Method for determining a torsion angle of a mirror body of an MEMS apparatus
A method comprises applying a driver voltage to an electrostatic comb drive of an MEMS apparatus and overlaying the driver voltage with a periodic voltage signal. The method further comprises determining a torsion angle of a mirror body of the MEMS apparatus based on the periodic voltage signal.
1. A method, comprising:
applying one or more driver voltages to one or more electrostatic comb drives of an MEMS apparatus, based on:
applying a first driver voltage to a first stator of the comb drive; and
applying a second driver voltage to a second stator of the comb drive;
overlaying the one or more driver voltages with one or more periodic voltage signals, based on:
overlaying the first driver voltage with a first periodic voltage signal; and
overlaying the second driver voltage with a second periodic voltage signal;
determining a measurement signal at a rotor of the one or more comb drives, wherein the measurement signal is based on the first periodic voltage signal and the second periodic voltage signal; and
determining a torsion angle of a mirror body of the MEMS apparatus based on the one or more periodic voltage signals.
2. The method as claimed in claim 1 , wherein the first periodic voltage signal and the second periodic voltage signal are substantially in anti-phase.
3. The method as claimed in claim 1 , wherein a frequency of the first periodic voltage signal and a frequency of the second periodic voltage signal are higher than a resonant frequency of the MEMS apparatus.
4. The method as claimed in claim 1 , wherein a frequency of the first periodic voltage signal and a frequency of the second periodic voltage signal are in a range from 1 MHz to 100 MHz.
5. The method as claimed in claim 1 , wherein an amplitude of the first periodic voltage signal and an amplitude of the second periodic voltage signal are in a range from 0.1 V to 1 V.
6. The method as claimed in claim 1 , wherein determining the torsion angle comprises:
mapping the measurement signal to the torsion angle based on a mapping of measurement signals at the rotor of the comb drive and torsion angles.
7. The method as claimed in claim 6 , further comprising:
generating the mapping during a calibration of the MEMS apparatus.
8. The method as claimed in claim 1 , wherein the measurement signal is based on a quotient
F
u
S
a
L
F
u
S
a
R
,
where:
FuSa L is the first periodic voltage signal, and
FuSa R is the second periodic voltage signal.
9. The method as claimed in claim 1 , wherein a amplitude of the first periodic voltage signal and is substantially the same as an amplitude of the second periodic voltage signal, and the condition
U F ˜U FuSa ·( C L −C R )
is satisfied, where:
U F is the measurement signal,
C L is a first capacitance between the first stator and the rotor,
C R is a second capacitance between the second stator and the rotor, and
U FuSa is the amplitude of the first periodic voltage signal or the amplitude of the second periodic voltage signal.
10. The method as claimed in claim 1 , further comprising:
regulating an amplitude of the first periodic voltage signal and an amplitude of the second periodic voltage signal to cause the condition
FuSa L ·C L +FuSa R ·C R =0
to be satisfied, where:
FuSa L is the amplitude of the first periodic voltage signal,
FuSa R is the amplitude of the second periodic voltage signal,
C L is a first capacitance between the first stator and the rotor, and
C R is a second capacitance between the second stator and the rotor.
11. The method as claimed in claim 1 , wherein the driver voltage is an AC voltage and the mirror body is a resonantly operated mirror body.
12. The method as claimed in claim 1 , wherein the driver voltage is a controllable DC voltage and the mirror body is a quasi-statically operated mirror body.
13. The method as claimed in claim 1 , wherein the first periodic voltage signal and the second periodic voltage signal comprise noise-like pseudorandom signals.
14. The method as claimed in claim 1 , wherein the first periodic voltage signal and the second periodic voltage signal comprise frequency-spread signals.
15. The method as claimed in claim 1 , further comprising:
verifying the torsion angle of the mirror body before electromagnetic radiation is reflected by the mirror body.
16. An MEMS apparatus, comprising:
a mirror body;
one or more electrostatic comb drives for twisting the mirror body based on one or more driver voltages,
wherein a first driver voltage is applied to a first stator of the comb drives, and
wherein a second driver voltage is applied to a second stator of the comb drives;
a unit for overlaying the one or more driver voltages with one or more periodic voltage signals,
wherein the first driver voltage is overlaid with a first periodic voltage signal, and
wherein the second driver voltage is overlaid with a second periodic voltage signal;
a first unit for determining a measurement signal at a rotor of the one or more comb drives, wherein the measurement signal is based on the one or more periodic voltage signals; and
a second unit for determining a torsion angle of the mirror body based on the one or more periodic voltage signals.
17. The MEMS apparatus as claimed in claim 16 , further comprising:
a memory storing a mapping between the measurement signal and the torsion angle.
18. The MEMS apparatus of claim 16 , wherein the measurement signal is mapped to the torsion angle based on a mapping of measurement signals at the rotor of the comb drive and torsion angles.
19. The MEMS apparatus of claim 18 , wherein the mapping is generated during calibration of the MEMS apparatus.
20. The MEMS apparatus of claim 16 , wherein the first periodic voltage signal and the second periodic voltage signal are substantially in anti-phase.
21. The MEMS apparatus of claim 16 , wherein a frequency of the first periodic voltage signal and a frequency of the second periodic voltage signal are higher than a resonant frequency of the MEMS apparatus.