Abstract:
A document transport utilizes a pneumatic pinch force generator in lieu of a conventional spring-loaded pinch roller, thereby minimizing problems associated with pinch roller inertia and debris collection.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to apparatus to transporting documents past one or more document processing stations. More particularly, the invention relates to pinch force generation at various drive wheels or capstans of document transport apparatus. 
     FIGS. 1 a,    1   b,    1   c  illustrate the basic components of a conventional document transport system for stopping a document  102  after traveling at high speed in transport  100  so that information can be printed on document  102  with document processing apparatus, such as a printer  104 . Printing magnetic ink character (MICR) amount fields on a check is a typical example of documents being processed. However, this invention applies to any other device that requires a document to be transported accurately in order to process it. 
     FIGS. 1 a, b, c  illustrate the case of a relatively short document  102 . In the document&#39;s stopped position at printer  104 , only one drive roller, in this case capstan  112 , is in contact with the document  102 . Typically, document  102  is moved at high speed up to a print station  104  with an entrance transport  106 , usually running at a high, constant speed. A typical entrance transport includes an input drive roller  108  and a companion pinch roller  110 , between which document  102  travels. When document  102  is in the grip of the capstan  112  and its associated pinch roller  114  only, capstan  112  and hence document  102  is decelerated to the desired stop position relative to the document processing station, in this example, print station  104 . 
     Edge sensor  116  is positioned a known distance from the desired stop position. Motion of the capstan  112  is controlled by a single motor (not shown) which is a part of a servo feedback control loop. Such methods of positioning documents are well known to those practiced in the art of document processing. 
     After printing on document  102  using hammer bank  118 , print drum  120  and ribbon  121  of print station  104 , document  102  is accelerated up to the speed of the exit transport  122  by the capstan  112 . The exit transport  122 , usually running at high, constant speed, moves document  102  to other devices for further processing or to a document transport exit via drive roller  124  and its associated pinch roller  126 . 
     Pinch rollers  110  and  126  are normally spring loaded against the entrance and exit drive rollers  108  and  124 , respectively, and pinch roller  114  against the capstan  112  to provide drive force for the document  102 . This is likewise common practice in the art. 
     During deceleration of document  102  by capstan  112 , pinch roller  114  must also undergo this same deceleration. However, as a practical matter, pinch rollers, such as  114 , have considerably more inertia than a document, such as a check. Therefore, the inertia of pinch roller  114  can carry document  102  with it and cause the document  102  to go past its intended stop position, if document  102  slips on capstan  112 . 
     Previous practice increased the force on pinch roller  114  to help prevent document slippage or sliding with respect to capstan  112 . However, large pinch forces can result in excessive loads on capstan  112 , pinch rollers  110 ,  114  and  126  and their support systems and bearings, causing premature failure of these components. Large pinch forces also require capstan drive motors to provide large amounts of power thereby wasting energy. 
     The above problems with pinch rollers also apply during the document&#39;s acceleration. In this case, document  102  won&#39;t accelerate as fast as capstan  112 . This, in turn, leads to two negative effects. First, documents behind document  102  being processed may crash into it. Second, document  102  may not get up to the exit transport speed before it enters the nip of the exit transport, thereby causing poor document control. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect of this invention, a document transport including at least one drive roller includes apparatus for providing pinch force to a document abutting the drive roller. A nozzle has an inlet and an outlet, the outlet facing the drive roller and spaced therefrom for permitting documents to pass therebetween. A source of compressed fluid, such as air, is coupled to the inlet of the nozzle thereby enabling it to provide pinch force pneumatically by a compressed fluid flow towards the drive roller. 
     In another aspect of the invention, a document transport system for carrying documents past a document processing station includes an entrance transport including at least one entrance drive roller adapted to propel documents into the transport system, a capstan positioned downstream of the at least one entrance drive roller, the capstan positioned upstream of the document processing station and adapted to propel documents into the document processing station, an exit transport including at least one exit drive roller adapted to propel documents away from the processing station, and a pneumatic pinch force generator positioned opposite at least one of the at least one entrance drive roller, the capstan and the at least one exit drive roller for applying pinch force to a document passing between the pneumatic pinch force generator and at least one of the at least one entrance drive roller, the capstan and the at least one exit drive roller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the invention will become apparent from a detailed description, taken in conjunction with the drawing, in which: 
     FIGS. 1 a,    1   b,  and  1   c  depict a prior art document transport arrangement for passing documents by a document processing station; 
     FIG. 2 sets forth a first embodiment of a pinch force generating arrangement for a document transport arranged in accordance with the principles of the invention; and 
     FIG. 3 sets forth an alternative embodiment of a pinch force generating arrangement of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In essence, the invention eliminates the inertia of a conventional pinch roller by eliminating the pinch roller itself. The pinch roller&#39;s primary function is to provide pinch force between document  102  and a drive element, such as capstan  112 . This pinch force can be provided in accordance with the invention by a high velocity fluid jet as shown in FIG.  2 . 
     A nozzle  204  is positioned so that it points towards the location on capstan  112  where it is desired to produce a pinch force. Nozzle  204  is connected to a pressure regulator  208  via appropriate tubing  206 . 
     Pressure regulator  208  is connected to a source of compressed fluid, such as air, at compressor  212  via tubing  210 . Compressor  212  provides a high pressure supply of fluid, preferably air. Regulator  208  provides a means of adjusting for, or maintaining a desired pressure at, the outlet  204   a  of nozzle  204 . 
     The resultant air jet at outlet  204   a  impinges on document  102 , thereby forcing document  102  against capstan  112 . This provides the requisite pinch force between document  102  and capstan  112 , thereby preventing documents from slipping on capstan  112  during acceleration and deceleration of document  102 . Lower pinch forces are usable with the invention, since the invention eliminates the need to deal with pinch roller inertia. 
     It will be apparent to those skilled in the art that the pneumatic pinch force generator shown in FIG. 2 could be used with other elements in the document transport system apart from capstan  112 . Indeed, such pinch force generators could be placed anywhere in a conventional system which in the past would have used conventional spring-loaded pinch rollers. 
     In most document processors, there is space between documents flowing in the transport. An air jet from nozzle  204  impinges on capstan  112  during this time. An additional advantage of the pneumatic pinch force generator is that the air jet helps keep capstan  112  free of debris and paper dust. This cleansing action, in turn, helps maintain a high coefficient of friction between capstan  112  and document  102 , permitting high values of acceleration and deceleration without document slippage. 
     In some document processors, printing occurs on the back of the documents prior to the document being engaged by the capstan. Endorsing of checks is one example. Because document speeds may be very high, as much as 300 inches per second or higher, ink applied to the document at a preceding station may not be dry before the document reaches the capstan. As a result, some ink may get transferred from the document to the capstan. An additional advantage of the pneumatic pinch force generator as shown in FIG. 2 is that it helps keep the capstan  112  dry. This also helps maintain high coefficient of friction between capstan  112  and document  102 , again permitting high values of document acceleration or deceleration along the transport path. 
     FIG. 3 sets forth an alternative embodiment of the pneumatic pinch force generator of the invention wherein nozzle  304  directs a compressed fluid stream at the documents in a direction downstream of document travel. This embodiment is useful in the case of processing a set of documents having a large percentage of damaged leading edges or where there are documents made of very thin material. Air may spill out in a direction against the document flow when the air jet is impinging on capstan  112  perpendicularly to the path of document travel. A document approaching the capstan may have its leading edge turned back by this spillage. Hence, directing nozzle  304  slightly downstream in the direction of document flow prevents this problem. 
     The invention has been described with reference to exemplary embodiments. The scope and spirit of the invention are to be determined from appropriately interpreted claims herein.