Rotary actuator

Disclosed is a rotary actuator having a rotor and a stator which rotatably supports the rotor. The stator includes a coil bobbin, a stator coil, a pair of tapered poles and a yoke. The coil bobbin is formed from a non-magnetic material into a cylindrical shape and has the stator coil wound circumferentially thereabout. The pair of poles are disposed on the internal circumference of the coil bobbin. The yoke covers the outer surface of the coil bobbin and is in contact with the respective poles. The rotor comprises a rotary shaft and a diametrically polarized cylindrical magnet. The rotary shaft is inserted into the coil bobbin and is rotatably supported by the yoke. The magnet is carried by the circumference of the rotary shaft and is rotatable integrally therewith.

This application claims the priority of Japanese Patent Application No. 
2-106263 filed on Apr. 20, 1990 which is incorporated herein by reference 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a rotary actuator utilizing a 
solenoid. More particularly, this invention pertains to a rotary actuator 
having a rotor rotational range of not more than 180.degree.. 
2. Description of the Related Art 
A rotary actuator is known which consists of a rotor having a permanent 
magnet fixed on a rotary shaft and a stator having poles disposed to 
oppose each other at an interval of 180.degree. with the rotary shaft 
therebetween (see, e.g., Japanese Unexamined Patent Publication No. 
54-34013). 
This type of rotary actuator has a stator consisting of a cylindrical coil 
bobbin with slots extending axially on the circumference thereof. A stator 
coil is axially wound around the coil bobbin and a cylindrical yoke is 
fitted to the circumference of the bobbin. The poles are formed to 
protrude from the internal circumference of the yoke. 
The polarity of the poles may be changed by switching the direction that 
the stator coil is energized. This permits the rotor to be rotated under 
the magnetic interaction between the rotor and the stator. The described 
rotary actuator also has two stoppers for limiting the rotational range of 
the rotor. 
However, the stator coil in the above rotary actuator has a hollow coil. 
That is, the center of the coil has an opening. This opening increases the 
magnetic reluctance which in turn reduces the magnetic flux density. 
Accordingly, the rotational torque provided is small relative to the coil 
current. Thus, a relatively large actuator must be used to provide a 
designate torque. 
Such a rotary actuator suffers several other problems as well. To begin 
with, it requires the use of a winding machine having a complicated 
structure since the stator coil must be wound around the coil bobbin in 
the axial direction. Thus the assembly of the stator is troublesome. 
Further, the wires connected to the coil ends are easily detached since 
they are merely secured with an adhesive tape. 
Further, the above actuator suffers the disadvantage that two stoppers are 
required and such stoppers cannot accurately regulate the rotational range 
of the rotor. 
SUMMARY OF THE INVENTION 
Accordingly, it is a primary objective of the present invention to provide 
a rotary actuator which can output a greater torque than conventional 
actuators by effectively utilizing the magnetomotive force (magnetic force 
generated by the energization of the coil). 
To achieve the foregoing and other objects and in accordance with the 
purpose of the present invention, an improved rotary actuator is provided. 
The rotary actuator has a rotor and a stator which rotatably supports the 
rotor. The stator has a coil bobbin, a stator coil, a pair of tapered 
poles and a yoke. The coil bobbin is made of a non-magnetic material 
formed in a cylindrical shape with a stator coil wound circumferentially 
thereabout. A pair of poles are provided on the internal circumference of 
the coil bobbin. The yoke encases the coil bobbin and is magnetically 
connected to each of the poles. 
The rotor has a rotary shaft and a diametrically polarized cylindrical 
magnet. The rotary shaft is inserted into the coil bobbin and is rotatably 
supported by the yoke. The magnet is provided on the circumference of the 
rotary shaft and is rotatable integrally with the rotary shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As illustrated in the drawings, a preferred embodiment of the present 
invention will be described. As shown in FIG. 1, the rotary actuator 1 
contains a housing 3 to which a bracket 2 is welded, a coil unit 4, a 
rotor 5, a bearing 6 made of a magnetic material, a cover plate 8 and a 
lever 9. 
The housing 3 has a cylindrical shape with a bottom and is made of a 
magnetic material. Once assembled, the housing 3 cooperates with the cover 
plate 8 and bearing 6 to function as a yoke for the rotor 5. The housing 3 
has a notch 12 at the upper end for allowing wires 11 to pass 
therethrough. 
The coil unit 4 consists of a substantially cylindrical coil bobbin 13 made 
of a resin and a stator coil 14 wound therebout. The coil unit is inserted 
into the housing 3. As shown in FIG. 6, the upper end of the coil bobbin 
13 has an inner wall 16 and an outer wall 17 that are integrally formed 
with a predetermined space therebetween defining a groove 15. The groove 
15 provides a space for guiding the wires 11 and for connecting the wires 
11 with the stator coil 14. 
As shown in FIGS. 1 and 6, the opposing wall surfaces of the inner wall 16 
and the outer wall 17 have two pairs of serrated portions 21,22 and 
21',22', respectively, and notches 23,24,23',24' are formed on each side 
of the serrated portions 22 and 22' so that the serrated portions 22,22' 
can undergo elastic deformation. 
As shown in FIGS. 5 and 7, a pair of poles 26,27 are secured on the 
internal surface of the coil bobbin 13. These poles 26,27 are made of 
curved plates that curve in correspondence to the internal circumference 
of the bobbin. These poles 26,27 have substantially the same shape and are 
as shown in FIG. 7. Specifically, they have an enlarged arcuate contact 
surface 26A,27A, and a narrow contact surface 26B,27B. In the embodiment 
shown a short longitudinally extending section of the pole adjacent the 
enlarged contact surface 26A,27A has the same width as the enlarged 
contact surface. The pole then tapers gradually towards the narrow contact 
surface 26B,27B. The poles are disposed to oppose each other in such a way 
that one is inverted relative to the other. The poles 26,27 are secured 
onto the internal circumference of the coil bobbin 13 so as to constitute 
portions of the internal circumference, as shown in FIGS. 5 and 6. 
It should be noted that the wider contact surface 26A of a first pole 26 is 
exposed on the upper face of the internal wall of the coil bobbin 13. In 
contrast, the contact surface 27A of the second pole 27 is likewise 
exposed on the lower face of the coil bobbin 13, as shown in FIG. 6. 
As shown in FIG. 4, when the coil unit 4 is incorporated into the housing 
3, the contact surface 27A of the pole 27 is brought into contact with the 
bottom wall of the housing 3. The bearing 6 is fitted in the upper opening 
of the coil bobbin 13 which is partially in contact with the contact 
surface 26A of the pole 26. The cover plate 8 is further fitted in the 
upper opening of the housing 3 in such a way that the lower surface 
thereof may be contacted with the bearing 6. The housing 3, the bearing 6 
and the cover plate 8 thus cooperate to constitute the yoke. 
As shown in FIG. 8, a pair of wires 11 (first lead wire 11A, second lead 
wire 11B) are inserted through the lip 28 provided on the outer wall 17 
and held respectively in the groove 15 between the serrated portions 
21,21' and the serrated portions 22,22'. These lead wires 11A,11B are 
connected to the coil ends 31,31' of the stator coil 14 by connectors 
32,32'. 
As shown in FIGS. 1 and 4, the rotor 5 consists of a rotary shaft 41 and a 
cylindrical permanent magnet 42 secured thereon. The permanent magnet 42 
is polarized diametrically. In other words, as shown in FIGS. 4 and 5, the 
portions on the circumference of the permanent magnet 42 opposing to each 
other with an angle of 180.degree. with the rotary shaft 41 therebetween 
are magnetized as north (N) and south (S) poles respectively. It should be 
noted, however, that the permanent magnet 42 is uniformly polarized in the 
axial direction. 
The rotary shaft 41 is rotatably supported by the coil bobbin 13 through 
the bearing 6 and an second bearing 34. 
As shown in FIGS. 1 and 2, a cylindrical stopper 7 protrudes from the cover 
plate 8, and a resin sheath 35 covers the circumference of the stopper 7. 
The cover plate 8 has a rim 8A. The rim 8A and the internal wall surface 
of the housing 3 define an annular groove, as shown in FIG. 4. An 
ultraviolet curing resin or the like is poured into the gap between the 
cover plate 8 and the housing 3 along the groove whereby to enhance the 
airtightness of the housing 3. 
The upper end portion of the rotary shaft 41 penetrates through the center 
hole 47 of the cover plate 8 and protrudes upward, as shown in FIGS. 2 and 
3, and a resin lever 9 is fixed thereto. The lever 9 is a member for 
transmitting the output from the rotary actuator to other members. It has 
a D-shaped hole 37 at the proximal end portion thereof. The upper end 
portion of the rotary shaft 41 has a D-shaped cross section corresponding 
to the hole 37. Under the engagement of the upper end portion of the 
rotary shaft 41 and the hole 37, the lever 9 is rotated integrally with 
the rotary shaft 41. 
A C-shaped metal bushing 36 constitutes the majority of the inner 
circumference of the hole 37. The central portion of the bushing has a 
reduced height and is engaged by nubs formed integrally with the lever. A 
protrusion 9A, also formed integrally with the lever 9 extends into the 
open portion of the C-shaped bushing to form the D shaped opening 37. 
Accordingly, the metal bushing 36 is easily fabricated without requiring 
an intricate machining process to form the D-shaped opening. 
At the proximal end portion of the lever 9, a pair of tabs 45,46 protrude 
forming a V shape. Since the stopper 7 is disposed between the two tabs 
45,46, the lever 9 and the rotary shaft 41 may be turned within the angle 
(approx. 45.degree.) defined between the tabs 45 and 46, and their 
movement is limited by the stopper 7 being brought into abutment against 
the tabs 45,46. Incidentally, since the tabs 45,46 are molded integrally 
with the lever 9 and protrusion 9A using a die or the like, the positions 
of these tabs 45,46 can be designed with high accuracy. 
Next, the operation of the rotary actuator will be described referring to 
FIG. 4. A magnetomotive force is generated upon energization of the stator 
coil 14 to magnetize, for example, the upper end of the coil bobbin 13 to 
form a N pole and the lower end thereof to form a S pole. Such 
energization forms a closed magnetic path "A" as shown with the arrows in 
FIG. 4. This closed magnetic path A starts from the cover plate 8, 
continues through the side wall of the housing 3, the bottom wall of the 
housing 3 and the pole 27. It then diametrically intersects the permanent 
magnet 42, passes into pole 26 and through the bearing 6 before it returns 
to the cover plate 8. 
The right pole 27 shown in FIG. 4 is magnetized to form a N pole and the 
left pole 26 forms a S pole in this closed magnetic path A. Thus, the S 
pole and N pole of the permanent magnet 42 are attracted to the poles 27 
and 26, respectively to turn the rotary shaft 41 and the lever 9, (in this 
case counterclockwise). When one of the tabs 45,46, (for example the tab 
45), abuts against the stopper 7, the lever 9 stops rotating. 
When the stator coil 14 is energized counterclockwise, the left pole 26 is 
then magnetized to form a N pole and the right pole 27 forms a S pole. 
This turns the rotary shaft 41 and the lever 9 in a clockwise manner. When 
one of the tabs 45,46, for example the tab 46, abuts against the stopper 
7, the lever 9 quits rotating. Thus, the rotor 5 is rotated according to 
the direction that the stator coil 14 is energized. 
Winding the stator coil 14 circumferentially around the coil bobbin 13 
provides an easier coil winding operation than conventional winding 
operations where the coil is wound axially. Further, according to this 
constitution, the number of windings can be increased to increase the 
magnetomotive force of the stator coil 14 relative to the volume of the 
coil unit 4. 
In this embodiment, no vacancy is present at the center of the stator coil 
14. Rather, a pair of poles 26,27 are provided on the internal surface, so 
that there is no substantial air gap in the closed magnetic path "A" 
running through the magnetic materials except for the very minor one 
present between the stator and the rotor. Accordingly, an enhanced 
magnetic flux density can be obtained to enable full utilization of the 
magnetomotive force of the stator coil 14. This allows the rotary shaft 41 
to output a greater torque. 
This embodiment, in which the rotational extremities of the rotary shaft 41 
and the lever 9 are regulated by the single stopper 7, allows a simple 
structure for regulating the rotational range of the lever 9. Further, the 
rotational range of the lever 9 can be fixed with high accuracy by the 
angle defined between the pair of tabs 45,46. 
In the described embodiment, the wires 11 are securely held in the groove 
15 between the serrated portions 21,22 and 21',22' formed on the inner 
wall 16 and the outer wall 17. Accordingly, the wires 11 and the stator 
coil 14 are not easily disconnected even if the wires 11 are pulled 
accidentally. 
Moreover, the notches 23,24,23',24' formed on the outer wall 17 impart 
resilience to the serrated portions 22,22' of the outer wall 17, so that 
the serrated portions 22,22' exert adequate pressure onto the wires 11 to 
securely hold them with the corresponding serrated portions 21,21', 
respectively. 
The resin sheath 35 applied on the circumference of the stopper 7 moderates 
the impact when the tabs 45,46 impinge on the stopper 7 and prevents 
abrasion of these members. 
Although only one embodiment of the present invention has been described 
herein, it will be apparent to those skilled in the art that the present 
invention may be embodied in many other specific forms without departing 
from the spirit or scope of the invention. Therefore, the present examples 
and embodiments are to be considered as illustrative and not restrictive, 
and the invention is not to be limited to the details given herein but may 
be modified within the scope of the appended claims.