In factories and warehouses, it’s not uncommon to see robots moving items or tools from one station to another. For the most part, robots can navigate easily across open layouts. But they have a much harder time winding through narrow spaces to carry out tasks such as reaching for a product at the back of a cluttered shelf or moving around a car’s engine parts to unscrew an oil cap.

Engineers have developed a robot designed to extend a chain-like appendage that is flexible enough to twist and turn in any necessary configuration, yet rigid enough to support heavy loads or apply torque to assemble parts in tight spaces. When the task is complete, the robot can retract the appendage and extend it again, at a different length and shape, to suit the next task.

The appendage design is inspired by the way plants grow, which involves the transport of nutrients in a fluidized form up to the plant’s tip. There, they are converted into solid material to produce, bit by bit, a supportive stem. Likewise, the robot consists of a “growing point,” or gearbox, that pulls a loose chain of interlocking blocks into the box. Gears in the box then lock the chain units together and feed the chain out, unit by unit, as a rigid appendage.

Grippers, cameras, and other sensors could be mounted onto the robot’s gearbox, enabling it to meander through an aircraft’s propulsion system and tighten a loose screw or reach into a shelf and grab a product without disturbing the organization of surrounding inventory, among other tasks.

The new “growing robot” can be programmed to grow, or extend, in different directions, based on the sequence of chain units that locked and fed out from the growing tip, or gearbox. (Image courtesy of researchers, edited by MIT News)

The design of the new robot addresses the “last one foot problem” — an engineering term referring to the last step, or foot, of a robot’s task or exploratory mission. While a robot may spend most of its time traversing open space, the last foot of its mission may involve more nimble navigation through tighter, more complex spaces to complete a task. Engineers have devised various concepts and prototypes to address the last one foot problem including robots made from soft, balloon-like materials that grow like vines to squeeze through narrow crevices. But such soft, extendable robots aren’t sturdy enough to support end effectors or add-ons such as grippers, cameras, and other sensors that would be necessary in carrying out a task once the robot has reached its destination.

Once the team defined the general functional elements of plant growth, they looked to mimic this in a general sense in an extendable robot. They designed a gearbox to represent the robot’s “growing tip,” akin to the bud of a plant, where as more nutrients flow up to the site, the tip feeds out a more rigid stem. Within the box, they fit a system of gears and motors that works to pull up a fluidized material — in this case, a bendy sequence of 3D-printed plastic units interlocked with each other, similar to a bicycle chain. As the chain is fed into the box, it turns around a winch, which feeds it through a second set of motors programmed to lock certain units in the chain to their neighboring units, creating a rigid appendage as it is fed out of the box.

The robot can be programmed to lock certain units together while leaving others unlocked, to form specific shapes, or to “grow” in certain directions. In experiments, they were able to program the robot to turn around an obstacle as it extended or grew out from its base. When the chain is locked and rigid, it is strong enough to support a one-pound weight. If a gripper were attached to the robot’s growing tip, or gearbox, the robot could potentially grow long enough to wind through a narrow space, then apply enough torque to loosen a bolt or unscrew a cap.

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