Patent Publication Number: US-2005138768-A1

Title: Caster

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a caster, more particularly to a caster including a swivel shaft which is riveted at a point thereof to retain an antifriction bearing unit thereon, thereby steadily supporting an appliance and permitting free movement of the appliance.  
      2. Description of the Related Art  
      Referring to  FIGS. 1 and 2 , a conventional caster  1  is shown to include a fork frame  12  with a bearing seat  121 , and two legs  122  for rotatably mounting a wheel  11  therebetween by a rivet shaft  14 , an antifriction bearing unit  13 , and a swivel shaft  15 . The antifriction bearing unit  13  includes first and second outer race members  132 , 133  disposed over and underneath the bearing seat  121 , respectively, and having first and second rivet holes  136 , 137  which are aligned with a rivet hole  123  in the bearing seat  121 , and a plurality of first and second balls  131 , 134  disposed between the first outer race member  132  and the bearing seat  121 , and between the bearing seat  121  and the second outer race member  133 , respectively. The swivel shaft  15  includes a distal segment  151  which is adapted to be connected securely to an appliance (not shown) to be moved, and a proximate segment  153  which extends downwardly from the distal segment  151 , which is inserted into the rivet hole  123 , and which is fitted into the first rivet hole  136  such that an enlarged head  152  which is formed around the proximate segment  153  adjacent to the distal segment  151  is disposed upwardly of the first outer race member  132 . A lower portion  154  extends downwardly from the proximate segment  153  to project outwardly of the second outer race member  133  and a washer  135 . The lower portion  154  is riveted to form a point  155  so as to fasten the second outer race member  133  and the washer  135 .  
      The impact force during riveting of the lower portion  154  may be transmitted to the first and second outer race members  132 , 133  to reduce the distance therebetween, thereby adversely affecting the turning of the fork frame  12  relative to the swivel shaft  15 . On the contrary, insufficient impact force applied to the lower portion  154  may result in unsteady connection between the swivel shaft  15  and the bearing seat  121 . Moreover, the dimension of the proximate segment  153  of the swivel shaft  15  has to be controlled precisely so as to fit into the first rivet hole  136  in the first outer race member  132 , thereby resulting in inconvenient formation of the swivel shaft  15  and the first outer race member  132 .  
     SUMMARY OF THE INVENTION  
      The object of the present invention is to provide a caster which can overcome the aforementioned problems associated with the prior art.  
      According to this invention, a caster includes a fork frame having a bearing seat and two legs which respectively extend downwardly in an upright direction from the bearing seat and which are spaced apart from each other in a transverse direction relative to the upright direction. The bearing seat has a larger rivet hole extending therethrough along a swivel axis in the upright direction.  
      A wheel is mounted between the legs for rotation about a wheel axis in the transverse direction.  
      A first antifriction bearing includes a first outer race member which is disposed over the bearing seat and which has a first smaller rivet hole that is aligned with the larger rivet hole along the swivel axis.  
      A second antifriction bearing includes a second outer race member which is disposed underneath the bearing seat and which has a second smaller rivet hole that is aligned with the larger rivet hole along the swivel axis so that the first and second smaller rivet holes and the larger rivet hole form a combined rivet hole.  
      A swivel shaft extends along the swivel axis, and includes a proximate segment which is configured such that when inserted into the combined rivet hole, the proximate segment is fitted into the first and second smaller rivet holes, and cooperates with the first and second outer race members to define an annular space, a head which is formed around the proximate segment and which is disposed upwardly of the first outer race member, and a point which is opposite to the head along the proximate segment and which projects outwardly of the second smaller rivet hole.  
      A tubular bracing member, which is made from a material that is more rigid than the proximate segment along the swivel axis, is sleeved movably on the proximate segment, and is configured to fit into the annular space such that when the point is riveted, the first outer race member abuts against the head through the tubular bracing member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of the invention, with reference to the accompanying drawings, in which:  
       FIG. 1  is an exploded perspective view of a conventional caster;  
       FIG. 2  is a partly sectional side view of the conventional caster;  
       FIG. 3  is an exploded perspective view of the first preferred embodiment of a caster according to this invention;  
       FIG. 4  is a partly sectional side view of the first preferred embodiment;  
       FIG. 5  is a partly sectional side view of the second preferred embodiment according to this invention; and  
       FIG. 6  is a partly sectional side view of the third preferred embodiment according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Before the present invention is described in greater detail, it should be noted that same reference numerals have been used to denote like elements throughout the specification.  
      Referring to  FIGS. 3 and 4 , the first preferred embodiment of a caster according to the present invention is adapted to be assembled to an underside of an appliance (not shown). The caster is shown to comprise a fork frame  3 , a wheel  2 , an antifriction bearing unit  4 , a swivel shaft  5 , and a tubular bracing member  45 .  
      The fork frame  3  includes a bearing seat  32  and two legs  31  which respectively extend downwardly in an upright direction from the bearing seat  32  and which are spaced apart from each other in a transverse direction relative to the upright direction. The bearing seat  32  has a larger rivet hole  321  which extends therethrough along a swivel axis in the upright direction.  
      The wheel  2  is mounted between the legs  31  by a pin  30  for rotation about a wheel axis in the transverse direction.  
      The antifriction bearing unit  4  includes first and second antifriction bearings  43 , 44 . The first antifriction bearing  43  includes a first outer race member  41  which is disposed over the bearing seat  32  and which has a first smaller rivet hole  411  that is aligned with the larger rivet hole  321  along the swivel axis, a first inner race  322  which is formed on an upper surface of the bearing seat  32 , and a plurality of balls  431  which are interposed between the first outer race member  41  and the first inner race  322 . The second antifriction bearing  44  includes a second outer race member  42  which is disposed underneath the bearing seat  32  and which has a second smaller rivet hole  421  that is aligned with the larger rivet hole  321  along the swivel axis so that the first and second smaller rivet holes  411 , 421  and the larger rivet hole  321  form a combined rivet hole, a second inner race  323  which is formed on a lower surface of the bearing seat  32 , and a plurality of balls  441  which are interposed between the second outer race member  42  and the second inner race  323 .  
      The swivel shaft  5  is made from a malleable material, and extends along the swivel axis. The swivel shaft  5  includes a distal segment  51  which is adapted to be connected securely to the appliance, and a proximate segment  53  which extends downwardly from the distal segment  51  and which is inserted into the combined rivet hole. The proximate segment  53  is configured to be fitted into the first and second smaller rivet holes  411 , 421  and to cooperate with the first and second outer race members  41 , 42  to define an annular space  46 . A manufactured head  52  is formed around the proximate segment  53  adjacent to the distal segment  51 , and is disposed upwardly of the first outer race member  41 . A point  54  is formed opposite to the head  52  along the proximate segment  53  and projects outwardly of the second smaller rivet hole  421 .  
      The tubular bracing member  45  is made from a material that is more rigid than the proximate segment  53  along the swivel axis, and is sleeved movably on the proximate segment  53  to fit into the annular space  56 . Thus, when the point  54  is riveted to fasten the second outer race member  42 , the first outer race member  41  abuts against the head  52  through the tubular bracing member  45 . By means of the tubular bracing member  45 , the impact force during riveting is transmitted to the head  52  primarily through the tubular bracing member  45 .  
      The method of forming a swivel joint for the caster of this invention includes the following steps:  
      (1) forming the larger rivet hole  321  in the bearing seat  32  of the fork frame  3 ;  
      (2) forming the first smaller rivet hole  411  in the first outer race member  41 ;  
      (3) forming the second smaller rivet hole  421  in the second outer race member  42 ;  
      (4) disposing the first outer race member  41  over the bearing seat  32  such that the first smaller rivet hole  411  is aligned with the larger rivet hole  321  along the swivel axis to form the combined rivet hole;  
      (5) forming the manufactured head  52  around the proximate segment  53  of the swivel shaft  5  and the point  54  that is opposite to the manufactured head  52  along the proximate segment  53 , and that is made from a malleable material;  
      (6) inserting the proximate segment  53  into the combined rivet hole so as to form the annular space  46 ;  
      (7) sleeving the tubular bracing member  45  on the proximate segment  53  to fit into the annular space  46 ;  
      (8) disposing the second outer race member  42  underneath the bearing seat  32  such that the point  54  protrudes outwardly of the second smaller rivet hole  421 ; and  
      (9) riveting the point  54 .  
      By means of the tubular bracing member  45  which has upper and lower edges respectively abutting against the first and second outer race members  41 , 42 , to maintain the distance between the first and second outer race members  41 , 42 , and since the impact force is transmitted to the manufactured head  52  primarily through the tubular bracing member  45  during riveting the point  54 , the gap between the second outer race member  42  and the second inner race  323 , and the gap between the first outer race member  41  and the first inner race  322  can be maintained, thereby resulting in smooth rolling of the balls  441 , 431 . Moreover, precision of the dimension of the swivel shaft  5  for fitting into the first smaller rivet hole  411  in the first outer race member  41  can be reduced for facilitating formation of the swivel shaft  5 .  
      Referring to  FIG. 5 , the second preferred embodiment of a caster according to this invention is shown to be similar to the first preferred embodiment, except that the second outer race member  42  and the tubular bracing member  45  are integrally formed with each other. Hence, the aforesaid steps (7) and (8) can be performed simultaneously in the process of forming the caster.  
      Referring to  FIG. 6 , the third preferred embodiment of a caster according to this invention is shown to be similar to the first preferred embodiment, except that the first outer race member  41  and the tubular bracing member  45  are integrally formed with each other. Thus, the tubular bracing member  45  is inserted into the larger rivet hole  321  in the bearing seat  32  in step (2) of the method of this invention.  
      While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.