Synthesis of a six-link mechanism for generating the ankle motion trajectory using shadow robot control method

Document Type : Research Article


1 Biomechatronics and Cognitive Engineering Research Lab, School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran

2 Department of Mechanical Engineering, Shahid Beheshti University, Tehran, Iran


In this paper, a one degree of freedom (1 DOF) Stephenson type III mechanism is synthesized to generate the human ankle gait trajectory by considering prescribed timing. The produced trajectory must be consistent with the natural motion of the human foot in terms of position and timing. In this regard, we used the robust and effective shadow robot algorithm that synthesizes the mechanism’s dimensions and considers prescribed timing, which is a crucial topic in gait rehabilitation devices. In this method, a mechanism with multiple fixed links is replaced by a hypothetical equivalent shadow robot with several degrees of freedom. Then, optimizing a suitable controller for the shadow robot leads to finding optimal mechanism dimensions. Afterward, the adjustability of this mechanism for generating other similar ankle gait trajectories is shown. Adjustability has been accomplished through the little change in the crank and coupler link sizes. The optimized mechanism generates ankle movement for different people with different leg lengths and has the least spatial and timing error. The reasonable error confirms the usage of the mechanism in gait rehabilitation devices.


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