Patent Publication Number: US-6341698-B1

Title: Sheet stacking device

Description:
FIELD OF THE INVENTION 
     The present invention relates to a stacking device, and more particularly, to a stacking device for stacking sheet material. The present invention is particularly applicable in stacking cut-to-length sheets from a generally continuous source, and shall be described with particular reference thereto. It will, of course, be appreciated that the present invention has other broader applications and may be used in stacking other types of sheet material. 
     BACKGROUND OF THE INVENTION 
     Many types of sheet material are produced by a process wherein individual sheets are cut from a generally continuous strip or web of material. It is then necessary to stack these “cut-to-length sheets” for packaging and/or shipping. In the process of stacking and/or shipping these “cut-to-length sheets”, it is often desirable to minimize the contact between the sheets and the stacking device so as not to damage the sheets. 
     The present invention provides a device for stacking sheet material, such as cut-to-length sheets that are cut from a generally continuous source, that minimizes physical handling and gripping of the sheet. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a sheet stacking device, comprised of a sheet support bed comprised of a plurality of side-by-side rollers. Each of the rollers is freely rotatable about a respective roller axis. A support bed drive assembly is provided for moving the sheet support bed in a predetermined direction along a closed path. The path has an upper horizontal run and a lower horizontal ran and is dimensioned such that a gap exists between a leading end and a trailing end of the sheet support bed. The gap moves along the path as the sheet support bed moves along the path. A roller control assembly is provided for selectively controlling rotation of each of the rollers about its respective roller axis. A controller selectively and sequentially controls the operation of the support bed drive assembly and the roller drive assembly. The stacking device is operable to perform the following operational steps: 
     a) causing the support bed drive assembly to move the sheet support bed to a sheet receiving position on the upper run of the path; 
     b) causing the roller control assembly to allow the rollers to rotate freely to receive a sheet to be stacked on the support bed; 
     c) causing the support bed drive assembly to move the sheet support bed at a predetermined speed along the path to move the sheet to a “stacking position”; 
     d) when the sheet is at the stacking position, causing the roller control assembly to rotate the roller in a predetermined direction at a predetermined speed while the support bed continues to move along the path, wherein the rollers are operable to convey the sheet in a direction opposite the direction of the support bed at a speed wherein the sheet remains essentially stationary at the “stacking position”; 
     e) continuously driving the sheet support bed along the path and continuously rotating the roller wherein the sheet becomes unsupported as the trailing end of the sheet support bed passes under the sheet and the sheet drops through the gap onto the sheet support bed as it moves along the lower run; 
     f) causing the rollers along the lower run to rotate at a predetermined speed in a predetermined direction wherein the sheet is conveyed in a direction opposite the direction of the support bed at a speed wherein the sheet remains essentially stationary at a position essentially below the stacking position; and 
     g) continuously driving the sheet support bed along the path and continuously rotating the roller along the lower run wherein the sheet becomes unsupported as the trailing end of the sheet support bed passes under the sheet and the sheet drops through the gap onto a stacking platform. 
     In accordance with another aspect of the present invention, there is provided a sheet stacking device, comprised of a sheet support bed having a first end and a second end. The sheet support bed is comprised of a plurality of side-by-side rollers, each of the rollers being freely rotatable about an associated roller axis. A drive assembly moves the sheet support bed in a predetermined direction along a closed path, the path having a horizontal upper run and a horizontal lower run, and is dimensioned such that a space exists between the first end and the second end of the sheet support bed as the sheet support bed moves along the path. A roller control assembly selectively and sequentially controls rotation of select ones of the rollers at select intervals during a stacking operation, wherein the stacking device is operable to: 
     receive a sheet to be stacked on the sheet support bed when the support bed is disposed along the upper run; 
     convey the sheet along the upper run on the support bed to a “staking position” on the upper run; 
     cause the roller control assembly to rotate rollers disposed along the upper run in a direction such that the sheet remains essentially in the stacking position as the sheet support bed continues to move along the path, the sheet dropping through the space between the first and the second end of the sheet support bed onto the rollers of the sheet support bed on the lower run when the support bed moves from the upper run to the lower run; and 
     cause the roller control assembly to rotate rollers disposed along the lower run in a direction such that the sheet remains essentially in the stacking position as the sheet support bed continues to move along the path, the sheet dropping through the space between the first end and the second end of the sheet support bed onto a stack of sheets when the support bed moves from the lower run to the upper run. 
     In accordance with another aspect of the present invention, there is provided a method of stacking sheet material, comprising the steps of: 
     a) conveying a sheet to be stacked onto the surface of a sheet support bed, the support bed comprised of a plurality of side-by-side rollers, each of the rollers being rotatable about a respective roller axis, the support bed being movable in a predetermined direction along a closed path having a horizontal upper run and a horizontal lower run, the path dimensioned such that a space exists between distal ends of the support bed, the space moving along the path as the support bed moves along the path; 
     b) moving the support bed along the path to move the sheet along the upper path run toward a stacking position; 
     c) causing the rollers along the upper run to rotate when the sheet reaches the stacking position, the roller rotating in a direction such that the sheet remains essentially stationary on the support bed at the stacking position as the support bed continues to move along the path, the sheet falling generally vertically onto the support bed on the lower run when the space moves under the sheet; 
     d) causing the rollers along the lower run to rotate in a direction such that the sheet falling on the support bed from the upper run remains essentially stationary on the support as the support bed continues to move along the path, the sheet falling from the lower run of the support bed when the space moves under the sheet; and 
     e) collecting the sheet at a stacking location below the lower run. 
     It is an object of the present invention to provide a stacking device for stacking sheet material. 
     It is another object of the present invention to provide a stacking device for stacking “cut-to-length sheets” from a generally continuous source of sheet material. 
     It is another object of the present invention to provide a device as described above having means for detecting defects on a cut-to-length sheet. 
     It is a still further object of the present invention to provide a stacking device as described above that diverts cut-to-length sheets with defects from the stacking operation. 
     It is a still further object of the present invention to provide a stacking device that minimizes contact with the sheet material to be stacked. 
     These and other objects and advantages will become apparent from the following description of a preferred embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, preferred embodiments of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
     FIG. 1 is a partially sectioned, side elevational view of a sheet-stacking device, illustrating a preferred embodiment of the present invention; 
     FIG. 2 is a top plan view of the sheet stacking device shown in FIG. 1; 
     FIG. 3 is a sectional view taken along lines  3 — 3  of FIG. 1; 
     FIGS. 4A-4M are schematic side elevational views of the sheet stacking device shown in FIG. 1, illustrating a sequence involved in stacking a sheet; 
     FIGS. 5A and 5B are schematic side elevational views of the sheet stacking device shown in FIG. 1, illustrating a sequence for diverting a defective sheet from the stacking process; 
     FIG. 6 is a schematic view showing two stacking devices in alignment for stacking sheets of different size or for sequentially stacking of sheets of the same size; and 
     FIG. 7 is a schematic control diagram showing a control system for the stacking device shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same, FIGS. 1-3 show a sheet stacking device  10  illustrating a preferred embodiment of the present invention. Sheet stacking device  10  is adapted to receive individual sheets, designated S, of a planar material at a first position relative thereto, and to stack such sheets S into a vertical stack at a second position. 
     In the drawings, sheet stacking device  10  is shown together with a sheet cutting device  20  that is operable to cut to length sheets S from a generally continuous length of material (not shown). Sheet cutting device  20  in and of itself forms no part of the present invention, and is shown solely for the purpose of illustration. Sheet cutting device  20  merely represents a source of “cut-to-length sheets” S to be stacked. It will be appreciated from a further reading of the specification that sheets S need not be cut from continuous roll, but may be formed in a flat planar configuration by any suitable process. 
     In the particular embodiment shown, the material to be cut into sheets S is guided along a predetermined path by guide rollers  22 . A cutting assembly  24  is provided along the path to cut the sheet material into sheets S of predetermined lengths. FIG. 1 shows a cutting assembly  24  comprised of a movable upper cutting die  26  and a stationary lower cutting die  28 . Supports  32 ,  34  on opposite sides of cutting assembly  24  support the material relative to cutting dies  26 ,  28 . Cutting assembly  24  is operable to repeatedly shear like sized sheets S from the roll material and to provide individual sheets S to stacking device  10  at the aforementioned first position. 
     Sheet stacking device  10  is disposed adjacent to the supply path at a predetermined elevation relative thereto to receive sheets S from sheet cutting device  20 . Broadly stated, sheet stacking device  10  is comprised of a frame assembly  40 , a sheet transport assembly  60 , a roller control assembly  120  and a stacking assembly  180 . 
     Frame Assembly 
     Frame assembly  40  is comprised of two spaced-apart plates  42 ,  44  that are vertically oriented and parallel to each other. Plates  42 ,  44  define the side walls of sheet stacking device  10  and are supported by vertical legs  46 , as best seen in FIG.  1 . Transverse beams  48  connect plates  42 ,  44  to each other and define a predetermined spacing therebetween. In the embodiment shown, legs  46  and beams  48  are formed of rectangular pipe. 
     Sheet Transport Assembly 
     Sheet transport assembly  60  is disposed between plates  42 ,  44 . Sheet transport assembly  60  is basically comprised of a plurality of rollers  72  that are movable along an endless path. The path of rollers  72  is generally defined by a pair of elongated, upper tracks, designated  64  and  65 , and a pair of elongated lower tracks  66  and  67 , that are best seen in FIG.  3 . Upper tracks  64  and  65  are mirror images of each other, and lower tracks  66  and  67  are also mirror images of each other. Lower tracks  66  and  67  are attached to side plates  42 ,  44 , respectively such that the upper surfaces thereof are in horizontal alignment with each other, as seen in FIG.  3 . Likewise, upper tracks  64  and  65  are attached to side plate  42 ,  44  such that the upper surfaces thereof are in horizontal alignment. Tracks  64 ,  65 ,  66  and  67  are attached to side plates  42 ,  44  by conventional fasteners  68 . In the embodiment shown, the upper surfaces of upper tracks  64  and  65  and lower tracks  66  and  67  are slightly convex from one end to the other, as best seen in FIG.  1 . As will be appreciated from a further reading of the specification, the upper surfaces of tracks  64 ,  65 ,  66  and  67  need not be slightly convex to practice the present invention. These surfaces may be flat. In the particular embodiment shown, the upper surface of upper tracks  64 ,  65  are slightly convex for better contact with flexible belt  132  that is described in greater detail below. In the embodiment shown, the upper surfaces of lower tracks  66  and  67  are slightly convex to provide greater contact with rail  162  that is described in greater detail below. Upper tracks  64  and  65  define an “upper run” for rollers  72 , while lower tracks  66  and  67  define a “lower run” for roller  72 . 
     Referring now to FIG. 3, the construction of each roller  72  is best seen. Each roller  72  is comprised of a roller body  74  that is generally cylindrical in shape. Bores  76  are formed in each end of roller body  74 . Bores  76  are dimensioned to receive a roller bearing  78  therein. A shaft  82  is mounted within each roller bearing  78  and extends axially outward from the ends of roller body  74 . Each shaft  82  has a track bearing  84  mounted thereon. Track bearing  84  is disposed on shaft  82  to rest upon the respective surfaces of upper and lower tracks  64 ,  65 ,  66  and  67 . 
     The free ends of shafts  82  extend into hubs  94  formed on conveyor belts  92 . In the embodiment shown, conveyor belts  92  are endless loops, having hubs  94  integrally formed thereon. Conveyor belts  92  are preferably formed of a flexible polymer material, such as nylon. A conveyor belt  92  is provided at each end of roller  72 . Each conveyor belt  92  extends around a drive sprocket  96  and an idler sprocket  98 . The inner surface of conveyor belt  92  includes splines adapted to interact with teeth on drive sprockets  96  and idler sprockets  98 . Drive sprockets  96  are mounted onto a drive shaft  102  for simultaneous rotation by a drive motor  104 . Drive motor  104  is fixedly mounted onto side plate  42 . Idler shafts  106  connect idler sprockets  98  to the frame  40 . Drive motor  104  is preferably a stepping motor having control means (not shown) to control movement of conveyor belts  92  and rollers  72  in a predetermined sequence as shall be described in greater detail below. 
     As shown in FIGS. 1 and 2, a little more than one-half of hubs  94  of conveyor  92  have rollers  72  mounted therein. As best seen in FIGS. 1 and 2, rollers  72  are mounted onto conveyor  92  to form a generally continuous roller bed  110  (i.e., a support bed comprised of adjacent rollers  72 ) and a gap or space  112  separating the distal ends of roller bed  110 . 
     A sensor  116  is located at the end of the “upper run” of belt  92 , as best seen in FIGS. 1 and 2. Sensor  116  is positioned to sense the edge of a sheet S moving along the upper run of the path of rollers  72 , as shall be described in greater detail below. 
     A scanner  118  is mounted to frame assembly  40  and extends parallel to the axes of rollers  72 . Scanner  118  is disposed above belt  92  and is disposed to be able to scan sheets moving along the upper run of belt  92 . 
     Roller Control Assembly 
     In accordance with the present invention, roller control assembly  120  is provided to interact with rollers  72  so as to control the rotation thereof. In the embodiment shown, roller control assembly  120  is comprised of a movable brake device  130  and a stationary brake device  160 . Movable brake device  130  is basically comprised of a flexible belt  132 . Brake belt  132  is a generally continuous loop that is mounted around a drive sprocket  134  and an idler sprocket  136 . Drive sprocket  134  and idler sprocket  136  include teeth that operatively interact with splines formed on brake belt  132 . Drive sprocket  134  and idler sprocket  136  are mounted on the distal ends of an elongated beam  138  (best seen in FIG.  3 ). Drive sprocket  134  is mounted onto a drive shaft  142  that extends from a drive motor  144 . Drive motor  144  is mounted on side plate  44  and is operable to controllably drive belt  132  about a path that is generally parallel to the path of conveyor belt  92 . In the embodiment shown, beam  138  and belt  132  are mounted to pivot about drive shaft  142 . An actuator  152  is fixedly mounted to frame assembly  40  to reciprocally move the end of beam  138 . In the embodiment shown, actuator  152  is a cylinder (either pneumatic or hydraulic) that is attached at one end to beam  138  and at the other to frame assembly  40 . Actuation of the cylinder is operable to move brake belt  132  between a first position shown in FIG. 1 wherein brake belt  132  is in contact with the surface of rollers  72 , and a second position wherein brake belt  132  is away from, and not in contact, with rollers  72 . As best seen in FIG. 2, brake belt  132  is disposed near side wall  44  and engages only one end of rollers  72 , thereby leaving the space above the center portions of rollers  72  unobstructed. 
     Referring now to FIGS. 1 and 3, stationary brake device  160  is best seen. Stationary brake device  160  is generally comprised of an elongated rail  162  that extends along a major portion of the lower run. As best seen in FIG. 3, rail  162  has an L-shaped cross-section and is mounted to side plate  44  by conventional fasteners  68 . A brake pad  164  formed of a tough, frictional material is disposed on the bottom surface of rail  162 . Brake pad  164  is disposed to engage the upper surface of rollers  72  as they move along the lower path run. To this end, the leading edge  168  of rail  162  is contoured to engage rollers  72  as they move around idler sprocket  98 . In the embodiment shown, rail  162  is slightly concave to match the convex surface of lower track  66 . 
     Stacking Assembly 
     Stacking assembly  180 , best seen in FIG. 1, is generally comprised of a stacking platform  182  supported by a movable support. In the embodiment shown, stacking platform  182  is supported on a rod  184  that extends from a base  186 . Stacking platform  182  is preferably operable to move downward a predetermined distance each time a sheet S is stacked thereon. In this respect, stacking platform  182  may be supported by a compression spring (not shown), wherein stacking platform will lower as the weight thereon increases. Alternately, rod  184  and base  186  may be comprised of a conventional hydraulic or pneumatic cylinder, or a mechanical screw device, that is operably controlled to lower stacking platform  182  after a predetermined number of sheets S have been stacked thereon. As shown in FIG. 1, stacking platform  182  is disposed at one end of sheet stacking device  10  and is generally centrally located between side plates  42 ,  44  below rollers  72 . 
     Operation 
     Referring now to FIGS. 4A through 4M, the operation of sheet stacking device  10  shall be described. In FIGS. 4A through 4M, the components of stacking device  10  have been in some cases simplified and enlarged for the purposes of illustration and easier identification. In this respect, the relative size of rollers  72  and movable brake device  130  have been enlarged for easier identification. Further, to reduce the complexity of the drawings, the slightly convex shape of upper tracks  64  and  65  and lower tracks  66  and  67  are not shown. (As indicated above, the upper surface of tracks  64 ,  65 ,  66  and  67  may be flat without deviating from the present invention). In addition, for a clearer visual illustration, movable brake device  130  is shown as being movable in its entirety relative to roller bed  110  rather than being pivotable about drive shaft  142 , as in FIGS. 1-3. It will be appreciated by those skilled in the art that the simplification of the drawings shown in FIGS. 4A-4M are for the purposes of illustration only, and are not intended to suggest a structural change in the device heretofore described. 
     Referring now to FIG. 4A, roller bed  110  is shown in a preferred first position to receive a sheet S from sheet cutting device  20 . In its initial operating position, movable brake device  130  is in its second position, wherein belt  132  is not in contact with rollers  72 . In the embodiment shown, a section of the generally continuous sheet material is fed onto the upper surface of rollers  72  by drive rollers  22 . Since belt  132  does not engage rollers  72 , rollers  72  are free to rotate about their respective axes. As the sheet material is being fed onto roller bed  110 , drive motor  104  causes drive sprocket  96  to rotate and move belt  92  in the direction shown. Since rollers  72  are free-wheeling, roller bed  110  may move to a predetermined position without exerting any influence on the sheet material. 
     FIG. 4B shows roller bed  110  of stacking device  10  continuing to move in a counter-clockwise direction as the sheet material is being fed onto roller bed  110 . When a predetermined length of the sheet material has been fed onto roller bed  110  by drive rollers  22 , movement of roller bed  110  ceases at a predetermined location. When in the predetermined position, upper die  26  from cutting device  24  moves downward to shear sheets S from the generally continuous length of sheet material. At approximately the same time, movable brake  130  moves downward such that belt  132  engages the upper surface of rollers  72 . Importantly, as indicated above, belt  132  of movable brake  130  engages only one end of rollers  72  and does not come in contact with the sheet material resting thereon. 
     With a sheet S resting upon the surface of rollers  72 , drive motor  104  is energized to cause roller bed  110  to move in a counter-clockwise direction along the upper path. At the same time, motor  144  of movable brake device  130 , causes belt  132  to move in a clockwise direction as shown in FIG.  4 D. In accordance with the present invention, conveyor belt  92  and control belt  132  are timed to move at the same speed. As a result of the motion of both belts at the same speed, rollers  72  move along the upper run in a “locked” position. In other words, each roller maintains a stationary position relative to its respective roller axis. As a result, sheet S moves along the upper run toward sensor  116  as best seen in FIGS. 4D and 4E. As shown in FIG. 4E, as rollers  72  move around idler sprocket  98 , onto the lower run, each individual roller moves away from engagement with belt  132  and comes into contact with stationary brake device  160 . As the surface of rollers  72  come into contact with brake pad  164 , (as illustrated in FIG.  3 ), rollers  72  begin to rotate in a counter-clockwise direction about their respective axes as illustrated in FIG.  4 E. As roller bed  110  continues to move around idler sprocket  98  from the upper run to the lower run, sheet S is carried to a predetermined position relative to sensor  116 . When sheet S reaches a predetermined position relative to sensor  116 , a signal generated by sensor  116  causes the controller (not shown) to deactivate motor  144  of movable brake device  130  thereby stopping the motion of belt  132 . With belt  132  still engaging rollers  72  of roller bed  110  that remain on the upper run, but with belt  132  now being stationary, the rollers that still engage belt  132  begin to rotate in a clockwise direction as illustrated in FIG.  4 F. As roller bed  110  continues to move from the upper run to the lower run, the clockwise rotation of rollers  72  still in contact with belt  132 , basically maintain sheet S in a stationary position relative to stacking device  10 . In this respect, the clockwise rotation of rollers  72  on the upper run influence the sheet S in a direction to the right as shown in the drawings. However, the motion of roller bed  110  to the left effectively cancels the motion imparted by the rotation of rollers  72  and causes sheet S to basically remain stationary in its stacking position. 
     As roller bed  110  continues to move from the upper run to the lower run, support for sheet S will begin to disappear as rollers  72  move from under sheet S as illustrated in FIGS. 4G and 4H. As support for sheet S on the upper run disappears, sheet S drops down onto the lower run where it comes in contact again with the upper surfaces of rollers  72 . Because of the counter-clockwise rotation of rollers  72  along the lower run (imparted by stationary brake device  160 ), sheet S effectively remains stationary relative to the moving roller bed  110  as illustrated in FIGS. 4J and 4K. Eventually, as all of the rollers  72  forming roller bed  110  move from the upper run to the lower run, sheet S falls completely onto the lower run as shown in FIG.  4 K. The counter-clockwise rotation of rollers  72  along the lower run effectively maintain sheet S stationary as roller bed  110  continues to move in a counter-clockwise direction along the lower run and back up onto the upper run. The counter-clockwise rotation of rollers  72  along the lower run maintains the sheet S in a position above stacking platform  182 . As the rollers  72  move from under sheet S, sheet S drops onto stacking platform  182 . 
     As shown in FIGS. 4K,  4 L and  4 M, stacking device  10  is preferably timed such that as one sheet S is dropping onto stacking platform  182 , roller bed  110  is returning to its initial starting position and another length of the sheet material is being driven onto rollers  72  on the upper run by drive rollers  22 . 
     The present invention thus provides a sheet stacking device that conveys a sheet material to a first position along an upper run and thereafter maintains the sheet in this relative vertical position by controlling the direction of rotation of the individual rollers  72  as the roller bed  110  moves along a closed path. As a result of the rotation of the rollers, the sheet basically drops from the upper run onto the lower run as roller bed  110  moves from the upper run to the lower run. Thereafter, sheet S is dropped onto a stacking platform  182  as the rollers along the lower run move from under sheet S. Importantly, sheet S is not pinched or squeezed between two surfaces, but merely rests upon the upper surfaces of rollers  72  and is conveyed by the rotation of such rollers from the upper run to the lower run to the stacking platform. Thus, minimal contact is exerted on sheet S as it is stacked. 
     Referring now to FIGS. 5A and 5B, another aspect of the present invention is illustrated. In accordance with this aspect of the present invention, the upper surface of each sheet S is scanned for defects or imperfections by scanner  118  as it moves along the upper run of belt  92 . If a defect or flaw is detected in the surface of a sheet S, such sheet S is diverted from the stacking operation. The defective sheet is diverted from the stacking process by conveying it off the upper run into a scrap bin  192 . The defective sheet S is conveyed off of roller bed  110  by continuing to drive belt  132  when the defective sheet S reaches the sheet stacking position (shown in FIG.  4 F). If drive belt  132  continues to move with roller bed  110 , the defective sheet S will be conveyed off of the end of sheet stacking device  10  into scrap bin  192 , as schematically illustrated in FIGS. 5A and 5B. Thus, once a defective sheet S is sensed by scanner  118 , the control unit that controls the operation of sheet stacking device  10 , can control motor  144  of movable brake device  130  to cause belt  132  to continue its clockwise rotation beyond the sheet stacking position. This prevents rotation of rollers  72  and causes the defective sheet to be conveyed into scrap bin  192 . Roller bed  110  would then continue back to its initial sheet-receiving position to receive the next sheet S for stacking from sheet cutter  20 , as illustrated in FIG.  5 B. 
     It will, of course, be appreciated that scanner  118  need not be located directly above the upper run of conveyor belt  92  or even be part of sheet stacking device  10 . The means for scanning and detecting defects may be part of sheet cutter  20  or be located before sheet cutter  20 . 
     Referring now to FIG. 6, a pair of stacking devices designated  10  and  10 ′, illustrate another embodiment of the present invention. Sheet stacking device  10  is the same device as heretofore described. Sheet stacking device  10 ′ may be the same (not shown) as sheet stacking device  10 , or may be a shorter version of stacking device  10  adapted to stack sheets of a different size, as illustrated in FIG.  6 . 
     By providing two identical stacking devices  10  in a row, one device  10  could be stacking sheets S while a stack of sheets S is being removed from the other. This enables continuous cutting and stacking of sheets S without the down time to remove a stack of sheets from platform  182 . 
     Alternatively, sheet stacking device  10 ′ may be adapted to stack different size sheets than stacking device  10 , as shown in FIG.  6 . In this respect, the size of rollers  72  and roller bed  110  may be modified and/or the timing of the operation of stacking device  10 ′ may be adjusted to stack sheets of a different size. Such a dual stacking arrangement allows cutting device  20  to be used to cut sheets S of more than one size. 
     In both of the foregoing configurations, sheets S to be stacked on stacking device  10 ′ would be conveyed across stacking device  10  by controlling the operation of belt  132  of movable brake device  130 , in a manner as previously described. 
     A device  10  in accordance with the present invention, lends itself to numerous modifications and arrangements for stacking a wide variety of sheet material in a number of different ways. 
     FIG. 7 is a schematic block diagram of a control system for controlling a stacking device  10 , as heretofore described. As illustrated, a central processor controls the operation of motors  104 ,  144  and actuator  152  based on feedback from motors  104 ,  144  (preferably stepper motors) and data received from sensor  116 , scanner  118  and sheet cutting device  20 . 
     The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.