BACKGROUND OF THE INVENTION The present invention deals with equipment used to process photographic film. More particularly, the present invention deals with rollers mounted to a roller rack for use in film processing.

A more detailed description of film processors is set forth in the Kulus U.S. Patent No. 4,937,607. It is common for sheets of film to be moved or transported through film processors by rollers. The rollers are arranged so that, as the developer or processor is activated, the rollers begin to turn. The rollers are positioned so that, as they turn, sheets of film are gripped by the rollers and transported through various processing steps.

For example, a film processor typically includes a developer chemical bath. The sheets of film to be developed are moved through the bath. The chemical reaction produced when the film is introduced in the chemical bath develops the film.

In order to transport the film through the chemical bath, a roller rack is typically mounted within the developer solution. Several pairs of rollers are arranged within the roller rack. Each pair is arranged so that the surfaces of the rollers in the pair are in contact with one another. The sheets of film to be exposed to the chemistry are inserted between a first pair of rollers. As the first pair of rollers turns, the rollers grip and transport the film down into the chemical bath. Several other sets of rollers transport the film through the bath.

A final set of rollers is typically mounted for receiving and removing the sheets of film from the chemical bath. As the rollers in the various sets grip

SUBSTITUTE SHEET

and transport the sheets through the chemical bath, they also act to exert pressure on both sides of the film rolling across the entire surface of the film thereby removing the chemicals from the film. In many types of developers, the amount of time which the film is exposed to the chemical bath determines the degree to which the film is developed. Also, in many chemistries, such as lith chemistry (which is widely used in the graphic arts industry) the byproducts of the chemical reaction used to develop the film tend to retard further reaction. Therefore, if chemical byproducts are left on the film when the film is exposed to another chemical treatment or as the film is passed through the chemical bath, this will lead to an undesirable retardation of the chemical reaction used to develop the film.

Also, one type of film processor includes a developer tank holding developer chemicals, a fix tank holding fix chemicals, and a wash tank holding a wash. If developer chemicals are carried by the film into the fix tank, the developer and fix chemicals tend to neutralize one another resulting in poor quality film processing.

A common problem in prior film processors resulted from the inability of manufacturers to fabricate rollers that were perfectly cylindrical. For example, as the roller is manufactured, it may obtain an arced shape. Further, even after the roller is manufactured, it may be bent so that it is no longer perfectly straight and cylindrical. When such a non- cylindrical roller is used to transport film through the chemical bath, even if a corresponding roller in the roller pair used to grip and transport the film from the chemical bath is perfectly cylindrical, the result is

nonuniform contact by the rollers across the surface of the film.

Although this nonuniform contact may be adequate to transport the film from the chemical bath, the nonuniform contact does not completely remove the chemical byproducts which adhere to the film as it is moved through the bath. This results in portions of the film having the byproducts removed, and other portions having the chemical byproducts still clinging to the film.

The chemical byproducts formed and/or other chemicals that diffuse out of the film which remain clinging to the film from the chemical reaction retard the desired chemical reaction on those portions of the film where the byproducts have adhered to the film. The result is that, on the portions of the film where no byproducts remain from the previous chemical reaction, the film is developed to a desired degree. However, on those portions of film where the byproducts have adhered, and the desired chemical reaction is retarded, the film is under developed.

This non-uniformity or imperfection in development is known by several names including "roller marks", "artifacts", "banana marks" or "film faults". However, they all result from nonuniform development of the film and appear as lighter or darker marks across the surface of the developed film.

In the past, some attempts have been made to achieve better transport of the film through the chemical bath. Such attempts included the use of soft foam rubber rollers in transporting the film. However, these soft rollers are extremely expensive relative to other rollers, and require much more maintenance.

SUMMARY OF THE INVENTION

The present invention includes an apparatus suitable for use in film processing. A roller rack has one or more pairs of rollers mounted in the roller rack. The rollers are positioned to transport film during film processing. Each roller has a center diameter corresponding to an approximate center of the rollers along the length of the roller. Each roller also has first and second end diameters corresponding to first and second ends of the rollers. The center diameter of at least one of the rollers is larger than the first and second end diameters of that roller.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a diagram of one typical film processor.

FIG. IB shows a roller rack suitable for use in processing film.

FIG. 2 shows a pair of rollers known in the prior art. FIG. 2A shows a pair of rollers implementing one embodiment of the present invention.

FIG. 2B shows the rollers of FIG. 2A in a position rotated approximately 180° from that shown in FIG. 2A. FIG. 2C shows a pair of rollers implementing a second embodiment of the present invention.

FIG. 2D shows a pair of rollers implementing a third embodiment of the present invention.

FIG. 2E shows a pair of rollers implementing a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A shows one example of a typical film processor 3. Processor 3 includes processing liquid tanks 4, 5 and 6 and a dryer 7. Photosensitive sheets

are transported through processor 3 along path 8.

During processing, the photosensitive sheets follow path 8 between a plurality of roller pairs 9 located in roller racks in various processing stations such as processing liquid tanks 4, 5 and 6, as well as dryer 7. The various roller pairs 9 form a transport system for transporting the sheets of photosensitive material through processor 3, and define path 8 which extends through processor 3. In one typical type of photo processor, liquid tank 4 contains developer solution (a chemical solution for reducing exposed silver ions) , liquid tank 5 contains fix solution (a chemical solution for removing undeveloped silver ions) , and liquid tank 6 contains a wash solution. A photosensitive sheet is sequentially passed through developer, fix and wash solutions to chemically process and develop the photographic images latent in the film. The photosensitive sheet is then passed through a dryer portion in a processor where, in this preferred embodiment, tempered air is directed at the sheet of film from both sides so that the sheet is dried for additional handling. It should be noted that FIG. 1A merely shows one embodiment of a typical processor 3. Other processors may include more processing liquid tanks, more roller pairs, or other processing steps.

FIG. IB shows a typical roller rack, generally shown at 10, used in processing film. Roller rack 10 includes a frame-like structure 12 and two sets of rollers. Typically, a roller rack may include four or more sets of rollers for guiding and transporting the film. However, for the sake of simplicity, the present invention will be described with respect to two sets. A first set of rollers is shown at 14 and a second set

of rollers is shown in phantom at 15 in FIG. IB. Roller rack 10 is suitable for use in a tank 13 which may be developer tank 4, fix tank 5 or wash tank 6 shown in FIG. 1A. The first set of rollers 14 includes roller 16 and roller 18. Rollers 16 and 18 each have a first end, 16A and 18A, respectively. Similarly, rollers 16 and 18 each have a second end, 16B and 18B, respectively. Rollers 16 and 18 are mounted at their first and second ends to rack 12.

In this preferred embodiment, rollers 16 and 18 are mounted to rack 12 in a similar fashion at their first ends and second ends. Therefore, for clarity's sake, the mounting arrangement of rollers 16 and 18 will be described only with respect to their second ends 16B and 18B.

Rollers 16 and 18 are each provided with mounting tabs 20 and 22, respectively. Mounting tabs 20 and 22 are inserted in slot 24 in rack 12. Tabs 20 and 22 are also engaged by retaining spring 26. Retaining spring 26 urges tabs 20 and 22, and consequently the second ends 16B and 18B of rollers 16 and 18, towards one another. A similar retention spring is mounted on the first ends of rollers 16 and 18. Thus, rollers 16 and 18 are urged into contact with one another within roller rack 12. Rollers 16 and 18 are driven for rotation by a motor or gear train (not shown) during film processing.

The second set of rollers 15 is mounted within slot 28 in rack 12 and is shown in phantom in FIG. IB. Set 15 includes rollers 17 and 19 and is mounted in a similar fashion to rollers 16 and 18.

During film processing, sheets of film such as sheet 30, (which may be typically from 20 square inches

in size to several thousand square inches in size) are first fed down into the chemical bath in rack 12 between rollers 17 and 19. As rollers 17 and 19 rotate during the developing process, they grip film 30 and transport it into the chemical bath in rack 12 along dashed arrow 21. Then the film is guided up from the chemical bath to the bottom side of rollers 16 and 18. As rollers 16 and 18 rotate, they grip film 30 and transport it from the chemical bath in rack 12 out of rack 12 into, for example, another chemical bath or another processing station.

Where the chemical bath contains developer chemicals, film 30 is moved through the chemical bath at a desired rate so that it is exposed to the chemicals for a desired amount of time. The chemicals in the chemical bath react with the film to develop the film.

Rollers 16 and 18 not only act to transport film 30 from the chemical bath, but also to roll across the surface of film 30 and thereby remove any chemicals or chemical reactants which are still clinging to film 30 from the chemical bath. By repeatedly moving film 30 through various chemical baths and washes, the film is developed to a desired extent.

FIG. 2 shows a common problem with prior art rollers. Rollers 32 and 34 are prior art rollers which are ideally formed as perfect cylinders. However, due to inaccuracies in forming the rollers, or some type of post-forming damage, roller 34 has become bent. It should be noted that the bend shown in FIG. 2 is typically on the order of one to ten thousandths of an inch from cylindrical. However, the deformation in roller 34 has been greatly exaggerated in FIG. 2 for the purpose of clarity.

If rollers 32 and 34 were used as rollers 16

and 18 shown in FIG. 1, problems in developing would occur. Since the ends of roller 32 and 34 are in contact, film 30 would be gripped between rollers 32 and 34 and transported through the chemical bath. However, since roller 34 is deformed from an ideal cylindrical shape, and since a gap 36 appears between rollers 32 and 34, rollers 32 and 34 would not uniformly contact the surface of film 30 along the length of the rollers. Thus, rollers 32 and 34 would be at least partially ineffective in uniformly removing chemical byproducts from film 30 which cling to film 30 as it proceeds through the chemical bath.

Since chemical byproducts of chemical reactions, particularly with lith chemistry which is widely used in film processing for graphic arts, tend to retard the chemical reaction, the byproducts which rollers 32 and 34 fail to remove from film 30 tend to retard further chemical reaction in the developer bath.

This results in the surface of film 30 being exposed to nonuniform chemical reactions. Therefore, those portions of film 30 upon which the chemical byproducts remain tend to be developed to a different degree than those areas from which all of the byproducts are removed. This nonuniform development causes artifacts or film faults in the finally developed film product.

Further, rollers 32 and 34 can be 26 inches long, 48 inches long or even longer. Thus, placement of retention springs around the mounting tabs on the ends of rollers 32 and 34 does not remedy the problem of having a gap 36 between the centers of rollers 32 and 34. While the ends of roller 32 and 34 are urged into contact with one another throughout rotation of rollers 32 and 34, the centers of the rollers form gap 36 for at least a portion of the rotation of rollers 32 and 34.

FIG. 2A shows one embodiment of the present invention. FIG. 2A shows a pair of rollers including a new roller 38 implementing the present invention, as well as deformed roller 34. Roller 38 has a first end 38A, a second end 38B and a center 38C. In this preferred embodiment, the diameters of roller 38 at its ends, 38A and 38B, are approximately equal. In addition, the diameter at the center of 38C, is larger than the diameters at ends 38A and 38B. In other words, roller 38 is generally formed as a crowned roller.

The crown on roller 38 is adequate to fill the deformation in roller 34. Further, when the rollers rotate approximately 180°, FIG. 2B shows the position of rollers 34 and 38. Without retention springs urging the mounting tabs or rollers 34 and 38 together, ends 34A and 38A would separate as would ends 34B and 38B. However, retention springs, such as retention spring 26 discussed with reference to FIG. IB, urge ends 34A and 38A, as well as 34B and 38B together. The retention springs effectively bend roller 34 over the crown on roller 38.

Thus, when retention springs hold the ends of rollers 34 and 38 together, there is uniform contact along the axial length of rollers 34 and 38 throughout the rotation of rollers 34 and 38. Hence, as rollers 34 and 38 grip film 30 and transport it through the chemical bath, rollers 34 and 38 remove in a uniform manner chemical byproducts clinging to film 30. Therefore, the chemicals in the chemical bath are applied to film 30 in the desired manner. This substantially eliminates any nonuniform development of film 30 due to remaining chemical byproducts because of deformed or bent rollers.

FIG. 2C shows a second embodiment of the present invention including roller 42. Roller 42 has an exterior surface which is convex in shape. Thus, it has a center diameter which is larger than its end diameters.

FIG. 2D shows a third embodiment of the present invention. FIG. 2D includes rollers 44 and 46. In the embodiment shown in FIG. 2D, both rollers 44 and 46 are crowned rollers formed in bi-conical shapes (i.e., where the bases of the cones are co-planar in plane 47) .

FIG. 2E shows a fourth embodiment of the present invention. FIG. 2E includes roller 48. Roller 48 has an exterior shaped as a double taper (i.e., where the bases of the cones are in different planes 49 and 51) . Thus, it has a center diameter larger than its end diameters.

All of the embodiments shown in FIGS. 2A, 2C,

2D and 2E help to eliminate non-uniform development caused by deformed rollers. It should also be noted that pairs of rollers with any of the shapes shown could be used as a roller set.

Although the rollers shown in FIGS. 2A, 2C, 2D and 2E can vary in length, they are typically 26 inches or 48 inches. For a 26 inch long roller, it has been found that a very effective crown is 4.0 mils. It should be noted that by indicating the crown is 4.0 mils, that means that the center diameter on the roller is larger than the end diameters by an amount equal to two times the crown. In other words, for a 4.0 mil crown, the center diameter of the roller would be 8 mils larger than the end diameters.

In addition, for a commonly used (but less typical) roller of 48 inch length, substantially

effective crown measurements are in a range from approximately 5 mils to 15 mils with the optimum being approximately 10 mils.

It has been observed that the optimum crown, not only varies with the length of the roller, but it also varies with the roller stiffness and the amount of pressure used to hold the mounting tabs on the rollers together. In other words, the optimum crown on the roller depends on the spring tension in retention spring 26. As the spring tension increases, the optimum crown also increases. For the ranges of optimum crown given above, the spring tension was varied between approximately 100 and 1000 grams.

Also, the size of the crown is a function of the crown shape. For example, with the double-taper configuration shown in FIG. 2E, less crown is required to achieve desired performance.

It should also be noted that the present invention, although described in this specification with reference to lith chemistry, can also be used very effectively with other, more recent hybrid-type chemistries.

CONCLUSION By using the present invention, substantially uniform contact is achieved between film 30 and the rollers mounted in roller rack 12. The uniform contact essentially provides complete removal of chemical byproducts and other soluble chemicals that diffuse from the film emulsion clinging to film 30 from the chemical bath in tank 13, thus providing for uniform development of film 30. The more uniform development effectively eliminates roller marks, or film faults from the film providing a better end product. Also, the crowned rollers of the present invention are valuable for

unifor ly removing liquid carried into a dryer used in film processing, and in removing that liquid carried from tarik-to-tank in the processor.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.