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Putting on a robotic balancing act.

Putting on a robotic balancing act

Even among basketball players, Manute Bol of the WashingtonBullets stands out as being exceptionally tall and thin. Now, researchers at Carnegie-Mellon University in Pittsburgh have designed and built a kind of Manute Bol of robots--a tall, slender machine poised precariously on a roller-skate base. Remarkably, the robot balances itself. Anyone who has held the lower end of a 6-foot pole and tried to keep the pole vertical can appreciate the difficulty of accomplishing this feat.

In fact, the robot manages to keep its balance in much thesame way a person would keep a pole vertical. The robot moves its base in the direction in which the robot happens to be leaning at any given moment. Constant adjustments back and forth keep the robot upright.

But civil engineer Irving J. Oppenheim and graduate studentLyman Petrosky have gone one step further. They've added to the challenge by putting in a joint halfway up the robot's trunk. Thus, the robot can bend down at its waist, going, as if it were doing calistenics, from a vertical stance to touching its toes. Even through this additional movement, it maintains its balance.

Oppenheim's 6-foot-tall robot consists of two 3-foot sectionsof perforated aluminum mounted on a pivoted base carrying a set of motor-driven wheels. Another motor controls movement at the waist. The aluminum trunk, with a square cross section, is about 3 inches wide. One sensor--a "floor feeler'--measures the angle between the ankle-height pivot link and the floor. Another counts motor rotations so that it's possible to sense how far along its path the robot has moved. A third device allows the researchers to determine the waist angle.

All of the data are fed by cable to a computer, which analyzesthe data and sends appropriate control signals back to the robot. The cable also transmits the power needed to run the robot's motors. The researchers use a joystick connected to the computer for commanding the robot to move from place to place and to bend.

The key component enabling the robot to keep its balance isthe computer program governing its operation. Although the idea of balancing a rod (an inverted pendulum) has long been a standard laboratory exercise in control theory, Petrosky developed a new, innovative mathematical approach that improves on older methods and greatly increases the robot's stability.

"When this robot stands undisturbed, you're not really awarethat it's doing active balancing,' says Oppenheim. "It looks as if it were planted in the ground.' And the machine isn't delicate. "It's very difficult to knock it over,' he says. When struck, the robot may briefly skitter away or swing wildly, but, unless its wheels slip or the motors need more power than they can deliver, it returns to its former position.

Oppenheim and Petrosky are using their robot to study howa machine may be designed to use its own weight to help it do a particular job. For instance, human beings, by tugging and pulling instead of relying just on the strength of their arms, can move relatively heavy objects. A lightweight robot with a similar capability may someday be able to accomplish what now requires a much heavier machine.

Although Oppenheim's robot can hold a camera about assteadily as a human being, it isn't equipped yet for turning a valve, stuffing a basketball into a basket or other chores where a long, vertical reach is handy. The Department of Energy, which is funding the research, is interested in tall, light robots that could work within tightly confined spaces in nuclear power plants and other hazardous environments (SN: 7/12/86, p.28). It may even be possible to use the principles applied in a self-balancing robot to improve the stability of construction machinery such as cranes.
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Title Annotation:6-foot-tall robot that balances itself
Publication:Science News
Date:Jul 25, 1987
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