Patent Publication Number: US-2023161334-A1

Title: Automatic inspection system and wireless slave device

Description:
TECHNICAL FIELD 
     The present invention relates to an automatic inspection system and a wireless slave device for inspecting a facility such as a plant. 
     BACKGROUND ART 
     In sites such as a power plant, a chemical plant, and a steel plant, facilities such as a motor, a compressor, and a turbine are installed. When components such as bearings and insulators deteriorate due to aging of the facilities, an abnormal sound is generated. Conventionally, an operation in which a worker hears an operation sound of a facility to determine whether the facility is normal has been performed. However, in order for a worker to distinguish abnormal sounds, it is necessary to have many years of experience. Furthermore, since the worker walks around a wide site and inspects the facilities with his/her own ears, a load on the worker is large. In recent years, the aging of skilled workers who can distinguish abnormal sounds has progressed, and it is also difficult to secure new workers. 
     Therefore, a technique disclosed in PTL 1 is known as a technique for monitoring a monitoring target object. A monitoring device disclosed in PTL 1 incorporates a radio device and an antenna connected to the radio device. The radio device transmits acoustic data and image data processed by an information processor and receives control signals of a microphone and a camera. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2009-273113 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     A conventional monitoring device disclosed in PTL 1 wirelessly transmits acoustic data of a monitoring target object to a monitoring processing device at a place away from the monitoring target object. Then, the monitoring processing device can calculate a frequency spectrum from the acoustic data collected by the monitoring device and detect an occurrence of an abnormality in a monitoring target facility by a neural network model. The data size of the acoustic data transmitted from the monitoring device is large although the data size varies depending on the frequency of the sound generated by the measurement target and the like. Therefore, the processing of measuring and analyzing the acoustic data, which is performed by the monitoring processing device becomes heavy, and the power consumption in the monitoring processing device tends to increase. 
     In addition, in a case where a sensor device is installed, in a so-called retrofitting manner, in an on-site facility of the plant, there is not always an outlet near the facility, and it is difficult to obtain a wired power supply capable of supplying power to the sensor device. Therefore, the sensor device needs to operate a built-in battery as a power source. However, when the sensor device performs processing with high power consumption (for example, processing of transmitting acoustic data having a large data size), the built-in battery runs out immediately, the frequency of battery replacement increases, and the usability of the sensor device deteriorates. 
     The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce power consumption of a sensor device that collects sound generated by an inspection target object. 
     Solution to Problem 
     In order to solve the above problems, according to an aspect of the present invention, an automatic inspection system includes a wireless slave device and a wireless master device. 
     The wireless slave device is configured to include a sound collection unit that collects sound generated from an inspection target object, an analysis unit that analyzes the collected sound to obtain a degree of difference between the collected sound and normal sound learned in advance and sound state information of the collected sound, as an analysis result, a wireless communication unit that wirelessly transmits data including the analysis results to a wireless master device, and a power supply unit that supplies power to the sound collection unit, the analysis unit, and the wireless communication unit. 
     The wireless master device is configured to perform processing of receiving and managing the data from the wireless slave device, and transmitting the analysis result extracted from the data to a monitoring terminal that monitors a state of the inspection target object. 
     Advantageous Effects of Invention 
     According to at least an aspect of the present invention, the wireless slave device does not transmit data in all frequency bands of sound collected from an inspection target object, as an analysis result, but transmits the degree of difference from the normal sound and the sound state information of the collected sound to the wireless master device as the analysis result. Therefore, it is possible to reduce the data size of the data transmitted from the wireless slave device to the wireless master device, and reduce the power consumption of the wireless slave device. 
     Objects, configurations, and advantageous effects other than those described above will be clarified by the descriptions of the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram illustrating an overall configuration example of an automatic inspection system according to a first embodiment of the present invention. 
         FIG.  2    is a diagram illustrating a configuration example of a packet including an analysis result according to the first embodiment of the present invention. 
         FIG.  3    is a block diagram illustrating an internal configuration example of a wireless master device and a monitoring terminal according to the first embodiment of the present invention. 
         FIG.  4    is a block diagram illustrating a hardware configuration example of a computer constituting a wireless slave device according to the first embodiment of the present invention. 
         FIG.  5    is a block diagram illustrating a hardware configuration example of a computer constituting a wireless relay, the wireless master device, and the monitoring terminal according to the first embodiment of the present invention. 
         FIG.  6    is a flowchart illustrating an example of processing performed by the wireless slave device according to the first embodiment of the present invention. 
         FIG.  7    is a flowchart illustrating an example of processing performed by the wireless relay and an example of processing performed by the wireless master device according to the first embodiment of the present invention. 
         FIG.  8    is a graph illustrating a temporal change of an abnormality degree according to the first embodiment of the present invention. 
         FIG.  9    is a block diagram illustrating an internal configuration example of a learning result setting terminal connected to the wireless slave device according to the first embodiment of the present invention. 
         FIG.  10    is a flowchart illustrating an example of processing of the learning result setting terminal according to the first embodiment of the present invention. 
         FIG.  11    is a view illustrating an example of a place of mounting the wireless slave device according to the first embodiment of the present invention. 
         FIG.  12    is a diagram illustrating a first configuration example (single manager) of a multi-hop network of the automatic inspection system according to the first embodiment of the present invention. 
         FIG.  13    is a diagram illustrating a second configuration example (multi-manager) of the multi-hop network of the automatic inspection system according to the first embodiment of the present invention. 
         FIG.  14    is a diagram illustrating a third configuration example (multi-manager) of the multi-hop network of the automatic inspection system according to the first embodiment of the present invention. 
         FIG.  15    is a block diagram illustrating an overall configuration example of an automatic inspection system according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments for embodying the present invention will be described with reference to the accompanying drawings. In the present specification and the attached drawings, components having substantially the same functions or configurations are designated by the same reference signs, and repetitive description will be omitted. 
     In an automatic inspection system according to each embodiment described below, data obtained by collecting sound (operating sound) generated in an on-site facility such as a plant is analyzed, and a degree of difference between sound data and normal sound, and sound state information of the collected sound are transmitted to a wireless master device as an analysis result. 
     First Embodiment 
     First, a configuration example and an operation example of an automatic inspection system according to a first embodiment will be described with reference to  FIGS.  1  to  14   . 
     [Overall Configuration of Automatic Inspection System] 
       FIG.  1    is a block diagram illustrating an overall configuration example of an automatic inspection system  1  according to a first embodiment. The automatic inspection system  1  is applied to, for example, a plant such as a power plant, a chemical plant, a steel plant, or a substation, or a building such as a building. The automatic inspection system  1  includes wireless slave devices  10  and  10 ′, a wireless relay  20 , a wireless master device  30 , and a monitoring terminal  40 . Various types of data can be transmitted and received between the wireless slave devices  10  and  10 ′ and the wireless relay  20  and between the wireless relay  20  and the wireless master device  30 , via a wireless communication path L 1 . Various types of data can be transmitted and received between the wireless master device  30  and the monitoring terminal  40  via a wireless communication path L 2 . Various types of data may be able to be transmitted and received between the wireless master device  30  and the monitoring terminal  40  via a wired communication path. 
     The plant is provided with facilities for generating sound, such as a motor, a pump, a compressor, a turbine, and a boiler. At least a portion of the facility that is provided in the plant and generates sound serves as a monitoring target (inspection target) by the automatic inspection system  1 . In the following description, a facility as a monitoring target is referred to as an “inspection target object”. A wireless slave device  10  (an example of a slave device) is provided near an inspection target object A 2 . The wireless slave device  10  may be provided in contact with the inspection target object A 2  or may be provided away from the inspection target object A 2 . In addition, a configuration in which different wireless slave devices  10  and  10 ′ are provided for different inspection target objects A 2  and B 3 , respectively, and the inspection target objects A 2  and B 3  are monitored by the respective wireless slave devices  10  and  10 ′ may be made. In addition, a configuration in which the wireless slave device  10  and the wireless slave device  10 ′ may be provided for one inspection target object A 2 , and different parts of the inspection target object A 2  are monitored by the wireless slave device  10  and the wireless slave device  10 ′, respectively may be made. The wireless slave device  10  will be described below. 
     [Wireless Slave Device] 
     The wireless slave device  10  is used as a “sound sensor device” that collects sound generated from the inspection target object A 2  and detects features of the sound. Therefore, the wireless slave device  10  collects the sound generated from the inspection target object A 2 , analyzes the collected sound to obtain the degree of difference between the sound data and the normal sound as an analysis result, and transmits data including the analysis result to the wireless master device  30 . Here, the amplitude of the sound is a displacement based on a silent state. The data including the analysis result is a packet D 1  having the detailed configuration illustrated in  FIG.  2    to be described later. In the following description, the data including the analysis result is referred to as the packet D 1 . 
     The wireless slave device  10  includes, for example, a sound collection unit  11 , an analysis unit  12 , a wireless communication unit  13 , and a power supply unit  14 . Each unit provided in the wireless slave device  10  is stored in a housing having a waterproof and dustproof function. Here, the wireless slave device  10  will be described as a device in which a sensor function and a wireless communication function are integrated. A device in which a sensor function unit (sound collection unit  11  and analysis unit  12 ) and a wireless communication function unit (wireless communication unit  13 ) which are configured separately are connected via a signal line may be handled as the wireless slave device  10 . 
     The sound collection unit  11  includes an analog-to-digital (AD) conversion unit (not illustrated) in the sound collection unit  11 . The AD conversion unit in the sound collection unit  11  samples and quantizes the amplitude of an analog signal of sound collected from the inspection target object A 2  at the predetermined interval (for example, every 10 minutes or every 1 hour), converts the analog signal into a digital value, and outputs the digital value to the analysis unit  12 . 
     The analysis unit  12  analyzes the digital value of the sound input from the sound collection unit  11 , and obtains the degree of difference between the collected sound and the normal sound learned in advance, and sound state information of the collected sound as an analysis result. The analysis unit  12  transmits the analysis result to the wireless communication unit  13 . The analysis unit  12  includes a learning result  15 , a feature extraction unit  16 , and an abnormality-degree and sound-state-information calculation unit  17 . 
     The learning result  15  is data of the normal sound learned in advance by a learning result setting terminal  7  illustrated in  FIG.  9    to be described later, and is information in which the sound of the inspection target object A 2  that normally operates is learned. The learning result  15  indicates a feature or the like obtained in a manner that the intensity of an electrical signal obtained by converting the normal sound by the sound collection unit  11  is calculated for each frequency based on recording information recorded in advance by the learning result setting terminal  7 , and the autocorrelation is obtained for each predetermined time. The learning result  15  is registered in advance in the wireless slave device  10  by the learning result setting terminal  7 , for example, when the wireless slave device  10  is installed. 
     The feature extraction unit  16  extracts a feature of the electric signal based on the electric signal input from the sound collection unit  11 . That is, the feature extraction unit  16  can extract the feature of sound generated by the inspection target object A 2  from the sound collected by the sound collection unit  11 . The feature of the sound contained in the learning result  15  or extracted by the feature extraction unit  16  is a parameter characterizing the sound generated for each inspection target object A 2 . For example, in a predetermined period, the frequency (high and low) of sound included in an audible area can be exemplified as the feature. 
     The abnormality-degree and sound-state-information calculation unit  17  calculates the degree of difference between the feature extracted by the feature extraction unit  16  from the sound collected by the sound collection unit  11 , and the learning result  15  of the normal sound. An example of a method of calculating the degree of difference will be described. First, the abnormality-degree and sound-state-information calculation unit  17  randomly samples a plurality of features of the sound indicated by the learning result  15  and a plurality of features of the sound collected by the sound collection unit  11 . Then, the abnormality-degree and sound-state-information calculation unit  17  individually inputs sets of sampled features to the Gaussian mixture model or the like, and calculates a score for each set. Then, the abnormality-degree and sound-state-information calculation unit  17  obtains a difference between the calculated scores to obtain the degree of difference (also referred to as an “abnormality degree” below) between the feature extracted by the feature extraction unit  16  and the learning result  15  of the normal sound. Information (information regarding the state of the sound) that has an influence on the degree of difference at this time is “sound state information”. For example, the sound state information indicates at least one of the frequency band of the collected sound and the magnitude (intensity) of the output for each frequency. 
     The abnormality-degree and sound-state-information calculation unit  17  can calculate statistical information (see  FIG.  8    described later) such as an average of the abnormality degree and standard deviation of the abnormality degree by repeating the above processes a plurality of times. In addition, the abnormality-degree and sound-state-information calculation unit  17  repeats the above processes to calculate the sound state information of the sound collected by the sound collection unit  11  based on the feature extracted by the feature extraction unit  16  from the sound collected by the sound collection unit. 
     The wireless communication unit  13  wirelessly transmits the packet D 1  in which destination information of the wireless master device  30  is added to the analysis result obtained by the analysis unit  12 , to the wireless master device  30  via the wireless relay  20  at a predetermined timing. This process is performed in a manner that the wireless communication unit  13  communicates with a wireless communication unit  21  of the wireless relay  20 . The packet D 1  including the analysis result is transmitted to the wireless relay  20  as indicated by the wireless communication path L 1 , and is further transmitted from the wireless relay  20  to the wireless master device  30 . 
     The power supply unit  14  supplies power stored in a built-in battery  58  (see  FIG.  4    described later) incorporated in the wireless slave device  10  to operate the sound collection unit  11 , the analysis unit  12 , and the wireless communication unit  13 . It is assumed that the type of built-in battery  58  is not limited. Note that the wireless slave device  10  may be provided with a power generation unit (not illustrated) that feeds the generated power to the power supply unit  14 . 
     [Wireless Relay] 
     The wireless relay  20  constitutes a portion of a sensor network stretched around the plant, and can transfer the packet D 1  transmitted from the wireless slave devices  10  and  10 ′ to the wireless master device  30  as described above. 
     The portion of the sensor network may include a sound sensor network capable of detecting abnormal sound generated from inspection target objects A 2  and B 3  and diagnosing the states of the inspection target objects A 2  and B 3 . In this case, in addition to the sound sensor network, the sensor network may include a sensor network capable of detecting at least one or more types of information of the temperature, the humidity, the pressure, the voltage value, the current value, the frequency, the resistance value, the flow rate, the flow velocity, the color, the image, and the like. Alternatively, all of the sensor networks provided in the plant may be constituted by the sound sensor network. 
     The wireless relay  20  can receive the packet D 1  wirelessly transmitted from one wireless slave device  10  or a plurality of wireless slave devices  10  and  10 ′, and then wirelessly transmit the packet D 1  to the wireless master device  30 . In addition, the wireless relay  20  can transfer the respective packets D 1  received from the plurality of wireless slave devices  10  and  10 ′ to the wireless master device  30 . Specifically, the wireless relay  20  can wirelessly communicate with the plurality of wireless slave devices  10  and  10 ′ and transmit the packet D 1  received from each of the wireless slave devices  10  and  10 ′ to the wireless master device  30 . Here, the wireless master device  30  issues an instruction of a transmission order of the packet D 1  to the plurality of wireless slave devices  10  and  10 ′, and wirelessly receives the data received from the wireless slave devices  10  and  10 ′ by the wireless relay  20 , via the wireless relay  20  according to the transmission order. 
     For example, the wireless master device  30  instructs the plurality of wireless slave devices  10  and  10 ′ sequentially selected by a polling method, to transmit the packet D 1  via the wireless relay  20 . The wireless slave devices  10  and  10 ′ having received the instruction from the wireless master device  30  sequentially transmit the packet D 1  to the wireless relay  20 . Then, the wireless relay  20  sequentially transmits the packets D 1  received from the wireless slave devices  10  and  10 ′ to the wireless master device  30  in the instructed transmission order. Therefore, the wireless master device  30  can receive the packet D 1  while avoiding collision between the packets D 1  transmitted from the plurality of wireless slave devices  10  and  10 ′ via the wireless relay  20 . 
     Note that, as illustrated in  FIGS.  12  to  14    to be described later, between a plurality of wireless slave devices  10  and  10 ′ close to each other, the wireless slave devices  10  and  10 ′ can transfer the packet D 1  to the wireless relay  20  by a so-called bucket relay method (multi-hop routing). At this time, the wireless slave device  10 ( 3 ) (see  FIGS.  12  to  14   ) that performs bucket relay of the packet D 1  functions as the wireless relay that relays the packet D 1 . 
     Although  FIG.  1    illustrates an example in which only one wireless relay  20  is provided, a plurality of wireless relays  20  may be provided. Further, the wireless communication path L 1  may not include the wireless relay  20 . In this case, the wireless slave device  10  can wirelessly and directly communicate with the wireless master device  30 . 
     [Wireless Master Device] 
     The wireless master device  30  manages data (packet D 1 ) received from the wireless slave device  10  via the wireless relay  20 . Therefore, for example, the wireless master device  30  has a function of interpreting the content of the packet D 1  (for example, referred to as a data parsing function) and storing the content as a file. The contents of the data described in this file may be obtained by converting the analysis result transmitted from the wireless slave device  10  into text, or may be obtained by converting bits or byte information of the packet into text as it is. As the format of the file, various types such as tab delimiter, space delimiter, and comma delimiter may be considered, and may be freely designed by a worker. 
     The wireless master device  30  transmits the analysis result (including the abnormality cause if there is an abnormality) extracted from the data to the monitoring terminal  40  based on a request from the monitoring terminal  40  that monitors the states of the inspection target objects A 2  and B 3 . Therefore, the wireless master device  30  retains the analysis result received from the wireless slave device  10 . The wireless master device  30  detects, for example, a state change of the inspection target objects A 2  and B 3  deteriorated over time, based on the degree of difference between the feature of the sound collected by the sound collection unit  11  and the learning result  15  of the normal sound. The feature is represented by the average value of the abnormality degrees of the inspection target objects A 2  and B 3  and the standard deviation of the abnormality degrees, which are obtained from the analysis result. Then, the wireless master device  30  notifies the monitoring terminal  40  of a probability of the abnormality in the inspection target objects A 2  and B 3  (including the abnormality cause if there is an abnormality) based on the detected state change of the inspection target objects A 2  and B 3 . The wireless master device  30  includes a wireless communication unit  31 , a data storage unit  32 , and a data disclosure unit  33 . 
     The wireless communication unit  31  communicates with the wireless relay  20 . 
     The data storage unit  32  extracts data including an analysis result from the packet D 1  received from the wireless slave device  10 , and stores the data in association with the time when the wireless master device  30  collects the packet D 1 . As a result, the data storage unit  32  converts the data extracted from the packet D 1  into time-series data. In a case where the data storage unit  32  does not have a storage capacity capable of retaining all pieces of the time-series data, a configuration in which the data to be retained is transferred to an external information processing apparatus or an information storage device to retain all pieces of the information in the entire system may be made. 
     The data disclosure unit  33  provides the monitoring terminal  40  with the time-series data retained by the data storage unit  32  and the probability of the abnormality in the inspection target objects A 2  and B 3  (including the abnormality cause if there is abnormality) in response to a request from the monitoring terminal  40 . 
     [Monitoring Terminal] 
     The monitoring terminal  40  is used by a worker to monitor the states of the inspection target objects A 2  and B 3  through the wireless master device  30 . The monitoring terminal  40  performs a process of determining and disclosing the states of the inspection target objects A 2  and B 3  by using the analysis result (including the abnormality cause if there is an abnormality) received from the wireless master device  30 . 
     [Configuration of Packet] 
       FIG.  2    illustrates a configuration example of the packet D 1  including the analysis result. 
     The packet D 1  includes a header and a data section. In the data section, data representing the abnormality degree and data representing sound state information are stored as the analysis result. The data representing the abnormality degree includes the average value of the abnormality degree and the value of the standard deviation of the abnormality degree. 
     The header includes a network address (for example, an IP address) for specifying the wireless master device  30  at which the packet D 1  finally arrives, or destination information represented by identification information of the wireless master device  30  or the like. 
     The average value of the abnormality degree is a value obtained by averaging the abnormality degree calculated for each predetermined timing by the abnormality-degree and sound-state-information calculation unit  17  in a unit time. 
     The standard deviation of the abnormality degree is a value of the standard deviation calculated by the abnormality-degree and sound-state-information calculation unit  17  based on the average value of the abnormality degree. 
     [System of Wireless Master Device and Monitoring Terminal] 
     Next, the system of the wireless master device  30  and the monitoring terminal  40  will be described with reference to  FIG.  3   . 
       FIG.  3    is a diagram illustrating the system of the wireless master device  30  and the monitoring terminal  40 . The data storage unit  32  of the wireless master device  30  stores an abnormality degree  321 , an abnormality cause  322 , sound state information  323 , and other information  324 . 
     The wireless master device  30  stores the time-series data including the abnormality degree  321  and the sound state information  323  received by the wireless communication unit  31  in the data storage unit  32 . The data storage unit  32  is configured to associate the sound state information  323  with the abnormality cause  322  so that the worker can quickly specify the abnormality cause when the abnormality occurs. As an association method, for example, in an event in which a difference from the normal time appears in a specific frequency band such as bearing deterioration of a motor, the specific frequency band is associated with bearing deterioration (abnormality cause  322 ) in advance as the sound state information  323 . In addition, regarding an unknown abnormality in advance, the sound state information  323  of the sound obtained when the abnormality occurs, and the abnormality cause  322  at this time are stored in the data storage unit  32  in association with each other, and thus it is possible to immediately handle a similar abnormality occurrence. As an example, the association between the sound state information  323  and the abnormality cause  322  is performed by a manual input using an input device (not illustrated) such as a mouse or a keyboard included in a computer  60  of the wireless master device  30  or the monitoring terminal  40 . 
     The other information  324  is more detailed sound state information at the time of abnormality or when abnormality is suspected. The other information  324  is, for example, information for each frequency of sound data, such as the frequency with the highest intensity for the sound data collected by the wireless slave device  10  or how much the intensity of which frequency has changed. As a specific example, the other information  324  is power spectrum information around the frequency band in which the occurrence of the abnormality is detected in the sound data. In the wireless master device  30 , for example, in a case where the data disclosure unit  33  determines that it is necessary to determine the abnormality cause (the abnormality degree is equal to or greater than a threshold value, or the like), or in accordance with an instruction from the worker via the monitoring terminal  40 , the wireless slave device  10  is requested to provide more detailed information of the corresponding portion (information (power spectrum or the like) regarding a frequency band having a high abnormality degree or the periphery). Then, the wireless master device  30  stores the information acquired from the wireless slave device  10  in the data storage unit  32  as the other information  324 . 
     The monitoring terminal  40  outputs a graph display or the like of time-series data to a display, a printer, or the like as a monitoring result of the states of the inspection target objects A 2  and B 3 . The monitoring terminal  40  may have a function of performing data analysis processing such as clustering processing on the time-series data retained by the data storage unit  32  of the wireless master device  30 . As a result, the monitoring terminal  40  can also analyze an abnormality degree trend  41  (fluctuation pattern) of the abnormality degree  321  and the abnormality cause  42  (abnormality cause  322 ) when an abnormality is detected, for each inspection target object. 
     [Hardware Configuration of Each Device] 
     Next, a hardware configuration example of the computers  50  and  60  constituting the respective devices in the automatic inspection system  1  will be described with reference to  FIGS.  4  and  5   . 
       FIG.  4    is a block diagram illustrating a hardware configuration example of the computer  50  constituting the wireless slave device  10 . Note that a hardware configuration example of the computer  50  constituting the wireless slave device  10 ′ is similar to that of the wireless slave device  10 . Thus, in the following description, a hardware configuration example of the computer  50  constituting the wireless slave device  10  will be described focusing on the wireless slave device  10 . 
     The computer  50  is hardware used as a computer used in the wireless slave device  10 . The computer  50  includes a micro processing unit (MPU)  51 , a main storage device  52 , an auxiliary storage device  53 , and a bus  54 . The computer  50  further includes a microphone  55 , an input and output circuit  56 , a communication circuit  57 , and a built-in battery  58 . The blocks are communicably connected to each other via a bus  54 . 
     The MPU  51  reads program codes of software for realizing each function of the wireless slave device  10  according to the present embodiment from the auxiliary storage device  53 , loads the program codes into the main storage device  52 , and executes the program codes. Therefore, in addition to a boot program and various parameters, a program for causing the computer  50  to function is recorded in the auxiliary storage device  53 . The auxiliary storage device  53  permanently records a program, data, and the like necessary for the MPU  51  to operate, and is used as an example of a computer-readable non-transitory recording medium storing a program executed by the computer  50 . As the auxiliary storage device  53 , a non-volatile memory including a semiconductor memory or the like is used. 
     Variables, parameters, and the like generated in the middle of arithmetic processing of the MPU  51  are temporarily written in the main storage device  52 , and the variables, the parameters, and the like are appropriately read by the MPU  51 . In the wireless slave device  10 , the function of each unit in the wireless slave device  10  is realized by the MPU  51  executing a program. Furthermore, in the wireless slave device  10 , a digital value received from the sound collection unit  11  (microphone  55 ) is temporarily stored in the auxiliary storage device  53 , and the analysis result of the analysis unit  12  is also temporarily stored in the auxiliary storage device  53 . 
     The microphone  55  is a device that collects sound generated by the inspection target object A 2  and outputs a digital value of the sound. Here, it is known that sound in an ultrasonic area higher than an audible area is generated when an abnormality starts to occur in the inspection target object A 2 . Therefore, the microphone  55  may have a function capable of collecting not only audible sound but also sound outside the audible area, for example, an ultrasonic wave generated by the inspection target object A 2 . By collecting and analyzing the ultrasonic wave emitted from the inspection target object A 2 , the wireless slave device  10  can easily detect the abnormality of the inspection target object A 2  accurately and early. 
     The input and output circuit  56  is an interface for inputting and outputting a digital signal. The input and output circuit  56  has a function of outputting a digital signal input from the microphone  55  to the feature extraction unit  16  of the analysis unit  12 . 
     For example, a network interface card (NIC), a low-power wireless module for the Internet of Things (IoT), or the like is used as the communication circuit  57 , and various types of data can be transmitted and received between devices via a wireless communication path including a wireless local area network (LAN), a multi-hop low-power radio wave, or the like connected to the NIC. In the wireless slave device  10 , the wireless communication unit  13  can control the operation of the communication circuit  57  to transmit the packet D 1  to the wireless relay  20  or transfer the packet D 1  received from another wireless slave device  10  to the wireless relay  20 . 
     The built-in battery  58  is mounted on the wireless slave device  10 , and supplies power to each unit in the computer  50  under the control of the power supply unit  14  illustrated in  FIG.  1   . The built-in battery  58  according to the present embodiment is assumed to be a primary battery. However, the built-in battery  58  may be a secondary battery. 
       FIG.  5    is a block diagram illustrating a hardware configuration example of the computer  60  constituting the wireless relay  20 , the wireless master device  30 , and the monitoring terminal  40 . 
     The computer  60  is hardware used as a computer used in the wireless relay  20 , the wireless master device  30 , and the monitoring terminal  40 . The computer  60  includes an MPU  61 , a main storage device  62 , an auxiliary storage device  63 , a bus  64 , a communication circuit  65 , and a user interface device  66 . The blocks are communicably connected to each other via a bus  64 . 
     The MPU  61  reads program codes of software for realizing each function of the wireless relay  20 , the wireless master device  30 , and the monitoring terminal  40  according to the present embodiment from the auxiliary storage device  63 , loads the program codes into the main storage device  62 , and executes the program codes. 
     Variables, parameters, and the like generated in the middle of arithmetic processing of the MPU  61  are temporarily written in the main storage device  62 , and the variables, the parameters, and the like are appropriately read by the MPU  61 . In the wireless relay  20 , the function of controlling the wireless communication unit  21  to transfer the packet D 1  received from the wireless slave devices  10  and  10 ′ to the wireless master device  30  is realized by the MPU  61 . In the wireless master device  30 , the wireless communication unit  31  controls the operation of the communication circuit  65  to capture the packet D 1  transferred from the wireless relay  20 , and the MPU  61  stores various types of data extracted from the data section of the packet D 1  in the data storage unit  32 . Further, in the wireless master device  30 , the function of disclosing the data extracted from the data storage unit  32  by the data disclosure unit  33  to the monitoring terminal  40  is realized by the MPU  61 . In the monitoring terminal  40 , the function of receiving the data subjected to the disclosure processing by the data disclosure unit  33  and presenting the data to the worker through the user interface device  66  is realized by the MPU  61 . 
     As the auxiliary storage device  63 , for example, a hard disk drive (HDD), a solid state drive (SSD), a flexible disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory, or the like is used. In addition to the OS and various parameters, a program for causing the computer  60  to function is recorded in the auxiliary storage device  63 . The auxiliary storage device  63  permanently records a program, data, and the like necessary for the MPU  61  to operate, and is used as an example of a computer-readable non-transitory recording medium storing a program executed by the computer  60 . In the wireless master device  30 , the function of the data storage unit  32  is realized by the auxiliary storage device  63 . In the monitoring terminal  40 , the function of accumulating the analysis result transmitted from the wireless master device  30  is realized by the auxiliary storage device  63 . 
     For example, an NIC or the like is used as the communication circuit  65  in the monitoring terminal  40 , and various types of data can be transmitted and received between devices via a wireless communication path including a wireless LAN or the like connected to the NIC or a wired communication path. In the wireless relay  20  and the wireless master device  30 , a low-power wireless module for IoT or the like is used for the communication circuit  65 . In the wireless relay  20 , the wireless communication unit  21  can control the operation of the communication circuit  65  to transfer the packet D 1  received from the wireless slave device  10  to the wireless master device  30 . In the wireless master device  30 , the wireless communication unit  31  controls the operation of the communication circuit  65  to receive the packet D 1  transmitted from the wireless relay  20 . Further, the wireless master device  30  can transmit data to the monitoring terminal  40  through the communication circuit  65 . In the monitoring terminal  40 , a wireless communication unit (not illustrated) controls the operation of the communication circuit  65  to receive data transmitted from the wireless master device  30 . 
     As the user interface device  66 , for example, a liquid crystal display monitor, a touch panel device, a mouse, a keyboard, or the like is used. The worker can check the data displayed on the user interface device  66  and input various commands through the user interface device  66 . The user interface device  66  is mainly provided in the monitoring terminal  40 . The user interface device  66  may not be provided in the wireless relay  20  and the wireless master device  30 . 
     In a case where the computer  60  is mounted on the wireless master device  30  and the monitoring terminal  40 , power can be supplied from a wired power supply to each unit, but the description of the power supply will be omitted. In addition, in a case where there is no supply of power from an external power supply to the wireless relay  20 , the wireless relay  20  may also include a built-in battery. 
     [Processing of Wireless Slave Device] 
     Next, an example of processing performed by the wireless slave device  10  will be described with reference to  FIG.  6   . 
       FIG.  6    is a flowchart illustrating an example of the processing performed by the wireless slave device  10 . Detailed description of processing that is similar to the processing performed by the wireless slave device  10  and is performed by the wireless slave device  10 ′ will be omitted. 
     The wireless slave device  10  monitors whether a predetermined timing has arrived (S 11 ). When the predetermined timing has not arrived (S 11 : NO), the wireless slave device  10  continues to monitor the arrival of the timing again. 
     When the predetermined timing has arrived (S 11 : YES), the wireless slave device  10  supplies power from the power supply unit  14  to the sound collection unit  11  to activate the microphone  55  (S 12 ). The predetermined timing may be a predetermined or undefined period. Furthermore, the wireless slave device  10  may set the predetermined timing in accordance with an instruction from the wireless master device  30  transmitted to the wireless slave device  10  via the wireless relay  20 . 
     The sound collection unit  11  collects the operating sound of the inspection target object A 2  (S 13 ). The operating sound collected by the sound collection unit  11  is input to the analysis unit  12  (S 14 ). 
     The analysis unit  12  analyzes the operating sound input from the sound collection unit  11 , and detects the degree of difference between the normal sound and the operating sound, as an analysis result, based on the learning result  15  of the normal sound learned in advance and the feature extracted from the operating sound (S 15 ). Here, the analysis unit  12  calculates the abnormality degree and the sound state information and obtains the abnormality degree and the sound state information as the analysis result. The analysis unit  12  transmits the analysis result to the wireless communication unit  13  (S 16 ). 
     The wireless communication unit  13  generates the packet D 1  based on the analysis result received from the analysis unit  12  and transmits the packet D 1  to the wireless relay  20  (S 17 ). 
     [Processing of Wireless Relay and Wireless Master Device] 
     Next, an example of processing performed by the wireless relay  20  and the wireless master device  30  will be described with reference to  FIG.  7   . 
       FIG.  7    is a flowchart illustrating an example of processing performed by the wireless relay  20  and an example of processing performed by the wireless master device  30 . 
     First, processing of the wireless relay  20  will be described. 
     When receiving the packet D 1  including the analysis result (abnormality degree and sound state information) from the wireless slave device  10  (S 21 ), the wireless relay  20  transfers the packet D 1  including the analysis result to the wireless master device  30  (S 22 ). The packet D 1  transmitted from the wireless slave device  10  reaches the wireless master device  30  in accordance with the network address or the identification information included in the header even in a case where the packet D 1  passes through another device in the middle. 
     When receiving the packet D 1  including the analysis result (abnormality degree and sound state information) from the wireless slave device  10  via the wireless relay  20  (S 31 ), the wireless master device  30  extracts the analysis result from the packet D 1  and converts the analysis result into data (S 32 ). The conversion into data is to register the time information of the time when the packet D 1  has been collected and the analysis result in the data storage unit  32  as time series data by storing the time information and the analysis result in association with each other. In a case where the data disclosure unit  33  determines, from the analysis result, that there is an unknown abnormality (in a case where the abnormality degree is higher than a threshold value and the abnormality cause is not associated), the data disclosure unit  33  stores the sound state information of the collected sound in association with the abnormality cause (S 33 ). This processing may be performed by the data storage unit  32 . 
     Then, the wireless master device  30  transmits time-series data (an example of the analysis result) in response to a request from the monitoring terminal  40 , and the monitoring terminal  40  determines the state of the inspection target object A 2  from the analysis result and discloses the state (S 34 ). The time-series data disclosed in response to the request is displayed on a predetermined user interface of the user interface device  66  in the monitoring terminal  40 . 
     [Average Value and Standard Deviation of Abnormality Degree] 
       FIG.  8    is a graph illustrating a temporal change of the abnormality degree. In  FIG.  8   , the vertical axis represents the abnormality degree, and the horizontal axis represents time. In addition, the vertical line plotted on the horizontal axis represents the timing at which the wireless slave device  10  transmits the average value of the abnormality degree and the standard deviation of the abnormality degree as the analysis result. 
       FIG.  8    illustrates both the average value of the abnormality degree and the standard deviation of the abnormality degree, which are calculated by the abnormality-degree and sound-state-information calculation unit  17 . The abnormality-degree and sound-state-information calculation unit  17  can calculate the average value of the abnormality degree of the inspection target object A 2 , and positive and negative standard deviations for the average value of the abnormality degree. In  FIG.  8   , the broken line on the upper side of the average value of the abnormality degree is represented as the positive standard deviation, and the broken line on the lower side of the average value of the abnormality degree is represented as the negative standard deviation. 
     The probability of the abnormality occurring in the inspection target object A 2  is represented by the point that both the average value of the abnormality degree and the standard deviation of the abnormality degree are high over a predetermined period or longer. Then, the abnormality-degree and sound-state-information calculation unit  17  can detect the abnormality in the inspection target object A 2  in a case where the abnormality degree becomes higher than a predetermined threshold value. In a case where the abnormality-degree and sound-state-information calculation unit  17  detects the abnormality in the inspection target object A 2 , that is, in a case where both the average value of the abnormality degree and the standard deviation of the abnormality degree, which are obtained from the analysis result by the data disclosure unit  33 , are high over a predetermined period or longer, the wireless master device  30  can notify the monitoring terminal  40  of the occurrence of the abnormality in the inspection target object A 2  by issuing an alarm or the like to the monitoring terminal  40 . 
     However, in a case where the standard deviation of the abnormality degree has a value equal to or greater than a predetermined value even though the average value of the abnormality degree is high, there is a high probability that the abnormality-degree and sound-state-information calculation unit  17  has erroneously detected the abnormality in the inspection target object A 2 . On the other hand, in a case where the average value of the abnormality degree is high over a predetermined period or longer, and the standard deviation of the abnormality degree continues continuously has a value smaller than a predetermined value, there is a high probability that the abnormality-degree and sound-state-information calculation unit  17  has correctly detected the abnormality in the inspection target object A 2 . 
     Therefore, for example, in a case where the average value of the abnormality degree is equal to or greater than the threshold value and the standard deviation of the abnormality degree is equal to or greater than a predetermined value SD 1 , the data disclosure unit  33  of the wireless master device  30  determines that the abnormality-degree and sound-state-information calculation unit  17  has erroneously detected the abnormality in the inspection target object. On the contrary, in a case where the average value of the abnormality degree is equal to or greater than the threshold value and the standard deviation of the abnormality degree is smaller than the predetermined value SD 1 , the data disclosure unit  33  determines that the abnormality-degree and sound-state-information calculation unit  17  has correctly detected the abnormality in the inspection target object. 
     The data disclosure unit  33  specifies the abnormality cause  322  from the sound state information  323  of the sound in which the abnormality is detected. Then, the data disclosure unit  33  notifies the monitoring terminal  40  of information (for example, identification information) on the inspection target object A 2  having a high probability that an abnormality has occurred, and the abnormality cause. When the worker who operates the monitoring terminal  40  confirms this notification (the identification information and the abnormality cause of the inspection target object A 2 ), the worker can perform an early inspection of the inspection target object A 2  and take measures such as repair and replacement of the inspection target object A 2  as necessary. 
     In a case where there is a high probability that the abnormality-degree and sound-state-information calculation unit  17  has erroneously detected an abnormality, the wireless master device  30  does not issue an alarm to the monitoring terminal  40 . On the other hand, in a case where there is a high probability that the abnormality-degree and sound-state-information calculation unit  17  has correctly detected the abnormality, the wireless master device  30  issues an alarm to the monitoring terminal  40  to attract the attentions of the worker. As described above, since the wireless master device  30  can determine the accuracy of the abnormality by using the average value of the abnormality degree and the standard deviation of the abnormality degree, the alarm does not occur frequently even though the abnormality becomes instantaneously high. Note that, the predetermined value SD 1  may be appropriately changed in accordance with the type of the inspection target object A 2  and the state of the inspection target object A 2  deteriorated over time. In addition, the predetermined value SD 1  may be set to a different value in accordance with the positive and negative standard deviations. 
     In the conventional abnormality detection method, the worker listens to the sound of the inspection target object A 2  with his/her own ear to determine whether or not the abnormality has occurred. Thus, when the sound of the inspection target object A 2  is not sufficiently large as indicated at the time t 1 , it is not possible to detect the abnormality. On the other hand, in the abnormality detection method according to the present embodiment, the worker is notified of the detection of the abnormality at the time t 2  earlier than the time t 1 , based on the point that both the average value of the abnormality degree and the standard deviation of the abnormality degree are high. Therefore, by using the abnormality detection method according to the present embodiment, the worker can take measures for the abnormality in the inspection target object A 2  at a timing earlier than a timing in the conventional abnormality detection method. In addition, when the abnormality is detected, an abnormality cause is specified based on the sound state information at this time and the worker is notified of the abnormality cause. Thus, the worker can quickly grasp the abnormality cause. 
     [Setting of Learning Result] 
     Meanwhile, the load of the processing of learning a normal sound is high. Thus, it is not appropriate to cause the wireless slave device  10  having limited available power and storage area to perform the learning processing. Therefore, when the wireless slave device  10  is installed, the worker prepares the learning result setting terminal  7  and performs an operation to set the learning result  15  in the wireless slave device  10 . Therefore, an example of the configuration and processing of the learning result setting terminal  7  that sets the learning result  15  will be described with reference to  FIGS.  9  and  10   . 
       FIG.  9    is a block diagram illustrating an internal configuration example of the learning result setting terminal  7  connected to the wireless slave device  10 . 
       FIG.  10    is a flowchart illustrating an example of processing of the learning result setting terminal  7 . 
     As the learning result setting terminal  7 , a notebook or tablet computer device or the like that can be carried by the worker is used. The computer  60  illustrated in  FIG.  5    may be applied as the hardware configuration of the learning result setting terminal  7 . The learning result setting terminal  7  includes a signal processing unit  71 , a feature extraction unit  72 , and a learning model generation unit  73 . 
     First, the worker connects the learning result setting terminal  7  to the wireless slave device  10  at the time of installation of the wireless slave device  10  (S 41 ). Then, the signal processing unit  71  performs various types of signal processing such as input processing, noise removal, amplification processing, and the like of the digital signal of the sound output from the sound collection unit  11  of the wireless slave device  10  (S 42 ). 
     Then, the feature extraction unit  72  extracts the feature of the sound generated by the inspection target object A 2  based on the digital signal processed by the signal processing unit  71  (S 43 ). The operation of setting the learning result  15  by using the learning result setting terminal  7  is often performed when the worker knows in advance that the operation of the inspection target object A 2  is normal. Therefore, the feature of the sound extracted by the feature extraction unit  72  is handled as the feature of the normal sound. 
     Then, the learning model generation unit  73  generates a learning model by using the extracted feature as an input (S 44 ). The learning model generation unit  73  is realized by using artificial intelligence (AI), for example. Here, in the case of inspection target objects A 2  of the same model, even though the installation places are different, the features of the sounds are often similar. Therefore, the learning model generation unit  73  can improve the accuracy of the learning model by repeating the processing of generating the learning model based on the feature extracted for the sound generated by many inspection target objects A 2 . 
     Then, the learning model generation unit  73  sets the learning result  15  generated using the learning model, in the wireless slave device  10  (S 45 ). After the setting of the learning result  15  is completed, this processing is ended. As described above, the wireless slave device  10  itself can perform processing of obtaining the degree of difference between the sound collected by the sound collection unit  11  and the normal sound learned in advance, as the analysis result, by using the appropriate learning result  15  set by the learning result setting terminal  7  even though the learning processing is not performed. 
     Note that  FIGS.  9  and  10    illustrate an example in which the learning result setting terminal  7  performs the learning processing. For example, a cloud server accessible by the learning result setting terminal  7  via the Internet may perform the learning processing. In this case, the learning result setting terminal  7  does not generate the learning model, but transmits digital data of the sound collected by the sound collection unit  11  to the cloud server and requests the cloud server to perform the learning processing. Then, the learning result setting terminal  7  receives the learning result  15  calculated by the cloud server from the cloud server, and performs processing of setting the learning result  15  in the wireless slave device  10 . 
     In the automatic inspection system  1  according to the first embodiment described above, the sound collection unit  11  is provided in the wireless slave device  10 , and the wireless slave device  10  activates the sound collection unit  11  at a predetermined timing (for example, periodically) and causes the sound collection unit  11  to collect the operating sound of the inspection target object A 2 . In the automatic inspection system  1 , instead of transmission of sound data in the entirety of the frequency band in which the sound collection unit  11  can collect sound from the wireless slave device  10  to the wireless master device  30 , the packet D 1  including the degree of difference from the normal sound learned in advance, which is a small portion of the sound data, and the sound state information of the collected sound as the analysis result is transmitted to the wireless master device  30 . Therefore, it is possible to reduce the data size of the packet D 1  of the analysis result transmitted from the wireless slave device  10  to the wireless master device  30  in comparison to the data size of the sound data collected by the sound collection unit  11  as it is. 
     In addition, since the wireless slave device  10  is intermittently driven and transmits the packet D 1  having the minimum size from which the wireless master device  30  can extract the analysis result, it is possible to reduce the power consumption of the wireless slave device  10 . Therefore, the wireless slave device  10  can reduce the power energy required to transmit the analysis result once and suppress the power consumption of the built-in battery  58 . As a result, since the lifespan of the built-in battery  58  in the wireless slave device  10  is prolonged, it is possible to reduce the frequency of battery replacement of the wireless slave device  10 . 
     In addition, by associating the sound state information with the abnormality cause in the wireless master device  30 , when an abnormality is detected in the collected sound, the worker can quickly identify (grasp) the abnormality cause based on the sound state information. Then, by quickly specifying the abnormality cause, the worker can perform planned and efficient maintenance. For example, when the bearing of the motor is deteriorated, the worker can check the stock, purchase a replacement part as necessary, and plan the replacement work time and securing the worker. 
     In addition, the wireless slave device  10  transmits, to the wireless master device  30 , a portion of information extracted from the sound data acquired from the inspection target object A 2  over a long period. The wireless master device  30  manages the characteristics of the sound data acquired by the wireless slave device  10 . When detecting an abnormality, the wireless master device  30  notifies the monitoring terminal  40  of the probability of the abnormality occurring in the inspection target object A 2  and the abnormality cause. Therefore, the worker who uses the monitoring terminal  40  can remotely monitor the state of the inspection target object A 2 , and it is possible to reduce the opportunity to approach the inspection target object A 2  and inspect the abnormal sound. Therefore, it is possible to not only reduce the operation cost of the inspection target object A 2 , but also improve the usability of the automatic inspection system  1 . 
     If the wireless master device  30  is within the range of a communicable distance of the wireless slave device  10 , the wireless relay  20  may not be provided in the automatic inspection system  1 , and the wireless slave device  10  may be configured to directly communicate with the wireless master device  30 . 
     In addition, the sound collection unit  11  may not include the AD conversion unit and may be configured to output an analog signal of the sound generated by the inspection target object A 2 . In this case, the analysis unit  12  is configured to include an AD conversion unit at a preceding stage of the feature extraction unit  16 . The AD conversion unit of the analysis unit  12  samples and quantizes the amplitude of the analog signal of the sound input from the sound collection unit  11  at a predetermined cycle, converts the analog signal into a digital value, and outputs the digital value to the feature extraction unit  16 . The subsequent processing is performed in a similar manner to the processing of each unit according to the first embodiment. 
     [Configuration Example in which Microphone is Separated from Wireless Slave Device] 
       FIG.  11    is a diagram illustrating an example of a place of mounting the wireless slave device  10 . 
     The wireless slave device  10  illustrated in  FIG.  1    incorporates the sound collection unit  11 , and the wireless slave device  10  is installed at a position away from the inspection target object A 2 . However, as illustrated in  FIG.  11   , the sound collection unit  11  provided in the wireless slave device  10  may be configured to be detached from the housing of the wireless slave device  10 , separated from the wireless slave device  10 , and attachable to the inspection target object A 2 . 
     Since the size of the sound collection unit  11  (microphone  55 ) is smaller than the size of the housing of the wireless slave device  10 , the sound collection unit  11  can be directly attached to the inspection target object A 2 . For example, in a case where the inspection target object A 2  is an electric motor, the sound collection unit  11  can be directly attached to the bearing of the electric motor or the outside of an electric motor cover. Since the sound collection unit  11  is directly attached to each unit of the electric motor as described above, the sound collected by the sound collection unit  11  is less likely to be influenced by the environmental sound around the electric motor. 
     The sound collection unit  11  and the wireless slave device  10  are connected by a power line and a signal line extended from the wireless slave device  10 . The power line and the signal line are housed in a cable  5  that connects the sound collection unit  11  and the wireless slave device  10 . The sound collection unit  11  is operated by power supplied from the power supply unit  14  (built-in battery  58 ) through the power line. In addition, the sound collection unit  11  outputs a digital signal of the sound collected from the inspection target object A 2  to the analysis unit  12  of the wireless slave device  10  through the signal line. The analysis unit  12  can analyze the sound based on the digital signal of the sound generated only from the inspection target object A 2 , which does not include the surrounding noise. 
     FIRST CONFIGURATION EXAMPLE OF MULTI-HOP NETWORK (SINGLE MANAGER) 
       FIG.  12    is a diagram illustrating a first configuration example (single manager) of a multi-hop network of the automatic inspection system  1  according to the first embodiment of the present invention. 
     As illustrated in  FIG.  1   , the automatic inspection system  1  includes a plurality of wireless slave devices  10  and  10 ′ and the wireless relay  20 . Normally, the wireless relay  20  being a destination to which the wireless slave devices  10  and  10 ′ first transmit the packet D 1  is determined in advance. However, the environment in which the wireless slave devices  10  and  10 ′ are installed is often in a plant in which facilities having various shapes are arranged. Therefore, when the wireless slave devices  10  and  10 ′ are installed, and then a new facility  6  is installed, it is not possible to transmit the packet D 1  from the wireless slave devices  10  and  10 ′ to the wireless relay  20 . 
     Here, a multi-hop network according to a first configuration example configured by the automatic inspection system  1  will be described. In the multi-hop network, a plurality of wireless slave devices  10  and  10 ′ can transfer the packet D 1 . An example in which wireless slave devices  10 ( 1 ) to  10 ( 4 ) denoted by the reference signs ( 1 ) to ( 4 ) are provided in the multi-hop network in order to identify a plurality of wireless slave devices  10  and  10 ′ will be described. In addition, an example in which wireless relays  20 ( 1 ) and  20 ( 2 ) denoted by the reference signs ( 1 ) and ( 2 ) are provided in the multi-hop network in order to identify a plurality of wireless relays  20  will be described. 
     The wireless slave device  10 ( 1 ) collects sound generated from the inspection target object A 2 , and the wireless slave device  10 ( 2 ) collects sound generated from the inspection target B 3 . Then, the wireless slave devices  10 ( 3 ) and  10 ( 4 ) collect sound generated from different locations of an inspection target object C 4 . For example, packets D 1  are transmitted from the two wireless slave devices  10 ( 1 ) and  10 ( 2 ) to the wireless relay  20 ( 1 ) illustrated on the left side of  FIG.  12   . In addition, it is assumed that the packets D 1  are also transmitted from the two wireless slave devices  10 ( 3 ) and  10 ( 4 ) to the wireless relay  20 ( 2 ) illustrated on the right side of  FIG.  12   . 
     However, it is assumed that a facility  6  is installed between the wireless relay  20 ( 2 ) illustrated on the right side of  FIG.  12   , and the two wireless slave devices  10 ( 3 ) and  10 ( 4 ), and thus a direct communication between the wireless relay  20 ( 2 ), and the two wireless slave devices  10 ( 3 ) and  10 ( 4 ) is not possible. As described above, when the wireless slave devices  10 ( 3 ) and  10 ( 4 ) among the plurality of wireless slave devices  10 ( 1 ) to  10 ( 4 ) detects that transmission of the packet D 1  to the wireless relay  20 ( 2 ) is not possible, another wireless slave device  10 ( 2 ) capable of transmitting data to another wireless relay  20 ( 1 ) is requested to transfer the packet D 1 . 
     Therefore, the wireless slave devices  10 ( 3 ) and  10 ( 4 ) that cannot transmit the packet D 1  to the wireless relay  20 ( 2 ) search for the wireless slave devices  10 ( 1 ) and  10 ( 2 ) capable of transmitting the packet D 1  to the other wireless relay  20 ( 1 ). The wireless slave devices  10 ( 3 ) and  10 ( 4 ) that cannot transmit the packet D 1  transfer the packet D 1  to the wireless slave device  10 ( 2 ) capable of transmitting the packet D 1 . At this time, the wireless slave device  10 ( 3 ) transmits the packet D 1  of the wireless slave device  10 ( 3 ) to the wireless slave device  10 ( 2 ), and further transfers the packet D 1  transmitted from the wireless slave device  10 ( 4 ) to the wireless slave device  10 ( 2 ). 
     The other wireless slave device  10 ( 2 ) transfers the packet D 1  transmitted from the wireless slave devices  10 ( 3 ) and  10  ( 4 ) to the wireless relay  20 ( 1 ). That is, the wireless slave device  10 ( 2 ) transmits the packet D 1  of the wireless slave device  10 ( 2 ) to the wireless relay  20 ( 1 ), and also transmits the packet D 1  transmitted or transferred from the wireless slave device  10 ( 3 ) to the wireless relay  20 ( 1 ). Since the automatic inspection system  1  constitutes the multi-hop network in this manner, all the wireless slave devices  10 ( 1 ) to  10 ( 4 ) can transmit the packets D 1  to the wireless master device  30  via the wireless relay  20 ( 1 ). 
     Note that, when the wireless slave devices  10 ( 2 ) and  10 ( 3 ) continue to transfer the packet D 1  over a long period, the power consumption of the built-in battery  58  in the wireless slave devices  10 ( 2 ) and  10 ( 3 ) becomes higher than that of the other wireless slave devices  10 ( 1 ) and  10 ( 4 ). Therefore, the monitoring terminal  40  may be notified of the presence of the wireless slave device  10 ( 2 ) that has started to transfer the packet D 1  transmitted from the other wireless slave devices  10 ( 3 ) and  10 ( 4 ), through the wireless master device  30 ( 1 ). With this notification, the worker can know a situation in which the wireless slave devices  10 ( 3 ) and  10 ( 4 ) and the wireless relay  20 ( 2 ) cannot perform wireless communication. Then, the worker can take measures such as movement of the wireless slave devices  10 ( 3 ) and  10 ( 4 ) to positions at which the worker can communicate with the wireless relay  20 ( 2 ) or movement of the facility  6 . 
     The monitoring terminal  40  can monitor the state of the inspection target object A 2  at a place away from the plant where the inspection target object A 2  is installed via the external Internet. 
     SECOND CONFIGURATION EXAMPLE OF MULTI-HOP NETWORK (MULTI-MANAGER) 
       FIG.  13    is a diagram illustrating a second configuration example (multi-manager) of the multi-hop network of the automatic inspection system  1  according to the first embodiment of the present invention. 
     Here, a multi-hop network according to a second configuration example configured by the automatic inspection system  1  will be described. The automatic inspection system  1  can constitute a multi-hop network without the wireless relay  20 . An example in which wireless master devices  30 ( 1 ) and  30 ( 2 ) denoted by the reference signs ( 1 ) and ( 2 ) are provided in the multi-hop network in order to identify a plurality of wireless master devices  30  will be described. That is, in this multi-hop network, the wireless relays  20 ( 1 ) and  20 ( 2 ) illustrated in  FIG.  12    are replaced with two wireless master devices  30  ( 1 ) and  30 ( 2 ). The wireless master devices  30 ( 1 ) and  30 ( 2 ) are connected to the monitoring terminal  40  via a communication network such as the Internet. 
     In the multi-hop network, a plurality of wireless slave devices  10  and  10 ′ can transfer the packet D 1 . For example, packets D 1  are transmitted from the two wireless slave devices  10 ( 1 ) and  10 ( 2 ) to the wireless master device  30 ( 1 ) illustrated on the left side of  FIG.  13   . In addition, it is assumed that the packets D 1  are also transmitted from the two wireless slave devices  10 ( 3 ) and  10 ( 4 ) to the wireless master device  30 ( 2 ) illustrated on the right side of  FIG.  13   . 
     However, it is assumed that a facility  6  is installed between the wireless master device  30 ( 2 ) illustrated on the right side of  FIG.  13   , and the two wireless slave devices  10 ( 3 ) and  10 ( 4 ), and thus a direct communication between the wireless master device  30 ( 2 ), and the two wireless slave devices  10 ( 3 ) and  10 ( 4 ) is not possible. As described above, when the wireless slave devices  10 ( 3 ) and  10 ( 4 ) among the plurality of wireless slave devices  10 ( 1 ) to  10 ( 4 ) detects that transmission of the packet D 1  to the wireless master device  30 ( 2 ) is not possible, another wireless slave device  10  ( 2 ) capable of transmitting data to another wireless master device  30 ( 1 ) is requested to transfer the packet D 1 . 
     Therefore, the wireless slave devices  10 ( 3 ) and  10 ( 4 ) that cannot transmit the packet D 1  to the wireless master device  30 ( 2 ) search for the wireless slave devices  10 ( 1 ) and  10 ( 2 ) capable of transmitting the packet D 1  to the other wireless master device  30 ( 1 ). The wireless slave devices  10 ( 3 ) and  10 ( 4 ) that cannot transmit the packet D 1  transfer the packet D 1  to the wireless slave device  10 ( 2 ) capable of transmitting the packet D 1 . At this time, the wireless slave device  10 ( 3 ) transmits the packet D 1  of the wireless slave device  10 ( 3 ) to the wireless slave device  10 ( 2 ), and further transfers the packet D 1  transmitted from the wireless slave device  10 ( 4 ) to the wireless slave device  10 ( 2 ). 
     The other wireless slave device  10 ( 2 ) transfers the packet D 1  transmitted from the wireless slave devices  10 ( 3 ) and  10 ( 4 ) to the wireless master device  30 ( 1 ). That is, the wireless slave device  10 ( 2 ) transmits the packet D 1  of the wireless slave device  10 ( 2 ) to the wireless master device  30 ( 1 ), and also transmits the packet D 1  transmitted or transferred from the wireless slave device  10 ( 3 ) to the wireless master device  30 ( 1 ). Since the automatic inspection system  1  constitutes the multi-hop network in this manner, all the wireless slave devices  10 ( 1 ) to  10 ( 4 ) can transmit the packets D 1  to the monitoring terminal  40  via the wireless master device  30 ( 1 ). 
     Note that, when the wireless slave devices  10 ( 2 ) and  10 ( 3 ) continue to transfer the packet D 1  over a long period, the power consumption of the built-in battery  58  in the wireless slave devices  10 ( 2 ) and  10 ( 3 ) becomes higher than that of the other wireless slave devices  10 ( 1 ) and  10 ( 4 ). Therefore, the monitoring terminal  40  may be notified of the presence of the wireless slave device  10 ( 2 ) that has started to transfer the packet D 1  transmitted from the other wireless slave devices  10 ( 3 ) and  10 ( 4 ), through the wireless master device  30 ( 1 ). With this notification, the worker can know a situation in which the wireless slave devices  10 ( 3 ) and  10 ( 4 ) and the wireless master device  30 ( 2 ) cannot perform wireless communication. Then, the worker can take measures such as movement of the wireless slave devices  10 ( 3 ) and  10 ( 4 ) to positions at which the worker can communicate with the wireless master device  30 ( 2 ) or movement of the facility  6 . 
     THIRD CONFIGURATION EXAMPLE OF MULTI-HOP NETWORK (MULTI-MANAGER) 
       FIG.  14    is a diagram illustrating a third configuration example (multi-manager) of the multi-hop network of the automatic inspection system  1  according to the first embodiment of the present invention. 
     Here, a multi-hop network according to a third configuration example configured by the automatic inspection system  1  will be described. The multi-manager configuration of the multi-hop network according to the second configuration example illustrated in  FIG.  13    may include a wireless relay  20  as illustrated in  FIG.  14   . 
     The automatic inspection system  1  illustrated in  FIG.  14    can constitute a multi-hop network in a form including a plurality of wireless relays  20  and a plurality of wireless master devices  30 . In this multi-hop network, the wireless relay  20 ( 1 ) is connected to the wireless slave devices  10 ( 1 ) and  10 ( 2 ), and the wireless relay  20 ( 2 ) is connected to the wireless slave devices  10 ( 3 ) and  10 ( 4 ). The wireless relay  20 ( 1 ) and the wireless master device  30 ( 1 ) are connected, and the wireless relay  20 ( 2 ) and the wireless master device  30 ( 2 ) are connected. The wireless master devices  30 ( 1 ) and  30 ( 2 ) are connected to the monitoring terminal  40  via a communication network such as the Internet. 
     Also in the multi-hop network according to the third configuration example, it is assumed that the facility  6  is installed between the wireless slave devices  10  ( 3 ) and  10 ( 4 ), and the wireless relay  20 ( 2 ), and the wireless relay  20 ( 2 ) and the two wireless slave devices  10 ( 3 ) and  10 ( 4 ) cannot directly communicate with each other. In this case, the wireless slave devices  10 ( 3 ) and  10 ( 4 ) search for another wireless slave device  10 ( 2 ). The wireless slave device  10  ( 4 ) transmits the packet D 1  to the wireless slave device  10 ( 3 ). The wireless slave device  10 ( 3 ) transmits the packet D 1  created by the wireless slave device  10 ( 3 ) itself to the wireless slave device  10 ( 2 ), and transfers the packet D 1  received from the wireless slave device  10  ( 4 ) to the wireless slave device  10 ( 2 ). Then, the wireless slave device  10  ( 2 ) transfers the packet D 1  to the wireless relay  20 ( 1 ), and thus the packets D 1  of the wireless slave devices  10 ( 3 ) and  10 ( 4 ) are transmitted from the wireless relay  20 ( 1 ) to the wireless master device  30 ( 1 ), and are transmitted from the wireless master device  30 ( 1 ) to the monitoring terminal  40  via the communication network. 
     Since the automatic inspection system  1  constitutes the multi-hop network according to the third configuration example in this manner, all the wireless slave devices  10 ( 1 ) to  10 ( 4 ) can transmit the packets D 1  to the monitoring terminal  40  via the wireless relay  20 ( 1 ) and the wireless master device  30 ( 1 ). Note that, in order to prevent the continuous transfer of the packet D 1  over a long period, the processing of notifying the monitoring terminal  40  that the wireless slave devices  10 ( 2 ) and ( 3 ) have started to transfer the packet D 1  is similar to the multi-hop network according to the first configuration example. 
     Second Embodiment 
     Next, a configuration example and an operation example of an automatic inspection system according to a second embodiment will be described with reference to  FIG.  15   . The inspection target object changes in temperature in accordance with the state of the inspection target object in many cases. Therefore, in the second embodiment, as compared with the first embodiment, a temperature sensor  18  is provided in the wireless slave device  10 , so that a configuration in which a temperature element is provided as the state information of the facility at the time of the abnormality is made. 
       FIG.  15    is a block diagram illustrating an overall configuration example of an automatic inspection system  1 A according to the second embodiment of the present invention. A wireless slave device  10 A according to the present embodiment further includes the temperature sensor  18 . Note that detailed description of a wireless slave device  10 A′ having the similar configuration to the wireless slave device  10 A and detailed description of the same portions as the wireless relay  20 , the wireless master device  30 , and the monitoring terminal  40  according to the first embodiment will be omitted. 
     The temperature sensor  18  is a device that is installed at a position away from the inspection target object A 2  (facility) by a predetermined distance and measures the temperature of the surface of the inspection target object A 2  at a predetermined timing (for example, a predetermined period). It is desirable that the temperature sensor  18  be disposed so as to be able to measure the temperature of a portion of the inspection target object A 2  at which heat generation is expected. In the present embodiment, an infrared sensor (radiation thermometer) or the like capable of measuring the temperature in a non-contact manner is used as the temperature sensor  18 , but a contact type temperature sensor such as a thermistor is not excluded. Similar to the sound collection unit  11 , the temperature sensor  18  desirably includes an AD conversion unit therein. In a case where the temperature sensor  18  does not include an AD conversion unit, an AD conversion unit (not illustrated) is provided in the wireless slave device  10 A, and the AD conversion unit converts an output signal of the temperature sensor  18  into a digital value. 
     The wireless communication unit  13  converts the temperature measured by the temperature sensor  18  into packet data (generates a packet D 1 ) together with the analysis result obtained by the analysis unit  12  (the abnormality degree and the sound state information of the sound data of the inspection target object A 2 ), as the state information of the inspection target object A 2 . The wireless communication unit  13  wirelessly transmits the packet D 1  in which destination information of the wireless master device  30  is added, to the wireless master device  30  via the wireless relay  20  at a predetermined timing. 
     The wireless master device  30  stores data including the temperature of the inspection target object A 2  as the state information at the time of sound collection, in the data storage unit  32  together with the abnormality degree and the sound state information of the sound data received by the wireless communication unit  31 , in association with the time of receiving the data. That is, the wireless master device  30  extracts the pieces of data from the packet D 1  and converts the data into time-series data. 
     The data disclosure unit  33  uses the temperature of the inspection target object A 2  as a material for reinforcing the determination at the time of determining the abnormality or identifying the abnormality cause. For example, when detecting the abnormality in the inspection target object A 2  based on the abnormality degree  321  in  FIG.  8   , the data disclosure unit  33  confirms the abnormality in the inspection target object A 2  if the measured temperature of the temperature sensor  18  is equal to or greater than a predetermined value. 
     Note that the data disclosure unit  33  may determine that the inspection target object A 2  is abnormal when the abnormality degree  321  of the sound data is lower than a threshold value (for example, the average value) by several percentages in  FIG.  8   , but the measured temperature of the temperature sensor  18  is equal to or greater than the predetermined value. As a result, in a case where an abnormality is suspected from the abnormality degree  321 , or in a case where it is not possible to determine an abnormality only from the abnormality degree  321 , it is possible to reliably determine the abnormality in the inspection target object A 2  by using the measured temperature of the temperature sensor  18 . 
     In addition, in a case where, in  FIG.  8   , the abnormality degree of the sound data is lower than the threshold value (for example, the average value) by a predetermined value or several percentages, but the measured temperature of the temperature sensor  18  is equal to or greater than the predetermined value, the data disclosure unit  33  may request the wireless slave device  10 A to transmit more detailed information (other information  324 ) in order to determine the abnormality in the inspection target object A 2  and specify the abnormality cause. As described above, in a case where the abnormality of the inspection target object A 2  is suspected from the abnormality degree  321  and the measured temperature of the temperature sensor  18 , more detailed information (the other information  324 ) regarding the sound collected from the wireless slave device  10 A is acquired. In this manner, the abnormality determination and specifying of the abnormality cause can be performed in consideration of more detailed information. 
     In addition, when detecting the abnormality in the inspection target object A 2  based on the abnormality degree in  FIG.  8   , the data disclosure unit  33  may specify the abnormality cause of the inspection target object A 2  based on the sound state information and the measured temperature of the temperature sensor  18 . By storing the sound state information  323  and the measured temperature of the temperature sensor  18  in the data storage unit  32  in advance in association with the abnormality cause  322 , the data disclosure unit  33  can specify the more accurate abnormality cause  322  based on the sound state information  323  and the measured temperature of the temperature sensor  18 . 
     The automatic inspection system  1 A according to the second embodiment described above has the following effects in addition to the effects similar to those of the automatic inspection system  1  according to the first embodiment. In the present embodiment, when an abnormality is determined or an abnormality cause is specified, it is possible to perform more accurate abnormality determination and specifying of the abnormality cause in consideration of the temperature of the inspection target object measured by the temperature sensor  18  in addition to the abnormality degree and the sound state information of the collected sound. 
     Note that it should be noted that the present invention is not limited to each of the above-described embodiments, and it goes without saying that various other application examples and modification examples can be taken as long as the gist of the present invention described in the claims is not deviated. Each constituent element of the present invention can be freely selected, and an invention having a selected configuration is also included in the present invention. Furthermore, the configurations described in the claims can be combined in addition to the combinations specified in the claims, and the configurations and the processing methods in the embodiments can be appropriately changed within the scope of achieving the object of the present invention. 
     Control lines and information lines in the drawings, which are considered necessary for the descriptions, are illustrated, and not all the control lines and the information lines in the product are necessarily shown. In practice, it may be considered that almost all components are connected to each other. 
     REFERENCE SIGNS LIST 
     
         
           1  automatic inspection system 
           2  inspection target object 
           10  wireless slave device 
           11  sound collection unit 
           12  analysis unit 
           13  wireless communication unit 
           14  power supply unit 
           15  learning result 
           16  feature extraction unit 
           17  abnormality-degree and sound-state-information calculation unit 
           20  wireless relay 
           21  wireless communication unit 
           30  wireless master device 
           31  wireless communication unit 
           32  data storage unit 
           33  data disclosure unit 
           321  abnormality degree 
           322  abnormality cause 
           323  sound state information 
           324  other information 
           40  monitoring terminal 
           41  abnormality degree trend 
           42  abnormality cause 
           58  built-in battery