Patent Publication Number: US-2007117064-A1

Title: Dental handpiece with improved grease retention

Description:
RELATED APPLICATIONS  
      This application is a Continuation In Part of U.S. patent application Ser. No. 11/151,933 filed Jun. 13, 2005, which is a Continuation application of U.S. patent application Ser. No. 10/371,033 (Case MID-30D) filed Feb. 20, 2003, which claims the benefit from Provisional Application No. 60/359,962 filed Feb. 27, 2002. 
    
    
     TECHNICAL FIELD  
      The present invention is directed toward dental handpieces of the type employing greased bearings. More particularly, the invention is directed toward a dental handpiece having improved grease retention even with repeated exposure to conventional sterilization practices. The handpiece has at least one bearing retainer with a unique geometry of grease retention grooves.  
     BACKGROUND OF THE INVENTION  
      Dental handpieces of many types, including the air-driven type are known to have an outer housing which often includes a neck portion. Within the chamber of the housing is a rotor adapted to be driven by air supplied through the handle and neck. The housing often includes upper and lower openings that are axially aligned with a rotor being supported for rotation by upper and lower bearing assemblies. The rotor often includes a bur tube that extends substantially between the openings and has a central bore axially aligned with those openings. The lower end of the bore conventionally receives a gripping chuck that is often fixed to the bur tube. Such a dental handpiece is disclosed for example, in U.S. Pat. No. 4,089,115 which is hereby incorporated by reference for such disclosure.  
      The bearing assemblies often include a plurality of balls held within a retainer. Foe example, U.S. Pat. No. 3,994,544 discloses such a ball and retainer bearing assembly, and is hereby incorporated by reference for such disclosure. It was a stated object of the invention of that patent to provide for a bearing for a high-speed turbine, such as may be used in a dental handpiece, and wherein the balls and retainer assembly were greased. Greasing of the bearing assemblies has proven to be a useful and desirable method of reducing friction between the balls and their supporting structure, leading to reduced wear, noise, heat build-up during use and overall improved operability of the handpieces. However, dental handpieces are unique in their use of greased bearings because of their intended use. More particularly, dental handpieces are often run at high speeds of up to 450,000 rpm or greater. Further, after each use, the handpiece must be carefully sterilized before it is used with another patient. Sterilization processes often include the use of high temperature, humidity and pressure. Such processes rapidly degrade the grease packing associated with the handpiece bearings. The grease must often be repacked repaired or otherwise compensated for, which is a time consuming and often difficult job.  
      A need exists therefore for a grease packed dental handpiece with improved grease retention characteristics. The handpiece should be improved with respect to the length of time and number of sterilization and use procedures that it can be subjected to before for example, repacking is necessary. The dental professional and the patient would both benefit from such a handpiece in the form of improved product quality, improved dental procedure efficiency and overall reduced dental procedure costs.  
     SUMMARY OF THE INVENTION  
      It is therefore, an object of the invention to provide a dental handpiece.  
      It is another object of the invention to provide an improved grease-packed dental handpiece.  
      It is another object of the invention to provide a dental handpiece improved with respect to its grease retention characteristics.  
      These and other objects of the invention that will become apparent from the following discussion, are accomplished by the invention as hereinafter described and claimed.  
      These and other objects of the invention, which will become apparent from the present disclosure, are carried out by the invention as hereinafter described.  
      In general, a dental handpiece of the type having a rotary member supported by at least one bearing assembly, wherein said at least one bearing assembly has an annular retainer and a plurality of balls at least partially supported by said annular retainer, the improvement comprising a grease retention groove in a surface of said annular retainer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side elevational view of the rotor assembly  10 , having a retainer element according to the present invention.  
       FIG. 2  is a perspective view of a retainer element according to the present invention.  
       FIG. 3  is a perspective view of an alternative embodiment of a retainer element according to the present invention.  
       FIG. 4  is a perspective view of an alternative embodiment of a retainer element according to the present invention.  
       FIG. 5  is a perspective view of an alternative embodiment of a retainer element according to the present invention. 
    
    
     PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION  
      The present invention has application to any dental handpiece where it is advantageous to provide for improved grease retention properties. Such properties are especially advantageous in dental handpieces that are subjected to repeated use and sterilization under harsh conditions of high heat and moisture. The present invention may therefore, find application in any handpiece driven by electric motor, pressurized air or the like.  
      The handpiece selected for illustration is an air-driven rotor assembly  10  having a pair of ball bearing assemblies  13  and  14  supporting rotor  15   a  for rotation, and including a conventional chuck  15 . The rotor includes any conventional driving means such as for example, an air-turbine  16  for rotatably driving rotor  15   a . The turbine depicted in  FIG. 1  is a radial-flow turbine that is driven by air, but of course, can be of any conventional design.  
      Bearing assemblies  13  and  14  are each provided with a plurality of balls  20  supported by annular retainers  21  and  22 . The invention will be exemplified with reference to bearing retainer  21 , it being understood that at least one and preferably both retainers  21  and  22  have the structure according to the present invention.  
      Dental handpiece rotor assembly  10  is of the type wherein grease (not shown) is packed into the head, such that the balls are physically coated or contacted by the grease during use. As turbine  16  causes rotor  15   a  to rotate, rotor  15   a  is supported by bearing assemblies  13  and  14 . Hence, balls  20  support rotation of rotor  15   a . In other words, rotor  15   a  is journaled within bearing assemblies  13  and  14 . As is conventional, balls  20  are rollingly supported by retainer  21  within ball apertures  23  which prevents adjacent balls  20  from touching each other. The presence of grease helps to reduce the friction encountered between the contacting parts. According to the present invention, retainer  21  has structure to facilitate the physical retention of grease in proximity to such contacting parts, assuring its continued, affective presence even after repeated use and sterilizations, at least compared to conventional handpieces. By “at least partially supported” as used herein with respect to the balls  20  and the retainer  21  it is meant that the ball apertures  23  prevent adjacent balls  20  from physically contacting or touching each other.  
      In order to facilitate such grease retention, retainer  21  is provided with at least one groove  30  in a surface thereof. By “surface” it is meant some external surface. For example, retainer  21  shown in  FIG. 2  has an inner surface  31 , and outer surface  32 , ball retention aperture surfaces  33 , upper surfaces  34  and lower surfaces  35 . Further, retainer  21  shown in  FIG. 2  has an inner annular groove  30   a  disposed on inner surface  31 , a first outer annular groove  30   b  disposed upon outer surface  32 , and a second outer annular groove  30   c  also disposed upon outer surface  32 .  
      In the embodiment of the invention depicted in  FIG. 2 , first outer annular groove  30   b  and second outer annular groove  30   c  are spaced apart such that ball apertures  23  are positioned therebetween. Further, there is preferably an overlapping or cut-away portion of each groove  30  and a portion of each ball aperture  23 , such as at overlapping portion  40 . Overlapping portion  40  allows for ingress of grease held within a groove  30  into ball aperture  23  to thereby lubricate a ball  20  held therein.  
      It will be appreciated that any number, size, depth, location or shape of groove  30  is within the scope of the invention. Further, as will be more fully explored below, the invention can be carried out with other than a groove, such as with a hole, aperture, depression, detent, dimple, cut, void, slice or the like, and need not be annular or even regularly spaced.  
      For example,  FIG. 3  illustrates an embodiment of the present invention having first and second outer annular grooves  30   b  and  30   c , but no inner groove.  
       FIG. 4  illustrates an embodiment of the invention wherein a plurality of straight grooves  50  extending between upper and lower surfaces  34  and  35 . In this illustration, straight grooves  50  are regularly spaced between each ball aperture  23 , but need not be so. Further, grooves  50  need not be straight but may be any shape or configuration.  
       FIG. 5  illustrates a retainer  21  having an inner annular groove  30   a , and also having a plurality of grease retaining dimples or voids  51 , in this case, positioned within ball aperture surfaces  33 . It will be appreciated that voids  51  can be positioned upon any external surface of retainer  21  and still be within the scope of the invention, and that any number of such voids  51  may be employed.  
      The size, shape, depth, spacing and location of all grooves  30 ,  50  or voids  51  may be varied and all fall within the scope of the invention. Each such aspect will be varied based upon the optimal end use conditions of the device with which the given retainer  21  is employed.  
      It has been found that the presence of grooves  30 ,  50  or voids such as voids  51 , improve the useful life of a grease packed handpiece with which they are employed. It is believed that the grooves  30 ,  50  or voids  51  provide a place for excess amounts of greased to congregate or collect, beyond the amount of grease otherwise capable of being positioned proximate to the respective components. This improved collection helps to ensure a supply of grease beyond that of conventional dental handpieces. A handpiece according to the present invention thus has a longer life of use and sterilization, as compared to an otherwise similar handpiece without the inventive structure. This serves to improve the overall bearing life and hence the overall life of the handpiece, as well as ensuring that noise and friction reduction are maintained for longer periods of time than is otherwise possible.  
      It should be apparent therefore, that the present invention provides an advantage and an improvement over known dental handpieces. While in the foregoing, embodiments of the invention have been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.