In recent years, soft robots have provided a desirable approach to solving complex tasks in a simple, cost-effective, and compliant manner. BASF’s California Research Alliance (CARA) facilitated the research collaboration with the University of California (UC) San Diego. The endeavor led by Yichen Zhai, Albert de Boer, Martin Faber, Rohini Gupta, and Michael T. Tolley has resulted in the successful desktop fabrication of monolithic soft robotic devices produced with embedded fluidic control circuits. These innovative grippers were manufactured with Ultrafuse® TPU using Fused Filament Fabrication (FFF), which both created a highly functional and complex device as well as utilizing a material which improved the safely level of the soft robot when working in close contact with humans.

Most soft robots are pneumatically actuated and fabricated by molding and assembling processes that typically require many manual operations and limit complexity. Through desktop FFF, three-dimensional printing provides an accessible alternative with less manual work as well as the capability of generating more complex structures. Due to both material and process limitations, FFF-printed soft robots can often have a high effective stiffness and contain many leaks which limits their applications. To solve this issue, the team developed an innovative design to fabricate soft, airtight pneumatic robotic devices while simultaneously printing actuators with embedded fluidic control components. They demonstrated this approach by printing the actuators an order of magnitude softer than those previously fabricated using FFF and capable of bending to form a complete circle. Similarly, they printed pneumatic valves that control a high-pressure airflow with low control pressure.

By combining the actuators and valves, the team was able to demonstrate a monolithically printed electronics-free autonomous gripper that not only maintained the airtightness and soft actuation performance of each component but could be manufactured in a one-shot 3D printing workflow in 16 hours and 19 minutes. The entire fabrication process of the gripper required no post-treatment, post-assembly, or repair of manufacturing defects, making this approach highly repeatable and accessible.

A similar approach could be applied to the design and fabrication of a range of pneumatic devices with embedded sensing and control circuits. The first key design rule for obtaining airtight structures is to print them using a single, continuous toolpath for each soft pneumatic device, known as an Eulerian path. A second key design rule is to create structures with very thin walls, measuring about two traces thick, which results in structures with low stiffness comparable to silicone-molded parts.

The monolithic autonomous gripper, which was fabricated in an uninterrupted 3D printing workflow, was ready to use immediately after printing. The gripper was designed to autonomously pick up and release objects with simple controls and could be a useful manipulation tool in various applications such as manufacturing and farming. In the fabrication process, there was no manual operation such as assembly or adjustment required, implying that the process and design are easily reproducible using a similar desktop 3D printer. With these predefined toolpath rules, all parts and the combined system were in the same printing standard to maintain the working performance and airtight quality.

Building on the fabrication method as well as the actuator and valve designs, the team demonstrated a fabrication approach that is uniquely enabled by 3D printing. The design rules developed through this collaboration of BASF and UC-San Diego resulted in the successful creation of air-tight, high-performance autonomous pneumatic devices. With different combinations of these “building blocks,” customized complex robots can be designed and manufactured in monolithic printing processes.

Detailed information about this project was recently published as the cover story in Science Robotics and can be found at: Desktop fabrication of monolithic soft robotic devices with embedded fluidic control circuits | Science Robotics