Abstract:
An apparatus for providing pinch force control to an entrance transport element in a document handling system. The entrance transport element includes a drive roller element and a pinch roller element and a pinch force relief mechanism coupled to the pinch roller element. The pinch force relief mechanism is positionable between a pinch force mode and a non-pinch force mode. A control element is adapted to control actuation of the pinch force relief mechanism between the pinch force mode and the non-pinch force mode. When the control element places the pinch force relief mechanism in the pinch force mode, the pinch roller element is positioned such that a pinch force is exerted on a document. Conversely, when the control element places the pinch force relief mechanism in the non-pinch force mode, the pinch roller element is positioned such that a pinch force is prevented from being exerted on the document.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to document handling systems, and more particularly, to the control of entrance transport element pinch force on documents of various lengths. 
     2. Discussion 
     Document handling systems, such as check processors, tag printers and ticket printers, are used to process a variety of documents at high speeds. FIG. 1 illustrates a conventional system used in a document handling system for stopping a document in a high speed transport so it can be printed on with a printer. As shown, the conventional system typically includes an entrance transport element  12  having a drive roller element  14  and a corresponding pinch roller element  16 . The system also includes a capstan element  18 , a pinch roller element  20  corresponding to the capstan element  18 , an edge sensor  22 , a hammer bank  24 , a print drum  26 , a ribbon  28 , and an exit transport element  30 . The exit transport element includes a drive roller element  32  and a corresponding pinch roller element  34 . In the example shown, MICR amount fields are being printed on a check  10 . 
     Documents come in a variety of weights and lengths. For example, in check processing, the document lengths range from about 5 inches to 9 inches. FIG. 1 illustrates the case of a relatively short document  10 . In particular, FIG. 1 a  shows a document  10  moving toward a print station. As shown, the entrance drive element  14  and pinch roller element  16  are in contact with the document  10 . Typically, a document  10  is moved at high speed up to a print station by the entrance transport element  12 . When the document  10  is in the grip of the capstan element  18  only, the capstan element  18 , and hence the document  10 , is decelerated to the desired stop position, shown in FIG. 1 b . For precise positioning, the leading edge  10   a  of the document is sensed by the edge sensor  22 . The edge sensor  22  is a known distance from the desired stop position. The motion of the capstan element  18  is controlled by a single motor (not shown) which is part of a servo loop. 
     After printing, the document  10  is accelerated up to the speed of the exit transport element  30  by the capstan element  18 . The exit transport element  30 , usually running at high, constant speed, moves the document  10  to other devices for further processing shown in FIG. 1 c.    
     As is conventionally known, each of the pinch roller elements  16 ,  20  and  34  are normally spring loaded against the entrance  12  and exit  30  drive roller elements and against the capstan element  18 , respectively, in order to provide drive force for the document. A pinch force F p  is generated by the interaction of the drive roller element  14  or  32  or capstan element  18  and the respective pinch roller element. The pinch force F p  is applied to the document  10  generally perpendicular to the path of travel. 
     If the document  10  is short enough, it will not be under the influence of the entrance transport element  12  while the capstan element  18  is decelerating it and holding it in the print position. 
     However, because some document processing, such as check processing, requires that multiple documents of varying length be processed, reliable document transporting dictates that at least one drive or capstan roller element be contacting the document at all times. As such, drive roller and capstan element spacing needs to be small to reliably transport short documents. Unfortunately, this results in long documents being under the influence of a drive roller and capstan element for a greater period of time, which has an undesirable effect on document handling apparatus performance. 
     FIG. 2 illustrates printing on a relatively long document  10 ′ using conventional methods. As best shown in FIG. 2 b , a long document  10 ′ is under the influence of the entrance transport element  12  when the capstan element  18  is decelerating and attempting to maintain the document position during printing. To keep the document  10 ′ from buckling, from slipping forward during deceleration, and to help the capstan element  18  hold the document  10 ′ in position, the small pinch forces F p  are typically used at the entrance transport element  12  to allow the drive roller element  14  to slip. Unfortunately, this action usually compromises document transport reliability since there is still some force on the document due to the friction between the document  10 ′ and the entrance drive roller  14  when the document  10 ′ is being driven by  12  with low drive force during its approach to the print station. 
     SUMMARY OF THE INVENTION 
     It is an thus object of the present invention to provide shorter stopping and starting times to improve throughput in document processing equipment. 
     Another object of the present invention is to remove the entrance transport pinch force during document deceleration and stop during document processing, and then return the pinch force just after processing is completed and the document is delivered to the exit transport. 
     The present invention is directed to an apparatus for providing pinch force control to the entrance transport element in a document handling system. The document handling system includes an entrance transport element comprising a drive roller element and a pinch roller element. A pinch force relief mechanism is coupled to the pinch roller element and is positionable between a pinch force mode and a non-pinch force mode. The apparatus also includes a control element adapted to control actuation of the pinch force relief mechanism between the pinch force mode and the non-pinch force mode. When the control element places the pinch force relief mechanism in the pinch force mode, the pinch roller element is positioned such that a pinch force is exerted on a document. Conversely, when the control element places the pinch force relief mechanism in the non-pinch force mode, the pinch roller element is positioned such that no pinch force is exerted on the document. 
     Accordingly, depending upon document length, the pinch force is automatically removed from entrance transport element, preventing external forces from affecting the positioning of the document. 
     Furthermore, a dashpot may be added to better control motion of the pinch force relief mechanism. 
    
    
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Additional objects, features, and advantages of the present invention will become apparent from studying the following detailed description and claims when taken in conjunction with the accompanying drawings, in which: 
     FIGS. 1 a ,  1   b  and  1   c  are a plan view of a conventional system for transporting documents, wherein the document is relatively short; 
     FIGS. 2 a ,  2   b , and  2   c  are a plan view of a conventional system for transporting documents, wherein the document is relatively long; 
     FIGS. 3 a ,  3   b , and  3   c  are a plan view of a preferred embodiment of the document pinch force control apparatus according to the principles of the present invention; 
     FIG. 4 is a block diagram of a preferred motor control according to the principles of the present invention; 
     FIG. 5 is a block diagram of a preferred algorithm for controlling the pinch force relief mechanism; and 
     FIGS. 6 a ,  6   b  and  6   c  are a plan view of another preferred embodiment of the document pinch force control apparatus, according to the principles of the present invention, wherein the apparatus includes a dashpot. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings show merely exemplary embodiments of the present invention for purposes of illustration only, and one skilled in the art will readily recognize that the principles of the invention are well adapted for application to devices other than document handling systems as well as to document handling systems other than the one shown in the drawings. Furthermore, one skilled in the art will readily appreciate that various adaptations of the preferred embodiments may be combined or otherwise modified without departing from the scope of the invention. 
     This invention may be applied to any device that requires a document to be stopped in an accurate position in order to process it or perform some process on it. 
     FIGS. 3 a ,  3   b , and  3   c  show a document  110  in a transport. As shown, the transport includes an entrance transport element  112 . The entrance transport element  112  includes a drive roller element  114  and a corresponding pinch roller element  116 . The pinch roller element  116  for the entrance transport  112  is allowed to rotate about a pinch roller shaft  116   a . The system also includes a capstan element  118 , a pinch roller element  120  corresponding to the capstan element, an edge sensor  122 , a hammer bank  124 , a print drum  126 , a ribbon  128 , and an exit transport element  130 . The exit transport element includes a drive roller element  132  and a corresponding pinch roller element  134 . 
     As shown in FIG. 3 a , initially only the entrance transport element  112  is in contact with the document  110 . The document  110  is moved at high speed up to a print station by the entrance transport element  112 . When the document  110  is in the grip of the capstan element  118 , the capstan element  118 , and hence the document  110 , is decelerated to the desired stop position. For precise positioning, the leading edge  110   a  of the document is sensed by the edge sensor  122 . The edge sensor  122  is a known distance from the desired stop position. The motion of the capstan element  118  is controlled by a single motor (not shown) which is part of a servo loop. 
     The apparatus of the present invention includes a pinch force relief mechanism  152  and a control element  154 . The pinch force relief mechanism  152  is coupled to the entrance pinch roller element  116  and includes a link member  156 , a power supply  158  and an output shaft  160 . The link member  156  has a first end  156   a  fixed to the pinch roller shaft  116   a  and a second end  156   b  connected to the output shaft  160 . The power supply  158 , preferably an electric motor, applies a torque T to the output shaft  160  when it is energized with electric current. As shown in FIG. 3 a , when the direction of current provides counterclockwise motor torque, a pinch force F p  is produced between the drive  114  and pinch rollers  116  via the connections between the output shaft  160 , the link member  156 , the pinch roller shaft  116   a  and pinch roller  116   b . Alternatively, as shown in FIG. 3 b , when current is cut off from the motor  158 , no torque T is applied to the output shaft  160 . As such, the first end  156   a  of the link member  156  and the pinch roller element  116  are displaced away from the drive roller element  114 , thereby removing the pinch force F p . 
     It is well known that document tracking systems can keep track of the position of a document in a transport by using edge sensors and appropriate electronic logic or computers. It is also well known that such tracking systems can measure the length of a document and have access to the length information at any position of the document along the track where an edge sensor is located. As such, these features will be understood by one of ordinary skill in the art and will not be discussed in detail. 
     The control element  154  selectively activates the pinch force relief mechanism  152  between a pinch force mode and a non-pinch force mode. Specifically, the control element  154  selectively activates the motor  160 . FIG. 4 is a block diagram illustrating the motor control. As shown, an electrical signal from the edge sensor (process block  50 ) is input into a controller (process block  56 ). Likewise, an electrical signal indicating the document length in the tracking system (process block  52 ) is input into the controller  56 . In addition, an electrical signal indicating the capstan element servo position (process block  54 ) is input into the controller  56 . The controller  56  includes either hardwired logic or a computer (microprocessor) to implement an algorithm for controlling the pinch force relief mechanism (see FIG.  5 ). An electrical signal from the controller  56  is then fed to an amplifier  58  which turns the motor current on or off, depending on the nature of the controller signal. 
     The Flowchart of FIG. 5 illustrates an algorithm for turning the motor current off and on. The algorithm initiates as decision block  70  inquires if the document is long enough to engage the entrance transport while printing. 
     If the answer to the inquiry is affirmative, the leading edge of a document is detected by the edge sensor, as shown in process block  72 . Motor current is then turned off ( 74 ). This removes the torque T being generated by the motor  158  and also removes the pinch force F p  as illustrated in FIG. 3 b . The pinch force relief mechanism  152  is thus in a non-pinch force mode. Although the entrance transport pinch force F p  is removed, the document  110  is still well controlled by the pinch force F p  of the capstan element  118  since the edge sensor  122  is downstream of the capstan element  118 . Although the entrance pinch roller  116  shown in FIG. 3 b  leaves contact with the document  110 , it may alternatively remain in contact even if the pinch force is zero. 
     The document  110  is decelerated to document processing position, as shown in process block  76 . The document processing is then performed (decision block  78 ). After the document processing is complete, the motor current can be turned on to re-apply the pinch force F p . Also, the capstan element  118  accelerates the document  110  (process block  80 ) toward and up to the speed of the exit transport element  130 . Re-applying the pinch force F p  of entrance transport element  112  (process block  82 ) at the instant of capstan element  118  acceleration helps the capstan element  118  accelerate the document  110 . 
     If the answer to the inquiry in decision block  70  regarding document length is negative, motor current is left on. This allows the torque T generated by the motor  158  to continue and also allows the pinch force F p  of entrance transport element  112  to be exerted. The pinch force relief mechanism  152  is thus in a pinch force mode. The document  110  is decelerated to document processing position, as shown in process block  76 . The document processing is then performed (decision block  78 ). After the document processing is complete, the motor current continues to apply the pinch force F p  to the entrance transport element  112 . The capstan element  118  accelerates the document  110  (process block  80 ) toward and up to the speed of the exit transport element  130 . Applying the pinch force F p  of the entrance transport element  112  (process block  82 ) at the instant of capstan element  118  acceleration helps the capstan element accelerate the document  110 . 
     FIGS. 6 a ,  6   b , and  6   c  illustrate another preferred embodiment of the document pinch force control apparatus, according to the principles of the present invention, wherein the apparatus further includes a dashpot  300 . Components that are similar to those described with reference to the first preferred embodiment are annotated with similar reference numerals incremented by  100 . 
     As shown in the conventional systems of FIGS. 1 a ,  1   b , and  1   c  and FIGS. 2 a ,  2   b  and  2   c , the pinch roller elements  16 ,  20 , and  34  appear substantially distorted. It is known in the art that soft pinch roller elements often provide more reliable document handling, especially with documents that have folds, staples, or other mutilations. As such, the rollers of pinch roller elements are often made of a soft material such as elostomer. 
     Because of the soft nature of the pinch roller, considerable elastic energy can be stored in the pinch roller element when the pinch force is applied. When the pinch force is removed, the stored elastic energy is released, much of which is converted to kinetic energy. 
     The present invention is adapted to be used with soft pinch rollers while also preventing the elastic energy from being converted to kinetic energy. Specifically the embodiment shown in FIGS. 6 a ,  6   b , and  6   c  include the dashpot  300  connected to the pinch roller shaft  216   a . The dashpot  300  preferably includes a plunger  302  and a cup  304 , as shown in FIGS. 6 a ,  6   b  and  6   c . One end of plunger  302  is connected to the pinch roller shaft  216   a . The other end is disposed inside the cup  304 . The cup  304  is suitably fixed to the frame of the machine (not shown). The cup includes a side  304  and a base  304   b . A small clearance exists between the plunger  302  and the side  304   a  of the cup. 
     When the pinch force at the entrance transport element  212  is removed, as shown in FIG. 6 b , the pinch roller shaft  216   a  moves away from the pinch point as the elastic energy is being released. The plunger  302  moves toward the base  304   b  of the cup. Air in the base  304   b  of the cup is forced out between the small clearance between the plunger  302  and side  304   a  of the cup. This action produces viscous drag forces which consume a large portion of the elastic energy of the plunger  302 . Therefore, there is much less elastic energy converted to kinetic energy. With smaller kinetic energy, the motion of the pinch roller element  216  and pinch force relief mechanism  252  is much smaller. The pinch force can then be returned in a more timely fashion. 
     It can thus be seen that the present offers certain advantages over conventional techniques in the art. Depending upon document length, the pinch force is automatically removed from the entrance transport element, thereby preventing external forces from affecting the positioning of the document. This not only improves performance, but also improves service life of the components of the pinch roller elements. In addition, when a dashpot is included as part of the apparatus, an even more precise control of the pinch force relief mechanism can be obtained. 
     The foregoing discussion and drawing discloses and describes merely an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion that various changes, modifications and variations may be made therein without departing from the scope of the invention as defined in the following claims.