Dynamic modeling and simulation of the omnidirectional locomotion of a mobile manipulator robot with four Swedish wheels and an independent suspension system

Abstract

Omnidirectional wheeled locomotion is often utilized by robots intended to work in indoor environments due to its high manoeuvrability in confined spaces. CHARMIE, a human-inspired mobile manipulator that aims to assist patients with mobility limitations, employs four Swedish wheels supported by an independent suspension to navigate through domestic environments. Multibody dynamics is one of the main tools which plays a pivotal role in this robot’s mechanical development and optimization. This work expands CHARMIE’s previously validated multibody model to include its locomotion and suspension systems. For this purpose, a new module is incorporated which adds 12 bodies with 16 associated degrees of freedom to the model. The suspension system allows the wheels to move vertically and slightly adjust their orientation, determining the robot’s altitude, roll angle, and pitch angle. The locomotive system combines the active and passive velocities of the omnidirectional wheels to determine the robot’s linear velocity in the two directions along the ground plane, as well as the yaw angle. The focus of this analysis is to assess the robot’s stability and safety in a computational environment. A complex model can be computed since real-time results are not required. This model considers the effects caused by the wheel friction, the weight transfer due to the robot’s motion, and the dynamics of the DC motors. The main contributions of the present study are the level of detail of the model, the analysis of the dynamics of a complex manipulator alongside its locomotion, and the inclusion of a suspension system on an omnidirectional locomotion. The results obtained were vital to further optimize CHARMIE’s mechanical parameters (such as suspension stiffness), as well as to define safe workspace considerations and parameters that had to be included in the robot’s trajectory planning.