Abstract:
This invention relates to an apparatus for assuring media feeding, comprising: an impression drum having a media gripper; an input feed unit located substantially adjacent to the impression drum for feeding a sheet of media; and a servo motor operatively connected to the input feed unit such that a change in operating characteristics of the servo motor is detected if the sheet of media is properly retained by the gripper.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to an apparatus for assuring media feeding, comprising: an impression drum having a media gripper; an input feed unit located substantially adjacent to the impression drum for feeding a sheet of media; and a servo motor operatively connected to the input feed unit such that a change in operating characteristics of the servo motor is detected if the sheet of media is properly retained by the gripper.  
         [0003]     2. Description of the Related Art  
         [0004]     Prior to the present invention, as set forth in general terms above and more specifically below, it is known, in the printing art to employ sensors at the entrance between the impression drum and the intermediate transfer drum in order to detect the media leading-edge position and timing. While this system is capable of detecting the leading edge and timing of the media, this solution requires additional sensors inside of the printing device. Also, the leading edge position and timing of the media are detected outside of the media grippers that can result in an inadequate detection of paper stick to blanket (PSTB). Finally, the sensors of this system may send faulty alarms due to dirt and paper dust adversely affecting the sensors. Consequently, a more advantageous system, then, would be provided if such sensors can be avoided.  
         [0005]     It is also known, in the printing art to employ a pressurized system to determine if the media is located against the impression drum. In this manner, a vacuum is applied to the impression drum. If a sheet of media is located on the impression drum, a change in the vacuum properties is detected. While this system is capable of detecting the presence the media, this solution requires additional sensors inside of the printing device. Also, the system is not capable of detecting if the media is properly located within grippers. Finally, the vacuum sensors of this system may send faulty alarms due to vacuum ports becoming inadvertently clogged. Therefore, a further advantageous system, then, would be provided if such a vacuum system could be avoided.  
         [0006]     It is apparent from the above that there exists a need in the art for a method and apparatus for assuring proper media feeding such that the proper retention of the media within the grippers can be detected without the use of sensors or other complicated systems so as to avoid paper stick to blanket (PSTB). It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.  
       SUMMARY OF THE INVENTION  
       [0007]     Generally speaking, an embodiment of this invention fulfills these needs by providing an apparatus for assuring media feeding, comprising: an impression drum having a media gripper; an input feed unit located substantially adjacent to the impression drum for feeding a sheet of media; and a servo motor operatively connected to the input feed unit such that a change in operating characteristics of the servo motor is detected if the sheet of media is properly retained by the gripper.  
         [0008]     In certain preferred embodiments, the input feed unit is a plurality of rollers that create a nip to feed the sheet of media towards the impression drum. Also, if a change in the torque on servo motor is detected then it can be assumed that the sheet of media is properly retained by the gripper. Finally, if a change in the velocity of the servo motor is detected, then it can be assumed that the media has not been properly retained by the grippers.  
         [0009]     In another further preferred embodiment, a method and apparatus is presented for assuring proper media feeding such that the proper retention of the media within the grippers can be detected without the use of sensors or other complicated systems so as to avoid paper stick to blanket (PSTB).  
         [0010]     The preferred method and apparatus for assuring media feeding, according to various embodiments of the present invention, offers the following advantages: ease-of-use; elimination of extraneous sensors; improved detection times; reduced printer downtime; decreased paper stick to blanket occurrences; and reduced blanket damage. In fact, in many of the preferred embodiments, these factors of elimination of sensors, improved detection times, reduced printer downtime, decreased paper stick to blanket occurrences, and reduced blanket damage are optimized to an extent that is considerably higher than heretofore achieved in prior, known method and apparatus for assuring media feeding.  
         [0011]     The above and other features of the present invention, which will become more apparent as the description proceeds, are best understood by considering the following detailed description in conjunction with the accompanying drawings, wherein like characters represent like parts throughout the several views and in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic illustration of a method and apparatus for assuring proper media feeding wherein the media has reached the grippers on time, according to another embodiment of the present invention;  
         [0013]      FIG. 2  is a schematic illustration of a method and apparatus for assuring proper media feeding wherein the media has missed the grippers, according to another embodiment of the present invention;  
         [0014]      FIG. 3  is a graphical illustration of paper velocity at various feed stages (time (ms) versus paper velocity (mm/s)), according to the prior art;  
         [0015]      FIG. 4  is a graphical illustration of paper velocity with servo detection at various feed stages (time (ms) versus paper velocity (mm/s)) as the media enters into the grippers properly, according to another embodiment of the present invention; and  
         [0016]      FIG. 5  is a graphical illustration of paper velocity with servo detection at various feed stages (time (ms) versus paper velocity (mm/s)) as the sheet of media misses the grippers, according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     The paper stick to blanket (PSTB) phenomenon is one of the main reasons for blanket (the soft material that is wrapped around the ITM drum) damage due to its interaction with jammed media. When PSTB occurs, the printer stops printing and the operator must then get to the blanket. The jammed media and any residual ink must be cleaned from the blanket. During this operation, the image may be fused to the blanket and then the operator is forced to replace the blanket. Also, in some cases, the jammed media may become bent and this bend may cause a mechanical defect in the blanket, which may also force the operator to place to blanket. It is to be kept in mind that under normal operating conditions, it takes about 30 milliseconds between the time the grippers are closed and the grippers reach the next drum. Clearly, media jamming is an issue and, even greater, is the concern of how to quickly determine that a media jammed has occurred in order to avoid undue amounts of lost downtime.  
         [0018]     With this background in mind, apparatus  2  for assuring proper media feeding is illustrated in  FIGS. 1 and 2 . Apparatus  2  includes, in part, conventional ITM drum  4 , conventional impression drum  6 , conventional grippers  8 , input feed unit  10 , a sheet of the media  12 , servo motor  14 , and servo motor controller  16 . Preferably, input feed unit  10  includes a plurality of rollers that create a nip. This nip interacts with media  12  in order to feed media  12  towards impression drum  6  and grippers  8 . Servo motor  14 , preferably, is operatively connected to input feed unit  10  and is any suitable electromechanical mechanism that supplements a primary control operated by comparatively feeble force through servo motor controller  16 . It is to be understood that controller  16  can be part of servo motor  14  or located outside of servo motor  14 .  
         [0019]      FIGS. 1 and 2  illustrate two scenarios that can occur with respect to apparatus  2 . In the first scenario, media  12  properly enters into grippers  8 , as illustrated in  FIG. 1 . In  FIG. 1 , input feed unit  10  pushes the media  12  to cause the media  12  to move towards the nip between ITM drum  4  and impression drum  6  and at the right time, apply a tension force. Media  12  properly enters into grippers  8 . Grippers  8  will pull media  12  against input feed unit  10  and servo motor  14 . This pulling creates a negative pulling force (tension mode) on servo motor  14 . It is to be understood that the pulling force of grippers  8  should be greater than the driving force of servo motor  14  on input feed unit  10  so that grippers  8  are capable of pulling media  12  through input feed unit  10  but not great enough to rip or otherwise adversely affect media  12  or pull media  12  out of grippers  8 . At this point, servo motor controller  16  will detect a change at the velocity levels (or current levels) of servo motor  14  and will cause input feed unit  10  to accelerate the velocity of media  12  so that it is equal to the process velocity (the velocity of media  12  at grippers  8 ) in order to avoid unnecessary tension upon media  12 . In this manner, the proper gripping of media  12  by grippers  8  can be quickly and easily detected.  
         [0020]     With respect to  FIG. 2 , input feed unit  10  pushes the media  12  to cause the media  12  to move towards the nip between ITM drum  4  and impression drum  6  and at the right time, apply a tension force. In this Figure, media  12  misses grippers  8 . It is to be understood that media  12  may miss the grippers  8  for a variety of reasons. For example, there may be a delay in the conveyor (not shown) that feeds media  12  into input feed unit  10 . Also, media  12  may be skewed when it reaches grippers  8 . Also, there may be a malfunction in the mechanical system which controls the gripper&#39;s actuation. Finally, there may be a malfunction in input feed unit  10  which feeds media  12  into grippers  8 . Due to the fact that media  12  misses or otherwise does not properly engage with grippers  8 , there will be no tension force on servo motor  14  on that will resist against grippers  8  and pull media  12  away from grippers  8 . In this manner, servo motor controller  16  will detect a decreased change in velocity level (or current level) of servo motor  14  and stop media  12  from entering into the nip between ITM drum  4  and impression drum  6 . Consequently, PSTB will be efficiently detected and prevented.  
         [0021]     To demonstrate further proof of the concepts of the present attention,  FIGS. 3-5  are presented. With respect to  FIG. 3 , a conventional current input feed unit operation is driven by a stepper motor, according to the prior art. As shown in the graph, media reaches the input feed unit, stops, and, at the right moment, the media is fed into the impression drum grippers. During the movement of the media, the input feed unit accelerates and decelerates the media until the media reaches the grippers. When the grippers close, the media velocity is equal to the process velocity (the velocity of the grippers). The input feed unit drives the media at this velocity until the trailing edge of the sheet of media exits the input feed unit.  
         [0022]      FIG. 4  is a graphical illustration showing how the media enters into the grippers properly, according to the present invention. As shown in  FIG. 4 , grippers  8  ( FIGS. 1 and 2 ) will pull media  12  against servo motor  14  to create a negative pulling force (tension mode) on servo motor  14 . The pulling force of grippers  8  should be greater than the force applied by input feed unit  10  and servo motor  14  so that grippers  8  will pull media  12  through input feed unit  10 . Servo motor controller  16  will detect a change in velocity levels (or current levels) of servo motor  14  and will accelerate the velocity of media  12  through input feed unit  10  so that it is equal to the process velocity (the velocity of grippers  8 ) in order to avoid unnecessary tension on media  12 . In this manner, the proper retention of media  12  within grippers  8  can be efficiently detected.  
         [0023]      FIG. 5  is a graphical illustration showing how the media missed the grippers, according to present invention. As shown in  FIG. 5 , input feed unit  10  will apply a tension force to media  12 . Due to the fact that media  12  misses grippers  8 , there will be no tension force on media  12  by grippers  8  that will pull media  12 . Due to this loss of tension force, the velocity of media  12  will be reduced. Servo motor controller  16  will detect this change in velocity of media  12  through input feed unit  10  and stop media  12  from entering into the nip between ITM drum  4  and impression drum  6 . In this manner, PSTB will be efficiently detected and prevented.  
         [0024]     The present invention can be embodied in any computer-readable medium for use by or in connection with an instruction-execution system, apparatus or device such as a computer/processor based system, processor-containing system or other system that can fetch the instructions from the instruction-execution system, apparatus or device, and execute the instructions contained therein. In the context of this disclosure, a “computer-readable medium” can be any means that can store, communicate, propagate or transport a program for use by or in connection with the instruction-execution system, apparatus or device. The computer-readable medium can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor media. More specific examples of a suitable computer-readable medium would include, but are not limited to, a portable magnetic computer diskette such as floppy diskettes or hard drives, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable compact disc. It is to be understood that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a single manner, if necessary, and then stored in a computer memory.  
         [0025]     Those skilled in the art will understand that various embodiment of the present invention can be implemented in hardware, software, firmware or combinations thereof. Separate embodiments of the present invention can be implemented using a combination of hardware and software or firmware that is stored in memory and executed by a suitable instruction-execution system. If implemented solely in hardware, as in an alternative embodiment, the present invention can be separately implemented with any or a combination of technologies which are well known in the art (for example, discrete-logic circuits, application-specific integrated circuits (ASICs), programmable-gate arrays (PGAs), field-programmable gate arrays (FPGAs), and/or other later developed technologies. In preferred embodiments, the present invention can be implemented in a combination of software and data executed and stored under the control of a computing device.  
         [0026]     It will be well understood by one having ordinary skill in the art, after having become familiar with the teachings of the present invention, that software applications may be written in a number of programming languages now known or later developed.  
         [0027]     Once given the above disclosure, many other features, modifications or improvements will become apparent to the skilled artisan. Such features, modifications or improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.