Patent Publication Number: US-2004043821-A1

Title: Fitting structure for knobs

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a fitting structure for knobs particularly suitable for fitting to shaft members of rotation drive members of motors and the like.  
       [0003] 2. Description of the Prior Art  
       [0004] To describe a fitting structure for knobs according to the prior art with reference to a drawing, FIG. 6 shows an exploded perspective view of a fitting structure for knobs according to the prior art.  
       [0005] A rotation drive member  51  consisting of an electric motor has a substantially cylindrical body  51   a  and a columnar shaft member  51   b , such as a rotation shaft or the like, protruding outward from the tip of the body  51   a . This shaft member  51   b  is rotated as prescribed by supplying electric power to the body  51   a  from a terminal (not shown) and, when no power is supplied to the body  51   a , the shaft member  51   b  has a prescribed revolving torque in either the clockwise or the counter-clockwise direction.  
       [0006] A fitting member  52  consisting of a synthetic resin member and formed by molding; a base  53 ; an annular first fitting portion  54  provided on the same circle as the base  53  sharing the center; and a second fitting portion  55  concentric with and having a greater diameter than the first fitting portion  54 . The first fitting portion  54  and the second fitting portion  55  are formed in a collar shape, some protruding outward from the center axis of the base  53 .  
       [0007] The base  53  has a front wall  53   a  formed to be a substantially flat face, and a cylindrical side wall  53   b  extending backward from the circumference of the front wall  53   a . The annular first fitting portion  54  and the second fitting portion  55  are arranged protruding outward from the rear end of the cylindrical side wall  53   b.    
       [0008] The front wall  53   a  of the base  53  has a round through holes  53   c  positioned at the center of the front wall  53   a.    
       [0009] A cylindrical member  53   d  consisting of a metallic material and integrated by insert molding is arranged within the through holes  53   c.    
       [0010] Into the cylindrical member  53   d  is inserted the shaft member  51   b  of the rotation drive member  51 , and the cylindrical member  53   d  is fitted to the shaft member  51   b  with a suitable means such as a screw (not shown). This fitting integrates the fitting member  52  with the shaft member  51   b  to enable the fitting member  52  to rotate together with the shaft member  51   b.    
       [0011] A knob  56  consisting of a synthetic resin material and formed by molding has a disk-shaped front wall  56   a , a cylindrical side wall  56   b  extending backward from the circumference of the front wall  56   a , a plurality (e.g. four) of hooks  57  protruding inward in the cylindrical side wall  56   b  and positioned on the same circle, and a plurality (e.g. four) of keep pieces  58  protruding inward within the cylindrical side wall  56   b  and positioned on the same circle. The hooks  57  and the keep pieces  58  are also positioned on the same circle.  
       [0012] In a state in which this knob  56  is arranged in front of and to concentrically cover the fitting member  52 , each of the hooks  57  of the knob  56  is engaged with the annular first fitting portion  54 , and each of the keep pieces  58  is kept in contact with and over the second fitting portion  55  to couple the knob  56  and the fitting member  52 .  
       [0013] This coupling results in arrangement of the side wall  53   a  of the fitting member  52  within the side wall  56   b  of the knob  56 .  
       [0014] Next will be described how the conventional knob fitting structure described above is assembled.  
       [0015] First, the cylindrical member  53   d  integrated with the fitting member  52  is fitted to the shaft member  51 b of the rotation drive member  51 .  
       [0016] Then, the front wall  56   a  of the knob  56  is arranged over and opposite the front wall  53   a  of the fitting member  52  to cover the front wall  53   a  so as to position the side wall  53   b  of the fitting member  52  within the side wall  56   b  of the knob  56 .  
       [0017] When the knob  56  in this state is pressed in the direction of the axis of the shaft member  51   b , the hooks  57  ride over the top of the first fitting portion  54  and are engaged with the first fitting portion  54 , and the keep pieces  58  are arranged in contact with and over the second fitting portion  55 .  
       [0018] The engaging of the hooks  57  with the first fitting portion  54  and the contact of the keep pieces  58  with the second fitting portion  55  cause the knob  56  to be fitted onto the fitting member  52 .  
       [0019] However, the knob fitting structure described above involves the problem that, when the knob  56  is to fitted to the fitting member  52  by pressing in, if the knob  56  is pressed in a state of being inclined relative to the fitting member  52 , the fitting member  52  is shaken to make the knob  56  difficult to be fitted and to make the hooks of the knob  56  to be engaged at the same time, adding to the difficulty of fitting.  
       [0020] Also the fitting of the knob  56  in a state of being only hooked onto the fitting member  52  invites the problem that the knob  56  slips relative to the fitting member  52 .  
       SUMMARY OF THE INVENTION  
       [0021] An object of the present invention is to solve the problems noted above, and provide a fitting structure for knobs that facilitates fitting of the knob to its fitting member.  
       [0022] A fitting structure for knobs according to the invention is provided with a fitting member fitted to a shaft member and a knob arranged concentrically with the fitting member and fitted to a front face of the fitting member, wherein the fitting member has a base having a flat portion, a stopper protruding forward from the base, and a through hole provided in the flat portion, the knob has a plurality of projections positioned on the same circle, and in fitting the knob to the fitting member, when the knob is rotated while being pressed backward in a state in which the projections are kept in contact with the flat portion, the projections slide on and in contact with the flat portion and when the projections hit against the stopper and the rotation of the knob is stopped, the projections and the through hole become opposite each other to enable the knob and the fitting member to be coupled to each other after the projections are fitted into the through hole.  
       [0023] As this configuration enables the knob to be readily and reliably positioned relative to the fitting member, the fitting is simplified, resulting in a knob fitting structure in which, even if the knob is pressed in a state in which it is inclined relative to the fitting member, the projections enable the knob to be kept in a normal state by the flat portion and reliable coupling of the knob and the fitting member with no fear of slipping of the knob can be ensured.  
       [0024] In the fitting structure for knobs according to the invention, the base has a cylinder protruding forward in its central part, and the projections perform rotary actions with the cylinder as a guide.  
       [0025] This configuration, in which rotary actions are performed with the cylinder as a guide, can provide a knob fitting structure enabling the knob and the fitting member to be reliably coupled while the knob is maintained in an even more normal state.  
       [0026] In the fitting structure for knobs according to the invention, the through hole is formed adjacent to the stopper.  
       [0027] This configuration can provide a knob fitting structure ensuring reliable and easy positioning of the knob, simple and inexpensive assembling, and freedom from slips and excess play of the knob.  
       [0028] In the fitting structure for knobs according to the invention, a plurality of the stoppers and the through holes are provided.  
       [0029] This configuration can provide a knob fitting structure ensuring well balanced, stable and reliable fitting of the knob to the fitting member.  
       [0030] In the fitting structure for knobs according to the invention, the base of the fitting member has an annular fitting portion on the same circle, the knob has a plurality of hooks on the same circle, and the hooks of the knob are engaged with the fitting portion of the fitting member to couple the knob and the fitting member to each other.  
       [0031] This configuration can provide a knob fitting structure that facilitates fitting of the knob to the fitting member and ensures reliable fitting.  
       [0032] In the fitting structure for knobs according to the invention, the knob may have a plurality of keep pieces arranged on the same circle, each of the keep pieces may be positioned between the hooks of the knob, and each of the keep pieces is kept in contact with the fitting portion of the fitting member.  
       [0033] This configuration, as the knob is kept in contact with the fitting portion of the fitting member by the keep pieces, can provide a knob fitting structure in which the knob can be stably fitted to the fitting member.  
       [0034] In the fitting structure for knobs according to the invention, a position in which the fitting portion of the fitting member is engaged with the hooks of the knob is farther outward in a radial direction than a position in which the projections of the knob are fitted into the through hole of the fitting member.  
       [0035] This configuration, wherein the knob is engaged with the fitting member in a position having a greater diameter than the projections of the knob, can provide a knob fitting structure in which the knob can be stably engaged.  
       [0036] The fitting structure for knobs according to the invention is further provided with a rotation drive member of which the shaft member is rotatable, wherein the fitting member is fitted to the shaft member.  
       [0037] This configuration can provide a knob fitting structure enabling rotary action of the knob to achieve its normal coupling to the fitting member.  
       [0038] In the fitting structure for knobs according to the invention, the rotation drive member comprises a motor.  
       [0039] This configuration can provide a less costly knob fitting structure as its rotation drive member comprises a motor of a simple structure.  
       [0040] A fitting structure for knobs according to the invention is provided with a fitting member fitted to a shaft member and a knob arranged concentrically with the fitting member and fitted to a front face of the fitting member, wherein the fitting member has a base, a plurality of arcwise guides protruding forward from the base and provided on the same circle, gaps each provided between adjacent guides, and guide faces each provided at a top of one or another of the guides and inclined relative to the base, the knob has a plurality of projections positioned on the same circle, and in fitting the knob to the fitting member, when the knob is pressed backward in a state in which the projections are kept in contact with the guide faces, the projections are guided on the guide faces, the knob or the fitting member is rotated so as to enable the projections to approach the base and, after the projections are positioned in the gaps, the knob and the fitting member are enabled to be coupled to each other.  
       [0041] This configuration can provide a knob fitting structure which is easy to fit because the knob can be readily and reliably positioned relative to the fitting member and, even if the knob is pressed in a state in which it is inclined relative to the fitting member, the projections enable the knob to be kept in a normal state by the guides and reliable coupling of the knob and the fitting member can be ensured.  
       [0042] In the fitting structure for knobs according to the invention, the projections of the knob are held between adjacent ones of the guides of the fitting member.  
       [0043] This configuration can provide a knob fitting structure ensuring easy positioning of the knob relative to the fitting member, simple and inexpensive assembling, and freedom from slips of the knob.  
       [0044] In the fitting structure for knobs according to the invention, the fitting member is provided with through holes bored in the parts of the base positioned between the gaps, and the projections of the knob are fitted into the through holes.  
       [0045] This configuration can provide a knob fitting structure ensuring even more reliable and easy positioning of the knob, simple and inexpensive assembling, and freedom from slips and excess play of the knob.  
       [0046] In the fitting structure for knobs according to the invention, the projections of the knob are arranged to form a cross.  
       [0047] This configuration can provide a knob fitting structure in which the projections are arranged in a well balanced way, and therefore stable and reliable fitting of the knob to the fitting member is ensured.  
       [0048] In the fitting structure for knobs according to the invention, the guide faces, inclined in the same direction relative to the base, are formed at the tops of the plurality of guides of the fitting member.  
       [0049] This configuration, because the guide faces therein are inclined in the same direction, can provide a knob fitting structure that is simply and inexpensively configured.  
       [0050] In the fitting structure for knobs according to the invention, the base of the fitting member has an annular fitting portion on the same circle, the knob has a plurality of hooks on the same circle, and the hooks of the knob are engaged with the fitting portion of the fitting member to couple the knob and the fitting member to each other.  
       [0051] This configuration can provide a knob fitting structure enabling the knob to be easily and reliably fitted to the fitting member.  
       [0052] In the fitting structure for knobs according to the invention, the knob has a plurality of keep pieces arranged on the same circle, each of the keep pieces is positioned between the hooks of the knob, and each of the keep pieces is kept in contact with the fitting portion of the fitting member.  
       [0053] This configuration, as the knob is kept in contact with the fitting portion of the fitting member by the keep pieces, can provide a knob fitting structure in which the knob can be stably fitted to the fitting member.  
       [0054] In the fitting structure for knobs according to the invention, a position in which the fitting portion of the fitting member is engaged with the hooks of the knob is farther outward in a radial direction than a position in which the projections of the knob are arranged in the gaps.  
       [0055] This configuration, wherein the knob is engaged with the fitting member in a position having a greater diameter than the projections of the knob, can provide a knob fitting structure in which the knob can be stably engaged.  
       [0056] In the fitting structure for knobs according to the invention, the base of the fitting member may have a front wall and a cylindrical side wall extending backward from a circumference of the front wall, the front wall is provided with the guides protruding forward, the knob has a front wall and a cylindrical side wall extending backward from the circumference of the front wall, the front wall of the knob is fitted with the projections protruding backward in a state of being positioned in the cylindrical side wall, and the side wall of the fitting member is positioned within the side wall of the knob.  
       [0057] This configuration can provide a knob fitting structure permitting ready positioning of the knob relative to the fitting member and excelling in assembling ease.  
       [0058] The fitting structure for knobs according to the invention is further provided with a rotation drive member of which the shaft member is rotatable, wherein the fitting member is fitted to the shaft member, and the fitting member rotates together with the shaft member when the knob is fitted.  
       [0059] This configuration provides a knob fitting structure allowing the knob to readily fitted to the fitting member fitted to the rotating shaft member and permitting normal coupling of the knob to the fitting member by pressing the knob in. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0060]FIG. 1 shows an exploded perspective view of a fitting structure for knobs in a first mode of implementing the present invention.  
     [0061]FIG. 2 shows a section of a knob and a fitting member pertaining to the knob fitting structure along line  2 - 2  in FIG. 1.  
     [0062]FIG. 3 shows a section of the knob and the fitting member pertaining to the knob fitting structure along line  3 - 3  in FIG. 1.  
     [0063]FIG. 4 shows an exploded perspective view of a fitting structure for knobs in a second mode of implementing the invention.  
     [0064]FIG. 5 shows a section of a knob and a fitting member pertaining to the knob fitting structure in the second mode of implementing the invention.  
     [0065]FIG. 6 shows an exploded perspective view of a fitting structure for knobs according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0066] A fitting structure for knobs embodying the present invention in a first embodiment will be described below. FIG. 1 shows an exploded perspective view of a fitting structure for knobs in a first mode of implementing the invention; FIG. 2; a section of a knob and a fitting member pertaining to the knob fitting structure along line  2 - 2  in FIG. 1; and FIG. 3, a section of the knob and the fitting member pertaining to the knob fitting structure along line  3 - 3  in FIG. 1.  
     [0067] A rotation drive member  1  consisting of an electric motor has a substantially cylindrical body  1   a  and a shaft member  1   b  such as a columnar rotation shaft protruding outward from the tip of the body  1   a . This shaft member  1   b  is rotated as prescribed by supplying electric power to the body  1   a  from a terminal (not shown) and, when no power is supplied to the body  1   a , the shaft member  1   b  is configured to have a prescribed revolving torque in either the clockwise or the counter-clockwise direction.  
     [0068] A fitting member  2  consisting of a synthetic resin material and formed by molding has a base  3 , a plurality of (e.g. two) stoppers  4  protruding forward from the base  3  and provided on the same circle as the base  3  sharing the center, and an annual fitting portion  5  provided on the same circle as the base  3  sharing the center.  
     [0069] The base  3  has a round flat portion  3   a , a plurality of (e.g. two) first rectangular through holes  3   b  provided on a straight line passing the center of the flat portion  3   a , a cylinder  3   c  protruding forward in the central part of the flat portion  3   a  of the base  3 , a round second through holes  3   d  provided in the central part of the cylinder  3   c , and a cylindrical side wall  3 e extending backward from the circumference the flat portion  3   a  with its diameter expanding as it extends. The stoppers  4  and the first through holes  3   b  are formed on or in the flat portion  3   a , and the first through holes  3   b  are formed adjoining the stoppers  4 .  
     [0070] The fitting portion  5  is formed in a collar shape protruding outward from the side wall  3   e  of the base  3 , and two grooves  3   f  are formed, spanning these fitting portion  5  and side wall  3   e , in a direction parallel to the axis of the base  3  and in opposite positions in the base  3 .  
     [0071] A cylindrical member  3   g  consisting of a metallic material and integrated by insert molding is arranged within the second through holes  3   d.    
     [0072] Into the cylindrical member  3   g  is inserted the shaft member  1   b  of the rotation drive member  1 , and the cylindrical member  3   g  is fitted to the shaft member  1   b  with a suitable means such as a screw (not shown). This fitting integrates the fitting member  2  with the shaft member  1   b  to enable the fitting member  2  to rotate together with the shaft member  1   b.    
     [0073] A knob  6  consisting of a synthetic resin material and formed by molding has a round front wall  6   a ; a cylindrical side wall  6   b  extending backward from the circumference of the front wall  6   a  with its diameter expanding as it extends; a plurality (e.g. two) of projections  7  protruding backward (inward) in a state in which they are positioned within the side wall  6   b  of the front wall  6   a  and on the same circle; a plurality (e.g. two) of hooks  8  protruding inward within the cylindrical side wall  6   b  and positioned on the same circle; and a plurality (e.g. four) of keep pieces  9  protruding inward within the cylindrical side wall  6   b  and positioned on the same circle. The hooks  8  and the keep pieces  9  are positioned on the same circle, and the keep pieces  9  are arranged between the hooks  8 .  
     [0074] Further, a plurality (e.g. two) of projections  7  are arranged on a straight line passing the center axis, namely at equal intervals of 180 degrees each, and each of these projections  7  has an L overall shape, whose top  7   a  is formed in an arc shape.  
     [0075] The plurality (e.g. two) of hooks  8  are positioned farther outward in the radial direction than the projections  7  are and on the same straight line as the positions in which the projections  7  are arranged.  
     [0076] The plurality (e.g. four) of keep pieces  9  are positioned farther outward in the radial direction than the projections  7  are and between the hooks  8  to form a cross.  
     [0077] In a state in which this knob  6  is arranged in front of and to concentrically cover the fitting member  2 , the tops  7   a  of the projections  7  are fitted into the first through holes  3   b , and the hooks  8  of the knob  6  are engaged with the fitting portion  5  of the fitting member  2 , while the keep pieces  9  are kept in contact with and over the fitting portion  5  to fit the knob  6  and the fitting member  2  coupled to each other.  
     [0078] This coupling results in positioning of the base  3  of the fitting member  2  within the side wall  6   b  of the knob  6 .  
     [0079] Next will be described how the above-described knob fitting structure in the first embodiment of the invention is assembled.  
     [0080] First, the cylindrical member  3   g  integrated with the fitting member  2  is fitted to the shaft member  1   b  of the rotation drive member  1 .  
     [0081] Then, when the knob  6  is turned with the tops  7   a  of the projections  7  projecting backward (inward) from the front wall  6   a  of the knob  6  kept in contact with the flat portion  3   a  of the base  3  of the fitting member  2 , the projections  7  turn, guided by the outer circumference of the cylinder  3   c . This regulates the position of the knob  6  in a normal state relative to the fitting member  2 .  
     [0082] Thus, as the knob  6  is turned clockwise, for instance, while being pressed in the axial direction of the shaft member  1   b  (backward), the projections  7  slide over the flat face  3   a  in frictional contact with it, and hit against the stoppers  4  to stop the rotation of the knob  6 .  
     [0083] Then, when this knob  6  is stopped, the projections  7  and the first through holes  3   b  are opposite each other, the knob  6  shifts in the axial direction (backward), and the projections  7  are fitted into the first through holes  3   b.    
     [0084] At the same time as this fitting of the projections  7  into the first through holes  3   b , the hooks  8  are engaged with the fitting portion  5  of the fitting member  2 , and the keep pieces  9  are kept in contact with the fitting portion  5 .  
     [0085] The engaging of the fitting portion  5  with the hooks  8  and the fitting of the tops  7   a  of the projections  7  into the first through holes  3   b  cause the knob  6  and the fitting member  2  to be coupled to each other.  
     [0086] Incidentally, although the projections of the knob are arranged on the same straight line in the first preferred embodiment of the invention described above, the appropriate arrangement is not limited to this, but it is adequate for one, three or more projections to be arranged in a prescribed position or positions, and one or more through holes formed opposite the projection or projections in the fitting member.  
     [0087] Further, while the rotation drive member having a shaft member consists of a motor in the first embodiment described above, the appropriate configuration is not limited to this, but the rotation drive member may consist of a rotary electrical part or mechanical part, such as an encoder.  
     [0088] Next, a fitting structure for knobs embodying the present invention in a second embodiment will be described below. FIG. 4 shows an exploded perspective view of a fitting structure for knobs in a second mode of implementing the invention, and FIG. 5, a section of a knob and a fitting member pertaining to the knob fitting structure shown in FIG. 4. The same constituent parts as in the first mode of implementing the invention are assigned respectively the same reference signs, and their description is dispensed with.  
     [0089] A fitting member  20  consisting of a synthetic resin material and formed by molding has a base  21 ; a plurality (e.g. eight) of arcwise guides  22  provided on the same circle as the base  21  sharing the center; a plurality (e.g. eight) of gaps  23  each provided adjoining guides  22 ; guide faces  22   a  each provided at the top of a guide  22 ; an annular first fitting portion  24  provided on the same circle as the base  21  sharing the center; and a second fitting portion  a  on the same circles the first fitting portion  24  and having a greater diameter than the first fitting portion  24 . The first fitting portion  24  and the second fitting portion  24   a  are formed in a collar shape protruding outward from the central axis of the base  21 .  
     [0090] The base  21  has a front wall  21   a  formed to be a substantially flat face, and a cylindrical side wall  21   b  extending backward from the circumference of the front wall  21   a , and to the front wall  21   a  are fitted the plurality of arcwise guides  22  protruding forward. The annular first fitting portion  24  and the second fitting portion  24   a  are arranged protruding outward from the rear end of the cylindrical side wall  21   b.    
     [0091] The guide faces  22   a  of the guides  22  are inclined in the same direction relative to the front wall  21   a  of the base  21 .  
     [0092] The front wall  21   a  of the base  21  has a plurality (e.g. eight) of rectangular first through holes  21   c  positioned between the gaps  23  and a round second through  21   d  position at the center of the front wall  21   a.    
     [0093] Further, a cylindrical member  21   e  consisting of a metallic material and integrated by insert molding is arranged within the second through holes  21   d.    
     [0094] Into the cylindrical member  21   e  is inserted the shaft member  1   b  of the rotation drive member  1 , which is fitted to the cylindrical member  21   e  or the shaft member  1   b  with a suitable means such as a screw (not shown). This fitting integrates the fitting member  20  with the shaft member  1   b  to enable the fitting member  20  to rotate together with the shaft member  1   b.    
     [0095] A knob  25  consisting of a synthetic resin material and formed by molding has a round front wall  25   a ; a cylindrical side wall  25   b  extending backward from the circumference of the front wall  25   a  with its diameter expanding as it extends; a plurality (e.g. four) of projections  26  protruding backward (inward) in a state in which they are positioned within the side wall  25   b  of the front wall  25   a  and on the same circle; a plurality (e.g. four) of hooks  27  protruding inward within the cylindrical side wall  25   b  and positioned on the same circle; and a plurality (e.g. four) of keep pieces  28  protruding inward within the cylindrical side wall  25   b  and positioned on the same circle. The hooks  27  and the keep pieces  28  are positioned on the same circle, and the keep pieces  28  are arranged between the hooks  27 .  
     [0096] Further, a plurality (e.g. four) of projections  26  are arranged to form a cross, namely at equal intervals of 90 degrees each, and each of these projections  26  has an L overall shape, whose top  26   a  is formed in an arc shape.  
     [0097] The plurality (e.g. four) of hooks  27  are positioned farther outward in the radial direction than the projections  26  are and on the same straight line as the positions in which the projections  26  are arranged to form a cross.  
     [0098] The plurality (e.g. four) of keep pieces  28  are positioned farther outward in the radial direction than the projections  26  are and between the hooks  27  to form a cross.  
     [0099] In a state in which this knob  25  is arranged in front of and to concentrically cover the fitting member  20 , the projections  26  of the knob  25  are positioned in the gaps  23  of the fitting member  20 , and the tops  26   a  of the projections  26  are fitted into the first through holes  21   c.    
     [0100] The hooks  27  of the knob  25  are engaged with the annular first fitting portion  24 , and the keep pieces  28  are kept in contact with and over the second fitting portion  24   a  to couple the knob  25  and the fitting member  20  to each other.  
     [0101] This coupling results in positioning of the side wall  21   b  of the fitting member  20  within the side wall  25   b  of the knob  25 .  
     [0102] Next will be described how the above-described knob fitting structure in the second mode of implementing the invention is assembled.  
     [0103] First, the cylindrical member  21   e  integrated with the fitting member  20  is fitted to the shaft member  1   b of the rotation drive member  1 .    
     [0104] Then, the tops  26   a  of the projections  26  projecting backward (inward) from the front wall  25   a  of the knob  25  are brought into contact with the guide faces  22   a  of the guides  22  of the fitting member  20 . This regulates the position of the knob  25  in a normal state relative to the fitting member  20 .  
     [0105] Then, as the knob  25  is pressed in the axial direction of the shaft member  1   b , the tops  26   a  of the projections  26  are pressed against the inclined guide faces  22   a , resulting in, for instance, clockwise turning of the fitting member  20  and shifting of the tops  26   a  to the positions of the gaps  23  of the fitting member  20 . That is, the shaft member  1   b  is rotated by pressing the knob  25  in the axial direction.  
     [0106] The rotations of the shaft member  1   b  and the fitting member  20  cause the knob  25  to shift in the axial direction, the projections  26  to be positioned so as to be caught in the gaps  23 , and the tops  26   a  to be fitted into the first through holes  21   c  between the gaps  23 .  
     [0107] At the same time as this fitting of the projections  26  into the first through holes  21   c , the hooks  27  of the knob  25  are engaged with the fitting portion  24  of the first fitting member  20 , and the keep pieces  28  are kept in contact with the second fitting portion  24   a.    
     [0108] The engaging of the first fitting portion  24  with the hooks  27  and the fitting of the tops  26   a  of the projections  26  into the first through holes  21   c  cause the knob  25  and the fitting member  20  to be coupled to each other.  
     [0109] Incidentally, although through holes are provided in the parts of the base positioned between the gaps in the second preferred embodiment of the invention described above, the through holes can be dispensed with.  
     [0110] Further, although the projections of the knob are arranged to form a cross in the above-described second embodiment of the invention, the appropriate arrangement is not limited to this, but it is adequate for one, two or more projections to be arranged in a prescribed position or positions.  
     [0111] Also, although the guide faces of the guides are inclined in one direction relative to the base in the above-described second embodiment, the appropriate arrangement is not limited to this, but it is adequate to incline the guide faces alternately in different directions.  
     [0112] Further, although the rotation drive member having a shaft member is a motor in the above-described second embodiment, the appropriate rotation drive member is not limited to this, but may as well be a rotary mechanical part or electrical part.  
     [0113] As hitherto described, in the fitting structure for knobs according to the invention, a fitting member has a base having a flat portion, stoppers protruding forward from the base, and through holes provided in the flat portion; the knob has a plurality of projections positioned on the same circle; and in fitting the knob to the fitting member, when the knob is rotated while being pressed backward in a state in which the projections are kept in contact with the flat portion, the projections slide on and in contact with the flat portion, and when the projections hit against the stoppers and the rotation of the knob is stopped, the projections and the through holes become opposite each other to enable the knob and the fitting member to be coupled to each other after the projections are fitted into the through hole. As this arrangement enables the knob to be readily and reliably positioned relative to the fitting member, the fitting is simplified, resulting in a knob fitting structure in which, even if the knob is pressed in a state in which it is inclined relative to the fitting member, the projections enable the knob to be kept in a normal state by the flat portion and reliable coupling of the knob and the fitting member can be ensured.  
     [0114] In the fitting structure for knobs according to the invention, the base may have a cylinder protruding forward in its central part, and the projections perform rotary actions with the cylinder as guide. This configuration, in which rotary actions are performed with the cylinder as a guide, can provide a knob fitting structure enabling the knob and the fitting member to be reliably coupled while the knob is maintained in an even more normal state.  
     [0115] In the fitting structure for knobs according to the invention, the base of the fitting member may have an annular fitting portion on the same circle, the knob has a plurality of hooks on the same circle, and the hooks of the knob are engaged with the fitting portion of the fitting member to couple the knob and the fitting member to each other. This configuration can provide a knob fitting structure that facilitates fitting of the knob to the fitting member and ensures reliable fitting.  
     [0116] In the fitting structure for knobs according to the invention, the position in which the fitting portion of the fitting member is engaged with the hooks of the knob may be farther outward in the radial direction than the position in which the projections of the knob are fitted into the through hole of the fitting member. This configuration, wherein the knob is engaged with the fitting member in a position having a greater diameter than the projections, can provide knob fitting structure in which the knob can be stably engaged.  
     [0117] As described above, in the fitting structure for knobs according to the invention, the fitting member has a base, a plurality of guides protruding forward from the base, gaps each provided between adjacent guides, and guide faces each provided at the top of one or another of the guides and inclined relative to the base, wherein the knob has a plurality of projections positioned, and in fitting the knob to the fitting member, when the knob is pressed backward in a state in which the projections are kept in contact with the guide faces, the projections are guided on the guide faces, the knob or the fitting member is rotated so as to enable the projections to approach the base and, after the projections are positioned in the gaps, the knob and the fitting member are enabled to be coupled to each other. This configuration can provide a knob fitting structure which is easy to fit because the knob can be readily and reliably positioned relative to the fitting member.  
     [0118] In the fitting structure for knobs according to the invention, the fitting member may be provided with through holes bored in the parts of the base positioned between the gaps, and the projections of the knob are fitted into the through holes. This configuration can provide a knob fitting structure ensuring even more reliable and easy positioning of the knob, simple and inexpensive assembling, and freedom from slips and excess play of the knob.  
     [0119] In the fitting structure for knobs according to the invention, the guide faces, inclined in the same direction relative to the base, may be formed at the tops of the plurality of guides of the fitting member. This configuration, because the guide faces therein are inclined in the same direction, can provide a knob fitting structure that is simply and inexpensively configured.