FIELD OF THE INVENTION

The invention relates to the field of transmission devices for converting input motion into output motion, in particular for converting input rotary motion into output rotary oscillating motion. The invention also relates to a driving device having a motor delivering input rotary motion, the motor being coupled to the transmission device. The invention also relates to an aerial vehicle comprising the driving device to provide output rotary oscillating motion to drive wings of the aerial vehicle.

BACKGROUND OF THE INVENTION

Transmission devices which convert a rotary motion, from for example a rotating electric motor, such as a DC motor, into a rotary oscillating motion are known. These transmission devices often consist of linkage or string-based mechanisms. Although these mechanisms function quite well for normal sized transmission devices, they are not ideal for miniaturized applications. Due to their complex nature, i.e. they consist of a high number of parts and they include moving hinges, they are difficult and thus expensive to manufacture. So, mass production of said mechanisms is cumbersome.

For certain applications it is desirable to have an as small as possible transmission mechanism. The abovementioned linkage and string-based mechanisms have limitations regarding their miniaturization. This is a clear disadvantage for small scale applications. The main reason is the high number of parts necessary.

Some applications require a lightweight transmission mechanism. Again, the complexity and high number of parts necessary for the said transmission mechanisms impose limitations regarding the weight/mass. This is another disadvantage.

One of the possible applications for a transmission device converting rotary into rotary oscillating motion could be a flapping wing device. An example is the Delfly

(http://www.delfly.nl) micro air vehicle, MAV, which has a wingbeat arrangement such that a so-called double clap and fling is realized with four wings. In order to miniaturize micro air vehicles, the transmission mechanism needs to be as small as possible whilst maintaining a symmetrical, rotary oscillating motion of the flapping wings. The flapping mechanism needs to produce a high frequency flapping motion with high amplitude in order to provide enough thrust. At the same time it needs to be lightweight and compact.

The Delfly MAV has wings flapping with a 40° angular amplitude. The wings are driven by a linkage mechanism. The main disadvantage of linkage mechanisms, as mentioned, is their complexity. They consist of many parts and include moving hinges. This limits their further miniaturization and requires high production costs. Another disadvantage is the slightly asymmetrical wing motion inherent to linkage mechanisms. So, a difficulty lies in achieving a high amplitude rocking motion that is, at the same time, symmetric.

Thus there is a need for a transmission device, and driving device including the transmission device, for driving wings. The transmission device should have a simple design, that is lightweight, efficient, easy to manufacture and allows miniaturization.

Additionally, there is a need for such a transmission device that converts a rotary motion into a high frequency rotary oscillating motion with a high amplitude that is, at the same time, symmetrical.

SUMMARY OF THE INVENTION

It would be desirable to provide a transmission device, driving device and aerial vehicle having a simple structure. It would also be desirable to provide a transmission device, driving device and aerial vehicle allowing a light weight. It would also be desirable to provide a transmission device, driving device and aerial vehicle having low inertia. It would also be desirable to provide an alternative transmission device, driving device and aerial vehicle.

To better address one or more of these concerns, in a first aspect of the invention a transmission device for converting input rotary motion into output rotary oscillating motion is provided. The transmission device comprises:

an input axis extending perpendicular to a virtual plane, wherein the input axis intersects the virtual plane at an input axis intersection point;

a number, N, of output axes (N being an integer at least equal to 2, and even) extending parallel to each other, wherein the output axes are spaced and perpendicular to the virtual plane, and wherein the output axes intersect the virtual plane at respective output axis intersection points;

a primary engagement member being configured to rotate about the input axis, and comprising M primary sectors (M being an integer at least equal to 1 ) of at most 180°/M of a circular surface having an effective first radius and a central axis coaxially with the input axis, wherein the primary sectors are evenly distributed along a circumference defined by the first radius;

N secondary engagement members each being configured to rotate about a respective one of the output axes, at least two of the secondary engagement members comprising a secondary sector of a circular surface having an effective second radius and a central axis coaxially with the corresponding output axis;

wherein the transmission device is constructed and arranged to rotate any one of the secondary engagement members in opposite direction to a direction of rotation of an adjacent secondary engagement member; and

wherein each one of the primary sectors, when the primary engagement member is rotated in one direction, is configured to consecutively engage the secondary sector of at least two of the secondary engagement members for rotary oscillating motion of the secondary engagement members.

The input axis and the output axes define axes of rotation, and may either be virtual axes, or physical axes supported in appropriate bearing structures known as such. In case of virtual axes, the primary and secondary engagement members are supported in appropriate bearing structures known as such to allow for rotation thereof.

A primary or secondary engagement member can be made in different shapes and sizes, and can be made from different materials, such as a metal or a plastic material. For a primary or secondary engagement member, it is sufficient to comprise the primary sectors and secondary sectors, respectively, as defined above, and functioning as defined above. A remainder of each primary or secondary engagement member may be arbitrarily shaped and sized, may be made from other materials, or may be even omitted. In some embodiments, a secondary engagement member may be disk-shaped. Hence, this feature contributes to the transmission device having low weight and low inertia.

A surface of a primary or secondary sector of a primary or secondary engagement member, respectively, is circular, i.e. the surface, as seen in a tangential direction, generally follows (a part of) a circle, and is delimited by a leading edge and a trailing edge in different angular positions. In some embodiments, the surface is profiled. In some embodiments, the surface is flat, convex or concave.

A surface of a primary or secondary sector of a primary or secondary engagement member has an effective first or second radius, respectively, and a central axis, relative to which the first or second effective radius is measured. Herein, the term 'effective radius' relates to a radius which is effective in transmission of angular movement in the

engagement of a primary sector with a secondary sector, where the angular speed of the primary and secondary engagement members depends on a ratio of the effective first and second radii. The transmission device according to the invention may be constructed from a low amount of material and components to allow the primary and secondary sectors to be formed, and their function to be performed. Also for this reason, the transmission device may be lightweight, and may have low inertia.

The transmission device according to the invention allows for a high degree of miniaturization. The transmission device has a relatively low number of parts, and therefore is easy to manufacture at relatively low cost, which makes the transmission device suitable for mass production.

In the transmission device, in a first phase, when the primary engagement member is rotated in a rotational direction, a primary sector of the primary engagement member engages a secondary sector of a first one of the secondary engagement members along the 180°/M surface of the primary sector. During this engagement, the primary engagement member rotates in the rotational direction, and drives and rotates the first one of the secondary engagement members in an opposite rotational direction. Also during this engagement, a second one of the secondary engagement members adjacent to the first one of the secondary engagement members driven by the primary engagement member, is rotated in the rotational direction. Thus, in the first phase of engagement between the primary engagement member and a first one of the secondary engagement members, the two adjacent first and second ones of the secondary engagement members rotate in opposite rotational directions.

In a second phase, the primary sector of the primary engagement member, still rotating in the same rotational direction as before, engages a secondary sector of the second one of the secondary engagement members. During this engagement, the primary engagement member still rotates in the rotational direction, and drives and rotates the second one of the secondary engagement members in an opposite rotational direction. Also during this engagement, the first one of the secondary engagement members adjacent to the second one of the secondary engagement members driven by the first engagement member, is rotated in rotational direction. Thus, then the two adjacent first and second ones of the secondary engagement members again rotate in opposite rotational directions, however, both oppositely to the rotational directions in the previous phase.

The angle through which the secondary engagement member (engaging the primary engagement member) moves, at a given angle of rotation of the primary engagement member, depends on the ratio of the effective first radius of the primary engagement member and the effective second radius of the secondary engagement member.

As indicated above, in the first and second phases, both the first one and the second one of the secondary engagement members move in rotary oscillating manner. This makes the transmission device well-suited to actuate one or more pairs of wings of an aerial vehicle, wherein the wing movements are generated by the secondary engagement members rotating around the output axes, which may function as a virtual or physical hinge axis for the wings. The wings may also be connected, such as fixedly connected, or elastically connected, to the respective secondary engagement members, e.g. at an end of each wing.

Each primary sector has a circular surface of at most 180°/M. In case this circular surface is equal to 180°/M, in operation of the transmission device the primary sector always contacts a secondary sector of a consecutive one of the secondary engagement members. More in particular, at the moment when a leading edge of a primary sector comes into contact with a secondary sector, the same primary sector at its trailing edge loses contact with an adjacent secondary sector it previously was in contact with. Furthermore, at the moment when a trailing edge of a primary sector comes into contact with a secondary sector, the direction of movement of the surface of the primary sector is opposite to the direction of movement of the surface of that secondary sector. Since the movement of the surface of the primary sector is imperative, the movement of the surface of the secondary sector is reversed almost instantly.

In some applications, this almost instantaneous reversal of direction of rotation of the secondary engagement member may be disadvantageous. Hence, in an embodiment of the transmission device, the circular surface of each primary sector extends over less than 180°/M, such as less than 0.9·180°/Μ to soften the angular speed reversal of the secondary engagement members. With this feature, during a (brief) time period none of the secondary engagement members is driven by the primary engagement member.

In practice, the secondary engagement members may experience some force counteracting their rotational movement. For example, if the secondary engagement members actuate pairs of wings, an air resistance acting on the wings may produce such counteracting force. During said time period of non-engagement of the secondary engagement members with the primary engagement member, this counteracting force will slow down the rotational movement of the secondary engagement member, thus making the difference between the speed of the surface of the primary sector and the speed of the surface of the secondary sector smaller. In some embodiments, the counteracting force acting on the secondary engagement member during said time period may even be such that the surface of the secondary sector, at the end of said time period, has come to a stop. In other embodiments, the counteracting force acting on the secondary engagement member during said time period may even be such that the speed of the surface of the secondary sector, at the end of said time period, has its direction reversed to be in the same direction as the speed of the surface of the first sector of which the leading edge contacts the surface of the second sector. In some embodiments, the counteracting force acting on the secondary engagement member during said time period may even be such that the speed of the surface of the surface of the secondary sector, at the end of said time period, is in the same direction as, and is substantially equal to the speed of the surface of the first sector of which the leading edge contacts the surface of the second sector. In any event, the counteracting force acting on the secondary engagement member during said time period of non-engagement with the primary engagement member may soften the angular speed reversal of the secondary engagement members to some extent, or to a great extent, or even completely.

In an embodiment of the transmission device, at least one secondary engagement member is coupled to a spring member, such as a torque spring member. The secondary engagement member may have a neutral angular position in which the spring member does not exert a torque on the secondary engagement member, and may have at least one biased angular position different from the neutral angular position, in which biased angular position the spring member exerts a torque on the secondary engagement member driving the secondary engagement member back to the neutral angular position thereof. The spring member has one part coupled to the secondary engagement member, and another part coupled to a stationary structure, such as a frame or housing or body of the transmission device, or the device of which the transmission device forms part. The spring member produces a counteracting force/torque on the secondary engagement member when it is rotated away from its neutral angular position in any one of its two opposite rotation directions. A spring characteristic of the spring member is selected such that in a

transmission device in operation a desired dynamic behaviour of the secondary engagement member is obtained, taking into account all mechanical aspects of a mechanical system in which the transmission device is included.

When one secondary engagement member is coupled to a spring member, the transmission device being constructed and arranged to rotate any one of the secondary engagement members in opposite direction to a direction of rotation of an adjacent secondary engagement member, all secondary engagement members are mechanically coupled to each other, whereby the spring member produces a counteracting force/torque on all secondary engagement members when they are rotated away from their neutral angular position in any one of their two opposite rotation directions.

The secondary engagement members may be coupled to tertiary engagement members or other parts (such as wings) as explained below, such that a (direct) coupling of a spring member to a tertiary engagement member or other part is to be considered as an (indirect) coupling of the spring member to the secondary engagement member.

In some embodiments of the transmission device, more than one secondary engagement member is coupled to a respective spring member. In some embodiments of the transmission device, all secondary engagement members are coupled to respective spring members.

The spring member acts as an energy storage element, and thereby may flatten and/or reduce a load of a motor driving a transmission device including at least one spring member.

In some embodiments including the spring member or members, a primary sector angle preferably is less than 180°/M, such as less than 0.9*180°/M. As explained above, in such a transmission device, when it is in operation, there is a time period between a primary sector contacting a secondary sector, and the primary sector contacting a next secondary sector. In this time period, the spring member is active to decelerate and, depending on the design, reverse the rotational movement of the next secondary sector, whereby the rotary oscillating motion of the secondary engagement members becomes more uniform.

In some embodiments, the spring member is made of metal, such as steel, or plastic. In some embodiments, the spring member is elongated, and is configured to be twisted or bent around its longitudinal axis. In some embodiments, the spring member comprises a wound wire structure.

In an embodiment of the transmission device, the primary engagement member has M non-engagement sectors of at least 180°/M, the non-engagement sectors alternating with the primary sectors. Each non-engagement sector, when the primary engagement member is rotated, is configured not to engage the secondary engagement members, in particular a secondary sector thereof.

The non-engagement sectors ensure that there is no physical contact between the primary engagement member and the secondary engagement member opposite the non- engagement sector. In some embodiments, a non-engagement sector of the primary engagement member is provided by a sector-shaped part of the primary engagement member having a radius being smaller than the effective first radius. In other embodiments, a non-engagement sector of the primary engagement member comprises little or no material at all.

As defined above, the transmission device is constructed and arranged to rotate any one of the secondary engagement members in opposite direction to a direction of rotation of an adjacent secondary engagement member. In an embodiment of the transmission device, for this purpose each secondary engagement member comprises at least one coupling sector of a circular surface having an effective coupling sector radius and a central axis coaxially with the corresponding output axis, and the at least one coupling sector of each one of the secondary engagement members engages a coupling sector of an adjacent secondary engagement member.

An advantage of the coupling sectors is that the output rotary oscillating motion of the transmission device is obtained in a simple manner at the second engagement members, and that the rotary oscillating motion of the different second engagement members is synchronized.

In an embodiment, the transmission device further comprises N tertiary engagement members each being configured to rotate about a respective one of the output axes, and each comprising at least one tertiary sector of a circular surface having an effective third radius and a central axis coaxially with the corresponding output axis, wherein the at least one tertiary sector of each one of the tertiary engagement members engages a tertiary sector of an adjacent tertiary engagement member. A tertiary engagement member may be disk-shaped. Hence, this feature contributes to the transmission device having low weight and low inertia.

In some embodiments, engagement between a primary sector and a secondary sector, between coupling sectors, and/or between tertiary sectors can be based on friction, wherein the cylindrical surface of one of the sectors engages or contacts the cylindrical surface of another sector, and the movement of said one of the sectors leads to a movement of said other sector through frictional engagement.

In other embodiments, at least one of these engagements consists of interacting profiles, such as teeth, of the circular surfaces of engaging sectors. In such embodiments, the primary engagement member comprises partial gears, and the secondary and tertiary engagement members may be partial or full gears.

In an embodiment of the transmission device, each primary sector and each secondary sector are provided with a series of teeth, wherein the series of teeth of each primary sector consecutively engages with the series of teeth of the secondary sector of different secondary engagement members.

In another embodiment of the transmission device, each primary sector and each secondary sector are provided with a friction surface, wherein the friction surface of each primary sector consecutively frictionally engages with the friction surface of the secondary sector of different secondary engagement members.

In an embodiment of the transmission device, each coupling sector is provided with a series of teeth, wherein the series of teeth of the at least one coupling sector of each one of the secondary engagement members engages with the series of teeth of a coupling sector of an adjacent secondary engagement member. In an embodiment of the transmission device, each tertiary sector is provided with a series of teeth, wherein the series of teeth of the at least one tertiary sector of each one of the tertiary engagement members engages with the series of teeth of a tertiary sector of an adjacent tertiary engagement member. Each tooth of each series of teeth may extend radially and axially relative to the corresponding central axis of the corresponding

engagement member. An effective radius of sector provided with teeth is slightly smaller than the distance between the central axis and the tops of the teeth.

In an embodiment of the transmission device, each primary sector and each secondary sector are provided with a friction surface, wherein the friction surface of each primary sector consecutively frictionally engages with the friction surface of the secondary sector of different secondary engagement members, and each coupling sector is provided with a series of teeth, wherein the series of teeth of the at least one coupling sector of each one of the secondary engagement members engages with the series of teeth of a coupling sector of an adjacent secondary engagement member.

An advantage of this embodiment is that a synchronization of the secondary engagement members is ensured through the interengaging series of teeth of the coupling sectors, whereas, at first contact between a leading edge of a surface of a primary sector (moving in one direction) with a surface of a secondary sector (which may have a different direction and/or different speed of movement), the frictional engagement between the primary sector and the secondary sector may absorb or cushion this contact. This effect may be also be advantageously applied when the embodiment has primary sectors of less than 180°/M.

In an embodiment of the transmission device, each primary sector and each secondary sector are provided with a friction surface, wherein the friction surface of each primary sector consecutively frictionally engages with the friction surface of the secondary sector of different secondary engagement members, and each tertiary sector is provided with a series of teeth, wherein the series of teeth of the at least one tertiary sector of each one of the tertiary engagement members engages with the series of teeth of a tertiary sector of an adjacent tertiary engagement member.

An advantage of this embodiment is that a synchronization of the tertiary

engagement members (and thereby of the secondary engagement members when they are coupled to the third engagement members) is ensured through the interengaging series of teeth of the tertiary sectors, whereas, at first contact between a leading edge of a surface of a primary sector (moving in one direction) with a surface of a secondary sector (which may have a different direction and/or different speed of movement), the frictional engagement between the primary sector and the secondary sector may absorb or cushion this contact. This effect may be also be advantageously applied when the embodiment has primary sectors of less than 180°/M.

In an embodiment of the transmission device, the input axis intersection point is at equal distance from all output axis intersection points, and each one of the primary sectors of the primary engagement member, when the primary engagement member is rotated in one direction, is configured to consecutively engage the secondary sector of each secondary engagement member.

This has the advantage of a compact construction of the transmission device, in particular when the input axis intersection point and two output axis intersection points corresponding to adjacent second engagement members define a line or a triangle. When N is at least equal to 4, and the output axis intersection points are corner points of an N-sided regular polygon, the input axis intersection point is located centrally in the polygon.

In an embodiment of the transmission device, the secondary engagement members are fixed to the tertiary engagement members, to be rotatable together.

In a second aspect of the invention, a driving device is provided. The driving device comprises the transmission device according to the first aspect of the invention, and a motor operatively coupled to the primary engagement member of the transmission device for rotating the primary engagement member.

In an embodiment of the driving device, the motor is an electric motor. The electric motor may be powered by a battery, a fuel cell, one or more photovoltaic cells, or any other electric power supply. An electric motor can be controlled adequately by electronic circuitry to provide a speed of rotation of the primary engagement member of the transmission device, e.g. based on locally (i.e. in or near the driving device) or remotely provided control signals, and/or e.g. based on local or remote sensor signals. Control signals may be provided wirelessly to the driving device. On the other hand, also at least one fuel (such as petrol) powered motor can be used in the driving device.

In a third aspect of the invention, an aerial vehicle is provided. The aerial vehicle may be a micro air vehicle, MAV. The aerial vehicle comprises a driving device according to the second aspect of the invention, and further comprises wings driven by the driving device in rotary oscillating manner.

With the driving device of the present invention, including the transmission device of the present invention, a high amplitude rocking motion of the wings, flapping in a

synchronized way, can be obtained. With N = 4, two pairs of wings may be actuated to obtain a clap-and-peel aerodynamic mechanism, which occurs twice per wing beat cycle when adjacent wings approach each other.

The aerial vehicle according to the present invention, employing the transmission device of the present invention, can be easily manufactured from a relatively low number of parts, and allows for a high degree of miniaturization. The aerial vehicle may be lightweight. A symmetrical, high-frequency wing movement with a high amplitude is possible.

In an embodiment of the aerial vehicle, the wings are coupled to the secondary engagement members and/or to the tertiary engagement members of the transmission device.

In an embodiment, the aerial vehicle comprises at least one spring member (directly) coupled between a secondary engagement member and a body of the aerial vehicle. In another embodiment, the aerial vehicle comprises at least one spring member (directly) coupled between a tertiary engagement member and a body of the aerial vehicle. In these embodiments, the spring member may be a torque spring member.

In an embodiment, the aerial vehicle comprises at least one spring member coupled between a wing and a body of the aerial vehicle. In another embodiment, the aerial vehicle comprises at least one spring member coupled between two wings of the aerial vehicle. In these embodiments, the spring member may be a linear spring member.

The spring member produces a counteracting force/torque on the secondary engagement member, tertiary engagement member, or wing, when it is rotated in at least one of its two opposite rotation directions. A spring characteristic of the spring member is selected such that in a transmission device in operation a desired dynamic behaviour of the secondary engagement member, tertiary engagement member, or wing, is obtained, taking into account all mechanical aspects of the aerial vehicle in which the spring member is included.

These and other aspects of the invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 a schematically depicts a front view of a first embodiment of a transmission device according to the invention, in a first operational position thereof.

Figure 1 b schematically and partly diagrammatically depicts a cross-sectional view of the transmission device of Figure 1 a, taken along the line lb, included in an embodiment of a driving device according to the present invention.

Figure 1c schematically depicts a front view of the embodiment of the transmission device of Figure 1 a, in a second operational position thereof.

Figure 2a schematically depicts a front view of a second embodiment of a

transmission device according to the invention.

Figure 2b schematically and partly diagrammatically depicts a cross-sectional view of the transmission device of Figure 2a, taken along the line lib, included in an embodiment of a driving device according to the present invention.

Figure 3a schematically depicts a front view of a third embodiment of a transmission device according to the invention.

Figure 3b schematically and partly diagrammatically depicts a cross-sectional view of the transmission device of Figure 3a, taken along the line lllb, included in an embodiment of a driving device according to the present invention.

Figure 4a schematically depicts a front view of a fourth embodiment of a transmission device according to the invention.

Figure 4b schematically and party diagrammatically depicts a cross-sectional view of the transmission device of Figure 4a, taken along the broken line IVb, included in an embodiment of a driving device according to the present invention.

Figure 5a schematically depicts a front view of a fifth embodiment of a transmission device according to the invention.

Figure 5b schematically and party diagrammatically depicts a cross-sectional view of the transmission device of Figure 5a, taken along the line Vb, included in an embodiment of a driving device according to the present invention.

Figure 6a schematically depicts a front view of a sixth embodiment of a transmission device according to the invention.

Figure 6b schematically and party diagrammatically depicts a cross-sectional view of the transmission device of Figure 6a, taken along the line VIb, included in an embodiment of a driving device according to the present invention.

Figure 7a schematically depicts a front view of a seventh embodiment of a transmission device according to the invention. Figure 7b schematically and party diagrammatically depicts a cross-sectional view of the transmission device of Figure 7a, taken along the line Vllb, included in an embodiment of a driving device according to the present invention.

Figure 8a schematically depicts a front view of a eighth embodiment of a

transmission device according to the invention.

Figure 8b schematically and party diagrammatically depicts a cross-sectional view of the transmission device of Figure 8a, taken along the line Vlllb, included in an embodiment of a driving device according to the invention.

Figure 9a schematically, and in top view, illustrates an embodiment of an aerial vehicle having one pair or two pairs of wings according to the invention, and provided with a motor and transmission device according to the invention.

Figure 9b schematically, and in front view, illustrates an embodiment of the aerial vehicle having one pair of wings of Figure 9a.

Figure 9c schematically, and in front view, illustrates an embodiment of the aerial vehicle having two pairs of wings of Figure 9a.

DETAILED DESCRIPTION OF EMBODIMENTS

Figures 1a, 1 b and 1 c depict a transmission device 100 and driving device according to a first embodiment of the invention.

A primary engagement member 102 is rotatable around an input axis 104 in a rotational direction as indicated by arrow 106. The primary engagement member 102 comprises three (M = 3) primary sectors 108 of a = 60° (180°/M) of a circular, e.g. cylindrical surface 109. Each primary sector 108 has a central axis coaxially with the input axis 104, and has a first radius R1. The three primary sectors 108 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 102 further comprises three non-engagement sectors 1 10 of 60° (180°/M) which alternate with the primary sectors 108.

The primary sectors 108 may extend over less than 60°, whereas the non- engagement sectors 1 10 may extend over more than 60°.

A first secondary engagement member 120 is rotatable about an output axes 124. A second secondary engagement member 122 is rotatable about an output axis 126. The secondary engagement members 120, 122 are depicted having a circular, e.g. cylindrical surface 128 having a central axis being coaxially with the corresponding output axis 124, 126. The secondary engagement members 120, 122 each have a second radius R2.

Each one of the primary sectors 108, when the primary engagement member 102 is rotated in the rotational direction of arrow 106, is configured to consecutively engage the first secondary engagement member 120 and the second secondary engagement member 122. If the primary sectors 108 extend over 60°, at any time one of the primary sectors 108 engages one of the secondary engagement members 120, 122.

The first secondary engagement member 120 and the second secondary

engagement member 122 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 120 in a rotational direction of arrow 130 leads to a rotation of the second secondary engagement member 122 in a rotational direction of arrow 132, opposite to the rotational direction of arrow 130.

Thus, starting from the angular position of primary engagement member 102 as depicted in Figure 1 a, and rotating the primary engagement member 102 in the rotational direction of arrow 106 over 60° until an angular position of the primary engagement member 102 according to Figure 1c is reached, the second secondary engagement member 122 is rotated by the primary engagement member 102 over (R1/R2)-60° in the rotational direction of arrow 132 through engagement between the primary sector 108 and a secondary sector of the second secondary engagement member 122. During this rotation of the primary engagement member 102, the primary engagement member 102 is not in engagement with the first secondary engagement member 120, since a non-engagement sector 1 10 of the primary engagement member 102 faces the first secondary engagement member 120, however, the first secondary engagement member 120 is in engagement with the second secondary engagement member 122, and is rotated thereby in the rotational direction of arrow 130 over (R1/R2)-60°.

Then, starting from the angular position of primary engagement member 102 as depicted in Figure 1 c, and while rotating the primary engagement member 102 in the rotational direction of arrow 106 further over 60° until an angular position of the primary engagement member 102 according to Figure 1 a is reached again, the first secondary engagement member 120 is rotated by the primary engagement member 102 over

(R1/R2)-60° in the rotational direction of arrow 134 opposite to that of arrow 130 through engagement between the primary sector 108 and a secondary sector of the first secondary engagement member 120. During this rotation of the primary engagement member 102, the primary engagement member 102 is not in engagement with the second secondary engagement member 122, since a non-engagement sector 1 10 of the primary engagement member 102 faces the second secondary engagement member 122, however, the second secondary engagement member 122 is in engagement with the first secondary engagement member 120, and is rotated thereby in the rotational direction of arrow 136 opposite to that of arrow 132 over (R1/R2)-60°.

Thus, it can be recognized that a continued rotation of the primary engagement member 102 in the rotational direction of arrow 106 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 120, 122 across a range of (R1/R2)-60°. This implies that only a secondary sector of (R1/R2)-60° of the circular surface 128 of the first and second secondary engagement members 120, 122 is in engagement with any primary sector 108 of the primary engagement member 102, and that only a coupling sector of (R1/R2)-60° of the circular surface 128 of the first and second secondary engagement members 120, 122 is in engagement with each other, so that portions of the primary engagement member 102 never coming into contact with the first and second secondary engagement members 120, 122 may be shaped arbitrarily as long as the non-contact condition is maintained.

Referring to Figure 1 b, a motor 150 may be coupled (directly through a physical connection 152, or through a transmission or gear) to the primary engagement member 102 to drive and rotate the primary engagement member in the rotational direction of arrow 106. The combination of the motor 150 and the transmission device 100 forms a driving device.

A torque spring member 156 may be coupled (directly through a physical connection 154, or through a transmission or gear) to one of the first and second secondary

engagement members 120, 122, whereby the first and second secondary engagement members 120, 122 have a neutral angular position in which the torque spring member 156 does not exert a torque on the first and second secondary engagement members 120, 122, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 156 exerts a torque on the first and second secondary engagement members 120, 122 driving the first and second secondary engagement members 120, 122 back to the neutral angular position thereof. In Figure 1a, one biased angular position of the first and second secondary engagement members 120, 122 is shown, and in Figure 1 c, another biased angular position of the first and second secondary engagement members 120, 122 is shown, whereas a neutral angular position of the first and second secondary engagement members 120, 122 is centrally between said biased angular positions according to Figures 1 a and 1c.

Each one of the first and second secondary engagement members 120, 122 may have a respective torque spring member 156.

Wings 160, 162 (only schematically indicated in Figures 1 a and 1 c) may be coupled to the first and second secondary engagement members 120, 122, respectively, whereby the motor 150 drives the wings 160, 162 in a synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first and second secondary engagement members 120, 122 through a physical connection, such as physical connection 154. The combination of motor 150, transmission device 100 and wings 160, 162 may be part of an aerial vehicle having the wings 160, 162 flapping to fly the aerial vehicle. Instead of, or in addition to the torque spring member 156, at least one spring member 164, 166, such as a linear spring member, may be coupled between at least one of the wings 160, 162 and a body 168 of the aerial vehicle. In Figure 1 a, the spring member 164 is stretched and produces a maximum spring force, whereas the spring member 166 is relaxed and produces a minimum spring force. This situation is reversed after the primary engagement member 102 has rotated a ⁰ in the rotational direction of arrow 106.

Furthermore, at least one spring member may be coupled between the wings 160,

162.

The engagement between the first sector 108 and the second sectors may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the coupling sectors may be based on friction or based on interengaging series of teeth.

Figures 2a and 2b depict a transmission device 200 and driving device according to a second embodiment of the invention.

A primary engagement member 202 is rotatable around an input axis 204 in a rotational direction as indicated by arrow 206. The primary engagement member 202 comprises two (M = 2) primary sectors 208 of a = 90° (180°/M) of a circular, e.g. cylindrical surface 209. Each primary sector 208 has a cylinder axis coaxially with the input axis 204, and has a first radius R1. The two primary sectors 208 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 202 further comprises two non-engagement sectors 210 of 90° (180°/M) which alternate with the primary sectors 208.

The primary sectors 208 may extend over less than 90°, whereas the non- engagement sectors 1 10 may extend over more than 90°.

A first secondary engagement member 220 is rotatable about an output axis 224. A second secondary engagement member 222 is rotatable about an output axis 226. The secondary engagement members 220, 222 are depicted having a circular, e.g. cylindrical surface 228 having a central axis being coaxially with the corresponding output axis 224, 226. The secondary engagement members 220, 222 each have a second radius R2.

Each one of the primary sectors 208, when the primary engagement member 202 is rotated in the rotational direction of arrow 206, is configured to consecutively engage the first secondary engagement member 220 and the second secondary engagement member 222. If the primary sectors 208 extend over 90°, at any time one of the primary sectors 208 engages one of the secondary engagement members 220, 222.

The first secondary engagement member 220 and the second secondary

engagement member 222 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 220 in a rotational direction of arrow 230 leads to a rotation of the second secondary engagement member 222 in a rotational direction of arrow 232, opposite to the rotational direction of arrow 230.

Thus, starting from the angular position of primary engagement member 202 as depicted in Figure 2a, and rotating the primary engagement member 202 in the rotational direction of arrow 206 over 90°, the second secondary engagement member 222 is rotated by the primary engagement member 202 over (R1/R2)-90° in the rotational direction of arrow 232 through engagement between the primary sector 208 and a secondary sector of the second secondary engagement member 222. During this rotation of the primary

engagement member 202, the primary engagement member 202 is not in engagement with the first secondary engagement member 220, since a non-engagement sector 210 of the primary engagement member 202 faces the first secondary engagement member 220, however, the first secondary engagement member 220 is in engagement with the second secondary engagement member 222, and is rotated thereby in the rotational direction of arrow 230 over (R1/R2)-90°.

Then, after having rotated the primary engagement member 202 from the angular position as depicted in Figure 2a over 90°, and while rotating the primary engagement member 202 further in the rotational direction of arrow 206 over 90° until an angular position of the primary engagement member 202 according to Figure 2a is reached again, the first secondary engagement member 220 is rotated by the primary engagement member 202 over (R1/R2) ⁰ in a rotational direction opposite to that of arrow 230 through engagement between the primary sector 208 and a secondary sector of the first secondary engagement member 220. During this rotation of the primary engagement member 202, the primary engagement member 202 is not in engagement with the second secondary engagement member 222, since a non-engagement sector 210 of the primary engagement member 202 faces the second secondary engagement member 222, however, the second secondary engagement member 222 is in engagement with the first secondary engagement member 220, and is rotated thereby in a rotational direction opposite to that of arrow 232 over (R1/R2)-90°

Thus, it can be recognized that a continued rotation of the primary engagement member 202 in the rotational direction of arrow 206 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 220, 222 across a range of (R1/R2)-90°. This implies that only a secondary sector of (R1/R2)-90° of the circular surface 228 of the first and second secondary engagement members 220, 222 is in engagement with any primary sector 208 of the primary engagement member 202, and that only a coupling sector of (R1/R2)-90° of the circular surface 228 of the first and second secondary engagement members 220, 222 is in engagement with each other, so that portions of the primary engagement member 202 never coming into contact with the first and second secondary engagement members 220, 222 may be shaped arbitrarily as long as the non-contact condition is maintained.

Referring to Figure 2b, a motor 250 may be coupled (directly through a physical connection 252, or through a transmission or gear) to the primary engagement member 202 to drive and rotate the primary engagement member in the rotational direction of arrow 206. The combination of the motor 250 and the transmission device 200 forms a driving device.

A torque spring member 256 may be coupled (directly through a physical connection 254, or through a transmission or gear) to one of the first and second secondary

engagement members 220, 222, whereby the first and second secondary engagement members 220, 222 have a neutral angular position in which the torque spring member 256 does not exert a torque on the first and second secondary engagement members 220, 222, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 256 exerts a torque on the first and second secondary engagement members 220, 222 driving the first and second secondary engagement members 220, 222 back to the neutral angular position thereof. In Figure 2a, one biased angular position of the first and second secondary engagement members 220, 222 is shown.

Each one of the first and second secondary engagement members 220, 222 may have a respective torque spring member 256.

Wings 260, 262 (only schematically indicated in Figure 2a) may be coupled to the first and second secondary engagement members 220, 222, respectively, whereby the motor 250 drives the wings 260, 262 in a synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first and second secondary engagement members 220, 222 through a physical connection, such as physical connection 254. The combination of motor 250, transmission device 200 and wings 260, 262 may be part of an aerial vehicle having the wings 260, 262 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 256, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 260, 262 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between the wings 260, 262.

The engagement between the first sector 208 and the second sectors may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the coupling sectors may be based on friction or based on interengaging series of teeth. Figures 3a and 3b depict a transmission device 300 and driving device according to a third embodiment of the invention. A primary engagement member 302 is rotatable around an input axis 304 in a rotational direction as indicated by arrow 306. The primary engagement member 302 comprises four (M = 4) primary sectors 308 of a = 45° (180°/M) of a circular, e.g. cylindrical surface 309. Each primary sector 308 has a central axis coaxially with the input axis 304, and has a first radius R1. The four primary sectors 308 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 302 further comprises four non-engagement sectors 310 of 45° (180°/M) which alternate with the primary sectors 308.

The primary sectors 308 may extend over less than 45°, whereas the non- engagement sectors 1 10 may extend over more than 45°.

A first secondary engagement member 320 is rotatable about an output axis 324. A second secondary engagement member 322 is rotatable about an output axis 326. The secondary engagement members 320, 322 are depicted having a circular, e.g. cylindrical surface 328 having a central axis being coaxially with the corresponding output axis 324, 326. The secondary engagement members 320, 322 each have a second radius R2.

Each one of the primary sectors 308, when the primary engagement member 302 is rotated in the rotational direction of arrow 306, is configured to consecutively engage the first secondary engagement member 320 and the second secondary engagement member 322. If the primary sectors 308 extend over 45°, at any time one of the primary sectors 308 engages one of the secondary engagement members 320, 322.

The first secondary engagement member 320 and the second secondary

engagement member 322 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 320 in a rotational direction of arrow 330 leads to a rotation of the second secondary engagement member 322 in a rotational direction of arrow 332, opposite to the rotational direction of arrow 330.

Thus, starting from the angular position of primary engagement member 302 as depicted in Figure 3a, and rotating the primary engagement member 302 in the rotational direction of arrow 306 over 45°, the second secondary engagement member 322 is rotated by the primary engagement member 302 over (R1/R2)-45° in the rotational direction of arrow 332 through engagement between the primary sector 308 and a secondary sector of the second secondary engagement member 322. During this rotation of the primary

engagement member 302, the primary engagement member 302 is not in engagement with the first secondary engagement member 320, since a non-engagement sector 310 of the primary engagement member 302 faces the first secondary engagement member 320, however, the first secondary engagement member 320 is in engagement with the second secondary engagement member 322, and is rotated thereby in the rotational direction of arrow 330 over (R1/R2)-45°. Then, after having rotated the primary engagement member 302 from the angular position as depicted in Figure 3a over 45°, and while rotating the primary engagement member 302 further in the rotational direction of arrow 306 over 45° until an angular position of the primary engagement member 302 according to Figure 3a is reached again, the first secondary engagement member 320 is rotated by the primary engagement member 302 over (R1/R2)-45° in a rotational direction opposite to that of arrow 330 through engagement between the primary sector 308 and a secondary sector of the first secondary engagement member 320. During this rotation of the primary engagement member 302, the primary engagement member 302 is not in engagement with the second secondary engagement member 322, since a non-engagement sector 310 of the primary engagement member 302 faces the second secondary engagement member 322, however, the second secondary engagement member 322 is in engagement with the first secondary engagement member 320, and is rotated thereby in a rotational direction opposite to that of arrow 332 over (R1/R2)-45°

Thus, it can be recognized that a continued rotation of the primary engagement member 302 in the rotational direction of arrow 306 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 320, 322 across a range of (R1/R2)-45°. This implies that only a secondary sector of (R1/R2)-45° of the circular surface 328 of the first and second secondary engagement members 320, 322 is in engagement with any primary sector 308 of the primary engagement member 302, and that only a coupling sector of (R1/R2)-45° of the circular surface 328 of the first and second secondary engagement members 320, 322 is in engagement with each other, so that portions of the primary engagement member 302 never coming into contact with the first and second secondary engagement members 320, 322 may be shaped arbitrarily as long as the non-contact condition is maintained.

Referring to Figure 3b, a motor 350 may be coupled (directly through a physical connection 352, or through a transmission or gear) to the primary engagement member 302 to drive and rotate the primary engagement member in the rotational direction of arrow 306. The combination of the motor 350 and the transmission device 300 forms a driving device.

A torque spring member 356 may be coupled (directly through a physical connection

354, or through a transmission or gear) to one of the first and second secondary

engagement members 320, 322, whereby the first and second secondary engagement members 320, 322 have a neutral angular position in which the torque spring member 356 does not exert a torque on the first and second secondary engagement members 320, 322, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 356 exerts a torque on the first and second secondary engagement members 320, 322 driving the first and second secondary engagement members 320, 322 back to the neutral angular position thereof. In Figure 3a, one biased angular position of the first and second secondary engagement members 320, 322 is shown.

Each one of the first and second secondary engagement members 320, 322 may have a respective torque spring member 356.

Wings 360, 362 (only schematically indicated) may be coupled to the first and second secondary engagement members 320, 322, respectively, whereby the motor 350 drives the wings 360, 362 in a synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first and second secondary engagement members 320, 322 through a physical connection 354. The combination of motor 350, transmission device 300 and wings 360, 362 may be part of an aerial vehicle having the wings 360, 362 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 356, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 360, 362 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between the wings 360, 362.

The engagement between the first sector 308 and the second sectors may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the coupling sectors may be based on friction or based on interengaging series of teeth.

When comparing the transmission device 200 of Figures 2a, 2b to the transmission device 300 of Figures 3a, 3b, it can be seen that the embodiment of Figures 2a, 2b is more compact than the embodiment of Figures 3a, 3b. It can further be seen that the angular range of rotary oscillating motion, as determined by (180°/M) (R1/R2) = a° R1/R2, of the wings 260, 262 of the embodiment of Figures 2a, 2b is smaller than that of the wings 360, 362 of the embodiment of Figures 3a, 3b. An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables M, R1 and R2. Figures 4a and 4b depict a transmission device 400 and driving device according to a fourth embodiment of the invention. The transmission device 400 has a lower portion which is identical to the transmission device 100 as shown in Figures 1a, 1 b and 1 c. A description of this portion is given below.

Referring to Figures 4a and 4b, a primary engagement member 102 is rotatable around an input axis 104 in a rotational direction as indicated by arrow 106. The primary engagement member 102 comprises three (M = 3) primary sectors 108 of a = 60° (180°/M) of a circular, e.g. cylindrical surface 109. Each primary sector 108 has a central axis coaxially with the input axis 104, and has a first radius R1. The three primary sectors 108 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 102 further comprises three non-engagement sectors 110 of 60° (180°/M) which alternate with the primary sectors 108.

The primary sectors 108 may extend over less than 60°, whereas the non- engagement sectors 1 10 may extend over more than 60°.

A first secondary engagement member 120 is rotatable about an output axes 124. A second secondary engagement member 122 is rotatable about an output axis 126. The secondary engagement members 120, 122 are depicted having a circular, e.g. cylindrical surface 128 having a central axis being coaxially with the corresponding output axis 124, 126. The secondary engagement members 120, 122 each have a second radius R2.

Each one of the primary sectors 108, when the primary engagement member 102 is rotated in the rotational direction of arrow 106, is configured to consecutively engage the first secondary engagement member 120 and the second secondary engagement member 122. If the primary sectors extend over 60°, at any time one of the primary sectors 108 engages one of the secondary engagement members 120, 122.

The first secondary engagement member 120 and the second secondary

engagement member 122 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 120 in a rotational direction of arrow 130 leads to a rotation of the second secondary engagement member 122 in a rotational direction of arrow 132, opposite to the rotational direction of arrow 130.

Thus, starting from the angular position of primary engagement member 102 as depicted in Figure 4a, and rotating the primary engagement member 102 in the rotational direction of arrow 106 over 60°, the second secondary engagement member 122 is rotated by the primary engagement member 102 over (R1/R2)-60° in the rotational direction of arrow 132 through engagement between the primary sector 108 and a secondary sector of the second secondary engagement member 122. During this rotation of the primary

engagement member 102, the primary engagement member 102 is not in engagement with the first secondary engagement member 120, since a non-engagement sector 1 10 of the primary engagement member 102 faces the first secondary engagement member 120, however, the first secondary engagement member 120 is in engagement with the second secondary engagement member 122, and is rotated thereby in the rotational direction of arrow 130 over (R1/R2)-60°.

Then, after having rotated the primary engagement member 102 from the angular position as depicted in Figure 4a over 60°, and while rotating the primary engagement member 102 further in the rotational direction of arrow 106 further over 60° until an angular position of the primary engagement member 102 according to Figure 4a is reached again, the first secondary engagement member 120 is rotated by the primary engagement member 102 over (R1/R2)-60° in the rotational direction of arrow 134 opposite to that of arrow 130 through engagement between the primary sector 108 and a secondary sector of the first secondary engagement member 120. During this rotation of the primary engagement member 102, the primary engagement member 102 is not in engagement with the second secondary engagement member 122, since a non-engagement sector 1 10 of the primary engagement member 102 faces the second secondary engagement member 122, however, the second secondary engagement member 122 is in engagement with the first secondary engagement member 120, and is rotated thereby in the rotational direction of arrow 136 opposite to that of arrow 132 over (R1/R2)-60°.

Furthermore, the transmission device 400 comprises a third secondary engagement member 420 being rotatable around rotation axis 424 and having a radius R3, and a fourth secondary engagement member 422 being rotatable around rotation axis 426 and having a radius R3. The first secondary engagement member 120 and the third secondary engagement member 420 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 120 in a rotational direction of arrow 130 leads to a rotation of the third secondary engagement member 420 in a rotational direction of arrow 430, opposite to the rotational direction of arrow 130. The second secondary engagement member 122 and the fourth secondary engagement member 422 engage each other, such that a rotation of the second secondary engagement member 122 in a rotational direction of arrow 132 leads to a rotation of the fourth secondary engagement member 422 in a rotational direction of arrow 432, opposite to the rotational direction of arrow 132.

According to Figure 4b, also the third secondary engagement member 420 and the fourth secondary engagement member 422 engage each other, such that a rotation of the third secondary engagement member 420 in a rotational direction of arrow 430 leads to a rotation of the fourth secondary engagement member 422 in a rotational direction of arrow 432. However, an engagement between the third secondary engagement member 420 and the fourth secondary engagement member 422 is not essential, and furthermore the radius R3 of the third secondary engagement member 420 and the fourth secondary engagement member 422 may be different from, or equal to, a radius R2 of the first secondary engagement member 120 and the second secondary engagement member 122.

It can be recognized that a continued rotation of the primary engagement member 102 in the rotational direction of arrow 106 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 120, 122 across a range of (R1/R2)-60°, and also leads to a synchronized rotary oscillating movement of the third and fourth engagement members 420, 422 across a range of (R1/R3)-60°. This implies that only a secondary sector of (R1/R2)-60° of the circular surface 128 of the first and second secondary engagement members 120, 122 is in engagement with any primary sector 108 of the primary engagement member 102, and that only a secondary sector of (R2/R3)-60° of the circular, e.g. cylindrical surface 428 of the third and fourth secondary engagement members 420, 422 is in engagement with a secondary sector of (R1/R2)-60° of the circular surface 128 of the first and second secondary engagement members 120, 122, so that portions of the primary engagement member 102 never coming into contact with the first and second secondary engagement members 120, 122, as well as portions of the first, second, third and fourth secondary engagement members 120, 122, 420, 422 never coming into contact with each other, may be shaped arbitrarily as long as this non-contact condition is maintained.

Referring to Figure 4b, a motor 150 may be coupled (directly through a physical connection 152, or through a transmission or gear) to the primary engagement member 102 to drive and rotate the primary engagement member in the rotational direction of arrow 106. The combination of the motor 150 and the transmission device 400 forms a driving device.

A torque spring member 156 may be coupled (directly through a physical connection

154, or through a transmission or gear) to one of the first, second, third and fourth secondary engagement members 120, 122, 420, 422 whereby the first, second, third and fourth secondary engagement members 120, 122, 420, 422 have a neutral angular position in which the torque spring member 156 does not exert a torque on the first, second, third and fourth secondary engagement members 120, 122, 420, 422, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 156 exerts a torque on the first, second, third and fourth secondary engagement members 120, 122, 420, 422 driving the first, second, third and fourth secondary engagement members 120, 122, 420, 422 back to the neutral angular position thereof. In Figure 4a, one biased angular position of the first, second, third and fourth secondary engagement members 120, 122, 420, 422 is shown.

Each one of the first, second, third and fourth secondary engagement members 120, 122, 420, 422 may have a respective torque spring member 156.

Wings 160, 162, 460, 462 (only schematically indicated in Figure 4a) may be coupled to the first, second, third and fourth secondary engagement members 120, 122, 420, 422, respectively, whereby the motor 150 drives the wings 160, 162, 460 and 462 in a

synchronized rotary oscillating manner. Wings 160 and 460 move towards and away from each other. Also wings 162 and 462 move towards and away from each other. In an alternative embodiment, wings may be physically connected to the first, second, third and fourth secondary engagement members 120, 122, 420, 422 through physical connections, such as physical connections 154, 454. The combination of motor 150, transmission device 400 and wings 160, 162, 460, 462 may be part of an aerial vehicle having the wings 160, 162, 460, 462 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 156, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 160, 162, 460, 462 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between a pair of the wings 160, 162, 460, 462.

The engagement between the first sector 108 and the second sectors of the first and second secondary engagement members 120, 122 may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the coupling sectors may be based on friction or based on interengaging series of teeth.

An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables M, R1 , R2 and R3. Figures 5a and 5b depict a transmission device 500 and driving device according to a fifth embodiment of the invention. The transmission device 500 has an upper portion which is identical to the transmission device 200 as shown in Figures 2a and 2b. A description of this portion is given below.

A primary engagement member 202 is rotatable around an input axis 204 in a rotational direction as indicated by arrow 206. The primary engagement member 202 comprises two (M = 2) primary sectors 208 of a = 90° (180°/M) of a circular, e.g. cylindrical surface 209. Each primary sector 208 has a central axis coaxially with the input axis 204, and has a first radius R1. The two primary sectors 208 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 202 further comprises two non-engagement sectors 210 of 90° (180°/M) which alternate with the primary sectors 208.

The primary sectors 208 may extend over less than 90°, whereas the non- engagement sectors 210 may extend over more than 90°.

A first secondary engagement member 220 is rotatable about an output axis 224. A second secondary engagement member 222 is rotatable about an output axis 226. The secondary engagement members 220, 222 are depicted having a circular, e.g. cylindrical surface 228 having a central axis being coaxially with the corresponding output axis 224, 226. The secondary engagement members 220, 222 each have a second radius R2.

Each one of the primary sectors 208, when the primary engagement member 202 is rotated in the rotational direction of arrow 206, is configured to consecutively engage the first secondary engagement member 220 and the second secondary engagement member 222. If the primary sectors extend over 90°, at any time one of the primary sectors 208 engages one of the secondary engagement members 220, 222.

The first secondary engagement member 220 and the second secondary

engagement member 222 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 220 in a rotational direction of arrow 230 leads to a rotation of the second secondary engagement member 222 in a rotational direction of arrow 232, opposite to the rotational direction of arrow 230.

Thus, starting from the angular position of primary engagement member 202 as depicted in Figure 5a, and rotating the primary engagement member 202 in the rotational direction of arrow 206 over 90°, the second secondary engagement member 222 is rotated by the primary engagement member 202 over (R1/R2)-90° in the rotational direction of arrow 232 through engagement between the primary sector 208 and a secondary sector of the second secondary engagement member 222. During this rotation of the primary

engagement member 202, the primary engagement member 202 is not in engagement with the first secondary engagement member 220, since a non-engagement sector 210 of the primary engagement member 202 faces the first secondary engagement member 220, however, the first secondary engagement member 220 is in engagement with the second secondary engagement member 222, and is rotated thereby in the rotational direction of arrow 230 over (R1/R2)-90°

Then, after having rotated the primary engagement member 202 from the angular position as depicted in Figure 5a over 90°, and while rotating the primary engagement member 202 further in the rotational direction of arrow 206 over 90° until an angular position of the primary engagement member 202 according to Figure 2a is reached again, the first secondary engagement member 220 is rotated by the primary engagement member 202 over (R1/R2) ⁰ in a rotational direction opposite to that of arrow 230 through engagement between the primary sector 208 and a secondary sector of the first secondary engagement member 220. During this rotation of the primary engagement member 202, the primary engagement member 202 is not in engagement with the second secondary engagement member 222, since a non-engagement sector 210 of the primary engagement member 202 faces the second secondary engagement member 222, however, the second secondary engagement member 222 is in engagement with the first secondary engagement member 220, and is rotated thereby in a rotational direction opposite to that of arrow 232 over (R1/R2)-90°

Furthermore, the transmission device 500 comprises a third secondary engagement member 520 being rotatable around rotation axis 524 and a fourth secondary engagement member 522 being rotatable around rotation axis 526. The first secondary engagement member 120 and the third secondary engagement member 520 engage each other at coupling sectors thereof, such that a rotation of the first secondary engagement member 120 in a rotational direction of arrow 130 leads to a rotation of the third secondary engagement member 520 in a rotational direction of arrow 530, opposite to the rotational direction of arrow 130. The second secondary engagement member 122 and the fourth secondary engagement member 522 engage each other, such that a rotation of the second secondary engagement member 122 in a rotational direction of arrow 132 leads to a rotation of the fourth secondary engagement member 522 in a rotational direction of arrow 532, opposite to the rotational direction of arrow 132. According to Figure 5b, also the third secondary engagement member 520 and the fourth secondary engagement member 522 engage each other, such that a rotation of the third secondary engagement member 520 in a rotational direction of arrow 530 leads to a rotation of the fourth secondary engagement member 522 in a rotational direction of arrow 532.

It can be recognized that a continued rotation of the primary engagement member 202 in the rotational direction of arrow 206 leads to a synchronized rotary oscillating movement of the first, second, third and fourth secondary engagement members 220, 222, 520, 522 across a range of (R1/R2)-90°. This implies that only a secondary sector of (R1/R2)-90° of the circular surface 228 of the first and second secondary engagement members 220, 222 is in engagement with any primary sector 208 of the primary engagement member 202, that only a coupling sector of (R1/R2)-60° of the cylindrical surface 228 of the first and second secondary engagement members 220, 222 is in engagement with each other, and that only a secondary sector of (R1/R2)-90° of the circular, e.g. cylindrical surface 528 of the third and fourth secondary engagement members 520, 522 is in engagement with a secondary sector of (R1/R2)-90° of the circular surface 128 of the first and second secondary engagement members 220, 222, so that portions of the primary engagement member 202 never coming into contact with the first and second secondary engagement members 220, 222, as well as portions of the first, second, third and fourth secondary engagement members 220, 222, 520, 522 never coming into contact with each other, may be shaped arbitrarily as long as this non-contact condition is maintained.

Referring to Figure 5b, a motor 250 may be coupled (directly through a physical connection 252, or through a transmission or gear) to the primary engagement member 202 to drive and rotate the primary engagement member in the rotational direction of arrow 206. The combination of the motor 250 and the transmission device 500 forms a driving device.

A torque spring member 256 may be coupled (directly through a physical connection 254, or through a transmission or gear) to one of the first, second, third and fourth secondary engagement members 220, 222, 520, 522, whereby the first, second, third and fourth secondary engagement members 220, 222, 520, 522 have a neutral angular position in which the torque spring member 256 does not exert a torque on the first, second, third and fourth secondary engagement members 220, 222, 520, 522, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 256 exerts a torque on the first, second, third and fourth secondary engagement members 220, 222, 520, 522 driving the first, second, third and fourth secondary engagement members 220, 222, 520, 522 back to the neutral angular position thereof. In Figure 5a, one biased angular position of the first, second, third and fourth secondary engagement members 220, 222, 520, 522 is shown.

Each one of the first, second, third and fourth secondary engagement members 220, 222, 520, 522 may have a respective torque spring member 256.

Wings 260, 262, 560, 562 (only schematically indicated in Figure 5a) may be coupled to the first, second, third and fourth secondary engagement members 220, 222, 520, 522, respectively, whereby the motor 250 drives the wings 260, 262, 560 and 562 in a

synchronized rotary oscillating manner. Wings 260 and 560 move towards and away from each other. Also wings 262 and 562 move towards and away from each other. In an alternative embodiment, wings may be physically connected to the first, second, third and fourth secondary engagement members 220, 222, 520, 522 through physical connections, such as physical connections 254, 554. The combination of motor 250, transmission device 500 and wings 260, 262, 560, 562 may be part of an aerial vehicle having the wings 260, 262, 560, 562 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 256, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 260, 262, 560, 562 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between a pair of the wings 260, 262, 560, 562. The engagement between the first sector 208 and the second sectors of the first, second, third and fourth secondary engagement members 220, 222, 520, 522 may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the coupling sectors may be based on friction or based on interengaging series of teeth.

An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables M, R1 and R2.

Figures 6a and 6b depict a transmission device 900 and driving device according to sixth embodiment of the invention.

A primary engagement member 902 is rotatable around an input axis 904 in a rotational direction as indicated by arrow 906. The primary engagement member 902 comprises one (M = 1) primary sector 908 of a = 180° (180°/M) of a circular, e.g. cylindrical surface 909. The primary sector 908 has a central axis coaxially with the input axis 904, and has a first radius R1.

The primary engagement member 902 further comprises a non-engagement sector 910 of 180° (180°/M) which alternates with the primary sector 908.

The primary sector 908 may extend over less than 180°, whereas the non- engagement sector 910 may extend over more than 180°.

A first secondary engagement member 920 is rotatable about an output axis 924. A second secondary engagement member 922 is rotatable about an output axis 926. The secondary engagement members 920, 922 are depicted having a circular, e.g. cylindrical surface 928 having a central axis being coaxially with the corresponding output axis 924, 926. The secondary engagement members 920, 922 each have a second radius R2.

The primary sector 908, when the primary engagement member 902 is rotated in the rotational direction of arrow 906, is configured to consecutively engage the first secondary engagement member 920 and the second secondary engagement member 922. If the primary sector 908 extends over 180°, at any time the primary sector 908 engages one of the secondary engagement members 920, 922.

The first secondary engagement member 920 and the second secondary

engagement member 922 do not engage each other. The first secondary engagement member 920 is coupled through coupling 958 to a first tertiary engagement member 940 having a third radius R3 and which is rotatable around the rotation axis 924. The second secondary engagement member 922 is coupled through coupling 958 to a second tertiary engagement member 942 having third radius R3 and which is rotatable around the rotation axis 926. The couplings 958 preferably are mechanical couplings such that the first secondary engagement member 920 and the first tertiary engagement member 940 rotate together, and such that the second secondary engagement member 922 and the second tertiary engagement member 942 rotate together. Alternatively, the first secondary engagement member 920 and the first tertiary engagement member 940 may be made in one part, and the second secondary engagement member 922 and the second tertiary engagement member 942 may be made in one part. The first tertiary engagement member 940 and the second tertiary engagement member 942 engage each other at tertiary sectors thereof, such that a rotation of the first tertiary engagement member 940 in a rotational direction of arrow 930 leads to a rotation of the second tertiary engagement member 942 in a rotational direction of arrow 932, opposite to the rotational direction of arrow 930. Thereby, the first and second tertiary engagement members 940, 942 may be considered to synchronize the movements of the first and second secondary engagement members 920, 922. Thus, starting from the angular position of primary engagement member 902 as depicted in Figure 6a, and rotating the primary engagement member 902 in the rotational direction of arrow 906 over 180°, the second secondary engagement member 922 is rotated by the primary engagement member 902 over (R1/R2)- 180° in the rotational direction of arrow 932 through engagement between the primary sector 908 and a secondary sector of the second secondary engagement member 922. During this rotation of the primary engagement member 902, the primary engagement member 902 is not in engagement with the first secondary engagement member 920, since a non-engagement sector 910 of the primary engagement member 902 faces the first secondary engagement member 920, however, the first tertiary engagement member 940 is in engagement with the second tertiary engagement member 942, and is rotated thereby in the rotational direction of arrow 930 over (R1 R2) - 180°

Then, after having rotated the primary engagement member 902 from the angular position as depicted in Figure 6a over 180°, and while rotating the primary engagement member 902 further in the rotational direction of arrow 906 over 180° until an angular position of the primary engagement member 902 according to Figure 6a is reached again, the first secondary engagement member 920 is rotated by the primary engagement member 902 over (R1/R2) ⁰ in a rotational direction opposite to that of arrow 930 through engagement between the primary sector 908 and a secondary sector of the first secondary engagement member 920. During this rotation of the primary engagement member 902, the primary engagement member 902 is not in engagement with the second secondary engagement member 922, since a non-engagement sector 910 of the primary engagement member 902 faces the second secondary engagement member 922, however, the second tertiary engagement member 942 is in engagement with the first tertiary engagement member 940, and is rotated thereby in a rotational direction opposite to that of arrow 932 over

(R1/R2)- 180°

Thus, it can be recognized that a continued rotation of the primary engagement member 902 in the rotational direction of arrow 906 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 920, 922 and of the first and second tertiary engagement members 940, 942 across a range of (R1/R2)- 180°. This implies that a secondary sector of (R1/R2)- 180° of the circular surface 928 of the first and second secondary engagement members 920, 922 is in engagement with the primary sector 908 of the primary engagement member 902. This further implies that tertiary sectors of (R1/R2)- 180° of the circular, e.g. cylindrical surfaces 944 of the first and second tertiary engagement members 940, 942 are in engagement with each other.

Portions of the primary engagement member 902 never coming into contact with the first and second secondary engagement members 920, 922, as well as portions of the first and second tertiary engagement members 940, 942 never coming into contact with each other, may be shaped arbitrarily as long as this non-contact condition is maintained.

Referring to Figure 6b, a motor 950 may be coupled (directly through a physical connection 952, or through a transmission or gear) to the primary engagement member 902 to drive and rotate the primary engagement member 902 in the rotational direction of arrow 906. The combination of the motor 950 and the transmission device 900 forms a driving device.

A torque spring member 956 may be coupled (directly through a physical connection 954, or through a transmission or gear) to one of the first and second secondary

engagement members 920, 922, or to one of the first and second tertiary engagement members 940, 942, whereby the first and second secondary engagement members 920, 922 and first and second tertiary engagement members 940, 942 have a neutral angular position in which the torque spring member 956 does not exert a torque on the first and second secondary engagement members 920, 922 and first and second tertiary

engagement members 940, 942, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 956 exerts a torque on the first and second secondary engagement members 920, 922 and first and second tertiary engagement members 940, 942, driving the first and second secondary engagement members 920, 922 and first and second tertiary engagement members 940, 942 back to the neutral angular position thereof. In Figure 6a, one biased angular position of the first and second secondary engagement members 920, 922 and first and second tertiary engagement members 940, 942 is shown.

Each one of the first and second secondary engagement members 920, 922 and first and second tertiary engagement members 940, 942 may have a respective torque spring member 956.

Wings 960, 962 (only schematically indicated in Figure 6a) may be coupled to the first and second secondary engagement members 920, 922, respectively, whereby the motor 950 drives the wings 960, 962 in a synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first and second secondary engagement members 920, 922 or to the first and second tertiary engagement members 940, 942 through a physical connection, such as physical connection 954. The combination of motor 950, transmission device 900 and wings 960, 962 may be part of an aerial vehicle having the wings 960, 962 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 956, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 960, 962 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between the wings 960, 962. The engagement between the first sector 908 and the second sectors of the first and second secondary engagement members 920, 922 may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the tertiary sectors of the first and second tertiary engagement members 940, 942 may be based on friction or based on interengaging series of teeth.

An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables R1 , R2 and R3.

Figures 7a and 7b depict a transmission device 600 and driving device according to a seventh embodiment of the invention. The transmission device 600 has an upper portion which is similar to the transmission device 200 as shown in Figures 2a and 2b.

A primary engagement member 602 is rotatable around an input axis 604 in a rotational direction as indicated by arrow 606. The primary engagement member 602 comprises two (M = 2) primary sectors 608 of a = 90° (180°/M) of a circular, e.g. cylindrical surface 609. Each primary sector 608 has a central axis coaxially with the input axis 604, and has a first radius R1. The two primary sectors 608 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 602 further comprises two non-engagement sectors 610 of 90° (180°/M) which alternate with the primary sectors 608.

The primary sectors 608 may extend over less than 90°, whereas the non- engagement sectors 610 may extend over more than 90°.

A first secondary engagement member 620 is rotatable about an output axis 624. A second secondary engagement member 622 is rotatable about an output axis 626. The secondary engagement members 620, 622 are depicted having a circular, e.g. cylindrical surface 628 having a central axis being coaxially with the corresponding output axis 624, 626. The secondary engagement members 620, 622 each have a second radius R2.

Each one of the primary sectors 608, when the primary engagement member 602 is rotated in the rotational direction of arrow 606, is configured to consecutively engage the first secondary engagement member 620 and the second secondary engagement member 622. If the primary sectors extend over 90°, at any time one of the primary sectors 608 engages one of the secondary engagement members 620, 622.

The first secondary engagement member 620 and the second secondary

engagement member 622 do not engage each other. The first secondary engagement member 620 is coupled through coupling 656 to a first tertiary engagement member 640 having a third radius R3 and which is rotatable around the rotation axis 624. The second secondary engagement member 622 is coupled through coupling 656 to a second tertiary engagement member 642 having third radius R3 and which is rotatable around the rotation axis 626. The couplings 656 preferably are mechanical couplings such that the first secondary engagement member 620 and the first tertiary engagement member 640 rotate together, and such that the second secondary engagement member 622 and the second tertiary engagement member 642 rotate together. Alternatively, the first secondary engagement member 620 and the first tertiary engagement member 640 may be made in one part, and the second secondary engagement member 622 and the second tertiary engagement member 642 may be made in one part. The tertiary engagement members 640 and 642 engage each other at tertiary sectors thereof, such that a rotation of the first tertiary engagement member 640 in a rotational direction of arrow 630 leads to a rotation of the second tertiary engagement member 642 in a rotational direction of arrow 632, opposite to the rotational direction of arrow 630. Thereby, the first and second tertiary engagement members 640, 642 may be considered to synchronize the movements of the first and second secondary engagement members 620, 622.

Thus, starting from the angular position of primary engagement member 602 as depicted in Figure 7a, and rotating the primary engagement member 602 in the rotational direction of arrow 606 over 90°, the second secondary engagement member 622 is rotated by the primary engagement member 602 over (R1/R2)-90° in the rotational direction of arrow 632 through engagement between the primary sector 608 and a secondary sector of the second secondary engagement member 622. During this rotation of the primary

engagement member 602, the primary engagement member 602 is not in engagement with the first secondary engagement member 620, since a non-engagement sector 610 of the primary engagement member 602 faces the first secondary engagement member 620, however, the first tertiary engagement member 640 is in engagement with the second tertiary engagement member 642, and is rotated thereby in the rotational direction of arrow 630 over (R1/R2)-90°.

Then, after having rotated the primary engagement member 602 from the angular position as depicted in Figure 7a over 90°, and while rotating the primary engagement member 602 further in the rotational direction of arrow 606 over 90° until an angular position of the primary engagement member 602 according to Figure 7a is reached again, the first secondary engagement member 620 is rotated by the primary engagement member 602 over (R1/R2) ⁰ in a rotational direction opposite to that of arrow 630 through engagement between the primary sector 608 and a secondary sector of the first secondary engagement member 620. During this rotation of the primary engagement member 602, the primary engagement member 602 is not in engagement with the second secondary engagement member 622, since a non-engagement sector 610 of the primary engagement member 602 faces the second secondary engagement member 622, however, the second tertiary engagement member 642 is in engagement with the first tertiary engagement member 640, and is rotated thereby in a rotational direction opposite to that of arrow 632 over

(R1/R2)-90°

Thus, it can be recognized that a continued rotation of the primary engagement member 602 in the rotational direction of arrow 606 leads to a synchronized rotary oscillating movement of the first and second secondary engagement members 620, 622 and of the first and second tertiary engagement members 640, 642 across a range of (R1/R2)-90°. This implies that a secondary sector of (R1/R2)-90° of the circular surface 628 of the first and second secondary engagement members 620, 622 is in engagement with any primary sector 608 of the primary engagement member 602. This further implies that tertiary sectors of (R1/R2)-90° of the circular, e.g. cylindrical surfaces 644 of the first and second tertiary engagement members 640, 642 are in engagement with each other.

Portions of the primary engagement member 602 never coming into contact with the first and second secondary engagement members 620, 622, as well as portions of the first and second tertiary engagement members 640, 642 never coming into contact with each other, may be shaped arbitrarily as long as this non-contact condition is maintained.

Referring to Figure 7b, a motor 650 may be coupled (directly through a physical connection 652, or through a transmission or gear) to the primary engagement member 602 to drive and rotate the primary engagement member 602 in the rotational direction of arrow 606. The combination of the motor 650 and the transmission device 600 forms a driving device.

A torque spring member 656 may be coupled (directly through a physical connection 654, or through a transmission or gear) to one of the first and second secondary

engagement members 620, 622, or to one of the first and second tertiary engagement members 640, 642, whereby the first and second secondary engagement members 620, 622 and first and second tertiary engagement members 640, 642 have a neutral angular position in which the torque spring member 656 does not exert a torque on the first and second secondary engagement members 620, 622 and first and second tertiary

engagement members 640, 642, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 656 exerts a torque on the first and second secondary engagement members 620, 622 and first and second tertiary engagement members 640, 642, driving the first and second secondary engagement members 620, 622 and first and second tertiary engagement members 640, 642 back to the neutral angular position thereof. In Figure 7a, one biased angular position of the first and second secondary engagement members 620, 622 and first and second tertiary engagement members 640, 642 is shown. Each one of the first and second secondary engagement members 620, 622 and first and second tertiary engagement members 640, 642 may have a respective torque spring member 656.

Wings 660, 662 (only schematically indicated in Figure 7a) may be coupled to the first and second secondary engagement members 620, 622, respectively, whereby the motor 650 drives the wings 660, 662 in a synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first and second secondary engagement members 620, 622 or to the first and second tertiary engagement members 640, 642 through a physical connection, such as physical connection 654. The combination of motor 650, transmission device 600 and wings 660, 662 may be part of an aerial vehicle having the wings 660, 662 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 656, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 660, 662 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between the wings 660, 662.

The engagement between the first sector 608 and the second sectors of the first and second secondary engagement members 620, 622 may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the tertiary sectors of the first and second tertiary engagement members 640, 642 may be based on friction or based on interengaging series of teeth.

An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables M, R1 , R2 and R3.

Figures 8a and 8b depict a transmission device 700 and driving device according to a seventh embodiment of the invention. The transmission device 700 has an upper portion which is similar to the transmission device 600 as shown in Figures 7a and 7b. A description of this portion is given below.

A primary engagement member 602 is rotatable around an input axis 604 in a rotational direction as indicated by arrow 606. The primary engagement member 602 comprises two (M = 2) primary sectors 608 of a = 90° (180°/M) of a circular, e.g. cylindrical surface 609. Each primary sector 608 has a central axis coaxially with the input axis 604, and has a first radius R1. The two primary sectors 608 are evenly distributed along the circumference defined by the first radius R1.

The primary engagement member 602 further comprises two non-engagement sectors 610 of 90° (180°/M) which alternate with the primary sectors 608.

The primary sectors 608 may extend over less than 90°, whereas the non- engagement sectors 610 may extend over more than 90°. A first secondary engagement member 620 is rotatable about an output axis 624. A second secondary engagement member 622 is rotatable about an output axis 626. A third secondary engagement member 720 is rotatable about an output axis 724. A fourth secondary engagement member 722 is rotatable about an output axis 726. The secondary engagement members 620, 622, 720, 722 are depicted having a circular, e.g. cylindrical surface 628, 728 having a central axis being coaxially with the corresponding output axis 624, 626, 724, 726. The secondary engagement members 620, 622, 720, 722 each have a second radius R2.

Each one of the primary sectors 608, when the primary engagement member 602 is rotated in the rotational direction of arrow 606, is configured to consecutively engage the first secondary engagement member 620, the second secondary engagement member 622, the third secondary engagement member 720, and the fourth secondary engagement member 722. If the primary sectors extend over 90°, at any time one of the primary sectors 608 engages one of the secondary engagement members 620, 622, 720, 722.

The secondary engagement members 620, 622, 720,722 do not engage each other.

The first secondary engagement member 620 is coupled through coupling 656 to a first tertiary engagement member 640 having a third radius R3 and which is rotatable around the rotation axis 624. The second secondary engagement member 622 is coupled through coupling 656 to a second tertiary engagement member 642 having third radius R3 and which is rotatable around the rotation axis 626. The third secondary engagement member 720 is coupled through coupling 756 to a third tertiary engagement member 740 having a third radius R3 and which is rotatable around the rotation axis 724. The fourth secondary engagement member 722 is coupled through coupling 756 to a fourth tertiary engagement member 742 having third radius R3 and which is rotatable around the rotation axis 726. The couplings 656, 756 preferably are mechanical couplings such that the first secondary engagement member 620 and the first tertiary engagement member 640 rotate together, and such that the second secondary engagement member 622 and the second tertiary engagement member 642 rotate together, such that the third secondary engagement member 720 and the third tertiary engagement member 740 rotate together, and such that the fourth secondary engagement member 722 and the fourth tertiary engagement member 742 rotate together. Alternatively, the first secondary engagement member 620 and the first tertiary engagement member 640 may be made in one part, the second secondary engagement member 622 and the second tertiary engagement member 642 may be made in one part, the third secondary engagement member 720 and the third tertiary engagement member 740 may be made in one part, and the fourth secondary engagement member 722 and the fourth tertiary engagement member 742 may be made in one part. The tertiary engagement members 640, 642, 740, 742 engage each other at tertiary sectors thereof, such that a rotation of the first tertiary engagement member 640 in a rotational direction of arrow 630 leads to a rotation of the second tertiary engagement member 642 in a rotational direction of arrow 632, opposite to the rotational direction of arrow 630. At the same time, the third tertiary engagement member 740 rotates in a rotational direction of arrow 730, and the fourth tertiary engagement member 742 rotates in a rotational direction of arrow 732. Thereby, the first, second, third and fourth tertiary engagement members 640, 642, 740, 742 may be considered to synchronize the movements of the first, second, third and fourth secondary engagement members 620, 622, 720, 722.

Thus, starting from the angular position of primary engagement member 602 as depicted in Figure 8a, and rotating the primary engagement member 602 in the rotational direction of arrow 606 over 90°, the second secondary engagement member 622 and the third secondary engagement member 720 are rotated by the primary engagement member 602 over (R1/R2)-90° in the rotational direction of arrows 632, 730, respectively. During this rotation of the primary engagement member 602, the primary engagement member 602 is not in engagement with the first secondary engagement member 620 and the fourth secondary engagement member 722, since non-engagement sectors 610 of the primary engagement member 602 face the first secondary engagement member 620 and the fourth secondary engagement member, however, the first, second, third and fourth tertiary engagement members 640, 742, 740, 742 are in engagement with each other, and are rotated thereby in the rotational direction of arrows 630, 632, 730, 732 over (R1/R2)-90°.

Then, after having rotated the primary engagement member 602 from the angular position as depicted in Figure 8a over 90°, and while rotating the primary engagement member 602 further in the rotational direction of arrow 606 over 90° until an angular position of the primary engagement member 602 according to Figure 8a is reached again, the first secondary engagement member 620 and the fourth secondary engagement member 722 are rotated by the primary engagement member 602 over (R1/R2) ⁰ in a rotational direction opposite to that of arrows 630, 732, respectively. During this rotation of the primary engagement member 602, the primary engagement member 602 is not in engagement with the second secondary engagement member 622 and the third secondary engagement member 720, since non-engagement sectors 610 of the primary engagement member 602 face the second secondary engagement member 622 and the third secondary engagement member 720, however, the first, second, third and fourth tertiary engagement members 640, 642, 740, 742 are in engagement with each other, and are rotated thereby in a rotational direction opposite to that of arrows 630, 632, 730, 732 over (R1/R2)-90°.

Thus, it can be recognized that a continued rotation of the primary engagement member 602 in the rotational direction of arrow 606 leads to a synchronized rotary oscillating movement of the first, second, third and fourth secondary engagement members 620, 622, 720 and 722, and of the first, second, third and fourth tertiary engagement members 640, 642, 740 and 742 across a range of (R1/R2)-90°. This implies that a secondary sector of (R1/R2)-90° of the circular surface 628, 728 of the first, second, third and fourth secondary engagement members 620, 622, 720 and 722 is in engagement with any primary sector 608 of the primary engagement member 602. This further implies that tertiary sectors of

(R1/R2)-90° of the circular, e.g. cylindrical surfaces 644, 744 of the first, second, third and fourth tertiary engagement members 640, 642, 740 and 742 are in engagement with each other.

Referring to Figure 8b, a motor 650 may be coupled (directly through a physical connection 652, or through a transmission or gear) to the primary engagement member 602 to drive and rotate the primary engagement member 602 in the rotational direction of arrow 606. The combination of the motor 650 and the transmission device 700 forms a driving device.

A torque spring member 656 may be coupled (directly through a physical connection 654, or through a transmission or gear) to one of the secondary engagement members 620, 622, 720, 722 or to one of the tertiary engagement members 640, 642, 740, 742, whereby the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742 have a neutral angular position in which the torque spring member 656 does not exert a torque on the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742, and biased angular positions different from the neutral angular position, in which biased angular positions the torque spring member 656 exerts a torque on the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742 driving the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742 back to the neutral angular position thereof. In Figure 8a, one biased angular position of the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742 is shown.

Each one of the secondary engagement members 620, 622, 720, 722 and tertiary engagement members 640, 642, 740, 742 may have a respective torque spring member 656.

Wings 660, 662, 760, 762 (only schematically indicated in Figure 8a) may be coupled to the first, second, third and fourth tertiary engagement members 640, 642, 740, 742, respectively, whereby the motor 650 drives the wings 660, 662, 760 and 762 in a

synchronized rotary oscillating manner. In an alternative embodiment, wings may be physically connected to the first, second, third and fourth secondary engagement members 620, 622, 720, 722 through a physical connection, such as physical connection 654, 754. Wings 660 and 760 move towards and away from each other. Also wings 662 and 762 move towards and away from each other. The combination of motor 650, transmission device 700 and wings 660, 662, 760, 762 may be part of an aerial vehicle having the wings 660, 662, 760, 762 flapping to fly the aerial vehicle.

Instead of, or in addition to the torque spring member 656, at least one spring member, such as a linear spring member, may be coupled between at least one of the wings 660, 662, 760, 762 and a body of the aerial vehicle. Furthermore, at least one spring member may be coupled between a pair of the wings 660, 662, 760, 762.

The engagement between the first sectors 608 and the second sectors of the first and second secondary engagement members 620, 622 may be based on friction or based on interengaging series of teeth. Similarly, the engagement between the tertiary sectors of the first, second, third and fourth tertiary engagement members 640, 642, 740, 742 may be based on friction or based on interengaging series of teeth.

An appropriate angular range of rotary oscillating motion can be selected by selecting a combination of variables M, R1 , R2 and R3.

In the different Figures, the rotation axes 104, 204, 304, 404, 504, 604, 904 of the respective primary engagement members each are input axes. In the different Figures, the rotation axes 124, 126, 224, 226, 324, 326, 424, 426, 524, 526, 624, 626, 724, 726, 924, 926 of the respective secondary and tertiary engagement members each are output axes. When the plane of the drawing is considered a virtual plane, each input axis intersects the virtual plane at an input axis intersection point, and each output axis intersects the virtual plane at an output axis intersection point. In the embodiment of Figures 5a and 8a, the output axis intersection points are corner points of a N-sided regular polygon (in this case, a square), and the input axis intersection point is located centrally in the polygon.

The primary sectors of the primary engagement members, and/or the secondary sectors and/or coupling sectors of the secondary engagement members, and/or the tertiary sectors of the tertiary engagement sectors may be provided with teeth, in particular series of teeth. The teeth of the primary sectors may engage with the teeth of the secondary sectors. The teeth of a coupling sector of a secondary engagement member may engage with the teeth of a coupling sector of an adjacent secondary engagement member. The teeth of a tertiary sector of a tertiary engagement member may engage with the teeth of a tertiary sector of an adjacent tertiary engagement member. Figures 9a, 9b and 9c schematically illustrate an aerial vehicle 810 comprising a body

81 1 , and a transmission device 812 coupled to a motor 814, which in turn is coupled to a battery 816 to power the motor 814. The aerial vehicle 810 may have two wings 820, 822 (Figure 9b), or may have four wings 820, 822, 824 and 826 (Figure 9c) coupled to the transmission device 812, whereby the wings 820, 822, 824 and 826 may be driven in rotary oscillating motion as illustrated by double arrows 828.

If, according to Figure 9b, the aerial vehicle 810 has two wings 820 and 822, the transmission device 812 may e.g. be a transmission device as illustrated in Figures 1 a, 1 b, 1 c, 2a, 2b, 3a, 3b, 7a and 7b.

If, according to Figure 9c, the aerial vehicle 810 has four wings 820, 822, 824 and 826, the transmission device 812 may e.g. be a transmission device as illustrated in Figures 4a, 4b, 5a, 5b, 8a and 8b.

As explained in detail above, a transmission device converts input rotary motion into output rotary oscillating motion. It has an input axis and N output axes (N at least equal to 2, and even) extending parallel to each other. A primary engagement member is rotatable about the input axis, and comprises M primary sectors (M at least equal to 1) of at most 180°/M of a circular surface having a first radius and a central axis coaxially with the input axis. The primary sectors are evenly distributed along the circumference defined by the radius. N secondary engagement members each are configured to rotate about a respective one of the output axes, and comprise a secondary sector of a circular surface having an effective second radius and a central axis coaxially with the corresponding output axis. Any one of the secondary engagement members rotates in opposite direction to a direction of rotation of an adjacent secondary engagement member. Each one of the primary sectors, when the primary engagement member is rotated in one direction, consecutively engages the secondary sector of at least two of the secondary engagement members. The transmission device may be used in a driving device for an aerial vehicle.

As required, detailed embodiments of the present invention are disclosed herein.

However, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the invention.

The terms "a'Van", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The term coupled, as used herein, is defined as connected, although not necessarily directly.