Robotic Fly Trap

The robot has a bi-stable unsymmetrical laminated carbon fiber reinforced prepreg (CFRP) structure, which has a bi-stable mechanism  similar to the Venus flytrap.

The robot has shape memory alloy springs which can be triggered to snap through. The leaves close in about 100ms; almost the same speed as that of the Venus flytrap.  

Design

The leaf of the flytrap robot is a cross-ply bi-stable CFRP structure, and the triggering actuator is an SMA spring actuator. The shape of the artificial leaf mimics that of the flytrap leaf, which has  different radii of curvature in two stable states. To close and open the artificial leaf, actuation has to generate a curvature change. 

The leaf of the flytrap has different curvatures at different stable shapes. When the leaf is open, its shape is almost flat; when the leaf is closed, the shape is dome-like. 

The flytrap robot has three components:

• Two bistable CFRP leaves
• Two SMA coil springs at each leaf 
• A supporter that holds the leaf. 

The center part of the straight edge of the artificial leaf with a large curvature is mounted on top of the supporter, which acts like the midrib ofthe flytrap, and two mounted leaves are opposite each other. The SMA wire and MFC actuator of the previous common unbending actuation generate a small deformation.

CFRP  

The bistability of the asymmetric CFRP laminate is based on the directional characteristics of CFRP ply. A single CFRP ply consists of unidirectional carbon fibers and epoxy resin. The tensile modulus of the CFRP ply is about ten times higher in the carbon fiber’s axial direction than in the fiber’s lateral direction because the modulus in the lateral direction depends only on the adhesion of the resin matrix between fibers. Thermal expansion of the CFRP has directional features. The coefficient of thermal expansion (CTE) in the lateral direction is about one hundred times thatin the fiber’s axial direction.