Composite vibratory in-plane accelerometer

• US 10,234,477 B2
• Filed: 09/23/2016
• Issued: 03/19/2019
• Est. Priority Date: 07/27/2016
• Status: Active Grant

• Current Assignee: Nxtant Incorporated
• Original Assignee: Google LLC (Alphabet Inc.)
• Inventors: Anac, Ozan, Huang, Xiaojun
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): Roberts, Herbert K
• Application Number:
  US15/275,188
• Publication Number:
  US 20180031601A1
• Time in Patent Office: 907 Days
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/051 Translation according to an axis parallel to the substrate
• CPC Class Codes: B81B 7/008 MEMS characterised by an electronic circuit specially adapted for controlling or driving the same B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01C 19/5762 the sensing mass being connected to a driving mass, e.g. driving frames
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: G01P 15/097 by vibratory elements
• 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 2015/0808 for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

Systems and methods are described herein for detecting and measuring inertial parameters, such as acceleration. In particular, the systems and methods relate to vibratory inertial sensors implementing time-domain sensing techniques. Within a composite mass sensor system, a sense mass may oscillate at a frequency different from its actuation frequency, allowing flexibility when integrating the sensor into drive systems without sacrificing sensitivity.

Claims

1. A composite mass system, comprising:

a sense mass, wherein the sense mass responds to an inertial parameter in a first direction at a first frequency in the first direction;

a drive mass flexibly coupled to the sense mass, wherein the drive mass is driven in the first direction at a second frequency;

a first time-domain switch configured to generate an output voltage based on a first current generated in part by the sense mass moving relative to a support structure; and

logic circuitry in signal communication with the first time-domain switch and configured to;

determine a time interval based on the output voltage; and

calculate the inertial parameter based on the time interval.

2. The composite mass system of claim 1, wherein a resonant frequency of the sense mass is different from a resonant frequency of the drive mass.

3. The composite mass system of claim 2, wherein the first frequency is the resonant frequency of the sense mass, and the second frequency is the resonant frequency of the drive mass.

4. The composite mass system of claim 1, wherein the drive mass is flexibly coupled to the sense mass via coupling springs that are compliant in the first direction.

5. The composite mass system of claim 4, further comprising an anchor structure rigidly coupled to the support structure, wherein the drive mass is mechanically coupled to the anchor structure via drive springs.

6. The composite mass system of claim 5, wherein a spring constant of the coupling springs is lower than a spring constant of the drive springs.

7. The composite mass system of claim 5, further comprising an arm having a major axis that passes radially from the anchor structure to the drive mass, wherein the drive springs are coupled to the arm and configured to cause the drive mass to move substantially in the first direction as the arm is rotated about an axis perpendicular to a plane defined by the first direction and the major axis.

8. The composite mass system of claim 7, wherein the first direction is substantially tangential to the rotation of the arm.

9. The composite mass system of claim 5, wherein a spring constant of the coupling springs increases as oscillation frequency increases and decreases as oscillation frequency decreases.

10. The composite mass system of claim 1, wherein the drive mass is driven via a comb drive.

11. The composite mass system of claim 1, wherein the time-domain switch comprises a first half coupled to the sense mass and a second half coupled to the support structure.

12. The composite mass system of claim 1, wherein the time-domain switch comprises a plurality of time-domain switches.

13. The composite mass system of claim 1, further comprising a second time-domain switch configured to generate a second voltage based on a second current generated in part by the sense mass, wherein the first current is out of phase with the second current.

14. The composite mass system of claim 13, wherein the logic circuitry is further configured to linearly combine a signal generated from the first time-domain switch with a signal generated from the second time-domain switch.

15. The composite mass system of claim 1, wherein the second frequency is higher than the first frequency.

16. The composite mass system of claim 15, wherein the inertial parameter is acceleration.

17. A method for determining an inertial parameter, comprising:

responding to an inertial parameter in a first direction with a sense mass in the first direction at a first frequency;

driving, in the first direction at a second frequency, a drive mass that is flexibly coupled to the sense mass;

generating, from a first time-domain switch, an output voltage based on a first current generated in part by the sense mass moving relative to a support structure;

determining a time interval based on the output voltage; and

calculating the inertial parameter based on the time interval.

18. The method of claim 17, further comprising oscillating the sense mass at a resonant frequency of the sense mass and driving the drive mass at a resonant frequency of the drive mass.

19. The method of claim 17, wherein the drive mass is flexibly coupled to the sense mass via coupling springs that are compliant in the first direction.

20. The method of claim 19, wherein the drive mass is mechanically coupled to an anchor structure via drive springs;

and

wherein the anchor structure is rigidly coupled to the support structure.

21. The method of claim 20, wherein a spring constant of the coupling springs is lower than a spring constant of the drive springs.

22. The method of claim 17, wherein the drive mass is driven via a comb drive.

23. The method of claim 17, wherein a first half of the time-domain switch is coupled to the sense mass and a second half of the time-domain switch is coupled to the support structure.

24. The method of claim 23, further comprising generating, from a second time-domain switch, a second voltage based on a second current generated in part by the sense mass, wherein the first current is out of phase with the second current.

25. The method of claim 24, further comprising linearly combining a signal generated from the first time-domain switch with a signal generated from the second time-domain switch.

26. The method of claim 17, wherein a resonant frequency of the sense mass is different from a resonant frequency of the drive mass.

27. The method of claim 17, wherein the inertial parameter comprises an acceleration.