In this thesis, the redundancy resolution and failure analysis of Cable-Driven Parallel Manipulators (CDPM) are investigated. A CDPM consists mainly of a Mobile Platform (MP) actuated by cables. Cables can only apply force in the form of tension. So, to design a fully controllable CDPM, the manipulator has to be redundantly actuated (e.g., by using redundant cables, external force/moment or gravity). In this research, the redundancy resolution of planar CDPMs is investigated at the kinematic and dynamic levels in order to improve the manipulator safety, reliability and performance, e.g., by avoiding large tension in the cables that may result in high impact forces, and avoiding large MP velocities that may cause instability in the manipulator, or on the contrary, by increasing the cable tensions and the stiffness for high-precision applications. The proposed approaches are utilized in trajectory planning, design of controllers, and safe dynamic workspace analysis where collision is imminent and the safety of humans, objects and the manipulator itself are at risk. The kinematic and dynamic models of the manipulator required in the design and control of manipulators are examined and simulated under various operating conditions and manufacturing automation tasks to predict the behaviour of the CDPM. In the presented research, some of the challenges associated with the redundancy resolution are resolved including positive tension requirement in each cable, infinite inverse dynamic solutions, slow-computation abilities when using optimization techniques, failure of the manipulator, and elasticity of cables that has a significant role in the dynamics of a heavy loaded manipulator with a large workspace. Optimization-based and non-optimization-based techniques are employed to resolve the redundancy of CDPM. Depending on the advantages and disadvantages of each method, task requirements, the used redundancy resolution technique, and the objective function suitable optimization-based and non-optimization-based routines are employed. Methodologies that could combine redundancy resolution techniques at various levels (e.g., position, velocity, acceleration, and torque levels) are proposed. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-09-26 22:39:34.35

Musculoskeletal dynamics is a branch of biomechanics that takes advantage of interdisciplinary models to describe the relation between muscle actuators and the corresponding motions of the human body. Muscle forces play a principal role in musculoskeletal dynamics. Unfortunately, these forces cannot be measured non-invasively. Measuring surface EMGs as a non-invasive technique is recognized as a surrogate to invasive muscle force measurement; however, these signals do not reflect the muscle forces accurately. Instead of measurement, mathematical modelling of the musculoskeletal dynamics is a well established tool to simulate, predict and analyse human movements. Computer simulations have been used to estimate a variety of variables that are difficult or impossible to measure directly, such as joint reaction forces, muscle forces, metabolic energy consumption, and muscle recruitment patterns. Musculoskeletal dynamic simulations can be divided into two branches: inverse and forward dynamics. Inverse dynamics is the approach in which net joint moments and/or muscle forces are calculated given the measured or specified kinematics. It is the most popular simulation technique used to study human musculoskeletal dynamics. The major disadvantage of inverse dynamics is that it is not predictive and can rarely be used in the cause-effect interpretations. In contrast with inverse dynamics, forward dynamics can be used to determine the human body movement when it is driven by known muscle forces. The musculoskeletal system (MSS) is dynamically under-determinate, i.e., the number of muscles is more than the degrees of freedom (dof) of the system. This redundancy will lead to infinite solutions of muscle force sets, which implies that there are infinite ways of recruiting different muscles for a specific motion. Therefore, there needs to be an extra criterion in order to resolve this issue. Optimization has been widely used for solving the redundancy of the force-sharing problem. Optimization is considered as the missing consideration in the dynamics of the MSS such that, once appended to the under-determinate problem, \human-like" movements will be acquired. \Human-like" implies that the human body tends to minimize a criterion during a movement, e.g., muscle fatigue or metabolic energy. It is commonly accepted that using those criteria, within the optimization necessary in the forward dynamic simulations, leads to a reasonable representation of real human motions. In this thesis, optimal control and forward dynamic simulation of human musculoskeletal systems are targeted. Forward dynamics requires integration of the differential equations of motion of the system, which takes a considerable time, especially within an optimization framework. Therefore, computationally efficient models are required. Musculoskeletal models in this thesis are implemented in the symbolic multibody package MapleSim that uses Maple as the leverage. MapleSim generates the equations of motion governing a multibody system automatically using linear graph theory. These equations will be simplified and highly optimized for further simulations taking advantage of symbolic techniques in Maple. The output codes are the best form for the equations to be applied in optimization-based simulation fields, such as the research area of this thesis. The specific objectives of this thesis were to develop frameworks for such predictive simulations and validate the estimations. Simulating human gait motion is set as the end goal of this research. To successfully achieve that, several intermediate steps are taken prior to gait modelling. One big step was to choose an efficient strategy to solve the optimal control and muscle redundancy problems. The optimal control techniques are benchmarked on simpler models, such as forearm flexion/extension, to study the efficacy of the proposed approaches more easily. Another major step to modelling gait is to create a high-fidelity foot-ground contact model. The foot contact model in this thesis is based on a nonlinear volumetric approach, which is able to generate the experimental ground reaction forces more effectively than the previously used models. Although the proposed models and approaches showed strong potential and capability, there is still room for improvement in both modelling and validation aspects. These cutting-edge future works can be followed by any researcher working in the optimal control and forward dynamic modelling of human musculoskeletal systems.

In this dissertation, we developed a method that uses the redundant information implicitly generated inside a random network coding network to apply error correction to the transmitted message. The obtained results show that the developed implicit error correcting method can reduce the effect of errors in a random network coding network without the addition of redundant information at the source node. This method presents numerous advantages compared to the documented concatenated error correction methods. We found that various error correction schemes can be implemented without adding redundancy at the source nodes. The decoding ability of this method is dependent on the network characteristics. We found that large networks with a high level of interconnectivity yield more redundant information allowing more advanced error correction schemes to be implemented. Network coding networks are prone to error propagation. We present the results of the effect of link error probability on our scheme and show that our scheme outperforms concatenated error correction schemes for low link error probability. / Thesis (M.Ing. (Computer Engineering))--North-West University, Potchefstroom Campus, 2010.

In this dissertation, we developed a method that uses the redundant information implicitly generated inside a random network coding network to apply error correction to the transmitted message. The obtained results show that the developed implicit error correcting method can reduce the effect of errors in a random network coding network without the addition of redundant information at the source node. This method presents numerous advantages compared to the documented concatenated error correction methods. We found that various error correction schemes can be implemented without adding redundancy at the source nodes. The decoding ability of this method is dependent on the network characteristics. We found that large networks with a high level of interconnectivity yield more redundant information allowing more advanced error correction schemes to be implemented. Network coding networks are prone to error propagation. We present the results of the effect of link error probability on our scheme and show that our scheme outperforms concatenated error correction schemes for low link error probability. / Thesis (M.Ing. (Computer Engineering))--North-West University, Potchefstroom Campus, 2010.

The purpose of this thesis is to demonstrate that two-girder or two-web structural systems can be employed to design efficient bridges with an adequate level of redundancy. The issue of redundancy in two-girder bridges is a constraint for the bridge designers in North America who want to take advantage of efficiency in this type of structural system. Therefore, behavior of two-girder or two-web structural systems after failure of one main load-carrying component is evaluated to validate their safety. A procedure is developed to perform system-level reliability analysis of bridges. This procedure is applied to two bridge concepts, a twin steel girder with composite deck slab and a concrete double-T girder with unbonded external tendons. The results show that twin steel girder bridges can be designed to fulfill the requirements of a redundant structure and the double-T girder with external unbonded tendons can be employed to develop a robust structural system.

The purpose of this thesis is to demonstrate that two-girder or two-web structural systems can be employed to design efficient bridges with an adequate level of redundancy. The issue of redundancy in two-girder bridges is a constraint for the bridge designers in North America who want to take advantage of efficiency in this type of structural system. Therefore, behavior of two-girder or two-web structural systems after failure of one main load-carrying component is evaluated to validate their safety. A procedure is developed to perform system-level reliability analysis of bridges. This procedure is applied to two bridge concepts, a twin steel girder with composite deck slab and a concrete double-T girder with unbonded external tendons. The results show that twin steel girder bridges can be designed to fulfill the requirements of a redundant structure and the double-T girder with external unbonded tendons can be employed to develop a robust structural system.

The probabilistic safety assessment of engineering systems involving high-consequence low-probability events is stochastic in nature due to uncertainties inherent in time to an event. The event could be a failure, repair, maintenance or degradation associated with system ageing. Accurate reliability prediction accounting for these uncertainties is a precursor to considerably good risk assessment model. Stochastic Markov reliability models have been constructed to quantify basic events in a static fault tree analysis as part of the safety assessment process. The models assume that a system transits through various states and that the time spent in a state is statistically random. The system failure probability estimates of these models assuming constant transition rate are extensively utilized in the industry to obtain failure frequency of catastrophic events. An example is core damage frequency in a nuclear power plant where the initiating event is loss of cooling system. However, the assumption of constant state transition rates for analysis of safety critical systems is debatable due to the fact that these rates do not properly account for variability in the time to an event. An ill-consequence of such an assumption is conservative reliability prediction leading to addition of unnecessary redundancies in modified versions of prototype designs, excess spare inventory and an expensive maintenance policy with shorter maintenance intervals. The reason for this discrepancy is that a constant transition rate is always associated with an exponential distribution for the time spent in a state. The subject matter of this thesis is to develop sophisticated mathematical models to improve predictive capabilities that accurately represent reliability of an engineering system. The generalization of the Markov process called the semi-Markov process is a well known stochastic process, yet it is not well explored in the reliability analysis of nuclear power plant systems. The continuous-time, discrete-state semi-Markov process model is a stochastic process model that describes the state transitions through a system of integral equations which can be solved using the trapezoidal rule. The primary objective is to determine the probability of being in each state. This process model ensures that time spent in the states can be represented by a suitable non-exponential distribution thus capturing the variability in the time to event. When exponential distribution is assumed for all the state transitions, the model reduces to the standard Markov model. This thesis illustrates the proposed concepts using basic examples and then develops advanced case studies for nuclear cooling systems, piping systems, digital instrumentation and control (I&C) systems, fire modelling and system maintenance. The first case study on nuclear component cooling water system (NCCW) shows that the proposed technique can be used to solve a fault tree involving redundant repairable components to yield initiating event probability quantifying the loss of cooling system. The time-to-failure of the pump train is assumed to be a Weibull distribution and the resulting system failure probability is validated using a Monte Carlo simulation of the corresponding reliability block diagram. Nuclear piping systems develop flaws, leaks and ruptures due to various underlying damage mechanisms. This thesis presents a general model for evaluating rupture frequencies of such repairable piping systems. The proposed model is able to incorporate the effect of aging related degradation of piping systems. Time dependent rupture frequencies are computed and the influence of inspection intervals on the piping rupture probability is investigated. There is an increasing interest worldwide in the installation of digital instrumentation and control systems in nuclear power plants. The main feedwater valve (MFV) controller system is used for regulating the water level in a steam generator. An existing Markov model in the literature is extended to a semi-Markov model to accurately predict the controller system reliability. The proposed model considers variability in the time to output from the computer to the controller with intrinsic software and mechanical failures. State-of-the-art time-to-flashover fire models used in the nuclear industry are either based on conservative analytical equations or computationally intensive simulation models. The proposed semi-Markov based case study describes an innovative fire growth model that allows prediction of fire development and containment including time to flashover. The model considers variability in time when transiting from one stage of the fire to the other. The proposed model is a reusable framework that can be of importance to product design engineers and fire safety regulators. Operational unavailability is at risk of being over-estimated because of assuming a constant degradation rate in a slowly ageing system. In the last case study, it is justified that variability in time to degradation has a remarkable effect on the choice of an effective maintenance policy. The proposed model is able to accurately predict the optimal maintenance interval assuming a non-exponential time to degradation. Further, the model reduces to a binary state Markov model equivalent to a classic probabilistic risk assessment model if the degradation and maintenance states are eliminated. In summary, variability in time to an event is not properly captured in existing Markov type reliability models though they are stochastic and account for uncertainties. The proposed semi-Markov process models are easy to implement, faster than intensive simulations and accurately model the reliability of engineering systems.

ABSTRACT A DEPENDABLE COMPUTING APPLICATION G&uuml / ng&ouml / r, Ugur M.S., Department of Electric and Electronics Engineering Supervisor : Prof. Dr. Hasan Cengiz G&uuml / ran April 2005, 129 pages This thesis focuses on fault tolerance which is kind of dependable computing implementation. It deals with the advantages of fault tolerance techniques on Single Event Upsets (SEU) occurred in a Field Programmable Gate Array (FPGA). Two fault tolerant methods are applied to floating point multiplier. Most common SEU mitigation method is Triple Modular Redundancy (TMR). So, two fault tolerance methods, which use TMR, are tested. There are three printed circuit boards (PCBs) and one user interface software in the setup. By user interface software running on a computer, user can inject fault or faults to the selected part of the system, which uses TMR with voting circuit or TMRVC TMR with voting and correction circuits on floating point multiplier. After inserting fault or faults, user can watch results of the fault injection test by user interface software. One of these printed circuit boards is called as a Test Pattern Generator. It is responsible for communication between the Fault Tolerant Systems and the user interface software running on a computer. Fault Tolerant Systems is second PCB in the setup. It is used to implement fault tolerant methods on fifteen bits floating point multiplier in the FPGA. First one of these methods is TMR with voter circuit (TMRV) and second one is TMR with voter and correction circuits (TMRVC). Last PCB in the setup is Display PCB. This PCB displays fault tolerant test result and floating point multiplication result. All the functions on Test Pattern Generator and Fault Tolerant Systems are implemented through the use of a Field Programmable Gate Array (FPGA), which is programmed using the Very High Speed IC Description Language (VHDL). Implementation results of the used methods in FPGA are evaluated to observe the performance of applied methods for tolerating SEU.

In addition to its intrinsic importance during quiet standing, posture also serves as the background for a wide variety of other critical motor tasks. The hierarchical nature of the motor control system suggests that the different layers may be responsible for different aspects of posture. I tested the hypothesis that spinal reflexes are organized according to optimal principles of stability, control accuracy, and energy. I found that there were no globally stable muscle activation patterns for muscles operating near optimal fiber length, suggesting that the intrinsic viscoelastic properties of muscle are insufficient to provide limb stability. However, for stiffer muscles a stable limb could be created by selectively activating muscles based on their moment-arm joint angle relationships. The optimal organization of length and velocity feedback to control and stabilize the endpoint position of a limb could not be produced from a purely muscle controller, but required neural feedback to improve endpoint performance, reduce energetic cost, and produce greater coordination among joints. I found that while muscles at near optimal fiber length were insufficient to provide limb stability, the length feedback provided by the autogenic stretch reflex was sufficient to stabilize. Length feedback was also sufficient to produce the directional tuning of muscle activity and constrained ground reaction forces as is observed in experiments. These results have implications for controlling powered prosthetic devices, suggesting that subdividing the responsibility for stability among hierarchical control structures will simultaneous improve stability and maneuverability of the devices.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains ix, 185 p. : ill. Includes abstract. Includes bibliographical references (p. 87-91).