Capacitance-type inertial detecting device

• US 6,997,054 B2
• Filed: 05/14/2004
• Issued: 02/14/2006
• Est. Priority Date: 05/15/2003
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Tsugai, Masahiro
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/845,504
• Publication Number:
  US 20040226377A1
• Time in Patent Office: 641 Days
• Field of Search: 735/143.2, 735/142.9, 735/040.4, 735/041.2, 735/041.4, 735/143.8, 735/141.8, 735/142.4
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

An inertial detecting device for detecting a change in capacitance of a sensor element caused by inertial force includes a displaceable unit. The displaceable unit includes a movable mass member which is displaceable in the direction of an inertial force and is supported in a space by a pair of beams fixed on the substrate. At least one pair of detection units for detecting the displacement of the displaceable unit are provided on the substrate. The detection unit includes a drive unit and a pair of sensing electrodes which are disposed opposite to the displaceable unit. Any gap can be freely set between the sensing electrode and the movable mass member, thereby changing the sensitivity of the detecting device in a wide range.

Claims

1. An inertial detecting device for detecting a change in capacitance of a sensor element caused by an inertial force, the sensor element comprising:

a substrate and a structure bonded to the substrate with a gap between at least part of the structure and the substrate, wherein,

the structure includes a displaceable unit and at least one pair of detection units for detecting displacement of the displaceable unit,

the displaceable unit includes a movable mass member displaceable along an inertial force direction, a pair of beams which are connected to the movable mass member and support the movable mass member in a space opposite the gap, and a pair of anchors which support the beams and are bonded to the substrate,

each of the detection units includes a respective pair of sensing electrodes, respective sensing electrodes of each pair being disposed on opposite first and second sides of the displaceable unit, each of the sensing electrodes is supported opposite and spaced from the substrate, and each pair of sensing electrodes defines a respective pair of variable gaps between the sensing electrodes and the displaceable unit, each pair of variable gaps having a respective different width when the displaceable unit is not displaced, and

each of the detection units includes a drive unit for moving each sensing electrode toward and away from the displaceable unit.

2. The inertial detecting device according to claim 1, wherein the sensor element comprises a damper including a pair of damping electrodes, the damping electrodes being disposed on opposite sides of the displaceable unit and forming damper gaps with the displaceable unit, narrower than the gaps of the sensing electrodes of the detection units and the displaceable unit, the damper contacting the displaceable unit, upon displacement of the displaceable unit, before the sensing electrodes of the detection units contact the displaceable unit.

3. The inertial detecting device according to claim 1, wherein the sensor element has respective different measurement ranges set by respective detection units, and the detecting device comprises an automatic range-changing mechanism which compares output voltage of the sensor element with a measurement range-defining threshold voltage and selects one of the detection units to provide an optimal measurement range according to the comparison.

4. The inertial detecting device according to claim 1, wherein the sensor element has respective different measurement ranges set by changing the variable gap stepwise, and the detecting device comprises an automatic range-changing mechanism which compares output voltage of the sensor element with a measurement range-defining threshold voltage and changes measurement range by changing the variable gap according to the comparison.

5. The inertial detecting device according to claim 1, wherein the drive unit is connected with the sensing electrode via an insulating layer.

6. The inertial detecting device according to claim 5, wherein the drive unit comprises a pair of fixed electrodes, fixed on the substrate, and a drive electrode which is displaceable by an electrostatic attraction between the fixed electrodes and the drive electrode.

7. The inertial detecting device according to claim 5, further comprising a feedback mechanism which applies a voltage to the drive unit for moving the sensing electrodes so that after a displacement, a gap between the movable mass member and the sensing electrodes returns to an original value, before the displacement.

8. The inertial detecting device according to claim 5, further comprising a feedback mechanism which changes potential difference between the movable mass member and the sensing electrodes, so that an electrostatic attraction cancels displacement of the movable mass member.

9. The inertial detecting device according to claim 5, further comprising a drift compensating mechanism for compensating temperature dependency of zero point output and sensitivity by applying a voltage to the drive unit to equalize gaps between the movable mass member and the sensing electrodes.

10. The inertial detecting device according to claim 1, further comprising a C-V converter for converting a change in capacitance into a voltage, the converter storing equal quantities of charge in a pair of capacitors defined by a pair of the sensing electrodes and the movable mass member.