JPH0540593Y2 - - Google Patents

Description

[Detailed explanation of the idea] 〔Technical field〕 This invention relates to a reflective photoelectric switch.

[Background technology]

In a reflective photoelectric switch, light emitted from a light emitting element such as a light emitting diode is reflected by an object to be detected, and this reflected light is received by a light receiving element to detect the presence of the object to be detected.

Among these reflective photoelectric switches, there is a reflective photoelectric switch that detects the detected object only when the position of the detected object as seen from the switch is within a predetermined distance range (detectable area). . This detectable area is usually set based on the intensity of reflected light that changes depending on distance.

However, in a reflective photoelectric switch, if the reflectance of the surface of the object to be detected differs, even if the intensity of the projected light is the same, the intensity of the reflected light will differ. Therefore, in the case of a reflective photoelectric switch that can set a detectable area as described above, if a detected object has a low reflectance, even if the detected object is in the detectable area, the light reception signal output from the light receiving element will be too weak. It may be determined that the detected object exists further away than the detectable area. Conversely, a detected object with a high reflectance may be determined to exist within the detectable area even though it is farther away than the detectable area because the received light signal is too strong.

In order to prevent such malfunctions due to differences in the reflectance of the surface of the detected object, a reflective photoelectric switch as described below was devised.

That is, it includes a light receiving means that receives light reflected from the object to be detected and outputs two series of light reception signals, and a calculation means that calculates the ratio of the two series of light reception signals. Accordingly, the object to be detected is detected.

In a reflective photoelectric switch equipped with this calculating means, if the position of the detected object is the same, even if the reflectance of the detected object is different, the ratio of the two series of received light signals, that is, the output output from the calculating means. The signals will be the same. Therefore, there is an advantage that if the object to be detected is at the same distance, it can be accurately detected regardless of the reflectance.

FIG. 5 is a graph showing the relationship between the position of the object to be detected within the detectable area and the two series of received light signals. The farther you go to the right in the diagram, the further away you are from the switch.

Curves A and A' represent the received light signals of one series, that is, channel 1, and curves B and B' are
It represents the received light signal of the other series, ie, channel 2. Solid curves A and B indicate light reception signals when the object to be detected has a high reflectance (for example, a blank sheet of paper), and the amount of light reception signals is high. Broken curves A′ and B′ are for low reflectance (for example, black paper)
This shows the received light signal in the case of the detected object, and the amount of the received light signal is smaller overall compared to curves A and B. Also, the received light signal of channel 1 changes as the distance increases. The received light signal of channel 2 exhibits a characteristic in which the signal amount decreases as the distance increases. Such light-receiving characteristics for each channel are set based on the characteristics of the light-receiving element and the configuration of the light-receiving circuit connected to the light-receiving element.

Therefore, when the objects to be detected are placed at the same position, even if the reflectance of the objects to be detected is different, the ratio between the amount of received light signals of channel 1 and the amount of received light signals of channel 2, that is, the calculation means The output signal will be the same, and as described above, accurate detection will be possible regardless of the reflectance.

However, in the case of a detected object with low reflectance, when the distance from the photoelectric switch exceeds a certain value, the amount of reflected light becomes too small, and as shown by curve B', the minimum received signal amount of channel 2 E ₀ It will drop below.

Since an accurate received light signal cannot be obtained in the range below the minimum received light signal amount E ₀ , the ratio between the received light signal amount of channel 1 and the received light signal amount of channel 2 will also be an inaccurate value, and the calculation means will It becomes impossible to detect the object to be detected based on the output signal of.

In other words, with the reflection type photoelectric switch having the structure described above, when detecting objects with low reflectivity,
Even if it is within the detectable area, if the distance from the photoelectric switch becomes too far, it will not be able to be detected. In other words, there is a maximum detection distance l ₀ of a low reflectance detected object.

As a result of these studies, we found that the conventional reflective photoelectric switch, which uses the ratio of two series of received light signals, is completely unaffected by the difference in reflectance of the detected object.
It was thought that accurate detection could be performed at all times, but in reality it was found that objects with low reflectivity located beyond the maximum detection distance could not be detected, and that the reflectance affected detection performance. Ivy.

The above-mentioned minimum received light signal amount E ₀ is determined by the characteristics of the light receiving element and circuit, but such characteristics are
Since it changes slightly depending on manufacturing processing conditions, etc., the maximum detection distance l ₀ of a low reflectance object to be detected may also differ depending on the photoelectric switch manufactured.

However, for photoelectric switches of the same model, it is desirable to keep the maximum detection distance l ₀ constant at the manufacturing stage. Furthermore, it is better to have the same maximum detection distance l ₀ even for a plurality of photoelectric switches used at the same time. Furthermore, it may be necessary to change the maximum detection distance l ₀ during the use stage depending on the purpose of use and required performance.

In such a case, for example, by changing the amplification factor of the amplifier in channel 2, the strength of the received light signal can be changed, and the maximum detection distance l ₀ can be adjusted. However, if the amplification factor of channel 2 is changed, the amplification factor of channel 1 must also be changed in order not to change the ratio of the received light signal, that is, the output signal of the calculation means. If the amplification factor of channel 1 is not changed, the calculation means must be readjusted so that the output signal does not change. In either case, complicated and time-consuming work is required. Furthermore, the configuration of the circuit required to make such adjustment becomes complicated, making it impractical. Furthermore, when the amplification factor of the received light signal is increased, there is also the disadvantage that noise is also amplified.

Other means and devices for adjusting the maximum detection distance l ₀ are conceivable, but for practical use they must not only be able to make appropriate adjustments, but also have simple adjustment work and circuit configuration. It is also required that the adjustment range be stable.

[Purpose of invention]

In view of the above-mentioned circumstances, this device uses an output signal calculated by a calculation means to calculate the ratio of the two series of received light signals as described above, thereby achieving accurate detection regardless of the difference in reflectance of the detected object. Reflective photoelectric switches, which are now capable of detection, can appropriately adjust the maximum detection distance _l0 for objects with low reflectance, and are simple in adjustment work and circuit configuration, and have a stable adjustment range. The purpose is to provide a type photoelectric switch.

[Disclosure of invention]

In order to achieve the above-mentioned purpose, this device includes a light projection means that irradiates light onto a detectable area, and outputs two series of light reception signals upon receiving the light reflected by the object to be detected existing in the detectable area. In a reflective photoelectric switch, the reflective photoelectric switch is provided with a light receiving means and also has a calculating means for calculating the ratio of the two series of light receiving signals, and the object to be detected is detected based on the output signal of the calculating means. , is equipped with a means to adjust the maximum detection distance of low reflectance detected objects,
As the maximum detection distance adjusting means, the light emitting means is provided with a transistor in which the light emitting diode is connected to the collector side, the resistor element is connected to the emitter side, and a lighting control signal is input from the base side, and A variable resistor for independently adjusting the amount of current flowing through the light emitting diode is disposed on the emitter side or base side of the transistor, and a knob for adjusting the variable resistor is disposed on the surface of the photoelectric switch. This article focuses on a reflective photoelectric switch that is characterized by:

The reflective photoelectric switch according to this invention will be described below.
A detailed explanation will be given with reference to drawings showing an example thereof.

FIG. 2 shows an electrical system block diagram of an example of the reflective photoelectric switch according to this invention.

The pulse generation circuit 1 outputs a continuous pulse signal. The drive circuit 2 receives the pulse signal and drives the light receiving diode 3 to emit light. The light emitted from the light emitting diode 3 is reflected by the object to be detected, photoelectrically converted by the light receiving elements 4 and 5, and then amplified by the amplifier circuits 6 and 7 and output as two series of light receiving signals. In other words, the light receiving elements 4 and 5 and the amplifier circuits 6 and 7 constitute a light receiving means that outputs two series of light receiving signals. Calculation circuit (calculation means)
8 calculates the ratio of the two series of received light signals. The signal processing circuit 9 determines the output signal sent from the calculation circuit 8, and when it determines that there is an object to be detected,
A detection signal is given to the output circuit 10. On the other hand, the pulse signal is also sent to the signal processing circuit 9,
The discrimination operation is performed only when light is being projected. The detection signal is normally output when it is determined that the object to be detected is present three to five times in a row.

FIG. 1a shows a specific example of the circuit configuration of the drive circuit 2 and the light emitting diode 3 which is a light source.

The pulse signal is input to the base of transistor Q1. During the pulse input period, transistor Q1
is conductive, so a current flows through the light emitting diode 3. Then, by changing the resistance value of the variable resistor VR1, the current flowing through the light emitting diode 3 changes, so the light emission intensity (light amount) can be adjusted. As can be seen from the above circuit configuration, changing the resistance value of the variable resistor VR1 does not affect other circuits, so only the light emission intensity can be adjusted independently. In this circuit, the resistor connected to the emitter side of the transistor Q1 is also used as a variable resistor.

FIG. 1b shows another circuit configuration. If you change the resistance value of variable resistor VR2, the pulse voltage applied to resistor R1 will change, so
During the pulse input period, the amount of current flowing through the light emitting diode 3 when the transistor Q2 is turned on can be changed. In this case as well, the light emitting intensity (light amount) of the light emitting diode 3 can be adjusted without affecting other circuits.
can be adjusted independently.

In addition, in the circuits shown in FIGS. 1a and 1b, in which the light emission intensity can be adjusted, the light emitting diode 3 is connected to the collector side of the transistor, and the lighting control signal is input from the base side, and the light emitting diode 3 is connected to the collector side of the transistor. A variable resistor is placed on the emitter side or the base side of the transistor, and the amount of current is determined on the emitter side or base side, and is virtually unrelated to the collector side where the light emitting diode is located, so the light intensity adjustment range is limited. is the forward voltage drop of the light emitting diode
Not affected by VF variations. As a result, the object detection distance adjustment range determined by the light amount adjustment range becomes extremely stable.

In this way, when the emission intensity of the light emitting element 3 changes, the intensity of the light reception signal output from the channel 2 also changes, so as shown in Figure 4, the maximum detection distance for a detected object with low reflectance is ₁ , l ₂ , or l ₃ , which can be adjusted freely.

Conversely, if there are variations in the light emission intensity of the light source (light emitting diode) among multiple photoelectric switches, the maximum detection distance will vary as l ₁ , l ₂ , or l ₃ , but the variable resistance of each photoelectric switch By adjusting the detector, the maximum detection distance can be unified to, for example, l ₁ .

In this way, when the variable resistor is adjusted to change the emission intensity, the strength of the light reception signal changes, so a photoelectric switch whose detection is affected by the strength of the light reception signal cannot perform accurate detection. Therefore, in such a photoelectric switch, it is necessary to adjust the sensitivity of the light receiving circuit in accordance with changing the emission intensity.

However, in the case of this invention, since the ratio of the two series of received light signals is taken, it is not affected at all by the strength of each received light signal. Even if the light emission intensity changes, the signal amount from the calculation means does not change, and there is no need to readjust the light receiving circuit or the like. Therefore, the maximum detection distance can be easily adjusted whether during the manufacturing process or during use. The circuit configuration required to realize this adjustment of the maximum detection distance is extremely simple, requiring only one additional variable resistor.

To adjust the variable resistor, as shown in Figure 3, attach the variable resistor to the outer surface 20a of the photoelectric switch case.
Providing an adjustment knob 22 for VR1 is convenient for making adjustments during use.

The adjustment work can be done as follows. First, among objects with various reflectances that need to be detected, the object with the lowest reflectance, that is, the object with the lowest reflectance, is placed at a position desired to be set as the maximum detection distance. What is necessary is to operate the photoelectric switch and turn the knob 22 while observing the status and movement of the operation indicator lamp and the notification means to adjust the state so that the object to be detected can be reliably detected.

This invention is not limited to the above embodiments. The variable resistor is not limited to one in which the resistance value changes continuously, but may also be one in which a mechanical switch or an electronic switch is used and the resistance value changes in steps.

As the two light-receiving elements 4 and 5 for obtaining two series of light-receiving signals, one one-dimensional optical position detection element (PSD element) may be used, or two light-receiving diodes may be used. .

For example, if a PSD element is used as the light-receiving element and the two series of light-receiving signals obtained have characteristics that vary differentially as shown in Figure 5, the position within the detectable area The amount of output from the calculation circuit changes depending on. Therefore, if the detection signal is obtained only when the output from the calculation circuit is within a certain range, it is possible to detect only objects within a narrower fixed range within the detectable area. can.

The type of reflective photoelectric switch is also not particularly limited, and there are usually those called limited reflection type and area reflection type.

[Effect of idea]

Since the reflective photoelectric switch according to this invention has the configuration described above, it can achieve the following effects.

Effects (1) Since the maximum detection distance for objects with low reflectivity can be adjusted, the performance of photoelectric switches that eliminate malfunctions due to differences in reflectance can be further improved by using the ratio of the two series of received light signals mentioned above. can be done.

This is because the reflective photoelectric switch that uses the ratio of two series of received light signals, which is the underlying technology of this invention,
As described above, there are variations in the maximum detection distance of low reflectance detection objects, and in this respect, there is a possibility that detection may become inaccurate.

However, with this invention, the maximum detection distance for low-reflectance objects can be adjusted simply by adjusting the adjustment switch, so it is possible to eliminate the difference in maximum detection distance between photoelectric switches, and to
It becomes possible to reset the maximum detection distance.

As a result, by combining the two techniques of using the ratio of the two series of light reception signals mentioned above and being able to adjust the maximum detection distance of a low reflectance detected object, it is possible to improve the reflectance. It is possible to more reliably eliminate the influence of differences in detection performance on detection performance, making it possible to further improve the performance of the photoelectric switch.

Effect (2) The light intensity adjustment operation of the light emitting diode can be easily performed to change the maximum detection distance of a low reflectance detected object.

This is because the adjustment knob for the variable resistor is provided on the surface of the photoelectric switch, allowing easy adjustment on the user's side.

Effect (3) The adjustment range of maximum detection distance is stable.

This is because the light intensity adjustment range of the light emitting diode, which determines the adjustment range of the maximum detection distance, is not affected by variations in the forward voltage drop V _F of the light emitting diode.

The light emitting diode is connected to the collector side of the transistor, a lighting control signal is input from the base side, and a variable resistor for adjusting the amount of current is arranged on the emitter side or the base side of the transistor, The amount of current is determined on the emitter side or the base side and is virtually unrelated to the collector side where the light emitting diode is located, so the light amount adjustment range is not affected by variations in _VF of the light emitting diode.

Effect (4) The maximum detection distance adjustment circuit is very simple.

This is achieved by adding a variable resistor to adjust the maximum detection distance to the reflective photoelectric switch circuit that uses the ratio of the two series of received light signals, and
This is because it is sufficient to appropriately arrange other elements accordingly.

Effect (5) Appropriate adjustment of the maximum detection distance for objects with low reflectivity can be made.

This is because the amount of current flowing through the transistor, which determines the amount of light from the light emitting diode, can be adjusted independently using a variable resistor. If the light intensity of the light emitting diode cannot be changed independently, for example, if the light intensity change is linked to a change in the detectable area,
Even if the maximum detection distance can be changed, this results in the inconvenience that even objects outside the desired detection area will be detected.

[Brief explanation of drawings]

Figures 1a and b are circuit diagrams showing specific configuration examples of a light emitting element and a drive circuit in a reflective photoelectric switch according to this invention, respectively, and Figure 2 is a circuit diagram of an example of a reflective photoelectric switch according to this invention. An electrical system block diagram, Fig. 3 is a perspective view of the exterior of this photoelectric switch, Fig. 4 is a line diagram for explaining the state of movement of the maximum detection distance when the emission intensity of the light source is changed, and Fig. 5 2 is a diagram showing the relationship between the position of the object to be detected within the detection area and the amount of received light signals of two series. 3... Light emitting diode, 4, 5... Light receiving element,
6, 7...Amplification circuit, 8...Calculation circuit, VR1,
VR2...variable resistor.

Claims (1)

[Scope of utility model registration request] The light projecting means for irradiating light onto a detectable area, and the light receiving means for receiving the light reflected by the object to be detected existing in the detectable area and outputting two series of light reception signals, and the two series In a reflection type photoelectric switch, which also includes calculation means for calculating the ratio of received light signals, and the detection object is detected based on the output signal of the calculation means, A means for adjusting a maximum detection distance of an object is provided, and as the maximum detection distance adjustment means, in the light projecting means, the light emitting diode is connected to the collector side, the resistor element is connected to the emitter side, and lighting is controlled from the base side. A transistor to which a signal is input is provided, a variable resistor for independently adjusting the amount of current flowing through the light emitting diode is provided on the emitter side or base side of the transistor, and a photoelectric switch is provided. A reflective photoelectric switch characterized in that a knob for adjusting the variable resistor is disposed on the surface thereof.