Dubbed the neuroArm, it’s the brainchild of neurosurgeon Dr. Garnette Sutherland and his team of researchers.
The neuroArm is designed to operate on the head of a patient sitting in an MRI machine. A surgeon at a workstation controls the arm using real-time MR imaging as a guide. And the robot’s hand is actually steadier than that of a human surgeon. A surgeon’s hand is stable to about 100 microns, say developers, but the neuroArm is good to about 25 microns.
MacDonald, Dettwiler, and Assoc. (MDA), makers of the Space Shuttle’s Canadarm, did the main engineering work. One of the tricky parts of the design was coming up with nonmagnetic motors and bearings. “Magnetic materials in the MRI field generate artifacts on the image the doctor uses to make decisions,” explains Alan Feinstein, CEO of Nanomotion Ltd., part of Johnson Electric’s Medtech group. Nanomotion supplied the motors that power neuroArm’s six axes.
The Nanomotion motors use PZT, a piezoelectric ceramic, to move a small ceramic finger back and forth. The finger rotates a ceramic ring, thus creating motion through friction. The motors are adapted from versions originally used in vacuum environments for semiconductor manufacturing. This involved converting stainless-steel parts to ceramic and coming up with fully ceramic bearings.
“The motor is putting pressure into the work surface. That means you need a certain amount of stiffness in the structure it works against,” says Feinstein. “We normally need a stiffness of about 40 N/micron. But the robot’s stiffness was low because of the plastic and ceramic bearings. We had to collaborate closely with designers to make sure we didn’t cause too much wear or noise despite compromises on stiffness.”
The PWM signals driving the motors could also potentially interfere with MRI signals, so Nanomotion built in a tunable filter that shifts the motor drive pulse frequency out of harm’s way.
MacDonald, Dettwiler, and Associates Ltd.,
Univ. of Calgary
neuroArm video and information,