A Novel Metamorphic Foot Mechanism With Toe Joints Based on Spring-Loaded Linkages

The toe joints play an important role in human walking and running movement patterns. In this letter, we propose a design method for metamorphic foot structures based on spring-loaded linkages to realize metatarsal-toe switching by using the self-recovery and self-stabilization properties of the spring-loaded linkages. We constrain the degrees of freedom (DOFs) of the foot mechanism by using the singular position characteristic of the four-bar mechanism to compensate for the lack of rigidity when the foot mechanism is in the toe line state. In addition, the structural parameters are calculated based on the static analysis method, and the validity of the design method is verified by simulation using Adams software. Finally, the compliance of the metatarsal state and the stability of the toe line state are demonstrated by physical prototyping and experiments. The results show that the novel metamorphic foot mechanism provides a uniform solution to cope with both walking and running movement modes.