IEEE Robotics & Automation Magazine - September 2022 - 37

The robot refers to the multimodal sensory data and then
intelligently recognizes the gait of the patient to output
proper assistance at different joints. Specifically, the encoders
are used to measure the flexion/extension of the robot's
joints, the inertial measurement units are used to measure
the angle of the lower limb and the acceleration information,
and the pressure sensors embedded in both shoes are
used to inspect the contact status.
Interaction Mode
BEAR-H provides three rehabilitation modes, i.e., weight
support, training, and intelligent interaction. The differences
among multiple modes, summarized in Table 2, are
as follows:
●
Compliant Actuation
Wearing a robotic exoskeleton involves substantial physical
interactions, hence the safety of patients is always the main
concern. Many robotic exoskeletons in the market are driven
with rigid actuators (see Table 1). Although the structure of
rigid actuators is relatively simple, it is unable to provide additional
flexibility for the movement of the human body. More
importantly, as the output force of the rigid actuator is directly
transferred to the robot joint, forces that are too large might
cause physical damage to the human body.
BEAR-H is designed with the deployment of compliant
The weight support mode is designed for early stages of
rehabilitation. Under this mode, the motion at the patient's
healthy side is converted to the trajectory for the disabled
side according to the walking pattern between two legs.
The robot is controlled to track the trajectory to provide
assistance for the disabled side while compensating for the
weight of the healthy side.
●
In the training mode, the robot is controlled to follow a
predefined trajectory to provide assistance for the patient.
The therapist monitors the progress of the training and
adjusts the frequency and level of assistance if necessary.
This mode is designed for patients whose motor functionalities
are partially restored.
●
In the intelligent interaction mode, the level of assistance
and frequency of the robot's trajectory is automatically
adjusted online by monitoring the patient's walking pattern.
This mode is designed for rehabilitation at the recovery
stage, where the patient is able to walk independently
with several abnormal patterns.
These multiple modes can meet the demand of patients
with different backgrounds, and a criterion is also proposed
to identify the patient's degree of severity (see Table 2). Both
the of training and intelligent interaction belong to active
training modes, which is important for pushing the patient to
master the normal and regular gait pattern. For patients with
dyskinesias, active training is even more significant in the
sense that a closed loop is established in the central neural
system to repair the disordered functionality and lead to a
positive long-term training effect.
The following development of this article mainly
focuses on the intelligent interaction mode to specify generation
of the intelligent gait pattern. Note that the initial
frequency of the robot's trajectory in the intelligent interaction
mode is set as 0.3 Hz, and it is progressively scaled
up or down to suit the actual walking frequency of the
patient. When the rate of synchronization is higher than
75%, the corresponding frequency and level of assistance
is displayed in the touch panel. In addition to the aforementioned
modes, BEAR-H also has the ability of customizing
a highly individualized gait according to
specific body parameters, which can better suit patients
with different conditions.
actuators, which makes it safe from a structural point of view.
The compliant actuator is developed by referring to the concept
of series elastic actuator [15], where an elastic element is
installed between the driving motor and the robot joint. This
design has the following attractive features:
●
The elastic property is explored to store the excessive energy
and thus counterbalance too large an impact.
●
The output torque/force can be obtained by simply measuring
the deflection of the elastic element (usually with
the encoders' reading on both ends of the element).
●
The actuator is backdrivable such that a certain level of free
motion is allowed for the patient.
Although various designs of compliant actuators have
been reported in the literature, BEAR-H is the first commercialized
exoskeleton robot (i.e., a medical product with an
official registration) that converts the prototype of compliant
actuators into an actual implementation. The structure of
compliant actuators used in BEAR-H is illustrated in Figure 2.
The motor drives the motion of the rope coiled around a
spool, and the curved spring is then pulled by the rope via a
rotary table, and then the motion is transmitted to the output
rod so as to realize the rotation of the robot joint by the end.
Such a design achieves a balance between the small size, lightweight,
high-density output, and relatively low cost, thus
guaranteeing the actual implementation. Table 3 summarizes
the specifications of the developed compliant actuators.
Gait Synchronization
BEAR-H considers seven phases of the human gait, as listed
in Table 4, and each phase is initiated with a gait event. The
seven phases of healthy subjects nearly follow the same
Table 2. The interaction modes.
Mode
Weight
Support Training
Degree of
severity
Serious:
without a
complete
gait cycle
Level of
assistance
Purely
passive
following
Moderate: with
a complete
gait cycle but
with abnormal
patterns
Active
assistance by
following the
predefined gait
trajectory
Intelligent Interaction
Mild: with several
complete cycles but
with abnormal patterns
Active assistance with
online synchronization
of patients' gait (with
the optional function of
individualized trajectory)
SEPTEMBER 2022 * IEEE ROBOTICS & AUTOMATION MAGAZINE *
37
IEEE Robotics & Automation Magazine - September 2022

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - September 2022
