A Decomposition of Interaction Force for Multi-Agent Co-Manipulation

TL;DR

This work addresses the lack of a general, frame-invariant definition of interaction force in multi-agent co-manipulation by proposing the net force decomposition. The method partitions the measured boundary force into $f_{\parallel}$ and $f_{\perp}$ relative to the net force $f_{net}$, enabling consistent interpretation across any number of agents and all six DOFs using onboard sensors. Applied to HH and HR data, the approach reveals distinct behavioral patterns, including a notable tendency toward maintaining system tension and differential alignment strategies between human and robot partners. The findings support the potential for more intuitive, lower-level robotic control in co-manipulation and motivate future enhancements in gravity compensation and behavior-to-control mappings for real-time coordination.

Abstract

Multi-agent human-robot co-manipulation is a poorly understood process with many inputs that potentially affect agent behavior. This paper explores one such input known as interaction force. Interaction force is potentially a primary component in communication that occurs during co-manipulation. There are, however, many different perspectives and definitions of interaction force in the literature. Therefore, a decomposition of interaction force is proposed that provides a consistent way of ascertaining the state of an agent relative to the group for multi-agent co-manipulation. This proposed method extends a current definition from one to four degrees of freedom, does not rely on a predefined object path, and is independent of the number of agents acting on the system and their locations and input wrenches (forces and torques). In addition, all of the necessary measures can be obtained by a self-contained robotic system, allowing for a more flexible and adaptive approach for future co-manipulation robot controllers.

Figures (18)

• Figure 1: Net Force Method: Visualisation of $f_\parallel$ and $f_\perp$
• Figure 2: (a) Ranges of angles, $\theta$, between $F_{net}$ and $F_{self}$. Ranges are chosen for the categories of interest. Aligned orthogonal and antagonistic ranges are each within $\pm$ 5 degrees of 0, $\pm$90, and 180 degrees respectively, while acute and obtuse ranges cover the remaining area. (b) Density plot showing the relative frequency of angles $\theta$ between $F_{self}$ and $F_{net}$ across each study by 5-degree increments.
• Figure 3: A comparison of HH and HR behaviors during increasing and decreasing velocity periods. Note: human followers tend to align their forces when the speed of the system is increasing while robots are antagonistic. The opposite behaviors are also observed when the system is slowing down during which humans become antagonistic while robots are aligned.
• Figure 4: Alignment range occurs when the agent force and the net force are within 5 degrees
• Figure 5: Acute angles with respect to the net force.