Abstract:
There is described a roller assembly which may be utilized in a linear or serial printer. The roller assembly includes a platen roller including a central axle being exposed at opposing ends of the roller and a frame for mounting the platen at both exposed axle ends.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a continuation application of prior application Ser. No. 10/743,235, filed on Dec. 22, 2003 by Michael N. Burdenko and entitled ROLLER ASSEMBLY. 
   REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of provisional application Ser. No. 60/436,277, filed Dec. 23, 2002. 

   TECHNICAL FIELD 
   The present invention relates to roller assemblies and particularly to roller assemblies, such as platen roller assemblies, having spring biased rollers. 
   BACKGROUND 
   Cylindrical rollers are widely used in a variety of apparatuses including linear or serial printers. One particular type of cylindrical roller is a platen roller, which is used to bias or support print media. Platen rollers are typically characterized by a relatively larger diameter roller section for providing a flatter foundation for the print media, and a relatively smaller diameter axle. In some applications, it is desirable for platen rollers to be movably mounted and biased for pressuring print media against a print head. Movement of such platen rollers needs to be free in certain directions and constrained in other directions. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a roller assembly, comprising a platen roller including a central axle being exposed at opposite ends of the platen roller, and a frame for mounting the platen at both exposed axle ends. The frame includes a separate fork structure adapted for mounting each exposed axle end, with each fork structure being adapted to constrain a respective axle end from moving away from the frame. Also included is a bias mechanism cooperatively associated with each fork structure and being adapted to push the respective axle end away from the frame and against the fork structure and to allow movement of a respective axle end towards the frame and against the bias mechanism. 
   Each exposed axle end may include a bearing and the fork structure may be adapted to retain the bearing and to allow movement of the bearing directly towards the frame. The bias mechanism may include a bearing retainer which is biased away from the frame by the bias mechanism and adapted to engage the bearing. 
   Each fork structure may also be adapted to constrain the bearings from lateral movement with respect to the frame. Each fork structure may include a pair of members extending from the frame and adapted to extend around opposite sides of an axle end. Each pair of members of the fork structure may be separated by a first space having a sufficient size to allow a bearing to pass axially there through. Also, one fork structure of the frame may have an additional spacing between the pair of members which additional spacing is sufficiently large enough to allow the platen roller to pass axially there through. The first space and the additional spacing may be located proximally to the frame. The platen roller may be adapted to be assembled to the frame by passing the roller axially through the additional spacing of the one fork structure, passing a bearing through the first spacing between the other fork structure of the frame and installing the bias mechanisms in each fork structure to bias each axle end away from the frame. 
   The above variations provide a simplified roller assembly with a minimum number of parts, which may be assembled without the use of tools. This feature of the roller assembly is particularly important when it is necessary to make repairs in the field since the roller can be changed without having to be realigned with respect to the print head. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of various preferred embodiments thereof taken in conjunction with the accompanying drawing wherein: 
     The FIGURE is a perspective view of a roller assembly. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The FIGURE shows a perspective view of a roller assembly  10 , which generally includes a frame  12  and a platen roller  14 . Roller  14  includes a cylindrical surface  16  and a central axle  17  having a pair of exposed ends  18 . Each exposed end  18  has a bearing  20  mounted thereupon to allow each exposed end  18  to be mounted and enable low frictional rotation of central axle  17 . Cylindrical surface  16  may be rubber coated as shown. 
   Frame  12  includes a main body  21  and a pair of fork structures  22  mounted on opposing ends of main body  21 . Frame  12  may be mounted by means of a pair of holes  24 , which may be threaded. Each fork structure  22  includes a pair of members  26 , which extend away from the main body  21  like tines on a fork. Member  26  includes a distal end  28  which is adapted, in cooperation with the distal end of fellow fork member  26 , to constrain a bearing  20  from moving away from frame  12  and main body  21 . The distal ends  28  of each respective fork structure  22  may even be connected; however, the lack of connection provides a lower profile for clearing print media handled by platen roller  14 . 
   Each bearing  20  is biased away from frame  12  and main body  21  by a cylindrical bias mechanism  30  to allow good conformance, for example, to a mating print head. The present bias mechanisms  30  each includes an adjustment screw section  32 , a spring bias mechanism  34 , and a bearing retainer  36 . The inwardly facing sides  29  of fork members  26  are shaped to constrain the bearings  20  and bearing retainers  36  from moving laterally with respect to frame  12 . The inwardly facing sides  29 , bearings  20  and retainer  36  may be very accurately fabricated to substantially eliminate such lateral movement. Bearings  20  and bearing retainers  36  are allowed to move towards main body  21  of frame  12 , which is also the axial direction of cylindrical bias mechanisms  30 . 
   The stiffness of spring bias mechanism  34  can be sufficient to maintain roller  14  in its desired position and prevent it from moving laterally. In a preferred embodiment, bearing retainer  36  is provided with two shoulders (not shown) to prevent the roller  14  from moving laterally to contact the inner surfaces of fork member  26 . The shoulders of the retainer extend over, and contact and slide along, the inner surfaces of fork member  26 . 
   Each adjustment screw section  32  may be turned to create the desired amount of pressure from spring bias mechanism  34  on bearing retainer  36 . The separate bias mechanisms  30  on a single frame  12  may be set to apply the same or different pressures depending upon the application. In this manner, bearing roller  14  may be set up to provide the desired amount of pressure against a print head. Assembly  10  thereby provides an independent suspension to each end of axle  17 , which enables roller  14  significant freedom of movement for conforming to the application. 
   Bearing  20  is shaped like a ball bearing; however any suitable bearing may be used depending upon the application. Higher speed rotation may require a ball bearing, whereas lower speed rotation may be handled by a sleeve bearing. A suitable sleeve bearing may be provided by fabricating the current bearing  20  and bearing retainer  36  as a single piece. 
   Although bias mechanisms  30  are set up to bias bearings  20 , the present structure may also be used without allowing such movement for bearings  20 , depending upon the application Also adjustment screw sections  32  may be tightened to create sufficient pressure against bearing retainers  36 . 
   Also, the current disclosure is not intended to be limited to platen rollers and may be applied to any suitable application, and especially to those requiring pressure and position adjustment for the roller. 
   Construction of the current assembly is simple and does not require any assembly tools. Each fork structure  22  includes sufficient space  40  between its respective members  26  to allow a bearing  20  to pass there between during the assembly process of roller assembly  10 . At least one of the spaces  40  for each assembly  10  further includes additional space for allowing roller surface  16  to also pass between the respective members  26  of at least one fork structure  22 . Spaces  40  are located proximally to frame  12  or main body  21 . 
   The above described spacing, along with the other design features of roller assembly  10 , significantly reduces the complexity of constructing assembly  10 . Bearings  20  are first pressed upon exposed axle ends  18 . Then roller  14  is at least partially inserted through a space  40  which is large enough to accommodate roller surface  16 . Then, each bearing  20  is passed through a space  40  of a respective pair of members  26  and is pushed away from frame  12  or main body  21  and against the distal ends  28  of members  26 . This is followed by the installation of bearing retainers  36  and the remainder of bias mechanisms  30 . Adjustment screw sections  32  are then adjusted to create the proper amount of pressure against bearings  20  to retain the roller  14  within assembly  10 . In this manner, assembly  10  maybe the easily and efficiently assembled. 
   The roller assembly of the invention may be incorporated in any thermal printer apparatus. In a preferred embodiment, at least one such roller assembly is incorporated in the thermal printer apparatus disclosed and claimed in commonly assigned U.S. patent application Ser. No. 10/743,235, filed on even date herewith the entire disclosure of which is hereby incorporated by reference herein. 
   Although the invention has been described in detail with respect to various preferred embodiments it is not intended to be limited thereto, but rather those skilled in the art will recognize that variations and modifications are possible which are within the spirit of the invention and the scope of the appended claims.