JPH05322914A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To adjust the initial value of a variable capacitor effectively and positively in a capacity-pickup type acceleration sensor. CONSTITUTION:An acceleration sensor is provided with a fixed rod member 1 having a, dielectric 2, which is embedded in the axial direction. In the fixed rod member 1, a movable member 3, which can be displaced in the axial direction in response to external acceleration, is mounted. A Pair of electrodes 4 and 5, which are arranged so as to face the dielectric 2 and constitute a variable capacitor, are formed in the movable member 3. A regulating means 6 is arranged so as to act on the movable member 3 elastically and regulates the initial position of the movable member 3. An adjusting member 7 is arranged so as to be separated from the movable member 3 with the regulating means 6 in-between. The adjusting member 7 is mounted on the fixed rod member 1 so that the position in the axial direction can be adjusted. The initial position of the movable member 3 is adjusted through the regulating means 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to a capacitor pickup type acceleration sensor for detecting a displacement amount of a movable member in response to an external acceleration as a change in capacitance.

[0002]

2. Description of the Related Art A conventional capacitor pickup type acceleration sensor which has been widely used has a differential capacitor system. FIG. 4 shows a conventional differential capacitor type acceleration sensor. This acceleration sensor is composed of a pair of fixed substrates 101 and 102 which are arranged to face each other. An upper fixed electrode 103 is formed on the inner surface of the fixed substrate 101, and a lower fixed electrode 104 is formed on the inner surface of the other fixed substrate 102. A movable electrode 105 is interposed between the pair of fixed electrodes 103 and 104. One variable capacitor 106 is formed between the upper fixed electrode 103 and the movable electrode 105, and the other variable capacitor 107 is formed between the lower fixed electrode 104 and the movable electrode 105.
Is formed. These pair of variable capacitors 106 and 107
Constitutes a differential capacitor. The movable electrode 105 is generally made of a conductive thin plate and is displaced between the pair of fixed electrodes 103 and 104 in response to external acceleration. Due to this displacement, a differential capacitance change occurs between the pair of capacitors 106 and 107, and external acceleration is detected.

FIG. 5 shows a conductive thin plate 10 constituting a movable electrode.
8 shows a general plane shape of No. 8. The thin plate 108 includes a fixed portion 109, a movable portion 110, and a beam portion 111 that connects them.
Consists of. The beam portion 111 is for bending the movable portion 110, and requires extremely delicate processing and precise dimension and shape in order to increase sensitivity to external acceleration and detection accuracy.

FIG. 6 shows an end face shape of the thin plate 108. For example, in order to detect a relatively small external acceleration of about several G, the beam portion 111 is required to have an extremely delicate elastic characteristic, and the movable portion 110 is bent due to its own weight.

[0005]

In the above-mentioned conventional example, since the movable portion of the conductive thin plate member is supported by the delicate beam portion, the neutral position of the movable electrode is affected by various external influences. There was a problem that it was not stable. Therefore, it is difficult to perform the initial setting for keeping the pair of variable capacitors in balance.
Even if an attempt was made to electrically correct the capacity imbalance, there were various effective factors, and there was no effective means. In particular, due to the influence of the ambient temperature, the movable electrode is liable to be thermally deformed, it is difficult to keep the balance of the capacitance over a wide temperature range, and the detection accuracy of the external acceleration is adversely affected.

[0006]

In view of the above-mentioned problems of the prior art, the present invention is an improved capacitive pickup type acceleration sensor having a structure capable of stable initial setting of capacitance and having excellent detection accuracy. The purpose is to provide. In order to achieve this object, the acceleration sensor according to the present invention uses a fixed rod member having a dielectric material embedded along the axial direction. A movable member is mounted on the fixed rod member so as to be axially displaceable in response to an external acceleration. The movable member is provided with a pair of electrodes that face the dielectric embedded in the fixed rod member and that constitute a variable capacitance. Furthermore, it is equipped with regulation means,
The movable member is arranged so that it can act elastically to regulate the initial position of the movable member. In addition, an adjusting member is arranged axially away from the movable member with the restricting means in between. The adjusting member is mounted on the fixed rod member so that the axial position with respect to the movable member can be adjusted, and adjusts the initial position of the movable member via the restricting means.

Preferably, the regulating means is a spring member having a predetermined length interposed between the adjusting member and the movable member. Alternatively, the restricting means may use an air damper located in the space between the adjusting member and the movable member.
More preferably, the regulating means is capable of adjusting its elastic force in order to control the amount of displacement of the movable member with respect to external acceleration.

[0008]

According to the above-mentioned structure, the movable member is displaced in response to the axial acceleration until it is balanced with the elastic action or elastic force of the regulating means. As a result, the pair of electrodes provided on the movable member relatively move with respect to the dielectric material interposed therebetween, and a capacitance change occurs. This change in capacitance is proportional to the amount of displacement of the movable member and represents the magnitude of external acceleration. In a state where no external acceleration is applied, that is, in an initial state, the movable member is held at the initial position by the restricting means. At this time, in order to set the initial value of the variable capacitance to a preset value, it is necessary to finely adjust the initial position or rest position of the movable member. Therefore, while the capacitance value is being monitored, the adjusting member is moved along the axial direction, and the rest position of the movable member is finely adjusted via the restricting means. When the adjustment is completed, the adjusting member is fixed to the fixed rod member. It is also possible to adjust the elastic force of the restriction means in order to control the displacement amount of the movable member, that is, the sensitivity to external acceleration.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an acceleration sensor according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view showing an embodiment of the present acceleration sensor. As shown in the figure, the acceleration sensor is assembled using the fixed rod member 1 made of an insulating material. A dielectric 2 is embedded inside the fixed rod member 1 along the axial direction thereof. The dielectric 2 is made of a material having a larger dielectric constant than the fixed rod member 1, for example, dielectric ceramics. A movable member 3 having a cylindrical shape is attached to the fixed rod member 1. The movable member 3 is engaged with the fixed rod member 1 so as to be freely movable without generating a substantial kinetic frictional force. For this reason, the outer peripheral surface of the fixed rod member 1 and the inner peripheral surface of the movable member 3 are lubricated. This lubrication treatment is performed by coating a lubricating coating or impregnating the contact surface with a lubricant. With this structure, the movable member 3 can be displaced in the axial direction, that is, the longitudinal direction of the fixed rod member 1 in response to an external acceleration. A pair of electrodes 4 and 5 are formed on the inner peripheral surface of the movable member 3 and are separated from each other in the diametrical direction. That is, the pair of electrodes 4 and 5 with respect to the dielectric 2.
The capacitance changes due to the relative displacement of.

The acceleration sensor further includes a regulating means 6 which is arranged so as to be elastically actable on the movable member 3 and regulates the initial position of the movable member. In this embodiment, the restricting means 6 is composed of a coil spring member having a predetermined length and elastic force. This spring member abuts the movable member 3 at one end and is fixed at the other end. Therefore, in the non-acceleration state, that is, in the initial state, the movable member 3 is regulated in its initial position in a state of hitting one end of the spring member 6. At this time, a predetermined initial capacitance or reference capacitance is given according to the relative positional relationship between the pair of electrodes 4 and 5 and the dielectric 2. However, this reference capacitance is generally deviated from a given target value unless adjustment is made.

The adjusting member 7 is arranged apart from the movable member 3 with the regulating means 6 in between. The adjusting member 7 fixes the other end of the spring member constituting the regulating means 6 and is attached to the fixed rod member 1 so that the axial position with respect to the movable member 3 can be adjusted. In this embodiment, the adjusting member 7 is a nut and is screwed to the bolt portion of the fixed rod member 1. By rotating the adjusting member 7, its axial position can be adjusted. For example, when the adjusting member 7 is moved to the left side in the drawing, the regulating means 6 is also moved to the left side accordingly. As a result, the initial position of the movable member 3 also moves to the left until it contacts one end of the regulating means 6. In this way, the adjusting member 7 can finely adjust the initial position of the movable member 3 via the regulating means 6.

In this embodiment, a coil spring member having a predetermined elastic force is used as the regulating means 6. The movable member 3 is displaced in response to an external acceleration until it balances with the elastic force. The amount of displacement of the movable member 3 can be controlled by adjusting this elastic force. That is, when the elastic force of the spring member is increased, the displacement amount of the movable member 3 is decreased and the detection sensitivity is decreased. On the contrary, when the elastic force is reduced, the displacement amount per unit external acceleration increases and the detection sensitivity increases.

Next, another embodiment of the acceleration sensor according to the present invention will be described in detail with reference to FIG. As illustrated, the fixed rod member 11 is attached along the central axis direction of the cylindrical case 18. The fixing rod member 11 is made of an insulating material having a relatively small dielectric constant, such as polycarbonate (containing 30% of glass) or glass.
Inside the fixed rod member 11, the dielectric 12 is provided along the axial direction.
Is buried. The dielectric 12 has a relatively large permittivity and is made of, for example, dielectric ceramics. As the dielectric ceramics, for example, those having a dielectric constant of several hundreds and a temperature change of several percent or less per degree are used. By using such a material, it is possible to obtain an acceleration sensor having high detection sensitivity and small temperature dependence. The diameter of the cylindrical case 18 can be reduced to about several mm. Around the fixed rod member 11, a ring-shaped movable member 13 is attached so as to be displaceable along the axial direction. This movable member 13 is also made of an insulating material molded product, for example, polycarbonate. In order to ensure responsiveness to external acceleration, the movable member 13 is supported via a bearing 19, and the inner peripheral surface of the movable member 13 and the fixed rod member 11 are supported.
It substantially eliminates kinetic friction with the outer peripheral surface. A pair of electrodes 14 and 15 divided in the diameter direction are formed on the inner peripheral surface of the movable member 13, and the dielectric 12 is wrapped from above and below to form a variable capacitance. Movable member 1
Along with the displacement of 3, the relative position of the dielectric 12 interposed between the pair of electrodes 14 and 15 fluctuates, causing a capacitance change.

A ring-shaped adjusting member 17 is arranged apart from the movable member 13 in the axial direction. This adjusting member 17
Are mounted so as to be movable along the fixed rod member 11. That is, it can be moved by loosening the screw 20 penetrating the side wall of the adjusting member 17, and can be fixed at a desired position by tightening it. A regulating means is interposed between the adjusting member 17 and the movable member 13. In the present embodiment, this restricting means comprises a ring-shaped air tube 16 and has a desired axial dimension. By adjusting the axial position of the adjusting member 17, the initial position of the movable member 13 is adjusted via the air tube 16. This adjustment is made so that a preset initial capacitance value is obtained. With the external acceleration applied, the air tube 16 elastically acts on the movable member 13, and the movable member 13 is displaced until the elastic force and the acceleration force are balanced. The displacement amount per unit acceleration is appropriately adjusted by changing the internal pressure of the air tube 16. That is, the air tube 16 acts as an air damper. Although the air tube 16 is used in the present embodiment, an air bag or an air damper may be formed by hermetically sealing the space between the adjusting member and the movable member instead.

FIG. 3 shows a cross section of the acceleration sensor shown in FIG. 2 taken along the line AA. As shown, the dielectric 12
Has a cylindrical shape and is embedded along the central axis of the fixed rod member 11, and can be obtained by molding or the like. A ring-shaped movable member 1 is provided around the fixed rod member 11.
3 is installed. A pair of electrodes 14 and 15 are formed on the inner peripheral surface of the movable member 13. As is apparent from the figure, the variable capacitance is composed of the pair of fixed electrodes 14 and 15 and the movable dielectric 12 interposed therebetween. The electrodes 14 and 15 are connected to external terminals in order to detect a capacitance change. The combination of the fixed rod member 11 and the movable member 13 is housed in a protective cylindrical case 18. The cylindrical case 18 is preferably made of a conductive material such as metal in order to shield the variable capacitance from external noise.

By the way, in the conventional differential capacitor type acceleration sensor shown in FIG. 4, since the movable electrode 105 which is sensitive to the change in ambient temperature is used, the output characteristic of the sensor has temperature dependency. As described above, the detection error occurs. In order to remove the detection error, it is necessary to correct it by using a circuit-like means. However, since the thermal deformation modes of the movable electrodes themselves are different from each other and a slight difference occurs in the assembling, the temperature dependence of each acceleration sensor varies, and there is no predictability or regularity. Therefore, in reality, there is currently no effective circuit correction means.

In view of this point, in the present invention, in addition to the above-mentioned means for adjusting the initial capacity, the temperature dependence is substantially eliminated or the temperature dependence having a regularity is forcibly imparted. Mechanical correction means can be incorporated into the acceleration sensor. The example will be described with reference to FIG. 2 again. In this example, the additional air tube 21 is used as the correction means. The air tube 21 is arranged on the opposite side of the movable member 13 from the air tube 16 described above. In this example, a pair of air tubes 16 and 21
In order to eliminate the play of the movable member 13 sandwiched between the two, it is appropriate that one end surface portion of the case 18 has a structure capable of movement adjustment along the axial direction. Effective temperature compensation is performed by providing a linear pressure-dependent pressure difference between the pair of air tubes.

Now, the internal pressure of one air tube 16 is PA, the volume is VA, the temperature is TA, the gas molecular weight is NA, and its tube length is LA, and the internal pressure of the other air tube 21 is PB and the volume is When VB, temperature is TB, gas molecular weight is NB, and its tube length is LB, the pressure difference between the two is given by the following equation. PA-PB = NA * R * TA / VA-NB * R * TB / VB However, R is a gas constant. Since the gas temperature is equal to the ambient temperature T, TA = TB = T, and if the same kind of gas is used, NA =
Since NB = N, the above equation can be modified as follows. PA-PB = NRT (1 / VA-1 / VB) Here, since the air tube volumes VA and VB are respectively proportional to the air tube lengths LA and LB, the above equation can be modified as follows. PA-PB = kT (1 / LA-1 / LB) where k is a proportional constant. As is clear from this formula,
The pressure difference PA-PB between the pair of air tubes is linearly proportional to the ambient temperature T. Therefore, when the proportionality constant k and the air tube lengths LA and LB are appropriately set, when there is linearity in the temperature dependency of the displacement of the movable member used in the acceleration sensor, temperature correction is performed so as to cancel it. Is possible. Alternatively, various fluctuation factors can be absorbed to give the acceleration sensor regular temperature dependence. In this case, correction using an external circuit can be performed very easily.

[0019]

As described above, according to the present invention, the movable member is mounted around the fixed rod member so as to be displaceable in the axial direction in response to the external acceleration, and the initial position of the movable member is set. By adopting a structure in which an adjusting member for adjusting the above is attached to the fixed rod member, the initial value of the variable capacitance composed of the pair of electrodes formed on the movable member and the dielectric embedded in the fixed rod member can be extremely reduced. The effect is that it can be easily adjusted. Further, there is an effect that the response sensitivity to external acceleration can be adjusted very easily by changing the elastic force of the regulating means interposed between the adjusting member and the movable member or the mass itself of the movable member. Furthermore, there is an effect that irregular output fluctuations due to ambient temperature changes can be eliminated and output changes can be corrected as compared with the related art.

[Brief description of drawings]

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

FIG. 2 is a schematic vertical sectional view showing another embodiment of the acceleration sensor according to the present invention.

FIG. 3 is a schematic cross-sectional view of the acceleration sensor shown in FIG. 2 taken along line AA.

FIG. 4 is a schematic diagram showing a conventional acceleration sensor.

FIG. 5 is a plan view of a movable electrode used in a conventional acceleration sensor.

FIG. 6 is a side view of a movable electrode used in a conventional acceleration sensor.

[Explanation of symbols]

 1 Fixed Rod Member 2 Dielectric 3 Movable Member 4 Electrode 5 Electrode 6 Restricting Means 7 Adjusting Member

Claims (5)

[Claims] 1. A fixed rod member having a dielectric material embedded along an axial direction, and a pair of electrodes arranged to face the dielectric material to constitute a variable capacitor and responding to an external acceleration. A movable member mounted on the fixed rod member so as to be displaceable in the axial direction, and a restricting means arranged to elastically act on the movable member and restricting an initial position of the movable member. , Which is arranged apart from the movable member with the regulating means in between and is attached to the fixed rod member so that the axial position can be adjusted, and the initial position of the movable member is adjusted via the regulating means. An acceleration sensor including an adjusting member for controlling the acceleration. 2. The acceleration sensor according to claim 1, wherein the restricting means comprises a spring member interposed between the adjusting member and the movable member. 3. The acceleration sensor according to claim 1, wherein the restricting means is an air damper located in a space between the adjusting member and the movable member. 4. The acceleration sensor according to claim 1, wherein the regulating means has an elastic force that can be adjusted to control the amount of displacement of the movable member with respect to external acceleration. 5. The acceleration sensor according to claim 1, further comprising correction means for correcting the temperature dependence of the variable capacitance.