METHOD FOR CONTROLLING POSITION OF A LINEAR MEMS MIRROR WITH VARIABLE RESOLUTION AND/OR LIGHT INTENSITY

• US 20170285327A1
• Filed: 09/29/2016
• Published: 10/05/2017
• Est. Priority Date: 03/30/2016
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Limited (STMicroelectronics NV)
• Inventors: Duvdevany, Offir, Sharon, Dadi, Sourani, Sason
• Granted Patent: US 10,642,025 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G02B 7/1821 for rotating or oscillating mirrors
• CPC Class Codes: G03B 21/008 using micromirror devices

Abstract

The method for controlling an angular position of a MEMS mirror, includes: applying a first driving moment to the MEMS mirror to generate a rotational scanning movement of the mirror; and, at a zooming instant, applying a second driving moment to the MEMS mirror, wherein the second driving moment is equal to the first driving moment plus an extra moment. The extra moment may be a DC offset. After a transient period of time from zooming instant, a third driving moment M₂=k{dot over (θ)}₂t is applied. The first and third driving moment are variable linearly with time. The driving moments are applied to torsional springs of the mirror.

Claims

1. A method for controlling an angular position of a MEMS mirror, comprising:

applying a first driving moment to the MEMS mirror, applying the first driving moment generating a rotational scanning movement of the mirror; and

performing a zooming by applying a second driving moment to the MEMS mirror, wherein the second driving moment is equal to the first driving moment plus an extra driving moment.

2. The method according to claim 1, wherein the extra driving moment is a fixed moment.

3. The method according to claim 1, wherein the first driving moment is variable linearly with time.

4. The method according to claim 3, wherein the first and second driving moments are applied to torsional springs of the mirror and the first driving moment is given by the equation:

k{dot over (θ

)}₁t=M₁

wherein k is a stiffness constant of the springs, {dot over (θ

)} is a first derivative of an angular position of the mirror, and t is time.

5. The method according to claim 1, wherein the first and second driving moments are applied to torsional springs of the mirror and the extra driving moment (M−

M₁) is equal to;

6. The method according to claim 1, comprising applying a third driving moment M₂=k{dot over (θ

)}₂t after a transient period of time t from a zooming instant, wherein k is a stiffness constant of the springs, and {dot over (θ

)}₂ is a speed of the mirror.

7. The method according to claim 6, wherein applying the first driving moment comprises rotating the MEMS mirror at a first constant speed {dot over (θ

)}₁ and applying the third driving moment comprises rotating the MEMS mirror at the speed {dot over (θ

)}₂, which is constant.

8. The method according to claim 1, comprising:

reading from a conversion table a control electrical quantity corresponding to an instant driving moment; and

controlling rotation of the MEMS mirror according to the control electrical quantity read from the conversion table.

9. An optical device comprising:

a MEMS mirror including a reflective structure and an actuator configured to apply driving moments to the reflective structure; and

a processing unit, the processing unit including a speed controller configured to cause the actuator to apply to the reflective structure a first driving moment that generates a rotational scanning movement of the reflective structure; and

the speed controller being configured to cause the actuator to apply a second driving moment to the reflective structure at a zooming instant, wherein the second driving moment is equal to the first driving moment plus an extra driving moment.

10. The optical device according to claim 9, wherein the MEMS mirror has torsional springs configured to be controlled by the first and second driving moments, and the first driving moment M₁ is given by the equation:

k{dot over (θ

)}₁t=M₁

wherein k is a stiffness constant of the springs and {dot over (θ

)} is a first derivative of an angular position of the reflective structure.

11. The optical device according to claim 10, wherein the actuator is configured to apply the first and second driving moments to the torsional springs of the mirror and the extra moment (M−

M₁) is equal to;

12. The optical device according to claim 9, wherein the speed controller is configured to cause the actuator to apply a third driving moment M₂=k{dot over (θ

)}₂t after a transient period of time from the zooming instant.

13. The optical device according to claim 12, comprising a conversion table having an input coupled to the processing unit, the speed controller being configured to provide to the conversion table one or more signals corresponding to the first, second and third driving moment, and the conversion table being configured to supply a control electrical quantity to the MEMS mirror.

18. The optical device according to claim 12, wherein the speed control means include a processing unit and a conversion table having an input coupled to the processing unit, the processing unit being configured to provide to the conversion table one or more signals corresponding to the first, second and third driving moment, and the conversion table being configured to supply a control electrical quantity to the MEMS mirror.

14. An optical device comprising:

a MEMS mirror; and

speed control means for applying a first driving moment to the MEMS mirror to generate a rotational scanning movement thereof, and for applying a second driving moment to the MEMS mirror at a zooming instant, wherein the second driving moment is equal to the first driving moment plus an extra driving moment.

15. The optical device according to claim 14, wherein the MEMS mirror has torsional springs configured to be controlled by the first and second driving moments, and the first driving moment M₁ is given by the equation:

k{dot over (θ

)}₁t=M₁

wherein k is a stiffness constant of the springs and {dot over (θ

)} is a first derivative of an angular position of the MEMS mirror.

16. The optical device according to claim 15, wherein the speed control means are for applying the first and second driving moments to the torsional springs of the mirror and the extra moment (M−

M₁) is equal to;

17. The optical device according to claim 14, wherein the speed controller speed control means are for applying a third driving moment M₂=k{dot over (θ

)}₂t after a transient period of time from the zooming instant.