A NOVEL GAIT-INSPIRED FOUR-BAR LOWER LIMB EXOSKELETON TO GUIDE THE WALKING MOVEMENT

Abstract

Background: Walking is a complex process that involves rhythmic movement of lower limb along with the coordination of brain, nerves and muscles. If the coordination is disturbed, gait may be effected or disordered. Therefore, it should be treated effectively and efficiently using assistive devices/exoskeletons. The exoskeletons and assistive devices may be embedded with the linkage and other mechanisms to imitate the behavior of human lower limb. However, these mechanisms are synthesized using the complex conventional procedures. Thus, a new gait-inspired algorithm is proposed in this study for synthesizing a four-bar mechanism for exoskeletons.Methods: This paper presents a design of four-bar linkage for lower limb exoskeleton to support walking. A new gait-inspired algorithm to synthesize four-bar linkage is also proposed which uses two phases of gait, namely, the swing phase and the stance phase, for lower limb exoskeleton. The trajectory is derived for each phase of the gait and is combined with the optimization techniques. The trajectory passes through 10 precision points in each phase giving a total of 20 precision points for one gait cycle. The optimization is performed in two stages. The first stage deals with the minimization of error between the desired and the generated foot trajectories; whereas, the second stage deals with the minimization of error between the desired and generated hip trajectories of the linkage. Besides the gait-inspired four-bar linkage synthesis, a hybrid teaching-learning-particle-swarm-optimization (HTLPSO) technique is also used to solve the problem.Results: A well-established genetic algorithm (GA) and a new hybrid (HTLPSO) algorithm are used to compare the results of the tracking error of the linkage. It is found that the HTLPSO optimization algorithm performs better in comparison to GA for the problem considered here. Finally, a solid model of the proposed design for lower limb exoskeleton is presented. Moreover, the obtained linkage tracks all the prescribed points accurately and the simulation of designed linkage has been demonstrated using stick diagram for one gait cycle.Conclusion: The proposed method has simplified the synthesis procedure to a great extent, and a feasible design is obtained using the optimization algorithm. The mechanism obtained using the proposed method can walk smoothly which is validated through stick diagram. The proposed mechanism can be used for exoskeleton, assistive devices, bipeds etc. Moreover, the proposed method may be extended to six- and eight-bar mechanisms.