Ricoh recirculating ink printhead

US 2015/0306875 A1
WO 2015/163487 A1
Inkjet head that circulates ink
Ricoh Printing Systems America, Inc.

The benefits of circulating ink through the actuator chambers of ink jet printheads is now well known. The chambers are easily and quickly primed, air bubbles can be displaced, inks with a tendency for pigment settling or separation can be used, and fresh ink is brought to the nozzles reducing the requirements for nozzle maintenance.

Oct-15aInk passes from an inlet manifold 302 through passageway 225 into the actuator chamber 221. In this design a second passageway 223 close to the nozzle allows ink to return to a separate manifold 304. Ink being supplied to the printhead is fed under a positive pressure, and a negative pressure is applied to the return path.

Oct-15bOverall though, the average pressure is slightly negative by arranging the negative pressure to be higher than the positive. Therefore there is enough differential pressure to achieve the continuous flow through the actuator chambers and a net negative pressure at the meniscus.

The ink flow paths and pressure chambers within the printhead are made up from a stack of etched stainless steel plates that are bonded together. Note that as the inlet and outlet manifolds are both the same side of the actuator chambers, then the overall width of the printhead is minimised.

Lexmark’s recirculating thermal ink jet printhead design

US 2013/0182022
On-chip fluid recirculation pump for micro-fluid applications
Lexmark International, Inc.

There have been a lot of developments of recirculation architectures within printheads since the launch of the Xaar system.  Already we have reviewed Canon and Hewlett-Packard’s proposals for thermal ink jet recirculation, and here is Lexmark’s.

Recirculation systems enable fresh ink to be brought to the actuator chambers and nozzles.  This is particularly important for fixed array printheads.  With scanning heads, ink can be ejected from each nozzle during the period when the head is outside of the substrate width.  This is not possible for fixed arrays.

With small nozzle sizes and relatively volatile aqueous inks, evaporation of the ink solvent from the nozzle may cause an increase in local ink viscosity and hence a deterioration in jetting properties within a second or two of becoming idle.  To maintain nozzle performance this means ensuring each nozzle fires drops within that period to bring fresh ink to the nozzle.

Nozzle failures are often more noticeable for fixed arrays as it is not possible to cover up defects by multiple passes.  Therefore it is necessary to be even more careful in keeping nozzles working with a fixed array.  To keep nozzles working, drops can be fired onto web substrates between pages.  The amount of ink consumed can be considerable.  Lexmark estimates heavy users, printing large multi-page jobs, may lose 15% of the ink to nozzle maintenance.  However light users printing only short jobs infrequently may consume 80% of the ink on maintenance.  As well as excess ink consumption the printhead life is shortened, as only perhaps 20% of the actuator cycles are used for printing.  The use of recirculation within the printhead can therefore eliminate a lot of external nozzle maintenance, ink wastage and increase the working life of the printhead.

Jul13

Various schemes are proposed, but all involve the passage of ink through the actuator chamber from one side to the other, driven by a pump.  Here the ink flows in from the manifold via inlets 60, through channels 65 to heater chambers 22.  Heaters 12 generate bubbles to fire drops from nozzles 24.  The ink circulation path continues via channels 75 and through outlet 60, driven by pump 50.  The pump is another heater, similar to the drop generators, but of course with no corresponding nozzle.

When the pump heater is actuated, ink flows preferentially through the large area outlet rather than back to the heater chambers.  When the drop generator heaters are actuated, ink preferentially flows from the nozzle rather than back to the inlet or to the recirculation outlet.

Note that the flow doesn’t have to be continuous.  The printer can determine which nozzles have not been fired for the past one or two seconds, and then drive the pumps corresponding to just those nozzles.