A Series Elastic, Compact Differential Mechanism
Differential mechanisms allow the designers of robotic and prosthetic grippers and hands to create devices that require a minimal number of motors in order to grasp a plethora of everyday life objects, leading to light-weight, compact, and low-cost implementations. The working principle of differential mechanisms is simple. They allow the distribution of the forces exerted by a single actuator to multiple outputs (e.g., fingers). This reduction in the number of motors leads to underactuation, which is the use of fewer motors than the available degrees of freedom. But differentials need also to be power-efficient, compact, adaptive, and lightweight. Most of the existing solutions lack at least one of these attributes. In this work, we focus on the design, modeling, and development of a compact, adaptive, series elastic differential. The proposed mechanism consists of four elastic elements connected in series with the four output attachments. The compression of the elastic elements during grasping allows the gripper or hand to conform to the object’s shape. The efficiency of the differential mechanism is experimentally validated using two different types of experiments, measuring: i) the maximum achievable tension load at the outputs, and ii) the maximum achievable compliance of a single output when all other outputs are blocked. The proposed differential has been employed for the development of a gripper and its efficiency has been assessed by executing grasping tasks with several everyday life objects. The device can be easily replicated using additive manufacturing and off-the-shelf materials and is disseminated in an open-source manner.
GitHub project: https://github.com/newdexterity/Differentials