A robust loop-shaping approach to fast and accurate nanopositioning

Peer reviewedPreprin

Superheat control for air conditioning and refrigeration systems: Simulation and experiments

Ever since the invention of air conditioning and refrigeration in the late nineteenth century, there has been tremendous interest in increasing system efficiency to reduce the impact these systems have on global energy consumption. Efficiency improvements have been accomplished through component design, refrigerant design, and most recently control system design. The emergence of the electronic expansion valve and variable speed drives has made immense impacts on the ability to regulate system parameters, resulting in important strides towards efficiency improvement. This research presents tools and methodologies for model development and controller design for air conditioning and refrigeration systems. In this thesis, control-oriented nonlinear dynamic models are developed and validated with test data collected from a fully instrumented experimental system. These models enable the design of advanced control configurations which supplement the performance of the commonly used proportional-integral-derivative (PID) controller. Evaporator superheat is a key parameter considered in this research since precise control optimizes evaporator efficiency while protecting the system from component damage. The controllers developed in this thesis ultimately provide better transient and steady state performance which increases system efficiency through low superheat set point design. The developed controllers also address the classical performance versus robustness tradeoff through design which preserves transients while prolonging the lifetime of the electronic expansion valve. Another notable contribution of this thesis is the development of hardware-in-the-loop load emulation which provides a method to test component and software control loop performance. This method alleviates the costs associated with the current method of testing using environmental test chambers

Architecture of a network-in-the-Loop environment for characterizing AC power system behavior

This paper describes the method by which a large hardware-in-the-loop environment has been realized for three-phase ac power systems. The environment allows an entire laboratory power-network topology (generators, loads, controls, protection devices, and switches) to be placed in the loop of a large power-network simulation. The system is realized by using a realtime power-network simulator, which interacts with the hardware via the indirect control of a large synchronous generator and by measuring currents flowing from its terminals. These measured currents are injected into the simulation via current sources to close the loop. This paper describes the system architecture and, most importantly, the calibration methodologies which have been developed to overcome measurement and loop latencies. In particular, a new "phase advance" calibration removes the requirement to add unwanted components into the simulated network to compensate for loop delay. The results of early commissioning experiments are demonstrated. The present system performance limits under transient conditions (approximately 0.25 Hz/s and 30 V/s to contain peak phase-and voltage-tracking errors within 5. and 1%) are defined mainly by the controllability of the synchronous generator

Advances in Spacecraft Systems and Orbit Determination

"Advances in Spacecraft Systems and Orbit Determinations", discusses the development of new technologies and the limitations of the present technology, used for interplanetary missions. Various experts have contributed to develop the bridge between present limitations and technology growth to overcome the limitations. Key features of this book inform us about the orbit determination techniques based on a smooth research based on astrophysics. The book also provides a detailed overview on Spacecraft Systems including reliability of low-cost AOCS, sliding mode controlling and a new view on attitude controller design based on sliding mode, with thrusters. It also provides a technological roadmap for HVAC optimization. The book also gives an excellent overview of resolving the difficulties for interplanetary missions with the comparison of present technologies and new advancements. Overall, this will be very much interesting book to explore the roadmap of technological growth in spacecraft systems

Distributed Sensing and Stimulation Systems Towards Sense of Touch Restoration in Prosthetics

Modern prostheses aim at restoring the functional and aesthetic characteristics of the lost limb. To foster prosthesis embodiment and functionality, it is necessary to restitute both volitional control and sensory feedback. Contemporary feedback interfaces presented in research use few sensors and stimulation units to feedback at most two discrete feedback variables (e.g. grasping force and aperture), whereas the human sense of touch relies on a distributed network of mechanoreceptors providing high-fidelity spatial information. To provide this type of feedback in prosthetics, it is necessary to sense tactile information from artificial skin placed on the prosthesis and transmit tactile feedback above the amputation in order to map the interaction between the prosthesis and the environment. This thesis proposes the integration of distributed sensing systems (e-skin) to acquire tactile sensation, and non-invasive multichannel electrotactile feedback and virtual reality to deliver high-bandwidth information to the user. Its core focus addresses the development and testing of close-loop sensory feedback human-machine interface, based on the latest distributed sensing and stimulation techniques for restoring the sense of touch in prosthetics. To this end, the thesis is comprised of two introductory chapters that describe the state of art in the field, the objectives and the used methodology and contributions; as well as three studies distributed over stimulation system level and sensing system level. The first study presents the development of close-loop compensatory tracking system to evaluate the usability and effectiveness of electrotactile sensory feedback in enabling real-time close-loop control in prosthetics. It examines and compares the subject\u2019s adaptive performance and tolerance to random latencies while performing the dynamic control task (i.e. position control) and simultaneously receiving either visual feedback or electrotactile feedback for communicating the momentary tracking error. Moreover, it reported the minimum time delay needed for an abrupt impairment of users\u2019 performance. The experimental results have shown that electrotactile feedback performance is less prone to changes with longer delays. However, visual feedback drops faster than electrotactile with increased time delays. This is a good indication for the effectiveness of electrotactile feedback in enabling close- loop control in prosthetics, since some delays are inevitable. The second study describes the development of a novel non-invasive compact multichannel interface for electrotactile feedback, containing 24 pads electrode matrix, with fully programmable stimulation unit, that investigates the ability of able-bodied human subjects to localize the electrotactile stimulus delivered through the electrode matrix. Furthermore, it designed a novel dual parameter -modulation (interleaved frequency and intensity) and compared it to conventional stimulation (same frequency for all pads). In addition and for the first time, it compared the electrotactile stimulation to mechanical stimulation. More, it exposes the integration of virtual prosthesis with the developed system in order to achieve better user experience and object manipulation through mapping the acquired real-time collected tactile data and feedback it simultaneously to the user. The experimental results demonstrated that the proposed interleaved coding substantially improved the spatial localization compared to same-frequency stimulation. Furthermore, it showed that same-frequency stimulation was equivalent to mechanical stimulation, whereas the performance with dual-parameter modulation was significantly better. The third study presents the realization of a novel, flexible, screen- printed e-skin based on P(VDF-TrFE) piezoelectric polymers, that would cover the fingertips and the palm of the prosthetic hand (particularly the Michelangelo hand by Ottobock) and an assistive sensorized glove for stroke patients. Moreover, it developed a new validation methodology to examine the sensors behavior while being solicited. The characterization results showed compatibility between the expected (modeled) behavior of the electrical response of each sensor to measured mechanical (normal) force at the skin surface, which in turn proved the combination of both fabrication and assembly processes was successful. This paves the way to define a practical, simplified and reproducible characterization protocol for e-skin patches In conclusion, by adopting innovative methodologies in sensing and stimulation systems, this thesis advances the overall development of close-loop sensory feedback human-machine interface used for restoration of sense of touch in prosthetics. Moreover, this research could lead to high-bandwidth high-fidelity transmission of tactile information for modern dexterous prostheses that could ameliorate the end user experience and facilitate it acceptance in the daily life

Study and implementation of a digital control of dual-gated electrolyte-gated organic field-effect transistors for cell stimulation and recording

openL’elettronica organica sta diventando particolarmente attraente per le applicazioni di biosensing, grazie ai suoi vantaggi come il basso costo dei materiali e dei processi di fabbricazione, la biocompatibilità e l’alta sensibilità. I transistor organici ad effetto di campo con gate elettrolitico (EGOFETs) sono stati ampiamente studiati negli ultimi anni in questo campo, per la loro peculiare abilità di operare a tensioni molto basse, grazie all’elevata apacità di double-layer che si ottiene all’interfaccia con l’elettrolita. Tuttavia, il contatto con l’ossigeno e l’umidità in soluzioni acquose è dannoso per le funzionalità del transistor, modificandone le caratteristiche elettriche (variazione della tensione di soglia) e degradandolo. Questa tesi si concentra sulla stabilizzazione del punto operativo dell’EGOFET, attraverso lo sviluppo di un controllo digitale che sfrutta un gate aggiuntivo per controllare la tensione di soglia del canale di conduzione liquid-gated. Abbiamo costruito un sistema di controllo completo che permette di ottenere un segnale di uscita ben definito per misure a lungo termine. In particolare, abbiamo mirato alla registrazione e alla stimolazione di segnali extracellulari, testando diversi metodi per rilevare e preservare ipotetici segnali di potenziale d’azione. Tutte le configurazioni sono state testate da simulazioni e prove sperimentali. Il controllo digitale include strumenti di autotuning per fornire robustezza rispetto al degrado delle proprietà dei dispositivi. Diversi parametri del sistema di controllo possono essere tarati a seconda delle priorità che vogliamo prendere in considerazione. Per quanto riguarda una futura implementazione con cellule reali, sono stati provati diversi rivestimenti per la semina delle cellule, al fine di analizzare il loro effetto sulle proprietà elettriche. I dispositivi rivestiti conservati in aria hanno mostrato un comportamento a effetto campo per circa un mese. Questa tesi fa parte di un progetto più ampio chiamato Project Proactive 2018 "Fully printed organic array of bidirectional reference-less sensors for neuronal interfacing", led by the Principal Investigator Prof. Andrea Cester, in collaborazione con: • VIMM Veneto Institute of Molecular Medicine • DiSC Dipartimento di Scienze Chimiche, UNIPD • ICMAB Institut de Ciència de Materials de BarcelonaOrganic electronics is becoming particularly attractive for biosensing applications, thanks to its advantages such as low-cost materials and fabrication processes, biocompatibility and high sensitivity. Electrolyte-Gated Organic Field Effect Transistors (EGOFETs) have been widely investigated in recent years in this field, due to their peculiar ability to operate at very low voltages, thanks to the high double-layer capacitance given by the interfaces with the electrolyte. However, the contact with oxygen and humidity in acqueous environment is detrimental for the functionality of the transistor, changing its electrical characteristics (threshold voltage shift) and degradating it. This dissertation is focused on the stabilization of the operating point of the EGOFET, by means of the development of a digital control that exploits an additional gate to control the threshold voltage of the liquid-gated conduction channel. We built up a complete control system that allows to achieve a well-defined output signal for long term measurements. In particular, we targeted extracellular recording and stimulation, by testing different methods to detect and preserve hypothetical action potential signals. All the configurations have been tested by simulations and experimental evidences. The digital control includes autotuning tools to give robustness to the degradation of the devices properties. Several parameters of the control system can be tuned depending on the priorities we want to take into account. With regard to a future implementation with real cells, different coatings for cell seeding have been tried, in order to analyze their effect on the electrical properties. The coated devices stored in air showed a field-effect behaviour for approximately one month. This thesis is part of a broader project called Project Proactive 2018 "Fully printed organic array of bidirectional reference-less sensors for neuronal interfacing", led by the Principal Investigator Prof. Andrea Cester, in collaboration with: • VIMM Veneto Institute of Molecular Medicine • DiSC Dipartimento di Scienze Chimiche, UNIPD • ICMAB Institut de Ciència de Materials de Barcelon

Modeling and tracking control of a novel XYθz stage

A XYθz stage is designed and experimentally tested. This developed stage is driven by three piezoelectric actuators (PZTs) and guided by a flexure hinge based mechanism with three symmetric T-shape hinges. It was manufactured monolithically by using wire electrical discharge machining technology. In addition, considering the both electrical and mechanical characteristics, a third-order dynamic model of the 3-DOF system has been established to investigate the relationship between the input voltage and the output displacement of the entire system. The parameters of the third-order dynamic model were estimated by using the system identification toolbox. Furthermore, decoupling control is also proposed to solve the existed coupling motion of the stage. In order to compensate the hysteresis of PZT, the inverse Bouc-Wen model was utilized as a feedforward hysteresis compensator. Finally, extensive experiments were performed to verify the good decoupling and tracking performances of the developed stage

ADV preview based nonlinear predictive control for maximizing power generation of a tidal turbine with hydrostatic transmission

As the development of tidal turbines attracts more and more attention in recent years, reliable design and efficient control of tidal turbines are becoming increasingly important. However, the majority of existing tidal turbines still utilize traditional fixed ratio geared transmissions and the associated control designs focus on simple feedback controllers that use measurements or possibly estimates of the turbine itself or current local tidal profile. Therefore, the measurement and control are inevitably affected by the inherent delay with respect to the current tidal speeds. This paper proposes a novel tidal turbine with continuously variable speed hydrostatic transmissions and a nonlinear predictive controller that uses short-term predictions of the approaching tidal speed field to enhance the maximum tidal power generations when the tidal speed is below the rated value. The controller is designed based on an offline finite-horizon continuous time minimization of a cost function, and an integral action is incorporated into the control loop to increase the robustness against parameter variations and uncertainties. A smooth second order sliding mode observer is also designed for parameter estimations in the control loop. A 150 kW tidal turbine with hydrostatic transmission is designed and implemented. The results demonstrate that the averaged generator power increases by 6.76% with this preview based nonlinear predictive controller compared with a classical non-predictive controller