JPH0865950A - Motor and optical scanner using the same - Google Patents

Abstract

PURPOSE: To eliminate seizure due to the contact of dynamic pressure bearing surfaces by stably maintaining a high speed rotation for a long period. CONSTITUTION: A motor has a dynamic pressure bearing for bearing a first holding member 2 for holding a magnet 21 and a second holding member 3 for holding a coil 31 via fluid. The coil 31 is energized to relatively rotate the members 2 and 3. The dynamic pressure bearing of the motor is formed of the outer periphery 23 of the member 2 and the inner periphery 35 of the holder 3, and nickel-phosphorus plating 25a in which polytetrafluoroethylene is dispersed is provided at least at one bearing surface of both the surfaces 23, 35. Further, the motor is mounted with a polygon mirror 1 for scanning a luminous flux from a light source at the small-diameter part 24 of the member 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor having a dynamic pressure bearing and an optical scanning device in which a polygon mirror is rotationally driven by the motor.

[0002]

2. Description of the Related Art A laser scanning motor, a magnetic drum motor, a gyro motor, or a motor that rotates at high speed such as a high-speed spindle motor is capable of rotating at high speed. A hydrodynamic bearing that supports the rotor (rotating shaft) is used. For example, as shown in FIG. 5, a laser scanning motor for constraining rotation of a polygon mirror includes a polygon mirror 1 and a first holding member (rotor) 2 to which a magnet 21 for rotation driving is attached and which rotates. Of the second holding member 3 and the second holding member (stator) 3 that holds the coil 31 for use as a bearing member, and faces the outer peripheral surface 23 of the first holding member 2 and the second holding member 3 with a slight gap 8 therebetween. A dynamic pressure bearing is configured with the peripheral surface 35. The first holding member 2 further includes
The balance plate 11 and the thrust magnet 22 for correcting the rotational balance of the polygon mirror 1 are attached,
The second holding member 3 includes a thrust magnet 32 that cooperates with the thrust magnet 22 to generate a floating force in the first holding member 2, and a stator core 33 that forms a part of the second holding member 3. And the case body 34 are attached. The second holding member 3 is fitted and fixed to the holder 4.

In this dynamic pressure fluid bearing, since a dynamic pressure is generated during rotation to levitate and support the rotating shaft, a very narrow fixed bearing gap is formed between the rotating shaft and the bearing member. . For this reason, unless the outer peripheral surface (bearing surface) of the rotating shaft and the inner peripheral surface (bearing surface) of the bearing member are precisely finished so that unnecessary protrusions do not occur, the rotating shaft and the bearing member will not rotate during rotation. There is a risk of causing frictional heat upon contact and causing a so-called seizure phenomenon in which the shaft and the bearing are adhered to each other due to melting of the contact portion. This seizure phenomenon generally causes wear due to contact when the bearing load capacity is low at the time of start and stop, but also occurs when contact occurs at high speed due to vibration when external force is applied. .

On the other hand, in this type of high-speed rotary motor, the weight is reduced and the rise time is shortened.
It is required to arrange the magnet 21 for driving rotation and the coil 31 for driving inside the portion constituting the dynamic pressure bearing to make the motor compact and minimize the runout and tilt of the rotary shaft. In the case of the dynamic pressure bearing having such a structure, since the bearing shape and structure are complicated, it is much more advantageous to machine the aluminum alloy in terms of machining cost. It is desired that both the second holding members 3 be made of aluminum or the like.

Therefore, in order to improve the wear resistance of aluminum and the like, a hard alumite treatment is applied to the inner peripheral surface 35 of the second holding member 3 serving as the bearing member, and the outer peripheral surface 23 of the first holding member 2 serving as the rotor. Has been conventionally subjected to Ni-P electroless plating containing SiC particles.

[0006]

However, when the hard alumite treatment and the Ni-P electroless plating containing SiC fine particles are applied, both materials have very high hardness and excellent wear resistance, but impurities in the plating reaction. Since it is a plating solution in which a large amount of SiC can be said to be generated, reaction unevenness is likely to occur and projections are formed on the coating film. There is a problem that the contact of 35 causes seizure. Then, in order to prevent uneven reaction of plating, it is necessary to make the process control extremely strict, and the yield is deteriorated.

In particular, when a member having a large mass such as the polygon mirror 1 is attached to the outside of the dynamic pressure bearing of the motor as in the optical scanning device, the polygon eccentric rotation of the polygon mirror 1 and the instability of the attachment work cause contact. It is easy to be burned by. When baking occurs, there is a risk that the heat generated by the motor may adversely affect the surrounding precision members such as the lens.

An object of the present invention is to provide a motor that maintains stable high speed rotation for a long period of time and does not cause seizure due to contact between the dynamic pressure bearing surfaces. Another object of the present invention is to provide an optical scanning device that can maintain stable quality for a long period of time by using a motor that does not cause seizure between dynamic pressure bearing surfaces.

[0009]

In order to achieve the above object, the invention of claim 1 has a first holding member for holding a magnet and a second holding member for holding a coil, which are borne by a fluid. In a motor having a dynamic pressure bearing portion, the first holding member and the second holding member are relatively rotated by energizing a coil, at least one bearing surface of the dynamic pressure bearing portion is Nickel-phosphorus plating in which tetrafluoroethylene is dispersed is applied.

Further, in the invention of claim 2, the polygon mirror for scanning the light flux from the light source, the first holding member for holding the magnet, and the second holding member for holding the coil are borne by the fluid. It has a dynamic pressure bearing portion, and is provided with a motor that relatively rotates the first holding member and the second holding member by energizing the coil, and the polygon mirror is rotationally driven by this motor. In the optical scanning device, at least one bearing surface of the dynamic pressure bearing portion of the motor is plated with nickel-phosphorus in which polytetrafluoroethylene is dispersed.

Further, according to the invention of claim 3, in the optical scanning device of claim 2, the film thickness of the nickel-phosphorus plating in which polytetrafluoroethylene is dispersed is 10 μm or less.

[0012]

Therefore, in the motor of claim 1, since the bearing surface is plated with nickel-phosphorus in which polytetrafluoroethylene having a low coefficient of friction is dispersed, the hardness is high, the wear resistance is excellent, and the friction is good. The bearing can have a low coefficient. Moreover, during operation, due to partial heat generation due to contact between the bearing surfaces, the polytetrafluoroethylene deposited on the bearing surface melts and forms a lubricating film, so that the bearing can have a very low friction coefficient.
Further, even if the coating is worn, the polytetrafluoroethylene deposited during plating is continuously exposed, so that a low friction coefficient can be maintained.

In addition, according to the invention of claim 2, as a motor for driving the polygon mirror, nickel-phosphorus plating in which polytetrafluoroethylene having a low friction coefficient is dispersed is applied to the bearing surface thereof, so that the rotation is locked. There is no need for adverse effects on other precision parts and repair work due to useless heat generation due to the above.

Further, in the third aspect of the present invention, similarly, unnecessary heat generation due to the rotation being locked does not adversely affect other precision parts or repair work, and the thickness of the plating film is reduced. Since the thickness is 10 μm or less, the surface roughness of the plated surface does not deteriorate and abrasion is unlikely to occur. Further, even if the plated surface is almost lost due to wear, the dimensional accuracy between the bearing surfaces changes only by a value of 10 μm or less, and has little influence on the dynamic pressure characteristics.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the motor and the optical scanning device of the present invention. This motor reflects a light flux from a light source (not shown) by a polygon mirror 1 which is a rotary polygon mirror and converges it as a minute beam diameter on a photosensitive drum by various lenses such as an Fθ lens (not shown) to form an electrostatic latent image. It is used in an optical scanning device for writing.

The main structure of this motor is as follows:
The polygon mirror 1 and a rotation driving magnet 21 are attached to rotate a first holding member 2 and a second holding member 3 holding a driving coil 31.
The balance plate 11 and the thrust magnet 22 that correct the rotational balance of the polygon mirror 1 are further attached to the first holding member 2, and the second holding member 3 is
A thrust magnet 32 for generating a floating force on the first holding member 2 in cooperation with the thrust magnet 22;
The stator core 33 and the case body 34, which form a part of the second holding member 3, are attached. The second holding member 3 is fitted and fixed to the holder 4.

The polygon mirror 1 is fitted into the small diameter portion 24 of the first holding member 2, and the small diameter portion 24 and the large diameter portion 25 thereof are arranged.
Positioning is performed by abutting the flat surface portion of the mirror 1 to the connecting portion 28 that connects the and. Then, the balance plate 11 is attached to the small-diameter portion 24 of the first holding member 2 with the screw 14, whereby the mirror 1 is connected to the balance plate 11 and the connecting portion 28 via the mirror pressing plate 12 and the plate spring 13. It is sandwiched between and fixed. The balance plate 11 is an adjusting member when the center of gravity of the entire rotating body deviates from the normal position due to a processing error of the first holding member 2 or an assembly error when mounting the polygon mirror 1, the magnet 21, and the like. is there. The adjustment is
This is performed by forming one or a plurality of recessed holes 11a whose diameter and depth are set in a position near the outer periphery of the balance plate 11. By this adjustment, vibration such as wow and flutter and collision between bearing surfaces are eliminated and reduced. Further, near the center of the balance plate 11, there is provided a hole 11b which communicates with a dynamic pressure bearing portion which will be described later and allows air inside the motor to escape to the outside. Each part 11c is provided.

The first holding member 2 is made of an aluminum material, and the rotation driving magnet 21 is attached to the inner peripheral surface of the large-diameter portion 25 via a yoke 27. A frequency generator magnet 26 is mounted on the surface opposite to the surface on which the mirror 1 is mounted. The outer peripheral surface 23 of the first holding member 2 is provided with a plurality of doglegged grooves 29 for generating dynamic pressure, and constitutes one of the bearing surfaces of the dynamic pressure bearing portion. The entire outer peripheral surface 23 including the grooves 29 is plated with nickel-phosphorus 25a in which polytetrafluoroethylene is dispersed by a method described later.
The thrust magnet 3 attached to one end of the second holding member 3 is provided on the inner peripheral surface of the small diameter portion 24 of the first holding member 2.
The thrust magnet 22 is attached at a position facing 2 and by the attraction force of both magnets 22 and 32,
The first holding member 2 is maintained in a non-contact state with the second holding member 3 in the thrust direction. This attractive force is generated by reversing the polarities of the opposing magnetic poles of the two magnets 22 and 32 as shown in FIG.

In the minimum diameter portion 3a located at one end of the second holding member 3, the minimum diameter portion 3 is arranged so that the thrust magnet 32 faces the thrust magnet 22 as described above.
The small-diameter portion 3b adjacent to a has a driving coil 31 held in the medium-diameter portion 3c adjacent to the small-diameter portion 3b so that the frequency generator circuit board 36 faces the frequency-generator magnet 26. The stator cores 33 forming a part of the second holding member 3 are attached so as to face the magnets 21. At the large-diameter portion 3d located at the other end of the second holding member 3, a cylindrical case body 34 forming a part of the second holding member 3 with respect to the outer peripheral surface 23 of the first holding member 2. It is mounted so as to surround it with a gap 8. Further, a drive circuit board 37 having a circuit pattern for energizing the drive coil 31 is attached to the large diameter portion 3d on the surface opposite to the attachment surface of the case body 34.

The case body 34 is made of an aluminum material, and the case body 34 has a plurality of ventilation holes 34a penetrating in the axial direction and a plurality of communication holes 34b for communicating the ventilation holes 34a with the gap 8. (In this embodiment, two are installed at opposite positions on the inner peripheral surface). The inner peripheral surface 35 of the case body 34 constitutes the other of the bearing surfaces of the dynamic pressure bearing portion, and the surface is plated with nickel-phosphorus 25a in which polytetrafluoroethylene is dispersed by a method described later. Has been done. The case body 34 is fixed to the holder 4 with the screw 7.

The holder 4 has a cylindrical shape with a bottom, and a case body 34 is placed in the center thereof. Then, the motor is mounted on the holder 4 so as to be in contact with the ventilation hole 4a communicating with the space formed between the holder 4 and the case body 34 and the driving circuit board 37 attached to the second holding member 3. The mounting portion 4b, the circular fixing portion 4c on which the fixed portion 34c of the case body 34 is mounted, and the hole 4d into which the screw 7 is inserted to fix the case body 34 are provided.

FIG. 2 shows a surface treatment process diagram of the outer peripheral surface 23 of the first holding member 2. First, wash the first holding member 2 with water.
The surface is washed by the step of pickling-water washing. Next, the first holding member 2 is immersed in a plating material obtained by dispersing polytetrafluoroethylene in a nickel hypophosphite solution,
Electroless nickel-phosphorus plating in which polytetrafluoroethylene is dispersed (hereinafter referred to as electroless Ni-P-PT
Called FE plating). In this electroless Ni-P-PTFE plating, the support base 9 is provided with a non-penetrating hole 91, and the hole 91 is formed.
Then, the small diameter portion 24 of the first holding member 2 is put in, and the outer peripheral surface 23 of the large diameter portion 25 is plated. In addition, this electroless Ni-P-
PTFE plating uses polytetrafluoroethylene 20
Containing volume% or more, PH 5 to 5.5, and about 90 ℃
It is performed in the liquid. Then, the surface treatment is completed through a washing-drying process. The inner peripheral surface 35 of the case body 34 is also surface-treated in the same process, although the jig used is different.

The bearing surfaces 23 and 35 obtained by the above surface treatment process have much less unevenness on the plated surface as compared with the generally used barrel plating method. That is,
In the barrel plating method, the members placed in the basket contact each other during plating, so the plating surface is in a sea-island shape, although the size is very small. . The cross-sectional state is shown in FIG. The large-diameter portion 25 of the first holding member 2 is a layer (hereinafter, referred to as PT) obtained by applying electroless Ni-P-PTFE plating on a base material of an aluminum material.
It has a two-layer structure on which an FE layer) 25a is placed, and the outer peripheral surface 23 is constituted by this structure. PT
In some places of the FE layer 25a, there is an unplated portion 25b. Then, the average of the difference in the irregularities generated on the surface of the plated surface (hereinafter referred to as surface roughness) becomes large, and the so-called surface roughness becomes poor. On the other hand, in the construction method of the above-described embodiment, since the plating surfaces do not come into contact with each other, the plating surface has almost no plating-free portion as shown in FIG. 4 showing the cross-sectional state. Become. The thickness of the PTFE layer 25a is about 5 μm. If the thickness of the PTFE layer 25a exceeds 10 μm, the surface roughness deteriorates, causing wear. In addition, the gap 8
When the thickness exceeds about 10 μm, the generation of dynamic pressure deteriorates. Therefore, even if the PTFE layer 25a having a thickness exceeding 10 μm is formed, even if the complete PTFE layer remains, it does not function as a dynamic pressure bearing and is wasted. May be. Therefore, the PTFE layer 2
The wall thickness of 5a is preferably 10 μm or less. Also,
Considering the abrasion of the PTFE layer 25a, thickening the PTFE layer 25a is not preferable in terms of the dimensional accuracy of the gap 8. When the PTFE layer 25a has a value of less than 0.5 μm, it is preferable in terms of surface roughness, but the role of the PTFE layer 25a tends to end early due to abrasion, so 0.5 μm or more is preferable. Further, even if the plated surface is almost lost due to wear, the dimensional accuracy between the bearing surfaces changes only by a value of 10 μm or less, and has little influence on the dynamic pressure characteristics. If both sides 23 and 35 are plated to a thickness of 10 μm, a total of 20
The change in value is less than or equal to μm, which is within the allowable range, although it is a little problem in terms of dimensional accuracy between bearing surfaces. However, it is preferable that the total thickness of the plated surfaces of both surfaces 23 and 35 is 10 μm or less in total.

Next, driving of the polygon mirror motor configured as described above will be described.

When a drive signal is input to the drive circuit of the drive circuit board 37, the energization of the drive coil 31 is started. Then, due to the interaction between the coil 31 and the magnet 21, the second holding member 3 starts to rotate, and the polygon mirror 1 integrally fixed thereto also starts to rotate. Then, as a medium of dynamic pressure, air is taken into the gap 8 from the plurality of ventilation holes 34a provided in the case body 34 through the communication holes 34b as shown by the arrow in FIG. As shown by the arrow in FIG. 1, this air is taken in through the ventilation hole 4a of the holder 4, passes through the filter 38 attached to the case body 34, and passes through the plurality of ventilation holes 34a.
It came in a. The air taken into the gap 8 is supplied to a plurality of V-shaped grooves 29 for generating a dynamic pressure, and a dynamic pressure is generated between the air and the inner peripheral surface 35 of the case body 34. As a result, bearings are provided in the radial direction, and high-speed rotation of the polygon mirror 1 is achieved. This rotation is normally 1 to 30,000 rpm, but it is from several thousand rpm to 10 rpm depending on the number of faces of the polygon mirror 1 and the printing density.
It can handle up to 10,000 rpm. When the polygon mirror 1 is rotated at a high speed, the air under the polygon mirror 1 is also blown out due to viscosity, and that portion becomes negative pressure, and as shown by the arrow in FIG.
The air inside and the air inside the gap 8 are taken in. In this way, a continuous air flow is created, and high speed rotation due to dynamic pressure is maintained.

The bearing surfaces 23, 3 are affected by the attitude of the motor at the start of driving, external impact during rotation, and attitude changes.
Even if 5 comes into contact, electroless N
Since the i-P-PTFE plating 25a is applied, the effects of polytetrafluoroethylene having a low coefficient of friction hardly cause seizure of both surfaces 23 and 35, and the motor rotation is not stopped.
Even if the two surfaces 23 and 35 frequently come into contact with each other, partial heat generated by the contact melts the polytetrafluoroethylene to form a lubricating film, so that seizure does not occur. Also, if the PTFE layer 25
Even if “a” is worn, the polytetrafluoroethylene is continuously exposed, so that a low friction coefficient can be maintained.

The gap 8 communicates with the space in which the driving coil 31 and the various magnets 21, 26, 22, 32, 36 are placed, and further, the balance plate 11
It communicates with the outside through the hole 11b. This allows
An air flow path in the internal space is formed as shown by the arrow in FIG. The air introduced into the internal space has two roles of releasing the air from the dynamic pressure bearing portion and cooling the motor, and also has a role of holding the first holding member 2 at the regular position. That is, when an axial disturbance is applied to the first holding member 2 and the first holding member 2 attempts to be displaced upward or downward, the displacement is suppressed by the orifice effect of the hole 11b of the balance plate 11. To be done.

In this embodiment, the heat of the motor is taken away by the flow of air through the plurality of ventilation holes 34a, so that the cooling effect can be improved without adding any parts such as a fan. Unlike the coating, the PTFE layer 25a of this embodiment is processed by electroless plating, so that the thickness of the coating can be controlled, and the dimensional accuracy of the gap 8 and the bearing surfaces 23 and 3 can be controlled.
The surface roughness of No. 5 becomes easy to manage, and post-processing is unnecessary or reduced.

The above embodiment is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, electrophotographic nickel-boron plating in which polytetrafluoroethylene is dispersed instead of electroless Ni-P-PTFE plating also prevents seizure. In addition, after performing electroless Ni-P-PTFE plating, heat treatment is performed to obtain N serving as a base.
It is possible to further increase the hardness of the i-P film. Also, depending on the temperature of the heat treatment, only polytetrafluoroethylene melts, covering the Ni-P film that is the base,
The surface roughness is improved.

Further, in the above embodiment, both bearing surfaces 2
Electroless Ni-P-PTFE plating is applied to 3, 35, which is very excellent in terms of preventing seizure, but only one of the bearing surfaces 23, 35 has electroless Ni-.
Even if P-PTFE plating is applied and nickel-phosphorus electroless plating containing conventional silica fine particles or hard alumite treatment is applied to the other, there is an effect of improving seizure prevention as compared with the conventional configuration. In addition, electroless Ni-P-PTF
In order to improve the adhesion of the E-plating, in order to improve the adhesion of the plating, nickel-phosphorus plating is electrolessly plated as a base plating on an aluminum base material, and then this electroless Ni is used.
-P-PTFE plating may be applied. Furthermore, nickel-phosphorus electroless plating containing fine silica particles and hard alumite-treated ones are added to this electroless Ni-P-PT.
FE plating may be applied.

The first holding member 2 and the case body 34 may be made of stainless steel or SK material instead of the aluminum material, but the aluminum material is excellent in workability and drivability, and the cost can be reduced. Become. Further, a part of the second holding member 3 is the stator core 33 or the case body 34, and the second holding member 3
Are three separate members, but a part or all of them may be integrated to form two members or one member.

The fluid for generating the dynamic pressure may be liquid such as oil instead of gas such as air. In the embodiment, the first holding member holding the magnet is rotated, but the second holding member holding the coil may be rotated.

[0034]

As is apparent from the above description, in the motor of the first aspect of the present invention, the bearing surface is plated with nickel-phosphorus in which polytetrafluoroethylene having a low friction coefficient is dispersed. The bearing can have a high friction coefficient, a high wear resistance, and a low friction coefficient. Moreover, during operation, partial heat generation due to contact between the bearing surfaces melts polytetrafluoroethylene on the bearing surface to form a lubricating film, so that the bearing can have a very low friction coefficient. Further, even if the coating is worn, polytetrafluoroethylene is continuously exposed, so that a low friction coefficient can be maintained. For this reason,
It is possible to provide a motor that maintains stable high-speed rotation for a long period of time and does not cause seizure due to contact between bearing surfaces.

In addition, in the invention of claim 2, the rotation is locked because the bearing surface of the motor for driving the polygon mirror is plated with nickel-phosphorus in which polytetrafluoroethylene having a low friction coefficient is dispersed. Unnecessary heat generation caused by this does not adversely affect other precision parts in the apparatus, and extra repair work does not occur. For this reason,
An optical scanning device that can maintain stable quality for a long period of time can be provided.

Further, according to the third aspect of the invention, since the thickness of the nickel-phosphorus plating in which polytetrafluoroethylene is dispersed is 10 μm or less, the surface roughness of the plated surface does not deteriorate and wear occurs. Hateful. Further, even if the plated surface is almost lost due to wear, the dimensional accuracy between the bearing surfaces changes only by a value of 10 μm or less, and has little influence on the dynamic pressure characteristics. Therefore, it is possible to provide an optical scanning device that can maintain more stable quality.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is a surface treatment process diagram of a bearing surface used in an embodiment of the present invention.

FIG. 3 is a sectional view showing a surface condition of a bearing surface plated by a barrel plating method.

FIG. 4 is a cross-sectional view showing a surface condition of a bearing surface plated by the method shown in the embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts of a polygon mirror motor used in an optical scanning device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Polygon mirror 2 1st holding member 3 2nd holding member 21 Magnet 23 Bearing surface 25a Nickel-phosphorus plating (PTFE layer) 31 in which polytetrafluoroethylene was dispersed 31 Coil 35 Bearing surface

Claims (3)

[Claims] 1. A dynamic pressure bearing portion for bearing a first holding member for holding a magnet and a second holding member for holding a coil through a fluid, and by energizing the coil, In a motor in which a first holding member and a second holding member are relatively rotated, at least one bearing surface of the dynamic pressure bearing portion is plated with nickel-phosphorus in which polytetrafluoroethylene is dispersed. A motor characterized by. 2. A dynamic pressure bearing portion for bearing a polygon mirror for scanning a light beam from a light source, a first holding member for holding a magnet and a second holding member for holding a coil through a fluid. By energizing the coil,
An optical scanning device comprising a motor configured to relatively rotate the first holding member and the second holding member, wherein the polygon mirror is rotationally driven by the motor,
An optical scanning device characterized in that nickel-phosphorus plating in which polytetrafluoroethylene is dispersed is applied to at least one bearing surface of a dynamic pressure bearing portion of the motor. 3. The optical scanning device according to claim 2, wherein the film thickness of nickel-phosphorus plating in which polytetrafluoroethylene is dispersed is set to 10 μm or less.