The present application is based on Japanese Patent Application No.  2001-178404, the entire contents of which are incorporated herein by reference. 
The present invention relates to a relatively small-sized motor, such as a motor for feeding an optical pickup in an optical disk drive apparatus or the like, and a method of manufacturing the same, and more particularly to a technique for improve the accuracy of such a motor. 
In many cases, high dimensional accuracy and rotational accuracy are required for small-sized motors depending on their applications.  For instance, in a motor for feeding an optical pickup in an optical disk drive apparatus or the like, there is a need to move the optical pickup smoothly, and it is required that the stopping position accuracy is to be high.  Referring now to FIG.  4, a description will be given of an example of a conventional motor of this type. 
In FIG.  4, a stator portion of the motor includes a stator set consisting of a stator core 1 and drive coils 3 each wound around a bobbin 13 circumscribing this stator core 1 as well as a stator set consisting of a stator core 2 and drive coils 4 each wound around a bobbin 19 circumscribing this stator core 2.  These two stator sets are fixed by being superposed in the axial direction.  This motor is a stepping motor, and each of the stator cores 1 and 2 has a plurality of pole teeth arranged at equal intervals in a cylindrical shape on its inner peripheral side.  An outer side surface of a bent side 10a at one end side of a frame 10, which is formed in a U-shape with both end faces bent orthogonally in the same direction and with a long bottom, is fixed to an end face on an axially outer side of the stator core 1. 
A hole with a diameter of xcfx86B is formed in a bent side 10b at the other end side of the frame 10, and a bearing 11, which consists of an outside-diameter portion having the same diameter as the aforementioned xcfx86B and an outside-diameter portion larger than the same, has its outside diameter xcfx86B portion fitted and fixed in this hole from the inner side of the frame 10.  The bearing 11 has a recess for receiving one end portion of an output shaft 6, and has a semispherical recess for receiving an approximately half of a steel ball 12 in a bottom of this recess.  A conical recess provided at a distal end of the output shaft 6 is fitted over the steel ball 12 fitted in the semispherical recess. 
The bent side 10a at the one end side of the frame 10 is also provided with a hole with substantially the same diameter xcfx86D as the aforementioned diameter xcfx86B, and the output shaft 6 is passed through this hole.  One end side of the output shaft 6 is formed as a small-diameter portion 6a, and this small-diameter portion 6a is inserted in holes defining inner peripheral sides of the stator cores 1 and 2.  The inside diameter xcfx86C of the stator cores 1 and 2 is larger than the diameters xcfx86B and xcfx86D of the holes formed in the bent sides 10a and 10b of the frame 10.  A slide bearing 8 whose outside diameter is substantially the same as the aforementioned inside diameter xcfx86C is fitted on an inner periphery of a bearing member fixed to an end face of the stator core 2 having the inside diameter xcfx86C, such that the slide bearing 8 is slidable along the inner periphery of the bearing member. 
The slide bearing 8 has a recess on its inner end side, and an approximately half portion of a steel ball 7 is thrust into this recess, while the remaining approximately half portion of the steel ball 7 is fitted in a conical recess formed in an end face of the small-diameter portion 6a which is the one end side of the output shaft 6.  The slide bearing 8 has its proximal portion urged in a direction in which it enters an inner periphery of the stator core 2 by a leaf spring 9 fixed to an outer end of the stator core 2.  The steel ball 7 presses the output shaft 6 by this urging force to cause the steel ball 12 at the distal end of the output shaft 6 to be pressed against the bearing 11.  Thus the output shaft 6 is rotatably supported by the bearings 8 and 11 via the steel balls 7 and 12, and the load in the direction of thrust is thereby received.  A hollow cylindrical magnet 5 is fitted and secured on an outer peripheral side of the small-diameter portion 6a of the output shaft 6, and the output shaft 6 and the magnet 5 constitute the rotor of the motor. 
Magnetic poles are formed in the magnet 5 at equal intervals in the circumferential direction, and as the drive coils 3 and 4 are alternately energized by a power supply in the form of pulses, the rotor rotates through predetermined angles.  A lead screw is formed on the output shaft 6 between the bent sides 10a and 10b of the frame 10, and as a portion of an object to be driven, such as an unillustrated optical pickup, or a member substantially integrated therewith, is engaged with this lead screw, the object to be driven is moved back and forth along the output shaft 6 in correspondence with the rotation of the output shaft 6. 
The above-described motor is a compact motor with an outside diameter of 6 mm or less in the case of driving an optical pickup, or one with a width of 6 mm or thereabouts in the case of an oval motor.  With such a small-sized motor, since there is a need to make smaller the air gap between the inner periphery of the stator and the outer periphery of the rotor magnet 5, high accuracy of concentricity is required for respective component units.  However, a further increase in the accuracy of individual components involves higher cost, which is undesirable since a highly sophisticated production technique is required. 
In addition, to obtain concentricity for the main body portion of the motor and the output shaft 6, during assembly a pin gage is inserted through a hole defining an inner periphery of the main body portion of the motor and the holes formed in the bent sides 10a and 10b of the frame 10, and the main body of the motor and the frame 10 are fixed in a state in which the relative positional offset, inclination, and a deviation in concentricity are eliminated.  However, since the inside diameter of the main body portion and the diameter of the holes formed in the bent sides 10a and 10b of the frame 10 differ, as described above, a pin gage having a step needs to be used correspondingly.  As such, however, if the pin gage is provided with a step, there is a possibility that the pin gage itself loses its concentricity between the large-diameter portion and the small-diameter portion.  Hence, there is a drawback in that the concentricity of the pin gage is reflected as it is on the concentricity of the main body portion of the motor and the output shaft, so that the concentricity varies. 
In particular, with the motor for feeding an optical pickup in an optical disk drive apparatus, the span of the bent sides 10a and 10b of the frame 10 is 50 to 60 mm or thereabouts and is thus long.  Therefore, if the frame 10 is inclined even slightly when it is fixed, the position for supporting the distal end of the output shaft becomes offset by a large degree, so that unless the hole diameter on the distal end side of the frame is measured directly to control concentricity, the accuracy of concentricity required for this type of motor cannot be ensured. 
The invention has been devised in view of the above-described conventional art, and its object is to provide a motor which has a motor body and a frame for holding its output shaft, and which makes it possible to obtain concentricity of the motor body and the output shaft with high accuracy and minimize the clearance between the stator and the rotor, as well as a method of manufacturing the same. 
(1) In accordance with the invention, there is provided a method of manufacturing a motor including a cylindrical rotor having a magnet, a stator having a cylindrical inner peripheral surface opposing to an outer periphery of the rotor, an output shaft of the rotor projecting from a first axial end side of the stator, and a frame fixed to the first axial end side of the stator to pivotally support the output shaft at a distal end thereof, the method comprising the steps of:
forming holes in the frame at a portion where the distal end of the output shaft is pivotally supported and at a portion where the stator is fixed, wherein the holes have diameters identical to a diameter of the inner peripheral surface of the stator;
simultaneously inserting a round rod-shaped positioning jig having a diameter slightly smaller than the diameter of the holes into a hole defining the inner peripheral surface of the stator and into the two holes in the frame, and causing the positioning jig to abut against the inner peripheral surfaces of the holes so as to effect positioning; and
fixing a first side of the frame to the first axial end side of the stator. 
(2) The method of manufacturing a motor according to (1), further comprising the steps of:
providing a bearing member having a slide bearing an outer wall of which is cylindrical and which pivotally supports the output shaft of the rotor on a side which opposite to a distal end thereof, the bearing member being adapted to hold the slide bearing so as to be axially movable on a second axial end side of the stator as the outer wall of the slide bearing is brought into sliding contact with an inner wall of the bearing member by using the inner wall as a guide;
forming the inner wall of the bearing member with a diameter identical to that of the inner peripheral surface of the stator;
simultaneously inserting the positioning jig into the hole defining the inner peripheral surface of the stator and the two holes in the frame, and causing the positioning jig to abut against the inner peripheral surfaces of the holes so as to effect positioning; and
fixing the first side of the frame to the first axial end side of the stator, and fixing the bearing member to the second axial end side of the stator. 
(3) In accordance with the invention, there is provided a motor comprising:
a cylindrical rotor having a magnet;
a stator having a cylindrical inner peripheral surface opposing to an outer periphery of the rotor;
an output shaft of the rotor projecting from a first axial end side of the stator; and
a frame fixed to the first axial end side of the stator to pivotally support the output shaft at a distal end thereof, the frame being provided with holes at a portion where the distal end of the output shaft is pivotally supported and at a portion where the stator is fixed;
wherein the holes have a diameter identical to a diameter of the inner peripheral surface of the stator, and
a central axis of the inner peripheral surface of the stator and central axes of the two holes in the frame are concentrically aligned. 
(4) In accordance with the invention, The motor according to (3), further comprising:
a bearing member having a slide bearing an outer wall of which is cylindrical and which pivotally supports the output shaft of the rotor on a side thereof opposite to a distal end thereof, the bearing member being adapted to hold the slide bearing so as to be axially movable on a second axial end side of the stator as the outer wall of the slide bearing is brought into sliding contact with an inner wall of the bearing member by using the inner wall as a guide;
wherein the first side of the frame is fixed to the first axial end side of the stator, and the bearing member is fitted to the second axial end side of the stator,
the inner wall of the bearing member is formed with a diameter identical to that of the inner peripheral surface of the stator, and
respective central axes of the inner wall of the bearing member, the inner peripheral surface of the stator, and the two holes in the frame are concentrically aligned. 
(5) In accordance with the invention, the motor according to (3), wherein a lead screw is formed on the output shaft, and as one of a portion of an optical pickup and a member substantially integrated with the optical pickup is engaged with the lead screw, the motor is formed for use in feeding the optical pickup.