JP2928193B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color printer, and more particularly, to an image forming apparatus of a type in which a color image is obtained by forming toner images of respective colors on a photosensitive member so as to overlap each other. About.

[0002]

2. Description of the Related Art A color printer includes a photoreceptor that moves in one direction at a constant period, and a plurality of exposing units arranged in the moving direction of the photoreceptor. There is a type in which a color image is obtained by superimposing images on each other. The exposure unit is provided with a number corresponding to the number of color separations of a color image, and each exposure unit has a number of light emitting diodes (hereinafter, referred to as LEDs) arranged in a direction substantially orthogonal to the moving direction of the photoconductor. Are arranged. Such an exposure device scans the photosensitive member in one direction by sequentially emitting light in one direction in each LED.

The LEDs of the exposure device are arranged at a very small interval from each other, and each exposure device emits light while sequentially emitting light in the scanning direction based on color-specific data for each line in the image data. Expose the body. When the first exposing device forms a latent image on the photoreceptor, a developing device corresponding to the exposing device develops the latent image to form a first color toner image. The same toner image forming process is sequentially performed by the other exposing units and developing units, and toner images of the respective colors are superimposed and formed at the synchronous positions of the photoconductors.

[0004] In the above-mentioned conventional color printer, it is difficult to assemble the exposure unit to the printer body while strictly aligning the LEDs at minute intervals. If the positions of the LEDs of the respective exposure devices are shifted from each other, the positions where the dot patterns of the latent images corresponding to the respective separated colors are shifted from each other will cause a problem that the color image is disturbed. A writing device for improving this problem is described in, for example, Japanese Patent Application Laid-Open No. Hei 5-84972. The writing device described in the publication has a plurality of exposure units arranged in the moving direction of the photoconductor, and each exposure unit is provided with a larger number of LEDs than the number of output dots in the scanning direction. In the writing device, a plurality of vertical reference lines extending in the moving direction of the photoconductor are provided at equal intervals, and L
By performing light emission while selecting the ED, correction between the respective exposure units in the scanning direction is performed. Also, by providing a horizontal reference line in the moving direction and changing the light emission timing by a time corresponding to the distance between each selected LED and the horizontal reference line, correction between the exposure units in the moving direction can be performed. Do.

In the above-described writing apparatus, LEs arranged in the scanning direction are used.
A method of dividing D into blocks and emitting light is not adopted. Therefore, for example, in a case where the selected LEDs are controlled to simply emit light sequentially in the scanning direction, the dot pattern formed by the LEDs that sequentially emit light from one end to the other end is inclined at the same angle. It becomes longer in the moving direction of the photoconductor.

In view of this, a color in which the length of a dot pattern formed at a time in the moving direction is reduced by dividing the LEDs arranged in the scanning direction into a plurality of blocks and emitting the LEDs sequentially for each block. Printers have been proposed. FIG. 5 is a plan view schematically showing a main part of an image forming unit of the color printer. FIG. 5 shows only exposure units 30b and 31b corresponding to yellow and magenta, which are color separations of a color image. Exposure units corresponding to other separation colors are omitted. Referring to FIG.
The depiction of b and 31b with respect to each other by one LED is for convenience of explanation. This shift causes a shift of one dot in one direction on the photoconductor 17. Such a shift is caused by an error in accuracy of a member for assembling the exposure units 30b and 31b to the printer main body.

The exposing units 30b and 31b are arranged at predetermined intervals in the moving direction A in relation to the endless belt-shaped photosensitive member 17 moving in the direction of arrow A. Exposure unit 30
b and 31b are provided with LEDs 40a to 40o and LEDs 41a to 41o, respectively, arranged at minute intervals in the scanning direction. The control unit (not shown) controls the exposing device 30b such that five consecutive LEDs 40a to 40d from the reference position (D1).
40e, 40f to 40j and 40k to 40o are recognized as individual LED groups B1, B2 and B3, respectively. Each LE based on the color-specific data for one line in the image data
From the second D2, the third D3, and the fourth D4 among the boundary portions D1 to D4 of the D group, light is emitted sequentially toward the front boundary portions D1, D2, and D3, respectively. Control. In the exposure device 31b, the reference position (D
5) continuous LEDs 41a to 41e from 1), 4
1f to 41j and 41k to 41o are recognized as individual LED groups B1, B2, and B3, respectively, and are controlled in the same manner as the exposure unit 30b.

When the exposure is started based on the data for one line, each LED sequentially emits light from the right side to the left side in the drawing of the LED groups B1 to B3. During this time, since the photoconductor 17 moves in the movement direction A, the dot patterns Y and M that are slightly inclined in the same direction A are formed in the print area P of the photoconductor 17 by the exposure units 30b and 31b. . In FIG. 5, for convenience, the formation positions of the dot patterns Y and M are shifted in the movement direction A, but actually, they are formed so as to overlap each other using a time difference.

FIG. 6 is a plan view schematically showing a dot pattern formed by overlapping using the exposure units 30b and 31b. 40c ′ to 40m ′ and 41d ′ to
40n ′ are LEDs 40 located in the print area P, respectively.
The dots are formed by c to 40 m and 41 d to 40 n. Since the exposing devices 30b and 31b are shifted from each other by one LED in the scanning direction, as shown in the figure, the dot patterns Y and M cause a color shift in a state shifted by one dot in the scanning direction, respectively. ing.

[0010]

SUMMARY OF THE INVENTION Dot patterns Y and M
Overlap, the dots 40c 'and 41d' and the dot 4
0d 'and 41e', dots 40f 'to 40i' and 4
1g 'to 41j', dots 40k 'to 40m' and 41
1 ′ to 41n ′ are slightly shifted in the movement direction A, respectively.
However, the dot 40e 'formed first and the dot 41f' formed last are farthest apart from each other at the start of exposure, so that they are greatly shifted in the moving direction A. This phenomenon similarly occurs between the dots 40j 'and 41k'. The distance a traveled by the photoconductor 17 from when the first LED of the LED group emits light to when the last LED of the adjacent LED group emits light is a shift amount delayed by four dots.

As described above, according to the above-described conventional light emission control, a new problem that a color image is particularly disturbed near the boundary portions D2 and D3 of the LED groups B1 to B3 of the respective exposure devices 30b and 31b and the color image is disturbed. Occurs.

In view of the above, the present invention has a plurality of light emitting elements while alleviating the problem that the dot pattern formed by the light emitting elements such as LEDs at one time becomes longer in the moving direction of the photosensitive member. It is an object of the present invention to provide an image forming apparatus capable of obtaining a good color image by minimizing the amount of displacement between dot patterns formed by each light emitting element group as much as possible.

[0013]

In order to achieve the above object, an image forming apparatus according to the present invention comprises: a photosensitive member moving in one direction; and a plurality of exposure means arranged in the moving direction of the photosensitive member.
The color image is formed by exposing the photoconductor by a plurality of light emitting elements arranged in the exposure unit and arranged in a direction substantially perpendicular to the moving direction, and forming toner images of respective colors on the photoconductor by overlapping each other. In a type of image forming apparatus,
The same number of consecutive light emitting elements are recognized as individual light emitting element groups from the corresponding reference position of each exposure means, and the odd numbered light emitting element groups of each light emitting element group are determined based on the color-specific data for each line in the image data. Or, a light emitting number for sequentially setting a light emitting number to a light emitting element sequentially from a light emitting element adjacent to an even-numbered boundary portion to an even-numbered or odd-numbered boundary portion on both sides adjacent to the odd-numbered or even-numbered boundary portion. It is characterized by comprising setting means and light emission control means for sequentially controlling light emission of the light emitting elements of each light emitting element group according to the light emission number.

The light emission control means of the present invention sequentially controls the light emitting elements of each light emitting element group by controlling the light emitting elements corresponding to the light emitting numbers to actually emit light, and controlling the light emitting elements corresponding to the light emitting numbers. Control to obtain only the timing without actually causing the light emitting element to emit light. As a result, unnecessary dots are not formed, and a desired color image can be obtained only by dots of necessary color-specific data.

In the image forming apparatus according to the present invention, the light emitting elements adjacent to the odd-numbered or even-numbered boundaries are directed to the even-numbered or odd-numbered boundaries adjacent to the odd-numbered or even-numbered boundaries. Since the light emitting elements are sequentially controlled to emit light, the dot pattern formed on the photoreceptor is
As a whole, a substantially sine wave (or cosine wave) shape is inclined from every other boundary to the upstream side in the moving direction of the photoconductor. Therefore, even if the boundary to be controlled is slightly shifted in the direction substantially perpendicular to the moving direction of the photoconductor for each exposure device, the dots that should overlap each other do not greatly shift. This alleviates the problem that the dot patterns formed by the light emitting elements at one time become longer in the moving direction of the photoconductor, while reducing the amount of deviation between the dot patterns formed by each light emitting element group as much as possible. Can be done.

Here, it is preferable that the apparatus further comprises a storage means for temporarily storing the image data when the image data is transmitted from the host device.

[0017]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a side view showing a color printer (image forming apparatus) according to an embodiment of the present invention.

The color printer 11 includes a driving roller 12,
Movement direction A by driven roller 13 and guide member 15
An endless belt-shaped photoreceptor 17 rotatably supported on
A paper cassette 20 for accommodating recording paper 19; The color printer 11 further includes a discharge tray 21 on which the discharged recording paper 19 on which an image has been formed is placed, and control means 18 such as a microcomputer. A paper feed roller 22 is provided at the front of the paper feed cassette 20. A timing roller 25 that feeds the recording paper 19 from the paper feed cassette 20 in synchronization with the toner image on the photoreceptor 17 and a toner image on the photoreceptor 17 are recorded on a transport path formed by each guide plate 23. A transfer device 26 for transferring to the paper 19 is provided. A fixing device 27 for thermocompression-bonding the recording paper 19 to which the toner image has been transferred;
A paper discharge roller 29 for discharging the recording paper 19 after fixing onto the paper discharge tray 21 is provided.

At a position facing the surface of the photoconductor 17 facing downward, a number of image forming units 30, 31, 32, 33 corresponding to the number of separated colors of the color image are arranged in the moving direction A of the photoconductor 17. It is arranged in. The image forming units 30 and 31 include a charger 30a, an exposure unit 30b, and a developing unit 30c, respectively.
A charging device 31a, an exposure device 31b, and a developing device 31c are provided. Each of the image forming units 32 and 33 includes a charger 32a, an exposing unit 32b, and a developing unit 32c, and a charging unit 33a, an exposing unit 33b, and a developing unit 33c. Image forming unit 30,
31, 32, and 33 correspond to four types of separation colors, yellow, magenta, cyan, and black, respectively.

FIG. 2 is a plan view schematically showing the main part of the image forming unit of the color printer 11. In the figure, the exposure units 30b corresponding to the separation colors of yellow and magenta, respectively,
Only 31b is shown and other exposure units are omitted. In the figure, the exposure devices 30b and 31b are drawn with a shift of one LED in the scanning direction orthogonal to the movement direction A for the sake of convenience of description. A minute shift occurs. This shift is caused by the exposure unit 3
This is caused by an error in the accuracy of each part when assembling Ob and 31b to the printer body. Exposure units 30b, 31b
Includes LEDs 40a to 40o and LEDs 41a to 41o, which are arranged at predetermined intervals in the movement direction A and are arranged at minute intervals in the scanning direction, respectively, in relation to the photoreceptor 17. On the side of the exposure device 30b, the LED 40
c to 40 m, and the LED 41 d on the side of the exposure unit 31 b.
４０40n are located.

FIG. 4 is a block diagram schematically showing the configuration of the control means 18. As shown in FIG. The control unit 18 includes a storage unit 35 as a storage unit and a calculation unit 36 as a light emission number setting unit.
And a light emission control unit 37 as light emission control means.

The storage unit 35 temporarily stores the image data sent from the host computer 39 as a host device. The calculation unit 36 determines the reference position (D
5) continuous LEDs 40a to 40e from 1), 4
0f-40j and 40k-40o are individually LED
Recognize as groups B1, B2 and B3. Exposure unit 3
5b continuous LED 41a to 41e, 41f to 41j, and 41k to 41b from the reference position (D1) in 1b.
41o are recognized as individual LED groups B1, B2 and B3, respectively. The calculating unit 36 further determines the LEDs 40e, 40f, 4f adjacent to the even-numbered boundaries D2, D4 of each LED group based on the color-specific data for each line in the image data.
0o, 41e, 41f and 41o, the odd-numbered boundary portions D on both sides adjacent to the even-numbered boundary portions D2 and D4.
The light emission number is sequentially set to the LED toward 1, D3. The light emission control unit 37 sequentially controls the light emission of the LEDs of the LED groups B1, B2, and B3 in both of the exposure units 30b and 31b according to the light emission number transmitted from the calculation unit 36.

Next, the exposure means 30 is controlled by the control means 18.
The operation at the time of forming an image by controlling b and 31b will be described.

When image data is sent from the host computer 39 to the control means 18, the image data is stored in the storage unit 35.
Is stored once. Next, the arithmetic unit 36 stores the
Image data from the LEDs 40 adjacent to the boundaries D2 and D4 based on the color-specific data for each line.
Light emission numbers are sequentially set to the LEDs from e, 40f, 40o, 41e, 41f, 41o toward the boundaries D1, D3, respectively.

When printing is started, the light emission control unit 37
According to the light emission number set by the calculation unit 36, the exposure unit 30
LEDs 40e, 40 adjacent to the boundaries D2, D4 of b
The LEDs are sequentially emitted from f, 40o toward the boundaries D1, D3. At this time, the photoconductor 17 is
0a, it moves in the movement direction A in a state of being uniformly charged in advance, so that it is exposed by each LED that emits light sequentially, and a dot pattern Y is placed in the print area P as a latent image corresponding to the first color (yellow). It is formed. This latent image is 1
The image is developed by the developing device 30c as a yellow toner image for the line. LED4 at a position outside printing area P
Oa, 40b, 40n, and 40o do not contribute to the formation of a yellow toner image even if they emit light.

The photosensitive member 17 is further moved while holding the yellow toner image on the peripheral surface, and the photosensitive member 17 is subjected to a second color (magenta) image forming process. That is, the light emission control unit 37 causes the LEDs 41e, 41f, and 41o to sequentially emit light from the LEDs 41e, 41f, and 41o toward the boundaries D1 and D3 according to the light emission number set by the calculation unit 36. At this time, the photoconductor 17 is uniformly charged in advance by the charger 31a and moves in the movement direction A while holding the yellow toner image.
Exposure is performed by the ED, and a dot pattern M is formed in the print area P as a latent image corresponding to the second color. This latent image is developed as a magenta toner image for one line by the developing device 31.
Developed by c. L at a position outside printing area P
The EDs 41a to 41c and 40o do not contribute to the formation of a magenta toner image even if they emit light.

FIG. 3 is a plan view schematically showing a dot pattern formed by being superposed by the exposing devices 30b and 31b. The yellow toner image and the magenta toner image formed in the above steps are mutually shifted by one dot in the scanning direction. Here, in the conventional light emission control described with reference to FIG. 5, the light emission direction of a large number of LEDs is one direction, whereas in the light emission control according to the present invention, the light emission direction in two directions is sequentially separated from the boundary. Light emission shifts. As a result, both toner images are separated from every other boundary part D2, D4.
Has a substantially sine-wave (or cosine-wave) shape as a whole, which is inclined toward the upstream side in the moving direction of the photosensitive member 17 from the center. For this reason, in FIG. 6, the dots 40e 'and 41 formed farthest apart are shown.
f 'and 40j' and 41k 'overlap at almost the same position. Other dots 40c 'and 41d', dots 40d 'and 41e', dots 40f 'to 40i' and 41g 'to 41j', dots 40k 'to 40m' and 4
The dot shift between each of 1l 'to 41n' is shown in FIG.
Is the same as The maximum shift amount between dots in FIG. 2 is a distance b between a dot formed earlier and a dot formed one dot later on the upstream side, and the distance b
Is a / 4 as compared with the shift amount a in FIG.

Actually, the third step is carried out at the formation positions of the yellow toner image and the magenta toner image by the same process.
The cyan toner image of the color and the black toner image of the fourth color are sequentially superimposed and formed. The color toner image formed on the photoconductor 17 is transferred onto the recording paper 19 fed by the timing roller 25 by applying a high voltage from the transfer device 26. The recording paper 19 to which the color toner image has been transferred is thermally fixed by a fixing device 27 and then discharged onto a discharge tray 21 by a discharge roller 29.

As described above, in the color printer 11 according to the present invention, while the problem that the dot patterns Y and M formed while the plurality of LEDs emit light becomes longer in the moving direction A, the LED group The amount of deviation between the dot patterns Y and M formed by B1 to B3 is also reduced as much as possible, and a good color image with extremely small color deviation can be obtained.

The light emission control unit 37 is not limited to the above configuration.
Are the LEDs 40 adjacent to the odd-numbered boundary portions D1 and D3.
a, 40j, 40k, 41a, 41j, 41k, and the like, in which the emission numbers are sequentially set to the LEDs toward the even-numbered boundaries D2, D4 on both sides adjacent to the odd-numbered boundaries D1, D3, respectively. It can also be configured. In this case, the same effect as described above can be obtained.

Although the present invention has been described based on the preferred embodiment, the image forming apparatus such as a color printer of the present invention is not limited to the configuration of the above-described embodiment, but is limited to the above embodiment. An image forming apparatus in which various modifications and changes are made from the configuration of the embodiment is also included in the scope of the present invention.

[0032]

As described above, according to the image forming apparatus of the present invention, while the problem that the dot pattern formed by the light emitting element at one time becomes longer in the moving direction of the photoreceptor is alleviated, a plurality of dot patterns are formed. The amount of deviation between the dot patterns formed by each light emitting element group having the light emitting elements can be reduced as much as possible. This allows
A good color image can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view illustrating a color printer according to an embodiment of the present invention.

FIG. 2 is a plan view schematically showing a main part of an image forming unit of the color printer of FIG.

FIG. 3 is a plan view schematically showing dot patterns formed by overlapping using different exposure devices.

FIG. 4 is a block diagram schematically illustrating a configuration of a control unit in FIG. 1;

FIG. 5 is a plan view schematically showing a main part of an image forming unit of a conventional color printer.

6 is a plan view schematically showing dot patterns formed by using different exposure devices in FIG. 5 in an overlapping manner.

[Explanation of symbols]

 11 Color Printer 17 Photoconductor 30b, 31b Exposure Unit 35 Storage Unit 36 Operation Unit 37 Light Emission Control Unit 39 Host Computer 40a-40o LED 41a-41o LED B1, B2, B3 LED Group

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/44 B41J 2/45 B41J 2/455

Claims (2)

(57) [Claims] 1. A photoconductor that moves in one direction and a plurality of exposure units arranged in the moving direction of the photoconductor, and a plurality of light emitting units arranged in the exposure unit and arranged in a direction substantially orthogonal to the moving direction. An image forming apparatus of a type in which a photoconductor is exposed by an element and a color image is obtained by forming a toner image of each color on the photoconductor so as to overlap each other, wherein each of the plurality of exposure units converts the color image into The same number of light-emitting elements, which are arranged corresponding to each of the constituent colors and are consecutive from the corresponding reference position of each exposure means, are recognized as individual light-emitting element groups, respectively, and color-specific data for one line in the image data. Based on the light emitting elements adjacent to the odd-numbered or even-numbered boundary of each light-emitting element group, the same number toward the even-numbered or odd-numbered boundary on both sides adjacent to the odd-numbered or even-numbered boundary of An image forming apparatus comprising: a light emitting number setting unit configured to sequentially set a light emitting number for each of the optical elements; and a light emitting control unit configured to sequentially control light emission of the light emitting elements of each light emitting element group according to the light emitting number. . 2. The image forming apparatus according to claim 1, further comprising storage means for temporarily storing the image data when the image data is transmitted from a host device.