Note: Descriptions are shown in the official language in which they were submitted.
~25615Z
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to a
three-phase brushless motor and, more particularly, to a
three-phase brushless motor particularly adapted for audio
and video equipment.
Description of the Background
There have been proposed heretofore flat,
miniaturized three-phase brushless motors in which the
stator coils are distributed uniformly about a stator plate
and in which the coils are connected either in series or
parallel. Some sort of electromagnetic transducer is
employed to sense the relative rotational position of the
magnetic poles on the rotor and produce appropriate
switching signals so that the proper currents can flow
through the coils arranged on the stator. One kind of
heretofore proposed brushless three-phase motor involves the
use of three such electromagnetic transducers, however, this
causes a problem when it is desired to miniaturize the motor
because the positional accuracy of the transducers is
critical and, also, the transducers occupy more than a
nominal physical space on the stator plate.
~Z5615Z
To overcome this drawback, a brushless three-phase
motor has been proposed in which only two electromagnetic
transducers are employed, with a resistive summing network
used to provide a third input for the three phases of the
stator windings. In that situation, a different problem
arises in that the waveforms of the electromagnetic
transducer elements are flattened and saturated so that the
slope ofthe summed or composite signal at the zero crossing
is made gradual, thereby leading to an increase in
rotational torque ripple of the motor.
OBJECTS AND SUMMARY OF THE INVENTION
. .
Accordingly, it is an object of the present
invention to provide a three-phase brushless motor that can
eliminate the above-noted defects inherent in the prior art.
Another object of this invention is to provide a
three-phase brushless motor that supplies an accurate drive
current to the stator coils so that rotational torque ripple
is suppressed.
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It is another object of this invention to provide
a three-phase brushless motor that can reduce rotational
torque ripple even thouqh variation exist in the
characteristics of at least two magnetic transducers
elements and the positional accuracy thereof.
It is a further object of this invention to
provide a three-phase brushless motor that is suitable for
use with a video tape recorder, an audio tape recorder, a
phonograph turntable, and the like.
According to one aspect of the present invention,
a three-phase brushless motor is provided in which two
electromagnetic transducer elements are provided to detect
the rotational position of a rotor and in which the
electromagnetic transducer elements are disposed on a stator
so as to produce a composite output signal having a phase
difference of 120 relative to the output signals of the
Fespective electromagnetic transducer elements. The outputs
from the electromagnetic transducer elements are fed to a
control signal generator that produces drive current signals
fed to the stator coils to provide rotational drive of the
motor. In such three-phase brushless motor, auxiliary
magnetic poles having opposite polarity to those o~
main magnetic poles are disposed on the vicinity a portion
of the rotor which is in opposing relationship to the
electromagnetic transducer elements mounted on the stator,
and are positioned having an electrical angle of
substantially ~45 from the boundaries between respective
North and South poles of the main magnetic poles, so that
waveforms of the composite signals and the output signals
from the electromagnetic transducer elements have a steep
slope at the zero crossing points.
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S03113
According to the three-phase brushless motor of
the present invention, because the auxiliary magnetic poles
are of the opposite polarity to those of the main magnetic
poles and are disposed in the vicinity of the opposing
portion of the rotor relative to the electromagnetic
transducer elements at a position with an electrical angle
of substantially i45 from the boundary between the North
pole and the South pole of the main magnetic poles, the
waveforms of the composite signal and the output from the
transducers themselves will have a steep slope at the zero
crossing points. Even if the various characteristics of the
electromagnetic transducer elements, as well as the
positional accuracy thereof, have a typical variation,
rotational torque ripple is still satisfactorially
suppressed.
The above and other objects, features, and
advantages of the present invention will become apparent
from the following detailed description of illustrative
embodiments thereof to be read in conjunction with the
accompanying drawings, in which like reference numerals
represent the same or similar elements.
BRIEF DESCRIPTIO~ OF THE DRA~ S
Fig. l is a cross-sectional representation of a
brushless motor known in the prior art;
Fig. 2 is a top plan view of a stator plate
~howing stator windings of a three-phase brushless motor
known in the prior art:
Fig. 3 is a schematic representation of a rotor
for use in the motor of Fig. l;
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1~56152.
Fig. 4 is a schematic diagram of a control circuit
useful in producing current pulses for driving the motor of
~ig. l;
Pig. 5 is a graphical representation of various
signal waveforms present in the circuit of Fig. 4;
Fig. 6 is a top plan view of another embodiment of
a stator plate and stator windings as known in the prior
art;
Fig. 7 is a schematic diagram of a drive circuit
similar to that of Fig. 4 intended for use with the stator
of Fig. 6;
Fig. 8 is a graphical representation of various
signal waveforms present using the drive circuit of Fig. 7;
Fig. 9 is a schematic representation of a rotor
for use in a three-phase brushless motor disclosed in the
United States Patent No. 4,585,979;
~ ig. 10 is a graphical representation of signal
waveforms found in a motor employing the rotor of Fig. 9;
~ ig. 11 is a graphical representation of signal
waveforms found in a modified motor using a rotor of Fig. 9;
Pig. 12 is a schematic representation of a rotor
for use in a three-phase brushless motor according to an
embodiment of the present invention;
Fig. 13 is a graphical representation of various
signal waveforms present in a motor employing the rotor of
Pig. 12;
Fig. 14 is a schematic representation of a rotor
for use in a three-phase brushless motor according to
another embodiment of the present invention;
.
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Fig. 15 is a schematic representation of a rotor
for use in a three-phase brushless motor according to still
another embodiment of the present invention;
Fig. 16 is a schematic presentation of a rotor for
use in a three-phase brushless motor according to yet
another embodiment of the present invention in which
rotational position detecting elements are provided;
Fig. 17 is a schematic representation of a
cylindrical rotor according to an embodiment of the present
invention;
Fig. 18 is a schematic representation of a
cylindrical rotor according to another embodiment of the
present invention;
Fig. 19 is a schematic representation of a further
embodiment of a cylindrical rotor according to the present
invention in which a rotational position detecting element
is employed;
Fig. 20 is a schematic representation of still a
further cylindrical rotor according to the present
invention;
Fig. 21 is a schematic representation of a flat
rotor for use in a three-phase brushless motor according to
an embodiment of the present invention; and
Fig. 22 is a schematic representation of a flat
rotor for use in a flat three-phase brushless motor
according to a further embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Fig. 1 is a cross-sectional representation of a
known three-phase brushless motor that is particularly
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adapted for miniaturization and has a generally flat
profile. More particularly, a stator 1 is provided in
opposition to rotor 2 that is mounted on a rotary shaft 3.
The stator l is formed on a base plate 4, which is shown in
more detail in Fig. 2. As seen in Fig. 2, the stator 1 is
provided with base plate 4 that is substantially circular in
shape and has six flat stator coils Ll, L2,...L6 mounted on
base plate 4, so as to have or encompass an equal angular
range, which is shown for example in Fig. 2 as being a 60
geometrical angle. The electrical arrangement relative to
the several flat stator coils is such that the opposing
coils are electrically connected either in series or in
parallel to each other, for example, coils Ll and L4 are
connected, coils L2 and L5 are connected and coils L3 and L6
are connected.
The details of rotor 2 are shown in Fig. 3, in
which it is seen that rotor 2 is formed of a disc shaped
magnetic element having eight magnetic North and South poles
alternately magnetized over an equal angular range. Pecause
this is a brushless motor, at predetermined positions on the
stator, more particularly, mounted on base plate 4, are
disposed electromagnetic transducer elements. More
specifically, Hall effect element Hl is arranged between
coils Ll and L6, Hall effect element H2 is arranged between
coils Ll and L2, and Hall effect element H3 is arranged
between coils L2 and L3. In this embodiment, although the
geometrical angle between adjacent Hall effect elements Hl,
H2, and H3 is 60, rotor 2 is provided with eight poles so
that the Hall elements are disposed in a relative positional
relationship having an electrical angle of 240.
': ~
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~.
Referring then to Fig. 4, the Hall effect elements
Hl, H2, and H3 are each connected between ground and a power
supply source at terminal 5, and the respective output
signals from the three Hall effect elements are fed to a
control signal generator 6, which in a conventional
embodiment is formed as an integrated circuit. Control
signal generator 6 provides six output lines connected to
respective base terminals of NPN-type transistors 7a, 7b,
8a, 8b, 9a, and 9b. The collector circuits of transistors
7a, 8a, and 9a are connected to a power supply source
terminal 10 that has a positive DC bias voltage applied
thereto. The emitters of transistors 7a, 8a, and 9a are
connected respectively to the collectors of the respective
transistors 7b, 8b, and 9b. The emitter circuits of
transistors 7b, 8b, and 9b are connected to ground
potential. The nodes between the emitters and collectors of
the respective pairs of transistors are connected to the
various stator coils. More specifically, the
emitter-collector node of transistors 7a and 7b is connected
to a series circuit of stator coils Ll and L2, the
emitter-collector node of transistors 8a and 8b is connected
to a series circuit of stator coils L2 and L5, and the
emitter-collector node of transistors 9a and 9b is connected
to a series circuit of stator coils L3 and L6. The free end
of coils of L4, L5, L6 are connected together in the known
manner.
In this embodiment, when Hall effect elements Hl,
H2 and H3 produce at their outputs the squarewave signals
that are sequentially different in phase by an electrical
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angle of 240, as seen in Fig. 5 at waveforms A, B, and C,
respectively, if the current flowing through the series
circuit of stator coils Ll and L4 is represented as Ia, the
current flowing through stator coils L2 and L5 is Ib, and
the current flowing through stator coils L3 and L6 is Ic,
control signal generator 6 operates to produce control
signals such that the currents Ia, Ib, and Ic differ in
phase by 120. As seen in the waveforms D, E, and F of Fig.
5, from an electrical angle viewpoint these currents will
become positive currents during 120, zero curr~nts during
the next 60, negative currents during the subsequent 120,
and zero currents during the final 60, which sequence is
then repeated.
Because the known three-phase brushless motor
described above requires three Hall effect elements, a
correspondingly large number of wires are required for
interconnection between the Hall effect elements and the
drive circuit and also the driving power required for the
Hall effect elements must be considered when providing a
power efficient motor. Moreover, as such three-phase
brushless motor is miniaturized, the ability to accurately
position the Hall effect elements becomes diminished and
also the physical space within which to mount the Hall
effect elements is reduced. Therefore, the above-described
three-phase brushless motor having three Hall effect
elements has been found to be lacking.
Another known three-phase brushless motor is
represented in Figs. 3, 6, and 7 in which it is seen only
that only two Hall effect elements, Hl and H2, are employed.
As seen in Fig. 6, two Hall effect elements Hl and H2 are
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~256~52 S03113
employed to detect the rotational position of the rotor and
are disposed at positions to produce a relative electrical
angle of 120 or 240. The output signals from these Hall
effect elements thereby produce a composite signal having a
phase difference of 120, relative to the output signals
from each of the respective electromagnetic transducer
elements Hl, H2. This composite signal and the two output
signals from the respective Hall effect elements Hl and H2
can then be used to supply the drive currents to the stator
coils Ll, L2,...L6. Accordingly, in an arrangement having
a stator and rotor formed similarly to those in Figs. 2 and
3, and following the teaching of the known embodiment in
Fig. 6, the two Hall elements then are arranged in relative
positional relationship with an electrical angle of 240
and, as seen in Fig. 7, the DC voltage is then applied at
power source terminal S through a resistor 11 to the two
Hall elements Hl and H2 as a bias voltage. Now in this
embodiment, the output obtained from the first and second
ootput terminals al and a2 of first Hall effect element Hl
is applied to the corresponding input terminals of control
signal generator 6, and the output signal obtained at
::
terminals bl and b2 of Hall effect element H2 is applied to
the third and fourth input terminals of control signal
,
generator 6. In order to provide the necessary signals now
that the third Hall effect element has been eliminated, a
resistive signal adding circuit is formed of a series
circuit of resistors 12 and 13 connected between the first
terminals of the two Hall effect elements and a resistive
series circuit made up of resistors 14 and 15 connected
between the second output terminals of the two Hall effect
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~ 25 6 15 2 S03113
.
elements. The connections to the control signal generator 6
are then made at the nodes of the series resistive circuits
and, specifically, the node between resistor 14 and 15 is
connected to fifth input terminal of control signal
generator 6, and the node between series resistors 12 and 13
is connected to a sixth input of control signal generator 6.
In this embodiment it is assumed that all of resistors 12,
13, 14, and 15 have the same resistance value R, which is
selected to be substantially greater than the resistance
values of the Hall effect elements Hl and H2.
Now, assuming that the output voltage values at
the first and second terminals a1 and a2 of Hall effect
element Hl are taken as Va and Va', and the output voltage
at the first and second output terminals bl and b2 of second
Hall effect element H2 are taken as Vb and Vb', the voltage
value fed to the fifth input terminal of control signal
generator 6 can be expressed as:
Vc = (1/2) (Va' + Vb') (1)
Similarly, a voltage value Vc' that would be supplied to the
sixth input terminal of control signal generator 6 can be
expressed as:
Vc' = (1/2) (Va + Vb) (2)
Therefore, the input signal c applied between the fifth and
sixth input terminals of control signal generator 6 can be
represented as:
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12561~Z~
S03113
c = vc - vc' = - (1/2) (Va - Va') - (1/2) (Vb - Vb')
(3)
In this case, the input signal then applied
between the first and second input terminals of control
signal generator 6, that is, the output signal of Hall
effect element Hl, is represented by the following:
a = Va - Va' (4)
Similarly, the input signal applied at the third and fourth
input terminals of control signal generator 6, that is, the
output signal of Hall-effect element H2 is represented by
the following:
b = Vb - Vb' (5)
Therefore, substituting the above values, it is seen that
the signal applied between the fifth and sixth input
terminals of control signal generator 6 can be represented
as:
c = - (l/2) ~a + b) (~)
Accordingly the signals having the waveforms represented at
A, B, and C of Fig. 5 are supplied to the input side of
control signal generator 6. The remaining circuit elements
$n the motor control system represented in Fig. 7 are
connected in exactly the same fashion as described in
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relation to Fig. 4. Therefore, the rotor of the motor is
rotated by the circuit arrangement represented in Fig. 7
exactly it was in accordance with the circuit arrangement of
Fig. 4.
Because in the arrangement of Figs. 6 and 7 the
number of Hall effect elements has been reduced from three
to two, the corresponding extent of interconnecting wirings
has also been correspondingly reduced, and the power
consumption has also been reduced, this embodiment is
advantageous in miniature motor applications. Nevertheless,
when a rotor in which North poles and South poles are
magnetized with an equal angular spacing, as seen for
example in Fig. 3, as used as rotor 2 of the three-phase
brushless motor and such rotor is rotated, the waveforms of
the output signals from Hall effect elements Hl and H2 have
the upper portions thereof flattened because of saturation.
This waveform distortion is represented at waveforms 51 and
S2 at A in Fig. 8, in which the compssite waveform S3, that
is, the signal C formed of waveforms Sl and S2, has a
gradual inclination or slope at the zero crossing point.
Therefore, the zero crossing point of the composite waveform
cannot be accurately determined and it is this signal, as
represented at waveform C of Fig. 8, that is fed to control
signal generator 6.
As seen more clearly in waveform C of Pig. 8, the
composite signal C is one in which the phases at the
trailing and leading edges of the square wave representation
are displaced from the normal by a phase error represented
at Zl' Z2' and Z3. Waveforms B and D of Fig. 8 illustrate
the waveforms obtained from output signals Sl and S2 of the
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~256~52
Hall effect elements Hl and H2, respectively. Now, when the
signals having waveforms represented at B, C and D of Fig. 8
are fed to the respective input terminals of control signal
generator 6, the drive current to be supplied to stator
coils Ll, L2, ... L6 are derived therefrom and the rotor is
then driven accordingly, however, the unevenness of the
rotation torque will become greater in the vicinity of the
zero crossing points of the composite signal S3, as
represented by the waveform E in Fig. 8. In such case, it
has been found that the rotational torque ripple is
increased by more than 23.4~.
To overcome the above-described disadvantageous
elements of the prior art, one solution provides a
brushless three-phase motor wherein a rotor is as
shown in Fig. 9. In this rotor four North poles and four
South poles are alternately magnetized on a disc made of
magnetic material with an equal angular spacing. These
North and South poles then form the main North and South
magnetic poles 2a. Auxiliary magnetic poles 2b are
provided that are arranged at the respective outer
peripheries of the main magnetic poles 2a and are
provided with the opposite polarity to that of the
corresponding main magnetic pole. The auxiliary poles 2b
then are arranged to substantially pass over the
electromagnetic transducers Hl and H2 of the stator. In the
three-phase brushless motor, which employs a rotor as
represented in Fig. 9,
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two Rall effect elements Hl and H2, provided to detect the
rotational position of the rotor, are arranged ha~ing a
positional relationship with an electrical angle of 240,
and the respective output signals from these Hall effect
elements when combined to form the composite will provide a
composite signal having a phase difference of 120 relative
to the output signals from the two Hall effect elements.
Thus, the drive currents to be supplied to the stator coils
Ll, L2,...L6 are determined by the composite signals and the
output signals from the two Hall effect elements, whereby
the three-phase brushless motor is driven to rotate.
In the case of the motor described in relation to
Fig. 9, because in that embodiment the auxiliary magnetic
poles 2b have the opposite polarity to those of the main
magnetic poles 2a and are provided at the opposing portion
of the rotor relative to the two Hall effect elements, when
the rotor is rotated the waveforms of the output signals
produced by the two Hall effect elements will not be
saturated but will have a relatively large inclination, that
is, the slope in the zero crossinq vicinity, as represented
by waveforms S4 and S5 at A in Fig. 10. Because the
composite signal c, as shown in waveform S6 of Fig. 10, has
a relatively sharp inclination or slope at the zero crossing
point, the composite signal represented in waveform C of
Fig. 10 does not have the phase difference problems
associated with the system described hereinabove. The
waveforms of output signals S4 and S5 derived from the two
Hall effect elements are seen at B and D of Fig. 10, and
when the signals having waveforms as shown in B, C, and D
are supplied to inputs of the control signal generator 6 to
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produce the drive currents drive the stator coils L~,
L2,...L6, the rotor is rotated ~y such drive currents with
relatively small unevenness or ripple in the rotational
torque. The rotational torque ripple is quite small and is
seen at waveform E in Fig. 10. Such rotational torque
ripple has been found to be as low as 6.3%.
Nevertheless, in order to obtain a torque ripple
as low as 6.3~, the output sensitivity, unbalanced voltag~s,
mounting positions, and the like of the Hall effect elements
must be determined with a high degree of accuracy. For
example, when the unbalanced voltage of the two Hall effect
elements are respectively 3.5~ and 6.3~, the output
difference therebetween is 10.5%. This is represented by
the waveforms at A of Fig. 11, in which it is seen that the
waveform S4' and S5' of the two Hall effect elements and the
waveform S6' of the composite thereof, can be employed to
produce a drive signal represented in waveform B in which
torque ripple is increased to approximately 13.7~. If such
torque ripple is increased due to the unbalanced voltages of
the Hall effect elements, for example, then when the motor
is employed in a video tape recorder or audio tape recorder
or record player or the like, which require a high
rotational accuracy and low wow and flutter, the previously
proposed motor is not suitable.
The present invention solves the above-described
drawbacks in the heretofore proposed three-phase brushless
motors and turning to Fig. 12 one embodiment of the present
invention is shown. In Figs. 12 and 13, the same reference
numerals corresponding to the motors described in the
preceding Figs. are employed and further description need
256 ~5 2 S03113
not be provided in detail. Referring then to Figs. 12 and
13, the stator will first be described and will consist
substantially of the stator that was described hereinabove
in relation to Fig. 6 in which six coils are provided
connected either pairs, either in series or in parallel, and
in which two electromagnetic transducer elem~nts, for
example, Hall effect elements, are employed. As described
hereinabove the Hall elements are placed in relative
positional relationship having an electrical angle of 240.
The Hall effect elements and the stator coils may be
connected as described hereinabove in relation to Fig. 7.
Assuming then that the stator is as shown in Fig.
6, the rotor provided by the present invention is seen in
Fig. 12 in which North and South poles are formed being
alternately magnetized on a disc made of magnetic material,
each having an equal angular spacing. In this embodiment,
main magnetic poles 2a and auxiliary magnetic poles 2b
having opposite polarities to those of ~he main magnetic
poles are magnetized on the disc at the position having an
electrical angle of substantially +45 from the boundary
between the North and South poles of the eight main magnetic
poles 2a and are arranged on the outer peripherial portions
thereof. The auxiliary magnetic poles 2b are arranged on
the periphery of the rotor so as to be in alignment and pass
over the electromagnetic transducer elements that are
affixed to the stator.
In this embodiment, and similar to the example of
the three-phase brushles~ motor employing only two Hall
effect elements, because the two Hall effect elements Hl and
H2 employed to detect the rotational position of the rotor
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~256152 S031 13
-
are placed in a relative positional relation having an
electrical angle of 240, the output signals from the Hall
effect elements produce a composite signal having a phase
difference of 120 relative to the outputs of the two Hall
elements, and the drive currents to be supplied to stator
coils Ll, L2,...L6 are determined by the composite signal,
as well as the output signals form the two Hall elements.
By using a circuit similar to Fig. 7, along with the Hall
elements, the three-phase brushless motor is driven to
rotate.
The waveforms produced by the two Hall effect
elements are shown generally in Fig. 13 and in the
embodiment of Fig. 12, because the auxiliary magnetic poles
2b, having opposite polarities to those of the main magnetic
poles 2a, are disposed in the vicinity of the opposing
portions of the rotor relative to the Hall effect elements
at positions having an electrical angle of substantially
~45 from th~ boundary between the respective South and
North poles of the main magnetic pole 2a, when the rotor is
rotated the waveforms of the output signals from the Hall
effect elements will not be saturated but will have signal
waveforms having sharp inclinations or slopes, as
represented by waveforms S7 and S8 at A of Fig. 13.
In waveform A of Fig. 13, signal S7 is a one-dot
chain line and signal S8 is represented by a two-dot chain
line, and the solid line Sg is the composite signal c formed
from the waveform S7 and S8. It is clearly seen that signal
Sg has a sharp slope at the zero crossing point.
Accordingly, the zero crossing point is determined and the
composite signal, as represented in waveform D of Fig. 13,
: . --18--
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is feed to the fifth and sixth input terminals of control
signal generator 6, as shown for example in Fig. 7. The
leading edge and the trailing edge of the squarewave of the
composite signal, having a waveform shown at D in Fig. 13,
are determined at the zero crossing points of waveform A of
Fig. 13. The waveforms of output signals S7 and S8, as
produced by the two Hall effect elements are shown at B and
D, respectively, of Fig. 13, and the signals having
waveforms B, C, and D of Fig. 13 are fed to control signal
generator 6 to obtain the drive currents that are fed tc the
stator coils Ll, L2,...L6, so that the rotor is rotated
thereby. Using this embodiment, regardless of the
variations in the characteristics of the Hall elements
employed, the rotational torque is quite even and the torgue
characteristic is shown for example at waveform E of Pig.
13. A torque curve having a waveform such as seen in E in
Fig. 13 has a rotational torque ripple of approximately
7.54, whereas although this torque curve is similar to the
torque curve shown at waveform B in Fig. 11, it is noted
that the torque curve in which there was an unbalanced
voltages of 3.54 and 6.54 in the Hall effect elements
resulted in an output difference of 10.5%. The rotational
torque ripple shown at B in Fig. 11 is 13.74, thus, the
:: :
present invention provides a substantial improvement
thereover.
Another embodiment of the three-phase brushless
motor according to the present invention is shown in Fig.
14, in which there are four main magnetic poles 2a and in
which the auxiliary magnetic poles 2b are disposed at the
outer peripheral portions of the main magnetic poles 2a at
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positions having an electrical angle of substantially +45
from the boundary between the respective North poles and
South poles.
In Fig. 15, another embodiment of a rotor provided
according to the present invention is shown in which there
are four magnetic poles and in which each main magnetic pole
2a is extended to the side surface and the auxiliary
magnetic poles 2b are disposed at positions with an
electrical angle of substantially +45 from the bGundary
between the respective North poles and the South poles. In
the embodiment of Fig. 15, the auxiliary magnetic poles 2b
are only arranged in the radial surface and are not in the
planar surfaces of rotor 2. The portion of rotor 2 not
shown in symmetrical.
Fig. 16 discloses an embodiment of the present
invention in which four main magnetic poles 2a form rotor 2
and in which auxiliary poles 2b of the same polarity as main
magnetic poles 2a are arranged on the radial surface of
rotor 2 and are disposed at positions having an electrical
angle of substantiall~ +45 from the boundary between
respective North poles and South poles. The auxiliary
magnetic poles are formed by means of a rotational position
detecting main magnetic pole 2c arranged as a thin magnetic
pole area on the peripherial surface of the rotor 2 and
being of an opposite magnetic polarity relative to the
respective main magnetic pole 2a and being displaced, for
example, by an electrical angle of 180 from the main
magnetic pole. In an embodiment differing from that of Fig.
16, the phase difference between the main magnetic pole 2a
and the rotational position detecting main magnetic pole 2c,
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the electrical angle can be 60, 120, 240, and 300, which
result in different amounts of the radial surface of the
main magnetic poles being covered by the thin magnetic pole
area that forms the detecting magnetic pole. Again, the
portion of rotor 2 not shown is symmetrical.
An example of a rotor being formed substantially
cylindrically for use with a cylindrical motor is shown in
Fig. 17, in which the main magnetic pole 2a is formed of
four poles. In the embodiment of Fig. 17, the auxiliary
magnetic poles 2b are arranged at an electrical angle of
substantially _45 from the boundary between the respective
North and South poles at the end and on the side surface or
cylindrical surface of the rotor 2.
Fig. 18 is an embodiment of a rotor for use with a
cylindrical brushless, three-phase motor in which main
magnetic pole 2a is formed of four magnetic poles. The
auxiliary magnetic poles 2b are arranged in the end surface
of the rotor 2 and are disposed at positions having an
electrical angle of substantially ~45 from the respective
boundary between the respective North poles and South poles
of the main magnetic pole 2a. The embodiment of Fig. 18 can
be to adapted to correspond to the embodiment of Fig. 16, in
which the end surfaces of the main magnetic poles 2a are
covered with the rotational position detecting magnetic
poles 2c having any one of the phase difference electrical
angles of 60, 120, 180, 240, and 300 relative to the
respective main magnetic poies 2a. The thin magnetic pole
area forming the detecting magnetic pole 2c defines the
auxiliary magnetic poles 2b as being disposed with
electrical angles of substantially ~45 from the boundaries
between the respective North and South poles of the
main magnetic poles.
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--
A specialized embodiment of cylindrical rotor 2 is
shown in Fig. l9, in which there are four main magnetic
poles 2a and in which the diameters of the main magnetic
poles 2a on the side surface and the rotational positioning
detecting main magnetic poles 2c are made different from
each other resulting in a diametrical step difference
forming a flange and a phase difference of any one of
electrical angles 60, 120, 180, 240, and 300 can be
selectively obtained. Also in the embodiment of Fig. 19,
the auxiliary magnetic poles 2b are exposed by the thin
magnetic area 2c at positions having an electrical angle of
substantially ~4~ from the boundary between the respective
North and South poles of the main magnetic pole 2a.
Fig. 20 is an example of an embodiment of rotor 2
in which the rotation positioning main magnetic poles 2c are
disposed on the end surface of rotor 2 that has
substantially the same shape as that in the embodiment of
~ig. l9. In the embodiment of Fig. 20, the auxiliary
magnetic poles 2b are exposed by the thin magnetic area 2c
at positions having an electrical angle of substantially
l45 from the boundary between the respective North and
South poles of the main magnetic poles 2a.
A rotor 2 for use in a flat brushless three-phase
motor is shown in Fig. 21, in which there are four main
magnetic poles 2a. In this embodiment, the rotational
position detecting main magnetic poles 2c are concentrically
formed at the outer periphery of the main magnetic poles 2a,
and the auxiliary magnetic poles 2b are disposed at
positions having an electrical angle of substantially _45
from the respective boundaries between the North poles and
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~256152 s03113
South poles of the rotational position detecting main
magnetic poles 2c. According to the embodiment of Fig. 21,
it is also possible to provide a phase difference equal to
any of various electrical angles such as 60, 120, 180,
240, and 300 between the main magnetic pole 2a and the
rotational position detecting main magnetic poles 2c.
~ ig. 22 illustrates an embodiment of rotor 2 for
use with a flat motor in which main magnetic poles 2a and
the rotational position detecting main magnetic poles 2c are
separated concentrically and in which the rotational
position detecting main magnetic poles 2c are disposed on
the side surface of the outer ring. The auxiliary magnetic
poles 2b are disposed at positions having an electrical
angle of substantially ~45 from the respective boundary
between the North pole and South pole of the rotational
position detecting main magnetic pole 2c. In this
embodiment as in the embodiments above, the main magnetlc
pole 2a and the rotational position detecting main magnetic
pole 2c may have phase differences other than the 180 as
shown, for example, 60, 120, 240, and 300.
The present invention also contemplates rotors of
various shapes in addition to those described above in which
the main magnetic pole can serve as the rotational position
detecting main magnetic pole, or the rotational position
detecting main magnetic poles can be formed independently
and assembled into the final structure. When the rotational
position detecting main magnetic poles are prepared
independently, it is possible to provide a phase difference
between the rotational position detecting main magnetic pole
and the main magnetic pole. Nevertheless, the auxiliary
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~ 1~56152 503~13
be arranged to Substa ti
1 and H2 f the stat0r
the number of main poles in the rotor need not be limited to
the four or eight pole embodiments described hereinabove,
arrangements such as two
be emP1oyed. ~urtherm
necessary to employ Hall effect elements and other
g ic transducers can be em l
tanCe elements and the li~
embdiments two electrO
p sed having a relative ele t i
brUShless mOtor accOrdin
invention can be formed using only two electromagnetic
transducer provided at a position having an electric angle
f 1200.
~ herefore, according to the present invention
described hereinabove, a three-phase brushleaa motor can be
driven in an acceptable fashion to rotate by using only two
electromagnetic transducer elements and in which the
characteristics of the electromagnetic transducer elements
: and their assembly accuracy can have variations yet still
provide a motor in which rotational torque ripple is
suppressed.
The above description is provided for a various
embodiments of the invention, however, it will be apparent
: that nany nodiflcations and variations oould be effected by
one skilled in the art without departing from the spirit or
cope of the novel concepts of the invention, which should
be determined only by the appended claims.
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