Slidable Sheet Separator for an Image Forming Device

Abstract

A sheet separator and apparatus utilizing the same for separating media sheets in an image forming device. The apparatus includes a supporting member for supporting a stack of media sheets, a pick assembly to pick media sheets and to feed the media sheets to a processing assembly of the image forming device, and a media dam having at least one sheet separator. Each sheet separator includes a casing inclined at a predetermined angle to the supporting member, a biasing member and a base member slidable within the casing. A plurality of detents in the form of steps or teeth are provided on a sheet receiving surface of the base member and the biasing member act to separate a top most media sheet from an adjacent media sheet to prevent double feeding of media sheets.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

This application is related to U.S. Ser. No. ______, entitled “SHEET SEPARATOR HAVING MULTI AXIS MOTION FOR AN IMAGE FORMING DEVICE (Docket No. P37), also assigned to the assignee of the present application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

REFERENCE TO SEQUENTIAL LISTING, ETC.

None.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates generally to image forming devices, and more particularly, to a media dam having a slidable sheet separator for separating media sheets in an image forming device.

2. Description of the Related Art

Typically, an image forming device (such as a printer) includes an apparatus for separating media sheets picked from an input stack and fed into a feed (motion) path of the imaging forming device for an imaging operation (such as printing). Specifically, such an apparatus includes a sheet separator intended to prevent picking of more than one media sheet at a time.

A variety of means, such as compliant devices including media retarding elements, have been used as sheet separators in image forming devices to accomplish picking of a single media sheet at a time. Further, the compliant devices are used along with a plurality of resistive elements spaced at usually a fixed frequency along a media in a feed path of a media sheet when being picked from an input tray. Such compliant devices are typically of lengths spanning around only a height of a stack of media sheets provided in the input tray. Thus, the compliant devices may be incapable of effectively separating the media sheets being fed into the feed path. One type of resistive elements is in the form of a plurality of dimples on the surface of the media dam, sometimes referred to as a dimpled dam. With dimples, the media sheet being fed encounters a high resistive force resulting in the pick assembly being induced to increase its pick force resulting in a higher force normal to the media stack which in turn increases the possibility of double feeding of the media, particularly when the media is in a humid environment. Higher pick force also requires greater power from the motor driving the pick assembly with motor stall more likely to occur, especially when feeding heavier media. It would be advantageous to have a sheet separator that can adjust to the required pick force for a particular media while giving a high resisting force to the second media sheet that has been fed during a double feed condition.

Also, many apparatuses have been designed that include plain or smooth media dams composed of a plurality of fixed metal wear strips provided in the face of the media dam that serve as sheet separators in input trays carrying the media sheets. Such apparatuses also include a pair of pick rolls that are rotated for feeding the media sheets towards the plain dams. In such apparatuses, a change in feed direction by reversing the pick rolls helps in separating extra media sheets. However, these apparatuses do not effectively prevent multi-feeds of media sheets into a feed path for a printing operation.

It has also been observed that most of the conventional sheet separators on a media dam have the tendency to leave an edge damage mark corresponding to their respective locations on edges of the media sheets. Such marks are undesirable as the marks represent visible defects on printed media sheets. Although, manufacturers of printers/media sheet separators are struggling to eliminate such defects, the problem of separating of the top media sheet from the underlying media sheet without any damage thereto still continues to prevail.

Accordingly, there persists a need for an effective and efficient sheet separator that assists in the separation of a media sheet from underlying media sheets without causing edge damage to the media sheets.

SUMMARY OF THE DISCLOSURE

An apparatus for separating media sheets in an image forming device comprises a supporting member for supporting a stack of media sheets, a pick assembly disposed upon the stack of media sheets for picking media sheets from the stack of media sheets and feeding the media sheets into a feed path to a processing assembly of the image forming device; and a media dam positioned at a predetermined angle with respect to the supporting member, the media dam positioned adjacent to both the leading edges of the media sheets in the stack and to the pick assembly. The media dam has at least one slidable sheet separator comprising a casing, a base member and a biasing member. The base member is positioned within the casing by the biasing member at an initial position with respect to the stack of media sheets. The base member slides within the casing from a force applied by one of the biasing member and one or more media sheets fed from the stack by the pick assembly. Further a plurality of detents in the form of steps on a sheet-receiving surface of the base member are provided. At least one of the plurality of detents receives and separates a topmost media sheet from an adjacent media sheet when picked by the pick assembly allowing the topmost media sheet to be fed to into the feed path to the processing assembly while resisting movement of the adjacent media sheet into the feed path. In other forms the slidable sheet separator may be detachably attached to the media dam or molded within it. Further the risers of each detent of the plurality of detents may be oriented vertically relative to a respective leading edge of each fed media sheet when each fed media sheet arrives at the at least one sheet separator. Each riser of each detent of the plurality of detents may have a height of about 0.5 mm and a tread depth of about 0.3 mm. The interior angle between the riser and tread produces a minimum resisting force by the base member on the adjacent media sheet that is always higher than a driving force by the pick assembly applied to the adjacent media sheet. In one embodiment the interior angle is in the range of 50 degrees to 70 degrees. The base member and the plurality of detents of the each sheet separator may be made of glass bead filled polyoxymethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned features and advantages of the present disclosure, as well as other features and advantages, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings.

FIG. 1 illustrates a portion of an apparatus for separating media sheets in an image forming device, in accordance with an embodiment of the present disclosure.

FIG. 2 illustrates a perspective view of the apparatus of FIG. 1, in accordance with an embodiment of the present disclosure.

FIG. 3 illustrates a sheet separator of the apparatus of FIGS. 1 and 2, in accordance with an embodiment of the present disclosure.

FIG. 4 illustrates a side view of the sheet separator of FIG. 3, (without a casing thereof) for depicting a plurality of detents, in accordance with an embodiment of the present disclosure.

FIGS. 5A-5D schematically illustrate the movement of one embodiment of the sheet separator during a double feeding of media sheets.

FIG. 6 illustrates a double feeding of media sheets occurring on one detent of a sheet separator.

FIG. 7 illustrates the forces acting on a sheet separator during feeding of a media sheet.

FIG. 8 illustrates the forces acting on the detent profile of a sheet separator during feeding of a media sheet.

DETAILED DESCRIPTION

It is to be understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present disclosure. It is to be understood that the present disclosure is not limited in its application to the details of components set forth in the following description. The present disclosure 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. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

The present disclosure provides an apparatus for separating media sheets in an image forming device, such as a printer. The apparatus includes a supporting member adapted to support a stack of media sheets. Further, the apparatus includes a pick assembly configured to be disposed upon the stack of media sheets. The pick assembly is adapted to pick media sheets from the stack of media sheets and to feed the media sheets to a processing assembly of the image forming device. The apparatus further includes at least one sheet separator configured adjacent to the stack of media sheets and the pick assembly. Each sheet separator is configured to separate the media sheets being fed from the stack of media sheets to the processing assembly. The apparatus and components thereof of the present disclosure are explained in detail in conjunction with FIGS. 1-5.

FIG. 1 depicts apparatus 100 having a media dam 102 for separating media sheets in an image forming device (not shown) and FIG. 2 illustrates a perspective view of the apparatus 100. As depicted in FIGS. 1 and 2, the apparatus 100 includes a supporting member 110. Media dam 102 may be integrally formed with supporting member 110 or may be placed in an abutting relationship with supporting member 110. The media dam 102 has a sheet receiving surface 104 comprised of a generally planar arrangement of slidable and fixed media separators 130, 142 that separate and guide media sheets being fed into a feed path of to an image forming device. The supporting member 110 supports a stack 10 of media sheets 12 (as shown in FIG. 1). For the purpose of this description, the supporting member 110 is depicted to be a rectangular tray for carrying the stack 10 of media sheets 12. Here media dam 102 may form a front or downstream wall of the tray (in relation to the media feed direction A). As illustrated media dam 102 forms a front or downstream wall 113 (in relation to the media feed direction A) of the tray. However, the supporting member 110 may be configured to have any shape and size depending on the type of the image forming device. Further, the supporting member 110 may be provided along with the image forming device, and may be detachably attached to the image forming device. Additionally, the supporting member 110 may be capable of supporting a large number of media sheets, such as the media sheets 12. For example, the supporting member 110 may be capable of supporting a sheet capacity of around 500 media sheets 12. However, it is to be understood that the configuration in terms of capacity of the supporting member 110 should not be considered as a limitation to the present disclosure. Further, the media sheets 12 for use in the apparatus 100 may be of any available size, such as A4, A3, Legal and the like.

The apparatus 100 further includes a pick assembly 120 disposed upon the top of the stack 10 of media sheets 12 (as shown in FIG. 1). The pick assembly 120 picks the media sheets 12 from the stack 10, and feeds in a feed direction indicated by the arrow A the media sheets 12 into the media dam 102 where it bends to slide over the sheet receiving surface 104 then on to a processing assembly (not shown) of the image forming device. The term “processing assembly,” as used herein above and below relates to a printing station of the image forming device that refers to a location where a printing operation may be performed.

As depicted in FIG. 1, the pick assembly 120 includes a transmission 122 and a pair of pick rolls 124 being placed/disposed about a leading/front edge of the stack 10 of media sheets 12. Each of the pick rolls 124 of the exemplary pick assembly 120 may have a diameter of about 30 millimeters (mm). Additionally, the pick rolls 124 may be in contact with the media sheets 12 at a distance of about 17 mm to 20 mm from respective front edges of the media sheets 12. Provided in support 110 is a pair of openings 112 in which idler rolls 114 are mounted that are used to reduce wear on the pick rolls 124 when no media sheet is present on support member 110. The use of the idler rolls 114 is optional. It should be understood that the pick assembly 120 may also include other components such as a pick roll shaft, a clutch mechanism, a drive motor and the like, as known in the art. The operation of the illustrated pick assembly 120 to pick or feed media sheets is well known to those of skill in the art.

The media dam 102 of apparatus 100 of FIGS. 1 and 2 also includes at least one slidable sheet separator 130 and at least one fix sheet separator 142 provided on the media dam 102 adjacent to the leading edge of the stack 10 of media sheets 12 and the pick assembly 120. In one embodiment a moveable sheet separator 130 is provided opposite each pick roll 124. The slidable and fixed sheet separators 130, 142 define a sheet receiving surface 104. Slidable and fixed sheet separators 130, 142 may be raised slightly above the surface of the media dam 102 in the range of 0.1 mm to about 2.0 mm, with the slidable sheet separators 130 being raised slightly higher by about 0.1 mm than the fixed sheet separators 142. Slidable and fixed sheet separators 130, 142 may be in close proximity to the stack 10 of media sheets 12 such that a portion of the leading edges of the media sheets lies against a portion of the surface of the slidable sheet separator 130. Typically this occurs at a lower portion of the stack 10 near supporting member 110 but may extend the entire height of the stack 10. Fixed sheet separators 142 (plain or smooth dams) composed of metal wear strips in the media dam 102. The sheet separators 142 may also assist in separating the media sheets 12. Further, the pick rolls 124 may be closely spaced to the sheet separators 130, 142 by about 20 mm.

The slidable sheet separator 130 separates the media sheets 12 being fed from the stack 10 to the processing assembly and to inhibit double feeds of two or more media sheets 12. As the media sheets 12 are being moved, the slidable sheet separator 130 is initially struck by the leading edges the media sheets 12 being moved by the pick assembly 120 and the interaction of sheet separator 130 and the fed media sheet or sheets 12 separates a top most media sheet N from the following media sheets N+1, N+2, etc. located below as the media sheets 12 are being moved to the processing assembly. Although, the processing assembly has not been shown in the Figures for the purpose of simplicity, the processing assembly is downstream of the sheet separator 130 in the feed direction A.

As depicted in FIGS. 1-3, the media dam and sheet separators 130 that includes a casing 132 and sheet separators 142 are inclined at a predetermined angle, such as an obtuse angle (e.g., 107 degrees) with respect to the supporting member 110 and with respect to the stack 10. The casing 132 keeps the sheet separator 130 laterally fixed in relation to the media dam 120 and in relation to the stack 10 of media sheets 12.

The sheet separator 130 includes a base member 134 that is slidable within the casing 132. Further, the base member 134 of the sheet separator 130 is biased to provide a resisting force at the predetermined angle (such as an obtuse angle) relative to the stack 10 of media sheets 12. For example, the base member 134 may be positioned at an angle of about 17 degrees from a vertical plane or 107 degrees with respect to supporting member 110. It is to be understood that the angle at which the base member 134 is positioned relative to the stack 10 of media sheets 12, should not be considered as a limitation to the present disclosure, and may be modified depending on the type of the image forming device. Such an alignment of the base member 134 facilitates the separation of the media sheets 12. Further, the height of the base member 134 is approximately equal or greater than to the maximum sheet capacity of supporting member 110 (for example about 50 mm for 500 sheets of 20 pound paper). As shown it extends from slightly below a top surface 111 of support member 110 to proximate the top of the media dam 102. The base member 134 may be composed of glass bead filled polyoxymethylene to prevent wear and maintain rigidity. However, it should be understood that the base member 134 may be composed of any other such material known in the art.

Referring to FIGS. 2 and 3, the sheet separator 130 also includes a spring 136 to provide a biasing force in the plane in which the base member 134 sits within the casing 132 that is applied when the top most media sheet N of the media sheets 12 is fed into media dam 120 as it is separated from the below adjacent N+1 media sheet. Specifically, the spring 136 assists in pushing the base member 134 to an original position once the top most media sheet N of the media sheets 12 is separated from the below adjacent media sheet N+1. As illustrated, the spring 136 may be compressed as the base member 134 slides in a first direction (upwardly) when the top most media sheet N is driven by pick assembly 120 into the media dam 102 and base member 134 allowing top most media sheet N to separate from the stack 10 of media sheets 12 and move over a sheet receiving surface 140 of base member 134 in the feed direction A. Once the separated media sheet N begins moving over the sheet receiving surface 140 of base member 134 and starts moving towards the processing assembly, the spring 136 expands sliding the base member 134 within casing 132 in a second direction (downwardly) opposite to the first direction. Accordingly, the sheet separator 130 acts as a self-adjusting sheet separator.

As depicted in FIGS. 1-6, the base member 134 of sheet separator 130 includes a sheet receiving surface 138 with a plurality of lateral detents 139 in the form of to steps (having a riser R and a tread T formation). The base member 134 further includes flanges 140 extending along both sides of the base member 134 from the bottom to the top of the base member 134 with the lateral detents 139 extending between the flanges 140. Flanges 140 are smooth and slide within casing 132. The detents 139, and in particular the outer edges E formed between the treads T and risers R form a rippled or serrated sheet receiving surface 138 over which the separated media sheet N may slide (as depicted in an enlarged portion in FIG. 3). The detents 139 may also be in the form of serrations or teeth. The detents 139 are arranged along a portion of the height and a portion of width of the base member 134. As depicted in FIG. 3, detents 139 extend between the flanges 140 from the bottom to near the top of the base member 134. The detents 139 are used to separate the top most media sheet N from any below adjacent media sheets N+1 that may also be moving with top most media sheet N as it is being fed. For the purpose of simplicity, the sheet separator 130 has been depicted without the casing 132 thereof in FIG. 4.

Each detent of the detents 138 has a height H for the riser R of about 0.5 millimeter (mm) and a tread depth D of about 0.3 mm (see FIG. 8). Further, the height H of the each detent of the detents 138 may be modified as per the requirements and based on a manufacturer's preferences and or thickness of the media sheets. The depth D of the treads is shallow to facilitate the movement of separated media sheet across sheet receiving surface 138 of base member 134 so that the leading edge of the separated media sheet does not catch on sheet receiving surface 138 as it continues in the feed direction A once it is separated and moving singly. Additionally, the detents 139 may be composed of glass bead filled polyoxymethylene to prevent wear and maintain rigidity. However, it should be understood that the detents 139 may be composed of any other such material known in the art. Further, the detents 139 and the base member 134 may be formed as a single rigid molded component for cost-effectiveness. Alternatively, the detents 139 may be configured separately and may be attached to the base member 134 by an attachment means, such as an adhesive and the like.

In use, the supporting member 110 carries the stack 10 of media sheets 12 thereupon. The pick rolls 124 of the pick assembly 120 to rotate to pick the media sheets 12 one-by-one. However, the pick assembly 120 may pick more than one media sheet from the stack 10 of media sheets 12 at the same time. This is referred to as a double feed. As the topmost media sheet N is being picked, the media sheet or media sheets (N+1, N+2 etc.) beneath it are sometimes drawn together with it. This usually happens when the resisting force between the topmost media sheet N and the next media sheet N+1 is less than the net driving force F_dp of the media pick assembly 120. Double feeding may also occur on a media having edge weld or media cohesion. Thereafter, the picked media sheets 12 arrive at the sheet receiving surface 138 of the base member 134. Subsequently, the arrangement of the base member 134 and the detents 139 may facilitate in bubble formation at the respective leading edges of the one or more media sheets arrived at the sheet separator 130, thereby, allowing the arrived double fed media sheets to separate prior to proceeding to the processing assembly of the image forming device. Further, the bubble action caused by the base member 134 and the detents 139 further allows the top most media sheet N to curve and slide over the detents 139 of the base member 134, for an easy separation from the adjacent media sheet N+1. Such an arrangement also prevents the leading edge of each of the double fed media sheets from undergoing any damage while being separated. Bubble formation or bubbling is a slight lifting or floating of the leading edge portion of a media sheet as compared to buckling where the media sheet will deform upwardly, forming a reverse U-shaped section a short distance from the leading edge of the media sheet.

Illustrated in FIGS. 5A-5D, is an exemplary operation of the sheet separator 130 with a two media sheets 12 being double fed by pick assembly 120. In FIG. 5A top most media sheet N and below adjacent media sheet N+1 are shown being driven into the base member 134 of sheet separator 130 that is in its initial or rest position indicated by the line IP. A leading edge of media sheet N is shown striking and engaging the riser R of detent 139-1 while a leading edge of media sheet N+1 is shown striking and engaging the riser R of detent 139-2 at about the respective midpoints indicated by the small circle on each riser. Of the leading edges may strike at riser at other than its midpoint. This facilitates bubble formation at respective leading edges of these media sheets when they arrive at the sheet separator 130 (along a feed direction indicated by arrow A in FIGS. 1 and 4). Contact angles Φ1, Φ2 are formed with respect the risers R of detents 139-1, 139-2 and media sheets N, N+1 respectively. In FIG. 5B, the force of media sheets N, N+1 striking base member 134 is sufficient to overcome the spring bias force provided by the spring 136 and causes base member 134 to rise as indicated by the upward arrow from its initial position shown by the line IP in FIGS. 5A-5D. Contact angle Φ1 becomes more acute or diminishes faster than contact angle Φ2 allowing the leading edge media sheet N to slip upward along the riser of detent 139-1. As base member 134 continues to rise at FIG. 5C, the leading edge of media sheet N moves upwardly along the face of the riser R of detent 139-1 and making contact angle Φ1 diminish even further. Contact angle Φ2 at the leading edge of media sheet N+1 at detent 139-2 also becomes more acute but at a lesser rate of change than the rate of change occurring for contact angle Φ1 because of a force applied to it by the bending of top most media sheet N. At FIG. 5D, media sheet N has reached the outer edge E of detent 139-1 and has disengaged from or exited from detent 139-1 and slipped past it to continue its motion along sheet receiving surface 138 of base member 134. Media sheet N as it bends upwardly applies a downward force to media sheet N+1 inhibiting the upward motion of media sheet N+1 along riser R of detent 139-2. This prevents media sheet N+1 from reaching the outer edge E of detent 139-2 and slipping past the riser R of detent 139-2. Once top most media sheet N has slipped past detent 139-1, its force applied to base member 134 has been reduced to a level that the downward biasing force of spring 136 returns base member 134 back to its initial position IP as indicated by the downward arrow. The leading edge of media sheet N+1 that is engaged with riser R of detent 139-2 is taken back down by base member 134 making angle Φ2 slightly more obtuse. These actions allows top most media sheet N to separate from the below adjacent media sheet N+1 and prevents adjacent media sheet N+1 from being further fed.

A similar sequence occurs if three medias sheets are simultaneously picked causing media sheets N+1, N+2 to become separated from top most media sheet N. While media sheets N and N+1 are shown striking two adjacent detents, the same separation actions occur if the two media sheets strike the same detent. FIG. 6 illustrates this condition where the top most media sheet N has just slipped by the outer edge E of detent 139-1 while the below adjacent media sheet N+1 is still being restrained by the riser R of detent 139-1. The leading edge of media sheet N+1 is restrained by the riser of detent 139-1 while the leading edge of the top most media sheet N eventually disengages and slips by the outer edge E of the detent 139-1.

Positioning of the base member 134 having the detents 139 thereon with respect to the stack 10 of media sheets 12, aids in formation of bubbles at the respective leading edges of the one or more fed media sheets when the one or more media sheets arrive at the sheet separator 130, causing the each media sheet to slightly separate from the adjacent media sheet (which also has been picked by the pick assembly 120). The bubble formation, which is a momentary action, allows the top most fed media sheet N to slip over the detents 139 of the base member 134 to proceed singly to the processing assembly, while the lower adjacent media sheet is restrained by the detents 139 from proceeding further towards the processing assembly. Such a mechanism takes the advantage of the base member 134 that has detents 139 having a riser R height H that is greater than the thickness of each media sheet of the media sheets 12. This allows the slidable sheet separator to be used with a variety of media thickness.

Further, the positioning of the base member 134 at the predetermined angle relative to the stack 10 of media sheets 12 facilitate orienting the risers R of detents 139 more vertically relative to the respective leading edges of the one or more media sheets that are being feed. Such an orientation of the detents 139 on the inclined base member 134 assists in the bubbling action occurring on the each media sheet arriving at the sheet separator 130, thereby, assisting in separation of the each media sheet N from the adjacent media sheet N+1. It will be evident that the detents 139 may be allowed to orient at any specific angle, as per the requirements of the image forming device and the manufacturer's preference.

The sheet separator 130, as described above, is shown to be detachably attached to a portion of the media dam 110 at the predetermined angle with respect to the stack 10 (as depicted in FIG. 2). Specifically, the sheet separator 130 may be detachably fixed in the apparatus 100 by means of snap latches, at the predetermined angle with respect to the supporting member 110. Alternatively, the sheet separator 130 may be formed as an integral component of the apparatus 100. Further, the casing 132 of the sheet separator 130 may also be molded into the supporting member 110 of the apparatus 100, and the base member 134 along with the detents 139 may then be slidably received with the casing 132.

After the media has been picked, the force supplied by the media sheet N itself will drive base member 134 upward, preventing the pick assembly 120 from exerting a greater force on the stack 10 of media sheets 12. From work-energy principle, the total changed in kinetic energy is equal to the total work done to the base member 134 (equal to the product of the external force applied by the media to the sliding dam and the distance it traveled, plus the negative work of gravity (due to sliding dam's weight and elevation), plus the negative work in overcoming the frictional resistance plus the negative work done by the maximum deflection of the spring 136. By doing this, the energy applied by the pick mechanism 120 is reduced and the excess energy of pick mechanism 120 in driving the media sheet N is transformed to useful work.

As illustrated by the vector diagram of FIG. 7, the optimized weight W of to the base member 134 of sheet separator 130 may be calculated using Eq. 1.

$\begin{array}{cc}W=F_{\mathrm{dm}}\left(\frac{\sin \Theta -{\mu }_{\mathrm{sc}}\cos \Theta }{\cos \Theta +{\mu }_{\mathrm{sc}}\sin \Theta }\right)& \mathrm{Eq}.1\end{array}$

F_dm=driving force on media sheet from pick assembly 120
Θ=angle of base member 134 with respect to supporting member 110
α=interior angle between riser R and tread T of detent 139 on base member 134
μ_SC=coefficient of friction between base member 134 and media sheet
F_fSC=frictional force between base member 134 and casing 132
N_SC=normal force acting on base member 134 and casing 132
Illustrative weights for member for media driving force of in the range of 100-300 grams are in a corresponding range of 20 to 40 grams. The weight vector is shown at the center of gravity, indicated at 134.

The profile of detents 139 of the base member 134 provides the media a higher resisting force (Ff_SM) required to separate the media sheets. FIG. 8 shows the forces acting in the detent profile. Ff_SM is the friction force of base member 134 rubbing against the media. μ_SM is the coefficient of friction between base member 134 and the media. N_SP is the normal reaction force on base member 134 while angle α is the angle between the riser R and tread T.

Ff_SM=μ_SMN_SP  Eq. 2

The angle α of the riser R of detent 139 is chosen to produce a minimum resisting force on the adjacent media sheet that is always higher than the maximum net driving force on the adjacent media sheet to ensure single sheet feeding. Summing up the forces acting on the detent profile will give the angle α:

α=Tan⁻¹(1/μ_SM)  Eq. 3

For media feed speeds in the range of 5 ips to 13 ips (inches per second) which translates into the force F_dm exemplary values for the weight W for base member 134 are in the range of 20 grams to 40 grams, and the angle α is in the range of 50 degrees to 70 degrees when the angle between the media separator 130 and the supporting member 110 is in the range of 100 degrees to 110 degrees. Exemplary ranges the for the height H of the risers R of detents 139 is in the range of 0.3 mm to 0.8 mm and for the depth of the tread T of detents 139 is in the range of 0.2 mm to 0.4 mm.

Based on the foregoing, the present disclosure provides an efficient and effective apparatus (such as the apparatus 100), employing a sheet separator (such as the sheet separator 130), for separating media sheets in an image forming device, such as a printer. Specifically, the apparatus employing the sheet separator of the present disclosure, serves as a robust arrangement for preventing multi-feeds into a feed path of an image forming device. More specifically, the configurations of base member (such as the base members 134 and detents 139 of the sheet separator of the present disclosure assist in an effective and efficient separation of media sheets in the image forming device. Further, the apparatus 100 and the sheet separator 130 are suitable for implementation in printers having L-shaped, C-shaped and S-shaped feed paths, for printing operations. Additionally, the sheet separator of the present disclosure may also be incorporated as a separating media dam in a detachable supporting member (tray) of an image forming device by molding features into the detachable supporting member, thereby, reducing part count and overall machine cost. Moreover, use of the sheet separator of the present disclosure, averts any damage to the media sheet being separated, thereby, averting any deterioration of quality of the finally printed media sheet.

The foregoing description of several embodiments of the present disclosure has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the disclosure be defined by the claims appended hereto.

Claims

1. An apparatus for separating media sheets in an image forming device, the apparatus comprising:

a supporting member for supporting a stack of media sheets;

a pick assembly disposed upon the stack of media sheets for picking media sheets from the stack of media sheets and feeding the media sheets into a feed path to a processing assembly of the image forming device; and

a media dam positioned at a predetermined angle with respect to the supporting member, the media dam positioned adjacent to both the leading edges of the media sheets in the stack and to the pick assembly, the media dam having at least one slidable sheet separator, the at least one slidable sheet separator comprising: a casing; a biasing member for applying a biasing force at the predetermined angle to the base member; a base member positioned within the casing by the biasing member at an initial position with respect to the stack of media sheets, the base member slidable within the casing from a resultant force applied by one of the biasing member and one or more media sheets fed from the stack of media sheet by the pick assembly; and a plurality of detents in the form of steps on a sheet-receiving surface of the base member, at least one of the plurality of detents engaging and separating a topmost media sheet from an adjacent fed media sheet when picked by the pick assembly allowing the topmost media sheet to be fed into the feed path to the processing assembly while resisting movement of the adjacent fed media sheet into the feed path.

2. The apparatus of claim 1, wherein each of the at least one sheet separator is detachably attached to the media dam.

3. The apparatus of claim 1, wherein the casing of the at least one sheet separator is molded within the media dam.

4. The apparatus of claim 1, wherein the biasing member comprises a compression spring for returning the base member to the initial position after the top most media sheet is separated from the adjacent media sheet.

5. The apparatus of claim 1, wherein a riser of each detent of the plurality of detents is oriented vertically relative to a respective leading edge of each fed media sheet when each fed media sheet arrives at the at least one sheet separator.

6. The apparatus of claim 1, wherein the base member facilitates bubble formation at respective leading edges of the top most media sheet and the adjacent media sheet when the top most media sheet and the adjacent media sheet arrive at the base member.

7. The sheet separator of claim 1, wherein each riser of each detent of the plurality of detents has a height that is greater than the thickness of the media sheet being fed.

8. The apparatus of claim 7, wherein each riser of each detent of the plurality of detents has a height of about 0.5 mm.

9. The apparatus of claim 1, wherein a tread of each detent of the plurality of detents has a depth of about 0.3 mm.

10. The apparatus of claim 1, wherein an interior angle a between the riser and the tread of each detent produces a minimum resisting force by the base member on the adjacent media sheet that is always higher than a driving force by the pick assembly applied to the adjacent media sheet.

11. The apparatus of claim 10, wherein the interior angle α is in the range of 50 degrees to 70 degrees.

12. The apparatus of claim 1, wherein the height of the base member of the at least one sheet separator is longer than a height of stack of media sheets.

13. The apparatus of claim 1, wherein the base member and the plurality of detents of the each sheet separator are composed of glass bead filled polyoxymethylene.

14. A sheet separator for a media dam for separating media sheets being fed by a pick assembly from a stack of media sheets into the media dam and then to a processing assembly in an image forming device, the sheet separator comprising:

a casing inclinable at a predetermined angle with respect to the leading edges of the media sheets in the stack;

a base member slidably received in the casing and positioned at an initial position with respect to the leading edges of the media sheets of the stack, the base member having a plurality of stepped detents forming a sheet receiving surface on the base member; and

a biasing spring for applying a biasing force at the predetermined angle to the base member at the initial position;

the base member being slidable upwards at the predetermined angle within the casing by a driving force applied by the fed media sheet, at least one of the plurality of stepped detents being struck by and engaging a leading edge of a top most fed media sheet and when present a leading edge of an adjacent fed media sheet, the struck at least one detent and the biasing spring facilitating the separation of the top most fed media sheet from the adjacent fed media sheet for feeding to the processing assembly with the biasing spring returning the base member to the initial position after the leading edge of top most fed media disengages with the struck at least one detent.

15. A sheet separator in a media dam for separating media sheets being fed from a stack of media sheets to a processing assembly in an image forming device, the sheet separator comprising:

a base member positionable with the media dam and inclinable at a predetermined angle with respect to the stack of media sheets;

a biasing member for applying a biasing force to the base member at the predetermined angle to place the base member in a first position when positioned with the media dam; and

a plurality of detents in the form of steps on a sheet-receiving surface of the base member, for engaging a leading edge of a fed media sheet.

16. The sheet separator of claim 15, wherein a riser of each detent of the plurality of detents is oriented vertically relative to a respective leading edge of each fed media sheet when each fed media sheet arrives at the at least one sheet separator.

17. The sheet separator of claim 16, wherein the plurality of detents of the base member facilitate bubble formation at respective leading edges of the top most media sheet and the adjacent media sheet when the top most media sheet and the adjacent media sheet arrive at the base member.

18. The sheet separator of claim 15, wherein each riser of each detent of the plurality of detents has a height that is greater than the thickness of the media sheet being fed.

19. The sheet separator of claim 18, wherein each riser of each detent of the plurality of detents has a height of about 0.5 mm.

20. The sheet separator of claim 15, wherein a tread of each detent of the plurality of detents has a depth of about 0.3 mm.

21. The sheet separator of claim 15, wherein an interior angle α between the riser and the tread of each detent produces a minimum resisting force by the base member on the adjacent media sheet that is always higher than a driving force by the pick assembly applied to the adjacent media sheet.

22. The sheet separator of claim 21, wherein the interior angle α is in the range of 50 degrees to 70 degrees.

23. The sheet separator of claim 15, wherein the height of the base member of the at least one sheet separator is longer than a height of stack of media sheets.

24. The sheet separator of claim 15, wherein the base member and the plurality of detents of the each sheet separator are composed of glass bead filled polyoxymethylene.