Patent Publication Number: US-10761483-B2

Title: Mechanical part, timepiece, and method of manufacturing a mechanical part

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a mechanical part, a timepiece, and a method of manufacturing a mechanical part. 
     2. Related Art 
     Mechanical timepieces comprise many wheels and numerous other mechanical parts. Mechanical parts such as wheels are disposed with a staff member inserted to a hole formed in the center of the rotating member having a plurality of teeth formed around the outside circumference. 
     Conventionally, such mechanical parts are machined from metal materials, but in more recent years silicon has also been used as a material for manufacturing mechanical parts for timepieces. Because mechanical parts made from a silicon substrate are lighter than parts made from a metal substrate, the inertia of the mechanical parts is also lower and improved energy transfer efficiency can be expected. 
     In addition, because silicon can be processed using technologies such as photolithography and etching, and can therefore be shaped with a high degree of freedom, using a silicon substrate also offers the benefit of improved precision processing mechanical parts. 
     EP1705533B1 describes a mechanical part that has a metal staff member inserted to a rotating member made of silicon, and is secured by a metal fastening member (washer). A protrusion (pin) that fits into a hole in the rotating member is disposed to the fastening member of the mechanical part described in EP1705533B1. By this pin fitting into the hole in the rotating member, separation of the rotating member from, and rotation of the rotating member relative to, the staff member are suppressed. 
     However, with the mechanical part described in EP1705533B1, machining processes such as cutting and grinding are required to form a pin (protrusion) on the metal fastening member. When the staff member and rotating member are secured by the fastening member, the hole in the rotating member and the protrusion on the fastening member must be aligned in the circumferential direction (rotational direction). This increases the number of processing and assembly steps, possibly increasing the cost of production. 
     In addition, if there is any deviation in processing precision during the machining process forming the protrusion on the fastening member, the positions of the staff member and fastening member may shift or vary when the staff member and fastening member are fastened together, or a gap may form between the staff member and fastening member, and the quality of the mechanical part may therefore drop. 
     SUMMARY 
     The present invention is directed to solving at least part of the foregoing problem, and can be achieved by the embodiments or examples described below. 
     EXAMPLE 1 
     A mechanical part according to this example includes: a staff member; a rotating member including a first hole in which the staff member is inserted, and a rib extending toward the staff member; and an annular fastening member configured to affix the rotating member to the staff member, the fastening member disposed in contact with the rib with part of the fastening member deformed and protruding into the first hole. 
     The configuration of a mechanical part according to this aspect of the invention has an annular fastening member configured to affix a rotating member to a staff member. Because the fastening member is disposed to contact the ribs of the rotating member, the position of the rotating member is fixed in the axial direction of the staff member. Furthermore, because part of the fastening member has a part (referred to below as a protrusion) that deforms and protrudes into the first hole, the position of the rotating member in the circumferential direction (direction of rotation) of the staff member is also fixed. As a result, a mechanical part that suppresses separation and rotation of the rotating member to the staff member can be provided. 
     EXAMPLE 2 
     Preferably in a mechanical part according to this example, the first hole is formed surrounded by a plurality of the ribs; and the fastening member is formed so that the part of the fastening member overlapping the first hole of the rotating member protrudes in the axial direction when seen in plan view from the axial direction of the staff member. 
     With the configuration of a mechanical part according to this example, because the part of the fastening member that overlaps the first hole surrounded by the rib protrudes in the axial direction past the part that overlaps the rib of the rotating member in plan view, the protrusion is formed desirably according to the shape of the first hole. Deviation and variation in the position of the fastening member to the rotating member can therefore be effectively suppressed. 
     EXAMPLE 3 
     Preferably in a mechanical part according to this example, the Vickers hardness of the fastening member is less than the Vickers hardness of the rotating member. 
     Because the Vickers hardness of the fastening member is less than the Vickers hardness of the rotating member in the configuration of a mechanical part according to this example, part of the fastening member can be plastically deformed and a protrusion formed by press fitting the fastening member to the rotating member. 
     More specifically, after disposing the fastening member in contact with the rib of the rotating member, the fastening member can be pressed to form the protrusion. As a result, the need for cutting, grinding or other machining process to form a protrusion on the fastening member can be eliminated, and positioning the fastening member and the rotating member in the circumferential direction can be eliminated. 
     In addition, because the part of the fastening member that overlaps the first hole can be made to protrude to the rotating member side past the part that overlaps the rib, deviation and variation in the position of the fastening member to the rotating member can be effectively suppressed, and the gap between the rotating member and fastening member can be reduced. 
     EXAMPLE 4 
     Preferably in a mechanical part according to this example, the staff member has, on the opposite side of the rotating member as the fastening member, a protrusion configured to protrude to an outside in a radial direction; and the diameter of the first surface of the fastening member that contacts the rib is less than or equal to the diameter of the surface of the protrusion that contacts the rotating member. 
     In this configuration of a mechanical part according to the invention, when pressing and plastically deforming part of the fastening member, force is transferred from the first surface of the fastening member to the rotating member supported by the surface of the protrusion from the staff member. Because the diameter of the first surface of the fastening member that contacts the rib is less than or equal to the diameter of the surface of the protrusion that contacts the rotating member, the force applied to the rotating member by pressing the fastening member is supported in the area of the surface of the protrusion contacting the rotating member. As a result, warping or other deformation or damage to the rotating member by pressing on the fastening member can be suppressed. 
     EXAMPLE 5 
     Preferably in a mechanical part according to this example, the diameter of a second surface of the fastening member, which is the opposite side as the first surface, is greater than or equal to the diameter of the first surface. 
     In this configuration of a mechanical part according to the invention, the diameter of the second surface to which force is applied when pressing on the fastening member is greater than or equal to the diameter of the first surface that contacts the rib. As a result, the diameter of the second surface used to push the fastening member can be increased, and the fastening member can be easily pressed into position, without making the diameter of the first surface that contacts the rib greater than the diameter of the surface that contacts the rotating member. 
     EXAMPLE 6 
     Preferably in a mechanical part according to this example, the rotating member has a rim part with a plurality of teeth, and a flexible part and a second hole disposed between the ribs and the rim part. 
     In this configuration of a mechanical part according to the invention, because there is a flexible member between the rib and rim, stress on the rib is relieved, and a holding force sufficient for the rib to hold the staff member is achieved, by the elasticity of the flexible member. 
     EXAMPLE 7 
     A timepiece according to another aspect of the invention has a mechanical part according to the invention as described above. 
     Because a mechanical part according to the invention as described above is used in a timepiece configured according to this aspect of the invention, a cost-competitive timepiece with outstanding quality and high precision can be provided. 
     EXAMPLE 8 
     Another aspect of the invention is a manufacturing method of a mechanical part including: a process of forming a rotating member having a rib extending toward a center part, and a first hole enclosed by the rib; a process of inserting a staff member into the first hole of the rotating member; a process of inserting the staff member into a hole in an annular fastening member so that the fastening member contacts the rib of the rotating member; and a process of pressing the fastening member to deform part of the fastening member to protrude into the first hole of the rotating member. 
     The manufacturing method of a mechanical part according to this aspect of the invention inserts a staff member to a first hole in a rotating member, and then inserts the staff member to a hole in an annular fastening member so that the fastening member contacts a rib of the rotating member. Because the fastening member is then pressed so that part of the fastening member deforms and protrudes into the first hole in the rotating member, a protrusion can be formed on the fastening member after inserting the staff member to the hole in the fastening member. 
     More specifically, because a protrusion does not need to be previously formed on the fastening member, machining processes such as cutting and grinding to form a protrusion on the fastening member are not needed, and there is no need to position a protrusion in the first hole of the rotating member when inserting the staff member to the hole in the fastening member. As a result, the production cost of the mechanical part can be reduced because the number of processing and assembly steps can be reduced. 
     In addition, because the part of the fastening member that overlaps the first hole in the rotating member protrudes into the first hole, a protrusion matching the shape of the first hole can be formed. As a result, because deviation and variation the positioning of the rotating member can be suppressed, and the gap between the rotating member and fastening member can be reduced, separation and rotation of the rotating member on the staff member can be suppressed by the fastening member, and a mechanical part with excellent quality can be manufactured. 
     EXAMPLE 9 
     In a manufacturing method of a mechanical part according to another example, in the process of inserting the staff member into a hole in the fastening member, the inside diameter of the hole in the fastening member is smaller than the outside diameter of the staff member. 
     Because the inside diameter of the hole in the fastening member is smaller than the outside diameter of the staff member, the fastening member can be spread to the outside by inserting the staff member into the hole in the fastening member in the manufacturing method of a mechanical part according to this aspect of the invention. Because the stress produced at this time secures the fastening member to the staff member, the rotating member can be more reliably fixed on the staff member by the fastening member. 
     Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view from the front side of the movement of a mechanical timepiece according to a preferred embodiment of the invention. 
         FIG. 2  is a plan view of the escapement according to a preferred embodiment of the invention. 
         FIG. 3  is an oblique view of an escape wheel as an example of a mechanical part according to the invention. 
         FIG. 4  is a section view through A-A′ in  FIG. 2 . 
         FIG. 5  is a plan view of an escape wheel as an example of a rotating member according to the invention. 
         FIG. 6  is an enlarged partial section view of area D in  FIG. 4 . 
         FIG. 7  is an enlarged partial section view of area B in  FIG. 2 . 
         FIG. 8  is an enlarged partial section view of area C in FIG.  3 . 
         FIG. 9  is a flow chart describing the method of manufacturing an escape wheel according to the invention. 
         FIG. 10  is a schematic section view illustrating the process of inserting a staff member to the fastening member. 
         FIG. 11  is a schematic section view illustrating the process of inserting a staff member to the fastening member. 
         FIG. 12  is a schematic section view illustrating the process of inserting a staff member to the fastening member. 
         FIG. 13  is a schematic section view illustrating the process of inserting a staff member to the fastening member. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of the invention is described below with reference to the accompanying figures. Note that this embodiment of the invention describes a mechanical timepiece as an example of a timepiece according to the invention. As an example of a mechanical part according to the invention, this embodiment also describes an escape wheel, which is an example of a wheel embodying a mechanical part in a movement of a mechanical timepiece. Note also that to show different layers and members in a size large enough to be recognized and understood, the scale of the layers and members may differ from the actual scale and size. 
     Embodiment 1 
     Mechanical Timepiece 
     A mechanical timepiece  1  is described first as an example of a timepiece according to this embodiment of the invention.  FIG. 1  is a plan view from the front side of the movement of a mechanical timepiece according to this embodiment of the invention. As shown in  FIG. 1 , a mechanical timepiece  1  according to this embodiment has a movement  10 , and a casing not shown that holds the movement  10 . 
     The side of the movement as shown in  FIG. 1  is referred to as the front side, and the opposite side of the movement is referred to as the back side. The movement  10  has a main plate  11  embodying the substrate. A dial not shown in disposed on the back side of the main plate  11 . Note that the wheel train assembled on the front side of the movement  10  is referred to as the front wheel train, and the wheel train assembled on the back side of the movement  10  is referred to as the back wheel train. 
     A winding stem guide hole  11   a  is formed in the main plate  11 , and a winding stem  12  is assembled freely rotatably inside the winding stem guide hole  11   a.    
     The position of the winding stem  12  on its axis of rotation is determined by a switching mechanism including a setting lever  13 , yoke  14 , yoke spring  15 , and setting lever jumper  16 . A winding pinion  17  is disposed freely rotatably to the guide shaft part of the winding stem  12 . 
     In this configuration, when the winding stem  12  is pushed in along the axis of rotation to the first winding stem position (zero stop) closest to the center of the movement  10  and the winding stem  12  is then turned, the winding pinion  17  turns through rotation of an intervening sliding pinion not shown. Rotation of the winding pinion  17  causes the crown wheel  20  meshed with the winding pinion  17  to turn. Rotation of the crown wheel  20  causes the ratchet wheel  21  meshed with the crown wheel  20  to turn. Rotation of the ratchet wheel  21  then winds the main spring (drive power source) not shown housed inside the barrel wheel  22 . 
     The front wheel train of the movement  10  includes, in addition to the barrel wheel  22  (mechanical part) described above, a center wheel (mechanical part)  25 , a third wheel (mechanical part)  26 , and a fourth wheel (mechanical part)  27 , and functions to transfer torque from the barrel wheel  22 . Also disposed on the front side of the movement  10  are an escapement  30  and regulator  31  for controlling rotation of the front wheel train. 
     The center wheel  25  is a wheel that meshes with the barrel wheel  22 . The third wheel  26  is a wheel that meshes with the center wheel  25 . The fourth wheel  27  is a wheel that meshes with the third wheel  26 . The escapement  30  is a mechanism controlling rotation of the front wheel train described above, and includes an escape wheel (mechanical part)  35  that meshes with the fourth wheel  27 , and a pallet fork (anchor striker) (mechanical part)  36  that advances and causes the escape wheel and pinion  35  to rotate isochronally. The regulator  31  is a mechanism that regulates the escapement  30  described above, and includes a balance (mechanical part)  40 . 
     Escape Wheel and Pinion 
     The escape wheel and pinion  35  of the escapement  30  according to this embodiment of the invention is described in detail next. 
       FIG. 2  is a plan view of the escapement according to this embodiment of the invention.  FIG. 3  is an oblique view of an escape wheel as an example of a mechanical part according to the invention.  FIG. 4  is a section view through A-A′ in  FIG. 2 .  FIG. 5  is a plan view of an escape wheel as an example of a rotating member according to the invention. 
     As shown in  FIG. 2  to  FIG. 4 , the escape wheel and pinion  35  of the escapement  30  includes an escape wheel  101  as a rotating member, a pinion (rotary staff)  102  affixed coaxially (on axis O 1 ) to the escape wheel  101 , and an annular fastening member  130  holding the escape wheel  101  and pinion  102  together. 
     Below, the direction along the axis O 1  of the escape wheel  101  and pinion  102  is referred to simply as the axial direction, the direction perpendicular to the axis O 1  is referred to as the radial direction, and the direction of rotation around the axis O 1  is referred to as the circumferential direction. Note also that the axis O 1  side of the radial direction is referred to as the inside, and the side away from the axis O 1  is referred to as the outside. 
     As shown in  FIG. 2  to  FIG. 5 , the escape wheel  101  is a disc of a uniform thickness throughout, and the front side  101   a , which is one side, and the back side  101   b , which is the opposite side as the one side, are flat. The escape wheel  101  is made from monocrystalline silicon or other material with a crystal orientation, or from a metal material. The escape wheel  101  has ribs  112 , a hole  115  as a first opening, flexible parts  113 , holes  113   a  and holes  113   b  as second openings, and a rim  111 . 
     A plurality of ribs  112  are disposed in the center of the escape wheel  101 , and are formed curving to the inside toward the pinion  102 . In this embodiment of the invention, the escape wheel  101  has three ribs  112 . 
     The hole  115  is a through-hole formed so as to be surrounded by the multiple ribs  112 . The pinion  102  is inserted to the hole  115 , and is held by the inside peaks of the three ribs  112 . As a result, the pinion  102  is supported with the axis O 1  thereof positioned in the center of the escape wheel  101 . 
     The flexible parts  113  are parts connected to the ribs  112  and rim  111 , and are formed as multiple spokes. Each flexible part  113  extends in an arc radiating in two branches from the adjacent rib  112  to the inside circumference side of the rim  111 . The holes  113   a  are through-holes formed so as to be surrounded by a rib  112 , a flexible part  113 , and the rim  111 . The other holes  113   b  are through-holes formed so as to be surrounded by a flexible parts  113  and the rim  111 . 
     Because there are flexible parts  113  between the ribs  112  and rim  111 , stress applied to the ribs  112  is relieved by the flexibility of the flexible parts  113 , while the ribs  112  have sufficient holding power to hold the pinion  102 . 
     The rim  111  is disposed around the escape wheel  101 . Around the outside circumference of the rim  111 , a plurality of teeth  114  with a specific hook shape are formed projecting to the outside in the radial direction. 
     As shown in  FIG. 2 , the multiple teeth  114  of the escape wheel and pinion  35  engage the pallet  36 . The pallet  36  has a T-shaped anchor  142   d  formed by three anchor beams (lever and pallets)  143 , and a pallet staff  142   f , which is a pivot. The anchor  142   d  is configured to pivot on the pallet staff  142   f . Note that the ends of the pallet staff  142   f  are supported rotatably by the main plate  11  described above and an anchor bridge not shown. 
     Of the three anchor beams  143 , a pallet stone  144   a  and  144   b  is disposed to two of the anchor beams (pallets)  143 , and a guard pin  145  is disposed to the distal end of the remaining one anchor beam (lever)  143 . The pallet stones  144   a  and  144   b  are rubies shaped like rectangular columns, and are affixed to the anchor beams  143  by adhesive, for example. 
     When the pallet  36  thus comprised pivots on the pallet staff  142   f , pallet stone  144   a  or pallet stone  144   b  contacts the distal end of a tooth  114  of the escape wheel and pinion  35 . The anchor beam (lever)  143  to which the guard pin  145  is attached then contacts a banking pin not shown, thereby preventing the pallet  36  from pivoting further in the same direction. As a result, rotation of the escape wheel and pinion  35  is also stopped temporarily. 
     Because the substantially of the escape wheel  101  is silicon, and the escape wheel  101  can therefore be formed using technology such as photolithography or etching, parts can be easily formed to the desired shape, and processing precision thereof can be improved. Furthermore, by using silicon for the substrate of the escape wheel  101 , the escape wheel  101  can be made lighter than if it was made from a metal substrate, the inertia of the escape wheel  101  can be reduced, and energy transfer efficiency can be improved. 
     As shown in  FIG. 3  and  FIG. 4 , the pinion  102  has tenons  121   a  and  121   b , an escape pinion  122 , a press-fit staff  123 , and a flange  124  as a protruding shoulder. The tenons  121   a  and  121   b  are disposed to the distal axial ends of the pinion  102 . Of the tenons  121   a  and  121   b , the one tenon  121   a  on one axial end is supported rotatably by a wheel train bridge not shown, and the other tenon  121   b  on the other axial end is supported rotatably by the main plate  11  described above. 
     The escape pinion  122  is formed near the one-end tenon  121   a  of the pinion  102 . The escape pinion  122  meshes with the teeth of the fourth wheel  27  (see  FIG. 1 ) described above. By the escape pinion  122  meshing with the fourth wheel  27 , torque from the fourth wheel  27  is transferred to the pinion  102 , and the escape wheel and pinion  35  turns. 
     The press-fit staff  123  is larger in diameter than the tenons  121   a  and  121   b  described above. The press-fit staff  123  is inserted from the back side  101   b  to the hole  115  surrounded by the multiple ribs  112  of the escape wheel  101 . The press-fit staff  123  is disposed inside the hole  115  in contact with the inside peaks of the ribs  112  with part of the press-fit staff  123  protruding from the front side  101   a  of the escape wheel  101  to the other axial end. 
     The diameter of the inscribed circle  115   a  (see  FIG. 2  and  FIG. 5 ) to the peaks of the three ribs  112  projecting toward the press-fit staff  123  of the pinion  102  when the pinion  102  is not inserted to the hole  115  (see  FIG. 5 ) is designed to be smaller than the diameter of the press-fit staff  123  of the pinion  102 . Therefore, when the pinion  102  is inserted to the hole  115  of the escape wheel  101 , the ribs  112  contacting the press-fit staff  123  deform to the outside in the radial direction. The pinion  102  is positioned and held in the center of the escape wheel  101  by the stress produced by this deformation. 
     The flange  124  are formed to project to the outside in the radial direction between the escape pinion  122  and the press-fit staff  123  of the pinion  102 . The flange  124  is disposed on the opposite side of the escape wheel  101  as the fastening member  130  with the escape wheel  101  therebetween. The diameter of the flange  124  is larger than the diameter of the press-fit staff  123 . The diameter of the flange  124  is therefore larger than the diameter of the inscribed circle  115   a  to the peaks of the three ribs  112 . 
     The face  125  on the tenon  121   b  of the flange  124  (see  FIG. 6 ) contacts the back side  101   b  of the escape wheel  101  (ribs  112 ). This determines (limits) the position of the escape wheel  101  in the axial direction of the pinion  102  (the direction toward the one-end tenon  121   a ). 
     The pinion  102  is made from a metal material that offers excellent rigidity and heat resistance, and good excellent processability by cutting, machining, and grinding, for example. The pinion  102  is preferably made from carbon steel. 
     The fastening member  130  is an annular member with a hole  130   a  (see  FIG. 4 ). The fastening member  130  is round in plan view (see  FIG. 2 ). The pinion  102  is inserted inside the hole  130   a  in the fastening member  130 . In other words, the fastening member  130  is pushed onto the press-fit staff  123  of the pinion  102  from the other-end tenon  121   b  side. 
     The fastening member  130  is disposed in the axial direction of the pinion  102  on the other-end tenon  121   b  side of the escape wheel  101  opposite the flange  124  with the escape wheel  101  therebetween. The inside diameter of the hole  130   a  in the fastening member  130  is designed to be smaller than the outside diameter of the press-fit staff  123  part of the pinion  102 . Therefore, the fastening member  130  is affixed to the pinion  102  when the fastening member  130  is pushed onto the pinion  102  (that is, when the pinion  102  is inserted inside the hole  130   a  of the fastening member  130 ). 
     The detailed configuration of the fastening member  130  is described next with reference to  FIG. 6  to  FIG. 8 .  FIG. 6  is an enlarged partial section view of area D in  FIG. 4 .  FIG. 7  is an enlarged partial section view of area B in  FIG. 2 .  FIG. 8  is an enlarged partial section view of area C in  FIG. 3 . 
     As shown in  FIG. 6 , the fastening member  130  has a large diameter part  131 , and a small diameter part  132  connected to the large diameter part  131  in the axial direction. The hole  130   a  passes through the large diameter part  131  and small diameter part  132 . The fastening member  130  is installed with the small diameter part  132  facing the escape wheel  101 . 
     The surface of the small diameter part  132  on the escape wheel  101  is referred to below as first surface  133  (first surface). This first surface  133  of the small diameter part  132  contacts the front side  101   a  of the escape wheel  101  (ribs  112 ). The surface of the large diameter part  131  on the opposite side as the escape wheel  101  is referred to as the second surface  135  (second surface). The diameter D 2  of the first surface  133  of the small diameter part  132  is less than or equal to the diameter D 3  of the face  125  of the flange  124 . The diameter D 1  of the second surface  135  of the large diameter part  131  is greater than or equal to the diameter D 2  of the first surface  133  of the small diameter part  132 , and is preferably greater than or equal to diameter D 3  of the face  125  of the flange  124 . 
     The fastening member  130  is disposed so that it touches and partially deforms the ribs  112 , and protrudes into the hole  115 . More specifically, the fastening member  130  has a protrusion  134  formed to protrude in the axial direction from the first surface  133  of the small diameter part  132  that contacts the front side  101   a  of the ribs  112  (escape wheel  101 ). 
     As shown in  FIG. 7 , when seen in plan view from the axial direction of the pinion  102 , the small diameter part  132  of the fastening member  130  has a part  132   a  that overlaps the ribs  112  of the escape wheel  101 , and a part  132   b  that overlaps the hole  115  in the escape wheel  101 . In other words, the small diameter part  132  of the fastening member  130  has parts  132   a  that contact the first surface  133  of the ribs  112  ((see  FIG. 8 ), and parts  132   b  that do not contact the ribs  112 . 
     As shown in  FIG. 8 , the part  132   a  of the small diameter part  132  that overlaps the ribs  112  contacts the front side  101   a  of the ribs  112  with the first surface  133 . As a result, the position of the escape wheel  101  in the axial direction of the pinion  102  (the direction toward the other-end tenon  121   b ) is fixed. As a result, the escape wheel  101  is affixed to the pinion  102  between the fastening member  130  and flange  124 . 
     The part  132   b  of the small diameter part  132  that overlaps the hole  115  protrudes in the axial direction from the first surface  133  of the part  132   a . The part  132   b  of the small diameter part  132  that protrudes from the first surface  133  to the inside of the hole  115  in the axial direction is the protrusion  134 . This protrusion  134  contacts the inside surface (the surface along the axial direction) of the ribs  112  in the circumferential direction (the direction of rotation of the escape wheel  101  and pinion  102 ). As a result, the position of the escape wheel  101  is limited in the circumferential direction. The distance the protrusion  134  protrudes from the first surface  133  is preferably greater than or equal to 3 μm. 
     As described above, because the position of the escape wheel  101  in the axial direction and the circumferential direction is determined by the fastening member  130 , the escape wheel  101  is prevented from separating from and rotating on the pinion  102 . 
     The fastening member  130  is formed from a metal material that has excellent processability, including machining and grinding, and is softer than the escape wheel  101 . More specifically, the Vickers hardness (VH) of the fastening member  130  is lower than the Vickers hardness of the escape wheel  101 . The Vickers hardness (VH) of the fastening member  130  is preferably also lower than the Vickers hardness of the pinion  102 . The material of the fastening member  130  in this example is brass. 
     The Vickers hardness of brass depends on the composition, but is typically 50 HV to 200 HV. 
     When the escape wheel  101  is made from monocrystalline silicon, the Vickers hardness of the escape wheel  101  is approximately 1040 HV. 
     When the pinion  102  is made from carbon steel, the Vickers hardness is approximately 210 HV to 300 HV. 
     The fastening member  130  may be made from an aluminum alloy, bronze, iron, or a titanium alloy. 
     As described in detail below, in this embodiment of the invention the protrusion  134  is formed by applying pressure to the fastening member  130  with the fastening member  130  in contact with the escape wheel  101 , causing plastic deformation of part of the fastening member  130  (part  132   b  of the small diameter part  132 ). By forming the protrusion  134  in this way, the protrusion  134  can be formed to match the shape of the hole  115  (the shape of the ribs  112 ), and there is no need to specifically position the fastening member  130  to the escape wheel  101 . In addition, an offset or deviation in the position of the fastening member  130  to the escape wheel  101  can be suppressed. 
     Method of Manufacturing an Escape Wheel 
     A method of manufacturing an escape wheel and pinion  35  as an example of a mechanical part according to this embodiment of the invention is described next.  FIG. 9  is a flow chart describing the method of manufacturing an escape wheel according to the invention.  FIG. 10  to  FIG. 13  are schematic section views illustrating the process of inserting a staff member to the fastening member.  FIG. 10  to  FIG. 13  are enlarged partial section views of main parts of  FIG. 4 . 
     As shown in  FIG. 9 , a method of manufacturing an escape wheel and pinion  35  as an example of a mechanical part according to this embodiment of the invention includes a process of forming the toothed part of the rotating member (escape wheel  101 ), a process of forming the pinion  102  (staff part), a process of forming the fastening member  130 , and a process of assembling these to make an escape wheel and pinion  35 . 
     The process of forming the toothed part of the escape wheel  101  includes step S 01  to step S 06 . First, a silicon wafer is prepared as a substrate (step S 01 ). By forming the escape wheel  101  from silicon, the escape wheel  101  its parts can be formed to the desired shape using technologies such as photolithography and etching, and processing precision can be improved. 
     Next, a photoresist is applied to the surface of the substrate by spin coating or spray coating, for example (step S 02 ). The photoresist applied in step S 02  may be made from either a negative or positive photoresist material. 
     Next, the photoresist applied to the surface of the substrate is exposed using photolithographic technology (step S 03 ), and developed (step S 04 ). As a result, a photoresist pattern is formed as a mask (etching mask) corresponding to the desired plane shape of the escape wheel  101  shown in  FIG. 5 . 
     Next, using the photoresist pattern formed in step S 03  and step S 04  in  FIG. 9  as a mask, the substrate is etched by an anisotropic etching process such as deep reactive ion etching (DRIE) (step S 05 ). As a result, the substrate is etched deeply perpendicularly from the surface through the photoresist pattern, and the outside shape of an escape wheel  101  having ribs  112 , a hole  115 , flexible parts  113 , holes  113   a  and holes  113   b , and a rim  111  as shown in  FIG. 5  is acquired. 
     Next, the photoresist (photoresist pattern) is removed (step S 06  in  FIG. 9 ). In step S 06 , the photoresist can be removed by, for example, wet etching that dissolves and strips the photoresist with white fuming nitric acid (WFNA) or an organic solvent, or by oxygen plasma asking. This completes the process of forming the escape wheel  101 . 
     Note that when anisotropic etching is applied to the substrate in step S 05 , a mask protecting the back side of the substrate may be formed. By forming a protective mask on the back side of the substrate, the substrate will not be etched from the back in step S 05 , changing the shape of the side walls (the sides along the axial direction) of the ribs  112  can be prevented, and a escape wheel  101  having the cross sectional shape as shown in  FIG. 4  can be acquired. 
     The process of forming the pinion  102  includes step S 11  and step S 12  in  FIG. 9 . The process of forming the pinion  102  is executed separately from the process of forming the escape wheel  101  in step S 01  to step S 06 . 
     First, a member that will become the pinion  102  is prepared (step S 11 ). The pinion  102  preferably has sufficient rigidity to function as a staff, and heat resistance. Because carbon steel is a material with excellent rigidity and heat resistance, and can be easily processed by machining and grinding, carbon steel is particularly well suited as the material of the pinion  102 . Note that tantalum (Ta) and tungsten (W) may also be used. 
     Next, the member that becomes the pinion  102  is mechanically processed by cutting and grinding, for example (step S 12 ). As a result, a pinion  102  having tenons  121   a  and  121   b , an escape pinion  122 , a press-fit staff  123 , and a flange  124  such as shown in  FIG. 3  and  FIG. 4  can be acquired. 
     The process of forming the fastening member  130  includes step S 21  and step S 22  in  FIG. 9 . The process of forming the fastening member  130  is also executed separately from the process of forming the escape wheel  101  in step S 01  to step S 06 , and the process of forming the pinion  102  in step S 11  and step S 12 . 
     First, a member that will become the fastening member  130  is prepared (step S 21 ). The material of the fastening member  130  has good processability by machining or grinding, for example, and a Vickers hardness that is lower than the Vickers hardness of the escape wheel  101 , such as brass or other metal material. 
     Next, the member that becomes the fastening member  130  is mechanically processed by cutting and grinding, for example (step S 22 ). As a result, a fastening member  130  having a large diameter part  131 , a small diameter part  132 , and an hole  130   a  such as shown in  FIG. 6  and  FIG. 7  is shaped. 
     The process of assembling the escape wheel and pinion  35  includes step S 31  to step S 33  in  FIG. 9 . 
     First, the pinion  102  formed in step S 11  and step S 12  is inserted to the escape wheel  101  formed in step S 01  to step S 06  (step S 31 ). In step S 31 , the pinion  102  is inserted to the inscribed circle  115   a  (see  FIG. 5 ) to the peaks of the three ribs  112  inside the hole  115  in the escape wheel  101  so that the face  125  of the flange  124  contacts the back side  101   b  of the ribs  112  (see  FIG. 6 ). 
     As described above, the diameter of the inscribed circle  115   a  inside the hole  115  of the escape wheel  101  is designed to be smaller than the diameter of the press-fit staff  123  of the pinion  102 . As a result, when the pinion  102  is inserted to the hole  115 , stress is applied to the escape wheel  101  pushing the ribs  112  contacting the press-fit staff  123  to the outside in the radial direction. In addition, the elasticity of the flexible parts  113  disposed between the ribs  112  and rim  111  relieves the stress applied to the ribs  112  and suppresses damage to the escape wheel  101  while positioning and holding the pinion  102  in the center of the escape wheel  101  with appropriate force. 
     Next, the pinion  102  is inserted into the hole  130   a  of the fastening member  130  that was formed in step S 21  and step S 22  (step S 32 ). 
     As shown in  FIG. 10 , the fastening member  130  is first placed with the small diameter part  132  facing the escape wheel  101  onto the other-end tenon  121   b  side of the pinion  102  that was inserted to the escape wheel  101  in step S 31  above. 
     Then, as shown in  FIG. 11 , the fastening member  130  is pushed in the axial direction onto the press-fit staff  123  part of the pinion  102 . 
     As shown in  FIG. 12 , the fastening member  130  is then pushed onto the pinion  102  until the first surface  133  of the small diameter part  132  of the fastening member  130  contacts the front side  101   a  of the ribs  112  of the escape wheel  101 . As a result, the pinion  102  is inserted into the hole  130   a  of the fastening member  130 . 
     In  FIG. 12 , of the small diameter part  132  of the fastening member  130 , the part on the right side of the pinion  102  is the part  132   a  (see  FIG. 7 ) that overlaps the ribs  112  in plan view along the axial direction, and the part on the left side of the pinion  102  is the part  132   b  (see  FIG. 7 ) that overlaps the hole  115 . 
     Next, the fastening member  130  is pressed in the axial direction to the escape wheel  101  side from the position shown in  FIG. 12  (step S 33  in  FIG. 9 ). At this time, a rib  112  intercedes between the flange  124  and the part of the small diameter part  132  of the fastening member  130  on the right side of the pinion  102  (part  132   a ), but the hole  115  is between the part of the small diameter part  132  of the fastening member  130  on the left side of the pinion  102  (part  132   b ) and the flange  124 , and a rib  112  is not present. 
     As described above, the Vickers hardness of the fastening member  130  is less than the Vickers hardness of the escape wheel  101 , and is less than the Vickers hardness of the pinion  102 . As a result, when the fastening member  130  is pressed down, the parts  132   b  that do not contact the ribs  112  plastically deform and protrude in the axial direction further inside the hole  115  than the parts  132   a  that contact the ribs  112 . As a result, as shown in  FIG. 13 , a protrusion  134  protruding in the axial direction is formed on the fastening member  130 . The distance the protrusion  134  protrudes from the first surface  133  of part  132   a  is preferably greater than or equal to 3 μm. 
     As described above, the inside diameter of the hole  130   a  of the fastening member  130  is smaller than the outside diameter of the press-fit staff  123  part of the pinion  102 . As a result, when the fastening member  130  is pushed onto the press-fit staff  123 , the fastening member  130  is pushed to the outside in the radial direction and affixed to the press-fit staff  123 . Because the escape wheel  101  is thus fixed between the fastening member  130  and flange  124 , separation of the escape wheel  101  from the pinion  102  can be prevented. 
     In addition, because a protrusion  134  protruding into the hole  115  is formed on the part  132   b  of the fastening member  130 , rotation of the escape wheel  101  relative to the pinion  102  can be suppressed. 
     As a different method of manufacturing the escape wheel and pinion  35  according to this embodiment of the invention, the fastening member  130  may conceivably be preformed with a protrusion  134 . 
     In this case, a machining process of cutting or grinding, for example, to form the protrusion  134  on the fastening member  130  is required in step S 22 . Then when inserting the pinion  102  to the hole  130   a  of the fastening member  130  in step S 32 , the protrusion  134  functioning as a key or fastening member must be desirably positioned to the hole  115  of the escape wheel  101 . As a result, processing in step S 22  and assembly in step S 32  involve more steps, and the production cost increases according. 
     Furthermore, if processing precision in the machining process forming the protrusion  134  of the fastening member  130  varies in step S 22 , deviation or variation may also occur when positioning the protrusion  134  in the hole  115  of the escape wheel  101  in step S 32 , or a gap may occur between the escape wheel  101  (ribs  112 ) and the fastening member  130 , and the quality of the escape wheel and pinion  35  may drop. 
     In this embodiment of the invention, the protrusion  134  is formed not in step S 22  but in step S 33  by press fitting the fastening member  130  and plastically deforming part of the fastening member  130 . As a result, compared with the conceivable alternative method described above, there is no need for a cutting, grinding, or other machining step to form the protrusion  134  in step S 22 , and there is no need to specifically position the protrusion  134  of the fastening member  130  to the hole  115  of the escape wheel  101  in step S 32 . As a result, the number of steps required to produce the escape wheel and pinion  35  is reduced, and the production cost of the escape wheel and pinion  35  can be reduced. 
     Furthermore, because a protrusion  134  is formed on the part  132   b  that overlaps the hole  115  of the escape wheel  101  in a plan view of the fastening member  130 , a protrusion  134  can be formed precisely according to the shape of the escape wheel  101 . 
     In addition, because the first surface  133  of the part  132   a  that overlaps the ribs  112  of the fastening member  130  is pushed against the front side  101   a  of the ribs  112  by pressing the fastening member  130  into place, the gap between the escape wheel  101  (ribs  112 ) and the fastening member  130  (part  132   a ) can be reduced. The quality of the escape wheel and pinion  35  can thereby be improved. 
     However, force is also applied to the escape wheel  101  (ribs  112 ) held between the fastening member  130  and the flange  124  by press fitting the fastening member  130  in step S 33 . If the diameter D 2  (see  FIG. 6 ) of the first surface  133  of the small diameter part  132  of the fastening member  130  is greater than the diameter D 3  (see  FIG. 6 ) of the face  125  of the flange  124  that supports the escape wheel  101 , the area to which force is applied from the small diameter part  132  to the escape wheel  101  becomes greater than the area supported by the flange  124 . Therefore, the part of the escape wheel  101  that is positioned outside of the flange  124  is not supported by the flange  124  against the force applied from the first surface  133 , and warping or other deformation of the escape wheel  101  or other damage may result. 
     In this embodiment of the invention, because the diameter D 2  of the first surface  133  of the small diameter part  132  of the fastening member  130  is less than or equal to the diameter D 3  of the face  125  of the flange  124 , the part of the escape wheel  101  to which force is applied from the small diameter part  132  is smaller than the area supported by the flange  124 . Therefore, warping or other deformation or other damage to the escape wheel  101  in step S 33  can be suppressed. 
     Because force is applied to the second surface  135  of the large diameter part  131  when press fitting the fastening member  130 , the diameter D 1  of the second surface  135  of the large diameter part  131  is preferably large. If the fastening member  130  does not have a small diameter part  132 , and the diameter D 1  of the second surface  135  of the large diameter part  131  is greater than the diameter D 3  of the face  125  of the flange  124 , warping or other deformation or other damage to the escape wheel  101  may occur as described above. 
     In this embodiment of the invention, the fastening member  130  has a large diameter part  131  an a small diameter part  132 , and the diameter D 1  of the second surface  135  of the large diameter part  131  is greater than or equal to the diameter D 2  of the first surface  133  of the small diameter part  132 . The diameter D 1  of the second surface  135  of the large diameter part  131  whereby the fastening member  130  is pushed can therefore be increased without making the diameter D 2  of the first surface  133  of the small diameter part  132  larger than the diameter D 3  of the face  125  of the flange  124 . Therefore, the fastening member  130  can be easily pushed in step S 32  and step S 33 . In addition, if the diameter D 1  of the second surface  135  of the large diameter part  131  is made larger than the diameter D 3  of the face  125  of the flange  124 , the fastening member  130  can be easily pressed into place. 
     Through the steps described above, manufacturing an escape wheel and pinion  35  as a mechanical part can be completed in a single continuous manufacturing process. 
     The invention is described above with reference to a preferred embodiment thereof, but the invention is not limited thereto and can be modified and adapted in many ways without departing from the scope of the accompanying claims. Some examples of such variations are described below. 
     Variation 1 
     The configuration and plane shape of the escape wheel  101  described as an example of a rotating member according to the invention is not limited to the configuration shown in  FIG. 5 . The configuration of the escape wheel  101  (including such parts as the ribs  112 , hole  115 , flexible parts  113 , and rim  111 ) may differ, and the shape in plan view may also differ. 
     Variation 2 
     The configuration and plane shape of the fastening member  130  according to the invention is not limited to the configuration shown in  FIG. 6 . For example, the fastening member  130  may have a trapezoidal shape in section view with a taper that decreases in diameter with proximity to the escape wheel  101 , and in plan view may have a non-round shape. 
     Variation 3 
     In the manufacturing method of an escape wheel according to the invention, after inserting the pinion  102  to the escape wheel  101  in step S 31 , an oxidation process that forms a silicon oxide film of silicon dioxide (SiO 2 ) may be formed on the surface of the escape wheel  101 . By applying an oxidation process to the escape wheel  101 , the mechanical strength of the escape wheel  101  can be improved by the silicon oxide film formed on the surface of the escape wheel  101  from a material containing silicon. The oxidation process is preferably a thermal oxidation process at a high temperature of 1000° C. or higher. 
     Variation 4 
     A escape wheel and pinion  35  is described as an example of a mechanical part in the foregoing embodiment, but the invention is not so limited. The configuration and manufacturing method of a mechanical part according to the invention can also be applied to other mechanical parts. 
     The invention being thus described, it will be obvious that it may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 2017-097043, filed May 16, 2017 is expressly incorporated by reference herein.