JPH05333055A - Acceleration detector - Google Patents

Abstract

PURPOSE:To obtain an electrode taking-out structure capable of preventing a drift dependent on temperature and fatigue failure of an acceleration detector. CONSTITUTION:A sensor board 7 is mounted on a sensor base 10. It is provided with a lower side fixing board 1 having an electrode pattern conducted over both faces thereof and an upper side fixing board 2, which has the electrode pattern conducted over both the faces, opposed to and arranged over the lower fixing board 1 through a specified clearance. A conduction plate lies within another clearance between both the boards and there is a movable electrode part capable of displacement in accordance with acceleration between the inner face side electrode patterns of both the fixing board. The conduction plate is conducted in the electrode pattern of at least either of the fixing boards 1, 2. A flexible board 3 has a wiring pattern 4 pressure-welded to the outer side electrode patterns of both the fixing boards 1, 2 and a pair of the fixing boards 1, 2 are sandwiched from upward and downward in a bent condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential capacitance type acceleration detecting device having a laminated structure. More specifically, it relates to an electrode connection method in a laminated structure.

[0002]

2. Description of the Related Art An acceleration detecting device is a kind of dynamic sensor and is used for controlling a moving body, a machine tool, a transportation facility or the like. For example, a vehicle control system such as an active suspension, an anti-lock brake system, a traction control, etc. has been actively developed in recent years as a means for improving driving performance and safety of an automobile.
As a sensor required for such a control system, a high-performance acceleration detecting device is required to detect the posture and motion of the automobile. As a method of detecting the acceleration, there are generally a method of detecting a displacement of a mass that moves according to the acceleration and a method of detecting a stress or a strain generated in a support that supports the mass. When the mass is increased, the detection amount is also increased in proportion to increase the accuracy, but the response to acceleration is reduced and the impact resistance is deteriorated.

FIG. 8 shows an example of a conventional acceleration detecting device called a differential transformer system. Cylindrical coil bobbin 1
Reference numeral 01 is an excitation coil 102 and a pair of detection coils 103.
A and 103B are wound. Also, the coil bobbin 10
An iron ball 104 is inserted into the hollow portion 1 so as to be movable along the axial direction. An alternating current is applied to the exciting coil 102, and an alternating magnetic field passing through the center of the coil bobbin 101 is generated. Therefore, an electromagnetic induction current is generated in the pair of detection coils 103A and 103B wound around the same coil bobbin. At this time, when the acceleration is not applied, the iron ball 104 is located in the central portion, and since the pair of detection coils are placed under the same condition with respect to the alternating magnetic field, there is no output difference in the electromagnetic induction current. .. When acceleration is generated in the axial direction of the coil bobbin 101, the iron ball 104 is displaced against the coercive force given by the magnet and is biased to one side of the pair of detection coils. For this reason, the inductance for each detection coil changes relatively, and a difference occurs in the electromagnetic induction current. The acceleration can be detected based on this current difference. However, in this differential transformer method, since the iron ball having a large mass is held through the magnet, its displacement amount depends on the frequency of acceleration, and there is a resonance point with a high Q value, which may cause resonance breakdown. There is Further, the coil bobbin 101 may be displaced in a direction orthogonal to the axis. If a guide is provided to regulate this, friction may occur and the detection output may have hysteresis.

FIG. 9 shows a cantilever type acceleration detecting device constructed by using a silicon semiconductor substrate. The circuit portion 131 is integrally formed on the fixed end of the silicon semiconductor substrate, and the beam portion 133 is formed between the weight portion 132 and the fixed end by etching or the like. A piezoresistive element is provided in the beam portion, and the stress generated in the beam portion is detected as a change in the resistance value of the piezoresistance to obtain an acceleration output. Although this method can be miniaturized, it is difficult to form the beam 133 symmetrically with respect to the moving direction of the weight 132, and the linearity of the output is poor and the output is affected by a temperature change. There is a drawback that occurs. In addition, the configuration of the circuit unit 131 is complicated to compensate for the drift.

FIG. 10 shows a differential capacitance type acceleration detecting device. This method is disclosed, for example, in U.S. Pat. No. 4,694,687.
No. The differential capacitance method is the most stable in principle, and is particularly suitable for detecting a low frequency of about 1 G or acceleration in a DC region. The differential capacitance system has a structure in which a movable electrode is interposed between a pair of fixed electrode patterns, and forms a pair of parallel plate capacitors. When the movable electrode is displaced according to the acceleration, a capacitance difference appears between the pair of capacitors, which is detected as a change in impedance.
As shown in the drawing, one fixed electrode pattern 152 is formed on the inner surface of the lower substrate 151. This board 151
A diaphragm 154 is superposed on the above with a spacer 153 interposed therebetween. A movable electrode 155 which is elastically supported is formed in the center of the diaphragm 154 and faces the fixed electrode 152 described above. This diaphragm 15
An upper fixed substrate 157 is further stacked on the substrate 4 via a spacer 156. A fixed electrode facing the movable electrode 155 is also formed on the inner surface of the substrate 157. A through hole pattern 158 for connecting electrodes is formed on the outer surface thereof. Electrical terminal connections to the pair of fixed and movable electrodes are pins 159, 160, 1
Via 61. These pins penetrate the stacked substrates and make contact to the corresponding electrodes. These pins are fixed to the through hole pattern 158 by, for example, soldering.

[0006]

The differential capacitance method described above has the advantage that the detection output is linear in principle with respect to acceleration. Further, the dielectric medium forming the capacitor is a gas such as air and has almost no temperature dependence.
Furthermore, since the electrode interval can be set finely and precisely through the spacer, the capacitance of the capacitor can be made large and the detection accuracy is high. Further, the resonance Q value is lowered due to the damper effect of air or the like, and the frequency response is good.

While having such advantages, the differential capacitance type acceleration detecting device has a laminated structure in which a plurality of plate materials are stacked. In this case, it is necessary to consider the fixing method of the laminated structure, the countermeasure against external impact, the insulating method between the substrates, the electrode connection extraction, and the like. There is a risk that drift due to temperature will occur due to structural reasons. For example,
As shown in FIG. 10, when the electrodes are taken out using the pins 159 to 161, thermal stress is generated between the pins and the substrate due to the difference in the coefficient of thermal expansion, etc., and the fixed electrodes are distorted, resulting in a slight error in the gap between the electrodes. The resulting temperature-dependent drift occurs. Further, due to the difference in the coefficient of thermal expansion of each component, stress may be generated in the connection portion such as soldering, which may cause fatigue fracture.

[0008]

In view of the above-mentioned problems of the prior art, the present invention improves the electrode lead-out structure in a differential capacitance type acceleration detecting device to suppress temperature-dependent drift and prevent fatigue damage. To aim for things. At the same time, it is an object of the present invention to improve the assemblability of the acceleration detecting device having the laminated structure. The following measures have been taken in order to achieve this object. That is, the acceleration detecting device according to the present invention has one fixed substrate having electrode patterns which are conducted over both surfaces and one fixed substrate which has electrode patterns which are similarly conducted over both sides. At least one fixed substrate and a fixed substrate opposite to each other with a predetermined gap interposed therebetween, and a movable electrode portion interposed in the gap and capable of being displaced between inner electrode patterns of both fixed substrates according to acceleration. A conductive plate that is electrically connected to the electrode patterns, and a connection flexible substrate that has a wiring pattern that presses against the outer electrode patterns of both fixed substrates and that sandwiches a pair of fixed substrates from above and below in a bent state. It is configured.

Preferably, the conductive plate has a central portion fixed in the gap, and has a structure for elastically supporting the movable electrode portion arranged around the central portion. Further, the one substrate has a central electrode pattern on the inner surface side thereof, which is electrically connected to the central portion of the conductive plate, and a peripheral electrode pattern which faces the movable electrode portion of the conductive plate. Further, the central portion of the conductive plate is electrically connected to the central electrode pattern of the one substrate through a conductive spacer.

[0010]

According to the present invention, through the flexible substrate,
Electrical connection and extraction for the fixed electrode pattern and the movable electrode portion that constitute the capacitor are performed. Since the flexible substrate has excellent flexibility or elasticity and can absorb stress caused by temperature change, temperature-dependent drift can be suppressed without giving strain to the laminated structure of the acceleration detection device. Further, unlike soldering or the like, the flexible substrate is electrically connected to the electrode pattern by pressure contact, so there is no fear of fatigue damage or the like. Further, since a pair of fixed substrates are sandwiched between the flexible substrates from above and below to make electrical connection, the assembling property can be remarkably improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic perspective view showing an embodiment of an acceleration detecting device according to the present invention. This acceleration detecting device includes one fixed substrate or the lower fixed substrate 1. The fixed substrate 1 has electrode patterns formed on both sides thereof so as to be electrically connected by through holes or the like. The other fixed substrate or the upper fixed substrate 2 is arranged to face the lower fixed substrate 1 with a predetermined gap therebetween. Similarly, the upper fixed substrate 2 also has electrode patterns formed on both sides thereof so as to be electrically connected by through holes or the like. A conductive plate is interposed in the gap between the pair of fixed substrates 1 and 2. This conductive plate has a movable electrode portion that can be displaced between the inner side electrode patterns of both fixed substrates 1 and 2 according to acceleration. The conductive plate is adapted to be electrically connected to at least one fixed substrate, for example, the electrode pattern of the lower fixed substrate 1. The pair of fixed substrates 1 and 2 are sandwiched from above and below by a flexible substrate 3 for connection.
The flexible substrate 3 has a wiring pattern 4 and is pressed against the outer surface side electrode patterns of both the fixed substrates 1 and 2. That is, the flexible substrate 3 is attached in a bent state by the nut 6 via the washer 5, and constitutes the sensor block 7 as a whole. The sensor block 7 is fixedly supported by a main shaft 8 which penetrates the center thereof.
Further, the sensor block 7 is mounted on the sensor base 10 via the damper member 9. Sensor base 10
Four terminals 11 are planted on the upper part of the upper part, and the electrode pattern of the fixed substrate and the movable electrode portion of the conductive plate are electrically taken out to the corresponding terminals 11 via the flexible substrate 3.

FIG. 2 is an exploded perspective view of the sensor block 7 shown in FIG. The main shaft 8 described above is planted in the center of the damper member 9 via a pedestal 11. A cut portion 12 is provided on the side surface of the main shaft 8 and a bolt portion 13 is formed on the top portion.

The flexible substrate 3 is composed of a pair of disk portions 14 and 15 and a tongue portion 16 which are connected to each other. One disc portion 14 is inserted into the main shaft 8 through an opening provided in the central portion and placed on the pedestal 11. In this state, the bush 17 is attached to the main shaft 8. Bush 17 is almost D
It has an irregular shape and is positioned in alignment with the cut portion 12 of the main shaft 8.

The lower fixed substrate 1 with respect to the bush 17
Is installed. As shown in the figure, a central electrode pattern 18 and a peripheral electrode pattern 19 which are electrically separated from each other are formed on the inner surface of the lower fixed substrate 1. A guard electrode pattern 20 is formed between the two electrode patterns. These inner surface side electrode patterns are guided to the outer surface side electrode patterns through the through holes. Further, the lower spacer 21
The conductive plate 22 is overlaid via. The conductive plate 22 is composed of a central portion 23 and a movable electrode portion 24 located around the central portion 23. The movable electrode portion 24 is elastically supported by the central portion 23. That is, the movable electrode portion 24 can be displaced in the axial direction of the main shaft 8 in response to external acceleration. The central portion 23 of the conductive plate 22 has a central electrode pattern 18 formed on the inner surface of the lower fixed substrate 1 via a conductive spacer 21.
Electrically connected to. Further, the upper fixed substrate 2 is overlaid via another spacer 25. Divided electrode patterns are formed on the outer surface side of the upper fixed substrate 2, and are electrically connected to the electrode patterns formed on the inner surface side through through holes. The other disk portion 15 of the flexible substrate 3 is brought into contact with the outer electrode pattern in a bent state. The components thus stacked are fixed by pressure contact with each other by the above-mentioned nut 6 via washers 26 and 27. The nut 6 engages with a bolt portion 13 protruding from the top of the main shaft 8.

Next, the main components of the acceleration detecting device according to the present invention will be described in detail with reference to FIGS. FIG. 3 shows a planar shape of the conductive plate 22. As shown in the figure, the conductive plate 22 has a disk shape, and has a central portion 23 and a peripheral movable electrode portion 24 which is flexibly extended from the central portion 23 and is displaceable in the direction perpendicular to the main surface. The movable electrode portion 24 has a ring shape and is connected to the outer peripheral end of the central portion 23 along the inner peripheral end thereof by, for example, three leaf springs 28. In addition, an opening 29 is formed in the central portion 23 to allow the bush 17 shown in FIG. 2 to pass therethrough. Conductive plate 22 having such a shape
Can be obtained by patterning an elastic metal member such as stainless steel by etching. When problems such as rust and corrosion do not occur, it is possible to use materials having better workability such as Cu and Be-Cu.

FIG. 4 shows the planar shape of the lower fixed substrate 1, in which the portion A represents the inner electrode pattern and the portion B represents the outer electrode pattern. The fixed substrate 1 is made of, for example, an electrically insulating material such as ceramic, and a ring-shaped peripheral electrode pattern 19 is formed on the inner surface thereof. The electrode pattern 19 can be composed of, for example, a conductive thick film electrode applied by using a printing technique. As is clear from a comparison between FIG. 3 and FIG. 4, the peripheral electrode pattern 19 and the movable electrode portion 24 have substantially the same shape, and when they are arranged opposite to each other, a capacitive element using a gas such as air as a dielectric substance Constitute. An opening 30 for allowing the bush 17 shown in FIG. 2 to penetrate is formed in the central portion of the fixed substrate 1. A central electrode pattern 18 is formed so as to surround the opening 30. The electrode pattern 18 is for electrical connection with a conductive plate 22 made of a conductive metal material, and is electrically connected to each other by the spacer 21 described above in this example. Further, the guard electrode pattern 20 is interposed between the central electrode pattern 18 and the peripheral electrode pattern 19 as described above.
The guard electrode pattern 20 is designed to be grounded to prevent an unnecessary capacitance component from being formed between the central electrode pattern 18 and the peripheral electrode pattern 19 on the fixed substrate 1.

As shown in part B of FIG. 4, an electrode pattern divided into four is formed on the outer surface of the fixed substrate 1 so as to surround the opening 30. It includes a segment pattern 18S that conducts to the center electrode pattern 18, another segment pattern 19S that conducts to the peripheral electrode pattern 19, and a further segment pattern 20S that conducts to the guard electrode pattern 20. The remaining segment patterns are dummy. Each of these segment patterns is connected to the corresponding electrode pattern on the inner surface side through a through hole h. Although not shown, the upper fixed substrate 2 also has a similar electrode pattern structure.

FIG. 5 is a plan view showing the wiring pattern shape of the flexible substrate 3. This flexible substrate can be processed, for example, by forming a predetermined wiring pattern on the surface of a polyimide film by etching and then punching it using a die. As described above, the flexible substrate 3 has the pair of disk portions 14 and 15 and the tongue portion 16 which are connected to each other.
One disk portion 14 has a plurality of pad patterns 18P and 19P so as to match with the segment patterns shown in the portion B of FIG.
P, 20P are formed. That is, the pad pattern 18
P contacts the corresponding segment pattern 18S and is guided to the land electrode for the output terminal OUT provided on the tongue portion 16. The other pad pattern 19P abuts on the corresponding segment pattern 19S and is guided to the land pattern for one input terminal IN1. Still another pad pattern 20P abuts on the corresponding segment pattern 20S and is guided to the land pattern for the ground terminal GND.

Similarly, the other disc portion 15 is pressed against the outer surface side of the upper fixed substrate 2 in a state of being bent with respect to the one disc portion 14. For example, the pad pattern 31P formed on the disk portion 15 is electrically connected to the peripheral electrode pattern formed on the upper fixed substrate 2, and is also guided to the land pattern for the other input terminal IN2. Similarly, the guard electrode pattern formed on the upper fixed substrate 2 is also grounded via the pad pattern 32P.

FIG. 6 is an equivalent circuit diagram of the sensor block 7 shown in FIG. The movable electrode portion 22 is connected to the output terminal OUT via the flexible substrate as described above. The lower peripheral electrode pattern 19 forms one capacitance C1 and is connected to the input terminal IN1 via the flexible substrate. Further, the upper peripheral electrode pattern 31 forms the other capacitance C2 and is connected to the other input terminal IN2 via the flexible substrate. In addition, both the upper and lower guard electrode patterns 20 are connected to the ground terminal GND via the flexible substrate. These 4
The drive circuit 33 is connected to the terminals of the book. The drive circuit 33 applies an AC voltage having an amplitude V0 between a pair of input terminals, and an output signal having an amplitude VS corresponding to the acceleration is obtained at the output terminal.

Now, the area of the electrode pattern is S, the gap between the electrodes when there is no acceleration is d0, the acceleration is α, and the movable electrode portion 2
When the spring constant of 2 is K and the mass of the movable electrode portion is M, the electrode intervals are d1 = d0 + KαM and d2 = d0-K.
given in αM. On the other hand, the capacitance value is C1 = εS / d1, C
2 = εS / d2 Note that ε is the dielectric constant of the gas sandwiched between the electrode gaps. A pair of input terminals IN1,
When an AC voltage V0 having an angular frequency ω is applied between IN2,
The potential of the movable electrode portion 22, that is, the amplitude VS of the signal appearing at the output terminal OUT is determined by the impedance Z = 1 / of the capacitor.
It is given as follows using the relational expression of jωC. VS = Z2V0 / (Z1 + Z2) = d2V0 / (d1 + d2) = (d0-KαM) V0 / 2d0 = V0 / 2-γα (γ = KMV0 / 2d0 constant) As is apparent from the above equation, the output voltage VS is the acceleration α Has a linear relationship with. In the present invention, the electrical connection from each electrode of the sensor block to the terminal is made by pressure welding using a flexible substrate or the like. Contact resistance can be suppressed to an extremely low level by making surface contact and applying a sufficient pressure contact force. The frequency of the input alternating voltage is 15kHz
If the values of the capacitors C1 and C2 are 20 pF, the impedance due to these capacitors is 530 kΩ. On the other hand, since the contact resistance is at most about several Ω, there is no problem at all.

Finally, FIG. 7 is a schematic sectional view showing an acceleration detecting device in which a sensor block and a driving circuit are integrally incorporated. The sensor base 10 on which the sensor block 7 is mounted is caulked and fixed to the post 35 of the casing 34. The sensor block 7 is hermetically sealed by a cap 36, and the inside thereof is filled with an inert gas. As mentioned above, the sensor base 10 has four terminals 1
1 penetrates. The upper end of each terminal is electrically connected to the tongue portion 16 of the flexible substrate 3. Further, the lower end portion of the terminal 11 penetrates the circuit board 37 and is electrically connected through the connector 38. The circuit board 37 has the drive circuit 33 shown in FIG. 6 mounted thereon. Circuit board 37
Is covered with an electromagnetic shield 39 and is protected by a cover 40 engaging with the casing 34. Finally, the connector pin 41 is connected to the circuit board 37 penetrating the sensor base 10 to supply power to the drive circuit or take out an output signal.

In the above embodiment, the conductive plate is fixed between the pair of fixed substrates via the spacer.
However, the present invention is not limited to this, and the center portion of the conductive plate may be made thicker than the peripheral movable electrode portion and directly fixed and supported. Further, in the above-described embodiment, the conductive plate is electrically connected to one fixed substrate, but the present invention is not limited to this. A structure may be used in which electrical connection is made to both the upper and lower fixed substrates. Further, in the above-mentioned embodiment, the conductive plate has the central portion fixed and the peripheral portion movable, but the present invention is not limited to this. The structure may be such that the peripheral portion is fixed and the central portion is the movable electrode.

[0024]

As described above, according to the present invention, since the electrode is taken out by using the flexible substrate, the stress due to the difference of the thermal expansion coefficient can be absorbed and the output signal of the temperature dependence. There is an effect that the drift can be reduced or eliminated. Further, the flexible substrate has excellent flexibility, and even if it repeatedly contracts due to a temperature change, fatigue failure is unlikely to occur, and the reliability of the acceleration detection device can be improved. further,
Since the flexible board is assembled by pressure contact in a bent state, there is an effect that the assembling property is remarkably improved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a sensor block portion of an acceleration detection device according to the present invention.

FIG. 2 is an exploded perspective view of a sensor block.

FIG. 3 is a plan view of a conductive plate.

FIG. 4 is a schematic view showing an electrode pattern of a fixed substrate.

FIG. 5 is a schematic plan view showing a wiring pattern shape of a flexible substrate.

FIG. 6 is an equivalent circuit diagram of the acceleration detecting device according to the present invention.

FIG. 7 is a schematic cross-sectional view showing an example of an acceleration detection device in which a sensor block and a drive circuit are integrally incorporated.

FIG. 8 is a schematic diagram showing an example of a conventional acceleration detection device.

FIG. 9 is a schematic perspective view showing another example of a conventional acceleration detection device.

FIG. 10 is a schematic exploded perspective view showing still another example of the conventional acceleration detection device.

[Explanation of symbols]

 1 Lower Fixed Board 2 Upper Fixed Board 3 Flexible Board 4 Wiring Pattern 7 Sensor Block 10 Sensor Base 11 Terminal 18 Central Electrode Pattern 19 Peripheral Electrode Pattern 21 Spacer 22 Conductive Plate 23 Center Part 24 Peripheral Movable Electrode Part 25 Spacer

Claims (4)

[Claims] 1. A fixed substrate having conductive patterns on both sides thereof, and an electrode pattern having conductive patterns on both sides thereof, and having a predetermined gap between the fixed substrates. And the other fixed substrate disposed opposite to each other, and a movable electrode portion that is interposed in the gap and that can be displaced between the inner surface side electrode patterns of both fixed substrates according to acceleration, and at least one fixed substrate electrode pattern. An acceleration detecting device comprising: a conductive plate having electrical continuity; and a connecting flexible substrate which has a wiring pattern in pressure contact with the outer surface side electrode patterns of both fixed substrates and which sandwiches a pair of fixed substrates from above and below in a bent state. 2. The acceleration detecting device according to claim 1, wherein the conductive plate has a central portion fixed to the gap and elastically supports the movable electrode portion arranged around the central portion. 3. The substrate according to claim 2, wherein the one substrate has a central electrode pattern on its inner surface side that is electrically connected to a central portion of the conductive plate and a peripheral electrode pattern that faces a movable electrode portion of the conductive plate. Acceleration detection device. 4. The acceleration detecting device according to claim 3, wherein a central portion of the conductive plate is electrically connected to a central electrode pattern of the one substrate through a conductive spacer.