Patent Application
20050285923
The present invention relates generally to an apparatus and method for processing an imaging material, and more specifically an apparatus and method for thermally developing an imaging material employing varying spacing between rollers forming a transport path.
Photothermographic film generally includes a base material coated on at least one side with an emulsion of heat sensitive materials. Once the film has been subjected to photo-stimulation by optical means (e.g., laser light), or “imaged”, the resulting latent image is developed through the application of heat to the film. In general, the uniformity in the density of a developed image is affected by the manner in which heat is transferred to the emulsion of heat sensitive material. During the developing process, uneven contact between the film and supporting structures can result in non-uniform heating of the film which, in-turn, can result in an uneven image density and other visual artifacts in the developed image. Therefore, the uniform transfer of heat to the heat sensitive materials during the developing process is critical in producing a high quality image.
Several types of thermal processing machines have been developed in efforts to achieve optimal heat transfer to sheets of photothermographic film during processing. One type of thermal processor, commonly referred to as a “flat bed” thermal processor, generally comprises an oven enclosure within which a number of evenly spaced rollers are configured so as to form a generally horizontal transport path through the oven. Some type of drive system is employed to cause the rollers to rotate, such that contact between the rollers and a piece of imaged film moves the film through the oven along the transport path from an oven entrance to an oven exit. As the film moves through the oven, it is heated to a required temperature for a required time period necessary to optimally develop the image.
While flat-bed type thermal processors are effective at developing photothermographic film, variations in image density can occur as the film moves through the oven. For instance, as a piece of film is transferred from one roller to the next, the lead edge can butt or “stub” into the next roller along the transport path until it eventually rides over the roller and is moved on to the next downstream roller. When the film stubs into a downstream roller, the force, although small, can be sufficient to cause a change in the velocity of the film as it moves along the transport path. Depending on the films rigidity, this velocity change may cause the film to either lift off from or to remain too long in contact with the surface of preceding rollers along the transport path and cause those areas of the film proximate to the roller surfaces to be heated differently than adjacent areas. A less rigid film may lift off from the roller surface and result in less heating to such areas than adjacent areas, while a more rigid film may remain for longer than a desired time on the roller surface and result in more heating to such areas than adjacent areas. In another instance, as the film moves along the transport path, the trailing edge may not maintain a desired contact with the roller surfaces and also in uneven heat transfer to the trailing edge.
Such non-uniform heating can produce variations in image density in the developed image which appear in the form of visible bands across the film. This effect is commonly referred to as “cross-width” or “cross-web” banding. Too much heating can result in “dark” bands, while too little heating may result in “light” bands. Furthermore, because the rollers are evenly spaced, the banding effect is reinforced at the same locations on the film as it moves from roller to roller along the transport path, and thus becomes increasingly visible as the film is processed.
Such cross-web banding is of particular concern in thermal processors employing heated rollers, such as that described by U.S. patent application Ser. No. ______ entitled “Flat Bed Thermal Processor Employing Heated Rollers”, (Kodak Docket No. 87968/SLP) filed on Jun. 22, 2004, assigned to the same assignee as the present application, and herein incorporated by reference. It is also more of a concern with rollers forming an initial portion of the transport path, as the difference in heat transfer to the film caused by its being lifted from or stalling on the roller surfaces is lessened as the film nears a desired developing temperature along the latter portions of the transport path.
It is evident that there is a continuing need for improved photothermographic film developers. In particular, there is a need for a flat bed type thermal processor having a roller system that substantially eliminates the above described cross-web banding effect.
In one embodiment, the present invention provides a thermal processor for thermally developing an image in an imaging material. The thermal processor includes an oven and a plurality of rollers positioned to form a transport path and, through contact with the imaging material, configured to move the imaging material through the oven along the transport path. Each roller has an initial contact point and a final contact point with the imaging material as the imaging material moves along the transport path. A spacing between the rollers is varied such that a distance between a final contact point and an initial contact point of at least a first pair of rollers along the transport path is different from a distance between a final contact point and an initial contact point of at least a second pair of consecutive rollers along the transport path.
By varying the spacing between consecutive pairs of rollers along transport path, different areas of the imaging material are in contact with upstream rollers when a leading edge of the imaging material contacts a next downstream roller. As a result, the present invention results in more uniform heat transfer to the imaging material and, thus, improved image quality, since the same area(s) of the imaging material are not repeatedly separated from or stalled on the surface of an upstream roller each time the imaging material passes from the upstream roller to a downstream roller.
These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other.
The following is a detailed description of the preferred embodiments of the invention, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several figures.
Reference is made to U.S. patent application Ser. No. 10/815,027 entitled “Apparatus and Method For Thermally Processing An Imaging Material Employing a Preheat Chamber,” filed on Mar. 31, 2004, assigned to the same assignee as the present application, and herein incorporated by reference.
Reference is made to U.S. patent application Ser. No. ______ entitled “Flat Bed Thermal Processor Employing Heated Rollers”, (Kodak Docket No. 87968/SLP) filed on Jun. 22, 2004, assigned to the same assignee as the present application, and herein incorporated by reference.
An upper group of rollers 44 and a lower group of roller 46, each having a cylindrical surface 48 and a rotational axis 50, are rotatably mounted to opposite sides of enclosure 34. In one embodiment, a portion of upper rollers 44 and lower rollers 46 include internal heating elements 52, as described by previously incorporated U.S. patent application Ser. No. ______ entitled “Flat Bed Thermal Processor Employing Heated Rollers”, (Kodak Docket No. 87968/SLP) filed on Jun. 22, 2004. The rollers 44 of the upper group and the rollers 46 of the lower group are staggered horizontally from one another and are vertically offset so as to overlap a horizontal plane, such that rollers 44 from the upper group and rollers 46 from the lower group alternate to form a sinusoidal-like transport path 54 through oven 35. One or more of the rollers 44 and 46 can be driven such that contact between the cylindrical surfaces 48 of rollers 44 and 46 moves imaging material 32 along transport path 54. A thermal processor having a similar roller configuration is described by U.S. Pat. No. 5,869,860 (Struble et. al.), which is herein incorporated by reference.
Rollers 44 and 46 are horizontally spaced such that a horizontal distance (A1) 56 between the rotational axes 50 of the pair consecutive rollers 46a and 44a is different from a horizontal distance (A2) 58 between the rotational axes 50 of the next pair of consecutive rollers 44a and 46b. Similarly, a horizontal distance (A3) 60 between the next pair of consecutive roller 46b and 44b is different from both A156 and A258. Thereafter, the horizontal distances between the rotational axes of each of the remaining consecutive pairs of rollers 44 and 46 along transport path 54 are substantially equal to A360. In one embodiment, distance A156 is less than distance A258, and distance A360 is less than distance A258 but greater than distance A156. In one embodiment, the horizontal distance between rotational axes of any given pair of consecutive rollers is different from the horizontal distance between rotational axes of any other given pair of consecutive rollers. As will be more fully illustrated by
Imaging material 32 enters oven 35 at entrance 36 at an ambient temperature. As imaging material 32 moves along transport path 54, imaging material 32 is initially heated by upper and lower heat sources 40a and 40b, and by internally heated rollers 46a, 44a, 46b, and 44b, with the greatest amount of thermal energy transferred to imaging material 32 being provided by internally heated rollers 46a, 44a, 46b, and 44b. Since the temperature difference between imaging material 32 and oven 35 decreases as imaging material 32 moves through oven 35, the majority of thermal energy transfer to imaging material 32, and thus the greatest rate of temperature increase of imaging material 32, occurs during this initial period. As imaging material 32 nears the desired temperature, the amount of heat transferred to imaging material 32 is substantially reduced. As such, non-internally heated rollers 46c, 44c, 46d, 44d, and 46e essentially move imaging material 32 the remaining distance along transport path 54 to exit 38, while upper and lower heat sources 40a and 40b maintain the non-internally heated rollers 46c, 44c, 46d, 44d, and 46e, and imaging material 32 at the desired temperature.
While the heating of imaging material 32 is described above with respect to an initial portion of the rollers including an internal heating element, transfer of thermal energy to the imaging material would be similar even if none of the rollers included internal heating elements. In such an instance, as illustrated below by
As imaging material 32 moves along transport path 54, imaging material 32 is successively transferred from an upstream roller to a downstream roller. When imaging material 32 is transferred from the upstream roller to the downstream, from roller 44b to roller 46c for example, a leading edge 61 of imaging material 32 may “stub” into downstream roller 46c before traveling over the cylindrical surface 48 of downstream roller 46c and continuing on to the next roller 44c. When leading edge 61 stubs into downstream roller 46c, the impact can cause a change in the velocity of imaging material 32 as it moves along transport path 54. Depending on the rigidity of imaging material 32, the velocity change may cause imaging material 32 to lift from or to stay too long in contact with upstream roller 44b, potentially resulting in an “uneven” heat transfer to imaging material 32. Additionally, as a trailing edge 62 of imaging material 32 is transferred from an upstream roller to a downstream roller, it may not maintain a desired contact with the upstream roller and thus, may also result in uneven heat transfer to trailing edge 62. Such incidences of uneven heat transfer can occur each time imaging material 32 passes from one roller to the next along transport path 54.
By varying the horizontal distances between the rotational axes of consecutive pairs of rollers along transport path 54, particularly along the initial portions of transport path 54 where the largest amount of thermal energy transfer to imaging material 32 occurs, thermal processor 30 according to the present invention, reduces cross-web banding effects by causing different areas of imaging material 32 to be in contact with an upstream roller, such as roller 46b, when leading edge 61 “stubs into” a next downstream roller, such as roller 44b. Varying the horizontal distances between the rotational axes of rollers in this fashion results in more uniform heat transfer to imaging material 32 and, thus, improved image quality, since the same area(s) of imaging material 32 are not repeatedly in contact with the surface of an upstream roller each time the imaging material passes from the upstream roller to a downstream roller.
As described in U.S. Pat. No. 5,869,860 (Struble et al.), bending imaging material 32 through use of a sinusoidal-like transport path 54 increases the “stiffness” of imaging material 32 and reduces the occurrence of thermally-induced wrinkles and resulting variations in image density of developed imaging material 32. In order to maximize the reduction of such wrinkles, an initial bend should be introduced to imaging material 32 as soon as possible after it enters oven 35 at entrance 36. With this in mind, the closer roller 44a is positioned to initial roller 46a, and thus the smaller distances A158 and D163 are made, the sooner the initial bend will be introduced to imaging material 32.
However, if second roller 44a is positioned too close to initial roller 46a, a bend having an undesirable “stub angle” may be created in imaging material 32 relative to third roller 46b. A stub angle (θ) is illustrated at 80 in
As such, in one embodiment, distance Al 56 between initial roller 46a and second roller 44a is based on a maximum allowable stub angle. In one embodiment, roller 44a is positioned relative to roller 46a such that distance A156 and associated distance D163 result in a stub angle 80 substantially equal to, but not in excess of the maximum allowable stub angle. In one embodiment, distance A156 and associated distance D163 are respectively less than distance A360 and associated distance D374, while distance A360 and associated distance D374 are respectively less than distance A258 and associated distance D268. In one preferred embodiment, spacing between rollers 46a, 44a, and 44b is adjusted such that distances A156, A258 and A360, respectively, are substantially equal to 11 millimeters, 18 millimeters, and 16 millimeters.
As described above, only the horizontal distances (i.e. A1, A2, and A3) between rotational axes 50 of rollers 44 and 46 have been described as being varied in order to cause different areas of imaging material 32 to be in contact with an upstream roller when leading edge 61 contacts the next downstream rollers (the “contact areas”) so as to reduce potential cross-web banding effects. However, it should be noted that variations in the “contact areas” of imaging material 32 can also be achieved by varying an amount of vertical overlap VO 82 between upper rollers 44 and lower rollers 46. Such vertical overlap may be adjusted for each roller 44, 46 along transport path 54. However, as described by the Struble et al. Patent, changes in vertical overlap VO 82 may be affected by other factors, such as the size and type of imaging material 32, and also by stub angle 80 limitations. Consequently, variations in the “contact areas” of imaging material 32 achieved by varying vertical overlap 82 may not be as great as those achieved by varying the distances between rotational axes 50 of rollers 44 and 46. Nonetheless, variations in the “contact areas” of imaging material 32 can be achieved by varying the distances between rotational axes 50 of rollers 44, 46 and/or by varying the amount of vertical overlap 82 between upper rollers 44 and lower rollers 46. Furthermore, such variations in “contact areas” may also be achieved by varying the outside diameters of rollers 44 and 46.
Preheat chamber 134 has an entrance 136 and an exit 138, and includes upper and lower heat sources, 140a and 140b, and a plurality of upper rollers 144 and lower rollers 146. In a fashion similar to that of dwell chamber 34, the plurality of upper rollers 144 and lower rollers 146 are rotatably mounted to opposite sides of preheat chamber 134 and positioned in a spaced relationship so as to contact imaging material 32 and to form a transport path 54 through preheat chamber 134 from entrance 136 to exit 138. Upper rollers 144 are horizontally offset from lower rollers 146 and vertically positioned such that upper rollers 144 and lower rollers 146 overlap a horizontal plane such that transport path 54 through preheat chamber 134 is sinusoidal-like in form. One or more of the rollers 144 and 146 can be driven such that contact between rollers 144 and 146 and imaging material 32 moves imaging material 32 through preheat chamber 134. In one embodiment, a portion of upper rollers 144 and lower rollers 146 include an internal heater 152.
Also in a fashion similar to that of dwell chamber 34, the rotational axes 150 of rollers 144 and 146 are spaced at varying distances along transport path 54. Distance A156 separates the rotational axes of the first pair of consecutive rollers, distance A258 separates the second pair of consecutive rollers, a distance A4162 separates the third pair of consecutive rollers, a distance A5164 separates a fourth pair of consecutive rollers, and distance A360 separates the remaining pairs of consecutive rollers.
Upper and lower heat sources 140a and 140b of preheat chamber 134 respectively include heat plates 166 and 168 and blanket heaters 170 and 172, and upper and lower heat sources 40a and 40b of dwell chamber 34 respectively include heat plates 174 and 176 and blanket heaters 178 and 180. Blanket heaters 170, 172, 178 and 180 can be configured with multiple zones, with the temperature of each zone being individually controlled. In one embodiment, as illustrated, heat plates 166, 168, 174, and 176 are shaped so as to partially wrap around a circumference of rollers 44, 46, 144, and 146 such that the rollers are “nested” within their associated heat plate, which more evenly maintains the temperature of the rollers.
As imaging material 32 moves through preheat chamber 134, upper and lower heat sources 140a and 140b and rollers 144, and 146 having internal heaters 152, heat imaging material 32 from an ambient temperature to substantially the first temperature. As imaging material 32 moves through dwell chamber 34, upper and lower heat sources 40a and 40b and rollers 44, and 46 having internal heaters 52, heat imaging material 32 from substantially the first temperature to substantially the second temperature. By varying the spacing between rollers of preheat chamber 134 and dwell chamber 34, particularly where the greatest amount of thermal energy is transferred to imaging material (i.e. those portions of transport path 54 formed by rollers having internal heaters 52, 152), thermal processor 30 as illustrated by
While rollers 144 and 146 of preheat chamber 134 are described as being variably spaced along transport path, varying of the spacing between rollers of preheat chamber 134 is not as critical as varying the spacing between the rollers of dwell chamber 34 since the temperature of preheat chamber 134 is less than a development temperature of imaging material 32 and thus, substantially no development takes place in preheat chamber 134. As such, in one embodiment, rollers 144 and 146 can be evenly spaced along transport path 54 such that distances A1, A2, A3, A4, and A5 are substantially equal distances.
A plurality of generally parallel rollers 244 (ten are shown), each having a cylindrical surface 248 and a rotational axis 250, are rotatably mounted to opposite sides of enclosure 34. Rollers 244 are spaced such that cylindrical surfaces 248 form a generally horizontal transport path 254 through oven 35 from entrance 36 to exit 38. A roller 256 forms a nip with a first roller of the plurality 244 at oven entrance 36. One or more of the rollers 244, 256 can be driven such that cylindrical surfaces 248 frictionally engage imaging material 32 to move imaging material 32 through oven 35 along transport path 254. It should be noted that, unlike the thermal processors illustrated by
Rollers 244 are horizontally spaced such that horizontal distances A1 through A9, illustrated at 258, between the rotational axes 250 any consecutive pair of rollers 244 is different from any other consecutive pairs of rollers 244. By varying the horizontal distances between the rotational axes 250 of consecutive pairs of rollers 244 forming transport path 254, thermal processor 30 according to the present invention reduces cross-web banding effects by causing different areas of imaging material 32 to be in contact with an upstream roller when leading edge 61 contacts the next downstream roller.
The invention has been described in detail with particular reference to a presently preferred embodiment, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.
