JPH0154950B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotor for a stepping motor. More particularly, the present invention relates to a rotor for a stepping motor that uses radially magnetized plastic bonded magnets as the rotor core.

The structure of the rotor of a conventional so-called hybrid stepping motor is shown in Figure 1.
It basically consists of a cylindrical permanent magnet (1), a rotor core (2) made of ring-shaped laminated steel plates, and (3) a shaft. The laminated steel plate 2 has a large number of salient poles on its outer periphery as shown at 4, for example, 50 salient poles. These salient poles form a gap with the salient poles of a stator (not shown), and lines of magnetic force flow through this gap to operate the motor. Here, the reason why the steel plates are laminated is to prevent heat loss due to eddy current. The permanent magnet No. 1 is cylindrical with a shaft hole in the center, and conventionally it is generally made of a sintered body of ferrite or rare earth alloy, with N and S poles at both ends in the axial direction.
They are magnetized so that they each have a pole. This N,
The south pole brings N and S magnetic field lines to the salient poles of the laminated core arranged around it, respectively.

However, conventional rotors have the following drawbacks. The laminated core shown in Fig. 1 and 2 for both N and S poles is usually made of at least 10 or more core pieces glued together, but the aforementioned gap between the rotor and stator improves the rotational characteristics of the motor. Therefore, it is usually extremely small, less than 0.5 mm. However, since ten or more core pieces are laminated, irregularities often occur on the outer periphery of the salient pole due to dimensional errors in the core pieces. This unevenness makes the gap uneven, so if the motor performance deteriorates or is severe, there is a risk of contact with the stator. For this reason, conventionally, it has been necessary to grind the laminated salient pole portions using various methods to obtain a smooth salient pole without unevenness. That is, a process of laminating with high precision and a finishing process of grinding after lamination were required. In addition, permanent magnets are originally magnetized so that the magnetic flux of a cylindrical magnet is concentrated on both end faces in the axial direction. However, as shown in FIG. 1, since it is actually necessary to guide the magnetic flux to the salient poles of the rotor core, the magnetic flux is extracted from the circumferential direction near both ends of the permanent magnet. For this reason, the direction of the magnetic flux is forced to bend, and from the standpoint of the magnetic circuit, leakage magnetic flux becomes large.
The magnetic flux generated from the permanent magnet was not fully utilized. Therefore, even if high-performance permanent magnets were used, the magnetic flux density passing through the gap between the rotor and stator would be small, resulting in a drawback that the motor performance would not improve much. Furthermore, due to the hard and brittle nature of conventional sintered permanent magnets, many steps are required to accurately drill holes for shafts, and the yield is also low. Ta. Furthermore, similar problems have arisen not only when drilling holes for shafts, but also when determining the outer diameter and length of magnets with high accuracy. In addition, when assembling a permanent magnet with a shaft, it is ideal to directly hammer it into place in order to prevent uneven rotation, but in reality, since it is a sintered magnet, it is prone to cracking and chipping, so Usually, a soft metal such as an aluminum cylinder is inserted into a hole in the magnet and forcefully engaged with the shaft. Note that a method of combining parts using an adhesive has also been used, but with this method, it is difficult to obtain a rotor with good rotational accuracy due to uneven application of the adhesive. Next, when assembling the parts finished as described above to form a rotor,
In order to improve rotational accuracy, that is, to minimize rotational wobbling, the assembly process itself usually requires special jigs and tools, and requires advanced technology. Furthermore, in general, the greater the weight of the entire rotor, the greater the moment of inertia.
It is difficult to operate the motor with low current consumption, but with the conventional rotor configuration described above, everything is made of metal and the weight of the rotor must be quite large, making it unsuitable for reducing current consumption. It was hot.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new stepping motor rotor that fundamentally solves the drawbacks of conventional rotors. The details of the present invention will be specifically explained below to clarify the contents and advantages of the present invention. The present invention provides a stepping motor having a rotor using permanent magnets, in which the rotor has a rotor core composed of a ring-shaped plastic bonded magnet magnetized in the radial direction and has a large number of salient poles on the outer periphery, and a rotating shaft. The present invention also provides a stepping motor rotor comprising a cylindrical body connecting the rotor and the shaft. The present invention also provides a rotor for a stepping motor, characterized in that the cylindrical body is omitted in some cases, and a rotor core made of a ring-shaped plastic bonded magnet is directly connected to a rotating shaft. It is.

The plastic bonded magnet used in the present invention is:
A magnet made of powdered permanent magnetic material bonded with plastic. Permanent magnet materials include ferrite, rare earth alloys, alnico, Mn-Al alloy, etc., but Ba ferrite and Sr are usually used.
Ferrite and SmCO ₅ , Sm ₂ (Co, Fe, Cu,
M) ₁₇ , M is preferably a rare earth alloy such as Zr, Hf, Ti, etc. from the viewpoint of magnetic properties and other reasons. Both thermoplastic and thermosetting plastics are used as binders. Examples of thermoplastic plastics include polyethylene, ethylene vinyl acetate (EVA), nylon, polypropylene, and modified polyolefins. Examples include Fuaidh. Examples of thermosetting plastics include epoxy and phenol. Injection molding, compression molding, extrusion molding, hot pressing, and impregnating methods are used as magnet molding methods for bonding magnet material powders using plastic.

Plastic bonded magnets obtained by these methods are characterized by superior dimensional accuracy compared to magnets produced by conventional sintering methods.

The large number of salient poles provided on the outer periphery of the plastic bonded magnet in the present invention are as shown in 4 in FIG. , the number of salient poles, etc. are not limited. Further, the salient poles are formed at the same time as the magnet is molded by the above-mentioned molding method, and a metal mold, press mold, plastic mold, or ceramic mold is processed to form the salient poles. The reason for this is that, as mentioned above in the drawbacks of the conventional method, it is essential that the salient poles have good precision without any unevenness, and it is better to form the salient poles during magnet molding because it is better to form the salient poles when molding the magnet. Moreover, it has the advantage of not requiring post-processing such as grinding.

Radial magnetization refers to magnetizing a ring-shaped magnetic body so that lines of magnetic force radiate outward from the center of the circle. Therefore, in a ring-shaped magnet, the inner circumference becomes the N pole or S pole, the outer circumference becomes the S pole or N pole, and the middle between the outer diameter and the inner diameter of the ring becomes a circular magnetic neutral point. .

Conventionally, the magnet was magnetized in the direction of the shaft axis, and therefore the direction in which the magnetic flux was extracted was different from the direction of magnetization, resulting in a large amount of leakage magnetic flux and poor efficiency.
On the other hand, if a ring-shaped magnet magnetized in the radial direction is used as in the present invention, the magnetic flux is used in the same direction as the magnetization direction, resulting in less leakage and higher efficiency. Can be used magnetically.

Magnetization may be performed during the magnet molding or after molding. Furthermore, the use of so-called anisotropic magnets in which magnetic powder is aligned and oriented during magnet molding results in higher performance magnets, which is advantageous in terms of motor performance. Of course, there is nothing wrong with using an isotropic magnet if the objective in terms of motor performance can be achieved.

Generally, it is difficult to form fine salient poles in a sintered magnet, and furthermore, if an attempt is made to provide radial anisotropy, cracks will occur during the sintering process. For this reason,
Conventionally, a rotor core made of ring-shaped laminated steel plates was attached to a cylindrical sintered magnet. According to the invention, plastic bonded magnets are used as magnets. Thereby, a large number of salient poles can be formed on the outer periphery of the magnet itself, which is magnetized in the radial direction.

In addition, this plastic bonded magnet is used as it is as a rotor core, but since this magnet contains plastic, it is not a good conductor at least, so unlike conventional rotors, a steel plate is used to prevent heat generation due to eddy current. There is no need to take measures such as lamination, and the advantage is that the one-piece plastic bonded magnet can be used as is. Furthermore, since the plastic bonded magnet has a certain degree of elasticity, it has the advantage of being less prone to cracking or chipping when it is hammered into engagement with a cylinder or shaft, and is easy to handle.

The rotating shaft is made of the same metals and alloys as those used in conventional rotors, and is used in the present invention as is.

In the present invention, the cylindrical body that connects the rotor core and the shaft eliminates uneconomical problems such as the need to increase the size of the magnet if a plastic bonded magnet is directly connected to the shaft in the case of a relatively large stepping motor. It is used for this purpose. Therefore, in the case of a small stepping motor or in cases where the magnet size can be increased, this cylindrical body may not be necessary. The material of the cylindrical body can be metal, plastic, ceramic, etc., or a combination thereof, but when trying to construct a magnetic circuit between the rotor cores for N and S poles and the cylindrical body, ferromagnetic materials are used. It is best to use at least a portion of the cylinder made of metal or ceramics, which helps improve motor performance. Furthermore, if it is desired to reduce the weight of the rotor as a whole, it is advisable to use a plastic cylinder for at least part of the rotor. When using a plastic cylindrical body, integral molding with the above-mentioned plastic bonded magnet or ferromagnetic cylindrical body by two-color molding, insert method, outsert method, etc. is also possible; in the case of a metal or ceramic cylindrical body, However, it is possible to obtain a magnet-cylindrical body with sufficiently good adhesion by using the insert method, outsert method, etc.

Stepping motor rotor 3 of the present invention
Cross-sectional views of two specific examples are shown in FIGS. 2A, 2B, and 2C.

In FIG. 2A, a cylinder 2 is assembled to each of two rotor cores 1, and 3 is a shaft.

Fig. 2B shows a case in which the cylinder 2 is common and is used for both rotor cores, and Fig. 2C shows a case in which there is no cylinder and the rotor core is directly assembled to the shaft.

As for the combination method, it is more preferable to forcibly engage at least the shaft and the cylindrical body. If the above-mentioned plastic bonded magnet and cylinder are integrally formed by molding, assembly of the rotor is completed by simply mating the cylinder and the shaft. Or, more advantageously,
It is also possible to complete the entire rotor in one molding process by insert molding the shaft or even the shaft and cylinder when molding the plastic bonded magnet.

In any of the above three specific examples, two rotor cores for the north pole and the south pole can be simultaneously molded using a single mold. In this case, N
A rotor with excellent relative positional accuracy between the pole salient pole and the S pole salient pole can be easily obtained.

As stated above, the rotor of the present invention is
By using permanent magnets with high dimensional accuracy that are plastic bonded to the rotor core, the disadvantages of conventional rotors are overcome, and the rotor is characterized by various advantages.

The present invention will be specifically described below with reference to Examples.

Example 1 Example 1 will be described with reference to FIG.

A pellet containing 93% by weight of magnetic powder obtained by hot kneading rare earth magnetic powder (2-17 type compound) and nylon 12 was injection molded to form a pellet with an outer diameter of 22 mm and an inner diameter of 14 mm.
A pair of spur gear-shaped rotors with a width of 5 mm and 50 salient poles on the outer periphery were fabricated. An electromagnet is installed in the injection mold in advance, and a magnetic field is applied to the mold cavity in the radial direction at the same time as injection.
In this way, the rotor core 1 taken out after demagnetization
The magnetic particles are oriented in the radial direction. The rotor core was pulse magnetized so that one salient pole had an N pole and the other salient pole had a S pole. The surface magnetic flux density of the N and S poles was 1300-1400 Gauss. Next, it is made of iron alloy (SS-41) with an outer diameter of 14 mm and an inner diameter of 10 mm.
A cylindrical body 2A having a length of 13 mm and a protrusion in the center, and a cylindrical body 2B made of PBT resin and having an outer diameter of 10 mm, an inner diameter of 5 mm, and a length of 13 mm were manufactured. These and the shaft 3 (diameter 5 mm) made of stainless steel (SUS316) were assembled by forced engagement.

In this embodiment, since the combinations are arranged in the order of metal-plastic-metal-plastic from the shaft 3 toward the core at the outer periphery, a feature is that the hammer-fitting can be performed easily. Comparing the rotor of this example with a conventional rotor having the structure shown in Fig. 1 and having almost the same dimensions, the weight of the rotor of this example is 40% smaller, and the surface The magnetic flux density has become 3 to 4 times higher. Therefore, the product of the present invention is a rotor that combines reduced current consumption due to weight reduction and improved motor performance due to increased magnetic flux.

Example 2 Example 2 will be described with reference to FIGS. 4 and 5.

A pair of plastic bonded rare earth alloy magnets having 50 salient poles and having an outer diameter of 15 mm as shown in FIG. 4 were prepared in the same manner as in Example 1. After this was magnetized in the radial direction, it was forcibly fitted to the shaft (Fig. 5). Although this embodiment is an example in which the cylindrical body is omitted, there is no break in the magnetic circuit between the north and south poles, resulting in a lightweight, high-performance rotor. It goes without saying that if the characteristics of the magnets in the rotor core are sufficiently compatible with the motor performance, there is no need to construct a magnetic circuit.

Example 3 In order to produce a rotor with excellent relative positional accuracy between the N and S poles of the rotor core, a salient pole for the N pole and a salient pole for the S pole were placed in the same cavity of an injection mold. A two-color mold for integral molding was prepared, which could be used to form the cylindrical body and the cylindrical body at the same time. After the PBT resin was first molded, a magnetic powder kneaded pellet was immediately molded in a magnetic field while leaving the cavitation on the PBT portion. Thus, by injection molding,
As shown in FIG. 6, a pair of rotor cores (for N and S poles) made of plastic bonded magnets and a cylindrical body (made of PBT resin) were integrally molded.

According to the molding method of this example, the relative position of the salient pole for N pole and the salient pole for S pole (when the salient poles face each other without any deviation or when they face each other with a half pitch difference) positional relationship), it is possible to obtain an integrated product that is assembled with precision, and unlike the conventional case where the N-pole rotor core and the S-pole rotor core were made separately, it is not necessary to assemble them once at a time. No need to pay special attention to relative positioning, good rotational accuracy,
Moreover, it is possible to obtain a rotor that is excellent in mass production. In addition, although the two-color molding method was used in this example, if the entire rotor is small,
In some cases, both the rotor core and the cylindrical body are made of only the material constituting the magnet.

As described above, the present invention uses plastic bonded magnets as the rotor core to reduce the weight of the rotor and thus reduce power consumption.
This invention brings about a number of advantages, including an increase in the magnetic flux density generated in the gap between the rotor and stator, which in turn improves motor performance, simplifies the manufacturing process for each rotor part, and simplifies rotor assembly.

[Brief explanation of drawings]

FIG. 1 is a simplified diagram showing a conventional rotor. Second
Figures A, 2B and 2C are cross-sectional views of rotors according to three embodiments of the present invention. FIG. 3 is a sectional view of a rotor according to a first embodiment of the invention. 4 and 5 are simplified illustrations of a rotor core and rotor formed in accordance with a second embodiment of the invention. FIG. 6 is a simplified diagram of a rotor formed in accordance with a third embodiment of the invention. 1...Rotor core, 2...Cylinder body, 3...Shaft.

Claims (1)

[Claims] 1. In a stepping motor rotor,
The rotor core comprises a rotating shaft and a rotor core attached to the rotating shaft, and the rotor core is made of a ring-shaped plastic bonded magnet having a large number of salient poles on the outer periphery and magnetized in the radial direction. Features a rotor. 2. The rotor according to claim 1, wherein the rotor core is attached to the rotating shaft via a cylinder. 3. The rotor core includes a N-pole rotor core and a S-pole rotor core that are spaced apart from each other in the axial direction of the rotating shaft, and the N-pole rotor core and the S-pole rotor core The rotor according to claim 1, wherein the rotor and the rotor are integrally formed. 4. The rotor core includes a N-pole rotor core and a S-pole rotor core that are spaced apart from each other in the axial direction of the rotating shaft, and the N-pole rotor core and the S-pole rotor core 3. The rotor according to claim 2, wherein the cylindrical body and the cylindrical body are integrally formed.