JPH037052A - Yoke structure of pm type stepping motor - Google Patents

Abstract

PURPOSE:To prevent bending of tooth even for a micro step angle and to utilize flux of rotor magnet efficiently by coupling pole teeth through a band bridge and setting the thickness of the pole tooth thicker than that of the bridge. CONSTITUTION:Relation between a bridge 34 and motor torque is set such that reduction of torque is low if the thickness of the bridge 34 is about 20% of the thickness of pole teeth 32, 33. When the length of the bridge 34 is about 30% of the length of the pole teeth 32, 33, reduction of torque is low. Since motor characteristic, rejection rate of product and gap accuracy are improved when compared with a conventional motor having no bridge 34, the gap can be shortened and the flux can be utilized effectively. By such arrangement, higher torque can be produced when compared with a conventional motor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a stator yoke of a PM stepping motor.

[Prior Art] Stepping motors and DC motors are widely used in the world for controlling information equipment. Among them, PM
Type stepping motors are widely used in magnetic recording devices such as FDDs and HDDs, printers, etc. because positioning can be controlled using an oven loop and they are inexpensive. PM
A type stepping motor has a stator having a plurality of pole teeth arranged in the circumferential direction, a coil wound around each pole tooth to generate magnetic flux, and a plurality of magnetized magnets on the outer peripheral surface facing the stator pole teeth. It consists of a rotor with permanent magnets.

FIG. 5 is a cross-sectional view of a conventional stepping motor.
21 is an outer yoke, 22 is an inner yoke, one set of the outer yoke and the inner yoke constitutes a stator yoke, and the motor is composed of two sets of stator yokes. 23 and 24 are flanges attached to the outer yoke. , 25 is a yoke, 26 is a permanent magnet attached to the yoke 25, and 27 is a motor shaft. The yoke 25, the permanent magnet 26, and the motor shaft 27 constitute a rotor. The bearings 28 each have a flange 23
and 24. 29 is an excitation coil. FIG. 6 is a perspective view of the outer yoke and the inner yoke;
The outer yoke 21 and the inner yoke 22 each have independent pole teeth 3.
2 are arranged in plural in the circumferential direction.

[Problems to be Solved by the Invention] However, in the conventional technology as described above, reducing the step angle due to the demand for precision and high precision of equipment requires increasing the number of pole teeth and narrowing the width of the pole teeth. Must,
However, narrowing the width of the pole teeth reduces the mechanical strength of the pole teeth, making them more likely to bend. If the pole teeth contact the rotor or bend, the gap between the rotor magnet and the pole teeth will widen. This has resulted in problems such as a decrease in effective magnetic flux, deterioration in motor characteristics, and deterioration in step position accuracy.

Therefore, the present invention is intended to solve such problems, and its purpose is to provide a high-performance and inexpensive PM that does not have tooth bending even at minute step angles and efficiently uses the magnetic flux with the rotor magnet. type stepper motor structure is provided.

[Means for solving the problem] An outer yoke having a plurality of pole teeth arranged in the circumferential direction;
In a PM stepping motor, which is composed of a stator yoke that is constructed by combining inner yokes with a plurality of pole teeth arranged in the same circumferential direction, and a multi-pole magnetized rotor magnet, the pole teeth of adjacent outer yokes and It is characterized by the pole teeth of the inner yoke being connected by a bridge.

It is also characterized by the relationship tp>tb, where the thickness of the pole teeth is tp and the thickness of the bridge is tb.

[Operation: A PM type stepping motor has a yoke structure with multiple pole teeth in the circumferential direction, and each pole tooth is constructed independently by bending a plate, so the mechanical strength of the pole teeth is increased by bending the plate. The strength is determined by the thickness of the part and the width of the pole teeth.
For this reason, when using a motor with a minute step angle, the mechanical strength becomes weak due to the narrow face width of the bent portion of the pole teeth, making it easy to bend and ensuring dimensional accuracy. This may cause the accuracy to deteriorate. Therefore, by attaching a band-shaped bridge that connects the pole teeth and changing the shape of the pole teeth from individual to continuous, the mechanical strength is increased so that they do not bend easily. At the same time, high precision can be achieved by preventing unexpected bending or returning due to springback during machining.

In this type of motor, a current is passed through a coil to excite the stator yoke between the rotor, which has multiple pole teeth combined with each other and a multipolar magnetized permanent magnet. Torque is generated by the action of magnetic flux between it and the permanent magnet. In order to use the excited magnetic flux effectively, it is necessary to prevent the magnetic flux from wrapping around between the pole teeth and to increase the magnetic flux that interacts with the rotor magnet.

The yoke structure of the present invention increases the magnetic resistance between the pole teeth, reduces the wraparound of magnetic flux between the pole teeth, and connects the rotor magnet with the pole. In order to effectively use the magnetic flux acting on the teeth, the relationship tp>tb must be satisfied. It is desirable that the bridge thickness tb be as thin as possible within a range that can prevent tooth bending.

[Example] FIG. 1 is a plan view of the pole teeth of the yoke of the present invention, and FIG.
The figure is a cross-sectional view of a pole tooth. The outer yoke 21 has a plurality of interdigitated pole teeth 32 arranged in the circumferential direction. Similarly, the inner yoke 22 also has a plurality of mutually combined pole teeth 33 arranged in the circumferential direction. A bridge 34 is provided between the pole teeth 32 of the outer yoke and the pole teeth 33 of the inner yoke to connect the pole teeth.

FIG. 3 is a diagram showing the relationship between bridge thickness tb and motor torque, and the bridge thickness is expressed as a ratio to the plate thickness of the pole teeth. The thickness of the bridge is 20% of the thickness of the pole tooth.
It can be seen that if this is the case, there is little decrease in torque and it can be used satisfactorily. In addition, it is thought that up to about 40% can be used depending on the purpose. FIG. 4 is a diagram showing the relationship between the length of the bridge and the motor torque, and similarly to the above, the length of the bridge is shown as a ratio to the length of the pole teeth. The thickness of the bridge is 20% of the thickness of the pole teeth.
It is. If the bridge length is about 30% of the pole tooth length, it can be used with less decrease in torque.

With the motor structure of the present invention, the number of pole teeth of the outer yoke is 50, the number of pole teeth of the inner yoke is 50, and the number of magnetization of the rotor permanent magnet is 200 per rotation.
I made a step motor. Pole tooth thickness 1. 2mm,
The length of the pole teeth is 6 mm, the plate thickness of the bridge is 0.2 mm, and the bridge length is 1.5 mm.

For comparison, we made a motor with a conventional structure without a bridge with the same specifications as above and compared it. However, since the conventional motor has curved teeth and lacks gear accuracy, the motor was made 0.05 mm larger than the motor of the present invention.

The results of the comparison are shown in Table-1.

The motor torque indicates the ratio of the conventional motor torque when the motor of the present invention is taken as 1. It can be seen that the stepping motor using the structure of the present invention is superior in motor characteristics and manufacturing defect rate compared to conventional motors. Regarding gap accuracy, conventional motors tend to have tooth bending, so the accuracy is poor and it is difficult to close the gap and use magnetic flux effectively. On the other hand, the present invention has good accuracy, so it was possible to close the gap and use magnetic flux effectively.

[Brief explanation of the drawing]

FIG. 1 is a plan view of the pole tooth of the present invention, FIG. 2 is a sectional view of the pole tooth of the present invention, FIG. 3 is a diagram showing the relationship between bridge thickness and motor torque, and FIG. 4 is a diagram of the bridge A diagram showing the relationship between length and motor torque, FIG. 5 is a sectional view of a conventional stepping motor, and FIGS. 6(a) and 6(b) are perspective views of an outer yoke and an inner yoke. [Effects of the Invention] As described above, according to the present invention, by connecting adjacent pole teeth of a motor yoke having a plurality of pole teeth in the circumferential direction with a bridge, the step angle becomes small and the motor yoke becomes thin and easy to bend. This not only compensates for the strength of the pole teeth and prevents tooth bending, but also increases the positional accuracy of the pole teeth to improve step angle accuracy and gap accuracy, making it possible to obtain torque that exceeds that of conventional motor structures. . Furthermore, it has the effect that it is possible to reduce costs by improving manufacturing yield by preventing tooth bending. 21 ・ 22 ・ 23. 25 ・ 26 ・ 27 ・ 28 ・ 29 ・ 30 ・ 31 ・ 32, ・Outer yoke, inner yoke 24... flange, yoke, permanent magnet, motor shaft, bearing, coil, dowel, reference hole 33... pole teeth/bridge

Claims (2)

[Claims] (1) A stator yoke configured by combining an outer yoke with a plurality of pole teeth arranged in the circumferential direction and an inner yoke with a plurality of pole teeth also arranged in the circumferential direction, and a multi-pole magnetized A yoke structure for a PM type stepping motor, characterized in that adjacent pole teeth of an outer yoke and adjacent pole teeth of an inner yoke are connected by a bridge in the PM type stepping motor made of rotor magnets. (2) The yoke structure for a PM stepping motor according to claim 1, characterized in that, where tp is the thickness of the pole teeth and tb is the thickness of the bridge, the relationship tp>tb holds true.