JP2014096715A - Photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a threshold correction process at an appropriate timing irrespective of the length and rate of a light incidence period.SOLUTION: A photoelectric sensor that repeatedly projects and receives light and samples an amount of light received while comparing the sampled amount of light received with a threshold to detect an object discriminates between a first period in which the amount of light received exceeds a predetermined reference value Plarger than the threshold and a second period in which the amount of light received falls below P, and in response to a cumulative number of samples in the first period reaching a preselected numeral value N, determines a degree of reduction in the N samples of the amount of light received relative to a desired value of the amount of light received and corrects the threshold on the basis of the degree. The numerical value N is selected at a numerical value decreasing with decreasing percentage of the length of the first period to the total length of the first period and the second period, and is selected from two or more prepared numerical values.

Description

  The present invention provides a light projecting unit that projects light for detection, a light receiving unit that receives the projected light or reflected light thereof, and a light receiving unit obtained by operating the light projecting unit and the light receiving unit. The present invention relates to a photoelectric sensor including a control unit that detects an object by comparing a sampled received light amount with a preset threshold value while repeating a process of sampling the amount.

  In general, a photoelectric sensor receives a light projected from a light projecting unit by a light receiving unit, detects a object by a change from a light incident state to a non-light incident state, and the projected light. The reflected light from the irradiated object is received by the light receiving unit, and it can be divided into a reflection type sensor that detects the object by a change from the non-light incident state to the light incident state. Furthermore, an optical fiber type photoelectric sensor configured to be compatible with both transmissive and reflective specifications has been developed (see Patent Document 1).

  In any type of photoelectric sensor, processing for adjusting sensitivity and setting a threshold value is necessary to ensure detection accuracy. Regarding this type of setting process, Patent Document 1 discloses a value having a predetermined distance from the target value after adjusting the light projection power and the light receiving gain so that the amount of light received at the time of incident light becomes a predetermined target value. It is described that the threshold value is set (paragraph 0088 of Patent Document 1).

In addition, a photoelectric sensor having a function of automatically correcting a threshold value with respect to attenuation of received light amount due to deterioration of a light projecting unit or a light receiving unit has been developed.
For example, Patent Document 2 determines whether or not the amount of change in the received light amount signal at the time of detection or non-detection is greater than or equal to a preset reference level, and determines that the amount of change is greater than or equal to the reference level. It describes that the threshold value is automatically corrected under the condition that it has continued for a predetermined number of times (see paragraphs 0016 and 0038 of Patent Document 2).

  Further, in Patent Document 3, when a work is in one of a state where it exists in a detection area or a state where it does not exist, a predetermined ratio is set to an average value of the amount of received light sampled under that state. Multiplication is performed and the threshold value is corrected by the multiplication value (see paragraphs 0028 to 0031 and the like in Patent Document 3).

JP 2004-101446 A JP 2003-172785 A Japanese Patent No. 4730898

  Since the correction of the threshold value should be performed following the degree of decrease in the amount of received light, it is desirable to use the amount of received light during the light incident period in which the attenuation state can be easily determined. Further, since the received light amount may fluctuate suddenly due to noise light or the like, it is desirable to use a plurality of received light amount data as described in Patent Documents 2 and 3.

  From the above, it is considered appropriate to use a plurality of received light amounts sampled during the light incident period for correcting the threshold, but it is not desirable to fix the sampling number. The length of the light incident period varies depending on the moving speed of the detection object, the interval between the objects, and the like, and also varies depending on whether the sensor is a transmission type or a reflection type. Even if the length of the light incident period is different, if the light projecting unit and light receiving unit repeat operations in the same cycle, the deterioration over time should occur to the same extent, but the number of received light amount data used for correction If is fixed, the time required to obtain the number of received light quantity data necessary for correction varies. In particular, if the light incident period is shortened, the time required to obtain the number of received light quantity data necessary for correction becomes longer, and as a result, the received light quantity greatly decreases before the correction is performed, and light reception during the light incident period is performed. There is a possibility that the margin for the amount threshold is insufficient and the detection operation becomes unstable.

  Further, in the invention described in Patent Document 3, it is preferable that the threshold value is corrected every sampling of the amount of received light when it is determined that the threshold value is to be corrected (see paragraph 0031 of Patent Document 3). )), However, the calculation burden on the control unit increases, and it may be difficult to speed up the detection process. Since the amount of light received is gradually attenuated over time, there is no need to correct the threshold every sampling.

  The present invention has been made paying attention to the above problem, and it is an object of the present invention to perform threshold value correction processing at an appropriate timing regardless of the length and ratio of the light incident period.

In order to solve the above problems, the control unit of the photoelectric sensor according to the present invention is provided with the following determination means, selection means, and correction processing means.
The discriminating means compares the sampled received light amount with a predetermined reference value higher than the threshold value, and discriminates between a first period in which the received light amount exceeds the reference value and a second period in which the received light amount falls below the reference value. To do. It is desirable that the reference value is set above the threshold by at least the minimum margin required to ensure detection accuracy.

  The selection means selects one of two or more numerical values prepared in advance, and the numerical value decreases as the ratio of the length of the first period to the total length of the first period and the second period decreases. Run as selecting.

  The correction processing means counts the total number of samplings during the first period, and counts the target value of the predetermined amount of received light in response to the count value reaching the numerical value selected by the selection means. The threshold value for object detection is corrected based on the degree of decrease in the received light amount of each sampling, and the count value is reset.

  According to the above configuration, the total sampling number in the first period in which the amount of received light having a certain degree of margin with respect to the threshold is incident is selected (hereinafter, this number is referred to as N). The threshold value can be corrected using the amount of light received by sampling N times. The value of N is automatically selected according to the ratio of the length of the first period to the total length of the first period and the second period, but the value of N decreases as the ratio decreases. The threshold value can be corrected at an appropriate timing regardless of the length and ratio of the light incident period.

  In the first embodiment of the photoelectric sensor, the selection unit individually counts the number of received light amounts in the first period and the second period for each period, and in response to the period switching occurring. The ratio of the total number of received light amounts in the first period and the second period immediately after the switching and the number of received light samples in the latest first period is obtained, and the numerical value to be selected is determined based on this ratio. .

  According to the above embodiment, in accordance with the switching from the first period to the second period, or the switching from the second period to the first period, the total length of the first period and the second period immediately after the switching A numerical value to be selected as N is determined based on the ratio of the length of the first period to the length, and the threshold value is corrected using the number of sampling data during the first period corresponding to the selection. Therefore, for example, the ratio between the first period and the second period is changed because the detection object is changed, or the ratio between the first period and the second period is changed because the detection object moves at irregular intervals. Even if there is a variation, the threshold value can be corrected at an appropriate timing by changing the value of N according to the change or variation.

  In the photoelectric sensor according to the second embodiment, the correction processing unit calculates a ratio between the average value of the received light amounts of the samplings and the target value of the received light quantity, which is the target of the counting during the first period, and calculates the ratio. The threshold value for object detection is lowered by a value corresponding to. In this way, the threshold value can be appropriately corrected according to the degree of decrease in the amount of received light with respect to the initially set target value.

The photoelectric sensor of the second embodiment can be further provided with a display unit for displaying the sampled received light amount. In this case, the control unit is provided with display light reception amount correction means for correcting the received light amount to be displayed on the display unit to a value higher by a value corresponding to the ratio between the average value of the received light amount and the target value of the received light amount. be able to.
According to this configuration, even if the actual amount of received light decreases, the amount of received light on the display is maintained at a level almost the same as that immediately after the sensitivity adjustment is completed, so the user confirms the detection result on a constant basis. be able to. In addition, it is possible to prevent the user from misunderstanding that the decrease in the amount of received light is due to some abnormality.

  According to the present invention, the threshold value correction process can be performed at an appropriate timing regardless of the degree of length of the light incident period and the degree of the ratio between the light incident period and the non-light incident period. Therefore, even if the amount of received light during the light incident period is attenuated, it is easy to secure a margin of the amount of received light with respect to the threshold value, and stable detection can be performed.

It is a perspective view which shows the external appearance of an optical fiber type photoelectric sensor. It is a perspective view which shows the state which opened the upper surface cover of the photoelectric sensor of FIG. It is the figure which looked at the upper surface containing the operation part and display part of the said photoelectric sensor from the front. It is a block diagram which shows the electric constitution of the said photoelectric sensor. It is a graph which shows the relationship between the change of light reception amount, and the timing of correction | amendment of a threshold value for each of the case where the ratio of light incident period is long, and a short case. 6 is a graph showing an example in which the threshold value is not appropriately corrected for the same change in the amount of received light as in FIG. It is a graph which shows the relationship between the change of received light quantity, and the timing of correction | amendment of a threshold value about the case where a light-incident state and a non-light-incident state switch at high speed. It is a flowchart which shows the procedure of the correction process of a threshold value. It is a flowchart which shows the procedure of a detection process.

1 and 2 show the appearance of an optical fiber photoelectric sensor to which the present invention is applied.
The photoelectric sensor 1 includes a main body 10 and a pair of optical fibers 11 and 12 attached to the front surface of the main body 10. The optical fiber 11 is for light projection, and the other optical fiber 12 is for light reception. Head portions 11A and 12A each including a lens or the like are attached to the tip portions of the optical fibers 11 and 12, respectively. The actual optical fibers 11 and 12 can be longer than the illustrated state.

  The optical fibers 11 and 12 are inserted into the insertion ports 11B and 12B on the front surface of the main body 10, respectively. A light projecting portion is provided in the vicinity of the insertion port 11B of the light projecting optical fiber 11, and a light receiving unit is provided in the vicinity of the insertion port 12B of the light receiving optical fiber 12. A connection cable 14 is drawn from the back surface of the main body 10.

  When the sensor 1 is used, the head portions 11A and 12A of the optical fibers 11 and 12 are arranged to face each other with a predetermined distance therebetween. The light emitted from the light projecting unit is emitted from the head unit 11A through the optical fiber 11, and the light incident on the head unit 12A on the light receiving side reaches the light receiving unit through the optical fiber 12. When an object enters between the head portions 11A and 12A, the light from the head portion 11A toward the head portion 12A is blocked, so that the amount of light received by the light receiving portion decreases.

  The received light amount data generated by the light receiving unit is input to the control unit (CPU), and it is determined whether or not the optical path is blocked by comparison with a threshold value registered in advance, and the determination result is output. .

  In the example of FIG. 1, the photoelectric sensor 1 functions as a transmissive sensor that receives light projected from the light projecting unit by the light receiving unit and discriminates that the light path is shielded from “object present”. However, it is also possible to attach a common head portion to the tips of the optical fibers 11 and 12 so that the sensor 1 functions as a reflective photoelectric sensor that receives reflected light from an object. is there.

  A display unit 100 and a plurality of push button switches SW <b> 1 to SW <b> 5 are provided on the upper surface of the main body unit 10. The cover 13 is put on the upper surface when in use, but the cover 13 is opened at the time of setting or the like, and the operation of the pushbutton switches SW1 to SW5 becomes possible. FIG. 2 is a perspective view of the main body 10 with the cover 13 being opened, and FIG. 3 is a front view of the upper surface. Since the cover 13 is transparent, the display on the display unit 100 can be confirmed via the cover 13 even when the cover 13 is attached.

The configuration of the upper surface will be described with reference to FIGS.
In this embodiment, a push button switch SW1 is provided at a position closer to the front surface of the main body, a display unit 100 is provided behind the push button switch SW1, and four push button switches SW2, SW3, SW4 are provided behind the display unit 100. , SW5 is deployed. In addition, although the button part of pushbutton switch SW2, SW3 is united, the switch main body (not shown) in the housing | casing 10 is each independent.

The display unit 100 is provided with a pair of indicators 101 and 102 and five indicator lights 111 to 115. The display devices 101 and 102 are a combination of four 7-segment LEDs, and display numbers and alphabetic character strings of up to 4 digits, respectively.
For example, when the tuning process described later is completed, the maximum value of the received light amount adjusted by this process is displayed on the display unit 101, and the numerical value set as the detection threshold is displayed on the display unit 102. Thereafter, when the process proceeds to the detection process, the display unit 101 displays the current amount of received light, and the display unit 102 displays a threshold value.

  The front pushbutton switch SW1 is a switch used for a tuning process described later. In the following description, this switch SW1 is referred to as “tuning button SW1”. A pair of push button switches SW2 and SW3 behind the display unit 100 are used to change menus and numerical values displayed on the display devices 101 and 102.

  The push button switch SW4 is a switch for switching between the measurement mode and the setting mode. When any setting is made in the setting mode, the set content is confirmed. When the measurement mode is switched by the push button switch SW4, measurement and detection processing is started with the set contents.

  The push button switch SW5 is for switching the output format of the sensor 1. Specifically, there is a “light on mode” that turns the output on when the amount of received light exceeds a threshold, or a “dark on mode” that turns the output on when the amount of received light is lower than the threshold. Selected. In general, when the sensor 1 is a transmission type, the dark on mode is selected, and when the sensor 1 is a reflection type, the light on mode is selected.

The display 111 lights up when the detection signal from the sensor 1 is turned on.
The indicator lamp 112 is lit when the light-on mode is selected, and the indicator lamp 113 is lit when the dark-on mode is selected. The indicator lamp 114 is lit when a process for adjusting the received light amount on the display described later is set to be effective, and the indicator lamp 115 is lit during and after the tuning process.

FIG. 4 shows the electrical configuration of the photoelectric sensor 1.
In this sensor 1, in addition to the light projecting unit 103 and the light receiving unit 104, a memory 106 storing a program, a display unit 100, an operation unit 110, an external device interface 107, an output unit 108, a power source, in addition to the light projecting unit 103 and the light receiving unit 104 The unit 109 and the like are connected.

  The display unit 100 includes the above-described indicators 101 and 102 and indicator lamps 111 to 115, and the operation unit 110 includes push button switches SW1 to SW5. The light projecting unit 103 includes an LED 131 and an LED drive circuit 132, and the light receiving unit 104 includes an amplifying circuit 142 and an A / D conversion circuit 143 in addition to a photodiode (PD) 141. In the light projecting unit 103, a driving current flows from the LED drive circuit 132 to the LED 131, and a light projecting process is performed. In the light receiving unit 104, the output from the photodiode 141 is processed by the amplification circuit 142 and the A / D conversion circuit 143, thereby generating digital data representing the amount of received light (hereinafter referred to as “light reception amount data”). .

  The CPU 105 samples the received light amount data from the light receiving unit 104 at a constant period while controlling the operations of the light projecting unit 103 and the light receiving unit 104 according to the program stored in the memory 106, and the sampled received light amount data is obtained. Compare with threshold. The result of this comparison is output as a detection signal via the output unit 108 or the external device interface 107.

  When the setting mode is selected by the switch SW4 shown in FIGS. 2 and 3, a setting menu is displayed on each of the displays 101 and 102 of the display unit 100. The user performs a desired setting while switching the menu display using the switches SW2 and SW3.

  When the tuning button SW1 is operated in the measurement mode, a setting process called “tuning” is performed. Tuning is a batch of sensitivity adjustment processing and threshold setting processing, which are indispensable settings for detection processing. Regardless of whether the sensor is used as a transmission type or a reflection type, the tuning is performed at a certain level. Implemented based on criteria.

  In this embodiment, a plurality of types of tuning processes are prepared for each purpose of use of the sensor 1, and the sensitivity and threshold value are automatically set to a state suitable for the purpose by performing a simple operation for each type of tuning. The rules for sensitivity adjustment and threshold setting are set so that Hereinafter, two typical types of tuning processing will be briefly described.

<Two-point tuning>
This tuning is executed when the sensor 1 is used for the purpose of determining the presence or absence of an object. The user performs the operation of pressing the tuning button SW1 in a short time twice, but one operation is performed in a state where a detection object (hereinafter referred to as “work”) is arranged in the detection area, and the other operation is performed. It is done in a state where the work is not deployed. Either may or may not be deployed.

  In the sensitivity adjustment process, the maximum value that can be displayed on the display units 101 and 102 (hereinafter referred to as “display maximum value”. The maximum display value in this example is “9999”) is set as the target value for the first time. The magnification of the target value for the larger value of the received light amount (first received light amount) and the received light amount (second received light amount) obtained during the second operation is obtained and The intensity of the drive current of the light projecting unit 103 and the amplification magnification of the light receiving unit 104 are adjusted so that the amount of received light can be increased. Further, the first received light amount and the second received light amount are multiplied by the above-described magnifications, respectively, and an intermediate value of the received light amounts after the multiplication is set as a threshold value.

<Moving work tuning>
In this tuning, the moving workpiece is detected, the sensor output is set to the detection state while the workpiece is passing the detection area, and the sensor 1 is operated so that the output is not detected when the passage is completed. Implemented when you want. When performing tuning, the user moves the workpiece under the same conditions as at the time of detection, and during the period when the workpiece is in the detection area and the workpiece is not in the detection area, the tuning button Press and hold SW1.

  In the sensitivity adjustment process, similarly to the two-point tuning, the maximum received light amount and the minimum received light amount during the period in which the tuning button SW1 is operated are specified with the display maximum value as the target value. Then, the magnification of the target value with respect to the maximum received light amount is obtained, and the intensity of the drive current of the light projecting unit 103 and the amplification magnification of the light receiving unit 104 are adjusted so that the received light amount is increased to this magnification. Further, the maximum received light amount and the minimum received light amount are respectively multiplied by the above magnifications, and an intermediate value of each received light amount after the multiplication is set as a threshold value.

  As described above, in the tuning process of this embodiment, the received light amount during the light incident period and the received light amount during the non-light incident period are obtained, and the sensitivity is adjusted so that the former received light quantity becomes a predetermined target value. The threshold value suitable for discriminating between the light incident state and the non-light incident state is automatically set using the received light amount of each period according to the adjusted sensitivity. Sensitivity parameters and threshold values set in the tuning process are registered in the memory 106, and these registered data are also applied in the measurement process after the tuning process.

  However, as time elapses, the amount of received light may gradually decrease as the heads at the tips of the optical fibers 11 and 12 become dirty or misaligned, and the LEDs 131 and the photodiodes 141 deteriorate. When the degree of reduction in the amount of received light increases, the margin with respect to the threshold value of the light receiving unit during the light incident period decreases, and the S / N ratio decreases. During the detection process, the measurement value and threshold value of the received light amount are displayed on the display devices 101 and 102. When the displayed received light amount is lower than the initial value and the margin for the threshold value is reduced, The user may misunderstand that something is wrong.

  In consideration of the above problems, the sensor 1 of this embodiment automatically corrects the threshold value according to the actual attenuation of the received light amount, and adjusts the received light amount displayed on the display unit 100 by tuning processing. It is possible to maintain a state close to the adjusted value. Further, the threshold value on the display is maintained as the initial value.

  FIGS. 5A and 5B are graphs showing the relationship between the change in the amount of received light and the correction of the threshold value. In any graph, the range in which the received light amount exceeding the threshold value is obtained on the horizontal axis (time axis) corresponds to the light incident period, and the range in which the received light amount below the threshold value is not input. Corresponds to the light period.

  For example, when the sensor 1 is set to a transmission type and detection is performed on a plurality of workpieces sequentially conveyed to the detection area, a change in the amount of received light as shown in FIG. 5A can be obtained. However, when a workpiece conveyed under the same conditions is detected by setting the sensor to a reflective type, a change in the amount of received light as shown in FIG. 5 (2) is obtained. In either case, the amount of light received during the light incident period is initially maintained near the target value, but gradually decreases as time elapses.

Therefore, in this embodiment, a predetermined value P ₀ higher than the threshold value is used as a reference value, and a period during which a received light amount exceeding the reference value P ₀ is obtained (hereinafter referred to as “first period”) and a reference value P ₀ are set. In response to the fact that the total number of times of sampling during the first period has reached a predetermined upper limit N while discriminating the period during which the received light amount is lower (hereinafter referred to as “second period”), the N times The average value of each received light amount is obtained by sampling, and the threshold value is corrected based on the ratio between the average value and the target value.

  However, the length of the light incident period varies depending on the movement speed of the workpiece and the interval between the workpieces. In particular, in the reflection type sensor that detects the workpiece by the light incident state, the light incident period tends to be short. The upper limit value N should not be fixed. If the period of light projection and light reception is constant, the degradation of the LED 131 and the photodiode 141 will be about the same, and there should be no difference in other factors that reduce the amount of received light. It is desirable to be performed at a timing without any problem. When the above correction process is performed with the value of N fixed, variation in timing at which correction is performed increases. In particular, when the light incident period is short, if a value larger than the number that can be sampled in that period is set to N, correction is not performed unless a plurality of light incident periods have passed, and the amount of light received with respect to the threshold value during that period. There is a risk of malfunction due to loss of the margin.

  In view of the above problem, in this embodiment, two numerical values that can be set as the upper limit value N are prepared (specifically, one numerical value is “256” and the other numerical value is “64”). If the ratio of the length of the first period to the total length of the first period and the second period is equal to or greater than a predetermined value α, N = 256, and if the above ratio is less than α, N = 64. The above threshold value correction process is executed. The total number of samplings is reset to zero when the threshold value is corrected. Therefore, if the lengths of the first period and the second period do not vary greatly, the threshold value is set at an appropriate time interval. It becomes possible to correct.

  The smaller numerical value “64” of the two numerical values selected as the upper limit value N is determined based on the standard number of samplings performed while one workpiece passes through the detection area. Is. Also, a numerical value considered to be the minimum necessary to distinguish the light incident period having a length corresponding to the 64 samplings from the non-light incident period is set as α.

  FIG. 5A corresponds to an example in which the ratio of the length of the first period to the total length of the first period and the second period is α or more and the threshold is corrected with N = 256. FIG. 5B corresponds to an example in which the ratio of the length of the first period to the total length of the first period and the second period is smaller than α, and the threshold value is corrected by N = 64. For convenience of explanation and illustration, in any case, immediately before switching from the first period to the second period, the total number of samplings during the first period reaches the upper limit value N, and the threshold value is corrected. The correction timing is not limited to this, and correction is performed at an arbitrary time point in the first period.

  FIG. 6 shows a case where correction is performed with the upper limit value N set to 256 with respect to the change in the amount of received light similar to the example of FIG. As shown in FIG. 6, when the ratio of the length of the first period to the total length of the first period and the second period is small and the upper limit value N is set to a large value, the threshold value is corrected. The number of times played is greatly reduced. As a result, even if the difference between the amount of light received during the light incident period and the target value increases, correction is not performed, and there is a possibility that the margin for the threshold of the amount of light received during the light incident period is insufficient.

  On the other hand, in the example of FIG. 5 (2), by setting the upper limit value N to a small value, the threshold value is set based on the N received light amounts acquired in the immediately preceding light incident period at an appropriate interval. Can be corrected. Therefore, even if the difference between the amount of light received during the light incident period and the target value increases, it is easy to ensure a margin of the amount of light received during the light incident period with respect to the threshold value.

  In FIG. 7, the length of the light incident period and the first period is the same as that of the example of FIG. 5 (2) and FIG. 6, but the second period is also shortened similarly to the first period. An example of threshold correction when the ratio of the length of the first period to the total length of the period and the second period is greater than or equal to α will be described. In this case, since the upper limit value N is set to 256, the amount of received light is corrected through a plurality of first periods. However, since the interval between the first periods is short, a large interval is required between each correction. Will never open.

  If the upper limit value N is selected not by the ratio of the length of the first period to the total length of the first period and the second period but only by the length of the first period, the value of N is also obtained in the example of FIG. It is assumed that the threshold value can be corrected every first period. However, if it does so, the frequency of correction | amendment will increase and it will increase the load of CPU105 which needs to respond | correspond to the state which switches a light incident state and a non-light incident state at high speed. Further, if the period of light projection or light reception is the same as in other examples, the reduction in the amount of received light will be about the same, so that no merit of increasing the frequency of correction can be found.

  In this embodiment, since the upper limit value N is selected based on the ratio of the length of the first period to the total length of the first period and the second period, the CPU 105 is not subjected to an excessive burden and is in the light entering period. The threshold value can be corrected at a frequency at which a margin with respect to the threshold value of the received light amount can be secured.

FIG. 8 is a flowchart showing a specific procedure of the threshold correction process, and is executed in parallel with the detection process shown in FIG. In the flowchart, N _ON is the number of received light amounts during the first period, N _OFF is the number of received light amounts during the second period, and N _SMP is the total number of sampling times during the first period. N _ON indicates the length of the first period, and N _OFF indicates the length of the second period.
This threshold value correction process is executed as a process for obtaining the threshold adjustment magnification D. The initial value of the magnification D is set to “1” in step S21 of FIG. 9, and the threshold value is automatically changed by changing the value of D. If D is close to 1 or 1, no substantial threshold change occurs.

With reference to FIG. 8, a specific procedure of the threshold correction process will be described.
Steps S1 and S2 are preparation processes. In step S1, based on the threshold value TH set by the target value and tuning process that is used to tune the process executed immediately before, determining the value of the reference value P _0. For example, we obtain the value d corresponding to 1% of the difference between the target value and the threshold value, the TH + d and P _0.
In step S2, the initial value of N is set to 64, and the initial values of the values of N _ON , N _OFF and N _SMP are set to 0, respectively.

When ready, it acquires the received light amount P which is sampled by the detection process, while repeating the process (step S3, S4) for comparing the value of the P and the reference value P _0, according to the determination result of step S4 processing Execute. The hourly received light amount P is stored in the log data area in the memory 106 for a certain period.

When the amount of received light P is equal to or less than the reference value P ₀ , that is, when the second period is entered (step S4 is “NO”), the process returns to step S3 only by the process of incrementing N _OFF (step S5). By repeating this step S5 while the second period continues, the length of the second period is derived.

When the amount of received light P is greater than P ₀ , that is, when the first period is entered (step S4 is “YES”), a process of incrementing the total number of samplings N _SMP during the incident period (step S6), A process of comparing the previous acquired received light amount with the reference value P ₀ (step S7), a process of incrementing N _ON (step S13), and a process of comparing the incremented N _SMP with the upper limit value N (step S14) are executed. Is done.

The determination in step S7 is “YES” only immediately after switching from the second period to the first period. In this case, it is determined in step S8 whether or not N _ON is greater than 0. However, since N _ON = 0 in the first period after the start of processing, step S8 is “NO”. Then, the process proceeds to step S13.

In the first period the second and subsequent, since the sampling number N _ON in the first period of one step before is counted, step S8 becomes "YES", the process proceeds to step S9.
In step S9, the number of samplings N _ON during the first period (indicating the length of the first period one stage before) and the number of samplings N _OFF during the second period (indicating the length of the immediately preceding second period). ) To obtain a ratio N _ON / (N _ON + N _OFF ), and further compare this ratio with a predetermined value α. Here, when N _ON / (N _ON + N _OFF ) ≧ α (“YES” in step S9), the value of N is set to 256 (step S10), and N _ON / (N _ON + N _OFF ) < If α (step S9 is “NO”), the value of N is set to 64 (step S11).

When the value of N is determined by the above processing, N _0N and N _OFF are returned to zero in step S12, and then step S13 and step S14 are performed.
Thereafter, until the total number of samplings N _SMP during the first period reaches the upper limit value N set in step S10 or step S11, the determination in step S14 becomes “YES”, and steps S3, S4, S6, S7 , S13, and S14 are repeated in this order, and the values of N _ON and N _SMP increase. Also, the way the light receiving amount P of the repetition if it becomes P ₀ below, steps S3, S4, S5 becomes sequentially processing flow state, the value of N _SMP is maintained. The value of N _ON is also maintained until entering the first period again and executing step S12.

In the first period, when the total number of samplings N _SMP reaches the upper limit value N (step S14 is “NO”), the process proceeds to step S15, and each received light amount corresponding to the N times of sampling is read from the log data area. The average value of these is calculated. In the following step S16, the target value is divided by the average received light amount calculated in step S15, and the divided value is set as the adjustment magnification D. Further, in step S17, N _SMP is returned to 0, and the process returns to step S3.

Note that in the first first period after the start of processing, step S8 is “NO”, so steps S9 to S12 are not executed. However, since “64” is set as the upper limit value N in step S2, step S8 is performed. There is no problem in the processing of S14.
Even when the total number of samplings N _SMP reaches 64, which is the initial value of N, in the first first period after the start of processing, steps S15, S16, and S17 are executed. Since the amount of light received during the period is normally maintained in the vicinity of the target value, the magnification D is a value close to 1, and there is a high possibility that the threshold value is substantially maintained. Thereafter, as long as the amount of deviation of the received light amount indicating the light incident state from the target value is not large, the threshold value is maintained at substantially the initial level.

If the amount of light received by the receiving light is lowered to a state below the reference value P _0, only the treatment with the procedure of Step S3, S4, S5 is repeated, the value of N _OFF is growing.
Although not shown in FIG. 8, in this embodiment, error notification is performed when N _OFF exceeds a predetermined allowable value. As a result, when the amount of received light is reduced to such an extent that the accuracy of detection cannot be ensured, an error notification informs the user that it is necessary to perform maintenance or re-tuning processing of the light projecting unit 103 or the light receiving unit 104. It can be tightened.

FIG. 9 shows a procedure of detection processing in the photoelectric sensor 1 described above.
This detection process is started in response to the completion of the above-described tuning process and the return to the measurement mode, and the threshold TH set in the tuning process and the adjustment magnification D are set to the initial values. After executing the process set to 1 (step S21), the loop of steps S22 to S27 is repeated.

  In step S22, the received light amount data is sampled from the light receiving unit 104, and the sampled value is stored in the log data area as the received light amount P. In step S23, a value (P × D) obtained by multiplying the received light amount P by the magnification D is displayed on the display unit 101 as the current received light amount. The other indicator 102 continues to display the threshold value TH displayed during the tuning process.

  In step S24, the received light amount P is compared with a threshold value TH / D corrected by the magnification D. If P> TH / D (“YES” in step S24), it is determined that the light is incident (step S25). If P ≦ TH / D (“NO” in step S24), the light is not incident. Determination is made (step S26). When the determination is completed, the process proceeds to step S27, and the determination result is output by turning on or off the detection signal.

  As described above, since the threshold value correction process shown in FIG. 8 is performed in parallel with the above detection process, when the magnification D is updated in step S16 of the threshold value correction process, The value of D used in S23 and S24 is also updated. Since the value of D is obtained by dividing the target value by the average value of the N received light amounts indicating the latest light incident state, the value of D increases as the received light amount decreases. Therefore, the value displayed in step S23 is larger than the actually sampled received light amount P, and the value TH / D compared with the received light amount P in step S24 is smaller than the initial threshold value TH.

According to the above series of processing, each time the total received light amount N _SMP reaches the upper limit value N and the magnification D is updated in the first period, the detection threshold value is corrected, and the received light amount during the light incident period is corrected. It is possible to perform stable detection while maintaining a long margin for the threshold value. Further, the magnification D used for the correction of the threshold value makes it possible to maintain the received light amount displayed during the light incident period at a value in the vicinity of the initial target value. Based on this, the detection operation can be confirmed. In addition, it is possible to prevent the user from misunderstanding that an abnormality has occurred due to a decrease in the amount of received light.
However, the adjustment of the received light amount on the display is an arbitrary process, and this adjustment process can be canceled in the setting mode.

  In the above embodiment, the ratio of the length of the first period to the total length of these periods is obtained for each set of the continuous first period and second period, and the value of the upper limit value N is calculated based on the ratio. Even if the above-mentioned ratio changes due to a change in the workpiece to be detected or the above-mentioned ratio varies greatly due to a large variation in the interval between the workpieces, the threshold value depends on the change or variation. The correction timing can be flexibly changed.

In the above embodiment, the threshold value is corrected immediately when the total number of samplings N _SMP during the first period reaches the upper limit value N. However, the present invention is not limited to this. The correction timing may be slightly delayed, for example, correction processing may be performed when the first period when the number of times reaches the upper limit is completed.

In the above embodiment, two numerical values that can be set as the upper limit value N of the total sampling number N _SMP during the first period are prepared. However, the present invention is not limited to this. One or more may be prepared and one of the candidates may be selected as N based on the ratio of N _ON to (N _ON + N _OFF ). In this case, by allowing small numbers as the proportion of N _ON is reduced is selected as N, it is possible to correct the threshold value at a proper spacing.

When the length of the first period and the second period and the ratio between the two do not fluctuate greatly, the upper limit value N is selected and the selection is maintained before the amount of received light is greatly reduced, and then the selection is made. The threshold value may be corrected based on the generated N. For example, based on the first period and the second period for a plurality of cycles, the average value of the ratio of the length of the first period to the total length of the first period and the second period is obtained, and the average value is compared with α Then, the upper limit value N is selected, and thereafter, the total number of samplings N during the light incident period N _SMP reaches the threshold value N by using each received light amount by the N times of sampling. May be corrected.

DESCRIPTION OF SYMBOLS 1 Photoelectric sensor 100 Display part 103 Light projection part 104 Light reception part 105 Control part 106 Memory 108 Output part

Claims (4)

A light projecting unit for projecting light for detection, a light receiving unit for receiving the projected light or its reflected light, and operating the light projecting unit and the light receiving unit to sample the amount of light received by the light receiving unit. A photoelectric sensor comprising a control unit that detects an object by comparing a sampled received light amount with a preset threshold value while repeating the processing,
The controller is
Discrimination that compares the sampled received light amount with a predetermined reference value higher than the threshold value to determine a first period in which the received light amount exceeds the reference value and a second period in which the received light amount falls below the reference value Means,
The process of selecting one of two or more numerical values prepared in advance is selected as the ratio of the length of the first period to the total length of the first period and the second period decreases. Selection means to perform as
The total number of times of sampling during the first period is counted, and when the count value reaches the numerical value selected by the selection means, it becomes the target of the counting with respect to a predetermined target value of received light amount. Correction processing means for correcting the threshold for object detection based on the degree of decrease in each received light amount and resetting the count value,
A photoelectric sensor comprising:   The selection means individually counts the number of received light amounts in the first period and the second period for each period, and when the period is changed, the first period and the nearest period 2. The photoelectric sensor according to claim 1, wherein a ratio between a total number of received light amounts in the second period and a number of received light amounts in the latest first period is obtained, and a numerical value to be selected is determined based on the ratio. .   The correction processing unit calculates a ratio between an average value of the received light amounts of the samplings that are targets of the counting during the first period and a target value of the received light quantity, and detects the object by a value corresponding to the ratio. The photoelectric sensor according to claim 1, wherein the photoelectric sensor is lowered. The photoelectric sensor according to claim 3,
A display unit for displaying the sampled received light amount is provided, and the received light amount to be displayed on the display unit is increased by a value corresponding to a ratio between the average value of the received light amount and the target value of the received light amount. A photoelectric sensor, wherein the control unit is provided with display light reception amount correction means for correcting the value.

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