Redundant supervisory control system, and redundancy switching method of the same

A redundancy switching method for a redundant supervisory control system having a pair of network loops in parallel in a single loop network, the redundant supervisory control system including:

• a pair of controllers each collecting input data from a controlled subject, and outputting control data based on the input data;
• a plurality of remote input/output units each connected to both of the pair of network loops in the single loop network for collecting the input data from the controlled subject, transmitting the input data to both of the controllers, and outputting, to the controlled subject, the control data transmitted from an active one of the pair of controllers currently executing control;
• communication cables each connecting the pair of controllers and the plurality of remote input/output units to make the pair of network loops in parallel in the single loop network;
• and
• a pair of redundant control interface units for mutually monitoring abnormality statuses of the pair of controllers, and setting a control right allowing any one of the pair of controllers to execute control in an active state, and the other controller to be in a standby state, and
• the redundant control system being configured to control the controlled subject by performing communications in two directions of clockwise and counterclockwise in any one of the pair of network loops in the single loop network composed of the pair of controllers, the plurality of remote input/output units and the communication cables, in accordance with a predetermined communication protocol,
• wherein each of the pair of controllers includes:
• a pair of first loop interface units each communicate the input data and the control data in the two directions with the counterpart controller and the remote input/output units, and judges whether the input data is normally received;
• a first switching controller which selects, among the pair of first loop interface units, one of the first loop interface units which is capable of performing normal reception, based on results of the judgments of the respective first loop interface units;
• a first data distributor-selector which receives the input data outputted from one of the first loop interface units selected by the first switching controller, and distributes the control data among the pair of first loop interface units;
• and
• a control computation unit which receives the input data outputted from the first data distributor-selector, performs arithmetic processing on the input data, and outputs, as the control data, the result of the arithmetic processing to the first data distributor-selector, and
• wherein each of the plurality of remote input/output units includes:
• a pair of second loop interface units each communicate the input data and the control data in the two directions through each one of the pair of network loops with the pair of the controllers, and judges whether the control data is normally received;
• a second switching controller which selects, among the pair of second loop interface units, one of the second loop interface units which is capable of performing normal reception based on results of the judgments of the second loop interface units;
• a second data distributor-selector which outputs the control data outputted from one of the second loop interface units selected by the second switching controller, and distributes the input data collected form the controlled subject among the pair of second loop interface units;
• and
• an input/output unit which transmits the control data outputted from the second data distributor-selector to the controlled subject, and transmits the input data from the controlled subject to the second data distributor-selector,
• the redundancy switching method comprising:
• detecting reception information on whether the input data and the control data are received normally at the receiver sides in each of the pair of network loops;
• selecting one of the pair of first loop interface units for each of the pair of controllers and one of the pair of second loop interface units for each of the plurality of remote input/output units which are capable of performing reception, based on the reception information;
• judging connection statuses of the pair of network loops based on the reception information;
• and
• setting a control right each of the pair of controllers again, based on a result of the network loop judging step,
• wherein the pair of redundant control interface units cause a control to continue without switching the control rights, in a case where the pair of redundant control interface units judge that portions respectively in the pair of network loops do not overlap with one another, each of the portions starting from each of the pair of controllers to a location of a failure;
• and
• the pair of redundant control interface units set the control right in one of the pair of controllers again, in a case where failures occur in a plurality of portions in each of the pair of network loops, and where the pair of redundant control interface units judge that the communication statuses of the respective network loop are different from one another in a range where each of the controllers can access the remote input/output units.