PLC Controller System Buffer Memory for Seamless Control Switching
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Solution Overview
Problem
Existing controller systems face challenges in seamlessly switching control subjects for a control target without interrupting the control process or causing data inconsistencies when an abnormality occurs, due to the large size of I/O signal data and low reliability of main memory data in PLCs.
Innovation Solution
A controller system with a higher level control device that allocates programs to multiple PLCs for parallel execution, utilizing input and output buffer memories to manage and switch data seamlessly, ensuring stable control subject switching without data contradictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is copied from the main memory of the PLC in which the abnormality has occurred to the other PLC via the Ethernet, then the control subject can be switched, but the copy time substantially exceeds one execution cycle of the PLC and control interruption occurs
Solution Approach 1:
The patent applies preliminary action by pre-copying I/O signal data from each PLC's main memory to its own communication unit's buffer memory before any abnormality occurs. This pre-positioning of data allows immediate switching without copy delays when a failure occurs, as the backup PLC already has the necessary data in its communication unit.
Solution Approach 2:
The patent introduces communication unit buffer memories as intermediary storage between the PLC main memory and the control target. These buffer memories act as intermediaries that hold I/O signal data, allowing fast local access and switching without requiring direct copying between PLCs via Ethernet during failure scenarios.
2Stability of the object's composition
If the PLC executes programs to control the control target, then the control process continues, but when switching control subjects the output data must not contradict execution results obtained so far
Solution Approach 1:
The patent creates and maintains duplicate copies of I/O signal data in each PLC's communication unit buffer memory. When switching control subjects, the backup PLC already possesses a copy of the current I/O data state, allowing it to continue control without contradiction. The higher-level control device manages this copying process and coordinates the switching based on failure detection.
Data Source
AI summary
A PLC system includes a plurality of I/O devices each connecting a control target of each of a plurality of PLCs to each of the plurality of PLCs, and a PC. Each one of the plurality of PLCs stores first output data obtained by executing a self-assigned program to control the control target connected to each PLC, and stores second output data obtained when the PC or another PLC executes another program allocated to the PC or the other PLC to control the control target connected to the one PLC. Each of the plurality of PLCs outputs one of the first output data and the second output data to the I/O device connected to each PLC based on selection information transmitted from the PC.