Communication device, communication system, and synchronous control method

A communication system in which a first communication device connected to a synchronous master that outputs a synchronous pulse regularly and a plurality of second communication devices connected to a synchronous target are connected through a network, wherein

• the synchronous master includes
• a synchronous-signal transmission unit that outputs a synchronous pulse with a predetermined cycle, and
• a communication-delay-time measurement unit that measures a communication delay time from the synchronous master to the second communication devices connected to the synchronous target and that sets a synchronous-pulse output value calculated on a basis of the communication delay time for each of the second communication devices,
• the first communication device includes a synchronous-packet transmission unit that transmits a synchronous packet to all the second communication devices connected to the network upon receiving the synchronous pulse from the synchronous master, and
• the second communication device includes
• a first communication unit that communicates with the first communication device or another second communication device,
• a second communication unit that communicates with the synchronous target,
• n (n is an integer of 2 or more) counters that count a predetermined period of time,
• a counter control unit that, upon receiving the synchronous packet from the first communication unit with a predetermined cycle, causes the counters to count a cycle that is n times as long as the predetermined cycle and controls the counters such that counts of the counters are cleared at different timings, and
• a synchronous-pulse output unit that outputs a synchronous pulse to the synchronous target through the second communication unit when there is a counter whose count value after being cleared becomes equal to the synchronous-pulse output value.

A synchronous control method in a communication system in which a first communication device connected to a synchronous master that outputs a synchronous pulse regularly and a plurality of second communication devices connected to a synchronous target are connected through a network, the method comprising:

• a first step of, by the first communication device, transmitting a synchronous packet to all the second communication devices connected through the network upon receiving the synchronous pulse from the synchronous master;
• a second step of, by the second communication device, clearing, among n (n is an integer of 2 or more) counters, a counter that has counted the number equal to a synchronous-pulse output value and starting counting anew upon receiving the synchronous packet;
• and
• a third step of, by the second communication device, outputting a synchronous pulse to the synchronous target connected to the second communication device when, among the n counters, there is the counter that has counted a value equal to a synchronous-pulse output value that is set according to a length from the synchronous master connected through the network.