Dynamic Modeling of Branched Robots using Modular Composition

TL;DR

This paper introduces a modular dynamic modeling approach for branched robots, enabling reuse of subsystem models, including black boxes, with a graph-based interconnection method, validated on complex robotic systems.

Contribution

It presents a novel systematic modular procedure for dynamic modeling of branched robots, accommodating black box subsystems and using graph representations for model composition.

Findings

Model accuracy comparable to state-of-the-art libraries

Demonstrated on 24-DoF and 30-DoF robots

Validated for closed-loop control applications

Abstract

When modeling complex robot systems such as branched robots, whose kinematic structures are a tree, current techniques often require modeling the whole structure from scratch, even when partial models for the branches are available. This paper proposes a systematic modular procedure for the dynamic modeling of branched robots comprising several subsystems, each composed of an arbitrary number of rigid bodies, providing the final dynamic model by reusing previous models of each branch. Unlike previous approaches, the proposed strategy is applicable even if some subsystems are regarded as black boxes, requiring only twists and their time derivatives, and wrenches at the connection points between those subsystems. To help in the model composition, we also propose a weighted directed graph representation where the weights encode the propagation of twists and their time derivatives, and wrenches between the subsystems. A simple linear operation on the graph interconnection matrix provides the dynamics of the whole system. Numerical results using a 24-DoF fixed-base branched robot composed of eight subsystems show that the proposed formalism is as accurate as a state-of-the-art library for robotic dynamic modeling. Additional results using a 30-DoF holonomic branched mobile manipulator composed of three subsystems demonstrate the fidelity of our model to a modern robotics simulator and its capability of dealing with black box subsystems. To further illustrate how the derived dynamic model can be used in closed-loop control, we also present a simple formulation of a model-based wrench-driven pose control for branched robots.