JP4107254B2 - Object detector - Google Patents

Description

  The present invention relates to an object detector that measures a physical quantity that varies depending on the position of an object to be detected and detects the object in a non-contact manner based on the measurement result.

  Typical examples of this type of object detector include a proximity switch and a photoelectric switch. The proximity switch has a detection unit including a coil and an oscillation circuit. A general proximity switch uses a phenomenon in which the oscillation amplitude decreases as the metal body approaches due to electromagnetic coupling between the metal body to be detected and the coil, and turns on when the oscillation amplitude becomes smaller than a predetermined threshold value. State (the state in which an object is detected. The same applies to the following). In addition, there is a type of proximity switch that detects an object using a change in oscillation frequency.

  There are two types of photoelectric switches: a transmission type switch in which a light projecting unit and a light receiving unit are arranged to face each other, and a reflection type switch in which a light projecting unit and a light receiving unit are arranged on the same side. The transmission type switch is turned on in response to the amount of light received on the light receiving unit side shifting from a value larger than the threshold value to a value smaller than the threshold value. On the other hand, the reflection type switch is turned on when the amount of received light has shifted from a value smaller than the threshold value to a value larger than the threshold value.

  Some of the proximity switches and photoelectric switches described above can change the threshold value for object detection. The following patent document 1 is mention | raise | lifted as the well-known example.

Patent 3040518

  In the above-mentioned Patent Document 1, objects to be detected are installed at a first reference position to be detected and a second reference position to be detected, and measured values (actual measurement data) obtained at the respective reference positions. Is used to obtain reference data as a comparison determination reference for object detection. The reference data corresponds to the above-described threshold value, and Patent Document 1 describes that an average value of two actually measured data is set as a threshold value as a specific example. Further, Patent Document 1 describes that margin data corresponding to the magnitude of the difference between the two measured values is created and displayed when the threshold value is set.

  According to the invention described in Patent Document 1, it is possible to confirm whether or not sufficient detection accuracy can be ensured by the set threshold value by displaying the margin. However, since this display is performed after setting the threshold value, if the displayed margin is not sufficient, the user needs to change the first or second reference position and perform setting again. is there. However, it is not easy for a general user to find out how much the margin is sufficient when the distance between the first and second reference positions is sufficient.

  In order to solve the above-described problem, it is conceivable to present the user with a minimum distance that should be secured as the distance between the first and second reference positions. However, the measured value in the object detector may vary depending on various noise components even if the position of the detected object is constant. For example, in the case of a proximity switch, it is affected by the vibration of the device in which the proximity switch is installed and the electromagnetic waves generated in the vicinity. In the case of a photoelectric switch, it is affected by ambient light and the reflectance of the surface of the object to be detected. Since the fluctuation range of the measurement value due to these noises varies depending on the installation environment or purpose of use of the object detector, the distance recommended between the first and second reference positions is indicated to the user. It is extremely difficult.

  The present invention has been made paying attention to the above-mentioned problem. In order to set a threshold value for object detection, an object is arranged in order at two reference positions and a teaching operation is performed at each position. It is an object of the present invention to make it possible to easily set an appropriate threshold value by efficiently advancing the teaching work of (1).

  An object detector according to the present invention includes a measurement unit that measures a physical quantity that varies depending on the position of an object to be detected, and a detection that detects the presence or absence of an object by comparing a measurement value by the measurement unit with a predetermined threshold value. Means, a first teaching signal indicating that the object is at a detection position, and a second teaching signal indicating that the object is at a non-detection position, in the order of first, second or second, first Setting means for inputting and setting the threshold value using the measurement value of the measurement means at the time of input of each teaching signal. Furthermore, the object detector of the present invention is provided with a display unit at an appropriate position of the machine body, and the setting means performs the first time between the input of the first teaching signal and the input of the second teaching signal. Performing a process of calculating a margin of the current measured value with respect to a measured value when the teaching signal is input, and a process of displaying information indicating the magnitude of the calculated margin on the display unit. Features.

When the object detector is a proximity switch, the measurement means can include a detection coil, an oscillation circuit, a detection circuit, and the like. Further, when the object detector is a photoelectric switch, the measuring means can include a light projecting unit such as an LED or a light receiving unit such as a photodiode. With these configurations, an analog signal (a signal indicating an oscillation amplitude, an oscillation frequency, an amount of received light, etc., which is changed in accordance with the position of the object, hereinafter referred to as a “detection signal”) can be obtained. . Further, the measurement means can include an integration circuit for smoothing the detection signal and an A / D conversion circuit for digitally converting the detection signal.
It should be noted that a part or the whole of the configuration for generating the detection signal in the measurement means can be made independent from the main body of the object detector with the head part.

The detection means can be configured as a logical operation circuit including a comparator or the like, but is preferably configured by a computer in which a program for comparison processing is incorporated.
Similarly, the setting means can be constituted by a computer in which a program for realizing the function of this means is incorporated.

  It is desirable that the first and second teaching signals are input by operating an operation unit provided at an appropriate position of the machine body constituting the object detector. However, the present invention is not limited to this, and each teaching signal may be input from the outside via an input terminal.

  The first teaching signal can be considered to indicate that the object to be detected is placed at a position where the object should be reliably detected (position where the object detector should be turned on). Hereinafter, the position of the object indicated by the first teaching signal is referred to as an “operation side reference point”. This operation-side reference point can be considered to correspond to the first reference position of Patent Document 1.

  The second teaching signal can be considered to indicate that the object to be detected is placed at a position where the object should not be detected (a position where the object detector should be turned off). Hereinafter, the position of the object indicated by the second teaching signal is referred to as “return-side reference point”. This return-side reference point can be considered to correspond to the second reference position of Patent Document 1.

  The user places the object to be detected at the operation-side reference point, inputs the first teaching signal, moves the object to the return-side reference point, and inputs the second teaching signal. A reference position can be taught. Alternatively, after the object is placed at the return side reference point and the second teaching signal is input, the object may be moved to the operation side reference point and the first teaching signal may be input.

Hereinafter, an operation performed by the user to input a teaching signal is referred to as a “teaching operation”. In addition, teaching that an object is placed at the operation-side reference point or the return-side reference point is expressed as “teach reference point”.
In the preferred teaching work, the object detector is fixedly installed and the object is moved. However, the present invention is not limited to this, and the object is fixedly arranged at a predetermined position, and the object detector head unit or the entire body is moved, A reference point may be taught.

Note that “the margin of the current measured value relative to the measured value when the first teaching signal is input” is the ratio of the difference between the two measured values and the noise width of the measured value, or the difference between the two. A value based on is included.
The noise width of the measured value originates from the detector itself (for example, CPU clock noise or internal power supply ripple), and is due to the internal noise on the measured value regardless of the external environment. The disturbance noise that comes from the outside of the detector and comes on the measured value of the detector can be considered. Here, the noise width can be any of internal noise, disturbance noise, or a combination of both.

  According to the present invention, when the user moves the object in the direction of the other reference point after teaching the operation-side reference point or the return-side reference point, the measurement value obtained at the time of the teaching and the current object The latter margin with respect to the former measurement value is calculated based on the measurement value reflecting the position, and information indicating the magnitude is displayed on the display unit. Here, as the distance between the taught reference point and the object increases, the value of the margin also increases, so that the user can indicate that the display unit has a sufficiently large margin and the other reference point. It is possible to recognize a position suitable for Therefore, by placing the object at the recognized position and performing the second teaching operation, based on the measured value acquired according to the first teaching operation and the measured value acquired according to the second teaching operation. Appropriate threshold can be set.

  In a preferred aspect of the object detector of the present invention, the setting means compares the calculated value with a predetermined reference value every time the margin is calculated, and shifts from a state where the margin is lower than the reference value to a state where the margin is higher. In this case, the display mode on the display unit is changed. For example, when the margin exceeds the reference value, the display color is changed, a predetermined mark is displayed near the margin display, or a notification lamp is turned on. can do. According to such a method, even a user who is unfamiliar with the setting can easily determine an appropriate position for the second teaching operation.

In the object detector according to another preferred aspect, the display unit includes a numerical display capable of displaying a number indicating the margin. In this way, the specific size of the margin can be grasped.
In addition, the display unit can display the measured value at the present time, the magnitude of the set value when the threshold value is set at the current time, and the like together with the margin.

  According to the present invention, when teaching the operation-side reference point and the return-side reference point for setting the threshold for object detection, after teaching one of the reference points, a sufficient margin can be obtained by displaying on the display unit. The other reference point can be taught by checking the position where the degree can be secured. Therefore, since the user can efficiently perform the teaching work for setting the threshold value, it is possible to easily set an appropriate threshold value.

  FIG. 1 shows the appearance of a proximity switch according to an embodiment of the present invention. In the proximity switch of this embodiment, a head part 1A in which a detection coil is accommodated, a preamplifier part 1B in which an oscillation circuit, a detection circuit, and the like are accommodated, and an amplifier part 2 including a CPU are respectively connected to shield cables 3 and 4. Connected through. The head unit 1A and the preamplifier unit 1B function as a detection unit 1 which will be described later, depending on the distance from the detection surface (front surface) of the head unit 1A to a metal object to be detected (hereinafter referred to as “object”). A detection signal (representing oscillation amplitude) whose magnitude changes is output. The amplifier unit 2 determines the presence or absence of an object using this detection signal, and outputs the determination result to the outside.

  An operation unit and a display unit including a plurality of switches are provided on the upper surface of the amplifier unit 2 of this embodiment, and the upper part thereof is protected by the lid unit 20. FIG. 2 shows a detailed configuration of the upper surface when the lid 20 is removed. In the figure, a display unit 21 is provided on the left hand, and an operation unit 22 is provided on the right hand.

  The display unit 21 includes an LED lamp 211 (hereinafter simply referred to as “lamp 211”) and four LED displays 212, and two sets of these combinations are arranged (hereinafter referred to as one set). (The combination of the eye lamp 211 and the LED display 212 is referred to as “display unit 21a”, and the combination of the second set of lamp 211 and the LED display 212 is referred to as “display unit 21b”.) The first set of display units 21a is configured by red LEDs, and the second set of display units 21b is configured by green LEDs.

  The operation unit 22 is provided with two selection keys 221, 222, a confirmation key 223, changeover switches 224, 225, and the like. The selection keys 221 and 222 and the confirmation key 223 are used in the setting mode. The changeover switch 224 is for switching between the setting mode and the normal operation mode, and the other changeover switch 225 is an operation of the output circuit 29 (on / off from the output circuit 29) to be described later when an object is detected. Signal). In the setting mode, a character string indicating a setting item or a numerical value indicating a setting value is displayed on the display unit 21, and the display is switched according to the operation of the selection keys 221 and 222, and the confirmation key 223 is operated. The selection of items and set values are determined accordingly. In the setting mode, a process for setting a threshold value for detecting an object is performed. In this setting, the selection keys 221 and 222 teach the operation-side reference point and the return-side reference point. Functions as a teaching operation key.

FIG. 3 shows a circuit configuration of the proximity switch.
In FIG. 3, the detection coil 10 of the head unit 1 </ b> A and the oscillation circuit 11 and the detection circuit 12 of the preamplifier unit 1 </ b> B are shown as a detection unit 1 in one block. In FIG. 3, the detection unit 1 includes the shielded cable 4 that connects the preamplifier unit 1 </ b> B and the amplifier unit 2. Reference numeral 201 in the figure denotes a connector on the amplifier unit 2 side with respect to the shielded cable 4, and 202 denotes a power supply circuit in the amplifier unit 2. The power supply circuit 202 is supplied with DC power from outside and supplies driving power to the circuits of the amplifier unit 2 and the detection unit 1.

  In addition to the CPU 23, the amplifier unit 2 includes an integration circuit 24, an A / D conversion circuit 25, an EEPROM 26, a communication circuit 27, an input circuit 28, an output circuit 29, and the like. The CPU 23 is connected to the operation unit 22 (including various switches 221 to 225) and the display unit 21 (including the LED indicators 212 and the lamp 211).

  The CPU 23 includes a ROM in which a program is stored. The EEPROM 26 stores setting data such as a threshold value for object detection. The output circuit 29 outputs an on / off signal (for example, a digital signal that becomes a high level when “there is an object”) indicating the determination result obtained by the object detection process. The input circuit 28 is used to input a signal from the outside when starting the object detection process in response to the trigger signal. The communication circuit 27 is used for exchanging information with an external device such as a personal computer when performing detailed settings in the setting mode or when performing detailed processing using measured values.

  In the above description, the oscillation amplitude of the oscillation circuit 11 decreases as an object approaches the detection coil 10. The detection circuit 12 outputs a detection signal indicating the magnitude of the oscillation amplitude to the amplifier unit 2. This detection signal is smoothed by the integration circuit 24 on the amplifier unit 2 side, then digitally converted by the A / D conversion circuit 25 and input to the CPU 23. This data input is performed at regular time intervals based on an output pulse from a timing generation circuit (not shown), and the CPU 23 takes in the input data every hour as a measured value of the oscillation amplitude at that time, and this measured value. Are averaged every predetermined number of units. Then, the averaged measurement value (hereinafter referred to as “average measurement value”) is compared with a threshold value in the EEPROM 26 to determine the presence or absence of an object, and the determination result is output from the output circuit 29. To do.

  FIG. 4 shows a theoretical curve representing the relationship between the position of the object to be detected with respect to the detection surface of the head unit 1A and the measured value. In FIG. 4, on the horizontal axis representing the position, the direction from the right to the left of the page is the direction approaching the head portion 1A. On the vertical axis indicating the measurement value, the value increases along the direction from the bottom to the top of the page.

  Further, FIG. 4 shows the principle of setting a threshold for object detection. Similar to the conventional proximity switch, this setting method is performed in accordance with an operation for teaching two points of the operation side reference point L1 and the return side reference point L2. In this teaching operation, the selection keys 224 and 225 of the operation unit 22 are set to be operated.

  The user sets an object at the position of the operation side reference point L1 with the boundary position of the range considered to be necessary to reliably detect the object to be detected, and uses the selection key 224 or 225. To perform the first teaching operation. Next, the user moves the object to the return side reference point L2 using the position L2 that is a predetermined distance away from the operation side reference point L1 as the return side reference point with respect to the head portion 1A, and selects the selection key 224 or 225. To perform the second teaching operation. Contrary to the above, first, an object is set at the position of the return side reference point L2, and after performing the first teaching operation, the object is moved to the operation side reference point L1, and then the second teaching operation is performed. May be performed.

  The CPU 23 samples a predetermined number of measurement values in accordance with the first and second teaching operations and obtains an average value thereof. The smaller average value is recognized as the average measured value AD1 corresponding to the operation side reference point L1, and the larger average value is recognized as the average measured value AD2 corresponding to the return side reference point L2. Further, the CPU 23 obtains a value AD0 (desirably an average value of AD1 and AD2) between these average measured values AD1 and AD2, and sets this AD0 as a threshold value.

  According to the theoretical curve of FIG. 4, when the object is located on the head portion 1A side from the position L0 corresponding to the threshold value AD0, the measured value falls below the threshold value AD0 and is determined to be “object present”. The When the object is located farther than the position L0 with respect to the head unit 1A, the measured value exceeds the threshold value AD0, and it is determined that “no object”.

  However, when the distance between the operation side reference point L1 and the return side reference point L2 is small, the difference between the average measured values AD1 and AD2 is smaller than the resolution of the AD conversion circuit 25 or slightly higher than the resolution. There is a possibility. In such a case, it is substantially impossible to set the threshold value AD0.

  In actual measurement, even when the position of the object has not changed, the measurement value varies due to vibrations of the device in which the proximity switch is installed, noise from the surroundings, and the like. The width of this variation varies depending on the installation environment of the proximity switch. Therefore, even if the difference between the average measured values AD1 and AD2 exceeds the resolution of the AD conversion circuit 25, if the difference is smaller than the fluctuation range of the measured value due to the surrounding environment, the object is moved to the operation side reference point. It is difficult to reliably determine and determine the case of being at L1 and the case of being at the return side reference point L2.

  Therefore, in order for the proximity switch to stably execute the operation that is turned on when the object is at the operation side reference point L1 and is turned off when the object is at the return side reference point L2, the average is used. It is necessary to adjust the positions of the points L1 and L2 so that the difference between the measured values AD1 and AD2 is sufficiently larger than the fluctuation range of the measured values. However, as described above, since the fluctuation range of the measured value varies depending on the installation environment of the proximity switch, the preferable distance between the operation side reference point L1 and the return side reference point L2 also varies depending on the installation environment. Moreover, it is difficult for a general user to determine how much distance should be provided between the points L1 and L2.

  In view of the above points, in this embodiment, after receiving the first teaching operation, until the second teaching operation is performed, the first measurement operation is performed for each measurement value at a predetermined time interval. A margin for the measurement value at the time of the teaching operation is obtained and displayed on the display unit 21.

The margin of this embodiment is calculated based on the average value and fluctuation range of the measured values sampled during the first teaching operation. Here, to simplify the explanation, it is assumed that the operation-side reference point L1 is taught in the first teaching operation, the average measured value obtained during this teaching operation is AD1, the fluctuation range of the measured value is ΔD1, and the margin If the average measured value obtained at the time of calculating the degree is AD, the margin Q is obtained by the following equation (1). Note that the fluctuation range ΔD1 is a difference between the maximum value and the minimum value of the sampled measurement values.
Q = (AD−AD1) / ΔD1 (1)

FIG. 5 schematically shows the ability of the proximity switch described above to detect a change in position when an object located at the operation-side reference point L1 moves in a direction away from the head unit 1A.
V in the figure indicates a difference in measured value corresponding to the resolution of the proximity switch. Hereinafter, this V is referred to as a “reference value V”. W is a reference value for determining the suitability of the margin Q obtained by the equation (1), and is set to a value larger than ΔD1 of the equation (1).

  The non-detectable region in the figure is a range where the difference between the average measured value AD and the average measured value AD1 at the operation side reference point L1 is equal to or less than the reference value V. When the moved object is located within this range, the separation between AD and AD1 is practically impossible, and it cannot be determined that the object has moved from the operation-side reference point L1.

  In the unstable region in the figure, the difference between the average measured value AD and the average measured value AD1 at the operation-side reference point L1 is larger than the reference value V, but the margin Q according to the above equation (1) is larger than the reference value W. It is a range that becomes smaller. When the moved object is located in this range, there is a possibility that the same measurement value may be obtained even when the object remains at the operation-side reference point L1, and it is determined that the object is moving reliably. It becomes difficult to do.

  With respect to the above two areas, the stable area is a range in which the margin Q exceeds the reference value W. When the object after movement is located within this range, a measurement value exceeding the maximum measurement value at the operation side reference point L1 is always obtained, and it is reliably determined that the object has moved away from the operation side reference point L1. can do.

  In the proximity switch of this embodiment, after accepting the first teaching operation, the margin Q based on the equation (1) is obtained and displayed on the display unit 21, so the user confirms this display. However, the second teaching operation can be performed when a value exceeding the reference value W is displayed by moving the object along either the direction approaching the head unit 1A or the direction moving away from the head unit 1A. As a result, the fluctuation range caused by the surrounding environment (ΔD1 in the equation (1)) between the measured value when the object is located at the operation side reference point L1 and the measured value when the object is located at the return side reference point L2. Each reference point can be taught in such a way that a larger difference occurs.

  Since the presence / absence determination of the object is performed based on the threshold value AD0, the average measured values AD1, AD2 at the reference points L1, L2 and the threshold value AD0 also exceed the fluctuation range ΔD1, respectively. It is desirable to make a difference. Therefore, if the reference value W is set to a value that is twice or more than ΔD1, the object is stably turned on when the object is at the operation side reference point L1, and stable when the object is at the return side reference point L2. Then, the threshold value AD0 can be set so as to be turned off.

  In the proximity switch of this embodiment, in the threshold setting mode, the margin Q is displayed on one of the display portions 21a and 21b, and the measured value when the margin Q is obtained on the other display portion. (Corresponding to the above-mentioned average measured value AD. In the following, this is referred to as the current value AD). Furthermore, in this embodiment, when performing the above display, it is determined whether the displayed current value AD or margin Q corresponds to the undetectable region, unstable region, or stable region in FIG. The display pattern is changed according to the determination result.

  For example, when it is determined that the area falls under the undetectable region, both the numerical value display indicating the current value AD and the margin Q and the lamp 211 are displayed blinking (hereinafter, this display pattern is referred to as a display pattern A). If the current value AD is determined to be an unstable region, the current value AD is fixedly displayed, but the margin Q and the lamp 211 are blinked (hereinafter, this display pattern is referred to as a display pattern B). In addition, when it is determined that it falls within the stable region, both the current value AD and the margin Q are fixedly displayed, and the respective lamps 211 are continuously lit (hereinafter, this display pattern is referred to as a display pattern C). By changing the display pattern in this manner, even a user unfamiliar with the setting can easily determine a position suitable for performing the second teaching operation, and the teaching work can be performed efficiently.

  FIG. 6 shows a procedure related to the threshold value setting process in the proximity switch, and FIG. 7 shows a display example of the display unit 21 during the setting process. Hereinafter, a detailed flow for setting a threshold value will be described along the flow of FIG. 6 with reference to FIG. Note that “ST” in FIG. 6 and the following description means a step (STEP). Moreover, in FIG. 7, the code | symbol with respect to the display part 21 is described only in the figure of (1), (2) The code | symbol of the following figures is abbreviate | omitted.

The procedure of FIG. 6 starts when an operation for selecting a threshold setting process from various setting items is performed in the setting mode.
In the first ST1, a predetermined number of measurement values are sampled. In the next ST2, the sampled measurement values are averaged, and the obtained measurement average value is displayed as the current value together with the existing threshold value. The existing threshold value is a threshold value currently stored in the EEPROM 26 and is a default threshold value in the proximity switch in the initial state.

In ST3, the presence / absence of the first teaching operation is checked. If the first teaching operation is not performed, the process returns to ST1. Thereafter, the loop of ST1 to ST3 is repeatedly executed until the first teaching operation is performed.
(1) in FIG. 7 shows a display example in ST2. The numerical value indicating the current value is displayed on the first display portion 21a, and the numerical value indicating the threshold value is displayed on the second display portion 21b. ing. If the position of the object changes while the loops of ST1 to ST3 are repeated, the display on the first display unit 21a also changes accordingly.

  Here, when the user places the object to be detected at an appropriate position and performs the first teaching operation, ST3 becomes “YES”, and the process proceeds to ST4 and subsequent steps.

  In ST4, the same number of measurement values as in ST1 are sampled, and in ST5, the average measurement value and the fluctuation range are calculated. Although not shown in FIG. 6, according to the execution of ST4 and ST5, the display on the display unit 21 is in the state shown in (2) of FIG. 7 for a predetermined time. This display state means “teaching in progress”, the first display portion 21a has a character string “tEch” meaning “teach” in English, and the second display portion 21b has “2Point”. A character string “2Pnt” meaning “is displayed.

  When the processes of ST4 and ST5 are completed, the steps of ST6 to ST10 are repeated until the second teaching operation is performed. In ST6, the same number of measurement values as in ST1 and ST4 are sampled. In ST7, these measurement values are averaged, and the obtained average measurement value is set as the current value AD.

  In the next ST8, the margin Q is calculated using the current value AD and the average measured value and fluctuation range obtained in ST5. In the calculation process of the margin Q, after obtaining the absolute value of the difference between the average measured value obtained in ST5 and the current value AD in accordance with the above-described equation (1), the result is used as the fluctuation range. Performs an operation that divides by.

  In ST9, the current value AD and the margin Q are used to determine which of the three regions shown in FIG. 5 is included in the current object, and display patterns A, B, Select one of C. That is, when the difference between the current value AD and the average measured value obtained in ST5 is equal to or less than the reference value V, it is determined that the object is in the undetectable region, and the display pattern A is selected. When the difference between the current value AD and the average measured value obtained in ST5 is larger than the reference value V and the margin Q is smaller than the reference value W, it is determined that the object is in an unstable region, and the display pattern Select B. Further, when the margin Q is equal to or greater than the reference value W, it is determined that the object is in the stable region, and the display pattern C is selected.

When the display pattern is selected in this way, in ST10, the current value and the margin are displayed according to the selected display pattern.
(3) of FIG. 7 is a display example in ST10. This example is based on the display pattern C at the final stage. The current value is fixedly displayed on the first display unit 21a, and the margin is displayed on the second display unit 21b. The lamp 211 of 21b is lit. In the illustrated example, the margin is displayed in units of%.

  When the second teaching operation is performed at a predetermined time, ST11 becomes “YES” and the process proceeds to ST12, and the same number of measurement values as ST1, 4, 6 are sampled. In the next ST13, the average of the respective measured values is obtained, and the obtained value is set as the average measured value corresponding to the second teaching operation.

  In the next ST14, the average measured value obtained in ST5 is compared with the average measured value obtained in ST13. Then, the calculation is performed by subtracting AD1 from AD2 with the smaller value as the average measured value AD1 corresponding to the operation side reference point L1 and the larger value as the average measured value AD2 corresponding to the return side reference point L2. The obtained difference value is compared with the reference value V.

  When the value of the difference is larger than V, the process proceeds from ST14 to ST15, an average of the average measured values AD1, AD2 is obtained, and the average value is set as a threshold value AD0. In the next ST16, the current value (here, the average measured value obtained in ST13) and the threshold value AD0 are displayed on the display unit 21. Further, in ST17, the existing threshold value in the EEPROM 26 is updated to the threshold value AD0, and then the process is terminated.

(4) and (5) of FIG. 7 show a detailed example of the display process of ST16. (4) is a state immediately after the threshold value is calculated in ST15. The character string “2Pnt” meaning “2Point” is displayed on the first display portion 21a, and the second display portion 21b is displayed on the second display portion 21b. A numerical value (1730) indicating the threshold value AD0 is displayed. In addition, the lamp 211 is in a state of being lit only by the first display unit 21a.
(5) is the time when a predetermined time has elapsed from the display of (4). The display on the first display unit 21a is switched to a numerical value indicating the current value, and both the display units 21a and 21b are The lamp 211 is turned on.

  Since the user can perform the second teaching operation at an arbitrary position regardless of the value of the margin Q, the difference between the measurement average values AD2 and AD1 is the difference between the measured average values AD2 and AD1 when the teaching operation is incorrect. There is a possibility that the reference value V or less. In this case, ST14 is “NO” and the process proceeds to ST18, and a predetermined error display is executed on the display unit 21 (for example, “EEEE” is displayed on each display unit 21a, 21b). In this case, when a predetermined time elapses from the display, the process returns to ST1, so that the user can redo the teaching work from the beginning.

  According to the above procedure, after the object is placed at either the operation side reference point L1 or the return side reference point L2 and the first teaching operation is executed, the object is moved while checking the display on the display unit 21. The threshold value AD0 can be set to an appropriate value by performing the second teaching operation when the display state as shown in FIG.

  In the proximity switch disclosed in the above-mentioned Patent Document 1, the margin cannot be confirmed unless the operation side reference point L1 and the return side reference point L2 are taught. The teaching work must be performed again. In addition, since the position where the second teaching operation is performed can only be selected sensibly, there is a possibility that the teaching work must be repeated many times.

  On the other hand, according to the proximity switch of this embodiment, the user sets either the operation-side reference point L1 or the return-side reference point L2 according to the purpose, and performs the first teaching operation at the set position. After that, the position suitable for the second teaching operation can be determined based on the display on the display unit 21. Therefore, it is possible to set an appropriate threshold value in one teaching operation, and it is possible to greatly reduce the labor for setting the threshold value.

  Further, Patent Document 1 only discloses that the difference between the measurement values obtained during each teaching operation is divided by the minimum unit of measurement values (that is, resolution), and is calculated as a margin. In this case, the fluctuation of the measured value due to noise becomes larger than the margin, and there is a possibility that malfunction may occur in detection. On the other hand, in this embodiment, the fluctuation range of the measured value is obtained in accordance with the first teaching operation, and the margin that becomes smaller as the fluctuation range is larger is calculated, so at any reference point L1, L2. In addition, the presence / absence determination of the object at the position can be performed stably.

  In the example of FIGS. 6 and 7, the current value is displayed together with the margin between the first teaching operation and the second teaching operation. However, instead of displaying the current value, the current value is displayed. You may make it display the threshold value at the time of employ | adopting.

  In the procedure shown in FIG. 6, after the first teaching operation is performed, the margin is calculated and displayed every time the average measured value AD is obtained. However, the present invention is not limited to this. . For example, the fluctuation amount of the average measured value AD within a predetermined time is extracted, and when the fluctuation amount is equal to or less than the fluctuation width obtained in ST5, it is considered that the object has stopped, and the calculation and output of the margin are performed. You may make it perform. In this case, since the margin is displayed when the user stops the object to perform the second teaching operation, it is determined whether or not the stop position is suitable for the teaching operation. The teaching operation can be performed above.

In addition, in the calculation of the margin in this embodiment, the average value and the fluctuation range of the measurement values sampled at the first teaching operation and the average value of the measurement values sampled at the margin calculation time are used. May be obtained from measured values sampled at the time of margin calculation. Further, when the teaching operation is not performed, for example, the margin may be calculated using the fluctuation range of the measured value acquired immediately after the power is turned on.
In addition, when the fluctuation of noise due to the external environment is not large, instead of the fluctuation range of the measured value, the internal noise of the proximity switch (for example, signal noise due to power supply ripple, CPU clock noise, etc.), etc. The margin may be calculated using a predetermined fixed value.

It is a perspective view which shows the external appearance of the proximity switch to which this invention was applied. 3 is a top view illustrating a detailed configuration of a display unit 21 and an operation unit of the amplifier unit 2. FIG. It is a block diagram which shows the electric constitution of a proximity switch. It is a graph which shows the relationship between the position of the object with respect to 1 A of head parts, and a measured value with the principle concerning the setting process of a threshold value. It is explanatory drawing which shows typically the capability to detect an object. It is a flowchart which shows the procedure of the setting process of a threshold value. 11 is an explanatory diagram illustrating a display example of the display unit 21. FIG.

Explanation of symbols

1 detector 1
2 Amplifier section 2
DESCRIPTION OF SYMBOLS 10 Detection coil 11 Oscillation circuit 12 Detection circuit 21 Operation part 22 Display part 21
23 CPU23
24 integration circuit 25 A / D conversion circuit 26 EEPROM
29 Output circuit

Claims (3)

Measuring means for measuring a physical quantity that changes depending on the position of the object to be detected, detecting means for detecting the presence or absence of an object by comparing a measurement value by the measuring means with a predetermined threshold, and the object at the detection position A first teaching signal indicating the presence and a second teaching signal indicating that the object is in the non-detection position are input in the first, second or second, first order, and each teaching signal is input In an object detector comprising: setting means for setting the threshold value using a measurement value of the measuring means at
There is a display at the right place on the aircraft,
The setting means calculates a margin of a current measured value with respect to a measured value at the time when the first teaching signal is input between the input of the first teaching signal and the input of the second teaching signal. An object detector characterized by executing a process and a process of displaying information indicating the calculated degree of margin on the display unit.   The setting means compares the calculated value with a predetermined reference value every time the margin is calculated, and changes the display pattern on the display unit when the margin shifts from a state below the reference value to a state above the reference value. The object detector according to claim 1, wherein the object detector is changed.   The object detector according to claim 1, wherein the display unit includes a numerical display capable of displaying a number indicating the margin.

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