Advances in the Development of a Spherical Rover for Planetary Exploration - Part 2 : Modelling and Control

The thesis focuses on the advances in the design, performance analysis and control strategy of a spherical rover actuated by a 2-dof pendulum. Designed for space exploration, the choice of rover's spherical shape offers several advantages. The presence of a continuous solid shell provides effective protection for the internal mechanism and makes the rover suitable for harsh environments, as it is immune to overturning and efficient in absorbing impacts. The design goals include the ability to move at a constant speed over 15º slope surfaces incline and to overcome 10-cm-height steps. To address the inherent limitations of the design, a gyroscope system is included. The gyroscope system provides auxiliary propulsion to the main system, allowing enhanced performances. This feature is based on the physical principle of angular momentum conservation. The work has been divided in two theses. In the following, an introductory summary of previous work is presented. Given the complete design of the robot, it is possible to proceed with the functional and performance study, both in terms of motor capabilities and electronic efficiency, considering multiple scenarios. The appropriate sizing of the internal battery is calculated in order to continuously power the entire system for one hour. The robot is modeled in a multi-body simulation environment using Simulink/Simscape, replicating the entire plant system, including the precise internal mechanisms. Different versions of the plant have been developed. A first one consider every single components, inertia and relative motion among them. A second compact form version ,by simplifying the redundant connections, presents an analogous behavior as the first one and it is used for further analysis. The last version presents a simple shape made by connecting macro-group-components, and is used for studying the motion of the robot in real-time simulation. A beginning set of tests simulate the plant over different surfaces, in particular when the terrain is only uphill, only downhill or has sinusoidal shape. The tests present an open loop system where the robot behavior has been analyzed either putting a constant reference from simulink, or connecting a joystick device via USB port. Therefore, starting from the aforementioned plant system, the thesis proposes the development of a corresponding closed loop controller system capable of maneuvering the spherical ROV. Given a linear speed input the robot can be controlled along a straight path, and follows curved trajectories by auxiliary imposing the pendulum angle during lateral oscillation. Every virtual data input to the controller is sourced from a sensor previously defined and implemented into the simulation. The controller development features a multi-closed-loop structure, consisting of PID controllers and saturation blocks. The results obtained from the Model-in-the-Loop (MiL) tests demonstrate optimal speed control during longitudinal trajectories, strongly reducing the internal mechanism oscillations. Furthermore, the controller efficiently maneuvers the robot through movements on the plane in real time.