Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 112-121). Also available in electronic version.

As robotic manipulators become more prevalent, particularly in hazardous environments or for repetitive tasks, demand continues for increased performance and decreased cost. In some applications, both can be achieved by reducing the weight of the manipulator. However, reduced weight often leads to significant structural flexibility and vibration which, for most tasks, is generally regarded as detrimental to performance. Although there has been a great deal of research in the area of controlling flexible manipulators to follow a desired trajectory, much less work has been directed towards choosing the trajectory itself. The objective of this work is to optimize point-to-point motions in joint space to reduce vibration. This problem is formulated as one of functional optimization and the applicable methods of solution are reviewed. An indirect method is chosen that allows modular software development by preserving the integrity of existing nonlinear dynamics models. Numerical results are compared with trajectories generated by other means and show a significant reduction in vibration possible by optimization, particularly for varying joint paths. Finally, the effectiveness of the trajectory optimization scheme is further evaluated for high-speed, large-angle motions of an experimental nonplanar two-link flexible manipulator. Such results are lacking in the literature, but are very important for assessing the utility of trajectory optimization in the presence of modelling and tracking errors. Again, significant reductions in vibration are demonstrated by using the global optimization approach for trajectory generation. / Graduate

M.Ing. (Mechanical Engineering) / In this study a manipulator was developed by using system design methods. The main aim was to develop a robot which could be used as a packer in an industrial environment. Pneumatic silinders have been used with great success but up to now seldom in areas where positional accuracy is required. To design a manipulator which is able to operate in a varying work space it must be supplied with specialized sensors. For this reason research was done into image processing. Most of the relevant techniques of image processing arc discussed shortly with particular emphasis on the method of moment invariants for object recognition. Another important aspect covered in the project is the way by which articulated mechanical systems can be modelled kinematically and dynamically. The kinematical description was especially studied and in particular the method introduced by Denavit and Hartenberg and the method of general matrix transformations.

Please read the abstract in the section “front” of this document / Dissertation (MSc (Applied Science))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / MSc / unrestricted

This thesis discusses the possibility of attaining closed loop end piece control of a servo controlled manipulator by externally modifying the independent control loop set point of each robot link. This procedure leaves the existing servo control loops intact and thus has the benefit of acquiring the advantages of an advanced control strategy while retaining the inherent reliability and stability of the existing control loops. Algorithms are proposed for compensating for known disturbance torques, eliminating end piece position errors, and applying specified forces to the surroundings with the end piece. These algorithms are demonstrated for the three degree of freedom case using a simulation package ROBSIM.FOR which simulates the response of a servo controlled manipulator to set point inputs. To compensate for known disturbance torques the torques generated by the robot control system are assumed to be directly proportional to the changes in set points. These approximate relations are used to estimate the adjustment in set points necessary to generate the required additional joint torques. Simulation results show that this method is effective in compensating for gravity disturbance torques. The Jacobian relates changes in position of the end piece to changes in joint angles. Using the Jacobian combined with a weighting factor to prevent overshoot an algorithm is developed which drives end piece position errors to zero. The transpose of the Jacobian is used to relate forces exerted on the surroundings by the end piece to generated joint torques. The required torques are created by adjusting the set points. Simulation results indicate that this method can be used to exert specified forces. Force control is more difficult to achieve than position control because the robot interacts physically with its surroundings. The ability of the robot to exert forces depends strongly on the robot's configuration. All work in this thesis can be generated using the single program ROBSIM.FOR. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Nitrogen (N) is a chemical constituent for almost all biological molecules including proteins, DNA, RNA, lipids and is therefore vital for life. The ultimate source of nitrogen is the atmospheric dinitrogen (N2) but that only becomes bioavailable through a process of nitrogen fixation, the process that converts N2 to ammonia (NH3). The industrial Haber-Bosch process and biological nitrogen fixation account for the majority of nitrogen fixed every year. However, due to its high temperature, pressure and fossil fuel requirements, Haber-Bosch is an expensive process. Every year, approximately 3% of the global energy demand is used to manufacture ammonia through Haber-Bosch process. On the other hand, biological systems produce ammonia by reducing dinitrogen at ambient temperature and pressure using an anaerobic enzyme called nitrogenase. Research in understanding the mechanism of nitrogenase could eventually allow researchers to mimic the enzyme and fix nitrogen efficiently at standard temperature and pressure. In this research nitrogenase of Azotobacter vinelandii was studied to understand the mechanism of delivery of electrons/protons to the active site and how these accumulated reducing equivalents are used for substrates reduction. Through a series of studies, it has been demonstrated that the electrons and protons are added to the active site in a concerted manner which are then stored as bridging hydrides. The accumulated hydrides are used in four different mechanisms, namely reductive elimination, hydride protonolysis, migratory insertion and proton coupled electron transfer, to catalyze the reduction of varieties of unsaturated molecules. This fundamental understanding of molecular detail of nitrogenase catalysis could eventually help in development of more efficient, robust and selective catalysts.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Psychology. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Vita. / Includes bibliographies. / by Marc H. Raibert. / Ph.D.

The separation efficiency of a triboelectrostatic separation (TES) for fine coal cleaning depends profoundly on the surface charges of the particles involved. In general, the larger the difference between the charges of the particle to be separated, the higher the separation efficiency. The premise that coal and mineral matter can be triboelectrically charged differently serves as a basis for the TES process. In order to improve the separation performance, it is apparent that a highly efficient charger is needed for the TES unit, as well as the information on the triboelectrification mechanisms of the coal and mineral matter. Tribo- or contact electrification is a phenomenon in which electrical charge is usually transferred form one material to another, when two dissimilar materials are brought into rubbing or contact. In the present work, the triboelectrification mechanisms of coal, quartz, and pyrite were investigated in an in-line static mixer charger. A new in-situ charge-measuring device has been developed, in which an in-line mixer charger is located in side a Faraday cage. This makes it possible to observe the charging mechanisms of the particles when they pass through the mixer. This device was used to study the tribocharging mechanisms of coal, quartz, and pyrite as functions of the air velocity, particle feed rate, particle size, temperature, ash content, and the work functions of the materials that make up the in-line mixer. Evidence suggests that the charge transfer mechanisms of coal and mineral matter be due to electrons. A new turbocharger designed and developed in the present study has been tested and used to investigate the triboelectrification mechanisms of coal and quartz. The charge measurements were conducted using a developed on-line charge-measuring device, which is based on the principle of the Faraday cage. The tribocharging mechanisms of coal and quartz were investigated as functions of the particle feed rate, particle size, rotor-blade rotation speed, ash content, and the type of the materials used to construct the turbocharger. The information on the charging mechanisms of the coal and quartz will be useful for improving the triboelectrification process and subsequently the design of a TES unit. / Ph. D.

No description available.

Gravitational waves detection is a challenging scientific objective, faced by scientist in the last 100 years, when Einstein theorized their existence. Despite multiple attempts, it was only in 2016 that the first observation of a gravitational wave was officially announced. The observation, worth a Nobel Prize, was made possible thanks to a worldwide collaboration of three large ground-based detectors. When detecting gravitational waves from ground, the noisy environment limits the frequency bandwidth of the measurement. Thus, the type of cosmic events that are observable is also limited. For this reason, scientists are developing the first gravitational waves detector based in space, which is a much quieter environment, especially in the sub-Hertz bandwidth. The space-based detector is named laser interferometer space antenna (LISA) and its launch is planned for 2034. Due to the extreme complexity of the mission, involving several new technologies, a demonstrator of LISA was launched and operated between 2015 and 2017. The demonstrator mission, called LISA Pathfinder (LPF), had the objective to show the feasibility of the gravitational waves observation directly from space, by characterizing the noise affecting the relative acceleration of two free falling bodies in the milli-Hertz bandwidth. The mission was a success, proving the expected noise level is well below the minimum requirement. The free-falling bodies of LPF, called test masses (TMs), were hosted inside dedicated electrode housings (EH), located approximately 30 cm apart inside the spacecraft. When free falling, each TM stays approximately in the center of the EH, thus having milli-meter wide gaps within the housing walls. Due to the presence of such large gaps, the TMs were mechanically constrained by dedicated mechanisms (named CVM and GPRM) in order to avoid damaging the payload during the launch phase and were released into free fall once the spacecraft was in orbit. Prior to the start of the science phase, the injection procedure of the TMs into free-fall was started. Such a procedure brought each TM from being mechanically constrained to a state where it was electro-statically controlled in the center of the EH. Surprisingly, the mechanical separation of the release mechanism from the TM caused unexpected residual velocities, which were not controllable by the electrostatic control force responsible for capturing the TM once released. Therefore, both the TMs collided with either the surrounding housing walls or the release mechanism end effectors. It was possible to start the science phase by manually controlling the release mechanism adopting non-nominal injection strategies, which should not be applicable in LISA, due to the larger time lag. So, since any release mechanism malfunctioning may preclude the initialization of LISA science phase, the GPRM was extensively tested at the end of LPF, by means of a dedicated campaign of releases, involving several modifications to the nominal injection procedure. The data of the extended campaign are analyzed in this work and the main conclusion is that no optimal automated release strategy is found for the GPRM flight model as-built configuration that works reliably for both the TMs producing a nominal injection procedure. The analysis of the in-flight data is difficult since the gravitational referencesensor of LPF is not designed for such type of analysis. In particular, the low sampling frequency (i.e., 10 Hz) constitutes a limiting factor when detecting instantaneous events such as collisions of the TM. Despite the difficulties of extracting useful information on the TM residual velocity from the in-flight data, it is found that the main cause of the uncontrollable state of the released TM is the collision of the TM with the plunger, i.e., one of the end-effectors of the GPRM. It is shown that the impact is caused by the oscillation of the plunger or by the elastic relaxation of the initial preload force that holds the TM. At the end of the analysis, some improvements to the design of the release mechanism are brie y discussed, aimed at maximizing the probability of performing a successful injection procedure for the six TMs that will be used as sensing bodies in the LISA experiment.