GB2603186A

GB2603186A - Shape memory alloy actuator control

Info

Publication number: GB2603186A
Application number: GB2101315.6A
Authority: GB
Inventors: Kist Renè; Howarth James; Benjamin Simpson Brown Andrew
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2021-01-29
Filing date: 2021-01-29
Publication date: 2022-08-03
Also published as: CN114810524A; GB202101315D0

Abstract

A method of controlling a system which includes a shape memory alloy (SMA) actuator, comprising determining if the system is in motion and how long for such that it indicates whether or not the shape memory alloy actuator will be subjected to mechanical shock, if the system will undergo shock then the controller controls the current in the SMA actuator in order to mitigate or reduce damage from the shock. The controlling of the current may include reducing the current to 0. The controller may make use of accelerometers and may monitor for a free-fall condition. The controller may be monitoring 3 non-planar axes to make the determination. The method may be implemented in a controller, the controller may be fitted to a module, the module may be fitted to a device. A computer program may be created which executes the method.

Description

Shape memory alloy actuator control

Field

The present invention relates to a method or methods of reducing damage to a shape memory alloy (SMA) actuator arising from mechanical shock, particularly mechanical shock following an impact caused by a device containing the SMA actuator being dropped and falling to the floor or being tapped against a surface.

Background

io Shape memory alloy (SMA) actuators for use in electronic devices such as smart phones and tablets need to be robust and not break tinder adverse mechanical shock. When powered, SMA wire is subject to a greater stress under mechanical shock conditions such as tumble, tap, micro drop and vibration condition tests than it is when the SMA wire is at a lower temperature.

Summary

According to a first aspect of the invention, there is provided a method comprising determining whether a shape memory alloy actuator comprising at least one shape memory alloy wire is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock. The method further comprises, upon positive determination, controlling current to the at least one shape memory alloy wire so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.

io The mechanical shock may comprise an impact, for example, hitting the floor after a drop, or a tap against a surface. The mechanical shock may include shock caused by drop, tap, tumble and/or micro drop tests. The mechanical shock may include shock caused by vibration, for example while the SMA actuator is attached to a moving vehicle. The mechanical shock may cause a mechanical stress on the at least one shape /5 memory alloy wire.

The method may further comprise monitoring the state of motion of the shape memory alloy actuator and processing the state of motion and generating a signal indicative of the state of motion.

Upon positive determination that the shape memory alloy actuator is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock, the current may be removed from the at least one shape memory alloy wire. Or

Determining that the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock may comprise receiving a signal from an accelerometer indicative that the shape memory alloy actuator is in free-fall.

Determining that the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock may comprise receiving a value below a pre-determined figure from each of three axes not on a single plane of an accelerometer. -3 -

Determining whether the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock may comprise receiving a signal from a gyroscope indicative of spinning.

Determining whether the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock may comprise receiving a signal from an optical sensor.

The at least one shape memory alloy wire may comprise at least one first shape memory io alloy wire and least one second shape memory alloy wire. The method may further comprise controlling current to the at least one second shape memory alloy wire, wherein the current control to the at least one second shape memory alloy wire occurs after and/or is of less magnitude than the current control to the at least one first shape memory alloy wire.

A moving portion of the shape memory alloy actuator may be moved closer to the end-stop of the shape memory alloy actuator.

A moving portion of the shape memory alloy actuator may be positioned in a predetermined position. The predetermined position may be a parking position in which the moving portion is held.

The above may be done by, upon positive determination, controlling current to the at least one shape memory alloy wire. Or

The method may further comprise determining the direction of motion of the shape memory alloy actuator, determining the orientation of the shape memory alloy actuator with respect to its direction of motion, and controlling current to the at least one shape memory alloy wire in dependence on the orientation of the shape memory alloy actuator with respect to its direction of motion so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.

The method may further comprise determining whether the shape memory alloy actuator is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to a second mechanical shock, and upon positive -4 -determination, controlling current to the at least one shape memory alloy wire so as to reduce damage arising from the mechanical shock when it occurs.

The second mechanical shock may be simultaneous to the first mechanical shock, for example a vibration mechanical shock while an impact mechanical shock is occurring.

The second mechanical shock may be after the first mechanical shock, for example, the second mechanical shock may be caused by a rebound or bounce from the first mechanical shock.

io Controlling the current to the at least one shape memory alloy wire may be sufficient to reduce the temperature of the shape memory alloy wire to below the martensite finish temperature of the shape memory alloy wire. This may occur before the mechanical shock or a subsequent mechanical shock.

According to a second aspect of the invention, there is provided a controller comprising memory and at least one processor. The at least one processor is configured to determine whether a shape memory alloy actuator comprising at least one shape memory alloy wire is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock and upon positive determination, control current to the at least one shape memory alloy wire so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.

According to a third aspect of the invention, there is provided a module comprising the Or controller.

The module may further comprise at least one sensor operatively connected to the controller, and at least one shape memory alloy actuator comprising at least one shape memory wire.

According to a fourth aspect of the invention, there is provided a device comprising the controller.

The device may be a portable device and maybe, for example, a portable electronic 35 device. The device may be a hand-holdable device such as a smartphone, a tablet, a laptop personal computer or a notebook computer. -5 -

According to a fifth aspect of the invention there is provided a computer program which, when executed by at least one processor, causes the at least one processor to perform the method of the first aspect of the invention.

According to a sixth aspect of the invention there is provided a computer program product comprising a computer-readable medium, which stores the computer program. -6 -

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure lisa schematic block diagram of a hand-holdable device including a camera module; Figure 2 is a perspective view of the axes of motion; Figure 3 is a perspective view of a four-wire shape memory alloy (SMA) actuator; Figure 4 is a perspective view of an eight-wire shape memory alloy actuator; io Figure 5 is a side view of an eight-wire shape memory alloy actuator; Figure 6 is a schematic of an electronic device prior to impact; Figure 7 is a process flow diagram of a method of controlling current to SMA wires; Figure 8 is a schematic of the martensite phase fraction of an SMA wire against temperature; and is Figure 9 is a schematic of a moving portion of an SMA actuator. -7 -

Description

Referring to Figure 1, an electronic device 1 includes an electronic device controller 2 and at least one camera module 3.

The camera module 3 includes a shape memory alloy (SMA) actuator 4 (herein also referred to as an "SMA actuator assembly", or simply an "actuator"). The SMA actuator 4 includes at least one SMA we 5. The camera module 3 further includes an SMA actuator controller 6 operatively connected to the SMA actuator 4. The SMA actuator controller 6 further includes at least one processor 7 and memory 8. The camera module includes a sensor unit 9 which may comprise an accelerometer 10 and/or a gyroscope 11. The sensor unit 9 maybe an inertial measuring unit (1MU). The IMU 9 is operatively connected to the SMA actuator controller 6. The camera module 3 further comprises image sensor 12.

/5 The camera module 3 may include more than one SMA actuator 4. As will be explained in more detail later, each SMA actuator 4 may move either the image sensor 12 or a lens (not shown) relative to each other with six degrees of freedom. Each SMA actuator 4 may be controlled by a single SMA actuator controller 6, or alternatively, each SMA actuator 4 may be controlled by a different SMA actuator controller 6. The sensor module 9 may be located elsewhere on the electronic device 1, and not on the camera module 3. There may be more than one sensor module 9 in different locations and the data from each module 9 may be provided to the one or more SMA actuator controller 6. If more than one sensor module 9 provides data to a single SMA actuator, the processor 7 of the SMA actuator 6 may perform processes to combine the information, Or which may be from different parts of the electronic device 1.

The electronic device controller 2 can provide the camera module with data about the state of the electronic device, for example, battery level, use data and data about other external factors such as temperature, altitude and the like.

The electronic device 1 maybe a hand-holdable device, for example a smartphone. The electronic device 1 maybe a measuring or monitoring device. The electronic device 1 may be, or may be part of, a vehicle, for example unmanned aerial vehicle (UAV). -8 -

Referring also to Figure 2, possible types of movement (or degrees-of-freedom) which the electronic device iand camera module 3 may be subject to are illustrated.

The sensors unit 9 senses motion of the camera module 3 while the electronic device 1 is moving. The accelerometer 10 measures linear motion, for example giving the rate of change of linear motion in three axes, and the gyroscope 11 measures rotational motion in three axes. A first degree-of-freedom (DOF) Tx corresponds to movement parallel to (along) the first axis x. A second DOF Ty corresponds to movement parallel to (along) the second axis y. A third DOF Tz corresponds to movement parallel to (along) a third /0 axis z. In some examples, the third axis z (also referred to as the "primary axis") may be oriented substantially parallel to an optical axis 0 (Fig. 4) of a lens (not shown) and the third DOF Tz may correspond to movement of the lens (not shown) towards or away from the image sensor 6. The third axis z is not in the same plane as formed by the first and second axes x, y and may be perpendicular to the plane formed by the first and /5 second axes x, y. The first, second and third (or primary) axes x, y, z may form a right-handed Cartesian coordinate system. A fourth DOF Rx corresponds to rotation about an axis parallel to the first axis x. A fifth DOF Ry corresponds to rotation about an axis parallel to the second axis y. A sixth DOE Rz corresponds to rotation about an axis parallel to the primary axis z. In some examples, one or more of the axes x, y, z may be attached to (and move and/or rotate/tilt with) a first part, a second part, or any other elements of an SMA actuator assembly 4 or image sensor 12.

The motion data from the sensor unit 9 is provided to the SMA actuator controller 6. The processor 7 of the SMA actuator controller 6 analyses the data received from the Or sensor unit 9 and controls the current provided to the SMA wires 5 in the SMA actuator 4. The memory 8 may include the software or firmware which includes the instructions for analysing the data from the sensor unit 9. In some examples, the motion data from the sensor unit 9 is used for optical image stabilisation (01S). Under normal operation, for example when a user is holding the electronic device 1, the camera module 3 may be subject to motion caused by external factors such as user movement, wind, vibrations and the like. The motion of the camera module 3 in six degrees of freedom is sensed by the sensor unit 9 and provided to the SMA actuator controller 6. After analysis of the motion by the processor 7, the SMA actuator controller 6 controls the current to the SMA wires 5 in the SMA actuator 4 which compensates the movement caused by the external factors. In this way, the image sensor 12 and or lens (not shown) can be moved -9 -relative to each other and provide a stable image recording conditions, despite the movement of the camera module 3.

Referring to Figure 3, an example of a "four-wire" SMA actuator 3 is shown. The actuator 3 is equivalent to that described in WO 2013/175197 Al, which is incorporated by reference.

In the SMA actuator 3, each of the first and second structures 15 takes the form of a flat, annular plate having a rectangular outer perimeter and a circular inner perimeter. The /0 first structure 15 is supported on a base (not shown). Four SMA wires 5, 52, 53, 54 are each attached at one end to respective first crimps 21,, 212, 213, 214 (also referred to as "static" crimps) which are fixedly attached to (or formed as part of) the first structure 15. The other end of each SMA wire Si, 52, 53, 54 is attached to a respective second crimp 221, 222, 223, 224 (also referred to as a "moving" crimp) which is fixedly attached /5 to (or formed as part of) the second structure 17.

The first and second structures 15, 17 may each take the form of respective patterned sheets of metal, e.g., etched or machined stainless steel, which may be coated with an electrically-insulating dielectric material. The first and second structures 15, 17 are each provided with a respective central aperture aligned with an optical axis (not shown) allowing the passage of light from a lens assembly 3 mounted to the second structure 17 to an image sensor 12 supported on the base (not shown).

The four SMA wires 51,52,53, 5,, may be perpendicular to the optical axis or inclined at a Or small angle to a plane perpendicular to the optical axis. Generally, in a set, the four SMA wires 5,, 5_, 5" 54 are non-collinear.

The actuator 3 includes a number of bearings (not shown) spaced around the optical axis 0 to bear the second structure 17, 18 on the first structure 15, 16. Preferably, at least three bearings are used in order to assist in providing stable support. Each bearing (not shown) may be a plain bearing which may be in the form of cylinder, and may be attached to, or formed as part of, the first structure 15. The bearings (not shown) may be made from any suitable material(s)..

The actuator 3 will generally also include biasing means such as one or more springs or flexure arms arranged and configured to maintain the first and second structures 15, 17 -10 -in contact (via the bearings) and/or to urge the first and second structures 15, 17 towards a neutral (for example central) relative position when the SMA wires Si, 52, 53, 54 are not powered.

Details relevant to manufacturing actuator assemblies similar to the actuator 3 can be found in WO 2016/189314 Al which is incorporated herein in its entirety by this reference.

Although not shown in Figure 3, the actuator 3 may be provided with end stops to provide limits on lateral movement of the second structure 17 relative to the first structure 15. In this way, the SMA wires Si, 52, 53, 54 can be protected from overextension resulting from, for example, impacts to which a device (not shown) incorporating the actuator 3 may be subjected (for example by being dropped).

is In operation, the SMA wires 5,, 52, 53, 54 are selectively driven -for example by the abovedescribed SMA actuator controller 6 -to move the second structure 17 relative to the first structure 15 at least in any lateral direction (i.e. direction perpendicular to the optical axis 0) as described, for example, in WO 2013/175197 At Referring to Figures 4 and 5, a camera lens assembly 25f comprising an example of an "eight-wire" shape memory alloy actuator 4 will now be described.

The camera lens assembly 25 comprises a static portion 26 and a lens holder 27 holding a lens 28 (shown in dotted outline), or more generally any number of lenses, having an Or optical axis 0. As described in more detail below, the lens holder 27 is supported on the static portion by eight SMA actuator wires 5, four of which are visible in Figure 1. The lens holder 27 is capable of movement with respect to the static portion 26, driven by the SMA actuator wires 5, with six degrees of freedom, that is three orthogonal translational degrees of freedom (Tx, Ty, Tz) and three orthogonal rotational degrees of freedom (Rx, Ry, Rz). In this example, the lens holder 271S supported solely by the SMA actuator wires 5, but as an alternative the lens holder 27 could additionally be supported by a suspension system which permits the movement with the six degrees of freedom, for example formed by one or more flexures. The static portion 26 preferably also includes a screening can 29 (for clarity, not shown in Figure 4 and shown cut away in cross-section in Figure 5) rigidly attached to the base plate and extending around the lens holder 27 with enough clearance to allow full movement of the lens holder 27.

In more detail, the static portion 26 comprises a base plate 30 and two static posts 31 provided on opposite corners of the base plate 30. The static posts 31 which may be affixed to the base plate 26 or formed integrally with the base plate 26 as one piece.

Two crimp assemblies 32 are affixed to each of the two static posts 31. The base plate 26 also rigidly mounts an image sensor 12 on which the lens 28 focuses an image.

The lens holder 27 includes two moving posts 33 aligned with the corners of the base plate 26 intermediate the static posts 31. Two crimp assemblies 34 are affixed to each of /0 the moving posts 33. The SMA actuator wires 5 are connected between the static portion 26 and the lens holder 27 by being crimped at one end to a crimp assembly 32 of the static portion and at the other end to a crimp assembly 34 of the lens holder 27. The crimp assemblies 32 and 34 provide both mechanical and electrical connection. The crimp assemblies 34 on the lens holder 27 at each corner are electrically connected /5 together.

The SMA actuator wires 5 have the same configuration around the lens holder 27 as the SMA actuator wires 5 in the camera apparatus described in W02011/104518. Specifically, two SMA actuator wires 5 are arranged on each of four sides around the optical axis 0, and are inclined with respect to the optical axis (i.e. at an acute angle greater than o degrees) in opposite senses to each other and crossing each other, as viewed perpendicular to the optical axis 0. Thus, in particular, each of the SMA actuator wires 30 is inclined with respect to the optical axis 0 of the lens element 27 and with respect to each other. Reference is made to W02o11/m4518 for further details Or of the arrangement of the SMA actuator wires 5. Selective contraction of the SMA actuator wires 5 drives movement of the lens holder 27 in any of the six degrees of freedom. Contraction and expansion of the SMA actuator wires 5 is generated by application of drive signals or current thereto. The SMA actuator wires 5 are resistively heated by the drive signals and cool by thermal conduction to the surroundings when the power of the drive signals is reduced.

Thus, the SMA actuator wires 5 may be used to provide both an AF function by translational movement of the lens holder 27 along the optical axis 0 and an OIS function by translational movement of the lens holder 27 perpendicular to the optical 35 axis 0.

-12 -The drive signals may be generated in a control circuit (e.g. SMA actuator controller 6) and supplied to the SMA actuator wires 5. Such a control circuit may receive an input signal representing a desired position for the lens holder 27 and generates drive signals having powers selected to drive the lens holder 27 to the desired position. The power of the drive signals may be either linear or varied using pulse width modulation. The drive signals may be generated using a resistance feedback control technique, in which case the control circuit measures the resistance of the SMA actuator wires 5 and uses the measured resistance as a feedback signal to control the power of the drive signals. Such a resistance feedback control technique may be implemented as disclosed in any of W02013/175197, W02014/076463, W02012/066285, W02012/020212, W02011/104518, W02012/038703, W02010/089529 or W02010029316.

As shown in Figure 5 (but omitted from Figure 4 for clarity), the static portion 26 also includes end-stops 35 having end-stop surfaces 36 which face the lens holder 27 and are arranged to limit the movement of the lens holder 27 by contacting it. There is an end-stop 35 corresponding to each SMA actuator wire 5. Figure 5 shows the two SMA actuator wires 5 and the two corresponding end-stops 35 on one side of the camera lens assembly 25, the other SMA actuator wires 5 on the other sides of the camera lens assembly 25 having corresponding end-stops 35 in the same configuration. In this example, each end-stop surface 36 extends orthogonally to the direction along the corresponding SMA actuator wire 5. Thus, the end-stop surfaces 36 are inclined with respect to the optical axis 0 at a complementary angle to the angle at which the SMA actuator wires are inclined with respect to the optical axis 0, the two end-stop surface 36 shown in Figure 5 being inclined in opposite senses to each other. Or

This arrangement of the end-stop surfaces 36 provides improved protection of the SMA actuator wires 5 from damage caused by impacts. In the worst case for an SMA actuator wire 5 in the event of an impact to the camera lens assembly 25, for example caused by the camera lens assembly 25 being dropped, a high impulse force is applied in the direction along the line of the SMA actuator wire 5 in the direction away from the static portion 26. When the camera lens assembly 25 receives the force, the lens holder 27 will be propelled away from the static portion 25 and contact the end-stop surface 36 which limits that movement and thereby saves the SMA actuator wire 5 from being damaged by receiving too much strain. Due to the position of the end-stop surface 36, the SMA actuator wire 5 may be saved from snapping, or from reaching the point where it is useful for life is shortened by strain fatigue. Due to the inclination of the end-stop -13 -surfaces 36 to extend orthogonally to the direction along the corresponding SMA actuator wire 5, this is achieved without restricting the degree of movement of the lens holder 27.

In the example shown in Figures, each end-stop surface 36 is positioned in line with the corresponding SMA actuator wire 5, that is in line with the crimp assembly 32 at the end of the SMA actuator wire 5. In this arrangement, the strain of the SMA actuator wires is restricted regardless of rotation of the lens holder 27. Where packaging constraints prevent an end-stop surface 36 being positioned in line with the /0 corresponding SMA actuator wire 5, a similar protective effect may be achieved by any one or more of the end-stop surfaces 36 being positioned not in line with the corresponding SMA actuator wire 5. In that case, the optical assembly may be arranged to prevent rotation of the lens holder 27.

/5 In the example shown in Figure 5, the end-stop surfaces 36 are formed on the inner surface of the screening can 29, for example by the end-stops being mounted to the screening can 29, or formed as an integral part of the screening can 29. This is convenient for manufacture. More generally, the end-stop surfaces 36 may be formed on the inner surface of any part of the static portion. For example, any one or more of the end-stops 35 may be mounted to the base plate 30, or formed as an integral part of the base plate 30. Similarly, some end-stop surfaces 36 may be formed on the inner surface of the screening can 29 and others may be formed on the inner surface of an end-stop mounted to the base plate 30, or formed as an integral part of the base plate 30. There will now be described some modified designs of the camera lens assembly.

Or For brevity, only the modifications will be described and the camera lens assembly otherwise has the construction described above.

Mechanical shocks Referring to Figure 6, the electronic device 1 may stiffer from intentional or unintentional mechanical shock.

For example, the electronic device 1 may fall from a height h above a surface 40 onto a surface 40, for example, by being dropped by a user, or being disturbed from a previously stable or controlled position, for example by a gust of wind. The surface 40 may be for example a table, or a floor. Then the electronic device 1 contacts the surface 40, the device 1 may suffer one or more mechanical shocks, for example an impact.

-14 -These impacts will also affect the SMA actuator 4 and the SMA actuator wires 5. For example, an impact such as this may damage the SMA wires 5. Damage to the SMA wires 5 may be more likely when the SMA actuator 4 is powered, that is, that there is current provided to the SMA wires 5 to heat them. The SMA actuator 4 may be powered when, for example, the camera of the electronic device 1 is in use. Such an instance could occur when a user is trying to take a photo using the electronic device iand drops the device 1 during operation.

The electronic device 1 may be subject to secondary unintentional impacts, for example, _to after rebounding from the floor 40 after a first impact. Secondary impacts may be as damaging or more damaging to SMA wires 5 as a first impact, despite the accelerations involved being of a lower magnitude.

A second mechanical shock may be simultaneous to a first mechanical shock, for /5 example a vibration mechanical shock while an impact mechanical shock is occurring. A second mechanical shock may be after the first mechanical shock, for example, the second mechanical shock may be caused by a rebound or bounce from the first mechanical shock.

The electronic device 1 may be subject to further mechanical shocks, for example, during a so-called tumble. The electronic device 1 may be subject to mechanical shock(s) caused by vibration, for example while the device 1 is attached to a moving vehicle.

Or The electronic device 1 may be subject to intentional mechanical shocks, for example a smartphone being tapped against the surface of a payment device will cause an impact mechanical shock.

Detection of imminent mechanical shock The detection of an imminent mechanical shock can aid the protection of SMA wires 5 in SMA actuators 4. if an imminent mechanical shock is detected, steps can be taken to reduce the damage inflicted on the SMA wires 5 and the SMA actuator 4. For example, reducing or removing the current from the SMA wires 5 allows the wires 5 to cool. Typically, the cooler (and hence less taut) the SMA wires 5, the less likely they are to be damaged by a mechanical shock. Preferably, the SMA wires are cooled to below the martensite finish temperature for the particular SMA used.

-15 -A typical period in which an electronic device 1 may fall from a user's hand to the floor 40 is around 140 ms. The typical time to detect that the drop has occurred is, in some examples, around 100 to 120 ms, and the typical cooling time of an SMA wire 5 is between 100 and 120 ms. Decreasing the detection time would allow action to be taken sooner, and for the SMA wires 5 to be cooler when an impact occurred, thus reducing the damage caused to them. The SMA wires 5 do not need to be completely cooled to reduce damage, even a small magnitude of cooling reduces the damage caused to the wires 5 by impact.

By monitoring the motion in the three linear axes, Tx, Ty, Tz, using the accelerometer 10, the SMA actuator controller 6 can detect when the sensor unit 9 and therefore the camera module 3, including the SMA actuator 4 and SMA wires 5, are in a freefall state when the acceleration falls below a threshold in all three axes. Ideally the threshold will is be close to zero, but the thresholds above zero may be appropriate under certain circumstances. Rotational data from the gyroscope 11 can augment the accelerometer data to provide more accurate readings of a freefall, and/or information about the rotational state of the camera module 3. The rotational information can also be used to determine whether the camera module is in a tumble state. Information from all six axes Tx, Ty, Tz, Rx, Ry and Rz, can also determine whether the camera module is subject to a vibration stimulus. Such motion information can also be used to determine whether the electronic device 1 is about to be tapped against a surface, for example during the motion of tapping a payment system with a smartphone. In certain circumstances, data from an optical sensor, for example image sensor 12, maybe Or combined with motion data from the sensor unit 9 to provide a more rapid determination of motion state or a more accurate state of motion.

Referring to Figure 7, the SMA actuator controller 6 monitors the state of motion of the camera module 3 provided by the senor module 9 (step Si). If the SMA actuator controller 6 determines that the camera module 3 is in a state of motion for a given amount of time indicative that the camera module 3 and the SMA actuator 4 will be subject to a mechanical shock (step 52), the SMA controller 6 can check whether the SMA actuator 4 is in an "on" state (step 53), (e.g. powered). If the SMA actuator 4 is in an "on" state, the SMA actuator controller 6 can take mitigating action (step S4). The mitigating action may be controlling or reducing the current provided to at least one SMA wire(s) 5 in the SMA actuator 4. The mitigating action may include controlling or -16 -reducing or removing the current to one or more SMA wire(s) 5 before controlling or reducing the current to a second SMA wire(s) 5. The control or reduction in current for each SMA wires may be at different times and at different magnitudes. The given amount of time in step 52 may be a time between o and too ms, between o and 75 ms, between o and 50 ms, between o and 25 ms or about to ms.

The SMA actuator controller 6 then determines whether it is safe for the SMA actuator 4 to return to it default state, for example in a powered state to perform image stabilization (step S5). If so, the SMA actuator controller 6 return to monitoring the io state of motion of the camera module 3 provided by the sensor unit 9 (step Si). The SMA actuator controller 6 may detect that a second mechanical shock is imminent, in which case, the SMA actuator controller continues to control the current provided to the SMA wires 5. For a second imminent mechanical shock, the control of the current to the SMA wires may be different than to the first control of the current to the SMA wires, depending on the motion of the camera module 3 and the type of shock that is expected.

The SMA actuator controller 6 may also determine the direction of motion of the SMA actuator 4 and the orientation of the SMA actuator 4 with respect to its direction of motion using data from the sensor unit 9. The SMA actuator controller 6 may use the direction and orientation information to determine which SMA wires 5 are most at risk of an imminent mechanical shock (e.g. those that will tend to be stretched), and control the current to the at least one shape memory alloy wires accordingly so as to reduce damage to the wires 5 when the shock occurs. Or

Referring to Figure 8, when the SMA actuator 4 is in a powered state, an SMA wire 5 is at a temperature 'F2, also referred to as a "hot" temperature. At time n, the SMA actuator controller detects that a mechanical shock is imminent and reduces current to the SMA wire 5. The SMA wire 5 cools and at time t, reaches the martensite finish temperature Tim,. At tip, the damage caused by mechanical shock to the SMA wire 5 is reduced to an acceptable level.

Referring to Figure 9, a first SMA wire Si maybe attached to a first crimp 21" for example at or near an end of the first SMA wire 5,. The first crimp 21i maybe attached 35 to a part of the SMA actuator 4. The first SMA wire Si may be attached to a moving portion 41 of the SMA actuator 4. The first SMA wires at a certain temperature has a -17 -length L.1. An end-stop (or endstop) 42 may also be attached to part of the SMA actuator 4. The moving portion 41 may initially be at a distance s from the end-stop 42. The moving portion 41 may be further attached to a second SMA wire 52 which is in turn attached to the SMA actuator 4 via a second crimp 222.

Upon the determination of an imminent mechanical shock, the SMA actuator controller 6 controls the current to the SMA wires 51, 52 to move the moving portion 41 to the distance 52 of the end-stop 42. For example, the SMA actuator controller 6 may reduce or stop the current to the first SMA wire 5, while still providing current to the second SMA wire 52 such that the moving portion 41 moves to a distance s2 from the end-stop 42, as illustrated.

In some examples, once the moving portion 41 has been moved to such a position, the moving portion may be "parked" or temporarily fixed in the position by either a /5 physical clamp (not shown) or by magnetic forces (for example, as disclosed in Fig. 8 and the accompanying description in WO 2021/005351 Al, which is incorporated by reference). This reduces further stress and/or strain on the SMA wires 5 and therefore decreased the chance of damage during mechanical shock.

Modifications It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design and use of shape memory alloy actuators, shape memory alloy actuator controllers and component parts thereof and which may be used Or instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

-18 -Claims 1. A method comprising: determining whether a shape memory alloy actuator comprising at least one shape memory alloy wire is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock; and upon positive determination, controlling current to the at least one shape memory alloy wire so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.
2. A method according to claim 1 further comprising monitoring the state of motion of the shape memory alloy actuator and processing the state of motion; and generating a signal indicative of the state of motion.is
3. A method according to claim 1 or 2 wherein, upon positive determination that the shape memory alloy actuator is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock, the current is removed from the at least one shape memory alloy wire.
4. A method according to any one of claims ito 3 wherein determining that the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock comprises receiving a signal from an accelerometer indicative that the shape memory alloy actuator is in free-fall.Or
5. A method according to any one of claims 1 to 3 wherein determining that the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock comprises receiving a value below a pre-determined figure from each of three axes not on a single plane of an accelerometer.
6. A method according to any one of claims ito 5 wherein determining whether the shape memory alloy actuator is in the state of motion indicative that the shape memory alloy actuator will be subject to mechanical shock comprises receiving a signal from a gyroscope indicative of spinning.
7. A method according to any one of claims 1 to 6 wherein determining whether the shape memory alloy actuator is in the state of motion indicative that the shape -19 -memory alloy actuator will be subject to mechanical shock comprises receiving a signal from an optical sensor.
8. A method according to any one of claims 1 to 7 wherein the at least one shape memory alloy wire comprises at least one first shape memory alloy wire and least one second shape memory alloy wire, the method further comprising: controlling current to the at least one second shape memory alloy wire, wherein a change in the current control to the at least one second shape memory alloy wire occurs after and/or is of different magnitude than a change in the current control to the io at least one first shape memory alloy wire.
9. A method according to any one of claims 1 to 8 wherein, upon positive determination, controlling current to the at least one shape memory alloy wire so as to move a moving portion of the shape memory alloy actuator closer to an end-stop of the /5 shape memory alloy actuator.
10. A method according to any one of claims 1 to 9 wherein, upon positive determination, controlling current to the at least one shape memory alloy wire so as to position a moving portion of the shape memory alloy actuator in a predetermined position, optionally wherein the predetermined position is a parking position in which the moving portion is held.
A method according to any one of claims 1 or in further comprising: Or determining the direction of motion of the shape memory alloy actuator; determining the orientation of the shape memory alloy actuator with respect to its direction of motion; and controlling current to the at least one shape memory alloy wire in dependence on the orientation of the shape memory alloy actuator with respect to its direction of motion so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.
12. A method according to any one of claims ito 11 further comprising: determining whether the shape memory alloy actuator is in a state of motion for 35 a given amount of time indicative that the shape memory alloy actuator will be subject to a second mechanical shock; and -20 -upon positive determination, controlling current to the at least one shape memory alloy wire so as to reduce damage arising from the second mechanical shock when it occurs.
13. A method of any one of claims ito 12 wherein the controlling of current to the at least one shape memory alloy wire is sufficient to reduce the temperature of the shape memory alloy wire to below the martensite finish temperature of the shape memory alloy wire.rcr
14. A controller comprising: memory; and at least one processor configured to: determine whether a shape memory alloy actuator comprising at least one shape memory alloy wire is in a state of motion for a given amount of time indicative that the shape memory alloy actuator will be subject to mechanical shock; and upon positive determination, control current to the at least one shape memory alloy wire so as to reduce damage of the at least one shape memory alloy wire arising from the mechanical shock when it occurs.
15. A module comprising the controller of claim 14.
16. A module according to claim 15 further comprising: at least one sensor operatively connected to the controller; and Or at least one shape memory alloy actuator comprising at least one shape memory wire.
17. A device comprising the controller or module of any one of claims 14 to 16.
18. A computer program which, when executed by at least one processor, causes the at least one processor to perform the method of any one of claims ito 13.
19. A computer program product comprising a computer-readable medium, which stores the computer program according to claim 18.