JP2587436Y2 - Step motor rotor structure - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor structure of a step motor, and more particularly to improvement of a rotor and improvement of characteristics of a step motor.

[0002]

2. Description of the Related Art In recent years, with the downsizing of equipment, a step motor for driving has also been required to be reduced in size, and a small and high torque motor has been desired.

[0003] A multi-pole magnetized permanent magnet rotor and two
In a rotor structure of a PM type step motor having four stator yokes which receive a magnetomotive force by two exciting coils, a rotor using a plastic permanent magnet made by an injection molding method using a conventional step motor is shown in FIG. There is a gate for injection molding, and the gate is cut off by the gate cutout 4, that is, forcibly opening the molding die after injection molding. Because there is a part, permanent magnet 3
Is shortened by the height of the gate cutout 4, and the effective length L of the stator cannot be fully utilized.
It is known that it is important for the stepper motor characteristics and torque to be uniform that the magnetic circuits of the stator blocks A5 and B6 are uniform. For uniformity of the magnetic circuit, the left and right stator blocks A5 and B6 have the same dimensions from the center position of the stator.
It is desirable that the permanent magnets 3 have the same magnetic force. Therefore, the permanent magnets 3 are symmetrically equal in length from the center of the stator, and the effective permanent magnet length of the rotor is short. Therefore, the facing area between the magnetic pole teeth of the stator and the permanent magnet is smaller than when the effective length L of the stator is fully utilized.

In addition, since the length of the permanent magnet of the rotor is a dimension in consideration of the height variation of the injection molding gate notch 4, that is, a short dimension that can absorb the height variation, the length of the permanent magnet 3 is made smaller than the end face of the permanent magnet 3. The distance between the end faces of the bearing 7 increases, the thrust gap increases, and the amount by which the rotor can move relatively freely in the thrust direction increases.

[0005]

It is known that the maximum static torque of the stepping motor increases almost in proportion to the area of the stator between the pole teeth of the stator and the permanent magnet 3 of the rotor. Similarly, it is known that an increase in the facing area leads to an increase in the torque.

As described above, in the conventional rotor structure, the permanent magnet 3 must be shortened by twice the height of the injection-molding gate cutout 4, and the area of the stator facing the magnetic pole teeth is reduced. Therefore, the motor has low torque and is inefficient. In addition, since the thrust gap is large, the amount of movement of the rotor in the thrust direction is large, which affects positioning accuracy, and causes large inconveniences such as noise and vibration. As the step motor becomes smaller, the influence of the height of the cutout 4 of the gate for injection molding becomes larger. As the number of times of injection molding increases, the wear of the mold also increases, the height of the gate cutout 4 increases, and the height of about 0.1 mm initially becomes 0.5 mm or more when the number of injection molding times exceeds tens of thousands of times. Has also become. This causes a change in the amount of thrust gap of the rotor depending on the production lot of the permanent magnets 3, and also leads to a shift from the optimum configuration position of the permanent magnets 3 with respect to the stator. The optimal displacement of the permanent magnet 3 causes the magnetic circuit to be non-uniform, and the characteristics of the step motor deteriorate.

In order to eliminate the influence of the gate cutout 4 for injection molding, a method of removing the gate cutout of the manufactured permanent magnet by secondary processing is adopted. However, in addition to the high cost due to the secondary processing, the magnet particles covered with plastic are exposed to the surface in a bare state due to removal by cutting or the like, and the corrosion resistance is reduced and rust is generated. To prevent this, rust prevention treatment such as coating must be performed, which is a factor of cost increase.

[0008] The countermeasure against the gate break 4 in the injection molding can be dealt with by devising the mold structure. For example, it is possible to solve the problem if a sink portion is provided in the gate portion and its periphery, and the gate cutout 4 can be controlled to be equal to or less than the height of the sink portion. However, in recent miniaturization and cost reduction of the step motor, improvement of dynamic torque by low inertia moment and reduction of the amount of expensive magnet material used are adopted. Therefore, the material thickness of the permanent magnet is reduced. It is getting thinner. In the case of a sink gate, it is difficult or impossible to process a thin-walled product due to the structure of a molding die. That is, there is a limit in reducing the gate diameter due to the relationship between the permanent magnet particle diameter and the diameter of the gate.
mm. When the thickness of the magnet material is about 1.0mm, it is difficult to manufacture the injection molding die using the sink gate method, or it takes a lot of man-hours to maintain the product in order to control the quality of the product. There is a problem that can not be done. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a step motor with excellent maximum static torque and high-speed response at low cost.

[0009]

In order to achieve the above-mentioned object, the rotor structure of the stepping motor according to the present invention is a stator which receives a magnetomotive force by a permanent magnet rotor which is magnetized on the outer periphery and two exciting coils. In the rotor structure of the PM type step motor having four yokes, the permanent magnets 3 constituting the rotor are made by an injection molding method, and the gate cutouts 4 for injection molding of the two permanent magnets are arranged inside facing each other. This is the configuration that

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of an embodiment of a stepping motor using a rotor structure according to the present invention. A permanent magnet 3 is fixed to a magnet spacer 2 fixed to a shaft 1. The permanent magnet 3 is made of a neodymium-based plastic magnet containing plastic by injection molding. 2
In the permanent magnet of the body, there is a gate cutout 4 for injection molding, the gates facing each other, and are housed within a distance of 1.2 mm between the permanent magnets.

The total length of the two permanent magnets was set to a value that secured the minimum clearance with the bearing and 0.1 mm on one side, so that the effective length L of the stator could be used to the maximum. Compared with the conventional method, the total length of the permanent magnet 3 can be increased by 1.0 mm, and the effective facing area between the magnetic pole teeth of the stator and the permanent magnet can be increased by 20%.

Since the facing area between the magnetic pole teeth of the stator and the permanent magnet can be increased by 20%, the maximum static torque is:
15 g of conventional 13 g-cm at 4.5 V applied voltage
An improvement of -cm and a 15% increase was obtained. Note that the root of the magnetic pole teeth of the stator corresponding to the intermediate permanent magnet space where the two permanent magnets are arranged is a portion bent by press working, and the air gap with the rotor is smaller than that of the main magnetic pole teeth. Is much larger. Therefore, even if the permanent magnets 3 do not face each other, the characteristics of the step motor are not affected. Rather, an increase in detent torque (torque generated without passing a current through the coil) can be prevented, and the characteristics of the step motor tend to be improved.

The production of the permanent magnet 3 is the same as that of the conventional injection molding die, so that the production cost of the die does not increase. Further, by displacing the gate cut-outs 4 facing each other of the two permanent magnets in the circumferential direction, the rotor can be assembled up to a maximum height of 1.2 mm of the injection-formed gate cut-outs 4. Compared to the conventional case where the thickness is controlled to 0.5 mm or less, the frequency of maintenance such as replacement of the gate bush of the molding die is reduced, and the inspection of the gate height is not required. Although two permanent magnets 3 were used, the improvement in dimensional accuracy of the parts was obtained due to the short length, the dimensional inspection process could be omitted due to the improvement in dimensional accuracy, and expensive magnet materials were used. There was no cost disadvantage because there was no increase in usage.

As a ripple effect, an intermediate portion between the two permanent magnets 3, that is, a space portion has an effect of reducing the rotor inertia moment, and there is no increase in the inertia moment as compared with the conventional method, and the stepping motor has no effect. Improved the high-speed responsiveness.

Further, the magnetic circuit is a stator block A
It is known that being independent between the stator blocks B6 is advantageous in the characteristics of the stepping motor.
In the present invention, since the permanent magnet 3 is separated into two bodies, the independence of the magnetic circuit composed of the stator block A5 and the stator block B6 with the permanent magnet 3 is increased, and characteristics such as torque and static angle error of the step motor are improved. It is advantageous and promotes the effect of improving characteristics.

The gate 4 for injection molding of a permanent magnet is
In the case of a part, the balance of the rotating body is lost, causing vibration and noise.
The problem can be solved by forming a pseudo gate substantially equal to the gate cutout 4 at a position 180 ° symmetrical to the gate, that is, a protrusion.

In the embodiment of the present invention, although the magnet spacer 2 is used for the rotor, it is apparent that the same effect can be obtained even if the permanent magnet 3 is directly fixed to the shaft 1 without using the magnet spacer 2. .

The gap in the thrust direction of the rotor can be set small because it is not affected by the gate cut-out 4. Since the gap does not change depending on the production lot, an appropriate position between the stator and the rotor is secured. As a result, a constant maintenance of the magnetic circuit was obtained. The stability of the step motor characteristics was increased, and the vibration and noise could be reduced.

[0019]

As described above, according to the present invention, by increasing the effective length of the rotor, the effective length L of the stator can be fully utilized, and the facing area between the stator and the rotor can be increased. This has the effect that the characteristics of the step motor, such as the maximum static torque and dynamic torque, can be improved at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view of a step motor showing an embodiment of the present invention.

FIG. 2 is a sectional view of the rotor showing the embodiment of the present invention.

FIG. 3 is a sectional view of a conventional step motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shaft 2 Magnet spacer 3 Permanent magnet 4 Injection molding gate cutout 5 Stator block A 6 Stator block B 7 Bearing L Effective length of stator

Continuation of the front page (56) References JP-A-63-198559 (JP, A) JP-A-2-72671 (JP, U) JP-A-62-168484 (JP, U) JP-A-6-17382 (JP) , U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02K 37/00-37/24 H02K 15/03

Claims (1)

(57) [Scope of request for utility model registration] In a rotor structure of a PM type stepping motor comprising a permanent magnet rotor multipolarly magnetized on an outer periphery and four stator yokes receiving a magnetomotive force by two exciting coils, a permanent magnet constituting the rotor is an injection motor. A rotor structure for a step motor, wherein the injection molding gates of two permanent magnets are formed by a molding method and are installed inwardly facing each other.