CN112236596B

CN112236596B - Shape memory alloy actuation device

Info

Publication number: CN112236596B
Application number: CN201980037779.5A
Authority: CN
Inventors: 斯蒂芬·邦廷; 马克-赛巴斯蒂安·肖尔茨
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2018-06-21
Filing date: 2019-06-21
Publication date: 2024-01-02
Anticipated expiration: 2039-06-21
Also published as: GB2574869A; WO2019243846A1; GB201810214D0; CN112236596A; GB2574869B

Abstract

The SMA actuation apparatus (1) comprises a support structure (2) and a lens element (20) supported on the support structure by a suspension system (30) that directs movement driven by a length of SMA actuator wire (41). The present technology relates to minimizing the overall height of an SMA actuation apparatus in a direction of movement.

Description

Shape memory alloy actuation device

The present technology relates generally to a shape memory alloy (SMA, shape memory alloy) actuation apparatus in which at least one length of SMA actuator wire (at least one length of SMA actuator wire) drives movement of a movable element relative to a support structure. In particular, the present technology relates to minimizing the overall height of an SMA actuation apparatus in a direction of movement, the SMA actuation apparatus being an optical device in which at least one length of SMA actuator wires drives movement of a lens element relative to a support structure along an optical axis of the lens element.

According to the present technique, there is provided a shape memory alloy actuation apparatus comprising: a support structure; a lens element comprising at least one lens supported on a support structure by a suspension system (suspension system) arranged to guide movement of the movable element relative to the support structure in a movement direction inclined at a first acute angle greater than 0 degrees relative to an optical axis of the lens element; at least one length of shape memory alloy actuator wire connected between the support structure and the movable element for driving movement of the movable element relative to the support structure, the at least one length of shape memory alloy actuator wire being inclined at a second acute angle relative to the optical axis that is greater than the first acute angle.

Since the moving direction is inclined at an acute angle of more than 0 degrees with respect to the optical axis, the lens element can be allowed to have a component of lateral movement perpendicular to the optical axis. However, such lateral movement is acceptable in many applications. Furthermore, this has the advantage of reducing the forces transmitted through the suspension system and also the advantage of reducing the gain. Thus, at least one length of SMA actuator wire is inclined at a second acute angle, greater than the first acute angle, relative to a plane orthogonal to the direction of movement. This means that at least one length of SMA actuator wire is still tilted with respect to the direction of movement, but the angle of the length of SMA actuator wire with respect to the normal to the optical axis is reduced, which allows the overall height of the SMA actuation apparatus to be reduced while maintaining the extent of travel and maintaining good control.

The at least one length of shape memory alloy actuator wire may extend in a plane orthogonal to the optical axis of the lens element. In this case, the SMA actuator wires have a minimum extent of projection along the optical axis.

Alternatively, the SMA actuator wires may extend at an angle of greater than 0 degrees relative to a plane orthogonal to the optical axis. In this case, the SMA actuator wires have a range of projection along the optical axis, but this can be controlled by adjusting the acute angle to fit within the dimensional limits of some other components of the SMA actuation apparatus.

Preferred features of the present technology are set out in the appended dependent claims.

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

FIG. 1 is a perspective view of a first SMA actuation apparatus;

FIG. 2 is an exploded view of a first SMA actuation apparatus;

FIG. 3 is a side view of the first SMA actuation apparatus;

fig. 4-6 are plan views of different bearing arrangements (bearing arrangement) for the first SMA actuation apparatus;

FIG. 7 is a cross-sectional view of an alternative bearing for the first SMA actuation device, the cross-section taken perpendicular to the direction of movement of the bearing;

FIG. 8 is a side view of the alternative bearing of FIG. 7;

FIG. 9 is a cross-sectional view of an alternative bearing for the first SMA actuation device, the cross-section taken perpendicular to the direction of movement of the bearing;

FIG. 10 is a side view of the alternative bearing of FIG. 9;

FIG. 11 is a perspective view of a second SMA actuation apparatus;

FIG. 12 is a perspective view of a step during the manufacture of a second SMA actuation device;

FIG. 13 is a perspective view of a third SMA actuation apparatus;

FIG. 14 is a side view of a strut element used during the manufacture of the third SMA actuation device; and

fig. 15 and 16 are schematic side views of two alternative forms of a fourth SMA actuation apparatus.

The present technology relates generally to minimizing the overall height of an SMA actuation apparatus, which is an optical device, in a direction of movement, wherein at least one length of SMA actuator wires drives movement of a lens element relative to a support structure along an optical axis of the lens element.

The use of SMA actuator wires to drive translational movement of a movable element relative to a support structure is known. SMA actuator wires are of particular advantage in miniature devices and can be applied in a wide range of consumer electronic devices including hand held devices (e.g. cameras and mobile phones).

For example, such SMA actuator wires may be used in an optical device (e.g. a camera) for driving translational movement of a camera lens element along its optical axis, e.g. to achieve focusing (autofocus, AF) or zooming. Such cameras may be small and relatively low cost and provide a large number of functions for taking not only photographs, but also video calls, scanning, object recognition, security, etc. Examples of SMA actuation arrangements for cameras of this type are disclosed in WO2007/113478, WO2009/056822 and WO 2017/134456.

Such SMA actuator wires may similarly be used in optical devices, such as cameras, for driving translational movement of a camera lens element transverse to an optical axis, for example to provide Optical Image Stabilization (OIS). Examples of SMA actuation arrangements for cameras of this type are disclosed in WO2013/175197 and WO 2014/083318.

WO2007/113478 discloses an example of an SMA actuation apparatus which is a camera in which a camera lens element is supported on a support structure by a suspension system comprising a flexure (flextube) guiding translational movement along an optical axis. Movement of the lens element along the optical axis is driven by a plurality of lengths of SMA actuator wires extending at an acute angle of greater than 0 degrees relative to a direction of movement parallel to the optical axis. Angling the length of SMA actuator wires away from the direction of movement in this manner increases the amount of movement compared to SMA actuator wires extending in the direction of movement. To maximize the amount of travel, it is desirable to maximize the length of the SMA actuator wire for that length. When the angle between the length of SMA actuator wire and the plane orthogonal to the optical axis is reduced, various problems arise as follows. Lateral forces (forces) on the suspension system (e.g., bearing arrangement of the bearings) increase, which may, for example, hinder the functionality of the suspension system in constraining degrees of freedom other than the desired movement along the optical axis and/or increase friction. Furthermore, control problems are increased due to an increase in gain, which is the ratio of the amount of movement to the change in length of the length of SMA actuator wire. Thus, to minimize these types of problems, it is desirable that the line angle not be too small, thereby limiting the height of the SMA device along the optical axis to be minimized.

In fig. 1 and 2, an SMA actuation apparatus 1 is shown, the SMA actuation apparatus 1 being a camera. The SMA actuation apparatus 1 comprises a support structure 2, the support structure 2 having an image sensor 3 mounted thereon.

The support structure 2 comprises a base 4, the base 4 being a rigid plate. The image sensor 3 is fixed to the front side of the base 4. In the arrangement shown in fig. 1 in which the SMA actuation apparatus 1 is controlled by means of a Hall sensor 9, the support structure 2 supports an IC chip 5 fixed to the rear side of the base 4. Alternatively, resistance control may be used to control the SMA actuation apparatus 1, in which case the IC chip 5 may be external to the SMA actuation apparatus 1. As described further below, the control circuit is implemented in the IC chip 5.

The support structure 2 further comprises a chassis 6, the chassis 6 protruding from the base 4 and may be a molded part. As described below, the chassis 6 serves as a mounting platform for the various components and also defines any reference features required during assembly. The chassis 6 has a central hole 7 aligned with the image sensor 3. In the arrangement shown in fig. 1, the support structure 2 further comprises a flexible printed circuit 8 fixed to the outside of the chassis 6. Typically, the flexible printed circuit 8 provides VDD, GND, SCL and SDA connection pads (not shown). On the flexible printed circuit 8, the hall sensor 9 is fixed close to a magnet 26 supported by the support structure 6.

The SMA actuation apparatus 1 further comprises a protective cover (shield can) 10, which protective cover 10 fits to the base 4 and covers all other components described below to prevent physical damage and dust ingress.

The SMA actuation apparatus 1 further comprises a lens element 20, in this example the lens element 20 being a movable element. The lens element 20 comprises a lens holder 25, the lens holder 25 holding the lens 21, but alternatively there may be a plurality of lenses. The lens 21 may be made of glass or plastic. The lens element 20 has an optical axis O aligned with the image sensor 3 and is arranged to focus an image on the image sensor 3. The lens element 20 also has a protrusion 22, the protrusion 22 being formed on a side of the optical axis O that protrudes laterally.

In the presence of the hall sensor 9, the lens carrier 25 of the lens element 20 is also mounted on the support structure 2 with respect to the magnet 26 positioned by the hall sensor 9, so that the hall sensor 9 senses the position of the lens element 20 along the optical axis O.

The SMA actuation apparatus 1 is a micro-optical device. In some examples of micro-optical devices, the lens 21 (or lenses when provided) may have a diameter of at most 20mm, preferably at most 15mm, more preferably at most 10 mm.

Although in this example the SMA actuation apparatus 1 is a camera, this is not generally necessary. In some examples, the SMA actuation apparatus 1 may be an optical device in which the movable element is a lens element, but without an image sensor. In other examples, the SMA actuation apparatus 1 may be a type of apparatus that is not an optical device and in which the movable element is not a lens element and there is no image sensor.

The SMA actuation apparatus 1 further comprises a suspension system 30, the suspension system 30 supporting the lens element 20 on the support structure 2. The suspension system 30 is configured to guide movement of the lens element 20 along an optical axis O (thus, in this example, the optical axis O is the direction of movement) relative to the support structure 2, while limiting movement of the lens element 20 relative to the support structure 2 in other degrees of freedom, e.g., translational movement in a direction orthogonal to the direction of movement, and rotational movement about any one of a set of three orthogonal axes. The suspension system 30 includes a bearing arrangement, which will be described in more detail below.

The SMA actuation apparatus 1 further comprises two lengths of SMA actuator wires 40, the lengths of SMA actuator wires 40 being arranged as follows to drive movement of the lens element 20 along the optical axis O. The two lengths of SMA actuator wire 40 are part of a piece (a piece of) SMA actuator wire 41, the piece of SMA actuator wire 41 being connected at each end to the support structure 2 by crimped portions (crimp portions) 42 fixed at opposite angles at the top of the chassis 6. The crimp portion 42 crimps the piece of SMA actuator wire 41 to provide both a mechanical and an electrical connection. The piece of SMA actuator wire 41 is also connected to the lens element 20 by hooking around the protrusion 22. Thus, each of these lengths of SMA actuator wires 40 is connected at one end to the support structure 2 and at the other end to the lens element 20.

These lengths of SMA actuator wire 40 have an angled V-shaped arrangement of the type disclosed in WO2007/113478, as described below.

These lengths of SMA actuator wires 40 have an angle of 90 degrees therebetween when viewed along the optical axis O, which in this example is the direction of movement. More generally, the orientation of the lengths of SMA actuator wires 40 may be varied such that the angle between them, as viewed along the optical axis O, has any magnitude less than 180 degrees, preferably in the range 70 to 110 degrees.

Furthermore, the SMA actuator wires 40 of each length are inclined in the same direction (in the same sense) and at the same acute angle θ with respect to a plane orthogonal to the optical axis O, which in this example is the direction of movement, as shown in fig. 3. In this example, the angle θ is selected to be in the range of a lower limit of 5 degrees, or more preferably 8 degrees, to an upper limit of 15 degrees, or more preferably 12 degrees, with respect to a plane orthogonal to the moving direction. Thus, for example, the angle θ is relatively small compared to WO 2007/113478. This allows the overall height of the SMA actuation apparatus 1 along the optical axis O to be reduced because the extent to which these lengths of SMA actuator wires 40 project along the optical axis O is reduced.

This low value of angle θ increases the gain, which is the ratio of the amount of movement to the change in length of the length of SMA actuator wires 40, and the strain on the length of SMA actuator wires 40 that requires an increase in power of the drive signal. These factors may make it more difficult to maintain stability of the position of lens element 20. Surprisingly, however, it has been found that in practice, in SMA actuation apparatus 1, the stability of lens element 20 may actually be maintained over such angular ranges. This is due in part to the suspension system 30 being formed as a bearing arrangement (described in more detail below) because the bearings resist increased lateral forces. This also benefits from the lens 21 being made of glass, since the extra mass means that the extra lateral force from the SMA actuators 40 of these lengths is advantageous compared to using plastic, allowing a viable device to be manufactured. However, making the lens heavier will lower the resonant frequency, which may cause environmental vibrations to be a problem. Since the decrease in line angle also lowers the resonant frequency, there is a lower limit to the acceptable line angle range.

While it is advantageous to select the angle θ in the range of 8 degrees to 12 degrees, this is not required and the angle θ may be selected to have other values, such as values in excess of 12 degrees or in excess of 15 degrees.

The lengths of SMA actuator wires 40 drive the lens element 20 along the optical axis O upon application of a drive signal that causes heating and cooling of the lengths of SMA actuator wires 40. These lengths of SMA actuator wires 40 are resistively heated by the drive signal and cooled by heat conduction from the surrounding environment as the power of the drive signal is reduced. These lengths of SMA actuator wires 40 contract when heated to drive movement of the lens element 20 in a first direction (upward in fig. 1 and 2) along the optical axis O.

The SMA actuation apparatus 1 further comprises a compression spring 11, which compression spring 11 is connected between the base 4 of the support structure 2 and the lens element 20 and acts as a resilient biasing element for these lengths of SMA actuator wire 40. Thus, as the lengths of SMA actuator wires 40 cool, the compression springs 11 drive movement in opposite directions (downward in fig. 1 and 2) along the optical axis O. Thus, the temperature of these lengths of SMA actuator wires 40, and thus the position of the lens element 20 along the optical axis O, can be controlled by controlling the power of the drive signals.

The control circuit implemented in the IC chip 5 generates the drive signals and supplies them to the lengths of SMA actuator wires 40 connected thereto. The control circuit receives an input signal representing a desired position of the lens element 20 along the optical axis O and generates a drive signal having a power selected to drive the lens element 20 to the desired position. The power of the drive signal may be linear or may be varied using pulse width modulation (pulse width modulation).

The drive signal may be generated using closed loop control based on the output of the hall sensor 9 sensing the position of the lens element 20 along the optical axis O.

Alternatively, the drive signal may be generated using a resistive feedback control technique, which may for example be as in WO2013/175197; WO2014/076463; WO2012/066285; WO2012/020212; WO2011/104518; WO2012/038703; implementations are disclosed in any of WO2010/089529 or WO2010029316, each of which is incorporated herein by reference in its entirety.

The suspension system 30 will now be described with reference to fig. 4 to 6, fig. 4 to 6 showing three different bearing arrangements of the rolling bearing 31.

The suspension system 30 comprises a bearing arrangement of a plurality of rolling bearings 31. Each of the rolling bearings 31 comprises a bearing surface 32 on the support structure 2, in particular on the chassis 6, and a bearing surface 33 on the lens element 20, in particular on the lens carrier 25. Each of the rolling bearings 31 further comprises one or more balls 34 arranged between the bearing surfaces. Thus, the balls 34 act as rolling bearing elements, however, other types of rolling bearing elements, such as rollers, may alternatively be used.

Ideally, the bearing surface 32 on the support structure 2 has a low surface roughness in order to minimize friction and dynamic tilting. In some cases it may be sufficient that the bearing surface 32 be a plastic molded surface. More preferably, the bearing surface 32 is made of metal. When the chassis 6 is a molded element, this is achieved by the bearing surface 32 being the surface of a metal insert 35 arranged in the chassis 6. Similarly, alternatively or additionally, the bearing surface 33 on the lens element 20 may be a metal surface forming a surface of a metal insert arranged in a lens carrier, which is also a molded element.

Forming bearing surface 32 (and/or bearing surface 33) from metal imparts a smooth surface upon which balls 34 may run and allows for achieving the desired dynamic tilting performance. Defects in bearing surface 32 and bearing surface 33 may cause dynamic tilting. Such defects may take the form of surface curvature and surface roughness. If the number of balls 34 is reduced, or in the case of a plurality of balls 34, if the distance between the contact points of the upper and lower balls 34 is reduced, the influence of the defects of the bearing surfaces 32 and 33 on the dynamic tilting increases.

Three different bearing arrangements of the bearing 31 are arranged as follows.

The first bearing arrangement shown in fig. 4 comprises four bearings 31a-31d arranged as follows.

In each of the bearings 31a-31d, the bearing surface 32 on the support structure 2 is a planar surface, while the bearing surface 33 on the lens element 20 is a groove (although alternatively the bearing surface 32 on the support structure 2 may be a groove and the bearing surface 33 on the lens element 20 may be a planar surface). Here, as well as other positions where the bearing surface is a groove, the following applies. As the balls 34 roll, the grooves of the bearing surface 33 come into contact with the balls 34 along a pair of parallel lines. The planar surface on the bearing surface 33 is substantially parallel to the pair of parallel lines of contact in the groove of the bearing surface 33.

Since a planar surface is included on the bearing surface 32, each of the bearings 31a-31d restricts movement of the bearing surface 32 and the bearing surface 33 toward each other, but does not restrict lateral movement of the bearing surface 32 and the bearing surface 33.

The two bearings 31a, 31b are positioned against the protrusion 22 on opposite sides of the protrusion 22 as seen along the optical axis O. These bearings 31a, 31b comprise a plurality of balls 34, typically three balls 34, as shown in fig. 1 and 2. In the case where three or more balls 34 are provided, the inner ball 34 may be smaller in diameter than the outer two balls 33, and serve as spacers.

Because the bearings 31a, 31b are positioned against the protrusion 22, these bearings 31a, 31b apply a force to the position of the lens element 20 proximate to the length of SMA actuator wire 40, which helps limit rotation about an axis orthogonal to the plane containing the optical axis O (i.e., the axis into the page in fig. 3 and the axis lateral in fig. 4). This is because the couple of forces (couple) between the forces exerted by the SMA actuator wires 40 and the bearings 31a, 31b of these lengths is reduced when viewed perpendicular to the optical axis O compared to the bearings 31a, 31b located further away. This effect is improved by providing a plurality of balls 34 in the bearings 31a, 31b, which increases the length of the bearings 31a, 31b along the optical axis O. Thus, the dynamic tilting performance depends on the spacing of the two outer balls 34 in the bearings 31a, 31b and the flatness of the bearing surfaces 32 and 33.

The other bearings 31c, 31d are positioned close to the location where these lengths of SMA actuator wires 40 are connected to the chassis 6. Thus, the bearings 31c, 31d provide a limit to rotation about an axis near the compression spring 11 in a plane orthogonal to the optical axis O. Since the main function of the other bearings 31c, 31d is to prevent such rotation, the other bearings 31c, 31d may each comprise a single ball 33. Rotation of the lens element 20 about this axis is undesirable during normal operation, but is important for controlling unpowered drop events (unpowered drop events).

The other two bearings 31c, 31d are required, since in general the rotation allowed by the bearings 31a, 31b positioned against the protrusions in the plane orthogonal to the optical axis O can occur in either direction. However, the other bearings 31c, 31d must be arranged such that only one of the two balls 33 is in contact with the support structure 2 and the lens element 20, in order not to unduly limit the system.

Thus, in the first bearing arrangement, four bearings 31a-31d are used to prevent rotation, but the design requires several parts with tight tolerances in order to be able to be assembled without undue limitation. The second bearing arrangement and the third bearing arrangement provide a simplified design which provides loose tolerances and ease of assembly due to the reduced number of parts.

The second bearing arrangement shown in fig. 5 comprises only two bearings 31a, 31b. For the respective bearings 31a, 31b in the first bearing arrangement, these bearings 31a, 31b are positioned against the protrusion 22 on opposite sides of the protrusion 22 when seen along the optical axis O, and comprise a plurality of balls 34, typically three balls 34. In the case where three or more balls 34 are provided, the inner ball 34 may be smaller in diameter than the outer two balls 33, and serve as spacers. In this way, these bearings 31a, 31b help to limit rotation about an axis orthogonal to the plane containing the optical axis O, and the above explanation of the respective bearings 31a, 31b in the first bearing arrangement with respect to this effect applies equally to the second bearing arrangement.

However, the bearing surfaces 32 and 33 of the bearings 31a, 31b are changed compared to the first bearing arrangement for restricting rotation in a plane orthogonal to the optical axis O. In particular, in one of the bearings 31a, the bearing surface 32 on the support structure 2 and the bearing surface 33 on the lens element 20 are each grooves. As the balls 34 roll, each of the grooves of the bearing surface 32 and the grooves of the bearing surface 33 come into contact with the balls 34 along a pair of parallel lines that are parallel to each other.

In the other bearing 31b, there is still a case where the bearing surface 32 on the support structure 2 is a planar surface and the bearing surface 33 on the lens element 20 is a groove (however alternatively the bearing surface 32 on the support structure 2 may be a groove and the bearing surface 33 on the lens element 20 may be a planar surface).

This asymmetric arrangement of bearings 31a, 31b limits the movement of lens element 20 for rotation in a plane orthogonal to optical axis O. Conceptually, this limitation can be understood by considering grooves on the bearing surface 32 and the bearing surface 33 of the bearing 31a, which limit the movement of all degrees of freedom except for the rotation about the axis passing through the bearing 31a itself, which is itself limited by the other bearing 31 b. Because the other bearing 31b comprises a planar bearing surface 33, this constraint is imposed without unduly limiting the overall bearing arrangement.

The third bearing arrangement shown in fig. 6 comprises only three bearings 31a-31c. As in the first bearing arrangement, two of these bearings 31a, 31b are positioned against the projection 22 on opposite sides of the projection 22 when viewed along the optical axis O, and comprise a plurality of balls 34, typically three balls 34. In the case where three or more balls 34 are provided, the inner ball 34 may be smaller in diameter than the outer two balls 33, and serve as spacers. In this way, these bearings 31a, 31b help to limit rotation about an axis orthogonal to the plane containing the optical axis O, and the above explanation of the respective bearings 31a, 31b in the first bearing arrangement with respect to this effect applies equally to the third bearing arrangement.

However, in contrast to the first bearing arrangement, the two bearings 31a, 31b are asymmetrically arranged such that they apply a force couple to the lens element 2 in a plane orthogonal to the optical axis O. Such a couple generated by the two bearings 31a, 31b in the third bearing arrangement tends to generate a rotation in a specific direction, compared to the first bearing arrangement, in which rotation in a plane orthogonal to the optical axis O may be in either direction. Thus, only a single further bearing 31c may be provided to limit the rotation, which bearing 31c is positioned against the lens element 22 in a position in which it prevents the rotation. Since the main function of the other bearing 31c is to prevent such rotation, the other bearing 31c may comprise a single ball 33.

In this further bearing 31c, the bearing surface 32 on the support structure 2 is a planar surface and the bearing surface 33 on the lens element 20 is a groove (although alternatively the bearing surface 32 on the support structure 2 may be a groove and the bearing surface 33 on the lens element 20 may be a planar surface). In this way, the limitation of rotation can be imposed without excessively limiting the overall bearing arrangement.

Although the rolling bearing 31 is described above, the rolling bearing 31 may alternatively be replaced by a plain bearing (plain bearings).

In one example, a first type of slide bearing 41 illustrated in fig. 7 and 8 may be used. The sliding bearing 41 comprises an elongated bearing surface 43 on one of the support structure 2 and the lens element 20. The slide bearing 41 further comprises a protrusion 45 formed on the other of the support structure 2 and the lens element 20, the end of the protrusion 45 forming a bearing surface 46 bearing on the elongated bearing surface 43. Although two tabs 45 are shown in the example of fig. 8, generally any number of one or more tabs 45 may be provided. The elongate bearing surface 43 and the bearing surface 46 are conformal (in this example planar) allowing relative movement of the lens element 20 with respect to the support structure 2. Desirably, the elongated bearing surface 43 and the bearing surface 46 have a coefficient of friction of 0.2 or less.

In another example, a second type of slide bearing 51 shown in fig. 9 and 10 may be used. The sliding bearing 51 comprises a channel 52 on one of the support structure 2 and the lens element 20, the inner surface of the channel 52 forming a bearing surface 53. The slide bearing 51 comprises a protrusion 55 formed on the other of the support structure 2 and the lens element 20, the end of the protrusion 55 forming a bearing surface 56 supported on the bearing surface 53. Although two tabs 55 are shown in this example, generally any number of one or more tabs 55 may be provided. The elongate bearing surface 53 and the bearing surface 56 are conformal, in this example both planar, allowing relative movement of the lens element 20 with respect to the support structure 2. Desirably, the elongated bearing surface 53 and the bearing surface 56 have a coefficient of friction of 0.2 or less.

In each of the slide bearing 41 and the slide bearing 51, the material of the bearing surfaces 43, 46, 53, 56 is selected to provide smooth movement and long life. The bearing surfaces 43, 46, 53, 56 may be integral with the underlying component or may be formed of a surface coating. Suitable materials include, for example, PTFE or other polymeric bearing materials or metals.

It may be surprising that the sliding bearing can be used adequately for applications in which the lens element 20 is guided in movement along the optical axis O, provided that the lens element 20 needs to move smoothly over its lifetime without jamming (slip) and slipping. However, it has been found that the sliding bearing functions adequately by controlling the forces experienced by the bearing in the plane and perpendicular to the direction of movement within a suitable range. Thus, compared with the rolling bearing 31, the sliding bearing can provide a similar function of restricting movement in degrees of freedom other than along the optical axis O while reducing some or all of the above problems, as described below.

Because of the reduced number of parts, the manufacturing of the SMA actuator arrangement is simplified and the assembly of the bearings is easier to perform because there are no rolling bearings to operate. Similarly, the risk of the rolling bearing elements falling off the bearing in use due to insufficient mechanical constraints is eliminated.

Furthermore, the use of sliding bearings may allow for a reduction in the height of the SMA actuation arrangement along the optical axis, which is required for miniaturization of cameras and other optical devices. In particular, the overall height of the bearing surface may be reduced compared to a bearing comprising rolling bearing elements, while providing the required degree of dynamic tilting.

More generally, the rolling bearing 31 may also be replaced by any one of the following types of bearings: a jewel bearing; a fluid bearing; a magnetic bearing; a flexible bearing; or a composite bearing. Furthermore, the rolling bearing 31 may also be replaced by a rocker bearing or a pivot bearing, wherein the bearing element pivots or oscillates on the moving element and the stationary element.

The second SMA actuation apparatus to the fourth SMA actuation apparatus will now be described. Each of the second to fourth SMA actuation apparatus is a modified version of the first SMA actuation apparatus 1. Thus, only the changes will be described, in addition to the second to fourth SMA actuation arrangements having the structure of the first SMA actuation arrangement 1 as described above.

A second SMA actuation apparatus 60 is shown in fig. 11. In the second SMA actuation apparatus 60, the SMA actuator wires 40 of the two lengths in the first SMA actuation apparatus 1 are replaced by a single straight SMA actuator wire 61, the straight SMA actuator wire 61 being connected to the support structure 2 by a crimp portion 62 fixed to the projection and to the lens element 20 by a crimp portion 63 fixed to the lens carrier 25. The crimp portion 62 and the crimp portion 63 crimp the SMA actuator wire 61 to provide both a mechanical connection and an electrical connection.

The SMA actuator wires 61 have the same configuration as one of the lengths of SMA actuator wires 40 in the first SMA actuation apparatus 1 and are therefore inclined at an acute angle θ of greater than 0 degrees with respect to a plane orthogonal to the optical axis O.

The manufacture of the second SMA actuation apparatus 60 is simplified compared to both the first SMA actuation apparatus 1 and the angled V-shaped arrangement of WO2007/113478 in that there is only a single length of SMA actuator wire 61 and there is no need to hook the SMA actuator wire 61 onto the projection 22. The tilting of the SMA actuator wires 61 maintains the advantage of providing gain in terms of movement and is beneficial in minimizing the height of the second SMA actuation apparatus 60 along the optical axis O.

The SMA actuator wires 61 produce a substantial lateral force when compared to known arrangements using 2, 4, or 8 SMA actuator wires, which typically provide some balance of the lateral forces produced by the different SMA actuator wires. However, it has been recognized through analysis and experimentation that, surprisingly, these lateral forces can be substantially counteracted by the suspension system 30 due to the bearing arrangement using the bearings 31.

The assembly of the second SMA actuation apparatus 60 may be performed using the method disclosed in WO2016/189314, for example, as shown in fig. 12. The method uses a strut member 65, the strut member 65 being shaped to include a sacrificial strut body (sacrificial strut body) 66 and crimp tabs 67 held apart by the sacrificial strut body 66.

The SMA actuator wire 61 is placed in a known tension, for example, starting from a reel, across the crimping tab 67, and the crimping tab 67 is folded over and pressed against the SMA actuator wire 61 by a closing tool (not shown) to form a crimping portion 62 and a crimping portion 63 that hold the SMA actuator wire 61. The crimp portion 62 and the crimp portion 63 are then attached to the support structure 2 and the lens element 20, respectively, for example by mechanical means or adhesive means.

Thereafter, the sacrificial post body 66 is removed, leaving the crimp portions 62 and 63 attached to the support structure 2 and the lens element 20, respectively.

In the second SMA actuation apparatus 60, it is necessary to electrically connect both ends of the SMA actuator wire 61. This connection is direct at the support structure 2, as it is where the flexible circuit board 8 is located. The connection at the lens element 20 may be made in any suitable way, for example by a flexible connector or by some other component of the SMA actuation apparatus 60, such as the compression spring 11, or a flexure (if used as the suspension system 30).

The second actuation device 60 generates half the amount of force in the direction along the optical axis O compared to the first SMA actuation device 1. A third SMA actuation apparatus 70 that generates the same force as the first SMA actuation apparatus 1 is shown in fig. 13.

In the third SMA actuation apparatus 70, the single piece SMA actuator wires 41 hooked over the projection in the first SMA actuation apparatus 1 are replaced by two lengths of SMA actuator wires 71, the two lengths of SMA actuator wires 71 each being connected to the support structure 2 by a crimp portion 72 fixed to the projection 22 and each being connected to the lens element 20 by a crimp portion 73 fixed to the lens bracket 25. The crimp portions 72 and 73 crimp the SMA actuator wires 71 to provide both a mechanical and an electrical connection.

The two lengths of SMA actuator wires 71 have the same configuration as the lengths of SMA actuator wires 40 in the first SMA actuation apparatus 1 except for the manner of connection at the projection 22. Thus, the SMA actuator wire 71 has an angled V-shaped arrangement of the type disclosed in WO2007/113478, as described below.

The SMA actuator wires 71 of the two lengths have an angle of 90 degrees between them when viewed along the optical axis O, which in this example is the direction of movement. More generally, the orientation of the lengths of SMA actuator wires 71 may be varied such that the angle between them, as viewed along the optical axis O, has any magnitude less than 180 degrees, preferably in the range 70 to 110 degrees.

Furthermore, the SMA actuator wires 71 of each length are inclined in the same direction and at the same acute angle θ with respect to a plane orthogonal to the optical axis O, which in this example is the direction of movement. These lengths of SMA actuator wires 71 are also positioned at the same height along the optical axis O. In this example, the angle θ is selected to be in the range of 8 to 12 degrees with respect to a plane orthogonal to the direction of movement. This provides the same advantages as using such an angle in the first SMA actuation apparatus 1, and the explanation regarding this aspect of the first SMA actuation apparatus 1 applies equally to the third SMA actuation apparatus 70.

However, while it is advantageous to select the angle θ in the range of 8 degrees to 12 degrees, this is not required and the angle θ may be selected to have other values, such as values in excess of 12 degrees or in excess of 15 degrees.

The manufacture of the second SMA actuation apparatus 70 is simplified compared to both the first SMA actuation apparatus 1 and the angled V-shaped arrangement of WO2007/113478 in that there is no need to hook the lengths of SMA actuator wires 71 onto the projections 22 and the crimp portions 73 may each be attached to the projections 22. The tilting of these lengths of SMA actuator wires 71 maintains the advantage of providing gain in terms of movement and is beneficial in minimizing the height of the third SMA actuation apparatus 70 along the optical axis O.

In the third SMA actuation apparatus 70, in order to provide electrical connection with two lengths of SMA actuator wires 71, electrical connectors 78 are provided on the lens element 2, forming electrical connections between the lengths of SMA actuator wires 71. In one type of embodiment, the SMA actuator wires 71 and the electrical connector 78 of the two lengths may each be part of a single piece SMA actuator wire. In another type of embodiment, the two lengths of SMA actuator wires 71 may be separate pieces of SMA actuator wires, and the electrical connector 78 may be a separate component, such as a conductive track or metal element molded into the lens carrier 24 that connects the two crimp portions 73, or alternatively a body integral with the crimp portions 73. Thus, an electrical connection with the SMA actuator wires 71 of the two lengths can be made at the support structure by the crimp portions 72, which is direct in that it is where the flexible circuit board 8 is located. This allows the drive signal to be provided by the SMA actuator wires 71 in two lengths in series without any electrical connection being required at the lens element 20.

The assembly of the third SMA actuation apparatus 70 may be performed using the method disclosed in WO2016/189314, for example, as shown in fig. 12.

For each length of SMA actuator wire 71, the method may use a separate strut element 75 and then assemble each length of SMA actuator wire 71 by performing the assembly method of a single wire 61 twice in the second SMA actuation assembly 60 as described above.

Alternatively, the method may use a single strut element 75, the single strut element 75 being shaped to include a sacrificial strut body 76 and crimp tabs 77 for the SMA actuator wires 71 of the two lengths held apart by the sacrificial strut body 76. The strut element 75 has a 90 degree bend at the bend line 78 so that two lengths of SMA actuator wire 71 may be attached in their respective orientations.

The lengths of SMA actuator wires 71 are placed under known tension, for example, starting from a spool, across the crimping tabs 77, and the crimping tabs 77 are folded over and pressed over the lengths of SMA actuator wires 71 by a closing tool (not shown) to form the crimping portions 72 and 73 that hold the lengths of SMA actuator wires 71. The two lengths of SMA actuator wires 71 and the electrical connector 78 may be part of a single piece of SMA actuator wire, or alternatively the two lengths of SMA actuator wires 71 may be separate pieces of SMA actuator wire 71 and the electrical connector 78 may be part of the strut element 75.

The crimp portion 72 and the crimp portion 73 are then attached to the support structure 2 and the lens element 20, respectively, for example by mechanical means or adhesive means.

Thereafter, the sacrificial post body 76 is removed, leaving the crimp portions 72 and 73 attached to the support structure 2 and the lens element 20, respectively.

The third SMA actuation apparatus 70 may be modified to change the configuration or number of SMA actuator wires 71 of these lengths, including by way of non-limiting example arrangements in which: parallel inclined length SMA actuator wires 71 on the same side of the SMA actuation apparatus 70; an SMA actuator wire 71 providing intersecting lengths of opposite movement on one side of the SMA actuation apparatus 70; or two pairs of parallel lengths of SMA actuator wires 71 on adjacent sides of the SMA actuation apparatus 70.

Two alternative forms of fourth SMA actuation apparatus 80 are shown in fig. 15 and 16.

In the fourth SMA actuation apparatus 80, the bearing arrangement forming the suspension system 30 is changed such that the bearing 31 guides the movement of the lens element 20 relative to the support structure 2 in a movement direction M that is inclined at a first acute angle α of more than 0 degrees relative to the optical axis O of the lens element 20. Even with such modifications, the suspension system 30 remains limited to movement of the lens element 20 in other degrees of freedom relative to the support structure 2, such as translational movement in a direction orthogonal to the direction of movement, and rotational movement about any one of a set of three orthogonal axes.

Thus, the lens element 20 is allowed to have a component of lateral movement perpendicular to the optical axis O. However, such lateral movement may be acceptable in many applications. In addition, this has the advantage of reducing the force transmitted through the suspension system 30 and also the advantage of reducing the gain.

These lengths of SMA actuator wires 40 are inclined relative to the optical axis O at a second acute angle β that is greater than the first acute angle α. This means that the lengths of SMA actuator wires 40 remain tilted with respect to the movement direction M, but the angle θ of the lengths of SMA actuator wires 40 with respect to the normal to the optical axis O decreases. This allows the overall height of the fourth SMA actuation apparatus 80 to be reduced while maintaining the degree of travel and maintaining good control. In the fourth SMA actuation apparatus 80, the critical angle in determining the performance of these lengths of SMA actuator wires 40 is no longer the angle θ between these lengths of SMA actuator wires 40 and the plane orthogonal to the optical axis O, but rather the angle γ between these lengths of SMA actuator wires 40 and the plane orthogonal to the direction of movement M of the lens element 20 relative to the support structure 20. Thus, the size of the fourth SMA actuation apparatus 80 along the optical axis O is no longer limited by these lengths of SMA actuator wires 40.

In a first form of the fourth SMA actuation apparatus 80 shown in fig. 15, the lengths of SMA actuator wires 40 extend in a plane orthogonal to the optical axis O. In this case, the lengths of SMA actuator wires 40 have a minimum extent of projection along the optical axis O.

In a second form of the fourth SMA actuation apparatus 80 shown in fig. 16, the lengths of SMA actuator wires 40 extend at an angle θ of greater than 0 degrees relative to a plane orthogonal to the optical axis O. In this case, these lengths of SMA actuator wires 40 have a range projected along the optical axis O, but this can be controlled by adjusting the angle θ to fit within the dimensional limits of some other component of the SMA actuation apparatus. For example, the extent of the SMA actuator wires 40 of these lengths projected in the optical axis O direction may be arranged to be the same as or smaller than the extent of the bearing arrangement of the bearing 31 projected in the optical axis O direction.

It should be appreciated by those skilled in the art that while the foregoing has been described as being considered the best mode and other modes of the present technology have been performed where appropriate, the present technology should not be limited to the specific constructions and methods of the preferred embodiments disclosed in the present specification. Those skilled in the art will recognize that the present technology has a wide range of applications and that the embodiments may be modified in a wide range without departing from any of the inventive concepts defined in the appended claims.

Claims

1. A shape memory alloy actuation apparatus comprising:

a support structure;

a lens element comprising at least one lens supported on the support structure by a suspension system, the suspension system being arranged to guide movement of the lens element relative to the support structure in a direction of movement, the direction of movement being inclined at a first acute angle greater than 0 degrees relative to an optical axis of the lens element;

at least one length of shape memory alloy actuator wire connected between the support structure and the lens element for driving movement of the lens element relative to the support structure, the at least one length of shape memory alloy actuator wire being inclined relative to the optical axis at a second acute angle that is greater than the first acute angle.

2. The shape memory alloy actuation apparatus according to claim 1, wherein the suspension system comprises a bearing arrangement.

3. Shape memory alloy actuation device according to claim 2, wherein the bearing arrangement comprises at least one rolling bearing comprising bearing surfaces on the support structure and the lens element and at least one rolling bearing element arranged between the bearing surfaces.

4. A shape memory alloy actuation apparatus according to claim 3, wherein the at least one rolling bearing element comprises a plurality of bearing elements.

5. The shape memory alloy actuation apparatus of any of claims 2 to 4, wherein a range of the length of shape memory alloy actuator wire projected in the direction of the optical axis is the same as or less than a range of the bearing arrangement.

6. The shape memory alloy actuation apparatus of any of claims 1-4, wherein the length of shape memory alloy actuator wire extends at an angle greater than 0 degrees relative to a plane orthogonal to the optical axis.

7. The shape memory alloy actuation apparatus of claim 5, wherein the length of shape memory alloy actuator wire extends at an angle greater than 0 degrees relative to a plane orthogonal to the optical axis.

8. Shape memory alloy actuation apparatus according to any one of claims 1-4 and 7, wherein the suspension system is arranged to limit movement of the lens element relative to the support structure in degrees of freedom other than movement of the lens element relative to the support structure in the direction of movement.

9. A shape memory alloy actuation apparatus according to claim 5, wherein the suspension system is arranged to limit movement of the lens element relative to the support structure in degrees of freedom other than movement of the lens element relative to the support structure in the direction of movement.

10. The shape memory alloy actuation apparatus according to claim 6, wherein the suspension system is arranged to limit movement of the lens element relative to the support structure in degrees of freedom other than movement of the lens element relative to the support structure in the direction of movement.

11. The shape memory alloy actuation apparatus of any of claims 1-4, 7 and 9-10, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

12. The shape memory alloy actuation apparatus according to claim 5, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

13. The shape memory alloy actuation apparatus according to claim 6, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

14. The shape memory alloy actuation apparatus according to claim 8, wherein the support structure has an image sensor mounted thereon, the lens element being arranged to focus an image on the image sensor.

15. The shape memory alloy actuation apparatus of any of claims 1-4, 7, 9-10, and 12-14, wherein the at least one lens has a diameter of at most 20 mm.

16. The shape memory alloy actuation apparatus according to claim 5, wherein the at least one lens has a diameter of at most 20 mm.

17. The shape memory alloy actuation apparatus according to claim 6, wherein the at least one lens has a diameter of at most 20 mm.

18. The shape memory alloy actuation apparatus according to claim 8, wherein the at least one lens has a diameter of at most 20 mm.

19. The shape memory alloy actuation apparatus according to claim 11, wherein the at least one lens has a diameter of at most 20 mm.