U.S. patent number 3,855,704 [Application Number 05/332,605] was granted by the patent office on 1974-12-24 for foot-operated speed control for air-driven tool.
Invention is credited to Dwight A. Booth.
United States Patent |
3,855,704 |
Booth |
December 24, 1974 |
FOOT-OPERATED SPEED CONTROL FOR AIR-DRIVEN TOOL
Abstract
A foot-operated speed control for an air-driven dental handpiece
includes a solid control block having a central vertical cavity
defining an upper piston chamber, a lower air inlet chamber, and a
restricted passage between the two chambers. An air inlet passage
extends from a surface inlet port through the control block into
the inlet chamber, and an air outlet passage extends from the
piston chamber through the control block to a surface outlet port.
A piston portion of a one-piece piston-poppet projects from an
upper opening of the piston chamber. A tapered stem portion of the
piston-poppet extends downwardly and flares outwardly from the
bottom of the piston into the restricted passage, with a lower end
of the stem in sealing engagement with a wall of such passage when
the piston is in an upper position. A foot-operated button exerts a
downward pressure directly against the top of the piston sufficient
to move the piston downwardly within its chamber, causing the
lower, sealing end of the stem to move into the air inlet chamber
so that the tapered portion of the stem at the lower end of the
restricted passage provides a variable orifice permitting air to
flow to the piston chamber and outlet passage. The effective size
of the orifice increases with the downward movement of the piston
to increase air pressure in the piston chamber and outlet passage.
Piston chamber air pressure counterbalances applied foot pressure
to determine the position of the piston-poppet and thus the outlet
pressure.
Inventors: |
Booth; Dwight A. (Portland,
OR) |
Family
ID: |
23298983 |
Appl.
No.: |
05/332,605 |
Filed: |
February 15, 1973 |
Current U.S.
Class: |
433/101;
251/63 |
Current CPC
Class: |
A61C
1/0023 (20130101) |
Current International
Class: |
A61C
1/00 (20060101); A61c 001/10 () |
Field of
Search: |
;32/DIG.3,28,22
;251/122,295,35,63 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Peshock; Robert
Assistant Examiner: Lever; J. Q.
Attorney, Agent or Firm: Klarquist, Sparkman, Campbell,
Leigh, Hall & Whinston
Claims
I claim:
1. A foot control for controlling the speed of an air-driven motor,
said control comprising:
a control block,
means defining a cavity extending into said block from an upper
surface opening thereof,
said cavity including an upper piston chamber, a lower inlet air
chamber and a narrow neck passage means interconnecting said
chambers;
means defining an inlet air passage extending through said block
into said inlet air chamber from an inlet air port at a surface
portion of said block;
means defining an outlet air passage extending from a portion of
said cavity above said inlet chamber through said block to an
outlet air port at a surface portion of said block;
and means defining a one-piece combination piston-poppet means
movable within said cavity, including a piston portion movable
within said piston chamber in sealed engagement with the walls of
said chamber and a narrower stem portion extending downwardly from
said piston portion into said neck passage and having a maximum
diameter less than the diameter of said piston portion;
said stem portion including sealing means operable to close said
neck passage means when said piston is in an upper position within
said piston chamber;
said stem portion including said sealing means being movable
downwardly into said inlet air chamber solely under foot pressure
to open said neck passage means upon downward movement of said
piston under foot pressure from said upper position and being
movable upwardly solely under air pressure acting in opposition to
said foot pressure to close said neck passage.
2. A control according to claim 1 including a foot pressure
operated piston actuator means separate from and movable relative
to said piston portion and having a contact portion adapted to
engage directly an upper surface of said piston portion upon
application of foot pressure to said actuator means.
3. Apparatus according to claim 2 wherein said piston portion has a
convexly curved upper surface engageable by said contact portion to
enable downward movement of said piston through application of foot
pressure to any surface area on an upper surface of said actuator
means.
4. Apparatus according to claim 3 wherein said actuator means
comprises a depressible actuator button and said contact portion
projects downwardly toward said piston from a central undersurface
portion of said button, said button being mounted for limited
universal movement in alignment with said piston portion, whereby
foot pressure applied to any upper surface portion of said button
causes said contact portion to engage and depress said piston
portion.
5. A control according to claim 1 wherein said stem portion
includes a tapered portion tapering outwardly in a downward
direction along said stem portion from said piston portion to said
sealing means, said tapered stem portion providing a gradually
variable orifice at the opening of said neck passage means into
said inlet air chamber upon downward movement of said piston within
said piston chamber.
6. A control according to claim 5 wherein said stem portion tapers
gradually outwardly in a downward direction from said piston
portion and terminates at a lower sealing end portion of smaller
diameter than said neck passage means and carrying said sealing
means for sealed engagement with the interior wall of said neck
passage means.
7. Apparatus according to claim 1 wherein said cavity extends
vertically through said block from said upper surface opening to a
bottom surface opening thereof, a base plate mounting said block
and means sealing said bottom surface opening against said base
plate, a housing enclosing the sides of said block and fixed to
said base plate, a single large depressible foot button separate
from and of substantially larger diameter than said piston portion
centered within and closing an upper opening of said housing and
including contact means extending downwardly from a central lower
surface portion of said button for engaging an upper surface of
said piston portion and moving said piston portion downwardly upon
application of a downward foot pressure to said button.
8. A control according to claim 1 wherein said piston and stem are
relatively sized and shaped such that air back pressure within said
piston chamber exerts a differential pressure acting upwardly
against bottom surface portions of said piston sufficient to move
said piston-poppet means upwardly to close said neck passage means
in the absence of foot-applied downward force acting against the
upper surface of said piston portion.
9. A control according to claim 1 including piston-poppet moving
means operable to move said piston-poppet means downwardly and
upwardly within said cavity to open and close said neck passage,
said moving means comprising solely a rigid depressible
footoperated actuator means in direct engagement with an upper
surface portion of said piston portion for effecting downward
movement of said piston-poppet means upon application of foot
pressure to said actuator means, and air pressure acting upwardly
against bottom surface portions of said piston-poppet means for
effecting upward movement of said piston-poppet means.
10. A control according to claim 2 wherein the foot pressure
applied to said actuator means required to effect downward movement
of said piston-poppet means within said cavity varies directly with
and is solely a function of the air pressure in said piston
chamber.
11. A manually operated fluid valve comprising:
a valve block including a valve cavity extending inwardly of said
block from a surface opening therein,
a movable valve member movable axially within said cavity solely by
manual pressure in a valve-opening direction and solely by fluid
pressure in the opposite valve-closing direction, whereby said
valve is characterized by the absence of springs for effecting
movement of said valve member,
said movable valve member including a valve piston movable axially
within a first cavity section and including piston sealing means in
fluid sealing engagement with the walls of said first cavity
section to prevent escape of fluid from said surface opening,
said movable valve member including a valve stem extending axially
from a bottom surface portion of said piston within a second cavity
section and including stem sealing means in fluid sealing
engagement with the walls of said second cavity section and spaced
axially from said piston sealing means,
said stem sealing means being movable out of fluid sealing
engagement upon movement of said piston under manual pressure in a
valve-opening direction,
a fluid inlet port in said block opening into said cavity upstream
of said stem sealing means when said stem is in sealing engagement
with said second cavity section,
a fluid outlet port in said block opening into said cavity between
said piston sealing means and said stem sealing means, whereby
movement of said piston under manual pressure in a valve opening
direction enables fluid flow from said inlet port into said valve
cavity and past said stem sealing means into said outlet port,
said stem and piston being sized such that fluid back pressure from
said outlet port acting between said piston sealing means and said
stem sealing means creates a variable differential pressure
proportional to said back pressure acting upwardly against said
piston in opposition to said manually applied pressure and tending
to move said valve member in a valve closing direction so that
manual pressure is required to open said valve.
12. A valve according to claim 11 wherein said piston and said stem
comprise a one-piece said valve member.
13. A valve according to claim 11 wherein said second cavity
section is of smaller diameter than said first cavity section and
said inlet port is in a third cavity section of larger diameter
than said second cavity section, said stem sealing means being
movable from sealing engagement with the walls of said second
cavity section into said third cavity section to enable fluid flow
past said stem sealing means upon movement of said piston in a
valve-opening direction under manual pressure.
14. A valve according to claim 11 wherein said piston is of larger
diameter than the largest-diameter portion of said stem and has a
larger bottom surface area against which back pressure acts than
any opposed upper surface portion of said stem.
15. A valve according to claim 11 wherein said stem tapers
gradually and progressively outwardly in an axial direction from
its intersection with the bottom of said piston to said stem
sealing means to provide a variable orifice within said cavity upon
variable movement of said valve member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a foot-operated speed control for
an air-driven tool and particularly for an air-driven dental
handpiece.
2. Description of the Prior Art
Conventional known foot-operated air pressure regulators for
controlling the speed of air-driven tools usually employ a poppet
or diaphragm-type valve and a system of multiple balance springs
for controlling the position of the diaphragm of poppet and thus
the outlet air pressure from the regulator. In one common type of
foot control used for controlling the speed of a dental handpiece,
there are, in addition to the foot control actuator, four separate
springs, two with separate spring caps, a piston, a separate poppet
actuated by a plunger on the piston, together with attendant O-ring
seals, all telescoped within a single valve body. This results in a
very complex interrelationship of a large number of separate parts
to achieve what is essentially a single simple object of
controlling the outlet air pressure from the device through a
variable orifice.
The use of mechanical balance springs in such controls also tends
to isolate the foot from the outlet pressure of the control, and
thus the foot is not sensitive to the speed of the controlled tool
and the control tends to be insensitive to changes in applied foot
pressure. The result is that the foot control of speed tends to be
less precise than would be desirable in many applications.
The large number of parts in conventional foot-controlled pressure
regulators require substantial assembly and service time, resulting
in high initial and maintenance costs. Such prior controls are also
more subject to malfunction than would be the case with a control
having fewer parts and complexities.
Some prior foot controls also have the disadvantage of not being
operable when pressure is applied to one particular portion of the
foot actuator button or pedal.
SUMMARY OF THE INVENTION
Principal objects of the present invention are to provide a
simplified foot control wih (1) a minimum number of separate
operational parts, (2) great sensitivity to changes in applied foot
pressures and therefore precise speed control, and (3) a
foot-operated actuator operable when pressure is applied to any
point on its foot-engaging surface.
At least some of the foregoing objects are achieved in the present
invention through the elimination of all mechanical balance springs
and the use of a single one-piece combination piston-poppet
providing a variable orifice between the inlet air chamber and a
piston chamber of the cavity.
A further feature of the invention helping to carry out the
foregoing objects is the balancing of the piston-poppet within the
cavity solely with air pressure acting at one side of the piston
and foot pressure transmitted directly into the opposite side of
the piston. The only essential moving parts are the foot actuator
itself and the single-piece piston-poppet.
Another feature of the invention which provides a precise speed
control is the design of the piston-poppet itself. The
piston-poppet is characterized by a piston moving in sealed
engagement with the walls of a piston chamber and a tapered
stemlike poppet portion extending downwardly from the piston into a
narrow passage between the piston chamber and an air inlet chamber
to seal these chambers from one another when the piston is in its
upper position. When the wide lower, sealing end of the tapered
stem is pushed into the air inlet chamber by downward movement of
the piston, the stem taper provides a variable orifice which
increases in size as the piston moves progressively downward.
A further feature of the invention is the use of air pressure in
the piston chamber when the poppet is open as an air spring to
balance the foot pressure applied directly to the upper surface of
the piston through the foot button, thus eliminating the need for
any mechanical balance spring. Since the air pressure in the piston
chamber and thus outlet air pressure increase with the size of the
orifice provided by the tapered stem, the foot pressure required to
maintain a given outlet air pressure and thus a given speed of the
controlled tool varies directly with such pressure and speed, the
operator is provided with a highly speed-sensitive control that can
be directly sensed by the foot.
The foregoing and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description which proceeds with reference to the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a perspective view of a foot control in accordance with
the invention as viewed from above the control;
FIG. 2 is a sectional view through the control of FIG. 1, taken
approximately along the line 2--2 of FIG. 1; and
FIG. 3 is a perspective view of the control block within the cover
of the device as shown in FIG. 2, with such cover removed.
DETAILED DESCRIPTION
With reference to the drawing, FIG. 1 discloses a foot control
including a circular base plate 10 fastened to a cover or housing
12 having a central opening 12a through which a depressible
foot-operated actuator button 14 projects. Cover 12 has an opening
12b in its rim through which a pair of flexible air tubes 16, 18
extends. Tube 16 extends from a source of air pressure, and tube 18
leads to an air-driven tool or to another control component for
such a tool, such as a master on-off control unit, neither of which
are shown. As shown in FIG. 2, cover 12 is of largely solid
construction to give the control considerable weight, thus reducing
its mobility when placed on the floor. The rim of the cover is
provided with an annular groove 12c which seats an elastomer bumper
ring 13.
Referring to FIG. 3, tubes 16 and 18 are connected to suitable slip
connectors 20, 22, respectively, at inlet and outlet ports 24, 26
respectively, at one side surface 28c of a solid control block 28.
Block 28 is affixed to base plate 10 centrally within cover 12.
As will be evident from FIG. 2, control block 28 includes a central
vertical cavity indicated generally at 30 passing completely
through the block from its upper surface 28a to its lower surface
28b. This cavity includes an enlarged upper piston chamber portion
32 and a lower air inlet chamber portion 34 connected by a
restricted neck passage 26. The air inlet port 24 leads into an air
inlet passage 38 which opens into the lower air inlet chamber 34.
Similarly, outlet port 26 opens into an air outlet passage 40 which
opens into a lower portion of the piston chamber 32. Inlet passage
38 can be bored in a straight line at a slight horizontal angle
directly into lower chamber 34 from inlet port 24. However, outlet
passage 40 requires three intersecting bores, including one
vertical and two horizontal, as will be evident from FIGS. 2 and 3.
The vertical bore extends upwardly into block 28 from its bottom
surface 28b and is sealed by an O-ring 41 at such surface. The
upper horizontal bore extends into the block from side surface 28c
and is closed by a cap 43 at such surface.
The lower end opening of cavity 30 is closed by base plate 10 and
air-sealed by an O-ring seal 42. However, the upper end opening of
the cavity remains open to receive a one-piece combination
piston-poppet member indicated generally at 44. The piston-poppet
includes a large piston portion 46 movable vertically within piston
chamber 32 and has an upper surface 46a normally projecting from
the flanged upper end opening of such chamber at top surface 28a of
the control block. The piston is adapted to move in sealed
engagement with the wall of the piston chamber and for this purpose
is provided with an O-ring seal at 48.
A stem-like poppet portion 50 of the piston-poppet extends
downwardly from the bottom surface of piston 46 into restricted
neck passage 36 between the piston and air inlet chambers. Stem 50
tapers or flares slightly outwardly from its intersection with the
piston to a generally cylindrical lower sealing end portion 52
provided with an O-ring seal 54 to air-seal the upper and lower
chambers from one another when O-ring 54 enters the lower end of
neck passage 36. This occurs, as shown in FIG. 2, when the piston
is in an upper position within its piston chamber.
However, downward movement of the piston through application of
downward force to its upper surface shifts O-ring 54 on lower end
52 of the poppet stem 50 into air inlet chamber 34. When this
occurs, the inversely tapered stem 50 above such lower end permits
air to flow from the inlet air chamber through neck passage 36 to
the piston chamber, with the effective size of such passage or
orifice varying with the position of the piston within its chamber.
Thus the tapered stem provides a variable orifice at the neck
passage and thus a variable pressure drop across the orifice. This
then provides a variable pressure in the piston chamber and in the
outlet passage 40 leading from such chamber.
Upper surface 46a of piston 46 is convexly curved. Foot button 14
has a central downward projection 14a on its undersurface which
engages directly upper surface 46a of the piston when the button is
depressed by the operator's foot. Although a coil spring 58 extends
between a spring seat portion of the push botton's bottom surface
and the top surface 28a of the control block, this spring serves no
operational function. Instead it merely helps center-position the
pedal with respect to the valve block and provides some resistance
to downward pressure on the foot button when the air system is
de-energized.
A small notch 60 provided at an upper inner wall portion of piston
chamber 32 serves as an air bleed passage to depressurize the
piston chamber and the outlet air passage when there is no foot
pressure on button 14. This feature prevents the air-driven turbine
of the controlled tool from coasting after the foot button is
released.
OPERATION
To operate the foot control, the air pressure system into which the
control is connected is first energized. If the system is activated
with the piston-poppet in its "up" or "off" position, it will
remain in such position until button 14 is depressed. If, however,
the air system is activated with the piston-poppet in an initial
"down" or "on" position but with no foot pressure on button 14, air
entering the air inlet chamber 34 flows through neck passage 36
past tapered stem 50 to piston chamber 32, where air pressure
acting against the bottom surface of piston 46 pushes the piston
upwardly until O-ring 54 on stem portion 52 closes neck passage 36,
cutting off air pressure to the air motor to be driven. This is the
condition of the control as shown in FIG. 2.
As the operator depresses foot button 14, the upward pressure of
spring 58 is easily overcome, and button contact portion 14a
engages convex surface 46a of the piston, no matter what part of
button 14 is depressed. Thereafter, continued foot pressure on
button 14 pushes piston-poppet 44 downwardly in its cavity 30,
closing bleed hole 60 in piston chamber 32, and shifting stem end
52 with O-ring 54 down into inlet air chamber 34 to open neck
passage 36 to air flow from lower chamber 34 to upper piston
chamber 32.
As foot pressure on button 14 continues to shift piston-poppet 44
downwardly, the effective size of the orifice defined by stem 50
and its passage 36 increases because of the reverse taper of the
stem. As the effective size of the orifice increases, the pressure
drop across the orifice decreases, and thus the pressure in the
piston chamber and the outlet passage 40 therefrom increases,
causing a corresponding increase in the speed of the air-driven
motor connected to tube 18.
At the same time, as stem 50 moves downwardly to increase the
effective size of neck passage 36, the upward pressure acting on
the bottom of piston 46 increases, requiring a corresponding
opposing foot pressure to maintain a given position of the
piston-poppet and thus a given speed. Any increase in speed desired
requires a corresponding increase in applied foot pressure
sufficient to overcome the resisting air pressure acting on the
bottom of the piston. In this sense foot pressure and counteracting
air pressure replace the usual mechanical balance springs of
conventional foot controls and make the present foot-operated speed
control directly variable with variations in applied foot pressure.
Conversely the control button, and thus the operator's foot, become
"speed sensitive."
A decrease in foot pressure causes the previously balanced air
pressure acting upwardly on piston 46 to shift the piston-poppet
upwardly, whereby the tapered stem reduces the effective size of
the orifice or opening at the bottom of neck passage 36,
consequently reducing air pressure in the piston chamber and outlet
passage until such air pressure again is in balance with the
applied foot pressure. Release of all pressure on the foot button
causes the air pressure in piston chamber to push the piston-poppet
upwardly until it returns to its upper, FIG. 2 position sealing
closed the neck passage. In this "closed" position of the
piston-poppet, residual air pressure in the piston chamber and
outlet passage is bled to atmosphere through bleed hole 60,
preventing the air-driven motor from coasting.
Having illustrated and described what is presently a preferred
embodiment of the invention, it should be apparent to persons
skilled in the art that such embodiment can be modified in
arrangement and detail without departing from the spirit and scope
of the invention. I claim as my invention all embodiments and their
equivalents that come within the true spirit and scope of the
following claims.
* * * * *