This paper examines a coordinated feedback and feedforward control design strategy for precision motion control (PMC) systems. It is assumed that the primary exogenous signals are repeated; including disturbances and references. Therefore, an iterative learning control (ILC) feedforward strategy can be used. The introduction of additional non-repeating exogenous signals, including disturbances, noise, and reset errors, necessitates the proper coordination between feedback and feedforward controllers to achieve high performance. A novel ratio of repeated versus non-repeated signal power in the frequency domain is introduced and defined as the repetitive-to-non-repetitive (RNR) ratio. This frequency specific ratio allows for a new approach to delegating feedback and feedforward control efforts based on RNR value. A systematic procedure for control design is given whereby the feedback addresses the non-repeating exogenous signal content ( RNR < 0 dB}) and the feedforward ILC addresses the repeating signal content ( RNR > dB). To illustrate the design approach, two case studies using different nano-positioning devices are given.
B. E. Helfrich et al., "Combined H∞-feedback Control and Iterative Learning Control Design with Application to Nanopositioning Systems," IEEE Transactions on Control Systems Technology, Institute of Electrical and Electronics Engineers (IEEE), Mar 2010.
The definitive version is available at https://doi.org/10.1109/TCST.2009.2018835
Mechanical and Aerospace Engineering
Nano-CEMMS Center, University of Illinois
Keywords and Phrases
Iterative Learning Control (ILC); Nanopositioning; Precision Motion Control (PMC)
Article - Journal
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