Abstract:
A detection system for remotely determining the speed of a rotating tool tip in a pneumatic dental handpiece. A means for detecting the speed of the rotating tool tip monitors a periodic mechanical function at the pneumatic hose connected to the handpiece. The monitored periodic mechanical function serves to provide feedback that is used to control the speed of the rotating tool tip. The means for detecting the speed of the rotating tool detects a mechanical function of the rotating tool tip, which in transmitted to a controller. The controller in turn regulates the operation of an air supply valve in response to the detected mechanical function. The valve regulates the flow of air to the handpiece. By continuously adjusting the flow of air through the valve into the pneumatic hose, the speed of the rotating tool is maintained at the desired cutting speed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to apparatus for controlling the rotational speed of a pneumatic dental handpiece by detecting and monitoring a periodic mechanical function produced by the handpiece. 
       BACKGROUND OF THE INVENTION 
       [0002]    In dental treatments with current pneumatic handpieces, a tool tip or burr is rotated at a speed higher than the desired cutting speed. These speeds can be as high as 450,000 revolutions per minute (rpm). When cutting load is applied, this pneumatic system is slowed significantly, adversely affecting cutting capability. The dental practitioner must maintain a useful system speed for cutting by carefully balancing cutting load and pneumatic pressure in order to properly accomplish the cutting operation. Water is also typically provided during the cutting operation to cool the cutting surface as well as the tool surface. 
         [0003]    Knowledge of the speed of the rotating burr and/or the rotating turbine under load is desirable and necessary to control speed at a useful value. Prior art devices detect the rotating speed of a pneumatic handpiece by a magnetic resistance element, or elastic control elements assembled near the tool tip. 
         [0004]    For example, U.S. Pat. No. 5,567,154 issued to Wohlgemuth on Oct. 22, 1996, entitled “Dental Turbine Drive Having Means of Automatic Speed Control,” (the &#39;154 patent) and U.S. Pat. No. 5,496,173 issued to Wohlgemuth on Mar. 5, 1996, entitled “Dental Handpiece Having an Automatically Controlled Turbine Drive,” (the &#39;173 patent) both disclose speed control by a control element in the form of a proportional valve placed in an air turbine exhaust path that throttles open as the turbine speed is decreased due to lowered centrifugal force on an elastic element, and conversely throttles closed as the turbine speed is increased. The control element adds cost and complexity to the handpiece. Such a control element also is subject to degradation during sterilization of the handpiece. The &#39;154 patent further includes as a second element a pressure chamber that responds to changes in pressure to further support the control element. Devices incorporating these features are currently being marketed. 
         [0005]    U.S. Pat. No. 4,493,643 issued Jan. 15, 1985, to Tachibana, entitled “Dental Handpiece Having Non-contact Rotational Speed Detection Device” (the &#39;643 patent) discloses speed detection by a cylindrical rotor of magnetic material and coil windings to produce an induction pulse generator. Such detection means adds cost and complexity to the handpiece and also is subject to degradation during required sterilization of the handpiece. 
         [0006]    U.S. Pat. No. 3,865,505 issued to Flatland on Feb. 11, 1975, entitled “Speed Governor for a Dental Handpiece,” (the &#39;505 patent) discloses speed control by a proportional bypass valve placed in the turbine supply path that throttles open as the turbine speed is decreased due to lowered discharge pressure in the exhaust channel, and conversely throttles closed as the turbine speed is increased. It too is inferior because it adds cost and complexity to the handpiece, and its control apparatus is subject to degradation during sterilization of the handpiece. Devices incorporating these features are currently being marketed. 
         [0007]    These prior art methods are impractical or undesirable as they add cost to the handpiece. These devices also can require relatively large structures within the handpiece, making them difficult and uncomfortable to hold, while also leading to integration problems as a result of this bulky but required size. Depending on the design, the sensors/control elements of these prior art units also can be difficult to protect from damage during handpiece sterilization. What is desired is a detection system that remotely detects the drill speed and regulates the drill speed based on the detected drill speed. Such a system does not rely on detecting exhaust pressure to determine rotational speed. Ideally, the detection system is not subject to damage as a result of handpiece sterilization. 
       SUMMARY OF THE INVENTION 
       [0008]    A detection system remotely determines the speed of a rotating tool tip in a pneumatic dental handpiece. The present invention does not rely on a control element operated by exhaust air pressure that is installed in a handpiece. The dental handpiece has a proximal end and a distal end, the rotating tool tip, also referred to as a bur, being located at the distal end. A means for detecting the speed of the rotating tool tip monitors a periodic mechanical function at a location away from the distal end of the handpiece, such as at or within a fluid hose, such as a pneumatic hose, connected to the handpiece. The monitored periodic mechanical function is related to the rotational speed of the tool tip. The monitored periodic mechanical function serves to provide feedback that is used to control the speed of the rotating tool tip. 
         [0009]    The means for detecting the speed of the rotating tool is in communication with a controller. It detects a mechanical function associated with the rotating tool tip, which is transmitted to the controller, typically as a signal. The controller receives the signal, calculates the rotational speed of the rotating tip, compares the calculated speed to a pre-set speed range and regulates the operation of a fluid supply valve in response to the detected mechanical function by adjusting the valve to meter the flow of a drive fluid to maintain the rotational speed of the tip within the pre-set speed range. The valve thus regulates the flow of the drive fluid, preferably air under pressure, to the handpiece. By continuously adjusting the flow of the pressurized drive fluid through the valve, as required, into the pneumatic hose, the speed of the rotating tool is maintained within the desired cutting speed range. 
         [0010]    The present invention relies on a means for detecting a mechanical function related to the speed of the tip, such as a vibration, that is located in the handpiece, or within the pneumatic hose attached to the handpiece, or in a coupling positioned between the pneumatic hose and the handpiece. Thus, it does not necessarily rely on “cylindrical rotor of magnetic material” and/or coil windings to produce an “induction pulse generator,” which is difficult to sterilize. Neither does it depend upon a sensor being located within the handpiece that is susceptible to damage by sterilization. Since it is not installed in the handpiece, such as an elastic control element operated by centrifugal force, it does not require sterilization. The means for detecting speed being located remotely from the handpiece allows the handpiece size to be both smaller as well as ergonomically designed for the comfort of the user, here the dentist. Thus, the pneumatic handpiece of the present invention can duplicate the operating “feel” of more compact electric motor handpieces. Nevertheless, the present invention contemplates sensors that have high temperature capability that can survive repeated sterilizations so that they can be installed within the handpiece. 
         [0011]    Another advantage of the present monitoring and feedback system of the present invention is that increased torque and power will be delivered by the pneumatic handpiece delivered over a wider range of operating speeds during its use. 
         [0012]    Still another advantage of the present invention is that the tool tips, typically burs and diamonds, will have a longer life. Since the pneumatic motor can operate at a lower speed, the handpiece itself also should have a longer life in addition to generating less noise during free-running operation. 
         [0013]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic cross sectional view of the control system for a dental handpiece of the present invention. 
           [0015]      FIG. 2  is a schematic cross sectional view of a handpiece coupled to a supply hose using the novel coupling of the present invention. 
           [0016]      FIG. 3  is a cross-sectional view of the female assembly of the coupling of the present invention. 
           [0017]      FIG. 4  is an exploded view of the female assembly of  FIG. 3 . 
           [0018]      FIG. 5  is a cross-sectional view of the male assembly of the coupling of the present invention. 
           [0019]      FIG. 6  is an exploded view of the male insert of  FIG. 5 . 
           [0020]      FIG. 7  is a cross-sectional view of the recognition valve assembly of the male assembly of  FIG. 5 . 
           [0021]      FIG. 8  depicts the coupling with the male assembly inserted into female assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention comprises a pneumatic dental handpiece  10  coupled to a pneumatic supply hose  40 . The dental handpiece  10  has a proximal end  12 , a distal end  14  and a body  16  extending between the proximal end  12  and the distal end  14 . A handpiece head  18  is located at the distal end  14 , the head housing a rotating turbine assembly  17  into which is inserted a bur  20  or tool tip. Bur  20 , on assembly into head  18 , extends away from the distal end  14  of the handpiece  10 . Depending on the handpiece design, the bur can extend substantially parallel to an axis through handpiece  10 , the axis extending between the proximal end  12  and the body  16  of the handpiece. The bur may extend substantially perpendicular to this axis. Alternatively, the bur may extend at any angle therebetween. As shown in  FIG. 1 , the bur extends at an angle to the axis between parallel and perpendicular. The proximal end  12  of the handpiece  10  includes a handpiece coupling  22  designed to interface with a pneumatic hose coupling  32  forming a first end of pneumatic hose  40 , thereby forming an airtight joint that supplies air to the rotating turbine assembly through a drive air passageway in the handpiece extending from the proximal end to the distal end. The pneumatic supply hose  40  preferably is flexible, having a first coupling end  33  and an opposed second end  42  connected to a pressurized air supply  44  by any suitable coupling. 
         [0023]    The pneumatic supply hose  40  includes an air supply passageway  60  and an exhaust passageway  50  for providing drive air to the handpiece. An air supply control valve  100  is connected to the air supply passageway  60 , as shown for example in  FIG. 1  at the second end  42  of the supply hose  40 , to regulate the flow of drive air from air supply  44  into air supply passageway  60 . A water supply passageway  72  connected to a water supply  74  may also be included in supply hose  40 , or a separate water supply hose connected to a water supply may be provided. Drive air from air supply  44  passes through supply valve  100  into air supply tube  60  and into the handpiece  10  to drive the turbine and attached bur. The drive air is directed from the proximal end  12  of the hand piece  10 , through the handpiece to the distal end  14  where it is used to drive turbine assembly  17  and thereby tool tip  20 . Return air is then transported through the handpiece to the proximal end and then to the exhaust tube  50 , where it is exhausted remotely from the handpiece. A separate supply of pressurized air sometimes referred to as chip air, may be provided to interact with the water supply to provide a water spray through a separate chip air supply passageway  76 . A fine mist water spray can be achieved at the distal end by placing the water supply passageway  72  coaxially and within the chip air supply passageway  76 . 
         [0024]    It will be understood by those skilled in the art that while pneumatic hose  40  is shown with an air supply passageway  60  and an exhaust passage way  50 , any equivalent structure that transports drive air from air supply  44  through a valve to the handpiece  10  to drive bur  20  and then exhausts the air from the handpiece may be utilized. One such structure may include a separate air supply tube and a separate exhaust tube or port. 
         [0025]    The present invention further includes a means for detecting a mechanical function  7 . As used herein, a mechanical function is any periodic mechanical artifact that is generated by operation of the handpiece  10 . A mechanical artifact includes but is not limited to any periodic mechanical vibration of the handpiece, a pressure, an acoustic wave or an oscillation resulting from its operation. The means for detecting may also include an electrical or a magnetic speed detection means, or combination of electrical and mechanical speed detection means in the handpiece that provides an indication of rotational speed of the bur or turbine in a periodic fashion, and is used as a basis to adjust the rotational speed of the bur to attempt to maintain the speed of the bur as a load is applied to the bur. In a preferred embodiment, the mechanical function detected is the periodic vibration of the rotating tool transmitted through the handpiece, and preferred means for detecting this mechanical function is an accelerometer. However, depending upon the mechanical function monitored, the means for detecting may vary. The means for detecting can include any sensor that can detect and monitor a periodic mechanical function, such as a pressure transducer, a sound transducer, a linear variable differential transformer (LVDT), a microphone or an acoustic device for detecting acoustic transmissions from operation of the handpiece. A pressure transducer may be used to detect the mean pressure in the handpiece. Alternatively, the pressure transducer may be used to detect the difference in pressure between the inlet and outlet pressure or to detect pressure pulsations. The means for detecting may also be any means (optical or other) for detecting periodic vibrations in the handpiece, since such vibrations are indicative of the tool tip rotational speed. The means for detecting may also be an optical speed detection means to detect an optical signal from an optical signal generator associated with the rotating tool. The means for detection may also be a Hall Effect detector that uses magnetic and electrical impulses to determine rotational speed. In a Hall Effect device, a rotating magnet generates an electrical field, which field can then be detected. 
         [0026]    The means for detecting a mechanical function  70  is a detector that preferably is located in the pneumatic hose coupling  32 . However, its location is not so restricted and it may alternatively be located in the flexible supply hose  40  or in the pneumatic handpiece  10  itself, although a proximal end location  12  may be preferable when size is a consideration. 
         [0027]    In one preferred embodiment, the detector is located in a novel pneumatic hose coupling  102  depicted in  FIG. 2   a  wherein the female assembly  104  is assembled to the proximal end  12  of handpiece  10 , while the male assembly  106  is assembled to the supply hose  40 .  FIG. 2   b  is a cross-section of  FIG. 2   a  along c-c. This novel coupling  102  includes a female assembly  104  and a male assembly  106 . In  FIG. 2 , the female assembly  104  is assembled to the proximal end  12  of handpiece  10 , while the male assembly  106  is assembled to the supply hose  40 . This novel coupling  102  satisfies the prerequisites of a coupling, which include being a light weight and compact mechanism that permits quickly and properly connected the handpiece  10  to the supply hose  40 , as well as allowing the handpiece to swivel on its connection during operation to prevent the hose from twisting. In addition, coupling  102  provides an additional mechanism to ensure that the proper handpiece is coupled to the supply hose and that the turbine supply air flow is properly restricted. Stated alternatively, coupling  102  prevents the air pressure provided to handpiece  10  from exceeding a predetermined limit. Coupling  102  also can be fabricated at a significantly lower cost. In addition, because of the novel design, the male assembly can be fabricated with a significant weight reduction. This further reduces fatigue experienced by the dental professional over the course of a workday. 
         [0028]      FIGS. 3 and 4  depict female assembly  104  of coupling  102 , while  FIGS. 5 and 6  depict male assembly  106  of coupling  102 . The coupling system is particularly suited for use with a dental handpiece having a detection system that remotely monitors the rotational speed of a tip, but is not so limited. Fundamentally, coupling  102  comprises female assembly  104  having a passageway for drive air to drive the handpiece tip comprising a diameter having a predetermined axial location, and a male assembly  106  that mates to the female assembly  104  and also having a passageway for drive air to drive the handpiece tip. The male assembly  106  further comprises a movable ring  164  having a first position that blocks the drive air passageway or port  140  of the male assembly  106  when the male assembly  106  is removed from the female assembly  104 . The male assembly has a second position that retracts from the drive air passageway or port  140  when the male assembly  106  is assembled to the female assembly  104 , thereby providing an aperture of predetermined size for flow of drive air from the drive air passageway in the male assembly  106  to the drive air passageway in the female assembly  104  as a result of movement of the ring  164  due to application of an external force that moves the ring, here contact with diameter  116  in the female assembly  104 . A spring  166  biases ring  164  into the first position in which drive passageway or port  140  is closed when the external force is removed so that substantially no drive air moves through port  140 . The applied external force is sufficient to counteract the spring force and allow the ring to move to the second position in which an aperture is opened. The applied external force is selected to counteract the spring force to provide an aperture having a preselected size. This is an important aspect of the invention, since this predetermined size permits flow of a predetermined amount of air. This predetermined amount of air determines the maximum air flow, and hence air pressure that is allowed to pass to the female assembly and hence to the handpiece from the male assembly. 
         [0029]      FIG. 3  depicts a preferred embodiment of female assembly  104  assembled to the proximal end  12  of handpiece  10 , while  FIG. 4  is an exploded view of female assembly  104 . A pair of tubes  112 ,  114 , preferably stainless steel, is positioned between a front female coupler  110  and a rear female coupler  118 . As depicted in  FIGS. 3 and 4 , conduit  112  is a chip air tube and conduit  114  is a chip water tube. However, depending upon the design of the handpiece, these may be interchanged. The chip water tube  114  and the chip air tube  112  are in fluid communication with the water supply passageway and the chip air supply passageway in the handpiece. Front female coupler  110  further includes a critical diameter  116  that controls the drive air pressure delivered to the handpiece, as will become evident. Female assembly  104  includes O-ring  120  assembled in groove  130  in rear female coupler  118 . This groove  130  provides a seal between the inner diameter of the handpiece and the outer diameter of female assembly  104  at rear female coupler  118 . Rear female coupler  118  further includes a plurality of apertures  122 .  FIGS. 3 and 4  depict three apertures  122  at about 120° along diameter  132  of rear female coupler, although more apertures or as few as two apertures can be located on this diameter. Each aperture houses a bearing  124  that permit free rotation of male assembly  106  inside of female assembly  104 . These bearings are also captured in circumferential groove  172  of male insert  133 , see  FIGS. 5 and 8 , permitting female assembly  104  to be quickly connected or disconnected from male assembly  106  by application of an axial force in the appropriate direction. Leaf spring  126  retains bearing  124  in position within aperture  122 . Threaded nut  128  locks female assembly  104  within proximal end  12  of handpiece. Threaded nut may be used in conjunction with a thread adhesive applied to female assembly to provide additional safeguards to prevent the loosening of female assembly  104  within the handpiece over extended periods of time. 
         [0030]      FIG. 5  depicts a cross-sectional view of male assembly  106  of the coupling of the present invention. Male assembly  106  comprises male insert  133 , which further comprises male coupler housing  134  having an axial cavity and insert  136 , and recognition valve assembly  137 .  FIG. 6  depicts an exploded view of male insert  133 . Insert  136 , preferably made of a plastic material, but which may be made from any suitable material, is introduced into the cavity of male coupler housing  134  which engages insert  136 , preferably made from stainless steel, but which also may be made from any suitable material. Insert  136  is firmly affixed into male coupler housing  134  by any suitable means, which in the preferred embodiment is accomplished by adhesive bonding. Insert  136  includes a first end that is inserted into coupler housing  134  and a second end that includes a plurality of ports that supply air and water from supply hose  40 . These ports include chip water port  138 , drive air port  140 , and chip air port  142 . The male coupler housing  134  includes a pair of drive air seals  146 , a pair of chip air seals  148  and a chip water seal. These seals direct the flow of these fluids into the appropriate regions of female assembly  104  when the male assembly  106  is properly assembled into female assembly  104 . Male insert further includes exhaust air ports  44  to channel exhaust air from the handpiece. Electrical wiring conveniently may be channeled through these exhaust air ports  144  to other regions of the male assembly  106  or to the female assembly or to the handpiece itself. Male insert  133  further includes a sensor housing  168  to house the means for detecting a mechanical function  70 , which preferably is a sensor. Counterbore  170  accepts a brass barb from the pneumatic supply hose  40 , thereby capturing the hose to insert  136 . When insert  136  is plastic, as in the preferred embodiment, a brass hose barb deforms into the plastic forming counterbore  170  and securing the barb to the counterbore. Thus, coupling  102  conveniently provides a design that not only permits rapid assembly and disassembly of the handpiece to the pneumatic hose supply, but also provides a desirable location to house the sensor so that it can perform its monitoring/feedback function, yet can be readily removed so that it is not subject to the harsh conditions of sterilization. Other advantages of the coupling are will become evident. 
         [0031]      FIG. 7  is a detailed cross-sectional representation of recognition valve assembly  137 . In its simplest form, recognition valve assembly  137  is a body having a passageway for air that can communicate directly or indirectly with an air supply. The recognition valve assembly  137  further includes a ring  164  movable from a first position that blocks the air passageway to a second position that retracts from the drive air passageway, the second position providing an opening or aperture of predetermined size for flow of drive air from the drive air passageway of the male assembly and either directly or indirectly to the handpiece as a result of movement of the ring from a force external to the male assembly, the predetermined size of the opening providing a predetermined air flow and hence a maximum predetermined air pressure when the ring is in the second position. This maximum predetermined air pressure can be used to provide the handpiece with a pressure rating. 
         [0032]    In a preferred embodiment, assembly  137  includes a light source  160 , which is the source of light at the distal end of handpiece  10 . Light is transmitted to the distal end by a fiber optic (not shown) in handpiece  10 . Contact  162  provides an electrical connection for light source  160 . Contact  162  can be connected to a power source by wires passing through the exhaust air ports  144  as previously discussed. Recognition valve assembly  137  further includes a drive air passageway or port  140  that extend to ring  164 . This ring  164  is movable from a front position to a second position. When male assembly  106  is assembled into female assembly  104 , seals  148  and  150  direct chip air and chip water from the supply hose through the male assembly  106  and into the appropriate tubes  112 ,  114  in the female assembly  104  and then into the handpiece. Seals  146  secure the passageways so that drive air passes from supply hose  40  into drive air port  140  in male insert  132  which continues into recognition valve assembly  137 , female assembly  104  and into handpiece. 
         [0033]    Recognition valve assembly  137  and its interaction with female assembly  104  provide the further advantage of controlling the flow of air, and hence the maximum air pressure flowing into handpiece  10 . Ring  164  assembled onto recognition valve assembly  137  is movable. Spring  166  biases ring into a closed position when male assembly  106  is removed from female assembly  104 . However, when male assembly  106  is inserted into female assembly  104  by application of the appropriate axial force, ring  164  in a preferred embodiment interacts with diameter  116  in female assembly  104  as bearings  124  are forced into groove  172  of male assembly, the action moving ring  164  and overcoming the biasing force of spring  166 , thereby providing an opening for drive air flow from drive air passageway or port in male assembly  106  to drive air passageway in female assembly  104  and hence to handpiece  10 . In as much as this opening is fixed, but predetermined, the amount of air flowing through the opening is also predetermined. Since the air flow is fixed by the interaction of ring  164  of male assembly  106  with diameter  116  of female coupling, the drive air flow is fixed, but can be modified. Thus, the coupling can provide a maximum air flow rate by controlling the interaction of ring  164  with diameter  116 . To modify the flow of air, the relationship of diameter  116  and ring  164  is modified. In a preferred embodiment, diameter  116  is machined axially either closer to the handpiece or further from the handpiece to decrease or increase the size of the opening and hence the flow of air. Alternatively, the location of ring  164 , the size of ring  164  or the geometry of ring  164  can be modified so that interaction with diameter will increase or decrease the size of the opening. In this way, the coupling can provide a maximum pressure rating for a handpiece. Thus, a handpiece can be provided with a coupling that rates the handpiece based on the maximum flow of drive air through the coupling at, for example, 45 psia, 50 psia, 55 psia and so on. While the preferred embodiment envisions application of force to ring  164  by diameter  116  to move ring  164  to second position, any other method or structure that applies force to ring  164  to bias the ring to second position is contemplated. 
         [0034]      FIG. 8  depicts coupling  102  assembled, with male assembly  106  assembled into female assembly  104 . Coupling  102  is assembled into proximal end  12  of handpiece  10 , and supply hose  40  is attached to male assembly  106 . Bearings  124  are seated into groove  172 , providing the quick disconnect feature. As can be seen, seals  146 ,  148  and  150  provide pathways for drive air, chip air and chip water from supply hose  40  to handpiece  10 . Ring  164  contacts diameter  116 , moving ring  164  to create a opening  180  of predetermined size that determines the maximum predetermined air pressure of the handpiece through which drive air flows, as discussed above. A sensor or means for detecting a mechanical function  70  is housed in housing  168 , not visible in  FIG. 8 , but visible in  FIG. 5 , located in coupling  102 . 
         [0035]    The present invention also contemplates detectors located in the distal end  14  when the detector or sensor can be sealed so that sterilization can be accomplished without damaging the detector or if the detector or sensor is otherwise capable of withstanding the harsh environment of repeated sterilizations. The detector can be unsealed if it is resistant to degradation due exposure to the fluids and temperatures used in the required sterilization procedures. The detector  70  is in communication with a controller  90 . The signal detected by detector  70  is a periodic signal indicative of the rotational speed of tool tip  20  or air turbine assembly  17  that is transmitted to the controller  90 . Although detector  70  is depicted as wired to controller  90  by means of embedded sensor wire leads  80 , as shown in the accompanying  FIG. 1 , the present invention contemplates wireless communication between the detector  70  and the controller  90 , such as by transmission of RF signals as is well known. 
         [0036]    Controller  90  may include a signal conditioner  92 , which conditions and amplifies the signal received from detector  70 , an optional analog to digital (ND) converter  94 , that converts an analog signal to a digital signal if the signal transmitted by the detector  70  is not digital, a digital signal processor  96 , and a scaled analog output  98 . Controller  90  is in communication with air supply valve  100 , which is preferably an electronically controlled air supply valve. Such a valve can be controlled with a solenoid, for example. The output of the controller opens and closes the valve as required to maintain the speed of the tip within a predetermined range. Increasing or decreasing the amount of air from the air supply through air supply valve  100  increases or decreases the speed of the tip, which airflow is controlled by the feedback from detector  70 . Since the speed of the bur is monitored by the sensor or detector  70 , which is then used to vary the drive air from the air supply via controller  90  to maintain the bur or air turbine at a substantially constant speed, the result is a closed loop speed control system. 
         [0037]    In a preferred embodiment, the closed loop control of a pneumatic dental handpiece is accomplished by sensing a periodic mechanical function of the handpiece indicative of the rotational speed of the tool tip, vibrations, generated by operation of the rotating tool tip  20  via a detector  70 , such as an accelerometer, mounted in the hose coupling  32 . The signal generated is delivered to the signal conditioner by wire leads  80  fed within the supply hose  40  back to the location of the supply valve  100 . The conditioned signal then is filtered or narrowed to oscillations within the expected operating range of the instrument, and converted into a digital approximation. Within the controller  90 , and specifically by digital signal processor  96 , a Fourier Transform of the digital signal is calculated, and the fundamental frequency corresponding to rotational speed is selected via a logic algorithm. This rotational speed is compared against a pre-set operating speed target to calculate a proportional adjustment of the supply valve  100  to meter the proper volume of air through it. 
         [0038]    The handpiece of the present invention that includes the closed loop control, when fitted with a coupling  102  provides the advantages of having a sensor that is readily removable so that the sensor is not subject to failure due to exposure to the harsh conditions of sterilization. Furthermore, if the sensor should fail, it is housed in male insert  133 , so that the male insert can be removed from the hose assembly and replaced with a new male insert. Alternatively, the sensor  170  can be removed from the sensor housing  168  and replaced. Coupling permits the handpiece to be rated based on a maximum pressure, which somewhat simplifies the operation of the fluid supply valve in response to the detected mechanical function. By incorporating the maximum pressure rating of the handpiece, the algorithm can also limit the maximum pressure required from the fluid supply valve, simplifying the feedback to the fluid supply valve. Even if the algorithm does not provide this control, the mechanical features of the coupling will automatically control the air flow. In addition, the preferred coupling provides a quick disconnect feature, allowing the separation of the handpiece  10  from the pneumatic hose supply  40 . Furthermore, the separation can be accomplished by the unique design of the male assembly and female assembly without having to close the supply of air from the supply hose. 
         [0039]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.