Browsing by Subject "Robots--Dynamics."
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Item Open Access 3D dynamic modeling of spherical wheeled self-balancing mobile robot(Bilkent University, 2012) İnal, Ali NailIn recent years, dynamically stable platforms that move on spherical wheels, also known as BallBots, gained popularity in the robotics literature as an alternative locomotion method to statically stable wheeled mobile robots. In contrast to wheeled platforms which do not have to explicitly be concerned about their balance, BallBot platforms must be informed about their dynamics and actively try to maintain balance. Up until now, such platforms have been approximated by simple planar models, with extensions to three dimensions through the combination of decoupled models in orthogonal sagittal planes. However, even though capturing certain aspects of the robot’s motion is possible with such decoupled models, they cannot represent inherently spatial aspects of motion such as yaw rotation or coupled inertial effects due to the motion of the rigid body. In this thesis, we introduce a novel, fully-coupled 3D model for such spherical wheeled balancing platforms. We show that our novel model captures important spatial aspects of motion that have previously not been captured by planar models. Moreover, our new model provides a better basis for controllers that are informed by more expressive system dynamics. In order to establish the expressivity and accuracy of this new model, we present simulation studies in dynamically rich situations. We use circular paths to reveal the advantages of the new model for fast maneuvers. Additionally, we introduce new inverse-dynamics controllers for a better attitude control and investigate within simulations the capability of sustaining dynamic behaviors. We study the relation between circular motions in attitude angles and associated motions in positional variables for BallBot locomotion.Item Open Access Smith predictor based controller design for a flexible robot arm(Bilkent University, 2013) Taşdelen, UğurIn this thesis, a new Smith predictor based controller is proposed for a flexible robot arm. A typical robot arm model includes high order modes with integral action from torque input to velocity output. Here we can also consider the effect of possible delays between the plant and the controller. The controller structure considered has an extended Smith predictor form. The designs use controller parametrization for stability and they also achieve certain performance objectives via interpolation conditions based on the disturbance rejection and setpoint tracking properties. This parametrization method allows widest freedom in controller parameters and this results in improved performance, both in set-point response and disturbance rejection. Free parameters in the controller determines the location of closed-loop poles. A hierarchical structure is used to extend Smith predictor structure to the position control loop. By protecting proposed structure, different approaches are shown to control the position. Compared to existing Smith predictor based designs, disturbance attenuation property with respect to periodic disturbances at a known frequency is improved. A two-degree of freedom controller structure is shown to be helpful in shaping the transient response under constant reference inputs. Stability robustness properties of this system are also investigated. Simulation results demonstrate the effectiveness of the proposed controller.Item Open Access Tracking and regulation control of a two-degree-of-freedom robot arm(Bilkent University, 2012) Güler, SametIn this thesis, servomechanism synthesis for a two-degree-of-freedom (2-DOF) serial chain revolute-revolute joint robot arm that achieves internal stability, reference signal tracking, and torque disturbance regulation is considered. We first derive the dynamic equations of the robot arm with Euler-Lagrange method by ignoring the effects of friction. Then, using system identification methods, we derive a plant model based on data obtained from a real system through experiments. We then employ PD and PID controllers along with the gravity compensation method to stabilize the system using the passivity properties. Alternatively, we linearize the system model and examine the performance of the same controllers. A linear controller is synthesized by invoking the internal model principle and is directly applied to the nonlinear plant model. The proposed fifth order linear controllers at each channel of the robot arm suffices to achieve not only tracking of step, ramp, and sinusoidal signals at one frequency, but also regulation of step, ramp, and sinusoidal disturbances. It is shown via simulations that, even though the plant model is nonlinear, the synthesized linear controller performs better than the commonly used PID controllers.