Shaping the Dynamics of a Low-Stiffness Positioning System by Mechatronic Design for Enabling Stable Unity Gain Feedback

Abstract

The paper presents a method for enabling feedback control of a mechatronic system without a dedicated controller by tailoring structural modes of the mechanical structure for loop shaping by design. Structural modes are in general unwanted effects in positioning systems and are by design typically well separated from the frequency range over which control is effective. They can, however, also be deliberately integrated to shape the resulting loop gain of the control loop, to overcome the need for a dedicated position controller and enable unity gain feedback. The method employs a structural mode with antiresonance-resonance-pattern together with a damping mechanism to obtain the required phase lead for feedback control of a low-stiffness positioning system. It is validated by an experimental setup with one degree-of-freedom (DoF), designed for a crossover frequency of 130 Hz and a phase margin of 50 deg. An adjustable electromagnetic damper is integrated to study the effects of parameter variations. The designed closed-loop controlled system achieves a bandwidth of 240 Hz, and is capable of tracking step inputs and rejecting external impacts with settling times a factor of 2–5 smaller than in the detuned case.