Patent Publication Number: US-2020297375-A1

Title: Frequency control method and system for ultrasonic surgical tool

Description:
BACKGROUND 
     Technical Field 
     The invention includes frequency controlling field, especially, a frequency controlling method and system of ultrasonic surgical instrument. 
     Description of the Related Art 
     Ultrasonic surgical instrument, like ultrasonic scalpel, phacoemulsification, and ultrasonic bone scalpel. The application of these instruments has been about 20 years. Comparing with other surgical system, these ultrasonic surgical instruments have many advantages. For instance, the ultrasonic scalpel has the advantages of less smoke, larger surgical vision, less thermal damage, simultaneous cutting, coagulation and separation, no electrical damage, self-cleaning and less sticking with tissue. 
     Ultrasonic surgical instrument, like ultrasonic scalpel, comprises ultrasonic generator, ultrasonic handpiece and ultrasonic blade; the ultrasonic generator is an electric signal source which is used to drive handpiece and blade and the blade acts on the tissue to achieve cutting and coagulation effect; this kind of cutting needs high frequency, like 55 KHz, and large vibration amplitude, like 50-100 um; the resonant frequency is easy to drift by impedance and temperature. For the high efficiency of the instrument, the driving frequency should be put at resonance around, which requires the frequency tracking function of the instrument. 
     When the system works at the resonant frequency, the phase difference of current and voltage of the instrument is zero. Normally, for the best efficiency, the phase locking point is set at zero. The frequency tracking function is usually the ability to track zero phase. But in some cases, the system doesn&#39;t exist in the zero phase. For example, in the condition of high impedance, the phase difference at resonance is lower than zero and working around a non-zero phase point may be still a good solution. When the system has the zero phase, but still leaving the system to work in the non-zero phase point makes the system inefficient. 
     BRIEF SUMMARY 
     Disclosed herein is a method and system of controlling frequency of an ultrasonic surgical instrument, in order to solve the problem of the low efficiency and instability of the surgical instrument, when the phase at the resonance frequency is less than zero. 
     For this purpose, the invention offers several embodiments:
         A method of controlling frequency of the ultrasonic surgical instrument includes:
           Obtain the maximum phase difference of the current and voltage of the ultrasonic surgical instrument;   Obtain the first determination result, by checking whether the maximum value is less than zero;   When the maximum value of the first determination result is not less than zero, tune the frequency of the ultrasonic surgical instrument to the frequency of zero phase difference;   When the maximum value of the first determination result is less than zero, tune the frequency of the ultrasonic surgical instrument to the frequency which comes from subtracting a presetting value from the maximum value.   Optionally, obtain the phase locking point from subtracting a presetting value from the maximum value, including:   According the phase locking formula:   
               

         ph _lock= ph _now− ph _delta  (1)
             to calculate phase locking point, where, ph_lock is phase locking point, ph_now is the maximum phase difference, ph_delta is first presetting value.   Optionally, ph_delta is 0-10 degree.   Optionally, after tuning the frequency of surgical instrument according the phase locking point, including:
               Obtain the current of surgical instrument;   Calculate the theoretical phase difference according to the current;   
               Tune the frequency of surgical instrument according to the theoretical phase difference.   Optionally, calculate the theoretical phase difference according working current, including:
               According to the formula:   
                       

         ph _max= a *current+ b   (2)
                 Calculate maximum phase difference, where, ph_max is theoretical phase difference, current is working current, a and b are known coefficients.       Optionally, tune the frequency of surgical instrument according to theoretical maximum phase difference, including:
               Let ph_max=ph_now, calculate the second phase difference according to the phase locking point formula;   When the second determination result is less than zero, tune the frequency of the surgical instrument to the frequency of the second phase difference;   When the second determination result is no less than zero, tune the frequency of the surgical instrument to the frequency of zero phase difference.   
               Optionally, tune the frequency of the surgical instrument according to the maximum phase difference, including:
               Obtain the third determination result according to if the theoretical maximum phase difference is less than zero;   When the third determination result is less than zero, maintain the frequency of the surgical instrument;   When the third determination result is no less than zero, tune the frequency of the surgical instrument to the frequency of zero phase difference.   
                   A method of controlling frequency of an ultrasonic surgical instrument includes:
           Obtain the phase difference of current and voltage of surgical instrument; Obtain the first determination result according to if the maximum value is less than zero;   When the maximum value of the first result is less than zero, increasing the current of surgical instrument and obtain the voltage value; when the voltage is higher than nominal voltage level, stop increasing the current; obtain the phase locking point from subtracting a presetting value from the maximum value; tune the frequency according to the phase locking point;   When the first determination result is no less than zero, tune the frequency of the surgical instrument to the frequency of zero phase difference.   
           A system of controlling frequency of an ultrasonic surgical instrument includes:
           Acquisition circuitry, for obtaining the phase difference of the current and voltage of the surgical instrument;   Determination circuitry, for determining if the maximum value is less than zero and obtaining the first determination result; The first tuning circuitry, when the result of first determination is no less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference;   The second tuning circuitry, when the result of first determination is less than zero, tune the frequency to the point coming from subtracting a presetting value from maximum value; tune the frequency of the surgical instrument according to the phase locking point.   
           A system of controlling frequency of an ultrasonic surgical instrument includes:
           Acquisition circuitry, for obtaining the phase difference of the current and voltage of the surgical instrument;   Determination circuitry for determining if the maximum value is less than zero and obtaining the fourth determination result;   The first tuning circuitry. When the maximum value of the first result is less than zero, increasing the current of surgical instrument and obtain the voltage value; when the voltage is higher than nominal voltage level, stop increasing the current; obtain the phase locking point from subtracting a presetting value from the maximum value; tune the frequency according to the phase locking point;   The second tuning circuitry. When the first determination result is no less than zero, tune the frequency of the surgical instrument to the frequency of zero phase difference.   
               

     According to the embodiments provided in the invention, the invention disclosed below technical benefits:
         The invention offers the method of controlling frequency of the ultrasonic surgical instrument. When the maximum phase difference value of the current and voltage is less than zero, preset a phase locking point below the maximum value and tune the frequency to the phase locking point. This method resolves the problem of the inability and low efficiency of the surgical instrument, when the phase difference at the resonant frequency is less than zero, which improves the stability and efficiency of the instrument.   The invention offers the method of controlling frequency of the ultrasonic surgical instrument. When the maximum phase difference value of the current and voltage is less than zero, increase the current of surgical instrument to increase the phase difference of the current and voltage to approach or exceed zero. This method resolves the problem that the inability and low efficiency of the surgical instrument, when the phase of resonant frequency is less than zero, which improves the stability and efficiency of the instrument.       

    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The described embodiments, however, both as to organization and methods of operation, may be best understood by reference to the following description, taken in conjunction with the accompanying drawings. While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will now occur to those skilled in the art without departing from the invention. 
         FIG. 1  illustrates a logic flow diagram of the first embodiment of controlling the frequency of surgical instrument. 
         FIG. 2  illustrates a logic flow diagram of the second embodiment of controlling the frequency of surgical instrument. 
         FIG. 3  illustrates a logic flow diagram of the third embodiment of controlling the frequency of surgical instrument. 
         FIG. 4  illustrates a logic flow diagram of the fourth embodiment of controlling the frequency of surgical instrument. 
         FIG. 5  is a schematic diagram of the phase locking of the surgical instrument. 
         FIG. 6  is a schematic diagram of the first embodiment of the frequency controlling of the surgical instrument. 
         FIG. 7  is a schematic diagram of the second embodiment of the frequency controlling of the surgical instrument. 
     
    
    
     DETAILED DESCRIPTION 
     Before explaining various embodiments of methods of controlling frequency of ultrasonic surgical instrument in detail, it should be noted that the illustrative embodiments are not limited in application or use to the details of construction and arrangement of parts of illustrated in the accompanying drawings and description. Basing on the embodiments of the invention, the embodiments obtained by those skilled in the art without departing from the invention is protected by the scope of the invention. 
     The purpose of the invention is to provide a method of controlling frequency of ultrasonic surgical instrument, which solves the problem of low efficiency and instability, in the case of the phase at the resonant frequency does not cross zero point. 
     Detailed description is illustrated below with drawings and embodiments. 
     Embodiment 1 
       FIG. 1  is the logic flow diagram of embodiment 1 of controlling frequency of surgical instrument. As shown in  FIG. 1 , a method of controlling frequency of ultrasonic surgical instrument, use ultrasonic scalpel as an example, includes:
         Step  101 , obtain the maximum phase difference of the current and voltage of surgical instrument.   Step  103 , when the maximum is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference. When the phase difference of current and voltage is higher than zero, it indicates the surgical instrument could work at the resonant condition which means the highest efficiency.   Step  104 , when the maximum value is less than zero, obtain the phase locking point by subtracting a presetting point from maximum value. When the phase difference of current and voltage is less than zero, the zero phase set point would not work because of the non-existed zero point.   According to phase locking formula:       

         ph _lock= ph _now− ph _delta  (1)
         Calculate the phase locking point:
           Where, ph_lock is the phase locking point, ph_now is the maximum phase difference, ph_delta is the first presetting point.   
           Step  105 , tune the frequency of surgical instrument according to the phase locking point.   The phase locking electric circuit could achieve tuning function.     FIG. 5  is the schematic diagram of phase locking, including:
           Ultrasonic surgical instrument  501 , current phase detector  502 , voltage phase detector  503 , phase discriminator  504 , controller  505  and power amplifier  506 .   The detected current and voltage signals of the surgical instrument  501  are fed to phase discriminator  504 , which sends the result to the controller  505 . The controller  505  tunes the frequency of surgical instrument according to the result. The driving signal with the corrected frequency feeds the power amplifier  506  to drive the surgical instrument  501 . This is a feedback closed loop to make sure the surgical instrument  501  working at the resonant frequency.   In the case of minus maximum phase difference of current and voltage, the invention improves the efficiency and stability of the surgical instrument through lowering the phase locking point.   
               

     Embodiment 2 
       FIG. 2  is the logic flow diagram of embodiment of controlling frequency of surgical instrument. As shown in  FIG. 2 , a method of controlling frequency of ultrasonic surgical instrument, includes:
         Step  201 , obtain the phase difference of the current and voltage of surgical instrument.   Step  202 , determine if the maximum value is less than zero.   Step  203 , when the maximum is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference.   Step  204 , when the maximum value is less than zero, obtain the phase locking point by subtracting a presetting point from maximum value.   Step  205 , tune the frequency of surgical instrument according to the phase locking point.   According to phase locking formula:       

         ph _lock= ph _now− ph _delta  (1)
         Calculate the phase locking point:
           Where, ph_lock is the phase locking point, ph_now is the maximum phase difference, ph_delta is the first presetting point. Tune the frequency of surgical instrument according to the phase locking point.   
           Step  206 , obtain the current of surgical instrument.   Step  207 , calculate the maximum phase difference according to the current.       

     Experimentally, in the same others conditions, when higher is the current, the bigger is the phase difference. And this could be estimated by the linear function: 
         ph _max= a *current+ b   (2)
         Where, ph_max is the theoretical phase maximum value, current is the electrical current, a and b are known coefficients from experiment.   Step  208 , calculate the second phase difference according to the maximum theoretical phase difference. Let ph_now=ph_max, and calculate the phase difference according the formula (1).   Step  209 , determine whether the second phase difference is less than zero.   Step  210 , when the second phase difference is less than zero, tune the frequency of the surgical instrument according to the second phase difference and raise the current. Specifically, tune the frequency of surgical instrument to the frequency with respect to second phase difference and raise the current, then return to Step  206 .   When the second phase difference is not less than zero, do Step  203 , tune the frequency of surgical instrument to zero phase difference.       

     In the embodiment, in the condition of minus phase difference of surgical instrument, determine the condition that if theoretical maximum phase difference is less than zero, through the current of surgical instrument and tune the frequency according to phase locking formula. This improves the efficiency and stability of surgical instrument. 
     Embodiment 3 
       FIG. 3  is the logic flow diagram of embodiment of controlling frequency of surgical instrument. As shown in  FIG. 3 , a method of controlling frequency of ultrasonic surgical instrument, includes:
         Step  301 , obtain the phase difference of the current and voltage of surgical instrument.   Step  302 , determine if the maximum value is less than zero.   Step  303 , when the maximum is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference.   Step  304 , when the maximum value is less than zero, set the phase locking point to a lower one, like −50 degree.   Step  305 , tune the frequency of the surgical instrument according to the phase locking point.   Step  306 , obtain the current of surgical instrument.   Step  307 , calculate the theoretical phase difference according to the current. Specifically, calculate the maximum phase difference according to formula 2.   Step  308 , determine if the maximum theoretical phase difference is less than zero.   Step  309 , when the maximum theoretical phase difference is less than zero, maintains the frequency of surgical instrument, raise the current and returns to Step  306 .   When the theoretical phase difference is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference and return to Step  303 .       

     In the embodiment, when surgical instrument works in the nonzero phase difference condition, tune the frequency of surgical instrument to the zero phase difference frequency if the maximum phase difference obtaining from current is not less than zero. When the surgical instrument works in high impedance condition which means the phase difference of resonant frequency may be less than zero, constantly forcing surgical instrument work in nonzero phase difference condition makes the low efficiency. The invention dynamically changes the set point according to the real maximum phase difference improving the efficiency of surgical instrument. 
     Embodiment 4 
       FIG. 4  is the logic flow diagram of embodiment of controlling frequency of surgical instrument. As shown in  FIG. 4 , a method of controlling frequency of ultrasonic surgical instrument, includes:
         Step  401 , obtain the phase difference of the current and voltage of surgical instrument.   Step  402 , determine if the maximum value is less than zero.   Step  403 , when the maximum is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference.   Step  404 , when the maximum is less than zero, raise the current of surgical instrument. When the voltage of surgical instrument excesses nominal voltage, stop raising current.   Step  405 , set a phase locking point by subtracting a presetting point from maximum value.   Step  406 , tune the frequency according to phase locking point       

     This embodiment realizes changing the current of surgical instrument within the limit of nominal voltage by the fact that the higher current, the bigger phase difference. This improves the maximum phase difference and the efficiency of surgical instrument. 
     The invention offers methods of frequency controlling and solves low efficiency and instability of surgical instrument in the condition of minus phase difference. 
     Embodiment 5 
       FIG. 6  is a schematic diagram of frequency controlling of surgical instrument of one embodiment. As shown in  FIG. 6 , the frequency controlling system of surgical instrument includes, acquisition circuitry  601 , determination circuitry  602 , first tuning circuitry  603 , second tuning circuitry  604 . 
     Acquisition circuitry  601 , for acquiring maximum phase difference of current and voltage of surgical instrument. 
     Determination circuitry  602 , for determining if the maximum is less than zero, obtain the first determination result. 
     First tuning circuitry  603 , when the maximum value of first determination result is not less than zero, tune the frequency of surgical instrument to the frequency of zero phase difference. 
     Second tuning circuitry  604 , when the maximum value of first determination is less than zero, obtain the phase locking point by subtracting a presetting point from the maximum value. Tune the frequency of the surgical instrument to phase locking point. 
     Embodiment 6 
       FIG. 7  is a schematic diagram of frequency controlling of surgical instrument of one embodiment. As shown in  FIG. 7 , the frequency controlling system of surgical instrument includes, acquisition circuitry  701 , determination circuitry  702 , first tuning circuitry  703 , second tuning circuitry  704 . 
     Acquisition circuitry  701 , for acquiring maximum phase difference of current and voltage of surgical instrument. 
     Determination circuitry  702 , for determining if the maximum is less than zero, obtain the fourth determination result. 
     The first tuning circuitry  703 , when the first determination result is less than zero, raises the current of surgical instrument; monitoring the voltage, when the voltage obtained is higher than the nominal voltage of surgical instrument, stop raising; obtain the phase locking point by subtracting a presetting value from maximum value; and tune the frequency to corresponding phase locking point. 
     The second tuning circuitry  704 , when the first determination result is not less than zero, tunes the frequency of surgical instrument to zero phase difference point. 
     Various embodiments are described in the invention, the difference between different embodiments are illustrated. The similarity of different embodiments could be referenced by each other. 
     While the invention has been particularly shown and described with reference to preferred embodiments, it could be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention. So, the description is not understood as the limit of the invention.