Apparatus for decorating beverage cans using a flexographic process

A decorator for cylindrical objects, such as beverage cans and the like. The cylindrical members are carried by mandrels which are sequentially presented to rotating printing plates. A plurality of mandrels are carried by a mandrel cluster and the printing plates are carried by plate wheels. The decorator is capable of utilizing flexographic inks wherein the surface of the cylindrical body can be printed with a first ink, the ink rapidly dried, followed by the application of the second ink. The mandrels are compliantly supported on the mandrel cluster by pneumatic cylinders supplied with both high and low pressure air so that the spring rate of the complaint support may be varied to ensure uniform printing. Synchronization of the rotation of a mandrel with the rotation of a printing plate carried by a plate cylinder is critical so that the second image is precisely in register with respect to a first applied image. A particular feature is the utilization of synchronized electric motors to rotate the various parts of the decorator with each electric motor having an encoder and wherein an electronic controller controls the rotational position of each motor so as to effect the synchronization of the several motors and the precise registration of the components.

FIELD OF THE INVENTION 
The current invention concerns an apparatus and method for decorating 
cylindrical members, such as beverage cans and the like. More particularly 
the invention concerns a decorator for decorating can bodies using a 
flexographic process. 
BACKGROUND OF THE INVENTION 
Generally, can-type beverage containers are of a two-piece construction, 
with one piece including an integral body and bottom and the other piece 
being a separately applied lid. Since such cans are cylindrical, they must 
be printed or decorated by rolling the required decorative ink onto the 
can body. 
Traditionally, can bodies were decorated in multiple colors using a 
decorator that sequentially applied colored inks in the desired image to a 
transfer blanket by way of a separate printing plate for each color. Such 
a can decorating press is disclosed in U.S. Pat. Nos. 3,223,028 (Brigham) 
and 3,227,070 (Brigham et al.). The application of the various color inks 
to the blanket is synchronized by mechanical gears. After the multicolored 
image has been applied to the blanket, the blanket applies the image to 
the can in one revolution of the can. The can is mounted on a free 
spinning mandrel. Although the can may be pre-spun prior to printing, as 
disclosed in U.S. Pat. No. 4,138,941 (McMillin et al.) during the printing 
process its rotation is driven by frictional contact with the transfer 
blanket. 
The art work on the aforementioned printing plates is so arranged that each 
color is separated from the adjacent color by very narrow non-printing 
areas, known as "trap lines". These "trap lines" serve to confine each 
color to its own design configuration and prevents undesirable bleeding of 
one color into another. The inks required for use with transfer blankets 
must be formulated to have a high tack and a paste like viscosity. The 
high viscosity ensures that the ink will stay within the trap lines, thus 
avoiding the bleeding of one color into another. The high tackiness also 
serves to increase the driving friction between the transfer blanket and 
the can that is necessary to allow the blanket to rotate the can. 
Unfortunately, the such high tack viscous inks are very slow drying and 
require large curing ovens. Further, the inks emit undesirable solvent 
vapors into the environment. 
Decorating cans using a flexographic process offers several advantages. 
First, flexographic inks are water based and do not emit significant 
quantities of volatile organic hydrocarbons. Consequently, they are 
environmentally benign. Second, they are quick drying and do not require 
oven curing after application. Third, since they are quick drying, the 
trap lines between each color image can be dispensed with resulting in a 
more aesthetically pleasing appearance, as well as the ability to 
overprint several colors in a "dry trap" process. 
Unfortunately, use of flexographic inks presents a number of serious 
difficulties that have heretofore made them impractical for use in 
decorating cans in a high speed operation, except in rather limited 
applications, such as printing random numbers on cans otherwise decorated 
using the traditional blanket transfer process, as disclosed in U.S. Pat. 
No. 4,884,504 (Sillars). First, they cannot be applied to a transfer 
blanket as the inks would run together. Accordingly, in order to utilize 
the flexographic inks, they must be applied directly to the can using a 
separate printing plate for each color. Consequently, the point of contact 
of each printing plate with the can must be precisely in registration with 
the point of contact of the other printing plates. 
Satisfying this precise registration requirement is made more difficult by 
the fact that flexographic inks are not tacky. The lack of tackiness can 
cause a friction driven can to slip relative to the printing plate, 
resulting in an image that is out of register. Consequently, the cans must 
be positively driven while they are in contact with the printing plate to 
ensure that the surface speed of the can matches that of the printing 
plate. The net result is that a decorator utilizing flexographic ink has a 
number of components which must be precisely indexed and synchronized. 
Although mechanical gearing can be utilized to properly index and 
synchronize the components, such gears are subject to wear, causing poor 
quality decoration. 
A second difficulty associated with flexography is that it is difficult to 
ensure uniform contact pressure of the entire can surface over a single 
printing plate and difficult to ensure uniform contact pressure between 
different printing plates. Non-uniform contact pressure results in 
non-uniform decorating. 
It would be desirable to provide a decorator for beverage cans, using a 
flexographic process, that did not require the use of mechanical gearing 
to synchronize and index the components and that ensured uniform contact 
pressure of the printing plates against the cans. 
SUMMARY OF THE INVENTION 
It is an object of the current invention to provide an apparatus and method 
for decorating cylindrical objects, such as beverage cans, using a 
flexographic process. 
It is another object of the current invention that the apparatus not rely 
on mechanical gearing to synchronize and index its various components. 
It is still another object of the current invention that the apparatus 
ensure that the printing plates contact the object to be decorated with 
uniform pressure. 
These and other objects are accomplished in a decorator for applying an 
image to cylindrical objects using a flexographic process, comprising (i) 
a first printing plate mounted on a first support structure, at least a 
first portion of the image being formed on the first printing plate, (ii) 
carrying means for carrying the cylindrical objects into contact with the 
first printing plate, and (iii) compliant support means for supporting the 
carrying means on a second support structure, the compliant support means 
having pneumatic means for imparting compliancy thereto. 
In one embodiment of the invention, the first support structure comprises a 
first plate wheel, the carrying means comprises a mandrel adapted to be 
inserted into one of the cylindrical objects, the second support structure 
comprises a mandrel cluster, and the pneumatic means comprises a piston 
operating within a piston cylinder. In addition, in this embodiment, the 
decorator comprises (i) a second plate wheel on which a second printing 
plate, having a second portion of the image formed therein, is mounted, 
(ii) a first source of pressurized air, (iii) means for placing the piston 
cylinder in flow communication with the first pressurized air source, 
whereby air in the piston cylinder from the first pressurized air source 
provides compliancy for the compliant support means, (iv) a shaft for 
driving rotation of the mandrel, (v) a support plate for supporting the 
shaft, (vi) a support frame having means for slidably supporting the 
support plate thereon, the piston and piston cylinder mounted on the 
support frame, the piston operatively coupled to the support plate, (vii) 
motors operatively coupled to rotate the first and second plate wheels, 
the mandrel cluster, and the mandrel, and (viii) an electronic controller 
programed with logic for controlling the rotation of each of the motors, 
whereby the first and second portions of the image are transferred to the 
surface of the cylindrical objects.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail, reference is first made to FIGS. 1 
and 2 wherein there is illustrated the details of a decorator 10 according 
to the current invention. The decorator 10 includes a mandrel cluster 12 
and upper and lower printing plate wheels 64 and 66, respectively. As 
explained in detail below, cans 94 to be decorated are carried by the 
mandrel cluster 12 into sequential contact with printing plates 78 and 79 
mounted on the plate wheels 64 and 66, respectively. 
The upper and lower plate wheels 64 and 66 are supported on a stand 56 
having a pair of uprights 58 carried by a base plate 60 and joined 
together at their tops by a cross brace 62. The plate wheels 64 and 66 
include shafts 68 and 69, respectively, that are rotatably journalled in 
sleeves (not shown) carried by the upright 58. Electric motors 82 and 84 
are attached to the shafts 68 and 69, respectively, of the upper and lower 
plate wheels 64 and 66. Encoders 112 and 114, which may be of the optical 
type, are mounted on the motors 82 and 84, respectively. As shown in FIG. 
2, the motors 82 and 84 are coupled to the shafts 68 and 69 for direct 
drive. However, the motors could also drive the shaft indirectly via a 
timing belt or gearing. Each shaft 68 and 69 carries a hexagonal hub 72 
having extending therefrom six radial spokes 74 that support a circular 
rim 76. 
The rim 76 of each plate wheel 64 and 66 carries a pair of diametrically 
opposed flexographic printing plates 78 and 79, respectively, that are 
adjustably mounted on the rim 76 by means of a compliant mount 80. Each of 
the printing plates in each pair has the same image formed therein. That 
image constitutes the entire decoration to be applied to the can in a 
single color. Additional printing wheels carry other plates for decorating 
with additional colors may also be used. The image formed on the printing 
plates 78, 79 may comprise any graphical representation, including a 
background for other images, alphanumerics, depictions of objects or 
people, etc. 
As shown in FIG. 1, each of the plate cylinders 64, 66 has associated 
therewith an inker 86. Each inker 86 includes a tray 88 in which ink is 
maintained at a prescribed level. An inker roll 90 is mounted for rotation 
within the tray 88 and has associated therewith a doctor blade 92. As the 
inker roll 90 rotates, it picks up ink from the tray 88, with the excess 
ink being doctored off by blade 92. From the roll 90, the ink is 
transferred to the printing plates 78 and 79 as they rotate past the 
inkers 86 so as to place the printing plates in rolling contact with the 
rolls 90. Each roll 90 is driven by an electric motor (not shown) 
controlled, by an electronic controller discussed below, so that its 
surface speed is equal to that of the printing plates 78 and 79. 
The decorator also includes a mandrel cluster 12 having a support stand 24. 
The stand 14 has a base plate 16 and a pair of spaced uprights 18, each 
having a base plate 20. The uprights 18 are joined together by transverse 
members 22 and 24. The mandrel cluster 12 also has a shaft 26 which is 
suitably journalled in sleeves 28 carried by the uprights 18. The mandrel 
cluster 12 is driven by an electric motor 54 attached to one end of the 
shaft 26. An encoder 113, discussed further below, is mounted on the 
motor. As shown in FIG. 2, the motor 54 is coupled to the shaft 26 for 
direct drive. However, the motor 54 could also drive the shaft 26 
indirectly via a timing belt or gearing. The shaft 26 has a hexagonal hub 
30 from which six pairs of circumferentially spaced spokes 32 extend 
radially. Each pair of spokes 32 has a rectangular mandrel support frame 
36 attached to its distal end, there being six support frames equally 
circumferentially spaced around the mandrel cluster 12. 
As shown in FIG. 5, an electric motor 40 is mounted, via screws 156 and a 
ball bushing mount 38, within each support frame 36. An encoder 176 is 
mounted on each mandrel motor 40. A mandrel support housing 46, mounted on 
a mounting plate 42, is slidably supported on each support frame 36 by 
three pairs of guide rods 130, 131 and 132, as explained further below. A 
mandrel shaft 48 is disposed through each support housing 46 and supported 
therein by bearings 34. As shown in FIG. 6, the mandrel shaft 48 has a 
sprocket 160 on one end that is driven by a flexible drive timing belt 52 
driven by the motor 40 via sprocket 162. 
As shown in FIG. 5, a mandrel 50 is attached to the end of the mandrel 
shaft 48 opposite the end driven by the timing belt 52. The outside 
diameter of the mandrels 50 is only slightly less than the inside diameter 
of the cans 94 so that the cans are stably supported on the mandrels, as 
shown in FIG. 2. 
In operation, cans 94 to be decorated are loaded onto the mandrels 50, as 
shown in FIG. 2, while the mandrel cluster is rotating in a clockwise 
direction at a rotational speed .omega..sub.mc, as indicated in FIG. 1. 
Methods for loading cans onto rotating mandrels are well known in the art 
-- see, for example, U.S. Pat. No. 4,138,941 (McMillin et al.), hereby 
incorporated by reference in its entirety -- and are not discussed further 
herein. 
The cans 94 are held on the mandrels 50 by vacuum and ejected after 
decoration by pressurized air. As shown in FIG. 5, a vacuum source 122, 
which may be a vacuum pump, is connected, via a valve manifold 128 and 
tubing 150, to an air tight plenum 126 formed in each mandrel support 
housing 46. The mandrel shaft 48 is hollow and has a radial hole 124 which 
places an axial passage 154 in the mandrel 50 in air flow communication 
with the plenum 126. Thus, the vacuum source 122 draws air into the axial 
hole 154 in the mandrel 50, thereby applying a negative pressure that 
holds the can 94 onto the mandrel. A source of pressurized air 158, which 
may be a compressor, is also connected to the valve manifold 128 so that, 
by appropriate actuation of the valving in the manifold, pressurized air, 
rather than vacuum, is transmitted to the axial hole 154 in the mandrel 
50, thereby causing the can 94 to be ejected from the mandrel. 
In order to ensure uniform contact pressure by the printing plates 78 and 
79 along the entire length of each can 94, the mandrels 50 must be rigidly 
supported. However, as explained further below, the mandrels 50 must also 
be free to move in the radial direction. Thus, according to the current 
invention, the mandrel support housing 46 is slidably supported on the 
support frame 36. Specifically, as shown in FIGS. 4 and 5, the mounting 
plate 42 on which the mandrel support housing 46 is mounted has three 
pairs of guide rods 130, 131 and 132 extending from its radially inward 
facing surface. These guide rods slide in close fitting holes in the 
support frame 36 so that the mandrels 50 are free to move substantially 
only in the radial direction, without undergoing significant tilting as a 
result of forces applied to the can 94 during printing. In addition, the 
center pair of guide rods 131 has collars formed thereon that slide within 
linear bearings 136 to provide additional rigidity. A collar 134 disposed 
at the distal end of each of the guide rod pairs 130 and 132 acts as a 
stop to limit the radial travel of the mandrel 50. 
Notwithstanding the rigid sliding support arrangement discussed above, the 
contact between the can 94 and the printing plates 78 and 79 imposes a 
moment 174 that tends to rotate the mandrel 50 clockwise, as viewed in 
FIG. 5, so that it tilts inward. Such inward rotation would cause uneven 
printing since the contact pressure at the open end 170 of the can 94 
would be greater than at the closed end 172. According to the current 
invention, this problem is solved by causing the mandrel timing belt drive 
52 to impart a downward acting force on the mandrel shaft gear 160 shown 
in FIG. 6. This downward acting force creates a moment 175, shown in FIG. 
5, that counteracts moment 174, thereby preventing the clockwise rotation 
of the mandrel. In the preferred embodiment, the downward acting force is 
created by an adjustable tensioner in conjunction with the drive chain 52. 
The adjustable tensioner is illustrated in simplified form in FIG. 6 and 
has a sprocket 164 attached to a rod 166 pivotally supported by an air 
cylinder 168. By adjusting the pressure within the air cylinder 168, the 
amount of tension in the timing belt drive 52, and therefore the amount of 
force pulling the sprocket 160 downward, can be varied so as to ensure 
that even contact pressure is achieved along the entire length of the can 
94. 
As shown in FIG. 3, if undisturbed, the mandrel cluster 12 would transport 
each can 94 so that it traveled in a circular path 118. As a result of 
contact with the printing plate 78, the can 94 must be displaced radially 
inward by an amount d so as to travel in the path 120. Thus, sufficient 
compliancy must be incorporated into the mandrel support system to allow 
for this radial displacement. Moreover, since the spring rate of the 
compliant support system determines the contact pressure of the cans 
against the printing plates, ideally, the spring rate should be adjustable 
so that the optimum pressure can be obtained. 
According to the current invention, compliancy is obtained by providing the 
mandrels 50 with a pneumatic support system. As shown in FIGS. 4 and 5, a 
piston rod 138 having a piston 140 at its distal end is attached to each 
of the guide rods 132. Each piston 140 slides within a piston cylinder 142 
supplied with either high pressure air 146 or low pressure air 148 from a 
valve manifold 144 via tubing 152 -- it should be understood that the 
terms "high" and "low" pressure as used herein refer to the relative 
values of the pressure of the air 146 and 148. The valve manifold is 
capable of operation in at least two states. In the first state, the high 
pressure air 146 is supplied to the piston cylinder 142. In the second 
state, the low pressure air 148 is supplied to the piston cylinder. The 
valve manifold 144 is supplied with air from a pressurized air source, 
which may be the aforementioned source 158, via tubing 184. The pressure 
of the air 146 and 148 may be individually adjusted via pressure 
regulators 178. 
Compliancy of the mandrel 50 support is achieved by translating the radial 
displacement d of the mandrel into reciprocal motion of the piston 140, 
thereby compressing the air supplied to the piston cylinder 142. The 
spring rate associated with this compliancy -- that is, the amount of 
resisting force applied by the compressed air in response to a given 
displacement d -- determines, in part, the magnitude of the contact 
pressure between the can 94 and the printing plates 78 and 79. According 
to the current invention, this spring rate can be readily adjusted by 
varying the pressure of the air 146 and 148 supplied to the cylinder 142 
-- for example, by using the pressure regulator 178 shown in FIG. 5. 
As shown in FIG. 1, the plate wheels 64 and 66 are arranged vertically. 
Thus, gravity will cause a variation in the contact pressure between the 
upper and lower plate wheels. Specifically, when a can 94 is in contact 
with a printing plate 78 on the upper plate wheel 64, the combined weight 
of the can 94, mandrel 50, housing 46 and mounting plate 42 will subtract 
from the force generated in the piston cylinders 142 as a result of the 
deflection of the mandrels 50. As a result, the contact pressure of the 
can against the printing plate 78 is reduced. By contrast, when the can is 
in contact with a printing plate 79 on the lower plate wheel 66 this 
weight will add to the contact pressure. Thus, according to an important 
aspect of the current invention, the valve manifold 144 is supplied with 
both high pressure 146 and low pressure 148 air. The difference in 
pressure between air 146 and 148 is such that the effect of gravity on the 
radially outward force pressing the can into the printing plates is 
exactly offset. 
In the preferred embodiment, the valving in the valve manifold 144 is 
automatically actuated by an electronic controller, discussed further 
below, so that high pressure air 146 is supplied to each mandrel support 
piston 140 prior to that mandrel moving into contact with the upper plate 
wheel 64. After each mandrel has contacted the upper plate wheel 64, the 
controller actuates the valve manifold 144 associated with that mandrel so 
that low pressure air 148 is supplied to its piston 140 prior to contact 
being made with the lower plate wheel 66. Thus, according to the current 
invention, uniform contact pressure is achieved with respect to printing 
by both the upper wheel printing plates 78 and the lower wheel printing 
plates 79 by varying the spring rate of the pneumatic support according to 
the circumferential position of mandrel. 
For various reasons, it sometimes is advisable to avoid printing with 
respect to a particular mandrel 50 -- for example, because it is detected 
that a can 94 was not mounted, or was improperly mounted, on that mandrel. 
According to the current invention, printing can be prevented with respect 
to each mandrel, on an individual basis, by retracting it radially inward 
so as to avoid contact with the printing plates. This is accomplished by 
using tubing 183 to connect a vacuum source, such as source 122, 
previously discussed, to the valve manifold 144 associated with each 
mandrel pneumatic support, as shown in FIG. 5. When it is determined that 
no printing should occur with respect to a particular mandrel 50, the 
aforementioned controller automatically actuates the valving in the valve 
manifold 144 for that mandrel so that the vacuum source is connected to 
its piston cylinder 142. As a result of air 149 being drawn out of the 
piston cylinder 142 by the vacuum source, the piston 140 is withdrawn, 
thereby retracting the mandrel support housing 46 so that the mandrel 50 
does not contact the printing plates. 
As shown in FIG. 1, rotation of the mandrel cluster 12 brings each of the 
cans 94 sequentially into contact with one of the plates 78 and 79 on each 
of the upper and lower plate wheels 64 and 68, respectively. As discussed 
further below, the rotational speed .omega..sub.c of the can 94 relative 
to its axis, as set by the mandrel motor 40, the rotational speed 
.omega..sub.mc of the mandrel cluster 12, as set by its motor 54, and the 
rotational speed .omega..sub.pw of the plate wheels 64 and 66, as set by 
their motors 82 and 84, are each closely synchronized so that the surface 
speed of the can 94 matches that of the plates 78 and 79, thereby causing 
the cans 94 to roll over the plates 78 and 79 without smearing. 
Accordingly, the speed of the mandrel cluster motor 54, the plate wheel 
motors 82 and 84, and each of the mandrel motors 40 are controlled so that 
r.sub.pw .omega..sub.pw =r.sub.c .omega..sub.c +r.sub.mc .omega..sub.mc, 
where r.sub.pw, r.sub.c and r.sub.mc are the radii of the plate wheels 64 
and 66, the cans 94 and the mandrel cluster 12, respectively, as shown in 
FIG. 1. As discussed below, according to the current invention, this 
synchronization is accomplished by an electronic controller. 
In order to reduce the complexity of the calculations required to control 
the speed and registration of the various components, the diameter of the 
mandrel cluster 12 and the plate wheels 64 and 68 should be multiples of 
the diameter of the can 94. In the preferred embodiment, the diameter of 
the mandrel cluster is eight times the diameter of the cans 94, so that 
r.sub.mc =8 r.sub.c. In addition, the diameters of the plate wheels 64 and 
68 and the diameter of the mandrel cluster 12 are equal -- that is, 
r.sub.pw =r.sub.mc. Thus, since there are six mandrels and two printing 
plates per plate wheel, .omega..sub.pw =3 .omega..sub.mc. 
In addition to the speed synchronization discussed above that is necessary 
to prevent smearing, the rotation of the plate wheels 64 and 66 must also 
be indexed to the mandrel cluster 12 so that when a can 94 is transported 
into position adjacent a plate wheel, one of the printing plates on the 
wheel is in position to initially contact the can at a predetermined 
location on the printing plate. In addition, for a given distance between 
the plate wheels 64 and 66, the proper relationship between the rotational 
speed of the mandrel cluster and the rotation speed of the cans must be 
maintained so that the can undergoes the proper number of revolutions in 
the time it takes for the can to travel from a printing plate 78 on the 
upper plate wheel 64 to a printing plate 79 on the lower plate wheel 66. 
This ensures that the image printed by a printing plate 79 on the lower 
plate wheel 66 is in registration with the image printed by a printing 
plate 78 on the upper plate wheel 64. 
In the preferred embodiment, speed regulation and indexing are performed on 
a continuous basis by an electronic controller 180, shown in FIG. 7. In 
the preferred embodiment, the controller 180 is a micro-processor based 
multi-axis servo motion and logic controller programed for controlling the 
speed and shaft position of several motors. Such controllers, 
pre-programed so as to allow the user to develop application programing 
for controlling motor speed and position, as well as other functions, are 
commercially available from various suppliers -- for example, the 
MAX/CONTROL model two axis motion controller supplied by Creonics, Inc., 
Lebanon, N.H., and the DMC-230 model three axis motor controller supplied 
by Galil Motion Control, Inc., Palo Alto, Calif. Since each plate wheel 
and mandrel motor is individually controlled, depending on the number of 
plate wheels and mandrels -- that is, depending on the total number of 
motors to be controlled -- a number of such controllers may be networked 
together to form the controller 180. Since, in the preferred embodiment, 
there are a total of nine motors to be controlled (i.e., one mandrel 
cluster motor, two plate wheel motors and six mandrel motors) two Creonics 
MAX/CONTROL and two Galil DMC-230 controllers are networked together. 
As shown in FIG. 7, conductors connect the encoders 112, 113, 114 and 176, 
associated with each of the motors 54, 82, 84 and 176, to the controller 
180, wherein the pulses from each encoder are accumulated, as discussed 
below. In addition, conductors connect the motors 54, 82, 84 and 176 to 
the controller 180, wherein signals are generated that, after suitable 
amplification by amplifiers (not shown), control the speed of each motor. 
Also, conductor 182 connects the controller 180 to the valve manifold 128 
and conductors 181 connect the controller to the valve manifold 144 for 
each mandrel. 
By way of illustration, a simplified logic diagram of one approach to 
synchronizing the speed and maintaining the registration of the mandrel 
cluster, plate wheels and mandrels is shown in FIGS. 8 and 9. Such logic 
can be readily programed, using techniques well known to those in the 
computer programing arts, into the controller 180. Appendices I and II, 
attached hereto, show the codes for the programs developed for the 
aforementioned Galil DMC-230 and Creonics MAX/CONTROL model electronic 
motor controllers, respectively, according to the current invention, using 
the commands provided for in the programing supplied with these 
controllers. As explained further below, in the preferred embodiment, the 
six mandrel motors 40 and the plate wheel motors 82 and 84 are slaved to 
the mandrel cluster motor 54. Thus, the program for the Galil DMC-230 
model controllers shown in Appendix I controls the six mandrel motors 40 
and the program for the Creonics MAX/CONTROL model controllers controls 
the plate wheel motors 82 and 84 and the mandrel cluster motor 54, as well 
as other logic functions, such as the actuation of the valves in the valve 
manifolds 128 and 144. 
Referring to FIG. 8, in steps 260-278, the "home" position for the mandrel 
cluster and each plate cylinder is set when an index signal is received. 
The index signal may be a once per encoder revolution pulse on a separate 
encoder output, with the encoder having been coupled to its respective 
drive shaft so that the pulse is generated at a predetermined 
circumferential orientation of the component -- for example, for the 
mandrel cluster encoder 113, the index point might be when a particular 
mandrel was at 12 o'clock, for the upper plate wheel encoder 112, the 
index point might be when the leading edge of one of the printing plate 78 
was at 6 o'clock, etc. Alternatively, encoders generating uniform pulses 
may be used and limit switches 186, the output from which is connected to 
the controller 180, installed on each component so that a switch is 
tripped at a predetermined orientation of each component by a "dog" 185, 
as shown in FIG. 2. In either case, the controller 180 would be programed 
to ignore index signals after the first signal for each component so that, 
after initializing, the pulses are continuously accumulated so long as the 
components continue to rotate. 
In order to obtain greater accuracy with respect to the index location, the 
controller 180 may be programed with logic (not shown) that adjusts the 
pulse count at initialization by a predetermined amount -- for example, if 
it was desired to generate the index signal for the upper plate wheel 64 
when the leading edge of one of the printing plates reached precisely the 
6 o'clock position but, because of inaccuracies in positioning, the index 
signal generator, whether a pulse from the encoder or a limit switch, 
produced a signal prematurely, the controller 180 would be programed to 
initially subtract a predetermined number of pulses from the pulse count 
after initialization. This approach also allows the registration to be 
adjusted "on the fly." 
Referring to FIG. 9, in step 200, each of the motors 54, 82, 84 and 40 is 
started and manually brought up to their approximate design operating 
speed by the controller 180. Next, in steps 202 and 204, the controller 
180, which determines the speed of the mandrel cluster motor 54 by 
measuring the frequency of the output pulses from the mandrel cluster 
motor encoder 113, regulates the output signal to the mandrel cluster 
motor 54 until the predetermined optimum operating speed for the mandrel 
cluster motor is attained. In the preferred embodiment, the operating 
speed of the mandrel cluster 12 is approximately 400 RPM. 
In step 208, the pulse count accumulated for each component is sensed, the 
pulse count for the mandrel cluster 12 being identified as P.sub.mc and 
the pulse count each of the remaining eight components -- that is, the two 
plate wheels and the six mandrels -- being identified as P.sub.1 . . . 
P.sub.8. 
In the preferred embodiment, the controller 180 slaves the mandrel motors 
40 and the plate wheel motors 82 and 84 to the rotation of the mandrel 
cluster motor 54. If the components are properly synchronized and 
maintained in the correct registration, a predetermined relationship -- 
that is, a certain ratio X -- will be maintained between the cumulative 
pulse count from the mandrel cluster motor encoder 113 and the cumulative 
pulse counts from the encoders 176, 112 and 114 associated with the 
mandrel and plate wheel motors 40, 82 and 84, respectively. Thus, in steps 
210 to 224, after each pulse count, the controller 180 compares the ratio 
of the pulse counts from each mandrel and plate wheel motor encoder with 
respect to the pulse count from the mandrel cluster motor encoder 113 to 
the predetermined ratios X.sub.1 . . . X.sub.8 that will result in 
synchronization and registration. If the ratio associated with any of the 
slaved motors deviates from the predetermined quantity, the controller 180 
generates a signal which increases or decreases the speed of that motor 
accordingly until the correct ratio of the cumulative pulse counts is 
obtained. Alternatively, once the components have been indexed so that 
proper registration is obtained, the controller 180 can be programed with 
logic to control each motor to a predetermined speed which is known to 
maintain registration. Such open loop control is possible because of the 
inherent accuracy of the controller and encoders. 
As previously discussed, the controller 180 is also programed with logic to 
actuate the valve manifold 144 associated with each mandrel 50 so that 
pressure is supplied to the pistons 140 to retract or extend the mandrels 
during the appropriate position intervals. Logic for performing this 
function is shown in FIG. 10. In step 280, the pulses from the encoder 113 
are accumulated during each revolution of the mandrel cluster 12. In steps 
282 and 284, the controller compares the pulse count to predetermined 
quantities and generates signals to actuate the various valve manifolds 
144 accordingly in steps 286 and 288. 
As previously discussed, the controller 180 is also programed with logic to 
actuate the valve manifold 144 associated with each mandrel 50 so that the 
pressure of the air supplied to the pistons 140 alternates from high to 
low pressure as the mandrels rotates into position to contact the upper 
and lower plate wheels, respectively. Logic for performing this function 
is shown in FIG. 11. In step 228, the pulses from the encoder 113 are 
accumulated during each revolution of the mandrel cluster 12. In steps 230 
to 244, the controller compares the pulse count to predetermined 
quantities that are indicative of the circumferential position of each 
mandrel and generates signals to actuate the various valve manifolds 144 
accordingly -- for example, a pulse count of Y.sub.1 indicates that 
mandrel no. 1 will shortly contact one of the printing plates 78 on the 
upper print wheel 64, hence, when such a pulse count is reached, the 
controller 180 generates a signal to actuate the valve manifold 144 
associated with mandrel no. 1 so that low pressure air 148 is supplied to 
the piston 140 of mandrel no. 1. Similar logic allows vacuum or pressure 
to be applied to each mandrel as cans are loaded or unloaded, 
respectively. 
The process by which the can bodies 94 is decorated is called "dry trap 
printing" whereby the can surface is printed with a first quick dry ink, 
followed by the application of a second ink to the dried first ink 
surface. This "dry trap" process allows overprinting of transparent inks 
thereby forming a third color. This is not achievable with the blanket 
applied paste inks heretofore used in can decorating. Thus, in FIG. 11 
there is illustrated a portion of a can body 94 to which a first ink 
stripe 106 is applied followed by the application of a second ink stripe 
108 so that the two ink stripes overlap in portion 110. The ink in the 
overlapping portion 110 will be overprint to blend the colors of the two 
inks of the stripes 106 and 108. 
While only two plate cylinders 64 and 66 have been illustrated, it is to be 
understood that additional plate cylinders may be utilized. This would 
require that the axis of the plate cylinders be relocated. 
Although only a preferred embodiment of the decorator has been specifically 
illustrated and described herein, it is to be understood that the 
invention may embody other specific forms without departing from the 
spirit and scope of the invention as defined by the appended claims. 
LIST OF REFERENCE NUMERALS 
10 Decorator 
12 Mandrel cluster 
14 Mandrel support stand 
16 Mandrel support stand base plate 
18 Mandrel support stand uprights 
20 Base plate for upright 
22, 24 Transverse members 
26 Mandrel cluster shaft 
28 Mandrel cluster sleeve 
30 Mandrel cluster hub 
32 Mandrel spoke 
34 Mandrel mounting plate 
36 Mandrel motor mounting plate 
38 Mandrel motor ball bushing mount 
40 Mandrel motor 
42 Mounting plate 
44 Mandrel base plate 
46 Mandrel housing 
48 Mandrel shaft 
50 Mandrel 
52 Mandrel drive connection 
53 Mandrel cluster motor 
56 Plate cylinder stand 
58 Plate cylinder upright 
60 Base plate for upright 
62 Plate cylinder stand cross brace 
64, 66 Plate cylinders 
68 Plate cylinders shaft 
70 Plate cylinders shaft sleeve 
72 Plate cylinders shaft hub 
74 Plate cylinders spoke 
76 Plate cylinders rim 
78 Printing plate 
80 Printing plate mount 
82 Upper plate cylinder motor 
84 Lower plate cylinder motor 
86 Inker 
88 Inker tray 
90 Inker roll 
92 Inker doctor blade 
94 Can 
106, 108 Ink stripes 
110 Overlapping portion of ink stripes 
112-114 Encoders 
118 Undisturbed can path 
120 Actual can path during contact 
122 Vacuum source 
124 Hole in mandrel shaft 
126 Mandrel housing plenum 
128 Vacuum manifold 
130-132 Guide rods 
134 Stop 
136 Linear bearing 
138 Piston shaft 
140 Piston 
142 Piston cylinder 
144 Air pressure manifold 
146 High pressure air 
148 Low pressure air 
150, 152 Tubing 
154 Hole in mandrel 
156 Screws 
158 Pressure source 
160, 162 Sprockets 
164 Idler sprocket 
166 Lever 
168 Air cylinder 
170 Open end of can 
172 Closed end of can 
174, 175 Moments 
176 Mandrel motor encoders 
178 Pressure regulator 
180 Electronic controller 
181, 182 Conductors 
183, 184 Tubing 
185 Dog 
186 Switch 
200-284 Logic steps 
##SPC1##