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Spherical Induction Motor Eliminates Robot’s Mechanical Drive System
PITTSBURGH— More than a decade ago, Ralph Hollis invented the ballbot, an elegantly simple robot whose tall, thin body glides atop a sphere slightly smaller than a bowling ball. The latest version, called SIMbot, has an equally elegant motor with just one moving part: the ball.
The only other active moving part of the robot is the body itself.
The spherical induction motor (SIM) invented by Hollis, a research professor in Carnegie Mellon University’s Robotics Institute, and Masaaki Kumagai, a professor of engineering at Tohoku Gakuin University in Tagajo, Japan, eliminates the mechanical drive systems that each used on previous ballbots. Because of this extreme mechanical simplicity, SIMbot requires less routine maintenance and is less likely to suffer mechanical failures.
The new motor can move the ball in any direction using only electronic controls. These movements keep SIMbot’s body balanced atop the ball.
Early comparisons between SIMbot and a mechanically driven ballbot suggest the new robot is capable of similar speed — about 1.9 meters per second, or the equivalent of a very fast walk — but is not yet as efficient, said Greg Seyfarth, a former member of Hollis’ lab who recently completed his master’s degree in robotics.
Induction motors are nothing new; they use magnetic fields to induce electric current in the motor’s rotor, rather than through an electrical connection. What is new here is that the rotor is spherical and, thanks to some fancy math and advanced software, can move in any combination of three axes, giving it omnidirectional capability. In contrast to other attempts to build a SIM, the design by Hollis and Kumagai enables the ball to turn all the way around, not just move back and forth a few degrees.
Though Hollis said it is too soon to compare the cost of the experimental motor with conventional motors, he said long-range trends favor the technologies at its heart.
“This motor relies on a lot of electronics and software,” he explained. “Electronics and software are getting cheaper. Mechanical systems are not getting cheaper, or at least not as fast as electronics and software are.”
SIMbot’s mechanical simplicity is a significant advance for ballbots, a type of robot that Hollis maintains is ideally suited for working with people in human environments. Because the robot’s body dynamically balances atop the motor’s ball, a ballbot can be as tall as a person, but remain thin enough to move through doorways and in between furniture. This type of robot is inherently compliant, so people can simply push it out of the way when necessary. Ballbots also can perform tasks such as helping a person out of a chair, helping to carry parcels and physically guiding a person.
Until now, moving the ball to maintain the robot’s balance has relied on mechanical means. Hollis’ ballbots, for instance, have used an “inverse mouse ball” method, in which four motors actuate rollers that press against the ball so that it can move in any direction across a floor, while a fifth motor controls the yaw motion of the robot itself.
“But the belts that drive the rollers wear out and need to be replaced,” said Michael Shomin, a Ph.D. student in robotics. “And when the belts are replaced, the system needs to be recalibrated.” He said the new motor’s solid-state system would eliminate that time-consuming process.
The rotor of the spherical induction motor is a precisely machined hollow iron ball with a copper shell. Current is induced in the ball with six laminated steel stators, each with three-phase wire windings. The stators are positioned just next to the ball and are oriented slightly off vertical.
The six stators generate travelling magnetic waves in the ball, causing the ball to move in the direction of the wave. The direction of the magnetic waves can be steered by altering the currents in the stators.
Hollis and Kumagai jointly designed the motor. Ankit Bhatia, a Ph.D. student in robotics, and Olaf Sassnick, a visiting scientist from Salzburg University of Applied Sciences, adapted it for use in ballbots.
Getting rid of the mechanical drive eliminates a lot of the friction of previous ballbot models, but virtually all friction could be eliminated by eventually installing an air bearing, Hollis said. The robot body would then be separated from the motor ball with a cushion of air, rather than passive rollers.
“Even without optimizing the motor’s performance, SIMbot has demonstrated impressive performance,” Hollis said. “We expect SIMbot technology will make ballbots more accessible and more practical for wide adoption.”
The National Science Foundation and, in Japan, Grants-in-Aid for Scientific Research (KAKENHI) supported this research. A report on the work was presented at the May IEEE International Conference on Robotics and Automation in Stockholm, Sweden.
Video by: Carnegie Mellon University
About Carnegie Mellon University: Carnegie Mellon (www.cmu.edu) is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 13,000 students in the university’s seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation.
Carnegie Mellon University
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Pittsburgh, PA 15213
Contact: Byron Spice For immediate release:
412-268-9068 October 4, 2016
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Neural networks work so well because they roughly reflect the structure of the underlying universe around us, new research suggests.
Servosila, a robotics technology company, announced a launch of a new line of robotic arm manipulators specifically targeted at mobile robotics market.
“Servosila Robotic Arms are the first manipulators specifically designed for mobile robots,” – said the company’s spokesperson, – “it is very easy to retrofit any existing robotic chassis or a torso with a Servosila Robotic Arm”.
Servosila Robotic Arms are attachable payload modules for mobile service robots or other robotic platforms. Servosila Robotic Arms shall typically be mounted on a chassis or a torso of a mobile robot and be powered by an on-board power supply system of the host robotic platform.
The robotic arms can be used both outdoors and indoors. The arms are water-tight, dust-proof and function properly in the rain and in the snow. The arms are designed to withstand impacts, collisions with obstacles and, in general, the harsh treatment so common to mobile robotics applications.
The servo drives and external electrical connectors of the robotic arms are water-tight and dust-proof (IP68 rating). The entire arm can be occasionally submersed in water without any adverse effects on its performance. The robotic arms may be operated in cold or hot weather.
Mobile robots tend to bump into things and hit obstacles while on the move. The harsh nature of outdoor mobile robotics applications caused a profound effect on the design of Servosila Robotic Arms, especially on the internal structure of servo drives and their harmonic reduction gears.
There are no exposed cables on the outside of the robotic arms that could be torn off when a mobile robot moves through bushes or forests.
Numerous protection measures built into electronic servo controllers and mechanical parts of Servosila Robotic Arms ensure reliable operation on-board of outdoor mobile service robots.
Servosila Robotic Arms are lightweight by design. For a given lifting capability, Servosila Robotic Arms have a significantly lower weight than their industrial counterparts. The lower weight of a Servosila Robotic Arm enables a mobile robot equipped with the arm to operate longer on a single battery charge, keep its center of gravity lower for better balance, climb stairs easier or have a superior mobility.
When not in an active use, Servosila Robotic Arms can folded into a very compact form that doesn’t occupy much space on the top of a robotic chassis or on the side of a torso. This feature protects the robotic arm of a mobile robot in case of an unexpected collision with an obstacle or whenever a rough terrain is encountered by the mobile robotic platform. The compact folded form also comes handy during transportation.
By folding its robotic arm into the compact form, the robot frees up its working area for other payloads to operate in. This is useful in case the robot is equipped with additional payloads other than the robotic arm.
Photo Credits: Servosila Limited (Hong Kong)
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