JPS5950138B2 - Photoelectric detection circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a photoelectric detection circuit.

Photoelectric detection circuits are applied to optical encoders, photoelectric switches, etc.

Optical encoders are devices that convert relative positions and displacements into digital signals, and are used as elements of control loops for reading angles and coordinates, generating synchronization signals, and operating and monitoring remote controls, and are widely used in information equipment, measurement, and Used in observation instruments, machine tools, and cargo handling equipment.

In addition, photoelectric switches are widely used as non-contact switches for detecting the presence, position, and phase of objects, as well as proximity switches using reflected light, mark sensors, curve tracers, and the like. The operation of this optical detection circuit may become uncertain due to the quality of the power supplied, external noise, noise generated by the detector itself, etc. To prevent this, sufficient hysteresis is provided in the circuit. I try to have it.
In digital circuits, the operational sensitivity to the above noise is sufficiently reduced, so this is not a problem, but in analog circuits that amplify minute signals, the size of the nozzle is more than 1000 times larger than the signal. When converting analog to digital via a voltage comparator, the ringing noise generated when the digital circuit switches enters the analog signal via the power supply, which is detected by the comparator, forming a closed loop in which the digital circuit operates. and easily cause oscillation. FIG. 1 shows an example of a conventional photoelectric detection circuit.

In this figure, voltage Vcc reaches a light emitting diode 4, which is the light source of the device, via a current limiting resistor 3, and drives it. The light from the light emitting diode 4 passes through the encoder code plate or object 5 and the slit 6 and enters the phototransistor 7 . The voltage at the output terminal P1 of the phototransistor 7 becomes m due to the resistors 8 and 10, and is applied to the non-inverting input of the voltage comparator 9. Further, the voltage n determined by the fixed resistor 1 and the variable resistor 2 is applied to the inverting input of the voltage comparator 9 as a reference voltage. Now, when the voltage m is greater than the voltage n, the output of the voltage comparator 9 becomes ``1'', and this output ``1'' is applied to a digital circuit (not shown) such as a counter. At the same time, a current from a power source (not shown) with voltage Vcc flows through resistors 12, 11, and 10, and the voltage at point P is the voltage m plus the hysteresis voltage determined by resistors 12, 11, and 10. It becomes ivy. The disadvantage of this method is that the noise generated during switching of the digital circuit (not shown) connected to the voltage comparator 9 and the line 1 is transferred to the power supply line 11, and this noise is transferred to the phototransistor 7.
The voltage reaches the point P1 via the resistors 12, 11, and 10, and the voltage comparator 9 is thereby activated. Regarding this drawback, since the noise transmission characteristics of the photo transistor 7 and the resistors 12, 11, and 10 are different from the nominal characteristics and are unknown, no compensation measures can be taken. The present invention has been made in view of the above points, and it is an object of the present invention to provide a photoelectric detection/output circuit that operates reliably and is not affected by noise.

According to this invention, a photovoltaic cell is used as a photodetector, the electromotive force of the photovoltaic cell is converted from a light emitter, and this electromotive force is compared with a reference voltage, and if the electromotive force is large, it is fed back positively to the light emitter. The circuit is designed to have bisserin 2 gas characteristics.

The optical sensor (photovoltaic cell) is connected to the power supply line only on one side (common line) and is disconnected from the other side (Vcc line), thereby avoiding the influence of noise. Hereinafter, the present invention will be described in detail based on one embodiment of the accompanying drawings.

In FIG. 2, a voltage Cc is led to a power supply line (Vcc line) 11, and drives a light emitting diode 4 connected to this line 11 via a current limiting resistor 3.

The light emitted from the light emitting diode 4 passes through the code plate or object 5 of the encoder and the slit 6 and enters the silicon photoelectric element (photocell) 14, which causes the element 14 to generate an electromotive force. One terminal of the silicon photoelectric element 14 is connected to the non-inverting input terminal of the voltage comparator 9, and the other terminal is connected to the power supply line (common line) 13. Further, a current-voltage converter resistor 15 is connected in parallel to the D silicon photoelectric element 14. The electromotive force of the silicon photoelectric element Jl4 becomes a voltage m1 via this resistor 15 and is applied to the non-inverting input terminal of the voltage comparator 9. A reference voltage fixed resistor 1 and a reference voltage variable resistor 2 are connected in series to the power supply line 11.

Further, a midpoint P2 between these resistors 1 and 2 is connected to an inverting input terminal of a voltage comparator 9 via a line 14. As a result, the voltage Cc becomes the voltage n1 at the point P2, and this voltage n1 is applied to the inverting input of the voltage comparator 9 via the line 14 as a comparison reference voltage in the voltage comparator 9. Voltage comparator 9 receives voltage m1 from silicon photoelectric element 14.
and a reference voltage n1, and when m1>n1, a signal 8r is outputted, and when m1<n1, a signal ``0'' is outputted and guided to a line 12.

A digital circuit (not shown) such as a counter is connected to this line 12. Further, this line 12 is connected to the anode of the light emitting diode 4 via a feedback limiting resistor 13. Furthermore, this line 12 is also connected to the power supply line 11 via a pull-up resistor 12. Now, if the output signal strength of the voltage comparator 9 changes from O'' to 1, a feedback current flows from the power supply line 11 through the pull-up resistor 12 and the feedback limiting resistor 13 to the light emitting diode 4.
flows into. Therefore, the current flowing into the light emitting diode 4 increases as the sum of the current passing through the current limiting resistor 3, the pull-up resistor 12, and the feedback limiting resistor 13. As a result, the amount of light emitted by the light emitting diode 4 increases, and the electromotive force of the silicon photoelectric element 14 also increases, and as a result, the output of the voltage comparator 9 has hysteresis. FIG. 3 shows another embodiment of the invention. In this embodiment, the value of the reference voltage n1 is changed according to the voltage m1 from the photovoltaic cell 14.

That is, a light emitting diode 17 is connected to the power line 11 via a current limiting resistor 16, and the light emitting diode 17 emits light due to the voltage applied from the power line 11. This light is the code plate of the encoder or the object 18
The light then passes through the slit 19 and enters the silicon photoelectric element 20 . This silicon photoelectric element 20 has one terminal connected to the inverting input terminal of the voltage comparator 9, and the other terminal connected to the power supply line 13. Further, a variable resistor 21 is connected in parallel. The encoder code plate or object 18 is in communication with the encoder code plate or object 5 and such that the increase or decrease of light passing through it is in opposite phase to the increase or decrease of light passing through the encoder code plate or object 5. will be installed. That is, when the amount of light incident on the silicon photoelectric element 14 increases, the amount of light incident on the silicon photoelectric element 20 decreases, and conversely, when the amount of light incident on the silicon photoelectric element 14 decreases, the amount of light incident on the silicon photoelectric element 20 decreases. Increase efficacy. As a result, the voltages M and N input to the voltage comparator 9 are such that when the voltage M increases, the voltage N,
On the contrary, when the voltage ml decreases, the voltage N increases, and the voltage comparator 9 is driven in a push-pull manner. The feedback current of the voltage comparator 9 flows into the light emitting diode 4 via the resistor 13 as in the embodiment shown in FIG. In such a structure, the two input circuits of the voltage comparator 9 have substantially the same configuration, and noise due to disturbance etc. is transmitted in the same manner and is canceled out by the common mode removal action of the voltage comparator 9. As explained above, according to the present invention, a photovoltaic cell such as a silicon photoelectric element is used as an optical sensor instead of a phototransistor, and the optical sensor and the power source are connected only through one side (common line). In addition, the positive feedback of the comparator to provide hysteresis characteristics is applied to the light emitter side, which prevents noise from flowing into the comparator from the power supply line, ensuring reliable circuit operation. It has the effect of being able to

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an example of a conventional photoelectric detection circuit.
FIG. 2 is a block diagram showing one embodiment of the invention, and FIG. 3 is a block diagram showing another embodiment of the invention. 4, 7... Light emitting diode, 5, 18...
...Encoder code plate or object, 6,9...
・Slit, 7...Photo transistor,
14,20...Silicon photoelectric element, 9...
...Voltage comparator.

Claims (1)

[Claims] 1. A light emitting means that emits an amount of light according to an input electrical signal, a photovoltaic cell that receives light from the light emitting means and generates an electromotive force according to the amount of received light, and an output of the photovoltaic cell and a reference voltage. A photoelectric detection circuit comprising a comparator that compares the two signals and generates a binary output depending on the magnitude of the two signals, and positively feedbacks the output signal of the comparator to the input of the light emitting means.