JPH0432777A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To stably adjust the balance of neutral-point capacity by composing at least one fixed electrode of a conductive pattern which is formed on a fixed substrate and adjustable in electrode area. CONSTITUTION:A couple of fixed substrates 1 and 2 are arranged opposite each other across a specific gap, one fixed electrode is formed on the internal surface of the upper substrate 1, and the other fixed electrode is formed on the internal surface of the lower substrate 2. A conductive plate member 3 is interposed between the couple of fixed electrodes and has a center part and a peripheral part which is coupled flexibly with the center part to constitute a movable electrode. Each fixed electrode is formed at the peripheral part of the internal surface of each fixed substrate opposite the movable electrode. Then at least one fixed electrode is composed of the conductive pattern which is formed on the fixed substrate and adjustable in electrode area so that a couple of neutral point capacity values are balanced with each other. This adjustment is made by what is called a trimming system, so the neutral point capacity values can be balanced after adjusting operation is repeated plural times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitive acceleration sensor for accurately detecting low accelerations of several G or less in a frequency band of several tens of Hz or less. This type of acceleration sensor is mounted on, for example, an automobile and used for automatic control of a drive mechanism or a braking mechanism.

[Conventional technology]

A capacitance detection type acceleration sensor generally includes a pair of fixed electrodes that are arranged opposite to each other with a predetermined gap therebetween, and a movable electrode that is neutral between the pair of fixed electrodes and is arranged opposite to each fixed electrode. A guise consisting of. This movable electrode forms a pair of neutral point capacitances on its front and back surfaces, each corresponding to the electrode area of the corresponding fixed electrode, and is displaced from the neutral point toward the fixed electrode in response to external acceleration. In response to this displacement, the balance between the pair of neutral point capacitances is disrupted and external acceleration is detected.

Acceleration sensors having such a configuration generally have a laminated structure. FIG. 6 shows a conventional laminated structure. An upper fixed substrate 44 is placed at the top of the laminated structure, and a lower fixed substrate 52 is placed at the bottom. As shown in the figure, an electrical pattern 52 for interlayer connection is formed around the surface of the lower fixed substrate 52, and a lower fixed electrode 58 separated by a separator 56 is formed in the center thereof. There is. Although not shown, an upper fixed electrode is similarly formed at the center of the upper fixed substrate 44. A conductive plate member 48 is arranged in the middle of the laminated structure. This conductive plate member 48 is connected to a peripheral portion 6B forming a supporting fixed portion and a movable mold 1.
464.

The central movable electrode 64 is flexibly supported by the peripheral portion 66 via three leaf spring pieces 63. Therefore, the movable electrode 64 can be displaced in the thickness direction of the laminated structure in response to external acceleration. The peripheral portion 66 is sandwiched from above and below by a pair of spacers 46 and 50, and is supported and fixed between a pair of fixed substrates 44 and 52.

An opening for forming a displacement space for the movable electrode 64 is provided in the center of each spacer.

[Problem that the invention seeks to solve]

In the conventional example shown in FIG. 6, the upper fixed electrode and the movable electrode 6
4 forms a first variable capacitor.

The neutral point capacitance when the movable electrode 64 is at the neutral point is the area of the side fixed electrode, dl is the distance between the movable electrode 64 at the neutral point and the upper fixed electrode, and ε is the dielectric constant of the medium air. On the other hand, the lower fixed electrode 58 and the movable electrode 64 form a second variable capacitor. Its neutral point capacitance is expressed as C2-ε. However, S2 is the area of the lower fixed electrode 58 and d
2 is the distance between the movable electrode 64 and the lower fixed electrode 58 at the neutral point.

Generally, the distances d1 and d2 between the electrodes are set to several tens of μm, but since there are variations in the accuracy of the spacer thickness and the flatness of the movable and fixed electrodes, the neutral point volume 1
Thc1 and C2 actually fluctuate from their set values within a range of several percent to ten-odd percent, respectively.

Therefore, if no adjustment means are taken, it is extremely difficult to maintain a balance between the pair of neutral point capacitances in each acceleration sensor. Therefore, conventionally, electric circuit processing has been performed in order to eliminate the above-mentioned fluctuations and maintain the balance of the neutral point capacitance. That is, adjustments were made by applying an electrical offset to cancel out the difference in neutral point capacitance. However, with electrical adjustment, it is difficult to eliminate the unbalance of the neutral point capacitance over the entire operating temperature range, and errors due to fluctuations in the dielectric constant ε due to temperature changes, temperature drift of the electric circuit, etc. There was a problem in that it was extremely difficult to make adjustments including this. Another problem is that it is difficult to maintain the linearity of the acceleration detection characteristics over the entire output range by adjusting the electrical circuit.

[Means for solving problems]

In view of the above-mentioned conventional problems, an object of the present invention is to provide a capacitance detection type acceleration sensor having a structure capable of stably adjusting the balance of the neutral point capacitance.

In order to achieve this object, the acceleration sensor according to the present invention has two basic components: a pair of fixed electrodes facing each other with a predetermined gap therebetween; and a sensor disposed neutrally between the pair of fixed electrodes. It consists of a movable electrode. This movable electrode forms a pair of neutral point capacitances corresponding to the area of each electrode in opposition to each fixed electrode, and functions to be displaced from the neutral point in response to external acceleration. As a characteristic feature of the present invention, at least one of the fixed electrodes is composed of a conductive pattern formed on a fixed substrate and capable of adjusting the electrode area. It is possible to adjust and set the point capacitances so that they are balanced with each other.

Preferably, the conductive pattern is composed of a main pattern portion having a constant electrode area and a divided pattern portion that can be selectively cut at the main pattern portion.

More preferably, a conductive plate member interposed between the pair of fixed electrodes is provided. This conductive plate member has a central portion that is fixedly supported between a pair of fixed electrodes, and a peripheral portion that is flexibly connected to the central portion and constitutes a movable electrode. In addition, each fixed electrode is formed on the periphery of the corresponding fixed substrate, facing the movable electrode.

[For production]

According to the present invention, at least one fixed electrode is composed of a conductive pattern formed on a fixed substrate and whose electrode area can be adjusted. The electrode area can be adjusted to balance the pair of neutral point capacitances with each other. That is, after assembling the acceleration sensor, one of the neutral point capacitances having a fixed value is first measured in a state where no external acceleration is applied.

Next, measure the other neutral point capacitances. The electrode area of the conductive pattern is adjusted based on the difference in the measured values.

Since this adjustment is performed by a so-called trimming method, the neutral point capacitance can be balanced after repeating the adjustment several times. For example, the conductive pattern is composed of a main pattern portion having a fixed electrode area, a plurality of subdivided pattern portions that can be selectively cut from the main pattern portion, and a pair of neutral pattern portions. It is sufficient to cut each division pattern according to the difference in point capacitance. Incidentally, the capacitance decreases in proportion to the decrease in electrode area. Therefore, the total electrode area of the conductive pattern is set in advance to be larger than the area of other opposing fixed electrodes, and the neutral point capacitance formed by the other opposing fixed electrodes is always set before adjustment. By making the size larger, reliable adjustment work can be performed.

According to an embodiment of the present invention, a conductive plate member interposed between a pair of fixed electrodes is provided. A central portion of the conductive plate member is supported and fixed by a pair of fixed substrates,
The peripheral portion is flexibly connected to the central portion to constitute a movable electrode.

That is, since the free end of the movable electrode is supported by the central portion, it is hardly affected by distortions in the central portion caused by thermal expansion or the like. Therefore, since only thermal warping occurs in the movable electrode, fluctuations in the neutral point are small.

Therefore, the adjustment work is also made more efficient. On the other hand, the sixth
In the conventional structure shown in the figure, the movable electrode is constituted by the central part of the conductive plate member and is flexibly supported by the peripheral part, so it is easily affected by distortion occurring in the peripheral part. Stress deformation occurs and the neutral point fluctuates greatly. Therefore, the adjustment work itself must be extensive.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partially cutaway sectional view showing the structure of a capacitance detection type acceleration sensor according to the present invention. As shown in the figure, this acceleration sensor has a pair of fixed substrates 1 and 2 that are placed opposite to each other with a predetermined gap in between. One fixed electrode is formed on the inner surface of the upper fixed substrate 1, and a fixed electrode is similarly formed on the inner surface of the lower fixed substrate 2. A conductive plate member 3 is interposed between the pair of fixed electrodes. The conductive plate member 3 has a central portion that is supported and fixed between a pair of fixed substrates 1 and 2, and a peripheral portion that is flexibly connected to the central portion and forms a movable electrode. . Further, each of the fixed electrodes described above is formed at the periphery of the inner surface of each fixed substrate, facing the movable electrode. With this structure, the movable electrode is neutral between the pair of fixed electrodes, and forms a pair of neutral point capacitors corresponding to the area of each electrode, facing each fixed electrode. Further, in response to external acceleration, it is displaced from the neutral point and external acceleration is detected based on a change in capacitance.

In this embodiment, the center portion of the conductive plate member 3 is sandwiched between a pair of conductive spacers 4 and 5 from above and below. Since these spacers are conductive, they have the function of connecting the movable electrode to the fixed substrate side and taking out the electrode.

The above-described upper fixed substrate 1, spacer 4, and conductive plate member 3
, a laminated structure consisting of the spacer 5 and the lower fixed substrate 2 is mounted on the circuit board 7 via the connection substrate 6. These laminated structures are housed inside the case 8 while being mounted on the circuit board 7 and are almost completely covered by the cover 9. The case 8 and cover 9 are made of conductive material and are externally grounded to form a shield. A terminal 10 for external connection is mounted on the end of the circuit board 7 protruding from the case 8. The terminal IO is connected to the fixed electrode and the movable electrode by interlayer surface contact via metal patterns and through holes formed on the front and back surfaces of each substrate.

The above-mentioned laminated structure has a coupling screw II passing through its center.
are connected to each other and fixed together with the circuit board 7 to the case 8. A leaf spring 12 and a spring 13 are interposed between the lower surface of the top of the coupling screw 11 and the upper surface of the upper fixed substrate 1, and press each layer to each other.

Further, a plurality of parallel pins 14 are inserted between the upper fixed board 1 and the lower fixed board 2 to maintain the parallelism of both boards 1 and 2.

Next, the main components used in this acceleration sensor will be explained in detail with reference to FIGS. 2 to 4. FIG. 2A is a plan view showing the inner surface, that is, the back surface, of the upper fixed substrate 1. FIG. An annular fixed electrode 15 is formed on the back surface of the substrate 1 .

This fixed electrode 15 is made of conductive material whose electrode area: A can be adjusted by trimming. That is, the conductive pattern consists of a main pattern portion 16 having a constant electrode area and a plurality of divided pattern portions 17 that can be selectively cut from the main pattern portion 16. Each divided pattern portion 17 is connected to a common pattern 18 formed on the front surface side of the substrate 1 via a through hole. One end of the common pattern 18 is electrically connected to the main pattern portion 16 formed on the back side of the substrate 1 via a through hole.

Therefore, each divided pattern portion 17 can be selectively cut from the common pattern 18 by laser beam irradiation or the like. This cutting operation can be performed from the surface side of the upper fixed substrate 1, so that the workability is extremely excellent. A dummy electrode 19 is formed at the center of the back surface of the substrate 1, and a screw hole 20 into which the coupling screw 11 is screwed is formed at the center of the dummy electrode 19. Furthermore, four through holes 21 are formed at the four corners of the substrate 1, into which the parallel bottles 14 are inserted.

In the above embodiment, the area of the fixed electrode is adjusted by selectively cutting the divided pattern portions 17, but the invention is not limited to this.

For example, a structure may be adopted in which adjustment work is performed by selectively connecting a plurality of fixed electrodes 17 separated in advance to the main pattern portion 1B.

FIG. 2B is a plan view showing the inner surface of the lower fixed substrate.

As shown in the figure, a lower fixed electrode 22 is formed around the inner surface of the lower fixed substrate 2. This lower fixed electrode 22
The electrode area is set in advance to be smaller than the total electrode area of the conductive pattern described above. For example, in this embodiment, the inner diameter of the annular lower fixed electrode 22 is set to be slightly larger than the inner diameter of the upper fixed electrode 15, which also has an annular shape. As explained in the operation section, capacitance is proportional to the electrode area, so in this example, the capacitance formed by the upper fixed electrode 15 is equal to the capacitance formed by the lower fixed electrode 22. It is always set large at the initial stage compared to the capacity. Therefore, it is possible to always effectively adjust the capacitance by selectively cutting each divided pattern portion 17. Note that a connection electrode 23 is formed at the center of the inner surface of the lower fixed substrate 2, and a screw hole 24 into which the coupling screw 11 is screwed is formed at the center of the connection electrode 23.

In addition, there are through holes 2 at the four corners of the board 2 for locking the parallel bottles 14.
5 is formed.

FIG. 3 shows the planar shape of the conductive plate member 3. FIG. The plate member 3
is made of a conductive elastic member such as stainless steel, and has a central portion 26 and an annular peripheral portion 27. An opening 28 is formed in the center of the central portion 26, through which the coupling screw 11 is inserted and fixed between the pair of fixed substrates 1 and 2. The peripheral portion 27 is flexibly supported by a plate piece 29 and constitutes a movable electrode. That is, the movable electrode 27
is supported at its free end by the central portion 26 via a leaf spring piece 29, and is displaced in the perpendicular direction in response to external acceleration. Unlike the conventional structure shown in FIG. 6, the movable electrode 27 is supported at the free end, so it is not affected by distortion due to thermal stress etc. generated in the central portion 26, does not warp, and is stably held at the neutral point. be done. Therefore, adjustment of the balance between the pair of neutral point capacitances can be done within a small range.

FIG. 4 shows the planar shape of the spacer 4. As shown,
The spacer 4 has a disk shape, and its outer diameter is approximately equal to the outer diameter of the connection electrode 23 formed on the inner surface of the lower substrate 2 shown in FIG. The outer diameter of the central portion 26 of the member 3 is also approximately equal.

Spacer 5 also has a similar shape. The pair of spacers 4 and 5 sandwich the center portion 26 of the conductive plate member 3 from both sides and are fixed by the pair of fixed substrates 1 and 2.

In particular, the central portion 26 of the conductive plate member 3 and the connection electrode 23 formed on the inner surface of the lower fixed substrate are electrically connected to each other via the conductive spacer 5.

Finally, FIG. 5 is a schematic block diagram showing the electrical connections of this acceleration sensor. As shown in the figure, the portion surrounded by the broken line represents the acceleration sensor body, and the portion outside the broken line represents the external drive circuit. The acceleration sensor body and the external drive circuit are connected to each other via a connection terminal 10 shown in FIG. The connection terminal 10 is actually the output terminal OUT, the first
It has an input terminal INI, a second input terminal IN2, and a pair of ground terminals GNDI, 2. The upper fixed electrode 15 is connected to the input terminal INI, the lower fixed electrode 22 is connected to the second input terminal IN2, and the movable electrode 27 is connected to the output terminal OUT. Further, the case 8 and the cover 9 are externally grounded via a pair of ground terminals GND1 and GND2.

First, the neutral point capacity adjustment work will be explained with reference to FIG.

In the assembled state, the first neutral point capacitance formed between the fixed electrode 15 and the movable electrode 27 is usually larger than the second neutral point capacitance formed between the fixed electrode 22 and the movable electrode 27. larger than. First, in a no-acceleration state,
The capacitance between the second input terminal IN2 and the output terminal OUT is measured. Next, the capacitance between the first input terminal INI and the common output terminal OUT is measured. The electrode area of the upper fixed electrode 15 is adjusted according to the difference, and the work is finished when the picture electrode capacity is finally balanced.

Next, the operation of this acceleration sensor will be explained. Pulses having mutually opposite phases and equal amplitude are input between the pair of input terminals INI and IN2 using, for example, an AC power supply 30. At this time, if the movable electrode 27 is at the neutral point, there is no difference between the pair of capacitances, so a zero level voltage appears at the output terminal OUT. On the other hand, if the movable electrode 27 is displaced in response to external acceleration, the pair of capacitances will be unbalanced, and a detection pulse will appear at the output terminal OUT. The phase of the detection pulse is determined by the direction of the acceleration, and the amplitude is determined by the magnitude of the acceleration, that is, the amount of displacement of the movable electrode 27.

External acceleration is measured by analyzing such detection pulses.

〔Effect of the invention〕

As described above, according to the present invention, at least one of the fixed electrodes is composed of a conductive pattern formed on a fixed substrate and whose electrode area can be adjusted, and the electrode area is set so that a pair of neutral point capacitances are equal to each other. It can be adjusted to balance. With this configuration, the capacitance detection type acceleration sensor can stably set its operating neutral point, and has the effect that the neutral point can be set with little fluctuation even with temperature changes. Particularly, by configuring the conductive elastic plate member in which the central portion is fixed and the peripheral portion is made into a movable electrode, an acceleration sensor with a small neutral point fluctuation range can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a schematic partially cutaway sectional view showing the structure of the acceleration sensor according to the present invention, FIG. 2A is an inside plan view of the upper fixed substrate, FIG. 2B is an inside plan view of the lower fixed substrate, and FIG. The figure is a plan view of the conductive plate member, Fig. 4 is a plan view of the spacer, and Fig. 5 is a plan view of the conductive plate member.
FIG. 6 is a circuit diagram showing electrical connections of an acceleration sensor according to the present invention, and FIG. 6 is an exploded perspective view showing the configuration of a conventional acceleration sensor. 1... Upper fixed substrate 3... Conductive plate member 5... Spacer 8... Case 10... Connection terminal 15... Upper fixed electrode 17... Divided pattern portion 22... Lower fixed electrode 2...Lower fixed board 4...Spacer 7...Circuit board 9...Cover 11...Coupling screw 16...Main pattern portion 18...Common pattern 23...・Connection electrode 26...Central part 27...Movable electrode 29...Plate spring piece Applicant: Cor No. 5, Co., Ltd. "-Figure" Figure 6

Claims (4)

[Claims] 1. A pair of fixed electrodes are arranged opposite to each other with a predetermined gap between them, and a pair of neutral point capacitors are formed between the pair of fixed electrodes and opposite to each fixed electrode according to the area of each electrode, and an external In a capacitance detection type acceleration sensor that has a movable electrode that is displaced from a neutral point in response to acceleration, at least one fixed electrode is composed of a conductive pattern formed on a fixed substrate and whose electrode area can be adjusted. An acceleration sensor characterized by: 2. 2. The acceleration sensor according to claim 1, wherein the conductive pattern includes a main pattern portion having a constant electrode area and a divided pattern portion that can be selectively cut from the main pattern portion. 3. 3. The acceleration sensor according to claim 2, wherein the total electrode area of the conductive pattern is set larger than the area of other opposing fixed electrodes. 4. A conductive plate member is provided between a pair of fixed electrodes, and the conductive plate member includes a central portion that is fixedly supported and a peripheral portion that is flexibly connected to the central portion and constitutes a movable electrode. 2. The acceleration sensor according to claim 1, wherein the fixed electrode is formed on the periphery of the fixed substrate so as to face the movable electrode.