JPH02103415A - Photoelectric displacement detector - Google Patents

Abstract

PURPOSE:To make it possible to improve interpolation accuracy and to improve response scanning speed by providing reference-light passing windows that are arranged in the vicinities of secondary lattices of an index scale, and providing reference-light photodetectors which transduce the light that has passed through the windows into electricity. CONSTITUTION:Longitudinal reference-light passing windows 341 and 342 are provided at the sides of secondary lattices 20a and 20b and 20c and 20d. Reference-light photodetectors 361 and 362 which transduce the light that has passed through the windows into electricity are provided. Two-phase detected signals (a-r1)-(c-r2) and (b-r1)-(b-r2) are formed based on outputs (a)-(d) and r1 and r2 of displacement detecting photodetectors 22a-22d and the photodetectors 361 and 362 in a signal processing circuit 40. When an index scale is moved to a main scale relatively, the vibrating components in said two-phase detected signals are fluctuated, but a DC component is not included. Therefore, the stable detected signal can be obtained. Highly accurate interpolation division is performed, and the highly accurate measured signal is obtained. Since the average values of the signals (a)-(d) in the photodetectors 361 and 362 are obtained, corrections with the reference signal r1 and r2 do not become excessive, and the adequate correction can be performed.

Description

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

The present invention relates to a photoelectric displacement detector, and in particular can correct DC level fluctuations in a displacement detection signal to generate a stable detection signal, thereby improving interpolation accuracy and increasing response scanning speed. The present invention relates to a photoelectric displacement detector that can be improved. [Prior Art] A light-transmissive index scale in which a main scale with a periodic main lattice formed thereon is fixed to one of opposing members, and a corresponding periodic sub-lattice formed in the other member;
A detector including an illumination system including a light source and a light receiving element that photoelectrically converts light from the illumination system modulated by the main grating and the sub grating is fixed, and changes periodically according to relative displacement of both members. A photoelectric displacement detector that generates a detection signal that
It is popular in the field of measuring the aging of machine tool tools. FIG. 10 shows an example of a conventional reflective photoelectric displacement detector, which includes a light emitting diode 10 as a light source, a collimator lens 12 that uses the light emitted from the light emitting diode 10 as a parallel illumination beam, A main scale 14 forming a periodic main grating 16, and a light-transmissive index scale 18 forming a corresponding periodic sub-grating 2o, which is arranged to be movable relative to the main scale 14.
and a displacement detection light-receiving element 22 for photoelectrically converting the reflected light beam R from the parallel illumination system that has been reflected by the main grating 16 of the main scale 14 and passed through the sub-grating 20 of the index scale 18. A periodic detection signal is generated according to the relative displacement between the main scale 14 and the index scale 18. In such a photoelectric displacement detector, the sub-grating 20
As shown in FIG. 11, there are usually two light receiving elements 22 on the index scale 18 in the direction parallel to the grating scale (up and down direction in the figure) and two in the longitudinal direction of the main scale (horizontal direction in the figure). For example, a total of 4 sub-lattice 20
The phase of a is set to the reference value O°, and the phase of the sub-grating 20b is -9
0'', the phase of the sub-grating 20c is +18°, and the phase of the sub-grating 20d is +90'', and as shown in FIG. Among the displacement detection signals a to d obtained by 22d, the difference (a − C) and (b
-d), a two-phase detection signal which is a differential signal is generated. In Figure 11, 24.2
6 is a differential amplifier. In this way, it is possible to obtain two-phase detection signals whose phases are different from each other by 90°, and by performing direction discrimination and electrical interpolation, highly accurate measurement can be performed. At this time, by employing the differential method as described above, it is possible to correct DC level fluctuations of the displacement detection signal and phase fluctuations due to changes in parallelism between the main scale 14 and the index scale 18. However, the main scale 14 has a length of, for example, 30 mm.
Long objects of 0 n or more are generally produced by positioning with a stepper, using a short object as an original plate, and exposing while transferring. Therefore, the thickness (shade) of the chrome that makes up the grating scale varies depending on the position in the longitudinal direction, so the reflectance and transmittance vary, and the line width also varies slightly, making it extremely difficult to manufacture uniformly. For example 8
In the case of a main grid with a main scale of μm pitch, the line width is 0.
．． The variation in the detection signal was about 2 μm, that is, about 2.5%, and when other factors were taken into account, the variation in the detection signal was sometimes about 10%. If there are variations in the longitudinal direction, the DC level of the received light output will change, and even if the differential method described above is adopted, if there is a difference in DC level fluctuation between the two differential phases,
There was a problem in that fluctuations in the DC level could not be sufficiently corrected. In particular, when the light source is provided in the center of the sub-grating in a reflective displacement detector, differential two-phase (sub-grating 20a
200.20b and 20d) becomes large, and the relative difference in DC level fluctuation becomes large.

[Problem to be achieved by the invention]

The present invention has been made to solve the above-mentioned conventional problems, and is a photoelectric displacement sensor capable of correcting DC level fluctuations of a displacement detection signal, improving interpolation accuracy, and improving response scanning speed. The objective is to provide a detector.

[Means for achieving the object 1] The present invention comprises a main scale having a main grating fixed to one member that moves relatively, and a light source and a sub-grid fixed to the other member moving relatively. A photoelectric sensor that includes a formed index scale and a displacement detection light-receiving element that photoelectrically converts light modulated by at least the main grating and the sub-grating, and generates a periodic detection signal according to the relative displacement of both members. The type displacement detector includes a reference light passing window disposed near the sub-grating of the index scale, and a reference charging light receiving element that photoelectrically converts the light that has passed through the reference light passing window, and a reference light receiving element is provided. The above object has been achieved by correcting the DC level fluctuation of the displacement detection signal obtained by the displacement detection light receiving element using the reference signal obtained by the element. [Operations and Effects] The present invention has been made with the focus on the fact that the closer the optical detection is to the displacement detection section, the greater the effect of the optical (2) detection for correcting DC level fluctuations. That is, for example, as in the example shown in FIG. Reference charging light receiving elements 328 to 32d are provided for photoelectrically converting the respective light beams. Then, as shown in FIG. 2 for the case of the sub-lattice 20a, the sub-lattice 20a
Reference light passing window 3 corresponding to the displacement detection signal a that has passed through a
The difference (a-ra) between the reference signal ra that has passed through 0a and the difference between the displacement detection signal C that has passed through the sub-grating 20G and the reference signal rc that has passed through the corresponding reference light passing window 300 (ara) -
By using (c-ra) as a detection signal, fluctuations in the DC level can be reliably corrected. Therefore, interpolation accuracy is improved and response scanning speed is also improved.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. A first embodiment of the present invention is a device similar to that shown in FIG.
As shown in FIG. 3, a vertically long reference light passing window 341 provided next to the sub-gratings 20a and 20b, and a vertically long reference light passing window 342 provided next to the sub-gratings 20c and 20d,
Similarly, vertically elongated reference light receiving elements 36+ and 362 are provided which photoelectrically convert the light passing through the reference light passing windows 341 and 342. The other configurations are the same as the example shown in FIG. 1, so the explanation will be omitted. As shown in FIG. 4, a signal processing circuit 40 for forming two-phase detection signals from the outputs of the displacement detection light receiving elements 22a to 22d and the reference light receiving elements 361 and 362 similar to that shown in FIG. an operational amplifier (op-amp) OPl whose amplification factor is made variable by a variable resistor VR1 for amplifying the output signal a of the light-receiving element 22a; and the light-receiving element 2
Variable resistor VR2 for amplifying the output signal of 2b
an operational amplifier OP2 whose amplification factor is made variable by a variable resistor VR3 for amplifying the output signal C of the light receiving element 220, and an output signal d of the light receiving element 22d. an operational amplifier OP4 whose amplification factor is made variable by a variable resistor VR4 for amplifying the reference light receiving element 361; and an operational amplifier OP4 whose amplification factor is made variable by a variable resistor VR5 for amplifying the output signal r1 of the reference light receiving element 361. An operational amplifier OP5, an operational amplifier OP6 whose amplification factor is made variable by a variable resistor VR6 for amplifying the output signal r2 of the reference light receiving element 362, and a differential signal (a- rt), and a differential signal (b-r) of the outputs of the operational amplifiers OP2 and OF2.
+), and the operational amplifier O
An operational amplifier OP9 that outputs a differential signal (C-rz) between the outputs of P3 and OF2, and an operational amplifier 0P that outputs a differential signal (d-rz) between the outputs of the operational amplifiers OP4 and OF2.
10, an operational amplifier 0P11 that outputs the differential signal (a-rl) (C-rz) of the outputs of the operational amplifiers ○P7 and OR3 as one of the two-phase detection signals, and a differential signal of the outputs of the operational amplifiers OP8 and 0P10. (br-r+)-(d
rz) as the other of the two-phase detection signals. In this embodiment, when the index scale 18 is moved relative to the main scale 14, the two-phase detection signal at that time becomes as shown in FIG. It becomes something that is not. Therefore, an extremely stable detection signal can be obtained, and highly accurate interpolation and division can be performed to obtain a highly accurate measurement signal. In this embodiment, the reference light passing windows 30a and 30b, 30c and 30d in the example shown in FIG. 1 are made common, and the reference light receiving elements 361 and 362 have
Since the average signal is obtained, the correction by the reference signal does not become excessive, and appropriate correction can be performed. Next, a second embodiment of the present invention will be described in detail with reference to FIG. This second embodiment has a second
The gratings 20a to 20d are arranged in a straight line, and corresponding reference light passing windows 30a to 30d and reference light receiving elements 32a to 32d are provided close to the lower side thereof. Other points are the same as those in the first embodiment, so detailed explanation will be omitted. In the explanation so far, reference light passing windows 30a, 30b, 30c, 30d, 341 .
342 were just passing windows with no grating formed therein, but as in the modified example shown in FIG. A grating in orthogonal directions may be formed to limit the amount of light. Next, a third embodiment of the present invention will be described with reference to FIG. In this third embodiment, the reference light passing window 42a is provided in each sub-grating 2.
It is provided in close contact with the outside of 0a. When the area of the sub-grating 20a and the area of the reference light passing window 42a are made the same so that the amount of light is substantially equal,
There is no need for electrical leveling, and adjustment is easy. In this embodiment, since the center of gravity of the sub-grating 20a and the center of gravity of the reference light passing window 42a coincide with each other, directionality can be eliminated and a good reference signal can be obtained. Next, a fourth actual droplet example of the present invention will be described with reference to FIG. In this fourth embodiment, in an apparatus similar to the third embodiment,
A separation band 4 is provided between the sub-grating 20a and the reference light passing window 42a.
4a is provided. According to this fourth embodiment, mixing of signal light and reference light can be prevented. Next, a fifth embodiment of the present invention will be described with reference to FIG. In this fifth embodiment, in an apparatus similar to the third embodiment,
Sub-grating 46 and reference light passing window 48 formed around it
are circular and concentric, respectively. According to this embodiment, directionality is completely eliminated. In this fifth embodiment as well, similarly to the fourth embodiment,
A separation band is provided between the sub-grating 46 and the reference light passing window 48,
The degree of light separation may be increased. In each of the third to fifth embodiments, the reference light passing windows 42a, 48 are connected to the sub-gratings 20a, 46.
However, it is also possible to reverse the arrangement of the two so that the center side serves as the reference light passing window and the peripheral side serves as the sub-grating window. In each of the above embodiments, the present invention was applied to a reflection type linear displacement detector, but the scope of application of the present invention is not limited to this, and is applicable to a transmission type linear displacement detector and a rotational displacement detector. It is clear that the same applies to detectors.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an arrangement example of a sub-grating on an index scale and a reference light passing window for explaining the present invention in detail. FIG. FIG. 3 is a diagram showing a detection signal, a reference signal, a corrected detection signal, and a two-phase detection signal; FIG. 4 is a block diagram showing the configuration of the signal processing circuit of the first embodiment, FIG. 5 is a front view showing the main parts of the second embodiment of the present invention, and FIG. 6 is a reference in the above embodiment. FIG. 7 is a front view showing a modification of the light passing window; FIG. 7 is a front view showing the configuration of main parts of the third embodiment of the present invention; FIG. 8 is a front view showing the structure of main parts of the fourth embodiment. , FIG. 9 is a front view showing the main structure of the fifth embodiment, FIG. 10 is a sectional view showing the structure of an example of a conventional reflective photoelectric displacement detector, and FIG. FIG. 12 is a front view showing the index scale in the conventional example. FIG. 12 is a diagram showing examples of signal waveforms at various parts in the conventional example. 14... Main scale, 16... Main grating, 18... Index scale, 20a to 20d, 46... Sub grating, 22a to 22d... Light receiving element, a-d... Displacement detection signal , 30a - 30d , 34 + , 342.42.48
...Reference light passing window, 32a to 32d, 36+, 362...Reference light receiving element, ra, rb, rclrd, r+, r2...Reference signal, 40...Signal processing circuit.

Claims (1)

[Claims] (1) A main scale on which a main grating is formed, which is fixed to one member that moves relatively; an index scale on which a light source and a sub-grating are formed, which are fixed to the other member that moves relatively; and at least the above-mentioned A photoelectric displacement detector that includes a displacement detection light-receiving element that photoelectrically converts light modulated by a main grating and a sub-grating, and that generates a periodic detection signal according to the relative displacement of both members, wherein the index A reference light passing window disposed near the sub-grating of the scale and a reference light receiving element for photoelectrically converting the light passing through the reference light passing window are provided, and a reference light receiving element obtained by the reference light receiving element is provided. A photoelectric displacement detector characterized in that a DC level fluctuation of a displacement detection signal obtained by the displacement detection light receiving element is corrected using a signal.