Acceleration sensitive switch

• US 20060219536A1
• Filed: 06/17/2005
• Published: 10/05/2006
• Est. Priority Date: 03/29/2005
• Status: Active Grant

• Current Assignee: Agency For Science Technology and Research
• Original Assignee: Agency For Science Technology and Research
• Inventors: Tay Eng Hock, Francis, Lee, Ki Bang
• Granted Patent: US 7,284,432 B2
• Time in Patent Office: Days
• US Class Current: 200/61.45R
• CPC Class Codes: G01P 15/0891 with indication of predetermined acceleration values G01P15/135 takes precedence
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

An acceleration sensitive switch arrangement (208) includes an acceleration sensitive variable capacitor(200), a detection circuit(202) for detecting a capacitance value of the variable capacitor(200), and a switching circuit (204) responsive to a comparison between the detected capacitance and a threshold value.

Claims

1. An switching arrangement sensitive to acceleration, the switching arrangement comprising:

an acceleration sensitive variable capacitor;

a detection circuit for detecting a capacitance value of the variable capacitor; and

a switching circuit responsive to a comparison between the detected capacitance and a threshold value.

2. The switching arrangement of claim 1, wherein the variable capacitor comprises a base with at least one first electrode thereon and a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base.

3. The switching arrangement of claim 2, wherein the spring applies a first force to the mass in a direction away from the base.

4. The switching arrangement of claim 2, wherein the first electrode is adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the electrode and the mass.

5. The switching arrangement of claim 1, wherein the detection circuit comprises a voltage supply and a resistive load.

6. The switching arrangement of claim 5, wherein the voltage supply is an alternating voltage supply.

7. The switching arrangement of claim 1, wherein the switching circuit comprises a differential amplifier providing a first input voltage and a potentiometer providing a second input voltage to an electronic switch.

8. The switching arrangement of claim 7, wherein the first input voltage corresponds to the detected capacitance and the second input voltage corresponds to the threshold value.

9. The switching arrangement of claim 8, wherein the electronic switch is triggered positive upon the second input voltage becomes larger than the first input voltage.

10. The switching arrangement of claim 8, wherein the threshold value is variable by adjusting the potentiometer to change the second input voltage.

11. An acceleration sensitive variable capacitor comprising:

a base with at least one first electrode thereon;

a mass forming a second electrode resiliently suspended by at least one spring a first predetermined distance from the base, the spring applying a spring force to the mass in a direction away from the base; and

the first electrode being adapted to provide an electrostatic attractive force to the mass, the attractive force being inversely proportional to the distance between the first electrode and the mass,

wherein the attractive force overcomes the spring force and draws the mass towards the base upon the mass being moved, due to acceleration, to within a second predetermined distance from the base.

12. The acceleration sensitive variable capacitor of any one of claims 11, wherein the mass includes at least one spacer formed on the surface facing the base.

13. The acceleration sensitive variable capacitor of claim 12, wherein the spacer is electrically insulated so as to prevent the mass to form electrical contact with the first electrode when the mass moved to the second predetermined distance.

14. The acceleration sensitive variable capacitor of claim 11, wherein a layer of insulator formed on the first electrode separating the mass and the first electrode when the mass moved to the second predetermined distance.

15. The acceleration sensitive variable capacitor of claim 11, wherein at least one third electrode is formed on the base, adjacent to the first electrode, and having same electrically potential with the mass.

16. The acceleration sensitive variable capacitor of claim 15, wherein the spacer comes into contact with the third electrode when the mass moved to the second predetermined distance.

17. The acceleration sensitive variable capacitor of any one of claims 11 to 16, wherein the capacitance of the capacitor increases to a maximum, indicative of the capacitor undergoing a predetermined level of acceleration, upon the mass moved to the second predetermined distance.

18. The acceleration sensitive variable capacitor of claim 17, wherein the maximum capacitance of the capacitor being variable so as to vary the level of acceleration required to move the mass to the second predetermined distance.

19. The acceleration sensitive variable capacitor of claim 18, wherein the maximum capacitance of the capacitor is variable by changing voltage supplied to the first electrode and the mass.

20. The acceleration sensitive switch of claim 19, wherein the capacitance between the first electrode and the mass is measured by a detection circuit comprising a voltage supply and a resistive load.