JPH01103131A - Motor - Google Patents

Abstract

PURPOSE:To prevent the outer peripheral surface of a rotary body and the inner peripheral surface of a fixed bearing from coming in contact with each other, by limiting the diameter of the rotary body according to working rotational frequency, and by controlling the expanded degree of the rotary body due to a centrifugal force, to be a fixed degree or less. CONSTITUTION:The outer peripheral surface 21 of a rotary body 12 and the inner peripheral surface 24 of a fixed bearing 11 are confronted with each other at a specified interval. On the outer peripheral surface 21 of the rotary body 12, groups 18 are, formed. Then, between the rotary body 12 and the fixed bearing 11, a dynamic pressure bearing is formed, and the dynamic pressure bearing is rotatably supported. The groups 8 are inclined at specified angles to the central axis at both the upper and lower end sections of the rotary body 12, and are formed so that the upper side group and the lower side group may be formed inclined in the directions opposite to each other. Then, the average diameter of a diameter for connecting the center line of the thickness of the cylindrical rotary body 12 is selected to come to a value within a specified range according to working rotational frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric motor in which one rotating body is supported by a hydrodynamic bearing.

(Prior art) A hydrodynamic bearing is constructed by providing a groove on either the outer circumferential surface of a cylindrical rotating body constituting a rotor or the inner circumferential surface of a fixed bearing that rotatably supports the outer circumferential surface of this cylindrical rotating body. There is an electric motor in which a magnet is fixed to the inner circumferential surface of the cylindrical rotating body, and a driving coil is arranged opposite to the magnet.

(Problem to be Solved by the Invention) In order for the dynamic pressure bearing to work effectively in the electric motor as described above, it is better to increase the diameter of the cylindrical rotating body and increase the angular velocity. Therefore, if the diameter of the rotating body is made too large, when the rotating body is rotated at high speed, the centrifugal force will cause the rotating body to bulge outward and come into contact with the inner circumferential surface of the fixed bearing placed on the outer circumferential side. In some cases, burn-in occurred, which was a fatal flaw. In addition, since the magnet fixed to the inner circumference of the rotating body has low rigidity, the magnet acts as a centrifugal force, but does not contribute to maintaining rigidity and promotes the expansion of the cylindrical rotating body due to the centrifugal force.
This increases the risk of bearing seizure. In particular, resin-bonded or rubber-bonded magnets, which have become widely used in recent years, have almost no rigidity, so when they are used in electric motors, there is an even greater risk of bearing seizure.

The present invention was made in order to solve the problems of conventional electric motors with hydrodynamic bearings, and the diameter of the rotating body is limited to the number of rotations used, thereby preventing the swelling of the rotating body due to centrifugal force. An object of the present invention is to provide an electric motor capable of suppressing the amount below a certain value, thereby preventing contact between the outer circumferential surface of a rotating body and the inner circumferential surface of a fixed bearing, and eliminating seizure of the bearing part.

(Means for solving problems) The present invention relates to an electric motor having a hydrodynamic bearing.

It is characterized in that the average diameter, which is the diameter connecting the centers of the wall thicknesses of the cylindrical rotating body, is configured within the range shown in the following table for the number of rotations used.

The present invention also provides a structure in which a magnet is fixed to the inner circumferential surface of the cylindrical rotating body under the interposition of a cylindrical yoke, and the yoke is bulged due to centrifugal force between the yoke and the inner circumferential surface of the cylindrical rotating body. The cylindrical rotating body is characterized in that the average diameter, which is the diameter connecting the centers of the wall thicknesses of the cylindrical rotating body, falls within the range shown in the following table for the number of rotations used.

(Function) The permissible limit for swelling of the rotating body due to centrifugal force is about 2 μm in radius, and it is desirable to keep it to 2.3 μm or less at most. Centrifugal force is greatly influenced by the rotation speed of the rotating body and the average diameter of the rotating body, but by configuring these within the ranges shown in the tables above, it is possible to suppress the expansion of the rotating body due to centrifugal force within the above allowable limits. Can be done.

In addition, by forming a relief between the yoke and the inner circumferential surface of the cylindrical rotating body to prevent the yoke from expanding due to centrifugal force,
The average diameter of the rotating body can be increased relative to the rotation speed of the rotating body.

(Example) Hereinafter, an example of the electric motor according to the present invention will be described with reference to the drawings.

1 to 3 show examples of rgAa 711 motors for rotating magnetic heads used in video tape recorders, digital audio tape recorders, and the like. In FIGS. 1 to 3, reference numeral 11 is a cylindrical fixed bearing, and a cup-shaped frame 25 is attached to the bottom of the fixed bearing 11.
The frame 25 is fixed in place, and a column 19 is press-fitted into a hole in the center of the frame 25 . A part of the outer periphery of the fixed bearing 11 protrudes like a flange and serves as a fixed drum 26 formed in a cylindrical shape.

A cylindrical rotating body 12 is dropped into the inner peripheral side of the fixed bearing 11. A thrust bearing screw 27 is screwed into the center of the rotating body 12, and the lower end of the screw 27 passing through the center of the shoulder of the rotating body 12 is a thrust bearing 28 at the upper end of the column 19.
is placed on top. An annular magnet 16 is fixed to the outer periphery of the upper end of the support column 19, and an annular magnet 15 is also fixed to the rotating body 12 so as to face the magnet 16. The opposing surfaces of each magnet 15 and 16 are magnetized with the same polarity, and the repulsive force causes the screw 27 and the bearing 28 to be magnetized.
This prevents excessive load from being applied to the thrust bearing.

The outer circumferential surface 21 of the rotating body 12 and the inner circumferential surface 24 of the fixed bearing 11 face each other with a predetermined gap therebetween. As shown in FIG. 2, a groove 18 is formed on the outer circumferential surface 21 of the rotating body 12.
A dynamic pressure bearing is thus formed between the rotating body 12 and the fixed bearing 11, and the rotating body 12 is rotatably supported via this dynamic pressure bearing. The grooves 18 are formed at both the upper and lower ends of the rotating body 12 so as to be inclined at a predetermined angle with respect to the central axis, and the directions of inclination of the upper groove and the lower groove are opposite. The groove 18 may be formed on the inner peripheral side of the fixed bearing 11.

A rotating drum 20 is fixed to the upper end of the rotating body 12. The outer diameter of the zero-rotating drum 20 is approximately the same as the outer diameter of the fixed drum 26, and a magnetic head 30 is mounted on the lower surface of the rotating drum 20 near the outer periphery. is attached.

Coils constituting a rotary transformer 23 are mounted on opposing surfaces of the fixed drum 26 and the rotating drum 20 so as to face each other, and send and receive signals between the magnetic head 30 and an external circuit.

An iron core 31 for forming a magnetic path is fixed to the outer periphery of the pillar 19. Drive coils 17 having an appropriate number of phases are arranged on the iron core 31 . On the other hand, a cylindrical yoke 13 is fixed to the inner circumferential side of the rotating body 12, and a cylindrical magnet 14 is further fixed to the inner circumferential side of this yoke 13. The magnet 14 faces the outer peripheral surface of the iron core 31 with a predetermined gap therebetween, and is magnetized to have an appropriate number of poles in the circumferential direction.

If the energization of the drive coils 17 of each phase is controlled according to the rotational position of the rotary body 12, a rotational torque is generated in the magnet 14, and the rotary body 12 and the rotary drum 20, which are integral with the magnet 14, are rotationally driven. As the rotating body 12 rotates, the dynamic pressure bearing formed between the groove 18 on the outer circumferential surface 21 of the rotating body 12 and the inner circumferential surface 24 of the fixed bearing 11 functions, and the fixed bearing 11 displaces the rotating body 12. Radial support in contact.

Note that the object to be rotationally driven is arbitrary, and if a rotating polygon mirror is fixed to the rotating body 12 instead of the rotating drum 20 in the above example, an optical deflector can be constructed.

Now, centrifugal force is generated by the rotation of the rotating body 12.

This centrifugal force increases as the rotational speed of the rotating body 12 increases, and as a result, the rotating body 12 expands outward as shown by the chain line in FIG. Since the mutual spacing between the dynamic pressure bearing, which is made up of the inner circumferential surface 24 of the fixed bearing 11 and the fixed bearing 11, is extremely small, there is no risk that the rotating body 12 and the fixed bearing 11 will come into contact with each other due to the swelling of the rotating body 12, resulting in seizure. As mentioned above. Therefore, in the above embodiment, the average diameter, which is the diameter connecting the centers of the wall thicknesses of the cylindrical rotating body 12, is configured to be within the range shown in the table set forth in claim 1 for the number of rotations used.

The basis of the above configuration will be explained below. As shown in FIG. 4, when the cylindrical rotating body 12 rotates around the central axis,
The increase δ in the radius of the rotating body 12 due to the J center force is.

However, γ: heavy density g/cn+2) r: average radius (am) g: 980 (am/S'') E: Young's modulus (
g/cm2) ω: Angular velocity (1/S). Furthermore, as shown in FIG. 5, when the yoke 13 is fixed to the inner circumferential surface of the rotating body 12 and the magnet 14 is further fixed to the inner circumferential surface, the magnet 14 becomes a resin-bonded or rubber-bonded magnet. If the rotating body 12 and the yoke 13 are made of a material with an extremely low Young's modulus compared to the materials of the rotating body 12 and the yoke 13, the increase in the radius of the rotating body 12 due to centrifugal force δ is.

However, ω: Angular velocity (1/S) g: Acceleration of gravity (980cm/S”) γl: Density of rotating body 12 (g/cm') γ1: Density of yoke 13 (
g/cm3) γ,: Density of magnet 14 (g/cm'
) R5: Turning radius of rotating body 12 (C■) ■! = Average radius of workpiece 13 (C) R9: Average radius of magnet 14 (am) E S Young's modulus of rotating body 12 (g/am") R2: Young's modulus of yoke 13 (g/c+w"), Thickness of the rotating body 12 (am): t, Thickness of the yoke 13 (am), Thickness of the magnet 14 (C). Therefore, in Fig. 5, the rotating body 12 is made of an aluminum alloy, the yoke 13 is made of mild steel, and the magnet 14 is made of a rubber magnet (ferrite magnetic powder is bonded with a rubber binder, commonly known as a "polymag"). The expansion of the rotating body due to centrifugal force in this case is determined by applying equation (2). Here, the rigidity of the rubber magnet is extremely small, and the density γ of the aluminum alloy is 2.7, and the Young's modulus E is 7.3.
The density γ2 of X10' mild steel is 7.9. Young's modulus E2 is 21
The density γ of the X 10′ rubber magnet is 4. For example, the thickness t of the rotating body 12 is 0.3.
When the thickness of the yoke 13 is t = 0.08 and the thickness of the magnet 14 is 0.16, the swelling due to centrifugal force δ is
(μm) calculated for the average radius and rotational speed of the rotating body are shown in Table 1.

Table 1 Swelling (μm) The fitting clearance of hydrodynamic bearings is usually set to about 3 to 7 μm on one side, taking bearing rigidity, processing accuracy, etc. into account, but the processing accuracy of roundness (usually 1 μm or less)1 Runout of shaft during rotation (usually 1
(μm or less), even if the above fitting gap is set slightly thick, the allowable bulge of the rotating body is 2 μm in radius.
The limit is about m, and it is necessary to keep it to 2.3 μm or less at most.In Table 1, the thick line indicates the limit of allowable bulge, and the upper left range of this thick line is the allowable range.Table 1 In No. 1, the diameter of the rotating body is expressed as a radius, so if this is expressed as a diameter by 2 ∆ and the allowable range is determined, the result will be as shown in the table shown in Claim 1. As is clear from Table 1, in this type of electric motor, the larger the diameter of one rotating body, the less it can withstand high-speed rotation, and it can be seen that there is a limit to high-speed rotation, which is one of the major functions of hydrodynamic bearings. Therefore, in the present invention, by setting the range of the average diameter (or radius) of the rotating body relative to the number of rotations used, the excellent functions of the hydrodynamic bearing can be utilized to the maximum extent.

Next, the swelling caused by the centrifugal force caused by the high-speed rotation of the 0-rotator, which will be explained with reference to the embodiments of FIGS. 6 and 7, is caused not only by the centrifugal force of the cylindrical rotor 12 itself.

The centrifugal force of the yoke 13 and the magnet 14, especially the latter, greatly contributes. Therefore, if the swelling force due to the centrifugal force of the magnet 14 is not transmitted to the rotating body 12, or even if it is transmitted, it is very small, the swelling of the rotating body 12 will be small, and the average diameter of the rotating body for the number of rotations used will be increased. can do. Figures 6 and 7 illustrate such an embodiment. The example in Figure 6 is.

Only the upper end of the outer periphery of the yoke 13 is fitted and fixed to the inner periphery of the rotating body 12, and a large diameter part is formed in the lower half of the inner periphery of the rotating body 12, which serves as a relief part 36 for the bulge of the yoke 13. It is something. The example in FIG. 7 shows the inner peripheral surface of one rotating body 12 and the yoke 13.
A gap 38 is formed between the outer peripheral surface of the yoke 13 and the yoke 1 as a relief part for the bulge of the yoke 13.
3 is partially adhered with a rubber-based or acrylic-based adhesive 40, and the transmission of the expansion force of the yoke 13 to the rotating body 12 is alleviated by the adhesive 40 having low rigidity. In the examples shown in FIGS. 6 and 7, the shoulder portion of the cylindrical rotating body 12 on which the rotating drum of the rotating magnetic head or the rotating polygon mirror is placed and fixed is made to act as a reinforcing rib. It has become.

According to the embodiments shown in FIGS. 6 and 7, the swelling force due to the centrifugal force of the magnet 14 and the yoke 13 is canceled by the relief portion 36 or the adhesive 40, and is hardly transmitted to the rotating body 12, so that the swelling force is not transmitted to the rotating body 12. The amount of swelling in No. 12 becomes smaller. Therefore, it is possible to increase the average diameter or radius of the rotating body relative to the number of rotations used. Table 2 shows the bulge δ due to centrifugal force in relation to the average radius of the rotating body and the number of rotations, assuming that the conditions such as the material and wall thickness of each part are the same as in the previous embodiment.

Table 2 Bulge (μm) In Table 2, the thick line indicates the limit of allowable bulge, and as in Table 1, the limit of bulge of the rotating body is 2.3 μm.
m, and a thick line is drawn around this point. The upper left range of the thick line is the permissible range.

Table 2 also shows the diameter of the rotating body in terms of radius.

If this is doubled and expressed as a diameter, and the allowable range is determined, the table shown in claim 2 will be obtained.

Although the calculations were made assuming that the material of the rotating body 12 is an aluminum alloy in each of the embodiments, almost the same values can be obtained even if the material is made of steel. That is, γ/ in the above equation (1)
This is because E is direct in the case of aluminum alloys, whereas it is direct in the case of steel, and there is almost no difference between the two.

Therefore, even if the material of the rotating body 12 changes, there is almost no change in the results shown in Tables 1 and 2.

(Effects of the Invention) According to the present invention, the average diameter, which is the diameter connecting the centers of the wall thicknesses of one cylindrical rotating body, is suppressed within a certain range with respect to the number of rotations used, so that it is fixed to the outer circumferential surface of one rotating body. It is possible to prevent seizure of the dynamic pressure bearing portion by preventing contact with the inner circumferential surface of the bearing. In addition, by forming a relief part between the cylindrical rotating body and the yoke on the inner circumferential side of the yoke to prevent swelling of the yoke due to centrifugal force, the average diameter of the cylindrical rotating body can be made larger relative to the operating speed. be able to.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the electric motor according to the present invention, and FIG. 2 is a partially sectional front view of a hydrodynamic bearing section of the same embodiment.
Fig. 3 is a longitudinal cross-sectional view showing how the bearing portion swells due to centrifugal force, Fig. 4 is a longitudinal cross-sectional view showing the relationship between the average radius and the swell of the cylindrical rotating body, and Fig. 5 is the same as the rotating body. FIG. 6 is a vertical cross-sectional view showing the relationship between the average radius and wall thickness of each part, which is the basis for calculating the amount of body expansion; FIG. 6 is a vertical cross-sectional view showing the main parts of another embodiment of the electric motor according to the present invention; FIG. 7 is a longitudinal cross-sectional view showing a main part of still another embodiment of the electric motor according to the present invention. 11... Fixed bearing, 12... Cylindrical rotating body, 1
4... Magnet, 17... Drive coil, 1
8...Groove, 21...Outer circumferential surface of cylindrical rotating body, 24...Inner circumferential surface of fixed bearing, 13...Yoke, 36.38...Relief portion. Enamel 40

Claims (1)

[Claims] 1. A hydrodynamic bearing is formed by providing a groove on either the outer circumferential surface of a cylindrical rotating body or the inner circumferential surface of a fixed bearing that rotatably supports the outer circumferential surface of this cylindrical rotating body. In an electric motor in which a magnet is fixed to the inner circumferential surface of the cylindrical rotating body and a driving coil is arranged opposite to the magnet, the diameter is the diameter connecting the center of the wall thickness of the cylindrical rotating body. An electric motor characterized in that its average diameter falls within the range shown in the following table for the number of rotations used. 2. A hydrodynamic bearing is formed by providing a groove on either the outer circumferential surface of the cylindrical rotating body or the inner circumferential surface of a fixed bearing that rotatably supports the outer circumferential surface of the cylindrical rotating body, and the cylindrical rotating body is In an electric motor in which a magnet is fixed to the inner circumferential surface of the body under the interposition of a cylindrical yoke, and a driving coil is arranged opposite to this magnet, the yoke and the inner circumferential surface of the cylindrical rotating body In addition to forming a relief part for the expansion of the yoke due to centrifugal force between An electric motor characterized by: