JPH08233605A - Capacitance type encoder - Google Patents

Abstract

PURPOSE: To constitute an encoder compact and high in angle resolution and accuracy by forming the electrode of a stator by combining three kinds of electrodes of specific shape so as to generate a correct sine wave signal in relation to a turning angle. CONSTITUTION: The electrode 22 of a rotor is formed into such shape that sector parts with a radius (r) and sector parts with a radius R are alternately arranged every angle of 45 deg.. The electrode of a stator is formed of three kinds of shape, that is, a power supply electrode (E-electrode) 121 formed as a circle with a radius rE at the center part around a rotary shaft, and signal output F (F0 -F5 ) electrodes 122 and signal output G (G0 -G5 ) electrode 123 formed being spaced on the outside. A signal detected in this electrode constitution becomes such a signal that sine wave of four cycles per one rotation is shifted in phase by π/6, and as to the accuracy, the sine wave rate becomes a high level (about 0.5% or less) to a turning angle. When this signal is resolved into pulses by an R/D converter to measure, a signal of one pulse to the rotation angle 10 minutes can be obtained with about 1% accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type encoder for detecting a rotational position of a motor, which utilizes a capacitance change of electrodes facing each other.

[0002]

2. Description of the Related Art Conventionally, as an encoder for detecting a rotational position of a motor, for example, an encoder utilizing a magnetic system or an optical system has been put into practical use. However, these methods have problems that the power consumption is large and it is very difficult to realize the miniaturization and the improvement of the angular resolution at the same time. As a method for solving these problems, the electrostatic capacitance method has been attracting attention. Of these, for low power consumption,
For example, it has been put to practical use for a micrometer and the like as seen in JP-A-59-183329.

[0003]

However, since the method described above is a method of generating a pulse, there is a problem that the angular resolution is poor and the size cannot be reduced because of problems such as the division accuracy of the electrodes. Therefore, it is an object of the present invention to provide a small-capacity capacitive encoder having a structure in which the electrodes of the fixed body have two specific shapes and having a high resolution with respect to the rotation angle.

[0004]

In order to solve the above-mentioned problems, the present invention provides a fixed body having electrodes, which are circularly provided at regular intervals on the surface of an insulator, and a disc-shaped insulator. A rotating body having an electrode provided, the electrode of the fixed body and the electrode of the rotating body are opposed to each other with a gap, and the rotational position is detected by detecting a change in capacitance between both electrodes. In the capacitance type encoder, the electrode of the rotating body has a shape in which fan portions having a radius r and fan portions having a radius R larger than the radius r are alternately arranged at regular intervals, and the electrode of the fixed body is the electrode. Radius r when the rotation angle is θ based on a circular part (E part electrode) with radius r _E smaller than the fan part radius r of the rotor and polar coordinates with the center of the circle as the origin
Between the F portion electrode and a portion surrounded by a curve f (θ), which has the respective arcs at regular intervals and extends outward from one end of the arc and then returns to the other end. And a portion surrounded by a curve g (θ) (G portion electrode) which has circular arcs of the radius R at regular intervals and which extends inward from one end of the circular arc and then returns to the other end. It is configured to be.

[0005]

With the above-mentioned means, since the two kinds of curves are combined as the electrode for signal generation of the fixed body, an accurate sine wave signal with respect to the rotation angle can be obtained. Therefore, the accurate analog signal of the sine wave can be used as it is as the position signal, so that the position resolution can be detected with high accuracy, and the compact encoder can be obtained.

[0006]

EXAMPLES Specific examples of the present invention will be described below with reference to the drawings. FIG. 1 is a partial sectional view showing an encoder of the present invention. In the figure, 1 is a fixed body, 2 is a rotating body, and 3 is a rotating shaft. The fixed body 1 has an electrode 12 provided on one surface of an insulating plate 11 and a signal processing unit 4 provided on the other surface. The rotating body 2 is provided with an electrode 22 on one surface of a circular insulating plate 21, and the rotating shaft 3 is fixed to the center of the circle on the other surface. The fixed body 1 and the rotating body 2 have both electrodes 12, 22.
Are opposed to each other with a certain gap maintained. These electrodes were manufactured by using a high-precision photolithography technique used in semiconductor manufacturing in order to make the accuracy higher, in addition to the usual electrode manufacturing process of a printed circuit board. The electrode shape of the rotating body 2 is shown in FIG. The electrode 22 has an angle of 45 °
Each of them has a shape in which fan portions having a radius r and fan portions having a radius R are alternately arranged. When the angle is θ and n is 0, 1, 2, 3 by polar display with the center of the circle as the origin, the fan part should be in the range of nπ + π / 4 to (n + 1) π / 2 at the angle θ. There is. The shape of the electrode 12 of the fixed body 1 is shown in FIG. The electrode 12 has a circular electrode 121 (hereinafter referred to as an E electrode) having a diameter r _E (where r _E is smaller than r) in the center with the rotation axis 3 as the center, and has a space on the outside thereof. The formed F part electrode 122 for signal output and the G part electrode 123 for signal output are formed in three kinds of shapes. The F portion electrode 122 is an electrode of a portion surrounded by a circle having a radius r and a curve f (θ) when the rotation angle of the circle is θ in polar coordinates, and is F ₀ , F ₁ , F ₂ , F ₃ , F ₄ , F ₅
There are 6 of them. The curve f (θ) has m of 0, 1, 2, 3,
4 and 5, and θ is represented by the following formula (1) with mπ / 3 ≦ θ ≦ mπ / 3 + π / 4. f (θ) = {(R ² −r ² ) sin 4 (θ−mπ / 3) + r ² } ^1/2 ... (1) The G part electrode 123 is located between the F part electrodes 122. , G is an electrode in a portion surrounded by a circle having a radius R and a curve g (θ), and there are six electrodes G ₀ , G ₁ , G ₂ , G ₃ , G ₄ , and G ₅ . In the curve g (θ), m is 0, 1, 2, 3, 4, 5, and θ is (m−1) π / 3 + π / 2 ≦ θ ≦ (m−1) π.
It is expressed by the following equation as a range of / 3 + 3π / 4. g
(Θ) = {r ² − (r ² −R ² ) sin 4 (θ− (m−
1) π / 3-π / 2)} ^1/2
(2) FIG. 4 shows connection of electrodes for signal output of the fixed body 1. The F part electrode 122 and the G part electrode 123 are
₀ and G ₁ and F ₃ and G ₄ , G ₀ and F ₂ , G ₃ and F ₅ , F ₁
, G ₂ , F _4, and G ₅ are connected every other line, and are connected to diagonal pairs, so that a total of 3 sets of outputs can be obtained. FIG. 5 shows a connection circuit between the electrode 12 of the fixed body 1 and the signal processing unit 4. The E section electrode 121 that supplies power is connected to the AC power supply 41, and the above-mentioned three sets of outputs are connected in series from the full-wave rectifier circuits 421 to 423 to the smoothing circuits 431 to 433, respectively, and are connected to the output terminal 44. Has been done. Now, when an AC voltage is applied to the E section electrode 121, three sine waves are obtained at the output terminals 441 to 443, respectively, and FIG. 6 shows the combined result. These signals are signals in which four cycles of sine waves are shifted by π / 6 per revolution. It can be seen that those accuracies have a high level of the sine wave ratio within 0.5% with respect to the rotation angle. Therefore, when this signal was decomposed into pulses using an R / D converter (not shown) and measured, a 1-pulse signal could be obtained with an accuracy of 1% for a rotation angle of 10 minutes. Furthermore, the present invention was applied to the control of an AC servomotor and the effect was investigated. FIG. 7 is a block diagram thereof. FIG. 8 is a block diagram in the case of using a conventional encoder that generates a pulse with a rotation angle. In the motor control sequence circuit 7 of this system, the difference between the angle signal command 71 and the pulse signal from the encoder 5 is taken by the differential circuit 72, and is calculated by the controller 73. Next, the signal from the control unit 73 and the signal obtained by converting the pulse signal from the encoder 5 into a sine wave by the pulse-sine wave conversion circuit 76 are multiplied by the multiplication circuit 74, and the AC servo motor 5 is passed through the power conversion circuit 75. To control. However, by using the 4-pole 3-phase encoder of the present invention, the control unit 73 becomes unnecessary and the R / D conversion circuit 77 is used instead of the pulse-sine wave conversion circuit 76.
Since it uses, it has a simple structure. Then, the performance was changed within 5/60 degrees in the rotation angle, and the effect of enabling highly accurate control was observed. In this example, 1
Although it was possible to obtain three phases of sinusoidal waves with four cycles for rotation, the cycle and phases can be made smaller by changing the number of electrodes of the fixed body and the connection method.

[0007]

As described above, according to the present invention, it is possible to generate an accurate sine wave signal with respect to the rotation angle by using a combination of two fixed electrode shapes of the fixed body. Therefore, there is an effect of obtaining a small-sized and highly accurate capacitance type encoder.

[Brief description of drawings]

FIG. 1 is a side view showing a capacitance type encoder of the present invention.

FIG. 2 is a plan view showing an electrode shape of a fixed body of the present invention.

FIG. 3 is a plan view showing an electrode shape of a rotating body of the present invention.

FIG. 4 is a connection circuit diagram showing the connection relationship of the fixed body electrodes of the present invention.

FIG. 5 is a block diagram of a signal processing circuit used in the capacitance type encoder of the present invention.

FIG. 6 is a characteristic diagram showing output values in the present invention.

FIG. 7 is a sequence circuit diagram in which the capacitance type encoder of the present invention is applied to a servo motor.

FIG. 8 is a sequence circuit diagram in which a conventional encoder is applied to a servo motor.

[Explanation of symbols]

1: Fixed body 5: Encoder 11: Insulation plate 6: AC servomotor 12: Electrode 7: Motor control sequence circuit 121: E part electrode 71: Angle signal command 122: F part electrode 72: Differential circuit 123: G part electrode 73: control part 2: rotating body 74: multiplication circuit 21: insulating plate 75: power conversion circuit 22: electrode 76: pulse-
Sine wave conversion circuit 221: Circular part 77: R / D conversion circuit 222: Fan part 3: Rotating shaft 4: Signal processing part 41: AC power supply 42: Full wave rectification circuit 43: Smoothing circuit 44: Output terminal

Claims (3)

[Claims] 1. A fixed body comprising a fixed body having electrodes provided on the surface of an insulator in a circular shape at regular intervals, and a rotating body having electrodes provided on the surface of a disc-shaped insulator. The electrode of and the electrode of the rotating body face each other with a gap,
In a capacitance encoder that detects a rotational position by detecting a change in capacitance between both electrodes, the electrodes of the rotating body include a fan portion having a radius r and a fan portion having a radius R larger than the radius r. The electrodes of the fixed body are circular portions (E portion electrodes) having a radius r _E smaller than the fan radius r of the rotating body, and polar coordinates with the center of the circle as the origin. A portion surrounded by a curve f (θ), which has arcs with a radius r at a constant interval when the rotation angle is represented by θ, extends outward from one end of the arc and then returns to the other end (F) Part electrode) and the F part electrode, and a curve g which has arcs of the radius R at regular intervals and each arc extends inward from one end of the arc and then returns to the other end.
A capacitance type encoder comprising a portion (G portion electrode) surrounded by (θ). 2. The angle of the fan portion of the electrode of the rotating body is represented by polar coordinates with the center of the circle as the origin and n is 0, 1,
2 and 3, the angle θ is nπ + π / 4 to (n + 1)
It should be in the range of π / 2, and the curve f of the fixed body should be
In (θ), m is 0, 1, 2, 3, 4, 5, and θ is mπ /
When the range is from 3 to mπ / 3 + π / 4, [(R ²
−r ² ) sin4 (θ−m / 3) + r ² ] ^1/2 , and the curve g (θ) represents θ by (m−1) π / 3 + π /
From 2 to (m-1) π / 3 + 3π / 4,
^{[R 2 - (r 2 -R 2} ) sin4 {θ- (m-1) π /
3- [pi] / 2}] ^1/2 . The capacitance type encoder according to claim 1, wherein 3. The electrodes of the F portion of the fixed body are _arranged from F ₀ to F
A six to _5, the G unit electrode and six from G ₀ to G _5, F _0, G ₀ and F ₀ as a starting point, F _1, G _1, · ·
., F ₅ and G ₅ permutations are combined every 3 pieces to form 6 pairs, and the pairs are connected in parallel every 3 pieces. Capacitive encoder.