Patent Publication Number: US-2015073453-A1

Title: Medical device

Description:
This application claims the benefit of Japanese Patent Application No. 2013-188263, filed on Sep. 11, 2013. The content of the aforementioned application is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a medical device. 
     2. Related Art 
     Hitherto, as a technique relating to a medical device that ejects a fluid, for example, a technique disclosed in JP-A-2008-82202 has been known. JP-A-2008-82202 discloses a medical device in which pulsation is given to a fluid by driving a piezoelectric element, and an affected part is incised or excised by ejecting a liquid to which pulsation is given onto the affected part. 
     However, in the medical device disclosed in JP-A-2008-82202, there is a desire for a user&#39;s convenience to be attempted to be further improved. Besides, in the medical device of the related art, a reduction in the size of, a reduction in the cost of, the resource saving of, the manufacturing facilitation of, an improvement in the usability of the device, and the like have been required. 
     SUMMARY 
     An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms. 
     (1) An aspect of the invention provides a medical device that ejects a fluid. The medical device includes: a fluid ejection portion that includes an ejection tube having an opening for ejecting the fluid and a pulsation generation portion, communicating with the ejection tube, which generates pulsation to the fluid; a control portion that controls a frequency of the pulsation by controlling the pulsation generation portion; a measurement portion that measures a movement velocity of the fluid ejection portion; a receiving portion that receives an instruction for setting a specific frequency and a specific movement velocity from a user; a setting portion that sets the specific frequency and the specific movement velocity on the basis of the instruction from a user; and a calculation portion that calculates a control constant using the specific frequency and the specific movement velocity. The control portion controls the frequency in accordance with the movement velocity so that a value which is calculated by the same method as a method of calculating the control constant using the frequency and the movement velocity falls within a predetermined range including the control constant. 
     A force for excising an object has a correlation with the number of pulsating flows ejected per unit length of the object. According to such an aspect, control is performed so that the number of pulsating flows ejected per unit length of the object comes close to the number which is set by an instruction from a user, thereby it is possible to maintain an excision force which is set by the instruction from a user. 
     (2) In the medical device described above, the setting portion may set the frequency at a timing when the setting instruction is received, to the specific frequency, and may set the movement velocity at a timing when the setting instruction is received, to the specific movement velocity. 
     According to this configuration, when the setting portion receives the setting instruction at a timing when a user&#39;s favorite excision force is realized, it is possible to maintain a user&#39;s favorite excision force. 
     (3) In the medical device described above, the calculation portion may calculate the control constant by dividing the specific frequency by the specific movement velocity, and the control portion may control the frequency so that a value of the frequency comes close to a value obtained by multiplying the control constant and the movement velocity together. 
     According to this configuration, it is possible to calculate the number of pulsating flows ejected per unit length of the object as the control constant, and to easily control the frequency. 
     (4) In the medical device described above, the control portion may control the frequency so that when the movement velocity is larger than a predetermined upper limit threshold, the frequency has a value smaller than a value of the frequency in a case where the frequency is controlled using the control constant. 
     According to this configuration, when the movement velocity becomes greater than the predetermined upper limit threshold, the frequency has a small value. Therefore, for example, when the movement velocity becomes greater against a user&#39;s intention, it is possible to reduce an excision force. 
     (5) In the medical device described above, the control portion may control the frequency so that when the movement velocity is less than a predetermined lower limit threshold, the frequency has a value smaller than a value of the frequency in a case where the frequency is controlled using the control constant. 
     According to this configuration, when the movement velocity is less than the predetermined lower limit threshold, the frequency has a small value. Therefore, for example, when the apical end of the fluid ejection tube continues to remain at the same position of the object which is undesired against a user&#39;s intention, or when a user interrupts the excision of the object or the like and thus the movement velocity becomes lower, it is possible to reduce an excision force. 
     (6) In the medical device described above, the control portion may perform control so that an output of the pulsation generation portion is reduced when the movement velocity is larger than a predetermined upper limit threshold. 
     According to this configuration, when the movement velocity becomes greater than the predetermined upper limit threshold, the output of the pulsation generation portion is reduced. Therefore, for example, when the movement velocity becomes greater against a user&#39;s intention, it is possible to reduce an excision force. 
     (7) In the medical device described above, the control portion may perform control so that an output of the pulsation generation portion is reduced when the movement velocity is less than a predetermined lower limit threshold. 
     According to this configuration, when the movement velocity is less than the predetermined lower limit threshold, the output of the pulsation generation portion is reduced. Therefore, for example, when the apical end of the fluid ejection tube continues to remain at the same position of the object which is undesired against a user&#39;s intention, or when a user interrupts the excision of the object and thus the movement velocity becomes lower, it is possible to reduce the excision force. 
     Not all of a plurality of components included in the respective aspects of the invention described above are essential. In order to solve some or all of the aforementioned problems, or to achieve some or all of the effects described in this specification, regarding some components of the plurality of components, it is possible to appropriately perform change, deletion, replacement with other new components, and deletion of a portion of limited contents. Further, in order to solve some or all of the aforementioned problems, or to achieve some or all of the effects described in this specification, some or all of the technical features included in an aspect of the invention described above can also be combined with some or all of the technical features included in other aspects of the invention, to thereby form an independent aspect of the invention. 
     For example, an aspect of the invention can be realized as device including one or more elements within six elements of the fluid ejection portion, the control portion, the measurement portion, the receiving portion, the setting portion, and the calculation portion. That is, this device may or may not include the fluid ejection portion. In addition, the device may or may not include the control portion. In addition, the device may or may not include the measurement portion. In addition, the device may or may not include the receiving portion. In addition, the device may or may not include the setting portion. In addition, the device may or may not include the calculation portion. The fluid ejection portion may be configured as, for example, a fluid ejection portion provided with an ejection tube having an opening for ejecting the fluid and a pulsation generation portion, communicating with the ejection tube, which generates pulsation in the fluid. The control portion maybe configured as, for example, a control portion that controls a frequency of the pulsation by controlling the pulsation generation portion. The measurement portion may be configured as, for example, a measurement portion that measures a movement velocity of the opening. The receiving portion may be configured as, for example, a receiving portion that receives an instruction for setting a specific frequency and a specific movement velocity from a user. The setting portion may be configured as, for example, a setting portion that sets the specific frequency and the specific movement velocity on the basis of the instruction from a user. The calculation portion may be configured as, for example, a calculation portion that calculates a control constant using the specific frequency and the specific movement velocity. In addition, the control portion may be configured as, for example, a control portion that controls the frequency in accordance with the movement velocity so that a value which is calculated by the same method as a method of calculating the control constant using the frequency and the movement velocity falls within a predetermined range including the control constant. Such a device can be realized, for example, as a medical device that ejects a fluid, but can be realized by devices other than the medical device that ejects a fluid. According to such an aspect, it is possible to solve at least one of various problems of a reduction in the size of, a reduction in the cost of, the resource saving of, the manufacturing facilitation of, an improvement in the usability of a device, and the like. Some or all of technical features of each aspect of the medical device that ejects a fluid stated above can be applied to this device entirely. 
     The invention can also be implemented as various forms other than the device. For example, the invention can be implemented as forms such as a method of manufacturing a medical device that ejects a fluid, a method of controlling a medical device that ejects a fluid, a computer program for realizing the control method, a non-transitory recording medium having the computer program recorded thereon, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a diagram illustrating a configuration of a medical device as an embodiment of the invention. 
         FIG. 2  is an enlarged cross-sectional view illustrating a portion of an internal configuration of a handpiece. 
         FIG. 3  is a diagram illustrating an example of a waveform of a drive voltage which is applied to a piezoelectric element. 
         FIG. 4  is a diagram illustrating a correspondence relation between the waveform of the drive voltage and a modified state of a diaphragm. 
         FIG. 5  is a diagram illustrating a relationship between a drive frequency F [Hz] of the drive voltage which is applied the piezoelectric element and a depth [mm] where an affected part is excised, in a graph form. 
         FIG. 6  is a diagram illustrating a relationship between a movement velocity V [mm/s] of a fluid ejection tube and the drive frequency F [Hz] of the drive voltage which is applied to the piezoelectric element. 
         FIG. 7  is a diagram illustrating a control pattern in a medical device as a second embodiment. 
         FIG. 8  is a diagram illustrating a control pattern in a medical device as a third embodiment. 
         FIG. 9  is a diagram illustrating a control pattern in a medical device as a fourth embodiment. 
         FIG. 10  is a diagram illustrating a control pattern in a medical device as a fifth embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Next, embodiments of the invention will be described in the following order on the basis of the embodiments. 
     A. First Embodiment 
     B. Second Embodiment 
     C. Third Embodiment 
     D. Fourth Embodiment 
     E. Fifth Embodiment 
     F. Modification Example 
     A. FIRST EMBODIMENT 
       FIG. 1  is a diagram illustrating a configuration of a medical device  100  as an embodiment of the invention. The medical device  100  has a function as a scalpel for performing medical treatment such as incision or excision of an affected part of a patient by ejecting a fluid onto a biological tissue which is an affected part. 
     The medical device  100  includes a fluid container  10 , a fluid supply mechanism  12 , a handpiece  14 , a control device  16 , and an ejection switch  18 . The fluid container  10  and the fluid supply mechanism  12  are connected to each other by a connection tube  19   a,  and the fluid supply mechanism  12  and the handpiece  14  are connected to each other by a connection tube  19   b.  In the present embodiment, the connection tubes  19   a  and  19   b  are formed of a resin. 
     The fluid container  10  accommodates a physiological saline solution as a fluid which is supplied to the handpiece  14 . Here, the fluid container  10  may accommodate other fluids, such as, for example, pure water or a drug solution which are not harmful even during ejection onto a biological tissue, instead of the physiological saline solution. 
     The fluid supply mechanism  12  supplies a fluid accommodated in the fluid container  10  to the handpiece  14  through the connection tubes  19   a  and  19   b.  In the present embodiment, a pump is used as the fluid supply mechanism  12 . 
     The handpiece  14  is an appliance which is manipulated by an operator with the handpiece held in his/her hand, and includes a fluid ejection tube  20 , a pulsation generation portion  22 , and a housing  24 . When a drive voltage is applied through a voltage application cable  17   a,  the pulsation generation portion  22  gives pulsation to a fluid which is supplied through the connection tube  19   b.  The fluid to which pulsation is given is ejected from an opening  20   a  of an apical end of the fluid ejection tube  20  at high speed. An operator incises, excises or the like, for example, an affected part by applying a fluid, ejected from the handpiece  14 , to which pulsation is given, to a biological tissue which is an affected part of a patient. Meanwhile, hereinafter, a fluid to which pulsation is given is also called a pulsating flow or a pulse flow. Meanwhile, the magnitude (volume ejected by one-time driving) and the intensity of a pulsating flow is changed when the magnitude of a drive voltage is changed, and the frequency of occurrence of the pulsating flow is changed when the drive frequency of a drive voltage is changed. 
     The control device  16  controls a drive voltage which is applied to the pulsation generation portion  22  through the voltage application cable  17   a,  and controls the start and stop of the fluid supply mechanism  12  through a control cable  17   b.    
     The ejection switch  18  is a switch which is manipulated by an operator, and is connected to the control device  16  through a control cable  17   c.  In the present embodiment, the ejection switch  18  is a foot switch which is manipulated by an operator using his/her foot. 
     When the ejection switch  18  is turned on by an operator, the control device  16  instructs the fluid supply mechanism  12  to start a supply of a fluid, and applies a drive voltage to the pulsation generation portion  22 . A fluid to which pulsation is given is ejected at high speed from the opening  20   a  of the apical end of the fluid ejection tube  20  of the handpiece  14 . 
     In the present embodiment, the handpiece  14  further includes an acceleration sensor  25  and an information acquisition switch  26 . The acceleration sensor  25  is provided in the vicinity of the apical end of the housing  24 , and detects acceleration. In the present embodiment, the acceleration sensor  25  is a semiconductor-type 3-axis acceleration sensor. The detected acceleration is supplied to the control device  16  through a control cable  17   d.  the information acquisition switch  26  is a switch which is depressed by an operator. When the information acquisition switch  26  is depressed by an operator, a signal indicating that the information acquisition switch  26  is depressed is supplied to the control device  16  through a control cable  17   e.    
     The control device  16  calculates the movement velocity V of the fluid ejection tube  20  on the basis of the acceleration detected by the acceleration sensor  25  and a positional relation between the acceleration sensor  25  and the fluid ejection tube  20 . In addition, the control device  16  sets the movement velocity V of the fluid ejection tube  20  at a timing when the information acquisition switch  26  is depressed, as a specific movement velocity Vs, and sets the drive frequency F of a drive voltage which is applied to the pulsation generation portion  22  at the timing, as a specific drive frequency Fs. The reason for setting the specific movement velocity Vs and the specific drive frequency Fs will be described later. In addition, the control device  16  also functions as a receiving portion  16   a,  a setting portion  16   b,  a calculation portion  16   c,  and a control portion  16   d  which are described later. 
       FIG. 2  is an enlarged cross-sectional view illustrating a portion of the internal configuration of the handpiece  14 . The pulsation generation portion  22  that gives pulsation to a fluid supplied from the fluid supply mechanism  12  is provided in the inside of the housing  24  of the handpiece  14 . The pulsation generation portion  22  includes a piezoelectric element  30 , a diaphragm  32 , a first case  34 , a second case  36 , and a third case  38 . 
     In the pulsation generation portion  22 , an inlet channel  40 , a fluid chamber  42 , and an outlet channel  44  are formed as a channel through which a fluid supplied from the fluid supply mechanism  12  passes. In the present embodiment, the inlet channel  40  and the outlet channel  44  are formed in the first case  34 , and the fluid chamber  42  is formed between the first case  34  and the diaphragm  32 . The connection tube  19   b  is connected to the inlet channel  40 , and the fluid ejection tube  20  is connected to the outlet channel  44 . 
     The diaphragm  32  is a disk-shaped metal sheet, and the outer circumference portion thereof is interposed between the first case  34  and the second case  36  and is fixed thereto. 
     The piezoelectric element  30  is an actuator which is operated by a drive voltage applied from the control device  16 . The piezoelectric element  30  changes the volume of the fluid chamber  42  formed between the diaphragm  32  and the first case  34 , to thereby change the pressure of a fluid within the fluid chamber  42 . In the present embodiment, the piezoelectric element  30  is a laminated piezoelectric element, and is configured such that one end thereof is fixed to the diaphragm  32  and the other end thereof is fixed to the third case  38 . 
     When a drive voltage applied to the piezoelectric element  30  becomes greater, the piezoelectric element  30  extends, and the diaphragm  32  is pushed to the piezoelectric element  30  and bends to the fluid chamber  42  side. When the diaphragm  32  bends to the fluid chamber  42  side, the volume of the fluid chamber  42  decreases, and the fluid within the fluid chamber  42  is extruded from the fluid chamber  42 . In the present embodiment, the inside diameter of the outlet channel  44  is larger than the inside diameter of the inlet channel  40 . That is, since the inertance of the outlet channel  44  is smaller than the inertance of the inlet channel  40 , the fluid within the fluid chamber  42  is extruded from the fluid chamber  42  through the outlet channel  44 . 
     On the other hand, when the drive voltage applied piezoelectric element  30  becomes lower, the volume of the fluid chamber  42  becomes greater due to a reduction in the size of the piezoelectric element  30 , and a fluid is supplied from the inlet channel  40  into the fluid chamber  42 . 
     Since the drive voltage applied to the piezoelectric element  30  repeats turn-on (maximum voltage) and turn-off (0 V) at a high frequency (for example, 400 Hz), the enlargement and reduction of the volume of the fluid chamber  42  are repeated, and pulsation is given to the fluid. The fluid extruded from the fluid chamber  42  is ejected from the nozzle  20   a  (opening  20   a ) of the apical end of the fluid ejection tube  20 . 
       FIG. 3  is a diagram illustrating an example of a waveform of a drive voltage which is applied to the piezoelectric element  30 . In  FIG. 3 , the horizontal axis represents a time, and the vertical axis represents a drive voltage. One cycle of the waveform of the drive voltage is composed of a rising period in which a voltage increases, a falling period in which a voltage decreases, and an idle period in which a voltage is not applied. 
     In the present embodiment, the waveform of the drive voltage in the rising period is offset in a positive voltage direction, and is a waveform of ½ cycle of an SIN waveform of which the phase is shifted by −90 degrees. The waveform of the drive voltage in the falling period is offset in a positive voltage direction, and is a waveform of ½ cycle of the SIN waveform of which the phase is shifted by +90 degrees. The cycle of the SIN waveform in the falling period becomes greater than the cycle of the SIN waveform in the rising period. 
     In the present embodiment, when the magnitude of the drive voltage is changed, the maximum value of the waveform shown in  FIG. 3  is changed. In addition, when the frequency of the drive voltage is changed, the waveform in the rising period and the falling period is not changed, and the length of the idle period is changed. 
       FIG. 4  is a diagram illustrating a correspondence relation between the waveform of the drive voltage and the modified state of the diaphragm  32 . Meanwhile, in  FIG. 4 , a reinforcement member  51  is provided between the piezoelectric element  30  and the diaphragm  32 . In the idle period (a), since the drive voltage is not applied, the piezoelectric element  30  does not extend, and the diaphragm  32  does not bend. In the rising period (b), since the drive voltage becomes greater, the piezoelectric element  30  extends, the diaphragm  32  bends to the fluid chamber  42  side, and the volume of the fluid chamber  42  decreases. 
     Since the drive voltage becomes maximum at a timing in (c) of the drawing, the length of the piezoelectric element  30  also becomes maximum, and the volume of the fluid chamber  42  becomes minimum. Since the drive voltage becomes lower in the falling period (d), the piezoelectric element  30  starts returning to its original dimensions, and the volume of the fluid chamber  42  starts returning to its original dimensions. Since the drive voltage is not applied in the idle period (e), the piezoelectric element  30  returns to its original dimensions, and the volume of the fluid chamber  42  returns to its original dimensions. A series of operations shown in (a) to (e) of the drawing are repeated, and thus the fluid within the fluid chamber  42  is extruded to the fluid ejection tube  20 . 
       FIG. 5  is a diagram illustrating a relationship between the drive frequency F [Hz] of the drive voltage applied to the piezoelectric element  30  and the depth [mm] to which an affected part is excised, in a graph form. A solid line J shown in  FIG. 5  shows a case where the fluid ejection tube  20  is moved at a constant velocity with respect to an affected part, and only the drive frequency F is changed. On the other hand, a broken line B shown in  FIG. 5  shows a case where the movement velocity V and the drive frequency F of the fluid ejection tube  20  are adjusted so that the number N of pulsating flows (hereinafter, also simply called “ejection number N”) ejected per unit length of an affected part becomes constant. In the example shown in  FIG. 5 , the movement velocity V and the drive frequency F of the fluid ejection tube  20  are adjusted so that the ejection number N per unit length is 1,000 shots/mm. 
     According to  FIG. 5 , it can be understood that when the ejection number N per unit length increases, the excision depth increases. In addition, when the ejection numbers N per unit length are the same as each other, even when the movement velocity V and the drive frequency F of the fluid ejection tube  20  are different, it can be understood that the excision depths are substantially the same as each other. That is, it can be understood that an excision force for excising an affected part has a correlation with the ejection number N per unit length. 
       FIG. 6  is a diagram illustrating a relationship between the movement velocity V [mm/s] of the fluid ejection tube  20  and the drive frequency F [Hz] of the drive voltage which is applied to the piezoelectric element  30 . As shown in  FIG. 6 , when the drive frequency F is controlled in accordance with the movement velocity V of the fluid ejection tube  20 , the ejection number N per unit length becomes constant. In the present embodiment, the control portion  16   d  controls the drive frequency F in accordance with the measured movement velocity V so that the ejection number N per unit length falls within a predetermined range. In this manner, even when the movement velocity V of the fluid ejection tube  20  is changed, the excision force can be made substantially constant, and the depth to which the affected part is excised can be made substantially constant. In the present embodiment, the control device  16  controls the drive frequency F so as to maintain the excision force at a timing when the information acquisition switch  26  is depressed by an operator. The details of control are as follows. 
     The receiving portion  16   a  receives an instruction for setting the specific drive frequency Fs and the specific movement velocity Vs from an operator. In the present embodiment, the receiving portion  16   a  receives a signal indicating that the information acquisition switch  26  is depressed through the control cable  17   e.    
     The setting portion  16   b  sets the specific drive frequency Fs and the specific movement velocity Vs on the basis of the instruction from an operator. In the present embodiment, the setting portion  16   b  sets the drive frequency F at a timing when the information acquisition switch  26  is depressed to the specific drive frequency Fs, and sets the movement velocity V of the fluid ejection tube  20  at a timing when the information acquisition switch  26  is depressed to the specific movement velocity Vs. 
     The calculation portion  16   c  calculates a control constant Ns using the set specific drive frequency Fs and the set specific movement velocity Vs. In the present embodiment, the calculation portion  16   c  calculates the control constant Ns by dividing the specific drive frequency Fs by the specific movement velocity Vs. 
     The control portion  16   d  controls the drive frequency F in accordance with the movement velocity V of the fluid ejection tube  20  so that a value calculated by the same method as a method of calculating the control constant Ns using the drive frequency F and the movement velocity V of the fluid ejection tube  20 , that is, the ejection number N per unit length falls within a predetermined range including the control constant Ns. In the present embodiment, the control portion  16   d  controls the drive frequency F so that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. Therefore, even when the movement velocity V of the fluid ejection tube  20  is changed, it is possible to easily control the drive frequency F, and to maintain the excision force at a timing when the information acquisition switch  26  is depressed. 
     In this manner, according to the present embodiment, control is performed so that the ejection number N per unit length comes close to the number (control constant Ns) which is set by an instruction from a user. Therefore, even when the movement velocity V of the fluid ejection tube  20  is changed, it is possible to maintain the excision force which is set by an instruction from an operator. 
     Further, according to the present embodiment, when a user depresses the information acquisition switch  26  at a timing when a favorite excision force is realized, it is possible to maintain the excision force at a timing when the favorite excision force is realized. Meanwhile, the fluid ejection tube  20  and the pulsation generation portion  22  are equivalent to a “fluid ejection portion” according to the invention. 
     B. SECOND EMBODIMENT 
       FIG. 7  is a diagram illustrating a control pattern in a medical device  100  as a second embodiment. The basic configuration of the second embodiment is the same as that of the above-mentioned first embodiment. When the ejection switch  18  is depressed by an operator and is turned on, the fluid supply mechanism  12  and the pulsation generation portion  22  are driven. On the other hand, when the ejection switch  18  is not depressed by an operator and is turned off, the fluid supply mechanism  12  and the pulsation generation portion  22  are stopped. 
     In the present embodiment, the control portion  16   d  controls the drive frequency F so that when the movement velocity V of the fluid ejection tube  20  is larger than a predetermined upper limit threshold Va, the drive frequency F has a value smaller than the value of the drive frequency F in a case where the drive frequency F is controlled using the control constant Ns. Meanwhile, the predetermined upper limit threshold Va may be set on the basis of the specific movement velocity Vs. For example, the predetermined upper limit threshold Va may be preferably a value greater than the specific movement velocity Vs, and may be preferably, for example, a value of 1.2 times the specific movement velocity Vs. A specific control method of the drive frequency F is as follows. 
     The calculation portion  16   c  calculates the control constant Ns in the same manner as that in the first embodiment, and calculates a second control constant Ns 2  by multiplying the control constant Ns and a predetermined constant less than 1 together. For example, the calculation portion  16   c  calculates the second control constant Ns 2  on the basis of the following expression. 
       Ns2= Ns× 0.5 
     The control portion  16   d  compares the movement velocity V of the fluid ejection tube  20  with the predetermined upper limit threshold Va. When the movement velocity V of the fluid ejection tube  20  is equal to or less than the predetermined upper limit threshold Va, the control portion  16   d  controls the drive frequency F so that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. 
     On the other hand, when the movement velocity V of the fluid ejection tube  20  is greater than the predetermined upper limit threshold Va, the control portion  16   d  controls the drive frequency F so that the value of the drive frequency F comes close to a value obtained by multiplying the second control constant Ns 2  and the movement velocity V of the fluid ejection tube  20  together. 
     In this manner, when the movement velocity V of the fluid ejection tube  20  is greater than the predetermined upper limit threshold Va, the ejection number N per unit length becomes smaller than the ejection number N per unit length in a case where the movement velocity V of the fluid ejection tube  20  is equal to or less than the predetermined upper limit threshold Va. 
     Therefore, according to the present embodiment, when the movement velocity V of the fluid ejection tube  20  becomes greater against an operator&#39;s intention, the ejection number N per unit length has a small value, and thus it is possible to reduce the excision force. For example, when the movement velocity V of the fluid ejection tube  20  becomes greater against an operator&#39;s intention, and the apical end of the fluid ejection tube  20  moves to an undesired position of an affected part, it is possible to reduce the excision force. As a result, it is possible to improve the safety of the medical device  100 . 
     C. THIRD EMBODIMENT 
       FIG. 8  is a diagram illustrating a control pattern in a medical device  100  as a third embodiment. The basic configuration of the third embodiment is the same as that of the above-mentioned first embodiment. In the present embodiment, when the control portion  16   d  controls the drive frequency F so that when the movement velocity V of the fluid ejection tube  20  is smaller than a predetermined lower limit threshold Vb, the drive frequency F has a value smaller than the value of the drive frequency F in a case where the drive frequency F is controlled using the control constant Ns. Meanwhile, the predetermined lower limit threshold Vb may be set on the basis of the specific movement velocity Vs. For example, the predetermined lower limit threshold Vb may be a value less than the specific movement velocity Vs, and may be, for example, a value 0.8 times the specific movement velocity Vs. A specific control method of the drive frequency F is as follows. 
     The calculation portion  16   c  calculates the control constant Ns in the same manner as that in the first embodiment, and calculates a third control constant Ns 3  by multiplying the control constant Ns and a predetermined constant less than 1 together. For example, the calculation portion  16   c  calculates the third control constant Ns 3  on the basis of the following expression. 
         Ns 3= Ns× 0.5 
     The control portion  16   d  compares the movement velocity V of the fluid ejection tube  20  with the predetermined lower limit threshold Vb. When the movement velocity V of the fluid ejection tube  20  is equal to or greater than the predetermined lower limit threshold Vb, the control portion  16   d  controls the drive frequency F so that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. 
     On the other hand, when the movement velocity V of the fluid ejection tube  20  is less than the predetermined lower limit threshold Vb, the control portion  16   d  controls the drive frequency F so that the value of the drive frequency F comes close to a value obtained by multiplying the third control constant Ns 3  and the movement velocity V of the fluid ejection tube  20  together. 
     In this manner, when the movement velocity V of the fluid ejection tube  20  is less than the predetermined lower limit threshold Vb, the ejection number N per unit length becomes smaller than the ejection number N per unit length in a case where the movement velocity V of the fluid ejection tube  20  is equal to or greater than the predetermined lower limit threshold Vb. 
     Therefore, according to the present embodiment, when the movement velocity V of the fluid ejection tube  20  becomes lower, the ejection number N per unit length has a small value, it is possible to reduce the excision force. For example, when the apical end of the fluid ejection tube  20  continues to remain at the same position of an affected part which is undesired, against an operator&#39;s intention, or when an operator interrupts the excision of an affected part or the like and thus the movement velocity V becomes lower, it is possible to reduce the excision force. As a result, it is possible to improve the safety of the medical device  100 . 
     D. FOURTH EMBODIMENT 
       FIG. 9  is a diagram illustrating a control pattern in a medical device  100  as a fourth embodiment. The basic configuration of the fourth embodiment is the same as that of the above-mentioned first embodiment. In the present embodiment, the control portion  16   d  reduces the magnitude of the drive voltage which is applied to the piezoelectric element  30  when the movement velocity V of the fluid ejection tube  20  is larger than the predetermined upper limit threshold Va while the drive frequency F is controlled in the same manner as that in the above-mentioned first embodiment. Meanwhile, the predetermined upper limit threshold Va maybe set on the basis of the specific movement velocity Vs. For example, the predetermined upper limit threshold Va may be a value greater than the specific movement velocity Vs, and may be, for example, a value 1.2 times the specific movement velocity Vs. A specific control method of the drive frequency F and the drive voltage is as follows. 
     The control portion  16   d  compares the movement velocity V of the fluid ejection tube  20  with the predetermined upper limit threshold Va. When the movement velocity V of the fluid ejection tube  20  is equal to or less than the predetermined upper limit threshold Va, the control portion  16   d  controls the drive frequency F so that the maximum value of the drive voltage which is applied to the piezoelectric element  30  is set to a predetermined value E, and that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. 
     On the other hand, when the movement velocity V of the fluid ejection tube  20  is greater than the predetermined upper limit threshold Va, the control portion  16   d  controls the drive frequency F so that the maximum value of the drive voltage which is applied to the piezoelectric element  30  is set to a predetermined value Ea smaller than the above-mentioned predetermined value E, and that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. Meanwhile, Ea may be a value smaller than E, may be, for example, a value of 0.5 times E, and may be 0. 
     In this manner, when the movement velocity V of the fluid ejection tube  20  is greater than the predetermined upper limit threshold Va, the intensity of a pulsating flow which is ejected from the fluid ejection tube  20  becomes lower than the intensity of a pulsating flow in a case where the movement velocity V of the fluid ejection tube  20  is equal to or less than the predetermined upper limit threshold Va. 
     For example, when the movement velocity V of the fluid ejection tube  20  becomes greater against an operator&#39;s intention, and the apical end of the fluid ejection tube  20  moves to an undesired position of an affected part, it is possible to reduce the excision force. As a result, it is possible to improve the safety of the medical device  100 . 
     E. FIFTH EMBODIMENT 
       FIG. 10  is a diagram illustrating a control pattern in a medical device  100  as a fifth embodiment. The basic configuration of the fifth embodiment is the same as that of the above-mentioned first embodiment. In the present embodiment, the control portion  16   d  reduces the magnitude of the drive voltage which is applied to the piezoelectric element  30  when the movement velocity V of the fluid ejection tube  20  is smaller than the predetermined lower limit threshold Vb while the drive frequency F is controlled in the same manner as that in the above-mentioned first embodiment. Meanwhile, the predetermined lower limit threshold Vb may be set on the basis of the specific movement velocity Vs. For example, the predetermined lower limit threshold Vb maybe a value less than the specific movement velocity Vs, and may be, for example, a value of 0.8 times the specific movement velocity Vs. A specific control method of the drive frequency F and the drive voltage is as follows. 
     The control portion  16   d  compares the movement velocity V of the fluid ejection tube  20  with the predetermined upper limit threshold Va. When the movement velocity V of the fluid ejection tube  20  is equal to or greater than the predetermined lower limit threshold Vb, the control portion  16   d  controls the drive frequency F so that the maximum value of the drive voltage which is applied to the piezoelectric element  30  is set to the predetermined value E, and that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. 
     On the other hand, when the movement velocity V of the fluid ejection tube  20  is less than the predetermined lower limit threshold Vb, the control portion  16   d  controls the drive frequency F so that the maximum value of the drive voltage which is applied to the piezoelectric element  30  is set to a predetermined value Eb smaller than the above-mentioned predetermined value E, and that the value of the drive frequency F comes close to a value obtained by multiplying the control constant Ns and the movement velocity V of the fluid ejection tube  20  together. Meanwhile, Eb may be a value smaller than E, may be, for example, a value 0.5 times E, and may be 0. 
     In this manner, when the movement velocity V of the fluid ejection tube  20  is less than the predetermined lower limit threshold Vb, the intensity of a pulsating flow which is ejected from the fluid ejection tube  20  becomes lower than the intensity of a pulsating flow in a case where the movement velocity V of the fluid ejection tube  20  is equal to or greater than the predetermined lower limit threshold Vb. 
     Therefore, according to the present embodiment, when the movement velocity V of the fluid ejection tube  20  becomes lower, it is possible to reduce the excision force. For example, when the apical end of the fluid ejection tube  20  continues to remain at the same position of an affected part which is undesired, against an operator&#39;s intention, or when an operator interrupts the excision of an affected part or the like and thus the movement velocity V becomes lower, it is possible to reduce the excision force. As a result, it is possible to improve the safety of the medical device  100 . 
     F. MODIFICATION EXAMPLE 
     Meanwhile, the invention is not limited to the above-mentioned embodiments, and can be implemented in various aspects without the gist of the invention. For example, the following modifications can be made. 
     Modification Example 1 
     In the above-mentioned embodiment, a user interface for receiving an instruction for setting the specific drive frequency Fs and the specific movement velocity Vs from an operator may be connected to the control device  16 . In addition, the setting portion  16   b  may set the specific drive frequency Fs from the average value of the drive frequency F in the past specific period, on the basis of the instruction from an operator. In addition, the setting portion  16   b  may set the specific movement velocity Vs from the average value of the movement velocity V of the fluid ejection tube  20  in the past specific period, on the basis of the instruction from an operator. 
     Modification Example 2 
     In the above-mentioned embodiment, the calculation portion  16   c  may calculate the control constant Ns by dividing the specific movement velocity Vs by the specific drive frequency Fs. In this case, the control portion  16   d  may control the drive frequency F so that the drive frequency F comes close to a value obtained by dividing the movement velocity V of the fluid ejection tube  20  by the control constant Ns. 
     Modification Example 3 
     In the above-mentioned embodiment, the control device  16  may calculate the movement velocity V of the fluid ejection tube  20  on the basis of an image or a moving image which is captured by a camera provided to the handpiece  14  or a camera provided at a position other than the handpiece  14 . In addition, in the above-mentioned embodiment, a camera, a sensor or the like that detects the movement (velocity) of an affected part may be provided, and the control device  16  may calculate a relative velocity between an affected part and the fluid ejection tube  20 . 
     Modification Example 4 
     In the above-mentioned embodiment, the pulsation generation portion  22  may be a mechanism that generates air bubbles by irradiating a fluid with a laser and generating pulsation due to the air bubbles. In this case, an optical fiber cable for perform irradiation with a laser may be connected to the pulsation generation portion  22 . In addition, the pulsation generation portion  22  may be a mechanism that generates air bubbles using an electric heater and generates pulsation. 
     Modification Example 5 
     In the above-mentioned embodiment, the release of the specific drive frequency Fs and the specific movement velocity Vs which are set may be performed when an operator stops the depression of the ejection switch  18 , or when an operator depresses the information acquisition switch  26  again. In addition, a button for releasing the specific drive frequency Fs and the specific movement velocity Vs which are set may be separately provided. 
     Modification Example 6 
     The controls performed in the above-mentioned first embodiment to the fifth embodiment may be appropriately combined. 
     Modification Example 7 
     A portion of functions realized by software in the above-mentioned embodiment may be realized by hardware, or a portion of functions realized by hardware may be realized by software. 
     The invention is not limited to the aforementioned embodiments, examples, and modification examples of this specification, and can be implemented by various configurations without the gist of the invention. For example, technical features in the embodiments, examples, and modification examples which correspond to the technical features in the respective aspects described in the summary of the invention can be appropriately replaced or combined in order to solve some or all of the aforementioned problems, or to achieve some or all of the aforementioned effects.