JP6684087B2 - Optical encoder - Google Patents

Description

  The present invention relates to an optical encoder using optical means, and more particularly to an optical encoder using triple diffraction grating technology.

  The optical encoder is used to detect the movement amount and / or the reference position of the object, and various configurations are known. Of these, an optical encoder that detects the amount of movement of an object using a triple diffraction grating technique has a light source that emits light and a scale that has a periodic optical pattern and that moves relative to the light source. And a photodetector for detecting the light emitted from the light source and passing through the scale. The photodetector is formed by arranging a plurality of detectors, for example, photodiodes, and each detector is capable of detecting four phase portions having different phases by 90 degrees in a light-dark pattern having a constant period. , Four groups electrically connected in each cycle, that is, A phase, B phase, -A phase (hereinafter referred to as "AB phase"), and -B phase (hereinafter referred to as "BB phase") are detected. It is divided into each group. The signals detected by these four groups differ in phase by 90 degrees from each other, and for example, the A phase and the AB phase are inverted signals whose phases differ by 180 degrees (Patent Document 1).

  An optical encoder using the triple diffraction grating technique, which has a function of detecting the reference position in addition to the movement amount of the scale, includes an incremental pattern that is a periodic pattern for detecting the movement of the object on the scale. And an index pattern for detecting the reference position, which are provided separately from each other, and a photodetector for periodic pattern detection for detecting light that has passed through the incremental pattern in the photodetector, and the index pattern. There is known a configuration in which reference position detecting photodetectors that detect the generated light are separately provided at separate positions. Then, a reference position signal (Z-phase pulse signal) is obtained based on the detection signal from the reference position detection photodetector (Patent Document 2).

Japanese Patent No. 4658452 Japanese Patent No. 4869628

  However, in the conventional technique for obtaining the reference position signal (Z-phase pulse signal) based on the detection signal from the reference position detection photodetector, as described above, the incremental pattern and the index pattern provided on the scale are separated from each other. A photodetector for periodic pattern detection, which is arranged at a position and is provided in the photodetector, for detecting light that has passed through the incremental pattern, and a photodetector for reference position detection that detects light that has passed through the index pattern. However, if the scale, the light source, and the photodetector are installed at different positions, the light originally incident on the incremental pattern will be incident on the index pattern to detect the reference position. It is generated by the light that has passed through the index pattern because it will be detected by the photo detector And the reference position signal (Z-phase pulse signal) stable to, there is a disadvantage that can not be reliably detected.

  It is an object of the present invention to solve this inconvenience and to provide an optical encoder using a triple diffraction grating technique capable of stably and reliably detecting a reference position signal (Z-phase pulse signal).

In order to achieve the above object, an optical encoder according to claim 1 of the present invention includes a light source that emits light, a scale that is formed with an optical pattern, and is movable relative to the light source. An optical encoder provided with a photodetector for detecting light that has been emitted and has passed through the optical pattern, wherein the optical pattern of the scale has a reflective portion and a non-reflective portion alternately in the moving direction of the scale. At least one aperiodic index pattern is arranged in the arranged periodic incremental pattern, and the photodetector detects the incremental pattern and the incremental pattern is detected. A photodetector for detecting the index pattern between the two photodetectors sandwiched between the photodetectors and two adjacent photodetectors in the moving direction of the scale. Of one obtained by arranged in a pattern, have a signal processing circuit for generating a reference position signal based on the detection signal of the photodetector for detecting the index pattern, the aperiodic index pattern, the incremental pattern The non-reflecting portion, the reflecting portion, and the non-reflecting portion have a width of approximately 1: 3: 1 so as to be sandwiched between the reflecting portions, and the width of each non-reflecting portion is substantially the same as that of the reflecting portion of the incremental pattern. Or arranged such that the non-periodic index pattern is sandwiched between the non-reflective portions of the incremental pattern so that the reflective portion, the non-reflective portion, and the reflective portion have a width of approximately 1: 3: 1. Further, the width of each of the reflective portions is arranged to be substantially the same as the non-reflective portion of the incremental pattern, and a photodetector for detecting the incremental pattern. , Four photodetectors corresponding to the respective phase portions are periodically arrayed so that the four phase portions of the light-dark pattern having a constant cycle and different in phase by 90 degrees can be detected. The photodetectors to be detected are divided into eight photodetectors into three groups, one, one, and three first to fourth groups, and the photodetectors for incremental pattern detection are arranged in succession. The first, second, and fourth photodetectors of the four photodetectors are replaced by the photodetectors of the first group, and the third photodetector of the following four is replaced by the photodetectors of the second group. Replacing, replacing the third photodetector of the following four with the photodetector of the third group, and replacing the first, second, and fourth photodetectors of the following four with the photodetection of the fourth group The signal processing circuit is replaced by the eight Pulse signals generated by comparing the detection signals of the index pattern detection photodetector with the reference signals with the differential signals obtained by differentially amplifying the detection signals of the first and fourth groups. , A differential signal obtained by differentially amplifying each detection signal of the second and third groups and a pulse signal generated by comparing the differential signal of the first and fourth groups with each other to obtain a reference position signal. To do.

According to the optical encoder of claim 1 of the present invention, the index pattern is arranged in the array of the incremental patterns of the scale, and the index pattern detecting photodetector is arranged in the array of the incremental pattern detecting photodetectors. As a result, erroneous incidence of light on the patterns and the photodetectors corresponding to the patterns due to variations in mounting positions of the light source, scale, and photodetector is eliminated, and the reference position signal can be detected stably and reliably. In addition to the above effect, the reference position signal is obtained by differentially amplifying and logically operating the detection signals of the eight photodetectors for index pattern detection arranged at predetermined positions in the photodetector array for incremental pattern detection. Allows for light or offset light that has passed through an incremental pattern other than the detection signal described above. By canceling the brute signal, and a reference position signal more stably, an effect that can be more reliably detected.

The schematic perspective view showing one embodiment of the present invention. Also a side view. Similarly, an explanatory view showing an example of an array state of reflective portions and non-reflective portions in the light source slit and the scale, and an array state of each detector for incremental pattern detection and index pattern detection in the photodetector. Similarly, a comparison table showing the relative positional relationship between the incremental pattern detecting photodetector and the index pattern detecting photodetector at the start of each phase. Similarly, a configuration diagram showing an example of a detection signal processing circuit that processes a detection signal of the photodetector for detecting an index pattern. Similarly, a voltage waveform diagram before and after differential amplification by the detection signal processing circuit. Similarly, a voltage waveform diagram after being converted into a pulse signal by the detection signal processing circuit.

  An embodiment in which the present invention is applied to a reflection type optical encoder using a triple diffraction grating technique will be described below with reference to the accompanying drawings. As shown in FIGS. 1 and 2, the optical encoder includes an encoder head 1 and a scale 2, and the encoder head 1 and the scale 2 are relatively movable in the X direction.

  The encoder head 1 comprises a light source 4 such as an LED and an IC 5 mounted on a PCB substrate 3, and a large number of photodetectors 6 such as photodiodes capable of photoelectric conversion are arranged inside the IC 5 to form a photodetector array. (Hereinafter referred to as "PD array".) 6A is configured. On the upper surface of the light source 4, a light source slit (hereinafter referred to as “slit”) 7 formed of a glass substrate or the like capable of transmitting light and having an optical light shielding portion 10a and a light transmitting portion 10b is provided as a first diffraction grating. Are arranged as. The light source 4 and the IC 5 have their upper surfaces at substantially the same height and are covered with the transparent resin 8. Therefore, the slit 7 is provided at substantially the same height as the surface of the PD array 6A (see FIG. 2).

  The light emitted from the light source 4 is transmitted through the transmissive portion 10b of the slit 7, is transmitted through the transparent resin 8, and is composed of a glass substrate or the like and has an optical reflective portion 9a and a non-reflective portion 9b. The light enters the scale 2, which is a grating. The light reflected by the reflecting portion 9a of the scale 2 again passes through the transparent resin 8 and enters the PD array 6A. L in the figure indicates an optical path. Further, as the scale 2 moves in the X direction, the optical path reflected by the scale 2 changes. The wavelength of the light emitted from the light source 4, the pitch of the transmissive portions 10b of the slits 7, and the pitch of the periodic pattern of the scale 2 are configured to meet the requirements of the optical encoder based on the triple diffraction grating technique. Then, depending on the respective relationships among the pitch of the photodetectors 6 in the PD array 6A, the pitch of the periodic pattern of the scale 2, the distance between the light source 4 and the periodic pattern, and the distance between the PD array 6A and the periodic pattern. Then, a bright-dark pattern similar to the second diffraction grating of the scale 2 is optically generated as the third diffraction grating on the PD array 6A.

  Subsequently, each configuration of the slit 7, the scale 2, and the PD array 6A will be described in more detail with reference to FIG. As shown in FIG. 3 (a), the light-shielding portion 10a and the light-transmitting portion 10b of the slit 7 are formed to have the same width 2W (W indicates a predetermined length), so that the light-shielding portion 10a has an equal interval 2W. It is placed in advance. Further, as shown in FIG. 3B, in the incremental pattern, which is a periodic pattern of the scale 2, the reflective portions 9a and the non-reflective portions 9b arranged alternately have the same width W, and The reflecting portions 9a are arranged at equal intervals W. On the other hand, as an index pattern which is a non-periodic pattern, a reflective portion 11a having a width of 3W and a non-reflective portion 11b having a width of W located on both sides thereof are formed in the incremental pattern. The index pattern and the incremental pattern form a bilaterally symmetrical pattern with a center line M passing through the widthwise center of the reflecting portion 11a as an axis. The index pattern in this embodiment is formed by converting one non-reflective portion in the incremental pattern into a reflective portion. In addition, in the present embodiment, the index pattern and the incremental pattern form a left-right symmetrical pattern with the center line M passing through the widthwise center of the reflecting portion 11a as an axis, but a left-right asymmetric pattern is formed. Is also good.

  As shown in FIG. 3C, in the PD array 6A, a large number of photodetectors 6 each having a width slightly smaller than the width W of each of the reflective portion 9a and the non-reflective portion 9b of the scale 2 are arranged at equal intervals. I will do it. Although the photodetector 6 is slightly narrower than each width W due to the physical structure, the periodic pattern pitch of the scale 2 and the optical pitch of the photodetector 6 in the PD array 6A are substantially equal. Of these, each photodetector 6 for detecting an incremental pattern detects one of four phases of A phase, B phase, AB phase, and BB phase, and the detection target is A phase, B phase, AB phase. The phase and the BB phase are periodically arranged in this order. For convenience of explanation, the photodetectors 6 are shown as A, B, AB, and BB, respectively, corresponding to the phases to be detected. Further, in the array of the photodetectors 6 for detecting the incremental pattern, a total of 8 photodetectors 6z in 4 groups for detecting the index pattern and generating the Z-phase pulse signal are provided. The detector 6 is replaced and arranged, and the regions of the PD array 6A used therein are shown as Z1 to Z4 for each group for convenience of explanation.

  FIG. 3C shows a first group Z1 of three photodetectors, a second group Z2 of one photodetector, a third group Z3 of one photodetector, and a fourth group Z4 of three photodetectors. In the arrangement of (1), when the A phase starts, that is, when the first photodetector of the first group Z1 corresponds to the photodetector 6 that detects the A phase, the arrangement area in the PD array 6A is shown. Specifically, in the four photodetectors 6 of A to BB, the three photodetectors 6 of the first A, the second B, and the fourth BB are replaced with the photodetectors 6z of the first group Z1. Substituting and following four photodetectors 6 of A to BB, the photodetector 6 of the third AB is replaced with the photodetector 6z of the second group Z2, and the following four photodetectors 6 of A to BB. The photodetector 6 of the third AB is replaced with the photodetector 6z of the third group Z3, and the first A, second B, and fourth BB among the four photodetectors 6 of A to BB are three. The photodetector 6 of No. 4 is replaced with the photodetector 6z of the fourth group Z4.

  Further, the use area in the photodetectors of each group Z1 to Z4 in the PD array 6A at the start of each of the B phase, the AB phase, and the BB phase is different from the above, and in these cases, it is as shown in FIG. As can be understood from FIG. 4, the relative positional relationship of the groups Z1 to Z4 in the arrangement of the photodetectors of the PD array 6A at the start of any of the phases A, B, AB, and BB. Is the same.

  In the above configuration, the light emitted from the light source 4, passing through the slit 7, and reflected in the incremental pattern forms a bright-dark pattern on the PD array 6A, and the bright-dark pattern is the photodetector 6 for detecting the incremental pattern. Detected in. The detection signal output from the photodetector 6 for detecting the incremental pattern is processed by a known signal processing circuit (not shown) to detect the relative movement amount of the scale 2 with respect to the encoder head 1.

  3B, in the incremental pattern which is the periodic pattern of the scale 2, as described above, the reflective portions 9a and the non-reflective portions 9b arranged alternately are formed with the same width W. As a result, the reflecting portions 9a are arranged at equal intervals W. Then, as an index pattern that is a non-periodic pattern, a non-reflective portion 11b having a width of 3W and reflective portions 11a having a width of W located on both sides thereof are formed in the incremental pattern. The index pattern and the incremental pattern form a bilaterally symmetrical pattern with a center line M passing through the widthwise center of the reflecting portion 11a as an axis. The index pattern in this embodiment is formed by converting one non-reflective portion in the incremental pattern into a reflective portion. In addition, in the present embodiment, the index pattern and the incremental pattern form a left-right symmetrical pattern with the center line M passing through the widthwise center of the reflecting portion 11a as an axis, but a left-right asymmetric pattern is formed. Is also good. The index pattern in the another embodiment configuration of FIG. 3B is formed by converting one reflective portion in the incremental pattern into a non-reflective portion. The scale and the PD array at that time have the configurations shown in FIGS. 3A and 3B, and are similar to those of the reflection type optical encoder using the triple diffraction grating technique shown in FIG. The configuration of an applied embodiment is formed.

  Next, a signal processing circuit for generating the reference position signal (Z-phase pulse signal) from the index pattern detection signal will be described with reference to FIG. When light is incident on the photodetector 6z for detecting the index pattern and the photoelectrically converted current signal is output from the photodetector 6z of each group Z1 to Z4, the current signal of the first group Z1 is converted into the current-voltage conversion circuit. 12a, the current signal of the second group Z2 is input to the current-voltage conversion circuit 12c, the current signal of the third group Z3 is input to the current-voltage conversion circuit 12d, and the current signal of the fourth group Z4 is converted to current-voltage. It is input to the circuit 12b. Each of the current-voltage conversion circuits 12a, 12b, 12c, 12d converts the input current signal into a voltage signal and outputs it.

  The output signal of the first group Z1 and the output signal of the fourth group Z4 are input to the differential amplifier circuit 13a, and the differential signal of the output signals is amplified and output by the differential amplifier circuit 13a. The output signal of the second group Z2 and the output signal of the third group Z3 are input to the differential amplifier circuit 13b, and the differential signal between the output signals is amplified and output by the differential amplifier circuit 13b. Then, in a comparison circuit 14 such as a window comparator, the output of the differential amplifier circuit 13a and a reference voltage are compared to generate a binarized pulse signal, and the output of the differential amplifier circuit 13a and the difference are generated. The output of the dynamic amplifier circuit 13b is compared to generate a binarized pulse signal. Each pulse signal output from the comparison circuit 14 is input to the AND circuit 15 and is logically operated to output a Z-phase pulse signal as a reference position signal from the output terminal 16. Although the logical operation is performed using the AND circuit 15 in FIG. 5, the logical operation may be performed using a NAND circuit or the like.

  Next, the generation of the reference position signal in this embodiment will be further described based on FIGS. 6 and 7. FIG. 6 shows output waveforms (a), (b), (c), (d) of the current-voltage conversion circuits 12a, 12b, 12c, 12d and output waveforms (e), (e) of the differential amplifier circuits 13a, 13b. f), where the vertical direction represents the voltage value and the horizontal direction represents the distance in the X direction of FIG. 1. Further, W in FIG. 6 corresponding to one cycle of the waveform shows a state in which the scale 2 shown in FIG. 1 is moved by W in the X direction of FIG. FIG. 7 shows the output waveforms (g) and (h) of the comparison circuit 14 that binarizes the outputs of the differential amplifier circuits 13a and 13b and the output waveform of the AND circuit 15 that is the reference position signal (Z-phase pulse signal) ( i).

  As shown in FIG. 6, the difference between the output of the current-voltage conversion circuit 12a input in the waveform (a) to the differential amplifier circuit 13a and the output of the current-voltage conversion circuit 12b input in the waveform (b) is amplified. The waveform (e) is output from the differential amplifier circuit 13a. On the other hand, the difference between the output of the current-voltage conversion circuit 12c input in the waveform (c) to the differential amplifier circuit 13b and the output of the current-voltage conversion circuit 12d input in the waveform (d) is amplified by the waveform (f). It is output from the differential amplifier circuit 13b. Here, the difference between the waveform (a) and the waveform (b) and the difference between the waveform (c) and the waveform (d) are that the light emitted from the light source 4 is reflected by the reflecting portion 11 a of the scale 2. It is caused by the incident light intensity dependency (location dependency) when reflected and incident on each photodetector 6z in the Z1 to Z4 regions of the PD array 6A.

  As shown in FIG. 7, the output of the differential amplifier circuit 13a input to the comparison circuit 14 with the waveform (e) is compared with the reference voltage, binarized, and output as the pulse signal of the waveform (g). The output of the differential amplifier circuit 13b input to the comparison circuit 14 with the waveform (f) is compared with the output of the waveform (e) of the differential amplifier circuit 13a and binarized to obtain the waveform (h). It is output as a pulse signal. The outputs of the waveforms (g) and (h) output from the comparison circuit 14 are input to the AND circuit 15 to be logically operated and output as the reference position signal (Z-phase pulse signal) of the waveform (i). It

The present invention is not limited to the above-described embodiments, and is applicable to, for example, not only the reflection type but also the transmission type optical encoder. The width of the reflective portion 11a of the index pattern, considering the detection accuracy of the moving amount and the reference position, that about three times the width of the reflective portion 9a of the incremental pattern is preferred, it was confirmed experimentally.

1 Encoder head 2 Scale 3 PCB board 4 Light source 5 IC
6 Photodetector 6A PD array 6Z Index pattern detection photodetector 7 Slit 8 Transparent resin 9a, 11a Reflecting part 9b, 11b Non-reflecting part 10a Light-shielding part 10b Transmissive part 12a, 12b, 12c, 12d Current-voltage converting circuit 13a, 13b Differential amplifier circuit 14 Comparison circuit 15 AND circuit 16 Output terminal

Claims (1)

A light source that emits light, a scale that is formed with an optical pattern and is movable relative to the light source, and a photodetector that detects light emitted from the light source and passing through the optical pattern In the optical encoder, the optical pattern of the scale is a non-periodic index pattern in a periodic incremental pattern in which reflective portions and non-reflective portions are alternately arranged in the moving direction of the scale. At least one is disposed, and the photodetector is a photodetector for detecting the incremental pattern, one sandwiched between the photodetectors for detecting the incremental pattern, and two adjacent indexes. Photodetectors for detecting patterns are arranged in a fixed pattern in the moving direction of the scale, while detecting the index patterns. Have a signal processing circuit for generating a reference position signal based on a detection signal that the photodetector,
The non-periodic index pattern is sandwiched between the reflective portions of the incremental pattern so that the non-reflective portion, the reflective portion, and the non-reflective portion have a width of about 1: 3: 1, and the non-reflective portion has a width of about 1: 3. The width is arranged as substantially the same width as the reflective portion of the incremental pattern,
Alternatively, the non-periodic index pattern is sandwiched between the non-reflective portions of the incremental pattern so that the reflective portion, the non-reflective portion, and the reflective portion have a width of approximately 1: 3: 1, and each of the reflective portions. The width of is arranged as substantially the same width as the non-reflective portion of the incremental pattern,
The photodetector for detecting the incremental pattern has four photodetectors corresponding to the respective phase portions periodically so as to detect the four phase portions having different phases by 90 degrees in the light-dark pattern having a constant period. Arranged in
The photodetector for detecting the index pattern is divided into eight photodetectors into three groups, one, one, and three first to fourth groups, and the photodetectors for incremental pattern detection are provided. The first, second, and fourth photodetectors of any four consecutive photodetectors of the above are replaced with the photodetectors of the first group, and the third photodetector of the following four photodetectors of the second group is replaced. A photodetector, the third photodetector of the following four is replaced with the photodetector of the third group, and the first, second, and fourth photodetectors of the following four are replaced by the fourth photodetector. Replaced with a group photo detector,
The signal processing circuit voltage-converts each detection signal of the eight index pattern detection photodetectors and differentially amplifies each detection signal of the first and fourth groups to obtain a reference signal. And a pulse signal generated by comparing the differential signals obtained by differentially amplifying the detection signals of the second and third groups with the differential signals of the first and fourth groups. An optical encoder characterized by performing a logical operation to obtain a reference position signal .

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