Safety Critical Control System Using Redundant State Machine Paths
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Solution Overview
Problem
Current safety-critical control systems face challenges in achieving high reliability and simplified implementation due to susceptibility to stray voltage, increased complexity, and resource-intensive software maintenance, particularly in environments requiring high safety margins.
Innovation Solution
A safety-critical control system utilizing a transmitter and receiver state machine apparatus with a control bus, where the system can only be engaged with corresponding commands from multiple inputs, ensuring reliable operation through redundant and shielded communication lines and state machine transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If single signal systems are used, then the system is simple to implement, but the system is susceptible to stray voltage activated control inputs
Solution Approach 1:
The control signal is segmented into multiple distinct conduction paths (at least two separate paths) between the control element and the safety critical device. Each path carries the same control signal independently, and the safety critical device requires matching signals from all paths to activate. This segmentation prevents stray voltage on a single path from activating the device, while maintaining relatively simple implementation by using duplicate signal paths rather than complex processing.
2Productivity
If serial control systems are used, then control signals can be transmitted efficiently, but the system experiences increased overhead and complexity creating different failure modes
Solution Approach 1:
The patent combines parallel redundant signal paths with state machine logic to create a unified control architecture. Multiple control paths are merged at the receiver through state machine validation, where the receiver tracks the state of each path and only activates the safety critical device when all paths converge to the correct state. This merging approach maintains the efficiency of serial control while adding redundancy, and the state machine automation reduces the overhead burden by providing clear state transition rules.
3Reliability
If advanced microprocessors are used to ruggedize the system, then environmental threats are better resisted, but substantial resources including time and personnel are required to write and maintain complex software
Solution Approach 1:
The patent uses state machines as simplified computational models that can be implemented in hardware or firmware without requiring complex microprocessor software. The state machine logic copies the essential control functionality into a structured format with defined states and transitions, which can be directly implemented in programmable logic devices or hardwired logic. This copying approach provides ruggedized control resistant to environmental threats while avoiding the software complexity and maintenance burden of advanced microprocessors.
Data Source
AI summary
This disclosure involves a method of controlling a safety critical control device, the method comprising: sending user inputs to a first state machine, identifying user inputs by the first state machine, determining the correct state to communicate to a second state machine, the correct state being determined by selecting one state of a plurality of states depending on the user inputs, communicating the correct state to a second state machine through a control bus, and determining the correct state for the second state machine based on communication from the control bus.