Disclosed herein is a swing-arm type linear d.c. brushless motor, wherein at least one coreless type armature coil such as an air-core armature coil is arranged on the inner wall of a linear motor body and a field magnet is formed by magnetizing a magnet member with a single pair of N/S poles so as to permit the generation of thrust in a predetermined direction face to face with only one active conductor of said at least one armature coil and which does not contribute to the generation of reverse thrust. The field magnet is opposite through an air-gap in the axial direction to only the active conductor portion, and is supported relatively and swingably through the air-gap. It is suitable for use in small, economical and high-speed magnetic head positioner mechanisms more useful in small-capacity magnetic disk units and the like and capable of performing position detecting, feed control, etc.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a swing-arm type linear d.c. brushless motor 
(hereinafter called "swing-arm type linear motor") suitable for use in a 
rotating magnetic positioner mechanism, which is useful for feeding a 
magnetic head of a magnetic disk unit having a relatively small capacity, 
or the like. 
2 Description of the Related Art 
A demand for high-density recording of information has resulted in frequent 
use of magnetic disk units. These magnetic disk units use a magnetic head 
for conducting read and write transfer of information from and into a disk 
are equipped with a magnetic head positioner mechanism for moving the 
magnetic head to a predetermined position. 
Magnetic head positioner mechanisms include both linear and rotating types. 
The former is suitable for use in large-capacity magnetic disks, and the 
latter is suitable for use in a small-and medium-capacity magnetic disks. 
A recent demand for small and/or portable units has resulted in a need for 
smaller, lower capacity and economical magnetic disk units. Also, magnetic 
head positioner mechanisms suitable therefor have been required. 
In conventional magnetic head positioner mechanisms, the following means 
are used to permit the control of the feed ratio and position of a 
magnetic head. One of plural magnetic disks is sacrificed to contain 
positional information (such a magnetic disk is so-called a "positional 
information disk") so as to control the feed ratio and position of the 
magnetic head by information detected by the magnetic head and feeding it 
back to a control system. 
However, the recent demand for small and/or portable units, has been met by 
small-size, small-capacity and economical magnetic disk units such as 
those using only one magnetic disk and those having no positional 
information disk even when plural magnetic disks have been used. 
Here, since a magnetic disk unit having no postional information disk can 
not detect the feed ratio and position of its magnetic head, it must be 
provided with some other means for this purpose. 
For such a detecting means, it has been known to use a linear potentiometer 
from which linear electric signals are output. However, it requires an A/D 
converter and hence has drawbacks in that it becomes complicated, large, 
and is costly. 
Although there is a method arranging encoder as another method, it is 
necessary to use a highly precise, large-size and expensive encorder in 
order to detect the microfeed and position of the magnetic head. It is 
hence difficult to provide a small-size, small-capacity and economical 
magnetic disk unit. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a small-size and economical 
swing-arm type lines motor suitable for use in a small, economical and 
high-speed magnetic head positioner mechanism more useful in 
small-capactiy megnetic disk units and the like and capable of performing 
position detecting, feed control and so forth. 
Another object of this invention is to provide a small-size and economical 
swing-arm type linear motor having a high-speed linear magnetic encoder 
capable of effecting position detecting, feed control, etc. with extreme 
ease and high precision in a magnetic disk unit making use of as few as 
only one magnetic disk, for example, a small-capacity magnetic disk unit 
making of no positional information disk. 
The principal of this invention is accomplished by providing a swing-arm 
type linear motor comprising at least one coreless type armature coil such 
as an air-core type armature coil arranged on the inner wall of a linear 
motor body; and a single magnetic pole type field magnet formed by 
magnetizing a magnet member with a single pair of N/S poles as to permit 
the generation of thrust in a predetermined direction with only one active 
conductor portion, which does not contribute to the generation of reverse 
thrust, of said at least one armature coil, said field magnet opposite 
through an air-gap in the axial direction to said one active conductor 
portion, and being supported swingably through the air-gap. 
Other objects of this invention are attained by the following means: (1) 
said at least one armature coil is formed as two air core type coils 
arranged adjacently so as not to overlap each in a position opposite to 
the field magnet, thereby obtaining required thrust only by adjacent 
active conductor portions, which do not contribute to the generation of 
reverse thrust, of the two armature coils, and the width of the magnetic 
pole of the field magnet is defined more narrowly than that between both 
conductor portions positioned on the outer sides of the two armature 
coils; (2) the field magnet is formed so as to have almost the same width 
as that of the armature coil; (3the field magnet is formed by magnetizing 
a portion of a flat magnet member swingably supported with one pair of N/S 
poles, said portions of the magnet member facing one available conductor 
portion not contributing to the generation of reverse thrust; (4) the 
magnet member having the field magnet is joined with a rotating shaft 
supported swingably at a position on which the magnetic pole forming the 
field magnet is not magnetized; (5) the portion, which is not magnetized 
with the field magnet, of the magnet member is extended to form integrally 
a magentic head attaching part projecting from the swing-arm type linear 
motor body; (6) a plurality of fine-pitch magnetic poles are formed on the 
predetermined positions of the magnet member forming the field magnet in 
such a manner that circumferentially-adjacent magnetic poles are different 
in pole from another, so as to form linear magnetic encoder magnetic poles 
and a magnetic sensor adapted to obtain magnetic encoder signals of at 
least A phase and B phase is arranged at a fixed position facing the 
linear magnetic encoder magnetic poles through a space, whereby a linear 
magnetic encoder is composed with the linear magnetic encoder magnetic 
poles and the magnetic sensor; (7) the linear magnetic encoder magnetic 
poles are formed on a surface, which does not face the armature coil, of 
the magnet member; and (8) the linear magnetic encoder magnetic poles are 
formed on a surface, which is on the same plane as that facing the 
armature coil, but does not form the field magnet, of the magnet member. 
The above and other objects features and advantages of the present 
invention will become apparent from the following description and appended 
claims, taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
In the following embodiments, swing-arm type linear motors having a linear 
magnetic encoder formed therein will be described. If it is not desired to 
use the linear magnetic encoder, it is only necessary to form no linear 
encoder magnetic pole constituting the linear magnetic encoder on a magnet 
member. 
First Embodiment of the Invention 
FIG. 1 illustrates a vertical cross-sectional side view of a swing-arm type 
linear motor 1 having a linear magnetic encoder according to the first 
embodiment of this invention. FIGS. 2 and 3 are explanatory illustrations 
illustrating the facing relation between armature 5-1, 5-2, 6-1, 6-2 and a 
field magnet 12 and the shapes thereof applicable to the swing-arm type 
linear motor 1 shown in FIG. 1. FIG. 4 is a partially cutaway perspective 
view of the swing-arm type linear motor 1 shown in FIG. 1. The swing-arm 
type linear motor 1 according to the first embodiment of this invention 
will hereinafter be described by reference to FIGS. 1 to 4. 
A body 2 of the swing-arm type linear motor 1 having a linear magnetic 
encoder is formed in the shape of an elongated and squared C in vertical 
section and in the shape of a fan in plan by elements 2a and 2b composed 
of a magnetic material. Sidewalls 2c and 2d are formed on both sides of 
the element 2a and an opening 3 is defined betweeen both sidewalls 2c and 
2d. 
As illustrated in FIGS. 2 through 4, two sets of each two adjacent air-core 
type armature coils 5-1 and 5-2 as wall as 6-1 and 6-2 formed in the shape 
of a flat sectorial frame are arranged respectively on the lower side and 
the upper side of the elements 2a and 2b facing an inner space 4 of the 
body 2 of the swing-arm type linear motor 1. A first stator armature 5A is 
composed by the armature coils 5-1, 5-2, while a second stator armature 6A 
is composed by the armature coils 6-1, 6-2. A field magnet 12, which will 
be described subsequently, is swung realtively and reciprocally in an 
air-gap 16 between the stator armatures 5A and 6A. Namely, this embodiment 
indicates a linear d.c. brushless motor of a double-side exciting 
structure. 
In these armature coils 5-1, 5-2, 6-1, 6-2, respectively one active 
conductor portion 5-1b, 5-2a, 6-1b, 6-2a extending radially from a fixing 
a shaft 7 as center, which will be described subsequently, and generates 
no reverse thrust but contribute to the genration of thrust in desired 
directions. 
Conductor portions 5-1c, 5-1d, 5-2c, 5-2 d, 6-1c, 6-1d, 6-2c, 6-2d, 
oriented in the circumferentail direction, do not contribute to the 
generation of thrust and are thus inactive. 
Other active conductor portions 5-1a , 5-2b, 6-1a, 6-2b contribute to the 
generation of reverse thrust and serve as conductor portions contributing 
to the generation of thrust, in themselves, when they face the field 
magnet 12. However, they are not used for the generation of thrust in this 
invention. This is due to the fact that when the conductor portions 5-1a, 
5-2b, 6-1a, 6-2b face the field magnet 12, the thrust produces thereby 
acts as reverse thrust against the thrust produced by the active conductor 
portions 5-1b, 5-2a, 6-1b, armature coils 5-1, 5-2, 6-1, 6-2. 
Therefore, the field magnet 12 is caused to face only the active conductor 
portions 5-1b, 5-2a, 6-1b, 6-2a of the armature coils 5-1, 5-2, 6-1, 6-2 
so as to generate required thrust, thereby avoiding the generation of the 
reverse thrust by the conductor portions 5-1a, 5-2b, 6-1a, 6-2b. For this 
reason the conductor portions 5-1a, 5-2b, 6-1a, 6-2b are redundant. 
However, since the armature coils 5-1, 5-2, 6-1, 6-2 in such a shape can 
be formed more economically and easily than those of any other shapes, and 
the armature coils 5-1, 5-2, 6-1, 6-2 can be formed at a low cost compared 
with a magnet member 11 as described below, the flat magnet member 11, 
composed of a material as described below, the armature coils 5-1, 5-2, 
6-1, 6-2 are used as a swinger and stators, respectively, in this 
invention. 
A cylindrical rotating shaft 8 around the above fixing shaft 7 is 
swingably, supported by means of bearings 9, 10 provided respectively in 
both upper and lower ends of the inner periphery of the rotating shaft 8. 
To the rotating shaft 8, the magnet member 11 is fixed at a below 
described portion not magnetized with the field magnet 12. Almost the half 
of the magnet member 11, which is defined by the rotating shaft 8 as a 
boundary and is facing the above-described stator armatures 5A, 6A, is 
formed as a sectorial part 11A so as to form the field magnet 12. The 
remaining portion of the magnet member 11 is formed as a magnetic head 
guiding member 11B in the shape of an elongated plate, which is adapted to 
attach a magnetic head for reading and writing the information of magnetic 
disks in a magnetic disk unit (not illustrated) on its front end. The 
rotating shaft 8, which serves as a support, swingably supports the magnet 
member 11 in such a manner that the outer portions of both sectorial part 
11A and magnetic head guiding member 11B move along arc-shaped tracks 
having the rotating shaft 8 as a center. 
The sectorial part 11A of the magnet member 11 is magnetized with N and S 
poles on its upper and lower surface, respectively, to form the field 
magnet 12 having a single pair of poles. Of course, such magnetization may 
be turned the other way. The reason why the field magnet 12 is not formed 
into two or more alternating N and S magnetic poles adjacent to each other 
on one plane is that if a magnet material almost equal in size to the 
sectorial part 11A, which acts as a swinger, is magnetized with two or 
more alternating poles, the swing stroke of the field magnet 12 as the 
swinger can not be made long. When a field magnet is formed into two or 
more alternating magnetic poles, a sectorial part forming the field magnet 
must be made larger, resulting in a drawback that responsiveness to field 
flux becomes poor. 
The field magnet 12 (sectorial part 11A) in the present embodiment is 
formed so as to have an opening angle smaller than the angle between both 
outer sides of the active conductor portions 5-1a or 6-1a of the armature 
coil 5-1 or 6-1 and the active conductor portion 5-2b or 6-2b of the 
armature coil 5-2 or 6-2. Therefore, field magnet 12 may not be forced 
substantially with reverse thrust generated by the conductor portions 
5-1a, 5-2b, 6-1a, 6-2b, of the armature coils 5-1, 5-2, 6-1, 6-2. Namely, 
while reciprocally swinging, the field magnet 12 faces either the active 
conductor portions 5-1b and 6-1b or 5-2a and 6-2a of the armature coils 
5-1, 5-2, 6-1, 6-2 get thrust without fail. The armature coils 5-1 and 6-1 
as well as 5-2 and 6-2 are electrically connected so as to successfully 
generate thrust in the same direction without fail by the active conductor 
portions 5-1b and 6-1b or 5-2a and 6-2a of the armature coils 5-1 and 6-1 
or 5-2 and 6-2 when electric current is caused to flow therein. 
A plurality of fine-pitch alternating N and S magnetic poles are magnetized 
on the peripheral surface of the sectorial part 11A, which is 
perpendicular to the plane forming the field amount magnet 12 of the 
magnet member 11, in such a manner that adjacent magnetic poles are 
different in pole from each other along the circumferential direction and 
each magnetic pole is oriented in radial direction, so as to form linear 
magnetic encoder poles 13. A magnetic sensor capable of detecting magnetic 
encoder signals of A phase and B phase, for example, a magnetroresistance 
element (MR sensor) 15, is arranged on an inner sidewall of the element 
2a, which is opposite to the linear magnetic encoder magnetic poles 13 
through a space 14. 
A linear magnetic encoder is composed with the linear magnetic encoder 
magnetic poles 13 and the magnetroresistance element 15. 
The output from the magnetroresistance element 15 is transmitted to a 
control circuit system through a lead wire not illustrated. 
Therefore, when the stator armatures 5A and 6A are energized and controlled 
by signals from the control circuit system, the field magnet 12 gets 
thrust in a predetermined direction and magnitude and hence swings in a 
predetermined direction and to a predetermined position, whereby a 
magnetic head (not illustrated) attached to the other half portion of the 
magnetic member 11, i.e. , the magnetic head guiding member 11B is swung 
to a prescribed position. By the swing of the field magnet 12, the linear 
magnetic encoder magnetic poles 13 are swung relatively to the 
magnetroresistance element 15. Accordingly, magnetic encoder signals 
detected by the magnetroresistance element 15 allow the field magnet 15 to 
make the controlled movement in the predetermined direction through a 
closed loop, thereby successfully swing the magnetic head under control to 
a position in a predetermined direction at a prescribed rate. 
It may be noted that in the case of above-described linear magnetic 
encoder, even when the magnetizing precision of the linear magnetic 
encoder magnetic poles 13 is relatively rough, no problem will be caused 
by making use of a means for electrically improving its resolution which 
have been devised variously. 
Second Embodiment of the Invention 
FIG. 5 is a vertical cross-sectional side view of a swing-arm type linear 
motor 51 having a linear magnetic encoder according to the second 
embodiment of this invention. FIGS. 6 and 7 are explanatory illustrations 
illustrating the facing relation between armature coils 5-1, 5-2, 6-1, 6-2 
and a field magnet 12 and shapes thereof and the region of linear magnetic 
encoder magnetic poles 63 as to the swing-arm type linear motor 51 shown 
in FIG. 5. FIG. 8 is a partially cutaway perspective view of the swing-arm 
type linear motor 51 shown in FIG. 5. 
The swing-arm type linear motor 51 equipped with a linear magnetic encoder 
according to this embodiment is different from the linear motor 1 in that 
the linear magnetic encoder magnetic poles 63 formed on a region of a 
surface, which is on the same plane as that formed with the field magnet 
12, but is not formed with the field magnet 12, of a magnet member 11, and 
a magnetroresistance element 15 is arranged on an inner top wall of the 
element 2a, which is opposite to the linear magnetic encoder magnetic 
poles 63 through an air gap 66, thereby composing the linear magnet 
encoder. However, since other structures therein are the same as those of 
the swing-arm type linear motor in the first embodiment, their structures 
are designated by the same reference characters and their description will 
be omitted. 
In the case of the second embodiment, linear magnetic encoder signals for Z 
phase can be obtained with ease. Therefore, it is convenient to magnetize 
with linear magnetic encoder magnetic poles for Z phase in advance and to 
arrange a magnetroresistance element capable of obtaining linear magnetic 
encorder signal for Z phase in addition to the linear magnetic encoder 
signals of A phase and B phase. 
Modified Emobodiments 
Although the swing-arm type linear motors 1 and 51 having a double-side 
exciting structure, in which the stator armatures 5A, 6A are arranged on 
both sides opposite to the field magnet 12, and having a linear magnetic 
encoder have been described in the above-mentioned embodiments, the linear 
motors may have a single-side exciting structure wherein any one of the 
stator armatures 5A and 6A is arranged on only one side. 
Although the cases, where the magnetroresitance elements have been used as 
the magnetic sensors for the linear magnetic encoder, have been described, 
a Hall element, Hall IC, magnetic head or the like may be used as a 
magnetic sensor. However, if two magnetic sensors are required in order to 
obtain magnetic encoder signals of both A phase and B phase, such sensors 
must be arranged with a phase difference of 90 degrees in terms of 
electric angle to each other. 
Although the most desirable cases, wherein two air-core type armature coils 
have been arranged adjacently so as not to overlap each other on a plane, 
have been described in the above embodiments, three or more of armature 
coils may be used or they may also be arranged so as to overlap each other 
if the armature coils are arranged so that conductor portions contributing 
to the generation of reverse thrust are not be positioned where they come 
to face the field magnet. Alternatively, only one armature coil may be 
used if desired thrust can be obtained thereby. 
The stator armatures composed by the air-core type armature coils, which 
were formed by winding a wire, have been described. However, those 
composed by sheet coils, which have been formed by a means such as etching 
or punching of a conductor, or printed coils, etc. may be used if coreless 
armatures can be composed thereby. 
Furthermore, both field magnet and linear magnetic encoder magnetic poles 
have been formed on the magnet member in each of the above embodiments. In 
each case, a yoke material may be interposed between the field magnet and 
the linear magnetic encoder magnetic poles so that the strong magnetic 
force of the field magnet does not adversely affect the magnet member. 
Alternatively, a yoke material may be laminated on a magnet member to be 
magnetized with a field magnet and a member for forming linear magnetic 
encoder magnetic poles may be affixed on the yoke material. 
ADVANTAGES OF THE INVENTION 
The swing-type linear motors according to this invention are coreless type 
linear d.c. brushless motors. Therefore, they can reciprocally swing 
smoothly and fast without cogging. When used in a magnetic head 
positioner, the swing-arm type linear motor allows a magnetic head to move 
smoothly and fast to a desired position. In addition, it is expected to 
lengthen their span of life because they have a brushless motor structure. 
Moreover, since the swing-arm type linear motors of this invention make 
effective use of magnet materials whose performance has been increasing of 
late years in particular, they can generate large thrust though they are 
relatively small, although their structures become very simple. In 
addition, the swing-arm type linear motors have an effect that units of 
good performance can be composed at a low cost and in a small size. 
Furthermore, the swing-arm type linear motors have been composed by the 
magnet member as a swinger, on which the field magnet of a sole magnetic 
pole structure has been formed, and the air-core type armature coils as 
stators. They hence have an advantage that it is possible to make their 
stroke relatively long though they are of small sizes. 
In particular, high-powered magnets, such as neodymium-boron-iron type 
magnets, having a thickness no more than about 1 mm, but possessing high 
magnetic force have been produced in recent years. The practice of the 
predetermined magnetization by making use of such a strong magnet material 
makes the present invention more useful. 
By making use of the swing-arm type linear motors having the linear 
magnetic encoder according to this invention, magnetic head positioner 
mechanisms can be composed at a low cost and in a small size without 
provision of a large-size and expensive linear potentiometer or encoder 
and without sacrificing one of plural magnetic disks to detect the feed 
ratio and position of the magnetic head. 
Having now fully described the invention, it will be apparent to one of 
ordinary skill in the art that many changes and modifications can be made 
thereto without departing from the spirit or scope of the invention as set 
forth herein.