JPH09311009A - Position sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low cost position sensor with high accuracy superior in durability by a constitution wherein a guard electrode holding a specific voltage is provided between electrodes of which voltages are varied in a plurality of variable capacities. SOLUTION: Each of first and second fixed electrodes 23, 24 is in a semicircle shape around a shaft 21. A movable electrode 22 is in a semicircle shape, is supported by the shaft 21 and is shared by the first and second fixed electrodes 23, 24 so that an electrostatic capacity is formed in each of the gaps. A guard electrode 25 is formed between the first fixed electrode 23 and second fixed electrode 24 and is set in a common voltage. The guard electrode 25 holding a constant voltage is provided between the electrodes of which voltages are varied in a plurality of variable capacities. Even when a voltage of one of the electrodes in the plurality of variable capacities is varied, a voltage of the other electrode is not varied because the guard electrode 25 having the constant voltage is placed between adjacent other electrodes so that the capacitance is accurately maintained and position detection can be accurately executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position sensor,
In particular, the present invention relates to a position sensor that varies a plurality of capacitances according to the position of a position detection target and detects the position of the position detection target according to the plurality of capacitances.

[0002]

2. Description of the Related Art Conventionally, there have been sliding resistance potentiometers, differential transformers and the like as position sensors for detecting a rotation angle or a linear position of a position detection target. FIG. 10 shows a schematic configuration diagram of a sliding resistance type potentiometer.

The sliding resistance type potentiometer 1 is provided with a line resistance 2 and a contact 3 which is slidable with respect to the line resistance 2 in the direction of arrow D, and the contact 3 depending on the position of the position detection target.
Is displaced and the position of the contact 3 is detected by obtaining the divided voltages V1 and V2 of the voltage V applied to the line resistance 2.

FIG. 11 shows a schematic configuration diagram of a differential transformer. The differential transformer 11 is mainly composed of a drive coil 12, detection coils 13 and 14, and a core 15, and displaces the core 15 in the arrow E direction according to the position of the position detection target and drives it according to the position of the core 15. Coil 13 to detection coil 13
By changing the magnetic flux supplied to the detection coil 14, the position of the core 15 is detected according to the signals generated in the detection coils 13 and 14, and the position of the position detection target is detected.

[0005]

However, since the sliding resistance type potentiometer, which is a conventional position sensor, has a structure in which the electrode is slid on the resistance film, a failure due to abrasion is likely to occur and the abrasion resistance is improved. There was a problem such as becoming expensive.

Further, since the differential transformer is non-contact, there is no failure due to wear, but the structure is complicated and therefore expensive.
Further, there is a problem that it is difficult to reduce the size due to the presence of the coil. The present invention has been made in view of the above points,
It is an object of the present invention to provide an inexpensive and accurate position sensor that has excellent durability.

[0007]

According to a first aspect of the present invention, there is provided a position sensor having a plurality of variable capacitors which are coupled to a position detection target and have a capacitance variable according to the position of the position detection target. It is characterized in that a guard electrode held at a constant potential is provided between electrodes of which the potential is variable among a plurality of variable capacitors.

According to the first aspect of the present invention, the potential of one of the plurality of variable capacitors fluctuates by providing the guard electrode held at a constant potential between the electrodes of which the potential is variable among the plurality of variable capacitors. Even in such a case, since the guard electrode having a constant potential exists between the adjacent other electrode, the potential of the other electrode is not changed, the capacitance can be accurately held, and the position can be accurately detected.

According to a second aspect of the present invention, there is provided a position sensor having a plurality of variable capacitors which are coupled to a position detection target and whose capacitance is variable according to the position of the position detection target, wherein the potential of the plurality of variable capacitors is variable. One electrode holds the other electrode at a constant potential during charging and discharging.

According to the second aspect of the present invention, among the plurality of variable capacitors, between the electrodes whose potential is variable, one electrode holds the other electrode at a constant potential during charging / discharging. Since charging and discharging can be performed without being affected by fluctuations, it is possible to obtain electric charges according to the capacity at that time from a plurality of variable capacities, and it is possible to accurately measure the capacity, thus enabling accurate position detection. .

[0011]

1 to 3 are block diagrams of a first embodiment of the present invention. 1 is a sectional view taken along the line CC ′, and FIG.
FIG. 3 is a sectional view taken along line BB ′ of FIG. The position sensor 20 of the present embodiment mainly includes a shaft 21 that is coupled to a position detection target and that is rotated according to the position of the position detection target, a movable electrode 22 that is fixed to the shaft 21 and that has a variable capacitance, and a movable electrode 22. First and second fixed electrodes 23 that are provided so as to face each other and obtain an electrostatic capacitance according to an area facing the movable electrode 22,
24, the guard electrode 25 connected between the first fixed electrode 23 and the second fixed electrode 24, the movable electrode 22, the first and second fixed electrodes 23, 24, the guard electrode 25 are connected, and the position Circuit board 26 on which a measuring circuit for detecting
It is composed of

The shaft 21 is formed by molding a metal into a rod-shaped body having a step portion 21c composed of a small diameter portion 21a and a large diameter portion 21b. The small diameter portion 21a of the shaft 21 is rotatably inserted into the bush 27, and the large diameter portion 21b is coupled to the position detection target. The bush 27 is made of a metal 27a.
The small diameter portion 21a of the shaft 21 is inserted into the center hole 27b, and is positioned on the plate 28 by the flange portion 27a. The bush 27 supports the end surface of the large diameter portion 21b of the shaft 21 around the center hole 27b and positions the shaft 21 with respect to the bush 27.

The plate 28 is formed by forming a metal plate into a substantially square shape and forming a holding hole 28a at the center thereof. Plate 2
The bush 27 is press-fitted and fixed in the holding hole 28 a of No. 8. At this time, the collar portion 27a of the bush 27 hits the periphery of the holding hole 28a and the bush 27 is positioned on the plate 28.

The plate 28 has columns 29, 30,
It is held by 31 and 32. Pillars 29, 30, 31,
32 is made of metal and has three members 29a, 2 respectively.
9b, 29c, 30a, 30b, 30c, 31a, 31
b, 31c, 32a, 32b, 32c. One end of each of the members 29a, 30a, 31a, 32a is fixed to the plate 28, and the other end thereof is the first and second fixed electrodes 2.
3, 24, and the guard electrode 25 is connected to the first printed wiring board 33.

The first printed wiring board 33 is the plate 2
It has almost the same shape as 8, and the columns 29, 30,
Members 29a, 30a, 31a, 3 constituting 31, 32
One end of 2a is fixed. A through hole 33 is formed in the center of the first printed wiring board 33 to allow the shaft 21 to penetrate therethrough.
a is formed, and the first fixed electrode 23 is printed in a semicircular shape centering on the through hole 33a, and the second fixed electrode 24 is printed as the remaining semicircle of the first fixed electrode 23. The first fixed electrode 23 and the second fixed electrode 24 are insulated from each other, and the first fixed electrode 23 and the second fixed electrode 24 are insulated from each other.
The guard electrode 25 is provided between the first and second fixed electrodes 2 and
3, 24 are formed in an insulated state.

The members 29a, 30a, 31a, 32a forming the columns 29, 30, 31, 32 are members 29b, 30b, 31b forming the columns 29, 30, 31, 32 via the first printed wiring board 33. , 32b.
The members 29b, 30b, 31b, 32b have one end fixed to the first printed wiring board 33 and the other end fixed to the second printed wiring board 34.

The second printed wiring board 34 is the plate 2
8 and the first printed wiring board 33 have substantially the same shape, and the members 29b, 30b, 31b, 32b are fixed to the four corners thereof. The second printed wiring board 34 has through holes 3
The first fixed electrode 23 is printed in a semicircular shape around the center 4a, and the second fixed electrode 24 is printed as the remaining semicircle of the first fixed electrode 23. As with the first printed wiring board 33, the first fixed electrode 23 is printed. A guard electrode 25 is formed between the first fixed electrode 23 and the second fixed electrode 24. The first printed wiring board 33 and the second printed wiring board 34 are the first and second fixed electrodes 23 of the first printed wiring board 33.
24, the surface on which the guard electrode 25 is formed and the first and second fixed electrodes 23, 24 of the second printed wiring board 34,
The surface on which the guard electrode 25 is formed faces, and the first
And, the patterns of the second fixed electrodes 23, 24 and the guard electrode 25 are arranged so as to face each other.

The first printed wiring board 33 and the second printed wiring board 34 include the first and second fixed electrodes 23 and 24 of the first printed wiring board 33 and the guard electrode 25, respectively.
Also, the first and second fixed electrodes 23 and 24 of the second printed wiring board 34 and the guard electrode 25 are connected to each other by the first flexible printed wiring board 35. Further, the first printed wiring board 33 is connected to the circuit board 26 on which the measurement circuit is formed by the second flexible wiring board 36, and the first and second fixed electrodes 2 are connected.
3, 24 and the guard electrode 25 are connected to the circuit board 26.

The members 29b, 30b, 31b, 32b forming the columns 29, 30, 31, 32 are members 29c, 30c forming the columns 29, 30, 31, 32 via the second printed wiring board 34. It is connected to 31c and 32c. The members 29c, 30c, 31c, 32c have one end fixed to the four corners of the second printed wiring board 34 and the other end fixed to the circuit board 26 on which the measurement circuit is formed. Prop 2
9, 30, 31, 32 are members 29a, 29b, 29
c, 30a, 30b, 30c, 31a, 31b, 31
c, 32a, 32b, 32c are continuous, and electrically connect the plate 28, the first and second printed wiring boards 33, 34, and the circuit board 26.

The movable electrode 22 is formed by forming a metal plate into a substantially semicircular shape, and a mounting hole 22a is formed in the center thereof, and the mounting hole 22a has a small diameter portion 21a of the shaft 21.
Is inserted. Metal rings 37 and 38 are press-fitted and fixed to the small diameter portion 21 a of the shaft 21. Movable electrode 22
Is sandwiched by the rings 37 and 38 and held by the shaft 21.

At this time, the movable electrode 22 is provided between the first printed wiring board 33 and the second printed wiring board 34 in the first area.
And the first formed on the second printed wiring boards 33, 34.
The second fixed electrodes 23, 24 and the guard electrode 25 are arranged so as not to come into contact with each other. At this time, the spring 39 is arranged between the ring 37 and the plate 28 in a compressed state. The spring 39 extends in the arrow A direction between the ring 37 and the plate 28 and presses the shaft 21 in the arrow A1 direction. The shaft 21 is pressed in the direction of arrow A1 by the spring 39, the end of the large-diameter portion 21b is pressed against the periphery of the bush 27 by the step portion 21c, and is reliably positioned with respect to the plate 28, and the movable electrode 22 is moved to the first position. Between the first printed wiring board 33 and the second printed wiring board 34, the first
And the first formed on the second printed wiring boards 33, 34.
The second fixed electrodes 23, 24 and the guard electrode 25 are securely arranged so as not to contact with each other.

The movable electrode 22 is connected to the plate 28 via a ring 37 and a spring 39. The plate 28 is connected to the circuit board 26 via columns 29, 30, 31, 32 and is connected to the common potential. Therefore, the movable electrode 22 is held at the common potential. The guard electrodes 25 formed on the first and second printed wiring boards 23, 24 are connected to the support columns 29, 30, 31, 32 and are held at a common potential like the movable electrode 22.

As described above, the first electrostatic capacitance C _a is formed between the first fixed electrode 23 and the movable electrode 22, and the second electrostatic capacitance C _a is formed between the second fixed electrode 24 and the movable electrode 22. Capacitance C
_b is formed. Next, a variable capacity operation will be described with reference to the drawings.

FIG. 4 shows an explanatory view of the operation of the movable capacitance portion according to the first embodiment of the present invention. When the movable electrode 22 is rotated by rotating the shaft 21, and the movable electrode 22 is rotated,
Movable electrode 22, first fixed electrode 23, second fixed electrode 2
4, in order to form a semi-circular, opposed area S1 of the movable electrode 22 constituting a first capacitance C _a and the first fixed electrode 23
And the movable electrode 22 which constitutes the second capacitance C _b and the second
The area S2 facing the fixed electrode 24 changes.

Here, the facing areas S1 and S2 are the same as those of the movable electrode 22 with respect to the first and second fixed electrodes 23 and 24 shown in FIG.
At the position shown in (A), the area S1 is equal to the area S2. Further, when the shaft 21 is rotated in the direction of the arrow B1 by the angle θ1, when the movable electrode 22 reaches the position shown in FIG. 4B, the area S1 increases and the area S2 decreases. Further, the shaft 21 is angled θ2 (90 °) in the direction of arrow B1.
When the movable electrode 22 is rotated by only the position shown in FIG. 4C, the area S1 becomes maximum and the area S2 becomes zero.

Generally, the capacitance C of a parallel plate capacitor is
Is approximately the area of the electrodes and d is the distance between the electrodes,

[0027]

[Equation 1]

Where ε is the dielectric constant, and when the medium between the electrodes is air, ε = ε ₀ = 8.8542 × 10 ^-11 [C ² N ^-1 m ^-2 ]
It is. Therefore, by rotating the shaft 21 and the movable electrode 22 as shown in FIG. 4, the electrostatic capacitance between the movable electrode 22 and the first fixed electrode 23 and the movable electrode 22 and the second fixed electrode 24. Therefore, the capacitance can be changed.

Now, the first and second fixed electrodes 23, 24
Is r ₁ , the radius of the central hole is r ₀ , the movable electrode 22 and the first fixed electrode 22, the movable electrode 22 and the second fixed electrode 24.
And the distance between the movable electrode 22 and the first fixed electrode 23 is d.
And the number of pairs with the second fixed electrode 24 is n, and the rotation angle of the shaft 21 is θ, the variable electrode 22 and the first fixed electrode 23.
When obtaining a second capacitance C _b between the first capacitance C _a, the movable electrode 22 and the second fixed electrode 24 between,

[0030]

[Equation 2]

It is calculated by the above equations (1) and (2).
First and second capacitance C_a, C _bOn the circuit board 26
It is connected. In the circuit board 26, equations (1) and (2)
The first and second capacitances C obtained by_a, C_bof
The rotational position of the shaft 21 is detected from the ratio.

From equations (1) and (2)

[0033]

(Equation 3)

Can be represented by Therefore, from the formula (4), the variable electrode 24 and the first fixed electrode 25, which are the first variable capacitor 22a, are formed.
And the electrostatic capacitance C _a of the second variable capacitance 22 b and the electrostatic capacitance C _{b of} the second fixed electrode 26 are constant regardless of the angle θ of the shaft 27. I understand.

Here, equations (1), (2) and equations (4),
(5) shows that the capacitances C _a , C _b and (C _a −C _b ) are functions of the distance d and the radii r ₀ , r ₁ .
If these values change due to temperature changes, the capacitance C
_It also shows that _a and C _b also change.

However, from equations (1) and (2) and equations (4) and (5),

[0037]

(Equation 4)

The equations (6), (7) and (8) represent the capacity ratio C _a
/ (C _a + C _b ), C _b / (C _a + C _b ), (C _a −C
_b ) / (C _a + C _b ) is the rotation angle −180 ° ≦ θ ≦ 0 ° and
Each of them is proportional to the angle θ in the range of 0 ° ≦ θ ≦ 180 °, and these capacitance ratios are functions of only θ and do not depend on the parameters of the shape such as the interval d and the radii r ₀ , r _1. The rotation angle θ of the shaft 21 can be detected.

Although the capacity is varied according to the rotation angle θ of the shaft 27, the capacity is not limited to this, and the capacity may be varied according to the position on the straight line. 5 to 7 are configuration diagrams of the second embodiment of the present invention. 5 shows a sectional view taken along the line CC ', FIG. 6 shows a sectional view taken along the line AA', and FIG. 7 shows a sectional view taken along the line BB '. In the figure, those parts that are the same as those corresponding parts in FIGS. 1 to 3 are designated by the same reference numerals, and a description thereof will be omitted.

The position sensor 41 of this embodiment is interlocked with two
One position sensor is built in, and the fixed electrode is made of a metal plate. The position sensor 41 is composed of first to fourth movable electrodes 42, 43, 44 and 45 and first to fourth fixed electrodes 46, 47, 48 and 49. The position sensor 41 of the present embodiment includes a support body 50 so as to surround the first to fourth movable electrodes 42, 43, 44, 45 and the first to fourth fixed electrodes 46, 47, 48, 49.
It is configured to be stored in a and 50b.

The supports 50a and 50b are made of a semi-cylindrical insulator, and the plate 28 is fixed to one end and the circuit board 51 is fixed to the other end. First to fourth movable electrodes 4
2 to 45 are sandwiched by metal rings 52 to 56 and held by the shaft 21, and the first to fourth movable electrodes 4 are
2 to 45 are held so as to be arranged in an insulating state between the first to fourth fixed electrodes 46 to 49.

Further, the first and second movable electrodes 42 to 45
Is connected to the plate 2 via the rings 52 to 56 and the spring 39.
8, the plate 28 is connected to the circuit board 51 via a lead wire (not shown), and is held at a common potential. On the other hand, the first to fourth fixed electrodes 46 to 4
9 is a leg part 57,58,59,60 and a support body 50a,
A lead wire 61 inserted through a small hole formed in 50b,
It is connected to the circuit board 51 via 62, 63 and 64.

The first to fourth movable electrodes 42 to 45 and the first to fourth fixed electrodes 46 to 49 have a semicircular shape,
The first movable electrode 42 and the second movable electrode 43 are overlapped with each other in the arrow C direction, and the third movable electrode 44 and the fourth movable electrode 45 are overlapped with each other in the arrow C direction.
The second movable electrodes 42 and 43 and the third and fourth movable electrodes 44 and 45 are attached with a phase difference of 180 °.

First fixed electrode 46 and second fixed electrode 47
Means that the third fixed electrode 48 and the fourth fixed electrode 49 are arranged side by side in the arrow D direction. The first fixed electrode 46 and the second fixed electrode 47 are inserted between the first movable electrode 42 and the second movable electrode 43, and
The fixed electrode 48 and the fourth fixed electrode 49 are inserted between the third movable electrode 44 and the fourth movable electrode 45.

The first and second movable electrodes 42, 43 and the first
A first capacitance C _a1 is generated by the fixed electrode 46 of
First and second movable electrodes 42, 43 and second fixed electrode 4
The second electrostatic capacitance C _b1 is generated by 7, and the third electrostatic capacitance C _a2 is generated by the third and fourth movable electrodes 44 and 45 and the third fixed electrode 48, and the third electrostatic capacitance C _a2 is generated. The fourth movable electrodes 44, 45 and the fourth fixed electrode 49 generate a fourth capacitance C _b2 .

When the shaft 21 rotates and the first capacitance increases, the second and third capacitances decrease and the fourth capacitance increases. Further, when the first capacitance decreases, the second and third capacitances increase and the fourth capacitance decreases. According to the configuration of this embodiment, the first and second movable electrodes 42, 43 and the third and fourth movable electrodes 44, 4
5 is installed with the shaft 21 as a shaft and a phase difference of 180 ° from each other, so that the first and second fixed electrodes 46, 4
Since the seventh and third and fourth fixed electrodes 48 and 49 are always shut off by the second or fourth movable electrodes 43 and 45 held at the common potential, the first and second fixed electrodes 46 and 4 are
The fluctuation of the potential of 7 does not affect the third and fourth fixed electrodes 48 and 49.

In this embodiment, since there is no guard electrode between the first fixed electrode 46 and the second fixed electrode 47 and between the third fixed electrode 48 and the fourth fixed electrode 49, these electrodes are not provided. The mutual influence between them can be eliminated by the circuit described below. FIG. 8 shows a circuit configuration diagram of a circuit board according to a second embodiment of the present invention.

The circuit shown in FIG. 8 shows a processing circuit for the first and second electrostatic capacitances C _a1 and C _b1 or the third and fourth electrostatic capacitances C _a2 and C _b2 , respectively. The circuit board 51 has a capacitance C
_a, it is a circuit which outputs a pulse signal of a duty ratio corresponding to the rotation angle θ from the C _b shaft 21.

The first capacitance C _a has a resistance R _1a ,
The charging circuit including R _2a and the switch SW _2a and the discharging circuit including the inverter INV1, the AND gate G1, and the switch SW _1a are connected to each other, and the second electrostatic capacitance C _b has a resistance R
_A charging circuit including _1b and R _2b , a switch SW _2b, and a discharging circuit including an inverter INV2, an AND gate G2, and a switch SW _1b are connected.

The voltage B of the first electrostatic capacitance C _a is supplied to the input terminal of the comparator CMP1. Comparator C
MP1 uses the voltage B of the first capacitance C _a as the reference voltage V
Compared with _REF, it outputs a signal Q1 that becomes high level when the voltage B of the first electrostatic capacitance C _a becomes larger than the reference voltage V _REF . Non-inverted output signal Q1 of the comparator CMP1 is supplied to the switch SW _2a of the charging circuit. The switch SW _2a turns on when the output signal Q1 is at a low level, and rapidly charges the first electrostatic capacitance C _a .

[0051] Further, the inverted signal / Q1 by inverting the non-inverted output signal Q1 of the comparator CMP1, the inverters INV1 and AN of the discharge circuit for discharging the second capacitance C _b
It is supplied to the D gate G1 and discharge control of the second capacitance C _b is performed. The discharge circuit detects the rising edge of the output signal / Q of the comparator CMP1 and turns on the switch SW _1b to discharge the second capacitance C _b . Second capacitance C
The voltage E of _b is supplied to the input terminal of the comparator CMP2. The comparator CMP2 compares the voltage E of the second capacitance C _b with the reference voltage V _REF to determine the second capacitance C
_When the voltage E of _b becomes larger than the reference voltage V _{REF, the} non-inverted output signal Q2 which becomes the high level is output. The non-inverted output signal Q2 of the comparator CMP2 is supplied to the switch SW _{2b of the} charging circuit. The switch SW _2b is turned on when the non-inverted output signal Q2 is at low level, and the second capacitance C
Quickly charge _b .

The non-inverted output signal / Q2 obtained by inverting the non-inverted output signal Q2 of the comparator CMP2 is supplied to the inverter INV2 and the AND gate G2 of the discharge circuit for discharging the first electrostatic capacitance C _a . The discharge of the capacitance C _a is controlled. The discharge circuit detects the rising edge of the output signal / Q of the comparator CMP2 and turns on the switch SW _1a to discharge the first electrostatic capacitance C _a .

FIG. 9 shows an operation waveform diagram of the circuit board according to the first embodiment of the present invention. 9A shows the waveform of the output A of the AND gate G1, FIG. 9B shows the waveform of the voltage B of the first capacitance C _a , and FIG. 9C shows the non-inverted output signal Q1 (of the comparator CMP1. C) waveform, Figure 9 (d) shows comparator CM
Waveform of inverted output signal / Q1 (/ C) of P1, FIG. 9 (e)
Is the waveform of the output D of the AND gate G2, and FIG.
9E shows the waveform of the voltage E of the electrostatic capacitance C _b , FIG. 9G shows the waveform of the non-inverted output signal Q2 (F) of the comparator CMP2, FIG.
(H) is the inverted output signal / Q2 of the comparator CMP2
The waveform of (/ F) is shown.

As shown in FIG. 9, the switch SW is activated at time t1.
_{When 1a} is turned on and the first capacitance _Ca is discharged, the first capacitance
The electrostatic capacitance C _a resistor charged with limited current by R _1a is started, the voltage B of the first capacitance C _a gradually rises. At this time, the non-inverted output signal Q2 (F) of the comparator CMP2 becomes high level and the switch S
W _2b is turned on, and the voltage E of the second electrostatic capacitance C _b is held at a predetermined voltage. Since the second capacitance C _b is in the charged state, the non-inverted output signal Q2 (F) of the comparator CMP2 is at low level.

Next, when the voltage B of the first electrostatic capacitance C _a reaches the reference voltage V _REF at time t2, the comparator CMP
The non-inverted output signal Q1 (C) of 1 becomes low level, the switch SW _2a is turned on, the first capacitance C _a is rapidly charged and saturated, and the voltage B of the first capacitance C _a is Is held at a constant value.

At this time, the inverted output signal / Q (/ C) of the comparator CMP1 is inverted from low level to high level. Inverted output signal / Q of comparator CMP1
When (/ C) is inverted from the low level to the high level, the inverter INV2 and the AND gate G2 detect this, the switch SW _1b is turned on, the second electrostatic capacitance C _b is discharged, and the non-inversion of the comparator CMP2 is performed. Output signal Q2
Invert (F) to high level. Comparator CMP
When the non-inverted output signal Q2 (F) of 2 becomes high level,
The switch SW _2b is turned off, and charging is started only by the current from the resistor R _1b .

At time t3, the voltage E of the second capacitance C _b is
_{Reaches the} reference voltage V _REF , the non-inverted output signal Q2 (F) of the comparator CMP2 is inverted and becomes low level,
The switch SW _2b is turned on, the second capacitance C _b is rapidly charged, the voltage of the second capacitance C _b is saturated rapidly, and is kept at a constant voltage.

At this time, the inverted output signal / Q2 (/ F) of the comparator CMP2 is inverted and becomes high level, the switch SW _1a is turned on, the first electrostatic capacitance C _a is discharged, and the same operation as at the time t1 is performed. This operation is repeated. From the above, the non-inverted output signal Q2 (F) of the comparator CMP2
Is a low level period T _a is determined by a time constant according to the capacitance of the first electrostatic capacitance C _a , and a high level period T _b is a second level.
Is determined by a time constant according to the capacitance of the electrostatic capacitance C _b . Therefore, the non-inverted output signal Q2 of the comparator CMP2
(F) Low-level period T _a and high-level period T _b
The rotation angle θ of the shaft 21 can be obtained from the duty ratios of and as shown in Expressions (6) to (8).

[0059] At this time, in the first capacitance C _a is charged to the second is the voltage of the capacitance C _b is held at a constant voltage, in the second capacitance C _b is charged in the opposite second since the first voltage of the capacitance C _a is held at a constant voltage, it can reduce the interaction between the first capacitance C _a and the second capacitance C _b.

Therefore, accurate position detection is possible. With the above processing circuit, the rotational position of the shaft 21 by the first and second electrostatic capacitances C _a1 and C _b1 and the rotational position of the shaft 21 by the third and fourth electrostatic capacitances C _a2 and C _b2 are respectively set. For example, the detected position of the shaft 21 based on the first and second electrostatic capacitances C _a1 and C _b1 and the detected result of the rotational position of the shaft 21 based on the third and fourth electrostatic capacitances C _a2 and C _b2. The average of and is output as the rotation position detection result of the shaft 21.

According to this embodiment, when one of the first and second electrostatic capacitances C _a1 and C _{b1 fails} , the third and fourth electrostatic capacitances C _a2 and C _b2. The detection result of the rotational position of the shaft 21 is used as the detection result of the rotational position of the shaft 21, and if any one of the third and fourth electrostatic capacitances C _a2 and C _b2 is defective, the first and second The rotational position detection result of the shaft 21 based on the electrostatic capacitances C _a1 and C _{b1 is taken as} the rotational position detection result of the shaft 21. At this time, the defects of the first to fourth capacitances C _a1 , C _b1 , C _a2 , and C _b2 can be detected by monitoring the output of each processing circuit. For example, the first to fourth capacitances C _a1 , C _b1 ,
When there is a defect in C _a2 and C _b2 , one cycle of the output pulse of the output of the processing circuit is abnormally long or short, and therefore the abnormality can be detected by relating the cycle of the output pulse. When an abnormality is detected in this way, the output of the other processing circuit is output as the rotation position detection result of the shaft 21.

As described above, the reliability of detecting the rotational position of the shaft 21 can be improved.

[0063]

As described above, according to claim 1 of the present invention, by providing the guard electrode held at a constant potential between the electrodes of which the potential is variable among the plurality of variable capacitors, a plurality of variable capacitors can be provided. Even if the potential of one of the electrodes changes, there is a guard electrode with a constant potential between the other adjacent electrodes, so the potential of the other electrode does not change and the capacitance can be held accurately. It has features such as accurate position detection.

According to the second aspect, among the plurality of variable capacitors, between the electrodes whose potentials are variable, one electrode holds the other electrode at a constant potential during charging / discharging. Since charging and discharging can be performed without being affected by fluctuations, it is possible to obtain electric charges according to the capacity at that time from a plurality of variable capacities, and it is possible to accurately measure the capacity, thus enabling accurate position detection. It has features such as

[Brief description of drawings]

FIG. 1 is a sectional view taken along the line C-C ′ of the first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line A-A ′ of the first embodiment of the present invention.

FIG. 3 is a sectional view taken along the line B-B ′ of the first embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 5 is a sectional view taken along the line C-C ′ of the second embodiment of the present invention.

FIG. 6 is a sectional view taken along the line A-A ′ of the second embodiment of the present invention.

FIG. 7 is a sectional view taken along the line B-B ′ of the second embodiment of the present invention.

FIG. 8 is a circuit configuration diagram of a measuring circuit according to a second embodiment of the present invention.

FIG. 9 is an operation waveform diagram of the measurement circuit according to the second embodiment of the present invention.

FIG. 10 is a configuration diagram of a conventional example.

FIG. 11 is a configuration diagram of another example of the related art.

[Explanation of Codes] 20, 41 Position Sensor 21 Shaft 22 Movable Electrode 23 First Fixed Electrode 24 Second Fixed Electrode 25 Guard Electrode 26 Circuit Board 27 Bush 28 Plate 29-32 Strut 33 First Printed Wiring Board 34 Fourth Second printed wiring board 35 First flexible printed wiring board 36 Second flexible printed wiring board 37, 38 Ring 39 Spring

Claims (2)

[Claims] 1. A position sensor having a plurality of variable capacitors coupled to a position detection target and having a capacitance that varies according to the position of the position detection target, the inter-electrodes having a variable potential among the plurality of variable capacitors. A position sensor characterized in that a guard electrode held at a constant potential is provided in the position sensor. 2. A position sensor having a plurality of variable capacitors, which are coupled to a position detection target and have a capacitance variable according to the position of the position detection target, between electrodes of which the potential is variable among the plurality of variable capacitors. In the position sensor, one electrode holds the other electrode at a constant potential during charging and discharging.