JPS5937783B2 - Capacitive rotation detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitive rotation detection device that detects the rotation speed, rotation angle, etc. of a rotating body using changes in capacitance.

Conventional devices that utilize changes in capacitance, for example, configure a so-called variable capacitor by rotating a rotating electrode plate connected to the rotating shaft of the object to be measured relative to a fixed electrode plate facing across an air gap. It is known that a high-frequency signal is amplitude-modulated by a capacitance that changes depending on the rotation angle, and the amplitude-modulated high-frequency signal is amplified and then detected to obtain a pulse signal corresponding to the rotation speed.

However, the amount of change in capacitance in the above device is very small, and the stray capacitance of the variable capacitor itself is often larger.

Therefore, the amount of change in capacitance due to the rotation of the object to be measured is extremely small compared to the capacitance of the entire variable capacitor, and a major drawback is that malfunctions are easily caused by slight fluctuations in the power supply voltage, external noise, etc. It was hot. The present invention aims to eliminate the above-mentioned drawbacks, and as a means thereof, changes in capacitance value are performed by detecting a phase shift with respect to a reference pulse.One embodiment of the present invention will be described below with reference to the drawings. explain.

FIG. 1 shows a capacitance changing device according to the present invention, that is, a variable capacitor, in which 1 is a rotor, 2 is a stator, and 3 is a rotating shaft.

The rotor 1 is fixed to a rotating shaft 3, and rotates together with the rotating shaft 3, which is connected to an object to be measured and rotates. This rotor 1 is
A plurality of comb-shaped wing electrodes 1a are formed on the peripheral edge thereof. On the other hand, the stator 2 has a substantially ring-shaped shape, and wing electrodes 2a are formed in a one-to-one correspondence with the wing electrodes 1a of the rotor 1 from the periphery toward the center. In this embodiment, a so-called rotor-grounded variable capacitor in which the rotating shaft 3 is grounded is configured. Therefore, the capacitance of this variable capacitor is maximum when the wing electrodes 1a and 2a of the rotor 1 and stator 2 are facing each other, and is minimum when the wing electrodes 1a and 2a are farthest from facing each other. capacity. In this embodiment, wing electrodes 1a, 2
Since eight pieces a are formed each, a peak value of capacitance occurs every time the rotating shaft 3 rotates 45 degrees.

Therefore, if the number of wing electrodes is increased as much as possible, the frequency of occurrence of the peak capacitance value will increase, and so-called resolution can be improved. FIG. 2 shows a circuit of one embodiment of the device of the present invention, in which 0SC is a square wave oscillator, D1
and D2 is a diode for preventing reverse current from flowing; CDl is a first charging/discharging circuit;
It consists of a fixed resistor Rref and a trimmer capacitor Cref. CD2 is a second charging/discharging circuit, and includes a second fixed resistor RV and a variable capacitor Cv.

Here, the variable capacitor Cv corresponds to that shown in FIG. Q1 and Q2 are buffer circuits for waveform shaping, and these buffer circuits are ordinary C-MOS buffer circuits that switch at a predetermined threshold voltage determined by the input voltage. PD is a phase comparator and has two input terminals R1 and V and two output terminals U and D1. FF is the so-called R-S
It is a flip-flop and has two input terminals S and R and two output terminals Q and Q. The circuit of this embodiment has the above-mentioned configuration, and its operation will next be explained with reference to FIG. In addition, Fig. 3A to Fig. 3H
The waveforms shown in FIG. 2 are waveforms at portions A to H shown in FIG. The square wave oscillator 0SC supplies a square wave (FIG. 3A) with a predetermined pulse width to the subsequent circuit. 1st
The charging/discharging circuit CDl is charged by the pulse, and after the pulse is inverted to zero level, the first resistor Rref
and the trimmer capacitor Cref [FIG. 3B]. In addition, in FIG. 3, the discharge curve is shown as a straight line for convenience. The time constant in this embodiment is preferably determined as follows.

That is, the resistance Rre in the first charging/discharging circuit CDl
The resistance value of f and the resistance Rv in the second charging/discharging circuit CD2
On the other hand, the capacitance value of the trimmer capacitor Cref in the first discharge circuit CDl is set to be equal to the strain capacitance of the capacitor Cv in the second charging/discharging circuit CD2 and half of the capacitance change due to rotation. Set to sum. For example, if the strain capacitance of capacitor Cv is 40 pF and the capacitance change due to rotation is 5 pF, trimmer capacitor Cref
The capacitance value is 40pF+2.5pF=42.5pF.

Note that the resistance values of resistors Rref and Rv are square wave oscillator 0S.
It will be clear from FIG. 3B that it is determined based on the frequency of C. The output voltage of the first charge/discharge circuit CDl [Fig. 3B] is then supplied to the first buffer circuit Q1, and as shown in Fig. 3C, it is switched at a predetermined threshold level and kept constant. is shaped into a square wave with a pulse width of .

On the other hand, the pulses from the square wave oscillator 0SC are simultaneously supplied to the second charging/discharging circuit CD2 via the diode D2 to charge the second charging/discharging circuit CD2.

Here, the capacitor C in the second charging/discharging circuit CD2
Since the capacitance of v changes with the rotation of the object to be measured, the discharge power curve after the pulse from the square wave oscillator 0SC is reversed to zero level varies depending on the rotation angle of the object to be measured. Become. In other words, the object to be measured is now rotating, and the change in capacitance of the variable capacitor Cv due to this rotation is shown in Figure 3 P.
If the capacitance changes as shown in the diagram (only the capacitance change due to rotation is shown), then at the peak of the capacitance value, the second discharge circuit C
The time constant at D2 becomes maximum and the slope of the discharge curve becomes gentle, so that the output voltage waveform of the second discharge circuit CD2 is observed as shown in FIG. 3D. The waveform of FIG. 3D is supplied to the second buffer circuit Q2, where it is switched at a predetermined threshold level as in the case of the first buffer circuit Q1, and the variable capacitor Cv as shown in FIG. A square wave with a pulse width corresponding to the capacitance change is obtained. The outputs of the two square waves thus obtained, ie, the waveforms shown in FIG. 3C and FIG. 3E, are supplied to the next stage phase comparator PD.

The phase comparator PD is sensitive to the falling edge of the two output pulses and operates as follows. That is, its output end U
1, as shown in FIG. 3F, a second buffer circuit Q
The output is generated by the fall of the pulse from the first buffer circuit Q1 (FIG. 3E), and is restored by the fall of the pulse from the first buffer circuit Q1 (FIG. 3C). On the other hand, as shown in FIG. 3G, the output terminal D1 generates an output due to the fall of the pulse of the first buffer circuit Q1 [FIG. 3C], and the second buffer circuit Q2 [FIG. Figure 3E]
It is designed to be restored by the falling edge of the pulse.
Therefore, if the falling time of the pulse shown in FIG. 3E is earlier than the falling time of the pulse shown in FIG. An output signal is obtained at the output terminal D1, and a change in capacitance value can be detected by the lead or lag of the phase. The above-mentioned two pulse signals obtained in the phase comparator PD are respectively supplied to terminals S and R of a known R-S flip-flop FF, and finally output to the output terminal Q as shown in FIG. 3H. One pulse signal corresponding to one capacitance change is obtained.

As described above, the present invention provides first and second charging/discharging circuits CD that are charged and discharged by the output pulses of the square wave oscillator 0SC.
l, CD2 is provided, and the rotating shaft 3 of the variable capacitor Cv in the second charging/discharging circuit CD2 is related to the object to be measured so that the time constant of its discharge is changed based on the rotation angle,
In addition, the discharge time constant in the first charging/discharging circuit CDl is set to approximately the middle between the maximum value and the minimum value of the discharge time constant of the second charging/discharging circuit CD2, and Since capacitance value changes are detected based on the phase difference of the obtained pulses, capacitance changes are reliably detected even when the amount of capacitance change in variable capacitor Cv is extremely small compared to the total capacitance of variable capacitor Cv including the stray capacitance. It has the remarkable effect of being able to

In this embodiment, the first charging/discharging circuit CDl is provided to obtain the reference pulse (FIG. 3C), but the present invention is not limited to this, and it is possible to obtain a pulse of a predetermined width in synchronization with the oscillator 0SC. For example, it may be replaced with a circuit such as a monostable multivibrator. Furthermore, if necessary, a circuit whose unit is the circuit shown in FIG.
, the reference pulse generation circuit consisting of the first buffer circuit Q1 may be used in common and a plurality of units may be arranged in parallel to obtain various detection signals. It goes without saying that design changes are possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the shape of the variable capacitor in the present invention;
FIG. 2 is a circuit diagram of one embodiment of the present invention, and FIGS.
Figure H is a diagram showing the waveforms of each part in the circuit diagram of Figure 2,
FIG. 3P is a diagram for explaining the state of one capacitance change of the variable capacitor shown in FIG. 1. 1... Rotor, 2... Stator, 3...
... Rotation axis, 0SC ... Square wave oscillator,
CDl...First charging/discharging circuit, CD2...
...Second charging/discharging circuit, Q,...First buffer circuit, Q2...Second buffer circuit, Cv.
...Varicon, PD...Phase comparator, F
F...R-S flip-flop.

Claims (1)

[Claims] 1 A reference pulse generation circuit that generates a reference pulse of a predetermined width based on the output pulse of a square wave oscillator, and a reference pulse generation circuit that repeats charging and discharging by the output pulse of the square wave oscillator, and the time constant during discharge is equal to that of the measured object. a charging/discharging circuit configured to vary depending on the rotation angle; a buffer circuit generating a pulse having a pulse width corresponding to a discharge time constant based on a discharge curve in the charging/discharging circuit; and the reference pulse and the discharge time. and a phase comparator for detecting a phase difference between the pulse width of the reference pulse and the pulse width corresponding to the discharge time constant, the pulse width of the reference pulse being between the maximum value and the minimum value of the pulse width corresponding to the discharge time constant. A capacitive rotation detection device characterized in that it is configured to perform settings.