JPH03267719A - Reference position detector and encoder using the same - Google Patents

Abstract

PURPOSE:To obtain large tolerance to sensitivity variation and high stability by providing luminous flux irradiating means, reflecting individual detecting means for a reference position signal having a phase difference from reflected light from reflecting slits on a body moving relatively with luminous flux and an irradiated position, and coincidence time point specifying means for both intensity values which are larger than a specific level at two specific places. CONSTITUTION:The light reflective slits 11 and 12 are arranged so that they are overlapped with each other in the slit advancing direction, the width of their overlapping part is smaller than the width of an image formation spot of the luminous flux, and when the signal outputs of two photodetectors are larger than the specific level and match each other, the slits are irradiated with the luminous flux to area which is larger than a half. Then the intersection P1 of wavelengths V1 and V2 moves up and the amplitude of the mean value V4 increases, so that the permissible range of a voltage Vr is expanded. Consequently, the setting of the voltage Vr is facilitated and the permissible range which is sufficiently wide can be secured even when the V4 is affected by the variation in the quantity of light and the variation in the sensitivity of a photodetecting element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is mainly used in encoders that detect displacement, and relates to a method of detecting a reference position.

[Prior Art] A conventional example of a method for detecting a reference position in an encoder such as a linear encoder or a rotary encoder is shown in Fig. 6(a).
Shown below. In this example, one light beam 2 is projected onto a light reflective slit 1 formed on the same substrate as the moving or rotating scale of the encoder, and the reflected light 3 is sent to the photodiode 4.
It receives light and converts it into electricity. The light-receiving current of the photodiode 4 is converted into a voltage by a current-voltage conversion circuit 5, and then compared with a predetermined voltage value Vr by a comparator 6 to obtain a reference position signal vO, which is converted to the base position of the encoder, i.e. It was at the zero position. FIG. 6(b) shows an example of waveforms at each part of the processing circuit when the slit moves to the left (in the direction of the arrow) in the figure.

In such an example, if the light intensity of the light flux or the sensitivity of the photodiode changes due to changes in temperature, the magnitude of the light-receiving current may increase or decrease as shown in the example waveform on the right side of the figure (b). Since the reference position signal V
This method has a problem in that the reference position cannot be detected accurately because the timing of occurrence of o is deviated.

Therefore, in order to solve this problem, the applicant of the present application has published Japanese Patent Application Laid-Open No. 62
−． In Japanese Patent No. 163923, a device having a configuration as shown in FIG. 7(a) is proposed.

In the figure, when the slit moves in the direction of the arrow, the waveforms at each part of the processing circuit are as shown in FIG. 7(b). In this example, two light reflective slits 11.12 are arranged side by side along the moving direction so that their areas do not overlap, and two light beams 21.2 are split from the same light source.
2 is irradiated onto each slit position, and these reflected lights 31 and 32 are individually received by photodiodes 41 and 42. The light-receiving current is converted into voltage by current-voltage conversion circuits 51 and 52 (waveforms V1 and V2), and then compared in magnitude by a comparator 61, and the intersections P1 and P2 of the two waveforms are detected (waveform V3).

On the other hand, the two output values of the current-voltage conversion circuits 51 and 52 are averaged by an average value circuit 71 (waveform V4), and compared with a constant voltage Vr by a comparator 62 to a predetermined level V.
A portion equal to or greater than r is detected (waveform V5). The logic circuit 81 extracts the portion A at which the output V3 of the comparator 61 is inverted, which is the portion above the predetermined level (the high level section of waveform 5), as the reference position signal Vo. This makes it possible to accurately detect the reference position.

Note that the predetermined voltage Vr here needs to be set to an intermediate value between the two intersections P1 and P2 of the outputs of the current-voltage conversion circuits 51 and 52, as shown in the same figure (b) as the permissible range of Vr. .

With this method, even if the light intensity of the light flux or the sensitivity of the phototied changes due to changes in temperature, the two received light signals change proportionally and integrally, so the position of the intersection point P1 does not change and can be accurately referenced. Can detect location.

[Problem to be solved by the invention] However, in the above example, the predetermined voltage Vr needs to be set to an intermediate value between the two intersection points P1 and P2 of the outputs of the current-voltage conversion circuit 51 and 52, so this value The allowable value is a little less than 1/2 of the amplitude of the received light signal. Also, since the average light amount v4 is affected by changes in light amount and sensitivity changes of the light receiving element, Vr
The allowable range is actually narrower than this. Considering these, it is desired to provide a method with a wider tolerance range for stabilizing the device.

[Purpose of the Invention] The present invention has been made to solve the above-mentioned problems, and has a simple structure and a high tolerance for changes in light amount and sensitivity of the light receiving element (a highly stable reference position pressure detection device layer). The present invention also aims to provide an encoder using the device.

[Means for Solving the Problems] A reference position detection device of the present invention that solves the above problems includes means for irradiating a light beam to two predetermined locations, and a means for irradiating a light beam onto two predetermined locations, and a means for displacing a displacement object that moves relative to the irradiation light beam. a light amount detection means for individually detecting two reference position signals having a phase difference by respectively detecting reflected light or transmitted light from the two irradiated locations; and means for specifying as the reference position of the displaced object a point in time when the intensities of the two reference position signals obtained by the light amount detection means match at a predetermined level or higher, and the output of the two signals match at a predetermined level or higher. The slit is characterized in that the slit is arranged so that at a point in time, an area larger than half of the light beam is irradiated onto the slit.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1(a) is a block diagram of an embodiment of the reference position detection device according to the present invention, and the same reference numerals as in FIG. 7 represent the same or similar members. Further, FIG. 1(b) shows an example of waveforms at each part of the processing circuit when the slit moves in the direction of the arrow.

In FIG. 1(a), compared to the previous FIG. The width of the portion is set smaller than the width of the imaging spot of the light beam. That is, the slit is arranged so that when the outputs of two signals obtained by the two photodetectors match at a predetermined level or higher, an area larger than half of the luminous flux is irradiated onto the slit. . Note that since the circuit configuration is the same as that shown in FIG. 7 above, a detailed explanation of the operation will be omitted.

With such a configuration, vl in FIG. 1(b)
, ■2 The point P1 where the two waveforms intersect near the center moves upward, and the amplitude of their average value ■4 increases. In other words, the permissible range of voltage Vr is wider than that shown in FIG.
Since r can be set over a wider range, the setting becomes easier.

In addition, even when affected by changes in the amount of light or changes in the sensitivity of the light-receiving element, it is possible to secure a sufficiently wider tolerance range for V than before.

Note that if the overlap width of the slits becomes larger than the width of the irradiated light beam (width of the imaging beam spot on the scale advancing direction side), Vl and v2 will intersect at a small change point, and the reference position will change. The width of the overlap of the slits needs to be smaller than the width of the illuminated beam, since the detection becomes ambiguous.

Now, FIGS. 2(a) and 2(b) show a modification of the above embodiment, and the same reference numerals as in FIG. 1 represent the same or similar members. Note that in both figures of FIG. 2, the circuit for processing the signals detected by the photodiodes 41 and 42 is the same as that shown in FIG. 1, and is therefore omitted.

In FIG. 2(a), the light-reflective slits 11 and 12 are arranged in an array with no overlap in the displacement direction, similar to the conventional example shown in FIG. 7(a). The positions are irradiated with a phase difference as shown in the figure. Here, if both slits are displaced in the direction of the arrow, the signal obtained will be similar to that shown in FIG. 1(b).

Further, in FIG. 2(b), two light beams are irradiated onto a single reflective slit 13 at an interval slightly narrower than the width of the slit J3 in the displacement direction. If the slit 13 is now displaced in the direction of the arrow, the obtained signal will be similar to that shown in FIG. 1(b).

That is, for these examples as well, as with the first example, 2
The slit is arranged so that an area larger than half of the luminous flux is irradiated to the slit when the outputs of the two signals obtained by the two photodetectors match at a predetermined level or higher, and the voltage Vr The permissible range of voltage Vr is wider than that shown in FIG. 7, and the voltage Vr can be set within a wider range.

In addition, although the case of reflected light was described in each of the above-mentioned embodiments, the case of transmitted light can also be considered in the same way. Also, the same idea is valid even if the light and dark are reversed.

Furthermore, it goes without saying that the angle of incidence on the slit and the shape of the light beam are not limited to the above configuration.

Next, an embodiment in which the above reference position detecting device is used as an encoder will be described with reference to FIGS. 3 and 4 using v1.

FIG. 3(a) is a diagram showing a scale plate used in a linear encoder, with a slit (diffraction grating) for measuring the amount of movement.
The reference position detection slit described above is formed on the scale plate.

On the other hand, Fig. 3(b) shows a detailed part of a rotating disk plate used in a rotary encoder, and shows a slit (diffraction grating) for measuring the amount of movement along the rotation direction of the rotating disk plate.
The reference position detection slit described above is provided in a part of the inside thereof.

FIG. 4 shows an example of the configuration of an encoder having these scale plates and rotating disks. A beam of light emitted from a coherent light source 101 such as a semiconductor laser passes through a Heems blister 10.
2, the beam is split into two beams, and the beam is incident on a single point on a diffraction grating 103, which is a slit for measuring the amount of movement formed on a scale plate or rotating disk plate as shown in FIG.

In addition, although not shown in the figure, an optical system for slit detection as shown in Fig. 1(a) is provided, which optically detects the slit for detecting the reference position on the scale plate or rotating disk plate. The configuration is such that the zero position of the encoder can be obtained in this way.

Reflection optical system 1 from diffraction grating 103 due to the incidence of the light beam
Both of the higher-order diffraction lights, here the ±1st-order diffraction lights, generated in the 04 direction are reflected by the reflection optical system 104 and re-enter the diffraction grating 103 at substantially the same position. The reflective optical system 104 constitutes a so-called cat's eye optical system. Here, the ±1st-order re-diffracted light generated by re-incidence returns along substantially the same optical path as that at the time of incidence. The interference light formed by this ±1st-order re-diffracted light is transmitted to the polarizing beam splitter 1.
The signal is detected by photodetectors 106 and 107 as a two-phase periodic signal with a phase difference of 90 degrees by the polarizer 04 and the deflection plate. The detection signals obtained by these photodetectors 106 and 107 are interpolated in the pulse output circuit 108 in order to increase the detection resolution, and divided pulses are obtained by detecting the zero cross point of the waveform of each signal. This is output as a detection pulse corresponding to the displacement of the diffraction grating. In this way, a number of detection pulses corresponding to the amount of relative displacement (amount of rotation or amount of movement) of the diffraction grating with respect to the incident light beam are outputted from the output terminal of the pulse output circuit 108. Furthermore, the direction of rotation and direction of movement are also detected.

Note that the optical arrangement of the encoder is not limited to the above embodiment, and can take various forms, such as an arrangement using a transmission type diffraction grating.

FIG. 5 shows an example of the use of the encoder, and is a system configuration diagram of a drive system using the encoder. An encoder 111 is connected to the drive output part of a drive means 110 having a drive source such as a motor, actuator, or internal combustion engine, or to the moving part of a driven object, and encodes the amount of rotation, rotation speed, amount of movement, or movement speed along with the τ position. etc. is detected. The detection output of the encoder 111 is fed back to the control means 112, and the control means 112 transmits a drive signal to the drive means 110 so that the state set by the setting means 113 is achieved. By configuring such a feedback system, it is possible to maintain the driving state set by the setting means 113 without being affected by disturbances. Such a drive system can be widely applied to, for example, machine tools, manufacturing machines, measuring instruments, recording instruments, and not only these, but also general devices having drive means.

[Effects of the Invention] As described above, the present invention provides a device with high tolerance to changes in the amount of light and changes in the sensitivity of the light receiving element.

[Brief explanation of drawings]

Fig. 1 is a diagram of an embodiment of the reference position detection device according to the present invention, Fig. 2 is a modification of the embodiment shown in Fig. 1, and Fig. 3 is a diagram of an encoder scale plate when the present invention is applied to an encoder. 4 is a block diagram of the encoder of the present invention, FIG. 5 is a system block diagram of a drive system using the encoder, and FIG. 6 is a conventional example of a reference position detection device. 7 is a diagram of a conventional example of a reference position detection device proposed by the applicant of the present application, and the main symbols in the figure are: 1.11.12... slit for reference position detection, 2.
21.22...Incoming light flux, 3.31.32...Reflected light flux, 4.41.42...Photodiode, 5.51.
52...Current voltage conversion circuit, 6.61.62...
・Comparator, 71...Averaging circuit, 81...Logic circuit,

Claims (2)

[Claims] (1) A means for irradiating a light beam to two predetermined places, a reflection or transmission slit provided on a displacement object that moves relative to the irradiated light beam, and reflected light from the two irradiated places. or a light amount detection means that individually detects two reference position signals having a phase difference by respectively detecting transmitted light, and the intensity of the two reference position signals obtained by the light amount detection means match at a predetermined level or more. and means for specifying a point in time as a reference position of the displaced object, and when the outputs of the two signals match at a predetermined level or higher, an area larger than half of the luminous flux is irradiated onto the slit. A reference position detection device characterized in that the reference position detection device is arranged so that the (2) A light source that generates a coherent light beam, which is movable relative to the light beam from the light source, and has a scale for detecting the amount of displacement and a reflection or transmission slit for the reference position formed on the surface. means for measuring the displacement of the displacement object by irradiating the light beam from the light source onto the displacement detection slit and detecting light from the scale; means for irradiating a luminous flux to two predetermined locations, a reflection or transmission slit provided on a displacement object that moves relative to the irradiation luminous flux, and a reflection or transmission slit from the two irradiated locations. A light amount detection means that detects each light and individually detects two reference position signals having a phase difference, and a time point when the intensities of the two reference position signals obtained by the light amount detection means match at a predetermined level or more. and means for identifying the displaced object as a reference position, and when the outputs of the two signals match at a predetermined level or higher, an area larger than half of the luminous flux is irradiated onto the slit. A reference position detection device characterized in that it is arranged as follows.