Steering Angle Plausibility Check for Driverless Vehicle Safety
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Solution Overview
Problem
Existing driverless transport vehicles face challenges in reliably detecting vehicle movement using a minimum number of encoders that do not have to be fail-safe, particularly in omnidirectional vehicles with complex kinematics, where ensuring safe navigation and collision avoidance is critical.
Innovation Solution
A device and method that utilize plausibility checks between steering angle signals and travel distance signals from individual wheels, allowing for fail-safe movement detection without the need for complex or redundant encoder systems, by assuming consistent wheel control and using tolerance values to compensate for minor deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fail-safe encoders or redundant encoders are used per wheel to reliably detect wheel movement, then measurement precision and reliability are improved, but device complexity and cost increase
Solution Approach 1:
The patent uses steering angle signals from steered wheels as a copy or substitute for direct encoding of all wheel movements. By detecting steering angles of steered wheels and using these signals to infer the movement state of non-steered wheels through plausibility checks, the system achieves reliable movement detection without requiring fail-safe encoders on every wheel, thus reducing device complexity while maintaining safety
Solution Approach 2:
The evaluation unit performs plausibility checks by comparing steering angle signals from multiple steered wheels against each other and against expected kinematic relationships. This feedback mechanism validates the consistency of wheel movement data and detects anomalies, providing reliable safety verification without requiring redundant encoders on all wheels
2Device complexity
If a minimum number of non-fail-safe encoders are used to detect wheel movement, then device complexity is reduced, but reliability of movement detection deteriorates
Solution Approach 1:
The patent replaces the mechanical/physical redundancy of multiple fail-safe encoders with a computational/electronic solution. Instead of using redundant physical sensing components, the system uses software-based plausibility checks that compare steering angle signals and validate them against the vehicle's known kinematic model, achieving safety through intelligent evaluation rather than physical redundancy
Solution Approach 2:
The steered wheels themselves provide the information needed for safety verification through their steering angle signals. By monitoring the steering angles of steered wheels and checking their consistency with each other and with the vehicle's kinematic constraints, the system makes the wheels self-verify their own movement state without requiring external redundant sensing
3Reliability
If plausibility checks are performed on steering angle signals from steered wheels, then reliability of movement detection is improved without additional encoders, but device complexity increases due to evaluation requirements
Solution Approach 1:
The evaluation unit performs multiple functions using the same steering angle signals: it determines vehicle position, calculates vehicle speed, verifies safety conditions, and detects anomalies. By making the evaluation unit multi-functional, the patent avoids adding separate systems for each function, thereby improving reliability without proportionally increasing device complexity
Solution Approach 2:
The system changes the parameter being monitored from direct wheel speed/position (which would require encoders on all wheels) to steering angle of steered wheels. This parameter change allows the use of existing steering sensors for multiple purposes including safety verification, avoiding the need for additional complex sensing hardware while improving reliability
Data Source
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AI summary
The invention relates to a driverless transport vehicle (10) with at least three wheels (12, 14, 16, 18) designed as individual wheels. At least two of the wheels are individually steered and each has a steering device. At least some of the wheels are driven so that their rotational speeds are controlled. The vehicle further comprises a steering angle detection device (28) for detecting the steering angles (α, β, γ, δ) of the at least two steered wheels and for outputting corresponding steering angle signals, as well as an evaluation unit (32) to which the steering angle signals are supplied. The evaluation unit has a plausibility check unit (34) that performs a plausibility check of the steering angle signals and outputs a safety signal if the plausibility check is unsuccessful.