Needle detector

Abstract

To provide a needle detector which can more appropriately detect metal foreign matters.SOLUTION: A needle detector inspects whether or not metal foreign matters are mixed in an inspection object, when the inspection object conveyed in a defined conveyance direction DR passes through specific space. The needle detector comprises: a permanent magnet 21 which generates a magnetic field applied to the specific space; a plurality of detection coils 22 which produce current according to change of the magnetic field; and a processing circuit 31 which detects the metal foreign matters, based on the change of the current generated in the detection coil 22. The processing circuit 31 executes: processing which takes in the current generated in the detection coil 22, and calculates a response value indicating a level of response of the detection coil 22 with respect to the metal foreign matter based on a value of the taken in current; processing which calculates a synthetic value by adding together the response values corresponding to the plurality of detection coils 22; and processing which detects the metal foreign matter by comparing the synthetic value with a threshold value of the response value.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a meter reading machine. [Background technology]

[0002] Conventionally, there exists a needle detector as described in, for example, Patent Document 1. The needle detector detects metallic foreign bodies mixed in the inspection object by conveying the inspection object on a conveyor belt and passing the inspection object through a detection head. The inspection object is a product such as a sewn product. The foreign body is, for example, a metallic foreign body such as a sewing needle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-189412 A Summary of the Invention [Problem to be solved by the invention]

[0004] Needle detectors, including the one disclosed in Patent Document 1, are required to detect metallic foreign bodies more appropriately. [Means for solving the problem]

[0005] The needle detector that solves the above problem is configured to inspect whether or not a metallic foreign object is present in an inspection object transported in a specified transport direction when the inspection object passes through a specific space. The needle detector includes a permanent magnet configured to generate a magnetic field to be applied to the specific space, a plurality of detection coils configured to generate a current corresponding to a change in the magnetic field, and a processing circuit configured to detect the metallic foreign object based on the change in the current generated in the detection coil. The processing circuit is configured to execute a process of taking in the current generated in the detection coil and calculating a reaction value indicating the degree of reaction of the detection coil to the metallic foreign object based on the value of the current taken in, a process of calculating a composite value by adding up the reaction values ​​corresponding to the plurality of detection coils, and a process of detecting the metallic foreign object through a comparison between the composite value and a reaction value threshold value.

[0006] According to this configuration, by combining the reaction values ​​corresponding to the respective detection coils, the difference in detection sensitivity according to the passing height of the metallic foreign object is suppressed, and therefore the processing circuit can appropriately detect the metallic foreign object regardless of the passing height of the metallic foreign object.

[0007] In the above-mentioned needle reading machine, the processing circuit may be configured to calculate the reaction value by performing an inversion process on the waveform of the current taken in from the detection coil. The inversion process is a process of inverting a negative region of the waveform of the current to a positive region.

[0008] According to this configuration, by combining the reaction values ​​of the detection coils calculated through the inversion process, it is possible to suppress the difference in detection sensitivity according to the passing height of the metallic foreign matter. The above-mentioned needle detector may have a display device configured to display a plurality of indicator regions corresponding to the plurality of detection coils. The detection coils may be arranged in a row at equal intervals in a direction perpendicular to the conveying direction. In this case, the processing circuit may be configured to light up or blink the indicator region corresponding to the detection coil that reacted to the metallic foreign object when the metallic foreign object is detected.

[0009] According to this configuration, an operator can visually check the indicator area to recognize the position of the metallic foreign object in the direction in which the multiple detection coils are arranged. The above-mentioned needle detector may have two sets of the permanent magnet and the plurality of detection coils. In this case, one set may be disposed on the upstream side in the conveying direction, and the other set may be disposed on the downstream side in the conveying direction.

[0010] According to this configuration, pairs of a permanent magnet and a plurality of the detection coils are provided at two locations, one on the upstream side and one on the downstream side in the conveying direction, which makes it possible to prevent metallic foreign matter from going undetected. Effect of the Invention

[0011] According to the needle detector of the present invention, metallic foreign matter can be detected more appropriately. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view of an embodiment of a needle detector. [Diagram 2] FIG. 2 is a perspective view showing an internal configuration of a detection head according to an embodiment. [Diagram 3] 5 is a schematic diagram showing a state in which a magnetic field is applied from a permanent magnet to a detection coil according to the embodiment; FIG. [Figure 4] 10 is a schematic diagram showing how a magnetic field applied to a detection coil from a permanent magnet changes with the approach of a metallic foreign object according to an embodiment; FIG. [Diagram 5]1A is a graph showing the change over time in the value of a current generated in a detection coil according to one embodiment, and FIG. 1B is a graph showing the change over time in a reaction value according to one embodiment. [Figure 6] FIG. 2 is a front view showing a screen of the display device according to the embodiment; [Figure 7] 1 is a graph showing the relationship between the position of a detection coil and a reaction value according to an embodiment. [Figure 8] FIG. 13 is a box plot showing the variation in reaction value when the passing height of a metallic foreign object according to a comparative example is changed. [Figure 9] 11 is a graph showing the relationship between the position of the detection coil and a composite value according to an embodiment. [Figure 10] FIG. 13 is a box plot showing the variation in composite value when the passing height of a metallic foreign object according to an embodiment is changed. [Figure 11] FIG. 13 is a box plot of reaction values ​​for seven patterns of different sizes and passing heights of metallic foreign matter according to a comparative example. [Figure 12] FIG. 11 is a box plot of reaction values ​​for seven patterns of different sizes and passing heights of metallic foreign matter according to an embodiment. [Figure 13] 13 is a graph showing the relationship between the position of a detection coil and a reaction value according to another embodiment. [Figure 14] FIG. 13 is a box plot of reaction values ​​for seven patterns of different sizes and passing heights of metallic foreign matter according to another embodiment. [Figure 15] FIG. 13 is a perspective view of a needle detector according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An embodiment of the needle detector will be described below. The needle detector is a device that inspects whether or not a metallic foreign object is present in an object to be inspected. The object to be inspected is, for example, a product such as a sewn product. The metallic foreign object is a magnetic body, for example, a sewing needle, a marking pin, or a broken needle.

[0014] <Overall composition> As shown in FIG. 1, the needle detector 10 has a base 11. The base 11 is, for example, a rectangular box that is installed on the installation surface of an inspection space in a factory. A first side frame 11A and a second side frame 11B are provided on the upper part of the base 11. The first side frame 11A and the second side frame 11B are hollow columnar bodies extending in the long side direction of the base 11. The first side frame 11A and the second side frame 11B are also arranged at an interval in the short side direction of the base 11.

[0015] The first side frame 11A has a display device 12. The display device 12 is, for example, a touch panel. The touch panel has a screen, and by touching the display on the screen, it is possible to input data or instruct the operation of the meter reading machine 10. The screen of the display device 12 is exposed on the upper surface of the first side frame 11A.

[0016] The needle detector 10 has a conveyor belt 13. The conveyor belt 13 is provided between the first side frame 11A and the second side frame 11B. The conveyor belt 13 is an endless belt-shaped member having a predetermined thickness, and extends along the first side frame 11A and the second side frame 11B. The conveyor belt 13 is stretched over a plurality of rollers (not shown). The rollers include a drive roller and a driven roller.

[0017] The drive roller is rotatably supported between a first end of the first side frame 11A and a first end of the second side frame 11B. The driven roller is rotatably supported between a second end of the first side frame 11A and a second end of the second side frame 11B. The second end is an end of the first side frame 11A and the second side frame 11B opposite to the first end.

[0018] The drive roller rotates, for example, by driving a motor provided inside the first side frame 11A or the second side frame 11B. The driven roller rotates by transmitting the rotational force of the drive roller via the conveyor belt 13. The conveyor belt 13 rotates in accordance with the rotation of the multiple rollers so as to convey the test object TG placed on the conveying surface in a conveying direction DR. The conveying surface is the surface of the conveyor belt 13 on which the test object TG is placed. The conveying direction DR is the traveling direction of the conveyor belt 13.

[0019] The needle detector 10 has a detection head 14. The detection head 14 is a part of the needle detector 10 for detecting metallic foreign matter. The detection head 14 is supported by the first side frame 11A and the second side frame 11B. The detection head 14 is disposed, for example, near the center of the long sides of the first side frame 11A and the second side frame 11B. The detection head 14 protrudes upward from the upper surfaces of the first side frame 11A and the second side frame 11B.

[0020] The detection head 14 has an upper head 14A, a lower head 14B, and two connecting frames 14C. The upper head 14A and the lower head 14B are box-shaped bodies each having a rectangular cross-sectional shape, and extend in a direction perpendicular to the traveling direction of the conveyor belt 13. The two connecting frames 14C extend in a direction perpendicular to the conveyor surface of the conveyor belt 13, and connect both ends of the upper head 14A and both ends of the lower head 14B. The upper heads 14A face each other at a predetermined interval in a direction perpendicular to the conveyor surface of the conveyor belt 13. The lower head 14B is inserted inside the conveyor belt 13 in a non-contact state.

[0021] The inspection object TG transported by the transport belt 13 passes between the upper head 14A and the transport surface of the transport belt 13 in a non-contact state. <Internal configuration of detection head 14> Next, the internal configuration of the detection head 14 will be described.

[0022] As shown in Fig. 2, the detection head 14 has a permanent magnet 21. The permanent magnet 21 is housed inside the lower head 14B. The permanent magnet 21 is a plate-shaped member having a rectangular cross-sectional shape, and extends in the long side direction of the lower head 14B. The length of the permanent magnet 21 in the long side direction is the same as or slightly longer than the width of the conveyor belt 13. The width is the length in the direction perpendicular to the conveying direction DR of the conveyor belt 13.

[0023] The detection head 14 has a plurality of detection coils 22. The number of detection coils 22 is, for example, 10. The detection coils 22 are accommodated inside the upper head 14A. The detection coils 22 are arranged in a row at equal intervals in the long side direction of the upper head 14A. The detection coils 22 are arranged corresponding to the space surrounded by the upper head 14A, the lower head 14B, and the two connecting frames 14C. The axial direction of the detection coils 22 is the up-down direction. The distance between the upper surface of the permanent magnet 21 and the lower end of each detection coil 22 is equal.

[0024] 3, the permanent magnet 21 is a two-pole magnet, and an N pole and an S pole are magnetized in the short side direction of the permanent magnet 21. The short side direction is a direction along the conveying direction DR of the conveyor belt 13. A magnetic field H directed from the N pole to the S pole is applied to the detection coil 22 by the permanent magnet 21.

[0025] As shown in Fig. 4, when a metallic foreign matter FR is present in the inspection object TG, the metallic foreign matter FR is transported in the transport direction DR together with the inspection object TG by the transport belt 13. When the metallic foreign matter FR approaches the magnetic field H as it is transported, the magnetic field H changes. When the magnetic field H changes, a current Iw is generated in the detection coil 22 by electromagnetic induction. The current is an induced current and is very weak. It is possible to detect the metallic foreign matter FR based on the current Iw generated in the detection coil 22.

[0026] <Processing circuit 31> 2, the meter reading device 10 has a processing circuit 31. The processing circuit 31 is, for example, a PLC (Programmable Logic Controller) and includes any one of the following three configurations A1, A2, and A3.

[0027] A1. One or more processors that operate according to a computer program, which is software. The processor includes a CPU (Central Processing Unit) and a memory. A2. One or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), that perform at least some of the processing.

[0028] A3. A hardware circuit that combines two configurations A1 and A2. The memory is a computer-readable medium that stores a program that describes processes or instructions for the computer. In this embodiment, the computer is a CPU. The memory includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The CPU executes various processes by executing the programs stored in the memory at a set calculation cycle.

[0029] The processing circuit 31 controls the driving of the motor 32. The processing circuit 31 controls the rotation speed and the rotation direction of the conveyor belt 13 by controlling the driving of the motor 32. The processing circuit 31 controls the display of the display device 12, and controls the operation of the meter reading machine 10 based on instructions input by operating the screen of the display device 12.

[0030] Both ends of the detection coil 22 are connected to the processing circuit 31. Although Fig. 2 shows a state in which both ends of one detection coil 22 are connected to the processing circuit 31, in reality, both ends of all detection coils 22 are connected to the processing circuit 31. The processing circuit 31 takes in the current Iw generated in each detection coil 22, and detects a metallic foreign matter FR based on the value of the taken-in current Iw.

[0031] As shown in Fig. 5(a), the processing circuit 31 amplifies the current Iw received from each detection coil 22. As shown in Fig. 5(b), the processing circuit 31 performs an inversion process on the waveform of the amplified current Iw to obtain a reaction value. The inversion process is a process of inverting the negative region of the waveform of the current Iw to a positive region. The reaction value is a value indicating the degree of reaction of each detection coil 22 to the metallic foreign matter FR, and is used to determine the presence or absence of the metallic foreign matter FR.

[0032] The processing circuit 31 compares the reaction value corresponding to each detection coil 22 with a determined reaction value threshold value Rth. The reaction value threshold value Rth is a standard for determining the presence or absence of a metallic foreign matter FR, and is set according to the detection sensitivity of the needle detector 10. The detection sensitivity can be set, for example, in 10 stages through the screen operation of the display device 12. The higher the detection sensitivity, the smaller the metallic foreign matter FR can be detected. The detection sensitivity of the needle detector 10 is set based on an iron ball equivalent value. The iron ball equivalent value is a value obtained by converting the size of the metallic foreign matter FR into the diameter of an iron ball.

[0033] When all the reaction values ​​corresponding to the detection coils 22 are less than the reaction value threshold value Rth, the processing circuit 31 determines that the inspection object TG does not contain a metallic foreign matter FR having a size equal to or greater than the detection sensitivity setting value. When at least one of the reaction values ​​corresponding to the detection coils 22 is equal to or greater than the reaction value threshold value Rth, the processing circuit 31 determines that the inspection object TG contains a metallic foreign matter FR. When it is determined that the inspection object TG contains a metallic foreign matter FR, the processing circuit 31 executes a predetermined process. The process includes, for example, a process of stopping the movement of the conveyor belt 13, a process of moving the conveyor belt 13 in the direction opposite to the conveying direction DR to return the inspection object TG to the end of the conveyor belt 13, and a process of notifying that the inspection object TG contains a metallic foreign matter FR.

[0034] The processing circuit 31 individually processes and manages the value of the current Iw generated in each detection coil 22. For example, the processing circuit 31 displays the detection position of the metallic foreign matter FR on the screen of the display device 12 based on the position of the detection coil 22 where the reaction value is equal to or greater than the reaction value threshold value Rth. The detection position is a position in the width direction of the conveyor belt 13. The width direction is a direction perpendicular to the conveying direction DR.

[0035] As shown in Fig. 6, the screen of the display device 12 is, for example, rectangular. A detection position display section 41 is displayed on the screen. The detection position display section 41 includes ten indicator areas 41A-41J. The indicator areas 41A-41J are arranged in a row in the short side direction of the screen. The indicator areas 41A-41J correspond to the ten areas when the conveying surface of the conveyor belt 13 is divided into ten areas in a direction perpendicular to the conveying direction DR. Each area corresponds to a detection coil 22. The direction perpendicular to the conveying direction DR is the width direction of the conveyor belt 13.

[0036] The processing circuit 31 lights or blinks the indicator areas 41A-41J corresponding to the detection coils 22 whose reaction values ​​are equal to or greater than the reaction value threshold value Rth. The lighting or blinking of at least one of the indicator areas 41A-41J indicates at which position in the width direction of the conveyor belt 13 the reaction to the metallic foreign matter FR is strong. The operator can visually recognize the position of the metallic foreign matter FR in the width direction of the conveyor belt 13.

[0037] In addition to the detection position display section 41, the screen also displays a sensitivity display section 42, a number of inspections display section 43, a speed display section 44, and a mode display section 45. The sensitivity display section 42 displays the currently set detection sensitivity of the needle detector 10. The number of inspections display section 43 displays the total number of inspections, the number of good products, the number of defective products, and the number of round trips of the inspection target TG. The speed display section 44 displays the transport speed of the inspection target TG. The mode display section 45 displays the operation mode of the needle detector 10.

[0038] Also displayed on the screen are a menu button 46, a stop button 47, a count reset button 48, and a return distance setting button 49. These buttons are virtual buttons displayed on the screen. The menu button 46 is operated when performing various settings of the meter detector 10. When the menu button 46 is touched, various menu items or various setting screens are displayed. The stop button 47 is operated when stopping the operation of the meter detector 10. The count reset button 48 is operated when resetting the count value displayed on the inspection number display unit 43. The return distance setting button 49 displays the currently set return distance. The return distance is the distance by which the conveyor belt 13 is moved in the opposite direction to the conveying direction DR in order to return the inspection target TG to the end of the conveyor belt 13 when a metal foreign matter FR is detected.

[0039] <Difference in detection sensitivity of needle detector 10> Next, a description will be given of the detection sensitivity difference of the needle detector 10. The detection sensitivity difference is "unevenness" in the detection sensitivity.

[0040] As shown in FIG. 7, the processing circuit 31 monitors the reaction values ​​of 10 channels corresponding to the 10 detection coils 22. A channel number from "1" to "10" is assigned to each detection coil 22. The detection coils 22 are arranged in the order of their channel numbers. In FIG. 7, the reaction values ​​of the 10 channels are indicated by the shading of the characteristic lines. As an example, the reaction value indicates the maximum reaction value corresponding to each detection coil 22 when a metal foreign matter FR of a predetermined size passes through the detection head 14 at a constant passing height. The passing height is the distance from the conveying surface of the conveyor belt 13 to the metal foreign matter FR.

[0041] However, the needle detector 10 configured in this manner has the following concerns: If the reaction values ​​corresponding to the detection coils 22 are managed separately, there is a risk that a large difference in detection sensitivity will occur depending on the passing height of the metallic foreign matter FR.

[0042] FIG. 8 shows the variation in the reaction value when the diameter of the iron ball and the passing height are changed. More specifically, FIG. 8 shows an example of the variation in the reaction value when the iron ball is passed through the detection head 14 a predetermined number of times for each passing height. The predetermined number is, for example, 125 times. The size of the metal foreign matter FR is converted into the diameter of the iron ball that provides the most stable detection operation. The diameter of the iron ball is an iron ball conversion value obtained by converting the size of the metal foreign matter FR into the diameter of the iron ball. The detection sensitivity of the needle detector 10 is set based on the iron ball conversion value. In FIG. 8, the degree of variation in the reaction value is represented by a rectangular "box" and a "whiskers" represented by straight lines. The difference in the passing height is indicated by the shading of the "box" and the "whiskers".

[0043] As shown in Figure 8, when the diameter of the iron ball is "φ0.8 mm", as the passing height of the iron ball is increased in increments of 10 mm from "0 mm" to "120 mm", the reaction value gradually decreases with the increase in passing height. After the passing height reaches a certain height, the reaction value gradually increases with the increase in passing height. In addition, after the passing height reaches a certain height, the degree of variation in the reaction value increases with the increase in passing height.

[0044] Note that an increase in the degree of variation in the reaction value means that the difference between the maximum and minimum reaction values ​​increases, and an increase in the passing height means that the metallic foreign matter FR approaches the detection coil 22.

[0045] When the diameter of the iron ball is φ1.0mm, as the passing height of the iron ball is increased by 10mm from 0mm to 120mm, the reaction value gradually decreases with the increase in passing height. After the passing height reaches a certain height, the reaction value gradually increases with the increase in passing height. Basically, the reaction value when the diameter of the iron ball is φ1.0mm is greater than the reaction value when the diameter of the iron ball is φ0.8mm.

[0046] However, depending on the degree of variation in the reaction values, the range of reaction values ​​when the diameter of the iron ball is "φ0.8 mm" may overlap with the range of reaction values ​​when the diameter of the iron ball is "φ1.0 mm". The range is determined by the maximum and minimum reaction values. Even when the diameter of the iron ball is "φ1.0 mm", the degree of variation in the reaction values ​​increases as the passing height increases after the passing height reaches a certain height.

[0047] If the diameter of the iron ball is φ1.2mm, when the passing height of the iron ball is increased by 10mm from 0mm to 120mm, the reaction value gradually decreases with the increase in passing height. After the passing height reaches a certain height, the reaction value gradually increases with the increase in passing height. Basically, the reaction value when the diameter of the iron ball is φ1.2mm is greater than the reaction value when the diameter of the iron ball is φ1.0mm.

[0048] However, depending on the degree of variation in the reaction values, the range of reaction values ​​when the diameter of the iron ball is "φ1.0 mm" may overlap with the range of reaction values ​​when the diameter of the iron ball is "φ1.2 mm". Even when the diameter of the iron ball is "φ1.2 mm", the degree of variation in the reaction values ​​increases as the passing height increases after the passing height reaches a certain height.

[0049] Therefore, the processing circuit 31 may determine that the inspection target TG contains a metal foreign matter FR due to the variation in the reaction value. For example, even if the detection sensitivity of the needle detector 10 is set to the iron ball equivalent value of "φ0.8 mm", the processing circuit 31 may erroneously detect a metal equivalent to the iron ball equivalent value of "φ1.0 mm". Also, even if the detection sensitivity of the needle detector 10 is set to the iron ball equivalent value of "φ1.0 mm", the processing circuit 31 may erroneously detect a metal equivalent to the iron ball equivalent value of "φ0.8 mm" or a metal equivalent to the iron ball equivalent value of "φ1.2 mm". When the inspection target TG is a sewn product, the metal is a metal accessory of the sewn product, such as a button, a fastener, or a hook.

[0050] Therefore, in this embodiment, in order to suppress erroneous detection of the metallic foreign matter FR, the processing circuit 31 has the following configuration. <Reaction value synthesis process> The processing circuit 31 synthesizes the reaction values ​​for the 10 channels corresponding to the 10 detection coils 22. Specifically, the processing circuit 31 calculates a synthetic value Rc by adding up the reaction values ​​corresponding to the respective detection coils 22. The processing circuit 31 compares the synthetic value Rc with a reaction value threshold value Rth to determine whether or not a metal foreign matter FR is present in the inspection object TG. The synthetic value Rc is expressed by the following formula (1).

[0051] Rc=R1+R2+R3+R4+R5+R6+R7+R8+R9+R10…(1) Here, "R1 to R10" are reaction values ​​for 10 channels corresponding to the 10 detection coils 22.

[0052] For example, the waveform of the response value when the response values ​​of the 10 channels shown in FIG. 7 are synthesized is as follows. As shown in FIG. 9, the waveform of the composite value Rc is a waveform obtained by connecting the peak values ​​of the waveforms of the response values ​​for the 10 channels shown in FIG. 7. The waveform corresponds to the position of each detection coil 22. The position is the position of the detection coil 22 in the width direction of the conveyor belt 13, and is also the passing position of the metallic foreign matter FR in the width direction of the conveyor belt 13. The processing circuit 31 monitors the composite value Rc. The processing circuit 31 can recognize the maximum value of the response value corresponding to each detection coil 22 even during the calculation of the composite value Rc. For this reason, it is also possible to display the detection position of the metallic foreign matter FR on the screen of the display device 12.

[0053] FIG. 10 shows an example of the variation in the composite value Rc when the diameter of the iron ball and the passing height are changed. More specifically, FIG. 10 shows an example of the variation in the composite value Rc when the iron ball is passed over the detection head 14 a predetermined number of times for each passing height. The predetermined number is, for example, 125 times. However, for the sake of convenience of explanation, the composite value Rc shown in FIG. 10 is a value calculated by omitting the response value when the passing height is "110 mm" and the response value when the passing height is "120 mm". The composite value Rc is a value indicating the degree of reaction of each detection coil 22 to the metal foreign matter FR. The composite value Rc is also a response value.

[0054] As shown in Fig. 10, when the diameter of the iron ball is "φ0.8 mm", when the passing height of the iron ball is increased by 10 mm from "0 mm" to "100 mm", the composite value Rc increases or decreases slightly but is almost constant regardless of the passing height. Also, the degree of variation in the composite value Rc is smaller than when the reaction value corresponding to each detection coil 22 is monitored individually regardless of the passing height (see Fig. 8).

[0055] When the diameter of the iron ball is "φ1.0 mm", even when the passing height of the iron ball is increased in increments of 10 mm from "0 mm" to "100 mm", the composite value Rc increases or decreases slightly but remains almost constant regardless of the passing height. Furthermore, the degree of variation in the composite value Rc is smaller than when the reaction values ​​corresponding to each detection coil 22 are monitored individually, regardless of the passing height (see FIG. 8). For this reason, the range of the composite value Rc when the diameter of the iron ball is "φ1.0 mm" does not overlap with the range of the composite value Rc when the diameter of the iron ball is "φ0.8 mm".

[0056] When the diameter of the iron ball is "φ1.2 mm", as the passing height of the iron ball is increased in 10 mm increments from "0 mm" to "100 mm", the composite value Rc gradually decreases as the passing height increases. After the passing height reaches a certain height, the composite value Rc gradually increases as the passing height increases. However, the degree of variation in the composite value Rc is smaller than when the reaction values ​​corresponding to each detection coil 22 are monitored individually, regardless of the passing height (see FIG. 8). For this reason, the range of composite values ​​when the diameter of the iron ball is "φ1.2 mm" does not overlap with the range of composite values ​​Rc when the diameter of the iron ball is "φ0.8 mm".

[0057] In this way, by combining the reaction values ​​corresponding to each detection coil 22, the range of the composite value Rc for a specific iron ball size is prevented from overlapping with the range of the composite value Rc for other iron ball sizes. That is, the detection sensitivity difference is suppressed. Therefore, the processing circuit 31 is prevented from erroneously determining that the inspection target TG contains a metal foreign object FR. For example, even though the detection sensitivity of the needle detector 10 is set to the iron ball equivalent value "φ0.8 mm", the processing circuit 31 is prevented from erroneously detecting a metal equivalent to the iron ball equivalent value "φ1.0 mm". Also, even though the detection sensitivity of the needle detector 10 is set to the iron ball equivalent value "φ1.0 mm", the processing circuit 31 is prevented from erroneously detecting a metal equivalent to the iron ball equivalent value "φ0.8 mm" or a metal equivalent to the iron ball equivalent value "φ1.2 mm". Therefore, the processing circuit 31 can appropriately detect a metal foreign object FR of a desired size regardless of the passing height of the metal foreign object. The passing performance of accessories is also improved.

[0058] It can be seen from Fig. 11 and Fig. 12 that the reaction value at the conveying height near the upper head 14A is particularly suppressed. Fig. 11 shows reaction values ​​of seven patterns B1 to B7 with different diameters of the iron ball and different passing heights when the reaction values ​​corresponding to each detection coil 22 are monitored individually. For convenience of explanation, the operation mode of the needle detector 10 that monitors the reaction values ​​corresponding to each detection coil 22 individually is called the reference mode. Fig. 12 shows the composite value Rc of seven patterns B1 to B7 with different diameters of the iron ball and different passing heights when the composite value Rc is monitored. For convenience of explanation, the operation mode of the needle detector 10 that monitors the composite value Rc is called the composite coil mode. The conveying height near the upper head 14A is, for example, 90 mm to 120 mm.

[0059] B1. Diameter of iron ball: φ0.8mm Passing height: 20mm B2. Diameter of iron ball: φ0.8mm Passing height: 90mm B3. Diameter of iron ball: φ0.8mm Passing height: 120mm B4. Diameter of iron ball: φ1.0mm Passing height: 20mm B5. Diameter of iron ball: φ1.0mm Passing height: 90mm B6. Diameter of iron ball: φ1.0mm Passing height: 120mm B7. Diameter of iron ball: φ1.2mm Passing height: 20mm As shown in Fig. 11, when the operation mode of the meter reading device 10 is the reference mode, for example, the maximum value of the response value of pattern B3 is slightly more than "180". In contrast, as shown in Fig. 12, when the operation mode of the meter reading device 10 is the composite coil mode, for example, the maximum value of the composite value Rc, which is the response value of pattern B3, is "100". In other words, by adopting the composite coil mode as the operation mode of the meter reading device 10, the maximum value of the response value of pattern B3 can be reduced from "180" to "100".

[0060] For the remaining patterns B2, B5, and B6, whose conveying height is near the upper head 14A, the maximum response value (see FIG. 12) when the operation mode of the needle detector 10 is the composite coil mode is significantly reduced compared to the maximum response value Rc (see FIG. 11) when the operation mode of the needle detector 10 is the reference mode.

[0061] In addition, in patterns B2, B3, B5, and B6 where the conveying height is near the upper head 14A, the range of the reaction value when the operation mode of the needle detector 10 is the composite coil mode (see FIG. 12) is significantly narrower than the range of the composite value Rc, which is the reaction value when the operation mode of the needle detector 10 is the reference mode (see FIG. 11). In other words, by adopting the composite coil mode as the operation mode of the needle detector 10, the range of the reaction value of patterns B2, B3, B5, and B6 can be significantly narrowed.

[0062] <Effects of the embodiment> This embodiment provides the following advantages. (1) The needle detector inspects whether or not a metallic foreign object FR is present in the inspection object TG when the inspection object TG, which is transported in a predetermined transport direction DR, passes through a specific space. The specific space is a space surrounded by an upper head 14A, a lower head 14B, and two connecting frames 14C. The needle detector 10 has a permanent magnet 21, a plurality of detection coils 22, and a processing circuit 31. The permanent magnet 21 generates a magnetic field that is applied to the specific space. The detection coil 22 generates a current Iw according to a change in the magnetic field. The processing circuit 31 detects the metallic foreign object FR based on the change in the current generated in the detection coil 22.

[0063] The processing circuit 31 executes a process of taking in the current Iw generated in the detection coil 22 and calculating a reaction value indicating the degree of reaction of the detection coil 22 to the metallic foreign matter FR based on the value of the current Iw taken in. The processing circuit 31 executes a process of calculating a composite value Rc by adding up the reaction values ​​corresponding to the multiple detection coils 22. The processing circuit 31 executes a process of detecting the metallic foreign matter FR by comparing the composite value Rc with a reaction value threshold value Rth.

[0064] According to this configuration, the difference in detection sensitivity according to the passing height of the metallic foreign matter FR is suppressed by combining the reaction values ​​corresponding to the detection coils 22. Therefore, the processing circuit 31 can appropriately detect the metallic foreign matter FR regardless of the passing height of the metallic foreign matter FR.

[0065] (2) The processing circuit 31 calculates a reaction value by performing an inversion process on the waveform of the current Iw received from the detection coil 22. The inversion process is a process of inverting the negative region of the waveform of the current Iw to positive. With this configuration, the reaction values ​​of the detection coils 22 calculated through the inversion process are combined to reduce the difference in detection sensitivity according to the passing height of the metallic foreign matter FR.

[0066] (3) The needle detector 10 has a display device 12 configured to display a plurality of indicator areas 41A-41J corresponding to the plurality of detection coils 22. The detection coils 22 are arranged in a row at equal intervals in a direction perpendicular to the conveyance direction DR. When a metallic foreign matter FR is detected, the processing circuit 31 lights up or blinks the indicator areas 41A-41J corresponding to the detection coils 22 that have reacted to the metallic foreign matter FR. With this configuration, an operator can visually check the indicator areas 41A-41J to recognize the position of the metallic foreign matter FR in the direction in which the detection coils 22 are arranged.

[0067] (4) The needle detector 10 has two sets of a permanent magnet 21 and a plurality of detection coils 22. One set is disposed on the upstream side of the conveying direction DR, and the other set is disposed on the downstream side of the conveying direction DR. According to this configuration, the sets of the permanent magnet 21 and the plurality of detection coils 22 are provided at two locations, one on the upstream side and one on the downstream side of the conveying direction. This makes it possible to suppress the metal foreign matter FR from being missed when detected.

[0068] <Other embodiments> This embodiment may be modified as follows. The meter reading device 10 may have an intermediate coil mode as an operation mode.

[0069] As shown in FIG. 13, the processing circuit 31 calculates nine virtual reaction values ​​based on the reaction values ​​of ten channels corresponding to the ten detection coils 22 shown in FIG. 7 above. The processing circuit 31 calculates one virtual reaction value using two reaction values ​​corresponding to two adjacent detection coils 22. Each detection coil 22 is arranged in the order of channel number. For example, a virtual reaction value obtained from the reaction value corresponding to the detection coil 22 of channel number "1" and the reaction value corresponding to the detection coil 22 of channel number "2" complements the valley between the reaction value corresponding to the detection coil 22 of channel number "1" and the reaction value corresponding to the detection coil 22 of channel number "2". When the number of detection coils 22 is ten, a total of nine virtual reaction values ​​are calculated. The processing circuit 31 monitors a total of 19 reaction values.

[0070] FIG. 14 shows the reaction values ​​of the seven patterns B1 to B7, which have different diameters and passing heights of the iron ball, when a total of 19 reaction values ​​are monitored individually. For example, consider the reaction value of pattern B4. The range of reaction values ​​of pattern B4 shown in FIG. 14 is narrower than the range of reaction values ​​of pattern B4 shown in FIG. 11. This is because the interval between two reaction values ​​corresponding to two adjacent detection coils 22 is supplemented by a virtual reaction value. Incidentally, FIG. 11 shows the reaction values ​​of the seven patterns B1 to B7, which have different diameters and passing heights of the iron ball, when a total of 10 reaction values ​​corresponding to each detection coil 22 are monitored individually.

[0071] Therefore, by adopting the intermediate coil mode, the difference in detection sensitivity in the width direction of the conveyor belt 13 is suppressed compared to the case of adopting the basic mode. This improves the detection capability of the needle detector 10 for detecting metal foreign matter FR. Depending on the product specifications, the operation mode of the needle detector 10 may be switched between the composite coil mode and the intermediate coil mode by operating the display device 12.

[0072] As shown in Fig. 15, the needle detector 10 may have two detection heads 14. The detection heads 14 are disposed on the upstream side and downstream side of the conveying direction DR. The two detection heads 14 are disposed, for example, obliquely with respect to the conveying direction DR. The two detection heads 14 are inclined in opposite directions with respect to the conveying direction DR.

[0073] The detection head 14 has the following characteristics. That is, when a metallic foreign object FR such as a sewing needle enters the detection head 14 parallel to the extension direction of the detection head 14, the detection sensitivity decreases. Therefore, even if the metallic foreign object FR passes through the detection head 14, the metallic foreign object FR may not be detected. In this regard, when the two detection heads 14 are installed at different angles, for example, even if the metallic foreign object FR enters parallel to the upstream detection head 14, it does not enter parallel to the downstream detection head 14. Therefore, even if the upstream detection head 14 cannot detect the metallic foreign object FR, the downstream detection head 14 can detect the metallic foreign object FR. Therefore, it is possible to suppress the metallic foreign object FR from being overlooked. In addition, it is possible to appropriately detect the metallic foreign object FR.

[0074] Depending on the product specifications, the processing circuit 31 may not perform the inversion process of inverting the negative region of the waveform of the current Iw to positive. In this case, the value of the current Iw taken in from each detection coil 22 becomes the reaction value of each detection coil 22. The processing circuit 31 calculates the composite value Rc by adding up the reaction values ​​of each detection coil 22.

[0075] The number of the detection coils 22 is not limited to 10. The number of the detection coils 22 may be more or less than 10. The number of the detection coils 22 is set appropriately depending on, for example, the size of the meter reading device 10.

[0076] The shape of the permanent magnet 21 is not limited to a plate shape. The permanent magnet 21 does not have to be a single member. The permanent magnet 21 may have any shape or configuration as long as it can apply a magnetic field H to the detection coil 22. For example, the permanent magnet 21 may have a first magnet group and a second magnet group. The first magnet group and the second magnet group each have a plurality of columnar magnets arranged in a row in a direction perpendicular to the conveying direction DR of the conveyor belt 13. The columnar magnets are two-pole magnets having a rectangular cross-sectional shape, and are magnetized with N and S poles in the vertical direction. However, the magnetic poles of the columnar magnets constituting the first magnet group and the magnetic poles of the columnar magnets constituting the second magnet group are opposite to each other. For example, the columnar magnets constituting the first magnet group are arranged so that the N poles face upward, while the columnar magnets constituting the second magnet group are arranged so that the S poles face upward. The first magnet group and the second permanent magnet group are spaced apart by a predetermined distance in the conveying direction DR of the conveyor belt 13. Even in this manner, the magnetic field H can be applied to the detection coil 22.

[0077] <Other technical ideas> Next, the technical ideas that can be understood from the above-described embodiment will be additionally described below. The meter reading machine has an intermediate coil mode as an operating mode, and the operation mode of the meter reading machine can be switched between the composite coil mode and the intermediate coil mode by operating the display device. [Explanation of symbols]

[0078] 10...Meter detector 12...Display device 21...Permanent magnet 22…Detection coil 31... Processing circuit 41A~41J…Indicator area DR: Transport direction FR…Metal foreign matter TG: Test subject

Claims

1. A needle detector configured to inspect whether a metal foreign object is present in an inspection object when the inspection object is conveyed in a predetermined conveying direction and passes through a specific space, a permanent magnet configured to generate a magnetic field that is applied to the particular space; a plurality of detection coils configured to generate a current in response to changes in the magnetic field; and a processing circuit configured to detect the metallic foreign object based on a change in the current in the detection coil. The processing circuit acquires the current generated in the detection coil, and calculates a reaction value indicating the degree of reaction of the detection coil to the metallic foreign object based on the value of the acquired current; A process of calculating a composite value by adding up the reaction values ​​corresponding to the plurality of detection coils; and detecting the metallic foreign object through a comparison of the composite value with a reaction value threshold.

2. The processing circuit is configured to calculate the reaction value by performing an inversion process on the waveform of the current captured from the detection coil; 2. The needle detector according to claim 1, wherein the inversion process is a process of inverting a negative region of the waveform of the current to a positive region.

3. a display configured to display a plurality of indicator regions corresponding to a plurality of said detection coils; The detection coils are arranged in a row at equal intervals in a direction perpendicular to the conveying direction, 3. The needle detector according to claim 1, wherein the processing circuit is configured to light up or blink the indicator area corresponding to the detection coil that reacts to the metallic foreign object when the metallic foreign object is detected.

4. The magnet includes two sets of the permanent magnet and the detection coils, 3. The needle detector according to claim 1, wherein one pair is disposed on the upstream side in the conveying direction, and the other pair is disposed on the downstream side in the conveying direction.

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