JPH1158814A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve printing quality without reducing a life of an LED element by a method wherein a shift quantity of an electrostatic latent image in each block in a subscanning direction is reduced, the image is formed on a photosensitive body. SOLUTION: There is provided an image forming apparatus wherein multiple LED elements arranged in a line are divided into plural blocks, the LED elements are controlled to be energized in accordance with image data by shifting the times by each block and an electrostatic latent image is formed on a photosensitive body that moves in a subscanning direction relatively with respect to the LED elements by virtue of the emissions of the LED elements. By paying attention on the fact that the electrostatic latent image formed on the photosensitive body is shifted among each of the blocks in the subscanning direction, a total emission time period of the LED elements per one main scanning line is set to a level not greater than one second of a cycle time of the main scanning line synchronism signal, thereby reducing the shift quantity of the electrostatic latent image formed on the photosensitive body by each block in the subscanning direction.

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.

[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 device, an LED that combines an LED array and a lens array as optical writing means has been used.
An image forming apparatus using an array head 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.

In an image forming apparatus using an LED array head, all (n) LED elements in an LED array are
Each time light emission is performed, the current required for light emission increases, and the current capacity required for the power supply of the device increases. For this reason, there is a problem that the size of the power supply is increased and its cost is increased, and a heat radiation measure is required, so that an LED array head is enlarged and its cost is increased. Therefore,
Conventionally, an LED element is divided into a plurality of blocks, and a time is shifted for each block in one main scanning line.
A technique has been developed in which the element emits light to reduce the current required for light emission of the LED element.

[0004]

However, in the technology of controlling the lighting by dividing the LED element into a plurality of blocks,
Since the LED array head and the photoreceptor move relative to each other in the process of sequentially emitting the LED elements for each block in the main scanning line, the electrostatic latent image formed on the photoreceptor is sub-scanned between the blocks. There is a problem that the printing quality is degraded due to the displacement in the direction.

Japanese Patent Application Laid-Open No. Hei 5-147262 discloses an invention in which one pixel is formed on a photosensitive member by causing an LED element divided into a plurality of blocks to emit light a plurality of times at different times. . As a result, the amount of shift in the sub-scanning direction between the blocks of the electrostatic latent image formed on the photoconductor is reduced. In this case, as the number of times the LED element emits light per pixel increases, the shift amount of the electrostatic latent image between the blocks in the sub-scanning direction decreases, and the printing quality improves. However, an increase in the number of times the LED element emits light per pixel leads to an improvement in printing quality, but has a problem in that the control circuit is complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the print quality by reducing the amount of shift in the sub-scanning direction of each block of an electrostatic latent image formed on a photosensitive member without shortening the life of an LED element. Is to obtain an image forming apparatus capable of performing the above.

[0007]

According to a first aspect of the present invention, there is provided an image forming apparatus, wherein a plurality of LED elements arranged on a line are divided into a plurality of blocks, and the LED elements are shifted in time for each block. Is controlled in accordance with the image data, and LE is controlled.
In an image forming apparatus in which an electrostatic latent image is formed on a photoreceptor relatively moved in the sub-scanning direction with the LED element by light emission of the D element, the total light emission time of the LED element per main scanning line is determined by the main scanning line. It was set to less than half the period of the synchronization signal.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an LED array head including a photosensitive member, a plurality of LED elements arranged on a line, and a lens array; Moving means for relatively moving the body and the LED array head in the sub-scanning direction; and an LED array driving section for dividing the LED elements into a plurality of blocks and controlling the lighting of the LED array by shifting the time for each block according to image data. Control means for setting the total light emission time of the LED elements per main scanning line to １ ／ or less of the period of the main scanning line synchronization signal.

Here, in claims 1 and 2, "LE
The “total light emission time of the D element” is the sum of the light emission times of the LED elements for all blocks.

Therefore, according to the first or second aspect of the present invention, the lighting of the LED elements is controlled so that the time is shifted for each block in one main scanning line. For this reason, the electrostatic latent image formed on the photoconductor is
Since the D element is relatively moved, each block of the LED element is shifted in the sub-scanning direction. On the other hand, according to the first or second aspect of the present invention, the LED per one main scanning line is provided.
The total light emission time of the element is 1 / the cycle of the main scanning line synchronization signal.
Since the time is set as short as 2 or less, the amount of deviation in the sub-scanning direction of each block of the electrostatic latent image formed on the photoconductor is small. Thereby, the print quality is improved.

[0011]

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. An LED array head 2 is provided so as to be in close proximity to a photosensitive member 1 having a photosensitive drum configuration. The photoreceptor 1 is rotatably held by a support mechanism (not shown) and is rotationally driven by a motor (not shown) as a drive source. Accordingly, a moving means for relatively moving the photoconductor 1 and the LED array head 2 in the sub-scanning direction by the support mechanism and the motor is configured. In addition, LED
The array head 2 has a large number of LED elements 3 (see FIG. 2).
Are arranged in a straight line, and a lens array 5 interposed between the LED array 4 and the photoconductor 1. Each LED element 3 in the LED array 4 emits light under the lighting control of the LED array controller 6 to which image data is transferred. At this time, LED
The 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 3 in the LED array 4 is transmitted in accordance with the image data.
Emits light. Then, the emitted light is irradiated and imaged on the photoconductor 1 through the lens array 5 to form an electrostatic latent image on the photoconductor 1. Here, in the present embodiment,
The rotation speed of the photoconductor 1 is set to 180 mm / sec (linear speed). The sensitivity of the photoconductor 1 is 0.13 lux ·
In about s, the potential of the photoconductor 1 drops to 1/2, and 0.23 lu
At about x · s, the potential of the photoconductor 1 drops to 1/5,
The sensitivity is set such that the potential of the photoconductor 1 drops to 1/10 at about lux · s. Further, the light quantity of the LED element 3 is 3 μW, and the light emission time of the LED element 3 is 3 μS.

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
The 1-dot binary image data of “0” or “1” is converted to the LED array control unit 6 by the clock signal CLOCK output from the transmitter 13 included in the ED array control unit 6.
Memory 14 (FIFO: First-In F
DATA as dot data DATA via irst-Out)
It operates in such a manner that the dot data is input sequentially from 1 and each dot data DATA is internally sent to a built-in register. When all the n pieces of 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 3 corresponding to the image data (dot data DATA) of "1" emits light by the width of the strobe pulse STB by the LED driver 12 (see the timing charts of FIGS. 4 and 5).

FIG. 3 is a block diagram showing a circuit configuration of the LED array control unit 6. First, the LED array controller 6
Is the main scanning line synchronization signal / L from the controller unit 7.
Using SYNC (in FIG. 4) as a trigger, the FIFO memory 14 fetches one-dot binary image data for one line from an external device. Also, the FIFO memory 14
Is the main scanning line synchronization signal / L from the controller unit 7.
With SYNC (in FIG. 4 and FIG. 5) as a trigger, the image data is sequentially transmitted as dot data DATA to the LED array driving unit 8 as DATA1 to n by the clock signal CLOCK generated from the transmitter 13 (FIGS. 4 and 5). 5). 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. And LE
In the D array control unit 6, the AND of the LED array drive unit 8
A strobe pulse generator 15 is connected to input a strobe pulse STB to the gate 11. The strobe pulse generator 15 includes, for example, a counter,
It is composed of a comparator and the like, and periodically generates a set of five strobe pulses (see timing charts in FIGS. 4 and 5). The strobe pulse STB generated by the strobe pulse generation unit 15 is LE
The signal is input to the AND gate 11 of the D array driving unit 8.

In this embodiment, the LED element 3 is divided into five blocks for forming one main scanning line, and corresponds to image data (dot data) which is "1" among the LED elements 3 in each block. The LED element 3 emits light only when the corresponding strobe pulse STB rises. In FIG. 4, the strobe pulse STB is shown as a strobe pulse STBＳＴ for convenience. In this case, the strobe pulse STB causes the LED element 3 of the block 1
Is changed to L in block 2 by the strobe pulse STB.
The ED element 3 selectively emits the LED element 3 of the block 3 by the strobe pulse STB, the LED element 3 of the block 4 by the strobe pulse STB, and the LED element 3 of the block 5 by the strobe pulse STB. The correspondence between the strobe pulse STB and the block of the LED element 3 is as follows.
This is realized by dividing the AND gate 11 into five blocks corresponding to each block of the LED element 3 and inputting the strobe pulse STB to the AND gate 11 of each block in the order of. Here, the time during which each of the strobe pulses STB rises is 3 μm.
S, and the light emission time of the LED element 3 that emits light at the rise of each of the strobe pulses STB is set to be equal to or less than half the period of the main scanning line synchronization signal / LSYNC as the total light emission time per main scanning line. ing. Such a setting is performed based on the rotation speed of the photoconductor 1 with the strobe pulse S in the strobe pulse generator 15.
This is achieved by adjusting the output timing of the TB. In this sense, the strobe pulse generator 15 functions as a control unit.

Next, an electrostatic latent image formed on the photoconductor 1 by an amount corresponding to the interval y of each strobe pulse STB due to the movement of the photoconductor 1 and the LED element 3 in the sub-scanning direction due to the rotation of the photoconductor 1 Shifts. For this reason, as shown in FIG. 6, the transfer image TI formed by developing such an electrostatic latent image and transferring it to the transfer paper also shifts in the sub-scanning direction for each block of the LED element 3. Become. On the other hand, in the present embodiment, the LED elements 3 per one main scanning line are used.
Is set to a short time equal to or less than の of the cycle of the main scanning line synchronization signal / LSYNC,
The shift amount y in the sub-scanning direction of the electrostatic latent image formed on the photoconductor 1 is extremely small. Therefore, deterioration of image quality due to a shift in the sub-scanning direction of the electrostatic latent image formed on the photoconductor 1 is small, and a high-quality image can be obtained.

Here, in this embodiment, the LED element 3
Is turned on once per pixel, so that the LED element 3 emits light a plurality of times per pixel to reduce the amount of shift in the sub-scanning direction for each block of the electrostatic latent image.
The control circuit is simplified and the life of the LED element 3 is prolonged.

In the embodiment, by increasing the sensitivity of the photoconductor 1 or increasing the light amount of the LED element 3, a sufficient exposure amount to the photoconductor 1 can be obtained without lowering the rotation speed of the photoconductor 1. And the printing speed can be increased.

Further, in the present embodiment, it is assumed that the capacity of the shift register 9 of the LED array driving section 8 is prepared for image data (dot data) for one main scanning line. On the other hand, in the embodiment, it is also possible to prepare only the capacity (m pieces) corresponding to the LED elements 3 for each block to be lit at a time, in the capacity of the shift register 9. In this case, the FIF
M image data (dot data) from O memory 14
Is transferred to the shift register 9, the latch operation by the latch 10 is executed, the strobe pulse STB is sent to the AND gate 11, and the LED elements 3 of the corresponding block are selectively turned on. The operation of transferring data (dot data) to the shift register 9 and executing the same operation is repeated. Thereby, the capacity of the shift register 9 can be saved.

Further, in the present embodiment, the transfer speed of image data sent from the outside and the LED array driving unit 8
The FIFO memory 14 is used because the transfer speed of the dot data DATA to be sent is different from the transfer speed of the dot data DATA. However, if the transfer speeds of the two data are the same, the FIFO memory 14 need not be used.

[0021]

According to the present invention, when controlling the lighting of the LED elements by shifting the time for each block, the total light emission time of the LED elements per one main scanning line is set to less than half the period of the main scanning line synchronization signal. , The amount of shift in the sub-scanning direction of each block of the electrostatic latent image formed on the photoreceptor can be reduced, so that the print quality can be improved. In addition, since the number of times of lighting of the LED element is one per pixel, the LED element emits light a plurality of times per pixel to reduce the amount of shift in the sub-scanning direction for each block of the electrostatic latent image. By simplifying the control circuit, L
The life of the ED element can be extended.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic structure of a writing unit of an LED array printer as one 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 of writing image data to a FIFO, timing of writing dot data from a FIFO to a shift register, and L based on dot data.
6 is a timing chart showing drive timing of an ED element.

FIG. 5 is a timing chart of writing dot data from a FIFO to a shift register, and L based on the dot data.
6 is a timing chart showing the drive timing of the ED element in more detail.

FIG. 6 is a schematic diagram showing a shift of an LED element for each block in an image formed on a transfer sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 LED array head 3 LED element 4 LED array 5 Lens array 8 LED array drive part 15 Control means

Claims (2)

[Claims] 1. A plurality of LED elements arranged on a line are divided into a plurality of blocks, and lighting control of the LED elements is performed according to image data while shifting the time for each block.
In an image forming apparatus configured to form an electrostatic latent image on a photoconductor that relatively moves in the sub-scanning direction with the LED element by light emission of the LED element, the total light emission time of the LED element per main scanning line An image forming apparatus wherein the period is set to a half or less of a period of a main scanning line synchronization signal. 2. An LED array head comprising: a photoreceptor; a plurality of LED elements arranged on a line; and a lens array; and an LED array head arranged to face the photoreceptor; and the photoreceptor and the LED array head. Moving means for relatively moving in the sub-scanning direction; an LED array driving section for dividing the LED elements into a plurality of blocks and controlling lighting of the LED array by shifting the time for each block in accordance with image data; Control means for setting the total light emission time of the LED element per one half or less of the cycle of the main scanning line synchronization signal.