BarrettHand™ Articles

Mechanical Engineering

Space-Age Robots Come Down to Earth

Lighter robotic arms and more dextrous hands, originally designed to perform critical tasks in outer space and other hazardous environments, are getting ready to conquer the factory floor.

By Michael Puttré

Over the past several years, the robotics industry appears to have undergone a renaissance. Traditional robots – those with bulky arms and hands that pick and place parts for machining – are increasingly being outfitted with slimmer arms and more dexterous hands. This emphasis on dexterity is a promising development because robots often can perform operations requiring precise hand movements – such as assembling parts, painting, and sewing – far faster than humans. The resulting time and labor savings could give automated companies a considerable edge.

For instance, an experienced seamstress generally needs at least five minutes to sew a sports coat. A robotic arm developed by Philipp Moll, a mechanical engineer and managing partner of Moll Automatische Nähsysteme GmbH in Alsdorf bei Aachen, Germany, can do the job in just 20 seconds. With such technology, Moll said, "the European textile industry can regain its competitiveness."

The trend toward lighter, more flexible robotic arms and hands has its roots in technology dating back to the 1940s. In the postwar rush to develop nuclear weapons, many safety practices now standard in the industry either hadn't been established or were ignored. As a result, injuries and fatalities among workers who handled nuclear material climbed. Teleoperated arms were developed to put workers at a safer distance from the hazardous material.

Such applications demanded flexibility rather than strength. Only small amounts of nuclear material had to be moved at a time, but it had to be handled very delicately. Thus, hardware had to operate with little friction and no backlash. Above all, it had to be easy to control. Slim, light arms fit the bill.

Over the years, lighter, more flexible hardware began to play a critical role in other environments, such as in the operating room and in space. Philipp Moll, for example, first applied his design for a slender arm with an integrated sewing mechanism in 1985 to help surgeons close incisions faster during surgery. George Schlöndorff, an ear, nose, and throat specialist and plastic surgeon at the Aachen Technical College clinic in Aachen, Germany, has been using a Moll sewing arm to close incisions in patients' throats after tumors have been removed. Because the arm sews much faster than he can – a surgeon normally takes 30 to 60 seconds to sew a single stitch, while the Moll arm can sew 40 stitches a minute – operations take less time and patients suffer less stress. Although the device is still considered in the testing stage, it is now being used routinely at the clinic.

Lighter, more flexible robotic arms were also designed for unmanned space missions by the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology in Cambridge, Mass. In 1987, MIT began working with the National Aeronautics and Space Administration's Jet Propulsion Laboratory to adapt teleoperator technology to control robots on unmanned space vehicles. The two groups developed the Whole Arm Manipulator (WAM), an arm and wrist system with seven degrees of freedom. WAM's mechanisms are driven by brushless electric actuators that operate smoothly with no backlash and little friction. NASA is evaluating WAM for use on the proposed space station.

Commercial Use
Moll's sewing arm and the WAM, as well as other devices like them, are quickly being adapted for commercial use. A customized version of Philipp Moll's sewing arm is already being used to manufacture seat covers for cars. A manufacturer of headrests also plans to use a second spinoff of the technology. Moll is in the early stages of negotiations with textile manufacturers to identify ways to automate their operations.

William Townsend, president and chief executive officer of Barrett Technology Inc. in Cambridge, Mass., formed his company in 1988 to commercialize the WAM technology. Two of the company's products, the BarrettArm and BarrettWrist, are direct descendants of models designed for the Jet Propulsion Laboratory for use in space. Both products can be used for spraying, finishing, and contouring applications and for mobile applications (such as transporting hazardous material in nuclear power plants or weapons disposal sites), particularly in environments that are cluttered or dangerous to humans.

The aluminum and steel BarrettArm and Wrist consists of a base, a spherical shoulder joint and inner link, a revolute elbow joint, and a forearm link. Shoulder rotation and roll ranges are 260 degrees each; shoulder pitch and elbow joint ranges are 240 degrees each. The optional wrist mechanism and optional hand mechanism complete the robot. Wrist roll and hand roll are 330 degrees each, and wrist pitch is 180 degrees. A fully configured Barrett robot weighs about 70 pounds.

The BarrettArm links are slender and, with seven degrees of freedom, they are capable of maneuvering through cluttered environments when performing tasks. The wrist, elbow, and shoulder joints each have a backdrivable Moog series 303 actuator that provides a high degree of force control. Barrett's control software features a teach [mode] for recording manual motions for the robot to perform at variable speeds. (With [teachmode on], users can "teach" a Barrett robot to paint a horizontal surface, for example, by tapping three points on the floor to define the surface to be sprayed and indicating that the surface is 6 feet above the floor. Users do not have to write trajectory codes.)

NASA's Johnson Space Center provided much of the funding for the development of another Barrett product, the BarrettHand, because the center needed a lightweight, dexterous hand that could work with the BarrettArm in space vehicle applications. (Most robotic hands then available were too heavy to work with the design.) The basic hand technology, licensed from the University of Pennsylvania, features human-scale fingers, thumb, and palm that enable the hand to clasp objects much as a human does. Each two-link finger and thumb has a dedicated brushless Barrett MiniMotor. The fingers and thumb are functionally identical, except each finger can pivot about two axes of the palm up to 180 degrees. Finger rotation is provided by another minimotor.

The BarrettHand has position- and force-sensing capabilities. When grasping an object, the finger base and tip links move together. If a base link encounters an object it stops, while the tip link keeps moving until it makes contact with the object as well. If the tip links encounter an object first, the whole finger assembly stops moving. The hand has up to 11 pounds of holding force.

A fully-configured turnkey [hand] robot costs about $29,500. Barrett made its first commercial sale of [the hand] late last year to the Korean Institute of Science and Technology. Potential Japanese customers have expressed interest in the robot as well. The robot hasn't found a job in space yet, but if it finds one here on earth, it will be one more sign that the robotics industry has come of age.

Michael Puttré is a former associate editor of Mechanical Engineering.

Publish Date: January, 1995

Redistributed with permission from Mechanical Engineering magazine. © 1995, ASME International.

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