Body Weight Support System for LOPES2

LOPES2 (LOwer-extremity Powered ExoSkeleton) is a robotic device for gait training and assessment of motor function in stroke survivors. Large forces applied by LOPES2 are experienced as uncomfortable by the patient, affecting rehabilitation efficiency. A Body Weight Support System (BWSS) is therefore required for unloading the lower extremities in patients who are unable to carry their own body weight. A previous design of a BWSS for LOPES2 was unsuccessful. The goal of this project is to propose a simpler, less costly and more appropriate redesign. The most important user requirements are easy patient (un)mounting from and to a wheelchair, adjustable support force which is constant during operation and a mechanism which prevents the patient from falling. The problem is subdivided into functionalities, being a constant force source, a transmission, allowing horizontal movement, falling security and adjustment of height and force. Solutions for these functionalities are analysed theoretically, after which a concept-design is proposed. Prototypes will be built for the constant force source and the transmission. A non-circular pulley is chosen as a constant force source, while a lever-transmission is used as transmission. A small-scale prototype showed adjustable constant force behaviour, but with a peak error of 8% in an extreme situation. Horizontal movement is made possible with the use of a series hinge-linear guidance. The operator can adjust the operation height with an electrical worm-drive winch. This winch, combined with mechanical falling endstops, can be used as an elevator to quickly mount and unmount patients.