Positioning Control System Integrator Windup Prevention
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Solution Overview
Problem
Positioning control systems using pneumatic cylinders face challenges in achieving high accuracy and rigidity due to the stick-slip phenomenon caused by frictional forces, and existing disturbance observers suffer from integrator windup, leading to reduced control performance.
Innovation Solution
A positioning control system incorporating a disturbance observer with a saturation element in a positive-feedback minor loop, which includes a low-pass element and a saturation element in the forward path, to restrain integrator windup and enhance control capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a disturbance observer with integrator characteristics is used to improve control accuracy, then positioning precision is improved, but integrator windup occurs leading to reduced control performance
Solution Approach 1:
The control system is segmented into a main feedback loop and a minor positive feedback loop. The saturation element is specifically placed in the minor loop to prevent integrator windup, while the main loop maintains integrator characteristics for accurate disturbance estimation and positioning control.
Solution Approach 2:
The saturation element acts as an intermediary component in the minor positive feedback loop. It mediates between the integrator output and the summing junction, preventing excessive integration (windup) while allowing the integrator to function properly for disturbance observation in the main control loop.
2Measurement precision
If control gain is increased to improve positioning accuracy, then positioning precision is improved, but the command values become too large requiring saturating elements
Solution Approach 1:
The control system separates the high-gain disturbance observer path from the main control path by introducing a minor positive feedback loop with a saturation element. This segmentation allows high control gain for accuracy while the saturation element prevents command values from becoming excessively large.
3Measurement precision
If a static pressure bearing is used to reduce frictional forces, then positioning accuracy is improved, but damping characteristics deteriorate increasing convergence time
Solution Approach 1:
The system employs a disturbance observer that estimates frictional disturbances and feeds back compensating signals. This feedback mechanism compensates for the poor damping characteristics of static pressure bearings, maintaining positioning accuracy while avoiding the need for mechanical damping modifications that would increase convergence time.
Data Source
AI summary
A positioning control system has a disturbance observer for estimating a disturbance from a displaced distance of a cylinder of a controlled object, and feeding back an estimated disturbance. The positioning control system also includes a saturation element and a low-pass element disposed in a feedback loop including the disturbance observer, and a saturated value changer for changing a saturated value of the saturation element based on a deviation. The saturation element is disposed in a forward path of a positive-feedback minor loop, whereas the low-pass element is disposed in a feedback path of the positive-feedback minor loop.