JPH05304457A - Photoelectric switch - Google Patents

Abstract

(57) [Summary] [Purpose] To keep the brightness of the light emitting pulse constant even when adjusting the detection distance of the photoelectric switch. [Structure] The output Vosc of the oscillation circuit 11 and the output Vavg of an averaging circuit 14 for averaging the output are set to a variable resistor 13
Give to both ends of. Then, the output Vb of the variable resistor 13 is converted into a current by the transistor 15 to control the light emission current of the light emitting diode 16. By doing this, the variable resistor 13
Thus, the average current becomes constant even if the peak value is changed. Then, the brightness becomes constant for the adjuster regardless of the peak value level, and the detection distance can be adjusted easily.

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 characterized by its sensitivity adjustment.

[0002]

2. Description of the Related Art In a conventional photoelectric switch, for example, as shown in FIG. 5, an output of an oscillation circuit 1 for generating a clock signal is applied to a light projecting element drive circuit 2 and a signal processing circuit 3 to project a light projecting element 4.
Is pulse-lighted, a light-receiving element 5 is provided at a position facing the light-projecting element 4 or at a position for receiving reflected light from an object, the signal is waveform-shaped through the amplifier circuit 6, and the output of the oscillation circuit 1 is output. The signal processing circuit 3 integrates and shapes the output as a gate signal, and outputs it from the output circuit 7. However, in the reflection type photoelectric switch, the object is arranged at the object detection position corresponding to the pulse-driven light projecting element 4, and the light receiving sensitivity is changed by changing the peak value of the light projecting pulse to detect the detection distance. Was being adjusted.
In this case, in order to facilitate the adjustment of the detection distance, a visible light emitting element such as a red light emitting diode is used as the light projecting element. By doing so, the irradiation position of the red light becomes clear, and the detection position and the distance can be easily adjusted.

[0003]

However, in such a conventional photoelectric switch, the brightness of the red light emitting diode becomes darker when the peak value of the light emitting pulse is lowered in order to shorten the detection distance and lower the sensitivity. Therefore, there is a drawback that the irradiation position and the detection distance are difficult to understand.

The inventions of claims 1 and 2 of the present application have been made in view of the problems of the conventional photoelectric switch, and in the photoelectric switch in which the light receiving sensitivity is adjusted on the light projecting side, A technical problem is to make it possible to easily adjust the sensitivity by always keeping the brightness of the light projecting element constant.

[0005]

According to the invention of claim 1 of the present application, an oscillation circuit for generating a light-emission pulse, a light-emission element for emitting visible light, and a light-emission element driven based on the output of the oscillation circuit. And a signal processing circuit for detecting an object based on a change in output of the light receiving element. The optical element driving means has a peak value adjusting means for adjusting the peak value of the light emitting pulse and a peak value adjusted by the peak value adjusting means every time the light emitting pulse is given from the oscillation circuit, and the average current thereof is And a projection level setting means for setting equal projection levels.

According to the second aspect of the present invention, an oscillation circuit for generating a light projection pulse, an averaging circuit for averaging the light projection pulses generated by the oscillation circuit, an output of the averaging circuit and an output of the oscillation circuit. Is connected to both ends, and the variable resistor that outputs the midpoint as an adjustment signal, the light projecting element drive circuit that outputs the variable resistor and converts it into a current according to the voltage level, and the light projecting element drive circuit A light emitting element that is connected and driven by the light emitting current to emit visible light, a light receiving element that receives the light emitted from the light emitting element, and a signal processing circuit that detects an object based on the output change of the light receiving element. And are provided.

[0007]

According to the invention of claim 1 of the present application having such a feature, the peak value of the projection pulse is adjusted by the peak value adjusting means in order to adjust the detection distance of the object.
The light emitting current having the adjusted peak value and the average current being equal is set. When a person visually adjusts the brightness of the light projection spot, the brightness of the light projection spot is constant because it is determined not by the peak value but by the average current.
Also in the invention of claim 2 of the present application, the light emitting pulses are averaged by the averaging circuit, the output of the oscillation circuit and the output of the averaging circuit are connected to both ends of the variable resistor, and set by the variable resistor from the midpoint thereof. It has a peak value and the average current is constant. By driving the light projecting element based on this voltage, a light projecting spot with a constant brightness is obtained during visual adjustment.

[0008]

1 is a block diagram showing the structure of a light projecting portion of a photoelectric switch according to an embodiment of the present invention. Oscillator circuit 11
Is an oscillating circuit for generating a periodic light emitting pulse, and a diode 12 is connected to the ground point of the oscillating circuit. The output Vosc of the oscillator circuit 11 is connected to one end of the variable resistor 13 and the input end of the averaging circuit 14.
The averaging circuit 14 averages the output Vosc of the oscillator circuit 11, and the output Vavg is connected to the other end of the variable resistor 13. The variable resistor 13 is a peak value adjusting means for setting the peak value of the projection pulse of the photoelectric switch, and the base of the transistor 15 for driving the projection element is connected to the midpoint thereof. The emitter of the transistor 15 is a resistor R1
Is connected to the power supply Vcc via a light emitting diode 16 which is a light projecting element. Here, the light emitting diode 16 is a light emitting diode that emits visible light. A capacitor C for preventing a rapid change in voltage is connected to the power source Vcc. Further, a constant current source 17 for giving a bias current to the light emitting diode 16 until the light emission starts is connected between the collector of the transistor 15 and the ground terminal.

FIG. 2A is a diagram showing an example of the oscillation circuit 11. The oscillation circuit 11 is composed of a plurality of inverters and a CR circuit, and the ground end thereof is grounded via the diode 12 connected in the forward direction as described above.

Further, as shown in FIG. 2B, the averaging circuit 14 has an integrating circuit having a large time constant for integrating the output of the oscillating circuit 11, and the averaging output by this integrating circuit is passed through a voltage follower. Is being output. When the smoothness is insufficient, the circuit shown in FIG. 2B may be serially connected. Further, in order to output this average level, it may be configured by a constant voltage circuit instead of the integrating circuit and the voltage follower.

Next, the operation of this embodiment will be described. The solid line in FIG. 3A shows the light projection pulse Vosc of the oscillation circuit 11. Here, the projection pulse Vosc has a peak value of Vh,
The low level value is Vl. Since Vl is determined by the diode 12 as described above, it is the same as the forward drop voltage V _{BE of the} diode 12. The period of the light projection pulse Vosc is T and the pulse width is τ. The output of the averaging circuit 14 has a level Vavg, which is the average of the outputs, as indicated by the broken line in FIG. Vavg is expressed by the following equation. Vavg = {Vl (T-τ) + Vh · τ} / T (1)

Now, the light projection level is adjusted by the variable resistor 13, and its set value is set to θ as shown in FIG. 4 (a). Then, in the divided voltage output Vb shown in FIG. 4B, the peak value is Vhb, the L level is Vlb, the period is Tb, the pulse width is τb, the pulse peak value is Vhl, and the average value of these is Vh.
Given avgb, the following relationship holds between them. τb = τ (2) Tb = T (3) Vhb = (Vh-Vavg) θ + Vavg (4) Vlb = (Vl-Vavg) θ + Vavg (5)

The average value Vavgb of the output Vb of the variable resistor 13 is expressed by the following equation from FIG. 4 (b). Vavgb = {Vlb (Tb- [tau] b) + Vhb * [tau] b} / Tb (6) Here, if formulas (1) to (5) are substituted into formula (6), the following formula is obtained. Vavgb = {Vl (T−τ) + Vh · τ} / T (7) From equations (1) and (7), it is understood that Vavgb and Vavg are equal.

On the other hand, the peak value Vhl of Vb is given by equation (4),
From (5), it is shown as follows. Vhl = Vhb−Vlb = (Vh−Vl) θ (8) As is clear from the equation (8), the peak value of Vb should be proportional to the set value θ of the variable resistor 13 for adjusting the projection amount. Becomes

The adjusted output Vb thus obtained is applied to the base of the transistor 15, and the base voltage regulates the current of the light emitting diode 16 which is a light projecting element. Since a constant current is flowing from the constant current source 17 to the light emitting diode 16, the brightness thereof is directly changed by the current flowing through the transistor 15. Therefore, the light emitting diode 16 can be pulse-lighted with the brightness corresponding to the voltage Vb. Here, the voltage Vb resulting from the voltage division has the following characteristics. (1) The average value Vavgb of the result of voltage division is equal to Vavg regardless of the setting of the variable resistor 13. (2) The peak value Vhl of the voltage division result is proportional to the set value θ of the variable resistor 13. (3) The voltage division result is equal to Vavg when θ of the variable resistor 13 is 0 (MIN). (4) The result of voltage division is that the setting of the variable resistor 13 is θ = 1 (MA
X) is equal to Vosc. In this way, the average value of the projected current can be kept constant.

In this embodiment, the average current of the light projecting element is made constant even after the adjustment, regardless of the adjustment of the peak value. However, after the adjustment, the variable resistor Vb is adjusted according to the output of the oscillation circuit.
It is also possible to reduce the power consumed by the light projecting element by selecting the voltage set to.

[0017]

As described in detail above, according to the present invention, even if only the peak value of the light projection pulse is changed by adjustment, the average value of the light projection pulse can always be kept constant. Therefore, even when the detection distance and the sensitivity are adjusted by adjusting the peak value of the light emitting pulse of the light emitting element, it is recognized by the adjuster that the brightness of the light emitting spot does not change. Therefore, the effect that the detection position of the photoelectric switch can be easily adjusted is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a light projecting unit of a photoelectric switch according to an embodiment of the present invention.

FIG. 2A is a circuit diagram showing an example of an oscillator circuit used in this embodiment, and FIG. 2B is a circuit diagram showing a configuration of an averaging circuit.

FIG. 3A is a waveform diagram showing outputs of an oscillation circuit and an averaging circuit, and FIG. 3B is a waveform diagram showing a midpoint output of a variable resistor.

FIG. 4A is a diagram showing setting of the variable resistor 14;
(B) is a figure which shows the output voltage.

FIG. 5 is a block diagram showing an overall configuration of a conventional photoelectric switch.

[Explanation of symbols]

 11 oscillator circuit 12 diode 13 variable resistor 14 averaging circuit 15 transistor 16 light emitting diode 17 constant current circuit

Claims (2)

[Claims] 1. An oscillating circuit for generating a light emitting pulse, a light projecting element for emitting visible light, a light projecting element driving means for driving the light projecting element based on an output of the oscillating circuit, and the light projecting device. In a photoelectric switch including a light receiving element that receives light emitted from an element, and a signal processing circuit that detects an object based on an output change of the light receiving element, the light projecting element driving means includes a light projecting pulse A peak value adjusting means for adjusting the peak value, and a projection value for setting a projection level having a peak value adjusted by the peak value adjusting means every time a light projecting pulse is given from the oscillation circuit and having the same average current. A photoelectric switch comprising: a light level setting means. 2. An oscillation circuit for generating a light projection pulse, an averaging circuit for averaging the light projection pulses generated by the oscillation circuit, an output of the averaging circuit and an output of the oscillation circuit are connected to both ends. A variable resistor that outputs the midpoint thereof as an adjustment signal, a light projecting element drive circuit that outputs the variable resistor and converts the current into a current that corresponds to the voltage level, and that is connected to the light projecting element drive circuit. A light projecting element that is driven by a light projecting current and emits visible light, a light receiving element that receives light emitted from the light projecting element, and a signal processing circuit that detects an object based on an output change of the light receiving element. A photoelectric switch comprising: