Using piezoelectric materials, researchers have replicated the muscle motion of the human eye to control cameras. Designed to improve the operation of robots, the technology could help make robotic tools safer and more effective in MRI-guided surgery and other medical device applications.
Conducted by PhD candidate Joshua Schultz under the direction of assistant professor Jun Ueda at the Georgia Institute of Technology (Georgia Tech; Atlanta), the new control system is based on a piezoelectric cellular actuator that uses a biologically inspired technology enabling a robot eye to move more like a real eye. “For a robot to be truly bioinspired, it should possess actuation, or motion generators, with properties in common with the musculature of biological organisms,” Schultz explains. “The actuators developed in our lab embody many properties in common with biological muscle, especially a cellular structure. Essentially, in the human eye muscles are controlled by neural impulses. Eventually, the actuators we are developing will be used to capture the kinematics and performance of the human eye.”
Piezoelectric materials expand or contract when electricity is applied to them, transforming input signals into motion. While this principle serves as the basis for piezoelectric actuators used in many applications, it use in robotics applications has been limited because of piezoelectric ceramic's minuscule displacement.
The cellular actuator concept developed by the research team was inspired by biological muscle structure that connects many small actuator units in series or in parallel. "Each muscle-like actuator has a piezoelectric material and a nested hierarchical set of strain amplifying mechanisms,” Ueda says. “We are presenting a mathematical concept that can be used to predict the performance as well as select the required geometry of nested structures. We use the design of the camera positioning mechanism’s actuators to demonstrate the concepts.”
The scientists’ research shows mechanisms that can scale up the displacement of piezoelectric stacks to the range of the ocular positioning system. In the past, the piezoelectric stacks available for this purpose have been too small.
“Each muscle-like actuator consists of a piezoelectric material and a nested hierarchical set of strain amplifying mechanisms,” Ueda remarks. “Unlike traditional actuators, piezoelectric cellular actuators are governed by the working principles of muscles—namely, motion results by discretely activating, or recruiting, sets of active fibers, called motor units." Motor units are linked by flexible tissue, which serves a two-fold function, according to Ueda. It combines the action potential of each motor unit and presents a compliant interface with the world, which is critical in unstructured environments.
For more information on this technology, see Georgia Tech's article on Robot Vision.
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