Patent Publication Number: US-11383952-B2

Title: Sheet stacker having movable arms maintaining stack quality

Description:
BACKGROUND 
     Systems and methods herein generally relate to sheet stacking devices and more particularly to sheet stacking devices that maintain stack quality. 
     Many flexible materials are available in sheet form, including print media, plastic sheeting, metallic sheets, foam materials, etc. It can be more efficient from a processing standpoint to stack these sheets during various stages of processing. In one example, after sheets of print media have received print markings, they are often stacked. 
     Stacking devices (stackers) are often used to perform such stacking operations. It is useful for such stacking devices to produce stacks in which all sheets lay flat and where the edges of all sheets are aligned. Many times, sheets are inverted just prior to being stacked; however, if the sheets do not fully complete the flipping process involved with inverting the sheets, this can result in sheets being folded under other sheets or in sheets irregularly piling upon one another. 
     SUMMARY 
     Various exemplary sheet stacking apparatuses herein include (among other components) a frame and at least one round member (e.g., disk), a first arm, a second arm, and a stacking surface (all directly or indirectly connected to the frame). A first hinge directly or indirectly connects the first arm to the frame and a second hinge directly or indirectly connects the second arm to the frame. 
     The round member is adapted to rotate, and the round member is positioned relative to the stacking surface to move the sheets toward the stacking surface when rotating. The first arm is rotatable around the first hinge to rotate the first arm between a first position (closed) and a second position (open). The second arm is similarly rotatable around the second hinge to rotate the second arm between a third position (closed) and a fourth position (open). 
     The second arm is longer than the first arm and extends closer to the stacking surface than the first arm when the first arm is in the first position (closed) and the second arm is in the third position (closed). The round member has leading edge receivers adapted to accept leading edges of the sheets, and the first arm is positioned to direct the leading edges of the sheets into the leading edge receivers of the round member when the first arm is in the first position (closed). 
     Thus, the first arm is positioned to bias the leading edges of the sheets toward the round member when in the first position (closed), but the first arm is positioned to bias the trailing edges of the sheets in a direction approximately parallel to the stacking surface when in the second position (open). Similarly, the second arm is positioned to bias the sheets toward the round member when in the third position (closed), but the second arm is positioned to not bias the trailing edges of the sheets toward or away from the round member to allow the sheets to lift off the round member when in the fourth position (open). 
     Additionally, a processor can be directly or indirectly connected to the first hinge and the second hinge. The processor is adapted to control the first hinge to only rotate the first arm to the second position (open) for a first type of sheet (e.g., lower beam strength sheets). However, the processor is adapted to control the second hinge to rotate the second arm to the fourth position (open) for both the first type of sheets and a second type of sheets (the first type of sheets have a lower beam strength relative to the second type of sheets). Further, a sensor can be directly or indirectly connected to the processor. The sensor detects whether the sheets are the first type of sheets or the second type of sheets. For example, the sensor (which can be, or include, multiple sensors of different types) can automatically detect the length of the media, the weight of the media, the humidity, temperature, and/or other environmental conditions within the stacking device, etc. 
     In greater detail, the first arm is rotatable around the first hinge to position the first arm in the first position (closed) when contacting the leading edges of both the first type of sheets and the second type of sheets. However, the first arm is rotatable around the first hinge to position the first arm in the second position (open) only when contacting the trailing edge of the first type of sheets; and the first arm does not rotate around the first hinge, but maintains the position of the first arm in the first position (closed), when contacting the trailing edge of the second type of sheets. 
     With respect to the second hinge, the second arm is rotatable around the second hinge to position the second arm in the third position (closed) when contacting the leading edges of both the first type of sheets and the second type of sheets. However, the second arm is rotatable around the second hinge to position the second arm in the fourth position (open) when contacting the trailing edges of both the first type of sheets and the second type of sheets. 
     Various sheet stacking methods herein include a number of steps, some of which include rotating the first arm around the first hinge to rotate the first arm between the first position (closed) and the second position (open). The first arm is positioned to bias sheets toward the round member when in the first position (closed). The first arm is positioned to not bias the sheets toward the round member when in the second position (open). The round member has leading edge receivers adapted to accept leading edges of the sheets, and the first arm is positioned to direct the leading edges of the sheets into the leading edge receivers of the round member when the first arm is in the first position (closed). 
     This processing also rotates the round member. The round member is positioned relative to the stacking surface to move the sheets toward the stacking surface when rotating. The process of controlling the first arm can control the hinge to position the arm to allow the trailing edge of a sheet to move from the round member in a direction approximately parallel to the stacking surface when the arm is in the second position (open). 
     In greater detail, in this processing, the first arm is rotated to the first position (closed) and the second arm is rotated to the third position (closed) when contacting the leading edges of both the first type of sheets and the second type of sheets. However, the arms operate differently on the trailing edges. Specifically, the first arm is rotated to the second position (open) only when contacting the trailing edge of the first type of sheets; and the first arm does not rotate, but maintains the first position (closed), when contacting the trailing edge of the second type of sheets. With respect to the second arm, in contrast the second arm rotates to the fourth position (open) when contacting the trailing edges of both the first type of sheets and the second type of sheets. 
     These and other features are described in, or are apparent from, the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary systems and methods are described in detail below, with reference to the attached drawing figures, in which: 
         FIG. 1  is a schematic perspective view diagram illustrating stacking devices herein; 
         FIGS. 2A-6B  are schematic cross-sectional view diagrams illustrating the stacking devices shown in  FIG. 1  herein; 
         FIG. 7  is a schematic diagram of a printing device that uses the stacking devices shown in  FIG. 1 ; and 
         FIG. 8  is a flowchart showing processing herein. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, when sheets are being inverted just prior to being stacked, if the sheets do not fully complete the flipping process, this can result in sheets being folded under other sheets or in sheets irregularly piling upon one another. The present inventors have found that different beam strength sheets will suffer from such problems differently. 
     More specifically, the present inventors have found that when longer length media, lighter weight media, and/or higher humidity condition are present, such conditions can reduce the relative beam strength of the sheets. These lower beam strength conditions can result in the trailing edge of the sheets not properly unfolding or uncurling, which may cause the trailing edge to not travel fully to the trailing end of the stacking surface, preventing the sheet from lying flat stacking surface. This can reduce the stack quality because some sheets may be folded under other sheets or other sheets may be irregularly piled upon one another. In contrast, with devices that produce high stack quality, all the sheets lie flat and the edges of such sheets are all aligned with one another. 
     In view of this, the devices and methods described herein use multiple arms, between which the sheets pass, to compensate for relatively low beam strength sheets. One of these arms (a first arm) is only rotated open for the trailing edges of sufficiently low beam strength sheets to help those sheets flip. Another of these arms (a second arm) rotates open for the trailing edges of both the lower and medium beam strength sheets. For sufficiently high beam strength sheets, neither arm may open when the trailing edges pass between the first and second arms. In contrast, to help direct the leading edges of sheets into a rotating disk that performs the flipping (inversion) process, both arms always remain closed for all leading edges of all sheet beam strengths. 
       FIGS. 1-5D  illustrate examples of such sheet stacking apparatuses herein. As shown in  FIGS. 1-5D , these devices include (among other components) what is generically referred to herein as a “frame”  110 . The frame  110  can comprise many different components of the apparatus, which are elements of the apparatus and which are directly or indirectly connected to each other. Thus, the frame herein can include any or all of the various elements that physically support the enumerated components discussed below. In the attached drawings, identification numeral  110  is used to indicate the different items that can be considered this generically defined “frame.” All the individual components discussed below are in a fixed location (even though many of the following components move, rotate, etc., in their fixed locations relative to the frame  110 ) and therefore all the following components are directly or indirectly connected to the frame  110  in some way. 
     With greater specificity,  FIG. 1  is a perspective view drawing that shows a stacking system  100  (apparatus, device, etc.) that includes a paper feeder device  104  that moves sheets  102  toward a curved paper guide  106 . The paper feeder device  104  and/or the curved paper guide  106  can include elements that move and control the sheets  102  including, roller nips, belts (vacuum and/or friction), rollers, slides, alignment guides, sheet position sensors, etc. Such elements are known and are not discussed in detail to maintain reader focus on the salient elements herein. 
     As can be seen in  FIG. 1 , sheets  102  are moved by at least the paper feeder device  104  to the curved paper guide  106 , which inverts the sheets  102  and directs the sheets  102  to a rotational device  120  which completes the sheet flipping (inversion). The rotational device  120  accepts the leading edges of the sheets  102 , while spinning/rotating, to move the leading edges to the sheets  102  to leading end  108 A of a stacking surface  108 . The rotational device  120  does not accept the trailing edge of the sheet  102 , but instead allows the trailing edges of the sheets  102  to unfold (uncurl, flip, etc.) and fall toward a trailing end  108 B (opposite the leading end  108 A) of the stacking surface. This operation inverts the sheet  102 , relative to their position in the paper feeder device  104 , and creates a stack of the sheets  102  on the stacking surface  108 . 
       FIG. 2A  is a cross sectional drawing showing a portion of the stacking system  100  in greater detail. Specifically,  FIG. 2A  shows that the rotational device  120  includes one or more disks  124 . The disk  124  is a round mechanical component that rotates and that can be hollow or solid, thin or thick, etc., with a rounded exterior; and, therefore can take the form of a cylinder, flat disk or wheel (thin or thick), etc. Multiple disks can be center-connected to a common axel which can be rotated by a motor or other device to rotate all disks  124  synchronously together.  FIG. 2A  also illustrates a pair of nip rollers  112 , one or more of which can rotate to drive the sheets  102  along the curved paper guide  106 . 
     As shown in  FIG. 2A , the disk  124  can include slots, cavities, openings, etc., that are referred to generically as “leading edge receivers”  122 , and that are configured and shaped to receive the leading edges of sheets of media. As the rotational device  120  continuously rotates, the leading edge of the sheets  102  runs into the planar surface of a notched alignment structure  114  that is connected to the leading end  108 A of the stacking surface  108 . As shown in  FIG. 1 , the notched alignment structure  114  has notches that allow only the disks  124  to pass through the notched alignment structure  114 ; however, the leading edges of the sheets  102  contact the remaining non-notched planar surface of the notched alignment structure  114 , stopping the sheets  102  on the stacking surface  108  and aligning the leading edges of the stacked sheets  102  along the planar surface of the notched alignment structure  114 . When the leading edge of the sheets  102  runs into the notched alignment structure  114 , this stops movement of the sheets  102  on the stacking surface  108  and pulls the sheets  102  from the leading edge receiver  122 . Note that while the drawings illustrate that the disks  124  have two leading edge receivers  122 , more or less leading edge receivers  122  could be included in each disk  124 . 
     While the structure shown in  FIGS. 1-2A  generally works very well with most media types, when longer length media, lighter weight media, and/or higher humidity condition are present and such reduces the relative beam strength of the sheets  102 , the trailing edge of the sheets  102  may not properly unfold or uncurl and may not travel fully to the trailing end  108 B of the stacking surface  108 , preventing the sheet  102  from lying flat stacking surface  108 . This is shown, for example, in  FIG. 2B  where the sheet  102  is shown with a slight buckle (e.g., fold, S-shape, opposing alternating curve shapes (opposing arch shapes), etc.) when compared to the mostly uniform single continuous curved arch shape of the sheet  102  shown in  FIG. 2A . 
     If the sheet  102  shown in  FIG. 2B  does not fully unfold, the next sheet  102  will not have a flat surface upon which to lie, causing the next sheet  102  to also fold (or at least not lie flat) and the same can continue with the following sheets, eventually resulting in an irregular stack of sheets or a jam of multiple sheets irregularly piled together. 
     As shown in  FIG. 2C , the structures and methods herein address this issue. More specifically, the present inventors discovered that the sheet  102  will undesirably buckle if the trailing edge  102 B of relatively low beam strength sheets continues to travel along trajectory (direction) T 1  because this trajectory T 1  forces/drives the trailing edge  102 B of the sheet  102  downward and more toward the stacking surface  108 , promoting the undesirable buckle shown in  FIGS. 2B-2C . In contrast, the present inventors discovered that if the trailing edge  102 B of the sheet  102  can be directed to travel in a trajectory T 2  that is relatively more parallel to the stacking surface  108  (relative to trajectory T 1 ) the undesirable buckle can be avoided for relatively low beam strength sheets. 
     The exemplary structures illustrated in the drawings cause the trailing edge  102 B of the sheet  102  to travel in the trajectory T 2  that is relatively more parallel to the stacking surface  108  (e.g., relative to trajectory T 1 ). For example,  FIG. 3A  is a partial and more detailed view of the structure shown in  FIGS. 1-2C  and includes a first arm  132  and a second arm  136 , a first hinge  130  directly or indirectly connecting the first arm  132  to the frame  110 , and a second hinge  134  directly or indirectly connecting the second arm  136  to the frame  110 .  FIGS. 3B-5B  show how the structure shown in  FIG. 3A  operates with different sheet beam strengths to direct the trailing edge  102 B of the sheet  102  to travel in the trajectory T 2  that is relatively more parallel to the stacking surface  108  (e.g., by opening a first arm  132  as shown in  FIG. 4A  and discussed below). 
     These “arms”  132 ,  136  can be paddles, baffles, guides, bars, projections, etc., and have the ability to maintain or change the trajectory of the sheets  102 . The first arm  132  is rotatable around the first hinge  130  to rotate the first arm  132  between a first position (closed,  FIG. 3B ) and a second position (open,  FIG. 5A , discussed below). The second arm  136  is similarly rotatable around the second hinge  134  to rotate the second arm  136  between a third position (closed,  FIG. 3B ) and a fourth position (open,  FIG. 4A , discussed below). The second arm  136  can be longer than the first arm  132  and can extend closer to the stacking surface  108  than the first arm  132  when the first arm  132  is in the first position (closed) and the second arm  136  is in the third position (closed). The sheets  102  pass between the first arm  132  and the second arm  136 . 
       FIG. 3B  shows the same structure shown in  FIG. 3A  with a generic sheet  102  that has been fed into one of the leading edge receivers  122  of the round member  124 . As can be seen in  FIG. 3B , the sheets  102  pass between the first arm  132  and the second arm  136  when moving from the curved paper guide  106 , past the first and second arms  132 ,  136 , to the stacking surface  108 . 
     In  FIG. 3B  the leading edge  102 A of the sheet  102  is shown within the leading edge receiver  122 . Additionally,  FIG. 3B  shows that the first arm  132  is in the first position (closed) and the second arm  136  is in the third position (closed). Therefore, when the first and second arms  132 ,  136  are closed they are positioned to direct the leading edge  102 A of the sheet  102  into the leading edge receivers  122  of the round member  124  (and this is the machine state maintained for all leading edges of all sheets). 
     As noted above, these structures generally work very well with most media types. However, when longer length media, lighter weight media, and/or higher humidity condition are present and such factors reduce the relative beam strength of the sheets, the trailing edge of the sheets may not properly unfold or uncurl, preventing the sheets from lying flat. In order to illustrate these situations and the unique way in which the structures and methods herein address these issues,  FIGS. 4A-4B  illustrate a sheet  142  having a relatively higher beam strength,  FIGS. 5A-5B  illustrate a sheet  144  having a relatively medium beam strength, and  FIGS. 6A-6B  illustrate a sheet  146  having a relatively lower beam strength (where medium beam strength is between high and low beam strengths). 
     More specifically,  FIGS. 4A, 5A, and 6A  illustrate the processing state where the trailing edges  142 B,  144 B, and  146 B of the sheets  142 ,  144 , and  146  have just lost contact with the round member  124 .  FIGS. 4B, 5B, and 6B  illustrate the processing state where the next sequential sheet has been fed into the leading edge receiver  122  of the round member  124  and where the trailing edges  142 B,  144 B, and  146 B of the sheets  142 ,  144 , and  146  have almost fully (or fully) uncurled to lie flat on the stacking surface  108  or lie flat on top of other sheets that are on the stacking surface  108 . 
     In the realm of sheets, beam strength is known to mean, for example, the tendency for an unsupported sheet to maintain, or return to, a flat state. For purposes herein, beam strength is considered a sheet&#39;s own unsupported, unaided ability to unfold (uncurl) when released from a curved surface so as to return to a flat state on its own and without manipulation by external components. Higher beam strengths correspond to a greater ability to self-unfold or self-uncurl, while lower beam strengths correspond to the opposite. The beam strength will vary depending upon the weight (e.g., g/cm 2 ), stiffness, length, etc., of the sheets, as well as the environmental conditions (humidity, temperature, etc.). Therefore, the very same sheet (same type, weight, length, etc.) may have a higher beam strength in one environment (e.g., lower humidity) and a lower beam strength in a different environment (e.g., higher humidity). 
     The distinction between a relatively lower beam strength sheet and a relatively higher beam strength sheet varies based upon the different environmental conditions, sheet conditions, machine conditions, user definition of stack quality, etc. Therefore, no absolute measures of beam strengths are presented here. Instead, broadly a relatively higher beam strength is higher than a relatively lower beam strength, with a medium beam strength being between the two. 
     Additionally, the relatively lower beam strength will, for a given machine and a given environment, produce stacking errors that are above a “stack quality standard” that may be established by an operator or may be industry standards. Therefore, when sheets of a specific brand, type, length, weight, etc., used in a specific stacking machine that is subjected to specific environmental conditions (e.g., humidity, temperature, etc.) results in stacking errors that are below a user&#39;s subjective expected “stack quality” standard, such sheets can be classified as relatively lower beam strength sheets. Correspondingly, sheets that do not result in such stacking errors or where the stack quality is above the minimum quality standard, under the same conditions, environment, machine, etc., are classified as relatively higher beam strength sheets. The classification of different lengths, weights, types, brands, etc., of sheets (for different environmental conditions) can be found empirically for each specific machine/environment or potentially from industry-standard records if such are established. 
     As shown in  FIG. 3A , the first arm  132  is rotatable around the first hinge  130  and the second arm  136  is rotatable around the second hinge  134  to position both the first arm  132  and the second arm  136  in the closed position (first and third positions, respectively) when contacting the leading edges of all types of beam strength sheets (high, low, and medium beam strength sheets, all of which are represented generically in  FIG. 3A  using the identification number  102 ). This positioning helps guide all leading edges  102 A of all sheets  102  into the leading edge receiver  122  of the round member  124 . However, different positions are utilized for the first and second arms  132 ,  136  for the trailing edges of sheets that have different beam strengths, as shown in the following examples illustrated in  FIGS. 4A-6B . 
     In a first example for relatively higher beam strength sheets  142 , shown in  FIG. 4A , the first and second arms  132 ,  136  are both left in the closed position (first and third positions, respectively) when the trailing edge  142 B of the higher beam strength sheets  142  passes between the first and second arms  132 ,  136 . At this processing state shown in  FIG. 4A , the leading edge of the sheet  142 A has already become firmly positioned against the notched alignment structure  114 , preventing the sheet  142  from sliding along, or moving horizontally relative to, the stacking surface  108 . 
     Maintaining the first and second arms  132 ,  136  in the closed position as the trailing edge  142 B passes between the first and second arms  132 ,  136  causes the trailing edge  142 B to be released from the surface of the disk  124  only after the trailing edge  142 B passes by the distal end of the longer second arm  136  (the distal end of the second arm  136  is the end furthest away from the second hinge  134 ). However, this does not result in decreased stack quality because the relatively higher beam strength sheets  142  will have a relatively higher ability/tendency to return to a flat position (e.g., snap back to a flat position) and there is, therefore, no need to rotate either the first arm  132  or the second arm  136  to the open position for such higher beam strength sheets  142 . Allowing the first and second arms  132 ,  136  to remain in the closed position for both the leading edge  142 A and the trailing edge  142 B of the higher beam strength sheets  142  reduces wear on the components and reduces energy consumption (energy is used to rotate the arms). 
       FIG. 4B  illustrates the processing state where the next sequential relatively higher beam strength sheet  142  has been fed into the leading edge receiver  122  of the round member  124  and where the trailing edge  142 B of the previous sheet  142  has almost fully (or fully) uncurled to lie flat on the stacking surface  108  or lie flat on top of other sheets that are on the stacking surface  108 . Note that both the first and second arms  132 ,  136  are in the closed position as the leading edge  142 A passes between the first and second arms  132 ,  136  in  FIG. 4B . 
     In a second example for relatively medium beam strength sheets  144  (relatively lower beam strength than sheets  142 ), shown in  FIG. 5A , the first arm  132  is left in the closed position (first position) but the second arm  136  is rotated around the second hinge  134  to the open position (fourth position) when the trailing edge  144 B of the medium beam strength sheets  144  passes between the first and second arms  132 ,  136  to not apply any bias to the sheets. At this processing state shown in  FIG. 5A , again the leading edge of the sheet  144 A has already become firmly positioned against the notched alignment structure  114 , preventing the sheet  144  from sliding along, or moving horizontally relative to, the stacking surface  108 . 
     Maintaining the first arm  132  in the closed position, but the second arm  136  in the open position, as the trailing edge  144 B passes between the first and second arms  132 ,  136  causes the trailing edge  144 B to be released from the region of the roller nips  112  after the trailing edge  144 B passes by the proximal end of the longer second arm  136  (the proximal end of the second arm  136  is the end closest to the second hinge  134 ) allowing the trailing edge  144 B to move away from the disk  124 . Note that in  FIG. 5A , the medium beam strength sheet  144  separates from the region of the roller nips  112  a distance further away from the stacking surface  108  relative to when the higher beam strength sheet  142  separates from the surface of the disk  124  in  FIG. 4A , creating a broader arc in the sheet  144  in  FIG. 5A , relative to more narrow arc of the sheet  142  shown in  FIG. 4A . This broader arc helps prevent the relatively medium beam strength sheet  144  sheet from the folding shown in  FIG. 2B , thereby maintaining high stack quality even for medium beam strength sheets  144 . 
     The processing state shown in  FIG. 5A  therefore does not result in decreased stack quality because the medium beam strength sheets  144  will have a relatively medium ability/tendency to return to a flat position (e.g., snap back to a flat position) and there is, therefore, no need to rotate both the first arm  132  and the second arm  136  to the open position for such medium beam strength sheets  144  because only rotating the second arm  136  to the open position is sufficient for medium beam strength sheets  144 . Allowing the first arm  132  to remain in the closed position for both the leading edge  144 A and the trailing edge  144 B of the medium beam strength sheets  144  reduces wear on the components of the first arm  132  and reduces energy consumption; however, rotating the second arm  136  to the open position for medium beam strength sheets  144  prevents irregular stacking and stacking jams, thereby maintaining the user-established stack quality. 
     Again,  FIG. 5B  again illustrates the processing state where the next sequential relatively medium beam strength sheet  144  has been fed into the leading edge receiver  122  of the round member  124  and where the trailing edge  144 B of the previous sheet  144  has almost fully (or fully) uncurled to lie flat on the stacking surface  108  or lie flat on top of other sheets that are on the stacking surface  108 . As shown in  FIG. 5B , the second arm  134  has been rotated back to the closed position for the next sheet so that both the first and second arms  132 ,  136  are in the closed position as the leading edge  144 A of the next sheet  144  passes between the first and second arms  132 ,  136  to ensure the leading edge  146 A is fed into the leading edge receiver  122  of the round member  124 . 
     In a third example for relatively lower beam strength sheets  146  (relatively lower beam strength than sheets  144 ) shown in  FIG. 6A , the first and second arms  132 ,  136  are both rotated to the open position (second and fourth positions, respectively) when the trailing edge  146 B of the lower beam strength sheets  146  passes between the first and second arms  132 ,  136 . At this processing state shown in  FIG. 6A , the leading edge of the sheet  146 A has already become firmly positioned against the notched alignment structure  114 , preventing the sheet  146  from sliding along, or moving horizontally relative to, the stacking surface  108 . 
     Rotating the first and second arms  132 ,  136  to the open position as the trailing edge  146 B passes between the first and second arms  132 ,  136  causes the trailing edge  146 B to be released from the region of the roller nips  112  after the trailing edge  144 B passes by the proximal end of the longer second arm  136  and to be pushed (redirected) away from the disk  124  by the first arm  132  in a trajectory (e.g., T 2 ) that is approximately (e.g., within 20% of) parallel to, or at least relatively more parallel to, the stacking surface  108 . 
     Movement of the trailing edge  146 B in trajectory T 2  is not hindered by the second arm  136  because it also is in the open position. Because the trailing edge  146 B is pushed away from the surface of the disk  124  by the first arm  132 , there is no decrease in stack quality even for relatively lower beam strength sheets  146 . More specifically, the force imparted by the open first arm  132  to the trailing edge  146 B is in a direction more parallel to the stacking surface  108  (e.g., horizontal direction) relative to the processing states shown in  FIGS. 4A-5B  (which allow the trailing edges  142 B,  144 B to move in a direction more perpendicular to the stacking surface  108  (e.g., more in a downward direction). This redirection of the trailing edge  146 B by the first arm  132  creates an even broader arc in the sheet  146  in  FIG. 6A , relative to more narrow arcs of the sheets  142  and  144  shown in  FIGS. 4A and 5A , respectively. This broader arc helps prevent the relatively lower beam strength sheet  146  from the folding shown in  FIG. 2B . 
     Again,  FIG. 6B  illustrates the processing state where the next sequential relatively lower beam strength sheet  146  has been fed into the leading edge receiver  122  of the round member  124  and where the trailing edge  146 B of the previous sheet  146  has almost fully (or fully) uncurled to lie flat on the stacking surface  108  or lie flat on top of other sheets that are on the stacking surface  108 . Note that both the first and second arms  132 ,  136  are rotated back to the closed position as the leading edge  146 A passes between the first and second arms  132 ,  136  in  FIG. 6B  to ensure the leading edge  146 A is fed into the leading edge receiver  122  of the round member  124 . 
     Therefore, the structures and methods herein address the issue of trailing edges of low beam strength sheets  146  not properly unfolding or uncurling by selectively opening the first and second arms  132 ,  136 . Specifically, for sufficiently low beam strength sheets, not only does the second arm  136  open to allow the inherent uncurling/unfolding ability of the sheet  146  to move the trailing edge of the low beam strength sheet away from the round member  124 , the first arm  132  additionally pushes the trailing edge  146 B of the low beam strength sheet  146  away from the round member  124  in a trajectory approximately perpendicular to the stacking surface  108 . Thus, the force imparted by the open first arm  132  is in the direction relatively more parallel to the stacking surface  108 . In this way, the open first arm  132  provides additional force to the sheet&#39;s own uncurling and unfolding ability to combat the tendency of such low beam strength sheets  146  to fold or buckle, thereby maintaining high stack quality. 
       FIG. 7  illustrates many components of printer structures  204  herein that can comprise, for example, a printer, copier, multi-function machine, multi-function device (MFD), etc. The printing device  204  includes a controller/tangible processor  224  and a communications port (input/output)  214  operatively connected to the tangible processor  224  and to a computerized network external to the printing device  204 . Also, the printing device  204  can include at least one accessory functional component, such as a user interface (UI) assembly  212 . The user may receive messages, instructions, and menu options from, and enter instructions through, the user interface or control panel  212 . 
     The input/output device  214  is used for communications to and from the printing device  204  and comprises a wired device or wireless device (of any form, whether currently known or developed in the future). The tangible processor  224  controls the various actions of the printing device  204 . A non-transitory, tangible, computer storage medium device  210  (which can be optical, magnetic, capacitor based, etc., and is different from a transitory signal) is readable by the tangible processor  224  and stores instructions that the tangible processor  224  executes to allow the computerized device to perform its various functions, such as those described herein. Thus, as shown in  FIG. 7 , a body housing has one or more functional components that operate on power supplied from an alternating current (AC) source  220  by the power supply  218 . The power supply  218  can comprise a common power conversion unit, power storage element (e.g., a battery, etc.), etc. 
     The printing device  204  includes at least one marking device (printing engine(s))  240  that use marking material, and are operatively connected to a specialized image processor  224  (that is different from a general purpose computer because it is specialized for processing image data), a media path  236  positioned to supply continuous media or sheets of media from a sheet supply  230  to the marking device(s)  240 , etc. After receiving various markings from the printing engine(s)  240 , the sheets of media can optionally pass to a finisher/stacker  234  which can fold, staple, sort, etc., the various printed sheets. The stacking system  100  discussed above can be included internally within the printing device  204  at any location where sheet stacking is needed, or externally as part of, for example, the finisher/stacker  234 . Also, the printing device  204  can include at least one accessory functional component (such as a scanner/document handler  232  (automatic document feeder (ADF)), etc.) that also operate on the power supplied from the external power source  220  (through the power supply  218 ). 
     The processor  224  can be directly or indirectly connected to, and can automatically control, the paper feeder device  104 , the nip rollers  112 , rotational device  120 , etc. Additionally, the processor  224  can be directly or indirectly connected to, and can automatically control, the first hinge  130  and the second hinge  134  so that the processor  224  can control the rotation of the first arm  132  and the second arm  136 . 
     More specifically, the processor  224  is adapted to control the first hinge  130  to only rotate the first arm  132  to the second position (open) for trailing edges of low beam strength sheets  146 . However, the processor  224  is adapted to control the second hinge  134  to rotate the second arm  136  to the fourth position (open) for both the first type of sheets  146  and a second type of sheets  142  or  144  to not apply any bias to such sheets (again, the first type of sheets  146  have a lower beam strength relative to the second type of sheets  142  or  144 ). 
     Further, as shown in  FIG. 7 , a sensor  208  can be directly or indirectly connected to the processor  224 . The sensor  208  can automatically detect whether the sheets  102  are the first type of sheets  146  or the second type of sheets  142 ,  144  (or such information can be manually entered through the user interface  212 ). For example, the sensor  208  (which can be, or include, multiple sensors of different types) can automatically detect the length of the media (media length sensor(s)), the weight of the media (media thickness/weight per area sensor), the humidity (hygrometer), temperature (thermometer), and/or other environmental conditions within the stacking device, etc. 
     The one or more printing engines  240  are intended to illustrate any marking device that applies marking material (toner, inks, plastics, organic material, etc.) to continuous media, sheets of media, fixed platforms, etc., in two- or three-dimensional printing processes, whether currently known or developed in the future. The printing engines  240  can include, for example, devices that use electrostatic toner printers, inkjet printheads, contact printheads, three-dimensional printers, etc. The one or more printing engines  240  can include, for example, devices that use a photoreceptor belt or an intermediate transfer belt or devices that print directly to print media (e.g., inkjet printers, ribbon-based contact printers, etc.). 
       FIG. 8  is flowchart illustrating exemplary methods herein. The processing described herein may, in some situations, be more useful for longer sheets; and, therefore, sometimes the processing herein may not be performed for smaller sheets. This is reflected in item  300  in  FIG. 8  where the sheets length is compared to an established minimum sheet length and the following processing only occurs for sheets that exceed the previously established minimum sheet length. 
     When performed, this processing activates sheet movement components (e.g., the paper feeder device, the nip rollers, rotational device, etc.) in item  301 . The round member is positioned relative to the stacking surface to move the sheets toward the stacking surface when rotating in item  301 . Specifically, these methods rotate the first arm around the first hinge to rotate the first arm between the first position (closed) and the second position (open). The first arm is positioned to bias sheets toward the round member when in the first position (closed). The first arm is positioned to not bias the sheets toward the round member when in the second position (open). The round member has leading edge receivers adapted to accept leading edges of the sheets, and the first arm is positioned to direct the leading edges of the sheets into the leading edge receivers of the round member when the first arm is in the first position (closed). The process of controlling the first arm can control the hinge to position the arm to allow the trailing edge of a sheet to move from the round member in a direction approximately parallel to the stacking surface when the arm is in the second position (open). 
     Therefore, as shown in item  302  in  FIG. 8 , in this processing, the first and second arms are kept closed when contacting the leading edges of both the first type of sheets and the second type of sheets. However, the arms operate differently on the trailing edges. 
     Specifically, as shown in item  304 , for the trailing edge of sufficiently high beam strength (higher beam strength) sheets, this processing leaves both arms closed and processing returns to item  302  to await the leading edge of the next sheet. Alternatively, in item  306 , for the trailing edge of sufficiently low beam strength (lower beam strength) sheets, this processing rotates both arms to the open position. In another alternative, in item  308 , for the trailing edge of beam strength sheets that are between the higher and lower beam strengths (medium beam strength) this processing leaves the first arm closed, but rotates the second arm to the open position. 
     While item  304  immediately returns to processing the leading edge of the next sheet, because items  306  and  308  have rotated at least one arm to the open position, in item  310  this processing closes any open arms for the next sheet and returns processing to item  302 . 
     Therefore, with the methods herein, the first arm is rotated to the second position (open) only when contacting the trailing edge of the lower beam strength sheets (first type of sheets) as shown in item  306 ; and the first arm does not rotate, but maintains the first position (closed), when contacting the trailing edge of the second type of sheets (medium and high beam strengths) as shown in items  304  and  308 . With respect to the second arm, the second arm rotates to the fourth position (open) when contacting the trailing edges of both the first type of sheets  306  and the second type of sheets  308  and may only remain closed when contacting the highest beam strength sheets in item  304 . 
     Herein, terms such as “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”, “over”, “overlying”, “parallel”, “perpendicular”, etc., used herein are understood to be relative locations as they are oriented and illustrated in the drawings (unless otherwise indicated). Terms such as “touching”, “on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., mean that at least one element physically contacts another element (without other elements separating the described elements). Further, the terms automated or automatically mean that once a process is started (by a machine or a user), one or more machines perform the process without further input from any user. Additionally, terms such as “adapted to” mean that a device is specifically designed to have specialized internal or external components that automatically perform a specific operation or function at a specific point in the processing described herein, where such specialized components are physically shaped and positioned to perform the specified operation/function at the processing point indicated herein (potentially without any operator input or action). In the drawings herein, the same identification numeral identifies the same or similar item. 
     It will be appreciated that the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Unless specifically defined in a specific claim itself, steps or components of the systems and methods herein cannot be implied or imported from any above example as limitations to any particular order, number, position, size, shape, angle, color, or material.