JPH0285714A - Encoder with reference position detecting system - Google Patents

Abstract

PURPOSE:To efficiently lead a luminous flux from a reference position detecting section to two photodetectors separated remotely by setting each element of a reference position detecting system by using a light transmission means and optical fiber. CONSTITUTION:A luminous flux emitted from a laser 1 is made incident on a deflection beam splitter 3 and divided into two linearly polarized rays of light of a reflected and transmissive luminous fluxes having nearly same light quantities after the luminous flux is changed into parallel rays of light by means of a collimator lens 2. The reflected luminous flux is changed to circularly polarized rays of light through a 1/4 wave plate 4 and made incident on the position M1 of a radiated grating 7 on a disk 6 after passing through a prism 16. Then the diffracted rays of light of the grating 7 are reflected 8 and again made incident on the nearly same position M1 on the grating 7 after the rays of light are transmitted through the same optical path in the opposite direction. Thereafter, the rays of light of specific number of order re-diffracted by the grating 7 are made incident on the splitter 3 as linearly polarized rays of light which are different in the polarized direction from that of the incident time through the wave plate 4 by 90 deg.. Thus the luminous flux from a reference position detecting section 22 can be transmitted efficiently to photodetectors 14 and 15.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an encoder having a reference position detection system suitable for photoelectrically measuring the moving state of a moving object. A light flux, especially a coherent light flux, is incident on the diffraction grating, and the diffracted light from the diffraction grating is made to interfere with each other to form interference fringes, and the movement state of a moving object is measured by counting the bright and dark fringes of the interference fringes. The present invention relates to an encoder that includes a reference position detection system that effectively and accurately obtains a reference position signal.

(Prior art) Conventionally, measuring instruments capable of measuring in submicron units use a coherent light beam such as a laser to form interference fringes from diffracted light from a diffraction grating provided on a moving object. Linear encoders and rotary encoders that utilize interference fringes or reference position signals obtained from rectangular slits are well known.

As these encoders become smaller and have higher resolution, it is necessary to obtain a reference position signal (origin signal) with high repeatability, which is used to read the interference fringes from the diffraction grating and measure the displacement of a moving object. has been done.

For example, an incremental type rotary encoder is provided with a periodic radiation grating and a pattern that generates a reference signal indicating a reference position at one point during one rotation.

The pattern of the reference signal at this time consists of reflective parts, non-transparent parts, etc., and the pattern is determined using a pattern detection system based on the presence or absence (or distance) of the pattern.

The present applicant previously disclosed in Japanese Patent Application Laid-Open No. 62-200223 a rotating disk having a diameter of 20 mm and a number of pulses per rotation (sine wave frequency) stoo.

We proposed a rotary encoder with approximately 20,250 grids. In the same bulletin, as shown in FIG. 7, a reference position signal is generated by, for example, providing a rectangular reflective slit 75 on a rotating disk 74-F, which is the object to be measured, and a light beam 71 having a rectangular or long elliptical cross section. The reflected light beam is sent to a cylindrical lens 73 and a half mirror 7.
Detection is performed by two light receiving elements 86 and 87 whose positions are shifted so that the detection timing is different.

The same publication proposes a rotary encoder that can theoretically determine a reference position with a higher resolution than the width of a rectangular reflection slit by comparing the output signals from both light receiving elements 86 and 87 with a comparator 78. ing.

On the other hand, in an encoder, there are cases where the light receiving elements 86, 81 cannot be installed inside the encoder device. for example,
At sites such as electric welding where strong electric field or strong magnetic field noise is generated near the encoder or under high temperature conditions, a light beam based on a pattern provided on the moving object to be inspected is guided to the outside using an optical fiber etc. to eliminate noise and temperature. It is necessary to guide light to the light-receiving element under an environment free from such problems.

However, as shown in FIG. 8, for example, if a condensing optical member 81° 82 (for example, a gradient index rod lens, etc.) is simply attached to the entrance surface of the optical fiber, the area where the amount of luminous flux is most concentrated will be the optical member 81. This corresponds to the boundary of .82.

For this reason, there was a problem that a large amount of light was removed from the optical members 81 and 82, resulting in a decrease in the S/N ratio of the light receiving element and a deterioration in detection accuracy.

(Problems to be Solved by the Invention) The present invention aims to detect a reference position signal related to a moving object with high precision while effectively utilizing a luminous flux when measuring the moving state of a moving object to be tested. The object of the present invention is to provide an encoder having a reference position detection system with a simple configuration.

(Means for solving the problem) A light beam is made incident on a rectangular pattern provided on a scale plate connected to a moving object to be inspected, and the reflected or transmitted light beam from the pattern is used to move the moving object to be inspected. When receiving light with two light-receiving elements whose positions are shifted with respect to the direction, and obtaining a reference position signal regarding the test moving object using the output signals from the two light-receiving elements, the reflected light flux or the transmitted light from the pattern The light flux is guided to the two light receiving elements via an optical fiber. In particular, in the present invention, the reflected or transmitted light beam from the pattern is guided to the rear and front light distributing finders via a wavefront splitting means or a light guiding means that guides the traveling directions of the two regions in different directions. It is a feature.

(Embodiment) FIG. 1 is a schematic diagram of an optical system of an embodiment when the present invention is applied to a rotary encoder.

In this embodiment, the luminous flux emitted from the laser 1 is made into a parallel luminous flux by the collimator lens 2 and is incident on the polarizing beam splitter 3.
It is split into two linearly polarized beams. The reflected light flux passes through a 174-wavelength plate 4, becomes circularly polarized light, passes through a prism 16 having two reflecting surfaces, and then is provided with a radial diffraction grating on a disc 6 connected to the rotating object to be measured. The beam is incident on position M1 of the radiation grating 7. (The diffracted light of a specific order among the transmitted diffracted light incident on the radiation grating 7 and diffracted is reflected by the reflecting means 8, and the same optical path is reversed to make it re-enter the radiation grating 7 at approximately the same position Ml. Then, the diffracted light of a specific order re-diffracted by the radiation grating 7 is converted into linearly polarized light having a polarization direction 90 degrees different from that when it is incident through the 174-wave plate 4, and is made incident on the polarizing beam splitter 3.

In this embodiment, from the polarizing beam splitter 3 to the reflecting means 8
The round trip optical path of the diffracted light of a specific order is the same.

FIG. 2 is an explanatory diagram of one embodiment of the reflecting means shown in FIG. 1.

In the figure, a reflecting mirror 40 is arranged approximately on the focal plane of a condensing lens 41, and only the diffracted light of a specific order that is incident parallel to the condensing lens 41 passes through an opening 43 of a mask 42, and the reflecting mirror 40 After being reflected by a mask 4, the diffracted light of other orders is
2. It is shielded from light.

Returning to Figure 1, the 2 beams split by the polarizing beam splitter 3
Of the two light beams, the transmitted light beam is converted into circularly polarized light through the 174-wavelength plate 5, and is made incident on a position M2 on the radiation grating 7 on the disk 6, which is approximately symmetrical with respect to the rotation axis 50 and the position M1. Then, out of the transmitted diffracted light that is incident on the radiation grating 7 and diffracted, a specific number of diffracted lights are caused to travel backward along the same optical path by a reflecting means 9 similar to the reflecting means 8 described in Moe's description, so that the diffracted light is caused to travel in the substantially concave position M of the radiation grating 7.
2 is re-injected. Then, the diffracted light of a specific order re-diffracted by the radiation grating 7 is converted into linearly polarized light with a polarization direction different by 90 degrees from that when it is incident through the I/4 wavelength plate 5, and is made incident on the polarization double splitter 3.

At this time, the transmitted light beam also has the same round-trip optical path of the diffracted light of a specific order from the polarizing beam splitter 3 to the reflecting means 9, as in the case of the above-mentioned reflected light beam.

After being superimposed with the diffracted light incident through the reflection means 8, it is made into circularly polarized light through the 174-wave plate 10, and split into two beams by the light splitter 11, with each beam having a polarization direction of 45 degrees. Through polarizing plates 12 and 13 arranged at an angle, both light beams are made to enter each light receiving means 14 and 15 as linearly polarized light with a phase difference of 90 degrees. The intensity of the interference fringes of the two beams formed by the light receiving means 14 and 15 is detected.

On the other hand, in this embodiment, among the light flux directly guided from the laser 1, the light flux from a separately provided light source (not shown), or the light flux incident on the position M of the radiation grating 7 and diffracted, the reflection means 8
Diffracted light of a specific order, for example -m order, m
A light beam 101 consisting of diffracted light beams of +1st order etc. is reflected by a reflecting mirror 18.
Through the beam splitter 19 and the cylindrical lens 21, the beam is made to form an elongated circle and is made incident on the reference position detection section 22 provided on the disk (scale plate) 6.

FIG. 3(A) is a schematic diagram of a main part when obtaining a reference position signal using the reference position detection section 22 at this time.

The reference position detection section 22 consists of a reflective surface of, for example, a rectangular slit. Then, the light beam reflected by the reference position detection section 22 is collected by the cylindrical lens 21, and the half mirror 19
The light is made incident on a light guide means 31 made of an optical path splitting prism having two regions that guide the light in mutually different directions.

The incident light beams are made incident by the light guiding means 31 at different angles to the condensing optical member 32. The optical member 32 has two points 32A whose luminous flux differs depending on the incident angle,
The light is focused on 32B.

For example, if a gradient index rod lens is used as the optical member 32, the light can be focused on two different points on the end face of the lens.

In this embodiment, by arranging the incident surfaces of the two optical fibers 33 and 34 at the condensing points 32A and 32B at this time, the two light beams from the optical member 32 are efficiently directed to the two corresponding light receiving elements 24A and 24B. It is guiding light.

The two light beams at this time are transmitted to two light receivers 24A and 2.
A reference position signal is obtained by photoelectrically receiving light with the light receiving means 24 having 4B.

The light receiving means 24 has two integrated light receiving surfaces.
It may also be composed of two light receiving elements. As a result, in this embodiment, a reference signal is obtained for measuring the rotational state of the disk 6, for example, one reference signal for each rotation.

In this way, by using a light beam whose irradiation cross section is linear and by making the reflection slit also have a similar linear shape, the influence of dust, scratches, etc. is reduced.

FIG. 3(B) is an explanatory diagram schematically showing a situation when a reflective surface having a width P as the reference position detecting section 22 approaches a convergence area of a light beam having a width Pa.

In this example, the light beam from the laser is transferred to a beam splitter.
A part of the light is reflected by the cylindrical lens 21 and condensed into a line near the reference position detection section 22 on the disk 6. When the disk 6 reaches a certain position as the disk 6 moves, the reflective surface 2 of the reference position detection section 22
reflected by 2a.

At this time, if the reflecting surface 22a is moving from left to right as shown in FIG. incident.

When the reflecting surface 22a further moves to the right, the light also enters the light receiver 24B. As a result, the light receiver 24A and the light receiver 24B
There is a moment when the amount of incident light becomes equal.

In this embodiment, two light receivers 24A and 24B are used at this time.
The position where the output signals from the two are equal is defined as a reference position, and a Z-phase signal is generated.

FIGS. 4(A) to 4(E) show how the amount of light incident on the two light receivers 24A and 24B changes in the relative relationship between the reflecting surface 22a and the width Pa of the light beam converging area in the third embodiment. FIG.

As is clear from the figure (B), it is preferable to set Pa=2P in order to accurately detect a two-phase signal. When Pa≦P in the figure (E), it becomes difficult to accurately detect the zero position.

FIGS. 5A, 5B, and 5C are schematic diagrams of other embodiments of the light guiding means 31 according to the present invention. Of these, the figure (A) shows a case in which a prism has a refracting action on only one side for the incident light beam 101, and the figure (B) shows a case in which two prisms having the same or different apex angles are opposed to each other. In the case of a prism, the entrance end face of a gradient index rod lens is processed to have a roof shape, as shown in FIG. 3(C).

In addition, in this embodiment, any optical member can be used as long as it divides the incident light beam 101 into two regions and refracts the two regions in mutually different traveling directions.

FIGS. 6A to 6E are schematic diagrams of main parts of other embodiments of a reference position detection system for obtaining a reference position signal according to the present invention.

In the same figure (A), a reflected light beam 101 from a reference position detecting section 22 on a disk (scale plate) 6 is condensed by a silitorical lens 21, and is passed through a half mirror 19 to a wavefront dividing means 61 as a light guiding means. It is input to.

The wavefront splitting means 61 has a reflecting surface 62 in an area corresponding to approximately half of the area through which the incident light flux passes. The incident light beam 101 is divided into two light beams, a transmitted light beam and a reflected light beam, and each light beam is made to enter a condenser lens 63, 64.

The condensing lenses 63 and 64 condense the light beams onto the incident surfaces of the optical fibers 33 and 34, respectively. Thereby, the light flux is efficiently guided to the light receiving elements 24A and 24B via the optical fibers 33 and 34.

In this embodiment, the light beam incident on the condenser lens 63.64 is divided by the boundary of the reflective surface 62, so that the light beam near the boundary where the amount of light is large is efficiently guided to the condenser lens 63.64. Optical axis (center axis) of condensing lens 63.64
are placed offset from each other.

Each of the embodiments shown in FIGS. 6(B) to (E) is different from the embodiment shown in FIG.
The only difference is the light guiding means placed in the optical path leading to the
The other configurations are exactly the same.

In the embodiment shown in FIG. 6(B), the light guide means 65 is composed of two prisms: a prism 65b having a half mirror 65a and a prism 65d having a total reflection mirror 65c.

The half mirror surface 65a divides the light beam 101 into two light beams: a reflected light beam and a transmitted light beam. After the transmitted light beam is reflected by the total reflection surface 65c, only one side of the light beam is incident on the condenser lens 63, and the other light beam is passed through the light shielding member 66.
It is blocked from light.

Also, of the light beams reflected from the half mirror surface 65a, only one side of the light beams is allowed to enter the condenser lens 64, and the other light beams are blocked by a light shielding member 66. As a result, two light receiving elements 24
The detection timings of the luminous fluxes A and 24B are made different.

In this embodiment, the boundary line between blocking and transmitting both light beams is the disk 6.
It is set so that when the upper reference position detection section 22 is located at the center of the luminous flux irradiation area, it becomes the position where the maximum luminous flux is incident.

In the embodiment shown in FIG. 6(B), the boundaries of the shielding members 66 are shifted from each other in the direction of shielding more light and the opposite direction, as shown in FIGS. 6(C) and (D). You may do so.

Alternatively, the light shielding member 66 may be omitted by shifting the positions of the condenser lenses 63 and 64 from each other as shown in FIG. 6(E).

Although each of the embodiments described above has been described with respect to a rotary encoder, the present invention can be applied to a linear encoder in exactly the same manner.

(Effects of the Invention) According to the present invention, by setting each element of the reference position detection system using a light guide means and an optical fiber as described above, the light flux from the reference position detection unit can be efficiently transmitted to two far apart locations. It is possible to achieve an encoder having a reference position detection system that can guide light to a light receiving element, prevent a decrease in the S/N ratio, and detect the moving state of a moving object with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment when the present invention is applied to a rotary encoder, FIGS. 2, 3, (A), and (B) are explanatory diagrams of a portion of FIG. 1, and FIG. 4 is an explanatory diagram of the output signals obtained from the two light receiving elements 24A and 24B for the reference position signal shown in FIG. 1, and FIG.
A schematic diagram of another embodiment of the light guiding means in FIG. 6(A), FIG.
) to (E) are schematic diagrams of other embodiments of the reference position detection system according to the present invention, and FIGS. 7 and 8 are schematic diagrams of conventional reference position detection systems. In the figure, 1 is the laser, 2 is the collimator lens, 3.19
is a beam splitter 14, 5, 10 is a 174 wavelength plate,
6 is a disk, 7 is a radiation grating, 8 and 9 are reflecting means, 11 is a light splitter, 12.13 is a polarizing plate, 14, 15, 24A, 2
4B is a light receiving element, 21 is a cylindrical lens, 22 is a reference position detection unit, 31, 61.65 is a light guiding means, 32° 63, '64 is a condensing lens, 33.34 is an optical fiber, and 66 is a light shielding member. . Patent applicant: Canon Co., Ltd. No. 1 M No. 4 β (K) 1 101 Su, Shi No. 6 Kasumi (D) ([)

Claims (2)

[Claims] (1) A light flux is made incident on a rectangular pattern provided on a scale plate connected to a moving object to be inspected, and the reflected or transmitted light flux from the pattern is shifted in position with respect to the moving direction of the moving object to be inspected. When receiving light with two light-receiving elements, and obtaining a reference position signal regarding the moving object to be detected using the output signals from the two light-receiving elements, the reflected light flux or transmitted light flux from the pattern is transmitted through an optical fiber. An encoder having a reference position detection system characterized in that light is guided to two light receiving elements. (2) The reflected light flux or the transmitted light flux from the pattern is guided to the optical fiber after passing through a wavefront splitting means or a light guide means that guides the traveling directions of the two regions of the light flux in different directions. An encoder having a reference position detection system according to claim 1.