Modeling, design and control of normal-stressed electromagnetic actuated fast tool servos

Abstract

The normal-stressed electromagnetic actuated fast tool servo (FTS) plays an important role in modern ultra-precision manufacturing due to its high actuation force density and fast dynamics response. In order to promote the design and control of the normal-stressed electromagnetic actuated FTS, this paper proposes a comprehensive dynamics model based on the principles of magnetic equivalent circuits, which can be described as a Hammerstein-like structure. The electromagnetic phenomena, including hysteresis, magnetic saturation, and eddy currents, as well as the coupling between electromagnetic and mechanical dynamics are explicitly represented in the model. Based on a simplified version of this model, an integrated optimal design method for simultaneously determining actuator and mechanism parameters of the FTS is developed with full consideration of various practical physical limitations, which is then systematically verified through the finite element analysis (FEA). Afterwards, the comprehensive model of the assembled FTS prototype is identified and experimentally verified with a two-step identification strategy. Finally, a dual-loop control scheme is employed to improve tracking accuracy while suppressing the hysteresis and lightly damped resonance. Both open-loop and closed-loop performance of the FTS prototype validate the feasibility and effectiveness of the proposed model and methods.