Design, Development and Characterization of a Wrap Spring Clutch/Brake Mechanism as a Knee Joint for a Hybrid Exoskeleton

Subra Mani, Vishnu Aishwaryan

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Design, Development and Characterization of a Wrap Spring Clutch/Brake Mechanism as a Knee Joint for a Hybrid Exoskeleton

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Evolution had played a significant role in structuring on how humans stand, walk or run. The nervous system plays a major role in the control of locomotion and injuries to the system can lead to gait abnormalities or disabilities. A Spinal Cord Injury (SCI) causes lack of signal communication between the central nervous system and the muscle fibers leading to deprived or no activation of the muscles thus resulting in paraplegia or quadriplegia.\r\rOver the past decade wearable robotics and exoskeletons have been gaining outstanding recognition in the field of medical, assistive and augmentative robotics and have led to numerous new innovative mechanisms in the mechanical engineering field. Due to fast paced research activities, the critical importance and performance of mechanisms such as wrap spring clutch/brake,Wafer Disc brakes are overlooked or used ineffectively. So, researchers tend to create new actuators from scratch and have limited their use of previously available resources, which has prevented us to explore the potential of these devices.The research presented focuses on developing a mechanism (“A Wrap Spring Clutch/Brake Mechanism”) from scratch using a trade study approach. This thesis addresses the fundamental relationship between coefficient of friction, interference, spring diameter and the holding torque of the mechanism using analytical, testing and simulation results. The human biomechanical data during ground level walking was used as design targets to develop the mathematical model of the system. Data from the testing stated that these targeted goals have been achieved by the design. This mechanism is used as a Knee Joint for the Hybrid EXoskeleton (HEX) GEN-1 project which is developed at the Automation and Interventional Medicine (AIM) Robotics Research Laboratory to rehabilitate the SCI.

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