Soft robotic fabric gripper with gecko adhesion and variable stiffness

Fluid-driven soft grippers possess conformable grasping characteristics that differ from their rigid counterparts. Despite advances, their inherent low-stiffness due to constituent materials causes them to be inferior in many high-load applications. Existing fabrication methods of soft grippers that mostly rely on molding silicone elastomers, despite being simple, are not easily scalable. This article presents the design of a soft robotic fabric gripper that can be fabricated by a facile and highly scalable process of apparel engineering. The proposed robotic gripper features a multi-fingered design that comprises hydraulic-driven, sheet-shaped fabric bending actuators. Its performance is enhanced by incorporating a bio-inspired gecko adhesive and a thermo-responsive variable stiffness filament. Experimental studies demonstrate that adding the variable stiffness filament and gecko adhesive improves the holding force of the gripper up to 655 % and 507 % in the gripping and pull-out configurations, respectively. The variable stiffness filament features a relatively good cooling speed of only 31 s by ambient cooling. A simple analytical model was also developed to characterize the deformation of the fabric bending actuators. To monitor the gripper bending motion, a new soft fabric sensor comprising a conductive composite of liquid metal and carbon particles was developed. The sensor was configured in a sheet-like shape and can be easily integrated into the gripper, which has been usually absent for other fabric grippers. The materials employed by this gripper design are commercially available for a reasonable budget, enabling the gripper to be both cost-effective and have potential applications where both gentle grasping and high load capacity are required.