Design of a Clutch–Spring Knee Exoskeleton for Running

Abstract

Because the leg is known to exhibit springlike behavior during the stance phase of running, several exoskeletons have attempted to place external springs in parallel with some or all of the leg during stance, but these designs have failed to permit natural kinematics during swing. To this end, a parallel-elastic exoskeleton is presented that introduces a clutch to disengage the parallel leg-spring and thereby not constrain swing-phase movements of the biological leg. A custom interference clutch with integrated planetary gear transmission, made necessary by the requirement for high holding torque but low mass, is presented and shown to withstand up to 190 N·m at 1.8 deg resolution with a mass of only 710 g. A suitable control strategy for locking the clutch at peak knee extension is also presented, where only an onboard rate gyroscope and exoskeletal joint encoder are employed as sensory inputs. Exoskeletal electromechanics, sensing, and control are shown to achieve design critieria necessary to emulate biological knee stiffness behaviors in running.

A Wearable Sensory Textile‐Based Clutch with High Blocking Force

“…Considering that clutches are normally serially coupled with elastic bands, the same configuration was proposed (Figure 6a), [3,13,21] and the STBC was worn as a knee clutch (see Video S1, Supporting Information). Considering that clutches are normally serially coupled with elastic bands, the same configuration was proposed (Figure 6a), [3,13,21] and the STBC was worn as a knee clutch (see Video S1, Supporting Information).…”

“…[3,4,8,11] In such unpowered devices, a combination of clutches and elastic elements enables energy storage from human motions (engaged mode) and its release (disengaged mode) at desired moments. [12][13][14] The challenge is to replace natural metabolic sources with solutions that can be comfortably donned, worn, and doffed while making the human body more efficient during movements. Indeed, in unpowered exoskeletons, conventional clutches are still bulky and heavy, thereby affecting their wearability.…”

“…[12][13][14] The challenge is to replace natural metabolic sources with solutions that can be comfortably donned, worn, and doffed while making the human body more efficient during movements. [13] Electrorheological and magnetorheological fluids have been successfully used for designing new classes of clutches, due to the low number of mechanical components needed and for the possibility to tune the withstanding of forces because of their analog behavior in response to electric and magnetic fields. [15,16] In particular, important advancements in wearable clutches were achieved.…”

Clutched Elastic Actuators

“…Type 2C-3S CEAs have been applied both in parallel to a motor [21][22][23][24] and without a motor [25][26][27][28][29][30][31][32]. There are four studies with a completely different implementation of this type of CEA.…”

Interaction Force Modeling for Joint Misalignment Minimization Toward Bio-Inspired Knee Exoskeleton Design

“…(a) A representative knee exoskeleton developed by Herr et al[11], (b) The computational model of the human-exoskeleton interaction. The red cylinder with an ellipsoid end (femoral condyle) and gray cylinder represent femur and tibia respectively.…”