JP2909338B2 - 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, and a height gauge for displaying a measured value on a liquid crystal display device or the like, a device utilizing a capacitance type displacement sensor is promising. A capacitive displacement sensor has a large number of electrodes disposed on a fixed element such as a main scale and a movable element such as a slider that moves relative to the fixed element. The displacement amount is detected by extracting a signal of a periodic capacitance change occurring between the patterns.

Among such displacement sensors, an absolute type displacement sensor has a coarse scale signal for detecting a coarse displacement amount, a fine scale signal for detecting a fine displacement amount, and an intermediate signal if necessary, depending on the shape of the electrode pattern. Each periodic square wave signal of the medium scale signal for detecting the displacement can be output. Then, the phase data obtained from these demodulated signals are combined to detect the absolute displacement (position) of the movable element.

[0004]

The phase of each square wave signal of such an absolute displacement sensor is carried by an edge, so that phase data can be obtained only at the edge.
For this reason, the sampling timing of each of the coarse and fine phase data naturally shifts. During the movement of the displacement sensor, information at different sensor positions is sampled due to the shift of the sampling timing, and in some cases, the synthesis of coarse / fine phase data may fail. The possibility of the occurrence of the combining error increases as the moving speed of the displacement sensor increases, and when the combining error occurs, the data display during the movement of the displacement sensor is not smooth.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an absolute-type displacement measuring device in which a displacement sensor moving speed at which data synthesis failure occurs is increased to a practically sufficient level. Aim.

[0006]

SUMMARY OF THE INVENTION A displacement measuring device according to the present invention comprises a displacement sensor for outputting an output signal corresponding to a relative positional relationship of a movable element with respect to a fixed element; Demodulation means for obtaining a periodic square wave signal for detecting the displacement amount of at least a coarse scale and a fine scale having phase information at an edge, and detecting phase information from each of the periodic square wave signals obtained by the demodulation means. Phase detecting means for obtaining coarse-scale and fine-scale phase data, averaging means for sampling each of the coarse-scale and fine-scale phase data a plurality of times and averaging each, and phase for the coarse-scale or fine-scale phase data. A sampler that determines one sampling timing in close proximity to one sampling timing of data. And a synthesizing means for synthesizing the coarse scale and fine scale phase data obtained by the averaging means to obtain an absolute displacement amount of the movable element with respect to the fixed element. .

[0007]

According to the present invention, the sampling control is performed so that the difference between the timings at which the coarse and fine scale phase data is taken in is reduced, and the sampling timing of each phase data is made closer. As a result, even when the displacement sensor is moving at a relatively high speed, a situation in which the data synthesis fails can be prevented.

[0008]

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

As shown in FIG. 2, the ABS sensor 1 includes a main scale 22 as a fixed element and a slider 21 as a movable element opposed to the main scale 22 with a small gap therebetween.
And The slider 21 is movable with respect to the main scale 22 in the measurement axis x direction. The transmission electrodes 23 are arranged on the slider 21 at a predetermined pitch Pt0. The transmission electrode 23 is capacitively coupled to the first reception electrode 24a and the second reception electrode 24b arranged at the pitch Pr on the main scale 22. Receiving electrodes 24a, 2
4b is a pitch Pt1, Pt adjacent to each other along the arrangement direction.
One to one for the first transmission electrode 25a and the second transmission electrode 25b at t2.
Are connected respectively. The transmission electrodes 25a and 25b are respectively connected to the first detection electrodes 26a and 26 provided on the slider 21 side.
6b and the second detection electrodes 27a, 27b.

The transmitting electrodes 23 are commonly connected every seven electrodes to form a plurality of electrode groups of eight electrodes. .., H having a phase shift of 45 ° in the measurement mode.
It is supplied as. More specifically, these drive signals Sd are signals chopped by high-frequency pulses, and are generated and output from the transmission waveform generation circuit 2 in FIG.

The pitch Wt of the electric field pattern generated when the drive signal Sd is supplied to the transmission electrode 23 is eight times the pitch Pt0 of the transmission electrode 23, and the pitch Wt is
The pitch 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 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. .

The receiving electrodes 24a and 24b and the 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 1 of this embodiment, the coarse displacement (coarse scale),
In order to detect three levels of displacement, an intermediate displacement (medium scale) and a fine displacement (dense scale), the transmission electrodes 25a and 25b are actually used as the reception electrodes 24a and 24b.
, And the pitch is changed by D1 and D2, respectively. The deviation amounts D1 and D2 are functions of the distance x in the measurement direction from the reference position x0, and can be expressed by the following equation (1).

[0013]

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

The transmission electrodes 25a and 25b are deviated from the reception electrodes 24a and 24b in this manner, and the detection electrodes 26a and 25b are deflected.
a, 26b, 27a, 27b at the pitch Wr1 (= 3Pt
1) and Wr2 (= 3Pt2), the displacement amounts D1 (x), D2
Detection signals B1, B2, C1 in which a small cycle of the detection electrodes 25a, 25b is superimposed on a large cycle corresponding to (x).
, C2. The signals B1 and B2 have a large cycle in opposite phase and a small cycle in phase. Accordingly, a signal having a large cycle can be obtained from the difference between the two signals, and a signal having a small cycle can be obtained from the sum of the two signals. The same applies to the detection signals C1 and C2. Here, the electrode pattern is set so that the large period of the detection signals B1 and B2 is several tens times the small period, and the large period of the detection signals C1 and C2 is several tens times the large period of the detection signals B1 and B2. Thus, the displacement of each level can be obtained by the calculation of the following equation (2).

[0015]

## EQU2 ## C1-C2 (coarse scale) B1-B2 (medium scale) (B1 + B2)-(C1 + C2) (dense scale)

These operation output signals C 1 -C 2, B 1-
B2, (B1 + B2)-(C1 + C2) are the coarse scale demodulation circuit 3, the medium scale demodulation circuit 4, the fine scale demodulation circuit 5, the coarse phase detection circuit 6, the medium phase detection circuit 7, and the fine phase detection circuit 8, respectively. Is processed. The demodulation is performed by generating a periodic square wave signal CMP having phase information at edges, through processes such as sampling, mixing, low-pass filtering, and binarization of a transmission waveform at a chop frequency. Will be The phase detection circuits 6, 7, and 8 output the phase of each input signal as a digital value using the 0 ° drive signal Sd output from the transmission waveform generation circuit 2 as a reference signal.

Each phase data of the digital value output from these phase detection circuits 6, 7, 8 is subjected to a plurality of sampling and averaging processes. This is due to reduction of display flicker and offset cancellation of operational amplifiers and comparators in the demodulation circuits 3, 4, and 5. The averaging circuit 9 is a part for averaging the phase data obtained by sampling a plurality of times from each of the phase detection circuits 6, 7, and 8. In order to optimize the sampling timing of each phase data,
A differentiating circuit 13 and a sampling control circuit 14 are provided. Details of these averaging circuit 9, differentiating circuit 13 and sampling control circuit 14 will be described later.

Each phase data obtained from the averaging circuit 9 is weighted and synthesized by a synthesis circuit 10. An offset value stored in an offset storage unit (not shown) such as an EEPROM is also supplied to the synthesizing circuit 10 so that the offset amount of the synthesized value can be adjusted. The output of the synthesizing circuit 10 is converted in an operation / display circuit 11 into, for example, an electrode arrangement pitch into an actual dimension value, and the obtained actual dimension value is sent to the LCD display 1 via a display decoder.
2 is displayed.

The system controller 15 includes the synthesizing circuit 1
0, enable signal ENB for operation / display circuit 11
1. An enable signal ENB2 for other circuits, various other reset signals, and a clock signal are generated to control the operation of the entire system.

The averaging circuit 9 samples each of the coarse, medium, and fine scale phase data a plurality of times and adds and samples them.
Arithmetic operation units 92, 94, 96 and register 9
1,93,95. Among the coarse, medium, and fine scale square wave signals CMPF, CMPM, and CMPC, the largest cause of display flicker that directly reflects on the least significant digit of display data is the fine scale square wave signal CMPF. is there. Therefore, in this embodiment, the fine scale demodulation circuit 5
Are sampled four times and averaged, and the output square wave signals CMPC and CMPM of the coarse scale and middle scale demodulation circuits 3 and 4 are sampled twice and averaged. On this occasion,
With reference to the sampling timing of the fine-scale square wave signal CMPF, the sampling timing of the medium-scale and coarse-scale square wave signals CMPM and CMPC is determined at a position closest to the sampling timing.

The sampling control is performed by the differentiating circuit 13 and the sampling control circuit 14. The differentiating circuit 13 is configured to output the square wave signals CMPC and CMP obtained from the coarse, medium, and fine scale demodulating circuits 3, 4, and 5, respectively.
This is a circuit that outputs pulses at the edges of M and CMPF.
More specifically, the differentiating circuit 13 generates the square wave signals CMPC, C
MPM, CMPF rising edge differential pulse CR
P, MRP, FRP, double edge differential pulse CEP, ME
P, FEP, and the falling edge differential pulses CFP, MFP of the square wave signals CMPC, CMPM are generated. FIG. 4 shows the input / output relationship of the differentiating circuit 13.

The sampling control circuit 14 receives the output pulses of the differentiating circuit 13 and sends the transfer clocks CCK, MCK, FCK and the reset pulse CRES to the registers 91, 93, 95 in the averaging circuit 9, respectively.
B, MRESB and FRESB are generated. FIG. 3 shows a specific circuit example. The control circuit 14 is roughly divided into a coarse scale sampling control circuit unit 14
C, a medium scale sampling control circuit section 14M and a fine scale sampling control circuit section 14F.

Sampling control circuit 1 for fine scale
4F is a register clock FCK for sampling the fine scale phase data four times based on the enable signal ENB2 , the rising edge differential pulse FRP and both edge differential pulses FEP obtained from the fine scale square wave signal CMPF. And a register reset signal FRESB. The sampling control circuit unit 14M for the middle scale includes an enable signal ENB2 , a rising edge differential pulse MRP, and a falling edge differential pulse MFP obtained from the square wave signal CMPM for the middle scale.
And a register clock MCK and a register reset signal MRE for sampling the middle scale phase data twice based on both edge differential pulses MEP.
Generate SB. The coarse scale sampling control circuit unit 14C coarsely calculates the coarse signal based on the enable signal ENB2 and the rising edge differential pulse CRP, falling edge differential pulse CFP, and both edge differential pulses CEP obtained from the coarse scale square wave signal CMPC. It generates a register clock CCK and a register reset signal CRESB for sampling the scale phase data twice.

The operation of sampling fine scale phase data as a reference will be described with reference to FIG. As shown in FIG. 5, after the enable signal ENB2 becomes "1", a reset signal FRESB for resetting the register 95 is output by the first rising differential pulse FRP, and thereafter, the reset signal FRESB is synchronized with both edge differential pulses FEP. Up to the fourth register clock FCK is generated. Then, at each rising edge of the clock FCK, the phase data from the fine scale phase detection circuit 8 and the contents of the register 95 are added by the arithmetic unit 96, and the averaged data after four times addition is obtained. At the falling edge of the fourth pulse of the two-edge differential pulse FEP, the output node A of the flip-flop F / F1 becomes "0", and thereafter, the reset signal FRESB and the clock signal FC
K is not output.

At the falling edge of the third pulse of the two-edge differential pulse FEP, the output node B of the flip-flop RS-F / F1 becomes "1". The output node B of the RS-F / F1 is connected to the medium scale sampling control circuit 14M.
, And sampling control circuit section 14C for coarse scale
Is input as a reference signal for sampling timing of medium scale and coarse scale phase data.

Next, the mid-scale phase data sampling operation will be described. After the enable signal ENB2 becomes "1", a register reset signal MRESB is output in synchronization with the rising edge differential pulse MRP, and both edge differential pulses are output. Register clock MCK in synchronization with MEP
Is output. The result obtained by adding the content of the register 93 to the phase data from the phase detection circuit 7 at the rise of the clock MCK is written in the register 93 for the middle scale. Next, when the rising edge differential pulse MRP is input, a register reset signal MRESB is output and the register 9
3 is cleared.

Here, after the output node B of the RS-F / F1 of the fine scale sampling control circuit section 14F becomes "1", the falling edge differential pulse MFP comes, or both edge differential pulses MEP are output. When the node B becomes "1" after the rising edge and before the rising edge differential pulse MRP comes, the register reset signal MR
ESB and clock signal MCK are not output. The sampling operation of the coarse scale phase data is the same as the medium scale phase data sampling operation.

The above sampling operation is digitally processed, and is converted into the phase data CMPF and CMP.
FIG. 6 shows the relationship when the M and CMPC signals are input. Regarding the fine-scale square wave signal CMPF, four consecutive edges F1 and F1 from the first rising edge after the enable signal ENB2 becomes “1”.
At 2, F3 and F4, the phase data is sampled and averaged.

As for the square wave signal CMPM of the middle scale, at the time of the first two edges M1 and M2, the RS-F / F1 of the fine scale sampling control circuit section 14F.
Is not "1" and the next edge M
At time 3, the contents of the register 93 are reset. When the phase data of the two edges M3 and M4 is sampled, the node B becomes "1" at the edge F3 of the fine-scale square wave signal CMPF, and no further sampling is performed. Therefore, the average value of the middle scale phase data is (M3 + M4) / 2. The phase data of the coarse scale is almost the same, and sampling ends at the edge C4 after the edge F3, and is obtained as the average value (C3 + C4) / 2 of the phase data of the two edges C3 and C4.

Accordingly, deviations TFM and TFC between the average value sampling point t1 of the fine scale phase data, the average value sampling point t2 of the middle scale phase data, and the average value sampling point t3 of the coarse scale phase data are kept small. . Incidentally, FIG. 7 shows the sampling timing when the above-described sampling control is not performed, in comparison with FIG. This is because the fine scale phase data takes an average of four edges F1 to F4 from the first rising edge after the enable signal ENB2 becomes "1", and the middle rising phase edge data also has the first rising edge. This is the case where the average of the two edges M1 and M2 and the average of the two edges C1 and C2 from the first rising edge are also obtained for the coarse scale phase data. in this case,
The average sampling timing shifts TFM and TFC are shown in FIG.
It is clearly larger compared to.

As described above, according to this embodiment, since the sampling timing of each phase data is close,
Even when the displacement sensor is moving at a relatively high speed, a situation in which the combination fails can be prevented.

In this embodiment, fine scale data is used as a reference for sampling timing control, and the number of times of data sampling is set to four. This is because fine scale data has the greatest effect on display flicker as described above. That's why. However, in order to prevent the failure of data synthesis, it is not always necessary to use the dense scale data as a reference for sampling, and other phase data may be used as a reference. Further, in the embodiment, a displacement sensor having three scales of coarse, medium, and dense is used, but the present invention is not limited to this, and a displacement sensor having at least two scales of coarse and dense is used. It is effective in the case.
Further, the sampling circuit of FIG. 3 in the embodiment is an example, and the sampling may be performed by a microprocessor or the like according to the same rule as the circuit of FIG.

[0033]

As described above, according to the present invention, by adjusting the data sampling, a synthesis error is hardly generated, and therefore, the absolute data can be displayed smoothly even while the displacement sensor is moving at a relatively high speed. A mold displacement measuring device can be provided.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of an ABS sensor in FIG. 1;

FIG. 3 is a diagram illustrating a configuration of a sampling control circuit of FIG. 1;

FIG. 4 is a diagram illustrating output signals of the differentiating circuit of FIG. 1;

5 is a diagram showing operation waveforms of the sampling control circuit of FIG.

FIG. 6 is a diagram illustrating timing of data sampling according to the embodiment.

FIG. 7 is a diagram showing timing of data sampling in a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... ABS sensor, 2 ... Transmission waveform generation circuit, 3 ... Coarse scale demodulation circuit, 4 ... Medium scale demodulation circuit, 5 ... Dense scale demodulation circuit, 6 ... Coarse phase detection circuit, 7 ... Medium phase detection circuit, 8 ... Dense Phase detection circuit, 9 ... Averaging circuit, 91, 9
3, 95 ... register, 92, 94, 96 ... arithmetic unit, 10
... Synthesis circuit, 11 ... Operation / display circuit, 12 ... Display unit, 1
3 ... differentiation circuit, 14 ... sampling control circuit, 15 ... controller.

Claims (1)

(57) [Claims] 1. A displacement sensor for outputting an output signal corresponding to a relative positional relationship of a movable element with respect to a fixed element, and at least a coarse scale and a fine scale each having an edge with phase information by processing an output signal of the displacement sensor. Demodulation means for obtaining a periodic square wave signal for detecting the amount of displacement, and a phase for detecting phase information from each of the periodic square wave signals obtained by the demodulation means to obtain coarse scale and fine scale phase data. Detecting means, averaging means for sampling each of the coarse-scale and fine-scale phase data a plurality of times, respectively, and averaging them; and Sampling control means for determining the sampling timing of the other, and the averaging means. The phase data of the coarse scale and fine-scale by combining the displacement measuring apparatus characterized by comprising a synthesizing means for obtaining the absolute amount of displacement of the movable element relative to the fixing element.