Servo Position Control With Pre-Switched Friction Compensation
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Solution Overview
Problem
Existing position control systems face challenges in accurately compensating for kinetic friction errors due to varying frictional relationships between objects, limiting their applicability across different controlled objects and mechanisms.
Innovation Solution
A control system that includes a control device and servo driver connected via a field bus, utilizing a kinetic friction compensating method where torque offsets are determined and applied prior to changes in the moving direction of the command speed, based on identified kinetic friction characteristics, to minimize position deviations and enhance tracking accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If kinetic friction compensation is performed using conventional methods, then position control accuracy is improved, but the method cannot be generally applied to different controlled objects due to varying friction characteristics
Solution Approach 1:
The invention changes the parameters of friction compensation by dynamically adjusting the torque offset based on the actual moving direction of the controlled object rather than relying on predetermined friction characteristics. The control device calculates the actual moving direction from position feedback and switches torque offsets accordingly, making the system adaptable to different controlled objects without requiring recharacterization.
Solution Approach 2:
The system performs self-characterization by automatically identifying friction characteristics through excitation commands and position feedback during operation. The control device executes identification commands, measures position responses, and derives friction parameters on-the-fly, eliminating the need for external characterization procedures and enabling universal application across different controlled objects.
2Speed
If torque offset switching is performed at command speed direction change, then response speed is improved, but position deviation occurs due to shaft operation delay
Solution Approach 1:
The invention applies preliminary action by switching the torque offset in advance based on the actual moving direction before the command speed direction changes. The control device calculates the actual moving direction from position feedback and proactively adjusts the torque offset to compensate for the upcoming direction change, preventing position deviation caused by shaft operation delay while maintaining fast response.
3Device complexity
If friction compensation is performed without considering actual moving direction, then device complexity is reduced, but position control accuracy deteriorates
Solution Approach 1:
The invention implements feedback by continuously monitoring the actual position of the controlled object and calculating the actual moving direction from position differences between control cycles. This feedback mechanism enables the system to dynamically switch torque offsets based on real moving direction, significantly improving position control accuracy while adding minimal complexity through simple position difference calculations.
Data Source
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AI summary
A control device, a control program and a control system are provided. The control device includes: a first identification device for giving a first command as a command value to a drive device and determining a torque required for the controlled object to execute the first command; a second identification device for giving a second command as the command value and a third command as a compensation command to the drive device and determining a preceding switching time based on a response from the controlled object; a command value updating device for sequentially updating the command value based on a predetermined target trajectory; and a compensation command updating device for sequentially updating the compensation command based on the command value. The compensation command updating device updates the compensation command according to a moving direction after a reversal of the moving direction of the controlled object in the target trajectory.