Printhead assembly having printhead modules in channel
View Patent ↗A printhead assembly ( 10 ) for an A4 pagewidth drop on demand printer includes a number of printhead modules ( 11 ) situated along a metal channel ( 16 ). The metal channel ( 16 ) is typically of a special alloy called “Invar 36”. Preferably the channel ( 16 ) is nickel plated to help match it to the coefficient of thermal expansion of silicon, being the major component of each individual printhead module ( 11 ). The channel ( 16 ) captures the printhead modules ( 11 ) in a precise alignment relative to each other and the similar coefficient of thermal expansion of the “Invar” channel ( 16 ) to the silicon chips allows similar relative movement during temperature changes.
1. A printhead assembly for a pagewidth drop on demand ink jet printer, comprising:
a U-channel extending substantially across said pagewidth;
an array of printhead modules secured to the channel so as to extend substantially across said pagewidth; and
wherein the channel is a metallic channel having a coefficient of thermal expansion substantially identical to that of a material from which the printhead modules are primarily formed.
2. The printhead assembly of claim 1 wherein the material from which the printhead modules are primarily formed is silicon.
3. The printhead assembly of claim 1 wherein the channel consists essentially of nickel iron alloy.
4. The printhead assembly of claim 3 wherein the channel is nickel plated.
5. The printhead assembly of claim 1 wherein the channel consists essentially of “Invar 36”.
6. The printhead assembly of claim 1 wherein the channel comprises walls of a selected thickness and wherein the channel is nickel plated to 0.056% of said wall thickness.
7. The printhead assembly of claim 1 wherein an elastomeric ink delivery extrusion extends along the channel, between a floor of the channel and the printhead modules.
8. The printhead assembly of claim 7 wherein walls of the channel impart force on the printhead modules so as to form a seal between ink inlets on each module and outlet holes that are formed on the elastomeric ink delivery extrusion.
9. The printhead assembly of claim 8 wherein the printhead modules are captured in a precise alignment relative to each other.
10. The printhead assembly of claim 1 wherein each printhead module has an elastomeric pad on one side thereof, the pad serving to “lubricate” the printhead modules within the channel to take up thermal expansion tolerances without loss of alignment of the modules.
11. The printhead assembly of claim 1 wherein the channel is cold rolled, annealed and nickel plated.
12. The printhead assembly of claim 1 wherein the channel has cut-outs at each end to mate with snap-fittings on printhead location moldings.
13. A method of assembling a printhead assembly for a pagewidth drop on demand ink jet printer, the method comprising the steps of:
(a) providing a U-channel to extend substantially across said pagewidth, the channel having a pair of opposed sidewalls and a base from which the sidewalls extend,
(b) applying a force to flex the sidewalls of the channel apart at a location along the channel where a printhead module is to be installed into the channel,
(c) placing a printhead module into the channel at said location,
(d) releasing the force such that the printhead module is retained by the walls of the channel,
(e) repeating steps (b) to (d) at consecutive locations spaced along the channel until all modules of the assembly have been installed in the channel.