JPH03199714A - Bearing device - Google Patents

Abstract

PURPOSE:To change the value of viscosity to an optimum value in accordance with a rotational speed by applying variable voltage to electric viscous fluid with which a clearance between a rotary shaft and a sliding bearing in filled, in the case of the sliding bearing used for a polygon mirror driving motor in a laser beam printer or the like. CONSTITUTION:A cylindrical sliding bearing part 2 is protrusively provided in a housing 1, and a bearing cylinder 3 is fitted into an internal peripheral part of the sliding bearing part 2. A stator 6 is constituted of an iron core 4 on which an armature coil 5 is wound. A part between a rotary shaft 7, in which a groove 7a is formed, and a rotary shaft 3 is filled with ER(Electro Rheological) fluid 13 serving as electric viscous fluid. A control part 20 is connected to an armature 15 by a lead wire 21 and connected to the rotary shaft 7 through conductive magnetic fluid from the lead wire 21. The housing is connected to the control part 20 by a lead wire 22 and grounded. Thus by placing the ER fluid 13 in an electric field, viscosity is changed in accordance with voltage. Any surplus load is eliminated by requlating the voltage by the control part so as to set the viscosity in an optimum value in accordance with a rotational speed.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a bearing device having a sliding bearing portion.

(Prior Art) For example, a motor for driving a polygon mirror in a laser beam printer or the like uses a sliding bearing in which a rotating shaft is provided with a groove for generating dynamic pressure. Oil lubrication ensures smooth rotation. In other words, as is well known, dynamic pressure is generated between the rotating shaft and the bearing due to its rotation, and this pressure causes oil to act as a lubricant between the shaft and the bearing, allowing the shaft to rotate without coming into contact with the bearing. A smooth rotational state is maintained.

(Problems to be Solved by the Invention) In such a motor, the rotation speed of the polygon mirror, that is, the rotation speed of the rotation shaft, may be changed in order to change the printing speed, resolution, etc., for example. However, in such a case, in a motor with the conventional configuration as described above, when the rotational speed is set to a value larger than a predetermined value, the viscosity of the oil as a lubricant is too large for the rotational speed. This creates an extra load on the rotating shaft, lowering efficiency and increasing heat generation. On the other hand, when the rotational speed is set lower than a predetermined value, the viscosity of the oil as a lubricant becomes smaller than the value required at that rotational speed, contrary to the above, and the sliding bearing There was a problem in which the rotational accuracy of the rotating shaft deteriorated due to the inability to function properly.

In other words, the viscosity of oil used as a lubricant is usually adapted to the specified rotational speed of the rotating shaft, so if the rotational speed of the rotating shaft is changed, the viscosity of the oil will deviate from its optimum value, causing an excess load. This may cause the rotational accuracy to deteriorate.

The present invention has been made in view of the above circumstances, and its object is to provide a bearing that can efficiently and stably maintain a rotating shaft in accordance with the rotational speed even when the rotational speed is changed. We are here to provide you with the equipment.

[Structure of the Invention] (Means for Solving the Problems) The present invention is directed to a bearing device having a sliding bearing portion for holding a rotating shaft. The present invention is characterized in that it is constructed by providing an electrorheological fluid and a voltage applying means for applying a variable voltage to the electrorheological fluid.

(Function) According to the bearing device of the present invention, when the rotational speed of the rotating shaft is set lower than a predetermined value, the electrorheological fluid is placed in a large electric field by applying a voltage using the voltage applying means. By increasing its viscosity, the rotation accuracy of the rotating shaft by the sliding bearing portion can be maintained well. In addition, when the rotational speed of the rotating shaft is set higher than a predetermined value, the viscosity of the electrorheological fluid can be reduced by applying a voltage lower than the above voltage using the voltage applying means and placing the electrorheological fluid in a small electric field ψ. This prevents the sliding bearing portion from being an extra load on the rotating shaft, thereby preventing a decrease in efficiency, and suppressing heat generation in the sliding bearing portion.

In this case, the electrorheological fluid generally refers to ER(P, 1ec
When placed in an electric field, its viscosity increases depending on the magnitude of the electric field, and the reaction is reversible and short-lived (several meters).
It has the property of occurring in seconds). Therefore, by changing the applied voltage according to the rotational speed of the rotating shaft, the viscosity of the electrorheological fluid can be quickly changed, resulting in excellent controllability.

(Example) The following is a first example of the case where the present invention is applied to a bearing of a polygon mirror drive motor used in a laser beam printer, etc.
An embodiment will be described with reference to FIGS. 1 to 3.

First, in Figure 1, which shows the overall configuration of the motor in cross section,
The stator housing 1 is formed of a metal such as aluminum into a cylindrical shape with a bottom, and has a cylindrical sliding bearing part 2 protruding from the center, and a bearing sleeve 3 on the inner circumference of the sliding bearing part 2. It is fitted. Further, an armature core 4 is fixed at a predetermined position on the inner peripheral wall surface of the stator housing 1, and an armature coil 5 is wound around the armature core 4, thereby forming a stator 6. Above bearing tube 3
A rotating shaft 7 made of a conductive metal such as stainless steel is pushed through the rotating shaft 7, and a herringbone groove 7a for generating dynamic pressure is formed on the outer circumference of the rotating shaft 7. Although not included, spiral grooves for generating dynamic pressure are also formed. Further, a rotor housing 8 and a polygon mirror 9 are fixed to the rotating shaft 7 via an insulating sleeve 10.

The rotor housing 8 has a cylindrical shape, and the sliding bearing portion 2
A rotor magnet 11 is attached to the outer peripheral surface of the armature core 4 at a predetermined distance from the armature core 4.

In this case, the rotor magnet 11 is made of, for example, a manganese-aluminum-carbon (Mn-AI-C) material. The rotor 12 is constructed as described above.

Now, between the rotating shaft 7 and the bearing sleeve 3 described above, an electrorheological fluid, ER (Elcctro
Rheological) fluid 13 is filled.

A non-contact conductive terminal 15 is provided at the end 2a of the sliding bearing 2 with an insulating spacer 14 interposed therebetween.

As shown in an enlarged view in FIG. 2, this non-contact conductive terminal 15 includes an electrode plate 16 made of a magnetic metal material. magnet 17
．． It is composed of a magnetic pole plate 18 and one conductive magnetic fluid, and forms a magnetic circuit R via the rotating shaft 7, and the conductive magnetic fluid 19 is held by the magnetic flux generated in this magnetic circuit R by the magnet 17. It has become. The non-contact conductive terminal 15 is connected from the control unit 20 to a lead wire 21 disposed through the back surface of the stator housing 1, and from the lead wire 21 through the electrode plate 16 and the conductive magnetic fluid 19. It is designed to be electrically connected to the rotating shaft 7. In this case, since conduction is established via the conductive magnetic fluid 19, no loss such as friction occurs between the rotating shaft 7 and the non-contact conductive terminal 15. On the other hand, the stator housing 1 is connected to the control section 20 by a lead wire 22 and is grounded. As a result, the control unit 20
By applying a voltage between the lead wires 21 and 22, a voltage is applied between the rotating shaft 7 and the sliding bearing part 2,
As a result, the ER fluid 13 is placed in an electric field. The control unit 20 is an electrical component provided to rotationally drive the motor, and in addition to the above-mentioned functions, the control unit 20 provides a predetermined armature current and a position detection unit provided on the bottom of the stator housing 1. The rotor 1 is
Controls such as detecting the position of 2 are performed.

Next, in order to explain the operation of this embodiment, first, the characteristics of the ER fluid will be explained with reference to FIG.

That is, as schematically shown in FIG. 3, the ER fluid contains fine particles (dispersoids) with a diameter of 1 to 100 μm in a solvent (dispersion medium).
N existed. Now, in the state where no voltage is applied between electrode plates A and B (see figure (a)), the fluid behaves like a general fluid because it is electrically neutral. As shown in b), when a DC voltage is applied between electrodes A and B, the charge of fine particles N in the solvent is attracted to each electrode A and B, resulting in a polarized state, and each fine particle N is attracted to each other and becomes a chain. As a result, a force acts between electrodes A and B to counteract shear stress, and the viscosity between the electrodes essentially increases. Since such changes occur several milliseconds after the voltage is applied, they can be considered to occur almost simultaneously.Furthermore, the degree of such changes in viscosity is approximately proportional to the magnitude of the applied voltage. Therefore, a desired viscosity can be set by controlling the magnitude of the applied voltage.

Now, in the motor of this embodiment, the rotating shaft 7 is driven to rotate under the control of the control section 20 using a well-known control method. At this time, if the rotational speed of the rotating shaft 7 is set to the low speed side, the magnitude of the dynamic pressure generated by the rotation of the rotating shaft 7 is small, so the voltage v1 between the lead wires 21 and 22 is
Apply. As a result, the ER fluid 13 is placed in an electric field, and the viscosity of the ER fluid 13 increases.
The rotating shaft 7 is maintained in a stable rotating state by the bearing sleeve 3 and the ER fluid 13. On the other hand, when the rotational speed is set on the high speed side, the dynamic pressure generated by the rotation of the rotating shaft 7 is large, and even if the viscosity of the ER fluid 13 is low, the rotating state can be maintained in a sufficiently stable manner. On the other hand, if the viscosity is high, it becomes a load that reduces the rotational force of the rotating shaft 7, reducing the efficiency of rotation. Therefore, in this case, ER fluid 1
The viscosity is lowered by setting the voltage applied to V2 to V2 (V2 - V+), which is lower than Vl. Thereby, the rotating shaft 7 is held without reducing the efficiency of rotation.

According to this embodiment, the viscosity of the ER fluid 13 is made variable by changing the applied voltage from the control unit 20, so the viscosity can be set to the optimum viscosity each time according to the rotational speed of the rotating shaft 7. In addition, the rotating shaft 7 can be maintained in a stable rotating state, and there is no need to act as an extra load on the rotating shaft 7, thereby preventing a reduction in its efficiency.

FIG. 4 shows a second embodiment of the present invention, which differs from the first embodiment in that the sliding bearing portion 2 is fixed to the stator housing 1 via an insulating member 24, and Since the insulating sleeve 10 of the rotor 12 is eliminated and the rotor housing 8 and polygon mirror 9 are directly fixed to the rotating shaft 7, electrically, the lead wire 21 is grounded and the control unit 2
0, a voltage is applied to the lead wire 22.

With this configuration, the same effects as in the first embodiment can be obtained except that the polarity of the applied voltage is reversed.

In each of the above embodiments, ER is used as the electrorheological fluid.
Although the case where the fluid 13 is used has been described, the present invention is not limited to this, and an ER fluid in which a surfactant is added to a solvent may be used.

Further, in each of the above embodiments, the voltage applied to the ER fluid 13 has been explained as being in two stages, but the voltage is not limited to this, and the voltage can be applied in multiple stages according to the rotational speed of the rotating shaft, including the case where no voltage is applied. Alternatively, it may be applied continuously in order to set the optimum viscosity based on the relationship between the applied voltage and the viscosity.

Further, in each of the above embodiments, the rotary shaft 7 is provided with a herringbone 7a and a spiral 7J7b for generating dynamic pressure, but the structure is not limited to this and may be provided on the bearing sleeve 3 side. Alternatively, the present invention may be applied to a sliding bearing having no groove for generating dynamic pressure.

In each of the above embodiments, the present invention is applied to a motor for driving a polygon mirror, but the present invention is not limited to this, but can be applied to general bearing devices having a sliding bearing, such as a motor for driving a cylinder of a VTR. It is something.

[Effects of the Invention] As explained above, according to the bearing device of the present invention, an electrorheological fluid is filled between the rotating shaft and the sliding bearing portion, and a variable voltage is applied to the electrorheological fluid by the voltage applying means. With this configuration, the viscosity of the electrorheological fluid can be set to an optimal value according to the rotational speed of the rotating shaft, and the rotational state of the rotating shaft can be maintained accurately and stably. It has the excellent effect of being able to efficiently maintain a rotating state without becoming a load.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention.
2 is a partially enlarged view of a non-contact conductive terminal, FIGS. 3(a) to 3(c) are schematic diagrams for explaining the characteristics of the ER fluid, and FIG. 4 is a longitudinal side view of the overall configuration. is the second aspect of the present invention
FIG. 2 is a diagram corresponding to FIG. 1 showing an embodiment of the present invention. In the drawing, 1 is a stator housing, 2 is a sliding bearing part,
3 is a bearing cylinder, 6 is a stator, 7 is a rotating shaft, 12 is a rotor, 13 is an ER fluid (electrorheological fluid), 15 is a non-contact conductive terminal, and 20 is a control unit (voltage application means).

Claims (1)

[Claims] 1. In a device having a sliding bearing for holding a rotating shaft, an electrorheological fluid filled between the rotating shaft and the sliding bearing, and a voltage for applying a variable voltage to the electrorheological fluid. A bearing device comprising applying means.