Introduction to the special issue on control of high-precision motion systems

Driven by increasing societal, economic, and technological pressures , high-precision motion systems must achieve ever increasing speed and accuracy requirements. Motion systems are used in many different application areas, including hard disk drives (HDDs) in consumer electronics, wafer steppers and scanners in nano-scale manufacturing machines, electron and atomic force microscopes for nano-scale imaging, and (nano-) printing devices. Despite the large differences in the application areas, these motion systems share a common aspect: control is essential for achieving the speed and accuracy requirements. The main goal of this special issue is to bring together the control challenges encountered in different high-precision motion systems that are of current interest. These challenges include modelling of complex and high-dimensional dynamics, feedback and tracking control, feedforward and model inversion, position-dependent and time-dependent behavior of both system dynamics and disturbances, flexible system behavior and spatial performance , nonlinear dynamics and control, and repetitive versus non-repetitive disturbances. Overall, 34 manuscripts have been received. All manuscripts have been thoroughly reviewed, and a total of 18 resulting papers have been accepted and included in this special issue. The papers are ordered according to the following aspects: (1) feedforward design and learning, (2) feedback design and flexible systems, (3) optimal control, (4) nonlinear systems, (5) disturbance analysis, observation, and control. Feedforward design and learning. In Altin and Barton [1] a signal based iterative learning control scheme based on L 1 adaptive feedback is presented. The proposed scheme effectively deals with parametric uncertainties, and is demonstrated to achieve high performance in a simulation study on a motion system. An extension to filter-based feedforward control and input shaping is presented in Boeren et al. [3]. The authors show that the proposed extension enables high performance for point-to-point stage positioning while avoiding a full plant inversion and its related stability issues. In addition, a data-driven tuning procedure is proposed and implemented on an industrial motion system. Aspects of input shaping are also considered by Yang et al. [17] with a focus on high band-width tracking control. The authors successfully implemented their method on a piezoelectric stage, achieving a significant increase in tracking bandwidth. A paradigm shift from feedforward control for rigid-body positioning systems to flexible systems is presented by Ronde et al. [13]. The authors propose a spatial feedforward controller to address the position-dependent stage dynamics over an entire surface instead of only optimizing the performance at the sensor location, as is traditionally …