Robotics make inspecting and replacing cutter discs on tunnel boring machines safer and faster.
Robotics are finding a real application in tunnelling projects, where there are real, tangible safety benefits in putting robots instead of humans in high-risk places.
Nowhere is this being better demonstrated than in Hong Kong on the 4.2km long sub-sea tunnels that constitute the most challenging part of the 21km under sea Tuen Mun to Chek Lap Kok Link.
One of the most ambitious projects currently under way in Hong Kong, it is fraught with risk.
High risk project
The ground is poor, the tunnel is deep – up to 55m deep – and the water pressures are huge – up to 5.5bar.
The contractor is Bouygues subsidiary Dragages Hong Kong, which has rolled out two key robotic innovations to significantly reduce the amount of human intervention needed in the cutter heads of the giant 17.63m diameter tunnel boring machines – the world’s biggest.
The two robots – the Snake and the Telemach – working alongside a Mobydic telemetry system - have been specifically developed to reduce the need for manual operations in hyperbaric conditions.
Off the shelf
Both have effectively been bought off the shelf, more-or-less, from robotics companies after Bouygues learned the hard way that it is a construction company not a robotics one.
“Five years ago we tried to build some robots. It was a big mistake,” explains Bouygues technical director Christophe Portenseigne. “Our business is not building robots. In factories robots stay in one place. In our industry, they need to move,” he says, to illustrate just one of the complexities of building robots from scratch for construction projects.
But getting companies to build one-offs for one-off projects is hard.
“Companies don’t want to work with us to develop bespoke robots, as we are a one-off,” he adds. Instead Bouygues now works with specific robotics suppliers to modify existing robots.
Aeroplane wing inspections
“The Snake we bought from the UK,” he explains. “It was designed to explore inside the wings of aeroplanes,” he adds. The first one was not robust enough. Now we have worked with them to build a second.
“So it is co-development, “he adds.
The skill, then, is finding and adapting the right robots and making them work as a system.
Here, in the Tuen Mun tunnel it starts with Mobydic. Mobydic is a system of sensors incorporated into disc cutters in the heads of the TBMs that enable wear on the cutters to be monitored, as well as providing real-time geological mapping of the rock face.
But nothing beats a visual inspection and the second innovation is Jet-Snake, a remote controlled robotic exploration arm equipped with a high pressure jet that can clean cutters and allow their condition to be assessed from the comfort of the TBM pilot’s cabin.
The Jet-Snake was bought, more-or-less off the shelf, from UK robotics firm OC Robotics.
And it is providing obvious safety benefits.
“We prefer losing a camera than a colleague,” observes Bouygues engineering and systems department manager Pierre Moulin.
Those cutters that then need replacing? Well, that is where the Telemach comes in – a teleoperated (remote control) system that allows safer replacement of TBM disc cutters.
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The traditional option is using teams of workers, operating under hyperbaric conditions, to go in front of the cutterhead and manually lift out the worn cutters and lift back in new ones. These teams have to work in extreme conditions that include confined dark spaces, up to 5 bar of pressure, 100% humidity and 40°C. It is uncomfortable, strenuous, and there are obvious safety implications. It is about the most extreme environment likely to be encountered on a civil engineering project.
But work by Bouygues’s research and development team has dramatically reduced the number of these human interventions.
To lead the effort, the contractor hired Patrice Robert – previously of Renault Automation and Kuka Robotics UK – as director of robotics. Robert is responsible for a team of five engineers and a cohort of specialist suppliers. It was quite an effort for the team to get to where it is today – successfully operating the Telemach at Tuen Mun.
But it is worth it, says Robert.
“Changing cutter discs is dangerous and takes time,” he notes. And time is money: “TBMs are stopped for 46% of the time they are in the ground – and half of the stops are due to cutter head disc changes,” he explains.
But the path to developing the Telemach required Bouygues to push its technical envelope beyond what had ever been seen in the tunnelling sector. To facilitate automated installation and removal of the cutter disc it had to rethink the cutter discs themselves and trialled six full-scale prototypes before validating the model.
The new disc is considerably more manoeuvrable. Comprising just one part versus the 11 components that make up most disc cutters, it weighs in at 220kg instead similar to the usual 305kg.
Indeed, as a spin-off benefit the new cutter disc is so successful that its personnel prefer to use it when manual changes are required.
But the central piece of the innovation is a robotic arm that is able to work in aggressive and high-pressure ground conditions. It is an off-the-shelf robot modified by Bouygues to withstand up to 7 bar of pressure. Bouygues has given the robot stereoscopic vision and fitted it with sensors that can it can control force.
This is crucial, says Robert: “Else it is like pulling on a stuck drawer,” he says.
Positioning is important
The Telemach robot is installed behind the cutterhead, accessing the cutters through an access hatch. The siting is important – at 3 o’clock, on the periphery of cutterhead. From there it can access the outer 50% of the cutters, which typically are 80% of those that will need changing as they cutters travel further and therefore do more work.
Trials began last year and the results were near-immediate. “The best manual replacement time is 45 minutes,” says Robert. “With the Telemach it is 25 minutes.”
Now 50% of the discs are changed robotically, eliminating the time and risk associated with people working in compressed air.
Innovation the French way
To Portenseigne is it simply “driving innovation the French way”.
“We don’t count on-the-project innovation as innovation,” he states. “For example, we don’t count building the longest, the fastest as innovation. That’s good project delivery.
“But we are used to innovating, so we can show the process,” he adds.
“Mobydic was 10 years of testing and development, and initially it was a mess. But now everyone wants it,” he observes.
Bouygues has a formal process for using live sites as trial sites. “R&D is a project like any other, with a schedule and cost controls,” explains Portenseigne. “So of the 40 R&D projects we have underway at any time, each has a project manager or project team with a board member sponsoring it, and bought into it and responsible for it.
Learning by failing
“On site we cannot fail. But when it comes to innovation we can fail,” he says, adding that team structure means that when an innovation starts failing, those involved can act fast to stop it impacting the project. “You have to learn so you can end prototype one and move to prototype two. Sometimes we stop completely,” he adds.
It’s a bracing approach, but one that bears fruit. And not always the fruit that was expected – take the Telemach.
“Sometimes the breakthrough is not what we were expecting,” notes Portensigne. “In order to have robots changing cutter head discs we had to redesign the mechanism and in doing that we made it three times faster for divers to do it – even without the robot.
“This made it possible for the robot, by making it lighter, made it quicker for men,” he observes.