Method and apparatus for an external media buffer

Abstract: An external media transport buffer (10) has a carriage (20) supported for linear motion on parallel guide rails (22) between an imagesetter (12) and a processor (14). A pair of transport rollers (26) is mounted for rotation on the carriage (20). Two sensors (60,62) are mounted within the buffer (10) to detect media movement. A first sensor (60) is positioned at an entrance to the buffer (10) and a second sensor (62) is positioned on the carriage (20) on an exit side of the transport rollers (26). Signals are sent from the sensors to a roller transport motor (50) and carriage transport motor (30) and the signals are coordinated to start and stop the motors according to a predetermined sequence. A leading end (70) of media enters the nip of the transport rollers (26) and is held in the nip as the carriage (20) travels from the imagesetter (12) to the processor (14). A slack loop (78) of media forms between the carriage (20) and the imagesetter (12) as the imagesetter feeds the media to the buffer (10) faster than the carriage (20) travels to the processor (14). A movable media guide (74) is used in a first position to guide the media from the imagesetter (12) into the nip of the transport rollers (26). As the carriage (20) begins to travel away from the imagesetter (12) and the leading end of the media is held in the roller nip, the movable guide (74) drops down to a second position so that the slack loop (78) may form easily. Upon the trailing end (80) of the media entering the buffer (10) and a ready signal from the processor (14), the transport rollers (26) deliver the leading end (70) of media into the processor transport rollers (86). Upon complete removal of the media by the processor (14), the carriage returns to the imagesetter (12) and the movable media guide (74) returns to its initial position.

Description: The invention is related to media handling and transport systems, and more specifically to systems used in the imaging technology industry to temporarily store and transport photosensitive media between an image-setting device and an image-processing device. The image-setting and image-processing devices are each equipped with internal media transport systems designed to handle and transport the media within that particular device at the operating speed required by that device. Typically the media transport system of the image-setting device operates at a faster speed than that of the image-processing device. This poses a problem when the two devices are used together in an on-line operating mode, in which the media is transported directly from the image-setting device to the image-processing device rather than to an intermediate storage take-up cassette that is transferred manually from one device to the other. In the on-line operating mode, the media needs to be buffered between the image-setting device and the image-processing device because of the difference in operating speeds of the respective media transport systems. During on-line operation it is desirable to avoid down time of the image-setting device due to a slower operating speed of the image-processing device. It is also desirable to minimize the amount of floor space used by an on-line operating system. It is further desirable to minimize the cost of an on-line operating system. Another problem encountered in media transporting systems is caused by the thickness and stiffness of the media. Plate materials having a thickness of approximately 0.3 mm (12 mils (1 mil = 1/1000 inch)) are more difficult to handle in media transport systems compared to media 0.1mm (4 mils) thick. Because this media is stiffer and harder to bend, generally a media transport path requires a large radius of curvature. Further, an inherent curvature at the leading end of a media supply or sheet causes difficulties with media loading. Sudden buckling and/or misfeeding due to the natural curl of the media can occur and disrupt the media handling or imaging as a result. It is therefore advantageous to prevent buckling and misguiding of the media during loading of media into a media handling system. US-A-5 110 104 discloses a sheet transporting apparatus having a sheet storage device capable of storing sheets and provided in the middle of a sheet transport path and a carriage unit with a sheet discharge mechanism for transporting a sheet to the sheet storage device and capable of reciprocating motion substantially above the sheet storage device. In view of the above difficulties encountered in media handling and transport systems, it is accordingly a general object of the invention to provide an external media transport mechanism for buffering media between an image-setting device and an image-processing device used together in an on-line operating mode. It is an object of the invention to minimize the amount of floor space required by an external media transport mechanism used with an image-setting device and an image-processing device in an on-line operating mode. It is further an object of the invention to accommodate media of varying stiffness and thickness during loading of the media into an external media transport mechanism and thereby prevent buckling of the media during transport. An apparatus and a method for buffering a sheet of media between a first media handling station and a second media handling station according to the present invention are defined in claim 1 and claim 5. The features and objects of the invention will become apparent in the following description taken in connection with the accompanying drawings, in which: Figures 1A-D are sequential partial sectional side views of the stages of operation of an external buffer according to the invention in combination with an imagesetter and a processor; Figure 2 is an illustrative view of an external buffer according to the invention; Figure 3 is a partial sectional front view of a pair of media transport rollers used in an external buffer according to the invention; and Figure 4 is a partial sectional side view of a second embodiment of an external buffer according to the invention in combination with an imagesetter and a processor. Referring to Figures 1A and 2 it is shown that an external media buffer, generally indicated as 10, is positioned between an imagesetter, generally referred to as 12, and a processor, generally referred to as 14. In the imagesetter 12, media 16 is fed from a continuous web supply roll to a recording support surface to be imaged and then delivered as cut sheets into the buffer 10 by a media transport system 18. The buffer 10 has a carriage 20 which is supported for linear motion on two horizontally spaced parallel guide rails 22. The guide rails 22 traverse a width spanning between the imagesetter 12 and the processor 14. The guide rails 22 are attached to the interior of a buffer housing 24 or may alternatively be directly attached to the exterior of the imagesetter 12 and the processor 14, respectively. A pair of media transport rollers 26 is mounted within the carriage 20 in a direction lengthwise perpendicular to the guide rails 22. The rollers 26 are positioned vertically below and in between the guide rails 22 and are mounted for rotation by bearings 27 mounted within the carriage end plates 28, shown in Fig. 3. A drive roller 26b is driven by means of a motor 30 mounted on an end plate 28, while the other is an idler roller 26a driven through rolling contact with the drive roller 26b or through media movement in the nip of the rollers 26 transferring the rotation of the drive roller 26b to the idler roller 26a. In Fig. 3, it is shown that the drive roller 26b has a drive gear 32 mounted onto its end shaft 34 that is driven by a gear connection (not shown) with the motor 30. The drive gear 32 is fitted with an overrunning clutch 36 allowing the end shaft 34 and the attached drive roller 26b to have one-way rotation with respect to the drive gear 32. The idler roller 26a is equipped with a break mechanism 40 on its end shaft 42 to seize rotation of the idler roller 26a and consequently of roller pair 26. It will be appreciated that the break mechanism can be an electro-magnetic brake, a friction disk brake, or other suitable means for stopping rotation of the idler roller. A carriage drive motor 50, shown in Fig. 2, is attached to a top side 52 of the carriage 20 and is engaged with a lead screw 54 that spans across the buffer housing 24 (Fig. 1A). The lead screw 54 is fixed to the interior of the buffer housing 24 parallel to the guide rails 22. The motor 50 and lead screw 54 are engaged through a nut 56 interface. The nut 56 has internal threads which engage the lead screw 54 such that when the motor 50 rotates the nut 56, the carriage 20, restricted from rotation about the lead screw 54 by engagement with the guide rails 22, is translated linearly along the guide rails 22. It will be appreciated that the carriage may alternatively be driven by a friction drive wheel in direct contact with one of the guide rails or by other suitable means. In Fig. 1A, it is shown that two sensors 60, 62 are mounted within the buffer 10 to detect media 16 movement by means of mechanical interrupt switches. Signals from the switches are relayed to the buffer roller motor 30 and carriage motor 50 to start and stop the motors according to a predetermined sequence. A first sensor 60 is positioned at an entrance to the buffer 10 and a second sensor 62 is positioned on the carriage 20 on an exit side of the buffer rollers 26. It will be understood that the location of the first sensor can be within the image-setting device for instance if the walls between the buffer and the image-setting device are removed to integrate the two units. Further, the sensors can be mechanical interrupt switches, optical sensors or a combination of both. Now, with reference to Figs. 1A-1D the operation of the buffer 10 will be described. In Fig. 1A, while the carriage 20 is in a media pick-up position, a leading end 70 of media 16 is fed at speed V1 into the buffer 10 through a media guide 72 by the media transport system 18 of the imagesetter 12. The first sensor 60 senses the leading end 70 of the media entering the buffer and activates the buffer rollers 26 to rotate. A movable media guide 74 is initially in a horizontal position to serve as a guide for the media 16 into the nip of the rollers 26. The media 16 moves along the guide 74 as the leading end 70 approaches the nip of the rotating buffer rollers 26. In Fig. 1B, the media 16 passes through the rollers 26 and reaches the second media sensor 62. In response to the sensor's signal, the roller motor 30 (Fig. 2) is stopped and the idler roller brake mechanism 40 is activated to stop the buffer rollers 26 from rotating and to hold the leading end 70 stationary with respect to the buffer rollers 26. Once the leading end 70 is gripped by the rollers 26, the carriage motor 50 (Fig. 2) turns on to transport the carriage 20 along the rails 22 at speed V2. The leading end 70 is held in the nip of the rollers 26 at the second media sensor 62 while speed V1 is greater than speed V2. As the carriage 20 begins to travel away from the imagesetter, the movable guide 74 automatically pivots down from the horizontal position to an angled position due to a linkage 75 between the movable guide 74 and a follower 76 that moves along a template 77 as the carriage is transported. The angled position allows a slack loop 78 to form and prevents bucking of the media in an upward direction which can result in sudden jerking of the media 16 causing media jams in the transport system of the imagesetter or wrinkling of the media. The slack loop 78 grows larger as the leading end 70 is held between the buffer rollers 26 and the media 16 continues to enter the buffer 10 from the imagesetter 12. It will be appreciated that the movable media guide can alternatively be pivotally attached to the interior of the buffer housing to pivot down from a horizontal position toward the housing wall and be operated by a motor that responds to the second sensor's signals. The linkage, follower and template are not needed in this alternative embodiment. Referring to Fig. 1C, a storage bin, generally indicated as 79, located below the carriage 20 is essentially an open space for the media 16 to form a slack loop in. The trailing end 80 of the media 16 enters the buffer 10 and drops down into the bin 79. The carriage 20 continues to travel along the rails 22 to the processor 14 side where the leading end 70 becomes aligned with an exit guide 82 adjacent to the processor and the carriage 20 is in the delivery position. Then, the processor 14 is checked to see if it is ready to accept the sheet of media 16 stored in the buffer 10. Upon a signal from the first sensor 60 indicating the media 16 is no longer entering the buffer 10 and a signal from the processor 14 indicating it is ready, the brake mechanism 40 (Fig. 4) is shut off and the buffer rollers 26 are rotated to transport the leading end 70 of the sheet into the processor 14. In the meantime, the imagesetter is in the process of imaging the next job and as the transport system of the imagesetter is empty, upon completion the job can be cut from the web and delivered as a sheet to the transport system of the imagesetter. Referring now to Fig. 1D, a processor input sensor 84 senses the media 16 as it enters the processor rollers 86. In response to the sensor's 84 signal, the processor transport rollers 86 are turned on and the rotation of the buffer rollers 26 is stopped. The overrunning clutch assembly 36 (Fig. 3) on the drive roller 26b allows the media 16 to be pulled out from the buffer rollers 26. When the sheet of media 16 leaves the buffer rollers 26, the second sensor 62 sees the empty buffer rollers 26 and in response the carriage motor 50 is driven in a reverse direction to begin the return of the carriage 20 to the imagesetter 12 side of the buffer 10. As the carriage 20 is positioned adjacent to the imagesetter 12, the follower 76 on the template 77 causes the movable media guide 74 to pivot to the horizontal position, so that the next sheet of media can be fed into the buffer 10 and the sequence then repeated. A second embodiment of the media buffer is shown in Fig. 4 in which a feature for media loading is shown. The buffer elements in Fig. 4 are referred to with the same reference numerals as those corresponding elements in Figs. 1A-D. To assist with loading the media 16 into the buffer 10 from the imagesetter 12, the media 16 is pre-deflected by media guides 90 along the media path to account for the stiffness and the natural curl of the media 16. The buffer rollers 26 are positioned vertically below the media path of the imagesetter 12 relative to the previous embodiment, for cooperation with downward deflecting guides 90. The guides 90 serve to pre-deflect the media 16 to a curved shape opposite from its natural curvature, to prevent buckling of the media 16 during input loading into the buffer 10, and to urge the media 16 into a pre-loop curvature, so that the slack loop 78 will form downwardly, as in Fig. 1B. The carriage 20 is in the media pick-up position adjacent to the imagesetter 12 to pick-up the leading end 70 of the media 16 from the media transport system 18 of the imagesetter 12. The leading end 70 is fed at speed V1 into the buffer 10 through the downward deflecting media guides 90 of the buffer 10. The first sensor 60 senses the leading end 70 of the media entering the buffer 10 and activates the buffer rollers 26 to rotate. The movable media guide 74 is initially in a horizontal position to serve as a guide for the media 16 into the nip of the rollers 26. The media 16 moves along the guide 74 as the leading end 70 approaches the nip of the rotating buffer rollers 26. The buffer rollers 26 have a center axis C-C that is angled with respect to a vertical axis to further urge the media into the pre-loop curvature 92 as the leading end 70 enters the nip of the buffer rollers 26. The pre-loop configuration 92 is easily formed for thick, stiff media by the combination of buffer rollers being located vertically below the media path of the imagesetter, the downward deflecting media guides, and the angled center axis C-C of the buffer rollers 26. As in the previous embodiment, the media 16 then passes through the rollers 26 and reaches the second media sensor 62 when the buffer rollers 26 stop to hold the leading end 70 stationary with respect to the buffer rollers 26. Then the process of loading the media is then complete, and continuing operation of the buffer 10 proceeds in the same manner as the previous embodiment to deliver the media to the processor rollers 86. In the embodiment depicted in Fig. 4, the processor rollers 86 can be positioned slightly above the horizontal plane of the buffer rollers to facilitate the loading of the media into the processor rollers. It will be appreciated by those skilled in the art that in the above described embodiments the buffer rollers that serve as a means for gripping the leading end of the media during loading of the media into the buffer, can alternatively be replaced with a vacuum pick-up mechanism mounted on the carriage which cooperates with the media guides and sensors described in the preferred embodiment. Further, it will be appreciated that the external buffer can be used in many different applications and is not limited to media handling between an imagesetter and a processor. While this invention has been described in terms of a preferred embodiment, those skilled in the art will appreciate that various modifications, substitutions, omissions and changes may be made. Accordingly, it is intended that the scope of the present invention be limited solely by the scope of the following claims.

Claims: A buffering apparatus (10) for buffering a sheet of media (16) between a first media handling station (18) and a second media handling station (86), said sheet of media (16) having a leading end (70) and a trailing end (80), said leading end (70) of the media (16) being fed at a first speed (V1) into the buffering apparatus (10), said buffering apparatus comprising: a carriage (20) movably supported between the first media handling station (18) and the second media handling station (86), the carriage (20) further including a drive motor (50) for advancing the carriage from a pick-up position adjacent to the first media handling station (18) to a delivery position adjacent to the second media handling station (86) and back again, said carriage (20) being moveable at a second speed (V2) which is slower than the first speed (V1); a pair of media transport rollers (26) rotatably supported by the carriage (20) such that a longitudinal axis of the rollers (26) is perpendicular to the axis of motion of the carriage (20), said pair of media transport rollers (26) including a drive roller (26b) driven by a motor (30) and an idler roller (26a), the drive roller (26b) and the idler roller (26a) being in rolling contact with each other thereby forming a nip therebetween for transporting the sheet of media (16) through the nip when the drive roller (26b) is driven and for holding the sheet of media (16) when the drive roller (26b) is stopped; a first sensor (60) positioned near an entrance to the buffering apparatus (10) for detecting the leading end (70) of the sheet of media being delivered by the first media handling station (18) and for detecting the trailing end (80) of the sheet of media (16) as it exits the first media handling station (18); a second sensor (62) positioned proximate to an exit side of the transport rollers (26) for detecting the leading end (70) of the sheet of media (16) as it advances past the media transport rollers (26) and for detecting the trailing end (80) of the sheet of media as it exits the media transport rollers (26); means for starting rotation of the pair of media transport rollers (26) at the first speed (V1) to receive the leading end (70) from the first media handling station (18) in response to the leading end (70) passing the first sensor (60) thereby advancing the leading end (70) through the nip between the pair of rollers (26); and means for stopping the pair of rollers (26) to hold the leading end (70) in a stationary position in response to the leading end (70) passing the second sensor (62); means for moving the carriage (20) at the second speed (V2) to transport said pair of rollers (26) holding the leading end (70) from the first media handling station (18) to the second media handling station (86), the trailing end (80) of the media (16) being pulled behind the carriage (20); characterised by : pivotally movable media guide means (74) located between the pair of media transport rollers and said first media handling station, having a first substantially horizontal position for guiding the leading end (70) of the media sheet (16) received from the first media handling station (18) to the pair of media transport rollers (26), and a second angled position which allows the trailing end (80) and a slack loop (78) of the media (16) to be pulled behind the carriage (20) while the carriage (50) moves from the first media handling station (18) to the second media handling station (86). The buffering apparatus (10) according to claim 1 wherein the first media handling station (18) is internal to an imagesetter (12) and wherein the second media handling station (86) is internal to a processor (14). The buffering apparatus (10) according to any one of the previous claims further comprising brake means (40) for stopping rotation of and holding the idler roller (26a). The buffering apparatus (10) according to any one of the previous claims further comprising overrunning clutch means (36) for allowing the drive roller (26b) to have one-way rotation with respect to a drive gear (32) for said drive roller (26b). A method for buffering a media sheet (16) between a first media handling station (18) and a second media handling station (86) by a pair of media transport rollers (26) carried by a movable carriage (20), comprising the steps of: positioning the carriage (20) at a media pick-up position adjacent to the first media handling station (18) for receiving a leading end (70) of the media sheet (16) therefrom at a first continuous speed (V1); rotating the pair of media transport rollers (26) by an amount sufficient to receive the leading end (70) of the media sheet (16) between the pair of media transport rollers (26) and then stopping the rotation of the pair of media transport rollers (26) after the leading end (70) is advanced beyond the rollers (26); transporting the carriage (20) and the pair of media transport rollers (26) holding leading end (70) at a second continuous speed (V2) which is slower than the first continuous speed (V1), from the first media handling station (18) toward the second media handling station (86); characterised by the steps of: forming a slack loop (78) of media between the media transport rollers (26) moving at the speed (V2) and the first media handling station (18) which is feeding the sheet of media (16) at the speed (V1) said slack loop continuing to form until a trailing end (80) of the media sheet (16) is released from the first media handling station (18), said trailing end (80) being pulled behind the moving carriage (20); positioning a pivotally movable media guide (74) attached to the carriage (20) in a first substantially horizontal position when the carriage (20) is positioned at the media pick-up position for guiding the leading edge (70) between the pair of media transport rollers (26); and positioning the pivotally movable guide (74) in a second angled position as the carriage (20) moves away from the pick-up position, said angled position guiding the sheet of media (16) during the forming of the slack loop (78) The buffering method according to claim 5 further comprising the steps of: generating a first signal when said leading end (70) enters said buffer, said first signal being used to start the rotation of said pair of media transport rollers (26); generating a second signal when said leading end (70) is sufficiently received between the pair of media roller (26), said second signal being used to stop the rotation of the pair of media transport rollers (26) and to start transporting the carriage (20) toward the delivery position adjacent to the second media handling station (86); and generating a third signal when the leading end (70) is released from the first media handling station (18). The buffering method according to any one of claims 5 or 6, further comprising the step of: upon the release of the leading end (70) from the first media handling station (18) starting the rotation of the pair of media transport rollers (26) to advance the leading end (70) to the second media handling station (86). The buffering method according to claim 7 wherein said second media handling station (86) comprises a processor (14), the buffering method further comprising the step of generating a fourth signal from the processor (14) indicating that the processor (14) is ready to accept the leading end (70), the fourth signal being used to start the rotation of the pair of media transport rollers (26) to advance the leading end (70) to the processor (14). The buffering method according to any one of claims 5 - 8, further comprising the step of, after transporting the entire media sheet (16) beyond the pair of media transport rollers (26) to the second media handling station (86), then moving the carriage (20) at the second speed (V2) back to the media pick-up position adjacent to the first media handling station (18) for receiving a leading end (70) of another sheet of media (16).

Inventors: KRUPICA LIBOR, MCELWAIN WILLIAM L, KRUPICA, LIBOR, MCELWAIN, WILLIAM L.
Applicants: AGFA CORP, AGFA CORPORATION
Application year: 1995
Main classification: G03D13
IPC codes: B65H5, G03D13, G03D3