Autonomous Vehicle Steering Control With Yaw-Limited Path Tracking
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Solution Overview
Problem
Autonomous agricultural machines require robust navigation control systems to follow guidance paths accurately without operator oversight, as they must handle anomalies and corrections independently, which is challenging due to the absence of operator input.
Innovation Solution
A mobile machine with a chassis, ground-engaging elements, and actuators is equipped with a controller implementing a cascading control loop that adjusts the error slope to ensure the machine follows a reference path by combining an outer loop for determining the set heading and an inner loop for driving the machine, using a weighting algorithm to balance distance and reference heading errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the autonomous machine uses a cascading control loop with outer and inner loops to follow a reference path, then the navigation accuracy is improved, but the system complexity increases
Solution Approach 1:
The control system is segmented into two distinct loops: an outer loop that determines the set heading for reducing distance to the reference path, and an inner loop that drives the actuators to follow the set heading. This segmentation allows each loop to handle specific control tasks independently, improving navigation accuracy while maintaining manageable system complexity through modular design.
Solution Approach 2:
The cascading control loop implements feedback mechanisms where the outer loop continuously monitors distance to the reference path and adjusts the set heading accordingly, while the inner loop monitors actual heading and adjusts actuator commands. This multi-level feedback structure enables precise path following by continuously correcting deviations at different control levels.
2Speed
If the error slope value is increased to improve response speed, then the machine can correct heading errors faster, but the machine may overshoot or become unstable
Solution Approach 1:
The error slope value is made dynamic rather than fixed. The controller automatically adjusts the error slope based on the current operating conditions, specifically modifying it when the rate of change of set heading approaches the machine's maximum yaw rate. This dynamic adjustment allows the system to respond quickly when safe to do so while preventing overshoot and maintaining stability when near the machine's rotational limits.
Solution Approach 2:
The controller changes the error slope parameter adaptively based on the machine's current state and capabilities. By monitoring the rate of change of set heading and comparing it to the maximum yaw rate, the system modifies the error slope parameter in real-time, increasing it to improve response when capacity allows and decreasing it to prevent instability when approaching operational limits.
3Productivity
If the machine operates at high speed to improve productivity, then more ground can be covered, but the machine has reduced ability to correct heading errors
Solution Approach 1:
The controller dynamically adjusts the error slope parameter based on the machine's operating speed and yaw rate capabilities. When operating at high speeds where heading correction capability is reduced, the controller modifies the error slope to account for the slower response time, ensuring that heading corrections remain accurate and stable even during high-productivity operations.
Data Source
AI summary
A mobile machine including a chassis, a plurality of ground-engaging elements, actuators for driving movement of the ground-engaging elements and a controller for controlling each of the actuators to cause the mobile machine to follow a reference path. The controller is configured to implement a cascading control loop for controlling movement of the mobile machine, the cascading control loop including an outer loop and an inner loop. The outer loop is configured to determine a set heading for reducing a distance between the mobile machine and the reference path, the set heading being determined using an error slope parameter. The inner loop is configured to drive the actuators so that the mobile machine follows the set heading determined by the outer loop. The controller is configured to automatically adjust the error slope value so that the rate of change of the set heading does not exceed a maximum yaw rate.