Robust adaptive control of conjugated polymer actuators

Conjugated polymers are promising actuation materials for bio and micromanipulation systems, biomimeticrobots, and biomedical devices. Sophisticated electrochemomechanical dynamics in these materials, however,poses significant challenges in ensuring their consistent, robust performance in applications. In this paper aneffective adaptive control strategy is proposed for conjugated polymer actuators. A self-tuning regulator isdesigned based on a simple actuator model, which is obtained through reduction of an infinite-dimensionalphysical model and captures the essential actuation dynamics. The control scheme is made robust againstunmodeled dynamics and measurement noises with parameter projection, which forces the parameter estimates tostay within physically-meaningful regions. The robust adaptive control method is applied to a trilayer polypyrroleactuator that demonstrates significant time-varying actuation behavior in air due to the solvent evaporation.Experimental results show that, during four-hour continuous operation, the proposed scheme delivers consistenttracking performance with the normalized tracking error decreasing from 11% to 7%, while the error increasesfrom 7% to 28% and to 50% under a PID controller and a fixed model-following controller, respectively. In themean time the control effort under the robust adaptive control scheme is much less than that under PID, whichis important for prolonging the lifetime of the actuator

Robust adaptive control of conjugated polymer actuators

Conjugated polymers are promising actuation materials for bio- and micromanipulation systems, biomimetic robots, and biomedical devices. Sophisticated electrochemomechanical dynamics in these materials, however, poses significant challenges in ensuring their consistent, robust performance in applications. In this paper, an effective adaptive control strategy is proposed for conjugated polymer actuators. A self-tuning regulator is designed based on a simple actuator model, which is obtained through reduction of an infinite-dimensional physical model and captures the essential actuation dynamics. The control scheme is made robust against unmodeled dynamics and measurement noises with parameter projection, which forces the parameter estimates to stay within physically meaningful regions. The robust adaptive control method is applied to a trilayer polypyrrole (PPy) actuator that demonstrates significant time-varying actuation behavior in air due to the solvent evaporation. Experimental results show that, during 4-h continuous operation, the proposed scheme delivers consistent tracking performance with the normalized tracking error decreasing from 11% to 7%, while the error increases from 7% to 28% and to 50% under a proportional-integral-derivative (PID) controller and a fixed model-following controller, respectively. In the meantime, the control effort under the robust adaptive control scheme is much less than that under PID, which is important for prolonging the lifetime of the actuator

Force control of a tri-layer conducting polymer actuator using optimized fuzzy logic control

Conducting polymers actuators (CPAs) are potential candidates for replacing conventional actuators in various fields, such as robotics and biomedical engineering, due to their advantageous properties, which includes their low cost, light weight, low actuation voltage and biocompatibility. As these actuators are very suitable for use in micro-nano manipulation and in injection devices in which the magnitude of the force applied to the target is of crucial importance, the force generated by CPAs needs to be accurately controlled. In this paper, a fuzzy logic (FL) controller with a Mamdani inference system is designed to control the blocking force of a trilayer CPA with polypyrrole electrodes, which operates in air. The particle swarm optimization (PSO) method is employed to optimize the controller\u27s membership function parameters and therefore enhance the performance of the FL controller. An adaptive neuro-fuzzy inference system model, which can capture the nonlinear dynamics of the actuator, is utilized in the optimization process. The optimized Mamdani FL controller is then implemented on the CPA experimentally, and its performance is compared with a non-optimized fuzzy controller as well as with those obtained from a conventional PID controller. The results presented indicate that the blocking force at the tip of the CPA can be effectively controlled by the optimized FL controller, which shows excellent transient and steady state characteristics but increases the control voltage compared to the non-optimized fuzzy controllers

Modeling and inverse feedforward control for conducting polymer actuators with hysteresis

Conducting polymer actuators are biocompatible with a small footprint, and operate in air or liquid media under low actuation voltages. This makes them excellent actuators for macro- and micro-manipulation devices, however, their positioning ability or accuracy is adversely affected by their hysteresis non-linearity under open-loop control strategies. In this paper, we establish a hysteresis model for conducting polymer actuators, based on a rate-independent hysteresis model known as the Duhem model. The hysteresis model is experimentally identified and integrated with the linear dynamics of the actuator. This combined model is inverted to control the displacement of the tri-layer actuators considered in this study, without using any external feedback. The inversion requires an inverse hysteresis model which was experimentally identified using an inverse neural network model. Experimental results show that the position tracking errors are reduced by more than 50% when the hysteresis inverse model is incorporated into an inversion-based feedforward controller, indicating the potential of the proposed method in enabling wider use of such smart actuators

Materials science and the sensor revolution

For the past decade, we have been investigating strategies to develop ways to provide chemical sensing platforms capable of long-term deployment in remote locations1-3. This key objective has been driven by the emergence of ubiquitous digital communications and the associated potential for widely deployed wireless sensor networks (WSNs). Understandably, in these early days of WSNs, deployments have been based on very reliable sensors, such as thermistors, accelerometers, flow meters, photodetectors, and digital cameras. Biosensors and chemical sensors (bio/chemo-sensors) are largely missing from this rapidly developing field, despite the obvious value offered by an ability to measure molecular targets at multiple locations in real-time. Interestingly, while this paper is focused on the issues with respect to wide area sensing of the environment, the core challenge is essentially the same for long-term implantable bio/chemo-sensors4, i.e.; how to maintain the integrity of the analytical method at a remote, inaccessible location

Roadmap on semiconductor-cell biointerfaces.

This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world

Control of an IPMC soft actuator using adaptive full-order recursive terminal sliding mode

The ionic polymer metal composite (IPMC) actuator is a kind of soft actuator that can work for underwater applications. However, IPMC actuator control suffers from high nonlinearity due to the existence of inherent creep and hysteresis phenomena. Furthermore, for underwater applications, they are highly exposed to parametric uncertainties and external disturbances due to the inherent characteristics and working environment. Those factors significantly affect the positioning accuracy and reliability of IPMC actuators. Hence, feedback control techniques are vital in the control of IPMC actuators for suppressing the system uncertainty and external disturbance. In this paper, for the first time an adaptive full-order recursive terminal sliding-mode (AFORTSM) controller is proposed for the IPMC actuator to enhance the positioning accuracy and robustness against parametric uncertainties and external disturbances. The proposed controller incorporates an adaptive algorithm with terminal sliding mode method to release the need for any prerequisite bound of the disturbance. In addition, stability analysis proves that it can guarantee the tracking error to converge to zero in finite time in the presence of uncertainty and disturbance. Experiments are carried out on the IPMC actuator to verify the practical effectiveness of the AFORTSM controller in comparison with a conventional nonsingular terminal sliding mode (NTSM) controller in terms of smaller tracking error and faster disturbance rejection

Doctor of Philosophy

dissertationConducting polymer actuators have shown numerous improvements in mechanical performance over the last couple of decades, but can be better utilized in applications with the ability to adjust to unknown operating conditions, or improved during their lifetime. This work employs the process of sequential growth to initially fabricate polypyrrole-metal coil composite actuators, and then again for further actuator growth during its lifetime of operation. The novel synthesis process was first shown through the use of a custom testing apparatus that could support the sequential growth process by allowing different actuation and synthesis solutions to be controlled in the test cell, as well as facilitate mechanical performance testing. Open-loop testing demonstrated the actuator system performance for multiple growth stages over multiple input frequencies, and was then compared to the parameters identified to fit a simplified model during operation. The simplified model was shown to differentiate from the experimental data, but provided useful optimal growth prediction values with a performance cost evaluation algorithm. The model could predict the optimal growth determined by the experimental data to within one growth stage. Performance was improved by using a proportional-derivative feedback controller where the gains were calculated by the desired response at each growth stage for each sample. The cost performance was performed again with the closed-loop data, but did an inferior job of predicting the optimal amount of growth for each sample compared to the open-loop data. The simplified model accurately tracked the behavior changes through multiple stages of growth. The main contributions of this work include a novel testing apparatus and synthesis method for multiple growth steps, the implementation of a simplified model for tracking and optimal growth stage prediction, and the application of a model-based proportional-derivative feedback controller

Creeping and structural effects in Faradaic artificial muscles

Reliable polymeric motors are required for the construction of rising accurate robots for surgeon assistance. Artificial muscles based on the electrochemistry of conducting polymers fulfil most of the required characteristics, except the presence of creeping effects during actuation. To avoid it, or to control it, a deeper knowledge of its physicochemical origin is required. With this aim here bending bilayer tape/PPy-DBSH (Polypyrrole-dodecylbenzylsulphonic acid) full polymeric artificial muscles were cycled between −2.5 and 1 V in aqueous solutions with parallel video recording of the described angular movement. Coulo-voltammetric (charge-potential, QE), dynamo-voltammetric (angle-potential, αE), and coulo-dynamic (charge-angle, Qα) muscular responses corroborate that 10 % of the charge is consumed by irreversible reactions overlapping the polymer reduction at the most cathodic potentials. In parallel, the range of the bending angular movement (145°) shifts by 15° per cycle (creeping effect) pointing to the irreversible charge as possible origin of the irreversible swelling of the PPy-DBS film. Different slopes in the closed loop part of the QE identify the different reaction driven structural processes in the film: oxidation-shrinking, oxidation compaction, reduction-relaxation, reduction-swelling, and reduction-vesicle’s formation. Despite the irreversible charge fraction, the muscle motor keeps a Faradaic behaviour: described angles are linear functions of the consumed charge in the full potential range