Dual-CPU PLC Fallback Control for Power Drop Abnormalities
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Solution Overview
Problem
Existing control systems, such as those described in Patent Literatures 1 to 3, fail to allow selection between stopping and continuing the entire operation when an abnormality occurs, particularly when the CPU of a PLC or a controller has an abnormality.
Innovation Solution
A programmable logic controller (PLC) is designed with two independent central processing units (CPUs) and a selector to choose whether to stop or continue the operation of the second CPU when a voltage drop is detected in the internal power supply of the first CPU. This allows the PLC to select between a stop mode and a fallback mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PLC uses a single CPU for control operations, then the device complexity is reduced, but the reliability deteriorates because when the CPU has an abnormality, the devices cannot continue operating
Solution Approach 1:
The control system is segmented into multiple independent CPUs (first CPU and second CPU) that can operate autonomously. Each CPU has its own power supply monitoring circuit, allowing independent detection and response to abnormalities. This segmentation enables the system to isolate failures to individual CPUs while maintaining overall system operation through the remaining functional CPUs.
2Productivity
If the system automatically stops all operations when an abnormality is detected, then the safety is improved, but the productivity deteriorates because the entire system stops even when some components are functioning normally
Solution Approach 1:
The system dynamically adjusts its operational state based on the detected abnormality conditions. When a voltage drop is detected in one CPU's power supply, the system can selectively stop only the affected CPU while allowing other CPUs to continue operation. This dynamic response enables the system to maintain productivity by keeping functional components operational while isolating and stopping only the problematic segments.
3Reliability
If the power supply monitoring IC outputs a reset signal to all controllers when voltage drops, then the reliability is improved by preventing unstable operation, but the productivity deteriorates because all controllers stop including those without abnormalities
Solution Approach 1:
Each CPU has its own dedicated power supply monitoring IC that independently monitors its specific power supply voltage. When a voltage drop is detected, the monitoring IC generates a reset signal that is confined to and affects only the specific CPU whose power supply experienced the drop. This localized quality approach ensures that reliability protection is applied precisely where needed without causing unnecessary shutdowns of other functional components.
Data Source
AI summary
Central processing units can perform factory automation control independently of each other. A first output selector selects to stop or not to stop an operation of a second central processing unit when a voltage drop in an internal power supply in a first central processing unit is detected. A first reset signal output controller stops the operation of the second central processing unit when the first output selector selects to stop the operation of the second central processing unit, and does not stop the operation of the second central processing unit when the first output selector selects not to stop the operation of the second central processing unit.