Abstract:
An automatic drive circuit for an ultrasonic probe, such as a dental scaler insert, is operative with a probe which includes a magnetostrictive unit and a vibratory element to be set into vibration by the magnetostrictive unit upon energization of the magnetostrictive unit with an alternating magnetic field. An energizing coil is enclosed within a handle having a compartment for receiving the probe. The coil is located within the handle adjacent to the probe-receiving compartment for applying the alternating magnetic field to the magnetostrictive unit upon insertion of the probe into the handle and upon energizing the coil by the drive circuit. An oscillator of the drive circuit is coupled to the coil for applying an oscillatory current to the coil. The drive circuit includes a frequency sensor for sensing a frequency of the oscillatory current, the sensor outputting a signal designating a magnitude of the frequency. A further component of the drive circuit establishes a value of amplitude of the alternating current in response to the sensed value of the frequency. The circuitry relies on the inductance introduced via the magnetostrictive unit to the coil for automatically establishing the value of oscillation frequency commanded by the probe.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a circuit for driving an ultrasonic scaling probe suitable for use in dentistry, primarily for removal of plaque, cements, composites, etc. The invention utilizes an automatically tuned drive circuit. 
     Electronic circuits have been employed for driving ultrasonic dental scalers. By way of example. Sharp (U.S. Pat. No. 5,451,161) discloses such a circuit operative with a scaler insert for a hand piece of a dental scaler unit. The circuitry produces an oscillation at a frequency established by the insert, and employs the energizer coil of the hand piece as a feedback coil for operation of the circuit. Different scaler inserts are operative at different frequencies and, accordingly, the circuitry includes a manual switching of capacitors to adjust oscillation frequency. 
     As a further example, German patent 3,136,028 also employs the energizer coil as a part of a feedback portion of an oscillator circuit. Multiple frequencies of oscillation are obtained by use of a variable resistor and capacitor as a part of the oscillator circuit. Also, Sharp (U.S. Pat. No. 5,730,594) discloses a switch which operatively switches between an automatic tuning and a manual tuning of an oscillator circuit for the driving of the dental scaler. 
     The foregoing circuits suffer from the disadvantage of requiring manual intervention in the operation of the drive circuit to establish a specific frequency of operation as may be required by the specific choice of a scaler insert for the hand piece. In addition, the foregoing circuits, while providing for the capacity of enabling different frequencies of operation, do not have a facility for automatically establishing a desired amplitude of drive signal for the scaler insert as a function of the operating frequency, or even maintaining a constant amplitude throughout an operating frequency range of the drive circuit. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome and other advantages are provided by an automatic drive circuit for an ultrasonic probe wherein the probe includes a magnetostrictive unit and a vibratory element to be set into vibration by the magnetostrictive unit upon energization of the magnetostrictive unit with an alternating magnetic field. An energizing coil is enclosed within a handle, the handle having a compartment for receiving the probe. The coil is located within the handle adjacent the probe-receiving compartment for applying the alternating magnetic field to the magnetostrictive unit upon insertion of the probe into the handle and upon an energizing of the coil by the drive circuit. 
     In accordance with the invention, an oscillator of the drive circuit is coupled to the handle coil for applying an oscillatory current to the magnetostrictive element. The drive circuit includes a frequency detector for sensing the frequency of the magnetostrictive element. The detector&#39;s output signal designates a magnitude of the frequency. A component of the drive circuit establishes a value of amplitude of the alternating current in response to the sensed value of the frequency. The automatic circuit relies on the current introduced via the magnetostrictive element to a tapped coil for automatically establishing the value of oscillation frequency commanded by the probe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The aforementioned aspects and other features of the invention are explained in the following description, taken in connection with the accompanying drawing figures wherein: 
     FIG. 1 is an electrical schematic diagram of the drive circuit constructed in accordance with the invention; 
     FIG. 2 is a graph showing output voltage of the drive circuit as a function of insert performance for different frequency inserts; and 
     FIGS. 3 a  and  3   b  are graphs of waveforms of an output signal of the drive circuit with and without the presence of an insert. 
     Indentically labeled elements appearing in different ones of the figures refer to the same element but may not be referenced in the description for all figures. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a drive circuit  10  comprising an oscillator  12 , a power supply  14 , a frequency detector  16 , a sensor  72  and a timer  74 . The power supply  14  outputs power to the oscillator  12  between positive voltage terminal  18  and ground  20 . The oscillator  12  comprises two transistors Q 1  and Q 2 , three diodes D 1 , D 2  and D 3 , handle coil L 1 , one inductor L 2  and one tapped coil L 3 , four capacitors C 1 , C 2 , C 3  and C 5  and resistor R 1 . The tapped coil L 3  is center tapped to ground. One section, L 3 . 1 , of the tapped coil L 3  is connected between the emitter  22  of the transistor Q 2  and ground, and the second section L 3 . 2  of the tapped coil L 3  is connected in series with the capacitor C 1  between ground and the base  24  of the transistor Q 1 . 
     Resistor R 1  connects between the base  24  of transistor Q 1  to the terminal  18  of the power supply  14  for supplying base current to the transistor Q 1 . The emitter  26  of transistor Q 1  supplies base current to the base  28  of the transistor Q 2 , whereby the transistors Q 1  and Q 2  are connected as a Darlington pair. The diode D 1  is connected in back-biased manner between the emitter  26  and the base  24  of the transistor Q 1 . The diode D 2  is connected in back-biased manner between the emitter  22  of the transistor Q 2  and the base  24  of the transistor Q 1 . The handle coil L 1  connects the power supply terminal  18  to the collector  30  of the transistor Q 1  as well as to the collector  32  of transistor Q 2  for application of DC power to the transistors Q 1  and Q 2 . By way of example, the transistors Q 1  and Q 2  are shown as NPN type transistors. 
     The handle coil L 1  is carried within a handle  34 , and is connected to the oscillator  12  via contacts  36   a  and  b  of an interconnecting electric cord between the handle  34  and the drive circuit  10 . The oscillator  12  develops an oscillatory current which flows through the handle coil L 1 . An insert, constructed as a probe  38  having a vibratory tip  40  connected to a magnetostrictive element  42 , is inserted within a compartment  44  of the handle coil. The location of the compartment  44  relative to the handle coil L 1  allows for coupling of the magnetic field of the handle coil L 1  to the magnetostrictive element  42 . Thereby, an oscillating magnetic field produced within the handle coil L 1  by the current of the oscillator  12  is coupled into the magnetostrictive element  42  to produce therein vibratory movement which is coupled to the tip  40 . The handle coil L 1  with the probe  38  serves as a load for the oscillator  12 , and extracts power therefrom during operation of the oscillator  12 . The electric power outputted by the oscillator  12  is converted to mechanical vibratory power of the probe  38 . The insert, or probe  38 , is readily extracted from the compartment  44  by a dentist, or other user of the insert, to be replaced by some other insert as may be required to perform a specific task. 
     In the operation of the oscillator  12 , the inductance of the tapped coil section L 3 . 2  resonates with the capacitance of the capacitor C 1  in a feedback path which couples alternating current from the emitter circuit of the transistor Q 2  to the base  24  of the transistor Q 1 . This induces oscillation within the oscillator  12 . The Darlington pair of the transistors Q 1  and Q 2  presents a much higher impedance and signal amplification to the feedback path of tapped coil section L 3 . 2  and capacitor C 1  than would be provided by either one of the transistors Q 1  and Q 2  by itself. This increases the effect of gain of the feedback circuit and enlarges the frequency range of oscillation. The diodes D 1  and D 2  are in a state of nonconduction when the voltage at the base  24  of the transistor Q 1  becomes positive relative to the voltage at the emitter  22  of the transistor Q 2 . Current flows through the diodes D 1  and D 2  when the voltage at the base  24  of the transistor Q 1  becomes negative relative to the voltage at the emitter  22  of the transistor Q 1 . Therefore, during one portion of an oscillatory cycle of current in the tapped coil L 3 , current flows through the transistor Q 2  while, during reverse flow of current through the tapped coil L 3 , the a second portion of the oscillatory cycle, the current of the tapped coil L 3  flows through the diode D 2 . 
     The total of the collector currents of the transistors Q 1  and Q 2  flows through the handle coil L 1 . Thereby, the inductance of the handle coil L 1  plays a role in the turning of the oscillator  12  to oscillate at a specific oscillation frequency. The inductance of the handle coil L 1  and probe  38  is dependent, in part, on the amount of the magnetostrictive material present in the magnetostrictive element  42 . Therefore, upon interchange among the inserts, as by exchanging one probe  38  for another probe  38 , there is a change in the amount of the magnetostrictive material with a corresponding shift in the oscillation frequency of the oscillator  12 . By way of example, it is desirable to employ oscillation frequency of 25 kHz (kilohertz) and 30 kHz. Thus, in accordance with a feature of the invention, this shift in frequency is obtainable by simply interchanging probes. 
     In order to provide for a circuit wherein oscillatory current of the handle coil L 1  is able to flow, thereby to avoid generation of spikes and to absorb other irregularities in the inductor current, the capacitor C 2  is connected in parallel to the inductor L 2  to form a tank circuit which is connected to terminal  18  and, via the diode D 3  to the collector terminals of the transistors Q 1  and Q 2 . The diode D 3  is normally back-biased. The capacitance of the capacitor C 2  and the inductance of the inductor L 2  also produce a resonance which, in combination with the inductance of the handle coil L 1  and probe  38  and in combination with the inductance of the tapped coil L 3  and the capacitance of the capacitor C 1 , is operative to establish the frequency of oscillation. The direction of forward conductance in the diode D 3  provides a path for the flow of current in the handle coil L 1  during such part of the oscillation cycle wherein the transistors Q 1  and Q 2  are rendered nonconductive. 
     The foregoing operation of the oscillator  12  provides for energization of the handle coil L 1  with alternating current (AC) at the frequency established by the characteristics of a selected probe  38 . The operator holds the handle  34  to direct the probe  38  to a desired location wherein work is to be performed. 
     A characteristic of the oscillator  12 , as well as of other oscillator circuits of the prior art is depicted in FIG. 2 which shows that the insert&#39;s performance depends upon Power Supply  14  voltage. In particular, in the case of oscillator  12 , for the same insert&#39;s performance Power Supply  14  provides greater output voltage for a 25 kHz insert than for a 30 kHz insert. 
     In order to insure that the output voltage and performance at 30 kHz is to be the same as the output voltage and performance at 25 kHz, or, generally speaking, may have any desired relationship such as being even greater than the voltage at 25 kHz, the invention provides the feature of employing the frequency detector  16  to control the power supply  14  to provide a desired output supply voltage at terminal  18  as a function of oscillation frequency. This is accomplished in the following manner. 
     A fraction of the output voltage at the node  46  is obtained via a resistive voltage divider consisting of a series circuit of resistors R 2  and R 3 , and applied to a frequency-to-voltage converter  48  within the frequency detector  16 . The converter  48  is operative to convert the oscillation frequency to a voltage level, as is depicted at graph  50 . By way of example, as shown in graph  50 , a relatively high voltage is indicative of an oscillation frequency of 25 kHz and a relatively low voltage is indicative of an oscillation frequency of 30 kHz. The voltage outputted by the converter  48  serves as a command signal for operation of the power supply  14 . 
     The power supply  14  comprises three electronic gates  52 ,  54  and  56  which are constructed as transistor gating circuits, and represented in the figure by transistors. Also included in the power supply  14  are two resistors  58  and  60 , and three potentiometers Rpc, Rp 25  and Riv. Also included in the power supply  14  are a DC—DC converter  62  and a time-delay circuit  64 . In the operation of the power supply  14 , input voltage from an unregulated power source (shown at  65 ) is applied via line  66  to the converter  62  in response to operation of a foot switch ( 67 ) by the operator. The converter  62  converts the voltage on line  66  to the desired output voltage at terminal  18 . An electronic voltage adjustment at line  68  is incorporated into the converter  62  for establishing a desired value of the voltage at terminal  18  in accordance with a value of voltage established at line  68 . 
     To illustrate operation of the power supply  14 , the adjustment voltage on line  68  appears at node  70  which connects with two of the potentiometers Rp 25  and Riv, the electronic gates  52  and  54 , and via the potentiometer Rp 25  to the electronic gate  56 . For the case of 25 kHz, the converter  48  places the electronic gate  56  in a state of conduction, thereby connecting the potentiometer Rp 25  between node  70  and ground  20 . Thereby, the two potentiometers Rp 25  and Riv are connected in parallel, such that the potentiometer Riv is available for presetting the initial voltage at the node  70 , utilizing at 30 kHz probe  38 . The potentiometer Rp 25  is available for initial adjustment of the voltage outputted by the converter  62  at terminal  18 , using a 25 kHz probe  38 . In the case of the 30 kHz probe  38 , the converter  48  places the electronic gate  56  in a state a noncondition, thereby disconnecting the potentiometer Rp 25  so that the output voltage of the converter at terminal  18  is established by the setting of the potentiometer Riv. It is noted also that the voltage appearing at node  70  is obtained also in conjunction with the series connection of the potentiometer Rpc, the resistor  60  and the electronic gate  52  between the terminal  18  and the node  70 . In addition, there is a contribution to the voltage at the node  70  by the series connection of the resistor  58  and the electronic gate  54  between the terminal  18  and the node  70 . 
     In accordance with a further feature of the invention, there is provided a manual power adjustment via the potentiometer Rpc which may be located at a point of convenience, such as on a front panel of the electronic assembly of the drive circuit  10 . This potentiometer enables the user to increase or decrease voltage online  68  for a corresponding adjustment of voltage at terminal  18 . However, in order to insure that the proper voltage is present initially, there is provided an initial delay before the manual control of the potentiometer Rpc becomes effective. 
     A time delay of approximately 0.1 second is established when the foot switch turns on the drive circuit  10 . During this delay, a timing signal T 2  is provided by the delay circuit  64  and is applied to the electronic gate  54 , thereby placing the electronic gate  54  in a state of conduction. At this time, a timing signal T 1 , also provided by the delay circuit  64 , places the electronic gate  52  in a state of nonconduction. Thus, during this interval of time, the potentiometer Rpc is disconnected from the node  70 . However, current flows from terminal  18  via resistor  58  and the potentiometer Riv to establish a desired voltage at the node  70 . By way of example, this initial setting of the power supply  14  may provide a specific voltage at terminal  18 . 
     Further, in the operation of the power supply  14 , it is noted whether the converter  48  is requesting operation at 25 kHz or at 30 kHz, with a resulting placing of the electronic gate  56  in a state of conduction of nonconduction, as has been described above. Thereby, after the initial delay of approximately 0.1 seconds, the output voltage at terminal  18  has a desired value for operation at either the 25 kHz or 30 kHz. In particular, it is noted that the drive voltage, outputted by the oscillator  12  at node  46 , is essentially proportional to the power supply voltage at terminal  18  so that any alteration in the magnitude of the voltage at terminal  18  produces a corresponding change in the magnitude of the voltage at node  46  for driving the handle coil L 1  and the probe  38 . 
     The drive circuit  10  also includes a protective device having an operation which may be understood with reference to FIG. 3 a  and  b.  FIG. 3 a  and  b  shows the voltage at the node  46 . When the insert is present within the handle  34  as shown in FIG. 3 a,  there is a succession of positive signal pulses which include relatively small negative signal in an amplitude range of typically 0.1 to 0.2 volts. However, removal of the insert alters the balance of the inductances and capacitances of the oscillator  12  resulting in a much increased value of the negative signal, such that the negative signal have magnitudes in the range of, for example, 7 to 8 volts as in FIG. 3 b.  Capacitors C 3  and C 4  act as filters to differentiate the amplitude of negative signal to determine the absence or presence of a probe  38 . 
     The drive circuit  10  further comprises a sensor  72  of the value of the negative signal at the node  46 , and a timer  74  which is triggered by a signal outputted by the sensor  72 . Upon each detection of the occurrence of a large negative signal by the sensor  72 , the timer  74  is triggered to produce a delay of two seconds. This is accomplished by outputting a gate signal by the timer  74  having a duration of the aforementioned two seconds, the gate signal being applied to the converter  62 . The gate signal is effective to deactivate the power supply  14  during this interval of two seconds. At the conclusion of the gate signal, the power supply  14  is reactivated to energize the oscillator  12 . However, the foregoing sequence amends of the large negative signals will react earth in the event that the insert is missing from the handle. Accordingly, the foregoing operational sequence is repeated with a detection of the large negative signal by the sensor  72  and an activation of the timer  74  to deactivate the power supply  14 . The procedure is repeated until such time as the insert is replaced into the handle  34 . At this time the output voltage at terminal  18  is maintained. 
     The foregoing feature is advantageous in keeping the power supply  14  in substantially a continuous state of deactivation, other than during the occurrence of minor timer intervals associated with the intermittent negative signals. In practice, this feature enables the user to remove the insert and, in the event that the user fails to turn off the drive circuit  10 , the drive circuit  10  effectively turns itself off by not applying power to the handle coil L 1  of the handle  34 . 
     It is to be understood that the above described embodiments of the invention are illustrative only, and that modifications thereof may occur to those skilled in the art Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited only as defined by the appended claims.