To allow versatile manipulation of soft robots made of compliant materials with limited force transmission, variable stiffness has been actively developed, which has become one of the most important factors in soft robotics. Variable stiffness is usually achieved by a jamming mechanism using layers, granules, or chain structures, through vacuum pressure or cable-driven mechanism due to its simple and rapid actuation. However, such jamming mechanisms are not suitable for actual robotic applications that require large supporting forces or drastic changes in stiffness. In this article, a hybrid jamming structure that combines granules and a rigid chain structure is proposed to simultaneously increase the average stiffness change in all directions and the maximum force in a certain direction. The improved performance of the proposed structure was compared to that of conventional granular and chain jamming structures. Based on the analytical model of the proposed structure, the principles for designing the hybrid jamming structure were derived and experimentally verified. Finally, based on the hybrid jamming structures, a multilink hybrid jamming structure was developed as a wearable system to assist the upper limbs and a robotic arm structure.
Keywords: jamming structure; soft interaction; soft manipulation; variable stiffness structure; wearable system.