JPH02143113A - Optical encoder - Google Patents

Abstract

PURPOSE:To obtain the optical encoder which can measure the displacement of a movable body with high accuracy by arranging the 1st and 2nd grating patterns of a subscale almost closely in a direction intersecting orthogonally with the displacing direction of the movable body. CONSTITUTION:A grating pattern 7 is a pattern for leading an A-phase signal out of a corresponding photodiode and a grating pattern 8 is for leading a B-phase out similarly. The A-phase signal and B-phase signal are 90 deg. out of phase with each other, and the direction where a main scale 2 as the movable body varies can be decided from the A-phase signal and B-phase signal. Further, a grating pattern 9 is a pattern for leading out, the inverse of A which is 180 deg. out of phase with the A-phase signal, and the difference between the A-phase signal and the signal, the inverse of A is found to generate a period signal which is tolerant to disturbance such as an electromagnetic noise, thereby measuring the displacement quantity and displacing speed of the main scale 2 with the signal. Further, the difference between the B-phase signal and a signal, the inverse of B which is 180 deg. out of phase with the B-phase signal is calculated to measure the displacement quantity and displacing speed of the main scale 2.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an optical encoder having a main scale on which a predetermined grating pattern is formed and a subscale on which a plurality of grating patterns having different phases from each other are formed. Regarding encoders.

[Prior art]

Traditionally, one of the main scale and subscale is connected to a movable body such as a movable stage, and the main scale's lattice pattern (slit row) is illuminated with light from a light source to distinguish between the main scale's lattice pattern and the subscale's lattice pattern. 2. Description of the Related Art Encoders that detect the displacement of a movable body based on a photoelectrically converted output signal from a light receiving element that receives passing light are well known.

In such an encoder, in order to improve the resolution of displacement direction discrimination or displacement amount, a plurality of grating patterns are formed on the subscale, and the phases of these grating patterns with respect to the main scale grating pattern are made to differ from each other. , periodic signals with mutually different phases were obtained by the light receiving element.

However, in the conventional encoder, since a plurality of sub-scale grating patterns are provided along the displacement direction of the movable body, a problem arises in that the phase difference between the patterns shifts over time. In addition, since both are lined up in the direction in which the slits form a lattice pattern,
It is also not easy to accurately define the mutual phase difference.

Therefore, for example, as shown in FIG.
0 (mask) grid patterns 7.8 (or 9°10) are arranged in a direction almost perpendicular to the displacement direction X of the movable body (here, the main scale 2 is attached to the movable body). If so, the above problem can be solved.

However, as shown in FIG. 5, when grid patterns 7 and 8 are provided with rectangular slits 6 interposed therebetween for monitoring the intensity fluctuations of the light source 1, the light from the main scale pattern 7 and the grid pattern 8 is It was found that the phase difference of the periodic signal obtained by photoelectric conversion deviates significantly from the predetermined phase difference.

[Summary of the invention]

An object of the present invention is to provide an optical encoder that can accurately obtain a plurality of periodic signals having a predetermined phase difference.

In order to achieve the above object, the optical encoder of the present invention includes a main scale on which a grating pattern with a predetermined period is formed, and first and second grating patterns having mutually different phases with respect to the grating pattern of the main scale. and a subscale provided opposite to the main scale;
an illumination means for illuminating the main scale; light obtained through the lattice pattern of the main scale and a first lattice pattern of the sub-scale; and light obtained through the lattice pattern of the main scale and the second lattice pattern of the sub-scale. and a photoelectric conversion means for individually photoelectrically converting the light obtained from each light and outputting first and second periodic signals corresponding to each light and having mutually different phases, and one of the main scale and the sub scale is movable. In an optical encoder that is connected to a body and measures the displacement of the movable body based on the first and second periodic signals, the movable body displaces the first and second grating patterns of the subscale. It is characterized by being provided close to each other in a direction substantially perpendicular to the direction.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below, but before that, an additional explanation will be given regarding the above-mentioned device shown in FIG. 5, which shows the basic configuration of the optical encoder of the present invention.

In FIG. 5, 2 and 100 indicate the main scale and subscale, respectively, as described above.

Reference numeral 1 designates a light source such as an LED, and the light emitted from the light source 1 is turned into a substantially parallel light beam by a lens 5, and this parallel light beam illuminates a grating pattern 20 (slit row) of a predetermined period on the main scale 2. The light transmitted through the light transmitting portions (slits) of the grating pattern 20 illuminates the entire surface of the subscale 100.

Behind the subscale 100 are the grid patterns 7, 8, 9 . A plurality of photodiodes (hereinafter referred to as
It is called a photodiode array. ) is provided,
Each photodiode array photoelectrically converts incident light.

Lattice pattern 7, 8.9. of subscale 100. 10
A photoelectric conversion signal from a photodiode into which light is incident becomes a periodic signal due to the relative displacement of the sub scale 100 and the main scale 2 in the X direction.

On the other hand, the photoelectric conversion signal from the photodiode into which the light from the rectangular slit 6 is incident is not a periodic signal but a signal that changes in response to changes in the light emission intensity of the light source 1. Therefore, the light emission intensity of the light source I can be adjusted automatically or manually based on the signal from the first diode.

Further, as the photodiode, one whose sensitivity characteristic includes the emission spectrum of the light source 1 is used.

Now, the main feature of the present invention lies in the configuration of the subscale 100 as shown in FIG.

1 and 2 are explanatory diagrams showing one embodiment of the present invention, FIG. 1 is an enlarged view showing the arrangement of grating patterns in the subscale 100, and FIG. FIG. 3 is a diagram showing output signals from each photodiode.

The grating pattern 7 is a pattern for extracting an A-phase signal from a corresponding photodiode, and the grating pattern 8 is a pattern for extracting a B-phase signal from a corresponding photodiode. The period of the A-phase signal and the period of the B-phase signal are 90 degrees out of phase with each other.
The direction in which the main scale 2 (movable body) changes can be determined from the phase signal using a well-known technique.

Furthermore, the grating pattern 9 is a pattern for extracting an A-phase signal that is 180' out of phase with respect to the A-phase signal from the corresponding photodiode. A periodic signal (C-phase signal) that is resistant to disturbances such as noise is formed, and the displacement amount and displacement speed of the main scale 2 are measured using this signal.

Furthermore, the grating pattern 10 is a pattern for extracting an n-phase signal whose phase is shifted by 1000 with respect to the B-phase signal from the corresponding photodiode. By taking the differential of the n-phase signals, a predetermined periodic signal (n-phase signal) is formed, and the displacement amount and displacement speed of the main scale 2 are measured using this signal.

Of course, by combining the C-phase and n-phase signals, the amount of displacement of the main scale 2 can be measured with twice the resolution as when each phase is used alone.

The states of the periodic signals obtained through each of the grating patterns 7 to 10 are shown in FIG. In order to obtain such a periodic signal, the periods of the grating patterns 7 to 10 are approximately the same as the period of the grating pattern 20, and the main scale is 2σ.
The phase is sequentially shifted by 90 degrees with respect to the grating pattern 20. That is, grating patterns 7 and 8 are 90° out of phase with each other, and grating patterns 9 and 9 are 90° out of phase with each other.

In this embodiment, the grating patterns 7 and 8 are arranged close to each other in the direction perpendicular to the displacement direction X, and the grating patterns 9 and 10 are arranged close to each other in the direction perpendicular to the displacement direction X. For this reason, each periodic signal is susceptible to the influence of the azimuth error between the main scale 2 and the subscale 100, and therefore, the phase difference between each periodic signal is correctly set to 90''.

FIG. 3 shows the relationship between the distance between the grating pattern 7 and the grating pattern 8, the azimuth error, and the relative phase error amount between the A phase and the B phase.

In the graph shown in Figure 3, the length of the slit in the lattice pattern is 61, the width is w (w = o, 14 ・b), the distance between the slit ends of lattice patterns A and B is a, and b / a
The relationship between azimuth error and phase error is plotted using as a parameter. As is clear from FIG. 3, the smaller the distance between the grating patterns A and B, the smaller the influence of the azimuth error on the phase error.

Therefore, in this embodiment, the displacement direction of the main scale 2
Since the grating patterns 7.8 (9°10) are arranged close to each other in the direction orthogonal to An optical encoder capable of measuring displacement can be provided.

Returning to FIG. 1, 6 is a slit for monitoring the emission intensity of light source l, and from the corresponding photodiode,
An n-phase signal corresponding to the emission intensity of the light source 1 is obtained. This n-phase signal is used to adjust the emission intensity of the light source 1, as described above. The slits 6 are not present between the lattice patterns 7.8 and 9.10, thereby achieving the close arrangement of the lattice patterns 7.8 (lattice patterns 9.10) described above. ing.

Further, the subscale 100 in this embodiment is provided on a substrate on which a photodiode array is formed, and the ζ photodiode array and the subscale 100 are integrated. That is, after forming photodiode arrays (for A phase, B phase, human phase, n phase, and F phase) on a substrate, a grating pattern or a slit pattern is formed on each upper photodiode array △ by a method such as vapor deposition. , the photodiode array is masked by these patterns.

Therefore, the subscale 100 is provided on the substrate as a mask, and the areas indicated by numerals 6 to 10 in FIG. 1 are photodiode areas for the F phase, A phase, B phase, A phase, and n phase, respectively. It can be considered as

By adopting such a configuration, it is possible to achieve miniaturization of the light receiving means (sub scale + charge conversion element) that receives light from the main scale 2, and to provide a compact optical encoder.

Furthermore, when forming a photodiode array on a substrate, the photodiodes themselves may be patterned into a grid pattern to provide a function as a subscale.

FIG. 4 is an explanatory diagram showing another embodiment of the present invention;
As in the case shown in the figure, the basic configuration of the encoder is already shown in FIG. The difference between the subscale of this embodiment and the subscale of the previous embodiment lies in the shape of the slit 6 for extracting the F-phase signal. In this embodiment, the slit 6 is divided into two parts, and the lattice pattern 7 to lO is formed between these two parts.
has been established. Therefore, not only the grid patterns 7 and 8 and the grid patterns 9 and 10 are arranged close to each other, but also the grid patterns 7 and 10 and the grid patterns 8 and 9 are arranged close to each other.

With such a configuration, even if there is some error in the parallelism of the light that illuminates the subscale 100 via the main scale 2, the period obtained through the grating pattern arranged in the displacement direction of the main scale 2 can be maintained. Variation in phase error between signals is reduced.

Therefore, for example, the C-phase signal formed by the differential of the periodic signals obtained via the grating patterns 7 and 9 becomes accurate, and a highly accurate optical encoder can be provided.

Although the above two embodiments have been shown in this application, various forms of optical encoders can be provided based on the idea of the present invention.

For example, in each of the above embodiments, the linear encoder as shown in FIG. 5 has been described, but the present invention can also be applied to a rotary type encoder. Also, instead of attaching the main scale to a movable body, an l
The unit may be attached to a movable body and the main scale may be fixed to the main body of the device. Furthermore, instead of using a photodiode array, it is advantageous in terms of setting to use a divided sensor whose light-receiving surface is divided in correspondence with a subscale grating pattern.

〔Effect of the invention〕

As described above, according to the present invention, by arranging the first and second lattice patterns of the subscales close to each other in a direction substantially orthogonal to the displacement direction of the movable body, the interval between periodic signals due to the azimuth error between the main scale and the subscales is Since the phase error can be reduced, it is possible to accurately obtain a plurality of periodic signals having a predetermined phase difference, and it becomes possible to provide an optical encoder that can measure the displacement of a movable body with high precision.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are explanatory diagrams showing one embodiment of the present invention. FIG. 3 is a graph diagram showing the relationship between the distance between grating patterns, the azimuth error between the main scale and the subscale, and the amount of phase error between the A phase and the B phase. FIG. 4 is an explanatory diagram showing another embodiment of the present invention. FIG. 5 is a diagram showing the basic configuration of an optical encoder. 1...Light source 2...Main scale 6...Slits 7-10. 20...Lattice pattern 100...Subscale 箭子 emouth

Claims (1)

[Claims] A sub-scale having a main scale on which a grating pattern with a predetermined period is formed, and first and second grating patterns having mutually different phases with respect to the grating pattern of the main scale, and provided opposite to the main scale. a scale, an illumination means for illuminating the main scale, light obtained through a grating pattern of the main scale and a first grating pattern of the subscale, a grating pattern of the main scale and a second grating of the subscale. a photoelectric conversion means for individually photoelectrically converting the light obtained through the pattern and outputting first and second periodic signals corresponding to each light and having mutually different phases; In an optical encoder, one of which is connected to a movable body and which measures the displacement of the movable body based on the first and second periodic signals, the first and second grating patterns of the subscale are connected to the movable body. An optical encoder characterized in that the optical encoder is provided in close proximity to the direction substantially perpendicular to the direction in which the is displaced.