JP2006080896A - Detection switch, photoelectronic switch and detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection switch capable of avoiding erroneous determination caused by fluctuations of a physical value accompanied by a change in the lapse of time. <P>SOLUTION: This detection switch is provided with a photodetector 24 for receiving light from a detection target area and acquiring the amount of the received light, an amplifier circuit 25 and an A/D converter 26 for generating a detection value from the amount of received light according to predetermined offset and gain, a comparing part 41 for comparing the detection value with a predefined threshold and outputting a first level or second level being a comparison result as a detection result to the outside, a reference detection value storing part 42 for storing a preset reference detection value, and a correcting part 43 for correcting the offset or gain of the amplifier circuit 25 so as to place a difference or ratio between a first detection value which is a detection value generated from the amount of received light acquired by the photodetector 24 at an optional time and is a detection value when the comparison result is at the first level, and the reference detection value within a prescribed range. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention compares a detection value obtained from a physical quantity corresponding to a physical state of a detection object with a threshold value, and outputs a first level or a second level as a comparison result to the outside as a detection result, In particular, the present invention relates to a photoelectric switch and a detection method using the photoelectric switch.

  A photoelectric switch, a type of detection switch, projects light toward the detection target area, receives light from the detection target area, compares the detection value obtained from the received light amount with a threshold value, and compares The first level or the second level as a result is output to the outside as a detection result corresponding to the presence or absence of the detection target. In such a detection switch such as a photoelectric switch or a proximity switch, an erroneous determination may occur due to a temporal change in a physical quantity (for example, a received light quantity) corresponding to a physical state of a detection target. For example, if the physical quantity corresponding to the ON state decreases with time, the detected value obtained from the physical quantity is originally set to be larger than the threshold value, but becomes smaller than the threshold value with time. End up. As a result, for example, when the second level indicating the on state is to be output, an erroneous determination of outputting the first level indicating the off state occurs.

  As one of the conventional methods for avoiding the erroneous determination of the detection switch due to the temporal change as described above, for example, there is a method described in Patent Document 1. In this method, the threshold value is changed according to the temporal change of the physical quantity. Specifically, a predetermined number of physical quantities corresponding to an on state (for example, a second level output) and a physical quantity corresponding to an off state (for example, a first level output) are accumulated. If a predetermined number of physical quantities are accumulated, the distribution of the physical quantity in the on state and the distribution of the physical quantity in the off state are respectively obtained, and the threshold value is reset (updated) so as to be an intermediate value thereof.

  In this method, when a predetermined number of physical quantities are accumulated, it is determined from the output (discrimination result) of the detection switch whether the physical quantity corresponds to the on state or the physical quantity corresponds to the off state. For this reason, an appropriate threshold value cannot be set when there is a change in physical quantity with time that causes erroneous determination at that time. In addition, for example, when the presence or absence of a plurality of types of objects is determined using a photoelectric switch, if the light reflectance of the surface of each object is greatly different, the amount of reflected light (physical quantity) from the object also varies greatly. In such a case, the distribution of the physical quantity corresponding to the ON state becomes a wide and gentle distribution, and it becomes difficult to set an appropriate threshold value by the above method.

Further, in Patent Document 2, a differential value of an acquired change waveform of a physical quantity is obtained, and a location where the physical quantity (physical state to be detected) changes is determined by comparing the differential value with a differential threshold value. A detection switch for setting a plurality of threshold values from a plurality of physical quantities is described. In this method, when a plurality of types of objects having different physical states are detected, or when a plurality of parts having different physical states of one object are detected, a plurality of threshold values are set so as to be an intermediate value of the preceding and following physical quantities. Can be set. When the threshold value is appropriately set by this method, the erroneous determination of the detection switch due to the change with time as described above is also avoided. However, in this method, it is necessary to separate a threshold setting mode in which a differential value of a change waveform of a physical quantity is obtained to set a plurality of threshold values from an operation mode that is a normal measurement mode. That is, the threshold change setting is executed only in the threshold setting mode and not in the operation mode.
JP-A-9-284116 JP-A-8-340242

  As described above, conventionally, a detection switch has been proposed that avoids misjudgment caused by fluctuations in physical quantities due to changes over time by automatic resetting (updating) of threshold values, but detection generated from physical quantities. There is no proposal for avoiding the erroneous determination as described above by correcting the value in accordance with the change with time of the physical quantity.

  In view of the problems of the conventional detection switch as described above, an object of the present invention is to provide a detection switch capable of avoiding erroneous determination due to a change in physical quantity accompanying a change with time with a simple configuration. .

  A first configuration of a detection switch according to the present invention includes a physical quantity acquisition unit that acquires a physical quantity corresponding to a physical state of a detection target, a detection value generation unit that generates a detection value from the physical quantity according to a predetermined offset and gain, and a detection A comparison unit that compares a value with a predetermined threshold and outputs the first level or the second level as a comparison result to the outside as a detection result; a reference detection value storage unit that stores a preset reference detection value; The difference or ratio between the first detection value and the reference detection value when the comparison result is the first level, which is a detection value generated from the physical quantity acquired by the physical quantity acquisition unit at an arbitrary time, falls within a predetermined range. And a correction unit that corrects the offset or gain of the detection value generation unit.

  Here, “difference or ratio falls within a predetermined range” means that a difference is within a control error range centered on zero and a ratio is centered on 1. That is, it means that control (correction) is performed such that the difference or ratio between the first detection value and the reference detection value approaches zero or one. The first level is, for example, when there is no detection target (off state), and the physical quantity (first physical quantity) at this time is more stable than when there is a detection target. On the other hand, the second level is, for example, when the detection target is present (ON state), and the physical quantity (second physical quantity) at this time is the type and state of the detection target (surface light reflectance and flatness). ). According to the above configuration, the correction for adjusting the offset or gain when generating the detection value from the physical quantity is performed so that the first detection value generated from the first physical quantity that is relatively stable becomes the reference detection value. Done automatically. By this correction, it is possible to avoid erroneous determination caused by a change in physical quantity accompanying a change with time.

  In a second configuration of the detection switch according to the present invention, in the first configuration, the reference detection value storage unit is a detection value generated from the physical quantity acquired by the physical quantity acquisition unit at a predetermined time, and the comparison result is the first. The detection value at the 1st level is stored as a reference detection value. According to such a configuration, the detection value generated from the physical quantity when there is no object to be detected (off state) at a predetermined time, for example, at the start of operation of the equipment in which the detection switch is installed is automatically set as a reference. It is set and stored as a detection value.

  A third configuration of the detection switch according to the present invention further includes a reference detection value acquisition instruction unit for instructing acquisition of a reference detection value in the second configuration. According to such a configuration, the user can instruct the timing by the reference detection value acquisition instruction unit so that the detection value generated from the physical quantity acquired under appropriate conditions is acquired as the reference detection value. it can.

  The fourth configuration of the detection switch according to the present invention determines whether or not the difference or ratio between the first detection value and the reference detection value is within a predetermined first specified range in any of the above configurations. A first defined range discriminating unit is further provided, and the correction of the offset or gain by the correcting unit is executed only when the discrimination result is negative. That is, in the control cycle that is repeatedly executed, the process of correcting the offset or gain as described above is not executed every time, but the difference between the first detection value and the reference detection value is within a predetermined first specified range. In some cases, such processing is not executed. The offset or gain is corrected only when the difference between the two exceeds the first specified range. By doing so, it is possible to reduce the processing load on the microcomputer including the correction unit.

  According to a fifth configuration of the detection switch of the present invention, the second specified range determination for determining whether or not the difference or ratio between the first detection value and the reference detection value is within a second specified range wider than the first specified range. An error notification is executed when the determination result is negative. Error notification can be performed using a display, a buzzer, an external output, or the like. According to such a configuration, it is possible to notify the user when a change in physical quantity with time (deterioration) has progressed before the offset or gain cannot be corrected as described above, or when a detection switch has failed. It becomes.

  The sixth configuration of the detection switch according to the present invention further includes a specified range setting unit for setting the first specified range, the second specified range, or both specified ranges in the fourth or fifth configuration. It is characterized by being. According to such a configuration, the user sets specific numerical values of the first specified range for determining whether to perform offset or gain correction and the second specified range for determining whether to perform error notification. It becomes possible to do.

  According to a seventh configuration of the detection switch of the present invention, in any one of the configurations described above, the reference detection value or the first detection value is acquired after a predetermined delay time from the time when the comparison result is inverted from the second level to the first level. It is generated from the physical quantity to be performed. The physical quantity acquired by the detection switch usually changes in a rectangular wave shape, but the rising edge and the falling edge are not always steep. Rather, it often becomes smooth like an integrated waveform. According to the configuration of the present invention, it is possible to avoid an unstable level immediately after the comparison result is inverted from the second level to the first level, and to perform a stable reference detection value or first detection from a physical quantity acquired after a predetermined delay time. A value can be obtained.

  An eighth configuration of the detection switch according to the present invention is the same as the seventh configuration described above, further including a delay time setting unit for setting a delay time. According to such a configuration, it is possible to set a preferable delay time according to the waveform of the physical quantity acquired by the detection switch.

  According to a ninth configuration of the detection switch of the present invention, in any one of the configurations described above, the detection switch further includes a display that simultaneously displays the detection value, the threshold value, and any two of the gain and the offset. Features. According to such a configuration, the user can know information on gain or offset correction that is automatically executed.

  The tenth configuration of the detection switch according to the present invention is characterized in that, in any one of the configurations described above, the detection switch further includes a reference detection value adjusting unit for increasing / decreasing the reference detection value. According to such a configuration, particularly when the reference detection value is automatically set as in the second configuration, the user can increase or decrease the reference detection value according to the surrounding environment (for example, illuminance, etc.). Even more preferred.

  An eleventh configuration of the detection switch according to the present invention is characterized in that, in any of the above configurations, a threshold setting unit for setting a threshold is further provided. As described in each of the above configurations, the detection switch according to the present invention corrects the detection value by changing the offset or gain with a constant threshold even when the acquired physical quantity has a change over time. In addition to this, it is preferable that the threshold value can be changed and set. According to such a configuration, the threshold value can be set to a value close to the reference detection value in consideration that the detection value corresponding to the first level is corrected to the reference detection value. Thereby, even when the detection value corresponding to the second level fluctuates as in the case of detecting a plurality of types of detection objects, the possibility of erroneous determination is reduced. Note that the threshold value setting unit may automatically set the threshold value, or may be set manually by the user.

  A first configuration of a photoelectric switch according to the present invention (claim 12) is a light projecting unit including a light emitting element for projecting light toward a detection target region, and receives light from the detection target region. A light receiving unit including a light receiving element for acquiring the amount of received light, a detection value generating unit that generates a detection value from the amount of received light according to a predetermined offset and gain, and comparing the detection value with a predetermined threshold, and comparing results The comparison unit that outputs the first level or the second level as a detection result to the outside, the reference detection value storage unit that stores a preset reference detection value, and the received light amount acquired by the received light amount acquisition unit at an arbitrary time point The offset or gain of the detection value generator is corrected so that the difference or ratio between the first detection value and the reference detection value when the comparison result is the first level is within a predetermined range. A correction unit And butterflies. The configuration of this photoelectric switch corresponds to the first configuration of the detection switch described above, and the same operational effects can be obtained.

  A second configuration of the photoelectric switch according to the present invention (Claim 13) includes a light projecting unit including a light emitting element whose light emission amount is variable for projecting light toward the detection target region, and light from the detection target region. A light receiving unit including a light receiving element for receiving light and acquiring the amount of light received is compared with a detection value corresponding to the amount of light received, and a first level or a second level as a comparison result is detected. As a result, a comparison unit that outputs to the outside, a reference detection value storage unit that stores a preset reference detection value, and a detection value that is generated from the received light amount acquired by the received light amount acquisition unit at an arbitrary time, and is a comparison result And a correction unit that corrects the light emission amount of the light emitting element so that the difference or ratio between the first detection value and the reference detection value is within a predetermined range. This configuration is based on a configuration unique to the photoelectric switch, that is, the amount of received light, which is a physical amount acquired from the detection object, can be adjusted by changing the light amount (light emission amount) on the light projecting side. This is to correct the change with time. With this configuration, the same effect can be obtained without correcting the offset or gain.

  A detection method according to the present invention (claim 14) includes a step of acquiring a physical quantity corresponding to a physical state of a detection target, a step of generating a detection value from the physical quantity according to a predetermined offset and gain, and a predetermined detection value. From the step of outputting the first level or the second level, which is a comparison result, to the outside as a detection result, comparing with a threshold value, storing a preset reference detection value, and a physical quantity acquired at an arbitrary time point And a step of correcting an offset or a gain so that a difference or ratio between the first detection value and the reference detection value when the comparison result is the first level is within a predetermined range. It is characterized by being. This detection method corresponds to the first configuration of the above-described detection switch, and the same operation and effect can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing an external appearance of a photoelectric switch body according to an embodiment of the present invention. This photoelectric switch is a kind of detection switch, and an optical fiber type photoelectric switch is shown as an example. The photoelectric switch body 1 is provided with light emitting side optical fibers and light receiving side optical fiber connecting portions (insertion ports) 11 and 12 on the front side of a thin rectangular parallelepiped case 10. A cable connection (not shown) for power supply and detection signal output is provided on the back side. The recess 13 on the lower surface of the photoelectric switch body 1 is an attachment portion for attaching the photoelectric switch body 1 to a DIN rail (standard rail for equipment attachment). Usually, a plurality of photoelectric switch bodies 1 are arranged side by side and attached to a DIN rail.

  On the upper surface of the photoelectric switch body 1, an indicator 15 using an 8-digit (4-digit × 2) 7-segment LED, and an output indicator for displaying the on / off state of the detection output in a binary manner by turning on / off the light. A (light emitting diode) 16 is provided. Further, push button switches 17 to 20 used for setting a threshold value for detection determination, switching between operation modes and display modes, and the like are provided. The push button switch 18 is a swing type up / down push button switch.

  FIG. 2 is a block diagram showing a circuit configuration of the photoelectric switch according to the embodiment of the present invention. In this example, the light projecting side optical fiber 3 to which the light projecting head 3a is attached and the light receiving side optical fiber 4 to which the light receiving head 4a is attached are connected to the photoelectric switch body 1 (the optical fiber connecting portions 11 and 12 thereof), A reflective photoelectric switch is configured. The photoelectric switch body 1 includes a light emitting element (light emitting diode) 22 connected to the base end side of the light projecting side optical fiber 3 and a light receiving element (photodiode) 24 connected to the base end side of the light receiving side optical fiber 4. Built in. The light emitting element 22 and the light projecting side optical fiber 3 constitute a light projecting part, and the light receiving side optical fiber 4 and the light receiving element 24 constitute a light receiving part.

  The light emitted from the light emitting element 22 propagates through the light projecting side optical fiber 3, and is projected from the tip (light projecting head 3a) as shown by a broken line LB in FIG. In the drawing, the light is projected toward the workpiece WK that is the detection target. However, in order to actually detect the presence or absence of the workpiece WK, the light LB is projected toward a predetermined detection target region. . When the work WK is present in the detection target region, part of the light reflected by the work WK is incident on the light receiving side optical fiber 4 from the light receiving head 4 a and propagates through the light receiving side optical fiber 4 to reach the light receiving element 24. . At this time, the amount of light received by the light receiving element 24 increases. When the workpiece WK does not exist in the detection target region, such reflected light does not reach the light receiving element 24, and an increase in the amount of light received by the light receiving element 24 is not detected.

  Therefore, if the detection value generated from the amount of light received by the light receiving element 24 is compared with a predetermined threshold value, the first level (low level) or the second level (high level) as the comparison result is the work WK. Obtained as a detection result corresponding to the presence or absence. In the following description, the comparison result becomes the first level (low level) when the work WK does not exist in the detection target region (off state), and the comparison result becomes the second level when the work WK exists (on state). (High level). When a reflective photoelectric switch is configured, a head unit in which the light projecting head 3a and the light receiving head 4a are integrated is used.

  Further, if the light projecting head 3a and the light receiving head 4a are arranged so as to face each other, a transmissive photoelectric switch can be configured. In this case, when the work WK blocks the optical path from the light projecting head 3a to the light receiving head 4a, the amount of light received by the light receiving element 24 is reduced. Therefore, the detection value generated from the amount of received light is set to a predetermined threshold value. If compared, a detection result corresponding to the presence / absence of the workpiece WK is obtained in the same manner as described above. In addition, there are various types of photoelectric switches. For example, in what is called an amplifier separation type, a light emitting element and a light receiving element are built in a head portion, and the head portion and the sensor amplifier are connected by an electric cable instead of an optical fiber. The present invention is applicable to detection switches including various types of photoelectric switches.

  In FIG. 2, the photoelectric switch body 1 includes a drive circuit 23 for the light emitting element 22 and a processing unit (microcomputer) 28 for controlling the drive circuit 23. Further, an amplifying circuit 25 for amplifying an electric signal corresponding to the amount of light received output from the light receiving element 24 and an A / D converter 26 for converting the output voltage of the amplifying circuit 25 into a digital value are incorporated in the photoelectric switch body 1. ing. The amplification circuit 25 amplifies an electrical signal corresponding to the amount of received light according to a predetermined gain and offset, and the gain and offset can be adjusted (corrected) by the processing unit 28.

  The digital value obtained from the A / D converter 26 is input to the processing unit 28 as a detection value. The processing unit 28 compares the input detection value with a predetermined threshold value, and outputs the first level (for example, L level) or the second level (for example, H level), which is the comparison result, to the outside as the detection result. . That is, a detection result that is a binary signal indicating the presence or absence of the workpiece WK is output from the output circuit 27 to the external device. For example, when a 12-bit A / D converter 26 is used, a detection value obtained from the A / D converter 26 is a digital value within a range of 0 to 4095 (decimal number).

  A display circuit 30 corresponding to the display 15 and the output indicator 16 and a pushbutton switch circuit 31 corresponding to the pushbutton switches 17 to 20 are also built in the photoelectric switch body 1, and the processing unit 28 also controls these. In FIG. 2, the flow of data related to the received light amount and the detected value among the input / output signals of the processing unit 28 is indicated by solid arrows, and other control signals are indicated by broken arrows.

  FIG. 3 is a top view of the photoelectric switch shown in FIG. The display 15 provided in the photoelectric switch body 1 is an 8-digit 7-segment display, so that a 4-digit first display unit 15a and a 4-digit second display unit 15b are arranged side by side. It is configured. For example, during the detection operation, the detection value is displayed in decimal on the first display unit 15a (lower 4 digits), and the threshold value (set value) is displayed in decimal on the second display unit 15b (upper 4 digits). Various usage forms are possible. Or you may display the gain or offset of the amplifier circuit 25 on the 1st display part 15a or the 2nd display part 15b. As will be described later, in the photoelectric switch of this embodiment, the offset or gain is automatically corrected in order to compensate for the change in the amount of received light due to deterioration with time. In this case, by displaying the offset or gain, the user can easily know the change in the received light amount due to the correction amount, that is, the deterioration with time.

  Next, a usage example of the push button switches 17 to 20 will be briefly described. Each push button switch is also used for a plurality of functions, and the following use examples relate to some of the functions. First, when setting a threshold value, a push button switch 17 (hereinafter referred to as a set SW) and a push button switch 18 (hereinafter referred to as an up / down SW) are used. For example, as shown in FIG. 2, the set SW 17 is pressed with the work WK disposed, and then the set SW 17 is pressed again with the work WK removed from the optical path LB. As a result, an intermediate value (for example, 2000) between a detection value (for example, 3000) corresponding to the amount of received light when the workpiece WK exists in the detection target area (for example, 3000) and a detection value (for example, 1000) corresponding to the amount of received light when the workpiece WK does not exist. Is automatically set as the threshold value. As described above, the set threshold value is displayed on the second display unit 15b (or the first display unit 15a) of the display unit 15 by four digits. In addition, the threshold value set as described above can be increased or decreased using the up / down SW 18.

  Next, the pushbutton switch 19 (hereinafter referred to as mode SW) and the up / down SW 18 are used for setting the operation mode. If the mode SW 19 is kept pressed for a certain time (for example, 2 seconds) or longer, the setting of the operation mode can be changed, and the operation mode can be sequentially selected using the up / down SW 18. At this time, the selected operation mode is displayed on the display 15 in a simplified alphabet. For example, as shown in FIG. 4, six types of operation modes of “Fine”, “Turbo”, “Super Turbo”, “Ultra Turbo”, “High Speed”, and “Super Fine” are reversed by pressing the up / down SW 18. It changes in both directions.

  The six types of operation modes have circuit conditions such as an appropriate light emission amount (drive current of the light emitting element 22) and sensitivity (amplification degree of the amplification circuit 25) according to the size and distance of the work WK (detection target). Is provided to optimize the. For example, the “fine” mode is optimized for applications in which the distance from the projection head 3a to the workpiece WK is about 100 mm. “Turbo” mode is optimized for about 200 mm, “Super Turbo” mode is about 300 mm, and “Ultra Turbo” is optimized for about 400 mm. The “high speed” mode is an operation mode in which the response speed is increased so that the workpiece WK crossing the optical path LB relatively quickly can be detected. In the “super fine” mode, the light emission amount or sensitivity (amplification factor) is further lowered than in the “fine” mode. Thereby, even when the distance from the light projecting head 3a to the work WK is further shortened than in the “fine” mode, the amplifier circuit 25 or the A / D converter 26 is hardly saturated.

  In addition to the above operation modes, differential mode that performs differential operation of detection value change and outputs rising or falling edge detection signal, from received light amount after delay time (settable) from rising or falling edge Various modes such as a timer mode for generating a detection value are provided. Moreover, the display mode by the display 15 is also provided with a plurality of modes including the display example described above. The mode switching can also be changed by combining the pressing order of the push button switches 17 to 20 and the pressing method (for example, pressing for 2 seconds or more, pressing twice, etc.).

  Next, a method for correcting a change in the amount of received light caused by a change with time in the photoelectric switch of this embodiment will be described. In general, a photoelectric switch has a tendency that the amount of received light decreases due to a change (deterioration) with time. The main factor is due to deterioration of the light emitting element 22, dirt on the light receiving side, etc. In some conventional photoelectric switches, the light emission amount of the light emitting element 22 is received by the monitor light receiving element so that the light emission amount becomes constant. In some cases, the drive current of the light emitting element 22 is feedback-controlled. Alternatively, as described in the description of the background art, there is a method in which a threshold value serving as a reference for outputting a detection result is changed and set in accordance with a decrease in the amount of received light.

  In the photoelectric switch of the present embodiment, the offset or gain of the amplifier circuit 25 or the light emission amount is corrected so that the detection value generated from the light reception amount when the work WK does not exist becomes a preset reference detection value. The amount of light received when the workpiece WK is present varies depending on conditions such as the type and state of the workpiece WK, but the amount of light received when the workpiece WK is not present, that is, the amount of light received by the background light is relatively stable. Therefore, correction is performed using the detection value generated from the received light amount when the workpiece WK does not exist as described above. Hereinafter, the description will be divided into several examples.

  In this embodiment, the offset of the amplifier circuit 25 is corrected using the detection value generated from the amount of received light when the work WK does not exist. The amount of received light corresponds to a physical quantity corresponding to the physical state (existence / non-existence) of the workpiece WK. Further, the detection value generated from the amount of received light when the workpiece WK does not exist corresponds to the first detection value when the detection result (comparison result) is the first level (off level).

  FIG. 5 is a functional block diagram showing the configuration of the first embodiment of the present invention. The light receiving element 24 corresponds to a physical quantity acquisition unit that acquires a physical quantity (amount of received light) corresponding to the physical state (presence / absence) of the detection target (work WK). The amplification circuit 25 and the A / D converter 26 correspond to a detection value generation unit that generates a detection value from the amount of received light (physical quantity) according to a predetermined offset and gain. The processing unit (microcomputer) 28 includes a comparison unit 41 that compares an input detection value with a predetermined threshold value, a reference detection value storage unit 42 that stores a preset reference detection value, and an arbitrary time point The correction part 43 which correct | amends the offset of the amplifier circuit 25 is included so that the 1st detection value produced | generated from the light reception amount corresponded to the off level acquired by (2) may become a reference | standard detection value.

  Further, a threshold value setting unit 44 for setting a threshold value, a threshold value storage unit 45 for storing the set threshold value, and a reference detection value acquisition instruction for instructing acquisition and storage of a reference detection value A unit 46 is included in the processing unit 28. Each of the units 41 to 46 included in the processing unit 28 includes an arithmetic processing unit built in the microcomputer, a program stored in advance in the ROM, and a RAM as a data memory. The same applies to the functional configuration inside the correction unit 43 described later.

  The threshold value setting unit 44 obtains the threshold value by the operation as described above and stores it in the threshold value storage unit 45. In the above-described operation example, an intermediate value between the detection value (first detection value) when the workpiece WK does not exist in the detection target region and the detection value (second detection value) when it exists is automatically set as the threshold value. It has been explained that the set threshold value can be increased or decreased using the up / down SW 18. In the photoelectric switch of this embodiment, the first detection value is corrected so as to become the reference detection value and is stable. On the other hand, the second detection value varies depending on conditions such as the type and state of the workpiece WK. Therefore, when multiple types of workpieces WK are mixed and flow on the transfer line and sequentially pass through the detection target area of the photoelectric switch, the threshold value is set closer to the first detection value than the intermediate value between the two. However, the possibility of erroneous determination is reduced, which is advantageous.

  The comparison unit 41 compares the detection value input from the A / D converter 26 constituting the detection value generation unit with the threshold value, and the comparison result is a first level (off level) or a second level. (ON level) is output as a detection result. The detection result is output to an external device via the output circuit 27. Further, as described with reference to FIGS. 1 and 2, display control is performed so that the output indicator 16 is turned off or turned on according to the off level or on level of the detection result.

  FIG. 6 is a block diagram showing an internal functional configuration of the correction unit 43. The correction of the offset of the amplifier circuit 25 by the correction unit 43 is performed so that the difference (error) between the first detection value and the reference detection value falls within a predetermined range so that the first detection value becomes the reference detection value. To be executed. The predetermined range here means a control error range centered on zero. Therefore, offset correction is performed so that the difference between the first detection value and the reference detection value approaches zero as much as possible. For this processing, the correction unit 43 includes a comparison calculation unit that calculates a difference between the reference detection value read from the reference detection value storage unit 42 and the first detection value input from the A / D converter 26. 431 is provided.

  For example, if it is assumed that the reference detection value is 1000 and the first detection value is 800, the difference 200 between them is output from the comparison calculation unit 431. The difference 200 is given to the correction execution unit 433 via the first specified range determination unit 432. The correction execution unit 433 performs control (correction) so that the difference becomes zero by instructing the amplifier circuit 25 to increase the offset corresponding to the difference 200.

  The first specified range determination unit 432 determines whether or not the difference between the first detection value output from the comparison calculation unit 431 and the reference detection value is within a first specified range (for example, 0 to 100). The difference is given to the correction execution unit 433 only when the specified range is exceeded. That is, when the difference between the first detection value and the reference detection value is within the first specified range, the offset correction as described above is not executed, and the offset correction is executed when the first specified range is exceeded. The Thereby, the processing load of the processing unit 28 is reduced. The first specified range determining unit 432 can be omitted.

  Further, a second specified range discriminating unit 434 is provided, which is within a second specified range (for example, 0 to 500) in which the difference between the first detected value and the reference detected value is wider than the first specified range. It is determined whether or not there is. If the difference exceeds the second specified range, an error signal is output, and the processing unit 28 performs error notification according to the error signal. As a specific example of error notification, it is possible to display an error “Err” on the first display unit 15 a (or the second display unit 15 b) of the display 15. An error notification by a buzzer or the like may be performed. This error notification notifies the user that the deterioration of the light emitting element 22 has progressed or that the correction of the offset as described above is impossible or difficult due to a failure or the like.

  In addition, a specified range setting unit 435 for setting the first specified range, the second specified range, or both specified ranges is provided. The user can input the first specified range, the second specified range, or both specified ranges using the display 15 and the push button switches 17 to 20 as described with reference to FIG. The specified range setting unit 435 sets the input first specified range or second specified range in the memory of the first specified range determining unit 432 or the second specified range determining unit 434. One or both of the second specified range determining unit 434 and the specified range setting unit 435 can be omitted in the same manner as the first specified range determining unit 432.

  Returning to FIG. 5, the reference detection value storage unit 42 in the photoelectric switch of this embodiment receives the first input from the A / D converter 26 at a predetermined time in accordance with an instruction from the reference detection value acquisition instruction unit 46. The detection value (detection value corresponding to the off level) is stored as a reference detection value. For example, the user instructs acquisition of the reference detection value using the display 15 and the pushbutton switches 17 to 20 or external input at the time of installation of the photoelectric switch or at a regular time (for example, when the equipment is started at the beginning of the week). can do. At this time, it is necessary to leave the workpiece WK in the detection target area. The reference detection value acquisition instruction unit 46 instructs the reference detection value storage unit 42 to acquire and store the reference detection value in accordance with an instruction by a user operation. Alternatively, the reference detection value may be automatically acquired and stored in an initial processing routine that is executed only once by the program of the processing unit 28 when the photoelectric switch is energized.

  Further, as indicated by a broken line block in FIG. 5, a reference detection value adjustment unit 47 that increases or decreases the reference detection value set as described above may be provided. Similar to the above-described threshold value increase / decrease change, the user can change the reference detection value increase / decrease using the display 15 and the up / down SW 18. The reference detection value adjustment unit 47 changes the reference detection value stored in the reference detection value storage unit 42 in accordance with the user's increase / decrease change operation. Alternatively, an appropriate reference detection value may be manually set by the user regardless of the operation of the reference detection value acquisition instruction unit 46 and the input from the A / D converter 26. Such manual setting is possible using the display 15 and pushbutton switches 17-20. Similarly, the delay time setting unit 48 shown by the broken line block in FIG. 5 enables setting of the acquisition timing (delay time) when generating the reference detection value or the first detection value, as will be described later. Is to do.

  FIG. 7 is a flowchart of processing executed by the processing unit 28 regarding offset correction. The operations described using the functional block diagrams of FIGS. 5 and 6 are shown as a flow of processing executed by the program of the processing unit 28. Briefly avoiding duplication as much as possible. In step # 101, the processing unit 28 acquires a detection value. If the acquired detection value is not the first detection value corresponding to the off level (first level) (No in step # 102), that is, if it is the second detection value corresponding to the on level (second level), step Processing after # 103 is skipped.

  If the acquired detection value is the first detection value (Yes in step # 102), the difference D between the reference detection value and the first detection value is calculated in step # 103. In the next step # 104, the difference D is compared with the second specified range. If the difference D exceeds the second specified range (Yes), error processing is executed in step # 105. When the difference D is within the second specified range (No), the difference D is compared with the first specified range at step # 106. When the difference D exceeds the first specified range (Yes), offset correction is executed in accordance with the difference D as described above in step # 107. If the difference D is within the first specified range (No), step # 107 is skipped and the process ends.

  FIG. 8 is a diagram illustrating the acquisition timing of the received light amount when generating the reference detection value or the first detection value. The waveform showing the change in the amount of received light (detection value) in this figure assumes a case where a plurality of types of workpieces WK are mixed and flow on the conveyance line at almost regular intervals and sequentially pass through the detection target area of the photoelectric switch. is doing. Therefore, although the amount of received light (detected value) changes in a substantially rectangular wave shape, a certain amount of time is required for the rise and fall, and the level is unstable during that time. Therefore, avoiding an unstable level immediately after the detection result (comparison result) is inverted from the second level to the first level, the reference detection value or the first detection value is obtained from the received light amount acquired after a predetermined delay time (t1). It is preferable to generate a value. This delay time (t1) is preferably manually settable by the user by the delay time setting unit 48 described above.

  Further, even after the delay time (t1), the received light amount (detected value) is not constant, and usually varies with a certain amplitude as illustrated in FIG. Therefore, for the reference detection value, an average of a plurality of values sampled in a certain period (t2) may be taken. The minimum value of the plurality of values may be used as the reference detection value. Alternatively, an average value of a plurality of minimum values detected during a certain period (t2) may be used as the reference detection value. The delay time (t2) is also preferably manually settable by the user. In FIG. 8, the threshold value is set closer to the first detection value (first received light amount) according to the above-described reason. Thereby, even if the level of the second detection value (second received light amount) varies depending on the type of the work WK, the possibility of erroneous determination is reduced.

  As described above, in the photoelectric switch of this embodiment, the first detection corresponding to the off level (first level) even when the received light amount, which is the physical quantity corresponding to the presence / absence of the work WK, is decreased due to the change (degradation) with time. The offset of the amplifier circuit 25 is corrected so that the value approaches a preset reference detection value. This reduces the possibility of erroneous determination.

  In addition, as a feature of the present embodiment, the detection switch generates correction execution timing from a signal corresponding to the presence / absence of a detection target instead of an external input, thereby realizing automatic correction of the detection switch. This eliminates the need to stop the conveyor for conveying the detection object and change the detection switch to the setting mode, or to give a correction execution command to the detection switch from an external device. The maintainability of the equipment where the switch is installed is improved.

  Next, an embodiment in which the gain of the amplifier circuit 25 is corrected using the first detection value generated from the amount of light received when the work WK does not exist will be described. The functional configuration of this embodiment can also be described using the block diagrams shown in FIGS. The present embodiment will be described focusing on differences from the configuration of the first embodiment.

  In the present embodiment, the correction unit 43 corrects the gain of the amplifier circuit 25 so that the first detection value generated from the received light amount corresponding to the off level acquired at an arbitrary time becomes the reference detection value. Precisely, it is executed so that the ratio between the first detection value and the reference detection value falls within a predetermined range. The predetermined range here means a control error range centered on 1. Therefore, the correction of the gain is executed so that the ratio between the first detection value and the reference detection value approaches 1 as much as possible.

  In this embodiment, the comparison calculation unit 431 in FIG. 6 calculates a ratio between the reference detection value read from the reference detection value storage unit 42 and the first detection value input from the A / D converter 26. For example, if it is assumed that the reference detection value is 1000 and the first detection value is 800, the ratio 1.25 of both is output from the comparison operation unit 431. The ratio 1.25 is given to the correction execution unit 433 via the first specified range determination unit 432. The correction execution unit 433 performs control (correction) so that the ratio becomes zero by instructing the amplification circuit 25 to increase the gain corresponding to the ratio 1.25. The basic operations of the first specified range discriminating unit 432 and the second specified range discriminating unit 434 are the same as those in the first embodiment, but the first specified range and the second specified range are defined not by the difference range but by the ratio range. The point is different. The same applies to the specified range set by the specified range setting unit 435.

  FIG. 9 is a flowchart of processing executed by the processing unit 28 regarding gain correction. The operation described along the above functional block diagram is shown as a flow of processing executed by the program of the processing unit 28. Briefly avoiding duplication as much as possible. In step # 201, the processing unit 28 acquires a detection value. If the acquired detection value is not the first detection value corresponding to the off level (first level) (No in step # 202), that is, if it is the second detection value corresponding to the on level (second level), step Processing after # 203 is skipped.

  When the acquired detection value is the first detection value (Yes in Step # 202), the ratio R between the reference detection value and the first detection value is calculated in Step # 203. In the next step # 204, the ratio R is compared with the second specified range. If the ratio R exceeds the second specified range (Yes), error processing is executed in step # 205. When the ratio R is within the second specified range (No), the ratio R is compared with the first specified range at step # 206. When the ratio R exceeds the first specified range (Yes), the gain is corrected in accordance with the ratio R as described above at step # 207. If the ratio R is within the first specified range (No), step # 207 is skipped and the process ends.

  As described above, in the photoelectric switch of the present embodiment, the first detection value corresponding to the first level is set in advance even when the received light amount, which is the physical amount corresponding to the presence or absence of the workpiece WK, is reduced due to the change (degradation) with time. The gain of the amplifier circuit 25 is corrected so as to approach the reference detection value. This reduces the possibility of erroneous determination.

  Next, an embodiment in which the light emission amount of the light emitting element 22 is corrected using the first detection value generated from the light reception amount when the workpiece WK does not exist will be described. This embodiment will be described focusing on the differences from the configuration of the first or second embodiment.

  FIG. 10 is a functional block diagram showing the configuration of the third embodiment of the present invention. In this embodiment, the control (correction) target of the correction unit 43 is the drive circuit 23 of the light emitting element 22. The drive circuit 23 can increase or decrease the light emission amount of the light emitting element 22 by increasing or decreasing the current supplied to the light emitting element 22. When the light emitting element 22 is pulse-driven, the average current supplied to the light emitting element 22 can be increased or decreased by increasing or decreasing the duty factor, and the light emission amount can be increased or decreased. Therefore, the correction unit 43 of the processing unit 28 can perform feedback control of the light emission amount of the light emitting element 22 through the drive circuit 23 so that the first detection value approaches the reference detection value.

  The processing executed by the processing unit 28 regarding the correction of the light emission amount is the same as the flowchart of the first or second embodiment illustrated in FIG. 7 or FIG. In step # 107 or step # 207, the light emission amount may be corrected instead of the offset or gain. In the photoelectric switch of the present embodiment, even when the amount of received light, which is a physical quantity corresponding to the presence or absence of the workpiece WK, decreases due to change (deterioration) with time, the first detection value corresponding to the first level becomes the preset reference detection value. The amount of light emission is corrected so as to approach. This reduces the possibility of erroneous determination.

  In addition, you may implement combining said Example 1, Example 2, and Example 3 suitably. For example, both the offset and gain of the amplifier circuit 25 may be corrected so that the first detection value corresponding to the first level approaches a preset reference detection value. Offset or gain correction and emission amount correction may be combined.

  Further, the configuration of Example 3 is an embodiment specific to the photoelectric switch, but the configurations of Examples 1 and 2 are not limited to the photoelectric switch, but a proximity switch using a magnetic sensor and a proximity switch using a capacitance sensor. The present invention can be applied to various detection switches. That is, a physical quantity corresponding to the physical state of the detection target is acquired, a detection value is generated from the physical quantity according to a predetermined offset and gain, and the detection value is compared with a predetermined threshold value to determine the first level or the second level. The present invention can be widely applied to detection switches that output level detection results.

  In the first and second embodiments, the detection value generation unit corrects the offset or gain of the amplifier circuit 25 to control the first detection value to approach the reference detection value. You may perform by the internal process by the program of the part 28. FIG. In other words, the processing unit 28 executes a process of adding a digital quantity corresponding to the offset to the digital value that is the output of the A / D converter, and multiplying the digital quantity corresponding to the gain, and adjusts one or both of the digital quantities. By doing so, the first detection value may be controlled to approach the reference detection value.

  Further, the correction processing as shown in the flowcharts of FIGS. 7 and 9 may be executed every control cycle, but every predetermined time (for example, 10 minutes) (precisely, the detected value is first around the predetermined time). It may be executed when it is level. In this case, as described above, it is preferable to omit the first specified range determination unit 432.

  In the description of each embodiment, the amount of light received by background light (the amount of light received when there is no detection target) is relatively stable. Therefore, the detection level (off level) at this time is set to the first level or the reference level. Treated as a detected value. However, in an application where the on level is more stable than the off level, it is desirable to treat the on level as the first level or the reference detection value.

It is a perspective view which shows the external appearance of the photoelectric switch main body which concerns on embodiment of this invention. It is a block diagram which shows the circuit structure of the photoelectric switch which concerns on embodiment of this invention. It is a top view of the photoelectric switch shown in FIG. It is a figure which shows the example of a display transition of an operation mode. It is a functional block diagram which shows the structure of Example 1 of this invention. It is a block diagram which shows the internal function structure of a correction | amendment part. It is a flowchart of the process which a process part performs regarding the correction | amendment of offset. It is a figure which shows the acquisition timing of the light reception amount at the time of producing | generating a reference | standard detection value and a 1st detection value. It is a flowchart of the process which a process part performs regarding correction | amendment of a gain. It is a functional block diagram which shows the structure of Example 3 of this invention.

Explanation of symbols

15 Display 22 Light emitting element 24 Light receiving element (physical quantity acquisition unit)
25 Amplifier circuit (detection value generator)
26 A / D converter (detection value generator)
28 processing unit 41 comparison unit 42 reference detection value storage unit 43 correction unit 44 threshold setting unit 45 threshold storage unit 46 reference detection value acquisition instruction unit 47 reference detection value adjustment unit 432 first specified range determination unit 434 second Specified range discriminating unit 435 Specified range setting unit WK Workpiece (detection target)

Claims (14)

A physical quantity acquisition unit for acquiring a physical quantity corresponding to the physical state of the detection target;
A detection value generation unit that generates a detection value from the physical quantity according to a predetermined offset and gain;
A comparison unit that compares the detection value with a predetermined threshold and outputs the first level or the second level as a comparison result to the outside as a detection result;
A reference detection value storage unit for storing a preset reference detection value;
A difference or ratio between the first detection value and the reference detection value when the comparison result is the first level, which is a detection value generated from the physical quantity acquired by the physical quantity acquisition unit at an arbitrary time point, is within a predetermined range. And a correction unit that corrects an offset or gain of the detection value generation unit so as to enter the detection switch. The reference detection value storage unit stores, as a reference detection value, a detection value generated from the physical quantity acquired by the physical quantity acquisition unit at a predetermined time and when the comparison result is the first level. The detection switch according to claim 1. The detection switch according to claim 2, further comprising a reference detection value acquisition instruction unit for instructing acquisition of the reference detection value. A first defined range discriminating unit that discriminates whether or not a difference or ratio between the first detected value and the reference detected value is within a predetermined first specified range, and the determination result is negative 4. The detection switch according to claim 1, wherein only correction of the offset or gain by the correction unit is executed. A second specified range determining unit that determines whether a difference or ratio between the first detected value and the reference detected value is within a second specified range that is wider than the first specified range; The detection switch according to claim 4, wherein an error notification is executed when the result is negative. 6. The detection switch according to claim 4, further comprising a specified range setting unit for setting the first specified range, the second specified range, or both specified ranges. The reference detection value or the first detection value is generated from a physical quantity acquired after a predetermined delay time from the time when the comparison result is inverted from the second level to the first level. The detection switch according to any one of 1 to 6. The detection switch according to claim 7, further comprising a delay time setting unit for setting the delay time. The detection according to any one of claims 1 to 8, further comprising a display that simultaneously displays any two of the detection value, the threshold value, and the gain or offset. switch. The detection switch according to any one of claims 1 to 9, further comprising a reference detection value adjustment unit for increasing or decreasing the reference detection value. The detection switch according to any one of claims 1 to 10, further comprising a threshold setting unit for setting the threshold. A light projecting unit including a light emitting element for projecting light toward the detection target region;
A light receiving unit including a light receiving element for receiving light from the detection target region and acquiring the amount of received light;
A detection value generation unit that generates a detection value from the amount of received light according to a predetermined offset and gain;
A comparison unit that compares the detection value with a predetermined threshold and outputs the first level or the second level as a comparison result to the outside as a detection result;
A reference detection value storage unit for storing a preset reference detection value;
The difference or ratio between the first detection value and the reference detection value when the comparison result is the first level is a detection value generated from the light reception amount acquired by the light reception amount acquisition unit at an arbitrary time point. And a correction unit that corrects an offset or gain of the detection value generation unit so as to fall within a predetermined range. A light projecting unit including a light emitting element with a variable light emission amount for projecting light toward a detection target region;
A light receiving unit including a light receiving element for receiving light from the detection target region and acquiring the amount of received light;
A comparison unit that compares a detection value corresponding to the amount of received light with a predetermined threshold value, and outputs a first level or a second level as a comparison result to the outside as a detection result;
A reference detection value storage unit for storing a preset reference detection value;
The difference or ratio between the first detection value and the reference detection value when the comparison result is the first level is a detection value generated from the light reception amount acquired by the light reception amount acquisition unit at an arbitrary time point. And a correction unit that corrects the light emission amount of the light emitting element so as to fall within a predetermined range. Obtaining a physical quantity corresponding to the physical state of the detection object;
Generating a detection value from the physical quantity according to a predetermined offset and gain;
Comparing the detection value with a predetermined threshold value, and outputting the first level or the second level as a comparison result to the outside as a detection result;
Storing a preset reference detection value;
The difference or ratio between the first detection value and the reference detection value, which is a detection value generated from the physical quantity acquired at an arbitrary time and the comparison result is the first level, falls within a predetermined range. And a step of correcting the offset or gain as described above.

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