Combined MEMS accelerometer and gyroscope

• US 8,464,585 B2
• Filed: 10/20/2008
• Issued: 06/18/2013
• Est. Priority Date: 10/18/2007
• Status: Active Grant

• Current Assignee: Melexis Technologies NV (Sensinnovat BVBA), Universiteit Gent Vzw
• Original Assignee: Melexis Technologies NV (Sensinnovat BVBA), Universiteit Gent Vzw
• Inventors: Raman, Johan, Rombouts, Pieter
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US12/738,504
• Publication Number:
  US 20100307241A1
• Time in Patent Office: 1,702 Days
• Field of Search: 735/040.3, 735/040.4, 735/041.2, 735/041.4, 735/10, 735/11, 735/140.1, 735/140.2
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5755 the devices having a single sensing mass
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/14 by making use of gyroscopes gyroscopes per se G01C19/00
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

A MEMS structure for a combined gyroscope and accelerometer unit (100) based on in-plane vibratory movements comprises a proof mass (101) and comb-drives (102) operable to cause the proof mass (101) to resonate in the x-direction, commonly referred to as the primary mode. Under the influence of a rotation Ω_z around the z-axis, a Coriolis force acting in the y-direction results. This excites the secondary (or sense) mode. A set of parallel-plate capacitors 103 are provided to enable position readout along the secondary axis. In addition to the above, the comb-drive capacitors (102) of the primary mode can also be used for readout of position along the primary axis, and the parallel-plate capacitors (103) for actuation along the secondary axis. This can be achieved either by time-multiplexing these capacitors (102, 103) or by providing separate sets of capacitors (102, 103) for sensing and actuation along each axis. The unit can operate in separate ΣΔ force-feedback loops with respect to both axes. This force-feedback approach is already known for readout of the secondary mode of MEMS gyroscopes. It has not previously been applied to the primary mode of a gyroscope for the measurement of a component of acceleration.

Claims

1. A combined accelerometer and gyroscope unit comprising:

a proof mass;

primary actuating means operable to actuate the proof mass along a primary axis;

secondary actuating means operable to actuate the proof mass along a secondary axis;

secondary sensing means operable to sense a position of the proof mass along the secondary axis; and

primary sensing means operable to sense a position of the proof mass along the primary axis wherein Σ

Δ

force-feedback loops are set up for both the secondary axis and the primary axis wherein an input Vin is included in a primary Σ

Δ

force-feedback loop to force the proof mass to track a predefined movement.

2. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the accelerometer and gyroscope unit is a MEMS accelerometer and gyroscope unit.

3. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein both the primary actuating means and the primary sensing means are comb-drive capacitors.

4. A combined accelerometer and gyroscope unit as claimed in claim 3 wherein separate comb-drive capacitors are provided for actuating and for providing a readout signal.

5. A combined accelerometer and gyroscope unit as claimed in claim 3 wherein time multiplexing is used to allow the same comb-drive capacitors to be utilised both for actuating and for providing a readout signal.

6. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein both the secondary actuating means and the secondary sensing means are differential parallel plate capacitors.

7. A combined accelerometer and gyroscope unit as claimed in claim 6 wherein separate differential parallel plate capacitors are provided for actuating and for providing a readout signal.

8. A combined accelerometer and gyroscope unit as claimed in claim 6 wherein time multiplexing is used to allow the same differential parallel plate capacitors to be utilised both for actuating and for providing a readout signal.

9. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein separate Σ

Δ

force-feedback loops are provided for the primary axis and the secondary axis.

10. A combined accelerometer and gyroscope unit as claimed in claim 9 wherein a primary Σ

Δ

force-feedback loop has an input Vin.

11. A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop incorporates an electrical filter.

12. A combined accelerometer and gyroscope unit as claimed in claim 9 wherein at the end of each loop, a quantizer is provided to deliver digital output values.

13. A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop contains a mechanical feedback path.

14. A combined accelerometer and gyroscope unit as claimed in claim 13 wherein an electrical feedback path is also provided.

15. A combined accelerometer and gyroscope unit as claimed in claim 14 wherein the feedback loops include electrical filters.

16. A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop includes a first filter and a second filter and wherein the second filters have the same poles as the first filters.

17. A combined accelerometer and gyroscope unit as claimed in claim 15 wherein each loop includes a first filter and a second filter and wherein the second filters have different zeros to the first filters.

18. A combined accelerometer and gyroscope unit as claimed in claim 13 further including a controller filter to stabilize the loop.

19. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the unit further includes a tertiary actuating means operable to actuate the proof mass along a tertiary axis and/or tertiary sensing means operable to sense a position of the proof mass along the tertiary axis.

20. A combined accelerometer and gyroscope unit as claimed in claim 19 wherein the tertiary axis is substantially perpendicular to the plane containing the primary and secondary axes.

21. A combined accelerometer and gyroscope unit as claimed in claim 19 wherein both the tertiary actuating means and the tertiary sensing means are comb-drive capacitors.

22. A combined accelerometer and gyroscope unit as claimed in claim 21 wherein separate comb-drive capacitors are provided for actuating and for providing a readout signal.

23. A combined accelerometer and gyroscope unit as claimed in claim 22 wherein time multiplexing is used to allow the same comb-drive capacitors to be utilised both for actuating and for providing a readout signal.

24. A combined accelerometer and gyroscope unit as claimed in claim 23 wherein two sets of fingers comprising the comb-drive capacitors are of differing dimensions along the tertiary axis.

25. A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the unit is operated in a mode wherein a Σ

Δ

force-feedback loop is set up for only one of the secondary axis and the primary axis.

26. A sensor cluster comprising one or more combined accelerometer and gyroscope units according to claim 1.

27. A sensor cluster as claimed in claim 26 wherein the cluster includes one or more dedicated single axis or multi-axis accelerometers and/or one or more dedicated single axis or multi-axis gyroscopes.

28. A method of operating a combined accelerometer and gyroscope unit having a proof mass;

primary actuating means operable to actuate the proof mass along a primary axis;

secondary actuating means operable to actuate the proof mass along a secondary axis;

secondary sensing means operable to sense a position of the proof mass along the secondary axis; and

primary sensing means operable to sense a position of the proof mass along the primary axis, the method comprising the steps of;

setting up Σ

Δ

force-feedback loops for the both the secondary axis and the primary axis to measure both a component of rotation and two components of acceleration wherein an input Vin is included in a primary Σ

Δ

force-feedback loop to force the proof mass to track a predefined movement.

29. A method as claimed in claim 28 both the primary actuating means and the primary sensing means include comb-drive capacitors.