Showing papers by "Andrew J. Fleming published in 2015"

Simultaneous Optimization of Damping and Tracking Controller Parameters Via Selective Pole Placement for Enhanced Positioning Bandwidth of Nanopositioners

Abstract: Positive Velocity and Position Feedback (PVPF) is a widely used control scheme in lightly damped resonant systems with collocated sensor actuator pairs. The popularity of PVPF is due to the ability to achieve a chosen damping ratio by repositioning the poles of the system. The addition of a necessary tracking controller causes the poles to deviate from the intended location and can be a detriment to the damping achieved. By designing the PVPF and tracking controllers simultaneously, the optimal damping and tracking can be achieved. Simulations show full damping of the first resonant mode whilst also achieving bandwidth greater than the natural frequency of the plant, allowing for high speed scanning with accurate tracking.

A new electrical configuration for improving the range of piezoelectric bimorph benders

Abstract: This article describes a new electrical configuration for driving piezoelectric benders. The ‘Biased Bipolar’ configuration is compatible with parallel-polled, bimorph and multimorph benders. The new configuration is similar to the standard three-wire drive method where the top electrode is biased with a DC voltage and the bottom electrode is grounded. However, the new configuration uses an alternate DC bias voltage and adjusted range for the central electrode which allows the full range of positive and negative electric fields to be utilized. Using this technique, the predicted deflection and force can be increased by a factor of 2.2 compared to the standard two wire configuration and 1.3 times for the standard three wire configuration. These predictions were verified experimentally where the measured factor of improvement in displacement and force was of 2.4 and 1.3 compared to the standard two-wire and three-wire configurations.

Piezoelectric actuators with integrated high-voltage power electronics

Abstract: This paper explores the possibility of piezoelectric actuators with integrated high-voltage power electronics. Such devices dramatically simplify the application of piezoelectric actuators since the power electronics are already optimized for the voltage range, capacitance, and power dissipation of the actuator. The foremost consideration is the thermal impedance of the actuator and heat dissipation. Analytical and finite-element methods are described for predicting the thermal impedance of a piezoelectric bender. The predictions are compared experimentally using thermal imaging on a piezoelectric bender with laminated miniature power electronics.

Design of a two degree of freedom resonant miniature robotic leg

Abstract: This article identifies the design considerations for a two degree of freedom (DoF) miniature robotic leg utilizing piezoelectric bimorph actuators with a specific focus on the resonance modes of the system. An analytical model was developed using three independent lumped mass models with superposition for tuning the resonance frequencies and optimizing the performance of the leg. The model was verified both experimentally and using finite element analysis (FEA).

A closed-loop phase-locked interferometer for wide bandwidth position sensing

Abstract: This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interferogram. In this configuration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics, it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has an effectively unlimited bandwidth. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instrument is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, Ultrasonic devices, and sensors such as surface acoustic wave detectors.

Low-Order Damping and Tracking Control for Scanning Probe Systems

Abstract: This article describes an improvement to integral resonance damping control (IRC) for reference tracking applications such as Scanning Probe Microscopy and nanofabrication. It is demonstrated that IRC control introduces a low-frequency pole into the tracking loop which is detrimental for performance. In this work, the location of this pole is found analytically using Cardano's method then compensated by parameterizing the tracking controller accordingly. This approach maximizes the closed-loop bandwidth whilst being robust to changes in the resonance frequencies. The refined IRC controller is comprehensively compared to other low-order methods in a practical environment.

Optimization of near-field scanning optical lithography

Abstract: This article describes two- and three-dimensional optical simulations for determining optimal conditions for near-field scanning optical lithography. It was found that a combination of 30-nm thick photoresist and 50-nm thick anti-reflective coating will yield optimal results with 405 nm incident light and a hollow-cantilever probe with 100-nm aperture width. In addition to identifying the optimal conditions, the sensitivity of the resolution with respect to each parameter is explored and plotted. The mechanisms behind each trend are described with supporting simulation data.

Optimization and simulation of exposure pattern for scanning laser lithography

Abstract: Maskless optical lithography is a technique for writing patterns into an optically sensitive material (photoresist) without the use of a photomask. The patterning process involves exposing selected areas of the photoresist film to the sensitizing light to produce the desired pattern. Unfortunately, the exposure pattern required to produce the desired pattern (output) is not a simple function of the desired pattern due to the geometric properties and focusing limits of the optical beam. Thus, we seek a technique capable of generating an exposure pattern which will result in the desired pattern being transferred to the photoresist. This goal can be achieved by exploiting an inverse lithography technique (ILT) which has previously been used for mask design in micro-photolithography systems. The technique is carried out by interpreting process flow in terms of forward modelling and presenting a regularization term in a cost function of the optimization problem to approach an efficient solution. This reduction in computational complexity in parts of the optimization calculation, results in a much faster convergence than has been previously reported. Finally, the effectiveness of this method in terms of fidelity of the desired features and the time of the calculation are verified by computer simulation.

A closed-loop phase-locked interferometer for wide bandwidth position sensing.

Abstract: This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interferogram. In this configuration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics: it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has a bandwidth equal to that of the photodiode. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instrument is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, ultrasonic devices, and sensors such as surface acoustic wave detectors.

Digital-to-analog converter considerations for achieving a dynamic range of 1 ppm in precision mechatronics systems

Abstract: The resolution of precision mechatronic systems employing the best available instrumentation is presently limited by the noise and distortion performance of digital-to-analog converters. The sources of noise and distortion include quantization error, non-linearity, thermal noise, and semiconductor noise. A resistor string digital-to-analog converter topology employing noise-shaping is presented and the contribution of each noise source in this topology is described in order to specify the necessary parameters to achieve a given resolution.

Model-less FIR repetitive control with consideration of uncertainty

Abstract: Repetitive control (RC) is used to track and reject periodic exogenous signals by including a model of a periodic signal in the feedback path. The performance of RC can be improved by also including an. The accuracy of this filter is the main limitation to the RC bandwidth. The bandwidth is typically limited with a robustness filter — often a low-pass filter which attenuates the model at high-frequencies where the model-mismatch often occurs. In this paper, two robustness filter designs are compared. The first design is a brick-wall low-pass filter commonly used in the literature. The second design is based on the uncertainty between the inverse plant response filter and the measured response of the system. Experimental results demonstrate that the proposed method outperforms the traditional brick-wall filter approach.