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.
Highlights
Piezo-actuators are used extensively in high precision positioning devices due to their various desirable proprieties, such as high positioning accuracy, nanometre repeatable displacement resolution and a high level of stiffness [1,2]
This paper presents the strategic zero placement of the Proportional Integral (PI) controller to enhance the positioning bandwidth, thereby overcoming the limitations of tracking error
The pole of the Integral Resonant Controller (IRC) was precisely cancelled by the tracking controller using the traditional method, as is clear from Figure 5
Summary
Piezo-actuators are used extensively in high precision positioning devices due to their various desirable proprieties, such as high positioning accuracy, nanometre repeatable displacement resolution and a high level of stiffness [1,2]. Precision positioning stages currently have widespread use due to their popularity and use in a variety of applications [4,5] Their uses include Atomic Force Microscope (AFM), such as biological manipulation [6]. Another popular application is scanning probe microscopy, where the nanopositioner moves the surface in a raster pattern, which is used to generate a topographic image of the surface with a nanometre scale. This image is beneficial as it provides qualitative information about the sample surface, which could be useful in investigating the magnetic or electrical properties of the surface [7]
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