JP4671606B2 - Encoder light receiving circuit - Google Patents

Description

  The present invention relates to a light receiving circuit of an optical rotary encoder, and more particularly to a light receiving circuit suitable when a parallel light emitting diode that emits parallel light is used as a light emitting element.

  A light receiving circuit of a conventional optical rotary encoder is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-126812 (Patent Document 1). As shown in FIG. 6, the light receiving circuit 100 includes three sets of light receiving circuit portions 100a, 100b, and 100c, and photodiodes 101a, 101b, and 101c for each phase are connected to each. Each of the light receiving circuit portions 100a, 100b, and 100c includes a comparator 102 that converts the amplitude of a current, which is an electric signal converted from light energy of each photodiode, into a rectangular wave, and a variable resistor (R1) 103 that mainly adjusts the duty of the comparator 102. And a fixed resistor (R2) 104 that determines the amount of positive feedback of the comparator 102, a reference power source 105 that supplies a reference voltage to the comparator 102, and a bias resistor 106.

  And each structural member of each light-receiving circuit part is connected as follows. The positive input side of the comparator 102 is connected to the anode of the photodiode 101a, and the negative input side is connected to a reference power source 105 that outputs a reference voltage. The supply voltage Vcc of the power supply circuit 1 is supplied to the cathode of the photodiode 101a, and the supply voltage Vcc of the power supply circuit is supplied to the output side of the comparator 102 via the bias resistor 106. A variable resistor 103 is connected between the positive input side of the comparator 102 and the ground, and a fixed resistor 104 is connected between the positive input side and the output side of the comparator 102.

  The conventional light receiving circuit is configured as described above. For example, in the case of the light receiving circuit unit 100a, the current is a product of an electric signal converted from the light energy received by the photodiode 101a and the resistance value of the variable resistor 103. When the voltage is input to the input side of the comparator 102, the comparator 102 converts the reference voltage of the reference power source 105 and the voltage into a rectangular wave and outputs it from the output side. The light receiving circuit units 100b and 100c operate similarly. The variable resistor 103 is provided to adjust the duty of the rectangular wave output from the comparator 102 by changing the resistance value.

  On the other hand, an optical rotary encoder has a rotary slit plate in which a plurality of slits for displaying a rotation angle (rotation position) are formed on a flange portion formed on a rotary shaft connected to a detected shaft that is a rotation detection target. It has been. On this rotating slit plate, a light emitting unit such as a light emitting diode (LED) and a light receiving unit such as a photodiode are arranged with a fixed slit formed with slits having the same pitch as the slit, and a rotation detection target. By rotating the rotary slit plate via the rotary shaft 1 connected to the detection shaft, the transmitted light is detected and the rotation angle is measured. In a normal optical rotary encoder, a light emitting diode of a type that diffuses light emitted as a light emitting portion has been adopted. Since this diffusion type light emitting diode has a large light emission amount, a large output voltage is obtained from the photodiode, and a necessary and sufficient voltage is applied to the comparator 102. Therefore, the phase error from the origin signal caused by the hysteresis of the comparator 102 can be within an allowable range.

  However, when the light emission amount decreases due to deterioration of the light emitting diode, or when the light emission amount is small, for example, a parallel light LED is used, each phase of the U, V, and W phases is shown in FIG. Since the detection signal voltage Vd output from the photodiodes 101a, 101b, and 101c of the output signal is small, the output signal of the U-phase, V-phase, or W-phase with respect to the Z-phase output signal serving as the origin signal is determined by the hysteresis width of the comparator 102. However, there is a problem that the phase error t becomes large and exceeds the allowable error range.

In the circuit shown in FIG. 6, when R1 is the variable resistor 103, R2 is the fixed resistor 104, VOH is the output voltage when the output H of the comparator 102 is output, and VOL is the output voltage when the output L of the comparator 102 is output, The hysteresis width voltage Vth can be expressed by the following equation.
Vth = [R1 / (R1 + R2)]. (VOH-VOL)
As described above, there is means for increasing the resistance value of the variable resistor 103 as a countermeasure when the light emission amount of the light emitting diode is small, that is, when the input voltage Vd to the comparator 102 is small. In order to reduce the voltage Vth of the hysteresis width under this condition, the fixed resistor 104 is increased, but there is a limit to increasing the resistance value from the characteristics of the comparator 102. Therefore, the ratio of the hysteresis to the input voltage of the comparator 102 cannot be reduced, and the phase difference characteristic cannot be improved.

As another means, in order to increase the input voltage to the comparator 102, it is possible to reduce the rate of hysteresis by providing an amplifier circuit with the photodiode, but providing the amplifier circuit itself However, it is not possible to adopt this because it increases costs.
Japanese Patent Laid-Open No. 9-126812

  The problem to be solved by the present invention is an encoder capable of obtaining a detection signal with a small phase error by reducing the voltage of the hysteresis width even when the input voltage to the comparator is reduced due to the light emission amount of the light emitting diode being small. It is to provide a light receiving circuit.

In order to solve the above-mentioned problem, the invention according to claim 1 is that a plurality of light receiving circuit units that receive light respectively transmitted from a light emitting element through a plurality of slits formed in an encoder and convert the light into an electric signal. With
Each light receiving circuit unit has a comparator that converts the electric signal into a rectangular wave,
The light receiving circuit of the encoder in which the light receiving element is connected to the positive input side of the comparator, the reference voltage is connected to the negative input side, and a positive feedback resistor is connected between the output side and the positive input side In
A resistance voltage dividing circuit is provided between the output side of the comparator and the ground terminal, and one end of the positive feedback resistor is connected to the resistance voltage dividing circuit,
The gist is that the divided voltage obtained by dividing the output voltage of the comparator by the resistance voltage dividing circuit is positively fed back to the comparator.

  The invention according to claim 2 is summarized in that, in the invention of claim 1, the light emitting element is a parallel light emitting diode from which parallel light is emitted.

  According to the present invention, the voltage fed back to the comparator can be lowered by dividing the output voltage of the comparator by the resistance voltage dividing circuit, so that the hysteresis width voltage of the comparator can be reduced. As a result, even if the input voltage to the comparator is small, the hysteresis width can be reduced, and a detection signal with a small phase error from the origin signal due to hysteresis can be obtained. In addition, since a necessary detection signal can be obtained even if the light emission amount is reduced due to deterioration of the light emitting diode or the like, the margin is increased and the life of the optical rotary encoder can be extended.

  According to the second aspect of the present invention, a necessary detection signal can be obtained even when a parallel light emitting diode having a small light emission amount is used as the light emitting element. In addition, since parallel light is emitted from the parallel light emitting diode, a highly accurate detection signal can be generated even if the distance between the parallel light emitting diode, the rotating slit plate, the fixed slit, and the light receiving element such as a photodiode varies. In addition, since the interval becomes longer, a necessary detection signal can be obtained even if the amount of light decreases.

  The light receiving circuit of the encoder includes a plurality of light receiving circuit units that receive light that has passed through a plurality of slits formed in the encoder from the light emitting element and that the plurality of light receiving elements receive and convert them into electrical signals. Each light receiving circuit unit has a comparator for converting the electric signal into a rectangular wave, the light receiving element is connected to the positive input side of the comparator, a reference voltage is connected to the negative input side, A positive feedback resistor is connected between the output side of the comparator and the positive input side. Further, a resistance voltage dividing circuit is provided between the output side of the comparator and the ground terminal, and one end of the positive feedback resistor is connected to the resistance voltage dividing circuit, whereby the resistor voltage dividing circuit is connected to the comparator. The divided voltage divided by the circuit is positively fed back. By reducing the positive feedback voltage to the comparator, the hysteresis width voltage of the comparator is reduced, thereby reducing the hysteresis width and obtaining a detection signal with a small phase error from the origin signal due to hysteresis.

  FIG. 1 is a block diagram showing a configuration of a light receiving circuit of an encoder according to an embodiment of the present invention. The light receiving circuit 8 includes three sets of light receiving circuit portions 8a, 8b, and 8c of U phase, V phase, and W phase, and photodiodes 9a, 9b, and 9c of each phase are connected to each. Since the three sets of light receiving circuit portions 8a, 8b, and 8c have the same configuration, the U-phase light receiving circuit portion 8a will be described as a representative.

  The light receiving circuit unit 8a is provided with a comparator 10, and the anode of the photodiode 9a is connected to the positive input side. Between the positive input side and the ground, a variable resistor (R1) 11 for adjusting the duty of the comparator 10 is provided. It is connected. A reference power supply 13 that outputs a reference voltage is connected to the negative input side of the comparator 10. Further, the supply voltage Vcc of the power supply circuit is supplied to the output side of the comparator 10 via the bias resistor 14. Further, a voltage dividing circuit 17 in which two fixed resistors 15 and 16 are connected in series is connected between the output side of the comparator 10 and the ground, and between the voltage dividing circuit 17 and the positive input side of the comparator 10. Is connected to a positive feedback resistor 12.

  On the other hand, in the optical rotary encoder, two members having slits are interposed in the optical path between the light emitting element 1 such as a light emitting diode (LED) and the light receiving element 2 including the photodiodes 9a, 9b, and 9c. Among them, the member on the light receiving element 2 side is a rotating slit plate 3 that rotates together with the rotation angle object to be measured, and slits 3a are formed in a circular shape radially and at a predetermined pitch in the circumferential direction. The other member is a fixed slit plate 4, and slits 4 a are formed at equal intervals with the slit 3 a of the rotary slit plate 3. When the slits 3 a and 4 a are aligned, the light from the light emitting element 1 passes through the slits 3 a and 4 a and is detected by the light receiving element 2 disposed behind the rotating slit plate 3.

  FIG. 2 is a side view showing a substantial structure of the optical rotary encoder excluding the light receiving element 2. In FIG. 2, a rotating shaft 5 connected to a detected shaft provided on a detection target is rotatably supported by a housing 6 of the optical rotary encoder via a bearing 7. The rotary slit plate 3 is placed on a flange portion 5 a provided on the rotary shaft 5 and attached coaxially, and rotates integrally with the rotary shaft 5. The fixed slit plate 4 is attached to the housing 6 and faces the rotary slit plate 3. Then, by rotating the rotary slit plate 3, the light passing therethrough is detected by the photodiodes 9a, 9b, 9c of each phase, and the rotation angle is measured.

  As the light emitting element 1, a parallel light emitting diode is used in the present invention. As shown in FIG. 4, the parallel light emitting diode 20 is provided with a light emitting diode chip 22 on a stem 21, and the periphery thereof is covered with a resin case 23. An aspheric lens 24 is integrally formed on the upper portion of the case 23. The chip 22 emits light from a point light source, and this light is further converted into parallel light by an aspheric lens 24 and is emitted from above in the figure. Since this light is parallel light, it can be detected with high accuracy even if the intervals between the rotating slit plate 3 and the fixed slit plate 4 interposed in the optical path between the light source 1 and the light receiving element 2 are slightly varied. have. However, since the light emitted from the chip 22 is a point light source, there is a drawback that the amount of light emission is reduced as compared with a conventional light emitting diode.

  In the light receiving circuit of the encoder configured as described above, for example, regarding the U-phase light receiving circuit unit 8a, the current that is an electric signal converted from the light energy received by the photodiode 9a and the resistance value of the variable resistor 11 Is input to the input side of the comparator 10, the comparator 10 converts the reference voltage of the reference power supply 13 and the voltage into a rectangular wave and outputs it from the output side. The output voltage of the comparator 10 is divided by a voltage dividing circuit 17 in which two fixed resistors 15 and 16 are connected in series, and this divided voltage is positively fed back to the positive input side of the comparator 10 via the positive feedback resistor 12. .

In this circuit configuration, R1 is a variable resistor 11, R2 is a fixed resistor 12, R3 is a fixed resistor 15, R4 is a fixed resistor 16, VOH is an output voltage at the output H of the comparator 10, and VOL is an output L of the comparator 10. When the output voltage VOH ′ and VOL ′ at that time are voltages obtained by dividing by the voltage dividing circuit 17, the voltage Vth of the hysteresis width of the comparator 10 can be expressed by the following equation.
Vth = [R1 / (R1 + R2)]. (VOH′−VOL ′)
In this equation, by dividing the output voltage of the comparator 10 by the voltage dividing circuit 17, the output voltage at the output L of the comparator 10 and the output voltage at the output H are respectively reduced according to the voltage dividing ratio. The voltage difference becomes smaller according to the voltage division ratio.

  Therefore, as apparent from the above equation, the hysteresis width of the comparator 10 can be reduced, so that even if the input voltage input to the comparator 10, that is, the detection signal voltage Vd is reduced, as shown in FIG. In addition, the hysteresis width voltage Vth can be reduced. As a result, the phase error t for the U-phase, V-phase, and W-phase output signals with respect to the Z-phase output signal serving as the origin signal can be reduced to the allowable error range. As a result, it is possible to eliminate the drawback that the parallel light emitting diode has a small amount of light emission and to make use of only the feature points.

  In the above-described embodiment, the resistor provided between the positive input side of the comparator and the ground is a variable resistor. However, if it is not necessary to adjust the duty of the rectangular wave output from the comparator, it is changed to a fixed resistor. You may do it. Further, the present invention is not limited to the above-described embodiments and can be modified without departing from the present invention.

  The present invention can be applied to a light receiving circuit of an absolute type optical rotary encoder that detects an absolute rotation angle or an incremental type that detects a relative rotation angle.

It is a block diagram which shows the structure of the light receiving circuit of the encoder concerning one Embodiment of this invention. It is a perspective view which shows the fundamental structure of an encoder. It is a side view which shows the substantial structure of an encoder. It is sectional drawing which shows the structure of a parallel light emitting diode. It is a wave form diagram of the output signal of the light-receiving circuit of the encoder with this invention. It is a circuit diagram of the light receiving circuit of the conventional encoder. It is a wave form diagram of the output signal of the light receiving circuit of the conventional encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 3 Rotating slit board 8 Light receiving circuit 8a, 8b, 8c Light receiving circuit part 9a, 9b, 9c Photodiode 10 Comparator 11 Variable resistance (R1)
12 Positive feedback resistor (R2)
13 Reference power supply 15 and 16 Voltage dividing resistor 17 Voltage dividing circuit

Claims (2)

A plurality of light receiving circuit portions that receive light that has passed through a plurality of slits formed in the encoder from the light emitting element and that receive the plurality of light receiving elements and convert them into electrical signals,
Each light receiving circuit unit has a comparator that converts the electric signal into a rectangular wave,
The light receiving circuit of the encoder in which the light receiving element is connected to the positive input side of the comparator, the reference voltage is connected to the negative input side, and a positive feedback resistor is connected between the output side and the positive input side In
A voltage dividing circuit is provided between the output side of the comparator and the ground terminal, and one end of the positive feedback resistor is connected to the voltage dividing circuit,
A light receiving circuit for an encoder, wherein a divided voltage obtained by dividing the output voltage of the comparator by the voltage dividing circuit is positively fed back to the comparator.   2. The light receiving circuit for an encoder according to claim 1, wherein the light emitting element is a parallel light emitting diode that emits parallel light.

Images