Force sensor device

• US 5,834,646 A
• Filed: 04/28/1997
• Issued: 11/10/1998
• Est. Priority Date: 04/12/1995
• Status: Expired due to Term

• Current Assignee: Infineon Technologies AG
• Original Assignee: SensoNor ASA (Infineon Technologies AG)
• Inventors: Kvisteroy, Terje, Jakobsen, Henrik
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/848,301
• Time in Patent Office: 561 Days
• Field of Search: 73/514.29, 73/514.15, 73/704, 73/862.59, 73/702, 73/24.05, 73/24.06, 73/DIG. 1, 280/735
• US Class Current: 73/514.29
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01V 1/181 Geophones
• CPC Class Codes: G01V 1/186 Hydrophones
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

A force sensor device for sensing seismic force due to changes in acceleration or pressure, comprising mass-spring system formed by a resonant flexible plate forming system mass and suspended from a rigid frame by means of at least two beams forming system springs and located at different sides of the plate, the plate, frame and beams being made of a silicon. A vibration excitation device upon application of electric signals at an elected one of a plurality of specific frequencies interacts with the plate to create a corresponding specific vibration mode therein, and a detection device detects any vibration frequency change in the plate due to interaction between a stress field thereon caused by the seismic force and a stress field thereon caused by the vibration mode.

Claims

1. A force sensor device for sensing seismic force due to changes in acceleration or pressure, comprising mass-spring system formed by

a resonant flexible plate forming system mass and suspended from a rigid frame by means of at least two beams forming system springs and located at different sides of the plate, said plate, frame and beams being made of a silicon,

vibration excitation means which upon application of electric signals at an elected one of a plurality of specific frequencies interact with the plate to create a corresponding specific vibration mode therein, and

detection means for detecting any vibration frequency change in the plate due to interaction between a stress field thereon caused by said seismic force and a stress field thereon caused by the said vibration mode.

2. A force sensor device according to claim 1, wherein the beams have a thickness which is less than that of the plate.

3. A force sensor device according to claim 2, wherein one face of each of said beams is flush with a face of said plate.

4. A force sensor device according to claim 1, wherein said beams have a midplane being off-set and parallel to a midplane of the plate.

5. A force sensor device according to claim 1, wherein said system springs are formed by two beams of identical geometry with parallel longitudinal axes, each beam suspending the plate at an angle of 90 degrees to a respective suspension side thereof and forming an angle of 90 degrees with a connecting side of the frame.

6. A force sensor device according to claim 5, wherein the plate has a substantially oblong form.

7. A force sensor device according to claim 5, wherein the plate has a substantially oblong hexagonal form.

8. A force sensor device according to claim 5, wherein a center line of the plate forms an angle in the range of 15-75 degrees with a beam longitudinal axis.

9. A force sensor device according to claim 8, wherein said angle is 45 degrees.

10. A force sensor device according to claim 5, wherein said beams are located at regions of the plate which have maximum distance apart.

11. A force sensor device according to claim 1, wherein the excitation means being of a thermal excitation resistor type located in at least one of the beams.

14. A force sensor device according to claim 1, wherein the excitation means being of a piezoresistor type located in at least one of the beams.

15. A force sensor device according to claim 14, wherein said detection means comprising one or more piezoresistive elements located in at least one of said beams.

16. A force sensor device according to claim 15, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.

17. A force sensor device according to claim 1, wherein the excitation means being of a thermal excitation resistor type located in the plate.

18. A force sensor device according to claim 17, wherein said detection means comprising one or more piezoresistive elements located in at least one of said beams.

19. A force sensor device according to claim 18, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.

20. A force sensor device according to claim 17, wherein said detection means comprising one or more piezoresistive elements located in the plate.

21. A force sensor device according to claim 20, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.

22. A force sensor device according to claim 17, wherein said detection means comprising one or more piezoresistive elements located in the plate and at least one other of said beams.

23. A force sensor device according to claim 22, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.

24. A force sensor device according to claim 1, wherein the excitation means being of a piezoresistor type located in the plate.

25. A force sensor device according to claim 24, wherein said detection means comprising one or more piezoresistive elements located in at least one of said beams.

26. A force sensor device according to claim 25, wherein said detection means has a plurality of piezoresistive elements forming av Wheatstone bridge structure.

27. A force sensor device according to claim 1, wherein the excitation means being of a piezoresistor type located in the plate and at least one of the beams.

28. A force sensor device according to claim 27, wherein said detection means comprising one or more piezoresistive elements located in at least one of said beams.

29. A force sensor device according to claim 28, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.

30. A force sensor device according to claim 1, wherein the excitation means being of electrostatic type, wherein the detection means being capacitive type, wherein the plate is located in spaced apart relationship between said excitation means and said detection means, and wherein said plate electrically connects to a common electrical node of the excitation means and the detection means and forms a capacitor electrode element common to both said excitation means and said detection means.

31. A force sensor device according to claim 30, wherein the excitation means have electrodes facing one face of the plate to provide an electrostatic field varying according to an applied electrical signal of said specific frequency, and wherein the detection means have electrodes facing the other face of the plate to detect capacitance variation due to said stress field interaction.

32. A force sensor device according to claim 31, wherein the electrodes of the detection means are located on a lid covering said one face of the plate.

33. A force sensor device according to claim 30, wherein said excitation and detection means are located at regions midway between vibration nodes of the plate.

34. A force sensor device according to claim 1, wherein the excitation means being of electrostatic type, wherein the detection means being capacitive type, wherein the plate is located in spaced apart relationship with said excitation means and said detection means, and wherein said plate electrically connects to a common electrical node of the excitation means and the detection means and forms a capacitor electrode element common to both said excitation means and said detection means.

35. A force sensor device according to claim 34, wherein the excitation means have electrodes facing one face of the plate to provide an electrostatic field varying according to an applied electrical signal of said specific frequency, and wherein the detection means have at least one electrode facing said one face of the plate to detect capacitance variation due to said stress field interaction.

36. A force sensor device according to claim 35, wherein the electrodes of the excitation and detection means are located on a lid covering said one face of the plate.

37. A force sensor device according to claim 1, further comprising electronic circuitry having a first set of terminals connected to the excitation means to provide excitation signals thereto, and a second set of terminals connected to the detection means for receiving signals indicative of vibration frequency changes caused by said interaction of stress fields, means for monitoring an output signal from said detection means and threshold means initiating an operation signal to be delivered to a third set of terminals connected to peripheral equipment if a state of change in said output signal is above a specific threshold.

38. A force sensor device according to claim 37, wherein said peripheral equipment is a vehicle air bag inflating device.

39. A force sensor device according to claim 1, wherein the plate, the beams, the frame, the excitation means, the detection means and the electronic circuitry are located on a common silicon substrate.

40. A force sensor device according to claim 1, wherein said beams are located at regions of the plate which have maximum distance apart.

41. A force sensor device according to claim 1, wherein said excitation and detection means are located at regions midway between vibration nodes of the plate.

12. A force sensor device according to claim 12, wherein said detection means comprising one or more piezoresistive elements located in at least one of said beams.

13. A force sensor device according to claim 12, wherein said detection means has a plurality of piezoresistive elements forming a Wheatstone bridge structure.