Inertial deflection field tilting for bi-directional printing in ink jet printers

In a continuous type ink jet printer having a conventional charging electrode for charging ink drops in accordance with a signal to be recorded on a record receiving media, a pair of deflection electrodes is mounted in a rocker which pivots on a holder mounted on the carrier. As the carrier is accelerated from the stop condition to print speed, the acceleration of the carrier effects rotation of the rocker about the pivot and thus automatic tilt of the deflection electrodes backward from the direction of carrier movement thereby tilting or inclining the electric field formed between the electrodes to compensate for carrier movement. In the preferred form, a simple magnetic type latch is applied to retain the rocker in one position for printing in a first direction, and to enable quick release and reversal, under inertial control, when the carrier moves in the opposite direction.

CROSS REFERENCE TO RELATED APPLICATION 
See "Image Inclination Control for Ink Jet Printers", Ser. No. 075,911, of 
Fathergill et al, filed concurrently herewith. 
SUMMARY OF THE INVENTION AND STATE OF THE PRIOR ART 
The present invention relates to ink jet printers and more specifically 
relates to continuous type ink jet printers employing apparatus for 
controlling the inclination of print images (characters, patterns, etc.) 
by inertially tilting the deflection field in an ink jet printer. 
A typical change amplitude controlled continuous type ink jet printer is 
the IBM 6640 document printer which employs a single nozzle. In this type 
of printer, deflection of a charged ink drop in the vertical direction of 
the dot pattern is accomplished by controlling the charge amplitude on 
individual ink drops so as to produce differences in the amount of 
deflection between the ink drops as they pass between a pair of deflection 
electrodes. Deflection in the horizontal direction, however, is produced 
by movement of the carrier, the carrier having mounted thereon the nozzle 
for emitting a stream of ink drops, the charging electrode for charging 
the ink drops in accordance with the signals to be recorded, and the 
deflection electrodes. 
In the aforementioned document printer, the ink drops are scanned in a 
vertical direction, in the example instance from their lowest to their 
highest printing position. When a white space is to be left without any 
drop thereon, the ink drops are left uncharged or receive a minimal charge 
and are propelled towards a gutter for recirculation back to the ink 
supply system. As the raster in the ink jet printing machine progresses 
from its lowest to its highest deflected printing position, the carrier 
moves from left to right so that the raster slants in the direction of 
carrier motion. In the IBM 6640 document printer, the effect is nominally 
0.00417 inches (0.106 mm) on a vertical distance of 0.167 inches (4.24 
mm), or 1.43.degree.. In the example printer, the slant is eliminated by 
tilting the deflection plate assembly by 1.43.degree. in the opposite 
direction. 
Of course if it is desired to print from right to left, without slant 
correction, the slope of the characters being printed would appear at 
double the magnitude inasmuch as the deflection electrodes are tilted in 
the wrong direction. 
Other approaches may rely on the fact that the charge on a drop is roughly 
proportional to its height in the raster. Therefore, introduction of a 
second set of deflection electrodes with a horizontally disposed electric 
field therebetween may be employed to provide raster tilt. Such a system 
is described in U.S. Pat. No. 3,938,163. Compared to the primary 
deflection electrodes, the needed deflection in the horizontal direction 
is only about 2.5%, the length of the throw from the mid-point of the 
deflector being about twice as far from the page, and the deflector 
electrodes can be much closer together since deflection within them is 
quite small. For example, at a 0.030 inch (0.762 mm) spacing, a 0.010 inch 
(0.254 mm) length, and a 125 volt supply may be sufficient for a system 
such as the IBM 6640 document printer, thus making it feasible to 
electronically switch horizontal deflection voltage during carrier 
turnaround. However, even the 0.254 mm added to the length of throw (throw 
is defined as the distance that the drop must travel from the nozzle to 
the paper) increases the already difficult ink drop merge and scatter 
problem. 
In U.S. Pat. No. 4,167,741 to R. S. Heard and D. W. Phillips, filed on Dec. 
23, 1977, and entitled "Raster Slant Control in an Ink Jet Printer", means 
of varying the ink drop inclination by distortion of the electric field is 
described. In U.S. Pat. No. 4,138,688 is disclosed a method and apparatus 
for automatically controlling the inclination of patterns in ink jet 
printers by monitoring the carrier velocity and automatically feeding back 
a signal to an electric field distortion created by a voltage difference 
on the deflection electrodes to control the electric field dependent upon 
carrier velocity. In U.S. Pat. No. 3,895,386, issued on July 15, 1975 is 
disclosed the basic principle of offsetting one charge electrode with 
respect to the other charge electrode to effect an inclination or curving 
of the electric field formed between the electrodes, or in the alternative 
of skewing one of the electrodes relative to the second electrode to also 
effect an inclination of the electric field in order to compensate for the 
tilt. 
In view of the above, it is a principle object of the present invention to 
provide moveable deflection electrodes in a continuous amplitude control 
type inke jet printer, which electrode movement is controlled for both 
forward and reverse printing merely by carrier acceleration. 
Other objects and a more complete understanding of the invention may be had 
by referring to the following specification and claims taken in 
conjunction with the accompanying drawings.

Referring now to the drawings, and especially to FIG. 1 thereof, a typical 
ink jet printer 10 of the charge amplitude or continuous type is 
illustrated schematically therein. The printer comprises a drop generator 
or the like 11 to which is supplied ink as from an ink supply .The drop 
generator is vibrated in a conventional manner as by a piezoelectric 
crystal which is driven from a crystal driver so that ink is dispelled 
from a nozzle 11a in a stream 12. The ink stream breaks up within a 
predetermined distance from the nozzle in a charge electrode or ring 13, 
the ink drops 12a which form from the stream being charged by the charging 
electrode in accordance with signals representative of images or 
characters to be printed. Ink drops 12a then pass intermediate first and 
second deflection electrodes 14 and 15 respectively, between which 
electrodes is an electric field formed by a power supply 9 so that the 
drops are deflected, for example, along a path 12b. The deflected height 
of the drops is of course dependent upon the amplitude of the charges on 
the drops. The droplets impinge upon a record receiving means 16 for 
forming patterns such as images, characters, etc., in the present instance 
the letter "M" 17 being illustrated on the record receiving means 16. 
Typically, blank spaces in the amplitude control type ink jet printer are 
afforded by placing a low charge or no charge on the drops as they are 
formed within the charging electrode 13, these drops passing between the 
deflection plates 14 and 15 along path 12c where they impinge upon a 
gutter or the like 18 which allows ink to be recirculated back through an 
ink supply system (not shown) to the drop generator 11. 
The drop generator including the nozzle 11a as well as the charging 
electrode 13, deflection electrodes 14 and 15 and gutter 18 are mounted on 
a carrier 19 which is driven as by carrier drive means 20 to effect 
horizontal movement of the ink drop stream relative to the record 
receiving means 16, in the instance of FIG. 1 the carrier moves into and 
out of the plane of the drawing. 
In accordance with the invention, means are provided for effecting 
deflection field tilting by inertia to permit of bi-directional printing 
in an ink jet printer. To this end and referring first to FIGS. 2 and 3, 
the upper and lower deflection electrodes 14 and 15 respectively are 
mounted in spaced apart relation on a rocker member or yoke 22, the rocker 
member or yoke 22 being pivoted as at 21 to the carrier 19 along an axis 
transverse to the carrier motion. In order that the rotation of the rocker 
member 22 is limited, stop means operative in conjunction with the rocker 
member is provided. To this end, mounted on the carrier is a bridge frame 
structure 23 including a recessed portion 24 which limits the rocker 
member or yoke 22 rotation between a first position such as shown in FIG. 
2 and a second position which is shown in FIG. 3. This is accomplished by 
a resilient bumper means or insulator 25 (preferably energy absorbing 
rubber) mounted on the upper deflection electrode 14 which registers with 
the recess 24 in such a manner that the left edge 24a of the recess 24 
registers with the bumper 25 when the carrier 19 motion is to the right 
such as illustrated in FIG. 2, and with the righthand edge 24b of the 
recess 24 when the carrier motion is to the left such as illustrated in 
FIG. 3. (For purposes of this specification and claims, "acceleration" 
includes both positive and negative [sometimes called deceleration] 
acceleration). 
Although the electric or electrostatic field may be tilted as described 
above, it is desirable to maintain the predetermined position of the 
electric field during a print cycle (the printing of a single line of 
print in one direction), for example such as illustrated in FIG. 2 when 
the carrier is moving from left to right the print cycle is from left to 
right, while in the instance of FIG. 3, the print cycle is from right to 
left. The desireability of providing rocker position maintenance is that 
besides the primary acceleration forces which occur at reversal of carrier 
direction, or upon starting the carrier from a rest position, other 
secondary forces act on the tilting mechanism such as a bouncing of the 
bumper upon the stop afforded by the recess 24 or some disturbance in the 
acceleration forces while the velocity of the carrier is stabilizing. 
In order to maintain the position of the rocker member or yoke 22 and thus 
the position of the electric or electrostatic field intermediate the upper 
and lower deflection plates 14 and 15 respectively during a print cycle, 
means are provided for latching the rocker member or yoke 22 which can 
discriminate between the primary acceleration forces and the secondary 
forces which may occur such as the bouncing of the bumper or some other 
disturbance in acceleration forces. While overcenter spring latches or 
detents may be employed in this connection, in the preferred embodiment of 
this feature of the invention, a magnet spring combination such as 
illustrated in FIGS. 4, 5 and 6 is to be preferred. Referring now to FIG. 
4, the upper deflection electrode 14a may be preferably formed of a plate 
portion 26, terminal upstanding end portions 27 and 28 which serve, as 
will be more fully described hereinafter, as knockoff projections, and a 
sleeve like portion 29 defining a hollow core 30 therein. The bumper 25 
may be connected to the central portion of the sleeve member 29 and serves 
as described heretofor, in conjunction with the recess 24, to limit the 
motion of the rocker member or yoke 22 between the first position such as 
illustrated in FIG. 2 and the second position illustrated in FIG. 3. 
Within the sleeve member 29 is located a tension spring 31 which is 
connected at its opposite ends to first and second plungers 32 and 33 
respectively, the plungers passing through guide rings 32a and 33a and 
terminating in pole catchers or shoe members 34 and 35 respectively which 
are biased by the spring 31 into contact with the ends of the sleeve 29 or 
the guide rings 32a and 33a. A horseshoe like magnet 36 including 
depending first and second pole pieces 37 and 38 has terminal ends 37a, 
38a adapted to register respectively with the shoes 34 and 35 depending 
upon whether the rocker member or yoke 22 is in its first or second 
position. 
The position of the various elements described above and shown in FIG. 4 is 
such that the carrier has just moved from right to left and has come to a 
stop, the deceleration or negative acceleration causing the rocker member 
or yoke 22 to move counterclockwise about the pivot 21 effecting 
engagement of the bumper 25 against the lefthand edge 24a of the recess 
24. Alternatively, if the machine has been at rest, the position 
illustrated in FIG. 4 would occur immediately after startup of the carrier 
19 in the direction of the carrier motion illustrated in FIG. 2. 
Because of the proximity of the terminal end 37a of the magnet 36 to the 
pole catcher or shoe 34, an attraction occurs which causes the apparatus, 
immediately after startup of the carrier 19 in the direction shown in the 
arrow illustrated in FIG. 2, to engage the magnet and be held thereby 
under spring 31 tension. The position of the rocker member or yoke 22 and 
thus the electric field intermediate the deflection electrodes thus will 
remain as illustrated in FIG. 2 until carrier motion is reversed. Upon 
reversal of motion the yoke member 22 associated with the deflection 
electrodes 14 and 15 will tend to continue and cause clockwise rotation 
about the pivot 21 causing the bumper 25 to move away from its lefthand 
restraint or stop 24a. Because the shoe 35 is stopped by the guide ring 
33a in the terminal end of the sleeve 29, the spring 31 tends to apply 
increased tension upon the lefthand shoe 34 held by the terminal end 37a 
of pole piece 37. Moreover, the upstanding terminal end 27 (and 28) of the 
upper deflection electrode 14a is positioned with respect to the shoe 34 
to effect and interference fit so that it engages the shoe 34 such as 
illustrated in FIG. 6 acting as a knockoff projection for the shoe 34 
causing the shoe 34 to be removed from the terminal end 37a. 
In a like manner, when the carrier accelerates in the reverse direction, 
the pole catcher or shoe 35 contacts the pole piece terminal end 38a, the 
bumper 25 residing against the righthand edge 24b such as illustrated in 
FIG. 3. Knockoff of the shoe 35 occurs, in a like manner, due to the 
knockoff projection or upstanding terminal end portion 28 of the upper 
deflection electrode 14a upon reverse motion occurring to the carrier 
motion illustrated in FIG. 3. 
Thus the present invention provides an inertial direction field tilting 
mechanism to permit bi-directional printing in ink jet printers while 
correcting automatically for the character tilt which occurs due to the 
interaction of scan of the ink drops and carrier motion. 
Although the invention has been described with a certain degree of 
particularity it is understood that the present disclosure has been made 
only by way of example and that numerous changes in the details of 
construction, the combination and arrangement of parts, and the method of 
operation may be made without departing from the spirit and scope of the 
invention as hereinafter claimed.