JP2709017B2 - Photoelectric switch - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse-modulated optical photoelectric switch. 2. Description of the Related Art In general, a pulse-modulated light type photoelectric switch illuminates a light emitting element in pulses with a pulse signal having a predetermined period and a predetermined pulse width, receives the light emitting pulse with a light receiving element, and receives light. It is taken out as a signal. Then, the presence or absence of the detected object is detected based on the result of integrating the received light pulse signals. As described above, a conventional pulse-modulated light type photoelectric switch is generally pulse-lit for a fixed period as described above. Here, assuming that the pulse width of the pulse signal is the same, the longer the period, the shorter the light emission time of the light emitting means as a whole, and the longer life of the light emitting means and reduction of power consumption can be expected. However, conversely, the longer the pulse period, the slower the response speed of the photoelectric switch. In order to increase the response speed, the cycle is shortened. However, this has the problem that the life of the light emitting means cannot be prolonged, the power consumption cannot be reduced, and conflicting problems cannot be solved. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a photoelectric switch capable of increasing the response speed, extending the life of the light emitting means, and reducing power consumption. I have. [0005] The photoelectric switch of the present invention comprises a pulse oscillator, a light emitting means for periodically lighting by a pulse output from the pulse oscillator, and
A light receiving means for generating a light receiving pulse signal each time pulse light is received from the light emitting means, wherein the light receiving pulse signal of the light receiving means changes from a light receiving state to a non-light receiving state or from a non-light receiving state to a light receiving state. Means for shortening the cycle of the pulse oscillator,
After the change from the light-receiving state to the non-light-receiving state, or from the change from the non-light-receiving state to the light-receiving state, whether the light-receiving pulse signal is obtained a predetermined number of times continuously in response to the pulse light from the light-emitting means, Or a means for lengthening the cycle of the pulse oscillator based on the fact that a light receiving pulse signal has not been continuously obtained a predetermined number of times corresponding to the pulse light from the light emitting means. [0006] In this photoelectric switch, while the light receiving state or the non-light receiving state continues, the cycle of the pulse oscillator is long, and the life of the light emitting means can be prolonged and the power consumption can be reduced. When the light receiving pulse signal of the light receiving means changes from the light receiving state to the non-light receiving state or from the non-light receiving state to the light receiving state, the cycle of the pulse oscillator is shortened, and during this period, the response speed is increased. After the change, the period of the pulse oscillator becomes longer if the light receiving pulse signal is continuously obtained or not obtained a predetermined number of times corresponding to the pulsed light. That is, the cycle returns to the original state. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the light projecting unit 1T includes an RC self-excited pulse oscillator 4 including resistors 14, 16, 17, 18, and 19, a capacitor 15, diodes 20, 22, and a comparator 21, and the resistor 14 and the capacitor 1
A transistor 13 is connected in series with the time constant circuit 5 to form a control circuit together with the resistors 11 and 12. The pulse of the pulse oscillator is sent to a light emitting diode (LED) 27 through a current amplifying circuit including resistors 23 and 24 and a transistor 25 and further through a resistor 26, whereby the LED 27 is periodically turned on. The light receiving section 1R includes a phototransistor 29
And a waveform shaping circuit including resistors 28, 31 to 34, a capacitor 30, and a comparator 35, and among the output signals of the phototransistor 29, only a signal having a peak value equal to or higher than a certain level is converted into a rectangular wave by the waveform shaping circuit. I try to convert. The light receiving signal (light receiving pulse signal) thus formed into a rectangular wave is supplied to five flip-flops 36 to 40.
To the shift register. Each of these flip-flops uses the pulse of the pulse oscillator as a clock pulse, and inputs are performed at the timing of the clock pulse. Therefore, the first-stage flip-flop 36 particularly functions as a gate circuit that gates the light receiving signal by the pulse of the pulse oscillator 4. The output of each flip-flop is an OR gate 4
1 and the AND gate 42, and the received light signal is 5
When these are successively taken into this shift register, A
The output of the ND gate 42 becomes "H". The OR gate 41 becomes “H” when any one of the five flip-flops is also at “H”, and when the outputs of all the flip-flops are “L”, that is, the clock pulse 5 It becomes “L” when there is no light reception signal for a continuous number of times. Therefore, it can be seen that the shift register functions as a digital integrating circuit (an analog integrating circuit can also be used. In this case, the level of the integrated output is used instead of the OR gate 41 and the AND gate 42). When two detection circuits are provided, one detection level is made to correspond to the integrated output when one light reception signal is present within a predetermined time, and the other detection level is set when five light reception signals are generated successively. The output of the OR gate 41 and the output of the AND gate 42 are NAND gates 43 and 44, a NOR gate 46, and NO.
The signal is input to a flip-flop including a T circuit 45. The output of the first-stage flip-flop 36 and the output of the last-stage flip-flop 40 of the shift register are guided to an exclusive OR circuit 73, and the transistor 13 is controlled by this output. Next, the operation will be described with reference to a time chart of FIG. 2 showing signal waveforms at points A to G in FIG. When no light receiving signal is generated at first, assuming that the outputs of the flip-flops 36 to 40 are all "L", the output of the exclusive OR circuit 72 is "H", so that the transistor 13 is turned off. The capacitor 15 is charged through the resistor 71. Therefore, the resistance 71
And a pulse is generated at a period determined by the time constant of the capacitor 15. In other words, a pulse having a long cycle is generated from the pulse oscillator, and the LED 27 is lit for a long period. FIG. 2A shows the waveform of the lighting current of the LED 27, which is the waveform of the pulse of the pulse oscillator 4 and the waveform of the clock pulse of the shift register. The projection light from the LED 27 is stably blocked by an object to be detected (not shown), and at this time, pulse light (noise light) emitted from the LED of another photoelectric switch enters the phototransistor 29. It is assumed that a light receiving signal is generated as shown in FIG. That is, if the light receiving signal B is present while the clock pulse A is at "H", the output E of the flip-flop 36 becomes "H" as shown at E in FIG. Accordingly, the output D of the exclusive OR circuit 73 becomes "L", the transistor 13 is turned on, and the charging of the capacitor 15 is accelerated. At this time, a pulse having a short cycle is generated by the pulse oscillator, and the LED 27 is turned on in a short cycle. Therefore, the next pulse light (noise light) from another photoelectric switch does not overlap with the pulse of the pulse oscillator 4, and when the next pulse occurs, the output E of the flip-flop 36 is "L" and the flip-flop 37 Is "H", the other flip-flops 38
The outputs of .about.40 become "L". Therefore, the output of the exclusive OR circuit 73 becomes “H”, and the pulse cycle of the pulse oscillator 4 returns to the original. That is, a pulse having a long cycle is generated from the pulse oscillator, and the LED 27 is turned on in a long cycle. Since the pulse period is shortened in this way, even if pulse light from another photoelectric switch is incident, the light emission timings of the other photoelectric switches do not overlap for five pulses, and the AND gate 42 Does not become "H". When the object to be detected moves and changes from the display light receiving state to the light receiving state and its own projected light is stably received, the flip-flops 3 which were initially all at "L" level
6 to 40 become “H” sequentially from the first stage, so that the output D of the exclusive OR circuit 73 becomes “L” for 5 pulses until all flip-flops become “H”. The cycle becomes shorter. That is, a pulse with a short cycle is generated from the pulse oscillator, and the LED 27 is turned on in a short cycle. After that (the received light pulse signal is 5
(After successive times), a pulse having a long cycle is generated from the pulse oscillator, and the LED 27 is turned on for a long period (that is, returns to the original state). Since the outputs of the flip-flops 36 and 40 are different for five pulses even when the state changes from the state to the non-light receiving state, the pulse period is shortened during that time. In other words, in such a case, the cycle of the clock pulse for driving the shift register is shortened, so that the response time of the photoelectric switch is shortened. Since the pulse cycle at the time of this shortening determines the response time, if the required response time is set, the pulse cycle becomes longer in a normal state where the output is not inverted and the average flowing through the LED 27 is set. The current is reduced, preventing the LED 27 itself from deteriorating, and helping to reduce the power consumption of the photoelectric switch. According to the present invention, when the state changes from the non-light-receiving state to the light-receiving state or from the light-receiving state to the non-light-receiving state, the period of the pulse oscillator becomes short, and after that change, the period becomes long (the original period). The effect of achieving a long response time and a reduction in power consumption can be obtained while increasing the response speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a time chart showing signal waveforms at points A to G in the circuit of the embodiment. [Description of Signs] 4 pulse oscillator 27 light emitting element 29 light receiving element 36,..., 40 flip-flop (gate circuit, shift register) 73 exclusive OR circuit

Claims (1)

(57) [Claims] A photoelectric switch, comprising: a pulse oscillator; a light emitting unit that is periodically lit by a pulse output from the pulse oscillator; and a light receiving unit that generates a light receiving pulse signal each time pulse light from the light emitting unit is received. Means for shortening the cycle of the pulse oscillator based on a change in the light receiving pulse signal from the light receiving state to the non-light receiving state or from the non-light receiving state to the light receiving state; and a change from the light receiving state to the non-light receiving state. Or, after the point of change from the non-light receiving state to the light receiving state, a light receiving pulse signal is continuously obtained a predetermined number of times corresponding to the pulse light from the light emitting means, or the light receiving pulse signal is output from the light emitting means. Means for extending the cycle of the pulse oscillator based on the fact that the pulse light was not obtained continuously for a predetermined number of times in response to the pulsed light. Photoelectric switch, characterized in that.