JPH0984326A - Stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stepping motor having high efficiency over the range of a low frequency through a high frequency. SOLUTION: The stepping motor comprises a plurality of pectinated poles 5b, 6b, 7b, 8b so opposed coaxially with a rotor 4 made of multipolarly magnetized permanent magnet, stator yokes 5, 6, 7 8 formed of Fe metal, exciting coils 9 mounted on the outer periphery of the poles of the outer periphery of the yoke, wherein the stator yokes are surrounded by a cylindrical frame yoke 10. The frame yoke is formed of Fe-Cr alloy to suppress the generation of an eddy current in an AC magnetic field and to improve the pull-out torque on a high-frequency band. In the frame yoke having a small magnetic flux density, Fe-Cr is not magnetically saturated, and even in the low-frequency band, the pull-out torque equivalent to prior art or more is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PM type stepping motor having a rotor with a comb-shaped pole portion using a permanent magnet.

[0002]

2. Description of the Related Art In recent years, stepping motors have been required to reduce power consumption, increase output and increase efficiency. By the way, in the conventional stepping motor, the stator yoke and the frame yoke are configured by using an electromagnetic soft iron plate (SUY), a cold rolled steel plate (SPC), a galvanized steel plate (SEC), or the like.

However, these various materials (SU
Y, SPC, SEC) has good DC magnetic field characteristics, but has poor AC magnetic characteristics when the motor is actually driven. That is, since these steel materials have a low electric resistivity in a fluctuating magnetic field, a large amount of eddy current is generated, and as a result, iron loss is significantly increased. This becomes remarkable as the driving frequency becomes higher. Therefore, this causes a decrease in efficiency, which becomes a bottleneck for satisfying the demand for improving the efficiency of the stepping motor accompanying the battery drive of the office automation equipment.

Therefore, in order to solve the conventional problems, for example, a silicon steel plate or a soft ferrite is used for the stator yoke and the frame yoke (actually 3-10407).
7, Japanese Utility Model Laid-Open No. 62-135577), one in which a through hole is provided in a part of the stator yoke (flow path of eddy current) (Japanese Patent Laid-Open No. 3-283049), and various other proposals have been made.

[0005]

However, each of the improved stepping motors described above has the following problems, and none of them can sufficiently solve the problem of the efficiency reduction due to the eddy current.

That is, when soft ferrite is used, the saturation magnetic flux density is as low as 1/3 as compared with SUY and SPC, and not only a sufficient output torque cannot be obtained, but bending,
It cannot be drawn and its mechanical strength is weak. Moreover, there is a problem that the dimensional accuracy becomes rough, and it is difficult to put it into practical use.

Further, in the structure having the through hole, the output torque tends to decrease as the through hole is formed, and moreover, the number of processing steps increases and the cost also increases. Further, although the through-hole is formed in a portion other than the comb-teeth-shaped magnetic pole portion, the magnetic flux density is low except in the comb-teeth-shaped magnetic pole portion,
Since the eddy current loss is small, the effect of forming the through hole does not appear so much.

Silicon steel sheets have not been put to practical use because they have a problem that drawing is difficult as compared with SUY and SPC.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above-mentioned problems, suppress eddy current generation in a high frequency region as much as possible, and reduce iron loss. To improve the output torque and to provide a highly efficient stepping motor. It is another object of the present invention to provide a stepping motor that can obtain holding torque and torque in a low frequency region with properties equal to or higher than those of a conventional product while obtaining the characteristics in the high frequency region.

[0010]

In order to achieve the above-mentioned object, a stepping motor according to the present invention is provided with a rotor composed of a permanent magnet magnetized in multiple poles so as to be coaxially opposed to the rotor. A stator yoke having a plurality of comb-shaped magnetic pole portions, an exciting coil mounted on the outer periphery of the comb-shaped magnetic pole portion of the stator yoke, and a tubular frame yoke surrounding the exciting coil and the stator yoke. On the premise of a stepping motor provided with, the stator yoke is made of Fe-based metal, and the frame yoke is made of Fe-Cr-based alloy (claim 1).

Preferably, the Fe-Cr alloy is 10 to 20 wt% of Cr and 80 to 90 wt% of Fe.
(Claim 2).
That is, if it is less than 10 wt% of Cr, rust occurs and it cannot be used for a long period of time. The rust preventive power increases as the amount of Cr added increases, but if it exceeds 20 wt%, the rigidity increases, so that the workability is reduced to 20 wt% or less. Then, within this range, deep drawing can be easily performed. Even if the content exceeds 20 wt%, deep drawing is not impossible, but as the content increases, a greater force is required at the time of pressing or the yield decreases. Moreover, the addition amount of Cr is 2
When it is 0% or more, the magnetic properties are remarkably deteriorated.

Further, this applicable range (10 to 20 wt%)
Is subdivided into 10-15 wt% and 15-20 wt%
The former has the feature that it can exhibit the necessary rustproofing power under normal use environment such as indoors, and can minimize the deterioration of magnetic properties. In addition, the latter has a characteristic that the generation of rust can be suppressed even in a severe environment such as outdoors or at sea. Therefore, the content will be determined based on the environment in which it is used and the required specifications.

In any case, the content of Fe is C
Since it is determined corresponding to the content of r and does not refuse to contain a trace amount additive in the balance, the total of Fe and Cr does not necessarily have to be 100 wt%.

The Fe-Cr alloy has an electrical resistivity ρ of SU
It is 5 to 10 times higher than Y, SPC, and SEC. And since the eddy current is inversely proportional to the electric resistivity ρ of the yoke,
In the stepping motor of the present invention, the generation of eddy current is reduced as much as possible even when an alternating magnetic field is generated during motor driving. As a result, when such a material is used for the yoke, loss is reduced and a stepping motor with low power consumption can be realized. Since the eddy current is made difficult to flow in this way, the reverse magnetic field due to the eddy current is also reduced, and if the input current is kept constant, the total magnetic flux amount increases and the output torque increases. In other words, in order to obtain the same output torque, a small amount of current is passed through the exciting coil, and as a result, copper loss can be reduced. When the iron loss and the copper loss are thus reduced, the heat generation of the motor itself can be suppressed to a low level.

By the way, the Fe--Cr alloy is the conventional Fe
The output torque may be lower than that of the conventional motor because the saturation magnetic flux density is low in the low frequency region and below as compared with the system metals (SUY, SPC, SEC).

In the stator yoke, the pole tooth portion having a particularly small magnetic path cross-sectional area has the highest magnetic flux density. Therefore, if an Fe-Cr alloy is used there, it is considered to be Fe-based metal in the low frequency region and below due to the above reason. Compared with this, output torque is reduced.

On the other hand, since the frame yoke has a sufficiently large magnetic path cross-sectional area as compared with the stator yoke (comb-shaped magnetic pole portion), the magnetic flux density is low. Therefore, even if the frame yoke is made of the Fe-Cr alloy, magnetic saturation does not occur and the output torque does not decrease.

Therefore, in the present invention, the Fe-Cr alloy is used only for the frame yoke, and the stator yoke portion is formed of the conventional Fe metal, so that the frame yoke portion is prevented from lowering the torque in the low frequency region and below. The efficiency is improved by suppressing the eddy current flowing in the.

[0019]

1 and 2 show an embodiment of a stepping motor according to the present invention. In this embodiment, a two-phase type stepping motor will be described. As shown in the figure, a rotor 4 is formed by fixing a cylindrical permanent magnet 3 integrally around a shaft 1 via a resinous connecting member 2. The outer periphery of the permanent magnet 3 is magnetized in multiple divisions in the circumferential direction.

Since the present embodiment is a two-phase type stepping motor, the first to fourth stator yokes 5 to 8 are concentrically arranged around the rotor 4. Specifically, the first and second stator yokes 5 and 6 form a first phase, and the third and fourth stator yokes 7 and 8 form a second phase. And each stator yoke 5-5
Reference numeral 8 forms comb tooth-shaped magnetic pole portions 5b to 8b by bending the inner periphery of the flat ring-shaped flange portions 5a to 8a by 90 degrees in a predetermined direction. The pair of stator yokes (5 and 6, 7 and 8) face each other toward the tip side of the comb-teeth magnetic pole portions (5b and 6b, 7b and 8b), and each of the comb-teeth-shaped magnetic pole portions. It is inserted and placed in the unformed region of the tooth. The electrical angle between the first phase side and the second phase side is 90
Make sure to stagger.

Further, this stator yoke pair (5 and 6,
The exciting coil 9 composed of the coil portion 9b wound around the coil bobbin 9a is mounted around the outer periphery of 7 and 8). As a result, the exciting coil 9 is interposed between the flange portions (5a and 6a, 7a and 8a).

Then, the rotor 4, the stator yoke 5
8 to 8 and the excitation coil 9, a cup-shaped frame yoke 10 having a bottom is arranged concentrically around the outer circumference of the excitation coil 9. In other words, the above components are inserted and arranged in the frame yoke 10. In this state, the open side of the frame yoke 10 is covered with the cap 11.

Both ends of the shaft 1 and the cap 1 are formed in the through hole 10a formed in the center of the bottom surface of the frame yoke 10.
1 is inserted into each of the through holes 11a formed therein and is rotatably supported by a bearing, and an end portion of the shaft 1 on the cap 11 side penetrates through the through hole 11a and projects outward by a predetermined length.
Functions as an output shaft. A flange 12 for fixing the stepping motor to a predetermined position of another device is integrally formed on the outer surface of the cap 11 (see FIG. 1).

Since the shape and configuration of each component described above are basically the same as the conventional ones, when manufacturing the stepping motor of the present invention, the manufacturing facility currently used can be used as it is.

Here, in the present invention, each of the four stator yokes 5 to 8 is formed using an Fe-based metal. F
As the e-based metal, various conventionally used materials such as SEC, SUY, and SPC can be used. Then, the frame yoke 10 is formed by using a Fe—Cr based alloy having a predetermined composition ratio. An example of this Fe-Cr alloy is, for example, JIS S
US430, SUS410L, etc. can be used.

As a result, the eddy current generated in the frame yoke 10 due to the alternating magnetic field during driving of the motor can be suppressed as much as possible, and the efficiency is improved. Then, as the frequency becomes higher, the difference (difference from the conventional product) becomes more remarkable. On the contrary, in the low frequency region, although there is not much difference, magnetic saturation does not occur in the frame yoke 10, so that the holding torque and the pullout torque in the low frequency region are at least equal to or higher than those in the conventional case. Therefore, it is possible to obtain a highly efficient stepping motor with a torque equal to or higher than that in a wide range from the low frequency region to the high frequency region. In other words, the stepping motor for obtaining the same output torque can be downsized by the efficiency improvement by using the product of the present invention.

When Cr is set to 10 to 15 wt%, the required rust preventive power can be exerted in a normal indoor environment while maintaining a very good magnetic property range. It is suitable for use in offices (OA equipment, etc.). On the other hand, when the Cr content is 15 to 20 wt%, the rustproofing power is further improved, and therefore it is not used outdoors (for in-vehicle or outdoor equipment) or exported overseas (not affected by salt during transportation by ship). Because) is suitable for. In this case as well, although the magnetic characteristics are lower than those of the former case, the AC magnetic characteristics are better than those of the conventional one, so that the characteristics of the motor are improved.

* Experimental Results In order to demonstrate the effect of the present invention, the motor of the above-described embodiment and a conventional motor having the same shape (the difference is the material of the frame yoke) are manufactured, and the respective motor characteristics are shown. evaluated. The driving condition is two-phase excitation bipolar constant current chopper driving. The measured motor characteristics are a holding torque characteristic with respect to an input current and a pullout torque characteristic with respect to a frequency. However, the Fe-Cr alloy of the frame yoke contains 12 wt% of Cr.
I'm using As for the holding characteristics with respect to the input current, the results shown in Table 1 below were obtained.

[0029]

[Table 1] As shown in Table 1 above, the holding torque of the invention product at each of the same currents was almost the same value as the holding torque of the conventional product. The current that flows while the motor is in use is 0.4 to 0.5A. That is, it is understood that the holding torque, which is the static torque of the stepping motor according to the present invention, is equivalent to that of the conventional product.

As for the pullout torque characteristic with respect to frequency, the results shown in FIG. 3 were obtained. About 300pp
In the low frequency region of s, the pullout torque of the invention product is equivalent to that of the conventional product. Then, as the frequency becomes higher, the pullout torque decreases, but the ratio of decrease is smaller in the invention product than in the conventional product. That is, in the high frequency region, the product of the present invention has a higher pullout torque than the conventional product, and the difference becomes more significant as the frequency increases.

From the above two experimental results, in the stepping motor according to the present invention, the holding torque and the pullout torque in the low frequency region are at least equal to or higher than those of the conventional one, and the pullout torque in the high frequency region is conventional. It is found that the efficiency of the stepping motor according to the present invention is better than that of the conventional stepping motor over the entire range of frequencies because the stepping motor of the present invention exceeds that of the conventional stepping motor.

[0032]

As described above, in the stepping motor according to the present invention, the Fe-Cr alloy is used for the frame yoke and the Fe metal is used for the stator yoke, so that the eddy current flowing in the frame yoke is suppressed. Especially, the efficiency is improved and the torque is increased in the high frequency region. Further, even in the low frequency region and below, since the magnetic flux density is low in the frame yoke portion, the torque does not decrease due to the magnetic saturation, and the torque becomes equivalent to that of the conventional stepping motor. That is, the torque of the stepping motor can be made equal or improved over the entire frequency range.

Fe-C forming the frame yoke
Since the r-based alloy has a rust preventive effect, a special rust preventive treatment step such as plating coating is unnecessary, and the number of steps can be reduced. The Fe-Cr alloy has good deep drawing workability, and the stepping motor of the present invention can be manufactured by using conventional manufacturing equipment as it is.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an embodiment of a stepping motor according to the present invention.

FIG. 2 is an exploded perspective view thereof.

FIG. 3 is a characteristic diagram demonstrating the effect of the present invention.

[Explanation of symbols]

 3 Permanent Magnet 4 Rotor 5-8 Stator Yoke 5b-8b Comb Tooth-shaped Magnetic Pole 9 Excitation Coil 10 Frame Yoke

Claims (2)

[Claims] 1. A rotor (4) comprising a multi-pole magnetized permanent magnet (3), and a plurality of comb tooth-shaped magnetic pole portions (5b to 8b) provided so as to be coaxially opposed to the rotor. A stator yoke (5-8), an exciting coil (9) attached to the outer periphery of the comb-shaped magnetic pole portion of the stator yoke, and a tubular frame yoke (around the exciting coil and the stator yoke). 10), wherein the stator yoke is made of an Fe-based metal, and the frame yoke is made of an Fe-Cr-based alloy. 2. The Fe--Cr alloy has a Cr content of 10 to 10.
The stepping motor according to claim 1, wherein the stepping motor contains 20 wt% and Fe of 80 to 90 wt%.