Patent Application
20050280689
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 heating of rotatable members which form 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. Non-uniform heating can result in uneven density of the developed image. Uneven contact between the film and any supporting structures during the development process can also produce visible marks, patterns, and other visual artifacts on the developed image. Therefore, the uniform transfer of heat to the heat sensitive materials is critical in producing a high quality image.
Several types of processing machines have been developed in efforts to achieve optimal heat transfer to sheets of photothermographic film during processing. One type of processor, commonly referred to as a “flat bed” processor, typically comprises an oven enclosure within which a number of spaced rollers are configured so as to form a generally horizontal transport path through the oven, wherein some type of heat source is positioned along and in proximity to the transport path. In one configuration, a plurality of upper rollers and a plurality of lower rollers are staggered in a horizontal direction and slightly overlap a horizontal plane in a vertical direction to form a slightly sinusoidal, or corrugated, transport path through the oven. A drive system is employed to cause the rollers to rotate and move a piece of film through the oven along the transport path from an oven entrance to an oven exit. As the film moves along the transport path, the heat source heats the film to a temperature necessary to develop the image.
While flat bed type processors are effective at developing photothermographic film, variations in image density and can result from temperature variations between the rollers. Prior to any photothermographic film entering the oven, the rollers, along with other internal surfaces of the oven, are heated by the heat source to a desired temperature. As a piece of photothermographic film enters the oven and contacts the rollers, heat is transferred to the photothermographic film from both the heat source and from contact with the surfaces of the rollers. However, as heat is transferred from the rollers to the photothermographic film, the surfaces of the rollers can drop below the desired temperature and, consequently, begin to transfer less heat to the imaging material. This is particularly true of rollers that form an initial portion of the transport path.
As a result, a leading portion of a piece of photothermographic film may receive more heat than a trailing portion of the piece of photothermographic film. Likewise, later pieces of photothermographic film may receive less thermal energy from the rollers than earlier pieces of photothermographic film transported through the oven. As a result, heat is not uniformly transferred to the photothermographic film and, consequently, image density may vary between consecutively developed pieces of photothermographic film and even within a single piece of photothermographic film.
It is evident that there is a continuing need for improved photothermographic film developers. In particular, there is a need for a thermal processor that substantially reduces variations in image density resulting from variations in roller temperatures as described above.
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 rotatable members. The plurality of rotatable members are positioned to form a transport path, and through contact with the imaging material, are configured to move the imaging material through the oven along the transport path. At least one of the rotatable members includes an internal heater such that the at least one rotatable member heats the imaging material as the imaging material moves along the transport path. The internal heater is controllable to provide an amount of thermal energy based on processing parameters associated with the imaging material.
By providing thermal energy to the rotatable members, the rotatable members are better able to maintain a consistent temperature as is thermal energy is transferred from the rotatable members to the imaging material as the imaging material moves through oven along the transport path. As a result, temperature variations between the rotatable members is reduced, which substantially reduces variations in image density caused by non-uniform heat transfer to the imaging material. Additionally, by heating the rotatable members, thermal energy transferred from the rotatable members to the imaging material can replenished more quickly, which can increase the throughput of the thermal processor.
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.
A plurality of upper rollers 44 and a plurality of lower rollers 46 are rotatably mounted to opposite sides of enclosure 34 and positioned in a spaced relationship so as contact imaging material 32 and to form a transport path 48 through oven 35. One or more of the rollers 44 and 46 can be driven such that contact between rollers 44 and 46 and imaging material 32 moves imaging material 32 through oven 35 along transport path 48 from entrance 36 to exit 38. A portion of upper rollers 44, illustrated as rollers 44a and 44b, and a portion of lower rollers 46, illustrated as rollers 46a and 46b, include an internal heater 50, wherein each internal heater 50 provides thermal energy based on processing parameters associated with imaging material 32. Processing parameters associated with imaging material 32 can include data indicative of the type, dimensions, and age of imaging material 32, as well as data indicative of the speed at which imaging material 32 will be transported through oven 35.
Imaging material 32 enters oven 35 at entrance 36 at an ambient temperature. As imaging material 32 moves along transport path 48, imaging material 32 is initially heated by upper and lower heat sources 40a and 40b and by heated rollers 44a, 44b, 46a, and 46b. Based on the processing parameters, heated rollers 44a, 44b, 46a, and 46b provide an amount of thermal energy that, together with thermal energy provided by upper and lower heat sources 40a and 40b, causes imaging material 32 to be heated to substantially the desired temperature after contact with the final heated roller. As illustrated, the final heated roller is upper roller 44b. The remaining non-heated rollers, 44c, 44b, 46c, 46d, and 46c, then move imaging material 32 the remaining distance along transport path 48 to exit 38, wherein both imaging material 32 and non-heated rollers 44c, 44b, 46c, 46d, and 46c, are maintained as substantially the desired temperature by upper and lower heat sources 40a and 40b.
In one embodiment, as illustrated, upper rollers 44 are horizontally offset from lower rollers 46 and are vertically positioned such that upper rollers 44 and lower rollers 46 overlap a horizontal plane such that transport path 48 is undulating, or sinusoidal in shape. Positioning the upper rollers 44 and lower rollers 46 in this fashion causes imaging material 32 to be bent or curved as it moves along transport path 48. Curving imaging material 32 in this fashion increases a column stiffness of imaging material 32 and enables imaging material 32 to be heated and transported through oven 35 without a need for nip rollers or other pressure transporting means.
By providing thermal energy to rollers 44 and 46 via internal heaters 50, rollers 44 and 46 of thermal processor 30 are better able to maintain a consistent temperature as is transferred to imaging material 32 as imaging material 32 moves through oven 35 along transport path 48. As a result, thermal processor 30 substantially reduces temperature variations between rollers 44 and 46, thereby substantially reduces variations in image density caused by non-uniform heat transfer to imaging material 32. Furthermore, by internally heating rollers 44 and 46, thermal energy transferred from rollers 44 and 44 to imaging material 32 can be replenished more quickly than with oven heater 40 alone. As a result, the throughput (i.e., the amount of imaging material processed in a give time) of thermal processor 30 can be increased.
As described above in regard to
In one embodiment, based on the varying heat transfer characteristics among rollers 44 and 46 and on the processing parameters associated with imaging material 32, thermal controller 60 individually controls the power provided to internal heaters 50 of rollers 44 and 46 via paths 62 to thereby individually control the thermal energy provided to rollers 44 and 46. In one embodiment, thermal controller 60 provides an amount of thermal energy to the associated internal heater 50 of each roller 44 and 46 that is substantially equal to an amount of thermal energy expected to be transferred to imaging material 32 by each roller 44 and 46 as imaging material 32 moves along transport path 48. In one embodiment, thermal controller 60 provides an amount of thermal energy to the associated internal heater of each roller 44 and 46, such that the amount of thermal energy transferred to imaging material 32 by rollers 44 and 46 and by oven heater 40 is such that the ΔT between imaging material 32 and the rollers following roller 44b (i.e. 46c to 46e) is substantially equal to zero.
In one embodiment, thermal controller 60 individually controls the thermal energy provided to each roller 44 and 46 by controlling the current provided to internal heater 50 associated with each roller. In one embodiment, thermal controller 60 separately controls both a magnitude and duration of a current applied to each internal heater 50.
In one embodiment, thermal controller 60 includes a voltage regulator 67 that maintains a voltage level provided to internal heaters 50 via paths 62 at a substantially constant level regardless of fluctuations that may occur in the level of a power source voltage received via path 66. In one embodiment, thermal controller 60 includes a resistance compensator 68 configured to compensate for differences in resistive values of internal heaters 50 when determining an amount of current to be provided to each internal heater 50. In one embodiment, thermal controller 60 cross references the processing parameters with a look-up table stored in a memory 69 to determine an amount of current to provide to each of the internal heaters 50.
In one embodiment, thermal processor 30 includes a feeder section 70 into which imaging material 32 is loaded by a user. In one embodiment, as imaging material 32 is fed toward entrance 36 to oven 35, a sensor 72 provides indication to thermal controller 60 via a path 74 of when imaging material 32 passes a point on transport path 48 that is a known distance from the first heated roller, as illustrated roller 46a. Based on the speed that imaging material 32 is moving, which can be included as one of the processing parameters received via path 64, thermal controller 60, in one embodiment, provides a predetermined amount of thermal energy to each roller 44 and 46 via its associated internal heater 50 before each roller 44 and 46 contacts imaging material 32. This is described in great detail below by
In one embodiment, thermal processor 30 includes a reader system 76 configured to read the processing parameters associated with imaging material 32 from packaging in which imaging material is stored or from the imaging material itself, and to provide the processing parameters to thermal controller 60. In one embodiment, reader system 76 includes a bar code scanner to read processing parameters affixed to either the imaging material or imaging material packaging in the form of a bar code. In one embodiment, reader system includes a radio frequency (RF) transmitter/receiver configured to read processing parameters affixed to either the imaging material or imaging material packaging in the form of an RF tag device.
Segment 84 illustrates the temperature of imaging material 32 while it is in contact with roller 46a during a time period from T0 and T1, during which time the temperature of imaging material 32 rises from an ambient temperature to a temperature C1. Segment 86 corresponds to imaging material 32 being between rollers 46a and 44a during a time period from T1 to T2, during which time the temperature of imaging material 32 rises from temperature C1 to a temperature of C2. Segment 88 illustrates the temperature of imaging material 32 while it is in contact with roller 44a during a time period from T2 and T3, during which time the temperature of imaging material 32 rises from temperature C2 to a temperature C3.
Segment 90 corresponds to imaging material 32 being between rollers 44a and 46b during a time period from T3 to T4, during which time the temperature of imaging material 32 rises from temperature C3 to a temperature C4. Segment 92 illustrates the temperature of imaging material 32 while it is in contact with roller 46b during a time period from T4 and T5, during which time the temperature of imaging material 32 rises from temperature C4 to a temperature C5. Segment 94 corresponds to imaging material 32 being between rollers 46b and 44b during a time period from T5 to T6, during which time the temperature of imaging material 32 rises from temperature C5 to a temperature C6.
Segment 96 illustrates the temperature of imaging material 32 while it is in contact with roller 44b during a time period from T6 and T7, during which time the temperature of imaging material 32 rises from temperature C6 to a desired temperature. Segment 98 illustrates the temperature of imaging material 32 as it moves along transport path 48 beyond heater roller 44b, wherein imaging material 32 is maintained at the desired operating temperature by oven heater 40.
As illustrated by graph 80, the amount of the temperature increase of imaging material 32 due to contact with the heated rollers (i.e., 44a, 44b, 46a, and 46b), and thus the amount of thermal energy transferred to imaging material 32 by the rollers, decreases as imaging 32 moves through oven 35. As illustrated by graph 80, and as described above, the largest temperature increase of imaging material 32 due to roller contact occurs from contact with the first heated roller 46a and the smallest temperature increase occurs from contact with the final heater roller 44b.
In response to a position indication received from sensor 72 and to processing parameters associated with the first piece of imaging material 32, such as provided by reader system 76, thermal controller 60 determines, such as from the look-up table in memory 69, an amount of electrical current to provide to internal heater 50 of roller 46a and for what duration. The magnitude of electrical current and the duration it is applied to internal heater 50 determines the amount of thermal energy internal heater 50 provides to roller 56a, and is such that the amount of thermal energy provided by internal heater 50 to roller 46a is substantially equal to the amount of thermal energy expected to be absorbed from roller 46a by imaging material 32 while in contact with roller 46a.
For the example illustrated by
At time t2, imaging material 32 contacts and begins absorbing from roller 46a, Q watts of power as indicated at 110. Imaging material 32 is in contact with roller 46a from time t2 to time t3, during which time it absorbs an amount of thermal energy from roller 46a that is represented by the cross-hatched area 112. The hatched area 108 is substantially equal to the cross-hatched area 112, which represents that the amount of thermal energy provided to roller 46a by its associated internal heater 50 is substantially equal to the amount of thermal energy absorbed from roller 46a by imaging material 32 as it moves along transport path 48.
The above described process is repeated for the second piece of imaging material 32, and for each subsequent piece of imaging material 32 that is to be developed by thermal processor 30. While, as illustrated, the second piece 104 of imaging material 32 has substantially equal processing characteristics relative to the first piece 102 of imaging material 32, each consecutive piece of imaging material 32 can have different thermal requirements. As a result, thermal controller 60 may provide a different amount of current for a different duration to internal heater 50 of roller 46a for each consecutive piece of imaging material 32 processed by thermal processor 30. Furthermore, while graph 100 indicates the cessation of the provision of thermal energy to a given roller as coinciding with its contacting the imaging material (as indicated at times t2 and t5), the provision of thermal energy to a roller can be discontinue prior to contact with the imaging material or can continue to be provided to a roller after it contacts the imaging material, depending on thermal requirements of the imaging material.
In one embodiment, as illustrated, roller 46a includes a bearing 126, or other low-friction device, which is configured to slidably fit over a support shaft 128 such that roller 46a is free to rotate around the stub shaft 128. As illustrated, stub shaft 128 is hollow and is mounted to and extends through a side of enclosure 34 such that stationary internal heater 50 can be inserted into the hollow interior 122 of roller 46a. In other embodiments, internal heater 50 can rotate with roller 46a.
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 and lower rollers, 144 and 146. A portion of upper rollers 144 and lower rollers 146 include an internal heater 150, wherein each internal heater 150 provides thermal energy based on the processing parameters associated with imaging material 32. In a fashion similar to that of dwell chamber 133, 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 through preheat chamber 134 from entrance 136 to exit 138. One or more of the rollers 144 and 146 can be driven such that contact with between rollers 144 and 146 and imaging material 32 moves imaging material 32 through preheat chamber 134. In one embodiment, as illustrated, upper rollers 144 are horizontally offset from lower rollers 146 and are vertically positioned such that upper rollers 144 and lower rollers 146 overlap a horizontal plane such that transport path through preheat chamber 134 is undulating, or sinusoidal in shape.
Upper and lower heat sources 140a and 140b of preheat chamber 134 respectively include heat plates 152 and 154 and blanket heaters 156 and 158. Upper and lower heat sources 40a and 40b of dwell chamber 133 respectively include heat plates 160 and 162 and blanket heaters 164 and 166. Blanket heaters 156, 158, 164, and 166, and heat plates 152, 154, 160, and 162 can be configured with multiple zones, with the temperature of each zone being individually controlled. In one embodiment, as illustrated, heat plates 152, 154, 160, and 162 are shaped so as to partially wrap around a portion of the circumference of rollers 44, 46, 144, and 146 such that the rollers are “nested” within their associated heat plate. By nesting rollers 44, 46, 144, and 146 within heat plates 152, 154, 160, and 162 in this fashion, the temperature of the rollers can be more evenly maintained.
As imaging material 32 moves through preheat chamber 134, upper and lower heat sources, 140a and 140b, and heated rollers, 144 and 146, heat imaging material 32 from an ambient temperature to substantially the first temperature. As imaging material 32 moves through dwell chamber 133, upper and lower heat sources, 40a and 40b, and heated rollers, 44 and 46, heat imaging material 32 from substantially the first temperature to substantially the second temperature. While imaging material 32 contacts non-heated rollers of preheat chamber 134 and dwell chamber 133, upper and lower heat sources 140a/140b and 40a/40b respectively maintain imaging material 32 substantially at the first temperature and substantially at the second temperature.
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.
Parts List
