IEEE Robotics & Automation Magazine - June 2018 - 96

automatically disengage the torque between the exo skeleton and the user. These experimental results show
that the exoskeleton can lower lumbar compression by
reducing the need for muscular activity in the spine.
Furthermore, powering both HFE and HAA can effectively
reduce the lumbar spinal loading user experience when
lifting and lowering objects while in a twisted posture.
Emergence of a Powered Lower-Back Exoskeleton
Manual material handling involves the actions of lifting, lowering, and carrying heavy materials in industrial environments. Lifting and lowering actions can significantly load the
lumbar spine and increase an individual's risk of lower-back
injury [1]. Work-related injuries increase industrial costs and,
more importantly, have a severe impact on a worker's quality
of life [1]. There has been increasing research interest in the
use of a wearable, powered exoskeleton to provide back support and reduce a user's risk of musculoskeletal injuries commonly resulting from material handling. Most existing
back-support exoskeletons exert assistive forces between the
torso and thighs to reduce muscular activity at the lower back
and spinal loads to reduce the associated risk of injury [2].
Various exoskeleton prototypes have been developed for
back support or load-carrying assistance, such as the Mk2
[2]-[5], PLAD [6]-[8], WSAD [9], backX [29], HAL Lumber
Support [10], Power Assist Suit [30], Atoun Model A [31],
HuMan [32], Axo-Suit [33], and Hyundai H-WEX 2 backsupport exoskeleton for lift assistance [1]. The wearable exoskeleton design by Naruse et al. [11] can deliver an assistive
force sufficient to lift 60 kg. Naruse et al. also demonstrated
that this exoskeleton could considerably reduce the compression forces on the user's lower back as calculated by a simplified biomechanical model [1]. Kobayashi et al. developed a
wearable, pneumatic exoskeleton to assist users carrying loads
up to 30 kg [1]. A recent study by researchers at the University of California (UC), Berkeley, and UC, San Francisco,
showed a 60% average reduction in electromyography (EMG)
signals (i.e., muscle activations) at four of the most injuryprone lower-back muscle groups [1]. Electrodes were placed
over four erector spinae muscle groups for eight test subjects,
both wearing and not wearing the backX [29]. Not only do
exoskeletons allow users to reduce their muscle activity; they
also effectively reduce lumber compression in industrial handling activities, according to biomechanics modeling and
analysis studies [12]-[14].
Commercial exoskeletons used for back support usually
have powered hip joints that move in the sagittal plane. One
limitation of the current back-support exoskeletons is that
they do not provide back support in the frontal plane. A biomechanics study showed that individuals activate their gluteal
muscles, which support HAA during lifting tasks, to maintain
their balance and avoid twisting during asymmetric lifting
of heavy objects [8]. Furthermore, asymmetric lifting and
lowering actions are important factors in the incidence of
lower-back pain and can cause prolapsed discs [15]. When
individuals combine forward bending and lateral bending of
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IEEE ROBOTICS & AUTOMATION MAGAZINE

june 2018

their torso, the risk of work-related back injuries increases due
to compressive forces exerted on the facet joints [16]. Based
on epidemiological data, Snook et al. [17] showed that 33% of
costs incurred by companies related to workers' lower-back
pain is due to twisting and turning. A worker is usually instructed to avoid asymmetric lifting of heavy objects in the
workplace to reduce lumbar spinal loading. However, it has
been documented that losing symmetry during lifting and
lowering tasks is more likely to occur, which may result in
high loads on a worker's lumbar spine that can cause the
worker's trunk to twist [1]. Thus, a lower-back exoskeleton
with both sagittal and frontal plane back support is urgently
needed to effectively reduce an individual's lumbar spinal
loads due to twisting or losing symmetry while lifting and
lowering heavy objects.
Recently, soft exoskeletons [18] have received research
interest because, in contrast to traditional rigid exoskeletons
with unbending support frames, they can be worn like clothing. Soft materials, such as textiles and elastomers, are used in
the fabrication of soft exoskeletons, unlike the materials used
in traditional rigid exoskeletons. However, to date, soft wearable exoskeletons have presented their own inherent limitations, such as an absence of weight-support functionality
[19]. Given the current state of robotic technology, the implementation of a robotic lower-limb exoskeleton capable of
biological levels of joint torque and velocity will likely introduce nonnegligible mass, rotational inertia, and possibly
joint friction [20].
Safety is always the most important concern when it
comes to the physical human-robot interaction of wearable
lower-back exoskeletons; therefore, compliant actuators are
preferred for exoskeletons. SEAs have been widely used in
robotics because they offer a range of advantages over rigid
actuators. SEAs have the ability to deform and take on various
shapes, increasing adaptability and high-precision force control for enhanced user safety [21].
Building on previous research, this article presents a highpower, passively mechanical, and software-controlled actively
compliant lower-back augmentation exoskeleton with four
degrees of freedom that can assist in industrial material handling tasks. Our exoskeleton includes powered HAA and
HFE. Each actuation unit includes a modular and compact
SEA with a high torque-to-weight ratio. The unit provides
mechanical compliance at the interface between the exoskeleton and the user to ensure user safety.
Exoskeleton Design
Structure
We developed a wearable exoskeleton to assist industrial
workers when they lift and lower goods. The mechanical
design of the powered lower-back exoskeleton is illustrated in
Figure 1. It consists of three modules: the torso module, the
powered hip exoskeleton, and the support leg. The articulation of the powered hip exoskeleton is achieved with four single-axis revolute joints: one for each HFE joint, mounted on

IEEE Robotics & Automation Magazine - June 2018

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