• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 715
  • 55
  • 34
  • 24
  • 16
  • 5
  • 4
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 953
  • 953
  • 664
  • 220
  • 184
  • 126
  • 99
  • 88
  • 87
  • 83
  • 76
  • 65
  • 63
  • 59
  • 59
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Manipulator, Mounting and Integration, and Communication Brick Collection

Ljungström, Camilla January 2008 (has links)
The aim of this project is to add manipulation functionality to one of the NASA's Mars rovers through the integration of a robotic arm. The functionality is needed to enable retrieval of deployed communication bricks from the Martian surface. For this, a simple hook end-eector is designed and tested using a controller implemented on a computer. The manipulator is a ve degree of freedom robotic arm with revolute joints. It is a nonlinear MIMO system but can be approximated to be five highly decoupled linear SISO systems. The manipulator is controlled in joint space, where each joint follows a trajectory. The trajectory is generated as four sequential sub-trajectories, where the manipulator comes to rest at each transition point. We assume that the Martian surface is free of obstacles and that the manipulator can work in any position on the workspace. We also assume that the position of the hole on the communication brick is known. For controlling the end-eector in joint space, a trajectory-following PD-controller is constructed. When testing the controller the rst four joints (waist, shoulder, elbow and twist) follow the desired trajectory well. The last joint, wrist, follows the trajectory well for the rst period of time and then start to oscillate around the path curve. The controller was tuned by decreasing Kp value for the wrist joint. The reason for deciding to decrease Kp was to slow the system down and therefore gain an increased stability. Tuning resulted in a better behaving wrist joint controller which follows the desired trajectory in a satisfactory way. Oscillations in wrist have disappeared and the controller works as intended. We designed and manufactured an end-eector that was within the IRG price range. We established baseline communication with the manipulator, developed a standalone control software and implemented a software for collection of communication bricks. This controller was working properly and fullled the goal set at the beginning of the thesis to design a communication brick collecting manipulator.
142

Probabilistic Fault Isolation in Embedded Systems Using Training Data

Cornell, Axel January 2008 (has links)
In the heavy vehicle industry customers, laws and increasingly complex processes demand methods of supervising every aspect of a truck. Fault isolation systems are introduced to do just that. In order to assure a sustainable development new types of isolation systems are investigated to substitute the consistency based isolation systems of today. In this thesis an application of a probabilistic isolation method that ranks possible faults on their likeliness of being a fault in the process is implemented and evaluated as a possible future replacement of today's system. This method bases the isolation on training data collected from measurements on the process and observation of the process. The probabilistic isolation method is evaluated on hos it performs under different circumstances such as the effort of different amounts of training data and how well it performs if the tests and observations of the process are of varying quality. Solution to several problems that arise when this method is implemented are also investigated such as how the system handles cases where several faults occur at the same time, what happens if there are missing data in the observations of the system and how to solve problems that involve execution times which is important in embedded systems. The results that are derived show that this probabilistic isolation system performs well on the process as it is today and that this is a good substitute when developing for future processes. There is however a need for further development of the system such as improved isolation when there are several faults present in the process and questions on how to collect and store the training data still remain to be answered. A full scale implement would allow for better comparison with the current system and give more information on runtime and storage problems.
143

Estimating Rotational Speed with a Phase- Locked Loop

Willemsen, Niklas January 2008 (has links)
Volvo Construction Equipment Components AB (Volvo CE) develops electronic control systems for various vehicles in the field of construction equipment. Increasing demands on quality, safety and environmental care require more and more sophisticated and intelligent drive control systems. These new systems are dependant on high quality input data from various sensors. One of these sensors is of inductive type and is used for measuring rotational speed of a gear wheel, and the method of doing this is the subject of this thesis. The current method applied at Volvo CE for measuring this speed needs to be changed in order to cope with these new demands, especially at low velocities. The alternative method presented in this paper is based on Phase-locked loop (PLL) techniques, which is a closed loop frequency control system. In this thesis two different ways of implementing a PLL are investigated; a Quadrature phaselocked loop (QPLL) in software and a second order PLL in hardware. The QPLL is derived through optimization theory and implemented in Simulink. The second order PLL is the integrated circuit LM565 from the manufacturer National Semiconductor. The QPLL is tested in a wheel loader and compared with the current method used at Volvo CE today. The results show that in the general case the QPLL is not better than the current method but at fast retardations and when changes of the velocity directions occur the QPLL outperforms the current method. A drawback with the QPLL is its behaviour at constant low velocities where it tends to lose track of the signal. The hardware-PLL is tested in a test bench with similar working conditions as in a machine. The results show that this method has a limited frequency interval but in this interval the performance is as good as the current method and very robust. The conclusion of this thesis is that PLL methods are interesting and could improve the quality of the measurements when the velocity is changing very fast but in the general case the current method is just as good. Implementing a PLL would require some extra expenses in terms of additional hardware but with the results presented in this thesis it does not seem cost effective.
144

Pressure Control of a Pneumatic Actuator Using On/O Solenoid Valves

Jeddi Tehrani, Maisam January 2008 (has links)
Nowadays a very important aspect in heavy duty vehicles is the braking system. The braking system can be divided into EBS brakes, exhaust brake and retarder, where the latter is of interest in the present Master's Thesis. This thesis presents an investigation whether it is possible to substitute today's concept, i.e. controlling the air pressure to the retarder using a proportional-valve, with two so-called on/o®-valves and a pressure sensor, which will reduce expenses and contingently hysteresis phenomena seen in the current system. A non-linear model of the Electronic Control Unit (ECU) electrical drives, and the electrical, magnetic, mechanical, and pneumatic parts of the valves, is designed. A Proportional-Integral-Derivative (PID)-controller is designed based on the derived model. Two di®erent pulsing schemes have been investigated. However, just one of the approaches together with the results from the other one is presented in this thesis. In order to improve the control performance non-linear control and prediction methods are used so that required time response and robustness is achieved. Finally the modelled current and pressure are validated against the measured data, and a verification of the controller is done on the prototypes.
145

Object Oriented Modelling and Simulation of Kaplan Turbines

Lu Quilisch, Angela January 2008 (has links)
The aim of this thesis is twofold. The first and major one is to develop an objectoriented Kaplan turbine model to support control design for hydropower systems. The model is developed in the Modelica language and implemented in the Dymola simulation environment. Using the equation-based modelling formalism of Modelica, the model exploits water flow and pressure balance equations to capture the relationship between the hydraulic and mechanical energy. A particular feature of the model is a detailed description of how the water flow and turbine torque are affected by the wicket gate and turbine runner blade angles. The second aim of the thesis is to demonstrate how the Kaplan turbine model can be used to design hydropower control systems. To this end, a relatively complete hydropower system model is developed using the model components and several dam control strategies are evaluated. This study clearly demonstrates the utility of the model in the design of hydropower control systems.
146

Modeling and Control of Retarder using On/Off Solenoid Valves

Steinsland, Vidar January 2008 (has links)
The Retarder is one of the main components in Scania's trucks' braking system and is used to brake down the truck and for maintaining a steady speed on descents. This Master's Thesis aims to investigate if the current system which uses a proportional valve to control the air pressure in the Retarder, can be replaced with two on/o® solenoid valves and a pressure chamber to control the air pressure, which would result in a cheaper and more robust system. By varying the air pressure, the braking torque in the truck can be regulated. A model including electrical drives from a control unit, valves, pressure chamber and a regulating valve is derived. Using the model as reference, a controller is designed and implemented to control the valves, and thereby the pressure. Based on experience from employees at Scania and former research on on/o® control of an Exhaust Gas Recirculation system, a regular PID-controller is used as the base in the control. A pulsing scheme where the valves are activated separately is used to distribute the control signal to the two valves. Di®erent ways of applying the control signal are investigated, whether the valves run digital, i.e. 0 % or 100 %, or continuously by varying the PWM signal. A boosting action using non-linear control, and prediction are investigated in order to improve the control performance in such way that the required time response and robustness is obtained. The controller is eventually tested and veri¯ed on the real system.
147

Probabilistic Fault Isolation in Embedded Systems Using Prior Knowledge of the System

Selhammer, Anders January 2008 (has links)
Nowadays truck engines are controlled by an embedded control system which is a specially designed computer system. It is important that the embedded system is robust against possible faults that could appear when driving the vehicle since faults may cause the vehicle to stop unintended or even worse, crash. To prevent this tests in the system are designed to detect faults and further isolate the faulty behaviors for components. After the isolation fault tolerant control software is used to control the engine in the presence of the faults until the faults have been attended to by a mechanic. In this thesis an application of a probabilistic isolation method that ranks possible faults on their likeliness is presented. The method uses a Bayesian approach for the probability computations based on prior knowledge for ranking the faults in order to improve the result. The probabilistic isolation method is analyzed to show how the isolation performs and how the isolation differs when changing different parameters for the isolation such as test sensitivities and prior knowledge. Different solutions for problems that appear due to different circumstances are also described and evaluated. The solutions handle cases such as limited RAM and execution time, multiple faults and incomplete observations. The result shows a good performance for the probabilistic isolation method and the different solutions. However the method still needs further developments in order to achieve adequate trust for an implementation in vehicles. Future work is proposed and should include further improvements in the isolation of multiple faults.
148

Cylinder-Pressure Based Injector Calibration for Diesel Engines

König, Johan January 2008 (has links)
One way of complying with future emission restrictions for diesel engines is to use pressure sensors for improved combustion control. Implementation of pressure sensors into production engines would lead to new possibilities for fuel injection monitoring where one potential use is injector calibration. The scope of this thesis is to investigate the possibility of using pressure sensors for finding the minimal energizing time necessary for fuel injection. This minimal energizing time varies over the injector's lifetime and therefore requires a re-calibration. The necessary energizing time can be found by estimating the injected fuel mass at dierent rail-pressures during a calibration state operating under specific engine conditions. Two dierent approaches based onin-cylinder pressure were used for fuel mass estimation. The result is based on a comparison to a non pressure based production line calibration function. Both fuel mass estimations show a correlation with convincingly accuracy for calibration use but with the possibility of further improvements. One approach is shown to be less sensitive to signal osets but more sensitive to noise. The oset sensitiveness can be reduces by changing measurement positions depending on user requirements. Compensations for energy losses depending on engine speed and cylinder dierences are shown to be necessary for calibration accuracy. Moreover are both injected fuel mass and rail-pressure shown to influence the combustion.
149

Scheduling Smart Home Appliances in the Stockholm Royal Seaport

Wu, Jonas January 2012 (has links)
This thesis investigates the optimal scheduling of smart home appliances with respect to economic benefits (electricity bill) and reducing environmental impacts (CO 2 emissions) for the Stockholm Royal Seaport project. The aim of this project is to develop a new urban district developing in the eastern Stockholm which will house 10,000 new apartments and 30,000 new office spaces where modern living is combined with environmental thinking to create sustainable living. In a previous work the scheduling objective was to minimize electricity bill, subject to various constraints such as sequential processing and consumer preferences. In this work the optimization framework will be extended to consider the trade-off between electricity bill and CO 2 emission minimization. This is a main concern in the Royal Seaport project. The study of this thesis shows that a well balanced result between minimizing the electricity cost and reducing the CO 2 emissions for an unusual cold day in Sweden (2010-01-05) with three typical home appliances showed that for formulation suggested in a previous work one could save up to 35.9% of electricity costs as well as reducing the CO 2 emissions with up to 16.5 %. This saving is with respect to the worst case scheduling for that specific day. The trade-off analysis is based on multi-objective Pareto frontier exploration, which requires solving multiple schedules instead of one as in the previous single objective case. In addition, for practical implementation the smart home control devices that will be used in the Stockholm Royal Sea project apartments will have a CPU and memory similar to those of a smart phone. Therefore there exists a need for faster implementation. The studies in this thesis indicate that the proposed simplified formulation can lead to a almost sixfold speed up in solve time, while providing schedules similar to those by the previous approach. The solve time of the proposed formulation decreases when the number of breakpoints in the piecewise linear objective decreases. A variant of the Ramer-Douglas-Peucker algorithm is applied to reduce the number of breakpoints while guaranteeing the objective function error is within a pre-specified bound. Finally, extensions of the current framework are discussed.
150

Numerical Control: Performance Analysis and Implementation Issues

Vinikoff, Nicolas January 2012 (has links)
In this thesis, a digitalization method with nite word-length (resolu- tion N ) of a given stable analog controller guaranteeing the minimum dierence in terms of frequency responses is treated. The challenge has consisted in nding a relevant frequency responses mismatch met- ric and in relating it to the word niteness issue. The analog con- troller is represented in modal state-space form and digitalized with a stability-maintaining approximation (ramp invariance) for dierent sampling periods. It results in digital controllers with block diago- nal transition matrices whose coecients (poles) are inside the unit circle. The format is chosen to match the poles dynamical range. The matrix is then coded and the mismatch measure allows for the selection of the "best" poles coded controllers. The remaining ma- trices are then scaled and coded for these selected controllers. The measure is computed for each of them. The procedure nally gives the "optimal" coded controller. This algorithm is shown to perform well and better that a simple rounding after the analog controller discretization phase. iii

Page generated in 0.1341 seconds