JP4539401B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device that scans and exposes a scanning target such as a photosensitive member, and more particularly to a technique for suppressing a decrease in image quality in scanning exposure.

  FIG. 11 shows an example of a general optical scanning device. This optical scanning device is provided in an image forming apparatus such as a copying machine or a laser printer, and irradiates a light beam from a light source 91 through an optical system member 93 such as a polygon mirror 92, and is a photosensitive member as a scanned object. The exposure is performed by forming a beam spot by irradiation light on the surface of the body drum 1. As a means to increase the speed and resolution of such an optical scanning device, the rotation speed of the polygon mirror and the increase of the video clock can be mentioned, but since both the speeding up and the resolution increase are approaching the limit, I cannot expect a big effect. Therefore, efforts are being made to increase the number of light beams emitted from the light source at a time and to expose a large number of scanning lines in one scanning exposure.

A technique for scanning and exposing a scanning object with a plurality of light beams is conventionally known. Such scanning methods include an interlaced scanning method (for example, see Patent Documents 1 and 2) and an adjacent scanning method (for example, Patent Document 3). Reference). FIG. 12 shows an example of a beam spot formed by the interlace scanning method, and FIG. 13 shows an example of a beam spot formed by the adjacent scanning method. When scanning exposure is performed by the adjacent scanning method, a surface-emitting light source such as a surface-emitting laser diode array having a light-emitting portion arranged at a lattice point on a parallelogram virtual lattice is used. For example, a surface-emitting light source that forms 32 scanning lines is realized as shown in FIG. 14 using an 8 × 4 light-emitting unit. If the resolution at this time is 2400 dpi, the pitch of the adjacent scanning lines is approximately 10.6 μm. Hereinafter, the surface-emitting light source having this arrangement is referred to as “(conventional) surface-emitting light source 9”.
JP-A-5-176128 Japanese Patent No. 3227226 JP 2004-109680 A

  A surface-emitting light source easily realizes an increase in speed and resolution of an optical scanning device, but has a problem that an image defect is likely to occur. This is because if a large number of scanning lines are formed at once by a surface-emitting light source, a rotation (skew) error of the surface-emitting light source has a significant effect on the position where the beam spot is formed.

  FIG. 15 is a diagram comparing the position of the beam spot when the surface-emitting light source 9 of FIG. 14 is skewed by 2 ° with the normal position (reference position). FIG. 16 is a diagram showing scanning lines formed with the surface-emitting light source 9 skewed by 2 °. As shown in FIG. 15, the position of the beam spot is offset in the main scanning direction even at the reference position. This offset can be eliminated by adjusting the timing of scanning exposure. However, since the positional shift due to the skew generated in the surface light source 9 cannot be eliminated by adjusting the exposure timing, the scanning line is shifted as shown in FIG. This shift causes a small gap for each of four spots (in the case of an 8 × 4 light source) in one scan (hereinafter referred to as “first gap”), and further, the first scan and the second scan. A large gap (hereinafter referred to as a “second gap”) is generated between the scanning lines by the scanning. That is, the image formed at this time has a periodic shift depending on the lattice shape and the total number of the light emitting sources.

  Since the above-described image forming apparatus expresses an image with halftone dots which are minute periodic patterns, such a periodic shift causes interference with the image, and an unnecessary interference pattern such as moire is generated in the image. This interference pattern becomes image noise, which significantly degrades the image quality. For example, in the case of the example shown in FIG. 16, the first gap has a period of about 600 dpi, resulting in noise having high coherence with an image formed by a general image forming apparatus. In addition, when the second gap is reached, it is 19.1 μm, which is noise that can be visually detected without interference with the image.

In this way, even with an error of about 2 °, noise that cannot be ignored occurs in the formed image. As a result, even an error that is acceptable as a manufacturing tolerance of the image forming apparatus has become a source of noise that degrades the image quality.
The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for suppressing a decrease in image quality in an optical scanning device using a surface-emitting light source.

To achieve the above object, the present invention provides a virtual parallelogram lattice at a position of the end point and the start point of the vector represented by an integer multiple of a linear combination of two basis vectors using the start to the common a plurality of light emitting points that will be arranged in a lattice point forming the distance between the light emitting point which emits light to form a scan line adjacent in the scanning body, both in the size of the two basis vectors A surface-emitting light source having a plurality of light emitting points arranged so as not to be equal to each other, and light emitted from each of the plurality of light emitting points is converted into a light beam and led to a scanned object. An optical system member that forms a plurality of scanning lines in the sub-scanning direction on the scanning object by moving the irradiation points formed by irradiating each in the main scanning direction. Providing an optical scanning device.
Alternatively, the present invention is arranged in a lattice point forming a virtual parallelogram lattice at a position of the end point and the start point of the vector represented by an integer multiple of a linear combination of two basis vectors using the start to the common a plurality of light emitting points that will be, the how two light emitting points are arranged in two lattice points having any size and equal distance basis vectors but any not adjacent to one another in the scanning target scan line A surface-emitting light source having a plurality of light emitting points arranged so as to form a light source, and light emitted from each of the plurality of light emitting points is converted into a light beam and guided to a scanned object, and each light beam is irradiated An optical system member that forms a plurality of scanning lines in the sub-scanning direction on the scanned body by moving the irradiation points formed in the main scanning direction. Providing that the optical scanning device.
According to such an optical scanning device, it is possible to reduce the coherence of noise caused by the positional deviation of the light source, and thus it is possible to suppress the occurrence of interference patterns.

In these optical scanning devices, the light source may include parallel lines in which the number of light emitting points arranged on the parallel lines forming the lattice is different from other parallel lines.
Such an optical scanning device can also suppress the occurrence of interference patterns.

Further, in these optical scanning devices, a second light emitting point different from the first light emitting point in the second scanning is obtained with respect to a part of the scanning line formed by the first light emitting point in the first scanning. It is good also as a structure which irradiates a light beam.
In this case, a gap between the scanning line formed by the second light emitting point and the scanning line adjacent to the scanning line is adjacent to the scanning line formed by the first light emitting point and the scanning line. It is more preferable that the gap is different from the gap between the scanning lines.
In this way, it is possible to suppress the generation of interference patterns even when performing multiple exposure.

  The present invention can also be specified as an electrophotographic image forming apparatus equipped with the above-described optical scanning device.

  As described above, according to the present invention, it is possible to suppress the occurrence of an interference pattern in an optical scanning device using a surface-emitting light source, and as a result, it is possible to suppress a decrease in image quality.

[1: First embodiment]
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. In addition to the optical scanning device 10, the image forming apparatus 100 includes a photosensitive drum 1, a charger 2, a developing device 3, a transfer roll 4, a paper transport belt 5, and a fixing device 6. The optical scanning device 10 receives an image signal from an image output device such as a computer (not shown), and irradiates the surface of the photosensitive drum 1 uniformly charged by the charger 2 by irradiating the light beam corresponding to the image data. I do. An electrostatic latent image is formed in the portion irradiated with the light beam. The developing device 3 supplies toner to the electrostatic latent image to make it visible, and forms a toner image. The toner image formed on the photosensitive drum 1 is moved in the direction of arrow A in the figure, and is transferred onto a recording sheet conveyed by the sheet conveying belt 5 at a position facing the transfer roll 4. The recording paper is transported in the direction B in the figure by the paper transport belt 5, and the toner image is fixed by being heated and pressed by the fixing device 6. In this way, the image forming apparatus 100 forms an image on the recording paper.

  FIG. 2 is a diagram showing in detail the configuration of the optical scanning device 10 described above. The optical scanning device 10 includes an LD array 11, a collimating lens 12, a half mirror 13, a lens 14, a light detection sensor 15, an aperture 16, a cylindrical lens 17, a mirror 18, a polygon mirror 19, and fθ. Lenses 20 and 21 and cylindrical mirrors 22 and 23 are provided.

  The LD array 11 is a surface-emitting light source having a plurality of light emitting points by a laser diode. The LD array 11 of this embodiment is a multi-beam type array light source that irradiates 32 light beams to form 32 scanning lines. The collimating lens 12 collimates the beam light from the LD array 11. The half mirror 13 transmits a part of the beam light and guides it to the aperture 16, reflects a part thereof and guides it to the light detection sensor 15. The light detection sensor 15 receives the beam light imaged by the lens 14 and outputs a signal for controlling the light amount of the beam light. The aperture 16 is provided with an opening corresponding to the shape of the light beam, and shapes the light beam passing therethrough. The shaped beam light is applied to the polygon mirror 19 through the cylindrical lens 17 and the mirror 18.

  The polygon mirror 19 is a polygon mirror that is rotated in the direction of arrow C in the drawing by a control unit (not shown). The polygon mirror 19 reflects the beam light while rotating, thereby moving the beam light in a linear manner in the main scanning direction (the axial direction of the photosensitive drum 1). This beam light is imaged on the surface of the photosensitive drum 1 through the fθ lenses 20 and 21 and the cylindrical mirrors 22 and 23.

With the above configuration, the optical scanning device 10 irradiates the photosensitive drum 1 with the light beam modulated according to the input image signal. By receiving the beam light while the photosensitive drum 1 rotates, an electrostatic latent image corresponding to an image signal is formed on the surface of the photosensitive drum 1. The collimating lens 12, the half mirror 13, the aperture 16, the cylindrical lens 17, the mirror 18, the polygon mirror 19, the fθ lenses 20 and 21, and the cylindrical mirrors 22 and 23 receive the light from the LD array 11 on the photosensitive drum 1. It has a function that leads to Therefore, here, these are collectively referred to as “optical members”.

The schematic configurations of the image forming apparatus 100 and the optical scanning apparatus 10 are as described above. Next, the structure of the LD array 11 of the optical scanning device 10 of this embodiment will be described.
FIG. 3 is a diagram showing the arrangement of the light emitting points of the LD array 11 of the present embodiment. In the LD array 11 of the present embodiment, the light emitting points are arranged at points indicated by p _{1 to} p ₃₂ among points on the parallelogram lattice. Incidentally, subscript attached to the point _{p n} "n" corresponds to the order of the scanning lines, the pitch of the scanning lines and 2400dpi equivalent, or about 10.6 [mu] m.

The position of the light-emitting point p _n in the present embodiment is determined as follows. First, an inclination is defined so that tan θ = ½ in a right triangle having a long side connecting adjacent light emitting points, and four light emitting points are arranged along this inclination. At this time, the laser tilt and the optical magnification are determined so that adjacent light emitting points do not form adjacent scanning lines and one scanning line is formed between them, and this position is determined as the light emitting point p ₁ , Let p ₃ , p ₅ and p ₇ . The position formed by these light emitting points is hereinafter referred to as “first column”.

Next, the light emitting points p ₂ , p ₄ , p ₆ , and p ₈ are defined so as to fill the position where the scanning line is not formed in the previous stage, and this position is defined as the “second column”. At this time, the parallelogram is formed by the four points of the light emitting points p ₁ , p ₃ , p ₆ , and p ₈ , and thereafter, the light emitting points are sequentially formed at points where a parallelogram congruent with the parallelogram is formed. Should be arranged. That is, at this time, the light emitting points are arranged in the third column, the fourth column,.

At this time, as shown in FIG. 4, when the basis vectors r ₁ and r ₂ are defined toward the two light emitting points having the shortest distance from a certain light emitting point (here, the light emitting point p ₁ ). , All the light emitting points can be expressed by vector sums of integer multiples of the respective basis vectors r ₁ and r ₂ , that is, linear combinations.

When the light emitting points _pn are arranged in this way, the scanning lines formed by the irradiation points by the adjacent light emitting points in the LD array 11 are not adjacent to each other on the surface of the photosensitive drum 1, and conversely, are adjacent to each other on the surface of the photosensitive drum 1. The relationship that the light emitting points forming the scanning line are not adjacent to each other in the LD array 11 is satisfied. In this case, the adjacent light emitting points are light emitting points in which the distance between the light emitting points is equal to _{one of} the base vectors r ₁ and r ₂ , and the light emitting points have a relationship other than the light emitting points that are not adjacent to each other. It is a point. For example, the light emitting points adjacent to the light emitting point p ₆ in FIG. 4 are p ₁ , p ₄ , p ₈ , and p ₁₁ . As apparent from FIG. 3, the irradiation points by these light emitting points p ₁ , p ₄ , p ₈ and p ₁₁ are all adjacent to the scanning line formed by the light emitting point p _{6 on the} photosensitive drum 1. No scan line is formed.

The effect produced by the LD array 11 by this arrangement will be described in comparison with the conventional surface-emitting light source 9 shown in FIGS.
FIG. 5 is a diagram showing the position of the beam spot when the same 2 ° skew as in FIG. 15 occurs in the LD array 11. FIG. 6 is a diagram showing scanning lines formed on the photosensitive drum 1 in a state where a skew of 2 ° is generated in the LD array 11. As can be seen from a comparison of FIG. 6 with FIG. 16, in the LD array 11 of the present embodiment, the first gap is less noticeable than the surface-emitting light source 9, and the regularity thereof is reduced. Due to the decrease in regularity, the LD array 11 of this embodiment is less likely to generate an interference pattern such as moire. The second gap in the surface emitting light source 9 was 19.1 μm, whereas the second gap in the LD array 11 of the present embodiment was 12.7 μm, and the second gap was relaxed by about 35%. You can see that As shown in the above description, according to the LD array 11 of the present embodiment, it is possible to reduce the generation of noise and suppress the deterioration of image quality as compared with the conventional surface-emitting light source 9.

[2: Second Embodiment]
Subsequently, a second embodiment of the present invention will be described. The image forming apparatus of the present embodiment is different from the image forming apparatus 100 described above only in the light source portion of the optical scanning device. Therefore, the following description will be focused on the light source portion, and description of the portion having the same configuration as that of the image forming apparatus 100 of the first embodiment will be omitted as appropriate.

  FIG. 7 is a diagram showing the arrangement of the light emitting points of the LD array 21 of the present embodiment. In the LD array 21 of the present embodiment, light emitting points are arranged on a lattice defined by the same basis vectors as the LD array 11 of the first embodiment described above. In the LD array 11, four light emitting points are arranged in each of the first column to the eighth column. However, in the LD array 21 of this embodiment, three in the first column, the second, third, and sixth columns. The light emitting points are arranged in such a manner that there are five in the row, six in the fourth and fifth rows, and two in the seventh row, and the total number is 32. Thus, the light source part in the present invention may have a configuration in which the number of light emitting points in each column is different.

The effect produced by the LD array 21 by this arrangement will be described in comparison with the conventional surface-emitting light source 9 shown in FIGS. 14 to 16 and the LD array 11 of the first embodiment described above.
FIG. 8 is a diagram showing the position of the beam spot when a 2 ° skew similar to FIG. 15 occurs in the LD array 21. FIG. 9 is a diagram showing scanning lines formed on the photosensitive drum 1 with a 2 ° skew generated in the LD array 21. When FIG. 9 is compared with FIG. 16, relaxation of the first gap can be confirmed also in the present embodiment. Further, the second gap is 17.6 μm, and although it is inferior to the LD array 11 of the first embodiment as an effect, it can be seen that it is smaller than the second gap of the surface emitting light source 9.
As described above, the LD array 21 of the present embodiment can also reduce the generation of noise and suppress the deterioration of the image quality as compared with the conventional surface-emitting light source 9.

[3: Third Embodiment]
Subsequently, a third embodiment of the present invention will be described. Here, an example in which the surface of the photosensitive drum 1 is subjected to multiple exposure using the LD array 11 and the LD array 21 described in the first and second embodiments will be described.

  FIG. 10 shows scanning when double exposure is performed with each of the conventional surface-emitting light source 9 (a), the LD array 11 (b) of the first embodiment, and the LD array 21 (c) of the second embodiment. It is the figure which showed the line. In the drawing, the same 2 ° skew as that described above is shown. Referring to FIG. 10A, it can be seen that the first gap is not relaxed in the surface-emitting light source 9 when double exposure is performed. This is because the position of the light emitting point on the surface light source 9 changes in a regular order such as right → right → right → left → right → right → right → left... And the gap generated every four scanning lines. This is because the first scanning line and the second scanning line just overlap each other. On the other hand, in the examples of FIGS. 10B and 10C, the gap is originally small, and the gap generation interval does not overlap between the first scan line and the second scan line. It is even less noticeable. For this reason, the LD array of the present invention can reduce periodic noise caused by the first gap and suppress degradation of image quality even when scanning exposure is performed by the multiple exposure method.

[4: Modification]
Although the present invention has been described with reference to the three embodiments, the present invention is of course not limited to the embodiment described above. For example, the number of light emitting points is not limited to 32, but may be 16 or 64, or of course other numbers. Also, various modifications can be made to the arrangement of the light emitting points, and the lattice shape and the basis vector shown in the above-described embodiment may be changed in shape and direction.
In addition, the present invention can be specified as an optical scanning device as described above, and can also be specified as an image forming apparatus including the optical scanning device.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating in detail a configuration of an optical scanning device provided in the image forming apparatus of the embodiment. It is the figure which showed arrangement | positioning of the light emission point in the LD array with which the optical scanning apparatus of the embodiment is equipped. It is a figure for demonstrating arrangement | positioning of the light emission point in the LD array of the embodiment. It is the figure which showed the position of the beam spot when 2 degree skew generate | occur | produced in LD array of the embodiment. FIG. 6 is a diagram showing scanning lines formed on the photosensitive drum in a state where a skew of 2 ° is generated in the LD array of the same embodiment. It is the figure which showed arrangement | positioning of the light emission point of LD array in the 2nd Embodiment of this invention. It is the figure which showed the position of the beam spot when 2 degree skew generate | occur | produced in LD array of the embodiment. FIG. 6 is a diagram showing scanning lines formed on the photosensitive drum in a state where a skew of 2 ° is generated in the LD array of the same embodiment. It is the figure which showed the scanning line at the time of performing double exposure with each of the conventional surface emitting light source and the LD array of the present invention. It is the figure which showed an example of the general optical scanning device. It is the figure which illustrated the beam spot formed by the interlace scanning method. It is the figure which illustrated the beam spot formed by the adjacent scanning system. It is the figure which illustrated the conventional surface emitting light source which forms 32 scanning lines. It is the figure which compared the position of the beam spot when the conventional surface emitting light source skewed 2 degrees with the regular position. It is the figure which showed the scanning line formed in the state which the conventional surface emitting light source skewed 2 degrees.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 10 ... Optical scanning device, 11, 21 ... LD array, 12 ... Collimating lens, 13 ... Half mirror, 14 ... Lens, 15 ... Light detection sensor, 16 ... Aperture, 17 ... Cylindrical lens, 18 ... Mirror, 19 ... Polygon mirror, 20, 21 ... fθ lens, 22, 23 ... Cylindrical mirror, 1 ... Photosensitive drum, 2 ... Charger, 3 ... Developer, 4 ... Transfer roll, 5 ... Paper transport belt, 6 ... Fixing device

Claims (6)

A plurality of light emitting points at the location of the end point and the start point of vector represented the starting point by an integer multiple of a linear combination of two basis vectors commonly Ru are arranged in a lattice point forming a virtual parallelogram lattice a is the distance between the light emitting point which emits light to form a scan line adjacent in the scanning member are both either a plurality of light emitting are disposed so as not equally in the size of the two basis vectors A surface-emitting light source having a point;
The light emitted from each of the plurality of light emitting points is converted into a luminous flux and guided to the scanning target, and the irradiation points formed by irradiating each of the luminous fluxes are moved in the main scanning direction, respectively. An optical scanning device, comprising: an optical system member that forms a plurality of scanning lines that are continuous in a scanning direction on the scanned object. A plurality of light emitting points at the location of the end point and the start point of vector represented the starting point by an integer multiple of a linear combination of two basis vectors commonly Ru are arranged in a lattice point forming a virtual parallelogram lattice a is the how the light emitting points are arranged in two lattice points having any size and equal distance between two basis vectors and, but arranged both to form a scan line which are not adjacent to each other in the scanning target A surface-emitting light source having a plurality of light-emitting points,
The light emitted from each of the plurality of light emitting points is converted into a luminous flux and guided to the scanning target, and the irradiation points formed by irradiating each of the luminous fluxes are moved in the main scanning direction, respectively. An optical scanning device, comprising: an optical system member that forms a plurality of scanning lines that are continuous in a scanning direction on the scanned object. The light source is
The optical scanning device according to claim 1, wherein the number of light emitting points arranged on the parallel lines forming the grating includes parallel lines different from other parallel lines. A second light emitting point different from the first light emitting point in the second scan irradiates a part of a scan line formed by the first light emitting point in the first scan. The optical scanning device according to claim 1 or 2. A gap between a scan line formed by the second light emission point and a scan line adjacent to the scan line is a scan line formed by the first light emission point and a scan line adjacent to the scan line. The optical scanning device according to claim 4, wherein the optical scanning device is different from a gap between them.   An image forming apparatus comprising the optical scanning device according to claim 1.

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