JP2017096711A - Rotary encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotary encoder that can stably obtain a light reception signal without reducing productivity, using an interference effect due to diffraction of light.SOLUTION: A rotary encoder comprises: a light source device that includes a light emitting diode radiating light, and a lens collimating the light of the light emitting diode; a rotary slit plate that includes a first slit forming a diffraction grating in a circumferential direction radially from a center; a stationary slit that includes a second slit forming the diffraction grating in the circumferential direction radially from the center; and light reception unit that receives the light passing through the first and second slits and coming from the light source. A distance between the rotary slit plate and the stationary slit plate is a distance where the light passing through the first slit or second slit interferes due to diffraction, and a slit image is formed on the rotary slit plate or stationary slit plate, and a light emitting diameter of the light emitting diode is configured to be greater than six times, and less than 13 times an interval among the first slits or the second slits.SELECTED DRAWING: Figure 1

Description

  The present invention relates to, for example, a rotary encoder using a light source as an LED.

  As a rotary encoder that has high resolution, is easy to manufacture, and can be used even in high temperature environments, LEDs are used as the light source of the light source device, and the slit pitch and slit width of the fixed slit plate and rotary slit plate are made as small as possible. There is one in which the emission diameter of the LED is 6 times or less the slit pitch (see, for example, Patent Document 1).

JP 2008-1111843 A

  By the way, when the slit pitch and the slit width are set to a certain value, for example, smaller than 10 μm, the light passing through the fixed slit spreads due to the diffraction phenomenon, the light contrast is lowered, and a sufficient light reception signal can be obtained. Disappear. Therefore, there is a method of increasing the resolution of the received light signal obtained by the slit pitch and slit width, which does not decrease the light contrast due to the light diffraction phenomenon, by electric multiplication, but an electrical error occurs and the output is reduced. The accuracy of certain pulse signals may be reduced.

In order to obtain a good light reception signal, it is necessary to narrow the gap between the rotating slit plate and the fixed slit plate. However, when the gap between the fixed slit plate and the rotary slit plate is narrowed, the gap between the fixed slit plate and the rotary slit plate has a tolerance Δg in the production of the rotary encoder. If the value is reduced, the productivity will be significantly reduced.
When the interference effect is ideal, the received light signal has a good S / N ratio at a specific gap between the fixed slit plate and the rotating slit plate, but the more ideal the interference effect is, the gap In the range of the assembly tolerance Δg including the difference in S / N ratio, there is a problem that the received light signal is not stable.

  The present invention has been made to solve the above-described problems, and provides a rotary encoder that can obtain a stable received light signal without reducing productivity by using an interference effect due to diffraction of light. For the purpose.

  A rotary encoder according to the present invention includes a light source device having a light emitting diode that emits light and a lens that collimates the light of the light emitting diode, and a first slit that forms a diffraction grating radially from the center in the circumferential direction. A rotating slit plate, a fixed slit plate having a second slit that forms a diffraction grating in the circumferential direction radially from the center, and a light receiving unit that receives light from the light source device that has passed through the first and second slits. The distance between the rotating slit plate and the fixed slit plate is the distance at which the light passing through the first slit or the second slit interferes by diffraction and a slit image is formed on the rotating slit plate or the fixed slit plate. In other words, the light emitting diameter of the light emitting diode is set to be larger than 6 times and not larger than 13 times the interval between the first slits or the second slits.

  According to the present invention, the light passing through the first slit or the second slit interferes with the distance between the rotary slit plate and the fixed slit plate by diffraction, and a slit image is formed on the rotary slit plate or the fixed slit plate. The distance formed is set so that the light emitting diameter of the light emitting diode is larger than 6 times and not larger than 13 times the interval between the first slits or the second slits. As a result, a stable light receiving signal can be obtained within the tolerance Δg, so that the productivity of the rotary encoder is not lowered.

1 is a perspective view showing a schematic configuration of a rotary encoder according to Embodiment 1 of the present invention. Sectional drawing which shows schematic structure of the light source device used for the rotary encoder of FIG. The curve figure of the received light signal which shows the correlation with the gap between the rotation slit board in a red LED, and a fixed slit board, and S / N ratio. The fragmentary sectional view which shows the example of mounting of the rotary encoder which concerns on Embodiment 2 of this invention. The perspective view which shows schematic structure of the rotary encoder of FIG. FIG. 6 is a waveform diagram showing an example of the output of the rotary encoder in FIG. 5. The curve figure of the received light signal which does not utilize the interference effect which shows the correlation with the gap between the rotation slit board in a red LED, and a fixed slit board, and the amount of received light.

Embodiment 1 FIG.
1 is a perspective view showing a schematic configuration of a rotary encoder according to Embodiment 1 of the present invention, FIG. 2 is a sectional view showing a schematic configuration of a light source device used in the rotary encoder of FIG. 1, and FIG. 3 is a rotary slit in a red LED. It is a curve figure of the received light signal which shows the correlation with the gap between a board and a fixed slit board, and S / N ratio.
As shown in FIG. 1, the rotary encoder according to the first embodiment includes a light source device 10, a rotary slit plate 20 formed in a circular shape, a fixed slit plate 30 formed in a quadrangular shape, and a photodiode, for example. The light receiving part 40 comprised by these is provided. The rotary slit plate 20 and the fixed slit plate 30 have slits 21 and 31 (first slit and second slit) that form a diffraction grating radially from the center and in the circumferential direction. The shapes or materials of the rotary slit plate 20 and the fixed slit plate 30 are not limited.

  As shown in FIG. 2, the light source device 10 includes, for example, a lens support portion 11 formed in a cylindrical shape, a lens 12 fitted and supported in the lens support portion 11, and an axis of the lens support portion 11. For example, a red LED chip 13 (light emitting diode) arranged and a chip support portion 14 that supports the red LED chip 13 are provided. The lens 12 irradiates red light emitted from the red LED chip 13 with parallel light having parallelism with the optical axis X of the red LED chip 13. Note that although the red LED chip 13 is used as the light source of the light source device 10, an infrared LED chip that emits infrared light may be used as the light source instead.

  The red LED chip 13 has a light emission diameter D that is greater than 6 times and less than or equal to 13 times the slit pitch P of the rotary slit plate 20 and the fixed slit plate 30, for example, 10 μm. The red LED chip 13 is electrically connected to a lead wire (not shown), and emits red light having a wavelength of 610 nm to 750 nm at the time of lighting.

  The rotary slit plate 20 is rotatably mounted on the object to be measured, and slits 21 are provided radially from the center and at equal intervals (slit pitch P) in the circumferential direction. The fixed slit plate 30 is fixed, and slits 31 are provided at the same interval (slit pitch P) as the slits 21 of the rotary slit plate 20. That is, the slits 21 and 31 of the rotary slit plate 20 and the fixed slit plate 30 have the same slit pitch P and the same slit width. The slit width of the fixed slit plate 30 may be narrower or wider than the slit width of the rotary slit plate 20.

The gap G between the rotary slit plate 20 and the fixed slit plate 30 is such that the wavelength of red light is λ, and the natural number is n (1, 2, 3,...)
G = nP ² / λ (1)
It is set to be a relationship. That is, the distance G between the rotary slit plate 20 and the fixed slit plate 30 is a distance at which the light that has passed through the slit 21 interferes by diffraction and a slit image is formed on the fixed slit plate 30.

  In the above-described prior art (Patent Document 1), in order to obtain an interference effect (Talbot effect) due to light diffraction satisfactorily, the slit width is ½ of the slit pitch P (10 μm), and the LED emission diameter is slit. The diameter is smaller than 6 times the pitch P, and the wavelength λ is increased to 860 nm, for example. As shown in FIG. 3, the ideal interference effect according to this prior art can obtain a light reception signal c having a good S / N ratio within a specific range G of the gap G between the rotary slit plate and the fixed slit plate. Since the interference effect is ideal, the light reception signal c in the range of the assembly tolerance Δg including the gap G has a large S / N ratio difference, and the pulse signal obtained from the light reception signal c is not stable.

  On the other hand, in the first embodiment, as described above, the emission diameter D of the red LED chip 13 is larger than 6 times the slit pitch P (10 μm) and less than 13 times, and the wavelength λ is from 610 nm to 610 nm. The range of 750 nm is used, and the interference effect due to light diffraction is used.

  That is, the emission diameter D of the red LED chip 13 is made larger than before, and the wavelength λ is made shorter than before to suppress the interference effect. As a result, as shown in FIG. 3, in the specific gap G range b between the rotary slit plate 20 and the fixed slit plate 30, the received light signal d secures a minimum required S / N ratio and S / N. The fluctuation of the ratio can be kept small. By suppressing the fluctuation of the S / N ratio of the light reception signal d, the gap b can be widened. Note that a line a shown in FIG. 3 is a lower limit value of the S / N ratio of the received light signal d that can be used as a rotary encoder.

  As described above, according to the first embodiment, the emission diameter D of the red LED chip 13 is set to be larger than 6 times the slit pitch P (10 μm) and not more than 13 times, and the wavelength λ is in the range of 610 nm to 750 nm.

  With this configuration, in the specific gap G range b between the rotary slit plate 20 and the fixed slit plate 30, the minimum required S / N ratio fluctuation of the received light signal d can be suppressed, and the gap G range b Can be taken widely. Thereby, it is not necessary to increase the resolution of the received light signal generated by the light receiving unit 40 by electrical multiplication.

  Since the range b of the gap G can be widened, it is not necessary to reduce the tolerance Δg, and it is possible to provide a miniaturized and high-resolution rotary encoder that uses the interference effect without reducing the productivity of the rotary encoder.

  Furthermore, since the red LED chip 13 having a large emission diameter D is used as the light source of the light source device 10, it is possible to secure a light emission amount as compared with an LED having a smaller emission diameter than the red LED chip 13. Further, as described above, since the light source device 10 includes the red LED chip 13 having a large light emission diameter D, the light source device 10 can be used in a rotary encoder that does not use the interference effect, and the light source device 10 can be shared.

Embodiment 2. FIG.
4 is a partial cross-sectional view showing a mounting example of a rotary encoder according to Embodiment 2 of the present invention, FIG. 5 is a perspective view showing a schematic configuration of the rotary encoder of FIG. 4, and FIG. 6 is an output of the rotary encoder of FIG. FIG. 7 is a waveform diagram of a received light signal that does not use the interference effect and shows the correlation between the gap between the rotating slit plate and the fixed slit plate in the red LED and the amount of received light. In the second embodiment, the same reference numerals are used for the same or corresponding parts as in the first embodiment.

  The rotary encoder according to the second embodiment is coupled to a motor shaft 60, for example. As shown in FIG. 4, the rotary encoder includes an encoder shaft 50 coupled to a motor shaft 60, a shaft support portion 51 that rotatably supports the encoder shaft 50, and a circuit board attached to the shaft support portion 51. 52, the light source device 10 mounted on the surface of the shaft support 51 that faces the circuit board 52, the rotary slit plate 20 mounted on the end of the encoder shaft 50, and a distance L3 from the rotary slit plate 20. The fixed slit plate 30 is disposed and fixed to the support part 53 protruding from the circuit board 52, and the light receiving part 40 installed in the recess of the support part 53 and mounted on the circuit board 52. Although the red LED chip 13 is used as the light source of the light source device 10, an infrared LED chip may be used as the light source instead.

  L3 is a distance within an allowable range in which the tolerance Δg is included in the gap G calculated by the above equation (1), and is obtained from the difference of L2−L1. L1 is a tolerance Δg1, and L2 is a dimension within an allowable range including the tolerance Δg2. That is, the value obtained from the difference between L2 and L1 is set to be the distance L3.

  As in the first embodiment, the light source device 10 in the second embodiment emits red light having a light emission diameter D that is greater than six times the slit pitch P (10 μm) and less than or equal to 13 times and a wavelength of 610 nm to 750 nm. A red LED chip 13 is provided as a light source. As shown in FIG. 5, the rotary slit plate 20 has the same center, a track A on the outer peripheral side, a track C on the inner peripheral side, and a track B between the tracks A and C.

  On the tracks A and B, for example, A-phase and B-phase slits 21 (first slits) that are 90 ° out of phase with each other are provided at equal intervals in the circumferential direction. In this case, the A-phase slits 21 are arranged so that the phase advances by 90 ° with respect to the B-phase slits 21. Each of the A-phase and B-phase slits 21 has a narrow slit width in order to use the interference effect due to light diffraction, as in the first embodiment. Although the phase difference between the A-phase and B-phase slits 21 is 90 °, the phase difference is not limited to this and may be other than 90 °.

  On the track C, C-phase slits 22 (third slits) having a slit width larger than the A-phase and B-phase slits 21 are provided radially from the center and in the circumferential direction. That is, the slit width of the slit 22 is a size that does not use the interference effect. The number of C-phase slits 22 is the same as the number of magnetic poles of the motor, for example. This is so that the same number of outputs as the magnetic poles can be obtained every time the motor rotates once, and each magnetic pole can be detected. Thereby, the electric current sent through the coil of a motor can be controlled appropriately. The provision of the C-phase slits 22 on the rotating slit plate 20 is an example, and the number of slits 22 and the slit width differ depending on the use and specifications of the object to be measured. Further, the rotary slit plate 20 is provided with one Z-phase slit 23 serving as an origin of one rotation of the motor.

  The fixed slit plate 30 is disposed opposite to the A-phase and B-phase slits 31 (second slit) and the C-phase slit 22 disposed to face the A-phase and B-phase slits 21. A C-phase slit 32 (fourth slit) and a Z-phase slit 33 arranged to face the Z-phase slit 23 are provided. The light receiving unit 40 includes A phase and B phase light receiving units 41 and 42, a C phase light receiving unit 43, and a Z phase light receiving unit 44. These light receiving portions 41 to 44 are configured by photodiodes, for example, as in the first embodiment.

  In the rotary encoder configured as described above, when the encoder shaft 50 is rotated by the rotation of the shaft 60 of the motor, the rotary slit plate 20 rotates in the same direction as the rotation direction of the encoder shaft 50. When the rotation of the rotary slit plate 20 causes the A-phase and B-phase slits 21 of the rotary slit plate 20 and the A-phase and B-phase slits 31 of the fixed slit plate 30 to overlap, respectively, from the light source device 10. Red light passes through and is received by the A-phase and B-phase light receiving portions 41 and 42. In this case, a slit image (light stripe pattern) obtained by interference of a large number of diffracted lights that have passed through the respective slits 21 is received by the A-phase and B-phase light receiving units 41 and 42. The A-phase and B-phase light receiving units 41 and 42 generate a light reception signal d based on the amount of received light. As shown in FIG. 7, the light reception signal d has a minimum required S / N ratio in a specific range G of the gap G between the rotary slit plate 20 and the fixed slit plate 30.

The A-phase and B-phase light receiving units 41 and 42 shape the waveform based on the received light signals, respectively, and input the pulse signals shown in (1) and (2) of FIG. In this case, an A-phase pulse signal is output from the A-phase light receiving unit 41, and a B-phase pulse signal whose phase is delayed by 90 ° with respect to the A-phase pulse is output from the B-phase light receiving unit 42. With these two pulse signals, the rotational direction of the motor is detected, and the rotational position and rotational speed of the motor can be measured.
The A-phase and B-phase light receiving units 41 and 42 generate a light reception signal based on the amount of received light, and shape a waveform based on the generated light reception signal to generate a pulse signal. However, the present invention is not limited to this. It is not something. For example, the A-phase and B-phase light receiving units 41 and 42 may generate a light reception signal based on the amount of received light and input the light reception signal to the circuit board 52. In this case, the circuit board 52 is provided with a circuit that shapes a waveform based on the received light reception signal and generates a pulse signal.

When the C-phase slit 22 of the rotary slit plate 20 and the C-phase slit 32 of the fixed slit plate 30 overlap, the red light from the light source device 10 passes and is received by the C-phase light receiving unit 43. . The C-phase light receiving unit 43 generates a received light signal based on the received light amount, shapes the waveform based on the generated received light signal, and inputs the pulse signal shown in (3) of FIG. It is possible to measure which magnetic pole of the motor is detected from the number of pulse signals.
Although the C-phase light receiving unit 43 generates a light reception signal based on the amount of received light and shapes the waveform based on the generated light reception signal, the pulse signal is generated. However, the present invention is not limited to this. For example, the C-phase light receiving unit 43 may generate a light reception signal based on the amount of light received and input this light reception signal to the circuit board 52. In this case, the circuit board 52 is provided with a circuit that shapes a waveform based on the received light reception signal and generates a pulse signal.

  The light reception signal of phase C that does not use the interference effect decreases as the gap G increases, and the light emission amount decreases as the light emission diameter D of the red LED chip 13 decreases. Falls below the lower limit line a. In the second embodiment, as described above, since the emission diameter D of the red LED chip 13 is large and the amount of emitted light is large, the amount of received light is increased as shown by e2 in FIG. It will be in a state exceeding a.

Furthermore, when the Z-phase slit 23 of the rotary slit plate 20 and the Z-phase slit 33 of the fixed slit plate 30 overlap with each other due to the rotation of the rotary slit plate 20, the red light from the light source device 10 passes, Light is received by the Z-phase light receiving unit 44. The Z-phase light receiving unit 44 generates a received light signal based on the received light amount, shapes the waveform based on the generated received light signal, and inputs the pulse signal shown in (4) of FIG. This pulse signal is the origin of the rotational position of the motor.
Although the Z-phase light receiving unit 44 generates a light reception signal based on the amount of received light and shapes the waveform based on the generated light reception signal, the pulse signal is generated. However, the present invention is not limited to this. For example, the Z-phase light receiving unit 44 may generate a light reception signal based on the amount of received light, and input this light reception signal to the circuit board 52. In this case, the circuit board 52 is provided with a circuit that shapes a waveform based on the received light reception signal and generates a pulse signal.

  As described above, according to the second embodiment, the light emission diameter D is set to be larger than 6 times the slit pitch P (10 μm) and 13 times or smaller, so that the light emission amount can be secured as compared with the LED having a small light emission diameter, and interference is caused. C-phase and Z-phase outputs (pulse signals) that do not use the effect can also be obtained.

  In the second embodiment, on the tracks A and B of the rotary slit plate 20, A-phase and B-phase slits 21 that are 90 ° out of phase with each other are provided at equal intervals in the circumferential direction. In addition, the A-phase and B-phase slits 31 are provided to face the A-phase and B-phase slits 21, but the present invention is not limited to this. For example, the area including the tracks A and B may be a single track, and the slits 21 may be provided on the track at equal intervals in the circumferential direction. In this case, the A-phase and B-phase slits 31 on the fixed slit plate 30 are arranged at positions where their phases are shifted by 90 °.

  In the second embodiment, the A-phase and B-phase slits 21 that are 90 ° out of phase with each other are provided on the tracks A and B of the rotary slit plate 20 at equal intervals in the circumferential direction. Either one of the tracks A and B may be a track, and the slits 21 may be provided on the track at equal intervals in the circumferential direction. In this case, on the fixed slit plate 30, slits 31 for A phase and B phase are arranged on the left and right. That is, for example, when the left A-phase slit 31 and the slit 21 of the rotary slit plate 20 overlap, the slit 21 of the rotary slit plate 20 overlaps half of the right B-phase slit 31. To do. Thereby, pulse signals as shown in FIGS. 6A and 6B are obtained.

  Further, on the fixed slit plate 30, instead of disposing the A-phase and B-phase slits 31 on the left and right, respectively, for example, on the lower right side or the upper right side with respect to the A-phase slit 31. You may make it arrange | position the slit 31 for B phases. Also in this case, for example, when the left A-phase slit 31 and the slit 21 of the rotary slit plate 20 overlap, the slit 21 of the rotary slit plate 20 overlaps half of the B-phase slit 31. To do. Thereby, pulse signals as shown in FIGS. 6A and 6B are obtained.

  Further, in the second embodiment, the tracks A and B are on the outer peripheral side on the rotary slit plate 20, but the track C is on the outer peripheral side, and the tracks A and B are arranged between the tracks C and Z. Anyway. Further, on the rotary slit plate 20, the tracks C and Z may be disposed on the outer peripheral side, and the tracks A and B may be disposed on the inner side.

  In the first and second embodiments, the rotating slit plate 20 is disposed on the light source device 10 side. However, the fixed slit plate 30 is disposed on the light source device 10 side, and the rotating slit plate 20 is disposed in front of the light receiving unit 3. It may be a configuration.

  DESCRIPTION OF SYMBOLS 10 Light source device, 11 Lens support part, 12 Lens, 13 Red LED chip, 14 Chip support part, 20 Rotating slit board, 21, 22, 23 Slit, 30 Fixed slit board, 31, 32, 33 Slit, 40 Light receiving part, 41 A phase light receiving unit, 42 B phase light receiving unit, 43 C phase light receiving unit, 44 Z phase light receiving unit, 50 shaft, 51 shaft support unit, 52 circuit board, 53 support unit, 60 motor shaft, D emission diameter, G Gap, L1, L2, L3 distance, X optical axis.

Claims (4)

A light-emitting diode that emits light, and a light source device having a lens that collimates the light of the light-emitting diode;
A rotating slit plate having a first slit that forms a diffraction grating in a circumferential direction radially from the center;
A fixed slit plate having a second slit forming a diffraction grating in the circumferential direction radially from the center;
A light receiving unit that receives light from the light source device that has passed through the first and second slits,
The distance between the rotary slit plate and the fixed slit plate is such that light that has passed through the first slit or the second slit interferes by diffraction, and a slit image is formed on the rotary slit plate or the fixed slit plate. The distance formed,
A rotary encoder characterized in that a light emitting diameter of the light emitting diode is set to be larger than 6 times and not larger than 13 times the interval between the first slits or the second slits.   The rotary encoder according to claim 1, wherein a wavelength of light of the light emitting diode is in a range of 610 nm to 750 nm. The rotating slit plate is provided with at least a third slit that is closer to the center than the first slit, radially from the center and circumferentially, and has a width that does not cause interference due to light diffraction. And
The fixed slit plate is provided with a fourth slit radially arranged from the center and circumferentially inside the second slit and having a width that does not cause interference due to light diffraction. The rotary encoder according to claim 1 or 2. The rotating slit plate is provided with at least a third slit that is disposed on the outer peripheral side of the first slit, radially from the center and in the circumferential direction, and has a width that does not cause interference due to light diffraction. ,
The fixed slit plate is provided with a fourth slit radially arranged from the center and in the circumferential direction outside the second slit and having a width that does not cause interference due to light diffraction. The rotary encoder according to claim 1 or 2.

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