JPH06132801A - Photoelectric switch - Google Patents

Abstract

PURPOSE:To reduce an output voltage at the time of turning on a photoelectric switch and to add hysteresis to switching characteristics when a light beam is cut off or made incident. CONSTITUTION:A light emitting diode 5, output transistor Q1 and the parallel circuit of a resistor R1 are connected between terminals 1 and 2. A light receiving circuit 6 receives the light of the light emitting diode 5 and when any object is detected, a signal processing circuit 7 outputs a signal at an H level. At such a time, the transistor Q1 for switching is conducted, and a driving current flows to a load 3 connected to a DC power source 4. In this case, the current of the light emitting diode 5 is increased, and the quantity of lights is increased. At the same time, the driving currents of the light receiving circuit 6 and signal processing circuit 7 are increased as well. Therefore, the switching characteristics at the time of ON are stablized, and the adverse influence of noise from the load or power source is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric switch which detects the presence or absence of an object and connects and disconnects a load.

[0002]

2. Description of the Related Art A photoelectric switch includes a light emitter and a light receiver,
It has a signal processing circuit for discriminating the output of the light receiving portion and an output circuit for connecting and disconnecting the power source of the load. Then, the output circuit is operated by irradiating the detection area with a light beam from the light projecting section and discriminating the output of the light receiving section obtained depending on the presence or absence of the detection object. The intensity of the light incident on the light receiving unit changes when the object is located at the boundary of the detection region, or due to ambient light or the like. It is required to reduce the influence of such unstable incident light.

In the conventional photoelectric switch, for example, in Japanese Patent Publication No. 54-21070, in order to distinguish between disturbance noise and signal,
A photoelectric switch is shown in which the comparison voltage input to the comparator is changed when disturbance noise arrives, and the detection characteristic of the light beam has hysteresis.

[0004]

In such a pulsed light receiving circuit, a malfunction is prevented by temporarily interrupting the pulse signal from the light emitting portion when disturbance noise arrives. However, there is a drawback that a signal for detecting the state of the object cannot be obtained when the pulse signal is cut off. Further, in the DC two-wire type photoelectric switch, it is necessary to reduce the leakage current when it is turned off, and therefore it is necessary to reduce the light projection current of the light projecting unit. Therefore, there is a drawback that it is easily affected by ambient light, noise, etc. and lacks stability.

The present invention has been made in view of the above-mentioned conventional problems, and reduces the conduction resistance when the DC photoelectric switch is turned on, and adds hysteresis to the object detection characteristic to improve the noise resistance characteristic. It is an object of the present invention to realize a photoelectric switch having stable switching characteristics by improving the above.

[0006]

According to the present invention, a light projecting unit for emitting light to a detection region, a light receiving circuit for receiving light emitted from the light projecting unit to an object detection region, and a signal for the light receiving circuit are set to predetermined values. A signal processing circuit that discriminates based on a threshold level and outputs an object detection signal, an output circuit that outputs externally based on the object detection signal of the signal processing circuit, and a drive current for the light receiving circuit and the signal processing circuit when the output circuit is conductive Current control circuit to increase
It is characterized by including.

[0007]

According to the present invention having such characteristics, the light projecting section emits light to the object detection area, and the light receiving circuit receives light from the irradiated object detection area. The signal processing circuit discriminates the output of the light receiving circuit at a predetermined threshold level and outputs an object detection signal. The output circuit interrupts the drive current of the load connected to the DC power supply based on the output level of the object detection signal. The current control circuit increases the supply current to the light receiving circuit and the signal processing circuit when the output circuit is turned on. In this way, the hysteresis characteristic when the output circuit is intermittent is added.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A direct current two-wire type photoelectric switch according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing the overall configuration of the DC 2-wire type photoelectric switch of this embodiment. In this figure, a load 3 and a DC power supply 4 are connected in series between a pair of terminals 1 and 2. The light emitting diode 5 and the switching transistor Q are provided between the terminals 1 and 2.
1 is connected, and the resistor R1 is connected in parallel with the transistor Q1. The light emitting diode 5 is a diode that is provided in the light projecting unit, emits a light beam to the object detection area, and generates a reference voltage. The resistor R1 is a resistor that regulates the current of the light emitting diode 5 when the photoelectric switch is off.

On the other hand, the light receiving circuit 6 provided in the light receiving portion is a circuit that includes a light receiving element, for example, a photodiode, and receives light from the detection region. The signal processing circuit 7 is a circuit that amplifies the output of the light receiving circuit 6 and discriminates the signal at a predetermined threshold level to generate an object detection signal. The output is given to the base of the transistor Q1. Current control circuit 8
Is a circuit that controls the supply current supplied from the DC power supply 4 to the light receiving circuit 6 and the signal processing circuit 7. When the control voltage changes to a high or low level, the supply current is decreased or increased. The transistor Q1 is a switching transistor that connects and disconnects the current of the load 3, and its collector is connected to the cathode of the light emitting diode 5 and the control terminal of the current control circuit 8 to form an output circuit.

The direct current 2 of the first embodiment constructed as described above
The operation of the wire photoelectric switch will be described. At present, the detected object is in a position to block the light emitted from the light emitting diode 5 and no light beam is incident on the light receiving circuit 6, the output of the signal processing circuit 7 becomes L level, and the transistor Q1 is turned off. At this time, a minute current (leakage current) set by the resistor R1 flows through the light emitting diode 5, and the light emission intensity of the light emitting diode 5 is set to the necessary minimum. Therefore, only the leakage current flows from the DC power supply 4 to the load 3 and the load 3 is not driven.

Next, the sensing object moves and the light emitting diode 5
When the light emitted from is incident on the light receiving circuit 6, the signal processing circuit 7 outputs an H level signal. At this time, the transistor Q1 is turned on to supply the current of the DC power supply 4 to the load 3 and increase the light output of the light emitting diode 5. At this time, the forward voltage drop of the light emitting diode 5 is saturated, and the voltage is given to the current control circuit 8. Therefore, the supply current of the current control circuit 8 increases, and the light receiving circuit 6 and the signal processing circuit 7
The operation of can be stabilized.

As described above, the incident light on the light receiving circuit 6 often changes when an object enters or leaves the detection area. However, once the transistor Q1 is turned on, the output of the light emitting diode 5 is increased and the currents of the light receiving circuit 6 and the signal processing circuit 7 are increased, so that the on-state characteristics of the transistor Q1 are stabilized. Thus, the hysteresis characteristic of the photoelectric switch is added.

Next, a two-wire type photoelectric switch according to the second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a circuit diagram showing the overall configuration of a DC 2-wire photoelectric switch. In this figure, a load 3 and a DC power source 4 are connected in series between terminals 1 and 2, and a light receiving circuit 6, a signal processing circuit 7, and a switching transistor Q1 are provided in the light receiving portion, respectively, as in the first embodiment. Therefore, the description thereof will be omitted.

In this embodiment, a resistor R is connected in series between terminals 1 and 2.
2, the light emitting diode 5 is connected to form a light projecting unit. The output of the light receiving circuit 6 having a light receiving element is given to the signal processing circuit 7. The signal processing circuit 7 discriminates the output of the light receiving circuit 6 by a predetermined threshold value to simultaneously open and close the switching transistor Q2 in addition to the switching transistor Q1. A transistor Q3 and a resistor R4 are provided between the collector of the transistor Q1 and the terminal 1.
Are connected. The base and collector of the transistor Q3 are commonly connected, and further connected to the bases of the transistors Q4 and Q5 to form a current mirror circuit. The transistor Q4 has an emitter connected to the terminal 1 and a collector connected to the base of the transistor Q1. Also transistor Q
The emitter of 5 is connected to the terminal 1, and the collector is connected to the power supply terminals of the light receiving circuit 6 and the signal processing circuit 7. Transistor Q4
Is a first current control transistor for controlling the base current of the transistor Q1, and the transistor Q5 is a second current control transistor for controlling the drive current of the light receiving circuit 6 and the signal processing circuit 7.

A diode 9 is connected in the forward direction between the resistor R1 and the terminal 1. Diode 9 is transistor Q3
And a resistor R4, which is a diode for applying a reference voltage to the connected body in series, and may be the light emitting diode 5 of the light projecting unit. The resistor R4 is a diode D1 when the DC photoelectric switch is off.
Is a resistor for setting the drive current of the transistor Q4 and the reference current of the transistor Q4 together with the resistor R3 in series.

Here, the transistor Q shown in the alternate long and short dash line
3, Q4, Q5, resistors R4, R5 are connected to the transistor Q1.
A current control circuit 10A that increases the current of the diode 9 and increases the supply current of the light receiving circuit 6 and the signal processing circuit 7 when the switch is turned on is configured.

The direct current 2 of the second embodiment constructed as described above
The operation of the wire photoelectric switch will be described. If the detection object is not in the detection area, the light is blocked, the light beam is not incident on the light receiving circuit 6, and the output of the signal processing circuit 7 becomes L level. This turns off transistors Q1 and Q2,
No drive current flows through the load 3. At this time, a reference current flows from the power supply to the transistor Q3 via the resistors R4 and R3. For this reference current, the forward voltage of the diode 9 is Vf _1, and the base-emitter voltage of the transistor Q3 is Vf _1.
When _BE1, the _{(Vf 1 -V BE1) / R4} . A drive current equal to this reference current is given to the light receiving circuit 6 and the signal processing circuit 7 via the transistor Q5.

Next, when the detection object moves to the detection area, the light beam of the light emitting diode 5 becomes the light receiving circuit 6 and the output of the signal processing circuit 7 becomes H level. Therefore, the transistor Q
1, Q2 are turned on and the load is driven by transistor Q1. The reference current of the transistor Q3 at this time is the forward voltage of the diode 9 Vf ₂ (≈Vf ₁ ), and the base-emitter voltage V _BE2 (≈V of the transistor Q ₄ ).
When _BE1), a (parallel resistance value of Vf ₂ -V _BE2) / (R4 and R5). Therefore, the reference current increases, and the drive currents of the light receiving circuit 6 and the signal processing circuit 7 supplied via the transistor Q5 increase. Therefore, the light receiving sensitivity of the light receiving section is increased. Further, since the collector current of the transistor Q4 flows into the base of the transistor Q1, the operation of the transistor Q1 is stabilized. Since the output of the signal processing circuit 7 is positively fed back to the transistor Q1 via the transistors Q1, Q4, Q3, the conduction characteristic of the transistor Q1 is stabilized.

The diode 9 may be replaced by the light emitting diode 5. In this case, the reference current of the transistor Q4 when the DC photoelectric switch is off can be adjusted by adjusting the value of the resistor R3, and further the light receiving circuit 6
The intensity of the light beam incident on can also be adjusted.
By adding the hysteresis characteristic when the transistor Q1 is intermittent as described above, the noise resistance of the DC two-wire photoelectric switch is improved, and the chattering phenomenon that occurs when the light beam is blocked or transmitted excessively is prevented. The output of the unit can be stabilized.

Incidentally, FIG. 3 shows a circuit in the case where the second switching transistor Q2 is omitted in the direct current two-wire type photoelectric switch in the second embodiment. Also diode 9
Instead of this, a light emitting diode 5 is connected. It is the same as the second embodiment except that the resistor R5 is removed together with the transistor Q2. Also in this case, when the signal processing circuit 7 is turned on, the transistor Q1 is also turned on, the current of the light emitting diode 5 is increased, and the voltage across it is also increased. Therefore, the amount of light emitted from the light emitting diode 5 increases, and it functions as an optical hysteresis.

Next, a three-wire type photoelectric switch according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a circuit diagram showing the overall configuration of a DC 3-wire photoelectric switch. In this figure, a load 3 is connected between terminals 1a and 1b, and a DC power supply 4 is connected between terminals 1a and 2. The resistor R2 and the light emitting diode 5 are respectively provided in the light projecting portion, and the light receiving circuit 6, the signal processing circuit 7, the switching transistor Q1, and the diode 9 are respectively provided in the light receiving portion, as in the above-described embodiment. The description is omitted. The diode D1 may be the light emitting diode 5.

The output of the signal processing circuit 7 is a transistor Q.
It is given to the base of 1 and Q2 respectively. The switching transistor Q1 is an output circuit for connecting and disconnecting the current of the load 3 connected via the open collector terminal 1b. On the other hand, the transistor Q2 is a transistor that gives a control voltage to the current control circuits 11 and 12. The current control circuit 11 is connected between the DC power supply and the common base of the transistors Q1 and Q2, and reduces or increases the base current of the transistors Q1 and Q2 by changing its control voltage to high or low level.

Next, the operation of the photoelectric switch of the fourth embodiment will be described. When the detection object is present at the light shielding position, the light receiving circuit 6 has a low light receiving level, and the output of the signal processing circuit 7 becomes L level. Therefore, the transistors Q1, Q
2 is turned off, and the control voltages of the current control circuits 11 and 12 are at high levels. Therefore, the current supplied to the light receiving circuit 6 also becomes the minimum value.

Next, when the detection object moves from the position where the light beam of the light emitting diode 5 is blocked, the light receiving level of the light receiving circuit 6 becomes high and the output of the signal processing circuit 7 becomes H level. At this time, the transistors Q1 and Q2 are rendered conductive, and the level of the control voltage of the current control circuits 11 and 12 is lowered. Therefore, the current supplied to the current control circuits 11 and 12 increases, and the current supplied to the light receiving circuit 6, the signal processing circuit 7 and the base of the transistor Q1 increases. Therefore, the transistor Q
1 rapidly conducts, and load 3 connected to terminals 1a, 1b
To drive.

When the object moves at the boundary of the detection area at a low speed or moves with vibration, chattering also occurs in the light receiving level received by the light receiving circuit 6. However, since the supply current to the light receiving circuit 6 and the signal processing circuit 7 increases and the base current of the transistor Q1 also increases, the conduction of the transistor Q1 is completely maintained. Therefore, when the detected object passes between the light projecting portion and the light receiving portion, a hysteresis characteristic is added. Therefore, the output of the signal processing circuit 7 changes sharply, and the power source of the load can be stably disconnected.

[0026]

As described in detail above, according to the present invention, the switching speed of the photoelectric switch can be improved by adding the hysteresis characteristic when the output circuit is intermittent. Further, it is possible to prevent the chattering phenomenon that occurs when the light beam is blocked or transmitted excessively and to stabilize the output. Further, it is possible to reduce the influence of external noise generated from the DC power supply or the load and realize stable switching characteristics.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a DC 2-wire photoelectric switch according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a DC two-wire photoelectric switch according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a DC 2-wire photoelectric switch according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a DC 3-wire type photoelectric switch according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1, 1a, 1b, 2 terminals 3 load 4 DC power supply 5 light emitting diode 6 light receiving circuit 7 signal processing circuit 8, 10A, 10B, 11, 12 current control circuit 9 diode Q1 to Q5 transistor R1 to R5 resistance

Claims (4)

[Claims] 1. A light projecting unit for emitting light to a detection region, a light receiving circuit for receiving light emitted from the light projecting unit to an object detection region, and a signal of the light receiving circuit for discriminating at a predetermined threshold level. A signal processing circuit that outputs an object detection signal, an output circuit that outputs an output based on an object detection signal of the signal processing circuit, and a drive current for the light receiving circuit and the signal processing circuit when the output circuit is in conduction. And a current control circuit for increasing the current control circuit. 2. The light projecting unit includes a light emitting diode which is connected between a load and an output terminal of the output circuit and whose current increases when the output circuit is in a conductive state. Photoelectric switch. 3. The output circuit is energized by the output of the signal processing circuit and energized by the output of the signal processing circuit, and a first switching transistor that connects and disconnects the load and the DC power supply. 3. The photoelectric switch according to claim 1, further comprising a second switching transistor that increases the supply current of the current control circuit. 4. The current control circuit supplies a first current control transistor for controlling a base current of a first switching transistor of the output circuit, and a current supplied to the light receiving circuit and the signal processing circuit, respectively. A second current controlling transistor for controlling, and a current mirror circuit together with the first and second current controlling transistors, which are connected in series between a first switching transistor of the output circuit and a DC power source, The photoelectric switch according to claim 3, further comprising a current mirror transistor that generates a reference current larger than that when the DC photoelectric switch is turned on.