Autonomous Vehicle Path Control for Clothoid Tracking
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Solution Overview
Problem
Current controllers for autonomous vehicles are not suited to track general path segments, especially clothoid segments, due to their design limitations, leading to suboptimal transitions and increased off-path normal errors, as they assume unplanned transitions and use linear or nonlinear approaches that do not result in linear dynamics.
Innovation Solution
A controller and method that includes an input module for receiving normal error, heading, and curvature signals, a curvature rate module for calculating curvature rate output signals, and a communication module to guide autonomous vehicles along paths with clothoid segments, using nonlinear feedforward for output linearization and LQR methods to stabilize the system, making it easier to tune and handle steering rate limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current controllers use linear or nonlinear approaches to deal with disturbances, then they can handle unplanned transitions between path segments, but they do not result in linear dynamics in the off-path normal error and experience degradation in controller performance
Solution Approach 1:
The patent transforms the controller design by changing the parameter representation from linear or nonlinear disturbance approaches to a curvature rate-based parameterization. This allows the controller to achieve linear dynamics in the off-path normal error by using curvature rate as the key control parameter, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The patent replaces the traditional mechanical control approach (linear/nonlinear controllers dealing with disturbances) with a mathematical transformation approach (curvature rate module that computes desired curvature rate based on clothoid path parameters). This substitution eliminates the performance degradation issue while maintaining manageable complexity.
2Adaptability or versatility
If autonomous vehicles use paths with clothoid segments, then they can achieve drivable paths with continuous curvature rate, but current controllers cannot track these general segments well due to their design limitations
Solution Approach 1:
The patent introduces dynamics to the controller by using curvature rate (derivative of curvature with respect to path length) as the control variable. This allows the controller to track clothoid segments effectively, as clothoids are defined by linearly varying curvature rate. The curvature rate module computes the desired curvature rate dynamically, enabling accurate tracking of general path segments with continuous curvature variation.
Solution Approach 2:
The patent segments the path into clothoid segments with specific parameters (initial position, initial heading, initial curvature, rate of curvature, and path length). By treating each segment separately with its own curvature rate characteristics, the controller can achieve high precision in tracking each segment while maintaining overall path adaptability.
3Ease of operation
If controllers assume unplanned transitions between path segments, then they can switch to new path segments at some time ahead, but they experience path segment transitions as disturbances leading to degradation in controller performance
Solution Approach 1:
The patent applies preliminary action by computing the desired curvature rate in advance based on the known clothoid path parameters. Instead of reacting to transitions as disturbances, the controller proactively calculates the required curvature rate changes before transitions occur, using the six quantities that parameterize clothoid segments. This eliminates performance degradation while maintaining ease of operation.
Data Source
AI summary
A path controller for guiding an autonomous vehicle along a desired path may include an input module that may receive input signals such as, a normal error signal that indicates an off-path deviation of the autonomous vehicle relative to a desired path, a heading signal, and a curvature signal associated with the autonomous vehicle. The path controller may also include a curvature rate module that calculates a curvature rate output signal to guide the autonomous vehicle along the desired path and a communication module that communicates the curvature rate output signal to a steering control system.