Improvement and Analysis of Cam-Follower Mechanism for a Passive Parallel Lower Limb Exoskeleton

This research projects revolves around the improvement and analysis of a novel cam-follower mechanism for a passive parallel lower limb exoskeleton. The research objectives of this project is to determine the effectiveness of the cam-follower mechanism in matching the natural walking gait of the user and to determine the effectiveness of the mechanism in reducing the energy usage of the user while using the exoskeleton. The scope of the project only discusses on specific design of exoskeleton system, in which this project scopes revolves around the study
of full passive system which are completely void of external power supplies and focuses on parallel lower limb exoskeletons which are fully passive. The cam-follower mechanism draws inspiration from the retractable pen mechanism. The research was aided with the prototype of the leg unit of the exoskeleton that had been fabricated prior to this research project by the previous project holder. Through this research, it was found that the cam-follower mechanism is not suitable to be implemented into a passive parallel exoskeleton system. Through
bodystorming and physical testing, the mechanism forces the user to walk with an unnatural walking gait which causes the user to bend below the neutral centre of gravity a few times during a complete cycle besides causing the user to rock side to side in an unstable manner throughout the entire walking gait cycle. At certain positions of the walking gait, the user would have to exert more force to allow the components to rotate and function properly. Throughout the walking gait, the energy calculated during each sequence of the cam-follower mechanism was different. At sequence 1 to 2, the user has to compress approximately 0.22281 J to push the
ridged bushing far enough for it slide into its locked position in the cam profile. At sequence 2 to 3, the spring would push the ridge bushing into the cam profile at 0.00988 J while locking itself as well. At sequence 3 to 4, the user has to compress 0.06172 J worth of energy to push the ridges bushing out of the cam profile for it to be free to slide in which upon completion of compression, the spring will extend and push out with approximately 0.38575 J worth of energy to extend to its free length back at sequence 4 to 1. While the flow of energy in theory is correct, the energy given out by the spring in sequence 2 to 3 is not sufficient and the user faces strain
from insufficient energy and needs to se energy and effort from self to keep the body upright.