Friction Compensation Gain Determination for Machine Position Control
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Solution Overview
Problem
Friction in machine apparatuses, particularly at drive and load shafts, leads to position deviation and inaccurate control due to shaft torsion and mechanical backlash, which existing friction compensation methods fail to fully address.
Innovation Solution
A control device that calculates a torque command using a friction estimation and adjusts it with a predetermined gain based on the transfer function properties from the position command to position deviation, optimizing the gain for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If friction compensation is applied using a friction model, then the adjustment process becomes simpler, but the accuracy of friction force estimation may be insufficient due to shaft torsion and mechanical backlash
Solution Approach 1:
The patent introduces an intermediate shaft between the drive shaft and load shaft to transfer force. By modeling the friction compensation at the intermediate shaft rather than directly at the load shaft, the system accounts for shaft torsion and mechanical backlash effects, improving estimation accuracy while maintaining simple adjustment procedures
Solution Approach 2:
The patent replaces direct mechanical friction compensation with a computational model that calculates friction forces based on measured positions and velocities. This substitution of mechanical adjustment with mathematical modeling simplifies the adjustment process while improving accuracy through dynamic compensation
2Device complexity
If a fixed gain is used for friction compensation, then the control structure becomes simpler, but the position control accuracy deteriorates under varying operating conditions
Solution Approach 1:
The patent implements dynamic gain adjustment where the compensation gain varies based on operating conditions such as velocity and position. This dynamic approach adapts to changing friction characteristics during machine operation, maintaining high position control accuracy across different operating conditions while accepting increased control structure complexity
Solution Approach 2:
The patent changes the friction compensation parameters (gain values) based on operating conditions. By adjusting these parameters dynamically according to velocity, position, and load conditions, the system optimizes compensation accuracy for each operating regime without requiring complete redesign of the control structure
3Loss of time
If friction compensation is applied at the drive shaft, then the compensation force is applied earlier, but shaft torsion and mechanical backlash delay force transfer to the load shaft
Solution Approach 1:
The patent applies friction compensation at the drive shaft in advance, before the force needs to be transferred to the load shaft. By calculating and applying the compensation force at the point of origin (drive shaft), the system proactively counteracts friction effects, accounting for the time delay caused by shaft torsion and mechanical backlash in the force transfer path
Solution Approach 2:
The patent creates a computational model that copies the friction characteristics from the load shaft to the drive shaft. By modeling how friction manifests at the load shaft and translating this information to the drive shaft compensation point, the system achieves accurate compensation despite the spatial and temporal separation between where friction occurs and where compensation is applied
Data Source
AI summary
The purpose of the present invention is to further improve the accuracy of position control of a machine apparatus. A control device for a machine apparatus is equipped with: a speed control unit for calculating a torque command for the machine apparatus; a friction estimation unit for calculating an estimated value of the friction force produced by the machine apparatus; an amplitude phase adjustment unit for calculating a corrected friction value by multiplying the proportional gain by the friction force estimated by the friction estimation unit; and a correction unit for correcting the torque command by using the corrected friction value calculated by the amplitude phase adjustment unit. Furthermore, the proportional gain is determined on the basis of the gain properties of the transfer function of the machine apparatus from the position command to the position deviation.