Piezoelectric Shunt Control Research Articles

Sensorless Implementation of a PPF Controller for Active <inline-formula> <tex-math notation="TeX">$Q$ </tex-math></inline-formula> Control of an AFM Microcantilever

Reducing the cantilever quality (Q) factor in the atomic force microscope (AFM), when operating in tapping mode, allows for an increase in imaging speed. Passive piezoelectric shunt control has several advantages over alternative methods of cantilever Q factor reduction. However, this technique uses a passive electrical impedance to modify the mechanical dynamics of the cantilever, which limits the amount of Q factor reduction achievable. This paper demonstrates that further reductions in the cantilever Q factor may be obtained with the use of an active impedance in the piezoelectric shunt control framework. The active impedance parameters are designed in such a way that the piezoelectric shunt controller emulates a positive position feedback controller in a displacement feedback control loop. A significant reduction in cantilever Q factor is obtained using an active impedance compared with that achieved with a passive impedance. The improvement in scan speed using this control technique is demonstrated with AFM images of a test sample.

Sensorless Damping Control of a High Speed Flexure Guided Nanopositioner

The scan speed of the Atomic Force Microscope (AFM) is limited by the highly resonant nature of the nanopositioner which scans the sample relative to the probe tip. Feedback control may be used to dampen the resonance; however this requires external displacement sensors which may introduce high frequency noise into the feedback loop. In this work an active piezoelectric shunt control system, which requires no external feedback sensors, is designed to damp the resonance of a high speed flexure guided nanopositioner. The shunt impedance is designed in such a way that the closed loop transfer function from applied voltage to actuator displacement is equivalent to that of a displacement feedback system using a Positive Position Feedback (PPF) controller. This impedance design is an improvement over a passive impedance in that higher damping of the resonance is achievable. AFM images of a test sample were obtained to demonstrate the reduction of image artifacts when this control technique is applied.

Sensorless enhancement of an atomic force microscope micro-cantilever quality factor using piezoelectric shunt control

The image quality and resolution of the Atomic Force Microscope (AFM) operating in tapping mode is dependent on the quality (Q) factor of the sensing micro-cantilever. Increasing the cantilever Q factor improves image resolution and reduces the risk of sample and cantilever damage. Active piezoelectric shunt control is introduced in this work as a new technique for modifying the Q factor of a piezoelectric self-actuating AFM micro-cantilever. An active impedance is placed in series with the tip oscillation voltage source to modify the mechanical dynamics of the cantilever. The benefit of using this control technique is that it removes the optical displacement sensor from the Q control feedback loop to reduce measurement noise in the loop and allows for a reduction in instrument size.

$Q$ Control of an Atomic Force Microscope Microcantilever: A Sensorless Approach

The scan rate and image resolution of the atomic force microscope (AFM) operating in tapping-mode may be im proved by modifying the quality (Q) factor of the AFM micro cantilever according to the sample type and imaging environment. Piezoelectric shunt control is a new method of controlling the Q factor of a piezoelectric self-actuating AFM microcantilever. The mechanical damping of the microcantilever is controlled by an electrical impedance placed in series with the tip oscillation circuit. A synthetic impedance was designed to allow easy modification of the control parameters which may vary with environmental conditions. The proposed techniques are experimentally demonstrated to reduce the Q factor of an AFM microcantilever from 297.6 to 35.5. AFM images obtained using this method show significant improvement in both scan rate and image quality.

Multiple mode current flowing passive piezoelectric shunt controller

A method for multiple mode piezoelectric shunt damping will be presented in this paper. The proposed “current flowing” shunt controller has a number of benefits compared to previous shunt damping schemes; it is simpler to implement and requires small number of passive circuit elements. The passive control strategy is validated through experimentation on two piezoelectric laminated structures.