3 research outputs found
Virtual Physical Coupling of Two Lower-Limb Exoskeletons
Physical interaction between individuals plays an important role in human
motor learning and performance during shared tasks. Using robotic devices,
researchers have studied the effects of dyadic haptic interaction mostly
focusing on the upper-limb. Developing infrastructure that enables physical
interactions between multiple individuals' lower limbs can extend the previous
work and facilitate investigation of new dyadic lower-limb rehabilitation
schemes.
We designed a system to render haptic interactions between two users while
they walk in multi-joint lower-limb exoskeletons. Specifically, we developed an
infrastructure where desired interaction torques are commanded to the
individual lower-limb exoskeletons based on the users' kinematics and the
properties of the virtual coupling. In this pilot study, we demonstrated the
capacity of the platform to render different haptic properties (e.g., soft and
hard), different haptic connection types (e.g., bidirectional and
unidirectional), and connections expressed in joint space and in task space.
With haptic connection, dyads generated synchronized movement, and the
difference between joint angles decreased as the virtual stiffness increased.
This is the first study where multi-joint dyadic haptic interactions are
created between lower-limb exoskeletons. This platform will be used to
investigate effects of haptic interaction on motor learning and task
performance during walking, a complex and meaningful task for gait
rehabilitation.Comment: 6 pages, 9 figures, accepted at 2023 IEEE International Conference on
Rehabilitation Robotics (ICORR
Exoskeleton-Mediated Physical Human-Human Interaction for a Sit-to-Stand Rehabilitation Task
Sit-to-Stand (StS) is a fundamental daily activity that can be challenging
for stroke survivors due to strength, motor control, and proprioception
deficits in their lower limbs. Existing therapies involve repetitive StS
exercises, but these can be physically demanding for therapists while assistive
devices may limit patient participation and hinder motor learning. To address
these challenges, this work proposes the use of two lower-limb exoskeletons to
mediate physical interaction between therapists and patients during a StS
rehabilitative task. This approach offers several advantages, including
improved therapist-patient interaction, safety enforcement, and performance
quantification. The whole body control of the two exoskeletons transmits online
feedback between the two users, but at the same time assists in movement and
ensures balance, and thus helping subjects with greater difficulty. In this
study we present the architecture of the framework, presenting and discussing
some technical choices made in the design.Comment: 7 pages, 6 figures, submitted to 2024 IEEE The International
Conference on Robotics and Automation (ICRA
Haptic Transparency and Interaction Force Control for a Lower-Limb Exoskeleton
Controlling the interaction forces between a human and an exoskeleton is
crucial for providing transparency or adjusting assistance or resistance
levels. However, it is an open problem to control the interaction forces of
lower-limb exoskeletons designed for unrestricted overground walking. For these
types of exoskeletons, it is challenging to implement force/torque sensors at
every contact between the user and the exoskeleton for direct force
measurement. Moreover, it is important to compensate for the exoskeleton's
whole-body gravitational and dynamical forces, especially for heavy lower-limb
exoskeletons. Previous works either simplified the dynamic model by treating
the legs as independent double pendulums, or they did not close the loop with
interaction force feedback.
The proposed whole-exoskeleton closed-loop compensation (WECC) method
calculates the interaction torques during the complete gait cycle by using
whole-body dynamics and joint torque measurements on a hip-knee exoskeleton.
Furthermore, it uses a constrained optimization scheme to track desired
interaction torques in a closed loop while considering physical and safety
constraints. We evaluated the haptic transparency and dynamic interaction
torque tracking of WECC control on three subjects. We also compared the
performance of WECC with a controller based on a simplified dynamic model and a
passive version of the exoskeleton. The WECC controller results in a
consistently low absolute interaction torque error during the whole gait cycle
for both zero and nonzero desired interaction torques. In contrast, the
simplified controller yields poor performance in tracking desired interaction
torques during the stance phase.Comment: 17 pages, 12 figure