JPS6361916A - Position detecting device - Google Patents

Abstract

PURPOSE:To easily obtain a signal in a desired waveform shape by using a laser light source and a light quantity limiting means as a light source and irradiating periodic slits on a slit plate. CONSTITUTION:A laser diode 11, a collimator lens 12, a light quantity limiter 13, a moving slit plate 14, a fixed slit plate, and a photodetecting element 16 are provided. Then, light emitted by the light emission surface of the laser diode 11 becomes parallel luminous flux through the collimator lens 12 and is varied in light quantity distribution in a plane perpendicular to the luminous flux by the light quantity limiter 13 to irradiate the moving silt plate 14. Thus, the laser light which is varied in light quantity distribution is used to obtain parallel flux with low dispersion and the relative intensity distribution of the Fraunhofer diffracted image of the periodic slits due to the coherence of the laser light is varied to easily obtain the signal in the desired waveform shape.

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. 11 shows a conventional photoelectric encoder.

In FIG. 11, 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, 6
is a waveform shaping circuit.

The operation of the photoelectric encoder configured as described above will be explained below. A light beam emitted from a light source 1 is collimated by a collimator lens 2, and the light that passes through a slit on a rotating disk 3 and a slit on a fixed mask 4 is photoelectrically converted by a light receiving element 5, and a signal is output from a 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, so that the waveform shaping circuit 6
A sinusoidal waveform signal is outputted, 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.

This is a more compact and high-resolution alternative to the conventional photoelectric position detection device, which uses a slit plate between a light source and a photodetector to detect the output signal of the photodetector to determine the amount of displacement of the slit plate. For information on the revolutionary position detection device that makes it easy to
I suggested it earlier.

This is achieved by obtaining a parallel beam with low dispersion using a laser light source, and by obtaining the main maximum of the Fraunhorn 1 diffraction image of the periodic slit due to the coherence of the laser light, the clarity of the light and dark fringes increases and the bright part becomes a sharp beam. At the same time, by installing the first slit plate and the second slit plate at a distance such that the main thickest interval matches the slit interval, the first slit plate and the second slit plate are The interval between the slit plates can be increased, the influence of the interval accuracy between the first slit plate and the second slit plate is negligible, the life of the slit plate can be extended, and preforming and high resolution can be easily achieved. Ru.

Problems to be Solved by the Invention However, with the above configuration, □In order to obtain a desired waveform signal, it is necessary to form chimney fringes using the slits on the rotating disk and the slits on the fixed mask. Developing a new model requires a large amount of money and time, as the spacing and shape of the moiré fringes and the shape and dimensions of the light-receiving surface of the light-receiving element are checked on the actual product and optimized through trial and error. Further, the waveform adjustment has the problem that fine adjustment of moiré fringes is required by a highly skilled person.

In view of the above problems, the present invention provides a position detection device that easily obtains a desired waveform signal.

Means for Solving the Problems In order to solve the above problems, the position detection device of the present invention includes:
A photoelectric position detector uses a laser light source as a light source and a light amount limiting means to illuminate periodic slits on a slit plate, and uses a photodetector to detect bright and dark fringes in a Fraunhofer diffraction image caused by the periodic slits. It is equipped with the following.

According to the above-described configuration, the present invention uses a laser light source with a changed light intensity distribution to obtain a parallel beam with low dispersion, and obtains the main maximum of a 7-round hod diffraction image of a periodic slit due to the coherence of the laser beam. By changing the relative intensity distribution, a desired waveform signal can be easily obtained.

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 light amount limiter, 14 is a movable slit plate, and 15
1 is a fixed slit plate, and 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 boolean diode 11 is turned into a parallel beam by the collimator lens 12, and the light quantity distribution is changed in a plane perpendicular to the beam by the light quantity limiter 13, and the movable slit plate 14 is irradiated. do. As shown in FIG. 2, the illumination light amount distribution on the moving slit plate 14 is 81 to S.
It can be considered that N individual illuminations are superimposed.

Next, as shown in FIG. 3, on the movable slit plate 14, a large number of slits 17 with an opening width a are arranged at intervals d, and light is transmitted through the slits 17 and blocked in other parts. The transmitted light irradiates the fixed slit plate 15.

At this time, the Fraunhofer diffraction image of the illumination SN having the wavelength λ transmitted through the slit 17 is considered to be that the slit 17 has a very large number of identical rectangular slit openings arranged regularly, so the diffraction of the light from the flint 1 is the same. It is a combination of a regular array of apertures and a rectangular half-aperture. It is assumed that the direction of the slits 17 is parallel to the y-axis in FIG. 4, and that their centers are regularly arranged on the x-axis at a constant interval d. If the light source SN is toss a slit on the Xl-Y1 plane parallel to the Y1 axis and the center is on the x1 axis, the diffraction image PN
is a thin line centered on the x2 axis and parallel to the Y2 axis,
The intensity distribution I (PN) of the diffraction image is I (PN) = Io (P
N)lF(PN)12−・−・−(1). Engineering. (
PN) is the intensity distribution of the diffraction image in the rectangular half-aperture, a = −(sinθ + sinθ) ・, −,
-=・(3) λ 12 may be used, and IF(PN)+2 is the relative intensity of the diffraction image when N identical apertures are sequentially lined up at intervals d on the X-axis from the first aperture at the origin. In the distribution, δ=−(sinθ+
sin θ2) −・−・−−−−(6)λ 1 , and when the light source is a monochromatic light source with wavelength λ, I of equation (1)
(PN) in IF (PN)+2 (sinθ,+s
Fig. 5 is drawn as a function of inθ2) (Reference: Optical Technology Handbook [Asakura Shoten]).

Here, the laser diode 11 and the collimator lens 12 are used as the light source to perform parallel flux, so the equations (3) and (69) are, respectively, = 2Sln θ λ 2 .・・・・・・・・・
・(6), 2゛−=−=−(7) The condition for the main maximum is d sin θ22 mλ (m=o, ±1.±2 ・= −
) , , (The width of the main maximum of El is 2/N of the interval of the main maximum, and as N becomes a dog, the main maximum gradually becomes thinner and sharper.

Also, as shown in FIG. 5, the dotted line connecting the main maxima of each order of IF (PN) 12 is a rectangular half-opening. (pN) distribution.

The illumination S of the slit 16 determined as above
The Fraunhofer diffraction image at N is projected onto the fixed slit plate 16. As shown in FIG. 3, on the fixed slit plate 15, a large number of slits 18 with opening widths are spaced apart at intervals d, and the light passes through the slits IJ,,,)
The light is transmitted in the 18th part, and the light is blocked in the other parts, and the transmitted light irradiates the photodetecting element 16.

At this time, the interval between the main maxima of the Fraunhofer diffraction image by the illumination SN projected onto the fixed slit plate 16 matches the interval d between the slits arranged on the fixed slit plate. That is, the distance between the movable slit plate 14 and the fixed slit plate 160 is expressed by the following formula (8): m=1...
・When (9) L=M− (11) λ (M: 1, 2, etc.), as the movable slit plate 14 moves, The amplitude of the detection signal output from the photodetection element 16 becomes maximum.

Similarly, in the Fraunhofer diffraction images obtained by the illuminations 81 to SN, the intervals between the main maxima are equal, the width of the main maximum is inversely proportional to the number N of slits under the illuminations 81 to SN, and the amount of light is proportional to the number N of the slits. Proportional. Therefore, the lighting 81
The relative intensity distribution of the main maximum of the Fraunhofer diffraction image by illumination in which ~SN are superimposed, that is, the light quantity distribution is changed in a plane perpendicular to the light beam by the light quantity limiter 13 on the moving slit plate 14, is: It is a function of the light amount distribution of the illumination. Therefore, as the movable slit plate 14 moves, the waveform shape of the detection signal outputted from the photodetecting element 16 also becomes a function of the light amount distribution of the illumination, and the light amount distribution of the illumination is determined from the desired waveform shape. Can be done.

Here, the desired waveform shape signal is f(, (θ is 2 when the movable slit plate 14 moves by the slit interval d.
), then the relative intensity distribution of the main maximum q
(θ) is q('s=fl('s)...
...... (12), and the light intensity distribution of the illumination to obtain q( is h(N).

(N is the number of slits under illumination), then θ=□
・・・・・・・・・・・・(13) However, since N≧4M, ・・・・・・・・・・・・・・・(14) Therefore, the light intensity distribution h(N) of the illumination becomes Seek.

As a first example, when trying to obtain a sinusoidal waveform signal, f(θ)=sinθ...
,...(15)q(θ) = cosθ
・・・・・・・・・・・・(16)・・・・・・・・・
(17) If M=1.2, 4.8 and illumination is performed in the illumination scene distribution state shown in FIG. 6, a sinusoidal waveform signal will be obtained.

As a second example, a laser diode with a beam pattern shown in Fig. 7 is made into a parallel beam using a collimator lens with a focal length of 8M, and is illuminated from the fixed slit plate side, with a slit interval of 12 μm and a pattern shape of the fixed slit plate. The eighth
When arranged as shown in the figure, the beam pattern shown in Fig. 7 is considered to be a superposition of each illumination from 81 to SN as shown in Fig. 9, and contrary to the first embodiment, the amount of illumination light is Determine the waveform shape of the signal from the distribution. From the calculation results shown in FIG. 10, an approximate sinusoidal signal is obtained when the gap interval between the movable slit plate and the fixed slit plate is set to 1080 to 1440/im.

As described above, according to the first embodiment, a laser diode and a collimator lens are used as a light source, and the light amount distribution is changed in a plane perpendicular to the light beam by a light amount limiter to illuminate the movable slit plate. By projecting a Fraunhofer diffraction image generated by slits regularly arranged on a moving slit plate onto a fixed slit plate and detecting the main image, a desired waveform signal can be easily obtained without using moiré fringes. Can be done. In this embodiment, the movable slit plate is arranged on the light source side, but a fixed slit plate may be arranged on the light source side.

Further, according to the second embodiment, by setting a gap distance suitable for the beam pattern of a laser diode as a light source, it is possible to easily obtain an approximate sinusoidal waveform signal. In this example, illumination is performed from the fixed slit side, but even if illumination is performed from the movable slit side, due to the need for symmetry of the slit that contributes to the formation of a diffraction image when viewed from the diffraction image side. Since this is equivalent to illuminating only the portion of the fixed slit pattern projected onto the moving slit, the result is the same.

It goes without saying that the light amount limiter in the first embodiment may be any means for limiting the amount of light on the light source side, such as an optical filter, a light shielding plate, or limiting the length of a slit on the light source side.

Further, in this embodiment, a fixed slit plate is provided, but it goes without saying that the same effect can be obtained even if only the optical detection element having the slit function of the fixed slit plate is used, 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 provides a photoelectric position detector in which a parallel beam of low dispersion is obtained using a laser light source with a changed light intensity distribution, and a periodic slit of 7 due to the coherence of the laser beam is used.
By changing the relative intensity distribution of the main maximum of the Raunhoff 7 diffraction image, it is possible to realize a submerged position detection device that can easily obtain a desired waveform signal. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a position detection device according to an embodiment of the present invention, FIG. 2 is a light intensity distribution diagram of the illumination light flux in FIG. 1, FIG. 3 is a detailed diagram of the slit portion in FIG. 1, and FIG. is a positional relationship diagram of Fraunhofer diffraction, Figure 5 is a light intensity distribution diagram of a Fraunhofer diffraction image that combines a regular array of identical apertures and a rectangular half-aperture, and Figure 6 is a diagram of the illumination light intensity distribution for obtaining a sinusoidal waveform signal. A graph showing the calculation results, FIG. 7 is a beam pattern diagram of the laser diode used in the second embodiment, FIG. 8 is a pattern layout diagram of the fixed slit plate of the second embodiment, and FIG. Conceptual diagram showing the illumination state of the example, 1st
FIG. 0 is a graph showing the calculation results of the second embodiment, and FIG. 11 is a configuration diagram of a conventional photoelectric encoder. 11... Laser diode, 12...
・Collimator lens, 13...-light limiter, 14
...Moving slit plate, 15...Fixed slit plate, 16...Photodetection element. Name of agent: Patent attorney Toshio Nakao and one other person N-
-'-f9-1TJ 12- Cori f-q Ren 2 13--・Chut4 Kaiten 2nd Figure 3 Figure 4f Figure 6 Figure 7 Off Ay, is Anynoe (Dear-
ee) Figure 8 Field, Middle Figure 9

Claims (6)

[Claims] (1) A light source using a laser light source, a slit plate having periodic slits, and at least one photodetector for detecting a change in light amount due to movement of the slit plate, the light source and the In the photoelectric position detector, the slit plate is provided between the light source and the slit plate, and the amount of displacement of the slit plate is determined by detecting the output signal of the photodetector. 1. A position detection device comprising a limiting means, wherein the light and dark fringes of a Fraunhofer diffraction image produced by the periodic slits on the slit plate are detected by the photodetector to obtain an output signal having a desired waveform shape. (2) Light amount distribution h(N) of periodic slits on the slit plate by the light source and light amount limiting means and desired waveform shape f(θ)
But, {h(N)}＾2=Σ＾∞_K_=_N{f′[2π/
(K/M+1)}-f'[2π/(K/M)}/K, the position detection device according to claim 1. (3) Using a laser diode and a collimator lens as a light source, the distance between the periodic slit on the slit plate and the Fraunhofer diffraction image to be detected is adjusted so that the output signal has a sine wave shape depending on the light intensity distribution generated by the beam pattern of the laser diode. A position detection device according to claim 1, characterized in that: (4) It has a light source using a laser light source, two slit plates having periodic slits, and a photodetector that detects changes in light amount due to movement of the slit plates, and the light source and the photodetector In the photoelectric position detector, the two slit plates are provided between the light source and the slit plate on the light source side, and the displacement amount of the slit plate is determined by detecting the output signal of the photodetector. a light amount limiting means is provided, and the light and dark fringes of the Fraunhofer diffraction image generated by the periodic slits on the slit plate on the light source side are detected by the photodetector via the periodic slits on the slit plate on the photodetector side; A position detection device characterized by obtaining an output signal with a desired waveform shape. (5) The light amount distribution h(N) of the periodic slit on the slit plate on the light source side by the light source and the light amount limiting means and the desired waveform shape f(θ) are {h(N)}＾2=Σ＾∞_K_ =_N{f′[2π/
(K/M+1)]-f'[2π/(K/M)]}/K, the position detection device according to claim 4. (6) Using a laser diode and a collimator lens as a light source, the distance between the periodic slits on the slit plate on the light source side and the periodic slits on the slit plate on the photodetector side is determined by the light intensity distribution generated by the beam pattern of the laser diode. 5. The position detection device according to claim 4, wherein the output signal has a sinusoidal waveform.