Gravity-Balancing of Elastic Articulated-Cable Leg-Orthosis Emulator. (January 2019) - Alamdari, Aliakbar
Highlights: We propose multiple design candidates for leg exoskeleton to reduce or eliminate the leg weight during gait training, including: Perfect static balancing of leg using parallelogram and zero-free-length springs, Perfect static balancing of leg with four-bar mechanism and zero free-length springs, Leg exoskeleton with fixed four-bar based mechanism, Leg exoskeleton with reconfigurable four-bar mechanism, Approximate static balancing of leg with non-zero-free-length springs, We examined variant four-bar based mechanisms for leg exoskeleton and presented a general framework and methodology for their static balancing and kinetostatic design optimization for planar motion tasks, We demonstrate the compensation of these static torques at the joints caused by gravity yields a significant reduction of the torque requirement, and we can achieve an efficient design with smaller actuators. Abstract: In this paper, we propose static-balancing mechanisms to permit perfect and approximate compensation of gravitational loads for an articulated-cable leg-orthoses. Such gravity-compensation of loads (arising from both user's leg as well as attached orthosis) can significantly improve the transparency and performance of the rehabilitation exoskeletons for gait training. The direct application of traditional static balancing methodologies (e.g. adding balancing weights or even auxiliary linkages) places a very restrictive set of conditions for mass, inertial and geometric parameters to achieve balancing for all leg postures in the configuration space. Greater design freedom and flexibility to achieve balancing conditions can be obtained by coupling semi-active elastic elements (such as coil and torsion springs) together with linkages. The effectiveness of this approach is demonstrated on a scaled physical leg-orthosis emulator in terms of significant reduction of actuation to realize the gravity-compensation.