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Engineer's Toolbox: Frameless motor tech enables advanced mobility and manipulation for CHIMP humanoid robot

www.theroboticschallenge.org

A team from Carnegie Mellon University's National Robotics Engineering Center (NREC) is building a new class of robot to compete in the upcoming Defense Advanced Research Projects Agency's (DARPA) Robotics Challenge, called the DRC. It's a human-size robot that moves, not by walking, but on rubberized tracks on the extremities of each of its four limbs. Forty-nine frameless motors from Kollmorgen are one of the keys to this unique robot's all-important drive joints.

Though the appearance of the CMU Highly Intelligent Mobile Platform, or CHIMP, is vaguely simian, its normal mode of locomotion will be much like that of a tank, with the tracks of all four limbs on the ground. This configuration offers a particular advantage when moving over debris and rough terrain. But CHIMP can also move on the treads of just two limbs when needed, such as when it must use one or more limbs to open a valve or to operate power tools.

CHIMP will have to do that and more during the DARPA Robotics Challenge (DRC), in which robots will have human-like capabilities to respond to calamities such as the 2011 Fukushima nuclear plant disaster. Climbing ladders and driving vehicles are among the obstacles robots will face in environments engineered for people. The DRC kicked off on October 24, 2012, and is scheduled to run for approximately 27 months with three planned competitions: June 2013, December 2013, and December 2014.

The NREC entry, Tartan Rescue Team, is one of seven selected by DARPA for DRC Track A, in which each team will develop its own hardware and software.

CHIMP will be able to perform complex, physically challenging tasks through supervised autonomy. A remote, human operator will make high-level commands controlling the robot's path and actions, while the robot's on-board intelligence prevents collisions, maintains stability and otherwise keeps the robot from harm. The robot also will be pre-programmed to execute tasks such as grasping a tool, stepping on a ladder rung or turning a steering wheel without step-by-step direction from the human controller, circumventing the lag between command and execution.

"Humans provide high-level control, while the robot provides low-level reflexes and self-protective behaviors," says Tony Stentz, NREC director and Tartan Rescue Team leader. "This enables CHIMP to be highly capable without the complexity associated with a fully autonomous robot."

"This type of robot has tremendous potential," Stentz adds. Such a robot would be suitable for a variety of tasks for which NREC now develops wheeled, tracked, and other conventional robots, such as remote inspection and monitoring of hazardous industrial facilities. As a unit of Carnegie Mellon's Robotics Institute, NREC performs advanced applied research and prototyping for commercial and governmental clients.

The human-centered nature of the DRC challenges would seem to favor a dynamically stable humanoid robot, the choice of five of the seven Track A teams, Stentz acknowledges. But his team's focus on simplicity and dependability led them to choose tracked locomotion.

"When we walk or stand, our brains are actively controlling our balance all of the time," Stentz says. This dynamic balance makes people nimble and enables them to run. But it also greatly increases the complexity, computational requirements, and energy consumption of a machine. So CHIMP is designed with static stability; it won't fall down even if it experiences a computer glitch or power failure.

When necessary, however, the operator can control CHIMP's individual joints, enabling it to adapt its motion to particular circumstances or extricate itself from tight spots. And for this robot, it's all about the joints.

"In a pinch, it can do anything," Stentz says.

CHIMP uses Kollmorgen frameless motor technology in each of its drive joints to deliver advanced functionality and significant performance benefits for the Robotics Challenge. This advanced functionality also paves the way for new mobile manipulation and manufacturing automation applications.

"The CHIMP design explicitly avoids many of the dynamic stability issues associated with humanoid robots. Tracks on all four limbs provide CHIMP with better mobility and with stability while opening doors, using tools, and turning valves. Sensors at the head and limbs provide the perception and feedback needed for CHIMP to manipulate objects, remove debris, and travel safely through the environment," says National Robotics Engineering Center Business Development Director Steve DiAntonio. "The hardware components and software methods that form CHIMP are standalone technologies that, in their own right, offer new automation capabilities for facility maintenance, manufacturing, and material handling."

For example, CHIMP's drive joints, constructed of Kollmorgen motors integrated with gearing and housing components, actuate the robot's 50 degrees of freedom and deliver advanced mobility, multi-limb manipulation, and human-like grasping capabilities not found in today's industrial robots. These capabilities are made possible by four custom frameless motor sizes from Kollmorgen -- a total of 42 motors between the four sizes -- along with seven modified standard KBM series frameless motors.

Benefits of KBM series frameless motors include:

Direct load connection eliminates maintenance of gearboxes, belts, or pulleys; Zero backlash and compliance provides more responsive system performance; Eliminates coupling devices, reducing overall machine size; and

Embedded motor enables compact machine design.

Kollmorgen framelss motors.

"Kollmorgen engineers worked to design a compact and high-power-density motor, and worked hand and hand with CMU's engineers to develop the high-power joint that really makes the human-like capabilities possible," says Dave Graff, Kollmorgen regional sales manager for custom motor solutions.

Other CHIMP features include:

Like a chimpanzee, each extremity is equipped with a manipulator that enables it to grasp objects; Near-human strength and dexterity; On-board sensors build a texture-mapped, 3D model of the environment that CHIMP uses to maintain stability and prevent collisions; The same 3D model enables the operator to visualize the location and orientation of CHIMP and evaluate possible actions; The operator controls CHIMP using an immersive interface of a large screen monitor, keyboard, and mouse, choosing from multiple modes that blend manual and autonomous control of the robot.

The new drive joint design will help the CHIMP execute the DARPA Robotics Challenge (DRC) challenge tasks.

In addition to the Tartan Rescue Team, Carnegie Mellon has a second team in the DARPA Robotics Challenge. Team Steel, headed by Christopher Atkeson, professor of robotics and human-computer interaction, was selected as a Track B team. In Track B, teams develop software in a virtual competition, with a winner receiving a DARPA-provided humanoid Atlas robot for use in the live competition. The final DRC event will be next year, with the winner receiving $2 million.

Other CHIMP technology sponsors include: Faulhaber (represented by MICROMO in the U.S.), Honeywell, Robotiq, Oshkosh, Elmo Motion Control, THK, Pratt & Miller, Accurate Gear and Machine (AGM), and Eclipse Metal Fabrication.

For more information on the DARPA Robotics Challenge, please see: