JPH05164779A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain an acceleration sensor with which fault diagnoses or calibration can be performed without applying acceleration or vibration to the sensor from the outside. CONSTITUTION:A mass section 2 is provided at the center of a frame 1 having a frame-like shape and the section 2 is supported from both sides by the frame 1. Covers 4 and 5 are respectively stuck to the upper and lower surfaces of the frame 1. Recessed parts 4a and 5a are respectively provided on the internal surfaces of the covers 4 and 5 so that the section 2 can be displaced and a displacement detecting electrode 6 for detecting the displacement of the section 2 is provided on the bottom of the part 4a. In addition, a driving electrode 7 which vibrates the section 2 by acting an electrostatically attracting force on the section 2 by means of an AC voltage is provided on the bottom of the part 5a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor. Specifically, the present invention relates to an acceleration sensor that electrically detects displacement of a mass portion caused by acceleration or vibration as a capacitance change.

[0002]

BACKGROUND ART FIG. 4 shows a sectional view of a conventional acceleration sensor 30. In this acceleration sensor 30, a mass portion 32 is arranged in the center of a frame 31 having a rectangular frame shape, and the mass portion 32 is supported on the frame 31 in a cantilevered manner by four elastic beams 33. Has been done. The mass portion 32 can be freely displaced minutely in the thickness direction (X direction in FIG. 4) of the mass portion 32 by elastic deformation of the beam 33. The frame 31, the mass portion 32, and the beam 33 are made of a conductor such as metal.

Covers 34 and 35 made of an insulating material are superposed on the upper surface and the lower surface of the frame 31, and peripheral portions thereof are bonded to the frame 31 with an adhesive or the like. Recesses 34a, 35a are formed on the inner surfaces of the covers 34, 35 so that the mass portion 32 can be displaced. A displacement detecting electrode 36 is provided on the bottom of the recess 34a of the cover 34 on the upper surface side, and the electrode surface 32a of the mass portion 32 and the displacement detecting electrode 36 constitute a capacitor. Between the displacement detecting electrode 36 and the electrode surface 32a of the mass portion 32, the displacement detecting electrode 3 generated due to the displacement of the mass portion 32 is formed.
A detection circuit 38 that detects a change in capacitance between the electrode 6 and the electrode surface 32a, converts the change into a change in voltage, and outputs the change as a voltage signal is connected.

However, when the mass portion 32 supported by the beam 33 is subjected to elastic displacement due to acceleration in the X direction, the gap between the mass portion 32 and the displacement detection electrode 36 depends on the displacement amount of the mass portion 32. The capacitance changes as the amount changes. This change in capacitance is detected by the detection circuit 38, converted into a voltage signal indicating the magnitude of acceleration, and output.

For example, if the sensor 30 is attached to a window glass or a door, it can be used as a crime prevention sensor, and if it is used in an in-vehicle airbag system, the impact at the time of collision can be detected.

[0006]

In such an acceleration sensor, the beam is very thin compared to the mass portion and is easily damaged by an external impact, so that the beam is not only used at the time of shipment but also in an airbag system or the like. It is necessary to check whether the acceleration sensor is damaged even after being set in the device.

Further, when the acceleration sensor is shipped, it is necessary to inspect whether or not the measured value is accurately adjusted. Furthermore, for example, when the operating environment temperature is different, the beam may be thermally expanded or contracted, for example, and the displacement amount of the mass portion may be displaced. Therefore, the measured value may be displaced while the acceleration sensor is used. There is also. In such a case, it is necessary to calibrate the displacement of the mass portion and the measurement value of the acceleration sensor.

However, in the conventional acceleration sensor, the detected value cannot be obtained unless acceleration or vibration is applied from the outside. Therefore, if the acceleration sensor is attached to the inspection device and the acceleration or vibration is not applied from the outside, failure occurs. The diagnosis and adjustment of measured values or calibration could not be performed, and the inspection took time and effort. In particular, after the acceleration sensor has been attached to an airbag system or the like, the acceleration sensor must be removed once, and work such as failure diagnosis and calibration has been difficult.

Further, as described above, the beam is thinner than the mass portion and is easily damaged, but it has no function of protecting the beam from damage due to impact or the like.

The present invention has been made in view of the problems of the above-mentioned conventional examples, and an object of the present invention is not to require an inspection device or the like, but to perform failure diagnosis and measurement value measurement independently by the acceleration sensor. The purpose is to make adjustments and calibrations possible, and to add a function to protect the beam from impacts and the like.

[0011]

In the acceleration sensor of the present invention, a mass portion is swingably supported by a support by an elastic beam, and the displacement of the mass portion is electrically detected as a capacitance change. In the acceleration sensor, a displacement detection electrode for detecting displacement of the mass portion is arranged so as to face the electrode surface of the mass portion, and an electrostatic attractive force is applied to the mass portion so as to face the electrode surface of the mass portion. It is characterized in that a driving electrode for displacing is arranged.

[0012]

The acceleration sensor of the present invention has the displacement detecting electrode for detecting the displacement amount of the mass portion facing the electrode surface of the mass portion. If the displacement amount of the mass portion is known from the electric signal, the magnitude of acceleration or vibration applied to the acceleration sensor can be detected.

On the other hand, since this acceleration sensor has a driving electrode facing the electrode surface of the mass portion to displace the mass portion by applying an electrostatic attractive force, the driving electrode and the electrode of the mass portion By applying a DC voltage or an AC voltage to the surface, an electrostatic attractive force can be applied to the mass portion to displace or vibrate the mass portion.

Therefore, a voltage is applied to the driving electrode to displace or vibrate the mass portion, and at the same time, a pseudo acceleration or vibration is detected by the displacement detecting electrode to cause abnormal operation of the mass portion due to beam damage. It is possible to carry out a failure diagnosis such as. Further, if the relationship between the input signal to the drive electrode and the detection signal of the displacement detection electrode related to the normal acceleration sensor is measured in advance, the input signal to the drive electrode and the detection signal will have a normal relationship. The measurement values can be adjusted at the time of shipment. Further, even in the use state, the acceleration sensor can be calibrated so as to eliminate the error by monitoring the error of the measurement value.

Further, when the mass portion is largely displaced and may collide with the displacement detecting electrode or the like, if a proper electrostatic attractive force is applied between the driving electrode and the electrode surface of the mass portion, the mass portion It is possible to prevent the excessive displacement by damping the movement of the beam, and it is possible to prevent the beam from being damaged due to the collision between the mass portion and the displacement detecting electrode or the like. Further, when a large impact is applied, if a large electrostatic attraction is generated between the driving electrode and the electrode surface of the mass portion to fix the mass portion by suction,
It is possible to prevent the beam from being damaged.

[0016]

1 and 2 are a sectional view and a partially cutaway perspective view of an acceleration sensor 10 according to an embodiment of the present invention.
In this acceleration sensor 10, a mass portion 2 is disposed at the center of a frame 1 having a rectangular frame shape, and the mass portion 2 is supported by the frame 1 in a cantilevered manner by four elastic beams 3. There is. Therefore, the mass portion 2 can be freely minutely displaced in the thickness direction (X direction in FIGS. 1 and 2) by elastically bending the beam 3. In addition, frame 1
The beam 3 and the mass portion 2 are integrally formed of a crystalline silicon wafer by using a semiconductor manufacturing process, and are entirely conductive.

Covers 4 and 5 made of Pyrex glass are superposed on the upper and lower surfaces of the frame 1, and peripheral portions of the covers 4 and 5 are adhered to the frame 1 with an adhesive or the like. Recesses 4a and 5a are formed on the inner surfaces of the covers 4 and 5 so that the mass portion 2 can be displaced.
A displacement detection electrode 6 for detecting the displacement of the mass portion 2 is provided at the bottom of the mass a, and an electrostatic attractive force is applied to the mass portion 2 at the bottom of the recess 5 a of the cover 5 to allow the mass portion 2 to move. A driving electrode 7 for displacing or oscillating is disposed.

The beam 3 is formed in the capacitor composed of the electrode surface 2a on the upper surface side of the mass portion 2 and the displacement detecting electrode 6.
Also, a detection circuit 8 that detects a change in the capacitance of the capacitor through the frame 1 and that converts the change in the capacitance into a change in the voltage and outputs the change is connected. Further, an electrostatic attractive force is applied between the electrode surface 2b and the driving electrode 7 through the frame 1 and the beam 3 to the capacitor composed of the electrode surface 2b on the lower surface side of the mass portion 2 and the driving electrode 7. A drive circuit 9 for applying an AC voltage for vibrating the mass portion 2 is connected.

However, when acceleration is applied to the acceleration sensor 10, the mass portion 2 is displaced by the inertial force while elastically bending the beam 3, and the mass portion 2 is stopped at a position where the inertial force and the elastic restoring force of the beam 3 are balanced. .. Alternatively, the acceleration sensor 1
When vibration is applied to 0, the mass portion 2 also vibrates in accordance with the vibration. At this time, the gap amount between the mass portion 2 and the displacement detection electrode 6 changes according to the displacement amount of the mass portion 2, and the electrostatic capacitance between the electrode surface 2a of the mass portion 2 and the displacement detection electrode 6 changes. Change. This change in capacitance is detected by the detection circuit 8,
Since the voltage signal corresponding to the magnitude of the acceleration is converted and output, the acceleration can be known.

Further, the acceleration sensor 10 has a drive electrode 7 for self-diagnosis, and the drive circuit 9 to the mass portion 2 are provided.
When an AC voltage is applied between the electrode surface 2b of the above and the driving electrode 7, a varying electrostatic attractive force is exerted on the mass portion 2, so that the mass portion 2
Vibrates. Therefore, by using the driving electrode 7 and the driving circuit 9, it is possible to electrically generate pseudo vibration in the acceleration sensor 10.

Therefore, an AC voltage is applied from the drive circuit 9 to the drive electrode 7 to forcibly vibrate the mass portion 2 and, at the same time, the displacement detection electrode 6 and the detection circuit 8 displace the mass amount of the mass portion 2 or equivalent. Fault diagnosis can be performed by detecting various accelerations. That is, if the beam 3 is damaged, the mass portion 2 will not be displaced normally even if an AC voltage is applied to the drive electrode 7. Therefore, if the displacement detection electrode 6 monitors the displacement of the mass portion 2, the inspection can be performed. It is possible to easily self-diagnose a failure due to beam breakage or the like while being attached to a device such as an airbag system without applying mechanical vibration from the outside by the device or the like.

Particularly, if the drive circuit 9 and the detection circuit 8 are integrated, the acceleration sensor 10 is started up and at the same time the mass portion 2
After forcibly oscillating and detecting the displacement and checking whether the acceleration sensor 10 is normal or abnormal, if it is normal, the acceleration sensor 10 is put into an operating state to have a self-check function. You can also

If a normal output signal from the detection circuit 8 when a predetermined input signal is applied to the drive electrode 7 from the drive circuit 9 is measured in advance, the measured value can be easily adjusted at the time of shipment. be able to. In addition, it is possible to correct an adjustment error with the passage of time. Further, if the relationship between the input signal applied from the drive circuit 9 and the normal output signal detected by the detection circuit 8 is stored in the detection circuit 8 or the like, an error or deviation of the measured value due to a change in environmental temperature or the like will occur. It is also possible to add a self-calibration function that automatically corrects.

Further, the electrostatic attractive force of the driving electrode 7 can be used also for beam protection. For example, when excessive vibration is applied to the acceleration sensor 10 and the mass portion 2 may collide with the displacement detection electrode 6 or the covers 4 and 5,
A constant voltage is applied from the drive circuit 9 to the drive electrode 7 in synchronization with the detection signal of the detection circuit 8 at the timing when the mass portion 2 is displaced toward the displacement detection electrode 6 side. As a result, an electrostatic attractive force is generated between the drive electrode 7 and the mass portion 2,
The displacement of the mass portion 2 is damped, and the collision of the mass portion 2 with the covers 4, 5 and the like can be prevented, and the damage of the beam 3 can be prevented. Alternatively, when a larger impact is applied to the acceleration sensor 10 and the beam 3 may be damaged, a large DC voltage is applied from the drive circuit 9 to the drive electrode 7 to fix the mass portion 2 to the drive electrode 7 by suction. , Beam 3
It is also possible to prevent damage to.

FIG. 3 is a sectional view showing an acceleration sensor 20 according to another embodiment of the present invention. In the acceleration sensor 20, the displacement detecting electrode 6 and the driving electrode 7 are provided on the bottom surface of the recess 4a of the cover 4 on the upper surface side so as to face the electrode surface 2a on the upper surface side of the mass portion 2. Yes, the detection circuit 8 is connected between the displacement detection electrode 6 and the electrode surface 2a, and the drive circuit 9 is connected between the drive electrode 7 and the electrode surface 2a.

Therefore, even in the acceleration sensor 20, the mass circuit 2 is forcibly vibrated by applying an AC voltage between the driving electrode 7 and the electrode surface 2a of the mass circuit 2 by the driving circuit 9. be able to. Therefore, the acceleration sensor 20 is also similar to the acceleration sensor 10 of FIG.
The function of self-diagnosis of failure, adjustment of measured value, self-check function, self-calibration function, damping function of mass part, suction-fixing function of mass part, etc. can be achieved. However, when damping the mass portion 2, it is necessary to generate an electrostatic attractive force on the drive electrode 7 in synchronization with the timing at which the mass portion 2 moves away from the displacement detection electrode 6.

[0027]

According to the present invention, the acceleration or vibration is artificially generated by using the drive electrode, and the acceleration or vibration is detected by the displacement detection electrode to diagnose the malfunction of the mass portion or the like. can do. That is, the acceleration sensor can perform its own self-diagnosis without using an inspection device or the like while being attached to a device such as an airbag system.

Further, by applying a predetermined input signal to the driving electrode to displace or vibrate the mass portion, the displacement detecting electrode detects the level of acceleration or vibration to adjust the measurement value of the acceleration sensor. Can be done,
It is possible to calibrate the initial error of measurement values and the error over time.

Further, by applying an electrostatic attractive force between the driving electrode and the electrode surface of the mass portion, the movement of the mass portion can be damped or the mass portion can be adsorbed and fixed to the driving electrode side. It is possible to prevent the beam from being damaged due to the collision of the mass portion with the displacement detecting electrode or the like due to an impact or the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view of the above embodiment.

FIG. 3 is a sectional view showing an acceleration sensor according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional acceleration sensor.

[Explanation of symbols]

 2 Mass part 3 Beam 6 Displacement detecting electrode 7 Driving electrode 8 Detection circuit 9 Driving circuit

Claims (1)

[Claims] 1. An acceleration sensor in which a mass portion is swingably supported by a support by a beam having elasticity, and a displacement of the mass portion is electrically detected as a change in capacitance. Displacement detection electrodes are arranged facing each other to detect displacement of the mass portion, and drive electrodes are arranged so as to be opposed to the electrode surface of the mass portion and apply electrostatic attraction to the mass portion to displace the mass portion. Acceleration sensor characterized by.