Seal for ink jet printhead

An ink jet printer includes an ink jet printhead having a drop generator and an ink drop charging and catching assembly. An elastomeric seal mounted on a lever arm about a pivot remote from the charging and catching assembly seals the ink drop generator and charging and catching assembly when the ink jet printer is not in use.

FIELD OF THE INVENTION 
The present invention relates to continuous ink jet printing and more 
specifically to apparatus for sealing the area of the catcher in an ink 
jet printhead. 
BACKGROUND OF THE INVENTION 
In continuous ink jet printing, electrically conductive ink is supplied 
under pressure to a manifold region that distributes the ink to a 
plurality of orifices, typically arranged in a linear array(s). The ink 
discharges from the orifices in filaments which break into droplet 
streams. Individual droplets in the streams are selectively charged in the 
region of the break-off from the filaments, and charged drops are 
deflected by electrostatic forces from their original trajectories. The 
deflected drops may be caught and recirculated and the undeflected drops 
allow to proceed to a print receiving medium. 
When the ink jet printhead is not in operation, means must be provided to 
seal the printhead so that ink doesn't dry in the catcher face area, or 
weep from the jets and soil the apparatus or adjacent work surfaces. One 
approach to providing a seal is taught in U.S. Pat. No. 4,928,115 issued 
May 22, 1990 to Fagerquist, et al which discloses a seal over the 
printhead when the printhead is not in operation. The seal described in 
the '115 patent is a sealing wall that slides in a slot between a position 
where the ink jet charging and deflecting area is open and a position 
where the charging and deflection area is covered by the sealing wall. The 
mechanism for moving the sealing wall is located in front of the ink jet 
printhead and includes a bale arm that controls cams that move the sealing 
wall. 
This prior art arrangement suffers from a number of shortcomings. First, 
ink may enter the area between the sealing wall and the slot it slides in 
and when dry, effectively cement the sealing wall into the slot against 
proper movement. Furthermore, the mechanism for moving the sealing wall 
occupies a substantial amount of space in front of the printhead, thereby 
undesirably increasing the footprint of the printhead. Since such 
printheads are employed in bindery lines where it is desirable to place 
the printhead as near to the seam of a signature as possible, a minimum 
sized footprint is desirable. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
sealing mechanism on a continuous ink jet printhead that avoids the 
problems noted above. The ink jet printhead according to the present 
invention includes a sealing head of elastomeric material that is carried 
by a pivot arm, the pivot point of which is located a distance from the 
ink jet charge and deflection area to avoid contamination by ink. 
According to a further aspect of the present invention, the pivot arm is 
driveable by a solenoid to move the sealing head between open and closed 
positions, and the solenoid is coupled to the pivot arm through a slip 
joint that allows the printhead to be removed from the ink jet printer 
without disturbing the alignment between the sealing head and the 
printhead catcher.

MODES OF CARRYING OUT THE INVENTION 
Referring to FIG. 1, an ink jet printhead having a sealing mechanism 
according to the present invention is shown. The ink jet printhead, 
generally designated 10, includes a resonator 12, a catcher/charge plate 
assembly 14, and an elastomeric sealing head 16. The sealing head 16 is 
mounted on a pivot arm 18 that pivots about a pivot point 20. The pivot 
point 20 is located a distance away from the ink jet printhead thereby 
avoiding ink contact and fouling of the pivot point. The sealing head 16 
is movably urged into sealing engagement with the resonator 12 and 
catcher/charge plate 14 by a spring 22. The pivot am 18 is coupled to a 
solenoid 24 through a slip coupling 26 that allows the printhead assembly 
to be easily disconnected from solenoid 24 without disturbing the 
orientation of the print sealing head 16 with the resonator assembly 12 
and the catcher/charge plate 14. 
The elastomeric sealing head 16 defines a first lip 28 adapted to engage 
and seal against the bottom front edge of the resonator body 12 and a 
second lip 30 adapted to engage and seal against the bottom front edge of 
the catcher/charge plate assembly 14. 
As shown in FIG. 3, the elastomeric seal 16 further includes protrusions 32 
and 34 adapted to engage and seal the sides of the catcher/charge plate 
14. It should be noted that when the seal 16 is in engagement with the 
resonator 12 and the catcher/charge plate 14, no part of the seal 16 
contacts the bottom face of the resonator 12. Proper functioning of the 
ink jet printhead requires a gap g between the sealing head 16 and the 
bottom of the resonator 12 that is between a minimum distance wherein 
trapped ink is held in the gap by capillary forces and therefore prevents 
proper operation, and a maximum gap to ensure proper air flow around the 
printhead. 
In operation, the printhead is started with the sealing head 16 in the 
closed position as shown in FIG. 1. After a programmed start up period in 
which ink jet formation and stimulation are achieved, solenoid 24 is 
actuated in the direction of arrow A as shown in FIG. 2 to move the 
sealing head 16 away from the face of the catcher 14. 
In a preferred implementation of the sealing head 16 according to the 
present invention, a printhead having a one inch wide print bar with 132 
jets was provided with a silicone rubber seal configured as shown in FIG. 
3 and having a durometer shore A hardness of 30. The seal 16 was formed by 
compression molding. Lip 28 was 0.030" thick by 0.080" high. Lip 30 was 
0.035" thick by 0.017" long and arranged at an angle .alpha. of 
25.degree.. Sealing protrusions 32 and 34 were 0.030" thick by 0.052" 
deep. The front surfaces of the protrusions 32 and 34 were angled at an 
angle .beta. of 3.degree. from the vertical to match the angle of the 
printhead catcher face. The printhead was operated with the sealing head 
according to the present invention and the printhead was observed to 
operate satisfactorily in both start-up and operational modes. 
Advantages 
The printhead sealing mechanism according to the present invention is 
advantageous in that the mounting means are positioned at a distance from 
the ink in the ink jet printhead thereby avoiding the problem of dried ink 
preventing operation of the ink jet printhead sealing mechanism. The 
printhead sealing mechanism according to the present invention is also 
advantageous in that it employs less space directly in front of the 
printhead than the prior art mechanism. Furthermore, the slip joint 
mounting allows the ink jet printhead to be removed from the solenoid 
mechanism without disturbing the orientation between the sealing head and 
the ink jet printhead.