EP1359104A2

EP1359104A2 - Method and apparatus for buffer transfer of media sheets between components in an imaging system

Info

Publication number: EP1359104A2
Application number: EP03101167A
Authority: EP
Inventors: Richard Hawes
Original assignee: Agfa Corp
Current assignee: Agfa Corp
Priority date: 2002-05-02
Filing date: 2003-04-29
Publication date: 2003-11-05
Also published as: JP2003335432A; US20030205639A1

Abstract

The present invention is directed to a method and apparatus for compensating for a speed differential between an imaging system (42) and an on-line development/finishing processor (44) in an electronic pre-press system (40) using a transfer buffer (58) having a plurality of storage devices (74,76). Each storage device comprises a first section (102) having first and second surfaces, a second section (104) having first and second surfaces, and a system for securing the first and second sections together to form a storage device (74), wherein the storage device (74) has a substantially cylindrical shape and includes a capture slot (124) for capturing a leading end of the media (28), wherein the first surfaces of the first and second sections form the capture slot (124), and wherein the second surfaces of the first and second sections form an exterior surface (106) of the storage device.

Description

FIELD OF THE INVENTION

The present invention relates generally to the buffering and transferring of sheets of recording media between functional components having different processing speeds within an imaging system. More specifically, the present invention is directed to a method and system for compensating for a speed differential between an imaging system and an on-line development/finishing processor in an electronic pre-press system using a transfer buffer having a plurality of storage devices.

BACKGROUND OF THE INVENTION

In existing electronic pre-press systems, images to be printed by offset printing are generally scanned from photographic sources and digitized. The digitized images are then transmitted to a raster image processor (RIP) for half-tone screening and image rasterization. The rasterized image is then transmitted to an imaging system such as an imagesetter or platesetter where the rasterized image is recorded onto a supply of recording media. The recording media may comprise film, printing plates, etc.
Existing pre-press systems include independent functional units for recording images onto the recording media and for subsequent processing of the exposed recording media. A typical photographic imaging system operates to record a predefined image onto a supply of recording media, for example by first mounting the recording media onto the internal surface of a drum (e.g., in an internal drum imagesetter or platesetter), then exposing the recording media with a laser beam via a rotatable, optically reflective element. The recording media is typically supplied as a web or as a cut sheet. Subsequent to imaging, the imaged recording media is passed to a development/finishing processor. In the processor, the imaged recording media may undergo chemical processing during which the media is photographically developed, fixed and washed. Alternately, the imaged recording media may undergo mechanical finishing in the processor. If the recording media was supplied by a continuous web, each sheet of imaged recording media is cut prior to entry into the processor.
Early pre-press systems typically used off-line development processors. In such early systems, imaged recording media was collected onto a take up cassette connected to an output of the imaging system, and then manually transported to the off-line processor. More recent systems have coupled the imaging system to an on-line processor, which receives the imaged media directly and automatically from the imaging system.
A significant drawback of existing systems using on-line processors results from the different processing speeds of the imaging system and the processor. This and other problems have been addressed, for example, in U.S. Pat. No. 5,769,301 to Hebert et al. disclosing a media transport bridge for use in the transporting and buffering of imaged recording media between an imagesetter and a processor. When imaged recording media is output from the imagesetter, it is transferred to a bridge mechanism between the imagesetter and the processor. The bridge mechanism holds the imaged recording media for a predetermined period of time while waiting for the processor to become available. When the processor's availability is detected, the imaged recording media is transferred from the bridge to the processor, and the bridge thereafter becomes available to store a second sheet of imaged recording media from the imagesetter. However, during the time that the bridge is waiting for the processor to accept the second sheet of imaged recording media, the imagesetter may have to be stalled, waiting for the bridge to become available. Such stalling of the imagesetter potentially causes an unacceptable reduction in overall media throughput. Moreover, existing bridge mechanisms often have high profiles, resulting in undesirably large form factors for products in which they are included.
One system that obviates the above-described stalling is disclosed in U.S. Pat. No. 6,240,260 to Krupica et al. providing a transfer buffer having at least two storage devices for transferring imaged sheets of recording media between a drum of an imagesetter and a media processor. The transfer buffer is rotated to align a first storage device with a media path from the drum and to concurrently align a second storage device with an input to the media processor. A first sheet of the imaged recording media is transferred from the drum through a media path to the first storage device. The transfer buffer is rotated to align the first storage device with the input to the media processor and to concurrently align the second storage device with the media path from the drum. The first sheet of imaged recording media is transferred to the input of the media processor while a second sheet of imaged recording media is simultaneously transferred through the media path to the second storage device.
An example of a storage device 10 used in Krupica et al. is illustrated in FIGS. 1A, 1B, and 2. The storage device 10 generally comprises a roller-shaped body 12 having a surface 14. The body 12 is rotatable about an axle 16. A plurality of leaf springs 18 are fastened to the surface 14 via fasteners 20. A retaining rod 22 is fastened to the leaf springs 18 by fasteners 24. A wheel bearing 26 is coupled to each end of the retaining rod 22.
After imaging, as shown in FIG. 1A, an end of the imaged recording media 28 is displaced until it is positioned between the surface 14 and the bearings 26. At this point, the body 12 of the storage device 10 is rotated about its axle 16, which causes the retaining rod 22 to clamp down on the imaged recording media 28. As the body 12 begins to rotate, as shown in FIG. 1B, the leaf springs 18 contract and the bearings 26 pinch the imaged recording media 28 against the surface 14, thereby holding the media 28 in place as it wraps around the body 12.
The storage device 10 provides a convenient mechanism for capturing and storing a sheet of imaged recoding media 28 within the transfer buffer of Krupica et al. The storage device 10, however, has a high part count and is expensive to manufacture. Further, because of its shape, the body 12 is unbalanced during rotation. In addition, the clamping bar 22, bearings 26, and other components of the storage device 10 may damage the imaged recording media 28 as it is captured, wrapped around the body 12, and released.

SUMMARY OF THE INVENTION

The above-mentioned problems are solved by a storage device having the specific features set out in claim 1 and by a method having the specific features set out in claim 11. Specific features for preferred embodiments of the invention are set out in the dependent claims.
The present invention provides a system an apparatus and method for transferring and buffering sheets of imaged recording media between two components in an imaging system so as to compensate for any transfer speed differential between the components.
Generally, the present invention provides a storage device for media, comprising a first section having first and second surfaces, a second section having first and second surfaces, and a system for securing the first and second sections together to form a storage device, wherein the storage device has a substantially cylindrical shape and includes a capture slot for capturing a leading end of the media, wherein the first surfaces of the first and second sections form the capture slot, and wherein the second surfaces of the first and second sections form an exterior surface of the storage device. The present invention further provides a transfer buffer, comprising a plurality of storage devices and a drive system for rotating the transfer buffer to exchange positions of the plurality of storage devices, wherein each storage device comprises a first section having first and second surfaces, a second section having first and second surfaces; and a system for securing the first and second sections together to form a storage device, wherein the storage device has a substantially cylindrical shape and includes a capture slot for capturing a leading end of a supply of media, wherein the first surfaces of the first and second sections form the capture slot, and wherein the second surfaces of the first and second sections form an exterior surface of the storage device.
The present invention also provides a method for transferring sheets of recording media between first and second components of an imaging system, comprising rotating a transfer buffer to align a first storage device with the first component while concurrently aligning a second storage device with the second component, wherein the first and second storage devices each comprise a first section having first and second surfaces, a second section having first and second surfaces, and a securing system for securing the first and second sections together to form a storage device transferring a first sheet of the media from the first component to the first storage device moving the transfer buffer to align the first storage device with the second component while concurrently aligning the second storage device with the first component; and transferring the first sheet of the media from the first storage device to the second component while simultaneously transferring a second sheet of the media from the first component to the second storage device; wherein each storage device has a substantially cylindrical shape and includes a capture slot for capturing a leading end of a supply of media, wherein the first surfaces of the first and second sections form the capture slot, and wherein the second surfaces of the first and second sections form an exterior surface of the storage device.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention will best be understood from a detailed description of the invention and embodiments thereof selected for the purpose of illustration and shown in the accompanying drawings in which:
FIGS. 1A, 1B, and 2, illustrate a storage device of a transfer buffer in accordance with the related art.
FIG. 3 illustrates an electronic pre-press system including an internal drum imagesetter, a transfer buffer in accordance with the present invention, and an on-line processor.
FIGS. 4, 5, and 6, illustrate the operation of the transfer buffer of FIG. 3.
FIG. 7 illustrates a storage device in accordance with the present invention.
FIG. 8 is a cross-sectional view taken along line 7-7 of FIG. 7.
FIG. 9 is a flow chart outlining the operation of the pre-press system of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The features of the present invention are illustrated in detail in the accompanying drawings, wherein like reference numerals refer to like elements throughout the drawings. Although the drawings are intended to illustrate the present invention, the drawings are not necessarily drawn to scale.
FIG. 3 illustrates an electronic pre-press system 40 including an internal drum imagesetter 42, and an on-line development/finishing processor 44. The imagesetter 42 includes a media supply cassette 46 that supplies a web of photosensitive recording media 28, drum input rollers 48, an imaging drum 50, drum output rollers 52, web cutters 54, a first sensor 56, a transfer buffer 58, a second sensor 60, and a controller 62. The controller 62 automatically controls and runs a predetermined sequence of operations of the pre-press system 40. The processor 44 includes a pair of input rollers 64. Although described below with regard to an internal drum imagesetter, the transfer buffer 58 of the present invention may be used in conjunction with a wide variety of other types of internal drum, external drum, or flatbed imaging systems without departing from the scope of the present invention.
During operation of the pre-press system 40 of FIG. 3, a portion of the recording media 28 resident in the media supply cassette 46 is drawn onto the internal drum surface 66 of the imaging drum 50 by the drum input rollers 48 until the leading edge of the recording media 28 is detected by the sensor 56. Alternately, the media supply cassette 46 of FIG. 3 may be replaced by a source of precut sheets of recording media. A laser imaging system (not shown) of a type known in the art transfers and records an image onto the recording media 28 positioned on the internal drum surface 66 of the imaging drum 50. The output beam from the laser scanning system is scanned by a rotating mirror across the recording media 28 position on internal drum surface 66 in successive circumferentially extending bands or paths referred to as scan lines. The output beam of the laser imaging system exposes specific pixel locations on the recording media 28 along the scan lines to form the desired image. Because the imaged recording media 28 is associated with a single color component of the image, the laser scanning system is modulated according to those pixel locations that contain that color component.
After imaging, the imaged recording media 28 is transferred from the imaging drum 50 to the transfer buffer 58 via drum output rollers 52. The imaged recording media 28 is transferred by the drum output rollers 52 along a media path from the imaging drum 50 to an opening 68 located between a pair of platens 70. After a predetermined length of the imaged recording media 28 has passed by the first sensor 56, the web cutters 54 cut the imaged recording media 28.
The sheet of cut, imaged recording media 28 entering the transfer buffer 58 continues to be drawn into the transfer buffer 58 by drive rollers 72 until the trailing edge of the sheet of imaged recording media 28 is in the vicinity of the opening 68. Another length of the recording media 28 is drawn from the media supply cassette 46 into the imaging drum 50 by drum input rollers 48 until the leading edge of the recording media 28 is again detected by the sensor 56. The operations of the pre-press system 40 are controlled by a software program stored in the controller 62.
As described above, sheets of cut, imaged recording media 28 are displaced into the transfer buffer 58 after imaging. In the transfer buffer 58, the sheets of imaged recording media 28 are captured and wound around one of a plurality of storage devices before being transferred to the processor 44. In FIG. 3, the transfer buffer 58 includes two storage devices 74 and 76, although more than two storage devices could be used if desired.
FIG. 4 illustrates the transfer buffer 58 in its home position, with the nip between the drive rollers 72 aligned with the opening 68 between the platens 70. A sheet of imaged recording media 28 is shown being drawn by the drive rollers 72 toward the storage device 74. The storage device 74 captures the leading end of the sheet of imaged recording media 28, and is subsequently rotated to wind the media around its outer surface. The nip between drive rollers 78 is concurrently aligned with an opening 80 formed between platens 82, and the opening 80 is in turn aligned with a media input opening 84 of the processor 44. The pair of drive rollers 72 operate to draw the sheet of imaged recording media 28 into the storage device 74 until the trailing edge of the sheet is in the vicinity of the opening 68. The rollers 72 and 78 may comprise a pair of driven rollers or a driven roller in combination with an idler roller. After the cut sheet of imaged recording media 28 is wound around the storage device 74 in response to a rotation of the storage device 74 about its axis 86, the transfer buffer 58 is rotated about its axis 88 as shown in FIG. 5 to a subsequent orientation shown in FIG. 6 where the nip between the drive rollers 72 is aligned with the opening 80 between the platens 82, and the nip between the rollers 78 is aligned with the opening 68 between the platens 70. Drive systems such as a motor or the like may be used to rotate the storage devices 74, 76, and the transfer buffer 58. For clarity, the axes 86, 90 (see below), and 88 are also intended to depict the corresponding drive systems of the storage devices 74, 76, and the transfer buffer 58, respectively. Note that during rotation of the storage device 74 about its axis 86 within the transfer buffer 58, a portion of the sheet of imaged recording media 28 remains in contact with the drive rollers 72 so that the sheet can be subsequently easily removed from the storage device via the drive rollers 72.
In FIG. 6, the drive rollers 72 transfer the sheet of imaged recording media 28 from the storage device 74 to the processor 44. Another sheet of imaged recording media 28 is simultaneously transported through the opening 68 between the platens 70 to the nip between the drive rollers 78. The storage device 76 captures the leading end of the sheet of imaged recording media 28, and is subsequently rotated about its axis 90 to wind the media around its outer surface.
As the sheet of exposed recording media 28 exits the transfer buffer 58 and moves towards the processor 44, it is detected by sensor 60 (see FIG. 3), which operates to generate a media present signal.
The media present signal may be used to initiate driving of the input rollers 64 in the processor 44.
A storage device 74 (or 76) in accordance with the present invention is illustrated in FIGS. 7 and 8. The storage device 74 comprises first and second sections 102, 104. The first and second sections 102, 104, are each separately formed using an extrusion process from a lightweight and strong material such as an aluminum alloy or the like. During the extrusion process, an extrusion press is used to force a billet of material (e.g., a billet of an aluminum alloy) through a suitably designed die. A different die is used to form the first and second sections 102, 104, of the storage device 74. Generally, each die includes solid areas corresponding to the hollow portions of the corresponding section 102, 104, and hollow areas corresponding to the solid portions of the first and second sections 102, 104. As the material is forced into and through each die, a length of a product corresponding to the corresponding section 102, 104, is produced. The extruded product is then cut to length and machined to form the finished first and second sections 102, 104, of the storage device 74. Storage devices 74 of varying length can easily be produced by cutting the extruded product to the desired length.
When the first and second sections 102, 104, are connected together, the resulting storage device 74 has a substantially cylindrical shape as best seen in FIG. 8. The storage device 74 has a smooth exterior surface 106 to prevent damage to the imaged recording media 28 when it is wound around the storage device 74.
The first and second sections 102, 104, are captured and secured together using a pair of end plates 108. Each end plate 108 is attached to the first and second sections 102, 104, using screws 110 or other suitable securing hardware. The positions of the holes 112 for receiving the screws 110 are depicted in FIG. 8.
The first section 102 of the storage device 74 comprises a hub 114, an outer wall 116, and a plurality of radial spokes 118 extending between the hub 114 and the outer wall 116. The storage device 74 is rotated by a drive system via shafts 120 coupled to the ends of the hub 114. A first surface 122 of the first section 102 forms a portion of a curved capture slot 124 that is used to capture the leading end of the imaged recording media 28 as it is fed toward the storage device 74 by the drive rollers 72. As shown in FIG. 8, the capture slot 124 extends through a substantial portion of the storage device 74. The first surface 122 includes a rounded area 126 at the entry of the curved slot 124 to help guide the leading edge of the imaged recording media 28 into the curved slot 124 and to prevent damage to the leading edge of the imaged recording media 28 as it enters and exits the curved slot 124. The first surface 122 also includes a groove 128 that is configured to mate with a corresponding tongue 130 of the second section 104 of the storage device 74. A second surface 106A of the first section 102 forms a portion of the exterior surface 106 of the storage device 74. One or more sections 136 of the outer wall 116 may be provided with extra material (i.e., extra mass) to balance the storage device 74 during rotation.
The second section 104 of the storage device 74 is formed in the shape of a hollow crescent. A first surface 132 of the second section 104 forms a portion of the curved capture slot 124. The first surface 132 of the second section 104 includes a rounded area 134 at the entry of the curved slot 124 to help guide the leading edge of the imaged recording media 28 into the curved slot 124 and to prevent damage to the leading edge of the imaged recording media 28. A second surface 106B of the second section 104 forms a portion of the exterior surface 106 of the storage device 74.
The operation of the pre-press system 40 including the transfer buffer 58 of the present invention is detailed by the flow chart of FIG. 9. The operating sequence is controlled by the controller 62 which, in turn, is dependent upon software executed therein. At step 160, recording media 28 is provided to the imagesetter 42 from the media supply cassette 46. Recording media 28 may alternatively be supplied by a number of pre-cut sheets, for example stored in a stack. At step 162, the drum input rollers 48 displace the recording media 28 onto the internal drum surface 66 of the imaging drum 50. At step 164, the imagesetter 42 records a predetermined image onto the recording media 28 while it is located on internal drum surface 66 of the imaging drum 50. After or during the recording of the image onto the recording media 28 and prior to removal of the recording media 28 from the internal drum surface 66, the transfer buffer 58 is initialized at step 166. The steps of initialization include: (i) aligning the nip of the drive rollers 72 with the opening 68 between the platens 70, and (ii) aligning the nip of the drive rollers 78 with the opening 80 between the platens 82. In addition, the curved slot 124 of the storage device 74 is aligned with the opening 68 between the platens 70 to receive the leading edge of the imaged recording media 28. At step 168, once the initialization is complete, the imaged recording media 28 is removed from the imaging drum 50 by the drum output rollers 52 and unexposed recording media 28 is displaced onto the imaging drum 50 from the supply cassette 46 by the drum input rollers 48. At step 170, the sensor 56 detects the traversal of the leading edge of the imaged recording media 28 and activates the drive rollers 72 at the same transfer speed as both the drum input and output rollers 48 and 52. The transfer speed of the various drive rollers indicates to the controller 62 the exact position of the leading edge of the imaged recording media 28. The drive rollers 72 displace the leading edge of the imaged recording media 28 into the curved slot 124 of the storage device 74. At this point, the storage device 74 is activated at the same transfer speed as the other drive rollers, causing the imaged recording media 28 to be wrapped around the exterior surface 106 of the storage device 74.
When the appropriate length of the imaged recording media 28 has passed by the sensor 56, the web cutters 54 cut the imaged recording media 28 at step 172 into a sheet and the drum input and output rollers 48 and 52 stop rotating. The drive rollers 72 continue to rotate until the trailing edge of the sheet of imaged recording media 28 is in the vicinity of the opening 68. The unexposed recording media 28 on the imaging drum 50 is then imaged.
Meanwhile, at step 174, the transfer buffer 58 is moved to exchange the positions of the storage devices 74, 76. For instance, for the cylindrically shaped transfer buffer 58 illustrated in FIGS. 5 and 6, the transfer buffer 58 is rotated until the nip of the drive rollers 72 is aligned with the opening 80 between the platens 82 and the nip of the drive rollers 78 is aligned with the opening 68 between the platens 70. In this way, the sheet of imaged recording media 28 that has been previously wrapped around the storage device 74 is ready for transfer into the processor 44, while the storage device 74 is available to receive the next sheet of imaged recording media 28 from the imaging drum 50. At step 176, the drive rollers 72 and the storage device 74 are activated to unwrap and transfer the sheet of imaged recording media 28 through the opening 80 between the platens 82 into the media input opening 84 of the processor 44. When the sensor 60 detects the leading edge of the imaged recording media 28, it transmits an electronic signal to the controller 62 which, in turn, activates the input rollers 64 of the processor 44 at the same transfer rate as the drive rollers 72 and the storage device 74. When the trailing edge of the imaged recording media 28 being transferred into the processor 44 is detected by the sensor 60, the drive rollers 72 and the storage device 74 are deactivated.
The above described process is repeated for each subsequent sheet of imaged recording media 28. Thus, sheets of recording media 28 are simultaneously being loaded onto the imaging drum 50 or imaged, transferred from the imaging drum 50 into the transfer buffer 58, and transferred from the transfer buffer 58 to the processor 44. In this manner, the pre-press system 40 operates at a high level of efficiency.
It should be noted that the particular shape of the transfer buffer 58 is not critical to the principles of the invention. Hence, the transfer buffer 58 is not limited to the cylindrical shape described above. Further, the movement of the storage devices 74, 76, from one point to another within the transfer buffer 58 can be implemented by any known transfer means, such as via a belt or chain driven transfer system. For example, the transfer buffer 58 could cause the storage devices 74, 76, to move in a linear path or along a combination of linear and angular paths. Any path for transferring the media (via multiple storage devices) from one component to another within the pre-press system 40 is a viable alternative for implementing the concepts of the present invention. The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in light of the above teaching. Such modifications and variations that may be apparent to a person skilled in the art may be included within the scope of this invention.

Claims

A storage device (74,76) for media (28), comprising:

a first section (102) having a first surface (122) and a second surface (106A);

a second section (104) having a first surface (132) and a second surface (104); and

a system (108,110,112,128,130) for securing the first (102) and second (104) sections together to form said storage device (74), wherein the storage device (74) has a substantially cylindrical shape and includes a capture slot (124) for capturing a leading end of the media (28), wherein the first surface (122) of the first section (102) and the first surface (132) of the second section (104) form said capture slot (124), and wherein the second surface (106A) of the first section (102) and the second surface (106B) of the second section (104) form an exterior surface (106) of the storage device (74).
The storage device according to claim 1, wherein the securing system comprises a pair of end plates (108).
The storage device (74,76) according to any one of the previous claims, further comprising a drive system for rotating the storage device (74,76) to wrap the media about the exterior surface (106) of the storage device (74,76).
The storage device (74,76) according to any one of the previous claims, wherein the first (102) and second (104) sections comprise an extruded material.
The storage device (74,76) according to any one of the previous claims, wherein the capture slot (124) is curved.
The storage device (74,76) according to any one of the previous claims, wherein the first section (102) includes a groove (128), and wherein the second section (104) includes a tongue (130) for mating with said groove (128).
The storage device (74,76) according to any one of the previous claims, wherein the first section (102) comprises a hub (114), an outer wall (116), and a plurality of radial spokes (118) extending between the hub (114) and the outer wall (116).
The storage device (74,76) according to any one of the previous claims, wherein the second section (104) is crescent shaped.
The storage device (74,76) according to any one of the previous claims, wherein the first surface (122) of the first section (102) and the first surface (132) of the second section (104) include a rounded area (126,134) at an entry to the capture slot (124).
A transfer buffer (58), comprising:

a plurality of storage devices (74,76) according to any one of the previous claims; and

a drive system for rotating the transfer buffer (58) to exchange positions of the plurality of storage devices (74,76).
A method for transferring sheets of recording media (28) between first (42) and second (44) components of an imaging system (40), the method comprising:

rotating a transfer buffer (58) to align a first storage device (74) with the first component (42) while concurrently aligning a second storage device (76) with the second component (44), wherein the first (74) and second (76) storage devices each comprise a first section (102) having a first surface (122) and a second surface (106A), a second section (104) having a first surface (132) and a second surface (106B), and a securing system (108,110,112,128,130) for securing the first (102) and second (104) sections together to form said storage device (74,76);

transferring a first sheet of the media (28) from the first component (42) to the first storage device (74);

moving the transfer buffer (58) to align the first storage device (74) with the second component (44) while concurrently aligning the second storage device (76) with the first component (42); and

transferring the first sheet of the media (28) from the first storage device (74) to the second component (44) while simultaneously transferring a second sheet of the media (28) from the first component (42) to the second storage device (76);

wherein each storage device (74,76) has a substantially cylindrical shape and includes a capture slot (124) for capturing a leading end of a supply of media (28), wherein the first surface (122) of the first section (102) and the first surface (132) of the second section (104) form the capture slot (124), and wherein the second surface (106A) of the first section (102) and the second surface (106B) of the second section (104) form an exterior surface (106) of the storage device.