JP2000071508A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce generation of vertical stripes on the screen even in case that the light amount distribution in LED elements in irregular. SOLUTION: In forming an electrostatic latent image on a light sensitive member by the light emission of a large number of LED elements arranged on lines controlled according to an image data so as to be lit for emitting a light, a plurality of rows of light writing arrays comprising an LED array with the LED elements gathered and a lens array are provided so that dots 23 are formed in the sub scanning direction by the plurality of rows of the light writing arrays by switching the light writing arrays to be light-controlled. Since an unavoidable irregularity is generated in the light amount distribution in the LED elements in each light writing array, generation of vertical stripes comprising a continuous white stripe or black stripe in the sub scanning direction can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printer for forming an image by electrophotography using an LED array head,
The present invention relates to an image forming apparatus such as a digital copying machine and a facsimile and an image forming method.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus for forming an image by electrophotography, a laser light source and a polygon mirror for deflecting and scanning a laser beam are used as optical writing means for optically writing on a photosensitive member having a photosensitive layer. The mainstream is to use a laser scanning optical system based on the above. On the other hand, in recent years, in order to reduce the size and simplification of the entire apparatus, an image forming apparatus using an LED array head that combines an LED array including a large number of LED elements and a lens array as an optical writing unit has been developed. Has also attracted attention. The LED array is configured by arranging a large number of LED elements on a straight line. By controlling the lighting of each LED element according to image data, optical writing is performed on the photoconductor. An electrostatic latent image is formed on the image.

[0003]

However, in the LED array, it is practically impossible to manufacture all the LED elements so as to have uniform characteristics. For this reason, as illustrated in FIG. 11, there is a problem that the dot diameter of the dots formed by using the LED array head differs for each LED element. Here, in FIG. 11, each waveform indicates the exposure power in the main scanning direction of the LED array head, and the threshold level indicates a level at which the electrostatic latent image formed on the photoconductor formed by the exposure power is developed. Reference numeral 101 denotes a dot obtained by developing the electrostatic latent image formed on the photoconductor. In FIG. 11, the LED
The figure shows that the dot diameter of the dots formed using the array head differs for each LED element.

[0004] Here, as exemplified in FIG.
In an image forming apparatus using an array, dots are formed by the same LED element in the sub-scanning direction. Therefore, when a variation in dot diameter occurs, a vertical streak occurs in a line image in the sub-scanning direction. There is an inconvenience. The vertical streak includes a white streak in which an image is lost in white when the interval between dots is too large, and a black streak in which the image density becomes too high when the dot overlaps with the dot.

[0005] In addition, variations in dot diameter appear as variations in density on a formed image, which also has the disadvantage of deteriorating image quality.

[0006] An invention of an image forming apparatus in which the amount of light of each LED element is made uniform has been made, and is disclosed in, for example, Japanese Patent Application Laid-Open Nos. Hei 5-4376 and Hei 5-50653. However, the light emitted by the LED elements is radiated onto the photoreceptor through the lens array, thereby forming an electrostatic latent image on the photoreceptor. It is impossible to equalize the light amount distribution of all the dots due to variations and the like. Therefore, the technique of equalizing the light amount of each LED element does not solve the above-mentioned problem.

An object of the present invention is to provide an image forming apparatus capable of reducing the occurrence of vertical stripes on an image even when the light amount distribution in each LED element varies.

Another object of the present invention is to provide an image forming apparatus capable of reducing variations in image density even when variations in the light amount distribution in each LED element occur.

[0009]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: controlling a plurality of LED elements arranged on a line to emit light by controlling lighting according to image data; In an image forming apparatus configured to form an electrostatic latent image thereon, an LED in which LED elements are assembled
A plurality of optical writing arrays each composed of an array and a lens array are provided, and the optical writing array to be controlled for lighting is switched.

Accordingly, dots are formed by a plurality of rows of optical writing arrays in the sub-scanning direction. In this case, in each optical writing array, there is an unavoidable variation in the light amount distribution in each LED element, so that such a variation may cause continuous white stripes or black stripes in the sub-scanning direction. And therefore
The occurrence of vertical stripes is reduced.

According to a second aspect of the present invention, there is provided an image forming apparatus having an LE in which a photosensitive member and a plurality of LED elements are arranged on a line.
A plurality of rows of optical writing arrays, each of which has a D array and a lens array, and is arranged opposite to the photosensitive member;
An LED array drive unit for controlling the lighting of the D element and a selection unit for switching an optical writing array for controlling the lighting are provided.

Therefore, dots are formed by a plurality of rows of optical writing arrays in the sub-scanning direction. In this case, in each optical writing array, there is an unavoidable variation in the light amount distribution in each LED element, so that such a variation may cause continuous white stripes or black stripes in the sub-scanning direction. And therefore
The occurrence of vertical stripes is reduced.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the optical writing array for lighting control is switched at a cycle in which one line is a minimum unit.

Therefore, since image data is handled with one line as a minimum unit, image processing control is facilitated.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the optical writing array for controlling lighting is:
Switching is performed at a cycle of one line.

Accordingly, since the image data is handled in units of one line, the driving control of the LED array is facilitated.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, the optical writing array for controlling lighting is:
It can be switched at random intervals.

Therefore, the occurrence of regular dot dropouts and overlaps is avoided, and the occurrence of vertical stripes is reduced.

The invention according to claim 6 is the invention according to claims 1 to 5
The image forming apparatus according to any one of the above, further comprising a dot position adjusting unit that adjusts a dot position in the main scanning direction for each of the plurality of rows of optical writing arrays.

Therefore, displacement of each LED array in the main scanning direction due to provision of a plurality of LED arrays is prevented.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the dot position adjusting means adjusts the position of the optical writing array of one row less than the number of rows of the optical writing array.

Therefore, by adjusting the position of the optical writing array with reference to the optical writing array having no dot position adjusting means, the labor of the adjustment operation can be reduced by one optical writing array.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the plurality of rows of optical writing arrays are formed separately with a support, and the dot position adjusting means is provided separately. The support of the optical writing array formed of the body is adjusted in the main scanning direction.

Therefore, by adjusting the position of the separate optical writing array, the displacement of each LED array in the main scanning direction due to the provision of a plurality of LED arrays can be prevented.

[0025] The ninth aspect of the present invention relates to the first to fifth aspects.
In the image forming apparatus according to any one of the above, the plurality of rows of optical writing arrays are formed separately.

Therefore, a plurality of rows of optical write heads can be easily obtained without requiring a design change in the optical write array itself.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the image data is binary data representing one dot in binary.

Therefore, even under the optical writing condition in which the vertical streak is most likely to occur, the occurrence of the vertical streak is surely reduced.

According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, there is provided gradation means for performing gradation expression by an area gradation method in accordance with image data including gradation data. .

Therefore, even under such an optical writing condition in which the image density variation tends to occur, the image density variation is reduced.

According to a twelfth aspect of the invention, there is provided an image forming method comprising:
In an image forming method in which a large number of LED elements arranged on a line are controlled to emit light in accordance with image data to emit light, and an electrostatic latent image is formed on a photoreceptor by light emission of the LED elements, a plurality of rows of LEDs are provided. The LED element row to be controlled for lighting is switched from the element row.

Accordingly, a plurality of rows of LEs are provided in the sub-scanning direction.
Dots are formed by the D element rows. In this case, in each LED element row, there is a practically unavoidable variation in the light amount distribution in each LED element. Therefore, such a variation causes white streaks or black streaks to continue in the sub-scanning direction. Therefore, the occurrence of vertical stripes is reduced.

According to a thirteenth aspect of the present invention, in the image forming method according to the twelfth aspect, the optical writing array to be controlled for lighting is switched at a cycle in which one line is a minimum unit.

Accordingly, since image data is handled with one line as a minimum unit, image processing control is facilitated.

According to a fourteenth aspect of the present invention, in the image forming method according to the thirteenth aspect, the optical writing array for lighting control is switched at a cycle of each line.

Therefore, since the image data is handled in units of one line, the drive control of the LED array is facilitated.

According to a fifteenth aspect of the present invention, in the image forming method according to the thirteenth aspect, the optical writing array for lighting control is switched at random intervals.

Therefore, the occurrence of regular dot dropouts and overlaps is avoided, and the occurrence of vertical stripes is reduced.

According to a sixteenth aspect of the present invention, in the image forming method according to any one of the twelfth to fifteenth aspects, the image data is binary data representing one dot in binary.

Therefore, even under such an optical writing condition that vertical stripes are most likely to occur, the occurrence of vertical stripes is reliably reduced.

According to a seventeenth aspect of the present invention, in the image forming method according to any one of the twelfth to sixteenth aspects, gradation expression is performed by an area gradation method in accordance with image data including gradation data.

Therefore, even under the optical writing condition in which such image density variation tends to occur, the image density variation is reduced.

[0043]

An embodiment of the present invention will be described with reference to the drawings. This embodiment is an example of application to an LED array printer.

FIG. 1 is a schematic diagram showing a schematic structure of a writing unit of the LED array printer 1. Two LED array heads 3 (3
a, 3b) are provided. These LED array heads 3 include an LED array in which a large number of LED elements 4 (see FIG. 3) are arranged in a straight line, and a lens array interposed between the LED array and the photoconductor 2. It is constituted by an optical writing array (not shown except for the LED element 4). Each L in each LED array head 3
The ED elements 4 are connected to respective LED array control units 6 (in the figure, an LED array control unit A and an LED array control unit) to which image data is transferred via a selector 5 that generates a select signal SEL (see the timing chart of FIG. 7). (Indicated by a section B) to emit light. At this time, each LE
The D array controller 6 operates upon receiving necessary signals transmitted from the controller 7 having a microcomputer configuration. In other words, the main scanning line synchronization signal / LSYNC from the controller unit 7 is used as a trigger to trigger an external device, for example,
Image data is sent from the frame memory, the scanner, or the like to the LED array control unit 6 for each main scanning line, and each LED element 4 in the LED array emits light according to the image data. Then, the emitted light is irradiated and imaged on the photoconductor 2 through the lens array to form an electrostatic latent image on the photoconductor 2.

FIG. 2 is a block diagram showing a circuit configuration of the LED array drive unit 8 included in the LED array control unit 6. The LED array driving unit 8 includes a shift register 9,
Latch 10, AND gate 11, and LED driver 1
2 is a basic circuit element. The shift register 9 has L
Oscillator 13 included in ED array control unit 6 (see FIG. 3)
"0" by the clock signal CLOCK output from
Alternatively, 1-dot binary image data of “1” is stored in a FIFO memory 14 (FIFO memory) included in the LED array control unit 6.
O: First-In First-Out) via dot data DATA
, And operates internally to send each dot data DATA to the built-in register. n
When all of the dot data DATA are sent, the latch 10 latches the dot data DATA.
When the strobe pulse STB is input to the AND gate 11, only the LED element 4 corresponding to the image data (dot data DATA) of "1" emits light by the LED driver 12 for the width of the strobe pulse STB (FIG. 4). Timing chart).

FIG. 3 is a block diagram showing a circuit configuration of the LED array control section 6. First, the LED array controller 6
Fetches one-dot binary image data for one line from the external device by the FIFO memory 14. This FI
The FO memory 14 uses the main scanning line synchronizing signal / LSYNC as a trigger in the controller 7 to trigger the oscillator 13
The image data is sequentially transmitted as dot data DATA to the LED array driving unit 8 as dot data DATA by the clock signal CLOCK generated from (see the timing chart of FIG. 4). At this time, the LED array driving unit 8 is also reset by the main scanning line synchronization signal / LSYNC from the controller unit 7. In the LED array controller 6, a strobe pulse generator 15 is connected to input a strobe pulse STB to the AND gate 11 of the LED array driver 8. The strobe pulse generation unit 15 is configured by, for example, a counter, a comparator, and the like, and periodically generates a strobe pulse STB (see a timing chart in FIG. 4). The strobe pulse STB generated by the strobe pulse generator 15 is input to the AND gate 11 of the LED array driver 8. As a result, only the LED element 4 corresponding to the image data (dot data DATA) of “1” is supplied by the LED driver 12 to the strobe pulse ST.
Light is emitted for the width of B (see the timing chart of FIG. 4). Thus, the photoconductor 2 is exposed according to the image data, and an electrostatic latent image is formed on the photoconductor 2. The electrostatic latent image thus formed on the photoreceptor 2 is developed and transferred by an electrophotographic process, so that an image is formed on a recording medium (not shown) such as recording paper in accordance with image data.

Here, in FIG. 3, the LED array controller 6
3 shows the circuit configuration of only the LED array control unit A (see FIG. 1), but the LE connected to the selector 5
The D array controller B has exactly the same circuit configuration as the LED controller A shown in FIG.

FIG. 5 shows the LED array head 3 and its dot position adjusting means. (a) is a plan view thereof, and (b) is a side view thereof. First, each LED array head 3 is supported by a support 16 via a support structure 17. In the support structure 17, a pair of pins 19 provided in the LED array head 3 is inserted into a pair of long holes 18 formed in the support portion 16 and elongated in the main scanning direction, and these pins 19 are grasped by the catcher 20. It is constituted by. With such a structure, the LED array head 3 is movable in the main scanning direction, that is, the arrangement direction of a large number of LED elements, within a range in which the pin 19 moves in the elongated hole 18. And
A leaf spring 21 is interposed between the support 16 and one side of the LED array head 3, and the LED array head 3 is urged in one direction by the extension force of the leaf spring 21. Further, the LED array head 3 for such a biasing direction
A micrometer 22 is provided between the other side of the LED array head 3 and the support 16 so as to restrict the movement of the LED array head 3. Therefore, the position of the LED array head 3 can be finely adjusted by the micrometer 22 in the main scanning direction. Here, the dot position adjusting means is configured.

FIG. 6 is a schematic diagram showing the exposure power in the main scanning direction and the dot shapes in the main scanning direction and the sub-scanning direction obtained when only a single LED array head 3 is used. 6, each waveform indicates the exposure power of the LED array head 3 in the main scanning direction, and the threshold level indicates a level at which the electrostatic latent image formed on the photoconductor formed by the exposure power is developed. The same). Reference numeral 23 denotes dots obtained by developing the electrostatic latent image formed on the photoconductor 2. FIG. 6 shows a state in which the dot diameter of the dots 23 formed by using a single LED array head 3 is different for each LED element 4. For this reason, as shown in FIG. 6, due to the variation in the diameter of the dots 23 in the main scanning direction, a vertical streak occurs in the line image in the sub-scanning direction. In other words, a white streak in which an image becomes white due to an excessively large interval between the dots 23 and a black streak in which the image density becomes too high due to the overlapping of the dots 23 is formed.

From the above, in the present embodiment,
A drive control process of switching the LED array drive unit 6 to be driven and controlled to the LED array drive unit A and the LED array drive unit B line by line is performed. FIG. 7 is a timing chart showing a select signal and an image data transfer state for each LED array drive unit. FIG. 8 is a schematic diagram showing exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction.

The controller unit 7 having a microcomputer configuration sends a select signal S to the selector 5 at the timing of the falling edge of the main scanning line synchronizing signal / LSYNC.
Output EL. The select signal SEL is a binary signal of “H” or “L”. When the selector 5 receives the “H” select signal SEL, the LED array driving unit A
When the select signal SEL of “L” is received, switching is performed so as to send the image data to the LED array driving unit B. Here, the function of the selection means is executed. Such control is as shown in the timing chart of FIG.

By such drive control of each section, each LE is controlled.
The array shape of the dots 23 formed by the LED array heads 3 driven and controlled by the D array drive unit 6 is formed by the LED array head 3 driven and controlled by the LED array drive unit A, as shown in FIG. 23a to be driven and LE driven and controlled by the LED array driving unit B
The array shape is such that the dots 23b formed by the D array head 3 repeat every line. In FIG.
The difference in the diameter of the dot 23 between the dot 23a and the dot 23b on the same sub-scanning line is due to various variations in the LED elements 4 and variations in the focal depth of the lens array and the like. It is virtually unavoidable. In the LED array printer 1 of the present embodiment, such a variation naturally occurs, so that white stripes and black stripes do not continue in the sub-scanning direction, and vertical stripes do not occur. Reduced. Thereby, the image quality is improved.

Here, the switching of the LED array head 3 contributing to image formation is executed in a cycle for each line by the drive control of the controller unit 7. For this reason, since the image data is handled with one line as a minimum unit,
Image processing control in the controller unit 7 is facilitated.
Moreover, since the image data is handled in units of one line, the drive control of the LED array head 3 by the controller unit 7 is further facilitated.

The position of the LED array head 3 is adjustable in the main scanning direction. Therefore, each LED array head 3 is provided by providing a plurality of LED array heads 3.
In the main scanning direction can be prevented. In this case, if one of the LED array heads 3 is not provided with the dot position adjusting mechanism and the other LED array head 3 is provided with the dot position adjusting mechanism, the LED array head 3 having no dot position adjusting means is provided. By adjusting the position of the LED array head 3 on the basis of the above, the labor of the adjustment operation is reduced by one LED array head 3. In the present embodiment, since the two optical writing arrays each including the LED array and the lens array are separately formed as the two LED array heads 3, the position adjustment of each optical writing array becomes easy, and therefore, Is also simplified. The fact that the two optical writing arrays are separately configured as the two LED array heads 3 means that the optical writing array itself does not need to be changed in design. Can be obtained.

Further, in the LED array printer 1 of the present embodiment, binary data expressing one dot in binary is used as image data. For this reason, image formation is performed under optical writing conditions where vertical stripes are most likely to occur.
Even under such conditions, the occurrence of vertical stripes is reliably reduced.

In the embodiment, image data that does not represent one dot in binary, for example, image data having density gradation information, is used as image data.
An image may be formed using such image data.

In the embodiment, a structure in which two optical writing arrays each including an LED array and a lens array are provided in one LED array head 3 may be employed. The number is not limited to two, but may be three or more.

Further, in implementation, two LEDs
The switching timing of the array head 3 may not be performed using one line as the minimum unit.

FIGS. 9 and 1 show a second embodiment of the present invention.
Description will be made based on 0. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

FIG. 9 is a timing chart showing a select signal and an image data transfer state to each LED array driving unit. FIG. 10 is a schematic diagram showing exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction. It is. In the present embodiment, a random number generator is provided in the controller section 7, and the type of the select signal SEL generated at the falling edge timing of the main scanning line synchronization signal / LSYNC and output to the selector 5 is random. That is, the select signal SEL is a binary signal of “H” or “L”, but “H” and “L” are not repeated alternately, but “H” and “L” are randomly. appear. An example of such a select signal SEL is as shown in the timing chart of FIG.

As a result of such control, as shown in FIG. 10, the array shape of the dots 23 formed by the LED array heads 3 driven and controlled by the LED array drive units 6 is shown in FIG. L driven and controlled
The dots 23a formed by the ED array head 3 and the dots 23b formed by the LED array head 3 driven and controlled by the LED array driving unit B have an array shape in which one line is repeated at irregular intervals. Therefore, as in the case of the first embodiment, the occurrence of vertical stripes is reduced. Thereby, the image quality is improved.

Next, a third embodiment of the present invention will be described. The same parts as those in the first embodiment or the second embodiment are denoted by the same reference numerals, and the description is omitted.

In the present embodiment, the image data includes gradation information, and the controller 7 drives the LED array so as to realize gradation expression by the area gradation method based on such gradation information. The drive of the unit 8 is controlled. in this case,
As the area gradation method, a known method such as a dither method or an error diffusion method is employed. Then, when performing such an area gradation method, in the present embodiment, the switching processing of the LED array head 3 of the first embodiment or the second embodiment is performed. Accordingly, even under an optical writing condition in which the image density tends to vary, such as in the area gradation method, the variation in the image density is reduced.

[0064]

According to the first aspect of the present invention, there is provided an image forming apparatus comprising:
Since a plurality of optical writing arrays each including an LED array in which LED elements are assembled and a lens array are provided to switch the optical writing arrays for lighting control, it is not possible to avoid the light quantity distribution in each LED element in each optical writing array. By utilizing the occurrence of the variation, it is possible to avoid a situation in which white stripes and black stripes continue in the sub-scanning direction due to the occurrence of such variation, and it is possible to reduce the occurrence of vertical stripes.

According to a second aspect of the present invention, there is provided an image forming apparatus in which a photoconductor and a plurality of LED elements are arranged on a line.
A plurality of rows of optical writing arrays, each of which has a D array and a lens array, and is arranged opposite to the photosensitive member;
Since there is provided an LED array drive unit for controlling the lighting of the D element and a selecting means for switching the optical writing array for controlling the lighting, it is possible to utilize the inevitable variation in the light amount distribution of each LED element in each optical writing array. By doing so, it is possible to prevent white and black streaks from continuing in the sub-scanning direction due to the occurrence of such variations.
The occurrence of vertical stripes can be reduced.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the optical writing array to be controlled for lighting is switched at a cycle in which one line is a minimum unit. Minutes can be treated as the minimum unit, and therefore, image processing control can be facilitated.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, an optical writing array for controlling lighting is provided in one.
Since switching is performed in a cycle of each line, image data can be handled in units of one line.
The drive control of the LED array can be facilitated.

According to a fifth aspect of the present invention, in the image forming apparatus of the third aspect, the optical writing array to be controlled to be turned on is switched at a random cycle, thereby avoiding the occurrence of regular dot omission and overlap. Therefore, the occurrence of vertical stripes can be reduced.

The invention according to claim 6 is the invention according to claims 1 to 5
In the image forming apparatus according to any one of the above, since a dot position adjusting unit that adjusts a dot position in the main scanning direction is provided for each of the plurality of rows of optical writing arrays, a main unit of each LED array by providing a plurality of LED arrays The displacement in the scanning direction can be prevented, and therefore, a high-quality image can be obtained.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the dot position adjusting means adjusts the position of the optical writing array of one row less than the number of rows of the optical writing array. Therefore, by adjusting the position of the optical writing array with reference to the optical writing array having no dot position adjusting means, it is possible to reduce the labor of the adjustment work by one optical writing array.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the plurality of rows of optical writing arrays are formed separately with a support, and the dot position adjusting means is provided separately. Since the position of the support of the optical writing array formed of the body is adjusted in the main scanning direction, the position of the separate optical writing array is adjusted to provide a plurality of LED arrays. The displacement in the main scanning direction can be prevented.

The ninth aspect of the present invention relates to the first to fifth aspects.
In the image forming apparatus according to any one of the above, since the plurality of rows of optical writing arrays are formed separately, it is possible to easily obtain a plurality of rows of optical writing heads without requiring a design change to the optical writing array itself. it can.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the image data is binary data representing one dot in binary.
Even under such an optical writing condition where vertical streaks are most likely to occur, the occurrence of vertical streaks can be reliably reduced.

According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, there is provided a gradation means for performing gradation expression by an area gradation method in accordance with image data including gradation data. Therefore, even under the optical writing condition in which such image density variation easily occurs, the image density variation can be reduced.

According to a twelfth aspect of the present invention, there is provided an image forming method comprising:
Since the LED element rows to be controlled to be turned on are switched from among the plurality of LED element rows, the use of the fact that the inevitable variation in the light quantity distribution in each LED element occurs in each LED element row makes use of this. It is possible to avoid that white stripes and black stripes continue in the sub-scanning direction due to the occurrence of various variations, and to reduce the occurrence of vertical stripes.

According to a thirteenth aspect of the present invention, in the image forming method according to the twelfth aspect, the optical writing array to be controlled for lighting is switched at a cycle of one line as a minimum unit. It can be handled as a minimum unit, and therefore, image processing control can be facilitated.

According to a fourteenth aspect of the present invention, in the image forming method of the thirteenth aspect, the optical writing array to be controlled for lighting is switched at a cycle of one line, so that image data is handled in units of one line. Therefore, driving control of the LED array can be facilitated.

According to a fifteenth aspect of the present invention, in the image forming method of the thirteenth aspect, the optical writing array to be controlled to be turned on is switched at a random cycle, thereby avoiding the occurrence of regular dot omission or overlap. Can be
Therefore, generation of vertical stripes can be reduced.

According to a sixteenth aspect of the present invention, in the image forming method of any one of the twelfth to fifteenth aspects, the image data is binary data representing one dot in binary. The occurrence of vertical streaks can be reliably reduced even under optical writing conditions in which streaks easily occur.

According to a seventeenth aspect of the present invention, in the image forming method according to any one of the twelfth to sixteenth aspects, there is provided a gradation means for performing gradation expression by an area gradation method in accordance with image data including gradation data. Therefore, even under the optical writing condition in which such image density variation easily occurs, the image density variation can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic structure of an LED array printer as a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a circuit configuration of an LED array driving unit.

FIG. 3 is a block diagram illustrating a circuit configuration of an LED array control unit.

FIG. 4 is a timing chart showing the generation timing of each signal for driving an LED element based on dot data written in a shift register in the LED array driving section.

5A is a plan view and FIG. 5B is a side view of the LED array head and its dot position adjusting means.

FIG. 6 is a schematic diagram showing exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction obtained when only a single LED array head is used.

FIG. 7 is a timing chart showing a select signal and an image data transfer state for each LED array driving unit.

FIG. 8 is a schematic diagram showing exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction.

FIG. 9 is a timing chart showing a select signal and a state of transferring image data to each LED array drive unit according to a second embodiment of the present invention.

FIG. 10 is a schematic diagram illustrating exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction.

FIG. 11 is a schematic diagram showing, as an example of the related art, exposure power in the main scanning direction and dot shapes in the main scanning direction and the sub-scanning direction.

[Explanation of symbols]

 2 Photoconductor 4 LED element 8 LED array drive unit

Claims (17)

[Claims] A plurality of LED elements arranged on a line are controlled to emit light in accordance with image data to emit light;
In an image forming apparatus configured to form an electrostatic latent image on a photoconductor by light emission of a D element, a plurality of rows of an optical writing array including an LED array in which the LED elements are assembled and a lens array are provided, and the lighting control is performed. An image forming apparatus characterized by switching an optical writing array. 2. A photoreceptor, a plurality of rows of light writing arrays which are arranged opposite to the photoreceptor and include an LED array and a lens array in which a plurality of LED elements are arranged on a line, and the LED according to image data. LED for lighting control of the element
An image forming apparatus comprising: an array driving unit; and a selection unit that switches the optical writing array to be controlled for lighting. 3. The optical writing array for controlling lighting includes:
2. The method of claim 1, wherein the switching is performed in a cycle having a line as a minimum unit.
Or the image forming apparatus according to 2. 4. The optical writing array for controlling lighting includes:
The image forming apparatus according to claim 3, wherein the switching is performed in a cycle for each line. 5. The image forming apparatus according to claim 3, wherein the optical writing array for controlling lighting is switched at a random cycle. 6. The image forming apparatus according to claim 1, further comprising a dot position adjusting unit that adjusts a dot position in the main scanning direction for each of the plurality of rows of the optical writing arrays. 7. The image forming apparatus according to claim 6, wherein the dot position adjusting means adjusts the position of the optical writing array in a row one less than the number of columns of the optical writing array. 8. The optical writing array of a plurality of rows is formed separately with a support, and the dot position adjusting means main-scans the support of the optical writing array formed separately. The image forming apparatus according to claim 6, wherein the position is adjusted in the direction. 9. The image forming apparatus according to claim 1, wherein the plurality of rows of the optical writing arrays are formed separately. 10. The image forming apparatus according to claim 1, wherein said image data is binary data representing one dot in binary. 11. The image forming apparatus according to claim 1, further comprising: gradation means for performing gradation expression by an area gradation method in accordance with the image data including gradation data. 12. A plurality of LEDs arranged on a line
The device is controlled to emit light according to image data to emit light,
An image forming method in which an electrostatic latent image is formed on a photoreceptor by light emission of an ED element, wherein the LED element row to be turned on and off is switched among a plurality of LED element rows. Method. 13. The optical writing array for lighting control,
13. The image forming method according to claim 12, wherein the switching is performed in a cycle with one line as a minimum unit. 14. The optical writing array for lighting control,
14. The image forming method according to claim 13, wherein the switching is performed at a cycle of each line. 15. The optical writing array for controlling lighting includes:
14. The image forming method according to claim 13, wherein the switching is performed at a random cycle. 16. The image forming method according to claim 12, wherein said image data is binary data representing one dot in binary. 17. The image forming method according to claim 12, wherein gradation expression is performed by an area gradation method according to the image data including gradation data.