An Actively Controlled Variable Stiffness Structure via Layer Jamming and Pneumatic Actuation

Current robotics industry trends show an increased interest in the interaction between humans and robots in a variety of fields, ranging from collaborative robots in manufacturing to assisted medical devices in the medical field. One limiting factor in present applications is the ability to actively morph these robotic structures and control their stiffness using the same type of actuation system. This paper focuses on developing an actively controlled, variable stiffness structure that uses a pneumatic system for both morphing and locking the structure shape. The structure design integrates Pneumatic Artificial Muscles (PAMs) that are pressurized to control shape morphing. The pressurization of the PAM provides a radial force that allows bi-directional morphing based on the pressurization scheme. Layer Jamming, which utilizes varied friction between thin sheets based on pressure, is used to control the variable stiffness of the structure. In this paper, a control model is developed to predict the morphed curvature of the structure based on the input actuator pressure. This experimental control model is also validated using a theoretical pseudo-rigid-body model. The repeatability and accuracy of morphing is also discussed. Through experimental testing, a measure of the stiffness variation range of the structure is also developed. This novel research would positively impact the robotics field by creating lightweight morphing structures that are flexible and easily deformed, but also stiff with high load-carrying capability for increased human-robot interaction.