JPH04323513A - Displacement measurement device - Google Patents

Abstract

PURPOSE:To drastically improve reliability of a measured value by accurately detecting excessive speed limit even when a moving element of a detector is abruptly moved. CONSTITUTION:A phase signal (c) output from a demodulation circuit 3 is input into a cycle measurement part 7, by which a cycle Tn from an initial starting edge of the phase signal (c) to the next starting edge, for example, is measured. The measured value is temporarily stored in a register 8. A current cycle measured by the cycle measurement part 7 and a cycle one measurement cycle before that is stored in the register 8 are supplied to a calculation circuit 9, and sliding acceleration of a moving element of a detector 1 is detected based on the degree of change in both cycles. It is estimated from the detected acceleration that the moving element of the detector 1 exceeds a fixed speed limit, by the calculation circuit 9, and an overspeed alarm signal is output to a display part 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device using a displacement sensor applied to small measuring instruments such as digital calipers, digital micrometers, and height gauges.

0002

[Prior Art] Small displacement measuring devices such as digital calipers, digital micrometers, and height gauges that display measured values on liquid crystal display devices are generally low power consumption types that use capacitive displacement sensors. It is widespread. A capacitive displacement sensor has a large number of electrodes arranged on a fixed element such as a main scale and a movable element such as a slider that moves relative to the main scale. The amount of displacement is detected by extracting a signal of periodic capacitance changes occurring between patterns.

In this type of displacement sensor, the limit speed of the movable element is determined by the scale pitch and the frequency of the transmitted signal. Therefore, if the movable element moves at a speed exceeding this limit speed, an erroneous measurement value will be obtained. Therefore, conventionally, as shown in Fig. 2, the period of the phase signal obtained from the demodulated signal of the sensor is detected as the average sliding speed of the movable element of the displacement sensor, and this period is longer than a certain period. At certain points, a warning signal was output to notify the driver of excessive speed.

0004

[Problems to be Solved by the Invention] However, in such a conventional excessive speed detection method, as shown in FIG.
If the movable element of the sensor is suddenly moved and the acceleration is very large, the moving speed of the movable element will exceed the limit speed before the period of the phase signal reaches the limit period. For this reason, there is a problem in that erroneous measurements are not accurately detected and the reliability of the measured values is reduced.

[0005] The present invention has been made to solve these problems, and even when a moving element moves rapidly, it is possible to accurately detect an excess of the limit speed, thereby increasing the reliability of measured values. The present invention aims to provide a displacement measuring device that can significantly improve performance.

[0006]

[Means for Solving the Problems] A displacement measuring device according to the present invention includes a displacement sensor that outputs a detection signal whose phase changes depending on the amount of displacement of a movable element with respect to a fixed element, and a displacement sensor that outputs a detection signal whose phase changes depending on the amount of displacement of a movable element with respect to a fixed element. a demodulation circuit that demodulates and outputs a phase signal; a period detection means that detects the period of the phase signal output from the demodulation circuit; and a period detection means that detects the period of the phase signal output from the demodulation circuit; The vehicle is characterized by comprising an acceleration detection means for detecting the acceleration of the vehicle, and an alarm output means for outputting an overspeed warning based on the acceleration detected by the acceleration detection means.

[0007]

[Operation] According to the present invention, the period of the phase signal output from the demodulation circuit is detected by the period detecting means, and the moving acceleration of the movable element is detected from the change in the detected period. It is possible to predict in advance that an element will exceed the speed limit, and a warning can be issued at that point. Therefore, according to the present invention, even if the movable element moves suddenly, exceeding the limit speed can be accurately detected, and the reliability of measured values can be significantly improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of a displacement measuring device according to an embodiment of the present invention. This displacement measuring device is applied to small scale devices such as digital calipers, digital micrometers, and digital height gauges.

That is, the detector 1 is, for example, a capacitive incremental type or absolute type displacement sensor. This detector 1 has a large number of electrodes arranged on a fixed element such as a main scale, and a movable element such as a slider that faces the main scale and is movable. As the movable element moves relative to the fixed element, the electrode pattern is The amount of displacement is detected by extracting a signal of periodic capacitance changes that occur between the two. This detector 1 receives a transmission signal a containing a sine wave component having a specific phase and a predetermined cycle from a detector driving unit 2.
is supplied. The detector 1 outputs a detection signal b containing phase information determined by the displacement of the movable element relative to the fixed element and the transmission signal a. This detection signal b is input to the demodulation circuit 3. The demodulation circuit 3 demodulates the detection signal b to generate a demodulated signal as shown in FIG. 2, then shapes the waveform of this signal and outputs a phase signal c as shown in FIG. The phase signal c is input to the phase detection section 4. The phase detection section 4 detects the phase of the rising or falling edge of the phase signal c. The phase detected by the phase detection section 4 is supplied to a counting section 5, where it is counted and the amount of displacement is determined. The determined displacement amount is displayed on a display unit 6 such as a liquid crystal display device.

On the other hand, the phase signal c output from the demodulation circuit 3 is also input to the period measurement section 7. Period measurement section 7
measures the period Tn from one rising edge to the next rising edge of the phase signal c, for example. The measured value is stored in the register 8 only for one measurement cycle. Then, the current period Tn measured by the period measuring section 7 and the period Tn-1 one measurement cycle before stored in the register 8 are supplied to the arithmetic circuit 9, and based on the degree of change in both periods, the detector A sliding acceleration of the movable element is detected. In addition, the arithmetic circuit 9
It is predicted from the detected acceleration that the movable element of the detector 1 will exceed a predetermined speed limit, and an overspeed warning signal is output to the display section 6. The display unit 6 outputs a warning by sound or display to notify of erroneous measurement.

Here, if the theoretical limit speed of the movable element of the detector 1 is v0, the sliding speed is v, and the period of the phase signal c when the movable element is stationary is T0, then the phase signal c when the movable element is moving is The period T can be expressed by the following equation 1.

0012

[Math 1] T=T0/(1-v/v0)

[0013]
Now, if an overspeed warning signal is to be output at, for example, 80% of the limit speed, then T=5T0. With this device,
Two consecutive cycles are always measured, such as the cycles Tn-1 and Tn of the phase signal c in Fig. 2, and the acceleration is calculated from the degree of change, and then the movable element of the detector 1 exceeds the limit speed. I try to predict things. That is, the speed in the next cycle when detecting the cycle Tn is vn+1
Then, this speed vn+1 can be obtained by calculation as shown in Equation 2 below.

[0014]

[Math. 2] vn+1 /v0 =1+T0 /Tn-1 -2・T
0/Tn

[0015] In actual detection, it is not necessary to perform such calculations strictly; instead, the combinations of Tn-1 and Tn for outputting an alarm are divided into several patterns, and the actual measured values are It is only necessary to decide whether to issue a warning depending on whether the combination of the above corresponds to these patterns or not.

[0016]

As described above, according to the present invention, the moving acceleration of the movable element is detected from the change in the period of the phase signal output from the demodulation circuit, and from this moving acceleration, the moving element exceeds the limit speed. Since the system predicts this situation in advance and outputs a warning, it is possible to accurately detect exceeding the speed limit even when moving elements move rapidly, greatly improving the reliability of measured values. be able to.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram for explaining the operation of the displacement measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Detector, 2...Detector drive part, 3...Demodulation circuit, 4...Phase detection part, 5...Counter part, 6...Display part, 7...Period measurement part,
8...Register, 9...Arithmetic circuit.

Claims (1)

[Claims] 1. A displacement sensor that outputs a detection signal whose phase changes depending on the amount of displacement of a movable element with respect to a fixed element; a demodulation circuit that demodulates the detection signal from this displacement sensor and outputs a phase signal; a period detection means for detecting the period of the phase signal output from the demodulation circuit; an acceleration detection means for detecting the acceleration of the movable element relative to the fixed element from a change in the period detected by the period detection means; 1. A displacement measuring device comprising: warning output means for outputting an overspeed warning based on the acceleration detected by the means.