PLC Instruction Priority Queuing for Unresponsive CNC Timing
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Solution Overview
Problem
In CNC systems, when the CNC is unresponsive due to unresponsive timing or load on the bus, low-priority WINDW instructions are executed first, leading to delayed execution of higher-priority instructions, which is undesirable.
Innovation Solution
A PLC device with a special instruction control unit that sets priority for WINDW instructions and an instruction storage determining unit that queues instructions based on CNC operation state, ensuring higher-priority instructions are executed first when the CNC becomes responsive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PLC transmits low-priority WINDW instructions to the CNC, then the interface can process instructions in sequence, but the execution of high-priority instructions is delayed when the CNC is unresponsive
Solution Approach 1:
The patent implements dynamic priority management by allowing the PLC to transmit multiple WINDW instructions with different priority levels (first priority and second priority) to the CNC. When the CNC is unresponsive, the system dynamically switches to executing higher-priority instructions first, rather than following a fixed sequential order. This dynamic adjustment resolves the contradiction by making the execution order adaptable to real-time system state, ensuring critical instructions are not delayed by lower-priority ones during CNC unresponsiveness.
Solution Approach 2:
The patent applies preliminary action by having the PLC transmit and queue multiple WINDW instructions in advance with assigned priority levels before the CNC becomes unresponsive. The instructions are prepared and staged in the PLC's transmission buffer, allowing the system to immediately switch to high-priority execution when CNC unresponsiveness is detected, without waiting for the current sequential queue to complete. This preliminary preparation eliminates the time loss that would occur with reactive priority switching.
2Ease of operation
If the PLC executes WINDW instructions sequentially in the order they are coded, then the program structure remains simple, but high-priority instructions cannot be executed preferentially when needed
Solution Approach 1:
The patent applies local quality by assigning different priority attributes to different WINDW instructions based on their specific function and importance. Instead of treating all instructions uniformly with a single execution queue, the system creates differentiated transmission paths within the PLC for first-priority and second-priority instructions. This localized differentiation allows critical control functions to be expedited while maintaining simple sequential processing for less critical operations, thus improving productivity without significantly complicating the overall program structure.
Data Source
AI summary
To preferentially execute an instruction with higher priority in a case of the CNC being unable to respond due to being an unresponsive timing, load on the bus or the like. A PLC device includes: a special instruction control unit that sets a priority degree indicating a degree of priority for executing predetermined processing to a special instruction for performing the predetermined processing in a control device that controls an industrial machine, and transmits the special instruction in which the priority degree is set to the control device; an instruction storage determining unit that determines whether or not to queue the special instruction according to an operation state of the control device; and an instruction storage unit that sequentially stores the special instruction received, on the basis of a determination result of the instruction storage determining unit.