Journal Published Online: 07 March 2022
Volume 50, Issue 5

New Optimized Mechanism for Linking a Hydraulic Actuator to the Elbow Joint of an Upper Arm Exoskeleton



Many occupational activities require heavy load lifting. The presented upper limb exoskeleton provides support for such lifting processes. Actuation is performed by a hydraulic system. Hydraulics is selected because of its unrivaled force density to satisfy the central demands on exoskeletons for a high wearing comfort: low weight and small distance to the body. The demand for high wearing comfort requires a slim construction beside the arm where the hydraulic actuator is integrated. The hydraulic power is transferred from the power unit at the back to the differential cylinder beside the limb. Through the novel mechanism, a compact transfer of the linear cylinder motion to a rotary joint motion is enabled, and a lightweight construction is possible. The hydraulic cylinder is connected to a crank on the exoskeleton arm, and the piston rod hinge of the cylinder guides along a line at the upper arm and is connected via a connection rod to a second crank, which is also part of the lower arm. This system of kinematics achieves a low crank length, which is a major compactness requirement. The optimized kinematic structure defines the basic architectural structure on which the full exoskeleton construction is developed. The supply of the hydraulic cylinder is connected by hoses to the components placed in the backpack. The electro-hydraulic actuator consists of a speed variable electric motor and a constant displacement pump, which generates the cylinder pressure. A low-pressure accumulator and pressure sensors are connected to the closed hydraulic circuit. Only the elbow motion is supported by an actuator; the other exoskeleton joints are passive and transmit parts of the load to the backpack frame. Motion control is done by the wearer. The measured electromyography sensor signal is adjusted by desired percentage, and the control system generates a proportional torque on the elbow joint.

Author Information

Holl, Eva
Institute of Machine Design and Hydraulic Drives, Johannes Kepler University, Linz, Austria
Pages: 10
Price: $25.00
Reprints and Permissions
Reprints and copyright permissions can be requested through the
Copyright Clearance Center
Stock #: JTE20210677
ISSN: 0090-3973
DOI: 10.1520/JTE20210677