Patent Publication Number: US-2007096387-A1

Title: Method for controlling stack-advancing in a reproduction apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a Continuation-In-Part of pending U.S. patent application Ser. No 10/668,417, filed on Sep. 23, 2003, by Thomas K. Sciurba, et al., entitled “METHOD FOR CONTROLLING STACK-ADVANCING IN A REPRODUCTION APPARATUS” hereby incorporated by reference and herein assigned to the Eastman Kodak Company. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to a method for providing paper stack level calibration in a reproduction apparatus.  
     BACKGROUND OF THE INVENTION  
      In typical reproduction devices, such as copiers or printers, for example, information is reproduced on individual cut sheets of receiver material such as plain bond or transparencies. Receiver sheets of the various types are stored in stacks and respectively fed seriatim from such stacks when copies are to be reproduced thereon. The sheet feeder for the reproduction devices should be able to handle a wide range of sheet types and sizes reliably and without damage. Desirably, the sheets are accurately fed individually from the sheet stack without misfeeds or multifeeds.  
      Reproduction device sheet feeders are typically of two types, vacuum feeders or friction feeders. An exemplary vacuum sheet feeder is shown in U.S. Pat. No. 5,344,133, issued Sep. 6, 1994, in the name of Jantsch et al. In such an apparatus, a stack of sheets is stored in a supply hopper. A sheet feed head assembly, including a plenum, a vacuum source in flow communication with the plenum, and a mechanism, such as a feed belt associated with the plenum, transports a sheet acquired by vacuum in a sheet feeding direction away from the sheet supply stack.  
      Typically, in most vacuum sheet feeders, the sheet supply stack is supported to maintain the topmost sheet at the feed head assembly. A first positive several sheets in the supply stack to an elevation enabling the topmost sheet to be acquired by vacuum from the sheet feed head assembly plenum. Additionally, a second positive air supply typically directs a flow of air at an acquired sheet to assure separation of any additional sheets adhering to such topmost sheet.  
      It is clear that the sheet stack should be maintained in a particular positional relation with the sheet feed head assembly to assure desired feed from the stack. An exemplary control of a sheet stack is shown in U.S. Pat. No. 5,823,527, issued Oct. 20, 1998, in the name of Burlew et al. In such an apparatus, a sheet feeder is disclosed having a platform for supporting a stack of sheets, a feed head assembly for feeding sheets seriatim from the top of a sheet supply stack on the platform, a mechanism for moving the platform relative to the feed head assembly, and device for controlling operation of the platform moving mechanism. The control device can determine a selected parameter in response to examination of sheet stack parameters, and consequently produce a signal corresponding thereto. The speed of the platform moving mechanism is then set based on the parameter signal.  
      Modem reproduction devices have more than one sheet feeder to store different types of sheets. When running large print jobs without any stop page there is a need to switch over from one feeder to another. Normally the first stack is not run empty before switching over to the next stack. It is preferred to leave the minimum number of sheets necessary to insure that the feed source will not run out prior to switching. This maximizes the effective capacity of the supplies and minimizes the number of sheets that are likely to be exposed to undesirable environments for an extended period of time as a result of being left behind. Normally, feeding is switched to another feed source when a paper low condition is signaled. This is typically determined by sensing that the platform has reached a certain position, either through action of a switch, or feedback from a platform travel monitor, such as an encoder, potentiometer or step count from a step motor. The actuation point for this paper low condition is selected to insure that a sufficient number of receiver sheets is present to allow switching under all conditions. Due to the system architecture, the system tolerances and differences in the receiver sheet thickness, this actuation point is selected conservatively. This results in an excessive number of sheets remaining under most conditions.  
      The stack advancing is often performed with stepper motors. The height position of the stack is proportional to the number of steps a stepper motor is triggered. The paper supply controller needs data relating to the displacement of the stack supporting platform relative to a down switch for several reasons. The displacement data is used to determine the paper low status as well as enabling the paper out check and other functions. The paper low displacement is one parameter that determines how many sheets are left behind in a supply hopper after a continuous mode swap, wherein paper supplies are switched and filled alternately in order to provide continuous stream of sheets to the marking engine. As mentioned before, the displacement can be measured in terms of stepper motor steps applied. The mechanical tolerances in the stack advancing mechanism are such that no nominal value for each of these displacements would give an acceptable performance for all supplies of the reproduction apparatus. Although it is possible to manually calibrate the total possible displacement of an elevator, it is inconvenient to manually calibrate for paper thickness.  
      The embodiments described herein allow for more effectively controlling the level of a sheet stack and the switching over to the next stack.  
     SUMMARY OF THE INVENTION  
      According to various aspects of the invention, methods are provided for continuous feeding with a transition from one supply to another, and leaving a controlled number of sheets in the prior supply. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side elevational view of an exemplary receiver sheet supply and feeding apparatus.  
       FIG. 2  is a top plan view of the receiver sheet supply and feeding apparatus of  FIG. 1 , with portions removed or broken away to facilitate viewing.  
       FIG. 3  is a side elevational view of a cross-section of the receiver sheet supply and feeding apparatus taken along lines  3 - 3  of  FIG. 2 , particularly showing the platform elevating mechanism.  
       FIG. 4  is an end view, on an enlarged scale and with portions removed, of a portion of the receiver sheet supply and feeding apparatus, particularly showing the feed head assembly thereof, taken along the lines  4 - 4  of  FIG. 3 .  
       FIG. 5  is a schematic illustration of an exemplary reproduction device with two feeding apparatuses.  
       FIGS. 6-9  present a schematic illustrations of a different stack advancing scenes according to further aspects of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Addressing the problems with paper feeder supplies in reproduction devices described above, the present embodiments provide effective control of a paper stack in a reproduction apparatus with the capability of increasing the effective receiver sheet capacity.  
      According to an aspect of the present invention, the control of stack-advancing may be characterized by an elevator step calibration management system whereby each supply will calibrate itself for both the total possible displacement and the paper low displacement of a stack supporting platform. The calibration occurs in a fashion that is both continuous and independent from the user. The calibration procedure could be performed every time a stack has been renewed or the sheet attributes were changed.  
      According to another aspect of the invention, the number of elevator steps counted during the calibration procedure could be checked with preset values to eliminate malfunctions in the stack advancing control and devices.  
      According to another aspect of the invention the data derived from the calibration procedure could be used to control the switching over to the next stack and to calculate the limits for declaring elevator movement problems.  
      The present invention provides a number of advantages and applications as will be readily apparent to those skilled in the art. Utilizing the disclosed methods, the present invention allows increased effective receiver capacity without increasing the risk of running out of paper while feeding sheets and switching over to another stack.  
      The present embodiments described herein, provide the ability to more effectively control a paper stack in a reproduction device. The system and method have been implemented in a reproduction device utilizing a top feed vacuum feeder. However, it should be understood that the present embodiments can be implemented in a reproduction device that utilizes other types of feeders, including variations of the vacuum feeder or a friction feeder. Thus, the exemplary embodiments disclose a system and method that can be utilized to increase the efficiency for any type of reproduction machine.  
       FIG. 1  is a side elevational view of an exemplary receiver sheet supply and feeding apparatus according to one aspect of the invention. The receiver sheet supply and feeding apparatus  10  generally includes an open hopper  12  and an elevating platform  14  for supporting a stack of sheets. The sheet stack (not shown in  FIG. 1 ) supported on the platform  14  contains individual sheets suitable, for example, for serving as receiver sheets for having reproductions formed thereon in a copier or printer device. Sheets for receiving reproductions may be selected from a wide variety of materials and sizes, which altogether define the sheet attributes. For example, the sheets may be of a weight in the range of 49 grams per square meter (“gsm”) to 300 gsm index, and a size in the range of 8·times·10 inches to 14·times·18 inches, or larger, or smaller, depending upon the application.  
      The sheet stack supporting platform  14  is supported within the hopper  12  for substantially vertical elevational movement by a lifting mechanism (“L”). Preferably, the lifting mechanism L serves to raise the platform  14  to an elevation for maintaining the topmost sheet in the stack at a predetermined level during operation of the receiver sheet supply and feeding apparatus  10 , and to lower the platform to permit adding sheets thereto. The lifting mechanism L may include a motor (“M·sub·1”), attached to the outside of the upstanding front wall of the hopper  12 . Preferably, the motor M·sub·1 rotates a gear set  16  mounted on a shaft  18  extending from the upstanding rear wall of the hopper  12 . A pair of sprocket mounted lifting chains  20  are respectively interconnected by gears with the shaft  18  to be moved about a closed loop path when the shaft  18  is rotated by the motor M·sub·1. As shown in  FIG. 1 , the sheet stack supporting platform  14  is shown in its lowest position in phantom. This most bottom position of the platform  14  is detected with a down switch  21 .  
       FIG. 2  is a top plan view of the receiver sheet supply and feeding apparatus  10  of  FIG. 1 , with portions removed or broken away to facilitate viewing of a sheet feed head assembly  30 . The sheet feed head assembly  30  is generally located in association with the hopper  12 , so as to extend over a portion of the platform  14  in spaced relation to a sheet stack  50  supported thereon. The sheet feed head assembly  30  includes a ported plenum  32  connected to a vacuum source V, and an air jet device  40  connected to a positive pressure air source P. Preferably, the positive pressure air jet from the air jet device  40  levitates the top several sheets in the supported sheet stack  50 , while the vacuum at the plenum  32  is effective through its ports to cause the topmost levitated sheet from the stack  50  to thereafter be acquired at the plenum  32  for separation from the sheet stack  50 . Additional positive pressure air jets from the air jet device  40  helps to assure separation of subsequent sheets from the acquired topmost sheet. To further assure separation of sheets from the sheet stack, the lifting mechanism (for example, L in  FIG. 1 ) preferably presents the top sheet a specified distance from the vacuum plenum  32 .  
       FIG. 3  is a side elevational view of a cross-section of the exemplary receiver sheet supply and feeding apparatus  10  taken along lines  3 - 3  of  FIG. 2 , particularly showing the platform  14  lifting mechanism. Each of the lifting chains have a link  22  extending through respective slots  12   a  ( FIG. 1 ) in the front and rear upstanding walls of the hopper  12 . The links  22  are connected to a shaft  24   a  supported in brackets  24   b  extending from the underside of the platform  14 . Tension cables  26  are respectively connected, at the ends  26   a ,  26   b  thereof, to the front and rear upstanding wall of the hopper  12 . The cables  26  are respectively threaded over their associated first pulleys  24  and under second pulleys  28  mounted on a shaft  28   a  supported in the brackets  28   b  extending from the underside of the platform  14 .  
      In  FIG. 3 , the sheet stack supporting platform  14  is shown in its most elevated position in solid lines, and in its lowest position in phantom. During the operation of the lifting mechanism L, an appropriate signal to the motor M·sub·1 causes the motor to rotate the gear set  16  ( FIG. 1 ), such as either clockwise to lower the platform  14  toward the lowest position or counterclockwise to raise the platform toward its most elevated position. Rotation of the gear set  16  moves the lifting chains  20  ( FIG. 1 ) in their closed loop paths, thereby imparting vertical movement to the links  22 . This movement, in turn, moves the shaft  24   a , and thus the platform  14 , and as well as its brackets  24   b  and first pulleys  24 . The platform  14  is maintained substantially level in its movement by the action of the tension cables  26 , which cooperatively move the second pulleys  28 , and thus, the shaft  28   a  and the brackets  28   b  of the platform  14 .  
       FIG. 4  is an end view, on an enlarged scale and with portions removed, of a portion of the receiver sheet supply and feeding apparatus  10 , particularly showing the feed head assembly  30  thereof, taken along the lines  4 - 4  of  FIG. 3 . Preferably, maintaining the topmost sheet  51  at the predetermined level is accomplished by one or more sheet detecting switches  80 , which controls the operation of the motor M·sub·1 for actuating the lifting mechanism L, (more described below), to raise the platform  14  through a predetermined increment. On the other hand, lowering of the platform  14  is usually accomplished by some externally produced signal to the motor which tells the motor to rotate until the platform  14  reaches the down switch  21  that signals the motor M·sub·1 to stop, often bringing the platform  14  to its lowest position.  
      Of course, other precisely controllable lifting mechanisms, such as worm gears, lead screws, or scissors linkages are suitable for use in the elevation control for the sheet stack supporting platform  14  according to these embodiments, and other suitable mechanisms without limitation.  
      Preferably, the lower surface  32   a  of the plenum  32  of the sheet feed head assembly  30  has a particularly configured shape, so as to provide for a specific corrugation of an acquired sheet  51 . As the top sheets  51  in the supported sheet stack  50  are levitated, the topmost sheet  51  preferably contacts the outer winged portions  32   b  of the surface  32   a . A minimal pressure is exerted on the sheet  51  to help in forming a controlled corrugation to the sheet  51 . This establishes a consistent spacing for the center portion of the sheet  51  from the center portion of the plenum  32 . As such, the access time for a sheet  51  to be acquired at the plenum  32  is often repeatably consistent and readily predictable.  
      The interactions of the plenum  32  and the air jet device  40  attempt to assure that control over the sheet  51 , as it is acquired at the plenum  32 , is not lost. Further, corrugation of the sheet  51  contorts the sheet  51  in an unnatural manner. Since subsequent sheets  51  are not subjected to the same forces, at the same time, as is the topmost sheet  51 , such subsequent sheets  51  are unable to contort in the same manner. Accordingly, the subsequent sheets  51  are effectively separated from the topmost sheet  51  as it is being acquired at the plenum  32 .  
      As noted above, it is important for proper operation of the sheet supply and feeding apparatus  10 , according to this embodiment, for the level of the topmost sheet  51  in the stack  50  supported on the platform  14  to be maintained at a predetermined height relative to the plenum  32 . The level is selected to be in a range where the topmost sheet  51 , when levitated by the first air jet arrangement  42 , is close enough to the plenum  32  to be readily acquired by the vacuum forces from the plenum  32 , within a repeatable time frame, but yet far enough away from the plenum  32  to assure that the sheet being acquired is not pinned against the plenum  32 .  
      Preferably, each of the switches  80 , as noted above, are designed to detect the level of the topmost sheet  51 . Such switches  80 , as known in the art, could be for example, a paper guide that rides against the sheet  51  with very little downward pressure, at the highest level of acceptable corrugation, as found in U.S. Pat. No. 5,823,527, in the name of Burlew et al. Additionally, paper level actuators could be integrated into an optical switch so as to cause limited pressure on the sheet  51 . The switches  80  can be read during the feed interval, and if necessary, will transmit a signal to the lifting mechanism L to raise the platform  14  in one or more increments. Preferably the increments can maintain the proper sheet level. The location of the switches  80  at the highest level of acceptable corrugation is an advantage in that each of the switches  80  can sense the location of sheets  51  which may be severely curled and still not pin the sheet  51  to the plenum  32 .  
      Referring back to  FIG. 1 , to further assure separation of sheets from the sheet stack and the switching over to another stack, the lifting mechanism L can present the top sheet a desirable distance from the vacuum plenum, in response to a second signal that originates from a secondary source other than the switches  80 , such as by a microprocessor  90  executing source code, or hardware logic.  
       FIG. 5  is a scheme illustrating an exemplary reproduction device  500  with two feeding apparatuses  502 ,  504  similar as described above with  FIGS. 1-4 . In each of feeding apparatus  502 ,  504  there is a platform  506 ,  508  supporting stack  510 ,  512 . The platform  506 ,  508  is coupled with an elevating stepper motor  514 ,  516 . Sheets  518 ,  520  in a stack  510 ,  512  are separated and transported by a feed head assembly  522 ,  524 . The stack height is measured with level sensors  526 ,  528 . An additional paper out sensor  527 ,  529  gives a signal if no sheet  518 ,  520  is remaining on the platform  506 ,  508 . A reference position of the platform  506 ,  508  is detected with down switches  530 ,  532 . To count the number of separated and transported sheets  518 ,  520  an optical edge sensor  534 ,  536  is arranged in the transport path  538 ,  540 . The sheets  518 ,  520  are transported to a printing unit  542 . After printing the sheets  518 ,  520  are discarded in a piling apparatus  544 . The piling apparatus contains a platform  546  to discard the sheets  518 ,  520  in a stack  548 . The stack  548  is lowered with the help of a stepper motor  550  whereby the bottom position is detected with a down switch  552 .  
      As shown in  FIG. 5  all active and sensor elements are connected to a control system  554  for the reproduction device  500 . To input, process and display data the control system  554  is connected to a computer system  556  with a keyboard  558  and a monitor  560 . Preferably, software for controlling feeding, of types known in the art, is modified in accordance with the present invention to provide the functionality described herein.  
      With  FIGS. 6-9  it will be described below how the stack-advancing may be performed according to various further aspects of the invention. Referring now to  FIG. 6  (with reference to  FIG. 5 ), a first procedure is presented wherein a number of steps needed to advance the stacks  510 ,  512  from a bottom most to a top most position is determined. This procedure is preferably done when the printing unit  500  is manufactured and the feeding apparatuses  502 ,  504  are mounted, or by field service if they have to be changed or repaired. After starting the procedure by calling up a program in the computer system  556 , first a total possible displacement count is initialized to a nominal value N·sub·T. The Initialized value N·sub·T is stored in Non-Volatile Memory (“NVM”, for example battery-backed memory, flash memory, etc.), also referred to herein as “persistent memory”, within the control system  554 . Next a complete stack  510 ,  512  is advanced stepwise with the stepper motor  514 ,  516  while sheets  518 ,  520  are separated with the head assembly  522 ,  524 . This is performed with the control system  554 . Just before every feed the current step count N·sub·T,C of the motor  514 ,  516  is recorded. A successful feed is verified with a signal from the edge sensor  534 ,  536 . This procedure goes on until the paper out sensor  527 ,  529  generates a paper out signal. If so, the current step count N·sub·T,C, which is the total number of steps needed to feed a stack of sheets starting from the initial lowest position of platform  506 ,  508 , is saved as the new total possible displacement count N·sub·T in the NVM memory, thereby overwriting the nominal initialized value N·sub·T.  
      In  FIG. 6  there is shown a platform  506 ,  508  in a bottom-most position (solid lines) and a top-most position (dashed lines). The just-described procedure starts at the bottom-most position where the platform  506 ,  508  closes the down switch  530 ,  532 . This responds to the reference position with the step count zero. In vertical direction the step count is shown. After feeding all sheets  510 ,  512  the empty platform  506 ,  508  would activate the level sensor  526 ,  528  in the top-most position. In this position the step count reaches N·sub·T.  
      The new total possible displacement count N·sub·T may be checked to determine whether it lies in a predetermined range of values. If not an error message may be displayed on the monitor  560 . In this case a service person could do further checking.  
      Referring now to  FIGS. 5 and 6 , the number of steps needed for the stepper motor  514  ( FIG. 5 ) to advance the stack  510  for feeding K sheets may be determined, wherein K is the number of sheets  518  that should remain in the stack  510  before the scheduling of future feeding goes to the other stack  512  in a continuous mode. For example, K may be the maximum number of sheets that can potentially be scheduled in advance. This paper low displacement procedure is automatically realized by recording the number of steps N·sub·K required to feed K sheets at some point during the reproduction process before only K sheets are left in the stack  510 ,  512 .  
      A paper-low value, N·sub·L, may be determined by subtracting N·sub·K from N·sub·T. N·sub·L may be used to signal a user that paper is almost out in a particular hopper, or it may be used to initiate transfer to another paper supply when paper is feeding in continuous mode. Preferably, K corresponds to a number of sheet feeds already fed from a corresponding supply before N·sub·L is reached. This value N·sub·L is also stored in the memory, preferably volatile Random Access Memory (RAM) rather than NVM.  
      The system may be initialized with a value N·sub·L that represents a nominal paper-low value. For example, if it is determined that an access to the hopper  12  of apparatus  502  or  504  or a paper attributes change occurred, a paper-low displacement count may be initialized to a nominal low paper value N·sub·L. N·sub·L may be chosen to either correspond to a thickest possible paper to ensure that paper will never run out in a drawer or N·sub·L may be chosen to correspond to a thinnest possible paper to ensure that excess paper is not left in a drawer.  
      With the motor  514  the stack is advanced up to the level of the feed-head assembly  522 , as shown in  FIG. 7 . The arrival at the feed-head assembly is confirmed by the level sensor  526 . After the level sensor  526  is activated the current step count is recorded as N·sub·0 in the memory. K sheets are fed, and the corresponding step count N·sub·1 is recorded. The number of step counts corresponding to K sheets is  N ·sub· K=N ·sub·1 −N ·sub·0. Finally a new paper low nominal value N·sub·L may be calculated as the difference between the total possible displacement N·sub·T and N·sub·K,  N ·sub· L=N ·sub· T−N ·sub· K . The stack  510  has now the position shown in  FIG. 8 .  
      After determining the paper low value, N·sub·L, feeding may continue until the actual step count reaches N·sub·L. The platform  506  has then the level shown in  FIG. 9 . The scheduling from stack  510  will be stopped and is continued with feeding apparatus  504  activated with the control system  554 . The feeding out of apparatus  504  is done in the same way as described with feeding apparatus  502 .  
      While the switching over from one feeding apparatus  502  to the next feeding apparatus  504  has been described with the remaining sheet number K, it should be clear that the switching over could be delayed by feeding J additional sheets with the feeding apparatus  502 . For example, after paper low N·sub·L is reached, allow scheduling of J additional feeds in a manner to insure that not more than K feeds occur from that point prior to switching the supplies. I.e., if six additional feeds (J) are scheduled when paper low N·sub·L is reached, allow K−6 (k−J) more feeds to be scheduled prior to switching to feeding apparatus  504 .  
      The present embodiments described herein, provide the ability to more effectively and reliably control stack-advancing in a reproduction device, by automatically calibrating the counts for the stepper motors M 1 ,  514 ,  516 . Although described in the setting of a reproduction device utilizing a top feed vacuum feeder  502 ,  504  and switches  80 ,  526 ,  528  that generate a signal to indicate an increment, it should be understood that the present embodiments could be implemented in a reproduction device that utilizes other types of feeders and switches, or in an off-line configuration (a paper supply not connected to a reproduction device), or with a post-fuser inserter.  
      The disclosed method provides a number of advantages and applications. Utilizing the disclosed embodiments, the present invention allows better control over the number of sheets remaining during a continuous mode swap even if the sheet attributes and the mechanical tolerances change or vary from stack to stack.  
      It should also be understood that the programs, processes, methods and systems described herein are not related or limited to any particular type of hardware, such as TTL logic or computer software, or both. Various types of general purpose or specialized processors, such as microcontrollers may be used with or perform operations in accordance with the teachings described herein.  
      In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the present invention. For example, more or fewer elements may be used in the drawings and signals may include analog, digital, or both. While various elements of the preferred embodiments have been described as being implemented in hardware, in other embodiments in software implementations may alternatively be used, and vice-versa. For example, the said stepper motor, could be any type of motor with feedback for platform movement such as an encoder or a potentiometer.  
      Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope and spirit of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.