Abstract:
A multi-station screen printing apparatus includes a base member; a plurality of platens, each for supporting a substrate to be printed, the platens mounted radially in a rotatable manner about the base member; and a plurality of print heads mounted radially and non-rotatably about the base member above the platens. A first print head is mounted in a vertically pivotable manner and a second print head is mounted in a non-pivotable manner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to the field of textile printing apparatuses and more particularly, to a multi-head, carousel-type textile printing press having a vertically pivotal print head. 
         [0004]    2. Related Art 
         [0005]    Multi-station screen printing devices enable small printing shops to screen-print designs in multiple colors on articles such as shirts, jackets, and posters, to name but a few possible items. The substrate to be printed is supported on a flat surface called a platen while a number of print heads, each containing a different color of the design, are aligned with the platens for printing purposes. The platens are arrayed around a circle and supported by a sturdy base and pivot relative to the base for alignment with each of the separate print heads. 
         [0006]    The print heads, on the other hand, while also being arrayed about a circle, are on some machines fixedly mounted relative to the base and the platens are rotated into position beneath each print head for printing each separate color. To print a multi-color design, each of the platens is in turn aligned with a particular print head to apply a particular color ink and is subsequently brought into contact with the print head, generally by raising the platens, whereupon the screen printing process for that particular color is performed on the article. The platen bearing the substrate is then rotated to the next print head to apply the next ink color. It follows that the number of print heads determines the number of different colors that can be combined to produce a printed design. 
         [0007]    However, in the typical configuration for such machines there are usually fewer print heads than the number of platens for supporting the substrates, or workpieces. For example, on a printing machine having six platens there are at most five print heads. The reason for omitting one or more print head is to make it easier to add and remove substrates from the platens. The range of motion of the platens relative to the print heads is kept short in order to speed up the overall process of printing, since with a shorter range of motion the platens can move to each print head more quickly. Given this short range of motion, it is very difficult to add or remove the item to be printed from the platen when the platen is aligned with a print head. The solution therefore has been to omit one of the print heads so that the machine operator has unobstructed access to one of the platens. 
         [0008]    The practical result of this configuration, though, is that a customer who wants to have six-color printing capability must purchase a machine with eight or more platens (similarly, a customer desiring four-color printing capability must buy a six-platen machine, etc.). However, the addition of more platens to a printing machine increases the cost and size of the machine, while many smaller print shops cannot afford the higher cost and may not have the additional space needed for the larger machine. 
         [0009]    In another style of screen printing machine the print heads are mounted on pivoting arms, which pivot upwards between screening steps in order to allow the platens to rotationally change positions. As with the platens on the fixed head machines, the range of motion of the pivoting heads is limited in order to increase the overall speed of the screen printing process. Again, the limited range of motion of the pivoting print heads makes it difficult to add and remove articles from the platen, with the result that pivoting head printing machines also have at least one fewer print head than the number of platens, to allow unimpeded access to at least one of the platens. 
         [0010]    What is needed is a screen printing apparatus that maximizes the number of individual colors that can be printed while minimizing the cost and size of the machine. Such an apparatus preferably allows easy addition and removal of the substrate material while maintaining a high degree of alignment between colors and rapid turnover of substrate articles, such as t-shirts, towels, banners and the like. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, in keeping with the above advantages and goals, the invention is, briefly, a multi-station screen printing apparatus which includes a base member; a plurality of platens, each for supporting a substrate to be printed, the platens mounted radially in a rotatable manner about the base member; and a plurality of print heads mounted radially and non-rotatably about the base member above the platens. A first print head is mounted in a vertically pivotable manner and a second print head is mounted in a non-pivotable manner. 
         [0012]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a perspective view of a multi-station screen printing machine of generally known variety, but with a new, equalizing print station attached thereto. 
           [0015]      FIG. 2  is an enlarged perspective view of a portion of  FIG. 1  showing a pivoting print head support arm with a print head attached thereto. 
           [0016]      FIG. 3  is an enlarged perspective view of a hinge mechanism for attaching the pivoting print head support arm to a base unit of the printing machine of  FIG. 1 . 
           [0017]      FIG. 4  is a perspective view of a portion of the screen printing machine of  FIG. 1  with the pivoting print head support arm in the raised position. 
           [0018]      FIG. 5A  is an enlarged perspective view of the alignment mechanism on a pivoting print head support arm of the printing machine of  FIG. 1  in the raised position. 
           [0019]      FIG. 5B  is an enlarged perspective view of the alignment mechanism on a pivoting print head support arm of the printing machine of  FIG. 1  in the lowered position. 
           [0020]      FIG. 6  is a perspective view of the multi-station screen printing machine of  FIG. 1  having the pivoting print head support arm in the down position, wherein the platens are in the raised position for printing. 
           [0021]      FIG. 7  is a perspective view of a multi-station screen printing machine of  FIG. 1  having a pivoting print head support arm in the up position for removal of the substrate, wherein the platens are still in the raised position for printing. 
           [0022]    Throughout the drawings, like parts are indicated by like element numbers. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For clarity and simplicity of the figures, not all elements are shown in all figures. 
         [0024]    As illustrated in the figures, and particularly  FIGS. 1 ,  6  and  7 , a multi-station screen printing machine, generally designated  20 , has disposed around the perimeter thereof a plurality of platens  22 , each for supporting a substrate article  24  to be printed, and a plurality of print heads  26  for screen printing a number of individual colors of a design onto the substrate article  24 . Platens  22  and print heads  26  are mounted on support arms  28 ,  30 , respectively, that project radially from a common, substantially central area disposed on machine (press)  20 , such that print heads  26  are positioned above platens  22  during printing. Platens  22  are rotatably mounted to a base unit  32  while print heads  26  are mounted in a non-rotatable manner to the base unit  32 . At the distal ends of the platen support arms  28  are disposed flat surfaces, i.e. the platens  22  themselves. At the distal ends of print head support arms  30  are the components which together make up print heads  26 , including frame carriers  34  for holding printing screens  36 , slidable holders  38  (shown in  FIG. 4 ) for the squeegees, and various tubing for adding and removing ink to the screen in a conventional manner. 
         [0025]    Print heads  26  are attached to base unit  32  by a central shaft  42 , with print head support arms  30  being attached to a circular plate  44 , above which projects a tower  46 , as seen in  FIG. 2 . In a preferred embodiment at least one, but fewer than all, of the print head support arms is pivotably mounted to circular plate  44  such that pivoting print head support arm  30 A moves in a vertical plane, as circular plate  44  is raised and lowered in known fashion. Pivoting print head support arm  30 A is held onto circular plate  44  by a hinge  48 , for example, as shown most clearly in  FIG. 3 . The movement of pivoting print head support arm  30 A is preferably, effected by an air-driven piston  50  or by mechanical means such as a motor. As shown in  FIG. 4 , air-driven piston  50  is attached to tower  46  and to pivoting print head support arm  30 A, such that piston  50  raises and lowers the support arm  30  and the print head  26  associated therewith. Alternatively, pivoting print head support arm  30 A can be raised and lowered manually. 
         [0026]      FIG. 5A  shows that an adjustment device (or “stop”)  52  such as a screw, for example, can be situated on the circular plate  44  below the pivoting print head support arm  30 A to allow fine tuning of the final resting height of the pivoting arm in the lowered position. Pivoting print head support arm  30 A preferably can be raised to an angle of at least 25-30 degrees relative to horizontal with the result that the distal edge of associated print head  26  is raised approximately 23 inches from a corresponding one of platens  22 , giving ample room for adding or removing the substrate article  24  on or from such corresponding platen  22 . 
         [0027]    Remaining, non-pivoting print head support arms  30  can be stabilized by attachment of a support bar  54  between respective support arm  30  and tower  46 , as shown in  FIG. 1 . In addition, various wires and tubing are fed through tower  46  to individual print heads  26 , as necessary for operation of the printing functions. 
         [0028]      FIG. 2  illustrates platen support arms  28  fixedly attached to a lifting tube  56  which in turn is slidably mounted on central shaft  42 . Through conventional hydraulic, mechanical, or air-driven mechanisms. Lifting tube  56  is urged upwardly in order to bring platens  22  in close proximity beneath corresponding print heads  26  for printing purposes. In this embodiment, therefore, all of platen support arms  28  are raised and lowered in unison when lifting tube  56  is raised and lowered. 
         [0029]    The process of screen printing is outlined briefly as follows and as shown in  FIGS. 1 ,  6 ,  7 . Print head  26  containing a screen  36  and platen  22  containing a substrate  24  (a shirt, jacket, or poster, for example) are aligned adjacent to one another and brought into close contact by raising platen  22  ( FIG. 6 ). Ink is flooded onto screen  36  so that ink flows through screen  36  according to the design therein onto substrate  24 , and then excess ink is removed using a squeegee mechanism that moves across screen  36 . Print head  26  and platen  22  are then separated from one another, for example by lowering platen  22 , as shown in  FIG. 1 , and either substrate  24  is then removed or platen  22  is rotated and aligned with another print head  26  and the process is repeated for each print head  26  that contains a different color in the ultimate design. 
         [0030]    Print heads  26  are disposed above platens  22  so that ink does not spill when screen  36  is flooded and so that ink flows through screen  36  and onto substrate  24 . On some existing machines the print heads remain in a fixed position while the platens rotate, while on at least one other the print head(s) are mounted on pivoting arms that cause the print heads to rotate upwards away from the platens. Heretofore, however, these two very different styles of print heads, i.e. 1) fixed and 2) pivoting, have not been combined on a single machine. One reason this has not been done before is because pivoting heads in general are disfavored in the market due to a perception that they do not align as accurately with the platen as fixed printing heads; thus causing sloppy printing and a less than desirable end product. Furthermore, the mechanisms for operating pivoting heads are very different from fixed head machines, creating a basic incompatibility between the two types of systems. 
         [0031]    Thus, an important issue regardless of the type of machine used is maintaining proper alignment between the different color screens when the platens or print heads are rotated to new positions. Even small amounts of mis-alignment will cause noticeable defects in the final printed image. Therefore, as seen in  FIGS. 4 ,  5 A, and  5 B, in the new device an alignment tab  58  is used to maintain proper alignment between the screens of the various pivoting and non-pivoting print heads. Alignment tab  58  slides into a slot  60  that is bordered by a pair of rollers  62 , which help guide vertical movement of alignment tab  58  and permit smooth movement the tab into and out of slot  60 . In the embodiment illustrated, alignment tab  58  is mounted on the underside of pivoting print head support arm  30 A and slot  60  is mounted in a corresponding position on top of circular plate  44 , although other acceptable locations can be conceived. Provided that alignment tab  58  is relatively close to slot  60 , rollers  62  will guide tab  58  into the slot and thus will provide appropriate side-to-side alignment of pivoting print head support arm  30 A. 
         [0032]    Similarly, as seen in  FIG. 4 , alignment tabs  58  are mounted to the underside of circular plate  44  beneath each non-pivoting print head support arm  30  and complementary slots  60  with rollers  62  are mounted near the base of each platen support arm  28 . Alignment tabs  58  and slots  60  in this case help to properly align all platens  22  with print heads  26  for printing. 
         [0033]    It is also possible to modify an existing machine to add one or more pivoting print head support arms  30 A having print heads  26  such as those described above. In that case, one end of support arm  30 A must be pivotably anchored, for example via a hinge mechanism  48 , near the center of printing machine  20 . If the machine to be so retrofitted is similar to the one described above, a hinge  48  attached to pivoting print head support arm  30 A can be anchored to the circular plate  44  to which the other print head support arms  30  are fixed. In addition, a mechanism (e.g. a piston  50 ) for lifting the pivoting support arm  30 A, if automatic or semiautomatic operation is desired, is attached to support arm  30 A and to tower  46 . Finally, tubing and wiring are attached to supply ink and to control operation of print head  26  in the customary manner. 
         [0034]    As various modifications could be made to the exemplary embodiments, as described above with reference to the corresponding illustrations, without departing from the scope of the invention, it is intended that all matter contained in the foregoing description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.