JP5124091B2 - Abnormal light emission prevention device for light source laser of separate type reflection type photoelectric encoder - Google Patents

Description

The present invention relates to an abnormal light emitting device for preventing a light source a laser reflection type photoelectric encoder separate type, suitable in particular, for use with a laser diode (LD) in a separate type reflective photoelectric encoder according to the light source, separate The present invention relates to an apparatus for preventing abnormal light emission of a light source laser of a reflection type photoelectric encoder .

  As a separate photoelectric encoder in which the scale 10 and the detector 12 are separated, as shown in FIG. 1A, a transmission encoder in which the detector 12 is configured to sandwich the scale 10, and FIG. As shown in FIG. 2, there is a reflective encoder in which a detector 12 is configured to face the scale 10. In the figure, 16 is a light receiving element such as a photodiode (PD).

  When a semiconductor laser is used as the light source 14 of the detector 12, the laser beam 15 is not emitted to the outside in the former transmission type, but is not opposed to the scale 10 in the latter reflection type. Then, the laser beam 15 is emitted to the outside.

Therefore, it is necessary to suppress the intensity of the emitted laser beam 15 within a range that does not affect the human body. Further, even if an abnormality due to a component failure or disconnection occurs on the laser diode (LD) drive circuit, the radiation output must be suppressed within a range that does not affect the human body. In the case of the transmissive type, the laser light 15 does not directly go outside, so that even if an abnormality occurs on the drive circuit, there is usually no problem, but in the case of the reflective type, a problem may occur .

  Patent Document 1 discloses a semiconductor laser in which a value obtained by subtracting a control amount stored in a latch from a control amount changing in an automatic power control (APC) section is larger than a predetermined reference value. It is described that an increase in the drive current value of the drive current source is also stopped by generating an APC error signal by judging that some abnormality has occurred and stopping the further increase in the control amount. .

JP-A-9-321386

  Conventionally, however, there is a problem that the configuration is complicated and expensive.

The present invention, wherein those so has been made to solve the conventional problems, the reflected light is also monitored, which can abnormal emission of the laser, to reliably prevent a low cost, separate type of reflective photoelectric It is an object of the present invention to provide an apparatus for preventing abnormal light emission of a light source laser of an encoder .

The present invention includes a first light receiving means for directly detecting the light emission amount of a laser diode, a second light receiving means for directly detecting the amount of light reflected from a measurement object, and usually the second light receiving means. The amount of light emitted from the laser diode is feedback-controlled in accordance with the amount of reflected light from the measurement object detected in step 1, and when the measurement object disappears, the amount of light emitted from the laser diode detected by the first light receiving means. A laser diode drive circuit having a control loop for feedback control of the light emission amount of the laser diode in response to a window comparator for monitoring the voltage of the control loop, and a voltage of the control loop being predetermined. when out of range, the separate type, characterized by comprising: a light emission stop means for stopping the light emission of the reflection type photoelectric encoder The abnormal light emitting device for preventing source laser beam is obtained by solving the above problems.

  In addition, by providing a delay circuit for preventing the operation of the light emission stop means when the power is turned on, a malfunction at the rise when the power is turned on is prevented.

According to the present invention, any one of the elements on the control loop for feedback control of the light emission amount of the laser diode according to both the light emission amount of the laser diode and the reflected light amount from the measurement object is broken or damaged. In this case, since the laser emission is stopped immediately, an increase in cost can be minimized and abnormal light emission of the light source laser of the separate reflection type photoelectric encoder can be surely prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 2, the reference example is incorporated in the laser diode package 20 for feedback control of the light emission amount of the LD according to the light emission amount of the laser diode (LD) in the laser diode package 20, for example. A photodiode PD1, a current-voltage converter 32 for converting the output current of the PD1 to a control voltage V1, a control loop 30 including a differential amplifier 34 for amplifying the difference between the control voltage V1 and a reference voltage Vref, and an LD In a laser including an LD drive transistor Tr1 for controlling a drive current, a window comparator 36 including comparators Cmp1 and Cmp2 for monitoring the voltage of the control loop 30 and an output of the window comparator 36 are turned on / off. The analog light emission stop switch 38 and the light emission stop switch when the power is turned on. A delay circuit 40 including a capacitor C1 and a resistor R4 and an AND gate IC1 are provided to prevent the switch 38 from being turned off.

In this reference example , first, in normal operation, when the power is turned on, the LD of the laser diode package 20 emits light, and a current proportional to the optical power is generated in PD1. Then, the current is converted into the control voltage V1 by the current-voltage converter 32, and the current of the LD is controlled by the transistor Tr1 so that the reference voltages Vref and V1 of the positive input terminal of the differential amplifier 34 are equal. The variable resistor VR1 of the current-voltage conversion unit 32 is adjusted so that the optical power is optimal for use.

  In normal operation, abnormal light emission can be prevented in this manner. However, if an element on the control loop 30 fails or is damaged, the control voltage V1 cannot be maintained at the control reference voltage Vref, and control is performed. The voltage V1 is different from the reference voltage Vref in the positive or negative direction.

  Therefore, when the control voltage V1 falls outside the reference value Vref ± α set in advance by the window comparator 36, the output of the comparator Cmp1 or Cmp2 becomes low level, and the light emission stop switch 38 is turned off. Therefore, it becomes impossible to supply power to the LD, and the light emission of the LD is forcibly turned off.

  Since the power-on rise requires time for the LD to start emitting light, the light emission stop switch 38 is forcibly turned on only for the time constant time of the capacitor C1 and the resistor R4 of the delay circuit 40, and then sequentially controlled by the above operation. Monitor the voltage V1.

Next , embodiments of the present invention will be described in detail.

In the present embodiment, in the same circuit as the reference example , as shown in FIG. 3, the control loop 30 receives a photodiode PD2 that receives the reflected light from the measurement object, and converts the output current of the PD2 into a voltage. The current-voltage converter 42 and the diodes D1 and D2 are provided so that the higher output of the current-voltage converters 32 and 42 is the control voltage V1.

The other points are the same as in the reference example, and the description is omitted.

  In this embodiment, first, in normal operation, when the power is turned on, the LD of the laser diode package 20 emits light, and the light reflected from the photodiode PD1 incorporated in the laser diode package 20 and the measurement object is reflected. A current proportional to the optical power is generated in the photodiode PD2 that receives the light. The photocurrents generated in PD1 and PD2 are converted into voltages by current-voltage converters 32 and 42, respectively, and the higher voltage is selected by diodes D1 and D2 to become control voltage V1. The drive current of the LD is controlled by the transistor Tr1 so that the control voltage V1 becomes equal to the reference voltage Vref of the positive input terminal of the differential amplifier 34.

  Specifically, feedback is normally made with a reflected signal (PD2 side) from the measurement object, but when the measurement object is lost, PD1 functions as an optical power limiter. The variable resistors VR1 and VR2 of the current-voltage converters 32 and 42 are adjusted so that the optical power is optimal for use.

  On the other hand, when there is no reflection from the measurement object and an element on the control loop 30 fails or is damaged, the control voltage V1 cannot be maintained at the control reference voltage Vref, and the control voltage V1 is the reference voltage. It differs from the voltage Vref in the positive or negative direction.

  Therefore, when the control voltage V1 falls outside the reference value Vref ± α set in advance by the window comparator 36, the output of the comparator Cmp1 or Cmp2 becomes low level, and the light emission stop switch 38 is turned off. Therefore, it becomes impossible to supply power to the LD, and the light emission of the LD is forcibly turned off.

  In this embodiment, since the reflected light is also monitored, the operation is reliable.

In the embodiment, since the circuits were analog circuitry, construction is simple. In addition, it is also possible to comprise with a digital logic circuit like patent document 1. FIG. The light emission stopping means is not limited to an analog switch.

Further, in the above embodiment, the present invention has been applied to a Linear encoder, application of the present invention is not limited to this and can be similarly applied to a B over Tali encoder.

Diagram showing a typical configuration of a photoelectric encoder Circuit diagram showing configuration of reference example The circuit diagram which shows the structure of embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Laser diode package LD ... Laser diode PD1, PD2 ... Photodiode 30 ... Control loop 32, 42 ... Current-voltage conversion part 34 ... Differential amplifier 36 ... Window comparator 38 ... Light emission stop switch 40 ... Delay circuit Tr1 ... LD drive Transistor

Claims (2)

First light receiving means for directly detecting the light emission amount of the laser diode;
A second light receiving means for directly detecting the amount of reflected light from the measurement object;
Usually, the amount of light emitted from the laser diode is feedback-controlled according to the amount of reflected light from the measurement object detected by the second light receiving means, and when the measurement object disappears, the first light receiving means A laser diode drive circuit comprising a control loop for feedback-controlling the light emission amount of the laser diode according to the light emission amount of the detected laser diode,
A window comparator for monitoring the voltage of the control loop;
Light emission stop means for stopping light emission when the voltage of the control loop is out of a predetermined range;
An apparatus for preventing abnormal light emission of a light source laser of a separate type reflection type photoelectric encoder, comprising: 2. The apparatus for preventing abnormal light emission of a light source laser of a separate reflection type photoelectric encoder according to claim 1, further comprising a delay circuit for preventing the operation of the light emission stop means when the power is turned on.

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