Abstract:
A feeding and conveying system for feeding and conveying sheet material for printing, collating, or binding the sheet material, among other processes. The feeding and conveying system includes at least one feeder having a magazine containing a plurality of articles of sheet material, for example, signatures, a rotatable disk for separating the sheet material from the magazine, and a feed drum for transferring the sheet material from the magazine to a conveyor. The rotatable disk, having at least one separating blade, is reciprocally rotated to separate the sheet material from the magazine. The separation of the sheet material from the magazine may be aided by applying a source of vacuum to the sheet material, for example, by means of suckers. The feed drum may include one or more grasping devices for grasping and retaining the sheet material, for example, one or more grippers. The rotation of the separator disk may be controlled by a programmable controller. The feeding and conveying system provides for increased throughput while minimizing or eliminating misalignment of the sheet material during handling.

Description:
TECHNICAL FIELD 
     The present invention relates to sheet material handling systems, and more particularly to devices for separating signatures during the collating and binding of, for example, books. 
     BACKGROUND OF THE INVENTION 
     The binding and printing industries often rely on high-speed sheet material handling systems for printing, collating, and binding and otherwise handling sheet material, for example, sheets of paper. This sheet material, for example, individual sheets, newspapers, magazines, inserts and “onserts” (that is, referring to sheet material used when collating newspapers), books, brochures, and the like, is typically, stacked in containers or “magazines” or “hoppers” and withdrawn from the magazines or hoppers for further processing. One particular sheet material that is handled in the binding and printing industry is what is known in the art as “signatures”. Signatures are sheets of paper, that may have a spine fold, that contain at least two pages of text. Typically signatures contain 4 or more pages of text, for example, 30 or more pages of text. In the manufacture of books it is common to assemble the book on a collecting conveyor by sequentially withdrawing signatures from magazines, or hoppers, containing stacks of signatures. In producing a book, typically, a plurality of serially-arranged magazines, separating devices, and feeders are employed for gathering the printed sheets of, for example, signatures. 
     Typically, the separating devices separate and withdraw the sheet material from the magazines and feed the sheet material to a rotating drum. The rotating drum then feeds the sheet material to a conveyor which collects and transfers the separated printed sheets for collation, binding, or other operations. The separation of the sheet material from the stacked sheet material can be effected by a rotating disk separator aided by a suction device, known in the art as a “sucker”. One typical disk-type separator is disclosed in U.S. Pat. No. 6,193,229 B1, the disclosure of which is incorporated by reference herein in its entirety. The disk separator separates and feeds the sheet material to a rotating drum which accepts and retains the sheet material and conveys it to the conveyor. The disk separator, typically with the aid of the suction device, deflects the edge of the lower-most article of sheet material in the magazine stack. When the sheets to be withdrawn from the magazine are in the form of signatures, the deflected edge is typically the spine fold portion of the sheet. The rotating drum positioned below the disk separator typically includes some means of retaining the sheet material as it rotates, for example, devices known in the art as “grippers”. The conveyor which receives the sheet material is typically a horizontal conveyor. This horizontal conveyor may also receive sheet material from other, typically serially-positioned, feeding drums. A common drive mechanism typically drives the separator, suction device, feed drum, and the conveyer. 
     The throughput of such systems is dependent upon on how closely together the sheet material is spaced, and on how fast the sheet material is moved. Accordingly, the throughput of such systems may be optimized by spacing the sheet material as closely together as possible and by maximizing the speed of operation of each of the components. For example, the rotational speed of the separator disk is of fundamental importance to performance of such sheet material handling systems. The faster the separator disk can rotate from the position where it enters the stack of sheet material to the position where the sheet material is separated, the better the system throughput. 
     Another important considering in the operation of disk-type separators is the alignment of the sheet material with separator disk. Since the disk separators of such devices rotate at high speed and typically “bite into” the stack of sheet material in the magazine, misalignment of the sheet material and the disk can cause misfeeds, jamming, or even damage to the equipment. According to the prior art methods the disk separators rotate in one direction and thus repeatedly impact the stack of sheet material in essentially one direction. This repeated engagement of the disk with the stack can cause the stack or individual articles within the stack to migrate or move in the direction of rotation of the disk. This migration of the sheet material can result in the misalignment and its potential consequences mentioned above. This disadvantage of the prior art is overcome by one aspect of the present invention. 
     Commonly-assigned U.S. Pat. No. 6,193,229 B1 discloses a method and apparatus for improving the throughput of a sheet material feeding system having a disk-type separator. This improvement is provided by using a servo-motor-driven disk separator to vary the speed of rotation of the disk separator. The speed of the servo-motor is monitored and controlled by means of a servo-control system, that is, an automated feed-back control loop. Though the method and apparatus for feeding disclosed in U.S. Pat. No. 6,193,229 B1 provides an effective means for controlling and feeding sheet material, the present invention provides improvements which further enhance the effectiveness of disk-type sheet-material feeders. 
     SUMMARY OF THE INVENTION 
     The present invention provides methods and apparatus which address many of the limitations of prior art methods and apparatus. One aspect of the present invention is a feeder for delivering at least one article of sheet material to a conveyer. The feeder includes: a rotatable separator disk for separating stacked articles of sheet material; a servomotor mechanically coupled to the separator disk adapted to impart reciprocating rotation to the separator disk; and a rotatable feed drum oriented to receive the article separated by the separator disk and to transfer the article of sheet material to the conveyor. The articles of sheet material may be sheets of paper, signatures, newsprint, magazines, inserts, onserts, flyers, or brochures. It will be understood by those familiar with the art that the conveyor may be a collator or a gatherer. In one aspect of the invention, the servomotor reverses the rotation of the separator disk after the disk enters the stacked articles of sheet material. The feeder may further include a servo-control system coupled with the servomotor. The servomotor is typically adapted to rotate the disk in a first direction and rotate the disk in a second direction, opposite the first direction. The servo-control system is typically programmable. 
     One advantage of the present invention compared to the prior art is that the back and forth motion of the separator tends to prevent movement or migration of the sheet material in the magazine, which can characterize prior art systems having non-reciprocating motion of the disk. For example, the return stroke of the disk helps to compensate for any deflection of the stack of sheet material that occurs due to the separating stroke. Thus, according to one aspect of the present invention, misalignment of the sheet material with the separator disk or drum, which can cause misfeeds or otherwise interfere with proper operation of the feed system, is minimized or eliminated. 
     Another aspect of the present invention is a method for separating articles of sheet material. The method includes: providing a separator disk for separating at least one article of sheet material from a stack of sheet material; providing a servomotor for rotating the separator disk; and reciprocatingly rotating the separator disk to separate the articles of sheet material from the stack of sheet material. Reciprocatingly rotating is typically practiced by a) rotating the separator disk in a first direction and b) rotating the separator disk in a second direction, opposite the first direction. Steps a) and b) are typically repeated, for example, b) may be practiced immediately after a). Also, a) is typically practiced by accelerating the disk to first rotational speed and b) is practiced by accelerating the disk to second rotational speed; the first rotational speed may be about equal to the second rotational speed. 
     Another aspect of the present invention is a method for separating articles of sheet material and feeding the articles of sheet material to a conveyor. The method includes: providing a magazine containing at least one article of sheet material; providing a separator disk for separating at least one article of sheet material in the magazine; providing a feed drum oriented to receive the at least one separated article of sheet material and transfer the at least one separated article to the conveyor; reciprocatingly rotating the separator disk to separate the at least one article of sheet material from the magazine; transferring the at least one separated article of sheet material from the magazine to the feed drum; and transferring the separated at least one article of sheet material from the feed drum to the conveyor. This method may further include deflecting the edge of the article of sheet material prior to transferring the separated article from the magazine to the feed drum, for example, by applying a source of vacuum to the article of sheet material. 
     A still further aspect of the present invention is a system for separating articles of sheet material. The system includes: a rotatable separator disk for separating stacked articles of sheet material; a motor operatively connected to the separator disk for rotating the separator disk; and a programmable controller for controlling the operation of the motor. The programmable controller is typically programmed to operate the motor whereby the separator disk is reciprocatingly rotated, that is, the separator disk is rotated in a first direction and then rotated in a second direction, opposite the first direction, for example, immediately after rotating the disk in the first direction. 
     An even further aspect of the present invention is a feeder for delivering articles of sheet material to a conveyer. The feeder includes: a rotatable separator disk for separating stacked articles of sheet material; a motor operatively connected to the separator disk for rotating the separator disk; a programmable control system for controlling the operation of the motor; and a rotatable feed drum oriented to receive the articles of sheet material separated by the separator disk and transfer the articles of sheet material to the conveyor. The programmable control system is typically programmed to control at least the speed of rotation of the motor. In one aspect of the invention, the programmable control system is programmed to operate the motor whereby the separator disk is reciprocatingly rotated. 
     A still further aspect of the present invention is a method for separating articles of sheet material and feeding the articles of sheet material to a conveyor. The method includes: providing a magazine containing articles of sheet material; providing a separator disk driven by a motor for separating at least one article of sheet material in the magazine; providing a programmable controller system for controlling the rotation of the separator disk; providing a feed drum oriented to receive at least one separated article of sheet material and transfer the separated article of sheet material to the conveyor; rotating the separator disk in response to the programmable controller to separate at least one article of sheet material from the magazine; transferring the at least one separated article of sheet material from the magazine to the feed drum; and transferring the at least one separated article of sheet material from the feed drum to the conveyor. This method may further include deflecting an edge of the article of sheet material prior to transferring the separated article of sheet material from the magazine to the feed drum. Transferring the separated article of sheet material from the magazine to the feed drum is typically practiced by grasping the article with grippers mounted on the feed drum. Again, in one aspect of the invention, rotating the separator disk in response to the programmable controller is practiced by reciprocatingly rotating the separator disk. For example, in one aspect of the invention, reciprocatingly rotating the separator disk is practiced whereby misalignment of the articles of sheet material in the magazine is minimized. 
     These and other embodiments and aspects of the present invention will become more apparent upon review of the attached drawings, description below, and attached claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following detailed descriptions of the preferred embodiments and the accompanying drawings in which: 
     FIG. 1 is a side view of a feeding and conveying system for sheet material which incorporates one aspect of the present invention. 
     FIG. 2 is a side view of the sheet material feeder shown in FIG. 1 in accordance with one aspect of the present invention. 
     FIG. 3 is a top view of a separator disk that can be used with one aspect of the present invention. 
     FIG. 4 is a top view of a separator disk that can be used with another aspect of the present invention. 
     FIG. 5 is graph of various feed system parameters as a function of degree of drum rotation according to one aspect of the present invention. 
     FIG. 6 is a schematic block diagram of a servo-control system which can be used to control the feeding and conveying system shown in FIG. 1 in accordance with one aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a feeding and conveying system, generally designated with the reference numeral  10 , for feeding and conveying sheet material that employs one aspect of the present invention. The sheet material that can be fed and conveyed includes, but is not limited to, individual sheets, signatures, newspapers, magazines, books, booklets, brochures, inserts, or onserts, among other types of sheet material. Feeding and conveyer system  10  typically includes a conveyer  12 , and at least one, typically more than one, sheet material feeder  14 . Each feeder  14  includes a rotatable feed drum  16 , a magazine  18  of stacked sheet material  19 , and a separator disk  22  (see FIG. 2) driven by a servomotor  20 . Feeder  14  separates sheet material  19  from the magazine  18  and feeds it via drum  16  to conveyor  12 . Conveyor  12  may be collating conveyor, that is, a collator, or a gathering conveyor, that is, a gatherer, among other types of conveyors. For example, in one aspect of the invention, conveyor  12  receives onserts from feeder  14  which are placed on top of articles of sheet material, for example, other onserts, that are already on conveyor  12 . 
     The conveyer  12  is positioned with respect to the feed drums  16  for receiving sheet material from feed drum  16 . Feed drum  16  rotates and delivers sheet material  19 , typically one at a time, to conveyer  12 . Conveyer  12 , in accordance with one aspect of the invention, functions to gather, collate, or otherwise handle sheet material  19 . For example, feeding and conveying system  10  shown in FIG. 1 includes multiple feeders  14  and is configured to enable conveyer  12  to gather and collate sheet material for a binding machine, though the system shown in FIG. 1 may be used to convey sheet material to other types of machines. 
     FIG. 2 illustrates a detailed view of the components that comprise sheet material feeder  14  which feeds conveyor  12 . Conveyor  12  in FIG. 2 is a collating-type of conveyor, though other types of conveyors may be used. As noted above, feeder  14  includes a rotatable feed drum  16 , a magazine  18  of stacked sheet material  19 , and a separator disk  22  driven by a servomotor  20 . As shown in FIG. 2, feeder  14  typically also includes means for deflecting the edge of an article of sheet material  19  from the magazine  18 . One means for deflecting the edge of an article of sheet material  19  from the magazine  18  may be means for selectively applying a source of vacuum to the lower-most article of sheet material  19  in magazine  18 . In the aspect shown in FIG. 2, a device  21  known in the art as a “sucker” is used for selectively applying a source of vacuum. Sucker or suction device  21  is operatively connected to a source of vacuum (not shown) and is adapted to selectively apply the vacuum to the sheet material  19 , for example, as a synchronized function of the relative rotation of drum  16 . Suction device  21  is also typically pivotally mounted for rotation as indicated by double arrow  25 , that is, suction device  21  may be raised and lowered to engage and deflect sheet material  19 . Suction device  21  typically applies a vacuum to the surface of an article of sheet material  19  that varies from about 18 inches of Hg (that is, inches of mercury) to about 25 inches of Hg. 
     Separator disk  22  is mechanically coupled to servomotor  20 . Servomotor  20  typically rotates disk  22  at maximum speeds of between about 900 rpm and about 1200 rpm. Separator disk  22  is positioned adjacent to magazine  18  whereby at least a portion of the surface of disk  22  engages and separates at least one article of sheet material  19 , typically only one article  19  at a time. After an article of sheet material  19  is engaged and deflected by suction device  21 , disk  22  engages and deflects article of sheet material  19  whereby article  19  can be engaged and retained by drum  16 . Typically, only an edge of an article of sheet material  19  is deflected by suction device  21  and disk  22  and each article  19  is drawn out of the magazine by the rotation of drum  16 . According to one aspect of the present invention, the rotation of servomotor  20  and thus separator disk  22  is controlled whereby disk  22  is reciprocatingly rotated, that is, disk  22  is rotated in a first direction and then in a second direction, opposite the first direction, and preferably repeatedly. Each repeated rotation in one direction and then rotation in the second, opposite direction comprises a machine cycle for servomotor  20  and disk and typically undergoes between about 250 and about 350 machine cycles per minute. This reciprocal rotation of disk  22  will be discussed further with respect to FIG.  5 . 
     After sheet material  19  is engaged by and deflected by suction device  21  and separator disk  22  engages and further deflects and separates an article of sheet material  19 , the article of sheet material  19  is positioned to be captured by feed drum  16 . The separated article of sheet material on drum  19  is identified by reference number  24 . In the view shown in FIG. 2, feed drum  16  rotates in a counter-clockwise direction as indicated by arrows  23 . Typically, feed drum  16  includes some means for grasping and capturing article of sheet material  24  from magazine  18  and transferring it to conveyor  12 . One means of grasping, capturing, and transferring sheet material  24  is by means of hinged linkages  26  that are selectively opened and closed to grasp and release an article of sheet material  24 . Linkages  26  are known in the art as “grippers”. Drum  16  may have one or more grippers, and typically two or more grippers evenly spaced about the periphery of drum  16 . For example, in one aspect of the present invention three grippers  26  are used. Grippers  26  retain the separated sheet material  24  and transfer it with the rotation of drum  16  to conveyor  12 . When the sheet material  24  is in position over conveyor  12 , gripper  26  opens allowing sheet material  24  to fall, typically, simply under the force of gravity, upon conveyor  12 . The position of grippers  26 , that is, either opened or closed, is typically controlled and synchronized with the relative rotation of drum  16  and the operation of suckers  21  to ensure the uninterrupted movement of articles of sheet material  24  from magazine  28  to drum  16  to conveyor  12 . 
     FIG. 3 illustrates a top view of a separator disk  22  having a single protrusion or blade  30  that can be used to effect the present invention. Blade  30  has a leading edge  32  and a trailing edge  34 . Disk  22  also includes a recess  33  and a axial hole  35  for mechanically coupling disk  22  to servomotor  20 . According to one aspect of the present invention, separator disk  22  is reciprocally rotated by servomotor  20  (see FIG. 2) as indicated by arrows  36  and  37 . During operation, after the edge of the sheet material  19  is deflected by suction device  21  (see FIG.  2 ), the rotation of disk  22  in the direction of arrow  36  causes leading edge  32  of blade  30  to contact stacked sheet material  18  whereby the edge of the lower-most sheet material  24  enters recess  33 . Further rotation of separator disk  22  causes blade  30  to “bite” into stacked sheet material  18 , separating sheet material  24  from the stacked sheet material  18 . After separation of sheet material  24  from the stacked sheet material  18  is complete, trailing edge  34  of blade  30  exits stacked sheet material  18 . 
     According to one aspect of the present invention, after blade  30  separates an article of sheet material  24  from the stacked sheet material  18 , for example, after trailing edge  34  passes through stacked sheet material  18 , the rotation of disk  22  is slowed, stopped (typically momentarily) and then reversed by servomotor  20  whereby blade  30  passes through the stacked sheet material  18  in the direction of arrow  37 . That is, the direction of rotation of disk  22  is reversed. After blade  30  passes through stacked sheet material  18  in the direction arrow  37 , for example, after leading edge  32  passes through stacked sheet material  18  in the direction of arrow  37 , the rotation of blade  22  is again slowed and reversed whereby the next article of sheet material is engaged and deflected by blade  30 . According to one aspect of the present invention, this cycle of rotating disk  22  in the direction of arrow  36  and then in the direction of arrow  37 , that is, in reciprocally rotating disk  22 , is essentially continuously repeated as long as necessary, for example, at a rate of between about 250 and about 350 machine cycles per minute. In addition to effectively separating sheet material, this reciprocal rotation of disk  22 , among other things, minimizes the misalignment, or mis-registration, of the stacked sheet material that can occur when a separator disk, such as disk  22 , is continuously rotated in a single direction. Repeatedly engaging the stack of sheet material  18  in the same direction, as would happen when disk  22  is only rotated in one direction, that is, not reciprocated, can physically move or shift the stack  18  from its desired position in the feeder  14 , causing mis-alignment of, among other things, the stack  18  and the disk  22  and the stack  18  and the suction device  21 . This mis-alignment is minimized or eliminated entirely when the rotation of disk  22  is reciprocated according to the present invention. 
     FIG. 4 illustrates another separator disk  122  that can be used for the present invention, which is a variation of separator disk  22  shown in FIG.  3 . Separator disk  122  has two opposing protrusions or blades  130  and  130 ′. Blades  130 ,  130 ′ oppose each other to enable separator disk  122  to selectively rotate in either of the two directions indicated by double arrow  38 . Blades  130 ,  130 ′ have leading edges  132 ,  132 ′ and trailing edges  134 ,  134 ′, respectively. Disk  122  includes two recesses  133 ,  133 ′ and an axial hole  135 . Blades  130 ,  130 ′; leading edges  132 ,  132 ′; trailing edges  134 ,  134 ′; recesses  133 ,  133 ′; and axial hole  135  all operate and function in the same fashion as the corresponding features described with respect to FIG.  3 . Rotation in the two directions indicated by arrow  38  is desirable depending on how articles of sheet material  18  are stacked in feeder  14 . For example, having two reciprocating blades  130 ,  130 ′ on disk  122  doubles the throughput of feeder  14  compared to the single-bladed disk  22  shown in FIG.  3 . The reciprocal motion of disk  122  also provides the same magazine sheet material alignment benefits discussed with respect to the reciprocation of disk  22  above. The double-bladed disk  122  shown in FIG. 4 can also be used in “gatefold” applications, that is, wherein the fold edge of the sheet material (for example, signature) is located on the feeder side of hopper  18 . In gatefold applications, the operation of the feeder  14  is controlled so that the edge  130 ′ first engages the stack of sheet material in a counter-clock-wise direction as viewed in FIG.  4 . According to one aspect of the present invention, for example, having a programmable system  50 , this reversal of disk  122  operation can be effected by a simple electronic switch, for example, either a manual or an automated switch, for instance, a switch that changes the direction of rotation of servomotor  20 . 
     FIG. 5 illustrates a graph  100  showing profiles of various parameters of the feeding and conveying system  10  of one aspect of the present invention as a function of the rotation of drum  16 . The profiles that appear in FIG. 5 were computed for a feeder and conveyor system having the following parameters: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Drum 16 diameter: 
                 17 inches 
               
               
                   
                 Corresponding circumference 
                 53.4 inches 
               
               
                   
                 of drum 16: 
               
               
                   
                 No. of grippers 26: 
                 3 
               
               
                   
                 Corresponding length of 
                 120 degrees or 17.8 inches 
               
               
                   
                 drum arc between grippers: 
               
               
                   
                 Maximum length of signature: 
                 13.5 inches. 
               
               
                   
                   
               
             
          
         
       
     
     Curve  41  is a typical representation of a rotational speed profile of separator disk  22  as a function of the rotation of the drum  16  according to one aspect of the present invention. As shown on the left side of graph  100 , disk  22  is approximately stationary at a time when the position of drum  16  is at a point A, for example, at approximately −13 degrees from a reference position of drum  16 . This position of disk  22  is sometimes referred to as the “disk home position”. As controlled by servomotor  20 , in response to servo-control system  50  (see FIG.  6 ), disk  22  accelerates in a generally uniform fashion (for example, at a relatively constant angular acceleration) to a maximum speed B, for example, a speed of from about 600 rpm to about 900 rpm, depending upon the size and configuration of the sheet material being handled. The speed of disk  22  is typically maintained for a predetermined time interval, for example, speed B may be maintained for time interval corresponding to about 45 to about 55 degrees of rotation of drum  16 . As shown by curve  41 , the speed of disk  22  then decelerates in a generally uniform fashion (again, for example, at a relatively constant angular acceleration) whereby disk  22  comes to a momentary stop and then reverses direction and accelerates to a speed C rpm in the opposite direction, for example, a speed of from about 600 rpm to about 900 rpm. The magnitude of speed C may be the same as the magnitude of speed B. Again, the speed C is typically maintained for a predetermined time interval, which may be the same interval at which the speed B is maintained, for example, speed C may be maintained for time interval corresponding to about 45 to about 55 degrees of rotation of drum  16 . The speed of disk  22  then decelerates in a generally uniform fashion (again, for example, at a relatively constant angular acceleration) and is stopped at a time corresponding to the position of drum  16  of from about 300 to about 310 degrees. Disk  22  is then held stationary for a time period corresponding to about 20 to about 30 degrees of the rotation of drum  16 . Disk  22  then accelerates again and the above disk speed profile is repeated. Curve  42  represents the corresponding profile of the displacement of disk  22  as a function of the rotation of drum  16 . 
     The position of suckers  31  and grippers  26  are also illustrated in graph  100 . Curve  43  represents a typical profile of position of suckers  31 , for example, “up” or “down”, as a function of the rotation of drum  16 . As shown by curve  43  in FIG. 5, at a time corresponding to when drum  16  is oriented in line with the reference, that is, at the zero degree position, suckers  21  are “up”, that is, rotated into contact with the lower-most article of sheet material  19 . At this position in the profile, a vacuum is typically applied to suckers  21 . Shortly thereafter, suckers  21  are deflected at a relatively uniform speed and attain the “down” position at a time interval corresponding to drum position D, for example, between about 20 and about 30 degrees beyond the zero reference position. Typically, when the suckers are in the “down” position, that is, displaced from the lower-most article of sheet material  19 , the vacuum is turned off from suckers  21 . As shown by curve  43 , suckers  21  remain in the “down” position until the drum reaches orientation E, for example, at between about 320 degrees and about 330 degrees of drum  16  rotation. The suckers  21  are then raised at a relatively uniform velocity to the “up” position at about 360 degrees, or after one full rotation of drum  16 . During this deflection of suckers  21  the vacuum is again applied to suckers  21 . The position of sucker  21  then repeats this schedule. 
     The state of grippers  26 , that is, “opened” or “closed”, is represented by curve  44  in FIG. 5, again as a function of the rotation of drum  16 . At a point corresponding to drum orientation A, grippers  26  are in the “opened” positioned. Grippers  26  remain opened until drum  26  reaches a position F, for example, between about 70 degrees and 80 degrees of drum  16  rotation, at which point grippers  26  begin to close. At point G, for example, between about 80 and about 90 degrees, grippers  26  are “closed”. Grippers  26  then remain closed until drum  16  reaches a position H, for example, between about 215 degrees and about 225 degrees. Grippers  26  then partially open to an intermediate position to release an article of sheet material  24  before fully opening beginning at a point E in preparation for subsequent closing on the next article of sheet material. Again, as shown by curve  44 ; this gripper position profile is then repeated. 
     FIG. 5 also includes other reference information for the feeding and conveying system of the present invention. For example, point J is the position of the drum corresponding to the time when blade  30  of disk  22  (see FIG. 3) enters the stack  18 , for example, at a position of between about 30 degrees and about 40 degrees. Note that at this point, J, per curve  41 , disk  22  is rotating at is maximum speed; per curve  42 , disk  22  is approximately midway in its deflection from its reference location; per curve  43 , suckers  21  are closing; and per curve  44 , grippers  26  are open. According to the present invention the reciprocating rotation of disk  22 , and the corresponding operation of drum  16 , suckers  21 , and grippers  26  are synchronized. This synchronization can be practiced mechanically, for example, via cams and timing belts, or electro-mechanically, for example, via linkages operated by actuators that are controlled by electronics, for example, by digital control software. In one aspect of the invention, the speed and position of separator disk  22  is monitored and controlled by means of the servo-control system shown schematically in FIG.  6 . 
     FIG. 6 illustrates a servo-control system generally designated with the reference numeral  50  that can be used to practice one aspect of the present invention. Servo-control system  50  includes a servomotor  20 , a position transducer  52 , a servo-amplifier  54 , a comparator  56 , and a command signal generator  58 . Servo-control system  50  regulates and controls the operation of servomotor  20  to regulate and control the displacement, speed, and acceleration of separator disk  22 . Servo-control system  50  is programmable, for example, command signal generator  58  may be programmable. Servo-control system  50  may be programmed to regulate and control the displacement, speed, or acceleration of disk  22  in order to optimize the operation of disk  22  and feeder  14 . In one aspect of the invention, servo-control system  50  is programmed to regulate the displacement, velocity, and acceleration of disk  22  to the schedules shown in FIG. 5, though servo-control system  50  can be programmed for any displacement, velocity, or acceleration schedule desired. Servo-control system  50  may be manually operable at the feeder, may be controlled from a desktop computer, may be integrated into a network of control systems designed to optimize handling system throughput, or controlled by means of any conventional programmable device, for example, a computer or programmable logic controller (PLC). It will be apparent to those in the art that servo-control system  50  and servomotor  20  can be integrated with new feeder systems or be retrofit to existing feeders. 
     Servomotor  20  drives separator disk  22  in response to the control algorithm of control system  50 . Position transducer  52  provides an indication of the position of separator disk  22 . The position sensed by position transducer  22  is fed to comparator  56  via feed back loop  53 . Command signal generator  58  receives a position indication from drum  16  via electrical connection  55  and transfers a command position to comparator  56  via electrical connection  57 . Comparator  56 , via an appropriate algorithm, compares the command position and the feed back position of disk  22  and generates and error signal that is forwarded to amplifier  54  via connection  59 . Servo-amplifier  54  amplifies this error signal and provides an amplified error signal to servomotor  20  via connection  60  which increase or decreases the speed of disk  22  to eliminate the error and conform to the desired speed schedule for disk  22 , for example, the schedule defined by curve  41  in FIG.  5 . As a result, control system  50  coordinates the rotation of disk  22  with the rotation of drum  16 , so that, among other things, grippers  26  (see FIG. 2) are open and ready to receive an article of sheet material separator disk  22  separates an article of sheet material  24  from the stack of sheet material  18 . 
     Servomotor  20  is typically a variable speed servomotor that is mechanically coupled to and rotates separator disk  22 . According to one aspect of the invention, servomotor  20  includes an absolute encoder coupled with comparator  56  to deliver the position of separator disk  22  to comparator  56 . According to an alternate aspect of the invention, servomotor  20  includes an incremental encoder, or a resolver. 
     According to one aspect of the present invention, control system  50  controls the operation of servomotor  20  to effect a reciprocating rotation to separator disk  22 . One such reciprocating rotation is shown by curve  41  in FIG.  5 . This reciprocal rotation of disk  22  according to one aspect of the present invention provides an effective means of separating sheet material for feeding to, for example, a sheet-material-collating conveyor. Compared to prior art methods, this reciprocal separation, among other things, minimizes or eliminates misalignment of the sheet material in the magazine that can occur during non-reciprocating separation that characterizes the prior art. 
     While the invention has been particularly shown and described with reference to preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made to the invention without departing from the spirit and scope of the invention described in the following claims.