Safety Signal Circuit Testing With Independent CPU Coordination
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Solution Overview
Problem
Creating a safety signal test program for machine tools that require high safety levels is costly due to the need for coordination between CPUs, and simultaneous signal changes cannot detect shorts effectively.
Innovation Solution
A control device with a first and second controller, each equipped with timing and test control units, performs independent safety signal circuit tests based on elapsed time, confirming test completion and detecting input signals to facilitate CPU coordination without manual program creation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a safety signal test program is created with manual coordination between CPUs, then the test can be performed, but the development cost and time increase significantly
Solution Approach 1:
The system enables self-service testing where the safety signal circuit automatically performs tests on itself. The first and second controllers independently execute test routines without requiring external coordination programs, reducing development complexity while maintaining test reliability through automated self-verification of safety signals
Solution Approach 2:
The safety signal test function is segmented into independent first and second controllers, each capable of autonomously executing test routines. This segmentation eliminates the need for complex inter-CPU coordination programs while ensuring comprehensive safety signal verification through distributed testing capabilities
2Productivity
If multiple safety signals are changed simultaneously during testing, then the test speed increases, but shorts between signals cannot be detected
Solution Approach 1:
The safety signal test employs periodic action by sequentially changing signals in a predetermined order rather than simultaneously. The first controller changes signals in a first sequence while the second controller changes signals in a second sequence, ensuring that shorts can be detected while maintaining efficient test execution through systematic periodic testing
3Measurement precision
If a comprehensive coordination program is created for CPU synchronization, then test accuracy improves, but the number of program steps and development cost increase
Solution Approach 1:
The system applies preliminary action by pre-establishing independent test routines in the first and second controllers that are designed to work autonomously. This preliminary preparation eliminates the need for complex runtime coordination programs, reducing development effort while ensuring accurate signal changes through pre-planned test sequences
Data Source
AI summary
A control device has first and second control units. The first unit includes a timing unit which measures elapsed time and instructs the start of a first safety signal circuit test based on the time, and a first circuit test control unit which, when a safety signal circuit output signal has been output to a first circuit, or output thereof has stopped, detects whether a safety signal circuit input signal is input, and executes the first safety signal circuit test. The second unit is provided with an implementation verifying unit which verifies whether the first safety signal circuit test is complete, and a second circuit test control unit which, after verification, when a safety signal circuit output signal is output to a second circuit, or when output thereof has stopped, detects whether a safety signal circuit input signal is input, and executes a second safety signal circuit test.