Abstract:
An oscillator includes an electromechanical energy conversion element and an elastic body. The elastic body is bonded with the electromechanical energy conversion element by metallic bonding and is configured to be driven by deformation of the electromechanical energy conversion element.

Description:
[0001]    This application is based on and claims the benefit of priority from Japanese Patent Application No. 2011-072712 filed on 29 Mar. 2011, the contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an oscillator, a vibration actuator, a lens barrel, a camera and a bonded product, as well as a bonding method of the oscillator and bonded product. 
         [0004]    2. Related Art 
         [0005]    A vibration actuator causes an electromechanic energy conversion element to deform by a driving signal, so that an elastic body bonded with the electromechanic energy conversion element is driven. Accordingly, the vibration actuator causes a relative movement member in pressure contact with the elastic body to move. For bonding the electromechanic energy conversion element with the elastic body, an adhesive and an adhesive layer are generally used (see Japanese Unexamined Patent Application Publication No. H5-261647). 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention, an oscillator includes an electromechanical energy conversion element and an elastic body. The elastic body is bonded with the electromechanical energy conversion element by metallic bonding and is configured to be driven by deformation of the electromechanical energy conversion element. 
         [0007]    According to another aspect of the present invention, a method for producing an oscillator includes bonding an electromechanical energy conversion element and an elastic body by metallic bonding to produce the oscillator. The elastic body is configured to be driven by deformation of the electromechanical energy conversion element. 
         [0008]    According to further aspect of the present invention, a bonded product includes a first member and a second member. The second member is bonded with the first member by vacuum bonding at room temperature. The vacuum bonding includes surface activation. Either one of the first member and the second member is metal-plated. 
         [0009]    According to the other aspect of the present invention, a method for bonding a first member with a second member includes: applying metal plating to either one of the first member and the second member; and bonding the first member with the second member by vacuum bonding at room temperature. The vacuum bonding includes surface activation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a front view of a vibration actuator according to an exemplary embodiment; 
           [0012]      FIG. 2  is a conceptual diagram of a camera using the vibration actuator of  FIG. 1 ; and 
           [0013]      FIG. 3  is a flowchart describing steps of a method for bonding a driving body and a piezoelectric element by surface activated bonding (SAB) at room temperature. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    An oscillator, a vibration actuator provided with the oscillator, a lens barrel provided with the vibration actuator, a camera provided with the lens barrel, and a method for bonding the oscillator as an embodiment of the present invention will be described with reference to the drawings. 
         [0015]      FIG. 1  is a front view of a vibration actuator  100 . 
         [0016]      FIG. 2  is a conceptual diagram of a lens barrel  300  provided with the vibration actuator  100  and a camera  200  to which the lens barrel  300  is attached. 
         [0017]    As shown in  FIG. 1 , the vibration actuator  100  according to the present embodiment includes a base member  10  and a rotor  120  placed on the base member  10 . 
         [0018]    The base member  10  is formed of a metallic material such as stainless steel in a hollow cylindrical shape, through which a supporting shaft  15  is centrally inserted and fixed. At an end portion of the base member  10  facing the rotor  120 , six supporting concavities  11  that accommodate driving mechanisms  30  (described later) are provided in a peripheral direction, for example. 
         [0019]    The rotor  120  is rotatably supported by the supporting shaft  15 . 
         [0020]    On an outer peripheral surface of the rotor  120 , a gear  125  is formed to output a rotational force. The rotor  120  is supported by the driving mechanisms  30 . 
         [0021]    The number of the driving mechanisms  30  is six, which are supported respectively by the six supporting concavities  11  provided in the peripheral direction. Each of the driving mechanisms  30  includes: a lifter  31  that lifts the rotor  120 ; a slider  32  that causes the rotor  120  to move in a rotational direction; a lift driving unit  33  disposed between the lifter  31  and the base member  10 ; and a slide driving unit  34  disposed between the lifter  31  and the slider  32 . 
         [0022]    A lifter  31  is accommodated in each of the six supporting concavities  11  at the base member  10 . An upper face of the lifter  31  projects upward from an upper face of the base member  10  by a predetermined amount. 
         [0023]    The lift driving unit  33  and the slide driving unit  34  are each provided with two piezoelectric elements arranged in parallel with each other. Each piezoelectric element is a rectangular plate formed of piezoelectric zirconate titanate (PZT), for example, and provides a piezoelectric effect. An oscillation mode resulting from the piezoelectric effect is a thickness-shear mode. The lift driving unit  33  is disposed between an outer face of the lifter  31  and an inner wall surface of the supporting concavity  11 . The lift driving unit  33  is bonded with the outer face of the lifter  31  by vacuum bonding at room temperature. 
         [0024]    The slider  32  is provided on an upper face of the lifter  31  via the slide driving unit  34 . An upper face of the slider  32  is a flat driving surface  32 A with which the rotor  120  is held in pressure contact. 
         [0025]    A driving voltage is applied respectively to the lift driving unit  33  and the slide driving unit  34  by a driving circuit controlled by a control device (not illustrated). The driving voltage causes the lift driving unit  33  to oscillate so as to drive the lifter  31  to vertically move. Accordingly, the slide driving unit  34  oscillates to drive the slider  32  to move in a peripheral direction R. 
         [0026]    Among the six driving mechanisms  30 , a group of alternate driving mechanisms  30  is in the same phase and operates in a different phase from another group of alternate driving mechanisms  30 . As a result, the driving mechanisms  30  of the same group alternately support the rotor  120  in the peripheral direction R and drive the rotor  120  to move relative to the base member  10 , thereby continuously driving the rotor  120  to rotationally move in the peripheral direction R. 
         [0027]      FIG. 2  is a conceptual diagram of the camera  200  to which the lens barrel  300  provided with the vibration actuator  100  is attached. 
         [0028]    The camera  200  includes a camera body  201  having an imaging device  202 , and the lens barrel  300 . The lens barrel  300  is an interchangeable lens that is mountable to and detachable from the camera body  201 . It should be noted that although the lens barrel  300  is an interchangeable lens in the present embodiment, the present invention is not limited thereto. It may alternatively be possible that the lens barrel  300  is formed integral with a camera body. 
         [0029]    The lens barrel  300  includes: a focusing lens  301 ; a cam barrel  302 ; the vibration actuator  100 ; and a housing  303  that surrounds these components; and the like. The vibration actuator  100  is disposed in an annular gap between the cam barrel  302  and the housing  303 . The vibration actuator  100 , in which the gear  125  of the rotor  120  is configured to engage with a gear formed on an outer periphery of the cam barrel  302 , drives the cam barrel  302  to rotationally move. In this manner, the vibration actuator  100  drives the focusing lens  301  while the camera  200  is in a focusing operation. 
         [0030]    The cam barrel  302  is provided inside the housing  303  to be movable in a direction parallel to an optical axis OA according to a rotational operation performed by the vibration actuator  100 . The focusing lens  301  is supported by the cam barrel  302 . The focusing lens  301  moves in a direction of the optical axis OA, following movement of the cam barrel  302  driven by the vibration actuator  100 . In this manner, focusing is adjusted. Although not illustrated, the lens barrel  300  includes a plurality of lens groups in addition to the focusing lens  301 . 
         [0031]    The focusing lens  301  is driven by the vibration actuator  100  according to a position of an object, focusing is adjusted, and an image of the object is formed on an imaging surface of the imaging device  202 . The imaging device  202  converts the image of the object thus formed into an electric signal, which is A/D converted to obtain image data. 
         [0032]    Next, a method for bonding the lifter  31  and the lift driving unit  33  according to the present embodiment will be described. In the present embodiment, the lifter  31  and the lift driving unit  33  are bonded by vacuum bonding at room temperature. As the vacuum bonding at room temperature, surface activated bonding at room temperature (SAB) is employed. 
         [0033]      FIG. 3  is a flow chart describing the method for bonding the lifter  31  and the lift driving unit  33 . 
         [0034]    First, the lifter  31  is washed to remove dust (dust removing step, S 1 ). Thereafter, the lifter  31  is soaked in a metal plating tank to apply metal plating to a bonding surface  31   a  of the lifter  31  to which the lift driving unit  33  is bonded (metal-plating step, S 3 ). It may be possible to use metal plating such as copper, tin, gold, silver, and nickel plating or the like. Experimental results reveal that copper plating is suitable in terms of bonding properties. It may be preferable but not necessary that the thickness of metal plating is in a range of 0.1 μm to 10 μm. 
         [0035]    It may be preferable but not necessary that a metal-plated surface and a surface of the lift driving unit  33  are flat so that these surfaces are better bonded. 
         [0036]    It may be preferable but not necessary that with respect to a surface roughness condition, Ra (an average value of roughness) and Rz (a maximum value of roughness) are both no greater than 1 μm. It may be preferable but not necessary that with respect to a geometric tolerance condition, the flatness is no greater than 0.5 μm over an entirety of the bonding surface. 
         [0037]    It may be preferable but not necessary that the metal-plated surface is not oxidized. Therefore, the metal-plated surface is subjected to a process for chemically removing an oxide film from a bonding surface (oxide film removing step, S 5 ). 
         [0038]    It may be preferable but not necessary that the oxide film removing step is performed immediately prior to bonding. 
         [0039]    The lift driving unit  33  is also washed to remove dust (dust removing step, S 11 ). Thereafter, a surface activation process is performed to sputter a bonding surface  33   a  of the lift driving unit  33 , so that the oxide film on the bonding surface  33   a  is removed (surface activation step, S 13 ). 
         [0040]    In this case, it may be preferable but not necessary that with respect to a surface roughness condition, Ra and Rz of the surface of the lift driving unit  33  are no greater than 1 μm so that bonding is better performed. 
         [0041]    It may be preferable but not necessary that with respect to a geometric tolerance condition, the flatness is no greater than 0.5 μm over an entirety of the bonding surface. 
         [0042]    Next, the metal-plated part of the lifter  31  is bonded with the surface-activated part of the lift driving unit  33  (bonding step, S 21 ). Here, the surface of the metal plating is a non-oxidized and activated surface. As a result, surface atoms of the metal plating of the lifter  31  are bonded with surface atoms of the activated surface of the lift driving unit  33 . Accordingly, the lifter  31  is bonded with the lift driving unit  33  at room temperature. 
         [0043]    Bonding of the lifter  31  and the lift driving unit  33  has been described above. Bonding of the lifter  31  and the slide driving unit  34 , as well as bonding of the slider  32  and the slide driving unit  34  are also performed by SAB. It may be that the lift driving unit  33  is bonded with the inner wall surface of the supporting concavity  11  by vacuum bonding at room temperature. 
         [0044]    The present embodiment described above has the following advantageous effects. 
         [0045]    (1) According to the present embodiment, there is no need to use an adhesive that inhibits transmission of oscillations between a piezoelectric body and an elastic body. 
         [0046]    As a result, the oscillations of the piezoelectric body are transmitted to the elastic body without attenuation. Accordingly, it is possible to increase the efficiency of transmitting the oscillations from the piezoelectric body to the oscillator. In this case, the vibration actuator with an elastic body of high oscillation transmission efficiency can quickly perform starting and stopping operations. 
         [0047]    A camera including the vibration actuator that can quickly perform starting and stopping operations can perform the focusing operation quickly, resulting in an increase in the user-friendliness associated with the camera. 
         [0048]    (2) In the manufacturing step of the oscillator  30 , it is possible to eliminate steps of: applying an adhesive; maintaining an adhesion state by a fixture; thermally curing the adhesive; removing the fixture; and the like, thereby increasing the productivity. 
         [0049]    In addition, it is possible to eliminate control of an amount of applied adhesive (thickness of applied adhesive), a temperature of the adhesive, a curing temperature, curing time and the like of the adhesive, thereby facilitating manufacturing control. 
         [0050]    (3) The lifter  31  is bonded with the lift driving unit  33  and the slide driving unit  34  at room temperature. The slider  32  is bonded with the slide driving unit  34  at room temperature. Accordingly, the lift driving unit  33  and the slide driving unit  34 , which are piezoelectric elements, will not be thermally deformed. Since the joining will not be damaged, it is possible to increase the efficiency of transmitting oscillation. 
       Modifications 
       [0051]    The present invention is not limited to the abovementioned embodiment and may also be embodied as follows. 
         [0052]    (1) It may alternatively be possible that the metal evaporation is applied to the lifter  31  and the slider  32  instead of the metal plating. 
         [0053]    (2) It may alternatively be possible that sputtering or etching is applied to the surfaces of the lifter  31  and the slider  32  instead of metal plating. 
         [0054]    (3) It may alternatively be possible that the metal plating is applied to the lift driving unit  33  and the slide driving unit  34  instead of the lifter  31  and the slider  32 , and the surface activation is applied to the lifter  31  and the slider  32 . 
         [0055]    (4) It may alternatively be possible to apply metal bonding between the lifter  31  and the lift driving unit  33 , between the lifter  31  and the slide driving unit  34 , and between the slider  32  and the slide driving unit  34  in the following manner: a) the surface activation is applied to both a first group of the lifter  31  and the slider  32  and a second group of the lift driving unit  33  and the slide driving unit  34  instead of applying the metal plating to one of the first and second groups; b) a metal foil (for example, a copper foil) is placed between the lifter  31  and the lift driving unit  33 , between the lifter  31  and the slide driving unit  34 , and between the slider  32  and the slide driving unit  34 , respectively; c) metal foils and these components are bonded by vacuum bonding at room temperature. 
         [0056]    (5) In the bonding step (S 21 ) of bonding the lifter  31  with the lift driving unit  33 , the lifter  31  with the slide driving unit  34 , and the slider  32  with the slide driving unit  34 , it may alternatively be possible that these components are held in pressure contact with each other. Since irregularities are flattened even if the bonding surface has a relatively higher roughness, it is possible to increase the bonding properties. 
         [0057]    (6) It may alternatively be possible to adopt vacuum bonding at room temperature using metal covalent bonding instead of metal bonding including surface activation. 
         [0058]    The above described embodiments and modifications may be used in suitable combinations, though detailed descriptions are not given herein. The present invention is in no way limited by the exemplary embodiments described above. 
         [0059]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.