JPH034022A - Dynamic pressure bearing structure for motor - Google Patents

Abstract

PURPOSE:To suppress damping in a thrust direction by providing a thrust direction position sensor, which detects positions of a permanent magnet in a rotary shaft insertion end and an electromagnet in a bearing part bottom end, in a bearing part and controlling supply power to the electromagnet based on sensor output. CONSTITUTION:A permanent magnet 5 is fixed to the insertion end of a rotary shaft 2 inserted into a bearing part 3, and an electromagnet 6, opposed to an insertion part of the rotary shaft 2, is mounted to the bottom part of the bearing part 3. A thrust position sensor 7, opposed to the lower surface of the permanent magnet 5, is provided in a space between this permanent magnet 5 and internal surfaces of the bottom part of the bearing part 3. A current control circuit 8 is connected to an output end of the thrust position sensor 7. In a flow of current in the electromagnet to support thrust of the rotary shaft 2, when its floating distance L is changed, output voltage of the sensor 7 is also changed in accordance with the change of the distance L, and excitation current in proportion to the change of the output voltage is allowed to flow in the electromagnet 6 to change magnetic repulsive force. Accordingly, damping in the thrust direction of a rotor 11, which contains the rotary shaft 2, is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a dynamic pressure bearing structure for a motor having a configuration in which the thrust load of a rotating shaft supported by dynamic pressure is supported by magnetic repulsion.

[Prior Art] Dynamic pressure bearing structures are used to support rotating shafts of, for example, scanner motors of laser beam printers, hard disk drive motors, cylinder drive motors of video tape recorders, and the like.

In this type of hydrodynamic bearing structure, two methods are available, one that uses dynamic pressure and the other that uses magnetic repulsion, to support the thrust load of the rotating shaft without generating mechanical contact friction. Are known.

A method that utilizes dynamic pressure is to provide a large number of arc-shaped grooves on the end face of the rotating shaft, extending from the center to the circumferential surface, and as the rotating shaft rotates, the fluid around the end face of the rotating shaft is transferred to the outer circumference with a wide groove width. By taking in the inner circumferential side where the groove width is narrower, dynamic pressure is generated at the center of the end face of the rotating shaft, and this force lifts the rotating shaft to support the thrust load.

In addition, a method using magnetic repulsion is to fix a permanent magnet to the end face of the rotating shaft, and also fix other permanent magnets facing this to the bottom of the bearing into which the rotating shaft is inserted. The magnetic repulsion of both magnets levitates the rotating shaft and supports the thrust load.

[Problems to be Solved by the Invention] However, in the conventional structure, the floating blade of the rotating shaft that is generated by dynamic pressure or magnetic repulsion requires a groove design for generating dynamic pressure on the end surface of the rotating shaft, and a permanent magnet that is magnetized. A fixed value was determined by the strength of the magnetism, and it was impossible to adjust this value arbitrarily.

Therefore, it was necessary to redesign each of the floating blades according to the magnitude of the load on the rotating shaft, and it was not possible to use a hydrodynamic bearing structure having a thrust load support structure in common for various loads.

Moreover, in the case of a motor that drives a rotating shaft supported in the thrust direction as described above, due to uneven rotation, variations in component dimensions, etc., the thrust direction of the rotating shaft is There is a problem in that there is a movement to align the magnetic center of the stator with the magnetic center of the rotor magnet, and this and the magnetically levitated blade cause the rotating shaft to be damped in the thrust direction.

An object of the present invention is to provide a dynamic pressure bearing structure for a motor that can have a thrust load support structure that can be used in common for various loads, or that can suppress damping in the thrust direction of the rotating shaft. .

[Means for Solving the Problems] In order to achieve the above object, in the dynamic pressure bearing structure of the motor of the present invention, an electromagnet facing the insertion end of the rotating shaft is provided at the bottom of the bearing portion into which the rotating shaft is inserted. Attach a permanent magnet to the insertion end of the rotating shaft opposite this electromagnet,
A thrust direction position sensor for detecting the position of the permanent magnet with respect to the electromagnet is attached to the bearing part, and a current control circuit is provided for controlling the current supplied to the electromagnet based on the output of this sensor. .

This generates magnetism. Thereby, the polarities of the facing surfaces of the permanent magnet fixed to the rotating shaft and the fixed iron core of the electromagnet that generated the magnetism become different from each other. Therefore, the magnetic repulsion between these different poles makes it possible to levitate the rotating shaft and support the thrust load. Further, the thrust direction position sensor detects the position of a permanent magnet fixed to the magnetically levitated rotating shaft with respect to the electromagnet. and,
The current control circuit controls the current supplied to the electromagnet based on the position detection of the sensor. Therefore, by adjusting the magnitude of the current given to the electromagnet using this current control,
The supporting force of the rotating shaft can be changed arbitrarily. Furthermore, by performing the above-described current control while the motor is operating, the position of the permanent magnet relative to the electromagnet, that is, the position of the rotating shaft in the thrust direction, can be held constant.

[Example] Hereinafter, an example in which the present invention is applied to a scanner motor for a laser beam printer shown in the drawings will be described.

In FIG. 1, reference numeral 1 denotes a motor housing made of a non-magnetic material, on which a rotary shaft 2 is rotatably supported via a dynamic pressure bearing structure. The hydrodynamic bearing structure includes a bearing portion 3, a herringbone groove 4, permanent magnets, an electromagnet 6, a thrust position sensor 7, and a control circuit 8.

The bearing part 3 is integrally provided approximately at the center of the motor housing 1, and has a cylindrical shape with only the upper end open. The rotating shaft 2 is inserted into this bearing part 3,
The outer circumferential surface of the rotating shaft 2 is closely opposed to the inner circumferential surface of the bearing portion 3 with a gap of several μ. Note that a bearing sleeve may be attached to the inner surface of the bearing portion 3 so that the inner circumferential surface thereof closely faces the outer circumferential surface of the rotating shaft 2.

The gap is filled with fluid. In this embodiment, the fluid is air, but it may also be a liquid lubricant such as grease. In addition, when filling the above-mentioned gap with liquid lubricant, a dynamic pressure bearing structure may be used in which a magnetic fluid seal is provided at the upper end opening of the bearing portion 3.

Herringbone f! A plurality of j4 are provided on the outer circumferential surface of the rotating shaft 2, for example, a pair of upper and lower ones. a4 is formed along the circumferential direction. Further, the permanent magnet 5 is magnetized in the axial direction (vertical direction in the figure), and is fixed to the lower end of the rotating shaft 2, that is, the insertion end.

The electromagnet 6 is fixed to the bottom of the bearing part 3, and the permanent magnet 5 is moved toward and away from the upper surface of the fixed iron core. By energizing the electromagnet 6, the upper surface of the fixed iron core has a polarity different from the polarity of the magnetic pole on the lower surface of the permanent magnet 5.

A Hall element, a Hall IC, or the like is used as the thrust position sensor 7, and this is attached to the bottom of the bearing portion 3 in correspondence with the permanent magnet 6. In the case of this embodiment, the sensor 7 is provided using the gap between the electromagnet 6 and the bottom inner surface of the bearing part 3. In this case, the sensor 7 is used to prevent damping of the rotating shaft 2 in the thrust direction. As shown in FIG. 2, it has an amplifier 9 connected to the output end of the sensor 7, and a transistor 10 as a current control element whose base is connected to the output end of the amplifier 9. And transistor 10
An electromagnet 6 is connected to the collector.

Further, a stepped portion is provided at the upper portion of the outer peripheral surface of the bearing portion 3, and the stator 11 is attached to the outer periphery of the bearing portion 3 by being hooked to this stepped portion. Further, a printed circuit board 12 is attached to the outer peripheral surface of the bearing portion 3 immediately below the stator 11. This circuit board 12 includes a position sensor 13 for detecting the rotational position of the rotor, the driving amplifier 9,
A transistor 10 and other circuit components are attached.

The upper end of the rotating shaft 2 passes through the center of a rotor yoke 14 and is fixed to the yoke 14. The rotor yoke 14 houses the stator 11 inside thereof, and has a ring-shaped rotor magnet 15 attached to its inner peripheral surface.

The rotor magnet 15 is magnetized along the thickness direction, and S poles and N poles are alternately provided on the inner surface along the circumferential direction. Note that the rotating shaft 2, rotor yoke 14, and rotor magnet 15 constitute a rotor.

Further, a polygon mirror 16 as a load is attached to the upper end of the rotating shaft 2 passing through the rotor yoke 14. This mirror 16 reflects the laser beam incident thereon and forms a spot image on the photosensitive drum via an optical system (not shown).

When the radial gap type DC brushless smoke manufactured by Joki Purchasing is driven, as the rotor rotates, a pair of upper and lower herringbone grooves 4 formed on the outer peripheral surface of the rotating shaft 2 collect the surrounding fluid. As a result, dynamic pressure is generated in the portions where these herringbone grooves 4 are provided, and this dynamic pressure supports the rotating shaft 2 without contacting the inner circumferential surface of the bearing portion 3.

When the motor is driven, the electromagnet 6 is excited at the same time, so magnetic repulsion occurs between the magnetic pole formed at the upper end of the fixed iron core of the magnet 6 and the permanent magnet 5 fixed at the lower end of the rotating shaft 2. The force causes the rotor with the rotating shaft 2 to levitate. In other words, the thrust load of the rotating shaft 2 can be supported.

In supporting this thrust load, the flying height A of the rotating shaft 2
When IL (see FIG. 1) changes, the distance between the thrust position sensor 7 and the permanent magnet 5 also changes, so the magnetic flux acting on the sensor 7 from the permanent magnet 5 changes. Therefore, the output voltage of the sensor 7 also changes accordingly.

This output change is amplified by amplifier 9 and applied to the base of transistor 10. Then, transistor 10
The degree of conductivity of the transistor 10 changes depending on the voltage between the base and emitter of the transistor 10, and an excitation current proportional to the degree of conductivity is caused to flow through the electromagnet 6.

By performing such current control, when the rotary shaft 2 approaches the electromagnet 6 regardless of the magnetic repulsion force, such as when the rotor is heavy, a larger amount of the excitation current is caused to flow. The above magnetic repulsion force is strengthened. On the other hand, when the rotor is light and the rotating shaft 2 is moved further away from the electromagnet 6 due to the magnetic repulsion, the excitation current decreases and the magnetic repulsion is weakened.

That is, by automatically adjusting the magnetic repulsion force as described above, damping of the rotor including the rotating shaft 2 in the thrust direction can be suppressed and its position can be maintained constant.

Note that the present invention is not limited to the above embodiment.

For example, instead of the current control circuit of the above embodiment, an electromagnet 6
In the case where a variable resistor (that is, a current control circuit) is provided in the current supply circuit to the
The magnetic force of the electromagnet 6 can be changed. Therefore, for example, by adjusting the resistance value of the variable resistor according to the difference in the magnitude of the load, a predetermined magnetic repulsion force can be obtained, and the dynamic pressure bearing structure can be shared. Also, similarly,
Although the magnetic force of the permanent magnet 5 fixed to the rotating shaft 2 varies widely, by adjusting the variable resistor, the variation in the permanent magnet 5 can be accommodated, and the quality of the hydrodynamic bearing structure can be improved.

Furthermore, it goes without saying that the present invention can also be applied to a dynamic pressure bearing structure included in an axial gap type brazire motor.

[Effects of the Invention] In the dynamic pressure bearing structure of the motor of the present invention described above, an electromagnet facing the insertion end of the rotating shaft is attached to the bottom of the bearing portion into which the rotating shaft is inserted, and the rotating shaft is rotated facing the electromagnet. A current control circuit that includes a permanent magnet attached to the insertion end of the shaft, a thrust direction position sensor that detects the position of this permanent magnet with respect to the electromagnet attached to the bearing, and that controls the current supplied to the electromagnet based on the output of this sensor. With this configuration, damping of the rotating shaft in the thrust direction can be suppressed, or a hydrodynamic bearing structure having a thrust load support structure can be used in common for various loads.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a longitudinal sectional view of a brushless motor equipped with a dynamic pressure bearing structure, and FIG. 2 is a circuit diagram showing current control of an electromagnet. 2... Rotating shaft, 3... Bearing section, 4... Herringbone groove Fig. 1

Claims (1)

[Claims] In a hydrodynamic bearing structure for a motor that supports the thrust load of a rotating shaft by magnetic repulsion, an electromagnet facing the insertion end of the rotating shaft is attached to the bottom of the bearing portion into which the rotating shaft is inserted, and the electromagnet is mounted opposite to the electromagnet. A permanent magnet is attached to the insertion end of the rotating shaft, a thrust direction position sensor for detecting the position of the permanent magnet with respect to the electromagnet is attached to the bearing part, and a current is supplied to the electromagnet based on the output of this sensor. A dynamic pressure bearing structure for a motor, characterized by being equipped with a current control circuit that controls.