Trajectory Tracking Control for Mobile Units
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Solution Overview
Problem
Existing trajectory tracking control systems for mobile units, such as robots, face instability and accuracy issues when tracking paths with varying curvatures due to direct incorporation of curvature changes in the control loop, leading to disturbances in feed-forward control and reduced tracking accuracy.
Innovation Solution
A trajectory tracking control system that approximates the target path to an arc, calculates curvature based on the mobile unit's moving speed and control cycle, and adjusts feed-forward control to match actual operational units, with the option to stop feed-forward control when position or orientation errors exceed predetermined limits, ensuring accurate tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If feed-forward control is continuously applied based on target path curvature, then the mobile unit can proactively respond to path changes, but the motion becomes unstable when curvature changes discontinuously and tracking accuracy deteriorates when deviation is large
Solution Approach 1:
The patent applies dynamics by making the feed-forward control adaptive rather than static. The control amount is dynamically adjusted based on the magnitude of curvature change and the current tracking deviation. When curvature changes are small and deviation is within acceptable limits, feed-forward control is applied to improve response speed. When curvature changes discontinuously or deviation exceeds thresholds, feed-forward control is reduced or suspended to maintain stability, thus resolving the contradiction between responsive speed and motion stability.
2Adaptability or versatility
If curvature of target path is directly incorporated into control loop, then the mobile unit can respond to path curvature, but the motion becomes unstable due to direct reflection of discontinuous curvature changes
Solution Approach 1:
The patent applies beforehand cushioning by introducing curvature change amount calculation and threshold-based filtering before the curvature information enters the control loop. Instead of directly using raw curvature values that may contain discontinuous changes, the system calculates the change amount between consecutive curvature values and only applies feed-forward control when changes are within acceptable thresholds. This cushioning mechanism prevents discontinuous curvature changes from directly causing instability while maintaining adaptability to genuine path curvature variations.
3Force
If feed-forward control is always applied, then the mobile unit can anticipate path changes, but when deviation is large, the feed-forward control acts as disturbance to feed-back control and reduces tracking accuracy
Solution Approach 1:
The patent applies partial action by selectively applying feed-forward control only when tracking deviation is within acceptable limits. When deviation exceeds the threshold, the system partially suspends feed-forward control to prevent it from acting as a disturbance to the feed-back control mechanism. This ensures that when the mobile unit is significantly off-track, the control system focuses on correction through feed-back control rather than potentially conflicting feed-forward commands, thereby maintaining tracking accuracy while preserving the benefits of feed-forward control during normal operation.
Data Source
AI summary
A trajectory tracking control system according to the invention controls a robot (1) to track a target path (100). In this system, the target path (100) is approximated to an arc, and the curvature of the arc is calculated. At this time, the curvature is calculated in accordance with the moving speed of the robot (1). Then, the control of the robot (1) is set in accordance with the calculated curvature.