[net.text] Laser Printer Woes

amr@rti-sel.UUCP (Alan Roberts) (06/18/86)

Hello,

My organization has two Imagen laser printers, one of the older, 
wet-process, 240 dpi printers, and a model 8/300, dry-process, 
300 dpi printer.  We just brought up TeX on VAX/VMS and a
translator for the Imagen, and seem to be having problems with 
the newer 8/300 Imagen. 

The problem surfaced when I was drawing some horizontal lines with
LaTeX.  The lines that resulted were longer than specified.  The 
problem gets worse as the line length increases (i.e. a 5 inch line 
is 1/16 inch too long, a 6.5 inch line is almost 1/8 inch too long).  
Vertical lines are much more accurate.  When I translated the same
DVI file for our 240 dpi Imagen, the line lengths were accurate.

I have checked the two versions of my translator, and the only
difference in software I have is the setting of the resolution
value (which is set correctly for both printers).  I was still
sure it was a software problem, until one of the Imagen gurus
here built a test job which contained raw Impress commands to
draw the lines.  We ran the test to both printers, and suprise, 
the older printer was accurate, while horizontal lines on the new 
printer exhibit the same errors.

I have had one comment to the effect that all printers using the
dry-process Canon engine are showing this kind of error.  Has 
anyone else had this problem?  Is it possibly a firmware error
of some sort (either Imagen's or whatever microcontroller runs
the Canon engine) that I can hope to get fixed, or is there some 
optical/mechanical accuracy tradeoff made in going to the 
admittedly convenient print cartridge?  

We also have LaTeX documents which translate and print perfectly 
on the older printer, but mysteriously relocate sections of the 
page on the 8/300 (despite having more buffer memory on the new 
printer).  This problem leads me to hope that its a firmware 
bug causing me grief.  I'd appreciate hearing from anyone who has 
been down this path before.
-- 


					Cheers,

					Alan Roberts
					Research Triangle Institute
					(decvax!mcnc!rti-sel!amr)

henry@utzoo.UUCP (Henry Spencer) (06/25/86)

> The problem surfaced when I was drawing some horizontal lines with
> LaTeX.  The lines that resulted were longer than specified.  The 
> problem gets worse as the line length increases...
> Vertical lines are much more accurate.  When I translated the same
> DVI file for our 240 dpi Imagen, the line lengths were accurate.

There is a known "problem" with the little Canon engine.  The vertical
resolution is determined by how far the paper moves between scan lines,
which I think is a matter of gear ratios in the engine.  So that's
pretty much fixed.  The horizontal resolution is determined by the dot
rate at which the controller sends video to the engine.  The "problem"
with the engine is that the right video rate for horizontal=vertical
resolution is almost BUT NOT QUITE equal to one of the standard crystal
frequencies.  So most of the controller manufacturers are lazy and use
the standard crystal, even though the result is slightly wrong.

I measure the resolution as 298.5/inch horizontal by 302.5/inch vertical
on my LaserJet Plus.  As they say, "your mileage may vary".
-- 
Usenet(n): AT&T scheme to earn
revenue from otherwise-unused	Henry Spencer @ U of Toronto Zoology
late-night phone capacity.	{allegra,ihnp4,decvax,pyramid}!utzoo!henry