Abstract:
In a frictional stirring weld apparatus for bonding elements with a rotary tool, a head is movable with respect to the elements to position and orient the rotary tool so that a pin of the rotary tool is aligned along a boundary between first surfaces and a shoulder of the rotary tool faces to second surfaces extending radially outward from the first surfaces, and to generate a relative movement between the rotary tool and the elements along the second surfaces, and a compensating member is capable of holding thereon the rotary tool, at least partially rotatable on the rotational axis with respect to the head to rotate the rotary tool, and supported on the head movably along the rotational axis with respect to the head so that a positional relationship between the rotary tool and a combination of the elements is adjustable in a direction parallel to the rotational axis.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an apparatus and method for frictional stirring weld for elements to be bonded in which apparatus and method a thermal energy is generated by a friction between a rotary tool and the elements to make the elements plastically deformable, and a stir by the rotary tool causes a connection by the plastic deformation between the elements.  
           [0002]    In a prior art frictional stirring weld apparatus as disclosed by JP-A-11-226758 (on pages 5 and 6, and FIGS. 4 and 5), a head holding a rotary tool is not movable in each of attitude and position with respect to elements to be bonded so that the rotary tool is positioned and oriented in such a manner that a pin of the rotary tool is aligned along a boundary between first surfaces of the elements and a shoulder of the rotary tool faces to second surfaces extending radially outward from the first surfaces.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    An object of the present invention is to provide an apparatus and method for frictional stirring weld in which apparatus and method a positional relationship between a rotary tool and a combination of elements to be bonded can be adjusted easily so that a friction between the rotary tool and the elements and a stir by the rotary tool on the elements are performed securely and sufficiently for the frictional stirring weld.  
           [0004]    A frictional stirring weld apparatus for bonding elements with a rotary tool including a pin extending along a rotational axis of the rotary tool to be inserted between first surfaces of the elements facing to each other, and a shoulder to be pressed against second surfaces of the elements extending radially outward from the first surfaces respectively, according to the present invention, comprises, a head movable with respect to the elements to position and orient the rotary tool in such a manner that the pin is aligned along a boundary between the first surfaces and the shoulder faces to the second surfaces, and to generate a relative movement between the rotary tool and the elements along the second surfaces, and a compensating member which is capable of holding thereon the rotary tool, at least partially rotatable on the rotational axis with respect to the head to rotate the rotary tool, and supported on the head movably along the rotational axis with respect to the head so that a positional relationship between at least one of the pin and shoulder and a combination of the elements is adjustable in a direction parallel to the rotational axis.  
           [0005]    In a frictional stirring weld method for bonding elements with a rotary tool including a pin extending along a rotational axis of the rotary tool to be inserted between first surfaces of the elements facing to each other, and a shoulder to be pressed against second surfaces of the elements extending radially outward from the first surfaces respectively, the pin is inserted between the first surfaces, and a relative movement between the rotary tool and the elements along the second surfaces is generated in such a manner that the pin is aligned along a boundary between the first surfaces and the shoulder faces to the second surfaces, rotating the rotary tool on the rotational axis, and pressing the shoulder against the second surfaces,  
           [0006]    wherein a positional relationship between a head supporting thereon the rotary tool to be positioned and oriented in such a manner that the pin is arranged between the first surfaces and the shoulder faces to the second surfaces and a compensating member which holds thereon the rotary tool and is supported on the head at least partially rotatably on the rotational axis with respect to the head to rotate the rotary tool and movably along the rotational axis with respect to the head is adjusted to determine a positional relationship between at least one of the pin and shoulder and a combination of the elements in a direction parallel to the rotational axis so that the frictional stirring weld is performed between the elements.  
           [0007]    Since the compensating member capable of holding thereon the rotary tool is at least partially rotatable on the rotational axis with respect to the head to rotate the rotary tool, and supported on the head movably along the rotational axis with respect to the head so that a positional relationship between at least one of the pin and shoulder and a combination of the elements is adjustable in a direction parallel to the rotational axis, the positional relationship between at least one of the pin and shoulder and a combination of the elements is adjusted in the direction without a movement of the head or with minimizing the movement of the head. Therefore, the positional relationship between the rotary tool and the combination of the elements can be adjusted easily while a friction between the rotary tool and the elements and a stir by the rotary tool on the elements are performed securely and sufficiently for the frictional stirring weld.  
           [0008]    If a positional relationship detector measures an actual value corresponding to an actual positional relationship between the rotary tool and the combination of the elements in the direction, and the compensating member is movable with respect to the head along the rotational axis in such a manner that a difference between the measured actual value and a desirable value corresponding to a desirable positional relationship between the rotary tool and the combination of the elements in the direction is not more than a predetermined degree, the positional relationship between the rotary tool and the combination of the elements in the direction is kept at a desirable degree. It is preferable for easily measuring the positional relationship that the positional relationship detector is stationary with respect to the compensating member in the direction so that the positional relationship detector is movable together with the rotary tool in the direction. It is more preferable for easily and correctly measuring the positional relationship that the compensating member has a first compensating member part being rotationally stationary with respect to the head and supported on the head movably in the direction with respect to the head, and a second compensating member part being capable of holding the rotary tool, stationary with respect to the first compensating member in the direction and supported on the first compensating member part in a rotatable manner with respect to the first compensating member part on the rotational axis to rotate the rotary tool, and the positional relationship detector is stationary with respect to the first compensating member part in the direction so that the positional relationship detector is movable together with the rotary tool in the direction.  
           [0009]    The positional relationship detector may be capable of measuring, as the actual value, one of an actual distance between the rotary tool and at least one of the elements, an actual force applied to the rotary tool, an actual power for driving the rotary tool and an actual electric current supplied to an electric motor for driving the rotary tool, and the desirable value is corresponding one of a desirable distance (corresponding to the actual distance) between the rotary tool and the at least one of the elements, a desirable force (corresponding to the actual force) to be applied to the rotary tool, a desirable power (corresponding to the actual power) for driving the rotary tool and a desirable electric current (corresponding to the actual electric power) to be supplied to the electric motor for driving the rotary tool, for example, the at least one of the pin and shoulder is moved toward or urged more strongly into the elements along the rotational axis, when the actual distance is significantly more than the desirable distance, the actual force for keeping the rotation on the rotational axis, press against the elements and/or movement along the second surface is significantly less than the desirable force, the actual power for keeping the rotation on the rotational axis, press against the elements and/or movement along the second surface is significantly less than the desirable power and/or the actual electric current for keeping the rotation on the rotational axis, press against the elements and/or movement along the second surface is significantly less than the desirable actual electric current. In this case, when one of the actual distance between the rotary tool and at least one of the elements, the actual force applied to the rotary tool, the actual power for driving the rotary tool and the actual electric current supplied to an electric motor for driving the rotary tool is measured as the actual value, and the desirable value is corresponding one of the desirable distance between the rotary tool and the at least one of the elements, the desirable force to be applied to the rotary tool, the desirable power for driving the rotary tool and the desirable electric current to be supplied to the electric motor for driving the rotary tool, it is preferable that at least one of a rotational velocity of the rotary tool, a velocity of the rotary tool along the second surface and a velocity of the rotary tool in a direction perpendicular to the second surface or parallel to the rotational axis is kept substantially constant or as constant as possible.  
           [0010]    If the positional relationship detector is stationary with respect to the compensating member in the direction so that the positional relationship detector is movable together with the rotary tool in the direction, the positional relationship detector may measure, as the actual distance between the rotary tool and the at least one of the elements, an actual distance between the positional relationship detector and the at least one of the elements, and the desirable distance between the rotary tool and the at least one of the elements may be a desirable distance between the positional relationship detector and the at least one of the elements. The positional relationship detector may measure, as the actual force, one of an actual torque for driving rotationally the rotary tool and an actual force applied to the rotary tool in the direction, and the desirable force may be corresponding one of a desirable torque (corresponding to the actual torque) for driving rotationally the rotary tool and a desirable force (corresponding to the actual force in the direction) to be applied to the rotary tool in the direction. In this case, when the positional relationship detector measures, as the actual force, one of the actual torque for driving rotationally the rotary tool and the actual force applied to the rotary tool in the direction, and the desirable force is corresponding one of the desirable torque for driving rotationally the rotary tool and the desirable force to be applied to the rotary tool in the direction, it is preferable that at least one of the rotational velocity of the rotary tool, the velocity of the rotary tool along the second surface and the velocity of the rotary tool in the direction perpendicular to the second surface or parallel to the rotational axis is kept substantially constant or as constant as possible.  
           [0011]    It is preferable for keeping an integrity of welded joint irrespective of a variation in thickness of the elements, that is, a desirable depth of the pin in the elements or a desirable protrusion length of the pin from the shoulder pressed against the second surfaces that the pin and the shoulder are separable from each other to be movable along the rotational axis with respect to each other, the compensating member has a pin holder being capable of holding thereon, rotatable on the rotational axis with respect to the head to rotate the pin, and supported on the head, and a shoulder holder being capable of holding thereon the shoulder, rotatable on the rotational axis with respect to the head to rotate the shoulder, and supported on the head, and at least one of the pin holder and the shoulder holder is supported on the head movably in the direction with respect to the head so that a positional relationship between the shoulder and the pin is adjustable in the direction. The at least one of the pin holder and the shoulder holder may be movable along the rotational axis with respect to the head to adjust the positional relationship between the shoulder and the pin in the direction in such a manner that one of a difference between an actual electric current supplied to an electric motor for driving rotationally the pin holder and a desirable electric current to be supplied to the electric motor for driving rotationally the pin holder, a difference between an actual torque for driving rotationally the pin holder and a desirable torque for driving rotationally the pin holder and a difference between an actual temperature of a front end of the pin and a desirable temperature of the front end of the pin is not more than a predetermined degree, for example, the at least one of the pin holder and the shoulder holder is moved toward or urged into the elements when the actual electric current for keeping the rotation of the pin holder is significantly less than the desirable electric current, the actual torque for keeping the rotation of the pin holder is significantly less than the desirable torque and/or the actual temperature of the front end of the pin is significantly less than the desirable temperature. Also in this case, it is preferable that at least one of the rotational velocity of the rotary tool, the velocity of the rotary tool along the second surface and the velocity of the rotary tool in the direction perpendicular to the second surface or parallel to the rotational axis is kept substantially constant or as constant as possible.  
           [0012]    It is preferable for easily controlling the movement of head and/or the compensating member that relative movements in a direction traversing the direction between the compensating member and the rotary tool and between the compensating member and the head, and a swing motion of the rotational axis with respect to the head are prevented irrespective of an orientation of the rotational axis, that is, even when the orientation of the rotational axis can be changeable desirably, or the head is movable in both attitude and position with respect to the elements.  
           [0013]    Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic view showing a compensating member of the present invention with a rotary tool thereon, and a head.  
         [0015]    [0015]FIG. 2 is a schematic view showing a compensating member of the present invention with the rotary tool thereon and the head attached to a welding machine.  
         [0016]    [0016]FIG. 3 is a partially cross-sectional view showing another compensating member of the present invention with the rotary tool and a positional relationship detector thereon.  
         [0017]    [0017]FIG. 4 is a partially cross-sectional view showing another compensating member of the present invention with the rotary tool and another positional relationship detector thereon.  
         [0018]    [0018]FIG. 5 is a schematic view showing another compensating member of the present invention with the rotary tool thereon and the head attached to another welding machine.  
         [0019]    [0019]FIG. 6 is a schematic view showing another compensating member of the present invention with the rotary tool thereon and the head attached to another welding machine.  
         [0020]    [0020]FIG. 7 is a cross-sectional view showing another compensating member of the present invention with the rotary tool thereon.  
         [0021]    [0021]FIG. 8 is a diagram showing an experimentally obtained relationship between an electric current for rotationally driving a pin, and a pin protrusion length relative to a thickness of elements to be bonded.  
         [0022]    [0022]FIG. 9 is a diagram showing an experimentally obtained relationship between a temperature of a front end of the pin, and the pin protrusion length relative to the thickness of the elements to be bonded.  
         [0023]    [0023]FIG. 10 is an experimentally obtained relationship among a moved distance of the rotary tool in a direction perpendicular to a rotational axis of the rotary tool, the thickness of the elements and the pin protrusion length.  
         [0024]    [0024]FIG. 11 is a cut view of welded area obtained when the pin protrusion length is not adjusted relative to the thickness of the elements to be bonded.  
         [0025]    [0025]FIG. 12 is a cut view of welded area obtained when the pin protrusion length is adjusted relative to the thickness of the elements to be bonded.  
         [0026]    [0026]FIG. 13 includes a cross-sectional view of the head and the compensating member of the present invention with the rotary tool thereon on which compensating member the pin protrusion length from a shoulder of the rotary tool can be desirably adjusted, a cross-sectional view showing an axially driving mechanism of the compensating member, and a cross-sectional view showing the axially driving mechanism and a compensating member guide mechanism. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    (Embodiment 1)  
         [0028]    A frictional stirring weld (FSW) apparatus of column-type having five axes for movements as shown in FIG. 2 includes three axes X, Y and Z for straight movements perpendicular to each other, an axis for rotational movement C which axis is parallel to the axis Z, and an axis for rotational movement A which axis is perpendicular to the axis for rotational movement C. Since a rotary tool  1  of the FSW apparatus is pressed by a significantly great force into a boundary between elements  7  to be bonded, the FSW apparatus needs to have a significantly great rigidity against the significantly great force. The force for pressing the rotary tool into the boundary varies in accordance with a kind of the elements  7 , a thickness of the elements  7 , an outer shape of the rotary tool  1 , a rotational velocity of the rotary tool  1 , a proceeding velocity of the rotary tool  1  along the elements  7  and so forth, and particularly increases in accordance with an increase of the thickness of the elements  7 . In the FSW apparatus, a column  50  is movable on a base  51  in a direction parallel to the axis Y, a work piece table  52  is movable on the base  51  in a direction parallel to the axis X, and a head block  53  is movable on the column  50  in a direction parallel to the axis Z. A head  6  supported by the head block  53  is rotatable by a servo-motor  8  on the axis for rotational movement C and on the axis for rotational movement A. The rotary tool  1  is rotationally driven by a motor  54 , and is supported by the head  6  through a combination of a shift member  3  (as the claimed first compensating member part) and a rotatable spindle  2  (as the claimed compensating member or the claimed second compensating member part) so that a positional relationship between the rotary tool  1  and the elements  7  is adjusted in a direction parallel to a rotational axis of the rotary tool  1  between the rotary tool  1  and the head  6 .  
         [0029]    As shown in FIG. 1, the rotary tool  1  including a pin  12  and a shoulder  11  is detachably fixed to the spindle  2  while a rotational axis of the rotary tool  1  and that of the spindle  2  are identical to each other, the spindle  2  is rotatably supported on the shift member  3  and stationarily with respect to the shift member  3  in the direction, and the shift member  3  is supported on the head  6  movably in the direction parallel to the common rotational axis of the rotary tool  1  and the spindle  2  and rotationally stationarily with respect to the head  6 , so that the rotary tool  1  is movable along the rotational axis with respect to the head  6  to adjust a positional relationship between the rotary tool  1  and the elements  7  in the direction. The shift member  3  may be moved with respect to the head  6  in the direction by a mechanical drive, a hydraulic drive or an electric drive.  
         [0030]    As shown in FIG. 3, a distance between a laser distance detector  35  and one of the elements  7  corresponding to an actual positional relationship between the rotary tool  1  and the elements  7  in the direction may be detected by the laser distance detector  35  fixed to the shift member  3  while irradiating a laser beam  36  from the laser distance detector  35  to the one of the elements  7  and receiving into the laser distance detector  35  the laser beam  36  reflected by the one of the elements  7 . The shift member  3  is moved with respect to the head  6  in the direction in such a manner that a difference between the measured distance and a desirable distance between the laser distance detector  35  and the one of the elements  7  corresponding to a desirable positional relationship between the rotary tool  1  and the elements  7  in the direction is not more than a predetermined degree, for example, ±0.05 mm. Since the positional relationship between the rotary tool  1  and the elements  7  in the direction is adjusted by the movement of the shift member  3  in the direction, a movement of the head  6  for the desirable positional relationship between the rotary tool  1  and the elements  7  in the direction and/or calculation for determining the movement of the head  6  for the desirable positional relationship between the rotary tool  1  and the elements  7  in the direction can be minimized.  
         [0031]    Alternatively, the actual positional relationship between the rotary tool  1  and the elements  7  in the direction may be estimated from or corresponds to (be substantially in proportion to) an actual force (torque or force in the direction) applied to the rotary tool  1 , an actual (electric or mechanical) power (output from or input into a motor) for driving rotationally the rotary tool  1  and/or moving the rotary tool  1  along the rotational axis, or an actual electric current supplied to an electric motor for driving rotationally the rotary tool and/or moving the rotary tool  1  along the rotational axis, and the desirable positional relationship between the rotary tool  1  and the elements  7  in the direction corresponds to a desirable force (torque or force in the direction) to be applied to the rotary tool  1 , a desirable power for driving rotationally the rotary tool and/or moving the rotary tool  1  along the rotational axis, or a desirable electric current to be supplied to the electric motor for driving rotationally the rotary tool and/or moving the rotary tool  1  along the rotational axis. The shift member  3  is moved with respect to the head  6  in the direction in such a manner that a difference between the actual positional relationship between the rotary tool  1  and the elements  7  in the direction and the desirable positional relationship between the rotary tool  1  and the elements  7  in the direction is not more than the predetermined degree.  
         [0032]    As shown in FIG. 4, the actual force (torque or force in the direction) applied to the rotary tool  1  may be measured by a load cell  37  arranged between the shift member  3  and the head  6 .  
         [0033]    (Embodiment 2)  
         [0034]    As shown in FIG. 5, a shift member  72 , a rotatable spindle  70  an a rotary tool  71  may be mounted a head  69  as an end of a robot arm  67 . The spindle  70  is rotationally driven by a motor  66 , and the head  69  is rotationally driven on the arm  67  by a motor  68  around a swing axis perpendicular to the rotational axis of the rotary tool  71 . The arm  67  is rotatable on an axis  64   c  perpendicular to the swing axis on an arm  65   b , the arm  65   b  is rotatable on an axis  64   b  parallel to the axis  64   c  on an arm  65   a , the arm  65   a  is rotatable on an axis  64   a  parallel to the axis  64   c  on a support member  73  of a rotary table  74 , and the rotary table  74  is rotatable on a base  75 . The arm  67  is rotationally driven with respect to the arm  65   b  by a rotary motor  62   c , a ball screw  61   c  driven by the motor  62   c , and a bearing joint  63   c , the arm  65   b  is rotationally driven with respect to the arm  65   a  by a rotary motor  62   b , a ball screw  61   b  driven by the motor  62   b , and a bearing joint  63   b , and the arm  65   a  is rotationally driven with respect to the support member  73  by a rotary motor  62   a , a ball screw  61   a  driven by the motor  62   a , and a bearing joint  63   a.    
         [0035]    (Embodiment 3)  
         [0036]    As shown in FIG. 6, a shift member  84 , a rotatable spindle  82  an a rotary tool  81  may be mounted a head  86  as an end of a first arm of a robot  80 . The spindle  82  is rotationally driven by a motor  83 , and the head  86  is rotationally driven on the first arm by a motor  85  around a swing axis perpendicular to the rotational axis of the rotary tool  81 . The first arm is rotatable on an axis C perpendicular to the swing axis on a second arm, the second arm is rotatable on an axis Q perpendicular to the axis C on a third arm, the third arm is rotatable on an axis B parallel to the axis C on a fourth arm  73 , and the fourth arm is rotatable on an axis A parallel to the axis C on a rotary table rotatable on an axis P perpendicular to the axis C.  
         [0037]    (Embodiment 4)  
         [0038]    In an embodiment of the invention as shown in FIG. 7, a pin  41  and a shoulder  40  of a rotary tool is separated from each other, the pin  41  is fixed to a first spindle shifter  64  as the claimed pin holder rotatable on the rotational axis of the pin  41  with respect to the head to rotate the pin  41 , and supported on the head movably along the rotational axis with respect to the head so that a positional relationship between the pin  41  and the elements  7  supported on a jig  43  is adjustable in a direction parallel to the rotational axis to keep an integrity of welded joint irrespective of a variation in thickness of the elements  7 , the shoulder  40  is fixed to a second spindle shifter  45  as the claimed shoulder holder rotatable on the rotational axis of the shoulder  40  with respect to the head to rotate the shoulder  40 , and supported on the head movably along the rotational axis with respect to the head so that a positional relationship between the shoulder  40  and the elements  7  supported on the jig  43  is adjustable in the direction parallel to the rotational axis to keep the integrity of welded joint irrespective of the variation in thickness of the elements  7 , and the rotational axes of the pin  41  and shoulder  40  are identical to each other, so that the positional relationship between the pin  41  and the elements  7  supported in the direction and the positional relationship between the shoulder  40  and the elements  7  in the direction can be adjusted independent of each other.  
         [0039]    As shown in FIG. 8, the electric current I supplied to a motor for driving rotationally the pin  41  increases gradually in accordance with an increase of a depth d of a front end of the pin  41  from an open surface of the elements  7  or a protruding length d of the pin  41  from the shoulder  40  pressed against the open surface of the elements  7  before the front end of the pin  41  reaches the jig  7 , and increases abruptly in accordance with the increase of the protruding length d of the pin  41  from the shoulder  40  when and after the front end of the pin  41  reaches the jig  7 . Therefore, the protruding length d of the pin  41  from the shoulder  40  is adjusted in such a manner that a difference between the electric current I actually supplied to the motor and a desirable electric current to be supplied to the motor just before the front end of the pin  41  reaches the jig  7  is not more than a predetermined degree so that the depth d of the front end of the pin  41  from the open surface of the elements  7  is kept sufficiently great for the integrity of welded joint, that is, a difference between the depth d of the front end of the pin  41  from the open surface of the elements  7  and the actual thickness of the elements  7  is significantly small as shown in FIG. 10 and the front end of the pin  41  is prevented from reaching the jig  7 . A torque may be supplied to each of the first and second spindle shifters  64  and  65  through a spline drive connection along the rotational axis, and the each of the first and second spindle shifters  64  and  65  may be driven along the rotational axis by a linear motor.  
         [0040]    As shown in FIG. 9, a temperature of the front end of the pin  41  increases gradually in accordance with the increase of the depth d of the front end of the pin  41  from the open surface of the elements  7  or the protruding length d of the pin  41  from the shoulder  40  pressed against the open surface of the elements  7  before the front end of the pin  41  reaches the jig  7 , and increases abruptly in accordance with the increase of the protruding length d of the pin  41  from the shoulder  40  when and after the front end of the pin  41  reaches the jig  7 . Therefore, the protruding length d of the pin  41  from the shoulder  40  is adjusted in such a manner that a difference between the actual temperature of the front end of the pin  41  and a desirable temperature of the front end of the pin  41  just before the front end of the pin  41  reaches the jig  7  is not more than a predetermined degree so that the depth d of the front end of the pin  41  from the open surface of the elements  7  is kept sufficiently great for the integrity of welded joint, that is, the difference between the depth d of the front end of the pin  41  from the open surface of the elements  7  and the actual thickness of the elements  7  is significantly small as shown in FIG. 10 and the front end of the pin  41  is prevented from reaching the jig  7 .  
         [0041]    As shown in FIG. 11, if the depth d of the front end of the pin  41  from the open surface of the elements  7  is not sufficient, the integrity of welded joint is deteriorated. As shown in FIG. 12, if the depth d of the front end of the pin  41  from the open surface of the elements  7  is sufficient, the integrity of welded joint is kept.  
         [0042]    (Embodiment 5)  
         [0043]    As shown in FIG. 13, a head  98  is rotatable by a servo-motor  91  through a servo-gear train incorporated in the head  98 . A rotary tool  90  is mechanically connected to the head  98  through a compensating mechanism  92 , and is rotationally driven by a shaft  97 . The rotary tool  90  includes a pin  94  and a shoulder  93  separable from each other so that the coaxial pin  94  and shoulder  93  can move along a rotational axis of the rotary tool  90  independent of each other. As shown in a cross sectional view along A-A in FIG. 13, the shoulder  93  can be moved along a guide  95  parallel to the rotational axis by a hydraulic cylinder  96  in the compensating mechanism  92  independent of the pin  94  to change the protruding length d of the pin  94  relative to the shoulder  93 . The pin  94  may be non-movable with respect to the head along the rotational axis, because the protruding length d of the pin  94  from the shoulder  93  can be adjusted by the movement of the shoulder  93  with respect to the head along the rotational axis.  
         [0044]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.