Patent Publication Number: US-7584953-B2

Title: Step spring auto-compensator mechanism

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   None. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   None. 
   REFERENCE TO SEQUENTIAL LISTING, ETC. 
   None. 
   BACKGROUND 
   1. Field of the Invention 
   The present invention provides a media feeding apparatus. More specifically, the present invention provides an auto-compensating mechanism in combination with a step-spring for providing appropriate normal force throughout the feeding of a media stack. 
   2. Description of the Related Art 
   Various mechanisms have been utilized to feed media into a printer or other peripheral. Various of these mechanisms utilize a tray or bin in order to support a stack media in which the upper most sheet of the stack may be advanced to a processing station or printing area for printing by a laser printer or inkjet printer, for example. In typical printing or duplicating devices, individual sheets of print media are advanced from the media tray to the processing station by utilizing a paper picking device. 
   With media picking devices a critical relationship exists between the pick roller and the media stack. More specifically the relationship involves a normal force between the pick roller and the media stack. The normal force must be within an operating range for the pick or media feed process to work properly. When too much normal force exists, multiple sheet of media may be fed resulting in paper jams. When too little normal force exists, media will not feed into the printing area. Some devices utilize a spring loaded paper stack to provide the normal force for picking. Despite extensive tuning of this normal force, usually only a very narrow range of media weights will run reliably on these devices. 
   Feeding of print media sheets from a stack has been significantly improved by an auto-compensating mechanism (ACM) shown and described in U.S. Pat. No. 5,527,026, issued to Padget et al. which overcomes problems with obtaining proper normal force. Auto-compensating media feeders address prior art issues in media feeding. A pick roll is mounted on the rotating swing arm and rests on the media stack. When the pick roll drive gear is initiated through a gear located on the pivot shaft with the swing arm, a torque is applied to the swing-arm through a gear transmission. The torque rotates the swing arm and pick roll into the media stack. This generates a normal force which is dictated by the buckling resistance of the media being picked. The normal force is no more than is required to buckle a single sheet of media plus the friction resistance between the first and second sheets. When the upper most sheet has moved, the normal force automatically relaxes and, thus, the auto-compensating mechanism will not deliver more normal force than what is required to feed a single sheet of media. 
   In a C-path feeding system, the ACM is disposed in a generally horizontal position when the media tray contains a full stack of media at upper positions, close to the horizontal, the down force created by the ACM is not high enough to consistently feed the microporous media because the normal force provided by the ACM is low. As the media stack height decreases during operation, the ACM moves through its operating positions during which time the normal force increases. At lower positions, i.e. positions away from the horizontal, the down force is high enough to allow for sheet feeding of the microporous media and the like. These systems are critically affected by various media characteristics including, but not limited to, density, net weight, stiffness and smoothness of the media surface. For example, lightweight media is fairly easy to move from a media stack. However, as media thickness and weight have increased with increased photo printing, the difficulty with consistent feeding throughout a media stack has increased. Even more recently, print feeding difficulties have occurred due to the use of microporous photo paper. The high coefficient of friction between sheets of microporous media tends to remove the ACM from its range of operating torque. Increased down force of the ACM has not alleviated this problem throughout the media stack feeding. 
   Given the foregoing deficiencies, it will be appreciated that an apparatus is needed which allows consistent media feeding of many types of media. 
   SUMMARY OF THE INVENTION 
   A media pick assembly comprises a media tray for retaining a stack of media in a peripheral, an auto-compensating mechanism disposed adjacent to the media tray, the auto-compensating mechanism movable through an operating range including a starting angular position and an ending angular position, and a media biasing member engaging the auto-compensating mechanism and providing a discontinuous force on the auto-compensating mechanism through the operating range. The discontinuous force may act on the auto-compensating mechanism based on a position of the auto-compensating mechanism. The down force is applied in a limited portion of the operating range corresponding to a height of the stack of media in the media tray. The biasing member disengages the auto-compensating mechanism at a preselected position. The limited angular range is between about 0 degrees and about 25 degrees. The biasing member is a leaf spring or a coil spring. The assembly has a total down force by the auto-compensating mechanism and the discontinuous force by the biasing member is between about 2 and 4 milli-newtons. One end of the biasing member is connected to a structure inside of the peripheral. One end of the biasing member is connected to or in contact with the auto-compensating mechanism. 
   A media pick assembly comprises a printer, an auto-compensating mechanism within the printer which transmits torque to a media pick tire, the auto-compensating mechanism increasing down force on a media stack during operation through a preselected angular range, a biasing member having a first end and a second end, the first end engaging a stationary part of the printer, the second end engaging the auto-compensating mechanism, the biasing member applying a discontinuous force to the auto-compensating mechanism through a limited portion of the preselected angular range. The auto-compensating mechanism moves from a substantially horizontal position downward to a lower limit during the preselected angular range. The auto-compensating mechanism creates a down force which is proportional to resistance created between media sheets, the down force being greater when the media stack is low than when the media stack is high. The biasing member engages the auto-compensating mechanism when the media stack is high or above a preselected height to increase down force in the limited portion of the preselected angular range. The biasing member is connected to or engages with the auto-compensating mechanism. The biasing member is connected to an internal portion of the printer. 
   A media pick biasing assembly for a peripheral having an auto-compensating mechanism comprises an auto-compensating mechanism rotatably connected to a drive shaft, the auto-compensating mechanism having a range of motion associated with feeding of media from a media tray in the peripheral, a biasing member connected to the peripheral and engaging the auto-compensating mechanism, the biasing member applying a force on the auto-compensating mechanism through a preselected angular range of motion of the auto-compensating mechanism. The auto-compensating mechanism moving from a first position to a second position. The biasing member engages the auto-compensating mechanism within the preselected range of motion between the first position and the second position. The preselected range of motion is about 0 degrees to about 25 degrees. The biasing member is one of a leaf spring and a coil spring. The biasing member creates additional downward force for the auto-compensating mechanism within the preselected range and additional downward force is inhibited outside the preselected angular range. 
   A method of feeding media from a media stack into a peripheral device using an auto-compensating device, comprises applying a discontinuous force on said auto-compensating mechanism when said media stack is above a preselected height; feeding media from said input tray with said auto-compensating device; and discontinuing applying said discontinuous force on said auto-compensating mechanism when said media stack decreases to said preselected height during feeding of said media. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of an exemplary multi-function peripheral; 
       FIG. 2  is a perspective view of the exemplary multi-function peripheral of  FIG. 1  with a cut-away portion; 
       FIG. 3  is a perspective view of the ACM with a step-spring; 
       FIG. 4  is a side sectional view of the ACM with step-spring; 
       FIG. 5  is a graphical representation of the relationship between the ACM force and the height of the media stack; 
       FIG. 6  is a side view of the media tray within the printer and the positioning of the ACM and multi-step spring with a full media stack; 
       FIG. 7  is a side view of the media tray within the printer and positioning of the ACM and multi-step spring with a nearly empty media stack; 
       FIG. 8  is a perspective view of an alternate embodiment of the biasing element; 
       FIG. 9  is a perspective view of an alternate embodiment of the biasing element; and, 
       FIG. 10  is a perspective view of an alternate embodiment of the biasing element. 
   

   DETAILED DESCRIPTION 
   It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings. 
   In addition, it should be understood that embodiments of the invention include both hardware and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software. As such, it should be noted that a plurality of hardware and software-based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible. 
   The term image as used herein encompasses any printed or digital form of text, graphic, or combination thereof. The term output as used herein encompasses output from any printing device such as color and black-and-white copiers, color and black-and-white printers, and so-called “all-in-one devices” that incorporate multiple functions such as scanning, copying, and printing capabilities in one device. Such printing devices may utilize ink jet, dot matrix, dye sublimation, laser, and any other suitable print formats. The term button as used herein means any component, whether a physical component or graphic user interface icon, that is engaged to initiate output. 
   Referring now in detail to the drawings, wherein like numerals indicate like elements throughout the several views, there are shown in  FIGS. 1-10  various aspects of a peripheral device. The apparatus provides a step spring in combination with an ACM for consistent feeding of multiple media types through various media stack heights consistent with feeding of the stack from a media tray during printing. 
   Referring initially to  FIG. 1 , an all-in-one device  10  is shown having an ADF scanner portion  12  and a printer portion  20 , depicted generally by the housing. The all-in-one device  10  is shown and described herein, however one of ordinary skill in the art will understand upon reading of the instant specification that the present invention may be utilized with a stand alone printer, copier, scanner or other peripheral device utilizing a media feed system. The peripheral device  10  further comprises a control panel  11  having a plurality of buttons  29  for making command selections or correction of error conditions. The control panel  11  may include a graphics display to provide a user with menus, choices or errors occurring with the system. 
   Referring to  FIGS. 1 and 2 , extending from the printer portion  20  is an input tray  22  and an exit tray  24  at the front of the device  10  for retaining media before and after a print process, respectively. The input and output trays  22 ,  24  of the printer portion  20  define start and end positions of a media feedpath  21  ( FIG. 2 ). The media trays  22 ,  24  each retain a preselected number of sheets defining a stack of media (not shown) which will vary in height based on the media type. One skilled in the art will understand that the media feedpath  21  is a C-path media feed due to the depicted configuration. 
   Referring now to  FIG. 2 , an interior cut-away perspective view of the all-in-one device  10  is depicted. The printer portion  20  may include various types of printing mechanisms including dye-sublimation, ink-jet printing mechanism or laser printing. For purpose of clarity, the printing components are not shown in  FIG. 2 , so that the ACM and step-spring arrangement are clearly depicted. For ease of description, the exemplary printer portion  20  is an inkjet printing device. With the interior shown, the printing portion  20  may include a carriage (not shown) having a position for placement of at least one print cartridge  23  ( FIGS. 6 ,  7 ). In the situation where two print cartridges are utilized, for instance, a color cartridge for photos and a black cartridge for text printing may be positioned in the carriage. As one skilled in the art will recognize, the color cartridge may include three inks, i.e., cyan, magenta and yellow inks. Alternatively, in lower cost machines, a single cartridge may be utilized wherein the three inks, i.e., cyan, magenta and yellow inks are simultaneously utilized to provide the black for text printing or for photo printing. Alternatively, a single black color cartridge may be used. During advancement, media M ( FIGS. 6 ,  7 ) moves from the input tray  22  to the output tray  24  through the substantially C-shaped media feedpath  21  beneath the carriage and cartridge  23 . As the media M moves into a printing zone, beneath the at least one ink cartridge, the media M moves in a first direction as depicted and the carriage and the cartridges move in a second direction which is transverse to the movement of the media M. 
   Referring again to  FIG. 1 , the scanner portion  12  generally includes an ADF scanner  13 , a scanner bed  17  and a lid  14  which is hingedly connected to the scanner bed  17 . Beneath the lid  14  and within the scanner bed  17  may be a transparent platen for placement and support of target or original documents for manually scanning. Along a front edge of the lid  14  is a handle  15  for opening of the lid  14  and placement of the target document on the transparent platen (not shown). Adjacent the lid  14  is an exemplary duplexing ADF scanner  13  which automatically feeds and scans stacks of documents which are normally sized, e.g. letter, legal, or A4, and suited for automatic feeding. Above the lid  14  and adjacent an opening in the ADF scanner  13  is an ADF input tray  18  which supports a stack of target media or documents for feeding through the auto-document feeder  13 . Beneath the input tray  18 , the upper surface of the lid  14  also functions as an output tray  19  for receiving documents fed through the ADF scanner  13 . 
   Referring now to  FIGS. 3-6 , an auto-compensating mechanism  30  is depicted positioned above the input tray  22  and mounted on a drive shaft  32  which defines a pivoting location for an auto-compensating mechanism (ACM)  30 . The ACM  30  comprises a housing  34  which extends from the drive shaft  32  at one end to an opposite end where at least one pick tire or drive roller  46  is located. The exemplary housing  34  is generally ovalized in shape having a depth in a third dimension wherein various components are located. However, the housing  34  may be various alternative shapes capable of housing the components described herein and capable of mounting adjacent to the media feedpath  21 . 
   The drive shaft  32  is substantially cylindrical in shape and comprises a gear  33  at one end. The gear  33  is operably engaged with a gear train (not shown) mounted on a transmission frame  25  within the printer portion  20 . The transmission frame  25  may also function as a motor mount  27  wherein a motor (not shown) may be operably engaging the transmission gear train driving the ACM  30 . At a side of the printer  20  opposite the frame  25 , the shaft  32  is pivotally supported for rotation by the motor and transmission gear train (not shown). The drive shaft  32  may comprise a milled portion  60  for engagement of the ACM  30 . By rotating the drive shaft  32 , the milled portion  60  transmits torque to the ACM  30  and gears therein. Within the housing  34 , the drive shaft  32  operates an ACM drive train  36  including at least one gear mounted on the shaft  32  inside the ACM  30 . 
   At a first end of the drive train  36  is a drive shaft gear  38 . The drive shaft  32  extends through the drive shaft gear  38  and is engaged therewith to transmit torque from the shaft  32  to the gear  38 . In turn, this causes the ACM  30  to pivot in a counter-clockwise direction (as shown in  FIG. 4 ) about the shaft  32 . With counter-clockwise rotation, the ACM  30  creates downward or normal force at the at least one pick tire  46  spaced from the shaft  32 . As the ACM  30  encounters resistance from the media stack M, the normal force increases. The drive shaft gear  38  and shaft  32  may be driven by a motor directly or indirectly by a gear transmission (not shown) mounted on the transmission frame  25 . One skilled in the art will understand such configuration and will be able to ascertain which system is most desirable in a given application. 
   Adjacent the drive shaft gear  38  is a first idle or transmission gear  40 . The first transmission gear  40  rotates about a shaft  41  extending through the ACM housing  34 . The shaft  41  extends generally parallel to the drive shaft  32 . The first transmission gear  40  is driven by the drive shaft gear  38  and drives a second transmission gear  42 . In addition to rotating about shaft  41 , the first transmission gear  40  orbits about drive shaft  32  as the ACM  30  moves through a stack of media from a first angle of operation to a second angle of operation. The first transmission gear  40  may have a number of teeth which is selected by one skilled in the art based on the angular velocity of the drive shaft  32  and the desired angular velocity at the pick tire  46 . 
   Adjacent the first transmission gear  40  is a second transmission gear  42  which also rotates about a shaft  43  extending through the ACM housing  34 . The shaft  43  is also generally parallel to the drive shaft  32 . The second transmission gear  42  rotates about the shaft  43  and orbits about the shaft  32  and drive shaft gear  38 . The second transmission gear  42  acts as a reversing gear to provide the desired rotational direction of the pick tire  46  relative to the tray  22 . The desired rotational direction is determined by the direction of media feed required to move the media into the media feed path  21 . Like the first transmission gear  40 , the second transmission gear  42  has a number of teeth selected based on input angular velocity of the first gear  40  and the desired angular velocity of the pick tire  46 . 
   Adjacent the second transmission gear  42  is a drive roller gear  44  which is operably connected to the drive roller or pick tire  46 . The drive roller gear  44  and pick tire  46  are coaxially disposed upon a shaft (not shown) extending through the ACM housing  34  which is parallel to the shaft  32  as well as the shafts  41 , 43  for the first and second transmission gears  40 ,  42 . The gear  44  rotates about the shaft as well as orbiting about drive shaft  32 . As previously indicated, the input angular velocity of gear  42  and the number of teeth of gear  44  determine the output angular velocity of the gear  44  and pick tire  46 . Because this angular velocity is known based on required speed of media in the media feed path  21 , the characteristics for gears  40 ,  42  may be calculated, as will be understood by one skilled in the art. 
   Disposed above the ACM  30  is a step spring or biasing member  50 . The spring or biasing member  50  may be utilized to force a component to bear against, to maintain contact with, to engage, to disengage, or to remain clear of some other component. The biasing member  50  is capable of storing energy when loaded and forced in one direction by the ACM and media M there below. As the ACM  30  operated and moves in the second direction, the member  50  is unloaded until it applies no force on the ACM  30 . The biasing member has the characteristic of maintaining its ability to be loaded within operating loads. The exemplary biasing member  50  is depicted as a leaf spring however various elastic bodies and shapes may be utilized and substituted for the leaf spring design. For instance, the biasing member  50  may be, for example, a flat spring, a spiral spring or a helical spring. Flat springs include, but are not limited to, elliptical leaf or half-elliptical leaf springs. The helical springs are generally formed of round cross-section wire or the like and may include a compression or tension springs, as well as torsion and cone shaped springs. 
   The biasing member  50  is connected at an upper end to an adjacent structure of the printer  20  (not shown for purpose of clarity). The connection may be by fastener or by unitary connection such as a weld. Alternatively, the biasing member  50  may be connected to and extend from the housing  34  at one end, while free to engage some internal printer structure at the other end. 
   Because the step spring  50  is positioned above the ACM housing  34 , as the ACM  30  moves toward a horizontal position, the free end of the step spring  50  engages the ACM housing  34 . As a result, the flexed step spring  50  places a force on the ACM  30  which is substantially constant. As the ACM  30  rotates counter-clockwise during media feed, the down force increases due to the operation of the ACM  30 . As the media stack height decreases during operation, the force applied by the step spring  50  remains generally constant until the spring force is disengaged from the ACM  30 . 
   Referring now to  FIG. 5 , a graph is depicted which compares the normal force of the ACM to the input paper stack height. Alternatively interpreted,  FIG. 5  depicts a relationship between the normal force of the ACM and the angular position of the ACM  30 . As previously indicated, the normal force created by an ACM is less when the ACM is disposed in a substantially horizontal position. However, the ACM  30  utilizes a step spring  50  to increase the down force when the media stack M is high so that the down force is within a desirable operating range and so that media with high coefficients of friction may be picked. 
   As depicted, line A depicts the normal force created by the ACM  30  without a step spring. During operation, the down force is greatest when the media stack is low. As the media stack M decreases in height, during media feeding, the torque increases such that additional spring force is not necessary. The media height is related to the position of the ACM  30  because the ACM  30  is close to a horizontal position when the media stack is high and angled from the horizontal as the height decreases during media feeding. 
   Beneath line A, line B depicts the force created by the step spring. The force is zero until the media height reaches a pre-selected position. In the present example, the paper height must reach six millimeters (6 mm) for the step spring  50  to engage. Once engaged, the step spring  50  increases its force on the ACM  30  until the height reaches another preselected height, for example about seven millimeters (7 mm) where the force becomes substantially constant. Between 6 mm and 7 mm, the spring  50  is loaded by engagement between the printer frame and ACM  30 . Although these dimensions are provided, one skilled in the art should realize that these dimensions may vary based on the tray  22  capacity and position of the ACM relative to the tray  22 . The spring force is discontinuous since at certain positions no force is applied by the spring  50  while at other positions the spring  50  does apply force to the ACM  30  thereby increasing the normal force applied by the ACM  30  to the media stack M. 
   Line C represents a summation of the normal force created by the ACM  30  and the step spring  50 . The normal force is greatest at the end of the chart where the input paper stack is at its lowest. This is because the down force applied by the ACM  30  is high although the force applied by the spring  50  is zero. As the media stack height increases, the down force decreases until a jump in down force is exhibited around the six millimeter (6 mm) stack height, corresponding to Line B. As the media stack height increases, the normal force applied by the ACM  30  decreases but the force is higher than that force of Line A because of the increase in force caused by spring  50 . The increase in down force of spring  50  maintains the total down force (spring  50 +ACM  30 ) within a preselected operating range. According to the present exemplary embodiment, a range of operation for the normal force may be between 2 and 4 milli-Newtons. Although this may vary depending on the characteristics previously described. Further, since the spring  50  force is generally constant, curvature of Line C is generally parallel to Line A. At a position where the normal force would normally be outside its range of operation, the spring force of the step spring  50  increases the total normal force applied to the media so that the apparatus provides a normal force within an operable range even though the media stack continues to increase in height. Through this increase in normal force, the ACM  30  is kept within an operating range which is desirable and useful for various types of media. 
   Operation of the device is now described. Referring to  FIG. 6 , a side view of the ACM  30  is depicted in the printer  20  disposed above a media input tray  22  having a full media stack M therein. The stack height corresponds to a height which is along the right side of the chart of  FIG. 5  so that the biasing member  50  is fully loaded. The ACM  30  is disposed in a substantially horizontal position due to the height of the media stack M. The horizontal position causes the spring  50  to be flexed against the ACM  30  and impart a down force on the ACM  30 . The step spring  50  imparts a maximum force when the tray  22  is completely filled with media M. 
   As drive shaft  32  rotates in a counter-clockwise direction, gears  40  and  42  rotate in their respectively proper directions so that the gear  44  and pick tire  46  turn in a clockwise direction for media feeding. Rotation of the drive shaft  32  causes the ACM  30  to create a down force until the upper sheet of media slips relative to the second sheet. When this slip occurs, the down force of the ACM  30  relaxes and a sheet of media is fed. In combination with the ACM  30 , the biasing member  50  maintains enough down force on the ACM  30  from its horizontal position through a preselected angular position to keep the media feed operating properly. 
   Referring now to  FIG. 7 , the ACM  30  is again depicted after feeding some of the media stack M such that the angular position of the ACM  30  has changed. As compared to  FIG. 6 , the ACM of  FIG. 7  has rotated downwardly, in a counter-clockwise direction from a substantially horizontal position to a position disposed away from the horizontal such that the spring  50  is not engaging the ACM  30 . In this position, as opposed to  FIG. 6 , the normal force of the ACM  30  is sufficient so not to require the spring  50 . Therefore, the spring  50  is discontinued from applying force to the ACM  30 . The position of the ACM in  FIG. 7  corresponds to the right hand side of the chart in  FIG. 5 . In terms of angular displacement, the biasing element  50  may engage the ACM  30  from a horizontal position through about twenty degrees (20°) from the horizontal. Below this angular position, the biasing member  50  disengages the ACM  30 . 
   Referring now to  FIGS. 8-10 , various alternative embodiments are depicted utilizing biasing elements or members to place a discontinuous force on the ACM  30 .  FIG. 8  depicts a perspective view of the media tray  22  with the ACM  30  disposed above one end of the tray. According to the embodiment depicted, a biasing element  150  is shown as a coil spring rather than a leaf spring as described in the previous exemplary embodiment. The coil spring is shown in a neutral, unflexed position with the ACM  30  disposed against the lower media support surface of the media tray  22 . When a media stack is inserted into the media tray  22 , the ACM  30  pivots about the drive shaft  32  upwardly towards a horizontal position with the media below the ACM. As the ACM reaches a pre-selected angular position, the coil spring  150  is engaged and places a down force on the ACM  30 . The coil spring  150  is depicted as depending from a print structure which is depicted as a flat plate  152 , which may represent, for example, the mid-frame of the printer, and is free at a lower end. However, one skilled in the art may realize that the coil spring  150  may be connected to the ACM  30  at a lower end while being free to move into engagement with the mid-frame or other structure at the upper end, in a configuration which is opposite that depicted in  FIG. 8 . 
   Referring now to  FIG. 9 , a second alternative embodiment of the step spring assembly  250  is depicted. According to the embodiment shown, an assembly  250  is provided comprising a shaft  252  extending through a movable end of the ACM  30 . The shaft  252  extends through the ACM  30  at or around the axis of the at least one pick tire  46 . The movable end of the ACM  30  moves through various elevations as the ACM  30  pivots about the shaft  32  and moves through its angular range of displacement. A shaft  252  extends generally across the media tray  22  and is connected to extension springs  254 ,  256  generally at ends thereof. The extension springs are shown in a substantially neutral position with the ACM  30  in a down position due to the media tray  22  being empty. When a stack of media is loaded into the media tray for printing, the ACM  30  pivots about the shaft  32  toward a generally horizontal position. As the ACM  30  reaches a pre-selected position moving upward towards a horizontal position, the extension springs  254 ,  256  move from the neutral unflexed position into a flexed position due to upward movement of the shaft  252  with the ACM  30 . Thus, when the media tray  22  comprises a stack of media, the ACM  30  pivots to a position where the extension springs  254 ,  256  place a discontinuous down force on the ACM  30 . As the media stack feeds into the peripheral, the ACM  30  moves downwardly and reaches a position where the springs  254 ,  256  are no longer placing a down force on the ACM  30 . Thus the force of the springs  254 ,  256  are discontinuous. Although two springs are depicted in the embodiment of  FIG. 9 , a single shaft which extends from one side of the ACM  30  as well as a single spring connected to that shaft may alternatively be utilized and is well within the scope of the described embodiment. 
   Referring now to  FIG. 10 , a third alternative embodiment is depicted. A biasing assembly  350  is depicted having a rod  352  extending through the ACM  30 . The rod  352  may depend from the printer mid-frame (not shown) and extend some pre-selected length such that the rod  352  does not interfere with feeding of a media stack from the media tray  22 . The ACM  30  comprises an elongated aperture  354  which allows the ACM  30  to move over the rod  352  during media feeding. As depicted, the media tray  22  is empty so that the ACM  30  is in a downward most position. When a media stack is inserted into the tray  22 , the ACM  30  pivots about the drive shaft  32  so that the ACM  30  moves upwardly along the rod  352 . At a pre-selected position, before the ACM is disposed in a horizontal orientation, the ACM  30  engages a weight  356  which is slideably positioned on the rod  352 . The weight  356  is supported in a preselected position relative to the rod  352  so that the ACM  30  is not affected by the weight until the ACM  30  reaches a specific height which is related to a full media stack being positioned in the tray  22 . Thus, as the ACM  30  operates to feed media into the printer, the ACM is loaded with a force of the weight  356  from the uppermost ACM position to a preselected angular position beneath the horizontal. For example, the angular range wherein the weight  356  is engaging the ACM  30  may be about 20 degrees. Once the ACM  30  reaches this lowermost position, the weight  356  is supported by ribs, protrusions, or the like extending from the rod  352  and the ACM  30  continues to feed the media without the force of the weight  356 . 
   In operation of the various embodiments depicted, one skilled in the art should understand that the media stack M is loaded into the media tray  22  causing the ACM  30  to rise to near an initial horizontal position. From this horizontal position or thereabouts, the discontinuous force is applied to the ACM  30  by the biasing element, for example,  50 . As the media begins feeding, the ACM  30  moves from the initial position through an angular range to preselected position where the force on the ACM  30  is discontinued. Beyond the preselected position where the force is discontinued, and as the media continues to feed, the only down force is created by the torque of the drive shaft  32 . When the media tray  22  is empty, a new stack of media is positioned in the tray  22  so that the ACM  30  rises to near a horizontal position and the discontinuous force is reapplied to the ACM  30 . 
   The foregoing description of several embodiments and method of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.