Contact Representation in Robotic Mechanical Systems Employing Reduced Models

Abstract

Contact interactions play a major role in the dynamic analysis of robotic arms, where they can be represented as unilateral constraints. However, incorporating these contacts into the system dynamic model is a challenging task, given the numerous ways to account for them. This paper presents and compares two different approaches to contact modelling, highlighting how adopting a different perspective can avoid constraint redundancies and indeterminate problems. To this end, a co-simulation setup is employed as the primary framework to address the differences in the contact modelling approaches and the corresponding formulations. In a co-simulation setup, a system is divided into subsystems that exchange information at pre-determined communication points through the interface. Between the communication time points, the subsystems are integrated independently while they require updated interface variables from other subsystems. Hence, it is necessary to approximate these variables. In a model-based approximation, a reduced model of the subsystem emulates its dynamic behaviour at the interface. This paper addresses challenges in developing a representative reduced order model for a mechanical subsystem with contacts and proposes solutions to incorporate changes in contact states in the reduced model. It will be shown how basic assumptions in the contact dynamic incorporation can influence the simulation outcome. To demonstrate the proposed solution, a robotic arm model and its operations are used as a case study.