WO1997016258A1

WO1997016258A1 - Screen angle adjusting alignment and selective screen drive actuating mechanism for screen printing press

Info

Publication number: WO1997016258A1
Application number: PCT/US1996/016611
Authority: WO
Inventors: Ivan B. Helmrich
Original assignee: Preco Industries, Inc.
Priority date: 1995-10-30
Filing date: 1996-10-18
Publication date: 1997-05-09
Also published as: AU7448796A

Abstract

A screen printing apparatus (10) is provided having a squeegee assembly (54) which includes a squeegee (64) movable across the screen (120) to force ink therethrough onto a substrate in engagement with the screen (120), wherein mechanism is provided for on-the-fly adjustment of the squeegee trailing peel angle of the screen (120) away from the substrate as the squeegee assembly (54) is moved across the screen. An elongated cam member adjacent the squegee assembly is mounted for pivotal movement adjacent the path of travel of the squeegee assembly (54) across the screen (120). A cam follower (100) carried by the squeegee assembly (54) engages the cam member (78) and effects swinging movement thereof during shifting of the squeegee assembly (54). Means connected to the cam member (78) and joined to the supporting frame for the screen (120) raises the screen frame (118) to progressively peel the screen (120) from the substrate as the squeegee assembly (54) is shifted across the screen (120). Means is also provided for selectively skewing the screen frame (118) with respect to the substrate supporting bed of the apparatus. Mechanism is further provided permitting the operator of the apparatus to selectively lift the screen frame (118) from the substrate supporting bed when the squeegee assembly (54) is lifted, or to shift only the squeegee assembly (54) away from the bed while leaving the screen frame (118) in position on the bed.

Description

SCREEN ANGLE ADJUSTING ALIGNMENT AND SELECTIVE SCREEN DRIVE ACTUATING MECHANISM FOR SCREEN PRINTING PRESS

Background of the Invention

1. Field of the Invention

This invention relates to screen printing apparatus having an image defining flexible, ink porous screen and a squeegee assembly including a squeegee movable across the screen for forcing ink through the screen onto a substrate in engagement with the screen. Mechanism is provided for on-the- fly adjustment of the squeegee-trailing progressive peel angle of the screen away from the substrate as the squeegee is moved across the screen.

Alignment means is also provided for selectively skewing the screen frame with respect to the substrate supporting bed of the apparatus. Mechanism is further provided which allows the operator of the apparatus to selectively lift the screen supporting frame away from the substrate supporting bed as the squeegee assembly is also shifted away from the bed, or for moving the squeegee assembly while leaving the screen frame in place on the bed.

2. Description of the Prior Art Screen printing apparatus conventionally includes a bed for supporting a substrate on which an image is to be printed, an image defining, flexible, ink porous carried by a supporting frame which is removably positioned on the bed, and a squeegee assembly having a squeegee which is movable across the screen to force ink through the screen onto the underlying substrate. Equipment of this type has been equipped with means for lifting the screen which trails the squeegee away from the substrate in order to prevent smearing of the still wet image that has been deposited on the substrate. The angle between the lifted screen and the substrate trailing the squeegee is generally known as the "peel angle." During makeready of the screen printing apparatus, it has been the prior practice to carry out a trial and error makeready procedure to determine the best screen peel angle for a particular job. This has involved setting a peel angle for each project and then running the screen printing press to determine what results are obtained for that setting. The peel angle is adjusted as necessary after observing the quality of the image and whether any smearing or other undesirable effects have been encountered. ln accordance with this procedure, makeready of the screen printing apparatus is often a time-consuming and expensive function of the overall job. Therefore, there has been a need for a makeready process for screen printing apparatus which allows the operator to adjust the screen peel angle on the fly as images are being printed in order to obtain optimum image quality in the least amount of time.

Prior screen printing equipment has also been provided with means for swinging or lifting the squeegee assembly relative to the screen frame and press bed for cleaning or maintenance of the squeegee. In most instances, the screen supporting frame was lifted manually from the bed for screen replacement and/or cleaning, or the screen frame could be raised only in association with the squeegee assembly. Thus, there has also been a need for reliable, inexpensive and selectively operable mechanism permitting the user of the apparatus to move the screen frame and the squeegee assembly away from the bed as a unit, or to shift only the squeegee assembly away from the screen frame while it rests on the press bed.

Summary of the Invention

The present invention is broadly concerned with screen printing apparatus having an image defining, flexible, ink porous screen and a squeegee assembly wherein the squeegee is movable across the screen to force ink through the screen onto an underlying substrate with means being provided for on-the-fly adjustment of the peel angle of the screen away from the substrate, thus significantly reducing makeready time for the screen press. It is an important object of the invention to provide screen printing apparatus as described which includes an elongated cam member adjacent the squeegee assembly and which is mounted for pivoting movement with respect to the path of travel of the squeegee assembly relative to the screen, a cam follower on the squeegee assembly operable to swing the cam member as the squeegee assembly is shifted, and means operated by the cam member for lifting the squeegee trailing end of the screen frame as the cam member is pivoted to thereby progressively lift the trailing portion of the screen. The pivot support for the cam member is selectively adjustable transversely of the path of travel of the squeegee assembly to vary the degree of lifting of the trailing end of the screen frame. Manually manipulable means is provided for permitting the operator to change the position of the cam member support block while the squeegee assembly is moving across the image defining screen. This ability to adjust the peel angle on-the-fly significantly decreases makeready time because it is no longer necessary to stop the press to perform each peel angle adjustment, in order to obtain optimum image quality. Screen press care and maintenance time is also lessened by virtue of the provision of mechanism for selectively connecting the squeegee assembly to the screen frame so that the frame is lifted with the squeegee assembly as desired, or the screen frame can be left in place as the squeegee assembly is raised for maintenance and cleaning purposes. Post and bushing alignment structure is provided on the bed and screen frame respectively so that when the frame unit is lifted, it will always return to a preselected position.

In those instances where skewing of the position of the screen frame with respect to the press bed is desirable, such skewing may be accomplished in a controlled and accurate manner. The improved post and bushing alignment structure is provided at all four corners of the screen frame thus allowing the frame to be skewed as desired while retaining registration by virtue of the fact that a single reference point is always maintained regardless of the degree of skewing of the frame unit as a part of initial setup, or lifting or removal of the frame from the press bed. In addition, the reference point post and bushing assembly may be adjusted in a direction across the lateral extent of the press bed.

Brief Description of the Drawings

Figure 1 is a front elevational view of the screen printing apparatus associated with a schematically illustrated conventional dryer unit;

Fig. 2 is a fragmentary enlarged side elevational view from the operator side of the screen printing apparatus;

Fig. 3 is a fragmentary enlarged end elevational view from the right-hand side of the apparatus as shown in Fig. 1 ; Fig. 4 is a fragmentary enlarged end elevational view of the opposite side of the apparatus depicted in Fig. 3;

Fig. 5 is a fragmentary vertical cross-sectional view taken substantially on the line 5-5 of Fig. 2 and looking in the direction of the arrows;

Fig. 6 is an enlarged fragmentary end elevational view similar to Fig. 3, but showing the frame unit in its normally raised position with respect to the underlying bed of the apparatus; Fig. 7 is an enlarged fragmentary front elevational view similar to Fig. 2, but showing the squeegee assembly in its fully operated position and with the left-hand end of the frame unit elevated;

Fig. 8 is a fragmentary enlarged plan view of the apparatus showing the squeegee assembly in its initial position, and with the frame unit raising cam bar in its neutral location essentially parallel to the path of travel of the squeegee assembly;

Fig. 9 is a fragmentary enlarged plan view similar to Fig. 9 but illustrating the cam bar in a skewed position for raising the end of the frame unit as depicted in Fig. 7;

Fig. 10 is an enlarged fragmentary plan view similar to Fig. 9 and illustrating the cam bar in its skewed location and the squeegee assembly in its fully actuated position;

Fig. 11 is an enlarged fragmentary plan view of the bed of the screen printing apparatus, showing the frame unit for the screen, and associated mechanism for adjusting the position of the frame unit on the screen printing apparatus bed;

Fig. 12 is an enlarged fragmentary plan view of the bed of the screen printing apparatus with the frame unit removed; Fig. 13 is an enlarged fragmentary plan view of one of the alignment block, post and bushing structures for the frame unit of the screen printing apparatus and provided with an elongated bushing opening for the alignment post;

Fig. 14 is an enlarged fragmentary plan view of the adjustable alignment block, post and bushing structure for the frame unit of the screen printing apparatus and provided with an cylindrical bushing opening for the alignment post; and

Figs. 15-17 are fragmentary enlarged cross-sectional views illustrating the path of travel of the squeegee assembly across the screen and further showing the manner in which the trailing end of the screen frame unit is lifted as the screen squeegee moves across the flexible screen.

Detailed Description of the Preferred Embodiments

Turning now to the drawings, and particularly Fig. 1 , screen printing apparatus is broadly designated by the numeral 10. The base unit 12 of apparatus 10 is provided with a main horizontal, generally rectangular bed 14 which overlies a web unwind shaft 16 and a rewind shaft 18. Web material 20 carried by shaft 16 unwinds from the roll 22, passes over a series of rollers 24, thence across bed 14, over web advancement vacuum belt assembly 26 and into dryer 28 of conventional construction. The web 20 after traversing through the dryer 28 is returned to the base unit 12 of apparatus 10 and after passing over roller 30 is rewound onto shaft 18 as roll 32.

A vertically shiftable, horizontal plate 34 carried by upright pneumatically actuated mechanism (not shown) at the rear of the base unit 10 reciprocates along the lengths of two upright, parallel, horizontally spaced rods 36. Horizontal arms 38 and 40 at opposite ends of the plate 34 extend forwardly over the upper surface of bed 14. Trapezoidal plates 42 and 44 carried by the innermost ends of arms 38 and 40 are in horizontal spaced alignment. Vertical blocks 46 and 48 connected to the arms 38 and 40 respectively serve as means for mounting two spaced, horizontal cylindrical bars 50 and 52. A squeegee assembly broadly designated 54 is reciprocably mounted on bars 50 and 52 for movement along the lengths thereof.

A central upright member 56 supported by bars 50 and 52, extending transversely thereof, and spanning the distance between such bars has a horizontal base plate 58 on the lower end thereof. A squeegee mounting unit 60 suspended from base plate 58 has a pivotal squeegee support 62 which in turn serves as the mounting structure for a removable flexible squeegee 64. A pair of upright pneumatically actuated cylinders 66 on mounting plate 58 are connected to the squeegee support 62 for raising and lowering squeegee 64. Two pneumatically actuated cylinders 68 mounted on plate 58 forwardly of cylinder 66 are operable to move the depending flood bar

70 toward and away from the underlying screen. An upright stop plate 74 is secured to the bars 50 and 52 between arm 38 and squeegee assembly 54.

Horizontal top plate 72 joins the upper ends of the cylinders 66 and 68. A tubular horizontal actuator 76 having a piston of magnetic material therein is aligned with and positioned between bars 50 and 52. The piston within actuator 76 is reciprocated by air under pressure alternately introduced at opposite ends of the actuator 76. In view of the fact that the member 56 is also of magnetic material, shifting of the piston within actuator 76 causes the entire squeegee assembly 56 to be moved in conjunction with the piston of the actuator 76. An elongated cam member 78 carried by trapezoidal plate 44, plate 72 and resting on the opposed trapezoidal plate 42 extends along the longitudinal lengths of the bars 50 and 52 above the squeegee assembly 54. The end 78a of member 78 has an opening therein which receives an upright pin 80 forming a part of a shiftable block assembly 82. As is apparent from

Figs. 8 and 9, the block assembly 82 has a central opening therein for reception of the end 78a of cam member 78. Block assembly 82 is restricted to reciprocable movement transversely of the bars 50 and 52, by positioning screws 84 which are received in respective elongated slots in the block assembly 82.

Block assembly 82 is reciprocable by shifting of rod assembly 86 which has a segment that passes through ear 88 on arm 40. A manually manipulable knurled knob 90 which is rotatable on the outermost end of rod assembly 86 may be rotated to effect reciprocation of rod assembly 86 and thereby transverse shifting movement of block assembly 82.

An adjustable length connector rod 92 pivotally secured to the end 78b of cam member 78 which rests on trapezoidal support plate 42, is also joined by a pivotal connector 94 coupled to a block 96 extending downwardly from the underside of a hinge plate 98 that is hingedly joined to arm 38. The plate 72 of squeegee assembly 54 supports a cam follower 100 (Figs. 8-10) which is positioned to ride along the elongated cam edge surface 102 of cam member 78. Viewing Figs. 8 and 9, it can be seen that hinge plate 98 has a pair of outwardly projecting ears 98a which are formed to present aligned upwardly opening grooves 98b at the outer extremities of the ears. The removable screen frame and clamp unit broadly designated

104 as shown in Figs. 5, 11 and 15-17, includes a main rectangular clamp frame 105 having two transversely L-shaped side frame elements 106 and 108 which are joined by L-shaped cross members having upright segments 110 and 112 joined by horizontal segments 114 and 116. Silk screen frame 118 is located within the frame unit 104 and held in position by conventional fasteners and pneumatically actuated components. A flexible screen 120 is removably supported by the frame 118 and conventionally is of ink porous nature having ink blocking areas defining the area of the image to be transferred to the substrate underlying the screen while positioned on the bed 14 of apparatus 10. A pair of transversely extending support bars 122 and 124 are carried by pillow blocks 126 on bed 14 above the surface thereof at opposite ends of the bars 122 and 124. Mounting members 128 and 130 adjustably secured to bar 122 carry upright cylindrical alignment posts 132 thereon while the mounting member 134 on bar 124 has an upright alignment cylindrical post

136 thereon. The outermost end of each of the posts 136 is of semi-spherical configuration. An elongated mounting block 138 secured to the end of bar 124 opposite mounting member 134 also carries an upright cylindrical alignment post which is provided with an outermost semi-spherical extremity. The securing element 142 of block 138 permits selective securement of block 138 to bar 124 at a selected position along the length of bar 124. It is to be seen from Fig. 11 that an element 144 of rectangular configuration is adjustably mounted on segment 116 in proximal relationship to the block 138. Fasteners 146 serve to fix the element 144 to frame unit 104 at any one of an infinite number of positions as determined by the length of the slot 148 in element 144 and which receives the fasteners 146.

An upright cylindrical post-receiving alignment bushing 150 is provided on the upper surface of element 144 and has an opening a cylindrical 150a therein of essentially the same diameter as cylindrical post 140. The mounting members 128, 130 and 134 each carry upright post-receiving alignment bushings 152. Each of the bushings 152 has an elongated opening 154 therein with the transverse axis of each opening 154 being essentially equal to the diameter of an associated post 132, while the longitudinal axis of each opening 152 is of greater length than the diameter of respective posts 132. As illustrated in Fig. 13, the longitudinal length of each of the openings

154 in the bushings 152 of members 130 and 134 are in alignment and parallel, and the longitudinal length of the opening 154 in the bushing 152 of member 128 is spaced from but parallel with the longitudinal lengths of the openings 154 in members 130 and 134. Each of the support bars 122 and 124 is reciprocable longitudinally thereof within respective pillow blocks 126. A bar adjustment assembly 153 on each of the bars 122 and 124 includes a sleeve 155 telescoped over the forwardmost end of a respective bar 124 (i.e., the ends of the bars facing the operator of the apparatus 10) and that is integral with a knurled cylindrical element 157. Inserts 159 threaded into the outermost end of each of the bars 122 and 124 is also in threaded engagement with the surrounding adjustment assembly 153. A coil spring 163 over the end of each bar 122 and 124 opposite adjustment assemblies 153 is trapped between a respective block 126 and a stop member 165 threadably mounted on the outermost end of a corresponding bar. The springs 163 serve to bias each of the bars 122 and 124 in a direction away from the front part of apparatus 10.

Returning to Fig. 2, it is to be seen that another hinge plate 156 is hingedly secured to arm 40 in opposition to and in horizontal alignment with hinge plate 98. The hinge plates 98 and 156 are of overall similar shape and therefore hinge plate 156 also has two integral outwardly turned ear portions 156a provided with upwardly opening aligned grooves 156b similar to grooves

98b. A pair of bale units 158 serve to releasably and selectively connect the hinge plates 98 and 156 to the underlying ends of frame unit 104. As can be observed from Figs. 3 and 4, each bale unit has a normally uppermost horizontal bight 160, and depending legs 162 at opposite ends of the bight section 160. If desired, turnbuckle structure 164 may be provided within each leg 162 as an integral part thereof for adjusting the lengths of respective legs. The lowermost extremity of each leg 162 is turned outwardly away from the opposite leg 162 of a corresponding bale 158 and is received within a block 166 forming a part of a respective segment 114 and 116. Air cylinders 168 and 170 carried by trapezoidal plates 42 and 44 respectively in underlying relationship to hinge plates 98 and 156 have pistons 172 which engage respective plates 98 and 156 for pivoting the latter about corresponding hinge lines upon actuation of the air cylinders 168 and 170. Adjustment screws 174 threaded through trapezoidal plates 42 and 44 respectively also engage the underface of each of the plates 98 and 156 to permit adjustment of the distance of the screen 120 from the upper surface of the substrate resting on bed 14 directly below the screen. As screws 174 are rotated toward and away from the hinge plates 98 and 156, the plates are pivoted to raise or lower the frame unit 104 carried by bale members 158 resting on the outer ends of hinge plates 98 and 156.

Operation

During initial setup of the apparatus 10, a flexible, ink porous screen 120 having ink blocking means thereon defining an image to be transferred to the web substrate supported by bed 14 is placed within the screen frame 118 off-press. The bales 158 are disconnected from the hinge plates 98 and 156 and swung downwardly in opposite directions away from the arms 38 and 40. The squeegee assembly 54 is raised by actuating the air cylinder connected to horizontal plate 34 which in turn lifts the arms 38 and 40 supporting the squeegee assembly, but the frame assembly 104 remains on bed 14 by virtue of disconnection of the bales 158 from that assembly. The screen frame 118 is then positioned within the clamp frame 105 of frame unit 104 while the latter rests on the bed 14. Next, the screen frame 118 is pulled against the stop screws 178 forming a part of clamp 105 of frame unit 104, while at the same time locating the frame 118 in engagement with the alignment stop 180. The air cylinders 182 located along the rear margin of the clamp frame 105 of frame unit 104 are actuated to clamp the screen frame 118 in the overall frame unit 104.

The squeegee assembly 54 is again lowered and bales 158 are reconnected to the plates 98 and 156. Thereupon, the squeegee assembly 54 is again raised. The frame unit 104 which carries the frame 118 clamped therein is also elevated to provide access to the top of bed 14.

A roll 22 of web material is placed on unwind shaft 16 and trained around rollers 24, and across bed 14 to the vicinity of vacuum drive belt 26. The web substrate lying on bed 14 is adjusted laterally as required to generally align the web with the overlying screen within frame 118. The frame unit 104 carried by squeegee assembly 54 is lowered so that the operator may view the image overlying the web substrate by looking through the screen itself.

Upon successive elevations of the frame unit 104, the web can be brought into overlying relationship to the vacuum drive belt 26. In this manner, the web can be incrementally shifted by the vacuum drive belt 26 so that the web can be threaded into the dryer 28, thence around the lowermost roller 30 adjacent rewind shaft 18, and finally connected to shaft 18. Ink is placed over the top of the screen 120 and apparatus 10 operated to print successive images on the web of material. Squeegee assembly 54 is shifted longitudinally of the support bars 50 and 52 by virtue of movement of the piston within tubular actuator 76. As the piston shifts from left to right viewing Fig. 2 for example, the squeegee 64 forming a part of assembly 54 moves across the surface of the screen 120 thereby forcing ink through the porous area of the screen onto the underlying substrate. Prior to initiation of the return stroke of the squeegee assembly 54, air cylinders 66 are actuated to lift squeegee support 62, thereby raising the squeegee 64 from the upper surface of screen 120. Next, air cylinders 170 are actuated to pivot hinge plates 98 and 156 thereby raising the frame unit 104 from the surface of the web substrate 20. At the same time, cylinders 68 are operated to lower the flood bar 70 into near engagement with the screen. The flood bar draws the bead 184 of ink that had accumulated ahead of the squeegee 64, back toward the leading edge of the screen 120.

Assuming that an adequate image is printed on the web substrate 20 to ascertain whether makeready adjustment of the peel angle of the screen from the substrate is required, the first image is normally transferred while cam member 78 is essentially parallel with the path of travel of squeegee assembly

54 across screen 120 (Fig. 8). In this instance, the margin of frame unit 104 which trails squeegee assembly 54 is not raised during travel of the squeegee assembly from left to right across the screen 120 viewing apparatus 10 from the perspective of the operator standing in front of such equipment as depicted in Fig. 1. Thus, the peel angle of the screen following squeegee 64 is essentially zero.

However, if the screen press operator determines that the portion of the flexible screen 120 immediately following the squeegee 64 should be lifted from the surface of the substrate to preserve image quality, the peel angle may be adjusted. This adjustment is accomplished by loosening the set screw 89 followed by rotation of the knurled knob 90 which shifts block 82 through the medium rod assembly 86, bringing the pin 80 defining the pivot point of cam member 78 toward the press operator. Shifting of the pivot point of cam member 78 which skews the longitudinal axis of cam member 78 with respect to the path of travel of squeegee assembly 54 as it moves from left to right viewing Fig. 9, the cam follower 100 of squeegee assembly 54 rides along the cam surface edge 102 of cam member 78 thereby exerting a Y-axis deflection force on cam member 78 which is converted to an X-axis movement of connector rod 92 to the left viewing Fig. 9. Shifting of the connector rod is converted into a vertical motion by pivoting of hinge plate 98 about its horizontal hinge axis. As can be seen from Fig. 7, lifting of the hinge plate 98 causes the associated bale unit 158 to be elevated, thus lifting the trailing edge portion of frame unit 104. This lifting movement of the left end of frame unit 104 as shown in Fig. 7 causes the screen 120 trailing squeegee 64 to be raised from the surface of the underlying web substrate. The peel angle α progressively increases as squeegee assembly 54 is moved across the horizontal extent of screen 120 (see Figs. 15-17).

Although apparatus 10 is normally capable of operating at cycle rates approaching one image per second, during makeready, the press will be operated at significantly lower cycle rates. In any event, the operator by viewing previously printed images emerging from the press can readily determine whether the progressively increasing peel angle α should be changed to obtain optimum image quality. This on-the-fly adjustment of the progressively increasing peel angle significantly decreases makeready time because it is not necessary stop the press and make adjustment in the peel angle between each incremental discontinuance of operation of the squeegee assembly 54.

At the time of transfer of successive images onto the substrate web 20 during first pass of the web through the press, and assuming that the image is again to be impressed with a different color, a registration mark in the form of indicia 176 is also printed on the web adjacent each image. This indicia is used to register subsequent images with the first printed image.

Before replacement of the image defining screen and an appropriate ink in the frame unit 104, it is desirable that the corner registration pin 140 be substantially aligned with the indicia 176 associated with respective images first printed on the web 20. This is to establish a primary point between the frame unit 104 and the image that has first been printed on the substrate. Accordingly, the position of post 140 is brought into visual alignment with the indicia 176 associated with each image printed on the web substrate 20. In order to accomplish this, fasteners 146 are loosened, and securing element

142 is rotated to allow mounting block 138 along with element 144 to be shifted along the length of support bar 116 until the post 140 is visually aligned with registration indicia 176, and with the bushing 150 likewise being brought into proper alignment with the indicia. The fasteners 146 are then tightened and element 142 likewise rotated to affix mounting block 138 to the bar 124.

Following replacement of the screen with the next image bearing screen, mounting of the screen frame unit on the machine using the procedure previously described, and application of the next colored ink to the screen, a series of images are printed onto the web substrate 20 over the first applied images. These second applied images indicate whether they are in correct alignment in the X and Y axes with the first applied images. Viewing Fig. 11 , the first step of proper alignment of successively applied images to web substrate 20 is to verify that the second applied image is aligned with the first applied image along the X-axis, i.e., the longitudinal length of the web. An X-axis sensor (not shown) reads the position of the indicia 176 and through servomechanism (again not shown) allows the operator to shift the point at which the web is stopped below the frame unit 104 until proper X-axis registration is obtained.

If the second applied images are out of Y-axis alignment with the first applied images, the operator rotates adjustment assemblies 153 made up of sleeves 155 and knob elements 157 to shift the bars 122 and 124 axially thereof as necessary to bring the second applied image into Y-axis alignment. As the posts 140 and 132 are shifted laterally of bed 14 as a result of their being mounted on respective bars 122 and 124, the frame unit 104 is shifted therewith by virtue of the fact that the bushings 152 receiving posts 132 and the bushing 150 receiving posts 140 are rigidly secured to frame unit 104.

Adjustment assemblies 153 are rotated in either of the directions of rotation as required to obtain Y-axis registration of the successively applied images.

In the event the successively applied images to the web substrate 20 are out of alignment in the θ axis, compensation for such misregistration may be accomplished by changing the adjustment assemblies 153 relatively to effect rotation of the screen frame unit 104 about a vertical axis. For example, if the adjustment assembly 153 associated with bar 122 is rotated, but adjustment assembly 153 of bar 124 is not adjusted, the frame unit 104 will be rotated about the axis of primary alignment pin 140. This rotation of frame unit 104 about the axis of pin 140 is accommodated by virtue of the fact that the openings 154 in bushings 152 are elongated in the X-axis direction, i.e,. along the length of the web 20. Rotational movement of the frame unit 104 about the axis of pin 140 results in a certain degree of movement of pins 132 in a Y direction. This transverse movement of pins 132 of the mounting members 128 on bar 122 is accommodated by virtue of the bias of spring 163 on bar 122 bearing against the pillow block 126.

Although the operation described above related to adjustment of only one of the assemblies 153 to effect rotation of the frame unit 104, it is to be understood that such rotational adjustment may be obtained by differential adjustment of assemblies 153 depending upon the nature of the alignment required between successively applied images. For example, one adjustment assembly 153 may be rotated in a direction to move the support bar toward the operator, while the other adjustment assembly 153 is rotated to move the opposed support bar in the opposite direction. The adjustment assemblies 153 may be manipulated as required to obtain image registration as visually observed by the operator.

It has previously been explained that the primary alignment pin 140 should be visually aligned with indicia 176 on the web substrate 20. In most instances, the indicia 176 will be printed on the substrate adjacent one edge of the web. However, in view of the fact that webs of varying widths will be printed using apparatus 10, and the registration indicia may or may not be in proximity to the edge but in fact may be near the center of the web, it can be seen that there is a need for a relatively wide range of adjustment positions of the primary alignment post 140. The mounting of primary pin supporting block 138 and its associated bushing mounting element 144 allow for shifting of the pin throughout the length of the support bar 124 so that the pin 140 may be aligned with an indicia substantially regardless of the position of the indicia on the web.

Another benefit of the ability of the operator to move the primary alignment pin 140 along the length of support bar 124 to a position in Y-axis alignment with an indicia on a substrate, where that indicia is centrally located with respect to the longitudinally length of bar 124, is to minimize the X-axis misregistration of successive images that would otherwise occur if the main alignment axis provided by pin 140 were required to always be at the corner of the frame unit 140, as for example shown in Fig. 11. It is also to now be appreciated that the operator of apparatus 10 may selectively: (1 ) raise and lower the squeegee support 62 with respect to frame unit 104 by actuation of air cylinders 66; (2) elevate the frame unit 104 and associated screen clamping frame 118 along with the squeegee assembly 54 by operation of the air cylinder which raises and lowers arms 38 and 40; and (3) raise the squeegee assembly 54 by actuation of the air cylinder connected to plate 34 between arms 38 and 40 while leaving the frame unit 104 in place on bed 14 as a result of prior disconnection of bale units 158 from hinge plates 98 and 156.

These independent operations are important because in screen printing, it is often necessary to lift the screen 120 so that the bottom can be cleaned to remove drying ink and stray fibers form the substrate. In this case, the entire print head including the squeegee assembly 54 and the frame unit 104 are lifted vertically to allow access to the bottom of the screen. In other instances, it is desirable to move the squeegee assembly with respect to the screen 120 so that the squeegee 64 and associated mechanism may be cleaned without loss of registration of the screen with images being printed.

In this case, disengagement ofthe bale units 158 from the hinge plates 98 and 156 allows the squeegee assembly 54 to be elevated independently of the frame unit 104. When the squeegee assembly 54 is lifted, the screen has not moved from its mount and registration is retained by the pins 132 and 140. Similarly, the pins 132 on bar 122 maintain registration of the screen even though the left-hand margin of the frame unit 104 may be lifted by hinge plate 98 to obtain a progressive peel angle between the substrate and the frame behind the squeegee 64 as it is moved across the screen.

Claims

Claims:

1. In screen printing apparatus provided with a bed for supporting a substrate on which an image is to be applied, a flexible, ink porous screen having ink blocking means thereon functioning to define said image, a frame unit for holding the screen and positionable adjacent the bed with the screen against a substrate on the bed, a squeegee assembly mounted for movement along a path of travel across the screen and provided with a squeegee which moves from a position adjacent one part of the frame unit toward a second part of the frame unit to force ink through the unblocked area of the screen onto the substrate, the combination with said frame unit of adjustable means for shifting said one part of the frame unit away from the bed as the squeegee is moved across the screen from a position adjacent said one part of the frame unit toward the second part of the frame unit, and including: an elongated cam member having a longitudinally extending cam edge surface; means pivotally mounting the cam member in a position along the path of travel of the squeegee assembly with the pivot axis for the member being associated with the second part of the frame unit; a cam follower on the squeegee assembly located to engage and ride along said cam edge surface of the cam member during movement of the squeegee assembly from a position at said one part of the frame unit toward the second part of the frame unit, said pivot axis of the cam member being located in a position to cause the cam member to be pivoted about said pivot axis therefor during movement of the squeegee assembly from said one part of the frame unit toward said second part of the frame unit; and means operated by the cam member during swinging thereof by the cam follower for lifting the end of the frame unit adjacent said one part thereof as the squeegee is moved across the flexible screen to thereby progressively lift the portion of the screen trailing said squeegee away from the substrate on said bed.

2. Apparatus as set forth in claim 1 , wherein said means for progressively lifting the end of the frame unit adjacent said one part thereof includes a swingable panel member overlying said one part of the frame unit, bale means joining the panel member to the frame unit adjacent said one part thereof, and means for swinging the panel member to lift the frame unit by the bale means as the panel member is pivoted by the cam member.

3. Apparatus as set forth in claim 1 , wherein said pivotal mounting means for the cam member includes adjustable structure for adjusting the position of the pivot axis of the cam member with respect to the path of travel of the squeegee assembly across the screen.

4. Apparatus as set forth in claim 3, wherein said adjustable structure includes components permitting adjustment of said position of the pivot axis of the cam member while the squeegee assembly moves along said path of travel across the screen.

5. Apparatus as set forth in claim 4, wherein said components of the adjustable structure includes a block receiving the pivotal end of said cam member, and manually manipulable mechanism for shifting the block transversely of the path of travel of the squeegee assembly.

6. In screen printing apparatus having a image defining flexible, ink porous screen and a squeegee assembly including a squeegee movable across the screen for forcing ink through the screen onto a substrate in engagement with the screen, the improvement comprising: means for peeling the portion of the screen trailing the squeegee away from the substrate as the squeegee is moved across the screen from one position thereof to a second position of the squeegee; and means for adjusting the angle of peel of the screen away from the substrate during movement of the squeegee across the screen.

7. The apparatus of claim 6, wherein the means for adjusting the angle of peel of the screen away from the substrate is operable to decrease or increase the peel angle during movement of the squeegee across the screen.

8. The apparatus of claim 7, wherein said selectively operable means includes selectively operable, manually manipulable components for decreasing or increasing the peel angle of the screen away from the substrate.

9. In screen printing apparatus provided with a bed for supporting a substrate on which an image is to be applied, a flexible, ink porous screen, a frame unit for holding the screen and positionable adjacent the bed with the screen against a substrate on the bed, and a squeegee assembly mounted for movement along a path of travel across the screen provided with a squeegee engageable with the screen, the combination with said frame unit of means for adjusting the position of the frame with respect to a substrate on the bed of: a plurality of upright positioning posts on the bed; a post-receiving alignment member on the frame unit for each of the positioning posts, all but one of the alignment members permitting limited relative shifting movement of a respective alignment member with respect to a corresponding positioning post; and means for adjustably fixing the frame unit in a selected position with respect to the bed.

10. The apparatus of claim 9, wherein each of the posts is of generally cylindrical configuration, said one alignment member being of cylindrical shape to generally complementally receive the associated positioning post.

11. The apparatus of claim 10, wherein said all but one alignment members is provided with an elongated opening therein removably receiving a respective positioning post, each of said elongated openings being of a transverse width approximately equal to the diameter of the post received therein and the longitudinal axis of each opening being of greater length than the diameter of the post received therein.

12. The apparatus of claim 11 , wherein the frame unit is of rectangular configuration with a post and alignment member being provided for each corner of the frame unit.

13. In screen printing apparatus provided with a bed for supporting a substrate on which an image is to be applied, a flexible, ink porous screen, a frame unit for holding the screen and positionable adjacent the bed with the screen against a substrate on the bed, and a squeegee assembly mounted for movement along a path of travel across the screen provided with a squeegee engageable with the screen, the combination with said frame unit and squeegee assembly of: means for shifting the squeegee assembly toward and away from the bed; and means for selectively connecting the squeegee assembly to the frame unit for moving the frame unit away from the bed as the squeegee assembly is shifted with respect to the bed whereby the squeegee assembly may be disconnected from the frame unit and moved with respect to the bed without the frame unit being connected thereto.

14. The apparatus of claim 13, wherein said frame unit is provided with opposed ends, said means for connecting the squeegee assembly to the frame unit including a pair of bales joined to opposite ends of the frame unit, pivotal panel members associated with each of said opposed ends of the frame unit, said bales being selectively connectable to respective panel members, and means for swinging the panel members to lift the frame unit with the squeegee assembly when the latter is moved away from the bed and the bale members are connected to corresponding panel members.

15. The apparatus of claim 14, wherein the bales frictionally engage corresponding panel members and may be disconnected therefrom by swinging the bales away from respective panel members.