Self-configuring robot mimics lifeforms

By Ted Smalley Bowen, Technology Research News

Scientists have long looked to nature for models when developing machines -- even machines that perform the unusual acts of pulling themselves apart and reconfiguring themselves.

Researchers from the University of Southern California have designed modular robots that move like snakes and spiders, and use a communication system akin to biological hormonal activity.

The self-assembling robots have the ability to rearrange themselves, and even exchange modules, making themselves bigger or more numerous, said Wei-Min Shen, an associate professor of computer science at the University of Southern California.

Eventually, this type of robot could change shape, size and locomotion method in order to navigate varied terrain or work in groups, traits that could be used for remote operations like search and rescue, and surveillance tasks, said Shen.

For instance, a robot could transform into a snake to pass through a narrow passage, rework itself to add legs to climb over an obstacle, and form a ring to roll quickly down a slope, according to Shen.

The robots are made up of identical, box-like modules constructed largely of off-the-shelf components. An individual module's functions are dictated by its position in a given configuration.

Each module includes a computer processor, batteries and a pair of motors that allow it to rotate up and down, and left and right. A single module can only wiggle on its own, but once two or more modules connect to form a structure, several different types of locomotion are possible, according to Shen.

The modules connect via one of four docking ports located on four sides of each module. The ports pair connectors with infrared communications systems that guide the connection process and allow modules to exchange hormone-like messages.

Connected modules communicate using these messages. In addition, modules from different robots can also communicate this way via open ports that are 30 centimeters or closer. This allows robots to coordinate actions and exchange modules.

The researchers have created several different configurations using the modules, including a robot with a three-module body and six legs, and an autonomous snake, Shen said.

The robots are self-sufficient, meaning they use the distributed communications system to move on their own. In addition, some of the robots are autonomous, meaning they can also reconfigure themselves without human intervention.

So far, autonomous robots constructed of the modules have been able to move only in snake-like fashion, but that should change, said Shen. "We are working to make all reconfiguration automatic," he added.

The autonomous snake can connect its head to its tail and form a loop in about three minutes, said Shen.

In addition, "a human operator can configure the robot any shape she wants with the four-way connectors on the modules," Shen said.

The key to the robot's self-sufficient and autonomous behavior is the hormone-like communication system, which allows modules to coordinate movements and reconfigurations.

The modules can broadcast messages to the other modules that make up a robot. These messages trigger the specific actions required for the robots to assemble, move and change shape.

Like biological hormones, the messages last only a certain length of time, trigger different actions in different receiving sites, and leave the execution and coordination of a local action to the module performing the action.

These properties are ideal for specifying tasks in a distributed system with minimal communications, according to Shen.

A module generates a hormone message when it receives a message from another module or from a human operator, or when its sensors detect certain conditions. "Every module can become a hormone generator, and can send out hormones to the entire network of modules," said Shen.

For instance, a snake robot module that contains a tilt sensor can keep the snake right side up, said Shen. "If this module detects that the snake is upside down, it will generate a sequence of hormones to other modules and the whole snake will perform a set wiggling to flip its body to the normal position."

The modules store generated hormones in a hormone template table. Each module typically has two or three template tables, a number limited by the size of the modules' memory, said Shen.

Hormone messages contain four variables, each of which has an expected range of parameters. The variables are HormoneType, ActionCode, ParameterValue and TimeToLive. Modules check each field's value against expected ranges, and discard hormones with erroneous values, Shen said.

As the hormone messages are passed between modules, the modules read them, follow their instructions to perform local actions, and, if needed, modify the messages and pass them on, or discard them when they reach their expiration date.

In cases when a number of hormones signal conflicting actions, a conflict resolution system determines the higher priority hormone.

"This is an interesting application of hormonal control to teams of robots working together. While others have explored hormonal control, I am not aware of other researchers who focused on multi-robot applications," said Ronald C. Arkin, professor and director of the Mobile Robot Laboratory at the Georgia Institute of Technology's College of Computing.

"Hormonal control provides a nice alternative to neural models of control for certain applications, specifically those which are often concerned with self-preservation and/or motional state," said Arkin. "Their use by this group to coordinate multiple robotic units is a nice extension of that idea."

The modular approach should lend itself to considerably larger robots, said Shen. "We can make a snake as long as we want. The snake can move in a caterpillar style. In principle, the size of the robot should not be a limiting factor for a successful reconfigurable robot, for it builds itself up as big as it likes," he said.

In order to make robots suitable for a range of environmental conditions, the researchers plan to modify the modules' housings. "We would like to make them waterproof, but that will be done in the future," Shen said.

The modular robot concept is general enough to have attracted the interest of a toy maker, in addition to the military, industrial and scientific communities, he said.

The researchers expect to have a workable, reconfigurable unit in roughly a year, according to Shen.

Shen's research colleagues on the hormone research were Peter Will, Behnam Salemi. Will and Andres Castano collaborated on the basic modular design, along with Ramesh Chokkalingam, Robert Kovac, and Behrokh Khoshnevis.

The researchers published a technical paper on the building block concepts in Proceedings of the IEEE/Robotic Society of Japan (RSJ) International Conference on Intelligent Robots Systems in Takamatsu, Japan, October 30-November 5.

They published a technical paper on the hormonal communication scheme in the proceedings of the International Conference on Intelligent Autonomous Systems in Venice, Italy, July 25-27, 2000.

The research was funded by the Defense Advanced Research Projects Agency.

Timeline:   1 year
Funding:  Government
TRN Categories:  Robotics
Story Type:   News
Related Elements:   Robot-as-insect video, Robot-as-snake video. Further videos available at; Technical paper "Mechanical Design of a Module for Reconfigurable Robots," Proceedings of the IEEE/RSJ International Conference on Intelligent Robots Systems October 30-November 5, 2000 in Takamatsu, Japan; Technical paper "Hormones for Self-Reconfigurable Robots," Proceedings of the Sixth International Conference on Intelligent Autonomous Systems, July 25-27, 2000 in Venice, Italy.


January 24, 2001

Page One

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Self-configuring robot mimics lifeforms

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