Patent Publication Number: US-8113503-B2

Title: Automatic warp compensation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Ser. No. 60/985,450 filed Nov. 5, 2007, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to apparatus and methods for prefeeders with automatic warp compensation. More particularly, the present disclosure relates to apparatus and methods for block pusher prefeeders with automatic warped board compensation. 
     BACKGROUND OF THE INVENTION 
     A prefeeder may be designed to handle blank sheets. The blank sheets are typically corrugated material. The prefeeder receives a stack of blank sheets, divides the stack into blocks, and feeds the blocks into a finishing machine in an intermittent shingled stream. Particularly, a block pusher prefeeder may receive the stack of blank sheets, lift the stack up, divide the stack into measured blocks, and then feed the sheets off the bottom of the block under a vertical stop in a continuous shingled stream for delivery into the finishing machine hopper. 
     With current block pusher technology, a stack of flat sheet stock enters the block pusher prefeeder. The lead edge of the stack is registered against a vertical stop, such as a backstop. The block pusher plate resides behind and to the top of the stack. When there is a call for another block of sheets, the stack rises, such that the stack is between the backstop and the block pusher plate. The block pusher plate then moves forward to push off a block of sheets from the top of the stack. In the standard configuration, the bottom of the block pusher plate is aligned with the top of the backstop, so as to produce a horizontal plane. This horizontal plane defines the separation point in the stack, wherein the sheet above the plane is the bottom sheet of the block and the sheet below the plane is the top sheet of the stack. 
     When there is down warp, the leading edge of the stack is lower than the trail edge of the stack. As a result, when the block pusher plate moves forward to deliver a block of sheets, the block pusher plate stalls due to the sheets that are captured/jammed between the block pusher plate and the backstop. When there is up warp, the leading edge of the stack is higher than the trail edge of the stack. When the block pusher plate moves forward to deliver a block of sheets, trailing sheets (i.e., sheets that are not aligned with the block or the stack) result. 
     Current block pusher prefeeders allow the operator to select a warp mode which lifts the block pusher plate. Elevating the bottom of the block pusher plate relative to the backstop allows the block pusher plate to convey forward and push a down warped block of sheets successfully off the stack. 
     Warp mode cannot be enabled permanently due to the potential for a trailing sheet condition when running flat, or non-warped, sheets. When the bottom of the block pusher plate and the top of the backstop are not correctly aligned in elevation (i.e., the bottom of the block pusher plate is above the top of the backstop), a scenario arises when running flat sheets where the bottom sheet(s) of the block, or the top sheet(s) of the stack, begin to move, but then stall and are no longer aligned with the block or the stack. This may causes issues with the manufacturing line efficiency. 
     With the selector switch for warp mode at the operator station, the operator is required to make the decision regarding when to use the warp mode and when to disable warp mode. Upon visual inspection of a stack, the operator can select a mode to allow the prefeeder to handle warp or select a mode where the prefeeder handles no warp. Use of a selector switch results in an increased risk for human error. For example, the operator may enable warp mode at times when warp mode is undesirable, thereby causing trailing sheets to occur. Similarly, the operator may disable warp mode at times when warp mode is desirable. Thus, the block pusher plate may stall against the back of the stack due to down warp. As an additional example, the operator may enable warp mode where warp mode is desirable (i.e., the stack contains warped sheets). However, the sheets at the bottom of the stack may be pressed flat due to the weight of the stack. That is, the amount of warp may diminish from the top of the stack to the bottom of the stack, and therefore, with warp mode enabled, trailing sheets may be present in the last few block pushes of the stack. Thus, to have an efficient operation, the operator must always be cognizant of whether warp is present in the stack and select the appropriate mode. 
     Thus, there is a need in the art for apparatus and methods for prefeeders with automatic warp compensation. There is a further need in the art for apparatus and methods for block pusher prefeeders with automatic warped board compensation. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention, in one embodiment, is an apparatus for feeding a stack of sheet stock to a finishing machine in blocks comprising a portion of the stack, wherein the apparatus automatically adjusts for warp in the sheet stock. The apparatus includes a backstop positioned generally near a lead edge of the stack, a block pusher plate positioned generally near a trail edge of the stack, and at least one sensor for determining a height differential between the stack at generally near a lead edge of the stack and the stack at generally near a trail edge of the stack. In one embodiment, the apparatus includes a lead edge sensor generally near the lead edge of the stack, and a trail edge sensor generally near the trailing edge of the stack. 
     The present invention, in another embodiment, is a method for pushing a portion of sheet stock from a stack of sheet stock. The method includes automatically compensating for warp present in the sheet stock. The method comprises obtaining a first measurement at generally near a lead edge side of the stack, obtaining a second measurement at generally near a trail edge side of the stack, comparing the first and second measurements, and pushing the portion of sheet stock from the stack with a block pusher plate when the second measurement is within a predetermined tolerance of the first measurement and, in some embodiments, an additional offset value. In one embodiment, obtaining a first measurement may include providing a first sensor for determining a distance from a known point above a lead edge side of the stack to the top of the lead edge side of the stack, and obtaining a second measurement may include providing a second sensor for determining a distance from a known point above a trail edge side of the stack to the top of the trail edge side of the stack. 
     The present invention, in yet another embodiment, is a method for feeding a stack of sheet stock to a finishing machine in blocks comprising a portion of the stack. The method automatically adjusts for warp in the sheet stock. The method includes determining a height differential between a lead edge side of the stack and a trail edge side of the stack and feeding a block of sheet stock from the stack based on the height differential. In one embodiment, a laser scanner is used for determining the height differential. In another embodiment, determining the height differential comprises determining the slope of the stack. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as forming the present invention, it is believed that the invention will be better understood from the following description taken in conjunction with the accompanying Figures, in which: 
         FIG. 1  is an elevation view of a prior art block pusher prefeeder. 
         FIG. 2A  is an elevation view of a flat stack of sheet stock between a block pusher plate and a backstop of a prior art block pusher prefeeder. 
         FIG. 2B  is an elevation view of the flat stack of sheet stock between the block pusher plate and backstop of  FIG. 2A , wherein the block pusher plate is pushing a block of sheets from the stack. 
         FIG. 2C  is an elevation view of a stack of down warped sheet stock between a block pusher plate and a backstop of a prior art block pusher prefeeder. 
         FIG. 2D  is an elevation view of the stack of down warped sheet stock between the block pusher plate and backstop of  FIG. 2D , wherein the block pusher plate is jammed while attempting to push a block of sheets from the stack. 
         FIG. 2E  is an elevation view of a stack of down warped sheet stock between a block pusher plate and a backstop of a prior art block pusher prefeeder in warp mode. 
         FIG. 2F  is an elevation view of the stack of down warped sheet stock between the block pusher plate and backstop of  FIG. 2E , wherein the block pusher plate is pushing a block of sheets from the stack. 
         FIG. 2G  is an elevation view of a flat stack of sheet stock between a block pusher plate and backstop of a prior art block pusher prefeeder in warp mode, wherein a trailing sheet results when the block pusher plate attempts a push. 
         FIG. 3  is an elevation view of a stack of sheet stock between a block pusher plate and a backstop of a block pusher prefeeder in accordance with one embodiment of the present disclosure, wherein a sensor is positioned above the lead edge of the stack and a sensor is positioned above the trail edge of the stack. 
         FIG. 4  is a flow diagram of a process of automatic warp compensation in accordance with another embodiment of the present disclosure. 
         FIG. 5A  is an elevation view of a stack of sheet stock between a block pusher plate and a backstop of a block pusher prefeeder in accordance with a further embodiment of the present disclosure, wherein the block pusher plate is in an “up” position. 
         FIG. 5B  is an elevation view of a stack of sheet stock between a block pusher plate and a backstop of a block pusher prefeeder in accordance with a further embodiment of the present disclosure, wherein the block pusher plate is in a “ready” position. 
         FIG. 6  is a flow diagram of a portion of a process of automatic warp compensation relating to positioning the block pusher plate in a position wherein the trail edge sensor can determine the distance to the trail edge of the stack. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure includes novel and advantageous apparatus and methods for prefeeders with automatic warp compensation. More particularly, the present disclosure relates to apparatus and methods for block pusher prefeeders with automatic warped board compensation. The applications of such devices may be exemplified in prefeeders for stacks of corrugated material, drywall, paper board, and other types of generally flat sheets of material where warp may be present. 
     Automatic warp compensation (AWC) of the present disclosure may take the operator out of the decision process. AWC may enable the prefeeder to adjust for warp in real time for each block push. Generally, AWC may evaluate the stack height at lead and trail edges of the stack and adjust the block pusher height to compensate for warp. Each block push may require a separate evaluation and potential block pusher height adjustment. 
     AWC may be used with any suitable block pusher prefeeder, such as bottom feeders, top feeders, and universal feeders. The apparatus and methods disclosed herein may be adapted for use with all such suitable block pusher prefeeders. Therefore, the illustrations of AWC in the figures, which may generally show AWC in combination with a block pusher bottom feeder, are exemplary and not limiting. 
     More specifically, AWC may use one or more sensors to capture measurements from a known point or height to the top of the stack at the lead edge and the trailing edge. The measurements from the one or more sensors may be compared and evaluated for stack height differential from the lead edge to the trail edge of the stack. The measurements may be used to determine if any warp in the sheets of the stack is present. If warp is present, the measurements may be used to determine how much. The measurements may further be used to determine where the block pusher plate could be adjusted vertically for correct warp compensation. After each block push, the stack may be reevaluated allowing the prefeeder to compensate for varying warp as the stack is processed. 
     As previously stated, a prefeeder receives a stack of sheet stock, divides the stack into blocks, and feeds the blocks into a finishing machine in a shingled stream. A block pusher prefeeder  100 , as illustrated in one embodiment in  FIG. 1 , may receive a stack of sheet stock  102 , lift the stack up, divide the stack into measured blocks  104 , and then feed the sheets off the bottom of the block under a vertical stop  106  in a continuous shingled stream  108  for delivery into a finishing machine hopper  110 . Particularly, a stack of flat sheet stock  102  enters the block pusher bottom feeder  100 . The lead edge  112  of the stack may be registered against a vertical stop, such as a backstop  114 . A block pusher plate  116  may reside behind and to the top of the stack  102 . When there is a call for another block of sheets  104 , the stack  102  may be raised, such that the stack  102  is between the backstop  114  and the block pusher plate  116 . The block pusher plate  116  may then move forward to push off a block of sheets  104  from the top of the stack  102 . As used herein, the terms “sheet stock” or “sheet(s)” may include corrugated material, drywall, paper board, and other types of generally flat sheets of material. 
     In an ideal situation, wherein the sheet stock is completely flat (i.e., no warp present), as illustrated  FIGS. 2A  and B, a block of sheets  104  may be pushed from the stack  102  by the block pusher  116  by generally aligning the bottom of the block pusher  116  with the top of the backstop  114 . However, sheet stock is not always flat and may have warp. When down warp, i.e., the leading edge of the stack is lower than the trail edge of the stack, is present, as illustrated in  FIGS. 2C  and D, one or more sheets  202  at the bottom of the block may become captured/jammed between the block pusher plate  116  and the backstop  114 , thereby stalling the block pusher plate  116 . 
     In a further embodiment, when down warp is present, the block plate pusher  116  may be raised vertically, such that the bottom of the block plate pusher  116  is above, and not aligned with, the top of the backstop  114 , as illustrated in  FIG. 2E . Therefore, when the block pusher plate  116  pushes a block of sheets  104  from the stack  102 , as illustrated in  FIG. 2F , the block pusher plate  116  does not stall on jammed sheets  202 . However, it may be undesirable to maintain the block pusher plate  116  at an increased height above the backstop  114  when warp is not present. For example, as illustrated in  FIG. 2G , if the bottom of the block pusher plate  116  is not aligned with the top of the backstop  114  when no warp is present, one or more trailing sheets  204  may result. 
     In one embodiment, one or more sensors may be used to evaluate the amount of warp present in the stack  102  at any given point in time. With reference to  FIG. 3 , a first sensor  302  may be positioned above the lead edge  112  of the stack  102 . The lead edge sensor  302  may be an optical sensor, ultrasonic sensor, etc. However, any sensor suitable for measuring distance may be used. The lead edge sensor  302  may be used to determine the distance D 1  between the lead edge sensor  302  and the lead edge  112  of the stack  102 . The lead edge sensor  302  may be operably attached to any suitable object in relation to the block pusher prefeeder  100 , including operably attached to the block pusher prefeeder  100  frame. In one embodiment, the lead edge sensor  302  may be stationary in relation to the block pusher prefeeder  100 . 
     A second sensor  306  may be positioned above a trail edge  308  of the stack  102 . The trail edge sensor  306  may be an optical sensor, ultrasonic sensor, etc. However, any sensor suitable for measuring distance may be used. The trail edge sensor  306  may be used to determine the distance D 2  between the trail edge sensor  306  and the trail edge  308  of the stack  102 . The trail edge sensor  306  may be operably attached to any suitable object in relation to the block pusher prefeeder  100 . In one embodiment, the trail edge sensor  306  may be stationary in relation to the block pusher prefeeder  100  while in other embodiments, the trail edge sensor  306  may move in relation to the block pusher prefeeder  100 . In further embodiments, the trail edge sensor  306  may be operably attached to the block pusher plate  116 . In one embodiment, the trail edge sensor  306  may be attached to the block pusher plate  116  frame. Thus, the trail edge sensor  306  may move with the block pusher plate  116 . 
     In one embodiment, when the distance D 1  is approximately equal to the distance D 2  within a desired tolerance, the block pusher plate  116  may be in position such that the block pusher plate  116  is ready for pushing a block  104  from the stack  102 . In relation to a stack of flat sheet stock, this may create a substantially horizontal plane extending from the top, or near the top, of the backstop  114  to the bottom of the block pusher plate  116 . In relation to a stack of warped sheet stock, this may create a generally non-horizontal plane extending from the top, or near top, of the backstop  114  to the bottom of the block pusher plate  116 . Therefore, AWC may adjust automatically and correctly for each block push of the stack  102 , depending on whether warp is present in the current block  104  at the top of the stack  102 . 
     During the process of pushing blocks from a stack, in accordance with one embodiment of the present disclosure, there may be generally three main steps. First, the distance from the lead edge sensor  302  to the top of the stack  102  at the lead edge  112  may be monitored. Then, the block pusher plate  116  may be adjusted vertically until the distance from the trail edge sensor  306  to the top of the stack  102  at the trail edge  308  is approximately within a desired range with respect to the distance from the lead edge sensor  302  to the top of the stack  102  at the lead edge  112 . Upon reading that the distance has converged to the appropriate range, the block pusher plate  116  height may be set, and the block pusher plate  116  may push the block  104  from the stack  102 . 
     Although AWC has so far been described as including a lead edge sensor  302  and a trail edge sensor  306 , the use of a lead edge sensor  302  and trail edge sensor  306  is only one exemplary apparatus and method for AWC. In other embodiments, AWC may use a greater or fewer number of sensors to obtain a measurement at the lead edge  112  of the stack and a measurement at the trail edge  308  of the stack. For example, in one embodiment, a single sensor may be used to take a measurement at the lead edge  112  and trail edge  308  of the stack. The sensor may be an optical sensor, ultrasonic sensor, etc. In further embodiments, any of the sensors described herein may be laser sensors, or laser scanners. 
     In further embodiments yet, the measurement obtained from the one or more sensors may be the height differential between the lead edge  112  and the trail edge  308  of the stack. In some embodiments, the measurement or measurements taken may not directly be the height differential between the lead edge  112  and the trail edge  308  of the stack, but may be used to mathematically calculate the height differential. Mathematically calculating may include, but is not limited to, manually calculating or using a processor, microprocessor, CPU, controller, etc. to mathematically calculate. For example, in one embodiment, a laser scanner, or other surface or horizontal scanner, may be used to obtain or determine the height differential between the lead edge  112  and the trail edge  308  of the stack. 
     In alternative embodiments, a mechanical device may be used to determine the height differential between the lead edge  112  and trail edge  308  of the stack. For example, in one embodiment, a mechanical device may be used to determine the slope of the stack. Using the length of the sheets in the stack, the height differential between the lead edge  112  and the trail edge  308  of the stack may be determined using the obtained slope. 
     In yet other embodiments, a topographical image of the stack may be obtained and used to determine the height differential between the lead edge  112  and the trail edge  308  of the stack. Any other suitable device or method for obtaining the difference of the height of the lead edge  112  of the stack and the height of the trail edge  308  of the stack may be used in accordance with the apparatus and methods of the present disclosure. 
     One embodiment of a process of performing AWC in accordance with the present disclosure will now be described with further detail. It is recognized that the process described herein is exemplary and is not the sole process by which AWC, in accordance with the present disclosure and falling within the scope of this specification, may be performed. Similarly, not all steps of the disclosed process need be necessarily included, and certain steps of the process may be eliminated without departing from the spirit and scope of the present disclosure. 
     With respect to the flow diagram shown in  FIG. 4 , at the beginning of a cycle (step  402 ), the stack  102  may be raised to a predetermined vertical position by the block pusher prefeeder  100  depending on the size of blocks  104  desired. The block pusher plate  116 , and thus the trail edge sensor  306 , may be in an “up” position, e.g., a position wherein the trail edge sensor  306  is higher than the lead edge sensor  302  and/or away from the stack  102 , as illustrated in  FIG. 5A . If the lead edge sensor  302  can sense the top of the lead edge  112  of the stack  102  (step  404 ), then the value of the distance from the lead edge sensor  302  to the top of the lead edge  112  of the stack  102  may be recorded (step  406 ). If the lead edge sensor  302  cannot sense the top of the stack  102 , or can otherwise not determine the distance to the stop of the stack, a fault/error may be triggered (step  408 ). 
     If the trail edge sensor  306  can sense the top of the trail edge  308  of the stack  102  (step  410 ), then the value of the distance from the trail edge sensor  306  to the top of the trail edge  308  of the stack  102  may be recorded (step  412 ). With reference now to  FIG. 6 , if the trail edge sensor  306  cannot sense the top of the stack  102  and if the block pusher plate  116  frame is not all the way down in a “push” position (step  602 ), then the block pusher plate  116  frame may be lowered into the push position (step  604 ). If the trail edge sensor  306  can now sense the top of the trail edge  308  of the stack  102  (step  606 ), then the value of the distance from the trail edge sensor  306  to the top of the trail edge  308  of the stack  102  may now be recorded. If the trail edge sensor  302  can still not sense the top of the stack  102 , then if the block pusher plate  116  is not fully retracted (step  608 ), the block pusher plate  116  may be retracted to a fully retracted position (step  610 ). If the trail edge sensor  306  can now sense the top of the trail edge  308  of the stack  102  (step  612 ), then the value of the distance from the trail edge sensor  306  to the top of the trail edge  308  of the stack  102  may now be recorded. If the trail edge sensor  306  can still not sense the top of the stack  102 , then the block pusher plate  116  may be moved towards the stack  102  until the trail edge sensor  306  senses the top of the stack  102  (step  614 ). The value of the distance from the trail edge sensor  306  to the top of the trail edge  308  of the stack  102  may then be recorded. If the trail edge sensor  306  can still not sense the stop of the stack  102 , then a fault may be triggered (step  616 ). 
     After the value of the distance between the lead edge sensor  302  and the lead edge  112  of the stack  102  and the value of the distance between the trail edge sensor  306  and the trail edge  308  of the stack  102  have been determined, the values may be compared. In one embodiment, if the value from the trail edge sensor  306  does not approximately match the value from the lead edge sensor  302  (step  414 ) to a desired tolerance, the block pusher plate may be adjusted vertically (step  416 ). In some embodiments, the block pusher plate may be adjusted if the values from the sensors  302  and  306  are not within about +/−0.25 inch. In other embodiments, the block pusher plate may be adjusted if the value from the sensors  302  and  306  are not within any desired tolerance range, including but not limited to, within about +/−0.5 inch, 0.75 inch, 1 inch, 1.5 inches, or any other suitable tolerance depending on the thickness of the sheets in the stack  102  and/or the desired specifications of the user. As the block pusher plate  116  is adjusted vertically to the correct position, the trail edge sensor  306  may provide continuous feedback relating to the distance between the trail edge sensor  306  and the trail edge  308  of the stack  102 . When the distance measured at the trail edge  308  approximately matches the distance measured by the lead edge sensor  302  at the lead edge  112  of the stack  102  to within the desired tolerance, the block pusher plate  116  may stop traveling vertically and may be ready to push the block  104  from the stack  102  (steps  418  and  420 ). The ready position, for one embodiment of AWC in accordance with the present disclosure, is illustrated in  FIG. 5B , wherein distance D 2  approximately matches D 1 . In alternative embodiments, it may be desirable that the lead edge sensor  302  and trail edge sensor  306  are aligned such that the ready position occurs at a point when distance D 2  does not approximately match distance D 1 . For example, in one embodiment, it may be desirable that at a ready position, D 2  may be at some desirable offset value or distance from D 1 . As used herein, an offset value or distance may include any suitable nonzero offset as well as a zero or substantially zero offset. As such, if the offset is zero or substantially zero, as previously described, distance D 2  may approximately match distance D 1  at the ready position. 
     In yet further embodiments, the trail edge sensor  306  may be used to determine the distance from the trail edge sensor  306  to the top of the trail edge  308  of the stack  102 . The block pusher plate  116  may be adjusted vertically to the correct position using a separate sensor, such as a potentiometer, encoder, laser, or any other suitable sensor. The separate sensor may be operably attached to any suitable object in relation to the block pusher prefeeder  100 . In one embodiment, the separate sensor may be stationary in relation to the block pusher prefeeder  100  while in other embodiments, the separate sensor may move in relation to the block pusher prefeeder  100 . In further embodiments, the separate sensor may be operably attached to the block pusher plate  116 . In one embodiment, the separate sensor may be attached to the block pusher plate  116  frame. Thus, the separate sensor may move with the block pusher plate  116 . 
     Once a block  104  has been called for (step  422 ), the block pusher plate  116  may push the block  104  from the stack  102  (step  424 ). If the block pusher plate  116  stalls (step  426 ), the block pusher plate  116  may be adjusted vertically (step  428 ) and may attempt another push on the block  104 . After a block  104  has been pushed from the stack  102 , the cycle may be completed and the block pusher plate  116  may be returned to a ready position (step  430 ). 
     Although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, as previously described, the use of a lead edge sensor and a trail edge sensor is exemplary and not limiting. Any suitable number of sensors or other suitable device or method for obtaining the difference of the height of the lead edge  112  of the stack and the height of the trail edge  308  of the stack may be used in accordance with the apparatus and methods of the present disclosure.