LOCOMOTION SYSTEM"

DESCRIPTION

TECHNICAL FIELD

The present invention relates to the field of systems to assist the movement of people with disabilities or reduced mobility, in particular it refers to stair-climbing wheelchairs.

The present invention refers more specifically to a stair-climbing wheelchair provided with a hybrid locomotion system according to the preamble of Claim 1. STATE OF ART

Today, enabling people with disabilities, or with reduced mobility, to climb architectural barriers safely and in a complete independent way is a felt concern. With respect to known solutions, such as for example fixed or movable stairlifts, there are alternative solutions aimed to solve such problem, as for example stair- climbing wheelchairs. The latter allow to combine in a single device both the ability to climb an obstacle and the functionality of a traditional electric wheelchair. Actually, such devices to climb obstacles such as single steps, sidewalks, stairs, even when there are no fixed structures intended to climb barriers and, compared to the traditional stairlifts, they usually allow the user to move about independently without requiring the presence of an assistant.

A widespread type of these stair-climbing wheelchairs is disclosed for example from Chinese patent document CN204072538U and from the wheelchair named with the tradename "TopChair", which provides a first locomotion system with motor-driven wheels for flat ground motion, and a second locomotion system with a motor-driven track for climbing on stairs.

The main disadvantage of this constructive solution is to require a double motorization system that, added to the implementation systems necessary to reconfigure the wheelchair, leads to problems of heavy weight and large dimensions. In addition, the track solution results poorly effective in managing the phases of entrance and exit from the stairs.

A solution aimed to solve such drawbacks is disclosed from European Patent Application EP1516797A2 and from the stair-climbing wheelchair named with the tradename "Scoiattolo". Such solution provides for a locomotion system with a cluster of wheels, more manageable during the phases of entrance and exit from the stairs, less cumbersome compared to current track solutions, and that can be used both for flat ground motion and climbing on stairs, without requiring a double motorization.

However, this solution is not equipped with motors for flat ground motion and has the disadvantage of allowing climbing architectural barriers only with the help of an assistant who keeps the wheelchair balanced. Actually, the wheelchair without an external aid does not show any condition of static balance, since in general the projection of its centre of gravity falls outside the area comprised between the wheel- stairs contact points, and almost always this area is reduced to an ideal segment between the contact points of the wheels, to the right and to the left, in contact with a single step.

A solution aimed at overcoming this drawback is disclosed in the Italian Patent IT1402989B1, which provides for a wheelchair with a locomotion system with a cluster of wheels both at the front and at the rear to ensure the static balance.

However, this solution has some criticality, particularly due to the movement of the clusters of wheels during the climbing of the stairs, since each cluster of wheels travels along a trajectory similar to a cycloid, generating continuous oscillations, scarcely comfortable for the user.

To limit these drawbacks, the publication "G. Quaglia, W. Franco, M. Nisi, "Evolution of Wheelchair, a Stair-climbing Wheelchair", Proceeding of the 14th World Congress in Mechanism and Machine Science, 2015, Taipei, Taiwan" discloses a hybrid locomotion system, with a motorized rear cluster of wheels and a non-motorized front track.

Despite the non-motorized front track allows to have a wheelchair which is substantially stable, lighter, less bulky and subject to less oscillations with respect to previously described wheelchairs, such solution does not ensure a correct distribution of contact forces in its front and rear support points, causing possible traction and grip problems of the wheelchair, in particular during the stair-climbing motion. Also, it is not able to generate a straight translational motion of the user of the wheelchair during the climbing of stair flights.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to overcome the drawbacks of the known art. In particular, it is an object of the present invention to provide a stair-climbing wheelchair with a hybrid locomotion system having characteristics of high safety and comfort for the user, and also a higher power autonomy.

Also, it is an object of the present invention to provide a stair-climbing wheelchair with a hybrid locomotion system having a simple and compact structure.

These and other objects of the present invention are achieved by a stair-climbing wheelchair incorporating the features of the appended claims, which form an integral part of the present description.

The basic idea of the present invention envisages to realize a stair-climbing wheelchair comprising a frame provided with a seat intended to accommodate a user to be transported, and a locomotion unit comprising a couple of clusters of wheels. Further, the wheelchair comprises passive supporting means that are movable between a stowed position wherein they are raised from the ground and an extracted position wherein they are in contact with the ground.

More in detail, the passive supporting means comprise a track configured in such a way that, in its extracted position, the frame rests at the front on the locomotion unit and at the rear on the track, and the stair-climbing wheelchair further comprises at least one mechanical device linked between the locomotion unit and the seat, adapted to cooperate with the track for compensating the oscillations of the seat generated by the movement of the couple of clusters of wheels, and configured in such a way as to allow a substantially translational motion of the seat during a stair- climbing motion of the stair-climbing wheelchair.

The choice of providing a front-wheel drive, by the locomotion unit with clusters of wheels and a rear support system on the track, allows a more regular and safer motion of the wheelchair during the stair-climbing motion, improving its static stability. Actually, this architecture allows, during the stair-climbing motion, to obtain a correct distribution of the contact forces at the rear and front support points of the wheelchair, loading more the locomotion unit to confer more grip during the traction stage and to avoid the occurrence of possible slipping.

It should be noted that in this description, the term "front/ at the front" is used to indicate the side of the wheelchair, and each individual component thereof, that a user has in front of him/ herself, while the term "rear/ at the rear" is used to indicate the side of the wheelchair, and each individual component thereof, that a user has behind him/ herself.

In addition, the idea of providing passive supporting means - i.e. non-motorized - reduces the number of sensors and actuators required for the wheelchair operation, giving greater compactness and structural simplicity to the structure.

Advantageously, at least one mechanical device of the wheelchair adapted to allow a translational motion of the seat during its motion comprises a cam-follower mechanism, wherein the cam is coupled to a connecting shaft connected to the couple of clusters of wheels, and wherein the follower is hinged to a supporting element integral with the seat.

Such solution increases the comfort for the user since it allows to compensate the oscillations of the seat generated by the cycloid trajectory of the geometric centre of the cluster of wheels during the stair-climbing stage. Also, the use of a cam-follower system, therefore a non-actuated system, allows to simplify the control system of the wheelchair and to reduce the power consumption required for its operation, thus improving the autonomy during the flat ground motion.

Further advantageous features of the present invention will become more apparent from the description that follows and from the appended claims, which form an integral part of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinbelow with reference to non-limiting examples, provided for the purposes of explanation, and not limitating, in the accompanying drawings. These drawings illustrate different aspects and embodiments of the present invention and, where appropriate, reference numbers illustrating components, materials and/ or similar elements in different figures are denoted by similar reference numerals.

Figures 1 and 2 illustrate an overall view respectively in flat ground motion and stair-climbing motion of a stair-climbing wheelchair according to the invention;

figures 3a, 3b and 3c illustrate respectively a front section view, a side section view and an enlarged detail of the side section view of a first constructive detail - the locomotion unit - of the stair-climbing wheelchair according to the invention;

figures 4a and 4b illustrate an overall view of a first and a second embodiment of a second constructive detail - the transmission assembly - of the stair-climbing wheelchair according to the invention;

figures 5a, 5b and 5c illustrate an overall view in a first operating position, a side view in a first operating position and an overall view in a second operating position of a detail of a third constructive detail - the frame - the stair-climbing wheelchair according to the invention;

figures 6 and 7 illustrate a simplified side view and a schematic view of an enlarged detail of the stair-climbing wheelchair according to the invention;

figures 8 and 9 illustrate an overall view of two different operative configurations of a fourth constructive detail - the track - of the stair-climbing wheelchair according to the invention;

figure 10 shows an overall view of a preferred embodiment of a fifth constructive detail - the track moving means - of the stair-climbing wheelchair according to the invention;

figures 11a, lib and 11c each illustrate a side view of the constructive detail of figure 10 in three different operating positions;

figures 12a and 12b illustrate an overall view and an enlarged detail of an alternative embodiment of the track moving means of the stair-climbing wheelchair according to the invention;

figures 13a, 13b, 13c and 14 illustrate an overall view of a first, a second and a third embodiment of a sixth constructive detail - the mechanical device compensating the oscillations of the seat - of the stair-climbing wheelchair according to the invention; figures 15 and 16, respectively, illustrate a first and a second embodiment of a seventh constructive detail - the seat - of the stair-climbing wheelchair according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible to various modifications and alternative constructions, some non-limiting embodiments, provided for explanatory purposes, are described in detail hereinbelow.

However, it should be understood that there is no intention to limit the invention to the specific illustrated embodiments, but, on the contrary, the invention is intended to cover all modifications, alternative constructions, and equivalents which fall within the scope of the invention as defined in the claims.

In the following description, therefore, the use of "for example", "etc.", "or", "either" indicates not exclusive alternatives without any limitation, unless otherwise indicated; the use of "also" means "including, but not limited to" unless otherwise indicated; the use of "includes / comprises" means "includes / comprises but not limited to" unless otherwise indicated.

Figures 1 and 2 illustrate overall views of a stair-climbing wheelchair 1 according to the invention. In particular, figure 1 shows the wheelchair 1 in flat ground motion conditions and figure 2 shows the wheelchair in stair-climbing motion conditions. In general terms, the stair-climbing wheelchair 1 comprises a frame 2, provided with a seat 3 intended to accommodate a user 100, in particular a user with disabilities or reduced mobility, and a locomotion unit 4 to allow the movement of the wheelchairs 1.

The stair-climbing wheelchair 1 is an electric wheelchair, i.e. which is provided with an electric motor assembly adapted to transmit a torque to operate a transmission assembly connected to the locomotion unit 4, and which will be discussed in more detail thereafter.

The wheelchair 1 further comprises passive supporting means (5, 6), idle or in any case non-motorized, connected to the frame 2, and movable between a stowed position wherein they are raised from the ground la, and an extracted position wherein they are in contact with the ground la.

In particular, the supporting means comprise a track 6 and a pair of pivoting wheels 5. In use, and in a condition of flat ground motion of the wheelchair 1 - as illustrated in figure 1 - it corresponds to a stowed position of the track 6 and to an extracted position of the pivoting wheels 5, in such a way that the track 6 is accommodated inside the volume occupied by the wheelchair 1, and the pivoting wheels 5 are in contact with the ground la.

On the contrary, during the stair-climbing motion of the wheelchair 1 - and as it can be seen in figure 2 - the track 6 is in the extracted position and is in contact with the stairs, and the pivoting wheels 5 are in stowed position, raised along the side of the frame 2.

Although in all embodiments which will be described in the present invention the pivoting wheels 5 of the wheelchair 1 are illustrated in such a way that during its flat ground motion, i.e. in their extracted position, i.e. in contact with the ground la, they are positioned at the rear of locomotion unit 4, the pivoting wheels 5 can also be arranged at the front of the locomotion unit 4, when they are in their extracted position, simply entailing a slight modification of the framework structure of the wheelchair 1 with respect to the illustrated examples.

With reference to figures 3a, 3b and 3c, the locomotion unit 4 comprises a couple of identical clusters of wheels 40 - of which only one is illustrated in the figures - positioned at the front of opposite sides of the frame 2 and mutually in axis.

Advantageously, the couple of clusters of wheels 40 is mounted at a distance such as to minimize the overall dimension of the wheelchair 1 and to confer the necessary mobility even in confined spaces (e.g., to allow an easy passage through the internal doors in buildings).

Each clusters of wheels preferably comprises three wheels 41, connected to a box-like body constituted by a supporting structure 42 - or planet carrier - and by a cover. However, alternative embodiments of the wheelchair 1 may provide for the use of a different number of wheels, such as for example two or four wheels, according to the design choices aimed at further reduced dimensions and weights of the wheelchair 1. In more detail, the planet carrier 42 comprises a central portion from which three supporting arms 43 extend, each for a respective wheel 41 and angularly equidistant from one another, and is provided with a housing 44 for accommodating a gear train therein.

In a preferred embodiment, the gear train is of the epicyclical type and comprises a sun gear 45, positioned centrally in the housing 44, integral with a drive shaft 45a and that meshes with three planet wheels 46, each positioned on a respective arm 43. Preferably, the sun wheel 45 and the related drive shaft 45a are hollow in order to enclose a shaft 42a integral with the planet carrier 42.

Each planet wheel 46 is hinged to the planet carrier 42 and allows to obtain the same direction of rotation between the sun wheel 45 and a second assembly of gears, in this case three gears 47. Each gear 47 of the second group of gears is arranged on a respective arm 43 and each meshes with a corresponding satellite wheel 46.

In addition, each gear 47 of the second group of gears is hinged to the planet carrier 42 and integral to a shaft 47a on which the wheel 41, preferably in rubber, is rigidly mounted, destined to come into contact with the ground la.

Therefore, each clusters of wheels 40 of the locomotion unit 4 has two degrees of freedom: the rotation of the sun gear 45 and the rotation of the planet carrier 42 respectively controlled by the drive shaft 45a and by the shaft 42a.

Figure 4a shows a first embodiment of the transmission assembly of the wheelchair 1 that, in order to simplify its structure and to ensure synchronous rotation of both cluster of wheels 40, provides a connecting shaft 48 that connects the shafts 42a controlling the rotation of the respective planet carriers 42.

Doing so, the couple of clusters of wheels 40 generally has three degrees of freedom since the rotations of both planet carriers 42 result coupled.

To control the three degrees of freedom of the locomotion unit 4, an electric motor assembly is provided, comprising three gear motors, indicated in figure 4a with the references 7a, 7b and 7c. Two of the three gear motors 7a and 7b are coupled to a respective drive shaft 45a connected to the sun wheel 45 of a corresponding planet carrier 42, while the remaining gear motor 7c is coupled to the connecting shaft 48 and is adapted to manage the rotation of both planet carriers 42 of the couple of clusters of wheels 40.

The gear motors (7a, 7b), i.e. those relating to the sun gears 45 of the planet carriers 42, can be both reversible and irreversible. In the case of reversibility of the gear motors 7a, 7b, the addition of a brake on the respective output shaft can be considered. The gear motor 7c coupled to the connecting shaft 48 is configured to ensure an irreversibility of the rotational motion, in such a way as to maintain the wheelchair 1 in position also when the motor assembly is not powered.

In an alternative embodiment illustrated in figure 4b, the connecting shaft, indicated with the reference 48a, connects the planet carriers of each cluster of wheels 40 and is mounted in a non-coaxial way with respect to the spin axis of the drive shafts 45a connected to the sun gears 45.

In this configuration two supporting elements 49 are provided integral with the frame 2, each disposed in the vicinity of the two planet carriers 42 and adapted to support the connecting shaft 48a.

Each supporting element 49 supports at one end a coaxial hinge to a respective drive shaft 45a of the sun gears 45, and at the other end a coaxial hinge to the connecting shaft 48a.

The connecting shaft 48a is coupled to the gear motor 7c adapted to control the motion of the two planet carriers 42, and to each of its ends a gear is keyed, which meshes with a corresponding gear mounted integral with a respective planet carrier 42 of the cluster of wheels 40. At the ends of the drive shafts 45a of the two sun gears 45, the gear motors 7a, 7b are mounted, adapted to control the rotation of the latter. In this case, preferably, the gear ratio between the gears mounted on the end of the connecting shaft 48a and the gears mounted integral with a respective planet carrier 42 is 3:1, so as to couple a complete rotation of the connecting shaft 48 with a 120° rotation of the cluster of wheels 40 during the stair-climbing motion, which corresponds to climbing a step.

Advantageously, such configuration allows to limit the overall dimension of the transmission assembly, and facilitates and simplifies the assembly thereof in the stair-climbing wheelchair 1, since it does not require the presence of shafts and coaxial motors entailing a greater constructive complexity, such as hollow shafts and multiple hinges, for example.

With reference to figures 5a, 5b, 5c, the frame 2 of the wheelchair 1 is shown. The frame 2 is constituted by a first and a second sub-frame mutually hinged by means of a couple of hinges (20a, 20b). Such coupling corresponds to hinge C in the diagram of figure 7. The first sub-frame comprises a structure provided with a first rod 2a and a second rod 2b, intended to connect reciprocally the other components of the wheelchair 1.

The two rods 2a, 2b are integral and parallel one another, i.e. they constitute a single rigid body that does not allow their relative rotation.

With reference to figures 6 and 7, each rod (2a, 2b) corresponds to segment PC. In particular, two drive shafts 45a of the respective sun gears 45 and two shafts 42a rotating the planet carriers 42 connected to the connecting shaft 48 are hinged in the point of the frame 2 indicated with P. The second sub-frame is constituted by a supporting element 30 integral with the seat 3 of the wheelchair 1, which corresponds to segment RC represented in figure 7.

Returning to figures 5a, 5b and 5c, and as previously stated, during the flat ground motion, the wheelchair 1 rests on two pivoting wheels 5, each mounted on one end of a movable rod 51, in such a way that, when the wheels are in contact with the ground la, they support the wheelchair 1 during the flat ground motion.

In the illustrated embodiment, each bar is hinged to the frame 2 at the opposite end of the end provided for the pivoting wheels 5. However, different embodiments can provide bars 51 hinged to the supporting element 30 of the seat 3.

Furthermore, although in the illustrated examples the movable bars 51 are hinged at one end of the frame 2 and, in particular, in correspondence of the planet carrier 42 of the cluster of wheels 40, they can be hinged at any other point belonging to the two bodies, provided that it allows the pivoting wheels 5 to move between the extracted position, in which they rest on the ground la - as illustrated in figures 5a, 5b, and the stowed position, in which they are raised from the ground la - as shown in figure 5c. The movement of the two movable bars 51 and of the relevant pivoting wheels 5 connected thereto occurs by the actuation of a linear or rotary actuator (not represented in the figures).

When climbing stairs, and in particular after having passed the transitory stage of entrance on the stairs and before of the transitory stage of exit, the motion of the wheelchair 1 is controlled by the coordinated action of the two reduction gears 7a, 7b coupled to the drive shafts 45a of the solar gears 45, and of the gear motor 7c coupled to the connecting shaft 48 moving the planet carriers 42.

In this condition of motion, the planet carriers 42 of each cluster of wheels 40 rotate synchronously in the motion of climbing each step, and the point indicated with P, which corresponds substantially to the geometric centre of each cluster of wheels 40, i.e. where the drive shaft 45a meshes, moves along a substantially cycloidal trajectory.

With reference to figures 6, 7, 8 and 9, the track 6, which comprises the hinge indicated with reference S, moves with a translational motion along a straight line, parallel to the plane lying on the edges of the steps of the stair.

Due to the cycloidal trajectory motion of P, the frame 2 - indicated schematically with the segment PC in figure 7 - oscillates and consequently also the supporting element 30 of seat 3 - indicated schematically in figure 7 with the segment RC - would oscillate if the two bodies were integral.

In order to obtain a translational motion for the supporting element 30 of the seat 3, the latter is hinged to the track 6 in correspondence of the hinge S, and the distance between the point R belonging to the supporting member 30 of the seat 3 and the point P belonging to the planet carrier 42 of the cluster of wheels 40, is controlled in such a manner as to compensate for the motion of P with respect to R.

Thus, the wheelchair 1 comprises at least one mechanical device linked between the locomotion unit 4 and the seat 3, adapted to cooperate with the track (6) for compensating the oscillations of the seat 3 generated by the movement of the couple of clusters of wheels 40, and configured in such a way as to allow a substantially translational motion of the seat 3 during the motion of the stair-climbing wheelchair 1.

In particular, such mechanical device comprises a first mechanism that allows to connect the supporting element 30 of the seat 3 to the track 6, and a second mechanism that manages the distance between P and R as a function of the rotation of the cluster of wheels 40. The first mechanism can move the track 6 between the stowed position for flat ground motion (in which the track 6 is raised and is not in contact with the ground la) and the extracted position in which the track 6 rests on the stair during the climbing motion.

The track 6 is idle, i.e. non-motorized, and at its maximum extension it preferably has a length greater than twice the maximum pitch between the steps of stairs that the wheelchair must climb (where pitch means the pitch is the hypotenuse of the triangle which has as catheti the riser and the tread of the step).

In order to reduce the overall dimension of the structure of the track 6, the wheelchair 1 preferably provides a telescopic track. The telescopic track of the embodiment illustrated in the figures comprises a first portion 6a on which the previously described hinge S is positioned, having a substantially rectangular structure, each opposite long side thereof is wound by a belt 61 and are connected at one end by a cross member 62.

Alternative embodiments may comprise a non-telescopic track, provided with a single belt (or for example with a rubber track), or a plurality of belts. In any case, the track 6 comprises one or more parts, connected to one another so as to be movable and such as to allow a retracted configuration in which the track 6 occupies a minimum volume, and an extended configuration of the latter in which it occupies a maximum volume.

Internally, the opposite long sides are provided with a linear guide 63 which constrains the sliding of a second telescopic portion 6b of the track 6.

The second telescopic portion 6b slides parallel inside the first fixed portion 6a, and it is also provided with belts 61 intended to come into contact with the plane of the stairs.

An actuator (not represented in the figures) allows to pass from the retracted configuration (figure 8) to the extended configuration (figure 9) of the telescopic track, and vice versa. The retracted configuration minimizes the overall dimension of the track 6 inside the volume occupied by the wheelchair 1 during the flat ground motion, while the extended configuration ensures a sufficient length of track 6 during the stair-climbing motion. Moreover, in the extended configuration of the track 6, the second telescopic portion 6b results extracted in such a way as to expand the track 6 in a direction which extends at the rear of the wheelchair 1.

The track 6 is shifted into the retracted or extended position by means of a mechanism connected to the supporting element 30 of the seat 3, which will be discussed in more detail shortly. With respect to such mechanism, the track 6 is further free to rotate about an axis perpendicular to the sagittal plane of the wheelchair 1 by means of a hinge 64, indicated with reference S in figure 7.

In the embodiment illustrated in the figures, both the fixed portion 6a and the telescopic portion 6b of the track 6 provide distinct contact surfaces by means of belts (i.e. two parallel and spaced apart half-rollers), however not illustrated alternative embodiments, and as previously mentioned, may provide a single contact surface for the fixed portion 6a and for the telescopic portion 6b, for example.

With reference to figures 10, 11a, lib and 11c, the mechanism allowing to shift the track 6 between the stowed position during the flat ground motion and the extracted position during the stair-climbing motion is shown. Such mechanism allows, moreover, to manage with continuity the distance of the frame 2 (especially that of the hinge indicated with letter C in figure 7) from the plane of the stairs during the different operative stages.

In a first alternative embodiment, not shown in figures, the mechanism provides a bar connecting the hinge S integral to the fixed portion 6a of the track 6 to a hinge connected to the supporting element 30 of the seat 3. Thanks to this mechanism, the hinge is moved in the plane leaving free the rotation of the fixed portion 6a of the track 6 with respect to the supporting element 30. This solution is similar to the example shown in figure 10, but deprived of the rods indicated by references 32 and 33.

A different alternative embodiment of such mechanism, illustrated in figure 10, provides two equal and parallel articulated parallelograms moving at the two sides of the track 6. Each articulated parallelogram is constituted by the supporting element 30 of the seat 3, which is hinged to the ends of two rods (31, 32), the latter in turn hinged to the opposite ends of a connecting rod 33, hinged to the fixed portion 6a of the track 6.

In this configuration, the two rods (31, 32) have the same length and the connecting rod 33 has a length equal to the distance between the hinges 34a and 34b provided on the supporting element 30 of the seat 3. The articulated parallelogram mechanism thus realized allows to move in the plane the hinge S of the fixed portion 6a of the track 6, while also translating the connecting rod 33, which is always parallel to the segment joining the hinges (34a, 34b) provided on the supporting element 30 of the seat 3.

This solution allows to introduce limitations to the rotation of the fixed portion 6a of the belt 6 with respect to the connecting rod 33, for example by adding contact surfaces on the latter, and allowing to improve the mobility control of the track 6, without introducing further actuation systems.

Figures 11a, lib and 11c show the track 6 provided with the articulated quadrangle mechanism in three different operating configurations that maintain its inclination constant with respect to the connecting rod 33.

Alternatively, a possible embodiment for the mechanism can provide the use of a single articulated parallelogram.

Preferably, and with reference to figures 12a and 12b, the articulated quadrangle mechanism provides a hook 36 integral with the telescopic portion 6b of the track 6 adapted to engage, in a closed track configuration, a pin 37 integral with the connecting rod 33. This solution makes the fixed portion 6a of the track 6 integral with the connecting rod 33 in the closed track configuration.

The motion system of the track 6 with respect to the supporting element 30 may also be implemented by mechanisms having two or three degrees of freedom actuated independently, that manage the relative position between the two elements.

Returning to figures 6 and 7, and as stated above, in order to obtain a substantially translational motion of the seat 3 during the stair-climbing motion of the wheelchair, this latter provides not only the mechanism just described that allows to connect the supporting element 30 of the seat 3 to the track 6, but also a second mechanism to manage the distance between the point R belonging to the supporting member 30 of the seat 3 and the point P belonging to the planet carrier 42 of the clusters of wheels 40, in such a way as to compensate for the motion of P with respect to R.

A first embodiment of this second mechanism, illustrated in figure 13a, provides a system with a cam and a follower. The cam 80 is integral with the connecting shaft 48 that connects the shafts 42a controlling the rotation of the planet carriers 42 of the clusters of wheels 40, then rotates together with the clusters of wheels; the follower 81 is for example a roller tappet, and it is hinged to the supporting element 30 of the seat 3.

In this way, by appropriately shaping the profile of the cam, the mechanism can control the distance between P and R - see figure 7 - so as to compensate the movement of point P during the rotation of the clusters of wheels 40 and can ensure a translational motion of the seat. This solution also allows to control the distance PR in a passive manner, i.e. by operating without the aid of control and actuated systems, but by exploiting the gear motors (7a, 7b, 7c) of the clusters of wheels 40, to the advantage of the constructive simplification of wheelchair 1.

Although the trajectory of the point P varies as the type of stairs to climb varies, and therefore different shapes of the cam profiles should be provided in function of these types, such variations are in any case reduced. Therefore, it is sufficient using a single cam profile, designed to compensate for most of the oscillations.

In figures 13b and 13c, and with further reference to figure 4b, the positioning of the cam 80a is elucidated, in the alternative embodiment of the transmission assembly of the wheelchair 1, in which the connecting shaft 48a connects the planet carriers of each cluster of wheels 40, and is mounted in a non-coaxial way with respect to the spin axis of the drive shafts 45a connected to the sun gear 45.

As mentioned previously, in this case, on each end of the connecting shaft 48a a gear wheel is keyed, which meshes with a corresponding gear mounted integral with a respective planet carrier 42 of the cluster of wheels 40.

Since such pair of gears preferably have a gear ratio of 3:1, such configuration allows to couple a complete rotation of the connecting shaft 48a with a 120° of rotation of the cluster of wheels 40, rotation corresponding to the climbing of a step during the stair- climbing motion of the wheelchair 1.

The cam 80a is integral with the connecting shaft 48a rotating together with the clusters of wheels, and is coupled to the follower 81a, the latter hinged to the supporting element 30 of the seat 3.

Advantageously, in this way a cam of reduced dimensions is obtained. Actually, the same displacement of the follower, with respect to the previously described solution, is obtained by a rotation of the cam of 360°, instead of 120°. This allows to have less stringent constraints on pressure angles of the mechanism, and therefore allows to obtain a smaller and less bulky cam.

On the other hand, the choice of using a mechanism with such configuration, entailing an architecture with basically larger volumes, and providing two pairs of additional gears, needs appropriate evaluations and comparisons in the executive design phase with respect to the embodiment illustrated in figure 13a.

An alternative embodiment, illustrated in figure 14, provides that the mechanism of motion compensation of P with respect to R is implemented by an active control by means of an actuator 9.

In this case, the actuator 9 is hinged at one end to the connecting shaft 48 of the planet carriers 42, and at the other end to the supporting element 30 of the seat 3. Such type of coupling is only a constructive example since, in general, in case of an active control of the distance between the point P and the point R, it is sufficient that one end of the actuator is connected to any point of the first sub-frame (2a, 2b) and the other end of the actuator to any point of the supporting element 30 of the seat. In a third alternative embodiment, not illustrated in the figures, the motion compensation mechanism of P with respect to R provides a combined use of the cam- follower mechanism and of the control system by means of the actuator, which were previously described.

The wheelchair 1 can also have different types of seat 3 installed, illustrated in figures 15 and 16, attached to the relevant supporting element 30, allowing to obtain a same structure of the wheelchair 1.

In a preferred embodiment, illustrated in figure 15, the seat 3 is fixed and rigidly connected to the relevant supporting element 30 by means of a generic link represented by the element indicated by the reference 35, such as for example a connecting bar.

Alternatively, and as shown in figure 16, a controlled degree of freedom can be added, regarding the positioning of the seat 3 with respect to the relevant supporting element 30.

In the example in the figure, this measure has been implemented by providing a hinge 36 for coupling the supporting element 30 and the seat 3, positioned in a generic point of the latter.

In alternative to the hinge 36, any other mechanism with a single degree of freedom could be used. In particular, a possible alternative solution could be the use of an articulated quadrangle. The introduction of a further degree of freedom requires, on the one hand, the introduction of an additional actuator 37, but allows to obtain an adjustment of the posture of the user 100 on the wheelchair, and the possibility to control and manage the centre of gravity position.

From the description above it is apparent how the described device allows to achieve the intended objects.

Therefore, it is apparent to a person skilled in the art that it is possible to make modifications and variants to the solution described with reference to the figures indicated above, without departing from the scope of protection of the present patent, as defined by the appended claims.

For example, further solutions not shown in the figures may relate to the use of passive articulated mechanisms, or other types of mechanisms, that control the distance PR in a way similar to that described regarding the cam, but using a different constructive embodiment of the mechanism.