Abstract:
A dental handpiece is disclosed including a turbine construction creating a radial in flow of air onto the impeller blades about the whole circumference of the turbine. An air guide inserted into the turbine housing and extending about the turbine defines a drive air supply chamber separated from the turbine housing and communicating with a drive air supply conduit. The air guide has a plurality of inlet openings for radially inwardly directing pressurized air from the drive air supply chamber into the turbine housing onto the turbine.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to handpieces for rotating tools and particularly to turbine driven medical or dental handpieces.  
       BACKGROUND OF THE INVENTION  
       [0002]     Numerous handpieces for rotating tools exist. Turbine driven handpieces are widely used in dental offices and medical labs around the world. Most handpieces include a handle portion, a connector at one end of the handle portion and a tool carrier drive head at the other end. The connector provides a connection of the handpiece to various air, water, light and power supply conduits, generally combined in a so called umbilical cord. The drive head houses a tool rotating assembly, generally composed of a tool mount or chuck, and a motor or turbine, rotatably mounted in the drive head for driving the chuck.  
         [0003]     Various different types of turbine arrangements are in use, all of which include a turbine in a turbine housing, a supply of pressurized air into the housing for driving the turbine and a set of bearings for rotatably supporting the turbine in the housing and the drive head. Since conventional dental handpieces are constructed to rotate the dental drill or burr at speeds of up to 500,000 rpm, the bearings are subject to large stress. Furthermore, asymmetrical thrust generated by drive air impinging tangentially on the turbine places additional stress on the bearings. This problem is addressed in PCT Application No. CA2003/001999 which teaches a dental handpiece including a drive head construction creating a radial inflow of turbine drive air onto the impeller blades about the whole circumference of the turbine. An annular drive air supply chamber and air vanes, shown as machined or molded integral with the drive head, serve to direct the drive air from the drive air supply chamber radially inwardly onto the turbine. Thus, drive air is supplied evenly about the turbine, providing a self-centering of the turbine by the drive air. However such a vane configuration is relatively expensive to manufacture and may affect assembly techniques, and time. Thus a need remains for a simpler structure for directing the turbine drive air radially inwardly to the turbine or a structure that facilitates manufacturing or reduces assembly time of the handpiece, especially the drive head portion.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an object of the present invention to obviate or mitigate at least one disadvantage of existing handpiece designs.  
         [0005]     In a first aspect, the present invention provides a medical or dental turbine handpiece having a handle, a drive head attached to the handle and defining a turbine housing, a turbine rotatably received in the turbine housing and a drive air supply conduit for supplying pressurized drive air to the turbine housing, including an air guide inserted into the drive head and extending about the turbine for defining a drive air supply chamber separated from the turbine housing and communicating with the drive air supply conduit, the air guide having a plurality of inlet openings for radially inwardly directing pressurized air from the drive air supply chamber into the turbine housing and onto the turbine. Preferably, the handpiece of further includes a drive air exhaust conduit for receiving drive air from the turbine housing, wherein the air guide further defines a drive air exhaust chamber separated from the turbine housing and communicating with the drive air exhaust conduit, the air guide further having a plurality of exhaust openings for allowing drive air to flow from the turbine housing into the drive air exhaust conduit.  
         [0006]     Preferably, the drive air supply chamber is an annular chamber extending substantially coaxially about the axis of rotation of the turbine. Preferably, the drive air exhaust chamber is an annular chamber extending substantially coaxially about the axis of rotation of the turbine. Preferably, the air guide is a generally cylindrical air ring substantially circumscribing the axis of rotation of the turbine. Preferably, the inlet openings are shaped inlet openings. Preferably, the exhaust openings are shaped exhaust openings. Preferably, the air guide is adapted to be removable from the drive head. Preferably, the plurality of inlet openings are evenly distributed about the axis of rotation of the turbine. Preferably, the plurality of exhaust openings are evenly distributed about the axis of rotation of the turbine. Preferably, the plurality of inlet openings and the plurality of exhaust openings are staggered with respect to one another. Preferably, the plurality of exhaust openings have a cross-sectional area larger than that of the plurality of inlet openings.  
         [0007]     Preferably, the shaped inlet openings form nozzles. Preferably, the nozzles are adapted to accelerate the drive air prior to said air impinging on the turbine. Preferably, at least one of the plurality of inlet openings is adapted to direct the turbine drive air onto the turbine in a generally radially inward direction towards the direction of rotation of the turbine. Preferably, the inlet openings are substantially circular. Preferably, the exhaust openings are substantially circular.  
         [0008]     In another aspect, the present invention provides a drive head for a medical or dental turbine handpiece defining a turbine housing adapted to rotatably receive a turbine, and a lower bearing and an upper bearing and adapted to connect to a drive air supply conduit for supplying pressurized drive air to the turbine housing, said drive head including a generally cylindrically shaped housing, having a substantially closed lower end and a substantially open upper end, and a progressively increasing bore extending from the closed end to the open end, wherein the drive head further including an air guide shoulder interposed between the lower end and the upper end adapted to receive an air guide for defining a drive air supply chamber separated from the turbine housing and communicating with the drive air supply conduit, the air guide having a plurality of openings for radially inwardly directing pressurized air from the drive air supply chamber into the turbine housing and onto the turbine.  
         [0009]     In another aspect, the present invention provides an air guide for a medical or dental turbine handpiece having a handle, a drive head attached to the handle and defining a turbine housing, a turbine rotatably received in the turbine housing and a drive air supply conduit for supplying pressurized drive air to the turbine housing, said air guide including a substantially cylindrical ring adapted to extend about the turbine for defining a drive air supply chamber separated from the turbine housing and communicating with the drive air supply conduit, the air guide having a plurality of inlet openings for radially inwardly directing pressurized drive air from the drive air supply chamber into the turbine housing and onto the turbine. Preferably, the medical or dental handpiece further includes a drive air exhaust conduit for receiving drive air from the turbine and the air guide further includes a substantially cylindrical ring adapted to extend about the turbine for defining a drive air exhaust chamber separated from the turbine housing and communicating with the drive air exhaust conduit, the air guide having a plurality of exhaust openings adapted to allow drive air to flow from the turbine into the drive air exhaust conduit.  
         [0010]     Preferably, the air guide includes an inlet portion having the inlet openings and an outlet portion having the outlet openings. Preferably, the inlet portion and the outlet portion are of unitary construction or separate component. Preferably, the inlet openings are shaped inlet openings. Preferably, the exhaust openings are shaped exhaust openings. Preferably, the air guide is adapted to be removable from the drive head. Preferably, the plurality of inlet openings are evenly distributed about the axis of rotation of the turbine. Preferably, the plurality of exhaust openings are evenly distributed about the axis of rotation of the turbine. Preferably, the plurality of inlet openings and the plurality of exhaust openings are staggered with respect to one another. Preferably, the plurality of exhaust openings have a cross-sectional area larger than that of the plurality of inlet openings. Preferably the shaped inlet openings form nozzles. Preferably the nozzles are adapted to accelerate the drive air prior to said air impinging on the turbine. Preferably, at least one of the plurality of inlet openings is adapted to direct the turbine drive air onto the turbine in a generally radially inward direction towards the direction of rotation of the turbine. Preferably, the inlet openings are substantially circular. Preferably, the exhaust openings are substantially circular.  
         [0011]     In another aspect, the invention provides a method of assembling a rotary tool drive head having a lower bearing, a turbine, an air guide, an upper bearing, and a closure, including the steps, in sequence, of providing a drive head having a turbine housing having a generally cylindrically shaped housing bore having an at least substantially closed end and an open end, and further including a lower bearing shoulder proximate to the closed end adapted to receive a lower end bearing, an air guide shoulder displaced axially towards the open end from the lower end bearing shoulder, said air guide shoulder adapted to receive the air guide, said air guide shoulder having a perimeter greater than the lower bearing shoulder, and said air guide adapted to receive an upper bearing; inserting the lower bearing into the housing bore through the open end of the housing; inserting the air guide or turbine into the housing bore through the open end of the housing; inserting the other of the air guide or the turbine into the housing bore through the open end; inserting the upper bearing into the housing bore through the open end of the head; and closing the open end with the closure. Preferably, the lower bearing, the air guide, the turbine, and the upper bearing are individually inserted into the housing bore in succession from the open end of the housing. The air guide and the turbine and the upper bearing may be pre-assembled into a sub-assembly and then the said sub-assembly is inserted into the housing bore through the open end of the housing.  
         [0012]     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
         [0014]      FIG. 1  is a perspective view of one embodiment of a dental handpiece in accordance with the present invention;  
         [0015]      FIG. 2  illustrates the shape and design of a drive head casing of one embodiment of a handpiece in accordance with the invention;  
         [0016]      FIG. 3   a - c  shows top, side, and cross-section views of the drive head casing of one embodiment of a handpiece in accordance with the invention,  FIG. 3   c  showing a cross-section through the drive head casing taken along the line A-A in  FIG. 3   b;    
         [0017]      FIG. 4  shows an axial cross-section through the drive head of one embodiment of a handpiece in accordance with the invention;  
         [0018]      FIG. 5   a - c  shows front, cross-section, and bottom views of a turbine in one embodiment of a handpiece in accordance with the invention,  FIG. 5   b  showing a cross-section through the turbine taken along the lines A-A in  FIG. 5   a;    
         [0019]      FIG. 6  illustrates a perspective view of an air guide of one embodiment of a handpiece in accordance with the invention; and  
         [0020]      FIG. 7  shows a side view of an air guide of one embodiment of a handpiece in accordance with the invention. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Generally, the present invention provides a handpiece for a rotatable tool  15  and in particular a medical or dental handpiece  10  and a method of assembling the handpiece. Although for the sake of simplicity reference is made in the following to a dental handpiece, all structural and functional features of the invention are equally applicable to medical handpieces and other handpieces for supporting high speed rotating tools.  
         [0022]     As is apparent from  FIG. 1 , one embodiment of the dental handpiece  10  in accordance with the invention includes a stem/handle portion  11 , a plug-in connection  12  for linkage with an umbilical cord (not shown) which, among other things, provides pressurized turbine drive air through a drive air supply conduit  75  and removes turbine drive air exhaust through a drive air exhaust conduit  85 , and a drive head  16  with a drive unit  20  for rotatably supporting and driving a rotatable tool  15 .  
         [0000]     Drive Unit  
         [0023]     The drive unit  20  of the dental handpiece  10  in accordance with the invention generally includes a turbine  50  ( FIGS. 3   a - c ) which is supported in a turbine housing  13  defined by a drive head casing  14 . The radial air flow turbine design requires that the drive air be supplied to the turbine  50  radially inwardly rather than tangentially. This is achieved in the illustrated embodiment in accordance with the invention by providing an air guide  100  inserted into the drive head casing  14  to define an annular drive air supply chamber  70  separated from the turbine housing  13  and communicating with the drive air supply conduit  75 . The drive air supply chamber  70  extends concentrically about the axis of rotation of the turbine  50 .  
         [0000]     Air Guide  
         [0024]     In a preferred embodiment, the air guide  100  is inserted into the drive head casing  14  about the turbine  50  to define the annular drive air supply chamber  70  and preferably also an annular drive air exhaust chamber  68 . The air guide  100  sealingly engages the drive head casing  14  and preferably other components of drive head  16  to seal the drive air supply chamber  70  from the turbine chamber  55 . Pressurized drive air is supplied to the turbine  50  from the drive air supply chamber  70  via openings  105  in the air guide  100 .  
         [0025]     Drive air from the drive air supply chamber  70  is directed by the air guide  100  radially into the turbine chamber  55  for impact with the impeller of the turbine  50 . Exhaust air from the turbine  50  is directed by the air guide  100  from the turbine chamber  55  to the drive air exhaust chamber  68 . In the preferred embodiment, the air guide  100  is in the form of an air ring  102  and is fittingly received in the drive head casing  14  to form the annular drive air supply chamber  70  and an annular drive air exhaust chamber  68 . The air guide  100  includes an inlet portion  165  and an exhaust portion  185 . Preferably the inlet portion  165  and the exhaust portion  185  are attached, or more preferably integral, but the inlet portion  165  and the exhaust portion  185  may be separate components and may differ in many ways, such as configuration or geometry. The drive head casing  14  may omit the exhaust portion  185  of the air guide  100  and be adapted to allow the drive air to flow directly from the turbine chamber  55  to the drive air exhaust chamber  68 .  
         [0026]     Preferably the air ring  102  sealingly engages an air guide shoulder  112  and a divider  120  of the drive head casing  14  to form the annular drive air exhaust chamber  68 . Although the divider  120  is shown formed with the drive head casing  14 , the divider  120  may be a separate component or components, may be formed with the air guide  100  or may be of any other configuration well known in the art to provide a drive air supply chamber  70  in cooperation with the air guide  100 . An upper bearing  27  having an upper bearing stator  151  sealingly engages the air ring  102  to form the annular drive air inlet chamber  70 . Although the inlet is shown above the outlet, one skilled in the art could appreciate that they could be reversed.  
         [0027]     A plurality of openings  105  in the form of inlet openings  107 , preferably shaped inlet openings  110  in the air ring  102  at least at two spaced-apart locations distributed about the axis of rotation direct turbine drive air from the annular drive air supply chamber  70  to radially impinge upon the turbine  50  in the turbine chamber  55 . The shaped inlet openings  110  may form nozzles  115  which direct or accelerate the drive air. A plurality of exhaust openings  109  in the form of shaped exhaust openings  132  in the air ring  102  at least at two spaced-apart locations distributed about the axis of rotation permit turbine drive air to pass from the turbine chamber  55  to the drive air exhaust chamber  68 . The shaped exhaust openings  132  may form nozzles  134  which direct or accelerate the drive air.  
         [0028]     The shaped inlet openings  110  and shaped exhaust openings  132  are collectively referred to herein as the shaped openings  140 . Preferably the air ring  102  includes a multiplicity of shaped openings  140 . More preferably the shaped openings  140  are evenly distributed about the axis of rotation of the turbine  50 . Preferably, the shaped openings  140  are distributed about the axis of rotation of the turbine  50  in a pair of staggered rows, with one row forming the shaped inlet openings  110  and the other row forming the shaped exhaust openings  132 . The shaped openings  140  may be of any desired shape to achieve the desired air flow, direction, aerodynamics and hydraulics. Preferably the shaped openings  140  are generally circular. Preferably the cross-sectional area of the exhaust openings  109  is greater than the cross-sectional area of the inlet openings  107 . The larger cross-section (for example by a larger diameter if the exhaust openings  109  and the inlet openings  107  are substantially circular) provides reduced back pressure to the turbine  50 . Preferably the shaped openings  140  have a diameter of between about 0.043″ to about 0.055″. Preferably the inlet portion  165  of the air ring  102  includes eight shaped openings  140  as shaped inlet openings  110  having a diameter of about 0.043″. Preferably the exhaust portion  185  of the air ring  102  includes eight shaped openings  140  as shaped exhaust openings  132  having a diameter of about 0.055″.  
         [0029]     The shaped openings  140  may form a passage orthogonal to the surface of the air ring  102  or may be directed in at least one direction. Preferably, the shaped openings  140  are directed at least partially tangential with respect to the turbine  50 . Preferably the shaped inlet openings  110  are directed at an angle at least partially in the direction of rotation of the turbine  50 . Preferably the shaped exhaust openings  132  are directed at an angle at least partially in the direction opposite to the direction of rotation of the turbine  50 .  
         [0030]     Preferably the air ring  102  is non-rotatably fixed in place by attachment to the drive head casing  14 , for example by a friction fit, adhesive, or other means known in the art. However, preferably, the air ring  102  is removable from the drive head casing  14 . The air ring  102  may be constructed of any suitable material. Preferably, the air ring  102  is constructed of 316 stainless steel.  
         [0000]     Progressive Cavity Drive Head  
         [0031]     In a preferred embodiment, the drive head casing  14  is configured to have a progressive cavity bore  150  having a cross-section which progressively increases from a closed end  152  (bottom end  156 ) through to an open end  154  (top end  158 ). Preferably, the closed end  152  of the drive head casing  14  is integrally formed with the drive head casing  14 , forming a generally cup-shaped drive head casing  14 . However, the closed end  152  of the drive head casing  14  may be detachably fixed to the drive head casing  14 , such as by a screwed, welded, adhesive, or other connection. As illustrated, the bottom end  156  of the drive head casing  14  is shown to be the closed end  152  and the top end  158  shown to be the open end  154 , but it would be readily apparent to one skilled in the art that the bottom end  156  could be the open end and that the top end  158  could be closed, with the cross-section of the bore  150  progressively increasing from the closed end to the open end.  
         [0032]     The bore  150  may be generally tapered or preferably have a stepped change in cross-section. Preferably, a lower bearing shoulder  160  receives a lower bearing stator  148  of a lower bearing  25 , and an air guide shoulder  112  receives the air ring  102 . The upper bearing stator  151  is supported by the air ring  102 , and a closure in the form of a cap  122  seals the drive head casing  14 . The progressive cavity bore  150  allows the assembly of the drive head casing  14  to be effected through the open end  154  in a simple and straightforward sequential manner. With the cap  122  removed, the lower bearing stator  148  may be inserted into the bore  150  through the open end  154  to rest on the lower bearing shoulder  160 , followed by the air ring  102  or turbine  50 . Preferably the air ring  102  is installed, followed by the turbine  50 . The upper bearing stator  151  is inserted and the drive head casing  14  closed by the installation of the cap  122 . Alternatively, the lower bearing stator  148 , the air ring  102 , the turbine  50 , and the upper bearing stator  151  are pre-assembled to form a sub-assembly, which is then inserted into the bore  150  through the open end  154 , and then installing the cap  122 .  
         [0033]     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.