Bonding Rigid and Soft Materials Using Flocking

One of the major challenges in the design and construction of soft-rigid hybrid systems is having robust bonding at soft-rigid interfaces. Soft robots tend to be compliant and adaptive but weak, while rigid robots tend to be strong and precise but uncompromising. Soft-rigid hybrid systems can provide a blend of both compliant interactions with environments as well as fast and precise body position controls. In this paper, we propose a fabrication strategy using flocking to achieve strong bonding between soft and rigid parts. Flocking is a fabrication method that bonds short fibers to fabrics or plastics. The fibers create a fuzzy surface texture on rigid components, which increases the surface area. In the context of soft robotic molding, flocked surface texture increases mechanical bonding between soft and rigid components and enables incorporation of rigid components with increased complexity or challenging placement that could be overmolded but not glued. In this paper, we investigate design parameters for flocking such as substrate materials, adhesives, and flocking materials; we recommend design and fabrication guidelines for the use of flocking to incorporate printed ABS and PLA components in silicone. To demonstrate the utility of flocking in a range of soft systems, we have fabricated several example soft systems with integrated components, including a pneumatic network (pneu-net) actuator, soft chambers connected to semi-rigid tubing, and a sensorized soft actuator. The performance of these demonstrations was comparable or exceeded that of silicone glues and allows for direct overmolding of complex structures, making flocking applicable and versatile in soft-rigid hybrid systems.