Motor structure

A motor structure of a claw pole type two-phase synchronous motor has a stator including two armature coils held between corresponding pairs of stator yokes and superposed on one another, and a rotor coaxially mounted on the stator and having a rotary shaft around which the rotor rotates so that a part of the chassis of a memory apparatus forms one of the stator yokes.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates to a motor structure and more particularly to 
a claw pole type two phase synchronous motor which can be used as a 
spindle motor in a memory apparatus such as an FDD (floppy disc drive 
apparatus), an HDD (hard disc drive apparatus) or a CD-ROM (compact disc 
ROM apparatus), all of which are referred to hereinafter as a "memory 
apparatus". 
2. Description of the Related Art 
Since a memory apparatus such as an FDD, an HDD or a CD-ROM must be rotated 
very accurately, a three phase brushless DC motor which rotates at a high 
accuracy has been used as a spindle motor of such a memory apparatus. 
However, this DC motor cannot be manufactured at a low cost, and thus it 
is undesirable to be used in the memory apparatus because the 
manufacturing cost of a memory apparatus must be reduced. 
A claw pole type two-phase synchronous motor can be speed-controlled in an 
open loop control system, making the use of a magnetic switching sensor 
unnecessary, whereby the structure of this motor can be simplified and its 
cost can be reduced. However, this motor is basically a stepping motor 
which has the disadvantages that large cogging, torque ripple, 
oscillation, noise and magnetic flux leakage are produced. Thus, the 
conventional claw pole type two-phase synchronous motor could not be used 
as a spindle motor for a memory apparatus. 
The conventional synchronous motor is manufactured separately from the 
chassis of a memory apparatus. Even when the spindle motor is assembled 
into the memory apparatus by using a jig, the center of rotation of the 
motor may be slightly displaced from the predetermined mounted position of 
the magnetic head of the memory apparatus, resulting in misalignment 
between the spindle of the motor and the head. 
A claw pole type two-phase synchronous motor which is operated at low 
cogging and small torque ripple is disclosed in U.S. patent application 
Ser. No. 08/662,448 filed on Jun. 10, 1996 assigned to the same assignee 
as the present application, the entire contents of which are incorporated 
herein by reference. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a claw pole type 
two-phase synchronous motor which can be manufactured at a low cost by 
reducing the number of components and improving yield, which operates 
stably at a high accuracy attained by increasing the assembling accuracy 
of the motor into a memory apparatus, and which can be used as a spindle 
motor of the memory apparatus. 
In order to achieve the object, a motor structure according to the present 
invention comprises a rotor and a stator disposed coaxially with the 
rotor. The stator comprises stator yokes made from a soft magnetic steel 
plate and superposed on one after another and armature coils each held in 
the corresponding pairs of the stator yokes. The rotor comprises a 
permanent magnet. Pole teeth are formed on a peripheral surface of each of 
the stator yokes by bending parts of the corresponding plate at 
substantially right angles with respect to the plate and are arranged 
opposed to the permanent magnet with a predetermined gap interposed 
between the pole teeth and the permanent magnet. Lead-out lines are drawn 
from the armature coils. The synchronous motor according to the present 
invention has the specific feature that a part of the chassis of a memory 
apparatus forms one of the stator yokes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be described in detail by way of preferred 
embodiments with reference to the accompanying drawings. 
In the embodiments of the present invention described hereinbelow, claw 
pole type two-phase synchronous motors are used as spindle motors. Thus, 
these motors are described as claw pole spindle motors. 
As shown in FIG. 1, a floppy disc drive apparatus comprises a chassis 1 
made of soft magnetic steel, a claw pole spindle motor 2, a magnetic head 
3 and a stepping motor 4 for driving a head actuator. The chassis 1 has a 
circular depressed mount which is formed by a drawing process as will be 
described later and in which the claw pole spindle motor 2 is mounted. 
Lead-out lines (not shown in FIG. 1) are drawn out from the claw pole 
spindle motor 2 as will be described later. 
FIGS. 2 and 3 show a first embodiment of the spindle motor according to the 
present invention. A cylindrical mount 1A is formed in the chassis 1 of 
the floppy disc drive apparatus by a drawing process. The circular bottom 
portion 1D of the circular depressed mount 1A comprises a circular flange 
6 formed at the central portion of the base portion 1D, for supporting a 
cylindrical oil-retaining bearing 10 and a stator yoke 5 (referred to 
hereinafter as the "lower stator yoke 5") formed around the flange 6. 
Circularly arranged and preferably equidistantly spaced trapezoidal 
portions 1B are punched out from the annular zone of the stator yoke 5 so 
that their roots or bases are on the inner circular edge of the stator 
yoke 5, and they extend radially outward. The number of the trapezoidal 
portions 1B is twenty-four in this embodiment but any number can be 
selected if required. The trapezoidal portions 1B are bent at their roots 
upward substantially at right angles with respect to the bottom portion 1D 
to form pole teeth 7 which are twenty-four in number in this embodiment 
and which are arranged circularly preferably at substantially equal 
intervals. 
The part of the annular zone other than the pole teeth 7 is used to connect 
the stator yoke 5 to the flange 6. It should be noted that the depressed 
mount 1A is not necessarily truly cylindrical but may has another shape as 
long as it can be used properly. A first armature coil 8 is inserted in 
the stator yoke 5 from above. 
A stator yoke 9 (referred to hereinafter as the "upper stator yoke 9") made 
of soft magnetic steel has the same number, the same size and the same 
arrangement of pole teeth 7 which are formed similarly to the lower stator 
yoke 5. The upper stator yoke 9 is placed from above on the first armature 
coil 8 held in the lower stator yoke 5, with the pole tooth 7 of both 
stator yokes 5 and 9 interdigitated preferably at substantially equal 
circumferential intervals. In this way, the first armature coil 8 is 
mounted in the depressed mount 1A in a state held between the upper and 
lower stator yokes 9 and 5. Here, the first armature coil 8, the upper and 
lower stator yokes 9 and 5 and the pole teeth 7 constitute a first 
armature coil assembly. 
Another upper stator yoke 9A and another lower stator yoke 9B both made of 
soft magnetic steel and having pole teeth 7A are formed in the same way as 
the upper stator yoke 9. A second armature coil 8A is held between the 
upper and lower stator yokes 9A and 9B with the pole teeth 7A 
interdigitated preferably at substantially equal circumferential 
intervals. The second armature coil 8A and the upper and lower stator 
yokes 9A and 9B and the pole teeth 7A constitute a second armature coil 
assembly. The second armature coil assembly is inserted in the depressed 
mount 1A from the above to be placed on the first armature coil assembly. 
One of the first and second armature coil assemblies is set in phase A and 
the other one is set in phase B. These armature coil assemblies are 
arranged so that the phase difference between the assemblies is 80.degree. 
to 90.degree. in an electric angle. 
Lead-out lines 16 are drawn out from the armature coils 8 and 8A, and the 
drawn-out portion 16a of the led-out lines 16 makes an angle .theta. with 
a straight line SM passing the central axis of the claw pole spindle motor 
2A and the center of the magnetic head 3, the angle .theta. being measured 
from the portion of the line SM as viewed from the magnetic head 3 (see 
FIG. 2). The angle .theta. is .+-.30.degree. to .+-.135.degree. 
(preferably, .+-.30.degree. to .+-.90.degree.) so that the magnetic fluxes 
leaking from the claw pole spindle motor 2A does not disadvantageously 
affect the performance of the magnetic head 3 and the drawn-out portion 
16a is made the shortest. 
As shown in FIG. 3, a cylindrical oil-retaining bearing 10 is placed in the 
central portions of the stator yokes 5 and 9, and 9A and 9B and fixed at 
the lower end thereof to the flange 6, i.e., the central part of the 
bottom portion 1D of the annular depressed mount 1A by means of a portion 
18 which is formed by molding a polymeric material on the outer peripheral 
surface of the bearing 10. The stator yokes 5, 9, 9A and 9B are fixed at 
the outer peripheral surfaces thereof to the cylindrical wall of the 
annular depressed mount 1A. These yokes are also fixed to the 
corresponding armature coils by means of a polymeric material. In this 
way, a stator 17 comprising both armature coil assemblies is formed. 
However, the yokes can be fixed together by means of plasma welding, 
caulking or the other suitable way. 
A disc-like hub 12 is made of a plastic magnetic material. A cylindrical 
rotor magnet receiving portion 12a is also made of a plastic magnetic 
material and is integrally and coaxially formed on the hub 12 so as to 
extend downward from the undersurface of the hub 12. A rotor magnet 13 is 
fixedly mounted on the outer peripheral surface of the rotor magnet 
receiving portion 12a. Interior of the rotor magnet receiving portion 12a, 
an inner cylindrical portion is coaxially formed 12b with its upper end 
integrally fixed to the undersurface of the hub 12. 
Eight magnetic poles for attracting a disc hub are formed on the hub 
surface of the hub 12, and forty-eight magnetic poles working as field 
magnets are formed on the rotor magnet 13. 
A rotary shaft 11 has an upper end portion extending through the central 
portion of the body of the hub 12 and fixed thereto. The rotary shaft 11 
extends through the inner cylindrical portion 12b. 
The rotary shaft 11, the hub 12 and the rotor magnet 13 constitute a rotor 
14. A drive pin 15 is formed on the upper surface of the hub 12 to 
transmit the rotation of the rotor 14 to an external rotary device. 
The rotary shaft 11 is inserted in the bearing 10 surrounded by a molded 
portion 18 in a state in which the inner cylindrical portion 12b receives 
the bearing 10 with a small gap provided between the inner peripheral 
surface of the portion 12b and the outer peripheral surface of the molded 
portion 18. Thus, the rotor 14 is securely mounted in the stator 17. In 
this way, the claw pole spindle motor 2A is manufactured. 
With the conventional spindle motor which does not contain, as an element, 
the chassis of a floppy disc drive apparatus, fine adjustment is required 
to set the spindle motor on the chassis in a correct position. 
In contrast, the claw pole spindle motor 2A according to this embodiment of 
the present invention uses, as an element thereof, a part of the chassis 1 
of a floppy disc drive apparatus. Thus, accurate positioning of the 
spindle motor 2A on the chassis 1 is ensured without necessity of 
adjustment which must be made in the conventional spindle motor. This 
improves the operational stability of the claw pole spindle motor 2A and 
reduces the number of parts to lower the cost of the memory apparatus. 
Further, the depressed mount 1A is formed by a drawing process, whereby 
the strength of the chassis 1 is enhanced. Thus, the spindle motor 2A of 
this embodiment can be used as a drive apparatus in a severe environment. 
In FIGS. 4 and 5 show a second embodiment of the claw pole spindle motor 2B 
according to the present invention. The motor 2B comprises a stator 17 and 
a rotor 14 coaxially mounted in the stator 17. The stator 17 has a first 
armature coil 8, a second armature coil 8A disposed under the first 
armature coil 8. However, the motor 2B does not have a cylindrical 
depressed mount 1A unlike the claw pole spindle motor 2A according to the 
first embodiment. The chassis 1 has a circular flange 6 and an annular 
zone 5b around the flange 6. 
Referring to FIG. 5, trapezoidal portions 19 circularly arranged preferably 
at substantially equal intervals are punched out from the annular zone 5b 
of a flat chassis 1 which zone is to be placed over the first armature 
coil 8 after the assembly of the first and second armature coils 8 and 8A 
has been completed. 
Each trapezoidal portion 19 radially outwardly extends by a length equal to 
the height of pole teeth 7 to be formed from a phantom circle having a 
diameter slightly (0.3 mm, for example) larger than the outer diameter of 
a rotor magnet 13. The trapezoidal portions 19 are bent downward 
substantially at right angles to form the pole teeth 7 arranged circularly 
preferably at substantially equal intervals. The number of the pole teeth 
7 formed from the chassis 1 may be twenty-four or another suitable number. 
Rectangular portions 20 arranged circularly preferably at substantially 
equal intervals are punched out from annular zone of the chassis 1. Each 
rectangular portion radially outwardly extends from a phantom circle 
defined by the roots of the rectangular portions 20 by a length equal to 
the height of a stator yoke 9 as will be described later. The rectangular 
portions 20 are bent downward at substantially right angles to form 
comb-shaped outer peripheral portions 5a. The annular zone 5b, the teeth 7 
and the outer peripheral portions 5a constitute an upper stator yoke 5. 
As shown in FIG. 4, a lower cylindrical stator yoke 9 for the first 
armature coil 8 comprises a ring-shaped bottom portion (horizontal 
portion), pole teeth 7 formed on the inner circular edge of the stator 
yoke 9 and an outer peripheral portions formed on the outer circular edge 
of the lower stator yoke 9. The pole teeth 7 have the same shape, size and 
the number and the arrangement of the teeth 7 of the chassis 1 and bent 
upward at substantially right angles with respect to the bottom portion of 
the lower stator yoke 9. 
The first armature coil 8 is placed in the lower stator yoke 9, and then 
the lower stator yoke 9 is fixed to the upper stator yoke from below by 
means of a polymeric material, with the pole teeth 7 of the upper and 
lower stator yokes interdigitated preferably at substantially equal 
intervals. The upper and lower stator yokes and the first armature coil 8 
are connected together by means of a polymeric material or any other 
suitable means and constitute a first armature assembly. 
The second armature coil 8A is held between a cylindrical upper stator yoke 
9B and a lower cylindrical stator yoke 9A having the same shape, size as 
the lower stator yoke 9 for the first armature assembly 8 in a state in 
which the upper stator yoke 9B is disposed upside down. In other words, 
each of them has a ring-shaped horizontal portion provided on the inner 
circular edge of the horizontal portion with pole teeth 7A and on the 
outer circular edge of the horizontal portion with a cylindrical outer 
peripheral wall. 
The horizontal portion, the teeth 7A and the outer peripheral wall also 
constitute a lower stator yoke 9A for the second armature coil 8A. The 
upper and lower stator yokes 9 and 9A and the second armature coil 8A are 
connected together by means of a polymeric material or any other suitable 
means and constitute a second armature coil assembly. The first and second 
armature coil assemblies are fixed together by means of welding shown at 
22. 
A cylindrical oil-retaining bearing 10 has an upper end portion passing 
through and fixed to the central portion of the flange 6, and extends 
downward from the flange 6. 
A rotary shaft 11 has an upper end passing through and fixed to the central 
portion hub 12. The rotary shaft 11 fixed to the hub 12 is inserted, and a 
cup-shaped rotor magnet receiving member 23 having a circular bottom 
portion 23a and a cylindrical outer peripheral wall 23b on which a rotor 
magnet 13 is mounted is inserted in a circular columnar space in the 
stator 17. The central portion of the bottom portion 23a of the rotor 
receiving member 23 is fixed at its disc-like bottom portion 23a to the 
lower end of the rotor shaft 11 by means of a screw 24, with a 
predetermined gap disposed between the pole teeth 7 and 7A and the rotor 
magnet 13. The rotary shaft 11, the hub 12, the rotor magnet receiving 
member 23 and the rotor magnet 13 constitute a rotor 14. 
The hub 12, the rotary shaft 11, the rotor receiving member 23 and the 
rotor magnet 13 constitute a rotor 14 and the upper surface of the hub 12 
is formed a pin 15 for transmitting the rotation of the rotor 14 to an 
external rotary device. The other elements and the parts are the same as 
those of the first embodiment and are indicated in FIG. 5 by the same 
reference numerals as those of the first embodiment, and a detailed 
description thereof is omitted. 
FIG. 6 shows a third embodiment of the claw pole spindle motor 2C which has 
a first armature coil assembly including a first armature coil 8 and a 
second armature coil assembly including a second armature coil 8A and 
disposed under the first armature coil assembly. The elements and parts 
other than those described below are the same as those described in the 
first and second embodiments. Thus, they are shown in FIG. 6 by the same 
reference numerals as those of the first and second embodiments and a 
detailed description thereof is omitted. 
A gear-shaped portion is punched out from the chassis 1 of a memory device. 
The remaining portions between the teeth of the punched-out gear-shaped 
portions extend radially inward and are shaped as pole teeth 7 to be 
formed. These remaining portions are bent downward at their roots at 
substantially right angles to be formed into pole teeth 7. Comb-shaped 
outer peripheral portions 5a are formed in the same way as in the second 
embodiment. The pole teeth 7, the comb-shaped outer peripheral portions 5a 
and the annular portion of the chassis 1 defined therebetween constitute 
an upper stator yoke 5 for the first armature coil 8. The upper stator 
yoke 5, a lower stator yoke 9 having the same structure as that of the 
first embodiment and a first armature coil 8 held by both stator yokes 5 
and 9 constitute a first armature coil assembly. 
Around a circular flange 6 there is integrally formed a lower stator yoke 
9A having trapezoidal pole teeth 7A formed at its inner circular edge and 
comb-shaped outer peripheral portions 5b formed at its outer circular 
edge. 
The pole teeth 7A are formed by bending the trapezoidal portions in an 
annular zone of the lower stator yoke 9A which extend radially outwardly 
from the inner circular edge of the lower stator pole 9A. The lower stator 
yoke 9A, an upper stator yoke 9B having the same structure as that of the 
second embodiment and a second armature coil 8A held between both stator 
yokes constitute a second armature coil assembly. 
The lower end of the cylindrical oil-retaining bearing 10 is fixed to the 
central portion of the flange 6 by means of a molded portion 18 formed on 
the outer peripheral surface of the bearing 10 in the same way as in the 
first embodiment. A rotary shaft 11 extends through the bearing 10 and is 
rotatably supported at its lower end on the flange 6. 
FIG. 7 shows a fourth embodiment of the claw pole spindle motor 2D. The 
spindle motors 2A to 2C of the first to third embodiments are of an inner 
rotor type and the spindle motor 2D of the fourth embodiment is of an 
outer rotor type. 
A cylindrical depressed mount 1C is formed in the chassis 1 of a memory 
apparatus. The central portion of the circular bottom portion of the mount 
1C is elevated to form a circular flange 26. 
The lower end of a cylindrical oil-retaining bearing 10 is fixed to the 
flange 26. The part of the bottom portion 5 except for the flange 26 forms 
a lower stator yoke. 
Circularly and preferably equidistantly arranged trapezoidal portions are 
punched out from an annular zone of the bottom portion 5 which is close to 
the outer circular edge thereof. The trapezoidal portions are bent upward 
at substantially right angles at their outer ends to form pole teeth 7. A 
first armature coil 8 is placed in the lower stator yoke formed by the 
bottom portion 5. 
An upper stator yoke 9 having downward extending pole teeth 7 formed on its 
outer edge and an inner wall formed at its inner edge is disposed on the 
first armature coil 8. The pole teeth 7 of the upper and lower stator 
yokes are interdigitated preferably at substantially equal intervals. 
These two stator yokes and the first armature yoke 8 held by them 
constitute a first armature coil assembly. 
On the first armature coil assembly there is coaxially and fixedly placed a 
second armature coil assembly comprising two stator yokes 9A, 9B having 
trapezoidal pole teeth 7A arranged circumferentially preferably at 
substantially equal intervals and inner walls formed on the inner edges of 
the stator yokes 9A, 9B, and a second armature coil 8A held between the 
stator yokes 9A, 9B. The inner walls of the first and second armature coil 
assemblies are firmly connected to the bearing 10 by means of a 
cylindrical molded portion 32. The first and second armature assemblies 
constitute a stator 31. 
A disk-shaped hub 27 is formed on its central portion with a disk-shaped 
hub portion 12c. The central portion of a cup-shaped rotor yoke 28 is 
fixed to the hub portion 12c of the hub 27. On the inner surface of the 
cylindrical outer peripheral wall portion or a skirt portion 28a of the 
rotor yoke 28 there is provided a cylindrical rotor magnet 13. 
The upper end portion of a rotary shaft 11 is inserted in the central 
portion of the hub 27 and fixed thereto. The hub 27, the rotary shaft 13, 
the rotor yoke 28 and the rotor magnet 13 constitute a rotor 30. On the 
upper surface of the hub 27 there is provided a drive pin 15 for 
transmitting the rotation of the rotor 30 to an external rotary apparatus. 
The rotor 30 is assembled into the stator 31 by inserting the rotary shaft 
11 in the bearing 10 and as well as inserting the outer peripheral wall 
portion 28a of the rotor yoke 28 in the space between the pole teeth 7 and 
7A and the outer peripheral wall 1C of the depressed mount 1C. In this 
state, the rotor magnet 13 is located in the space between the pole teeth 
7 and 7A. In this way, the claw pole spindle motor 2D is manufactured. 
The number of phases of the motor according to the present invention is not 
limited to two, and motors having more than two phases are available. In 
such motors, yoke coil assemblies, the number of which is equal to the 
number of the phases thereof and each of which comprises a pair of yokes 
and an armature coil held therebetween, are superposed on one another.