Abstract:
A vibratory driving device ( 1 ) comprising an electromechanical transducer ( 3 ) which causes mechanical displacement according to an applied voltage, a driving shaft ( 4 ) which is held so as to be displaced in its axial direction by the electromechanical transducer and which is provided on its surface with two resistive bodies ( 8 ) extending in the axial direction and connected to the electromechanical transducer at one end, a movable member ( 5 ) which slidably engages on the driving shaft so as to contact with the two resistive bodies to connect electrically the contacted points of the resistive bodies each other, a driving circuit ( 13 ) which applies a periodical driving voltage to the electromechanical transducer, and a measuring circuit ( 15 ) which measures electric resistance between the two resistive bodies can determine a position of the movable member and has a simplified wiring ( 7 ) with low risk of disconnection.

Description:
[0001]    This application is based on application No. 2009-174044 filed in Japan, the contents of which are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a vibratory driving device. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    For a vibratory driving device which oscillating a driving shaft with an electromechanical transducer to slidingly displace a movable member frictionally engaging on the driving shaft, JP-2000-205809-A and JP-2006-91208-A describe techniques in which the driving shaft consists of an resistive body and the movable member is used as an electric contact sliding on the resistive body, wherein a electric resistance between one end of the driving shaft and the movable member is measured to determine a position of the movable member. 
         [0004]    In these vibratory driving devices, it is required to connect conductive leads to the end of the driving shaft and the movable member so as to enable measuring a electric resistance between the end of the shaft and the movable member, in addition to the wiring for applying a driving voltage to the electromechanical transducer. Therefore, the wiring work is complicated in the vibratory driving device. Further, particularly the lead connected to the movable member is largely deformed due to the displacement of the movable member, and therefore the lead is at risk for disconnecting and breaking. 
       SUMMARY OF THE INVENTION 
       [0005]    In view of the above problems, an object of the present invention is to provide a vibratory driving device which can determine a position of a movable member and in which the wiring is simplified with low risk of disconnection. 
         [0006]    In order to achieve the objects of the present invention, there is provided a vibratory driving device comprising an electromechanical transducer which causes mechanical displacement according to an applied voltage, a driving shaft which is held so as to be displaced in its axial direction by the electromechanical transducer and which is provided on its surface with two resistive bodies extending in the axial direction, a movable member which slidably engages on the driving shaft so as to contact with the two resistive bodies to connect electrically the contacted points of the resistive bodies each other, a driving circuit which applies a periodical driving voltage to the electromechanical transducer, and a measuring circuit which measures electric resistance between the two resistive bodies. 
         [0007]    With this configuration, a position of the movable member can be calculated with measuring a resistance of a series circuit consisting of the two partial resistances of the resistive body in portions from the end to the movable member and the internal resistance of the movable member. According to the present invention, it is not required to wire to the largely displacing movable member. Therefore, the wiring is not exerted any strong stress, hence the vibratory driving device according to the present invention has a reduced risk of disconnection of the wiring. 
         [0008]    Further, in the vibratory driving device according to the present invention, the two resistive bodies may be electrically connected to electrodes of the electromechanical transducer respectively. 
         [0009]    With this configuration, the wiring for connecting the driving circuit serves as a wiring for connecting the measuring circuit and the resistive body. Therefore, only two wires are required to be wired to the vibratory driving device. 
         [0010]    Further, in the vibratory driving device according to the present invention, the resistive bodies may be made of resistive material applied beyond the drive shaft to the electromechanical transducer. 
         [0011]    With this configuration, forming of the resistive body and connecting the resistive body to the electromechanical transducer can be simultaneously carried out. Therefore, required production step is reduced. Moreover, this configuration significantly reduces the risk of a disconnection between the resistive body and the electromechanical transducer. 
         [0012]    Further, in the vibratory driving device according to the present invention, a predetermined conductive portion of the movable member may contact with the resistive body at a point. 
         [0013]    With this configuration, an electrically dividing point of the resistive body by the movable member is precisely defined according to the position of the movable member, hence the accuracy of the position measurement of the movable member is high. 
         [0014]    Further, in the vibratory driving device according to the present invention, the movable member may engage with a portion of the driving shaft where the resistive body is not provided, and the movable member may have a blush slidingly contacting with the resistive body. 
         [0015]    With this configuration, since the movable member engages with a portion where the resistive body is not provided, the displacing amount and the moving torque are stable. And, by arranging the brush in contact with the resistive body with a weak pressure, an attrition of the resistive body is prevented, and therefore a degrading of the measuring accuracy is prevented. Further, if a brush having a small contacting area is used, the electrically dividing point of the resistive body is secure so as to enhance the measuring accuracy of the position of the movable member. 
         [0016]    Further, in the vibratory driving device according to the present invention, the driving shaft may be covered with an insulating material and the resistive body may be formed on the insulating material. 
         [0017]    With this configuration, the driving shaft can be made from a conductive material. 
         [0018]    Further, in the vibratory driving device according to the present invention, the measuring circuit may measure a current when the driving circuit applies a direct-current voltage to the electromechanical transducer. 
         [0019]    With this configuration, the current of the electromechanical transducer is steady, and therefore any change in current value due to change of the partial resistance of the resistive body can be easily measured. 
         [0020]    Further, in the vibratory driving device according to the present invention, the measuring circuit may measure an average value of the current when the driving circuit applies the driving voltage to the electromechanical transducer. 
         [0021]    With this configuration, the measured current value is shifted by offset value proportional to the partial resistance of the resistive body with respect to the driving voltage. Therefore, the offset value is easily calculated by averaging the measured current value. 
         [0022]    Further, in the vibratory driving device according to the present invention, the measuring circuit may measure a peak value of the current when the driving circuit applies the driving voltage to the electromechanical transducer. 
         [0023]    With this configuration, a value of the inrush current is changed according to the partial resistance of the resistive body, therefore the position of the movable member is easily calculated by picking up the peak value of the current. 
         [0024]    Further, in the vibratory driving device according to the present invention may further comprise a controller which calculates the position of the movable member based on the electric resistance between the two resistive bodies measured by the measuring circuit. 
         [0025]    With this configuration, the vibratory driving device independently calculates the position of the movable member. 
         [0026]    In accordance with the present invention, a calculation of the position of the movable member is enabled by forming the two resistive bodies on the driving shaft, by electrically dividing the two resistive bodies with the movable member, and by measuring the series resistance of the partial resistance of the two resistive bodies. Therefore, the movable member is not needed to be wired. Hence the vibratory driving device according to the present invention can be produced with a simple wiring operation and has no risk of disconnecting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a schematic view of a vibratory driving device of first embodiment according to the present invention; 
           [0029]      FIG. 2  is a sectional view of the vibratory driving device in  FIG. 1 ; 
           [0030]      FIG. 3  is a circuit diagram of the vibratory driving device in  FIG. 1 ; 
           [0031]      FIG. 4  is a chart showing measured voltage depending on a position of the movable member in the vibratory driving device in  FIG. 1 ; 
           [0032]      FIG. 5  is a chart showing a waveform of measured voltages in the vibratory driving device in  FIG. 1 ; 
           [0033]      FIG. 6  is a schematic view of a vibratory driving device of second embodiment according to the present invention; 
           [0034]      FIG. 7  is a schematic view of a vibratory driving device of third embodiment according to the present invention; 
           [0035]      FIG. 8  is a sectional view of the vibratory driving device in  FIG. 7 ; 
           [0036]      FIG. 9  is a schematic view of a vibratory driving device of fourth embodiment according to the present invention; 
           [0037]      FIG. 10  is a schematic view of a vibratory driving device of fifth embodiment according to the present invention; 
           [0038]      FIG. 11  is an axial sectional view of the vibratory driving device in  FIG. 10 ; 
           [0039]      FIG. 12  is a schematic view of a vibratory driving device of sixth embodiment according to the present invention; 
           [0040]      FIG. 13  is a schematic view of a vibratory driving device of seventh embodiment according to the present invention; 
           [0041]      FIG. 14  is a schematic view of a vibratory driving device of eighth embodiment according to the present invention; and 
           [0042]      FIG. 15  is a circuit diagram of the vibratory driving device in  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0043]      FIG. 1  shows a vibratory driving device  1  as first embodiment according to the present invention. The vibratory driving device  1  comprises a weight  2  which is fixed to a chassis or like of an equipment, a piezoelectric element (electromechanical transducer)  3  of which one end in its elongating direction is held by the weight  2 , a driving shaft  4  of which one end is held by the other end of the piezoelectric element  3 , and a movable member  5  which frictionally engages slidably on the driving shaft  4 . 
         [0044]    The piezoelectric element  3  is formed by stacking up a plurality of layers of piezoelectric material with interposition of electrode layers and has external electrodes  6  the every other electrode layers on both sides. To the external electrodes  6 , conductive leads  7  are connected respectively. 
         [0045]    The driving shaft  4  has a columnar form with a diameter same with the width of the piezoelectric element  3 . For instance, the driving shaft  4  is formed by consolidating glass fibers with resin. And, the driving shaft  4  is provided on the both side surfaces respectively with resistive bodies  8  which are formed by applying resistive paint material in linear form with constant width and thickness in the axial direction of the driving shaft  4 . Further, the Driving shaft  4  is supported by guide members  9  slidably in the axial direction. 
         [0046]      FIG. 2  shows a configuration of the movable member  5 . The movable member  5  consists of a main body  10  which receives the driving shaft  4  and which is formed, for instance, from metallic material such as zinc, a cap member  11  which press the driving shaft  4  to the main body  10  and which is formed, for instance, from metallic material such as stainless steel, and a spring member  12  which clamps the main body  10  and the cap member  11  and which is formed, for instance, from beryllium copper. 
         [0047]    The main body  10  and the cap member  11  respectively contact at a point with the resistive body  8  of the driving shaft  4  to short circuit between the two contacting points of the resistive bodies  8  via the spring member  12 . 
         [0048]      FIG. 3  shows a circuit configuration of the vibratory driving device  1 . The vibratory driving device  1  has a driving circuit which applies a driving voltage between the two external electrodes  6  of the piezoelectric element  3 , and a measuring circuit  15  which is provided with a measuring resistance  14  for measurement of a current of the driving circuit  13 . 
         [0049]    The resistive bodies  8  of the driving shaft  4  are electrically divided by the movable member  5 . It is appropriate that the resistive bodies  8  have a resistance from several kilo ohms to several dozen of kilo ohms as a whole. An internal resistance of the movable member  5  is illustrated in  FIG. 3 , but the internal resistance of the movable member  5  in this embodiment is substantially ignorable. 
         [0050]    The driving circuit  13  is a full-bridge circuit which has four switching elements S 1 , S 2 , S 3 , S 4  and which connects one of the external electrodes  6  of the piezoelectric element  3  to a direct-current source  16  and connects other of the external electrodes  6  to the ground by turning on the switching elements S 1 , S 4  or the switching elements S 2 , S 3 . The switching elements S 1 , S 2 , S 3 , S 4  are turned on and off by the controller  17 . 
         [0051]    The driving circuit  13  applies a driving voltage in which the polarity is turned over periodically, by alternately turning on the switching element S 1 , S 4  and the switching element S 2 , S 3  cyclically. By controlling the duty ratio of this driving voltage, the driving shaft can be oscillated in an asymmetrical manner so as to displace slidably the movable member  5  on the driving shaft  4  in a desired direction. 
         [0052]    The measuring circuit  15  measures a grounding current of the driving circuit  13  transformed into a voltage by the measuring resistance  14 , with the switching element S 1 , S 4  of the driving circuit  13  turned on continuously to apply a direct-current voltage between the external electrodes  6 . In this embodiment, the measuring resistance  14  has a resistance around 200 ohms. And the measured voltage by the measuring circuit  15  is converted into digital and thereby recognized by the controller  17 . 
         [0053]    Since the piezoelectric element  3  can be assumed electrically as a capacitor, a direct current resistance between the external electrodes  6  is a resistance between the external electrodes  6  side ends of the resistive bodies  8  on the driving shaft  4 , that is sum of the partial resistances on the piezoelectric element  3  side among the partial resistances of the two resistive bodies  8  divided by the movable member  5 . 
         [0054]    In this embodiment, the surface resistance value of the resistive bodies  8  between the external electrodes  6  (resistance value of the partial resistances connected in series) is about 3 kilo ohms when the movable member  5  is positioned at the closest position to the piezoelectric element  3 , and is about 15 kilo ohms when the movable member  5  is positioned at the closest position to the distal end (opposite side to the piezoelectric element  3 ) of the driving shaft  4 . 
         [0055]    The partial resistances of the resistive bodies  8  increases in proportional to the position of the movable member. Therefore, as shown in  FIG. 4 , the measured voltage by the measuring circuit  15  has a negative proportional relation with the position of the movable member  5 . Accordingly, the controller  17  can calculate the position of the movable member  5  easily based on the measured voltage by the measuring circuit  15 . 
         [0056]      FIG. 5  shows measured voltages by the measuring circuit  15  when the periodical driving voltage is applied to displace slidingly the movable member  5  on the driving shaft  4 . In the chart, one cycle time of the driving voltage is about 7.5 msec, and the shown measured voltages are respectively in the case where the movable member  5  is located the position closest to the piezoelectric element  3  (proximal end) and in the case where the movable member  5  is located the position farthest from the piezoelectric element  3  (distal end). 
         [0057]    As shown in the chart, when the movable member  5  is positioned in the side of the piezoelectric element  3 , the grounding current of the driving circuit  13  is high. Therefore, the controller  17  can determine the position of the movable member  5  by integrating the measured voltage and calculating an average value of the measured voltage. In this embodiment, the average value of the measured voltage by the measuring circuit  15  is 0.39 V when the movable member  5  is located at the closest position to the piezoelectric element  3 , and the average value of the measured voltage by the measuring circuit  15  is 0.19 V when the movable member  5  is located at the farthest position from the piezoelectric element  3 . 
         [0058]    Alternatively, since the peak value of the grounding current of the driving circuit  13  changes, the peak value may be measured to calculate the position of the movable member  5 . In this embodiment, the peak value of the measured voltage by the measuring circuit  15  is 1.39 V when the movable member  5  is located at the closest position to the piezoelectric element  3 , and the peak value of the measured voltage by the measuring circuit  15  is 1.25 V when the movable member  5  is located at the farthest position from the piezoelectric element  3 . 
         [0059]      FIG. 6  shows a vibratory driving device  1   a  as second embodiment according to the present invention. It is to be noted that in the following description of the preferred embodiment of the present invention, components identical to those described before are designated by identical reference numerals to omit redundant explanation. In the vibratory driving device  1   a  as this embodiment, the driving shaft  4  consists of a shaft-like carbon solid  4   a  provided with a insulating layer  4   b  made of PPS resin on surface and with the resistive bodies  8  on the insulation layer  4   b . As this embodiment, to make the driving shaft from a conductive material, an electrical insulation between the two resistive bodies should be ensured by providing the insulating layer  4   b.    
         [0060]      FIG. 7  shows a vibratory driving device  1   b  as second embodiment according to the present invention. In the vibratory driving device  1   b  as this embodiment, the connected portion of the piezoelectric element  3  and the driving shaft  4  is supported by the supporting member  18 . As shown in  FIG. 8 , supporting member  18  surrounds three directions of the circumference of the piezoelectric element  3  to hold the piezoelectric element  3  and the driving shaft  4  with adhesive  19 . The resistive body  8  and the supporting member  18  can contact each other, depending on the condition of the assembling of the vibratory driving device  1   b . Accordingly, the supporting member  18  should be made from an insulating material to prevent the resistive bodies  8  from short circuiting. 
         [0061]      FIG. 9  shows a vibratory driving device  1   c  as third embodiment according to the present invention. As this embodiment suggests, surfaces of the main body  10  and the cap member  11  may have any shape for a surface contacting with the driving shaft  4 . Also, if the resistive bodies  8  are insulated each other and can be divided by the movable member  5 , the resistive bodies  8  may be provided in any arrangement. 
         [0062]      FIGS. 10 and 11  show a vibratory driving device  1   d  as fifth embodiment according to the present invention. In the vibratory driving device  1   d  as this embodiment, the movable member  5  and the main body  10  are formed, for instance, by machining of the stainless steel, so as to have respectively two inclined faces  20  slidingly contacting with the driving shaft. Each inclined face  20  is arranged to contact with the portion of the driving shaft  4  where the resistive bodies  8  are not formed. 
         [0063]    Further, the main body  10  and the cap member  11  respectively provided with a brush  21  which contacts slidingly to the resistive body  8  formed on the driving shaft  4  between the two inclined faces  20 . For instance, the brush  21  is made of a thin plate of beryllium cupper. And the contacting pressure of the brush  21  to the driving shaft  4  is designed sufficiently weaker in contras with the contacting pressure of the main body  10  and the cap member  11  to the driving shaft  4  caused by the spring member  12 . 
         [0064]    In this embodiment, since the main body  10  and the cap member  11  of the movable member  5  are frictionally engages with a portion of the driving shaft  4  where the resistive body is not formed, frictional force is stable and therefore the driving speed and the driving torque do not vary. Since the brushes  21  contact with the resistive bodies  8  with a small pressure, the resistive bodies  8  practically are not worn. Therefore, the resistivity of the resistive bodies  8  are not changed, hence the relation between the measured voltage by the measuring circuit  15  and the position of the movable member  5  is not changed. Furthermore, the brushes  21  contact in a point to the resistive bodies  8 , and therefore the electrically dividing point of the resistive bodies  8  is precisely defined according to the position of the movable member  5 , hence the accuracy of the position measurement of the movable member  5  is improved. 
         [0065]      FIG. 12  shows a vibratory driving device  1   e  as sixth embodiment according to the present invention. In the vibratory driving device le as this embodiment the main body  10  and the cap member  11  of the movable member  5  are, for instance, formed by injection molding with PPS and respectively integrated metallic members  22 ,  23  which is made of pressed stainless steel and form the two inclined faces  20  slidingly contacting with the driving shaft  4 , since the metallic members  22 ,  23  has inserted into the molds when the injection molding. 
         [0066]    The metallic member  23  of the cap member  11  extends partially to lateral sides to hold the brushes  21  which slidingly contact to the resistive bodies  8  of the driving shaft  4  respectively. In this embodiment, the metallic member  23  of the cap member  11  and two brushes  21  divide the resistive bodies  8  and short circuit between the divided points. Therefore, the main body  10 , the cap member  11  and the spring member  12  is not needed to be completely conductive, and can be made from an advantageous material chosen in view of mechanical property and workability. 
         [0067]      FIG. 13  shows a vibratory driving device  1   f  as seventh embodiment according to the present invention. In the vibratory driving device  1   f  as this embodiment, the brushes  21  are laterally protruding from the movable member  5 . With employing this configuration of the brushes  21 , while keeping a basic design of the movable member of a conventional vibratory driving device, a configuration according the present invention so as to divide two resistive bodies respectively and to connect the resulted partial resistances can be achieved, for instance, by inserting the brushes  21  respectively between the main body  10  and the spring member  12  and between the cap member  11  and the spring member  12 . 
         [0068]    Further  FIG. 14  shows a vibratory driving device  1   g  as eighth embodiment according to the present invention. In the vibratory driving device  1   g  as this embodiment, the two resistive bodies  8  are connected each other through a resistive body  8   a  which is formed on the distal end of the driving shaft  4 . In the case where the piezoelectric element  3  and the driving shaft  4  is formed in a rectangular columnar shape which is sliced from a plate-like base material, the resistive bodies  8  and the resistive body  8   a  can be formed by slicing the plate-like base material after dipping in to a resistive paint material. 
         [0069]      FIG. 15  shows an equivalent circuit of the vibratory driving device  1   g  as this embodiment. As, the circuit diagram teaches, if the resistance of the movable member  5  can be ignored, the partial resistance of the far side of resistive bodied  8  and the resistance of the resistive body  8   a  at the distal end of the driving shaft  4  does not influence the grounding current. 
         [0070]    The measuring circuit  15  of this embodiment further has a capacitor  24  and therefore is configured as a low pass filter which outputs a voltage representing an average value of the grounding current in an electrical manner. Accordingly, the controller  17  is not required to integrate the outputted voltage from the measuring circuit  15 , hence the controller  17  has a reduced arithmetic load. 
         [0071]    Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.