Design and Control of a Soft Combined Actuator

Soft pneumatic actuators (SPAs) are developing rapidly in the fields of human-robot interaction and cooperation, owing to their flexiblility, light weight and safety. They will neither cause harm to human nor break themselves. The main hurdles in application of SPAs are their poor load capability and motion accuracy. Because of the inherent compliance of the materials and structures, they are not able to ensure enough strength, i.e. heavy loads can’t be supported. Even light load will give rise to the considerable deformation, which severely affects their precision. Here, a novel soft actuator is proposed, with the capability of bearing the load heavier than itself, thanks to its variable stiffness structure. When working with heavy load, its movement accuracy can still be guaranteed. Meanwhile, since high nonlinearity exists in the working process of most SPAs, approximate models or finite element analysis should be used to obtain the solution. For our actuator, by contrast, the closedform analytical solutions can be got for the forward and inverse kinematics, making it more stable and reliable. We tested the variable-stiffness characteristics and motion accuracy, the mean error of our actuator is less than 10 mm with different weights, thus it holds prospects for a wide variety of applications.