JP2010085357A - Photoelectric sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric sensor having a simple configuration and capable of, for example, discriminating a front end and a back end of a detection object delivered at a predetermined speed and detecting the length of the delivering direction of the detection object. <P>SOLUTION: The photoelectric sensor includes: a differential calculating means for differentiating the amount of light received by an optical receiver; a rising-edge detecting means for detecting a rising edge with a large change of the increase in the received light amount by comparing the differential amount determined by the differential calculating means and a first threshold value; a falling-edge detecting means for detecting a falling edge with a large change of the decrease in the received light amount by comparing the differential amount and a second threshold value; and an output signal generating means which is set/reset by the output from each of the rising-edge detecting means and the falling-edge detecting means and generates an output signal from the detection point of the rising edge to the detection point of the falling edge or from the detection point of the falling edge to the detection point of the rising edge. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to, for example, a photoelectric sensor that optically detects the presence or absence of a detection object conveyed at a constant speed. In particular, the detection object is distinguished from a front end portion and a rear end portion of the detection target. The present invention relates to a photoelectric sensor that can easily detect the length in the transport direction.

  As a sensor for detecting the presence or absence of an object to be detected that is conveyed at a constant speed in an industrial production line or the like, there is a photoelectric sensor in which a projector and a light receiver are provided in pairs. In general, this type of photoelectric sensor receives light projected from the projector according to the presence or absence of the detected object by the light receiver, or is projected from the projector and reflected by the detected object. The received light is received by the light receiver, and the presence or absence of the detection object is determined from the change in the amount of light received by the light receiver. These photoelectric sensors are called transmissive photoelectric sensors or reflective photoelectric sensors.

By the way, depending on the usage environment (installation environment) of the photoelectric sensor, for example, the amount of light received by the light receiver changes due to the influence of dust, so the threshold value for determining the presence or absence of the detection object from the change in the amount of received light It is necessary to change according to the environment. In order to solve such a problem, a differential detection type photoelectric sensor that differentially processes the amount of light received by the light receiver and discriminates the differential signal at a predetermined threshold value to detect the presence or absence of a detection target has been proposed ( For example, see Patent Document 1).
JP 2004-119835 A

  However, in the conventional general differential detection type photoelectric sensor, the presence / absence of the detected object is merely determined instantaneously by simply discriminating the differential signal with a predetermined threshold value. For this reason, even if the differential signal is measured by a controller such as a PLC, there is a problem that it is impossible to determine which part of the detected object is detected. .

  The present invention has been made in consideration of such circumstances, and its purpose can be detected by distinguishing the front end portion and the rear end portion of the detected object conveyed at a constant speed, for example. An object of the present invention is to provide a photoelectric sensor having a simple configuration capable of easily detecting the length of a detected object in the transport direction.

In order to achieve the above-described object, the photoelectric sensor according to the present invention includes:
<a> Differentiation calculation means for differentiating the amount of light received by the light receiver to obtain the amount of change in the amount of received light
<b> Rising edge detection means for detecting a rising edge having a large increase in the amount of received light by comparing the amount of change obtained by the differential calculation means with a first threshold;
<c> Falling edge detection means for detecting a falling edge having a large decrease in the amount of received light by comparing the amount of change obtained by the differential calculation means with a second threshold value;
<d> An output signal that is set / reset by the output of each of the edge detection means to reach the falling edge detection time from the rising edge detection time, or from the falling edge detection time to the rising edge detection time And an output signal generating means for generating an output signal leading to.

  That is, the photoelectric sensor according to the present invention has a rising edge having a large increase in the amount of received light and a falling edge having a large decrease in the amount of received light from a differential signal obtained by differentiating the amount of light received by the light receiver. By independently detecting and generating an output signal indicated by the rising edge and the falling edge, the front end portion and the rear end portion of the detected object are distinguished, and the length of the detected object in the transport direction ( (Size) can be detected.

  Preferably, the output signal generation means selects an output signal from the detection time of the rising edge to the detection time of the falling edge or an output signal from the detection time of the falling edge to the detection time of the rising edge. Configured to generate automatically. The output signal generating means is a timer that is automatically reset when it is not reset by the output of the other edge detecting means by a preset time after being set by the output of one edge detecting means. It is preferable to realize the function.

  Note that the first and second threshold values given to the respective edge detection means may be set independently of each other, but may be variably set in conjunction with each other. In addition, there may be provided output signal selection means for selectively selecting a signal output from the rising edge detection means, a signal output from the falling edge detection means, and a signal generated by the output signal generation means and externally outputting them. preferable.

  According to the photoelectric sensor having the above configuration, a rising edge having a large increase in the amount of received light and a falling edge having a large decrease in the amount of received light are independently determined from a differential signal obtained by differentiating the amount of light received by the light receiver. Therefore, the change in the amount of received light due to the presence or absence of the detected object regardless of fluctuations in the amount of light received by the light receiver due to disturbance factors, in particular, of the detected object conveyed at a predetermined speed A front end part and a rear end part can be distinguished and detected.

  In addition, since a signal set and reset at the detection timing of the rising edge and the detection timing of the falling edge in the differential signal is generated as an output signal, the leading edge and the trailing edge of the output signal are defined as the front end portion of the detected object and The rear end portion can be easily distinguished and detected, and the length of the detected object can be easily detected from the signal width.

Hereinafter, a photoelectric sensor according to an embodiment of the present invention will be described with reference to the drawings.
This photoelectric sensor is provided with a pair of light projectors (light projecting elements) and light receivers (light receiving elements) (not shown). Basically, as shown in FIG. A received light amount detector 1 that detects the amount of light received by the device as an electrical signal, and a differential signal that indicates the magnitude of the change is generated by differentiating the received light amount signal detected by the received light amount detector 1. And a differential operation unit 2.

  The photoelectric sensor further includes a rising edge detector 3 that receives the differential signal obtained by the differential calculator 2 and detects a rising edge having a large increase in the amount of received light, and a large decrease in the amount of received light. A falling edge detection unit 4 for detecting a falling edge is provided in parallel. Incidentally, when the differential signal exceeds the first threshold value TH1, the rising edge detection unit 3 is configured to detect this as a rising edge in which the amount of received light has suddenly increased. Further, the falling edge detection unit 4 is configured to detect when the differential signal has turned around the second threshold value TH2 as a falling edge in which the amount of received light is rapidly reduced.

  The first threshold value TH1 is basically set as a positive (+) value with respect to the differential signal, whereas the second threshold value TH2 is negative (−) with respect to the differential signal. ) Value. The first and second threshold values TH1 and TH2 can be set independently according to the usage environment (installation environment) of the photoelectric sensor, but are provided so as to be variably set in conjunction with each other. It is also possible to keep it.

  In addition to the rising edge detection unit 3 and the falling edge detection unit 4, the photoelectric sensor according to the present invention is set by receiving one output of the edge detection units 3 and 4 and receiving the other output. A set / reset output section (output signal generating means) 5 is provided for generating an output signal (set / reset output) that is reset and takes a binary value. Specifically, the set / reset output unit 5 includes a flip-flop circuit. For example, the set / reset output unit 5 is set by receiving the output of the rising edge detecting unit 3 and reset by receiving the output of the falling edge detecting unit 4. An output signal that is turned on (ON) from the rising edge detection timing to the falling edge detection timing is generated. Alternatively, the set / reset output unit 5 is set by receiving the output of the falling edge detection unit 4 and resets by receiving the output of the rising edge detection unit 3 so as to rise from the detection timing of the falling edge. An output signal that is turned on (ON) over the edge detection timing is generated.

  The set / reset output unit 5 may have a timer function for automatically resetting the output when no reset signal is applied even when the preset elapsed time To has been reached since the set. Useful. Also, it is desirable that the timer time To can be variably set according to the usage conditions of the photoelectric sensor. In this embodiment, the output switch 6 that alternatively outputs the output of the rising edge detector 3, the output of the falling edge detector 4, and the output of the set / reset output unit 5 described above is output. It is incorporated as signal selection means.

  For example, when the photoelectric sensor configured as described above is used in a detection environment in which the amount of light received by the light receiver increases when an object to be detected exists, the set / reset output unit 5 detects the rising edge. The operation condition is set so that the output is set by receiving the output of the unit 3 and reset by receiving the output of the falling edge detection unit 4. Then, when the amount of light received by the light receiver increases due to the presence of the detected object as shown in FIG. 2 (a), the differential output (differential amount) of the received light amount by the differential operation unit 2 is shown in FIG. 2 (b). Thus, it changes to positive (+) when the amount of received light increases, and changes to negative (-) when the amount of received light decreases.

  Since the rising edge detector 3 detects a sudden increase in the differential amount at the first threshold value TH1 with respect to such a differential amount, the output of the differential amount is as shown in FIG. A pulse-like output that is turned on (high) at a rapidly increasing rising edge is generated. Further, since the falling edge detection unit 4 detects a sudden decrease in the differential amount at the second threshold value TH2, the output is a falling edge in which the differential amount has rapidly decreased as shown in FIG. A pulse-like output that is turned on (high) at the edge is generated.

  As a result, the set / reset output unit 5 is set in response to the output of the rising edge detector 3, and is reset in response to the output of the falling edge detector 4, as shown in FIG. In addition, an output signal that is turned on (high) from the detection timing of the rising edge to the detection timing of the falling edge is generated. Then, by monitoring the signal shown in FIG. 2 (e), it becomes possible to distinguish and detect the time point when the front end portion of the detected object is detected and the time point when the rear end portion of the detected object is detected, Further, it is possible to detect the detection time (detection width) from the front end portion to the rear stage portion of the detected object from the signal duration time. Therefore, if the detected object is conveyed at a predetermined conveying speed, for example, the length of the detected object in the conveying direction (the size of the detected object) can be detected from the detection time (detection width). It becomes possible.

  On the other hand, when the photoelectric sensor is used, for example, in a detection environment in which the amount of light received by the light receiver decreases when an object to be detected exists, the set / reset output unit 5 is connected to the falling edge detection unit. The operation condition is set so as to be reset upon receipt of the output of 4 and to be reset upon receipt of the output of the rising edge detector 3. Then, when the amount of light received by the light receiver decreases due to the presence of the detected object as shown in FIG. 3A, the differential output (differential amount) of the received light amount by the differential operation unit 2 is shown in FIG. Thus, it changes to negative (−) when the amount of received light decreases, and changes to positive (+) when the amount of received light increases.

  Since the rising edge detection unit 3 detects a sudden increase in the differential amount at the first threshold TH1, the output of the differential amount is as shown in FIG. A pulse-like output that is turned on (high) at a rapidly increasing rising edge is generated. Further, since the falling edge detection unit 4 detects a sudden decrease in the differential amount at the second threshold value TH2, the output is a falling edge in which the differential amount has rapidly decreased as shown in FIG. A pulse-like output that is turned on (high) at the edge is generated.

  Then, the set / reset output unit 5 is set in response to the output of the falling edge detection unit 4, and is reset in response to the output of the rising edge detection unit 3. As shown in FIG. An output signal that is turned on (high) from the detection timing of the falling edge to the detection timing of the rising edge is generated. Therefore, by monitoring the signal shown in FIG. 3 (e), the time point when the front end portion of the detected object is detected is distinguished from the time point when the rear end portion of the detected object is detected, as in the embodiment described above. It becomes possible to detect, and it is possible to detect the detection time (detection width) from the front end portion to the rear stage portion of the detected object from the signal continuation time. Therefore, if the detected object is conveyed at a predetermined conveying speed, for example, the length of the detected object in the conveying direction (the size of the detected object) can be detected from the detection time (detection width). It becomes possible.

  In addition, when detecting a state in which the detection object does not exist, such as when detecting a groove (notch) provided in the detection object, the same applies from the signal generated by the set / reset output unit 5. Needless to say, it can be detected. In addition, it is assumed that the conveyance of the detected object is stopped for some reason, and the set / reset output unit 5 remains set due to this. Therefore, in such a case, for example, as shown in FIG. 4, the set / reset output unit 5 is automatically reset when a predetermined time To elapses after the set / reset output unit 5 is set. It ’s good if you keep it. By providing such a timer function, it is possible to reliably prevent the unintentional signal output state from the set / reset output unit 5 from continuing. Further, when the set / reset output unit 5 is forcibly reset in this way, it is also useful to emit some event signal.

  Thus, in the differential detection type photoelectric sensor that detects the presence of the detected object from the differential value of the received light amount at the photoreceiver, as described above, the rapid decrease of the differential amount is individually detected, According to the photoelectric sensor according to the present invention having a function of generating a signal that is set / reset according to these detection results, the front end portion and the rear end portion of the detected object are monitored by monitoring the set / reset output. Can be detected separately, and further, the detection width (length in the transport direction) of the detection target can be detected.

  In addition to detecting a sudden increase in the differential amount of the received light amount, it is possible to improve the accuracy of object detection with a simple configuration that also detects a sudden decrease in the differential amount. Furthermore, since it is possible to accurately grasp which part of the detection object is detected, not only the detection of the object conveyed along the industrial production line, but also the conveyance interval of the object and the detection object The present invention has a great practical effect such that the present photoelectric sensor can be effectively used for detecting a space width of a groove (notch) provided.

  The present invention is not limited to the embodiment described above. For example, it is also useful to incorporate a length converter 7 that obtains the length of the detected object from the output of the set / reset output unit 5 as indicated by a broken line in FIG. Of course, the output switch 6 may be omitted and only the output of the set / reset output unit 5 may be obtained. In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

The principal part schematic block diagram of the photoelectric sensor which concerns on one Embodiment of this invention. FIG. 3 is an operation waveform diagram for explaining a typical operation mode of the photoelectric sensor shown in FIG. 1. The operation | movement waveform diagram for demonstrating another operation | movement form of the photoelectric sensor shown in FIG. FIG. 6 is an operation waveform diagram for explaining still another operation mode of the photoelectric sensor shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Received light amount detection part 2 Differential operation part 3 Rising edge detection part 4 Falling edge detection part 5 Set / reset output part (output signal generation means)
6 Output switch (output signal selection means)

Claims (6)

Differential operation means for differentiating the amount of light received by the light receiver to obtain the amount of change in the amount of received light;
A rising edge detecting means for detecting a rising edge having a large increase in the amount of received light by comparing the amount of change obtained by the differential calculation means with a first threshold;
A falling edge detecting means for detecting a falling edge having a large change in decrease in the amount of received light by comparing the amount of change obtained by the differential calculation means with a second threshold;
An output signal that is set / reset by the output of each of the edge detection means and reaches from the rising edge detection time to the falling edge detection time, or an output from the falling edge detection time to the rising edge detection time An output signal generation means for generating a signal.   The output signal generating means alternatively outputs an output signal from the rising edge detection time to the falling edge detection time or an output signal from the falling edge detection time to the rising edge detection time. The photoelectric sensor according to claim 1, which is generated.   The output signal generating means is provided with a timer function that automatically resets when not set by the output of the other edge detecting means by a preset time after being set by the output of one edge detecting means. The photoelectric sensor according to claim 1.   2. The photoelectric sensor according to claim 1, wherein the first and second threshold values given to the edge detection units are variably set independently of each other or in conjunction with each other. The light receiver is used in a pair with a light projector, and the light projected from the light projector according to the presence or absence of the target to be transported at a constant speed or the light to be detected from the light projector Receiving the light reflected by
The photoelectric sensor according to claim 1, wherein the output signal generation unit generates a signal corresponding to a length of the detected object in a conveyance direction. In the photoelectric sensor in any one of Claims 1-5,
Further, the apparatus further comprises output signal selection means for selectively selecting a signal output from the rising edge detection means, a signal output from the falling edge detection means, and a signal output from the output signal generation means and outputting them externally. A photoelectric sensor characterized by

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