PLC SFC Device Data Collection for Retrospective Analysis
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Solution Overview
Problem
Conventional programmable logic controllers face challenges in displaying all device outputs within a step and retrospectively confirming the operation process of a sequential function chart (SFC) program due to longer communication times and limited display of current device output states.
Innovation Solution
A programmable logic controller with a device data collecting unit, storing unit, and outputting unit that collects, stores, and outputs device data for each step of the SFC program, allowing for the display of all device outputs and retrospective confirmation of the operation process by storing data in a ring buffer structure and outputting it to a storage medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the communication time between the programmable logic controller and the engineering tool is reduced, then the execution speed is improved, but the completeness of device output display within a step deteriorates
Solution Approach 1:
The patent applies preliminary action by collecting and storing device output data during the execution of each step before the communication cycle completes. The PLC stores device outputs in a buffer memory during step execution, so that when communication occurs, all device outputs for that step are already captured and can be transmitted完整地 to the engineering tool, resolving the contradiction between fast execution and complete data display.
2Loss of time
If only the current device output state is displayed, then the communication time is reduced, but the ability to retroactively confirm the operation process deteriorates
Solution Approach 1:
The patent implements preliminary action by pre-collecting and storing device output data throughout the execution of each step in a buffer memory. This allows the system to not only display current device states but also retrieve and display historical operation data for troubleshooting, eliminating the need for repeated communications and enabling retrospective analysis without extending communication time.
Solution Approach 2:
The patent creates a copy of device output data by storing it in a buffer memory during execution. This copied data can be read and displayed by the engineering tool without requiring continuous communication with the PLC, allowing both current and historical device states to be viewed while minimizing communication overhead.
3Reliability
If all device outputs within a step are collected and stored, then the troubleshooting capability is improved, but the memory usage and data management complexity increase
Solution Approach 1:
The patent applies segmentation by organizing device output data into separate buffer memory areas corresponding to different steps in the SFC program. Each step has its own designated storage region, which simplifies data management by allowing the system to selectively collect, store, and retrieve data for specific steps without handling all device data uniformly, thus improving troubleshooting capability while managing complexity through structured organization.
Data Source
AI summary
A programmable logic controller executes an SFC program including a plurality of blocks, each including a step indicating an operation output and a transition indicating a transition condition. The programmable logic controller includes an SFC device data collecting unit for collecting device data of a device included in an active step for each scan at the time when the SFC program is executed, an SFC device data storing unit for storing the data collected by the SFC device data collecting unit, and an SFC device data outputting unit for outputting the data stored in the SFC device data storing unit to a memory card as a file for each of the steps or the blocks.