Motor

An electromagnetic drive apparatus comprises a stator yoke excited with supply of power to a coil, a rotor arranged as capable of being driven by excitation of the stator yoke so as to move a driven member, and a fixed member for positioning and supporting the rotor and the stator yoke. The stator yoke has a projecting portion or a recessed portion and the stator yoke is positioned and supported relative to the fixed member by the projecting portion or the recessed portion to provide a compact motor without causing a drop of efficiency in the power of the motor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention concerns a motor assembled without degrading motor 
performance. More particularly, the invention relates to a motor having a 
configuration suitable for a compact of motor and suitably applicable for 
example to lens driving motors. 
2. Related Background Art 
In the case of conventional motors, for example in a stepping motor, a 
method for positioning a stator yoke thereof to a fixed member was such 
that a fitting hole was formed in the stator yoke itself and the fitting 
hole was engaged with a shaft provided on the fixed member to position the 
stator yoke. 
The necessity of positioning the stator yoke relative to the fixed member 
is to maintain an adequate gap between a rotor and the stator yoke. 
Dispersion of the gap directly results in degrading the performance and 
stop accuracy, and, therefore, the position of the stator yoke needs to be 
precisely determined relative to the fixed member. For that purpose, it is 
conventional that a fitting positioning hole for a rotating shaft of the 
rotor and a positioning portion for the stator yoke are formed on the 
fixed member so as to restrict the dispersion of dimensional accuracy as 
much as possible. 
Meanwhile, miniaturized products are becoming commercially available, which 
increases demands also to miniaturize the motor itself mounted in such 
products. A first way for achieving miniaturization of a motor, for 
example the stepping motor itself, is usually to consider whether it is 
possible to simply miniaturize the motor configuration presently used as 
it is. Namely, it is a present status that the motor is designed as being 
miniaturized in the same positioning structure of the stator yoke to the 
fixed member as described above and in the same relation between the 
fitting hole of the stator yoke and the fitting shaft of the fixed member 
(at the same reduction ratio for the diameter of the shaft, the diameter 
of the hole, etc.). 
However, because the above conventional example employs a structure 
obtained by miniaturizing the motor configuration presently used as it is 
in order to miniature the motor, it is considered that the fitting hole 
for positioning the stator yoke also becomes smaller, and that the 
positioning shaft of the fixed member to fit in the fitting hole of the 
stator yoke also becomes slimmer with a decrease an the diameter of the 
fitting hole. 
Moreover, the fixed member is usually a molded part of a mold (for example, 
polycarbonate) being an insulating member, taking account of processing 
and cost. Thus, there is a limit (in view of molding and strength) to 
decreasing the diameter of the shaft for miniaturization as described 
above, and there occurs some cases that the diameter of the shaft of the 
fixed member cannot follow a miniaturization rate of the motor. In such 
cases, a method employed is to design the size of the shaft of the fixed 
member for positioning the stator yoke so as not to be decreased relative 
to the miniaturization of the motor. This is explained referring to FIG. 4 
and FIG. 5. 
FIG. 4 is a drawing to show a configuration of a conventional stepping 
motor, and FIG. 5 is a drawing to show a configuration of a compact model 
of the conventional stepping motor. In FIG. 4, 101, 102 denote stator 
yokes, 103 a rotor, and 104, 105 coils. In FIG. 5, 111, 112 designate 
stator yokes, 113 a rotor, and 114, 115 coils. In FIG. 4 and FIG. 5, 101a, 
102a, 111a, 112a are positioning fitting holes of respective stator yokes 
relative to the fixed member, and the diameters of the four holes are the 
same. 
Next explained are magnetic circuits in such states. First, chain 
double-dashed lines in FIG. 4 and FIG. 5 represent magnetic paths. As 
shown in FIG. 4, the magnetic paths are closed as passing through the 
inside of the stator and rotor. The stepping motors presently available 
are realized in that state. Changing this configuration into the one shown 
in FIG. 5 for miniaturization, the magnetic paths would run across the 
positioning holes of the stator yokes 111, 112, and thus, the magnetic 
circuits are closed so as to pass through the inside of the stator yokes 
111, 112 as avoiding the positioning holes 111a, 112a. 
However, because a rate of an area occupied by the positioning hole 111a, 
112a of stator yoke 111, 112 to the stator yoke 111, 112 is high, the 
stator yoke becomes thin in that portion, and it becomes impossible to 
keep a predetermined quantity of magnetic field passing through that 
portion. Namely, the stator yokes become magnetically saturated there, so 
that the motor can supply only the power resulting from passage of 
magnetic field at the level of magnetic saturation, resulting in a 
drawback that the efficiency drops. 
Another positioning method of stator yokes considered is a method for 
surrounding the stator yoke itself by the fixed member without perforating 
the stator yoke, which is poor in space efficiency, thus failing to 
achieve miniaturization. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above problems, and thus 
to provide a motor employing projecting portions or recessed portions for 
positioning of the stator yoke, thereby permitting positioning without 
forming the positioning holes. 
Another object of the present invention is to provide a motor arranged in 
such a manner that the projecting portions or recessed portions for 
positioning of the stator yoke are also utilized upon lamination of the 
stator yoke. 
Still another object of the present invention is to provide a motor which 
can be readily produced by employing a common configuration to two stator 
yokes in the motor. 
The other objects of the present invention will be apparent from the 
specific embodiments described below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The embodiments of the present invention will be explained with reference 
to the drawings. 
FIG. 1 is an exploded, perspective view of the stepping motor and FIG. 2 is 
a sectional view of the motor. In FIG. 1 and FIG. 2, reference numeral 1 
designates a stator yoke formed by stacking a plurality of (six) plates of 
a soft magnetic material and securing them to each other, in which the 
plates of the soft magnetic material are laminated as a stack of plates in 
a same shape. 
The plates of the soft magnetic material are shaped by press working (half 
press) so as to form projecting portions 1a on top faces thereof and 
recessed portions 1b on bottom faces thereof as positioning portions 
necessary when stacked. Namely, as shown in FIG. 2, the plates of the soft 
magnetic material are stacked so that their projecting portions 1a may be 
opposed to the recessed portions 1b. Actually, the projecting portions la 
are pressed into the recessed portions 1b, thereby achieving positioning 
and also forming a unit of stator yoke 1. 
Numeral 2 is a same component as the stator yoke 1, which can be the other 
stator yoke in the stepping motor of a two-phase type. The stator yoke 2 
is nothing but the stator yoke 1 turned over. Therefore, projecting 
portions 2a correspond to the projecting portions 1a and recessed portions 
2b correspond to the recessed portions 1b. 
Numeral 3 denotes a rotor of a plastic magnet, which can be rotated by 
excitation states of the stator yoke 1 and stator yoke 2, and which is 
integrally provided with a gear 3a for transmitting the rotating power of 
the rotor 3 to a driven member (not shown). Numerals 4, 5 represent coils 
for exciting the stator yoke 1 and stator yoke 2, respectively, and the 
coil 4 and coil 5 are formed as same parts. The coil 4 and coil 5 are 
arranged to excite the stator yoke 1 and stator yoke 2, respectively, when 
the power is supplied thereto through connection terminals 4a, 4b, 5a, 5b. 
Numeral 6 stands for a motor case for positioning and supporting the stator 
yoke 1 and stator yoke 2. Next explained is the positioning and supporting 
structure of the stator yoke 1 and stator yoke 2 to the motor case 6. 
First, the positioning method of the stator yoke 1 to the motor case 6 
utilizes the arrangement that the projecting portions la used upon 
stacking of the stator yoke 1 as described above project from the 
lowermost plate of the soft magnetic material, in which the projecting 
portions 1a are pressed into recessed portions 6a formed in the motor case 
6 so as to achieve positioning and support. On the other hand, the 
positioning method of the stator yoke 2 to the motor case 6 utilizes the 
arrangement that the lowermost plate of the soft magnetic material has the 
recessed portions 2b in contrast with the case of the stator yoke 1, in 
which projecting portions 6b formed in the motor case 6 are pressed into 
the recessed portions 2b so as to achieve positioning and support. 
Since the positioning and supporting method of the stator yokes 1, 2 to the 
motor case 6 employs the press-fitting relation between the projecting 
portions and the recessed portions, the invention can solve the problem 
occurring in the positioning and supporting method of the perforated 
stator yokes in the conventional example of FIG. 5 as discussed 
previously; that is, the invention can avoid the magnetically saturated 
state. 
Further, the motor case 6 rotatably supports the rotary shaft 3b of the 
rotor 3. Namely, the stator yokes 1, 2 and the rotor 3 are positioned with 
respect to the motor case 6, so that they are set only in a dimensional 
tolerance relation of only the motor case 6, which can maintain the 
dispersion of gaps between the rotor 3 and the stator yokes 1, 2, which 
affects the motor performance very much, at the minimum level, thus 
realizing a structure that can provide a stepping motor with high 
accuracy. 
Numeral 7 denotes a motor case cap, which rotatably supports the rotary 
shaft 3c of the rotor 3 and which has claws 7a-7d hooked on grooves 6c-6f 
of the motor case 6, thereby forming a unit of the stepping motor as an 
electromagnetic drive apparatus. 
(Embodiment 2) 
Referring to FIGS. 3A and 3B, Embodiment 2 is next explained as to an 
electromagnetic drive stop apparatus provided with the motor A in 
Embodiment 1 as a drive source. In FIGS. 3A, 3B, the stop apparatus is 
totally denoted by reference symbol B; and the motor A of Embodiment 1 is 
mounted in the stop apparatus B. The motor A is comprised of the 
components as explained in Embodiment 1, and, because the configuration of 
the motor A was already explained, the explanation thereof is omitted in 
this Embodiment 2. 
The configuration of the stop apparatus B is next explained. Reference 
numeral 11 designates an electrically conductive, annular, base plate, 
which has an aperture through which photographing light passes, and the 
electromagnetic drive apparatus (motor) A as described above is fixed by a 
known method to the annular base plate 11. 
Numeral 12 denotes an annular cam plate of an insulating member, and a 
plurality of known stop cams 12a are cut in the cam plate 12. Numeral 13 
represents a plurality of stop wings, and dowels 13a provided on the back 
faces of the respective stop wings 13 are fitted in the stop cams 12a of 
the cam plate 12. Numeral 14 stands for a rotary ring arranged to rotate 
about the optical axis and having an aperture through which the 
photographing light passes in the center, and top-face dowels 13b of the 
respective stop wings 13 are fitted in a plurality of holes 14a formed in 
the rotary ring 14. An outer periphery 14b of the rotary ring 14 is 
engaged with inner surfaces of separating projections 12b located at three 
positions on the cam plate 12, so that the ring 14 is rotatably supported 
by the cam plate 12. The rotary ring 14 has a gear portion 14c, and the 
gear portion 14c is formed so as to mesh with the gear portion 3a of the 
magnet rotor 3 in the motor A. 
Further, the rotary ring 14 has a protrusion 14d, and the protrusion 14d is 
set so as to be relatively slidable in an elongated hole 11a formed in the 
annular base plate 11. The cam plate 12 has three hooks 12c in total, and 
the hooks 12c are engaged with three notches 11b of the annular base plate 
11 so as to sandwich the rotary ring 14, thus forming a unit of the 
annular base plate 11, cam plate 12, stop wings 13, and rotary ring 14 as 
the stop apparatus B. This stop apparatus B is provided with a switch for 
detecting whether the stop is open or not. Numeral 15 represents a spring 
of an electrically conductive member, which is a component of the switch 
and which is put in a switch mounting portion 12d integrally formed with 
the cam plate 12. One end of the spring 15 is engaged with a protrusion 
12e of the cam plate 12 and the other end is engaged with a switch pin 16. 
The switch pin 16 is also an electrically conductive member, which is 
caulked to the annular base plate 11 so as to be always conductive with 
the annular base plate 11. Namely, the annular base plate 11 itself 
becomes electrically grounded because the upright portion 11C is connected 
to the ground pattern of the base plate which is not shown. A terminal end 
of the spring 15 is connected to the signal pattern of the base plate. The 
switch is arranged to detect an electric signal caused by engagement 
between the spring 15 and the switch pin 16. This contact/non-contact 
arrangement of the switch is realized by making the protrusion 14d of the 
rotary ring 14 hit one end of the spring 15 so as to turn the switch off 
as interrupting the contact between the spring 15 and the switch pin 16 
when the stop becomes open. The above describes the configuration of the 
stop apparatus B. 
Next explained is the operation based on the above configuration. When the 
power is supplied through the connection terminals 4a, 4b, 5a, 5b to the 
coils 4, 5, magnetic fields are formed in the stator yokes 2, 3 to act 
with a magnetic field of the magnet rotor 3, thereby forming closed 
magnetic paths. If the power is not supplied to the coil 5, the magnetic 
path caused by the coil 4 receiving the power becomes dominant, thereby 
generating a rotating torque in the magnet rotor 1 (the same can be 
applied to the case when the power is supplied only to the coil 5). When 
the power is supplied to the both coils 4, 5, the magnetic paths are 
similarly formed in the stator yokes 2, 3 to act with the magnet rotor 3, 
thus giving the rotating torque to the magnet rotor 3. On the other hand, 
the motor is arranged to perform drive of stepping motor conventionally 
known by supplying the power to the both coils 4, 5 as successively 
switching the current directions. This rotation rotates the rotary ring 14 
by a predetermined angle through meshing between the gear portion 3a of 
the magnet rotor 3 and the gear portion 14c of the rotary ring 14. This 
rotation of the rotary ring 14 moves the top-face dowels 13b of the stop 
wings 13 in the rotating direction. Then the back-face dowels 13a of the 
stop wings 13 effect the known stop opening and closing operation by 
rocking the stop wings 13 in an opening direction or in a closing 
direction, depending upon a relative relation with the stop cams 12a 
formed in the cam plate 12, thereby effecting exposure control. 
As explained above, the present invention effects the positioning between 
the stator yokes and the fixed member by the projecting portions or 
recessed portions formed in the stator yokes per se, which can suppress 
occurrence of magnetic saturation, which used to be caused in the 
conventional motors in the positioning and supporting arrangement of the 
perforated stator yokes with the shafts of the fixed member, resulting the 
making of the regions around the holes of the stator yokes thinner. 
Therefore, the present invention is free of degradation of motor 
performance and is effective for forming a compact motor. 
The present invention is arranged to effect positioning between the stator 
yokes and the fixed member by utilizing the positioning members for 
positioning the plurality of plates of the soft magnetic material, 
necessary for stacking of the laminated stator yokes, also for positioning 
the stator yokes with respect to the fixed member, thus presenting an 
effect to provide an electromagnetic drive apparatus (motor) that can 
achieve miniaturization in a simple configuration without degrading the 
motor performance, different from the magnetic saturation generating 
structure of the stator yokes in the conventional positioning method of 
the perforated stator yokes. 
Further, the present invention employs a common arrangement to the both 
stators in a two-phase motor in which the positioning method between the 
fixed member and the stator yokes includes positioning with the projecting 
portions of one stator yoke and positioning with the recessed portions of 
the other stator yoke relative to the fixed member (in the structure of 
stator yokes in which one can obtain by turning the other over), which can 
realize the common arrangement of two stator yokes, thus obviating a need 
to newly prepare two different stator yokes, and which can expect an 
effect of cost reduction. 
The present invention can achieve an actuator fully ready for recent 
miniaturization of products by applying the configuration of the motor 
having a above effects to the stop apparatus in optical devices and 
mounting it in the products.