Abstract:
In one embodiment, a bearing comprises a cylindrical bearing surface supporting a spherical journal surface. In another embodiment, a device comprises a shaft having a spherical journal surface supported inside and rotatable against a cylindrical bearing surface. In another embodiment, a sheet media feed mechanism comprises: a chassis; a motor mounted to the chassis; a rotatable shaft operatively coupled to the motor; a roller affixed to the shaft; an idler disposed opposite the roller; the idler and the roller engagable with one another to form a nip therebetween; bearings mounted to the chassis and supporting the shaft, each bearing having a cylindrical inner bearing surface; and the shaft having a spherical journal surface inside and rotatable against each bearing surface.

Description:
BACKGROUND  
       [0001]     In many printers, paper or other print media is fed into the printer with rollers mounted to one or more rotating shafts. These shafts are usually supported on each end with a cylindrical journal bearing. In a journal bearing, the stationary supporting part is called the “bearing” and that portion of the shaft directly supported the bearing is called the “journal.” In a cylindrical journal bearing, the bearing and the journal are both cylindrical—a cylindrical journal on the shaft fits into a cylindrical opening in the bearing. Very small clearances between the shaft journals and the support bearings are necessary to maintain the accurate paper feed required for good image quality. At the same time, the torque required to turn the shaft must remain low to prevent the paper feed motor from overheating or stalling during higher speed printing. With a conventional cylindrical journal bearing, the small clearances between the journals and the bearings means the journal bearings at each end of the shaft must be closely aligned to prevent the shaft journals from binding inside the bearings and increasing the motor torque needed to turn the shaft. Achieving good bearing alignment is very difficult, however, especially when the bearings at each end of the shaft are mounted to separate components in the printer. 
     
    
     DRAWINGS  
       [0002]      FIG. 1  is a perspective view of a shaft supported on journal bearings according to one embodiment of the invention.  
         [0003]      FIG. 2  is a partial section view of the bearings shown in  FIG. 1 .  
         [0004]      FIG. 3  is a perspective view of the outside of an inkjet printer.  
         [0005]      FIG. 4  is a perspective view of an inkjet printer such as the one shown in  FIG. 3  with the cover and other parts of the housing removed.  
         [0006]      FIG. 5  is a side elevation and partial section view of the inkjet printer of  FIG. 3 .  
         [0007]      FIG. 6  is a detail perspective view showing a connection between the media sheet output shaft and the chassis in the printer of  FIG. 4 .  
         [0008]      FIG. 7  is a perspective view of the media sheet output shaft in the printer of  FIG. 4  supported on journal bearings constructed according to one embodiment of the invention.  
         [0009]      FIG. 8  is an exploded perspective view of one end of the shaft of  FIG. 7  showing in detail one of the journal bearings supporting the shaft.  
         [0010]      FIGS. 9 and 10  are detail partial section views of one end of the shaft of  FIG. 7 . The shaft is aligned in  FIG. 9 . The shaft is misaligned in  FIG. 10 . 
     
    
     DESCRIPTION  
       [0011]     Embodiments of the invention were developed in an effort to reduce the adverse effects of misalignment in the bearings supporting printer media feed shafts while still maintaining the tight clearances needed for good image quality. Embodiments of the invention are directed to a bearing of the type commonly referred to as a journal bearing. In a journal bearing, the stationary supporting part is called the “bearing” and that portion of a moving part directly supported by the bearing is called the “journal.” The surfaces of each of these parts that move against one another are called the “bearing surface” and the “journal surface”, respectively.  
         [0012]      FIG. 1  is a perspective view of a shaft  10  supported at each end inside a cylinder  12  with journal bearings  14  constructed according to one embodiment of the invention.  FIG. 2  is a partial section view of a journal bearing  14 . Referring to  FIGS. 1 and 2 , shaft  10  is supported inside cylinders  12  on spherical journals  16  that protrude from shaft  10 . That portion of each cylinder  12  immediately adjacent to each journal  16  forms the bearings  18  for journals  16 . Each journal bearing  14  includes a journal  16  and supporting bearing  18 . Each journal  16  includes a spherical journal surface  20  that rotates against a cylindrical bearing surface  22  on each bearing  18 .  
         [0013]     One exemplary application for embodiments of the invention will now be described with reference to a media feed roller shaft in the inkjet printer shown in  FIGS. 3-5 . Embodiments of the new journal bearings, which use a spherical journal in a cylindrical bearing, allow the feed roller shaft to rotate freely in all directions without binding inside the bearing. This freedom of movement makes alignment between the bearings much less important for maintaining low motor torque. The clearance between the journal and bearing surfaces can be tight without significantly increasing the risk of binding.  
         [0014]     The contact between the journal and bearing surfaces in embodiments of the new journal bearings is smaller than that of conventional journal bearings. In a conventional journal bearing, the theoretical contact between the journal and bearing surfaces lies along a curved plane (along a line when the bearing is viewed in longitudinal section). In embodiments of the new journal bearings, the theoretical contact between the journal and bearing surfaces lies along a curved line (at a point when the bearing is viewed in longitudinal section). The pressure on the bearing at the contact area can be much higher in embodiments of the new bearings than the pressure in a conventional bearing under the same load. Exceptional freedom of movement, therefore, means higher contact pressures. It has been discovered, however, that higher contact pressures in a journal bearing can be tolerated in print media feed applications due to the light loading on the bearings. (Because it is not usually practicable to fabricate ideal bearing surfaces, the actual contact between the journal and bearing surfaces may be less than the theoretical contact. Nevertheless, the theoretical contact is used to describe the contact between the two surfaces because it would be virtually impossible to determine the actual contact of a non-ideal journal surface rotating against a non-ideal bearing surface.)  
         [0015]      FIG. 3  illustrates an inkjet printer  50 .  FIG. 4  shows inkjet printer  50  with cover  52  and other parts of housing  54  removed.  FIG. 5  is a side elevation and partial section view of inkjet printer  50 . Referring to  FIGS. 3-5 , printer  50  includes a cover  52  and a housing  54 . A sheet media tray  56  is positioned at the bottom of printer  50  along an opening  58  in housing  54 . Paper or other print media sheets  61  are stacked in tray  56  for input to printer  50  and printed sheets are output back through opening  58  over tray  56 . A supporting surface  60  helps suspend the trailing edge of the printed sheets over tray  56 .  
         [0016]     Printer  50  includes a chassis  62  that supports the operative components of printer  50 . Chassis  62  represents generally those parts of housing  54  along with other structurally stable elements in printer  50  that support the operative components of printer  50 . A printhead carriage  64  is driven back and forth along a guide rail  66  mounted to chassis  62 . Any suitable drive mechanism may be used to move carriage  64 . A reversing motor (not shown) coupled to carriage  64  through a belt and pulley system (not shown), for example, is one carriage drive mechanism commonly used in inkjet printers.  
         [0017]     Carriage  64  has stalls for holding one or more printheads  68 . In the printer shown in  FIGS. 3-5 , carriage  64  carries two printheads  68 —one printhead containing color ink for color printing and one printhead containing black ink for monochrome printing. Printheads  68  are also commonly referred to as print cartridges or ink cartridges. As best seen in  FIG. 5 , printheads  68  are positioned along a media path  70  such that each sheet of print media  61  passes directly under printheads  68 . The bottom of each printhead  68 , which faces media sheet  61 , includes an array of nozzles through which drops of ink are ejected onto media sheet  61 .  
         [0018]     An electronic printer controller  72  receives print data from a computer, scanner, digital camera or other image generating device. Controller  72  controls the movement of carriage  64  back and forth across media sheet  61  and the advance of media sheet  61  along media path  70 . Printer controller  72  is also electrically connected to printheads  68  through, for example, a flexible ribbon cable  74 . As carriage  64  carries printheads  68  across media sheet  61 , printer controller  72  selectively activates ink ejection elements in printheads  68  according to the print data to eject ink drops through the nozzles onto media sheet  61 . By combining the movement of carriage  64  across media sheet  61  with the movement of sheet  61  along media path  70 , controller  72  causes printheads  68  to eject ink onto media sheet  61  to form the desired print image.  
         [0019]     A top sheet  61  is “picked” from a stack of media sheets in tray  56  and fed along media path  70 . When a sheet is needed for printing, pick roller  76  is driven clockwise at the direction of controller  72  to grab top sheet  61  and feed it along media path  70  toward transport rollers  78 . Transport rollers  78  bear against idler rollers  79  to form a nip that moves sheet  61  along toward output rollers  80 . Output rollers  80  bear against idler arms  82  to form a nip that moves sheet  61  onto sheet output supporting surface  60 . Output rollers  80  are mounted on a shaft  84 . Output rollers shaft  84  is mounted at each end to chassis  62 . Output rollers shaft  84  is driven by a motor  86  through a gear train  88 .  
         [0020]     One of the connections between output rollers shaft  84  and chassis  62  is shown in detail in  FIG. 6 . Output rollers shaft  84  is shown in detail in  FIG. 7 . The journal bearings  90  and other components used to support the ends of shaft  84  in chassis  62  are shown in detail in  FIGS. 8-10 . Shaft  84  is aligned in  FIG. 9  and misaligned in  FIG. 10 . Referring to  FIGS. 6-10 , each journal bearing  90  includes a spherical journal  92  integral with or affixed to shaft  84  and a bearing  94  integral with or affixed to a mounting part  96 . Mounting part  96  is sized and shaped to form or hold bearing  94  while mounting securely into chassis  62 . Each journal  92  includes a spherical journal surface  98  that rotates against a cylindrical bearing surface  100  on each bearing  90 . In the embodiment shown in  FIG. 6-10 , bearing surface  100  is defined by the inside surface of a cylindrical bushing  102  pressed or over molded into bearing  94 . E-clips  104  pushed into grooves  106  on shaft  84 , or another suitable retainer, hold bearings  90  in position on shaft  84 . Splines  108  on one end of shaft  84  provide an operative connection between shaft  84  and gear train  88  ( FIG. 4 ). Forming bearing surface  100  in a bushing  102  discrete from the rest of bearing  90  and mounting part  96  allows the use of dissimilar materials for these parts. For example, where the characteristics of the bearing surface/journal surface interface require a comparatively tough, wear resistant material, bearing surface  100  can be formed in a bushing  102  and the rest of bearing  94  and mounting part  96  formed from a softer less expensive material.  
         [0021]     Carriage  64  and printheads  68  along with other hardware components necessary to deliver ink to the print media are referred to collectively as a print engine. For laser printers or other image forming devices, the print engine will include those components needed to deliver toner or another marking material to the print media. Rollers  76 ,  78  and  80  along with other hardware components necessary to transport the print media through printer  50  are referred to collectively as a media feed mechanism. Controller  72  includes the programming, processor and associated memory and electronic circuitry necessary to control the print engine, the feed mechanism, and the other operative components of printer  50 .  
         [0022]     The exemplary embodiments shown in the figures and described above illustrate but do not limit the invention. Other forms, details, and embodiments may be made and implemented. For example, embodiments of the invention are not limited to use in inkjet printers or even printers or printer media feed mechanisms, but may be use in many other devices and mechanisms. Hence, the foregoing description should not be construed to limit the spirit and scope of the invention, which is defined in the following claims.