JPH0445794B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of the Invention The present invention relates to a pulse modulation light type photoelectric switch,
In other words, regarding a type of photoelectric switch that projects pulsed light and performs a detection operation by extracting only the received light signal that is synchronized with this pulsed light, it is particularly sensitive to the pulsed light of another photoelectric switch whose period is similar to that of its own pulsed light. This invention relates to a pulse modulated light type photoelectric switch whose circuit configuration has been improved so that it does not malfunction in response to periodic noise light such as.

(b) Prior art and its problems Pulse-modulated light type photoelectric switches employ a so-called synchronization gate method, which extracts only the received light input synchronized with the emitted light pulse and prohibits the received light input during other periods. Therefore, it is effective in preventing malfunctions against discontinuous noise light. However, as shown in FIG. 1a, a plurality of photoelectric switches are often used side by side. In such a case, if the light projection range of the light projecting parts 1T, 2T and the light receiving range of the light receiving parts 1R, 2R of the photoelectric switch are wide,
Even though the light from the light emitting portion 1T of the photoelectric switch 1 is blocked by the object to be detected 3, the light from the light emitting portion 2T of the photoelectric switch 2 enters the light receiving portion 1R of the photoelectric switch 1. . And the light projector 1T,
Pulsed light with different phases and periods are projected from the 2T, but the periods of the pulsed lights are often similar, so the projecting unit 1
The timings of the T and 2T pulse lights may completely overlap, and in this case, the influence of the projection light of other photoelectric switches cannot be eliminated only by the synchronization gate method.

For this reason, conventionally, as shown in FIG. 1b, the light emitting range and light receiving range of the light emitting parts 1T, 2T and the light receiving parts 1R, 2R are narrowed, so that the projected light from other photoelectric switches is transmitted to another photoelectric switch. Consideration has been given to preventing the light from entering the light receiving section of the device. However, in this case, it becomes difficult to align the optical axes of the corresponding light projecting section and light receiving section, and if the optical axes are even slightly deviated due to vibrations, shocks, etc., there are disadvantages such as inconvenience in operation.

Furthermore, as shown in FIG. 1c, the light projecting parts 1T, 2T
It has been considered to alternately arrange the light receiving sections 1R and 2R, but if the surface reflectance of the object to be detected 3 is good, the reflected light will enter the light receiving sections of other photoelectric switches. It's inconvenient.

Furthermore, when multiple light emitters are arranged side by side, the light emitting timing is shifted so that they do not emit light at the same time, and a gate circuit is installed to selectively pass only the received light signal at the corresponding timing. There is also a way of thinking to avoid the influence. However, a control circuit is required to shift the light emission timing and sequentially emit light, and electrical connections are required to transmit synchronization signals to each of the light emitting and receiving parts of this control circuit, so the configuration is difficult. In addition to complicating the process and making the wiring work complicated, it also has the disadvantage that each photoelectric switch cannot be used independently.

(c) Purpose of the Invention In view of the above, the present invention has a light emitting/receiving range that allows easy optical axis adjustment, does not require mutual electrical connection when a large number of them are arranged side by side, and can be used to connect other photoelectric devices. It is an object of the present invention to provide a photoelectric switch that can prevent malfunctions by eliminating the influence of noise light such as light projected by the switch.

(d) Structure and Effects of the Invention According to the present invention, a pulse oscillator, a light emitting element that lights up in pulses in response to a pulse output from the pulse oscillator, and a light receiving device that receives light from the light emitting element and generates a light reception signal. a gate circuit for gating the received light signal with a pulse from the pulse oscillator; a counting circuit including the gate circuit and comprising a plurality of stages and counting signals input to the gate circuit; a logic circuit that detects a mismatch between the output of the gate circuit and the output of the final stage of the counting circuit; and in response to the mismatch output of the logic circuit,
Since it is equipped with a control circuit that shortens the pulse period of the pulse oscillator, when noise light is incident on the light receiving element and a light reception signal is generated, the projected light of the self and the other will overlap over many pulses. can be avoided, and malfunctions caused by optical noise can be prevented. Furthermore, as a result of the pulse period being shortened, the response time can be shortened.

Furthermore, since there is no need to narrow the light emitting/receiving range, there is no need to compromise the ease of aligning the optical axis, and there is no need to make electrical connections between multiple photoelectric switches when they are placed side by side. . Also,
The pulse period can be shortened only when changing from a light-blocking state to a light-receiving state, or from a light-receiving state to a light-blocking state, and the pulse period can be lengthened during normal times, extending the lifespan of the light emitting element and reducing power consumption. .

(E) Description of Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In Fig. 2, the light projecting section 1T
is equipped with an RC self-excited pulse oscillator consisting of low resistors 14, 16, 17, 18, 19, a capacitor 15, diodes 20, 22, and a comparator 21, and a transistor 13 is connected in series with the time constant circuit of the low resistor 14 and capacitor 15. are connected together with the low resistors 11 and 12 to form a control circuit. The pulses from the pulse oscillator pass through a current amplification circuit made up of resistors 23 and 24 and a transistor 25, and then are sent to a light emitting diode (LED) 27 via a resistor 26. The light receiving section 1R includes a phototransistor 29, a resistor 28,
31 to 34, capacitor 30, comparator 35
Among the output signals of the phototransistor 29, only signals having a peak value above a certain level are converted into rectangular waves by the waveform shaping circuit. The light reception signal thus made into a rectangular wave is sent to five flip-flops 36 to 36.
40 shift registers. Each of these flip-flops uses the pulse from the pulse oscillator as a clock pulse, and input is performed at the timing of this clock pulse. Therefore, the flip-flop 36 in the first stage in particular functions as a gate circuit that gates the received light signal with the pulse of the pulse oscillator. The output of each flip-flop is OR gate 41
and an AND gate 42, and when five consecutive light reception signals are taken into this shift register, the output of the AND gate 42 becomes "H". Further, the OR gate 41 becomes "H" when the output of any one of the five flip-flops is "H", and when the output of all the flip-flops is "L", that is, the output of the five flip-flops is "H". It becomes "L" when there is no light reception signal for a continuous period of time. Therefore, it can be seen that the shift register functions as a digital type integrating circuit (an analog type integrating circuit can be used, but in this case, an integrating circuit is used instead of the OR gate 41 and the AND gate 42). Two output level detection circuits are provided, and the detection level of one corresponds to the integrated output when one received light signal is received within a certain period of time.
The other detection level may be made to correspond to the integral output reached when five light reception signals occur in succession). The output of OR gate 41 and AND gate 42 is
NAND gates 43, 44, NOR gate 46,
The signal is input to a flip-flop consisting of a NOT circuit 45. Further, the output of the flip-flop 36 in the first stage of the shift register and the output of the flip-flop 40 in the final stage are led to the exclusive OR circuit 73,
The transistor 13 is controlled by this output.

Next, the operation will be described with reference to the time chart in FIG. 3, which shows the signal waveforms at points A to G in FIG. 2, respectively.

If the outputs of the flip-flops 36 to 40 are all "L" when no light reception signal is generated initially, the output of the exclusive OR circuit 73 is "H", so the transistor 13 is off.
Capacitor 15 is charged through resistor 71 . Therefore, pulses are generated at a period determined by the time constants of the resistor 71 and the capacitor 15. FIG. 3A shows the waveform of the lighting current of the LED 27, which is also the waveform of the pulse of the pulse oscillator and the waveform of the clock pulse of the shift register.
The projected light from this LED 27 is blocked by an object to be detected (not shown), and at this time, pulsed light emitted from the LED of another photoelectric switch enters the phototransistor 29, as shown in FIG. 3B. Suppose that such a received light signal is generated. This received light signal B
When the timing of the clock pulse A overlaps with the timing of the clock pulse A, the output E of the flip-flop 36 becomes "H" as shown in FIG. 3E. Therefore,
The output D of the exclusive OR circuit 73 becomes "L", the transistor 13 is turned on, and the capacitor 15
charges faster. Therefore, the next pulse light from another photoelectric switch and the pulse of the pulse oscillator do not overlap, and when the next pulse occurs, the output E of the flip-flop 36 is "L", the output of the flip-flop 37 is "H", The outputs of the other flip-flops 38-40 become "L". Therefore, the output D of the exclusive OR circuit 73 becomes "H",
The pulse period of the pulse oscillator returns to the original value.

Since the pulse period is shortened in this way, even if pulsed light from another photoelectric switch is incident, the light emission timing of the other photoelectric switch will not overlap for 5 pulses, and the AND gate 42 will not overlap. The output never becomes "H". When the object to be detected moves and changes from a light-shielding state to a light-receiving state and begins to receive its own projected light, the flip-flops 36 to 40, which were initially all "L", sequentially become "H" from the first stage. Therefore, during the five pulses until all the flip-flops become "H", the output D of the exclusive OR circuit 73 becomes "L" and the pulse period becomes short. Similarly, when transitioning from the light-receiving state to the light-blocking state, the flip-flop 3
Since the outputs of 6 and 40 differ for 5 pulses, the pulse period becomes shorter during that time. In other words, in such a case,
Since the period of the clock pulse driving the shift register is shortened, the response time of the photoelectric switch is shortened. The pulse period when this shortens determines the response time, so if you set it to the required response time, the pulse period will be long under normal conditions where the output is not inverted, and the average value flowing to the LED 27 will be reduced. This reduces the current, prevents deterioration of the LED 27 itself, and helps reduce power consumption of the photoelectric switch.

[Brief explanation of drawings]

Figures 1a, b, and c are schematic plan views showing the positional relationship between the light emitting part and the light receiving part of the photoelectric switch, Figure 2 is a circuit diagram of an embodiment of the present invention, and Figure 3 is the same as Figure 2. A of
It is a time chart showing the signal waveform at each point of ~G. 1T, 2T...Light emitter, 1R, 2R...Light receiver, 3
... object to be detected, 27... LED for light projection, 29... photo transistor (light receiving element), 36 to 40... flip-flop, 73... exclusive OR circuit.

Claims (1)

[Claims] 1 a pulse oscillator, a light emitting element that lights up in pulses in response to pulses output from the pulse oscillator, a light receiving element that receives light from the light emitting element and generates a light reception signal, and a light reception element that generates a light reception signal by receiving the light from the pulse oscillator. a gate circuit for gating by, a counting circuit including this gate circuit and consisting of multiple stages and counting signals input to the gate circuit, an output of the gate circuit and an output of the final stage of the counting circuit. 1. A photoelectric switch comprising: a logic circuit that detects a mismatch between the two; and a control circuit that shortens the pulse period of the pulse oscillator in response to the mismatch output of the logic circuit.