FEATURE
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Maximum power, maximum safety

Rob Coppinger investigates how the industry is containing lasers as powerful as Class 4

‘Class 3B and Class 4 lasers represent a serious hazard to the eyes and skin. Additionally, Class 4 lasers have the potential to damage surrounding infrastructure,’ says Paul Tozer, managing director of laser safety solutions company Lasermet. Rising to the challenge of these increasingly powerful lasers with more comprehensive protection for users and their facilities is driving advances in the safety market. The range of laser safety products now span any industry where lasers are used, from research science laboratories, to universities and engineering design institutions, to dentistry, the medical and beauty sectors and manufacturing facilities. Manufacturing is a leading user of the higher power Class 3B and Class 4 lasers.

One of the latest challenges for the industry is the design, development and manufacture of active laser guarding systems to protect personnel and building infrastructure against the destructive results of stray multi- kilowatt lasers.

Various companies have been designing passive enclosures for many years so customers can fully enclose their lasers safely and cost effectively. Today enclosures are now advancing to active systems.

One company’s patented active laser guarding system is called the Laser Jailer. That company is Tozer’s Lasermet. Lasermet was formed in 1987 and was run by its chairman, professor Bryan Tozer, who at the time had 25-years involvement in lasers. His son Paul is now MD and he explains that ‘the use of proven, CE certified laser blocking materials with their specified rating, ensures that laser beams are kept safely within the laser controlled area.’

A number of Lasermet’s Laser Jailer installations have already been completed in the UK and one of the larger ones has been installed at the University of Manchester. The company won the contract to supply and install active laser safety enclosures for three 16kW fibre laser robotic cells at the University of Manchester’s school of mechanical, aerospace and civil engineering.

The contract was to design and build three laser safety enclosures with active and passive shielding that meet the standard EN60825-4. Lasermet developed the Laser Jailer under BS EN ISO 13849-1:2008 so it was fail safe. These type of enclosures are for lasers, often employed with robots, for cutting and welding operations. At the school of mechanical, aerospace and civil engineering an IPG 16kW fibre laser with multiple outputs is used to deliver, through fibre, the laser light to three processing heads for cutting, welding and deposition processes. These three processing heads are mounted on three six-axis Kuka robots. Safety enclosures were required for each of the robotic processing cells.

The dimensions of the enclosures at Manchester are 4 x 3.5 x 2.5m and one of them has double wide doors at the entrance to accommodate large work-pieces using manual forklifts. Lasermet’s system is modular and as such can be installed on almost any scale; from small enclosures measuring around a cubic metre up to large rooms typically 10m x 10m x 3m. Lasermet’s fail safe technology cuts power to lasers producing stray beams in less than 50ms, preventing damage to the surrounding enclosure and possible injury to its users. Its dual channel ICS-15XM interlock control system is also linked to the relevant robot motion control circuitry. Lasermet’s safety system is hardware reliant and not dependent on software avoiding the problems of bugs and upgrades.

Family owned German laser system manufacturer Trumpf provides machines with extensive safety measures akin to Lasermet’s Laser Jailer. The company’s Ralf Kohlloeffel spoke to Electro Optics about how CO2 lasers were once all anyone had to worry about but the increasing range of powerful lasers meant enclosure safety has had to advance. For Trumpf’s latest product Kohlloeffel says: ‘At the end of 2009 we released the new generation of the 7000 series, offering solid state laser integration, higher optical energy efficiency and lower cost per part and higher performance with lower laser power compared to CO2 lasers.’ The changes seen with the 7000 series in the design of the enclosure and peripheries are because solid state lasers have more stringent needs compared to CO2 lasers due to the different wavelength of solid state lasers. ‘For that reason gaps where laser light can directly or indirectly penetrate the enclosure are totally forbidden for the use of solid state lasers,’ Kohlloeffel explains.

The rotary changer is a turning table and brings the part from the working area so the operator can safely start loading and unloading. However, Kohlloeffel admits that the rotary changer takes up a lot of space and so it is probably not appropriate for a job shop.

Another addition related to tackling the challenge of securing solid state laser beams with mechanical roof tops or shutters is the use of materials that absorb the energy from the solid state laser. ‘We started combining materials and now we know ways that are not working but we also know which are working. With this combination the entire roof of the enclosure is equipped and covered,’ Kohlloeffel tells Electro Optics.

In the enclosure the sides are reflective, guiding the laser radiation to the top, while the roof has an absorber to reduce the laser power dramatically to below the limits set by law.

Another safety measure is ensuring that any operator that steps on the machine’s table is not struck directly by laser radiation. For this problem Trumpf installed two laser scanners, located two metres above the floor. If someone is scanned in this area at a height above two metres inside the TruLaserCell while the laser is on and processing on the other side the machine stops automatically.

Trumpf’s latest development for machines with solid state lasers is the TruLaserCell 7040. It has been commercially available from the second quarter of 2011. One of Trumpf’s customers received it in January 2011 for testing. It is using the system in the dual station mode with its 3kW solid state laser from Trumpf, in a three shift operation.

Any operator will also wear protective eyewear. Lasermet is a distributor of laser safety eyewear in Europe. ‘We have been providing the optimum solution for eyewear for many years – to the appropriate standard – by sourcing from several manufacturers,’ says Tozer.

Laser Components also distributes eyewear. Its Bernhard Russell spoke to Electro Optics about the pros and cons of eyewear selection and use. ‘I used to replace my [safety] glasses every six months, they have a polymer frame and they get thrown on benches. The scratches thin the filter and it might still be eye safe but it is taking that risk, you’re thinning the material,’ he explains. ‘With Class 4 [lasers] your reactions aren’t quick enough and your eyesight will be destroyed in a fraction of a second. It is important that people get the right level of safety.’

A lot of eyewear is designed for a range of wavelengths. Some will filter out 780-840nm, others 315 to 400nm and then there are those that filter 800 to 950nm and above. The glasses with the wider range, from 700nm up to 1100nm have darker filters. ‘The more blocking you put on, the more the visibility is reduced. So instead of 50 per cent plus visibility you get 17 or 18 per cent,’ explains Russell. ‘Safety levels are creeping up now. Whereas before there was just a level of five, that is now six or seven. We are also finding [levels of] eight and [some products], one or two, at nine.’

Another aspect to eyewear design that arises when providing the greater protection needed with Class 4 lasers is the use of glass. ‘With CO2 [lasers] you will end up with glass filters in them. But unfortunately glass makes them very, very heavy. A lot of people don’t like that. When you’re looking down at something you need something that is very sturdy, and they don’t tend to be very comfortable’. Because of this, companies have been trying to reduce the weight. ‘We have found a trend in people wanting lighter, more comfortable eyewear. We have started seeing changes; where you could only find glass we’re now finding there is a polymer equivalent,’ Russell says. ‘Something polymer, a lighter [lens], if you’re wearing them all day it will make a big, big difference to your work’.

Russell explained that a lot of the new developments in eyewear have been developing technology to get away from glass but that ‘in certain circumstances you’ll never get away from glass’.

Russell has seen product changes over the last 10-15 years with glasses that were uncomfortable and bulky and heavy for a high level of protection are now becoming sleeker and more ‘wrap around’ in style. ‘We have several ranges ideal for people with prescription lenses,’ he adds.

Users have also demanded better visibility and there is a much wider range of clear options where there is a visibility of 90 per cent but still giving the blocking at the wavelength users need.

Prices for basic glasses through to the sleeker wrap around styles range from £25 to £300-£400.

Russell warns that people keep glasses longer than they should and that scratches, even on a £400 pair, mean the eyewear is giving the users less protection than it should. ‘If you have a cluster of scratches then replace it immediately, it is not worth taking the risk. [But] safety glasses should be the last line of defence. There should be other safety measures in place,’ including the enclosures.