JPH09284117A - Detection switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set a threshold level in following to a level even when the input level is fluctuated due to an environmental change or the like in the case of discriminating the input level. SOLUTION: A light is emitted from a light projection section 2 for each prescribed period and its reflected light is received by a light receiving section 3. The light receiving signal is A/D converted and discriminated by a discrimination means 13. In this case, the discrimination result and input level are stored in a data storage means 14. When a prescribed number of data is stored, a threshold level calculation means 15 discriminates each distribution of the discrimination result and calculates the threshold level to be an intermediate distribution level. Thus, the calculation processing of the threshold level is conducted stepwise so as to continue the light projection and discrimination for a prescribed period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection switch, such as a photoelectric switch or a proximity switch, which is characterized by a method of setting a threshold value corresponding to environmental changes.

[0002]

2. Description of the Related Art Conventionally, for example, a photoelectric switch irradiates an object detection area with light from a light projecting portion and receives transmitted light or reflected light. Then, the presence / absence of an object in the object detection area is determined based on whether or not the light receiving level exceeds a threshold value.
In such a conventional photoelectric switch, when the threshold value is set in the threshold value setting mode by a predetermined method, the presence or absence of an object is determined based on the set threshold value thereafter. This threshold setting method includes various methods such as detecting the light receiving level in the background where there is no object and the light receiving level when the object is placed at the detection position, and setting the threshold value at an intermediate level. It has been proposed and used conventionally. FIG. 9A is a graph showing the distribution of the received light level at the time when the threshold Th1 is set in the reflective photoelectric switch, and the distribution for each received light sensitivity when the photoelectric switch determines that it is the background and when it detects an object. It shows the situation. In the case of such distribution, if the threshold value Th1 can be set to the light receiving level intermediate between both distributions, the object can be detected without malfunction.

[0003]

However, according to such a conventional detection switch, since the threshold value once set does not change, the use environment changes and the light projection level and the light receiving sensitivity change during use. When the detection state changes due to factors such as the above, stable detection cannot be performed. For example, assuming that the overall light receiving level is lowered as shown in FIG. 9B due to a change in environment or a change in light amount, when the light receiving level is low even though the object is located in the detection area at the time of object detection, Since the threshold value Th1 is fixed, there is a case where an erroneous determination occurs. The hatching shown in FIG. 9B indicates the region where this erroneous determination occurs.
In order to avoid such a malfunction, the threshold value itself should be set as shown in FIG.
It must be changed like Th2 in (b). Also, when setting the threshold, a light receiving level at the time of object detection or a light receiving level of the background that is largely different from the normal value is obtained due to some abnormality, and it is set when this light receiving level is detected. The threshold does not become as shown in FIG.
There is a drawback that it becomes difficult to set an accurate threshold value.

The present invention has been made by paying attention to such a conventional problem, and even if there is a change in the environment, the threshold value is made to follow the change in the environment during the normal detection operation and the optimum value is automatically obtained. A technical issue is to be able to set a threshold value.

[0005]

According to a first aspect of the present invention, a detecting means for detecting an input level according to a physical state at a constant cycle and an output of the detecting means are discriminated by a threshold value to output a detection signal. Discriminating means, a data accumulating means for accumulating the input level and the discrimination result when the detection signal is output by the discriminating means, and detecting the distribution of the input level for each detection result accumulated in the data accumulating means. ,
A threshold value calculating means for calculating a threshold value between the respective distributions and setting a threshold value based on the threshold value in the judging means, wherein the threshold value calculating means is stepwise during each processing by the detecting means and the judging means. By performing the threshold value calculation process, detection and determination of a constant period are performed even during the threshold value calculation by the threshold value calculation means.

In the invention of claim 2 of the present application, the detection means outputs light projection pulses at a constant cycle, and light projection processing means for outputting light according to the light projection pulses of the light projection processing means. And a light-receiving unit that receives light from the light-projecting unit via the object detection area and outputs a light-reception level at each fixed cycle.

According to the invention of claim 1 of the present application having such a feature, the input level input by the detection means is determined by the determination means. Then, the discrimination result and the input level are accumulated by the data accumulating means. Then, when data exceeding a predetermined number is accumulated, a new threshold value is calculated based on the data. The threshold value is calculated by detecting the distribution of the input level for each detection result and calculating a new threshold value during this distribution. The threshold value calculated in this way is set as it is, or an offset amount that has been input in advance is added to the threshold value and set as a new threshold value in the determination means. Then, in order to operate the detection means and the determination means at a constant cycle even while the threshold calculation / setting processing is performed, the threshold calculation processing is performed stepwise.

[0008]

1 is a block diagram showing the overall structure of a reflective photoelectric switch according to an embodiment of the present invention. In the figure, the microcomputer 1 is provided with a light projecting section 2
Is connected. The microcomputer 1 causes the light projecting processing means 11 to apply a light projecting pulse to the light projecting unit 2 at regular intervals. The light projecting unit 2 drives a light emitting element such as an LED in accordance with a light projecting pulse to irradiate the object detection region with light, and the reflected light is received by the light receiving unit 3. The output of the light receiving unit 3 is input to the microcomputer 1 via the amplifier unit 4 that amplifies the light receiving signal. In addition to the light emission processing means 11, the microcomputer 1 includes an A / D converter 12 for A / D converting a light reception level signal input from the amplifier 4.
The light-receiving level converted by the A / D conversion unit 12 is discriminated by a threshold value, and a discrimination unit 13 for discriminating detection or non-detection of an object is provided. Further, in the present invention, the A / D conversion unit 12
Data storage means 1 for accumulating the received light level of each of the discrimination results
4 and a threshold value calculation means 15 for calculating a threshold value based on the accumulated data. Microcomputer 1
The determination result determined by is output to the outside by the output unit 5 as an object detection or non-detection signal. The display unit 6 displays the light receiving level, the threshold value, and the on / off output, as described later. Further, an input section 7 is provided for switching between the measurement mode and the threshold value setting mode and for inputting an increase and a decrease of the threshold value offset Uoff.

The data accumulating means 14 indicates the discrimination result discriminated by the discriminating means 13 and the ON level and OFF level inputted at that time, for example, the light receiving level when an object exists and the light receiving level when it is judged to be the background. The data is stored together with the determination result. The threshold calculation means 15 calculates and sets a threshold by statistical processing based on this data.

Next, the threshold setting process of this embodiment will be described in detail. FIG. 2 is a time chart during the operation of this embodiment, and FIG. 3 is a flowchart showing the operation. First, in setting the first threshold value, teaching is performed by some method conventionally used, and the mode is switched to the measurement processing mode as the first threshold value is set.
In the measurement processing mode, first, in the routine 21 shown in FIG. 3, the light projecting processing means 11 generates a light projecting pulse at regular intervals to perform the light projecting processing. FIG. 2A shows this light projection pulse. The light emitting element of the light projecting unit 2 is driven each time the light projecting pulse is output, and the light receiving signal obtained from the light receiving unit 3 corresponding to the light projecting pulse is amplified by the amplifier unit 4. Then, the amplified output is input to the A / D conversion unit 12 of the microcomputer 1. In the routine 22, A by the A / D converter 12
The / D conversion process is performed, and the routine proceeds to routine 23, where the presence or absence of an object is determined by the threshold value set at that time. The on / off determination processing routine 23 is a routine that realizes the function of the determination means 13, and the determination result is output to the output unit 5 and the display unit 6. Then, the process proceeds to step 24, and it is checked whether it is the data accumulation period. In the present embodiment, the light receiving level and the data of the object discrimination signal corresponding to each output of the light emitting pulse are stored in the data storing means 14 in the microcomputer 1. The data is either when an object is detected or when there is no object and only the background is present. Therefore, when the same type of articles are conveyed on the belt conveyor and used for article detection in the same state, if a predetermined number of data are accumulated, the distribution thereof is, for example, as shown in FIG.
A normal distribution or a distribution close to this can be obtained.

When a predetermined number of received light data are accumulated in this way, a threshold calculation operation is performed. In the present embodiment shown in FIG. 3, the calculation calculation process is divided into a plurality of stages, and the routine 26 first selects the calculation stage. Then, any one of the threshold value calculation operations 1 to N of the routines 27 to 29 is performed according to the operation stage. When the threshold value calculation process is completed, the threshold value update process is performed and the process returns to the light projecting process routine 21. When the new threshold value is set in this way, the determination processing according to the threshold value is performed by the subsequent routine 23. By dividing the threshold calculation processing into a plurality of stages in this way, the calculation processing time in each stage can be shortened sufficiently, and as shown in FIGS. 2A and 2C, the threshold calculation processing is performed. Even during this period, a light projection pulse is output at regular intervals, and the object discrimination processing can be continued as it is. Therefore, it is assumed that the number of stages of the arithmetic processing can maintain the light projection and the discrimination in a constant cycle. In this way, the user can obtain the determination result for each light projection pulse of a constant cycle without being aware of whether the threshold value calculation processing or the data accumulation is being performed.

In the final threshold value calculation operation of the routine 29, it is determined whether or not the automatic follow-up mode is set. If the automatic follow-up mode is set, the threshold value is updated. The update process may not be performed. In this way, the threshold can be automatically tracked only when the user needs it. Data is accumulated only when there is a trigger input after the determination processing by the routine 23.
If there is no trigger input, data may not be stored. This is to prevent incorrect data from being taken in, for example, when the photoelectric switch is not in the normal use position or when an object different from the normal one is placed in the background. It is conceivable that data will be accumulated only when is input.

Next, details of the threshold value calculation processing will be described. FIG. 5 is a flowchart collectively showing the threshold value calculation process without dividing it, and in practice, it is divided according to the operation time as shown in FIG. In the threshold value calculation process, as shown in FIG. 5, first, in step 31, the threshold value calculation condition is satisfied, and it is determined whether the calculation is possible. Here, it is determined whether or not the number of pieces of data for detecting the background and the number of pieces of data for detecting the object shown in FIG. 4 are both sufficient. If it is less than this, the threshold calculation process is not performed, and the received light data accumulation process is continued. Further, since the accurate threshold value cannot be calculated even when there is a large amount of either one of the data, the threshold value is not calculated when the ratio of the number of data is a predetermined number or more. If both data exceeds a predetermined number and the ratio is less than or equal to a predetermined value, the calculation condition is satisfied. Therefore, the process proceeds to step 32, and the average value AV1 of the object detection light receiving level when the detection output of the object is first obtained is calculated. To do. Next, in step 33, the standard deviation σ1 of the light receiving level for object detection is calculated. Next, at step 34, the first reference value L1 is calculated. First
In the reflective photoelectric sensor, the reference value L1 is higher than the threshold in the light receiving level at the time of object detection, so that the threshold is set to the average value AV1 of the object light receiving level or less. The standard value should also be decided so as to approach this. That is, in this case, AV1-kσ1 is set as the first reference value L1. The coefficient k uses a value of 2 or 3, for example, but it does not have to be an integer. FIG. 4 shows the reference value L1 when k is 2.

Next, the routine proceeds to step 35, where the average value AV2 of the light receiving level when it is judged to be the background is calculated. Then, in step 36, the standard deviation σ2 of the background light receiving level
Is calculated. Further, in step 37, the second reference value L2 of the background light receiving level is calculated. Also in this case, the threshold value is set to a level higher than the average light receiving level AV2 of the background as shown in the figure, so that AV2 + kσ2 is set to the second reference value L2. Then, the routine proceeds to step 38, where a new threshold value Thn is calculated between these two reference values L1 and L2. This new threshold value Thn is, for example, reference values L1 and L2.
The arithmetic mean value of is used. Then step 39
And the new threshold Th currently set.
It is determined whether or not the difference from n exceeds a predetermined value ε.
When the new threshold value Thn is significantly changed from the current threshold value Th, some kind of abnormality, for example, damage of the sensor or abnormality of the device is considered. Therefore, the threshold value changing process is not performed, the tracking limit output is output to the outside, and the error is displayed (step 40). If the change in the threshold value is not so large, the new threshold value Thn thus calculated is set as the recommended threshold value Thn of this photoelectric switch. Next, the procedure proceeds to step 41, where a user offset Uoff to be described later is set to this recommended threshold value.
Is added to obtain a new threshold Thu. Then step 42
Then, the updating process for replacing the new threshold value Thu with the threshold value Th is performed, the updated threshold value and the user offset value are displayed, and the process ends (step 43). In this way, if the threshold value does not change significantly, the optimum threshold value is set according to the fluctuation of the received light level.

When the threshold value calculation / setting process is completed, the received light data is again accumulated as shown in FIG. 2, and a new threshold value is calculated and set after the accumulation for a certain period of time.
By repeating the accumulation of data and the calculation and setting of the threshold value based on the data in this way, the optimum threshold value including the change even if there is a change in the environment, the amount of received light, the drop of the light projection level, etc. It will be set automatically. When a trigger signal is input from the input unit 7, data is stored,
A process of calculating and setting the threshold may be performed after the data is accumulated. In this case, the user can manually input the threshold update timing when the environment changes.

FIG. 6 is a diagram showing the panel surface of the display unit 6 during operation, and FIG. 7 is a conceptual diagram showing its display range. The display unit according to the present embodiment is provided with two bar graph indicators on the left and right. The bar graph display on the left side is the received light amount display section 51. Then, the central position of the received light amount display section 51 on the left side is set as the threshold level. The central threshold Th is fixedly drawn on the panel surface of the photoelectric switch. In the received light amount display section 51, five display elements are arranged above and below the threshold value,
Displays the received light level. In this display example, as shown in FIG. 7, the entire dynamic range of the light receiving unit 3 is displayed as it is as the light receiving amount of the light receiving amount display unit 51. Then, the light-reception level display section 51 divides the entire light-reception range of the light-reception amount into upper and lower halves at a threshold level, and divides this equally into ⅕ to correspond to the respective display elements. In this case, the amount of light received for one display element differs above and below the threshold value. The bar graph display on the right side is an enlarged display section 52 in which the light receiving level for one display element near the threshold is enlarged. In this case, since one element of the threshold value is enlarged by the enlargement display unit 52 around the threshold value, the new threshold value calculated by the photoelectric switch is displayed as the recommended threshold value Thn. Also, this enlarged display section 52
Offset value Uoff set by the user is the recommended threshold value T
It is displayed as the difference from hn. The recommended threshold Thn is always in the center of the enlarged display section 52, and the value obtained by adding the user offset to the recommended threshold Thn is the threshold Thu. This user offset can be changed up and down with the push button switches 54a and 54b. In FIG. 6A, since the light receiving level exceeds the set threshold value Thu, the object detection signal is output to the outside and the operation indicator lamp 53 is lit. FIG. 6
(B) shows a state in which the object detection signal is not output and the operation indicator lamp 53 is off because the light reception level is equal to or lower than the threshold Thu. In this way, the threshold value is always displayed in the center, so that the margin of the light receiving level can be easily recognized. Although the number of display elements is 5 in each of the upper and lower sides here, it is not limited to this and may be any number. In addition, the light receiving level around the threshold is 2
Although it is divided into five equal parts, it is not always necessary to divide the parts into five equal parts.

Further, the received light amount display unit 51 of the display unit 6 does not display the entire received light range of the received light level but the upper and lower fixed ranges around the threshold as shown in FIG. 8 on the received light amount display unit 51. Can also be considered. In this case, a certain range above and below the threshold value is divided into equal intervals, in this case, five, and a bar graph is displayed by making each correspond to each display element. The received light amount display unit 51 displays the amount of received light in a bar graph when the received light amount reaches this level, and the enlarged display unit 52 enlarges one display element near the threshold level and recommends the threshold value Thn and the user. Threshold value T including the set user offset Uoff
Similarly, hu is displayed. In this case, since the threshold value is always located at the center of the received light amount display section 51, the light reception level near the threshold value can be recognized in detail. Also, the margin during use can be recognized more accurately.

Although the reflective photoelectric switch has been described in the above-mentioned embodiment, it may be applied to a transmissive photoelectric switch. In this case, when an object is detected, the input level of the object is lowered, and in a normal state without an object, a high level light reception signal is obtained.
The distribution state shown in is reversed. In this case as well, the average value of each is added or subtracted by a coefficient multiple of the standard deviation so as to approach the intermediate threshold value side, and the first and second reference values are obtained. Although the present embodiment describes the photoelectric switch, the present invention detects not only the photoelectric switch but also an external physical state such as a high-frequency oscillation type proximity switch or an ultrasonic switch, and discriminates this with a threshold value to output. It can be applied to various types of detection switches.

[0019]

As described in detail above, according to the first and second aspects of the present invention, the optimum threshold value can be calculated according to the distribution state of the discrimination result. Even when the input level or the like changes due to the change of the surrounding environment, the excellent effect that the optimum threshold value can be always set following the change is obtained. Further, since the threshold value calculation process is performed stepwise, the threshold value calculation can be performed without changing the operation cycle of the detection means and the determination means corresponding thereto in a constant cycle. Therefore, there is an effect that the user can continue to use the data without being aware of whether the data is being accumulated or the threshold value is being calculated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a photoelectric switch according to an embodiment of the present invention.

FIG. 2 is a time chart showing the operation of the present embodiment.

FIG. 3 is a flowchart showing an operation of this embodiment.

FIG. 4 is a distribution chart showing a light receiving level and its frequency when a threshold value is set.

FIG. 5 is a flowchart showing a threshold value calculation process of this embodiment.

FIG. 6 is a display example showing a state of a display unit of the present embodiment.

FIG. 7 is a diagram showing a relationship between a light receiving level and a display unit.

FIG. 8 is a diagram showing a relationship between a display example of a display according to another embodiment and a light receiving level.

FIG. 9 is a diagram showing a light reception level and a threshold value of a conventional photoelectric switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microcomputer 2 Light emitting part 3 Light receiving part 4 Amplifier part 5 Output part 6 Display part 7 Input part 11 Projection processing means 12 A / D conversion part 13 Discrimination means 14 Data storage means 15 Threshold value calculation means

Continuation of the front page (51) Int.Cl. ⁶ Identification code Reference number within the agency FI Technical display location G01V 8/12 H01H 35/00 A H01H 35/00 H03K 5/08 R H03K 5/08 G01V 3/08 E / / G01V 3/08 9/04 K

Claims (2)

[Claims] 1. A detection means for detecting an input level according to a physical state in a constant cycle, a discrimination means for discriminating an output of the detection means by a threshold value and outputting a detection signal, and a detection signal output by the discrimination means. Data storage means for accumulating the input level and the discrimination result at the time, the distribution of the input level is detected for each of the detection results stored in the data storage means, and the threshold value is calculated between the distributions.
A threshold value calculation means for setting a threshold value based on this in the determination means, and the threshold value calculation means performs the threshold value calculation processing stepwise during the respective processing by the detection means and the determination means, A detection switch characterized in that detection and determination are performed in a constant cycle even while the threshold value is being calculated by the calculation means. 2. The light emitting processing means for outputting light emitting pulses at a constant cycle, and the light emitting portion for emitting light to an object detection area according to the light emitting pulses of the light emitting processing means. 2. The detection switch according to claim 1, further comprising: a light-receiving unit that receives light from the light-projecting unit via an object detection region and outputs a light-reception level at each constant cycle.