JPH06105525A - Stepping motor - Google Patents

Abstract

PURPOSE:To obtain a damping force independently of an inertia force of a rotor and to reduce vibration and noise due to rotation by installing a conductor-made damper which generates an eddy current loss adjacent to the magnet of a rotor or by installing a ferromagnetic body-made damper which generates a magnetic hysteresis loss on a stator. CONSTITUTION:In a stepping motor which has a rotor which is made by fastening a magnet 2 coaxially on a shaft 1 and a stator which has a pair of yokes 5 and a pair of coils 6 on the external face of the magnet 2, a ring-shaped damper 20 is installed between the pair of yokes 5. By using the damper 20 formed of a conductor, eddy current is generated inside due to the rotation of the magnet 2 and the damping force of the magnet 2 can be obtained due to eddy current loss. When the damper 20 is formed of a ferromagnetic body, magnetic hysteresis loss is generated inside and then damping force is obtained. The damping force can be obtained independently of the inertia force of the rotor, and therefore enough vibration-controlling effect can be obtained even if the size of the rotor is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small stepping motor used, for example, for driving a lens of a video camera, and more particularly to an improvement for reducing vibration accompanying rotation of the motor.

[0002]

2. Description of the Related Art Most commercially available video cameras in recent years have a structure in which a small stepping motor is built in a lens barrel and a lens is moved forward and backward by this motor to focus the lens.

As this type of stepping motor, the one shown in FIG. 5 is well known. Reference numeral 1 is a metal shaft, and a screw portion 1A is formed on the tip side thereof,
A cylindrical magnet 2 is fixed to the base end side, and the shaft 1 and the magnet 2 form a rotor.
The outer peripheral surface of the magnet 2 is magnetized so that a plurality of magnetic poles are arranged in the circumferential direction, and a pair of yokes 5 are arranged so as to surround the outer periphery thereof. An unillustrated female screw member is screwed into the screw portion 1A, and the female screw member advances and retracts an article such as a lens.

The yoke 5 is composed of an inner yoke member 4 and an outer yoke member 3 made of a soft magnetic material, and a coil 6 is housed between the pair of yoke members 3, 4. The inner yoke member 4 has pole teeth (not shown) facing the magnetic poles of the magnet 2, and the pole teeth of each inner yoke member 4 have different phases. As a result, when positive and negative currents are alternately applied to the pair of coils 6, the magnet 2 rotates stepwise in a predetermined direction.

A radial bearing 9 is provided on the end surface of one yoke 5.
Is fixed, the base end of the shaft 1 is rotatably supported, and a leaf spring 7 is fixed to the end face so that its free end 8 biases the base end of the shaft 1. The base end of a bracket 10 having a U-shape is fixed to the end surface of the other yoke 5. The tip of this bracket 10 is
The thrust bearing 11 is fixed to the thrust bearing 1 while being extended to a position facing the tip of the shaft 1.
1, the tip of the shaft 1 is rotatably supported. The yoke 5, the coil 6, the bracket 10 and the portions fixed to these constitute a stator.

[0006]

By the way, in the conventional stepping motor, the positive and negative rectangular wave voltages corresponding to the input pulse are applied to each coil 6 to drive the magnet 2. At that time, the magnet 2 is generated. Drive torque is 1
The rotation speed of the rotor is not constant because it fluctuates greatly during the pulse. For example, when the rotation angle and the time are plotted, a graph having a sawtooth amplitude as shown in FIG. 6 is obtained. Due to such fluctuations in the rotation speed, the stepping motor and the driven system vibrate and generate noise. In most video cameras of recent years, the recording microphone is arranged near the lens barrel, so that the microphone easily picks up noise caused by the stepping motor, which causes a decrease in the SN ratio of recording.

Therefore, recently, an elastic body such as rubber is interposed between the magnet and the shaft, and vibration is reduced by the cushioning action of the elastic body, or a weight is attached to the outer circumference of the shaft through the elastic body. Some have proposed a structure for reducing vibration by the moment of inertia of the weight and the buffering action of the elastic body. However, such a structure provided with a mechanical damper has a problem that the productivity is reduced due to the complexity of the structure, the downsizing of the motor becomes difficult, and the vibration damping effect is small in the small motor. It was

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a stepping motor capable of reducing vibration and noise accompanying rotation.

[0009]

A stepping motor according to a first aspect of the present invention comprises a rotor having a shaft on which a magnet is coaxially fixed, and a stator having a yoke and a coil arranged on the outer periphery of the magnet. In the stepping motor provided, a damper made of a conductor is provided adjacent to the magnet in the stator, which causes an eddy current loss inside the magnet as the magnet rotates.

On the other hand, a stepping motor according to a second aspect of the present invention is a stepping motor comprising a rotor having a shaft on which a magnet is coaxially fixed, and a stator having a yoke and a coil arranged on the outer periphery of the magnet. It is characterized in that the stator is provided adjacent to the magnet with a damper made of a ferromagnetic material which causes magnetic hysteresis loss inside the magnet as the magnet rotates.

It is preferable that the damper has an annular shape concentrically arranged on the outer periphery of the magnet, and the axial width thereof is 10 to 50% of the total length of the magnet.

[0012]

In the stepping motor according to the first aspect of the present invention, an eddy current is generated inside the damper made of a conductor with the rotation of the magnet and is converted into heat. Join. Since this braking force increases proportionally as the rotation speed of the magnet increases, the braking force serves to stabilize the rotation speed of the magnet, and vibration and noise from the stepping motor can be reduced.

On the other hand, in the stepping motor according to the second aspect of the present invention, the direction of the magnetization of the ferromagnetic damper changes with the rotation of the magnet, and the magnetic hysteresis loss occurs and changes to heat. As much as, braking force is applied to the magnet. This braking force serves to stabilize the rotation speed of the magnet, and vibration and noise from the stepping motor can be reduced.

According to the structure of claim 1 or 2, the braking force can be obtained without depending on the inertial force of the rotor. Therefore, even when the rotor is downsized, a sufficient vibration reducing effect can be obtained. is there.

[0015]

1 is a vertical sectional view showing an embodiment of a stepping motor according to the present invention. In FIG. 1, the same elements as those of the conventional example of FIG. 5 are denoted by the same reference numerals, and the description thereof will be omitted.

The main feature of this embodiment is that an annular damper 20 is interposed between a pair of yokes 5. The material of the damper 20 can be roughly classified into the following two types in terms of operation.

(1) Conductor The conductor damper generates an eddy current inside the magnet 2 as the magnet 2 rotates, and this eddy current loss causes the magnet 2 to move.
To obtain the braking force of. Although an eddy current loss will occur for some time if it is a conductor, a material having higher electric conductivity is preferable, and from that viewpoint, aluminum, copper, or an alloy thereof is preferable.

(2) Ferromagnetic material In the ferromagnetic material damper, magnetic hysteresis loss occurs inside the magnet 2 as the magnet 2 rotates. As the material having a larger magnetic hysteresis loss has a larger braking effect, the Fe, Fe-V system having a relatively large magnetic hysteresis loss,
Fe alloys such as Fe-Co and Fe-Cr alloys, ferroscopic sprayers, ferrites such as Ni-ferrite, and rare earth-cobalt alloys are particularly suitable. Of these,
A conductive material generates not only the braking force due to the magnetic hysteresis loss but also the braking force due to the eddy current loss, so that a stronger vibration preventing effect can be obtained and the size of the damper 20 can be reduced. Become.

The outer diameter of the damper 20 is almost equal to that of the yoke 5, and the amount of the gap between the inner peripheral surface 20A and the magnet 2 is about the same as the amount of the gap between the yoke 5 and the magnet 2 in terms of assembling workability. ing. The total length of the magnet 2 is longer than that of the conventional product by the length of the damper 20, and is sufficiently long to face the pole teeth of both yokes 5.

According to the studies made by the present inventors, the width t of the damper 20 is preferably about 10 to 50% of the total length of the magnet 2. If it is less than 10%, the braking force due to eddy current loss or magnetic hysteresis loss is insufficient, and it is difficult to obtain a sufficient vibration preventing effect. On the other hand, if it exceeds 50%, the driving force of the coil 6 becomes insufficient.

When the damper 20 is made of a conductor, a magnetic field P is formed inside the damper 20 from each N pole of the magnet 2 toward the adjacent S pole, as shown in FIG. An eddy current Q is generated inside the conductor damper 20 with the rotation of the. The eddy current Q is changed into heat, and a braking force is generated on the magnet 2 by the amount of this eddy current loss. Since this braking force increases proportionally as the rotation speed of the magnet 2 increases, it acts to make the rotation speed of the magnet 2 constant, and vibration and noise generated by the stepping motor can be reduced.

On the other hand, when the damper 20 is made of a ferromagnetic material, the direction of the magnetic field P in the damper 20 is alternately changed with the rotation of the magnet 2 in the same manner as described above, and magnetic hysteresis loss is generated to change to heat. Therefore, the braking force is applied to the magnet 2 by the amount of the magnetic hysteresis loss, and the rotation speed of the magnet 2 is made constant, so that the vibration and noise from the stepping motor can be reduced.

In any case, in the stepping motor of this embodiment, the effect of stabilizing the rotational speed of the rotor can be obtained without depending on the inertial force and elastic force of the rotor, so that it is sufficient even when the rotor is small. Vibration can be reduced. further,
Since only the damper 20 is added, the structure of the motor is not complicated and the productivity is not hindered, and the influence on the rotational balance is small.

Further, in this embodiment, since the damper 20 is interposed between the yokes 5, magnetic interference between the yokes 5 can be prevented. Therefore, there is also a side effect that it is possible to prevent an error in the rotor stop position due to magnetic interference and a reduction in rotation accuracy.

Next, FIG. 3 shows a second embodiment of the present invention.
In this example, so as to face the base end of the magnet 2,
The annular damper 22 is fixed to the end surface of the yoke 5. The material of the damper 22 may be the same as that of the above embodiment. Also in this example, the same vibration reduction effect as described above can be obtained.

FIG. 4 shows a third embodiment of the present invention, which is characterized in that an annular damper 24 is attached so as to face the tip of the magnet 2. A convex portion 24A is formed on the end surface of the damper 24, and the convex portion 24A is inserted and fixed to the inner circumference of the yoke 5. As a result, in this example, the braking force is obtained by the magnetic force acting between the convex portion 24A and the tip surface of the magnet 2.

It should be noted that although the dampers of the above-mentioned respective embodiments are all annular, they are not necessarily annular, and for example, an arc type can be implemented. In short, the effect of the present invention can be obtained in any shape, size, and installation position that causes eddy current loss or magnetic hysteresis loss inside the magnet as the magnet rotates.

Of course, the structure and shape of the motor may be changed as appropriate. For example, a shaft without the threaded portion 1A may be used, and the application of the motor of the present invention is not limited to driving a lens. Also,
The support structure of the shaft may be changed arbitrarily.

[0029]

As described above, as the magnet rotates, an eddy current is generated in the damper made of a conductive material and converted into heat. Therefore, a braking force is applied to the magnet by the amount of this eddy current loss. Since this braking force increases proportionally as the rotation speed of the magnet increases, the braking force serves to stabilize the rotation speed of the magnet, and vibration and noise from the stepping motor can be reduced.

On the other hand, in the stepping motor according to the second aspect of the present invention, the direction of the magnetization of the ferromagnetic damper changes with the rotation of the magnet, and the magnetic hysteresis loss is generated and converted into heat. As much as, braking force is applied to the magnet. With this braking force, the action of making the rotation speed of the magnet constant can be obtained, and the vibration and noise from the stepping motor can be reduced.

According to the structure of claim 1 or 2, since the braking force can be obtained without depending on the inertial force of the rotor, it is possible to obtain a sufficient vibration reducing effect even when the rotor is downsized. is there.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a stepping motor according to the present invention.

FIG. 2 is a sectional view showing a damper and a magnet of the same stepping motor.

FIG. 3 is a vertical sectional view of another embodiment of the present invention.

FIG. 4 is a vertical sectional view of still another embodiment of the present invention.

FIG. 5 is a vertical cross-sectional view showing a conventional stepping motor.

FIG. 6 is a graph showing a problem of a conventional stepping motor.

[Explanation of symbols]

 1 Shaft (Part of Rotor) 2 Magnet (Part of Rotor) 5 Yoke (Part of Stator) 6 Coil (Part of Stator) 10 Bracket (Part of Stator) 20, 22, 24 Damper

Claims (3)

[Claims] 1. A stepping motor comprising a rotor in which a magnet is coaxially fixed to a shaft, and a stator having a yoke and a coil arranged on the outer periphery of the magnet, wherein the magnet rotates adjacent to the magnet. A stepping motor, wherein a damper made of a conductor that causes an eddy current loss therein is provided in the stator. 2. A stepping motor comprising a rotor in which a magnet is coaxially fixed to a shaft, and a stator having a yoke and a coil arranged on the outer periphery of the magnet, wherein the magnet rotates adjacent to the magnet. A stepping motor, wherein a damper made of a ferromagnetic material that causes magnetic hysteresis loss therein is provided in the stator. 3. The damper according to claim 1, wherein the damper has an annular shape concentrically arranged on the outer periphery of the magnet, and the axial width thereof is 10 to 50% of the total length of the magnet. 2. The stepping motor according to 2.