3 research outputs found
Josef v. Karabacek's letter to Ignaz Goldziher
The cyclic and often linear torque-angle
relationship of locomotion presents the opportunity to innovate
on the design of traditional series-elastic actuators (SEAs). In
this paper, a novel modification to the SEA architecture was
proposed by adding a clutch in parallel with the motor within
the SEA—denoted as a CSEA. This addition permits bimodal
dynamics where the system is characterized by an SEA when
the clutch is disengaged and a passive spring when the clutch is
engaged. The purpose of the parallel clutch was to provide the
ability to store energy in a tuned series spring, while requiring
only reactionary torque from the clutch. Thus, when the clutch
is engaged, a tuned elastic relationship can be achieved with
minimal electrical energy consumption. The state-based model
of the CSEA is introduced and the implementation of the
CSEA mechanism in a powered knee prosthesis is detailed. The
series elasticity was optimized to fit the spring-like torqueangle
relationship of early stance phase knee flexion and
extension during level ground walking. In simulation, the
CSEA knee required 70% less electrical energy than a
traditional SEA. Future work will focus on the mechanical
implementation of the CSEA knee and an empirical
demonstration of reduced electrical energy consumption
during walking.United States. Dept. of Defense (National Defense Science and Engineering Graduate Fellowship Award 1122374
A Lightweight Soft Exosuit for Gait Assistance
Abstract-In this paper we present a soft lower-extremity robotic exosuit intended to augment normal muscle function in healthy individuals. Compared to previous exoskeletons, the device is ultra-lightweight, resulting in low mechanical impedance and inertia. The exosuit has custom McKibben style pneumatic actuators that can assist the hip, knee and ankle. The actuators attach to the exosuit through a network of soft, inextensible webbing triangulated to attachment points utilizing a novel approach we call the virtual anchor technique. This approach is designed to transfer forces to locations on the body that can best accept load. Pneumatic actuation was chosen for this initial prototype because the McKibben actuators are soft and can be easily driven by an off-board compressor. The exosuit itself (human interface and actuators) had a mass of 3500 g and with peripherals (excluding air supply) is 7144 g. In order to examine the exosuit's performance, a pilot study with one subject was performed which investigated the effect of the ankle plantar-flexion timing on the wearer's hip, knee and ankle joint kinematics and metabolic power when walking. Wearing the suit in a passive unpowered mode had little effect on hip, knee and ankle joint kinematics as compared to baseline walking when not wearing the suit. Engaging the actuators at the ankles at 30% of the gait cycle for 250 ms altered joint kinematics the least and also minimized metabolic power. The subject's average metabolic power was 386.7 W, almost identical to the average power when wearing no suit (381.8 W), and substantially less than walking with the unpowered suit (430.6 W). This preliminary work demonstrates that the exosuit can comfortably transmit joint torques to the user while not restricting mobility and that with further optimization, has the potential to reduce the wearer's metabolic cost during walking