JPH0411809B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an improvement of a photoelectric encoder that is capable of detecting the number of brightnesses of light caused by repeated overlapping of relatively displaced optical gratings using a photoelectric element, and measuring the distance of the relative displacement.

[Conventional technology]

The photoelectric encoder as described above is used by being attached to, for example, a machine tool, a measuring instrument, etc., and naturally there is a demand for its size and weight to be reduced. In response to such demands for downsizing and weight reduction,
The present applicant has proposed a compact encoder integrated with an illuminator, as disclosed in Japanese Patent Publication No. 14287/1987. As shown in FIG. 4, this small-sized encoder reflects light emitted from a light emitting diode 1 by a concave mirror-like reflective film 2, and passes the light to a first scale 3.
The light illuminates optical gratings 5 and 6 provided on the second scale 4, respectively, and reaches the light receiving element 7. By the way, in the photoelectric encoder using the reflective film 2 as described above, the light emitted from the light emitting diode 1 is diffused in the width direction of the optical gratings 5 and 6, that is, in the direction of the scale. There is a problem in that the rising and falling edges of the signal obtained from the light receiving element 7 become unclear due to the brightness and darkness caused by the repeated overlapping of the optical gratings 5 and 6. In this way, when the diffusion angle of illumination light is large, the first
The gap between the optical grating 5 and the optical grating 6 in the scale 3 and the second scale 4, that is, the grating interval S, cannot be increased. For example, in the case of an optical grating with a pitch of 20 μm, the grating spacing S must be approximately 10 μm or less, and the accuracy of the guide mechanism for relative movement of the first scale 3 and the second scale 4 must be considerably reduced. There is a problem that this increases the manufacturing cost. Here, if the paraxial focal length of the spherical reflective film 2 is f and the width of the light emitting part of the light emitting diode 1 is d, then the diffusion angle is proportional to d/f. Here, f is proportional to the radius, and the size of the diffusion angle is less affected by f. That is, the main cause of the diffusion of illumination light is the width d of the light emitting portion of the light emitting diode 1.

[Problems to be solved by the invention]

On the other hand, in order to increase f, the reflective film 2
It is also possible to increase the radius of the sphere, but this has the problem of increasing the size of the photoelectric encoder. Furthermore, in order to reduce d, it is possible to reduce the size of the light emitting portion of the light emitting diode 1, but if this is done, there is a problem that the amount of light emitted from the light emitting diode decreases.

[Purpose of the invention]

This invention was made in view of the above-mentioned conventional problems, and it is possible to maintain a sufficient amount of light emitted from a light emitting diode without increasing the size of the device, and to
An object of the present invention is to provide a photoelectric encoder that is less affected by diffusion of illumination light.

[Means for Solving the Problems] The present invention provides a method for moving a first scale, in which graduations made of optical gratings with a constant pitch are formed in parallel in the longitudinal direction, relative to the first scale in the longitudinal direction. a second scale having a scale formed of an optical grating having the same pitch as the optical grating on the first scale, the scale being arranged so as to face the scale of the first scale; an illuminator comprising a diode and illuminating the optical gratings of the first and second scales arranged opposite to each other from one side; A photoelectric encoder comprising a light receiving element configured to receive light from the illuminator and passing through optical gratings of the first and second scales. In addition, the slits are arranged parallel to the optical grating to achieve the above object. Further, the above object is achieved by forming the slit-shaped light-emitting portion of the light-emitting diode by depositing a metal film having a slit-shaped opening on the light-emitting surface. Further, the above object is achieved by setting the width of the slit of the light emitting part to 100 μm or less. Furthermore, the illuminator is attached to an outer surface of the second scale opposite to the optical grating forming surface, and the light emitting diode is provided with a light emitting portion facing opposite to the outer surface; and a spherical reflective film disposed surrounding the diode,
The above object is achieved by illuminating the optical grating of the second scale and the optical grating of the first scale after the light from the light emitting part is reflected by the spherical reflective film.

[Effect]

In this invention, the light emitting part of the light emitting diode is shaped like a slit, and the slit is arranged parallel to the optical grating, so that the light emitted from the light emitting part is directed in the width direction of the slit, that is, in the direction of the optical grating. There is little diffusion in the parallel direction, and only in the height of the optical grating, that is, in the width direction of the scale, so the rise and fall of light and darkness of the light received by the light-receiving element becomes clear, reducing measurement accuracy. do not have. Therefore, even if the grating spacing between the optical gratings on the first and second scales is increased, the measurement accuracy will not be reduced. Furthermore, since there is no need to downsize the light emitting diode, a sufficient amount of illumination light can be obtained. Furthermore, when the light emitting diode is surrounded by a spherical reflective film, there is no need to increase the radius of the reflective film.

【Example】

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, as shown in FIGS. 1 to 3, a first scale 1 has graduations formed of optical gratings 10 of a constant pitch arranged in parallel in the longitudinal direction.
2, and the first scale 12 is disposed so as to be movable relative to the first scale 12 in the longitudinal direction.
A second scale 16 is formed with an optical grating 14 having the same pitch as the optical grating 10 on the scale 12 and is arranged so as to face the scale of the first scale 12, and a light emitting diode 18, an illuminator 20 for illuminating the optical gratings 10, 14 of the first and second scales 12, 16 arranged oppositely from one side;
The light from the illuminator 20 is disposed between the optical gratings 10, 14 of the scales 12, 16, facing the illuminator 20, and passes through the optical gratings 10, 14 of the first and second scales. A photoelectric encoder comprising a light-receiving element 22 for receiving light, in which the light-emitting diode 18 is provided with a slit-shaped light-emitting portion 24, and the slit is arranged in parallel with the optical gratings 10, 14. It is. As shown in FIG. 3, the light emitting diode 18 has the slit-shaped light-emitting portion 24 formed by depositing a metal film 28 having a slit-shaped opening on the light-emitting surface 26. This light emitting diode 18 is a P-type GaAs18A
and N-type GaAs18B, and these are squares with one side of 400 μm,
The shape of the slit-like light emitting section 24 has a width W=
50 μm, length L = 350 μm, and GaAs substrate 1
It is arranged on the diagonal line of 8A and 18B. Reference numbers 18C and 18D in the figure are lead wires,
One lead wire 18C is a metal film 28 that also serves as an electrode.
The other lead wire 18D is connected to the metal film 2
8 and is connected to the opposite side. As shown in FIG. 2, the first scale 12 is a so-called main scale in a photoelectric encoder. On the other hand, the second scale 16 is formed short and is used as a so-called index scale, and its optical grating 14 has four optical gratings whose phases are shifted by 90 degrees.
It is formed from optical gratings 14A to 14D. These four optical gratings 14A to 14D are
They are arranged in a block shape, that is, in a box shape, at positions that can overlap the optical grating 10 on the scale 12. On the other hand, in the light emitting diode 18, the slit-shaped light emitting portion 24 is composed of four optical gratings 14.
At the central position of these optical gratings 14A to 14D,
It is arranged parallel to ~14D. Reference numerals 30A and 30B in FIG. 2 indicate transparent conductive films formed on the surface of the second scale in order to supply power to the light emitting diode 18, and these transparent conductive films 30A and 30B are connected via lead wires 32A and 32B. and is connected to a power source 34. The illuminator 20 is attached to an outer surface 16A of the second scale 16 opposite to the surface on which the optical grating 14 is formed, and the light emitting section 24 is attached to the outer surface 16A of the second scale 16.
The light emitting diode 18 is arranged in the opposite direction to A, and the spherical reflective film 36 is arranged surrounding the light emitting diode 18, and the light from the light emitting part 24 is reflected by the spherical reflection film 36. After being reflected by the film 36, the optical grating 14 of the second scale 16
and illuminates the optical grating 10 of the first scale 12. The spherical reflective film 36 is formed by applying epoxy adhesive to a lens 36A having a hemispherical surface using a hemispherical mold.
The hemispherical reflective film 36 is formed by depositing aluminum on the hemispherical surface of this lens 36A. Further, the light receiving element 22 includes four light receiving elements 22 corresponding to the four optical gratings 14A to 14D.
It is composed of A to 22D. Reference numerals 38A and 38B in FIG. 1 indicate difference calculators for calculating the difference between the electrical signals obtained by the four light receiving elements 22A to 22D to obtain a differential signal. In the above embodiment, optical gratings 10 and 14
When the pitch of these optical gratings is 20 μm, the spacing between these optical gratings, that is, the grating spacing S, can be set to about 40 μm. That is, conventionally, when the pitch of the optical grating was 20 μm, the grating spacing S was at most 10 μm, but in the case of the above embodiment, the grating spacing S could be made four times that of the conventional one. Furthermore, even if the radius of the spherical reflective film 36 is the same as before, the amount of light received by the light receiving element 22 is not reduced in any way compared to the conventional one, and the SN ratio of the obtained signal is almost the same as before. They were the same. Note that in the above embodiment, the light emitting diode 18
P-type GaAs18A and N-type GaAs18A forming
Both B are squares, but they may also be rectangles. However, when these P-type and N-type substrates are made into squares and the slit-shaped light-emitting portions 24 are formed on the diagonals thereof, there is an advantage that the light-emitting efficiency is high with respect to the injected current. Further, the light emitting diode 18 uses a gallium arsenide semiconductor substrate, which is
Other semiconductor substrates such as GaP and GaAlAs may also be used. Furthermore, the P-type and N-type substrates may be upside down compared to the embodiment, and the sides of these substrates may be coated with black paint. Further, in the above embodiment, the optical grating 14 of the second scale 16 is composed of four optical gratings 14A to 14D whose phases are shifted by 90 degrees, but the present invention is not limited to this. For example, in the case of the moire fringe method, the optical grating 14 of the second scale 16
It is sufficient that the pitch of the optical grating 10 of the first scale 12 is approximately equal to that of the optical grating 10 of the first scale 12, and furthermore, it is possible to obtain a signal whose phase is changed by 90 degrees depending on the position of the optical grating of the second scale. . Furthermore, in the above embodiment, the first scale 12 and the second scale 16 are linear encoders, but the present invention is not limited to this, and can naturally be applied to a rotary encoder. . Further, in the above embodiment, the optical gratings 10 and 14 are illuminated after the light emitted from the light emitting diode 18 is reflected by the spherical reflective film 36, but in the present invention, the spherical reflective film 36 By the light emission from the light emitting diode 18 without providing
It also applies to those that directly illuminate the optical gratings 10 and 14.

【Effect of the invention】

Since the present invention is configured as described above, the light illuminating the first and second scale optical gratings can be diffused in the width direction of the optical grating, that is, in the scale direction, without downsizing the light emitting part of the light emitting diode. It has the excellent effect of suppressing

[Brief explanation of drawings]

Fig. 1 is a sectional view including a partial block diagram showing an embodiment of a photoelectric encoder according to the present invention, Fig. 2 is a sectional view taken along the - line in Fig. 1, and Fig. 3 is a light emitting diode in the same embodiment. FIG. 4 is a sectional view showing a conventional photoelectric encoder. 10... Optical grating, 12... First scale, 1
4...Optical grating, 16...Second scale, 16A
...Outer surface, 18...Light emitting diode, 20...
Illuminator, 22... Light receiving element, 24... Light emitting section, 2
6... Light emitting surface, 28... Metal film, 36... Spherical reflective film.

Claims (1)

[Scope of Claims] 1. A first scale in which scales made of optical gratings with a constant pitch are formed in parallel in the longitudinal direction, and the first scale is disposed so as to be movable relative to the first scale in the longitudinal direction, and a second scale having a scale formed of an optical grating having the same pitch as that of the optical grating on the first scale, and arranged so that the scale faces the scale of the first scale; an illuminator that illuminates the optical gratings of the first and second scales arranged as shown in FIG.
A photoelectric encoder comprising: a light receiving element arranged opposite to the illuminator and receiving light from the illuminator that passes through optical gratings of the first and second scales, wherein the light emitting diode A photoelectric encoder comprising a slit-shaped light emitting section, and the slit is arranged parallel to the optical grating. 2. The photoelectric encoder according to claim 1, wherein the light emitting diode has the slit-shaped light emitting portion formed by depositing a metal film having a slit-shaped opening on the light emitting surface. 3. The photoelectric encoder according to claim 1 or 2, wherein the width of the slit of the light emitting section is 100 μm or less. 4. The illuminator is attached to an outer surface of the second scale opposite to the optical grating forming surface, and
The light-emitting diode has the light-emitting portion arranged in a direction opposite to the outer surface, and a spherical reflective film is arranged to surround the light-emitting diode,
Claim 1 or 2, wherein the light from the light emitting part is reflected by the spherical reflective film and then illuminates the optical grating of the second scale and the optical grating of the first scale. photoelectric encoder.