OPTICAL IMAGE STABILISATION

• US 20140055630A1
• Filed: 09/22/2011
• Published: 02/27/2014
• Est. Priority Date: 09/22/2010
• Status: Active Grant

• Current Assignee: Cambridge Mechatronics Limited
• Original Assignee: Cambridge Mechatronics Limited
• Inventors: Gregory, Thomas Matthew, Topliss, Richard
• Granted Patent: US 8,866,918 B2
• Time in Patent Office: Days
• US Class Current: 348/208.2
• CPC Class Codes: F03G 7/065 using a shape memory element
• CPC Class Codes: G02B 27/646 compensating for small deviations, e.g. due to vibration or shake movement of one or more optical elements for control of motion blur in cameras, projectors or printers G03B2205/0007; image stabilisation in cameras peculiar to the presence or use of an electronic image sensor H04N23/68
• CPC Class Codes: G03B 2205/0023 by tilting or inclining one or more optical elements with respect to the optical axis
• CPC Class Codes: G03B 2205/0076 using shape memory alloys
• CPC Class Codes: G03B 3/02 moving lens along baseboard
• CPC Class Codes: H04N 23/57 Mechanical or electrical details of cameras or camera modules specially adapted for being embedded in other devices
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors
• CPC Class Codes: H04N 23/6815 by distinguishing pan or tilt from motion
• CPC Class Codes: H04N 23/687 by shifting the lens or sensor position

Abstract

A camera apparatus capable of providing optical image stabilisation comprises: a support structure; a camera unit comprising an image sensor and a lens system; a suspension system comprising a plurality of flexure elements supporting the camera unit on the support structure in a manner allowing the camera unit to tilt; and a plurality of SMA actuators. A sensor arrangement, whose output is used as the basis for generating drive signals, is mounted on the camera unit. A control circuit generates drive signals for the SMA actuators, by deriving closed-loop control signals representative of a desired degree of variation in the power of the drive signals from the output signals of the sensor arrangement without dependence on any measurement of the resistance of the SMA actuators, and generating the drive signals with powers that varies from a set-point power in correspondence with the closed-loop control signal.

Claims

1. A camera apparatus comprising:

a support structure;

a camera unit comprising an image sensor and a lens system for focussing an image on the image sensor, the camera unit being supported on the support structure in a manner allowing the camera unit to tilt relative to the optical axis of the lens system;

a plurality of SMA actuators arranged to drive tilting of the camera unit;

a sensor arrangement mounted on the camera unit and arranged to generate output signals representative of the movement of the camera unit; and

a control circuit arranged to generate drive signals and supply them to the SMA actuators, wherein

the control circuit is arranged to derive closed-loop control signals representative of a desired degree of variation in the power of the drive signals from the output signals of the sensor arrangement for reducing the movement of the camera unit, without dependence on any measurement of the resistance of the SMA actuators, and

the control circuit is arranged to generate the drive signals with powers that vary from set-point powers in correspondence with the closed-loop control signal.

2. The camera apparatus according to claim 1, wherein the closed-loop control signals are, or include respective components that are, derived from the output signals of the sensor arrangement to be proportional to the position of the camera unit.

3. The camera apparatus according to claim 1, wherein the closed-loop control signals include respective components that are derived from the output signals of the sensor arrangement to be proportional to the position of the camera unit and further respective components derived from the output signals of the sensor arrangement to be proportional to the integral of the position of the camera unit.

4. The camera apparatus according to claim 1, wherein the sensor arrangement is arranged to generate output signals representative of the angular velocity of the camera unit.

5. The camera apparatus according to claim 4, wherein the sensor arrangement is a gyroscope sensor arrangement.

6. The camera apparatus according to claim 4, wherein the control circuit is arranged to integrate the output signals of the sensor arrangement to derive a measure of the position of the camera unit and to derive the closed-loop control signal from the derived measure of the position of the camera unit.

7. The camera apparatus according to claim 1, wherein the control circuit is arranged to select the set-point powers on the basis of a measure of ambient temperature in the vicinity of the SMA actuators.

8. The camera apparatus according to claim 7, wherein the control circuit includes a temperature sensor for measurement of the ambient temperature and said measure of the ambient temperature is derived from an output signal of the temperature sensor.

9. The camera apparatus according to claim 7, wherein the control circuit is arranged to determine said measure of temperature from measured electrical characteristics of the SMA actuators.

10. The camera apparatus according to claim 7, wherein the control circuit is arranged to derive an estimate of at least one characteristic temperature of the SMA actuation apparatus, including the ambient temperature in the vicinity of the SMA actuators, on the basis of the power of the drive current, using a thermal model that relates the at least one characteristic temperature of the SMA actuation apparatus to the power of the drive current.

11. The camera apparatus according to claim 7, wherein

the camera unit comprises:

a camera support on which the image sensor is mounted, the lens system being suspended on the camera support in a manner allowing movement of the lens system to change the focus of an image on the image sensor; and

at least one further SMA actuator connected between the camera support and the lens system for driving movement of the lens system to change the focus, and

the control circuit is arranged to determine said measure of temperature from measured electrical characteristics of the at least one further SMA actuator.

12. The camera apparatus according to claim 11, wherein

the control circuit is arranged to measure the resistance of the at least one further SMA actuator connected between the camera support and the lens system and to generate further drive signals based on the measured resistance and to supply the drive signals to the at least one further SMA actuator, and

the control circuit is arranged to determine said measure of temperature from measured electrical characteristics of the at least one further SMA actuator based on the measured resistance of the at least one further SMA actuator.

13. The camera apparatus according to claim 1, wherein the control circuit is arranged to select the set-point powers on the basis of the output signals of the sensor arrangement.

14. The camera apparatus according to claim 13, wherein the control circuit is arranged to perform a set-point power selection process comprising:

supplying the SMA actuators with dithered drive signals having a power that dithers and has a changing average power over a predetermined period;

monitoring the output signals of the sensor arrangement while said dithered drive signals are supplied; and

selecting the set-point powers to be the average power of the dithered drive signals when the output signals of the sensor arrangement indicate that the movement of the camera unit is maximised.

15. The camera apparatus according to claim 1, wherein the control circuit comprises:

a drive circuit arranged to generate the drive signals in correspondence with power control signals; and

a controller arranged to generate the power control signals.

16. The camera apparatus according to claim 15, wherein the controller is arranged to generate the power control signals by adding the closed-loop control signals to set-point control signals for causing the drive signal to have the set-point powers.

17. The camera apparatus according to claim 1, further comprising a suspension system comprising a plurality of flexure elements supporting the camera unit on the support structure.

18. The camera apparatus according to claim 1, wherein the plurality of SMA actuators consists of two SMA actuator subsystems each comprising plural SMA actuators connected between the camera unit and the support structure, the respective SMA actuator subsystems being arranged, on contraction of the actuators thereof, to drive displacement of the camera unit in opposite directions along the optical axis relative to the support structure, and each SMA actuator subsystem being arranged, on differential contraction of the actuators thereof, to drive rotation of the camera unit around a respective one of said notional axes.

19. A method of controlling a drive circuit to generate drive signals for SMA actuators that drive tilting of a camera unit comprising an image sensor and a lens system relative to a support structure from output signals of a sensor arrangement mounted on the camera unit, the method comprising:

deriving closed-loop control signals representative of a desired degree of variation in the power of the drive signals from the output signals of the sensor arrangement without dependence on any measurement of the resistance of the SMA actuators, and

generating power control signals for controlling the drive circuit to generate drive signals for the SMA actuators with powers that vary from a set-point power in correspondence with the closed-loop control signal.

20. A controller for controlling a drive circuit to generate drive signals for SMA actuators that are arranged drive tilting of a camera unit comprising an image sensor and a lens system relative to a support structure, from output signals of a sensor arrangement mounted on the camera unit, wherein:

the controller is arranged to derive closed-loop control signals representative of a desired degree of variation in the power of the drive signals from the output signals of the sensor arrangement without dependence on any measurement of the resistance of the SMA actuators, and

the control circuit is arranged to generate power control signals for controlling the drive circuit to generate drive signals for supply to the SMA actuators with powers that varies from a set-point power in correspondence with the closed-loop control signal.

21. The controller according to claim 20, wherein the controller is implemented in a semiconductor chip.

22. The controller according to claim 21, wherein the controller further comprises the sensor arrangement.

23. The control circuit comprising:

a controller according to claim 20, and

a drive circuit arranged to generate drive signals for SMA actuators, for driving tilting of a camera unit comprising an image sensor and a lens system relative to a support structure, in correspondence with the power control signals.