Innovations in laser printing
Over forty years of evolution and refinement have seen the laser printer become a ubiquitous technology for small business, the workhorse of the enterprise, and the engine of a revolution that changed publishing forever. It’s one of the key technologies of the last century, and its role is far from over. While inkjet printers can now equal them in terms of speeds and costs per page, nothing beats a laser printer when it comes to high-speed, high-volume workloads – and it’s unlikely that anything will soon.
Laser printers have their roots in electrophotography, as developed by the American patent lawyer, Chester Carlson. In 1938 Carlson discovered that you could create a copy of a page of text or images by reflecting light off the white areas of the paper onto a charged drum. The light would neutralise the charge on the drum, so that when oppositely-charged toner – fine particles of dry powder mixed with a colouring agent – was applied to the unexposed areas, it would stick. This toner could then be rolled from the drum onto a sheet of paper, where heat and pressure would fuse it to create a copy. This technique formed the basis of the first photocopiers, and led to the creation of one of the pioneering IT companies, Xerox.
In 1969 Gary Starkweather, a researcher for Xerox, had the idea of using a laser to draw a digital image on the copier drum, successfully demonstrating the principles of what would become the laser printer. Eight years later Xerox released the Xerox 9700 Electronic Printing System, which featured a 30dpi laser printer that could print at a speed of two pages per second. Yet this was a huge and highly expensive system, not the laser printer we know today. To make one into another took the talent and expertise at one of IT’s other pioneers: Hewlett Packard.
By the mid-1970s Canon had developed a prototype laser printer, which it demonstrated at the autumn 1975 National Computer Conference. Canon had an existing relationship with Hewlett Packard, and asked whether HP would be interested in bringing the technology to market. HP took Canon’s core technology and engineered its first laser printer – the HP2680A – around it. Released in 1980, it was still a high-end product designed to work with mini-computers, yet it paved the way for the first mass-market laser printer, the HP LaserJet.
The technology we use in laser printers today still stems back to that first LaserJet. Instructions arrive at the printer in the form of printer control language, which tells the printer what text and picture elements go where, and how they should be styled. The printer’s Raster Image Processor (RIP) transforms these instructions into a map of dot patterns, as they will be printed on the finished page. The drum is charged by a Corona wire or primary charge roller, then the laser, working through an arrangement of lenses and mirrors, etches the map created earlier onto the drum. This makes those areas negative so that the positively-charged toner particles will stick to them, and the page can then be transferred onto paper from the drum, ready to be bonded.
Released in May 1984, the LaserJet combined Canon’s latest print engine with an 8MHz Motorola processor and the third-generation of HP’s PCL printer command language to form a 300dpi, 8-page per minute printer capable of outputting text and graphics on the same page. The LaserJet Plus, released in September 1985, improved on that with soft fonts and larger graphics. In the same year Apple unveiled its LaserWriter, which used the PostScript page description language as an interface between the printer and early DTP software. Together the HP LaserJet, Apple’s LaserWriter and Aldus’ PageMaker publishing software created Desktop Publishing, Meanwhile the LaserJet fast became a key partner for the early MS-DOS and Windows PCs that were now flooding into the world of business.
Colour was the next big development. A colour laser printer works along the same basic principles, but where a mono laser printer has just one printer mechanism running one black pass over a white page, a colour laser has one to four printer mechanisms running four different passes, one Cyan, one Magenta, one Yellow and one Black, layering the four inks in dithered patterns to create an illusion of continuous tone. QMS was first to market with the QMS ColorScript Laser 1000 in 1993, but HP wasn’t far behind with a more cost-effective rival, the HP Color LaserJet, in 1994.
Since then it’s been onwards and upwards for the laser printer. We’ve seen speeds grow from 8ppm to 50ppm, resolutions move from 300dpi to 600, 1,200 and now 2,400dpi, and engines and control languages develop to allow for more complex documents, more detailed graphics and more accurate photo reproductions. And while we’re seeing Inkjet printers match those resolutions and those speeds, the laser printer still has some advantages. Where most Inkjet printers are built to handle a monthly workload between 250 and 3,000 pages, enterprise-grade lasers can cope with anywhere up to 20,000 pages every month. If a business needs to print large numbers of documents on plain paper, keeping costs down and text quality high, then a laser printer is still the way to go.
So what now for the laser printer? Over the last few years it’s become the heart of a new generation of multi-function devices that give you fast and reliable printing, scanning and copying capabilities in just the one appliance. We’ve seen lasers become more environmentally-friendly, with advanced energy-saving features, new toners and duplex printing all helping to drop the quantities of energy, paper and toner being consumed. Features like HP’s ePrintCentre technology are making it easier to print from anywhere or anything, so that you can email a document to your printer for output, or print from your smartphone or mobile phone. With NFC technology on-board, it only takes a touch.
Lasers are also becoming easier to manage and control, with Web-based tools that allow you to decide who can print in colour or print with the highest quality settings, and who can’t. Modern lasers even come with robust security features built in, so that users have to authenticate at the printer before a document will print, while encryption and embedded security keep data safe while it’s travelling to or being stored on the printer.
And laser technology hasn’t stopped developing. New super-toners promise to produce even better, sharper colour images more economically, while reducing the carbon dioxide emissions created in their production. Liquid toner technology, currently at use in high-end digital presses, might eventually drip down to enterprise lasers. Manufacturers have demonstrated printers capable of speeds of 100ppm, while researchers in Singapore have demonstrated techniques for printing at microscopic resolutions of up to 100,000dpi. We might even one day see printers that can reuse their own printouts, with scientists from the University of Cambridge using green lasers to heat the toner on the paper and remove it, creating a clean sheet ready for printing. The laser printer has always been a focus for new innovation, and that still holds true today.
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