Safety-Critical Switch Circuit for Validated State Latching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing safety systems for switches, such as single pole single throw switches, fail to distinguish between valid and invalid states due to issues like shorted contacts or unplugged cables, leading to unsafe operations in systems like unmanned aerial vehicles.
Innovation Solution
A switch circuit incorporating digital logic to validate, latch, and flag the output using a D-latch to prevent inadvertent switching due to switch bounce, disconnects, or power failures, ensuring the read switch position is valid before allowing state changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single pole single throw switch is used for safety control, then the device complexity is low, but the reliability is insufficient because the system cannot distinguish between valid and invalid states (shorted contacts, unplugged cables)
Solution Approach 1:
The switch control signal is segmented into multiple independent signals (e.g., two complementary signals instead of one). This segmentation allows the system to validate switch states by checking for expected relationships between signals, thereby distinguishing valid states from invalid states such as shorted contacts or unplugged cables.
Solution Approach 2:
A validation circuit acts as an intermediary between the physical switch and the control system. This intermediary monitors multiple switch signals, validates their relationships, and only passes validated states to the control system, preventing propagation of error states while maintaining system reliability.
2Reliability
If switch bounce is not addressed, then the device complexity remains low, but the reliability decreases due to inadvertent switching
Solution Approach 1:
The validation circuit performs preliminary validation of switch states before they are processed by the control system. By checking signal relationships and validating states in advance, the system prevents switch bounce and other transient errors from causing inadvertent switching, thereby improving reliability without requiring complex post-processing.
3Measurement precision
If multiple signals are monitored for validation, then the measurement precision of switch state detection is improved, but the loss of time increases due to additional validation processing
Solution Approach 1:
The validation process is implemented using hardware logic circuits instead of software-based validation. This substitution allows multiple switch signals to be monitored and validated simultaneously through parallel hardware processing, achieving high measurement precision without significant time loss, as the validation occurs in real-time rather than through sequential software checks.
Data Source
AI summary
A method, computer program product, and circuit for monitoring a plurality of signals as input from a switch. It may be detected whether a current state of the switch is valid based upon, at least in part, the plurality of signals. When the current state of the switch is valid, use of the current state of the switch may be enabled as an output. When the current state of the switch is invalid, use of the current state of the switch may be disabled while a previous valid state is held in memory and maintained on the output.