Contact robotics—close physical contact and cooperation between robots and humans— requires reliable, robust control of interaction. I will review some of the interesting and perhaps unique challenges of interaction control. Most control theory is permeated by a “signals” perspective: each system component is described as a mathematical operator that unilaterally determines its output (signals) as a function of its input (signals)—but not vice-versa. Composition of operators is straightforward and the result is modularity: behavior of a component is essentially unaffected by its assembly into a system, thereby dramatically simplifying design of complex machines. Unfortunately, the interactions due to physical contact are usually bi-lateral—each system affects the other. The “controlled system” blends the robot dynamics with those of the contacted object, which may be poorly or incompletely unknown. As a result the “signals” perspective doesn’t work well. I will review the mechanical physics of interaction, define what is meant by a “port” and show its usefulness for establishing impedance or admittance control. Drawing heavily on concepts from physical systems, I will review how a port-based perspective yields simple solutions for stabilizing contact, coping with (and taking advantage) of redundancy and selecting optimal behavior for different tasks.
Neville Hogan is Sun Jae Professor of Mechanical Engineering and Professor of Brain and Cognitive Sciences at the Massachusetts Institute of Technology, with research in robotics, motor neuroscience, and rehabilitation engineering. Awards include two honorary doctorates and the Rufus T. Oldenburger Medal from the Dynamic Systems and Control Division of the American Society of Mechanical Engineers.