Transfer assist blade

FIELD OF THE INVENTION

[0002] The present invention relates generally to a reprographic printing machine. More specifically, the present invention pertains to an apparatus for assisting the transfer of a developed image from an imaging surface, such as a photoconductive surface or intermediate image transfer surface, to a print sheet, such as paper, by optimizing the contact between the print sheet and the imaging surface. The present invention also pertains to such a transfer assist apparatus including a variable length transfer assist blade that may be adjusted for a plurality of different size print sheets.

BACKGROUND OF THE INVENTION

[0003]
FIG. 1 is a schematic illustration of a typical electrophotographic printing machine 10 that may employ a transfer assist blade according to the present invention (not shown in FIG. 1). The illustrated printing machine includes a conventional photoconductive layer or light sensitive surface 12 on a conductive backing in the form of a belt 14. The belt is mounted on a plurality of rollers journaled in a machine frame (not shown), in order to rotate the belt and cause the photoconductive surface 12 to pass sequentially through a plurality of reprographic process stations A through E.

[0004] The several generally conventional processing stations A through E in the path of movement of the photoconductive surface 12 may be as follows. A charging station A, where the photoconductive surface of the photoconductive belt 14 is uniformly charged. An exposure station B, where a light or radiation pattern of a document to be printed is projected onto the photoconductive surface to expose and discharge select areas of the photoconductive surface to form a latent image thereon. A developing station C, where developer material is applied to the photoconductive surface of the drum to generate a toner image on the photoconductive surface. A transfer station D, where the toner image is electrostatically transferred from the photoconductive surface to a print sheet. Finally, a cleaning station E, where the photoconductive surface is brushed or otherwise cleared of residual toner particles remaining thereon after image transfer.

[0005] In order to generate multi-color prints, there may be a group of process stations A through E for each of a plurality of colors. For example, there may be a group of stations A through E for each of yellow, cyan, magenta and black. One method of generating multicolor prints is to arrange all of the color stations around a single photoreceptor and generate a toner image on the photoreceptor for each color, one color at a time. After each individual color toner image is formed on the photoreceptor, it is transferred to an intermediate transfer surface before the next color toner image is generated. This is repeated for each color, thereby building up a full color toner image on the intermediate transfer surface. The full color toner image is then transferred from the intermediate transfer surface to the print sheet. The intermediate transfer surface may be formed on an intermediate transfer belt, roll, drum or other suitable structure. Alternatively, a separate photoreceptor may be provided for each color. In which case, each color toner image is formed on the corresponding photoreceptor and transferred to the intermediate transfer surface, thereby creating a multi-color toner image on the intermediate transfer surface. The multi-color toner image is then transferred from the intermediate transfer surface to the print sheet.

[0006] Another method of generating full color prints is to arrange all of the color processing stations around a single photoreceptor and form all of the color toner images, one on top of each other, during a single rotation of the photoreceptor. The full color toner image may then be transferred from the photoreceptor to the print sheet, eliminating the need for an intermediate transfer surface.

[0007] Print sheets, such as paper or other print substrate, supplied from a sheet feeding tray or sheet feeding module 16, are fed by a series of sheet feeding rollers and guide rails to the transfer station D. At the transfer station, the developed toner image is transferred from the photoconductive belt 14 (or intermediate transfer surface) to the print sheet. The print sheet is then stripped from the photoreceptor belt by a sheet stripper 18 and transported to a fusing station F, where a fuser 20 fuses the toner image onto the print sheet in a known manner. The print sheet, which now has an image fused to a first face thereof, is then transported by a plurality of rollers to an output tray or stacking module 26 for one-sided or simplex copying. It will be appreciated that the print sheet may pass directly into the stacking module. It will also be appreciated that the print sheet may be inverted prior to entering the stacking module or may be inverted and returned to the developing station for duplex printing.

[0008] The various machine operations are regulated by a controller (not shown) which is preferably a programmable microprocessor capable of managing all of the machine functions and subsystems. Programming conventional or general purpose microprocessors to execute imaging, printing, document, and sheet handling control functions with software instructions and logic is well known and commonplace in the art. Such programming or software will, of course, vary, depending on the particular machine configuration, functions, software type, and microprocessor or other computer system utilized. Those of skill in the software and/or computer arts can readily program the microprocessor and/or otherwise generate the necessary programming from functional descriptions, such as those provided herein, or from general knowledge of conventional functions together with general knowledge in the software and computer arts without undue experimentation. The operation of the exemplary systems described herein may be accomplished by conventional user interface control inputs selected by the operator from the printing machine consoles. Conventional sheet path sensors or switches may be utilized to keep track of the position of documents and print sheets in the machine.

[0009] The electrophotographic printing process and machine described above, and variations thereof, are well known and are commonly used for light lens copying and digital printing and photocopying. In digital printing and photocopying processes, a latent image is produced by modulating a laser beam or by selectively energizing light emitting diodes in an array of diodes. A digital original may be created digitally in any known manner, or may be a digital image of a hard copy that was previously scanned, digitized and stored in memory. In ionographic printing and reproduction, a charge is selectively deposited on a charge retentive surface in response to an electronically generated or stored image. It should be understood that a drum photoreceptor, or flash exposure may be alternatively employed.

[0010] The process of transferring charged toner particles from an image bearing member, such as the photoconductive member or an intermediate transfer member to a print sheet is accomplished in a reprographic machine by overcoming the adhesive and electrostatic forces holding the toner particles to the image bearing member. This has been accomplished, for example, via electrostatic induction using a corona generating device. The print sheet is placed in direct contact with the developed toner image on the photoconductive surface, while the reverse side of the print sheet is exposed to a corona discharge. The corona discharge generates ions having a polarity opposite that of the toner particles on the photoconductive surface. The ions electrostatically attract the toner particles from the image bearing member and into contact with the print sheet, thereby transferring the toner particles from the image bearing member to the print sheet. Other forces, such as mechanical pressure or vibratory energy, have also been used to support and enhance the electrostatic transfer process.

[0011] To achieve substantially complete transfer of the developed image to the print sheet, it is necessary for the print sheet to be in intimate uniform contact with image bearing surface. However, the interface between the image bearing surface and the print sheet is rarely uniform. Print sheets that have been mishandled, left exposed to the environment, or previously passed through a fixing operation (e.g., heat and/or pressure fusing) tend to be non-flat or uneven. An uneven print sheet makes uneven contact with the image bearing surface. In the event that the print sheet is wrinkled, the sheet will not be in continuous intimate contact with the image bearing surface. Wrinkles in the sheet cause spaces or air gaps to materialize between the developed toner powder image on the image bearing surface and the print sheet. When spaces or gaps exist between the developed image and the print sheet, various problems may result. For example, there is a tendency for toner not to transfer across the gaps, causing variable transfer efficiency and creating areas of low toner transfer or even no transfer. A phenomenon known as image transfer deletion. Clearly, image transfer deletion is undesirable in that portions of the desired image may not be appropriately reproduced on the print sheet.

[0012] One known approach for curing the transfer deletion problem is illustrated in U.S. Pat. No. 5,247,335 to Smith et al., which discloses a flexible blade member, or so-called transfer assist blade. A solenoid-activated lever arm moves the transfer assist blade from a non-operative position spaced from the print sheet, to an operative position in contact with the print sheet. When in the operative position, the transfer assist blade presses the print sheet into contact with the developed image on the photoconductive surface, thereby substantially eliminating wrinkles in the sheet and gaps between the sheet and the photoconductor.

[0013] U.S. Pat. No. 4,947,214 to Baxendell et al. and U.S. Pat. No. 5,227,852 to Smith et al. each disclose a transfer assist blade formed of two separately actuated segments, thereby providing a variable length transfer assist blade. A first of the segments is actuated when an 11 inch sheet is passing through the developing station. Both segments are actuated when a 14 inch sheet is passing through the developing station. A separate blade actuating motor and linkage arrangement is provided for each blade segment.

[0014] U.S. Pat. No. 5,300,993 to Vetromile and U.S. Pat. No. 5,300,944 to Gross et al. each disclose a variable length transfer assist blade apparatus formed of a plurality of blade segments. In order to accommodate print sheets of a plurality of cross-process dimensions, varying numbers of the blade segments are selectively actuate into and out of their operative position in contact with the print sheet by a cam shaft. The cam shaft has a plurality of lobes or cam segments of varying length. The cam shaft is rotated so that the lobe having a length that corresponds to the desired actuated or unactuated length of the transfer assist blade presses against the blade segments. Thus, the cam shaft deflects the desired number of blade segments into (see Gross et al.) or out of (see Vetromile et al.) contact with the photoconductive surface. The cam shaft disclosed by Vetromile et al. and Gross et al. enables the selective deflection of varying numbers of blade segments with a single drive motor that rotates the cam shaft.

[0015] For obvious reasons, it is desirable that the size or footprint of modern reprographic printing machines be as small as possible. As the size of the reprographic machines is reduced, the space available in the machine for the transfer assist blade and associated mechanisms is similarly reduced. Furthermore, the space between the corona generating device and the image bearing surface is extremely limited. The space limitations are multiplied in full color xerographic machines. A color xerographic printing machine typically has a plurality of sets of charging, developing and transfer stations, for example, one set for each of yellow, cyan, magenta and black, packed into the available interior space. Due to the limited space available in reprographic printing machines, the prior art variable length transfer assist blade systems are limited to providing segmented transfer assist blades having lengths corresponding to a relatively limited number of discrete sheet dimensions.

[0016] Many of the existing variable length transfer assist blade devices require a separate actuation motor and linkage for each blade segment. As the number of blade segments is increased, the number of motors and links is also increased. As a result, the cost and complexity of the system increases dramatically as the number of blade segments is increased. Furthermore, only a limited number of motors and associated linkage mechanisms will fit within the available space. On the other hand, existing devices that employ a single cam shaft to actuate all of the transfer assist blade segments eliminate the need for a separate drive motor and linkage for each blade segment. As the number of blade segments is increased, however, the number of cam lobes spaced around the periphery of the cam shaft must also increase. As the number of cam lobes spaced around the periphery of the cam shaft increases, the diameter of the cam shaft must be increased. The diameter of the cam shaft is limited by the available space within the reprographic machine. As a result, the number of cam lobes and the number of separately actuatable transfer assist blade segments are likewise limited.

[0017] The few discrete transfer assist blade dimensions available in the prior art devices may not always correspond to the dimension of the print sheets being processed for imaging in a reprographic printing machine. For example, a reprographic machine may be provided with a transfer assist blade having variable segmented lengths corresponding to print sheets having cross-process dimensions or width of 11″, 11.7″, 13″, and 14″. In the case where a 10″ paper width is to be processed through the transfer station, the 11″ blade segment is actuated. As a result, an inch of the transfer assist blade contacts the surface of the photoreceptor. The area of the blade that contacts the photoreceptor will, in most instances, pick up residual dirt and toner from the photoreceptor surface. The next job run which processes print sheets having a dimension greater than 10″ will have the residual dirt on the transfer assist blade transferred to the back side of the print sheet, resulting in an unacceptable print quality defect. More importantly, continuous frictional contact between the blade and the photoreceptor may cause permanent damage to the photoreceptor.

[0018] In the case of a print sheet having a dimension of, for example, 12.5″, the transfer assist blade segments corresponding to a print sheet dimension of 11.7″ may be actuated. In this case, the widthwise marginal regions of the print sheet extending beyond the 11.7 inches will not be pressed against the photoconductive surface by the transfer assist blade. As a result, the risk of transfer deletions intended to be eliminated by the transfer assist apparatus will not be prevented in those portions of the print sheet extending beyond the marginal regions of the blade member.

[0019] There is a need in the prior art for a variable length transfer assist blade mechanism having a large number of available lengths, in order to accommodate print sheets having a large number of different the cross-process dimensions or widths. Such a transfer assist blade must fit within the limited space available in modern electrostatographic printing and copying machines. It is also may be desirable for such a transfer assist blade device to be capable of switching from one width to another quickly enough to do so between pitches (i.e. in between immediately consecutive print sheets), and thereby avoid the need to skip a pitch.

SUMMARY OF THE INVENTION

[0020] An apparatus according to one form of the present invention includes a resilient contact blade having a blade root and a blade tip. The blade is movable from an inoperative position in which the blade root is spaced from the print sheet contacting the imaging member by a first distance and the blade tip is spaced from the print sheet to an operative position in which the blade root is spaced from the print sheet by a second distance that is greater than the first distance. A blade deflector located in the path of travel of the blade from the inoperative position to the operative position, wherein, while the blade is moving from the inoperative position to the operative position the blade engages the deflector. When the blade is in the operative position the blade is deflected by the deflector causing the blade tip to contact the print sheet and press the print sheet against the imaging member.

[0021] An apparatus according to another form of the present invention includes a contact blade, formed of a plurality of blade segments, mounted parallel to and spaced form the imaging surface. A plurality of blade lifters, one blade lifter for each of the blade segments, are individually movable from an inoperative position immediately adjacent to the blade segments to an operative position. When in the operative position the lifters engage the blade segments and deflect the blade segments causing tips of the blade segments to contact a the print sheet contacting the imaging surface and press the print sheet against the imaging surface. A lifter activating device for moving a current select number of adjacent blade lifters into the operative position. The current select number being selected such that a current number of adjacent blade segments having a cumulative length that is equal to a width of a current the print sheet currently contacting the imaging surface are deflected and contact with the current print sheet. A lifter locking member for engaging the current select blade lifters in the operative position and current non-selected blade lifters in the inoperative position while the current print sheet is in contact with the imaging surface.

[0022] Another form of the present invention includes a contact blade mounted parallel to and spaced from the imaging surface, the contact blade being formed of a plurality of blade segments. A plurality of blade lifters, one blade lifter for each of the blade segments, are individually movable from an inoperative position immediately adjacent to the blade segments to an operative position in which the lifters engage the blade segments. In the operative position the lifters deflect the blade segments causing tips of the blade segments to contact a print sheet contacting the imaging surface and press the print sheet against the imaging surface. A guideway extending along ends of the blade lifters remote from the contact blade. An elongate cam slidably mounted in the guideway, the cam having gear teeth formed along one side thereof. A pinion gear mounted adjacent to the guideway in engagement with the gear teeth on the cam. A motor operatively connected to the pinion gear for rotating the pinion gear, moving the cam in the groove, and thereby moving a select number of the blade lifters into the operative position. The select number being selected such that a select number of adjacent blade segments having a cumulative length that is equal to a width of a the print sheet contacting the imaging surface are deflected and contact the print sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will now be described, by way of example, with reference top the following drawings, of which:

[0024]
FIG. 1 is a diagrammatic illustration of an exemplary reprographic printing machine;

[0025]
FIG. 2 is side plan view of a transfer assist blade and associated actuating mechanism according to an embodiment of the present invention, showing the transfer assist blade in the unengaged position;

[0026]
FIG. 3 is an enlarged front plan showing the transfer assist blade and associated mechanism of FIG. 1 in the engaged position;

[0027]
FIG. 4 is a partially broken away perspective view of the transfer assist blade and associated mechanism of FIG. 1;

[0028]
FIG. 5 is a partial cross-sectional top view of the actuation mechanism of FIG. 1;

[0029]
FIG. 6 is a perspective view of the transfer assist blade and the blade holder of FIG. 1;

[0030]
FIGS. 7 and 8 are side plan and perspective views, respectively, of a blade lifter according to one form of the present invention; and

[0031]
FIGS. 9 through 12 are sequential cross-sectional views illustrating the operation of the transfer assist blade actuation mechanism of FIG. 1.

[0032] For a general understanding of the features of the present invention, reference is made to the drawings, wherein like reference numerals have been used throughout to identify identical or similar elements.

DESCRIPTION OF THE INVENTION

[0033] A transfer station D incorporating a transfer assist blade mechanism 40 according to one form of present invention is illustrated in FIGS. 2 through 4. The illustrated transfer station D includes a corona generating device 42 attached to base plate 44 that is mounted to the machine frame (not shown). The corona generating device (only shown in FIG. 2) charges a print sheet 30 (shown in FIG. 3) to the proper magnitude and polarity, so that the print sheet is tacked to photoconductive belt 14 and moves in unison with photoconductive belt in the direction of arrow S. As the print sheet moves in unison with the photoconductive belt, the toner image is electrostatically attracted from the belt 14 to the print sheet.

[0034] The transfer assist apparatus also includes a transfer assist blade 50. As the print sheet 30 moves into the transfer zone between the corona generating device 42 and the photoconductive belt 14, the transfer assist blade is pressed against the print sheet (As shown in FIG. 3). Thus, the transfer assist blade applies a uniform contact pressure to the print sheet as it passes through the developing station D, for pressing the print sheet into uniform contact with the photoconductive surface 12 of the photoreceptor belt 14.

[0035] The transfer assist blade 50 is secured in a blade holder 52 (also see FIG. 6) by wrapping one elongate edge of the blade around a retaining rod 54, and securely snapping or sliding the rod into a C-shaped retaining head formed on the blade holder (best seen in FIG. 3). The blade holder 52 is secured between a pair of pivot arms or blade brackets 56, only one of which is visible in FIGS. 2 and 3. The pivot arms are pivotally journaled on a pair of blade axles 58 that are affixed to a portion of the machine frame (not shown). Lower ends of the pivot arms are interconnected by a bar 60 that extends therebetween. A stepper motor 62 is secured to the base plate 44 or is otherwise secured to the machine frame. A crank arm 64 is secured to the output shaft of the stepper motor. The crank arm is connected to the bar by a link 66. The blade axles 58 are offset to one side of the pivot arms 56 by legs 68 that extend from the pivot arms.

[0036] With this construction, pivotal motion of the pivot arms in a clockwise direction about the axles, causes the transfer assist blade 50 to move generally down, away from the photoconductive belt 14, from an inoperative position shown in FIG. 2 (and in ghost in FIG. 3) to an operative position shown in FIG. 3. A blade deflector or lifter 70 is secured to the base plate, such that the blade lifter is located to engage a central portion of the transfer assist blade 50 when the blade is moved into the operative position. In order to move the transfer assist blade from the inoperative to the operative position, the pivot arms 56 only need to be pivoted about the axles 58 a small amount, for example 4 degrees. The force applied by the transfer assist blade 50 to the print sheet may be controlled by adjusting the degree of rotation of the pivot arms 56 under the control of the first stepper motor.

[0037] All terms of orientation, such as up, down, lower, upper, left, right, front and back, etc., are relative to the orientation of the apparatus as shown in the appended Figures. It will be appreciated that the apparatus may be employed in different orientations, such that upper and lower may, for example, be reversed or become left and right. Use of such terms of orientation in the description of the illustrated embodiment of the invention and in the appended claims is for the purpose of facilitating the description of the arrangement and interaction of the components of the invention relative to each other. As such, the use of such terms of orientation in the present description and in the appended claims is not intended to limit the invention to any particular orientation. The use of such terms is only intended to set forth the arrangement and interaction of the components relative to each other, whatever the orientation of the overall arrangement may be.

[0038] An optical sheet sensor (72 in FIG. 1) may be provided for detecting the leading edge of a print sheet as it enters the transfer station D, or as the print sheet travels through an area of the machine prior to delivery to the transfer station. The signal from the sensor is processed by the controller 34 for controlling the actuation of the transfer assist device 40. When a signal indicating an incoming print sheet is received by the controller from the sensor, the controller activates the first stepper motor 62 to rotate in a clockwise direction as viewed in FIGS. 2 through 4.

[0039] Rotation of the first stepper motor 62 in the clockwise direction causes the pivot arms 56 to pivot clockwise about the blade axles 58. This causes the blade holder 52 to move the root of the transfer assist blade generally down, away from the photoreceptor belt 14, from the inoperative position (shown in FIG. 2 and in ghost in FIG. 3) to the operative position (shown in solid lines in FIG. 3). When the root of the transfer assist blade moves down toward the operative position, the blade lifter 70 engages the central portion of the transfer assist blade 50. As the transfer assist blade continues to move into the operative position, the blade lifter causes the transfer assist blade to deflect upwardly, such that the tip of the blade contacts the underside of the print sheet 30 passing through the developing station D.

[0040] As the trailing edge of the print sheet passes the sheet sensor 72, the sensor again transmits a signal to the controller. Upon receiving this signal, the controller rotates the first stepper motor 62 in the counter-clockwise direction, thereby shifting the transfer assist blade 50 into its inoperative position as illustrated in FIG. 2, immediately before the trailing edge of the print sheet arrives at the transfer assist blade. In the inoperative position, the transfer assist blade 50 is spaced from the print sheet and the photoconductive belt, ensuring that blade does not scratch the photoconductive belt or accumulate toner particles therefrom which might otherwise be deposited on the backside of the next successive print sheet.

[0041] Also, when in the inoperative position the transfer assist blade is disengaged from and is not deflected by the blade lifter 70, and is therefore advantageously in a relaxed, un-flexed condition. Since the transfer assist blade spends more time in the inoperative position than in the operative position, the transfer assist blade will therefore be less likely to take a set and will have a longer life span than a blade in an arrangement the flexes the blade in the inoperative position.

[0042] The embodiment described herein and shown in the amended Figures is intended to disclose one form of the present invention by way of example only. It will be understood that the stepper motor and crank arm arrangement shown in FIG. 1 represents one of various means for selectively pivoting the pivot arms 56 for positioning the transfer assist blade 50. Numerous other apparatus or systems, such as a solenoid device, a cam assisted assembly, or other suitable mechanism, may alternatively be incorporated into the present invention in place of the illustrated stepper motor and crank arm for facilitating the same or a similar function. Similarly, the sheet sensor may be any type of sensor or switch that is suitable for detecting the presence of a print sheet.

[0043] The transfer assist apparatus according to one form of the present invention includes a variable length transfer assist blade 50. With particular reference now to FIGS. 4 and 5, the transfer assist blade 50 has a plurality of slits formed therein that separate the blade into a plurality of blade segments. A first or primary blade segment 80 and a plurality of smaller secondary or auxiliary blade segments 82 extending along a substantially common longitudinal axis substantially parallel to the surface 12 of belt 14. Each blade segment may be fabricated from a resilient, flexible material, as for example, Mylar, manufactured by E. I. DuPont de Nemours, Co. of Wilmington, Del. The plurality of blade segments cooperate, as discussed in further detail below, for providing a variable length transfer assist blade.

[0044] The primary transfer assist blade segment 80 has a length corresponding to the smallest process width dimension of a print sheet contemplated for use in the machine, for example, 5.5 inches. The transfer assist blade 50 blade is mounted in the blade holder 52 such that its outboard end 84 is in alignment with the outboard edge of the photoreceptor belt 14. The auxiliary transfer assist blade segments 82 can be of any length, but in most instances will be shorter than the primary assist blade segment 80 and may be, for example, 8.5 millimeters in length each. The cumulative length of the primary blade segment and the auxiliary blade segment matches the greatest process width dimension of a print sheet contemplated for use in the machine, typically the width of the photoconductive belt 14, which may be, for example, 14.33 inches. The number of available discrete variable transfer assist blade lengths corresponds with the overall number of blade segments 80 and 82. Thus, the greater the number of auxiliary blade segments 82, the greater the number of available blade lengths. The auxiliary blade segments are illustrated as all being of a common length. It will be appreciated, however, that the auxiliary blade segments may be of varying lengths that are selected to provide the desired discrete blade widths.

[0045] As best seen in FIGS. 4 and 5, the blade lifter 70 is formed of a plurality of individual blade lifters or deflectors. A primary blade lifter 90 is immovably affixed to the base plate 44 in a blade deflecting or operative position. The primary blade lifter may alternatively be formed as an integral unitary part of the base plate. A plurality of smaller auxiliary blade lifters 92 are mounted for reciprocal vertical movement relative to the base plate 44. Referring now to the partial cross-sectional top view of FIG. 5, a vertical guide channel 94 is formed in the base plate for each of the auxiliary blade lifters. Vertical guide ribs 96 extend from the sides of the channels 94. The ribs are slidably received within vertical grooves 98 (see FIGS. 7 and 8) formed in the sides of each auxiliary blade lifters 92. Thus, the auxiliary lifters 92 are guided in the vertical direction by the ribs, which act as guide rails for the lifters. Cam followers 100 extend from the lower ends of the auxiliary blade lifters. A cam 110 is slidably mounted in a channel 112 formed, for example, in an extension of the second stepper motor's housing.

[0046] In order to selectively move the cam 110, a second stepper motor 114 is mounted to the base plate 44 or otherwise mounted to the machine frame. A pinion gear 116 is affixed to the output shaft of the second stepper motor. Gear teeth formed in the edge of the cam 110 mesh with the gear teeth on the pinion gear 116. The right end of the cam (as viewed in FIG. 4) tapers downward defining an upwardly facing inclined cam surface 118 (see FIG. 8). When the second stepper motor is rotated clockwise, the pinion gear moves the cam to the right in FIG. 4, as indicated by arrow X in FIG. 4. As the cam moves to the right, the cam surface 118 engages the cam followers 100 and pushes the auxiliary blade lifters up 92, one by one, from the lower inoperative position to the upper operative position as indicated by arrow Y in FIG. 4. The auxiliary blade lifters only need to move up far enough to engage and deflect the auxiliary blade segments 82. For example, a distance of approximately 3 millimeters may suffice, depending on the overall configuration of the system. Positive stops may be provided in the guide channel 94 to stop the blade lifters upward movement and accurately locate the auxiliary blade lifters in the operative position relative the belt 14.

[0047] When the second stepper motor 114 is rotated counterclockwise, the cam 110 moves to the left, out from under the movable lifters 92, one by one, such that the lifters 92 move back down to the inoperative position. In this manner, the pinion gear 116 moves the cam into a position that lifts a selective number of auxiliary blade lifters 92, which correspond to the desired operative blade segments 82, into the operative position. When the transfer assist blade 50 is subsequently moved by the first stepper motor 62 into the operative position, the raised auxiliary blade lifters 92 deflect the corresponding blade segments 82 against the print sheet 30. In this manner, the desired effective blade length is deflected into contact with the print sheet.

[0048] By way of example, when processing a print sheet having a 10″ process width in a machine having a 10″ long primary blade lifter 90 and primary blade segment 80, all of the auxiliary blade lifters are positioned in the lower inoperative position. Thus, only the primary blade segment 80 is deflected into contact with the print sheet 30. However, when the process width of the print sheet is greater than the length of the primary transfer assist blade segment 80, then select auxiliary blade lifters 92 adjacent to the primary blade lifter 90 are activated to deflect auxiliary blade segments 82 in to contact with the print sheet. The number of deflected auxiliary blade segments is selected such that the inboard edge of the activated auxiliary segments precisely corresponds to, or is just shy of the inboard edge of the print sheet. The print sheet is pressed against the surface of the photoconductive belt by both the primary transfer assist blade 80 and the deflected auxiliary transfer assist blade segments 82.

[0049] Operation of the above-described variable length transfer assist blade system is as follows. The transfer assist blade 50 is first placed into the inoperative position by the first stepper motor 62. While the blade is in the inoperative position, the number of auxiliary blade lifters 92 that correspond to the width of an incoming print sheet 30 are placed in the operative position by appropriately locating the cam 110 with the second stepper motor 114. When the incoming sheet enters the transfer region D, the first stepper motor 62 is activated to move the transfer assist blade into the operative position. As the transfer assist blade moves into the operative position, the primary blade segment 80 and the auxiliary blade segments 82 that correspond to the auxiliary blade lifters 92 in the upper operative position are deflected such that the tips of these blade segments contact the print sheet. The auxiliary blade segments 82 that correspond to the inactivated auxiliary blade lifters in the lower inoperative position remain undeflected and therefore remain in the inoperative position and do not contact the print sheet. Thus, only the blade segments 80 and 82 whose total combined width is equal to or somewhat less than the cross-process width dimension of the print sheet traveling through the transfer station are activated. Just prior to the print sheet exiting from the transfer region, the first stepper motor 62 is activated to move the blade holder to the inoperative position. Thus, all of the blade segments are disengaged form the blade lifters and move into the undeflected inoperative position spaced from the photoconductive belt as show in FIG. 2. This process is repeated for each consecutive sheet entering and exiting the transfer region.

[0050] The second stepper motor 114 retains the cam in a fixed position as long as print sheets 30 of the same cross-process dimension, or width, are entering the transfer region D. When a next sheet entering the transfer region has a different width than the preceding sheet just exiting the transfer region, then the second stepper motor must reposition the cam 110 to raise the correct number of blade lifters 92 into the operative position. The second stepper motor 114 must make the transfer assist blade width adjustment in the inter-document zone, i.e. between consecutive print sheets, while the blade holder 52 is in the inoperative position. In high speed printing machines, it may be necessary to skip a pitch (a section of the photoconductive belt equal to one sheet), in order to provide enough time for the second stepper motor to move the cam into the desired position before the next print sheet to be printed on enters the transfer region. Since this adjustment is only made when there is a change in print sheet width, skipping a pitch when making the transfer assist blade width adjustment is acceptable in most circumstances.

[0051] In some instances, skipping a pitch every time a transfer assist blade width adjustment must be made may be undesirable. This may be true for high-speed printers and copiers, particularly when printing on small print sheets. Skipping pitches decreases the overall output speed of the machine. Skipping pitches also requires additional programming to maintain synchronization of the toner images on the photoconductive belt with the incoming print sheets and maintain proper registration of the image with the print sheets.

[0052] Referring once again to FIGS. 2 through 4, an optional embodiment of the present invention includes a parking brake feature. The parking brake feature allows the second stepper motor 114 to adjust the position of the cam 110 in the middle of a pitch, i.e. while a print sheet is currently passing through the transfer station D, rather than only in the inter-document zone.

[0053] One possible form a parking brake includes a blade lifter locking member or parking brake 130 mounted between a pair of end flanges 132 (only one of which is visible in FIGS. 2 and 3). The end flanges are mounted for rotation about pair of pins 134 secured to the machine frame (not shown) and journaled through a central portion of the end flanges. The parking brake extends from one end of the end flanges for pivotal motion therewith into and out of engagement with the auxiliary blade lifters 92. A pair of links 136 connect the ends of the end flanges 132 remote from the parking brake to the pivot arms 56. The links 136 are connected to the pivot arms 56 at a location spaced from the axles 58 of the pivot arms 56. With this construction, when the pivot arms are pivoted by the first stepper motor 62 into the operative position, the links cause the end flanges to rotate about the pins. Rotation of the end flanges causes the parking brake 130 to pivot from an unparked or disengaged position clear of the auxiliary blade lifters (shown in FIG. 2 and in ghost in FIG. 3), to a parked or locked position engaging the auxiliary blade lifters 92 (shown in solid lines in FIG. 3).

[0054] The parking brake 130 has been described above as pivoting about pins 134 along with motion of the pivot arms, due to the links 136. It will be appreciated that other arrangements may be provided for selectively moving the parking brake. For example, the parking brake may translate, rather than pivot, and may be actuated by a separate stepper motor or solenoid. One of skill in the art will envision various arrangements for actuating the parking upon reviewing the present description and appended drawings, all of which are intended to be within the scope of the present invention and the appended claims.

[0055]
FIGS. 7 and 8 illustrate one possible form of the auxiliary blade lifters 92 for use with the parking brake embodiment of the present invention. According to this optional form, the lower end of each auxiliary blade lifter 92 is provided with a longitudinally extending bore 140. The cam follower 110 is formed on the lower end of a piston or plunger 142. An upper portion of the plunger is sized and shaped to be slidably received in the bore in the blade lifter. A compression spring 144 is located in the bore in the blade lifter, followed by the plunger. The plunger is pressed against the spring to pre-stress the spring and the plunger is then secured in the blade lifter by press fitting or otherwise securing a retaining pin 146 in a cross-bore provided in the plunger 142. A longitudinally extending slot 148 is provided in at least one side of the blade lifer 92 to provide access to the bore in the plunger for insertion of the pin. The retaining pin 146 has a length that is greater than the diameter or cross-section of the top of the plunger, such that the pin extends into the slot 148 and thereby retains the plunger 142 in the blade lifter 92. The slot 148 has a longitudinal length that is greater than or equal to the length of travel of the blade lifter 92 from the inoperative position to the operative position. Thus, the pin may travel up and down in the slot, providing the desired range of motion of the plunger 142 within the bore 140.

[0056] The side of each blade lifter facing the parking brake is provided with a shoulder 150 and a slot that defines a downwardly facing ledge 152. The shoulder and the ledge are spaced by a distance that is somewhat less than the travel distance of the blade lifter from the inoperative position to the operative position. The shoulder and the ledge are position to engage the parking brake 130 as follows. When a given blade lifter 92 is in the lower inoperative position (as shown in ghost in FIG. 3) and the parking brake 130 is in the braking position (as shown in solid lines in FIG. 3), the parking brake is located just above the shoulder 150 (dashed lines in FIG. 3). On the other hand, when a given blade lifter is in the upper operative position, then the parking brake is located just below the ledge 152 (solid lines in FIG. 3).

[0057] The proposed parking arrangement functions as illustrated in FIGS. 9 through 12, which show the sequence of operation. Before the first print sheet 30 arrives at the transfer station D the transfer assist blade 50 is located in the inoperative position, awaiting the arrival of a print sheet. The second stepper motor 114 is activated to move the cam 110 via the pinion gear 116, to the appropriate location that corresponds to the width of the first incoming sheet, as shown in FIG. 9. When in the appropriate location, the cam lifts a number of blade lifters 92-A, whose cumulative length is equal to or somewhat less than the width of the incoming first print sheet to the upper operative position. The remaining blade lifters 92-B remain in the lower inoperative position. The cam 110 must be in the desired position shown in FIG. 9 before the leading edge of the print sheet arrives at the transfer station D.

[0058] Once the print sheet arrives at the transfer station, as detected by the sensor, the first stepper motor 62 is activated to move the transfer assist blade 50 from the inoperative position (FIG. 2) to the operative position (FIG. 3). Since the parking brake 130 is connected to the pivot arms 56 via the links 136, the parking brake moves along with the transfer assist blade into the operative or parked position. In the parked position, the parking brake is located just above the shoulders 150 on the auxiliary blade lifters 92-B that are in the inoperative position and just below the ledges 152 on the auxiliary blade lifters 92-A that in the operative position. Thus, the parking brake parks or locks the auxiliary blade lifters 92 in position, such that the cam 110 may be moved without affecting the positions of the auxiliary blade lifters 92 or the auxiliary blade segments 82.

[0059] With the transfer assist blade 50 and the parking brake 130 in the operative position, the blade lifters 92 are locked in place as described above. As a result, when a next incoming print sheet is of a different width than a print sheet that is currently passing through the transfer station D, the cam 110 may be moved to a new position corresponding to the width of the incoming sheet without moving the auxiliary blade lifters 92 or altering the effecting transfer assist blade length. When the cam is moved to a new position with the parking brake in the operative locking position, for example, to the right underneath additional auxiliary blade lifters 92-C as shown in FIG. 9, the cam followers 100 of the additional auxiliary blade lifters 92-C are raised by the cam 110. The additional auxiliary blade lifters themselves, however, are locked in place by the engagement of the parking brake 130 with the shoulders 150 on the additional auxiliary blade lifters. Thus, the plungers 142 move up in the bores in the additional auxiliary blade lifters compressing the springs 144, but the additional auxiliary blade lifters 92-C remain in the inoperative position as shown in FIG. 9.

[0060] When the current sheet is about to exit the transfer region D, as detected by the sensor, the first stepper motor 62 is activated to move the transfer assist blade 50 to the inoperative position. The parking brake 130, which is connected to the pivot arms 56 by the links 136, moves along with the transfer assist blade into the inoperative position clear of the auxiliary blade lifters 92. As a result, the additional auxiliary blade lifters 92-C are unlocked or released, and are raised by the compressed springs into the upper operative position and become activated raised auxiliary blade lifters 92-A as shown in FIG. 11. As the next sheet moves into the transfer region, the first stepper motor 62 is activated, thereby moving the transfer assist blade and the parking brake into the operative position. Thus, the appropriate transfer assist blade segments 82 are deflected by the raised auxiliary blade lifters 92-A into contact with the next wider sheet.

[0061] When the next print sheet approaching the transfer station is narrower than sheet currently in the transfer station D, the process is reversed. The cam 110 is moved to the left prior to arrival of the next narrower sheet, while the current sheet is still within the transfer region and the auxiliary lifters 92 are locked in place by the parking brake as shown in FIG. 12. The transfer assist blade 50 and the parking brake 130 are maintained in the operative position until the current sheet is about to exit the transfer station. As a result, the cam moves out from below the cam followers 100 of the auxiliary blade lifters 92-D that are to be lowered for the next narrower sheet. However, auxiliary blade lifters 92-D remain locked in the operative position by engagement of the parking brake with the ledges 152 and remain in the raised operative position (see FIG. 12). When the current sheet is about to exit the transfer station, the transfer assist blade 50 and the parking brake 130 are moved into the inoperative position. At which point, the auxiliary blade lifters 92-D will drop to the inoperative position (not shown, but similar to FIG. 9).

[0062] While the present invention has been described in connection with an illustrative embodiment, it will be understood that the preceding description is not intended to limit the invention to the specifics of the disclosed embodiment. On the contrary, the description is intended to cover all alternatives, modifications, and equivalents that may be included within the spirit and scope of the invention as defined by the appended claims. Other aspects, features and embodiments of the present invention will become apparent to one of skill in the art upon reviewing the preceding description and the accompanying drawings.

[0063] For example, it will be understood that the rack and pinion arrangement of the pinion gear 116 and the cam 100 is only one of many systems that may be employed to activate the auxiliary blade lifters 92. For example, a cam shaft, lead screw, cable drive, or other well known mechanisms may be employed to activate the auxiliary blade lifters or an associated cam. The rack and pinion arrangement does have space saving advantages over many of the other options and may be the best choice when a large number of auxiliary blade lifters are desired and free space is within the machine limited. Thus, the disclosed rack and pinion arrangement is just one optional feature of the present invention.

[0064] The other features of the present invention, such as the reverse actuation of the transfer assist blade (i.e. actuation by moving the blade away from the photoconductive belt and into engagement with a stationary blade lifter) and the parking brake feature, may be employed separately or with alternative mechanisms without departing from the spirit of the present invention. When the parking brake feature is employed separately from the reverse actuation, then the transfer assist or contact blade may be stationarily mounted relative to the imaging surface or member. In this case, the blade lifters or deflectors move into contact with the stationary blade segments and deflect the blade segments into contact with the print sheet.

Transfer assist blade

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