JP2005242024A - Optical scanner and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately position a beam spot by reducing temperature rises of scanning lenses used in the optical scanner of a high-speed color printer and temperature rises and temperature deviations of scanning lenses for each optical scanner of a color machine and to realize the noise reduction and power-saving of the color machine. <P>SOLUTION: In the optical scanner, two light deflector 62a, 62b are attached to bearings provided on the same board of a motor housing 214 and each of the deflectors deflects two laser beams. Beams are made incident on respective reflecting surfaces while having a small angle in the vertical direction with respect to a main scanning flat surface. Moreover, heat emitted from motors is shielded by wind shielding plates and it do not affect scanning lenses 63. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning apparatus having a multi-beam writing optical system, which is used in an optical scanning apparatus using a polygon scanner, an image forming apparatus, a digital laboratory, and the like.

2. Description of the Related Art A tandem color image forming apparatus is known that uses two optical deflectors and deflects and scans a laser beam facing each optical deflector (see, for example, Patent Document 1).
According to this apparatus, the scanning lens for two of the four colors is disposed at a position sandwiched between two optical deflectors, and the scanning lens is disposed at a position facing the optical deflector. Therefore, the scanning direction is different for every two colors.
As a result, the temperature of the two-color scanning lens sandwiched between the light deflectors of the heating element is higher than that of the other scanning lenses. Especially when a resin scanning lens is used, the refractive index changes. Therefore, since the magnification of each color (at least every 2 colors) is different, color deviation tends to appear in the main scanning direction.
Also, since the optical housing in which the optical deflector and the scanning lens are installed is separated for each optical deflector, all the two components are required, and the size, weight, and cost of the optical scanning device are required. Will be doubled.

In order to realize high-speed printing and high image quality of a color machine, it is necessary to rotate an optical deflector at a high speed of 25000 rpm or more and with high accuracy in a tandem type image forming apparatus.
In particular, in a color image forming apparatus provided with an optical scanning device as a writing unit for a plurality of colors (yellow, magenta, cyan, black) as in a tandem type color machine, an optical deflector, a fixing device, etc. in each writing unit Due to temperature changes due to the heat generated by the lens, optical characteristics change due to changes in the shape and refractive index of the lens in the scanning device for each color, resulting in deviation of the laser beam spot position on the surface to be scanned and bending of the scanning line. There was a bug that occurred. As a result, the relative positions of the scanning lines for the respective colors are different, and color misregistration occurs, resulting in a problem that the quality of the color image is lowered.
Specifically, the temperature rise of the fθ lens as the scanning imaging lens closest to the optical deflector which is a heating element becomes a problem. When the polygon mirror unit and the scanning imaging lens are in the same space, the temperature of the fθ lens rises due to radiation by the air current of the polygon mirror. Actually, the temperature of the fθ lens is not raised uniformly, but the temperature distribution is particularly large in the main scanning direction, which is the longitudinal direction, due to the distance from the heat source (optical deflector), the difference in thermal expansion coefficient of each material, and the influence of airflow. I will have. If there is a temperature distribution in the main scanning direction, particularly the shape accuracy and refractive index of the fθ lens change, the spot position of the laser beam fluctuates, and the image quality deteriorates. This problem is particularly noticeable in the case of a resin lens having a large coefficient of thermal expansion and low thermal conductivity.

On the other hand, in the case of a high-speed printing machine, the photoconductors corresponding to a plurality of colors (four in the case of a tandem type) need to have a large outer diameter in order to ensure a long life, and the laser beam emitted from the optical scanning device Therefore, there is a demand for an optical scanning device that can cope with a wider interval for each color.
FIG. 8 is a diagram showing an example of a conventional color image forming apparatus.
In the figure, reference numeral 1 denotes a paper feeding device, 2 denotes a transfer belt, 3 denotes a photosensitive drum, 5 denotes an optical scanning device, 6 denotes a developing device, 10 denotes an image forming device, and 14 denotes a fixing device.
As shown in the figure, conventionally, one of the four photoconductors 3Y to 3K is associated with one optical deflector 5Y to 5K (hereinafter referred to as a four deflector system) so as to be able to cope with an arbitrary interval. However, since four optical deflectors that rotate at high speed are used, there is a problem that noise and power consumption increase.
There is also a method of deflecting all four colors with one optical deflector (one deflector method), but considering the optical path length, the degree of freedom corresponding to the interval between the photosensitive members is low, and the interval becomes long. Thus, it becomes difficult to cope with a high-speed printing machine. Furthermore, since the two colors are scanned opposite each other with respect to the rotation center of the optical deflector, the scanning directions for the two colors are different from each other. Therefore, the temperature distribution in the main scanning direction of the scanning lens induces local fluctuations in the refractive index, and an error is likely to occur in the synchronization detection timing, resulting in color misregistration.

JP-A-9-281976

  The present invention reduces the temperature rise of the scanning lens used in the optical scanning device of the high-speed color printer, the temperature rise of the scanning lens for each optical scanning device of the color machine, and the temperature deviation, and the positional deviation of the beam spot is improved. At the same time, it realizes noise reduction and power saving.

  In the first aspect of the present invention, the laser light source includes three or more laser light sources, a plurality of scanned surfaces corresponding to the plurality of laser light sources, and two optical deflectors. In the optical scanning device that distributes the beam by the two optical deflectors, deflects and scans in the main scanning plane, and collects the light on the surface to be scanned, the two optical deflectors are substantially at the center of the optical scanning device. Each of the optical deflectors deflects the beam on the side opposite to the side on which the other optical deflectors exist.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the drive circuit boards of the two optical deflectors are integrated.
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the rotation directions of the two optical deflectors are different.
According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, the two optical deflectors are configured using a bearing whose rotational direction is rotatable in both directions. .

According to a fifth aspect of the present invention, in the optical scanning device according to the third aspect, the two optical deflectors have a drive unit composed of a brushless motor, and at least one of the optical deflectors receives a rotational position detection signal. The rotation position detection signal is inverted and given to the other optical deflector.
According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, the two optical deflectors are integrated into a common motor housing. .

According to a seventh aspect of the present invention, in the optical scanning device according to any one of the first to sixth aspects, at least one of the beams incident on at least one of the two optical deflectors is The main scanning plane has an angle in the sub-scanning direction.
According to an eighth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the two optical deflectors have the other light with respect to the reflection surface of the one optical deflector. The rotational phase of the other optical deflector is controlled from the drive circuit of the one optical deflector so that the reflecting surface of the deflector has a desired phase relationship.

According to a ninth aspect of the present invention, in the optical scanning device according to the eighth aspect, the two optical deflectors have the same number of reflective surfaces and the same number of rotor poles, and the reflective surfaces of the two optical deflectors. And the magnetic pole positions are substantially in phase.
According to a tenth aspect of the present invention, in the optical scanning device according to the eighth aspect, the two optical deflectors use a rotating body that is magnetized after the reflecting member and the rotor magnet are fixed to each other. Features.

  The invention according to an eleventh aspect is characterized by a color image forming apparatus using the optical scanning device according to the first to tenth aspects.

  In the present invention, two optical deflectors are arranged adjacent to each other at substantially the center, and the optical deflector deflects the laser beam to the side opposite to the adjacent side. And power saving can be achieved.

FIG. 1 is a diagram showing an optical scanning device of the present invention.
FIG. 2 is a diagram showing an image forming apparatus to which the optical scanning device of FIG. 1 is applied.
FIG. 3 is a cross-sectional view for explaining the optical polarizer.
In FIG. 1, reference numeral 11 denotes a wind shield, 50 denotes an optical housing, 62 denotes an optical deflector, 63 denotes a scanning lens, 162 denotes a driving circuit, and 214 denotes a motor housing.
In FIG. 2, reference numeral 87 denotes a cover. Other reference numerals are the same as those in FIGS.
In FIG. 3, reference numeral 22 denotes a rotating body, 23 a bearing holder, 24 a coil winding, 25 a bearing member, 28 a polygon mirror, 30 a shaft, 211 a rotor magnet, 214 a motor housing, 215 a cover, 514 Each substrate is shown.
In FIG. 2, an optical scanning device 5 includes four photoconductors 3Y, 3M, 3C, and 3K (hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals, Y: yellow, M: magenta in the image forming apparatus. , C: cyan, and K: black) are arranged above the image forming units arranged in parallel.
Referring to FIG. 1, an optical scanning device 5 includes four light source units corresponding to four colors (not shown), two optical deflectors 62A and 62B, and a plurality of optical elements. Each of the laser beams from the two light source units is deflected and scanned.

The two optical deflectors 62A and 62B are arranged adjacent to the substantially central portion of the optical scanning device 5, and the two optical deflectors are installed in a single motor housing. Each is deflected to the adjacent side and the opposite side. By configuring the two optical deflectors as one optical deflection unit, the optical housing 50 can be attached and detached with a fixing screw. The laser beam incident on the reflecting surface of each optical deflector has a desired angle α in the sub-scanning direction with respect to the main scanning plane. Specifically, it is set to be 5 ° or less. Even if the laser beams for two colors do not have an angle, the following problems can be reduced if at least one laser beam has an angle. However, it is desirable that the laser beams A and C or the laser beams B and D of the two optical deflectors have the same incident angle because the optical elements before entering the optical deflector can be used in common.
Main scanning originally means relative movement of the laser beam on the surface to be scanned, and sub-scanning means relative movement of the surface to be scanned and the laser beam in a direction perpendicular to the main scanning direction. Yes. However, since all of the optical deflectors and other components are arranged strictly corresponding to the main scanning direction and the sub scanning direction, they actually coincide with the main scanning direction and the sub scanning direction on the surface to be scanned. Even if not, the corresponding directions will be referred to as the main scanning direction or the sub-scanning direction for convenience. Therefore, the main scanning plane means a virtual plane formed by moving the laser beam for main scanning.

When the incident angle is 5 ° or more, the scanning line is greatly bent on the surface to be scanned, and the diameter of the laser beam is increased, resulting in image deterioration. On the other hand, when the two laser beams are perpendicular and parallel to the reflecting surface (α = 0), the polygon mirror needs to have a large height (thickness) in the sub-scanning direction, and the windage loss during high-speed rotation increases. There is a defect.
FIG. 4 is a diagram showing the difference in power consumption depending on the surface thickness of the polygon mirror.
As can be seen from the figure, when the surface thickness is doubled, the power consumption starts to increase around the rotational speed exceeding 20000 rpm, and a significant difference appears at the frequently used 25000 rpm or higher.

  Two sets of scanning imaging optical systems (imaging lenses, optical elements of mirrors for turning back the optical path) for guiding each laser beam onto the scanned surfaces of the four photosensitive drums 3Y, 3M, 3C, and 3K are also provided. These components are housed in one optical housing 50. Four light source units (not shown) are composed of a semiconductor laser that is a light source and a collimating lens that collimates an outgoing laser beam of the semiconductor laser, and are arranged on the side wall of the optical housing 50. Further, the optical housing 50 is provided with a cover 87, and an opening through which the laser beam passes is provided at the lower part (photosensitive member side in FIG. 2) of the optical housing 50. The opening is dust-proof as a laser transmitting member. Glass is attached and almost sealed.

  The optical scanning device 5 converts the image data into a signal for driving the light source, and accordingly, the laser beam emitted from each light source unit passes through a cylindrical lens for correcting surface tilt (not shown) and reaches the optical deflectors 62A and 62B. Deflection scanning is performed by the polygon mirror portions 28A and 28B that are rotationally driven by the deflectors 62A and 62B. The laser beam obtained by deflecting and scanning the laser beam corresponding to two colors in one direction on one side by the polygon mirror reflecting surface 28a of the optical deflector 62A passes through the scanning lens 63, is folded by the folding mirror, and is reflected by the laser transmitting member. An electrostatic latent image is written by irradiating on the scanned surfaces of the photosensitive drums 3Y, 3M, 3C, and 3K for each color through the dustproof glass. Note that at least the scanning lens 63 is fixed to the optical housing 50 by bonding, and it is particularly preferable to bond only the central portion in the main scanning direction on the contact surface side of the scanning lens. The reason why it is good to bond at the center is that when expanding and deforming due to the thermal expansion of the lens, it spreads toward both ends with reference to the center, so that it expands freely with respect to temperature and does not deform in the main scanning direction. Further, it is possible to prevent the magnification error in the main scanning direction from being greatly deteriorated locally. Adhesive fixing that can be achieved at a low manufacturing cost by reducing the number of parts and simplifying the fixing process is most preferable.

In FIG. 3, the two optical deflectors 62 </ b> A and 62 </ b> B are disposed in one motor housing 214 to which a fixing member and a bearing of the rotation driving unit are fixed. The rotation directions of the respective optical deflectors are different so that the scanning direction is the same, such that if one is CW (clockwise), the other is CCW (counterclockwise). The air shield plates 11a and 11b and the upper cover 215 shield the high-temperature airflow accompanying the rotation of the polygon mirrors 28A and 28B, and the scanning lens 63 is shielded from heat and airflow. That is, the provision of the wind shielding plates 11a and 11b prevents the airflow generated by the rotation of the polygon mirror from directly hitting the scanning lens.
As the windshield plate, a glass plate capable of transmitting laser, having a smaller thermal expansion coefficient than that of resin and having a high thermal conductivity is preferable. Table 1 shows characteristic values of examples of suitable materials.

By setting the characteristic values as described above, the wind shield itself suppresses the temperature distribution in the main scanning direction (effect of thermal conductivity), and the wind shield that blows the high-temperature air flow of the polygon mirror expands in temperature. Therefore, it is possible to effectively prevent optical characteristics (a shape such as a curvature and a laser beam diameter due to a change in refractive index) from being deteriorated. Therefore, a resin that can easily be aspherical can be applied to the scanning lens that is not affected by the high-temperature airflow.
If the scanning lens is made of glass other than resin, it is difficult to produce an aspherical shape, which not only satisfies the desired optical characteristics, but also has the demerit that the manufacturing cost is high even if the optical characteristics are sacrificed. is there. Similarly, when the optical housing is made of a metal such as aluminum, the weight is greatly increased and the contact surface of the scanning lens becomes high temperature in a short time due to high thermal conductivity. It has a local temperature distribution. In addition, there is a demerit that the manufacturing cost becomes high.

The optical housing 50 is preferably made of a metal having a high thermal conductivity, and in particular, a material having a thermal expansion coefficient close to that of the scanning imaging lens 63 is preferable. Specifically, zinc, magnesium, aluminum or an alloy thereof is preferable, but zinc is most preferable.
The table below shows typical values.

By adopting the above materials and configuration, even if the temperature in the optical housing 50 rises due to heat generated by the optical deflector or the fixing unit, the scanning imaging lens 63 does not have a locally high portion, and the temperature distribution (especially the main component) The scanning direction is flattened and the deviation of the position of the scanning beam spot is suppressed. Since the above effect occurs for each color, color misregistration during image formation is small, and high image quality can be achieved.
The scanning imaging lens 63 is made of plastic and can easily achieve an aspherical shape by molding. However, the refractive index and the change in shape due to the influence of temperature rise are more remarkable than those of glass, and scanning imaging corresponding to all the colors. The upper temperature limit of the lens is 45 ° C. or lower, and the temperature distribution (main scanning direction) is 2 ° C. or lower. As a result, in addition to the beam spot position deviation, the beam diameter and scanning line bending are suppressed, and high image quality can be achieved. In addition to the temperature distribution within one color, the temperature distribution is also less effective in reducing color misregistration because the relative difference for each color is small.

  The drive circuit 162 controls the rotational speed of the two optical deflectors 62 and the rotational phase of the polygon mirror 28. Conventionally, the drive circuit provided for each optical deflector is integrated, and the substrate, power supply system, and noise filter function are integrated, and the rotational phase of the polygon mirror 28 is detected by the rotor magnet. The phase is adjusted with respect to the rotation reference clock of the optical deflector, and control is performed so as to obtain a desired phase relationship (separately described later). By integrating the drive circuit, it is possible to improve noise resistance and connect the wiring pattern and the motor harness at the shortest distance, thereby reducing electromagnetic noise. Furthermore, cost reduction is achieved by downsizing the board and reducing the number of parts.

Due to the above configuration, the wind noise of the polygon mirror 28 is compared with the case where four light deflectors for each color are used (particularly at a high speed of 25000 rpm or more) as shown in the conventional example of FIG. Noise reduction (silence), power consumption halved, and the effect on image banding due to vibration source reduction.
Furthermore, in a plastic scanning lens and optical housing that can be reduced in cost and weight, it is possible to reduce the temperature distribution of the scanning lens due to heat generated by the optical deflector accompanying high-speed rotation of 25000 rpm or more, and color misregistration occurs. Can be suppressed.

The image forming apparatus shown in FIG. 2 is a tandem type color image forming apparatus in which a plurality of photoconductors 3Y, 3M, 3C, and 3K are arranged in parallel. An optical scanning device 5, a developing device 6, a photosensitive member 3, an intermediate transfer belt 2, a fixing device 14, and a paper feed cassette 1 are laid out in order from the top of the apparatus.
On the intermediate transfer belt 2, photosensitive members 3Y, 3M, 3C, and 3K corresponding to the respective colors are arranged at equal intervals in the parallel order. The photoreceptors 3Y, 3M, 3C, and 3K are formed to have the same diameter, and members are sequentially disposed around the photoreceptors according to an electrophotographic process. The photoreceptor 3Y will be described as an example. A charging charger (not shown), a laser beam L1 based on an image signal emitted from the optical scanning device 5, a developing device 6Y, a transfer charger (not shown), and a cleaning device (not shown). Etc.) are arranged in order. The same applies to the other photoconductors 3M, 3C, 3K. That is, in the present embodiment, the photoconductors 3Y, 3M, 3C, 3K are to be scanned surfaces set for each color, and the laser beams L1, L2, L3,. L4 is provided to correspond to each.

The photoconductor 3Y uniformly charged by the charging charger rotates in the direction of arrow A, thereby sub-scanning the laser beam L1, and an electrostatic latent image is formed on the photoconductor 3Y. Further, a developing device 6Y that supplies toner to the photoconductor 3Y is disposed downstream of the irradiation position of the laser beam L1 by the optical scanning device 5 in the rotation direction of the photoconductor 3, and yellow toner is supplied. The toner supplied from the developing device 6Y adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, M, Y, and K monochromatic toner images are formed on the photoreceptors 3M, 3C, and 3K, respectively. The intermediate transfer belt 2 is disposed further downstream in the rotational direction than the position where the developing unit 6Y of each photoconductor 3Y is disposed. The intermediate transfer belt 2 is wound around a plurality of rollers 2a, 2b, and 2c, and is moved and conveyed in the direction of arrow B by driving a motor (not shown). By this conveyance, the intermediate transfer belt 2 is sequentially moved to the contact points of the photoreceptors 3Y, 3M, 3C, and 3K. The intermediate transfer belt 2 sequentially superimposes and transfers the single color images developed by the photoreceptors 3Y, 3M, 3C, and 3K, thereby forming a color image on the intermediate transfer belt 2. Thereafter, the transfer paper is conveyed from the paper feed tray 1 in the direction of arrow C, and the color image is transferred. The transfer paper on which the color image is formed is discharged to the fixing device 14 as a color image after fixing processing.
The above configuration can be applied to a digital laboratory. For example, although not shown in the figure, if each photosensitive member and its peripheral mechanism are removed, a conveyance belt is disposed so as to pass through the convergence positions of the light beams L1 to L4, and color photographic paper is passed therethrough. Image exposure can be performed directly on photographic paper. In this case, after four-color exposure, the photographic paper is developed by a dedicated developing device.

In FIG. 3, since the optical deflectors 62A and 62B have basically the same configuration except for the rotation direction, they will be described in detail in 62A. In the optical deflector 62A, a plurality of laser beams (A, B) corresponding to two colors are incident on the reflecting surface 28a on the polyhedron forming the polygon mirror portion, rotate at a high speed of 25000 rpm or more, and deflect and scan at a high speed.
In the bearing, the upper outer periphery of the shaft 30 made of martensitic stainless steel is fixed to the inner diameter portion 28m of the polygon mirror 28 made of an aluminum alloy having a polyhedron forming the polygon mirror portion. Martensitic stainless steel (for example, SUS420J2) is suitable because it can be quenched and has high surface hardness, and the shaft 30 has good wear resistance. A rotor magnet 211 is fixed below the polygon mirror 28 and constitutes an outer rotor type brushless motor together with the stator core 24a.
The reflection surface of the polyhedron forming the polygon mirror portion has an axial length (thickness) sufficient to deflect a predetermined laser beam, and specifically, it is set to 1 to 3 mm. The reason for setting within this range is that when the thickness is 1 mm or less, the plate is thin, so that the rigidity during mirror processing is low and the flatness deteriorates. If it is 3 mm or more, there is a problem that inertia is large as a rotating body, and start-up time becomes long.

Circumferential grooves 28i and 28k provided in the polygon mirror 28 reduce the weight of the rotating body 22 (an assembly of the polygon mirror 28, the shaft 30, and the rotor magnet 211) (inertia reduction, suppression of bearing wear deterioration due to mass reduction, and start-up time). In addition, it is used for the adhesive application part for balance correction. It is necessary to correct and maintain the balance of the rotating body 22 with high accuracy in order to reduce vibration at high speed rotation of 25000 rpm or more. As an unbalance correction part, a circle of the polygon mirror 28 is placed on the upper side in the axial direction across the center of gravity. The balance is corrected by applying an adhesive to each of the circumferential recesses 28i and the circumferential recesses 28k on the lower side. The unbalance amount is required to be 10 mg · mm or less. For example, the correction amount is kept at 1 mg or less at a location having a radius of 10 mm. In addition, when performing such minor corrections as described above, it is difficult to manage with an adhesive or the like, or when the amount is small, the adhesive strength is weak, and peeling and scattering are a problem during high-speed rotation of 40000 rpm or more. For this, it is preferable to carry out a method (a cutting with a drill or laser processing) for deleting a part of the parts of the rotating body 22.
Although it is conceivable to provide the circumferential groove 28k on the opposite surface (lower 28g side), when applying the adhesive to the groove opened downward, the rotating body 22 is removed from the bearing 25 and the rotating body 22 is removed. It is necessary to apply it after turning it upside down and fixing it, and it is not only necessary to go through a complicated process, but also because a desorption process with the bearing 5 is involved, oil splatters etc. each time, causing deterioration of the bearing It is not suitable because of the problem of triggering.

This structure has an advantage that there is no need to use a fixing member such as a leaf spring for the polygon mirror as in the prior art, so that there is no distortion on the polygon mirror reflecting surface due to the fixing pressure.
The rotor magnet 211 is a bonded magnet using resin as a binder. The rotor magnet 211 is press-fitted and fixed to the lower part of the polygon mirror 28 member. By press-fitting and fixing, the rotor magnet 211 does not move slightly even under high temperature and high speed rotation, and stable high speed rotation can be ensured. (As in the case of bonding or the like, it is possible to suppress a change in the balance of the rotating body and a vibration of the polygon scanner due to the high-speed rotation due to the difference in thermal expansion and the fine movement of the adhesive layer at a high temperature). Since the outer diameter portion is held, the structure is difficult to break due to centrifugal force during high-speed rotation.
The rotor magnet 211 may be an aluminum-manganese magnet, and is composed of an aluminum alloy polygon mirror 28 and a shaft made of an aluminum alloy whose surface is hardened or lubricated, so that the rotating body is entirely made of aluminum alloy between each component. The difference in thermal expansion between these components is made substantially equal, and fine movement between components due to temperature rise can be further prevented, and the high-accuracy balance of the rotating body can be further maintained. Aluminum-manganese magnets have high mechanical strength and do not break even with centrifugal force during high-speed rotation, high-purity aluminum has high reflectivity of polygon mirror reflecting surface 28a, and aluminum alloy shafts can be made lighter than stainless steel It has the effect of becoming.

The radial bearing constitutes a hydrodynamic bearing by an outer diameter of the shaft 30 and a bearing member 25 that is press-fitted or adhesively fixed in the bearing holder 23 (the bearing member 25 is composed of a copper-based oil-impregnated sintered member. Of the thermal expansion coefficient 1.6 × 10 ⁻⁵ / ° C.). In order to efficiently circulate the oil contained in the sintered member even at a high speed of 25000 rpm, a dynamic pressure generating means (not shown) is provided. The dynamic pressure generating means is provided on the outer peripheral surface of the shaft 30 or the inner peripheral surface of the bearing member 25, and is preferably provided on the inner periphery of the sintered member having good workability. The hydrodynamic bearing gap is set to 10 μm or less in diameter.
A suitable example of a radial bearing is a true dynamic bearing having a rotational direction corresponding to both the CW and CCW directions and having a long life even at a high speed of 25000 rpm or more. A circular bearing, a bearing with a groove (or ground trace) parallel to the axial direction, and a bearing having a surface shape of a sine wave or a harmonic component in the circumferential direction are suitable. A sintered oil-impregnated bearing or a ball bearing is also suitable. Moreover, although the case of oil was shown as an example of the fluid constituting the hydrodynamic bearing, it is used when the temperature of the bearing is 75 ° C. or higher which causes deterioration of the oil, or the operation time is 3000 hours or more cumulatively. In the case where high durability is required, an air dynamic pressure bearing is suitable.

The bearing holder 23 is made of brass (thermal expansion coefficient 1.8 × 10 ⁻⁵ / ° C.), aluminum alloy (thermal expansion coefficient 2.4 × 10 ⁻⁵ / ° C.) as a material having a thermal expansion coefficient similar to that of the bearing member 5. ) Is preferred. In the case of a material such as a polyimide resin (thermal expansion coefficient 4.5 × 10 ⁻⁵ / ° C.) having a large difference in thermal expansion coefficient, loosening occurs at a high temperature, which is not suitable. The bearing holder 23 has a tapered shape such that the outer diameter portion 23d and the outer diameter portion 23d are shrink-fitted into the lower portion and the outer diameter increases toward the lower portion of the shrink-fitted fit. A motor core 24a is caulked and fixed to the tapered portion. By adopting the taper shape, even if the shaft 30 sways in the bearing member 25 due to the unbalance of the rotating body 22, the swaying excitation force prevents stress from concentrating on the shrink-fit portion, This has the effect of reducing unbalanced vibration. The lower surface 23c of the bearing holder 23 is used for axial positioning of shrink fitting, and is fixed in contact with the same surface as the motor housing 214 during shrink fitting.
Further, since the bearing member 25 is impregnated with lubricating oil, it is necessary to set the temperature to 100 ° C. or less during shrink fitting (when the temperature exceeds 100 ° C., the lubricating oil deteriorates due to a chemical reaction). In the shrink fitting process, the motor housing 214 is held at a high temperature of 150 ° C. or higher, the hole (opposite surface to 23 d) is expanded in diameter than the outer diameter portion 23 d of the bearing holder 23, and the expanded diameter portion is in a room temperature state. The bearing holder 23 is inserted and then slowly cooled to be firmly fixed. At that time, a heat dissipating fin for a jig that can be attached and detached at the bottom of the bearing holder 23 is provided at the bottom of the bearing holder 23 so that the bearing member 25 does not reach 100 ° C. or higher, and the bearing member 25 is heated to a high temperature of 100 ° C. or higher. It is preventing. The shrink fit may be a step of fixing only the bearing holder 23 and, after completion of the shrink fit, gradually cooling to room temperature (25 ° C.) and then fixing the bearing member.

Although the bearing member 25 has been described above as being press-fitted or adhesively fixed to the bearing holder 23, it is appropriately selected depending on the following situation. The case where the press-fitting and fixing is suitable is a case where the bearing member 5 is used in an environment in which the bearing member 5 is in a high temperature state up to around 100 ° C. which is the upper limit temperature of use of the lubricating oil. On the other hand, in the case of adhesive fixing, in the vicinity of 100 ° C., the adhesive strength of the adhesive decreases, and the gap between the outer diameter of the bearing member 25 and the inner diameter of the bearing holder 23 may change (expand / contract), possibly causing peeling of the adhesive. Therefore, the adhesive fixing is suitable only when the temperature is 100 ° C. or lower.
Note that the method of fitting a part of the bearing holder to a conventional thin plate substrate and pressurizing and deforming it instead of shrink-fitting the bearing holder is a thin plate, which causes rattling of the fitting portion. Fixing rigidity becomes low, such as easy.
Since the bearing holder and the housing that hold the bearing member impregnated with the lubricating oil are fixed by shrinkage fitting as in this configuration, the bearing fixing portion is highly rigid, and the unbalance vibration of the rotating body can be reduced.

The axial bearing is a pivot bearing in which the convex curved surface 30a formed on the lower end surface of the shaft 30 and the thrust receiving member 27 are brought into contact with the opposing surface. The thrust receiving member 27 is preferably martensitic stainless steel, ceramic, or a metal member whose surface is hardened such as DLC (diamond-like carbon) treatment because generation of wear powder is suppressed as much as possible.
The rotating body (polygon mirror 28, shaft 30, and rotor magnet 211) is fitted and inserted into the bearing 25 from above in FIG.

The motor system is a system called an outer rotor type in which a magnetic gap is provided in the radial direction and the rotor magnet 211 is laid out on the outer diameter portion of the stator core 24a. The rotation drive refers to a signal output from the Hall element mounted on the substrate 514 by the magnetic field of the rotor magnet 211 as a position signal, and rotates by switching excitation of the winding coil by the driving IC. The rotor magnet 211 is magnetized in the radial direction and rotates by generating rotational torque with the outer periphery of the stator core 24a.
The rotor magnet 211 has a magnetic path open in the outer diameter and height direction other than the inner diameter, and a Hall element for switching the excitation of the motor is disposed in the open magnetic path. The reason why the magnet is open is that when a magnetic body (iron plate, stainless steel) is placed, the rotor magnet fixing part moves slightly due to the thermal expansion difference from the aluminum alloy of the polygon mirror material, and the balance of the rotating body changes at high temperatures. This is because of this. Since the magnetic circuit of the rotor magnet 211 is open, it is preferable that a magnetic shield member (not shown) is disposed around the rotor and is made of a nonconductive material such as resin. This is because if a conductive material such as a steel plate is present in the vicinity, the leakage flux of the rotor magnet accompanying high-speed rotation generates eddy currents and the motor loss increases.

FIG. 5 is a diagram showing an excitation sequence of two optical deflectors. FIG. 4A shows a sequence of one optical deflector in the CW direction, and FIG. 4B shows a sequence of the other optical deflector in the CCW direction.
The CW direction sequence of FIG.
The output of the Hall element that detects the rotational position of the rotor magnet is shown for each phase of UVW. For example, if the positive side is an N pole, the negative side is an S pole. In accordance with the Hall element output, the timing of the excitation current to each phase coil is set. For example, the positive side of the exciting current is a current flowing into the coil, and the negative side is a current flowing out of the coil. It rotates in the CW direction at the Hall element output timing shown in FIG. On the other hand, it is set to rotate in the CCW direction at the Hall element output timing shown in FIG. For setting, either the + side of the Hall element output is a comparator (comparison circuit) or the-side is compared, or the + power source of the Hall element of one optical deflector is inverted to the-power source, and the-power source is inverted to the + power source. As a result, the Hall element output is inverted, and CW and CCW can be set appropriately.

FIG. 6 is a diagram showing the number of faces of the polygon mirror and the number of magnetic poles of the rotor magnet. FIG. 4A shows the case where there are six mirror surfaces, and FIG. 6B shows the case where there are eight mirror surfaces.
The number of magnetic poles (number of N poles and S poles) of the rotor magnets of the two optical deflectors is the same as the number of faces of the polygon mirror. In addition, the phase relationship between the N-pole and S-pole and the polygon mirror is arbitrary, but the two optical deflectors have the same phase relationship. In order to obtain the same phase relationship, magnetization is performed after the rotor magnet is fixed to the polygon mirror member. During magnetization, phase alignment is performed by a phase positioning mechanism (not shown) so that the phase relationship between the polygon mirror surface and the magnetized yoke is always the same. As a result, even different rotating bodies can be manufactured such that the phase relationship between the polygon mirror surface and the rotor magnet is always constant.

With the above configuration, the phase relationship between the polygon mirrors of the two optical deflectors can be set to a desired relationship. What is desired is that the scanning timing of the four color laser beams in the two optical deflectors is 2 so that the scanning can be started at a predetermined timing at which the toner is transferred onto the intermediate transfer belt moving between the photosensitive members. This is the phase relationship of the polygon mirrors of the two optical deflectors. In order to match the phase of one optical deflector to the other optical deflector, the number of magnetic poles (number of N poles and S poles) of the rotor magnet and the number of faces of the polygon mirror are the same. The output and the phase of the polygon mirror are the same between the two optical deflectors. Therefore, this can be achieved by controlling the phase relationship between the Hall element output from one optical deflector and the other Hall element output to a desired relationship. The ideal timing is set for each image forming apparatus in advance, and is controlled by the drive circuit 162 so as to maintain a phase relationship that achieves the relationship.
If the phase relationship is not desired, the reflection surface of the polygon mirror when the laser beam is emitted for each color is in an arbitrary phase, so that the maximum is one reflection surface of the polygon mirror (one line in the sub-scanning direction). (In the first place, the driving of the photosensitive member and the driving of the polygon mirror are asynchronous).

Around the rotating body, the motor housing 214 and the wind shielding plates 11a and 11b (2 sheets) and the upper part are used to prevent heat transfer to the other optical elements and wind noise caused by heat generated by the wind damage of the polygon mirror. The cover 215 is substantially sealed. (The motor housing 214 has an opening window 214a for entering and exiting the laser beams A and B into the polygon mirror, and the wind shield plate 11a is fixed to the opening window 214a. The same applies to the laser beams C and D. .)
The glass plate 11a is preferably a glass plate that can transmit a laser beam and has little thermal expansion. The flatness of the glass plate is set to be 100 mR or more at the transmitted wavefront in an environment of a temperature of 100 ° C. or more reached during actual deflection operation.
In addition, the windshield plate 11a, particularly when the laser beam diameter (1 / e ² ) is 50 μm or less, is set with reference to a desired value in both the main scanning direction and the sub-scanning direction in order to prevent the laser beam diameter from deteriorating. It is necessary to arrange with high accuracy of ± 0.01 ° or less. In order to achieve a high-accuracy arrangement, the geometrical positions of the contact surface 214b with the laser beam entrance / exit window 214a and the contact surface 214c with which the optical deflector 62 is attached to the optical housing 50 are increased. A laser beam entrance / exit window 214a is integrally formed in the motor housing 214 so that the accuracy can be maintained.

In order to reduce noise due to wind noise, the upper cover member 215 may be a plurality of sheet metals (iron plate, aluminum plate, etc.). Even if the light deflector generates heat due to high-speed rotation, the high-temperature airflow is sealed by the wind shield plate 11, so that a portion where the temperature is locally increased due to the high-temperature airflow is eliminated, and the scanning lens 63 is moved in the main scanning direction. The temperature distribution is suppressed.
On the other hand, the turbulent flow caused by the wind-cutting of the polygon mirrors of the two optical deflectors affects the rotation unevenness, and the flare light of the laser beam becomes a problem due to the influence of the two openings for attaching the two wind shielding plates. In this case, it is preferable to provide a partition member 214d that does not transmit the laser beam between the two optical deflectors. The partition member 214d may be integrated with a metal (iron, aluminum) or a motor housing to be unified.

  In addition, the bearing holders of the two optical deflectors are fixed to the motor housing 214 and integrated as a motor housing. With such a configuration, the two reference surfaces 3d and 3c on which the bearing holder is fixed are provided. However, since it can be processed simultaneously (same chucking state) with respect to the mounting surface of the motor housing, it can be manufactured with the same degree of parallelism and perpendicularity. As a result, the axis tilt of the two optical deflectors is the same, including the phase, the scanning line is bent due to the axis tilt, the laser beam diameter is increased in all four colors, and variations in image quality become obvious. It has the effect of becoming difficult.

FIG. 7 is a view for explaining mirror surface processing of a polygon mirror surface.
In the drawing, reference numeral 421 denotes a cutting bit, 422 denotes a rotation center of the bit, 423 denotes a holding substrate, and 424 denotes a holding member.
As shown in the figure, the reflecting surface 28a of the polygon mirror is mirror-finished after at least the shaft 30 and the polygon mirror 28 are fixed by shrinkage fitting. Except for the polygon mirror reflecting surface portion of the polygon mirror 28, the diameter is smaller than the inscribed circle diameter of the polygon polygon. The reason is to avoid the tip of the cutting tool (cutting tool) 421 from colliding with the outer diameter part of the polygon mirror during mirror finishing.
The polygon mirror 28 first creates a polygonal column-shaped blank corresponding to the number of reflecting surfaces by a die (die casting, forging). Thereafter, the inner peripheral surface 28m into which the shaft 30 of the polygon mirror 28 is inserted by shrink fitting is processed with high accuracy (cylindricity of 3 μm or less). Thereafter, the spaced apart portions 28j and the periphery of the plurality of polyhedrons are cut. Thereafter, the shaft 30 is shrink-fitted, and the polygon mirror reflecting surface portion is mirror-finished. This process eliminates the need for high accuracy of the flatness and squareness of the polygon mirror mounting surface, which was conventionally required to maintain the surface tilt characteristics.

An embodiment in which the polygon mirror surface is processed based on the outer diameter of the shaft 30 will be described in detail.
The part to be used as a bearing is firmly held on the entire length and circumference to increase the holding force against the working force during processing. For holding the outer diameter, an oil compression diameter type holding member 424 having an inner diameter slightly wider than the outer diameter of the bearing is used. As for the holding member, the inner peripheral portion 424a is reduced in diameter by the hydraulic pressure rising by a hydraulic mechanism (not shown), and the shaft 30 is firmly fixed. Since this holding method is less likely to cause a bias in holding force in the axial direction, the occurrence of shaft runout is suppressed and it is suitable as a reference for high-precision machining.

It is a figure which shows the optical scanning device of this invention. It is a figure which shows the image forming apparatus to which the optical scanning device of FIG. 1 is applied. It is sectional drawing for demonstrating an optical polarizer. It is a figure which shows the difference in the power consumption by the surface thickness of a polygon mirror. It is a figure which shows the excitation sequence of two optical deflectors. It is a figure shown about the number of surfaces of a polygon mirror, and the number of magnetic poles of a rotor magnet. It is a figure explaining mirror surface processing of a polygon mirror surface. It is a figure which shows the example of the conventional color image forming apparatus.

Explanation of symbols

23 Bearing holder 24 Coil winding 25 Bearing member 28 Polygon mirror 30 Shaft 62 Optical deflector 214 Motor housing

Claims (11)

  A plurality of three or more laser light sources, a plurality of scanned surfaces corresponding to the plurality of laser light sources, and two optical deflectors, and beams from the plurality of laser light sources are transmitted by the two optical deflectors. In the optical scanning device that shares and deflects and scans on the main scanning surface and collects the light on the surface to be scanned, the two optical deflectors are disposed substantially adjacent to the central portion of the optical scanning device, The optical deflector deflects the beam on the side opposite to the side on which the other optical deflectors exist.   2. The optical scanning device according to claim 1, wherein drive circuit boards of the two optical deflectors are integrated.   3. The optical scanning device according to claim 1, wherein the rotation directions of the two optical deflectors are different.   4. The optical scanning device according to claim 3, wherein the two optical deflectors are configured using a bearing whose rotational direction is rotatable in both directions.   4. The optical scanning device according to claim 3, wherein the two optical deflectors have a drive unit composed of a brushless motor, at least one of the optical deflectors outputs a rotation position detection signal, and the other optical deflector receives the rotational position detection signal. An optical scanning device characterized in that the rotational position detection signal is inverted and given.   6. The optical scanning device according to claim 1, wherein the two optical deflectors are integrated in a common motor housing.   7. The optical scanning device according to claim 1, wherein at least one of the beams incident on at least one of the two optical deflectors is a sub-scanning beam with respect to the main scanning plane. An optical scanning device having an angle in a scanning direction.   8. The optical scanning device according to claim 1, wherein the two optical deflectors have a desired phase relative to a reflective surface of one optical deflector. An optical scanning device characterized in that the rotational phase of the other optical deflector is controlled from the drive circuit of the one optical deflector so as to satisfy the relationship.   9. The optical scanning device according to claim 8, wherein the two optical deflectors have the same number of reflection surfaces and the same number of rotor poles, and the reflection surfaces and magnetic pole positions of the two optical deflectors have substantially the same phase. An optical scanning device configured as described above.   9. The optical scanning device according to claim 8, wherein the two optical deflectors use a rotating body that is magnetized after fixing the reflecting member and the rotor magnet.   A color image forming apparatus using the optical scanning device according to claim 1.

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