Three-phase hybrid type stepping motor

Details Three-phase hybrid type stepping motor Three-phase hybrid type stepping motor

2001-05-21

2003-04-08

Mullins, Burton S. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S06700R, C310S254100

Reexamination Certificate

active

06545376

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-phase hybrid type stepping motor, and more particularly to a three-phase hybrid type stepping motor having a structure capable of reducing cogging torque and improving a torque waveform.
2. Description of the Prior Art
A conventionally implemented three-phase hybrid type stepping motor has twelve magnetic poles with windings as shown in
FIGS. 1A
,
1
B and
1
C or six magnetic poles with windings as shown in
FIGS. 2A
,
2
B and
2
C.
The conventionally implemented three-phase hybrid type stepping motor shown in
FIGS. 1A
,
1
B and
1
C is composed of a stator having twelve magnetic poles
2
arranged on the inner periphery of an annular yoke
1
at equal intervals, windings
3
wound around the respective magnetic poles
2
to form three-phase windings and multiple small teeth
4
provided at the tip end of each magnetic pole
2
, and a rotor
9
having two split rotor elements
7
, a permanent magnet
8
held therebetween and magnetized to two polarities of N and S in an axial direction, and fifty small teeth
6
formed on an outer periphery of each of the rotor elements
7
at a regular pitch, said rotor elements
7
being shifted from each other in angular position by a ½ pitch of the teeth
6
. The three-phase hybrid type stepping motor rotatably supports the rotor
9
, the rotor
9
being opposed to the stator
5
with a gap therebetween.
On the contrary thereto, in the three-phase hybrid type stepping motor shown in
FIGS. 2A
,
2
B and
2
C, each of the rotor elements
7
has forty small teeth
6
.
In the above-described three-phase hybrid type stepping motor, torque is generated between the rotor and the stator when the rotor is rotated without energizing the windings, and this torque is referred to as cogging torque.
A vernier method for unequalizing a pitch of the small teeth of the stator and that of the small teeth of the rotor was examined in order to reduce the cogging torque of the three-phase hybrid type stepping motor in the prior art. The examination is still insufficient and the satisfactory effect is not obtained. Therefore, it is an object of the present invention to elucidate the theory of the vernier method and obtain the effective vernier method having a high degree of freedom.
In the three-phase hybrid type stepping motor having twelve magnetic poles with windings shown in
FIGS. 1A
,
1
B and
1
C, a magnetic flux passing through one phase winding is not interlinked with a magnetic flux passing through the other phase winding. On the contrary, in the three-phase hybrid type stepping motor having six magnetic poles with windings shown in
FIGS. 2A
,
2
B and
2
C, a magnetic flux passing through one phase winding is interlinked with a magnetic flux passing through the other phase winding, and the quantity of the magnetic flux becomes twice that in the motor having the twelve magnetic poles, so that the torque becomes larger, and the electromagnetic energy can be absorbed and controlled easily because a relative inductance exists between the phases as a normal motor.
As shown in
FIGS. 2A
,
2
B and
2
C, the windings
3
of the magnetic poles facing each other and separated by 180° from each other are connected in series. The small teeth
6
of the N and S side rotor elements
7
are shifted from each other by 180° so that the top of small tooth of N side rotor element
7
is faced to the bottom of small tooth of S side rotor element
7
.
Taking an equivalent circuit of a magnetic circuit of the hybrid type twelve magnetic poles three-phase stepping motor shown in
FIGS. 1A
to
1
C into consideration, the equivalent circuit is as shown in
FIG. 3A
when the magnetic resistance in a magnet core is ignored for the sake of simplicity. In
FIG. 3A
, reference characters F
u
, F
v
, F
w
, denote magnetomotive forces of V, W phases winding poles (that is, stator poles with windings); P
i
(here i is 1 to 6), a permeance of the i-th winding pole on the N polarity side; and F
m
and P
m
, magnetomotive force and an internal permeance of the magnet. It should be noted that the permeances of the winding poles provided at axisymmetric positions are equal to each other and the same reference character is therefore used. Further, in regard to the windings at the axisymmetric positions are connected in series in the forward direction and are connected in series in the backward direction, respectively, the directions of the magnetomotive force to these poles are shown in the Figure. As shown in
FIG. 3A
, the same four circuit groups (sub circuits) are aligned in parallel, thereby equivalently replacing with one sub circuit by the circuit logic. This is shown in FIG.
4
A. In this case, a number of the equivalent winding poles is six in the three-phase motor.
SUMMARY OF THE INVENTION
A three-phase hybrid type stepping motor according to the present invention is characterized by comprising a stator and a rotor arranged concentrically with the stator and with an air gap therebetween, said stator having an annular stator yoke, a plurality of stator poles extending radially and formed at a regular pitch on the inner peripheral surface of the annular stator yoke, and stator windings of three-phase each wound around each stator pole, each of said stator poles having an even number of and at least four small stator teeth at the tip end thereof, said rotor having two split rotor elements and a permanent magnet held therebetween and magnetized so as to form N and S poles in the axial direction thereof, and a plurality of small rotor teeth formed at a regular pitch on the outer peripheral surface of each of said rotor elements, said two splitted rotor elements being shifted from each other in angular position by a ½ pitch of the small rotor teeth,
wherein said small stator teeth are composed of sets of two small stator teeth of the same width, and at least one pitch of the adjacent teeth is different from the other pitch of the other adjacent teeth, so that a vector sum of the tertiary or sixth harmonic of permeances of the small stator teeth included in each of said sets becomes substantially zero.
A three-phase hybrid type stepping motor according to the present invention is characterized by comprising a stator and a rotor arranged concentrically with the stator and with an air gap therebetween, said stator having an annular stator yoke, a plurality of stator poles extending radially and formed at a regular pitch on the inner peripheral surface of the annular stator yoke, and stator windings of three-phase each wound around each stator pole, each of said stator poles having an odd number of and at least five small stator teeth at the tip end thereof, said rotor having two split rotor elements and a permanent magnet held therebetween and magnetized so as to form N and S poles in the axial direction thereof, and a plurality of small rotor teeth formed at a regular pitch on the outer peripheral surface of each of said rotor elements, said two split rotor elements being shifted from each other in angular position by a ½ pitch of the small rotor teeth,
wherein said small stator teeth are composed of a first set of three small stator teeth including a small teeth positioned at the center of the stator pole and a second set of two small stator teeth of the same width, and at least one pitch of the adjacent teeth is different from the other pitch of the other adjacent teeth, so that a vector sum of the tertiary harmonic of permeances of the small stator teeth included in said first and said second sets becomes substantially zero.
A three-phase hybrid type stepping motor according to the present invention is characterized by comprising a stator and a rotor arranged concentrically with the stator and with an air gap therebetween, said stator having an annular stator yoke, a plurality of stator poles extending radially and formed at a regular pitch on the inner peripheral surface of the annular stator yoke, and stator windings of three-phase each wound around each st

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