Abstract:
A sensor and controller for a belt moving about a path, the sensor and controller including an analog sensor including a medium that changes a characteristic to give a signal that varies continuously with any lateral belt edge position, thus yielding improved resolution of actual belt edge position, and a control mechanism responsive to the changes in characteristics of the medium for more accurate edge position control.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to printing apparatus having an endless belt, and more particularly to a sensor for the edge of the belt and an actuator for controlling tracking of such belt. 
       BACKGROUND OF THE INVENTION 
       [0002]    In electrostatographic imaging and recording processes such as electrographic reproduction, an electrographic reproduction apparatus is utilized to form an electrostatic latent image on a primary image-forming member such as a dielectric surface and is developed with a thermoplastic toner powder to form a visible image. The visible thermoplastic toner powder image is thereafter transferred to a receiver, e.g., a sheet of paper or plastic, and the visible thermoplastic toner powder image is subsequently fused to the receiver in a fusing station using heat or pressure, or both heat and pressure. 
         [0003]    In the reproduction apparatus, various components, such as the primary image-forming member, the transport for the receivers, and/or the fuser may include a belt movable about a closed loop path. In each instance where a belt moving about a closed loop path is used, it is important that the particular belt be accurately controlled in the movement about the closed loop path such that it is steered for proper interrelation with other components of the reproduction apparatus as a reproduction is formed. Often a section of the circumference of the closed loop transport path, or a run of the path between path-defining rollers, must be held substantially constant in the location both axially and vertically to assure desired registration between apparatus elements. Since a most desirable, compact system uses a minimum of support/steering rollers, a sever requirement is placed on the steering method in order to satisfy the physical location consistency and accuracy. Motion of the belt in a direction perpendicular to the desired transport direction must be minimized to assure registration between the apparatus components in order to form a desirable image reproduction. 
         [0004]    In the past it was well known to track belt movement in a direction perpendicular to the transport direction by a common belt edge sensor having an array of optical sensors. The belt edge position is digitally deduced by determining which optical sensors of the array are (or are not) blocked by the belt as it is transported about the closed loop path. The overall resolution of the belt edge sensor is determined by the spacing between the optical sensors in the sensor array. As such, the ability to accurately steer the belt is dependent upon the finite relationship of optical sensor and their spacing. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is directed to a sensor and controller for a belt device for use in an electrographic reproduction apparatus. The belt edge sensor and controller includes an analog sensor that gives a signal that varies continuously with any lateral belt edge positioning thus yielding a better resolution of the actual edge position for more accurate edge control. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which: 
           [0007]      FIG. 1  shows a schematic side elevational view of a reproduction apparatus utilizing the belt edge sensor and tracking control actuator according to this invention; 
           [0008]      FIG. 2  is a view in perspective showing the belt support system for the reproduction apparatus utilizing the belt edge sensor and tracking control actuator according to this invention; 
           [0009]      FIG. 3  is a side elevational view of the belt edge the belt edge sensor and tracking control actuator as shown in according to this invention; 
           [0010]      FIG. 4  is a front elevational view of the belt edge receiver block of the belt edge sensor and tracking control actuator as shown in  FIG. 3 ; 
           [0011]      FIG. 5  is a top plan view of the belt edge receiver block of the belt edge sensor and tracking control actuator as shown in  FIG. 4 ; 
           [0012]      FIG. 6  is a side elevational view of the cooperative interrelation of the belt edge sensor and tracking control actuator according to this invention with the belt support system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring now to the accompanying drawings,  FIG. 1  shows a schematic side elevation view of a reproduction apparatus such as a well known digital printer  10 . The digital printer includes a plurality of receiver sheet supplies  12   a ,  12   b ,  12   c , and  12   d  in operative association with a receiver sheet transport path  14 . In order to accomplish desired printing, individual receiver sheets are fed seriatim from selected receiver sheet supplies for transport along the receiver sheet transport path  14  through a registration mechanism  16  to a plurality of imaging stations  18   a ,  18   b ,  18   c ,  18   d , and  18   e , by a moving belt sheet transport mechanism  20 , where color separation images are transferred to the respective receiver sheets, such as by any well known electrographic reproduction method. In such electrographic reproduction method, in each imaging station  18   a - 18   e , an electrostatic latent image is formed on a primary image-forming member such as a dielectric surface and is developed with a thermoplastic toner powder to form a visible image. The visible thermoplastic toner powder images are thereafter transferred in superimposed register to a receiver sheet, e.g., a sheet of paper or plastic. The combined visible thermoplastic toner powder image on the receiver sheet is transported by a second moving belt transport mechanism  22  through a fusing station  24 , and fused to the receiver sheet by the fusing station  24  using heat or pressure, or both heat and pressure. The fusing station  24  can include a roller, belt, or any surface having a suitable shape for fixing thermoplastic toner powder to the receiver sheet. 
         [0014]    The present invention is directed to a sensor and control for a belt used in the transport of receiver sheets in a printer apparatus. Of course, since the typical printer apparatus as described above has various other components (such as the primary image-forming member, or the fuser) which may include a belt movable about a closed loop path, this invention is suitable for use with such other components. Particularly, this invention will be described with reference to the receiver sheet transport  22  that spans the receiver sheet transport path between the last imaging station  18   e  and the entrance to the fuser station  24 . As best shown in  FIG. 2 , the receiver sheet transport  22  includes a continuous belt  26  entrained about two rollers  28 ,  30  to provide a closed loop path for the belt  26 . The rollers  28 ,  30  are supported by a frame  32 . Electrostatic chargers  34 ,  36  are mounted to the frame  32  respectively above and below the belt  26  adjacent to the roller  28  but could be separately supported. The charger  34  is a tack down charger that applies a charge that causes the receiver sheet to be held to the surface of the belt  26  by an electrostatic attraction, and charger  36  is a conditioning charger which removes residual charge from the belt surface prior to the arrival of the receiver sheet. A receiver sheet (not shown) is tacked to the belt  26  by the charger  34  so as to move from right to left across the top surface of the belt. The left (smaller) roller  28  is a steering roller mounted in a yoke  38 . A yoke  38  supports the steering roller  28  for rotation about the longitudinal axis of the roller and pivots about an axis A that is parallel to an imaginary line that passes from the center of the larger roller  30  to the center of the smaller roller  28  (perpendicular to the longitudinal axis) along which a receiver passes. 
         [0015]    The belt edge sensor and controller, according to this invention, is designated generally by the numeral  40 . The belt edge sensor, that can include an internal controller,  40  is shown mounted to the frame  32  on the underside of the belt  26 . The belt edge sensor could also include a sensor  41  located separately from the belt edge sensor. This could be part of a logic printer and control unit (LCU). The belt edge sensor  40  includes a sensor unit  42  formed of a rectangular block of material having a slot  44  therein to accommodate the belt edge  26   a  (see  FIGS. 3-5 ). The block of the sensor unit  42  has three apertures (orifices)  46   a ,  46   b ,  46   c  drilled in the block perpendicular to the belt surface that passes through the slot  44 . The block is positioned so that the nominal belt edge position is at the center of the middle of the three apertures  46   a ,  46   b , and  46   c . A medium, such as a low pressure fluid (e.g., air), is directed in a conduit  48 , at a constant flow rate, from a source S is passed through the three apertures  46   a ,  46   b ,  46   c  of the block of the sensor unit  42 . The pressure drop of the fluid flow through the three apertures  46   a ,  46   b ,  46   c  is proportional to how much of the aperture area is blocked by the belt surface. If the belt moves to block more of the aperture area, the pressure drop increases. Conversely, if the belt moves to block less of the aperture area, the pressure drop decreases. The actual value of the pressure drop is thus directly related, in an analog fashion, to the location of the belt edge, and can be readily used to provide accurate feed-back indicative of the location of the belt edge relative to the nominal position thereof. 
         [0016]    The feed-back indicative of the belt location can be used to generate a signal used to control steering of the belt to maintain the belt in the nominal position. While the feed-back could be in the form of a signal to control steering of the belt, in the preferred embodiment of this invention, the steering control is affected by using the pressure drop itself as the control signal. Accordingly, the belt edge sensor and controller  40  further includes a bladder assembly  50 . The bladder assembly  50 , shown in  FIG. 3 , has an inflatable bladder  52  connected by a conduit  54  to the conduit  48  so as to admit fluid pressure from the source S to inflate the bladder  52 . Such bladder inflation thus varies according to the actual pressure drop across the apertures  46   a ,  46   b , and  46   c  in the sensor unit  42  due to the change in pressure drop which changes the pressure in conduit  48 , and thus in conduit  54  connected to the bladder  52 . That is, the bladder  52  will inflate or deflate in direct proportion to the change in pressure drop caused by the increase or decrease in fluid pressure through the apertures  46   a ,  46   b , and  46   c  due to the sensed change in location of the belt edge in the slot  44 . 
         [0017]      FIG. 6  shows a bladder  52 , supported on a fixed plate  56 , engages an actuator arm  58  supported on a pivot pin  60 . A spring  62  urges the actuator arm  58  about the pivot pin  60  into positive engagement with a paddle portion  58   a  of one end of the actuator arm  58 . The bladder  52 , on change in pressure loss communicated thereto, pushes on the paddle portion  58   a , with an approximate 4:1 lever ratio, against the urging of the spring  62 . The motion of the actuator arm  58  is transmitted through a linkage  64  to the yoke  38  that holds the steering roller  28  and causes the yoke  38  to pivot counter-clockwise when the bladder  52  inflates and clockwise when the bladder deflates. Pivoting of the yoke  38 , in turn, rotates a center-pivoted steering roller  28  through approximately a 2″ range of motion. The pivoting of the steering roller  28  causes a corresponding lateral motion of the belt  26 . The lever  58 , and yoke  38  are positioned such that when the belt edge is at the preferred position (sensed by the sensor unit  40  with the belt edge in the slot  44 ), the yoke  38  is in a neutral position that causes no lateral belt motion. When the belt edge moves away from the preferred position in the slot  44 , the web edge sensor unit  40  causes a response in the bladder  52 , lever  58 , and yoke  38  that causes a lateral belt motion back to the preferred (neutral) belt position. The edge of belt  26  generally tracks in an axial direction such that the center of the three closely spaced apertures  46   a ,  46   b , and  46   c  is partially covered as noted above. The inner and outer two of the apertures come into play only if there is a major disturbance of the belt tracking system (such as for example during start-up). In normal operation the belt tracking system operates smoothly, in an analog fashion, for proportional movement with almost no lateral movement of the belt. When the belt is significantly disturbed (to an off-center location) the system recovers rapidly, with oscillations about either side of the center strongly damped. 
         [0018]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be affected within the spirit and scope of the invention. 
       PARTS LIST 
       [0000]    
       
           10  digital printer 
           12   a - 12   d  receiver sheet supplies 
           14  receiver sheet transport path 
           16  registration mechanism 
           18   a - 18   e  imaging stations 
           20  moving belt receiver sheet transport mechanism 
           22  second moving belt receiver sheet transport mechanism 
           24  fusing station 
           26  belt 
           28  belt support roller 
           30  belt support roller 
           32  frame 
           34  tack down charger 
           36  conditioning charger 
           38  roller support yoke 
           40  belt edge sensor and controller 
           41  controller 
           42  sensor unit 
           44  slot 
           46   a - 46   c  apertures 
           48  conduit 
           50  bladder assembly 
           52  bladder 
           54  conduit 
           56  fixed plate 
           58  control arm 
           58   a  paddle portion 
           60  pivot 
           62  spring 
           64  linkage 
         A axis