Method for controlling the position of a MEMS mirror
According to the present invention there is provided a method of controlling the position of a MEMS mirror in a MEMS device, wherein the MEMS device comprises, a MEMS mirror, a magnet which provides a magnetic field (B), an actuating means which operatively cooperates with the MEMS mirror so that it can apply a force to the MEMS mirror which can tilt the MEMS mirror about at least one rotational axis when the actuating means is provided with a drive signal, wherein the magnitude force applied by the actuating means to the MEMS mirror is dependent on the amplitude of the drive signal, and a detection coil which is mounted on the MEMS mirror, the method comprising the steps of, detecting a change in the resistance (R) of the detection coil so as to detect a change in temperature of the MEMS mirror; determining the drive signal amplitude required to maintain the MEMS mirror at a predefined angular position (Θ); providing the actuating means with a drive signal which has an amplitude which is equal to the determined drive signal amplitude.
1. An apparatus comprising:
a microelectromechanical system (MEMS) mirror;
a magnet to provide a magnetic field;
an actuator to receive a drive signal and to cooperate with the magnetic field to apply a force to the MEMS mirror to tilt the MEMS mirror about at least one rotational axis based in part on the drive signal;
a detection coil coupled to the MEMS mirror; and
a driver to provide the drive signal to the actuator, the driver to determine a change in the magnetic field provided by the magnet, determine a drive signal amplitude to maintain the MEMS mirror at a predefined angular position based in part on the change in the magnetic field and adjust the amplitude of the drive signal based on the drive signal amplitude.
2. The apparatus of claim 1 , the drive signal comprising a drive current, the actuator comprising a conduction coil to conduct the drive current in the magnetic field to apply a Laplace force to the MEMS mirror.
3. The apparatus of claim 2 , wherein the conduction coil is the detection coil.
4. The apparatus of claim 2 , the driver to determine a change in resistance of the detection coil and adjust the amplitude of the drive signal in response to the change in resistance of the detection coil.
5. The apparatus of claim 4 , the driver to determine the drive signal amplitude (I) based in part on the following equation:
I
=
K
n
*
B
*
S
*
Θ
cos
(
Θ
)
,
where K is a stiffness of the MEMS mirror, n is a number of turns in the conduction coil, S is an area of the MEMS mirror, B is the magnetic field, and Θ is the predefined angular position.
6. The apparatus of claim 5 , the conduction coil to surround a portion of the MEMS mirror, S corresponding to the area of the portion of the MEMS mirror.
7. The apparatus of claim 5 , the driver to:
determine a resistance of the detection coil; and
determine the stiffness of the MEMS mirror based in part on the determined resistance.
8. The apparatus of claim 1 , the driver to:
determine a difference between the predefined angular position and a second angular position; and
adjust the amplitude of the drive signal proportionate to the difference.
9. At least one non-transitory computer-readable storage medium comprising instructions that when executed by a processor, cause the processor to:
determine a change in resistance of a detection coil coupled to a microelectromechanical system (MEMS) mirror, the MEMS mirror to tilt about at least one rotational axis based in part on a drive signal and a magnetic field;
determine a drive signal amplitude to maintain the MEMS mirror at a predefined angular position based in part on the change in resistance; and
send a control signal to current source including an indication to adjust the amplitude of the drive signal based on the drive signal amplitude.
10. The non-transitory computer-readable storage medium of claim 9 , wherein the MEMS mirror is coupled to a conduction coil to conduct the drive current in the magnetic field to apply a Laplace force to the MEMS mirror.
11. The non-transitory computer-readable storage medium of claim 10 , wherein the conduction coil is the detection coil.
12. The non-transitory computer-readable storage medium of claim 10 , comprising instructions that when executed by the processor, cause the processor to adjust the amplitude of the drive signal in response to determining a change in resistance of the detection coil.
13. The non-transitory computer-readable storage medium of claim 10 , comprising instructions that when executed by the processor, cause the processor to determine the drive signal amplitude (I) based in part on the following equation:
I
=
K
n
*
B
*
S
*
Θ
cos
(
Θ
)
,
where K is a stiffness of the MEMS mirror, n is a number of turns in the conduction coil, S is an area of the MEMS mirror, B is the magnetic field, and Θ is the predefined angular position.
14. The non-transitory computer-readable storage medium of claim 13 , comprising instructions that when executed by the processor, cause the processor to:
determine a resistance of the detection coil; and
determine the stiffness of the MEMS mirror based in part on the determined resistance.
15. The non-transitory computer-readable storage medium of claim 13 , comprising instructions that when executed by the processor, cause the processor to:
determine a difference between the predefined angular position and a second angular position; and
adjust the amplitude of the drive signal proportionate to the difference.
16. The non-transitory computer-readable storage medium of claim 14 , comprising instructions that when executed by the processor, cause the processor to:
detect a further change in the resistance of the detection coil; and
adjust the amplitude of the drive signal proportionate to the difference based on detecting the further change.
17. The non-transitory computer-readable storage medium of claim 13 , comprising instructions that when executed by the processor, cause the processor to:
determine a change in the magnetic field; and
adjust the amplitude of the drive signal proportionate to the change in magnetic field.
18. The non-transitory computer-readable storage medium of claim 13 , comprising instructions that when executed by the processor, cause the processor to determine the stiffness (K) of the MEMS mirror based on the following equation:
Fr
=
1
2
*
π
*
K
J
,
where Fr is a resonant frequency of the MEMS mirror and J is a moment of inertia of the MEMS mirror.
19. The non-transitory computer-readable storage medium of claim 18 , comprising instructions that when executed by the processor, cause the processor to:
detect a voltage induced across the detection coil, the voltage induced based on the MEMS mirror freely oscillating about the at least one rotational axis;
determine a period of the induced voltage; and
determine the resonant frequency of the MEMS mirror based on the induced voltage and the period.
20. An apparatus comprising:
a microelectromechanical system (MEMS) mirror;
a magnet to provide a magnetic field;
actuator means to receive a drive signal and to cooperate with the magnetic field to apply a force to the MEMS mirror to tilt the MEMS mirror about at least one rotational axis based in part on the drive signal;
a detection coil coupled to the MEMS mirror; and
driver means to:
provide the drive signal to the actuator;
determine a change in resistance of the detection coil;
determine a drive signal amplitude to maintain the MEMS mirror at a predefined angular position based in part on the change in resistance; and
adjust the amplitude of the drive signal based on the drive signal amplitude.
21. The apparatus of claim 20 , wherein the MEMS mirror is coupled to a conduction coil to conduct the drive current in the magnetic field to apply a Laplace force to the MEMS mirror.
22. The apparatus of claim 21 , the driver mean to determine the drive signal amplitude (I) based in part on the following equation:
I
=
K
n
*
B
*
S
*
Θ
cos
(
Θ
)
,
where K is a stiffness of the MEMS mirror, n is a number of turns in the conduction coil, S is an area of the MEMS mirror, B is the magnetic field, and Θ is the predefined angular position.
23. The apparatus of claim 21 , the driver means to:
determine a change in the magnetic field; and
adjust the amplitude of the drive signal proportionate to the change in magnetic field.