JP7639355B2 - Master device, slave device, network system, communication control method, and computer program - Google Patents

Description

The present invention relates to a master device, a slave device, a network system, a communication control method, and a computer program.

In the field of factory automation (FA), various types of devices that share the work process are controlled. To enable the various controllers, remote I/O, and manufacturing equipment used in work in a certain area such as a factory facility to work in coordination, an industrial network system, also known as a field network, is constructed to connect these devices.

A typical industrial network system uses a master-slave network consisting of various slave devices and a master device. The slave devices are devices that control the equipment installed in the factory or collect data. The master device is a device called a PLC (Programmable Logic Controller), for example, that centrally manages these slaves. EtherCAT (registered trademark) and Ethernet/IP (registered trademark) are examples of such industrial network system formats (ETHERNET: registered trademark). In such an industrial network system, communication cables are stretched between each device to create a network.

A related technique is disclosed in Patent Document 1 below. Patent Document 1 relates to a mobile communication device having a data retransmission control function. The mobile communication device includes a setting unit that sets some of multiple wireless frames to dedicated retransmission frames according to the reception quality level of data at the receiving device, and a retransmission control unit that, upon receiving a failure response from the receiving device, reallocates and retransmits data that was not successfully received in a wireless frame corresponding to the reception timing of the failure response, and further allocates and retransmits the data in the dedicated retransmission frame. By setting the dedicated retransmission frame, the number of times data can be retransmitted is increased beyond the maximum number of retransmissions before the dedicated retransmission frame was set.

International Publication No. 2008/120275

In industrial network systems, noise can occur due to various factors, and this noise can cause communication to be impossible. The above-mentioned Patent Document 1 deals with failure responses by setting a dedicated retransmission frame and increasing the number of times data can be retransmitted beyond the maximum number of retransmissions before the dedicated retransmission frame was set.

However, Patent Document 1 relates to mobile communication devices, and this technology cannot be applied to industrial network systems.

The present invention was made in consideration of the above problems, and aims to realize a master device or the like that can avoid communication failures in an industrial network system even when the communication status of the communication network temporarily deteriorates.

To solve the above problems, the present invention adopts the following configuration.

A master device according to one aspect of the present invention includes a communication unit that communicates with multiple slave devices via a communication network, and a control unit that, upon receiving from one of the multiple slave devices via the communication unit that information regarding the signal quality of a communication cable is an abnormal value, changes the upper limit of the number of timeout detections of the multiple slave devices and transmits the changed upper limit of the number of timeout detections to the multiple slave devices via the communication unit.

According to the above configuration, the control unit transmits the changed upper limit value of the number of timeout detections to the multiple slave devices via the communication unit, so that it is possible to avoid communication failure even if the communication status of the communication network temporarily deteriorates.

In the master device according to the above aspect, the master device further includes a memory unit that stores an upper limit value of the number of timeout detections for each of the plurality of slave devices, and when the control unit receives from one of the plurality of slave devices via the communication unit that information relating to the signal quality of the communication cable is an abnormal value, the control unit increases the upper limit value of the number of timeout detections for each of the plurality of slave devices stored in the memory unit and transmits the upper limit value of the number of timeout detections corresponding to the plurality of slave devices via the communication unit.

With the above configuration, the upper limit of the number of timeout detections for each of the multiple slave devices stored in the memory unit is increased, making it possible to avoid situations in which the slave device is unable to send or receive packets.

In the master device according to the above aspect, when the control unit receives information from one of the multiple slave devices via the communication unit indicating that the information on the signal quality of the communication cable is an abnormal value, the control unit transmits the same upper limit value of the number of timeout detections to all of the multiple slave devices via the communication unit.

With the above configuration, the control unit transmits the same upper limit value for the number of timeout detections to all of the multiple slave devices via the communication unit, making it possible to avoid a situation in which a slave device whose information on the signal quality of the communication cable is normal is unable to send or receive packets.

In the master device according to the above aspect, when the control unit receives, via the communication unit, from a slave device whose information on the signal quality of the communication cable was an abnormal value, that the information on the signal quality of the communication cable is now a normal value, the control unit instructs the multiple slave devices to restore the upper limit of the number of timeout detections to the original value.

With the above configuration, multiple slave devices are instructed to return to the original upper limit value for the number of timeout detections, making it possible to respond when the communication state of the communication network returns to normal.

A slave device according to one aspect of the present invention includes a communication unit that communicates with a master device, and a control unit that acquires information about the signal quality of a connected communication cable, and if the information about the signal quality of the communication cable is an abnormal value, notifies the master device via the communication unit that the information about the signal quality of the communication cable is an abnormal value, and when a changed upper limit value for the number of timeout detections is received from the master device via the communication unit, sets the upper limit value for the number of timeout detections.

According to the above configuration, when the control unit receives the changed upper limit of the number of timeout detections from the master device via the communication unit, the control unit sets the upper limit of the number of timeout detections, so that it is possible to avoid communication failure even if the communication state of the communication network temporarily deteriorates.

A network system according to one aspect of the present invention is a network system including a master device and a plurality of slave devices, the master device including a first communication unit that communicates with the plurality of slave devices via a communication network, and a first control unit that, when receiving from any of the plurality of slave devices via the first communication unit that information on the signal quality of the communication cable is an abnormal value, changes the upper limit of the number of timeout detections of the plurality of slave devices and transmits the changed upper limit of the number of timeout detections to the plurality of slave devices via the first communication unit, and each of the plurality of slave devices includes a second communication unit that communicates with the master device, and a second control unit that acquires information on the signal quality of the communication cable, notifies the master device via the second communication unit that the information on the signal quality of the communication cable is an abnormal value when the information on the signal quality of the communication cable is an abnormal value, and sets the upper limit of the number of timeout detections when the changed upper limit of the number of timeout detections is received from the master device via the second communication unit.

According to the above configuration, the first control unit transmits the changed upper limit of the number of timeout detections to the multiple slave devices via the first communication unit, so that it is possible to avoid communication failure even if the communication status of the communication network temporarily deteriorates.

A communication control method according to one aspect of the present invention includes a step of changing the upper limit of the number of timeout detections of the multiple slave devices when a master device receives from one of the multiple slave devices that information on the signal quality of a communication cable is an abnormal value, and a step of transmitting the changed upper limit of the number of timeout detections to the multiple slave devices.

With the above configuration, the master device transmits the changed upper limit of the number of timeout detections to multiple slave devices, making it possible to avoid communication failure even if the communication status of the communication network temporarily deteriorates.

A computer program according to one aspect of the present invention is a computer program for causing a computer to execute a communication control method, the communication control method including the steps of: when receiving from one of a plurality of slave devices information indicating that the signal quality of a communication cable is an abnormal value, changing the upper limit of the number of timeout detections of the plurality of slave devices; and transmitting the changed upper limit of the number of timeout detections to the plurality of slave devices.

With the above configuration, the master device transmits the changed upper limit of the number of timeout detections to multiple slave devices, making it possible to avoid communication failure even if the communication status of the communication network temporarily deteriorates.

According to any one of the master device according to an aspect of the present invention, the slave device according to an aspect of the present invention, the network system according to an aspect of the present invention, the communication control method according to an aspect of the present invention, and the computer program according to an aspect of the present invention, it is possible to avoid communication failure even when the communication state of the communication network temporarily deteriorates.

2 is a block diagram showing a functional configuration of a master device included in the network system according to the embodiment of the present invention. FIG. 11A and 11B are diagrams illustrating changes made by the master device to the upper limit of the number of timeout detections. 1 is a diagram showing a schematic configuration of a network system including a master device according to an embodiment of the present invention; 10 is a flowchart illustrating a processing procedure of the master device. 10 is a flowchart for explaining a processing procedure of a PC or an HMI. FIG. 2 is a block diagram showing a functional configuration of a slave device included in a network system according to an embodiment of the present invention. 5 is a flowchart illustrating a processing procedure of a slave device according to an embodiment of the present invention.

Below, an embodiment of one aspect of the present invention (hereinafter also referred to as "this embodiment") will be described with reference to the drawings.

§1 Application example (Example of configuration of master device 10)
1 is a block diagram showing the functional configuration of a master device 10 included in a network system 1 according to an embodiment of the present invention. The network system 1 includes the master device 10, a hub device 17, slave devices 21a to 21e, and a PC (Personal Computer) 30.

The master device 10, the slave device 21a, and the PC 30 are connected by a communication network such as EtherCAT (registered trademark) or Ethernet/IP (registered trademark). In this embodiment, a case where these devices are connected to an Ethernet/IP (registered trademark) communication network is described, but this is not limited to this. The communication network may be, for example, a network system such as Mechatrolink (registered trademark) or CC-Link (registered trademark).

As shown in FIG. 1, master device 10 and slave device 21a are connected by communication cable 61. Similarly, slave device 21a and slave device 21b are connected by communication cable 62, and slave device 21b and hub device 17 are connected by communication cable 63. Hub device 17 and slave device 21c are connected by communication cable 64, hub device 17 and slave device 21d are connected by communication cable 65, and hub device 17 and slave device 21e are connected by communication cable 66. Slave devices 21a to 21b are connected by a daisy chain connection, and slave devices 21c to 21e are connected by a star connection.

Slave devices 21a to 21e have a circuit for controlling the physical layer (hereinafter referred to as a PHY circuit), and are capable of acquiring the SQI (Signal Quality Indicator) (information related to the signal quality of the communication cable) value of the communication cable connected by the PHY circuit.

The master device 10 includes a control unit (first control unit) 101, a memory unit 102, and a communication unit (first communication unit) 103. The communication unit 103 is connected to the slave device 21a and the PC 30 via a communication network such as Ethernet/IP (registered trademark). Note that communication between the communication unit 103 and the slave devices 21a to 21e is performed by cyclic communication.

The memory unit 102 is composed of RAM (Random Access Memory), flash memory, a hard disk, etc., and stores data referenced by the control unit 101 and is used as a primary memory area.

The memory unit 102 stores the upper limit of the number of timeout detections for each of the slave devices 21a to 21e. This upper limit of the number of timeout detections is set in advance by the user for each of the slave devices 21a to 21e. In addition, the same upper limit of the number of timeout detections may be set for all of the slave devices 21a to 21e.

When the control unit 101 receives a message from one of the slave devices 21a to 21e that the SQI value is abnormal, it reads out the upper limit of the number of timeout detections for each slave device 21a to 21e stored in the memory unit 102. The control unit 101 then changes the upper limit of each timeout detection count and transmits it to the corresponding slave device 21a to 21e via the communication unit 103. For example, the control unit 101 adds "1" to the upper limit of each timeout detection count and transmits it to the corresponding slave device 21a to 21e via the communication unit 103.

The control unit 101 may also add "1" to the largest upper limit value of the number of timeout detections for each slave device 21a to 21e stored in the memory unit 102, and transmit the same upper limit value of the number of timeout detections to all slave devices 21a to 21e.

Then, when the control unit 101 receives a notification via the communication unit 103 from a slave device whose SQI value was abnormal that the SQI value is now normal, it reads the upper limit value of the timeout detection count for each slave device 21a to 21e stored in the memory unit 102, and instructs the slave devices 21a to 21e to reset the number of timeout detections to the original value by transmitting the upper limit value of the timeout detection count corresponding to each slave device 21a to 21e.

Each of the slave devices 21a to 21e has an input port and an output port, and a communication cable is connected to each port. The slave devices 21a to 21e can obtain the SQI value of both the input port and the output port.

Each of the slave devices 21a to 21e periodically measures the SQI value of the communication cable connected to the slave device and determines whether the SQI value is abnormal. For example, each of the slave devices 21a to 21e acquires the SQI value of the communication cable at a 100 ms cycle (predetermined cycle), and sets the average of the SQI values acquired 10 times (predetermined number of times) as the SQI value of each slave device.

Then, each of the slave devices 21a to 21e compares the SQI value with a predetermined value to determine whether the SQI value is abnormal. For example, the predetermined value is "40," and if the SQI value is equal to or less than this value, the SQI value is determined to be abnormal.

As described above, communication between the master device 10 and the slave devices 21a to 21e is carried out by cyclic communication, with the master device 10 sending a packet to the slave device 21a. When the slave device 21a receives the packet, it writes data into the packet and sends it to the slave device 21b. In the same manner, packets are sent to the slave devices in sequence, and after the last slave device 21e writes data into the packet, it sends the packet to the master device 10. In this way, each of the slave devices 21a to 21e writes data into one packet in sequence and sends it, so that the master device 10 can obtain the data from each of the slave devices 21a to 21e at high speed.

If packets cannot be transmitted between master device 10 and slave device 21a, or between slave devices 21a to 21e, master device 10 will notify slave devices 21a to 21e that it has detected a timeout because it was unable to receive the packet within a specified time. Then, master device 10 will resend the packet.

Each of the slave devices 21a to 21e tolerates not being able to receive packets until the upper limit of the timeout detection count is reached. Therefore, if a small upper limit of the timeout detection count is set in a slave device other than the slave device in which communication is not possible, that slave device may detect the timeout first. To avoid this situation, if the SQI value of any of the communication cables 61 to 66 becomes abnormal, the master device 10 performs a process to change the upper limit of the timeout detection count for each of the slave devices 21a to 21e.

Figure 2 is a diagram showing a schematic diagram of the master device 10 changing the upper limit of the number of timeout detections for each of the slave devices 21a to 21e. The slave device 21a measures the SQI value of the communication cable 61 connecting the master device 10 and its own slave device 21a, and if the SQI value is abnormal, notifies the master device 10 that the SQI value is abnormal. The slave device 21a also measures the SQI value of the communication cable 62 connecting its own slave device 21a and slave device 21b, and if the SQI value is abnormal, notifies the master device 10 that the SQI value is abnormal.

The slave device 21b measures the SQI value of the communication cable 63 connecting the slave device 21b itself to the hub device 17, and if the SQI value is abnormal, notifies the master device 10 that the SQI value is abnormal. Note that the measurement of the SQI value of the communication cable 62 connecting the slave device 21a to the slave device 21b may be performed by either the slave device 21a or 21b.

Slave device 21c measures the SQI value of the communication cable 64 connecting its own slave device 21c to the hub device 17, and if the SQI value is abnormal, notifies master device 10 that the SQI value is abnormal. Slave device 21d measures the SQI value of the communication cable 65 connecting its own slave device 21d to the hub device 17, and if the SQI value is abnormal, notifies master device 10 that the SQI value is abnormal. Similarly, slave device 21e measures the SQI value of the communication cable 66 connecting its own slave device 21e to the hub device 17, and if the SQI value is abnormal, notifies master device 10 that the SQI value is abnormal.

For example, if the SQI value of the communication cable 62 connecting the slave devices 21a and 21b is below the abnormal value of "40", the slave device 21a notifies the master device 10 that the SQI value is abnormal. When the master device 10 receives notification from the slave device 21a that the SQI value is abnormal, it changes the upper limit of the number of timeout detections for each of the slave devices 21a to 21e and transmits the upper limit of the number of timeout detections to each of the slave devices 21a to 21e.

§2 Configuration example (Overall overview of network system 1)
3 is a diagram showing a schematic configuration of a network system 1 including a master device 10 according to an embodiment of the present invention. The network system 1 includes the master device 10, hub devices 15-17, slave devices 21a-21e, 22a-22c, and 23a-23c, a PC (terminal device) 30, and an HMI (Human Machine Interface) (terminal device) 40.

The network system may be, for example, a field network system made up of a group of manufacturing devices in a factory. The master device 10 may be, for example, a device such as a PLC.

Master device 10 is connected to multiple slave devices 21a-21c, 22a-22c, and 23a-23 via a communication network through hub devices 15 and 16. Slave device 21b is also connected to slave devices 21c-21e via hub device 17. For example, multiple slave devices 21a-21b, 22a-22c, and 23a-23c are connected by a daisy chain connection, and slave devices 21c-21e are connected by a star connection.

The PC 30 and the HMI 40 are connected to the master device 10 via the hub device 15, and transmit instructions to the master device 10 and transmit the upper limit of the timeout detection count of each of the slave devices 21a to 21e to the master device 10. When the master device 10 changes the upper limit of the timeout detection count of each of the slave devices 21a to 21e, the PC 30 and the HMI 40 receive the changed upper limit of the timeout detection count from the master device 10. The PC 30 and the HMI 40 may then display the changed upper limit of the timeout detection count on the display unit. The PC 30 and the HMI 40 are also referred to as terminal devices.

§3 Operation Example Fig. 4 is a flow chart for explaining the processing procedure of the master device 10. First, the control unit 101 judges whether or not a notification that the SQI value is an abnormal value has been received from any of the slave devices 21a to 21e via the communication unit 103 (S1). If no notification has been received from any of the slave devices (S1, No), the processing of step S1 is repeated.

In addition, when the control unit 101 receives a notification from any of the slave devices 21a to 21e that the SQI value is abnormal, the control unit 101 reads the upper limit value of the timeout detection count for each of the slave devices 21a to 21e stored in the memory unit 102, and adds 1 to the upper limit value of the timeout detection count. The control unit 101 then transmits the corresponding upper limit value of the timeout detection count to each of the slave devices 21a to 21e via the communication unit 103, and instructs them to change the upper limit value of the timeout detection count (S2).

Next, the control unit 101 determines whether the hold time has elapsed (S3). This hold time is the time for which the state is to be maintained after the upper limit value of the timeout detection count is changed. This hold time is assumed to be set in advance by the user. If the hold time has not elapsed (S3, No), the process of step S3 is repeated.

If the retention time has elapsed (S3, Yes), the control unit 101 determines whether or not a notification that the SQI value is normal has been received from the slave device whose SQI value was abnormal via the communication unit 103 (S4). If a notification that the SQI value is normal has not been received (S4, No), the process returns to step S2 and repeats the subsequent steps. In this case, the communication failure of the slave device whose SQI value was abnormal has not been resolved, so the number of timeout detections is changed again.

Also, if a notification is received via the communication unit 103 that the SQI value is normal (S4, Yes), the control unit 101 reads the upper limit value of the timeout detection count for each slave device 21a to 21e stored in the memory unit 102, and instructs the slave devices 21a to 21e to reset the number of timeout detections to the original value by transmitting the upper limit value of the timeout detection count corresponding to each slave device 21a to 21e (S5).

Finally, the control unit 101 determines whether or not to end the process (S6). For example, if an instruction to stop the system is received, it determines that the process is to be ended. If the process is not to be ended (S6, No), the process returns to step S1 and the subsequent processes are repeated. If the process is to be ended (S6, Yes), the process is ended as is.

Figure 5 is a flowchart for explaining the processing procedure of the PC 30 or the HMI 40. First, the PC 30 or the HMI 40 determines whether or not the timeout detection count change function has been enabled by the user (S11). If the timeout detection count change function has not been enabled (S11, No), the process ends.

Also, if the timeout detection count change function is enabled (S11, Yes), the PC 30 or HMI 40 notifies the master device 10 of the upper limit of the timeout detection count for each slave device 21a to 21e set by the user (S12).

Next, the PC 30 or HMI 40 notifies the master device 10 of the time for which the change to the upper limit of the number of timeout detections set by the user will be retained (S13).

Finally, it is determined whether or not to end the process (S14). If the process is not to be ended (S14, No), the process returns to step S12 and the subsequent processes are repeated. If the process is to be ended (S14, Yes), the process is ended as is.

(Example of the configuration of the slave device 21a)
6 is a block diagram showing the functional configuration of slave device 21a included in network system 1 according to an embodiment of the present invention. Slave device 21a includes a control unit (second control unit) 211, a storage unit 212, and a communication unit (second communication unit) 213. Note that since slave devices 21a to 21e have similar configurations and functions, only slave device 21a will be described as a representative.

The communication unit 213 is connected to the master device 10 and the slave device 21b via a communication network such as EtherCAT (registered trademark). Note that communication between the communication unit 213 and the slave devices 21b to 21e is performed by cyclic communication.

The memory unit 212 is composed of RAM, flash memory, a hard disk, etc., and stores data referenced by the control unit 211 and is used as a primary memory area.

The control unit 211 periodically acquires the SQI value of the communication cable 61 and stores it in the memory unit 212. For example, the control unit 211 acquires the SQI value of the communication cable 61 at a 100 ms cycle (predetermined cycle) and sets the average of the SQI values for 10 times (predetermined number of times) as the SQI value of the communication cable 61. The control unit 211 then determines whether the SQI value (average value) is equal to or lower than a predetermined abnormal value.

If the SQI value is abnormal, the control unit 211 notifies the master device 10 that the SQI value is abnormal via the communication unit 213. After that, when the control unit 211 receives an instruction to change the upper limit of the number of timeout detections from the master device 10 via the communication unit 213, it stores this upper limit of the number of timeout detections in the storage unit 212. The control unit 211 allows packets to be received in a non-received state based on this upper limit of the number of timeout detections.

After changing the upper limit of the number of timeout detections, the control unit 211 periodically acquires the SQI value of the communication cable 61 and determines whether the SQI value has recovered from an abnormal value to a normal value. If the SQI value has recovered from an abnormal value to a normal value, the control unit 211 notifies the master device 10 via the communication unit 213 that the SQI value has recovered from an abnormal value to a normal value.

Figure 7 is a flowchart for explaining the processing procedure of the slave device 21a according to an embodiment of the present invention. First, the control unit 211 acquires the SQI value of the communication cable 61 and determines whether the SQI value is an abnormal value (S21). If the SQI value is not an abnormal value (S21, No), the processing of step S21 is repeated.

If the SQI value is abnormal (S21, Yes), the control unit 211 notifies the master device 10 that the SQI value is abnormal via the communication unit 213 (S22). After that, the control unit 211 determines whether or not an instruction to change the upper limit of the number of timeout detections has been received from the master device 10 via the communication unit 213 (S23).

If an instruction to change the upper limit of the number of timeout detections has not been received (S23, No), the process of step S23 is repeated. If an instruction to change the number of timeout detections has been received (S23, Yes), the changed upper limit of the number of timeout detections is stored in the memory unit 212, and the upper limit of the number of timeout detections is changed (S24).

Next, the control unit 211 acquires the SQI value of the communication cable 61 and determines whether the SQI value is normal (S25). If the SQI value is not normal (S25, No), the process of step S25 is repeated. If the SQI value is normal (S25, Yes), the control unit 211 notifies the master device 10 via the communication unit 213 that the SQI value is normal (S26).

Next, the control unit 211 determines whether or not an instruction to reset the upper limit of the timeout detection count to its original value has been received from the master device 10 via the communication unit 213 (S27). If an instruction to reset the upper limit of the timeout detection count to its original value has not been received (S27, No), the process of step S27 is repeated. If an instruction to reset the upper limit of the timeout detection count to its original value has been received (S27, Yes), the control unit 211 resets the upper limit of the timeout detection count to its original value (S28).

Finally, the control unit 211 judges whether or not to end the process (S29). For example, if an instruction to stop the system is received, it judges that the process is to be ended. If the process is not to be ended (S29, No), the process returns to step S21 and the subsequent processes are repeated. If the process is to be ended (S29, Yes), the process is ended as is.

§4 Operation and Effects According to an embodiment of the present invention, the control unit 101 of the master device 10 transmits the changed upper limit value of the timeout detection count to the multiple slave devices 21a to 21e via the communication unit 103, so that it is possible to avoid communication failure even if the communication status of the communication network temporarily deteriorates.

In addition, the control unit 101 increases the upper limit of the number of timeout detections for each of the multiple slave devices 21a to 21e stored in the memory unit 102 and transmits the increased number, making it possible to avoid a situation in which the slave devices 21a to 21e are unable to transmit packets.

In addition, the control unit 101 transmits the same upper limit value for the number of timeout detections to all of the multiple slave devices 21a to 21e via the communication unit 103, making it possible to avoid a situation in which a timeout is detected in a slave device whose SQI value is normal.

In addition, when the control unit 101 receives information that the SQI value has returned to a normal value, it instructs the multiple slave devices 21a to 21e to restore the upper limit of the number of timeout detections to the original value, making it possible to respond when the communication state of the communication network has returned to normal.

In addition, when the control unit 211 of the slave device 21a receives the changed upper limit value of the timeout detection count from the master device 10 via the communication unit 213, the control unit 211 sets the upper limit value of the timeout detection count, so that it is possible to avoid communication failure even if the communication state of the communication network temporarily deteriorates.

[Software implementation example]
The functional blocks of the master device 10 and the slave device 21a (particularly, the control units 101 and 211) may be realized by a logic circuit (hardware) formed on an integrated circuit (IC chip) or the like, or may be realized by software.

In the latter case, the master device 10 and the slave device 21a are equipped with a computer that executes instructions of a program, which is software that realizes each function. This computer is equipped with, for example, one or more processors, and a computer-readable recording medium that stores the program. The object of the present invention is achieved by having the processor in the computer read and execute the program from the recording medium.

The processor may be, for example, a CPU (Central Processing Unit). The recording medium may be a "non-transient tangible medium" such as a ROM (Read Only Memory), tape, disk, card, semiconductor memory, programmable logic circuit, or the like. The computer may further include a RAM for expanding the program. The program may be supplied to the computer via any transmission medium capable of transmitting the program (such as a communication network or broadcast waves). One aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

The present invention is not limited to the above-described embodiments and examples, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments and examples.

1 Network system 10 Master device 15 to 17 Hub devices 21a to 21e, 22a to 22c, 23a to 23c Slave device 30 PC
40 HMI
61 to 66 Communication cable 101, 211 Control unit 102, 212 Memory unit 103, 213 Communication unit

Claims (8)

a communication unit for communicating with a plurality of slave devices via a communication network;
a control unit that, when receiving from any of the plurality of slave devices via the communication unit that information regarding the signal quality of the communication cable is an abnormal value, changes an upper limit of the number of timeout detections of the plurality of slave devices and transmits the changed upper limit of the number of timeout detections to the plurality of slave devices via the communication unit. the master device further includes a storage unit configured to store an upper limit value of the number of timeout detections for each of the plurality of slave devices;
2. The master device according to claim 1, wherein when the control unit receives from any one of the plurality of slave devices via the communication unit that information regarding the signal quality of the communication cable is an abnormal value, the control unit increases an upper limit value of the number of timeout detections stored in the memory unit for each of the plurality of slave devices, and transmits the upper limit values of the number of timeout detections corresponding to the plurality of slave devices via the communication unit. The master device according to claim 1, wherein the control unit, upon receiving from any one of the plurality of slave devices via the communication unit that information relating to the signal quality of the communication cable is an abnormal value, transmits the same upper limit value of the number of timeout detections to all of the plurality of slave devices via the communication unit. The master device according to any one of claims 1 to 3, wherein when the control unit receives, via the communication unit, from a slave device whose information on the signal quality of the communication cable was an abnormal value, that the information on the signal quality of the communication cable has returned to a normal value, the control unit instructs the multiple slave devices to restore the upper limit value of the number of timeout detections to the original value. A communication unit for communicating with a master device;
acquiring information regarding a signal quality of a communication cable to be connected, and if the information regarding the signal quality of the communication cable is an abnormal value, notifying the master device via the communication unit that the information regarding the signal quality of the communication cable is an abnormal value;
and a control unit that, when receiving from the master device via the communication unit an upper limit value for the number of timeout detections that has been changed in response to notification that the value has become abnormal , sets the upper limit value for the number of timeout detections. A network system including a master device and a plurality of slave devices,
the master device has a first communication unit that communicates with the plurality of slave devices via a communication network;
a first control unit that, when receiving information indicating that information regarding signal quality of a communication cable is an abnormal value from any one of the plurality of slave devices via the first communication unit, changes an upper limit of a number of timeout detections of the plurality of slave devices and transmits the changed upper limit of the number of timeout detections to the plurality of slave devices via the first communication unit;
Each of the plurality of slave devices includes a second communication unit that communicates with the master device;
acquiring information regarding a signal quality of the communication cable, and if the information regarding the signal quality of the communication cable is an abnormal value, notifying the master device via the second communication unit that the information regarding the signal quality of the communication cable is an abnormal value;
a second control unit that, when receiving a changed upper limit value for the number of timeout detections from the master device via the second communication unit, sets the changed upper limit value for the number of timeout detections. a step of changing an upper limit of the number of timeout detections of the plurality of slave devices when the master device receives information indicating that the signal quality of the communication cable is an abnormal value from any of the plurality of slave devices;
transmitting the changed upper limit value of the number of timeout detections to the plurality of slave devices. A computer program for causing a computer to execute a communication control method,
The communication control method includes a step of changing an upper limit of a number of timeout detection counts of the plurality of slave devices when receiving, from any one of the plurality of slave devices, information indicating that the signal quality of the communication cable is an abnormal value;
and transmitting the changed upper limit value of the number of timeout detections to the plurality of slave devices.

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