Speed Governor For A Dental Handpiece

Abstract

A speed governor is utilized in an air driven turbine dental handpiece having both an air inlet passage to said turbine and an air release passage from said turbine. A valve is included in the inlet passage and is moved in response to the velocity or to the pressure of air from the turbine in the outlet passage. The valve includes a valve body movable between different air flow positions in response either to a spring restrained vane or to a pressure responsive piston or diaphragm, the net result being to maintain the turbine velocity reasonably constant under varying load and at or below a predetermined maximum.

Description

Dental handpieces driven by air turbines have come into widespread use and operate at relatively high speeds of rotation. A difficulty is that the turbine speed under no load is sometimes much higher than the preferred maximum turbine speed. Also the turbine speed tends to vary greatly under changing load. The dentist is usually well occupied with other things and is not able to concentrate his attention on varying the air supply to the turbine in any effective way to control the turbine; for example, to keep it at a constant speed under different loads or at least to keep it from overspeeding when the load is removed from the turbine.

The best work with a handpiece is usually accomplished when the turbine maintains its selected or predetermined speed or runs within a small range from such speed despite substantial variations in load on the turbine.

It is therefore an object of the invention to provide a speed governor for a dental handpiece which is readily utilizable with the customary air turbine and is effective automatically to maintain the turbine speed at a predetermined value or within a selected range despite variations in load on the turbine.

Another object of the invention is to provide a speed governor for a dental handpiece which is quite small in its extent and can readily be housed and positioned within a handpiece which is acceptable in shape, size and balance.

Another object of the invention is to provide a speed governor for a dental handpiece that can operate satisfactorily for a protracted period despite some disadvantageous operating conditions.

A further object of the invention is to provide a speed governor for a dental handpiece which generally affords not only an improved handpiece but also an improved speed governor.

Other objects, together with the foregoing, are attained in the embodiments of the invention described in the accompanying description and illustrated in the accompanying drawings, in which:

FIG. 1 is a side elevation of a typical handpiece constructed pursuant to the invention;

FIG. 2 is a cross-section to a greatly enlarged scale, the plane of section being indicated by the line 2--2 of FIG. 1;

FIG. 3 is a cross-section to the same scale as FIG. 2, the plane of section being indicated by the line 3--3 of FIG. 2;

FIG. 4 is a cross-section, the plane of which is indicated by the line 4--4 of FIG. 2;

FIG. 5 is a view comparable to FIG. 2, to a slightly reduced scale, showing a modified form of governor in accordance with the invention;

FIG. 6 is a view comparable to FIG. 5 showing a further modified form of governor pursuant to the invention; and

FIG. 7 is a view comparable to FIG. 5 showing another modified form of governor.

In one typical instance the speed governor for a dental handpiece is incorporated in a handpiece, preferably inclusive of a head housing 6 made in two portions divided on a central plane 7 and removably held together by fasteners 8. Secured to the headpiece is a handle tube 9 removably secured to the headpiece and of a convenient size, weight and shape for holding in the hand. Within the headpiece there is afforded a turbine wheel 11 of a convenient kind mounted to rotate in bearings 12 and 13 elastically mounted in the headpiece 6 and carrying a sleeve 14 within which a dental burr 16 can be disposed.

The turbine wheel 11 is provided with propelling air through an inlet duct 21. This conveniently is a segregated portion within the handle tube 9 and requires only a portion of the handle adequately and appropriately to confine incoming air. The air supply, from any suitable pressure source, is carried to the entrance of the inlet duct 21 by a flexible tube 22.

Air normally flows in through the duct 21 under general control of an off-on valve, not shown, and is dicharged from a nozzle 23 onto the turbine wheel 11. The inlet, pressure air impinges upon and turns around with the turbine wheel. The air, now exhaust air, finally is released or discharged from the turbine housing 6 into a discharge duct 24. This is conveniently made up of the interior volume of the handle 9 except for the inlet duct 21. The released air can emerge from the handle 9 directly to the atmosphere or, if desired, a duct (not shown) similar to the tube 22 can be attached to communicate with and extend the discharge duct 24.

With the arrangement as so far described, the air flow into and from the turbine is not controlled in fine scale and the turbine speed therefor varies substantially with the load on the burr 16 and in some cases can even attain runaway speed.

Pursuant to the invention and as shown especially in FIGS. 2, 3 and 4, I provide within the handle 9 and intersecting the inlet duct 21 a valve body 26 having portions in each of the members of the head 6 and together defining a transverse circular-cylindrical chamber in which a valve member 27 is rotatable. The valve member 27 has a passageway 28 extending therethrough. The valve member 27 can rotate between one extreme position in which the passageway 28 is in effect a straight through continuation of the duct 21 and does no throttling and another position in which the passageway 28 is transverse to the inlet duct 21 and serves to block flow in such passage. The position of the valve member 27 thus controls the amount of air flow through the duct 21 to the turbine inlet.

The valve is made responsive to characteristics of air leaving the turbine through the discharge duct 24. For that reason the valve member 27 has a shaft extension 31 connected to the radial arm 32 of a vane 33 inclusive of a paddle 34 disposed in the air exit or release path. In order to modulate the position of the vane under different conditions, there is provided a spring 36 at one end having a hook 37 joined to the paddle 34 and at the other end having a similar hook 38 mounted on a lug 39 projecting from part of the head 6.

In the operation of this device it is not usually necessary to have the valve member 27 rotate for its entire range between full open and full close. Rather, the member 27 need only rotate through a portion of the full range since the main air shut-off to the tube 22 is customarily relied upon for the stop and go conditions. In any event when there is no load on the turbine and air is flowing in through the inlet duct 21, the air travels around with the turbine and leaves the turbine wheel through the release or discharge duct 24 in a fair approximation of laminar flow. It consequently travels in the discharge duct 24 at a relatively high velocity and displaces the vane paddle 34 to the right or clockwise in FIG. 2 sufficiently to rotate the valve member against the urgency of the spring 36 so as to throttle the incoming flow and thus reduce or limit the turbine speed.

When a load is put upon the turbine and the wheel correspondingly slows down in its rotational speed then the air stream traveling around with the wheel tends to break up and take on a turbulent flow characteristic. In general the velocity of the flow in the discharge duct 24 is reduced as far as its effect on the paddle 34 is concerned. The spring 36 then tends to move the valve member 27 to open slightly so as to afford more air flow to bring the turbine back to its designed or predetermined speed. With variations in load on the turbine wheel and with variations in speed of the turbine wheel, there is a corresponding but opposite effect in the valve 27. Thus the turbine speed is kept within the desired range automatically and without attention on the part of the handpiece user.

In a somewhat comparable fashion but with different mechanism the handpiece, as shown in FIG. 5, can be provided. In general this is the same structure as shown in the preceding figures except that incoming air in a duct 41 passes through a valve body 42 having a piston valve member 43 therein movable between positions which permit or block the incoming air flow. The outflowing or released air from the turbine wheel passes into the handpiece housing 44 through a duct 46. Some air passes outwardly for release whereas some air impinges upon a pitot tube 47. This is located within the housing 44 opposite the duct 46 and extends to a chamber 48 in one end of the valve body 42.

Reciprocable within the valve body 42 is a piston 49 connected to the valve member 43 and resisted in motion in one direction by a spring 51. The spring is in a chamber 52 in the body 42. From the chamber 52 ports 53 leas to the interior of the housing 44 which is usually at or very close to atmospheric pressure.

In the operation of this device when there is no load on the turbine the incoming air spins around with the wheel and emerges from the duct 46 at a relatively high velocity. The pitot tube 47 transfers the pressure resulting from such velocity to the chamber 48 and displaces the piston 49 against the spring 51 in a downward direction, as seen in FIG. 5. Such movement of the valve member 43 tends to throttle the incoming air and to reduce the turbine speed.

When a load is impressed upon the turbine wheel and it correspondingly slows down, then the velocity of the air exiting from the passageway 46 is less and is more nearly turbulent. The pressure in the pitot tube 47 is correspondingly less and the spring 51 tends to displace the piston 49 upwardly, in FIG. 5, and to open the valve by lifting the valve member 43 in a corresponding amount. In this fashion the amount of air supplied to the turbine wheel is varied automatically in accordance with the turbine speed and particularly in accordance with air pressure resulting from the release velocity of the discharging air.

In another version of the device, as shown in FIG. 6, the construction is substantially as previously described except in this instance the inlet duct 61 leads into a valve body 62 having a passage 63 therein intersecting a cross bore 64 in which a piston valve 66 is disposed. The valve has a stem 67 joined to a flexible diaphragm 68 gripped between the body 62 and a cap ring 69. A chamber 70 between the diaphragm and the piston 66 is connected to the atmosphere through a balance tube 71.

In the operation of this device the incoming air in the duct 61 is free to travel through the body 62 and through a tube 72 into the turbine inlet nozzle 73. The air spins with the turbine and then emerges through an outlet duct 74 to the interior chamber 75 of the handpiece housing 76. The outlet to the atmosphere from the housing 76 is substantially restricted so that air discharging through the duct 74 is effective to build up a superatmospheric pressure within the housing 76.

The incoming air, if unrestricted, speeds the turbine wheel at a relatively high rate and the discharging air from the duct 74 builds up a relatively high pressure within the housing 76. This deflects the diaphragm 68 downwardly, in FIG. 6, and causes throttling of the incoming air. Thus, excessive speed of the turbine is prevented. However, when load comes onto the turbine and its speed decreases correspondingly, then the pressure of the air emanating from the discharge duct 74 is somewhat less and pressure on the diaphragm 68 is reduced. The valve 66 is correspondingly opened and additional air is supplied to maintain the turbine speed at its desired value.

In the arrangement shown in FIG. 7, most parts are similar to the FIG. 5 device in that an air supply duct 41 travels through the housing 44 to the turbine and a pitot tube 47 also is disposed within the housing. In this case, the duct and tube lead into a capsule 81 closed by a cap 82 and enclosing a reciprocating piston 83 operating in chambers 84 and 86. The pitot tube leads into the chamber 84 while the chamber 86 is open to substantially atmospheric pressure through a port 87. Integral with the piston 83 is a plunger 88 having a transverse through passage 89 controlling the air supply duct 41 and operating in a chamber 91. There is a bleed port 92 between the chamber 91 and a bleed outlet 94 to atmosphere controlled by an adjustable needle valve 93. A wrench hole 96 affords access for a tool to adjust the valve 93.

In operation, incoming air from the duct 41 passes through the passage 89 to impel the turbine. Some incoming air travels through a controlled leak around the plunger to the chamber 86 from which it readily discharges to atmosphere. Other incoming air travels through a controlled leak around the plunger 88 to the chamber 91. Exit therefrom to the atmosphere is restricted by the valve 93 in the bleed port 92. Hence, a super-atmospheric pressure is maintained in the chamber 91 during supply of high pressure air.

When the turbine tends to overspeed, the pressure in chamber 82 goes up and moves the plunger 88 downwardly to reduce the flow through the passage 89 and so slow the turbine. The plunger movement is resisted by air pressure in the chamber 91 which is sufficient also to lift the plunger and restore or augment the incoming air flow when the turbine slows down and reduces pressure in the chamber 84. In effect, the air in the chamber 91 acts as a cusion or spring and is adjustable to a desired value.

Claims

What is claimed is:

1. A speed governor for a dental handpiece comprising a head housing including an inlet duct and a discharge duct, an air turbine wheel mounted to rotate in said head housing, a handle extending from said head housing, means for supplying air through said handle and said inlet duct to the inlet side of said turbine wheel, means for releasing directly to the atmosphere air from said head housing in the vicinity of said turbine wheel, means for releasing air through said discharge duct and said handle from the discharge side of said turbine wheel, a valve in said inlet duct, means movable in position in response to released air flowing out through said discharge duct, and means in said head housing for connecting said movable means to control said valve.

2. A speed governor as in claim 1 in which said movable means is a vane in the path of air flowing in said discharge duct, and including a spring in said discharge duct for urging said vane in a direction opposite to the direction of flow of said air in said discharge duct.

3. A speed governor as in claim 1 in which said movable means responds to the pressure of air in said releasing means.