Abstract:
A light-weight upright shaft ( 14 ) supports cotton harvester doffers ( 12 ). An internally threaded mounting end ( 36 ) receives a bolt ( 38 ) which is stretchable to a greater degree than the shaft to provide a reliable shaft preload condition that prevents the doffers from spinning relative to the shaft. The shaft may be hollow and may have a diameter greater than conventional shafts to reduce weight and increase the stiffness and thereby increase critical speed. The preload structure does not require a nut and has increased thread engagement.

Description:
FIELD OF THE INVENTION 
     The present invention relates to doffer columns for spindle type cotton harvesters. 
     BACKGROUND OF THE INVENTION 
     Previously available doffers for spindle type cotton pickers include a stack of doffers, or pads, supported on a solid shaft. Some pads are in the shape of a flat disk with spacers inserted between each pad. The disks are sandwiched between the spacers, and a nut threaded on external threads at the end of the solid shaft tightly clamps the disks and spacer for rotation of the pads and spacers in unison with the solid shaft. Examples of such structures are illustrated in U.S. Pat. No. 4,819,415. Alternatively, the doffers may include integral axially extending hubs of cast aluminum in place of the separate spacers, such as shown in U.S. Pat. No. 5,014,502. If there is insufficient tensioning preload on the assembled doffer, the doffer can spin relative to the shaft. Once the pads begin to spin, the pads further loosen on the shaft, and the entire doffer column usually must be rebuilt. 
     The threaded stub shaft at the bottom of the doffer column receives a tensioning nut to provide the preload that sandwiches the doffers and spacers or hubs for rotation together with the doffer shaft. The small amount of mounting space at the lower end of the column usually requires a relatively thin nut with a minimal amount of thread engagement. 
     The doffer columns normally operate near the critical operating speed. If the doffer shaft is operated in an over-speed condition for even a short period of time, the shaft may bend. Therefore, increasing the critical operating speed of the doffer columns helps to eliminate shaft bending. 
     SUMMARY OF THE INVENTION 
     A doffer column includes a low weight doffer shaft supporting doffers and spacers or hubs. An internally threaded tensioning member at one end of the shaft tightly sandwiches the pads and spacers or hubs together for rotation in unison with the shaft. The tensioning member provides sufficient preload to prevent rotation of the pads relative to each other and to the shaft. In the embodiment shown, the tensioning member may be an elongated bolt threaded into a receiving member secured to the bottom of a hollow doffer shaft. The internal threads provide more thread engagement than the typical short external nut configuration of the prior art. The construction also facilitates use of a bolt that is sufficiently long for good bolt stretch to provide adequate preload for tight joints. A short external nut may be eliminated. The shaft may be of hollow construction with an outer diameter greater than the outer diameter of previously available solid shafts to decrease weight, increase stiffness and increases the critical speed of the doffer column. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a doffer column assembly, partially in section. 
         FIG. 2  is an enlarged view, partially in section, of the mounting and column preload assembly of the doffer column assembly of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , therein is shown a doffer column assembly  10  for the harvester row unit of a conventional cotton picker. The doffer column structure  10  includes doffers  12  supported on an upright shaft  14  for rotation about a shaft axis  15 . The doffers  12  are vertically spaced on the shaft  14  by spacers  16 . Alternatively, the spacers may be replaced by extended hubs on the doffers  12 . The doffers  12  rotate with the shaft  14  above rows of the spindles and unwrap and remove cotton from the spindles in the row. 
     Each of the doffers  12  includes a generally horizontal circular metal disk or base plate  22  supporting radially outward and downwardly directed lugs  24  in a conventional manner. A round aperture  26  of diameter slightly greater than the diameter of the shaft  14  is located in the center of the base plate  22 . The doffers  12  are slid into position on the shaft  14  with a spacer  16  inserted on the shaft between adjacent doffers. A retention assembly  28  and bearing assembly  30  mount a lower end  14 L of the upright shaft  14  to the base of floor of the harvester row unit. An upper mounting flange  32  secured to an upper end  14 U of the shaft  14  adjacent the uppermost doffer base plate  22  mounts the upper end  14 U to the row unit adjacent a row unit drive assembly (not shown) located in an upper portion of the row unit housing and drivingly connected to the flange  32 . The retention assembly  28  tensions the shaft  14  to firmly secure the doffers  12  and spacers  16  between the flange  32  and the bearing assembly  28  for rotation of the doffers and spacers in unison with the upright shaft. The retention assembly  28  preloads the shaft  14  sufficiently to prevent the doffers from rotating relative to the upright shaft  14 . 
     The retention assembly  28  includes an internally threaded member  36  supported at one of the mounting ends of the upright shaft  14  and a tensioning member  38  threaded into the internally threaded member  36  for sandwiching the doffers  12  and spacers  16  between the upper and lower ends for rotation in unison with the upright shaft  14 . The tensioning member  38  may be an elongated bolt having threads  40  engaging internal threads  42  of the member  36 . The member  36  may be fixed to the lower end  14 L of the shaft  14  by any suitable connecting method. For example, the member  36  may be fabricated from metal and friction welded at location  46  to the end of the shaft  14 . The member  36  may also be connected by arc welding or brazing. 
     As shown in  FIG. 2 , the member  36  has an upper end  36 U with an outer diameter approximately equal to the outer diameter of the shaft  14  with a stepped bore  48 , the upper end of which defines the internal threads  42  and the lower end of which defines an enlarged unthreaded bore portion  50 . A lower end  36 L has a diameter slightly less than the diameter of the upper end  36 U. Other configurations of the member  36  may also be used, including but not limited to an internally member formed in or inserted into the end of the shaft  14 . 
     The tensioning member  38  as shown includes a headed end  56  opposite the threads  40  for receiving a tool. A washer  58  is secured between an inner race  60  of the bearing assembly  30  and the headed end  56 . A slinger  64  is positioned on the lower end  36 L and abuts the upper end of the inner race  60 . A cup-shaped shield  66  opens downwardly over the slinger  64  and the bearing assembly  30  and is secured between the lowermost spacer  16  and the slinger  64  for rotation in unison with the inner race  60 , slinger  64 , and shaft  14 . 
     In the configuration wherein the tensioning member  38  comprises a bolt such as shown in  FIG. 2 , the bolt is fabricated from a material the has the ability to stretch to a greater extent than the shaft  14  as the bolt is tightened during assembly. Therefore, the preload for the assembly is dependent on the degree the member  38  is threaded into the member  36 . As the bolt is tightened, the washer  58 , inner race  60 , slinger  64 , and shield  66  are sandwiched between the headed end  56  and the lowermost spacer  16  which extends downwardly around the member  36  from the lowermost doffer  12 . The radially inwardmost portions of the bases  22  of doffers  12  and the spacers  16  (or the doffer hubs) are firmly secured between the bearing assembly  30  and the flange  32  for rotation together. The preload is sufficient to prevent relative rotation between doffer column components. The offset of a stepped portion  36   a  from the shield  66  facilitates vertical movement of the member  36  relative to the bearing assembly  30  as the bolt head  56  is rotated to adjust the preload. Since a bolt head rather than a thin nut may be used at the bottom of the column, adjustments may be made more easily and more thread engagement may be provided. 
     By way of example only without limitation, an M16×90 bolt, 8.8 grade, is used for the tensioning member  38 . The shaft  14  is hollow with an outer diameter of approximately 1.5 inches (3.8 cm) and is fabricated from metal DOM tubing (ASTM 513 type 5 MD). The outer diameter is greater than the diameter of most previously available conventional doffer column solid shafts. The spacers  16  have a preselected axial length to properly space the doffers  12 , and as shown the tensioning member  38  and threaded member  36  have mutual thread engagement approximately equal to the preselected axial length for a firm, reliable connection. A similar length of unthreaded bolt shank  38   b  facilitates the necessary member stretch for providing the shaft preload condition necessary to assure non-slippage of the doffers  12  relative to the shaft  14  and the spacers  16 . The hollow construction facilitates the elimination of a heavier, solid innermost shaft that extends from end to end so that stiffness and critical speed of the doffer column are increased while weight is reduced. 
     Having described a preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.