Note: Descriptions are shown in the official language in which they were submitted.
-
;3
Background and Summary
-
The high speed operation of conventional air driven
contra angle handpieces tends to accelerate bearing wear and
gives rise to a need for bearing replacement at periodic
intervals. Because of the small size of the parts and the
precision with which they must be fitted together, bearing
replacement for such dental handpieces is still commonly a
factory rebuilding operation requiring the skill of highly
trained workers. Such reconstruction is, unfortunately, rela-
tively expensive and time consuming. Since down-time for a
given handpiece depends on the availability of trained workers
capable of carrying out such reconstruction, and since the
number of such skilled workers is limited, it is not uncommon
for dentists to wait days or even weeks for factory rebuilding
of their handpieces.
Efforts have been made to simplify the rebuilding of
such handpieces so ~hat dentists might perform the work them-
selves, but such efforts have been only marginally successful.
A common approach has been to form a rigid cartridge consisting
essentially of a rotor (which includes a bur tube), a pair of
bearing assemblies, and a shell which securely locks the bear-
ings in alignment and at the proper pre-load. When replace-
ment becomes necessary, the dentist removes the cap from the
handpiece housing, withdraws the old cartridge, and replaces
it with a new self-contained cartridge unit. Some United
States Patents Nos. disclosing such a cartridge arrangement
are 3,25S,527, 2,945,299, 3,324,553, 3,084,439, and 3,411,212.
- 2 -
~,,
. .. ~ .
~523~i3
Among the disadvantages of such a rigid
cartridge system are the increased bulk caused by the
secondary shell which locks the bearings and other
cornponents in proper operating relation and the require-
ri~
ment that the cartridge be manufactured to extremely close
tolerances so that it will fit precisely in existing
housings. The result is that a system utilizing a rigid
cartridge construction to permit ield replacement is
achieved only at relatively high cost and with some dis-
lo advantages of increased bulk and weight.
To avoid the disadvantages of rigid cartridge
systems, some manufacturers have marketed replacement rotor
subassemblies in which all of the replacement parts are
carried by spindles which only support the parts until they
are mounted within a handpiece housing. ~hile such sub-
assemblies are sometimes called "cartridges", they differ
from other cartridge systems because, among other things,
no shells are utilized for rigidly securing the parts
together in fixed relation. The bulk and weight arising from
the use of a cartridge shell are therefore avoided; however,
such a system does increase the possibility that some of the
components of the replacement assembly, such as the resilient
support rings for the bearings, r,lay be shifted out of position,
become damaged (the resilient rings may be pinched or cut by
malassembly), or fail to seat properly within a handpiece
housing unless considerable care is exercised in making
the replacement.
An object of this invention is thereEore -to
overcome the aforementioned disadvantages of prior
constructions. Specifically, it is an object to provide
a system which permits quick and simple field reconstruction
of a worn handpiece at relatively low cost and with
~ ;iZ3~3
virtually no risk of misalignment or faulty assembly of the
parts.
In the system of the present invention, no rigid
cartridge is used. The combination of parts which might for
convenience be referred to as a "cartridgel' is really a sub-
assembly having at least one rotor bearing assembly and
resilient support ring therefor, the latter serving the ulti-
mate purpose of cushioning the parts and reducing sound develop-
ment in a fully assembled handpiece. The or each such resilient
ring is protected against displacement during field replacement
by protective surroundin~ elements and by the remaining com-
ponents of the rotor cartridye replacement assembly. More
specifically, the lower beariny assembly and the resilient ring
which encircles it are surrounded by a flexible plastic cup
which is adapted to seat within the lower end of the head
housing of a dental handpiece. The flexible side wall of the
plastic cup has a slight taper which not only facilitates
insertion into the handpiece housing but also insures a secure
interfit between the cup and housing. In other words, the wall
of the plastic cup is capable of flexing inwardly to a limited
extent to conform to the inside dimensions of the head housingO
Such flexure of the cup's sic1e wall is facilitated by
a multiplicity of notches which are spaced circumferentially
about the rim of the cup and which define a multiplicity of
spring fin~ers formed integrally with the cup's side wall.
The spring fin~ers surround and retain the resilient support
ring for the lower bearing assembly and, especially when the
rotor cartridge or subassembly is mounted within the housing
3a
~ . ~
~5Z36~3
of a handpiece, such fingers exert a compressive force
on the ring which serves to hold the cup, ring, and
lower bearing assembly (along with other elements such
as, for example, a wave washer) frictionally together.
The security of such frictional engagement is increased
by reason of the fact that the resilient ring tends to
bulge or expand slightly into -the notches of the cup,
thereby reducing the possibility of independent relative
movement of the parts.
In addition to the above advantages, the flexible
plastic cup also serves as a non-metallic spacer between
the lower bearing assembly and the handpiece housing and,
along with the resilient support ring, further reduces
the transmission of sound generated during operation of
the high speed handpiece.
The rotor cartridge or subassembly is part of a
larger assembly which includes a housing cap and a support
tool for holding the parts together during shipment and
storage and for inserting and securing such parts in place
when handpiece reconstruction is re~uired. The tool
includes an enlarged upper retaining element in the form
of a wrench which is keyed to the threaded handpiece cap
so that, following insertion of the rotor subassembly into
the cavity of the handpiece housing, the wrench may be
~ .
rotated to secure the threaded cap in place. The tool
also includes a spindle which extends through both the cap
and the rotor cartridge, and a lower retaining element in
the form of a sleeve which is located at the lower end of
the spindle and which holds the cap and cartridge in place
upon that spindle until such time as removal is desired.
One of the retaining elements, either the wrench or sleeve~
~L~ 5Z3~
is removabie from the spindle to permit extractiGn of
the spindle aEter the replacement rotor assembly has
been secured within the handpiece housing. In the
embodiment disclosed, the removable member is the lower
retaining element which takes the form of a plastic
sleeve frictionally secured to the lower end of the spindle.
t~ Other features, objects, and advantages of the
system of this invention will become apparent from the
specification and drawings.
Drawings
Figure 1 is a fragmentary vertical sectional
view showing the head housing of a contra angle handpiece
equipped with the rotor assembly of this invention.
..
Figure 2 is an enlarged vertical sectional
view of a complete rotor cartridge replacement assembly.
Figure 3 is an enlarged perspective view
illustrating the relationship between the rotor cartridge
replacement assembly and the head housing of a dental
handpiece.
Figure 4 is an enlarged horizontal sectional
view taken along line 4-4 of Figure 2.
~ Description of Preferred Embodiment
. .
Referring to Figure 1, the numeral 10 designates
the handle of a contra angle air-driven dental handpiece r
the handle terminating in a head housing 11 having an
enlarged threaded opening 12 at its upper end and a
centrally apertured bottom wall 13 at its lower end.
An externally threaded cap 14 is secured to the upper end
~1523~3
of the housing to retain the rotor "cartridge" 15 within
the cavity 16 of the housing. The term "cartridge" will
be used herein as a matter of convenience aIthough it will
become apparent as the specification proceeds that the
parts so designated do not constitute a rigid unitary
cartridge but are instead a subassembly of the basic com-
ponents of the handpiece which are held securely together in
operative relationship only when they are fully mounted in
a handpiece as shown in Figure l.
The handle of the handpiece includes a tube 17 for
delivering drive air to the operating mechanism~ Tube l~
carries chip-blowing air and l~a delivers water to the work
area for cooling the bur and tooth during a cutting operation
and for clearing chips from the work area. Exhaust air dis-
charged from the turbine passes into the handle through
exhaust port 19.
Figures 3 and 4 depict the rotor subassembly or
cartridge removed from head housing 11 and carried by a
supporting tool 20 along with handpiece cap 14. The tool
includes a spindle 21 which extends axially through all of
the components of the cartridge 15 and through end cap 14,
an upper retaining element 22, and a lower retaining
element 23. One of the retaining elements is secured to
the spindle while the other is only frictionally held in
, ...
place and may be removed therefrom; in the preferred
embodiment illustrated, the lower element 23, which takes
the form of a resilient plastic sleeve~ is removably fitted
upon the lower end of the spindle while the upper retaining
element 22, which takes the form of an enlarged cylindrical
knob, is more permanently secured to the spindle's upper end.
The cylindrical knob 22 has a diameter greater than cap 14
and includes two (or more) eccentrically located pins 24
~S2363
which extend beyond the knob and which are positioned to be
received within sockets 25 in cap 14. The pins therefore key
the cap 14 and the supporting tool 20 against independent
relative rotation so that the tool may be used as a torsion
wrench to screw cap 14 into place. A transverse torque bar
26 may extend through the cylindrical body 22 and project
radially beyond that body to assist a user in applying the
required force in tightening (or loosening) a handpiece cap
14. It will be noted that pins 24 project from the upper sur-
lo face of cylindrical body 22 (Figure 3) as well as downwardly
into the sockets of cap 14; hence, the tool may be used as a
wrench to remove the old cap from an existing handpiece
requiring replacement of its operating mechanism without
disturbing the rotor subassembly supported on the opposite
side of the wrench.
The supporting tool 20, cap 14, and cartridge orrotor subassembly 15 together form a unitary rotor cartridge
replacement assembly designated generally by the numeral 27
in Figure 3. The assembly 27 represents all that is required
to permit a user to replace the operating mechanism of an air-
driven dental handpiece. By inverting the assembly, the
exposed stub ends~of pins 24 are used to engage and remove
the existing cap from a handpiece requiring rotor replacement.
After the worn or damaged mecnanism is removed from head
'`- housing 11, the new rotor cartridge or subassembly 15 is
inserted into the cavity 16 of the housing in the manner
depicted in Figure 3. The new cap 14 is scre~ed into place
using tool 20 as awrench. Thereafter, the resilient sleeve 23
is removed from the lower end of the spindle (an action which
may be achieved simply by lifting the tool by means of torque
bar 26), and the tool is removed from the rebuilt handpiece.
~5;~3~3
Referring in particular to Figures 2 and 3, the
rotor cartridge or subassembly 15 comprises a turbine rotor
28, upper and lower bearing assemblies 29 and 30, resilient
support rings 31 and 32 surrounding the outer races of the
upper and lower ball bearing assemblies, respectively, a
stator ring 33 having apertures 34 for directing drive air
axially against the vanes 35 of the turbine, a cup-shaped
,_ member 36 surrounding the lower bearing assembly 30 and a
resilient support ring 32, and a wave spring 37 ~or exerting
an axial pre-load from the outer race of the lower bearing
assembly and Eor urging the cup member 36 into properly seated
condition within the cavity of the handpiece's head housing.
Rotor 28 includes a bur tube 2~a which extends through a bore
in turbine 28b, it being understood that, if desired, the
turbine and bur tube may be integrally formed. A suitable
chuck 38 extends through the axial bore 39 of the bur tube and
is threadedly adjustable within that bore for the purpose of
clamping or releasing a dental bur (not shown) which in normal
handpiece operation would be mounted within the bore 40 of
the chuck. Bore 40, including bore portion 40a, extends com-
pletely through the chuck and that bore, combined with the
upper end of bur tube bore 39, together define an opening
which extends axially and completely throug}l rotor cartridge
15. Bore portion 40a is non-circular ~s~uare) in cross
section to receive the non-circular shaft of a suitable wrench
, tnot shown) used to apply torsional force to the chuck during
tightening or loosening of the chuck.
Cap 14 is similarly provided with an opening 41 co-
axial with opening 40. As shown in Figure 2, spindle 21 may
therefore extend axially through the central opening 41 and the
openings 39 and 4~ of bur tube 28a and chuck 38, respectively.
The spindle is dimensioned to be loosely received in the passage
or opening extending througn the cartridge lS and superimposed
cap 14, such parts being retained on the spindle because of the
Z3~;~
cylindrical knob or body 22 which engages the top surface
of the cap and the retaining sleeve 23 which engages the
bottom surface o~ rotor 28.
In the particular form of turbine illustrated in
the drawings, air passes in a generally axial direction
through the turbine blades, in contrast to a construction
~~ in which air impinges on the blades in a tangential or
radial direction. The former requires a stator, as
represented by stator ring 33, whereas in the latter cases,
as in a Pelton wheel turbine, a stator may be unnecessary.
It is to be understood, therefore, that a stator as such
is not an essential element of the rotor cartridge
subassembly unless an axial-flow turbine of the general
type depicted in the drawings is utilized. On the other
hand, some means must be provided for retaining the upper
resilient support ring 31 and, as shown in the drawings
(Figure 2), ring 33 also performs that function.
Cup-shaped member 36 is formed of a tough flexible
plastic material such as nylon, although it is believed
apparent that other materials having similar properties
may also be used. The cup includes a side wall 36a and an
integral end or bottom wall 36b, the latter being provided
with a central aperture 42 to accommodate the lower end of
rotor 28 and to permit the escape of cooling (and lubricating)
air passing through the lower bearing assembly 30 and wave
washer 37. The outer corner of the cup is beveled or
rounded at 43 ~Figure 2) and the side wall 36a has an outer
surface which is slightly rusto conical in shape, sloping
gradually upwardly and outwardly at an angle x within the
range of about 1 to 5 degrees from the vertical.
1~5Z3~;i3
~ he cavity of the cup retains the wave washer or
spring 37, the lower bearing assembly 30, and the
resilient support ring 32. As shown most clearly in
Figures 3 and 4, the sloping side wall of the cup is
provided with a plurality of circumferentially-spaced
notches which extend downwardly from the top of the cup
to a level intermediate the upper and lower limits of
side wall 36a. Such notches thereby define a plurality of
upstanding flexible fingers 45 formed as integral parts of
lo side wall 36a. Resilient ring 32 is squeezed or tightly
held between such fingers and the outer race of bearing
assembly 30 with the result that portions of the ring
expand or are forced limited distances into the notches
between the fingers (Figure 4). Such limited expansion of
the resilient ring into the notches assists in holding the
ring in place, that is, in preventing relative mo~ement
between the resilient support ring 32 and the cup 36.
Each finger 45 of the cup is provided with an
inwardly projecting lip or flange 46 at its upper end for
the purpose of retaining the resilient support ring 32
against upward axial displacement with respect to the cup.
It will be observed, however, that the inner surfaces of
the lips define an opening appreciably larger than the
inside diameter of resilient support ring 32 (or the outside
'~ diameter of bearing assembly 30) so that no direct contact
between the cup and bearing assembly occurs.
As part of the rotor cartridge 15, the tapered
cup 36 performs important functions in helping to guide
the lower end of a rotor cartridge replacement assembly
into place within the cavity o the head housing of a
dental handpiece, of protecting the resilient support ring
~~ ~ ~ ~ ~~ ~ ~ ~-- ~ _ ~ ~_ __ __~ _ ____~_~_~ ~_~____ _~~_ ___ __ _____ r ___. _ . _. _ __ . .__ _ _. ~ _
~5~3~ `
32 and spring washer 37 against displacement during
such an insertion step, and of reducing the transmission
of sound and vibration from the lower bearing assembly
to the head housing during handpiece operation. The cup
also serves to protect the lower bearing assembly against
forces which might otherwise cause slight misalignment of
the upper and lower bearing assemblies, since fingers 45
are capable of flexing slightly to accommodate such
differences and absorb such forces. In addi-tion, the
slightly frusto conical configuration of the cup's outer
surface permits greater dimensional tolerances during
manufacture while at the same time insuring that the cup
will fit firmly and properly within the head cavity of a
dental handpiece, thereby permitting a reduction in
manufacturing and selling costs without reducing quality
of construction or performance.
While in the foregoing I have disclosed a
preferred embodiment of the invention in considerable
detail for purposes of illustration, it will be understood
that many of these details may be varied without departing
from the spirit and scope of the invention.
,~ ~
- 12 -
