Network equipment and network systems

Abstract

To provide a network apparatus that can prevent disruption of network communication even when a slave device is detached from a network by removing a communication cable while the network is in an operation.SOLUTION: When a communication state detection unit (23A) detects that a signal from another apparatus has not arrived or that communication with another apparatus is performed in a one-sided contact state, a control unit (25) of a network apparatus (2N) cuts off communication by a second communication unit (22A).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a network device and a network system using the same. [Background technology]

[0002] In the field of factory automation (FA), various types of devices that share the work process are controlled. In order to link various controllers, remote I / O, and manufacturing devices used for work in a certain area such as a factory facility, industrial networks, also called field networks, that connect these devices are constructed.

[0003] A typical industrial network uses a master-slave system 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 slave devices.

[0004] 2. Description of the Related Art In conventional network systems, a technique is known in which a plurality of slave devices are daisy-chained to a master device (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-195329 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional technology described above, when a slave device is removed from a network by disconnecting the communication cable while the network is in operation, a problem occurs in that communication on the network is interrupted.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a network device and a network system that can prevent network communication from being interrupted when a slave device is removed from a network by disconnecting a communication cable while the network is in operation. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present disclosure employs the following configuration.

[0009] A network device according to one aspect of the present disclosure is a network device that is a slave device used in a network system to which a master device and a plurality of slave devices controlled by the master device are connected, and includes a first communication unit that communicates with other upstream devices, at least one second communication unit that communicates with other downstream devices, and a control unit that controls each unit of the network device, wherein the second communication unit has a communication status detection unit that can detect whether a signal from the other device has arrived, and further whether communication from the other device is occurring in a state where only some of a plurality of signal lines for communication from the other device are connected, and the control unit is configured to cut off communication by the second communication unit when the communication status detection unit detects that a signal from the other device has not arrived, or that communication from the other device is occurring in a state where only some of the plurality of signal lines for communication from the other device are connected.

[0010] According to the above configuration, even if a slave device is removed from a network by disconnecting the communication cable while the network is in operation, it is possible to prevent communication on the network from being interrupted.

[0011] In the network device relating to the above-mentioned aspect, the network device may include a plurality of the second communication units, and further include a switching circuit that switches connections between the plurality of the second communication units, and the control unit may be configured to control the switching circuit to daisy-chain other devices respectively connected to at least a portion of the plurality of second communication units, and when the second communication unit performs the disconnection, to switch to daisy-chain other devices excluding the second communication unit.

[0012] According to the above configuration, even if a slave device is removed from the network by disconnecting the communication cable while the network is in operation, a plurality of slave devices can be connected in a daisy chain while preventing a disruption of network communication.

[0013] Moreover, a network device according to another aspect of the present disclosure is a network device which is a slave device used in a network system to which a master device and a plurality of slave devices controlled by the master device are connected, the network device comprising: a first communication unit which communicates with other devices on an upstream side; and a control unit which controls each unit of the network device; and further comprising a plurality of second communication units which communicate with other devices on a downstream side, the plurality of second communication units being connected in a loop to the first communication unit, the second communication unit comprising: a communication state detection unit which can detect whether a signal from the other device has arrived, and further whether communication from the other device is being performed in a state where only a portion of a plurality of signal lines for communication from the other device are connected; and a switching unit which causes the other device to leave the network, and the control unit is configured to cause the switching unit to remove the other device from the network when the communication state detection unit detects that a signal from the other device has not arrived, or that communication from the other device is being performed in a state where only a portion of the plurality of signal lines for communication from the other device are connected.

[0014] According to the above configuration, even if a slave device is removed from the network by disconnecting the communication cable while the network is in operation, each second communication unit can connect multiple slave devices in a daisy chain while preventing communication on the network from being interrupted.

[0015] In the network device relating to the above-mentioned aspect, the communication status detection unit may be configured to detect, based on the amplitude value of a signal from another device, whether or not communication from the other device is taking place in a state in which only a portion of a plurality of signal lines for communication from the other device are connected.

[0016] According to the above configuration, highly accurate detection can be reliably performed in a state where only some of the plurality of signal lines are connected.

[0017] In the network device relating to the above-mentioned aspect, the communication status detection unit may be configured to detect, based on a pulse width value of a signal from another device, whether or not communication from the other device is taking place when only a portion of a plurality of signal lines for communication from the other device are connected.

[0018] According to the above configuration, highly accurate detection can be reliably performed in a state where only some of the plurality of signal lines are connected.

[0019] In the network device relating to the above-mentioned aspect, the communication status detection unit may be configured to detect, based on the value of a coding rule error in communication with another device, whether or not communication from the other device is being performed in a state in which only a portion of a plurality of signal lines for communication from the other device are connected.

[0020] According to the above configuration, highly accurate detection can be reliably performed in a state where only some of the plurality of signal lines are connected.

[0021] Moreover, a network system according to one aspect of the present disclosure is a network system to which a master device and a plurality of slave devices controlled by the master device are connected, and is configured such that any of the above network devices is connected as the slave device.

[0022] According to the above configuration, it is possible to configure a network system that can prevent communication on the network from being interrupted even when a slave device is removed from the network by disconnecting the communication cable while the network is in operation. Effect of the Invention

[0023] According to the present disclosure, it is possible to provide a network device and a network system that can prevent network communication from being interrupted even when a slave device is removed from a network by disconnecting a communication cable while the network is in operation. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is an explanatory diagram illustrating a configuration example of a network system according to a first embodiment of the present disclosure. [Diagram 2] 1 is a schematic configuration diagram showing a network device (slave device) according to a first embodiment of the present disclosure. [Diagram 3] 10 is a diagram illustrating the state of each part of the network device when the communication cable is pulled out from the slave device while the network is in operation. FIG. [Figure 4] 11A and 11B are diagrams illustrating a problem that occurs when a communication cable is pulled out on the slave device side while the network is in operation in a comparative example. [Diagram 5] 10A to 10C are explanatory diagrams illustrating the state of each part when the above problem occurs in the comparative example. [Figure 6] FIG. 11 is a diagram illustrating a state of each part of a network device according to a second embodiment of the present disclosure when a communication cable is pulled out from a slave device while the network is in operation. [Figure 7] FIG. 11 is an explanatory diagram illustrating a configuration example of a network system according to a fourth embodiment of the present disclosure. [Figure 8] FIG. 11 is a schematic configuration diagram showing a network device (slave device) according to a fourth embodiment of the present disclosure. [Figure 9] FIG. 11 is a schematic configuration diagram showing a network device (slave device) according to a fifth embodiment of the present disclosure. [Figure 10] 10 is a diagram for explaining an example of operation of the network device shown in FIG. 9 when a communication cable is pulled out on the slave device side while the network is in operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] [Embodiment 1] §1 Examples of application First, an example of a situation to which the present disclosure is applied will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is an explanatory diagram for explaining a configuration example of a network system according to an embodiment of the present disclosure. Fig. 2 is a schematic configuration diagram showing a network device (slave device) according to an embodiment of the present disclosure.

[0026] In the following description, an example will be given in which, for example, four slave devices 2A, 2B, 2C, and 2D are connected as multiple slave devices in network system 100 of this embodiment. In addition, when any of slave devices 2A to 2D constitutes a network device of this embodiment, it is also referred to as network device 2N.

[0027] A network system 100 of this embodiment is a network system in which a master device 1 is connected to a plurality of slave devices 2A to 2D controlled by the master device 1. A network device 2N of this embodiment is also connected to the network system 100 as one of the slave devices.

[0028] In addition, in the network system 100 of this embodiment, a case will be described in which the network device 2N is a slave device 2A. As shown in Fig. 1, this slave device 2A constitutes a branching slave device to which a plurality of slave devices, for example, three slave devices 2B, 2C, and 2D, are connected.

[0029] In addition, the network device 2N of this embodiment includes a first communication unit 21 that communicates with other devices on the upstream side in the network system 100, at least one second communication unit 22A, 22B, 22C that communicates with other devices on the downstream side in the network system 100, a switching circuit 24 that switches connections between the multiple second communication units 22A to 22C, and a control unit 25 that controls each part of the network device 2N.

[0030] The second communication units 22A, 22B, and 22C each have a communication status detection unit 23A, 23B, and 23C. The communication status detection units 23A to 23C can detect whether a signal from another device has arrived. The communication status detection units 23A to 23C can also detect whether communication is being performed with another device when the communication cable connector of the other device is in a one-sided contact state.

[0031] The switching circuit 24 has a port P0 connected to the first communication unit 21, and ports P1, P2, and P3 connected to the second communication units 22A, 22B, and 22C, respectively.

[0032] The control unit 25 changes the communication states (links) of the second communication units 22A-22C by controlling the ports P1-P3 of the switching circuit 24 based on the detection results of the communication state detection units 23A-23C. That is, the control unit 25 opens the ports P1-P3 to allow communication by the second communication units 22A-22C. On the other hand, the control unit 25 closes the ports P1-P3 to block communication by the second communication units 22A-22C.

[0033] Therefore, according to this embodiment, for example, communication state detection unit 23A detects a one-sided contact state, and in that case, causes slave device 2B to be removed from the network. Therefore, it is possible to configure a network device 2N and a network system 100 using the same that can prevent network communication from being interrupted even when slave device 2B is removed by pulling out the communication cable from slave device 2A while the network is operating.

[0034] §2 Configuration Example <Network System> In the example of FIG. 1, a network system 100 of this embodiment includes a master device 1 and a plurality of slave devices 2A to 2D connected to the master device 1. The master device 1 includes a master terminal 1a, a slave terminal 1b, and a slave terminal 2c.

[0035] In addition, the network system 100 of the present embodiment uses, for example, a network system conforming to the EtherCAT (Ethernet for Control Automation Technology: registered trademark) standard.

[0036] In the network system 100 of this embodiment, the master device 1 and the slave devices 2A to 2D are connected using, for example, communication cables as shown in FIG. 1, and communication is performed via the communication cables.

[0037] The master device 1 includes, for example, a PLC (Programmable Logic Controller). The master device 1 is configured to operate in accordance with a predetermined program set by an information processing device 3, thereby controlling each of the multiple slave devices 2A to 2D.

[0038] <Network devices> 2, the network device 2N of this embodiment includes a first communication unit 21, three second communication units 22A, 22B, and 22C, a switching circuit 24, and a control unit 25. In the network device 2N of this embodiment, communication state detection units 23A, 23B, and 23C are provided in the second communication units 22A, 22B, and 22C, respectively.

[0039] Further, the network device 2N of this embodiment constitutes the branching slave device, and slave devices 2B, 2C, and 2D connected to second communication units 22A, 22B, and 22C, respectively, are daisy-chained to the master device 1.

[0040] The first communication unit 21 is a functional block that is connected to the master device 1 via a communication cable via the communication device 5, and transmits and receives signals to and from the master device 1.

[0041] Further, second communication units 22A, 22B, 22C are functional blocks that are connected to slave devices 2B, 2C, 2D by communication cables, respectively, and transmit / receive signals to / from slave devices 2B, 2C, 2D.

[0042] The communication state detection units 23A to 23C are functional blocks that detect the amplitude value of the signal received by the second communication units 22A to 22C, respectively. When the detected amplitude value is equal to or greater than a preset first threshold value, the communication state detection units 23A to 23C determine that the signal from the slave devices 2B to 2D has normally reached the second communication units 22A to 22C, respectively, and notify the control unit 25, via the switching circuit 24, of a signal indicating that the communication by the second communication units 22A to 22C is normal.

[0043] Furthermore, when the detected amplitude value is less than a preset first threshold value, communication status detection units 23A-23C determine that the communication cable connectors of slave devices 2B-2D are in a one-sided contact state in the communication with slave devices 2B-2D, and notify control unit 25, via switching circuit 24, of a signal that communication by second communication units 22A-22C is in an abnormal state.

[0044] The one-sided contact state of the communication cable connector referred to here means a state in which the communication cable connector is in an incomplete contact state with the connector of the communication cable to be contacted. More specifically, the one-sided contact state means, for example, a state in which one of a pair of contact pins provided on the communication cable connector is in almost complete contact with the pin of the connector of the communication cable, and the other contact pin is not in contact.

[0045] Furthermore, in this one-sided contact state, although a large impedance mismatch occurs between the other slave device and the second communication section, signals can be transmitted.

[0046] In addition, in network system 100 of the present embodiment, it is possible to insert and remove slave devices from various manufacturers. However, the inventors of the present disclosure have found that, depending on the shape of the connectors of the communication cables connected to such various slave devices, when the connectors are pulled out, a one-sided contact state as described above may occur.

[0047] Furthermore, when the detected amplitude value is "0", the communication status detection units 23A-23C determine that no signal has reached the second communication units 22A-22C from the slave devices 2B-2D, and notify the control unit 25, via the switching circuit 24, of a signal indicating that communication by the second communication units 22A-22C is cut off.

[0048] Based on an instruction signal from the control unit 25, the switching circuit 24 sets the operating state of the ports P0, P1, P2, P3 to open or close, and sets the link state with the corresponding first communication unit 21 or second communication units 22A to 22C to on or off, respectively.

[0049] In addition, based on an instruction signal from the control unit 25, the switching circuit 24 connects the slave devices 2B, 2C, and 2D in a daisy chain in sequence to the master device 1, as shown by arrows D1, D2, D3, and D4 in FIG. 2.

[0050] In addition, based on an instruction signal from the control unit 25, for example, when communication by the second communication unit 22A is to be cut off, the switching circuit 24 switches so that the other slave devices 2C, 2D are daisy-chain connected except for the second communication unit 22A.

[0051] As a result, in the network device 2N of this embodiment, even if the slave device 2B is detached by, for example, unplugging the communication cable from the slave device 2A while the network is operating, the network device 2N can appropriately perform a switching operation to the slave devices 2C, 2D, preventing communication with the other slave devices 2C, 2D (i.e., network communication) from being interrupted (details will be described later).

[0052] The control unit 25 is a functional block that controls each component by executing information processing. When the control unit 25 receives a signal from the communication state detection units 23A-23C indicating that the communication by the second communication units 22A-22C is in an abnormal state, the control unit 25 controls the switching circuit 24 to cut off the communication by the second communication units 22A-22C. That is, the control unit 25 makes the switching circuit 24 close the states of the corresponding ports P1-P3, and turns off the states of the links with the corresponding second communication units 22A-22C.

[0053] The functions of the switching circuit 24 and the control unit 25 may be realized as an integrated IC (Integrated Circuit) chip.

[0054] §3 Example of operation <Switching action> An example of the operation of the network device 2N of this embodiment will be specifically described with reference to Fig. 3. Fig. 3 is a diagram for explaining the state of each part of the network device when the communication cable is pulled out on the slave device side while the network is in operation.

[0055] In the following, a switching operation will be described in a case where, for example, the communication cable is pulled out on the slave device 2B side during network operation in Fig. 2 to disconnect the slave device 2B. In addition, the following description will be given by taking as an example a case where the communication cable connector of the slave device 2B is pulled out in a one-sided contact state.

[0056] 3, the communication cable connector of slave device 2B has not been pulled out, and in network device 2N of this embodiment, slave device 2B is normally connected to second communication unit 22A. In other words, the communication cable connector of slave device 2B is normally in contact with second communication unit 22A until time T1.

[0057] In addition, the communication status detection unit 23A detects the value A0, which is greater than or equal to the first threshold, as the amplitude value of the signal received by the second communication unit 22A, and notifies the control unit 25 of a signal indicating that communication by the second communication unit 22A is normal.

[0058] As a result, the control unit 25 determines that the communication status at the communication cable connector of the slave device 2B is normal communication, turns on the link status of the second communication unit 22A, and further controls the switching circuit 24 to open the status of port P1.

[0059] Then, from the time when the operation of pulling out the communication cable connector of the slave device 2B starts at time T1 and ends at time T2, the above-mentioned one-sided contact state occurs in the network device 2N of this embodiment, and the slave device 2B is no longer normally connected to the second communication unit 22A.

[0060] In other words, during the period TH from time T1 to time T2, the connector for the communication cable of the slave device 2B is in a one-sided contact state, causing an impedance mismatch with the second communication unit 22A, and the connector is not in normal contact with the second communication unit 22A.

[0061] In addition, at time T1, the communication status detection unit 23A detects value A1, which is less than the first threshold value, as the amplitude value of the signal received by the second communication unit 22A, and notifies the control unit 25 of a signal indicating that communication by the second communication unit 22A is in an abnormal state.

[0062] As a result, at time T1, control unit 25 determines that the communication state at the communication cable connector of slave device 2B is not normal, and controls switching circuit 24 to turn off the link state of second communication unit 22A and to close the state of port P1. This cuts off communication by second communication unit 22A, and slave device 2B is electrically disconnected from network system 100.

[0063] Furthermore, at time T1, the control unit 25 controls the switching circuit 24 to cut off communication by the second communication unit 22A, so that at time T1, the control unit 25 switches so as to daisy-chain the slave device 2C (other device) except for the second communication unit 22A.

[0064] In other words, in FIG. 2, the control unit 25 controls the switching circuit 24 to connect port P0 and port P1 and transmit the signal received by the first communication unit 21 from the master device 1 to the slave device 2C via the second communication unit 22B.

[0065] Thereafter, after the operation of pulling out the communication cable connector of the slave device 2B is completed at time T2, in the network device 2N of this embodiment, the slave device 2B is completely separated from the second communication unit 22A. In other words, after time T2, the communication cable connector of the slave device 2B is completely separated from the second communication unit 22A.

[0066] Moreover, the detection result of the communication status detection unit 23A indicates a value of "0", indicating that communication with the connector is not possible, that is, a signal from the slave device 2B has not arrived, and notifies the control unit 25 of a signal indicating that communication by the second communication unit 22A is in a cut-off state. As a result, the control unit 25 does not instruct the switching circuit 24 to control the second communication unit 22A.

[0067] Here, during time period TH, due to a one-sided contact state of the communication cable connector of slave device 2B, unauthorized communication occurs between said connector and second communication unit 22A, as shown in Fig. 3. However, in network device 2N of this embodiment, at time T1 when communication state detection unit 23 detects the abnormality, the link state of second communication unit 22A is turned off and further the state of port P1 is turned closed, so that it is possible to perform a switching operation to slave device 2C without being affected by this unauthorized communication.

[0068] Furthermore, the unauthorized communication as described above occurs because the signal communication interval period (i.e., the transmission period of communication frames in the network) in the network system 100 is shorter than the time required to connect and disconnect the connector. In other words, in this embodiment, the corresponding slave device 2B is immediately electrically connected or disconnected upon detection of the one-sided contact state, so that the switching operation of the slave device 2B can be appropriately performed regardless of the transmission period of communication frames.

[0069] More specifically, for example, valid frames and meaningless frames (idle frames) flow in communication between two slave devices 2A and 2B. If a valid frame is flowing while a one-sided contact state occurs due to the pulling out operation of the communication cable connector of slave device 2B, the valid frame is destroyed and becomes an invalid frame. If such an invalid frame occurs two or more times in succession, communication between slave devices 2A and 2B is interrupted.

[0070] In contrast, in this embodiment, as described above, when a one-sided contact state is detected, the state of port P1 to which the corresponding slave device 2B is connected is immediately closed. As a result, in this embodiment, it is possible to prevent the next valid frame from becoming a corrupted invalid frame, and the next valid frame can be sent to the slave device 2C to appropriately perform switching operation to the slave device 2C.

[0071] In the following, the inappropriate switching operation will be specifically described with reference to Fig. 4 and Fig. 5. Fig. 4 is a diagram for explaining a problem that occurs when a communication cable is pulled out on the slave device side while the network is in operation in a comparative example. Fig. 5 is an explanatory diagram for explaining the state of each part when the above problem occurs in the comparative example.

[0072] The network device of the comparative example is similar to the network device 2N according to the first embodiment, except that the second communication units 122A to 122C do not have a function for detecting a one-sided contact state.

[0073] 4, the comparative example includes master device 11, branching slave device S1, and slave devices 12A, 12B, and 12C. Branching slave device S1 includes a first communication unit 121, three second communication units 122A, 122B, and 122C, and a switching circuit 124 having ports P10, P11, P12, and P13.

[0074] For example, the master device 11 is connected to the first communication unit 121, and for example, the other slave devices 12A, 12B, and 12C are connected to the second communication units 122A, 122B, and 122C, respectively.

[0075] In the comparative example, when the slave device 12A is disconnected by, for example, pulling out the communication cable from the branch slave device S1 while the network is in operation, the communication cable connector of the slave device 12A is in a one-sided contact state. As a result, in the comparative example, the signal from the master device 11 reaches the slave device 12A, as shown by the solid arrow D11 in FIG.

[0076] However, in the comparative example, as shown by dotted arrows D12, D13, and D14 in FIG. 4, the signal from the master device 11 is transmitted in an unauthorized manner, that is, the communication of a signal containing a large number of errors in the communication content, at a point where one-sided contact is established between the slave device 12A and the second communication unit 122A.

[0077] As a result, in the comparative example, the signal from master device 11 is not normally delivered to slave devices 12B, 12C, the daisy-chain connection of these slave devices 12B, 12C goes down, and a communication interruption occurs in the network of the comparative example.

[0078] Specifically, unlike the present embodiment, the comparative example does not include communication status detection units 23A-23C that detect a one-sided contact state, and therefore, unlike the present embodiment illustrated in Figure 3, even if the above-mentioned unauthorized communication occurs at time T1, the link status of the second communication unit 122A is not turned off, and the status of port P11 is not turned closed.

[0079] Therefore, in the comparative example, the signal from master device 11 continues to be transmitted to slave device 12A in a one-sided contact state (disconnected portion), and the signal does not reach slave devices 12B and 12C, causing a communication interruption in the network. In other words, in the comparative example, it becomes impossible to execute a daisy chain connection.

[0080] In contrast, in the network device 2N and network system 100 of this embodiment, the control unit 25 cuts off communication by the second communication unit 22A at time T1 when the one-sided contact state occurs, as shown in Fig. 3. As a result, in the network device 2N and network system 100 of this embodiment, even if the slave device 2B is detached online, it is possible to prevent communication with the other slave devices 2C, 2D from being interrupted.

[0081] The inventors of the present disclosure have found that the above-mentioned problems in the comparative example occur when, in an actual network system, a slave device is removed by unplugging the communication cable from the slave device while the network is in operation. The inventors of the present disclosure have found that by using the network device 2N and network system 100 of this embodiment, it is possible to prevent network communication from being interrupted even when a slave device is removed from the network by unplugging the communication cable while the network is in operation.

[0082] Furthermore, in this embodiment, the communication state detection unit 23A detects whether or not communication is being performed in the one-sided contact state based on the amplitude value of the signal from the slave device 2B (other device), and therefore can reliably detect the one-sided contact state with high accuracy.

[0083] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0084] The main difference between this embodiment and the above-mentioned embodiments is that the communication state detection units 23A to 23C detect whether or not communication is being performed in the one-sided contact state based on the value of the pulse width of the signal from the slave devices 2B to 2D. That is, the communication state detection units 23A to 23C of this embodiment are adapted to detect the one-sided contact state by detecting that the signal waveform becomes smaller than normal and therefore the detected pulse width becomes smaller when the one-sided contact state is in place.

[0085] That is, in this embodiment, communication state detection units 23A to 23C are functional blocks that detect the pulse width value of the signal received by second communication units 22A to 22C, respectively. When the detected pulse width value is equal to or greater than a preset second threshold value, communication state detection units 23A to 23C determine that a signal from slave devices B to 2D has reached second communication units 22A to 22C, respectively, and notify control unit 25, via switching circuit 24, of a signal indicating that communication by second communication units 22A to 22C is normal.

[0086] Furthermore, when the detected pulse width value is less than a preset second threshold value, communication status detection units 23A-23C determine that the communication cable connectors of slave devices 2B-2D are in a one-sided contact state in the communication with slave devices 2B-2D, and notify control unit 25, via switching circuit 24, of a signal that communication by second communication units 22A-22C is in an abnormal state.

[0087] Furthermore, when the detected pulse width value is "0", the communication status detection units 23A-23C determine that no signal has reached the second communication units 22A-22C from the slave devices 2B-2D, and notify the control unit 25, via the switching circuit 24, of a signal that communication by the second communication units 22A-22C is cut off.

[0088] An example of the operation of the network device 2N of this embodiment will be specifically described below with reference to Fig. 6. Fig. 6 is a diagram for explaining the state of each part of the network device according to the second embodiment of the present disclosure when the communication cable is pulled out on the slave device side during network operation. In the following explanation, the switching operation will be explained in the first embodiment, for example, when the slave device 2B is pulled out online, as in the case explained with reference to Fig. 3.

[0089] Up until time T1 in FIG. 6, the communication cable connector of slave device 2B has not been pulled out, and in network device 2N of this embodiment, slave device 2B is normally connected to second communication unit 22A.

[0090] That is, until time T1, the communication cable connector of slave device 2B is in normal contact with second communication unit 22A. In addition, communication status detection unit 23A detects value P0, which is equal to or greater than the second threshold value, as the pulse width value of the signal received by second communication unit 22A, and notifies control unit 25 of a signal indicating that communication by second communication unit 22A is normal.

[0091] As a result, the control unit 25 determines that the communication status at the communication cable connector of the slave device 2B is normal communication, turns on the link status of the second communication unit 22A, and further controls the switching circuit 24 to open the status of port P1.

[0092] Then, from the time when the operation of pulling out the communication cable connector of the slave device 2B starts at time T1 and ends at time T2, the above-mentioned one-sided contact state occurs in the network device 2N of this embodiment, and the slave device 2B is no longer normally connected to the second communication unit 22A.

[0093] In other words, during the period TH from time T1 to time T2, the connector for the communication cable of the slave device 2B is in a one-sided contact state, causing an impedance mismatch with the second communication unit 22A, and the connector is not in normal contact with the second communication unit 22A.

[0094] In addition, at time T1, the communication status detection unit 23A detects a value P1, which is less than the second threshold value, as the amplitude value of the signal received by the second communication unit 22A, and notifies the control unit 25 of a signal indicating that communication by the second communication unit 22A is in an abnormal state.

[0095] As a result, at time T1, the control unit 25 determines that the communication state at the communication cable connector of the slave device 2B is not normal, and controls the switching circuit 24 to turn off the link state of the second communication unit 22A and further to close the state of port P1.

[0096] As a result, communication by second communication unit 22A is cut off, and slave device 2B is electrically disconnected from network system 100.

[0097] Furthermore, at time T1, the control unit 25 controls the switching circuit 24 to cut off communication by the second communication unit 22A, so that at time T1, the control unit 25 switches so as to daisy-chain the slave device 2C (other device) except for the second communication unit 22A.

[0098] In other words, in FIG. 2, the control unit 25 controls the switching circuit 24 to connect port P0 and port P1 and transmit the signal received by the first communication unit 21 from the master device 1 to the slave device 2C via the second communication unit 22B.

[0099] Thereafter, after the operation of removing the communication cable connector of the slave device 2B is completed at time T2, in the network device 2N of this embodiment, the slave device 2B is completely separated from the second communication unit 22A.

[0100] That is, after time T2, the communication cable connector of slave device 2B is completely separated from second communication unit 22A. Also, the detection result of communication status detection unit 23A indicates a value of "0", indicating that communication with the above connector is not possible, that is, a signal from slave device 2B has not arrived, and a signal is sent to control unit 25 to the effect that communication by second communication unit 22A is cut off. As a result, control unit 25 does not instruct switching circuit 24 to control second communication unit 22A.

[0101] As described above, this embodiment provides the same effects as the first embodiment.

[0102] Furthermore, in this embodiment, the communication state detection unit 23 detects whether or not communication is being performed in the one-sided contact state based on the pulse width value of the signal from the slave device 2B (other device), and therefore, it is possible to reliably detect the one-sided contact state with high accuracy.

[0103] [Embodiment 3] The main difference between this embodiment and the above-described embodiments is that the communication state detection units 23A to 23C detect whether the communication is being performed in the above-described one-sided contact state based on the value of the coding rule error in the communication with the slave devices 2B to 2D.

[0104] That is, in this embodiment, the communication status detection units 23A to 23C are functional blocks that detect the value of a coding rule error in the communications between the second communication units 22A to 22C and the slave devices 2B to 2D, respectively. Specifically, the communication status detection units 23A to 23C perform a coding rule check on the signals received by the second communication units 22A to 22C, respectively, and determine whether the signals have been transmitted correctly or not.

[0105] If the result of the coding rule check is normal, each of the communication state detection units 23A to 23C notifies the control unit 25, via the switching circuit 24, of a signal indicating that the communication by the second communication units 22A to 22C is normal.

[0106] Furthermore, if the result of each of the coding rule checks is abnormal, each of the communication status detection units 23A to 23C determines that the communication cable connectors of each of the slave devices 2B to 2D are in a one-sided contact state, and sends a signal to the control unit 25, via the switching circuit 24, to the effect that the communication by the second communication units 22A to 22C is in an abnormal state.

[0107] Furthermore, if the communication status detection units 23A to 23C are unable to perform the coding rule check, they determine that no signal has reached the second communication units 22A to 22C from the slave devices 2B to 2D, and notify the control unit 25, via the switching circuit 24, of a signal that communication by the second communication units 22A to 22D is cut off.

[0108] As described above, this embodiment provides the same effects as the first embodiment.

[0109] The coding rule check can be performed based on, for example, the standard coding specification (4B5B coding (decoding)) of ETHERNET (registered trademark).

[0110] Furthermore, in this embodiment, the communication status detection unit 23 detects whether or not the communication with another device is being performed in the one-sided contact state based on the value of the coding rule error in the communication with another device, so that highly accurate detection of the one-sided contact state can be reliably performed.

[0111] [Embodiment 4] Another embodiment of the present invention will be described below with reference to Fig. 7 and Fig. 8. Fig. 7 is an explanatory diagram for explaining a configuration example of a network system according to a fourth embodiment of the present disclosure. Fig. 8 is a schematic configuration diagram showing a network device (slave device) according to the fourth embodiment of the present disclosure.

[0112] The main difference between this embodiment and the above embodiment is that a network device 2N is applied to the slave device connected in a daisy chain.

[0113] 7, in the network system 100 of the present embodiment, for example, four slave devices 2E, 2F, 2G, and 2H are daisy-chained as a plurality of slave devices. In addition, when any of the slave devices 2E to 2H constitutes a network device of the present embodiment, it is also referred to as a network device 2N. In the following description, a case where the network device 2N is applied to the slave device 2G is described as an example.

[0114] 7, the network device 2N of this embodiment includes a first communication unit 21, a second communication unit 22A, a switching circuit 24, and a control unit 25. The first communication unit 21 communicates with an upstream slave device 2F. The second communication unit 22A communicates with a downstream slave device 2H.

[0115] In addition, the network device 2N of this embodiment is provided with only one second communication unit 22A. The communication state detection unit 23A of this second communication unit 22A uses the communication state detection unit 23 of any one of the above-mentioned embodiments 1 to 3.

[0116] The switching circuit 24 has ports P0 and P1. The first communication unit 21 and the second communication unit 22A are connected to these ports P0 and P1, respectively. Furthermore, the ports P0 and P1 are configured to transmit signals as shown by arrows D5 and D6 in FIG.

[0117] In this embodiment, when the communication status detection unit 23A detects an abnormal state of communication by the second communication unit 22A, that is, when it detects a one-sided contact state of the communication cable connector of the slave device 2H, it turns off the link state with the second communication unit 22A at the time of detection, and cuts off communication by the second communication unit 22A. In addition, the control unit 25 closes the state of the port P1, and turns off the link state of the second communication unit 22A.

[0118] As a result, only port P0 is turned on, and a signal from the slave device 2F is transmitted to the slave device 2F via the first communication unit 21 and port P0. As a result, in this embodiment, the daisy-chain connection between the master device 1 and the slave devices 2E to 2G is maintained.

[0119] As described above, this embodiment provides the same effects as the first embodiment.

[0120] [Embodiment 5] Another embodiment of the present invention will be described below with reference to Fig. 9. Fig. 9 is a schematic configuration diagram showing a network device (slave device) according to a fifth embodiment of the present disclosure.

[0121] The main difference between this embodiment and the above-mentioned embodiment 1 is that the second communication unit is provided with a switching unit that, when a communication state detection unit in the second communication unit detects that a signal from another device is not arriving or that communication with the other device is being performed in a one-sided contact state, causes the other device to disconnect from the network in accordance with instructions from the control unit.

[0122] 9, in a network device 2N of this embodiment, a plurality of second communication units 22A-22C are connected in a loop to a first communication unit 21. Also, communication state detection units 23A-23C and switching units 24A-24C are provided in the second communication units 22A-22C, respectively.

[0123] When communication status detection units 23A-23C detect that a signal from slave device 2B-2D has not arrived or that the communication cable connector of slave device 2B-2D is in a one-sided contact state in communication with slave device 2B-2D, they notify control unit 25 of the detection.

[0124] When the communication state detection units 23A-23C detect that a signal from the slave device 2B-2D has not arrived or that the communication cable connector of the slave device 2B-2D is in a one-sided contact state during communication with the slave device, the switching units 24A-24C disconnect the slave device 2B-2D from the network in accordance with an instruction from the control unit 25.

[0125] <Switching action> An example of the operation of the network device 2N of this embodiment will be specifically described with reference to Fig. 10. Fig. 10 is a diagram for explaining an example of the operation of the network device shown in Fig. 9 when the communication cable is pulled out on the slave device side while the network is in operation.

[0126] In the following, a switching operation will be described in a case where, for example, the communication cable is pulled out on the slave device 2C side during network operation in Fig. 9 to disconnect the slave device 2C. In addition, the following description will be given taking as an example a case where the communication cable connector of the slave device 2C is pulled out in a one-sided contact state.

[0127] 10, in the second communication unit 22B, when the communication state detection unit 23B detects the one-sided communication state in the communication with the slave device 2C, the communication state detection unit 23B notifies the control unit 25 that the one-sided communication state has been detected. Then, the control unit 25 notifies the switching unit 24B of an instruction. Thereafter, the switching unit 24B cuts off the communication with the slave device 2C by the second communication unit 22B in accordance with the instruction from the control unit 25. As a result, as shown by the dotted arrow in FIG. 10, communication between the second communication unit 22B and the slave device 2C is no longer performed, and the switching unit 24B causes the slave device 2C to leave the network.

[0128] Furthermore, the switching unit 24B switches the communication path so that the second communication unit 22B is interposed between the second communication unit 22A and the second communication unit 22C, as shown by the arrow D6 in Fig. 10. As a result, in the network device 2N, as shown by the arrows D1, D5, D6, D7, and D8 in Fig. 10, a daisy chain connection is made in which the slave devices 2B and 2D other than the slave device 2C are sequentially connected to the master device 1.

[0129] As a result, in the network device 2N of this embodiment, even if the slave device 2C is removed from the network by, for example, unplugging the communication cable from the slave device 2A while the network is operating, the network device 2N can appropriately perform a switching operation to the slave devices 2B, 2D, preventing communication with the other slave devices 2B, 2D (i.e., network communication) from being interrupted.

[0130] As described above, this embodiment provides the same effects as the first embodiment.

[0131] In addition, in this embodiment, since the second communication units 22A-22C are provided with the switching units 24A-24C, respectively, unlike the first embodiment, it is possible to omit the installation of the switching circuit 24 in the network device 2N. As a result, in this embodiment, it is possible to reduce the number of components of the network device 2N, and it is also possible to configure each of the second communication units 22A-22C using, for example, one communication chip.

[0132] [Software implementation example] The functional blocks of the network device 2N (particularly, the control unit 25) may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

[0133] In the latter case, the control unit 25 includes a computer that executes instructions of a program, which is software that realizes each function. The computer includes, for example, one or more processors, and a computer-readable recording medium that stores the program. In the computer, the processor reads the program from the recording medium and executes it, thereby achieving the object of the present disclosure.

[0134] The processor may be, for example, a CPU (Central Processing Unit). The recording medium may be a "non-transitory tangible medium" such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like. The device may further include a RAM (Random Access Memory) for expanding the program.

[0135] The program may be supplied to the computer via any transmission medium capable of transmitting the program (such as a communication network or a broadcast wave). Note that 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.

[0136] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0137] In the above description, a configuration has been described that can prevent network communication from being interrupted even when a slave device is removed from a network by removing a communication cable while the network is in operation, but the present disclosure is not limited to this. Specifically, the present disclosure can prevent network communication from being interrupted, such as communication down in a daisy chain connection, even when a slave device is attached to a network by attaching a communication cable while the network is in operation. Furthermore, the present disclosure can prevent network communication from being interrupted in cases other than the above-mentioned insertion and removal of a communication cable, for example, when a part of the communication cable is broken.

[0138] In the above description, the communication state detectors 23A to 23C detect whether communication is being performed with another device when the connector for the communication cable of the other device is in a one-sided contact state, but the present disclosure is not limited to this, and the communication state detectors 23A to 23C may detect whether communication is being performed with the other device when only some of a plurality of signal lines for communication from the other device are connected. Specifically, the communication state detectors 23A to 23C can detect whether communication is being performed with the other device when, for example, only one of four signal lines is connected when the other device is inserted or removed. [Explanation of symbols]

[0139] 1 Master device 2A~2H Slave device 2N Network Equipment 21 First Communications Department 22A~22C Second communication section 23A~23C Communication status detector 24 Switching circuit 24A~24C Switching section 25 Control Unit 100 Network Systems

Claims

1. A network device which is a slave device used in a network system in which a master device and a plurality of slave devices controlled by the master device are connected, comprising: A first communication unit that communicates with another device on the upstream side; At least one second communication unit that communicates with another downstream device; A control unit that controls each unit of the network device, the second communication unit has a communication state detection unit that can detect whether a signal from another device has arrived and further whether communication from the other device is being performed in a state where only a part of a plurality of signal lines for communication from the other device is connected; The control unit is A network device which immediately cuts off communication by the second communication unit when the communication status detection unit detects that a signal from another device is not arriving, or that communication from the other device is being performed with only some of a plurality of signal lines for communication from the other device connected.

2. A plurality of the second communication units are provided, Further, a switching circuit is provided for switching connections between the second communication units, The control unit is Controlling the switching circuit to daisy-chain other devices respectively connected to at least some of the second communication units, The network device according to claim 1 , wherein when the second communication unit is caused to perform the cutoff, the second communication unit is excluded from the cutoff and other devices are switched to a daisy-chain connection.

3. A network device which is a slave device used in a network system in which a master device and a plurality of slave devices controlled by the master device are connected, comprising: A first communication unit that communicates with another device on the upstream side; A control unit that controls each unit of the network device, Further, a plurality of second communication units are provided for communicating with other downstream devices, A plurality of the second communication units are connected in a loop to the first communication unit, The second communication unit is a communication state detection unit capable of detecting whether a signal from another device has arrived and further whether communication from the other device is being performed in a state where only a part of a plurality of signal lines for communication from the other device is connected, and a switching unit for disconnecting the other device from the network, The control unit is A network device in which, when the communication status detection unit detects that a signal from another device is not arriving, or that communication from the other device is occurring with only some of a plurality of signal lines for communication from the other device connected, the switching unit immediately disconnects the other device from the network.

4. The network device according to any one of claims 1 to 3, wherein the communication status detection unit detects whether communication from another device is taking place when only a portion of a plurality of signal lines for communication from the other device are connected, based on the amplitude value of the signal from the other device.

5. The network device according to any one of claims 1 to 3, wherein the communication status detection unit detects whether or not communication from another device is taking place when only a portion of a plurality of signal lines for communication from the other device are connected, based on a pulse width value of a signal from the other device.

6. The network device according to any one of claims 1 to 3, wherein the communication status detection unit detects whether communication from another device is taking place when only a portion of a plurality of signal lines for communication from the other device are connected, based on the value of a coding rule error in communication with the other device.

7. A network system in which a master device and a plurality of slave devices controlled by the master device are connected, A network system, in which the network device according to claim 1 is connected as the slave device.

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