JPH04157319A - Encoder utilizing silhouette pattern - Google Patents

Abstract

PURPOSE:To obtain a favorable signal by using an array of minute photodetecting elements as a photosensor, and detecting the displacement of a pattern of a silhouette on the photosensor from outputs of the photodetecting elements at a bright part or at a dark part of the pattern of the silhouette. CONSTITUTION:A scale 5 formed in the shape of a disk has light permeability, with a grating pattern formed in the peripheral edge thereof. The grating is arranged in the rotating direction of the scale. The grating pattern is illuminated by a luminous flux from a linear light source 4. An area sensor as a photosensor 6 is provided at a position where a silhouette pattern is formed. The photodetecting surface of the photosensor 6 is restricted to the size of the pattern area by a light-shielding mask. Therefore, signals are output, only from elements receiving the Light or from elements not receiving the light. In this manner, the displacement of the silhouette pattern can be reliably detected as a displacement of a bright part or a dark part.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to an encoder that utilizes shadowgraph patterns.

[Prior Art] A shadow pattern corresponding to the grid pattern is generated by irradiating the grid pattern with a light beam from a linear light source, and a displacement of the shadow pattern due to the movement of the grid pattern is detected by an optical sensor to detect the grid pattern. A method of measuring the amount of movement is known (Japanese Patent Laid-Open No. 1-297513).

Since the present invention utilizes the above shadow picture pattern, the shadow picture pattern will first be briefly explained below.

In FIG. 4, numeral 10 indicates a linear light source, numeral 12 a lattice pattern, and numeral 14 a screen.

A grating pattern is one in which changes in transmittance or reflectance are repeated in a single period in one direction, but in the grating pattern 12 shown in FIG. 4, changes in transmittance are repeated in a single period in the vertical direction of the figure. It is something that

Regarding the grating pattern, the direction in which transmittance change or reflectance change is repeated in a single period is called the grating arrangement direction.
It is called. In FIG. 4, the vertical direction of the figure is the lattice arrangement direction of the lattice pattern 12. The lattice pattern 12 has a lattice pitch,
That is, it has ξ as the period of transmittance change in the grating arrangement direction.

The linear light source 10 has a length d in the lattice arrangement direction of the lattice pattern 12. Examples of linear light sources include A I G
It is preferable to use a semiconductor laser such as aAs or GaAs whose light emitting part is parallel to the lattice arrangement direction, but in this example, the light emitting part is circular with a diameter d.

When the light beam from the linear light source 10 is irradiated onto the grating pattern 12, diffracted light L□T is emitted from each irradiated portion of the grating pattern 12.
LZP L3+ L4t L5 etc. occur.

The region where these diffracted lights interfere with each other has a symbol 20.
Interference fringes like the one shown appear.

When the length d of the linear light source 10 and the grating pitch ξ of the grating pattern 12 satisfy the condition (1/10)≦(d/ξ)≦2 (1), the interference fringes 20 are referred to as a “shadow pattern”. call,
This shadow picture pattern is generated as if an ideal point light source was placed at the position of the linear light source 10 and the grating pattern 12 was enlarged as a geometric optical shadow picture. That is, the linear light source 10
The distance between and the grid pattern 12 and the distance between the grid pattern 12 and the screen 14 are bl and b, respectively, as shown in the figure.

Then, the silhouette pattern 20 is the lattice pattern 12 enlarged by ((b1+b,)/bl) times in the lattice arrangement direction. Moreover, the linear light source 10 is fixed and the grid pattern 1 is
2 in the grid arrangement direction, the shadow picture pattern 2o
is also displaced in the same direction as the grid pattern 12 while maintaining the silhouette relationship with the grid pattern 12. Therefore, the amount of movement of the grid pattern is determined by the silhouette pattern 2o ((b 1+ b z
> /b l>D, and by using the silhouette pattern, extremely minute displacements of the grating pattern itself can be measured with high precision.

The dimension of the linear light source 10 in the direction perpendicular to the drawing of FIG. 4 is not particularly limited. Furthermore, although coherent light is ideal for the light irradiated onto the grating pattern from a linear light source, even incoherent light beams from a light source such as an LED can be produced by using a slit with a length d as shown in Figure 5 (see Figure 5). (1)), an aperture (II) with an elliptical opening whose major axis or minor axis is d, or an aperture (III) with a circular opening whose diameter is d to form a lattice pattern. If the relationship between the above d and the grating pitch ξ satisfies the above (1), a shadow pattern can be generated.

By using the shadow picture pattern, the amount of movement of the grid pattern can be measured with high precision as described above, and therefore, by using the shadow picture pattern, an extremely accurate encoder can be realized.

The area where the silhouette pattern occurs is called a "pattern area." In FIG. 4, the pattern area looks like rugby balls stacked on top of each other, but this is because the light emitting part of the linear light source is circular with a diameter d. That is, in this case, since the cross-sectional shape of the beam of diffracted light due to the grating pattern is circular, the shape of the area where the light beams overlap in order to interfere becomes a rugby ball shape.

When a linear light source having an elliptical light emitting portion with a major axis diameter of d is used, the pattern area becomes a compact rugby ball shape as shown in FIG.

[Problem to be solved by the invention] Even in an encoder that uses a shadow pattern as described above,
The accuracy of the measurement depends on the signal-to-noise ratio of the signal from the optical sensor that detects the displacement of the silhouette pattern. In order to increase the S/N ratio of the photosensor output, the size of the light-receiving surface of the photosensor should be made approximately equal to the size of the bright part of the silhouette pattern.
Achieving this is not always easy.

Furthermore, if a single light-receiving optical sensor is used, if the position of the optical sensor is shifted due to vibration or impact, the accuracy of detecting displacement of the shadow pattern may deteriorate.

The present invention was made in view of the above-mentioned circumstances, and
The purpose is to provide a highly accurate encoder that uses shadow patterns.

[Means for Solving the Problems] The encoder of the present invention irradiates a light beam from a linear light source onto a grating pattern formed on a scale, and generates a silhouette pattern corresponding to the grating pattern by interference of diffracted light by the grating pattern. This encoder generates a lattice pattern and measures the amount of movement of the scale by detecting the displacement of the shadow pattern as the scale moves in the lattice arrangement direction using an optical sensor, and is characterized by the following points.

That is, ``an array of minute light-receiving elements is used as a light sensor, and the displacement of the shadow pattern is detected by the output from the light-receiving elements in the bright or dark areas of the shadow pattern on the light sensor.''

As a light sensor, you may use a unique array of tiny light-receiving elements according to the silhouette pattern, or you may use a CCD or MOS.
A type area sensor may also be used.

The array arrangement form of the light receiving elements in the optical sensor can be restricted to "below the pattern area of the silhouette pattern" (Claim 2).

Also if the scale has a chord pattern.

That is, when the encoder is an absolute type, the light receiving element arrangement in the light sensor is two-dimensional, and the arrangement position of the light sensor is determined so that one direction of the light receiving element arrangement is parallel to the track arrangement direction on the scale. (Claim 3).

Specifically, the scale can be configured into a cylindrical rotating shaft, a disk shape, a narrow plate shape, or the like.

[Function] In the encoder of the present invention, the optical sensor is composed of an array of minute light-receiving elements, and the output is from the elements that are actually receiving light or the elements that are not receiving light, so that a shadow pattern is generated. It is possible to reliably detect the displacement of the bright or dark part of the image. Furthermore, even if the position of the optical sensor shifts slightly due to vibration or shock, since the light-receiving elements are arranged in an array, the "shift" will hardly affect the array arrangement as a whole.

In order to restrict the array arrangement form of the light receiving elements in the optical sensor to be "below the pattern area of the silhouette pattern", for example, as shown in FIG. 2, or the minute light receiving elements 3 may be arranged according to the shape of the pattern area as shown in FIG. 2 (II). The size of regulation of the pattern area is not limited to the examples shown in FIGS. 1(I) and (II). Further, the array arrangement form may be set to be smaller than the pattern area, that is, smaller than the pattern area.

[Example] Specific examples will be described below.

FIG. 2(I) shows an example in which the present invention is implemented as a rotary encoder with a disk-shaped scale.

The scale 5 formed in the shape of a disk is transparent and has a lattice pattern formed on its periphery with the rotation direction as the lattice arrangement direction, and the linear light source 4 as described with reference to FIG.
An area sensor is disposed as a light sensor 6 at the position of a shadow pattern that is generated by being irradiated with a light beam from a light source.

The light-receiving surface of the optical sensor 6 is covered with a light-blocking mask as shown in Figure 1 (I).
As in the example above, the size of the pattern area is regulated, and signals are output only from elements that are receiving light or elements that are not receiving light. In this way, displacement of the silhouette pattern can be reliably detected as a displacement of its bright or dark portion.

In the example shown in FIG. 2 (II), the grating pattern 9A is formed directly on the shaft 9 of the motor 11, and the light from the LED 7 is transmitted through the aperture 8 as described in conjunction with FIG. 5 (III). A shadow pattern generated by irradiating the grid pattern 9A.

The optical sensor 6 (Fig. 2 (I)
(similar to that shown in ).

FIG. 3 shows an example in which the present invention is implemented as an absolute encoder.

The grid pattern 9B with the code pattern is the motor 11
It is formed on the shaft 9 of.

The light source device designated by reference numeral 4A has the same number of semiconductor lasers as the number of tracks in the lattice pattern 9A, arranged at positions corresponding to each track, so that the elongated direction of the light emitting portion corresponds to the lattice arrangement direction of each track. It is composed of

Therefore, if all the linear light sources of the light source device 4A are made to emit light, a shadow pattern will be generated for each track of the lattice pattern, and will be displaced all at once as the shaft 9 rotates.

The optical sensor 6A is an area sensor in which light-receiving elements are arranged two-dimensionally, and one arrangement direction of the light-receiving elements is made to correspond to the arrangement direction of the tracks in the grid pattern 9B. Therefore, the other arranging force (orthogonal to the one arranging direction) corresponds to the direction of displacement of the silhouette pattern.

By detecting the displacement of the silhouette pattern corresponding to each track, the absolute position of the shaft 9 with respect to its rotation can be detected.

In addition, in this case, by outputting a matrix signal from the optical sensor 6A, phase information of the output signal for each bit can be obtained, so phase division is possible, and the detection accuracy of the absolute position signal can be improved. .

As the form of the encoder, a well-known linear encoder (using a narrow plate-like scale having a lattice pattern arranged along a straight line in the elongated direction) is possible, and the form shown in Fig. 2 (I) is possible. It goes without saying that the linear encoder described above can also be implemented as an absolute encoder as described above.

[Effects of the Invention] As described above, according to the present invention, a novel encoder that uses shadow patterns can be provided. In this encoder, the optical sensor that detects the displacement of the silhouette pattern is composed of a miniature light receiving element arranged in a playback arrangement, so it is possible to obtain a good detection signal with a high S/N ratio, and it is also immune to the effects of vibration and shock. Hard to accept.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the characteristic parts of the present invention, Fig. 2 is a perspective view showing an embodiment, Fig. 3 is a perspective view showing another embodiment, and Figs. 4 to 6 are silhouette patterns. FIG. l... Light receiving surface of area sensor, 2... Light shielding mask, 3... Minute light receiving element, 4... Linear light source, 5...
- Scale, 6... optical sensor. 9B... Lattice pattern 7'ft with code pattern
)7 prisoners

Claims (1)

[Claims] 1. A grating pattern formed on a scale is irradiated with a light beam from a linear light source, and a shadow pattern corresponding to the grating pattern is generated by interference of diffracted light by the grating pattern, and the grating pattern of the scale is This is an encoder that measures the amount of movement of the scale by detecting the displacement of the shadow pattern as it moves in the array direction using an optical sensor. An encoder using a shadow pattern, characterized in that displacement of the shadow pattern is detected by output from a light receiving element in a bright part or a dark part of the pattern. 2. The encoder using a shadow pattern according to claim 1, wherein the array arrangement form of the light receiving elements of the optical sensor is restricted to be smaller than the pattern area of the shadow pattern. 3. In claim 1, the scale has a code pattern, the light-receiving element arrangement in the optical sensor is two-dimensional, and the optical sensor is arranged so that one direction of the light-receiving element arrangement is parallel to the track arrangement direction on the scale. An encoder that uses a shadow pattern and is characterized by having a fixed orientation.