A novel piezoelectric strain sensor for simultaneous damping and tracking control of a high-speed nanopositioner

Abstract—This paper presents a novel piezoelectric strain sensor for damping and accurate tracking control of a high-speed nanopo-sitioning stage. Piezoelectric sensors have the benefit of simple in-terface circuitry, low cost, high sensitivity, and high bandwidth. Although piezoelectric sensors have been successfully used as vi-bration sensors in smart structures, complications arise when they are used in a feedback loop for tracking. As piezoelectric strain sensors exhibit a capacitive source impedance, a high-pass filter is created, typically with a cut-off frequency of 1 to 10 Hz. This filter can cause significant errors and destabilize a tracking control system. Here, we overcome this problem by using a low-frequency bypass technique to replace the low-frequency component of the strain measurement with an estimate based on the open-loop sys-tem. Once the low-frequency filter is accounted for, any standard control system can be applied. In this paper, an analog integral resonant controller together with an integral tracking controller are implemented on a flexure-guided nanopositioner. The result-ing closed-loop bandwidth is experimentally demonstrated to be 1.86 kHz. The nanopositioner is installed in an Atomic Force Mi-croscope to obtain open- and closed-loop images at line rates of 40 and 78 Hz. Images recorded in closed loop show a significant improvement due to the elimination of nonlinearity. Index Terms—Atomic force microscope (AFM), control, high speed, nanopositioning, piezoelectric, strain sensor. I