Field of the invention

The present invention relates to damper mechanisms for reducing the kinetic energy of a moving body, particularly damper mechanisms for use in damping translational movement of a reciprocating device, as well as apparatus including such damper mechanisms and the use of such mechanisms.

Background to the invention

In applications where actuators are configured for high speed reciprocating movement, for example, in machining or valving applications, the operating stresses imparted on the components controlled by the actuators due to the rapid accelerations and decelerations as a result of initiation of movement, or arrest of movement, especially where the latter are by travel limiting stops, may reduce longevity, or, may produce undesirable rebound.

It would therefore be desirable to dampen any sudden arrests or sudden initiated motion so that these may be more gradual, thereby reducing such operating stresses, and/or rebound, particularly where such starting or stopping movements occur frequently. Further, in arrangements where the deceleration involves an impact against a stop, it would be desirable to dampen such an impact.

Summary of the Invention

According to a first aspect of the present invention, there is provided a damper mechanism comprising:

a first part;

a second part configured to pivot relative to the first part about an axis, the first and second parts having first and second opposed cam surfaces respectively, wherein relative translational movement between the first and second parts from a first configuration to a second configuration (e.g. end position) results in rotation of the second part relative to the first part about the axis; and

a damper coupled to the second part so as to damp rotation of the second part relative to the first part.

In one embodiment, the first and second opposed cam surfaces define first and second profiles respectively that in combination are configured such that the point of contact between the first and second opposed cam surfaces reduces in distance from the axis as the first part (or cam piece) and second part (or cam piece) move from the first configuration to the second configuration. In one embodiment, the first and second opposed cam surfaces define first and second profiles respectively that in combination are configured to increase (e.g. continuously increase) the amount of rotation of the second part per unit translation (e.g. per unit stroke), as the first and second parts move from the first configuration to the second configuration (i.e. the rotation per unit stroke increases as the stroke progresses).

In one embodiment, the damper is a rotary damper (e.g. a linear or non-linear rotary damper) torsionally coupled to the second part (e.g. by an axle). For example, the damper may be a rotary paddle damper, where a paddle is confined to move within a fluid-filled cavity with viscous damping. The rotary damper may also use other effects to generate the retarding torque and may for example use friction to provide some or all of the retarding torque required to damp the mass associated with the rotating cam part. The damper may be any means that provides a non-linear retarding torque on the rotating cam part.

In one embodiment, the damper is a speed dependent damper configured to provide increased damping with increased angular velocity as the first and second parts move from the first configuration to the second configuration, where the rate of rotation (with respect to the relative translation (e.g. stroke) of the second part relative to the first part) continuously increases as the first and second parts move from the first configuration to the second configuration. A damper based on viscous damping will provide a resistive force proportional to the speed of the damper (linear damping).

There is further provided a damper mechanism comprising:

a first part;

a second part configured to pivot relative to the first part about an axis, the first and second parts having first and second opposed cam surfaces respectively, wherein relative translational movement between the first and second parts from a first configuration to a second configuration results in rotation of the second part relative to the first part about the axis; and

a damper coupled to the second part so as to damp rotation of the second part relative to the first part;

wherein the first and second opposed cam surfaces define first and second profiles respectively that in combination are configured such that the point of contact between the first and second opposed cam surfaces reduces in distance from the axis as the first and second parts move from the first configuration to the second configuration. The effect of the point of contact approaching the axis is that the moment arm (the distance between the pivot/axis and the point of contact) decreases and hence the reaction force generated by the first and second opposed cam surfaces (caused by the relative translational movement) increases as the first and second parts approach the second configuration, such that it is easier for the damper to damp the translation energy of the components. If, for example, the damper is arranged to provide a constant resisting torque throughout the stroke, this torque becomes progressively bigger in comparison with the generated torque and so can reduce the forces acting on a device driving the relative translational movement between the first and second parts and hence, reduce the likelihood of rebound or an abrupt stop as such a device is brought to a stop.

The effect of the point of contact approaching the (pivot) axis (i.e. the moment arm reducing) is that, as the stroke progresses, for a given small increment of stroke, the rotation per unit stroke increases as the stroke progresses. (The rotation per unit stroke can be shown to be inversely proportional to the moment arm.) Hence, when the moment arm is at its longest in the first configuration, relative translation will not generate much rotation of the second part, whereas as the stroke progresses, the relative translation generates progressively more rotation per unit stroke. If a speed dependent damper is used that increases damping force as a function of speed, the resisting torque will also increase as a function of speed. Hence, this effect can be exploited to provide a further enhancement of the effective damping action as the stroke progresses.

In a preferred embodiment, the first and second profiles are configured in combination such that the locus of the point of contact between the first and second opposed cam surfaces lies on a straight line (i.e. has a linear trajectory) passing through the axis. In this way, the first and second profiles are configured to minimise sliding therebetween (e.g. non-rubbing) at the point of contact between the first and second opposed cam surfaces. In this way, wear on the first and second cam surfaces may be reduced and the damping mechanism may be made available for use in unlubricated environments.

In one embodiment, one of the first and second profiles has an equiangular spiral geometry and the other is substantially planar (the only profile match to provide the aforementioned linear trajectory). These profiles are inherently configured such that the rate of rotation with stroke increases at an exponentially increasing rate as the first and second parts move towards the second configuration.

An equiangular spiral (also known as a logarithmic spiral or growth spiral) is a particular example of a curved profile with a radius of curvature that decreases in radius with decreased distance from the axis, but other curved profiles with this quality may also be used (and which may also lie on the said vertical locus so as to be non-rubbing).

Preferably, the spiral angle of the equiangular spiral profile is no more than 30°, more preferably no more than 20°, and ideally no more than 15°. Cam profiles with angles of no more than 30° avoid large bearing forces being exerted on components supporting the cam profiles. A constant angle of 8-12° has been found to give especially good results.

In one embodiment, one of the first and second profiles has a curved profile with a compound spiral (i.e. varying spiral angle) geometry. Where non-rubbing action is desired, the other profile will be a unique match for the selected compound equiangular spiral geometry (so as to achieve the afore-mentioned vertical locus for the contact points). The compound geometry may be selectively configured so as to achieve tuned damping as the first and second parts move from the first configuration to the second configuration.

Such a compound spiral geometry may include a section with a spiral angle of less than 5° (or less than 3°) so as to provide a rapid change in the damping action as the first and second parts translate relatively from the first configuration to the second configuration; it may be provided midway between those two configurations and allows a rapid switching action i.e. force reversal such that an accelerating moving device may rapidly become a decelerating one.

In a preferred embodiment, the second part is configured to rotate about an axis without translating relative thereto, and the first part is configured to translate relative to that axis. Conveniently, the second part rotates about an axis without translating relative thereto and the first part translates relative to that axis; this may be a stationary axis, or one that is relatively fixed in the context of the immediate damper mechanism. An embodiment with a (relatively) fixed axis means that the damper is easier to configure and there is likely to be less overall moving mass requiring damping by the damper.

Alternatively, the second part may be configured to rotate about the axis and translate relative to that axis; in that case, the first part may be stationary. The latter arrangement is likely to be more complex if the pivot axis is moving.

In one embodiment, the damper mechanism further comprises a stop to prevent further pivotal movement of the second part relative to the first part when the second part reaches the second configuration. In one embodiment, the damper mechanism further comprises a reset mechanism for returning the first and second parts from the second configuration to the first configuration.

A double-action damper mechanism may be provided which, in addition to any of the above features, further comprises:

a third part; and

a fourth part pivotal relative to the third part about a further axis and coupled to the damper or to a further damper, the third and fourth parts having third and fourth opposed cam surfaces respectively, wherein relative translational movement between the third and fourth parts from a third configuration to a fourth configuration results in rotation of the fourth part relative to the third part about the first defined or further axis. In this way, a bi-directional damper mechanism may be provided capable of providing damping to a reciprocating translation of a device.

The second and fourth parts may be rotatably coupled (e.g. by the axle) such that they rotate with one another. This provides the damper device with the additional benefit of being self-resetting thereby obviating the need for a dedicated reset mechanism.

In one embodiment, the first-defined axis and the further axis are co-axial such that the second and fourth parts pivot around a common axis.

In one embodiment, the third and fourth profiles are substantially identical to the first and second profiles respectively.

Conveniently, the first and second parts and the third and fourth parts are arranged symmetrically with respect to a mid-stroke position, where the end positions of the stroke correspond to the second and fourth configurations. In a particularly preferred embodiment, the first configuration of the first part and second part corresponds to the fourth configuration of the third and fourth parts, while the second configuration of the first part and second part corresponds to the third configuration of the third and fourth parts, such that a device only undergoes a linear reciprocating stroke within the ongoing constraint of the action of the double-acting cam mechanism.

Alternatively, a device may translate during a linear reciprocating stroke unhindered and only be acted upon by a double-acting damper mechanism that has the first and second parts, and third and fourth parts, respectively located. at each end of the that stroke.

In one embodiment, the first and third parts are sub-parts of a common component. In one embodiment, the first and second parts and the third and fourth parts are configured such that relative translational movement between the third and fourth parts from a third configuration to a fourth configuration causes the first and second parts to reset by moving substantially from the second configuration to the first configuration, and/or vice versa. Preferably, the damper mechanism is configured so that the inactive cam pair (e.g. first and second parts in the above case) are not in contact during the resetting i.e. without the first and second opposed cam surfaces making contact, and vice versa.

Conveniently, the fourth part is torsionally coupled to the same damper as the second part.

The third and fourth parts may have any one or more of the features specified above in respect of the first and second parts. In particular, it may be that:-

(i) the third and fourth profiles are configured in combination such that the locus of the point of contact between the third and fourth opposed cam surfaces lies on a straight line passing through the axis.

(ii) one of the third and fourth profiles has an equiangular spiral geometry and the other is substantially planar.

(iii) one of the third and fourth profiles has a compound spiral geometry.

(iv) the fourth part is configured to rotate about an axis without translating relative thereto, and the third part is configured to translate relative to that axis.

(v) a stop is provided to prevent further pivotal movement of the fourth part relative to the third part when the fourth part reaches the fourth configuration.

(vi) a reset mechanism is provided for returning the third and fourth parts from the fourth configuration to the third configuration.

There is further provided apparatus comprising a damper mechanism, as described above, and a device configured to follow a linear path, the device being configured to drive the relative translational movement between the first and second parts, and, if present, the third and fourth parts, thereby damping its own movement.

The damper mechanism may be configured such that the first and second parts, and/or the third and fourth parts, are reset in their respective first (or third) configurations by virtue of their motion being constrained with respect to the moving device.

For example, the device may be a reciprocating device and the damper mechanism a double action damper mechanism configured to provide damping at each end of the reciprocating stroke of the device. In particular, the apparatus may comprise robotic apparatus, reciprocating apparatus, such as, for example, high speed linear actuators, machining apparatus, valve-controlling apparatus or other apparatus involving repetitive, controlled movements of components, and optionally, comprises an actuator assembly forming part of or operatively linked to the damper mechanism.

The present damper may be used progressively to decelerate a relatively moving device or body, in particular, so as to lessen its impact, or the impact of a connected component, against a surface, stop or another body, and discourage rebound.

There is further provided the use of a damper mechanism as specified above to damp the motion of a moving device, wherein the damper mechanism comprises a first part, and a second part pivotable relative to the first part about an axis, the first and second parts having first and second opposed cam surfaces, respectively, wherein the moving device is configured to drive relative translational movement between the first and second parts from a first configuration to a second resulting in rotation of the second part relative to the first part about the axis, wherein a damper is coupled to the second part so as to damp rotation of the second part relative to the first part, thereby damping the relative translation movement with the result that the motion of the moving device is damped, optionally bringing it to a halt.

Thus, the present damper mechanism may be used progressively to decelerate a relatively moving device, in particular, so as to lessen its rebound or impact, or the impact of a connected component, against a surface, stop or another body.

Such a use may involve a damper mechanism or apparatus with any one or more of the features as specified above.

In addition, in accordance with the present invention, there is provided a damper mechanism comprising:

a first part;

a second part pivotable relative to the first part about an axis, the first and second parts having first and second opposed cam surfaces respectively, wherein relative translational movement between the first and second parts from a first configuration to a second configuration results in rotation of the second part relative to the first part about the axis; and

a damper for damping rotation of the second part relative to the first part;

wherein the first and second opposed cam surfaces define first and second profiles respectively that in combination are configured to increase (e.g. continuously increase) the rate of rotation of the second part relative to the first part as the first and second parts move from the first configuration to the second configuration (i.e. the rotation per unit stroke increases as the stroke progresses).

The present invention further provides any novel feature or combination of features described above.

Brief Description of the Figures

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of a damper mechanism in accordance with a first embodiment of the present invention;

Figure 2 shows a series of illustrations of the damper mechanism of Figure 1 as the second part moves from the first configuration to the second configuration;

Figure 3 is a detailed view of components of the damper mechanism of Figure 1 when the second part is in the first configuration;

Figure 4 is a graph of cam rotation φ plotted against cam translation x as the second part moves from the first configuration towards the second configuration;

Figure 5 shows graphs of predicted displacement, velocity and acceleration of a device connected to the damper mechanism of Figure 1 ;

Figure 6 is a detailed view of alternative cam components with more tailored profiles for a damper mechanism in accordance with a second embodiment of the present invention;

Figure 7 shows graphs of predicted displacement, velocity and acceleration of a device connected to the damper mechanism of Figure 6;

Figure 8 is a schematic view of a damper mechanism in accordance with a third embodiment of the present invention;

Figure 9 is a schematic view of a damper mechanism in accordance with a fourth embodiment of the present invention;

Figures 10-13 show components used in the construction of a damper mechanism in accordance with a fifth embodiment of the present invention;

Figure 14 shows the damper mechanism incorporating the components of Figures

10-13 when fully constructed; and,

Figure 15 is a schematic view of a damper mechanism in accordance with a sixth embodiment of the present invention. Detailed Description of Specific Embodiments

Figure 1 illustrates operation of a single action damper mechanism 10 according to a first embodiment of the present invention . This embodiment uses a constant angle cam arrangement and comprises a first translational part 20 connected to a device 30 with mass m _v and a second part 40 pivotable relative to the first part 20 about a fixed pivot axis P and torsionably coupled to a rotary paddle damper 50 having inertia J _p and configured to generate a damping moment M _f .

First and second parts 20, 40 have first and second opposed cam surfaces 22, 42 respectively whereby relative translational movement between the first and second parts 20, 40 from a first translational configuration x = 0 to a second translational configuration x _f results in rotation of the second part 40 relative to the first part 20 about the pivot axis P from a first angular position φ = 0 ° to a second angular position <jp _f .

Figure 2 are a series of illustrations at respective angular positions φ as the second part 40 rotates about the pivot axis P due to translation of first part 20 through its stroke from left to right (as shown by arrow).

By converting the translation of the first part, which may be over only a short (e.g. horizontal) stroke length, into a rotation, a torque is generated with a moment arm (perpendicular (e.g. vertical) distance from the axis to the line of action of the force) that may be selected to be of any desired length, depending on the height selected for the cam pieces, thereby amplifying the forces involved. Moreover, by selection of the respective cam profiles, the manner of the damping action may be "tuned" over the stroke length to achieve the desired velocity and accelerations in the device being damped.

As illustrated in Figure 2, the first and second profiles 24, 44 are configured such that the moment arm i.e. the height h of the line of contact (shown as a dotted line) between the first and second opposed cam surfaces relative to pivot axis P progressively reduces as the first and second parts 20, 40 move from the first configuration to the second configuration. This results in the torque generated by the first and second opposed cam surfaces 22, 42 decreasing as the first and second parts 20, 40 approach the second configuration, thereby progressively increasing the effective damping action of paddle damper 50.

As illustrated, first cam surface 22 has a first profile 24 that is substantially planar and second cam surface 42 has a second profile 44 that is curved with an equiangular spiral geometry (i.e. constant spiral angle geometry) that decreases in radius (of curvature) with decreased distance from pivot axis P (see discussion below). First and second profiles 24, 44 are in combination thus configured to exponentially increase the rate of rotation of the second part 40 relative to the first part 20 as the first and second parts 20, 40 move from the first configuration to the second configuration in response to a force F _a applied to device 30. This force may be applied throughout the entire stroke and may be of constant magnitude (e.g. where the device is a valve being moved by a pneumatic actuator). In this way, damping resistance generated by paddle damper 50 increases as the mechanism moves towards the second configuration (e.g. end position), thereby increasing the damping action of the mechanism as the translational movement between the first and second parts 20, 40 approaches the second configuration and the speed of rotation of second part 40 increases. This is turn progressively reduces the overall forces acting left to right in the stroke direction on device 30 and reduces the propensity for device 30 to rebound as it slows to stop in the second configuration. Further advantageously, the equiangular spiral geometry acts to reduce rubbing and consequential wear on the first and second opposed cam surfaces 22, 42 as there should be only rolling friction (i.e. minimal sliding) between the two surfaces at their point of contact. (The locus of the contact point between the two surfaces of the equiangular spiral cam arrangement follow a vertical line through the pivot during the pivoting of the curved cam piece such that the contact points of each piece instantaneously share the same velocity vector throughout the pivoting and hence do not move relative to one another.) Such a damper mechanism may therefore be suitable for use in an unlubricated environment.

A single paddle, paddle damper has been shown although other paddle arrangements (e.g. two opposed paddles) or other types of rotary damper may alternatively be used. Where a paddle damper is used, it is possible to tune the damper's action to achieve the desired degree of resistance, e.g. overall or throughout different parts of the stroke. For example, GB343213 teaches a paddle damper where the degree of resistance offered to the paddle by a fluid in a dashpot may be adjusted as required by adjustment of the proximity of the dashpot walls (i.e. non-linear clearance). Non-linear damping may also be achieved by using a pattern of holes arranged within the cavity to effect a change in the damping characteristics, or squeeze film effects at each end of the cavity.

Device 10 as illustrated is a single acting device (damping in one direction). It may be a one-shot device, or a device that acts occasionally and requires resetting thereafter. In that case, a reset mechanism, for example, a (linear or rotary) return spring may be provided for returning the first and second parts 20, 40 from the second configuration to the first configuration. This may be suitably applied to any appropriate component of the coupled components, for example, as a rotary spring acting about point P attached for example to the paddle damper or second part 40 or other component rotatably coupled therewith, or a linear spring attached to the first part 20. The reset mechanism may be a mechanism built in to the device 30 whose motion is being damped e.g. by an appropriately configured link, cam, dog or gab or the like.

Figure 3 shows in more detail the first and second profiles 24, 44 at <p _f = 0° of the two cam parts/pieces of the constant spiral angle cam. In this embodiment, second cam surface 42 has a constant spiral angle of 10° (the same angle as the lowermost vertex of part 20) and a height of 0.022847m. This rotates by an angle <p _f = 50° over a 4 mm stroke.

Figure 4 is a graph showing the angle of rotation φ of second part 40 relative to the first part 20 plotted against translation x of first part 20 (i.e. stroke) relative to pivot axis P. It therefore shows how the angle of rotation φ of the spiral angled cam piece 40 about the pivot changes (i.e. continuously increases) as a result of the extent of the stroke of the translating cam piece 20. For the first half of the stroke, second part 40 rotates through around 7° and around 43° over the second half of the stroke (i.e. to reach the second configuration). This strongly non-linear (actually logarithmic) relationship acts to bring device 30 to a smooth controlled stop.

Figure 5 shows graphs of predicted displacement, velocity and acceleration of device 30 over the stroke based on a simulation model of damper mechanism 10. As illustrated, the time to complete the stroke is predicted to be around 5.7 milliseconds and the final kinetic energy of device 30 is small as the first and second parts 20, 40 approach the second configuration. In practice, the stroke completion is likely to be swifter than illustrated since other damping mechanisms (such as frictional loss in bearings/inertial fluid films) which have not been simulated are likely to provide additional damping.

In accordance with a second embodiment of the invention, Figure 6 depicts a damper mechanism with a variable spiral angle cam (or "compound cam"). The two cam pieces 7 and 9 have respective selectively configured profiles that modify the damping action over the stroke in order to achieve a tailored damping action, as illustrated with reference to Figure 7 below.

In this mechanism, both cam pieces have highly curved and only marginally curved (i.e. nearly straight) sections and together are matched (i.e selectively paired) so as to achieve substantially non-rubbing wear, by virtue of the locus of the contact point again describing a vertical line passing through the pivot (a selected profile requiring a unique corresponding other profile), as in the case of the constant angle spiral cam. However, by selectively varying the spiral angle of the cam it is possible to control the rate of change of the height of the contact point (i.e. the "moment arm" of the actuator force) throughout the stroke and thus modify the motion of a moving device that is being decelerated by the damper mechanism. In this preferred compound cam, one cam has a spiral angle varying during the stroke from 1 ° to 30°, the upper and lower ends having angles of about 30°, while the nearly straight mid-section has a spiral angle of only about 1 °.

Figure 7 shows graphs of predicted displacement, velocity and acceleration of a device being decelerated by this damper mechanism over the stroke, based on a simulation model. It will be appreciated that the taller, compound cam is capable of achieving a larger initial acceleration due to the long moment arm at the start of the stroke, and because of the small spiral angle over the mid-section, the moment arm rapidly reduces with stroke so as to permit fast switching between acceleration and deceleration. If it is desired to minimise component stress for example in a device being actuated (e.g. reciprocated) over a short travel time, then it will usually be desirable to use constant acceleration to the midpoint, for maximum velocity at mid-stroke, and constant deceleration from then until the end of the stroke. Such an optimal motion profile is nearly achieved as shown in Figure 7.

Figure 8 is a sectional view of a third embodiment of the invention involving an alternative single cam mechanism where a pivoting cam piece is caused to translate with a body it is decelerating, the translation causing it (by virtue of a second static cam piece) to rotate about a pivot point that is not stationary. This embodiment again uses an equiangular spiral cam piece in combination with a planar cam piece.

Referring to Figure 8, the damper mechanism 10' thus comprises a second translation part or cam piece 40' which translates from a to c during its stroke and a first stationary part or cam piece 20' that provides a static reaction force thereagainst, so as to cause part 40' to pivot about a moving pivot axis P' as it translates. Second translation part 40' is coupled to a device (not shown) requiring damping so that they translate together over the stroke, but part 40' is still free to pivot and that part is also coupled to a rotary paddle damper (also not shown) where the energy is dissipated. For example, the paddle damper and translation part 40' may be torsionally coupled to a shaft so that they rotate together, while the device is rigidly coupled to, or even integrally formed with, a bearing, housing or the like supporting that shaft. Since the pivot axis P' and associated components (e.g. damper) are translating, which leads to complexity, this embodiment is of more limited application.

As in the first embodiment, first and second parts 20', 40' define first and second opposed cam surfaces 22', 42' respectively with a substantially planar first profile 24' and a curved equiangular spiral geometry second profile 44' as before, the first and second profiles 24', 44' again being in combination configured to decrease the height of the point of contact (labelled Sa-Sc) as second part 40' pivots relative to first part 20' from a first configuration to a second configuration and hence, continuously increase the rate of rotation. In that regard, damper mechanism 10' operates in the same manner as damper mechanism 10.

It is helpful to consider the forces involved in an example with a static cam piece. Three positions along the stroke axis are highlighted, a, b and c. These stroke locations are associated with contact points between the cam surface and the counterface defined by distances normal from the stroke axis of Sa, Sb and Sc.

If a force is applied to point p to move it from left to right, a torque is produced about point p as a result of the rolling of the spiral surface on the counterface. If a rotary damping device (eg, friction, viscous damper etc) is torsionally coupled to point p then this torque may be reacted by the damper, ie, the rotary motion is then resisted by the damper and as this rotary motion is a direct result of the linear motion of point p, the linear motion is also resisted, ie, damped.

If, as an option, the force on point p is maintained for the entire stroke (e.g. driven by an actuator), then to bring this point to rest in a damped, ie, non abrupt manner, the effect of the resisting torque from the damping device needs to increase as the stroke progresses. This is achieved by the intrinsic action of the two rolling counterfaces. When point p is at position a, the torque resulting from an applied left to right force F as point p is Sa x F. Inspection of the figure shows that, similarly, as the stroke progresses through points b and c the following inequality will result:

Sa x F > Sb x F >Sc x F

This shows that the torque induced by an applied force, F, at point p reduces as the stroke progresses from left to right. If (for example) a constant resisting torque, Tr, is applied about point p by the chosen damping device then the resisting force, Fr, about point p progresses thus:

Tr/Sa < Tr/Sb < Tr/Sc

The resisting force therefore increases with the stroke as compared to the constant driving force, leading to an overall deceleration.

It is also evident from the diagram that as the stroke progresses, for a given small increment of stroke, the rotation per unit stroke increases as the stroke progresses. If a speed dependent damping device were optionally to be used, for example a damper that increases damping force as a function of speed then the resisting torque and hence resisting force will also increase as a function of speed. The resulting increase of damping of the motion of point p with speed then also becomes a natural function of the rolling geometry of the two rolling counterfaces. The mechanism 10' optionally includes a stop 60 to prevent further pivotal movement of second part 40' relative to first static part 20' when second part 40' reaches the second configuration. However, the stop 60 could act against another component torsionally coupled to the second part 40', for example, a brake lever, or even the rotary paddle damper, so as indirectly to limit the translation of part 40'. Again, the cam mechanism may be a one-shot mechanism or may include a reset mechanism (not shown) for returning the second part 40' from the second configuration to the first configuration for occasional re-use or for returning it for more frequent re-use (e.g. repeated reciprocating movement).

Figure 9 shows a bi-directional damper mechanism 100 comprising first and second cam mechanisms 110, 210 according to a fourth embodiment of the invention.

First cam mechanism 110 comprises a first translational part 120A/first pivotable part 140A pairing, the first translational part 120A being connected to a reciprocating device (not shown) and the first pivotable part 140A being mounted on a rotatable axle 150 defining pivot axis P" and having coupled at one end thereof a rotary paddle damper 160. First translational part 120A/first pivotable part 140A pairing includes first and second opposed cam surfaces 122A, 142A respectively defining a substantially planar first profile 124A and a curved equiangular spiral geometry second profile 144A, the first and second profiles 124A, 144A in combination being configured to increase the rate of rotation and decrease the height of the point of contact as first pivotable part 1 0A pivots relative to first translational part 120A from a first configuration to a second configuration.

Second cam mechanism 210 comprises a second translational part 120B/second pivotable part 140B pairing, the second translational part 120B being connected to the reciprocating device and the second pivotable part 140B being mounted on rotatable axle 150. Second translational part 120B/second pivotable part 140B pairing defines third and fourth opposed cam surfaces 122B, 142B respectively defining a substantially planar first profile 124B and a curved equiangular spiral geometry second profile 144B identical to first and second profiles 124A, 144A but each facing in the opposite direction thereto, whereby the third and fourth profiles 124B, 144B in combination are configured to increase the rate of rotation and decrease the height of the point of contact as second pivotable part 140B pivots relative to second translational part 120B from a third configuration to a fourth configuration.

In use, first cam mechanism 110 operates to provide a damping action in a first direction during a first phase of a reciprocating movement of the reciprocating device to be damped and second cam mechanism 210 operates to provide a damping action in a second direction opposed to the first direction during a second phase of the reciprocating movement of the reciprocating device, with rotation of the first pivotable part 140A during transition from the first configuration to second configuration causing rotation of the second pivotable part 140B from the fourth configuration to the third configuration to reset the second cam mechanism 210 ready for damping when the motion of the reciprocating device next changes direction. Similarly, rotation of the second pivotable part 140B during transition from the third configuration to the fourth configuration causes rotation of the first pivotable part 140A from the second configuration to the first configuration to reset the first cam mechanism 1 10 ready for damping when the motion of the reciprocating device returns back to the previous direction.

The first translational part 120A/first pivotable part 140A pairing are configured to move substantially from the second configuration to the first configuration without the first and second opposed cam surfaces 122A, 142A making contact and the second translational part 120B/second pivotable part 140B pairing are configured to move substantially from the fourth configuration to the third configuration without the third and fourth opposed cam surfaces 122B, 142B making contact. However, at any time at least one of the opposed cam surface pairs are in contact so there is no discontinuous behaviour.

Figures 10-13 show components for forming a bi-directional damper mechanism 200 according to the fifth embodiment of the invention, as illustrated in detail in Figure 14, based on the principle described in relation to the double cam mechanism of Figure 9.

Bi-directional damper mechanism 200 includes a first cam mechanism 210 including a first translational part 220A/first pivotable part 240A pairing, the first translational part 220A being connected to a reciprocating device (not shown) and the first pivotable part 240A forming part of a two-way cam component 245 mounted on a rotatable axle 250 defining pivot axis P'" and having coupled at one end thereof a rotary paddle damper 260 configured to pivot over a predetermined angular range within a fluid-filled recess 270 defining opposed paddle stops 272, 274. First translational part 220A/first pivotable part 240A pairing includes first and second opposed cam surfaces 222A, 242A respectively defining a substantially planar first profile 224A and a curved equiangular spiral geometry second profile 244A, the first and second profiles 224A, 244A in combination being configured to increase the rate of rotation and decrease the height of the point of contact as first pivotable part 240A pivots relative to first translational part 220A from a first configuration to a second configuration.

Second cam mechanism 220 comprises a second translational part 220B/second pivotable part 240B pairing, the second translational part 220B being connected to the reciprocating device and the second pivotable part 240B again forming part of two-way cam component 245. Second translational part 220B/second pivotable part 240B pairing defines third and fourth opposed cam surfaces 222B, 242B respectively defining a substantially planar first profile 224B and a curved equiangular spiral geometry second profile 244B identical to first and second profiles 224A, 244A but each facing in the opposite direction thereto whereby the third and fourth profiles 224B, 244B in combination are configured to increase the rate of rotation and decrease the height of the point of contact as second pivotable part 240B pivots relative to second translational part 220B from a third configuration to a fourth configuration.

In use, bi-directional damper mechanism 200 operates in the same way as mechanism 100.

In accordance with a sixth embodiment of the invention, Figure 15 depicts a damper mechanism with two interacting cam pieces 82 and 84 with respective planar and circular cam profiles. Cam piece 82 is coupled to a moving device (not shown) and translates from left to right remaining in contact with circular cam piece 84, which is configured to rotate about the illustrated fixed pivot point. Thus, linear motion input is converted into rotational output of curved cam piece 84 about the pivot. That cam piece is coupled to a damper (e.g. a rotary damper) that resists the rotation, thereby damping the linear motion of cam piece 82 and hence, damping the motion of the device.

The moment arm of the contact point moves down towards the pivot as the cam pieces move from a first configuration to a second (end) configuration (where they may come to a halt with the assistance of a stop), and hence, the reaction forces generated by the opposed cam profiles increase making it progressively easier for the damper to damp the translating motion. Again the reduction in moment arm means that as the stroke progresses, for a given small increment of stroke, the rotation per unit stroke increases.

In this embodiment, the locus of the contact point does not follow a straight line towards the pivot. The instantaneous velocities of each piece at the contact point is marked with arrows and it may be seen that the contact point on the circle moves perpendicular to a line joining it to the fixed pivot and hence the relative velocity between the two pieces is non-zero and there will be rubbing wear. This may be acceptable in a lubricated environment, especially where the mechanism is used infrequently, and it may exhibit very effective damping.

In this "rubbing" embodiment, a greater variety of cam profiles are possible (since the locus of contact is not constrained to a linear trajectory), but otherwise the choice of associated damper, or the choice of which cam piece moves or rotates may be as described above for the earlier non-rubbing embodiments.

It will be appreciated that the damper mechanism according to the invention comprises a cam mechanism designed to convert a linear (motion) input into a rotary (motion) output so as to allow translational energy from a moving device to be transferred into rotational energy that can be dissipated by means of a suitable damper, where the rate at which the energy is transferred can be controlled, and indeed tuned, by selection of suitable interacting cam profiles of the cam mechanism. Moreover, spiral geometry profiles may be used in order to provide only rolling contact between the interacting profiles, thereby reducing wear and making the damping apparatus suitable for unlubricated environments. Furthermore, compound spiral geometries (where the spiral angle changes with the stroke) may be utilised in order to achieve tuned damping over the stroke.

While the invention has been described by reference to specific embodiments, it should be understand that the invention is not limited to the described embodiments and numerous modifications may be made within the scope of the present invention. Thus, alternative single-action or double-action damper mechanisms may also be used to those illustrated and alternative dampers may be employed to the single paddle, paddle dampers illustrated in the present embodiments.