JP2000275925A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent color image to be obtainable at high speed by eliminating the need of useless toner consumption as well as highly accurate toner mark detecting means, and highly accurately overlapping the image, with high reliability. SOLUTION: A color image forming device which let detecting laser beams 3 reflected by optical reflection planes 30 by optical detecting mans 31 by providing plural optical reflection planes 30 on a part of a photoreceptor drum 1 surface, and respectively distributes 4 laser beams 3 at a specified angle for forming an electrostatic latent image corresponding to the basic color image on the single photoreceptor drum 1. In accordance with this detection signal, by adjusting the image read-out timing of the respective laser beam 3, on the photoreceptor drum 1, the device is made possible to highly accurately laminate monochrome color images, and possible to obtain the color image of the high quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming a single color image on an image recording medium, and sequentially forming a color image on the image recording medium.

[0002]

2. Description of the Related Art There are various image forming methods for forming a color image on an image forming medium such as a sheet of paper. For example, an electrostatic image (electrostatic latent image) is formed on a photosensitive drum and a toner is used. Electrophotography method to visualize and transfer to paper
There are known an ink jet system in which an image is formed by directly spraying an ink droplet onto a sheet, and a silver halide photographic system in which an image is exposed to a photosensitive coloring material and recorded. In a printing apparatus using an electrophotographic system, one of three primary colors (yellow, magenta, and cyan) for forming a color image on a photosensitive drum is used as a toner.
A method in which a process of forming an image and transferring it to a sheet is repeated three times (in some cases, four times including black), and an image forming unit for forming a single-color toner image is arranged in black and three primary colors in the sheet transport direction, and the sheet is sequentially printed. A method of forming a color image by superimposing a single-color image on top, arranging image forming means for the basic primary colors in the photoconductor transport direction, and superimposing the single-color images sequentially on the photoconductor surface to form a color image on paper at once Examples include a transfer method.

In particular, a color image is created on the surface of a photoreceptor,
The method of collectively transferring images onto a sheet can achieve a color image forming speed three to four times as fast as the method of sequentially superimposing single color images on a sheet at the same photoconductor surface speed. It is possible. Also, when compared with a system in which image forming units for the number of basic colors are arranged in the paper transport direction (tandem configuration), both are suitable for a high-speed color image forming apparatus, but the tandem configuration has various mechanical characteristics. ,
On the other hand, it is difficult to keep the superposition accuracy of each single-color image at high accuracy because the single-color images are superimposed on the uneven paper. On the other hand, the method of forming a color image on the surface of the photoconductor has an advantage that the superposition accuracy is relatively easily improved because the single-color image is superimposed on the surface of the single photoconductor. However, in this method, in order to form images of the second and subsequent colors, a photoreceptor having a front color toner image formed on its surface is irradiated with irradiation light for forming the images of the second and subsequent colors (multiple exposure). There is a need. At present, in the case of an image forming process using a dry toner, which is the mainstream in the electrophotographic system, the toner particle size is large (7 to 13 μm), and since the toner has not been heat-fixed, the translucency is poor and the second and subsequent colors are used. And there is a disadvantage that a high-quality color image cannot be obtained because an electrostatic latent image is not sufficiently formed. An electrophotographic method using a liquid developer is a method capable of overcoming this drawback and achieving both high-speed image formation and high-quality image formation, and its value is being reviewed in recent years. One of the advantages is a toner particle size of a submicron size. When this liquid developer is used, the above-described problem at the time of multiple exposure with a dry toner has been solved.

Further, the advantage of a wet electrophotographic color image forming apparatus using a liquid developer is that it is economical to obtain a sufficient image density with a small amount of toner, and it is possible to realize a print-like texture. In addition, energy can be saved because fixing can be performed on paper at a relatively low temperature.

[0005] Regardless of the method, in order to create a color image, it is necessary to superimpose the monochrome images with high accuracy.
If the accuracy is not good, it becomes impossible to obtain a high-quality image such as blurred image, insufficient sharpness, and insufficient color reproducibility. In general, the overlay deviation is not conspicuous visually and the overlay accuracy for obtaining high image quality is 0.1 mm or less, and various proposals for improving the overlay accuracy have been made. For example, a mark for detecting a misalignment between the single-color images is formed on a sheet conveying medium, and the image forming position is to be corrected based on the detected misalignment data. These proposals are intended to improve the image registration accuracy in the tandem configuration, but wasteful toner consumption due to marks for detecting deviation, additional mark cleaning means, and a long recording time due to loss time for detecting deviation. This has significantly impaired the merchantability of the image forming apparatus, such as increasing the time and increasing the cost due to the highly accurate mark detection means.

On the other hand, as a proposal for high-precision image superposition by multiple exposure, there is a method in which one of a plurality of laser beams is synchronized with a reference beam. In this proposal, only the other beam is adjusted with a single beam as a reference.For example, when the ambient temperature changes, the beam imaging position shifts due to thermal deformation of the optical system element, and each laser when exchanging the photoconductor There is no description of a detection method and a correction method for an image registration error generated due to an image position shift caused by a shift between the beam and the photosensitive member relative position.

Further, when there is a slight error in the photoconductor driving speed, only the synchronization is performed for each beam. Therefore, it is impossible to reduce the image superposition error due to the photoconductor speed error. There is a problem that the image superposition accuracy cannot be satisfied unless the driving is performed with very high accuracy.

In order to solve these problems, four-color images of yellow, magenta, cyan, and black are formed on the surface of the photosensitive drum.
In order to improve the image overlay accuracy in an image forming apparatus that creates a full-color image by sequentially overlaying the images, the inventors of the present proposal applied a writing laser to the surface of the photosensitive drum in the prior application (Japanese Patent Application No. 10-332848). Providing a member for reflecting light;
A high-precision image overlay in which four laser beams for forming respective color images are reflected from the reflecting member on the drum by a light detection sensor and converted into electric signals, and these signals are used as image writing timings. A matching method was proposed. According to this method, since a single-color image of four colors is formed based on the position of the reflection member on the surface of the photosensitive drum, the superposition accuracy of the superimposed full-color image can be extremely high. Although the surface of the photosensitive drum is always cleaned by a cleaner or the like, since the image material such as toner adheres, the surface of the writing laser beam reflecting member may be temporarily covered with the toner or the like, and the reflectance may be reduced. Since the timing of image formation is performed by detecting the reflected light from the reflective member, an image cannot be formed unless the reflected light from the reflective member is reflected with a sufficient amount of light.

[0009]

As described above, in the conventional method in which means for detecting an overlay error is provided in order to improve the overlay accuracy and obtain a high-quality color image, the overlay error is reduced. The amount of toner consumed by forming a mark for detection increases. In addition, since the mark image has no relation to the recording image to be output, it is necessary to remove the mark image without transferring it to the paper. Therefore, it is essential to provide a cleaning means, and the photoconductor is deteriorated due to mechanical stress such as cleaning. The time was shortened, and the life of the photoconductor was shortened. That is, there is a problem that leads to an increase in running cost including the photoconductor and the toner. Further, in order to realize a detection unit for detecting a registration error mark formed by a dot image having a dot size related to the recording resolution with high accuracy and detecting a registration error between each monochrome image, the detection unit itself is required. Detection accuracy (assuming that the overlay deviation allowable amount is about 0.1 mm, the detection accuracy is 0.02 in consideration of the overlay error generation factor analysis and the accuracy allocation based on the error analysis of the components of the image forming apparatus).
mm or less), and at the same time, there are fluctuations and variations in the image forming process for forming the marks and the driving accuracy of the constituent elements. There is a problem that a burden is imposed not only on the hardware but also on software such as a detection sequence. Further, the time required for outputting an image is delayed due to the loss time for the mark detection and the calculation of the overlay error, which is one of the factors that make it impossible to satisfy the high-speed output required for the image forming apparatus.

On the other hand, in the conventional method of synchronizing with one of a plurality of laser beams, only the relative positioning between the laser beams can be performed, and the image forming position determined by the relative position between the photosensitive member and the beam is not determined. There was a problem that the images could not be accurately aligned, and thus the image overlay accuracy could not be sufficiently improved. In addition, a mechanism that can attach a photoconductor, which is a consumable product and needs to be replaced several tens of times during the life of the apparatus, with sufficient accuracy at the time of replacement is required, which complicates the apparatus configuration. In addition, the driving speed of the photoconductor needs to be set with high accuracy, and a high-precision drive transmission mechanism and the photoconductor driving by high-precision speed control are required, which has a problem of an increase in apparatus cost.

Further, the method of detecting the reflected light of the writing laser beam by the reflection member on the surface of the photosensitive drum has a problem that an image cannot be formed due to a reflected light detection error caused by contamination on the surface of the reflection member.

As described above, according to the conventional method, there is a problem that a high-quality color image having no image registration error cannot be formed at a high speed.

According to the present invention, it is possible to correct image registration misregistration of a formed color image with high accuracy without wasteful toner consumption and a highly accurate toner mark detecting means. It is another object of the present invention to provide a color image forming apparatus which can be obtained at the same time.

[0014]

In order to achieve the above object, a first aspect of the present invention is to distribute irradiation light such as a plurality of laser beams on the surface of an image recording medium such as a photosensitive drum which is driven to rotate, and to distribute the irradiation light. Means for forming an electric image such as an electrostatic latent image on the surface of the image recording medium by the irradiation light, and providing a means for converting the electric image formed by each irradiation light into a visible image of a different color; In an image forming apparatus provided with means for sequentially forming a color image by superimposing on a recording medium surface and transferring the image to an image transfer medium such as paper, a part of the surface of the image recording medium is irradiated with irradiation light for image formation. It is characterized in that only a plurality of reflecting members are provided in the direction of travel of the image recording medium and the direction orthogonal thereto.

According to a second aspect of the present invention, there is provided a detecting means for receiving reflected light from an irradiating light reflecting member provided on the surface of an image recording medium such as a photosensitive drum and converting the reflected light into an electric signal. According to the present invention, an image forming timing by irradiation light is determined according to a detection signal.

According to a third aspect of the present invention, the plurality of reflecting members provided on the surface of the image recording medium are arranged all around the moving direction of the image recording medium, and select a specific reflecting member when forming one image. The image forming timing is determined in accordance with the reflected light detection signal from the specific reflecting member.

[0017]

The first embodiment of the present invention will be described below.

The image recording medium 1 shown in FIG. 1 is a photosensitive drum in which an organic or amorphous silicon photosensitive layer is provided on a conductive substrate. The image recording medium 1 is uniformly charged by a well-known corona charger or scorotron charger 2-1 and then exposed to an image-modulated laser beam 3-1 to form an electrostatic latent image on the surface. . Thereafter, the developing device 4-1 for storing the liquid developer
Thereby, the electrostatic latent image is visualized. The liquid developer or toner adhering to the electrostatic latent image may be directly transferred to a sheet by the transfer device 5 in the transfer step, but here, the second charger 2-2 and the second laser exposure 3- 2 to form a second electrostatic latent image, and a first developing device 4
-1 is developed by a second developing device 4-2 which stores a second developer of a color different from that of the liquid developer stored in -1. Therefore, after the second development, two color toner images are formed on the image recording medium 1. Similarly, third and fourth developments are performed, and a full-color toner image is formed on the image recording medium 1. This toner image is transferred to a sheet by the transfer device 5, and may be directly transferred to the sheet, or may be transferred to the sheet 9 via the intermediate transfer medium 6 as illustrated in FIG. Is also good. In the transfer from the image recording medium 1 to the intermediate transfer medium 6 and in the transfer from the intermediate transfer medium 6 to the paper 9, either transfer using an electric field or transfer using pressure (and heat) can be used. In general, many liquid developers can be fixed on paper at room temperature. However, fixing may be performed by heating the pressure roller 7 or the like.

Laser beam 3 for forming an electrostatic latent image
-1, 3-2, 3-3, and 3-4 scan the surface of the photosensitive drum 1 in a direction orthogonal to the rotation direction by rotating the polygon mirror 10, which is a polyhedral mirror, at a high speed by the polygon motor 11. Each beam is emitted light from an independent semiconductor laser light source (not shown), is deflected on the same surface of the polygon mirror 10, narrows down to a small spot of about 0.06 mm on the drum surface, and In the surface scanning, the fθ lens 12 and 1 for keeping the scanning speed constant in the axial direction of the photosensitive drum.
3, the light is distributed to prescribed positions on the surface of the photosensitive drum 1 by the folding mirror assemblies 20-1 to 20-8. While scanning the surface of the photosensitive drum 1, each laser beam is controlled to blink in accordance with image information to be formed, thereby forming a necessary electrostatic latent image.

A configuration for scanning a laser beam will be described with reference to FIG. The figure shows folding mirrors 20-1 to 20- for distributing light to the photosensitive drum 1 for simplicity of explanation.
8 is omitted. In the present embodiment, diffused light from the four semiconductor laser light sources 21-1, 21-2, 21-3, and 21-4 is converted into collimated lenses 23-1, 23-2, and 23-3.
At 23-4, the light is converted into substantially parallel light, and the half mirrors 24-1 and 24-1,
The two laser beams are condensed at substantially the same position by 24-2 and 24-3, pass through the cylindrical lens 25, and irradiate the deflection surface of the polygon mirror 10. The four laser beams are simultaneously deflected by the polygon mirror deflecting surface, pass through the fθ lenses 12 and 13, and are distributed by a folding mirror (not shown) at a specified position on the photosensitive drum at a specified incident angle.

FIG. 3 shows the arrangement of the optical system on the laser beam scanning plane. The emitted light of the semiconductor laser 21-1 is converted into parallel light by the collimator lens 23-1, but is focused only by the cylindrical lens 25 in a direction orthogonal to the scanning to form an image on the polygon mirror deflection surface 10. The laser beam deflected by the polygon mirror deflecting surface 10 forms an image on the photosensitive drum surface 1 which is conjugate to the polygon mirror deflecting surface due to the optical characteristics of the fθ lenses 12 and 13.

This is a widely known technique for suppressing the beam position fluctuation on the photosensitive drum surface 1 due to the inclination of the polygon mirror deflection surface 10. With this configuration, even if the accuracy of the deflection surface of the polygon mirror is not extremely high, the beam imaging position on the photosensitive drum surface differs for each polygon mirror surface, and the output image does not have uneven shading called banding.

In the color image forming apparatus of the present embodiment, a color image is formed by superimposing monochromatic images of different colors formed by respective laser beams.
If the imaging position of the distributed laser beam is shifted, the color image is shifted in registration, and the image quality is significantly deteriorated. In the embodiment according to the present invention, the reflection surface 30 of the laser beam is provided on the surface of the photosensitive drum 1 as shown in FIG. Although the figure shows only 3-1 and 3-2 of the four beams for simplification of the description, the surface of the photosensitive drum 1 is scanned by the polygon mirror 10 and the laser beam Reflected light 40-1 is generated. Although the details of the reflection surface 30 will be described later, since the reflection surface 30 is provided on the surface of the photosensitive drum 1, the reflection surface 30 moves in accordance with the rotation of the photosensitive drum. If the reflected light when the reflecting surface 30 moves to the scanning position of each laser beam is detected, and the image writing timing of each laser beam is determined based on the detection signal, the image on the photosensitive drum formed by each laser beam is obtained. Is formed at a position based on the beam reflecting surface 30, even if the light distribution position of each laser beam is shifted, the formation position of each monochromatic image on the photosensitive drum 1 is correct, and the color image is superimposed on the superimposed color image. The gap disappears.

In this embodiment, the reflected laser beam 40-1 is used.
The light detecting means 31 is installed at a position substantially equal to the distance from the photosensitive drum surface 1 to the polygon mirror deflecting surface 10 and at a position after the reflected beam 40-1 has passed through the fθ lenses 13 and 12. As described above, since the polygon mirror deflection surface 10 has an optical system configuration in which the laser beam is focused in a direction orthogonal to the scanning, the photosensitive drum reflection surface 3
The reflected beam 40-1 from the lens surface 0 through the fθ lens is reflected at the reflection surface
If the diffused light reflected by 0 is condensed again and the light detecting means 31 is installed at this position, the amount of received light per unit area is high, and the detection sensitivity can be increased. Further, since the light receiving surface of the light detecting means is substantially optically conjugate with the photosensitive drum surface, there is an advantage that the beam imaging position on the light receiving surface does not vary even if the reflected beam emission angle from the reflecting surface 30 varies. is there. That is, when distributing each laser beam to a predetermined position around the photosensitive drum 1, the laser beam is incident at a predetermined position on the surface of the photosensitive drum 1 due to a mounting failure of a folding mirror or the like. Even in the case where the angle has an error from the specified value, the beam imaging position at the light receiving section of the optical detection means 31 that is optically conjugate to the reflected beam emission angle does not shift, and the reflected beam can be detected.

The light detecting means 31 is a light detecting element having a light receiving surface of a Si photodiode as shown in FIG.
When light enters the light receiving surface 200, an electric signal is generated. In some cases, four laser beams are distributed on the polygon mirror deflection surface in directions different from each other in a direction orthogonal to the scanning direction.
The size of the light receiving surface of No. 1 was set to a width such that all reflected laser beams could be detected at the detection position.

The details of the reflecting surface 30 are shown in an enlarged view in FIG. In this embodiment, only four 0.1 mm square minute reflecting members are arranged in the laser scanning direction. The arrangement interval was set to 0.8 mm so that the laser beam scanning position was shifted by the maximum amount or more. When the laser beam scans the minute reflecting member, reflected light corresponding to the reflecting member is obtained, and the reflected light is detected by a reflected light detecting means 31 described later to obtain a reflected light detection signal pulse. Generate

First, a method of generating an image forming timing signal in a direction orthogonal to laser beam scanning, that is, in a sub-scanning direction in the present embodiment will be described.

As shown in FIG. 2, a reflection mirror 47 for receiving a laser beam for each laser beam scanning and a laser beam detecting means 46 are provided upstream of the photosensitive drum 1 in the scanning direction.
Is provided separately from the light detecting means for detecting the reflected beam by the reflecting member on the photosensitive drum surface. When an image is formed on the photosensitive drum by laser beam scanning, a laser scanning signal synchronized with the scanning from the detecting unit 46 is obtained each time scanning is performed. On the other hand, each time the laser beam passes through the four reflecting members in FIG. 8, a pulse signal corresponding to the position of the reflecting member is obtained. FIG. 9 shows a timing chart of these signals. FIG. 11 shows a circuit block for generating these signals. An image forming timing signal which is inverted at the first pulse edge of the reflected beam detection signal is generated by the gate circuit, and an image is recorded from the laser scanning signal after the image forming timing signal is inverted.

With this configuration, even if toner or the like adheres to any one of the reflecting members 30 on the photosensitive drum surface and a sufficient amount of reflected beam is not generated, the reflected beam from the other reflecting member can be generated. As a result, an image forming timing signal can be generated. FIG. 10 shows a timing chart in the case where one of the reflecting surfaces of the reflecting members 30 is dirty and a reflected beam detection signal cannot be obtained. Even if the first detection signal is not obtained, the second, third, and fourth signals are obtained, so that the image forming timing signal can be generated. The laser scanning signal for recording an image includes the reflected beam from each reflecting surface. There is no difference from the case of normal detection. As a result, the image writing position in the sub-scanning direction can be determined with high reliability without errors caused by contamination of the reflection surface, and thus, the image registration accuracy when the images of the respective colors are superimposed is increased. Will be able to keep it.

A method for improving the accuracy of superimposing images by a light receiving signal of a reflected laser beam will be described. FIG. 6 is a block diagram of a circuit that determines an image writing timing in synchronization with a reflected laser beam detection signal. Photosensitive drum 1
The reflected light beams 40-1, 40-2, 40-3, and 40-4 from the reflecting surface 30 (not shown) provided on the surface are detected by the light detecting means 31 and converted into electric signals. Detection signals are generated by the light detection means 31 at the same interval as the time when the photosensitive drum 1 moves between the four laser beams to which the light is distributed, and the image writing timing generation circuit 51 synchronizes the detection signals Y, A write timing signal for each of M, C, and K images is generated. On the other hand, the image processing circuit 52 decomposes the image data into YMCK single-color image data, and converts the image data corresponding to the number of scannings of the laser beam into line buffers 53-1, 53-2, 53-3, and 53.
-4 and stored in a line buffer in synchronization with the image forming timing signal.
2, 54-3 and 54-5. Each semiconductor laser 2
1-1, 21-2, 21-3, and 21-4 blink according to the image data, and form an electrostatic latent image on the photosensitive drum. FIG. 12 is a timing chart for explaining signals for forming a one-color image. FIG. 12 is a timing chart for forming a four-color image.

As described above, since the laser light source for forming each monochrome image is driven, the formation position of each monochrome image on the photosensitive drum is the same position with respect to the laser beam reflecting surface 30.
Almost no overlay error is found in the superimposed color images, and a high-quality output color image can be obtained.

Next, a method of generating an image writing timing signal in the scanning direction of the laser beam, that is, in the main scanning direction will be described.

The image writing timing in the main scanning direction is determined by a scanning signal from the light detecting means 46. Rotation speed of polygon motor for driving polygon mirror and light detecting means 46
According to the positional relationship, the laser beam is turned on so that the laser beam irradiates the light detecting means 46 to obtain a scanning signal. As shown in the timing chart of FIG. 7, the image formation, that is, the driving timing of the laser beam, is performed after a certain delay time dy, dm, dc, dc from the edge of the scanning signal generated every time the laser beam scans. The control is performed by generating a laser blinking signal corresponding to the image data. By setting the delay times dy, dm, dc, and dk for each monochromatic image, it is possible to shift the image forming position in the laser beam scanning direction. The position in the scanning direction of each monochrome image is determined from the time interval between the scanning signal and the signal detected by the light detecting means 31 from the reflected beam from the reflecting surface 30. FIG. 13 shows a signal timing chart. When the time between the laser scanning signal and the detection signal of the light detecting means 31 is counted based on the clock count value between the two edges, the light detecting means 46 (FIG. 2) for generating the laser scanning signal outputs the reflection surface 30 of the photosensitive drum surface. The respective laser arrival times up to are obtained, and the delay time d shown in FIG. 7 is set so that each monochrome image is formed at a fixed position in the scanning direction with respect to the reflection surface 30.
Change y, dm, dc, dk. With this correction sequence, the single-color image forming position in the laser beam scanning direction is the same for each image, and the overlay error in the color image is eliminated.

More specifically, the delay times dy, dm, dc,
A method for setting dk will be described. The time from the laser scanning signal pulse edge to the laser beam reflected light detection pulse edge is counted by the delay time counting circuit of FIG.
The counted reference clock data is taken into the image processing circuit, and the image processing circuit calculates a delay time for a transfer start timing when transferring image data for one laser scan to the laser drive circuit, and calculates an image line buffer. The delay time data dy, dm, dc,
Set dk. In this figure, for simplification of description, only a line buffer circuit for black image data is described, but a similar circuit is provided for yellow, magenta, and cyan image data. The delay time counting circuit does not need to be provided for each beam in the present embodiment because the delay time is not counted simultaneously for laser beams for forming yellow, magenta, cyan, and black images.

As described above, the delay time is set. However, if the reflection surface 30 is contaminated with toner or the like and a sufficient amount of reflected beam cannot be obtained, the image forming position cannot be determined correctly. In this embodiment, since a plurality of reflection members are provided as shown in FIG. 8, a plurality of reflected beam detection signals can be obtained as shown in FIG. FIG. 15 shows a case where the first reflection member does not have a sufficient reflectance due to dirt and a detection signal cannot be obtained. The delay time counting circuit counts the time from the laser scanning signal edge to the reflected beam detection signal pulse edge from the second reflecting member, and obtains data CT1 '. If the first reflecting member is normal, the counted delay time is CT1, and the delay time when transferring the image data is CT1
In this case, a value obtained by integrating a predetermined delay time dt for forming an image from a position separated by a predetermined distance from the first reflecting member may be used. In the present embodiment, since the distance between the respective reflecting members is set to be longer than the distance in which the laser beam can fluctuate, the image processing circuit determines the magnitude of the delay time CT1 ′ to determine the order of the detection signal pulse. Can be determined. Even if the detection signal from the first reflecting member is not obtained as in the present example, CT1 ′
Is determined, it is determined that the detection signal from the second reflection member is the first detection signal from the laser signal edge. The delay time for transferring the image data is the first and second from the counted delay time CT1 '.
If the time dl during which the laser beam passes between the second reflecting members is subtracted and a value obtained by integrating the constant delay time dt described above is obtained, the image forming start position is a position based on the first reflecting member. Is determined with high accuracy.

In this embodiment, only the laser beam corresponding to the one-color image has been described. However, the same applies to the laser beam corresponding to the other color, and the image forming position can be set based on the first reflecting member. Therefore, it is possible to make the superimposition accuracy of the superimposed images extremely high. Furthermore, even if a part of the reflection surface is contaminated, it is possible to realize highly reliable superposition.

In this embodiment, as shown in FIG. 5, the reflecting surface 30 is provided on the drum so that the reflected light 40-1 irradiates the light receiving surface of the light detecting means 31 provided substantially at the same position as the polygon mirror deflecting surface 10. It is provided at an angle to the surface. Specifically, a groove 33 is formed in the tube portion of the photosensitive drum 1 and the reflecting surface 3 is formed.
0 is formed. A transparent cover member 32 made of an acrylic material is buried in the groove 33 in order to prevent a foreign material such as a developing material from entering the groove 33 and contaminating the reflection surface to lower the reflectance.

FIG. 16 shows a second embodiment according to the present invention. In this embodiment, a laser beam reflecting member is provided on the periphery of the photosensitive drum every 45 degrees in the rotation direction. Immediately before the timing of forming an image, with the reflecting member located at the shortest position in the first laser beam as a reference, a yellow image is formed by the first laser beam and a magenta image is formed by the second beam based on a reflected light detection signal from the reflecting member. , The image writing timing of the cyan image using the third beam and the image writing timing of the black image using the fourth beam. This eliminates the need to rotate the photosensitive drum excessively to generate each image forming timing signal,
By rotating the photosensitive drum by a maximum of 45 ° to generate an image writing timing signal by the first beam, an image writing signal can be obtained. It is possible to reduce the dead time until image formation, and it is possible to shorten the printing process.

In addition to the embodiments described above, a plurality of reflecting members are provided at both ends of the photosensitive drum, and using the reflected beam detection signals from the two members, the displacement due to the inclination of the scanning position of the laser beam or the laser It is also possible to correct an overlay shift caused by a beam scanning width magnification shift. In these cases, the method may be performed in the same manner as described above.

In this embodiment, the components for forming an electrostatic latent image by a laser beam have been described. However, the embodiment 4 is not particularly limited to a laser optical system. For example, an electrostatic latent image is formed by a line head such as an LED head. Obviously, it is also applicable to elements.

Further, the photodetecting element using a Si photodiode has been described as an example of the photodetecting means. However, any means for receiving a laser beam and converting it into an electric signal can be used.

[0042]

As described above, according to the present invention,
A plurality of members for reflecting a laser beam are provided on a part of the surface of a photoreceptor serving as an image recording medium, and a color image is formed based on light detection signals of reflected beams from the plurality of reflecting members. There is no beam detection error, and thus, high reliability and high-accuracy image superposition are possible. As a result, a high-quality color image can be obtained. In addition, since a toner mark for detecting a misalignment is not required, useless toner consumption, a mark detection unit, a mark cleaning unit, and the like are not required.
This can contribute to a reduction in device cost and a reduction in running cost.

[Brief description of the drawings]

FIG. 1 is a side view showing a schematic configuration of a color image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram of a laser beam scanning device according to an embodiment of the present invention.

FIG. 3 is a layout diagram of a laser beam optical system according to an embodiment of the present invention.

FIG. 4 is a schematic perspective view of a light detection unit.

FIG. 5 is a diagram illustrating an optical arrangement according to an embodiment of the present invention.

FIG. 6 is a circuit block diagram for generating image write timing according to the embodiment.

FIG. 7 is a timing chart for explaining an image position in the main scanning direction in the fifth embodiment.

FIG. 8 is a perspective view illustrating a first embodiment according to the present invention.

FIG. 9 is a timing chart for explaining the start of image recording in this embodiment.

FIG. 10 is a timing chart illustrating a case where a part of a detection signal is missing in the embodiment.

FIG. 11 is a circuit block diagram for generating an image recording signal in the embodiment.

FIG. 12 is a timing chart for explaining the start of formation of a four-color image in the sub-scanning direction in the embodiment.

FIG. 13 is a timing chart for explaining the start of formation in the main scanning direction in the present embodiment.

FIG. 14 is a circuit block diagram for performing image formation in the main scanning direction in the present embodiment.

FIG. 15 is a timing chart illustrating a case where a part of the detection signal is missing in the embodiment.

FIG. 16 is a perspective view for explaining a second embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Laser beam 10 Polygon mirror 11 Polygon motor 12, 13 fθ lens 20, 47 Folding mirror 21 Semiconductor laser 23 Collimator lens 24 Half mirror 25 Cylindrical lens 30 Light reflecting surface 31, 46 Light detecting means 33 Reflecting member 40 Reflected light 45 lenses

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 H04N 1/29 C 5C074 H04N 1/04 B41J 3/00 D 1/113 G03G 21/00 372 1/29 H04N 1/04 D 104A F term (reference) 2C362 BA52 BA69 BB30 BB31 BB40 BB47 CA22 CA38 CB59 2H027 DA38 DE02 EB04 EC06 EC07 EC20 ED02 ED06 EE02 EE07 EF09 2H030 AA01 AD12 AD17 BB02 BB16 BB02 BB16 BB16 BB16 BB02 BB16 BB02 ABB01 CA89 CA98 DA02 5C072 AA03 BA19 HA02 HA06 HA12 HB08 HB11 QA14 QA17 XA01 XA05 5C074 AA02 AA10 AA12 BB03 BB17 BB26 CC22 CC26 DD15 DD24 EE02 EE04 EE20 FF15 GG09 GG12 HH02

Claims (3)

[Claims] 1. A method of distributing a plurality of irradiation lights on a surface of an image recording medium driven to rotate, forming an electric image on the surface of the recording medium by the respective irradiation lights, and converting the electric images into different colors of one color. A part for forming a color image by sequentially superimposing the different one color visible images on the surface of the image recording medium, and transferring the color image to an image transfer medium; and a part of the surface of the image recording medium. A color image forming apparatus, wherein a plurality of members for reflecting the irradiation light are provided in a traveling direction of the image recording medium and a direction orthogonal to the traveling direction. A detecting means for receiving reflected light from an irradiation light reflecting member provided on a surface of the image recording medium and converting the reflected light into an electric signal; 2. The color image forming apparatus according to claim 1, wherein the forming timing is determined. 3. A plurality of reflecting members provided on the surface of the image recording medium are arranged all around the moving direction of the image recording medium, select a specific reflecting member when forming one image, and select the specific reflecting member. 2. The color image forming apparatus according to claim 1, wherein the image forming timing is determined according to a detection signal of light reflected from a reflection member.