Abstract:
A gear apparatus includes a spur gear including teeth and to be rotated around a rotation axis, a rotation mechanism to rotate the spur gear, a limitation member including tooth to be engaged with the teeth of the spur gear, the limitation member to limit the rotation of the spur gear, a movement mechanism to move the limitation member in the radial direction of the rotation axis such that the tooth of the limitation member is engaged with the teeth of the spur gear, an input mechanism to input power to actuate the movement mechanism, a transmission mechanism to transmit the power input by the input mechanism to the movement mechanism, and an accumulation mechanism provided in the transmission mechanism and to accumulate the power input by the input mechanism when a tip of the tooth of the limitation member contacts a tip of the tooth of the spur gear.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2007-161485, filed Jun. 19, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a gear apparatus to limit the rotation of a spur gear. 
         [0004]    2. Description of the Related Art 
         [0005]    Various gear apparatuses to limit the rotation of a spur gear are used. 
         [0006]    In a gear apparatus of Jpn. Pat. Appln. KOKAI Publication No. 2006-212357, a rotation limitation member is moved toward a spur gear, an engaging portion of the limitation member is engaged with the teeth of the spur gear, and so the rotation of the spur gear is limited. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In an aspect of the present invention, a gear apparatus includes: a spur gear including teeth and to be rotated around a rotation axis; a rotation mechanism to rotate the spur gear; a limitation member including tooth to be engaged with the teeth of the spur gear, the limitation member to limit the rotation of the spur gear; a movement mechanism to move the limitation member in the radial direction of the rotation axis such that the tooth of the limitation member is engaged with the teeth of the spur gear; an input mechanism to input power to actuate the movement mechanism; a transmission mechanism to transmit the power input by the input mechanism to the movement mechanism; and an accumulation mechanism provided in the transmission mechanism and to accumulate the power input by the input mechanism when a tip of the tooth of the limitation member contacts a tip of the tooth of the spur gear. 
         [0008]    In an aspect of the present invention, an electric bending endoscope includes: a drive apparatus including a clutch mechanism; a bending portion to be bent by the drive apparatus; and a gear apparatus provided in the drive apparatus, wherein the gear apparatus includes: a spur gear including teeth and to be rotated around a rotation axis; a rotation mechanism to rotate the spur gear; a limitation member including tooth to be engaged with the teeth of the spur gear, the limitation member to limit the rotation of the spur gear; a movement mechanism to move the limitation member in the radial direction of the rotation axis such that the tooth of the limitation member is engaged with the teeth of the spur gear; an input mechanism to input power to actuate the movement mechanism; a transmission mechanism to transmit the power input by the input mechanism to the movement mechanism; and an accumulation mechanism provided in the transmission mechanism and to accumulate the power input by the input mechanism when a tip of the tooth of the limitation member contacts a tip of the tooth of the spur gear. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
           [0010]      FIG. 1  is a perspective view showing an endoscope system in a first embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic diagram showing a power transmission mechanism in the first embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic diagram showing the power transmission mechanism in the first embodiment of the present invention along the III-III line of  FIG. 2 ; 
           [0013]      FIG. 4  is a perspective view showing a clutch mechanism in the first embodiment of the present invention; 
           [0014]      FIG. 5  is a sectional view showing the clutch mechanism in the first embodiment of the present invention cut along the V-V line of  FIG. 4 ; 
           [0015]      FIG. 6  is an exploded perspective view showing the clutch mechanism in the first embodiment of the present invention; 
           [0016]      FIG. 7A  is a schematic diagram showing the clutch mechanism in a released state in the first embodiment of the present invention; 
           [0017]      FIG. 7B  is a sectional view showing the clutch mechanism in the released state in the first embodiment of the present invention; 
           [0018]      FIG. 8A  is a schematic diagram showing the clutch mechanism in a stopped state in the first embodiment of the present invention; 
           [0019]      FIG. 8B  is a sectional view showing the clutch mechanism in the stopped state in the first embodiment of the present invention; 
           [0020]      FIG. 9A  is a schematic diagram showing the clutch mechanism in a connected state in the first embodiment of the present invention; 
           [0021]      FIG. 9B  is a sectional view showing the clutch mechanism in the connected state in the first embodiment of the present invention; 
           [0022]      FIG. 10  is a front view showing a clutch mechanism in a first modification of the first embodiment of the present invention; 
           [0023]      FIG. 11  is a sectional view showing the clutch mechanism in the first modification of the first embodiment of the present invention; 
           [0024]      FIG. 12  is a front view showing a clutch mechanism in a second modification of the first embodiment of the present invention; 
           [0025]      FIG. 13  is a sectional view showing the clutch mechanism in the second modification of the first embodiment of the present invention; 
           [0026]      FIG. 14  is a sectional view showing a positioning mechanism in a second embodiment of the present invention; 
           [0027]      FIG. 15  is a schematic diagram showing a clutch mechanism in a first referential embodiment of the present invention; 
           [0028]      FIG. 16  is a schematic diagram for explaining the operation of the clutch mechanism in the first referential embodiment of the present invention; 
           [0029]      FIG. 17  is a schematic diagram showing a clutch mechanism in a second referential embodiment of the present invention; and 
           [0030]      FIG. 18  is a schematic diagram showing a clutch mechanism in a third referential embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Embodiments of the present invention will hereinafter be described with reference to the drawings. 
         [0032]      FIGS. 1 to 9B  show a first embodiment of the present invention. 
         [0033]    An electric bending endoscope  20  (hereinafter simply referred to as an endoscope  20 ) of an endoscope system includes an elongate insertion portion  22  to be inserted into a body cavity. A bending portion  24  to be operated to be bent is provided at the distal end of the insertion portion  22 , and an insertion and removal portion  26  is provided at the proximal end of the insertion portion  22 . Here, the insertion and removal portion  26  includes an angle mechanism therein, and an angle wire extending out of the angle mechanism is inserted through the insertion portion  22 , and coupled to the distal end of the bending portion  24 . Further, the insertion and removal portion  26  is removably inserted into a motor unit  28 , and a drive apparatus for actuating the angle mechanism is provided in the motor unit  28 . As described later, a clutch mechanism is provided in the drive apparatus and the drive apparatus functions as a gear apparatus. The motor unit  28  is held by a holding apparatus  30  such that the motor unit  28  is movable and fixable, and rotatable about its central axis. Moreover, the motor unit  28  is connected to a video processor  34  via a universal cord  32 , and an operation portion  38  to be held and operated by an operator is connected to the video processor  34  via an electric cord  36 . The operation portion  38  is provided with a changeover switch  40  and a bending switch  42 . When the changeover switch  40  is switched between a connection position and a release position, the clutch mechanism of the drive apparatus is switched between a connected state and a released state. When the bending switch  42  is operated, the angle mechanism is actuated by the drive apparatus of the motor unit  28 , the angle wire is moved back and forth, and so the bending portion  24  is bend. 
         [0034]    The drive apparatus functioning as the gear apparatus will be described with reference to  FIGS. 2 to 6 . 
         [0035]    A power transmission mechanism  44  is explained with reference to  FIGS. 2 and 3 . 
         [0036]    A drive shaft of a motor  46  is connected to an output shaft  72  at a reduction gear ratio via gear train in a gear unit  47 . Here, a fixing gear  66  as an annular gear is interposed between the gear train. The fixing gear  66  is switchable between a fixing state unrotatable about its central axis and a fixing-released state rotatable. In the case where the fixing gear  66  is in the fixing state, when the drive shaft of the motor  46  is rotated, the gear train are sequentially rotated and the output shaft  72  is rotated at a reduced rotation velocity. On the other hand, in the case where the fixing gear  66  is in the fixing-released state, even when the drive shaft of the motor  46  is rotated, the gear train idles and rotation torque is not transmitted to the output shaft  72 . 
         [0037]    A clutch mechanism  74  of the drive apparatus is explained with reference to  FIGS. 4 to 6 . 
         [0038]    In the clutch mechanism  74 , the fixing gear  66 , a connection cam  76  and a release cam  78  are sequentially provided in the direction of the rotational axis of the fixing gear  66 . The connection cam  76  and the release cam  78  are in the shape of long plate perpendicular to the rotational axis of the fixing gear  66 , and rotatable between a connection position and a release position about a rotational axis coaxial with the rotational axis of the fixing gear  66 . Connection guide holes  80  penetrate at both ends of the connection cam  76  in symmetry with respect to the rotational axis, and release guide holes  82  penetrate at both ends of the release cam  78  in symmetry with respect to the rotational axis. A connection cam face  84  is formed by the end side surface defining the connection guide hole  80  in the connection cam  76 , while a release cam face  86  is formed by the rotational axis side surface defining the release guide hole  82  in the release cam  78 . A cam pin  88  is inserted through the connection guide hole  80  of the connection cam  76  and the release guide hole  82  of the release cam  78 , and the cam pin  88  protrudes from a limitation member  90  disposed radially outside the fixing gear  66 . Both side surfaces of the limitation member  90  forms slide surfaces  92 , slide surfaces  92  are supported slidably in the radial direction of the fixing gear  66 , and the limitation member  90  is movable in the radial direction of the fixing gear  66 . 
         [0039]    In the case where the connection cam  76  and the release cam  78  are integrally rotated in phase, when the connection cam  76  and the release cam  78  are rotated from the release position to the connection position, the cam pin  88  slid along the connection cam face  84  on the end side in the connection cam  76 , and so the limitation member  90  is moved to the radially inside connection position inwardly in the radial direction of the fixing gear  66 . When the connection cam  76  and the release cam  78  are rotated from the connection position to the release position, the cam pin  88  slid along the release cam face  86  on the rotational axis side in the release cam  78 , and so the limitation member  90  is moved to the radially outside release position outwardly in the radial direction of the release cam  78 . 
         [0040]    Teeth  91  to engage with external teeth  67  of the fixing gear  66  are formed in a radially inner portion of the limitation member  90 . When the limitation member  90  is at the connection position, the teeth  91  of the limitation member  90  are engaged with the external teeth  67  of the fixing gear  66 , and the fixing gear  66  is brought into an unrotatable fixing state by the limitation member  90  which is circumferentially unrotatable. On the other hand, when the limitation member  90  is at the release position, the teeth  91  of the limitation member  90  are separated from the external teeth  67  of the fixing gear  66 , and the fixing gear  66  is brought into the rotatable fixing-released state. 
         [0041]    When the fixing gear  66  is in the fixing state, the transmission of power by the power transmission mechanism  44  is possible. This is the connected state of the clutch mechanism  74 . When the fixing gear  66  is in the fixing-released state, the respective gears idle and so the transmission of power by the power transmission mechanism  44  is impossible. This is the released state of the clutch mechanism  74 . 
         [0042]    The configuration of the drive apparatus as the gear apparatus is explained with reference to  FIGS. 4 to 6 . 
         [0043]    As described above, a cam mechanism is used as a movement mechanism, and when the connection cam  76  as a movement member is rotated from the release position to the connection position, the limitation member  90  is moved inwardly in the radial direction of the fixing gear  66 , and the teeth  91  of the limitation member  90  are engaged with the external teeth  67  of the fixing gear  66 . Moreover, when the limitation member  90  is not engaged with the fixing gear  66 , the driving force of the motor  46  of the drive apparatus is cut off, and the fixing gear  66  and the output shaft  72  is freely rotatable independent of the driving force of the motor  46 . 
         [0044]    The release cam  78  as an input member is electrically rotatable from the release position to the connection position. 
         [0045]    A pair of receiving holes  96  penetrates in each of the release cam  78  and the connection cam  76 , and extends in the circumferential direction of the rotational axis in symmetry with respect to the rotational axis. When the release cam  78  and the connection cam  76  are in phase, the receiving hole  96  of the release cam  78  and the receiving hole  96  of the connection cam  76  are disposed to overlap each other. An input side receiving surface  98  is formed at the releasing direction side end of the receiving hole  96  of the release cam  78 , and output side receiving surface  100  is formed at the connecting direction side end of the receiving hole  96  of the connection cam  76 . An compression spring  101  as a elastic member is received in the overlapped receiving holes  96  of the release cam  78  and the receiving hole  96  of the connection cam  76 , and one end of the compression spring  101  is supported by the input side receiving surface  98  of the release cam  78 , while the other end thereof is supported by the output side receiving surface  100  of the connection cam  76 . 
         [0046]    In the release cam  78 , a clearance surface  102  is formed by the end side surface defining the release guide hole  82  in opposition to the rotational axis side release cam face  86 . 
         [0047]    In addition, a drive pin  104  protrudes from a connection cam  76  side surface of the release cam  78 . The drive pin  104  is inserted into the connection guide hole  80  of the connection cam  76 . When the release cam  78  and the connection cam  76  is in phase, the drive pin  104  contacts a drive surface  106  formed by a releasing direction side surface of the connection guide hole  80 . 
         [0048]    Next, the actuation of the drive apparatus as the gear apparatus in the present embodiment will be described. 
         [0049]    When the bending portion  24  of the endoscope  20  is bent, the changeover switch  40  is switched from the release position to the connection position in order to switch the clutch mechanism  74  from the released state to the connected state, and then the bending switch  42  is operated in order to bend the bending portion  24 . 
         [0050]    As shown in  FIGS. 7A and 7B , when the clutch mechanism  74  is in the released state, the release cam  78  and the connection cam  76  are in phase and in the release position, and the limitation member  90  is in the release position, and the fixing gear  66  is rotatable. When the changeover switch  40  is switched from the release position to the connection position, the release cam  78  is electrically rotated from the release position to the connection position. When the release cam  78  is rotated, the connection cam  76  is pressed by the slightly compressed and deformed compression spring  101  and thus rotated in the same direction as the rotational direction of the release cam  78 , and the cam pin  88  is slid on the end side connection cam face  84  in the connection cam  76 , and so the limitation member  90  is moved inwardly in the radial direction of the fixing gear  66 . 
         [0051]    As shown in  FIGS. 8A and 8B , when the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the tip of the external tooth  67  of the fixing gear  66 , the tip of the tooth  91  of the limitation member  90  contacts the tip of the external tooth  67  of the fixing gear  66 . In this case, the release cam  78  keeps rotation to the connection position, but the movement of the limitation member  90  and the rotation of the connection cam  76  are once stopped, the compression spring  101  between the connection cam  76  and the release cam  78  is compressed and deformed, and so the power is accumulated as elastic energy. In addition, while the connection cam  76  is being stopped and the release cam  78  is rotating, there is no interference between the release cam  78  and the cam pin  88  owing to the function of the end side clearance surface  102  in the release cam  78 . In this manner, while the release cam  78  is disposed in the connection position, the limitation member  90  and the connection cam  76  are stopped at a stop position between the release position and the connection position, and the fixing gear  66  remains rotatable. 
         [0052]    Then, when the bending switch  42  is operated, the motor  46  of the drive apparatus is driven. As the clutch mechanism  74  is not in the connected state, the respective gears idle, and the fixing gear  66  is also rotated. Further, when the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of a root between the external tooth  67  of the fixing gear  66 , the stopping of the limitation member  90  and the connection cam  76  is released, the compressed and deformed compression spring  101  reset, and so the power is input to the connection cam  76 , and the connection cam  76  is rotated in the same direction as the rotational direction of the release cam  78 . 
         [0053]    As shown in  FIGS. 9A and 9B , as the connection cam  76  is rotated, the cam pin  88  is slid on the end side connection cam face  84  in the connection cam  76 , the limitation member  90  is radially inwardly moved to the connection position, the limitation member  90  is engaged with the fixing gear  66 , and the fixing gear  66  is fixed. When the fixing gear  66  is fixed, the transmission of power by the power transmission mechanism  44  is enabled, the angle mechanism is actuated by the drive apparatus, and the bending portion  24  is bent. 
         [0054]    On the other hand, when the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 , the release cam  78  and the connection cam  76  are integrally rotated to the connection position substantially in phase with each other, and the limitation member  90  is moved to the connection position without being stopped, and so the limitation member  90  is engaged with the fixing gear  66 . 
         [0055]    In addition, when an operator of the endoscope  20 , for example, a medical doctor judges that the bending portion  24  needs to reset into a linear state, the changeover switch  40  is switched from the connection position to the release position, and so the release cam  78  is electrically rotated from the connection position to the release position. Consequently, as shown from  FIGS. 9A and 9B  to  FIGS. 7A and 7B , the drive pin  104  of the release cam  78  contacts the releasing direction side drive surface  106  in the connection cam  76  and drives the connection cam  76 , and the connection cam  76  is rotated from the connection position to the release position integrally with the release cam  78 . Then, the cam pin  88  is slid along the end side release cam face  86  in the release cam  78 , the limitation member  90  is moved from the connection position to the release position, the engagement of the fixing gear  66  and the limitation member  90  is released, and the fixing of the fixing gear  66  is released. When the fixing of the fixing gear  66  is released, the transmission of power by the power transmission mechanism  44  is impossible, and the angle mechanism is free, and the bending portion  24  reset to the linear state. 
         [0056]    Therefore, the drive apparatus as the gear apparatus in the present embodiment includes the following effect. 
         [0057]    In the drive apparatus of the present embodiment, when the release cam  78  is rotated, the connection cam  76  is rotated via the compression spring  101 , and the limitation member  90  is thus moved toward the fixing gear  66 . When the tip of the tooth  91  of the limitation member  90  contacts the tip of the external tooth  67  of the fixing gear  66 , the movement of the limitation member  90  and the rotation of the connection cam  76  are once stopped, and the power is accumulated as elastic energy by the compression and deformation of the compression spring  101 . Then, when the fixing gear  66  is rotated and the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 , the connection cam  76  is again rotated by the reset of the compression spring  101 , the limitation member  90  is again moved, and the limitation member  90  is engaged with the fixing gear  66 . Therefore, an operational failure in the gear apparatus is prevented. 
         [0058]      FIGS. 10 and 11  show a first modification of the first embodiment of the present invention. 
         [0059]    In the present modification, a tension spring  108  is used as an elastic member. An input side coupling portion  110  is formed in the release cam  78  and one end of the tension spring  108  is coupled to the input side coupling portion  110 . An output side coupling portion  112  is formed in the connection cam  76  and the other end of the tension spring  108  is coupled to the output side coupling portion  112 . The input side coupling portion  110  and the output side coupling portion  112  are disposed on the same circumference with respect to the rotational axis of the release cam  78  and the connection cam  76 . When the release cam  78  and the connection cam  76  is in phase, the input side coupling portion  110  is disposed on the connecting direction side and the output side coupling portion  112  is disposed on the releasing direction side. 
         [0060]    When the release cam  78  is electrically rotated, the connection cam  76  is pulled by the slightly pulled and deformed tension spring  108  and thus rotated in the same direction as the rotational direction of the release cam  78 . When the tip of the tooth  91  of the limitation member  90  contacts the tip of the external tooth  67  of the fixing gear  66 , as in the first embodiment, the release cam  78  keeps rotation to the connection position, but the movement of the limitation member  90  and the rotation of the connection cam  76  are once stopped, and the tension spring  108  between the connection cam  76  and the release cam  78  is pulled and deformed, and power is accumulated as elastic energy. When the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 , the stopping of the limitation member  90  and the connection cam  76  is released, the pulled and deformed tension spring  108  resets, the power is input to the connection cam  76 , and the connection cam  76  is rotated in the same direction as the rotational direction of the release cam  78 . 
         [0061]      FIGS. 12 and 13  show a second modification of the first embodiment of the present invention. 
         [0062]    In the present modification, a torsion spring  114  is used as an elastic member. As in the first modification, the input side coupling portion  110  is formed in the release cam  78 , and the output side coupling portion  112  is formed in the connection cam  76 . 
         [0063]    When the release cam  78  is electrically rotated, the connection cam  76  is urged by the slightly twisted and deformed torsion spring  114  and thus rotated in the same direction as the rotational direction of the release cam  78 . When the tip of the tooth  91  of the limitation member  90  contacts the tip of the external tooth  67  of the fixing gear  66 , the torsion spring  114  between the connection cam  76  and the release cam  78  is twisted and deformed, and so power is accumulated as elastic energy. When the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 , the twisted and deformed torsion spring  114  resets, and so the power is input to the connection cam  76 . 
         [0064]      FIG. 14  shows a second embodiment of the present invention. 
         [0065]    In the drive apparatus of the present embodiment, the fixing gear  66  is positioned in advance such that the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66  in order to prevent the tip of the tooth  91  of the limitation member  90  from contacting the tip of the external tooth  67  of the fixing gear  66 . 
         [0066]    That is, one end of a leaf spring  116  as an urging member is fixed to a housing, and a spherical member  118  as a lock member is provided at the other end of the leaf spring  116 . The spherical member  118  is inserted and locked between the external teeth  67  of the fixing gear  66  by urging force of the leaf spring  116 . The limitation member  90  is disposed such that the phase of the tip of the tooth  91  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66  when the spherical member  118  is locked between the external teeth  67  of the fixing gear  66  and thus the fixing gear  66  is positioned. 
         [0067]    In addition, when the engagement of the fixing gear  66  and the limitation member  90  is being released, the fixing gear  66  is rotatable by the rotation of the motor  46  of the drive apparatus regardless of the urging of the spherical member  118  toward the fixing gear  66  by the leaf spring  116 . That is, when the motor  46  of the drive apparatus is driven, the fixing gear  66  is rotated while the spherical member  118  is pushed out by the external teeth  67  of the fixing gear  66  and the spherical member  118  falls between the external teeth  67  of the fixing gear  66  by the urging of the leaf spring  116 , and these are repeated. 
         [0068]    In the gear apparatus of the present embodiment, the tip of the tooth  91  of the limitation member  90  is prevented from contacting the tip of the external tooth  67  of the fixing gear  66 , and so an operational failure in the gear apparatus is prevented. 
         [0069]    Referential embodiments of the present invention will now be described. 
         [0070]    In the referential embodiments of the present invention, the fixing gear  66  is rotated by the movement of the limitation member  90 , and so the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 . 
         [0071]      FIGS. 15 and 16  show a first referential embodiment of the present invention. 
         [0072]    Referring to  FIG. 15 , a movement direction M of the limitation member  90  does not pass through the rotation axis of the fixing gear  66 , and the rotation axis of the fixing gear  66  is disposed eccentrically with respect to the movement direction M of the limitation member  90 . Moreover, in the limitation member  90 , the teeth  91  are provided side by side in parallel with the tangential direction of the fixing gear  66 . 
         [0073]    Referring to  FIG. 16 , when the limitation member  90  is moved toward the fixing gear  66 , if the teeth  91  of the limitation member  90  contact the external teeth  67  of the fixing gear  66 , press force F in the movement direction M of the limitation member  90  acts from the teeth  91  of the limitation member  90  to the external teeth  67  of the fixing gear  66 . Due to component force Ft of the press force F, in the tangential direction of the fixing gear  66 , the fixing gear  66  is rotated, and so the phase of the root between the external teeth  67  of the fixing gear  66  corresponds to the phase of the tip of the tooth  91  of the limitation member  90 . As the limitation member  90  is further moved, the teeth  91  of the limitation member  90  are engaged with the external teeth  67  of the fixing gear  66 . 
         [0074]    As described above, the fixing gear  66  is rotated by the movement of the limitation member  90 , the phase of the tip of the tooth  91  of the limitation member  90  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 , and the limitation member  90  is engaged with the fixing gear  66 . Therefore, an operational failure in the gear apparatus is prevented. 
         [0075]      FIG. 17  shows a second referential embodiment of the present invention. 
         [0076]    In the present referential embodiment, as the limitation member  90 , a limitation member  90  to be engaged with the fixing gear  66  over quarter circumference of the fixing gear  66  is used. 
         [0077]      FIG. 18  shows a third referential embodiment of the present invention. 
         [0078]    In the present referential embodiment, first and second limitation members  90   a,    90   b  are used. A movement direction M 1  of the first limitation member  90   a  is the radial direction of the fixing gear  66 . A movement direction M 2  of the second limitation member  90   b  is the tangential direction of the fixing gear  66 . In the second limitation member  90   b,  teeth  91   b  are provided side by side in the tangential direction of the fixing gear  66 , and the second limitation member  90   b  functions as a so-called rack gear. Moreover, the gear apparatus is provided with a stopper  120  for stopping the movement of the second limitation member  90   b  in the state where the second limitation member  90   b  is engaged with the fixing gear  66 . When the second limitation member  90   b  is engaged with the fixing gear  66 , the phase of the tip of the tooth  91   a  of the first limitation member  90   a  corresponds to the phase of the root between the external teeth  67  of the fixing gear  66 . 
         [0079]    When the limitation members  90  are engaged with the fixing gear  66 , the second limitation member  90   b  is moved toward the fixing gear  66  in the tangential direction of the fixing gear  66  ahead of the first limitation member  90   a.  When the tooth  91   b  of the second limitation member  90   b  contact the external tooth  67  of the fixing gear  66 , force in the tangential direction of the fixing gear  66  acts on the external tooth  67  of the fixing gear  66  from internal tooth  90 b of the second limitation member  90   b,  the fixing gear  66  is rotated, and the phase of the roots between the external teeth  67  of the fixing gear  66  sequentially corresponds to the phase of the tips of the internal teeth  90   b  of the second limitation member  90   b,  and thus the internal teeth  90   b  of the second limitation member  90   b  are engaged with the external teeth  67  of the fixing gear  66 . When the second limitation member  90   b  is engaged with the fixing gear  66 , the phase of the root between the external teeth  67  of the fixing gear  66  corresponds to the phase of the tip of the teeth  91   a  of the first limitation member  90   a.  Then, as the first limitation member  90   a  is moved toward the fixing gear  66  in the radial direction of the fixing gear  66 , the first limitation member  90   a  is engaged with the fixing gear  66  without contact of the tip of the external teeth  67  of the fixing gear  66  and the tip of the teeth  91   a  of the first limitation member  90   a.    
         [0080]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.