Design and development of a control system for TASI Docking mechanism prototype

This thesis presents the design procedure of a control system to implement over a docking mechanism, developed for on-orbit servicing of cooperative satellites. The mechanism's prototype is part of the SAPERE-STRONG mission, with the aim of performing an active docking procedure between low-mass satellites, recovering the residual misalignment during the last approach and dissipating the energy associated with the relative velocities between spacecrafts upon contact. The chaser element is the active part and consist of a central docking mechanism, with a sliding probe structure. The control development started from the study of the mechanical behaviour of the mechanism and of the available electrical hardware to implement. The technical specifications of actuators, motors drivers and sensors are examined and a suitable control architecture has been selected. The final solution consist of a central control system, where an Arduino MEGA board is the master controller and the motors drivers are the slave elements. So the control algorithm was implemented onto Arduino board, which manages the actuators motions and the sensors measurements, communicating with driver through rs232 serial communication protocol. The docking procedure consist of several phases: the preliminary mechanism positioning, the alignment, the soft docking, the probe re-centering, the retraction and the hard docking stage. They are executed by the use of a finite state machine. The motion of the motors and the mechanical movements are performed using the closed loop position and velocity control theory. The results of the first design iteration are tested over a dedicated test bench in no load conditions, where it is checked if the devices work properly and if the control algorithm runs without issues. After, the electrical components are mounted over the mechanism and the laboratory tests are done. A set of mating trials between the two parts are performed and the control parameters are regulated in order to meet the requirements. Also a PCB shield is designed, in order to integrate all the additional Arduino hardware onto a single board. The final obtained result is a working prototype of an active docking mechanism, ready to be subjected to the final mating test, which consist of a docking simulation by using a robotic arm. The active part will be still while the passive one will be mounted over the manipulator, that simulates the relative motion between the docking halves through apposite trajectory generation techniques.