JPS59210322A - Photoelectric position detection system - Google Patents

Abstract

PURPOSE:To generate a stable signal through small-sized constitution by obtaining two out-of-phase position signals from three photodetectors arranged so as to obtain the out-of-phase signals. CONSTITUTION:The photodetectors (a), (b), and (c) are arranged at intervals a quarter as large as one cycle of slits. Signals A, B, and C obtained by the detectors (a), (b), and (c) shift in phase from one another by a quarter cycle; and a subtractor 14 obtain a signal A-B and a subtractor 15 obtain a signal C-B. Further, an inversion type adder 16 obtains a signal A+C, with which the brightness of an LED is held constant through an LED driving circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric detection method for detecting changes in position or angle.

Conventionally, potentiometers, inductosyns, photoelectric encoders, etc. have been used to detect changes in position or angle. In recent years, with the advancement of semiconductors, photoelectric encoders have come into widespread use.

Figure 1 shows the principle of a photoelectric encoder.

Light from light source 1 passes through slit plate 4 or 6
The movement of the slit plate is detected by the photodetector. Usually 2. As shown in Fig. 2, the detectors are arranged with their detection positions shifted by 1/4 of one slit period, and as shown in Fig. 6 (A), (
As shown in B), the direction of movement is detected by the phase advance and lag of the signals obtained from signals 2 and 6. However, a dark current normally flows through a photodetector even when the light is dialyzed. Moreover, complete light shielding is permanent, and therefore the output does not become O even at the original light shielding position as shown in FIG. Also, the brightness of the light source changes over time.
As the temperature changes, the sharpness of the signal from the photodetector also changes. For this reason, it becomes difficult to set the threshold when the signal from the photodetector is waveform-shaped and converted into a rectangular wave. In order to eliminate these drawbacks, configurations as shown in FIGS. 4 and 5 are used.

Six additional photodetectors are added, 2 and 3 are the same as the photodetectors in Figure 2, and 2' and 3' are engraved into 4 instead of 2 and 3, respectively.
The slits are arranged so as to be shifted by 1/2 of one period of the slits. 5
The detector detects the brightness of the light source 1 and performs sphere control via the intensifier 6 so that the brightness of the light source 1 is constant.

When the sets of 2.21, 6, and 6/ are obtained as a signal through a subtracter, a periodic signal is obtained as shown in Figure 6, which is free from the influence of dark current or light leakage, and as mentioned above, the brightness of the advent is obtained. Since the amplitude is constant, the signal amplitude 1'' is also constant, and a stable signal can be obtained by selecting OV as the threshold potential when shaping the waveform into a rectangular wave. However, in FIGS. 4 and 5, a total of five detectors are required.

The present invention is an improved version of the structure shown in FIGS. 4 and 5, and the original J-shaped diagram is shown in FIG. 7-8. In the figure 2. Ro, 2'.

In place of photodetector 61, photodetectors a, l), and C are arranged shifted by 1/4 of one period of the slit.

a.

Addition and subtraction are performed between the outputs obtained from b and c. 4.5
The same effect as the configuration shown in the figure is obtained.

FIG. 9 shows a circuit diagram of an example of the present invention.

As the light source 1, a light emitting diode (LED) is used.

The waveform diagram of each part of FIG. 9 as the slit No. 4 moves is as shown in FIG.

Through 12, A, B, and C become (i5).

As shown in FIG. 10, the symbols A, B, and C are signals whose phase is delayed by 1/4 period -j. 0・r'43'
The J unit 14 executes A-13, and the subtractor 15 executes C.
-B is executed. There is a 1/4 period as a phase difference between (A-B) and (C-B), and both signals are dark N
The waveform is free from the influence of IL light leakage. Therefore, the waveform is shaped, and when obtaining the rectangular wave of E, 4iQ can be detected by using Ov as the threshold potential.

The inverting adder 16 performs addition of the A and C signals.
, +C signals are obtained. As shown in the figure, the A and C signals are out of phase by 180° for the 11iL portion of the alternating current. After performing the nose cutting, the alternating current portion disappears and the A and +C signals are only proportional to the brightness of the light source. is obtained.

This A+C signal controls L E 1) to maintain a constant brightness through the 17 L E 1) drive circuits.

As described above, although the present invention can obtain the same effects as those shown in FIGS. 4 and 5, the number of expensive photodetectors can actually be reduced to six in total, making it possible to reduce costs. Furthermore, since the photodetector group can be made small, it has the advantage that a small photoelectric encoder can be constructed.

4. f) i'+simple t152 light in Figure 1m Figures 1 and 2 are explanatory diagrams of the principle of the photoelectric position detection method, and the waveform diagram generated when moving in one direction in the 6th section ) is a waveform diagram when moving to the other side, Figure 4.5 is an example diagram of the conventional method,
FIG. 6 is a waveform diagram thereof, FIGS. 7 and 8 are illustrations of an example of the present invention, FIG. 9 is a block diagram thereof, and FIG. 10 is a waveform diagram thereof.

a　b　C・・・Photodetector 14.15 弗・・・Subtractor 16-・φ・Adder Applicant: Canon Co., Ltd. ＋　　　) Figure 6 7th item δth familiarization

Claims (1)

[Claims] A photoelectric position detection system characterized in that it is configured to obtain two position signals with different phases from six photodetectors arranged so that = signals with different phases can be obtained from each photodetector.