Direct current motor

A direct current motor comprising the field magnet pole of a permanent magnet and an armature having a plurality of armature windings. The field magnet pole has at least four magnetic poles and the angular spacing is equal to 360 degrees divided by the number of the magnetic poles, and at least one of the armature windings has an angular spacing which is (2n - 1) times the width of the field magnet pole, where n is a positive integer of 2 or more, and control means for successive switching, rendering said armature windings conductive, is provided.

BACKGROUND OF THE INVENTION 
The present invention relates to a direct current motor and more 
particularly to a direct current motor provided with armature windings 
with a specific angular space. 
Recently, various types of direct current motors have been proposed. Most 
of them employ lap windings or wave windings, and, in other improved 
direct current motors, only part of the lap windings or the wave windings 
has been improved, and they have various drawbacks including that the wow 
and flutter characteristics are poor (U.S. Pat. Nos. 4,107,587 and 
4,227,107). 
SUMMARY OF THE INVENTION 
The above-described drawbacks in the prior art direct current motors have 
been successfully eliminated by the present invention. 
An object of the present invention is to provide a direct current motor 
with armature windings whose construction is free from the conventional 
principles of lap windings and wave windings. 
Another object of the present invention is to provide a direct current 
motor of the type described, with high torque ripple frequencies and less 
mechanical and electrical noise in comparison with the conventional direct 
current motors. 
According to the present invention, in order to attain these objects, in a 
direct current motor with an armature having a plurality of armature 
windings, which is rotatable relative to the field magnet poles of a 
permanent magnet, the number of the field magnet poles is four or more and 
the angular space is equal to 360.degree. divided by the number of 
magnetic poles, and at least one of the armature windings has an angular 
space which is (2n-1) times the width of the field magnet poles, where n 
is a positive integer of 2 or more. The direct current motor according to 
the present invention is further provided with control means for 
successive switching, rendering the armature windings conductive. 
These and other objects of the invention will become apparent from the 
following description of embodiments thereof when taken together with the 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a cross section of a semi-conductor 
motor according to the present invention. Reference numeral 1 represents a 
magnet rotor, which is fixed to a rotating disc 2 by an adhesive. The 
rotating disc 2 serves as a support member for supporting the magnet rotor 
1 which constitutes a field magnet pole and to close the magnetic path of 
the magnet rotor 1. By press-fitting a boss 3 into the central portion of 
the rotating disc 2 and also press-fitting a rotating shaft 4 into the 
central portion of the boss 3, the magnet rotor 1, the rotating disc 2, 
the boss 3 and the shaft 4 are united integrally. Armature windings 5 are 
disposed so as to face the magnet rotor 1 and are fixed to the upper 
surface of a bottom plate 6 by an adhesive. In the outer peripheral 
portion of the bottom plate 6, there are formed holes 6-1 and 6-2 through 
which the bottom plate 6 may be mounted on a support (not shown). A boss 8 
is press-fitted into the central portion of the bottom plate 6, and the 
boss 8 is provided with bearings 9 and 10. The bearings 9 and 10 are made 
of a oil-less metal, each having an opening portion in the central portion 
thereof, whereby the rotating shaft 5 can be passed through the bearings 9 
and 10, and the magnet rotor 1, the rotating disc 2, the boss 3 and the 
shaft 4 can be rotatably supported. 
Referring to FIG. 2, there is shown a developed view of an example of the 
magnetic rotor 1 and the armature windings 5 which constitute the 
essential portions of the D.C. motor according to the present invention. A 
motor which is constructed of two magnetic poles 1-1 and 1-2 which are 
encircled by the dotted line 11, and armature windings 12 and 13 indicated 
by the dotted lines in the figure, is a conventional two-phase motor. The 
armature windings 12 and 13 are superimposed on each other. The angular 
spacing of each of the armature windings 12 and 13 is the same as that of 
the magnet rotors 1-1 and 1-2 which constitute the field magnet poles. 
Therefore, when the magnet rotor 1 has 8 magnetic poles, the angular 
spacing of one pole is 45 degrees, so that the angular spacing of the 
armature windings is also 45 degrees (360.degree./8=45.degree.). 
Furthermore, these armature windings are superimposed in double layers. As 
the number of poles of the magnet rotor increases, the angular spacing of 
the armature windings has to be decreased, so that production of such 
armature windings is difficult in practice. In particular, if the armature 
windings have to be superimposed on each other, producing such armature 
windings will become more difficult. 
Therefore, according to the present invention, the angular spacing of the 
armature windings can be set in an easy manner for production thereof 
without superimposing the armature windings. Specifically, an armature 
winding fraction 12B is phase-shifted at the in-phase position of the 
magnet rotor 1, so that the armature winding fraction 12B is located at a 
position 5-1B. Furthermore, an armature winding fraction 13A of an 
armature winding 13 is phase-shifted at the in-phase position of the 
magnet rotor 1, so that the armature winding fraction 13A is located at a 
position 5-2A. An armature winding fraction 13B is also phase-shifted at 
the in-phase position of the magnet rotor 1, so that the armature winding 
fraction 13B is located at a position 5-2B. Thus, the armature windings 
5-1 and 5-2 are capable of performing exactly the same function as that of 
the armature windings 12 and 13. The angular spacing of each of the 
armature winding 5-1 and 5-2 is 135 degrees, which is three times the 
angular spacing of each of the armature windings 12 and 13 (i.e., 2n-1=3, 
when n=2). In this case, both the armature windings are phase-shifted to 
treble the angular spacing. However, the angular spacing can be trebled by 
phase-shifting either of the armature windings 12 or 13. 
Another method of accomplishing the present invention will now be 
explained. 
If the armature windings are arranged with respect to a magnet rotor having 
8 magnetic poles in the conventional manner as shown in FIG. 2, armature 
windings 12, 13, 14, 15, 16, 17, 18 and 19 and at least 8 double windings 
are required. In one end of the armature winding 12 and in the opposite 
end of the armature winding 14, the phase of the current which flows 
through them is the same, but the direction of the flow of the current is 
opposite. Therefore, one armature winding 5-1 is formed by connecting the 
armature windings 12 and 14 to each other. Likewise, in one end of 
armature winding 17 and in the opposite end of the armature winding 19, 
the phase of the current which flows through them is the same, but the 
direction of the flow of the current is opposite. Therefore, another 
armature winding 5-2 is formed by connecting the armatures 17 and 19 to 
each other. Since the armature windings 13, 15, 17 and 19 are shifted by 
90 degrees of electrical angle relative to the armature windings 12, 14, 
16 and 18, the armature winding 5-1, which is prepared by synthesizing the 
armature winding 12 and the armature winding 14, is shifted by 90 degrees 
of electrical angle relative to the armature winding 5-2 which is prepared 
by synthesizing the armature winding 17 and the armature winding 19. 
FIG. 2A is a view similar to FIG. 2 in which it is emphasized that the 
angular spacing of each of the armature windings, for example, winding 
fractions 12A and 12B, is the same as that of each of the field magnet 
poles 1-1. Torques produced at the fractions 12A and 12B are in the same 
direction because the polarities of the magnetic poles facing the winding 
fractions are in opposite directions. Under Fleming's left-hand rule, 
rotation of the motor is thus achieved. 
Position sensors 7-1 and 7-2 are Hall devices. A voltage is applied to the 
voltage-applying terminals 20, 21, 22 and 23 of the Hall devices through 
resistors 24, 25, 26 and 27. One output terminal 28 of the Hall device 7-1 
is connected to the base of a transistor 33 through a resistor 32, while 
the other output terminal 29 of the Hall device 7-1 is connected to the 
base of a transistor 35 through a resistor 34. One output terminal 30 of 
the Hall device 7-2 is connected to the base of a transistor 37 through a 
resistor 36, while the other output terminal 31 of the Hall device 7-2 is 
connected to the base of a transistor 39 through a resistor 38. A 
collector of the transistor 35 is connected to the base of a transistor 41 
through a resistor 40. A collector of the transistor 39 is connected to 
the base of a transistor 43 through a resistor 42. 
Therefore, when output signals are generated at the output terminal 28 of 
the Hall device 7-1 and at the output terminal 30 of the Hall device 7-2, 
the transistors 33 and 37 are energized (ON), and an electric current 
flows from a grounded power source 44 to a negative power source 45 
through the armature windings 5-1 and 5-2. On the other hand, when output 
signals are generated at the output terminal 29 of the Hall device 7-1 and 
at the output terminal 31 of the Hall device 7-2, the transistors 35 and 
39 are energized (ON), and, accordingly, the transistors 41 and 43 are 
also energized (ON), so that the electric current flows from a positive 
power source 46 to the grounded power source 44 through the armature 
windings 5-1 and 5-2. This conduction switching is performed successively 
with a phase difference of 90 degrees of electric angle. Therefore, the 
magnet rotor is rotated, generating torque. In the state shown in FIG. 2, 
an output signal is generated at the output terminal 30 of the Hall device 
7-2, so that the transistor 37 is energized (ON) through the resistor 36, 
and the electric current flows from the grounded power source 44 to the 
armature winding 5-2 in the direction of the arrow, so that the magnet 
rotor is rotated, generating torque. 
This embodiment has been explained by use of the transistors. However, it 
is apparent that other semi-conductor switching elements can be employed 
in place of the transistors. The same thing applies to other embodiments 
according to the present invention, which will be mentioned hereinafter. 
Referring to FIG. 3, a further embodiment of a D.C. motor according to the 
present invention will now be explained. The main differences between the 
motor in FIG. 2 and the motor in FIG. 3 are that, in the motor in FIG. 3, 
the number of poles of the magnet rotor is greater, and further that, in 
the motor in FIG. 2, the armature windings are rendered conductive 
reciprocatively by use of a two-power source system, while, in the motor 
in FIG. 3, one-way conduction is performed by use of a 
four-armature-windings system. The specific reasons for those differences 
will now be explained. 
When a D.C. motor is employed for driving a direct turntable or for direct 
driving of cassette tapes, the wow and flutter characteristics are greatly 
affected by the cogging and torque ripples of the D.C. motor itself. The 
cogging can be avoided by making the motor coreless. The simplest and 
least expensive way to avoid the torque ripples is to absorb the high 
frequency torque ripples by mechanical inertia by increasing the switching 
frequency as much as possible. Therefore, in this embodiment, in 
comparison with the motor in FIG. 2, the number of magnetic poles is 
increased to 18 in FIG. 3. In fact when making the motor in practice, the 
number of magnetic poles was further increased to 60. However, since it is 
difficult to make a drawing of the circuits in that case, in the 
embodiment shown in FIG. 3 the number of magnetic poles is 18. 
Referring to FIG. 4, there is shown the magnetization of the magnet rotor 
1. As can be seen from the figure, the angular spacing of the 
magnetization of one magnetic pole is 20 degrees (360.degree./18). 
According to a conventional arrangement of armature windings, double 
layered armature windings are arranged with 20 degrees of angular spacing 
as shown in FIG. 6. As mentioned previously, in this embodiment the number 
of magnetic poles is 18 since the illustration of a magnet rotor having 
more than 18 magnets is very difficult. As a result, the angular spacing 
of each of the armature windings is 20 degrees, so that each armature 
winding appears to be in a fan shape and conventional winding can be 
easily done. However, in the case where the magnet rotor has 60 magnetic 
poles and the angular spacing is 6 degrees, the winding may be done as if 
it is done around an almost rectangular member and, actually, when such 
coiling is done, the portions indicated by reference numerals 47 and 48 in 
FIG. 6 bulge out, deviating from an ideal shape. Further, it is impossible 
to make an ideal arrangement of those improperly shaped armature windings. 
Therefore, formation of the armature windings in a shape for performing 
winding easily, by increasing the angular spacing thereof, and a simple 
arrangement method for the armature windings, are desired. 
The angular spacing of the armature windings in the case where the magnet 
rotor has 18 magnetic poles as shown in FIG. 3 will now be explained. When 
winding is performed in a conventional armature winding procedure, the 
armature windings are superimposed in double layers as indicated by the 
dotted lines 49 and 52 and the magnet rotor 1 is rotated as a four-phase 
semi-conductor motor. Here attention is paid to the armature winding 
fractions 49-A, 49-B, 50-A, 50-B, 51-A, 51-B, 52-A and 52-B which generate 
torque of the armature winding 49 and 52. The armature fractions 49-A to 
52-B generate torque in the same direction, even if they are shifted to an 
in-phase position with respect to the magnet rotor 1, so long as the 
current flow direction is the same. Therefore, an armature winding 53 can 
be made by shifting the armature winding fraction 49-B to a position 
indicated by reference numeral 53-B and by connecting the armature winding 
fraction 49-B to the armature winding fraction 49-A. Thus, an armature 
winding having an angular space which is three times the angular space of 
the armature winding 49 (i.e., 2n-1=3, when n=2) is achieved. As a matter 
of course, the armature winding fraction 49-B can be shifted to 53-C and 
to 53-D. In this case, the armature windings whose angular spaces are an 
odd number of times the angular space of the armature winding 49, such as 
5 times (2n-1=5, when n=3) or 7 times (2n-1=7, when n=4), can be 
successively obtained. 
As in the case where the armature winding fraction 49-B is shifted, the 
armature winding fraction 50-A is shifted to a position indicated by 
reference numeral 54-A, and the armature windinng fraction 50-B to a 
position indicated by reference numeral 54-B, whereby an armature winding 
54 can be obtained. 
Furthermore, by shifting the armature winding fraction 51-A to a position 
indicated by reference numeral 55-A, and the armature winding fraction 
51-B to a position indicated by reference numeral 55-B, an armature 
winding 55 can be obtained. Furthermore, by shifting the armature winding 
fraction 52-A to a position indicated by reference numeral 56-A, and the 
armature winding fraction 52-B to a position indicated by reference 
numeral 56-B, an armature winding 56 can be obtained. 
The thus obtained armature windings 53 to 56 can be rendered conductive by 
four-phase conduction in exactly the same manner as in the case where the 
armature windings 49 to 52 are employed. Therefore, one terminal of each 
of the armature windings 53 to 56 is connected to a positive power source 
terminal 57, and the other terminals of the armature windings 53 to 56 are 
respectively connected to the collectors of the transistors 58 to 61, 
while the emitters of the transistors 58 to 61 are connected to a negative 
power source terminal 58. As mentioned previously, the transistors 58 to 
61 are for controlling the four-phase conduction. In the arrangement of 
the armature windings shown in FIG. 3, a hole is formed in the central 
portion of a winding frame for the armature windings, since the angular 
space of the armature windings is increased, so that the armature windings 
are secured to the bottom plate 6 shown in FIG. 1 by screws through the 
hole. According to this method, the armature windings can be easily 
arranged properly, so long as the accuracy of the above-mentioned members 
is high. Further, the angular spaces of the armature windings can be made 
large. Consequently, an ideal arrangement of the armature windings can be 
accomplished almost in an ideal shape. 
In the case where the armature windings can be disposed by regulating their 
positions in a well known way, without employing the winding frame, the 
position sensors, such as Hall devices, or the one chip semi-conductor 
switching elements, can be secured to the holes of the armature windings. 
The advantages of the present invention will now be further explained. The 
angular spaces of the armature windings that can be actually wound range 
from about 30 degrees to 90 degrees. Therefore, in the conventional magnet 
rotor which is in conformity with the above-mentioned angular spaces, the 
maximum number of magnetic poles is 12. In such a magnet rotor, if the 
electric current which flows through the armature windings is switched by 
the conventional switching method, torque ripples take place due to the 
low switching frequency, and such torque ripples cannot be eliminated by 
mechanical inertia. As a result, the wow and flutter characteristics are 
considerably degraded. In order to prevent this, the current curve of the 
electric current which flows through the armature windings is controlled 
so as to reduce the torque ripples, thereby improving the wow and flutter 
characteristics. Therefore, motors for use with acoustic apparatus, such 
as direct-drive turntables, are very expensive due to the above-mentioned 
control problems. 
However, according to the present invention, the angular spaces of the 
armature windings can be increased as shown in FIG. 5 and the number of 
magnetic poles of the magnet rotor 1 can be increased significantly. For 
example, as mentioned previously, the number of the magnetic poles of the 
magnet rotor 1 can be increased to 60, and the angular space of the 
armature windings can be made 6.times.(2n-1) degrees, where n is a 
positive integer of 2 or more. Therefore, although the waveform of the 
current which flows through the armature windings is in the shape of 
square waves, the frequency of the torque ripples is so high that the 
torque ripples can be absorbed by the mechanical intertia. As a result, 
according to the present invention, the advantage of remarkably improving 
the wow and flutter characteristics can be achieved successfully. 
Conventionally, in order to increase the rotation accuracy of the magnet 
rotor, a feed-back mechanism is employed for the control of the rotation 
of the magnet rotor. However, according to the present invention, a motor 
having excellent wow and flutter characteristics can be obtained even if 
the motor is rotated in a similar rotation principle to that of a 
synchronization motor by applying an input with a pretermined frequency to 
the motor. Furthermore, the motor according to the present invention has 
advantages with respect to production efficiency over the prior-art 
motors. 
The present invention is not limited to two-phase and four-phase motors, 
but it can be applicable to three-phase and other motors. 
Referring to FIG. 7, a further embodiment of a D.C. motor according to the 
present invention, which is a three-phase motor, will now be explained. In 
the three-phase motor, the angular space of the field magnets is 
360.degree./14.div.25.7.degree.. When the three-phase winding is performed 
in accordance with the conventional lap winding procedure, the armature 
windings are superimposed on each other as indicated by the broken lines 
in FIG. 7, and the angular space of the armature is limited to 
360.degree./14 degrees. In contrast to this, in the present invention, an 
armature winding fraction 62-B of an armature winding 62 is shifted to the 
magnetic field of the magnet rotor 1 and located at a position indicated 
by reference numeral 65-B, and an armature winding fraction 62-A is 
connected to an armature winding fraction 65-B, so that an armature 
winding 65 is obtained. An armature winding fraction 63-A of the armature 
winding 63 is shifted to a position indicated by reference numeral 66-A, 
and an armature winding fraction 63-B is shifted to a position indicated 
by reference numeral 66-B and an armature winding fraction 66-A and an 
armature winding fraction 66-B are connected to each other, so that an 
armature winding 66 is obtained. Furthermore, an armature winding fraction 
66-A of an armature winding 64 is shifted to a position indicated by 
reference numeral 67-A, and an armature winding fraction 64-B is shifted 
to a position indicated by reference numeral 67-B, and an armature winding 
fraction 67-A and an armature winding fraction 67-B are connected to each 
other, so that an armature winding 67 is obtained. The angular space of 
each of the armature windings 65, 66 and 67 is three times the angular 
space of each of the armature windings 62, 63 and 64 (i.e., 2n-1=3, when 
n=2). One end of each of the armature windings 65 to 67 is connected to a 
positive power source 68, while the other ends of the armature windings 65 
to 67 are respectively connected to the collectors of transistors 69 and 
71. The emitters of the transistors 69 and 71 are connected to a negative 
power source 72. The thus connected armature windings 65 to 67 are 
rendered conductive exactly in the same order as in the case of the 
armature windings 62 to 64. The phase shifting of all the armature 
windings is not necessarily required. Furthermore, it is not always 
necessary to dispose uniformly the phase-shifted armature windings. 
Therefore, the number of the magnetic poles can be increased as in the 
position indicated by broken lines such as 1-14 and 1-15 for increasing 
the torque ripple frequencies, thereby improving the wow and flutter 
characteristics. 
In all the so far explained embodiments, the present invention is applied 
to semi-conductor motors in which a magnet rotor constituting field 
magnetic poles is rotated. However, the present invention can be applied 
to a commutator motor employing a commutator and a brush for rendering 
each armature winding and, a stator constituting a field magnet pole. 
Referring to FIG. 8, there is shown an example of such a commutator motor. 
The magnet rotor and and armature windings for the motor will now be 
explained by referring to those shown in FIG. 2. The reference numerals 
common to FIG. 2 and FIG. 8 indicate substantially the same members having 
the same functions. Reference numeral 75 represents a commutator 
comprising commutator bars 75-1, 75-2, . . . , 75-16. Reference numerals 
76 and 77 represent brushes to which an electric current is supplied from 
positive and negative D.C. power sources 78 and 79. The brushes 76 and 77 
are in sliding contact with the commutator bars 75-1, 75-2, . . . , 75-16, 
so that each armature winding is rendered conductive. The commutator bars 
75-1, 75-5, 75-9 and 75-13 are electrically connected to each other by a 
conductive member. Likewise, the commutator bars 75-2, 75-6, 75-10 and 
75-14 are connected to each other, the commutator bars 75-3, 75-7, 75-11, 
75-15 are connected to each other and the commutator bars 75-4, 75-8, 
75-12 and 75-16 are connected to each other, by conductive members. In the 
arrangement shown in FIG. 8, electric current flows through the armature 
winding 5-2 in the direction of the arrow, generating torque, so that each 
armature winding and the commutator 75 are rotated. The present invention 
can be applied to any other commutator motors. 
Furthermore, in the so far mentioned embodiments, the armature windings of 
a flat type are employed. However, the present invention can be applied to 
cylindrical type armature windings and to core type armatures. 
Thus, there is provided in accordance with the invention a D.C. motor which 
has the advantage discussed above. The embodiments described are intended 
to be merely exemplary and those skilled in the art will be able to make 
variations and modifications in them without departing from the spirit and 
scope of the invention. All such modifications and variations are 
contemplated as falling within the scope of the claims.