Patent Publication Number: US-2006012937-A1

Title: Piezoelectric actuator driver

Description:
TECHNICAL FIELD  
      The present invention relates to a driver of a piezoelectric actuator, and particularly to improvement in the driver of the piezoelectric actuator for switching and driving a plurality of piezoelectric actuators mechanically moving each of the plural mechanism components directly or indirectly installed on the driver.  
     BACKGROUND ART  
      Conventionally, as shown in  FIG. 7A , a piezoelectric actuator  1  is constituted in such a manner that thin piezoelectric sheets  5  and  7  are attached to opposed surfaces of a rectangular conductive plate  3 , and electrodes  5   a  and  7   a  are disposed on the opposed surfaces which are not brought into contact with the plate  3  in each piezoelectric sheet  5  and  7 , with the plate  3  serving as common electrodes, wherein the electrodes  5   a  and  7   a  are connected to positive terminals P 1  and negative terminals P 2 , the plate  3  is connected to a common terminal P 3 , and while supporting one end (left end in the figure) in the longitudinal directions of the plate  3  in an open-sided shape, the other end (right end in the figure) is formed in an open end. Note that a support member of the piezoelectric actuator  1  is not shown in  FIG. 7  (see  FIG. 8 ).  
      In the piezoelectric actuator  1  thus constituted, for example, when positive potential + is applied to a positive terminal P 1  and a common terminal P 3  by short-circuiting both terminals (between the electrode  5   a  of the piezoelectric sheet and the plate  3 ), according to the polarization directions of the piezoelectric sheets  5  and  7 , for example, the plate  3  is bent so that the open end is displaced in the upward direction as shown by broken line in  FIG. 7A .  
      Meanwhile, when a negative potential − is applied to the common terminal P 3  and a negative terminal P 2  by short-circuiting both terminals (between the plate  3  and the electrode  7   a  of the other piezoelectric sheet  7 ), for example, the open end is displaced in the downward direction as shown by one-dot chain line in the figure.  
      Then, the piezoelectric actuator  1  is used as various driving sources, such as a needle selecting driver of knitting needles of a knitting machine, by utilizing a bending motion by dint of such a piezoelectric phenomenon.  
      Specifically, as shown in  FIG. 8 , the aforementioned plural piezoelectric actuators  1  (shown by dividing into  1   a ,  1   b ,  1   c ,  1   d ,  1   e ,  1   f ,  1   g , and  1   h  in the figure) are arranged on a side wall  9   a  in a long and narrow insulating box-shaped case  9  in parallel to each other at prescribed intervals apart from one another, with the one ends supported in an open-sided shape and the other ends as the open end inserted into operation holes  11  formed on the side wall  9   b  opposed to the side wall  9   a  in the case  9  with a certain play. Then, operation pieces  13  as mechanical components fixed to the other ends are protruded with a certain play from the operation holes  11 .  
      All of the plural piezoelectric actuators  1   a  to  1   h  (including the operation pieces  13 ) supported by the case  9  are the same actuators, and  FIG. 9  is a view of the case  9  viewed from the side of the side wall  9   b  of the case  9 , specifically from the tip end side of the operation piece  13 .  
      When a positive/negative direct current drive voltage is applied from a power supply section  15  to such plural piezoelectric actuators  1   a  to  1   h  through a controller  17 , each of the piezoelectric actuators  1   a  to  1   h  is bent and the operation pieces  13  protruding from the operation holes  11  of the case  9  are displaced. This contributes to moving a selecting needle lever not shown (mechanism component) by means of the operation pieces  13 .  
      Then, when the controller  17  switches and selects the drive voltage applied to the plural piezoelectric actuators  1   a  to  1   h , the piezoelectric actuators  1   a  to  1   h  can be used as a needle selecting driver of the knitting needles of the knitting machine, for example.  
      A general patent document according to such a kind of piezoelectric actuator includes a patent document 1 (Japanese Patent Laid Open No. 5-302251).  
      Further, the structure as shown in  FIG. 10  is given as an example of the structure of selectively controlling the drive voltage applied to the plural piezoelectric actuators  1   a  to  1   h  by the controller  17 .  
      Specifically, phototransistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , Q 7  and Q 8 , which are connected in series respectively, are disposed corresponding to the plural piezoelectric actuators  1   a  to  1   h . A collector of one of the phototransistors Q 1  is connected to the phototransistor Q 2  through a resistor R 1  from a positive side feeder line  19 , and an emitter of the other phototransistor Q 2  is connected to a negative side feeder line  21  through a resistor R 2 .  
      The positive terminal P 1  in the piezoelectric actuator  1   a  is connected to the positive side feeder line  19 , the negative terminal P 2  is connected to the negative side feeder line  21 , and joints of the phototransistors Q 1  and Q 2  are connected to common terminal P 3  of the piezoelectric actuator  1   a.    
      Similarly, the phototransistors Q 3  to Q 8  are also connected to the positive side and negative side feeder lines  19  and  21  through resistors R 3  to R 8 , and the piezoelectric actuators  1   b  to  1   d  are also connected to the joints of the phototransistors Q 3  to Q 8  and the positive side and negative side feeder lines  19  and  21 .  
      In addition, light emitting diodes D 1  and D 2 , D 3  and D 4 , D 5  and D 6 , and D 7  and D 8  connected in series are disposed in proximity to and corresponding to the photo transistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , and Q 7  and Q 8  connected in series.  
      The light emitting diodes D 1  to D 8  are emitted by selectively being energized by a switching control section  23 , and the driver of the aforementioned piezoelectric actuators is thus formed.  
      In  FIG. 10 , the aforementioned controller  17  is formed by the phototransistors Q 1  to Q 8 , light emitting diodes D 1  to D 8 , and the switching control section  23 .  
      Note that in  FIG. 10 , the light emitting diodes D 1  to D 8  are connected by one line from the switching control section  23 . However, actually the light emitting diodes D 1  to D 8  are connected by individual wiring corresponding to the light emitting diodes D 1  to D 8 . Such wiring is simplified in  FIG. 8  so as to be easy to understand.  
      Then, for example, when the driver of the piezoelectric actuator is used in the needle selecting driver, for example, and the piezoelectric actuator  1   a  out of the plural piezoelectric actuators  1   a  to  1   d  is on-controlled, the open end is displaced in the upward direction through the conduction control of only light emitting diode D 1  selectively by the switching control section  23 . Meanwhile, the tip end is displaced in the downward direction through the conduction control of only light emitting diode D 2  selectively.  
      Similarly, in the other piezoelectric actuators  1   b  to  1   h  also, the tip end is displaced through the conduction control of only either of the light emitting diodes D 3  or D 4 , D 5  or D 6 , and D 7  or D 8 , and after a specified on-control period has passed, all the piezoelectric actuators  1   a  to  1   h  are simultaneously off-controlled.  
      In addition, in the aforementioned driver of the piezoelectric actuator, as shown in  FIG. 7B , the piezoelectric sheets  5  and  7  function as a kind of capacitors C 1  and C 2 . Therefore, even when the drive voltage is applied to the piezoelectric sheets  5  and  7  of each of the piezoelectric actuators  1   a  to  1   h  to on-control the plural piezoelectric actuators  1   a  to  1   h , any large current is prevented from running over the on-control period. Therefore, it is considered that power saving of the overall device is easily achieved.  
      In addition, in the driver of the piezoelectric actuators thus constituted, the resistors R 1  to R 8  connected between the phototransistors Q 1  to Q 8  and the positive side and negative side feeder lines  19  and  21  have a current limit function to suppress a drive current flowing through the phototransistors Q 1  to Q 8  so as not to increase the power consumption for the entire driver due to increased drive current, which occurs when one of the phototransistors is switched to the other in the phototransistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , and Q 7  and Q 8 , thereby causing both of the phototransistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , and Q 7  and Q 8  to be temporarily conducted or a rapid current change to occur, resulting in a large drive current.  
      However, in the driver of the aforementioned piezoelectric actuators, a large drive current is inhibited from running through the piezoelectric sheets  5  and  7 , which constitute the plural piezoelectric actuators  1   a  to  1   h , during the on-control period thereof. However, in the piezoelectric sheets  5  and  7 , namely, in each of the piezoelectric actuators  1   a  to  1   h , the capacitors C 1  and C 2  are equivalently formed. In addition, capacitance of such capacitors has a large level of about 150 to 600 nF, and therefore a large drive current is easy to run through the piezoelectric sheets  5  and  7  immediately after the on-control of the piezoelectric actuators  1   a  to  1   h.    
      Then, with any one of the piezoelectric actuators  1   a  to  1   b  on-controlled, when another one of the piezoelectric actuators  1   a  to  1   h  is duplicately on-controlled, flow of a large drive current occurs frequently, to easily raise power consumption of the overall driver.  
      In order to avoid above situation, it needs to cope with increase in the drive current by a treatment such as making the wiring of the feeder line thick, which causes easy increase in cost.  
      The present inventors carefully study on the piezoelectric actuators  1   a  to  1   h , and the function and an equivalent circuit thereof. As a result, the present inventors focus on the point that the piezoelectric actuators  1   a  to  1   h  have the function as capacitors equivalently, and in addition each of the piezoelectric actuators  1   a  to  1   h  is electrically connected in parallel, and the piezoelectric sheets  5  and  7  of the piezoelectric actuators  1   a  to  1   h , which are off-controlled, are discharged. The present invention is thus completed.  
      In order to solve the aforementioned problem, the present invention is provided, and an object of the present invention is to provide the driver of the piezoelectric actuator capable of suppressing the power consumption of an overall device low, by drastically reducing the drive current, during on/off switching control in the driver for driving the plural actuators.  
     DISCLOSURE OF THE INVENTION  
      In order to solve the aforementioned problem, the present invention provides plural actuators in which a first and a second piezoelectric sheets are attached to opposed surfaces of a plate interposed between the first and the second piezoelectric sheets, comprising: 
          plural actuators mechanically moving a mechanical component directly or indirectly connected to each of the piezoelectric actuators;     a positive side feeder line directly or indirectly connected to the opposite side of the first piezoelectric sheet to the side attached to the plate;     a negative side feeder line directly or indirectly connected to the opposite side of the second piezoelectric sheet to the side attached to the plate; and     a controller selectively applying a positive or a negative drive voltage to the first and the second piezoelectric sheets so that the piezoelectric sheets are on-controlled and charged, by connecting the positive side or the negative side feeder line to the plate side of the first or the second piezoelectric sheet.        

      In addition, the controller has a function to off-control the drive voltage applied to the first or the second piezoelectric sheet of the piezoelectric actuator selectively on-controlled, and simultaneously with this, on-controls the drive voltage to be applied to the first or the second piezoelectric sheet of the piezoelectric actuator to be selectively on-controlled next, so that the piezoelectric sheet of the piezoelectric actuator thus on-controlled next is charged. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block circuit diagram showing an embodiment relating to a driver of a piezoelectric actuator according to the present invention.  
       FIG. 2  is a waveform chart explaining a switching operation of the driver of the piezoelectric actuator according to the present invention.  
       FIG. 3  is a schematic equivalent circuit diagram of the piezoelectric actuator of the present invention.  
       FIG. 4  is a circuit diagram for explaining the operation of the piezoelectric actuator of the present invention.  
       FIG. 5  is a view for explaining the operation of the piezoelectric actuator of the present invention.  
       FIG. 6  is a block circuit diagram showing other embodiments relating to the driver of the piezoelectric actuator according to the present invention.  
       FIG. 7  is a sectional view A and an equivalent circuit diagram B showing a general constitution of the piezoelectric actuator.  
       FIG. 8  is a sectional view showing a constitution example to which the piezoelectric actuator is applied.  
       FIG. 9  is a side view of an essential part of  FIG. 8 .  
       FIG. 10  is a block circuit diagram showing the driver of a conventional piezoelectric actuator. 
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION  
      Embodiments of the present invention will be explained with reference to the drawings of the present invention hereunder. Note that the parts identical to those in the conventional example are assigned the same numerals without further explanation.  
       FIG. 1  is a block diagram showing an embodiment relating to a driver of a piezoelectric actuator according to the present invention.  
      In  FIG. 1 , each of the plural piezoelectric actuators  1   a ,  1   b ,  1   c ,  1   d ,  1   e ,  1   f ,  1   g , and  1   h  is composed of a conductive plate  3 , and a piezoelectric sheet (first piezoelectric sheet)  5  and a piezoelectric sheet (second piezoelectric sheet)  7  attached to the opposed surfaces of the conductive plate  3 , as shown in  FIG. 7A  for example, wherein electrodes  5   a  and  7   a  are provided on the opposed surfaces not touching on the plate  3  of each of the piezoelectric sheets  5  and  7 , with the plate  3  serving as a common electrode of each of the piezoelectric sheets  5  and  7 .  
      The electrodes  5   a  and  7   a  of the piezoelectric sheets  5  and  7  are connected to a positive terminal P 1  and a negative terminal P 2 , and the plate  3  is connected to a common terminal P 3 , so as to be supported by a box-shaped case  9  (not shown in  FIG. 1 ) in an open-sided shape, as shown in  FIG. 8 .  
      Note that in  FIG. 1 , the piezoelectric actuators  1   a  to  1   h  are not shown, however they are formed in the same way as the piezoelectric actuator  1  of  FIG. 7 .  
      As shown in  FIG. 8 , a positive side feeder line  19  and a negative side feeder line  21  are extended from a power supply section  15 , serving as lines to supply a positive DC power supply of about +50 V to +100 V, and a negative DC power supply of about −50 V to −100 V. Then, common resistors Ra and Rb for current limitation are inserted and connected in series in the middle thereof, respectively.  
      Phototransistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , and Q 7  and Q 8 , in which emitters and collectors are mutually connected in series, are disposed corresponding to the piezoelectric actuators  1   a  to  1   h.    
      Each collector of each of the phototransistors Q 1 , Q 3 , Q 5 , and Q 7  is directly connected to the positive side feeder line  19  on the side of the power supply section of the common resistor Ra, not through the common resistor Ra.  
      Each emitter of the phototransistors Q 2 , Q 4 , Q 6 , and Q 8  is connected to the negative side feeder line  21  on the side of the power supply section of the common resistor Rb.  
      Joints of the phototransistors Q 1  and Q 2 , Q 3  and Q 4 , Q 5  and Q 6 , and Q 7  and Q 8  are connected to common terminals P 3  of the piezoelectric actuators  1   a ,  1   b ,  1   c , to  1   h.    
      Positive terminals P 1  of the piezoelectric actuators  1   a ,  1   b ,  1   c , to  1   h  are connected to the terminal Sa of the common resistor Ra of the positive side feeder line  19  on the side opposite to the power supply section. Meanwhile, negative terminals P 2  of the piezoelectric actuators  1   a ,  1   b ,  1   c  to  1   h  are connected to a terminal Sb of the common resistor Rb of the negative side feeder line  21  on the side opposite to the power supply section.  
      Designation marks Ca 1  and Ca 2  in  FIG. 1  correspond to equivalent capacitors formed in the piezoelectric actuator  1   a  (corresponding to C 1  and C 2  in  FIG. 7B ). The same can be said for the designation marks Cb 1 , Cb 2 , Cc 1 , Cc 2 , and Ch 1 , Ch 2 .  
      The light emitting diodes D 1  and D 2 , D 3  and D 4 , D 5  and D 6 , and D 7  and D 8  are connected in series in a forward direction. The light emitting diode D 1  and the phototransistor Q 1 , the light emitting diode D 2  and the phototransistor Q 2 , the light emitting diode D 3  and the phototransistor Q 3 , the light emitting diode D 4  and the phototransistor Q 4 , the light emitting diode D 5  and the phototransistor Q 5 , the light emitting diode D 6  and the phototransistor Q 6 , the light emitting diode D 7  and the phototransistor Q 7 , and the light emitting diode D 8  and the phototransistor Q 8 , are correspondingly disposed in proximity to each other, respectively.  
      The light emitting diodes D 1  and D 2 , D 3  and D 4 , D 5  and D 6 , and D 7  and D 8  are connected to a switching control section  25 . Then, by this switching control section  25 , any one of the light emitting diodes D 1  to D 8  is switched and conducted to emit light.  
      The present invention is characterized by timing of sequentially selectively conduct-control of the plural light emitting diodes D 1  to D 8 , by the switching control section  25 .  
      Specifically, as shown in  FIG. 2 , for example, the switching control section  25  controls the plural piezoelectric actuators  1   a  to  1   h  by switching, in such a manner that the piezoelectric actuator  1   a  is on-controlled by applying the drive voltage thereto, and after a specified elapsed period of time previously set, the piezoelectric actuator  1   a  (more correctly piezoelectric sheets  5  and  7 ) is off-controlled by turning off the drive voltage applied to the piezoelectric sheets subjected to on-control, simultaneously with this, the next piezoelectric actuator  1   b  is on-controlled by applying the drive voltage thereto, then simultaneously with this, the drive voltage applied to the piezoelectric actuator  1   b  is off-controlled, and simultaneously with this, further next piezoelectric actuator  1   c  is on-controlled by applying the drive voltage thereto, and thereafter onward, such a control of the drive voltage is sequentially repeated.  
      Designation mark  27  in  FIG. 1  indicates the controller  27  constituted of the aforementioned phototransistors Q 1  to Q 8 , the light emitting diodes D 1  to D 8 , and the switching control section  25 . In the controller  27 , as described above, the switching control section  25  has a function to sequentially selectively switch and control the piezoelectric sheets  5  and  7  of each of the piezoelectric actuators  1   a  to  1   h , so that the drive voltage is applied thereto from the feeder lines  19  and  21 .  
      A connection structure of the equivalent capacitors Ca 1  to Ch 2  of the aforementioned piezoelectric actuators  1   a  to  1   h  and the controller  27  is shown in  FIG. 3 .  
      In  FIG. 1  also, the light emitting diodes D 1  to D 8  are connected by one line from the switching control section  25 . However, actually the light emitting diodes D 1  to D 8  are connected by individual wiring so that the light emitting diodes D 1  and D 2 , D 3  and D 4 , D 5  and D 6 , and D 7  and D 8  are corresponded. Then, in the same way as  FIG. 10 , any one of the light emitting diodes D 1  to D 8  is selected to allow emission control.  
      Then, specifically, when only light emitting diode D 1  is selectively conduct-controlled by the operation of the switching control section  25 , the phototransistor Q 1  is on-operated by receiving the light from the light emitting diode D 1 , and the piezoelectric sheet  5  (not shown in  FIG. 1 . Similarly not shown hereafter) of the piezoelectric actuator  1   a  is short-circuited by the positive drive voltage.  
      Meanwhile, the positive and negative drive voltages are applied to both sides of the piezoelectric sheet  7  of the piezoelectric actuator  1   a  (not shown in  FIG. 1 . Similarly not shown hereafter), and the capacitor Ca 2  is thereby charged, and the open end (operation piece  13 ) of the piezoelectric actuator  1   a  is displaced in the upward direction.  
      Then, the phototransistor Q 1  is off-operated by the off-control of the light emitting diode D 1  by the switching control section  25 , and the piezoelectric sheet  7  of the piezoelectric actuator  1   a  is discharged, and the open end thereof (operation piece  13 ) is returned to an original position.  
      When only light emitting diode D 2  is selectively conduct-controlled, the phototransistor Q 2  is on-operated by receiving the light from the light emitting diode D 2 , and the piezoelectric sheet  7  of the piezoelectric actuator  1   a  is short-circuited by the negative drive voltage.  
      Meanwhile, the capacitor Ca 1  is charged by applying the positive and negative drive voltages to both sides of the piezoelectric sheet  5  of the piezoelectric actuator  1   a , and the open end thereof (operation piece  13 ) is displaced in the downward direction.  
      Then, the phototransistor Q 2  is off-operated by the off-control of the light emitting diode D 2 , and the open end thereof (operation piece  13 ) is returned to the original position, simultaneously with discharge of the piezoelectric sheet  5  of the piezoelectric actuator  1   a.    
      Next, the operation of the driver of the piezoelectric actuators thus constituted will be explained, when the piezoelectric actuators  1   a  to  1   h  are on-controlled in this order, for example.  
      When the switching control section  25  selectively conduct-control only light emitting diode D 1 , the phototransistor Q 1  is on-operated and the positive side drive voltage is applied from the feeder line  19  to the piezoelectric actuator  1   a  through the common resistor Ra, thereby short-circuiting the piezoelectric sheet  5  of the piezoelectric actuator  1   a  by the positive drive voltage.  
      Meanwhile, the positive and negative drive voltages are applied to both sides of the piezoelectric sheet  7  of the piezoelectric actuator  1   a , and the capacitor Ca 2  is thereby charged.  
      The switching control section  25  functions to off-control the light emitting diode D 1 , after elapsed period of time of driving the piezoelectric actuator  1   a , and simultaneously with this, on-operate the phototransistor Q 3  by selectively conduct-controlling only light emitting diode D 3 .  
      Therefore, the capacitor Ca 2  of the piezoelectric actuator  1   a  is discharged in association with off-control of the piezoelectric actuator  1   a , and meanwhile, the capacitor Cb 2  is charged by short-circuiting the piezoelectric sheet  5  of the piezoelectric actuator  1   b  by the positive drive voltage, thereby applying the positive and negative drive voltages on both sides of the piezoelectric sheet  7  of the piezoelectric actuator  1   b.    
      At this time, as shown in  FIG. 3 , the piezoelectric sheet  7  (Capacitor Cb 2 ) is charged, while discharging current I mainly from the piezoelectric actuator  1   a  (capacitor Ca 2 ) runs to the piezoelectric sheet  7  (capacitor Cb 2 ) of the piezoelectric actuator  1   b  through the negative side feeder line  21 . Thereafter onward, this is sequentially repeated from the next actuators  1   c  to  1   h.    
      Specifically, the piezoelectric actuator  1   a  is on-controlled to charge the capacitor Ca 2 , and the piezoelectric actuator  1   a  is off-controlled to discharge the capacitor Ca 2  to produce discharging current I. Then, by this discharging current I, the capacitor Cb 2  of the piezoelectric actuator  1   b  to be on-controlled next is charged.  
      Then, the piezoelectric actuators  1   a  to  1   h  to be on-controlled is sequentially charged by the discharging current from the capacitor Ca 2  of the piezoelectric actuator  1   a  which is off-operated immediately before on-operated.  
      For this reason, during on/off switch control, current running through the common resistors Ra and Rb is made to be close to “zero” or extremely small, thus not too requiring power supply from the positive or negative side feeder lines  19  and  21  by on/off switching.  
      Hereafter, by using formulas or the like, consideration is given to the reason for not too requiring power supply from the positive or negative side feeder lines  19  and  21 , by the discharging current from the capacitors Ca 1  to Ch 2  of any one of the piezoelectric actuators  1   a  to  1   h  to charge the capacitors Ca 1  to Ch 2  of any other one of the piezoelectric actuators  1   a  to  1   h.    
      In order to simplify the consideration, two-sheet constitution to drive only piezoelectric actuators  1   a  and  1   b  in  FIG. 1  is considered as shown in  FIG. 4 .  
      Here, the capacitors Ca 1  and Ca 2  of the piezoelectric actuator  1   a  and the phototransistors Q 1  and Q 2  selectively on/off controlling the capacitors Ca 1  and Ca 2  are defined as a channel CH 1 , and the capacitors Cb 1  and Cb 2  of the piezoelectric actuator  1   b  and the phototransistors Q 3  and Q 4  selectively on/off controlling the capacitors Cb 1  and Cb 2  are defined as a channel CH 2 .  
      Such channels CH 1  and CH 2  are independently provided, and either of the phototransistor Q 1  or Q 2 , or the phototransistor Q 3  or Q 4  is on-operated, and the energy balance in this case is shown as follows.  
      Specifically, energy obtained by subtracting “dissipated energy at resistors Ra and Rb” and “dissipated energy due to offset of the holding energy polarity” from “inputted energy” from a power source E, becomes a capacitor holding energy in the capacitors Ca 1  to Cb 2 .  
      In a case of one-sheet constitution of the piezoelectric actuator  1   a , if the operation of the phototransistors Q 1  and Q 2  are taken into consideration, a current route in  FIG. 4  is shown in  FIG. 5A , where current i is expressed by formula 1.  
             i   =         2   ⁢   E     R     ⁢     ⅇ     -     t   CR                   [     Formula   ⁢           ⁢   1     ]             
 
      An amount of energy dissipation at the resistors Ra and Rb is expressed by formula 2.  
               Wu   +   Wd     =       2   ⁢     ∫       i   2     ⁢   R   ⁢     ⅆ   t           =     4   ⁢     CE   2                 [     Formula   ⁢           ⁢   2     ]             
 
      An amount of energy input from the power source E is expressed by formula 3.  
               2   ⁢   E   ⁢     ∫     i   ⁢     ⅆ   t           =     4   ⁢     CE   2               [     Formula   ⁢           ⁢   3     ]             
 
      In addition, in the case of two-sheet constitution of the piezoelectric actuators  1   a  and  1   b , when the operation of the phototransistors Q 1  and Q 3 , in which the current i is allowed to run in the same direction, is taken into consideration, the current rout of  FIG. 4  is shown in  FIG. 5B , and the current i is expressed by formula 4.  
             i   =       E   R     ⁢     ⅇ     -     t     2   ⁢   CR                     [     Formula   ⁢           ⁢   4     ]             
 
      An amount of energy dissipation at the resistors Ra and Rb is expressed by formula 5.  
               Wu   +   Wd     =       2   ⁢     ∫     2   ⁢     i   2     ⁢   R   ⁢     ⅆ   t           =     8   ⁢     CE   2                 [     Formula   ⁢           ⁢   5     ]             
 
      An amount of energy input from the power source E is expressed by formula 6.  
               2   ⁢   E   ⁢     ∫       (     2   ⁢   i     )     ⁢     ⅆ   t           =     8   ⁢     CE   2               [     Formula   ⁢           ⁢   6     ]             
 
      Further, in the case of two-sheet constitution of the piezoelectric actuators  1   a  and  1   b , when the operation of the phototransistors Q 1  to Q 4 , in which the current i is allowed to run in an opposite direction, is taken into consideration, the current route is shown in  FIG. 5C , and the current i is expressed by formula 7.  
             i   =       δ   ⁡     (   t   )       ⁢           ⁢     (         1   C     ⁢     ∫     i   ⁢     ⅆ   t           =     2   ⁢   E   ⁢     :     ⁢           ⁢       )               [     Formula   ⁢           ⁢   7     ]             
 
      The current i does not run through the resistors Ra and Rb.  
      Accordingly, the amount of energy dissipation at the resistors Ra and Rb is close to “zero”, and the amount of energy input from the power source E is expressed by formula 8.  
               2   ⁢   E   ⁢     ∫       (     2   ⁢   i     )     ⁢     ⅆ   t           =       2   ⁢     E   ·   2   ·   2     ⁢   CE     =     8   ⁢     CE   2                 [     Formula   ⁢           ⁢   8     ]             
 
      As described above, from the consideration using the formulas, it is found that the energy during on/off switch control of the piezoelectric actuators  1   a  and  1   b  moves directly between the piezoelectric actuators  1   a  and  1   b  not through the resistors Ra and Rb. The same can be said for the piezoelectric actuators  1   a  to  1   h.    
      Then, energy movement between the piezoelectric actuators  1   a  and  1   b  during on/off switch control is increased, thereby improving a transient characteristic and improving on/off switching performance of the overall device, and in addition, drastically reducing the amount of energy dissipation (amount of heat generation) at the resistors Ra and Rb, and the power consumption of the overall device can be reduced.  
      In this way, the driver of the piezoelectric actuator of the present invention has the plural piezoelectric actuators  1   a  to  1   h , each of which is composed of a plate  3  and piezoelectric sheets  5 ,  7  attached to the opposed surfaces of the plate interposed between the piezoelectric sheets  5  and  7 , and also has the controller  27  which functions to charge the piezoelectric sheets  5  and  7  by selectively on-controlling either of them by connecting the electrodes  5   a  and  7   a  of the opposed surfaces of the plate  3 , of the piezoelectric sheets  5  and  7  of each of the piezoelectric actuators  1   a  to  1   h , to the positive side or the negative side feeder line  19 ,  21 , and in this condition, by applying the drive voltage to the piezoelectric sheets  5  and  7  of any one of the piezoelectric actuators  1   a  to  1   h  which is selected to be on-controlled, from the positive side or the negative side feeder line  19  or  21  on the side of the plate  3 .  
      In addition, the controller  27  has the function to off-control the drive voltage applied to the piezoelectric sheets  5  and  7  of any one of the piezoelectric actuators  1   a  to  1   h  which is selected to be on-controlled, and simultaneously with this, charge the piezoelectric sheets  5  and  7  of any other one the piezoelectric actuators  1   a  to  1   h  to be on-controlled next by turning on the drive voltage applied thereto.  
      Therefore, for example, the discharging current runs when the piezoelectric actuator  1   a  is subjected to on-control to charge the capacitor Ca 2 , and the piezoelectric actuator  1   a  is subjected to off-control to discharge the capacitor Ca 2 , and by this discharging current, the capacitor Cb 2  of the piezoelectric actuator  1   b  to be on-controlled next is charged.  
      Any one of the piezoelectric actuators  1   a  to  1   h  to be on-controlled is sequentially charged by the discharging current from any one of the capacitors Ca 1  to Ch 2  of any one of the piezoelectric actuators  1   a  to  1   h  which is off-controlled immediately before being on-controlled. Therefore, the charging current which is apt to be increased at on/off switching needs not to be supplied so much from the positive or negative side feeder lines  19  and  21 .  
      Accordingly, in the driver driving the plural piezoelectric actuators  1   a  to  1   h , the drive current during on/off control of the piezoelectric actuators  1   a  to  1   h  can be drastically reduced, and the power consumption of the overall device can thereby be suppressed low.  
      In addition, resistors R 1  to R 8  for current limitation inserted per every piezoelectric actuators  1   a  to  1   h  can be reduced to the common resistors Ra and Rb. Moreover, such resistors R 1  to R 8  with small sizes can be used at a low cost and wiring is simplified, which achieves a cost reduction and improved productivity. Note that the number of components can also be reduced by omitting the resistors Ra and Rb for current limitation.  
      In the present invention, any one of the piezoelectric actuators  1   a  to  1   h  is off-controlled to produce discharging current, and by this discharging current from the capacitor, any other one of the piezoelectric actuators  1   a  to  1   h  to be driven next is on-controlled. Therefore, it is preferable that on-control timing of any other one of the piezoelectric actuators  1   a  to  1   h  to be on-controlled next is simultaneously with or immediately after off-control of any one of the piezoelectric actuators  1   a  to  1   h  subjected to on-control. In transition, the effect is decreased by half after charging to some extent the piezoelectric actuators  1   a  to  1   h  subjected to on-control.  
      preferably, the controller  27  of the present invention has the function to on-control the piezoelectric sheets  5  and  7  of any other one of the piezoelectric actuators  1   a  to  1   h  to be driven next, so that the drive voltage is applied thereto at a timing of off-controlling the drive voltage applied to the piezoelectric sheets  5  and  7  of any one of the piezoelectric actuators  1   a  to  1   h.    
      Incidentally, as shown in  FIG. 6 , the driver of the piezoelectric actuator according to the present invention may also be constituted by connecting the phototransistors Q 1 , Q 3 , Q 5 , and Q 7  to the positive side feeder line  19  through the terminal Sa of the common resistor Ra on the side opposite to the power supply section, or by connecting the phototransistors Q 2 , Q 4 , Q 6 , and Q 8  to the negative side feeder line  21  through the terminal Sb of the common resistor Rb on the side opposite to the power supply section. Other constitution is the same as that of  FIG. 1 , and the same effect can be obtained.  
      As described above, when the phototransistors Q 1  to Q 8  are connected to the positive side and negative side feeder lines  19  and  21  through the common resistors Ra and Rb on the side of the power supply section, the influence of fluctuation in the power supply voltage to the phototransistors Q 1  to Q 8  is diminished during on/off switch control of the phototransistors Q 1  to Q 8  (piezoelectric actuators  1   a  to  1   h ), and preferably a stable operation can thereby be easily realized.  
      The aforementioned each of the piezoelectric actuators  1   a  to  1   h  is arbitrarily constituted, and for example, may be composed of only piezoelectric plates  3  and  5 , or may have plural piezoelectric plates  3  and  5  and the plate  3  may be laminated, and also the supporting body is not limited to the constitution of the aforementioned case  9  of  FIG. 8 .  
      The present invention is useful for the constitution of sequentially switching and controlling the piezoelectric sheets directly or indirectly connected from the positive side or negative side feeder lines  19  and  21  directly, or sequentially controlling and switching the capacitors Ca 1 , Cb 1 , Cc 1 , and Ch 1 , or the capacitors Ca 2 , Cb 2 , Cc 2 , and Ch 2 .  
      According to the present invention, the switching mechanism of the controller  27  for switching the drive power source from the feeder lines to the plural piezoelectric actuators  1   a  to  1   h , is not limited to the aforementioned combination of the light emitting diodes D 1  to D 8  and the phototransistors Q 1  to Q 8 , but may be a contactless switch by only transistor for turning on and off the power source, and the switching control section  25  may be formed in accordance with the switching mechanism.  
      Note that when the light emitting diodes D 1  to D 8  are combined with the phototransistors Q 1  to Q 8 , an insulating state between the feeder lines  19 ,  21 , and the controller  17  side is easily formed and a stable operation can thereby be realized.  
      The driver of the piezoelectric actuator according to the present invention is not limited to the driver for driving the knitting needles of the knitting machine as described above, but applicable as a drive source mechanically moving a mechanical component directly or indirectly connected to each of the plural piezoelectric actuators having piezoelectric sheets, such as an ink jet drive source and a dot wire drive source in a printer.  
     
       FIG. 1 
     
     
         
          TO POWER SUPPLY SECTION  
           19  POSITIVE SIDE FEEDER LINE  
           21  NEGATIVE SIDE FEEDER LINE  
           25  SWITCHING CONTROL SECTION  
           27  CONTROLLER  
          COMMON RESISTOR Ra  
          COMMON RESISTOR Rb  
          TERMINAL Sa  
          TERMINAL Sb  
          PIEZOELECTRIC ACTUATOR 
 
  FIG. 2  
 
           1   a  PIEZOELECTRIC ACTUATOR  
           1   b  PIEZOELECTRIC ACTUATOR  
           1   c  PIEZOELECTRIC ACTUATOR 
   FIG. 3   
           19  POSITIVE SIDE FEEDER LINE  
           21  CONTROLLER  
          Sa TERMINAL  
          Sb TERMINAL  
           27  CONTROLLER 
   FIG. 6   
          TO POWER SUPPLY SECTION  
           19  POSITIVE SIDE FEEDER LINE  
           21  NEGATIVE SIDE FEEDER LINE  
          COMMON RESISTOR Ra  
          COMMON RESISTOR Rb  
           25  SWITCHING CONTROL SECTION  
          PIEZOELECTRIC ACTUATOR 
 
  FIG. 7  
 
           1  PIEZOELECTRIC ACTUATOR  
          P 1  POSITIVE TERMINAL  
          P 2  POSITIVE TERMINAL  
          P 3  COMMON TERMINAL  
           5  PIEZOELECTRIC SHEET  
           5   a  ELECTRODE  
           7  PIEZOELECTRIC SHEET  
           7   a  ELECTRODE  
           3  PLATE 
   FIG. 8   
           1   a ,  1   b  PIEZOELECTRIC ACTUATOR  
           3 , 5  PIEZOELECTRIC SHEETS  
           9  CASE  
           9   a  SIDE WALL  
           9   b  SIDE WALL  
           11  OPERATION HOLE  
           12  OPERATION PIECE  
           15  POWER SUPPLY SECTION  
           17  CONTROLLER 
   FIG. 9   
           9  CASE  
           9   b  SIDE WALL  
           11  OPERATION HOLE  
           13  OPERATION PIECE 
   FIG. 10   
           17  CONTROLLER  
           19  POSITIVE SIDE FEEDER LINE  
           21  NEGATIVE SIDE FEEDER LINE  
           23  SWITCHING CONTROL SECTION  
          PIEZOELECTRIC ACTUATOR