JPH02103416A - Photoelectric displacement detector - Google Patents

Abstract

PURPOSE:To make it possible to improve interpolation accuracy and to improve response scanning speed by arranging a second index scale on the opposite side of a first index scale with a main scale in-between. CONSTITUTION:An index scale 34 is arranged on the opposite side of an index scale 18 with a main scale 14 in-between. Secondary lattices 36 (36a-36d) as reference-light passing windows are formed. In DC-level detecting photodetectors 38 (38a'-38d'), light passing a main lattice 16 and the windows 36 undergoes optoelectronic transducing operation. The DC level fluctuations of detected displacement signals (a)-(d) obtained in displacement detecting photodetectors 22 (22a-22d) are corrected by using detected DC level signals a'-d' obtained in the photodetectors 38. Two-phase detected signals (a+a')-(c+c') and (b+b')-(d+d') are formed in a signal processing circuit 40 based on the outputs (a)-(d) and a'-d'. The amplitude signals in said two-phase detected signals are fluctuated, but the DC component becomes constant. Therefore, the stable detected signals are obtained, and highly accurate interpolation division can be performed and the highly accurate measured signals can be obtained.

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 displacement detection signal, and therefore improves interpolation accuracy. The present invention relates to a photoelectric displacement detector capable of improving response scanning speed.

[Conventional technology]

A main scale having a periodic main lattice formed thereon is fixed to one of the facing members, and a light-transmissive index scale having a corresponding periodic sub-lattice formed to 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 feed rate of machine tool tools. FIG. 12 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 20, 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. 13, the light-receiving elements 22 are normally arranged on the index scale 18, two in the direction parallel to the grating scale (in the vertical direction in the figure) and two in the longitudinal direction of the main scale (in the left-right 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 set to 19
0°, the phase of the sub-grating 20C is +180°, n1
When the phase of the grating 20d is set to +90°, as shown in FIG. The difference (a − c), (b
-d), a two-phase detection signal which is a differential signal is generated. In Figure 13, 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 of the chrome that makes up the grating scale (11! light) varies depending on the longitudinal position, so the reflectance and transmittance vary, and the line width also varies slightly, making it extremely difficult to manufacture uniformly. be. For example, in the case of a main grating with a main scale having a pitch of 8 μm, the line width varies by about 0.2 μm, that is, by about 2.5%, and when other factors are taken into account, the variation in the detection signal sometimes becomes 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
20C120b 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 first task is to provide a detector. The present invention also makes it possible to prevent measurement errors caused by reverse light incident from the back side of the main scale in a reflective photoelectric displacement detector using a reflective main scale that is transparent to light. The second objective is to provide a reflective photoelectric displacement detector.

[Means to achieve the task]

The present invention provides a main scale having a light transmittance and having a main lattice formed therein, which is fixed to one member that moves relatively;
A light source, a first index scale on which a sub-grating is formed, and a displacement detection light-receiving element that photoelectrically converts light modulated by at least the main grating and the sub-grating, which are fixed to the other member that moves relatively. In the photoelectric displacement detector that generates a periodic detection signal according to the relative displacement of both members, a reference light passing window is provided on the opposite side of the first index scale indicated by +iff across the main scale. The formed second index scale and a DC level detection light receiving element that photoelectrically converts the light that has passed through the main grating and the reference light passing window are provided, and a DC level detection signal obtained by the DC level detection light receiving element is provided. The first problem has been achieved by correcting the DC level fluctuation of the displacement detection signal obtained by the displacement detection light receiving element using the displacement detection light receiving element. Further, the present invention provides a method that is fixed to one member that moves relatively.
a light-transmissive main scale on which a main grating is formed; an index scale on which a light source and a sub-grating are formed; the index scale is fixed to the other member that moves relatively; and the index scale is modulated by at least the main grating and the sub-grating. In a photoelectric displacement detector that includes a displacement detection light receiving element that photoelectrically converts either reflected light or transmitted light, and generates a periodic detection signal according to the relative displacement of both members, the main grating and the sub-grating A DC level detection light receiving element is provided that photoelectrically converts the other light modulated by the grating, and a DC level detection signal obtained by the DC level detection light receiving element is used to detect displacement obtained by the displacement detection light receiving element. By correcting the DC level fluctuation of the signal, the first
This goal has been achieved. The present invention also provides the following features: being fixed to one member that moves relatively;
A reflective main scale having a light transmittance on which a main grating is formed, an index scale on which a light source and a sub-grating are formed, which are fixed to the other relatively moving member, and at least the main grating and the sub-grating. In a reflective photoelectric displacement detector that includes a displacement detection light receiving element that photoelectrically converts modulated light and generates a periodic detection signal according to the relative displacement of both members, the index is placed between the main scale. The second problem is achieved by providing a shielding cover on the opposite side of the scale to prevent reverse light from irradiating the main grating from the back side of the main scale.

[Action and effect]

In the present invention, when using a main scale having optical transparency, (1) If it is a reflective type photoelectric displacement detector, transmitted light is not used; (2) Displacement detection signal a (signal obtained by detecting reflected light 1 in case of reflective type, signal obtained by detecting transmitted light in case of transmissive type) As shown in Fig. 1<A), the signal) usually not only has an AC component necessary for displacement detection, but also has a DC component a'' superimposed thereon that causes a measurement error; The DC level of the signal obtained by detecting the light (transmitted light for reflective type, reflected light for transparent type) (referred to as DC level detection signal) a l
As shown in FIG. 1(B), is a signal that fluctuates in the opposite direction to the DC component of the displacement detection signal a shown in FIG. 1(A); (4) Therefore, the displacement detection signal By adding a and the DC level detection signal a', the added signal a+
This was done by focusing on the fact that the DC level a''+a' of a' becomes insensitive to the influence of variations and fluctuations in the width of the scale line, and becomes almost constant, as shown in Figure 1 (C). That is, as in the example shown in FIG. 2 or FIG. By disposing an index scale 34 of 2 and photoelectrically converting the light passing through the main grating 16 and the reference light passing window (36a) with the light receiving element 38a' for DC level detection, the light as shown in FIG. 1(B) is generated. A DC level detection signal a' can be obtained, and using this DC level detection signal a',
DC level fluctuations in the displacement detection signal a can be corrected. Therefore, interpolation accuracy is improved and response scanning speed is also improved. Furthermore, as in the example shown in FIG. 11, for example, by providing a light receiving element 38 for detecting a DC level that photoelectrically converts the light that is not used for displacement detection among the light modulated by the main grating 16 and the sub-grating 20. A similar effect can also be obtained. In addition, when using a reflective type photoelectric displacement detector with a reflective main scale that is optically transparent, the displacement detection signal fluctuates due to the back incident light that illuminates the main grating from the back side of the main scale, making the measurement difficult. Although it may cause an error, as in the example shown in FIG. By providing the shielding cover 42 for preventing the intrusion of light, such problems can be solved.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. The first embodiment of the present invention, as shown in FIGS. 2 to 4,
A reflective main scale 1 having a light transmitting property and having a main grating 16 fixed to one relatively moving member.
4, and a light source 32 fixed to the other member that moves relatively.
, four sub-gratings 20a whose phases differ from each other by 90°
20d is formed on the first index scale 18 (
(see FIG. 3), and the main grating 16 and each sub-lattice 20a.
A reflective type detector 30 including four displacement detection light receiving elements 22a to 22d that photoelectrically convert the light modulated by 20d to 20d, respectively, and generates a periodic detection signal according to the relative displacement of both members. In the photoelectric displacement detector, four sub-gratings 36a' to 36d' as reference light passing windows are disposed on the detector 30 on the opposite side of the first index scale 18 with the main scale 14 in between. a second index scale 34 (see FIG. 4) formed with
Four DC level detection light receiving elements 388' to 38d' are provided, each photoelectrically converting the light that has passed through the DC level detection light receiving elements 388' to 38d'. is used to correct DC level fluctuations of the displacement detection signals ad given by the displacement detection light receiving elements 22a to 22d. Above the first index scale 18, as shown in detail in FIG. 3, there is an n1 grating 20a consisting of graduation lines in the same direction (vertical direction in the figure) as the main grating 16 formed on the main scale 14. ~20d are 90° in phase with each other
There are four arranged in different locations. On the other hand, above the second index scale 34,
As shown in detail in FIG. 4, four sub-gratings 36a' to 36d', which are made up of scale lines in the horizontal direction of the figure, are arranged for adjusting the light m. Here, the distance p between the sub-gratings 20a to 20d on the first index scale 18 and the main grating 16 on the main scale 14 and the sub-gratings 36a' to 36d' on the second index scale 34 from the main grating 16 are also the same. It is desirable that the distance q between them be optically approximately equal. When this interval p=q, the first index scale 18
The effective areas of the upper sub-grating 20a and the sub-grating 36a' on the second index scale 34, the same 22b and 36b', the same 22C and 360', and the same 22d and 36d' are the same as those of the displacement detection light receiving elements 22a to 22d. The amount of light that reaches the DC level detection light receiving elements 38a' to 38d' are made to be approximately the same. In addition, the interval p,! : When q is set differently, the ratio of the effective areas of the corresponding sublattices 2oa to 20d and 36a' to 36d can be made to correspond to p/Q. 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 DC level detection light receiving elements 388' to 38d' includes a fifth
As shown in the figure, a variable resistor VR is used to add and amplify the output signals a and a' of the light receiving elements 22a and 38a'.
1, and a variable resistor V for adding and amplifying the output signals c and c' of the light receiving elements 22c and 38c'.
The output signals S, b' of the operational amplifier OP2 whose amplification factor is made variable by R2 and the light receiving elements 22b and 38b' are
an operational amplifier OP3 whose amplifier is made variable by a variable resistor VR3 for adding and amplifying the signals, and a variable resistor for adding and amplifying the output signals d and d' of the light receiving elements 22d and 38d'. OR3 whose amplification factor is made variable by VR4 and the output signal of the operational amplifier OP1 (
a+a') and the output signal of operational amplifier OP2 (+, +c)
an operational amplifier OP5 that outputs the differential signal (a + a') - (c + c') as one of the two-phase detection signals;
A differential signal (b
+b')-(d+d') 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. 1(C) above,
Although the imaging width component varies, the DC component remains constant. 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 sum of the corresponding displacement detection signals a to d and DC level detection signals a' to d' (a + a') to (d
+d') for each operational amplifier OP1~. Since it is amplified by P4, the signal processing circuit 40
The configuration is simple. Note that the configuration of the signal processing circuit 40 is not limited to that shown in FIG. 5, and for example, as shown in FIG.
-d Sa '~d' each, variable resistor VRII~vR
Operational amplifier 0P11 with variable amplification factor by ia
~0P18 amplify and operational amplifiers 0P19~0P22 output the displacement detection signals a~d1 DC level signal a'
~d', the differential signals of each phase (a − c), (
c'-a')(fll-d) and (d'-b') are obtained, and operational amplifiers 0P23 and ○P24 are used to generate a differential signal (a-c)-(c
'-a') = (a +a') -(c
+c'), (1)-d)-(d'-b
' ) = (b + b' ) - (d
+d) can also be obtained and used as a displacement detection signal for each phase. In this case, each detection signal a-d, a'-d
Since it is possible to adjust the level for each sub-grid 36a' to
It is also possible to omit the scale stripes 36d' for adjusting the optical distance and use them as mere passing windows. Further, in this embodiment, the second index scale 34 and the DC level detection light receiving elements 38a' to 38d
' blocks the reverse incident light that illuminates the main grating 16 from the back side of the main scale 14 (right side in the figure), so it is possible to prevent the displacement detection signals a to d from being affected by the reverse incident light. . Note that instead of the second index scale 34, etc., a shielding cover 42 may be provided on the detector 30, as in the second embodiment shown in FIG. In FIG. 7, 44 is a pace (one of the relative moving members) to which the lower part of the main scale 14 is fixed. In the above embodiments, the present invention was applied to a reflection type photoelectric displacement detector, but when applied to a transmission type displacement detector, the first index scale 18
The pattern of the sub-gratings 20a to 20d and the pattern of the sub-gratings 36a' to 36d' of the second index scale 34 are interchanged. Next, a third embodiment of the present invention will be described in detail with reference to FIGS. 8 to 10. In this second embodiment, the DI gratings 208 to 20d (see FIG. 9) on the first index scale 18 and the light receiving probes 22a to 22d for displacement detection are arranged in a straight line, and
Correspondingly, the sub-gratings 36a' to 36d' (see FIG. 10) on the second index scale 34 and the light receiving elements 388' to 38d' for DC level detection are also arranged in a straight line. Other points are the same as those in the first embodiment, so detailed explanation will be omitted. In the explanations so far, the sub gratings 368' to 36 on which scale stripes are formed are used as reference light passing windows.
d' was used, but in cases where the level can be adjusted by other methods, as in the case of a signal processing circuit as shown in FIG. It is also possible to use a simple passage window or the like. Next, a fourth embodiment of the present invention will be described in detail with reference to FIG. This fourth embodiment includes a transmission-type main scale 14 formed with a main grating 16 and having optical transparency, which is fixed to one member that moves relatively, and a main scale 14 that is fixed to the other member that moves relatively. A light source 32, an index scale 18 on which a sub-grating 20 is formed, and the main grating 16 and the sub-grating 20.
In a transmission-type photoelectric displacement detector that includes a displacement detection light receiving element 22 that photoelectrically converts transmitted light modulated by the main grating 16 and generates a periodic detection signal according to the relative displacement of both members, the main grating 16 and a DC level detection light receiving element 38 that photoelectrically converts the other of the light (reflected light) modulated by the main grating 16 and the sub-grating 20, and converts the light from the light source 32 in the direction of the main scale 14, and The reflected light modulated by the grating 20 is sent to the light receiving element 3 for DC level detection.
8 and a half mirror 50 or beam splitter for making the light incident on it! A light receiving element 52 for monitoring the amount of light from the light source is provided for monitoring the light amount of the light source 32, and the DC level detection signal a' obtained by the light receiving element 38 for detecting the DC level is used to obtain the DC level detection signal a' obtained by the light receiving element 22 for detecting displacement. This is to correct the DC level fluctuation of the displacement detection signal a. In the figure, 12 is a collimator lens, and 54.56 is a condensing lens. The output of the light receiving element 46 for monitoring the amount of light from the light source is fed back to, for example, a power supply circuit for the light [32], and is controlled so that the amount of light irradiated by the light source 32 is constant. Note that the light receiving element 46 for monitoring the light source light weight may be omitted. Further, although the present embodiment is of a transmission type, it can also be made of a reflection type by replacing the functions of the displacement detection light receiving element 22 and the DC level detection light receiving element 38. In all of the embodiments described above, the present invention was used in linear displacement detectors, but it is clear that the scope of application of the present invention is not limited thereto, and can be similarly applied to rotational displacement detectors.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing examples of a displacement detection signal, a DC level detection signal, and a corrected detection signal for explaining the present invention in detail. FIG. 2 is a photoelectric displacement detector according to the present invention. 3 is a front view showing the first index scale used in the first example; FIG. 4 is a front view showing the second index scale, FIG. 5 is a circuit diagram showing an example of the signal processing circuit, FIG. 6 is a circuit diagram showing another example of the signal processing circuit, and FIG. 7 is a main part configuration of the second embodiment of the present invention. FIG. 8 is a cross-sectional view showing the main structure of the third embodiment. FIG. 9 is a front view of the first index scale used in the third embodiment. FIG. 10 is a front view showing the first index scale used in the third embodiment. 11 is a sectional view showing the main part configuration of the fourth embodiment of the present invention, and FIG. 12 is an example of a conventional reflective photoelectric displacement detector. FIG. 13 is a front view showing the index scale in the conventional example, and FIG. 14 is a diagram showing examples of signal waveforms at various parts in the conventional example. 14... Main scale, 16... Main grid, 18.34... Index scale, 20a ~ 2
0d, 20-... sublattice, 22a-22d, 22-
...Light receiving element for displacement detection, a-d...Displacement detection signal, 32...Light source, 368' to 36d'...Sub-grating (reference light passing window), 3
8a' to 38d', 38... Light receiving element for DC level detection, a' to d'... DC level detection signal, 40... Signal processing circuit, 42... Shielding cover

Claims (5)

[Claims] (1) A light-transmissive main scale on which a main grating is formed, which is fixed to one relatively moving member, and a main scale on which a light source and a sub-grating are formed, which is fixed to the other relatively moving member. 1, 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. In the photoelectric displacement detector, a second index scale provided with a reference light passing window is disposed on the opposite side of the first index scale across the main scale.
and a DC level detection light receiving element that photoelectrically converts the light that has passed through the main grating and the reference light passing window, and using a DC level detection signal obtained by the DC level detection light receiving element. . A photoelectric displacement detector, characterized in that it corrects DC level fluctuations in a displacement detection signal obtained by the displacement detection light receiving element. (2) The photoelectric displacement detector according to claim 1, wherein the main scale is of a reflective type, and the second index scale is disposed on the opposite side of the light source with the main scale in between. Photoelectric displacement detector. (3) The photoelectric displacement detector according to claim 1, wherein the main scale is of a transmission type, and the second index scale is arranged on the same side of the main scale as the light source. Photoelectric displacement detector. (4) A light-transmissive main scale on which a main grating is formed, which is fixed to one relatively moving member, and an index on which a light source and a sub-grating are formed, which are fixed to the other relatively moving member. a scale, and a displacement detection light-receiving element that photoelectrically converts either the reflected light or the transmitted light modulated by at least the main grating and the sub-grating, and periodic according to the relative displacement of both members. A photoelectric displacement detector that generates a detection signal is provided with a DC level detection light receiving element that photoelectrically converts the other of the light modulated by the main grating and the side grating, and the DC level detection light receiving element A photoelectric displacement detector characterized in that the obtained DC level detection signal is used to correct the DC level fluctuation of the displacement detection signal obtained by the displacement detection light receiving element. (5) A reflective main scale with optical transparency, on which a main grating is formed, which is fixed to one member that moves relatively, and a light source and a sub-grating that are fixed to the other member, which moves relatively. 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. In a reflective photoelectric displacement detector, a shielding cover is provided on the opposite side of the index scale across the main scale to prevent back-incoming light from irradiating the main grating from the back side of the main scale. Features of photoelectric displacement detector.