Variable Stiffness Forearm


                                                                            Figure 1  Variable Stiffness Forearm in the assembly of Soft Humanoid Robot

Variable Stiffness forearm is inspired by snake ghonus which can inflate its body became stiffer and protect itself from an enemy.

    Figure 2  Russel’s Viper Snake (ghonus

The Variable Stiffness Forearm is the soft foam part that acts as a forearm to the hand of the soft-robot. It has three Variable Stiffness Links embedded into the PU foam.

                                                                                  Figure 3  Finite Element Analysis of Variable stiffness Forearm in ANSYS.

Each Variable Stiffness Link consists of a silicon rubber pipe covered by fibreglass. When pressurized air is passed across this enclosed link, the silicon rubber pipe will try to expand while the fibreglass will try to constraint the pipe from expanding, Thus making the link stiff after injecting pressurized air. Three such links are the first joint by two PDMS connectors at 120-degree angular difference from the Centre of the connector. This assembly is now to be embedded into PU foam. Thus a 3D printed mold enclosure was designed to pour in the foam solution as shown in the figure. The inner surface of the mold was covered by sealing tape to obtain a foam skin and thus the PU foam cast Variable Stiffness Forearm was manufactured.

The first manufactured iteration had square connectors whereas the second iteration contained modified circular connectors.

Figure 4 Variable stiffness links assembly in forearm mold

Figure  5Variable Stiffness Link

   Figure 6 Variable Stiffness Forearm with Square and Circular end Connectors