M.Ing. (Mechanical Engineering) / Please refer to full text to view abstract

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The accurate control of a positioning system that exhibits scalar hysteresis requires a control strategy that incorporates compensation for the hysteresis. One approach is to develop a compensator based on an inverse hysteresis operator. This method uses an open loop control in which the inverse operation adjusts the actuator input to compensate for the hysteresis in the system. When this is accomplished, the composite operation produces a linear relationship between a reference input and the system output. The difficulty of this method lies in developing an accurate model of the hysteresis for which an inverse operator can be obtained. In this work, a system with hysteresis is modeled by a generic model based on a Preisach type operator. First, it is shown that the operator has an inverse and that both have approximations that are convergent. Then, simulation and experimental data are used to demonstrate the ability of the operator to accurately model a hysteresis relationship. This lays the foundation for then demonstrating the concept of inverse compensation. / Ph. D.

The medical community has expressed a need for flexible medical instruments. Hence, this work investigates the possibility to use "flexible fluidic actuators" to develop such flexible instruments. These actuators are driven by fluid, i.e. gas or liquid, and present a flexible structure, i.e. an elastically deformable and/or inflatable structure. Different aspects of the study of these actuators have been tackled in the present work:<p>• A literature review of these actuators has been established. It has allowed to identify the different types of motion that these actuators can develop as well as the design principles underlying. This review can help to develop flexible instruments based on flexible fluidic actuators.<p>• A test bench has been developed to characterize the flexible fluidic actuators.<p>• A interesting measuring concept has been implemented and experimentally validated on a specific flexible fluidic actuator (the "Pneumatic Balloon Actuator", PBA). Ac- cording to this principle, the measurements of the pressure and of the volume of fluid supplied to the actuator allow to determine the displacement of the actuator and the force it develops. This means being able to determine the displacement of a flexible fluidic actuator and the force it develops without using a displacement sensor or a force sensor. This principle is interesting for medical applications inside the human body, for which measuring the force applied by the organs to the surgical tools remains a problem.<p>The study of this principle paves the way for a lot of future works such as the implemen- tation and the testing of this principle on more complex structures or in a control loop in order to control the displacement of the actuator (or the force it develops) without using a displacement or a force sensor.<p>• A 2D-model of the PBA has been established and has helped to better understand the physics underlying the behaviour of this actuator.<p>• A miniaturization work has been performed on a particular kind of flexible fluidic actu- ator: the Pleated Pneumatic Artificial Muscle (PPAM). This miniaturization study has been made on this type of actuator because, according to theoretical models, minia- turized PPAMs, whose dimensions are small enough to be inserted into MIS medical instruments, could be able to develop the forces required to allow the instruments to perform most surgical actions. The achieved miniaturized muscles have a design similar to that of the third generation PPAMs developed at the VUB and present a total length of about 90 mm and an outer diameter at rest of about 15 mm. One of the developed miniaturized PPAMs has been pressurized at p = 1 bar and it was able to develop a pulling force F = 100 N while producing a contraction of 4 %.<p>Propositions have been made regarding a further miniaturization of the muscles. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Combining the advantages from electric motor and the pneumatic actuator, the hybrid pneumatic-electric actuator is expected to be safe, low-cost, clean, high power to weight ratio, and to provide precise position control. In this thesis, the modeling and control of an improved hybrid pneumatic-electric actuator prototype is presented. The actuator’s main components consist of a low-friction pneumatic cylinder, two on/off solenoid valves, and a small DC motor. The cylinder and motor are connected to a common output shaft using gears. The shaft rotates a single-link robot arm. Its position is measured by an incremental encoder. The prototype was improved by incorporating faster switching valves, flow controls, a faster valve drive circuit, a high resolution encoder rather than the existing linear potentiometer, more accurate pressure sensors and stronger gears. A system dynamic model without the valve dynamic was developed identified and validated using open-loop experiments. The valve models for a discrete input and PWM input were then developed and validated separately. The use of bipolynomial function and artificial neural network fitting methods for modeling the valve mass flow rates were compared. The combined system model with valve dynamics was validated experimentally. Two model-based nonlinear position controllers, using the backstepping and discrete-valued model predictive control (DVMPC) methods, were designed, simulated and extensively tested. Testing was done with the actuator operating using the cylinder alone, the motor alone and in hybrid mode using the cylinder and motor together. Operating in the hybrid mode reduced the root-mean-square error (RMSE) up to 80%. A stability analysis for the backstepping control including the valve modeling error, friction model error, and electric motor torque modeling error was performed. Compensation terms were designed to improve the performance for the two controllers. Additional stability analyses were performed for backstepping controller with a feedback term and the DVMPC with motor control. A payload estimation algorithm was proposed and shown to enhance the robustness of the DVMPC operating in vertical configuration. Simulations and experiments demonstrated that the model-based controllers performed well for both vertical and horizontal configurations. Regarding robustness to payload mismatch, if the payload was within the load capacity of the hybrid actuator, the model-based controllers were both insensitive to the payload variations in horizontal configuration. The backstepping controller was also robust to the payload variations in the vertical configuration. In experiments, the backstepping control in hybrid actuation mode produced a RMSE of 0.0066 radian for a 2 Hz sine wave desired position trajectory with a 0.3 radian amplitude. With DVMPC, this value decreased to 0.0045 radian. These tracking errors were shown to be 30 to 50% less than those produced by a modified linear position plus velocity plus acceleration controller. / Master of Applied Science (MASc)

This study develops the foundation of a digitally implemented control system for the radial positioning of the read/write heads of an optical disk drive system. Topics addressed are: sample rate selection, state reconstruction, closed-loop system response, disk track-following filters, and measurement noise filters. Consideration is given to the unmodeled dynamic's influence on system performance, system sensitivity to parameter variations, and a one sample computational delay. What has been concluded from this work is that the system must be further desensitized to parameter variations, and, at this stage of the development of the control scheme, neither a computational delay nor the unmodeled dynamics degrade system performance significantly.

CIVINS / Field studies have demonstrated that it is possible to evaluate the state of many shipboard systems by analyzing the power drawn by electromechanical actuators. One device that can perform such an analysis is the non-intrusive load monitor (NILM). This thesis investigates the use of the NILM as a supervisory control system in the engineering plant of gas-turbine-powered vessel. Field tests demonstrate that the NILM can potentially reduce overall sensor count if used in a supervisory control system. To demonstrate the NILM's capabilities in supervisory control systems, experiments are being conducted at the U.S. Navy's Land-Based Engineering Site (LBES) in Philadelphia, Pennsylvania. Following a brief description of the LBES facility and the NILM itself, this thesis presents testing procedures and methodology with results obtained during the extensive field studies. This thesis also describes the on-going efforts to further demonstrate and develop the NILM's capabilities in supervisory control systems. / CIVINS / US Naval Academy (USNA) author.

Following the studies of natural frequency based damage detection methods, an advanced technique for damage detection and localization in beam-type structures using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage on the change of the natural frequencies of the damaged structure to realize the high detection sensitivity. Based on the vibration characteristic tuning procedure, a scan-tuning methodology for damage detection and localization is proposed. From analytical simulations, both crack and delamination damage in the beams are detected and located with over 20% change in the natural frequencies. Finite element method (FEM) simulations are conducted to verify the effectiveness of the proposed methodology. / October 2016

Over the past few decades, surface dielectric barrier discharge (SDBD) actuators have been studied extensively as aerodynamic flow control devices. There has been extensive research on producing SDBD plasmas through excitation by sinusoidal high voltage in low-speed flows, resulting in local acceleration of the flow through the electrohydrodynamic (EHD) effect. However, high-speed flow control using SDBD actuators has not been considered to the same extent. Control through thermal perturbations appears more promising than using EHD effects. SDBDs driven by nanosecond repetitively pulsed (NRP) discharges (NRP SDBDs) can produce rapid localized heating and have been used to produce better flow reattachment in high-speed flows. While surface actuators based on NRP DBDs appear promising for high-speed flow control, the physics underlying the plasma/flow coupling are not well understood and the actuators have yet to be fully characterized or optimized. In particular, methods for tailoring the plasma characteristics by varying the actuator’s electrical or geometrical characteristics have not been thoroughly explored.<div>In the current work, NRP SDBD actuators for control of high-speed flows are developed and characterized. As discussed previously, it is believed that the mechanism for high-speed flow control by these plasmas is thermal perturbations from rapid localized heating. Therefore, the goal is to design actuators that produce well-defined filamentary discharges which provide controlled local heating. The electrical parameters (pulse duration, PRF, and polarity) and electrode geometries are varied and the optimal configurations for producing such plasma filaments over a range of ambient pressures are identified. In particular, single and double sawtooth shaped electrodes are investigated since the enhanced electric field at the electrode tips may permit easier production of “strong” (i.e. higher temperature) filaments with well-defined spacing, even at low pressure. Time-resolved measurements of the gas temperature in the plasma will be obtained using optical emission spectroscopy (OES) to assess the thermal perturbations produced by the actuators. To the author’s knowledge, these will be the first such measurements of temperature perturbations induced by NRP SDBDs. The plasma structure and temperature measurements will be correlated with schlieren visualization of the shock waves and localized flow field induced by the discharges. Finally, the optimized actuators will be integrated into a high-speed flat plate boundary layer and preliminary assessment of the effect of the plasma on the boundary layer will be conducted.<br></div>