JP2005140596A - Detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection device, capable of easily setting a threshold value to be a specific detection condition of detection level on a reference value of detection level of detection signal output by a detector under a specific measuring condition, of easily confirming minimum value of peak value in the increasing side of the detection signal or the maximum value of bottom value in reducing side of the detection signal, regardless of the characteristics of the object to be detected, and setting a proper threshold, even when each state level is unstable. <P>SOLUTION: An extreme value detector detects a local maximum value of a detection level exceeding a specific threshold and a local minimum value of a detection level undergoing the threshold. The local maximum value and the local minimum value detected by the extreme value detector are held in a memory. When the update local maximum value detected by the extremum value detector is smaller than the local maximum value, or when the update local minimum value detected by the extremum value detector is smaller than the local minimum value stored in the memory, the information stored in the memory is renewed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a detection apparatus, and more particularly to a detection apparatus suitable for detecting the proximity of an object, such as a photoelectric sensor, a high-frequency proximity sensor, or a capacitive proximity sensor.

  Recently, various detection devices have been applied. As this detection device, for example, a photoelectric sensor that detects the proximity of an object, a high-frequency proximity sensor, a capacitive proximity sensor, or a turbidity sensor that detects the turbidity of a solution, temperature, humidity, magnetism, etc. There are those that detect various physical quantities. For example, the photoelectric sensor is a detection device including a projector and a light receiver, and can be roughly classified into a transmission type and a reflection type. The transmission type photoelectric sensor basically has a configuration in which a light projector (light projecting unit) and a light receiver (light receiving unit) are opposed to each other with a predetermined distance. Then, when an object enters the optical path formed between the projector and the light receiver, the proximity of the object is detected by detecting a change in the amount of light received (detected amount) blocked by the object.

  On the other hand, a reflective photoelectric sensor has a configuration in which a light projector (light projecting unit) and a light receiver (light receiving unit) are arranged with their optical axes aligned, and the light emitted from the light projector is reflected by an object. An object is detected by detecting light with a light receiver. In other words, the reflection type photoelectric sensor has no reflected light from the object when there is no object on the optical axis, and when there is an object on the optical axis, the reflected light with the intensity corresponding to the distance to the object is not emitted. Object detection is performed by using the received light.

  The photoelectric sensor is a detection device that detects the optical state in the optical path formed between the light projector and the light receiver in this manner as a change in the amount of light received (detected amount) by the light receiver. It is used for various purposes such as detection and object determination. Specifically, the photoelectric sensor compares a predetermined set value (threshold value) with the amount of received light, and determines the presence or absence of an object between the projector and the light receiver based on a level difference between the set value and the received light amount. It is used as a photoelectric switch that outputs a value. In this type of photoelectric switch, it is important to set a threshold value for determining the presence or absence of an object.

In general, a peak value and a bottom value of the received light level are held, and an average value of the held peak value and bottom value is set as a threshold value (see, for example, Patent Document 1).
JP-A-9-167951

  However, in the above-described detection device, for example, a photoelectric switch for detecting the presence or absence of an object, there is a problem that an error occurs in the detection of the object if the threshold value of the light reception level for determining the presence or absence of the object is mistaken. Specifically, as shown in FIG. 9, when the average value of the maximum value (peak value) and the minimum value (bottom value) of the detection level of the detection signal output from the detection unit of the photoelectric sensor is set as the threshold value, the detection signal Depending on the level, there is a concern that the object is erroneously detected as having an object even when the object is not present, or the object is erroneously detected as having an object even though there is no object.

  Further, in the conventional detection device described above, when the detection target cannot be stopped in the detection target area of the photoelectric switch so that the detection target object moves on the conveyor, the peak value is displayed from the display unit of the photoelectric switch. The bottom value can be obtained, but the peak value below the peak value or the bottom value above the bottom value cannot be obtained and it cannot be determined whether the threshold value is appropriate. was there.

In general, therefore, it is necessary to confirm the detection state of the photoelectric switch by using a plurality of inspection objects in advance and verify whether or not it is erroneously detected, and there is a problem that threshold setting becomes complicated. In addition, when the shape of the inspection object, surface processing, or the like is changed, it is necessary to check the detection state of the photoelectric switch each time, and there is a problem that efficient sensing cannot be performed.
The present invention has been made in response to such a conventional situation, and the object thereof is to easily set an appropriate threshold value in a detection apparatus, and to detect changes that vary depending on the characteristics of a detection object. The minimum value of the peak value on the signal increase side or the maximum value of the bottom value on the detection signal decrease side can be easily confirmed, and even if the detection level of each peak value or bottom value is unstable An object of the present invention is to provide a detection device capable of setting an appropriate threshold value.

In order to achieve the above-described object, the detection apparatus according to the present invention sets a threshold value that is a predetermined detection condition for the detection level, using the detection level of the detection signal output by the detector under a predetermined measurement condition as a reference value. A detection apparatus comprising threshold setting means and a comparator that outputs a detection signal by comparing a detection level of the detector with the threshold,
An extreme value detection unit for sequentially detecting the maximum value of the detection level exceeding the threshold and the minimum value of the detection level below the threshold;
A storage unit that holds the maximum value and the minimum value detected by the extreme value detection unit, and
When the maximum value detected by the extreme value detection unit is smaller than the maximum value held in the storage unit, or when the minimum value detected by the extreme value detection unit is larger than the minimum value held in the storage unit, Updating means for updating the maximum value or the minimum value held in the storage unit to the maximum value or the minimum value detected by the extreme value detection unit, respectively;
And a display unit for displaying the maximum value or the minimum value held in the storage unit.

  For this reason, the maximum value taking the minimum value among the maximum values exceeding the threshold value can be displayed as the peak value, and the maximum value among the minimum values falling below the threshold value can be displayed as the bottom value. By using these values, Thus, it is possible to appropriately set the threshold value serving as the reference value for the detection level. That is, the maximum value and the minimum value output from the display unit can be used as reference values for setting a threshold value that serves as a reference for the detection level of the detection signal of the detector.

Preferably, the storage unit is configured to hold a history of the maximum value and the minimum value of the detection level.
For this reason, it is possible to obtain various statistical information such as the tendency of the maximum value and the minimum value of the detection level, the variation state, and the average value from the history information of the maximum value and the minimum value held in the storage unit.
Specifically, the detector in the detection apparatus according to the present invention includes a light projector and a light receiver that form a predetermined optical path as described in claim 4, and the light emitted from the light projector or the reflected light thereof is the light receiver. And a photoelectric sensor for detecting the optical condition in the optical path from the detection level.

  As described above, in the detection apparatus according to the present invention, the detection signal maximum value of the detection signal that exceeds the predetermined threshold and the minimum value of the detection level that falls below the threshold value are detected from the detection signals output by the detector. The difference between the maximum value and the minimum value can be displayed while keeping the detection signal of the minimum level of the maximum value and the detection signal of the maximum level of the minimum value as a history. Even when the state levels are unstable, it is possible to set an appropriate threshold by using the maximum value and the minimum value. Further, by using the history information of the maximum value and the minimum value described above, it can be determined whether the detection signal on the increase side or the decrease side of the detection signal has a large variation, and should be set as a threshold value. It is possible to appropriately determine the detection level. In addition, since the threshold value, the maximum value, and the minimum value are held as history information, for example, when the detection apparatus according to the present invention is applied to an inspection process of a manufactured product, the history information can be used as inspection information. It has a great effect on practical use.

Hereinafter, an embodiment of a detection device according to the present invention will be described with reference to the drawings, illustrating a photoelectric sensor that detects the presence or absence (proximity) of an object.
FIG. 1 is a detection apparatus according to an embodiment of the present invention, and shows a schematic configuration of a photoelectric sensor. In this figure, 1 is a projector made up of a light emitting diode (LED) that emits laser light with a wavelength of 660 nm, for example, and 2 is a light receiver made up of a photodiode (PD) that receives the laser light directly or its reflected light. . These projector 1 and light receiver 2 may constitute a transmissive photoelectric sensor, or may constitute a reflective photoelectric sensor. Here, light is directly projected from the projector 1 onto a predetermined object detection target area, and the light receiver 2 receives reflected light of the light emitted from the projector 1 by the detection target existing in the object detection target area. A reflective photoelectric sensor that determines the presence or absence of a detection target will be described.

  The light receiver 2 used in this photoelectric sensor outputs a signal having a level corresponding to the intensity of received light (amount of received light). The photoelectric sensor provided with the light receiver 2 captures a change in the detection level R of the light receiver 2 by crossing the detection object using a transport mechanism (not shown) in the detection target region, for example, and detects the presence or absence of the detection target. It comes to judge. That is, as shown in FIG. 9, when the detection target reaches the detection target region, the laser light emitted from the projector 1 is reflected by the detection target and the light reaching the light receiver 2 gradually increases. Then, the detection level R of the light receiver 2 gradually increases. When the detection target reaches the substantially central portion of the detection target region, the amount of reflected light is maximized, and the detection level R of the light receiver 2 is also maximized. Thereafter, as the detection target moves away from the detection target region as the detection target moves, the output level R gradually decreases because the amount of light reflected by the detection target decreases. Thus, when the detection target is in the detection target region, the change in the detection level R has the maximum value, that is, the maximum value. Conversely, when the detection target is not in the detection target region, the change in the detection level R has a minimum value, that is, a minimum value.

  By the way, the output signal (detection level) output from the light receiver 2 is amplified through a preamplifier (head amplifier) including a frequency selection filter (not shown) and then converted into a digital signal through an A / D converter 3. Then, it is taken into the signal processing circuit 5 including the control unit 4 such as a microcomputer every 200 μs, for example. The signal processing circuit 5 compares the threshold value SH set in the threshold value setting unit 6 with the detection level R detected by the light receiver 2 provided from the A / D converter 3, and detects the object in the detection target region. A level determination unit (comparator) 7 that outputs a determination signal indicating the presence or absence is provided. A determination signal from the level determination unit (comparator) 7 is externally output as a detection signal of the photoelectric sensor.

Incidentally, the threshold value SH set in the threshold value setting unit 6 will be described in detail later, but in the case of a reflective photoelectric sensor, the amount of light reflected by the detection object (reflection) when the detection object passes through the detection object region. A reference value of a detection determination level for detecting an object is set based on whether or not (light quantity) exceeds a predetermined amount (threshold value).
The signal processing circuit 5 detects that the detection level R output from the A / D converter 3 is higher than the threshold value SH set in the threshold setting unit 6 and is output from the A / D converter 3. When the signal includes a maximum value, a peak value holding unit 8a is provided for holding the maximum value. The signal processing circuit 5 outputs the detection level R output from the A / D converter 3 when the detection level R is lower than the threshold value SH set in the threshold value setting unit 6 and from the A / D converter 3. When the minimum value is included in the detection signal, a bottom value holding unit 8b for holding the minimum value is provided. These hold units 8a and 8b serve as extreme value detection units for detecting a maximum value and a minimum value in the detection level R, respectively.

  The signal processing circuit 5 is provided with a storage unit 9 including a peak value storage unit 9a and a bottom value storage unit 9b that hold the values held by the peak value hold unit 8a and the bottom value hold unit 8b, respectively. Although details will be described later, the storage unit 9 holds values (maximum value and minimum value) held by the peak value holding unit 8a and the bottom value holding unit 8b, respectively.

  The signal processing circuit 5 holds a peak value comparison unit 10a and a bottom value hold unit 8b that compare the maximum value held by the peak value hold unit 8a and the maximum value held by the peak value storage unit 9a. There is provided a bottom value comparison unit 10b for comparing each value of the minimum value and the minimum value held in the bottom value storage unit 9b. Further, the signal processing circuit 5 is provided with a peak value display unit 11a and a bottom value display unit 11b for displaying the maximum value and the minimum value respectively held in the peak value storage unit 9a and the bottom value storage unit 9b.

The detection apparatus according to the present invention configured as described above is characterized in that the maximum value of the minimum detection level among the maximum values included in the detection signal exceeding the threshold set in the threshold setting unit 6 is stored in the storage unit. The minimum value of the maximum detection level among the minimum values included in the detection signal below the threshold set in the threshold setting unit is stored in the storage unit 9.
That is, when the detection level R of the detection signal exceeds the threshold set in the threshold setting unit 6, the peak value holding unit 8a detects the maximum value included in the detection signal having a level higher than this threshold. Then, this maximum value is held in the peak value storage unit 9a. Next, the peak value holding unit 8a detects the maximum value included in the detection signal in which the detection level R of the detection signal again exceeds the threshold set in the threshold setting unit 6. At this time, the peak value comparison unit 10a compares the latest maximum value held by the peak value hold unit 8a with the previous maximum value held in the peak value storage unit 9a. Then, when the latest maximum value is lower than the previous maximum value, the control unit 4 updates the maximum value held in the peak value storage unit 9a to the latest maximum value (update means). The updated maximum value (peak value) is displayed by the peak value display unit 11a.

  On the other hand, when the detection level R of the detection signal is lower than the threshold set in the threshold setting unit 6, the bottom value holding unit 8b detects a minimum value included in the detection signal having a level lower than the threshold. Then, the minimum value is held in the bottom value storage unit 9b. Next, the bottom value holding unit 8b detects the maximum value included in the detection signal in which the detection level R of the detection signal again falls below the threshold set in the threshold setting unit 6. At this time, the bottom value comparison unit 10b compares the latest minimum value held by the bottom value holding unit 8b with the previous minimum value held by the bottom value storage unit 9b. When the latest minimum value is higher than the previous minimum value, the control unit 4 updates the minimum value held in the bottom value storage unit 9b to the latest minimum value (update means). The updated minimum value (bottom value) is displayed by the bottom value display unit 11b.

An embodiment of the detection apparatus according to the present invention having such characteristics will be described with reference to the flowchart of FIG. 2 showing the operation of the photoelectric sensor for detecting the presence (proximity) of an object. Incidentally, it is assumed that a temporary threshold value (peak value) SH is previously set in the threshold value setting unit 6 as a threshold value of the detection level R of the detection signal for detecting the presence or absence of the detection object.
First, the control unit 4 of the signal processing circuit 5 sets the counter variables X and Y to 1, and the peak value variable P (1) held in the peak value storage unit 9a to the maximum value and bottom value of the detection level R of the detection signal. The minimum value of the detection level R of the detection signal is set in the bottom value variable B (1) held in the storage unit 9b to initialize the variable [step S1]. Incidentally, the peak value storage unit 9a and the bottom value storage unit 9b have, for example, configurations such as array variables as described later.

  Then, the peak value holding unit 8a and the bottom value holding unit 8b respectively compare the detection level R of the detection signal with the temporary threshold value SH set in the threshold value setting unit 6 [Step S2]. When the detection level R of the detection signal is larger than the temporary threshold value SH set in the threshold setting unit 6 in step S2, the peak value holding unit 8a detects the local maximum value included in the detection signal and takes it into the variable P [step S3]. Next, the peak value comparison unit 10a compares the maximum value P captured by the peak value holding unit with the array variable P (X) of the peak value storage unit 9a [step S4]. When the peak value comparison unit 10a determines that the maximum value P captured by the peak value hold unit 8a in step S4 is smaller than the array variable P (X) of the peak value storage unit 9a, the peak value comparison unit 10a peaks the captured maximum value P. The value is stored in the array variable P (X) of the value storage unit 9a [Step S5]. The stored maximum value is displayed by the peak value display unit 11a [step S6]. Next, the control unit 4 increments the counter variable X of the array variable to capture the next maximum value [Step S7], and returns to Step S2. When the peak value comparison unit 10a determines in step S4 that the maximum value P captured by the peak value holding unit 8a is equal to or greater than the array variable P (X) of the peak value storage unit 9a, the next maximum value is obtained. To return to step S2.

  On the other hand, when the value of the detection level R of the detection signal is smaller than the temporary threshold value SH set in the threshold value setting unit 6 in step S2, the bottom value holding unit 8b detects the minimum value included in the detection signal and sets the variable B [Step S8]. Next, the bottom value comparison unit 10b compares the minimum value B captured by the bottom value holding unit 8b with the array variable B (X) of the bottom value storage unit 9b [Step S9]. When the bottom value comparison unit 10b determines that the minimum value B captured by the bottom value holding unit 8b in step S9 is smaller than the array variable B (X) of the bottom value storage unit 9b, the bottom value comparison unit 10b uses the captured minimum value B as the bottom value. It is stored in the array variable B (X) of the value storage unit 9b [Step S10]. The stored minimum value is displayed by the bottom value display unit 11b [step S11]. Next, the control unit 4 increments the counter variable Y of the array variable to capture the next minimum value [step S12], and returns to step S2. When the bottom value comparison unit 10b determines in step S9 that the minimum value B captured by the bottom value holding unit 8b is equal to or less than the array variable B (X) of the bottom value storage unit 9b, the next minimum value is determined. To return to step S2.

When the detection level R of the detection signal is equal to the provisional threshold value SH in step S2, a change in the detection level R taken in by the light receiver 2 is waited [step S2].
The detection device according to the present invention that operates according to such a procedure will be described with a specific example. Here, in order to facilitate understanding, the algorithm for detecting the maximum value and the algorithm for detecting the minimum value will be described separately. The detection level R of the detection signal output from the A / D converter 3 assumes a value in the range of [0 to 100], and the threshold setting unit 6 has [50] set as the temporary threshold SH. And Therefore, in step S1 of the flowchart described above, the array variable P (1) has [100] as the maximum value that the detection level R can take, and the array variable B (1) has the minimum value that the detection level R can take [ 0] is assigned to initialize variables.

  Now, it is assumed that the detection level R exceeds the temporary threshold SH = [50] and the maximum value of the first detection level R becomes [92] as shown in FIG. At this time, the peak value holding unit 8a takes the maximum value [92] into the variable P in step S3 as described above. Since the maximum value P = [92] is smaller than P (1) = [100] initialized by the array variable, the maximum value P held by the peak value holding unit 8a is the peak value storage unit 9a in step S5. And this value is displayed by the peak value display section 11a. In step S7, the control unit 4 increments the counter variable X so that X = [2].

  Next, the peak value holding unit 8a detects the next maximum value included in the detection signal. Incidentally, when the detection signal changes in the detection level R as shown in FIG. 3, the next maximum value P is [87]. This value is smaller than the array variable P (1) in the peak value storage unit 9a. Accordingly, the local maximum value P is held in the array variable P (2) of the peak value storage unit 9a and displayed by the peak value display unit 11a in step S5. In step S7, the control unit 4 increments the counter variable to set X = [3].

  Thereafter, similarly, the peak value hold unit 8a detects the next maximum value included in the detection signal. At this time, when the maximum value P is [96] as shown in FIG. 3, it is larger than the previously detected maximum value [87]. Therefore, the control unit 4 determines in step S4 that the maximum value P is larger than the previous maximum value held in the peak value storage unit 9a, and prepares for the detection of the next maximum value. Then, the peak value hold unit 8a detects the next maximum value included in the detection signal. At this time, when the maximum value P is [82] as shown in FIG. 3, it is smaller than the previously detected maximum value [87]. Accordingly, the local maximum value P is held in the array variable P (3) of the peak value storage unit 9a in step S5 and displayed by the peak value display unit 11a. In step S7, the control unit 4 increments the counter variable X to detect the next maximum value.

Incidentally, the maximum value held in the peak value storage unit 9a in this way is held as an array variable in a table format as shown in FIG. 4, for example.
Next, an algorithm for detecting a minimum value in the detection apparatus according to the present invention will be described.
First, it is assumed that the detection level R of the detection signal output from the A / D converter 3 falls below the temporary threshold SH = [50] as shown in FIG. 5, and the first minimum value becomes [25]. At this time, the bottom value holding unit 8b takes the minimum value [25] into the variable P in step S8 as described above. Since this minimum value B = [25] is larger than B (1) = [0] initialized by the array variable, it is stored in the bottom value storage unit 9b and displayed by the bottom value display unit 11b in step S10. . In step S12, the control unit 4 increments the counter variable Y to Y = [2].

  Next, the bottom value holding unit 8b detects the next minimum value included in the detection signal. Incidentally, when the change of the detection level R as shown in FIG. 5 is taken, the next minimum value B is [40]. This value is smaller than the array variable B (1) in the bottom value storage unit 9b. Accordingly, the minimum value B is held in the array variable B (2) of the bottom value storage unit 9b and displayed by the bottom value display unit 11b in step S10. In step S12, the control unit 4 increments the counter variable to Y = [3].

  Thereafter, similarly, the bottom value hold unit 8b detects the next minimum value included in the detection signal. At this time, as shown in FIG. 5, when the minimum value B is [20], the value is smaller than the previously detected minimum value [40]. Therefore, the control unit 4 determines that the minimum value B held in the bottom value holding unit 8b in step S9 is larger than the previous minimum value held in the bottom value storage unit 9b, and detects the next minimum value. Prepare. Then, the bottom value holding unit 8b detects the next minimum value included in the detection signal. At this time, when the minimum value B is [48] as shown in FIG. 5, it is a value larger than the previously detected minimum value [40]. Accordingly, the minimum value B is held in the array variable B (3) in the bottom value storage unit 9b and displayed by the bottom value display unit 11b in step S10. In step S12, the control unit 4 increments the counter variable Y to detect the next minimum value.

Incidentally, the minimum value held in the bottom value storage unit 9b in this way is held as an array variable in a table format as shown in FIG. 6, for example.
Thus, the detection apparatus according to the present invention configured as described above includes the maximum value of the detection level that exceeds the threshold value set in the threshold value setting unit 6 by the hold unit (extreme value detection unit) 8 and the detection level that is below the threshold value. Are detected and held, and these extreme values (maximum value and minimum value) are held in the storage unit 9. Then, when the maximum value detected by the extreme value detection unit is smaller than the maximum value held in the storage unit 9, or the minimum value detected by the extreme value detection unit is larger than the minimum value held in the storage unit 9. At this time, the control unit 4 updates the maximum value or the minimum value held in the storage unit to the maximum value or the minimum value detected by the extreme value detection unit, respectively. The updated local maximum value and local minimum value are displayed on the display unit 11. That is, the maximum value taking the minimum value among the maximum values exceeding the threshold value can be displayed on the display unit 11 as the peak value, and the maximum value among the minimum values falling below the threshold value can be displayed as the bottom value on the display unit 11. , It is possible to appropriately set a threshold value serving as a reference value for the detection level in the threshold value setting unit 6.

Further, since the maximum value and minimum value information of the detection level R of the detection signal is stored as a history in the storage unit 9, the detection level R of the detection level R is determined from the history information of the maximum value and the minimum value stored in the storage unit 9. Various statistical information such as the tendency of the maximum value and the minimum value, the state of variation, and the average value can be calculated.
Incidentally, in addition to the display unit 11 described above, the threshold setting unit 6 performs threshold setting by bringing a terminal device (for example, a personal computer or a portable handy terminal) close to the detection device or connecting a communication line, although not particularly shown. The maximum value and the minimum value held in the storage unit 9 may be displayed. By doing in this way, the history information of the maximum value and the minimum value held in the storage unit 9 is analyzed by, for example, application software installed in a personal computer, and calculation of appropriate threshold information is performed. It becomes possible to easily set an appropriate threshold value in the threshold setting unit 6.

  The present invention is not limited to the embodiment described above. For example, as shown in FIG. 7, the present invention can also be applied to a high-frequency (inductive) proximity sensor that utilizes the fact that the current flowing in the oscillation circuit changes due to the electromagnetic induction effect accompanying the proximity of the object to be detected. This high frequency (inductive) proximity sensor is configured to include a detection coil L that constitutes a part of a high frequency oscillation circuit, and a conductive detection object S (for example, in the vicinity of the detection coil L). This is a detection device that utilizes the fact that the internal resistance component and the self-inductance component of the detection coil L change due to the electromagnetic induction action when (metal) is present or approaches. The oscillation circuit of the high-frequency proximity sensor forms an LC parallel resonance circuit between the detection coil L and a capacitor C connected in parallel, and is oscillated and driven by an oscillator 12.

The output of the oscillator 12 is amplified and output to a level suitable as an input signal for the detection circuit 13 at the next stage. The analog signal output from the detection circuit 13 is converted into a digital signal (reception level) corresponding to the level of the high frequency signal by the A / D converter 3 and applied to the signal processing circuit 5.
In principle, the high-frequency (inductive) proximity sensor configured as described above detects the presence or absence of the detection object S close to the detection coil L, changes the internal resistance component of the detection coil L, that is, for detection. This is considered as a change in Q of the coil L. This change in Q is detected as a change in the amplitude of the oscillator 12.

Also in the high-frequency proximity sensor configured as described above, the amplitude of the high-frequency oscillation circuit changes when the detection object S comes close to the detection coil L, similarly to the above-described photoelectric sensor. With the detection level R of the embodiment described above, it is possible to set an appropriate threshold as a threshold for detecting the detection target S.
Alternatively, the inspection apparatus according to the present invention can be applied to a capacitance-type proximity sensor that utilizes the fact that the capacitance changes due to the electrostatic induction accompanying the proximity of an object to be detected as shown in FIG. is there. This capacitive proximity sensor is provided with a detection capacitor C that detects the proximity of an object, and a coil L that constitutes a resonance circuit with the detection capacitor. An oscillator 12 is provided that oscillates and drives a resonance circuit including the detection capacitor C and the coil L. As the oscillation output of the oscillator 12, a voltage signal proportional to the frequency is output by the f / V converter 14 for converting the frequency into a voltage. The voltage signal converted by the f / V converter 14 is applied to the A / D converter 3 and converted to a digital signal, and then applied to the signal processing circuit 5 described above.

  In principle, the electrostatic induction type proximity sensor configured as described above changes the capacitance of the detection capacitor C when the detection object (dielectric) S is brought close to the detection capacitor C. Is detected as a change in the oscillation frequency of the LC resonance circuit composed of the coil L and the capacitor C, and the presence of an object is detected. This change in oscillation frequency is converted into a digital signal (reception level) by the f / V converter 14 and the A / D converter 3. Then, when the value of this digital signal, that is, the oscillation frequency of the LC oscillation circuit reaches a predetermined frequency (threshold), it can be detected that the detection object S is present. For this reason, even if there is an error in setting the threshold value, it is possible to set an appropriate threshold value that does not cause a detection error by referring to the history information of the maximum value and the minimum value of the level of the detection signal. It becomes.

  In addition, the detection apparatus according to the present invention can be applied to various sensors without departing from the gist thereof.

The block diagram which shows the structure of the photoelectric sensor which concerns on one Embodiment of this invention. The flowchart which shows the algorithm which detects the extreme value (local maximum value and local minimum value) of the detection apparatus which concerns on one Embodiment of this invention. The graph which shows an example of the detection level of the detection signal which the detector of the photoelectric sensor shown in FIG. 1 outputs. The figure which shows an example of the variable structure (array variable) of the memory | storage part which hold | maintains the maximum value of the detection level of the detection signal shown in FIG. The figure which shows an example of the detection level of the detection signal which the detector of the photoelectric sensor shown in FIG. 1 outputs. The figure which shows an example of the variable structure (array variable) of the memory | storage part which hold | maintains the minimum value of the detection level of the detection signal shown in FIG. The block diagram which shows schematic structure of the high frequency type proximity sensor using a high frequency signal. The block diagram which shows schematic structure of the electrostatic capacitance type proximity sensor using an electrostatic induction phenomenon. The graph which shows the change of the detection level of the detection signal of a general detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light projector 2 Light receiver 3 A / D converter 4 Control part 5 Signal processing circuit 6 Threshold setting part 7 Comparison part 8 Hold part 8a Peak value hold part 8b Bottom value hold part 9 Storage part 9a Peak value storage part 9b Bottom value storage Part 10 Comparison part 10a Peak value comparison part 10b Bottom value comparison part 11 Display part 11a Peak value display part 11b Bottom value display part

Claims (4)

Threshold value setting means for setting a threshold value that is a predetermined detection condition of the detection level using the detection level of the detection signal output by the detector under a predetermined measurement condition as a reference value, and comparing the detection level by the detector with the threshold value And a detection device comprising a comparator that outputs a detection signal,
An extreme value detection unit for sequentially detecting the maximum value of the detection level exceeding the threshold and the minimum value of the detection level below the threshold;
A storage unit that holds the maximum value and the minimum value detected by the extreme value detection unit, and
When the maximum value detected by the extreme value detection unit is smaller than the maximum value held in the storage unit, or when the minimum value detected by the extreme value detection unit is larger than the minimum value held in the storage unit, Updating means for updating the maximum value or the minimum value held in the storage unit to the maximum value or the minimum value detected by the extreme value detection unit, respectively;
A detection apparatus comprising: a display unit that displays a maximum value or a minimum value held in the storage unit.   The detection apparatus according to claim 1, wherein the maximum value and the minimum value output by the display unit serve as reference values for setting a threshold value serving as a reference for a detection level of a detection signal of the detector.   The detection device according to claim 1, wherein the storage unit holds a history of the maximum value and the minimum value of the detection level.   The detector includes a light projector and a light receiver that form a predetermined optical path. The light emitted from the light projector or reflected light thereof is received by the light receiver and the optical condition in the optical path is detected from the detection level. The detection device according to claim 1, wherein the detection device is a photoelectric sensor.

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