published_or_final_version / abstract / toc / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

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This project details the construction and development of, and experimentation with a mobile service courier robot named Meercat. This robot has been built from the ground up using parts sourced from various places. The application for this service robot is the delivery of internal mail parcels between the buildings situated on the campus of the Council for Scientific and Industrial Research (CSIR) in Pretoria. To achieve this, the robot has to be able to localise and navigate through indoor office and laboratory environments and over outdoor tarred roads which interconnect the various buildings. Not many robots are intended for operation in both indoor and outdoor environments, and to achieve this, multiple sensing systems are implemented on the platform, where the correct selection of sensing inputs is a key aspect. Further testing and experiments will take place with algorithms for localisation and navigation. As a limited budget was available for the development of this robot, cost-effective solutions had to be found for the mechanical, sensing and computation needs. The Mechatronics group from the Mechatronics and Micro Manufacturing (MMM) competency area at the CSIR is involved with the development of various autonomous mobile robots. The particular robot developed in this project will be an addition to the CSIR’s current fleet of robots and will be used as a stepping stone for experimentation with new sensors and electronics, and the development of further positioning and navigation algorithms. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Controlling a system with chaotic nature provides the ability to control and maintain orbits of different periods which extends the functionality of the system to be flexible. A system with diverse dynamical behaviours can be achieved. Trajectory flows of chaotic systems can be periodically stabilised using only small perturbations from the controlled parameter. The method of chaos control is the Ott-Grebogi-Yorke method. In non-chaotic systems large system parameters changes are required for performance changes. A sagittal plane biped model which is capable of exhibiting periodic and chaotic locomotion was researched and investigated. The locomotion was either periodic or chaotic depending on the design parameters. Nonlinear dynamic tools such as the Bifurcation Diagram, Lyapunov Exponent and Poincaré Map were used to differentiate parameters which generated periodic motion apart from chaotic ones. Numerical analytical tools such as the Closed Return and Linearization of the Poincaré Map were used to detect unstable periodic orbit in chaotic attractors. Chaos control of the model was achieved in simulations. The system dynamic is of the non-smooth continuous type. Differing from other investigated chaotic systems, the biped model has varying phase space dimensions which can range from 3 to 6 dimensions depending on the phase of walking. The design of the biped was such that its features were anthropomorphic with respect to locomotion. The model, consisting of only the lower body (hip to feet), was capable of walking passively or actively and was manufactured with optimal anthropometric parameters based on ground clearance (to avoid foot scuffing) and basin of attraction simulations. During experimentation, the biped successfully walked down an inclined ramp with minimal aid. Real time data acquisitions were performed to capture the results, and the experimental data of the walking trajectories were analysed and verified against simulations. It was verified that the constructed biped exhibits the same walking trend as the derived theoretical model. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

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For mobile robots to navigate autonomously, one of the most important and challenging task is localisation. Localisation refers to the process whereby a robot locates itself within a map of a known environment or with respect to a known starting point within an unknown environment. Localisation of a robot in unknown environment is done by tracking the trajectory of a robot whilst knowing the initial pose. Trajectory estimation becomes challenging if the robot is operating in an unknown environment that has scarcity of landmarks, is GPS denied, is slippery and dark such as in underground mines. This dissertation addresses the problem of estimating a robot's trajectory in underground mining environments. In the past, this problem has been addressed by using a 3D laser scanner. 3D laser scanners are expensive and consume lot of power even though they have high measurements accuracy and wide eld of view. For this research work, trajectory estimation is accomplished by the fusion of an ego-motion provided by Time of Flight(ToF) camera and measurement data provided by a low cost Inertial Measurement Unit(IMU). The fusion is performed using Kalman lter algorithm on a mobile robot moving in a 2D planar surface. The results shows a signi cant improvement on the trajectory estimation. Trajectory estimation using ToF camera only is erroneous especially when the robot is rotating. The fused trajectory estimation algorithm is able to estimate accurate ego-motion even when the robot is rotating. / [Durban, South Africa] : University of KwaZulu-Natal, 2013.

This thesis presents advances in the state-of-the-art in legged locomotion through the development of bounding and galloping gaits as well as new modes of hybrid wheeled-leg modes of locomotion. Two four-legged running robots, Scout II and PAW, are examined, the latter of which is distinguished by actuated wheels at the ends of its legs. / First, hybrid modes of locomotion are demonstrated which use legs to dynamically reposition wheels at specific locations with respect to the body. These modes improve the stability and tire-wear of turning and braking manoeuvres and allow pitch-controlled slope ascent and descent in a wheeled-leg vehicle such as the PAW robot. / Second, through hip actuation, passive leg compliance and controlled wheel action it is possible to make the same vehicle run using a dynamically stable legged gait called the bound. Experimental evidence of this is presented and compared to similar experiments on the same robot with mechanically blocked wheels, a 3D simulation of the same, as well as bounding on a completely different quadrupedal robot, Scout II. While a casual observer finds no difference in blocked-wheel and active wheel control modes, detailed examination of the gaits reveals lower speeds and efficiency as well as decreased repeatability when the wheels are actively controlled. / A new method of forward speed control is presented for the bounding gait using liftoff, as opposed to touchdown, leg angles. The liftoff angle method of speed control is shown to be particularly suited to fine-tuning of certain gait performance indices. / Third, the underactuated bounding gait is extended to demonstrate, for the first time, that robotic galloping is possible and that it can be achieved in two underactuated quad-rupedal robots and with varying levels of decoupled control. In the Scout II robot the front leg pair and rear leg pairs function independently; while in the PAW robot galloping is achieved with no controlled coupling between any of the four legs. The rotary gallop gait demonstrated by both robots is characterized by a significant yaw component and is compared to another bound-derived turning gait which uses liftoff angles to produce yaw. In particular, the correspondence of lead leg to yaw direction in both cases is found to match results from biology. In contrast, while it is thought that animals pivot about their lead leg to turn, the rotary gallop demonstrated by these robots shows that yaw occurs primarily in the leg behind the lead leg.