JP2967413B1 - Rotary differential capacitive angle converter - Google Patents

Abstract

An object of the present invention is to provide a rotary differential capacitance type angle converter for detecting a rotation angle θ with high accuracy without using a large amplitude AC signal source or feedback control for temperature compensation. SOLUTION: A ring-shaped fixed electrode 1 arranged on a fixed portion so as to be concentric with a rotating shaft 4 is opposed to the fixed electrode 1 while keeping an appropriate space, and four electrodes 2 are arranged on the same plane.
a, 2b, 2c, and 2d are arranged in a ring shape, and are fixed to the four-divided electrode 2 in which the opposed electrodes 2a, 2b, 2c, and 2d are electrically connected to each other, and insulated from the rotating shaft 4 Then, a pair of electrodes 2a, 2
c or a shape that can cover only the electrodes 2b and 2d, and is constituted by a rotating blade 3 that rotates in the space between the fixed electrode 1 and the four-divided electrode 2. Accordingly, when one of the capacitances of the two capacitors C _a and C _b composed of the fixed electrode 1 and the four-divided electrode 2 increases in proportion to the angle, the other decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary differential capacitance type angle converter for accurately detecting an angular position of a mirror or the like directly attached to a rotary shaft of a motor or the like.

[0002]

2. Description of the Related Art Conventionally, a rotary differential capacitance type angle converter of this type will be described with reference to FIGS. 11 and 12. As shown in FIG. Electrodes 2a, 2b, 2c, and 2d are arranged in a ring.
It is composed of a split electrode 2 and a butterfly-shaped rotary blade 3 attached to a rotary shaft 4.
As shown in FIG. 13, the opposing electrodes 2a and 2c and the electrodes 2b and 2d are electrically connected.
Now, the capacitance between the electrodes 2a, 2b, 2c, 2d is represented by C2a, C2a,
Expressed as 2b, C2c and C2d, the electrical equivalent circuit of this angle converter can be expressed by two capacitors Ca and Cb having the fixed electrode 1 as a common terminal.

[0003]

(Equation 1)

[0004]

(Equation 2) Normally, a dielectric having a relative dielectric constant of about 6 to 7 is used for the rotating blade 3, so that the effective dielectric constant between the electrodes 2a, 2b, 2c, and 2d changes with the rotation of the rotating blade 3, and Ca and Cb are changed.
When the angle of the rotary blade 3 is represented by θ with respect to the angle when the angles are equal, Ca and Cb can be written as the following equations.

[0005]

(Equation 3)

[0006]

(Equation 4) Here, k is a proportional constant, and C0 is Ca at the reference angle position.
And the capacity of Cb.

From the equations of Equations 3 and 4,

[0008]

(Equation 5) Therefore, if Ca−Cb is electrically detected, a signal proportional to the rotation angle θ can be obtained. Conventionally, a diode direct detection circuit shown in FIG. 18 is used for this detection. In this circuit, the AC power supply VS applied to the common terminal of Ca and Cb is represented by VS as amplitude and ω as angular frequency.

[0009]

(Equation 6) And the CR of the rectification detection circuit is

[0010]

(Equation 7) If the time constant is selected so as to satisfy the following, the detection outputs Va and Vb can be regarded as DC voltages.

Under this condition, the DC current Ia flowing through the resistor R becomes equal to the average current flowing through the capacitor Ca, so that the following relationship is obtained with reference to FIG.

[0012]

(Equation 8) However,

[0013]

(Equation 9) Where VD is the forward voltage drop of diode D. Number 8
By solving the equation

[0014]

(Equation 10) Is obtained. The same can be derived for Vb, and the result is an expression obtained by replacing Ca in expression 10 by Cb. However, f = ω / 2π.

[0015]

However, the conventional rotary-differential-capacitance type angle converter requires that the detection voltage of the equation (10) be proportional to Ca.

[0016]

[Equation 11] It is necessary to Also, the forward voltage drop of the diode varies logarithmically with the flowing current and further decreases with temperature. In order to make these effects sufficiently negligible and to further increase Va sufficiently under the equation (11), a voltage of 100 V or more is required as VS. A transformer is necessary to generate such a high voltage, and an angle shield must be provided with an electromagnetic shield or guard ring to prevent unnecessary radio wave radiation from the transformer.
This complicates the configuration of the angle converter. Further, in order to prevent discharge due to high voltage, it is necessary to use a dielectric material for the rotating blades and widen the distance between the electrodes. As a result, Ca and Cb become extremely small, so that a change in capacitance due to rotation is necessarily reduced. Therefore, it is necessary to pay close attention to the configuration of the angle converter so as to minimize the influence of the parasitic capacitance and the electric field at the electrode end, and the configuration is inevitably complicated. Furthermore,
Ca and Cb also vary with temperature, and their temperature coefficients are γ
given that,

[0017]

(Equation 12)

[0018]

(Equation 13) It is expressed as Here, ΔT is a temperature change from the reference temperature. In this case,

[0019]

[Equation 14] Therefore, it is necessary that the frequency or amplitude of the AC signal applied to Ca and Cb have a temperature dependency of 1 / (1 + γΔT) so that the detection outputs Va and Vb do not change with temperature. Become. Conventionally, this temperature compensation is
+ Cb is detected and fed back to the AC signal source to control its amplitude, or a temperature change is detected by a separately provided capacitor and the frequency or amplitude of the AC signal source is controlled by its signal. However, in these feedback controls, the configurations of the signal processing circuit and the angle converter become complicated, and when high-speed response is required, instability is caused.

As is apparent from the above description, the reason why a large-amplitude AC signal source must be used is a circuit system in which the currents flowing through the capacitors Ca and Cb are directly detected by diodes. Ratio calculation in the AC frequency domain applied to the two capacitors instead of the DC domain

[0021]

(Equation 15) I do. Alternatively, the problem can be solved by a method of performing the above-described ratio calculation by a switched capacitor technique. The ratio operation cancels out the temperature changes of the two capacitors, but the most important in this solution is to find a signal processing circuit in which the parasitic capacitance between the ground and the ground necessarily associated with the angle converter does not affect the ratio operation. It is in.

Therefore, an object of the present invention is to provide a rotation angle difference provided with a signal processing circuit for detecting the rotation angle θ with high accuracy without using feedback control for temperature compensation and a correction circuit for eliminating parasitic capacitance. An object of the present invention is to provide a dynamic capacity type angle converter.

[0023]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a rotary differential capacitance type angle converter according to the present invention has a ring-like shape disposed on a fixed portion so as to be concentric with a rotation axis. A fixed electrode, a four-divided electrode in which four electrodes are arranged in a ring shape on the same plane, facing the fixed electrode while keeping a space as appropriate, and opposite electrodes are electrically connected to each other; A rotating blade that is fixed to the rotating shaft in an insulated state and has a shape capable of covering only one set of the four-divided electrodes, and that rotates in a space between the fixed electrode and the four-divided electrodes; When one of the capacitances of the two sets of capacitors Ca and Cb composed of the fixed electrode and the four-divided electrode increases in proportion to the angle of the rotation axis in accordance with the rotation of the rotary blades , The rotary differential capacitance type angle having the feature of decreasing the other In the power converter, each terminal of the capacitor is connected to the output terminal of the operational amplifier or the inverting input terminal of the operational amplifier which is a virtual ground so that the parasitic capacitor such as stray capacitance is not affected. , And the other capacitor constitutes a differentiating circuit as a differentiating capacitor. The output of the differentiating circuit is inverted in polarity and fed back to the integrating circuit to obtain (Ca−Cb) / (Ca + C).
b) a signal processing circuit for outputting a voltage proportional to the signal processing circuit;

Further, a ring-shaped fixed electrode arranged concentrically with the rotation axis on the fixed portion, and opposed to the fixed electrode while keeping an appropriate space, four electrodes are formed in a ring on the same plane. And the electrodes facing each other are electrically connected to each other, and are fixed to the rotary shaft in an insulated state so that only one set of the four-divided electrodes can be covered. And two sets of capacitors each including a fixed blade and the four-divided electrode in accordance with the rotation of the rotary blade. When the capacitance of Ca and Cb increases in proportion to the angle of the rotation axis and one of them increases, the other decreases, and is not affected by parasitic capacitance such as stray capacitance. like,
The common terminal of the two capacitors is connected to the inverting input terminal of the operational amplifier that is a virtual ground, and the other terminals are alternately connected to the constant voltage source or the output terminal of the operational amplifier via a switch, Two sets of capacitors Ca and C
b is charged with voltages of opposite polarities and then connected in parallel to each other by connecting capacitors Ca and Cb to output a voltage proportional to (Ca−Cb) / (Ca + Cb) as angle information. It has a circuit.

FIG. 1 shows a circuit configuration for performing signal processing in the AC frequency domain according to the present invention. In FIG. 1, a block 11 includes two capacitors Ca and Cb of the rotary differential capacitive angle converter of the present embodiment. , A unity gain inverting amplifier, a block 10 is an adder, a block 12 is a subtractor, an AC signal source is applied to a terminal 9, and an operation result is output from a terminal 14. Is output.

Now, the AC voltage applied to the terminal 9 is Vs,
If the output voltage of the terminal 14 is Vo and the analysis in the frequency domain is performed,

[0027]

(Equation 16) Is obtained. By rearranging the above equation for Vo and substituting the equation of equation 16,

[0028]

[Equation 17] The amplitude of the output signal does not depend on the temperature change of the capacitors Ca and Cb but is proportional to the rotation angle θ. Therefore, the output signal is

[0029]

(Equation 18) When this output signal is detected by the synchronous detection circuit shown in FIG. 7, the detection output Eo becomes

[0030]

[Equation 19] And becomes a DC voltage proportional to θ.

FIG. 8 is a principle diagram of the present embodiment for performing the operation of the expression (15) by the switched capacitor technique. The switches 43 and 45 are analog switches which are opened and closed by a two-phase clock φ shown in FIG. , A switch 44 is an analog switch which is opened and closed by a two-phase clock -φ shown in FIG. 9, Ca and Cb are two capacitors of a rotary differential capacitance type angle converter, a terminal 42 is a DC voltage source 48, and a terminal 46 is a DC voltage source. The voltage is connected to a DC voltage source 49 having the same voltage as that of the voltage source 48 and having the opposite polarity.

Assuming that the voltage of the DC voltage source 42 is Er and the voltage of the DC voltage source 46 is -Er, Ca is charged to + Er and Cb is charged to -Er at the φ clock of FIG. At the next -φ clock, the analog switches 43 and 45 are turned off, the analog switch 44 is turned on, the two capacitors are connected in parallel, and the output E47 at that time is

[0033]

(Equation 20) And a voltage proportional to the angle θ is obtained without depending on the temperature change of Ca and Cb.

[0034]

FIG. 2 shows an embodiment of the present invention shown in FIG. 1. In FIG. 2, an integrating and differentiating circuit block 11 shown in FIG. 1 is an integrating circuit with an operational amplifier 15 and a differentiating circuit with an operational amplifier 16. The one unit gain inverting amplification block 13 is realized by an inverting amplifier using an operational amplifier 17. Further, the integration circuit of the operational amplifier 15 also functions as the addition block 10 in FIG. 1, and the integration circuit of the operational amplifier 16 also functions as the subtraction block 12 in FIG. 1, so that the configuration is simplified.
As yet another feature, the common terminal of the two capacitors of the rotary differential capacitive angle converter has an operational amplifier 1 that can be regarded as an ideal voltage source.
5, the other two electrodes are connected to the operational amplifiers 15 and 1 respectively.
6 are connected to the six virtual ground points, the parasitic capacitances necessarily associated with the three electrodes of the rotary differential capacitive angle converter do not affect the operation.

FIG. 10 shows an embodiment of the present invention shown in FIG. 8. Each analog switch of this circuit is driven by a two-phase clock φ and -φ shown in FIG. Thus, a negative feedback circuit of the operational amplifier 50 is formed, and the inverting input terminal is set to a virtual ground point. At this time, one capacitance Ca of the rotary differential capacitance type angle converter is + E
r and the other capacitor Cb is charged to -Er. Next -φ
At the time of clocking, the capacitors Ca and Cb are both connected to the output terminal of the operational amplifier 50. The operation of Expression 29 is performed by the operation of one cycle. Also in the present embodiment,
The common electrode (fixed electrode 1) of the two capacitors is connected to the operational amplifier 50.
, The other two electrodes (terminals 5 and 6 in FIG. 13) are connected to the voltage sources 48 and 4 at the time of φ clock.
9. At the time of the -φ clock, since it is connected to the output terminal of the operational amplifier 50 which can be regarded as an ideal voltage source, it is not affected by the parasitic capacitance inevitably attached to the three electrodes of the rotary differential capacitance type angle converter. Is calculated.

[0036]

According to the signal processing mode of the present invention, without controlling the frequency or amplitude of the high-frequency sine signal applied to the rotary differential capacitance type angle converter, the temperature change of the two capacitors of the converter can be controlled. Accurate offset angle information can be obtained.

Further, according to the signal processing mode of the present invention, the rotation angle can be detected with high accuracy without being affected by the parasitic capacitance between the three capacitance electrodes of the rotary differential capacitance type angle converter and the ground. it can. Further, since the signal applied to the rotary differential capacitance type angle converter is a high-frequency sine wave signal having an amplitude of about 10 V or a DC voltage of about 10 V, the distance between the electrodes can be made much smaller than before, and the rotating blades Since a metal piece or a processed printed circuit board can be used for 3, a rotary differential capacitance type angle converter having extremely high angle conversion sensitivity can be realized. These features of the present invention are extremely useful in practical use, and can be widely applied to a scanner or the like that scans a laser beam with a mirror attached to a rotating shaft of a motor.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a signal processing form in an AC frequency domain of a rotary differential capacitance type angle converter according to the present invention.

FIG. 2 is a circuit diagram of the signal processing mode of FIG.

FIG. 3 is a block diagram of a synchronous detection circuit.

FIG. 4 is a principle diagram of a signal processing mode by a switched capacitor technique.

FIG. 5 is a waveform diagram of a two-phase clock for driving the analog switch of FIG. 4;

FIG. 6 is a circuit diagram of the signal processing mode of FIG. 4;

FIG. 7 is a perspective view of a rotary differential capacitive angle converter with the signal processing form of the present invention in mind.

8 is a vertical sectional front view of the rotary differential capacitive angle converter shown in FIG. 7;

FIG. 9 is a connection diagram of the quadrant electrode of FIGS. 7 and 8;

FIG. 10 is a signal processing circuit of a conventional rotary differential capacitance type angle converter.

FIG. 11 is a waveform diagram showing a relationship between a sine wave applied to a conventional rotary differential capacitance type angle converter and an output voltage.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Fixed electrode 2 4 divided electrode 2a electrode 2b electrode 2c electrode 2d electrode 3 Rotating blade 4 Rotating axis 5 terminal 6 terminal 10 Addition block 11 Integral / differential circuit 12 Subtractor 13 Unit gain inverting amplifier 14 Terminal 15 Operation amplifier 16 Operation amplifier 17 Operation Amplifier 18 terminal 37 signal processing circuit 38 synchronous pulse generation circuit 39 analog switch 40 low-pass filter 41 terminal 42 terminal 43 analog switch 44 analog switch 45 analog switch 46 terminal 47 terminal 48 DC voltage source 49 DC voltage source 50 operational amplifier 51 terminal 52 terminals 53 terminals 54 Capacity

Claims (2)

(57) [Claims] 1. A ring-shaped fixed electrode arranged on a fixed portion so as to be concentric with a rotation axis, and opposed to the fixed electrode while keeping an appropriate space, and four electrodes are formed in a ring on the same plane. And the electrodes facing each other are electrically connected to each other, and are fixed to the rotary shaft in an insulated state so that only one set of the four-divided electrodes can be covered. And two sets of capacitors each including a fixed blade and the four-divided electrode in accordance with the rotation of the rotary blade. When the capacitance of Ca and Cb increases in proportion to the angle of the rotation axis and one of them increases, the other decreases, and is not affected by parasitic capacitance such as stray capacitance. So that each terminal of the capacitor The output terminal of the calculation amplifier or,
Connected to the inverting input terminal of the operational amplifier, which is a virtual ground,
One capacitor constitutes an integrating circuit as an integrating capacitor, and the other capacitor constitutes a differentiating circuit as a differentiating capacitor. The output of the differentiating circuit is inverted in polarity and fed back to the integrating circuit to obtain (Ca−C
b) A rotary differential capacitance type angle converter comprising a signal processing circuit for outputting a voltage proportional to / (Ca + Cb). 2. A ring-shaped fixed electrode arranged concentrically with a rotation axis on a fixed portion, and opposed to the fixed electrode while keeping a suitable space, and four electrodes are formed in a ring on the same plane. And the electrodes facing each other are electrically connected to each other, and are fixed to the rotary shaft in an insulated state so that only one set of the four-divided electrodes can be covered. And two sets of capacitors each including a fixed blade and the four-divided electrode in accordance with the rotation of the rotary blade. When the capacitance of Ca and Cb increases in proportion to the angle of the rotation axis and one of them increases, the other decreases, and is not affected by parasitic capacitance such as stray capacitance. As shown in FIG. The terminal is connected to the inverting input terminal of the operational amplifier, which is a virtual ground, and the other terminals are alternately connected to the constant voltage source or the output terminal of the operational amplifier via switches, so that two sets of capacitors Ca, Switched capacitor signal processing for charging Cb with equal voltages of opposite polarities and then connecting capacitors Ca and Cb in parallel to output a voltage proportional to (Ca-Cb) / (Ca + Cb) as angle information. A rotary differential capacitance type angle converter comprising a circuit.