JP2007309917A - Photoelectric sensor with automatic sensitivity correction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric sensor with automatic sensitivity correction capable of appropriately performing automatic sensitivity correction, even if there is a rapid increase/decrease in the amount of light. <P>SOLUTION: An automatic sensitivity correcting means 10 corrects the reference amount of light A, when a rapid change in an amount of received light among the changes in the amount of received light spans a predetermined time or longer for automatic recovery; and since sensitivity correction is terminated without correcting the reference amount of light A, when the rapid change spans less than the predetermined time, appropriate automatic sensitivity correction can be performed, even if there is a rapid increase/decrease in the amount of the light received. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric sensor with automatic sensitivity correction that automatically performs sensitivity correction in response to a change in the amount of light received by a light receiving element.

  Conventionally, a photoelectric sensor such as a reflection type or a transmission type that constantly detects the amount of light emitted by the light projecting element itself by the light receiving element, and detects a transparent or opaque object according to the degree of decrease in the amount of received light ( (Including fiber type). When this photoelectric sensor is installed in a place under a bad environment where there is a lot of dust, water vapor, etc., the environmental factors impede the arrival of light and reduce the amount of received light. For this reason, the threshold value has been manually reset by the teaching function or the like, but it has been requested that the sensitivity can be automatically corrected for labor saving.

In this case, it is conceivable to automatically set an optimum threshold value for detection in accordance with a change in the amount of received light. As this prior art, it is known to set a threshold value so as to follow fluctuations in the amount of received light and perform stable detection even if the amount of received light varies (for example, Patent Document 1).
JP 2003-87107 A

  By the way, the decrease in the amount of received light proceeds due to the environmental factors, and if the amount of received light falls below the threshold for object detection, it becomes impossible to detect the object. It is necessary to remove environmental factors, and in this case, the amount of received light increases rapidly before and after cleaning. On the other hand, even when a transparent object is detected, the amount of received light may suddenly increase or decrease.

  However, the conventional automatic sensitivity correction method usually detects a change in the amount of received light that is sufficiently slower than the speed at which the sensor operates (a few milliseconds at the latest), and corrects the threshold value. In this conventional method, a process that cancels the sudden increase / decrease in the amount of received light and does not affect the correction is performed. It was difficult to distinguish, and appropriate automatic sensitivity correction could not be realized.

  An object of the present invention is to solve the above-described problems and to provide a photoelectric sensor with automatic sensitivity correction that can appropriately perform automatic sensitivity correction even when the amount of received light is suddenly increased or decreased.

  In order to achieve the above object, a photoelectric sensor with automatic sensitivity correction according to the present invention includes a light projecting element that projects light, a drive circuit that drives the light projecting element, a light receiving element that receives light, and reflection by an object. A photoelectric sensor having a control means for performing control to detect an object by comparing the amount of light received by light or light shielding with a threshold value set based on a reference light amount that is a reference amount of light for object detection. Then, during the object detection operation, the control means performs sensitivity correction for correcting at least the reference light amount in response to a change in the amount of light received by the light receiving element, and automatically returns to the object detection operation. The automatic sensitivity correction unit corrects the reference light amount when a sudden change in the received light amount is greater than or equal to a predetermined time for performing the automatic return process, Predetermined When less than between one in which to terminate the sensitivity correction without correcting the reference amount of light.

  According to this configuration, the reference light amount is corrected when a sudden change in the received light amount is greater than or equal to a predetermined time for performing the automatic return process, and the reference light amount is corrected when the change is less than the predetermined time. Therefore, even if there is a sudden increase or decrease in the amount of received light, automatic sensitivity correction can be performed appropriately.

  Preferably, the automatic sensitivity correction unit includes a light reception amount change time determination unit that determines whether or not a sudden change in the light reception amount among the changes in the light reception amount is equal to or longer than a predetermined time for performing the automatic return process; Correcting the reference light amount when it is longer than the time, calculating the threshold value based on this, storing the reference light amount and threshold value, and correcting the reference light amount when less than a predetermined time And a sensitivity correction processing unit that ends the sensitivity correction. Therefore, automatic sensitivity correction can be performed more appropriately even if the amount of received light suddenly increases or decreases.

  Preferably, the reference light amount is a received light amount of background reflected light that is projected from the light projecting element and detected by the light receiving element. Therefore, an object can be detected based on the reference light amount that is the amount of light received from the background.

  Preferably, the automatic sensitivity correction unit further includes an averaging processing unit that performs an averaging process of the received light amount received by the light receiving element, and the reference light amount is the received light amount that is averaged by the averaging processing unit. It is. Therefore, even if there is a variation in the amount of received light, the sensitivity correction can be prevented from being affected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a photoelectric sensor with automatic sensitivity correction according to the first embodiment of the present invention. This sensor includes a light projecting element 1 such as an LED (light emitting diode) that projects light, a drive circuit 4 that drives the light projecting element 1, a light receiving element 3 that receives light, and a detection signal output from the light receiving element 3. The amplifier 6 for amplifying the signal, the A / D converter 7 for A / D-converting the amplified detection signal, and the entire sensor, the amount of light received or reflected by the object W, and the amount of received light A control / processing unit (microcomputer) 5 is provided as a control means for performing control for detecting the object W by comparing a threshold value set based on a reference light amount A that is a reference received light amount.

  The sensor further includes a display unit 11 that displays the detection result, an output circuit 12 that outputs the detection result to an external device, an input circuit 13 such as various switches, and a connection circuit 14 that is connected to another photoelectric sensor. . The display unit 11, the input circuit 13, and the connection circuit 14 may be omitted.

  In this example, the present sensor is a reflective photoelectric sensor that detects a transparent or opaque object W placed in front of the background M, and is projected from the LED 1 through the lens 2. The light reflected by the background M passes through the object W, and the reflected light of the background M and the light passing through the object W are received by the light receiving element 3 via the lens 2. The reference light amount A includes, for example, the amount of reflected light of the background M out of the reflected light of the background M and the passing light (transparent body) of the object W that is projected from the light projecting element 1 and detected by the light receiving element 3. The threshold value is set by multiplying the reference light amount A by a predetermined ratio. In addition, this sensor may receive light by the light receiving element 3 after collecting light by providing a mirror (not shown).

  The control / processing unit 5 in FIG. 1 automatically returns to the object detection operation by performing sensitivity correction for correcting at least the reference light amount A in response to a change in the amount of light received by the light receiving element 3 during the object detection operation. Automatic sensitivity correction means 8 for performing automatic return processing is provided. The automatic sensitivity correction unit 8 corrects the reference light amount A when the change in the light reception amount among the changes in the light reception amount is equal to or longer than a predetermined time for performing the automatic return process, and corrects the reference light amount when the change is less than the predetermined time. The sensitivity correction is terminated without correcting A.

  As shown in FIG. 2, the automatic sensitivity correction unit 8 includes an averaging processing unit 16 that performs an averaging process on the amount of light received by the light receiving element. For example, the received light amount is averaged by performing calculation using the moving average method for each light projection cycle. Thereby, even if there is some variation in the level of the amount of received light, the sensitivity correction can be prevented from being affected. The automatic sensitivity correction unit 8 includes a light reception amount change time determination unit 17 that determines whether or not a sudden change in the light reception amount among the changes in the light reception amount is equal to or longer than a predetermined time for performing the automatic return process; When the time is more than the time, the reference light amount A is corrected, the threshold value is calculated based on the correction, and the reference light amount A and the threshold value are stored. When the time is less than the predetermined time, the reference light amount A is not corrected. And a sensitivity correction processing unit 18 for ending the sensitivity correction.

  The operation of the automatic sensitivity correction means 8 of the present invention will be described below using the flowchart of FIG. The automatic sensitivity correction means 8 performs an automatic sensitivity correction process according to software stored in a storage unit such as a ROM. This sensitivity correction is performed by detecting the received light amount of the reflected light of the background M by the light receiving element 3 using the received light amount of the reflected light of the background M as the reference light amount A as described above during the object detection operation.

  First, when the sensitivity correction cycle is started (step S1), it is confirmed whether the received light amount of the background M sampled for each light projection cycle is a level at which correction processing is possible (step S2). If the level of the received light amount of the background M is equal to or higher than the level that can be corrected, an integration process is performed, and the integration counter sequentially counts +1 (step S3). It is confirmed whether or not the total number of times has become n times or more (step S4). If n times or more, the received light amount of the background M is averaged (step S5). In this way, even if there is some variation in the level of received light amount of the background M, it is possible to prevent the sensitivity correction from being affected. If it is less than n times, there is no need for sensitivity correction, so the sensitivity correction cycle is terminated (step S17).

  Next, it is confirmed whether or not the average value of the received light amount of the background M is less than or equal to a threshold value set for performing the automatic return processing, that is, whether or not there is a sudden change in the received light amount of the background M (step). S6). If it is equal to or less than the threshold value, the light reception amount of the background M did not change rapidly, so the automatic return processing flag is cleared (step S7), and the average value of the light reception amount of the background M is within a correctable range. Whether or not is confirmed (step S8). If within the correctable range, a parameter recalculation / storage process for correcting the reference (reference light amount) of the received light amount of the background M is performed (step S16), and the sensitivity correction cycle is completed (step S17).

  If the received light level of the background M is less than the correctable level in step S2, it is confirmed whether the sampling interval is within a normal range (step S9). If within the normal range, the sensitivity correction cycle is terminated (step S17). If it is not within the normal range, in order to redo the correction of the reference light amount, a parameter clear process for clearing the parameter relating to the correction of the reference light amount is performed (step S10), and the sensitivity correction cycle is ended (step S17).

  If it is determined in step S6 that the threshold value set for performing the automatic return process is exceeded, whether or not the automatic return process is in progress is confirmed (step S11). If the automatic return processing is not in progress, automatic return processing and parameter initialization processing for initializing parameters for automatic return processing and automatic return processing are performed (step S12), and the reference light amount (background light amount reference) A Is newly set (step S13), and the sensitivity correction cycle ends (step S17).

  If the automatic return process is being performed in step S11, it is checked whether the difference between the previous reference light amount and the current received light amount is appropriate (step S14). It is confirmed whether or not the predetermined time (specified time) for performing the process is exceeded (step S15). If the time is longer than the specified time, for example, it is considered that the amount of received light is rapidly increasing due to improvement of environmental factors such as cleaning of lenses and mirrors (steady state). Since it is regarded as a sudden increase / decrease (transient state) of the amount of light received by the object W such as a transparent body, both can be distinguished.

  In step S15, if the time is equal to or longer than the specified time, since the state of rapid increase in the amount of received light continues due to the improvement of environmental factors, the parameter recalculation / storage process including the correction of the reference light amount A is performed (step S15). S16), the sensitivity correction cycle ends (step S17). If it is less than the specified time, the amount of light received by the temporary object W is suddenly increased or decreased, so that the sensitivity correction cycle ends without correcting the reference light amount A (step S17). If the difference between the previous reference light amount and the current received light amount is too large and appropriate in step S14, the reference light amount (background light amount reference) A is newly set (step S13), and then the sensitivity correction cycle. Ends (step S17).

  Thus, the present invention distinguishes between a sudden increase / decrease in the amount of light received by the object W and a sudden increase in the amount of received light due to the improvement of environmental factors, and automatically corrects the sensitivity even if there is a sudden increase / decrease in the amount of received light. It can be carried out.

  FIG. 4 is a block diagram showing a photoelectric sensor with automatic sensitivity correction according to the second embodiment. Unlike the first embodiment, the second embodiment is a transmissive photoelectric sensor, which projects light from the light projecting element 1 through the optical fiber 9, and this light is transmitted by the light receiving element 3 through the optical fiber 9. Received light. When the object W blocks the projected light, the amount of light received by the light receiving element 3 decreases, so the presence or absence of the object W is detected.

  The sensitivity correction of the second embodiment differs from the first embodiment in that the received light amount of the reflected light of the background M received by the light receiving element 3 is used as the reference light amount A based on this, and the light projection received by the light receiving element 3 is used. The amount of received light from the element 1 is set as a reference light amount A1, and the measurement is performed based on the reference light amount A1. When the sudden change in the amount of received light is not less than a predetermined time (specified time) for performing the automatic return process, the reference light amount A1 is corrected, and when it is less than the predetermined time, the sensitivity correction is terminated without correcting the reference light amount A1. . Other configurations are the same as those of the first embodiment.

  Thus, even in the transmission type photoelectric sensor of the second embodiment, there is a sudden increase / decrease in the amount of received light by distinguishing between a sudden increase / decrease in the amount of received light by the object W and a sudden increase in the amount of received light due to improvement of environmental factors. Also, sensitivity correction can be performed automatically and appropriately.

It is a block block diagram which shows the photoelectric sensor with an automatic sensitivity correction which concerns on 1st Embodiment of this invention. It is a block block diagram which shows an automatic sensitivity correction | amendment means. It is a flowchart which shows the sensitivity correction operation | movement of the photoelectric sensor of FIG. It is a block block diagram which shows the photoelectric sensor with an automatic sensitivity correction which concerns on 2nd Embodiment.

Explanation of symbols

1: Light projecting element 3: Light receiving element 5: Control means (control / processing section)
8: Automatic sensitivity correction means 16: Averaging processing unit 17: Received light amount change time determination unit 18: Sensitivity correction processing unit A, A1: Reference light quantity M: Background W: Object

Claims (4)

A light projecting element that projects light, a drive circuit that drives the light projecting element, a light receiving element that receives light, and the amount of light received by reflected or blocked light from an object, and a reference that is the amount of light received that serves as a reference for object detection A photoelectric sensor having a control means for performing control to detect an object by comparing with a threshold value set based on the amount of light,
The control means performs an automatic return process for automatically returning to the object detection operation by performing sensitivity correction for correcting at least the reference light amount in response to a change in the amount of light received by the light receiving element during the object detection operation. Equipped with automatic sensitivity correction means,
The automatic sensitivity correction unit corrects the reference light amount when a sudden change in the received light amount among the changes in the received light amount is equal to or longer than a predetermined time for performing the automatic return processing, and Photoelectric sensor with automatic sensitivity correction that finishes sensitivity correction without correcting the amount of light. In claim 1,
The automatic sensitivity correction means includes
A light-receiving-amount change time determination unit that determines whether or not a sudden change in the light-receiving amount among the changes in the light-receiving amount is equal to or longer than a predetermined time for performing the automatic return processing;
When the predetermined amount of time is exceeded, the reference light amount is corrected, and the threshold value is calculated based on the correction. The reference light amount and the threshold value are stored, and when the predetermined time is less than the predetermined time, the reference light amount is corrected. A sensitivity correction processing unit for ending the sensitivity correction without performing
Photoelectric sensor with automatic sensitivity correction. In claim 1,
A photoelectric sensor with automatic sensitivity correction, wherein the reference light amount is a received light amount of reflected light of a background projected from the light projecting element and detected by the light receiving element. In claim 1,
The automatic sensitivity correction unit further includes an averaging processing unit that performs an averaging process on the amount of received light received by the light receiving element, and the reference light amount is a received light amount averaged by the averaging processing unit. Photoelectric sensor with automatic sensitivity correction.

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