Development of a Hybrid Control Concept with Adaptive Force Control for Electromechanical Feed Axes

The cascaded position control of electromechanical feed axes is only capable to a very limited extent of reacting to non-linear process dynamics or changing machining conditions and thus compensating for undesirable deviations in quality or process parameters. The potential of this conventional control concept with PID-structures at machine level is now largely exhausted. The development of control concepts at process level, in which essential process variables are taken into account as control variables, still offers much room for improvement. In particular, the control of process forces is the focus of much research work. This paper presents a hybrid control concept that combines cascaded position control with an adaptive force controller that can adapt to changing behaviour of the controlled system in contact situations. The parameterisation of the force controller, the hybrid transition range with weighting function and confidence interval, as well as the adaptation concept are presented for a test rig that can be used as a forming or material testing machine. The final results show that the overall concept enables a rapid transition from position control to adaptive force control, which remains stable even in the event of drastic changes in the controlled system.