Local Loop Shaping for Rejecting Band-Limited Disturbances in Nonminimum-phase Systems with Application to Laser Beam Steering for Additive Manufacturing

Closed-loop disturbance rejection without sacrificing overall system performance is a fundamental issue in a wide range of applications from precision motion control, active noise cancellation, to advanced manufacturing. At the core of rejecting band-limited disturbances is the shaping of feedback loops to actively and flexibly respond to different disturbance spectra. However, such strong and flexible local loop shaping has remained underdeveloped for systems with nonminimum-phase zeros due to challenges to invert the system dynamics. This paper proposes a local loop shaping with prescribed performance requirements in systems with nonminimum-phase zeros. Pioneering an integration of the interpolation theory with a model-based parameterization of the closed loop, the proposed solution provides a filter design to match the inverse plant dynamics locally and as a result, creates a highly effective framework for controlling both narrow- and wide-band vibrations. From there, we discuss methods to control the fundamental waterbed limitation, verify the algorithm on a laser scanning platform in selective laser sintering additive manufacturing, and compare the benefits and tradeoffs over con- ventional direct inverse-based loop-shaping method. The results are supported by both simulation and experimentation.

Journal article