Screen printing apparatus

A multiple screen printing apparatus for multiple simultaneous printing in which the screen printing carrier head and the platen carrier head are indexed and locked together when the printing screens are down so as to provide precise registration. This indexing and locking arrangement resists degradation of the screen's registration during normal field use. Also, the apparatus has a precise microregistration adjustment system that permits adjustment of the printing screen attachment or screen clamping member relative to the screen carrier head by a controlled and guided adjustment movement in a single plane between a clamping plate and base member. This arrangement provides a coplanar locking so that no movement of the registration occurs during the clamping action.

This invention relates to screen printing equipment and especially (1) a 
screen registration assembly and (2) a screen printing apparatus whereby a 
plurality of screens rotate about a common point and may be simultaneously 
placed on a plurality of workpieces for screen printing. 
Screen printing has become a big business and continues to grow with the 
technology being used on T-shirts, caps, sleeves bumper stickers and other 
workpieces where screen printing is appropriate. One type of screen 
printing apparatus is where a multiplicity of screens are rotated about a 
common point to be placed over a plurality of work holders. The screens 
are rotated while in an elevated or raised position and then when they are 
over a workpiece to be printed are lowered onto the work. A number of 
colors are frequently printed on the same workpiece and each color must be 
registered with the others to give a satisfactory product. 
When only one screen is lowered at a time, registration with the workpiece 
is relatively easy. But if a multiplicity of screens are to be lowered at 
the same time, referred to as simultaneous printing or "all screens down" 
printing, registration at one work station may cause misregistration at a 
second work station because of imperfections in the equal spacing between 
the screens. Even if such spacing is set correctly at the factory, the 
machines will lose their initial settings in actual use. 
Also, when a screen is initially mounted into a screen holder onto the 
machine, it must be brought into initial alignment by adjusting the screen 
holder. In the past, this has been done by moving the clamping 
arrangement, which is loosely held, and then when proper registration is 
achieved, tightening the clamping arrangement to prevent any further 
relative movement. However, because of the usual type of movement 
associated with the clamping arrangement, the action of clamping against 
further movement tends to disturb the registration initially achieved. One 
popular form of such a clamping arrangement is a U-shaped member that, as 
a practical matter, clamps along a line rather than over a wide surface. 
The present invention improves the simultaneous printing apparatus so that 
as a practical matter all screen heads can be lowered and be acceptably 
registered for simultaneous printing and thus greatly increase the 
productivity of the machine. Although all heads can be used to print 
simultaneously with this invention, frequently only several heads are so 
used at one time but this is still a significant improvement over the 
normal apparatus. 
A still further improvement made by this invention is the prior adjustment 
of the registration of this screen prior to beginning the printing 
operation. This is accomplished by a better adjustment apparatus. Instead 
of a U-type of screen clamping arrangement, the adjustment mechanism now 
involves a controlled and guided precision movement of the screen clamp 
carrier as a sandwich between two guiding planes which serve to guide the 
adjustment after the adjustment has been correctly made, it is clamped and 
locked into the position by planar surfaces to prevent the distortions and 
movements that have occurred in the past. 
The above developments result in both a greatly improved apparatus for 
simultaneous screen printing and a greatly improved registration system 
for a simple, fast and accurate initial set up for multicolor printing. 
In multicolor printing with proper registration, one color must be 
accurately indexed to the preceding color with the next color being 
accurately indexed to these two colors, etc., to get a proper acceptable 
multicolor product. The apparatus of the new invention has one plane 
containing the screen arms and another plane containing the print station, 
both rotating about a common axis. 
In the past, a common method of indexing an individual print head to an 
individual print station was to have a screen arm with a steel tongue 
protruding from it on the order of 1/4 inch wide by 3 inches long. This 
tongue would be received by a pair of radial ball bearings that would 
index this tongue precisely with respect to its print station so that the 
two rotating planes are locked together. This worked fine for an 
individual station but if multiple screens were to be used simultaneously 
they would have to be positioned so as to be equiangular spaced apart in a 
precise manner. For example, the equiangles are 90.degree. in the case of 
a four station machine. 
While the present tolerances required can be achieved at the factory, 
adjustments and abuse and wear in the field make it difficult to maintain 
this equiangular relationship which is essential before simultaneous and 
highly productive screen printing can take place. For example, if the 
indexing is 1/3 the distance from the axis of rotation and the screen 
printing actually occurs 3 times this distance from the axis, then there 
is a multiplier of any error in the indexing of three times. For example, 
if the indexing is off 0.004 inch (which is slightly more than the width 
of a human hair), then the misregistration would be 0.012 inch which is 
easily seen on a screen printed object. So even a quarter of a degree of a 
360.degree. circle is more than enough to give a misregistration. 
Throughout this specification, a four station machine will primarily be 
described but it is to be understood that the quantity of stations can 
vary usually from two up to six or even higher. Usually, only 2 to 3 
operators are used on an apparatus at the same time although, 
theoretically one operator could be assigned to each station. Even with 
two people printing simultaneously, the productivity doubles over a single 
person operating the apparatus. 
The present invention has departed from the previous practice of indexing. 
There is no registration device on the screen arms themselves or on the 
platens and the steel bars going into roller bearings on each of the 
screen arms have been eliminated. It is believed that much of the wear 
takes place at this location to cause a degradation in the printing 
registration. The indexing and locking assembly of the present invention 
is located to lock the screen carrier head to the platen carrier head. The 
screen carrier head is a rotating member that carries the screen frames 
and is a one-piece member. Likewise, the platen carrier head is a rotating 
member that holds the platen supports or arms on which the platens are 
attached. Since these two carrier heads are one piece metal members, 
usually in the form of relatively flat aluminum plates, the precision 
location of the indexing provided at the factory is not substantially 
disturbed by actual field conditions so that the registration will not 
substantially degrade with use. Any movements of the platens or the 
screens such as by being replaced would not change the registration 
between the carrier heads themselves.

With reference to FIG. 1, there is shown a multiple screen printing 
apparatus 10 having a mounting base 11, a platen carrying assembly 12 and 
a screen carrying assembly 13. 
As seen in FIGS. 1 and 5, the platen carrying assembly 12 is attached to a 
vertical shaft 14 which rotates in a lower bearing 15 and an upper bearing 
16 which are attached to the mounting base. 
As used in this specification, "platen" is meant to be a variety of holders 
for various work which is to be printed. This work may be baseball caps, 
sleeves, T-shirts and other objects. 
The four platens 17 shown in FIG. 1 are those designed for holding 
T-shirts. The platens 17 are attached to the outer end of platen support 
beams or arms 18. The platen support beams are fixedly mounted to platen 
carrier head 19. 
Also mounted on platen carrier head 19 is an indexing and locking plunger 
20, which is better seen in FIG. 5, that consists of a pneumatic motor 21 
driving a plunger 22 having a conical end 23. The plunger 22 is located 
within guide sleeve 24. The pneumatic motor 21 is connected by pneumatic 
conduit 25 which runs from the motor to the vertical shaft 14. An internal 
pneumatic passageway 26 runs down the shaft 14 to a rotary air coupler and 
source of pneumatic pressure (not shown). 
Also shown on FIG. 1 with the screen carrying assembly 13 are four screen 
attachment and registration assemblies 27, each of which is pivotally 
mounted on a screen carrier head 28. With reference to FIG. 5, the screen 
carrier head 28 can be seen as rotary mounted to vertical shaft 14 by 
bearings 29 and thus concentrically and coaxially rotates with platen 
carrying assembly 12 and platen carrier head 19. 
An alternative is to have both platen carrier head 19 and screen carrier 
head 28 rotating independently about an axis such as shaft 14 rather than 
having the platen carrier head 19 fixed with regard to shaft 14. In this 
arrangement, it is essential that concentricity among all the components 
be obtained. When head 19 is fixed to shaft 14 then concentricity between 
heads 28 and 19 is not an absolute essential although such is desirable. 
In all situations, concentricity in equiangular spacing of the indexing 
and locking receiver cones or tongues must exist in screen carrier head 
28. 
Screen carrier head 28 has inserted therein an indexing and locking 
receiver 30 having a conical cavity complimentary to the conical end 23 of 
plunger 22. There is one indexing and locking receiver 30 for each screen 
attachment and registration assembly 27. When the screen carrier head 28 
is rotated relative to platen carrier head 19 to the next work station or 
platen and the screen is lowered to print a workpiece such as a T-shirt, 
the plunger 22 is actuated to the upper position. This causes a final 
centering or indexing of the platen carrier head 19 to the screen carrier 
head 28 and locks the two in fixed angular position so that during the 
printing accurate registration is maintained. 
This is a very important aspect to the invention and is the first time that 
a machine of this type has been able to achieve accurate positioning or 
indexing and locking of the stations so that all screens can print 
simultaneously by locking both the platen carrier head and the screen 
carrier head together by a direct arrangement between the two. Even though 
the indexing and locking is closer to the axis of rotation then normally 
the case, the arrangement permits an accurate positioning at the factory 
of the indexing and locking receivers and indexing and locking plunger 
which will not be disturbed by normal conditions of field use. Each screen 
printing station is indexed and locked with exact equiangular separation 
which in the case of four screens would be 90.degree., six screens would 
be 60.degree. and so forth. 
In addition to the male-female cone locking method shown in FIG. 5, a 
moving carriage mounted on the platen carrier head to engage an index 
tongue located on the screen carrier head as detailed in the next 
paragraph may be used as well as other alternatives so long as an accurate 
positioning or indexing and locking of the two carriers together is 
achieved so that the screens are spaced equiangular to one another. 
An alternative and preferred embodiment of the indexing and locking 
arrangement is shown in FIGS. 9, 10 and 11. The figures show an indexing 
and locking receiver tongue 80 equiangularly spaced around the bottom 
surface of screen carrier head 28. The tongue is shown in FIG. 10 as 
having two parallel vertically extending planes 81 and a rounded entry 82. 
On the opposite platen carrier head 19 is shown the horizontally moving 
indexing and locking plunger arrangement in which a carriage 83 slides on 
parallel guide shafts or rails 84 with nylon bearings in the form of 
bushings 85 located in the carriage 83. On the top surface of the carriage 
is located two guides or bumpers 86. Located in each guide 86 is a metal 
cam roller bearing 87 with hardened surfaces. Such bearings are obtainable 
from many suppliers. 
The guides or bumpers 86 are preferably made of a plastic such as nylon to 
absorb and dampen the impact and sound of the initial impact of the 
rounded entry 82 of tongue 80 when a pneumatic cylinder is actuated to 
move the carriage 83 and guide 86 to the left to cause the indexing and 
locking to take place. One of the guides 86 is fixed in position and the 
other guide 86 is adjusted in relation to the fixed guide and locked in 
position so the space between the roller bearings 87 is the distance 
between parallel planes 81. 
The parallel rails or guide shafts 84 for the carriage 83 parallel the 
radius of the platen carrier head. The movement for indexing and locking 
is outward which is to the left in FIGS. 9 and 10. The return of the 
carriage to the right and unlocked position is buffered by an elastomeric 
buffering surface or pad (not shown) located to the immediate left of rail 
support 88. The guide shaft or rails are carried at their other and outer 
end by support 89. 
The embodiment of FIGS. 9, 10 and 11 is an improvement over the cone 
arrangement since there is no pressure, which can be as much as 60 lbs., 
trying to push apart the two heads 19 and 28 and there is no requirement 
for tight radius tolerances. The equiangular spacing can be tightly 
controlled by the arrangement. 
The roller bearings 87 inside the guides or bumpers 86 is a preferred 
arrangement but an alternate is to have two larger roller bearings 87 with 
the same diameter as the guides 86 which would give an equal size window 
for the insertion of rounded entry 82 of indexing and locking tongue 80. 
The two larger bearings would not have the dampening provided for by 
bumpers 86 which are preferably made of nylon. 
With reference to FIG. 10, the position of the guides or bumpers 86 and 
roller bearings 87 are shown in their unlocked position by solid lines and 
in their actuated and indexed and locked position by the dotted lines. The 
dotted lines are to the left of the solid lines. 
Also shown in FIG. 1 are pneumatic switches 31 which are actuated by switch 
actuators such as cam 32 attached to the underside of the screen 
attachment and registration assembly 27 so that when the screen is lowered 
to the printing position the actuator cam 32 is moved with it to actuate 
pneumatic switch 31. This is best seen in FIGS. 2 and 3. In FIG. 2, the 
screen is shown in the raised position with the cam 32 out of engagement 
or contact with switch 31. In FIG. 1, the screen is in the lowered 
position where cam 32 has been rotated downward and to the right to 
actuate switch 31. As will be seen later, when any of the pneumatic 
switches are actuated by a screen being down, the platen carrier head and 
screen carrier head are locked together so that they cannot move relative 
to one another. 
With reference to FIGS. 2 through 4, there is shown the details of the 
screen attachment and registration assembly 27. The assembly 27 is 
pivotally mounted on the upper surface of the screen carrier head 28 at 
pivots 33 and 34 so that the printing screen can be raised and lowered 
about the pivot axis between pivots 33 and 34. 
At the outboard end of screen attachment and registration assembly 27 is a 
screen attachment member 35 having an outer attachment end in the form of 
a clamp 36 for clamping the edge of printing screen 37 in a well known 
manner. The screen attachment member 35 has an upper planar surface 38 and 
a lower planar surface 39 both of which planes are smooth and lie parallel 
to one another so that the thickness between the two is constant. At the 
inner end of screen attachment member 35 are two uprights 40 and 41 which 
serve as attachment points for turnbuckle adjustment means. 
Circular holes 42 and 43 are provided in the screen attachment member 35 so 
as to accommodate clamping screws 44 and 45. 
The screen attachment member 35 is sandwiched between clamping plate 46 and 
base member 47. Clamping plate 46 is a rectangular plate having a lower 
smooth planar surface 48 and four threaded holes 49 located at each corner 
of the plate. 
Base member 47 is attached near its inboard end to pivots 33 and 34 and at 
its most in board end has vertical risers 50 and 51 as attachment points 
for the turnbuckle adjustment means. 
Base member 47 also has an intermediate riser 52 as a third attachment 
point for the turnbuckle adjustments. 
At the outboard end of base member 47 there are two wings or extensions 53 
and 54 which are the same width as clamping plate 46. The innermost ends 
of the extensions 53 and 54 have a spring receiving pins 55 and 56. 
Coil springs (not shown) are attached at 55 and 56 and lead back to the 
screen carrier head where their other end is fastened. These coil springs 
serve to hold the screen attachment registration assembly 27 in the upward 
position when not printing but when the assemblies are lowered for 
printing the spring passes through the pivot point in an over-center 
action so that the screens are held in their down position while printing. 
Also, located in extensions 53 and 54 are oversized bolt holes through 
which pass four capture bolts 57. These capture bolts are free to slide in 
the holes which are slightly oversized to accommodate them as will be 
explained more fully below. 
Base member 47 also has a smooth planar surface 58 on the upper surface 
thereof over which the screen attachment member 35 is free to slide when 
not clamped down. 
As is seen best in FIGS. 2 through 3, the screen attachment member is 
sandwiched between the clamping plate 46 and the base member 47 so that 
the upper smooth planar surface of base member 47 is in contact with the 
smooth lower planar surface 39 of the screen attachment member 35 and the 
lower smooth planar surface of clamping plate 46 is in contact with the 
upper smooth planar surface of screen attachment member 35. The assembly 
is held together by capture bolts 57 which have their lower end headed and 
their upper end threadedly received into the threaded holes 49 of base 
member 47. Since the capture bolts 57 have their shanks smooth and 
slidable in oversize hole located in the extensions 53 and 54 of the base 
member, the base member is free to slide on the capture bolts for a 
restricted distance determined by the length of the capture bolts above 
the bolt head. 
A clamping arrangement is provided for the assembly by means of clamping 
screws 44 and 45 which are threadedly received into the base member 47 and 
are adapted to be loosened and tightened by two clamping knobs 59. The 
clamping screws 44 and 45 pass through oversized holes in the clamping 
plate 46 so that as the knobs 59 are tightened, they apply pressure to the 
ferrule spacer 60 which applies pressure to the clamping plate 46 to draw 
it closer to base member 47 and clamp screen attachment member 35 
therebetween. The ferrule 60 has an inside hole that is larger than the 
diameter of the clamping screw 44 and 45 but has an outside diameter 
greater than the oversized hole in the clamping plate 46. 
When the knob 59 are loosened and the clamping plate and base member are 
free to separate, they can separate only a small distance as shown in 
FIGS. 3a and 3b. In 3b, they are clamped tightly together holding the 
screen attachment member 35 therebetween so that the three members, i.e., 
base member clamping plate and screen attachment member are locked to one 
another. When the knob is loosened, the plates can separate but only to 
the extent permitted by the head 57 of the capture bolt which prevents any 
separation beyond approximately 0.015 of an inch and preferably only 
approximately 0.007 of an inch. This close spacing permits a controlled 
and guided adjusting movement of the base member relative to the screen 
attachment member which is confined to glide in a plane defined by the 
smooth planar surface of the base member below and the smooth planar 
surface of the clamping plate above. 
The controlled and guided adjustment movement is made by three turnbuckle 
adjusters 61, 62 and 63. The turnbuckle adjusters have knurled adjustment 
cylinders arranged so that adjustment cylinders 61 and 63 are parallel to 
one another and are connected respectively between attachment points 50 
and 40 and between attachment points 51 and 41 so that as they are 
adjusted in and out by turning the knurled cylinder they move screen 
attachment member in and out with respect to the base member. If only one 
adjuster is moved out, then a combined rotary movement and outward 
movement is achieved. If both adjustment cylinders 61 and 63 are turned to 
move the units out simultaneously, it moves only outward with no rotation 
around any adjustment attachment point. 
Adjustment cylinder or turnbuckle 62 is attached at one end to attachment 
point 40 and at the other end attachment point 52 and serves to move the 
screen attachment member primarily in a transverse direction relative to 
the base member although there may be some minor movement in other 
directions depending on the positions of the other adjustment cylinders. 
By using the three adjustment cylinders, the screen attachment member is 
rapidly adjusted to bring accurate registration to the printing screen. 
Since the movement is controlled and guided in a single plane by the 
parallel plane surfaces of the base member and clamping plate, when the 
clamping knobs 59 are tightened there is no distortion or movement away 
from the desired registration point. This is unlike previous devices that 
did not have the captured controlled and guided coplanar clamping 
arrangement as just described. One of the most popular previous devices 
utilized a U clamp where the metal is sprung into tight contact. This 
springing action resulted largely in merely line clamping which permits 
distortion away from the adjustment position during the clamping process. 
With reference to FIGS. 2 and 3, there is seen actuator cam 32 is connected 
to the base member 47 and moves therewith. It extends through a slot 64 in 
the screen carrier head 28 so as to be able to contact and actuate the 
pneumatic switch 31. Slots 64 better seen in FIG. 6 which shows the screen 
carrier head without the attachments. In addition to the four slots 64, 
the screen carrier head 28 has mounting holes 65 for the indexing and 
locking receivers 30. 
With reference to FIG. 7, there is shown the platen carrier head 19 without 
any of the attachments other than one platen support beam 18. The relative 
location of the pneumatic switch 31 and actuator cam 32 are also shown. 
Mounting holes 66 for the pneumatic motor 21 and indexing and locking 
plunger 20 precisely located on platen carrier head 19 so that when 
assembled the indexing and locking plunger is precisely located with 
respect to the indexing and locking receivers 30. It is to be noted that 
there is one indexing and locking receiver 30 for each of the screen 
attachment and registration assemblies 27 but there is preferably only one 
indexing and locking plunger 20. On some occasions a second plunger may 
also be used. It is to be noted that the plunger and the receivers are 
located near the periphery of their respective carrier heads. 
With reference to FIG. 8, there is shown a pneumatic circuit for the 
apparatus for which normally an air source is available in most shops. 
This is normally called "shop air" and is usually about 60 p.s.i.g. There 
is shown the four pneumatic switches 31 which are normally closed three 
way poppet valve switches. 
An operator frequently will not notice when he or she pulls the screen down 
that it may be somewhat misaligned but if the screen is anywhere near the 
correct position, the pneumatic switch will be operated and the piston 
cone or wedge or metal cam roller bearings of the indexing and locking 
plunger or carriage as it enters into a mating or complimentary receiver 
30 or 80 will rotate the two carrier heads into their final and correctly 
indexed correct position. 
While the indexing and locking plunger arrangement is preferably located on 
the bottom or platen carrier head, and the receivers located on the screen 
carrier or upper head, they could be reversed. What is important is that 
when the indexing takes place the two rotating carrier heads 19 and 28 are 
locked together precisely in the angularly correct positions when the 
screen is lowered it is in proper registration. 
The four pneumatic switches 31 are connected to a source of supply air and 
when actuated, serve to actuate an assigned pilot valve associated with 
the three way valve having four pilot valves 67 which is also connected 
with the source of supply pressure. The three way valve 67 is connected 
with the four way valve with associated pilot valve 68 which supplies air 
to the double acting pneumatic cylinder or motor 21 to cause it to move 
upward to the indexing and locking position and downward back to the 
unlocked position. The pneumatic motor could also have a normally biased 
downward piston with an actuated raised piston position. 
Although a pneumatic system is shown as most desirable, an electric or 
electropneumatic system could also be utilized. 
In operation, if any of the actuating pneumatic switches 31 are actuated 
because one of the printing screens is in the down position, its 
associated pilot valve causes the three way valve 67 to take a position to 
actuate the pilot valve associated with four way valve 68 to move the 
pneumatic motor or piston 21 into the indexing and locked position. If all 
of the screens are raised, all of the pneumatic switches 31 would be 
closed and the three way valve 67 would return to its normal position and 
four way valve 68 would return to its normal position to cause the 
pneumatic motor or cylinder 21 to drive the plunger to the downward and 
unlocked position. 
While the invention has been described with reference to a preferred 
embodiment it will be understood by those skilled in the art that various 
changes may be made and equivalents may be substituted for elements 
thereof without department from the scope of the invention. In addition, 
many modifications may be made to adapt a particular situation, material 
or component to the teachings of the invention without departing from the 
essential scope thereof. Therefore, it is intended that the invention not 
be limited to the particular embodiment disclosed but that the invention 
will include all embodiments falling within the scope of the appended 
claims.