PLC Interrupt Blocking Using Activation Permission Flags
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Solution Overview
Problem
Existing programmable logic controllers (PLCs) cannot prevent the activation of execution elements due to interrupt instructions, which can cause device failures during maintenance.
Innovation Solution
A programmable logic controller (PLC) with a flag data update receiver, interrupt receiver, and preventer mechanism that maintains the inactive state of execution elements when interrupt instructions are generated, using flag data to determine if activation is permitted or prohibited.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the PLC allows interrupt instructions to activate execution elements independently of transition conditions, then the responsiveness and adaptability of the control system is improved, but the reliability deteriorates because execution elements may be activated during maintenance causing device failures
Solution Approach 1:
The patent introduces a transition prevention flag as an intermediary mechanism between the interrupt instruction and the execution element activation. This flag acts as a mediator that can block the activation of execution elements during maintenance periods while still allowing interrupt instructions to be received and processed, thus resolving the contradiction between system responsiveness and maintenance safety
Solution Approach 2:
The system performs preliminary action by setting the transition prevention flag to a specific value before maintenance operations. This preliminary setting prevents execution element activation in advance, ensuring that even if interrupt instructions are generated during maintenance, the execution elements will not be activated, thereby preventing device failures
2Reliability
If the PLC maintains the inactive state of execution elements during maintenance by using flag data, then the reliability is improved, but the ease of operation deteriorates because the execution element cannot be activated even when needed
Solution Approach 1:
The transition prevention flag is designed to be dynamically changeable between different values. It can be set to prevent activation during maintenance, and changed to allow activation when maintenance is complete. This dynamic property resolves the contradiction by making the system adaptable to different operational states while maintaining reliability during maintenance and ease of operation when needed
Data Source
AI summary
In a programmable logic controller, a flag data update receiver receives an update of flag data indicating whether activation of a second execution element is permitted or prohibited. An interrupt receiver receives an interrupt instruction indicating a request for activating the second execution element independently of whether a transition condition is satisfied. An interrupt preventer maintains, when the interrupt instruction is received and latest flag data indicates that the activation of the second execution element is prohibited, an inactive state of the second execution element and outputs an interrupt invalidation error indicating that the interrupt instruction is invalidated. An executor activates the second execution element when the interrupt instruction is received and the latest flag data indicates that the activation of the second execution element is permitted.