JPH09203644A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output an origin signal even when a gap between a moving scale and a fixed scale is large, by providing an origin phase first circular slit having concentric slits, an origin phase second circular slit and an origin phase third circular slit of the same pitch as that of the first circular slit, an origin phase photodetecting element for detecting the amount of light passing through the origin phase third slit, etc. SOLUTION: An origin phase first circular slit 11 having concentric slits, an origin phase second circular slit 22 formed on a fixed scale 2 and having the same slit pitch as that of the slit 11, and an origin phase third circular slit 24 formed on the scale 2 and having the same slit pitch as that of the slit 11 are provided. A scattering light emitted from a light source 3 passes through the slit 22, and illuminates the slit 11 on a moving scale 1. The amount of a reflecting light from the scale 1 passing through the slit 24 on the scale 2 is detected.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to origin detection of an optical encoder.

[0002]

2. Description of the Related Art As a method of detecting the origin of an optical encoder using a diffractive three-grating optical system, there is the following conventional example (JP-A-61-212727). FIG. 5 is a block diagram of this conventional optical system. Hereinafter, this conventional example will be described. In this figure, the fixed optical grating 2 for displacement detection, which is attached to the fixed side of the light sources 10A and 10B and the detection target,
0 is formed on the surface of the reflection type main scale 18, an index scale 14 having movable optical gratings 16A and 16B for displacement detection attached to the movable side of the object to be detected, the fixed optical grating 20 for displacement detection, A light receiving element 24A for receiving the first optical signal for displacement detection modulated by the first movable optical grating 16A and converting it into a first electric signal for displacement detection Vx1, the fixed optical grating for displacement detection 20 and the second optical element. A light receiving element 24B for receiving the second optical signal for displacement detection modulated by the movable optical grating 16B and converting it into a second electric signal for displacement detection Vx2 is provided. The displacement detecting fixed optical grating 20 is, for example, a reflection grating having a bright line and a dark line having substantially the same width, and the displacement detecting movable optical gratings 16A and 16B are transmission gratings having the same pitch as the displacement detecting fixed optical grating 20. And the two are formed so that their phases are different from each other by 90 °. Therefore, the waveforms of the displacement detecting first electric signal Vx1 and the displacement detecting second electric signal Vx2 output from the light receiving element 24A are close to sine waves in which the electric signal pitch is S1 and the phases are different from each other by 90 ° as shown in FIG. It is a signal. Further, the main scale 18
An origin detecting fixed optical grating 30 is integrally formed on the upper side along with the displacement detecting fixed optical grating 20. The fixed optical grating 30 for origin detection is, for example, a reflection grating in which the widths of the bright line and the dark line are substantially equal. At least one reference mark 32 having an optical reflection characteristic is integrally formed on the origin detection fixed optical grating 30 in correspondence with the origin position and the number of detection. The index scale 14 has movable optical gratings 16A, 16A for detecting displacement.
The movable optical gratings for origin detection 16A, 16 similar to the movable optical grating for origin detection 34 integrally formed along B
A reference light detection window 38 integrally formed on the extension line of B is provided. The origin detecting movable optical grating 34 is a transmission grating having the same pitch as the origin detecting fixed optical grating 30. Therefore, the index scale 14 is provided by the light source 40 and the light receiving element 43 provided at corresponding positions.
On the other hand, when the main scale 18 is displaced in the direction of arrow C or in the opposite direction, the origin detecting first electric signal V01 having the pitch S2 as shown in FIG. 7 can be generated. The origin detection window 36 is a window that can transmit light uniformly,
When the main scale 18 is displaced in the direction of arrow C or in the opposite direction, the second optical signal V02 as shown in FIG. Can be generated. The reference light detection window 38 can generate a first reference voltage Vref1 that is hardly subjected to optical modulation by the optical grating 20. The light receiving elements 24A, 2
4B is connected to an encoder 60 as shown in FIG. 8, which is connected to a counter 62, which is connected to a display 64 for displaying the measured displacement amount. Further, the light receiving element 43 is connected via an amplifier 66 to a first comparator 68 for detecting the first intersection. Further, the light receiving element 46 is an amplifier 70.
Second comparator 7 for detecting the second intersection via
2 are connected. The light receiving element 48 is connected to a reference signal generator 74 for generating the first and second reference voltage signals Vref1 and Vref2. The first and second comparators 68 and 72 are connected to an absolute origin specifying circuit 76 for specifying an absolute origin. The absolute origin specifying circuit 76 is connected to the counter 62 to correct the count value of the counter 62. The second reference voltage Vref2 is adjusted by adjusting the constant of the electric circuit so that the point P0 of the second electric signal V02 coincides with the point P2 of the first electric signal V01 when the main scale 18 is displaced in the arrow direction. It is created by shifting the reference voltage Vref1. By doing so, first, the second comparator 72 detects the second intersection P0 at which the second electric signal V02 becomes equal to the second reference voltage Vref2, and then the first electric signal V01 becomes equal to the first reference voltage Vref1. The constant (N) th, for example, the first first intersection point P3 is detected by the first comparator 68, and the absolute origin specifying circuit 76 detects the first first intersection point P3.
The origin position was determined with high accuracy by setting 3 as the origin position. Since this optical system is a diffraction-type three-grating optical system, the first electric signal V01 is accurate even if the gap between the main scale and the index scale having slits with a slit pitch of several tens of μm is several millimeters. The origin phase can be detected accurately with this structure.

[0003]

However, in the conventional example, two means, that is, the reference mark detecting means and the origin detecting means are necessary, and the light source-optical grating-light-receiving element associated therewith is required. Therefore, the displacement including the detection system is required. There is a problem that the whole detection device becomes large and the signal processing for origin detection is complicated, and when the slit pitch becomes smaller, it is necessary to reduce the origin detection signal cycle S2 in order to improve the origin accuracy. In such a case, the change in the output signal of the reference mark detecting light receiving element 46 within the cycle S2 becomes small, so that it becomes difficult to adjust P0 and P2 to the same phase, and the origin detection accuracy deteriorates. was there.
Here, an object of the present invention is to provide an inexpensive optical encoder device that can accurately output an origin signal even if the gap between the movable scale and the fixed scale is wide, and that is small and has a simple structure. .

[0004]

In order to achieve the above object, the present invention is directed to a moving scale which is fixed to one member that moves relatively and has a plurality of first slits in the moving direction, and the other moving scale. Which is fixed to the member of FIG. 1 and is disposed between the light source that emits diffused light and the moving scale through a gap, and includes a second slit that functions as a light source slit and a third slit that functions as an index slit. Diffused light emitted from the fixed scale and the light source passes through the second slit on the fixed scale, irradiates the moving scale, and the reflected light from the moving scale is detected via the third slit. With a light receiving element,
In an optical encoder for detecting relative displacement of both members from a periodic variation of a detection signal of the light receiving element output, provided for origin detection on the moving scale,
An origin phase first circular slit having concentric circular slits, and an origin phase second circular slit formed on the fixed scale and having the same slit pitch as the origin phase first circular slit. Diffuse light emitted from the light source is provided separately from the origin phase third circular slit formed on the fixed scale and having the same slit pitch as the origin phase first circular slit, and the light receiving element. Origin phase light reception that detects the amount of light that passes through the origin phase second circular slit, irradiates the origin phase first circular slit on the moving scale, and detects the amount of the reflected light that passes through the origin phase third circular slit. Optical encoder consisting of elements. An optical encoder in which the slit pitches of the origin-phase second circular slit and the origin-phase third circular slit are each twice the slit pitch of the origin-phase first circular slit.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration diagram of an optical system of an optical encoder of the present invention. As shown in FIG. 1, the optical system is composed of a moving scale 1, a fixed scale 2, a light source 3, and light receiving elements 41A, 41B, 42. On the moving scale 1 surface, an incremental phase first slit 11 and an origin phase are provided. A first circular slit 12 is arranged, and an incremental phase second slit 21, an origin phase second circular slit 22, an incremental phase third slits 23A and 23B, and an original phase third circular slit are arranged on the surface of the fixed scale 2. 24 are arranged. The light source 3 is diffuse light,
The light emitted from the light source 3 passes through the second slit of the incremental phase and the second circular slit of the origin phase, respectively, and is reflected by the first slit 11 and the first slit 12 of the origin phase on the moving scale 1, respectively. The light quantity changes of the incremental phase reflected lights 51A and 51B and the origin phase reflected light 52 which are transmitted through the third slits 23A and 23B and the origin phase third circular slit 24 are detected by the incremental phase light receiving elements 41A and 41B and the origin phase light receiving element 42, respectively. However, the displacement amount and the origin position are detected. The optical system in the incremental phase has a diffractive structure as disclosed in, for example, U.S. Pat. No. 3,812,352, which means that the gap between the moving scale and the fixed scale is small even if the slit pitch is about several microns. There is a feature that you can take as large as several millimeters. FIG. 2 shows patterns of the incremental phase first slits 11 and the origin phase first circular slits 12 on the moving scale 1 of this embodiment. In the present embodiment, the slit pitch of the first phase first circular slit 12 is made equal to the slit pitch of the incremental phase. FIG. 3 shows the second slit 2 of the incremental phase on the fixed scale 2 of this embodiment.
1, the pattern of the origin phase second circular slit 22, the incremental phase third slits 23A and 23B, and the origin phase third circular slit 24 is shown. Incremental phase third slits 23A, 23B on the fixed slit 2
Are arranged so as to obtain signals having different phases by 90 °. Further, the pitch ratio of the incremental phase first slit 11, the incremental phase second slit 21, and the incremental phase third slit is 1: 1: 1 or 1: 2: 2, respectively. Further, the pattern of the origin-phase second circular slits 22 is an inverted pattern of the origin-phase first circular slits 12 on the moving scale 1 in FIG. 3, but the pattern may be the same, and the number of slits is different. Is also good. Although the pattern of the origin-phase third circular slit 24 is the same as the pattern of the origin-phase second circular slit 22 in FIG. 3, the pattern of the origin-phase first circular slit is reversed.
It may be the same pattern as the pattern. Origin phase first circular slit 12 and origin phase second circular slit 22 and origin phase third
The slit pitch ratio of circular slits is 1: 1: 1 respectively
Alternatively, it is configured with 1: 2: 2, and with such a configuration, a diffraction type optical system configuration similar to the incremental phase is obtained, and even if the slit pitch is about several microns, the gap between the moving scale and the fixed scale is It can be as large as a few millimeters. Further, at this time, due to the circular slit image formed on the surface of the origin phase third circular slit 24 and the moire fringe of the origin phase third circular slit 24, the change in the amount of light transmitted through the origin phase third circular slit 24 changes as shown in FIG. Further, in the present embodiment, the origin phase circular first slit pitch is made equivalent to the incremental phase first slit pitch, so that the pulse width of the origin phase signal can be always contained within one cycle of the incremental phase, and high accuracy can be obtained. can get. In addition, in applications where the pulse width of the origin phase signal may be outside one cycle of the incremental phase, the origin phase circular first slit pitch can be made larger than the incremental phase first slit pitch. Origin phase light receiving element 42
Since the amount of light that hits is determined by the area occupied by the origin-phase third circular slit, a sufficient amount of light can be obtained even if the slit pitch becomes small. Since the present optical system irradiates only with the light source 3, the device is small and the signal processing is very simple. By the means, the origin-phase first circular slit, the origin-phase second circular slit, and the origin-phase third circular slit have a diffractive configuration, so that the circular slit image is the origin even if the gap between the movable scale and the fixed scale is increased. A sharp origin signal is obtained by forming the circular slit image on the phase third circular slit and the moire fringe of the phase third circular slit. Further, although the linear encoder is applied in the above-mentioned embodiment, the scope of application of the present invention is not limited to this, and it is obvious that the rotary encoder is also applied.

[0006]

As described above, according to the present invention, since the circular slit is applied as the origin phase slit and the diffractive optical system is constructed, the fixed slit is used even if the slit pitch has a resolution of about several μm. The gap between the scale and the moving scale is sufficient, and the origin signal can be output with high accuracy.
Since the device is also simple and can be configured in a small size, it is possible to configure an inexpensive optical encoder with high resolution.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of an optical encoder of the present invention.

FIG. 2 is a diagram showing an incremental phase first slit and an origin phase first circular slit on a moving scale that is an embodiment of the present invention.

FIG. 3 is an embodiment of the present invention in which an incremental phase second slit and an incremental phase third on a fixed scale are provided.
It is a figure which shows a slit, an origin phase circular 2nd slit, and an origin phase circular 3rd slit.

FIG. 4 is a diagram showing a light amount detection signal transmitted through a third circular slit of the origin phase on the fixed slit of the embodiment.

FIG. 5 is a configuration diagram of an optical system of a conventional optical encoder.

FIG. 6 is a diagram showing a received light waveform obtained by a conventional light receiving element.

FIG. 7 is a diagram showing a light receiving waveform obtained by a light receiving element which is a conventional example.

FIG. 8 is a block diagram showing a circuit configuration of a conventional example.

[Explanation of symbols]

1 Moving scale 11 Incremental phase 1st slit 12 Origin phase 1st circular slit 14 Index scale 18 Main scale 16A, 16B Movable optical grating for displacement detection 2 Fixed scale 21 Incremental phase 2nd slit 22 Origin phase 2nd slit 23A, 23B Incremental Phase 3rd slit 24 Origin phase 3rd circular slit 20 Fixed optical grating for displacement detection 30 Fixed optical grating for origin detection 32 Reference mark 34 Movable optical grating for origin detection 36 Origin detection window 38 Reference light detection window 3, 10A, 10B, 40, 44, 48 Light source 24A, 24B, 41A, 41B Incremental phase light receiving element 42, 43, 44 Origin phase light receiving element 50 Reference voltage generating light receiving element 51A, 51B Incremental phase reflected light 52 Origin phase reflected light 60 Encoder 2 counters 68, 72 comparators 76 absolute origin specific circuit Vx1, Vx2 first electrical signal V02 second electrical signal Vref1 first reference voltage Vref2 second reference voltage point detection displacement detection electric signal V01 origin detection

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Nakajima No.2-1 Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu, Fukuoka Prefecture Yasukawa Electric Co., Ltd.

Claims (2)

[Claims] 1. A moving scale, which is fixed to one member that relatively moves and includes a plurality of first slits in the moving direction, and a light source that is fixed to the other member that relatively moves and emits diffused light, and the moving scale. And a fixed scale composed of a second slit functioning as a light source slit and a third slit functioning as an index slit and a diffused light emitted from the light source on the fixed scale. A light-receiving element that transmits the second slit of, irradiates the moving scale, and detects reflected light from the moving scale via the third slit,
In an optical encoder for detecting relative displacement of both members from a periodic fluctuation of a detection signal of the light receiving element output, an origin phase number which is provided for origin detection on the moving scale and has a concentric circular slit is formed. 1 circular slit, an original phase second circular slit having the same slit pitch as the original phase first circular slit formed on the fixed scale, and the same slit as the original phase first circular slit. Origin phase third formed on the fixed scale with a pitch
The circular slit and the light receiving element are provided separately, and diffused light emitted from the light source passes through the origin-phase second circular slit and irradiates the origin-phase first circular slit on the moving scale, and the reflected light is reflected. An optical encoder comprising an origin phase light receiving element for detecting the amount of light transmitted through the origin phase third circular slit on the fixed scale. 2. The optical encoder according to claim 1, wherein the slit pitches of the origin-phase second circular slit and the origin-phase third circular slit are each twice the slit pitch of the origin-phase first circular slit.