Voice Coil Actuators for Human-Robot Interaction
An Exploration of the use of Electromagnetic Voice Coils as Compliant, Force-
Controlled Actuators in Direct-Drive Robots for Visual and Tactile Interaction with
Humans

John McBean, Cynthia Breazeal
MIT Media Laboratory
Robotic Life Group
Cambridge, MA
jmcbean@mit.edu, cynthiab@media.mit.edu



Abstract—The growing field of human-robot interaction
(HRI) demands robots that move fluidly, gracefully,
compliantly and safely. This paper describes our recent work
in the design and evaluation of long-travel voice coil
actuators (VCAs) for use in robots intended for interacting
with people. The basic advantages and shortcomings of
electromagnetic actuators are discussed and evaluated in the
context of human-robot interaction, and are compared to
alternative actuation technologies. Voice coil actuators have
been chosen for their controllability, ease of implementation,
geometry, compliance, biomimetic actuation characteristics,
safety, quietness, and high power density.
Keywords- Voice coil, actuator, human-robot interaction,
HRI, tactile, compliance.

I.
II.
A.
INTRODUCTION
Comparisons of robot actuator technologies typically
reveal the appealing high power densities of
electromagnetic actuators, and the high pressures of
hydraulic, electro-active polymer (EAP), piezoelectric and
shape memory alloy (SMA) actuators. The conventional
metrics of comparison for these actuators tend not to
clearly identify which technologies are most suitable for
high degree of freedom robots intended for tactile
interaction with people. Such comparisons also tend to be
misleading in that they may overlook some of the bulky
infrastructure required for the implementation of the
actuators. Hydraulic actuators, for example, are
particularly attractive for their high pressures, low power
holding forces, and relatively high speeds. It should not be
overlooked, however, that hydraulic actuators are
conventionally messy, high maintenance, very stiff, and
require large amounts of material overhead for pumps,
fluid lines, valves, accumulators and the like. In the
selection and development of an appropriate actuation
technology for interactive robots, we have considered
conventional metrics of comparison (pressure, power
density, and controllability), but the relatively young field
of human-robot interaction (HRI) demands that substantial
consideration be given to the metrics of noise, quality of
motion, low inherent mechanical impedance (high
backdriveability), geometric configuration, robustness to
overloading, and safety.
We are designing and building a 6 degree of freedom
(DOF) direct-drive robotic arm, using voice coil actuators
(VCAs), that will serve as an evaluation platform for the
actuators themselves, for viable control systems for such
robots, and for testing of interactive modes and experiences
through HRI studies.
This paper will begin with brief descriptions of many
available actuation technologies. This will serve as
motivation for the work being done on voice coil actuators.
The paper will then describe the attributes of voice coil
actuators, their advantages and shortcomings (specifically
in the context of tactile human-robot interaction), and
design parameters that affect their performance. In section
IV, we will discuss the design and construction of the
actuators that we are using in our robotic arm, as well as a
brief description of the arm itself. We will show some
preliminary results in section V.A: actuator performance
curves and qualitative analyses of the actuators and the arm
as HRI demonstration and testing tools. Finally, section
V.B will summarize results this far, and propose potential
future work in the area of novel actuator design for the
emerging field of HRI.
BACKGROUND AND MOTIVATION – ACTUATOR
COMPARISON SYNOPSIS
Introduction
A comprehensive comparison of conventional actuator
technologies was published by Hollerbach, Hunter, and
Ballantyne in 1992 [1] and is still very much relevant
today. The vast majority of actuators used in robotic
systems to date employ one or more of the technologies
described in that paper. Many of these technologies have
been proven to be robust, cheap, and readily available.
Under a paradigm where robots are expected to be bulky,