Combined H∞ -Feedback and Iterative Learning Control Design with Application to Nanopositioning Systems

This paper presents a coordinated design framework for precision motion control (PMC) systems. In particular, the focus is on the design of feedback and feedforward controllers operating on systems that repeatedly perform the same tasks. The repetitive nature of the tasks suggests the use of Iterative Learning Control (ILC). However, in addition to the repeatability of the desired trajectory, the class of systems under study examines the effect of nonrepeating disturbances and possible reset errors. The rejection of uncertain, but bounded, disturbances suggests the use of H∞ design. The non-repeating disturbances and reset errors necessitate coordination of the feedback and feedforward designs. The assumption that the disturbances have a particular frequency distribution affords a frequency domain separation between the two controller degrees of freedom. Experimental results are given on a piezo-driven nanopositioning device demonstrating the benefits to the presented approach.