Alex,
I have written an article for Printed Circuit Design magazine on "Designing
Electronic Equipment for ESD Immunity". Part 1 appeared on pages 18-26 of the
July 2001 issue (volume 18 number 7), and Part 2 will be in the August issue.
Printers and copiers can be quite nasty generators of ESD, with the moving paper
acting like the belt of a Van de Graaf generator to generate voltages of
thousands of volts. One defense is to use tinsel or static-discharger brushes
to bleed charge off the paper (rule L4 in my article) as it leaves the printhead
area. Dogpile ( http://www.dogpile.com ) searches for antistatic +tinsel,
static +tinsel, static +brush*, and antistatic +brush* gave these hits, for
example:
* http://www.westmontinc.com/price.htm
* http://www.fraser-antistatic.co.uk/products.htm
* http://www.takk.com/takktins.htm
* http://kinetronics.com/
* http://www.stopstatic.com/printer.html
* http://www.chapman-static.com/oemtinsel.html
* http://www.amstat.com/html/passive.html
Another technique is to make plastic parts in the paper path of antistatic
materials, and make sure that every shaft has a grounding contact (usually on
one end of the shaft) to bleed off charge (rule L3). An alternative to the
grounding contact is to use conductive grease in the bearings (rule L5).
Establishing a "chassis ground" for any ungrounded device is difficult. About
the best you can do is choose a large piece of metal close to the
switches/operating controls, and tie circuit common, shields, and grounding
wires from the mechanism to it (rule B14).
John Barnes Advisory Engineer
Lexmark International
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