Device and method for stretching a screen on a roller frame

#The invention relates to screen printing. In particular, the invention involves a device for rapidly and evenly stretching a screen on a roller frame.

#The widely practiced art of screen printing generally involves the application of inks through taughtly stretched screens or meshes. For this purpose, a screen is typically stretched over, and fixed on, a rectangular (sometimes square) frame. There are two general types of frames which have gained common acceptance in the trade. First, there are frames designed for a single use. These frames are often made of wood. The screen is usually glued to the wood after being stretched over the frame. Second, there are frames which are designed for repeated use. These frames are often referred to as "roller frames" . Each of at least three sides (usually four sides) of a roller frame typically includes a cylindrical roller, a groove running substantially along the length of the roller, a bolt-like end portion which can be torqued by a wrench, and a locking mechanism for controlling the rotational freedom of the roller. One such roller frame is referred to as a Newman Roller.TM., and is sold by Stretch Devices of Philadelphia. Another such roller frame is sold by Diamond Chase Company, Inc. of Huntington Beach, Calif. The present invention involves the second-mentioned type of roller frame, i.e., reusable roller frames.

#Up until now, the conventional method of stretching a screen on a roller frame is a manual process requiring the following steps: (1) the screen is placed in the frame and secured to the frame by urging the mesh into the roller grooves, then inserting a dowel or flexible strip into each of the grooves; (2) the frame is placed on a table with the screen side down; (3) a wrench is applied to a bolt-like end portion of one of the sides of the frame, and torqued, thus stretching the screen; (4) a jam bolt is tightened to prevent the roller from further turning; (5) steps 3 and 4 are repeated sequentially for each of the other sides of the frame; and (6) the frame is then turned over and the tension of the screen is tested. This process is typically repeated two to five times before the proper tension for the screen is achieved. This manual process of stretching a screen on a roller frame usually takes between 5 and 45 minutes, depending on the skill of the operator.

#FIG. 1 is a perspective view of a screen stretching device in accordance with a preferred embodiment of the present invention.

#FIG. 2 is a top view of the device shown in FIG. 1.

#FIG. 3 is a side view of the device shown in FIGS. 1 and 2.

#FIG. 1 shows a preferred embodiment of the present invention. The device includes a table 12 which has a top surface 14 and a rectangular work area 16 defined on the top surface 14. Torsion stations 20a, 20b, 20c and 20d are located at or near the four corners of work area 16. The particular type of torsion station which is employed in the device illustrated in FIG. 1, may also be referred to as a "wrenching station" because the stations employ wrench heads 22a, 22b, 22c and 22d to torque, i.e., cause rotation of the cylindrical rollers which form the sides of roller frame 30. Further details of the device shown in FIG. 1 will now be described with reference to FIGS. 2-5.

#As shown in FIG. 2, roller frame 30 has four sides. Each side of roller frame 30 has a groove, such as 34, running substantially along the entire length of roller 32. The groove is used to fasten the screen to the cylinder before stretching. The screen material is fastened to the cylinder by urging the screen into the groove, then inserting a dowel or flexible strip into the groove. At least one end of roller 32 has an end portion, such as 36, which is configured to be gripped by wrench 22c. Most commonly, roller frames have two end portions on each side of the frame. The end portions are essentially "bolt-like" in that they have opposing flat surfaces which can be gripped by an open ended wrench. Each side of frame 30 also has a locking mechanism (not shown), for example, a "jam bolt" which screws in the end of the roller in the direction parallel with the core of the roller. Tightening of the jam bolt essentially locks or prevents further rotation of the cylinder.

#Frame 30 is held in place on work area 16 by frame stops 40a, 40b, 40c and 40d. Each of the wrenching stations has a slot 44a, 44b, 44c and 44d through which wrench heads 22a, 22b, 22c and 22d , respectively, connect to shaft structures which will be described in more detail below. Note that slots 44a, 44b, 44c and 44d are actually larger than what is shown in FIG. 2. The bottom view (FIG. 4) shows the actual relative dimensions of the slots. In FIG. 2, portions of slots 44b, 44c and 44d are covered by station plates 46b, 46c and 46d. Each torsion station has a station plate 46a, 46b, 46c and 46d. However, station plate 46a of station 20a (also referred to as station #1) is different from the other station plates because it is fixed, i.e., non-movable with respect to its X-Y position on top surface 14 and work area 16. Station plate 46b at station 20b (also referred to as station #2) is movable in the Y direction, but not in the X direction. In a similar fashion, station plate 46c of station 20c (also referred to as station #3) is movable in both the X direction and the Y direction. Station plate 46d of torsion station 20d (also referred to as station #4) is movable in the X direction, but not the Y direction.