Ink jet printing apparatus with adjustable print head

An ink jet printing apparatus comprises a print head, a reservoir, and a rigid articulated support assembly connecting the print head to the reservoir. The support assembly affords two degrees of rotational freedom for allowing adjustment of the print head relative to the reservoir, so that printing can be carried out on surfaces lying in various planes or moving in various directions without tilting the reservoir. The support assembly has an internal channel for conducting ink from the reservoir to the print head, and may be made of a thermally conductive material in order to maintain hot melt inks at the proper operating temperature using heat generated by heating elements in the reservoir and print head.

BACKGROUND OF THE INVENTION 
The present invention relates generally to an ink jet printing apparatus, 
and is specifically concerned with a hot melt ink jet printer in which an 
articulated arm is provided for connecting the ink reservoir to the print 
head so as to allow the print head to be positioned independently of the 
reservoir. 
A conventional hot melt ink jet printing apparatus includes a heated 
reservoir assembly for melting a solid ink pellet and a print head for 
ejecting the melted ink. Normally, the print head is directly mounted to 
the reservoir assembly in a manner such that there is no relative movement 
between the reservoir assembly and print head. The print head has an array 
of nozzles, usually forming a straight line. When mounted on the reservoir 
assembly, this line of nozzles is at a slight angle with respect to the 
horizontal. As the object to be printed is conveyed in a horizontal 
direction past the print head, the nozzles are actuated in a sequential 
manner in order to form dot-matrix characters on the surface of the 
object. The angle formed by the line of nozzles relative to the horizontal 
defines the height of the printed characters. 
Conventional hot melt ink jet printers with fixed print heads are not well 
suited to applications in which it is desired to print on a non-vertical 
surface of a horizontally moving object, or to move the object past the 
print head in a direction other than the horizontal. In some cases, it is 
possible to tip the entire ink jet apparatus so that the nozzles of the 
print head face the surface to be printed and line up properly with the 
direction of product movement. However, in instances where it is necessary 
to print on the top surface of the product, or where the product is being 
conveyed vertically during printing, this would require tipping the 
apparatus a full 90 degrees. Such tipping of the ink jet apparatus poses 
serious problems. Normally, the ink jet apparatus has one or more level 
sensors in the reservoir assembly for detecting when the ink is low and 
for shutting down the system to prevent de-priming. Tipping of the ink jet 
apparatus can set off these level sensors and cause a premature shutdown 
of the system. Furthermore, extreme tipping of the reservoir assembly can 
cause spillage of the ink if the print head is brought to for above or 
below the level of the reservoir. Such may also cause ink starvation or 
siphoning at the print head. 
An additional disadvantage of conventional hot melt ink jet printing 
apparatus concerns the height of characters printed. In order to increase 
the printed character height, the angle formed by the array of ink jet 
nozzles relative to the horizontal must be increased in order to increase 
the effective vertical spacing between successive nozzles. However, 
because the print head is fixedly mounted to the reservoir assembly, the 
print head and reservoir must be tilted as a unit in order to achieve this 
result. In addition to the physical difficulty involved in repositioning 
the entire reservoir and print head assembly, there is the additional 
problem that the operation of the ink level sensors can be adversely 
affected whenever the orientation of the reservoir is changed. Therefore, 
with typical hot melt ink jet printing apparatus, only small changes in 
character height can ordinarily be obtained. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the foregoing limitations and 
disadvantages of the prior art are substantially avoided by providing an 
ink jet printing apparatus which includes an ink jet print head, a 
reservoir for supplying ink to the print head, and rigid articulated 
support means carried by the reservoir and connected to the print head. 
The support mean affords two degrees of rotational freedom for allowing 
adjustment of the print head relative to the reservoir, and includes an 
internal channel extending from the reservoir to the print head for 
conducting ink to the print head. 
By virtue of the articulated support means, printing can be carried out on 
surfaces lying in various planes or moving in different directions, 
without tilting the ink reservoir. This makes it possible to avoid ink 
spillage and improper operation of the level sensors in the ink reservoir. 
Adjustment of the height of the printed characters is also facilitated. 
In a specific embodiment of the invention, the articulated support means 
comprises at least three rigid sections and at least two rotatable joints 
connecting these sections. The support assembly may be made of a thermally 
conductive material in order to maintain hot melt ink at the proper 
operating temperature using heat conducted from heating elements in the 
reservoir and print head. 
Other aspects of the present invention relate to a rotatable joint 
construction for use in an adjustable ink jet apparatus, and the provision 
of means to prevent siphoning of ink through the print head orifices, as 
described and claimed hereinafter.

Although throughout the following description the terms vertical and 
horizontal will be used extensively, it should be understood that the 
invention is not limited to operation in horizontal and vertical planes. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates an upper rear perspective view of a hot melt ink jet 
printing apparatus 20 constructed in accordance with the present 
invention. The apparatus includes a print head 22, a reservoir 24 for 
supplying ink to the print head 22, and an articulated support assembly 26 
connected to the reservoir 24 at one end 28 and rotatably supporting the 
print head 22 in an operable position at its remote end 30. The support 
assembly 26 has a continuous internal channel (not shown in FIG. 1) 
extending from the reservoir 24 to the print head 22 for carrying the ink. 
The support assembly 26 includes a plurality of serially interconnected, 
rigid sections hereinafter referred to as a pivot block support 32, joint 
block or elbow 34, and pivot block 36. Rotatable joints 38 and 40 connect 
the sections 32, 34 and 36 in series. 
A ribbon cable 42, a portion of which is shown in phantom in FIG. 1, is 
coupled to the print head 22 for carrying electrical control signals to 
the individual orifices (not shown in FIG. 1). The ribbon cable 42 also 
contains power lines for a heating element in the print head, ground 
lines, and additional lines which are connected to a temperature sensor in 
the print head. Piezoelectric devices associated with each orifice of the 
print head produce droplets 44 of ink on demand, and these droplets are 
directed at a moving substrate 46 in a controlled fashion for producing 
dot-matrix characters 48. The principles of operation of the print head 
per se are well known in the art and need not be described further herein. 
In FIG. 1, the print head 22 is shown in a first operating position for 
printing on a surface, such as the substrate 46, which lies in a vertical 
plane parallel to the face of the print head 22 and which moves 
horizontally in the direction of the arrow 50. The reservoir 24 is in flow 
communication with a melting chamber 52 which receives ink in solid form. 
A cover 54 protects the melting chamber from contamination. 
The pivot block support 32 includes a draw end block 56 in communication 
with the reservoir 24. An arm 58 extends outwardly from the draw end block 
56 as shown. The joint block or elbow 34 is coupled to the free end 60 of 
the arm 58 by means of a first pivot screw 62. The pivot block 36, which 
carries the print head 22, has an ink supply block 64 in communication 
with the print head 22 for supplying ink thereto. The ink supply block 64 
is coupled to the elbow 34 by means of a second pivot screw 66. 
The first pivot screw 62 defines a first pivot axis 68 which is fixed with 
respect to the reservoir 24 and which is parallel to the axis x of the 
fixed orthogonal coordinate system x, y, z shown in FIG. 1. For purposes 
of the description herein, the coordinate system x, y, z will be 
considered as being fixed relative to the reservoir 24, and hence the 
first pivot axis 68 will always remain parallel to the x axis. 
The second pivot screw 66 is coupled to the ink supply block 64 to define a 
second pivot axis 70, which is movable with respect to the reservoir. In 
the print head position shown in FIG. 1, the second pivot axis 70 is 
parallel to the z axis, which is itself parallel to the arm 58. In 
accordance with the present invention, however, the elbow 34 is rotatable 
about the first pivot axis 68 through a first pivot angle 72 of about 
90.degree.. As a result, the second pivot axis 70 is rotatable from a 
position in alignment with the z axis as shown in FIG. 1 to a position in 
alignment with the y or vertical axis. A pair of confronting stops 76 on 
the elbow 34 and radial arm 58 limits the first pivot angle 72. The pivot 
block 36, pivotally mounted to the elbow 34, is movable through a second 
pivot angle 74 of greater than about 90 degrees. This angle extends from 
below the X axis to beyond the Y axis. 
In FIG. 2, the ink jet printing apparatus 20 of FIG. 1 is illustrated in a 
lower front perspective view in the first position so that the print head 
22 is arranged to print on a vertical surface (not shown) moving generally 
parallel to the x-y plane in the x direction. Droplets of ink are produced 
by orifices 78 which are formed in an orifice plate 80. In a typical 
application, the orifice plate 80 is spaced about one-eighth of an inch 
from a substrate to be printed, such as the substrate 46 shown in FIG. 1. 
In the print head position of FIG. 2, the droplets of ink will be 
projected from the orifices 78 in a direction parallel to the z axis. 
An overflow orifice 81 is located in the melting chamber 52 to establish 
the maximum ink level in the printing system 20. A stop 83 between the 
elbow 34 and pivot block 36 prevents further counterclockwise rotation of 
the print head 22 about the pivot axis 70 beyond the position shown in 
FIG. 2. This maintains the orifices 78 above the overflow level so that 
the orifices do not release ink by siphoning action. 
FIG. 3 illustrates a fragmentary portion of the printing apparatus 20 of 
the present invention in which the print head 22 has been rotated about 
the fixed axis 68 so that the orifice plate 80 faces downwardly generally 
in the horizontal X-Z plane. In the arrangement of FIG. 3, the printing 
apparatus 20 is adapted to print on horizontal surfaces moving in a 
horizontal direction generally parallel to the x axis. The stop 76 
(visible in FIGS. 1, 2, 4 and 6) prevents the print head from moving below 
the overflow hole 81. 
FIG. 4 illustrates the printing apparatus 20 of the present invention with 
the print head 22 moved or rotated about the second pivot axis 70 from the 
first position shown in FIG. 2 to the third position. The row of orifices 
78 in the orifice plate 80 is aligned generally in the direction of the y 
axis. In the arrangement illustrated, the print head 22 is arranged to 
print to a surface lying in a vertical or x-y plane and moving in the 
vertical or y direction. Stops 85 between elbow 34 and pivot block 36 
prevent the print head 22 from traveling much beyond the vertical. 
It should be understood that, in accordance with the present invention, 
adjustment of the print head 22 to the third position may be accomplished 
by moving the print head from the first position (FIG. 2) directly to the 
third position (FIG. 4) by rotating the print head 22 about the second 
pivot axis 70. However, it is also possible to move the print head 22 into 
the third position (FIG. 4) from the second position (FIG. 3) by first 
rotating the print head 22 in the horizontal plane about second pivot axis 
70 through the second pivot angle 74, and then rotating the print head 22 
through the first pivot angle 72 about the first pivot axis 68. The print 
head 22 as illustrated in FIG. 3 may be moved from the second position, as 
shown, through any portion of the second pivot angle 74 to other 
orientations in the horizontal plane. It should be further understood that 
the invention is not limited to the three positions illustrated, and that 
other orientations are possible. 
In accordance with the present invention, it is possible to adjust the size 
or height of printing characters 48 (FIG. 5) by adjusting the skew angle 
82 of the print head 22. The skew angle 82 is defined as the angle between 
the center line 86 of the row of orifics 78 and the direction of movement 
88 of the substrate (not shown). In FIG. 5, the orifice plate 80 is 
illustrated at a first skew angle 82 (solid lines) and at a second skew 
angle 82' (phantom lines). The skew angles 82 and 82' are exaggerated for 
purposes of illustration. In FIG. 5, the vertical distance 90 between the 
first orifice 92 and the last orifice 94 defines the height of the smaller 
character 48A. Likewise, the vertical distance 96 between the first 
orifice 92 and last orifice 94 at the larger skew angle 82' defines the 
height of the larger character 48B. In the present invention, when the 
print head 22 is positioned in any one of the positions shown in FIGS. 
1-4, the specific skew angle may be adjusted for setting the character 
height. In all cases, the skew angle 82 is a lesser included angle within 
the second pivot angle 74. 
The row of orifices 78 lie along the center line 86 which is normal to the 
second pivot axis 70. The droplets 44 produced by the orifices 78 (FIG. 1) 
are directed at the substrate 46 in a direction perpendicular to said 
first pivot axis 68 and parallel to the second pivot axis 70. 
Referring to FIGS. 6-11, further details of the present invention will now 
be described. FIG. 6 illustrates in top plan view the ink jet printing 
apparatus 20 of the present invention with the ribbon connector removed 
for clarity. In this view, the print head 22, the reservoir 24 and the 
articulated support assembly 26 are illustrated as being in the second 
position, with the print head 22 facing downwardly for printing on a 
horizontal surface (not shown). The print head 22 lies at a skew angle 86 
about the second pivot axis 70. 
FIG. 7 is a simplified perspective drawing of the printing apparatus 20 of 
the present invention with an ink jet head cover 102 and a reservoir cover 
104 in place. The ribbon cable 42 is coupled at one end to a circuit card 
(not shown) mounted on the reservoir 24, and at its opposite end to the 
print head 22. The stops 76, 83 and 85 (FIGS. 1, 2, 4 and 6) prevent full 
rotation of the print head 22 below the overflow level, for the reasons 
noted previously. Such full rotation is also prevented in order to protect 
the ribbon cable 42 from damage. 
FIG. 8 is a rear elevation of the printing apparatus of the present 
invention illustrating the reservoir 24, the melting chamber 52, and the 
cover 54. The lower reservoir chamber housing 112 has a cylindrical bore 
114 for receiving a reservoir heating element 116. The heating element 116 
maintains the reservoir 24 at the proper operating temperature for hot 
melt ink. Similarly, as illustrated in FIG. 10, the print head ink chamber 
block 118 has a cylindrical bore 120 for receiving a print head heating 
element 122 therein for maintaining the print head 22 at the proper 
operating temperature. The articulated arm 26 coupled between the print 
head 22 and the reservoir 24, is made of a heat conductive material, such 
as aluminum, and is heated by conduction from the heat supplied by the 
reservoir heater 116 and the print head heater 122. 
In FIG. 9, the reservoir 24 is shown in a side sectional view. With the 
exception of the cap 54, which may be made of plastic, the reservoir 24 is 
made of a metal having good heat conduction properties, such as aluminum 
or steel. The melting chamber 52 of the reservoir has an upper reservoir 
chamber 124 formed therein. With the cap 54 removed, a pellet 126 of solid 
thermoplastic hot melt ink is supplied through the open top 128 of the 
melting chamber 52. The heating element 116, when actuated, supplies heat 
for raising the temperature of the entire reservoir 24 in order to melt 
the pellet 126 and thereby provide a supply of liquid ink 130 for the 
system. The cover 54 protects the ink 130 in the system from contamination 
and the overflow orifice 81 establishes an ink level below the level of 
the orifices 78. The upper reservoir chamber 124 is connected to a lower 
reservoir chamber 132 via exit ports 134 in the bottom wall 135 which 
extends into the side wall 136 of the chamber 124. The ink 130 flows into 
the lower chamber 132 through a filter 137. Ink flow, shown by the arrows 
138, moves laterally in the lower chamber 132 past the baffles 140, which 
enhance heat exchange between the reservoir 24 and the ink 130, to the 
lateral exit port 142 in the end wall 144. A chamber 146 is provided above 
the filter 137 to allow the ink to spread across the entire top surface of 
the filter. 
The ink flowing through the exit port 142 fills a supply chamber 148, which 
contains a draw tube 150. The draw tube 150 is an extension of the draw 
end block 56 of the pivot block support 32. The supply chamber 148 also 
contains a sensor element 152 which has first and second level detectors 
154 and 156. The first level detector 154 senses when the ink supply 130 
falls below a warning level so that a signal can be provided to the 
operator to add more ink. The second level detector 156 provides a system 
shutdown signal when the ink 130 falls below the level at which the system 
would lose its prime. 
The ink 130 is drawn up the draw tube 150 by pumping action provided by the 
piezoelectric actuators within the print head 22, and passes into a 
continuous internal channel 160 formed in the articulated arm 26. As shown 
in FIGS. 9 and 10, the internal channel 160 comprises a plurality of 
interconnected cylindrical bores in the articulated support assembly 26. A 
draw channel 162 is axially aligned within the draw tube 150 (FIG. 9), and 
a lateral channel 164 in the draw end block 56 is in communication with 
the draw channel 162. The feed channel 166 formed in the arm 58 
communicates with the lateral channel portion 164 and extends to the free 
end 60 of the arm 58. First and second pivot channels 168 and 170 are 
formed in the pivot block 36, as shown in FIG. 11. Each of the first and 
second pivot screws 62 and 66 has an axial channel 172 and a diametric 
channel 174 (FIGS. 10 and 11). The free end 60 of the arm 58 and the 
downstream end 175 of the pivot block 36 have respective stepped bores 
176, 177 formed therein. Each stepped bore 176, 177 has an enlarged 
stepped open end 178, 179 and a stepped intermediate portion 180, 181. The 
upstream end 182 of the pivot block 36 has a threaded opening 183 which 
confronts the enlarged open end 178 of the arm 58. The first pivot screw 
62 is fitted into the stepped bore 176 and is threadably secured to the 
pivot block 36 as shown in FIG. 11. Similarly, the supply block 64 has a 
threaded opening 183 which confronts the enlarged opening 179 in the 
downstream end 175 of the pivot block 36. The second pivot screw 66 is 
threadably secured to the supply block 64 through the stepped bore 179 in 
the downstream end 175 in pivot block 36. The enlarged open end 178 of the 
stepped bore 176 forms a first recess 184 around the first pivot screw 62. 
The intermediate portion 180 forms an annular chamber 185 around the first 
pivot screw 62. The annular chamber 185 communicates with the radial 
channel 166 in the radial arm 58 and the diametric channel 174 in the 
first pivot screw 62. 
By virtue of the foregoing arrangement, the ink is able to flow from the 
feed channel 166 about the pivot screw 62 in the annular chamber 185 to 
the diametric channel 174 and thence to the axial channel 172. Thus, it is 
not necessary for the diametric channel 174 to be aligned with the feed 
channel 166 in order for the ink to flow. An 0-ring seal 186 is provided 
in second recess 187 to seal the head 188 of the pivot screw 62 against 
the radial arm 58. An 0-ring 189 is provided in first recess 184. A washer 
190 overlying the 0-ring 189 is in confronting relation with the elbow 36 
to seal the pivot block 36 against the opposite side of the arm 58 as 
shown in FIG. 11. The second stepped bore 177 has a structure similar to 
that of the first stepped bore 176, and contains similar components. The 
details of the second stepped bore 177 are shown in FIG. 11 but are not 
further discussed herein. 
A supply channel 192 (FIG. 11) is formed in the ink supply block 64 for 
communication with a supply tube 194 (FIG. 10) in the print head 22. The 
supply tube 194 has a tapered tubular end 196 that is suitably sleeved in 
the supply channel 192. As indicated by the arrows 138, the ink flows via 
the first and second pivot channels 168 and 170 to the supply channel 192 
via the annular chamber 181 which is in communication with the respective 
axial and diametric channels 172 and 174 in the second pivot screw 66. The 
second pivot screw 66 is suitably threaded into the threaded bore 183 in 
ink supply block 64. The second stepped bore 177 in elbow 36 confronts the 
supply block 64 as shown. The second stepped bore 177 of the second joint 
40 is similar to the stepped bore 176 of the first joint 38, as previously 
described. The first recess 179, 0-ring 199, washer 200, intermediate 
chamber 181, second recess 201, and 0-ring 202 have the same functions of 
the corresponding parts described above. 
The first and second pivot screws 62 and 66 are tightened so that the 
0-rings 186, 189, 199 and 202 are sufficiently compressed to prevent 
leaks. The screw threads 203 of the first and second pivot screws 62 and 
66 are secured in their respective bores by an appropriate adhesive such 
as the material sold under the trademark "Loctite". 
Referring to FIG. 12, when it is desired to adjust the position of the 
print head 22 to any of the various positions hereinbefore described, the 
pivot screw locks 218 are loosened so that the various arm sections 32, 34 
and 36 may move with respect to each other but remain self-supporting. 
When the proper adjustment is achieved, the pivot screw locks 218 may be 
tightened by means of hex bolts 220. Thus, the pivot screw locks 218 
prevent the movement of the pivot screws 62 and 66 after the arm sections 
32, 34 and 36 are fixed in position. 
Referring once again to FIGS. 9-11, the various sections of the channel 160 
are formed by mechanical drilling from opposite ends of a particular piece 
until the channels intersect and therefore communicate. Sometimes, 
however, as in the case with the draw channel 162, the lateral channel 
164, and the feed channel 166, through-holes are drilled and the ends are 
closed with screw plugs 222. Screw plugs 222 are also used for reclosing 
the first and second pivot channels 168 and 170 as illustrated in FIG. 11. 
Operation of the ink jet printing apparatus of the present invention is 
illustrated in FIGS. 13-15. In FIG. 13, the printing apparatus 20 is shown 
with the print head 22 in the first position. The printing apparatus 20 is 
mounted on a supporting platform 210, shown in phantom. The articulated 
support assembly 26 coupled to the reservoir 24 supports the print head 22 
in an orientation such that the ink nozzles face the vertical side 
surfaces 224 of the cartons 226 carried by the moving conveyor belt 228 in 
the direction of arrows 230. In the arrangement of FIG. 14, the printing 
apparatus 20 is shown with the print head 22 in the second position for 
printing on the top surfaces 232 of the cartons 226 carried by the 
conveyor 228 in the direction of arrows 230. In the arrangement of FIG. 
15, the print head 22 is shown in the third position, in which printing 
may be carried out on the vertical surfaces 234 of cartons 239 carried by 
an elevator 240 moving upward in the direction of the arrows 242. 
In the various arrangements illustrated in FIGS. 13-15, it may be necessary 
to adjust the position of the printing apparatus 20 with respect to the 
cartons being printed. Such adjustments may be easily accomplished by 
adjusting the position of the platform 210 with respect to the belts 228 
or elevator 240. 
While the invention has been described in connection with specific 
embodiments thereof, it will be understood that the invention is capable 
of further modifications. For example, although the preferred embodiment 
utilizes single-axis rotatable joints to obtain the desired articulation 
of the print head, other types of rotatable joints, such as ball joints 
and the like, may be used instead. It may also be desired to fit a second 
print head and articulated support assembly to the reservoir so that two 
different character heights can be printed simultaneously. Finally, it may 
be desired to provide a supplementary heating element for the articulated 
support assembly 26 to prevent cooling of the ink, particularly in 
embodiments wherein the arm 58 is made longer to extend the reach of the 
print head. The appended claims are intended to cover any variations, uses 
or adaptations of the invention following, in general, the principles of 
the invention, and including such departures from the present disclosure 
as come in known and customary practice within the art to which the 
invention pertains.