Bao Kha Nguyen

Feedforward Control of Shape Memory Alloy Actuators Using Fuzzy-Based Inverse Preisach Model

This brief investigates a possible application of the inverse Preisach model in combination with the feedforward and feedback control strategies to control shape memory alloy actuators. In the feedforward control design, a fuzzy-based inverse Preisach model is used to compensate for the hysteresis nonlinearity effect. An extrema input history and a fuzzy inference is utilized to replace the inverse classical Preisach model. This work allows for a reduction in the number of experimental parameters and computation time for the inversion of the classical Preisach model. A proportional-integral-derivative (PID) controller is used as a feedback controller to regulate the error between the desired output and the system output. To demonstrate the effectiveness of the proposed controller, real-time control experiment results are presented.

A C. elegans-inspired micro-robot with polymeric actuators and online vision

The 1mm long nematode worm Caenorhabditis elegans (C. elegans) is one of the best characterized animals and an important biological model for studies of nervous system function and behavior. C. elegans locomotion is generated by the rhythmic contraction of muscles under the control and regulation of the animals nervous system. The final goal of this research is to build a robotic model mimicking this undulatory locomotion. Towards this end, a first prototype invertebrate wormbot using electroactive polymer is presented in this paper. The 25mm wormbot is made of a single ionic polymer-metal composite consisting of five segments that are controlled individually and can propagate a sinusoidal wave along the robot body similar to the movement of C. elegans. Solutions to the technical challenges of miniaturization, IPMC segmentation and small scale electrical wiring are also described. Finally, a digital image processing technique was developed for online sensory feedback. The system operates in real time and includes robust image noise removal.

Optimal proportional-integral-derivative control of shape memory alloy actuators using genetic algorithm and the Preisach model

Abstract Shape memory alloy (SMA) actuators, which have the ability to return to a predetermined shape when heated, have many potential applications in aeronautics, surgical tools, robotics, and so on. Although the number of applications is increasing, there has been limited success in precise motion control owing to the hysteresis effect of these smart actuators. The present paper proposes an optimization of the proportional-integral-derivative (PID) control method for SMA actuators by using genetic algorithm and the Preisach hysteresis model. In this work, the numerical Preisach model with geometrical interpretation is used for hysteresis modelling of SMA actuators. This model is then incorporated in a closed-loop PID control strategy. The optimal values of PID parameters are determined by using genetic algorithm to minimize the mean squared error between desired output displacement and simulated output. This is used to reduce hysteresis effects and improve accuracy for the displacement of SMA actuators.

Automatic extruder for processing recycled polymers with ultrasound and temperature control system

Melt viscosity is one of the main factors affecting product quality in extrusion processes particularly with regard to recycled polymers. However, due to wide variability in the physical properties of recycled feedstock, it is difficult to maintain the melt viscosity during extrusion of polymer blends and obtain good quality product without generating scrap. This research investigates the application of ultrasound and temperature control in an automatic extruder controller, which has ability to maintain constant melt viscosity from variable recycled polymer feedstock during extrusion processing. An ultrasonic modulation system has been developed and fitted to the extruder prior to the die to convey ultrasonic energy from a high power ultrasonic generator to the polymer melt. Two separate control loops have been developed to run simultaneously in one controller: the first loop controls the ultrasonic energy or temperature to maintain constant die pressure, the second loop is used to control extruder screw speed to maintain constant throughput at the extruder die. Time response and energy consumption of the control methods in real-time experiments are also investigated and reported this paper.

Viscosity Control for Extrusion Processes Using Recycled Polymers

The aim of this paper is to develop a new extruder control system for recycled materials which has ability to automatically maintain constant a polymer melt viscosity of mixed recycled polymers during extrusion, regardless of variations in the Melt Flow Index (MFI) of recycled mixed grade high density polyethylene (HDPE) feedstock. A closed-loop controller is developed to automatically regulate screw speed and barrel temperature profile to achieve constant viscosity and enable consistent processing of variable grade recycled HDPE materials. The experimental results of real time viscosity measurement and control using a 38mm single screw extruder with different recycled HDPEs with widely different MFIs are reported in this work.