Structural optimization of variable stiffness mechanism with particle jamming and core-frame

Abstract

As a collaboration between humans and robots becomes critical, stiffness control of the robot is essential for stability and efficiency of work. Therefore, research on the variable stiffness mechanism is being actively conducted in service robots, soft robots, and exoskeletons. The main types of variable stiffness mechanisms are jamming effect (particle jamming and layer jamming), shape memory polymer (SMP), and low melting point alloy (LMPA). The case of the jamming effect uses negative pneumatic pressure to change the stiffness. Because of that, it is possible to change the stiffness quickly, and it is easy to manufacture. However, both SMP and LMPA use thermal energy to increase the material’s stiffness. There is a risk of damage to humans or robots, and it takes much time to change the stiffness. Therefore, this study introduces a variable stiffness mechanism that combines particle jamming and core-frame. In addition, optimization studies are being conducted to use the jamming effect in industries. However, due to the randomness of particle jamming, the existing studies assumed that the variable stiffness mechanism was a simple beam or modeled it using hook’s law, so the accuracy was low. Therefore, in this study, five design variables are selected for particle and core-frame, the main elements constituting the variable stiffness mechanism. In addition, design variables are optimized through various FEM simulations. Furthermore, the simulation is proved by establishing a theoretical model for variable stiffness structure when the jamming effect occurs. Finally, the optimization of five design variables is proved through experiments.