Ink jet nozzle with tilted arrangement

#In ink jet printers, the printhead and recording medium are usually moved continuously relative to each other. During the movement, drops of ink are deflected to selected sites on the record medium along axes transverse to the path of motion. Because the drops are generated in succession from a nozzle, a straight line segment such as a character stroke, has an inclination in which the drops forming the segment do not lie on a line normal to the direction of motion.

#The usual correction for the inclination has been to alter the direction of the deflecting force field for the drops an amount which will result in a non-inclined column of marks forming the line segment. One form of compensation is that of tilting the deflecting electrodes in electrostatic printing such as shown in U.S. Pat. Nos. 3,641,588 and 3,813,676. Another method has been to distort the force field by offsetting or skewing the deflecting electrodes such as disclosed in U.S. Pat. No. 3,895,386. Yet another technique has been the addition of a pair of compensating deflecting electrodes along the drop flight path which are normal to the principal deflection electrodes and impart a correcting amount of deflection to that produced by the principal electrodes, as shown in U.S. Pat. No. 3,938,163.

#Frequently, it is desirable to record while the printhead is moving along both the forward and return strokes to increase printing throughput. The first two correction technques mentioned above require mechanical repositioning of the electrodes at the end of each line of print to provide a proper correction in the opposite direction. Such mechanical repositioning invites errors in the rapid adjustment necessary to maintain printing efficiency. When the printhead is moved in both directions with the same velocity, the positioning will be double the compensation amount, thus requiring the rapid movement of a relatively large mass. The last of the above-mentioned techniques has the disadvantage of increasing the drop flight path in order to acommodate the auxiliary electrodes. Such path extension necessitates greater flight time and the attendant adverse drop interaction and aerodynamic effects.

#FIGS. 1a and 1b are diagrams of a prior art ink jet recording apparatus illustrating the known technique of controlling drop placement with forward rastering;

#FIGS. 2a and 2b are diagrams similar to FIGS. 1a and 1b illustrating the known technique of controlling drop placement with reverse rastering;

#FIGS. 3a and 3b are diagrams similar to FIGS. 2a and 2b illustrating the known technique of drop omission in a recording series while using reverse rastering;

#In FIG. 1a, there is schematically illustrated a conventional ink jet recorder having a nozzle 10 from which issues an ink stream 11 that breaks into drops 12 within a charging ring 13. Ink is supplied under pressure to nozzle 10 and is perturbated by means not shown so as to break up into drops within the charging ring. The charging ring is connected to a signal generator 19 which induces selected charge levels in the drops. Drops 12 pass between a pair of electrostatically charged deflection electrodes 14, 15 which are effective to deflect upwardly above a gutter 16 any drops carrying an indeed charge thereon. Uncharged drops are intercepted by the gutter for disposal or reuse. The deflected drops continue on toward the surface 17 of a record member 18 where the drops form marks at the impact sites on the surface.

#With the conventional recording method, a line segment is recorded on the surface 17 of the record member by deflecting selected ones of the drops 12 to different levels so that a plurality of drops form a vertical succession of marks. Each drop in a recording series is given a larger induced charge at charging ring 13 so that the last drop to form the recorded line segment receives the greatest charge. The drops for recording a line segment are shown in flight just before impact with the recording member. It will be noted that there is a considerable amount of time that will elapse between the impact times of the first drop 21 and last drop 24 of the four drop series at the surface of the record member.

#Usually, recording occurs during relative movement between the printhead and recording member, indicated schematically by rolls 20. The effect of the delay in impact between neighboring drops is illustrated in FIG. 1b, a view of drop marks on recording surface 17 as seen from nozzle 10, in which the line segment slopes backward from the direction of motion of the recording member. As each of the selected drops is deflected from the path of the preceding drop, it encounters increased areodynamic drag which increases the original drop-to-drop spacing existing at the time of drop formation. The result of the slanted line segment in FIG. 1b can be corrected by tilting deflection electrodes 14 and 15 to compensate for the successive registration of droplets on the recording medium, which is moving relative to the printing means.