3D Printed Flexible Gripper With Capacitance Sensing
Authors: Moreno-Rueda David , Maynard Cole , Hernandez Julio , Tallman Tyler , Garcia Jose , Newell Brittany 
Published: November 2023

Abstract
Soft robotics has changed the way people think and interact with robots. Robots were traditionally perceived as metallic rigid structures. However, soft-robot implementation has become essential in many medical devices (where conditions are highly dynamic and are susceptible to physical contact), smartphones, and industrial and human-robot applications. Some of the key features these devices offer are high dexterity, compliance, large amplitude, repeatability of motion, and improved safety. Pneumatic actuation is the dominant technology in soft robotics in terms of ease of implementation, low mass, and fast response time. Pneumatically actuated soft robots are mainly used for manipulation and gripping due to their capacity to generate high forces with minimal weight. Manufacturing these devices has decreased the cost and time to manufacture while increasing flexibility of materials used in comparison to traditional metal robotic manufacturing. Particularly, soft robotics has allowed for production using 3D printing for manufacturing soft pneumatic actuators. This is advantageous due to the capability of customization and ease of fabrication by using elastomeric materials. Also, by using 3D-printing it is possible to produce complex shapes and therefore motions including bending, rotating, twisting, jumping, rolling, and their combinations with high precision. Pneumatic gripper robots in particular are often used in applications where specific forces are required or nonuniform shape lifting is needed. In these applications, sensing the robot’s grip is critical. This paper presents a pneumatic soft robot sensing and actuating system. This system consists of a flexible pneumatic actuator, that can create rotational or linear motion and due to connection of two actuators can in turn be used for gripping. The actuator is manufactured fully via 3D printing using the softest commercially available thermoplastic polyurethane (TPU) filament. Both the actuator and sensor produced were manufactured using fused deposition modeling (FDM) techniques. This actuator incorporates 3D printed capacitance-based sensors made from commercial conductive thermoplastic polyurethane and a custom conductive thermoplastic polyurethane material. The capacitance-based sensors enable a pressure analysis of the robot’s grip. Both the soft-actuator and the capacitance-based sensor have been previously characterized and manufactured separately. This work integrates the two for a real-world application and provides a comparison between the commercial material and a custom carbon nano-fiber-based conductive filament for sensor and actuator response optimization. The actuator’s deformation along with applied pressure when gripping was assessed in this work for robot performance optimization. Results showed linear responses for commercial material and 10 wt% custom materials. The 10 wt% custom material demonstrated the widest sensing range (36.2–49.1 pF) and lowest standard deviation compared to both the commercial and 7.5 wt % custom material demonstrating grip sensing capabilities.