JP2002217702A - Apc device for photoelectric switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an APC(Automatic Power Control) device for a photoelectric switch that enhances the accuracy of feedback control without the need for using a high-speed amplifier circuit so as to keep the light emission amount of a light emitting element constant. SOLUTION: A 1st switch 17 and a 2nd switch 18 are connected in series between a light receiving element 12 and an operational amplifier 16 in this order from the light receiving element 12. A midpoint P2 between the 1st switch 17 and the 2nd switch 18 is connected to ground via a 1st capacitor 20. Furthermore, a midpoint P3 between the 2nd switch 18 and the operational amplifier 16 is connected to ground via a 2nd capacitor 21. When the light emitting element 11 is lighted, first an APC circuit 10 reaches a 1st state where the 1st switch 17 is closed and the 2nd switch 18 is opened, and then reaches a 2nd state where both the 1st and 2nd switches 17, 18 are opened, When the light emission of the light emitting element 11 is stopped, the APC circuit 10 reaches a 3rd state where the 1st switch 17 is opened and the 2nd switch 18 is closed, and the APC circuit 10 restores to the 1st state when the light emitting element 11 is lighted.

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 an automatic power control (APC) device for maintaining a constant amount of light emitted from a light emitting element.

[0002]

2. Description of the Related Art A photoelectric switch is disclosed, for example, in JP-A-9-18.
No. 412, including a light-emitting element such as a laser diode, and a light-receiving element for receiving light emitted from the light-emitting element, light received by the light-receiving element by reflecting the light of the light-emitting element through a detection object, or It is often used to determine the presence or absence of a detected object by interposing the detected object between the light receiving element.

Since the photoelectric switch includes a possibility of erroneous output when the amount of light emitted from the light emitting element changes, an automatic power control (APC) device is incorporated to maintain the reliability of the photoelectric switch.

FIG. 1 shows a circuit of an APC device built in a conventional photoelectric switch. In the illustrated APC circuit 1, when the switch 2 is turned ON / OFF intermittently, the light emitting element 3 blinks in pulses. When the light emitting element 3 emits light, the light causes the APC circuit 1 to substantially form a feedback loop.

In the APC circuit 1, when the light emitting element 3 emits a pulse light, this light is input to the light receiving element 4, and a current generated according to the amount of light received by the light receiving element 4 is converted into a voltage Vb by the resistor 5. You. By controlling the voltage Vb, which is the light receiving result of the light receiving element 4, to be equal to the reference voltage V ₀ of the OP amplifier 6, the light emission amount of the light emitting element 3 can be kept constant.

[0006]

However, in order to realize automatic power control (APC) using pulsed light emission, a high-speed amplifier circuit having excellent responsiveness is required in order to enhance the accuracy of feedback control of the projected light amount. It needs to be adopted. This problem becomes significant as the pulse emission time is shortened, and is an important requirement.

SUMMARY OF THE INVENTION An object of the present invention is to provide an APC device for a photoelectric switch which can improve the accuracy of feedback control and maintain a constant light emission amount of a light emitting element without using a high-speed amplifier circuit. It is in.

A further object of the present invention is to reduce the pulse emission time without using a high-speed amplifier circuit.
APC of a photoelectric switch capable of maintaining a constant light emission amount of a light emitting element by improving the accuracy of feedback control under a circuit configuration including an analog device
It is to provide a device.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided a light-emitting element which emits light with a pulse, a light-receiving element which receives light emitted by the light-emitting element, and a light-emitting element which emits light. A light emission amount control unit for controlling an amount, and controlling the light emission amount control unit with an operation amount corresponding to an amount of light received by the light receiving element so as to maintain a constant amount of light emitted by the light emitting element. APC device of a photoelectric switch having an operation amount control unit for performing the operation amount control unit, wherein the operation amount control unit accumulates a current light reception result corresponding to an amount of light received by the light receiving element when the light emitting element emits light. First storage means for storing the light receiving element, second storage means for storing the previous light receiving result of the light receiving element corresponding to the current operation amount of the light emitting element at the time of light emission and holding the same, At the time of the next emission stop of the element Averaging means for averaging the current light reception result and the previous light reception result, and at the next light emission of the light emitting element, the light emission amount control with an operation amount based on the averaged light reception result. This is achieved by providing an APC device for a photoelectric switch characterized by controlling the means.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention, a light emitting element, switching means for causing the light emitting element to emit a pulse, a light receiving element for receiving light emitted by the light emitting element, and a light receiving element Are connected in series to a resistor for converting a current flowing according to the amount of light received by the light receiving element into a voltage, and a conductor for applying the voltage converted by the resistor to the negative input terminal of the OP amplifier. First and second switch means, a first capacitor connected between a ground point between the first switch means and the second switch means, and ground, the second switch means and the OP amplifier. A second capacitor connected between an intermediate point of the second and the ground, and a transistor, a base of the transistor is connected to an output terminal of the OP amplifier, and an emitter of the transistor is When the switching means is connected, the light-emitting element is connected to the collector of the transistor, and the light-emitting element emits light, first, the first switch means is turned on and the second switch means is turned off in a first state, Next, while the light emitting element remains emitting light, the first switch means is turned off and the second switch means is turned to a second state, and when the light emitting element stops emitting light, The first switch means is O
When the FF is performed and the second switch means is turned on to be in the third state, the light emission amount of the light emitting element is kept constant and the APC function is realized.

In another embodiment of the present invention, in a state where the light emitting element emits light, the first switch is turned on, the second switch is turned off, and then the light emission of the light emitting element is stopped. In this state, when the first switch is turned off and the second switch is turned on, the light emission amount of the light emitting element is kept constant.

In another embodiment of the present invention, comparing means for comparing the manipulated variable output from the manipulated variable control means with a predetermined reference value, and an APC function based on a signal from the comparing means. Further includes an abnormality determining unit that determines whether the APC function is operating normally, and a notifying unit that notifies an abnormality when the APC function is determined not to be operating normally in the abnormality determining unit. For example, the operator can be informed of a situation in which the light emitting element has deteriorated and the APC function does not operate normally. The above and other objects and advantages of the present invention will be apparent from the following detailed description of preferred embodiments of the present invention.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an APC device of a photoelectric switch according to an embodiment. FIG. 2 shows A of the embodiment.
2 shows a circuit of a PC device. The illustrated APC circuit 10 includes a light emitting element 11 and a light receiving element 12 as in the related art, and a feedback loop is formed substantially through transmission and reception of light between the light emitting element 11 and the light receiving element 12. Has become.

The light emitting element 11 is connected to the collector of the transistor 13 and the emitter of the transistor 13 is connected to the resistor 1
4 (R ₃ ) and the light emission control switch 15 (SW ₃ ). The transistor 13 constitutes a light emission amount control unit that controls the light emission amount of the light emitting element 11 as will be described later.

The APC circuit 10 includes an OP amplifier 16,
The light receiving element 12 is connected to a negative input terminal of the OP amplifier 16. A first switch 17 (S) is provided between the light receiving element 12 and the OP amplifier 16 in order from the light receiving element 12 side.
W ₁ ) and the second switch 18 (SW ₂ ) are connected in series.

The light receiving element 12 and the first switch 17 (S
W ₁₎ intermediate point P ₁ with the resistor for converting the current flowing depending on the amount of received light receiving element 12 receives the voltage 1
9 (R ₁ ). Further, an intermediate point P2 between the first switch 17 (SW ₁ ) and the second switch 18 (SW ₂ ) is grounded via the first capacitor 20. The second switch 18 (SW ₂ ) and the OP amplifier 1
6 and the intermediate point P3 is grounded via the second capacitor 21 (C ₂ ). As will be understood from the description below, the first capacitor 20 constitutes a first storage unit that stores and holds a voltage corresponding to the current amount of light received when the light emitting element 11 emits light. Further, as will be understood from the description below, the second capacitor 21 includes a second storage unit that stores and holds a light reception result corresponding to an operation amount related to a current light emission amount when the light emitting element 11 emits light. Make up.

A reference voltage V ₀ is applied to a positive input terminal of the OP amplifier 16. On the other hand, the output terminal of the OP amplifier 16 is connected to the base of the transistor 13.
The OP amplifier 16 constitutes an operation amount control means for controlling an operation amount of the light emission amount control means including the transistor 13. In order to stabilize the operation of the OP amplifier 16, it is preferable to provide a capacitor 22 (C ₃ ) between the output terminal of the OP amplifier 16 and the negative input terminal.
Further, in order to stabilize the potential during light emission of the light emitting element 12, a resistor 2 is connected between the OP amplifier 16 and the transistor 13.
3 (R ₂ ) and / or transistor 1
3 may be grounded via a capacitor 24 (C ₄ ).

FIGS. 2 to 4 are diagrams for explaining a series of controls related to the pulse light emission of the light emitting element 11 in a time-series manner.

FIG. 2 shows a light emission control switch 15 (SW ₃ ).
Indicates a first state in which the first switch 17 (SW ₁ ) is ON, the second switch 18 (SW ₂ ) is OFF, and the first switch 17 (SW ₁ ) is ON. FIG. 3 shows that the light emission control switch 15 (SW ₃ ) is ON, the first switch 17 (SW ₁ ) and the second switch 18 (SW ₂ ).
Indicate a second state in which both are turned off. FIG. 4 shows the light emission control switch 15 (SW ₃ ) and the first switch 17 (S
W ₁ ) are both OFF and the second switch 18 (SW ₂ ) is O
9 shows a third state that has been set to N.

The APC circuit 10 sequentially goes through a first state (FIG. 2), a second state (FIG. 3), and a third state (FIG. 4) to a first state.
By returning to the state (FIG. 2), the light emitting element 11 repeats the pulse blinking.

[0021]First state (FIG. 2)  Light emission control switch 15 (SW₃) Is ON,
The base potential of the transistor 13 (point P₄Potential V
₄The light emitting element 11 emits light with the amount of current specified in ()). This
When the light receiving element 12 receives the light of
The current flowing through the resistor 19 (R₁) Depending on the voltage (point P
₁Voltage V₁). In this first state, the first
Switch 17 (SW₁) Is ON, this first
Switch (SW₁) Point P₁Voltage V₁And P
₂Voltage V₂Is the same. Therefore, the first condensation
Sa20 (C₁) Is the voltage V₁Is applied (point P₂
Voltage is V₁), The first capacitor 20 (C₁)
Be charged.

[0022]Second state (FIG. 3)  Light emission control switch 15 (SW₃) Is still ON
Therefore, the light emitting element 11 continues to emit light. In this second state
Is the first switch 17 (SW₁) And the second switch 18
(SW₂) Are both OFF, the first capacitor 2
0 (C₁), The power corresponding to the amount of light received by
The pressure is sampled and held.

[0023]Third state (FIG. 4)  Light emission control switch 15 (SW₃) Is turned off,
Light emission of the light emitting element 11 is stopped. Therefore, point
To P₁Voltage V₁Is zero. In this third state,
2 switch 18 (SW₂) Is ON.
Of the second switch 18 (SW₂) Point P₂And P
₃And the second capacitor 21 (C₂)
Be charged. In this state, the first switch 17 (S
W₁) And the second switch 18 (SW₂) And the state,
The first switch 17 is turned off and the second switch is turned off.
When the switch 18 is turned on, the following explanation
As can be seen, the first capacitor 20 and the second capacitor
21 means for averaging the amount of electricity stored in
Will be achieved.

Thereafter, the first state to the third state are sequentially repeated.
In the process of switching, the second switch 18 (SW₂) Is turned off
Point P when you are₂, Point P₃Voltage to V
₂, V₃Then, the third state (the light emission control switch 15
(SW₃) Is OFF), the first and second first condensation
Since points 20 and 21 are conducting, point P₂, P
₃Is represented by V, V = (V₂× C₁+ V₃× C₂) / (C₁+ C₂) And the capacitance C of the first capacitor 20₁And the second conden
Capacitance C of sa21₂Weighted average value.

Therefore, the base voltage of the transistor 13 is
Pressure (point P₄Voltage V₄) Is the above weighted average
Is the point P₃(Negative side input of OP amplifier 16
End) voltage V₃And the reference voltage V of the OP amplifier 16₀And the ratio
Will be updated. From this, the OP amplifier
The voltage (V₃) Is the reference voltage (V
₀), The base voltage of the transistor 13
(Point P₄Voltage V ₄) Is updated in the downward direction,
Light emission control switch 15 (SW₃) Lights when ON
Since the amount of current flowing through the element 11 decreases, the light emitting element 11
The amount of light emission decreases.

[0026] updating the other hand, if falls below than the negative input terminal of the voltage _{(V 3)} is the reference voltage of the OP amplifier 16 _{(V 0),} in a direction in which the base voltage of the transistor 13 (voltage _{V 4} points _{P 4)} increases And the light emission control switch 15
When (SW ₃ ) is turned on, the amount of current flowing through the light emitting element 11 increases, so that the light emitting amount of the light emitting element 11 increases.

From the above, according to the above-described APC circuit 10, when the light emission of the light emitting element 11 that emits pulse light is stopped,
Since the light emission amount at the next pulse emission is controlled by the average value of the voltage corresponding to the light reception amount at the previous light emission and the voltage corresponding to the light reception amount at the previous light emission, the light emission of the light emitting element 11 is controlled. Increase in the amount → increase in the voltage V _{1 at} the point P ₁ → decrease in the base voltage V ₄ of the transistor 13 → decrease in the amount of light emitted from the light emitting element 11, while decrease in the amount of light emitted from the light emitting element 11 → voltage at the point P ₁ reduction of V ₁ → rise of the base voltage V ₄ of the transistor 13 → since an increase of quantity of light from the light emitting element 11, operates so as to hold the quantity of light from the light emitting element 11 to be constant.

Therefore, according to the APC circuit 10, as will be understood by those skilled in the art, the operation amount of the light emitting element 11 is not updated while the light emitting element 11 is emitting light by the pulse ON. The operation amount is updated each time the light emission of the light emitting element 11 is stopped by the pulse OFF, and the light reception amount at the time of the previous light emission is held at the time of the pulse OFF. From the circuit side, it is the same as DC lighting. And if it is equivalent to DC lighting, the output of the amplifier circuit only needs to generate a DC voltage, and therefore the output of the amplifier circuit does not fluctuate greatly. Is enough. This means that even if the APC circuit is formed of general-purpose and inexpensive analog devices, the amount of light emission can be kept constant under accurate feedback to the photoelectric element for pulse emission. . In the above-described embodiment described with reference to FIGS. 2 to 4, the first state, the second state, and the third state
Although the states have been described as being performed sequentially, it is needless to say that the object of the present invention can be achieved by directly changing from the first state shown in FIG. 2 to the third state shown in FIG.

FIG. 5 is a circuit diagram showing a modification of the APC circuit 10. The APC circuit 30 of the modification shown in FIG.
The positive input terminal of the OP amplifier 16 and the transistor 13
And a comparator 31 connected to the base. The other configuration is substantially the same as that of the above-described APC circuit 10, and the description thereof will be omitted by using the reference numerals used earlier.

In general, a photoelectric switch provided with an APC device automatically maintains a constant light emission amount even if a light emitting element is deteriorated by the APC function. When that happens, it is necessary to pass more current. However, the amount of current that can be passed through the light emitting element is generally finite, and if the current is passed to the limit value, the APC may not operate normally and the light emitting amount of the light emitting element may be reduced. This means
This is a problem that is directly connected to an erroneous output of the photoelectric switch.

In consideration of this point, the APC circuit 30 shown in FIG. 5 compares the reference voltage V ₀ of the OP amplifier 16, which is the amount of operation for the light emitting element 11, and the base voltage V ₄ of the transistor 13 with the comparator 31. Compare the base voltage V
₄ is detected to be equal to or higher than the reference voltage V ₀ , and this detection signal is taken into a CPU or a gate array built in the photoelectric switch, and the CPU or the gate array is attached to the photoelectric switch. For example, an alarm signal is output to a display means such as a liquid crystal, and A
It can be notified that the PC function is not operating normally. The operator who sees this can take necessary countermeasures such as replacement of the light emitting element 11. In the above embodiment, the reference voltage V ₀ which comparator 31, but taken from the OP amplifier 16 is an operation amount controlling means, which may naturally be set separately. Further, it goes without saying that, depending on the setting of the circuit, when the value of the base voltage becomes lower than the reference voltage, the above-mentioned values may be set so as to determine that the APC function is not operating normally. That is.

FIG. 6 shows an APC according to a second embodiment of the present invention.
It is a circuit diagram. In the APC circuit diagram 40 of the second embodiment, the light emitting element 11 is directly connected to the output terminal of the OP amplifier 16 so that it can be understood immediately as compared with the APC circuit 10 of FIG. Have been. That is, in the APC circuit 40 of the second embodiment, the transistor 13 is omitted, and the light emitting element 11 is directly controlled by the OP amplifier 16.

Therefore, in the second embodiment, it can be seen that the OP amplifier 16 is both the above-described operation amount control means and also the light emission amount control means of the light emitting element 11. That is, the output voltage V ₄ of the OP amplifier 16 (to be precise, the voltage at the point P ₄ after passing through the resistor R ₂ ) is
This defines an operation amount related to the anode voltage of the light emitting element 11.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a conventional APC device for a photoelectric switch.

FIG. 2 illustrates a circuit configuration of an APC device of the photoelectric switch according to the embodiment, and illustrates a first state in which a light emitting element emits light.

FIG. 3 is a diagram illustrating an APC circuit configuration of the photoelectric switch according to the embodiment, and illustrates a change from the first state in FIG. 2 to the next second state while the light emitting element emits light.

FIG. 4 is a diagram illustrating an APC circuit configuration of the photoelectric switch according to the embodiment, and illustrates a third state in which the pulse emission of the light emitting element is stopped.

FIG. 5 is a diagram illustrating a circuit configuration of an APC device according to a modified example.

FIG. 6 is a diagram illustrating a circuit configuration of an APC device of a photoelectric switch according to a second embodiment.

[Explanation of symbols]

Reference Signs List 10 APC circuit of first embodiment 11 Light emitting element 12 Light receiving element 15 Light emission control switch (SW ₃ ) 16 OP amplifier 17 First switch (SW ₁ ) 18 Second switch (SW ₂ ) 19 Resistance for current-voltage conversion (R) ₁ ) 20 First capacitor (C ₁ ) 21 Second capacitor (C ₂ ) 30 APC circuit of modified example 31 Comparator 40 APC circuit of second embodiment

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/04

Claims (4)

[Claims] A light-emitting element that is pulse-flashed; a light-receiving element that receives light emitted by the light-emitting element; a light-emission amount control unit that controls an amount of light emitted by the light-emitting element; To keep the amount of light emitted constant
A photoelectric switch having an operation amount control unit for controlling the light emission amount control unit with an operation amount according to an amount of light received by the light receiving element, wherein the operation amount control unit is configured to emit the light when the light emitting element emits light. First accumulation means for accumulating and holding a current light reception result corresponding to the amount of light received by the light receiving element, and a previous accumulation of the light receiving element corresponding to the current operation amount when the light emitting element emits light Second accumulation means for accumulating and holding the light reception result; and averaging means for averaging the current light reception result and the previous light reception result when the next light emission of the light emitting element is stopped. An APC device for a photoelectric switch, wherein, at the next light emission of the light emitting element, the light emission amount control means is controlled by an operation amount based on the averaged light reception result. 2. A comparison means for comparing the manipulated variable output from the manipulated variable control means with a predetermined reference value, and based on a signal from the comparison means, determines whether an APC function is working normally. 2. The AP of the photoelectric switch according to claim 1, further comprising: an abnormality determining unit that performs an abnormality, and a notifying unit that notifies the abnormality when the APC function is not working properly in the abnormality determining unit.
C device. 3. A light emitting element, switching means for causing the light emitting element to emit a pulse, a light receiving element receiving light emitted by the light emitting element, and a light receiving element connected to the light receiving element and received by the light receiving element A resistor for converting a current flowing according to the amount into a voltage, and first and second switch means arranged in series with a conductor for applying the voltage converted by the resistor to a negative input terminal of the OP amplifier; A first capacitor connected between an intermediate point between the first switch means and the second switch means and ground; and a first capacitor connected between an intermediate point between the second switch means and the OP amplifier and ground. A second capacitor, and a transistor, the base of the transistor being connected to the output terminal of the OP amplifier, the switching means being connected to the emitter of the transistor, Is the light emitting element connected to the collector of transistor, when said light emitting element emits light, first, the first switching means is turned ON, first the second switch means is OFF
State, and then the first light switch is turned off and the second light switch is turned off in a second state while the light emitting element emits light. Next, light emission of the light emitting element is stopped. Sometimes the first
An APC device for a photoelectric switch, wherein a light emission amount of the light emitting element is kept constant by setting a third state in which a switch means is turned off and a second switch means is turned on. 4. A light-emitting element, switching means for causing the light-emitting element to emit a pulse, a light-receiving element for receiving light emitted by the light-emitting element, and a light-receiving element connected to the light-receiving element and received by the light-receiving element A resistor for converting a current flowing according to the amount into a voltage, and first and second switch means arranged in series with a conductor for applying the voltage converted by the resistor to a negative input terminal of the OP amplifier; A first capacitor connected between an intermediate point between the first switch means and the second switch means and ground; and a first capacitor connected between an intermediate point between the second switch means and the OP amplifier and ground. A second capacitor, and a transistor, the base of the transistor being connected to the output terminal of the OP amplifier, the switching means being connected to the emitter of the transistor, A state in which the light emitting element is connected to the collector of the transistor, the first switch is turned on, the second switch is turned off in a state where the light emitting element emits light, and then the light emission of the light emitting element is stopped; An APC apparatus for a photoelectric switch, wherein the light emission amount of the light emitting element is kept constant by turning off the first switch means and turning on the second switch means.