| Inkjet Printheads Printers > Inkjet > Printheads |  | Navigation Icons Guide
|
This section is some further notes on inkjet printheads. They are just notes at present
Printheads
Thermal inkjet printheads are cheapest, but nevertheless a significant cost.
The cheapest possible cartridge would have a one chamber printhead and only print black. The printer would be so slow and the pages so unnatractive the printer wouldn't sell. Printheads are made by photolithographic techniques similar to chip making so manufacturers don't need to restrict themselves to one chamber. Processes that would produce on chamber can make 4, 8, 16, 32 or 64 chambers as they improve. The makers calculation has to balance the performance versus yield for head making with how attractive the printer is as a product.
A low cost design aims at a single printhead but to get colour it will have to supply three or four colours. Inks might be delivered from tanks above a printhead would need careful allignment.
If one head is to supply four inks it will be fairly complex and quite difficult to integrate into a cartridge. It is clearly cheaper to integrate the head into the cartridge than to have seperate head and ink assemblies - there is no need for an extra plastic moulding with gaskets and suchlike to seal the ink in. An integral cartridge is also least messy for the user; all they have to do is pull a sealing strip away from the nozzles and lock the cartridge in a cradle.
If the factory can put 300 chambers in a 4mm high chip then the printer can do half a line of mono characters at 1200 dpi for each sweep of the head. If the chip can be 8mm high with 600 chambers then the printer speed quadruples - or potentially the resolution goes up to 2400 dpi. If the factory can put four lines of 600 into the chip then the printer can do the same in colour.
The cheapest possible design is monochrome - one head and one colour of ink. However the main market for the cheapest printers is likely to be buying them as toys, and the customers ache for colour. The natural companion to cheap colour cameras are cheap colour printers.
Adding colour doesn't add much to manufacturing cost. A colour printer can use the same motors, it just needs a more complicated cartridge. The extra complication in the cartridge does add to innitial manufacturing cost. On the other hand the users have made the commitment to buy the printer and the cartridges are consumeable - so if they want to go on using the printer they have to buy them. The hilarious situation has sometimes happened that a new printer with a cartridge has sold for £50 - and new cartridges for £53. Users naturally think "I'll just buy a whole new printer"; actually they may not be able to - this sort of printer isn't on the market for long.
The cheapest manufacturing approach is to put all four colours into one cartridge. There is just one set of control connections. Obviously all four inks won't run out at the same time and a single cartridge tends to really irritate users - who say "but I never printed any colour".
Two cartridges - one for black the other for colour strikes a better balance. If users are mainly printing photographs then they will probably exhaust the cyan before the red (theres more green and blue in the world) and innevitably one colour will run out before the others.
Even low cost printers tend to have two cartridges, one black and an optional one for colour. In some designs the user can use a black or a colour cartridge but not both at the same time - decide on the job then put the cartridge in. Some designs have two different positions and can handle both at the same time, so the colour cartridge cut in for a colour photo.
Electronics in a printer can be complicated -an A4 colour page at 600dpi is potentially 95,040,000 bytes of information. A low cost inkjet will have to avoid anything expensive so all the complexity will be in the driver loaded onto the users PC. The printer unnavoidably needs the motor control chips for the carriage and paper feed motors. The controllers for the printhead chambers might sensibly be built into the printhead chip allowing the thing to be fed serial data and cutting down connection problems.
An inkjet printer probably needs to be able to print one line uninterupted - regardless of what the users PC is doing. Either the printer needs its own local memory to hold the line content, or it needs to be able to recover from the PC processor going off and doing other things.
If the printer has an 8 inch working wdth for the carriage and prints at 2400 dpi with 600 chambers in each head then there are 11,520,000 pixels for each colour. Thermal inkjet pixels are either on or off - they don't usually do greyscale. The memory buffer for one line in 4 colours is 5,760,000 bytes - not much by recent standards. It will take a couple of seconds to transfer that much data from the computer driver to the printer buffer so it may help to have 8 megabytes of buffer RAM and have most of the next line transfered before the first is complete. There will be a huge amount of redundancy in the transfer so it may also make sense to run-length compress the data, using rather less memory. A possible cost is that some patterns will be uncompressible and the printer may have to handle those lines slowly. Decompressing data and varying the motor speed is probably going to need a moderately powerful processor - but the cost savings on RAM will probably more than compensate.
--
© Graham Huskinson 2010
This page is like all those in the "book" section in being under development.
If you think this page is wrong in some respect or have better information on how things are done let us know. Click here.