JP4584228B2 - Stepping motor - Google Patents

Description

  The present invention relates to a hybrid type stepping motor (hereinafter referred to as a motor) used in office automation equipment that handles images such as facsimiles, ink jet printers, laser beam printers, and copiers.

  The motor used for each OA device as described above is required to achieve low vibration and low noise while achieving cost reduction, which is an absolute condition.

  On the other hand, the applicants of the present invention have proposed a motor structure in which a small amount of vibration and a large torque are taken out in Japanese Patent Application Laid-Open No. 2003-134788 filed earlier. FIG. 7 shows this structure, in which 1 is a stator on which a winding 3 is wound, 51 is a ring-shaped magnet with a single pole magnetized on its plane, and 21 and 22 are rotor cores sandwiching the magnet 51 with a rotor core. Two sets are prepared, and the motor shaft 4 is mounted as a core so that the magnetized magnetic poles of the magnet 51 are opposed to each other with the same pole. It is a stepping motor having a structure that is arranged to be the same.

In this type of motor, the radial suction forces F1, F2, F3, and F4 are generated in each of the four rotor cores as shown in FIG. 8, and are distributed and balanced by that amount compared to the conventional two configurations. Since there is no unbalanced moment force, the vibration and noise due to the clearance of bearings and the like are more advantageous than conventional machines, and low vibration and noise are reduced. In addition, this stepping motor can ideally obtain about twice as much torque as a conventional motor of the same physique.
In addition, Japanese Patent Application No. 2005-274974 proposes that the motor having this structure has good cost performance when the residual magnetic flux density of the ring magnet is 0.5 T or less.

Japanese Utility Model Laid-Open No. 52-59212 proposes a method using a plurality of ferrite magnets having a small residual magnetic flux density.
JP 2003-134788 A Japanese Patent Application No. 2005-274974 Japanese Utility Model Publication No. 52-59212

  In the motor structure disclosed in Japanese Patent Application No. 2005-274974 proposed by the applicant of the present invention, the residual magnetic flux density Br of the magnet is small and can be configured at low cost. In general, such motors need to be serialized so that the user can select the motor torque according to the load conditions used. In many cases, the output torque of the target motor is generated by fixing the radial dimension of the motor and changing the axial length. It is known that the conventional general motor has an optimum magnetic flux density distribution in a magnetic circuit determined by the Br of the magnet, the rotor core, and the stator core.

The motor structure of the present application is a structure in which two sets of rotors made of magnets magnetized in a single pole on the plane of a ring-shaped magnet are prepared and attached in the motor axial direction so that the magnetized magnetic poles of the magnets face each other at the same pole. There are many unclear points about the optimal magnetic circuit.
There is a method to increase only the stator core stack thickness as a method for taking out the motor torque greatly. However, in practice, the desired torque cannot be obtained unless the magnetic flux of the magnet is also increased.

  Further, in the motor configuration of the 8-pole stator structure disclosed in Japanese Utility Model Laid-Open No. 52-59212, there is no description of the magnetic circuit, and the configuration of the magnetic circuit is insufficient.

6a is a plan view of the rotor core 21 and the stator core of the two-phase four-pole stator structure related to the present application, and FIG. 6b is a plan view of the rotor core 22 and the stator core with the same positional relationship.
In FIG. 6a, in the phase A, the rotor small teeth 23 and the stator small teeth 52 are opposed to each other so that the magnetic resistance is small and the magnetic flux from the rotor flows most. On the other hand, the A ′ phase has the highest magnetic resistance because the convex portions of the rotor small teeth and the concave portions of the stator small teeth face each other, and the amount of magnetic flux flowing from the rotor is small. The B phase and the B ′ phase are opposed to the positions where the convex portions of the rotor small teeth and the stator small teeth overlap, and a magnetic flux having an intermediate size between the A phase and the A ′ phase flows in.
In FIG. 6b, since the rotor small teeth 23 and the stator small teeth 52 face each other at the convex portions and the concave portions in the A phase, the magnetic resistance is large and the magnetic flux from the rotor is minimized. On the other hand, in the A ′ phase, the convex portion of the rotor small teeth and the convex portion of the stator small teeth face each other, so that the magnetic resistance is the lowest and the amount of magnetic flux flowing from the rotor is large. The B phase and the B ′ phase are opposed to the positions where the convex portions of the rotor small teeth and the stator small teeth overlap, and a magnetic flux having an intermediate size between the A phase and the A ′ phase flows in.
As the amount of magnetic flux in the magnet is gradually increased, the amount of magnetic flux in each phase increases. However, if the amount of magnetic flux in the magnet is excessive, the amount of magnetic flux from the rotor core 21 increases most in the A phase in FIG. , The main magnetic pole and core back constituting the A phase are saturated. As a result, the magnetic flux that can no longer flow in the A phase returns to the rotor core as a leakage magnetic flux from the combination of the small teeth 23 of the rotor core 22 and the convex and concave portions of the stator small teeth 52 shown in FIG. Since this leakage flux ΦB flows in the opposite direction to the normal winding linkage flux ΦA, the actual linkage flux is weakened, resulting in a decrease in the A-phase back electromotive force. That is, there exists an optimum relationship between the magnet thickness and the rotor core thickness that maximizes the back electromotive force.
This phenomenon is common to all hybrid stepping motors having the same structure, and is the same for two-phase eight-pole motors and three-phase three-pole, six-pole motors.

一方，トルクは，逆起電力と電流の積である理論出力を機械的角速度ω_M＝ω/pで割ったものであるから，次式のように表せる。ここに，pは極対数すなわちステータまたはロータの小歯数である。

上式からわかるように，コイル巻数と小歯数を一定とすれば，トルクを大きくするにはコイルを通る平均磁束Φと定数kを大きくする必要のあることがわかる。
平均磁束Φと定数kの積が大きく取り出せる組み合わせが，トルクを大きく取り出せ，それは逆起電力が最大となるマグネット厚みとロータコア厚みの組み合わせと言える。 Next, the generated torque will be examined. In Figure 6a, valid main magnetic flux entering the A-phase coil is phi _A. Here, considering the case where the rotor rotates at the electrical angular velocity ω, the coil back electromotive force e _{A at} that time is expressed by the following equation. n is the number of turns of each phase coil, k is a constant, and φ _A = Φ cos θ.

On the other hand, the torque is the theoretical output, which is the product of the counter electromotive force and current divided by the mechanical angular velocity ω _M = ω / p. Here, p is the number of pole pairs, that is, the number of teeth of the stator or rotor.

As can be seen from the above equation, if the number of coil turns and the number of small teeth are constant, it is necessary to increase the average magnetic flux Φ passing through the coil and the constant k in order to increase the torque.
A combination that can extract a large product of the average magnetic flux Φ and a constant k can extract a large amount of torque, which can be said to be a combination of the magnet thickness and the rotor core thickness that maximizes the back electromotive force.

  The present invention has been made on the basis of such knowledge, and a motor that uses two ferrite magnets with the same shape in the plane perpendicular to the motor shaft, changing the thickness in the motor shaft direction, and increasing the number of motor outputs. The purpose of this series is to propose the optimum relationship between magnet thickness and rotor core thickness to achieve high output torque at low cost.

An object of the present invention is to provide a new index as an optimum design parameter of a motor. For this purpose, the magnetic flux density, interlinkage magnetic flux, counter electromotive force, torque, and the like are calculated using a three-dimensional magnetic field analysis, and the parameters are used to derive the maximum torque using the values.
As a result, the relationship between the ferrite magnet thickness Tm and the rotor core thickness Tc is Tm / Tc = 0.25 to 0.45, the maximum magnetic flux density of the rotor small teeth is 1.4 to 1.7 T, and the thickness of the main magnetic pole of the stator core By setting the ferrite magnet thickness and the rotor core thickness so that the maximum magnetic flux density difference between both ends and the center in the direction is 0.75 to 0.85 T, it is possible to extract the back electromotive force to the maximum.

When designing a high-resolution hybrid stepping motor, the present invention can be used to optimally set the relationship between the magnet thickness and the rotor core thickness in accordance with the total length of the motor so that the back electromotive force can be maximized. . In addition, a magnet having good cost performance such as a ferrite magnet having a residual magnetic flux density of 0.5T or less can be used efficiently.
In addition, since there are four rotor cores, the motor of this system is more balanced and balanced in the radial suction force than the conventional two, so the vibration and noise due to the clearance of bearings etc. are more advantageous than the conventional machine. Low vibration and low noise.

  A stator having a plurality of small teeth at the tip of the salient pole portion extending from the main pole, a core back portion integrally connecting the outer periphery of the main pole, and a two-phase winding wound around each main pole; It consists of two sets of rotors arranged in the stator in the axial direction via an air gap. The rotor set is sandwiched between the two rotor cores spaced apart from each other in the axial direction, and in the axial direction. Each rotor core has a plurality of (Nr) small teeth on its outer peripheral surface, and the two rotor cores in each set are shifted from each other in the 1/2 pitch circumferential direction of the small teeth. In the stepping motor which is arranged and arranged so that the polarities of the small teeth of the two adjacent rotor cores are the same, the relationship between the magnet thickness Tm and the rotor core thickness Tc is Tm / Tc = 0.25. The magnet thickness and rotor core thickness are set so that the maximum magnetic flux density of the rotor small teeth is 1.4 to 1.7 T and the maximum magnetic flux density of the main magnetic pole of the stator core is 0.75 to 0.85 T at 0.45. The motor structure is

  FIG. 1 shows a rotor set according to the present invention. The thickness of the two magnets 51 is Tm, and the thickness of each of the rotor cores 21 and 22 is Tc / 2. The core thickness of the central portion overlaps the rotor cores 21 and 22, and the thickness is represented by Tc. The total length of the rotor set can be expressed as 2 (Tc + Tm).

FIG. 2 shows the result of electromagnetic field analysis calculation by FEM (finite element method), using the magnet thickness Tm and rotor core thickness Tc of FIG. 1 as parameters.
The rotor core stacking thickness Tc corresponding to the four types of motor lengths was analyzed for A, B, C, and D according to the total length of the rotor assembly. The horizontal axis of the figure shows the thickness of the ferrite magnet, and the vertical axis shows the value of the A phase back electromotive force when the motor is rotated at 500 r / min. You can see that the value exists.

  Since the entire length of the rotor assembly is fixed, increasing the thickness of the magnet decreases the thickness of the rotor core. In the positional relationship between the rotor and the stator in FIG. 6, when the magnet thickness is increased, the amount of magnetic flux in each phase increases. However, when the limit point where the main magnetic pole and core back of the rotor and the stator are saturated is reached, A Magnetic flux that can no longer flow in the phase returns to the rotor core as leakage magnetic flux. Since this leakage flux ΦB flows in the opposite direction to the normal winding linkage flux ΦA, the actual linkage flux is weakened, resulting in a decrease in the A-phase back electromotive force.

  In FIG. 2, when the total length of the rotor assembly of A is 14 mm, Tc is 5.5 mm and Tm is 1.5 mm. When the total length of the rotor assembly of B is 18 mm, Tc is 7 mm and Tm is 2 mm. In the case of T, the Tc is 8 mm and the Tm is 3 mm, and in the case where the total length of the rotor assembly of D is 28 mm, the Tc is 10 mm and the Tm is 4 mm. This result could be confirmed not only by electromagnetic field analysis but also by a prototype motor.

  FIG. 3 relates to claim 1. Based on the result obtained in FIG. 2, the horizontal axis indicates the ratio Tm / Tc value of the ferrite magnet thickness Tm and the rotor core thickness Tc, and the vertical axis indicates the value of the back electromotive force. FIG. It can be seen that the Tm / Tc value at which the counter electromotive force is maximized is in the range of 0.25 to 0.45 in the range of the rotor assembly thickness of 14 mm to 28 mm.

  FIG. 4 relates to claim 2. The horizontal axis represents the magnet thickness Tm, and the vertical axis represents the magnetic flux density at the position where the counter electromotive force of the rotor small teeth 23 is maximum. When the relationship between the counter electromotive force and the ferrite magnet thickness Tm in FIG. 2 is plotted on FIG. 4, it can be seen that the maximum magnetic flux density of the rotor small teeth is distributed within 1.5 to 2T.

  FIG. 5 relates to claim 3, wherein the horizontal axis represents the magnet thickness and the vertical axis represents the maximum magnetic flux density difference of the stator main magnetic pole portion 2. When the relationship between the counter electromotive force and the ferrite magnet thickness in FIG. 2 is plotted on FIG. 5, the difference in magnetic flux density between the thickness direction both ends P and the central portion Q of the stator main pole is proportional to the counter electromotive force, and the maximum magnetic flux density is 0. It can be seen that it is distributed within .75 to 0.85T.

  FIG. 9 shows the vibration characteristics when the motor is driven at full step. The horizontal axis represents the motor rotation speed, and the vertical axis represents the vibration value in the radial direction of the motor case. The effect of the motor of the present invention can be seen in the vibration value in the section from the point where the resonance point near 100 r / min escapes to 450 r / min. In the two-phase four-pole motor of the present invention, a vibration reduction effect of 3 to 4G, and in a two-phase eight-pole motor, 1 to 3G is seen.

  FIG. 10 shows the relationship between the rotor core and the stator core of the two-phase eight-pole motor, and FIG. 11 shows the relationship between the rotor core and the stator core of the three-phase three-pole motor. Although the number of main magnetic poles varies, a magnetic circuit equivalent to the above-described two-phase four-pole motor is configured, and similar effects can be obtained.

  The basic technology of each element of the present invention has been established. By applying it to a two-phase stepping motor, the relationship between the ferrite magnet thickness Tm and the rotor core thickness Tc can be set optimally, and the cost performance can be maximized. It can be expected to significantly improve characteristics and reduce costs. As a stepping motor used in office automation equipment that handles images such as facsimiles, inkjet printers, laser beam printers, and copiers, it can achieve low vibration and low noise while achieving cost reduction, which is an absolute requirement. It can be widely used as a simple driving source.

The figure which shows the rotor assembly of the motor of this invention The figure which shows the characteristic of the motor of this invention The figure which shows the characteristic of the motor of this invention The figure which shows the characteristic of the motor of this invention The figure which shows the characteristic of the motor of this invention The top view which shows the relationship between the rotor core of the motor of this invention, and a stator core Structural diagram of motor according to the present invention The figure which shows the unbalanced moment force of the motor regarding this invention The figure which shows the vibration characteristic of the motor regarding this invention The top view which shows the relationship between the rotor core of the motor of this invention, and a stator core The top view which shows the relationship between the rotor core of the motor of this invention, and a stator core

1: Stator 2: Stator main magnetic pole 3: Winding 4: Motor shaft 5: Stator salient pole 6: Motor case 7: Motor case 8: Bearing 21: Rotor core 22: Rotor core 23: Rotor small tooth 51: Magnet 52: Small stator Teeth 53: Stator core back P: Stator main pole both ends Q: Stator main pole center

Claims (3)

A stator having a plurality of small teeth at the tip of the salient pole portion extending from the main pole, a core back portion integrally connecting the outer periphery of the main pole, and a winding wound around each main pole; It consists of two rotor sets arranged in the stator in the axial direction through an air gap. The rotor set is sandwiched between the two rotor cores spaced apart from each other in the axial direction, and the axial direction. Each rotor core has a plurality of (Nr) small teeth on the outer peripheral surface thereof, and the two rotor cores in each set are arranged in the circumferential direction of the 1/2 pitch of the small teeth. In the stepping motor which is arranged so as to be shifted and arranged so that the polarities of the small teeth of the two sets of adjacent rotor cores are the same,
Ferrite magnets as said magnet, a relationship between the thickness Tm and the rotor core thickness Tc of the magnet, and Tm / Tc = 0.25 to 0.45,
The maximum magnetic flux density of the motor radial direction component of the small teeth of the rotor core is 1.4 to 1.7 T,
In addition, the multiphase stepping motor is characterized in that the maximum magnetic flux density difference between both end portions P and the central portion Q in the thickness direction of the main magnetic pole of the stator is 0.75 to 0.85T . The multi-phase stepping motor according to claim 1 , wherein the stepping motor is a two-phase stepping motor having four or eight main magnetic poles. The multi-phase stepping motor according to claim 1 , wherein the stepping motor is a three-phase stepping motor having three or six main magnetic poles.

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