Needle detector

Abstract

When an inspection target (TG) being conveyed in a prescribed conveying direction (DR) passes through a specific space, a needle detector (10) inspects whether a metallic foreign body is mixed into the inspection target. The needle detector comprises: a permanent magnet (21) that generates a magnetic field to be applied to the specific space; a plurality of detection coils (22) that each generate a current corresponding to a change in the magnetic field; and a processing circuit (31) that detects the metallic foreign body on the basis of changes in the currents generated in the detection coils. The processing circuit executes: processing for capturing the currents generated in the detection coils and calculating reaction values indicating the degree of reaction of the detection coils with respect to the metallic foreign body on the basis of the values of the captured currents; processing for calculating a combined value by adding the reaction values corresponding to the plurality of detection coils; and processing for detecting the metallic foreign body by comparing the combined value with a reaction value threshold.

Description

meter reading machine

[0001] The present disclosure relates to a meter reader.

[0002] Conventionally, there have been needle detectors, such as that described in Patent Document 1. The needle detector detects metallic foreign matter mixed into the inspection object by transporting the inspection object on a conveyor belt and passing it through a detection head. The inspection object is a product such as a sewn product. The foreign matter is, for example, a metallic foreign matter such as a sewing needle.

[0003] JP 2012-189412 A

[0004] Needle detectors, including the one disclosed in Patent Document 1, are required to detect metallic foreign matter more appropriately.

[0005] A needle detector according to one aspect of the present disclosure is configured to inspect whether a metal foreign object is present in an inspection object transported in a predetermined transport direction as 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, multiple detection coils configured to generate currents in response to changes in the magnetic field, and a processing circuit configured to detect the metal foreign object based on changes in the currents generated in the detection coils. The processing circuit is configured to perform the following processes: take in the currents generated in the detection coils and calculate a reaction value indicating the degree of reaction of the detection coils to the metal foreign object based on the value of the current taken in; calculate a composite value by adding up the reaction values ​​corresponding to the multiple detection coils; and detect the metal foreign object by comparing the composite value with a reaction value threshold.

[0006] FIG. 1 is a perspective view of an embodiment of a needle detector. FIG. 2 is a perspective view showing the internal configuration of the detection head of FIG. 1. FIG. 3 is a schematic diagram showing how a magnetic field is applied from the permanent magnet of FIG. 2 to the detection coil of FIG. 2. FIG. 4 is a schematic diagram showing how the magnetic field applied from the permanent magnet of FIG. 2 to the detection coil of FIG. 2 changes as a metallic foreign object approaches. FIGS. 5A and 5B are diagrams explaining the processing of the processing circuit of FIG. 2. The graph of FIG. 5A shows the time change in the value of the current generated in the detection coil, and the graph of FIG. 5B shows the time change in the reaction value. FIG. 6 is a front view showing the screen of the display device of FIG. 2. FIG. 7 is a graph showing the relationship between the position of the detection coil of FIG. 2 and the reaction value. FIG. 8 is a box-and-whisker plot showing the variation in the reaction value when the passing height of a metallic foreign object is changed according to a comparative example. FIG. 9 is a graph showing the relationship between the position of the detection coil of FIG. 2 and the composite value. FIG. 10 is a box-and-whisker plot showing the variation in the composite value when the passing height of a metallic foreign object is changed according to one embodiment. Fig. 11 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. Fig. 12 is a box plot of reaction values ​​for seven patterns of different sizes and passing heights of metallic foreign matter according to one embodiment. Fig. 13 is a graph showing the relationship between the position of the detection coil and reaction value according to another embodiment. Fig. 14 is a box plot of reaction values ​​for seven patterns of different sizes and passing heights of metallic foreign matter according to another embodiment. Fig. 15 is a perspective view of a needle detector according to another embodiment.

[0007] A needle detector according to one embodiment will be described. The needle detector is a device that inspects whether or not a metal 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 metal foreign object is a magnetic material, such as a sewing needle, a safety pin, or a broken needle.

[0008] <Overall Configuration> 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 that extend in the long side direction of the base 11. Furthermore, the first side frame 11A and the second side frame 11B are arranged with an interval between them in the short side direction of the base 11.

[0009] 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 and instruct the operation of the meter reading device 10. The screen of the display device 12 is exposed on the top surface of the first side frame 11A. The display device 12 is both an output device and an input device.

[0010] 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.

[0011] 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 or the second side frame 11B opposite the first end.

[0012] 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 inspection object TG placed on the conveyor surface in a conveying direction DR. The conveying surface is the surface of the conveyor belt 13 on which the inspection object TG is placed. The conveying direction DR is the direction in which the conveyor belt 13 travels.

[0013] The needle detector 10 has a detection head 14. The detection head 14 is a part of the needle detector 10 that detects 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 top surfaces of the first side frame 11A and the second side frame 11B.

[0014] 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 each box-shaped with a rectangular cross section and extend in a direction perpendicular to the direction of travel of the conveyor belt 13. The two connecting frames 14C extend in a direction perpendicular to the conveying surface of the conveyor belt 13 and connect both ends of the upper head 14A to both ends of the lower head 14B. The upper heads 14A face each other at a predetermined distance in a direction perpendicular to the conveying surface of the conveyor belt 13. The lower head 14B is inserted inside the conveyor belt 13 in a non-contact manner.

[0015] The inspection object TG transported by the transport belt 13 passes in a non-contact state between the upper head 14A and the transport surface of the transport belt 13. <Internal Configuration of the Detection Head 14> Next, the internal configuration of the detection head 14 will be described.

[0016] 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 with a rectangular cross section, 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.

[0017] The detection head 14 has multiple detection coils 22. The number of detection coils 22 is, for example, 10. The detection coils 22 are housed inside the upper head 14A. The detection coils 22 are arranged in a row at equal intervals along the long side 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 vertical direction. The distance between the top surface of the permanent magnet 21 and the lower end of each detection coil 22 is equal.

[0018] 3, the permanent magnet 21 is a two-pole magnet, with a north pole and a south pole magnetized in the direction of the short side of the permanent magnet 21. The short side direction is the direction along the conveying direction DR of the conveyor belt 13. A magnetic field H directed from the north pole to the south pole is applied to the detection coil 22 by the permanent magnet 21.

[0019] As shown in Figure 4, if 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. As 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 therefore weak. It is possible to detect the metallic foreign matter FR based on the current Iw generated in the detection coil 22.

[0020] <Processing Circuit 31> In Fig. 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 one of the following three configurations A1, A2, and A3.

[0021] A1. One or more processors that operate according to a computer program, which is software. The processor includes a CPU (Central Processing Unit) and memory. A2. One or more dedicated hardware circuits, such as an application-specific integrated circuit (ASIC), that execute at least some of the various processes.

[0022] A3: A hardware circuit that combines the 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 RAM (Random Access Memory) and ROM (Read Only Memory). The CPU executes various processes by running the programs stored in the memory at a predetermined calculation cycle.

[0023] The processing circuit 31 controls the driving of the motor 32. The processing circuit 31 controls the rotation speed and rotation direction of the conveyor belt 13 by controlling the driving of the motor 32. The processing circuit 31 controls the display on the display device 12, and also controls the operation of the needle reading machine 10 based on instructions input by operating the screen of the display device 12.

[0024] 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 receives the current Iw generated in each detection coil 22, and detects a metallic foreign matter FR based on the value of the received current Iw.

[0025] As shown in Fig. 5A, the processing circuit 31 amplifies the current Iw received from each detection coil 22. As shown in Fig. 5B, the processing circuit 31 performs an inversion process on the waveform of the amplified current Iw to determine a response value. The inversion process inverts the negative region of the waveform of the current Iw to a positive region. The response value indicates the degree of response of each detection coil 22 to a metallic foreign matter FR and is used to determine the presence or absence of a metallic foreign matter FR.

[0026] The processing circuit 31 compares the reaction value corresponding to each detection coil 22 with a predetermined reaction value threshold Rth. The reaction value threshold 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 in, for example, 10 stages through screen operations on the display device 12. The higher the detection sensitivity, the smaller the metallic foreign matter FR that 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.

[0027] When the reaction values ​​corresponding to all the detection coils 22 are all less than the reaction value threshold 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. When at least one of the reaction values ​​corresponding to all the detection coils 22 is equal to or greater than the reaction value threshold Rth, the processing circuit 31 determines that the inspection object TG contains a metallic foreign matter FR. When the processing circuit 31 determines that the inspection object TG contains a metallic foreign matter FR, it 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 the inspection object TG that a metallic foreign matter FR has been contained.

[0028] The processing circuit 31 individually processes and manages the value of the current Iw generated in each of the multiple detection coils 22. The processing circuit 31 displays the detected position of the metallic foreign matter FR on the screen of the display device 12, for example, 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 conveyance direction DR.

[0029] 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 to 41J. These indicator areas 41A to 41J correspond to the ten areas when the conveying surface of the conveyor belt 13, which is arranged in a row along the short side of the screen, is divided into ten areas in a direction perpendicular to the conveying direction DR. Each of the ten areas corresponds to one detection coil 22. The direction perpendicular to the conveying direction DR is the width direction of the conveyor belt 13.

[0030] The processing circuit 31 lights or flashes the indicator areas 41A-41J corresponding to the detection coils 22 whose reaction values ​​are equal to or greater than the reaction value threshold Rth. The lighting or flashing of at least one of the indicator areas 41A-41J indicates the position in the width direction of the conveyor belt 13 where 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.

[0031] 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 detection sensitivity of the needle detector 10 that is currently set. 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.

[0032] 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 making various settings for the needle 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 needle detector 10. The count reset button 48 is operated when resetting the count value displayed in 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 direction opposite 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.

[0033] <Detection Sensitivity Difference of the Meter 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.

[0034] As shown in Fig. 7, the processing circuit 31 monitors response values ​​for 10 channels corresponding to the 10 detection coils 22. The 10 detection coils 22 are assigned channel numbers from "1" to "10." The detection coils 22 are arranged in channel number order. In Fig. 7, the response values ​​for the 10 channels are indicated by the shading of the characteristic lines. As an example, the response value indicates the maximum response 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.

[0035] However, the needle detector 10 configured in this manner has the following concerns: When the reaction values ​​corresponding to the plurality of detection coils 22 are managed separately, there is a risk that a large difference in detection sensitivity may occur depending on the passing height of the metallic foreign matter FR.

[0036] FIG. 8 shows the variation in the response 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 response 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 iron ball diameter is an iron ball equivalent 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 equivalent value. In FIG. 8, the degree of variation in the response value is represented by a rectangular "box" and straight "whiskers." Differences in passing height are indicated by the shading of the "box" and "whiskers."

[0037] 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 10 mm increments from "0 mm" to "120 mm", the reaction value gradually decreases as the passing height increases. After the passing height reaches a certain height, the reaction value gradually increases as the passing height increases. Furthermore, after the passing height reaches a certain height, the degree of variation in the reaction value increases as the passing height increases.

[0038] Note that an increase in the degree of variation in the reaction value means an increase in the difference between the maximum and minimum reaction values, and an increase in the passing height means that the metallic foreign matter FR is approaching the detection coil 22.

[0039] When the diameter of the iron ball is "φ1.0 mm", as the passing height of the iron ball is increased in 10 mm increments from "0 mm" to "120 mm", the reaction value gradually decreases as the passing height increases. After the passing height reaches a certain height, the reaction value gradually increases as the passing height increases. Basically, the reaction value when the diameter of the iron ball is "φ1.0 mm" is greater than the reaction value when the diameter of the iron ball is "φ0.8 mm".

[0040] 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 values ​​of the 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.

[0041] 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 "120 mm", the reaction value gradually decreases as the passing height increases. After the passing height reaches a certain height, the reaction value gradually increases as the passing height increases. Basically, the reaction value when the diameter of the iron ball is "φ1.2 mm" is greater than the reaction value when the diameter of the iron ball is "φ1.0 mm".

[0042] 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.

[0043] Therefore, due to variations in the reaction value, the processing circuit 31 may erroneously determine that a metal foreign matter FR is present in the inspection target TG. For example, even if the detection sensitivity of the needle detector 10 is set to an iron ball equivalent value of "φ0.8 mm," there is a risk of erroneously detecting a metal equivalent to an iron ball equivalent value of "φ1.0 mm." Furthermore, even if the detection sensitivity of the needle detector 10 is set to an iron ball equivalent value of "φ1.0 mm," there is a risk of erroneously detecting a metal equivalent to an iron ball equivalent value of "φ0.8 mm" or a metal equivalent to an iron ball equivalent value of "φ1.2 mm." If the inspection target TG is a sewn product, the metal is a metal accessory of the sewn product, such as a button, zipper, or hook.

[0044] Therefore, in this embodiment, the following configuration is adopted for the processing circuit 31 in order to suppress erroneous detection of metallic foreign matter FR. <Reaction Value Combination Processing> The processing circuit 31 combines the reaction values ​​for 10 channels corresponding to the 10 detection coils 22. Specifically, the processing circuit 31 calculates a composite value Rc by adding up the reaction values ​​corresponding to all of the detection coils 22. The processing circuit 31 compares the composite value Rc with a reaction value threshold value Rth to determine whether or not a metallic foreign matter FR is present in the inspection object TG. The composite value Rc is expressed by the following equation (1):

[0045] Rc=R1+R2+R3+R4+R5+R6+R7+R8+R9+R10 (1) where "R1 to R10" are response values ​​for 10 channels corresponding to the 10 detection coils 22.

[0046] For example, the waveform of the response value when the response values ​​for the 10 channels shown in FIG. 7 are combined is as follows. As shown in FIG. 9, the waveform of the combined value Rc is a waveform that connects the peak values ​​of the response value waveforms 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 combined value Rc. The processing circuit 31 can recognize the maximum value of the response value corresponding to each detection coil 22 even while calculating the combined value Rc. Therefore, it is possible to display the detection position of the metallic foreign matter FR on the screen of the display device 12.

[0047] 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, the composite value Rc shown in FIG. 10 is a value calculated by excluding 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 that indicates the degree of response of all detection coils 22 to the metallic foreign object FR. The composite value Rc is also a response value.

[0048] As shown in Figure 10, when the diameter of the iron ball is "φ0.8 mm" and the passing height of the iron ball is increased in 10 mm increments from "0 mm" to "100 mm," the composite value Rc remains almost constant regardless of the passing height, although there are some fluctuations. Furthermore, the degree of variation in the composite value Rc is smaller than when the reaction values ​​corresponding to the multiple detection coils 22 are monitored individually, regardless of the passing height (see Figure 8).

[0049] When the diameter of the iron ball is "φ1.0 mm," the composite value Rc remains almost constant regardless of the passing height, even when the passing height of the iron ball is increased in 10 mm increments from "0 mm" to "100 mm," although there are some fluctuations. Furthermore, the degree of variation in the composite value Rc is smaller than when the reaction values ​​corresponding to multiple detection coils 22 are monitored individually, regardless of the passing height (see Figure 8). Therefore, 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."

[0050] 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 multiple detection coils 22 are monitored individually, regardless of the passing height (see Figure 8). Therefore, the range of the composite value when the diameter of the iron ball is "φ1.2 mm" does not overlap with the range of the composite value Rc when the diameter of the iron ball is "φ0.8 mm."

[0051] In this way, by combining the response values ​​corresponding to multiple detection coils 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. In other words, the difference in detection sensitivity is reduced. This also reduces the possibility that the processing circuit 31 will erroneously determine that the inspection target TG contains a metallic foreign object FR. For example, even if the detection sensitivity of the needle detector 10 is set to an iron ball equivalent value of "φ0.8 mm," the processing circuit 31 will be prevented from erroneously detecting a metal object with an iron ball equivalent value of "φ1.0 mm." Furthermore, even if the detection sensitivity of the needle detector 10 is set to an iron ball equivalent value of "φ1.0 mm," the processing circuit 31 will be prevented from erroneously detecting a metal object with an iron ball equivalent value of "φ0.8 mm" or an iron ball equivalent value of "φ1.2 mm." Therefore, the processing circuit 31 can properly detect a metallic foreign object FR of the desired size regardless of the passing height of the metallic foreign object. Accessory passing performance is also improved.

[0052] 11 and 12 show that the response value at the transport height near the upper head 14A is particularly suppressed. FIG. 11 shows seven patterns B1 to B7 of response values ​​where the diameter of the iron ball and the passing height are different when the response values ​​corresponding to the multiple detection coils 22 are individually monitored. For convenience of explanation, the operating mode of the needle detector 10 that individually monitors the response values ​​corresponding to the multiple detection coils 22 is referred to as the reference mode. FIG. 12 shows the composite value Rc of seven patterns B1 to B7 where the diameter of the iron ball and the passing height are different when the composite value Rc is monitored. For convenience of explanation, the operating mode of the needle detector 10 that monitors the composite value Rc is referred to as the composite coil mode. The transport height near the upper head 14A is, for example, 90 mm to 120 mm.

[0053] B1. Iron ball diameter: φ0.8 mm Passing height: 20 mm B2. Iron ball diameter: φ0.8 mm Passing height: 90 mm B3. Iron ball diameter: φ0.8 mm Passing height: 120 mm B4. Iron ball diameter: φ1.0 mm Passing height: 20 mm B5. Iron ball diameter: φ1.0 mm Passing height: 90 mm B6. Iron ball diameter: φ1.0 mm Passing height: 120 mm B7. Iron ball diameter: φ1.2 mm Passing height: 20 mm As shown in Figure 11, when the operation mode of the needle detector 10 is the reference mode, for example, the maximum value of the response value of pattern B3 is slightly over "180". On the other hand, as shown in Figure 12, when the operation mode of the needle detector 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". That is, 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".

[0054] For the remaining patterns B2, B5, and B6, whose conveying height is near the upper head 14A, the maximum value of the reaction value when the operation mode of the needle detector 10 is the composite coil mode (see Figure 12) is significantly reduced compared to the maximum value of the composite value Rc, which is the reaction value when the operation mode of the needle detector 10 is the reference mode (see Figure 11).

[0055] In addition, in patterns B2, B3, B5, and B6 where the conveying height is near the upper head 14A, the range of the response 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 (see FIG. 11), which is the response value when the operation mode of the needle detector 10 is the reference mode. In other words, by adopting the composite coil mode as the operation mode of the needle detector 10, the range of the response value of patterns B2, B3, B5, and B6 can be significantly narrowed.

[0056] <Effects of the embodiment> This embodiment has the following effects. (1) The needle detector inspects whether or not a metallic foreign matter 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 the upper head 14A, the lower head 14B, and the two connecting frames 14C. The needle detector 10 has a permanent magnet 21, multiple 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 in response to changes in the magnetic field. The processing circuit 31 detects the metallic foreign matter FR based on changes in the current generated in the detection coil 22.

[0057] 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.

[0058] This configuration reduces the difference in detection sensitivity depending on the passing height of the metallic foreign matter FR by combining the reaction values ​​corresponding to the multiple detection coils 22. As a result, the processing circuit 31 can appropriately detect the metallic foreign matter FR regardless of the passing height of the metallic foreign matter FR.

[0059] (2) The processing circuit 31 calculates the response value by performing an inversion process on the waveform of the current Iw taken in from the detection coil 22. The inversion process inverts the negative region of the waveform of the current Iw to a positive region. With this configuration, by combining the response values ​​of the multiple detection coils 22 calculated through the inversion process, it is possible to reduce the difference in detection sensitivity depending on the passing height of the metallic foreign object FR.

[0060] (3) The needle detector 10 has a display device 12 configured to display multiple indicator areas 41A-41J corresponding to the multiple detection coils 22. The multiple 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 flashes the indicator areas 41A-41J corresponding to the detection coil 22 that 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 multiple detection coils 22 are arranged.

[0061] (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 a permanent magnet 21 and a 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 prevent metallic foreign matter FR from being missed when it is detected.

[0062] Other Embodiments This embodiment may be modified as follows: The needle detector 10 may have an intermediate coil mode as an operation mode.

[0063] As shown in FIG. 13 , the processing circuit 31 calculates nine virtual response values ​​based on the response values ​​for the ten channels corresponding to the ten detection coils 22 shown in FIG. 7 . The processing circuit 31 calculates one virtual response value using two response values ​​corresponding to two adjacent detection coils 22. The detection coils 22 are arranged in order of channel number. For example, a virtual response value calculated from the response value corresponding to the detection coil 22 with channel number "1" and the response value corresponding to the detection coil 22 with channel number "2" complements the valley between the response value corresponding to the detection coil 22 with channel number "1" and the response value corresponding to the detection coil 22 with channel number "2." If there are ten detection coils 22, virtual response values ​​for a total of nine channels are calculated. The processing circuit 31 monitors a total of 19 response values.

[0064] Figure 14 shows the response values ​​for seven patterns B1 to B7, each with different diameters and passing heights of the iron ball, when a total of 19 response values ​​are individually monitored. Consider, for example, the response values ​​for pattern B4. The range of response values ​​for pattern B4 shown in Figure 14 is narrower than the range of response values ​​for pattern B4 shown in Figure 11. This is because the gap between two response values ​​corresponding to two adjacent detection coils 22 is supplemented by a virtual response value. Incidentally, Figure 11 also shows the response values ​​for seven patterns B1 to B7, each with different diameters and passing heights of the iron ball, when a total of 10 response values ​​corresponding to 10 detection coils 22 are individually monitored.

[0065] 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 when the basic mode is adopted, thereby improving the detection capability of the needle detector 10 for detecting metallic 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.

[0066] As shown in Fig. 15, the needle detector 10 may have two detection heads 14. The detection heads 14 are arranged on the upstream side and downstream side of the conveying direction DR. Furthermore, the two detection heads 14 are arranged, 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.

[0067] The detection head 14 has the following characteristics. Specifically, when a metallic foreign object FR, such as a sewing needle, enters the detection head 14 parallel to the direction in which the detection head 14 extends, detection sensitivity decreases. As a result, there is a risk that the metallic foreign object FR will not be detected even if it passes through the detection head 14. In this regard, if 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 will 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 it. This makes it possible to prevent metallic foreign objects FR from being missed during detection. Furthermore, it is possible to properly detect the metallic foreign object FR.

[0068] 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 the detection coils 22.

[0069] The number of detection coils 22 is not limited to 10. The number of detection coils 22 may be more or less than 10. The number of detection coils 22 is set appropriately depending on, for example, the size of the meter reading device 10.

[0070] The shape of the permanent magnet 21 is not limited to a plate shape. Furthermore, the permanent magnet 21 does not have to be a single component. The permanent magnet 21 may have any suitable 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 include a first magnet group and a second magnet group. Each of the first magnet group and the second magnet group includes a plurality of cylindrical magnets arranged in a row in a direction perpendicular to the conveying direction DR of the conveyor belt 13. The cylindrical magnets are two-pole magnets with a rectangular cross section, and are magnetized with north and south poles in the vertical direction. However, the magnetic poles of the cylindrical magnets constituting the first magnet group and the second magnet group are opposite in orientation. For example, the cylindrical magnets constituting the first magnet group are arranged with their north poles facing upward, while the cylindrical magnets constituting the second magnet group are arranged with their south poles facing 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. In this manner, the magnetic field H can be applied to the detection coil 22.

Claims

1. A needle detector configured to inspect whether a test object transported in a prescribed transport direction contains metallic foreign matter as the test object passes through a specific space, the needle detector comprising: 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 matter based on the change in the current generated in the detection coil, the processing circuit being configured to execute the following processes: 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 matter based on the value of the current taken in; calculating a composite value by adding up the reaction values ​​corresponding to the plurality of detection coils; and detecting the metallic foreign matter through comparison of the composite value with a reaction value threshold.

2. The needle detector according to claim 1, wherein the processing circuit is 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 being a process of inverting the negative area of ​​the waveform of the current to a positive area.

3. A needle detector as described in claim 1 or claim 2, further comprising a display device configured to display a plurality of indicator areas respectively corresponding to a plurality of said detection coils, said plurality of detection coils being arranged in a row at equal intervals in a direction perpendicular to said conveying direction, and said processing circuit being configured to, when said metallic foreign object is detected, light up or blink said indicator area corresponding to said detection coil which has reacted to said metallic foreign object.

4. A needle detector as claimed in claim 1 or 2, comprising two sets of the permanent magnet and a plurality of the detection coils, one set being arranged on the upstream side of the conveying direction and the other set being arranged on the downstream side of the conveying direction.

5. A meter reading machine as described in claim 1 or claim 2, further comprising an input device configured to instruct the operation of the meter reading machine, the meter reading machine having a composite coil mode and an intermediate coil mode as operating modes, the composite coil mode being an operating mode of the meter reading machine that monitors the composite value, and the intermediate coil mode being an operating mode of the meter reading machine that monitors the reaction values ​​corresponding to a plurality of the detection coils and a virtual reaction value calculated based on two reaction values ​​corresponding to two adjacent detection coils among the plurality of the detection coils, and the processing circuit being configured to switch the operating mode of the meter reading machine between the composite coil mode and the intermediate coil mode in response to operation of the input device.

Images