At last HP has embraced single colour individually replaceable inks, but they have done it differently to the competition.
Read the Press Release: HP Launches its Fastest Home Photo Printer Yet
Most of the key ink-jet printer models from Canon and Epson have featured separately replaceable single colour ink cartridges for some time. Meanwhile, HP and Lexmark have soldiered on with combination ink cartridges that contain several colours or shades of ink and an integrated print head. HP and Lexmark have repeatedly insisted that this was the best strategy. But with this week's launch of the HP Photosmart 8250 printer, HP has apparently had a change of heart as the 8250 is the first consumer HP printer in recent years to feature single colour ink cartridges and a separate, non-disposable print head.
a: Pump, b: ink sensor, c: ink cartridges, d: print head, e: vent chamber.
So the Photosmart 8250 is something of a revolutionary printer for HP and in more ways than you might think. For a start, unlike most of its rivals (Brother being an exception), the ink tanks don't sit on the print head carriage but are connected to the print head via tubes. This means the print head has less inertia to deal with, which should translate into less printer wobble and potentially faster print head speeds. The arrangement of the ink tanks, tubing and print head is show in the diagram (looking vertically downwards) below:
The 8250 even has a clever solution to ink wasted when priming the print head to purge it of air; ink expelled during the process is basically hoovered back up to be re-used, which is, as far as I know, a first for consumer ink-jet printers. A vent chamber separates the ink from the air removed from the print head during pumping. The ink is pumped back into the cartridge and the air is purged from the system.
Single ink benefits
HP's new single colour ink cartridges have an unusual T-shape
The benefits of single colour ink tanks are clear: they give the user the comfort of knowing that no more usable ink remains in the cartridge when it is exhausted. With cartridges that contain three or so chambers, each with a different ink colour, only one chamber emptying rendered the whole cartridge and any remaining ink in the other chambers, useless.
Single ink cartridges, without the expense of an integrated print head, are also cheaper to buy individually, so there is a smaller hit on your wallet each time you need a new cartridge. Also, our own exhaustive experience is that overall ink cartridge costs in real life are measurably higher when using combined ink and print head cartridges.
Though there are disadvantages
However, there are some disadvantages. In some circumstances, you could find your printing interrupted more frequently as several different cartridges run out one after another in a short space of time. As there is usually more ink in separate ink cartridges, replacing several at once usually adds up to a substantial amount and can be more than a single combined multiple ink cartridge.
But another advantage of single ink tanks that HP has exploited is the ability to optimise the print head for printing speed. Print heads are complicated precision devices manufactured using silicon wafer production techniques. Keeping them small, substantially reduces individual head costs as you can fit more onto a wafer and the proportion of faulty heads will also be lower – all classic chip manufacturing indicators. It's why the print heads in ink cartridges that are meant for one-time use are usually small, with a relatively small number of ink jet nozzles.
The problem with having so few nozzles in a print head is that the print heads needs to make more passes over the paper to cover the same area as a wide print head with many more nozzles. Canon, especially, has concentrated on very wide print heads with thousands of nozzles compared to HP and Lexmark cartridges featuring small print heads with just a few hundred nozzles.
HP's new Photosmart 8250 has, like Canon and Epson, a separate print head designed to last the life of the printer and it has nearly four thousand nozzles in a generously wide swath. HP used to be enthusiastic about a 6x4 photo printing in a minute or so, but the new 8250 can print one in just 14 seconds.
When you have up to three ink cartridges, each with its own print head, which is typical of HP's printers to date, alignment of the three print heads is critical. But the separation of the ink tanks from the print head in HP's new Photosmart 8250 means a single print head is all that is required and this can be much more precisely configured. In HP's own words: "Normal manufacturing tolerances for customer-installed printheads can produce drop volume variations between colours that change every time a printhead is replaced. While encoding the drop volume on each printhead during manufacture allows printers to compensate for these variations, an alternative solution is to manufacture all the nozzles together to assure drop volume consistency across all colours for the life of the printer." Until a few weeks ago, I'd have been astonished to hear an HP representative saying that!
Fresh new heads?
One of the defensive claims manufacturers make for cartridges with integrated print heads is that each time you buy a new cartridge, you benefit from a fresh new print head. It sounds good, but Canon and Epson have proven that permanent print heads can deliver consistent performance over the life time of a printer. And believe me, after having fitted brand new ink cartridges to printers hundreds of times, duff print heads in brand new cartridges do exist.
There is also the issue of recycled cartridges. Recycling is a term that is associated with good, eco-friendly, practices. However, recycled ink-jet cartridges can be very problematic. For a start, can you be sure that the replacement third party ink that has been pumped into the cartridge is of good quality in terms of colour accuracy and resistance to fading? And how can you be sure the previous owner of the cartridge didn't abuse the cartridge, leaving the print head reliability suspect? Indeed, will you know how many times the cartridge has been refilled?
Big step forward?
Is HP's new ink-jet technology going to be killer? On paper, it looks great, but you have to remember that HP is basically electing to play the same game as Canon and Epson for the first time and they have been playing that game for longer. HP has taken the concept of single ink cartridges and fixed print heads a step further, but it remains to be seen if what HP delivers is substantially superior to relevant Canon and Epson offerings. One area HP does have a useful advantage in is print life through a tight matching of its inks and papers. Epson does have its own long-life ink system, so it's Canon that should be fearing HP most here, though we're expecting some announcements concerning developments in Canon's ink technology too.