Device for Applying a Flexible Halftone Screen Over a Camera Vacuum Platen

This invention relates to devices for applying halftone screens over a camera imaging platen.

Devices are known for causing a flexible halftone screen to be applied to the surface of a vacuum platen. See, for example, U.S. Patent to Schutt et al., U.S. Pat. No. 3,068,748. It is desirable to provide a device for applying the halftone screen which is somewhat simpler than the Schutt device, and is more compact so that the flexible screen is always stored on a single wound up roller and is laid flat upon being unwound without relative motion (rubbing) between the screen and the film positioned upon the screen. It is also desirable to rapidly replace flexible screens in the field.

In accordance with a preferred embodiment of the invention, a roller is rotatably supported upon a movable support frame which is translated back and forth over the surface of the platen. When the movable support frame assumes a first position, the flexible screen is fully wound up and stored about the roller. As the movable support frame is translated across the platen and the roller rotates in a first direction, the screen is unwound and laid flat upon the platen surface. On the other hand, the screen becomes wound up about the roller as the support frame is translated back across the platen. The roller is rotationally spring biased to maintain the screen tightly wound about the roller.

Other objects, features, and advantages of the present invention will become apparent upon the perusal of the detailed description taken in conjunction with the drawings in which:

FIGS. 1 and 2 schematically illustrate a basic principle of the invention;

FIG. 3 illustrates a side view of the roller together with the spring means for maintaining the screen in a tightly wound up condition about the roller; and

FIG. 4 illustrates further details of a preferred embodiment of the invention.

FIG. 1 schematically illustrates one principle of the invention. A vacuum platen 1 is provided having a sheet of film 2 positioned thereupon which is exposed to a focused image of an object on copyboard 3. Roller 4 has the flexible halftone screen wound up thereabout and a terminal portion of screen 6 is mechanically coupled to the frame of the camera at frame portions 7 and 7'. As the roller is translated across the platen in the direction indicated by arrow 8, the screen is laid flat over the platen. At the end of the translation of roller 4, the screen 6 covers film 2 as shown in FIG. 2. As the roller 4 is translated back across the platen in the direction of arrow 9, the screen is thereafter wound up about the roller. Further details of one constructed embodiment are illustrated in FIGS. 3 and 4. Roller 4' is rotatably and detachably coupled to a first movable frame portion 11 and a second movable frame portion 12 by means of detachable coupling device 13 and 14. Lead screws 16 and 16' are provided to translate the movable roller support across the platen. The lead screw or screws may be driven by a motor, not shown in the interest of clarity. A cross bar 18 may be provided to couple the first and second frame portions together. FIG. 2 illustrates terminal screen portion 6' being coupled to mechanical ground at 21. The screen is wound up about the roller in FIG. 2. As the movable roller support is translated across the platen by virtue of the aforementioned lead screws, the screen is applied and removed from the film surface as described hereinabove. A pulley 23, shown in FIG. 2, having grooves therein is provided wherein a flexible wire 24 for example is coupled to the pulley and is positioned within the grooves. The wire extends in a direction parallel to the surface of the platen and is coupled to mechanical ground at 26 via spring 27. This structure rotationally biases the roller in a second direction opposite to the direction of rotation which occurs when the screen is being unwound in a first direction indicated by arrow 29. This arrangement serves to maintain the screen in a tightly wound up condition about the pulley regardless of its position with respect to the surface of the platen. The use of this structure is greatly preferred so that the screen is laid flat over the platen. The spring means, of course, may take numerous forms, but it is preferred that it be of a type which asserts a constant force with respect to the pulley, regardless of the position of the movable roller with respect to the platen. The pulley may be rotatably supported within the first movable frame portion 11 by bearing 31.

The use of a detachable screen roller is commercially significant since the flexible halftone screen may be rapidly replaced in the field. In contrast with the prior art, the screen is compactly stored about the roller. Furthermore, it is laid flat over the platen without rubbing, which is deemed undesirable.

While a preferred embodiment of the invention has been described in detail, the teachings of this invention will readily suggest many other embodiments to those skilled in the art.