Patent Publication Number: US-2017351215-A1

Title: Movement for mechanical timepiece

Description:
TECHNICAL FIELD 
     This invention relates to a mechanical timepiece movement. 
     BACKGROUND ART 
     A mechanical timepiece movement includes a power source, a gear train mechanism having a plurality of gears which engages with each other, and an escapement and a governor. The gear train mechanism transmits power generated by the power source to the governor via the escapement and moves with a period controlled by the governor. The power source is a mainspring disposed within a barrel, for example. The mainspring of a manual watch is wound up as a user turns a crown, which is connected to a winding stem, with his or her fingers. The mainspring of an automatic winding watch is wound up as a rotor rotates in accordance with the motion of the watch. Torque is generated as the mainspring is released and is used as a power for driving the gear train mechanism, the governor, and the escapement. 
     The mainspring is not supposed to be further wound up beyond a state that the mainspring is wound up to a predetermined amount of winding (a fully-wound-up state); however, the mainspring may be further wound up from the fully-wound-up state. In particular, with the automatic watch, the mainspring in the fully-wound-up state may easily further wound up since the rotor rotates as the watch moves. Also, even with the manual winding watch, the mainspring may be further wound up from the fully-wound-up state. 
     When the mainspring is further wound up beyond the fully-wound-up state, the torque generated as the mainspring is released becomes higher than the torque generated as the mainspring is released from the fully-wound-up state. Accordingly, the torque transmitted to the governor via the gear train mechanism becomes higher than the torque expected from the fully-wound-up state. As a result, the oscillation of the governor becomes larger than expected, which leads to the occurrence of overbanking (overswinging) to regulate the maximum oscillation angle and an error in the isochronisms of the governor. 
     It has been proposed to uniformly reduce the torque generated from the fully-wound-up state of the mainspring and accordingly reduce the torque generated as the mainspring is further wound up beyond the fully-wound-up state so as to restrain the excessive amplitude of the governor. Also, a constant torque mechanism using the Remontoire mechanism has been proposed to prevent the variation of torque generated by the mainspring (Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2014-81334 A 
     SUMMARY 
     Technical Problem 
     However, uniformly reducing torque generated by the mainspring causes a problem which shortens the duration time of the governor from the fully-wound-up state. Further, in the art proposed in Patent Literature 1, energy generated by the mainspring is wastefully consumed since the constant torque mechanism consumes the energy (the torque generated by the mainspring) even when the excessive torque is not generated. 
     The present invention is made in view of the above problems. An object of the present invention is to provide a mechanical timepiece movement which prevents or restrains the transmission of torque to the governor when the excessive torque is generated by the power source and also avoids the wasteful consumption of energy when the excessive torque is not generated. 
     Solution to Problem 
     The present invention is a mechanical timepiece movement including a power source which generates torque; a governor; a gear train mechanism that transmits the torque generated by the power source to the governor, the gear train mechanism including a plurality of gears engaging with each other; and a moving mechanism that moves at least one of the gears of the gear train mechanism in a direction to reduce the transmission efficiency of the torque between the gears of the gear train mechanism when the torque generated by the power source is higher than a predetermined torque. 
     Advantageous Effects 
     According to the present invention, the mechanical timepiece movement can prevent or restrain the transmission of torque to the governor when the excessive torque is generated by the power source and can also avoid the wasteful consumption of energy when the excessive torque is not generated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top plan view of a movement of a mechanical portable timepiece (a wristwatch, for example) according to the first embodiment (Embodiment 1) of the present invention. 
         FIG. 2A  is a perspective view of a spring seat (an example of a moving mechanism) which roratably supports a pivot of a second wheel and shows a spring in a non-compressed state. 
         FIG. 2B  is a perspective view of the spring seat of  FIG. 2A  and shows the spring in a compressed state. 
         FIG. 3A  is a cross-sectional view along a vertical surface depicted with a line I-I in  FIG. 2A . 
         FIG. 3B  is a cross-sectional view along a vertical surface depicted with a line I-I in  FIG. 2A , which corresponds to the state of  FIG. 2B . 
         FIG. 4  is a back view of a gear train mechanism seen from the back side of the gear train mechanism of  FIG. 1 . 
         FIG. 5  is a graph showing barrel torque corresponding to an elapsed time from a wound-up state to a released state of a mainspring, and values obtained by multiplying the torque transferred to a balance wheel, which corresponds to the barrel torque, by a reduction ratio. 
         FIG. 6  is a perspective view of a spring seat, which is another example of a moving mechanism, in a movement according to the second embodiment (Embodiment 2) of the present invention. 
         FIG. 7A  is a perspective view of a spring seat, which is yet another example of a moving mechanism, in a movement according to the third embodiment (Embodiment 3) and shows the spring seat assembled and disposed in a main plate. 
         FIG. 7B  is an exploded perspective view of the spring seat shown in  FIG. 7A . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiments of a mechanical timepiece movement will be described with reference to the figures. 
     First Embodiment 
     (Configuration of Movement) 
       FIG. 1  is a schematic view illustrating a movement  100  of a mechanical portable watch (a wristwatch, for example) according to the first embodiment (Embodiment 1) of the present invention. The movement  100  shown in the figure includes a mainspring  1  as an example of a power source, a gear train mechanism  10 , an escape wheel  21  and an anchor  22  (an escapement), and a balance wheel  23  (a governor). The mainspring  1  is disposed within a rotary barrel  11 , which is a first wheel, in the gear train mechanism  10 . 
     The inner end of the mainspring  1  is hooked to a barrel arbor  11   a . Turning a crown (not shown) (in case of a manual watch) or rotating a rotor (in case of an automatic winding watch) rotates the barrel arbor  11   a  so that the mainspring  1  is wound around the barrel arbor  11   a . Then, torque is generated as the mainspring  1  wound around the barrel arbor  11   a  is released (referred to barrel torque hereinafter) and the torque rotates the rotary barrel  11  about the barrel arbor  11   a  which is a rotation axis. The barrel arbor  11   a  is rotatably supported by a main plate  91  (see  FIG. 2A, 2B  which will be described hereinafter) and a barrel plate. 
     The gear train mechanism  10  includes the rotary barrel  11 , a second wheel  12  (an example of a gear train to be moved), a third wheel  13  and a fourth wheel  14 . As described above, the rotary barrel  11  includes the mainspring  1  disposed therewithin and rotates around the barrel arbor  11   a . The rotary barrel  11  includes a gear  11   b  around the outer circumference of the barrel  11 . The second wheel  12  is integrally formed with a pinion  12   a,  a gear  12   b  and a tenon or pivot  12   c  which is provided as an axis of the pinion  12   a  and the gear  12   b.  Similarly, the third wheel  13  is integrally formed with a pinion  13   a,  a gear  13   b  and a tenon or pivot  13   c  which is provided as an axis of the pinion  13   a  and the gear  13   b.  The fourth wheel  14  is integrally formed with a pinion  14   a,  a gear  14   b  and a tenon or pivot  14   c  which is provided as an axis of the pinion  14   a  and the gear  14   b.    
     Each pivot  12   c,    13   c,    14   c  of the second wheel  12 , the third wheel  13 , and the fourth wheel  14  is rotatably supported by the main plate  91  and a gear train bridge. Accordingly, the second wheel  12 , the third wheel  13  and the fourth wheel  14  rotate about the pivot  12   c,    13   c ,  14   c,  respectively. The pinion  12   a  of the second wheel  12  engages with the gear  11   b  of the rotary barrel  11  to receive the barrel torque generated in accordance with the rotation of the rotary barrel  11 , which is a driving gear, and rotates about the pivot  12   c  which is a rotation axis. The pinion  13   a  of the third wheel  13  engages with the gear  12   b  of the second wheel  12  to receive the torque generated in accordance with the rotation of the second wheel  12 , which is a driving gear, and to rotate about the pivot  13   c  which is a rotation axis. The pinion  14   a  of the fourth wheel  14  engages with the gear  13   b  of the third wheel  13  to receive the torque generated in accordance with the rotation of the third wheel  13 , which is a driving gear, and to rotate about the pivot  14   c  which is a rotation axis. 
     The gear  14   b  of the fourth wheel engages with a pinion  21   a  of the escape wheel  21  to rotate the escape wheel  21 . The escape wheel  21  and the anchor  22  constitute an escapement, and the balance wheel  23  constitutes a governor. The escape wheel  21 , the anchor  22  and the balance wheel  23  interact with each other in a conventional manner to control the advancement and the speed of the gear train mechanism  10 . 
     (Configuration of Spring Seat) 
       FIG. 2A  is a perspective view of a spring-provided seat or spring seat  30  (an example of the moving mechanism) which rotatably supports the pivot  12   c  of the second wheel  12  (see  FIG. 1 ) and illustrates a spring  33  in a non-compressed state.  FIG. 2B  is a perspective view of the spring seat  30  shown in  FIG. 2A  and illustrates the spring  33  in a compressed state.  FIG. 3A  is a cross-sectional view along a vertical surface depicted with a line I-I in  FIG. 2A .  FIG. 3B  is a cross-sectional view along a vertical surface depicted with a line I-I in  FIG. 2A , which corresponds to the state of the spring member shown in  FIG. 2B . 
     The pivot  12   c  of the second wheel  12  is supported by the spring seat  30  shown in  FIGS. 2A, 2B, 3A and 3B . The spring seats  30  are provided in the main plate  91  disposed above the second wheel  12  and in the gear train bridge disposed below the second wheel  12 , respectively. Note that  FIGS. 2A, 2B, 3A and 3B  show the spring seat provided in the main plate  91 ; however, the spring seat  30  provided in the gear train bridge is identical to the one shown in  FIGS. 2A, 2B, 3A, 3B . The position of the main plate  91  may be replaced with that of the gear train bridge. The spring seat  30  includes a guide  31  (an example of a base member), a seat  32  and a spring  33  (an example of a biasing member). 
     The seat  32  has a circular shape in a plan view and includes a recess  32   a  formed inside the seat  32 , which receives an end stone  34 . The end stone  34  includes a bearing hole  34   a  for rotatably supporting the pivot  12   c  of the second wheel  12 . The pivot  12   c  is supported by the hole  34   a.  The guide  31  has a circular shape in a plan view and includes an elongate hole  31   a  formed inside the guide  31  for receiving the seat  32 . The elongate hole  31   a  is configured such as to allow the seat  32  to move in a longitudinal direction X. The outer circumference of the guide  31  is fitted into a hole formed in the main plate  91  and the guide  31  is fixed to the main plate  91 . 
     The spring  33  has a substantially S-shaped contour in a plan view. The spring  33  is disposed within the elongate hole  31   a  such that one and the other ends of the S-shaped spring  33  are placed along the longitudinal direction X of the elongate hole  31   a  of the guide  31 . The spring  33  is formed from a material which allows the S-shaped spring to elastically deform as a load beyond a predetermined value is applied between the one end and the other end of the S-shaped spring  33  in the longitudinal direction X. The one end and the other end of the S-shaped spring  33  is connected to the guide  31  and the other end is connected to the seat  32 . 
     As shown in  FIGS. 2A and 3A , the spring  33  biases the seat  32  and the end stone  34  toward an end  31   b  of the longitudinal direction X of the elongate hole  31   a  when the spring  33  is not elastically deformed. As shown in  FIGS. 2B and 3B , on the other hand, the seat  32  and the end stone  34  move away from the end  31   b  of the longitudinal direction X of the elongate hole  31   a  when the load exceeding the predetermined value is applied between the one end and the other end of the S-shaped spring  33  in the longitudinal direction X and the S-shaped spring elastically deforms. Resultingly, the pivot  12   c  of the second wheel  12  moves from a position shown in  FIG. 3A  to a position shown in  FIG. 3B  along the longitudinal direction X. Note that the spring seat  30  in Embodiment 1 is integrally formed with the guide  31 , the seat  32  and the spring  33 . 
       FIG. 4  is a back view of the gear train mechanism  10  shown in  FIG. 1 . The barrel torque is generated as the mainspring  1  disposed within the rotary barrel  11  is released. The barrel torque rotates the rotary barrel  11  in a direction of an arrow shown in  FIG. 4  (in the counterclockwise direction). The gear  11   b  of the rotary barrel  11  transmits the torque to the pinion  12   a  of the second wheel  12 . That is, the rotary barrel  11  corresponds to a driving gear as seen from the second wheel  12 . In accordance with the torque of the rotary barrel  11 , a load F 1  acts on the second wheel  12  from the rotary barrel  11 . On the average, the load faces a direction inclined at the friction angle relative to a tangential direction in common with the gear  11   b  and the pinion  12   a,  though the facing direction technically differs depending on the shapes of the teeth (teeth profiles) engaging with each other and the conditions of the engagement between the teeth. 
     Then, the torque transmitted to the second wheel  12  rotates the second wheel  12  in a direction of an arrow shown in  FIG. 4  (in the clockwise direction). The gear  12   b  of the second wheel  12  transmits the torque to the pinion  13   a  of the third wheel  13 . That is, the third wheel  13  corresponds to a driven gear as seen from the second wheel  12 . In accordance with the torque of the second wheel  12 , a load acts on the pinion  13   a  of the third wheel  13  from the gear  12   b  of the second wheel  12 . On the average, the load faces a direction inclined at a friction angle relative to a tangential direction in common with the gear  12   b  and the pinion  13   a,  though the facing direction technically differs depending on the shapes of the teeth engaging with each other and the conditions of the engagement between the teeth. In accordance with an action and reaction relationship, a reaction load F 2  acts on the second wheel  12  from the third wheel  13 . Similarly, on average, the reaction load F 2  acting on the second wheel  12  from the third wheel  13  faces to a direction inclined at the friction angle relative to the tangential direction in common with the gear  12   b  and the pinion  13   a.    
     Accordingly, the second wheel  12  receives the load F 1  from the rotary barrel  11  and the load F 2  from the third wheel  13 . The spring seat  30  shown in  FIGS. 2A, 2B, 3A, 3B  is positioned such that the longitudinal direction X of the elongate hole  31   a  coincides with the direction of a resultant force F 3  obtained from the vector addition of the two loads F 1 , F 2 . Here, the spring seat  30  is positioned in a direction such that the load F 3  acts on the second wheel  12 , and the seat  32  and the end stone  34  supporting the pivot  12   c  compress the spring  33  in the longitudinal direction X. 
     Note that the direction of the resultant force F 3  is a direction in which the pivot  12   c  of the second wheel  12  moves away from the rotary barrel  11 , which is the driving gear, and also moves away from the third wheel  13 , which is the driven gear. Accordingly, the longitudinal direction X of the elongate hole  31   a  is a direction in which the pivot  12   c  of the second wheel  12  moves away from the rotary barrel  11  and also moves away from the third wheel  13 . 
     (Operation of Movement) 
     In the movement  100  configured as described above, turning a non-illustrated crown or rotating a non-illustrated rotor rotates the barrel arbor  11   a  so that the mainspring  1  is wound around the barrel arbor  11   a . The barrel torque generated by the mainspring  1 , which is wound around the barrel arbor  11   a,  is sequentially transmitted from the rotary barrel  11  to the second wheel  12 , the third wheel  13 , the fourth wheel  14 , the escape wheel  21 , the anchor  22  and then the balance wheel  23 . 
       FIG. 5  is a graph showing the barrel torque with respect to an elapsed time from the wound-up state to the released state of the mainspring  1 , and values obtained by multiplying the torque transferred to the balance wheel  23 , which corresponds to the barrel torque, by a reduction ratio. As shown in  FIG. 5 , Tmax indicates the barrel torque in the state that the mainspring  1  (see  FIG. 1 ) is wound up to the predetermined amount of winding (the fully-wound-up state). The longer the elapsed time for releasing the mainspring  1  from the fully-wound-up state becomes, the lower the barrel torque becomes. As the barrel torque falls below a minimum value required to drive the balance wheel  23 , the gear train mechanism  10  does not move anymore and the movement of the watch stops. 
     The barrel torque Tmax corresponding to the fully-wound-up state is determined in advance. In accordance with the determined barrel torque Tmax, the specifications of the movement  100  such as oscillation angle of the balance wheel  23  are set. However, the mainspring  1  may be further wound up from the fully-wound-up state. During the further winding of the mainspring  1 , the barrel torque reaches a torque Tsmax beyond the torque Tmax in the fully-wound-up state as shown in the left side of  FIG. 5 . 
     Frictions such as contact friction or viscous friction in the gear train mechanism  10 , the escape wheel  21 , and/or the anchor  22  consume energy from the barrel torque while the energy is transmitted to the balance wheel  23 . For example, the gear train mechanism  10  consumes about 30% of the energy of the barrel torque, and the escape wheel  21  and the anchor  22  consume about 35% of the energy of the barrel torque. As a result, about 35% of the energy of the barrel torque is transmitted to the balance wheel  23 . 
     The barrel torque reaches the torque Tsmax beyond the torque Tmax during the mainspring  1  is further wound up from the fully-wound-up state since the maximum value of the oscillation angle of the balance wheel  23  is set in accordance with the assumed barrel torque Tmax. In this case, with the conventional movement which differs from Embodiment 1 of the present invention, the value obtained by multiplying the torque transferred to the balance wheel  23  by a reduction ratio also becomes torque (35% of the barrel torque Tsmax) higher than the assumed torque (35% of the barrel torque Tmax) as shown with a thinner line in  FIG. 5 . Then, the balance wheel  23  oscillates at an oscillation angle beyond the assumed angle, resulting in the occurrence of so called overbanking. 
     With the movement  100  of Embodiment 1 of the present invention, on the other hand, the spring seat  30  moves the second wheel  12  in a direction which reduces the transmission efficiency of the torque in the gear train mechanism  10  when the barrel torque is higher than the predetermined torque Tmax. The spring seat  30  does not move the second wheel  12  when the barrel torque does not exceed the predetermined torque Tmax. 
     Specifically, with the resultant force F 3  between the load F 1  (see  FIG. 4 ) from the barrel torque of the rotary barrel  11  and the load F 2  from the third wheel  13 , the second wheel  12  intends to move in the direction of the resultant force F 3 . Here, the pivot  12   c  of the second wheel  12  is supported by the end stone  34  and the end stone  34  is fixed to the seat  32 . However, the resultant force F 3  acting on the pivot  12   c  does not elastically deform the spring  33  when the barrel torque does not exceed the torque Tmax (see  FIGS. 2A and 3A ). Accordingly, the second wheel  12  is maintained in the state shown in  FIGS. 2A and 3A  when the barrel torque does not exceed the predetermined torque Tmax. In this state, about 30% of the energy of the barrel torque in the gear train mechanism  10  is consumed. 
     When the barrel torque exceeds the predetermined torque Tmax, on the other hand, the resultant force F 3  acting on the pivot  12   c  of the second wheel  12  elastically deforms the spring  33  (see  FIGS. 2B and 3B ). The deformation of the spring  33  moves the second wheel  12  in the longitudinal direction X so as to reduce the efficiency of the engagement between the gear  11   b  of the rotary barrel  11  and the pinion  12   a  of the second wheel  12  and accordingly to reduce the transmission efficiency of the torque from the rotary barrel  11  to the second wheel  12 . In addition, the movement of the second wheel  12  along the longitudinal direction X reduces the efficiency of the engagement between the gear  12   b  of the second wheel  12  and the pinion  13   a  of the third wheel  13  to reduce the transmission efficiency of the torque from the second wheel  12  to the third wheel  13 . 
     As described above, reducing the transmission efficiency of the torque in the gear train mechanism  10  increases the energy consumption of the barrel torque to about 35%, for example. Accordingly, the movement  100  of Embodiment 1 can reduce the barrel torque transmitted to the escape wheel  21  from the gear train mechanism  10  compared to the conventional movement which does not move the second wheel  12 . Therefore, about 30% of the energy of the barrel torque is transmitted to the balance wheel  23  since the escape wheel  21  and the anchor  22  still consume about 35% of the energy of the barrel torque. 
     As a result, as shown with a bold line in  FIG. 5 , the value obtained by multiplying the torque transmitted to the balance wheel  23  by the reduction ratio becomes a torque (30% of the barrel torque Tsmax) which is substantially the same as that of the assumed torque (35% of the barrel torque Tmax). Accordingly, the oscillation of the balance wheel  23  at an oscillation angle beyond the assumed angle is prevented or restrained and therefore the occurrence of so-called overbanking can be prevented or restrained. 
     According to the Embodiment 1 of the present invention, the movement  100  can prevent or restrain the transmission of the excessive barrel torque to the balance wheel  23  (the increase in the oscillation angle) even when the mainspring  1  generates the excessive barrel torque (the barrel torque exceeds the torque Tmax), and can also avoid wasteful energy consumption when the excessive barrel torque is not generated (the barrel torque does not exceed the torque Tmax). 
     Further, in the movement  100  of Embodiment 1, the spring seats  30  are provided such as to move, in the same direction, the end stones  34  (the end stone  34  of the spring seat fixed to the main plate  91  and the end stone  34  of the spring seat fixed to the gear train bridge) which support the pivot  12   c  of the second wheel  12  at the upper and the lower ends of the pivot, respectively. Hence, the upper and lower spring seats  30  move in the same direction as the direction in which the second wheel  12  is moved. Therefore, configuring the upper and lower spring seats  30  to move for the same distance with the consideration of the lateral pressure on the upper and lower pivots of the second wheel  12  can prevent the inclination of the second wheel  12  relative to the vertical direction when the second wheel  12  is moved. 
     Note that the mechanical timepiece movement according to the present invention is not limited to one which moves both of the upper and lower end stones supporting the pivot of the gear moved by the moving mechanism. Therefore, the moving mechanism such as the spring seat  30  may be disposed either at the upper side or the lower side of the pivot. The movement with the moving mechanism disposed either at the upper side or the lower side of the pivot can also reduce the efficiency of the engagement between the gears forming the train gear mechanism and accordingly reduce the transmitting efficiency of the barrel torque. 
     In the mechanical timepiece movement according to Embodiment 1, the spring  33  biases the end stone  34  with the elastic force (applies a load pressing the end stone) toward the end  31   b  closer to the rotary barrel  11  along the longitudinal direction X of the elongate hole  31   a.  As a load against the elastic force of the spring  33  acts on the end stone  34 , the spring  33  moves the end stone  34  in a direction away from the rotary barrel  11  for a distance corresponding to the magnitude of the acting load. That is, the heavier the load acting on the end stone  34  becomes, the longer the distance from the end stone  34  to the rotary barrel  11  becomes. 
     Then, the longer the distance from the end stone  34  to the rotary barrel  11  becomes, the lower the transmitting efficiency of the barrel torque from the rotary barrel  11  to the second wheel  12  becomes. According to the mechanical timepiece movement  100  of the Embodiment 1, the degree of the restraint of the torque transmitted to the balance wheel  23  increases as the amount of the barrel torque exceeding the predetermined torque Tmax becomes greater so that the variation of the torque transmitted to the balance wheel  23  can be restrained. In addition, in the mechanical timepiece movement  100  according to Embodiment 1, the moving mechanism can be achieved with a simpler configuration since the movement  100  does not include an independent sensor for sensing the magnitude of the barrel torque or a controller for controlling the degree of the transmission to the balance wheel  23  in accordance with values sensed by the sensor. 
     In the mechanical timepiece movement  100  according to Embodiment 1, the spring  33  providing elastic force biases the end stone  34 . However, the movement of the present invention is not limited to above movement in which the spring  33  biases the end stone. Therefore, the biasing member in the mechanical timepiece movement according to Embodiment 1 can be any member as long as it can provide a tension load or a compressing load on the end stone  34 . For example, the present invention may adopt an elastic member for providing elastic force such as a coil spring, a leaf spring or a rubber, or a magnetic member (a magnet) for providing magnetic force such as attraction and repulsion. In the mechanical timepiece movement  100  according to Embodiment 1, the seat  32  supports the end stone  34 . However, the seat  32  may be eliminated, and the end stone  34  may be directly biased by the spring  33 . 
     In the mechanical timepiece movement  100  according to Embodiment 1, the spring seat  30  is formed with the elongate hole  31   a,  and is integrated as a unit with the guide  31  fixed to the main plate  91  and the gear train bridge, with the seat  32  disposed within the elongate hole  31   a  and including the end stone  34 , and with the spring  33 . Since the guide  31 , the seat  32 , and the spring  33  cannot be separated from each other, the spring seat  30  can be easily handled compared to a spring seat configured with the guide  31 , the seat  32 , and the spring  33 , each of which is an independent element. 
     In addition, the moving mechanism (the spring seat  30 ) which moves the second wheel  12  may be mounted in the movement  100  only by fixing the guide  31  of the unitized spring seat  30  to the main plate  91  and the gear train bridge. Accordingly, in order to mount the moving mechanism to the main plate  91  and the gear train bridge, it is only required to open a hole for receiving the guide  31  on the main plate  91  and the gear train bridge, which makes the required work minimum. This prevents the configuration of the main plate  91  and the gear train bridge from being complicated compared to one configured by opening the elongate hole  31   a  on the main plate  91  and the gear train bridge, and then by placing the seat  32  and the spring  33  within the elongate holes. 
     Note that the mechanical timepiece movement of the present invention does not intend to eliminate the above described moving mechanism configured by opening the elongate hole  31   a  on the main plate  91  and the gear train bridge, and by placing the seat  32  and the spring  33  within the elongate hole. It is also possible to adopt the moving mechanism configured by opening the elongate hole  31   a  on the main plate  91  and the gear train bridge, and placing the seat  32  and the spring  33  within longitudinal the hole. 
     In the mechanical timepiece movement  100  according to Embodiment 1, the spring seat  30  moves the second wheel  12 . However, the movement of the present invention is not limited to one in which the moving mechanism moves the second wheel  12 . Accordingly, the spring seat  30  may move the rotary barrel  11 , the third wheel  13 , or the fourth wheel  14 . Further, if the gear train mechanism  10  includes other gears aligned with the balance wheel  23  in addition to the rotary barrel  11 , the second wheel  12 , the third wheel  13 , and the fourth wheel  14 , the spring seat  30  may be configured to move such other gears aligned with the balance wheel  23 . 
     Note that the axes of the above gears of the gear train mechanism  10  moved by the spring seat  30  is preferably not common with the axes of hands such as a hour hand, a minute hand and a second hand. The gears having the common axes with these hands discomforts a user who looks at the moving hands since the hands are also moved as the gears are moved by the spring seat  30 . Further, the spring seat  30  is not limited to one which moves only one of the gears forming the gear train mechanism  10 . The spring seat  30  may move more than one gear of the gear train mechanism  10 . 
     In the movement  100  of this embodiment, the longitudinal direction X of the elongate hole  31   a  of the spring seat  30  corresponds to the directions in which the pivot  12   c  of the second wheel  12  moves away from the rotary barrel  11 , which is a driving gear, and also moves away from the third wheel  13 , which is a driven gear. This reduces the efficiency of the torque transmission between the second wheel  12  and the rotary barrel  11  and between the second wheel  12  and the third wheel  13 . Accordingly, it can increase the reduction of the torque transmission efficiency relative to the distance for which the end stone  34  moves. In addition, a space required to move the end stone  34  can also be reduced. 
     Note that in the mechanical timepiece movement of the present invention, the longitudinal direction X of the elongate hole  31   a  may correspond to a direction in which the moving mechanism moves the gear away from at least one of a driven gear or a driving gear. Resultingly, the torque transmission efficiency between the gears of the gear train mechanism is reduced. 
     Second Embodiment 
       FIG. 6  is a perspective view of a spring-provided seat or spring seat  40  which is another example of the moving mechanism in the mechanical timepiece movement according to the second embodiment (Embodiment 2) of the present invention. The spring seat  40  has the same configuration as the spring seat  30  shown in  FIGS. 2A and 2B  with the exception of a spring  43  which is replaced with the spring  33 . The spring  33  in the spring seat  30  has a S-shaped contour in a plan view but the spring  43  of the spring seat  40 , on the other hand, has an ellipse annular contour in a plan view. The spring  43  is configured such that the shorter diameter direction of the ellipse annular contour extends along the longitudinal direction X of the elongate hole  31   a.    
     In the spring seat  40  of Embodiment 2 as configured above, a state in which the spring  43  biases the seat  32  is maintained and remains as shown in  FIG. 6  unless the barrel torque exceeds the predetermined torque Tmax. The seat  32  compresses the spring  43  in the shorter diameter direction and moves in the longitudinal direction X against the elastic force of the spring  43  when the barrel torque exceeds the predetermined torque Tmax. Resultingly, the seat  32  and the end stone  34  move in a direction away from the rotary barrel  11  and the third wheel  13 . Accordingly, the mechanical timepiece movement provided with the spring seat  40  of Embodiment 2 can provide an operation and an effect similar to the mechanical timepiece movement  100  provided with the spring seat  30  of Embodiment 1. 
     Third Embodiment 
       FIG. 7  is a perspective view of a spring-provided seat or spring seat  50  which is yet another example of the moving mechanism in the mechanical timepiece movement according to the third embodiment (Embodiment 3) of the present invention. The spring seat  50  is assembled and provided in the main plate  91 .  FIG. 7B  is an exploded perspective view of the spring seat shown in  FIG. 7A . The spring seat  50  differs from the spring seat  30  shown in  FIGS. 2A, 2B  and the spring seat  40  shown in  FIG. 6 . The spring seat  50  includes a guide  51   a  having an elongate hole  51   d  extending in a longitudinal direction X, a seat  52  housed within the elongate hole  51   d  and receiving the end stone  34 , and a spring  53  biasing the seat  52 , each of which is formed as an independent element. 
     It is necessary to prevent the seat  52  and the spring  53  from being separated from the guide  51   a  since the seat  52  and the spring  53  are independent from the guide  51   a.  Considering the above, in the spring seat  50 , the guide  51   a  is laminated with covers  51   b,    51   c  disposed on the top and bottom thereof as shown in  FIGS. 7A and 7B . Each of the covers  51   b,    51   c  has a hole  51   e,    51   f  which is smaller than the contour of the seat  52 . Note that the cover  51   b,  which is illustrated as the upper cover, may not necessarily has the hole  51   e.    
     The hole  51   e  of the cover  51   b  is formed such that the pivot  12   c  (see  FIGS. 3A and 3B ) supported by the end stone  34  does not interfere with the cover  51   b  as the seat  52  moves within a space of the elongate hole  51   d  in the longitudinal direction X. The spring  53  is a leaf spring made of an elastic member such as metal. The spring  53  generates elastic force to return the included angle θ of the leaf spring to the original angle as the included angle θ increases. The elastic force acts as biasing force which biases the seat  52  toward one of the ends. 
     In the spring seat  50  of Embodiment 3 as configured above, a state in which the spring  53  biases the seat  52  is maintained and remains as shown in  FIG. 7A  while the barrel torque does not exceed the predetermined torque Tmax. The seat  52  moves in the longitudinal direction X against the elastic force of the spring  53  when the barrel torque exceeds the predetermined torque Tmax. Resultingly, the seat  52  and the end stone  34  move in a direction away from the rotary barrel  11  and the third wheel  13 . Accordingly, the mechanical timepiece movement provided with the spring seat  50  of Embodiment 3 can provide an operation and an effect similar to the mechanical timepiece movement  100  provided with the spring seat  30  of Embodiment 1 or the spring seat  40  of Embodiment 2. 
     Note that in the Embodiments 1 and 2, the guide may be laminated with the covers  51   b,    51   c  disposed on the top and bottom of the guide as the spring seat  50  of Embodiment 3 if the spring seats  30 ,  40  of Embodiment 1, 2 are configured such that the seat  32  and the spring  33 ,  34  are formed separate from the guide  31 . 
     CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority from Japanese Patent Application No. 2015-000127, filed on Jan. 5, 2015, the disclosure of which is hereby incorporated by reference in its entirety.