JP2001083177A - Electret capacitor type acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance acceleration sensor of a relatively simple structure at a low manufacturing cost. SOLUTION: Split conductors 14a and 14b are made an electret so as to constitute a pair of capacitors C1 and C2 between the split conductors 14a and 14b and a metal fixed electrode 12. The split conductors 14a and 14b are oscillated in the reverse direction B by the moment of a mass block body 16 when an acceleration A is applied in the direction parallel to the surface of an oscillating body 14, for detecting the acceleration based on the difference in output between the capacitors C1 and C2 which accompanies the oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can detect acceleration by converting vibration into an electric signal.
The present invention relates to an electret condenser type acceleration sensor suitable for use in multi-axis applications and the like.

[0002]

2. Description of the Related Art Conventionally, acceleration sensors that have been put to practical use have been known to detect acceleration applied by various methods such as an electromagnetic type, a piezoelectric type, and a semiconductor type. Some of them detect acceleration applied by bending of a piezoelectric element.

[0003] As this kind of piezoelectric acceleration sensor,
For example, there is an acceleration sensor as shown in FIG. 5. This acceleration sensor is a piezoelectric element 3a formed in a donut shape on the front and back of a disk-shaped metal vibration plate 2 supported by a support 1a standing on a support plate 1. , 3b are coaxially bonded to form a bimorph type. This piezoelectric element 3
a and 3b are a small-diameter excitation electrode 4 and a large-diameter detection electrode 5;
Are formed so as to be coaxial double, and the excitation electrode 4 and the detection electrode 5 are connected to each other by a wire 6 formed by wire bonding or the like.
It is connected to printed circuit boards 9a and 9b provided with electronic components 7 such as a correction circuit. The printed circuit board 9
A and 9b are connected by a connecting pin 8, and an electric signal obtained from the electronic component 7 is taken out via an electric wire (not shown) which passes through the inside of the support 1a of the support plate 1.

[0006] This acceleration sensor is connected and used as shown in FIG. 6. When the piezoelectric elements 3 a and 3 b vibrate together with the vibrating plate 2, the potential generated at the detection electrode 5 is taken out and the acceleration applied from the outside is obtained. Can be detected. Such an acceleration sensor, for a constant acceleration,
As shown in FIG. 7, while a high Q can be obtained near the resonance point f ₀ , the frequency characteristic becomes flat in the middle and low frequency regions. Therefore, in general, a flat portion or f ₀ depends on the purpose of use. Use the nearby vibration output.

In this acceleration sensor, an AC voltage is externally applied to the piezoelectric elements 3a and 3b via an excitation electrode 4, and the diaphragm 2 is driven by the piezoelectric effect of the piezoelectric elements 3a and 3b.
Is vibrated, and the self-diagnosis of the quality of the sensor function or the presence or absence of a failure or the calibration of the detection level can be performed based on the potential of the detection electrode 5 generated by the vibration.

The arrows shown in the piezoelectric elements 3a and 3b shown in FIG. 6 indicate the polarization directions. The reason why the two piezoelectric elements 3a and 3b are connected in parallel as shown in the connection diagram of FIG. 6 is to cancel the pyroelectric charge due to a temperature change peculiar to the piezoelectric element.

In this prior art, the diaphragm 3 is supported by a column 1a standing upright at the center, but there are various types such as a type in which a disk-shaped peripheral portion is clamped and a type in which a rod-shaped diaphragm is fixed to a cantilever. There is a method. Some do not have a self-diagnosis function.
Needless to say, one sheet may be used instead of being divided into two as in 9b.

[0008]

However, since such a conventional acceleration sensor has a structure in which the piezoelectric elements 3a and 3b are bonded to the vibration plate 2, an adhesive layer is interposed therebetween. In addition, the excitation electrode 4 and the detection electrode 5 must be electrically connected to the printed circuit boards 9a and 9b by wire bonding or the like.
Since a plurality of piezoelectric elements are required, there is a problem that the structure is complicated, the production is troublesome, and the cost is increased.

Further, since the piezoelectric elements 3a and 3b are adhered to the vibrating plate 2 and integrated to form a vibrating body, the characteristics such as sensitivity may vary, and the temperature characteristics may easily deteriorate. there were.

Further, two piezoelectric elements 3a and 3b are connected in parallel to cancel the pyroelectric charge due to a temperature change peculiar to the piezoelectric element, but such a problem occurs because the piezoelectric element is used. It is. In addition, the piezoelectric element has poor response and poor conversion efficiency, and thus has a problem of low sensitivity level.

The present invention provides a high-performance acceleration sensor which has a relatively simple structure and can be manufactured at low cost.

[0012]

An electret capacitor type acceleration sensor according to the present invention has a metal fixed electrode and a divided conductor which is opposed to a facing surface of the metal fixed electrode via a gap and is divided into a pair or more. A vibrating body,
The metal fixed electrode or the split conductor is provided on one of the opposed surfaces of the metal fixed electrode or the split conductor, and forms at least one or more capacitors between the split conductor and the metal fixed electrode. An electret material for converting any one of the opposing surfaces into an electret, an insulator for holding the vibrating body so that the divided conductor can vibrate, and a boundary surface of the divided conductor or an outer periphery of each of the divided conductors A mass block body provided at an end and vibrating the divided conductor when acceleration is applied in a direction parallel to the plane of the vibrator, and an output difference between the capacitors caused by the vibration of the divided conductor is detected. And a detecting means for performing the detection.

In this case, when acceleration is applied in a direction parallel to the plane of the vibrating body, the divided conductor vibrates in the opposite direction due to a moment acting on the mass block body, and the divided conductor and metal The change in the capacitance of each capacitor formed between the fixed electrodes is extracted as an electric signal, and the output difference is detected, whereby the acceleration can be easily detected.

Since the acceleration sensor is composed of an electret capacitor as described above, the acceleration sensor can be manufactured with a relatively simple structure and at low cost. Further, since it is not necessary to use a piezoelectric element, it is possible to prevent deterioration of responsiveness and conversion efficiency due to pyroelectric charge, and also to prevent a decrease in sensitivity level. Thus, a high-performance acceleration sensor can be obtained.

In the electret condenser type acceleration sensor according to the present invention, the divided conductor is divided in plane symmetry and an acceleration detection axis is set in a symmetric direction of the divided conductor so that at least one or more detection axes are provided. The dividing conductor is divided so that
It is characterized in that an output difference of each of the capacitors caused by the vibration of the divided conductor divided in the same direction as the detection axis is detected.

In this case, by dividing and arranging the divided conductors in the same direction as the acceleration detection axis, the acceleration generated in one axis can be easily detected. Also, if the detection axes are set in a plurality of directions and the divided conductors are divided and arranged in the same direction as the respective detection axes, acceleration in multiple axes can be easily detected with respect to the same plane. Can be further improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is an explanation based on an embodiment of the present invention.

FIGS. 1 and 2 show a first embodiment of an electret condenser type acceleration sensor according to the present invention.

First, the configuration will be described. In FIG. 1, a metal fixed electrode 12 is provided on the bottom surface of a metal case that also serves as a ground shield. Note that this metal case 11
Although not shown, it is housed in the space defined by the support plate and the main body case as in the conventional example. Further, the fixed electrode 12 has a polymer film 12a as an electret material fixed to the upper surface by heat melting or the like, and the upper surface is electretized. In forming the electret, SiO2 may be used instead of the polymer film 12a.

A vibrating body 14 is opposed to the fixed electrode 12 via a disk-shaped spacer 13 having a thickness of several tens of μm. The vibrating body 14 and the fixed electrode 12 have a gap of several tens μm. Are separated by Further, the vibrating body 14 includes two divided conductors 14a and 14b formed by plating or vapor-depositing the surface of a plate-shaped member made of an insulating material. It is divided symmetrically.

Therefore, the fixed electrode 12 and the divided conductor 14
a and 14b are independently connected to capacitors C1 and C2, respectively.
And a so-called electret-type capacitor has 2
One will be formed.

The vibrating body 14 is held by the metal case 11 via a disk-shaped insulator 15 and the above-described fixed electrode 1
2, spacer 13, vibrator 14 and insulator 15 are metal case 1.
The upper end of 1 is fixed in the metal case 11 in a stacked state by fixing by caulking (indicated by reference numeral 11a).

The boundary surface 14c between the divided conductors 14a, 14b
Is in a state where the insulator is exposed, and the divided conductor 14
a and 14b are insulated.

A rectangular mass block 16 is fixed to the boundary surface between the divided conductors 14a and 14b by bonding or the like. The mass block 16 constitutes a weight and is parallel to the plane of the vibrating body 14. When an acceleration is applied in the axial direction (indicated by an arrow A), the divided conductors 14a and 14b vibrate in the opposite direction (indicated by an arrow B) by a moment.

The mass block 16 is not limited to a square shape but may be a cylinder.
It is not the boundary between 14a and 14b, but rather the divided conductors 14a and 14b.
b can be oscillated in the opposite direction.
As shown by a virtual line in (b), the outer peripheral ends of the divided conductors 14a and 14b may be used.

As shown in FIG. 2, the divided conductors 14a and 14b are connected to FETs (impedance converters) 17 and 18, respectively, and the capacitors C1 and C1 each formed by the fixed electrode 12 and the divided conductors 14a and 14b. The capacitance change of C2 is converted into a voltage by an electret, then impedance-converted by FETs 17 and 18, and output as an electric signal of opposite phase. The capacitors C1, C2
The change in the capacitance is converted into an impedance by the FETs 17 and 18 because the capacitances of the capacitors C1 and C2 are small.

The electric signals output from the FETs 17 and 18 are differentially output by a differential amplifier 19. In the present embodiment, the FETs 17 and 18 and the differential amplifier 19 constitute an application unit.

Next, the operation will be described.

When acceleration is applied in the direction of arrow A, the divided conductors 14a, 14a
b vibrates in the opposite direction (opposite phase) to the direction of arrow B.
At this time, since the distance between the divided conductors 14a and 14b with respect to the fixed electrode 12 changes, the capacitances of the capacitors C1 and C2 change by ± ΔC by the amount of the vibration change.

In the present embodiment, the change in the capacitance of the capacitors C1 and C2 is converted into a voltage of ΔV = Q / ΔC by the electretization and output, and the impedance is converted by the FETs 17 and 18 and output as an electric signal of the opposite phase. , By differential output by the differential amplifier 19,
An acceleration is detected.

As described above, in the present embodiment, the divided conductors 14
a, a pair of capacitors C between the metal fixed electrode 12 and 14b.
1, the divided conductors 14a, 14b are electretized so as to form C2, and when the acceleration A is applied in a direction parallel to the plane of the vibrating body 14, the divided conductors 14a, 14b are inverted by the moment of the mass block body 16. By vibrating in the direction B and detecting the acceleration based on the output difference between the capacitors C1 and C2 caused by the vibration, the acceleration sensor can be manufactured with a relatively simple structure and at low cost. Further, since it is not necessary to use a piezoelectric element, it is possible to prevent deterioration of responsiveness and conversion efficiency due to pyroelectric charges, and also to prevent a decrease in sensitivity level. Thus, a high-performance acceleration sensor can be obtained.

In this embodiment, the polymer film 12
Although a is provided on the fixed electrode 12 side to form the fixed electrode 12 as an electret, the invention is not limited to this, and the divided conductive bodies 14a and 14b may be provided as an electret by being provided on the divided conductive bodies 14a and 14b. In addition, the inner peripheral surface of the main body case that houses the metal case 11 is formed into an electret.
a and 14b may be opposed to each other.

In this embodiment, the divided conductors 14a,
Although 14b is divided plane-symmetrically, it does not have to be plane-symmetric.

FIGS. 3 and 4 show a second embodiment of the electret condenser type acceleration sensor according to the present invention, which is used for multi-axis applications. In the present embodiment, since only the configuration of the vibrating body and the configuration of the circuit are different from those of the first embodiment, the other configurations are the same as those of the first embodiment.
Only different points from the first embodiment will be described. Further, members (not shown) in this embodiment will be described with reference to FIG.

In FIG. 3, a vibrating body 21 is composed of a pair of conductive bodies 22.
a and 22b and a pair of conductors 23a and 23b. The divided conductors 22a and 22b are divided in plane symmetry, and an acceleration detection axis C is set in the symmetric direction. The divided conductors 23a and 23b are divided in plane symmetry and detect acceleration in the symmetric direction. Axis D is set.

Therefore, the fixed electrode 12 and the divided conductor 22
a and 22b are independently connected to capacitors C3 and C4.
And capacitors C5 and C6 are independently formed between the fixed electrode 12 and the divided conductors 23a and 23b. In this embodiment, four electret-type capacitors are formed.

The divided conductors 22a, 22b, 23a, 23b
A round mass block body 20 is fixed to the boundary surface by an adhesive or the like. This mass block body 20 constitutes a weight, and is in the detection axis C direction or the detection axis C direction which is an axial direction parallel to the surface of the vibrating body 21. When an acceleration is applied in the direction of the axis D, the paired divided conductors 22a and 22b or the divided conductors 23a and 23b vibrate in opposite directions by a moment.

The divided conductors 22a, 22b, 22c, 22d
Is in a state where the insulator is exposed, and the divided conductors 22a, 22b, 22c and 22d are insulated.

A divided conductor divided on the detection axis C
As shown in FIG. 4, 22a and 22b are connected to FETs 24 and 25, and the capacitance changes of the capacitors C3 and C4 formed by the fixed electrode 12 and the split conductors 22a and 22b are converted into voltages by the electret. The impedances are converted by the FETs 24 and 25 and output as electric signals of opposite phases. The electric signals output from the FETs 24 and 25 are differentially output by the differential amplifier 28.

The divided conductor divided on the detection axis D
23a and 23b are connected to FETs 26 and 27 as shown in FIG. 4, and the capacitance changes of the capacitors C5 and C6 formed by the fixed electrode 12 and the divided conductors 23a and 23b are converted into voltages by an electret. The impedances are converted by the FETs 26 and 27 and output as electric signals of opposite phases.

The electric signals output from the FETs 26 and 27 are differentially output by the differential amplifier 29. In the present embodiment, the FETs 24 to 27 and the differential amplifiers 28 and 29 constitute an application unit.

Next, the operation will be described.

First, when acceleration is applied in the direction of the detection axis C,
Conductive body divided by weight moment of mass block body 20
22a and 22b vibrate in opposite directions (opposite phases). At this time,
Since the distance between the divided conductions 22a and 22b with respect to the fixed electrode 12 changes, the capacitances of the capacitors C3 and C4 change by ± ΔC by the amount of the vibration change.

In this embodiment, the change in the capacitance of the capacitors C3 and C4 is converted into a voltage ΔV = Q / ΔC by the electretization and output, and the impedance is converted by the FETs 24 and 25 and output as an opposite-phase electric signal. Is output by the differential amplifier 28,
The acceleration in the direction of the detection axis C is detected.

On the other hand, when acceleration is applied in the detection axis D direction,
Conductive body divided by weight moment of mass block body 20
23a and 23b vibrate in opposite directions (opposite phases). At this time,
Since the distance between the divided conductions 23a and 23b with respect to the fixed electrode 12 changes, the capacitance of the capacitors C5 and C6 changes by ± ΔC by the amount of the vibration change.

In the present embodiment, the change in the capacitance of the capacitors C5 and C6 is converted into a voltage of ΔV = Q / ΔC by the electretization and output, and the impedance is converted by the FETs 26 and 27 and output as an opposite-phase electric signal. , By the differential output by the differential amplifier 29,
The acceleration in the direction of the detection axis D is detected.

As described above, in this embodiment, the detection axis is C,
D is set in two directions, and the divided conductors 22a, 22b and 23a, 23b are divided and arranged in the same direction as the respective detection axes C, D. In addition to the same effects as in the first embodiment, ,
Acceleration in multiple axes can be easily detected on the same plane, and acceleration detection accuracy can be further improved.

In this embodiment, the conductor is divided into four pieces. However, the conductor may be further divided so that more axial accelerations can be detected.

Further, in each of the above embodiments, the vibrating body 21 is circular, but may be square.

In each of the above embodiments, the acceleration sensor having no self-diagnosis function is described. However, when the self-diagnosis function is provided, a voltage is applied to one conductor of a pair of capacitors. Then, the conductor is driven, and the conductor constituting the other capacitor is vibrated by the vibration of the conductor, and self-diagnosis can be performed based on a change in the capacitance of the other capacitor due to the vibration of the conductor.

[0051]

As described above, according to the present invention, since the acceleration sensor is constituted by the electret capacitor, the acceleration sensor can be manufactured with a relatively simple structure and at low cost. In addition, since it is not necessary to use a piezoelectric element, it is possible to prevent deterioration of responsiveness and conversion efficiency due to pyroelectric charge, and
The sensitivity level can be prevented from lowering, and a high-performance acceleration sensor can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an electret capacitor type acceleration sensor according to the present invention, wherein (a) is a side sectional view and (b) is a top view of a vibrating body.

FIG. 2 is an equivalent circuit diagram of the sensor of the first embodiment.

FIGS. 3A and 3B are diagrams showing a second embodiment of an electret condenser type acceleration sensor according to the present invention, wherein FIG. 3A is a top view of the vibrating body and FIG. 3B is a side view of the vibrating body.

FIG. 4 is an equivalent circuit diagram of a sensor according to a second embodiment.

FIG. 5 is a view for explaining the prior art, and is a cross-sectional view showing a configuration thereof.

FIG. 6 is a partially enlarged cross-sectional view illustrating its use.

FIG. 7 is a graph showing the characteristics.

[Explanation of symbols]

 12 Metal fixed electrode 14, 21 Vibration body 14a, 14b, 22a, 22b, 23a, 23b Conductor 16, 20 Mass block body 17, 18, 24, 25, 26, 27 FET (detection means) 19, 20, 28, 29 Differential amplifier (detection means)

Claims (2)

[Claims] A vibrating body having a metal fixed electrode, a vibrating body facing a facing surface of the metal fixed electrode via a gap, and having a divided conductor divided into a pair or more, and opposing the metal fixed electrode or the divided conductor. Either one of the opposing surfaces of the metal fixed electrode or the split conductor is provided on one of the surfaces, and at least one pair of capacitors is formed between the split conductor and the metal fixed electrode. An electret material, an insulator that holds the vibrating body so that the divided conducting body can vibrate, and an insulator provided at a boundary surface of the divided conducting body or at an outer peripheral end of each of the divided conducting bodies. A mass block that vibrates the divided conductor when acceleration is applied in a direction parallel to a plane; and a detection that detects an output difference between the capacitors due to the vibration of the divided conductor. And an electret condenser type acceleration sensor. 2. The divided conducting body is divided into plane-symmetrical conductors and an acceleration detection axis is set in a symmetric direction of the divided conducting body, so that at least one detection axis is provided. 2. The electret condenser type acceleration sensor according to claim 1, wherein the detection unit detects an output difference of each of the capacitors due to vibration of the divided conductor divided in the same direction as the detection axis.