Abstract.
BACKGROUND: When using upper limb exoskeletons that assist the movement of physically weak people, safety should be the most important index.
OBJECTIVE: In this paper, a passively safe, cable-driven upper limb exoskeleton with parallel actuated joints, which perfectly mimics human motions, is proposed.
METHODS: Compared with the existing upper limb exoskeletons which are mostly designed only considering the realization of functional properties, and having poor wearabity, a passively safe prototype for motion assistance based on human anatomy structure has been developed in our design. This design is based on the prior exoskeleton structure with the adoption of a gravity balanced device.
RESULTS AND CONCLUSION: The gravity balanced mechanism was confirmed in theory and simulation, showing it has a positive effect on balance.
1. Introduction
Upper limb movement dysfunction caused by stroke and other diseases are more and more in the current society, and commensurately emerging out of a variety of upper limb rehabilitation exoskeleton. For a human-machine interactive system, a patient-friendly mechanism is acquired and safety should be the most important indicator of the design. Also it does not need extra actuated power in a fully passive system. This paper presents a passively safe cable driven upper limb exoskeleton. With adding a gravity balanced mechanism which composes a parallelogram linkage mechanism, pulleys and springs to the improved exoskeleton, the final structure can be achieved. The final exoskeleton can be a safe and low energy consumption mechanism. At the first time, a prototype 6-DOF exoskeleton with parallel actuated joints for motion assistance based on human anatomy structure is developed. It adopted a differential gear mechanism, and with large movement space and big stiffness [1]. There are many advantages in using cables: no backlash, no slippage, no lubrication, high efficiency, no speed limits and torque limited only by strength of cables. Due to the advantages of cable driven manipulators the gear driven mechanism was changed [2,3]. The later research is inspired by many related studies. John and Jessica developed a passively safe and gravitycounterbalanced anthropomorphic robot arm. In the design, a novel differential mechanism was adopt to counter balance the upper arm, motors and counterweights were located remotely to realize a better packaging and mass distribution [4]. Agrawal et al. presented a leg orthosis with passive gravity-balancing mechanism, achieved its performance evaluation on the walking experiment, and they believed the orthosis can be a potential rehabilitation device for individuals with severe muscle weakness [5]. They did some further researches related gravity-balancing, the principle involved in the mechanism can solve the planar and spatial balance problem with links, pulleys and springs. There is a premise of the establishment of the principle for example: the center of mass is on an end point of the auxiliary parallelogram mechanism [6,7]. Smith et al. presented a perfect balance system for active upper-extremity exoskeletons, and it adopted the principle of WREX which is a 4-dof orthosis that was designed by Tariq Rahman and Whitney Sample, et al. WREX can achieve gravity balance by utilizing rubber bands [8–10]. Safety is an important issue which can’t be ignored in the design of exoskeleton. It is hard to find the perfect solution in the existing exoskeletons. Compared with the design mentioned above, the rationale for the gravity balanced mechanism we designed and the mechanism used are more simple and easy to fulfill. It is an effective method to solve the spatial balance problem.
TBI Rehabilitation 