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Guiding a snake-arm robot into a tight spot

11 February 2013

OC Robotics' snake-arm robots are, as their name suggests, long, slender and flexible enough to fit through small openings and move around obstacles effortlessly with no prominent elbows to snag or cause damage to surrounding equipment. They are easily manoeuvred into position and are just as easily retracted without disturbing their environment - features that make them very attractive for certain duties at the Sellafield nuclear waste processing site.

However, these innovative robotic arms need the support of guiding mechanisms which provide a reliable method of introducing them into these confined workspaces. HepcoMotion's 'V principle' slide system, comprising a hardened and ground steel plate with 'V' shaped edges captured between pairs of correspondingly 'V' shaped ball bearings, has a proven track record in the nuclear industry and has been specified on previous OC Robotics projects encompassing visual and radiological inspection, remote handling, loose material sampling and water-jetting. 

Lightweight for portability and easy handling, but rigid enough to be cantilevered, HepcoMotion's HDS2 V principle slide proved to be the ideal choice for a recent application at Sellafield where its low maintenance and reliability are key requirements for the ‘no-go’ nuclear environment.

A beam comprising this heavy duty slide had previously been used in Sweden to form an X-Y gantry system where, again, the key criteria were low mass, high rigidity and ease of modification. These factors, plus HepcoMotion's willingness to machine the necessary components from stock in order to meet the client's specifications, made the HDS2 product the clear front runner. Favourable cost and the technical guidance provided by the company’s applications team also helped secure this order.

Meanwhile, back at Sellafield, the HDS2 forms the spine of a system on which the rail, supporting the snake arm both vertically and horizontally, is mounted. The Sellafield snake-arm weighs 70kg and is moved under close control at a speed of around 50mm per second. OC Robotics’ Tim Francois takes up the story:

“The fact that HepcoMotion can precision machine four metre long beams meant that the system could very easily be made compatible with our frame. The HDS2 system is also very easy to maintain, requiring minimal lubricant. We required a positional accuracy of 0.1mm but achieved much better, repeatable results in reality”

Rather than being classified as special requirements, corrosion resistant components and stainless steel slides are both standard choices within the HDS2 range. As a result, OC Robotics was able to specify a standard aluminium product to meet its low weight and corrosion resistance requirements for nuclear use. The fact that it needed minimal modification was an added bonus.

Now fully constructed, the bespoke snake arm was recently transported to Areva in France for pre-installation nuclear trials. And, according to Tim Francois, because the HDS2 system was so easily mountable on any frame it made these trials very simple to accomplish.

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