JPS59132311A - Optical scale - Google Patents

Abstract

PURPOSE:To improve resolution, by using a laser light source as a light source, splitting the light beam emitted from the laser light source into a plurality of beams by a diffraction grating, and projecting said beams on an index scale. CONSTITUTION:A scale 4 is divided into three parts. The grating constants of the parts are the same as shown in the Figure (a). The positions of the gratings are different by, O, W/4, and W/2 with respect to the gratings shown in the Figure (a). The laser beams divided into three parts are inputted to the respective parts of the index scale 4. The beams transmitted through both scales are received by detectors 5, 5', and 5'' comprising three photodiodes. In this constitution, the optical gratings having the small grating constant can be used, and the resolution can be improved.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention provides a light source, a scale comprising an optical grating having a constant lattice constant, and a source emitted from the light source that is projected onto the scale for the purpose of precision length measurement. and an optical grating having the same lattice constant as the above scale, and the patterns of both optical gratings are completely parallel or slightly spaced apart from the above scale by a minute distance of /''・1'&l''. includes an index scale provided so as to be tilted at The present invention relates to an optical scale that detects and performs photoelectric conversion to obtain a position signal of the scale.

BACKGROUND ART AND PROBLEMS Such optical scales are already in widespread use. Figure 1 is a perspective view of the main parts of such a conventional optical scale/lz (7). In the figure, l is a light source, 2 is a lens for projecting parallel light from the light source onto the scale, and 3 is a lens for projecting parallel light onto the scale. A scale consisting of an optical grating with a constant lattice constant 7, 4
The optical grating consists of a single optical grating having the same lattice constant as the above-mentioned scale, and is arranged so that the patterns of both optical gratings are completely parallel to each other or are tilted at a very small distance from the above-mentioned scale. In order to differentiate the direction of movement of the scale 3, the index scale 4 has two yC gratings that are offset from each other by 1/4 wavelength. 5 and 5' are detectors for detecting the source transmitted through each of the two optical gratings, and 6 is an arrow indicating the movable blade IoI of the scale 3. It is advantageous to use an optical grating with a low lattice constant to construct a high-resolution scale, but the lattice constant is 4.
As the light source becomes smaller, the contrast between the brightness and darkness of the moiré fringes decreases, and when using an incandescent lamp, L, or ED (light emitting diode) as a light source, the practical limit is about 4 microns, and 8 microns or larger is actually used. ing.

OBJECTS OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to enable the use of an optical grating having a small lattice constant without deteriorating the contrast between brightness and darkness of Moiré fringes, and to achieve high resolution 7.
An object of the present invention is to provide an optical scale of the kind mentioned at the outset.

SUMMARY OF THE INVENTION To achieve the above object, an optical scale according to the present invention includes a light source that is a laser light source, an original beam emitted from the laser light source that is split into a plurality of beams by a diffraction grating,
It is assumed that these beams are projected onto the scale.

Lasers are effective as light sources for optical systems that create Moiré fringes because they can concentrate energy in a narrow area with high density and have coherence.

Hereinafter, the present invention will be explained in more detail using examples with reference to the drawings, but these are merely illustrative, and it is understood that various modifications and improvements may be made without going beyond the scope of the present invention. Of course.

Embodiment FIG. 2 is a schematic diagram showing the configuration of an optical scale according to an embodiment of the present invention, and the reference numbers common to FIG. 1 refer to the same parts as in FIG. 1. A beam emitted from a light source 1 consisting of an oscillator tube or a quasi-laser iode and passing through a uremeter lens 2 is first divided into a plurality of beams through a diffraction grating 7 and made incident on a scale 3. If a coherent beam is incident on the diffraction grating 7, it will normally be diffracted into the 0th order, the 1st order, the ±2nd order, etc.
・It is divided into many luminous fluxes. However, since the phase grating allows most of the light quantity to be limited to three beams, the 70th order and the 1st order, it becomes an efficient light source as a moiré optical system.

3(b) and (C) are front views of two different embodiments of index scale optical gratings used in the optical scale according to the present invention; FIG.
) and (cl) are front views of scale optical gratings at positions corresponding to the VC7r
Scale 4 is divided into three parts, as shown in Figure 3(b) and (C), and their lattice constants are expressed by the third factor (
The lattice position is the same as that of the lattice shown in Figure 3(a), but the position of the lattice is set to W, which is the lattice constant, and O with respect to the lattice shown in Figure 3(a).
9τ, differs by i. The three divided laser beams are made incident on each part of the index-scale 4, and the beams transmitted from both scales are sent to a detector 5, which consists of three photodiodes. 5
', 5'' can be accepted.

The index scale does not have to be divided into three parts, but can be of one part, as shown in FIG. When the pattern of index scale 4, shown by group 9 of parallel lines, is tilted by a small angle θ with respect to scale 3 of the pattern with lattice constant WV, shown by group 8 of parallel lines, moiré fringes with width W, represented by yam, appear. . Therefore, the three beams are made incident on a portion corresponding to the light and dark phase Os 4 p Z Vc of the moiré fi4 shown in 10.11.12, and the transmitted light is received by three detectors.

Since a beam diffracted by the scale also occurs, the number of index e-scale, photodiode detectors may be increased to more than three. A method of converting charging outputs with different phases into phase signals is described, for example, in the Japanese Patent Publication No. 47
49621, and is not subject to the present invention, so it will not be described here.

As described in detail, the present invention enables the use of an optical grating having a small lattice constant without reducing the contrast between bright and dark moiré fringes, thereby obtaining an optical scale with a depth resolution r. be able to.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the main parts of a conventional optical scale, Figure 2 is a perspective view of the main parts of a conventional optical scale.
FIG. 3 is a block diagram schematically showing an optical scale 7 according to an embodiment of the present invention.
Figure 3(b) and (Cl are two different embodiments of the optical grating of the indexer scale used in the optical scale according to the invention); Japanese Patent Publication No. 59-132311
(3) The front view and FIG. 4 are diagrams showing the relationship 7 among the positions of the scale optical grating, the index scale optical grating, and the incident light beam according to another embodiment of the present invention. ■...i source, 2...lens, 3...scale, 4
...Index Q scale, 5. 5', 5"
- Detector, 6... Arrow indicating the direction of the moving force of the scale, 7... Diffraction grating, 8... - Group of rows of lines indicating the pattern of the scale, 9... Index - Scale pattern wR: bj group of parallel lines, 10.1], 12.
...Circle indicating the incident position of the original beam. Patent applicant: Sony Magnescale Co., Ltd. Figure 2, Figure 3 (0)

Claims (1)

[Claims] It consists of a light source, a scale consisting of an optical grating with a constant lattice constant, an optical system that projects an element emitted from the light source onto the scale, and an optical grating with the same lattice constant as the scale. An index scale is provided with an interval of "1" so that the patterns of both optical gratings are completely parallel or slightly inclined, and an index scale that transmits through both the above scale and the above index scale. a detector that detects the original, and detects moiré that moves as the scale moves;
In an optical scale that performs photoelectric conversion to obtain a position signal of the scale, the light source is a laser light source, and the original beam emitted from the laser light source is split into a plurality of beams by a diffraction grating, and these beams are transmitted to the scale. An optical scale characterized by projection.