Improved actuation apparatus

Abstract

An actuation apparatus which has a support structure having a first end and a second end, a first end piece and a second end piece coupled to the respective first and second ends of the support structure, each end piece being coupled to the support structure by a set of actuators. The apparatus has a central portion which is at least partially located in the support structure, the central portion having a first end and a second end coupled to the first and second end pieces respectively. The set of actuators comprises three or more actuator elements, which are symmetrically positioned on the end piece and extend substantially radially for connection with the support structure, and, when coupled and in its natural position, the end piece is offset with respect to the support structure so as to be non-coplanar, and wherein applying a control signal to one or the actuator elements moves the moveable element with respect to the support structure and wherein the central portion has a dimension which is variable to change the polar moment of inertia of the actuation apparatus.

Description

[0001] Title

[0002] Improved Actuation Apparatus

[0003] Field

[0004] The present invention relates to an actuation apparatus and in particular an actuation apparatus which has multiple degrees of freedom of movement and which is suitable for controlling movement of the apparatus or transmitting movement to a component or work piece.

[0005] Background

[0006] There are many applications for devices which can control or transmit movement based on a control signal.

[0007] Haptic technology (also kinaesthetic communication or 3D touch) is technology that can create an experience of touch by applying forces, vibrations, or motions to the user. These technologies can be used to create virtual objects in a computer simulation, to control virtual objects, and to enhance remote control of machines and devices (telerobotics). Haptic devices may incorporate tactile sensors that measure forces exerted by a user on the interface.

[0008] Single or dual frequency haptics are often used to give a user feedback confirmation of a button press, action, or to raise an alert. An example is a touch screen in a vehicle where a haptic device may be mounted on the rear of the screen, so when a user presses a virtual button on the screen the haptic device can vibrate to give confirmation to the user, through their fingertip, that the touch has been registered. For simple screens and buttons this response is adequate, but with more and more adoption of multifunction screens, buttons and multiple actions possible from one touch point, it is desirable to have a variety of haptic responses depending on which particular function has been pressed / activated by the user. Another example is a handheld game controller where players feel a haptic response though individual buttons or the whole controller body depending on some action or command within a game.Haptics used for vibration feedback in applications are usually of the (ERM), linear resonant actuator (LRA), or piezo type. All of these generally operate in one axis, and to achieve more than that multiple actuators have to be used. The LRA type has a vibration motor producing an oscillating force along a single axis. Multiple actuators are required to create movement along multiple axes. An example of this type of device is an ALPS Alpine haptic Heavy with 2 axis operation, one at 160Hz and the other at 320Hz. These are commonly used in computer game handheld controllers and behind touchscreens in automotive applications.

[0009] In both these applications the incumbent LRA or ERM technology is limited to single or dual axis response, and within a very limited operationally effective frequency range that, in the case of LRA, is fixed. In order to convey a variety of haptic feedback to the user, multiple separate haptic devices with different resonant frequencies have to be used which add cost, complexity and take space, none of which are desirable. Therefore, there is a requirement to create an improved mechanism.

[0010] WO2023105213 describes a mechanism fora camera lens that uses SMA elements to rotate a central piece which, in turn moves the lens towards or away from the fixed part and is reset via biasing mechanism. WO2019162694 discloses a fully floating lens located by 8 planar SMA wires in which a control system detects and processes resistance values in order to obtain positional control, feedback for closed loop control, and restriction of movement to a desired envelope. It is designed around a mobile phone camera where very limited physical movement is required.

[0011] Summary

[0012] It is an object of the invention, as defined in the appended claims, to overcome at least one of the above-referenced problems.It is also an object of the present invention to create an apparatus which may operate with an extended range of movement, over multiple degrees of freedom, over a wider range of frequencies and / or with the opportunity to vary the resonant frequency within a single device.

[0013] In accordance with a first aspect of the invention there is provided an actuation apparatus comprising:

[0014] a support structure having a first end and a second end;

[0015] a first end piece and a second end piece coupled to the respective first and second ends of the support structure, each end piece being coupled to the support structure by a set of actuators;

[0016] a central portion which is at least partially located in the support structure, the central portion having a first end and a second end coupled to the first and second end pieces respectively;

[0017] a controller which provides a control signal;

[0018] wherein the set of actuators comprises three or more actuator elements, which are symmetrically positioned on the end piece and extend for connection with the support structure, and, when coupled and in its natural position, the end piece is offset with respect to the support structure so as to be non-coplanar, and wherein applying a control signal to one or the actuator elements moves the central portion with respect to the support structure and wherein the central portion has at least one dimension which is variable so as to change the polar moment of inertia of the actuation apparatus with respect to rotation around one or more axes.

[0019] In at least one embodiment, the dimension is the length and / or breadth and / or height of the central portion to change the polar moment of inertia in one or more axes.

[0020] In at least one embodiment, variation in polar inertia in one or more axes provides the variation in natural frequency and therefore the frequency response.

[0021] In at least one embodiment, the central portion comprises one or more moveable parts.In at least one embodiment, a plurality of moveable parts is moveable with respect to one another to change the polar moment of inertia of the actuation apparatus.

[0022] In at least one embodiment, the moveable parts are moveable linearly.

[0023] In at least one embodiment, the moveable parts are moveable in two dimensions.

[0024] In at least one embodiment, the moveable parts are moveable in three dimensions.

[0025] In at least one embodiment, the moveable parts dynamically change their linear spring stiffness to offer one option to alter the resonant frequency of the apparatus.

[0026] In at least one embodiment, an SMA material is coupled to an antagonistic element.

[0027] In at least one embodiment, the antagonistic element is a second SMA material.

[0028] In at least one embodiment, the antagonistic element is a return spring.

[0029] In at least one embodiment the central portion comprises a shape memory alloy SMA material.

[0030] In at least one embodiment, the SMA comprises a straight wire.

[0031] In at least one embodiment, the SMA comprises a helix (spring),

[0032] In at least one embodiment, the SMA comprises a U-shaped device.In at least one embodiment, the SMA elements are selectively and partly or fully actuated in order to dynamically change the effective spring stiffness, and therefore the resonant frequency, of the system in one or more degrees of freedom.

[0033] In at least one embodiment, the SMA is a two-way trained SMA element wherein the dimensions of the central portion are varied by means of the two-way shape memory effect.

[0034] Advantageously, the present invention may be used as a dynamically adjustable haptic device giving variable frequency and haptic behaviours in 3 translation, 3 rotation, or any combination of those.

[0035] In at least one embodiment, the first and second end pieces are rigidly connected to the central portion.

[0036] In at least one embodiment, the offset is defined by the distance between the endpiece and a plane intersecting the end piece and parallel to the corresponding support structure.

[0037] In at least one embodiment, the actuators extend substantially radially from the end piece.

[0038] In at least one embodiment, the offset is defined by the angle between the endpiece and a plane intersecting the end piece and parallel to the corresponding support structure.

[0039] In at least one embodiment, the support structure comprises a frame.

[0040] In at least one embodiment, the support structure is substantially cubic in shape.

[0041] In at least one embodiment, the support structure is substantially cuboid in shape.In at least one embodiment, the support structure is substantially cylindrical in shape.

[0042] In at least one embodiment, the moveable element comprises a coupling for connecting the moveable element to an external device.

[0043] In at least one embodiment, the actuator element comprises a single actuator member.

[0044] In at least one embodiment, the actuator element comprises at least two actuator members of which at least two are nonparallel.

[0045] In at least one embodiment, at least two actuator members cross over one another.

[0046] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy material.

[0047] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy wire.

[0048] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy wire in tension.

[0049] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy element under compression.

[0050] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy wire operating in one way shape memory effect.

[0051] In at least one embodiment, the actuator member is, at least in part, a shape memory alloy wire operating in two way shape memory effect.In at least one embodiment, the coupling is a recess for insertion of at least part of the external device.

[0052] In at least one embodiment, the coupling features a magnetic interface for coupling of an external device.

[0053] In at least one embodiment, the external device is a user interface.

[0054] In at least one embodiment, the external device is a utensil.

[0055] In at least one embodiment, the external device is a mass.

[0056] In at least one embodiment, the control signal is provided by a motion detection system.

[0057] In at least one embodiment, the actuation apparatus is contained in a housing and the motion detection system detects movement of the housing and controls movement of the external device in the moveable element using the sets of actuators in response to said detected movement.

[0058] In at least one embodiment, the control signal transmits a haptic control signal to the actuation apparatus.

[0059] In at least one embodiment the haptic control system controls the sets of actuators to provide feedback to the user interface.

[0060] In accordance with a second aspect of the invention there is provided a haptic device which comprises an actuation apparatus in accordance with the first aspect of the present invention.Brief Description of the Drawings

[0061] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a schematic end view which shows an example of part of an actuation apparatus in accordance with the present invention;

[0062] Figure 2 is a schematic end view which shows an example of part of an actuation apparatus in accordance with the present invention;

[0063] Figure 3 is a schematic end view which shows an example of part of an actuation apparatus in accordance with the present invention;

[0064] Figure 4 is a schematic end view which shows an example of part of an actuation apparatus in accordance with the present invention;

[0065] Figure 5 is a top view of an actuation apparatus in accordance with the present invention;

[0066] Figures 6a to 6d describe an example of the present invention with variable polar moment of inertia;

[0067] Figures 7a to 7c show the example of figures 6a to 6d in a model from which polar moment of inertia values have been calculated as examples; Figures 8a to 8f are schematic diagrams which show features similar to those of figure 6;

[0068] Figures 9a and 9b are schematic diagrams which illustrate the possibility of using multiple orthogonal mechanism with two masses moving axially per axis to change the inertia in accordance with the present invention; and

[0069] Figure 10 is a schematic diagram of a control system 231 for the present invention.

[0070] Detailed Description of the Drawings

[0071] In at least one embodiment, the present invention provides an actuation apparatus which uses two sets of actuator arrays, capable of at least 3 degrees of freedom of movement and configured to be operated in co-operation with each other to significantly increase the range of movement and give multiple degrees of freedom of movement. The actuator apparatus may be used in numerousapplications as an actuation system. The central portion of the actuator has a dimension which is variable to change the polar moment of inertia of the actuation apparatus.

[0072] Advantageously, variation in polar inertia in one or more axes provides the variation in natural frequency and therefore the frequency response. Polar Moment of Inertia is a measure of an object's capacity to oppose or resist torsion when some amount of torque is applied to it on a specified axis. Polar Moment of Inertia also known as the second polar moment of area is a quantity used to describe resistance to torsional deformation. It is generally denoted as Iz or J.

[0073] For example, when related to haptic resonant devices that use angular oscillation rather than linear, this polar inertia defines how far from the virtual centre of rotation the effective mass lies. This in turn has a direct effect on the resonant frequency, the system behaving as a mass-spring-damper system. With the system as described herein the actuators which change the polar moment of inertia of the central portion are also capable of dynamically changing their spring stiffness which also effects the effective resonant frequency. The actuator configuration allows linear, rotational, or a combination, in up to 6 degrees of freedom, for the central portion movement and resonance.

[0074] In at least one embodiment, the actuator elements of the present invention may comprise shape memory alloy wires in tension as the individual actuators to allow a very small size and low power consumption. It will be appreciated that the overall mechanism described and claimed herein may be actuated by any suitable means. For example, hydraulic cylinders, linear ball screw actuators, piezo, springs, bimetal strips or any other method may be used to control movement of the moveable element and end piece with respect to the support structure / frame.

[0075] SMA materials in compression may also be used. An actuation apparatus made in accordance with the present invention may be of any suitable size, for example,the present invention has applications in microelectromechanical (MEMs) devices at micron scale to much larger scale heavy industrial applications.

[0076] Advantageously, by using two sets of actuators some distance apart, a much greater range of movement may be achieved and with up to 6 degrees of freedom (translation in X, Y, Z, and rotation in X, Y and Z). This gives a much improved user experience and extends the range of operation of the devices.

[0077] In at least one embodiment, the apparatus of the present invention may be attached to a work piece, such as a utensil, for application as an anti-tremor device. In addition, the work piece may be a mass rather than a utensil, in which case, the apparatus may be used in a low cost and energy efficient haptic device with up to 6 degrees of freedom.

[0078] In some embodiments of the present invention, a symmetrical or asymmetrical pattern of actuator elements, such as SMA wires, may be used in pairs where each wire is non-parallel to its partner. In addition, having a non-planar three-dimensional array allows for the use of 3 or 4 pairs arranged an equal angle apart (90 or 120 degrees in this instance) to create a balanced system at rest. The actuator elements are anchored to a frame or support structure and to a movable element such as a beam which is to be manipulated in space.

[0079] The invention may use 3 actuator elements in a set of actuators and two sets, one at each end of the moveable element. In principle there is no upper limit to the number of actuators within an array and the number of arrays in the system.

[0080] Figure 1 is a schematic end view of an example of an actuation apparatus in accordance with the present invention and illustrates the overall geometry of an example of the present invention. The central portion with variable dimension is not shown in this diagram.

[0081] In particular, figure 1 shows one end of the actuation apparatus 1. The actuation apparatus 1 comprises a support structure or frame 3 at the first end 5, a first endpiece 9, a set of actuators 13 with actuator elements 21, 23 and 25. In this example three actuator elements are shown and the axes of symmetry 29 are shown with an angle between the actuator elements being approximately 120°. In this example, each actuator element comprises a single actuator, for example, a wire or other similar component.

[0082] Figure 2 is a schematic end view of an example of an actuation apparatus in accordance with the present invention and illustrates the overall geometry of an example of the present invention. The central portion with variable dimension is not shown in this diagram. In particular figure 2 shows one end of the actuation apparatus 31. The actuation apparatus 31 comprises a support structure orframe 33 at the first end 35, a first end piece 39, a set of actuators 43 with actuator elements 51 , 53 and 55 and 57. In this example four actuator elements are shown and the axes of symmetry 59 are shown with an angle between the actuator elements being approximately 90°. In this example, each actuator element comprises a single actuator, for example, a wire or other similar component.

[0083] Figure 3 is a schematic end view of an example of an actuation apparatus in accordance with the present invention and illustrates the overall geometry of an example of the present invention. The central portion with variable dimension is not shown in this diagram. Figure 3 shows one end of the actuation apparatus 32. The actuation apparatus 32 comprises a support structure orframe 34 at the first end 36, a first end piece 40, a set of actuators 44 with actuator elements 46, 48 each of which have 2 actuator members 50. In this example four actuator members 50 are shown connected tangentially to the end piece 40.

[0084] Figure 4 shows an example of the present invention with actuator elements in pairs. These figures also illustrate the overall geometry of an example of the present invention. The central portion with variable dimension is not shown in this diagram.

[0085] Figure 4 is a schematic end view of an example of an actuation apparatus in accordance with the present invention. In particular figure 4 shows one end ofthe actuation apparatus 61. The actuation apparatus 61 comprises a support structure or frame 63 at the first end 65, a first end piece 69, a set of actuators 73 with actuator element 81, 83 and 85 and 87. In this example four actuator elements are shown and the axes of symmetry 89 are shown with an angle between the actuator elements being approximately 90°. In this example, the actuator element comprises a pair of intersecting actuator members for example, a wire or other similar component. The axis of symmetry 89 which defines the average position of the pairs of actuator elements is shown. The line of actuation is radial through the centre of the beam. In other embodiments, the line of actuation may be offset.

[0086] Figure 5 describes an example of the present invention for use as a haptic feedback mechanisms. It shows a structure 101 comprising the end s 109, 111, the central portion 115 which comprises a central beam 116 and a pair of blocks 118 positioned either side of the central beam adjacent to the end pieces 109 and 111. Figure 5 also shows a first end 105 of the frame 103, a first end piece 109, sets of actuators 113 with actuator elements 121, 123, 125 and 127 are shown and a second end 107 with actuator elements labelled 123, 125 and 127.

[0087] Figures 6a to 6d describe an example of the present invention with variable polar moment of inertia. Figure 6a is a perspective view and shows a device 131 comprising the end piece 139, 141, the central portion 145 which comprises a central beam 146 and a pair of blocks 148 positioned either side of the central beam adjacent to the end pieces 139 and 141. The frame at the first end 135, a first end piece 139, sets of actuators 143 and central beam 146 of the movable element 145 and actuator elements 151 and 153. The second end 137 with similar end piece 141 and a corresponding set of actuators 157 and 159.

[0088] In this example, the central beam 146 is suspended via actuator elements 151, 153, 157 and 159 and is either made from SMA, or is in two parts interconnected by an actuator of variable length, which could be made from SMA. This allows the overall dimension or dimensions to be changed dynamically, either at high or low frequency. By changing the dimensions this will also change the polarmoment of inertia in respect to rotation around both the axes situated orthogonally to the axis in which the dimension of the central portion orfloating beam assembly has been changed. Therefore, in a haptic resonant system this will change the frequency at which resonance occurs in those orthogonal axes. This system can therefore be used as a dynamically adjustable haptic device giving variable frequency and haptic behaviours in up to 3 translation, 3 rotation, or any combination of those provided suitably arranged variable dimension positional masses are positioned on 2 or all 3 of the axes.

[0089] During operation, the length of the central beam 146 can be varied to change the polar moment of inertia and therefore dynamically alter the resonant frequency. This is desirable to give different types and levels of haptic feedback but in one single haptic mechanism device. The central beam can even act as a resonator itself if the actuator is, for example a piezoelectric device which would give the effect of a multi-resonant system.

[0090] Figure 6b shows the device with the central beam in a first position in which the device 131 has a fixed linear (axial) inertia value of A Kg.m2, and a rotational moment of inertia about its centre of mass of B Kg.m2which is variable.

[0091] In figure 6c, the central portion 146 is an SMA material activated to reduce its length. Consequently, the central portion 146 and the overall device becomes shorter.

[0092] One method for achieving this reduction of length is to use a two-way trained shape memory alloy element. In this example we can apply an electrical current to the shape memory alloy, heating it to above the transition temperature, at which point it will revert to the hot memory state, which could be pre-trained as the shorter dimension. Upon removal of the joule heating the shape memory alloy will cool to ambient temperature and revert back to the previously trained ambient temperature (cooler) trained length.This change in length has the effect of not changing the axial linear inertia (A Kg.m2) but the rotational moment of inertia around a virtual centre reduces, as the effective distance of the two outer masses has reduced. Therefore, the rotational moment of inertia is less than B Kg.m2.

[0093] In figure 6d, the central portion 146 is an SMA material activated to increase its length. Consequently, the overall assembly becomes longer which has the effect of not changing the axial linear inertia (A Kg.m2), but the rotational moment of inertia around a virtual centre increases, as the effective distance of the two outer masses has increased, Therefore, the rotational moment of inertia is more than B Kg.m2. The length of the central portion 146 may be adjusted dynamically to vary the moment of inertia and frequency response of the device.

[0094] Figures 7a to 7c and the following tables show example calculations of the change in moment of inertia for the device of 6a to 6c where the central beam length is 5mm (fig.7a, 10mm (Fig.7b) and 20mm (fig.7c). To keep the central actuator mass constant the Computer Aided Design model used a fixed mass of 2grams, and the overall floating assembly has a mass of 5.07grams.

[0095] The effect of changing this element length can clearly be seen by comparing the variation in values of Py, Pz, Lxx, Lyy, and noting that the values of the remaining parameters stay the same.

[0096] 5mm

[0097] Mass = 5.07 grams

[0098] Centre of mass: (mm) X = -4.37 Y = 19.01 Z = -10.61

[0099] Principal axes of inertia (denoted as Px, Py, Pz) and principal moments of inertia (denoted as lx, ly, Iz): (grams* mm2) taken at the centre of mass.

[0100]

[0101] Moments of inertia: (grams. mm2)Taken at the centre of mass and aligned with the output coordinate system.

[0102]

[0103] 10mm

[0104] Mass = 5.07 grams

[0105] Centre of mass: (mm) X = -4.37 Y = 19.01 Z = -10.61

[0106] Principal axes of inertia and principal moments of inertia: (grams. mm2) taken at the centre of mass.

[0107]

[0108] Moments of inertia: (grams. mm2)

[0109] Taken at the centre of mass and aligned with the output coordinate system.

[0110]

[0111] 20mm

[0112] Mass = 5.07 grams

[0113] Centre of mass: (mm) X = -4.37 Y = 19.01 Z = -10.61

[0114] Principal axes of inertia and principal moments of inertia: (grams. mm2) taken at the centre of mass.

[0115]

[0116] Moments of inertia: (grams. mm2)

[0117] Taken at the centre of mass and aligned with the output coordinate system.

[0118]

[0119]

[0120] Where SMA is used to change the moment of inertia, the two-way shape memory effect can be used with joule heating, or one-way shape memory together with joule heating and a return spring or second antagonistic SMA element, to create the actuator movement and positional reset between the masses to vary the distance. In one example a single mass, one SMA element and one return spring may be used. The system of the present invention does not actually need to be balanced to have the centre of mass central to the beam. Where an SMA is used, the detail mechanism can be any suitable shape and will depend on the amount of movement desired. For example, straight wire, a helix (spring) or a U shape.

[0121] Figures 8a to 8f are schematic diagrams which show features similar to the central beam 146 and a pair of blocks or end pieces 148 of figure 6. Figure 8a shows a central beam assembly 161 with mass elements 163 and an SMA element 165 which changes the length of the central beam.

[0122] Figure 8b shows a central beam 171 with mass elements 173 and an SMA element 175 which changes the length of the central beam.

[0123] Figure 8c shows a central beam 181 with mass elements 183 and an SMA element 185 which changes the length of the central beam.

[0124] Figure 8d shows a central beam 191 with mass elements 193 and an SMA element 195 which changes the length of the central beam.

[0125] Figure 8e shows a central beam 201 with mass elements 203 and an SMA element 205 which changes the length of the central beam.

[0126] Figure 8f shows a central beam 211 with mass elements 213 and an angular actuator 215 which changes the length of the central beam.

[0127] Figures 9a and 9b illustrate the possibility of using multiple orthogonal mechanism with two masses moving axially to change the inertia. The cross shape 221 of figure 9a illustrates the two-dimensional version and the three-dimensional cross shape 223 of figure 9b illustrates the three-dimensional version. These allow a variation in moment of inertia in two and three dimensions.Figure 10 is a schematic diagram of a control system 231 for the present invention. In this example the control system receives a system input 233 which may be from an accelerometer measuring the movement of a housing or maybe a feedback signal from an electronic device which is used to generate a haptic. When the control system 235 receives the input signal an output is sent to the device 237. The output is used to control movement of the device. In the case of the haptic application, the control system will provide a signal which provides feedback to a user in connection with a signal from an electronic device, for example a mobile phone, touch screen, button press or computer game controller.

[0128] The present invention allows a wide range of motion in a single device within 6 degrees of freedom. Where used herein and unless specifically indicated otherwise, the following terms are intended to have the following meanings in addition to any broader (or narrower) meanings the terms might enjoy in the art:

[0129] In at least one embodiment, the present invention uses multiple SMA elements and has active biasing with the antagonistic design. Advantageously, this removes the need for any bearings and means the system reaction / reset time can be much faster and it automatically has 6 degrees of freedom without having to add further layers of complexity.

[0130] In at least one embodiment, the present invention the use of two sets of antagonistic elements giving a much greater range of movement in all 6 degrees of freedom. This also allows a forced return to position so the system can be used as a haptic vibration device both linear along an axis line, or by vibrating in rotation around an axis. Indeed any combination of these can be achieved, and the natural frequency in each degree of freedom can be set differently if desired to give a greater range of response and feel to the end user. The addition of the feature using a moveable element in one or more axes to move the end pieces apart to dynamically alter the natural frequency is highly advantageous and absent from the state of the art.Unless otherwise required by context, the use herein of the singular is to be read to include the plural and vice versa. The term "a" or "an" used in relation to an entity is to be read to refer to one or more of that entity. As such, the terms "a" (or "an"), "one or more," and "at least one" are used interchangeably herein.

[0131] As used herein, the term "comprise," or variations thereof such as "comprises" or "comprising," are to be read to indicate the inclusion of any recited integer (e.g. a feature, element, characteristic, property, method / process step or limitation) or group of integers (e.g. features, element, characteristics, properties, method / process steps or limitations) but not the exclusion of any other integer or group of integers. Thus, as used herein the term "comprising" is inclusive or open-ended and does not exclude additional, unrecited integers or method / process steps.

[0132] The foregoing description details presently preferred embodiments of the present invention. Numerous modifications and variations in practice thereof are expected to occur to those skilled in the art upon consideration of these descriptions. Those modifications and variations are intended to be encompassed within the claims appended hereto.

[0133] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims1. An actuation apparatus comprising:a support structure having a first end and a second end;a first end piece and a second end piece coupled to the respective first and second ends of the support structure, each end piece being coupled to the support structure by a set of actuators;a central portion which is at least partially located in the support structure, the central portion having a first end and a second end coupled to the first and second end pieces respectively;a controller which provides a control signal;wherein the set of actuators comprises three or more actuator elements, which are symmetrically positioned on the end piece and extend for connection with the support structure, and, when coupled and in its natural position, the end piece is offset with respect to the support structure so as to be non-coplanar, and wherein applying a control signal to one or the actuator elements moves the central portion with respect to the support structure and wherein the central portion has a dimension which is variable so as to change the polar moment of inertia of the actuation apparatus with respect to rotation around one or more axes.

2. The actuation apparatus as claimed in claim 1, wherein the dimension is the length and / or breadth and / or height of the central portion to change the polar moment of inertia in one or more axes.

3. The actuation apparatus as claimed in claim 2, wherein change in the polar moment of inertia provides the variation in natural frequency and therefore the frequency response.

4. The actuation apparatus as claimed in claims 1 to 3, wherein the central portion comprises one or more moveable parts.

5. The actuation apparatus as claimed in claim 4, wherein a plurality of moveable parts is moveable with respect to one another to change the moment of inertia of the actuation apparatus.

6. The actuation apparatus as claimed in claim 4 or 5, wherein the moveable parts are moveable linearly.

7. The actuation apparatus as claimed in claims 4 to 6, wherein the moveable parts are moveable in 2 dimensions.

8. The actuation apparatus as claimed in claims 4 to 6, wherein the moveable parts are moveable in three dimensions.

9. The actuation apparatus as claimed in claims 4 to 8, wherein the moveable parts dynamically change their linear spring stiffness to alter resonant frequency of the apparatus.

10. The actuation apparatus as claimed in any preceding claim, wherein the central portion comprises an SMA material.

11. The actuation apparatus as claimed in claim 10, wherein the SMA material is coupled to an antagonistic element.

12. The actuation apparatus as claimed in claim 11 , wherein the antagonistic element is a second SMA material.

13. The actuation apparatus as claimed in claim 12, wherein the antagonistic element is a return spring.

14. The actuation apparatus as claimed in claim 10, wherein the SMA comprises a straight wire.

15. The actuation apparatus as claimed in claim 12, wherein the SMA comprises a helix (spring).

16. The actuation apparatus as claimed in claim 12, wherein the SMA comprises a U- shapes device.

17. The actuation apparatus as claimed in claims 9 and 10 to 16, wherein the SMA elements are selectively and partly or fully actuated in order to dynamically change the effective spring stiffness, and therefore the resonant frequency, of the system in one or more degrees of freedom.

18. The apparatus as claimed in claims 10 to 17, wherein the SMA is a two-way trained SMA element and wherein dimensions of the central portion are varied by means of the two-way shape memory effect.

19. A haptic device which comprises an actuation apparatus as claimed in claims 1 to 17.

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