JPH0329208B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention provides a detector including a light emitting element and a light receiving element in relation to an object to be detected, and receives light emitted from the light emitting element. A photoelectric switch that detects the presence or absence of an object to be detected by applying a light reception signal obtained by receiving light to an amplifier set at an appropriate amplification factor and discriminating the output of the amplifier from a predetermined discrimination level. Regarding.

(b) Conventional technology FIG. 1 is an explanatory diagram of a conventional photoelectric switch.

Figure a schematically shows the configuration of a photoelectric switch in which the optimum operating conditions are selected depending on the distance at which the detector is installed by varying the amplification factor of the amplifier to which the received light signal is applied. In the same figure a, 1 is
This is a light projection drive circuit that drives a light projection element 2 such as an LED. Reference numeral 3 denotes a light-receiving element made of a phototransistor or the like that detects light reflected from the detection object 4. Therefore, the light projecting element 2 and the light receiving element 3 are as follows.
It constitutes a so-called reflection type detector.

5 is an amplifier whose amplification factor is varied by a variable resistor VR. 6 is a discrimination circuit in which a discrimination level E1 is set. 7 is based on the output of the discrimination circuit 6,
This is an output circuit that drives a next-stage relay, etc. (not shown).

On the other hand, in FIG. 5B, an appropriate operating condition is selected by varying the discrimination level E2 according to the set distance of the detector. In the figure, the same parts as in figure a are indicated by the same reference numerals. In addition,
5' is an amplifier with a fixed amplification factor.

Generally, there is a relationship as shown in FIG. 2 between the relative light receiving output of the light receiving element (the maximum light receiving output is 1) and the set distance (distance from the detector to the object to be detected). However, the figure illustrates a photoelectric switch using a glass fiber as a detector. For example, the output when the two are close to each other (section A, which is the output when the set distance is 2 to 3 mm in the same figure)
There is a difference of approximately 100 times between the distance and the output (portion B, which is the output when the set distance is 30 to 40 mm).

Therefore, in the case of the photoelectric switch shown in FIG. 1a, the amplification factor of the amplifier 5 is appropriately set in relation to the set distance of the detector so that the output of the amplifier 5 is approximately equal to the discrimination level E1. There is a need. However, the variable resistor used to set the amplification factor
For VR, the usable resistance range is usually about 5% to 100% of the total resistance, so the variable range of the amplification factor is about 20%.
The limit is twice as much. Therefore, in the case of this photoelectric switch, as shown in FIG. 2, where the relative light reception output changes significantly depending on the set distance, there is a drawback that the optimum amplification factor cannot be set for the entire set distance. Here, the optimum amplification factor is an amplification factor that provides operating conditions such that the photoelectric switch can reliably detect the object to be detected without being affected by disturbances.

On the other hand, in the case of the photoelectric switch shown in Fig. 1b, when the setting distance is short (part A in Fig. 2), the change in the detection distance is small with respect to the change in the relative received light output. The discrimination level can be set to high resolution. However, when the set distance is long (section B in FIG. 2), it is difficult to set the optimum discrimination level because the change in the detection distance becomes significantly large with respect to the change in the relative light reception output. Here, the optimum discrimination level refers to a discrimination level that provides operating conditions such that the photoelectric switch can reliably detect the object to be detected without being affected by disturbances.

(c) Purpose The purpose of the present invention is to provide a photoelectric switch that can set optimal operating conditions according to the set distance of a detector, even when the received light output changes significantly as the set distance of the detector changes. There is.

(d) Configuration The photoelectric switch according to the present invention includes a light projecting element that irradiates light onto an object to be detected, a light receiving element that receives light from the light projecting element and generates a light reception signal, and a light receiving element that receives light from the light receiving element. An adder circuit that adds a predetermined DC voltage to a signal, an amplifier circuit to which the output of this adder circuit is input and whose amplification factor is set to a larger value as the output decreases, and the output of this amplifier circuit and a discrimination level. and a discriminator that detects the presence or absence of a detection target by comparing these input signals, and the discrimination level is equal to the output of the amplifier circuit when the received light signal input to the amplifier circuit is zero. The difference is set to a minimum, and the DC voltage is set to be equal to the discrimination level when the output of the adder circuit is amplified at the maximum amplification factor of the amplifier circuit.

(e) Embodiment FIG. 3 is a block diagram schematically showing the structure of an embodiment of a photoelectric switch according to the present invention.

In this figure, the same parts as in FIG. 1 are designated by the same reference numerals. Reference numeral 8 denotes an amplifier that amplifies the light-receiving signal, which is the output of the light-receiving element 3, at a constant amplification factor. 9 is an adder circuit that adds DC voltage E3 to the output of amplifier 8. This adder circuit 9 and the next stage amplifier circuit 5
Specifically, as shown in Figure 4, the feedback resistance is
The light receiving signal amplified by the amplifier 8 is connected to one terminal of the amplifier circuit having VR through the resistor R1, and the resistor R2
are configured to apply a DC voltage E3 through the respective terminals.

The discrimination level E4 of the discriminator 6 is set in advance to a value equal to the output voltage of the amplifier circuit 5 when the light reception signal takes the maximum value (section A in FIG. 2). On the other hand, the DC voltage E3 can be detected at the maximum setting distance (B in Fig. 2).
When the output of the adder circuit 9 obtained by adding the output Eb of the amplifier 8 and the DC voltage E3 when installed in , is set to a value such that the output of the amplifier circuit 5 is equal to the discrimination level E4. Expressed mathematically, the voltage E3 is (Eb+E3×10
= E4 is preset to a voltage value that satisfies.

In this way, the DC voltage E3 and the discrimination level E
By setting 4, the difference between the output of the amplifier circuit 5 when the received light signal is zero and the discrimination level E4 is minimized as the amplification factor of the amplifier circuit 5 increases. That is, when the detector is installed near the object to be detected (section A in FIG. 2), the DC voltage E3 is sufficiently smaller than the output E6 of the amplifier 8, so it can be ignored. Therefore, in this case, the amplification factor of the amplifier circuit 5 is set to 1. On the other hand, if the detector is installed at the maximum distance from the object to be detected (second
(Part B in the figure), even if the output of the amplifier 8 is small, the DC voltage E3 is added to it, so even if the amplification factor of the amplifier circuit 5 is relatively small (for example, 10 times), it should be approximately equal to the discrimination level E4. be able to.

FIG. 5 shows the set distance of the detector and the variable resistor of the amplifier circuit 5 in the photoelectric switch according to this embodiment.
FIG. 3 is an explanatory diagram showing the correlation with the value of VR. However, the resistance value is indicated by the relative rotation angle (0 to 1) of the variable resistor VR (potentiometer), and this has a linear relationship with the amplification factor of the amplifier circuit 5.

In the figure, C1 shows the correlation when the conventional device shown in FIG. 1b is used, and C2 shows the correlation in the present embodiment shown in FIG. 3. As is clear from the figure, according to this embodiment, the change in the rotation angle of the variable resistor VR corresponding to the change in the set distance is smaller than that in the conventional device, so that the set distance of the detector can be optimally adjusted. The amplification factor can be easily set.

In the above embodiment, a so-called reflection type detector was taken as an example, but it goes without saying that a so-called transmission type detector may also be used.

(F) Effect The photoelectric switch according to the present invention is configured such that as the amplification factor of the amplifier to which the received light signal is applied increases, the difference between the output of the amplifier and the discrimination level when the received light signal is zero becomes smaller. Therefore, the optimum amplification factor can be easily set according to the set distance of the detector.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a conventional photoelectric switch, Figure 2 is an explanatory diagram showing the relationship between the relative light reception output of the light receiving element and the detection distance (distance from the detection part to the object to be detected), and Figure 3 is an explanatory diagram of the conventional photoelectric switch. A block diagram schematically showing the configuration of one embodiment of the photoelectric switch according to the invention, FIG. 4 is a circuit diagram showing a specific configuration example of the adder circuit 9 and the next stage amplifier 5, and FIG. The determined distance of the detector and the variable resistance of the amplifier 5 in such a photoelectric switch
FIG. 3 is an explanatory diagram showing the correlation with the value of VR. 1...Light emission drive circuit, 2...Light emission element, 3...
Light receiving element, 4... Sensing object, 5... Amplifying circuit,
6...discriminator, 7...output circuit, 9...addition circuit.

Claims (1)

[Scope of Claims] 1. A light emitting element that irradiates light onto an object to be detected, a light receiving element that receives light from the light emitting element and generates a light receiving signal, and a predetermined direct current applied to the light receiving signal of the light receiving element. An adder circuit that adds voltages, an amplifier circuit to which the output of this adder circuit is input and whose amplification factor is set larger as the output decreases, and the output of this amplifier circuit and a discrimination level are input. and a discriminator that detects the presence or absence of the detection target by comparing the levels, and the discrimination level is set at a level at which the difference between the output of the amplifier circuit and the output of the amplifier circuit when the received light signal input to the amplifier circuit is zero is set. , and the DC voltage is set to be equal to the discrimination level when the output of the adder circuit is amplified by the maximum amplification factor of the amplifier circuit.