JPH03284154A - Stepper motor - Google Patents

Abstract

PURPOSE:To reduce a detent torque, suppressing the variation of a magnetic energy for the rotating direction of a rotor, by providing ringlike bands in the bottom parts of stator poles the surfaces of which oppose to the rotor. CONSTITUTION:A first stator set 10 constituting a part of a stepper motor comprises a stator cup 11 and a stator plate 15. In the stator cup 11 and the stator plate 15, sinking comb-like stator poles 12 and 16 are provided opposing to a rotor respectively, and in their bottom parts, which oppose to the rotor, ringlike bands 13, each of which has the building-up width of 1, are provided respectively. Thereby, the ringlike bands short between the stator poles as magnetic circuits, and the variation of the magnetic resistance relative to the rotating direction of the rotor can be reduced. Therefore, by suppressing the variation of a magnetic energy when performing no current application, a detent torque is reduced, and the ratio of the torque when performing a current application to the detent torque is improved.

Description

[Detailed description of the invention] <Industrial application field> This invention relates to improvements in step motors.

<Prior Art> FIG. 7 is a perspective explanatory view showing an example of a conventional step motor. In the figure, reference numeral 1 denotes a rotor, which has a cylindrical magnet 2 on its outer circumferential surface that is magnetized with multiple poles in the circumferential direction, and has a rotor shaft 3 coaxially fixed thereto. The first component that constitutes the stator. The second stator set 50, 60 has a stator cup 51, a stator plate 55, a stator cup 61, and a stator plate 65, respectively. The stator cup 51.61 and the stator plate 5565 include a comb-shaped stator pole 52 facing the rotor 1,
56, 62, and 66 are provided respectively. And the first. Excitation coils 31 and 32 are wound around the second stator set 5060, respectively.

FIG. 8 shows the structure of the first stator set 50 of the step motor as described above. As shown in the figure, the stator pole 52 is bent at a right angle from a plane perpendicular to the axis of the stator cup 51, and a notch 53 is formed in the rising portion thereof. Further, a similar notch 57 is formed in the rising portion of the stator pole 56. Note that in the second stator set 60 as well, notches similar to those described above are formed at the rising portions of the stator poles 62 and 66. As a known technology related to such a step motor, for example,
There are those described in Publication No.-48384 and the like.

<Problem to be solved by the invention> In the step motor configured in this way, the coil 31
．． Even if 32 is not excited, a magnetic attraction force acts between the rotor magnet 2, which is a permanent magnet, and the stator poles 52, 56, 62, 66, and detent torque is generated to try to hold the rotor 1 in a fixed position. exists. If this detent torque is large, there is a problem in that it is difficult to rotate the rotor 1 when the step motor is not energized.

For example, if such a step motor is used in a control device that is configured to return the rotor to its initial position by an external biasing force when the power is not energized, the step motor will return to the initial position when the energization is cut off in an emergency. There is a risk that the motor will not return to its initial position.

This invention was made to solve the above problems, and its purpose is to provide a step motor that reduces detent torque and improves the ratio of torque generated when energized to detent torque. This is what I am trying to do.

<Means for Solving the Problems> The present invention has been made to achieve the above object, and includes a rotor having magnetic poles provided in the circumferential direction on the outer peripheral surface;
A step motor comprising first and second stator sets having stator poles arranged at a predetermined interval and facing the rotor, and a coil for exciting the first and second stator sets. ,
This step motor has an annular band formed at the base of the stator pole facing the rotor.

Function> The present invention is configured as described above, and the annular band short-circuits the stator poles in the form of a magnetic circuit to suppress changes in magnetic energy in the rotational direction of the rotor.
Reduce detent torque.

<Example> Hereinafter, an example of the present invention will be described based on FIG. 1. Note that in the following, parts common to the conventional example are indicated by common reference numerals, and redundant explanation will be omitted.

The step motor of the present invention includes a first stator set 10 shown in FIG. 1, and a second stator set 20 formed in the same shape as the first stator set 10 and arranged back to back. Therefore, in the following, the first stator set 10
I will mainly explain.

The first stator set 10 includes stator cups 11. each of which is formed by press working. Stator plate 15
It is composed of. The stator cup 11 and the stator plate 15 are provided with comb-like stator poles 12 and 16 facing the rotor 1, and an annular band portion 13 and a rising width β are respectively provided at the root portion facing the rotor 1. 17 is formed.

FIG. 2 shows the first stator set 10. It shows the positional relationship between the second stator set 20 and the rotor magnet 2. With this positional relationship, the detent torque when the step motor is not energized is represented by the curve Ta for the first stator set 10 alone, the curve Tb for the second stator set 20 alone, and the curve TD for Ta, Tb. It represents the total detent torque that is the result of combining .

FIG. 3 shows the magnetic energy distribution of the step motor after generating the detent torque To.

The curve shown by the broken line is the change in magnetic energy of a conventional stator set without the annular band portion 1317, and by providing the annular band portions 13 and 17, the change in magnetic energy can be reduced as shown by the curve shown by the solid line. I can do it.

This detent torque TO is determined from the magnetic energy W by the rotor magnet 2 as follows. Here, α indicates an electrical angle, and if expressed in terms of a mechanical angle θ, then if the number of magnetic pole pairs of the stator and rotor is P, then the relational expression α=Pθ may be set.

As a result, the expression for magnetic energy W is W=H
(at-bl)cos2a+W.

It is expressed as

A and S are the half amplitude of the detent torque of the first stator set 10 alone and the half amplitude of the detent torque of the second stator set 20, respectively.

By providing the annular bands 13 and 17, the magnetic resistance due to the air gap between the stator poles 12 and 16 and the rotor magnet 2 is reduced. Therefore, since the magnetic resistance change in the rotational direction of the rotor 1 becomes smaller, the third
As shown in the figure, the change in magnetic energy is also reduced, and the detent torque To can be reduced.

Here, the width of the annular bands 13, 17 is determined by the ratio to the axial length of the stator pole 12, 16 (see FIG. 4). In the embodiment, as a result of experiments with various width degrees Celsius, the torque ratio γ of the holding torque TH to the detent torque To shows a change curve shown in FIG. 5.

On the other hand, the relationship between the annular band width ratio A/L and the excitation current (2)/holding torque TH (torque current ratio) changes as shown by the curve in FIG.

In FIG. 5, as u/L increases, the torque ratio γ increases, but on the other hand, as shown in FIG. 6, the torque current ratio decreases, leading to a so-called decrease in efficiency. Therefore, the practical range of the annular band width ratio u/L is n/L, which is the range where the torque current ratio decreases little and the torque ratio γ is large.
=0.1 area (for example, J2/L = 0.1±0
．． 04 range), the decrease in excitation torque can be minimized and detent torque can be significantly reduced.

Note that the present invention is not limited to the above-mentioned explanation and the mouth side, and the embodiments thereof can be changed within a range that does not depart from the technical idea of the present invention. for example,
Even if the annular band is formed only on either side of the stator cup or stator plate of the stator set, a corresponding reduction in detent torque can be achieved.

<Effects of the Invention> As explained above, the step motor of the present invention includes a rotor having magnetic poles provided circumferentially on the outer peripheral surface, and stator poles provided at predetermined intervals and facing the rotor. In the step motor, the step motor includes first and second stator sets, and a coil that excites the first and second stator sets. Because of this structure, the annular band short-circuits the stator poles in the form of a magnetic circuit, thereby making it possible to reduce changes in magnetic resistance in the rotational direction of the rotor.

Therefore, it is possible to suppress changes in magnetic energy during non-energization, reduce detent torque, and improve the ratio of generated torque during energization to detent torque.

Further, by providing the annular band, the mechanical strength of the stator pole is increased, the stator pole is prevented from tilting in the radial direction, and the air gap with the rotor can be made uniform. Furthermore, the annular band increases the strength against twisting of the stator pole in the angular direction, and prevents deterioration of stepping accuracy due to twisting of the stator pole. This has the effect of improving the stepping accuracy by reducing the number of steps and increasing the mechanical strength of the stator pole.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a stator set in a step motor according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the relationship between detent torque and angle, and FIG. 3 is a curve diagram illustrating the relationship between magnetic energy and angle. Fig. 4 is a developed view of the stator pole and annular band, Fig. 5 is a curve diagram showing the relationship between the torque ratio and the annular band width, and Fig. 6 is a curve diagram showing the relationship between the torque current ratio and the annular band width. 7 is a perspective explanatory diagram of a step motor; FIG. 8 is a perspective view of a conventional stator set. 1. Rotor; 10. First stator set; 11. 21... Stator cup, 12.22... Stator pole, 13.23... Annular band, 15.25... Stator plate, 16.26... Stator pole, 17.27... Annular band portion, 20... second stator set. Lie-4dW♂yo (togu) Figure 7 Copper figure

Claims (1)

[Scope of Claims] A rotor having magnetic poles provided circumferentially on an outer peripheral surface, and first and second stator sets having stator poles provided at predetermined intervals and facing the rotor. , a step motor comprising a coil for exciting the first and second stator sets, characterized in that an annular band is formed at a root portion of a surface of the stator pole facing the rotor. motor.