JP2007240863A - Optical scanner, optical writing apparatus, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high quality images by reducing the color shifts due to temperature variation of an image forming apparatus, without causing cost increase or making the control complex. <P>SOLUTION: In the optical scanner, symbols 1 and 1' represent light sources, symbol 2 represents an optical deflector (polygon mirror), symbol 3 and 3' represent fθ lenses as scanning lenses, symbols 4 and 4' represent synchronization detection means, and symbols 6 and 6' represent faces to be scanned, respectively. The fθ lenses 3 and 3' constituting a scanning lens system are arranged to face each other with the optical deflector 2 between them on a main scanning plane and nearly line symmetrically with the rotation center 7 of the optical deflector 2 as a reference on the main scanning plane. The scanning lenses 3 and 3' have a non-power portion having no power in the main scanning direction, and synchronized luminous fluxes reaching the synchronization detection means 4 and 4' pass through the non-power portions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device for optically scanning a surface to be scanned, an optical writing device having the optical scanning device, a copying machine having the optical writing device, a printer, a facsimile, and a composite having at least two of these. The present invention relates to an image forming apparatus such as a printer or a plotter.

Optical scanning devices are widely known in connection with digital copying devices and laser printers. The scanning optical system is an optical system that is used in an optical scanning device and collects a light beam deflected by an optical deflector as a light spot on a surface to be scanned.
When an optical writing device or an image forming apparatus is configured using an optical scanning device, optical performance degradation due to tolerances of the optical elements and expansion / contraction of the optical elements due to temperature fluctuations is a problem. Along with the reduction in diameter, stabilization is desired.
High stability can be obtained by a method in which an adjustment mechanism is mounted on the optical element. However, since there is a demand for the layout and cost of the image forming apparatus, it is necessary to improve the stability with a structure as simple as possible.
Among the required stability, the main scanning position shift between the respective colors of the light spot formed by the scanning optical system corresponding to each color appears as visible degradation in the multicolor image.

The main scanning position of the light spot can be stabilized by adjusting the writing timing. A method based on so-called synchronization detection in which light receiving means is provided in a portion other than the writing range and the writing start timing is electrically adjusted is already widely known.
As a synchronization detection method, there are a method of receiving light at one end of a scanning line and a method of receiving light at both ends. In the latter method, since the reference of the writing start timing is provided at both ends of the scanning line, a high effect can be expected with respect to the reduction of the main scanning position deviation. However, in this case, since the scanning optical system requires two light receiving portions, if a multicolor image forming apparatus capable of color reproduction is configured, the number of light receiving portions and the corresponding electric control boards increases.
Therefore, there is a demand for a technique that can adjust the writing start timing with as few light receiving units as possible.
In addition, since a light beam used for synchronization detection (hereinafter referred to as “synchronous light beam”) serves as a reference for writing start timing, high stability with respect to the main scanning position is required as described above. The light receiving means is reached with a deterioration in optical performance due to tolerance and temperature fluctuation.

Patent Document 1 discloses an optical scanning device in which a notch is provided at the end of the scanning lens so that the synchronized light beam does not pass through the scanning lens and is not affected by the expansion and contraction of the scanning lens.
Similarly, Patent Document 2 discloses an optical scanning device in which a rib as a synchronous light beam passage portion is provided so that the synchronous light beam does not pass through the scanning lens and is not affected by expansion and contraction of the scanning lens. .

Japanese Patent Laid-Open No. 2002-98921 Japanese Patent No. 3293345

The topic related to the sync beam does not relate to the main scanning position of the light spot corresponding to the image of each color, but relates to the reduction and stabilization of the main scanning position deviation of the light spot in a certain single color.
In order to obtain a high-quality image, not only the main scanning position deviation of each color is reduced, but also the deviation between each color of the light spot main scanning position (hereinafter simply referred to as “color deviation”) is small, and temperature fluctuations, etc. Therefore, it is necessary to construct an optical scanning device and an optical writing device that are robust against color misregistration caused by.

  The present invention has a simple feature in the configuration of an optical scanning device, reduces color misregistration due to temperature fluctuations in the image forming apparatus, and realizes high image quality without increasing costs and complicating control. It is an object.

In order to achieve the above object, the present invention relates to the relationship between the “arrangement of the scanning lens system based on the optical deflector” and the condition that “the synchronous light beam is not affected by the expansion and contraction of the scanning lens system”. The aim is to reduce color misregistration due to temperature fluctuations by focusing on the above and optimizing it.
Specifically, in the first aspect of the present invention, the light source has 2n (n ≧ 1) light sources having m (m ≧ 1) light emitting sections, and m × n light beams of the light sources are light deflected. Synchronization for determining a writing timing on the scanned surface by scanning the scanned surface with light beams emitted from 2n light sources, entering substantially symmetrically with respect to the sub-scanning section including the rotation axis of the scanner In an optical scanning device having a detection means and having a scanning lens system for imaging m light beams on the surface to be scanned arranged to face the optical deflector, the synchronization detection means Synchronization detection is performed at one end of each scanning line, and the scanning lens system is arranged substantially symmetrically with respect to a line in the main scanning direction orthogonal to the rotation axis of the optical deflector.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, a spot position shift in the main scanning direction due to a temperature variation on a surface equivalent to the image plane of the synchronous light beam detected by the synchronous detection means. The amount is 5 μm / ° C. or less.

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the scanning lens system has a non-power portion having no power in the main scanning direction, and the synchronous light flux is the non-power. It is characterized by passing through the part.

  According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, the non-power portion has a power for correcting surface tilt of the optical deflector in the sub-scanning direction. To do.

  According to a fifth aspect of the present invention, in the optical scanning device according to the first or second aspect, the synchronizing light beam does not pass through the scanning lens system.

  According to a sixth aspect of the present invention, in the optical scanning device according to the first or second aspect, an opening is provided in the scanning lens system, and the synchronizing light beam passes through the opening.

  According to a seventh aspect of the present invention, in the optical scanning device according to the first, second, third, fifth, or sixth aspect, an inter-surface deviation of the surface tilt of the optical deflector is suppressed to 200 seconds or less. Features.

  According to an eighth aspect of the present invention, in the optical scanning device according to the first, second, third, fifth or sixth aspect, the synchronous optical system of the synchronous detection means for condensing the synchronous luminous flux on a light receiving unit is It has a function of correcting the influence of surface tilt of the optical deflector.

  According to a ninth aspect of the present invention, in the optical scanning device according to any one of the first to seventh aspects, the one side of the scanning lens system composed of one or more scanning lenses is arranged in the order from the optical deflector to L1. , L2,... Lj (j = 1, 2, 3,...), And the other side of the scanning lens system facing the optical deflector is L ′ in the order from the optical deflector. 1. When L′ 2,... L′ j (j = 1, 2, 3,...), Lenses having the same shape are used for Lj and L′ j in any j. It is characterized by.

  According to a ninth aspect of the present invention, the optical writing device includes a plurality of the optical scanning devices according to any one of the first to eighth aspects, and detects only the synchronous light flux of one optical scanning device, and the other The writing timing of the optical scanning device is electrically predicted from the detection signal of the synchronous light beam.

  According to a tenth aspect of the present invention, the optical writing device includes a plurality of the optical scanning devices according to any one of the first to eighth aspects, and the optical deflectors in these optical scanning devices have a common rotational axis. It is characterized by having.

  According to an eleventh aspect of the present invention, in the optical writing device according to the ninth aspect, the optical deflectors in the respective optical scanning devices have a common rotation axis.

  According to a twelfth aspect of the invention, in the optical writing device according to the tenth or eleventh aspect, the incident angles in the main scanning direction of the light beams of the respective stages incident on the same phase plane of the plural stages of optical deflectors are different. It is characterized by being.

  According to a thirteenth aspect of the present invention, in the optical writing device according to the twelfth aspect, each stage of the light beam incident on the same phase plane of the plurality of stages of optical deflectors is reflected at different reflection points in the main scanning direction. It is characterized by being deflected.

  According to a fourteenth aspect of the present invention, in the optical writing device according to the ninth aspect, all the light beams have an angle in the sub-scanning direction with respect to the normal line of the reflecting surface of the optical deflector. To do.

  In the invention described in claim 15, a plurality of image carriers are optically scanned by an optical writing device to form a latent image corresponding to each color, and the latent image is visualized by a developing means to form a color image. In the obtained image forming apparatus, the optical writing device is any one of claims 9 to 14.

  According to the present invention, color misalignment due to temperature fluctuation can be suppressed with a simple configuration and simple characteristics by combining a line-symmetric arrangement of a scanning lens system and a synchronous light beam that is not affected by temperature fluctuation.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
First, consider the combination of the arrangement of the scanning optical system and the synchronous beam passage portion of the scanning lens under the following assumptions.
As shown in Table 1, there are four combinations depending on the presence / absence of power of the synchronous light beam passage portion in the scanning lens and the difference between the line-symmetrical arrangement and the rotationally-symmetrical arrangement.

Assumption:
Equal temperature fluctuations (hereinafter referred to as “uniform temperature fluctuations”) occur on both sides of the optical deflector.
2 and 3, the image height h is taken upward, and the main scanning position deviation Δx due to temperature fluctuation is taken. When performing synchronous detection at one end, there is a method of detecting the scanning start end and end end, but since end end detection can be regarded as the start end of scanning by the next surface of the optical deflector, the scanning start will be described below. The discussion will focus on the edge detection method.
For simplicity, it is assumed that the temperature variation occurs uniformly in the optical scanning device. That is, the scanning lenses on both sides of the optical deflector are equally thermally expanded.

For the above four combinations, color misregistration that can occur when the scanning lens is deformed due to temperature fluctuation is evaluated.
A schematic optical layout of a line-symmetric arrangement (A and C in Table 1) is as shown in FIG. In FIG. 2, reference numerals 1 and 1 ′ denote a light source, 2 denotes an optical deflector (polygon mirror), 3 and 3 ′ denote an fθ lens as a scanning lens constituting a scanning lens system, and 4 and 4 ′ denote synchronous detection. Means 6 and 6 ′ respectively indicate scanned surfaces.
The fθ lenses 3 and 3 ′ are arranged so as to face the optical deflector 2 in the main scanning plane, and are arranged substantially line-symmetrically in the main scanning plane with respect to the rotation center 7 of the optical deflector 2. ing.

Since the scanning lenses 3 and 3 'are arranged substantially symmetrically, it is considered that a main scanning position shift in both scanning optical systems is generated by Δx1 on the image height h = (+) side and Δx2 on the h = (−) side. be able to.
There is a difference between A and C in Table 1 in that the light beam reaching the synchronization detection means 4, 4 'is affected or not affected by temperature fluctuations.
The schematic optical layout of the rotationally symmetric arrangement (B and D in Table 1) is as shown in FIG. Since the scanning lenses 3 and 3 ′ are arranged substantially rotationally symmetrically, it can be considered that a main scanning position shift in both scanning optical systems occurs Δx1 on the writing end side and Δx2 on the starting end side.
There is a difference between B and D in Table 1 in that the light beam reaching the synchronization detection means 4, 4 'is affected or not affected by temperature fluctuations.

The main scanning position shift can be described with respect to the image height h as shown in FIG. In FIG. 1, an arrow S indicates the scanning direction, and a broken line portion m on the scanning line indicates a non-light emitting region of the light source (the same applies to other drawings).
In the case of A, the synchronous light beams in the scanning optical systems on both sides cause a positional shift of Δx1 and Δx2 in the opposite directions. Therefore, the main scanning position shift generated in the scanning optical systems on both sides occurs in the form as shown in FIG. 4 in which the graph of FIG. 1 is shifted by Δx1 and Δx2 in the opposite directions, respectively.
Since the color misregistration is the difference between the two graphs, it is given by Δx1 + Δx2.
In the case of B, the synchronized light beams in the scanning optical systems on both sides cause a positional shift of Δx1 in the opposite directions. Therefore, the main scanning position shift generated in the scanning optical systems on both sides occurs in a form as shown in FIG. 5 in which the graph of FIG. 1 is shifted by Δx1 in the opposite direction. Since the color misregistration is the difference between the two graphs, it is given by Δx1 + Δx2.

Since A and B are affected by the deformation of the scanning lens, the synchronous light beam is always affected by “the deviation of the main scanning position generated at both ends of the scanning line even if it is arranged symmetrically with respect to the optical deflector 2. It can be seen that “sum (Δx1 + Δx2)” occurs as a color shift. At the same time, it is shown that color misregistration reduction cannot be expected only by arrangement.
In the case of C, the synchronized light beams in the scanning optical systems on both sides do not cause a position shift due to temperature fluctuation. For this reason, the main scanning position shifts that occur in the scanning optical systems on both sides are the same as those in the graph of FIG. 1, and are generated as shown in FIG. Color misregistration does not occur in this case.
Also in the case of D, the synchronous light beams in the scanning optical systems on both sides do not cause a position shift due to temperature fluctuation. Since the main scanning position shifts that occur in the scanning optical systems on both sides occur in opposite directions in terms of arrangement, they are generated as shown in FIG. 7 in which the graphs in FIG. 1 are superimposed in opposite directions.
| Δx1−Δx2 | remains as color misregistration.

Even in the case of D in which the synchronous light beam is not affected by temperature fluctuations, due to the rotational symmetry of the arrangement, a color shift always remains unless a main scanning position shift that is completely symmetric with respect to the image height h = 0 occurs. I understand.
From the above, it can be seen that C is the one that minimizes color misregistration in principle by the combination of the arrangement of the scanning optical system in the opposed scanning method and the non-powered portion of the synchronized light beam passage.
Actual temperature fluctuations do not occur uniformly throughout the optical scanning device. Let us assume that non-uniform temperature fluctuations occurred from the above. For example, it is assumed that temperature variation occurs in only one of the two scanning optical systems facing each other. In this case, it can be easily understood that the main scanning position deviation of any of the scanning optical systems in FIGS.
In either case, it can be seen that Δx1 or Δx2 remains even if the color misregistration is minimum. In other words, regarding the non-uniform temperature variation, it can be said that the arrangement of the scanning optical system and non-power alone are not effective.

In the present embodiment, based on the above consideration results, when uniform temperature fluctuations occur on both sides of the optical deflector, the color shift due to temperature fluctuations is reduced. “Combination with arrangement of optical system” is specified as type C in the combinations shown in Table 1.
Therefore, the optical scanning device in the present embodiment has the configuration shown in FIG. That is, this is an opposed scanning type optical scanning device having two scanning optical systems for condensing the light beam deflected by the optical deflector 2 as a light spot on the scanned surfaces 6 and 6 ′, and has the following characteristics. is doing.

First, it has 2n (n ≧ 1) light sources having m (m ≧ 1) light emitting sections, and m × n light beams of the light sources include sub-scans including the rotation axis of the optical deflector. A synchronization detecting means for scanning the surface to be scanned with light beams emitted from 2n light sources and determining writing timing on the surface to be scanned; The scanning lens system forms an image on the scanned surface disposed so as to face the optical deflector.
Second, synchronization detection is performed at one end of each scanning line, and the scanning lens system is arranged substantially symmetrically with respect to a line in the main scanning direction orthogonal to the rotation axis of the optical deflector, and is equivalent to the surface to be scanned. The spot position in the main scanning direction of the synchronous light beam on the flat surface is shifted by 5 μm / ° C. or less with respect to the temperature fluctuation.
Here, the “deviation accuracy of 5 μm / ° C. or less” is not uniquely obtained as a result of the C type shown in Table 1, but is an accuracy that can be obtained when the C type is used. is there.
Since the scanning optical system facing the deflector 2 as a center is substantially line symmetric with respect to the line 7 in the main scanning direction orthogonal to the rotation axis of the optical deflector 2, the expression “line symmetric arrangement” is used here. I will do it.

If the amount of spot position deviation is 5 μm / ° C. or less with respect to temperature fluctuation that actually occurs in the optical writing device, color deviation can be reduced.
As described above, the actual temperature fluctuation does not occur uniformly in the entire optical writing apparatus, but the deviation of the temperature distribution in the closed space of the optical writing apparatus is not so large. Can be fully enjoyed.

In the optical scanning device according to the present embodiment, the non-power portion of the scanning lenses 3 and 3 ′ and the synchronous optical system that condenses the synchronous light flux in the synchronous detection means 4 and 4 ′ to the light receiving unit is light deflected in the sub-scanning direction It is preferable to have the power to correct the surface tilt of the vessel 2.
Moreover, in the optical scanning device according to the present embodiment, it is preferable that the deviation between the surfaces of the reflecting surfaces of the optical deflector 2 is suppressed to 200 seconds or less. This is because the positional deviation in the sub-scanning direction when the synchronous light beam reaches the light receiving portion is reduced, and the determination of the writing timing is stabilized. That is, it is possible to reduce the deviation of the writing position with respect to each surface of the optical deflector.

In the present embodiment, since the two scanning optical systems are arranged substantially symmetrically with respect to the sub-scan section (in other words, the line 7 shown in FIG. 2) passing through the rotation axis of the optical deflector 2, the optical deflector. The light beam scanned corresponding to the rotation of 2 is scanned in a substantially line symmetrical manner on both sides of the optical deflector 2 although the scanning directions on the scanned surfaces 6 and 6 ′ arranged on both sides are reversed. Will be.
That is, the scanning lens system for providing desired imaging performance on the surface to be scanned is completely equivalent. That is, since the scanning lens having the same shape can be applied to both scanning optical systems, the production cost is reduced.
In FIG. 2, only the fθ lenses 3 and 3 ′ are shown as a representative of the scanning lens system, but the other scanning lenses constituting the scanning lens system are also arranged substantially line-symmetrically.
Here, the scanning lenses of the scanning lens system on one side are L1, L2,... Lj (j = 1, 2, 3,...) In order from the optical deflector 2, and the scanning lens on the other side facing each other. When the scanning lens of the system is L′ 1, L′ 2,... L′ j (j = 1, 2, 3,...) In order from the optical deflector 2, the shape of Lj at an arbitrary j Since the shape of L′ j is the same and the scanning lens having the same shape can be applied to both scanning optical systems, the production cost is reduced.
That is, the number of lenses and the number of steps of the optical scanning device can be reduced.

In the optical writing device using a plurality of the optical scanning devices described above, only the synchronous light beam of one optical scanning device is detected, and the writing timing of the other optical scanning device is electrically predicted from the synchronous light beam detection signal. (Second embodiment).
This is because the synchronous light flux in the present invention is strong against the main scanning position shift, and the reliability related to synchronous detection is increased. Therefore, even if the synchronization detection signal of another optical scanning device is electrically predicted, the writing timing of the all-optical scanning device can be satisfactorily determined.
This method (hereinafter referred to as “delay method”) makes it possible to reduce the number of light-receiving elements (synchronization detection means), thereby realizing a low-cost writing optical system.

A third embodiment will be described with reference to FIG.
In the present embodiment, the optical writing device 10 is configured by using a plurality of the optical scanning devices described above and overlapping them in the upper and lower stages.
In FIG. 8, reference numeral 5 denotes a folding mirror, and 6 denotes a photosensitive drum as a surface to be scanned.
In this case, since the rotation axis of the optical deflector 2 is common in the upper and lower stages, the number of parts of the optical deflector 2 that is relatively expensive in the optical writing device 10 can be reduced, and the cost is reduced.
Also, when performing synchronous detection using the above-described delay method, more accurate detection timing can be predicted because the phases of the upper and lower optical deflectors rotate on a common axis.

As shown in FIG. 9, the optical writing device 10 shown in FIG. 8 may have a configuration in which the incident angles of the upper and lower light beams to the optical deflector 2 are different (here, “giving a crossing angle”). (Fourth embodiment).
In FIG. 9, reference numeral 11 denotes a coupling lens, 12 denotes an aperture, and 13 denotes a cylindrical lens.
Thereby, it becomes possible to shorten the space | interval of an up-and-down stage to below the light emission point space | interval, and can implement | achieve size reduction.

Naturally, the upper and lower light beams given the crossing angle also differ in their optical characteristics and deflection angles by the optical deflector 2. In particular, vignetting may occur in one of the upper and lower stages in the synchronous light beam near the end of the deflection angle range.
Therefore, as shown in FIG. 10, the difference between the reflection points of the light beams in the upper and lower stages can be reduced (compensation for the difference in the upper and lower stages of the maximum writing width), and the optical characteristics of each scanning optical system can be reduced. Deviation can be suppressed (fifth embodiment).

The optical writing device described above has a form in which a light beam is incident and deflected in parallel to the normal line of the reflecting surface of the optical deflector 2. The present invention can also be applied to a case where a light beam is incident at an angle with respect to the normal line of the reflecting surface of the optical deflector 2 (sixth embodiment). Here, this method is called an oblique incidence method.
In the conventional horizontal scanning optical scanning device, as shown in FIG. 11A, in order to obtain the interval Z necessary for separating the light beams directed to the corresponding scanned surfaces, the polygons are arranged in two stages. A mirror 40 is used. Although it may be used in a single stage without being doubled, the thickness of the polygon mirror portion in the sub-scanning direction is increased, which is not suitable for speeding up and cost reduction.
On the other hand, in the oblique incidence optical system as in the present invention, it is not necessary to provide a plurality of light beams with a predetermined interval in the sub-scanning direction on the deflection reflection surface of the polygon mirror.
That is, as shown in FIG. 11B, a pair of light beams from a plurality of light sources having different angles in the sub-scanning direction with respect to the normal line of the reflecting surface of the polygon mirror 2 is the same polygon mirror 2 from the left and right in the figure. By making the light incident on different reflective surfaces, the polyhedron forming the deflection reflective surface of the polygon mirror 2 can be formed in a single stage, the thickness in the sub-scanning direction can be reduced, the inertia as a rotating body can be reduced, and the startup time can be shortened. .

As an advantage of the oblique incidence method, it is possible to write an image of four colors with a single stage optical deflector, so that the cost for configuring the optical writing apparatus can be reduced.
When the oblique incidence method is applied, scanning line bending and wavefront aberration degradation are unavoidable problems, so the surface shape of the scanning lens needs to correspond to the obliquely incident light beam, The effects of the present invention can be utilized as they are, and the cost can be reduced by combining them.

A seventh embodiment (multicolor image forming apparatus) will be described with reference to FIG.
In the laser color printer as the multicolor image forming apparatus (color image forming apparatus) according to the present embodiment, a photosensitive image carrier is provided along the extended surface of the intermediate transfer belt 21 stretched between the rollers 102a, 102b, and 102c. The drum-shaped photoconductors 20Y (yellow), 20M (magenta), 20C (cyan), and 20K (black) are arranged in parallel.
Around the photoreceptor 20Y, a primary transfer roller (not shown) provided inside a charging means (not shown), a common optical scanning device 105 as an exposure means, a developing means 106Y, and an intermediate transfer belt 21 in order counterclockwise. Further, a cleaning unit (not shown), a static elimination unit (not shown), and the like are arranged. The same applies to the photoconductors 20M, 20C, and 20K.

An electrostatic latent image of each color component image is formed on each photoconductor 20Y, 20M, 20C, 20K by each laser beam L1, L2, L3, L4 based on the image information of each color, and each developing means 106Y, 106M, 106C. , 106K.
The toner images of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 21. The superimposed image is collectively transferred by the secondary transfer roller 102d onto a transfer sheet (recording medium) fed from the sheet feeding cassette 111 at a predetermined timing. After the color image transfer, the intermediate transfer belt 21 is cleaned by a cleaning unit (not shown). The transfer paper is sent to the fixing device 114 where the color image is fixed by heat and pressure.
After the fixing, the transfer sheet is conveyed substantially vertically through the apparatus main body and is discharged to the sheet discharge tray 110 on the upper surface of the apparatus.
By using the optical scanning device 105 described in the first embodiment, extremely good image formation can be performed.

  Various types of “photosensitive image carrier” can be used. For example, a “silver salt film” can be used as the image carrier. In this case, a latent image is formed by writing by optical scanning, and this latent image can be visualized by processing by a normal silver salt photographic process. Such an image forming apparatus can be implemented as an “optical plate making apparatus” or an “optical drawing apparatus” for drawing a CT scan image or the like.

As the photosensitive image carrier, a “coloring medium (positive printing paper) that develops color by the thermal energy of the light spot during optical scanning” can be used. In this case, a visible image is directly displayed by optical scanning. Can be formed.
A “photoconductive photoreceptor” can also be used as the photosensitive image carrier. As the photoconductive photoconductor, a sheet-like material such as zinc oxide paper can be used, or a “selenium photoconductor or organic photo-semiconductor such as“ repetitively used in a drum shape or belt shape ”is used. Can do.
When a photoconductive photoconductor is used as an image carrier, an electrostatic latent image is formed by uniform charging of the photoconductor and optical scanning by an optical scanning device. The electrostatic latent image is visualized as a toner image by development. The toner image is directly fixed on the photoconductor when the photoconductor is in the form of a sheet such as zinc oxide paper, and transfer paper or an OHP sheet when the photoconductor can be used repeatedly. It is transferred and fixed on a sheet-like recording medium such as (plastic sheet for overhead projector).

The transfer of the toner image from the photoconductive photosensitive member to the sheet-like recording medium may be directly transferred from the photosensitive member to the sheet-like recording medium (direct transfer method), or may be temporarily transferred from the photosensitive member to an intermediate transfer belt or the like. After transfer to the intermediate transfer medium, transfer from the intermediate transfer medium to a sheet-like recording medium (intermediate transfer method) may be performed.
Such an image forming apparatus can be implemented as an optical printer, an optical plotter, a digital copying apparatus, or the like.

As described above, the present invention has an effect of easily reducing the occurrence of color misregistration by using a combination of the line-symmetric arrangement of the scanning optical system and the condition that the synchronous light beam is not affected by temperature fluctuation.
In order to realize an optical scanning device with little color misregistration and strong against temperature fluctuation, it is effective to make the scanning optical systems of the respective colors as close as possible to equivalent ones. That is, even if the main scanning position shift occurs in each color, if the same position shift occurs in all the colors, the “color shift” that is the deviation amount of the main scanning position shift of each color does not occur.

The main scanning position deviation caused by temperature fluctuation will be described in more detail. In the scanning optical system, the light beam deflected by the optical deflector scans the surface to be scanned at a constant speed by the refraction / condensing action of the scanning lens. In the case of ideal constant velocity, a proportional relationship is established between the rotation angle θ of the optical deflector and the light spot position on the surface to be scanned.
In other words, the ideal light spot position (hereinafter referred to as “ideal image height”) is determined by the angle of the reflecting surface of the optical deflector, and the deviation from the ideal image height caused by some factor is the main scanning here. It is defined as misalignment. From this, it can be easily imagined that the main scanning position shift increases as the light beam passing through the scanning lens moves away from the optical axis.
In addition, since the rotational axis of the optical deflector is different from the reflecting surface, asymmetric scanning is performed with respect to the optical axis of the scanning lens. When the scanning position deviation is plotted by the image height h, an asymmetric shape is obtained as shown in FIG.

(About the non-power of the synchronous beam passage part)
In order to prevent only the synchronized light flux from being affected by temperature fluctuations, the following method can be considered. If an appropriate method is selected according to the scanning optical system, the effect of the present invention can be sufficiently expected.
(1) Design a synchronous optical system that does not pass through any scanning lens.
(2) An air layer (aperture) is provided in the synchronous light beam passage portion in the scanning lens to avoid refraction by the scanning lens.
(3) The synchronous light beam passage portion in the scanning lens is formed in a parallel plate shape in the main scanning direction so that the scanning lens is not affected even if deformation occurs.
The method (1) is the most effective for stabilizing the synchronous beam. However, as the optical scanning device becomes smaller and the scanning lens becomes thinner, the beam shaping optical system in front of the optical deflector, the synchronized light beam passage part, and the scanning lens become a layout that concentrates in the vicinity of the optical deflector. May be a foothold when you plan for a simple layout.
The methods (2) and (3) are methods that can avoid the problem (1). However, since secondary processing is required at the time of forming the scanning lens, the scanning lens becomes expensive.
In the present invention, whichever method (1) to (3) is used, it means that “the synchronized light beam passes through the non-power part”.

(About low power)
In addition, when the optical scanning device of the present invention is applied to the multi-beam method, the line image imaging optical system to the scanning optical system are “shared by a plurality of light beams” for each coupled light beam, thereby Since the image forming optical system and below can be configured in the same manner as the single beam type optical scanning device, it is possible to realize a multi-beam type optical scanning device that is extremely stable against mechanical fluctuations.
When the multi-beam method is used, the same writing speed can be realized with a smaller number of rotations of the optical deflector than with a single beam. Therefore, the optical deflector can be driven with low power, and an energy saving optical scanning device can be realized.
As the light source of the multi-beam type optical scanning device, an LD array type or a “beam combining type” can be used. In the case of using an LD array type light source, it is possible to effectively reduce the thermal and electrical influence between the light emitting sources and perform good multi-beam optical scanning by setting the interval between the light emitting sources to 10 μm or more. It becomes possible.
In the above-described oblique incidence method, an optical writing device can be configured with a single stage optical deflector. That is, by applying the oblique incidence method, the height of the deflecting means (polygon mirror) (height in the sub-scanning direction) is low and the contact area with the air is smaller than that of the two-stage, so that it is influenced by the windage loss. Power consumption is suppressed, and as a result, the optical writing device can be driven with low power.

It is a figure explaining main scanning position shift. It is a schematic diagram of the optical scanning device of the line symmetrical arrangement which concerns on the 1st Embodiment of this invention. It is a schematic diagram of the optical scanning device of rotation symmetrical arrangement. It is a figure explaining the main scanning position shift in line symmetrical arrangement. It is a figure explaining the main scanning position shift in a rotation symmetrical arrangement. It is a figure explaining a main scanning position shift in case of a line symmetry arrangement and a synchronous beam passage part is non-power. It is a figure explaining a main scanning position shift in the case of rotation symmetry arrangement and a synchronous light beam passage part being non-power. FIG. 9 is a schematic cross-sectional view of an optical writing device according to a third embodiment in which optical scanning devices are arranged in two stages. It is a schematic diagram at the time of changing the incident angle in the main scanning direction of the light beam of the upper and lower stages based on 4th Embodiment. It is a schematic diagram at the time of changing the reflection point of the light beam of the upper and lower stages based on 5th Embodiment. It is a figure explaining the incident method of a light beam, (a) is a figure which shows the conventional parallel incident method, (b) is a figure which shows an oblique incidence method. 1 is a schematic configuration diagram of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'Light source 2 Optical deflector 2a Rotating shaft 3, 3' Scan lens 4, 4 'Synchronous detection means 6, 6' Surface to be scanned

Claims (16)

having 2n (n ≧ 1) light sources with m (m ≧ 1) light emitting sections;
The m × n luminous fluxes of the light source enter substantially symmetrically with respect to the sub-scanning section including the rotation axis of the optical deflector,
Scan the surface to be scanned with light beams emitted from 2n light sources,
Synchronization detection means for determining the writing timing to the scanned surface;
In the optical scanning device having a scanning lens system for forming images of m light beams on the surface to be scanned disposed so as to face the optical deflector,
Synchronization detection by the synchronization detection means is performed at one end of each scanning line,
The optical scanning device according to claim 1, wherein the scanning lens system is disposed substantially symmetrically with respect to a line in a main scanning direction orthogonal to a rotation axis of the optical deflector. The optical scanning device according to claim 1,
An optical scanning apparatus characterized in that the amount of spot position deviation in the main scanning direction due to temperature fluctuations on the surface equivalent to the image plane of the synchronous light beam detected by the synchronization detection means is 5 μm / ° C. or less. The optical scanning device according to claim 1 or 2,
An optical scanning device characterized in that the scanning lens system has a non-power portion having no power in the main scanning direction, and the synchronous light flux passes through the non-power portion. The optical scanning device according to claim 3.
The optical scanning device according to claim 1, wherein the non-power portion has power for correcting surface tilt of the optical deflector in the sub-scanning direction. The optical scanning device according to claim 1 or 2,
An optical scanning device characterized in that the synchronizing light beam does not pass through the scanning lens system. The optical scanning device according to claim 1 or 2,
An optical scanning device, wherein an opening is provided in the scanning lens system, and the synchronous light beam passes through the opening. In the optical scanning device according to claim 1, 2, 3, 5 or 6,
An optical scanning device characterized in that the surface deflection of the optical deflector is suppressed to 200 seconds or less. In the optical scanning device according to claim 1, 2, 3, 5 or 6,
An optical scanning device characterized in that a synchronization optical system of the synchronization detection means for condensing the synchronization light beam on a light receiving unit has a function of correcting the influence of surface tilt of the optical deflector. The optical scanning device according to any one of claims 1 to 7,
The one side of the scanning lens system composed of one or more scanning lenses is expressed as L1, L2,... Lj (j = 1, 2, 3,...) In order from the optical deflector.
L′ 1, L′ 2,... L′ j (j = 1, 2, 3,...) In order from the optical deflector in the scanning lens system on the other side facing the optical deflector. Is written,
An optical scanning device characterized in that lenses having the same shape are used for Lj and L′ j in arbitrary j.   A plurality of optical scanning devices according to any one of claims 1 to 8, wherein only the synchronous light beam of one optical scanning device is detected, and the write timing of the other optical scanning devices is determined from the detection signal of the synchronous light beam. An optical writing apparatus characterized by electrically predicting.   9. An optical writing device comprising a plurality of optical scanning devices according to claim 1, wherein the optical deflectors in these optical scanning devices have a common rotation axis. The optical writing device according to claim 9.
The optical writing device according to claim 1, wherein the optical deflectors in the respective optical scanning devices have a common rotation axis. The optical writing device according to claim 10 or 11,
An optical writing apparatus characterized in that the incident angles in the main scanning direction of the light beams of the respective stages incident on the same phase plane of the plural stages of optical deflectors are different. The optical writing device according to claim 12,
An optical writing apparatus, wherein the light beams of each stage incident on the same phase plane of the plurality of stages of optical deflectors are deflected at different reflection points in the main scanning direction. The optical writing device according to claim 9.
An optical writing apparatus characterized in that all light beams have an angle in the sub-scanning direction with respect to the normal line of the reflecting surface of the optical deflector. In an image forming apparatus for forming a latent image corresponding to each color by performing optical scanning with an optical writing device on a plurality of image carriers, and visualizing the latent image with a developing unit to obtain a color image.
15. The image forming apparatus according to claim 9, wherein the optical writing device is one according to any one of claims 9 to 14.

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