Patent Publication Number: US-6338483-B1

Title: Single sheet feeder with selectively engageable prefeeding rolls

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to sheet feeding assemblies. In particular, this invention relates to feeding assemblies that control sheet registration and orientation. 
     2. Description of Related Art 
     Reproduction apparatuses must control sheet feeding to ensure that the original document sheet is fed in a straight, properly positioned manner to achieve accurate reproduction of the original document. Such reproduction apparatuses include copiers, scanners and facsimile machines, for example. It is also critical to feed a sheet accurately and in an aligned manner to prevent jamming of the sheet in the feed path. 
     There are many known sheet registration assemblies, commonly referred to as deskewing devices, that control feeding and correct misalignment. One example is U.S. Pat. No. 5,090,683 to Kamath et al. in which a sheet is initially fed to input drive rollers that convey the sheet to detectors that detect the leading edge of the sheet to signal the controller of the presence of the sheet in the assembly. Another example is U.S. Pat. No. 5,169,140 in which a sheet is initially driven with an undetected amount of skew to skew detectors and then driven differentially to deskew the sheet based on signals from the skew detectors. 
     An example of a sheet registration and deskewing device in use in an electrophotographic printing machine is shown in U.S. Pat. No. 5,678,159 to Williams et al and in U.S. Pat. No. 5,887,996 to Castelli. An example of use of a document deskewing system in a copier is shown in U.S. Pat. No. 4,428,667 to Phelps et al. 
     The above devices, however, engage and drive the sheet into the feed path before detection of the sheet. Thus, the sheet must be fed into the nip of the drive assembly prior to actuating the system, especially the deskewing system. This creates obstacles in the feed path that can create problems or require additional attention from the user. Many lightweight documents experience jamming or wrinkling when passing obstacles in the feed path. Also, the drive rolls that nip the sheet to activate the system constrict the latitude of possible sheet orientation upon input and requires greater care by the user. A system without initial obstacles that enabled easy use by all users would be desirable. 
     SUMMARY OF THE INVENTION 
     An aspect of this invention is to provide a feeding assembly that easily feeds sheets to a feed path with a high degree of accuracy. 
     Another aspect of this invention is to provide an assembly that has a user-friendly feel when a sheet is input to the device. Further, this invention allows a greater latitude in document input and registration during input to facilitate operation by a user. 
     An additional aspect to this invention is to provide an assembly that functions well with a full range of document weights. 
     A sheet feeding assembly according to the invention is used for feeding a sheet to a feed path. The assembly comprises a sheet input with a sheet detector that outputs a signal when a sheet is present at the input. A prefeeding mechanism is provided that is selectively engageable with the sheet at the input. A deskewing mechanism is disposed downstream of the prefeeding mechanism and controls orientation of the sheet. A controller is coupled to the sheet detector, the prefeeding mechanism and the deskewing mechanism to actuate the deskewing mechanism in response to the signal from the sheet detector and selectively engage the sheet with the prefeeding mechanism to drive the sheet to the deskewing mechanism. 
     The sheet feeding assembly can further comprise a limited slip clutch connected to the deskewing mechanism to cause the prefeeding mechanism to respond to the signal output from the sheet detector by moving the prefeeding mechanism toward the input. A sensor can be provided in proximity to the deskewing mechanism that detects a leading edge of the sheet to cause the prefeeding mechanism to disengage with the sheet upon a signal from the sensor. 
     The method of controlling a sheet feeding assembly to feed a sheet from an input to a feed path according to this invention comprises the steps of detecting the sheet at the input, actuating a driving apparatus, moving a prefeeding driving mechanism with the driving apparatus to engage the sheet, and manipulating the sheet with a deskewing apparatus to deskew the sheet with respect to the feed path. 
     The method can include actuating the driving apparatus with a limited slip clutch in response to detecting a sheet in the feed path to pivot the prefeeding driving mechanism toward a nip roll to engage the sheet. The method can also include automatically biasing the prefeeding driving mechanism away from the input when a sheet is not detected at the input and detecting a leading edge of the sheet within the feed path at the deskewing mechanism to disengage the prefeeding driving mechanism. 
     The invention also encompasses a reproduction assembly comprising an image reproduction device for reproducing images from an original document sheet. A sheet feed path extends from an input to an output past the image reproduction device. A self-actuating prefeeding device selectively engages a sheet at the input and drives the sheet into the feed path, and a controller controls engagement of the self-actuating prefeeding device based on presence of a sheet at the input of the feed path. 
     The reproduction assembly can further comprise a deskewing device located in the feed path downstream of the self-actuating prefeeding device for controlling orientation of the original document sheet being fed through the feed path. A sheet detector and a movable nip assembly may also be provided, wherein the deskewing device actuates the movable nip assembly to move into the feed path to engage a sheet at the input based on a signal from the sheet detector. 
     Other aspects, advantages and salient features of the invention will be become apparent from the following detailed description, which taken in conjunction with the drawings discloses preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
     FIG. 1 is a schematic bottom view of the prefeeding and deskewing assembly according to this invention; 
     FIG. 2 is a flowchart describing the operation of the device in accordance with this invention; 
     FIG. 3 is a schematic side view of the assembly shown in FIG. 1 prior to insertion of a sheet; and 
     FIG. 4 is a schematic side view of the assembly shown in FIG. 1 after insertion of a sheet. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The feeding assembly described herein is discussed in the context of a reproduction assembly, such as a copier, for purposes of illustration. However, the feeding assembly could be implemented in any type of reproduction apparatus, such as a printer, facsimile machine or scanner, or any device that feeds sheet material through a feed path. 
     FIG. 1 shows a feeding assembly  10  in accordance with this invention in a schematic overview as seen from the bottom of the assembly. The assembly is positioned at the input of a reproduction device  100  and includes a feed path indicated by arrow A. A registration guide  12  is provided at one edge of the feed path and extends in the direction of arrow A. A sheet detector  14 , in the form of a sensor switch, is located at the input. Sheet detector may be any type of sensor, such as a pivotal lever that is mechanically actuated by insertion of a sheet or an optical sensor that actuates when the optical path is obstructed, for example. A prefeeding mechanism  16  is positioned at the input adjacent to sheet detector  14 . 
     Prefeeding mechanism  16  includes at least one prefeed roll  18 , also called a nudger roll, supported on a prefeed roll pivot frame  20 . Any number or type of rolls  18  can be used depending on the intended use of the assembly and the preferred material to be fed into the device. Frame  20  pivots about pivot axis B—B. A biasing mechanism  22 , such as a return spring as shown in FIGS. 3 and 4, is positioned to abut frame  20  and normally bias frame  20  away from feed path A. Biasing mechanism  22  is shown as a helical spring, but could be embodied as any type of biasing mechanism such as a leaf spring or resilient fastener. It is also possible to eliminate biasing mechanism  22  and use a drive mechanism to move frame  20  away from feed path A when disengagement of prefeeding mechanism  16  is desired. 
     A pair of corrugating rolls  24  can be provided opposed to prefeed roll  18  to pinch the sheet upon engagement of prefeeding mechanism  16  with feed path A. As known, corrugating rolls  24  serve to corrugate or create ridges in the sheet to impart beam strength to the sheet to facilitate feeding. Of course, any type of nip assembly could be used, such as a friction roll, to drive the sheet into the assembly. 
     Prefeed roll  18  is carried by a drive shaft  26  that is coupled to a drive shaft  28 , such as an O-ring drive, which is in turn coupled to a drive  30 . A deskewing mechanism  32  is connected to drive  30  and preferably comprises a deskew roll  34  supported by a drive shaft  36 . However, any suitable deskewing mechanism  32  can be employed to control the orientation of a sheet in the feed path, including a combination of rolls that are selectively controlled with respect to velocity and lateral position. Examples of known deskewing mechanisms are disclosed in U.S. Pat. No. 5,601,283 to Pinckney and U.S. Pat. No. 5,278,624 to Kamprath et al., which are both incorporated herein by reference. 
     A movement translating mechanism  42 , preferably in the form of a limited slip clutch, is connected to prefeeding mechanism  16  to convey drive movement from drive  30  through O-ring drive  28  to drive shaft  26  to pivot frame  20 . By this, frame  20  is moved into position in feed path A when drive  30  is actuated. Any type of mechanism that creates a torque reaction against a drag clutch to translate the drive force from drive  30  to prefeeding mechanism  16  would be suitable. 
     A sensor  38  is provided adjacent to deskewing mechanism  32  in feed path A to detect a leading edge of the sheet being fed through the feed path. As discussed below, sensor  38  generates a signal used to deactivate or disengage prefeeding mechanism  16  when the sheet is being or has been deskewed. 
     A controller  40  is provided to control drive  30  based on signals from sheet detector  14  and sensor  38 . Controller  40  may be preprogrammed or selectively programmable depending on desired implementation of the feeding assembly. Preferably, controller  40  operates by one or more control programs. Such a control program is preferably implemented on a programmed general purpose computer. However, the control program can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, in an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA or PAL, or the like. In general, any device, capable of implementing a finite state machine that is in turn capable of implementing the process shown in FIG. 2 described below, can be used to implement the control program. The control program is preferably recorded on a storage medium, which can be embodied in any medium capable of storing a control program, including but not limited to a hard drive, a conventional floppy disk, compact disk or chip. 
     FIG. 2 illustrates the main process steps in accordance with this invention. In the following description, the various steps are represented by the reference symbol S. In operation, a document sheet D is introduced to the machine at the input of feed path A at S 1 . Prior to introduction of document sheet D, the assembly is at rest in the position shown in FIG. 3 with prefeeding mechanism  16  spaced from feed path A, with frame  20  naturally biased by spring  22 . As seen in FIG. 3, there are no obstructions such as feeding rolls or sheet registration guides at the input in this position. 
     When document sheet D is input, sheet detector  14  is activated at S 2 . Sheet detector sends a signal to controller  40  to start drive  30 , which drives O-ring drive  28  and deskewing mechanism  32  at S 3 . As seen in FIG. 3, roll  34  rotates, which causes O-ring drive  28  to rotate and clutch  42  to actuate. O-ring drive  28  causes drive shaft  26  to rotate. With clutch  42  actuated at S 4 , the torque reaction against limited slip clutch  42  by O-ring drive  28  compresses return spring  22 . This causes prefeed roll  28  to engage the opposed corrugating rolls  24  and create a nip through which document sheet D is fed at S 5 . At S 6 , deskewing begins with document sheet D fed to deskew rolls  34 . 
     When document sheet D advances to sensor  38 , a signal is sent to controller  40  at S 7  when the leading edge of document sheet D is detected. The clutch turns off at S 8 , which disengages prefeed roll  18  at S 9 . 
     The exact timing can be optimized for best deskew/sheet feed effect and may be customized for each particular machine depending on the particular intended usage. Also, the precise positioning and spacing of the elements can be varied based on the particular application. As shown in FIG. 1, prefeed roll  18  is spaced inward of registration guide  12  and before or upstream of the deskew roll  34 . For example, in one test device, the position of the prefeed roll was approximately 2.5″ from the registration guide and approximately 2.5″ from the deskew roll. 
     Using corrugating rolls  24 , the beam strength of document sheet D provides the drive force. Therefore, a broad range of paper weights can be fed without slip or damage when using such a corrugating input. 
     As can be appreciated from the operation described above, use of the prefeed/deskew action allows for even more inaccuracy in document placement for sheet acquisition, since prefeed roll  18  retracts after each prefeed. Therefore, there is no obstruction for a document sheet to overcome to be successfully handled. 
     While advantageous embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as set forth in the appended claims.