Browsing by Subject "Adaptive control systems."

Now showing 1 - 5 of 5

Open Access
Adaptive control of a one-legged hopping robot through dynamically embedded spring-loaded inverted pendulum template
(2011) Uyanık, İsmail
Practical realization of model-based dynamic legged behaviors is substantially more challenging than statically stable behaviors due to their heavy dependence on second-order system dynamics. This problem is further aggravated by the dif- ficulty of accurately measuring or estimating dynamic parameters such as spring and damping constants for associated models and the fact that such parameters are prone to change in time due to heavy use and associated material fatigue. In the first part of this thesis, we present an on-line, model-based adaptive control method for running with a planar spring-mass hopper based on a once-per-step parameter correction scheme. Our method can be used both as a system identifi- cation tool to determine possibly time-varying spring and damping constants of a miscalibrated system, or as an adaptive controller that can eliminate steady-state tracking errors through appropriate adjustments on dynamic system parameters. We use Spring-Loaded Inverted Pendulum (SLIP) model, which is the mostly used, effective and accurate descriptive tool for running animals of different sizes and morphologies, to evaluate our algorithm. We present systematic simulation studies to show that our method can successfully accomplish both accurate tracking and system identification tasks on this model. Additionally, we extend our simulations to Torque-Actuated Dissipative Spring-Loaded Inverted Pendulum (TD-SLIP) model towards its implementation on an actual robot platform. In the second part of the thesis, we present the design and construction of a onelegged hopping robot we built to test the practical applicability of our adaptive control algorithm. We summarize the mechanical, electronics and software design of our robot as well as the performed system identification studies to calibrate the unknown system parameters. Finally, we investigate the robot’s motion achieved by a simple torque-actuated open loop controller.
Open Access
Mechatronic design of a modular three-axis slider system for high-precision positioning applications
(2012) Ulu, Erva
Following the recent improvements in precision engineering related technology, interest for micro/nano-engineering applications are increased and various micro/nano-scale operations and products are developed. For micro/nano-scale applications, high-precision equipment including micro/nano-positioning devices with high accuracy and precision are required. In this thesis, mechatronic design of a three axes micro/nano-positioning device is discussed in detail. In order to satisfy nanometer level precision, an adaptive method to increase the available measurement resolution of quadrature encoders is presented. Performance characteristics of micro/nano-positioning devices usually include positioning accuracy of their each individual axis, operation range, maximum velocity and maximum acceleration. For this reason, permanent magnet linear motors (PMLM) are chosen as actuators in the presented design due to their outstanding characteristics. Moreover, in order to provide high-flexibility in terms of applications and simplify the control of the system, modularity is one of the main concerns while designing the micro/nano-positioning system presented here. Building the modular single axis slider system, three axes positioning device is constructed by assembling three of them perpendicularly. In this design, linear optical encoders are used as feedback sensors. Movement range of the designed system is 120mm in each direction. Since the available linear optical encoders have measurement resolution of 1µm, resolution of them is to be improved in software for sub-micron level positioning applications. For this purpose, a new method to increase the available measurement resolution of quadrature encoders is presented in this thesis. This method features an adaptive signal correction phase and an interpolation phase. Imperfections in the encoder signals including amplitude differences, mean offsets and quadrature phase shift errors are corrected by using recursive least squares (RLS) with exponential forgetting and resetting. Interpolation of the corrected signals is accomplished by a quick access look-up table calculated offline to satisfy linear mapping from available sinusoidal signals to higher order ones. With the conversion of the high-order sinusoids to binary pulses, position information is derived. By using the presented method, 10nm measurement resolution is achieved with an encoder with 1µm off-the-shelf resolution. Experiment results demonstrating the effectiveness of the proposed method are presented. Validation of the method is accomplished for several cases including the best resolution obtained. Practical constraints limiting the maximum interpolation number are also discussed in detail.
Open Access
An optimal solution for the multi-agent rendezvous problem appearing in cooperative control
(2008) Kölmek, Fatih
The multi-agent rendezvous problem appearing in cooperative control is considered in this thesis. There are various approaches to this topic as the objectives and problem set-ups vary in real-life rendezvous problems. Some of the applications can be given as the coordination of autonomous mobile robots or unmanned air vehicles (UAVs) for joint tasks, and motion planning for vehicle convoys. The problem is basically on providing a rendezvous for mobile agents at a specified or unspecified destination. What makes the topic interesting is maintaining a coordination between the mobile agents so that the agents reach the rendezvous point simultaneously. Early or late arrivals are not desired. An energy optimal solution is obtained for the problem. Imperfect road conditions, obstacles, internal problems of the agents or similar disturbances are also tried to be handled. As these factors are included in the problem, it is assumed that the agents communicate between each other at specified time instants exchanging information about their expected arrival times in order to maintain a common rendezvous time among the team. The solution is initially derived for rendezvous in one-dimensioned space. Then, the problem configuration is altered for two-dimensioned motions, and the target point is assumed to be moving in order to extend the solution to possible practical applications. The effect of increasing disturbance on the control input and time delays in the communication are also discussed.
Open Access
Optimal timing of an energy saving technology adoption
(2011) Harmankaya, Mehmet Fatih
In this thesis, we use two stage optimal control techniques to analyze the optimal timing of energy saving technology adoptions. We assume that the physical capital goods sector is relatively more energy intensive than consumption goods sector. First, we solve a benchmark problem without exogenously growing energy saving technology frontier. In such a case, the economy sticks either to the initial technology or immediately switches to a new technology, depending on the growth rate advantage compared to the obsolescence and adjustment costs. In the second step, we introduce exogenously growing energy saving technology frontier. The anticipated level of the technology provides incentives to delay the adoption and generates an interior switching time. Finally, we analyze numerically the e§ects of the speed of adjustment to the new technology, growth rate of technology, subjective time preference and planning horizon on the optimal timing of technology adoption.
Open Access
Parameter optimized controller design based on frequency domain identification
(1995) Köroğlu, Hakan
Recently, there has been a great tendency towards the development of iterative design methodologies combining identification with control in a mutually supportive fashion. In this thesis, we develop such an algorithm utilizing nonparametric frequency domain identification methods in order to realize the online iterative design of parameter optimized controllers for a system of unknown dynamics. The control design is based on the minimization of LQG (Linear Quadratic Gaussian) cost criterion with a two-degree of freedom control system. This is achieved by the approximation of an optimality relation, which is derived for a particular parametrization of one of the controllers, using the frequency domain transfer function estimates and application of this together with a numerical optimization algorithm. It is shown that, if the first controller is a FIR filter of length greater than or equal to two times the number of frequencies present in the reference input, the designed control system is optimal independent of the stabilizing second controller.