Precision referencing/latching system for document separation and transport in a scanning unit

Abstract: In a scanning unit such as a facsimile machine, an automatic document feeder transports individual sheets from a stack of documents along a document path over a scanning window to an output tray. Precise co-planar referencing is provided between a pick roller mounted on a frame beneath a document path and a document separator mechanism mounted on an upper guide member which moves between an open position for allowing manual access to the document path to a closed position for scanning document sheets. An integrated sheet metal chassis on the upper guide member provides a direct reference path between a central portion of the chassis which carries the document separator mechanism as well as Z axis and Y-axis (media transport direction) reference datums on both side edges of the channels which are engaged by a rigid vertical reference arm. A latching device is located closely adjacent to the reference datums to securely hold the upper guide member in a predetermined closed position, as well as determine positioning in the X axis. A pair of pivotal arms at the post-scanning end of the chassis allow clearance in the X-axis and Y-axis while providing secondary referencing in the Z-axis.

Description: BACKGROUND OF THE INVENTION This case relates generally to a scanning unit having rollers for selectively feeding individual document sheets along a document path past a scanning station comprising a frame having a rigid upper guide member. as known from US-A-4 508 444. Prior art scanning units have typically had a myriad of parts making up the document path. This has typically resulted in complicated referencing between adjoining parts which produces larger tolerance variations. Accordingly, misfeeds often occur, and the quality of scanning is often unsatisfactory, thereby resulting in bad outputs such as at a facsimile receiver. Prior solutions have failed to adequately deal with the problem, and the multiple parts have required more intervention during assembly of the products, and greater paper path disruption, as well as imprecise referencing between elements on a rigid frame and matching elements on an upper document guide which is typically move between a closed scanning position and an open position to allow manual accessibility. What is needed is a document picking and transport system which provides the advantages of improved reliability and output quality due to decreased assembly time and intervention, decreased part count, decreased interruption of the document path, and improved document control while scanning. BRIEF SUMMARY OF THE INVENTION In a scanning unit according to claim 1 an automatic document feeder transports individual sheets from a stack of documents along a document path over a scanning window to an output tray. Precise co-planar referencing is provided between a pick roller mounted on a frame beneath a document path and a document separator mechanism mounted on an upper guide member which moves between an open position for allowing manual access to the document path to a closed position for scanning document sheets. More specifically, an integrated sheet metal chassis on the upper guide member provides a predictable referencing scheme as follows: the position in the vertical Z axis is primarily determined by two shoulder datums on two vertical frame arms which respectively engage bottom datum surfaces on a flat portion of the chassis, and secondarily determined by a third shoulder on one or the other of the pivot arms at the post-scanning end of the chassis. However, the pivot arms are designed to preferably have some play in the X and Y axis directions to avoid overriding the positioning by the X and Y datums. The position in the Y axis is determined by two inclined lateral datum edges which respectively engage one side of their matching chassis apertures. The Y axis (i.e., document transport direction) datums are immediately adjacent to the primary Z axis datums. Finally, the position in the X axis is an equilibrium location determined by opposing outward forces exerted by two spring latches acting against latch seats formed in flange plates. The spring latches also provide a strong downward force against the latch seats to maintain constant intimate contact between the datum surfaces. A co-planar reference path is provided between a central portion of the chassis which carries the document separator mechanism and reference datums on a side edge of the chassis which are engaged by a rigid vertical reference arm. A latching device is located closely adjacent to the reference datums to properly position the datums and to securely hold the upper guide member in a predetermined closed position. This application is related to European patent applications EP-A-0 706 894 and EP-A-0 706 895, both prior art according to article 54(3) EPC, as well as European co-pending applications EP-A-0 707 972 and EP-A-0 707 974. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top perspective view of a facsimile machine incorporating a presently preferred embodiment of the invention; FIG. 2 is a back perspective view of the machine of FIG. 1 with its upper automatic document guide in open position exposing the document path past a scanning station; FIG. 3 is a presently preferred stripper or pick roller; FIGS. 4 and 5 are side view illustrating the dynamic action of the pick roller of FIG. 3 and a presently preferred separator assembly which together enable individual document sheets to be picked one by one from a stack; FIG. 6 is a side cut-away view of the scanner unit of the facsimile machine of FIG. 1; FIG. 7 is a partial isometric view of a chassis portion of an upper guide member in closed position on a frame; FIG. 8 is an enlarged fragmentary view of FIG. 7 looking up at the latching mechanism and certain reference datums; FIG. 9 is a complete side view of FIG. 7; FIG. 10 is a side view of the frame portion of FIG. 7 showing the transfer gears from a motor to the pick roller, pre-scanning primary drive roller and post-scanning (kickout) secondary drive roller; FIG. 11 is a side view of a chassis mounted on an upper guide member having a control/display member; FIG. 12 is a side view of only the chassis portion of FIG. 11; FIG. 13 is an enlarged fragmentary view of FIG. 12 showing a spring-biased limiter; FIG. 14 is a bottom view looking up at a portion of FIG. 11; and FIG. 15 is a top view of only the chassis portion of FIG. 11, with the separator assembly mounted thereon, and showing the spring-biased mounting of the pre-scanning and post-scanning pinch rollers. Detailed Description Of The Preferred Embodiments Generally speaking, the invention includes a scanning unit such as a facsimile machine, an automatic document feeder transports individual sheets from a stack of documents along a document path over a scanning window to an output tray. Precise co-planar referencing is provided between a pick roller mounted on a frame beneath a document path and a document separator mechanism mounted on an upper guide member which moves between an open position for allowing manual access to the document path to a closed position for scanning document sheets. An integrated sheet metal chassis on the upper guide member provides a direct reference path between a central portion of the chassis which carries the document separator mechanism as well as Z axis and Y-axis (media transport direction) reference datums on both side edges of the channels which are engaged by a rigid vertical reference arm. A latching device is located closely adjacent to the reference datums to securely hold the upper guide member in a predetermined closed position, as well as determine positioning in the X axis. A pair of pivotal arms at the post-scanning end of the chassis allow clearance in the X-axis and Y-axis while providing secondary referencing in the Z-axis. In that regard, the invention is best understood in connection with the illustrated embodiments shown in the drawings, as described in more detail below. Fig. 1 is a front perspective view of a facsimile machine 10 incorporating the preferred embodiment paper separator mechanism. Facsimile machine 10 contains a paper tray 12 which is downward directed so that a paper stack 14 placed into tray 12 is urged toward the receiving portion of machine 10 by gravity. The paper stack 14 enters a slot in the back of machine 10. A paper separation mechanism within machine 10 pulls one sheet of paper at a time from the bottom of the stack 14 so that printing on the sheet may be read and subsequently transmitted by the facsimile machine 10 in a well known manner. The sheet may also be copied by machine 10. In another embodiment, machine 10 is a printer which feeds in blank sheets of paper for printing thereon. The individual sheets of paper are then outputted through exit slot 16. A printing mechanism (not shown) is also provided in the complete machine 10 for printing received facsimile transmissions. The printing mechanism, which may be an inkjet or laser printer, can also be used when machine 10 is used as a copier or printer. Fig. 2 is a back perspective view of the facsimile machine 10 with its hinged top portion 17 lifted up to reveal the paper separation and paper transport mechanisms. Paper feed tray 12 has been removed in Fig. 2 for simplicity. When top portion 17 is in its closed position, shown in Fig. 1, and paper stack 14 is placed in paper tray 12, the front edge of the stack extending over shelf 18 abuts against a rubber stripper roller 20, and paper-feed springs 22 and 24 provide a downward force on paper stack 14. When stripper roller 20 rotates, the frictional force between roller 20 and the bottom sheet, and the frictional forces between the bottom sheet and the overlying sheets, pull the paper sheets further into machine 10. A rubber separator pad 26, biased downward by a separator spring 27 ( obscured in Fig. 2), effectively blocks all sheets but the bottom sheet so that only the bottom sheet directly contacted by the rubber stripper roller 20 is forwarded past separator pad 26. In one embodiment the average forwarding speed of stripper roller 20 is about 12 mm/sec. A downstream, rubber maim feed roller 30 is rotated so as to have a faster paper forwarding speed (e.g., 26 mm/sec.) than stripper roller 20. Thus, when the bottom sheet of paper is sufficiently forwarded by stripper roller 20 to be between main feed roller 30 and an opposing passive roller 32, the bottom sheet will be pulled by main feed roller 30 (rather than pushed by stripper roller 20) to ensure that the paper speed is constant and correct across window 34 or any printing mechanism. Stripper roller 20 is driven via a slip clutch, which allows stripper roller 20 to rotate at the increased forwarding speed of main feed roller 30 when a single sheet of paper simultaneously contacts both rollers 20 and 30. Main feed roller 30 forwards the paper over a window 34, below which resides the necessary optical detection electronics for detecting the printing on the bottom sheet. Such optical electronics can be conventional and will not be described in detail herein. If machine 10 were solely a printer, window 34 and the optical electronics may be replaced by a printing mechanism. A kick-cut roller 36, in conjunction with a passive opposing roller 38, has a 2% faster forwarding speed than main feed roller 30 to ensure that there is no slack in the paper between rollers 30 and 36. The pulling force of main feed roller 30 is approximately 13,5 N (3 pounds), while the pulling force of kick-out roller 36 is approximately 6,75 N (1.5 pounds), so the speed of the paper is controlled by maim feed roller 30 rather than kick-out roller 36. A single stepper motor drives each of the rollers 20, 30, and 36, and gear mechanisms and slip clutch mechanisms are used for driving rollers 20, 30, and 36 at the required rotational speeds and forces. The users of the facsimile machine 10, when placing the paper stack 14 in position on tray 12, will insert the stack 14 into machine 10 with varying amounts of forca depending upon what tactile feedback the user believes is required to indicate a proper positioning of the stack. If the expected tactile feedback force is very light, then no sheets may be grabbed by the rotating stripper roller 20, since there is insufficient friction between roller 20 and the bottom sheet. If the user expects a high degree of tactile feedback, the stack 14 will be wedged deeply between stripper roller 20 and the opposing springs 22, 24, and 27, thus possibly causing multiple sheets to be simultaneously forwarded downstream by stripper roller 20. The below-described stripper roller 20 and opposing spring assembly (comprising springs 22, 24, and 27 and separator pad 26) improve the separating function of the- stripper mechanism to compensate for the varying forces initially exerted on the paper stack 14 when the user inserts the stack 14 into machine 10. Fig. 3 is a perspective view of the preferred embodiment stripper roller 20. Stripper roller 20 includes eccentric kicker portions 40 and 42 located at the ends of the cylindrical middle portion 44 (also identified in Fig. 2). Stripper roller 20 is forcedly slipped over a stainless steel shaft 46 and is frictionally secured to shaft 46. Shaft 46 includes a flattened end 48 which is ultimately secured to a suitable slip clutch and gear mechanism within facsimile machine 10 for rotating stripper roller 20. A molded plastic shim 50 is attached to shaft 46 and includes an extension which is inserted under kicker portion 40 to create the eccentricity of kicker portion 40. An identical shim 51 is used to create the eccentricity of kicker portion 42. Figs. 4 and 5 illustrate the operation of the eccentric kicker portions 40 and 42 as the apex 60 makes a first revolution after a paper stack 14 is inserted into the facsimile machine 10. In Fig. 10, a user inserts a paper stack 14 in the direction shown by arrow 61 between paper-fed springs 22/24 and kicker portions 40/42 of roller 20. The user senses the resistance to further insertion of the paper stack 14 and releases the paper stack 14. The actual extent to which the paper stack 14 is inserted between roller 20 and paper-feed springs 22/24 thus varies depending upon the user. As the apex 60 is rotated toward the paper stack 14, the downward force applied by paper-feed springs 22/24 is thus increased (causing the friction between the kicker portions 40/42 and the bottom paper sheet to be increased). At the same time, the apex 60 of kicker portions 40/42 effectively reaches out to contact a greater bottom surface area of the bottom paper sheet so that the bottom sheet is pulled forward by the direct frictional contact with the kicker portions 40/42, while the other sheets are pulled forward with less force by their friction with this bottom sheet. The downward angle of paper-feed springs 22/24 causes the paper stack 14 to spread forward to resemble a staircase (Fig. 5 ), while the bottom sheet or bottom few sheets continue to be carried forward by the high friction between the kicker portions 40/42 and the bottom sheet. Fig. 5 illustrates the position of stack 14 after being carried forward during the first rotation of stripper roller 20 at the point where apex 60 has now completed its function and advanced the bottom sheet 64 or bottom few sheets to be in contact with the rubber separator pad 26. During this next stage, the friction between the bottom sheet 64 and the rotating roller 20 continues to push the bottom sheet 64 out from under separator pad 26, while the sheets overlying this bottom sheet 64 are held back by contact with separator pad 26 and slip with respect to the bottom sheet 64. After the bottom sheet 64 has exited from between separator pad 26 and stripper roller 20, the next sheet comes in direct contact with the rubber surface of the stripper roller 20 and is thus forced under the separator pad 26, while the separator pad 26, in conjunction with the angled paper-feed springs 22 and 24, hold back the remainder of the sheets. Once the bottom sheet being passed under separator pad 26 reaches the main feed roller 30 shown in Fig. 2, then the main feed roller 30 controls the forwarding of the bottom sheet, as previously described with respect to Fig. 2. Referring back to Figs. 1-2, it will be understood that top portion 17 generally constitutes an upper guide member which is held in a closed position during scanning by a pair of upstanding spring latches 70/71. The various document control components previously described including a composite separator assembly 72, and the passive rollers 32/38 are mounted in a rigid chassis 74 preferably made of sheet metal. Also directly mounted on the chassis are electrostatic discharge devices (ESD) such as conductive brushes 76 located adjacent the document path exit 16. The preferred embodiment provides a display window 78 on a display/control panel 80 which have respective circuit board components 82/84 shown by dotted lines which are sandwiched against the chassis 74. A ground plate (not shown) framing the display pane is directly grounded to the metallic chassis which also acts as a shield to protect the circuit board elements from damage by ESD. The chassis is grounded to the frame by a separate ground wire (not shown) and also through a metallic pivot hinge to be described hereinafter. The details of the scanner are best shown in Fig. 6, including a LED illumination array 86, an opaque baffle 88, a transparent scanning window 90, and mirrors 91/92/93 which transfer the optical signals from a document being scanned through a lens 94 to a CCD array 100. A limiter 95 having level portion 96, angled portion 97, lever arms 98, and mounting fingers 99 is spring biased to press a document somewhat tightly out of its normal position between the two drive rollers to a predetermined location in close proximity but preferably not touching the scanning window. The angled portion helps guide the document without obstructing the document path. A white background for calibration purposes is provided on bottom surfaces of the level and angled portions 96/97, such as Kimdura plasticized paper which is specialized optical material having suitable optical characteristics as well as suitable durability during normal use and cleaning. The limiter is spring loaded to exert a force of at least 0,5 N (1/10 of a pound) in order to overcome any counterbalancing from the document sheet. In reality, the actual spring force use is about five times that minimum amount to avoid the need for precise tolerances during manufacturing. In order to achieve the proper picking and transporting of document sheets past the scanning window, the following preferred specifications have been used for the driven rollers: diameter hardness doc. speed spr. force PickRoller 19 mm 30 shoreA 12.7 mm/sec N/A PreScanRoller 12.7 mm 50 shoreA 25.9 mm/sec 2 x 7,2 N (1.6 lbs) PostScanRoller 12.9 mm 50 shoreA 26.3 mm/sec 2 x 8,1 N (1.8 lbs) Figs. 7-9 show the details of the pivotal hinging, as well as the referencing and latching between the chassis of the upper guide member and the frame 101. The latch spring mechanism includes a base 102, a frame mounting pine 103, chassis lip 104, a V-shaped spring extension 105, and a chassis aperture 106. An upstanding arm 110 has a shoulder surface 111 which engages a Z-datum surface 112 on the chassis, and also has a tapered tongue 113 with a reference edge 114 to engage a reference seat 115 on the chassis and a non-reference edge which preferably has a slight clearance relative to the reference seat. Both of the V-shaped spring extensions push outwardly, as well as downwardly to securely engage the reference surfaces. Each pivotal arm 120 on the chassis potentially abuts a downwardly facing secondary datum 121 as it moves between open and closed positions in a pivoting slot 122 in the frame. A wire spring 125 is suspended between two bridge elements 126, 127 and passes through an aperture 128 and around the end of the lever arm of the limiter to provide the aforementioned spring biasing (see Fig. 13). In summary, there are Y-axis datums formed by the edge 114 of arm 110 of the frame and the mating surface of seat 115 of the chassis and Z-axis datums formed by the shoulder surface 111 on upstanding arm 110 and the mating surface 112 of the chassis as well as by pivotal arm 120 and secondary datum 121. Figs. 10 shows the gear train going from a motor shaft 130 through first and second transfer gears 131/132 to pick roller gear 133, through first transfer gear 131 to pre-scanning roller gear 134, and through third transfer gear 135 to post-scanning roller gear 136. The holes for the gear shafts are respectively shown in Fig. 9. Fig. 11 shows the chassis mounted on the upper guide member which has a slotted guide 138 with a flex-arm to temporarily hold the upper guide member in open position and a stop 139 to prevent opening the upper guide member too far. Fig. 12 shows the same view of the chassis separate from the upper guide member. Fig. 14 shows the positioning of the separation assembly and the two idler rollers as well as the mounting screw hole 140 for the wire spring. Slots 142/143 are for a first sensor flag to detect documents inserted for scanning, and a second sensor flag to detect a single document sheet which has already been picked and is headed for the scanning window. Fig. 15 shows one cantilever leaf spring 150 (its mate is not shown) mounted on a first hole 151 to provide a short cantilever arm 152, and a second identical cantilever leaf spring 154 (its mate is not shown) mounted on a second hole 155 to provide a longer cantilever arm 156. Each idler roller is a hollow hard plastic roller which is mounted on a stationary axle 158 held in lengthwise position by flange brackets 160 and held in Z-axis position by small holes 162 in each of the cantilever leaf springs. The cantilever leaf springs also include a positioning flange for mounting on their upstanding brackets 164.

Claims: A scanning unit such as a facsimile machine (10) having a pick roller (20) for selectively feeding individual document sheets along a document path past a scanning station (34; 86-94) comprising: a frame (101) having a pick roller (20) thereon in the document path; post-scanning arms (123) fixedly attached to and extending upwardly from said frame and having pivot slots (122); a rigid upper guide member (17, 74) having a separator assembly (72) thereon located upstream from said pick roller (20) and including pivoting legs (120) for engaging said pivot slots; pre-scanning arms (110) fixedly attached to and extending upwardly from said frame (101) and having first datum surfaces (111) in the Z-axis and second datum surfaces (114) in the Y-axis; Z-axis datums (112) on said guide member for engaging said first datum surfaces and Y-axis datums (115) on said guide member for engaging said second datum surfaces, whenever said upper guide member (17, 74) is moved from an open position allowing manual access to the document path to a closed position allowing scanning of document sheets, to achieve optimum positioning of said separator assembly (72) relative to said pick roller (20). The scanning unit of claim 1 wherein said Z-axis datums and/or said Y-axis datums are located on an edge portion of said guide member (17, 74) which edge is substantially co-planar with a central portion of said guide member. The scanning of unit of claim 1 or 2 wherein said pivoting legs (120) include secondary datums (121) for engaging said pivoting slots (122), the secondary datums providing referencing in the Z-axis. The scanning unit of one of the preceding claims which further includes a latching mechanism (70, 71) for holding said upper guide member (17, 74) in said closed position. The scanning unit of one of the preceding claims wherein said Z-axis (112) and Y-axis (115) datums are located in close proximity to each other on said guide member (74). The scanning unit of claim 4 or 5 wherein said latching mechanism (70, 71) is located in close proximity to said Z-axis datums and/or said Y-axis datums on said guide member (74). The scanning unit of claim 4, 5 or 6 wherein said latching mechanism includes two spring arms (70, 71) extending upwardly from said frame (101) and said upper guide member (17, 74) includes two latch seats (106) said spring arms engaging said latch seats to securely position said upper guide member in said closed position. The scanning unit of claim 7 wherein said two spring arms (70, 71) exert opposing outward forces against said latch seats (106) to establish an equilibrium position in the X-axis direction. The scanning unit of one of the preceding claims wherein said second datum surfaces include two inclined lateral datum edges (114) and said Y-axis datums include one side of a chassis aperture (115) for engaging said inclined lateral datum edges. The scanning unit of one of the preceding claims wherein said first datum surfaces include two shoulder datums (111) and said Z-axis datums include a bottom flat portion (112) of said upper guide member for engaging said shoulder datums. The scanning unit of one of the preceding claims wherein said rigid upper guide member (17) includes a rigid sheet metal chassis (74). The scanning unit of claim 11 wherein said Z-axis datums and/or said Y-axis datums and/or said pivoting legs are part of said metal chassis.

Inventors: SONNENBURG DENNIS NMI, WILCOX DARREN W, SONNENBURG, DENNIS, (NMI), WILCOX, DARREN W.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: B41J29
IPC codes: H04N1, B41J13, B65H3