System and method for controlling a vehicle
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Solution Overview
Problem
Autonomous vehicles with rate-limited servo steering systems face challenges in smoothly transitioning between path segments, leading to control system degradation and suboptimal path execution due to abrupt changes in curvature, which results in increased wear and tear and maintenance costs.
Innovation Solution
The implementation of a drivable path plan system that uses clothoid splines to connect tangentially aligned path segments, minimizing off-path normal error and lateral acceleration by identifying initial and final connection points, headings, and curvatures, and inserting calculated clothoid segments between these points to create a smoother transition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tangentially connected circular arc and straight line segments are used to construct desired paths, then path length optimality is improved, but path smoothness deteriorates due to abrupt curvature changes at transition points
Solution Approach 1:
The patent applies clothoid curves (spiral curves with linearly varying curvature) to replace the abrupt transitions between circular arcs and straight lines. The clothoid provides continuous curvature variation, eliminating sudden curvature changes while maintaining path efficiency. This resolves the contradiction by introducing a curved transition segment that preserves the overall path optimality while ensuring smoothness.
Solution Approach 2:
The patent changes the curvature parameter continuously along the transition path using clothoid curves, where curvature varies linearly with arc length. This parameter change approach allows the path to transition smoothly from zero curvature (straight line) to constant curvature (circular arc) without abrupt changes, resolving the smoothness issue while maintaining path length optimality.
2Ease of operation
If rate-limited servo steering systems are used in autonomous vehicles, then vehicle control capability is improved, but transition performance between path segments deteriorates due to finite steering rate causing lag
Solution Approach 1:
The patent pre-calculates the clothoid transition curves and identifies optimal connection points before executing the path. By preparing the smooth transition path in advance, the system can execute transitions more efficiently with the rate-limited steering system, reducing lag and improving transition performance while maintaining control capability.
3Device complexity
If abrupt transitions between path segments are executed, then path segment switching simplicity is improved, but vehicle wear and control system degradation increase
Solution Approach 1:
The patent introduces clothoid transition curves that provide smooth curvature variation between path segments. This eliminates abrupt transitions, reducing mechanical stress and wear on the vehicle while preventing control system degradation. The continuous curvature profile maintains reliability without significantly increasing switching complexity.
Solution Approach 2:
The clothoid curve acts as an intermediary transition segment between the circular arc and straight line segments. This intermediate element provides a smooth bridge that reduces abrupt changes, protecting the control system and reducing wear while maintaining a relatively simple switching mechanism.
Data Source
AI summary
Drivable path plan systems and methods for autonomous vehicles disclosed herein may receive original path plan data, including a first path element tangentially connected to a second path element at a transition connection point. A drivable path plan may be calculated for the autonomous vehicle between the first path element and the second path element using a clothoid spline. An initial connection point may be identified, as well as an initial heading and an initial curvature along the first path element, and a final connection point, a final heading, and a final curvature along the second path element. The clothoid spline may be inserted between the initial connection point along the first path element and the final connection point along the second path element.