Position Controller Friction Compensation for Overshoot Prevention
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Solution Overview
Problem
Conventional position controllers face issues with overshoot and resonance due to varying friction characteristics in machinery systems, leading to low robustness and instability, especially near zero speed.
Innovation Solution
A position controller with a feedforward system that estimates friction coefficients from disturbance torque and calculates a speed-integral-term feedforward gain to reduce the feedforward term, preventing overshoot and minimizing resonance by automatically adjusting the control gain based on estimated disturbance torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If viscous friction compensation torque is applied by multiplying actual speed by identified friction coefficient, then overshoot due to friction is prevented, but mechanical resonance is induced and control oscillates near zero speed
Solution Approach 1:
The invention changes the parameter of friction compensation from speed-proportional to position-proportional. Instead of multiplying friction coefficient by actual speed, the controller calculates compensation torque by multiplying friction coefficient by position deviation from the target position. This parameter change eliminates the sign inversion problem near zero speed while maintaining overshoot prevention effectiveness.
Solution Approach 2:
The invention inverts the conventional approach by using position deviation as the basis for friction compensation instead of actual speed. This inversion transforms the compensation mechanism from one that causes resonance and oscillation near zero speed to one that provides stable control while preventing overshoot.
2Manufacturing precision
If friction characteristics are optimized to prevent overshoot, then positioning accuracy is improved, but control robustness decreases when friction varies with temperature and time
Solution Approach 1:
The invention implements feedback by continuously monitoring position deviation and using it to adjust friction compensation torque in real-time. The controller calculates compensation based on current position error, automatically adapting to varying friction conditions without requiring manual re-tuning, thereby maintaining both positioning accuracy and control robustness.
Solution Approach 2:
The invention makes the friction compensation dynamic by linking it to position deviation rather than using fixed speed-proportional compensation. The compensation torque dynamically adjusts according to the instantaneous position error, allowing the system to adapt to changing friction characteristics while maintaining precise control.
3Stability of the object's composition
If speed-integral-term feedforward gain is reduced to prevent overshoot, then positioning stability is improved, but response speed decreases
Solution Approach 1:
The invention applies preliminary action by calculating friction compensation torque in advance based on position deviation before the actual positioning error occurs. This proactive compensation prevents overshoot without requiring reduction of the speed-integral-term gain, thereby maintaining both stability and fast response.
Data Source
AI summary
An objective is to obtain a high robust position controller and a controlling method therefor, with respect to their technique in which control gain, in order to prevent an overshoot due to frictions, is most suitably adjusted. The position controller having a feedforward system includes: a friction-coefficient-estimated-value setting unit for setting arbitrary friction-coefficient-estimated-values; an overshoot-prevention-gain calculator for determining speed-integral-term feedforward gain, based on estimated friction-coefficient values set by the friction-coefficient-estimated-value setting unit; and a speed feedforward multiplying unit for calculating the product of the speed-integral-term feedforward gain multiplied by a feedforward command value that is based on a positional command; the multiplication product from the speed feedforward multiplying unit being used to reduce the feedforward term.