The role of pre-tensioned springs in 3 pneumatic artificial muscles driven joint mechanisms with sliding mode controllers

During the past decade, soft robotics has become a growing new field, and researchers have developed different kinds of soft robots with different actuation technologies and mechanisms. Pneumatic artificial muscles (PAMs), as one kind of the most popular soft actuators, have been widely applied to robotic systems that assist persons. However, PAMs are highly nonlinear, which makes it difficult to achieve accurate force and motion control. Another major problem is their slow response. Efforts have been made to improve the accuracy and responses of PAMs. Adding pre-tensioned springs is one efficient way to improve responses of mechatronic systems. However, the role of pre-tensioned springs in different PAMs-driven mechanical structures has not been sufficiently investigated. In this study, two joint structures combining pre-tensioned springs and PAMs were modeled and their sliding mode controllers (SMC) were designed. The control results were compared with canonical antagonistic PAMs structure in simulation experiments. Moreover, a one-joint prototype actuated by 3 PAMs connected in series with two series-connected springs, was built and used to validate the simulated model. The results with both simulation models and the prototype mechanism showed that, one of joint structure with pre-tensioned springs could achieve better step response and control accuracy than the canonical antagonistic PAMs structure.

Recommended citation: Zhou, Zhongchao, Yuanyuan Wang, and Wenwei Yu. "The role of pre-tensioned springs in 3 pneumatic artificial muscles driven joint mechanisms with sliding mode controllers." Robotics and Autonomous Systems 151 (2022): 104017.
Download Paper | Download Slides