Patent Publication Number: US-2023159278-A1

Title: Device and method for detecting vertical tear in conveyor belt

Description:
TECHNICAL FIELD 
     The present invention relates to a device and method for detecting a vertical tear in a conveyor belt and particularly relates to a detection device and method that allow accurate detection of generation of a vertical tear in a conveyor belt while having high versatility at low cost. 
     BACKGROUND ART 
     A conveyor belt that runs hung around a conveyor device transports various conveyed objects to conveying destinations. Since various conveyed objects are fed into the conveyor belt, a crack (so-called vertical tear) extending in a longitudinal direction of the conveyor belt may be generated due to the conveyed objects or the like. Various devices that detect such a vertical tear in the conveyor belt have been proposed. 
     Conventionally, for example, loop coils embedded in the conveyor belt and a detection device disposed near the conveyor belt are used to detect a vertical tear generated in the conveyor belt (see Patent Document 1). A transmitter of the detection device emits high frequency waves to form a high frequency magnetic field, in which an induced current flows through the loop coils. Induced electromotive force is generated by the induced current in a reception unit of the detection device. As a result, whether a damage of the loop coils passing the placement position of the detection device is present is determined based on whether induced electromotive force is generated in the reception unit, and in a case where the loop coils are damaged, it can be determined that a vertical tear has been generated. 
     The loop coils are special products (exclusive parts) and are expensive because they are not general-purpose parts. The detection device that emits high frequency waves and detects induced electromotive force is also expensive. In addition, since the loop coils are expensive, it is difficult to sufficiently reduce an embedding pitch with respect to the conveyor belt, which is disadvantageous in accurately detecting generation of a vertical tear. Accordingly, there is room for improvement in accurately detecting whether a vertical tear has been generated in the conveyor belt while providing high versatility at low cost. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP 2016-204070 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a device and method for detecting a vertical tear in a conveyor belt which allow accurate detection of whether a vertical tear has been generated in a conveyor belt while having high versatility at low cost. 
     Solution to Problem 
     In order to achieve the aforementioned object, a detection device for a vertical tear in a conveyor belt, according to an aspect of the present invention, includes an embedded body embedded in the conveyor belt, a detector configured to wirelessly communicate with the embedded body without making contact with the conveyor belt, and a calculation unit connected to the detector. In the detection device, the embedded body includes an IC tag being passive, one side antenna unit connected to the IC tag, a coaxial cable including one end portion connected to the one side antenna unit, and the other side antenna unit connected to the other end portion of the coaxial cable; the IC tag and the one side antenna unit, and the other side antenna unit are disposed with an interval in a width direction of the conveyor belt and the coaxial cable extends in the width direction of the conveyor belt; and a radio wave is emitted from the detector toward the other side antenna unit, the calculation unit determines whether the detector has received a radio wave emitted, in response to the emitted radio wave, from the IC tag through the coaxial cable and the other side antenna unit, and then whether a vertical tear has been generated in the conveyor belt in a region where the coaxial cable is embedded is detected based on the determination result. 
     A method for detecting a vertical tear in a conveyor belt, according to an aspect of the present invention, uses an embedded body embedded in the conveyor belt, a detector configured to wirelessly communicate with the embedded body without making contact with the conveyor belt, and a calculation unit connected to the detector. In the method, the embedded body includes one side antenna unit connected to one end portion of a coaxial cable, the other side antenna unit connected to the other end portion of the coaxial cable, and an IC tag that is passive and connected to the one side antenna unit; and the one side antenna unit and the IC tag, and the other side antenna unit are disposed with an interval in a width direction of the conveyor belt and the coaxial cable extends in the width direction of the conveyor belt. The detection method includes: emitting a radio wave from the detector toward the other side antenna unit; determining by the calculation unit whether the detector has received a radio wave emitted, in response to the emitted radio wave, from the IC tag through the coaxial cable and the other side antenna unit; and detecting based on the determination result whether a vertical tear has been generated in the conveyor belt in a region where the coaxial cable is embedded. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, the embedded body has a simple structure including the passive IC tag, the coaxial cable, and the one side antenna unit and the other side antenna unit connected to both end portions of the coaxial cable. Accordingly, the embedded body can be formed of general-purpose parts, which is advantageous to reduce costs. Further, the detector may have specifications that allow wireless communication with the embedded body and thus can be formed of general-purpose parts, which is advantageous to reduce costs. 
     Furthermore, when the coaxial cable is embedded in the position in which a vertical tear is generated in the conveyor belt, the coaxial cable breaks. Thus, even when a radio wave is emitted from the detector toward the other side antenna unit, a radio wave is not emitted from the IC tag in response to the emitted radio wave. As a result, whether a vertical tear has been generated can be determined based on whether the detector has received the radio wave emitted through the other side antenna unit. In association with the cost reduction of the embedded body, an embedding pitch of the embedded body with respect to the conveyor belt can be sufficiently decreased compared to a case of a conventional loop antenna or the like, which is advantageous to accurately detect whether a vertical tear has been generated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an explanatory diagram illustrating a detection device for a vertical tear in a conveyor belt of an embodiment of the present invention, which is disposed on a conveyor device in a side view of the conveyor belt. 
         FIG.  2    is a cross-sectional view taken along A-A of  FIG.  1   . 
         FIG.  3    is an enlarged explanatory diagram illustrating the conveyor belt of  FIG.  1    in a cross-sectional view. 
         FIG.  4    is an enlarged view of the surroundings of the other side antenna unit of  FIG.  3   . 
         FIG.  5    is an enlarged view of the surroundings of one side antenna unit of  FIG.  3   . 
         FIG.  6    is an explanatory diagram illustrating the conveyor belt of  FIG.  3    in a plan view. 
         FIG.  7    is an explanatory diagram illustrating an embedded body of  FIG.  6    in a plan view. 
         FIG.  8    is an explanatory diagram illustrating the embedded body of  FIG.  7    in a bottom view. 
         FIG.  9    is an explanatory diagram illustrating the embedded body of  FIG.  7    in a side view. 
         FIG.  10    is an explanatory diagram illustrating another embodiment of the detection device in a cross-sectional view of the conveyor belt. 
         FIG.  11    is an explanatory diagram illustrating the conveyor belt of  FIG.  10    in a plan view. 
         FIG.  12    is an explanatory diagram illustrating a modified example of the placement of a detector in a cross-sectional view of the conveyor belt. 
         FIG.  13    is an explanatory diagram illustrating a modified example of the embedded body in an embedded state in a plan view of the conveyor belt. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A detection device and method for a vertical tear in a conveyor belt of the present invention will be described below based on embodiments illustrated in the drawings. 
     A detection device  1  for a vertical tear in a conveyor belt of the present invention, illustrated in  FIGS.  1  to  6    (hereinafter, referred to as a detection device  1 ), is placed on a conveyor device  14 . A conveyor belt  17  is mounted between a pair of pulleys  15   a ,  15   b  of the conveyor device  14 . The conveyor belt  17  is supported by a number of support rollers  16  between the pulleys  15   a ,  15   b . In the drawings, an arrow L indicates a longitudinal direction of the conveyor belt  17 , and an arrow W indicates a width direction of the conveyor belt  17 . 
     The conveyor belt  17  is formed integrally of an upper cover rubber  20 , a lower cover rubber  21 , and a core layer  18  disposed between the upper cover rubber  20  and the lower cover rubber  21 . The core layer  18  includes a plurality of steel cords  19  disposed side by side in the width direction W and extending in the longitudinal direction L. The core layer  18  is not limited to the steel cords  19  and may be a fiber layer formed of canvas or the like. The conveyor belt  17  includes other members as necessary. 
     On the carrier side of the conveyor device  14 , the lower cover rubber  21  of the conveyor belt  17  is supported by the support rollers  16 , and thus a central portion in the width direction W of the conveyor belt  17  is formed into a trough shape protruding downward. A conveyed object C is fed onto an upper surface of the upper cover rubber  20  to be transported. On the return side of the conveyor device  14 , the upper cover rubber  20  of the conveyor belt  17  is supported in a flat state by the support rollers  16 . 
     The detection device  1  detects the generation of a crack (so-called vertical tear) extending in the longitudinal direction L in the conveyor belt  17 . The detection device  1  includes embedded bodies  2  embedded in the conveyor belt  17 , a detector  10 , and a calculation unit  12 . In this embodiment, a warning device  13  is further provided. The warning device  13  may be optionally provided. 
     A number of the embedded bodies  2  are embedded at intervals in the longitudinal direction L. Wireless communication is performed between each of the embedded bodies  2  and the detector  10 . The frequency of radio waves used in wireless communication in the present invention is mainly an UHF band (different from country to country, but in the range of 860 MHz or higher and 930 MHz or lower; 915 MHz or higher and 930 MHz in Japan), and an HF band (13.56 MHz) can also be used. 
     As illustrated in  FIGS.  7  to  9   , the embedded body  2  includes an IC tag  3  that is passive, one side antenna unit  4  connected to the IC tag  3 , the other side antenna unit  5 , and a coaxial cable  6 . The one side antenna unit  4  is connected to one end portion of the coaxial cable  6 , and the other side antenna unit  5  is connected to the other end portion of the coaxial cable  6 . In this embodiment, the embedded body  2  is embedded in the lower cover rubber  21 , but may be embedded in the upper cover rubber  20 . In order to protect the embedded body  2  from the conveyed object C, the embedded body  2  is preferably embedded in the lower cover rubber  21  rather than the upper cover rubber  20 . 
     The commonly distributed specifications are adopted for the IC tag  3 , and for example, an RFID tag can be used. The size of the IC tag  3  is preferably as small as possible; for example, a length of 15 mm or less and more preferably 10 m or less, a width of 60 mm or less and more preferably 50 mm or less, and a thickness of 1 mm or less and more preferably 0.5 mm or less. In addition, the IC tag  3  having a heat resistance temperature of approximately 200° C. is used. 
     In addition to information specific to the tag such as an identification number thereof, any other necessary information is stored in the IC tag  3 . The IC tag  3  is disposed overlapping the one side antenna unit  4  and is connected to the one side antenna unit  4 . 
     The one side antenna unit  4  includes antenna plates  4   a ,  4   b  made of metal and formed on a substrate. The antenna plates  4   a ,  4   b  are disposed separated from each other. The other side antenna unit  5  includes antenna plates  5   a ,  5   b  made of metal and formed on a substrate. The antenna plates  5   a ,  5   b  are disposed separated from each other. 
     The size of the one side antenna unit  4  is preferably as small as possible; for example, a length of 15 mm or less and more preferably 10 mm or less, a width of 60 mm or less and more preferably 50 mm or less, and a thickness of 1 mm or less and more preferably 0.5 mm or less. The size of the other side antenna unit  5  is preferably as small as possible; for example, a length of 15 mm or less and more preferably 10 m or less, a width of 150 mm or less and more preferably 120 mm or less, and a thickness of 1 mm or less and more preferably 0.5 mm or less. In this embodiment, the one side antenna unit  4  is smaller than the other side antenna unit  5  and has an area of approximately 50% of that of the other side antenna unit  5 , but may have an area equivalent to that of the other side antenna unit  5 . 
     The commonly distributed specifications are adopted for the coaxial cable  6 . The coaxial cable  6  includes a core wire  7  serving as an inner conductor, an insulating layer  8  covering the periphery of the core wire  7 , and an outer conductor layer  9  covering the periphery of the insulating layer  8 . The outer diameter of the coaxial cable  6  is, for example, approximately 1 mm or more and 3 mm or less. 
     The core wire  7  is connected to one antenna plate  4   a  by soldering or the like at one end portion of the coaxial cable  6 , and is not connected to the other antenna plate  4   b . Also, the outer conductor layer  9  is connected to the other antenna plate  4   b  by soldering or the like, and is not connected to one antenna plate  4   a . The core wire  7  is connected to one antenna plate  5   a  by soldering or the like at the other end portion of the coaxial cable  6 , and is not connected to the other antenna plate  5   b . Also, the outer conductor layer  9  is connected to the other antenna plate  5   b  by soldering or the like, and is not connected to one antenna plate  5   a . The exposed surface of each of the one side antenna unit  4  and the other side antenna unit  5  is covered by an insulator. 
     The IC tag  3  and the one side antenna unit  4  are embedded in one end portion in the width direction W of the conveyor belt  17 , and the other side antenna unit  5  is embedded in the other end portion in the width direction W of the conveyor belt  17 . The IC tag  3  and the one side antenna unit  4  are disposed with an interval from the other side antenna unit  5  in the width direction W. The coaxial cable  6  is embedded in the conveyor belt  17  while extending in the width direction W. In this embodiment, as illustrated in  FIG.  6   , the coaxial cable  6  extends parallel to the width direction W and extends substantially at an inclination angle of 0° with respect to the width direction W. Each coaxial cable  6  is preferably extended to cover the entire width of the core layer  18 . 
     In manufacturing the conveyor belt  17 , the embedded bodies  2  are disposed in the lower cover rubber  21  having not been vulcanized or the upper cover rubber  20  having not been vulcanized, in a molding step; thereafter, through a vulcanization step, the embedded bodies  2  embedded in the conveyor belt  17  are integrated with the lower cover rubber  21  or the upper cover rubber  20 . In order to allow the one side antenna unit  4  and the other side antenna unit  5  to be firmly adhered to the lower cover rubber  21  or the upper cover rubber  20  into which the antenna units are to be embedded, a fiber layer or the like immersed in dipping liquid is interposed between an adhering surface of the lower cover rubber  21  or the upper cover rubber  2  and the antenna units in the molding step of the conveyor belt  17 . 
     The embedded bodies  2  are embedded at intervals of, for example, 5 m or more and 20 m or less in the longitudinal direction L. In other words, an embedding pitch P of the embedded bodies  2  is preferably in the range of 5 m or more and 20 m or less, and is more preferably an equal pitch. It is appropriate that the embedding pitch P of the embedded bodies  2  is approximately 10 m in consideration of detection accuracy of a vertical tear and costs. Note that in the drawings, the embedding pitch P is illustrated shorter than the real embedding pitch P. 
     The detector  10  is disposed at a position near the conveyor belt  10  to wirelessly communicate with the embedded bodies  2  without making contact with the conveyor belt  17 . The detector  10  includes a transmission unit of a radio wave R 1  and a reception unit of a radio wave R 2 . The detector  10  emits the radio wave R 1  toward the other side antenna unit  5 . Additionally, the detector  10  receives the radio wave R 2  emitted from the other side antenna unit  5  in response to the radio wave R 1  and acquires information that is stored in the IC tag  3  and is to be transmitted with the radio wave R 2 . 
     The commonly distributed specifications that allow wireless communication with a passive RFID tag or the like are adopted for the detector  10 . Thus, the IC tag  3  and the detector  10  form a Radio Frequency IDentification (RFID) system. 
     In this embodiment, the detector  10  is disposed on the return side of the conveyor device  14 , but may be disposed on the carrier side. The distance between the detector  10  and the other side antenna unit  5  when the other side antenna unit  5  comes closest to the detector  10  is set, for example, 1 m or less. In other words, the detector  10  is preferably placed at a position where the distance between the detector  10  and the other side antenna unit  5  is 1 m or less when the other side antenna unit  5  passes in front of the detector  10 . 
     The calculation unit  12  is connected by wire or wirelessly to the detector  10 . A computer or the like is used as the calculation unit  12 . Information acquired by the detector  10  is input to the calculation unit  12 . In addition, embedded position data (at least position data in the longitudinal direction L) of each IC tag  3  in the conveyor belt  17  is stored in the calculation unit  12 . 
     The warning device  13  notifies its surroundings of generation of a vertical tear. Examples of the warning device  13  can include an alarm, a warning lamp, and an alarm indicator. The warning device  13  is connected by wire or wirelessly to the calculation unit  12 , and the operation of the warning device  13  is controlled by the calculation unit  12 . When it is determined that a vertical tear has been generated, the calculation unit  12  activates the warning device  13 . 
     Next, an example of a procedure of a method for detecting whether a vertical tear has been generated, by using the detection device  1  will be described. 
     As illustrated in  FIGS.  1  to  3   , during operation of the conveyor device  14  (during running of the conveyor belt  17 ), the radio wave R 1  is emitted from the detector  10  toward the other side antenna unit  5 . When the embedded body  2  is in an undamaged condition, the radio wave R 1  is input to the IC tag  3  through the other side antenna unit  5 , the coaxial cable  6 , and the one side antenna unit  4 . The IC tag  3  emits the radio wave R 2  in response to the input radio wave R 1 . The radio wave R 2  is emitted toward the detector  10  through the one side antenna unit  4 , the coaxial cable  6 , and the other side antenna unit  5 . The detector  10  receives the radio wave R 2  and thus acquires the information stored in the IC tag  3  and transmitted with the radio wave R 2 . The information acquired by the detector  10  is input to the calculation unit  12 . 
     Meanwhile, in a case where a vertical tear has been generated in the conveyor belt  17 , the coaxial cable  6  breaks in the region where the vertical tear has been generated. Accordingly, even when the radio wave R 1  is emitted from the detector  10  toward the other side antenna unit  5 , the IC tag  3  does not emit the radio wave R 2  in response to the radio wave R 1 . Consequently, the radio wave R 2  is not received by the detector  10 , and the information acquired by the detector  10  is not input to the calculation unit  12 . 
     The calculation unit  12  determines whether the detector  10  has received the radio wave R 2 , based on whether information is input from the detector  10 . When the information is input to the calculation unit  12  from the detector  10 , it is determined that the detector  10  has received the radio wave R 2 . In the case of this determination result, it is assumed that the embedded body  2  is in an undamaged condition, and it is determined that there is no vertical tear generated in the region where the coaxial cable  6  is embedded (the generation of a vertical tear is not detected). 
     When no information is input to the calculation unit  12  from the detector  10 , it is determined that the detector  10  has not received the radio wave R 2 . In the case of this determination result, it is assumed that the coaxial cable  6  has broken, and it is determined that there is a vertical tear generated in the region where the coaxial cable  6  is embedded (the generation of a vertical tear is detected). 
     When the generation of a vertical tear is detected, the warning device  13  is activated, and the generation of a vertical tear is notified to the surroundings. Since the embedded position of each IC tag  3  in the conveyor belt  17  is stored in the calculation unit  12 , the embedded position of the IC tag  3  whose specific information cannot be acquired is determined. Consequently, the position (region) of the conveyor belt  17  in which a vertical tear has been generated can be identified. 
     The administrator who has recognized the generation of a vertical tear stops running of the conveyor belt  17  at an appropriate timing and handles the vertical tear, for example, by repairing the region in which the vertical tear has been generated. Running of the conveyor belt  17  is resumed after such handling is completed. 
     The detection device  1  has a simple structure in which the embedded body  2  includes the IC tag  3 , which is passive, the coaxial cable  6 , and the one side antenna unit  4  and the other side antenna unit  5  connected to both the end portions of the coaxial cable  6 . Thus, the embedded body  2  can be formed of general-purpose parts, which is advantageous to reduce costs. Further, the detector  10  may have specifications that allow wireless communication with the embedded body  2  and thus can be formed of general-purpose parts, which is advantageous to reduce costs. 
     Furthermore, at the position in which a vertical tear has been generated in the conveyor belt, the coaxial cable  6  breaks. Accordingly, even when the radio wave R 1  is transmitted from the detector  10  toward the other side antenna unit  5 , the radio wave R 2  is not emitted from the IC tag  3  in response to the radio wave R 1 . As a result, whether a vertical tear has been generated can be accurately determined based on whether the detector  10  has received the radio wave R 2  emitted through the other side antenna unit  5 . In association with the cost reduction of the embedded bodies  2 , the embedding pitch P of the embedded bodies  2  with respect to the conveyor belt  17  can be sufficiently decreased under the predetermined cost restriction compared to a conventional loop antenna or the like, which is advantageous to accurately detect whether a vertical tear has been generated. 
     In another embodiment of the detection device  1  illustrated in  FIGS.  8  and  9   , a tag side detector  11  is added to the foregoing embodiment. Other configurations are substantially the same as those in the foregoing embodiment. 
     The tag side detector  11  is disposed at a position near the conveyor belt  10  to wirelessly communicate with the embedded bodies  2  without making contact with the conveyor belt  17 . The tag side detector  11  includes a transmission unit of a radio wave R 3  and a reception unit of a radio wave R 4 . The tag side detector  11  emits the radio wave R 3  toward the one side antenna unit  4 . Additionally, the tag side detector  11  receives the radio wave R 4  emitted from the IC tag  3  through the one side antenna unit  4  in response to the radio wave R 3  and acquires information that is stored in the IC tag  3  and transmitted with the radio wave R 4 . Note that the frequency of the radio waves R 3 , R 4  preferably differs from the frequency of the radio waves R 1 , R 2 . 
     The commonly distributed specifications that allow wireless communication with a passive RFID tag or the like are adopted for the tag side detector  11  as in the case of the detector  10 . The tag side detector  11  and the detector  10  may have the same specifications. Thus, the IC tag  3  and the tag side detector  11  form a Radio Frequency IDentification (RFID) system. 
     In this embodiment, the tag side detector  11  is disposed on the return side of the conveyor device  14 , but may be disposed on the carrier side. The distance between the tag side detector  11  and the one side antenna unit  4  when the one side antenna unit  4  comes closest to the tag side detector  11  is set, for example, 1 m or less. In other words, the tag side detector  11  is preferably placed at a position where the distance between the tag side detector  11  and the one side antenna unit  4  is 1 m or less when the one side antenna unit  4  passes in front of the tag side detector  11 . The information acquired by the tag side detector  11  is input to the calculation unit  12 . 
     For example, in a case where the IC tag  3  has a failure while the coaxial cable  6  is not broken, even when the radio wave R 1  is emitted from the detector  10 , the radio wave R 2  is not emitted from the IC tag  3  in response to the radio wave R 1 . Accordingly, in the foregoing embodiment, there is a risk that it could be determined that a vertical tear has been generated even when the coaxial cable  6  is not broken. In order to avoid such a wrong detection, in this embodiment, the calculation unit  12  determines the intensity degree of reception by the tag side detector  11  of the radio wave R 4  emitted from the IC tag  3  through the one side antenna unit  4  in response to the radio wave R 3 . 
     In the case where the IC tag  3  is damaged, even when the radio wave R 3  is emitted from the tag side detector  11  toward the one side antenna unit  4 , the IC tag  3  does not emit the radio wave R 4  in response to the radio wave R 3 . Consequently, the radio wave R 4  is not received by the tag side detector  11 , and the information acquired by the tag side detector  11  is not input to the calculation unit  12 . As a result, when the calculation unit  12  determines that the tag side detector  11  has not received the radio wave R 4  (the reception intensity of the radio wave R 4  is zero), it is determined that the IC tag  3  has been damaged. 
     Meanwhile, in a case where the IC tag  3  is in an undamaged condition and the coaxial cable  6  is broken, the intensity of the radio wave R 4  emitted from the IC tag  3  in response to the radio wave R 3  changes (becomes weak) compared to a case where the coaxial cable  6  is in an undamaged condition. Accordingly, such characteristics of changing in the intensity of the radio wave R 4  are used. 
     The intensity (reference intensity) of the radio wave R 4  emitted from the IC tag  3  in response to the radio wave R 3  when the coaxial cable  6  is in an undamaged condition is determined and stored in the calculation unit  12  in advance. Then, the reference intensity is compared with the intensity of the radio wave R 4  emitted from the IC tag  3  in response to the radio wave R 3  and received by the tag side detector  11 , and whether the coaxial cable  6  is broken can be determined based on the comparison result. In a case where the intensity of the radio wave R 4  received by the tag side detector  11  is weaker than the reference intensity, it is determined that the coaxial cable  6  is broken. Thus, by a combination of determination of whether the radio wave R 2  has been received by the detector  10  and determination of the intensity degree of reception of the radio wave R 4  by the tag side detector  11 , breaking of the coaxial cable  6  can be more reliably determined. This is advantageous for accurate detection of generation of a vertical tear. 
     In the above-described manner, a damaged state of the coaxial cable  6  or a damaged state of the IC tag  3  can be determined based on the determination result of the intensity degree of reception of the radio wave R 4  by the tag side detector  11 . The embedded body  2  is a consumable, the life span of which expires in a certain period of time. By using the tag side detector  11 , the embedded body  2  not in an undamaged condition and the embedded position thereof can be determined, which is highly beneficial in efficiently performing maintenance for the embedded body  2 . 
     The one side antenna unit  4  and the other side antenna unit  5  can each protrude outward in the width direction W from the steel cord  19  disposed on the outermost end side in the width direction W. In such a structure, the radio waves used for wireless communication are less likely to be affected by the core layer  18  (steel cords  19 ), and the wireless communication distance to the detector  10  or the tag side detector  11  can be increased in some cases. 
     In each of the embodiments described above, the detector  10  and the tag side detector  11  are each disposed at a position on an inner side in the width direction W of the conveyor belt  1 , but may be disposed at a position on an outer side in the width direction W of the conveyor belt  1  as illustrated in  FIG.  12   . A sufficient space for placing the detector  10  and the tag side detector  11  is not ensured inside the conveyor device  14  in some cases. Under such a condition, the detector  10  and the tag side detector  11  are preferably disposed in an open space outside the conveyor belt  17 . With such an arrangement, maintenance work for the detector  10  and the tag side detector  11  can be easily performed. 
     The coaxial cable  6  can extend parallel to the width direction W, but may extend inclined with respect to the width direction W as illustrated in  FIG.  13   . In  FIG.  13   , the coaxial cable  6  extends at an inclination angle g of −30° with respect to the width direction W. Note that in  FIG.  13   , a negative inclination angle means downward-sloping, and a positive inclination angle means upward-sloping. 
     For example, the coaxial cable  6  can extend at an inclination angle g of +45° or smaller and −45° or smaller with respect to the width direction W. The coaxial cable  6  extends inclined with respect to the width direction W, which is advantageous in further reducing a change in bending rigidity (smoothly changing bending rigidity) when the conveyor belt  17  passes the surroundings of the pulleys  15   a ,  15   b , compared to a case where the inclination angle g is zero. 
     REFERENCE SIGNS LIST 
     
         
           1  Detection device 
           2  Embedded body 
           3  IC tag 
           4  One side antenna unit 
           4   a ,  4   b  Antenna plate 
           5  The other side antenna unit 
           5   a ,  5   b  Antenna plate 
           6  Coaxial cable 
           7  Core wire (inner conductor) 
           8  Insulating layer 
           9  Outer conductor layer 
           10  Detector 
           11  Tag-side detector 
           12  Calculation unit 
           13  Warning device 
           14  Conveyor device 
           15   a ,  15   b  Pulley 
           16  Support roller 
           17  Conveyor belt 
           18  Core layer 
           19  Steel cord 
           20  Upper cover rubber 
           21  Lower cover rubber 
         C Conveyed object