JPS6363916A - Optical type displacement detector - Google Patents

Abstract

PURPOSE:To facilitate the manufacture of an index scale, by forming a lattice pitch in a specified relationship according to intervals respectively between a diffusion light source consisting of laser diode and a main scale and an index scale to divide the pitch in to a plurality of segments optically. CONSTITUTION:A lattice 16 of a main scale 14 is arranged at a position separated by (u) from a laser diode 32 while a lattice 20 of an index scale 18 is arranged at a position separated by (v) from the lattice 16. The pitch of the lattice 20 is given by qapprox.=(u+v)Q/u when Q=P/m (m is integer of 2 or more) with the pitch of the lattice 16 represented by P. Changes in the quantity of light with relative movement of the scales 14 and 18 are received with light receiving elements 22A and B differing in the phase by 90 deg. from each other to obtain a 2-phase detection signal with the pitch Q and a higher harmonic component of m=4 is utilized. This facilitates the manufacture of the index scale.

Description

[Detailed description of the invention]

[Industrial Field of IJ 1111] The present invention relates to an optical displacement detector, and more particularly, to detecting the relative positions of two members by forming an optical grating that corresponds to a main scale formed with an optical grating. The present invention relates to an improvement in an optical displacement detector that detects changes in a photoelectric conversion signal caused by relative displacement with an index scale.

[Conventional technology]

In the field of machine tools, measuring instruments, etc., as shown in FIG. The first grating 16 and the grating 20 of the button 2 are fixed by fixing the provided index scale 18, a slider having an illumination means composed of a light source 10 and a collimator lens 12, and a photoelectric conversion means composed of a light receiving element 22, for example. Optical displacement measuring devices are in widespread use that measure displacement by photoelectrically converting changes in light caused by relative movement with the object, converting the resulting signal into pulses in a counting circuit, and counting. In such a measuring device, for example, the second grating 22 provided on the index scale 18 is divided into phases of 0", 90°, 180°, and 270°, as shown in FIG. , by adjusting the width of the preamplifiers 24A and 24B, the X of the index scale 18
Corresponding to the displacement in the direction, △sinθ, A CO3
A two-phase detection signal approximated by θ is obtained. In such a measuring device, as processing technology becomes more popular, it is required to further refine the measurement resolution, and the grating pitch P of the first grating 16 of the main scale 14
is becoming smaller. Conventionally, the grating pitch P is 20 μm
However, recently a specification of 10μ or less is required. Therefore, as a detector that is advantageous for high resolution, the so-called optical division method is used, in which the pitch t of the detection signal obtained with respect to the pitch P of the first grating of the main scale is a subdivision of P such as P/2. A detector that performs this has been proposed. The present applicant has also previously determined that the pitch P of the first grating on the main scale is the pitch P of the second grating on the index scale.
/n (n is an integer of 2 or more), a detector is proposed that can obtain a signal with a pitch of P/n as a detection signal. In this case, the first grating had a ratio of 131:1 between the light transmitting or reflecting part and the light shielding part, but the first grating had a main wave component of pitch P as well as a high component of pitch P/n. It has an A-wave component, and it is estimated that the detection signal was obtained by the combination of 1 m of this harmonic component and the second grating. This means that when the wavelength is λ, the lattice spacing is approximately (P/n)
The fact that good signals are obtained at integer multiples of 2/λ also proves it is a good idea. For example, assuming a grating F1(x) with a pitch of P as the first grating and a ratio of light transmitting or reflecting portions to light blocking portions at exactly 1:1, and performing Fourier analysis on this, excluding the constant, the following equation is obtained. become. F 1 (X) = 1/2 + 0.6 sin (2
πx /P) + 0.2Sin (3・2πx /P) 10Q, 1sin (5・2πx/P)+ ... Therefore, in addition to the fundamental wave, Fl(x) contains harmonics such as the 3rd and 5th orders. It can be seen that waves are included. Similarly, if Fourier analysis is performed assuming that the number of light transmitting or reflecting portions and light shielding portions in the first grating is 5=7, it is found that harmonics such as second order and fourth order are also included. Generally, the first grating is manufactured with the aim of achieving a ratio of 1:1 between the light transmitting or reflecting part and the light shielding part. However, due to variations in manufacturing technology, the ratio is not 1:1, so It is thought that harmonic components are included, and the above-mentioned detector utilizes these harmonic components.

[Problems to be solved by the invention]

However, this detector requires a collimator lens with high precision and a long focal length to collimate the illumination light into a well-paralleled beam. Therefore, there is a problem that the detector becomes larger. Furthermore, with increasing optical resolution, it is necessary to refine the pitch of the second grating on the index scale. Unlike the main scale, the index scale is not a wood-related problem because it is sufficient to have a number of index scales, but the problem remains that the yield deteriorates as the pitch becomes finer.

[Purpose of the invention]

The present invention was made to solve the above-mentioned conventional problems, and it does not require the use of a collimator lens with high precision and a long focal length, and the index scale can be easily processed.
An object of the present invention is to provide an optical displacement detector that performs optical division.

[Means to solve the problem]

The present invention provides an optical displacement detector including a diffused light source and a main scale formed with a first grating including a harmonic component with a grating pitch P and disposed at a distance U from the diffused light source. and Q=P/1 (ii is an integer greater than or equal to 2)
Then, the grating pitch qα(u +v) Q/ is arranged at a position where the distance from the first grating is V.
an index scale on which a second lattice of u is formed;
By including a light receiving element that generates a pitch Q detection signal by photoelectrically converting a change in light amount due to the overlapping of the image of the first grating by the diffused light source and the second grating when the two scales move relative to each other. , the above objective has been achieved. Further, in an embodiment of the present invention, the diffused light source is a point light source. Moreover, the fruit of the present invention f+l! In the i aspect, the point light source is further a laser diode. In another embodiment of the present invention, the point light source is provided with a lens for suppressing the angle of collapse 1+l in front of the light emitting part of the laser diode. Further, in another embodiment of the present invention, the diffused light source is a line light source oriented in the grating width direction of the first grating. Further, in an embodiment of the present invention, the interval V is defined as λ, which is the wavelength at the average value of the light sensitivity spectrum of the optical system, and the magnification M of this system is defined as M4 (u + v) /u, Vαn MQ' /λ (n is an integer greater than or equal to 1). (Operation) First, the detection principle of the present invention will be briefly explained. As shown in FIG. Here, assuming that the first grating 16 has a harmonic component of −th order (+a is an integer of 2 or more), the pitch Q (however, Q-P/l) is used instead of the first grating. It may be assumed that there is a grating represented by: Then, intuitively, an enlarged shadow of the grating with a pitch Q is formed on the image plane S which is spaced apart from the first grating 16 by a distance V.In reality, The light intensity distribution of the shadow changes variously depending on the values of U and V due to the effect of one loaf of time. Due to the spacer, the amplitude transmittance of light of the grating with pitch Q f(x)
is expressed by the following formula, Principles of Op
tics, 6th edLtion(MAX B
ORN & EMI L WOLF, Perg
The results of calculating the image distribution g (X) on the image plane S with the interval V using the theory of Fresnel diffraction described on page 383 of Amon Press, 1980 are shown below. f(x) = 1 + cos (2πx/Q)...
(1) Here, let λ be the gt value at the average value of the light spectrum in this optical system, taking into account the emission spectrum of the diffused light source 30 and the wavelength sensitivity of the light receiving element, and n
is a natural number (an integer vi of 1 or more), and is defined as the magnification M@M-(u + v )/11 of the first lattice of this system. When the distortion interval V is approximately equal to vl(0) expressed by the following equation (2), the relationship shown in the following equation (3) holds true, excluding the proportionality constant. VαV 1 (n') 1 = (n-0,5)MQ2/λ-・-(2>Q(X)
301 (X) y4+cos[4πUX/((u +v)Q)] ......(3) The above equation (2) is expressed as VtaV1(n)-u(n
-Q. 5) Equivalent to Q2/(λu - (n-0,5)Q2). However, since gl (x) does not change much even if ■ changes, equation (2) is not exact. On the other hand, when the interval V is approximately equal to v2(n) expressed by the following equation (4), the relationship of the following equation (5) holds true, excluding the proportionality constant. V = v 2 (n) = n MQ2 /λ (4) Re
(X) 3 g2 (x)=i +cos[2
[πu
, the grating pitch q is (U + v )Q/ (2u )
It can be seen that the detection signal can be obtained by arranging the second grating of . This shadow platform has a grid pitch that is 1/2 that of an intuitive shadow platform, and the first grid 16 has a Q
That is, the detection signal has a large characteristic in that when it is displaced by P/l, the detection signal changes by two pitches. On the other hand, from equations (4) and (5), the interval V is V2(I
I) The nearby image plane S has a grating pitch q of (u + v
) It can be seen that the detection signal can be obtained by arranging the second grid of Q/u. Since this shadow plate corresponds to an intuitive image, the first grid 1
The detection signal changes by 61 bits depending on the displacement of Q of 6, that is, P/If. 41. Although there are waveforms with various pitches on the image plane S corresponding to the harmonic components of the first grating 16, the second grating may be considered to filter a specific component among them. Up until now, there has been no diffused light source 30, especially a point light source, with a small light emitting part and a large output, and there has been little need for a large grating pitch P, so the present invention Such a detector has never been studied in depth. However, due to changes in the technical background such as the need to reduce the cost of laser diodes, which are ideal as point light sources, and to overcome problems associated with miniaturization of the grating pitch P, the inventor of the present application has investigated the above-mentioned method. (3
) and (5), and MI confirmed the practicality of the detector as described above. The present invention was made based on such research results, and the grating pitch of the first grating is P1, the grating pitch q of the second grating is (u + v) Q/u (u is the difference between the diffused light source and the first grating). The interval between the gratings, ■ is the interval between the first grating and the second grating, Q-P/s), and the main scale on which the first grating is formed is illuminated with a diffused light source, and the first grating is A detection signal with a pitch Q is generated by photoelectrically converting the change in the amount of light caused by the overlapping of the Shōbutsu and the second grating in the harmonic components of the second grating. Therefore, there is no need to use a collimator lens with high viscosity and a long focal length, and the index scale can be easily processed.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. The first embodiment of this 11th light uses the relationship of equations (4) and (5) above using the ■ order harmonic component, and as shown in Fig. 2, the main A main scale 14 includes a laser diode 32 that illuminates the scale 14, and a first grating 16 including a harmonic component with a grating pitch P, which is disposed at a distance U from the laser diode 32. A second grating with a grating pitch q arranged at a distance V from the first grating 16
an index scale 18 on which a lattice 20 of
When both the scales 14 and 18 move relative to each other, the phase of each of them is 0, which photoelectrically converts the change in the amount of light caused by the interaction between the first grating 16'# of the first grating 16 by the laser diode 32 and the second grating 20. It is comprised of two light receiving elements 22A, 22B with angles of 90° and 90°, and preamplifiers 24A, 24B that amplify the outputs of the light receiving elements 22A, 22B, respectively. Here, it is assumed that the first grating 16 has a -th order harmonic component, and in FIG. 2, the first grating is represented by a grating with a pitch Q-P/e. As the first grating, for example, a grating in which the ratio of light transmitting portions to light blocking portions is approximately 1:1 is used. As the laser diode 32, a laser diode (for example, HL-7801E manufactured by Hitachi, Ltd.) whose light emitting portion is approximately several μm square and whose wavelength λ is approximately 0.78 μl can be used. The distance V between the first grating 16 and the second grating 20 and the grating pitch q of the second grating 20 are made to satisfy the following relationship. v hn 1vlQ2/λ ・・・・・・(6)q
= (u + v) Q/u (7)
Here, n is an integer of 1 or more. u Body t: Ha, i=5, n=120, U, V
are both set to approximately 5I11m, and the grating pitch P of the first grating is 20 μs (Q−4 μl), the grating pitch q of the second grating 20 may be 8 μ− from the relationship in equation (7). Finally, the position of the laser diode 32 and index scale 18 may be finely adjusted to obtain a good signal. Further, the correction value of the variation in the interval V is approximately ±0.202/λ. On the other hand, regarding the deviation δ of the second grating 20, which is divided by the deviation δ in order to obtain a phase-shifted signal, in order to obtain a phase difference of 90°±10', the grating pitch q must be 8μ.
m, the deviation δ may be (2±0.2) μm. Therefore, it can be seen that the second grating 20 has twice the grating pitch and twice the deviation as compared to the conventional detector, and is easier to manufacture. Here, in the case of a vernier type detector, the second grating 20
The grating pitch q is set to an approximate value of equation (7), and division by phase is unnecessary, but the grating pitch q may be twice that of the conventional one. In addition, Iff due to the deviation between the pitch q of the second grating 20 and the pitch of the image caused by variations in the intervals U and V when the main scale 14 is displaced is
This can be avoided by reducing the width of B in the X direction. In the configuration of this embodiment, by displacing the main scale 14 in the ×X direction, the preamplifiers 24A, 24[3
From this, a two-phase detection signal with a pitch (=4 μl) is obtained. That is,

[=Q. Using this grid, u=51m1
If vα is set to 3111 m, the pitch of the detection signal becomes 5 μm because the magnification M=875. In other words, m −4 harmonic components are used. In the first embodiment, the laser diode 32 is used as it is as a point light source, but the type of point light source is not limited to this. For example, as shown in FIG. A diameter of 5 mm is placed on the front of the light emitting part of the
It is also possible to use one provided with a hemispherical lens 34 for suppressing the divergence angle of about 00 μm. In this case, the divergence angle of the illumination light from the laser diode 32 is suppressed,
Although the light receiving efficiency is improved, it is necessary to convert the value of g in equation (7) above to be larger than the actual interval. Further, as a point light source, a high-output light emitting diode, which is a hybrid of a laser diode and a light emitting diode, can also be used. Next, a third embodiment of the present invention will be described in detail. In this third embodiment, as shown in FIG. 4, a linear light source 40 made of, for example, a slit-shaped light emitting diode oriented in the grating width direction of the first grating 16 is used as a diffused light source. Regarding other points, the light receiving elements 22A, 22B
, 22C122D has phases of 0°, 180°, 90°, 27
The explanation is omitted since it is the same as the first embodiment except that four light emitting diodes are provided and divided by 0". When a general light emitting diode is used as a light source, a light emitting part is used to make it a point light source. If only a small value is used, the light emission output decreases, and the amplification degree of the preamplifier must be increased, resulting in a deterioration of the S/N ratio.For this reason, in this third embodiment, the light source is used as a line light source rather than a point light source. The light source 40 has already been proposed by the applicant.
A light emitting diode in which the light emitting portion 42 has a slit shape as shown in FIGS. 5 and 6 can be used. This light emitting diode is made by diffusing P-type GaAs into a slit-like shape with a width W of about 50 μm and a length L of about 400 μm on a substrate 44 of, for example, N-type GaAS, and an electric VM film 46 on the lower surface. Electrode on the top surface via insulating PTA48! ! J46 is vapor-deposited. 50 is a lead wire. Since such a light emitting diode emits light in a slit shape, the overall output does not decrease and is suitable as a linear light source. In this way, the slit-shaped light emitting portion 4 of the light emitting diode
By orienting the longitudinal direction of 2 in the grating width direction of the first grating 16 of the main scale 14, even if it is a linear light source in the grating line direction, it becomes a point light source in the X direction of the grating, and is essentially a point light source. Acts as a light source. In this case, a cylindrical lens for controlling divergence direction may be provided in front of the linear light source. In each of the above embodiments, the present invention was applied to a transmission type detector, but the scope of application of the present invention is not limited to this. For example, as in the fourth embodiment shown in FIG. The present invention can be similarly applied to type (7) type detectors. Further, as the first grating, any shape can be used as long as it has a harmonic component. Also, the actual BL! In example i, the invention both:
Although the second grating has been commonly used in linear displacement detectors in which two or more sections are provided, the scope of application of the present invention is not limited to this, and detection using a moiré stripe method in which the second grating has no sections is applicable. The present invention can be similarly applied to a rotary displacement detector (0-tary encoder). Effects of the Invention As described above, according to the present invention, a point light source or a line light source can be used as it is as a diffused light source, and there is no need to use a highly accurate collimator lens. In addition, since the pitch of the index scale can be made larger than before, excellent effects such as ease of manufacturing the index scale are obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the detection principle of the present invention, FIG. 2 is a sectional view for explaining the configuration of the first embodiment of the optical displacement detector according to the present invention, and FIG. 3 is a diagram for explaining the detection principle of the present invention. are the same (a cross-sectional view of a main part for explaining the configuration of the second embodiment, FIG. 4 is a perspective view for explaining the configuration of the third embodiment, and FIG. 5 is a cross-sectional view of the main part for explaining the configuration of the third embodiment). Figure 6 is a front view for explaining the configuration of the light source used in Figure 5.
7 is a cross-sectional view taken along the line, FIG. 7 is a sectional view for explaining the configuration of the fourth embodiment of the present invention, and FIG. 8 is a perspective view of the configuration of an example of a conventional optical displacement detector. be. 14... Main scale, 16... First grating, 18... Index scale, 20... Second grating, 22. 22A, 22B, 22C122D... Light receiving element, P, Q... - Grating pitch, U, V... spacing, 30... diffused light source, 32... laser diode, 34... hemispherical lens, 40... line light source.

Claims (6)

[Claims] (1) a diffused light source, a main scale on which a first grating including a harmonic component is formed with a grating pitch P, which is disposed at a distance u from the diffused light source, and Q=P/m( m is an integer of 2 or more), an index scale in which a second grating with a grating pitch q≒(u+v)Q/u is formed and is arranged at a position with an interval from the first grating. , a light-receiving element that photoelectrically converts a change in light amount due to the overlapping of the image of the first grating and the second grating caused by the diffused light source when both scales move relative to each other to generate a detection signal of pitch Q; An optical displacement detector characterized by: (2) The optical displacement detector according to claim 1, wherein the diffused light source is a point light source. (3) The optical displacement detector according to claim 2, wherein the point light source is a laser diode. (4) The optical displacement detector according to claim 2, wherein the point light source has a lens for suppressing a divergence angle disposed in front of a light emitting part of a laser diode. (5) The optical displacement detector according to claim 1, wherein the diffused light source is a line light source oriented in the grating width direction of the first grating. (6) The distance v is defined by the wavelength at the average value of the light sensitivity spectrum of the optical system being λ, and the magnification M of this system being M=
The first claim states that when defined as (u+v)/u, v≒nMQ^2/λ (n is an integer of 1 or more)
Optical displacement detector as described in section.