A soft humanoid hand developed by a team of engineers at Michigan State University has demonstrated a superior ability to perform a wide variety of tasks that involve grasping light, irregularly shaped objects. The hands may soon be ready to integrate into machines that increase the speed and accuracy of numerous industrial tasks, such as automated packaging, surgical robotics and fruit picking.
Dr. Changing Cao, the leader of the team, said the hand took about one and a half years to develop. He described the design as “a soft-hard flexible gripper.”
“It combines the advantages of the deformability, adaptability and compliance of soft grippers while maintaining the large output force originated from the rigidity of the actuator,” said Cao.
Cao added that a traditional rigid gripper helps to generate large forces, high accuracy and repeatability. Yet such a device requires a complex system to maintain control, as well as a robust planning strategy to manipulate.
Cao is the director of the Laboratory for Soft Machines and Electronics at Michigan State University (MSU). He is also an assistant professor in Packaging, Mechanical Engineering, and Electrical and Computer Engineering at MSU.
How It Works
Each finger of the hand is a flexible hybrid pneumatic actuator (FHPA), an independent small pump that applies pressurized air to bend. The FHPA has a leaf spring sheet on the bottom and an elastomeric bladder in the middle layer. The elastomeric bladder has the elastic properties of natural rubber.
“We have multiple bladders for certain designs of the hand,” said Cao.
When AI directs the FHPAs, each finger can respond as in a real hand. In a real hand, the brain controls the muscles that move the fingers. The muscles start in the forearm and connect to the finger bones through the flexor tendons. When the muscle moves, it pulls on the tendons, which in turn pull on the bones of the fingers.
The humanoid hand is similar in size to a real hand. It can be tailored larger or smaller, based on models for specific applications. The hand is placed on the end effector or gripper of a robot, a device connected to the end of a robot arm.
The covering of the hand is made of acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA) plastic rings. These materials are stiffer than rubber. They need to be stronger than the softer internal materials.
Cao said the team tested prototypes to complete different tasks that involved grasping objects.
“Our test set included a Rubik’s cube, table tennis ball, cylinder, banana, tomato, bottled juice, thin cylinder, and water glass. We also joined the humanoid hand with robotic arms to performing picking and packaging tasks,” said Cao.
Cao said the team is now optimizing the grasping speed and dexterity of the hand when mounted on robotic arms. This helps it get better at manipulation and do even more complex tasks.
“We will also make it smart in the coming future,” said Cao.
Next Steps
Cao said he anticipates the hand to be licensed through MSU Technologies, MSU’s technology licensing office.
The team, together with other collaborators at MSU, received a new National Science Foundation grant, which will be provided in fall 2020. The grant will allow for the continuation of work on soft robotics until 2024.
Cao said the team has also developed separate artificial skins for tactile sensing applications.
“We will combine these with our soft robotic components including the hand and ‘soft arms’ for responsive applications. My group is now doing this task together,” said Cao.
Like many things around the world, the project has been negatively affected by the COVID-19 pandemic, but the team has several invited papers on the hand that it will submit this year.
The team’s research was partially funded by the U.S. Department of Agriculture-National Institute of Food and Agriculture, an MSU Strategic Partnership Grant, the National Natural Science Foundation of China, and an MSU Startup Grant. Of the members of Cao’s team, Xiaomin Liu is a MSU Visiting Scholar, Shoue Chen is a MSU Ph.D. student, Dr. Xiaobo Tan is an MSU Foundation professor in the Department of Electrical and Computer Engineering, and Dexu Geng and Yunwei Zhao are affiliated with the School of Mechanical Engineering in Beihua University in Jilin, China.