CHAPTER
13
DESIGN OF LOWER-LIMB
EXOSKELETONS AND EMULATOR
SYSTEMS
Kirby Ann Witte
1
and Steven H. Collins
2
1
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States
2
Department of
Mechanical Engineering, Stanford University, Stanford, CA, United States
13.1 INTRODUCTION
Designing lower-limb exoskeletons is a difficult process with many inherent challenges. All exos-
keletons add mass and inertia to their user, which makes locomotion more energetically costly.
Exoskeletons also restrict natural movement by increasing the overall volume of the leg and by
resisting or completely inhibiting motion in some directions. The assistance provided by exoskele-
tons must effectively offset these innate costs before the user’s performance can be improved. This
requires exoskeletons to be lightweight and compact while ensuring safety and conforming to con-
straints such as desired degree of adjustability.
Designs range from soft to rigid and single jointed to full body, but all exoskeletons have the same
key components: frames, actuators, sensors, control hardware, and physical interfaces that connect to
the user. These features can be distributed in various ways, from a fully untethered system with all com-
ponents mounted on the user to an emulator testbed with many components located off-board.
This chapter provides guiding principles for design and case studies of effective approaches to
help developers begin the process of designing their own lower-limb exoskeletons. Topics include
the pros and cons of exoskeleton testbeds, selection of actuators, development of free body dia-
grams for evaluating loading and stresses, comfort and safety measures, tips for frame and joint
design, sensor selection, materials and manufacturing, series elasticity for improved torque tracking,
and a brief description of low-level control strategies.
13.2 EXOSKELETON EMULATOR TESTBEDS
Exoskeleton hardware is often complicated and expensive. Exoskeletons are usually built as an
untethered system with onboard power supply, control hardware, and actuation. Fitting all of this
into a compact packa ge that fits on a user without impeding movement often requires complex cus-
tom parts. Researchers often build exoskeletons and discover unsatis factory details, resulting in the
need for adjustments that require substantial redesign. This is discouraging, time-consuming, and
expensive, and can be largely avoided by beginning development with an exoskeleton emulator
system.
251
Wearable Robotics. DOI: https://doi.org/10.1016/B978-0-12-814659-0.00013-8
© 2020 Elsevier Inc. All rights reserved.
