Object-oriented Modelling of a Tracked Vehicle for Agricultural Applications

Mobile robots are a pillar of technologies that support agriculture 4.0, tracked mobile robots in particular are very suitable for agricultural applications. In this paper, the development of the multibody model of a tracked vehicle for agricultural applications is described, with the main goal to create a tool for the design of motion planning and control strategies in realistic conditions, in particular taking into account the characteristics of the terrain (terramechanics). Thanks to the modular approach enabled by the object-oriented modelling language Modelica, the complete suspension system as well as the interaction of tracks and grousers with the terrain have been described with a high level of accuracy. An extensive campaign of validation experiments has been carried out, mainly focused on the steering dynamics: on a rigid surface in indoor experiments and on a deformable surface in outdoor experiments. In indoor experiments the actual position of robot center of mass and its angular orientation were measured very accurately through a VICON motion capture system and an Inertial Measurement Unit (IMU), in outdoor experiments the motion capture system was replaced by a Real-Time Kinematic (RTK) Global Positioning System (GPS). This validation campaign has demonstrated the accuracy of the proposed model in representing the vehicle dynamics, clearly stating that it can be profitably adopted as a tool to design and validate novel planning and control strategies for agricultural robots.