JPH0545151A - Displacement measuring device - Google Patents

Abstract

PURPOSE:To enable a power consumption to be reduced and updating of a counter display when a movable element travels to be performed smoothly. CONSTITUTION:A circuit switching control portion 12 allows scale demodulation portions 3 and 4, phase detection portions 6 and 7. and an absolute counter portion 10 to be in stop state when a slider of an ABS (absolute) sensor 1 is traveling at a low speed or at halt and at the same time a dense scale demodulation portion 5, a dense phase detection portion 8, and an incremental counter portion 11 to be operated, thus enabling the device to be switched to an incremental counter operation. Also, the circuit switching control portion 12 enables the scale demodulation portions 3 and 4, the phase detection portions 6 and 7, and the absolute counter portion 10 to be in operation state when the slider is traveling at a high speed and at the same time the incremental counter portion 11 to be stopped, thus enabling the device to be switched to an absolute counter operation. The speed of the slider is detected by a speed detection portion 9.

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 using a displacement sensor applied to a small measuring instrument such as a digital caliper, a digital micrometer, a height gauge, etc. The present invention relates to a displacement measuring device using a so-called absolute type sensor capable of detecting various displacement amounts.

[0002]

2. Description of the Related Art Small displacement measuring devices such as digital calipers, digital micrometers, and height gauges for displaying measured values on a liquid crystal display device or the like are generally of low power consumption type using a capacitance type displacement sensor or the like. It is popular. A capacitance type 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 which moves relative to the fixed element, and the electrodes are moved as the movable element moves relative to the fixed element. The displacement amount is detected by extracting a signal of a periodic capacitance change generated between the patterns.

This type of displacement sensor is classified into two types, an incremental type and an absolute type, depending on the form of its output signal. The increment type measuring device detects the displacement amount by continuously counting the periodic signals generated by the movement of the slider from the reference position. On the other hand, the absolute type displacement sensor is a sensor that can obtain the absolute position of the movable element with respect to the fixed element without performing continuous counting operation. It is possible to output periodic signals with different pitches and fine pitches. Then, it is possible to detect the absolute displacement amount of the movable element by combining the phase information of the periodic signals of these respective pitches.

[0004]

However, of the above-mentioned two types of displacement measuring devices, in the incremental type measuring device, if the slider is moved too fast, the clock signal cannot follow the counting operation.
A counting error will occur. Counting errors can be prevented by setting the clock frequency high, but in this case,
Power consumption increases significantly. In particular, in a small displacement measuring device, a small power source such as a small button battery or a solar battery is inevitably used for downsizing. Therefore, it is desirable that the power consumed by the signal processing circuit that processes the signal from the displacement sensor is as small as possible.

On the other hand, in the absolute type displacement measuring device, a plurality of signal processing circuits are required to be provided in parallel in order to process the respective periodic signals of the coarse pitch, the intermediate pitch and the fine pitch. For this reason, there is also a drawback that the power consumption becomes large. In particular, movable elements such as sliders
Since most of the time is in the stopped state, it is not preferable to operate a plurality of circuits corresponding to each pitch even in such a stopped state because power is wasted.

Therefore, in the absolute type displacement measuring device, it is also considered that the phase information of the periodic signal of each pitch is sequentially read by one circuit to make the signal processing circuit common and reduce the power consumption. .. However, in this case, since the timing for capturing the phase information of the periodic signal of each pitch is shifted, the synthesis of the phase information does not work well when the slider is moving,
There is a problem in that the display value changes randomly, making it difficult to see the display value.

The present invention has been made in order to solve such a problem, and provides a displacement measuring device which can operate with low power consumption and can smoothly update the count display. To aim.

[0008]

A displacement measuring device according to the present invention responds to a first periodic signal having a coarse pitch corresponding to a displacement amount of a movable element with respect to a fixed element and a displacement amount of the movable element with respect to the fixed element. A displacement sensor that outputs a detection signal including a second periodic signal with a fine pitch, a first phase information corresponding to the coarse pitch and a second phase corresponding to the fine pitch from the detection signal output from the displacement sensor. Phase information detecting means for detecting phase information of the
Absolute displacement counting means for counting the absolute amount of displacement of the movable element with respect to the fixed element based on the phase information, and the amount of relative displacement of the movable element with respect to the fixed element based on the second phase information. Relative displacement counting means for counting, a speed detecting means for detecting a moving speed of the movable element with respect to the fixed element, and a moving speed of the movable element detected by the speed detecting means is faster than a predetermined speed. In this case, the displacement amount of the fixed element with respect to the movable element is calculated based on the output of the absolute displacement counting means, and the moving speed of the movable element detected by the speed detecting means becomes slower than a predetermined speed. In this case, the present invention is characterized by comprising a count combining means for calculating the displacement amount of the fixed element with respect to the movable element based on the output of the relative displacement counting means.

[0009]

According to the present invention, the moving speed of the movable element with respect to the fixed element is detected by the speed detecting means. Then, based on the detected speed information, when the movable element is moving at a low speed with respect to the fixed element, it is incremental (relative) based on the second phase information obtained from the periodic signal of the fine pitch. The counting operation is performed. As a result, a single circuit operates and power consumption is suppressed.

On the other hand, when the movable element moves beyond the speed that can be detected by the incremental counting, the speed detecting means detects this, and the measuring device detects the absolute value based on the first phase information obtained from the periodic signal of the coarse pitch. Shift to (absolute) counting operation. In this case, the circuit for the incremental counting operation is in the idle state, so that the power consumption is suppressed. At this time, the display of the lower digit of the displayed value changes at coarse intervals, but with a hand tool such as a caliper, when the sliding speed of the slider is high, the lower digit of the displayed value is not important information. Therefore, such a count display is acceptable. Moreover, since the upper digit of the display value is continuously updated, the display value is easy to see.

When it is detected that the moving speed of the movable element has decreased to a speed at which incremental counting can be performed without erroneous measurement again, the incremental counting operation starts again. At the time of this transition, it is desirable to read all the first and second phase information based on the periodic signals of all pitches and read the absolute position of the movable element.

As described above, according to the present invention, the incremental counting operation and the absolute counting operation are switched according to the moving speed of the movable element with respect to the fixed element, so that the displacement of the movable element can be increased without increasing the clock frequency. Can be detected with high accuracy, the display can be updated smoothly, and power consumption can be significantly suppressed.

[0013]

Embodiments of the present invention will be described below 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 length measuring devices such as a digital caliper, a digital micrometer, and a digital height gauge.

That is, the ABS sensor 1 is a capacitance type absolute type displacement sensor. The ABS sensor 1 is configured, for example, as shown in FIG. The slider 21, which is a movable element, is arranged to face the main scale 22, which is a fixed element, with a slight gap therebetween, and is movable in the measurement axis X direction. Slider 21
, The transmission electrodes 23 are arranged at a predetermined pitch Pt0. The transmission electrode 23 has a pitch Pr on the main scale 22.
First receiving electrode 24a and second receiving electrode 24 arranged in
It is capacitively coupled with b. The receiving electrodes 24a and 24b are
The first pitches Pt1 and Pt2 adjacent to each other along the arrangement direction
The transmission electrodes 25a and the second transmission electrodes 25b are connected in a one-to-one relationship. The transmission electrodes 25a and 25b are capacitively coupled to the first detection electrodes 26a and 26b and the second detection electrodes 27a and 27b provided on the slider 21 side, respectively.

The transmission electrodes 23 are commonly connected to every other seven electrodes to form eight electrode groups. These electrode groups include
Eight-phase periodic signals ah each having a phase difference of 45 °
Is supplied as the drive signal Sd. More specifically, these drive signals Sd are signals chopped by high frequency pulses as shown in FIG. The sin component of a large period is expressed by the following formula 1.

[0016]

## EQU1 ## Vn = Asin2.pi. {(T / T)-(n / 8)}

Here, A is the amplitude of the transmission signal Sd, T is the period of the transmission signal Sd, and n is the phase number (a, b, ..., H). The transmission signal Sd is generated and output from the transmission waveform generator 2 of FIG. The drive signal S is sent to the transmitting electrode 23
The pitch Wt of the electric field pattern generated by supplying d is 8 times the pitch Pt0 of the transmitting electrode 23, and this pitch Wt 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, etc., and is set to 3 in this example. Therefore, the reception electrodes 24a and 24b are always given a substantially constant weight to the eight continuous transmission electrodes 23.
Will be capacitively coupled. Receiving electrodes 24a, 24b
Is a device in which triangular (or sinusoidal) electrode pieces are arranged so as to sandwich each other. Each receiving electrode 24a,
The phase of the signal received by 24b is determined by the capacitive coupling area between the transmitting electrode 23 and the receiving electrodes 24a, 24b, which changes depending on the relative position between the slider 21 and the main scale 22.

Receiving electrodes 24a, 24b and transmitting electrode 25
If a and 25b are formed at the same pitch, the detection electrodes 26a, 26b, 27a and 27b are simply the slider 2
Although the periodic signal repeated every time the position of 1 in the x direction changes by the pitch Pr is detected, the ABS sensor 1 detects displacements at three levels of a coarse pitch, an intermediate pitch and a fine pitch. Therefore, the transmission electrode 25
Actually, a and 25b are deviated from the receiving electrodes 24a and 24b by D1 and D2, respectively. Deviation amount D1, D2
Are each a function of the distance x in the measurement direction from the reference position x0, and can be expressed by the following equation 2.

[0019]

## EQU2 ## D1 (x) = (Pr-Pt1) x / Pr D2 (x) = (Pr-Pt2) x / Pr

Further, the detection electrodes 26a, 26b, 27a,
The pitches Wr1 and Wr2 of the waveform pattern of 27b are 3P each.
It is set to t1 and 3Pt2. FIG. 4A shows the transmitter electrode 2.
3 is a graph showing a change in capacitance between the detection electrode 26a and one of the three electrodes, and FIG. 4B shows a change in the capacitance according to the position x between one of the transmission electrodes 23 and the detection electrode 26b. It is a graph which shows. As shown in FIG. 4, the capacitance of the detection electrode 24 is set to a large period λ1 based on the deviation amount D1 (x).
The period Pr having a small pitch of a changes in a superimposed manner. This capacity is shown in Equation 3 below.

[0021]

## EQU3 ## Cn (B1) = Bsin2π {(x / λ1)-(n / 8)} + Csin2π {(x / Pr)-(3n / 8)} + D Cn (B2) =-Bsin2π {(x / λ1 )-(N / 8)} + Csin2π {(x / Pr)-(3n / 8)} + D

Here, B is the amplitude of a large cycle, C is the amplitude of a small cycle, and D is the offset value. Therefore, the reception signal B1 detected by the detection electrodes 26a and 26b
, B2 are respectively expressed by the following formula 4.

[0023]

[Equation 4]

Here, the electrode patterns are arranged such 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 several tens times the large cycle of the detection signals B1 and B2. When set, the displacement of each level can be obtained by the following mathematical expression 5.

[0025]

[Equation 5] C1-C2 (coarse scale) B1-B2 (medium scale) (B1 + B2)-(C1 + C2) (fine scale)

These calculations are carried out by the coarse scale demodulator 3, the medium scale demodulator 4 and the fine scale demodulator 5 shown in FIG. The demodulation is performed, for example, by sampling the transmission waveform shown in FIG. 3 at a chop frequency, mixing the signals, and then performing low-pass filtering and binarization processing. As a result, each of the scale demodulators 3, 4, and 5 has a rectangular-wave phase signal CM in which phase information is carried by an edge.
P is output.

The phase signals CMPCOA. , CMPMED. , CMPF
INE is input to the coarse phase detector 6, the medium phase detector 7, and the fine phase detector 8, respectively. These phase detectors 6 to
8, the count value of the internal counter (not shown) is latched at the rising or falling timing of each phase signal CMP, so that each phase signal CMP and the reference phase signal CP
A value corresponding to the phase difference with O is detected.

The phase values output from the phase detectors 6 to 8 are input to the absolute counter 10. The absolute counter 10 combines the phase values output from the phase detectors 6 to 8 to calculate the absolute displacement amount of the slider 21 with respect to the main scale 22. The phase value output from the fine phase detection unit 8 is input to the incremental counting unit 11. Incremental counting unit 1
1 calculates the displacement of the slider 21 with respect to the main scale 22 by up-counting and down-counting the periodic change of the phase value output from the fine phase detection unit 8.

On the other hand, the phase signals CMPMED. ，
The CMPFINE is also input to the speed detector 9.
The speed detector 9 detects the phase signal CMPFINE when the slider 21 is moving at a low speed or is stopped.
The signal detects the moving speed of the slider 21,
Is moving at high speed, the phase signal CMPME
D. The moving speed of the slider 21 is detected by. The speed detector 9 outputs the detected slider speed information to the circuit switching controller 12.

The circuit switching controller 12 includes a slider 21.
Is moving slowly or is stopping, the scale demodulating units 3 and 4, the phase detecting units 6 and 7, and the absolute counting unit 10 are stopped, and the fine scale demodulating unit 5 and the fine phase detecting unit 8 are Also, the incremental counting unit 11 is put into an operating state and switched to the incremental counting operation. Further, the circuit switching control unit 12 controls the scale demodulation unit 3 when the slider is moving fast.
4, the phase detectors 6 and 7 and the absolute counter 10 are activated, and the incremental counter 1
Stop 1 and switch to absolute counting operation.

Further, since the change of the electrostatic capacity is as shown in the equation 3, as shown in FIG. 5, the phase of the transmission signal Sd during the counting operation by the coarse scale and the medium scale and the transmission signal during the counting operation by the fine scale are performed. It is different from the phase of Sd,
The circuit switching controller 12 switches the transmission signal Sd from the transmission waveform generator 2 according to the speed information from the speed detector 9. The count value of the absolute counting unit 10 and the count value of the incremental counting unit 11 are combined by the count combining unit 13.
The output of the counting / synthesizing unit 13 is displayed on the display unit 14 such as an LCD in a form appropriately converted into the actual displacement amount.

Next, the operation of the displacement measuring apparatus according to this embodiment having the above-mentioned structure will be described. FIG. 6 is a diagram showing the relationship between the slider speed v and the counting / speed detection mode. When the slider 21 is stopped or is moving at a slow speed, the circuit switching control unit 12 stops the scale demodulation units 3 and 4, the phase detection units 6 and 7, and the absolute counting unit 10 and sets the fine scale demodulation unit 5. The fine phase detector 8 and the incremental counter 11 are activated, and the transmission waveform generator 2 generates the transmission waveform Sd for the fine scale counting operation. As a result, the incremental counting operation is started, and the count value held in the absolute counting section 10 is sequentially added or subtracted. At this time, the speed detection unit 9 determines the slider 2 from the cycle of the phase signal CMPFINE output from the fine scale demodulation unit 5.
The moving speed of 1 is detected.

When the moving speed v of the slider 21 reaches about 80% of the theoretical limit speed v3 of the fine scale incremental counting, the circuit switching controller 12 causes the scale demodulators 3 and 4, the phase detectors 6 and 7, and the absolute controller. Counting unit 1
0 is the operating state, the fine scale demodulating unit 5, the fine phase detecting unit 8 and the incremental counting unit 11 are in the stopped state, and the transmission waveform generating unit 2 generates the transmission waveform Sd for the coarse scale and fine scale counting operations. .. As a result, the device shifts to the absolute counting mode. At this time, the lower digit of the display value is updated with a coarse interval, but when the slider is moving fast, the lower digit of the display value is not so noticeable, so there is no particular problem.
In this mode, the speed detector 9 operates in the medium scale demodulator 4
From the phase signal CMPMED. The moving speed of the slider 21 is detected from the cycle.

When the moving speed v of the slider 21 is reduced to about 15% of the speed v3, the incremental counting operation starts again, but at this time, it is necessary to transfer absolute displacement information to the counting / combining section 13. For this reason, the circuit switching control unit 12 operates all the scale demodulation units 3, 4, 5 and the phase detection units 6, 7, 8 only for the period required for this delivery, and calculates the absolute count value including the fine scale. .. In this case, the transmission signal Sd during the coarse scale / medium scale counting operation and the transmission signal Sd during the fine scale counting operation
Therefore, the transmission signal Sd is temporarily multiplexed during this period. FIG. 7 is a diagram showing a multiplexed signal M of a 45 ° phase transmission signal b1 for coarse and medium scales and a 135 ° phase transmission signal b2 for fine scales. In this way, the multiplexed signal M can be generated by synthesizing while maintaining the heights and directions of the edges of the transmission signals b1 and b2. When the absolute count value is obtained during this delivery period, the process thereafter shifts to the incremental count using the fine scale alone.

As a result of the above operation, when the slider 21 is moving at a low speed, the signal processing circuits for coarse scale and medium scale and the absolute counter 10 are in a rest state, and the slider 21 is moving at a high speed. At this time, the signal processing circuit for the fine scale and the incremental counting unit 11
And become dormant. By doing so, the operating clock frequency can be suppressed to a low level, and power consumption can be significantly reduced. Further, since the mismatch of the count composition caused by the different time to read the position information of each scale at the time of movement is prevented, the count display can be updated smoothly, and a display value without a feeling of strangeness can be obtained.

Further, as shown in FIG. 6, a hysteresis characteristic such that the speed v2 when shifting from the incremental counting operation to the absolute counting operation is set higher than the speed v1 when shifting from the absolute counting operation to the incremental counting operation. If you keep it, you can prevent the mode from switching frequently, and moreover,
Even when the transmission waveform is temporarily multiplexed at the time of transfer to the incremental counting operation, there is an advantage that the current operation clock can be sufficiently used.

In the above embodiment, counting was performed using three types of scales having different pitches, that is, a coarse scale, a medium scale, and a fine scale, but if accuracy is allowed, only the coarse scale and the fine scale are used. You may count.

[0038]

As described above, according to the present invention, the moving speed of the movable element with respect to the fixed element is detected by the speed detecting means, and when the movable element is moving at a low speed, a fine pitch When the movable element is moving at a high speed by performing the incremental counting operation based on the second phase information obtained from the periodic signal, the absolute counting operation based on the first phase information obtained from the periodic signal having a coarse pitch is performed. By doing so, the number of circuits to be operated is reduced, so that the power consumption can be greatly suppressed and the counting display can be made smooth. Therefore, according to the present invention, it is possible to realize a small length measuring instrument with low power consumption using, for example, a solar cell as a power source.

[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 an ABS sensor in the displacement measuring device.

FIG. 3 is a waveform diagram showing an example of a transmission signal supplied to the sensor.

FIG. 4 is a graph showing a change in capacitance with respect to position in the sensor.

FIG. 5 is a schematic diagram showing a phase relationship of transmission signals supplied to the sensor.

FIG. 6 is a graph showing a relationship between a moving speed of a slider of the sensor and a counting mode and a speed detection mode.

FIG. 7 is a waveform diagram showing an example of a multiplexed transmission signal supplied to the sensor.

[Explanation of symbols]

1 ... ABS sensor, 2 ... Transmission waveform generator, 3 ... Coarse scale demodulator, 4 ... Medium scale demodulator, 5 ... Fine scale demodulator, 6 ... Coarse phase detector, 7 ... Medium phase detector, 8 ... Fine Phase detection unit, 9 ... Speed detection unit, 10 ... Absolute counting unit, 11 ... Incremental counting unit, 12 ... Circuit switching control unit, 13 ... Count combining unit, 14 ... Display unit, 21 ... Slider, 22 ... Main scale, 23 ... Transmitting electrodes, 24
a ... 1st receiving electrode, 24b ... 2nd receiving electrode, 25a ... 1st transmission electrode, 25b ... 2nd transmission electrode, 26a, 26b ...
1st detection electrode, 27a, 27b ... 2nd detection electrode.

Claims (5)

[Claims] 1. A first periodic signal having a coarse pitch corresponding to a displacement amount of a movable element with respect to a fixed element and a second periodic signal having a fine pitch corresponding to a displacement amount of the movable element with respect to the fixed element.
A displacement sensor that outputs a detection signal including a periodic signal of the above, and the first phase information corresponding to the coarse pitch and the second phase information corresponding to the fine pitch are detected from the detection signal output from the displacement sensor. Phase information detection means,
Absolute displacement counting means for counting the absolute amount of displacement of the movable element with respect to the fixed element based on the first phase information, and the relative displacement of the movable element with respect to the fixed element based on the second phase information. Relative displacement counting means for counting various displacement amounts, speed detecting means for detecting a moving speed of the movable element with respect to the fixed element, and moving speed of the movable element detected by the speed detecting means is higher than a predetermined speed. When it becomes faster, the displacement amount of the fixed element with respect to the movable element is calculated based on the output of the absolute displacement counting means, and the moving speed of the movable element detected by the speed detecting means is higher than a predetermined speed. And a counting / combining means for calculating the amount of displacement of the fixed element with respect to the movable element based on the output of the relative displacement counting means. Displacement measuring device. 2. The displacement measuring device according to claim 1, wherein the absolute displacement counting means and the relative displacement counting means are selectively in an operating state. 3. The speed detecting means performs speed detection based on the second periodic signal when the movable element is moving at a speed lower than a predetermined speed, and the movable element is higher than the predetermined speed. 3. The displacement measuring device according to claim 1 or 2, wherein speed detection is performed based on the first periodic signal when moving at. 4. The speed of the movable element that switches from the relative displacement count to the absolute displacement count is set to be higher than the speed of the movable element that switches from the absolute displacement count to the relative displacement count. The displacement measuring device according to any one of items 1 to 3. 5. The absolute displacement counting means uses the first and second phase information when the speed of the movable element with respect to the fixed element decreases to switch from absolute displacement counting to relative displacement counting. The displacement measuring device according to any one of claims 1 to 4, wherein the displacement measuring device counts an absolute displacement amount of the movable element with respect to the fixed element.