JPH02147816A - Scale reader - Google Patents

Abstract

PURPOSE:To obtain the title reader which hardly receives the effect of the change of temperature at the time of measurement by making irradiating light have a line focus in parallel with the pattern line of a scale. CONSTITUTION:A laser light beam is splitted into two by a 1st beam splitter 3 and projected on the scale by means of separate optical paths, and the transmitted light or the reflected and diffracted light of the laser light beam is converged. The diffracted light beams splitted into two by a 2nd beam splitter 10 is photoelectrically converted so as to detect the relative moving quantity of the scale. Then, a 1st cylindrical lens 2 for making the line focus of the optical path parallel with the pattern line of the scale is placed before a spot where luminous flux enters the 1st beam splitter 3 and a 2nd cylindrical lens 8 is placed on a point where the interference light reflected from the scale of both optical paths is made coincident so as to cause the linear light of the optical path to return to the circular collimated beam of light.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical device that accurately reads the amount of movement of an optical scale.

<Prior Art> A technique for reading scale graduations using a laser light source is disclosed, for example, in Japanese Patent Laid-Open No. 130816/1983. However, this method cannot easily prevent fluctuations in the laser's oscillation wavelength due to temperature changes, and has the disadvantage that the device becomes large and expensive.

Therefore, the applicant of the present application first thought of a device that improved these points (Japanese Patent Application No. 146359/1989.62-146361).
) has been applied. It splits the laser light into P component light and S component light and irradiates it onto the scale through separate optical paths.
The reflected diffraction light is irradiated onto the graduations (pattern lines) of the scale, and movement is detected from the reflected diffraction light, which is a great improvement. However, since the light is applied as a spot on the scale, if there is minute dirt, dust, or scratches on the spot on the scale, accurate interference may not be achieved, resulting in a counting error.

Means for Solving the Problems of the Present Invention In the present invention, a method is used in which the irradiation light is focused in a linear form parallel to the pattern lines of the scale, and the reflected diffracted light is used. This attempts to cancel the irregularity of the fine surface shape on the scale.

<Example> In FIG. 1, the scale is opaquely marked with pattern lines 5 constituting a diffraction grating on a glass plate 6.
A reflective film 7 is attached to the bottom surface. A reader is provided on the scale, and as a result of relative movement between the scale and the reader, the reader counts interference fringes of reflected diffracted light interference light from the scale and detects the amount of movement. Therefore, the following explanation assumes that the reader is fixed and the scale is movable. At this time, the direction of movement is also detected using two detectors. The reader has the configuration described below. The light from the laser diode 1 is made into parallel light by the convex lens 16, and is received by the first cylindrical lens 2, and is reflected in one direction (
In the direction perpendicular to this (the Y direction), the light is focused.

Note that this narrowing method will be described later.

The light exiting the cylindrical lens 2 is split into two beams by a first beam splitter (for example, a polarizing beam splitter) 3, passes through another optical path 13, 13, and is redirected by reflective mirrors 4, 4'. on the scale surface,
In the figure, the light is irradiated obliquely from the left and right. Here, to explain the aperture in the Y direction by the first cylindrical lens 2, the light projected on the scale surface is parallel to the pattern line 5 in the X direction, and a narrow linear focus 17 is formed in the Y direction. Adjust the mounting position direction of the cylindrical lens 2 so as to create the following. The narrow beams incident on the scale surface of the pattern from the left and right are each diffracted, pass through the glass portion 6, and are reflected by the reflective film 7, and after the second diffraction, the incident angles are taken such that they overlap. Then, only the Y direction is magnified by the second cylindrical lens 8, which has a focal point (for example, on the scale plane) at the position of the overlapping left and right diffracted lights and is installed in the same direction as the first cylindrical lens 2. The light beam forms a parallel light beam that travels upward, and is converted into circularly polarized light by the wave plate 9. The beam is then split into two again by the second beam splitter 10, and each beam is split into two by the polarizing plate 11.
．． 11' causes interference, which is converted into an electrical signal by photoelectric elements 12, 12'. At this time, the polarizing plate 11.11'
is adjusted to, for example, a 90° phase difference so as to provide a phase difference necessary for discrimination in the moving direction of the scale.

Note that the treatment of the light exiting the second cylindrical lens 8 is based on the conventionally known technology described above, so its explanation will be omitted, but scale counting and movement direction discrimination are performed based on changes in electrical signals. In this reader, it is also possible to change the configuration of the scale. In other words, in the one shown in FIG. 1, the lights 13 and 13' irradiated on the scale are reflected by the reflective film 7 of the scale and then superimposed, so that the lights 13 and 13' irradiated on the scale are overlapped at a certain interval on the pattern line. There is. However, in FIG. 2, there is no reflective film, and the optical paths 13 and 13' enter the same point on the scale, are reflected by the reflective mirrors 14 and 14' provided at the reflection position, and are superimposed on the cylindrical lens 8. to go into.

The one in Figure 3 is a surface reflection type and diffracts only once, while the one in Figure 4 has a transmission scale and has two readers, one for the light emitting part and one for the light receiving part.
It is divided into two parts with a scale in between.

Effect> In the present invention, movement is detected using linear light parallel to the moving pattern line, so minute dust, dirt, and scratches attached to a part of the surface of the pattern line are detected by the linear focus. However, the overall effect is much smaller than that of the conventional focusing method, and therefore stable reading can be performed.

In addition, since the light beam is focused in the direction perpendicular to the pattern line (Y direction), even if the diffraction angle changes due to changes in the light source wavelength, the cylindrical lens 8 converts the light beam into parallel light beams, allowing for slight deviations in overlapping. There is almost no effect on the output signal. Therefore, it has the characteristic that it is less affected by temperature changes during measurement.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the configuration of the present invention;
FIG. 2 is an explanatory diagram of how the reader of the present invention responds when the configuration of the scale changes. 1... Laser diode 2... First cylindrical lens 3... First deflection beam splitter 5.
...Pattern line 6...Temporary glass 7...Reflection film 10...Second deflection beam splitter 11.11'...Deflection plate 12.12'...Photoelectric detector patent applicant Stock Company Tokyo Seimitsu t de 1 Diagram 1 Diagram Procedure 11 Correct writing method) Indication of the case Patent Application No. 1983-301795 Name of the invention Person who corrects the scale reading device Relationship with the case Patent applicant Address Mitaka City, Tokyo Shimorenjaku 9-7-1 No. 4゜5゜Date of amendment order: March 28, 1999 Shipping port) "Brief explanation of drawings" column of the specification subject to amendment (1) Page 7 of the specification of the present application 2nd to 4th line “2nd, 3rd”
, fourth..., corresponding explanatory diagram. ” is corrected as follows. "Figure 2 is an explanatory diagram of the present invention for a transmission type scale without a reflective film on the bottom surface of the scale, Figure 3 is an illustration of the invention for a reflection type scale, and Figure 4 is a transmission type scale with the scale on both sides. An explanatory diagram of the present invention when a projector and a receiver are installed.'' Procedural amendment (spontaneous) April 2/1, 1999 1, Indication of case Patent application No. 1983-301795 2, Name scale of the invention Reader 3, Relationship with the person making the amendment Patent applicant address 9-7-1-4, Shimorenjaku, Mitaka-shi, Tokyo Date of amendment 5 Target of amendment (1) The patent claim in the specification of the present application "Range" is corrected as shown in the attached sheet. (2) "Laser" on page 2, line 4 of the present specification is corrected to "laser." (3) "Laser" on page 2, line 7 of the present specification is corrected to "laser." (4) "Laser" on page 2, line 11 of the present specification is corrected to "Laser J." (5) "Laser" on page 3, line 18 of the present specification is corrected as "laser." (6) "Laser" on page 7, line 5 of the present specification is corrected to "laser." Attachment 2, Claims (1) Laser light is split into two by a first beam splitter, projected onto a scale by separate optical paths, the transmitted or reflected diffracted light is collected, and the second In a scale reading device that photoelectrically converts the diffracted light split into two by a beam splitter and detects the amount of relative movement of the scale, the light beam is placed before entering the first beam splitter, and its optical line focus is aligned with the pattern of the scale. It has a first cylindrical lens that is parallel to the line, and a second cylindrical lens that is placed at a point where the reflected interference light from the scales of both optical paths coincides, and that returns the optical linear light to circular parallel light. A scale reading device featuring:

Claims (1)

[Claims] (1) Laser light is split into two by a first beam splitter, projected onto a scale through separate optical paths, the transmitted or reflected diffracted light is collected, and the diffracted light is further split into two by a second beam splitter. In a scale reading device that photoelectrically converts the scale and detects the amount of relative movement of the scale, a first beam splitter is placed before the light beam enters the first beam splitter, and the focus of the optical line is parallel to the pattern line of the scale. A scale reading device comprising: a cylindrical lens; and a second cylindrical lens placed at a point where reflected interference light from the scales in both optical paths coincide, and which returns the linear light to circular parallel light.