Abstract:
A method for controlling and adjusting nudger drive friction force. The nudger drive friction force is measured and compared with a desired nudger belt friction force term needed for reliable feeding. Cable drum motor torque is responsively adjusted to obtain a desired nudger drive friction force.

Description:
FIELD OF THE INVENTION 
     The present invention relates to document processing equipment, and more particularly to adjusting document nudger drive friction force in a document feeding device. 
     BACKGROUND OF THE INVENTION 
     Document feeding devices are commonly used today to quickly move and sort a variety of documents. Documents are often stacked and automatically fed from the document stack. A feeding mechanism, typically including a nudger and a feedwheel/separator nip, is used to introduce each document to its document transport for processing and sorting. It is important to introduce each document singly, with consistent spacing to permit the fastest feed rate possible while still maintaining proper document spacing. 
     In high-speed equipment, a hopper is often used to supply documents toward the nudger. A stack of documents is placed in the hopper against a flag element, which is used to move the document stack toward the nudger during feeding. To move the document stack, the flag applies a force to the last document in the stack, thereby forcing the stack against a nudger belt. 
     It is common to apply the flag force with a spring, a weight, or a motor. Most commonly, an electric motor drives a cable drum which is interconnected to the flag element by a flexible cable. By applying an electric current to the motor, a known torque is applied to the drum. Rotation of the drum produces a tension on the flexible cable, and subsequently, a force on the flag element. 
     As the flag force moves the document stack along the hopper, the stack is supported by a hopper floor and is guided along a leading edge guide wall toward the nudger. Upon reaching the nudger, the nudger belt (driven by a nudger belt pulley) drives the documents from the stack toward the feedwheel/separator nip. At the feedwheel/separator nip, documents are separated to other transports for forwarding to upstream document processing stations and/or to sorters. 
     As is often the case in conventional systems, the nudger may inadvertently drive more than one document from the stack or may apply a force to a document when the trailing edge of a previous document has not yet left the feedwheel/separator nip. In such a circumstance, depending on inter-document friction and fragility of the document, document leading edge damage, overlapped document feeding, or document jamming may occur if the nudger drive friction force is too large. In contrast, if the nudger drive friction force is too small, a document may slip on the nudger belt and not be driven to the feedwheel/separator nip. 
     Furthermore, although the electric motor torque may be reliable and consistent, the normal force at the nudger due to the motor may vary due to losses between the motor and the nudger. These losses may be induced by cable bending, cable idler friction, flag guide friction, and/or variable friction between the differing documents and the hopper floor and leading edge guide. Also, the coefficient of friction between the nudger belt and the documents may vary depending upon the documents and the environmental conditions, and the age of the nudger belt material. 
     It is therefore desirable to adjust the nudger force in response to force changes caused by such variables in order to provide consistent document spacing. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is provided to alleviate some of the shortcomings of conventional systems. In a preferred embodiment of the present invention, a nudger drive friction force is measured and compared with a desired nudger belt friction force term needed for reliable feeding. Cable drum motor torque is responsively adjusted to obtain a desired nudger drive friction force. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
     FIG. 1 is a plan view of a preferred embodiment of a document feeder according to the principles of the present invention; 
     FIG. 2 is partial enlarged view of the nudger shown in FIG. 1; 
     FIG. 3 is an enlarged partial side view of the document feeder of FIG. 1; and 
     FIG. 4 is a block diagram showing a preferred methodology of the present invention with FIG. 5 giving a related logic diagram. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     FIG. 1 illustrates the typical elements of a document feeder  10 . As shown, a stack  12  of documents is placed in a hopper  14  (details not shown) between a flag element  16  and a nudger  18 . The flag element  16  is adapted to apply a flag force on the stack  12 , thereby forcing the stack  12  toward the nudger  18 . As shown, the nudger preferably includes a nudger belt drive pulley  18   a , a first nudger belt idler  18   b , a second nudger belt idler  18   c  and a nudger belt  18   d . As will be understood by one of ordinary skill in the art, the nudger belt  18   d  is operably disposed around the nudger belt drive pulley  18   a , the first nudger belt idler  18   b  and the second nudger belt idler  18   c . The second nudger belt idler  18   c  is preferably positionally adjustable to provide tensioning of the nudger belt  18   d.    
     In general, the flag force may be applied using a spring, a weight, or a motor arrangement. In the preferred embodiment shown, an electric motor  22  is adapted to provide a torque for applying the flag force. The electric motor  22  is mechanically coupled to and adapted to rotationally drive a cable drum  24 . As shown, the cable drum  24  and the flag element  16  are interconnected by a flexible cable  26  via a cable idler  28 . It will be understood that by applying an electric current to the motor  22 , a known torque is applied to the cable drum  24 , thereby providing tension on the flexible cable  26  which consequently produces a known force on the flag element  16 . 
     The document stack  12  is supported by a hopper floor (not shown) and is guided along a leading edge guide wall  14   a . A hopper sensor  30 , preferably optically reflective, is adapted to sense whether or not documents are in the hopper  14  and provide a signal in response thereto. If documents are in the hopper  14 , the nudger  18  drives the documents from the stack  12  toward a feedwheel  32  and separator  34  via a friction force between the nudger belt  18   d  and the document surface. At a feedwheel/separator nip  36 , documents are separated to other transports (not shown) for forwarding to other document processing stations and/sorters. As shown, a control unit  38  communicates with various sensors and electronics, including hopper sensor  30 , a feedwheel motor (not shown), and cable drum motor ( 22 ). 
     FIG. 2 shows a more detailed view of the nudger  18 . As shown, the nudger belt drive pulley  18   a  includes a hub  100  and a rim  102  interconnected by a plurality of spokes  104 . The hub  100  is operably fastened to a feedwheel motor shaft (not shown) by suitable mounting means. The nudger belt  18   d  wraps circumferentially around and is driven by the rim  102 . 
     The spokes  104  are slender relative to the size of the rim  102  and hub  100 . As such, if a torque T 1 , caused by the nudger belt friction force Ff, is applied to the rim  102 , the spokes  104  will bend slightly, thereby causing relative rotation between the rim  102  and the hub  100 . It is preferable that the spokes  104  remain relatively rigid in the radial direction, which is possible because the spoke  104  is much stiffer in tension/compression than in bending. 
     As further shown, a pair of strain gages  106  and  108  are bonded to the sides of two opposite spokes  104   a  and  104   b . As will be appreciated by one of ordinary skill in the art, additional strain gages may be added to the two spokes in order to increase the sensitivity. As is well known, the strain gages  106  and  108  are adapted to change electrical resistance when they are stretched or compressed, commonly called mechanical strain, and to produce a proportional electrical signal in response thereto. As such, a torque T 1  may be applied to the nudger drive belt pulley  18   a  as a result of nudger belt friction force Ff. In response, the spokes  104  are subjected to bending stresses and the strain gages  106  and  108  produce a proportional signal in response. It will be understood that if the torque T 1  is counterclockwise, the resulting stress in the spokes (and hence, strain in the strain gages) is compressive. 
     Bending stresses in the spokes  104  are also produced by the torque resulting from tension of the nudger belt  18   d . For example, in the configuration shown, if the nudger belt pulley  18   a  was rotated counterclockwise, the second strain gage  108  would be in compression while the first strain gage  106  would be in tension. It will be understood that if the rotation was clockwise, the first strain gage  106  would be in compression and the second strain gage  108  would be in tension. If the nudger belt pulley  18   a  was rotated 90 degrees from the position shown, axial stresses would be placed on the spokes  104   a  and  104   b  due to the nudger belt tension Ft. 
     To cancel out the effects of resistance changes in the strain gages  106  and  108  due to nudger belt tension Ft, yet maintain the effects of resistance changes in the strain gages  106  and  108  due to torque T 1  from the nudger belt friction force Ff, the strain gages  106  and  108  are connected in opposite arms of a Wheatstone bridge. The Wheatstone bridge is a commonly known for use in strain gage electronics, and, as such will not be discussed in further detail. 
     FIG. 3 is a side view of the feedwheel  32 , nudger belt drive pulley  18   a , and a drive motor  200  having a drive motor shaft  202 . As shown, the feedwheel  32  and nudger belt pulley  18   a  are preferably co-axially attached to the drive motor shaft  202 . A plurality of strain gage wires  204  are electronically coupled to the strain gages (not shown) and disposed along the spokes (not shown) toward the hub (not shown) and along the drive motor shaft  202  where they are connected to a plurality of slip rings  206 . As shown, the slip rings  206  are fastened to the motor shaft  202 . The slip rings  206  include wipers  208  for transferring electrical signals from the strain gages to wires  210  that are then routed to measurement and excitation electronic devices  212 . The method of transferring electrical signals to and from a rotating shaft using slip rings is well known to one of ordinary skill in the art, and as such, will not be described in further detail. 
     Turning now to FIG. 4, a block diagram illustrating the electronics of the present invention is shown. As shown in blocks  250  and  252 , bridge excitation voltage is applied to the strain gages. The strain gages are connected to a signal conditioning and amplification section (block  254 ) where two legs of the Wheatstone bridge are completed. When no load is applied, the Wheatstone bridge is balanced, and the relatively small electrical signals are amplified to be easily accepted by the control unit  38  which may be a microprocessor, hard wired logic, analog computer or any combination thereof. Preferably, the control unit  38  is a microprocessor. The control unit  38  is responsible for directing electronics of the cable drum motor (block  256 ) to supply more or less electrical current to the cable drum motor  22 . 
     In the system, a negative torque is applied to the nudger belt drive pulley due to losses as the nudger belt bends around the nudger belt drive pulley and the nudger idler pulleys and due to rotational friction in bearings (not shown) of the pulleys. This negative torque must be subtracted from a measured torque value during document feeding. To accomplish this, an electrical signal from the hopper sensor  30  is utilized to determine if documents are present. As shown in blocks  258  and  260 , a signal from the hopper sensor is conditioned and amplified and then sent to the control unit  38 . When no documents are present, the control unit  38  instructs the electronics of the feedwheel motor (block  262 ) to run for a short period of time, during which the nudger belt drive pulley torque is measured and stored as a reference torque value (block  264 ). The reference torque value is readily accessible for future operations, such as when documents are being fed. 
     With cross-reference to FIG. 5, the control unit  38  performs the operations to instruct the cable drum motor drive electronics (block  256 ). As shown in block  300 , a desired nudger belt friction force term is stored in the control unit  38 . From block  300 , the method advances to summing junction  302 , where the desired nudger belt friction force term and measured force values are compared. In the summing junction  302 , an error term is determined. From the summing junction  302 , the method advances to block  304 , where the error term is multiplied by gain and compensation algorithms which are commonly known in feedback control systems to produce a corresponding signal. The gain and compensation algorithms minimize steady state error while maintaining system stability. These techniques are familiar to those practiced in the art of feedback control systems. 
     From process block  304 , the methodology advances to process block  306 . In block  306 , the signal is translated into a cable drum motor current to increase or decrease the flag force as required. From block  306 , the method advances to block  308 . In block  308 , nudger belt pulley torque is measured to provide a measured nudger belt pulley torque term. The methodology advances to a summing junction  310 . As shown, the summing junction  310  corrects for the measured nudger belt pulley torque and the nudger belt drive torque (block  311 ). In block  312 , the result from the summing junction  310  is divided by the radius of the nudger drive pulley to produce the measured nudger belt friction force. The measured nudger belt friction force is then fed back to the summing junction  302  to be compared to the desired nudger belt friction force. 
     Accordingly, the nudger belt friction force can be controlled by adjusting the flag force applied to the document stack, thereby providing an improved document feeding system. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.