JP2007038546A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive image forming device which linearly regulates the light volume of each printing head in such a manner that the density is compensated to the density unevenness of the rotating cycle of a photo-sensitive body drum resulting from a focal point position variation of each printing head by the rotating deflection of the photo-sensitive body drum, and by which a high picture quality without density unevenness is obtained by a comparatively simple constitution. <P>SOLUTION: This image forming device is equipped with a light emitting element array unit being the printing head, a plurality of which are arranged into a zigzag shape in the main scanning direction of the photo-sensitive body. The image forming device is equipped with a synthesizing means, a control means, and a density sensing means. The synthesizing means synthesizes image data of each printing head into one line on the photo-sensitive body. The control means individually changes the light volume of the printing head. The density sensing means senses a toner image density on the photo-sensitive body which is formed by the printing head. A density sensing at least for one cycle portion of the photo-sensitive body is performed by the density sensing means. The image forming device is equipped with a control means which linearly adjusts the light volume of each printing head, based on the result of the density sensing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a digital copying machine, and a multifunction machine having an optical writing device using a light emitting element array unit such as an LED array.

2. Description of the Related Art Conventionally, in an image forming apparatus, a light emitting element array unit for writing an image pattern, for example, an LED print head (hereinafter referred to as a print head or LPH) in which the light emitting element is an LED is arranged on a photosensitive member (this method is referred to as this method). (Referred to as type 1), or data is transferred in parallel by a plurality of LPHs so that the divided image is combined with the image written in the first LPH on the photosensitive member again on one line ( This technique is called type 2) (see Patent Documents 1 and 2).
In the optical writing device described in Patent Document 1, in the optical writing device in which a plurality of LPHs are provided in the main scanning direction, the light amount adjustment is performed for each of the plurality of LPHs, and the light amount difference between the LPHs. Thus, an image having no density unevenness due to the image can be obtained.
The image forming apparatus described in Patent Document 2 includes an optical writing device in which a plurality of LPHs similar to Patent Document 1 are provided in the main scanning direction, and detects a focal position shift of each LPH with respect to the photosensitive drum. It is made to detect by means.
FIG. 10 is a schematic view showing a light emitting element array unit and a photosensitive drum. FIG. 11 is a schematic diagram showing the concentration in the state of FIG. FIG. 12 is a schematic view showing a state where the focal position of the light emitting element array unit is shifted with respect to the photosensitive drum.
10 and 12, reference numerals 2 and 3 denote light emitting element array units (LPH), and 9 denotes a photosensitive drum. As shown in FIG. 12, the LPHs 2 and 3 are tilted by a predetermined angle to correct the focal shift of the LPHs 2 and 3 so that an image without density unevenness caused by the focal shift between the LPHs 2 and 3 can be obtained. ing.
JP 2001-80118 A JP 2002-52757 A

However, by providing a means for changing the light quantity of each LPH as in Patent Document 1, it is possible to reduce the focal position variation of each LPH due to the rotational fluctuation of the photosensitive drum only by suppressing density unevenness due to the difference in the light quantity of adjacent LPH. The resulting density unevenness of the photosensitive drum rotation period cannot be resolved.
Further, as in Patent Document 2, the focal position deviation of each LPH with respect to the photosensitive drum is detected by the detecting means, and each LPH is tilted by a predetermined angle to correct the focal deviation, thereby causing the focal deviation between the LPHs. In the method of suppressing the density unevenness, since it is not possible to linearly correct the focal position fluctuation of each LPH due to the rotation fluff of the photoconductor drum, the density unevenness of the photoconductor drum rotation cycle due to this cannot be eliminated. In addition, the mechanism for inclining the angle of each LPH is complicated and the cost is increased.
Accordingly, an object of the present invention is to correct the shading with respect to density unevenness in the rotation cycle of the photosensitive drum caused by the focal position variation of each print head due to rotation flutter of the photosensitive drum in consideration of the above situation. Thus, an object of the present invention is to provide an inexpensive image forming apparatus capable of linearly adjusting the light amount of each print head and obtaining a high image quality without density unevenness with a relatively simple configuration.

In order to solve the above problems, the invention according to claim 1 is an image forming apparatus in which a plurality of light emitting element array units as print heads are arranged in a staggered manner along the main scanning direction of the photosensitive member. A combining unit that combines the image data of the print head into one line on the photoconductor; a control unit that individually varies the light amount of the printhead; and a toner image density on the photoconductor formed by the printhead. Density detecting means that detects at least one period of the photosensitive member by the density detecting means, and the control means linearly adjusts the light amount of the print head based on the detection result. It is characterized by that.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the density detecting means is provided in each of the print heads and is disposed near a joint between adjacent print heads.

  According to the present invention, the combining means for combining the image data of each print head into one line on the photosensitive member, the control means for individually changing the light amount of each print head, and the photosensitive formed by each print head. Density detecting means for detecting the density of the toner image on the body drum, the density detecting means detects the density of at least one cycle of the photosensitive drum, and based on the result, linearly determines the light quantity of each print head. The control means for adjusting the print head to each of the print heads so as to correct the shading with respect to the density unevenness in the rotation cycle of the photoconductor drum caused by the fluctuation of the focal position of each print head due to the rotation flutter of the photoconductor drum. Since the amount of light is adjusted linearly, it is possible to obtain a high image quality with a relatively simple configuration and without density unevenness at a low cost.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a type 1 image forming apparatus as a first embodiment of the present invention. In FIG. 1, the charging charger 1 uniformly charges the surface of the photosensitive drum 9.
The print head 2 is, for example, an LED print head (LPH) in which a light emitting element of a commonly used light emitting element array unit is an LED, and irradiates a charged photosensitive drum 9 surface with pattern light corresponding to an image. Then, an electrostatic latent image is obtained on the surface of the photosensitive drum 9.
The developing device 4 for developing the latent image is generally developed with a powder called toner. The toner on the developed image pattern is superimposed on a transfer paper (not shown) on the transfer charger 5, and the image is transferred to the transfer paper.
The separation charger 6 separates the transfer paper from the photosensitive drum 9, and the cleaning unit 7 cleans the transfer residual toner. Reference numeral 8 denotes a static elimination lamp that uniformly removes the residual potential on the photosensitive drum 9.
Here, one LPH 2 for writing an image pattern is arranged on the photosensitive drum 9 in FIG. 1, and the length in the width direction corresponds to the width of the transfer paper. For example, the A0 width transfer paper is used. If the writing device handles the above, the length of LPH is also equivalent to A0.

FIG. 2 is a schematic diagram showing a type 2 image forming apparatus as a second embodiment of the present invention. In FIG. 2, the charging charger 1 uniformly charges the surface of the photosensitive drum 9. The print heads 2 and 3 are, for example, LPHs using LEDs as light emitting elements that are generally used. The print heads 2 and 3 irradiate the charged surface of the photosensitive drum 9 with pattern light corresponding to an image, and the surface of the photosensitive drum 9 is statically irradiated. An electrostatic latent image is obtained. The developing device 4 for developing the latent image is generally developed with a powder called toner. The toner on the developed image pattern is superimposed on a transfer paper (not shown) on the transfer charger 5, and the image is transferred to the transfer paper. The separation charger 6 separates the transfer paper from the photosensitive drum 9, and the cleaning unit 7 cleans the transfer residual toner.
Reference numeral 8 denotes a static elimination lamp that uniformly removes the residual potential on the photosensitive drum 9. Further, a pulley 10 for driving the photosensitive drum 9 and a density detection sensor 12 provided for correcting the image density are shown.
Further, in order to detect the reference position of the photosensitive drum 9, the light shielding plate 14 disposed on the rotating peripheral surface of the rotating shaft of the photosensitive drum 9 can be detected on a face plate (not shown) that holds the photosensitive drum 9. A photosensitive drum position detection sensor 13 fixed in this manner is arranged.
FIG. 3 is a block circuit diagram showing a configuration including LPHs arranged in a zigzag pattern divided in the width direction. In the embodiment of FIG. 2, the LPHs 2 and 3 are divided in the width direction and arranged in a zigzag manner as shown in FIG. 3, and image writing is performed in three divisions.
2 and 3, specifically, the image data 16 is transferred to the LPH control circuit 15, where the image is divided into three in the width direction. Data of the divided images is transferred in parallel to the first LPH2, the second LPH3, and the third LPH3a.
However, the second and third LPHs 3 and 3a arranged downstream of the first LPH 2 in the rotation direction of the photosensitive drum 9 pass through the first LPH 2 and the second LPH 3 and the third LPH 3 through the delay circuits 17 and 17a. The data is transferred after being delayed by a delay time t ′ determined by the sub-scan interval of the LPH 3 a and the peripheral speed of the photosensitive drum 9, so that one line on the photosensitive drum 9 is transferred to the image written by the first LPH 2. It is designed to be synthesized.

FIG. 4 is a schematic diagram showing density unevenness when an image is written using Type 2. In FIG. Conventionally, when a plurality of LPHs 2, 3, and 3a are arranged in a staggered manner in the width direction and image writing is performed in a divided manner as in the embodiment of FIG. 2, the photosensitive drum 9 is exposed for each LPH 2, 3, and 3a. As a result, the density unevenness as shown in FIG. 4 is generated.
For this reason, conventionally, the adjacent LPH light quantity is selected by selecting the light quantity of the adjacent LPH that is the same or having a relatively small light quantity difference, or by providing means for changing the light quantity of each LPH as in Patent Document 1. Density unevenness due to the difference was suppressed.
In Type 2, the depth of focus of each LPH 2, 3, 3a with respect to the photosensitive drum 9 is approximately ± 100 μm or less, and it is necessary to adjust the focus adjustment of each LPH 2, 3, 3a with high accuracy.
However, it is difficult to eliminate variations in focus adjustment for the photosensitive drums 9 of the LPHs 2, 3, and 3a. In addition, the rotational flutter accuracy of the photosensitive drum 9 is also limited as the processing accuracy, especially when the writing width is a long one of A0 and A1 sizes.
The merit of the type 1 type image forming apparatus is that a high-quality image can be obtained with a simple configuration, but the LPH used in this method needs to cover the entire width direction of the document. For example, when A0 width writing is performed, LPH of A0 length is required, and the cost of parts of LPH becomes considerably high. As a result, the cost of the apparatus itself is increased. .
The merit of the type 2 image forming apparatus is a method developed to compensate for the disadvantages of the type 1 method, and the cost of parts is kept low by arranging a plurality of short LPHs. (By the way, the part cost of this LPH is proportional to the length in the width direction.)

FIG. 5 is a schematic diagram showing density unevenness in the photosensitive drum rotation period in a halftone image. As shown in FIG. 5, in the halftone image, an image having a conspicuous gray level in the rotation cycle of the photosensitive drum in the sub-scanning direction is generated due to the focus variation of each LPH due to the rotation flutter of the photosensitive drum.
In particular, when the focal shift of adjacent LPHs is shifted in the opposite direction with respect to the focal position center, the density is reversed at the joint, and density unevenness between the LPHs becomes conspicuous.
As described above, by providing the means for changing the light quantity of each LPH as in Patent Document 1, the focal position of each LPH caused by the rotation fluff of the photosensitive drum can be obtained only by suppressing the density unevenness due to the difference in the light quantity of adjacent LPH. The density unevenness of the photosensitive drum rotation period due to the fluctuation cannot be eliminated.
Further, as in Patent Document 2, the focal position deviation of each LPH with respect to the photosensitive drum is detected by the detecting means, and each LPH is tilted by a predetermined angle to correct the focal deviation, thereby causing the focal deviation between the LPHs. In the method of suppressing the density unevenness, since it is not possible to linearly correct the focal position variation of each LPH due to the rotation fluff of the photosensitive drum, the density unevenness of the rotation cycle of the photosensitive drum due to this cannot be eliminated. In addition, the mechanism for inclining the angle of each LPH is complicated and the cost is increased.
FIG. 6 is a block diagram illustrating a writing control unit of the image forming apparatus. In FIG. 6, the writing control unit 18 includes a density detection control unit 19, a first LPH light amount correction ROM 20, a second LPH light amount correction ROM 21, a third LPH light amount correction ROM 22, a light amount correction ROM read control unit 23, The image data / temperature correction data control unit 24 is configured.

FIG. 7 is a schematic view showing a concentration detection sensor arranged in the vicinity of the joint of each LPH. FIG. 8 is a schematic view showing a concentration detection sensor arranged at the center of each LPH. FIG. 9 is a diagram showing output data during the time TD corresponding to one cycle of the photosensitive drum of each density sensor.
Here, in the first embodiment of the present invention, for example, when the power of the image forming apparatus is turned on, a pattern image of a certain area is transferred to the photosensitive drum 9 (see FIG. 2) by the LPHs 2, 3, 3a. A pattern image of at least one cycle of the photosensitive drum 9 is exposed with a default light amount of 3, 3a.
As shown in FIG. 7, this pattern image can be detected by four density detection sensors 12 including a reflection type photosensor disposed near the joint of the first LPH2, the second LPH3, and the third LPH3a.
Here, the pattern image is a halftone image pattern such as a one-dot halftone dot pattern in which density unevenness is likely to appear remarkably. This pattern image is developed as a toner image by the developing unit 4 (see FIG. 2).
The density of this image is detected by each density detection sensor 12, and each detection data is sent to the density detection control section 19 in the writing control section 18 as shown in the block diagram of FIG. First, a light amount correction value for one cycle of the photosensitive drum 9 of each LPH 2, 3, 3a is obtained from each detection data.

Specifically, in the output data during the time TD corresponding to one cycle of the photosensitive drum 9 of each density sensor shown in FIG. 9, the portion where the image density is high on the circumference of the photosensitive drum 9 is the LPH 2, 3, 3a. Light amount correction data is created so that the light amount is low, and conversely the light portion is high.
As shown in FIG. 9, the correction timing is based on a light shielding plate 14 (see FIG. 2) for detecting the reference position of the photosensitive drum 9 and a reference by a position detection sensor 13 (see FIG. 2) of the photosensitive drum 9. From the position signal, for example, the time when the position where the image density of the first LPH density sensor output data 1 is the highest on the circumference of the photosensitive drum 9 is detected: the correction timing of the first LPH 2 is determined from T1, and the like. The correction timings of the second and third LPHs 3 and 3a are determined.
Each correction data is sent to the light quantity correction ROM 20, 21, 22 of each LPH 2, 3, 3a, sent from the light quantity correction ROM read control unit 23 to the density correction data control unit 24 that combines the image data and the density correction data, The final image data is transferred to each LPH 2, 3, 3a.

As described above, the exposure light amount of each LPH 2, 3, 3 a is linearly corrected in one cycle of the photoconductor drum 9, so that the rotational deflection of the photoconductor drum 9 and the focal position of each LPH 2, 3, 3 a are corrected. Image density unevenness due to deviation can be visually suppressed.
For example, since the image density check is performed every time the power is turned on, even if the light quantity of LPH 2, 3, 3a changes compared to the initial value, and even if the photosensitive drum 9 is replaced, high image quality without image density unevenness. Can always be maintained.
Also, if the light amount difference in one LPH is large, as shown in FIG. 8, when the arrangement position of each density detection sensor 12 is near the center of LPH2, 3, 3a, the density at the detected position is fed back. Therefore, density unevenness occurs.
Further, when the light amount difference between the light emitting element near the joint and the light emitting element near the center is large, density unevenness occurs at the joint. (There is no problem if there is no difference in the amount of light in one LPH or it is very small.)
For this reason, by disposing each density detection sensor 12 in the vicinity of the joint between the LPHs 2, 3, 3a, the difference in light quantity between adjacent light emitting elements can be minimized (FIG. 7). Further, density unevenness generated by the LPHs 2, 3, 3a can be reduced.

The above description of the preferred embodiment of the present invention includes a comparison with the prior art for convenience. Therefore, the configuration of the embodiment of the present invention will be described purely below.
As shown in FIGS. 2 and 3, the image forming apparatus connects a one-dimensional light emitting element array in which a plurality of light emitting elements are arranged at a predetermined density in the main scanning direction and the light from the light emitting element array to a photosensitive drum 9. A plurality of light emitting element array units (hereinafter referred to as print heads or referred to as LPH since the light emitting elements are referred to as LEDs) 2, 3, and 3a having image forming means for imaging along the main scanning direction of the photosensitive drum 9 Arrange them in a staggered pattern.
At that time, an optical writing device (not shown) for exposing the photosensitive drum 9 by irradiating light from each of the print heads 2, 3, 3 a and writing an electrostatic latent image is provided, and then developed by the developing unit 4. Form an image.
Combining means (delay circuits) 17 and 17a for synthesizing the image data 16 of each print head 2, 3 and 3a into one line on the photosensitive drum 9, and the light quantity of each of the print heads 2, 3 and 3a are individually varied. And a density detecting means (density detecting sensor) 12 for detecting the toner image density on the photosensitive drum 9 formed by the print heads 2, 3, 3a.
The density detection means 12 performs density detection for at least one cycle of the photosensitive drum 9, and based on the result, a control means (density detection control unit) that linearly adjusts the light quantity of each print head 2, 3, 3a. ) 19.
The density detection means 12 provided in each print head 2, 3, 3 a is arranged in the vicinity of the joint between the adjacent print heads 2, 3, 3 a. As a result, density fluctuations near the joints of the print heads 2, 3, 3a are detected.
Since the amount of light of each print head 2, 3, 3a can be linearly corrected and controlled based on this detection result, the amount of light at the joint of each print head 2, 3, 3a is accurately corrected without error, and is visually conspicuous. It is possible to reduce density unevenness at the joints of the print heads 2, 3, 3a.

1 is a schematic diagram illustrating an image forming apparatus of a type 1 system. FIG. 3 is a schematic diagram illustrating an image forming apparatus of a type 2 system. It is a block circuit diagram which shows the structure containing LPH divided | segmented into the width direction and arrange | positioned 3 in zigzag form. It is the schematic which shows the density nonuniformity at the time of performing image writing using Type 2. FIG. FIG. 6 is a schematic diagram showing density unevenness in a photosensitive drum rotation cycle in a halftone image. 3 is a block diagram illustrating a writing control unit of the image forming apparatus. FIG. It is the schematic which shows the density | concentration detection sensor arrange | positioned in the joint vicinity of each LPH. It is the schematic which shows the density | concentration detection sensor arrange | positioned in the center of each LPH. It is a figure which shows the output data between 1 period equivalent time: TD of the photoconductive drum of each density sensor. It is the schematic which shows a light emitting element array unit and a photoreceptor drum. It is the schematic which shows the density | concentration in the state of FIG. It is the schematic which shows the state which shifted the focus position of the light emitting element array unit with respect to the photosensitive drum.

Explanation of symbols

  2 print head (light emitting element array unit, first LPH), 3 second LPH (light emitting element array unit, second LPH), 3a third LPH (light emitting element array unit, third LPH), 9 Photosensitive drum, 15 LPH control circuit, 16 image data, 17 delay circuit, 17a delay circuit, 18 writing control unit, 19 density detection control unit, 24 density correction data control unit

Claims (2)

In an image forming apparatus in which a plurality of light emitting element array units, which are print heads, are arranged in a staggered manner along the main scanning direction of the photoconductor,
A combining unit that combines the image data of the print head into one line on the photoconductor; a control unit that individually varies the light amount of the printhead; and a toner image density on the photoconductor formed by the printhead. Density detecting means that detects at least one period of the photosensitive member by the density detecting means, and the control means linearly adjusts the light amount of the print head based on the detection result. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the density detecting unit is provided in each of the print heads and is disposed in the vicinity of a joint between adjacent print heads.

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