Abstract:
A piezoelectric actuator is formed in a manner which enhances the identifying function of markings provided thereon, and minimizes the influence on the markings when an electrode pattern on the piezoelectric actuator is shifted. The piezoelectric actuator has a piezoelectric element, an electrode pattern formed thereon, and at least one identifying marking formed on the electrode pattern, each identifying marking having a shape comprising multiple sides and being formed at a specific location of the electrode pattern for use in identifying a characteristic of the electrode pattern. In one embodiment, the piezoelectric element has a disk shape, the electrode pattern comprises a plurality of electrodes provided on an inner side of the piezoelectric element, selected electrodes being connected to each other in a desired pattern, and the identifying marking is formed on the electrode pattern proximate a peripheral edge of the piezoelectric-element and has at least three straight sides so that the area of the identifying marking is based on the length of its sides rather than a radius. Thus, shifting of the identifying marking with respect to the curved peripheral edge of the disk-shaped piezoelectric element results in reduction in area of the identifying marking on a linear basis rather than based on a squared value of a radius. In another embodiment, a plurality of identifying markings are arranged in a spaced-apart relation on the piezoelectric element.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a piezoelectric actuator in which a marking is formed at an electrode pattern on a piezoelectric element and a method of compensating a direction thereof. 
     In recent times, in the field of a micromotor, a piezoelectric actuator utilizing a piezoelectric element subjected to predetermined polarization processing has attracted attention. 
     In the procedure of fabricating the piezoelectric actuator, there is utilized a marking produced by forming a shape of an electrode pattern in identifying directions of polarization of respective divided electrodes in polarization processing, identifying a direction of a set position of the piezoelectric element in forming an electrode pattern for shortcircuiting, in identifying a direction of pasting a piezoelectric element on an elastic member in pasting operation, in identifying a direction of assembling a motor in assembling operation and in identifying a direction of attaching lead wires in attaching operation. 
     FIG. 17 shows a plane structure of a piezoelectric actuator according to a conventional example. 
     A piezoelectric actuator  100  according to the conventional example is installed with a piezoelectric element  101  produced by dividing a circular disk body in a fan-like shape in the peripheral direction, an electrode pattern  102  formed with electrodes  102   a ,  102   b ,  102   c ,  102   d ,  102   e  and  102   f  at every other divided portion in the fan-like shape of the piezoelectric element  101  in which the electrodes are shortcircuited at outer peripheral portions thereof, an electrode pattern  103  formed with electrodes  103   a ,  103   b ,  103   c ,  103   d ,  103   e  and  103   f  similarly in a fan-like shape in which the electrodes are shortcircuited at inner peripheral portions thereof and an entire face electrode, not illustrated, formed on a side of the piezoelectric element  101  opposed to the electrode patterns  102  and  103 , and further formed with a marking  104  in a semicircular shape at a portion of the outer peripheral portion of the electrode  102   a  in the fan-like shape of the electrode pattern  102  (for example, refer to JP-A-1-283074, JP-A-3-219681). 
     However, the above-described marking  104  in the semicircular shape cannot be set with an area larger than that illustrated above to avoid overlapping the entire face electrode formed on the opposed side. 
     Further, when the divided electrode  102 a in the fan-like shape and the piezoelectric element  101  are formed to shift from each other, there also causes a situation in which the position of the marking  104  cannot be detected by an image processing apparatus. The reason is as follows. 
     1) When a portion of the marking  104  rests on the outer periphery of the piezoelectric element  101 , the area of the marking  104  is extremely reduced in accordance with the radius of curvature of the circle. 
     2) The marking  104  is deviated from the outer periphery of the piezoelectric element  101  and the marking is not formed at all. 
     3) An area of a blank margin portion in a ring-like shape between the divided electrode  102 a in the fan-like shape and the outer periphery of the piezoelectric element  101  (portion not formed with the electrode pattern  102 ) is widened and the marking  104  cannot be discriminated from the blank margin portion. 
     Further, when dirt or dust having a shape and a size similar to those of the marking  104  is adhered to the electrode pattern  102  or  103 , there poses a problem in which the correct position of the marking cannot be detected. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a piezoelectric actuator and a method of compensating a direction thereof promoting a function of identifying a marking and minimizing adverse influence on a marking even when an electrode pattern is formed to shift. 
     That is, according to solving means of the problem, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator having a piezoelectric element forming an electrode pattern: 
     wherein the electrode pattern is formed with at least one marking in a shape comprising multiple sides (When the shape is closed, a polygonal shape is constituted. The same as follows.) for determining a direction of forming the electrode pattern of the piezoelectric element. 
     In the above-described solving means, the shape of the marking includes a shape comprising three sides (When the shape is closed, a tetragonal shape is constituted. The same as follows.), a shape comprising four sides (When the shape is closed, a pentagonal shape is constituted. The same as follows.) or other shape comprising multiple sides. Further, the position of the marking includes that of either of cases of forming the marking at an outer peripheral portion of the electrode pattern and at inside thereof. 
     The piezoelectric element includes shapes of a circular disk, a ring-like shape, a polygon and the like. 
     According to the solving means, the area surrounded by the shape comprising multiple sides becomes larger than an area surrounded by a semicircle and accordingly, the identifying function of the marking is promoted. Further, when the marking having the shape comprising multiple sides rests on the outer periphery of the piezoelectric element, the area is reduced in accordance with an internal angle of the shape comprising multiple sides and accordingly, a rate of reducing the area is smaller than that of reducing the marking in the semicircular shape. 
     Further, according to the piezoelectric actuator, the marking is featured in having a shape comprising three sides. 
     According to the solving means, an area surrounded by the shape comprising three sides becomes larger than the area surrounded by a semicircle and accordingly, the identifying function of the marking is promoted. Further, when the marking having the shape comprising three sides rests on the outer periphery of the piezoelectric element, the area is reduced by a constant rate and accordingly, the rate of reducing the area is smaller than that of reducing the marking in the semicircular shape. 
     Further, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator in which a piezoelectric element is divided in a peripheral direction and electrodes are formed at divided portions at least contiguous to each other to thereby constitute an electrode pattern: 
     wherein at least one marking for determining a direction of forming the electrode pattern of the piezoelectric element is formed on an inner side of an outer periphery of the electrode pattern and between the electrodes contiguous to each other in the electrode pattern. 
     In the above-described solving means, the shape of the piezoelectric element includes any of a circular disk shape, a ring-like shape, a polygonal shape and so on. Further, the respective electrodes formed at the divided portions include either of a system for connecting leads to the respectives and a system of shortcircuiting predetermined ones of the electrodes. 
     The shape of the marking includes a circular shape, a semicircular shape, a shape comprising two sides, a shape comprising three sides and other shapes comprising multiple sides as well. 
     According to the solving means, the marking is disposed on an inner side of an outer periphery of the electrode pattern and accordingly, even when the electrode pattern rests on the outer periphery of the piezoelectric element, no adverse influence is effected and sufficient identifying performance is ensured. 
     Further, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator having a piezoelectric element which is divided equally by n in a peripheral direction and in which p of consecutive divided portions polarized in one direction and p of consecutive divided portions polarized in a direction reverse to the one direction are alternately arranged and electrodes are formed at n of the divided portions of the piezoelectric element: 
     wherein the electrode pattern is formed with m of markings for determining a direction of forming the electrode pattern of the piezoelectric element at equal intervals (where m=n/(2×p), m: an optimum number of markings, n: a number of dividing the piezoelectric element, p: a number of consecution in the same polarization direction). 
     In the above-described solving means, the piezoelectric element includes any of a circular disk shape, a ring-like shape, a polygonal shape and so on. 
     The shape of the marking includes a circular shape, a semicircular shape, a shape comprising two sides, a shape comprising three sides and a shape comprising multiple sides as well. The position of the marking includes any of a case where it is formed at an outer peripheral portion of the electrode, a case where it is formed at inside of the electrode and a case where it is formed between electrodes. 
     According to the solving means, by recognizing any of the markings, a direction of polarization of the respective divided portion of the piezoelectric element can be specified. That is, the markings are formed at each unit (2×p) of an arrangement of a polarization direction polarized regularly and accordingly, when any of m of the markings is recognized, the directions of polarization of n of the divided portions become apparent. Further, the direction of the electrode pattern of the piezoelectric is compensated among the unit divided portions in the direction of polarization and accordingly, a rotational angle to be compensated for can be reduced. 
     Further, there is provided a method of compensating a direction of the piezoelectric actuator according to any one of the above-described piezoelectric elements, characterized in comprising the steps of: 
     recognizing the markings formed at the electrode pattern on the piezoelectric element, determining the direction of forming the electrode pattern of the piezoelectric element based on the recognized markings, determining an angle to be compensated by comparing the direction of forming and a set direction of the electrode pattern of the piezoelectric element and compensating the piezoelectric element in the set direction by pivoting the piezoelectric element by the compensated angle. 
     In the above-described solving means, the method of recognizing the marking includes either of a method by optical observation and a method by mechanical means of a camera or the like. 
     Further, the direction compensating method is used, for example, in adjusting a direction of the piezoelectric element when polarization is carried out, a direction of a set position of the piezoelectric element in forming the electrode pattern for shortcircuiting, a direction of pasting the piezoelectric element on an elastic body, a direction of assembling a motor in assembling operation and a direction of attaching lead wires in attaching operation. 
     According to the solving means, the marking formed at the electrode pattern on the piezoelectric element is clearly recognized, the direction of forming the electrode pattern of the piezoelectric element is determined based on the recognized marking, the angle to be compensated for is determined by comparing the direction of forming the electrode pattern of the piezoelectric element with the set direction and the piezoelectric element is compensated to the set direction by pivoting it by an amount of the angle of compensation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an explanatory view showing a plane structure of a piezoelectric actuator according to Embodiment  1  to which the invention is applied. 
     FIG. 2 is an explanatory view schematically showing a positioning device. 
     FIG. 3 is an explanatory view showing a plane structure of the piezoelectric actuator in an electrode forming step according to FIG.  1 . 
     FIG. 4 is an explanatory view showing a plane structure of the piezoelectric actuator in a polarizing step according to FIG.  1 . 
     FIG. 5 is an explanatory view showing a plane structure of the piezoelectric actuator in a step of forming shortcircuit electrodes according to FIG.  1 . 
     FIG. 6 is an explanatory view showing a plane structure of a piezoelectric actuator according to Embodiment  2  to which the invention is applied. 
     FIG. 7 is an explanatory view showing a plane structure of a piezoelectric actuator according to Embodiment  3  to which the invention is applied. 
     FIG. 8 is an explanatory view showing a plane structure of the piezoelectric actuator in an electrode forming step according to FIG.  7 . 
     FIG. 9 is an explanatory view showing a plane structure of the piezoelectric actuator in a polarizing step according to FIG.  7 . 
     FIG. 10 is an explanatory view showing a plane structure of the piezoelectric actuator in a step of forming shortcircuit electrodes according to FIG.  7 . 
     FIG. 11 is an explanatory view showing a plane structure in a polarizing step of a piezoelectric actuator in a first modified mode according to FIG.  7 . 
     FIG. 12 is an explanatory view showing a plane structure in a polarizing step of a piezoelectric actuator in a second modified mode according to FIG.  7 . 
     FIG. 13 is an explanatory view showing a plane structure of a piezoelectric actuator in a third modified mode according to FIG.  7 . 
     FIG. 14 is an explanatory view showing a plane structure of a piezoelectric actuator in a fourth modified mode according to FIG.  7 . 
     FIG. 15 is an explanatory view showing a plane structure of a piezoelectric actuator in a fifth modified mode according to. FIG.  7 . 
     FIG. 16 is an explanatory view showing a plane structure of a piezoelectric actuator in a sixth modified mode according to FIG.  7 . 
     FIG. 17 is an explanatory view showing a plane structure of a piezoelectric actuator according to a conventional technology. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed explanation will be given of embodiments according to the invention in reference to FIG.  1  through FIG. 16 as follows. 
     Embodiment 1 
     FIG. 1 shows a plane structure of a piezoelectric actuator. 
     A piezoelectric actuator  10  is provided with a piezoelectric element  11  and electrode patterns  12  and  13 . 
     In this case, the piezoelectric element  11  is formed in a circular disk shape by using, for example, barium titanate, lead titanate, lithium niobate, lithium tantalate or lead titanate/lead zirconate solid solution and a center hole  11   m  is formed at its center. 
     Further, the piezoelectric element  11  is divided equally in  12  in a fan-like shape in the peripheral direction, every other ones of divided portions  11   a ,  11   b ,  11   c ,  11   d ,  11   e  and  11   f  constitute one group and divided portions  11   g ,  11   h ,  11   i ,  11   j ,  11   k  and  11   l  constitute other group. Further, respective groups of the divided portions  11   a  . . .  11   f ,  11   g  . . .  11   l  are polarized in directions alternately reversed in the thickness direction as shown by FIG.  4 . That is, the divided portions  11   g  . . .  11   l  are alternately arranged with two consecutive divided portions polarized in one direction and two consecutive divided portions polarized in a direction reverse to the one direction. 
     The electrode pattern  12  is formed with electrodes  12   a ,  12   b ,  12   c ,  12   d ,  12   d  and  12   f  substantially in a fan-like shape at six locations in correspondence with the divided portions  11   a  . . .  11   f  and outer peripheral portions of the respective electrodes  12   a  . . .  12   f  are shortcircuited. 
     Further, the outer peripheral portion of the electrode  12   a  is formed with a marking  14  in a shape comprising three sides. The marking  14  is used as a reference in calculating a rotational angle to be compensated for in determining a direction of forming the electrode pattern of the current piezoelectric element  11 . 
     The electrode pattern  13  is formed with electrodes  13   a ,  13   b ,  13   c ,  13   d ,  13   e  and  13   f  substantially in a fan-like shape in correspondence with the divided portions  11   g  . . .  11   l  and inner peripheral portions of the respective electrodes  13   a  . . .  13   f  are shortcircuited. 
     Next, an explanation will be given of a method of fabricating the piezoelectric actuator  10 . 
     First, an explanation will be given of a positioning device used in the fabrication method. 
     FIG. 2 is a view schematically showing a positioning device. 
     A positioning device  30  is provided with an X, Y, Z axes robot  31 , a vacuum chuck  32  fixed at a front end of the X, Y, Z axes robot  31  and a CCD (Charge Coupled Device) camera  33  installed forward from the vacuum chuck  32 . Further, the CCD camera  33  is connected to an image processing apparatus  34  and the image processing apparatus  34  and the X, Y, Z axes robot  31  are connected to a control circuit  35 . 
     In this case, the X, Y, Z axes robot  31  comprises an arm  31   a  and an XYZ moving apparatus  31   b  for moving the arm  31   a  in X axis direction, Y axis direction and Z axis direction. 
     The vacuum chuck  32  sucks to chuck the piezoelectric element  11  and rotates the piezoelectric element in X-Y plane. 
     The image processing apparatus  34  comprises CPU (Center Processing unit), ROM (Read Only Memory), RAM (Random Access Memory), a display device, a storage device, an input/output interface and so on. 
     The control circuit  35  comprises CPU, ROM, RAM, an input/output interface and so on. 
     Further, the plane structures of the piezoelectric element  11  and electrode patterns  12  and  13  are photographed by the CCD camera  33  and the image data is outputted to the image processing apparatus  34 . The display device of the image processing apparatus  34  displays the piezoelectric element  11  and the electrode patterns  12  and  13  on the coordinate axes. 
     CPU of the image processing apparatus  34  calculates coordinates of the center of the center hole  11   m  of the piezoelectric element  11  and the marking  14  of the piezoelectric element  11  on the coordinate axes. Further, by comparing the coordinates of the center of the center hole  11   m  and a set position of the piezoelectric element  11 , a movement direction and a movement distance necessary for compensation are calculated. 
     Further, a rotational angle necessary for compensation is calculated by comparing a direction connecting the center of the center hole  11   m  and the coordinates of the marking  14  with the set direction of the piezoelectric element  11 . The above-described movement direction, the movement distance and the rotational angle necessary for compensation are outputted to the control circuit  35 . 
     The piezoelectric element  11  is sucked to chuck by the vacuum chuck  32 , moved in a direction of movement necessary for compensation by an amount of a distance of movement necessary for compensation by the X, Y, Z axes robot  31  and is rotated by an amount of the rotational angle necessary for compensation by the vacuum chuck  32 . 
     In this way, the piezoelectric element  11  is compensated to the set position and the set direction. 
     FIG. 3 shows a plane structure of a piezoelectric actuator in steps of forming electrodes. 
     Further, the electrodes  12   a  . . .  12   f  substantially in the fan-like shape are deposited by vapor deposition on the one group of the divided portions  11   a  . . .  11   f  and the electrodes  13   a  . . .  13   f  substantially in the fan-like shape are deposited by vapor deposition on the other group of the divided portions  11   g  . . .  11   l . Further, the marking  14  in the shape comprising three sides is formed at the outer peripheral portion of the electrode  12   a  and extended portions in an arc-like shape are formed on both sides of the outer peripheral portion. 
     By forming the marking  14  in the shape comprising three sides, even when the marking.  14  rests on the outer periphery of the piezoelectric element  11 , the area of the marking  14  is reduced by a constant rate and accordingly, the identifying function is not reduced extremely. 
     Arc-like electrodes  12   g ,  12   h ,  12   i  and  12   j  are deposited by vapor deposition on outer sides of the electrodes  12   b  . . .  12   f  in an arc-like shape in the peripheral direction. 
     The electrodes  13   b ,  13   d  and  13   f  are deposited by vapor deposition with extended portions extended in an arc-like shape from both sides of inner peripheral portions and the electrodes  13   a ,  13   c  and  13   e  are deposited by vapor deposition with projected portions projected in directions of the center of the circle. 
     FIG. 4 shows a plane structure of the piezoelectric actuator in a polarizing step. 
     By the CCD camera  33  of the positioning device  30 , the marking  14  and the center of the center hole  11   m  are recognized and the piezoelectric element  11  is set to the set position and the set direction. 
     In this case, an area surrounded by the shape comprising three sides of the marking  14  is wider than an area surrounded by a semicircle, the identifying function is promoted and accordingly, the marking  34  can be recognized by the image processing apparatus  34  further clearly. 
     Further, an electric field equal to or more than a negative coercive field is applied on the electrodes  12   a ,  12   c ,  12   e ,  13   b ,  13   d  and  13   f  and an electric field equal to or more than a positive coercive field is applied on the electrodes  12   b ,  12   d ,  12   f ,  13   a ,  13   c  and  13   e.    
     As a result, both of the one group of the divided portions  11   a  . . .  11   f  and the other group of the divided portions  11   g  . . .  11   l  are polarized in the thickness direction alternately in reverse directions. Further, (+) in the drawing designates a direction of polarization where the surface side is made positive and the rear face side is made negative and (−) designates a direction of polarization where the surface side is made negative and the rear face side is made positive. Further, dotted lines in the drawing show an arrangement of projections installed for bringing the piezoelectric element into the press contact with an elastic moving body. 
     FIG. 5 shows a plane structure of the piezoelectric actuator in a step of forming electrodes for shortcircuiting. 
     By the positioning device  30 , the center of the center hole  11   m  of the piezoelectric element  11  and the marking  14  are recognized and the piezoelectric element  11  is compensated for the set position and the set direction. 
     Next, a shortcircuit electrode  12   k  is deposited by vapor deposition among one extended portion of the electrode  12   a , the arc-like electrode  12   g  and the outer peripheral portion of the electrode  12   b , a shortcircuit electrode  12  is deposited by vapor deposition among the arc-like electrode  12   g , the arc-like electrode  12   h  and the electrode  12   c , a shortcircuit electrode  12   m  is deposited by vapor deposition among the arc-like electrode  12   h , the electrode  12   d  and the arc-like electrode  12   i , a shortcircuit electrode  12   n  is deposited by vapor deposition among the arc-like electrode  12   i , the electrode  12   e  and the arc-like electrode  12   j  and a shortcircuit electrode  12   p  is deposited by vapor deposition among the arc-like electrode  12   j , the electrode  12   f  and an extended portion of the electrode  12   a . Further, by shortcircuiting the electrodes  12   a  . . .  12   f , the electrode pattern  12  is formed. 
     A shortcircuit electrode  13   g  is deposited by vapor deposition among the projected portion of the electrode  13   a , an extended portion of the electrode  13   b  and an extended portion of the electrode  13   f , a shortcircuit electrode  13   h  is deposited by vapor deposition among the projected portion of the electrode  13   c , an extended portion of the electrode  13   b  and an extended portion of the electrode  13   d  and a shortcircuit electrode  13   i  is deposited by vapor deposition among the projected portion of the electrode  13   e , an extended portion of the electrode  13   d  and an extended portion of the electrode  13   f . Further, by shortcircuiting the electrodes  13   a  . . .  13   f , the electrode pattern  13  is formed. 
     As described above, according to the embodiment, the area surrounded by the shape comprising three sides of the marking  14  becomes larger than the area surrounded by the conventional semicircle and accordingly, the identifying function is promoted. 
     Further, the shape of the marking  14  is constituted by the shape comprising three sides and accordingly, even when the marking  14  rests on the outer periphery of the piezoelectric element  11 , the area is reduced by a constant rate and a rapid deterioration in the identifying function is prevented. 
     Further, the marking  14  is recognized, the angle to be compensated for in respect of the set direction of the piezoelectric element  11  is determined with the recognized marking  14  as a reference, the piezoelectric element  11  is pivoted in accordance with the determined angle to be compensated for and accordingly, the piezoelectric element  11  is compensated in the set direction. 
     Embodiment 2 
     FIG. 6 shows a plane structure of a piezoelectric actuator according to the embodiment 2 to which the invention is applied. 
     The piezoelectric actuator  10  is featured in that markings  14   a ,  14   b  and  14   c  having a shape the same as that of the marking  14  used in Embodiment  1  are formed at outer peripheral portions of the electrodes  12   a ,  12   c  and  12   e . Further, constitutions similar to those in Embodiment  1  are attached with the same notations and an explanation thereof will be omitted. 
     That is, the markings  14   a ,  14   b  and  14   c  are arranged at respective units of a regularly polarized arrangement among  12  of the divided portions  11   a  . . .  11   a  of the piezoelectric element  11  (twice as much as a number of the consecutive divided portions in the same direction of polarization) and are arranged at equal intervals. Further, by recognizing any one of the markings  14   a ,  14   b  and  14   c , directions of polarization of the respective divided portions  11   a  . . .  11   l  of the piezoelectric element  11  are specified. Accordingly, in positioning in connecting leads to the respective electrode patterns  12  and  13 , in positioning in assembling a motor, in positioning the piezoelectric actuator  10  to the projections of the elastic body, in positioning in vapor deposition of the shortcircuit electrodes and in positioning in carrying out polarizing operation, an angle to be compensated for is equal to or smaller than 60° and the angle to be compensated for becomes smaller than 180° when one marking is installed or 90° when two markings are installed. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 No. of divisions 
               
             
          
           
               
                   
                 No. of consecutive 
                   
               
               
                   
                 polarization direction 
                 Optimum No. of markings 
               
               
                 n 
                 p 
                 m 
               
               
                   
               
             
          
           
               
                 2 
                 1 
                 1 
               
               
                 4 
                 1 
                 2 
               
               
                   
                 2 
                 1 
               
               
                 6 
                 1 
                 3 
               
               
                   
                 3 
                 1 
               
               
                 8 
                 1 
                 4 
               
               
                   
                 2 
                 2 
               
               
                   
                 4 
                 1 
               
               
                 10 
                 1 
                 5 
               
               
                   
                 5 
                 1 
               
               
                 12 
                 1 
                 6 
               
               
                   
                 2 
                 3 
               
               
                   
                 3 
                 2 
               
               
                   
                 6 
                 1 
               
               
                 14 
                 1 
                 7 
               
               
                   
                 7 
                 1 
               
               
                 16 
                 1 
                 8 
               
               
                   
                 2 
                 4 
               
               
                   
                 4 
                 2 
               
               
                   
                 8 
                 1 
               
               
                 18 
                 1 
                 9 
               
               
                   
                 3 
                 3 
               
               
                   
                 9 
                 1 
               
               
                 20 
                 1 
                 10 
               
               
                   
                 5 
                 2 
               
               
                   
                 10 
                 1 
               
               
                   
               
             
          
         
       
     
     Table 1 shows a relationship among a number of dividing the piezoelectric element  11  in the peripheral direction, a number of consecutive divided portions in the same polarization direction and an optimum number of markings. 
     When the above-described number of markings is generalized, it is expressed by m=n/(p×2) (m: an optimum number of markings, n: a number of dividing the piezoelectric element, p: a number of consecutive divided portions in the same direction of polarization). 
     For example, when the number of divisions is set to 12, in the case where the number of consecutive divisions in the same polarization direction is 1, markings of 12/(1×2)=6 are formed at equal intervals. When the number of consecutive divisions in the same polarization direction is 2, markings of 12/(2×2)=3 are formed at equal intervals. When the number of consecutive divisions in the same polarization direction is 3, markings of 12/(3×2)=2 are formed at equal intervals. When the number of consecutive divisions in the same polarization direction is 6, a marking of 12/(6×2)=1 may be formed. Further, when any of the markings is recognized, the situation of the polarization direction of the piezoelectric element  11  becomes uniquely clarified. 
     Embodiment 3 
     FIG. 7 shows a plane structure of a piezoelectric actuator according to Embodiment 3 to which the invention is applied. 
     According to the piezoelectric actuator  10 , a marking  15   a  in a shape comprising three sides is formed between an electrode  12   q  of the electrode pattern  12  and the electrode  13   b  of the electrode pattern  13  which are contiguous to each other on inner sides of the outer peripheries of the electrode patterns  12  and  13  to each other. Similarly, a marking  15   b  is formed between the electrode  12   c  and the electrode  13   d  and a marking  15   c  is formed between the electrode  12   e  and the electrode  13   f.    
     According to such markings  15   a ,  15   b  and  15   c , even when the electrode patterns  12  and  13  are formed to shift from each other on the piezoelectric element  11 , the markings do not rest on the outer periphery of the piezoelectric element  11  and the identifying function is maintained. 
     Next, an explanation will be given of a method of fabricating the piezoelectric actuator. 
     FIG. 8 shows a plane structure of the piezoelectric actuator in a step of forming electrodes. 
     First, the electrodes  12   b  . . .  12   f ,  12   q  substantially in the fan-like shape are deposited by vapor deposition on one group of the divided portions  11   a  . . .  11   f  of the piezoelectric element  11 . Further, the marking  15   a  in the shape comprising three sides is formed between the electrode  12   q  and the electrode  13   b  contiguous to each other, further, similarly, the marking  15   b  is formed between the electrode  12   c  and the electrode  13   d  and the marking  15   c  is formed between the electrode  12   e  and the electrode  13   f.    
     In this case, the markings  15   a ,  15   b  and  15   c  are arranged at the respective number of the consecutive divided portions in the same polarization direction which is multiplied by 2, that is, at the respective minimum unit of expressing an arrangement in polarization directions and arranged at equal intervals. 
     Further, arc-like electrodes  12   g ,  12   h ,  12   i ,  12   j ,  12   r  and  12   s  are deposited by vapor deposition at the outer peripheral portion of the piezoelectric element  11 . 
     FIG. 9 shows a plane structure of the piezoelectric actuator in a polarizing step and FIG. 10 shows a plane structure of the piezoelectric actuator in a step of forming shortcircuit electrodes. 
     In the polarizing step, by the positioning device  30 , for example, the marking  15   a  and the center of the center hole  11   m  are recognized, the set direction and the set position of the piezoelectric element  11  are compensated for and polarizing operation similar to that in Embodiment 1 is carried out. 
     Next, in the step of forming the shortcircuit electrodes, by the positioning device  30 , for example, the marking  15   b  and the center of the center hole  11   m  are recognized and the set direction and the set position of the piezoelectric element  11  are compensated for. 
     In this case, only by recognizing a single one of the marking  15   b , the polarization directions of the respective divided portions  11   a  . . .  11   g  of the piezoelectric element  11  become apparent, the angle to be dispensed for is within a range of 60° and the piezoelectric element  11  is compensated to the set direction efficiently. 
     As shown by FIG. 10, a shortcircuit electrode  12   t  is formed among the arc-like electrode  12   r , the arc-like electrode  12   s  and the electrode  12   q  and in respect of other positions, similar to Embodiment 1, the shortcircuit electrodes  12   k ,  12 ,  12   m ,  12   n ,  12   p ,  13   g ,  13   h  and  13   i  are deposited by vapor deposition. 
     As has been described, according to the embodiment, other than achieving an effect similar to that in Embodiment 1, when the electrode patterns  12  and  13  are formed to shift from the piezoelectric element  11 , the markings  15   a ,  15   b  and  15   c  do not rest on the outer periphery of the piezoelectric element  11 , areas of the markings  15   a ,  15   b  and  15   c  are not reduced and accordingly, the identifying function is maintained. 
     Further, arrangement of the markings  15   a ,  15   b  and  15   c  is optimized and accordingly, by recognizing any one of the markings  15   a    15   c , directions of polarization of the divided portions  11   a  . . .  11   l  of the piezoelectric element  11  are clarified and the piezoelectric element  11  is efficiently compensated to the set direction. 
     Further, the embodiment may be modified as follows. 
     FIG. 11 shows a plane structure in the polarizing step in respect of a piezoelectric actuator according to a first modified mode of Embodiment 3. 
     According thereto, directions of polarization of the respective divided portions  11   a  . . .  11   f ,  11   g  . . .  11   l  are brought into a relationship reverse to that of the piezoelectric actuator according to Embodiment 3. 
     FIG. 12 is a plane structure in the polarizing step of a piezoelectric actuator according to a second modified mode of Embodiment 3. 
     According thereto, directions of polarization of the respective divided portions  11   a  . . .  11   f ,  11   g  . . .  11   l  are brought into a relationship where they are shifted by one divided portion to the counterclockwise direction from those of the piezoelectric actuator according to Embodiment 3. Further, in this modified mode, polarities of (+) and (−) may be switched. 
     FIG. 13 shows a plane structure of a piezoelectric actuator according to a third modified mode of Embodiment 3. 
     The piezoelectric actuator  10  is featured in that in place of the markings  15   a ,  15   b  and  15   c , markings  16   a ,  16   b  and  16 c in a shape comprising two sides are formed. 
     FIG. 14 shows a plane structure of a piezoelectric actuator according to a fourth modified mode of Embodiment 3. 
     The piezoelectric actuator  10  is featured in that in place of the markings  15   a ,  15   b  and  15   c  in the shape comprising three sides, markings  17   a ,  17   b  and  17   c  in a semicircular shape are formed. 
     FIG. 15 shows a plane structure of a piezoelectric actuator according to a fifth modified mode of Embodiment 3. 
     The piezoelectric actuator  10  is featured in that the marking  15   a  in the shape comprising three sides is formed between the electrode  12   q  and the electrode  13   a , the marking  15   b  in the shape comprising three sides is formed between the electrode  12   c  and the electrode  13   c  and the marking  15   c  in the shape comprising three sides is formed between the electrode  12   e  and the electrode  13   e.    
     FIG. 16 shows a plane structure of a piezoelectric actuator according to a six modified mode of Embodiment 3. 
     The piezoelectric actuator  10  is featured in that the markings  15   a ,  15   b  and  15   c  respectively in a quadrilateral shape are formed at intermediary positions in the diameter direction of the electrode patterns  12  and  13 . 
     According thereto, even when the electrode patterns  12  and  13  are formed to shift toward an outer diameter direction of the piezoelectric element  11 , there is achieved an advantage that the markings  15   a ,  15   b  and  15   c  suffer less adverse influence. 
     As has been described, an area surrounded by a shape comprising multiple sides becomes larger than the area surrounded by a semicircle and accordingly, the function of identifying markings is promoted. Further, when the marking having the shape comprising multiple sides rests on the outer periphery of a piezoelectric element, the area is reduced in accordance with an internal angle of the shape comprising multiple sides and accordingly, the rate of reducing the area is smaller than that of reducing the marking in the semicircular shape. 
     Further, an area surrounded by a shape comprising three sides becomes larger than the area surrounded by a semicircle and accordingly, the function of identifying the marking is promoted. Further, when the marking in the shape comprising three sides rests on the outer periphery of a piezoelectric element, the area is reduced by a constant rate and accordingly, the rate of reducing the area is smaller than that of reducing that of the marking in the semicircular shape. 
     Further, the marking is disposed on an inner side of an outer periphery of an electrode pattern and even when the electrode pattern rests on the outer periphery of a piezoelectric element, no adverse influence is effected and accordingly, sufficient identifying function is ensured. 
     Further, by recognizing the markings, directions of polarization of respective divided portions of a piezoelectric element can be specified and accordingly, when a direction of forming an electrode pattern of a piezoelectric element is compensated for, an angle to be compensated for can be reduced. 
     Further, the marking formed at an electrode pattern on a piezoelectric element is clearly recognized, the direction of forming an electrode pattern of a piezoelectric element is determined based on the recognized marking, an angle to be compensated for is determined by comparing the direction of forming the electrode pattern of the piezoelectric element with a set direction thereof, the piezoelectric element is pivoted by an amount of the angle to be compensated for and accordingly, the piezoelectric element is compensated to the set direction.