Abstract:
A screen-printing apparatus having pneumatically operated clamping devices for clamping one edge of a print screen frame to the print head of the apparatus. In a screen-printing operation where multiple print screens must be quickly interchanged, efficiency of time and energy may be achieved by a manually activated pneumatic clamping device that quickly secures and releases one edge of the screen frame to the print head. The screen-printing apparatus is not limited to a single print head, and multiple pneumatic clamping devices are envisioned for as many screen print heads as are mounted on the screen-printing apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/425,745, filed Nov. 13, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to screen-printing apparatus and, more specifically, to a screen-printing apparatus having pneumatically operated clamping devices for holding the edge of a rigid frame of a printing screen in order to permit faster and easier replacements of print screens. 
     2. Description of Related Art 
     Various types of manually operated screen-printing apparatus are known in the prior art. One commonly used type of construction is known as the Harco screen-printing machine made by Brown Manufacturing Company, as described in U.S. Pat. No. 4,809,604, issued to Harpold on Mar. 7, 1989, which is incorporated herein by reference. 
     The Harco machine typically includes four separate head units, each head unit being capable of holding one print screen by clamping onto an edge of the rigid frame surrounding the screen that contains the indicia. Each of the four heads is mounted onto a carousel that can be rotated to align any one of the four print screens with a textile article, such as a T-shirt or jersey, placed on a platen. Ink is then applied to the surface of the screen, passing through the unmasked portion of the screen to the exposed and aligned surface of the textile article. In addition to the typical four-head apparatus, similar manually operated apparatus have been equipped with one, two or six heads as well. In this and other similar devices, the print screens are generally clamped in place along an edge of the screen frame by hand using threaded knobs. Mounting and remounting of screens is time-consuming and labor-intensive, especially when multiple print screens having different indicia are required. 
     Improvements in screen-printing apparatus are known in the relevant art. Pneumatic or hydraulic devices for raising and lowering the print screen, for positioning the workpiece, and for stretching the screen on a frame are a few of the improvements disclosed in the related art. 
     U.S. Pat. No. 4,022,156, issued to Esterline on May 10, 1977, teaches a hydraulically operated work holder in which the device opens or closes a frame. U.S. Pat. No. 4,079,671, issued to Dubuit on Mar. 21, 1978, teaches a screen-printing machine for printing onto an article placed on a cylindrical support using a hydraulically or pneumatically actuated squeegee. 
     U.S. Pat. No. 4,442,772, issued to Bubley on Apr. 17, 1984, teaches a screen tensioning apparatus using a pneumatic tensioning device. U.S. Pat. No. 4,696,228, issued to David et al. on Sep. 29, 1987, describes a cantilevered support frame to hold a screen that includes a pneumatically actuated bladder. 
     U.S. Pat. No. 4,771,687, issued to Daunheimer on Sep. 20, 1988, teaches a pneumatically operated screen-printing apparatus for printing nonplanar workpieces in which the pneumatic device moves the screen into place on the workpiece. U.S. Pat. No. 4,829,894, issued to Gardner on May 16, 1989, teaches a balloon printing machine having a pneumatically operated squeegee. 
     U.S. Pat. No. 4,974,508, issued to Anderson et al. on Dec. 4, 1990, teaches a four-head manually operated screen-printing apparatus. U.S. Pat. No. 5,197,388, issued to Keast et al. on Mar. 30, 1993, teaches a clamping apparatus for use in the screen of curved articles wherein the curved workpiece is held in place by a spring biased clamp. 
     U.S. Pat. No. 5,235,908, issued to Froelicher et al. on Aug. 17, 1993, teaches a screen fabric stretching apparatus having pneumatic stretching components. U.S. Pat. No. 5,309,831, issued to Fuqua et al. on May 10, 1994, teaches a rotatable multicolor screen-printing apparatus having a powered squeegee device. 
     U.S. Pat. No. 5,454,307, issued to Chen on Oct. 3, 1995, teaches an apparatus for screen-printing shoe soles including pneumatically actuated clamping members. U.S. Pat. No. 5,740,732, issued to Karlyn et al. on Apr. 21, 1998, teaches an apparatus for simultaneously manufacturing a plurality of annularly shaped screen frames. 
     U.S. Pat. No. 5,913,263, issued to Hruska on Jun. 22, 1999, teaches a device using pneumatic devices to stretch printing screens. 
     None of the above inventions and patents, taken either singly or in combination, is seen to describe a manually operated screen-printing apparatus having a pneumatic clamping device for quickly and easily holding or releasing a printing screen as claimed. 
     SUMMARY OF THE INVENTION 
     The present invention is a screen-printing apparatus in which print screens are held in place by a pneumatically actuated clamping device. The screen-printing apparatus may includes at least one screen-holding head, each head having clamped to it an edge of a print screen frame. The apparatus uses switch actuated pneumatic cylinders to cooperatively engage or disengage clamps holding an edge of a print screen frame to the screen-printing apparatus. 
     When a complete set of jerseys for use by an entire sports team, e.g., for hockey or football, is produced, multiple screens having a variety of indicia are needed, necessitating frequent changing of the print screen during production. The screen=printing apparatus of the present invention reduces the time needed to interchange the print screens during production. 
     Accordingly, it is a principal object of the invention to provide a screen-printing apparatus in which an edge of a print screen is held in place by a pneumatically operated clamping device. 
     It is another object of the invention provide an apparatus including a plurality of print screen holding heads mounted on a carousel, each print head having pneumatic clamping devices. 
     It is a further object of the invention to provide an air distribution system that is centrally mounted within a carousel supporting a plurality of print screen holding heads, thereby allowing the carousel to rotate freely about the air supply without entangling the air supply tubes supplying each clamping device. 
     Still another object of the invention is to provide a screen-printing apparatus in which each print screen holding head includes a pair of pneumatic cylinders operated in tandem. 
     It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes. 
     These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a four-head screen-printing apparatus having pneumatic screen frame clamps according to the invention. 
     FIG. 2 is a detailed cross-sectional view of a screen frame clamped by a pneumatic cylinder in accordance with the present invention. 
     FIG. 3 is a front view of a dual cylinder screen head according to the present invention. 
     FIG. 4 is a plan view of the pneumatic distribution system for a four-head screen-printing apparatus according to the present invention. 
     FIG. 5 is a fragmented elevation view of a portion of the pneumatic supply system according to the present invention. 
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is a manual screen-printing apparatus which is modified to include pneumatic cylinders that are manually actuated to engage or disengage clamps that hold an edge of the frame of a respective print screen. 
     FIG. 1 shows a four-head manual screen-printing apparatus, designated generally in the drawings as  10 , having dual cylinders  20  mounted to each of the four print heads  50   a ,  50   b ,  50   c  and  50   d . Although the present modification is shown applied to a screen-printing apparatus having four heads, the modification may be similarly applied to a screen-printing apparatus having any number of print heads. An individual printing screen  28  is removably attached to each head  50   a ,  50   b ,  50   c  and  50   d  by means of a two-part clamping device that that cooperatively engages an edge of a screen-printing frame  22 . The screen-printing frame  22  encloses a screen  28  that is masked to print the desired indicia. Typical indicia include letters and numbers for use in sports-related wearable fabric articles, in which the height of the indicia vary in size from two inches, e.g., for use on the shoulder portion of the fabric article, to twelve inches for the backs of jerseys. 
     Each head  50   a ,  50   b ,  50   c  and  50   d  includes two pneumatic cylinders  20  that operate in tandem to cooperatively engage the edge of screen frame  22  between a movable portion  40  of the two-part clamp and a stationary portion  42  of the clamp. A two-position valve  52  operates the tandem cylinders  20  to either open the clamp or close the clamp, that is, by reciprocating movement of the movable portion  40  of the clamp toward, or away from, the stationary portion  42  of the clamp. 
     A textile or fabric workpiece, such as a T-shirt or jersey, which receives the indicia during the screen-printing operation, is initially placed onto a support platen  12 . The support platen  12  may be illuminated from below by a light source  14 , e.g., by a fluorescent lamp. The platen  12  may itself be mounted onto a support  16  that is movable linearly along the surface of the main body  38  of the screen-printing apparatus  10 . A linear scale on a bar  18  may be provided to assist in aligning the movable platen  12  to the appropriate position on the surface of main body  38  to accurately receive the indicia. 
     During the screen-printing operation, the platen  12  with the textile workpiece placed thereon is first fixed in position. Second, the carousel  70  holding the four heads  50   a ,  50   b ,  50   c  and  50   d , with each head  50   a ,  50   b ,  50   c  and  50   d  having a print screen frame  22  and screen  28  clamped thereon, is rotated, to move the appropriate screen  28  in place above the textile workpiece. Third, the print screen  28  is lowered by pivoting the head  50   a ,  50   b ,  50   c  or  50   d  on its arm  26  until the underside of the screen  28  contacts the exposed surface of the workpiece and is held in this position while screen-printing ink is applied onto the top surface of the screen  28 , and a squeegee (not shown) is then used to evenly distribute the printing ink over and through the screen  28  onto the textile workpiece. 
     After applying the indicia to the workpiece, the head  50   a ,  50   b ,  50   c  or  50   d  and the attached screen frame  22  is then raised to release the textile workpiece. At this point the operator may rotate the carousel  70  to present another print head  50   a ,  50   b ,  50   c  or  50   d  to the workpiece, interchange print screens  28  into the same print head  50   a ,  50   b ,  50   c  or  50   d , or apply the indicia to another workpiece. If no further indicia are required on this workpiece, the textile workpiece is removed from the platen  12  and placed into an oven to bake, thereby fixing the indicia in place on the surface of the textile workpiece. An optional flash heater (not shown) can be used to accelerate setting of the indicia ink composition during the process of screen-printing. 
     FIG. 2 shows one of the two pneumatic cylinders  20  having a piston  30  movable inside the cylinder  20 . The piston  30  is connected to the movable portion  40  of the clamping device through a threaded piston rod  56 . A bushing  36  acts to dampen the action of the movable clamp portion  40  when it travels upward. Preferably the pneumatic cylinder  20  has a cylindrical bore of 1.5 inches, a 2-inch stroke, and a maximum PSI of 1.7 times the line pressure, although the pneumatic cylinder  20  is not limited to these specifications. Any pneumatic cylinder that provides sufficient force to securely clamp the screen frame  22  to the head  50   a ,  50   b ,  50   c  or  50   d  is acceptable. 
     As shown in FIG. 2, a print screen frame  22  is held clamped in place by the pneumatic clamping device of the present invention. A print screen  28  is shown in the figure stretched beneath the underside of frame  22 , the frame  22  being firmly clamped to the head  50   a ,  50   b ,  50   c  or  50   d  when the movable clamp portion  40  holds the frame  22  against the stationary clamp portion  42 . 
     The movable clamp portion  40  is formed from lightweight aluminum stock approximately 0.250-inch thick and is designed to resist deflection due to torque applied to the surface of the movable clamp  40  by the pneumatic cylinders  20 . 
     Each pneumatic cylinder  20  is adjustably mounted on its own support mount  44 , which, in turn, is fastened by bolts to a support bracket  46  formed from 0.250-inch thick aluminum. The support bracket  46  is itself bolted, or otherwise suitably fastened, to the stationary clamp portion  42 , which is formed from 0.125-inch thick steel bent upwards 90 degrees along its length. The stationary clamp portion  42  is fastened (e.g., by welding) to a slotted angle bracket  68 . The two horizontal slots  66  in the slotted bracket  68  permit horizontal alignment of the printing screen frame  22  within print head  50   a ,  50   b ,  50   c  or  50   d.    
     The slotted bracket  68  is fastened to an angle support bracket  62  by fasteners (e.g., bolts) passing through horizontal slots  66  in the slotted bracket  68  and vertical slot  64  in the angle bracket  62 . The printing screen frame  22  can then be aligned vertically on the machine by adjusting the bracket  68  along the vertical slot  64 . The angle support bracket  62  is permanently fastened, such as by welding, to the tubular support  60 , which is slidably received by head support cross member  58 , which is itself welded to head support arm  26 . 
     FIG. 3 shows the tandem pneumatic cylinders  20  for one of the heads  50  with the movable clamp portion  40  in the “clamp open” position. Two pneumatic cylinders  20  are mounted on their respective mounting brackets  44 . Each of the mounting brackets  44  is then fastened to its respective support bracket  46 . The ends of the piston rods  56  of both cylinders are fastened (e.g., by a threaded connection) at separate points along the movable clamp portion  40 . Adjustments are made as necessary to ensure that the movable clamp portion  40  remains horizontally level with respect to the printing screen frame  22  to ensure accurate alignment when using the apparatus  10  and to ensure simultaneous operation of the cylinders  20 . 
     A 2-position, 4-way, normally closed/normally open, detented valve  52  with single-direction throw, the throw having a pinned lever, and with all ports except the exhaust ports having ⅛″ NPT threads, is mounted on its own support bracket  54 . The valve  52  is manually actuated by the lever to simultaneous operate cylinders  20 , causing the movable clamp portion  40  to securely clamp the edge of frame  22 . As disclosed, valve  52  has one air input port, two output ports, and a manual lever, the position of the lever determinative of which of the two output ports is connected to the air supply. Furthermore, valve  52  has integrated exhaust valves, (not shown), which bleed off excess air, allowing smooth motion of the movable clamp portion  40  and guarantee a controlled transition from a “clamp open” position to a “clamp closed” position and vice versa. 
     As shown in FIG. 4, the air distributed to each of the pneumatic cylinders  20  passes through a main supply line  100  into a main distributor  78  that is mounted on the carousel  70 . The air then flows outwardly and horizontally through two arms  76  to the two T-connections  74  at the ends of each arm  76  and into the valve air supply inlet lines  88  for each head. 
     The inlet lines  88  supply air to the inlet port of valve  52  and, depending upon whether the air is directed to the upper portion of cylinder  20 , to clamp the frame  22 , or to the bottom portion of the cylinder  20  to release the clamp, the air flow exits the first or second valve port and is distributed by lines  134  and  132  to a pair of manifolds, e.g. T-connections,  142  and  144 , respectively, to provide simultaneous operation of pneumatic cylinders  20 . 
     Thus, when valve  52  is set to the “clamp open” position, i.e., when releasing the print screen from the clamp, air flows through lines  34  to cause the tandem pistons to move the movable clamp portion  40  upwards, away from the stationary clamp portion  42 . Conversely, to clamp a screen frame  22  in place in a head  50 , the valve  52  is moved to the “clamp closed” position allowing air to flow through lines  32  causing the tandem pistons  56  to extend the movable clamp portion  40  downward cooperatively engaging one edge of frame  22 . Once clamped in place, the print screen can then be used for printing indicia onto a textile workpiece by moving the screen  28  downward onto the textile workpiece through the respective head support arm  26 . 
     FIG. 5 is a view of the main air distribution showing the compressor supply line  102  above the machine and having a quick disconnect connector  98 , which receives male connector stem  94 . Connector  94  has a stationary part and a 360 capable rotation part, permitting air to be continuously supplied into the vertical supply line  100  of the screen-printing apparatus  10  without applying rotational torque on connector  94  or on supply line  102  when carousel  70  is rotated. An air pressure regulator  92 , having a pressure gauge  96 , is used to adjust air pressure in the screen-printing apparatus. Although pressurized air at 60 psi is used in the preferred embodiment, air at any pressure within the operating range of pneumatic cylinders  20  is contemplated herein, as well as from any source which may include an air compressor, a tank of compressed air, or other supply of pressurized air. 
     Although the present embodiment discloses pneumatic cylinders  20  operating to clamp a screen frame  22  to each head  50  of a four-head manually operated screen-printing apparatus, the apparatus is also contemplated for use in any manually operated screen-printing apparatus that requires the ability to quickly and easily replace different printing screens in the screen holding heads of these machines, whether the apparatus has one, two or any number of heads. 
     It is further noted that the valve mounting bracket  54  has a generally S-shaped cross-section (not shown) so as to ensure that valve  52  extends a short distance away from the clamping portion of the head, thereby preventing an operator from inadvertently trapping their fingers or hand in the clamp when actuating the pair of pneumatic cylinders  20 . 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.