JPS623615A - Position detector - Google Patents

Abstract

PURPOSE:To obtain the titled small-sized high resolution detector by providing a photodetector at a distance to be situated in a projection area of the slits where the 3rd maximum of a diffraction pattern generating by the slits on the slit plates adjoins. CONSTITUTION:Light emitted from a laser diode 11 is made the parallel beams of flux with a collimator lens 12 and irradiates the moving slit plate 13. The plural slits 16 are arranged on the plate 13 and the light is transmitted through a slit part 16 part and intercepted on the other parts and the transmitted light irradiates the fixed slit plate 14. The light is transmitted through a slit part 17 and the transmitted light irradiates a photodetecting element 15. Then, the interval between the moving slit plate 13 and the fixed slit plate 14 can be enlarged and the influence of the interval accuracy can be made slight and the detector can be made small and highly resolable easily by providing the fixed slit plate at a position where the 3rd maximum of the diffraction pattern generating by the slits on the moving slit plate 13 coincides with the 1st maximum of the diffraction pattern generating by the adjacent slits.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a position detection device in a positioning device.

2. Description of the Related Art A positioning device that positions a mechanical device by detecting the rotation angle of the mechanical device using a position detection device is well known. Photoelectric encoders are widely used as such position detection devices. An example of the above-mentioned conventional photoelectric encoder will be described below with reference to the drawings.

FIG. 8 shows a conventional photoelectric encoder. In FIG. 8, 1 is a light source, 2 is a collimator lens, 3 is a rotating disk, 4 is a fixed mask, 6 is a light receiving element, and 8 is a waveform shaping circuit.

The operation of the photoelectric encoder configured as described above will be explained below. The light beam emitted from the light source 1 is made into parallel light by the collimator lens 2, and the light that passes through the slit on the rotating disk 3 and the slit on the fixed mask 4 is photoelectrically converted by the light receiving element 6, and a signal is output from the waveform shaping circuit 6. do. When the rotating disk 3 rotates according to the rotation of the member, the slits on the rotating disk 3 and the slits on the fixed mask 4 repeat matching and mismatching, and the waveform shaping circuit e
A sinusoidal signal is output, and by detecting this signal, the rotational position of the member is detected.

Conventionally, filament light bulbs and light emitting diodes have been used as light sources for this type of photoelectric encoder.

Problems to be Solved by the Invention However, with the above configuration, it is difficult to obtain parallel light beams with low dispersion due to the large light emitting area of filament light bulbs and light emitting diodes as light sources. The image of the slit would be blurred on the fixed mask, and the distance between the rotating disk and the fixed mask could not be made large; in general, when the slit distance was P, the value was L = P/2 to P. . Furthermore, as the degree of blur of the slit image changes as L changes, the sinusoidal waveform signal also changes, and in order to perform highly stable position detection, it is necessary to keep the change in L small. In order to solve the above problems with conventional photoelectric encoders, there are some that improve the flatness of the rotating disk and increase the precision of the rotating disk bearing, suppress the change in L, and achieve high resolution. In order to keep the changes in , L small, the operating temperature conditions and the load conditions on the rotating disk bearing are severely limited, so it is configured as a precision measuring instrument, and it is difficult to use it for general industrial purposes. There are also devices that use a high-intensity filament bulb and a long-focus collimator lens to obtain a relatively low-dispersion luminous flux, suppressing the effects of blurring on the slit image, making it resistant to changes in L, and achieving high resolution. Filament light bulbs, which are used to obtain light intensity, are susceptible to vibration and have problems in terms of lifespan, and the use of long focal length lenses to obtain low-dispersion luminous flux necessitates larger lighting systems, making it difficult to use for general industrial purposes. . The conventional examples described above have the problem that it is difficult to miniaturize and increase the resolution for general industrial use due to limitations in the mechanical configuration. In view of the above-mentioned problems, the present invention provides a compact, high-resolution position detection device that can be used for general industrial purposes. The position detection device is
In the photoelectric position detector, a laser light source is used as the light source, and the photodetector is installed at a distance such that the third maximum of the diffraction pattern generated by the slit on the slit plate is within the projection area of the slit adjacent to the slit. It has the following configuration.

Effects of the Invention With the above-described configuration, the present invention obtains a parallel beam with low dispersion using a laser light source and superimposes the slit diffracted light due to the coherence of the laser light, thereby making it possible to increase the distance between the slit plate and the photodetector. This makes it easy to improve the image quality and resolution.

Embodiment Hereinafter, a position detection device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of a position detection device in an embodiment of the present invention. In FIG. 1, 11 is a laser diode, 12 is a collimator lens, 13 is a movable slit plate, 14 is a fixed slit plate,
16 is a photodetecting element.

The operation of the optical portion of the position detection device configured as described above will be described below.

First, the light emitted from the light emitting surface of the laser diode 11 is turned into a parallel beam by the collimator lens 12, and irradiates the moving slit plate 13. As shown in FIG. 2, on the movable slit plate 13, a plurality of slits 16 having an opening width a are arranged at intervals P, and light is transmitted through the slits 16 and blocked at other parts. The transmitted light irradiates the fixed slit plate 14. At this time, the sleeve) 16a
The light intensity distribution P1(y) on the fixed slit plate 14 of the diffracted light of wavelength λ that has passed through is given by taking the coordinates as shown in FIG. 3, resulting in a pattern as shown in FIG. 4. .

Next, the light intensity distribution Pm(y) on the fixed slit plate 14 due to m slits is (m=1, 3, 5, ...>......・As given by (4) and shown in FIG. 2, on the fixed slit 14, one slit 17 with an opening width is arranged at an interval P, and light is transmitted through the slit 17. , other parts are blocked, and the transmitted light irradiates the photodetection element 15. If the relative difference between the slit 16 and the slit 17 is t, then the light intensity waveform p(t )
is (0≦t<p, m> 13 , l=1.3.s,
7-...-), and the light intensity waveform p (t) that irradiates the photodetecting element 16 at 0≦tap is the fifth
It becomes a sine wave shape as shown in the figure, and the maximum amplitude of the light intensity waveform p (t) is caused by the third maximum of the diffraction pattern caused by the slit 16a and the slit adjacent to the slit 16a, as shown in FIG. It can be seen that the first maximum of the diffraction pattern is obtained when the distance between the movable slit plate 13 and the fixed slit plate 14 matches. Furthermore, it can be seen that an amplitude close to the maximum amplitude can be obtained even at an interval such that the third maximum of the diffraction pattern generated by the slit 16a is within the projection area of the slit adjacent to the sleeve 16a. In addition, as shown in Fig. 5, when the opening width of the slit 16a is set to a=P/2, the opening width of the slit 17 is P/12, or the light intensity waveform p due to the change in the interval at 5P/12. It can be seen that the similarity of (t) is good.

Further, when the slit 18a is considered as a rectangular single aperture shown in FIG. 5 and Fraunhofer diffraction is determined, the intensity distribution Io(
If β is treated as a constant, it becomes as shown in Fig. 7.

Here, using the coordinates shown in FIG.
L at which the third maximum of the diffraction pattern caused by a matches the first maximum of the diffraction pattern caused by the slit adjacent to the slit 16a is defined as α≠2.
5. z=p.

If cos θ cape 1 is set, then Lo at which the maximum amplitude of the light intensity waveform p (t) given by equation (5) is obtained can be approximated by the following.

As described above, according to this embodiment, by using a laser diode and a collimator lens as a light source, it is possible to achieve high illuminance and low dispersion of illumination luminous flux by improving the efficiency of use of the amount of emitted light, and the slits on the movable slit plate P ) At λ, the distance between the movable slit plate and the fixed slit plate can be increased compared to the conventional example, and the influence of the accuracy of the interval between the movable slit plate and the fixed slit plate due to the mechanism configuration can be minimized, resulting in miniaturization and High resolution can be easily achieved.

Furthermore, when the slit width on the movable slit plate is P/2, by approximately setting the slit width on the fixed slit plate to 7P/12 or SP/12, the interval between the movable slit plate and the fixed slit plate can be changed. On the other hand, the similarity of the sine wave shape signal is improved, and the influence of the spacing accuracy between the moving slit plate and the fixed slit plate due to the mechanism configuration can be minimized.
Miniaturization and high resolution can be easily achieved.

In this embodiment, the movable slit plate is placed on the light source side, but a fixed slit plate may be placed on the light source side.

Furthermore, although a fixed slit plate was provided in this example,
Only the photodetecting element having the slit function of the fixed slit plate may be used.

In addition, in this example, the slit width on the movable slit plate was set to P/2 and the slit width on the fixed slit plate was determined, but the opposite is true when the fixed slit plate is placed on the light source side. Needless to say.

Further, in this embodiment, l and m are odd numbers in equations (4) and (5), but even numbers can be easily determined in the same manner, so a description thereof will be omitted.

Further, in this embodiment, a laser diode and a collimator lens are used as the light source, but it goes without saying that any laser light source that can provide a parallel beam may be used.

Effects of the Invention As described above, the present invention uses a laser light source as a light source in a photoelectric position detector, and adjusts the distance between the slit plate and the photodetector so that the third maximum of the diffraction pattern generated by the slit on the slit plate is By installing the photodetector at a distance that is within the projection area of the slit adjacent to the slit, the influence of the spacing accuracy between the slit plate and the photodetector due to the mechanism configuration can be minimized, resulting in miniaturization and It is possible to realize a position detecting device that can easily achieve high resolution.

[Brief explanation of drawings]

FIG. 1 shows that the position detection device according to the embodiment of the present invention has a =
In the light intensity distribution diagram on the fixed slit plate 14 at P/2, the fifth (7a, b, c, d, e are respectively b=12P/24.b:13P/24 (or b=
11P/24), b=14P/24(-4 or b=10
P/24). b=1SP/24 (or b=9P/24), b=16
A diagram of the light intensity waveform illuminating the photodetector element when P/24 (also b = 5P/24), Figure 5 is a positional relationship diagram of the rectangular half aperture, Fraunho 77
(Fraunhofer) diffraction light intensity distribution diagram, FIG. 8 is a configuration diagram of a conventional photoelectric encoder. 11... Laser diode, 12...
・Collimator lens, 13...Moving slit plate, 14...Fixed slit plate, 16...
Photodetection element. Name of agent: Patent attorney Toshio Nakao and 1 other person f3
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Claims (9)

[Claims] (1) In a photoelectric position detector, a slit plate is provided between a light source and a photodetector, and the amount of displacement of the slit plate is determined by detecting the output signal of the photodetector, in which a laser light source is used as the light source. A position detection device characterized by: (2) A photodetector is installed at a position such that the third maximum of the diffraction pattern generated by the slit on the slit plate is within the projection area of the slit adjacent to the slit. The position detection device described in section. (3) A patent claim characterized in that a photodetector is installed at a position where a third maximum of a diffraction pattern generated by a slit on a slit plate and a first maximum of a diffraction pattern generated by a slit adjacent to the slit match. The position detection device according to the second item in the range. (4) The position detection device according to claim 2, wherein the slit plate and the photodetector are installed at a distance of ap/2.5λ. (5) Providing a second slit plate between the light source and the photodetector,
A patent claim characterized in that the slit plate on the photodetector side is installed at a position such that the third maximum of the diffraction pattern generated by the slit on the slit plate on the light source side is within the projection area of the slit adjacent to the slit. The position detection device according to item 1. (6) The slit plate on the photodetector side was installed at a position where the third maximum of the diffraction pattern generated by the slit on the light source side coincided with the first maximum of the diffraction pattern generated by the slit adjacent to the slit. The position detection device according to claim 5, characterized in that: (7) The position detection device according to claim 5, wherein the slit plate on the light source side and the slit plate on the photodetector side are installed at a distance of ap/2.5λ. (8) The slit width on the slit plate on the light source side is P/2, and the slit width on the slit plate on the photodetector side is 7P/12 or 5P/12.
The position detection device described in section. (9) The position detection device according to claim 1, characterized in that a laser diode and a collimator lens are used as a laser light source.