Design of Hybrid Mechanism of a Lower-Limb Knee Exoskeleton for Torque Variation
Abstract - Research on effective lower-limb exoskeletons for knee joints has become an important requirement while the elderly population is growing at a high rate. To maintain independence and good quality of life, lower-limb mobility exoskeletons are expected to play a vital role for elderly people. It is anticipated that these will help the elderly to continue living in their own homes and carry out their daily activities. This research explores important issues in mechanisms design that need to be addressed to achieve the required functionalities of exoskeletons. This research attempted to combine several mechanisms to develop a novel hybrid mechanism, comprising a four-bar chain for poly-centricity and a scotch yoke for motion reversal. These could be useful as generic components in assistive exoskeletons which are envisaged to be in high demand in the future. The proposed new mechanism is coupled with a continuously variable transmission (CVT) element, which helps adjust the torque as required to perform various motions by different users with varying anthropological dimensions. This means that an exoskeleton that incorporates the new hybrid mechanism can provide the required level of assistance for a range of wearers that have different height, weight, build, and posture. The mathematical and geometrical modeling of the overall human and exoskeleton systems has been carried out using Pro/Engineer and MATLAB/Simulink software. For validation of the results, data of a standard gait cycle has been used to help determine the limits of angle covered by the knee joint during a walking cycle. The limiting value of torque is validated by the data obtained from the work carried out within the AAL Call 4 EXO-LEGS project.
Keywords - CVT-gearbox, Four-bar mechanism, Lower-limb Exoskeletons, Scotch-yoke Mechanism, Wearable Robots