 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-phase bipolar brushless D.C. motor
in which a stator is constituted by an armature and a rotor is constituted
by permanent magnets.
If in this motor the stator winding is arranged as the lap winding, the
motor produces the sinusoidal torque ripples thereby to be adapted for the
micro-motor, and instead if the stator winding is arranged as the wave
winding, the motor produces the trapezoidal torque ripples thereby to be
adapted for the power motor.
And this invention is devised to make into the bipolar system so that the
copper loss of the exciting coil can be minimized, thereby increasing the
efficiency, and to make into polyphase so that the utility of the coil can
be increased, thereby making the compact design of the motor possible and
improving the torque ripple. Also in this motor the commutation system
comprising a commutation encoder, a photo-sensor and a electronic
commutator is simply and safely constituted so that the starting and
rotation characteristics of the motor can be improved as well as the motor
having the simple construction can be manufactured, thereby reducing the
cost of production.
2. Description of the Prior Art
In a conventional shunt motor, since the field coils (exciting coils) are
wound on the rotor to have the proper number of poles and the coils
attaching the brushes thereto are wound on the rotor so that the rotor is
rotated, there are drawbacks that, during its use, the alien substances
such as dusts are jammed between the commutator segments or the brush must
be replaced with the new one due to the contact therebetween by breakdown
of insulation or the wear thereof.
SUMMARY OF THE INVENTION
An object of the present invention is, in order to solve the aforementioned
problems, to provide a multi-phase bipolar brushless D.C. motor in which
the permanent magnet instead of the field coil is used for the rotor, the
winding is wound on the stator as the independent winding, the commutation
encoder is fixedly mounted on the shaft of the rotor to be rotated, and
the photo-sensor is coupled operatively thereto to be connected with the
driving circuit, whereby the motor is smoothly started and rotated with
having a simple construction, and is manufactured of low cost of
production.
Accordingly, with this object in view, the present invention resides in a
multi-phase bipolar brushless D.C. motor comprising: a stator constituted
by M phases, each phase having a plurality of windings which are connected
in series and being connected independently of the winding connection of
the other phases; a rotor rotatably coupled to said stator and having N
permanent magnet poles; a commutation encoder fixed at one end of the
rotor shaft outside the motor and assuming a cylindrical form comprising a
circular plate and an annular ring, said annular ring having light
shielding portions and light detecting portions which function,
respectively, as the non-sensing and sensing area, and each of said light
detecting portions having opposite inclined portions each which is
inclined to the edge of said light shielding portions at a given angle; a
photo-sensor coupled operatively with said commutation encoder and being
constituted so that two photo-transistors are provided with respect to
each phase, each of said photo-transistors in said M phases being
arranged, in turn, one by one at intervals of predetermined shaft angle so
as to produce the positive pulse when registered with said sensing area of
said commutation encoder; an electronic commutator constituted in such a
manner that four power transistors are connected across the winding coil
of each phase of said stator, two of said transistors of each phase being
connected to one photo-transistor of said photo-sensor so that each phase
is provided with two photo-transistors so as to perform the determination
of the current direction according to said positive pulse of said
photo-transistors, thereby flowing the alternating current through the
winding coil to drive the motor; and an electric power source connected in
parallel to each phase of said electronic commutator.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better understood, and further advantages and use
thereof more readily apparent, when considered in view of the following
detailed description of exemplary embodiment, taken with the accompanying
drawings, in which:
FIG. 1 is a schematic diagram showing, partly in block form, the system of
a multi-phase bipolar brushless D.C. motor according to the present
invention;
FIG. 2A is a exploded perspective view showing the speed encoder, the speed
sensor, the commutation encoder, and the photo-sensor according to the
present invention;
FIG. 2B is a party sectional view showing the state in which the components
in FIG. 2A are combined together;
FIG. 3A is a circular independent connecting diagram of the winding coils
of the 3-phase 4-pole motor;
FIG. 3B is an arrangement diagram of the 4-pole rotor;
FIG. 3C is a serially developed independent connecting diagram of the
winding coils of the 3-phase 4-pole motor;
FIG. 4A represents schematically the driving circuit of the 3-phase motor;
FIG. 4B represents the constructions of the rotor, the connutation encoder
and the photo-sensor;
FIG. 5A represents a schematic construction of the 3-phase 4-pole motor;
FIG. 5B represents a schematic construction of the 4-phase 4-pole motor;
FIG. 6 shows waveform of the output torque ripples of FIG. 3A, 3B and 3C;
FIG. 7A and 7B represent respectively the theoretical position of the
photo-transistor and the waveform of the torque ripple;
FIG. 8A and 8B represent respectively the corrected position of the
photo-transistor and the waveform of the torque ripple;
FIG. 9A and 9B represent respectively the photo-transistor being attached
at the corrected angle to the commutation encoder and the waveform of
torque ripple;
FIG. 10A and 10B represent respectively the state where the
photo-transistor is attached to the optimally corrected position on the
commutation encoder and the waveform of torque ripple; and
FIG. 11 shows the arrangement of the sets of photo-transistor for use in
the forward and reverse rotation in the 3-phase 4-pole motor according to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Now, a multi-phase brushless D.C. motor according to the present invention
will be explained. It should be noted that, for a facile description, the
following explanation of the present invention will be made with reference
to a 3-phase 4-pole brushless D.C. motor of a preferred embodiment shown,
by way of example only, in the accompanying drawings.
Referring now to the several drawings, and especially to FIG. 1, there is
illustrated the system of the 3-phase 4-pole brushless D.C. motor
according to the preent invention, in block form. The 3-phase 4-pole
brushless D.C. motor of the present invention includes a rotary machine 1
having a stator 4 constituted by three phases A, B and C, each phase
having four windings 40 which are connected in series (see FIG. 3A).
Windings 40 of each phase of the stator 4 are connected independently of
the winding connection of the other phases, as can be understood from FIG.
3A and 3C, respectively, illustrating a circular independent connecting
diagram and a serially developed independent connecting diagram of the
winding coils of the 3-phase 4-pole motor according to the present
invention. The winding coil ends of each phase of the stator 4 are
connected to transistors of each corresponding phase of a electronic
commutator, as will be described. Thus, since the stator 4 assumes the
independent phase-connected winding form connected differently from the
.DELTA., or Y-connected winding form, the motor is constituted so that the
exciting condition of the winding coil of each phase is always constant,
even though the motor becomes of the polyphase motor. The rotary machine 1
also has a rotor 7 constituted by the permanent magnets. The rotor 7 is
constituted as four magnetic poles, as shown in FIG. 3B. It is understood
that the stator 4 can be constituted as two, three, four, five,... or n
phase, and the rotor 7 can be constituted as two, four, six, eight,... or
2n poles. Hence, the number of poles or phases can be easily increased, or
reduced as occasion demands, and the length, the thicknes, or the shape of
the rotary machine 1 can be easily modified as occasion demands.
As shown in FIG. 2, a rotor shaft 11of the rotary machine 1 is projected
outwardly from a bracket 12 which is fixed on the one side of the rotary
machine 1. Fixed on the end of the rotor shaft 11 are a commutation
encoder 2 and a speed encoder 3. Since the commutation encoder 2 and the
speed encoder 3 are fixed between the end of the rotor shaft 11 and a
washer 17 by means of screw means 16, the commutation encoder 2 and the
speed encoder 3 can be rotated together with the rotor shaft 11.
The speed encoder 3, as can be understood from FIG. 2A, assumes the disk
form which a plurality of light penetrating openings 31 are spaced and
disposed at the circumferential edge portion thereof so as to position
with respect to a speed sensor 6. The speed sensor 6 at the support
portion 25 thereof is fixed to a portion of a photo-sensor 5 by means of
screw means 26. When the speed encoder 3 is rotated, the speed sensor 6
detects a pulse corresponding to the rotation speed of the rotor 7 through
the light penetrating openings 31. The detected pulse is supplied to the
switching circuit through the encoder circuit so as to control the
electric power energy supplied to the winding coils, thereby controlling
the rotation speed of the rotor 7, as known in the art.
The commutation encoder 2, as can be understood from FIG. 2B, assumes the
cylindrical from having a circular plate 19 and an annular ring 20. The
annular ring 20 comprises light shielding portions 21 and light detecting
portions 22 which function as the non-sensing area and the sensing area
for the photo-sensor 5, respectively. It will be noted that in FIG. 1, 5,
7, 8 and 11 the commutation encoder 2 is illustrated in a developed form
for a facile illustration. Each of light detecting portions 22 has
opposite inclined portions 23 so as to modulate the exciting width by
adjusting of the distance between the photo-sensor 5 and the commutation
encoder 2, as will be described with reference to FIG. 8. Each of the
inclined portions 23 are inclined to the edge 27 of the light shielding
portion 22 at a given angle.
The number of the light detecting portions 22, i.e., the sensing areas is
determined by the following formula;
The number of the sensing areas=the number of poles in the rotor/2.
Accordingly, the number of the sensing areas of the preferred 3-phase
4-pole motor corresponds to two. Also, the width of the sensing area
corresponds to the shaft angle determined by the following formula;
##EQU1##
Hence, the width of the sensing area of the preferred 3-phase 4-pole motor
corresponds to the shaft angle of 60.degree., as shown in FIG. 5A. In the
case of the 4-phase 4-pole motor, as shown by way of another example in
FIG. 5B, the width of the sensing area corresponds to the shaft angle of
67.5.degree..
However, thus determined, the width of the sensing area for the
photo-sensor 5 can be slightly changed to modulate the exciting width in
the winding coil, if necessary. For example, in case that
photo-transistors (only one shown in FIG. 9) of the photo-sensor 5, as
will be described, are positioned in the position which the sensing area
therefor corresponds to the shaft angle of 60.degree., the winding coil
will result in the exciting in the area of poor torque because the
exciting width of the winding coil is not coincided with the pulse width
induced from the photo-transistor, i.e., the exciting width of the winding
coil is naturally greater than the pulse width of the photo-transistor due
to the time delaying of driving circuit and the exciting characteristic of
the winding coil. The exciting in the area of poor torque makes the copper
loss of the winding coil increased, which results in generating heat in
the motor, and degrating the efficiency. To eliminate these drawbacks, it
is necessary to change the width of the sensing area for the
photo-transistor having an effect on the exciting width in the winding
coil. This is accomplished by adjusting the distance between the sensing
point of the photo-transistors and the middle portion 24 of the light
detecting portion 22 because the light detecting portion 22 of the
commutation encoder 2 has opposite inclined portions 23. This adjustment
can be easily performed because the commutation encoder 2 and the
photo-sensor 5 are disposed on the rotor shaft 11 outside the rotary
machine 1. At this time, it is preferred for the adjustment of the
distance between the photo-transistors and the commutation encoder 2 to
set in the best position of torque ripple and in the most efficient
position of the motor in operation. When the photo-transistor is
positioned in the position displaced by the moving distance of
photo-transistor as illustrated in FIG. 10, the winding coil will result
in the exciting in the area of good torque. Thus, the commutation encoder
2 of the invention makes it possible to maximize the efficiency of the
motor by adjusting the distance between the photo-sensor 5 and the
commutation encoder 2.
Disposed on the rotor shaft 11 between the bracket 12 and the commutation
encoder 2 so as not to rotate together with the rotor shaft 11, as shown
in FIG. 2, is a semicircular support plate 50 for supporting the
photo-sensor 5 for producing the positive pulse when registered with the
sinsing area of the commutation encoder 2. The photo-sensor 5 assumes a
U-shaped form having a guide groove 59 for receiving and guiding the
annular ring 20 of the commutation encoder 2. As shown in FIG. 4B and 5,
the photo-sensor 4 is constituted by six photo-transistors PA.sub.1,
PB.sub.1, PC.sub.1, PA.sub.2, PB.sub.2 and PC.sub.2 so that two
photo-transistors are provided with respect to each phase. Each of
photo-transistors PA.sub.1, PB.sub.1, PC.sub.1 PA.sub.2, PB.sub.2 and
PC.sub.2 in A-, B-, and C-phase is arranged, in turn, one by one at
intervals of the shaft angle calculated by the following formula;
##EQU2##
Accordingly, the interval between each photo-transistors of the preferred
3-phase 4-pole motor corresponds to the shaft angle of 30.degree..
The interval between two photo-transistors of each phase is determined by
the following formula;
##EQU3##
Therefore, the interval between two photo-transistors PA.sub.1 and
PA.sub.2 of A-phase corresponds to the shaft angle of 90.degree., and also
the cases of B- and C-phases are the same as A-phase.
In the case of the 4-phase 4-pole motor as shown in FIG. 5B, the interval
between each photo-transistors corresponds to the shaft angle of
22.5.degree., and the interval between two photo-transistors of each phase
corresponds to the shaft angle of 90.degree..
In the brushless D.C. motor constructed thus, the number of
photo-transistors which can be turned on simultaneously within one sensing
area corresponds to the number of phases -1. Accordingly, the commutation
encoder 2 and photo-transistors according to the present invention becomes
of 2-phase 1-exciting, 3-phase 2-exciting, 4-phase 3-exciting, 5-phase
4-exciting, 6-phase 5-exciting,...so that the n-phase (n-1)-exciting motor
is construction, thereby performing the production of the multiphase
bipolar brushless D.C. motor.
In addition, in order to improve the efficiency and minimize the copper
loss, it is preferred for the photo-transistors of the photo-sensor 5 to
be set in the advanced commutation by ".theta..degree." as the best
position with the motor in driving. This reason are as follows:
As shown in FIG. 7 and 8, if the photo-transistor (only one shown) is
registered with the theoretical sensing position of the sensing area of
the commutation encoder 2 during the driving of the motor, the
photo-transistor will generate a positive pulse so as to be the transistor
Q of the electronic commutator "ON", which cause to flow a current in a
given direction of the winding coil, as will be described. Then, when the
photo-transistor is registered with the non-sensing area of the
commutation encoder 2 by the rotation of the commutation encoder 2, the
photo-transistor stops the generating of the positive pulse to allow the
transistors Q to be turned "OFF", thereby cutting off the current in the
winding coil. At this time, the starting and finishing time of exciting in
the winding coil shall be delayed by the degree of ".theta." as compared
with the starting and finishing time of the pulse signal generated from
the photo-transistor due to the time delaying of the transistor Q, and the
exciting characteristic of the winding coil. This time delaying of the
exciting in the winding coil results in the increase of the copper loss
and the lowering of efficiency of the motor due to the poor torque, as
shown in FIG. 7A. Accordingly, it is necessary to eliminate the portion of
poor torque by the advanced commutation of the photo-transistor with the
reverse direction to the rotating direction of the rotor 7. This advanced
commutation of the photo-transistor of the photo-sensor 5 can be easily
adjusted because the photo-transistor is disposed on the rotor shaft 11
outside the rotary machine 1.
Also, the photo-sensor 5 of the 3-phase 4-pole brushless D.C. motor
according to the present invention, as shown in FIG. 11, can be
constructed to rotate forwardly or reversely by providing the set of
photo-transistors PA'.sub.1 -PC'.sub.2 for use in the reverse rotation in
the symmetric position separated from the set of photo-transistors
PA.sub.1 - PC.sub.2 for use in the forward rotation advancedly positioned
by ".theta..degree." from the theoretical sensing position of
photo-transistor. In accordance with the selection of the set of the
photo-transistors for use in the forward or reverse rotation by
non-contacted electro-magnetic operation, the forward, or reverse rotation
of the motor is possible.
Referring now to FIG. 4A and 4B, there is illustrated the driving circuit
having the commutation system comprising the commutation encoder 2, the
photo-sensor 5, and the electronic commutator in accordance with the
present invention. The electronic commutator is constituted in such a
manner that 4 power transistors Q are connected across the winding coil of
each phase of the stator 4. Two of transistors Q connected across the
winding coil of each phase are connected to one photo-transistor of the
photo-sensor 5 so that each phase is provided with two photo-transistors,
thereby performing the determination of the current direction according to
the operation of the photo-transistors. Namely, one photo-transistor
PA.sub.1 of A-phase of the photo-sensor 5 is connected to the transistors
Q.sub.1 and Q.sub.4 so that, when the photo-transistor PA.sub.1 is turned
on, the transistors Q.sub.1 and Q.sub.4 are turned on to allow the current
to be flowed from the transistor Q.sub.1 to the transistor Q.sub.4. The
other photo-transistor PA.sub.2 of A-phase is connected to the transistor
Q.sub.2 and Q.sub.3 so that, when the photo-transistor PA.sub. 2 is turned
on, the transistors Q.sub.2 and Q.sub.3 are turned on to allow the current
to be flow from the transistor Q.sub.2 to the transistor Q.sub.3. The
photo-transistors in B- and C-phase are connected to the transistors in
the same way as the photo-transistors in A-phase.
Thus, the commutation system of the present invention is independently
arranged in every phase. Accordingly, as two photo-transistors are
provided with respect to one phase so that only the positive pulse in
used, the pulse dividing device can be removed, and since also each
photo-transistor of one phase is constituted so that it is turned off
while the rotor is rotated by the shaft angle of 30.degree. upon
alternating, the cross-fire prevention interlock can be removed. Hence,
since the complicated logic circuit is removed, the safe and simple
electronic commutator can be constructed.
Also, as illustrated in FIG. 1, the commutation system of each phase is
connected in parallel to one voltage controller, directly in case of D.C.
and through D.C. rectifier in case of A.C. so that the motor is composed
efficiently.
The operation of the preferred 3-phase 4-pole brushless D.C. motor
according to the present invention will now be described.
At first, the switch (not shown) of the power source is turned on to
energize the commutation system of the drive circuit.
So, each of photo-transistors PA.sub.1, PB.sub.1, PC.sub.1, PA.sub.2,
PB.sub.2 and PC.sub.2 of the photo-sensor 5 which is registered with one
sensing area of the commutation encoder 2 produces the positioning pulse,
and supplies the produced positive pulse to the electronic commutator to
allow the transistors Q.sub.1 -Q.sub.12 of the electronic commutator to be
turned on, thereby allowing the alternating current of the square wave to
be flowed through the winding coil of each phase as shown in FIG. 6.
Namely, when the photo-transistors PA.sub.1 and PB.sub.1 of A- and
B-phases are within the sensing area of the commutation encoder 2, both
the photo-transistors PA.sub.1 and PB.sub.1 produce the positive pulse.
Then, the transistors Q.sub.1 and Q.sub.4, and Q.sub.5 Q.sub.8 in A- and
B-phases are turned on so that the current of each phase flows,
respectively, from the transistor Q.sub.1 to Q.sub.4 and from the
transistor Q.sub.5 to Q.sub.8 so as to allow the corresponding alternating
current of the square wave to be flowed through the winding coil of A- and
B-phases, thereby driving the motor. In this case, since the width of the
sensing area for the photo-transistor producing the positive pulse to
transmit to the electronic commutator corresponds to the shaft angle of
60.degree., the photo-transistor PC.sub.1, PC.sub.2, and PA.sub.2 and
PB.sub.2 spaced respectively by the shaft angle of 90.degree. away from
the photo-transistor PA.sub.1 and PB.sub.2 are turned off. While the rotor
7 is rotated by the shaft angle of 30.degree. upon alternating, the
photo-transistor PA.sub.1 is turned off, as shown in FIG. 4B. Then, the
photo-transistor PC.sub.1 is newly positioned in the sensing area of the
commutation encoder 2 to produce the positive pulse. Accordingly, the
transistors Q.sub.5 and Q.sub.8, and Q.sub.9 and Q.sub.12 in B-and
C-phases are maintained in a state turned on so that the current of each
phase flows, respectively, from the transistor Q.sub.5 to Q.sub.8 and from
the transistor Q.sub.9 to Q.sub.12 so as to allow the corresponding
alternating current of the square wave to be flowed through the winding
coil of B- and C-phases, thereby driving the motor. In this case, the
photo-transistors PA.sub.1, PA.sub.2, PB.sub.2 and PC.sub.2 are turned
off, by reason as above-mentioned. While the rotor 7 is again rotated by
the shaft angle of 30.degree. upon the alternating, the photo-transistor
PB.sub.1 is turned off. Then, the photo-transistor PA.sub.2 is newly
positioned in the sensing area of the commutation encoder 2 to produce the
positive pulse. Accordingly, the transistors Q.sub.9 and Q.sub.12, and
Q.sub.2 and Q.sub.3 in C- and A-phases are maintained in a state turned on
so that the current of each phase flows, respectively, from the transistor
Q.sub.9 to Q.sub.12 and transistor Q.sub.2 to Q.sub.3 so as to allow the
corresponding alternating current of the square wave to be flowed through
the winding coil of C- and A-phases, thereby driving the motor. In this
case, the photo-transistor PA.sub.1, PB.sub.1, PB.sub.2 and PC.sub.2 are
at the position where it can not be turned on, by reason as
above-mentioned. Thus, the operation of the photo-sensor 5 and electronic
commutator of the commutation system is repeated to drive the motor.
On the other hand, as the speed encoder 3 is rotated by the rotor shaft 11
of the rotary machine 1, the speed sensor 6 detects the pulse from the
speed encoder 3. The detected pulse signal is supplied to the switching
circuit through the encoder circuit so as to controll the electric power
energy supplied to the winding coil, thereby controlling the rotation
speed of the rotor 7, as known in the art. Accordingly, the brushless D.C.
motor according to the present invention can be smoothly rotated.
From the above description, it will be readily seen that the brushless D.C.
motor of this invention is constructed so that a pair of photo-transistors
per a phas are arranged in the commutation encoder 2 so as to eliminate
the signal deviding device and the cross-fire prevention interlock,
thereby enabling the circuit to be simplified. Moreover, the brushless
D.C. otor of the invention is constituted so that the maximum current can
be applied to the independent winding coil for each phase, and the winding
coils can be utilized efficiently by the multiphasing (for example,
2-phase 1-exciting, 3-phase 2-exciting, 4-phase 3-exciting, 5-phase
4-exciting, 6-phase 5-exciting....)so as to realize a compact design.
Furthermore, the brushless D.C. motor of the invention allows a torque
ripple to be remarkably improved, and the copper loss to be minimized by
eliminating the portion having the poor torque by the advanced commutation
of the photo-transistors and the adjustment of the width of the sensing
area for the photo-transistor so that the heat generated from the motor is
minimized with improving the efficiency. Further, the brushless D.C. motor
of the inention can be constructed to rotate forwardly or reversely by
providing the set of photo-transistors used during the reverse rotation in
the symmetric position separated from the set of photo-transistors used
during the forward rotation. Also, the reduction of the captivity of the
transistor mounted in the driving edge having independent phase makes the
manufacturing cost reduced.
* * * * *
|
|
 |
|
 |
Description |
|
