Snake-arm robots are turning the corner in everything from car production to medical surgery, reveals Ben Gadd

The ancestry of nearly all modern robots can be traced back to the pioneering work of Unimate in the Sixties, when they began the hugely successful process of installing industrial robots on car production lines. Interest and investment in robotics has had the ups and downs of a runaway rollercoaster since then, but a recent advance appears to be slithering its way to success.

Since 2000, OC Robotics have focused on developing snake-arm robots which, before you start panicking, are no relation to the boa constrictors and pythons of this world. They have been developed to reach into nuclear reactors, aircraft wings and even difficult-to-access parts of the human body, such as the brain or the gall bladder. These long, slender, robotic arms can reach into confined spaces, more like flexible endoscopes - the optical tools that are used to look inside the body - than the powerful industrial robots used to assemble cars. Instead of rigid links, interconnected by joints like the human arm, they have a fluid, curving shape like a human spine.

The mathematics behind the arms aroused interest at OC Robotics, but it was the realisation that these mechanisms might solve a range of difficult tasks that provided the impetus to raise capital and start designing.

OPERATIONAL USES

The initial market pull came from medical surgery. In the mid-Nineties, discussions were held between OC Robotics and neurosurgeons about a device that could follow non-straight paths into the human body. In the brain this involved the fluid-filled ventricles that were like a 3D canal system to reach the lower brain, for example.

Such surgical tasks require a highly versatile and flexible device, one that can progress along curved paths without exerting forces on the surrounding tissue. Surgical devices have to be very safe, easy to use, robust and easily sterilised. These practical considerations led OC Robotics away from standard robot designs with motors at their joints.

HOW SNAKE-ARM ROBOTS WORK

The basic component of a snake-arm is a patented link, which functions in the same way as a vertebra. Each link articulates with respect to its neighbours and springs are used to stabilise the link structure so that when unloaded it will straighten out.

The shape of the arm is controlled by groups of three wires, 120 degrees apart, that pass through the core of the arm. The number of links and the number of segments can be varied according to the payload (what weight needs to be carried), length and curvature requirements of the arm. The shape of each segment can then be controlled independently by varying the length of each wire using motors.

"These robots are really about getting into awkward spaces," says Dr Rob Buckingham at OC Robotics. "The advantage of [them] is that you get a device that can steer around multiple corners."

He's not wrong: the robots can actually move in up to 30 different directions at once, which means they can flex and bend to fit into whatever space they happen to be in. You can move the arm around whilst holding the tip and still make it follow its nose. "The number of possible movements means the maths can become very interesting," adds Buckingham.

SECONDARY CHARACTERISTICS

The design of snake-arm robots means that there are a range of secondary features that give the device additional uses. One feature is that the arms have a constant diameter and are hollow. This is ideal for routing services to tip-mounted sensors and tools. It also means that a snake-arm can be used as a steerable hose, performing the tasks of a vacuum cleaner or a fuel line.

Having a constant arm diameter means that protecting the arm from the environment and vice versa becomes as simple as sleeving the arm in a flexible skin. This is essential in situations when it is important to stop the arm becoming contaminated - such as when it is being used in nuclear reactors - or to stop the arm contaminating the environment, when it is being used in surgery or food preparation. The snake-arm is also designed with a quick-release interface, which means it can be disposed of if need be.

APPLICATIONS

OC Robotics first contract in 2003 was for a snake-arm mounted on a remote-controlled vehicle for the Ministry of Defence in the UK. Two were then designed as part of the solution for repairing a leaking pipe in a Swedish nuclear reactor. Currently the company is conducting a project with Airbus, assessing how a snake-arm may be used for inspecting the inside of the wings on their aircraft in the future. "There are a lot of applications," said Dr Buckingham. "What this is all about is reaching the unreachable."

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