JPH05308269A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce the power consumption of the photoelectric switch. CONSTITUTION:A light emitting element 3 is intermittently driven with an output of an oscillation circuit 1 through a light emission circuit 2. Then an output of the oscillation circuit is expanded by a pulse width magnification circuit 21 and its output is given to a current source gate circuit 22. A current source gate circuit 22 operates a voltage generating circuit 23 to generate a reference voltage V+ which is always higher than a comparison voltage V-. Moreover, the comparison voltage V- is superimposed on an amplified output from a light receiving section. Thus, a couple of voltages are given to a comparator circuit 24 to reduce the current consumption. Furthermore, an object is sensed without malfunction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric switch, and more particularly to a photoelectric switch designed to reduce the current consumption on the light receiving portion side thereof.

[0002]

2. Description of the Related Art A conventional photoelectric switch, for example, as shown in FIG.
The light projecting element 3 is intermittently driven via the light projecting circuit 2. If there is an object in the irradiation area of the light projecting element 3, the light receiving element 4 receives the reflected light, and the preamplifier 5 and the main amplifier 6
The signal is amplified through and given to the comparison circuit 7. The comparator circuit 7 discriminates the amplified output by a predetermined threshold value, and the comparison output is gated by the gate circuit 8
Give to. The gate circuit 8 gives only the signal synchronized with the oscillation clock of the oscillation circuit 1 to the integration circuit 9 at the next stage. The integrating circuit 9 is a signal processing circuit that outputs an object detection signal to the outside via the output circuit 10 when a signal exceeding a predetermined level is continuously obtained a plurality of times.

[0003]

However, in such a photoelectric switch, it is necessary to reduce the current consumption in order to reduce the amount of heat generation and reduce the size. Especially in a two-wire type photoelectric switch, it is necessary to make the leakage current below a predetermined value, for example, 1 mA or less when the switch is turned off. As described above, the light projecting section intermittently drives the light projecting element 3 in accordance with the oscillation output of the oscillation circuit 1, and the light receiving section processes the light receiving signal only during this period. I'm wearing a gate. However, in the conventional photoelectric switch, current is always supplied to the preamplifier 5, the main amplifier 6, the comparison circuit 7 and the signal processing circuit of the subsequent stage regardless of the timing of oscillation of the oscillation circuit 1, and a wasteful current is generated. It had the drawback of consuming it.

The present invention has been made in view of the above problems of the conventional photoelectric switch, and supplies a current to the block of the light receiving circuit including the comparison circuit only in a necessary time zone to reduce the power consumption. It is a technical task to be able to achieve

[0005]

According to the present invention, a light projecting element for irradiating a detection region with light, an oscillator circuit for generating a light projecting pulse and intermittently driving the light projecting element, and an object detection by the light projecting element are provided. A light receiving element that receives an optical signal obtained through the region, an amplifier that amplifies the output of the light receiving element, a pulse width expansion circuit that expands the pulse width of the oscillation circuit and supplies power to the amplifier,
A comparison circuit that obtains an object detection signal by comparing a pair of voltages, and has a reference voltage of the comparison circuit and a predetermined voltage difference from the reference voltage,
The voltage generation circuit includes: a voltage generation circuit that generates a comparison voltage on which the output of the amplifier is superimposed and gives the comparison voltage to the comparison circuit; and a current source gate circuit that operates by the output of the pulse width expansion circuit to operate the voltage generation circuit. The reference voltage is always higher in rising and falling speed than the comparison voltage, and its level is set higher than the comparison voltage.

[0006]

According to the present invention having such characteristics, the output of the oscillation circuit is expanded by the pulse width expansion circuit, and the voltage generation circuit is operated by the current source gate circuit. The voltage generation circuit sets the reference voltage and the comparison voltage to be given to the comparison circuit, the rising and falling speed of the reference voltage is fast, and the level thereof is also set higher than the comparison voltage. In this way, the reference voltage is always higher than the comparison voltage when no object is detected and the output of the amplifier is not superimposed on the comparison voltage. When the output is obtained from the amplifier, this level is inverted, so that the object detection signal is output by the comparison circuit.
Therefore, the comparison circuit can obtain the object identification signal without causing a malfunction and without using a gate circuit for signal processing.

[0007]

2 is a block diagram showing the overall construction of a photoelectric switch according to a first embodiment of the present invention. The same parts as those of the conventional example described above are designated by the same reference numerals and detailed description thereof will be omitted.
Also in this embodiment, the light projecting element 3 is driven through the light projecting circuit 2 by the intermittent light projecting pulses from the oscillation circuit 1, and the light obtained from the light projecting element 3 through the object detection area is generated. The light is received by the light receiving element 4 and amplified through an amplifier including a preamplifier 5 and a main amplifier 6.

In the present embodiment, the output of the oscillator circuit 1 is given to the pulse width expansion circuit 21. Pulse width expansion circuit 2
Reference numeral 1 expands the pulse width before and after the output of the oscillation circuit 1, and the output controls the power supplies of the preamplifier 5 and the main amplifier 6 of the light receiving section. Also, pulse width expansion circuit 2
The output of 1 is given to the current source gate circuit 22. The current source gate circuit 22 controls the power supplies of the voltage generation circuit 23 and the comparison circuit 24. The comparison circuit 24 compares the reference voltage generated by the voltage generation circuit 23 with the comparison voltage on which the input signal is superimposed. The output of the comparison circuit 24 is given to the integration circuit 9. The integration circuit 9 detects whether or not the output of the comparison circuit 24 is continuously obtained in a predetermined cycle, and outputs the object detection signal to the outside through the output circuit 10 as in the conventional example described above.

FIG. 1 is a circuit diagram showing the configuration of a current source gate circuit 22, a voltage generation circuit 23, and a comparison circuit 24, which are the main parts of this embodiment. In this figure, the pulse width expansion circuit 2
The output of 1 is given to the input end 22a of the current source gate circuit 22. The resistor R1 is connected to this input end, and the other ends are connected to the resistors R2 and R3. Here, the resistance value of the resistor R2 is set to be larger than that of the resistor R3. Resistance R2
Is connected to the base of the transistor Q1. The emitter of the transistor Q1 is grounded, and the collector thereof is connected to the current mirror circuit composed of the transistors Q2 and Q3. The emitters of the transistors Q2 and Q3 are commonly connected to the power supply Vcc, and the bases thereof are commonly connected. The collector of the transistor Q2 is grounded via the resistor R4. The collector of the transistor Q3 is connected to the transistor Q1,
Further, it is connected to a current mirror circuit composed of transistors Q4 and Q5. The collector of the transistor Q4 is a resistor R
5, grounded via diode D1, and transistor Q
The collector of 5 is connected to a current mirror circuit composed of transistors Q6 and Q7. The collector of the transistor Q6 is grounded via the diode D2. The collector of the transistor Q7 is connected to the power source Vcc via the resistor R6, and the emitter thereof is grounded via the diode D3. Further, the amplified output of the amplifier 6 is given to the emitter end. The anode of the diode D3 is the transistor Q8.
, The base of the transistor Q8 is connected to the other end of the resistor R3, and the emitter is grounded.
The emitter terminal of the transistor Q7 and the collector terminal of the transistor Q4 of the voltage generation circuit 23 are given to the comparison circuit 24 as the comparison voltage V ₋ and the reference voltage V ₊ .

The comparison circuit 24 has a transistor Q9 which forms a current mirror circuit together with the transistors Q4 and Q5. The emitter of the transistor Q9 is connected to the power supply, and the collector of the transistor Q9 is connected to the transistors Q10 and Q11. The bases of the transistors Q10 and Q11 are connected to the V ₋ and V ₊ ends of the voltage generation circuit 23, respectively.
Transistors Q12 and Q13 are connected to the collectors of the transistors Q10 and Q11, respectively. The transistors Q12 and Q13 output the output identified here to the outside through the transistor Q14. The collector of the transistor Q14 is connected to the collector resistor R7, and the collector end is connected to the integrating circuit 9.

Next, the operation of this embodiment will be described. First, the oscillator circuit 1 outputs a periodic pulse as shown in FIG. 3A, and drives the light projecting element 3 via the light projecting circuit 2. Then, the pulse width expansion circuit 21 expands the pulse width of the signal as shown in FIG. 3B, and when the output is at the L level, power is supplied to the amplifier 5 and the main amplifier 6. This signal is also given to the current source gate circuit 22. Therefore, when the input to the current source gate circuit 22 is at H level, the transistors Q1 and Q8 are in the ON state, and V ₋ and V ₊ of the voltage generation circuit 23 are at almost zero level as shown in FIG. 3 (c). .. Here, the constant current I ₁ determined by the resistor R4 flows through the transistor Q2, and the substantially same current I ₂ flows through the transistors Q3 and Q1.

Now, at time t ₁ , the current source gate circuit 22
It is assumed that the input to is changed from H level to L level. Then, the transistors Q1 and Q8 are turned off. The current I ₂ of the transistor Q1 flows through the transistor Q4, the resistor R5, and the diode D1 because the transistor Q1 is turned off. This current is I ₂ ′. Therefore, the voltage on the V ₊ side of the comparison circuit 24 rises rapidly, and the voltage is expressed by the following equation. V ₊ = Vf 1 + I ₂ ′ × R5 And this current I ₂ ′ (≈I ₁ ) also flows through the transistor Q5 by the current mirror circuit (current I ₃ ). Therefore, at the same time, the current mirror circuit of the transistors Q6 and Q7 also flows into the transistor Q7 (current I ₄ ).
Since the transistor Q8 is off, the voltage V ₋ given to the comparison circuit 24 is expressed by the following equation. V ₋ = Vf3 Note that Vf1 and Vf3 are forward drop voltages of the diodes D1 and D3.

Here, after the time t ₁ , V ₊ rises quickly, and then V ₋ rises after a time delay due to the rise of the currents of the transistors Q4 and Q5 and Q6 and Q7 forming the current mirror circuit. This is transistors Q4 to Q7
It depends on the parasitic capacitance between collector and base of
When the current used is small, as in a DC two-wire photoelectric switch, the effect of parasitic capacitance is large and the time difference becomes large. Therefore, in the present invention, this is utilized to provide the time difference τ ₁ .

Next, at time t _2, when the output of the pulse width expanding circuit 21 rises, the transistors Q1 and Q8 are turned on. At this time, since the resistance value of the resistor R2 is larger than the resistance R3, the base current of the transistor Q1 becomes smaller than the base current of the transistor Q8. Therefore, the transistor Q8 is turned on first, the V ₋ side falls first, and V ₊ falls slightly later, as shown in FIG. 3C, and a time difference τ ₂ occurs. Therefore, as shown in FIG. 3C, the comparison voltage V ₋ is always smaller than the reference voltage V ₊ . Now, when the output of the pulse width expansion circuit 21 becomes L level at time t ₃ and H level at t ₄ , the same operation is repeated. At this time, the time of FIG.
When the object is close to t ₅ , reflected light from the object is obtained by the light projection pulse. This reflected light is passed through the light receiving element 4, the preamplifier 5, and the amplifier 6 to generate the voltage generation circuit 23.
To the base of the transistor Q7. Therefore, FIG.
As shown in (c), the potential on the V ₋ side rises as shown. In this case, the output of the comparison circuit 24 is inverted and a comparison output is obtained as shown in FIG. When this output is continuously obtained a plurality of times, it is output from the output circuit 10 via the integration circuit 9 as an object detection signal.

As described above, in this embodiment, the voltage generation circuit 23
Since one voltage of the comparison circuit 24 is always set to be lower than the other voltage by the output of, the output of the comparison circuit 24 is not obtained at the time of rising and the time of falling. Therefore, the output of the current source gate circuit 22 can be used as it is as a gate signal, it is not necessary to use a gate circuit on the output side of the comparison circuit 24, and the circuit configuration can be greatly simplified. By adding such a current source gate circuit, it is possible to significantly reduce current consumption. That is, the input to the current source gate circuit 22 is H
At the level, the current is I ₁ + I ₂ , and at the L level, the current is I ₁ , I ₂ ′ and I _{3 to} I ₅ . Assuming that the pulse width of the current source gate is T ₀ and one cycle is T, the reduction current by the current source gate is (I ₁ + I ₂ ′ + I ₃ + I ₄ + I ₅ ) − {I ₁ + I ₂ + (I ₃ + I _{4 + I 5) × T 0} / T} = (I 3 + I 4 + I 5) × (T-T 0) a / T. In addition to this, the currents of the preamplifier 5 and the amplifier 6 are reduced, and the used current can be significantly reduced.

FIG. 4 is a circuit diagram showing the configuration of the main part of a photoelectric switch according to the second embodiment of the present invention. In this figure, another example of the current source gate circuit 22A, the voltage generation circuit 23A, and the comparison circuit 24A is shown, and the other circuit configuration is the same as that of the first embodiment described above. In the present embodiment, the output of the pulse width expansion circuit 21 is connected to the resistors R2 and R3 via the resistor R1.
Are connected to each. Here, the resistance value of the resistor R2 is the resistance R3.
Keep it smaller. And the voltage generation circuit 2
The output of the amplifier 6 is connected to 3A at one end of the capacitor C1. The other end of the capacitor C1 is grounded via the resistor R4 and is connected to the base of the transistor Q3. The collector of the transistor Q3 is grounded, and the emitter is connected to the current mirror circuit composed of the transistors Q4 and Q5. The emitter of the transistor Q5 is connected to the power supply Vcc, and the collector is connected to the current mirror circuit composed of the transistors Q6 and Q7. The emitter of the transistor Q7 is grounded, and the collector is connected to the power supply Vcc via the current source I ₁ and the resistor R5. The collector of the transistor Q2 is connected to the constant current source I ₁ . The voltage generation circuit 23A sets the other end of the resistor R5 to the reference voltage V ₋ and sets the transistor Q3
Is applied to the comparison circuit 24A as the comparison voltage V ₊ .

Now, the comparison circuit 24A includes a transistor Q8,
Transistors Q10, Q1 in the collector circuit composed of Q9
A differential amplifier composed of 1 is connected to form a comparison circuit, and the common emitter ends of the transistors Q10 and Q11 are connected to the transistor Q12. Transistor Q12
Together with the transistors Q6 and Q7 form a current mirror circuit. The collector of the transistor Q11 is connected to the base of the output transistor Q13. The collector of the transistor Q13 is grounded via the resistor R6, and is supplied to the integrating circuit 7 as a comparison output.

Next, the operation of this embodiment will be described. Also in this embodiment, the light emitting pulse is periodically generated from the oscillation circuit 1 similarly to the respective parts of the first embodiment described above. This pulse width is expanded by the pulse width expansion circuit 21 and added to the current source gate circuit 22A, as in the first embodiment described above. Transistors Q1, Q2 is turned off at time t ₆ to the output of the current source gate falls in Fig. Therefore, V ₋ is expressed by the following equation. V ₋ = V _BE7 + I ₁ R5 Since the current I ₁ flows through the transistor Q7, the transistors Q6 and Q12 rise and the comparison circuit 24A operates. Since the current I ₂ flows through the transistor Q6, the current I ₃ also flows through the transistors Q4 and Q3 by the current mirror circuit of the transistors Q5 and Q4. This current causes V ₊ to rise. Here, the voltage of V ₊ is expressed by the following equation. _{V + = V BE3 + I 1} / hf3 × R4 ≒ V BE3 Thus V ₊ is V _- a current mirror circuit and the transistor Q3 of the transistors Q4, Q5 becomes that guests only slow stand standing rise time than occurs the time difference tau _3.

When the output of the pulse width expansion circuit 21 becomes H level at time t ₇ , the base voltages of the transistors Q1 and Q2 also become H level and these transistors are turned on. Therefore, both V ₊ and V ₋ are at almost zero level.
At this time, since the resistance value of the resistor R2 is smaller than R3, the base current of the transistor Q1 becomes larger than the base current of Q2, the V ₊ side falls first, and a time difference τ ₄ occurs. Moreover, since the current of the constant current source I ₁ flows through the transistor Q2,
The transistors Q7, Q6 and Q12 are turned off, and no current flows in the comparison circuit 24A. Therefore, only when the output of the pulse width expansion circuit 21 becomes L level, the comparison circuit 23A
Therefore, current is consumed in the voltage generation circuit 24A. When the output of the pulse width expansion circuit 21 is at H level, the constant current source I ₁
And only the current I _{3 of the} transistor Q4 flows. Therefore, assuming that the pulse period of the current source gate and the pulse width of the H level are T and T ₀ , respectively, the reduction current is expressed by the following equation. I ₁ + I ₂ + I ₃ + I ₄ − {I ₁ + I ₃ + (I ₂ +
I ₄ ) × T ₀ / T} = (I ₂ + I ₄ ) × (T−T ₀ ) /
T In addition to this current reduction, the currents of the preamplifier 5 and the amplifier 6 can also be reduced.

[0020]

As described above in detail, according to the present invention, the light receiving circuit and the signal processing circuit are operated only during the period when the signal is received by the light emitting pulse of the light emitting circuit which intermittently emits light. ing. Therefore, the effect that the current consumption of the photoelectric switch circuit can be greatly reduced as a whole can be obtained. Therefore, if the reduced current is increased, for example, by increasing the drive current of the light projecting element, it is possible to increase the detection distance. Further, since no erroneous output is generated from the comparison circuit when the current source gate circuit rises and falls, it is possible to reduce the gate circuit itself which limits the output of the comparison circuit only when the light projection pulse is at the H level. The circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part of a photoelectric switch according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing the overall configuration of a photoelectric switch of this embodiment.

FIG. 3 is a time chart showing a waveform of each part of the photoelectric switch according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a main part of a photoelectric switch according to a second embodiment of the present invention.

FIG. 5 is a time chart showing waveforms at various parts of the photoelectric switch according to the second embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a conventional photoelectric switch.

[Explanation of symbols]

 1 oscillator circuit 2 light emitting circuit 3 light emitting element 4 light receiving element 5 preamplifier 6 main amplifier 8 gate circuit 9 integrating circuit 10 output circuit 21 pulse width expansion circuit 22, 22A current source gate circuit 23, 23A voltage generation circuit 24, 24A comparison circuit

Claims (1)

[Claims] 1. A light projecting element for irradiating light to a detection area, an oscillation circuit for generating a light projecting pulse, and driving the light projecting element intermittently, and a light projecting element obtained from the light projecting element through an object detection area. A light receiving element that receives an optical signal that is received, an amplifier that amplifies the output of the light receiving element, a pulse width expanding circuit that expands the pulse width of the oscillation circuit and supplies power to the amplifier, and compares a pair of voltages. A comparison circuit that obtains an object detection signal; and a voltage generation circuit that generates a comparison voltage that has a reference voltage of the comparison circuit and a predetermined voltage difference from the reference voltage, and that superimposes the output of the amplifier, and supplies the comparison voltage to the comparison circuit. A current source gate circuit that operates according to the output of the pulse width expansion circuit to operate the voltage generation circuit, wherein the reference voltage of the voltage generation circuit has rising and falling speeds that are always faster than the comparison voltage, Is a photoelectric switch characterized by being set higher than the comparison voltage.