PM type stepping motor

Details PM type stepping motor PM type stepping motor

2000-09-07

2002-11-12

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S257000, C310S269000

Reexamination Certificate

active

06479911

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a PM type stepping motor, and more specifically, it relates to a PM type stepping motor capable of further reducing vibration and noise.
2. Description of Related Art
A conventional PM type stepping motor proposed by the present applicant is disclosed in Japanese Unexamined Patent Application Publication No. 10-136631. In this conventional PM type stepping motor, to effectively reduce the higher harmonic component of the detent torque, the polar teeth of the yokes of the stator unit are arranged so as to be deviated from positions at equal intervals. That is, when the polar teeth are shifted from positions of equal intervals, the higher harmonic component of the detent torque appearing in principle can be canceled out in the yokes and reduced.
Other conventional PM type stepping motors are disclosed in Japanese Unexamined Patent Application Publication No. 5-252719, Japanese Unexamined Patent Application Publication No. 8-126290, Japanese Unexamined Patent Application Publication No. 3-7050, Japanese Unexamined Patent Application Publication No. 9-233802, etc.
Of these, Japanese Unexamined Patent Application Publication No. 5-252719 discloses a two-phase PM type stepping motor in which a member consisting of a non-magnetic material is provided between first and second phases stacked together in the axial direction.
Japanese Unexamined Patent Application Publication No. 8-126290 discloses a method of joining yokes constituting the stator of a PM type stepping motor.
Japanese Unexamined Patent Application Publication No. 3-7050 discloses a PM type stepping motor in which adjacent polar teeth of the yoke are connected by a bridge.
Further, Japanese Unexamined Patent Application Publication No. 9-233802 discloses a PM type stepping motor which is equipped with a plate spring biasing the rotation shaft of the rotor in one axial direction.
SUMMARY OF THE INVENTION
In the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 10-136631, it is true that, for example, the fourth degree higher harmonic component of the detent torque, can be reduced. However, there is no possibility of both the fourth degree higher harmonic and the second degree higher harmonic being reduced. Further, in some parts, the gap between the polar teeth of the outer yoke and the polar teeth of the inner yoke is extremely small, so that the leakage flux flowing between those polar teeth increases, resulting in a reduction in the torque generated.
On the other hand, careful study made by the present inventors shows that in a PM type stepping motor, the vibration and noise attributable to the axial vibration of the polar teeth due to the electromagnetic force when the motor is driven are not negligible, apart from the vibration and noise attributable to the higher harmonic component of the detent torque periodically generated with respect to the rotation angle of the rotor due to the magneto motive force of the permanent magnet, as has been conventionally reported. However, in the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 10-136631, nothing is done to reduce the noise such as impact sound attributable to the axial vibration of the polar teeth.
In the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 5-252719, it is possible to prevent direct collision of the first phase and second phase polar teeth by means of the member provided between the phases. However, exclusively aiming at a reduction in detent torque, the technique does not adopt a construction in which collision of the member interposed between the phases with the polar teeth, and the sound caused by the collision of the member with the polar teeth has resulted in an increase in noise.
In the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 8-126290, there is provided no joining method as will prevent collision of the motor cover with the polar teeth, and the sound caused by the collision of the cover with the polar teeth has resulted in an increase in noise.
In contrast, in the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 3-7050, the strength of the base portions of the polar teeth is increased, so that a reduction in the vibration of the polar teeth due to the electromagnetic force when driving the motor can be expected. However, since it adopts a construction in which a bridge is provided, the number of parts is rather large, resulting in an increase in production cost.
Further, in the PM type stepping motor disclosed in Japanese Unexamined Patent Application Publication No. 9-233802, when the reaction force of the electromagnetic force causing the axial vibration of the polar teeth when driving the motor acts on the rotor side, the rotor also axially vibrates, involving elastic deformation of the plate spring and colliding with a member such as the bearing when displaced in the same direction as the biasing direction of the plate spring to thereby generate an impact sound.
The present invention has been made in view of the problems in the conventional techniques. It is one object of the present invention to provide a PM type stepping motor capable of further reducing the higher harmonic component of the detent torque and, further, to provide a PM type stepping motor capable of reducing the noise attributable to the axial vibration of the polar teeth and the rotation shaft due to the electromagnetic force when driving the motor.
According to one exemplary embodiment of the present invention, a PM type stepping motor may consist of a rotor in which N and S magnetic pole pairs of permanent magnets are alternately arranged circumferentially on the outer peripheral surface at a fixed pitch P
1
, and a stator surrounding the rotor. The stator may consist of a stator unit equipped with an outer yoke and an inner yoke, the outer and inner yokes having comb-teeth-like stator polar teeth in the inner periphery. Each of the outer and inner yokes is equipped with n sets of teeth groups each consisting of m stator polar teeth.
Assuming that the pitch of the stator polar teeth in the teeth group is P
2
and the pitch of the teeth groups is P
3
,
P
2
≠
P
1
,  (1)
P
3
≠m·
P
1
, and  (2)
P
3
≠m·
P
2
  (3),
where P
1
, P
2
and P
3
are electrical angles, and m and n are integers equal to or larger than 2.
According to another exemplary embodiment of the present invention, in the above PM type stepping motor, the teeth groups of the outer and inner yokes may be set such that an arbitrary one of the teeth groups of the outer yoke overlaps circumeferentially only one of the teeth groups of the inner yoke. That is, assuming, for example, that m=3, three polar teeth of an arbitrary teeth group of the outer yoke and three polar teeth of the teeth group of the inner yoke paired therewith are arranged circumferentially as: first of the outer yoke, first of the inner yoke, second of the outer yoke, second of the inner yoke, third of the outer yoke and third of the inner yoke, and do not circumferentially overlap other teeth groups. In the case of a plural phase PM type stepping motor in which a plurality of stator units are stacked together, it suffices that this relationship only holds true in each stator unit.
According to another exemplary embodiment of the present invention, in the above PM type stepping motor, the relationship:
P
2
=
P
1
{1
±i/u
}, and  (4)
P
3
=
P
1
{
m±i
′/(
n
·&ngr;′)}  (5)
holds true, where u is a positive integer, i is a positive integer which is not a multiple of u, i′ is a positive integer which is not a multiple of n, and &ngr;′ is the degree of main higher harmonic reduced.
According to another exemplary embodiment of the present invention, in the above PM type stepping motor, the relationship:
P
2
=
P
1
&lc

Affiliated with

Also associated with

Rating

PM type stepping motor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with PM type stepping motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PM type stepping motor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2987629