Fullscreen HTML5Med Res (??MB)HTML4

Advertising with high power lasers projected onto the sides of city buildings is soon to become a reality in Australia and in fact, we lead the world in the development of this technology. SILICON CHIP recently took a look at these highpowered lasers which are controlled by computer. By LEO SIMPSON Just when you thought that advertising had gone about as far as it could go, a brand new technology has popped into place to give the marketing people another way of delivering their message. Just recently, Sydney City Council has approved in principle the use of Laservision for advertising on the sides of large city buildings. And with Sydney leading the way, other Australian cities are sure to follow. Laservision is in fact the name of Laservision (Aust.) Pty Ltd. They have developed and own the technology for controlling high power lasers so thatthey can produce almost any image imaginable. The lasers they use to project images on the sides of buildings, the Sydney Opera House or at the State of Origin rugby league matches are big - 5 to 20 watts. They are also to take delivery of the world's most powerful visible laser, capable of producing 32 watts. While such a power rating may not seem big, in terms of lasers it really is big. And if you think about the really low efficiency of laser tubes, like less than .05%, then the power input to these devices is quite significant - tens of kilowatts. Mirror, mirror As you might expect, to make a high power laser write on a wall or cliff which may be a kilometre in the distance, you don't move the laser, you move the beam. It's all done with mirrors. But there's no way you can 76 SILICON CHIP accept that glib explanation and then move onto another subject. Laservision Australia has spent some 8 years developing the control technology for writing with lasers and they reckon they are still refining it. At the moment they have the only system available worldwide which can be programmed in real time to control a laser display. You can sign your signature on a digitiser panel and have it blown up to 50 metres wide by the laser - instantaneously. The result is that Laservision's system is booked for advertising and media displays all around the world. In fact, if you see an overseas sourced video news item featuring a large laser display, the chances ar.e that it is a Laservision show. Animated advertising So what are the ramifications of having permanent laser advertising on the sides of city buildings? One of the big advantages of laser vision advertising is that it does not require any large supporting structure. As long as there is a large blank wall in clear view, that is all that is needed. There is no need for a large bulky billboard structure which is costly to put up in the first place and then costly to pull down when it is no longer needed. The second big advantage comes about because of the immediate programmability of the Laservision 1 Co~™110111CA~TI((l r, Laservision displays can be projected from very long distances and onto odd shaped surfaces such as the Sydney Opera House sails. Mist and smoke from passing ferries makes the beam itself visible. This Laservision display during the recent State of Origin rugby league matches used a whopping 20 watt Argon laser. The large display is so bright that the full sportsground lighting was able to be left on for the whole display. system - that enables the display to be changed almost at will. For example, a large city Laservision diplay could be programmed to display a multiplicity of advertising messages which could be charged on a timeslot basis, just the same as TV. But interspersed with the advertising could be useful information to the passing parade of citizens; news bulletins, traffic and accident reports and so on. Where the laser billboard was visible to large numbers of motorists, as it inevitably would be, it would be possible for the local traffic or municipal authority to specify how much animation and how many changes per minute there is in the advertising. The idea behind this is that the advertising can be made less distracting to motorists in peak hour conditions. Actually, Laservision doesn't even need a flat wall on which to project a recognizable image. Since a laser beam is always in focus, it can produce an outline image on any surface, including the curved sails of the Sydney Opera House. What about the drawbacks of laser advertising on buildings? Are there any at all? Well, apart from the need to supply the power and control requirements of the laser, which we '11 get to in a moment, and the possible danger of people being injured by the laser, there aren't any real drawbacks, unless of course, you regard the advertising itself as a drawback. Is it possible to be injured by the laser? Absolutely. Laservision's 5 watt laser can lighl: a cigarette at 100 metres! If it got you in the eye, you'd be blind and that would be that. Even looking at the spot projected on a AUGUST 1990 77 Really, when you consider the above figures, high power lasers are hungry beasts but what little light they put out is coherent and that's what makes laser light so special- its concentrated beam diverges very little over long distances and it can even write on the clouds. In the future, Laservision hope to be working with solid state lasers which have much higher efficiency. Even now, there are solid state laser arrays capable of producing 5 watts but at present they can only work in the infrared region. Controlling the light fantastic This is the 3-phase power supply for Laservision's 5 watt model. Rated at 14 kilowatts, it is water cooled, as is the laser itself. nearby wall by a 5 watt laser is painful and it can set the wall smoking in a short time! So clearly, the laser can only be set in such a way that no-one is ever likely to come into contact with the beam. In fact, there are strict guidelines set down by the National Health and Medical Research Council of Australia which cover the safe use of lasers. Mind you, while the laser could light a cigarette at 100 metres and even burn a wall when focused to a stationary spot at close range, when scanning images at a distance there is no likelihood of damage to buildings. In principle, deflecting a laser beam to write a message is simple. One mirror deflects it in the X direction (ie, horizontal axis) while another mirror deflects it in the Y direction (Y axis). Continuously move both mirrors by very small amounts and the beam can be deflected extremely rapidly to produce an unbroken outline image which may be hundreds of metres wide and hundreds of metres high. Laservision's system does all this and a great deal Laser specifications Few people have ever come into contact with lasers and when they have, they have usually been small helium-neon instruments capable of putting out just a few milliwatts. On that basis, their power supply requirements have not seemed very demanding maybe a 50 watt power supply is all that is required. But when you scale up the power demands to feed a 5 watt laser, you realise just how inefficient these devices really are. Laservision commonly employs a 5 watt Argon (blue-green) or Krypton (red) laser. These are large instruments typically measuring 114cm long, 16.5cm wide and 18.6cm deep. They are heavy, weighing over 46 kilograms (102lbs). They use a 3-phase rack mounting power supply which looks reasonably impressive but it is not until you look at its power input specifications that you realise just what's involved: 40 amps per phase at 208 volts AC; that's just over 14 kilowatts! To supply that requirement from Australian 415V AC 3-phase mains supply takes a whopping transformer that weighs over 95kg! Where does all that power go'? Well, we said before that lasers are highly inefficient devices and so virtually all that power is ultimately turned into heat by the laser tube and its associated plasma coils. To get rid of the heat, the laser and the power supply must be water-cooled and in fact is fed by a substantial hose at 8.5 litres per minute. 78 SILICON CHIP This is the 5 watt Argon laser, sitting on top of its carrying case. In the future, solid state laser arrays will be much more efficient and a very small fraction of the size of this model. This view of the laser shows the two galvanometer scanners and their dichroic mirrors which are used to deflect the beam. Ordinary metallised mirrors are no good for this task as they are not sufficiently efficient as reflectors - the laser would burn a hole straight through them! Moving the mirrors While this tunnel effect looks spectacular, it is easily produced by a laser and a rotating mirror - no fancy laser scanning software is needed. more. For example, in every Laservision display (whether text, script or graphics), the image is unbroken. At no point does it start or finish - it is continuous. The control software does not reduce the apparent laser light output by blanking the laser during a retrace line from start to finish of an image; the software cleverly makes the laser spot write the image in such a way as to avoid any need for a retrace period. By doing so, they not only avoid reducing the apparent light output but they also avoid the need for the extra complication of an electronically controlled shutter. As you can imagine, the mirrors which deflect the laser beam must be controlled with extreme precision. And before we go any further we should perhaps describe the mirrors. The mirrors used to deflect the beam are not mirrors at all. They look like small pieces of glass and are, in fact, dichroic filters, similar to those used for beam splitting in colour TV cameras. At the light wavelengths for which they are designed, dichroic filters act as more efficient reflectors than conventional silvered (or aluminized) glass mirrors. This is important because low reflector efficiency quickly translates into heat rise and conventional mirrors would quickly burn out - the laser literally burns a hole right through them. The two small dichroic mirrors are each moved back and forth by devices which are referred to as galvanometer scanners. In essence, these are the same as the pointer deflection coil used in analog multimeters. In fact, they are virtually the same as the mirror galvanometer, a very precise instrument which is virtually a laboratory curiosity. Like the mirror galvanometer, these galvanometer scanners have a centre rest position and the mirror can be deflected symmetrically from each side of this centre rest position. The difference is that while mirror galvanometers were very sensitive, responding to mere microamps of current, these laser deflectors are high power devices with very fast response times. As well as having a fast response time, the : We keep it simple, · so you can look smart. ProtelEasytraxn, a fast, friendly, low-cost pr ogram for PCB design that lives up to its name. PC version $395 Macintosh® version $495. Ideal for students, hobbyists and prototype builders - a professional design system for PC's that supports multi-layer boards, including power and ground planes, up to 32 x 32 inches. Complete throughhole package includes pad-to-pad autorouter, editable ~ Protel Technology component library, metric/ in1perial grid system to 1 mi! (.001 inch) placement accuracy. Supports popular printers 2 Protel Easytrax and pen plotters, plus Gerber ®, Postscript®and N/C drill output. User files and libraries are compatible with both PC and Mac versions. So, you can get smart and take the Electronic Desi!Jn. A u tomation specialists 1· Product ofAustra ia © 1990 Protel Technology Pty Ltd affordable solution. GPO Box 204 Hobart Tasmania 7001 Australia Phone (002) 730100 (Int'l + 6102 730100) Fax (002) 730944 (Int'l+6102 730944) PC version requires XT/ AT/ 386/ 486 compatible ,vith 640K RAM ; DOS 2.0 o r later. Macintosh version re quires Mac Plus, SE o r II. Mac and M.\Cintosh are registered trade marks of Apple Compute r, Inc. Gerbe r is a registere d trademark o f Gerber Scientific , Inc. Postscript is a registered trademark of Adobe Systems, Inc. A90-S AUGUST 1990 79 galvanometer scanners have positional feedback [via separate coils) and temperature compensation so that the laser beam does not drift from its initial set-up position as the temperature changes. To provide the temperature compensation, the galvanometers have been provided with external heaters and thermocouples. The other reason for having positional feedback and temperature control is to make sure that the laser always follows the same path when scanning out a pattern - if it did not continually follow the same precise path [within a few millimetres at a distance of 1 kilometre) the image would be blurred and not as bright. In addition, the drive circuitry defines the limits of horizontal and vertical deflection of the laser beam [the scan "window"). This is an inbuilt safety feature so that even if the driving software goes awry the laser beam will not be deflected anywhere but at the target wall. The time for the laser to make one complete scan of the image is typically 20 milliseconds although it depends on how complicated the image is. Larger and more complicated images take longer to scan but once the scan frequency gets down below 20 Hertz or so, flicker begins to become a problem. Interestingly, the scan rate can be set to avoid flicker problems when the display is being recorded on film or video and the programming has time code facilities so that a laser display can be precisely choreographed into a video production schedule. 80 SILICON CHIP Laservision can project very complex images such as this one for a well known magazine. The images are vector scanned in outline and not "raster scanned" as in video technology. Note that this image is being produced in real time, direct from the digitiser tablet. Another interesting aspect of the software includes the ability to "keystone" the display so that it can be projected onto oblique roofs or for example, on the Sydney Cricket Ground during the recent State of Origin series. As well, images can be rotated, and animated to blend from one to another, expand, contract and so on. It is this ability to rapidly change images which make the Laservision display so entertaining to audiences at large entertainment venues. Apart from the power amplifiers, power supplies and other analog control circuitry, Laservision's control hardware includes a full size digital to analog control card which fits into a Toshiba T3200 laptop computer with a plasma display. It is used in conjunction with a digitiser panel for direct programming of the laser display. The photos included in this article show some of the spectacular displays which Laservision has produced. For us though, one of the most satisfying was the setup they did specially for the SILICON CHIP logo. They say there is nothing like having your name up in lights. With Laservision, that's especially true. Acknowledgement Acknowledgement: our thanks to Paul McCloskey of Laservision [Aust) Pty Ltd for his assistance in the preparation of this story and for supplying the photos.