Abstract:
A system for reducing torque disturbance includes a motor mechanically coupled to an endless belt. The motor is operable to drive the belt, and the belt has a seam that causes a torque disturbance to the system. The system includes a data structure having a set of values that indicates an amount of compensation for reducing the torque disturbance and a controller electrically coupled with the motor. The controller is configured to control the motor and reduce the torque disturbance based on the set of values in the data structure.

Description:
TECHNICAL FIELD 
   This invention relates to printing systems and methods and, more particularly, to systems and methods for canceling torque disturbance in devices using an endless belt. 
   BACKGROUND 
   Any discussion of the related art throughout the specification should in no way be considered as an admission that such related art is widely known or forms part of common general knowledge in the field. 
   Conventional printing machines often include a photoreceptor belt driven in a cyclical manner by a motor. The motor is typically controlled by a closed-loop feedback controller, such as a proportional-integral-differential controller. The closed-loop controller strives to achieve a desired belt velocity by incorporating feedback from operation of the machine. As shown by the jagged line in  FIG. 4 , the actual belt velocity closely approximates, but nonetheless varies from, the desired belt velocity. 
   In conventional machines having an endless belt, that is, a belt having two ends joined together to form a seam, the seam may cause undesirable errors, for example, a torque disturbance outside the bandwidth of the closed-loop system. For example, the operational frequency of the controller may not be adequate to timely detect and resolve the errors resulting from the seam. Instead the controller is late to correct the actual torque disturbance  420  ( FIG. 4 ) and causes a lagged disturbance  424 . 
   Some printing systems, for example, color printing systems benefit from higher degrees of accuracy due to the overlaying of different colored images over one another. Accordingly, it may be desirable to provide systems and method for reducing torque disturbance in devices having an endless belt, for example, printing systems. 
   SUMMARY 
   According to various aspects of the invention, a system for reducing torque disturbance may include a motor mechanically coupled to an endless belt. The motor may be operable to drive the belt, and the belt may have a seam that causes a torque disturbance to the system. The system may include a data structure having a set of values that indicates an amount of compensation for reducing the torque disturbance and a controller electrically coupled with the motor. The controller may be configured to control the motor and reduce the torque disturbance based on the set of values in the data structure. 
   In accordance with various aspects of the invention, a method for reducing torque disturbance may include controllably operating a motor to drive an endless belt in a cyclical manner, determining when a seam of the belt is expected cause a torque disturbance in a system, determining an amount of compensation for reducing the torque disturbance, and controllably operating the motor based on the amount of compensation to reduce the torque disturbance. 
   According to various aspects of the invention, a printing system may include a belt having two ends joined together to form a seam, a motor mechanically coupled to the belt, and an acoustic transfer assist device configured to transfer an image from the belt to a medium. The motor may be operable to drive the belt, and the assist device may include a vacuum source for drawing the belt toward the assist device. The vacuum source and the seam may cooperate to cause a torque disturbance to the system. The system may include a data structure having a set of values that indicates an amount of compensation for reducing the torque disturbance caused by the seam and a controller electrically coupled with the motor. The controller may be configured to control the motor and reduce the torque disturbance based on the set of values in the data structure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form part of the specification, illustrate various aspects of the present invention and, together with the description, describe those various aspects. Throughout the drawings, like numbers are used to represent like parts. 
       FIG. 1  is a schematic diagram of an exemplary printing machine in accordance with various aspects of the invention; 
       FIG. 2  is a schematic diagram of an exemplary acoustic transfer assist system for use with the exemplary machine of  FIG. 1 ; 
       FIG. 3  is a block diagram of an exemplary system for reducing torque disturbance in accordance with various aspects of the invention; 
       FIG. 4  is a combination schematic diagram and graph illustrating and exemplary torque disturbance and synchronization of a signal to reduce the torque disturbance; and 
       FIG. 5  is a flowchart illustrating an exemplary method for reducing torque disturbance in accordance with various aspects of the invention. 
   

   DETAILED DESCRIPTION 
   The following detailed description is provided to facilitate an understanding of some of the innovative features unique to the present invention. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
   Referring to the drawings and in particular to  FIG. 1 , an image forming device, for example, an electrophotographic printing machine  10 , is shown. The printing machine  10  creates an image in a single pass through the machine. It should be appreciated that the present invention may be used in an electrophotographic printing machine which utilizes an image on image process to create a color image on a sheet in a single pass through the machine, or which creates a single black toner image on a sheet. 
   The printing machine  10  uses a charge retentive member or imaging member in the form of a photoreceptor belt  12 , which travels sequentially through various process stations in the direction indicated by the arrow  13 . Belt travel may be achieved by mounting the belt  12  about a drive roller  14  and two tension rollers  16  and  18  and then rotating the drive roller  14  via a drive motor  20 . 
   As the photoreceptor belt  12  moves, each part of it passes through each of the subsequently described process stations. For convenience, a single section of the photoreceptor belt, referred to as the image area, is identified. The image area is the part of the photoreceptor belt which is to receive a toner powder image which, after being transferred to a substrate such as a sheet of paper, produces the final image. It should be appreciated that the photoreceptor belt may have a plurality of image areas, depending on the length of the belt and the size of the images. 
   As the photoreceptor belt  12  moves, the image area passes through a charging station A. A corona generating device  22  charges the image area to a relatively high and substantially uniform potential at the charging station A. The corona generating device  22  is powered by a high voltage power supply (HVPS). 
   After passing through the charging station A, the now charged image area passes through an exposure station B. At exposure station B, the charged image area is exposed to light, which illuminates the image area with a light representation of an image. The light representation discharges some parts of the image area so as to create an electrostatic latent image. While the illustrated embodiment uses a laser based output scanning device  24  or raster output scanner (ROS) as a light source, it is to be understood that other light sources, for example an LED printbar, can also be used with the principles of the present invention. It should also be appreciated that the present invention may be practiced in a light lens machine in which an image is formed by passing light through an original document to expose the photoconductive surface. 
   After passing through the exposure station B, the now exposed image area passes through a development station C. The development station C deposits an image of negatively charged toner  26  onto the image area. The toner is attracted to the less negative sections of the image area and repelled by the more negative sections. The result is a toner powder image on the image area. 
   The development station C incorporates a donor roll  27  in a development system  28 . An electrode grid  30  is electrically biased with an AC voltage relative to the donor roll  27  for the purpose of detaching toner therefrom so as to form a toner powder cloud in the gap between the donor roll  27  and the photoreceptor belt  12 . Both the electrode grid  30  and the donor roll  27  are biased at a DC potential for discharge area development (DAD). The discharged photoreceptor image attracts toner particles from the toner powder cloud to form a toner powder image thereon. 
   Thereafter, the toner powder image is advanced past a corotron member  34  to a transfer station D. At the transfer station D, the toner powder image is transferred from the image area onto a support sheet  36  (e.g. a sheet of paper, a transparency, or any other member adapted to receive marking particles thereon). It should be understood that the sheet  36  is advanced onto the photoreceptor belt  12  by a conventional sheet feeding apparatus schematically shown by reference numeral  39 . The sheet then advances through the transfer station D in the direction of arrow  38 . The transfer station D includes a transfer assist blade system  41  which is operable to apply uniform contact pressure to the sheet  36  as the sheet is advanced onto the photoreceptor belt  12  by the sheet feeding apparatus  39 . In particular, as the sheet is being advanced onto the photoreceptor belt  12 , a transfer assist blade (not shown) of the transfer assist blade system  41  presses the sheet  36  into contact with the toner powder image on the photoreceptor belt  12  thereby substantially eliminating any spaces between the sheet  36  and the toner powder image. One exemplary transfer assist blade system which may be used with the present invention is disclosed in U.S. Pat. No. 5,300,993 issued to Vetromile, the disclosure of which is totally incorporated herein by reference in its entirety. 
   The transfer station D further includes a transfer corona device  40  which sprays positive ions onto the sheet  36 . Also, at transfer station D, an acoustic transfer assist (ATA) system  44  is operable to impart vibrations to the photoreceptor belt  12  during operation of the corona device  40 . Operation of these devices  40 ,  44  cause the negatively charged toner powder image to move onto the sheet  36 . Positioned downstream relative to the transfer corona device  40  is a detack corona device  42  which facilitates removal of the sheet  36  from the photoreceptor belt  12 . 
   After being advanced through the transfer station D, the sheet  36  moves onto a conveyor (not shown) which advances the sheet to a fusing station E. The fusing station E includes a fuser assembly  46  which is operable to permanently affix the transferred powder image to the sheet  36 . Preferably, the fuser assembly  46  includes a heated fuser roller  48  and a backup or pressure roller  50 . When the sheet  36  passes between the fuser roller  48  and the backup roller  50 , the toner powder is permanently affixed to the sheet  36 . After fusing, a chute  52  guides the sheet  36  to a catch tray  54  for removal by an operator. 
   After the sheet  36  has separated from the photoreceptor belt  12 , the image area is advanced toward a cleaning station F. Upon arrival at the cleaning station F, residual toner particles on the image area are removed via a cleaning brush  58  located at the cleaning station F. The image area is then ready to begin a new marking cycle. 
   The various machine functions described above are generally managed and regulated by a controller  74  which provides electrical command signals for controlling the operations described above. The controller  74  may be any conventional controller, for example, a closed-loop feedback controller, such a proportional-integral-differential controller or the like. The controller  74  may control the operations based on various information, for example, velocity and position information relating to the photoreceptor belt  12 . Such information about the photoreceptor belt  12  may be provided by an encoder  76 , for example, an optical encoder, associated with, for example, one of the tension rollers  16 ,  18 , the drive roller  14 , or the motor  20 . 
   Turning now to  FIG. 2 , the ATA system  44  is shown in more detail. The ATA system  44  may be substantially similar to the ATA system disclosed in U.S. Pat. No. 6,157,804 issued to Richmond et al., the disclosure of which is totally incorporated herein by reference in its entirety. Since acoustic transfer assist systems in general are well known in the art, only some of the components of the ATA system  44  will be discussed herein in detail. Examples of some acoustic transfer assist systems are disclosed in the following U.S. Patents, the disclosure of each of such patents being totally incorporated herein by reference in its entirety: U.S. Pat. No. 5,515,148 issued May 7, 1996 entitled “Resonator Assembly Including a Waveguide Member Having Inactive End Segments”; U.S. Pat. No. 5,512,991 issued Apr. 30, 1996 entitled “Resonator Assembly Having an Angularly Segmented Waveguide Member”; U.S. Pat. No. 5,512,990 issued Apr. 30, 1996 entitled “Resonating Assembly Having a Plurality of Discrete Resonator Elements”; U.S. Pat. No. 5,512,989, issued Apr. 30, 1996 entitled “Resonator Coupling Cover for use in Electrostatographic Applications”; U.S. Pat. No. 5,357,324 issued Oct. 18, 1994 entitled “Apparatus for applying Vibratory Motion to a Flexible Planar Member”; U.S. Pat. No. 5,329,341 issued Jul. 12, 1994 entitled “Optimized Vibratory Systems in Electrophotographic Devices”; and U.S. Pat. No. 5,282,005 issued Jan. 25, 1994 entitled “Cross Process Vibrational Mode Suppression in High Frequency Vibratory Energy Producing Devices for Electrophotographic Imaging”. 
   As shown in  FIG. 2 , the ATA system  44  includes a horn-shaped transducer  60  having waveguide segments  62  that engage the backside (i.e., non-image side) of the photoreceptor belt  12  at the transfer station D. The ATA assembly  44  may include a housing  88  defining a cavity  90  in which the transducer  60  is located. The transducer  60  further has a piezoelectric element  64  that is driven by a drive circuit (not shown). The housing  88  further defines an opening  92  in the housing that is juxtaposed to the photoreceptor belt  12  at the transfer station D. A vacuum source  94  may be positioned in fluid communication with the cavity  90 . The vacuum source  94  may be operable to generate a vacuum of, for example, −50.0 mmHg within the cavity. When the vacuum source  94  is operated so as to generate a vacuum in the cavity  90 , the photoreceptor belt  12  is drawn toward the opening  92  thereby forcing a lower tip  96  of the transducer  60  into continuous engagement with the photoreceptor belt  12  during advancement of the belt  12  in the direction of arrow  98 . 
   Referring now to  FIG. 3 , a system  300  for reducing torque disturbance in the printing machine  10  is described. The system  300  may be embodied in the controller  74  or a separate controller associated with the printing machine  10 . The system  300  may comprise signals to and from the controller  74 , the motor  20 , the photoreceptor belt  12 , and the encoder  76 . 
   A reference signal is combined with system feedback from the encoder  76  at summation point  350 . Based on the output of summation point  350 , the closed loop compensator  374  determines an appropriate signal for controlling the motor  20 . During portions of the operation of the printing machine  10 , the photoreceptor belt  12  does not cause significant torque disturbance  380  in the system  300 . However, when the seam  15  of the photoreceptor belt  12  is near the acoustic assist device opening  92 , a brief loss of the vacuum force on the belt may occur, causing an undesirable amount of torque disturbance  380  to the system  300 . 
   When the controller  74  determines that the torque disturbance is expected to occur, the controller  74  can control the motor  20  with a compensation amount determined from a data structure  360 . The data structure  360  may comprise a lookup table, a mathematical algorithm, or a combination thereof. The compensation amount may be retrieved from a lookup table or determined by a mathematical algorithm. The compensation amount from the data structure  360  may be adjusted via gain factor  378  and may be combined with the output of the closed loop compensator  374  at summation point  370 . It should be appreciated that during operation of the printing machine  10  when the seam  15  is not at the opening  92  of the acoustic assist device  44 , the system  300  operates as a conventional closed-loop feedback system. 
     FIG. 4  illustrates an exemplary manner in which the controller  74  may identify when the torque disturbance  420  is expected to occur. The photoreceptor belt  12  may include a position marker  414  such as, for example, a hole, a cutout, a notch, or any other sensable feature, and the distance between the position marker  414  and belt seam  15  can be easily determined. For any given speed of the motor  20 , the belt seam  15  will be at the opening  92  of the acoustic transfer assist device  44  during substantially the same period of each cycle of the belt  12 . Thus, the number of pulses  476  of the encoder  76  occurring in the time period between detection of the position marker  414  and seam being at the opening  92  of the assist device  44  can be used to determine the time at which the torque disturbance is expected to occur. It should be appreciated that the number of pulses  476  shown in  FIG. 4  is only exemplary, and the actual number of pulses occurring in the time period between detection of the position marker  414  and seam being at the opening  92  of the assist device  44  may be more or less than the number illustrated. 
   As shown in  FIG. 4 , the compensation amounts determined from the data structure  378  define the compensation profile  430 . The compensation profile  430  is selected to reduce and/or substantially cancel the torque disturbance  420 , and to eliminate the lagging torque disturbance  424  caused by late correction of the torque disturbance  420 . 
   An exemplary operation  500  of the exemplary aspects described above with respect to  FIGS. 1–4  is described with respect to  FIGS. 5 . Referring to  FIG. 5 , the exemplary operation  500  commences at stage S 505 , for example, when the printing machine is printing images to a substrate. Control continues to stage S 510 , where a sensor (not shown) coupled with the controller  74  attempts to detect a position marker  414  of the belt  12 . For example, the belt  12  may include a hole, a cutout, a notch, or any other sensable feature. Control then continues to stage S 515 . 
   In stage S 515 , the controller  74  determines whether the position marker  414  is detected. If the position marker  414  is not detected, control returns to stage S 510 , where the sensor continues to attempt to detect the position marker  414 . If the position marker  414  is detected, control continues to stage S 520 , where the controller  74  begins counting encoder pulses. Control continues to stage S 525 . 
   Then, in stage S 525 , the controller  74  determines whether the torque disturbance is expected to occur at the present time. The controller  74  can make this determination because the number of encoder pulses between the time the position marker is detected and the expected time of the torque disturbance are substantially known. Control continues to stage S 530 . 
   Next, in stage S 530 , if it is determined that the torque disturbance is not expected to occur at the present time, control returns to stage S 520 , where the controller  74  continues to count encoder pulses and determine whether the torque disturbance is expected to occur (S 525 ). If, in stage S 530 , it is determined that the torque disturbance is expected to occur, control continues to stage S 535 . 
   In stage S 535 , the controller  74  controls the motor  20  with a compensation amount for reducing the torque disturbance. The compensation amount may be retrieved from a lookup table or determined by a mathematical algorithm. Control continues to stage S 540 . 
   Then, in stage S 540 , the controller  74  determines whether the expected end of the torque disturbance is reached, and control continues to stage S 545 . In stage S 545 , if it is determined that the expected end of the torque disturbance has not been reached, control returns to stage S 535 , where the controller  74  controls the motor  20  with a compensation amount for reducing the torque disturbance. 
   If, in stage S 545 , it is determined that the expected end of the torque disturbance has been reached, control continues to stage S 550 . In stage S 550 , the controller  74  may determine whether the reduction of the torque disturbance is satisfactory. The controller  74  may make this determination by timing the period between the encoder pulse where the torque disturbance is expected to begin and the encoder pulse where the torque disturbance is expected to end, that is, the period during which stage S 535  is executed. Control then continues to stage S 555 . 
   If, in stage S 555 , it is determined that the reduction of the torque disturbance is satisfactory, control continues to stage S 510 , where the controller  74  awaits another detection of the belt position marker  414 . If, in stage S 555  it is determined that the reduction of the torque disturbance is not satisfactory (either too much or too little), control continues to stage S 560 . In stage S 560 , the controller  74  may adjust the gain factor  378  for further operations  500 . Control then continues to stage S 510 , where the process is repeated beginning with stage S 510 . 
   The novel features of the present invention will become apparent to those of skill in the art upon examination of the disclosure or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only, because various changes and modifications will become apparent to those of skill in the art from this disclosure.