PLC Variable Reading Window for Synchronized Multi-Task Values
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Solution Overview
Problem
Industrial control devices face challenges in ensuring synchronization of variable values when multiple tasks are carried out concurrently, leading to inconsistencies in reading updated values of variables across tasks.
Innovation Solution
A control device and method that ensures synchronization of variable values by reading all updated values within the cycle of the task with the shortest cycle, preventing tasks from being executed during the reading period, and using association information to determine optimal reading times based on task cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple tasks are carried out concurrently in an industrial control device, then productivity is improved, but synchronization of variable values deteriorates
Solution Approach 1:
The patent applies preliminary action by determining the reading period in advance based on the shortest task cycle before executing multiple tasks concurrently. The control device calculates the required reading duration beforehand and establishes a dedicated reading period during which variable values are collected, ensuring that all tasks are completed within this predetermined timeframe. This prevents synchronization issues by proactively organizing the reading sequence rather than reacting to conflicts during execution.
Solution Approach 2:
The patent introduces an intermediary mechanism in the form of a dedicated reading period that mediates between multiple concurrent tasks and the variable reading process. This intermediate time slot acts as a buffer zone where variable values are collected from all tasks without interference from task execution. The reading period serves as a mediator that isolates the reading operation from task interference, ensuring consistent variable values are obtained from all concurrent tasks.
2Loss of time
If variable values are read during task execution, then response time is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-calculating the reading period duration based on the shortest task cycle before execution begins. This allows the system to establish an optimized reading window in advance that is sufficient to capture all variable updates without extending unnecessarily. By determining the reading period beforehand, the system minimizes the time variables remain unchanged while ensuring complete coverage of all task updates, thus reducing response time without sacrificing measurement precision.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the reading period parameter based on the actual task cycles. The control device monitors the execution time of multiple tasks and modifies the reading period duration accordingly. When tasks complete faster, the reading period is shortened; when tasks take longer, the period is extended. This adaptive parameter adjustment ensures optimal balance between response time and measurement precision under varying operational conditions.
Data Source
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AI summary
To read respective values as updated of a plurality of variables synchronization of which respective values is ensured while tasks are being carried out in a multi-tasking manner, a PLC 10 reads respective values as updated of variables A to C in such a manner as to complete reading the respective values as updated of the variables A to C during a time period from (i) a time point of a start of a single instance of a cycle of a task which cycle is shortest to (ii) a time point of an end of the single instance of the cycle.