Doctoral student, professor design world’s first biellipsoidal robotic thumb joint - The University of Tulsa
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Doctoral student, professor design world’s first biellipsoidal robotic thumb joint

Photograph of Joshua Schultz, BRAT’s director
Joshua Schultz, BRAT’s director

It’s not uncommon to see images of robots and robotic hands in the media and popular culture. This proliferation can give the false impression that the mechanical nuts and bolts for these complex technologies have all been resolved.

Taking up this challenge, The University of Tulsa’s Biological Robotics at Tulsa (BRAT) Research Group is broadly interested in giving robots the ability to perform useful tasks in the world everyday people inhabit, not just in lab and factory environments. “Creating dexterous, capable robotic hands that can pick up, retain, reorient, and place or insert any reasonably sized object they come across is critical to achieving that goal,” said Joshua Schultz, BRAT’s director and an associate professor of mechanical engineering.

An essential element is development of a thumb that’s capable of flexing and extending – opening and closing a hand’s grasp – as well as abducting and adducting – repositioning the thumb opposite fingers in a location that optimizes grasping or manipulating an object. Schultz and Spenser Pulleyking (BSME ’17), a BRAT member and doctoral student in the Department of Mechanical Engineering, recently had the results of their research in this area accepted for publication in IEEE/ASME Transactions on Mechatronics, one of the field’s most influential scientific journals.

Pulleyking is the lead author of the study, A Compliant Rolling Ellipsoidal Thumb Joint for the TU Hand. In this paper, he and Schultz present their work on a joint for the thumb of an anthropomorphic robotic hand designed entirely by TU students. Their major innovation is the development of a biellipsoidal joint, which consists of two ellipsoids – spheres stretched out to be longer in one direction – that roll over each other. “This type of joint allows the base of the thumb to rotate in two directions,” explained Pulleyking. “With a conventional pin joint, movement in only one direction is possible.” “Because an ellipse can roll over itself in two directions, much like the surface of the metacarpal rolls over the carpal nearest to it, our novel thumb joint elegantly puts two axes of rotation at the base of the thumb,” Schultz noted. A further advantage of ellipsoids is their ability to resist high compressive forces when pushed into each other. However, because ellipsoids alone can easily twist about a contact point or slide off each other, Pulleyking designed engineering components that could prevent those unwanted motions while also fitting in a tiny space (ca. 1 cm3).

The initial stages of Pulleyking’s work were supported by a National Science Foundation (NSF) grant on which Schultz was the principal investigator. The remainder of his dissertation will entail using the TU hand and measurements of the stretch that occur in the spring network to deduce what object the hand has grasped when it picks up an object in an unknown environment.

Pulleyking, Schultz, and their BRAT colleagues also intend to conduct grasping experiments using the Barrett WAM® robotic arm TU acquired as the result of another NSF grant in 2022.