JPWO2018163424A1 - Absolute encoder - Google Patents

Abstract

An absolute encoder (1) is provided with an optical pattern (10), detects a light from an optical pattern, a movable scale (2), a light emitter emitting light to be advanced to the optical pattern, A sensor (4) for outputting a signal representing the intensity of the detected light, and an operation unit (13) for obtaining the position of the scale based on the signal from the sensor. In the optical pattern, data encoded from unique data assigned to each possible position of the scale can be detected at a light intensity different from that of the first region (11) and the first region by the sensor It is replaced by the arrangement with the second region (12). The width of the light emitter is smaller than the width of the portion in which the first regions are continuously arranged and the width of the portion in which the second regions are continuously arranged.

Description

  The present invention relates to an absolute encoder that measures the position of an object to be measured.

  The rotary encoder measures the rotation angle of the measurement object by detecting the rotation angle of the scale rotated with the measurement object. The optical rotary encoder detects the reflected light or transmitted light from the optical pattern provided on the scale with a sensor, and obtains the rotation angle of the scale by arithmetic processing based on the signal from the sensor. In the optical pattern, a first area and a second area detectable at a light intensity different from that of the first area by the sensor are arranged.

  As types of rotary encoders, an incremental encoder and an absolute encoder are known. The incremental encoder comprises an incremental pattern which is an optical pattern in which a first area and a second area are arranged at a constant pitch. The incremental encoder integrates the number of pulse signals from the sensor to determine the rotation angle of the scale. The absolute encoder acquires data of the rotation angle which is the absolute position of the scale from the light intensity pattern detected by the sensor. In an absolute pattern which is an optical pattern provided on the scale of an absolute encoder, a bit string which is encoded data is replaced with an arrangement of a first area and a second area. In the absolute pattern, the first region and the second region are irregularly arranged.

  Patent Document 1 discloses a rotary encoder provided with a main slit plate which is an incremental encoder and an index slit plate opposed to the main slit plate. In the main slit plate and the index slit plate, slits for transmitting light are provided at regular intervals. The rotary encoder can perform measurement with high accuracy and high resolution by utilizing the Talbot effect due to the diffractive action at the slit.

  Further, Patent Document 2 discloses that a signal including a phase difference is acquired, and feedback control of the light source is performed using a light source adjustment signal obtained by adding the acquired signals. Signals containing phase differences from one another are obtained by detecting light from the incremental pattern. The rotary encoder enables measurement with high accuracy and high resolution by highly accurate feedback control of the light source.

Unexamined-Japanese-Patent No. 2002-257593 JP, 2016-61600, A

  As described above, in the absolute pattern, the first area and the second area are arranged at an irregular pitch. In the technique of Patent Document 1, it is a condition of the Talbot effect that slits with a constant interval are provided, so even if the technique of Patent Document 1 is applied to an absolute encoder, measurement with high accuracy and high resolution is difficult . Further, in the absolute pattern, since the first region and the second region are arranged at an irregular pitch, the intensity of light detected by the sensor changes depending on the portion where light is incident. It becomes. When the technology of Patent Document 2 is applied to an absolute encoder having no incremental pattern, the level of the light source adjustment signal obtained by using the light from the absolute pattern changes depending on the portion where the light is incident. In this case, the adjustment of the light source becomes unstable, which makes it difficult to perform measurement with high accuracy and high resolution.

  The present invention has been made in view of the above, and an object thereof is to obtain an absolute encoder capable of measuring the position of a measurement object with high accuracy and high resolution.

  In order to solve the problems described above and achieve the object, the absolute encoder of the present invention is provided with an optical pattern, a movable scale, a light emitter for emitting light to be advanced to the optical pattern, and an optical pattern And a sensor for outputting a signal representing the intensity of the detected light, and an operation unit for obtaining the position of the scale based on the signal from the sensor. In the optical pattern, data encoded from unique data assigned to each possible position of the scale can be detected in a first area and a light intensity different from that of the first area by the sensor. It has been replaced with an array of 2 regions. The width of the light emitter is smaller than the width of the portion in which the first regions are continuously arranged and the width of the portion in which the second regions are continuously arranged.

  The absolute encoder according to the present invention is effective in that the position of the object to be measured can be measured with high accuracy and high resolution.

A diagram showing a schematic configuration of an absolute encoder according to a first embodiment of the present invention Block diagram of angle calculation unit shown in FIG. 1 The figure which shows the example of intensity distribution of the signal input into the angle calculating part shown in FIG. The figure which shows the example of intensity distribution of the signal corrected by the intensity distribution correction part shown in FIG. A diagram for explaining edge detection for a portion in a frame VII of FIG. 4 A diagram for explaining the conversion from the signal shown in FIG. 4 to a bit string A diagram for explaining calculation of phase shift amount in the phase shift calculation unit shown in FIG. A diagram for explaining light amount adjustment by the light source control unit shown in FIG. Flow chart showing the procedure of light amount adjustment of the light source control unit in the first embodiment In the absolute encoder shown in FIG. 1, a first schematic diagram showing how light from a light emitter passes through an optical pattern and reaches an image sensor. In the absolute encoder shown in FIG. 1, a second schematic view showing a state in which light from the light emitter passes through the optical pattern and reaches the image sensor A diagram for explaining data to be replaced with the optical pattern shown in FIG. The figure which shows the example of the hardware constitutions of the absolute encoder which performs the function of the control part shown in FIG. Diagram for explaining light amount adjustment by the light source control unit of the absolute encoder according to the second embodiment Flow chart showing the procedure of light amount adjustment of the light source control unit in the second embodiment Diagram for explaining light amount adjustment by the light source control unit of the absolute encoder according to the third embodiment Flow chart showing the procedure of light amount adjustment of the light source control unit in the third embodiment

  Hereinafter, an absolute encoder according to an embodiment of the present invention will be described in detail based on the drawings. The present invention is not limited by the embodiment.

Embodiment 1
FIG. 1 is a view showing a schematic configuration of an absolute encoder 1 according to a first embodiment of the present invention. The absolute encoder 1 includes a scale 2 provided with an optical pattern 10 and a light emitting element 3 including a light emitter for emitting light to be advanced to the optical pattern 10. Also, the absolute encoder 1 includes an image sensor 4 which is a sensor that detects light from the optical pattern 10 and outputs a signal representing a pattern of the detected light intensity.

  The absolute encoder 1 is a rotary encoder including a rotatable scale 2. Scale 2 is a circular flat plate. The scale 2 and the shaft 6 of the motor to be measured are connected to each other with the position of the axial center AX of the shaft 6 aligned with the center point O of the scale 2. The scale 2 rotates with the rotation of the shaft 6. In FIG. 1, the illustration of the motor main body for rotating the shaft 6 is omitted.

  The optical pattern 10 is formed on the surface of the scale 2. The optical pattern 10 is an arrangement of a first area 11 and a second area 12 which can be detected by the image sensor 4 at a light intensity different from that of the first area 11. The first area 11 and the second area 12 are arranged in a line, annularly surrounding the area inside the outer edge of the scale 2. The first region 11 reflects the light from the light emitting element 3. The reflectance of the second region 12 is lower than the reflectance of the first region 11. The second region 12 has a reflectance lower than that of the first region 11 by absorbing or scattering the light from the light emitting element 3.

  In the case of a configuration in which light reflected from the optical pattern 10 is detected, a portion of the scale 2 on which the optical pattern 10 is formed is disposed at a position facing the light emitting element 3 and the image sensor 4. In one example, a scale 2 is a flat plate of metal material. One example of a metallic material is aluminum. The metallic material may be a reflective metallic material other than aluminum or a reflective material other than metallic material. The optical pattern 10 is formed by patterning a light absorbing film formed on the surface of the scale 2. One example of the light absorbing film is an oxide film formed by oxidizing the surface of a metal material. Of the surface of the scale 2, a region in which the light absorption film is left in patterning is the second region 12. A region between the regions where the light absorption film is left and which exposes the metal material is the first region 11. In the second region 12, a member for scattering light may be provided instead of the light absorption film.

  The light emitting element 3 which is a light source is disposed on the scale 2. One example of the light emitting element 3 is a point light source LED (Light Emitting Diode). The light emitting element 3 includes an LED chip which is a light emitting body that emits light. The light emitted from the light emitting element 3 obliquely enters the optical pattern 10. LEDs are heat resistant and have a long life as compared to LDs (Laser Diodes). The absolute encoder 1 is capable of performing stable measurement in a high temperature environment and prolonging the life of the light source as compared to the case where an LD is used because the LED is used as the light source.

  The image sensor 4 is disposed forward in the traveling direction of the light reflected from the light emitting element 3 by the optical pattern 10. The image sensor 4 is a complementary metal oxide semiconductor (CMOS) image sensor or a charge coupled device (CCD) image sensor. The image sensor 4 includes a plurality of photodiodes which are photoelectric conversion elements. The plurality of photodiodes are arranged in one dimension. The photodiode generates a signal charge upon receiving the light. The image sensor 4 converts an analog signal from each photodiode into a digital signal in an analog-to-digital converter. The image sensor 4 outputs a digital signal representing a pattern of light intensity detected by each photodiode. In FIG. 1, illustration of the photoelectric conversion element and the analog-to-digital converter is omitted.

  In the first embodiment, no lens system for collimating, converging, or diverging light is provided between the light emitting element 3 and the optical pattern 10 and between the optical pattern 10 and the image sensor 4. A lens system that collimates, converges, or diverges light may be provided between the light emitting element 3 and the optical pattern 10 or between the optical pattern 10 and the image sensor 4.

  The absolute encoder 1 includes a control unit 5 that is a functional unit that controls the entire absolute encoder 1. FIG. 1 shows a functional configuration of the control unit 5. The control unit 5 includes an angle calculation unit 13 which is a functional unit that obtains the rotation angle of the scale 2 based on the detection result of the light intensity in the image sensor 4. The angle calculation unit 13, which is a calculation unit, obtains a rotation angle that is the position of the scale 2 based on the signal from the image sensor 4. The absolute encoder 1 outputs absolute position data indicating the rotation angle obtained by the angle calculation unit 13. Further, the control unit 5 is a light source control unit 14 that is a functional unit that controls driving of the light emitting element 3, a storage unit 15 that is a functional unit that holds a look up table (LUT) 16, and an image sensor And a sensor control unit 17 that is a functional unit that controls the driving of the image forming apparatus. The function of the light source control unit 14 includes the function of a light amount adjustment unit that adjusts the light amount of the light emitting element 3.

  The LUT 16 associates and holds absolute position data indicating the rotation angle of the scale 2 and a bit string which is encoded data. One example of absolute position data is a numerical value representing a rotation angle by an arc degree method or a frequency method. The absolute position data may be unique data assigned to each rotation angle of the scale 2 and may be an address assigned every unit angle.

  The absolute encoder 1 shown in FIG. 1 detects the light reflected by the optical pattern 10 and obtains the rotation angle of the scale 2. The absolute encoder 1 may have a configuration for detecting the light transmitted through the optical pattern 10 instead of the configuration for detecting the light reflected by the optical pattern 10.

  In the case of a configuration in which light transmitted through the optical pattern 10 is detected, the portion of the scale 2 on which the optical pattern 10 is formed is disposed in the optical path between the light emitting element 3 and the image sensor 4. The scale 2 is a glass plate or a resin plate. The material of scale 2 may be another material that transmits light. The optical pattern 10 is formed by patterning of a metal film deposited on the scale 2. One example of the material of the metal film is chromium. The region from which the metal film is removed is the first region 11. The regions between the first regions 11 where the metal film is left become the second regions 12. The material of the metal film may be a light absorbing material other than chromium. The scale 2 may be a plate member having the first region 11 as an opening.

  In the absolute encoder 1, unique absolute position data is assigned to each rotation angle which is the absolute position of the scale 2. In the optical pattern 10 which is an absolute pattern, the encoded absolute position data is replaced with the arrangement of the first area 11 and the second area 12. The absolute encoder 1 extracts the encoded absolute position data from the patterns of the first area 11 and the second area 12 included in the image detected by the image sensor 4. In the optical pattern 10, the first regions 11 and the second regions 12 are arranged at an irregular pitch. The absolute encoder 1 obtains absolute position data indicating the rotation angle of the scale 2 at the time of detection of light by the image sensor 4 by decoding the data extracted from the patterns of the first area 11 and the second area 12 .

  In the first embodiment, the encoded data represented by the arrangement of the first area 11 and the second area 12 further includes the data obtained by the encoding from the absolute position data to the pseudo random code. It is data obtained by performing encoding to Manchester code. One example of a pseudorandom code is an M-sequence code. Of the bit string which is data obtained by encoding to Manchester code, bit “1” is replaced with the first area 11. Of the bit string, bit “0” is replaced with the second area 12.

  In the image sensor 4, the first area 11 is detected as a bright portion having a light intensity higher than that of the second area 12. The second area 12 is detected as a dark portion having a light intensity lower than that of the first area 11. Since the reflectance of the second region 12 is lower than the reflectance of the first region 11, the second region 12 is detected by the image sensor 4 at a light intensity different from that of the first region 11. Each photodiode, which is a pixel of the image sensor 4, detects the light intensity of the image projected on the image sensor 4 by sharing for each unit area. In the following description, an axis parallel to the direction in which the pixels are arranged in the image sensor 4 will be referred to as an X axis. By the rotation of the scale 2, the image of the optical pattern 10 projected on the image sensor 4 is moved in the X axis direction by the image sensor 4.

  Next, the configuration of the angle calculation unit 13 will be described. FIG. 2 is a block diagram of the angle calculation unit 13 shown in FIG. The signal 36 from the image sensor 4 is input to the angle calculation unit 13. The angle calculation unit 13 includes an intensity distribution correction unit 31 that is a functional unit that corrects the intensity distribution of the signal 36, and an edge detection unit 32 that is a functional unit that detects an edge that is a switch between high and low of the signal level. Equipped with Further, the angle calculation unit 13 includes a rough data calculation unit 33 which is a functional unit that calculates rough data of absolute position data based on the detected edge. The rough data calculation unit 33 reads the data 38 of the rotation angle from the LUT 16 shown in FIG. Furthermore, the angle calculation unit 13 is a phase shift calculation unit 34 that is a functional unit that calculates a phase shift amount of a pattern of the intensity distribution of light detected by the image sensor 4 and a functional unit that calculates absolute position information. And a position calculation unit 35.

  FIG. 3 is a diagram showing an example of the intensity distribution of the signal 36 input to the angle calculation unit 13 shown in FIG. The signal 36 represents the intensity of light detected at each pixel of the image sensor 4. The vertical axis shown in FIG. 3 represents the intensity I of the signal 36. The horizontal axis represents the position of the image sensor 4 in the X-axis direction. In the following description, a value representing a position in the X-axis direction may be referred to as “X value”.

  A plurality of peaks appear in the distribution of intensity I of signal 36. Each peak represents the intensity of light from the first region 11. Also, the bottom between the peaks represents the intensity of light from the second region 12. The peak level and the bottom level of the signal 36 vary due to the influence of various factors. Such factors may include the influence of the intensity distribution of the light emitted from the light emitting element 3 and the influence of the variation in sensitivity of each pixel of the image sensor 4.

  FIG. 4 is a diagram showing an example of the intensity distribution of the signal 37 corrected by the intensity distribution correction unit 31 shown in FIG. The intensity distribution correction unit 31 makes the levels of the peaks of the signal 36 uniform and makes the levels of the bottoms uniform by correcting the signal 36 shown in FIG. 3. The level of the peak of the signal 37 after correction is fixed, and the level of the bottom is also fixed. Thereby, the intensity distribution correction unit 31 obtains the signal 37 in which the intensity I changes between the H level which is the peak and the L level which is the bottom. The intensity distribution correction unit 31 outputs a signal 37 to the edge detection unit 32 and the light source control unit 14 illustrated in FIG. 1. The correction method in the intensity distribution correction unit 31 is arbitrary as long as the level of the signal 36 can be corrected.

  The edge detection unit 32 obtains an X value when the intensity I is a threshold level 39 set in advance. The edge detection unit 32 detects an edge that is the boundary between the bright part and the dark part on the basis of the threshold level 39. The X value corresponding to the threshold level 39 represents the position of the edge on the image sensor 4.

  FIG. 5 is a diagram for explaining edge detection for the portion in the frame VII of FIG. The edge detection unit 32 is an X value representing the position of two pixels corresponding to I (i-1) and I (i) which are intensity I lower than the threshold level 39 and intensity I higher than the threshold level 39. (I-1) and X (i) are detected. The pixel of X (i-1) and the pixel of X (i) are two pixels adjacent to each other in the X-axis direction. It is sufficient if one of I (i-1) and I (i) is lower than the threshold level 39 and the other is higher than the threshold level 39, and I (i-1) and I (i) in detection by the edge detection unit 32. The magnitude with) is irrelevant.

  The edge detection unit 32 obtains an edge position 42 which is an X value corresponding to the threshold level 39 by sub-pixel processing using two X values X (i−1) and X (i). One example of subpixel processing is linear interpolation of two points, X (i-1) and X (i). The edge detection unit 32 may obtain the edge position 42 by linear interpolation of three or more points or a method other than linear interpolation. The edge detection unit 32 obtains the edge position 42 of each edge in the signal 37.

  The rough data calculation unit 33 compares I (i-1) and I (i) detected by the edge detection unit 32 to determine whether the edge is a rising edge or a falling edge. The rising edge is an edge at which the intensity I rises from the L level to the H level due to the increase of the X value. The falling edge is an edge at which the intensity I falls from the H level to the L level due to the increase of the X value. When I (i) is larger than I (i-1) and I (i-1) <I (i) holds, the rough data calculation unit 33 determines that the edge is a rising edge. If I (i) is smaller than I (i-1) and I (i-1)> I (i) holds, the rough data calculation unit 33 determines that the edge is a falling edge.

  Next, the rough data calculation unit 33 converts the signal 37 into a bit string based on the edge determination result. FIG. 6 is a diagram for explaining conversion from the signal 37 shown in FIG. 4 to the bit string 41. As shown in FIG. The coarse data calculation unit 33 replaces the rising edge of the signal 37 with bit "1" and the falling edge with bit "0". In addition, the rough data calculation unit 33 calculates an interval between the edges, and determines how many times each interval corresponds to a preset basic period 44.

  The coarse data calculation unit 33 replaces the portion where the rising edge and the falling edge are adjacent to each other at the same interval as the basic cycle 44, with a bit string of “1” and “0”. In addition, the rough data calculation unit 33 replaces the portion where the rising edge and the falling edge are adjacent to each other at an interval corresponding to twice the basic period 44, to a bit string of “1”, “1”, “0”. . The coarse data calculation unit 33 replaces the portions where the falling edge and the rising edge are adjacent to each other at an interval corresponding to twice the basic cycle 44, with bit strings of “0”, “0”, and “1”. Thereby, the rough data calculation unit 33 converts the optical pattern 10 projected on the image sensor 4 into the bit string 41.

  The coarse data calculation unit 33 refers to the LUT 16 and reads data 38 of the rotation angle corresponding to the obtained bit string 41 from the LUT 16. Thereby, the rough data calculation unit 33 calculates rough data which is data of the rotation angle before correction in the absolute position calculation unit 35. The coarse data calculation unit 33 may perform error correction of the bit string 41 using the redundant bits added to the bit string 41. The absolute encoder 1 may obtain redundant bits associated with the bit string 41 by expanding the field of view of the image sensor 4 more than the field of view for obtaining an image of a portion of the optical pattern 10 corresponding to the bit string 41.

  FIG. 7 is a diagram for explaining the calculation of the phase shift amount 43 in the phase shift calculation unit 34 shown in FIG. The rough data obtained by the rough data calculation unit 33 indicates a rotation angle based on the pixel at the center Xc in the X-axis direction among the plurality of pixels. The phase shift calculating unit 34 searches the edge detected by the edge detecting unit 32 for one edge position 42 closest to the center Xc, and the phase shift amount 43 between the edge position 42 and the center Xc is detected. Calculate The phase shift calculating unit 34 may calculate the phase shift amount 43 based on two or more edge positions 42 in addition to calculating the phase shift amount 43 based on one edge position 42. The phase shift calculating unit 34 may obtain the result of edge detection from the rough data calculating unit 33 in addition to obtaining the result from the edge detecting unit 32. In this case, the rough data calculation unit 33 outputs the result of edge detection obtained from the edge detection unit 32 to the phase shift calculation unit 34. The calculation of the phase shift amount 43 in the phase shift calculation unit 34 may be simultaneous with the calculation of the rough data in the rough data calculation unit 33 or may be after the calculation of the rough data.

  The absolute position calculation unit 35 calculates the rotation angle indicating the absolute position of the scale 2 by adding the phase shift amount 43 calculated by the phase shift calculation unit 34 to the rough data calculated by the rough data calculation unit 33. . The absolute position calculation unit 35 outputs absolute position data 40 indicating the calculated rotation angle.

  Next, the operation of the light amount adjustment by the light source control unit 14 will be described. The amount of light emitted from the light emitting element 3 may change due to changes in the environmental conditions at the measurement location. One example of a change in environmental conditions is a rise in temperature. The light amount of the light emitting element 3 may decrease due to the temperature increase at the measurement location. In this case, the intensity of light incident on the image sensor 4 from the optical pattern 10 is reduced, whereby the overall amplitude of the signal 36 shown in FIG. 3 is reduced. The reduction of the amplitude of the signal 36 also reduces the amplitude of the signal 37 shown in FIG. 4, which may lower the accuracy and resolution of the calculation of the rotation angle in the angle calculation unit 13. The light source control unit 14 adjusts the light amount of the light emitting element 3 based on the detection result of the light intensity by the image sensor 4 so that the light amount of the light emitting element 3 becomes constant regardless of the change of the environment.

  FIG. 8 is a diagram for explaining light amount adjustment by the light source control unit 14 shown in FIG. The left side of FIG. 8 shows an example of the intensity distribution of the signal 37 at the standard temperature. The right side of FIG. 8 shows an example of the intensity distribution of the signal 51 from the intensity distribution correction unit 31 when the temperature rises above the standard temperature. The amplitude of the signal 51 is reduced relative to the amplitude of the signal 37. The light source control unit 14 according to the first embodiment calculates the ratio of the maximum value 52 of the intensity I of the signal 37 to the maximum value 53 of the intensity I of the signal 51, and uses the ratio to drive the drive current value of the light emitting element 3 Adjust the

  FIG. 9 is a flowchart showing a procedure of light amount adjustment of the light source control unit 14 according to the first embodiment. The light source control unit 14 acquires, from the intensity distribution correction unit 31, the signal 51 that has been corrected by the intensity distribution correction unit 31. In step S1, the light source control unit 14 detects the maximum value 53 of the intensity I in the acquired signal 51.

  In step S2, the light source control unit 14 calculates the ratio between the maximum value 53 detected in step S1 and the maximum value 52 of the intensity I in the signal 37 at standard time. In step S3, the light source control unit 14 adjusts the drive current value of the light emitting element 3 based on the ratio calculated in step S2. The light source control unit 14 adjusts the drive current value so that the light amount of the light emitting element 3 becomes the same as that at standard time by multiplying the drive current value by the ratio.

  The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution by the light amount adjustment of the light source control unit 14 even if the environmental conditions of the measurement place change. The light source control unit 14 may obtain the signal before correction in the intensity distribution correction unit 31 and adjust the light amount based on the maximum value of the intensity I in the signal. In addition, when the temperature at the measurement place is lowered, the light source control unit 14 can adjust the drive current value so that the light amount of the light emitting element 3 decreases, contrary to the case where the temperature rises.

  The light source control unit 14 may adjust the light amount of the light emitting element 3 also when there is a change in environmental conditions other than the temperature of the measurement place or conditions other than the environmental conditions. One example of conditions other than environmental conditions is the positional relationship between the scale 2 and the image sensor 4. The positional relationship between the scale 2 and the image sensor 4 can be changed by vibration of the scale 2 or the image sensor 4. If the positional relationship between the scale 2 and the image sensor 4 changes due to a change in the distance between the scale 2 and the image sensor 4, the intensity of light detected by the image sensor 4 may decrease. In this case, the light source control unit 14 performs adjustment to increase the light amount of the light emitting element 3, whereby the absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution.

  Next, the setting of the width of the light emitter and the widths of the first region 11 and the second region 12 will be described. In the first embodiment, the light emitter is the LED chip of the light emitting element 3. The LED chip has an opening provided on the side from which light is emitted. In Embodiment 1, the width of the light emitter is the width of the opening. In one example, the opening is formed by patterning a metal material provided on the semiconductor material. A light transmissive material may be provided in the opening. One example of a light transmissive material is a transparent electrode material. Also in the case where the light transmitting material is provided in the opening, the width of the opening is equal to the width of the light emitter. In FIGS. 10 and 11 described below, the openings are not shown.

  FIG. 10 is a first schematic diagram showing how the light from the light emitter 20 reaches the image sensor 4 through the optical pattern 10 in the absolute encoder 1 shown in FIG. In FIG. 10, the light beam reflected by the reflection in the first area 11 is replaced with the light beam transmitted through the first area 11. In FIG. 10 and FIG. 11 described below, the first region 11 is described as transmitting light from the light emitter 20. Note that the description of FIGS. 10 and 11 is applicable to the case of reflecting light in the first area 11 by including the folding of the light in the first area 11.

  Further, in FIG. 10 and FIG. 11, the straight line indicating the image sensor 4 represents the position of the light receiving surface of the image sensor 4. The curve shown above the straight line indicates the intensity distribution of light detected by the image sensor 4.

  The distance 23 shown in FIG. 10 is a distance between the light emitter 20 and the optical pattern 10 in the direction of the chief ray 25 of the light emitted from the light emitter 20. The distance 24 is a distance between the optical pattern 10 and the light receiving surface of the image sensor 4 in the direction of the chief ray 25. The distance 23 and the distance 24 are the same. In the first embodiment, a point light source refers to including a light emitter 20 of a size that can be regarded as a point as compared to the distance 23 between the light emitter 20 and the optical pattern 10.

  The plurality of pixels of the image sensor 4 are arranged in the X-axis direction. The chief ray 25 is perpendicular to the X axis. Here, in the X-axis direction, the direction of the arrow is the plus X direction, and the direction opposite to the arrow is the minus X direction. The width of the first region 11, the width of the second region 12, and the width of the light emitter 20 all refer to the width in the X-axis direction. The width of one first region 11 and the width of one second region 12 are unit widths of the optical pattern 10. The unit width of the optical pattern 10 is a width which is a unit of arrangement of the first region 11 and the second region 12.

  In the example shown in FIG. 10, the width 26 of the light emitter 20 is assumed to be the same as the unit width of the optical pattern 10. Further, FIG. 10 shows a portion of the optical pattern 10 in which first regions 11 and second regions 12 each having a unit width are alternately arranged. The two first regions 11 a and 11 b are the first regions 11 adjacent to each other with one second region 12 interposed therebetween. The light beam 21 is a light beam emitted from the end in the negative X direction of the light emitter 20 and incident on the end in the positive X direction of the first region 11 a. The light beam 22 is a light beam emitted from the end in the positive X direction of the light emitter 20 and incident on the end in the negative X direction of the first region 11 b.

  The light beam 21 and the light beam 22 are parallel to each other. Since the light ray 21 and the light ray 22 do not intersect with each other, the image sensor 4 can separate and detect the light from the first area 11 a and the light from the first area 11 b. Thereby, the image sensor 4 can detect the first area 11 and the second area 12 with high resolution by using the light emitter 20 having the same width 26 as the unit width of the optical pattern 10.

  FIG. 11 is a second schematic diagram showing how the light from the light emitter 20 passes through the optical pattern 10 and reaches the image sensor 4 in the absolute encoder 1 shown in FIG. FIG. 11 shows a portion of the optical pattern 10 including two continuously arranged first regions 11. In the example shown in FIG. 11, the width 26 of the light emitter 20 corresponds to twice the unit width of the optical pattern 10.

  The area 11 c is an area in which two first areas 11 of unit width are continuously arranged. The width of the region 11 c is the same as the width 26 of the light emitter 20. The first region 11 d is a first region 11 adjacent to the region 11 c with one second region 12 interposed therebetween.

  The light beam 27 is a light beam emitted from the end of the light emitter 20 in the negative X direction and incident on the end in the positive X direction of the region 11 c. The light beam 28 is a light beam emitted from the end in the positive X direction of the light emitter 20 and incident on the end in the negative X direction of the first region 11 d. The light rays 27 and 28 are not parallel to each other, but intersect each other on the light receiving surface of the image sensor 4. The image sensor 4 can detect the light of the area 11c and the light of the first area 11d separately from each other. Thus, the image sensor 4 can detect the first area 11 and the second area 12 with high resolution, using the light emitters 20 having the width 26 corresponding to twice the bit width.

  Temporarily, it is assumed that the width 26 of the light-emitting body 20 is expanded from the width of the area | region 11c from the state shown in FIG. In this case, the light ray 27 and the light ray 28 cross each other in front of the light receiving surface of the image sensor 4. In this case, in the image sensor 4, the light from the area 11c and the light from the first area 11d are detected without being separated from each other. In this case, it is difficult for the image sensor 4 to detect the first area 11 and the second area 12 with high resolution.

  In the first embodiment, the width 26 of the light emitter 20 is equal to or less than the maximum width of the portion of the optical pattern 10 in which the first regions 11 are continuously arranged. Further, the width 26 of the light emitter 20 is equal to or less than the maximum width of the portion of the optical pattern 10 in which the second regions 12 are continuously arranged. As a result, the image sensor 4 can separately detect the light from each of the first regions 11 and the light from each of the portions where the first regions 11 are continuously disposed, so The pattern 10 can be detected with high resolution. The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution.

  Next, encoding of data to be replaced by the optical pattern 10 will be described. FIG. 12 is a diagram for explaining data to be replaced with the optical pattern 10 shown in FIG. The bit string 55 is a bit string obtained by encoding absolute position data into a pseudorandom code. The bit string 56 is a bit string obtained by encoding the bit string 55, which is a pseudo random code, into a Manchester code.

  When the number of positions to which absolute position data is assigned is increased in order to improve the accuracy and resolution of measurement by the absolute encoder 1, the number of bits of the pseudorandom code also increases. As the number of bits of the bit string 55 increases, the frequency of the portion in which the bit “0” is continuous and the portion in which the bit “1” is continuous in the bit string 55 is increased. In one example, the rotation angle of the scale 2 causes the width of the portion where the plurality of first regions 11 representing the bit “1” are continuously disposed and the single first region 11 to be independently disposed. And the width of the part that is In this case, a difference may occur in the intensity of light detected by the image sensor 4 between the portion of the plurality of first regions 11 and the portion of one first region 11 due to the diffractive action of light. Since the intensity of light detected by the image sensor 4 varies depending on the rotation angle of the scale 2, the accuracy and resolution of the calculation of the rotation angle in the angle calculation unit 13 may be reduced.

  By encoding into Manchester code, the signal of bit “0” in the data before encoding is replaced with a signal transitioning from L level to H level. Also, the signal of bit "1" in the data before encoding is replaced with a signal that transitions from H level to L level. Thereby, bit "0" of bit string 55 which is a pseudorandom code is replaced with bit "01" in bit string 56 which is a Manchester code. Bit "1" of bit string 55 which is a pseudorandom code is replaced with bit "10" in bit string 56 which is a Manchester code.

  In the example shown in FIG. 12, the portion where three bits “1” are continuous in the bit string 55 is eliminated by being replaced with the bit “10” in the bit string 56. Thus, encoding into Manchester code eliminates three or more consecutive bits "0" and three or more consecutive bits "1". Also, the portion where bit "0" and bit "1" are continuous in bit string 55 is replaced with bit "0110" in bit string 56, resulting in a portion where two bits "1" are continuous in bit string 56. ing. A portion in which bit "1" and bit "0" in bit string 55 are continuous is replaced with bit "1001" in bit string 56, so that a portion in which two bits "0" are continuous is generated in bit string 56. . Thus, by encoding into Manchester code, the maximum number of consecutive bits "0" and the maximum number of consecutive bits "1" can both be two.

  The first area 11 and the second area 12 of the optical pattern 10 are arranged according to the bit string 56. The maximum width of the portion of the optical pattern 10 in which the first regions 11 are continuously arranged and the maximum width of the portion in which the second regions 12 are continuously arranged are the unit width of the optical pattern 10 Is twice as much. Since the maximum width is suppressed to twice the unit width, the absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution.

  Here, an advantage of the absolute encoder 1 in comparison with the incremental encoder will be described. In the case of an incremental encoder, the number of detected pulse signals is integrated to determine the rotation angle of the scale 2. In order to detect the rotation angle with respect to the origin, the home return operation is performed every measurement. Home position return means returning the rotation angle of the scale 2 to the home position. The absolute encoder 1 is capable of detecting the absolute position, so the operation of home return is unnecessary. For this reason, the absolute encoder 1 has an advantage that the time until the measurement is started can be shortened.

  All or any part of the functions of the control unit 5 shown in FIG. 1 may be executed on a CPU (Central Processing Unit) or a microcomputer. All or any part of the functions of the control unit 5 may be executed on a program analyzed and executed by a CPU or a microcomputer. Alternatively, all or any part of the functions of the control unit 5 may be implemented on wired logic hardware.

  FIG. 13 is a diagram showing an example of a hardware configuration of the absolute encoder 1 that executes the function of the control unit 5 shown in FIG. The absolute encoder 1 includes a communication unit 81 which is a communication interface, a CPU 82 which executes various processes, and an input / output unit 83 which is an input / output interface between the light emitting element 3 and the image sensor 4 shown in FIG. The absolute encoder 1 further includes a random access memory (RAM) 84 including a program storage area and a data storage area, and a read only memory (ROM) 85 which is a non-volatile memory. The bus 86 connects the communication unit 81, the CPU 82, the input / output unit 83, the RAM 84, and the ROM 85.

  The communication unit 81 transmits the data of the rotation angle which is the calculation result of the angle calculation unit 13 to the outside. The ROM 85 stores programs for various processes. The program may be recorded on a recording medium readable by a drive other than the ROM 85. The recording medium may be any of a portable recording medium, such as a CD-ROM, a DVD disk or a USB memory, or a flash memory, which is a semiconductor memory. The illustration of the drive and the recording medium is omitted in FIG.

  The program is loaded into the RAM 84. The CPU 82 develops a program in a program storage area in the RAM 84 and executes various processes. The data storage area in the RAM 84 is a work area in the execution of various processes. The functions of the angle calculation unit 13, the light source control unit 14 and the sensor control unit 17 are realized using the CPU 82. The LUT 16 shown in FIG. 1 is stored in the RAM 84. The function of the storage unit 15 is realized using the RAM 84.

  According to the first embodiment, the absolute encoder 1 has any of the width of the portion where the first regions 11 are continuously arranged and the width of the portion where the second regions 12 are continuously arranged. Also, by reducing the width of the light emitter 20, the first region 11 and the second region 12 can be detected with high resolution. Further, the data encoded into the bit string of the Manchester code is replaced with the first area 11 and the second area 12 so that the maximum width of the portion where the first areas 11 are continuously arranged and The maximum width of the portion where the second regions 12 are continuously arranged is suppressed to twice the unit width of the optical pattern 10. The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution. Furthermore, the absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution by adjusting the light amount of the light emitting element 3 by the light source control unit 14 which is a light amount adjusting unit. As described above, the absolute encoder 1 has an effect of being able to measure the rotation angle of the measurement object with high accuracy and high resolution.

Second Embodiment
FIG. 14 is a diagram for explaining light amount adjustment by the light source control unit 14 of the absolute encoder 1 according to the second embodiment. In the second embodiment, the light source control unit 14 serving as the light amount adjustment unit performs the light amount adjustment using the average values 63 and 64 instead of the maximum values 52 and 53 shown in FIG. The same parts as those of the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

  The left side of FIG. 14 shows an example of the intensity distribution of the signal 37 at the standard temperature. The right side of FIG. 14 shows an example of the intensity distribution of the signal 61 from the intensity distribution correction unit 31 when the temperature rises above the standard temperature. The amplitude of the signal 61 is reduced relative to the amplitude of the signal 37. Also, noise 62 having a level higher than the H level of the signal 61 is generated in the signal 61. The light source control unit 14 of the second embodiment calculates a ratio of the average value 63 of the intensity I of the signal 37 to the average value 64 of the intensity I of the signal 61, and uses the ratio to drive the drive current value of the light emitting element 3 Adjust the

  The first area 11 and the second area 12 of the optical pattern 10 are arranged in accordance with a bit string 56 which is a Manchester code shown in FIG. In the image detected by the image sensor 4, the number of the first regions 11 corresponding to the bit "1" and the number of the second regions 12 corresponding to the bit "0" are identical to each other or one It will be a difference of degree. Therefore, the average value 63 calculated from the standard time signal 37 can be regarded as constant regardless of the rotation angle. Therefore, the light source control unit 14 can perform adjustment to make the light amount of the light emitting element 3 constant based on the ratio of the average value 63 and the average value 64.

  FIG. 15 is a flowchart showing the procedure of light amount adjustment of the light source control unit 14 according to the second embodiment. The light source control unit 14 acquires from the intensity distribution correction unit 31 the signal 61 that has been subjected to the correction in the intensity distribution correction unit 31. In step S11, the light source control unit 14 detects the average value 64 of the intensities I in the acquired signal 61.

  In step S12, the light source control unit 14 calculates the ratio of the average value 64 detected in step S11 and the average value 63 of the intensity I in the signal 37 at the standard time. In step S13, the light source control unit 14 adjusts the drive current value of the light emitting element 3 based on the ratio calculated in step S12. The light source control unit 14 adjusts the drive current value so that the light amount of the light emitting element 3 becomes the same as that at standard time by multiplying the drive current value by the ratio. The light source control unit 14 can reduce the influence of the noise 62 in the light amount adjustment by performing the light amount adjustment using the average values 63 and 64.

  The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution by the light amount adjustment of the light source control unit 14 even if the environmental conditions of the measurement place change. As in the first embodiment, the light source control unit 14 may adjust the light amount based on the average value of the intensity I in the signal 36 before correction in the intensity distribution correction unit 31. The light source control unit 14 may adjust the light amount of the light emitting element 3 also when there is a change in environmental conditions other than the temperature of the measurement place or conditions other than the environmental conditions.

  According to the second embodiment, the absolute encoder 1 adjusts the light amount of the light emitting element 3 using the average values 63 and 64 by the light source control unit 14 which is the light amount adjusting unit. The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution. As described above, the absolute encoder 1 has an effect of being able to measure the rotation angle of the measurement object with high accuracy and high resolution.

Third Embodiment
FIG. 16 is a diagram for explaining light amount adjustment by the light source control unit 14 of the absolute encoder 1 according to the third embodiment. In the third embodiment, the light source control unit 14, which is the light amount adjustment unit, replaces the average values 63 and 64 shown in FIG. 14 and averages the maximum values 74A, 74B and 74C and the average of the maximum values 75A, 75B and 75C. Adjust the light amount using the value. The same parts as those of the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

  The left side of FIG. 16 shows an example of the intensity distribution of the signal 37 at a standard temperature. The right side of FIG. 16 shows an example of the intensity distribution of the signal 71 from the intensity distribution correction unit 31 when the temperature rises above the standard temperature. The amplitude of signal 71 is reduced relative to the amplitude of signal 37. Further, in the signal 71, a portion 73 where a peak is missing is generated. One example of a factor causing such a peak loss is that light is blocked by foreign matter that has entered the optical path between the optical pattern 10 and the image sensor 4.

  The light source control unit 14 according to the third embodiment divides the image sensor 4 into three areas 72A, 72B and 72C in the X-axis direction, and calculates the maximum values 75A, 75B and 75C of the signal 71 in each area 72A, 72B and 72C. calculate. Further, the light source control unit 14 calculates the maximum values 74A, 74B, and 74C of the signal 37 in the respective regions 72A, 72B, and 72C. The light source control unit 14 calculates the ratio of the average value of the maximum values 74A, 74B and 74C of the signal 37 to the average value of the maximum values 75A, 75B and 75C of the signal 71, and uses the ratio. Adjust the drive current value.

  FIG. 17 is a flowchart showing a procedure of light amount adjustment of the light source control unit 14 in the third embodiment. The light source control unit 14 acquires from the intensity distribution correction unit 31 the signal 71 that has been subjected to the correction by the intensity distribution correction unit 31. In step S21, the light source control unit 14 detects the maximum values 75A, 75B, and 75C of the intensity I in each of the areas 72A, 72B, and 72C from the acquired signal 71. In step S22, the light source control unit 14 calculates an average value of the maximum values 75A, 75B, and 75C detected in step S21.

  In step S23, the light source control unit 14 calculates the ratio between the average value calculated in step S22 and the average value of the maximum values 74A, 74B, and 74C in the signal 37 at the standard time. In step S24, the light source control unit 14 adjusts the drive current value of the light emitting element 3 based on the ratio calculated in step S23. The light source control unit 14 adjusts the drive current value so that the light amount of the light emitting element 3 becomes the same as that at standard time by multiplying the drive current value by the ratio. The light source control unit 14 adjusts the light amount using the average value of the maximum values 74A, 74B and 74C and the average value of the maximum values 75A, 75B and 75C in each of the areas 72A, 72B and 72C, thereby the image sensor 4 As compared with the case of using the average value of the entire intensity I, the influence of the dropout portion 73 in the light amount adjustment can be reduced.

  The light source control unit 14 is not limited to one that divides the image sensor 4 into three regions 72A, 72B, and 72C and detects the maximum values 75A, 75B, and 75C. The number of regions may be two, or four or more.

  The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution by the light amount adjustment of the light source control unit 14 even if the environmental conditions of the measurement place change. As in the first and second embodiments, the light source control unit 14 may adjust the amount of light based on the average value of the intensity I in the signal before correction in the intensity distribution correction unit 31. The light source control unit 14 may adjust the light amount of the light emitting element 3 also when there is a change in environmental conditions other than the temperature of the measurement place or conditions other than the environmental conditions.

  According to the third embodiment, the absolute encoder 1 uses the light source control unit 14 as the light amount adjustment unit to set the average value of the maximum values 74A, 74B and 74C and the maximum values 75A, 75B and 75C for each of the areas 72A, 72B and 72C. The light amount of the light emitting element 3 is adjusted using the average value. The absolute encoder 1 can obtain the rotation angle of the scale 2 with high accuracy and high resolution. As described above, the absolute encoder 1 has an effect of being able to measure the rotation angle of the measurement object with high accuracy and high resolution.

  The absolute encoders 1 of Embodiments 1 to 3 may be linear encoders instead of the rotary encoders. An absolute encoder 1 which is a linear encoder measures the position of a measurement object which operates in a linear direction. In this case, in the absolute encoder 1, unique absolute position data is assigned to each absolute position of the scale 2 in the linear direction. The absolute encoder 1 obtains the position of the scale 2 in the linear direction by decoding the detection result of the optical pattern 10 in the image sensor 4. The absolute encoder 1 which is a linear encoder can measure the position of a measurement object with high accuracy and high resolution.

  The configuration shown in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and one of the configurations is possible within the scope of the present invention. Parts can be omitted or changed.

  Reference Signs List 1 absolute encoder, 2 scale, 3 light emitting element, 4 image sensor, 5 control unit, 6 shaft, 10 optical pattern, 11, 11a, 11b, 11d first area, 11c, 72A, 72B, 72C area, 12 second Area, 13 angle calculation unit, 14 light source control unit, 15 storage unit, 16 LUT, 17 sensor control unit, 20 light emitters, 21, 22, 27, 28 rays, 23, 24 distances, 25 chief rays, 26 widths, 31 intensity distribution correction unit, 32 edge detection unit, 33 coarse data calculation unit, 34 phase shift calculation unit, 35 absolute position calculation unit, 36, 37, 51, 61, 71 signals, 38 rotation angle data, 39 threshold level, 40 absolute position data, 42 edge positions, 43 phase shift amounts, 44 basic periods, 52, 53, 74 A, 74 B, 74 C, 75A, 75B, 75C maximum value, 62 noise, 63, 64 average value, 55, 56-bit string, 81 communication unit, 82 CPU, 83 input / output unit, 84 RAM, 85 ROM, 86 bus.

In order to solve the problems described above and achieve the object, the absolute encoder of the present invention is provided with an optical pattern, a movable scale, a light emitter for emitting light to be advanced to the optical pattern, and an optical pattern And a sensor for outputting a signal representing the intensity of the detected light, and an operation unit for obtaining the position of the scale based on the signal from the sensor. In the optical pattern, data encoded from unique data assigned to each possible position of the scale is different from the first area having the same width as the unit width of the optical pattern and the first area in the sensor It is made detectable by light intensity and replaced with an arrangement with a second region of the same width as the unit width of the optical pattern . The width of the light emitter is smaller than the width of the portion in which the first regions are continuously arranged and the width of the portion in which the second regions are continuously arranged.

Claims (9)

A movable scale provided with an optical pattern,
A light emitter for emitting light to be advanced to the optical pattern;
A sensor that detects light from the optical pattern and outputs a signal representing the intensity of the detected light;
An arithmetic unit for determining the position of the scale based on the signal from the sensor;
In the optical pattern, data encoded from unique data assigned to each possible position of the scale can be detected at a first region and at a light intensity different from the first region by the sensor Is replaced with an array with the second region
The width of the light emitter is smaller than both the width of the portion in which the first regions are continuously arranged and the width of the portion in which the second regions are continuously arranged. Absolute encoder to be.   The maximum width of the portion where the first regions are continuously arranged and the maximum width of the portion where the second regions are continuously arranged are the first region and the second region. The absolute encoder according to claim 1, characterized in that it is twice the unit width of the arrangement of.   The absolute encoder according to claim 1 or 2, wherein the encoded data is a bit string of Manchester code.   The encoded data is characterized in that it is a bit string obtained by further coding the Manchester code to the bit string obtained by the coding of the unique data to a pseudo-random code. The absolute encoder according to claim 3. The scale is rotatable.
The absolute encoder according to any one of claims 1 to 4, wherein the calculation unit obtains a rotation angle which is a position of the scale.   The absolute encoder according to any one of claims 1 to 5, further comprising a light amount adjustment unit configured to adjust a light amount of the light emitter based on a detection result of light intensity by the sensor.   The light amount adjustment unit adjusts the light amount of the light emitter based on a ratio of the maximum value of the intensity of the signal from the sensor to the maximum value of the intensity of a standard signal. Absolute encoder as described in.   The light amount adjusting unit adjusts the light amount of the light emitter based on a ratio of an average value of intensities in the signal from the sensor and an average value of intensities in a standard signal. Absolute encoder as described in.   The light amount adjustment unit is configured to adjust the light amount based on a ratio of an average value of the maximum values of the signals in each area of the sensor to an average value of the maximum values of intensities in the areas of the standard signal. 7. The absolute encoder according to claim 6, wherein the amount of light is adjusted.

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