WO2023166320A1 - Sma actuator assembly - Google Patents

Sma actuator assembly Download PDF

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Publication number
WO2023166320A1
WO2023166320A1 PCT/GB2023/050514 GB2023050514W WO2023166320A1 WO 2023166320 A1 WO2023166320 A1 WO 2023166320A1 GB 2023050514 W GB2023050514 W GB 2023050514W WO 2023166320 A1 WO2023166320 A1 WO 2023166320A1
Authority
WO
WIPO (PCT)
Prior art keywords
sma
movable part
actuator assembly
assembly according
movement
Prior art date
Application number
PCT/GB2023/050514
Other languages
French (fr)
Inventor
Andrew Benjamin Simpson Brown
Oliver HART
Original Assignee
Cambridge Mechatronics Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB2202987.0A external-priority patent/GB2616298A/en
Priority claimed from GBGB2204617.1A external-priority patent/GB202204617D0/en
Application filed by Cambridge Mechatronics Limited filed Critical Cambridge Mechatronics Limited
Publication of WO2023166320A1 publication Critical patent/WO2023166320A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/02—Mountings, adjusting means, or light-tight connections, for optical elements for lenses
    • G02B7/023—Mountings, adjusting means, or light-tight connections, for optical elements for lenses permitting adjustment
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/58—Optics for apodization or superresolution; Optical synthetic aperture systems
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/02—Mountings, adjusting means, or light-tight connections, for optical elements for lenses
    • G02B7/04—Mountings, adjusting means, or light-tight connections, for optical elements for lenses with mechanism for focusing or varying magnification
    • G02B7/08—Mountings, adjusting means, or light-tight connections, for optical elements for lenses with mechanism for focusing or varying magnification adapted to co-operate with a remote control mechanism
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/02—Mountings, adjusting means, or light-tight connections, for optical elements for lenses
    • G02B7/04—Mountings, adjusting means, or light-tight connections, for optical elements for lenses with mechanism for focusing or varying magnification
    • G02B7/10—Mountings, adjusting means, or light-tight connections, for optical elements for lenses with mechanism for focusing or varying magnification by relative axial movement of several lenses, e.g. of varifocal objective lens
    • G02B7/102—Mountings, adjusting means, or light-tight connections, for optical elements for lenses with mechanism for focusing or varying magnification by relative axial movement of several lenses, e.g. of varifocal objective lens controlled by a microcomputer

Definitions

  • the SMA actuator assembly comprises a control circuit configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about the one or more movement axes and/or movement of the movable part along the one or more movement axes relative to the support structure between predetermined positions in a repeated pattern.
  • the predetermined positions may also be referred to as predetermined orientations.
  • Each predetermined position/orientation may be defined by a particular angular position or angular orientation of the movable part relative to the support structure.
  • the image sensor may be configured to capture an image at each of the predetermined positions.
  • the SMA actuator assembly comprises a second resilient element, wherein the one or more SMA wires comprises a second SMA wire which is configured to, on contraction, deform the second resilient element and wherein the second resilient element is configured to oscillate at a second frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions.
  • the second frequency may be the resonant frequency of the second resilient element in the direction of deformation by the second SMA wire.
  • the second SMA wire may be driven at the second frequency.
  • the one or more SMA wires are configured to, on contraction, drive movement of the at least part of the movable part along the primary axis in a first direction and wherein the actuator assembly comprises a biasing arrangement configured to cause movement of the at least part of the movable part in a second direction along the primary axis, opposite to the first direction, and wherein the bearing arrangement converts movement of the at least part of the movable part along the primary axis into movement along the loop.
  • an SMA actuator assembly comprising a support structure; a movable part supported on the support structure in a manner allowing tilt of the movable part relative to the support structure about two orthogonal tilt axes; two or more SMA wires arranged to tilt the movable part relative to the support structure about the two orthogonal tilt axes; a control circuit configured to apply drive signals to the two or more SMA wires so as to drive tilting of the movable part relative to the support structure between predetermined positions in a repeated pattern.
  • the four SMA wires comprise two pairs of SMA wires, each pair of SMA wire is arranged on opposite sides of the movable part when viewed perpendicularly to the two orthogonal tilt axes.
  • Some embodiments further comprise a bearing arrangement allowing tilt of the movable part relative to the support structure about the two orthogonal tilt axes.
  • FIGS. 2A and 2B are perspective and cross-sectional views of an SMA actuator assembly in accordance with embodiments of the present invention.
  • Two of the four SMA wires may be arranged to apply a torque to the movable part 20 in a first sense, e.g. clockwise, like the SMA wires 30 connected to the top right and bottom left corners of the movable part 20 in Figure 1A.
  • the other two SMA wires 30 may be arranged to apply a torque to the movable part 20 in a second, opposite sense, e.g. anti-clockwise, like the SMA wires 30 connected to the top left and bottom right corners of the movable part 20 in Figure 1A.
  • the four SMA wires 30 may be arranged in a loop at different angular positions around the axis, successive SMA wires being arranged to apply a force to the movable part in alternate senses.
  • the arrangement of SMA wires 30, when viewed perpendicularly to the two orthogonal tilt axes x-y (so when viewed along the z axis), may be rotationally symmetrical. This may achieve the benefits of a symmetrically balanced arrangement of SMA wires of making movement control simpler and more accurate.
  • the basic concept of super resolution imaging is that a number of images are captured each with the image offset on the image sensor by a different amount. The images are then combined and the additional information afforded by the additional images is used to create an image of higher resolution (and/or possibly higher quality) than that of the original images.

Abstract

An SMA actuator assembly comprising a support structure; a camera module supported on the support structure in a manner allowing tilt of the camera module relative to the support structure about two orthogonal tilt axes, wherein the camera module comprises an image sensor and a lens assembly arranged to focus an image onto the image sensor; two or more SMA wires arranged to tilt the camera module relative to the support structure about the two orthogonal tilt axes; a control circuit configured to apply drive signals to the two or more SMA wires so as to drive tilting of the camera module relative to the support structure between predetermined positions in a repeated pattern.

Description

SMA ACTUATOR ASSEMBLY
Field
The present application relates to an SMA actuator assembly, in particular for tilting or moving (e.g. shifting or translating) a movable part (such as a camera module) relative to a support structure between predetermined positions in a repeated pattern, for example for the purpose of achieving super-resolution imaging or wobulation of an image.
Background
There is a desire to improve the quality of images from miniature cameras, such as those incorporated in laptops. The space available for such miniature cameras is very constrained and the size of such miniature cameras is limited in size to only a few millimetres in a lateral direction (e.g. along a y axis) that is perpendicular to the optical axis of the camera.
There is also a desire to improve the resolution of projected or otherwise displayed images and to improve the fill of pixels in such images through wobulation. Small size and low power consumption are key requirements for many applications such as AR light engines.
Summary
According to an aspect of the present invention, there is provided an SMA actuator assembly comprising a support structure; a movable part supported on the support structure in a manner allowing: tilt of the movable part about one or more movement axes; and/or movement of the movable part along one or more movement axes relative to the support structure. The SMA actuator assembly comprises one or more SMA wires arranged to tilt the movable part relative to the support structure about the one or more movement axes and/or move the movable part along the one or more movement axes; and a control circuit configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about the one or more movement axes and/or movement of the movable part along the one or more movement axes relative to the support structure between predetermined positions in a repeated pattern.
The SMA actuator assembly is compact in size. The high energy density of SMA wires allows rapid actuation with high actuation force combined with comparably small space requirements. Additionally, tilting in a repeated pattern allows the SMA actuator assembly to achieve super-resolution imaging or wobulation, depending on the device or optical element combined with the SMA actuator assembly.
The control circuit may be relatively simple and thus compact by limiting the drive scheme of the SMA wires to a predetermined pattern. In the case that tilting is employed, the tilt motion driven by the SMA wires particularly reduces the size of a movement envelope required for effective super-resolution imaging or wobulation using SMA wires, thus working in concert with the compact SMA wires to allow provision of an even more compact SMA actuator assembly.
According to the present invention, there is also provided an SMA actuator assembly comprising a support structure; a movable part supported on the support structure in a manner allowing tilt of the movable part relative to the support structure about one or more movement axes (also referred to as one or more tilt axes) and/or movement of the movable part along one or more movement axes (or tilt axes); one or more SMA wires arranged to tilt the movable part relative to the support structure about the one or more movement axes and/or move the movable part along the one or more movement axes. The movable part may be a camera module.
In some embodiments, the SMA actuator assembly comprises a control circuit configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about the one or more movement axes and/or movement of the movable part along the one or more movement axes relative to the support structure between predetermined positions in a repeated pattern. The predetermined positions may also be referred to as predetermined orientations. Each predetermined position/orientation may be defined by a particular angular position or angular orientation of the movable part relative to the support structure. The image sensor may be configured to capture an image at each of the predetermined positions.
In some embodiments, the movable part comprises an optical device comprising a lens assembly defining an optical axis, wherein the one or more movement axes are perpendicular to the optical axis. The optical device may be a camera module comprising an image sensor, wherein the lens assembly is arranged to focus an image onto the image sensor.
In some embodiments, the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving super-resolution imaging with the camera module. So, the predetermined positions or orientations may be such that the image focused by the lens assembly onto the image sensor shifts by a sub-pixel distance on tilting or movement of the movable part from one of the predetermined positions to the next predetermined position. The sub-pixel distance is a distance that is less than a pixel pitch of the image sensor.
In some embodiments, the SMA actuator assembly comprises a projector for projecting an image, wherein the movable part comprises at least a portion of the projector such that tilting or movement of the movable part relative to the support structure moves the projected image. The control circuit may be configured to apply the drive signals to the one or more SMA wires for the purpose of achieving wobulation of the projected image.
In some embodiments, the movable part comprises a display panel for displaying an image. The control circuit may be configured to apply the drive signals to the one or more SMA wires for the purpose of achieving wobulation of the displayed image.
In some embodiments, the predetermined positions in the repeated pattern are arranged in two degrees of freedom. The predetermined positions may be arranged in a square, for example. The movable part need not stop at the predetermined positions, but may move continuously through the predetermined positions.
In some embodiments, the control circuit is configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about two orthogonal tilt axes relative to the support structure between the predetermined positions in the repeated pattern and wherein the one or more SMA wires comprise four SMA wires, optionally a total of four SMA wires in an arrangement capable of applying a torque to the movable part about an axis perpendicular to the two orthogonal tilt axes.
In some embodiments, two of the four SMA wires are arranged to apply a torque to the movable part in a first sense and the other two SMA wires are arranged to apply a torque to the movable part in a second, opposite sense.
In some embodiments, the four SMA wires are arranged in a loop at different angular positions around the axis which is perpendicular to the two orthogonal tilt axes, successive SMA wires being arranged to apply a force to the movable part in alternate senses.
In some embodiments, the four SMA wires are arranged such that respective subsets of two SMA wires are arranged to apply a force to the movable part in four respective directions along the two orthogonal tilt axes.
In some embodiments, the four SMA wires comprise two pairs of SMA wires, each pair of SMA wire is arranged on opposite sides of the movable part when viewed perpendicularly to the two orthogonal tilt axes. In some embodiments, the SMA wires of each pair of SMA wires cross over or overlap when viewed perpendicularly to the two orthogonal tilt axes.
In some embodiments, the four SMA wires are arranged to apply forces to the movable part that are in angular directions offset by 90 degrees from each other.
In some embodiments, the one or more SMA wires comprise two or more SMA wires which are arranged parallel to the one or more movement axes, optionally in a plane.
In some embodiments, the one or more SMA wires are arranged to be angled relative to the one or more movement axes.
In some embodiments, the control circuit is configured to apply drive signals to the one or more SMA wires so as to induce tilting or movement of the movable part between the predetermined positions at a predetermined frequency.
In some embodiments, a resonance frequency of tilting the movable part about the one or more movement axes or moving the movable part along the one or more movement axes is substantially equal to the predetermined frequency, in particular differs by less than 10%, preferably less than 5% or less than 1%, from the predetermined frequency.
In some embodiments, the SMA actuator assembly comprises a first resilient element, wherein the one or more SMA wires comprises a first SMA wire which is configured to, on contraction, deform the first resilient element and wherein the first resilient element is configured to oscillate at a first frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions. The first frequency may be the resonant frequency of the first resilient element in the direction of deformation by the first SMA wire. The first SMA wire may be drive at the first frequency.
In some embodiments, the SMA actuator assembly comprises a second resilient element, wherein the one or more SMA wires comprises a second SMA wire which is configured to, on contraction, deform the second resilient element and wherein the second resilient element is configured to oscillate at a second frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions. The second frequency may be the resonant frequency of the second resilient element in the direction of deformation by the second SMA wire. The second SMA wire may be driven at the second frequency. In some embodiments, the first resilient element is configured to tilt or move the movable part about or along a first axis and the second resilient element is configured to tilt or move the movable part about or along a second axis perpendicular to the first axis. The first frequency may be substantially equal to the second frequency. The first SMA wire may be driven at the same frequency as the second SMA wire. The phase difference between drive signals applied to the first SMA wire and drive signals applied to the second SMA wire may be 90 degrees.
In some embodiments, the SMA actuator assembly comprises a bearing arrangement allowing tilt of the movable part relative to the support structure about the one or more movement axes and/or movement of the movable part relative to the support structure along the one or more movement axes.
In some embodiments, the bearing arrangement is configured to allow tilting of the movable part relative to the support structure about two orthogonal tilt axes, wherein the bearing arrangement is arranged to constrain translational movement of the movable part along the two orthogonal tilt axes, optionally wherein the bearing arrangement is further arranged to constrain translational and/or rotational movement of the movable part along and/or about an axis perpendicular to the two orthogonal tilt axes.
In some embodiments, the bearing arrangement is arranged to constrain movement of the movable part along the two orthogonal tilt axes at a position that is offset along an axis perpendicular to the two orthogonal tilt axes from the force applied by the two or more SMA wires to the movable part.
In some embodiments, the bearing arrangement comprises a sheet material or flexure connected between the support structure and the movable part, optionally wherein the sheet material or flexure extends in the plane defined by the one or more movement axes.
In some embodiments, the bearing arrangement comprises a pivot or a plain bearing, in particular a spherical plain bearing, or wherein the bearing arrangement comprises a compliant bulk material, such as a rubber.
In some embodiments, the SMA actuator assembly is configured to tilt or move the moveable part such that at least part of the movable part moves in a loop when viewed along a primary axis which is perpendicular to the one or more movement axes, optionally wherein the loop is an ellipse, optionally wherein the loop is a circle. In some embodiments, the bearing arrangement is configured to guide at least part of the movable part to move in a loop as viewed along a primary axis which is perpendicular to the one or more movement axes, optionally wherein the loop is an ellipse, optionally wherein the loop is a circle.
In some embodiments, the one or more SMA wires are configured to, on contraction, drive movement of the at least part of the movable part along the primary axis in a first direction and wherein the actuator assembly comprises a biasing arrangement configured to cause movement of the at least part of the movable part in a second direction along the primary axis, opposite to the first direction, and wherein the bearing arrangement converts movement of the at least part of the movable part along the primary axis into movement along the loop.
In some embodiments, the bearing arrangement is configured to guide the at least part of the movable part along a helical path about the primary axis.
In some embodiments, the one or more SMA wires comprises a total of one SMA wire which induces the tilting or movement of the movable part between the predetermined positions.
According to the present invention, there is also provided an SMA actuator assembly comprising a support structure; a movable part supported on the support structure in a manner allowing tilt of the movable part relative to the support structure about two orthogonal tilt axes; two or more SMA wires arranged to tilt the movable part relative to the support structure about the two orthogonal tilt axes; a control circuit configured to apply drive signals to the two or more SMA wires so as to drive tilting of the movable part relative to the support structure between predetermined positions in a repeated pattern.
In some embodiments, the movable part comprises an optical device comprising a lens assembly defining an optical axis, wherein the two orthogonal tilt axes are perpendicular to the optical axis.
In some embodiments, the optical device is a camera module comprising an image sensor, wherein the lens assembly is arranged to focus an image onto the image sensor.
In some embodiments, the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving super-resolution imaging of the camera module.
In some embodiments, the SMA actuator assembly comprises a projector for projecting an image, wherein the movable part comprises at least a portion of the projector such that tilting of the movable part relative to the support structure moves the projected image. In some embodiments, the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving wobulation of the projected image.
In some embodiments, the movable part comprises a display panel for displaying an image.
In some embodiments, the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving wobulation of the displayed image.
In some embodiments, the predetermined positions in the repeated pattern are arranged in two degrees of freedom.
In some embodiments, the two or more SMA wires comprise a four SMA wires, optionally a total of four SMA wires in an arrangement capable of applying a torque to the movable part about an axis perpendicular to the two orthogonal tilt axes.
In some embodiments, two of the four SMA wires are arranged to apply a torque to the movable part in a first sense and the other two SMA wires are arranged to apply a torque to the movable part in a second, opposite sense.
In some embodiments, the four SMA wires are arranged in a loop at different angular positions around the axis, successive SMA wires being arranged to apply a force to the movable part in alternate senses.
In some embodiments, the four SMA wires are arranged such that respective subsets of two SMA wires are arranged to apply a force to the movable part in four respective directions along the two orthogonal tilt axes.
In some embodiments, the four SMA wires comprise two pairs of SMA wires, each pair of SMA wire is arranged on opposite sides of the movable part when viewed perpendicularly to the two orthogonal tilt axes.
In some embodiments, the SMA wires of each pair of SMA wires cross over or overlap when viewed perpendicularly to the two orthogonal tilt axes.
In some embodiments, the four SMA wires are arranged to apply forces to the movable part that are in angular directions offset by 90 degrees from each other. In some embodiments, the two or more SMA wires are arranged parallel to the two orthogonal tilt axes, optionally in a plane.
In some embodiments, the two or more SMA wires are arranged to be angled relative to the two orthogonal tilt axes.
In some embodiments, the control circuit is configured to apply drive signals to the two or more SMA wires so as to drive tilting of the movable part between the predetermined positions at a predetermined frequency.
In some embodiments, the resonance frequency of tilting the movable part about the two orthogonal tilt axes is substantially equal to the predetermined frequency, in particular differs by less than 10%, preferably less than 5% or less than 1%, from the predetermined frequency.
Some embodiments further comprise a bearing arrangement allowing tilt of the movable part relative to the support structure about the two orthogonal tilt axes.
In some embodiments, the bearing arrangement is arranged to constrain translational movement of the movable part along the two orthogonal tilt axes, optionally wherein the bearing arrangement is further arranged to constrain translational and/or rotational movement of the movable part along and/or about an axis perpendicular to the two orthogonal tilt axes.
In some embodiments, the bearing arrangement is arranged to constrain movement of the movable part along the two orthogonal tilt axes at a position that is offset along an axis perpendicular to the two orthogonal tilt axes from the force applied by the two or more SMA wires to the movable part.
In some embodiments, the bearing arrangement comprises a sheet material or flexure connected between the support structure and the movable part, optionally wherein the sheet material or flexure extends in the plane defined by the two orthogonal tilt axes.
In some embodiments, the bearing arrangement comprises a pivot or a plain bearing, in particular a spherical plain bearing, or wherein the bearing arrangement comprises a compliant bulk material, such as a rubber.
Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figures 1A and IB are schematic perspective and cross-sectional views of an SMA actuator assembly in accordance with embodiments of the present invention;
Figures 2A and 2B are perspective and cross-sectional views of an SMA actuator assembly in accordance with embodiments of the present invention;
Figures 3A and 3B are plan and side views of an SMA actuator assembly in accordance with embodiments of the present invention;
Figure 4 is a side view of an SMA actuator assembly in accordance with embodiments of the present invention;
Figure 5 is a plan view of an SMA actuator assembly in accordance with embodiments of the present invention; and
Figures 6A-D are schematic diagrams illustrating a particular method of achieving super-resolution imaging or wobulation.
Detailed description
Figures 1 and 2 schematically show SMA actuator assemblies 1 in accordance with the present invention. The SMA actuator assemblies 1 comprise a support structure 10 and a movable part 20. The movable part 20 is supported on the support structure 10 in a manner allowing tilt of the movable part 20 relative to the support structure 10 about two orthogonal tilt axes (the x and y axes in the depicted embodiments). In some embodiments, the SMA actuator assembly 1 comprises a bearing arrangement 40 that allows tilt of the movable part 20 relative to the support structure 10 about the two orthogonal tilt axes x,y.
Although movement of the movable part 20 is described herein with reference to a static support structure 10, it will be appreciated that this movement is merely relative. The support structure 10 need not be static, and may itself move either within a device into which the SMA actuator assembly 1 is incorporated or as part of such a device. The SMA actuator assembly 1 comprises two or more SMA wires 30. The SMA wires 30 are arranged to tilt the movable part 20 relative to the support structure 10 about the two orthogonal tilt axes x,y.
The SMA actuator assembly 1 further comprises a control circuit (not shown) configured to apply drive signals to the two or more SMA wires 30 so as to drive tilting of the movable part 20 relative to the support structure 10. The control circuit drives such tilting between predetermined positions in a repeated pattern. One example drive scheme that may be implemented by the control circuit is described with reference to Figure 3.
For example, the control circuit may apply PWM (pulse width modulated) control signals to the SMA wires 30. Supplying electrical power to the SMA wires 30 heats the SMA wires 30. Upon reaching a transition temperature, the SMA wire 30 starts contracting. The amplitude and/or frequency of SMA wire contraction can be controlled by supplying appropriate PWM control signals, thus allowing selective and targeted contraction of the SMA wires 30 in the arrangement so as to accurately move/tilt the movable part 20 relative to the support structure 10.
Movement in a repeated pattern
The control circuit drives tilting between predetermined positions in a repeated pattern. Such tilting between predetermined positions in a repeated pattern may be used in a variety of applications, for example to achieve super-resolution imaging or wobulation.
The predetermined positions in the repeated pattern may be at least two positions. So, the movable part 20 may repeatedly move between two predetermined positions. The predetermined positions in the repeated pattern may be four (or more) positions.
Preferably, the predetermined positions in the repeated pattern may be arranged in two degrees of freedom. The predetermined positions may form a square, for example. In general, the predetermined positions may form a triangle, pentagon, hexagon, or any other regular shape. The predetermined positions may be positioned along a loop, for example an elliptical (e.g. circular) path.
The predetermined positions may be stationary positions, so the movable part 20 may stop at each of the predetermined positions before moving on to the next of the predetermined positions.
Alternatively, the movable part 20 may move continuously between the predetermined positions, for example along a predetermined continuous path. Super-resolution imaging
In some embodiments, the movable part 20 comprises an optical device. The optical device may, for example, comprise a lens assembly defining an optical axis. The two orthogonal tilt axes x-y are perpendicular to the optical axis.
With reference to Figure 1, the optical device may be a camera module 21. The camera module 21 comprises an image sensor and the lens assembly. The lens assembly is arranged to focus an image onto the image sensor.
The control circuit may be configured to apply the drive signals to the SMA wires 30 for the purpose of achieving super-resolution imaging with the camera module 21. In particular, the control circuit drives movement of the movable part between predetermined positions in a repeated pattern, which in turn moves the image on the image sensor between predetermined image positions in the repeated pattern. The image on the image sensor may, for example, move by a sub-pixel distance between the predetermined image positions. Super-resolution imaging may then be achieved, for example, by combining two or more images that are captured at positions offset from one another by a sub-pixel distance.
For this purpose, the movable part 20 may be controllably moved/tilted between predetermined positions that are offset from each other such that the image on the image sensor moves, in a direction parallel to the light-sensitive region of the image sensor, by a sub-pixel distance. Light that falls onto a center of a pixel at one position (and so may be used to capture an image) thus falls between pixels at another position. The control circuit may drive the SMA wires 30 so as to controllably move the movable part 20 in this manner. A sub-pixel distance is a distance that is less than a pixel pitch of the light-sensitive region of the image sensor. The pixel pitch refers to the distance between the centeres of two adjacent pixels.
The movable part may be controllably moved such that the image on the image sensor moves to a positional accuracy of 0.5pm or smaller. Particular advantage is achieved in the case that the actuator arrangement comprises plural SMA wires, as SMA provides a high actuation force compared to other forms of actuator. This may assist in accurate positioning of the movable part relative to the support structure.
The predetermined positions may be offset from one another in a direction along a pixel row and/or along a pixel column of the light-sensitive region of the image sensor. The predetermined positions may comprise i) one or more positions that are offset from a starting position by a sub-pixel distance along a pixel row, and ii) one or more positions that are offset from a starting position by a sub-pixel distance along a pixel column. Optionally, the two or more positions may comprise one or more positions that are offset from a starting position by a sub-pixel distance along a pixel row and along a pixel column.
Images are captured at each of the predetermined positions using the image sensor. A controller may control the image sensor so as to capture the images. The controller may be implemented as part of the control circuit or as part of another circuit. Alternatively, the controller may be implemented as part of the processor that forms part of the portable electronic device.
The images may then be combined so as to form a super-resolution image, for example using the processor of the portable electronic device or the above-described controller. The super-resolution image has a resolution that is greater than the resolution of the individual images that are captured by the image sensor. For example, the two or more images may be combined by interleaving the two or more images.
Wobulation
With reference to Figure 2, the SMA actuator assembly 1 may comprise a projector 22. The projector 22 may project an image. The movable part 20 comprises at least a portion of the projector 22, such that tilting of the movable part 20 relative to the support structure 10 moves the projected image. The movable part 20 may, for example, comprise an light-emitting element, such as a laser or laser array, or a light-modifying element, such as a diffraction grating or reflection element. In either case, movement of the movable part 20 may move the projected image.
The control circuit is configured to apply the drive signals to the two or more SMA wires 30 for the purpose of achieving wobulation of the projected image. In this regard, wobulation may be achieved in general in a synonymous manner described with reference to super-resolution imaging. Instead of capturing an image with an image sensor at each predetermined position, the projector may project an image at each predetermined position. The image projected at each predetermined position may be a lower resolution image formed of a subset of pixels of a high-resolution image. The high-resolution image may thus be effectively split into multiple lower-resolution images that are projected in rapid succession. The movable part 20 may be moved between the predetermined positions in the repeated pattern at a frequency of greater than 30 Hz, preferably greater than 60 Hz, further preferably greater than 120 Hz, such that the succession of lower-resolution images is perceived by the human eye as one high-resolution image. Instead of providing a projector, the movable part 20 may comprise a display panel for displaying an image. The control circuit may be configured to apply the drive signals to the two or more SMA wires for the purpose of achieving wobulation of the displayed image.
Arrangement of SMA wires 30
Figures 1 and 2 depict two possible embodiments of arrangements of SMA wires 30 for driving tilt of the movable part 20 relative to the support structure 10. These arrangements of SMA wires 30 are particularly compact and so especially suitable for applications with limited space constraints. In general, any other arrangements of SMA wires 30 capable of tilting the movable part 20 relative to the support structure may be used.
In general, at least two SMA wires 30 are provided so as to allow tilting in at least two degrees of freedom. The two SMA wires 30 may be opposed by a resilient element, such as a spring.
Preferably, the SMA actuator assembly 30 comprises at least three SMA wires 30. This allows the tension in the SMA wires 30 to be controlled (as a third degree of freedom), allowing more accurate movement control of the movable part 20, which is particularly beneficial for the purposes of achieving super-resolution imaging and wobulation.
As shown in Figures 1 and 2, the SMA actuator assembly 1 may comprise four SMA wires 30, preferably a total of four SMA wires 30. This allows for a more symmetric arrangement of SMA wires 30, allowing more accurate and reliable movement control with less complexity in the drive scheme.
The SMA wires 30 may be connected between the movable part 20 and support structure 10. One end of each SMA wire 30 may be connected to the movable part 20 by a connection element 23, such as a moving crimp. The other end of each SMA wire 30 may be connected to the support structure 10 by a connection element 13, such as a static crimp. Alternatively, the SMA wires 30 may be connected at both ends to the support structure 10 or movable part 20 and hooked about a contact part with the movable part 20 or support structure 10, for example. Further alternatively, an intermediate mechanism may be provided between the SMA wires 30 and the movable part 20 and/or support structure 10 so as to transfer the force imparted by contraction of the SMA wires 30.
The SMA wires 30 may be in an arrangement as described in WO 2013/175197 Al, which is herein incorporated by reference. So, the SMA wires 30 may be in an arrangement capable of applying a torque to the movable part 20 about an axis z perpendicular to the two orthogonal tilt axes x,y. This allows the torque about the axis z to be controlled by the SMA wires 30, for example so as to reduce or mitigate rotation about the axis z. A bearing arrangement constraining rotation about the axis z may not be required with such an SMA wire arrangement, allowing the SMA actuator assembly 30 to be made more compact.
Two of the four SMA wires may be arranged to apply a torque to the movable part 20 in a first sense, e.g. clockwise, like the SMA wires 30 connected to the top right and bottom left corners of the movable part 20 in Figure 1A. The other two SMA wires 30 may be arranged to apply a torque to the movable part 20 in a second, opposite sense, e.g. anti-clockwise, like the SMA wires 30 connected to the top left and bottom right corners of the movable part 20 in Figure 1A. Put another way, the four SMA wires 30 may be arranged in a loop at different angular positions around the axis, successive SMA wires being arranged to apply a force to the movable part in alternate senses.
Furthermore, the four SMA wires may arranged such that respective subsets of two SMA wires are arranged to apply a force to the movable part in four respective directions along the two orthogonal tilt axes x,y. For example, the two SMA wires 30 provided on the left of Figure 1A may apply a force in the - x direction and the two SMA wires provided 30 on the right of Figure 1A may apply a force in the +x direction. The two SMA wires 30 connected to the top of the movable part 20 in Figure 1A may apply a force in the -y direction and the two SMA wires 30 connected to the bottom of the movable part 20 in Figure 1A may apply a force in the +y direction. This provides for a symmetrically balanced arrangement of SMA wires, making movement control simpler and more accurate.
In general, the arrangement of SMA wires 30, when viewed perpendicularly to the two orthogonal tilt axes x-y (so when viewed along the z axis), may be rotationally symmetrical. This may achieve the benefits of a symmetrically balanced arrangement of SMA wires of making movement control simpler and more accurate.
As shown in Figure 1A, the four SMA wires 30 may comprise two pairs of SMA wires. Each pair of SMA wire may be arranged on opposite sides of the movable part 20 when viewed perpendicularly to the two orthogonal tilt axes x-y (so when viewed along the z axis). This allows the SMA actuator assembly 1 to be made more compact along one of the orthogonal axes (here along the y axis), which is particularly useful in applications such as laptop cameras. The SMA wires 30 of each pair of SMA wires may cross over or overlap when viewed perpendicularly to the two orthogonal tilt axes x-y. This allows the SMA wires 30 to be made longer compared to a situation in which such overlap is not allowed (for a given orientation of the SMA wires). The SMA wires in each pair may be offset along the z axis, to avoid the SMA wires coming into direct physical contact or rubbing against each other on contraction. As shown in Figures 1A and 2A, the four SMA wires 30 may be arranged to apply forces to the movable part that are in angular directions offset by 90 degrees from each other. The SMA wires 30 may extend in angular directions offset by 90 degrees from each other. This provides for a particularly balanced arrangement of SMA wires.
The SMA wires 30 may be arranged parallel to the two orthogonal tilt axes x-y, optionally in a plane. This may reduce the size of the SMA actuator assembly in a direction perpendicular to the orthogonal tilt axes x-y (so along the z axis). There may be no need for a bearing arrangement constraining movement of the movable part 20 along the z axis.
So, as shown in Figs 1A and IB, the SMA wires 30 may be mounted at the top of the camera module 21. In this design, the SMA wires 30 lie in a plane normal to the optical axis and are at 90 degrees relative to each other. The wires are displaced slightly along the z axis so that they can cross without touching. The wires are at 90 degrees relative to each other so that the lines of force produced by the wires are all orthogonal. This is preferred (but not required) as it increases the symmetry of the motion of the actuator.
Similarly, as shown in Figs 2A and 2B, the SMA wires 30 are mounted at the top of the projector 22. In this design the wires lie in a plane normal to the optical axis and are in the SMA wire arrangement described in WO 2013/175197 Al .
Alternatively, the two or more SMA wires may be arranged to be angled relative to the two orthogonal tilt axes. This may be particularly useful, for example, when a plain bearing or rolling bearing is provided, because the angled SMA wires may bias the movable part 20 against the plain bearing or rolling bearing. So, the SMA wires could be angled down from the moving part 20 to the support structure. In this case, a bearing constraint to prevent the camera module 21 moving in the -z direction is advantageous.
Bearing arrangement 40
The SMA actuator assembly 1 may further comprise a bearing arrangement 40. The bearing arrangement 40 allows tilt of the movable part 20 relative to the support structure 10 about the two orthogonal tilt axes x,y. The bearing arrangement 40 is arranged to constrain translational movement of the movable part 20 along the two orthogonal tilt axes. So, translational movement of the movable part 20 along the x or y axes may be reduced or even prevented.
Optionally, the bearing arrangement is further arranged to constrain translational and/or rotational movement of the movable part 20 along and/or about an axis z perpendicular to the two orthogonal tilt axes x-y.
As shown in Figures IB and 2B, the bearing arrangement 40 is arranged to constrain movement of the movable part 20 along the two orthogonal tilt axes at a position that is offset along an axis z perpendicular to the two orthogonal tilt axes x-y from the force applied by the two or more SMA wires 30 to the movable part 20.
Figures IB and 2B show the bearing arrangement 40 in the form of a sheet material or flexure. The sheet material or flexure is connected between the support structure 10 and the movable part 20. The sheet material or flexure spans a gap between the support structure 10 and the movable part 20.
In particular, the sheet material or flexure extends along one or both of the two orthogonal tilt axes x-y. The sheet material or flexure may be flat, with a smaller extent along the z axis compared to the x or y axes. The sheet material or flexure may extend generally in the plane defined by the two orthogonal tilt axes x-y.
So, in the design of Fig IB, the camera module 21 is constrained from moving along the x and y axes by the sheet material or flexure that is connected to both the camera module 21 and the support structure 10 at the bottom of the camera module 21. The sheet material or flexure could be the FPC or a PCB that the image sensor of the camera module 21 is mounted on, or it could be an additional component such as sheet stainless steel.
Similarly, as shown in Fig 2B, the projector 22 is constrained from moving along the x and y axes by the sheet material or flexure that is connected to both the projector 22 and the support structure 10 at the bottom of the projector 22. This sheet material or flexure could be embodied by the FPC or PCB that the light emitting element is mounted on or could be an additional component such as sheet stainless steel.
Although the bearing arrangement 40 in Figures IB and 2B is embodied by a flexure, many other suitable bearing arrangements 40 are available. For example, the bearing arrangement 40 may comprise a pivot point about which the movable part pivots so as to tilt about the two orthogonal axes x-y. The bearing arrangement 40 may comprise a plain bearing, for example a spherical plain bearing such as a ball. The center of the sphere or ball may be at the intersection of the two orthogonal tilt axes x-y-
Further alternatively, the bearing arrangement 40 may comprises a compliant bulk material, such as rubber.
So, in a variant of any of the above designs, the flexure or sheet material could be replaced by a pivot or bearings providing lateral constraint. In a further variant, the flexure could be replaced by a rubber or compliant material that is placed under the camera module 21 or projector. This material could also be used to influence the resonant frequency.
The embodiments of the present invention have been described in combination with several examples of a bearing arrangement 40. However, in general, provision of a bearing arrangement 40 is not strictly required and the movable part 20 may be supported on the support structure 10 solely by the SMA wires 30. For example, the eight SMA wires of WO 2011/104518 Al, which is herein incorporated by reference, may support the movable part 20 and drive tilt of the movable part 20 relative to the support structure 10 in the absence of any bearing arrangement 40.
Resonance design
In some embodiments of the present invention, the SMA wires not only drives tilt of the movable part 20, but also acts as a spring that causes resonant motion at the desired frequency.
In this regard, the control circuit may be configured to apply drive signals to the two or more SMA wires so as to drive tilting of the movable part between the predetermined positions in the repeated pattern at a predetermined frequency.
The resonance frequency of tilting the movable part about the two orthogonal tilt axes may be substantially equal to the predetermined frequency. So, the resonance frequency may differs by less than 10%, preferably less than 5% or less than 1%, from the predetermined frequency.
The resonance frequency of the SMA actuator assembly may be influenced by the diameter, length of the SMA wires, height of the wires from the orthogonal tilt axes, the stiffness of the bearing arrangement (e.g. flexure) and the moment of inertia of the movable part (in use, so with camera module or portion of a projector, etc). By appropriately selecting these parameters, the SMA actuator assembly may be at or near resonant frequency at the desired frequency of motion. This may reduce power consumption of the SMA actuator assembly, because reduced force input is needed to drive movement of the movable part between the predetermined positions.
With reference to Figures 3A and 3B, a further embodiment is disclosed. Figure 3A is a plan view of the actuator assembly along an axis P and Figure 3B is a side view of the actuator assembly.
In the embodiment shown in Figures 3A and 3B, an SMA actuator assembly 1 comprises a support structure (not shown) and a movable part 20, indicated by a dashed line. The movable part 20 is supported on the support structure 10 in a manner allowing tilt of the movable part 20 relative to the support structure about two orthogonal tilt axes (the x and y axes in the depicted embodiment). In some embodiments, the SMA actuator assembly 1 comprises a bearing arrangement that allows tilt of the movable part 20 relative to the support structure about the two orthogonal tilt axes x,y. The movable part 20 may pivot about point 50, for example (shown in Figure 3B), which lies at the intersection between the two tilt axes.
The movable part 20 comprises a lens assembly 52 and an image sensor 54. The lens assembly 52 comprises one or more lenses and is arranged to focus an image onto the image sensor 54.
The assembly 1 comprises an SMA wire 30 which induces tilting of the movable part 20 about one of the two axes (the x-axis in the case of the embodiment shown in Figures 3A and 3B). The SMA wire 30 is connected at one end to the movable part 20 by a connection element 23, such as a moving crimp. The other end of the SMA wire 30 is connected to the support structure by a connection element 13, such as a static crimp. The assembly 1 further comprises a resilient element, specifically a spring 56 which is connected at one end to the movable part 20, e.g. to connection element 23 or via other connection means, and at the other end to the support structure (not shown) via connection element 58.
The assembly further comprises a control circuit (not shown). During operation, the control circuit directs control signals to the SMA wire 30. Supplying electrical power to the SMA wire 30 heats the SMA wire 30. Upon reaching a transition temperature, the SMA wire 30 starts contracting. This has the effect of compressing the spring 56. When the power to the SMA wire is removed and thus the SMA wire can extend, the spring 56 expands and drives oscillation of the movable component 20 about a tilt axis (the x axis in the case of Figure 4). Natural damping in the system will act to reduce the oscillation and so the SMA wire 30 is periodically powered-on to drive the oscillation of the movable component. The movable component may oscillate at a resonant frequency of the spring 56.
The actuator assembly 1 further comprises a second SMA wire 30 (not shown in Figures 3A and 3B for clarity). The second SMA wire 30 is perpendicular to the first SMA wire 30 (i.e. it is aligned with the x axis in Figures 3A and 3B) and is arranged in an analogous manner to the SMA wire 30 shown in Figures 3A and 3B (with a corresponding spring). The second SMA wire 30 is arranged to induce oscillation of the movable part 20 about second tilt axis (i.e. the y axis in Figures 3A and 3B). In this way, two SMA wire assemblies such as that shown in Figures 3A and 3B are arranged in series; one for each tilt axis. The result of the combination of the oscillations about the two tilt axes is that an end of the movable part which is opposed to point 50 follows a circular path (when viewed along the z-direction). Such motion may facilitate motion of the moveable part between a number of predetermined positions, e.g. four positions, at which a different image is captured (in the case of super-resolution imaging) or a different image is displayed/projected (in the case of wobulation). Each SMA wire assembly may be configured to cause motion of the movable part between two of the four positions.
The embodiment shown in Figures 3A and 3B employs tilting of the movable part 20 but the movable part 20 may instead (or additionally) be moved along the x and y axes, i.e. translated along the x and y axes. In such an embodiment, the movable component is not pivoted about a point or axis but instead is shifted along the x and y axes by the mechanism (i.e. the SMA wires 30 and the springs 56). This results in the whole movable part 20 following a circular path (when viewed along the z-direction).
With reference to Figure 4, a further embodiment is described. An SMA actuator assembly 1 comprises a movable part 20 and a support structure 10. The movable part 20 is supported on the support structure 10 in a manner allowing tilt of the movable part 20 relative to the support structure about two orthogonal tilt axes (the x and y axes in the depicted embodiment). In some embodiments, the SMA actuator assembly 1 comprises a bearing arrangement that allows tilt of the movable part 20 relative to the support structure 10 about the two orthogonal tilt axes x,y. The movable part 20 may pivot about point 50, for example, which lies at the intersection between the two tilt axes. The bearing arrangement 20 also allows translation of the movable part 20 along an axis H, which is perpendicular to the two tilt axes.
The movable part 20 comprises a lens assembly and an image sensor (neither of which are shown). The lens assembly comprises one or more lenses and is arranged to focus an image onto the image sensor. In other embodiments, the movable part may comprise a display, for displaying an image, an image projector, for projecting an image, an emitter or illumination source (or merely a part of any of these components).
The movable part comprises a guiding element 60 which engages with a bearing surface 62 disposed on the support structure 10. The guiding element may be disposed on an external surface of the movable part and may be a protrusion. The movable component is configured to move relative to the bearing surface 62. The bearing surface 62 follows a helical path about an axis H over most of its length (the path of the bearing surface behind the movable part as viewed in Figure 4 is indicated by a dotted line) and also comprises a step portion 64. Whilst the portion 64 is referred to as a step, as indicated in Figure 4, the corners of the step are smoothed to facilitate relative motion between the guiding element 60 and the bearing surface 62.
The assembly 1 further comprises a biasing arrangement 64 which is configured to bias the movable part 20 in a first direction 66, indicated by an arrow in Figure 4, along the axis H. The biasing arrangement 64 thus biases the guiding element 60 into contact with the bearing surface 62. The biasing arrangement 64 is a spring in the embodiment shown in Figure 4 but may instead comprise one or more magnets, one or more SMA wires or any other actuator. A biasing arrangement which does not require power (e.g. a spring) may be preferable to reduce the power consumption of the actuator assembly.
For any given position of the guiding element 60 relative to the movable part 20, the force of the biasing arrangement 64 (which acts in a downwards direction in Figure 4) will cause the guiding element 60 to move down, along the helical path of the bearing surface 62 which induces tilting of the movable part 20 about point 50. This motion will continue until the guiding element 60 reaches the step portion 64 of the bearing surface 62 (at which point the guiding element 60 is trapped in a well).
The assembly 1 further comprises an SMA wire 30 which is connected at one end to the movable part 20 by a connection element (not shown), such as a moving crimp. The other end of the SMA wire 30 is connected to the support structure by a further connection element (not shown). Once the guiding element 20 reaches the step portion 64, power is provided to the SMA wire which causes it to contract. This causes translation of the movable part 20 in a second direction 68 along axis H, opposed to the first direction, and in opposition to the action of the biasing arrangement 64. The SMA wire 30 is angled relative to the axis H (i.e. there is an acute angle between the SMA wire 30 and the axis H) such that on contraction of the SMA wire 30, the SMA wire pulls the guiding element 60 (as a result of the movement of the movable part 20) up and over the step portion 64 of the bearing surface 62. The SMA wire is angled relative to the axis H to ensure that the guiding element 60 continues along the bearing surface 62 in the desired direction around axis H. Once the guiding element 60 has moved over the step portion 64, the SMA wire 30 is powered off, which causes the SMA wire 30 to cool and expand and the SMA wire thus no longer opposes the force of the biasing arrangement 64 on the movable component. The biasing arrangement 64 thus acts to pull the movable part 20 along the axis H in direction 66 (downwards in Figure 4) and the guiding element 60 thus continues back down the helical path of the bearing surface 62.
This has the effect that the end of the movable part opposed to point 50 follows a circular path, as viewed along axis H. Accordingly, the SMA actuator assembly induces movement of the movable part (as thus the lens assembly and image sensor) between predetermined positions in a repeated pattern. The motion can therefore be used to implement super-resolution imaging, as explained above.
In embodiments in which the movable part comprises e.g. a display or image projector (or a part thereof), the motion provided for by the embodiment of Figure 4 may be used to implement wobulation of the displayed/projected image, as described above.
As for some other embodiments described herein, the assembly 1 further comprises a control circuit (not shown) for directing control signals to the SMA wire 30.
The movable part 20 in the embodiment shown in Figure 4 is configured to tilt about a pivot point 50 however the actuator assembly 1 may equally be configured to allow translation of the movable part along the x and y axes. In this way, instead of tilting about the x and y axes, the movable part is shifted along the x and y axes. Such an actuator assembly is configured as in Figure 4 but the bearing arrangement allows movement of the movable part along the x and y axes. The resulting motion will be such that the whole movable part 20 moves in a circular path, as viewed along the axis H.
An advantage of the embodiment shown in Figure 4 is that only a single SMA wire is required to move the movable part between a number of positions in a repeated pattern. This is beneficial in implementations in which power consumption is a particular concern (e.g. in head-mounted devices).
It will be appreciated that the connections between various elements in the embodiment of Figure 4 may need to be configured to allow rotation of one element relative to another. Further, variations to the embodiment of Figure 4 are envisaged, including: the bearing surface 62 may be provided on the movable part and the guiding element on support structure; the SMA wire may act to pull the guiding element 20 down along the helical path and the biasing arrangement may bias the movable part upwards (i.e. along direction 68) when the SMA wire is powered-off.
As explained above, a movable part may be moved between predetermined positions in a repeated pattern by tilting the movable component about one or more movement axes and/or by moving (e.g. translating) the movable part along one or more movement axes. With reference to Figure 6, an embodiment in which a movable component is translated along one or more movement axes to move between predetermined positions is described.
Figure 5 illustrates an SMA actuator arrangement 1 which is described in detail in patent application WO2013/175197, which is incorporated herein by reference. The following description is also provided. The SMA actuator assembly 1 comprises a movable part 15 which is configured to move relative to a support structure 4. The actuator assembly 1 comprises four SMA wires 11, 12, 13 and 14, which are each connected between the movable part 15 and the support structure 4. Each SMA wire is held in tension, thereby applying a force between the movable part 15 and the support structure 4 perpendicular to an axis O. In operation, the SMA wires 11 to 14 move the movable part 15 relative to the support structure 4 in two orthogonal directions (x and y, as labelled in Figure 6). Each of the SMA actuator wires 11 to 14 is arranged along one side of the movable part 15. Thus, the SMA wires 11 to 14 are arranged in a loop at different angular positions around the axis O. Thus, the four SMA actuator wires 11 to 14 consist of a first pair of SMA actuator wires 11 and 13 arranged on opposite sides of the axis O and a second pair of SMA wires 12 and 14 arranged on opposite sides of the axis O. The first pair of SMA wires 11 and 13 are capable on selective driving to move the movable part 15 relative to the support structure 4 in a first direction in the x-y plane, and the second pair of SMA wires 12 and 14 are capable on selective driving to move the movable part 15 relative to the support structure 10 in a second direction in said plane transverse to the first direction. Movement in directions other than parallel to the SMA wires 11 to 14 may be driven by a combination of actuation of these pairs of the SMA actuator wires 11 to 14 to provide a linear combination of movement in the transverse directions. Another way to view this movement is that simultaneous contraction of any pair of the SMA actuator wires 11 to 14 that are adjacent each other in the loop will drive movement of the lens element 2 in a direction bisecting those two of the SMA wires 11 to 14 (diagonally in Fig. 5, as labelled by the arrows X and Y).
Accordingly, by actuating the SMA wires 11 to 14 in various combinations, motion of the movable part 15 between different positions in the x-y plane may be achieved. Such motion could be used for the purposes of super-resolution imaging or wobulation, as described above. Example of a model of repeated movement for super-resolution
Figures 6A-D show an example method of repeated movement enabling super-resolution imaging.
The basic concept of super resolution imaging is that a number of images are captured each with the image offset on the image sensor by a different amount. The images are then combined and the additional information afforded by the additional images is used to create an image of higher resolution (and/or possibly higher quality) than that of the original images.
This simple model assumes that there is a gap between collecting the images and when the image can be moved to a new position. However, if a rolling shutter is used there is often no gap between frames when the image can be moved over the image sensor. This means that using this simple approach a frame needs to be dropped when the image is moved, and this decreases the rate at which images can be collected.
The image may thus be moved relative to the image sensor continuously in a circular manner while four images are collected per cycle. This allows images to be collected for super resolution while a rolling shutter is used.
The image may generally be moved over the image sensor in a continuous manner (motion has a constant speed or velocity) by moving the image sensor, other optical elements or both (e.g. in the camera module described herein).
In the first manifestation the motion is circular and the SMA wires (or other actuator) move the image over the image sensor in a complete circle once every four exposures. This is shown in Figures 6A-D. The timing of the actuator motion is locked to the exposures so that at the middle of the image an exposure starts when the image is at the top of the circle. In this case each of the four exposures can be directly equated to one of the super resolution pixels indicated by the grid shown in Figures 6A-D. Having the exposures correlated in this manner gives the best quality of image and so is done at the centre of the image.
At the top and the bottom of the image, four independent samples of light are still taken, but they are not arranged in a uniform square grid. This data is converted to a square grid to provide a super resolution image. The same method can be applied to creating a super-resolution image from images displayed on a display panel or projected by a projector, thus implementing wobulation.
Final paragraphs
In any of the embodiments described herein, the movable part may comprise one or more of the following: a light-emitting element (such as a laser or laser array), a light-modifying element (such as a diffraction grating or reflection element), a lens assembly, an image sensor, a display or an image projector (or a part of any of these components).
Although the SMA actuator assembly has been described in connection with a control circuit configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about the one or more movement axes and/or movement of the movable part along the one or more movement axes relative to the support structure between predetermined positions in a repeated pattern, this is not strictly required. The present invention extends to the provision of other features of the SMA actuator assembly described herein, such as the SMA wire arrangement of Figure 1 or the bearing arrangements described herein.
The above-described SMA actuator assemblies comprise an SMA wire. The term 'shape memory alloy (SMA) wire' may refer to any element comprising SMA. The SMA wire may have any shape that is suitable for the purposes described herein. The SMA wire may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA wire. It is also possible that the length of the SMA wire (however defined) may be similar to one or more of its other dimensions. The SMA wire may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two elements, the SMA wire can apply only a tensile force which urges the two elements together. In other examples, the SMA wire may be bent around an element and can apply a force to the element as the SMA wire tends to straighten under tension. The SMA wire may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA wire may or may not include material(s) and/or component(s) that are not SMA. For example, the SMA wire may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA wire' may refer to any configuration of SMA wire acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA wire may comprise two or more portions of SMA wire that are arranged mechanically in parallel and/or in series. In some arrangements, the SMA wire may be part of a larger piece of SMA wire. Such a larger piece of SMA wire might comprise two or more parts that are individually controllable, thereby forming two or more SMA wires.

Claims

Claims
1. An SMA actuator assembly comprising a support structure; a camera module supported on the support structure in a manner allowing tilt of the camera module relative to the support structure about two orthogonal tilt axes, wherein the camera module comprises an image sensor and a lens assembly arranged to focus an image onto the image sensor; two or more SMA wires arranged to tilt the camera module relative to the support structure about the two orthogonal tilt axes; a control circuit configured to apply drive signals to the two or more SMA wires so as to drive tilting of the camera module relative to the support structure between predetermined positions in a repeated pattern.
2. An SMA actuator assembly according to claim 1, wherein the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving super-resolution imaging of the camera module.
3. An SMA actuator assembly according to any preceding claim, wherein the predetermined positions in the repeated pattern are arranged in two degrees of freedom.
4. An SMA actuator assembly according to any preceding claim, wherein the control circuit is configured to apply drive signals to the two or more SMA wires so as to drive tilting of the movable part between the predetermined positions at a predetermined frequency.
5. An SMA actuator assembly according claim 4, wherein the resonance frequency of tilting the camera module about the two orthogonal tilt axes is substantially equal to the predetermined frequency, in particular differs by less than 10%, preferably less than 5% or less than 1%, from the predetermined frequency.
6. An SMA actuator assembly according any preceding claim, wherein the SMA actuator assembly comprises a first resilient element, wherein the one or more SMA wires comprises a first SMA wire which is configured to, on contraction, deform the first resilient element and wherein the first resilient element is configured to oscillate at a first frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions.
7. An SMA actuator assembly according any preceding claim, wherein the SMA actuator assembly comprises a second resilient element, wherein the one or more SMA wires comprises a second SMA wire which is configured to, on contraction, deform the second resilient element and wherein the second resilient element is configured to oscillate at a second frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions, optionally wherein the first resilient element is configured to tilt or move the movable part about or along a first axis and the second resilient element is configured to tilt or move the movable part about or along a second axis perpendicular to the first axis.
8. An SMA actuator assembly according to any preceding claim, wherein the two or more SMA wires comprise four SMA wires.
9. An SMA actuator assembly according to claim 8, where the two or more SMA wires comprise a total of four SMA wires in an arrangement capable of applying a torque to the camera module about an axis perpendicular to the two orthogonal tilt axes.
10. An SMA actuator assembly according to claim 9, wherein two of the four SMA wires are arranged to apply a torque to the camera module in a first sense and the other two SMA wires are arranged to apply a torque to the camera module in a second, opposite sense.
11. An SMA actuator assembly according claim 9 or 10, wherein the four SMA wires are arranged in a loop at different angular positions around the axis, successive SMA wires being arranged to apply a force to the camera module in alternate senses.
12. An SMA actuator assembly according any one of claims 9 to 11, wherein the four SMA wires are arranged such that respective subsets of two SMA wires are arranged to apply a force to the camera module in four respective directions along the two orthogonal tilt axes.
13. An SMA actuator assembly according any one of claims 9 to 12, wherein the four SMA wires comprise two pairs of SMA wires, each pair of SMA wire being arranged on opposite sides of the camera module when viewed perpendicularly to the two orthogonal tilt axes.
14. An SMA actuator assembly according to claim 13, wherein the SMA wires of each pair of SMA wires cross over or overlap when viewed perpendicularly to the two orthogonal tilt axes.
15. An SMA actuator assembly according any one of claims 9 to 14, wherein the four SMA wires are arranged to apply forces to the camera module that are in angular directions offset by 90 degrees from each other.
16. An SMA actuator assembly according to any preceding claim, wherein the two or more SMA wires are arranged parallel to the two orthogonal tilt axes, optionally in a plane.
17. An SMA actuator assembly according to any one of claims 1 to 15, wherein the two or more SMA wires are arranged to be angled relative to the two orthogonal tilt axes.
18. An SMA actuator assembly according to any preceding claim, further comprising a bearing arrangement allowing tilt of the movable part relative to the support structure about the two orthogonal tilt axes.
19. An SMA actuator assembly according to claim 18, wherein the bearing arrangement is arranged to constrain translational movement of the camera module along the two orthogonal tilt axes.
20. An SMA actuator assembly according to claim 19, wherein the bearing arrangement is further arranged to constrain translational and/or rotational movement of the camera module along and/or about an axis perpendicular to the two orthogonal tilt axes.
21. An SMA actuator assembly according to any one of claims 18 to 20, wherein the bearing arrangement is arranged to constrain movement of the camera module along the two orthogonal tilt axes at a position that is offset along an axis perpendicular to the two orthogonal tilt axes from the force applied by the two or more SMA wires to the camera module.
22. An SMA actuator assembly according to any one of claims 18 to 21, wherein the bearing arrangement comprises a sheet material or flexure connected between the support structure and the camera module, optionally wherein the sheet material or flexure extends in the plane defined by the two orthogonal tilt axes.
23. An SMA actuator assembly according to any one of claims 18 to 21, wherein the bearing arrangement comprises a pivot or a plain bearing, in particular a spherical plain bearing.
24. An SMA actuator assembly according to any one of claims 18 to 21, wherein the bearing arrangement comprises a compliant bulk material, such as a rubber.
25. An SMA actuator assembly comprising a support structure; a movable part supported on the support structure in a manner allowing tilt of the movable part relative to the support structure about one or more movement axes and/or movement of the movable part along one or more movement axes; one or more SMA wires arranged to tilt the movable part relative to the support structure about the one or more movement axes and/or move the movable part along the one or more movement axes; and a control circuit configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about the one or more movement axes and/or movement of the movable part along the one or more movement axes relative to the support structure between predetermined positions in a repeated pattern.
26. An SMA actuator assembly according to claim 21, wherein the movable part comprises a camera module, wherein the camera module comprises a lens assembly defining an optical axis and an image sensor, wherein the lens assembly is arranged to focus an image onto the image sensor, and wherein the one or more movement axes are perpendicular to the optical axis.
27. An SMA actuator assembly according to claim 26, wherein the control circuit is configured to apply the drive signals to the two or more SMA wires for the purpose of achieving super-resolution imaging with the camera module.
28. An SMA actuator assembly according to claim 21, wherein the SMA actuator assembly comprises a projector for projecting an image, wherein the movable part comprises at least a portion of the projector such that tilting or movement of the movable part relative to the support structure moves the projected image.
29. An SMA actuator assembly according to claim 25, wherein the control circuit is configured to apply the drive signals to the one or more SMA wires for the purpose of achieving wobulation of the projected image.
30. An SMA actuator assembly according to any preceding claim, wherein the predetermined positions in the repeated pattern are arranged in two degrees of freedom.
31. An SMA actuator assembly according to any preceding claim, wherein the control circuit is configured to apply drive signals to the one or more SMA wires so as to induce tilting of the moveable part about two orthogonal tilt axes relative to the support structure between the predetermined positions in the repeated pattern and wherein the one or more SMA wires comprise a total of four SMA wiresin an arrangement capable of applying a torque to the movable part about an axis perpendicular to the two orthogonal tilt axes.
32. An SMA actuator assembly according to any preceding claim, wherein the control circuit is configured to apply drive signals to the one or more SMA wires so as to induce tilting or movement of the movable part between the predetermined positions at a predetermined frequency.
33. An SMA actuator assembly according claim 32, wherein a resonance frequency of tilting the movable part about the one or more movement axes or moving the movable part along the one or more movement axes is substantially equal to the predetermined frequency, in particular differs by less than 10%, preferably less than 5% or less than 1%, from the predetermined frequency.
34. An SMA actuator assembly according to claim 32 or 33, further comprising a first resilient element, wherein the one or more SMA wires comprises a first SMA wire which is configured to, on contraction, deform the first resilient element and wherein the first resilient element is configured to oscillate at a first frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions.
35. An SMA actuator assembly according to claim 34, further comprising a second resilient element, wherein the one or more SMA wires comprises a second SMA wire which is configured to, on contraction, deform the second resilient element and wherein the second resilient element is configured to oscillate at a second frequency so as to cause the tilting or movement of the movable part between at least some of the predetermined positions, optionally wherein the first resilient element is configured to tilt or move the movable part about or along a first axis and the second resilient element is configured to tilt or move the movable part about or along a second axis perpendicular to the first axis.
36. An SMA actuator assembly according to any preceding claim, further comprising a bearing arrangement allowing tilt of the movable part relative to the support structure about the one or more movement axes and/or movement of the movable part relative to the support structure along the one or more movement axes.
37. An SMA actuator assembly according to claim 36, wherein the bearing arrangement is configured to allow tilting of the movable part relative to the support structure about two orthogonal tilt axes, wherein the bearing arrangement is arranged to constrain translational movement of the movable part along the two orthogonal tilt axes, optionally wherein the bearing arrangement is further arranged to constrain translational and/or rotational movement of the movable part along and/or about an axis perpendicular to the two orthogonal tilt axes.
38. An SMA actuator assembly according to any preceding claim, wherein the actuator assembly is configured to tilt or move the moveable part such that at least part of the movable part moves in a loop when viewed along a primary axis which is perpendicular to the one or more movement axes, optionally wherein the loop is an ellipse, optionally wherein the loop is a circle.
39. An SMA actuator assembly according to any one of claims 36 to 37, wherein the bearing arrangement is configured to guide at least part of the movable part to move in a loop as viewed along a primary axis which is perpendicular to the one or more movement axes, optionally wherein the loop is an ellipse, optionally wherein the loop is a circle.
40. An SMA actuator assembly according to claim 39, wherein the one or more SMA wires are configured to, on contraction, drive movement of the at least part of the movable part along the primary axis in a first direction and wherein the actuator assembly comprises a biasing arrangement configured to cause movement of the at least part of the movable part in a second direction along the primary axis, opposite to the first direction, and wherein the bearing arrangement converts movement of the at least part of the movable part along the primary axis into movement along the loop.
41. An SMA actuator assembly according to claim 39 or claim 40, wherein the bearing arrangement is configured to guide the at least part of the movable part along a helical path about the primary axis.
42. An SMA actuator assembly according to any preceding claim, wherein the one or more SMA wires comprises a total of one SMA wire which induces the tilting or movement of the movable part between the predetermined positions.
PCT/GB2023/050514 2022-03-03 2023-03-03 Sma actuator assembly WO2023166320A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB2202987.0A GB2616298A (en) 2022-03-03 2022-03-03 SMA actuator assembly
GB2202987.0 2022-03-03
GBGB2204617.1A GB202204617D0 (en) 2022-03-30 2022-03-30 SMA actuator assembly
GB2204617.1 2022-03-30

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