JP2015099079A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical encoder that can accurately detect an origin with a simple arithmetic circuit by using two optical scales.SOLUTION: The optical encoder includes: first and second optical scales 2-1 and 2-2; a light source 11; a first light-receiving sensor 15-1 having four-phase main sensor parts repeatedly and successively arranged at an interval of a sensor pitch in a main axis direction; a second light-receiving sensor 15-2 having four-phase sub-sensor parts repeatedly arranged; and a detection circuit for arithmetic processing of a detection signal. In the pattern 2-2 of the second optical scale, the pattern represented by two densities is reversed at one side of a predetermined position from the pattern at the other side. The detection circuit includes: first and second main difference arithmetic circuits 41 for computing difference in an A-phase and difference in a B-phase of the main sensor parts; first and second sub difference arithmetic circuits 42 for computing difference in the A-phase and difference in the B-phase of the sub-sensor parts; a synthesis circuit 43 for adding an output of the first main difference arithmetic circuit and an output of the first sub difference arithmetic circuit; and a determination circuit 46 for comparing an output of the synthesis circuit to a threshold to detect the origin.

Description

  The present invention relates to an optical encoder, and more particularly to an optical encoder that enables origin detection.

  Optical encoders are widely used for measuring shapes such as the length, thickness, inner and outer diameters of objects to be measured, and displacements such as rotation angles or movement amounts, and their configurations are also widely known. Optical encoders include a transmission type that detects light transmitted through the optical scale and a reflection type that detects light reflected by the optical scale, and the reflection type is often used for miniaturization. Hereinafter, a reflective linear optical encoder will be described as an example. However, the present invention is not limited to this, and any optical encoder can be applied.

  As described in Patent Documents 1 and 2, reflective linear optical encoders in recent years have applied a semiconductor manufacturing technique to improve the accuracy, miniaturization / thinning, and ease of assembly. A sensor substrate on which a light receiving sensor is integrally formed is used. The sensor substrate is arranged so that the illumination light from the light source is reflected by the optical scale with respect to the reflective optical scale, and a light pattern corresponding to the pattern of the optical scale is formed on the light receiving sensor. The reflective linear optical encoder measures the relative movement amount of the optical scale and the sensor substrate.

  In order to reduce the influence of manufacturing variation of each part, the light receiving sensor has first to fourth sensor parts. The first to fourth sensor units are arranged at the same width and in the same direction as the arrangement direction of the light and shade pattern of the optical scale (hereinafter referred to as the main axis direction) at the sensor pitch, and one set of the first to fourth sensor units is set. Are repeatedly arranged in the main axis direction by a predetermined number of sets. Therefore, the first sensor units are arranged at a 4-sensor pitch, and the other second to fourth sensor units are also arranged at a 4-sensor pitch. The number of sets is 13, for example. The detection signals of a plurality of (for example, 13) first sensor units are added to form a + A signal. Similarly, the detection signals of the plurality of second to fourth sensor units are also added to form + B, −A, and −B signals, respectively. By adding signals from a plurality of sensor units, it is possible to reduce the influence of variations in sensitivity of sensor units, uneven illumination light, assembly errors, and the like.

  The optical encoder measures a relative movement amount of the optical scale and the sensor substrate by reading a light and shade pattern (having different reflection intensities) periodically formed on the optical scale. However, only the relative movement amount can be measured, and the absolute position cannot be measured.

If the absolute position can be measured by the optical encoder, it is advantageous in the following points as compared with the measurement of only the relative position.
First, consider a case where a miscount occurs due to some external cause. In this case, since the origin does not exist, that is, the measurement reference point does not exist, it is impossible for the mechanism to detect the miscount. For this reason, there is a risk that all measured values after the occurrence of miscounting will be incorrect values.
On the other hand, in the case of having an origin, a miscount can be detected by using the origin as a reference, so that an incorrect value can be corrected each time.

Also, consider a case where the count value is lost during measurement due to external factors such as power loss. When the origin does not exist, it is impossible to return to the original state using only the optical encoder. On the other hand, when the origin exists, the value of the origin position is determined in advance, and the original state can be restored by retracting to the origin.
The above is very important when an optical encoder is used for measurement during actual machining.

  Therefore, an optical encoder generally includes an origin detection mechanism separately from an optical scale for detecting a relative position.

JP 2010-223631 A JP2012-103230A

Patent Document 1 proposes an origin detection mechanism having two optical scales formed in parallel on the same scale substrate. However, the described origin detection mechanism is not sufficient in the following points.
Since the gradient of the amplitude change of the signal used for the origin detection is small, it is difficult to detect the origin by comparison with the threshold with high accuracy. In addition, there is a possibility that detection is performed by shifting the origin position due to the influence of the light amount fluctuation of the light source.

Therefore, in order to detect the origin with high accuracy, it is necessary to provide a circuit for correcting the origin detection mechanism in addition to the optical scale detection circuit for detecting the relative position, which increases the size and cost.
Further, a Z-phase signal obtained by summing up the outputs of the four sensor units is generated, and an origin signal is generated in combination with the A-phase signal, and a deviation occurs with a reciprocal relative movement.

  An object of the present invention is to realize an optical encoder that uses two optical scales and can detect an origin with high accuracy with a simple arithmetic circuit.

  In the optical encoder of the present invention, one of two optical scales formed in parallel is a normal light / dark pattern in which the dark portion and the light portion have the same width, and the light / dark is repeated at the scale pitch. In the same manner, the density is repeated at the scale pitch, but the dark part and the light part are reversed at a predetermined position. In other words, one side of the predetermined position has the same density pattern as the density pattern of one optical scale, and the other side has a density pattern obtained by inverting the density pattern of one optical scale. .

  That is, the optical encoder of the present invention includes a first optical system, a second optical system, and a detection circuit. The first optical system includes a first optical scale having a first light and shade pattern that changes in a principal axis direction, a first light source that outputs the first illumination light of the first optical scale, and the first optical light by the first illumination light. A first light receiving sensor arranged to detect an image of a first gray pattern generated by illuminating the equation scale, and the first light receiving sensors are arranged in order in the main axis direction at a sensor pitch. It has a first sensor array in which a first sensor group composed of first to fourth main sensor units is repeatedly arranged a predetermined number of times in the main axis direction. The second optical system includes a second optical scale having a second light and shade pattern that changes in the principal axis direction, a second light source that outputs the second illumination light of the second optical scale, and a second optical light using the second illumination light. And a second light receiving sensor arranged to detect an image of the second gray pattern generated by illuminating the equation scale, and the second light receiving sensors are arranged in order in the main axis direction at a sensor pitch. A second sensor array in which a second sensor set including the first to fourth sub sensor units is repeatedly arranged a predetermined number of times in the main axis direction is provided. The detection circuit includes a detection circuit that performs arithmetic processing on the detection signal of the first light receiving sensor of the first optical system and the detection signal of the second light receiving sensor of the second optical system. The first optical scale and the second optical scale move relative to the first light source, the first light receiving sensor, the second light source, and the second light receiving sensor. The first light and shade pattern of the first optical scale has the same width of the dark portion and the light portion and repeats light and shade at the scale pitch. The second light and shade pattern of the second optical scale has the width of the dark portion and the light portion. In the same manner, light and shade are repeated at a scale pitch, and a dark portion and a light portion are reversed at a predetermined position. The detection circuit includes a first main difference calculation circuit that calculates a difference between outputs of the first and third main sensor units, and a second main difference calculation circuit that calculates a difference between outputs of the second and fourth main sensor units. A first sub-difference calculating circuit that calculates a difference between the outputs of the first and third sub-sensor units, a synthesis circuit that adds the output of the first main difference calculating circuit and the output of the first sub-difference calculating circuit, An origin determination circuit that detects the origin by comparing the output of the combining circuit with a threshold value.

  In the optical encoder of the present invention, the second shading pattern of the second optical scale is inverted at a predetermined position. Therefore, when the second light receiving sensor detects the second gray pattern on one side of the predetermined position, the output of the first main difference calculation circuit that calculates the difference between the outputs of the first and third main sensor units; The output of the first sub-difference calculating circuit that calculates the difference between the outputs of the first and third sub-sensor units is an in-phase signal, but the second gray pattern on the other side of the predetermined position is detected. In this case, the output of the first main difference calculation circuit and the output of the first sub difference calculation circuit are signals having opposite phases. Therefore, the output of the synthesis circuit that adds the output of the first main difference calculation circuit and the output of the first main difference calculation circuit becomes a signal with a large amplitude on one side of the predetermined position, and a small amplitude on the other side of the predetermined position. When the second gray level pattern detected by the second light receiving sensor moves from one side of the predetermined position to the other side, it changes from a large amplitude to a small amplitude, and the other of the predetermined positions. When moving from one side to the other, when changing from a small amplitude to a large amplitude, the change is reversed. In any case, since it changes between a large amplitude and a small amplitude, the amplitude change becomes steep, and the accuracy of detecting the change position is improved compared to the threshold value.

  The first optical scale and the second optical scale are adjacent to each other on a common scale substrate, and the first gray pattern and the second gray pattern are parallel to each other. Are preferably formed so as to match. The first light source, the first light receiving sensor, the second light source, and the second light receiving sensor are formed on a common sensor substrate, and the first light source and the second light source are formed as a common light source. In the two light receiving sensors, the first sensor array and the second sensor array are arranged in parallel on both sides of the common light source so that the positions of the first to fourth main sensor units and the first to fourth sub sensor units coincide with each other. It is desirable to be formed. Furthermore, the sensor substrate projects illumination light from the common light source reflected by the first light and shade pattern onto the first light receiving sensor and the illumination light from the common light source reflected by the second light and shade pattern on the scale substrate. It is desirable to arrange so as to be projected onto the second light receiving sensor.

  Thereby, the position adjustment of the sensor substrate and the scale substrate is facilitated, and the size and thickness can be reduced.

The scale pitch is twice the sensor pitch, and the sensor substrate is arranged such that the first density pattern and the second density pattern are projected on the scale board as a density pattern that is four times the sensor pitch. .
Thereby, it is possible to increase the amplitude of the detection signal and improve the resolution with a simple configuration.

The origin determination circuit includes an absolute value circuit that generates an absolute value signal of the output of the synthesis circuit, a low-pass filter that removes high-frequency components of the absolute value signal, and a comparison circuit that compares the output of the low-pass filter with a threshold value.
As a result, the positive / negative combined signal is changed to an absolute value signal having only a positive portion, and a signal close to the change in the peak value is obtained.

  Similar to a general optical encoder, the detection circuit calculates a phase within a cycle length that is four times the sensor pitch as one cycle from the outputs of the first main difference calculation circuit and the second main difference calculation circuit. calculate. Therefore, origin detection only needs to be able to determine which period length the origin is in. Therefore, the detection circuit detects in which period length the output change of the comparison circuit of the origin determination circuit has occurred, and determines in which period length the origin is in consideration of the moving direction.

The origin determination circuit determines when the output of the first main or sub-difference arithmetic circuit becomes the maximum value based on the output of the second main or sub-difference arithmetic circuit, and determines the maximum output of the first main or sub-difference arithmetic circuit. A threshold control circuit that changes the threshold of the comparison circuit of the origin determination circuit according to the value is provided.
As a result, even if the signal intensity changes due to deterioration of the first or second light source or the first or second light receiving sensor of the first or second optical system, the origin can be detected accurately.

  The optical encoder of the present invention uses only one of the two optical scales for movement detection and the other for origin detection, and simply adds a simple arithmetic circuit to a general circuit used for movement detection. There is an effect that the origin can be detected with high accuracy.

FIG. 1 is a diagram illustrating a main part of a reflective linear optical encoder according to an embodiment. FIG. 2 is a diagram illustrating a pattern of the light receiving unit. FIG. 3 is a diagram illustrating the positional relationship between the scale substrate and the sensor substrate. FIG. 4 is a diagram schematically illustrating a path in which light from the light source is reflected by the reflection pattern and projected onto the light receiving unit. FIG. 5 is a diagram illustrating a reflection pattern projected onto the light receiving unit. FIG. 6 is a diagram illustrating changes in detection signals accompanying changes in the relative positional relationship (length) between the scale substrate and the sensor substrate. FIG. 7 is a diagram illustrating a detection signal calculation circuit used in the optical encoder. FIG. 8 is a diagram illustrating changes in the A-phase signal and the B-phase signal accompanying changes in the relative positional relationship (length) between the scale substrate and the sensor substrate. FIG. 9 is a diagram illustrating a scale pattern in the reflective linear optical encoder according to the embodiment. FIG. 10 is a diagram illustrating a configuration of an arithmetic processing unit in the reflective linear optical encoder of the embodiment. FIG. 11 is a diagram illustrating a change in the sub-A phase signal output from the light receiving unit in accordance with a change in the relative positional relationship (length) between the scale substrate and the sensor substrate. FIG. 12 is a diagram showing changes in the sub-A phase signal and the synthesized signal obtained by synthesizing the main A-phase signal and the sub-A phase signal in accordance with the change in the relative positional relationship (length) between the scale substrate and the sensor substrate. is there. FIG. 13 is a diagram illustrating the relationship between the relative position signal calculated by the arithmetic circuit that calculates the signal of the light receiving unit and the origin signal generated by the origin detection described so far. FIG. 14 is a diagram illustrating a configuration of the threshold adjustment circuit.

FIG. 1 is a diagram illustrating a main part of a reflective linear optical encoder according to an embodiment.
The reflective linear optical encoder of the embodiment includes a scale substrate 1 on which two reflection patterns 2-1 and 2-2 are formed, a light source 11, a light transmitting member 13 on which a grating 12 is formed, and two pieces The light receiving elements 14-1 and 14-2 are formed, and the sensor substrate 10 is covered with a transparent resin material 16. The scale substrate 1 is fixed to one of the two members relatively moving in the uniaxial direction, and the sensor substrate 10 is fixed to the other, and the relative movement distance of the two members is measured. Here, the moving direction is referred to as the main axis direction.

  The reflection patterns 2-1 and 2-2 are formed of a transparent glass substrate and are formed on the surface facing the sensor substrate 10. The reflection pattern 2-1 is a reflection pattern formed with a scale pitch p2 in the principal axis direction, and chromium is vapor-deposited in the reflection portion, and light is transmitted between the reflection portions, so that a reflection pattern with the pitch p2 is formed. The The reflection pattern 2-2 will be described later. The reflection pattern 2-1 functions as a main optical scale, and the reflection pattern 2-2 functions as a sub optical scale.

The light source 11 is an LED, and the grating 12 is an optical pattern having a grating pitch p1. Light receiving portions 15-1 and 15-2 having patterns as shown in FIG. 2 are formed on the surfaces of the light receiving elements 14-1 and 14-2, respectively.
The light source 11, the reflection pattern 2-1 and the light receiving element 14-1 form a first optical system, and the light source 11, the reflection pattern 2-2 and the light receiving element 14-2 form a second optical system, respectively.

  FIG. 2 is a diagram illustrating patterns of the light receiving units 15-1 and 15-2. As shown in the figure, sensor portions PS1 to PS4 having the same width are formed in order in the main axis direction at the sensor pitch sp, and are repeatedly formed. In other words, the sensor units PS1 to PS4 are set as one set, and a plurality of sets are formed at a repetition pitch p3 = 4sp. In the embodiment, for example, 13 sets are formed, so the total number of sensor units is 52. The sensor units PS1 to PS4 are formed of, for example, photodiodes and operate as independent light receiving elements. The outputs of a plurality (here, 13) of sensor units PS1 are connected in common and become a detection signal + A. Similarly, the outputs of the plurality of sensor units PS2 to PS4 are connected in common and become detection signals + B, -A, and -B.

  The pattern light receiving portions 15-1 and 15-2 are formed symmetrically with respect to the plane in the principal axis direction passing through the center of the light source 11.

FIG. 3 is a diagram showing an arrangement relationship between the scale substrate 1 and the sensor substrate 10.
As shown in FIG. 3, the light from the light source 11 passes through the grating 12, and in the figure, the light in the left direction is reflected by the reflection pattern 2-1, projected onto the light receiving unit 15-1, and light in the right direction. Is reflected by the reflection pattern 2-2 and projected onto the light receiving unit 15-2.

  Since details of the configuration, arrangement, and projected pattern in FIGS. 1 to 3 are described in Patent Document 1, further description thereof is omitted.

FIG. 4 is a diagram schematically illustrating a path in which light from the light source 11 is reflected by the reflection pattern 2 and projected onto the light receiving unit 15.
As shown in FIG. 4, the reflection pattern 2 is a reflection pattern having a scale pitch p2 (= 20 μm), and the duty is 50%. Therefore, the width of the reflection portion 2R is p2 / 2 (= 10 μm). In the embodiment, the reflective portion 2R is projected onto the light receiving unit 15 as a pattern having a width p2 (= 20 μm). Therefore, the pitch of the pattern projected on the light receiving unit 15 is 2p2 (= 40 μm).

FIG. 5 is a diagram illustrating a reflection pattern projected onto the light receiving unit 15.
As shown in FIG. 5, in the light receiving unit 15, four sensor units PS1 to PS4 are arranged at a pitch p2 / 2 (= 10 μm). On top of this, the projected shading pattern is a shading pattern with a pitch of 2p2 (= 40 μm), and the duty is 50%. Therefore, the width of the dark portion 4A and the light portion 4B is p2 (= 20 μm).

  As shown in FIG. 2, the outputs of the plurality of sensor units PS1 to PS4 are connected in common and become detection signals + A, + B, −A, and −B.

  FIG. 6 is a diagram illustrating changes in detection signals + A, + B, −A, and −B accompanying changes in the relative positional relationship (length) between the scale substrate 1 and the sensor substrate 10. As shown in FIG. 6, the detection signals + A, + B, −A, and −B are sinusoidal signals having a period of 20 μm and are shifted by ¼ phase (90 °). In other words, the detection signals + A and -A are signals that are shifted by 1/2 phase (180 °), and the detection signals + B and -B are signals that are shifted by 1/2 phase (180 °).

FIG. 7 is a diagram illustrating a detection signal calculation circuit used in the optical encoder.
The arithmetic circuit calculates the difference between the outputs of the amplifier circuits 31 to 34 that amplify the detection signals + A, -A, + B, and -B, and the amplifier circuits 31 and 32, and outputs the A-phase signal PHASEA. A circuit 35 and a second difference calculation circuit 36 that calculates a difference between outputs of the amplification circuits 33 and 34 and outputs a B-phase signal PHASEB.

  FIG. 8 is a diagram illustrating changes in the A-phase signal PHASEA and the B-phase signal PHASEB accompanying changes in the relative positional relationship (length) between the scale substrate 1 and the sensor substrate 10. As described above, the detection signals + A and −A are signals that are shifted by 1/2 phase (180 °), and the detection signals + B and −B are signals that are shifted by 1/2 phase (180 °). Even if the amplification factor is 1, the A-phase signal PHASEA and the B-phase signal PHASEB are signals having amplitudes twice that of the detection signals + A, -A, + B, and -B. Also. The A-phase signal PHASEA and the B-phase signal PHASEB are signals that are shifted by ¼ phase (90 °).

  Therefore, by detecting the ratio of the values of the A-phase signal PHASEA and the B-phase signal PHASEB, a phase of less than 90 ° can be detected. Even in an optical encoder that is actually used, the scale pitch or sensor pitch can be detected. The position (length) is detected with a resolution of several tenths. The same applies to the reflective linear optical encoder of the embodiment.

  The configuration of the reflective linear optical encoder of the embodiment described above is described in Patent Document 1 and is widely known. The reflective linear optical encoder of the embodiment is different in the reflective pattern 2-2 and the arithmetic circuit.

FIG. 9 is a diagram illustrating the reflection patterns 2-1 and 2-2 in the reflective linear optical encoder of the embodiment.
As described above, the reflection pattern 2-1 is a reflection pattern formed with a scale pitch p2 = 20 μm in the principal axis direction, and the reflection portion R and the transmission portion T have the same width of 10 μm.

  The reflection pattern 2-2 has the same pattern as the reflection pattern 2-1 in the left portion of the predetermined position 5, and is transmitted through the reflection portion R of the reflection pattern 2-1 in the right portion of the predetermined position 5. It has a reflection pattern in which the portion T is inverted. Therefore, in the portion on the left side of the predetermined position 5 of the reflection pattern 2-2, the reflection portion R is 20 μm wide. Here, the predetermined position 5 is the origin.

  With respect to the scale substrate 1 having the reflection patterns 2-1 and 2-2 shown in FIG. 9, the sensor substrate 10 is arranged as shown in FIG. When the part 15-2 detects the reflected light of the left part of the predetermined position 5 of the reflection pattern 2-2, the output signals of the light receiving part 15-1 and the light receiving part 15-2 are the same. On the other hand, when the light receiving unit 15-2 detects the reflected light of the right part of the predetermined position 5 of the reflection pattern 2-2, the reflection pattern is formed on the surfaces of the light receiving unit 15-1 and the light receiving unit 15-2. Is projected with a deviation of 20 μm.

  The sensor units PS1 to PS4 of the light receiving unit 15-1 correspond to the main sensor unit, and the sensor units PS1 to PS4 of the light receiving unit 15-2 correspond to the sub sensor unit, respectively.

FIG. 10 is a diagram illustrating a configuration of an arithmetic processing unit in the reflective linear optical encoder of the embodiment.
Note that, in the reflective linear optical encoder of the embodiment, similarly to a general reflective linear optical encoder, the calculation for calculating the signal of the light receiving unit 15-1 that receives the reflected pattern of the reflective pattern 2-1. The circuit calculates the movement position with a resolution higher than the period of the scale pitch of the reflection pattern 2-1, but since this is widely known, a description thereof will be omitted. The reflective linear optical encoder of the embodiment is obtained by adding a different origin detection function to the position calculation function described above, and only the calculation processing related to the origin detection will be described.

  The arithmetic processing unit includes a first arithmetic circuit 41, a second arithmetic circuit 42, a synthesis circuit 43, an absolute value circuit 44, a low-pass filter 45, a determination circuit (comparator) 46, and a first pulse generation circuit 47. , A second pulse generation circuit 48, and an OR gate 49. These circuits are all realized by analog circuits.

  The first arithmetic circuit 41 has the circuit configuration shown in FIG. 7, and outputs the main A-phase signal PHASEA and the main B-phase signal PHASEB from the detection signals + A, -A, + B, -B output from the light receiving unit 15-1. Output. The second arithmetic circuit 42 has the circuit configuration shown in FIG. 7, and outputs the sub-A phase signal PHASEA and the sub-B phase signal PHASEB from the detection signals + A, −A, + B, −B output from the light receiving unit 15-2. Output. The first difference calculation circuit 35 and the second difference calculation circuit 36 in the first calculation circuit 41 correspond to a first main difference calculation circuit and a second main difference calculation circuit, and the first difference calculation in the second calculation circuit 42 is performed. The circuit 35 and the second difference calculation circuit 36 correspond to a first sub difference calculation circuit and a second sub difference calculation circuit.

  The synthesizing circuit 43 is an analog adder circuit, and adds the main A phase signal PHASEA and the sub A phase signal PHASEA to output a synthesized signal C.

  The absolute value circuit 44 inverts the negative part of the composite signal C that changes between positive and negative and converts it into a signal of only the positive part. Since the absolute value circuit is widely known, description thereof is omitted.

  The low-pass filter 45 removes high frequency components from the output of the absolute value circuit 44 and outputs a signal close to the change in peak value.

  The comparator 46 compares the output of the low-pass filter 45 with the threshold value Vth, and changes the output when the output of the low-pass filter 45 changes beyond the threshold value Vth. Specifically, the output of the comparator 46 changes from “1 (H: High)” to “0 (L: Low)” when the output of the low-pass filter 45 changes from a state larger than the threshold value Vth to a smaller state. When the output of the low-pass filter 45 changes from a state smaller than the threshold value Vth to a larger state, it changes from L to H.

  The first pulse generation circuit 47 generates a short pulse when the output of the comparator 46 changes from H to L. The second pulse generation circuit 48 is the same as the first pulse generation circuit 47. However, since the output of the comparator 46 is inverted by the inverter and input, when the output of the comparator 46 changes from L to H, a short pulse is generated. Is generated. Since the short pulse generation circuit is widely known, description thereof is omitted.

  The OR gate 49 combines the outputs of the first pulse generation circuit 47 and the second pulse generation circuit 48. In other words, the OR gate 49 passes the short pulse output from both the first pulse generation circuit 47 and the second pulse generation circuit 48.

Hereinafter, the principle of origin detection according to the present invention will be described.
FIG. 11 is a diagram illustrating a change in the sub-A phase signal PHASEA output from the light receiving unit 15-2 in accordance with a change in the relative positional relationship (length) between the scale substrate 1 and the sensor substrate 10. When the reflection at the predetermined position 5 of the reflection pattern begins to enter the light receiving unit 15-2 with the change in position, the projection pattern incident on the sensor units PS1 and PS3 of the light receiving unit 15-2 is partially out of phase. Become. For example, on the positive phase side, a reflection part (bright part) is incident on PS1, and a transmission part (dark part) is incident on PS3, whereas on the opposite phase side, a transmission part (dark part) is on PS1. Is incident, and a reflective portion (bright portion) is incident on PS3. Therefore, the signal on the positive phase side and the signal on the negative phase side cancel each other, and the amplitude of the sub A phase signal PHASEA decreases as the ratio of the negative phase increases. When the predetermined position 5 of the reflection pattern is projected at the center of the light receiving unit 15-2, half of the sensor part of the light receiving unit 15-2 outputs a signal in the normal phase and half outputs a signal in the reverse phase. The amplitude of the sub A phase signal PHASEA becomes zero. When the movement further proceeds, the ratio of the reverse phase signal increases, and when the other side (the right side in FIG. 9) of the predetermined position 5 of the reflection pattern is projected on the entire light receiving unit 15-2, the sub A phase signal PHASEA is projected. Is the same amplitude as the state in which the left portion of the predetermined position 5 of the reflection pattern is projected on the entire light receiving unit 15-2, but is a signal in reverse phase. Accordingly, at this time, the sub-A phase signal PHASEA is a signal having the same amplitude as that of the main A phase signal PHASEA and having a reverse phase.

  Although not shown in FIG. 11, even if it moves further, the sub-A phase signal PHASEA has the same amplitude as the main A phase signal PHASEA and is a reverse phase signal.

  FIG. 12 shows a composite signal C obtained by synthesizing the sub A phase signal PHASEA, the main A phase signal PHASEA, and the sub A phase signal PHASEA in accordance with a change in the relative positional relationship (length) between the scale substrate 1 and the sensor substrate 10. It is a figure which shows the change of.

  The composite signal C is a signal having an amplitude twice that of the secondary A-phase signal PHASEA in a state where only the left portion of the predetermined range 5 of the reflection pattern is projected onto the light receiving unit 15-2. When the right part of the predetermined position 5 of the reflection pattern is projected, the amplitude suddenly decreases, and when only the right part of the predetermined position 5 of the reflection pattern is projected to the light receiving unit 15-2, the amplitude is It becomes zero. Thus, when the composite signal C passes through the predetermined position 5, the amplitude changes from a large amplitude to a small amplitude or vice versa.

  However, the composite signal C is a signal that changes positively and negatively, and it is necessary to detect the amplitude and compare it with a threshold value. Therefore, in the arithmetic processing unit of FIG. 10, the absolute value circuit 44 inverts the negative part to make only the positive part of the signal, smoothes it with the low-pass filter 45, and compares the output of the low-pass filter 45 with the threshold value Vth.

  The composite signal C is a signal that changes from twice the amplitude of the main and sub-A phase signals PHASEA to zero amplitude, and the amplitude when the predetermined position 5 of the reflection pattern is projected on the center of the light receiving unit 15-2. 1/2. Therefore, if Vth is set to ½ of the amplitude of the composite signal C when only the left part of the predetermined position 5 of the reflection pattern is projected onto the light receiving unit 15-2, the predetermined position of the projected reflection pattern When 5 passes through the center of the light receiving unit 15-2, the output of the comparator 46 changes, and the first pulse generation circuit 47 and the second pulse generation circuit 48 generate short pulses accordingly. However, there are two moving directions, and the combined signal C changes from H to L in one moving direction, and from L to H in the other moving direction. In the case of one moving direction, when the composite signal C changes from H to L, a short pulse is generated on the right side of the predetermined position 5, and in the case of the other moving direction, the composite signal C changes from L to H. When changing, a short pulse is generated on the left side of the predetermined position 5. Therefore, the origin is detected in consideration of the fact that the short pulse generation position differs depending on the moving direction.

  As described above, in the reflective linear optical encoder of the embodiment, the signal of the light receiving unit 15-1 that receives the reflected pattern of the reflective pattern 2-1 is received as in the general reflective linear optical encoder. The calculation circuit for calculating calculates the movement position with a resolution higher than the cycle of the scale pitch of the reflection pattern 2-1.

  FIG. 13 is a diagram for explaining the relationship between the relative position signal calculated by the arithmetic circuit that calculates the signal of the light receiving unit 15-1 and the origin signal generated by the origin detection described so far.

  The arithmetic circuit that calculates the signal of the light receiving unit 15-1 uses one cycle when the sensor pitch is one cycle by utilizing the fact that the main A-phase signal indicates the sin component and the main B-phase signal indicates the -cos component. The phase within is calculated. In FIG. 13, phase zero in one cycle is when the main A-phase signal is zero and the main B-phase signal has a negative peak value. As shown in FIG. 12, the synthesized signal C has an amplitude halved at a phase of 180 ° in this period, and when moving to one side, a short pulse is generated at a phase slightly larger than the phase 180 ° and moves to the other side. Sometimes a short pulse is generated with a phase slightly smaller than 180 ° (FIG. 13 shows a short pulse generated when moving to the other side).

  In any case, since the origin signal is generated before and after the phase 180 ° of one cycle of the detection position by the arithmetic circuit that calculates the signal of the light receiving unit 15-1, the position of the phase 180 ° of the cycle in which the origin signal is detected. Is the origin.

  As described above, in the embodiment, when the composite signal C passes through the predetermined position (origin) 5, the amplitude changes from a large amplitude to a small amplitude or vice versa. In comparison, the accuracy in detecting the change position is improved.

  In the above embodiment, the threshold value Vth of the comparator 46 is fixed. If the first and second optical systems are stable, there is no particular problem. However, if the signal intensity output from the light receiving sensor changes due to the light amount of the light source 11, the sensitivity of the light receiving sensor, dirt, etc., an error occurs in the origin detection. Produce. Therefore, it is conceivable to adjust the light intensity of the light source 11 or the amplification factor of an amplifier that amplifies the output of the light receiving sensor so that the signal intensity output from the light receiving sensor becomes constant. It is also conceivable to change the threshold value Vth according to the signal intensity output from the light receiving sensor. Hereinafter, an example of a threshold adjustment circuit that changes the threshold Vth in accordance with the signal intensity output from the light receiving sensor will be described.

FIG. 14 is a diagram illustrating a configuration of the threshold adjustment circuit.
The threshold adjustment circuit receives the signals of the amplifiers 35-2 and 36-2 that amplify the A-phase and B-phase signals output from the second light receiving sensor 14-2 as input signals and outputs the output signals to the comparator 46. Note that even if the A-phase and B-phase signals output from the first light-receiving sensor 14-1 are received as input signals, the A-phase and B-phase signals output from the first light-receiving sensor 14-1 and the second You may make it receive the synthetic | combination A phase signal and synthetic | combination B phase signal which respectively combined the A phase signal and B phase signal which the light receiving sensor 14-2 outputs as an input signal. Further, the threshold adjustment circuit performs an adjustment operation only when the CPU 60 that controls the entire encoder outputs a pulse-shaped threshold adjustment control signal having a predetermined width, and holds the previous threshold when the threshold adjustment control signal is not output. . Further, the threshold adjustment process is performed by moving in one direction, that is, the direction in which the projected reflection pattern 2-2 changes from the normal phase to the reverse phase.

The threshold adjustment circuit includes a comparator 61, an AND gate 62, an A / D converter 63, a latch circuit 64, a D / A converter 65, and an amplifier 66.
The comparator 61 compares the sub B phase signal output from the amplifier 35-2 with the zero level, and generates a signal that rises to H when the sub B phase signal changes from negative to positive. The AND gate 62 allows the signal of the comparator 61 to pass only when the CPU 60 outputs the threshold adjustment control signal.

  The A / D converter 63 samples the sub-A phase signal output from the amplifier 36-2 when the signal of the comparator 61 rises from L to H, and converts it into a digital signal. Since the secondary A phase signal takes a peak value when the secondary B phase signal changes from L to H, the A / D converter 63 outputs a digital signal having a peak value of the secondary A phase signal.

  The latch circuit 64 latches and holds the digital signal output from the A / D converter 63 according to the latch signal output from the CPU 60. The latch signal output from the CPU 60 is a signal corresponding to the falling edge of the threshold adjustment control signal, for example.

  The D / A converter 65 converts the digital signal of the peak value of the sub A phase signal output from the latch circuit 64 into an analog signal and outputs the analog signal to the amplifier 66. The amplifier 66 outputs an analog signal corresponding to the peak value of the sub A phase signal to the comparator 46 as the threshold value Vth. Thereby, for example, the same analog signal level as the peak value of the sub-A phase signal is set as Vth. Therefore, even if the peak value of the sub A phase signal varies, Vth is set to the peak value of the sub A phase signal. As described above, the amplitude of the composite signal C changes from twice the amplitude of the main A-phase signal (= the amplitude of the sub-A phase signal) to zero, and thus setting the Vth in this way is the origin. A short pulse is generated when the predetermined position 5 is passed.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that the modification of each place is possible. For example, two reflection patterns 2-1 and 2-2 are formed on one scale substrate 1, and two light receiving elements 14-1 and 14-2 are formed on one sensor substrate 10 together with one light source 11. Been formed. However, if the positional relationship can be set precisely, even if the reflection patterns 2-1 and 2-2 are formed on the two scale substrates, two sensor substrates having one light source and one light receiving element are provided. It may be used or both. However, the configuration of the embodiment is desirable to facilitate assembly and realize a highly accurate positional relationship.

In the embodiment, a reflective scale is used. However, a transmissive scale may be used.
Furthermore, the arithmetic processing circuit is an example, and it is easily understood by those skilled in the art that various modifications for realizing a circuit for detecting a change in amplitude are possible.

  The present invention can be applied to various optical encoders.

DESCRIPTION OF SYMBOLS 1 Scale board | substrate 2-1, 2-2 Reflection pattern 5 Predetermined position 10 Sensor board | substrate 11 Light source 14-1, 14-2 Light receiving element 15-1, 15-2 Light receiving part 35 1st difference calculation circuit 36 2nd difference calculation circuit 41 1st arithmetic circuit 42 2nd arithmetic circuit 43 Composition circuit 44 Positive / negative judgment circuit 45 Zero cross detection circuit 46 Judgment circuit

Claims (6)

A first optical scale having a first light and shade pattern that changes in the main axis direction, a first light source that outputs the first illumination light of the first optical scale, and the first optical scale with the first illumination light. A first light receiving sensor arranged to detect an image of the first gray pattern generated by illuminating, wherein the first light receiving sensor is arranged in order at a sensor pitch in the main axis direction. A first optical system having a first sensor array in which a first sensor group including first to fourth main sensor units is repeatedly arranged in a predetermined number of sets in the main axis direction;
A second optical scale having a second shading pattern that changes in the principal axis direction; a second light source that outputs a second illumination light of the second optical scale; and the second optical scale using the second illumination light. And a second light receiving sensor arranged so as to detect an image of the second gray pattern generated by illuminating the light, and the second light receiving sensors are sequentially arranged at the sensor pitch in the main axis direction. A second optical system having a second sensor array in which a second sensor set including the first to fourth sub sensor units is repeatedly arranged a predetermined number of times in the main axis direction;
A detection circuit that performs arithmetic processing on a detection signal of the first light receiving sensor of the first optical system and a detection signal of the second light receiving sensor of the second optical system;
The first optical scale and the second optical scale move relative to the first light source, the first light receiving sensor, the second light source, and the second light receiving sensor;
The first light and shade pattern of the first optical scale has the same width as the dark portion and the light portion, and repeats light and shade at a scale pitch.
The second light and shade pattern of the second optical scale has the same width as the dark portion and the light portion, repeats the light and shade at the scale pitch, and the dark portion and the light portion are reversed at a predetermined position.
The detection circuit includes a first main difference calculation circuit that calculates a difference between outputs of the first and third main sensor units, and a second main difference calculation that calculates a difference between outputs of the second and fourth main sensor units. A circuit, a first sub-difference calculating circuit for calculating a difference between outputs of the first and third sub-sensor units, and a composition for adding the output of the first main difference calculating circuit and the output of the first sub-difference calculating circuit. An optical encoder comprising: a circuit; and an origin determination circuit that detects an origin by comparing an output of the synthesis circuit with a threshold value. The first optical scale and the second optical scale are adjacent to each other on a common scale substrate, and the first gray pattern and the second gray pattern are parallel to each other, and are dark on one side of the predetermined position. And the position of the light part matches, and on the other side, it is formed so that the dark part and the light part are reversed,
The first light source, the first light receiving sensor, the second light source, and the second light receiving sensor are formed on a common sensor substrate, and the first light source and the second light source are formed as a common light source, The first light receiving sensor and the second light receiving sensor have the first sensor array and the second sensor array in parallel on both sides of the common light source, the first to fourth main sensor units, and the first to fourth sensors. It is formed so that the position of the sub main sensor part matches,
The sensor substrate is configured such that illumination light from the common light source reflected by the first light and shade pattern is projected onto the first light receiving sensor and reflected by the second light and shade pattern with respect to the scale substrate. The optical encoder according to claim 1, wherein the optical encoder is disposed so that illumination light from the first light receiving sensor is projected onto the second light receiving sensor. The scale pitch is twice the sensor pitch,
The optical sensor according to claim 2, wherein the sensor substrate is arranged such that the first gray pattern and the second gray pattern are projected as a light / dark pattern four times the scale pitch with respect to the scale substrate. Type encoder. The origin determining circuit is
An absolute value circuit for generating an absolute value signal of the output of the synthesis circuit;
A low-pass filter for removing high-frequency components of the absolute value signal;
The optical encoder according to any one of claims 1 to 3, further comprising a comparison circuit that compares an output of the low-pass filter with a threshold value.   The detection circuit calculates a phase within a period length in which a length four times the sensor pitch is one period from outputs of the first main difference calculation circuit and the second main difference calculation circuit, and the origin The optical according to claim 4, wherein in which period length the output change of the comparison circuit of the determination circuit occurs is detected, and in which period length the origin is in consideration of a moving direction. Type encoder. The origin determining circuit is
Based on the output of the second main or sub-difference calculating circuit, it is determined when the output of the first main or sub-difference calculating circuit is the maximum value, and the maximum value of the output of the first main or sub-difference calculating circuit is determined. 6. The optical encoder according to claim 4, further comprising a threshold control circuit that changes the threshold value of the comparison circuit of the origin determination circuit.

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