WO2022263811A1

WO2022263811A1 - Voice coil motor actuator assembly

Info

Publication number: WO2022263811A1
Application number: PCT/GB2022/051496
Authority: WO
Inventors: Andrew Benjamin Simpson Brown
Original assignee: Cambridge Mechatronics Limited
Priority date: 2021-06-14
Filing date: 2022-06-14
Publication date: 2022-12-22
Also published as: CN117501167A; GB2607901B; GB202108466D0; GB2607901A

Abstract

An actuator assembly comprising a support structure, and a movable part movable relative to the support structure across a range of movement in two orthogonal directions perpendicular to a primary axis extending through the movable part. The assembly further comprising four voice coil motors (VCMs) arranged between the movable part and the support structure, and a controller configured to unidirectionally drive each of the four VCMs, thereby capable of producing forces for moving the movable part relative to the support structure to any position in said range of movement without applying any net torque to the movable part in the plane of the two orthogonal directions. The four VCMs arranged such that none of the forces produced by each of the four VCMs can be collinear.

Description

VOICE COIL MOTOR ACTUATOR ASSEMBLY

The present application relates to a voice coil motor (VCM) actuator assembly in which four VCMs drive movement of a movable part relative to a support structure.

It is known to use VCMs as actuators to drive movement of a movable part with respect to a support structure. Such actuators may be applied in a variety of devices including handheld devices, such as cameras and mobile phones. Such actuators may be applied in an optical device, such as a camera, for driving movement of a camera lens element in two orthogonal directions perpendicular to its optical axis, and/or driving movement of an image sensor in any direction laterally to its light- sensitive region, for example for optical image stabilisation (OIS).

In some applications, it is desirable to have actuators that can also drive rotation of a movable part relative to a support structure around a primary axis extending through the movable part. For example, in sensor-based OIS applications (wherein the image sensor is moved to achieve OIS) it is desirable to have actuators that can drive rotation of the image sensor around its primary axis (i.e. the axis extending through the centre of the image sensor and its light-sensitive surface, perpendicular to the light-sensitive surface) relative to the support structure, and that can also drive movement of the image sensor in any direction laterally to its light-sensitive surface relative to the support structure. Examples of such actuators are disclosed in JP2005184122A (Nikon Corp), JP2014067016A (Canon Inc), WO2013145793A (Olympus Corp) and WO2013175197A (Cambridge Mechatronics Limited).

VCM actuator assemblies capable of providing both rotation and lateral movement for e.g. OIS will now be described.

Summary

According to the present invention, there is provided an actuator assembly comprising a support structure, and a movable part movable relative to the support structure across a range of movement in two orthogonal directions perpendicular to a primary axis extending through the movable part. The actuator assembly further comprises four voice coil motors (VCMs) arranged between the movable part and the support structure, and a controller configured to unidirectionally drive each of the four VCMs, thereby capable of producing forces for moving the movable part relative to the support structure to any position in said range of movement without applying any net torque to the movable part in the plane of the two orthogonal directions. The four VCMs are arranged such that none of the forces produced by each of the four VCMs can be collinear. Having a controller configured to unidirectionally drive each of the four VCMs (i.e. configured to, for each coil of each VCM, only drive current in one direction; or, in other words, configured, for each coil of each VCM, to only drive current from a first end of the coil to a second end of the coil) can provide many benefits over a controller configured to bidirectionally drive VCMs. For example, such a controller may have a simpler design and comprise fewer components, allowing it to be cheaper and easier to manufacture, as well as be more compact.

Optionally, the four VCMs are arranged such that none of the forces produced by each of the four VCMs on the movable part can be codirectional.

Optionally, the four VCMs are arranged such that none of the forces produced by each of the four VCMs have a line of action passing through the primary axis.

Optionally, the movable part comprises an image sensor comprising a light-sensitive region (herein also referred to as a light-sensitive surface), and the primary axis is an axis orthogonal to the light- sensitive region of the image sensor. Moreover, the axis orthogonal to the light-sensitive region of the image sensor passes through the centre of the image sensor (including the centre of the light- sensitive region).

Alternatively, the movable part may comprise a lens assembly comprising one or more lenses. Where this is the case, the primary axis is the optical axis of the one or more lenses. Moreover, optionally, at least one of the one or more lenses is movable along the optical axis.

Optionally, each of the four VCMs comprise a coil fixed to the movable part and a corresponding magnet fixed to the support structure. For example, the four VCMs comprise four coils on the movable part, and four corresponding magnets (e.g. permanent magnets) on the support structure. Alternatively, each of the four VCMs comprise a magnet fixed to the movable part and a corresponding coil fixed to the support structure. For example, the four VCMs may comprise four magnets on the movable part, and four corresponding coils on the support structure. In both cases, the four coils/magnets fixed to the movable part may be arranged with two-fold rotational symmetry around the primary axis.

Optionally, the four VCMs are arranged such that the forces that can be produced by the four VCMs have two-fold rotational symmetry around the primary axis. Optionally, the movable part is capable of being rotated about the primary axis. In other words, optionally, the movable part is movable relative to the support structure in rotation about the primary axis.

Optionally, two of the four VCMs each apply a torque to the movable part in the plane of the two orthogonal directions around the primary axis in a first sense around the primary axis, and the other two VCMs apply a torque to the movable part in said plane around the primary axis in a second, opposite sense around the primary axis.

Optionally, the actuator assembly further comprises a suspension system supporting the movable part on the support structure in a manner allowing movement of the movable part relative to the support structure in the two orthogonal directions perpendicular to the primary axis.

Optionally, the four VCMs consist of two pairs of VCMs wherein the first pair of VCMs is arranged to be capable of being selectively driven to drive the movable part relative to the support structure in a first direction in said plane, and to generate a net torque to the movable part in said plane around the primary axis, and the second pair of VCMs is arranged to be capable of being selectively driven to drive the movable part relative to the support structure in a second direction in said plane transverse to the first direction, and to generate a net torque to the movable part in said plane around the primary axis that is in an opposite sense to the first pair of VCMs. Moreover, within each of the two pairs of VCMs, the two VCMs may be arranged on opposite sides of the primary axis. Alternatively, within each of the two pairs of VCMs, the two VCMs may be arranged on the same side of the primary axis at different distances from the primary axis.

Optionally, the movable part comprises a display, an emitter, or a part thereof. Where this is the case, the primary axis may be parallel to a general direction in which the display or emitter emits light.

The actuator assembly may correspond to (part of) an illumination source which may be for use in a 3D sensing system such as described in W02020/030916 or in an augmented reality (AR) display system.

Where the movable part comprises an emitter or a display (or a part thereof), the movable part may be moved to achieve wobulation, for example for the display of a super-resolution image (i.e. an image having a resolution higher than that of the intrinsic resolution of the emitter or display). In this case, a high-resolution image is displayed (or projected) by displaying a number of lower-resolution images at different positions in rapid succession. The image displayed at each position is a lower- resolution image formed of a subset of pixels of the high-resolution image. The movable part may be moved between the positions in a repeated pattern at a high frequency, for example greater than 30 Hz, preferably greater than 60 Hz, further preferably greater than 120 Hz. The succession of lower- resolution images is thus perceived by the human eye as one high-resolution image.

The display may be a display panel, for example a LCOS (liquid crystal on silicon) display, a MicroLED display, a digital micromirror device (DMD) or a laser beam scanning (LBS) system.

The emitter is configured to emit radiation (visible light or non-visible radiation, e.g. near infrared (NIR) light, short-wave infrared (SWIR) light). The emitter may comprise one or more LEDs or lasers, for example VCSELs (vertical-cavity surface-emitting lasers) or edge-emitting lasers. The emitter may comprise a VCSEL array. The emitter may otherwise be referred to as an illumination source and/or may comprise an image projector.

In the case that the movable part comprises a display, the display may define a plane and the primary axis may be perpendicular to the plane defined by the display. In any case, the primary axis may be aligned with a general direction in which light is emitted from the display. In the case that the movable part comprises an emitter, the emitter may define a plane and the primary axis may be perpendicular to the plane defined by the emitter. For example, the emitter may comprise a VCSEL array and the primary axis may be perpendicular to the plane of the VCSEL array. In any case, the primary axis may be aligned with a general direction in which radiation is emitted by the emitter.

Detailed Description

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

Fig. 1 is a schematic cross-sectional view of a camera apparatus;

Fig. 2 is a perspective view of the suspension system of the camera apparatus of Fig. 1;

Figs. 3 to 8 are plan views of different possible arrangements of VCMs in the camera apparatus of Fig. 1; and

Fig. 9 is a plan view of an alternative camera apparatus with the VCM arrangement of Fig. 7.

A camera apparatus 1 that is an example of a voice coil motor (VCM) actuation apparatus in accordance with the present invention is shown in Fig. 1, which is a cross-sectional view taken along the optical axis O. In order to clearly describe the main parts of the camera apparatus 1, the components of the VCMs are not shown in Fig. 1, but subsequently described with reference to Figs. 3 to 8. The camera apparatus 1 is to be incorporated in a portable electronic device such as a mobile telephone, media player or portable digital assistant.

The camera apparatus 1 comprises a lens element 2 supported on a support structure 4 by a suspension system 7, described in detail below, in a manner allowing movement of the lens element 2 relative to the support structure 4 in two orthogonal directions each perpendicular to the optical axis 0. Thus, the lens element 2 is a movable part.

The support structure 4 is a camera support supporting an image sensor 6 on the front side of the base 5 thereof. On the rear side of the base 5 there is mounted an 1C (integrated circuit) chip 30 in which the control circuit (herein also referred to as controller) is implemented, and also a vibration sensor 47 (e.g. a gyroscope sensor and/or an accelerometer).

The lens element 2 comprises a lens carrier 21 in the form of a cylindrical body supporting a lens 22 arranged along the optical axis O, although in general any number of lenses 22 may be provided. The camera apparatus 1 is a miniature camera in which the lens 22 (or lenses 22 if plural lenses are provided) has a diameter of at most 20 mm.

The lens element 2 is arranged to focus an image onto the image sensor 6. The image sensor 6 captures the image and may be of any suitable type, for example a CCD (charge-coupled device) or a CMOS (complementary metal-oxide-semiconductor) device. The lens 22 (or lenses 22 if plural lenses are provided) may be fixed relative to the lens carrier 21, or alternatively may be supported on the lens carrier in a manner in which the lens 22 (or at least one lens 22 if plural lenses are provided) is movable along the optical axis O, for example to provide focussing. Where the lens 22 is movable along the optical axis O, a suitable actuation system (not shown) may be provided, for example using a voice coil motor or SMA actuator wires, such as is described in WO2007/113478.

In operation, the lens element 2 is moved orthogonally to the optical axis O in two orthogonal directions, shown as X and Y relative to the image sensor 6. This is used to provide OIS, compensating for image movement of the camera apparatus 1, caused by for example hand shake.

The suspension system 7 is shown in isolation in Fig. 2 and arranged as follows. The suspension system 7 comprises four beams 71 connected between a support plate 72 that forms part of the support structure 4 and a lens plate 73 that forms part of the lens element 2 (and thus forms part of the movable part) and is connected to the rear end of the lens carrier 21 as shown in Fig. 1. The four beams 71 extend parallel to each other and to the optical axis 0, and therefore extend perpendicular to the orthogonal directions in which the lens element 2 moves, although they could extend at a non perpendicular angle, provided that they are transverse to the orthogonal directions.

The beams 71 are fixed to each of the support plate 72 and the lens plate 73 in a manner that the four beams 71 cannot rotate, for example by being soldered.

The beams 71 are positioned inside the support structure 4 and outside the lens carrier 21, the support plate 72 and the lens plate 73 having the same construction including respective apertures 74 and 75 aligned with the optical axis O to accommodate the lens element 2 and allow the passage of light to the image sensor 6. The beams 71 are equally spaced around the optical axis O, one at each corner of the camera apparatus 1.

The beams 71 thereby support the lens element 2 on the support structure 4 in said manner allowing movement of the lens element 2 relative to the support structure 4 in two orthogonal directions perpendicular to the optical axis O simply by means of the beams 71 bending, in particular in an S- shape. Conversely, the beams 71 resist movement along the optical axis O. The beams 71 may have any construction that provides the desired compliance perpendicular to the optical axis O, typically being formed by wires, for example metal wires.

In general, the suspension system 7 could have any alternative construction that allows movement of the lens element 2 relative to the support structure 4 in two orthogonal directions perpendicular to the optical axis O. For example, the suspension system 7 could employ ball bearings, plain bearings and/or flexures.

Movement of the lens element 2 may be driven by the actuator arrangements shown in Figs. 3 to 8. The actuator arrangements comprise a total of four VCM actuators 11 to 14. Each VCM actuator 11 to 14 has a corresponding coil fixed to the movable lens plate 73 and a corresponding magnet (e.g. a permanent magnet) fixed to the support structure 4 (not shown in the figures for clarity). The four VCM actuators 11 to 14 are arranged to drive movement of the lens element 2 relative to the support structure 4 in two orthogonal directions each perpendicular to the optical axis O (herein also referred to as the primary axis of the movable part). In other words, the four VCM actuators 11 to 14 are arranged to drive movement of the lens element 2 along a plane perpendicular to the optical axis

O.

VCM actuator arrangements Each of the VCM actuators 11 to 14 is configured to be driven unidirectionally. In other words, each of the VCM actuators 11 to 14 is configured to only be driven in a single predetermined direction in the above-mentioned plane. Moreover, the VCM actuators 11 to 14 are arranged such that none of the forces produced by each of the four VCM actuators 11 to 14 are codirectional. For example, in the actuator arrangements shown in Figs. 3 to 7, VCM actuator 11 is only configured to generate an electromagnetic force in the negative X direction, VCM actuator 12 is only configured to generate an electromagnetic force in the negative Y direction, VCM actuator 13 is only configured to generate an electromagnetic force in the positive X direction, and VCM actuator 14 is only configured to generate an electromagnetic force in the positive Y direction.

Each of the VCM actuators 11 to 14 is arranged at one side of the lens element 2 at different angular positions around the optical axis 0. The four VCM actuators 11 to 14 consist of a first pair of VCM actuators 11 and 13 arranged on opposite sides of the optical axis 0, and a second pair of VCM actuators 12 and 14 arranged on opposite sides of the optical axis 0. The first pair of VCM actuators 11 and 13 are capable on selective driving to move the lens element 2 relative to the support structure 4 in a first direction in said plane. The second pair of VCM actuators 12 and 14 are capable on selective driving to move the lens element 2 relative to the support structure 4 in a second direction in said plane transverse to the first direction. Movement in directions other than parallel to the first and second directions may be driven by a combination of actuation of these pairs of the VCM actuators 11 to 14 to provide a linear combination of movement in the transverse directions. Another way to view this movement is that simultaneous actuation of any pair of the VCM actuators 11 to 14 that are next to each other around the optical axis 0 will drive movement of the lens element 2 in a direction bisecting those two of the VCM actuators 11 to 14.

As a result, the VCM actuators 11 to 14 are capable of being selectively driven to move the lens element 2 relative to the support structure 4 to any position in a range of movement in two orthogonal directions perpendicular to the optical axis 0.

The position of the lens element 2 relative to the support structure 4 perpendicular to the optical axis 0 is controlled by selectively varying the electromagnetic forces generated by the VCM actuators 11 to 14. This is achieved by selectively varying the amount of current (herein also referred to as drive current) flowing through the coils of the VCM actuators 11 to 14.

The VCM actuators 11 to 14 are arranged such that none of the forces produced by the VCM actuators 11 to 14 are collinear. The VCM actuators 11 to 14 are also arranged such that none of the forces produced by the VCM actuators 11 to 14 have a line of action that passes through the optical axis 0. As a result, each VCM actuator 11 to 14 individually applies a torque to the lens element 2 in the plane of the two orthogonal directions around the optical axis O. Thus, the VCM actuators 11 to 14 are capable of being selectively driven to rotate the lens element 2 relative to the support structure 4 in said plane about the optical axis O.

Successive VCM actuators 11 to 14 around the optical axis O apply a force to the lens element 2 in alternate senses around the optical axis O. Each of the first pair of VCM actuators 11 and 13 apply a force to the lens element 2 in a first sense around the optical axis O (e.g. in an anticlockwise sense). Each of the second pair of VCM actuators 12 and 14 apply a force to the lens element 2 in a second opposite sense around the optical axis O (e.g. in a clockwise sense). In other words, the first pair of VCM actuators 11 and 13 generate a net torque to the lens element 2 in the first sense in the plane of the two orthogonal directions around the optical axis O, and the second pair of VCM actuators 12 and 14 generate a net torque to the lens element 2 in the second opposite sense in said plane around the optical axis O.

The amount of rotation of the lens element 2 relative to the support structure 4 about the optical axis O is controlled by selectively varying the electromagnetic forces generated by each of the VCM actuators 11 to 14.

When no rotation of the lens element 2 is required, the four VCM actuators 11 to 14 can apply cancelling torques when operated together. Thus, movement of the lens element 2 to any position in the range of movement may be achieved without applying any net torque to the lens element 2 in the plane of the two orthogonal directions around the optical axis O.

In the arrangements shown in Figs. 3 to 8, the forces produced by the first pair of VCM actuators 11 and 13 are parallel to each other, and the forces produced by the second pair of VCM actuators 12 and 14 are parallel to each other and perpendicular to the forces produced by the first pair of VCM actuators 11 and 13. However, this is not strictly necessary.

As shown in Figs. 3 to 5 and 8, the VCM actuators 11 to 14 may be arranged such that the forces produced by two of the four VCM actuators (e.g. VCM actuators 11 and 14 of Fig. 3) are directed towards a first notional point as viewed along the optical axis O, and the forces produced by the other two VCM actuators (e.g. VCM actuators 12 and 13 of Fig. 3) are directed towards a second notional point as viewed along the optical axis O. The first and second notional points being located on opposite sides of the optical axis O. As shown in Figs. 3 to 5, the VCM actuators 11 to 14 may be arranged such that said first and second notional points fall within the footprint of the movable part (i.e. the lens plate 73 and/or lens element 2) as viewed along the optical axis 0. Alternatively, as shown in Fig. 8, the VCM actuators 11 to 14 may be arranged such that said first and second notional points may fall outside the footprint of the movable part as viewed along the optical axis O. Alternatively, as shown in Figs. 6 and 7, the VCM actuators 11 to 14 may be arranged such that none of the forces produced by the VCM actuators 11 to 14 are directed towards common notional points as viewed along the optical axis O.

As shown in Figs. 3, 7 and 8, the coils of the VCM actuators 11 to 14 may be substantially equally spaced around the optical axis O. Alternatively, as shown in Figs. 4 to 6, two of the VCM actuators (e.g. VCM actuators 11 and 12 of Fig. 4) may be arranged to be closer to a first corner of the lens plate 73, and the other two VCM actuators (e.g. VCM actuators 13 and 14 of Fig. 4) may be arranged to be closer to a second opposing corner of the lens plate 73 as viewed along the optical axis O.

As shown in Figs. 4 to 7, the coils of the VCM actuators 11 to 14 may be arranged with two-fold rotational symmetry around the optical axis O.

As shown in Figs. 3 to 8, the four VCM actuators 11 to 14 may be arranged such that the forces produced by the four VCM actuators 11 to 14 have two-fold rotational symmetry around the optical axis O.

Controller

The coils of the four VCM actuators 11 to 14 are connected to the controller which generates drive signals for each of the VCM actuators 11 to 14 and supplies the drive signals to the VCM actuators 11 to 14.

The controller receives the output signals of the vibration sensor 47. The vibration sensor 47 detects the vibrations that the camera apparatus 1 is experiencing and its output signals represent those vibrations, specifically as the angular velocity of the camera lens element 2 in three dimensions.

The drive signals are generated by the controller in response to the output signals of the vibration sensor 47 so as to drive movement of the camera lens element 2 to stabilise an image focus by the camera lens 2 on the image sensor 6, thereby providing OIS. The drive signals may be generated using known feedback control techniques, for example, involving Hall effect sensors that provide an indication of the positioning of the lens element 2 relative to the support structure 4. The controller is configured to unidirectionally drive each of the four VCM actuators 11 to 14. In other words, the controller is configured to drive current through each coil in one predetermined direction only. This can provide many benefits over a controller configured to bidirectionally drive VCM actuators. For example, such a controller may have a simpler design and comprise fewer components, which allows it to be cheaper and easier to manufacture, as well as be more compact.

Alternatives

Any of the actuator arrangements discussed above may in general be applied to any type of movable part including ones other than a lens element.

For example, as shown in Fig. 9, any of the actuator arrangements discussed above may be used to move a movable image sensor assembly 730 comprising an image sensor 60 (instead of the lens element 2 and the lens plate 73), relative to a support structure of a camera apparatus for providing sensor-based OIS. Where this is the case, references to the optical axis 0 made above simply need to be replaced with references to the primary axis P of the image sensor 60 which extends through the centre of the image sensor 60 and its light-sensitive surface.

Moreover, for example, any of the actuator arrangements discussed above may be used to move any electronic component which is to be moved with respect to a support structure (e.g. a display, an emitter or part thereof).

In the above examples, each VCM actuator comprises a coil that is fixed to the movable lens plate 73 and a corresponding magnet (e.g. a permanent magnet) fixed to the support structure 4. Flowever, alternatively, the coils may be fixed to the support structure 4 and the magnets may be fixed to the movable lens plate 73 instead.

The coils of any of the actuator arrangements discussed herein may share magnets.

In general, it is not necessary for the VCM actuators 11 to 14 to be in a symmetrical or regular arrangement.

Various modifications to the camera apparatus 1 described above are possible. The lens plate 73 has a square shape as viewed along a primary axis but more generally could have any shape. The support structure 4 is illustrated schematically but could in general be any type of element suitable for supporting the lens element 2. More generally, the same type of actuator arrangements may in general be applied to any type of movable element including ones other than a lens element.

Claims

1. An actuator assembly comprising: a support structure; a movable part movable relative to the support structure across a range of movement in two orthogonal directions perpendicular to a primary axis extending through the movable part; four voice coil motors (VCMs) arranged between the movable part and the support structure; a controller configured to unidirectionally drive each of the four VCMs, thereby capable of producing forces for moving the movable part relative to the support structure to any position in said range of movement without applying any net torque to the movable part in the plane of the two orthogonal directions; and wherein the four VCMs are arranged such that none of the forces produced by each of the four VCMs can be collinear.

2. An actuator assembly according to claim 1, wherein the four VCMs are arranged such that none of the forces produced by each of the four VCMs on the movable part can be codirectional.

3. An actuator assembly according to claim 1 or 2, wherein the four VCMs are arranged such that none of the forces produced by each of the four VCMs have a line of action passing through the primary axis.

4. An actuator assembly according to any preceding claim, wherein the movable part comprises an image sensor comprising a light-sensitive region, and the primary axis is an axis orthogonal to the light-sensitive region of the image sensor.

5. An actuator assembly according to claim 4, wherein the axis orthogonal to the light-sensitive region of the image sensor passes through the centre of the image sensor.

6. An actuator assembly according to any one of claims 1 to 3, wherein the movable part comprises a lens assembly comprising one or more lenses, and the primary axis is the optical axis of the one or more lenses.

7. An actuator assembly according to claim 6, wherein at least one of the one or more lenses is movable along the optical axis.

8. An actuator assembly according to any preceding claim, wherein each of the four VCMs comprise a coil fixed to the movable part and a corresponding magnet fixed to the support structure.

9. An actuator assembly according to any of claims 1 to 7, wherein each of the four VCMs comprise a magnet fixed to the movable part and a corresponding coil fixed to the support structure.

10. An actuator assembly according to any preceding claim, wherein the four VCMs are arranged such that the forces that can be produced by the four VCMs have two-fold rotational symmetry around the primary axis.

11. An actuator assembly according to any preceding claim, wherein the movable part is capable of being rotated about the primary axis.

12. An actuator assembly according to any preceding claim, wherein two of the four VCMs each apply a torque to the movable part in the plane of the two orthogonal directions around the primary axis in a first sense around the primary axis, and the other two VCMs apply a torque to the movable part in said plane around the primary axis in a second, opposite sense around the primary axis.

13. An actuator assembly according to any preceding claim, further comprising a suspension system supporting the movable part on the support structure in a manner allowing movement of the movable part relative to the support structure in the two orthogonal directions perpendicular to the primary axis.

14. An actuator assembly according to any preceding claim, wherein the four VCMs consist of two pairs of VCMs and wherein: the first pair of VCMs is arranged to be capable of being selectively driven to drive the movable part relative to the support structure in a first direction in said plane, and to generate a net torque to the movable part in said plane around the primary axis, and the second pair of VCMs is arranged to be capable of being selectively driven to drive the movable part relative to the support structure in a second direction in said plane transverse to the first direction, and to generate a net torque to the movable part in said plane around the primary axis that is in an opposite sense to the first pair of VCMs.

15. An actuator assembly according to claim 14, wherein within each pair of VCMs, the two VCMs are arranged on opposite sides of the primary axis.

16. An actuator assembly according to claim 14, wherein within each pair of VCMs, the two VCMs are arranged on the same side of the primary axis at different distances from the primary axis.

17. An actuator assembly according to any of claims 1 to 3, or any of claims 8 to 16 when dependent on any of claims 1 to 3, wherein the movable part comprises a display, an emitter, or a part thereof.

18. An actuator assembly according to claim 17, wherein the primary axis is parallel to a general direction in which the display or emitter emits light.