JPH01163616A - Position detector - Google Patents

Abstract

PURPOSE:To improve phase detection accuracy by detecting the phase of a detection signal from the interval between a reference point and a singular point and phase cycle width. CONSTITUTION:Light from a semiconductor laser 1 is scanned on a code plate 4 at right angles to a moving direction through a polygon mirror 2 and a lens 3, a synchronizing signal from a photodetecting element 8 is inputted to a control circuit, and the detection signal from the photodetector 7 is inputted to the control circuit. The detection signal contains a binary code obtained by scanning binary code patterns 13 at the upper and lower parts of the code plate 4 and moire transmitted light quantity waveform obtained by scanning moire fringes formed through slits 11 and 12. The binary code is sent to a signal processing circuit to detect the rough absolute position of the code plate 4. The control circuit detects the fine position in each slit pit to the reference position and the rough absolute position in binary code is combined to detect the absolute position with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a position detection device, and more particularly to a position detection device that can be suitably used in an Abflu 1 type encoder that detects an absolute position with high precision. Conventional technology In recent years, optical scale type position detection devices have changed from the conventional method of detecting the transmitted light of periodic slits with a photodetector and increasing the resolution by dividing the detected signal in the amplitude direction. The method of arranging multiple sensors with different phases and scanning them to detect the phase signal, and increasing the resolution by phase detection, is attracting attention because it is possible to increase the resolution of the negative layer. ing.

The configuration of this phase division type position detection device will be explained with reference to Fig. F5. In FIG. 5, 31 is a code plate having regularly arranged slits 32, 33 is a mask, and 37I
is a light source, 35 is a lens, 36 is a light receiver, and 3[3
d is a photodetection element, 37 is an amplifier, 38 is a bandpass filter, SW, ~s W, photodetection elements 36a-36d
This is a switch that sequentially extracts signals from the The pitch of the slits 32 of the hood plate 31 is set at 5/'4 so that the detection signals are sequentially shifted in phase by 1]0°. has been completed.

In the above configuration, the light emitted from the light source 34 is transmitted to the lens 35.
The light becomes a parallel beam of light, and the light that passes through the Surino 132 and the mask 33 is detected by the photodetectors T'36a-36d.
The switch SW, -3W, is switched to switch at a certain timing to extract the signal, amplify the signal, and extract the fundamental wave component of the output signal using the bandpass filter 38.
The position within one slino pitch is detected by comparing the phase of the obtained sine wave signal with the switching phase.

Additionally, the present applicant previously filed Japanese Patent Application No. 62-198502';
Moiré fringes formed by a coat plate having regularly arranged slits and a mask movable relative to the code plate and having regularly arranged slits. In contrast, we have proposed a position detection device that detects the amount of transmitted light zt4L with a photodetector and detects the position within the slit pitch based on the phase of the detection signal.

Problems to be Solved by the Invention However, in the conventional phase detection force type position detection device, the detected 4y signal is denotally sampled, so the obtained sine wave signal contains distortion, and It is difficult to obtain varying amounts of light over a wide area or to perfectly match the sensitivity of the photodetector, so it is inevitable that the phase signal will be distorted and the detection position will be non-linear. ! There are problems such as causing a Q error.

On the other hand, in the position detection device previously proposed by the present applicant, since a continuous Φ output signal without distortion can be obtained by optical scanning, the problem described in item 1 can be basically solved. However, as shown in FIG. 4, the method for detecting the phase of the detection signal is to input the optical scanning synchronization signal and the moiré fringe detection signal to the control circuit 41, and to output the pulse signal from the force oscillator 12. It is input to the counter 44 via f-143, and the control circuit 41 outputs a 1-fold signal based on synchronous belief to open the date 43, and corresponds to the reference position of the detected phase from the generation of the 1-fold signal. After the reference time has elapsed, the detection signal reaches a predetermined threshold level and is lost.
Date 13 is closed with "D", (), and the number of pulses during that time is counted by the counter 44 to measure the time from the synchronization signal generation to the cross point, and the difference between this detection time and the reference time and the cycle of the moiré fringe are measured. One possible method is to detect the phase of the detection signal based on the ratio of the scanning time corresponding to the width, but in that case, the detection accuracy of the code board with respect to the moving object, the periodic change of the moiré fringe due to pitching during movement, or the oscillator's There is a problem in that the stability of the oscillation frequency is affected by changes in temperature.

Furthermore, problems caused by the mounting accuracy of the code plate and pitching during movement are not limited to the above-mentioned optical scanning method. This also occurs in a vernier method in which the mask's sulin l pinch is shifted and a plurality of photodetectors are provided for scanning.

In view of the above-mentioned conventional problems, the present invention has been developed to solve the problem of the circumference of moiré fringes due to the mounting accuracy of the code plate, pitching during movement, changes in vernier, stability of the oscillation frequency of the oscillator ('l: influence of shade, etc.). An object of the present invention is to provide a position detecting device that accurately detects a phase without any errors.

Means for Solving the Problems In order to achieve the object stated in item 1, the present invention provides a code plate having regularly arranged slints, and a code plate having regularly arranged slints movable relative to the hood plate and having regularly arranged slits. A position detection device that detects moiré fringes formed by a mask having 71- or the amount of transmitted light from a vernier with a photodetector, and detects the position within the slit beam/chi based on the phase of the detection signal J1τ. , comprising means for detecting a singular point of the detection signal, means for detecting a phase cycle width, and means for detecting the interval between the reference point and the singular point and the phase of the phase cycle 1 failure detection f8'';:, . It is characterized by the presence of

Operation Since the present invention has the above configuration, the detection signal is calculated by taking the ratio of the gap between the detected singular point and the reference point and the phase cycle width detected at each detection time by the phase cycle width detection means. The phase can be detected, and from this detected phase, the position relative to the reference position within the interval of each slot 71 can be detected. At the same time, the phase shift width is detected at each valley detection time, so the removal of the hood plate ( Even if the period of the moiré fringes or the vernier change due to the precision of the detection, or even if the frequency of the oscillator used to detect the singular point changes due to temperature changes, no detection error will occur.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 3.

In Figure 3, 1 is a semiconductor laser as a light source;
2 is a polygon mirror that scans the light; 3 is a lens that directs the scanning light; 4 is a code plate attached to a moving body (not shown) along the moving direction; 5 is a fixed mask;
6 is a lens for condensing the scanning light, 7 is a photodetector, and 8 is a photodetector element for generating a synchronizing signal for optical scanning. A large number of fine slits 11 are regularly formed in the code plate 4 so as to be parallel to the moving direction thereof, and the mask 5 has slits/112 which are inclined so as to produce moiré fringes when opened with the slits 7111. is formed. In this example, slits are formed between both ends to produce three moiré stripes. 11
It is formed by slanting it by 3 pitches. 13 is a binary code pattern formed to detect the rough position of the code plate 1, and its minimum detection width is equal to the slit 11.
It matches the pitch of 1. Further, the scanning light scans the binary code pattern 13 and the slit 11.

Next, using the detection signal output from the photodetector 7 and the optical scanning synchronization number 43 output from the photodetector element 8, the slit is scanned. A signal processing circuit for detecting the position within 1 pinch of 11 will be explained with reference to FIG.

The detection signal and synchronization signal are input to the control circuit 15. On the other hand, the pulse signal output from oscillator 1G is
The data is input to one first counter and one second counter 20 via the first date 17 and the second date 22-113, respectively. The first data 117 is opened by the l trigger signal outputted from the control circuit 15 based on the synchronization signal No. 43, and the first data 117 is opened at a reference time T3. (See FIG. 2), the detection signal is output when it crosses a predetermined threshold/subold level. It is configured to open and close according to the signals output from the control circuit 15 at the beginning and end of the width of one phase cycle of the detection signal.The output signals of the first and second counters 19 and 20 are 21 and performs calculations to be described later, thereby outputting calculation results corresponding to the phase of the detection signal.

Furthermore, after the first and second counters 19 and 20 are output, they are reset 21- by the 71 signal from the control circuit 15, and the arithmetic unit 21 receives the output signal from the counters by the control signal from the control circuit 15. Import and calculate.

Next, the operation of the position detection device having the above configuration will be explained.

First, the light emitted from the semiconductor laser 1 scans the code plate through the polygon mirror 2 and the lens 3 in a direction perpendicular to the direction of movement of the code plate. For each scan of the scanning light, as shown in FIG. A detection signal is output from the photodetector 7 and input to the control circuit 15. The detection number includes a binary code obtained by scanning three binary code patterns 13 formed on the second part of the code plate 4, a slit 11 of the code plate 4 and a slit 12 of the mask 5. It includes a moire fringe transmitted light amount waveform obtained by scanning the moire fringes formed by the 3D code plate 4, and a binary code obtained by scanning the 3-line binary code pattern formed at the bottom of the code plate 4.

A binary code from the detection signal input to the control circuit 15 is sent to a signal processing circuit (not shown), and by identifying this binary code, the absolute position of the code plate 4 is detected.

The first date 17 is opened by a trigger signal outputted from the control circuit 15 in response to the synchronization signal, and the time T from when the synchronization signal is output until reaching approximately the center of the scanning light beam 11 is . Fft after the period has elapsed.
Since the first counter 19 is closed by the signal output when the output (i) crosses the predetermined threshold level in the direction of the threshold, the first counter 19 is closed by the signal output when the output (i) crosses the predetermined threshold level. TI: Count the corresponding number of counts A per month.The above T time provides a reference point for minute position detection within the slit pitch, and the detection signal crosses this reference point. The position of the code plate 4 at the bottom becomes the reference position for position detection within the slit pitch.

Let C be the expected number of 1 callan in time.

Further, the second counter 20 outputs a count number B corresponding to the time Tc for scanning one phase cycle width of the detected symbol.

The output signals of the first and second counters 19.20 are input to the arithmetic unit 21, and (A-C)/B is calculated using the above-mentioned Callan numbers A, B, and C, and the calculation result is Output. Meaning of this calculation 1±, the time T from the generation of the synchronization signal to the cross point of the detection signal is measured 31, and the time T3 from the generation of the synchronization signal to the reference point is measured. difference T
-T, , and divides it by 1'c, which corresponds to the →noicle width of the moiré fringe, to detect the phase difference with the detection signal at the reference position shown by the broken line in Figure 2. By multiplying this calculation result by slit/1 bit/ch, it is possible to detect the minute position within each slit pitch that falls within the reference position, which can be compared with the rough absolute position based on the binary code. By combining them, the absolute t=J position can be detected with high precision.

Note that in Example 1)11; a semiconductor laser was used as the source, but an LED or the like may also be used. Furthermore, a Galve mirror or the like may be used instead of the polygon mirror as the scanning device. Further, as a means for rough position detection, any one-stage method other than the binary code pattern can be used.

Further, in the above embodiments, the light source side is scanned, but the present invention provides position detection in which phase is detected by providing a plurality of photodetectors that receive moiré fringes or transmitted light from a vernier, and scanning these photodetectors. It can also be applied to equipment.

Furthermore, the present invention is not limited to linear encoders as described in the embodiments mentioned above, but can also be applied to rotary encoders consisting of code plates or rotating disks.

Effects of the Invention According to the position detection device of the present invention, as described above, the singular point detection means of the detection signal, the phase shift width detection means, and the detection from the reference point and the singularity 7 ('height interval and phase shift width) Since we have a means for detecting the phase of the signal (Iiii),
The phase of the detection signal can be detected by taking the ratio of the interval between the detected singular point and the reference point and the phase cycle width detected at each detection time point by the phase M cycle width detection means, and from this detected phase It was possible to detect the position relative to the base f' position within each slot 21 interval, and at the same time, the phase cycle width was detected at each detection time, so the moiré pattern was determined by the accuracy of the code plate. Even if the period of the oscillator changes, or even if the frequency of the oscillator for detecting the singular point changes due to changes in temperature, etc., no detection error will occur, which is a great effect.

[Brief explanation of the drawing]

FIG. 1-t53 shows one embodiment of the present invention, FIG. 1 is a block diagram of the signal processing circuit, FIG. 2 is a waveform diagram of the operation 53j, and FIG. 3 is a general outline drawing of the position detection device. riS4 is a block diagram of a signal processing circuit considered in the preliminary stage of the present invention, and FIG. 5 is a perspective view of a conventional example. 1... Semiconductor laser 2...
・・・・・・Polygon mirror 4・・・・・・・・・・・・
...Coating plate 5 ......Mask 7 ...... Photodetector 8 ...... Photo detection element 11 ... −・・
...Slit 12... ...Slit 17...
......G S1 day) IS...
...pIS2'7'-119... ...
...First counter 20... Second counter 21... Arithmetic unit.

Claims (1)

[Claims] A photodetector detects the amount of transmitted light from the moiré fringes or vernier formed by a code plate having regularly arranged slits and a mask movable relative to the code plate and having regularly arranged slits. In a position detection device that detects the position within the slit pitch based on the phase of the detection signal, the detection signal has a singular point detection means, a phase cycle width detection means, and an interval between the reference point and the singular point. and means for detecting the phase of the detection signal from the phase cycle width.