JP3105565B2 - Manufacturing method of linear encoder and scale for linear encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a linear encoder and a method for manufacturing a scale for a linear encoder.

[0002]

2. Description of the Related Art A document describing the prior art according to the present invention is, for example, "Latest Precision Measurement Technology" (General Technology Center, published in 1987). According to this document, when the linear encoders are classified according to the detection method, there are a parallel slit type, a moire stripe type, a vernier stripe type, and a holographic scale type. In each case, position information is obtained using moiré fringes or interference fringes created from grid lines engraved on the scale. In order to increase the detection resolution, the grating pitch may be narrowed. However, in encoders other than those described above, a grating having a pitch of 4 μm is limited in consideration of a decrease in signal output due to a diffraction phenomenon.

On the other hand, the holographic scale method uses a fine diffraction grating and can measure the length with high resolution. On a commercially available holographic scale, a grid pitch of 0.5 μm and a resolution of 0.01 μm have been realized. However, the processing accuracy of the holographic scale is determined by the quality of the optical components used in the hologram manufacturing apparatus. For example, in the case of a linear encoder using a holographic scale, the effective length accuracy of the scale is determined by the size and surface accuracy of the two parabolic mirrors. Therefore, only an object of about 250 mm is realized on the holographic scale.

Japanese Patent Laid-Open Publication No. Sho 64-74414 discloses an example of the vernier stripe type encoder. This is because in the signal detection of the conventional vernier fringe encoder, the scale is illuminated by collimating a light beam from a light source with a collimator lens, and positional information is detected by moire fringes created by the transmitted light and the vernier. On the other hand, it is possible to obtain a periodic position signal by illuminating a diffused light from a light source on a scale. In any case, it is necessary to engrave grids at equal intervals on the scale with high accuracy, and particularly for long lengths, large-scale manufacturing equipment with high accuracy is required.

[0005] The scale used in the linear encoder is engraved with a highly processed grating.
The detection accuracy and resolution of the encoder are determined by the processing accuracy of the grating and the grating interval. Therefore, the grating is manufactured by using a ruling engine, using a reduction exposure apparatus for manufacturing an LSI, or using a high-precision optical element to perform two-beam interference. In any case, when the length of the scale to be manufactured is long, the processing apparatus is required to be large and highly accurate, and as a result, it is very expensive. In particular, the holographic scale cannot be made long, which has been a problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a linear encoder scale that can be easily lengthened, a linear encoder capable of detecting a signal corresponding to the scale, and a linear encoder scale. The purpose of the present invention is to provide a production method.

[0007]

To achieve the above object, the present invention provides (1)
In a linear encoder that forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information, strip-shaped grid patterns are arranged in a staggered manner, and the adjacent grid patterns slightly overlap each other. A linear encoder scale having: a plurality of detectors for reading position signals from the linear encoder scale; and a detecting means for detecting a phase difference between signals from the plurality of detectors, or (2) A) a linear encoder that forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information;
A linear encoder scale in which strip-shaped lattice patterns are arranged in a staggered manner, and adjacent lattice patterns have a slight overlapping portion, a plurality of detectors for reading position signals from the linear encoder scale, Switching means for switching a detector used in an overlapping portion of the grating so that one of the detectors detects reflected or transmitted light from the grating, and a phase difference between signals from the plurality of detectors. Or (3) a linear encoder that forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information. A linear encoder scale which is arranged in a staggered manner and has a slight overlap between the adjacent grid patterns; Switching between a plurality of detectors for reading position signals from a coder scale and detectors used at overlapping portions of the grating so that any one of the plurality of detectors detects reflected or transmitted light from the grating And a storage means for measuring and storing the phase difference of the signals from the plurality of detectors in advance, and using the phase difference to change the phase on the side newly selected so as to synchronize them. (4) In a linear encoder that forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information, strip-shaped grid patterns are arranged in a staggered manner and A linear encoder scale having a slight overlap between the lattice patterns that match each other, and a plurality of detectors for reading position signals from the linear encoder scale Consists of a piezoelectric element provided in Kaei mirror placed in one optical path of the two divided light beams, by driving the piezoelectric element,
To change the phase of the interference waveform by changing only one of the optical path lengths, or (5) When manufacturing a grating pattern formed on the scale by two-beam interference or a reduction exposure device, a staggered grating pattern Are manufactured by repeatedly exposing while sequentially moving in a uniaxial direction with one set of adjacent grid patterns as a minimum unit.
Hereinafter, a description will be given based on examples of the present invention.

FIG. 1 is a block diagram for explaining an embodiment of a linear encoder according to the present invention. In FIG. 1, reference numeral 1 denotes a scale, 2 denotes a diffraction grating, 3 denotes a detector A, and 4 denotes a detector B. . In this scale, rectangular areas having a linear diffraction grating perpendicular to the longitudinal direction are arranged in a staggered manner, and adjacent areas have some overlapping portions. In this way, by connecting the short scales to form the scale, it becomes possible to manufacture a long one by a processing machine for the short scale.

FIG. 2 is a diagram showing a method of detecting a position signal from a scale using a holographic scale type encoder. In the figure, 1a is a holographic scale,
5 is a light receiving element, 6 is a semiconductor laser, 7 is a half mirror,
Reference numeral 8 denotes a reflection mirror, and the other portions having the same functions as those in FIG. 1 are denoted by the same reference numerals.

In the signal detection according to the present invention, a position signal is output in accordance with the presence or absence of the hologram grating so that one of the two detectors shown in FIG. 1 or 2 always outputs a position signal. This is performed while switching between the detectors A and B that perform the output. Now, the output waveforms from the detectors A and B are shown in FIG.
(A) and (b) show. Both signals are out of phase with each other. This is because adjacent hologram gratings are displaced from each other. If the signal output is switched from A to B in this state, an error occurs in position detection. As shown in FIGS. 3 (a) and 3 (b), the signal phase of B is corrected by applying an electrical phase bias so as to be synchronized with that of A. In addition to the electric phase synchronization, a piezoelectric element is provided on the back surface of the reflection mirror 8 to obtain optical phase synchronization, and by driving the piezoelectric element, only one optical path length is changed to cause interference. The phase of the waveform can be changed.

FIG. 4 shows an embodiment of a signal detection circuit which performs the above-described phase correction even between different hologram gratings and always outputs a continuous sine wave signal. In the figure, 10 is an output signal of the detector A, 11 is an output signal of the detector B, 12 is a phase difference detection circuit, 13 is a subtractor, 14 is an adder, and 15 is an output. The signals 10 and 11 from the detectors A and B are input to a phase difference detection circuit 12, and the difference φ _i between the phases φ _A and φ _B of each sine wave signal
= Seek φ _A -φ _B. Here, i is the number of the phase connection portion counted from the start position. Now, assuming that the signal is switched from A to B, the signal B which has reached the overlapping portion and has not been input is input, and the phase difference φ _i is obtained. φ _i
At the same time, the two switches are switched to the B signal output side, and the B signal is output after the phase of φ _i is corrected. φ _i
Is fixed until the next overlap.

FIG. 5 shows another embodiment of a signal detection circuit different from that of FIG. In the figure, 16 is a phase shift amount memory (storage means), 17 and 18 are adders, 19 is an output,
The output signal and the B output signal are the same as in FIG. The phase difference between the diffraction gratings is a fixed value unless a change over time or a change in temperature is considered. Therefore, when the encoder is configured, the correction phase amount at each connection portion is obtained and stored in the memory, or when the encoder is used, a pre-scan is performed and the correction phase amount is obtained and stored. When the actual encoder is used, the correction is performed by reading the correction phase amount from the memory. As a result, the time required for detecting the phase difference at each connection portion can be reduced,
It can be used as an encoder even for those with a high moving speed. The above detection method is not limited to the holographic scale type encoder, and the other detection methods include two detectors and connect the phases of two obtained periodic signals in the same manner. is there.

FIG. 6 shows an example in which the present invention is applied to a vernier fringe encoder. In the figure, 20 is the index scale, 20
b is a main scale, 21 is a vernier stripe, 22 is a phototransistor, 23 is a collimator lens, and 24 is a lamp. When vernier fringes are formed using the same index scale, the phases of the vernier fringes formed between adjacent gratings appear differently. Each grating detects a position signal with four phototransistors and performs phase correction in the same manner as in the above case.

In addition to the electrical phase synchronization shown in FIGS. 4 and 5, it is also possible to perform optical phase synchronization. FIG.
8 is a configuration diagram of a detector that performs optical phase synchronization. FIG. 7 shows a reflection type, and FIG. 8 shows a transmission type.
In the figure, 25 is a scale, 26 is a reflecting mirror, 27a is PZT
(Piezoelectric element), 27 is a reflection mirror, 28 is a half mirror, 29 is a light guide laser, 30 is a light receiving element, 31 is an analyzer (λ / 4 plate), 32 is a beam splitter, and 33 is a polarizer. In both cases of the reflection type and the transmission type, a piezoelectric element is provided on the back surface of a reflecting mirror placed in one optical path of the light beam divided into two. By driving this piezoelectric element, it is possible to change only one optical path length and change the phase of the interference waveform.

FIG. 9 is a diagram showing a signal detection circuit in the case where a piezoelectric element is provided on a reflecting mirror. In the figure, 50 is a phase difference judging unit, 51 is an output, and 52 is a piezoelectric element driving unit. The detected phase difference by the phase difference detecting circuit 12, φ _A -φ _B, i.e., phi _i drives the piezoelectric element so that 0. φ _i
When = 0, the switch is switched to obtain an output. FIG.
FIG. 11 is a diagram showing a holographic scale manufacturing method.
In the figure, 40 is a laser beam, 41 is a mask, 42 is a photosensitive agent,
43 is a hologram substrate, 44 is a high precision stage (X direction), and 45 is a high precision stage (Y direction).

A diffraction grating is formed on a substrate coated with a photosensitive agent through a mask having openings as shown in FIG. 11A or 11B by interference of two light beams. Subsequently, the substrate is sequentially exposed while moving the substrate in the x or y direction so as to obtain a desired zigzag pattern. After the exposure is completed, this is developed, and the surface is subjected to metal evaporation to obtain a scale original. A copy of this original is used as the encoder scale. In particular, in the case of performing exposure using an opening as shown in FIG. 11B, the substrate needs to be moved only in one axis direction, so that the original plate can be easily manufactured and the occurrence of cosine error due to the inclination during the movement is suppressed. As a result, a highly accurate scale can be obtained. Even when a grating is manufactured by a reduction exposure machine, it is effective to make the pattern of the reduced original plate as shown in FIG. 11B for the same reason.

[0017]

As apparent from the above description, the present invention has the following effects. (1) An effect corresponding to the first and second aspects: a scale in which small lattice patterns are arranged in a staggered manner because of having two detection units is continuous as if it were one long lattice pattern. It is possible to read the position information in a long time, and it is not necessary to increase the size of the manufacturing machine in order to produce a long grid pattern and to increase the precision of the manufacturing machine in order to secure a uniform grid pitch over a long distance. As a result, an inexpensive linear encoder can be realized. (2) Effect corresponding to claim 3: Since exposure is performed using an aperture or a reduced pattern having a shape as shown in FIG. 2 (b), the substrate needs to be moved only in one axial direction and the original plate can be easily manufactured. Since the occurrence of a cosine error can be suppressed by the inclination during the movement, a highly accurate scale can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a linear encoder according to the present invention.

FIG. 2 is a diagram showing a method of detecting a position signal from a scale using a holographic scale encoder.

FIG. 3 is a diagram showing an output waveform from a detector.

FIG. 4 is a diagram illustrating a signal detection circuit.

FIG. 5 is a diagram illustrating another signal detection circuit.

FIG. 6 is a diagram showing an example applied to a vernier fringe encoder.

FIG. 7 is a configuration diagram of a detector (reflection type) that performs optical phase synchronization.

FIG. 8 is a configuration diagram of a detector (transmission type) that performs optical phase synchronization.

FIG. 9 is a diagram illustrating a signal detection circuit when performing optical phase synchronization.

FIG. 10 is a diagram illustrating a method for manufacturing a holographic scale.

FIG. 11 is a diagram illustrating openings in a mask.

[Explanation of symbols]

1 ... scale, 2 ... diffraction grating, 3 ... detector A, 4 ... detector B

Claims (5)

(57) [Claims] 1. A linear encoder which forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information, wherein the strip-shaped grid patterns are arranged in a staggered manner, and the adjacent grid patterns are adjacent to each other. A linear encoder scale having a few overlapping portions; a plurality of detectors for reading position signals from the linear encoder scale; and a detecting means for detecting a phase difference between signals from the plurality of detectors. A linear encoder. 2. A linear encoder which forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information, wherein strip-shaped grid patterns are arranged in a staggered manner, and the adjacent grid patterns are adjacent to each other. A linear encoder scale having some overlapping portions, a plurality of detectors for reading position signals from the linear encoder scale, and one of the plurality of detectors detects reflected or transmitted light from a grating. A linear encoder comprising: switching means for switching a detector used in an overlapping portion of a grating so as to detect; and a phase difference detection circuit for detecting a phase difference between signals from the plurality of detectors. 3. A linear encoder that forms a grid pattern on a scale and performs position detection by photoelectrically reading the pattern information, wherein strip-shaped grid patterns are arranged in a staggered manner, and the adjacent grid patterns are adjacent to each other. A linear encoder scale having some overlapping portions, a plurality of detectors for reading position signals from the linear encoder scale, and one of the plurality of detectors detects reflected or transmitted light from a grating. A switching unit for switching a detector used in an overlapping portion of the grating so as to detect, and a storage unit for measuring and storing a phase difference of signals from the plurality of detectors in advance, and using the phase difference. A linear encoder, wherein a phase on a newly selected side is corrected so that both are synchronized. 4. A linear encoder for forming a grid pattern on a scale and performing position detection by photoelectrically reading the pattern information, wherein the strip-shaped grid patterns are arranged in a staggered manner, and the adjacent grid patterns are adjacent to each other. A linear encoder scale having some overlapping portions, a plurality of detectors for reading a position signal from the linear encoder scale, and a reflecting mirror placed in one optical path of a light beam divided into two are provided. And a piezoelectric element,
A linear encoder wherein the phase of an interference waveform is changed by driving only one optical path length by driving the piezoelectric element. 5. When manufacturing a lattice pattern formed on a scale by two-beam interference or a reduction exposure machine, a staggered lattice pattern is sequentially moved in one axial direction using a set of adjacent lattice patterns as a minimum unit. A method for manufacturing a scale for a linear encoder, wherein the scale is manufactured by repeating exposure.