Combined Feed-forward and Feedback Control of Flexible Structures:
From Atomic Force Microscopes to Megawatt Wind Turbines
Lucy Y. Pao, University of Colorado at Boulder
Manipulators, machine tools, measurement and many other systems were in the past designed with rigid structures and operated at relatively low speeds. With an increasing demand for fuel efficiency, smaller actuators and speed, lighter weight materials are now often used in the construction of systems, making them more flexible. Flexible structures are also prevalent in space systems where lightweight materials are necessitated for fuel efficiency when carrying the structures into space. Achieving high-performance control of flexible structures is a difficult task, but one that is now critical to the success of many important applications, including the space shuttles’ remote manipulator system, satellites, megawatt wind turbines, robotic manipulators, gantry cranes, disk drives, tape systems and atomic force microscopes. The unwanted vibration that results from maneuvering a flexible structure often dictates limiting factors in the performance of the system.
We will discuss a general combined feed-forward and feedback control architecture and how it can be applied for controlling flexible structures. Depending upon the particular performance goals – such as tracking accuracy in a trajectory-following task or rapid settle time for point-to-point motion – there are different requirements for the controller. In many applications the actuators and sensors are separated by the flexible structure, leading to nonminimum phase characteristics that are challenging for control. Over the last few decades many feedback and feed-forward control methods have been developed for flexible structures. We will overview and compare several of these control methods, and we will outline our recent and ongoing investigations and applications in a few areas ranging from atomic force microscopes to megawatt wind turbines. We shall close by discussing a number of future challenges.
Lucy Y. Pao holds B.S., M.S. and Ph.D. degrees in electrical engineering from Stanford University, and she is currently the Richard and Joy Dorf Professor of Electrical, Computer and Energy Engineering at the University of Colorado at Boulder. She was a visiting scholar at Harvard University (2001-2002), a Visiting Miller Professor at UC Berkeley (fall 2008) and has just completed a term as a visiting scholar at the National Renewable Energy Laboratory. She has interests in the areas of control systems (with applications to flexible structures, atomic force microscopes, disk drives, tape systems, power converters and wind turbines), multisensor data fusion (with applications to unmanned autonomous vehicles, satellites and automotive active safety systems) and haptic and multimodal visual/haptic/audio interfaces (with applications to scientific visualization and spatial communication).