Soft robot is a new kind of robot with various freedom of movement and good environmental adaptability. However, low stiffness of the soft robot limits its practical carrying capacity. Therefore, it is meaningful to develop variable stiffness technology for soft robot. This paper summarizes the new variable stiffness technology in recent 5 years, introduces and analyzes its working principles including electrostatic adsorption principle, layer interference principle, self-locking origami mechanism, electrical/magnetorheological principle and minimum potential energy principle, variable stiffness performance and practical application. This paper also discusses the challenges for the current variable stiffness technology and the future development direction, and summarizes the potential research value of the new generation of variable stiffness technology.

soft robots  /  variable stiffness  /  origami  /  biomimetics  /  dielectric elastomer