Robotics system for the acquisition of nuclear images

This thesis presents the development of a robotic device that executes movements that correspond to those developed by a tomographic system used in imaging. The robotic device contains in its end effector a device for capturing radiological images using a gamma camera. The configuration of the robotic system obeys the structure of a cylindrical robot. The movement system of the robotic device is composed of: one swivel joint and two prismatic joints. The movement of each joint was driven by the action of direct current motors with encoder. The power stage to regulate the movement of the motors from the action of a digital system, was developed with a set of circuits of complete phase called H bridge. The controller developed to regulate the execution of the movement in each joint of the robotic device used a scheme called active disturbance rejection. This control method uses the compensation of the non modeled sections of the robotic device, as well as the disturbances and uncertainties that can affect the performance of the system in the image acquisition process. The estimation of the unknown section of the robotic system was made by proposing a set of extended states that are modulated by time varying parameters. The algorithm for estimating both the extended states and the time varying parameters was constructed from the application of an analysis obtained from the stability study of trajectory tracking error, state estimation and parameters. The main tool to develop the stability analysis was the application of the second method of Lyapunov using the concept of controlled function that is regularly used in the theory of adaptive control. To evaluate the proposed controller, a series of simulations were carried out from the Simulink tool of the Matlab software and experimental tests from the Tms-320-C-200 digital card from Texas Instruments. For the nuclear image acquisition system, the integration and evaluation of the elements of the gamma camera was carried out. This device consists of a parallel hole collimator, a LaBr₃ :Ce scintillation crystal, a 256-channel photomultiplier tube, and an electronic data acquisition system to process the signals from the photomultiplier tube. (Author)