JP2548495B2 - Displacement measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring apparatus applied to a small measuring instrument such as a digital caliper, and more particularly to an apparatus capable of measuring an absolute displacement of a movable element with respect to a fixed element of a displacement sensor. And a so-called absolute type displacement measuring device.

[0002]

2. Description of the Related Art As a small measuring instrument such as a digital caliper, a digital micrometer or a height gauge for displaying a measured value on a liquid crystal display device or the like, it is promising to use a capacitance type displacement sensor. In a capacitance type displacement sensor, a large number of electrodes are arranged on a fixed element such as a main scale and a movable element such as a slider which moves relative to the fixed element, and the electrodes are moved along with the movement of the movable element with respect to the fixed element. The displacement amount is detected by extracting a signal of periodic capacitance change generated between patterns.

Such displacement sensors are classified into two types, an incremental type and an absolute type, depending on the form of the output signal. The former measures the displacement amount by continuously measuring the periodic signal generated by the movement of the slider from the reference position. The latter is a coarse scale signal for coarse displacement detection, depending on the shape of the electrode pattern.
It is possible to output each periodic signal of the intermediate scale signal for detecting the intermediate displacement amount and the fine scale signal for detecting the fine displacement amount, and by combining the phase information of these periodic signals, the absolute element of the movable element can be detected. The displacement amount (position) can be detected.

There are two types of absolute value synthesizing errors in the absolute type displacement measuring device for performing phase detection and synthesizing as described above. The first is when the device itself is defective.
In this case, it is necessary to reliably display an error on the display. Secondly, although the device itself is not defective, an absolute value synthesis error occurs in operation. This is because the periodic signal containing the phase information obtained by demodulating the output signal from the displacement sensor can obtain the phase information only at that edge, and the data can be obtained only at one period interval of the signal. Because it is not possible. That is, there are cases in which the phases of the fine scale signal, the medium scale signal, and the coarse scale signal are naturally different, and there is a time difference between the phase information of one scale signal and the phase information of another scale signal. . When there is no relative movement of the slider with respect to the main scale (hereinafter simply referred to as sensor movement), that is, when the sensor is stopped, even if each scale information is not obtained at the same timing, there is no problem because it is information at the same scale position. . However, since the scale information at different timings becomes the information of different scale positions during the movement of the sensor, there occurs a situation in which the phase data cannot be combined when the sensor moves at a high speed.

Further, although the drive signal used for the capacitance type displacement sensor has a constant frequency, the effect equivalent to that of the frequency modulation is produced by the change in the facing relationship between the transmitting electrode and the receiving electrode due to the displacement sensor movement, When the sensor moves, the period of the demodulated periodic signal changes. The influence of this periodic fluctuation increases in the order of the fine scale signal, the intermediate scale signal, and the coarse scale signal. This change in cycle becomes a factor that further increases the difference in the phase data extraction timing from each scale signal, that is, the difference in the measurement position at each scale, and therefore a synthetic error occurs when the sensor moves at high speed.

[0006]

Among the composite errors in the above-mentioned absolute type displacement measuring device, it is desirable to clearly display the error due to the device failure.
On the other hand, the composition error caused by the high-speed movement of the sensor is not a defect of the apparatus itself but has the property of being resolved when the sensor movement becomes slow or stops, and therefore, it is not desirable to display the error if possible. It is possible to distinguish between the error due to device failure and the error due to sensor movement and display the error only for the former, but in order to distinguish between the two, a special detection circuit must be provided, which increases the cost of the device. Invite. The present invention, without increasing the cost,
It is an object of the present invention to provide an absolute displacement measuring device in consideration of error display so as to deal with the above-mentioned two kinds of combined errors.

[0007]

DISCLOSURE OF THE INVENTION A displacement measuring device according to the present invention is a displacement sensor that outputs an output signal according to the relative positional relationship of a movable element with respect to a fixed element, processes the output signal of this displacement sensor, and Demodulating means for obtaining at least two types of displacement amount detecting periodic signals of coarse scale and fine scale having phase information at the edge, and detecting phase information from the periodic signal obtained by this demodulating means, Phase detection means for obtaining the phase data of the fine scale, synthesis means for synthesizing the phase data obtained by the phase detection means to obtain the absolute displacement amount of the movable element with respect to the fixed element, and the synthesis means Further, it is characterized in that it is provided with a display means for digitally displaying the absolute displacement amount and displaying an error display only in the least significant digit when an error occurs.

[0008]

The composite error when the sensor is stopped is due to a defect in the device itself. In this case, the error signal is given only to the least significant digit of the display to display, for example, "E". This error display does not change even if refreshed, so that the device defect can be surely known.
On the other hand, when the sensor moves at high speed, a synthesis error often occurs, but unlike the case of a device defect, the synthesis error does not always occur throughout the entire display refresh cycle. Therefore, the error signal “E” is superimposed on the lowest digit because the display data changes by repeating the operation of sending an error signal or other numerical data to the lowest digit. However, it is not much different from the case where normal numerical data are refreshed one after another.

It can be said that the present invention focuses on the fact that the data display when the sensor is moved changes greatly as the digit becomes smaller. For example, consider a case where an error is displayed on all digits of the display. Even when the sensor moves at a high speed, the larger the digit changes, the smaller the change in the display value. Therefore, if the same error display is performed even for a large digit with a small display change, the error display becomes too conspicuous. This gives the user a feeling of distrust and anxiety, such as making the user misunderstand that the system is defective. In this respect, according to the present invention, since the error display is performed only on the least significant digit, the composite error display at the time of high speed movement of the sensor is inconspicuous, and the device defect can be surely recognized. Further, in the present invention, since no special circuit for distinguishing an error due to a device failure and an error due to sensor movement is required,
The cost of the device does not increase.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a system configuration of a displacement measuring device according to an embodiment of the present invention, and FIG. 2 is a configuration of an absolute capacitance displacement sensor (hereinafter referred to as an ABS sensor) 100 in FIG.

As shown in FIG. 2, the ABS sensor 100 has a main scale 22 which is a fixed element, and a slider 21 which is a movable element which is opposed to the main scale 22 with a slight gap therebetween. The slider 21 is the main scale 2
2 is movable in the measurement axis x direction. On the slider 21, the transmission electrode 23 has a predetermined pitch Pt0.
It is installed in. The transmission electrode 23 is the main scale 2
2 is capacitively coupled to the first receiving electrode 24a and the second receiving electrode 24b arranged at the pitch Pr. Reception electrode 24
a and 24b are pitches P that are adjacent to each other in the arrangement direction.
One-to-one connection is made to the first transmission electrode 25a and the second transmission electrode 25b of t1 and Pt2, respectively. Transmission electrodes 25a, 25b
Are the first detection electrodes 26 provided on the slider 21 side, respectively.
a, 26b and the second detection electrodes 27a, 27b are capacitively coupled.

The transmission electrodes 23 are commonly connected to every other seven electrodes to form a plurality of electrode groups each having eight electrodes. In the measurement mode, the eight-phase periodic signals a, b, ...
Is being supplied as. More specifically, these drive signals Sd are signals chopped with high frequency pulses, and are generated and output from the transmission waveform generating circuit 101 in FIG.

The pitch Wt of the electric field pattern generated by supplying the drive signal Sd to the transmitting electrode 23 is eight times the pitch Pt0 of the transmitting electrode 23, and this pitch Wt is
It is set to N times the pitch Pr of the receiving electrodes 24a and 24b. Here, N is preferably an odd number such as 1, 3, 5 or the like, and is set to 3 in this embodiment. Therefore, three to four receiving electrodes 24a and 24b are always capacitively coupled to the eight continuous transmitting electrodes 23. The receiving electrodes 24a and 24b are formed by sandwiching triangular or sinusoidal electrode pieces. The phase of the signal received by each of the receiving electrodes 24a and 24b is determined by the capacitive coupling area between the transmitting electrode 23 and the receiving electrodes 24a and 24b, and varies depending on the relative position between the slider 21 and the main scale 22. .

Receiving electrodes 24a and 24b and transmitting electrode 25
If a and 25b are formed at the same pitch, the detection electrodes 26a, 26b, 27a, and 27b simply detect a periodic signal that is repeated every time the position of the main scale 22 in the x direction changes by the pitch Pr. However, in the ABS sensor 100 of this embodiment, since the displacement amount of three levels of the coarse displacement amount (coarse scale), the intermediate displacement amount (medium scale) and the fine displacement amount (fine scale) is detected, the transmission electrode 25a and 25b are actually the receiving electrodes 24
The pitches are changed with respect to a and 24b to deviate by D1 and D2, respectively. The displacement amounts D1 and D2 are respectively set at the reference position x
It is a function of the distance x in the measurement direction from 0 and can be expressed as in the following Equation 1.

[0015]

## EQU1 ## D1 (x) = (Pr-Pt1) x / Pr D2 (x) = (Pr-Pt2) x / Pr

The transmitting electrodes 25a and 25b are thus displaced relative to the receiving electrodes 24a and 24b, and the detecting electrode 26
a, 26b, 27a, 27b with a pitch Wr1 (= 3Pt
1) and Wr2 (= 3Pt2), the deviation amounts D1 (x) and D2 from the detection electrodes 26 and 27 are set.
Detection signals B1, B2, C1 in which a small period of the detection electrodes 25a, 25b is superimposed on a large period corresponding to (x)
, C2 can be obtained. The signals B1 and B2 have a large period in opposite phase and a small period in phase. Therefore, a signal with a large period can be obtained from the difference between both signals, and a signal with a small period can be obtained from the sum of both signals. The same applies to the detection signals C1 and C2. Here, the electrode pattern is set so that the large cycle of the detection signals B1 and B2 is several tens of times the small cycle and the large cycle of the detection signals C1 and C2 is tens of times the large cycle of the detection signals B1 and B2. Thus, the displacement of each level can be obtained by the calculation of the following Expression 2.

[0017]

[Equation 2] C1-C2 (coarse scale) B1-B2 (medium scale) (B1 + B2)-(C1 + C2) (fine scale)

These operation output signals C1-C2, B1-
B2 and (B1 + B2)-(C1 + C2) are a coarse scale demodulation circuit 1021 and a medium scale demodulation circuit 102, respectively.
2, fine scale demodulation circuit 1023 and phase detection circuit 1
031, 1032, 1033. Specifically, the demodulation is performed by generating a rectangular wave periodic signal CMP having phase information at the edges through processing such as sampling at the chop frequency of the transmission waveform, mixing, low-pass filtering, and binarization. Be seen. Phase detection circuits 1031, 1032,
From 1033, the phase of each input signal is output as a digital value with the 0 ° drive signal Sd output from the transmission waveform generating circuit 101 as a reference signal.

These phase detection circuits 1031 to 1033
The digital values output from are weighted and combined by the combining circuit 104. The synthesizing circuit 104 has an EEPR
An offset value stored in an offset storage unit (not shown) such as an OM is also supplied, so that the offset amount of the combined value can be adjusted. The output of the synthesizing circuit 104 is converted into an actual dimension value, for example, by the electrode array pitch in the arithmetic circuit 106. The arithmetic circuit 106 is connected to a control circuit such as a microcomputer via an interface (not shown). The actual size value obtained by the arithmetic circuit 106 is displayed on the LCD display 108 via the display decoder 107.

The phase data obtained from the phase detection circuits 1031 to 1033 are also input to the synthesis error detection circuit 105. Here, if there is a large difference to some extent between the corresponding bit data of each phase data of the coarse scale, the medium scale, and the fine scale, a synthesis error is detected. On the other hand, the display decoder 107 and the LCD display 1
A selector 109 is provided at the least significant digit of 08. The selector 109 has a composition error detection circuit 105.
Controlled by the detection output of, the numerical data of the least significant digit (LSD) of the display decoder 107 or the error signal "E" is selectively transferred to the least significant digit of the LCD display 108.

In this embodiment, a solar cell 112 is used as a DC power source for driving the system. Further, the control circuit 110 controls the respective circuits so that the system is operated in the set display refresh cycle and the measurement operation is intermittently performed in the display refresh cycle. That is, the control circuit 110 includes a transmission waveform generation circuit 101 and a demodulation circuit 102 that is an analog circuit.
1-1023, and phase detection circuits 1031-1033
Drive signal ON1 for data extraction for intermittently operating
Coarse scale signal (CMP COA.), Medium scale signal (CMPMED.), Fine scale signal (CMP FIN) obtained from these phase detection circuits 1031 to 103 3.
The drive signal ON2 to be sent to the combination circuit 104, the arithmetic circuit 106 and the combination error detection circuit 105 for digitally processing and combining and displaying E) is generated. Control circuit 1
Reference numeral 10 supplies a reset signal, a clock signal and the like to each circuit in addition to a drive signal for turning on and off these circuits to control the operation of the entire system.

FIG. 3 is an enlarged view of the appearance of a digital caliper and its LCD display section, which is a more specific example of this embodiment. Although the LCD display 108 is a 5-digit digital display in this embodiment, FIG. 3B shows the case where the error display "E" is displayed at the lowest digit. When the phase error data cannot be combined for some reason and the composite error detection circuit 105 outputs an error detection signal, this causes the selector 109 to replace the LSD data of the display decoder 107 with the error signal “E” on the LCD. It will be sent to the least significant digit of the display 108.

In the case where the above-mentioned composition error occurs due to a defect in the system, a composition error signal is always output even when the displacement sensor is stopped, and the lowest digit of the LCD display 108 always displays the error indication "E". "It becomes. This allows the user to know the system failure. On the other hand, when the sensor moves at a high speed, the detected displacement amount changes, for example, at every display refresh cycle, and the numerical value displayed on the LCD display 108 is
Especially, the numerical value of the least significant digit changes rapidly. During this period, a synthesis error may occur due to a shift in the extraction timing of the phase data of each scale, or normal synthesis may be performed. In the cycle in which the synthesis error occurs, as described above, L
An error "E" is displayed on the least significant digit of the CD display 108, but since other numerical values are also displayed one after another, the error display "E" is not so noticeable.

[0024]

As described above, according to the present invention, an error display is not conspicuous with respect to a composite error which is not a device defect when a sensor is moved at a high speed, so that a device defect is generated without increasing the cost. In this case, it is possible to provide an absolute type displacement measuring device which gives a clear error display.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of an ABS sensor of the example.

FIG. 3 is a diagram showing an external appearance of a digital caliper and its display unit embodying the same embodiment.

[Explanation of symbols]

100 ... ABS sensor, 101 ... Transmission waveform generating circuit, 1
021 to 1023 ... Demodulation circuit, 1031 to 1033 ... Phase detection circuit, 104 ... Synthesis circuit, 105 ... Synthesis error detection circuit, 106 ... Operation circuit, 107 ... Display decoder, 108 ... LCD display, 109 ... Selector, 110
... control circuit, 112 ... solar cell.

Claims (1)

(57) [Claims] 1. A displacement sensor that outputs an output signal according to a relative positional relationship between a movable element and a fixed element, and at least a coarse scale and a fine scale that have phase information at their edges by processing the output signal of this displacement sensor. Demodulation means for obtaining the displacement amount detecting period signal, and phase detection means for detecting phase information from each of the period signals obtained by the demodulation means to obtain phase data of the coarse scale and the fine scale; The phase data obtained by the detecting means are combined to obtain the absolute displacement amount of the movable element with respect to the fixed element, and the absolute displacement amount obtained by the combining means is digitally displayed. A displacement measuring device, comprising: a display unit for displaying an error display only on the lowest digit.