Friction parameter identification and compensation using the ElastoPlastic friction model

This paper presents the application of a model-based feedforward friction compensation system based on the ElastoPlastic friction model. This nonlinear feedforward compensator, in combination with a linear feedback controller, is applied to a linear drive axis with recirculating ball bearings and a fine-positioning axis with crossed roller bearings. The developed friction compensator estimates the state of the ElastoPlastic friction model and thus the friction force. The compensator also adapts to local variations and variations over time due to wear. This feedforward system serves as an add-on friction compensation system and can be used with existing feedback control systems. Both linear axes are used in an optical measurement setup based on a modified Mahr MFU 100 measuring machine. The designed and implemented control system permits high-accuracy trajectory tracking control even for small velocities such as typical measurement velocities in surface metrology. The parameter identification procedure used for the identification of the ElastoPlastic friction model parameters is explained in detail. The trajectory tracking for the regarded hardware setups with and without friction compensation is compared in experiments, illustrating the performance of this feedforward system. Although the presented work was motivated by the mentioned measurement application, the presented modelling, identification and compensation techniques are not limited to this application and can be transferred to many mechanical systems with friction.