Note: Descriptions are shown in the official language in which they were submitted.
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AIR DRIVEN LOW SPEED DENTAL HANDPIECE MOTORS
Field of the Invent~.on
The present invention relates to air driven dental
equipment and, more particularly, to air driven, low speed
dental handpiece motors.
Backctround of the Invention
Air driven turbines have virtually supplanted all
other types of dental handpiece drives. High speed air
driven motors are typically located in a drive head which
receives the burr or other tool. These motors reach speeds
of hundreds of thousands revolutions per minute,. However,
because the heads need to be sterilized after each use, the
operating lives of such heads are relatively short.
There remains a very significant market for so-
called "low speed" motors. Such motors are generally
located in the grip portion of the handpiece and are
connected to the burr in a drive head spaced from the motor
through a train of gears and shafts. Such low speed motors
can achieve maximum burr speeds on the order of about 20,000
to 40,000 rpm depending upon manufacturer. The speed of
such motors typically can be varied by varying the air
supplied to the motor typically through a separate foot
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pedal control coupled with the air supply. However, it is
very difficult to vary speed with such foot controls.
In addition, some air driven motors may be
provided with speed control valves which limit maximum speed
of the motors and even permit reverse rotation of such
motors. Due to the miniature size of such motors and the
use of air, high precision parts must be used. Alignment of
these parts is important to assure smooth operation, long
life and minimum air leakage for high efficiency. Moreover,
due to their small size and air drives, resolution of the
maximum speed of such motors is difficult to achieve. The
valvir_g provided to vary air flow must be sufficiently small
to fit into the handpiece with the rotor to provide a self-
contained unit.
Summary of the Invention
In one aspect the invention is an air driven
dental handpiece motor comprising a tubular outer housing
sufficiently small in diameter to enable the housing to be
gripped in one hand using only fingers of the hand; a rotor
with a plurality of vanes rotatably supported in the
housing; a sun gear coupled with one axial end of the rotor;
a plurality of idler gears; a hub rotatably supporting the
plurality of idler gears in engagement with the sun gear; a
drive shaft coupled with the hub and axially aligned with
the rotor, the drive shaft projecting axially away from the
rotor; a drive gear coupled with an end of the drive shaft
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distal to the hub; a ring gear engaged with the plurality of
idler gears, the ring gear surrounding the sun gear and the
plurality of idler gears, the ring gear including a skirt
defining central bore extending axially away from the idler
gears, the bore receiving the hub and a portion of the drive
shaft; and a bearing located between the drive shaft and the
central bore of the ring gear skirt centering the drive
shaft with respect to the ring gear during rotation of the
drive shaft.
In another aspect the invention is an adjustable
air driven dental handpiece motor comprising: a tubular
housing; a rotor with a plurality of vanes supported for
rotation within a chamber within the housing; a valve member
within the housing; a valve plate within the housing between
the valve member and the chamber, a first air passageway
extending through the valve plate to the chamber and a
second air passageway separate from the first air passageway
extending from the chamber through the valve plate to the
valve member; and the valve member having an end face
contacting the valve plate, an air supply opening through
the valve member and the end face and an air exhaust opening
spaced from the air supply oper_ing at the valve.member end
face, the air supply opening includes a central slot defined
by two circumferentially extending, concentrically located
outer and inner walls connected by radius walls at their
circumferential ends, and at least two, generally
semicircular recesses in the valve member end face, one
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recess at each circumferential end of the central slot, at
least one of the valve member and the valve plate being
rotatable within the housing.
In yet another aspect the invention is an
adjustable air driven dental handpiece motor comprising: a
tubular housing; a rotor with a plurality of vanes supported
for rotation within a chamber within the housing; a valve
member within the housing; a valve plate within the housing
between the valve member and the chamber, a first air
passageway extending through the valve plate to the chamber
and a second air passageway separate from the first air
passageway extending from the chamber through the valve
plate to the valve member; and the valve member having an
end face contacting the valve plate, an air supply opening
through the valve member and the end face and an air exhaust
opening spaced from the air supply opening at the valve
member end face, the air supply openina~ includes a central
slot defined by two circumferentially extending,
concentrically located outer and inner walls connected by
radius walls at their circumferential ends, and an outer
recess in the end face extending from a central portion of
the central slot towards a circumferential outer. perimeter
of the end face, the outer recess and the central slot
defining a pair of circumferential walls of the end face on
either side of the outer recess, the circumferential walls
extending along an outer peripheral portion of the valve end
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face, and at least one of the valve member and the valve
plate being rotatable within the housing.
Brief Description of the Drawings
The foregoing summary, as well as the following
detailed description of preferred embodiments of the
invention, will be better understood when read .in
conjunction with the appended drawings. For the purpose of
illustrating the invention, there is shown in the drawings
embodiments which are presently preferred. It should be
understood, however, that the invention is not limited to
the precise arrangements and instrumentalities shown. In
the drawings:
Fig. 1 is a quarter sectioned and partially broken
away side elevational view of an air driven dental handpiece
motor of the present invention.
Fig. 2 is a cross section taken along the lines 2-
2 of Fig. ''
Fig. 2 is a cross section taken along lines 3-3 of
Fig. 1;
Fig. 4 is an expanded, cross-sectional view of the
rear support of the rotor;
Fig. 5 is a rear elevation of the valve plate;
Fig. 6 is a front elevation of the speed
adjustment valve;
Fig. 7 is a cross section taken along the lines 7-
7 of Fig. 6;
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Fig. 8 is a cross section taken along the lines 8-
8 of Fig. 6;
Fig. 9 depicts diagrammatically the control valve
of the motor 10 in the full forward drive position;
Fig. 10 depicts diagrammatically the control valve
of the motor 10 in throttled forward drive position; and
Fig. 11 depicts diagrammatically the control valve
of the motor 10 in the closed or neutral position; and
Fig. 12 depicts diagrammatically the control valve
of the motor 10 in the throttled reverse position; and
Fig. 13 depicts diagrammatically the control valve
of the motor 10 in the full reverse drive position.
Fig. 14 is a top plan view of the motor cylinder;
Fig. 15 and 16 are side elevations of the motor
cylinder viewed about 90° in either direction from F'ig. 14
about a central axis.
Detailed Description o~ ~refer:~°::~d Embodiments
Certain terminology is used in the following
description for convenience only and is not limiting. The
words "right," "left," "lower" and "upper" designate
directions in the drawings to which reference is made. The
words "inwardly" and "outwardly" refer to directions toward
and away from, respectively, the geometric center of the
and designated parts thereof. The words "front" and "rear"
refer to the opposing burr drive end and air supply end of
the motor. The terminology includes t:he words above
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specifically mentioned, derivatives thereof and words of
similar import.
Referring to the drawings, like numerals indicate
like elements throughout. A preferred, embodiment air driven
dental handpiece motor, indicated generally at 10 is shown
in Fig. 1. A front end 10a of the motor 10 is configurated
(i.e. sized and shaped) to mate with and, preferably,
releasably engage a drive head (not depicted) holding the
burr or other tool. The rear end lOb of the motor 10 is
configured to mate with and, preferably, releasably engage a
dental handpiece air supply coupling (not depicted) either
swivel or fixed back end type couplings. The overall
construction of such motors, couplings and handpieces is
well-known in the industry.
Motor 10 includes a generally tubular outer
housing 12, sufficiently small in diameter to enable the
housing 12 to be gripped and manipulated in only one hand by
an operator using only fingers of the hand like a pen or
other writing instrument. An air driven rotor indicated
generally at 14 is rotatably supported in the housing 12 on
bearings 20, 22. Referring to Fig. 2, rotor 14 is
preferably an assembly including a central hub 15 receiving
a plurality of vanes 16 in radial slots 15a extending the
length of the hub 15 and biased outwardly by springs 17.
Referring back to Fig. 1, a pair of stub shafts 18, 19
integral with the hub 15 extend from opposite axial ends of
the hub 15 and are received in the bearings 20, 22,
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respectively. A sun gear 24 is fixedly coupled to one axial
end of rotor 14 at the free, distal end of the rotor shaft
I9, projecting through the bearing 22. Referring to Figs. 1
and 3, an idler gear carrier indicated generally at 32
rotatably supports a plurality of idler gears 30,
suggestedly three in number. Carrier 32 includes a hub 35
fixedly supporting shafts 34, which rotatably support the
idler gears 30 in engagement with the sun gear 24. Carrier
32 further includes a drive shaft 3&, which is fixedly
coupled to hub 35 axially aligned with the rotor shafts 18,
19 and which project axially away from rotor 14. A crown-
type drive gear 38 is fixedly coupled with an end of a drive
shaft 36 distal to the hub 35. Drive gear 38 is exposed to
view at the "forward" end 10a of the motor 10 within the
. open forward end of housing 12. Referring also to Fig. 3, a
ring gear 40 is engaged with the idler gears 30 and
surrounds the idler gears 30 and sun gear 24. The ring gear
40 further includes a cylindrical skirt portion 42 defining
a cylindrical bore 44 extending axially away from idler
gears 30. Skirt portion 42 and bore 44 receive and surround
the hub 35 of the idler gear carrier 32 and a portion of the
drive shaft 36. According to an important aspect of the
invention, a bearing 46 is located between the drive shaft
36 of the idler gear carrier 34 and the ring gear 40 within
the central bore 44. Bearing 46 centers the drive shaft 36
with respect to the ring gear 40 during rotation. This
reduces by at least one the total number of tolerances built
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up between the drive shaft 36 and the bearing 46 and
provides the proper gear mesh as evidenced by smooth start-
up of the motor l0 at low inlet air pressures.
Motor l0 includes a number of other components at
least one function of which is to control and direct
pressurized air through the rotor 14. These are most
conveniently identified from the rear end lOb of the motor
where the air supply is introduced arid exhausted. The rear
end lOb of the motor is defined by an end cap 60. A speed
adjustment ring 62 is rotatably mounted on the end cap 60
and retained between a step on the end cap 60 and the rear
end of housing 12. The end cap 60 retains a speed
adjustment valve 66 in motor 10. Valve 66 is coupled to
ring 62 and end cap 60 by a ball 64, which travels along a
transverse slot 602 that extends circumferentially partially
around the end cap 60 through about 140° of arc. A valve
plate 68 abuts a forward end of the speed adjustment valve
66. A forward end of the end cap 60 is located in an
annular recess provided between the valve plate 68 and the
inner bore of housing 12, fixing the valve plate 68 and end
cap 60 with the housing 12. The end cap may be threaded to
the housing 12 or press fit into the annular recess. A
forward face of the valve plate 68 abuts a rear face of a
rear end plate 70. A rear face of a cylinder 72 abuts the
forward face of the rear end plate 70. A rear face of a
forward end plate 76 abuts a forward face of the cylinder
72. End plates 70, 74 and a bore 722 of cylinder 72 define
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a chamber in which rotor 14 rotates. Referring to Fig. 3,
the bore 722 is eccentrically located in cylinder 72 while
rotor hub 15 is centrally located thereby creating a rotary
vane motor with rotor 14. The planetary arrangement
5 including idler gears 30, carrier 34 and ring gear 40
reduces the speed and increases the torque passed to drive
gear 38. The depicted motor has a top forward speed of
about 5000 RPM. The rotor, however, has a top speed of
about 20,000 RPM. A 20,000 RPM motor is supplied simply by
10 substituting drive gear 38 for sun gear 24 on the end of
rotor shaft 19 and eliminating the rotary components of
motor 10 forward of that gear.
Fig. 4 depicts in expanded form, the components
supporting the rear end of rotor 14. A spring or wave
washer 80 and spacer 82 are located between valve plate 68
and bearing 20. Spacer 82 has a central opening
sufficiently large so that the spacer 82 bears only on the
outer race of bearing 20. Another spacer 84 on shaft 18
extends between the inner race of bearing 20 and the hub 15
of rotor 14 and is biased against hub 15 by spring washer
80, which also bears upon the inner race of bearing 20.
Spring washer 80 takes up wear in the rotor support and
enables a relatively light preload (e.g. about 24 ounces) to
be maintained on bearing 20, 22 during the life of the motor
10. This promotes longer bearing life and provides smoother
motor operation. Referring back to fig. 1, an alignment pin
86 extends from cylinder 72 through rear end plate 70 and
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into the valve plate 68 and keeps those components aligned.
Another spacer 88 is provided around stub shaft 19 at the
forward end of rotor 14 between its hub 15 and the inner
race of bearing 22. This arrangement is used in both 5,000
and 20,000 RPM versions of motor 10.
Figs. 5-8 show the valve components primarily
responsible for speed adjustment and reversal of the motor
in either 5,000 or 20,000 RPM versions. Valve plate 68
has a circular outer perimeter 681 and includes a circular
10 air inlet opening 682 therethrough near the circular outer
perimeter 681 of the valve 68 and a semicircular air outlet
or exhaust opening 682 intersecting the outer perimeter 681
approximately 117° away from the inlet air opening 682.
Valve stop pins 685 and 686 are located approximately 63°
apart. A blind bore 687 receives the end of alignment pin
86. Lastly, central bore 687 is provided to assure that the
adjustable valve member 66 seats fully against the valve
plate 68 to form an air seal. The rear face of valve plate
68 depicted in Fig. 5 abuts the front face of adjustment
valve member 66 depicted in Fig. 6,
Referring to Fig. 6, adjustable valve member 66
has a generally circular outer perimeter 661. Referring to
Figs, 6 and 7, a partially circumferential recess 662
extends approximately 210° around the lower circumferential
portion of the depicted valve face and provides a
circumferential channel connecting five uniformly sides
generally a rectangularly-shaped slot 663 which extend along
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the circumferential outer surface of the valve member along
the remainder of its length and provide air outlet channels.
Ends of the recess also define stops for pins 685, 686. An
air supply opening is indicated generally at 664, is
provided along the upper circumferential portion of the
valve member 66 and is symmetric with respect to the recess
662 and slots 663. Lastly, a slot 665 which extends part
way along the length of the valve member 66 from its rear
end and which receives ball 64 coupling valve member 66 with
the speed adjustment ring 62 is indicated in phantom.
Referring to Fig. 6, the primary structure of the
supply opening 664 is a central slot 664a which is elongated
in circumferential direction and extends entirely through
the face of the adjustable valve member 66. The central
slot 664a has two circumferentially extending concentrically
located outer and inner walls. The circumferentially
extending walls are radiused at their circumferential ends.
The radial ,1~:1h of central slot 664a is approximately
0.065". The air supply opening 664 further includes two
shallow, generally semicircular recesses or lands 664b, 664c
in line with the circumferential outer and inner walls of
the central slot 664a at each circumferential end of the
slot 664a. Centers of the semicircular recesses 664b, 664c
are located just beyond the radiused circumferential ends of
the central slot 664a. Referring to Fig. 8 where it is
shown, the depth of the recess 664b is only approximately
0.020". Recess 664c has the same depth.
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Referring back to Figs. 6 and 7, deeper central
recesses 664d and 664e are provided below (radially inwardly
from) and above (radially outwardly from) the central slot
664a. The inner recess 664d is a portion of a semicircle
approximately twice the width of the central slot 664a
centered at the center of the slot 664a. The upper, outer
recess 664e extends from the central slot 664a to the outer
perimeter 661 of the valve member and has a width equal to
the diameter defining recess 664d, which is approximately 25
percent greater than the diameter of the air inlet opening
682 of the valve plate 68. Referring to Fig. 7, the depths
of recesses 664d and 664e is approximately 0.07" in the
depicted embodiment. The overall valve radius is about
0.24". Central slot 664a and central recesses 664d and 664e
define two circumferential walls or arms 664f and 6648 on
either side of outer recess 664 along the outer peripheral
portion of the valve end face. Arms 664f and 664g seal
flush against the rear face of valve plate 68.
The recesses 664b-664e and walls 664f, 664g
present a varying air supply opening geometry to the
circular air inlet opening 682 of the valve plate 68 as the
adjustable valve member 66 is rotated with respect to the
valve plate 68 and air outlet opening 684. Figs. 9-13 show
various positions of the inlet and outlet openings 682, 684
of the valve plate 68 (in phantom) with respect to the air
supply opening 664 and partial circumferential recess 662
leading to the exhaust slots 663 of the valve member 66.
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In Fig. 9, the air inlet opening 682 of the valve
plate 68 is centered over the air supply opening 664 of the
adjustable valve member 66 providing full, direct and
maximum air flow. The effective air supply orifice diameter
presented to the circular inlet air opening 682 of valve
plate 68 is preferably at least equal to or slightly greater
than the effective orifice diameter of the circular inlet
air opening 682.
Fig. 10 depicts the adjustable valve member_ 66 in
a partially throttled position. In reaching that position,
the sharp edge of the radially outwardly located wall 664f
adjoining the air inlet opening 664a almost immediately
intersects and then partially covers the air inlet opening
682 in increasing degrees. Before the air inlet opening 682
passes completely from the outer recess 664e, a portion of
the air inlet opening 682 has begun to pass over the shallow
semicircular recess 664c. As the valve 66 continues to be
rotated, the shallow semicircular recess 664c passes across
and finally completely by the air inlet opening 682 until
the position shown in Fig. 11 is reached.
In Fig. 11, the forward end face of the adjustable
valve member 66 fully covers and closes the air..inlet
opening 682 of the valve plate 68 while another portion of
the adjustable valve member 66 forward end face covers the
semicircular air outlet opening 684 of the valve plate 68.
In this position, the motor 10 is considered to be in
neutral and has insufficient air flow to turn the rotor 14.
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As the adjustable valve member 66 is rotated
further in a counterclockwise direction as shown in Figs-. 12
and 13, the semicircular outlet air apening 684 of the valve
plate 68 begins to overlap the shallow semicircular recess
664b of the air supply opening 664 while air inlet opening
682 of the valve plate 68 starts overlapping the partially
circumferential recess 664 extending to the air exhaust
channels or slots 663 along valve member 66. As a result,
air begins to flow in a "reverse" direction through the
valve plate 68 "inlet" and "outlet° openings 682 and 684 and
through the remainder of the motor 10, thereby driving the
rotor 14 in a reverse direction. Fig. 13 depicts the full
open reverse orientation of the adjustable valve member 66
and valve plate 68 with the semicircular air outlet opening
684 of the valve plate 60 centered over the central slat
664a of air supply opening 664 and the deeper recesses 664d
and 664e around that slot. Contact of stop pins with the
ends ef the partial circumferential recess 662 are shown in
Figs. 9 and 13, the full forward and reverse positions of
valve member 68.
$y way of example; at full rpm, the supply
pressure and exhaust pressure of air supply through.the
adjustable valve member might be approximately 43 psi and 10
psi, respectively to pass air at a rate of 0.85 cu. ft./min.
through the motor ZO at full 20,000 rpm (unloaded). The
effective orifice provided by the circular air inlet opening
682 of the valve plate 68 and the air supply opening 664 of
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the adjustable valve member 66 is selected to provide
approximately half of the maximum air flow (e.g. 0.42 cu.
ft./min.) when the adjustable valve 66 is positioned in the
middle position between the full throttle and neutral
positions of the valve. That effective orifice size was,
for example, about 0.035 in. The deep central recesses 664d
and 664e provide spaces where air passing through central
slot 664a can be collected from ends of the slot and be
presented directly to the valve plate inlet 682 over an area
more uniformly surrounding the inlet 682. Arms 664f and
6648 provide immediate, gross speed adjustments in the
middle ranges. Shallow recesses 664b and 664c contribute to
that adjustment. The shallow, semicircular recesses 664b
and 664c, in particular, further provide fine adjustment at
the low speed ranges formerly lacking in earlier designs of
such motor, between the mid-speed position of valve member
66 and its-neutral position.
Completing the description of the air supply
system within the motor 10, Figs. 14 through 16 depict
details of the flow channels along cylinder 72. These
channels carry air between the valve plate 68 and the rotor
chamber 722 (Fig. 2). Referring further to Fig..l4, which -
is a top plan view of the cylinder 72 as it would be
positioned within the motor 10, blind-ended inlet and outlet
channels 724, 728 are provided in the outer cylindrical
surface of the cylinder extending from the rear end towards
the forward end at roughly symmetric positions on either
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side of the center line of the cylinder 72. Referring to
Fig. 15, a pair of jet hole 725, 726 are provided
extendingly radially through the cylinder wall and into its
hollow interior forming chamber 722 at angles selected to
5. strike the vane surfaces and rotate the rotor 14 in a
"forward" direction, Terminations of the holes are shown in
phantom. Jet hole 726 is spaced circumferentially from jet
hole 725 in a circumferentially extending recess 727
projecting from inlet channel 724 to space the jet holes
725, 726 sufficiently apart to enable them to simultaneously
strike separate vanes with their jets. An exhaust slot 729
extends completely through the side wall of cylinder 72 and
circumferentially about 135° around the outer circumference
of the cylinder 72 to collect air from between a number of
adjoining vanes at the same time. Slot 729 is a straight
cut milled into the wall of cylinder 72 for ease of
manufacture, but might take other shapes. It will be
appreciated that because of the specialization of the
channels 724 and 728 to optimize "forward" rotation of the
2Q rotor 14, motor 10 does net provide the same maximum speed
and torque in a reverse direction as it does in the forward
direction.
It will be appreciated by those skilled in the art
that changes could be made to the embodiments described
above without departing from the broad inventive concept
thereof. For example, while the semicircular air supply
opening recess geometries of the adjustable valve member are
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preferred, other non-circular but curvilinear recess and
wall geometries might be used. It is understood, therefore,
that this invention is not limited to the particular
embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present
invention as defined by the appended claims.
