Segway robot opens doors

By Eric Smalley and Kimberly Patch, Technology Research News

Researchers from Massachusetts Institute of Technology have crossed a robotic arm with the bottom half of a Segway to make a robot named Cardea that can traverse hallways and open doors.

Cardea, named after the Roman goddess of thresholds and door pivots, is the one-armed first prototype of a robot designed to have three arms and the ability to safely interact with humans at eye level.

The Segway scooter platform, with its dynamic balancing abilities, makes the arm practical, said Una-May O'Reilly, an MIT research scientist. "The Segway is... like an inverted pendulum," she said. "Regardless of where the weight is on top of it... the platform is able to move with balance."

This is important because when the robot arm moves, its center of mass shifts. Without dynamic balancing, a robot that has arms and stands as tall as a human would require a much larger base, said O'Reilly.

Cardea stands about five feet tall and weighs about 200 pounds. It consists of the Segway base, sonar sensors that help in navigation, a pair of cameras that form a rudimentary vision system, and a single arm capable of five degrees of freedom -- two at the shoulder, one at the elbow, and two at the wrist. It also has a kickstand in the form of spring-loaded legs that deploy when the robot is in danger of falling, usually due to low battery power.

The prototype is capable of navigating a hall, finding a door and pushing it open, according to O'Reilly. This demonstrates "that we have some of the pieces toward the issues and the challenges of mobile manipulation," she said.

The idea behind building a mobile robot that stands as tall as a human is to explore the ways a humanoid robot can interact with the world, and to make sure it interacts safely, said O'Reilly. The researchers are aiming to give the robot the abilities to recognize whether it's in a room or hallway, recognize and manipulate objects, take instructions, and learn. Given the ability to move around, Cardea can actively explore, she said.

Traditionally, robotic arms have been used to manipulate parts for manufacturing, but factory manipulators operate under a different set of assumptions and within a different realm, said O'Reilly. The environment must be structured in a way that allows them to anticipate, she said. "Parts have to be arranged perfectly so that the robotic arm can interact with them repetitively."

Moving a robotic arm outside a factory setting means teaching the robot to deal with an environment that is not necessarily structured in an organized fashion, said O'Reilly. The present incarnation of Cardea performs a level of mobile manipulation in an unstructured environment, she said. The challenge is making it both safe and able to deal with all the clutter of the real world, she added.

The researchers are aiming to augment the sonar sensors on Cardea's base with a heat-sensing system and improve its vision system with better panning ability and arm-vision system coordination, said O'Reilly. They are also planning to add a robotic hand to the arm, increase the number of arms to three, and give the robot a head, said O'Reilly.

The researchers used a type of robot arm previously designed for MIT's robot Cog. The arm was designed with safety in mind. Robotic manipulators tend not to be sensitive to objects or people, and so are in danger of hurting people or burning out their own motors when they meet an obstruction.

The arm contains a series elastic actuator system that, like biological muscle, provides a buffer between the actuator force and the load it is acting on. An embedded spring system senses forces interacting with the arm. The spring provides feedback about the load and also allows the actuator's motor to gradually apply the force needed to move the load. "We can actually use the spring model to control the arms, and the arms become much safer when they interact with things," said O'Reilly.

The researchers's plans for improving Cardea's arms call for adding two more and also giving the robot a third degree of freedom at each shoulder so that each arm has six degrees of freedom. The three arms will be of different lengths, and will have different end effectors, or hands, designed for different purposes. "You can imagine having different instruments at the ends of the arms, and with that we get more flexibility in terms of what the mechanical system can actually do when it has to interact with the world," said O'Reilly.

The current prototype has a simple knob for pushing open doors. The researchers are working on a hand that has three force-controlled fingers. Other hand possibilities include pincers, grippers, flippers and paddles.

The odd number of arms will also widen the robot's interaction abilities, said O'Reilly. "When you've got three arms you can carry something with two and then perform an operation on that object with the third," she said. And while two arms make a single pair, three arms can form three different pairs, she added.

Once Cardea gains a full complement of arms, the researchers will add a more sophisticated vision system that coordinates with the arms, said O'Reilly. "We want to try and understand the various vision-based manipulation problems and how to address them," she said.

Cardea will eventually gain a robotic head similar to the MIT robots Cog and Kizmet, said O'Reilly. "Then we can have a robot that moves around and has to deal with social interaction issues of human-to-robot at human-height level," she said. Cog is a stationary humanoid robot that consists of a head, arms and torso. Kismet is a stationary humanoid robotic head that is capable of facial expressions.

The researchers are also aiming to use Cardea to explore more general notions of behavior, said O'Reilly. The robot will, like its predecessors, learn by exploring its environment and manipulating objects, and interact with humans through facial expressions and tones of voice.

There's also the question of what social character an assistive robot should have, said O'Reilly. "If we were to have a robot [wondering] around the halls and available for assistance... what should the face look like, [and] how should the robot negotiate its interactions, take instructions and show that it's learned or is following them?"

The researchers are also looking at the issue of maintaining a robot that would never really have to power down, O'Reilly said. This would require that the robot understand when it is in need of energy and, for instance, plug itself into the wall, she said. Not having to turn off would be an advantage because complicated robots tend to have time-consuming startup procedures.

MIT's Cardea project is one of a dozen projects at universities and government labs around the country that involve building robots on Segway bases. The projects were initiated under the Defense Advanced Research Projects Agency (DARPA) Mobile Autonomous Robot Software (MARS) program.

The MIT robot and a similar NASA project "make a strong case for the marriage of mobility and manual skill," said Rod Grupen, an associate professor of computer science at the University of Massachusetts, Amherst. Grupen and colleagues are also developing a Segway-based robot under the DARPA program. "These projects... are among the very first to achieve a robot that interacts with people in a human scale environment," he said.

O'Reilly's research colleagues are Rodney Brooks, Paul Fitzpatrick, Lijin Aryananda, Jessica Banks, Aaron Edsinger, Eduardo Torres-Jara, Paulina Varchavskaya, Alana Laferty, Alex Moore, Jeff Weber, Charlie Kemp and Kathleen Richardson. The research is funded by DARPA and by a corporation.

Timeline:   Unknown
Funding:   Corporate; Government
TRN Categories:  Robotics; Human-Computer Interaction; Engineering
Story Type:   News
Related Elements:   Cardea Web site:


November 19/26, 2003

Page One

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