US 3889595 A
This disclosure is directed to a method and apparatus for screen printing in which a continuous sheet or web of material to be printed is advanced in the direction of feed relative to a rotating cylindrical printing screen to effect a continuous screen print in which both the rotation of the screen and the direction of feed of the material is reversed a predetermined amount each time the screen printing operation is interrupted for any reason. Upon commencing a successive printing operation, the method and apparatus operate to lower the printing screen as it rotates in a printing direction onto the advancing material so that the rotating screen effects registration with the advancing trailing edge portion of a previously printed portion of web to effect an overprint of the previously printed surface resulting in the avoidance of any smearing and/or waste between successive screen prints. The method and apparatus further contemplate a feed and unwind system operatively associated to facilitate splicing of successive rolls and/or effecting the removal of successive rolls of printed material without interruption of the printing operation.
Description (OCR text may contain errors)
United States Patent [1 1 Jaffa 1 1 CONTINUOUS ROTARY SCREEN PRINTING METHOD AND APPARATUS David Jaffa, Fairlawn, NJ.
 Assignee: Precision Screen Machines Inc.,
 Filed: July 3, 1972  Appl. No.: 268,522
 U.S. C1. 101/116; 101/118; 101/126; 101/129; 101/181; 242/584  Int. Cl..... B411 13/16; B41f 15/10; B41f 15/24  Field of Search l01/116,182,115,181, 101/126,120,129,119, 228,178, 248, 219,
[ 1 June 17, 1975 Primary Examiner-Edgar S. Burr Assistant Examiner-R. E. Suter  ABSTRACT This disclosure is directed to a method and apparatus for screen printing in which a continuous sheet or web of material to be printed is advanced in the direction of feed relative to a rotating cylindrical printing screen to effect a continuous screen print in which both the rotation of the screen and the direction of feed of the material is reversed a predetermined amount each time the screen printing operation is interrupted for any reason. Upon commencing a successive printing operation, the method and apparatus operate to lower the printing screen as it rotates in a printing direction onto the advancing material so that the rotating screen effects registration with the advancing trailing edge portion of a previously printed portion of web to effect an overprint of the previously printed surface resulting in the avoidance of any smearing and/or waste between successive screen prints. The method and apparatus further contemplate a feed and unwind system operatively associated to facilitate splicing of successive rolls and/0r effecting the removal of successive rolls of printed material without interruption of the printing operation.
11 Claims, 22 Drawing Figures PATENTEDJUN 17 1975 SHEET PATENTEDJUN 1 7 I975 maslses SHEET PATENTEDJUN 17 I975 SHEET 4 F/GZZ PATENTEUJUN 1 7 I975 SHEET Illlllfllllllilllll PATENTEDJUN 17 I975 SHEET PATENTEDJUN 17 ms SHEET am a CONTINUOUS ROTARY SCREEN PRINTING METHOD AND APPARATUS PROBLEM AND PRIOR ART Heretofore, considerable difficulty has been encountered in effecting proper registration between successive printing operations in the'event the printing operation was interrupted for'any reason, e.g., when changingrolls either at the feed end or take-off end of the operation. This was due to the extreme difficulty encountered in effecting proper registration of the rotary printing screen and'the end of the preceding print, whenever the operation was restarted. With the known method and apparatus. invariably a smear or blurr would result between successive printed portions of the web each time the printing operation was stopped and then recommenced. Thus each time the known rotary screen printers were stopped for any reason, some portion of the web ofprinted material was lost due to waste created by such blurring or smearing.
Another difficulty noted with existing rotary screen printing'methods andapparatus isthat the point at which the rotary printing screen means contact with the material being printed is backed up by a generally hard surface. For this reason the printing occurs at a line contact which limits the arriountof ink or dye deposited a nd/or penetration thereof into the material being printed,
Still another difficulty encountered in rotary screen printing is the need for securingthe material to the printing bed as itis being printed so as to insure positive registration and to m inimize shrinkage and particularly when theprinted sheet is made of plastic, e.g., vinyl websor sheets. I
Also with known printing methods and apparatus, it was heretofore necessary to stop the printing operation each time a new supply of material was required to be fed to the machine and/or removed therefrom. Because of these stoppages the problem of registration and waste between successive prints is further aggravated.
' OBJECTS An object of this invention is to. provide a method and apparatus for rotary screen printing in which registration between successive printedportions of a continuous strip or web is assured without the effect of smearing or blurring. i V v Another object os this invention is to provide a method and apparatus for rotary screen printing continuous webs and sheets in which the deposit of ink and/or penetration thereof on the material being printed is enhanced.
Another object is to provide a method and apparatus for rotary screen printing in which the material and the screen is reversed in relative predetermined relationship in the event the printing operation is interrupted for any reason.
Another object of this invention is to provide a method and apparatus for rotary'screen printing a continuous web or sheet in which the material is positively held in place throughout the printing cycle of operation to insure positive registration and to eliminate shrink age during the printing thereof.
Another object is to provide amethod and apparatus of rotary screen printing in which a new supply of material and/or a supply of printed material may be readily spliced or unspliced without effecting any interruption of the printing operation.
Another object is to provide a method and apparatus for rotary screen printing a continuous web or sheet in which the printing bed and/or the printed portion of the material is cooled so as to enhance the overall printing operation.
BRIEF SUMMARY OF THE INVENTION The foregoing objects and other features and advantages of this invention are attained by a rotary screen printing method in which a continuous strip or web or material to be printed is fed to and supported on an endless printing bed or blanket whereby the material is firmly adhered thereto, e.g., in the case ofa non-porous material by a negative pressure acting thereon. A rotary printing screen having a stencilled portion and associated squeegee is lowered onto the material whereby the ink is forced through the stencilled portion of the screen by relative movement between the screen and squeegee. The printing is effected by rotation of the printing screen relative to the moving printing bed and material which are connected in synchronous driving relationship.
Upon the termination of the printing operation for any reason the squeegee is first lifted out of contact with the screen slightly in advance of the printing bed and material coming to a full stop. The screen is then lifted away from the material being printed resulting in a minimum of any ink or dye being forced through the screen to leave any demarcation mark. Upon the printing bed coming to a complete stop, both the printing bed and material supported thereon together with the rotation of the printing screen are reversed a corresponding amount in synchronous timed relationship, a predetermined amount.
Upon starting up of the printing operation, the screen is lowered onto the material to engage the trailing edge portion of the previously printed section. In doing so the rotation of the screen and the linear movement of the printing bed or blanket and material thereon being synchronized for movement in the printing direction effects an overprint between successive prints and thereby results in a positive registration therebetween.
To enhance color penetration and/or the deposit of color on the material, a surface area contact is provided between the printing portion of the screen and the material and its printing bed. This is attained by allowing the material to circumscribe a circumferential surface portion or area ofthe printing screen during a printing operation.
To minimize any interruption of a printing operation the changing of the supply of material and/or the removal of a supply of printed material is effected by splicing and/or unsplicing'of the sheet as the printing opertion is being conducted. This is attained by providing an accumulation of material at the beginning and end of theprinting operation which enables the printing operation to continue as the changeover in supply is effected.
t The apparatus by which the continuous screen printing method may be automatically performed comprises a machine frame having an endless printing bed or blanket thereon upon which the material to be printed is supported and advanced through the printing cycle. The printing bed is perforated or porous and overlies a vacuum table which is subjected to a residual negative pressure during a printing operation to firmly adhere thereto the material being printed;
One or more rotary printing screens and associated squeegees are supported along spaced intervals on the machine from above the printing bed. Each of the rotary screens and associated squeegees is mounted for relative movement so as to be lowered and raised between a printing and non-printing position.
A reversible variable speed drive means is operatively connected to the printing blanket and the respective printing screen to effect thesynchronous drive thereof; A programming means is operatively connected to the drive means for sequencing the operating components and the reversibility of the drive means so that upon the termination of a printing operation the travel of-the printing blanket and the rotation of the screen is gradually reduced and then reversed a predetermined amount. Upon restarting the printing operation-the printing screen can thus be lowered onto the trailing edge of the preceding printed portion of the material to cause an overprint in registration with the previously printed portion.
Between printing screens there is disposed suitable heaters for effecting a drying of the inks or dyes between screen prints. The heaters are pivotally mounted to pivot to an inoperative position when the machine is stopped to eliminate any overheating during machine stoppage. Between the heater and the next succeeding printing screen there: is disposed a means to cool the portion of the web-printed by the preceding rotary printing screen.
To provide surface contact ,between the printing screen and the materialbeing printed to increase the amount of ink deposited or the amount of penetration, a means is provided to permit the material being printed to conform to a circumferential surface portion or area of the printing screen during a printing operation. The arrangement is such that the amount of available surface contact provided beteween the printing screen and the web can be varied within predetermined limits.
The apparatus further'includes a web'feed and takeoff system. operatively associated with the printing portion of the apparatus to enable successive rolls of web material to be spliced and unspliced without interruption in the printing operation. Each of the respective web feed and take-off systems includes an accumulator for accommodating a predetermined amount of material so as to enable aprinting operation to continue for a predetermined amount of time sufficient to make the necessary splice between successive rolls.
FEATURES A feature of this invention resides in the provision of a method and apparatus of continuously printing a continuous sheet of web material in which accurate registration is effected between successive prints upon an interrupted printing operation by effectingareversal of the printing bed andassociated rotary screen a corresponding predetermined amount.
Another feature residies in the provision of a screen printing method and apparatus in which registration of successive printing portions (upon interruption is' attained by effecting an overprint between successive printed portions of the continuous.web.-
Another feature resides in a method and apparatus 'of screen printing wherein the material being printed circumscribes a circumferential surface portion of a rotary printing screen during a screen printing operation.
Another feature resides in the provision of a residual vacuum means for maintaining the continuous web of material to the printing bed throughout the printing op eration.
.Another feature vresidesin the provision of a drive means for the printing bed or blanket and associated rotary printing screen which effects a slowing down of the respective movement thereof in the direction of feed as the printing operation is stopped and thereafter effecting a reversal in the movement of the printing bed and rotary screen a corresponding amount.
Another feature resides in the cooling of the printed material before passing under a rotary screen.
Another feature resides in the provision of a screen printing method andapparatus having a feed and takeoff system which permits uninterrupted printing during changeover between material supplies.
Another feature resides in the provision of a continuous. rotary screen printing machine in which the synchronization of the printing bed or blanket and the associated rotary screen is effected by two variable speed drives operatively associated with a programmer motor means.
Another feature of this invention resides in the provision whereby the rotary printing screens can be readily raised and'lowered between a printing and non-printing position without requiring any disengagement of their driving connections.
Another feature of this invention resides in the provision of utilizing a porous printing blanket.
Another feature of this invention resides in the provision of utilizing a foraminous covering over the surface of the printing blanket to create a soft printing surface which provides for a uniform distribution of the negative pressure forces being applied thereto.
Other features and advantages will become more readily apparent when considered in view of the drawings and specification in which:
' FIG. 1 is a sectional view of the left hand portion of a screen printing machine embodying the invention.
FIG. 2 is a sectional view of the right hand portion of the apparatus of FIG.'1.
FIG. 3 is an enlarged'detailed view of the vacuum pump to control the residual negative pressure in the table portion of the apparatus.
FIG. 4 is an enlarged detailed sectional view illustrating the contact area of the screen relative to the matei l FIG. -5 is an enlarged detail of the programming means.
FIG. 6 is a fragmentary end view of the rotary screen.
FIG. 7 is a side view of FIG. 6 illustrating the mounting for various diameter screen heads.
FIG. 8 is a perspective view of the lower head or base assembly of the rotary printing head.
FIG. 9 is a detailed perspective view of the upper head assembly.
. FIG. 10 is a detailed perspective view of a portion of the printing head assembly.
the head assembly. 2
FIG. is a bottom view of FIG.'14.
FIG. 16 is an end view of FIG. 14.
FIG. 17 is a side view of the upper rear portion of the head assembly.'
FIG. 18 is a bottom view of FIG. 17.
FIG. 19 is an end view of FIG. 17.
FIG. 20 is a side view of the in-feed accumulator.
FIG. 21 is a side view'of the take-off accumulator.
FIG. 22 is a sectional view ofa modified printing blanket construction.
DETAILED SPECIFICATION This invention is directed to an improved method of continuously screen printing an'uninterrupted sheet or web of material. The material to be printed is taken from a roll supply and fed to and supported on a movable printing bed or blanket. The material is held fast to the printing blanket in a manner so asto as sure positive registration and to avoid shrinkage. If the sheet or web to be printed is a porous or fabric material, the sheet is adhesively secured to the movable printing bed or blanket. Non-porous material, such as vinyl plastic sheets, are secured to the movable printing bed or blanket by subjecting the sheet to a residual'negative pressure. This is attained by providing the printing blanket with a series of small perforations or holes and passing the blanket over a perforated table top which is subjected to a negative pressure;
The printing blanket and material supplied thereon is then passed under one or more rotary printing screens which are adapted to be moved between a raised nonprinting position and a lowered printing position. In the printing position the rotary screen printing screen is rotated in contact with and in synchronization with the linear movement of the material relative thereto to ef feet the printing of the material.
the material is heated to enhance drying of the'inks or dyes; and thereafter passed in printing relationship'with a next succeeding'rotary screen. In'the printing of vinyl plastic the heated or dryed portion of the printed fabric is thereafter cooled by blowing cooling airthereat immediately prior to advancing the printed' sheet through the succeedingprinting operation, e.g'. during a multiple color printing'op'eration. Sufficient cooling air is applied to the heated or dryed portion of the printed sheet to cool the material to a temperature below IZO F. To
reduce any buildup of heat in the printing blanket, it too may be subjectedto a cooling by directing cooling air thereto at a point beyond the last of the printing screens. I
To avoid interrupting the printing operation, the material from the successive roll" supplies is spliced together so that a continuous uninterrupted sheetis printed. This is attained by accumulating a supply of the material to be printed to provide the-required.
amount of material which'can bep'rintedduring the time necessary to effect a splicebetween the end'of the material from one roll supply and the lead end of a'suc printed area of the material. In this. mannerany smear -ceeding supply roll. Also the removal of a supply of printed material may be effected without interrupting theprinting operation by providing for an accumulation of printed material to occur upon completion of the printing operation for a period of time necessary to effect the removal of the printed supply.
In the event the printing operation is to be stopped for any reason the squeegees associated with the, re-
spective screens are first lifted out of contact with the screen before the movement of the material in the direction of feed has come to a complete stop. The screen is then lifted off contact from the material whereby a minimum of color is forced through the screen to create any mark. With the screen off the material, the rotation of the screen is reversed and the printed. material is backed up a corresponding amount.
Upon commencing the printing operation again the printing screen and associated squeegee is lowered onto the printing surfaceso as to make contact with the trailing edge of the preceding printed portion of the sheet. In doing sol-the screen or screens are again rotated in the direction of printing as the materialis also being advanced from its backed up position in synchronization with *the' rotation of the screen and. with the screen being lowered into printing position to effect an overprint with the trailing edge of the preceding or blurring betweensuccessive printing operations is avoided as the screen and material are in register. To
avoid any overheating of the material in the interrupted printing operation the heaters are moved to a position to deflect the heat away from thematerial.
The foregoing methodmay be automatically performed by a screen printing apparatus 25 disclosed in the drawings. Referring to FIGS. 1 and 2, the screen printing apparatus 25 comprises a. screen printing portion 26, an infeed accumulator portion 27 and a takeup accumulator portion 28. The printing portion 26 comprises of a suitable frame structure 29 formed by a plurality of spaced upright leg portions 30 interconnected by longitudinally extending, and transversely extending frame members 31 and 32 respectively to define a substantially rectangularly shaped frame, assem- 'Journalled adjacent the respective end portions of the frame assembly29 are a pair of end rollers 33, 34
over which an endless belt or printing blanket 35 is threaded; The arrangement is such that the upper flight M to'be printedi v Disposed immediately subjacent the upper flight 35A of the printing bed or blanket 35 is atable top 36 which is fixed'to and supported on the frame structure 29. The table top36, as seen in FIG. 4 comprises a hollow structure to define therein a negative pressure, chamber 38 whichis substantially coextensive the length of the table. The upper surface 36Aof the table top 36 is provided with a plurality of holes or apertures 37 extending therethrough so as to be disposed in communication with the negative pressure chamber 38.
The printing blanket or bed- 35 is also-provided with a series of perforations .35B throughout'the surface area thereof so that during the operationof, the machine the upper surface of the blanket or bed 35 is brought under the influence of the negative pressure applied to the negative pressure chamber 38.
In lieu of a perforated printing blanket A, a porous or foraminous printing blanket may be used. The porous printing blanket has the advantage in that the printed material will not show the perforation outlines which may occur when a perforated blanket is utilized. Also a porous type blanket functions to more uniformly disperse the negative pressure being drawn thereon. Reference to FIG. 22 there is shown therein a modified printing blanket construction in which foraminous material, e.g., polyurethane, having open cellular structure 35C is bonded to the upper surface of the perforated printing blanket 35A. The modified blanket B of FIG. 22 supports the material M to be printed and provides a soft surface therefor through which the negative pressure can be readily utilized to hold a non-porous material M, e.g., a vinyl sheet or web to the upper surface of the foraminous material 35C.
The negative pressure chamber 38 of the table top 36 is operatively connected through suitable conduits 40 to a series of, vacuum pumps 41 which, when actuated, will subject the pressure chamber 38 to a negative pressure or vacuum. The respective vacuum pumps 41 are supported on aframe platform below the table at spaced intervals along the length of the frame. In this manner the respective sections of the table top 36 are serviced by their own vacuum pump 41.
Each of the vacuum blowers or pumps 41 is provided with means whereby the amount of residual vacuum or negative pressure imposed in the associated vacuum chamber may be controlled or varied. Referring to FIG. 3, the means for controlling the amount of residual vacuum or negative pressure imposed on the respective sections of the table 36 includes valve plate 42 which is pivotally mounted about a pivot 43 adjacent to the negative pressure outlet'44 of the vacuum pump 41. The valve plate 42 is provided with an opening or collar 42A to which a flexible conduit 40 is connected. The other end of the conduit 40 connects with the vacuum chamber 38. Connected to the free end of the valve plate is a linkage 45 which is threadably connected to a threaded adjusting shaft 46, and a handle or turn knob 47 is connected to the free end of the adjusting shaft 46. The arrangement is such that by effecting rotation of the control handle 47, in one direction or the other, the opening 42A of the valve plate is moved into and out of communication with the vacuum outlet opening 44 of the vacuum pump accordingly. Thus the intersecting cross-sectional areas of the conduit connection 42A with the negative pressure outlet 44 of the valve determines the amount of negative pressure which is being drawn on the associated section of the vaccum table 36. As seen in FIG. 3, an interconnecting link 48 interconnects the adjacent valve plates 42 of the respective vacuum pumps, so that the adjustment of each valve plate 42 may be effected simultaneously by the turning of the control handle 47.
Thus the degree or amount of negative pressure being drawn along the length of the vacuum table can be readily controlled by a single adjustment of the control handle 47.
Mounted on the frame 29 to extend transversely thereof are one or more printing heads 50. The respective printing heads are spaced at predetermined intervals along the length of the frame structure 29. It will be understood that the number of printing heads may be varied depending upon the colors and/or type of designs being printed.
Each printing head 50 is similarly constructed and comprises a lower head or base assembly 51 and an upper head assembly 52. The lower head assembly 51 comprises a pair of base castings 53, each being oppo- 5 sitely disposed and supported on the opposed upper frame members 31A. Rotatably journalled between suitable trunnion supports 54 on one of the base castings only is a driving worm wheel 55. 7
As best seen in FIGS. 11, and 12, the worm wheel 55 is operatively associated with a harmonic phase control unit 55A which permits for a full 360 index adjustment of a cylindrical or rotary printing screen as will be hereinafter described. The output shaft 56 of the harmonic phase control 55A has connected thereto a driving gear 67. A similar driving gear 57 is journalled to the opposed base casting. Pivotally connected about the opposed lower base castings 51 at 51A is the upper head assembly 52. The upper head assem ly includes opposed upper head castings 58, 58 which are pivoted to the respective lower base. castings 53, 53. Extending transversely between the respective upper head castings 5859 are a pair of interconnecting support rods 60. Connected between the support rods 60 area pair of screen support yokes 6161 arranged for supporting therebetween a cylindrical stencilled printing screen As best seen in FIG. 6, the printing screen 62 comprises a cylindrical sleeve portion which is stencilled to define a given design to beprinted. An end collar 63 is connected to each end of the cylindrical. screen 62, with a gear 64 connected to the end collar for effecting the drive of the screen as will be hereinafter set forth. A screen holder 63A rotatably supports the respective endcollars 63 on the screen yoke 61. As bestseenin FIG. 10, the screen holder 63A is provided with pin means 633 which are arranged to be received in appropriate retaining apertures 61A formed in the yoke 61.
The screen gears 64, when supported between yokes 6l61, are disposed so as to be in meshing arrangement with an idler gear 67 rotatably journalled to the respective upper head castings 58, 59. The idler gears 67 are in turn arranged to mesh with the screen driving gear 57. As will be hereinafter described the idler. gears 45 67 are arranged to roll about theperiphery of the driving gears 57 in meshing relationship therewith so that the upper head assembly, in moving the printing screen between a lowered printing position and a raised inoperative printing position moves without causing any disengagement of the gears of the drive train which includes gears 57, 67 and 64. Thus, the screen 62, as will be hereinafter described is always maintained in gear. or in synchronization with its driving means.
Referring to FIG. 7, it will be noted that screens62, 62' of varying size and/or diameters may be suitably supported between screen yokes 6161. As seen in FIG. 7, there is shown in dotted or phantom line, a showing of how a smaller screen 62' may be substituted for the larger screen 62 illustrated by the solid line showing. In either event the driven screen gears 64, 64' of the respective screens 62, 62. are arranged to mesh with the intermediate idler gears 67. The arrangement is such that varying size screens 62, 62 can be readily interchanged, depending upon the shape or repeat of agiven design. 1 v
Operatively associated with each printing head 50 or screen 62-is a squeegee assembly 70. Referring to FIG.
14, the squeegee assembly 70 includes a pair of pivoting arms 71, 72, each of which is pivoted at one end about pivot 71A, 72A to its respective upper head casting 58, 59. The other end of the respective pivoting arms 71, 72 is provided with a limit stop 73 in the form of a thread adjusting screw; which can be readily adjusted to limit the downward movement of the screen and associated squeegee, as will be hereinafter described.
Mounted on each arm 71, 72 intermediate the ends thereof, and arranged to extend upwardly through an opening 58A. 59A formed in the respective upper head castings 58, 59 isa squeegee holder support 74. A squeegee holder 75 and associated squeegee blade 76 is supported between the support holders 7474. As seen in FIG. 7, the squeegee blade 76 extends longitudinally through the cylindrical screen and is arranged to engage the inner circumferential portion of the screen to force the color therethrough during a screen printing operation.
Means are provided for effecting the movement of the respective screens 62 and their associated squeegee blades 76 between a raised inoperative or non-printing position and a lowered or operative, printing position. The operation of the screen 62 and associated squeegee 76 is such that when the machine or screen printing operation is stopped for any reason, the squeegee blade 76 is first lifted up or out of contact with the screen. The screen 62 is then lifted away or off the material M being printed. Upon restarting the printing operation the screen 62 is first lowered into printing position and thereafter the squeegee blade 76 engages the screen to commence the printing. Thus there is provided a limited loss of motion between the squeegee and its associated screen.
This operation or movement of the screen 62 and squeegee blade 76 between raised and lowered positions is attained by means of a piston and cylinder assembly 77. The piston rod 78 of the assembly 77 is connected to an operating rack 79 which is in meshing relationship with an eccentric or gear sector 80. A crank arm 81 is eccentrically interconnected between gear sector 80 and the pivoting arm 71 which supports the squeegee holder support 74 and associated squeegee holder 75 and squeegee holder 76.
In operation it will be noted that whenever the piston and cylinder assembly 77 is actuated the displacement of the rack upon extension of the piston rod 78 will effect rotation of the gear sector 80 to effect a displacement of the crank arm 81. As gear sector 80 is rotated clockwise as viewed in FIG. 14, the crank 81 will effect upward displacement of the pivot arm 71 and its associated squeegee holder 74 and blade 76. Slightly before the arm 81 approaches its high point, the stop 82 engages abutment 83 of the upper head casting 58, 59 whenever continued upward displacement of the crank arm 81 and arm 65 will effect a lifting of the upper printing head assembly 58, 59 and screen supported thereon off the material M.
Upon lowering of the upper printing head assembly 58, 59, a reverse movement is effected. That is, as the rack 79 is'moved to the right as viewed in FIG. 14, the crank arm 81 is moved to its lowered position whereupon the printing head 58, 59 is lowered to effect contact between the screen and the material, whereupon continued downward movement of the crank arm 81 and connected pivoting arm 71 to its low point, as
determined by stop 73, brings the squeegee blade 76 into Contact with the screen 62.
As will be hereinafter described the control of actuation of the piston and cylinder assembly 77 for timing the raising and lowering of the screen 62 and associated squeegee 76 between a printing and non-printing position is effected by the actuation of a suitable micro switch which is wired into the control circuit of the machine. It will be understood that the piston and cylinder assembly 77 controlling the actuation of the screen and associated squeegee may be either hydraulically or pneumatically operated with the micro switch controlling a solenoid valve which controls the flow of activating fluid to and from the cylinder of the assembly 77. The drive means 85' for effecting the drive of the printing bed or blanket 35 during a printing operation, in timed or synchronous relationship to the rotation of the respective printing head screen 62, comprises a main reversible motor 85 which is suitably mounted on the machine frame. The output shaft of the main motor 85 is coupled to a variable speed transmission unit or harmonic phase control unit 86 of a known construction. The output shaft 86A of the variable speed transmission unit 86 has a sprocket 87 connected thereto which is connected in driving relationship by a flexible chain drive 88 to a slip clutch 89, which couples the drive shaft 90 of the printing blanket 35 to the drive of the screen 62. i 1
The printing blanket drive shaft 90 extending to one side of the clutch 89 has. connected to the end thereof beveled gear 91 which is disposed in meshing relationship with the driven gear 92 of the end roller 33. On the screen drive side of the slip clutch 89 there is operatively connected thereto a second variable speed transmission unit 93. The output side of the transmission unit 93 is connected or coupled to a common drive shaft 94 for driving the respective printing head screens 62. As shown, a plurality ofworm sectors 95 are spaced along the common drive shaft 94, each worm sector 95 being disposed into meshing relationship with a driving worm wheel 55 of the respective printing head screens 62.
Operatively associated with the variable speed control unit 86 of the main motor 85 is a programming means 96 for sequencing the operating cycle of the machine. The programming means 96 comprises a reversible motor 97, the output shaft of which is connected to a suitable gear reduction unit 98. The output shaft of the gear reducer unit 98 is connected through a slip clutch 101 in driving relationship to shaft 99 which is coupled to the input of the variable speed transmission unit 86. The drive shaft 99 is effected by means of a flexible chain drive 100 coupling the output shaft of the reducer unit 98 and the slip clutch 101. As best seen in FIG. 5, the shaft 99 is provided with a section 99A which has spaced therealong a series of cam actuators 102, 103, 105, 104, and 106 in predetermined relationship of activating various micro-switches 102A, 103A, 105A, 104A, and 106A for sequencing the operation of the respective machine components as will be hereinafter described. For example, a cam actuator 102 is mounted for movement on the screw sector 99A for actuating a micro switch 102A to effect a reversal of the motors as will be hereinafter described when engagement is effected therebetween. Another cam actuator 103 is provided for effecting actuation of a microswitch 103A controlling the operation of the screen 62