[I wrote this up back in 2011, but didn't think to post it until now, so I'm just copying and pasting that writeup here. It's a bit jump-around-y but I don't
want to rewrite it. I've added a note and some paragraph breaks.]
This printer uses both an inkjet system and a laser system to produce prints
with photo-quality color and laser-quality text, at a high speed.
Duplexing should probably be done by sending the paper back through the paper path in the same direction, rather than pulling it back in the way most
printers do. If the paper is short enough, it can be flipped by sending it through a figure eight-shaped path.
There may be two paper paths for the laser system, one on each side of the drum.
For speed, the inkjet may use a print head that extends across the entire width of the paper, instead of a smaller head that traverses. Such a head
would probably move rapidly in a diagonal pattern, so it moves sideways relative to the forward-moving paper.
For printing both black and color on the same page, using the inkjet second may be more forgiving of alignment errors, because the inkjet can easily
adjust the image's position. The laser, on the other hand, would require more precise alignment. [2017: I'm not sure why I thought that.]
The printer should have two output trays, one for laser and one for inkjet. This eliminates the need for the laser system to wait for the inkjet system,
or vice versa. The two systems can then print their pages asynchronously, for re-stacking later. The sizes of the output trays would depend on the
anticipated use of the printer. For example, a printer that is expected be used for documents containing mostly text and a few color images would have
a large laser output tray and a smaller inkjet output tray.
A large laser output tray might require devices to ensure the pages don't flip over or get reordered. These might consist of a system of rollers that press
down the pages already in the stack and lift the leading edge of the page being deposited. This would probably require lowering the base of the output
tray relative to the output slot/rollers as paper is added. Another way is to have a fan blow each sheet down to meet others. This could be an
oscillating-blade fan to blow on different areas of the sheet at different times to make sure it falls straight. This could be assisted by a group of fans
that suck away the air below the falling sheet. These would have to be lifted up as the top of the stack rises.
An inkjet output tray might need a fan to dry the ink rapidly. In this case, the sheets could not be stacked rapidly.
Having two asynchronous output trays will require the pages to be combined into one stack having the pages in the proper order. There should be at
least two ways to perform this re-stacking operation: automatic and manual.
Automatic re-stacking sends each sheet from the larger output tray (or maybe just the laser output tray, if the paper path is not set up to send pages
from the inkjet's output back through the paper path) back through the paper path and interleaves them with the sheets from the other output tray.
This is better for documents that have approximately alternate color and black pages, but would take a long time for extremely long documents. Sheets
may be extracted by rollers from the bottom of the stack. The rollers may need to bounce the stack up and down at high frequency and low amplitude
(maybe in a wave motion) to achieve the proper amount of weight on the rollers so they can feed out the bottom sheet.
Manual re-stacking is done by hand. The printer gives instructions for how many sheets to take from each stack to properly combine them. This may
become an assisted manual mode in some circumstances, such as by having the printer measure how many sheets the user has removed from each
output tray and adjusting the instructions accordingly.
If the automatic re-stacking operation finishes interleaving the sheets, but there are still many sheets that need to be moved from the bottom to the
top of the stack in the same order, the printer may alert the user of this and give the user the option to stop automatic re-stacking and finish moving
the sheets by hand, to save time.