JP2006136108A - Stepping motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stepping motor capable of reducing detent torque with a simple constitution. <P>SOLUTION: This stepping motor 1, including a rotor 4, a first stator 10 disposed facing the rotor, a second stator 20 which faces the rotor, is disposed in parallel to an axial direction of a first stator and the rotor. A spacer 7 formed out of a soft magnetizer is disposed between the first stator 10 and the second stator 20. This stepping motor has a simple structure in which the spacer having magnetization is disposed between the first stator and the second stator, expediting the unification of the magnetization states on the first stator side and the second stator side. A state of firmly and magnetically coupling pole teeth of the first stator and the second stator with the rotor are reduced. Detent torque acting on the rotor can be reduced, thus providing the smoothly rotating stepping motor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a stepping motor, and more particularly to a stepping motor that can reduce detent torque.

  In electronic devices such as cameras, stepping motors are widely used as drive sources. The stepping motor rotates according to a pulse signal input from the outside. For example, a stepping motor built in a camera is used for opening / closing a sector and driving a zoom lens. Therefore, a stepping motor built in a camera or the like is required not only to perform step driving with high accuracy but also to rotate smoothly.

  There are various types of stepping motors. For example, there is a PM (permanent magnet) type stepping motor using a permanent magnet as a rotor. This PM-type stepping motor is widely adopted because of its relatively simple structure, but a detent torque (self-holding force) is generated because a permanent magnet is used. The detent torque is particularly apparent when the coil wound around the stator is not energized (when no power is applied), but it may affect the rotation of the rotor even when the rotor is rotating. If the detent torque is large, it becomes a load when the rotor rotates, so that smooth rotation is hindered, and vibration and noise may be induced when the rotor rotates. Therefore, a technique for reducing the detent torque has been studied for a PM type stepping motor.

  For example, in Patent Document 1, a spacer formed of a non-magnetic material is inserted between two stators formed of a magnetic material, and the distance between the stators is changed by rotating the spacer so as to slide. A stepping motor that reduces detent torque is disclosed.

JP-A-6-22532

  In Patent Document 1, when two stators disposed inside are magnetically connected, a leakage magnetic flux is generated from one stator to the other stator, and a detent torque is generated based on the leakage magnetic flux. The structure which suppresses is proposed. Patent Document 1 proposes a structure for weakening the magnetic coupling between two stators. Specifically, a rotatable spacer is disposed between two stators to increase the distance, and the distance between the stators is changed by rotating the spacer between the stators using the spacer as a non-magnetic material. Propose.

  However, when the above configuration is incorporated into a stepping motor, the structure becomes complicated. Particularly in recent years, the demand for downsizing of stepping motors has become stronger. Adding a complicated structure to the stepping motor that is miniaturized in this way is difficult in processing and causes a problem of cost increase.

  Accordingly, an object of the present invention is to provide a stepping motor capable of reducing detent torque with a simple configuration.

  The object is to provide a rotor, a first stator arranged opposite to the rotor, and a second stator arranged opposite to the rotor and arranged in parallel in the axial direction of the rotor. This can be achieved by a stepping motor having a spacer formed of a soft magnetic material between the first stator and the second stator.

  According to the present invention, with a simple configuration in which a magnetic spacer is disposed between the first stator and the second stator, the magnetization states of the first stator side and the second stator side are uniform. Can be achieved. As a result, it is possible to reduce the state in which the local portions (generally magnetic pole teeth) of the first stator and the second stator are magnetically strongly coupled to the rotor. Therefore, it is possible to provide a stepping motor that rotates smoothly with reduced detent torque acting on the rotor.

  In addition, the first stator includes a first annular stator portion having a ring-shaped base portion and a plurality of magnetic pole teeth arranged at equal intervals on the periphery of the base portion, and the second stator includes the ring-shaped base portion and the A second annular stator portion having a plurality of magnetic pole teeth arranged at equal intervals on the periphery of the base portion, and the spacer includes the base portion of the first annular stator portion and the base portion of the second annular stator portion. It can be set as the structure which is a ring-shaped soft magnetic body inserted between these. The rotor may be formed using a permanent magnet.

  According to the present invention, a stepping motor capable of reducing detent torque with a simple configuration can be provided.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. 1A and 1B are views showing an external appearance of a stepping motor 1 according to the embodiment. FIG. 1A is a perspective view, and FIG. 1B is a top view. FIG. 2 is an exploded perspective view showing the internal configuration of the stepping motor 1 so that it can be confirmed. The configuration of the stepping motor 1 will be described with reference to these drawings.

  The stepping motor 1 has a case formed of a substantially cylindrical case 6, an upper cover 2 that also serves as a bearing set on the upper side of the case 6, and a lower cover 3 that also serves as a bearing disposed on the lower side. ing. The case 6 is formed with two notches 6a and 6b for drawing out terminal pins to be described later.

  In the case 6, the rotor 4, the first stator 10 and the second stator 20 are accommodated. The first stator 10 and the second stator 20 are arranged in parallel in the axial direction of the rotor 4. A spacer 7 made of a soft magnetic material is interposed between the first stator 10 and the second stator. The spacer 7 magnetically connects the first stator 10 side and the second stator 20 side. The spacer 7 will be described later in detail.

  The rotor 4 is press-fitted and fixed to a rotor shaft 5 that is supported by the upper cover 2 and the lower cover 3 serving as bearings, and is rotatable. The rotor 4 is a permanent magnet having a 6-pole (3-pole S-pole and 3-pole N-pole) configuration in which S-pole and N-pole magnetic poles are alternately arranged on the outer peripheral surface at intervals of 60 degrees.

  The first stator 10 is formed by combining two annular stator portions 11 and 12, and an exciting coil 13 is disposed on the outer periphery thereof. The coil 13 is wound around a coil bobbin 14. Similarly, the second stator 20 is formed by combining two annular stator portions 21 and 22, and an exciting coil 23 is disposed on the outer periphery thereof. The coil 23 is wound around a coil bobbin 24. The four annular stator portions 11, 12, 21, 22 are made in the same shape using a soft magnetic material. The stepping motor 1 is a so-called claw pole type stepping motor, and each of the annular stator portions corresponds to the fact that the rotor 4 is a magnet having 6 poles, and three magnetic pole teeth are equally spaced on the inner periphery thereof. Has been placed.

  The first stator 10 has a configuration in which the six magnetic pole teeth are opposed to the six poles of the rotor 4 by setting the first stator 10 so that the magnetic pole teeth of the annular stator portions 11 and 12 mesh with each other. Similarly, with respect to the annular stator portions 21 and 22 of the second stator 20, the six magnetic pole teeth correspond to the six poles of the rotor 4 by being arranged in a state where the magnetic pole teeth mesh with each other. Terminal pins 15 for supplying power to the coil 13 are formed on the coil bobbin 14. A terminal pin 25 for supplying power to the coil 23 is formed on the coil bobbin 24. As shown in FIG. 1, when the stepping motor 1 is assembled, the terminal pin 15 protrudes outward through the notch 6a of the case 6, and the terminal pin 25 passes through the notch 6b of the case 6. Protrused outward.

  Now, in this stepping motor 1, as described above, it is formed of a soft magnetic material between the first stator 10 and the second stator 20, and is made of, for example, a ring-shaped member made of the same material as the stators 10 and 20. A spacer 7 is inserted. Specifically, the spacer 7 is disposed so as to be sandwiched between the annular stator portion 12 included in the first stator 10 and the annular stator portion 21 included in the second stator 20. As shown in FIG. 2, each of the annular stator portions 12 and 21 has a ring-shaped base portion 12a and 21a and three magnetic pole teeth 12b and 21b arranged on the periphery of the base portion. When the stepping motor 1 is assembled, the spacer 7 is positioned between the base portion 12a of the annular stator portion 12 and the base portion 21a of the annular stator portion 21 to form a state in which the base portion 12a and the base portion 21a are magnetically connected. .

  FIG. 3 is a cross-sectional view taken along the line AA in FIG. 3, it can be confirmed that the spacer 7 is positioned between the base portion 12a of the annular stator portion 12 and the base portion 21a of the annular stator portion 21 when the stepping motor 1 is assembled.

  Generally, magnetic flux from the rotor (magnet) side tends to concentrate on the magnetic pole teeth (local part) on the stator side, and a large detent torque is likely to be generated at the magnetic pole teeth. If the detent torque is large, it becomes a load when the rotor rotates, and the torque varies depending on the position of the rotor, which may cause a problem with unevenness. Further, it is desirable as a motor characteristic that the starting torque is constant from any position when energized from an arbitrary stop position. If the torque is uneven, a portion where the starting torque is small and a portion where the starting torque is large are generated, and there is a possibility that the motor does not start in a portion where the starting torque is small. Here, if the magnetic flux concentrated in the vicinity of the magnetic pole teeth can be dispersed in the area where the magnetic pole teeth do not exist (the part between the magnetic pole teeth), the magnetic flux in the vicinity of the magnetic pole teeth is relatively lowered to make the magnetization state on the stator side uniform Can be If the magnetization state on the stator side is homogenized, the detent torque can be weakened. From such a viewpoint, in the stepping motor 1, the magnetic spacer 7 is disposed between the annular stator portion 12 and the annular stator portion 21. That is, by disposing the annular spacer 7, the difference in magnetic flux density between the magnetic pole tooth portion and the portion between the magnetic pole teeth can be filled and the magnetization state can be made uniform.

  Further, the spacer 7 also serves to magnetically couple the first stator 10 side positioned on the upper side and the second stator 20 side positioned on the lower side. The spacer 7 homogenizes the internal magnetization state in each of the first stator 10 and the second stator 20 and homogenizes the external magnetization state between the first stator 10 and the second stator 20. Facilitate. The stepping motor 1 having such a spacer 7 can significantly reduce the detent torque as compared with the conventional stepping motor.

  A comparative stepping motor was manufactured with the same structure except that the spacer 7 was not inserted, and the detent torque reduction effect of the stepping motor 1 of this example was confirmed. The coil was not energized and was de-energized, and the detent torque at static rotation was measured. At that time, one N pole of the rotor 4 was used as a reference. When this reference N pole is placed at a certain angle, a detent torque that tries to rotate counterclockwise is applied (plus), and conversely, a detent torque that attempts to rotate clockwise is applied. The case was set to-(minus).

  FIG. 4 is a diagram showing the measurement result of the detent torque. From FIG. 4, the difference in detent torque (rotational torque) between the stepping motor 1 of this embodiment and the stepping motor of the comparative example can be confirmed. It can be confirmed from FIG. 4 that the detent torque is greatly reduced in the stepping motor 1.

  As described above, the stepping motor 1 can reduce the detent torque with a simple configuration in which the soft magnetic spacer 7 is disposed between the annular stator portion 12 and the annular stator portion 21.

  The said Example illustrated the case where the 1st and 2nd stators 10 and 20 were formed of the two cyclic | annular stator parts 11, 12 and 21,22. However, the present invention is not limited to such a structure. The present invention can be similarly applied to a structure in which each of the stators 10 and 20 is formed by one annular stator portion. Since the stepping motor of the present invention has a simple configuration in which soft magnetic spacers are arranged between stators arranged in parallel in the axial direction, it can be realized at a very low cost.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible. The present invention is preferably applied to a PM type stepping motor, but can be applied to other types of stepping motors when detent torque becomes a problem.

It is the figure which showed the external appearance of the stepping motor which concerns on embodiment, (A) is a perspective view, (B) is a top view. It is the disassembled perspective view shown so that the internal structure of a stepping motor could be confirmed. It is AA sectional drawing in FIG. 1 (A). It is the figure which showed the difference in the detent torque (rotation torque) in the stepping motor of a present Example, and the stepping motor of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stepping motor 4 Rotor 5 Rotor shaft 6 Case 7 Spacer 10 1st stator 12 Annular stator part 12a Ring-shaped base part 12b Magnetic pole tooth 20 Second stator 21a Ring-shaped base part 21b Magnetic pole tooth

Claims (3)

A rotor,
A first stator disposed opposite the rotor;
A stepping motor having a second stator facing the rotor and arranged in parallel in the axial direction of the rotor,
A stepping motor characterized in that a spacer formed of a soft magnetic material is disposed between the first stator and the second stator. The first stator includes a first annular stator portion having a ring-shaped base portion and a plurality of magnetic pole teeth arranged at equal intervals on the periphery of the base portion;
The second stator includes a second annular stator portion having a ring-shaped base portion and a plurality of magnetic pole teeth arranged at equal intervals on the periphery of the base portion;
The said spacer is a ring-shaped soft magnetic body inserted between the said base part of the said 1st annular stator part, and the said base part of the said 2nd annular stator part, The Claim 1 characterized by the above-mentioned. Stepper motor. The stepping motor according to claim 1, wherein the rotor is formed using a permanent magnet.

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