Forward Dynamics of Variable Topology Mechanisms - The Case of Constraint Activation

TL;DR

This paper addresses the complex dynamics of mechanisms with changing topology, proposing transition conditions for accurate modeling during topology switches, with applications to robotic joints.

Contribution

It introduces physically meaningful transition conditions for variable topology mechanisms using two different coordinate approaches.

Findings

Transition conditions enable better dynamic simulation of topology changes.

Results demonstrate the approach on planar and industrial robotic mechanisms.

Computational properties of the methods are analyzed.

Abstract

Many mechanical systems exhibit changes in their kinematic topology altering the mobility. Ideal contact is the best known cause, but also stiction and controlled locking of parts of a mechanism lead to topology changes. The latter is becoming an important issue in human-machine interaction. Anticipating the dynamic behavior of variable topology mechanisms requires solving a non-smooth dynamic problem. The core challenge is a physically meaningful transition condition at the topology switching events. Such a condition is presented in this paper. Two versions are reported, one using projected motion equations in terms of redundant coordinates, and another one using the Voronets equations in terms of minimal coordinates. Their computational properties are discussed. Results are shown for joint locking of a planar 3R mechanisms and a 6DOF industrial manipulator.