Enhanced Positioning Bandwidth in Nanopositioners via Strategic Pole Placement of the Tracking Controller

Abstract

Tracking triangular or staircase trajectories is a challenge for a piezo-driven nanopositioner due to vibration problems. The piezo-driven nanopositioner is a lightly-damped system because of its mechanical construction. These reference trajectories are high-frequency components that tend to excite the mechanical resonance of the nanopositioner, causing vibration and thus affecting the accuracy. The Integral Resonant Controller (IRC) is employed to damp the resonance and thereby furnish a larger gain margin for a high-gain tracking controller to be implemented. The IRC, however, introduces a low-frequency pole. Due to other control issues, such as hysteresis nonlinearity, Integral (I) or Proportional Integral (PI) tracking control is used as a tracking loop to address uncertainties (hysteresis). The traditional method using a PI controller has a limited positioning bandwidth. This paper presents the strategic zero placement of the PI controller to enhance the positioning bandwidth, thereby overcoming the limitations of tracking error. Using experimental validations to confirm the feasibility of the proposed method, it is shown that significant improvement regarding bandwidth and disturbance rejection are reported.

Experimental validation of the simultaneous damping and tracking controller design strategy for high‐bandwidth nanopositioning – a PAVPF approach

“…In this approach, the inner‐loop damping controller damps the dominant resonance of the nanopositioner axis while the tracking controller in the outer‐loop (typically integral or proportional–integral) is employed to suppress the effects of non‐linear hysteresis and creep. A significant body of work suggests that this approach is highly effective in delivering adequate performance and has significant potential to be improved/optimised further [24, 25].…”