Robots aid in particle physics research

A laser-welding system incorporating ABB IRB 140 six-axis robots is helping make critical components for the next generation of particle accelerator.

A laser-welding system incorporating ABB IRB 140 six-axis robots, developed for manufacturing critical components for the next generation of particle accelerator is "probably the most precise and demanding application of a standard robot ever devised" according to Chris Moore, Managing Director of Garrandale Systems, designer of the system.

The system was developed in collaboration with Ferranti Photonics for Accles and Pollock of Birmingham, which is manufacturing special, nonmagnetic, stainless-steel alloy tubing assemblies for the new Large Hadron Collider (LHC) for The European Organisation for Nuclear Research (CERN).

Planned for completion in 2007, the LHC, located 100m underground near CERN's headquarters near Geneva will be the largest particle physics apparatus ever built.

The LHC accelerates two beams of particles in opposite directions within a 27km ring of super conducting magnets held at temperatures approaching absolute zero.

The resultant collision between the two beams will help provide research information at the very edge of scientific knowledge.

Accles and Pollock, using the manufacturing system devised by Garrandale, is producing both "dipole" and "quadrapole" tube assemblies.

Dipole tubes are used to bend the path of accelerating particle beams and to keep them on course, whereas quadrapole tubes are used to focus the particle beams for collision at detector points.

Each variant of dipole and quadrapole tube is an extremely accurate and complex welded assembly, comprising a beam screen tube, cooling tube, cooling tube feedthroughs, beam screen fixed points, sliding rings, contact rings and cooling tube supports.

Garrandale's task was to design a manufacturing system and jig that could handle tubes in lengths of 15-18m long which have to be straight and accurate to extremely tight tolerances in all planes.

Welding specifications are extremely demanding - on one detail alone the tube assembly requires 0.3mm-diameter spot-welds every 1mm in axial length.

For the two particle accelerator rings that works out at 54,000,000 welds alone.

The position of the welds has to be within 10-15um to be effective, although the welds themselves are only 300um in diameter.

Commenting on the selection of a standard robot for these tasks Chris Moore said: "When surveying the market we could have gone for a specialist robot, however we knew the ABB IRB 140 was inherently precise by the nature of its design".

"ABB allowed us to check out the IRB 140's positional accuracy and repeatability during a demonstration at the company's Milton Keynes facility and the robot did indeed achieve 10um".

"In service it has performed every bit as good with no faults whatsoever".

The IRB140, ABB's smallest robot, provides an extremely compact automation solution while boasting one of the fastest cycle times of any articulated robot and an industry-leading payload for its size, 5kg.

The Garrandale system - contained within a temperature and humidity controlled environment and operated for safety reasons through remote CCTV - incorporates two ABB IRB 140 six-axis robots, which travel independently along linear tracks.

Each robot is equipped with Luxstar 100W ND:YAG laser welding head.

Laser welding was chosen because it is a high speed, precise technique ideal for the application, capable of producing very controlled weld penetration.

Other benefits of laser welding include low distortion, excellent aesthetics and reduced heat affected area.

Garrandale Systems take advantage of the ND:YAG laser's ability to focus through standard optics - thus the laser's lens is linked to a CCTV camera and used as a highly accurate positioning tool by the system operator, providing an extra check for the accuracy of weld positioning.

The Garrandale system uses fixed tooling to locate the screen tube assembly from below while an integrated sliding carriage moves along the tooling to position the cooling tubes as they are welded.

On either side of the tooling, linear tracks provide a seventh axis for the robot control system.

The robot-mounted lasers weld most features of the tube assembly, except for the cooling tube and feed through.

For cooling tube welding, the laser delivery heads are removed from the robots and located on a special tooling carriage with one of the robot track slides towing the carriage along.

The ABB robots work in close synchronisation moving along the linear track in a primary robot/secondary robot configuration - the robots even work together on a single weld, such as the circumferential weld of the contact ring.

Both robot controllers are linked through standard ABB software to effectively give a single robot control system.

To assist this and primary robot/secondary robot synchronisation, extensive use of ABB RobotWare advanced programming options has been made, including "World Zone" software.

World Zone software is especially useful when two robots are working in close proximity to prevent collision and establish working protocols.

Commissioned in March last year, the Garrandale system has operated faultlessly since it started operation for Accles and Pollock.

Chris Moore adds: "The combination of precision tooling and a standard, though high performance robot coupled to a high-level of robot programming, has produced incredible levels of accuracy and repeatability within the application for which we are all justly proud".

Garrandale's Operations Director and Senior Manager on the project Tony Hart sums up: "The project uncovered some challenging technical problems - probably the most difficult of which was achieving weld positional accuracy and repeatability on the relatively small and complex area of the tube assemblies".

"Garrandale Systems is extremely proud of the innovative way in which these challenges were overcome through our own research and development, and the technical discourse and collaboration between the customer, our project partners, suppliers and CERN engineers".

"To this end, the help and advice from ABB plus the exceptional positional accuracy and repeatability of the ABB robots, were invaluable in achieving these goals".

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