JPH0721418B2 - Displacement measuring circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a displacement measuring circuit that inputs a sensor output signal from a displacement detector and outputs a displacement measurement result, and particularly uses a capacitance type displacement sensor. The present invention relates to a displacement measuring circuit suitable for a small displacement measuring device.

[Prior Art] A displacement measuring device using a capacitance type sensor is small and has low power consumption. Therefore, a small displacement measuring device such as a digital micrometer, a caliper or a hide gauge is used. Often used in devices.

In a general capacitance type sensor, a plurality of supply electrodes are arranged at a predetermined pitch on a slider that moves on a scale, and pulse signals are supplied to these supply electrodes with a predetermined angle shift. Then, by utilizing the fact that the capacitance between these supply electrode and the detection electrode arranged on the scale changes depending on the relative position of the two, the phase information of the detection signal is extracted from the detection electrode side, The relative displacement with the slider is calculated. Further, usually, a receiving electrode is provided on the slider in a state of being insulated from the supply electrode, and a signal detected by the detecting electrode is taken out from the receiving electrode capacitively coupled thereto. As a result, in addition to the supply electrode and the reception electrode on the slider, an electronic circuit for supplying a pulse signal to these electrodes and detecting a sensor output, a liquid crystal display for displaying a measurement result, a displacement measurement of a key matrix, etc. A circuit can be mounted. Further, from the viewpoint of miniaturization of the sensor, there is an increasing number of cases where a 1-chip IC in which a digital circuit and an analog circuit are mixed is used as a main part of the displacement measuring circuit, and these circuits are mounted on a small board.

[Problems to be Solved by the Invention] However, such mixed analog and digital
In a displacement measurement circuit using an IC, digital signal noise is often placed on the analog input terminal of the IC connected to the reception electrode of the displacement sensor due to crosstalk from the digital circuit. Such crosstalk can be improved to some extent by designing the board pattern such as forming a shield pattern on the board. However, there is a problem in that the effective shield cannot be removed, the accuracy of the displacement measuring instrument is reduced, and the measured value becomes unstable and display flicker occurs.

The present invention has been made in view of such problems,
Stable and good measurement accuracy can be obtained even with a small board, and display flicker can be reduced, which can greatly increase the degree of freedom in board design, aiming to downsize the board and shorten the design period. An object of the present invention is to provide a displacement measuring circuit capable of performing the above.

[Means for Solving the Problems] A displacement measuring circuit according to the present invention includes an analog input circuit for inputting a sensor output signal from a displacement detector, a predetermined signal processing for the output of the analog input circuit, and a peripheral circuit. In a displacement measuring circuit constituted by disposing a digital circuit for outputting a digital signal for driving the circuit on the same substrate, the analog input circuit samples and inputs the sensor output signal in synchronization with an input synchronizing signal. And a digital circuit for changing the output state of the digital signal during a non-sampling period of the analog input circuit.

[Operation] According to the present invention, an analog input circuit for inputting the sensor output signal from the displacement detector is used as a switched capacitor type input circuit, and a digital signal output from a digital circuit arranged on the same substrate as this input circuit. The output state of the signal is changed during the non-sampling period of the analog input circuit. Therefore, even if noise from the digital signal line is added to the analog input signal line, the noise is generated during the period when the analog input signal is not captured, and the problem of crosstalk occurs. There is no.

Therefore, according to the present invention, it is possible to obtain stable and good measurement accuracy even with a small substrate, and to reduce display flicker, which can greatly increase the degree of freedom in substrate design. It is possible to reduce the size and shorten the design period.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an electrical configuration of a displacement measuring device according to an embodiment of the present invention.

This displacement measuring device comprises a capacitance type sensor 1 and a displacement measuring circuit 9 formed on the same substrate, and is mounted on a small measuring instrument such as a digital micrometer or a digital caliper. There is.

The displacement measuring circuit 9 is configured as follows. That is, the sensor output signal from the capacitance type sensor 1 is input to the switched capacitor type signal detection circuit 2 which is an analog input circuit. The switched capacitor type signal detection circuit 2 inputs the sensor output signal at a predetermined timing and outputs a phase signal indicating the displacement between the scale and the slider. This phase signal is input to the digital signal processing circuit 3. The digital signal processing circuit 3 constitutes a digital circuit together with a timing adjustment circuit 4 which will be described later, and calculates the measurement result based on the input phase signal.
Various digital signals are output in order to display the calculation result and supply the drive pulse to the capacitance type sensor 1. The timing of the digital signal is adjusted by the timing adjustment circuit 4, and the digital signal is supplied as a drive signal for the liquid crystal display device (hereinafter, referred to as LCD) 5, the key matrix 6, and the peripheral circuit 7. The key matrix 6 inputs information such as preset of display contents, hold and display switching to the digital signal processing circuit 3. In addition, the peripheral circuit 7
This is a circuit that has a power supply voltage drop detection function, an auto sleep function, a data output function, and the like.

Among the above circuits, the switched capacitor type signal detection circuit 2, the digital signal processing circuit 3 and the timing adjustment circuit 4 are integrated into one chip as a signal processing IC 8.

The capacitance type sensor 1 is configured, for example, as shown in FIG. The scale 11 is provided, for example, on a spindle of a micrometer. A slider 12 that moves with respect to the scale 11 is built in on the frame side. Plural supply electrodes 13 are formed on the slider 12 at a predetermined pitch. On the scale 11 side facing these supply electrodes 13, a plurality of detection electrodes 14 are arranged with a width and pitch that are, for example, three times the width and pitch of the supply electrodes 13.
Further, although different in the drawing, in reality, on the slider 12 side, a plurality of detection electrodes 14 and a receiving electrode 15 capacitively coupled,
The supply electrode 13 is arranged in an insulated state. For example, every two supply electrodes 13 are commonly connected to form three electrode groups. Drive signals R, S, and T obtained by chopping signals of three phases with a long period at high frequencies are supplied from the digital signal processing circuit 3 to these electrode groups. The signal received by the receiving electrode 15 is output to the switched capacitor type signal detection circuit 2 as a sensor output signal.

The switched capacitor type signal detection circuit 2 is, for example, a third
It is configured as shown in the figure.

That is, the analog input terminal 21 to which the sensor output signal from the capacitance type sensor 1 is input is connected to the output end of the reference voltage circuit 23 via the analog switch 22. Also,
The sensor output signal input from the analog input terminal 21 is
It is input to the non-inverting input terminal of the operational amplifier 26 of the voltage follower via the analog switch 24 and the capacitor 25, and is also input to the non-inverting input terminal of the operational amplifier 29 of the voltage follower via the analog switch 27 and the capacitor 28. Has been done. The analog switches 24 and 27 are on / off controlled by the SYNC1 and SYNC2 signals, respectively, and the analog switch 22 is on / off controlled by the DIS signal which is an input synchronization signal. As a result, a sample circuit is formed by the analog switches 22, 24, 27 and the capacitors 25, 28, and the input signal is alternately sampled at an appropriate timing.

The outputs of the operational amplifiers 26 and 29 are differentially combined by the MIX circuit 30,
The LPF (low pass filter) circuit 31 converts the analog signal into a smooth analog signal. This signal is input to the operational amplifier 32 which constitutes a comparator, and is compared there with a predetermined reference voltage Ref. And this operational amplifier 32
The output of is output as the phase signal CMP. The reference voltage circuit 23 outputs a predetermined reference voltage Ref. The timing pulse generation circuit 33 also generates and outputs a timing signal for turning on / off the analog switches 22, 24, 27 based on the clock signal CK.

Next, the operation of the displacement measuring device according to the present embodiment configured as described above will be described.

When the three-phase drive signals R, S, and T as shown in FIG. 4 are supplied to the supply electrode 13 of the electrostatic capacity type sensor 1, when the slider 12 is in the stopped state, it is synchronized with the drive signal and has a long cycle. A sensor output signal whose component is shifted by a phase determined by the relative position of the supply electrode 13 and the detection electrode 14 with respect to the drive signal is output from the reception electrode 15. When the slider 12 is driven, the relative position between the supply electrode 13 and the detection electrode 14 changes, so that the phase of the sensor output signal changes accordingly.

This signal is input to the switched capacitor type signal detection circuit 2.

FIG. 5 shows this switched capacitor type signal detection circuit 2
2 is a timing chart of.

While the DIS signal is at the high level, the input terminal 21 of the switched capacitor type signal detection circuit 2 is discharged,
Then, after the sensor output signal is captured, SYNC1, SY
With the NC2 signal, the sensor output signal is alternately sampled into the capacitors 25 and 28. Therefore, the operational amplifiers 26 and 29 output sampled values whose phases are different from each other by 180 °. These outputs are differentially combined by the MIX circuit 30 to remove common mode noise. Then, after being converted into a smooth sinusoidal analog value by the low-pass filter 31,
The operational amplifier 32 compares it with a predetermined reference voltage Ref and outputs it as a phase signal CMP.

When the phase signal CMP is output from the switched capacitor type signal detection circuit 2, the digital signal processing circuit 3
The displacement is calculated from the phase signal CMP, and the calculation result is output to the LCD 5 as display data. At this time, the timing adjustment circuit 4 adjusts the timing so that the change point of the drive pulse of the LCD 5 coincides with the non-sample period, as shown in FIG. This non-sampling period is SYNC1 or SYNC2.
This corresponds to the period from the end of the sampling by and the end of the next discharge period. The timing adjustment circuit 4 also applies to the drive pulses of the peripheral circuit 7 and the key matrix 6 output from the digital signal processing circuit 3.
Therefore, the timing is adjusted so that the output state of the digital signal changes only during the non-sampling period.

Therefore, according to the apparatus of the present embodiment, the output states of other digital signals do not change during the period in which the edge of the sensor output signal is detected, so that they are generated when these digital signals change. Noise does not affect the measurement result.

In the above embodiments, the switched capacitor type signal detection circuit 2 is taken as an example of the analog input circuit.
The configuration of the analog input circuit is not limited to this, and various circuits arranged in the input stage such as other switched capacitor type filters and demodulation circuits can be used.

Further, the drive signal for driving the displacement detector is not limited to the chopper drive signal as described above, but SIN wave, trapezoidal wave,
Other signals such as triangular waves and compression waves may be used, and especially 3
Nor is it limited to phases.

Further, the present invention can be applied not only to the capacitance type but also to a displacement measuring device using a photoelectric type sensor.

As described above, according to the present invention, the output state of the digital signal from the digital circuit is changed while the sensor output signal is not input from the displacement detector to the analog input circuit. Crosstalk due to signals will not be input to the analog input circuit. Therefore, stable and good measurement accuracy can be obtained even with a small board, and display flicker can be reduced, which can greatly increase the degree of freedom in board design, reduce board size, and reduce design time. It can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram of a displacement measuring device according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a configuration of a capacitance type sensor in the device, and FIG. 3 is a switched capacitor type signal detection circuit in the device. 4 is a waveform diagram showing a drive signal to the electrostatic capacity type sensor in the device, and FIG. 5 is a timing diagram showing the operation of the device. 1; Capacitance type sensor, 2; Switched capacitor type signal detection circuit, 3; Digital signal processing circuit, 4; Timing adjustment circuit, 5; Liquid crystal display, 6; Key matrix, 7; Peripheral circuit, 8; Signal processing IC, 9; Displacement detection circuit, 11; Scale, 12; Slider, 13; Supply electrode, 14; Detection electrode, 15; Reception electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01D 3/028 5/24

Claims (2)

[Claims] 1. An analog input circuit for inputting a sensor output signal from a displacement detector, and a digital circuit for performing a predetermined signal processing on the output of the analog input circuit and outputting a digital signal for driving a peripheral circuit. In the displacement measuring circuit arranged on the same substrate, the analog input circuit is a switched capacitor type input circuit for sampling and inputting the sensor output signal in synchronization with an input synchronizing signal, and the digital circuit. Is a circuit for changing the output state of the digital signal during a non-sampling period of the analog input circuit. 2. The displacement measuring circuit according to claim 1, wherein the displacement detector is a capacitance type displacement sensor.