JPH1081032A - Digital writing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform the distribution of a quantity of light by each of the LED elements of an LED head over a long time. SOLUTION: When a quantity-of-light correction part 518 changes the light emission duty ratio of an LED element (the correction level is calculated) in accordance with a signal for measuring the quantity of light (the detection value of a light emission level of the LED element is shown), the light emission duty ratio is also changed so that the light emission level of another adjacent LED element to the LED element is increased according to necessity (in the case when the detection value below a specified level is found).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital writing device using an LED head as a recording head.

[0002]

2. Description of the Related Art For example, an LED printer is equipped with a digital writing device using a one-dimensional LED head in which a plurality of LED (light emitting diode) elements are arranged in an array at a predetermined density in a main scanning direction as a recording head. The light emission of each LED element of the LED head is controlled in accordance with a signal (digital image information) corresponding to an image to be recorded, and the light information is image-formed and projected on a photoconductor to write an image. ing.

Such an LED printer has high reliability because there is no movable part such as a polygon mirror used in a laser printer. Also, in the case of a wide-width machine that requires large-format print output, an optical space for scanning the light beam in the main scanning direction is not required, and the apparatus can be downsized. It has been replaced.

A laser printer emits (lights) one light source (laser diode) having an output of about 10 mW.
While the light beam is scanned by a polygon mirror, fθ lens, and the like, the LED printer arranges the LED elements in the main scanning direction for each pixel, and emits a current of about 10 mA for each to emit light. I have.

Therefore, when a digital writing device equipped with an LED head is mounted on a printer that mainly outputs characters and has a relatively low image density or a plotter that outputs only line drawings such as figures, the printer or the plotter uses the LED head. Since only on / off control (binary control) for selectively emitting light from each LED element is performed, variation in the amount of light emitted from each LED element does not matter.

However, when a digital copying machine equipped with an LED head is mounted on a digital copying machine, the digital copying machine has a halftone (halftone) such as an original having a lot of black solids such as a poster original or a photograph. Since a large number of originals are sometimes copied, there is a problem in that the variation in the light emission amount of each LED element appears as density unevenness or white stripes.

Therefore, for example, Japanese Patent Application Laid-Open No. 62-200966
As disclosed in Japanese Patent Application Laid-Open No. H10-260, correction data corresponding to the characteristics (variation in the amount of light emission) of an LED array (LED head) is stored in a ROM in advance, and the drive current of each LED element is controlled based on the correction data. By doing, each LE
There has been proposed a device in which the variation in the light emission amount of the D element is reduced to make the light amount distribution uniform.

However, in the device for performing such control, the variation of the light emission amount of each LED element at the time of manufacturing the LED head is measured, and correction data is generated based on the result. In this case, the light emission amount of each LED element varies. In view of the above, there has been proposed an apparatus that detects the light emission amount (light emission luminance) of each LED element and changes the light emission duty ratio of the corresponding LED element according to each detected value to make the light amount distribution uniform. I have.

[0009]

However, such control can be performed when each LED element has deteriorated to some extent with time, but can be performed when any one of the LED elements has changed significantly. Becomes impossible. That is,
Since the light emission amount of the LED element that has changed greatly cannot be corrected, unevenness occurs in the light amount distribution of each LED element, which leads to deterioration of image quality.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in a digital writing device using an LED head as a recording head, the light quantity distribution of each LED element of the LED head can be made uniform over a long period of time. The purpose is to do.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a one-dimensional LED head in which a plurality of LED elements are arranged at a predetermined density in a main scanning direction, and each LED of the one-dimensional LED head.
A digital writing device comprising: a light amount detecting unit for detecting a light emitting amount of each element; and a light amount correcting unit for correcting a light emitting amount by changing a light emitting duty ratio of a corresponding LED element in accordance with each detection value by the unit. In the above, the light amount correcting means is controlled by the LED in accordance with the value detected by the light amount detecting means.
When the light emission duty ratio of the element is changed, the light emission duty ratio of another LED element adjacent to the LED element is changed as necessary.

[0012] For example, the light quantity correction means may change the light emission duty ratio so that the light emission quantity of another LED element adjacent to the LED element increases when the value detected by the light quantity detection means is equal to or less than a predetermined value. It is good to In this case, the predetermined value is set at 50, which is the rated value of the light emission amount of each LED element.
% Is desirable.

[0013]

Embodiments of the present invention will be specifically described below with reference to the drawings. First, an outline of a digital copying machine equipped with a digital writing device according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration example of a digital copying machine according to an embodiment of the present invention.

The digital copying machine includes an image reading device 100 for reading an image of a document, and an image information storage device 3 for storing image information read by the image reading device 100.
00, and a copier main body 2 including a printer device 500 for executing a series of processes for printing (copying) image information stored in the image information storage device 300 on transfer paper.
00 and an operation device 400 for inputting various information.

Next, the image reading apparatus 100 shown in FIG. 2 will be described with reference to FIG. FIG. 3 shows the image reading apparatus 100.
FIG. 2 is a schematic configuration diagram illustrating an example of a mechanism section. When an operator inserts an original from the insertion opening of the image reading apparatus 100, the original is conveyed on the upper surface of the contact glass 2 according to the rotation of the roller 1. Fluorescent lamp 4 is attached to the original being transported.
The reflected light is imaged on a CCD line image sensor (hereinafter simply referred to as “CCD”) 6 which is an image pickup device (photoelectric conversion device) via a lens 5, and an image of a document is read. .

The reflected light from the document imaged on the CCD 6 is converted into an analog image signal there and input to the image amplification circuit 101 in FIG. 2 where it is amplified and synchronized with the clock signal from the synchronization control circuit 105. And output. A
The / D conversion circuit 102 converts the analog image signal amplified by the image amplification circuit 101 into a multi-value digital image signal (digital image information) for each pixel.

The shading correction circuit 103 has an A / D
The digital image information converted by the conversion circuit 102 is subjected to processing for correcting distortion due to uneven light amount, stain on contact glass, uneven sensitivity of the CCD, and the like. The corrected digital image information is subjected to predetermined image processing by the image processing circuit 104, output to the image information storage device 300 as digitally recorded image information, and stored in the image memory unit (page memory) 3.
01 is written.

Further, the digitally recorded image information written in the image memory unit 301 is read out as appropriate and output to the digital writing device 506 of the printer device 500.
LED write control circuit 501 and LED driver circuit 50
The light is converted into infrared light by the LED head 503 via the LED head 2.
Note that control relating to writing and reading of digital recording image information to and from the image memory unit 301 is performed by the system control device 302.

Next, the copying machine main body 200 shown in FIG. 2 will be described with reference to FIG. FIG. 4 is a schematic configuration diagram illustrating an example of a mechanical unit of the copying machine main body 200. This copier body 2
In the figure, reference numeral 26 denotes a charging device for charging the photosensitive drum 25 rotated by a main motor (not shown) to -850V.
This is called a scorotron charger with a grid that charges uniformly.

Reference numeral 503 denotes a one-dimensional LED head in which a plurality of LED elements are arranged in an array at a predetermined density in the main scanning direction, and the light is irradiated on the photosensitive drum 25 via an SLA (Selfoc lens array). Is done. The light emission (lighting) of the LED head 503 is controlled in accordance with digitally recorded image information read from the image memory unit 301 by an LED writing control circuit 501 in FIG. Then, the charge on the photoreceptor surface flows to the ground due to the photoconductive phenomenon and disappears.

Here, in the LED head 503, a portion where the image density of the document is light (the binarized signal is at the non-recording level)
Are not emitted, and the LED elements corresponding to the portion where the image density of the document is high (the binarized signal is the recording level) are emitted. As a result, the non-irradiated portion of the photoreceptor drum 25 has a potential of -850 V and the infrared light radiated portion has a potential of about -100 V, so that an electrostatic latent image corresponding to the density of the image is formed.

The electrostatic latent image is developed by the developing unit 27. That is, the toner in the developing unit 27 is negatively charged by stirring, and the developing bias of −600 V is applied, so that the toner adheres only to the portion irradiated with the infrared light.

On the other hand, the transfer paper 11 (11a, 11b, 11
c) are stored in the three paper feeders 10 (10a, 10a).
b, 10c), and the transfer paper 11 of one of the selected paper feeding devices 10 is fed by a feed roller 12 (1c).
2a, 12b, 12c) and the cutter 13
After being cut to a predetermined length by (13a, 13b, 13c), it passes under the photosensitive drum 25 at a predetermined timing by a registration roller 24, and at this time, the transfer charger 2
3, the toner image is transferred.

The transfer paper on which the toner image has been transferred is then separated from the photosensitive drum 25 by a separation charger 28, transported by a transport belt 31 and sent to a fixing unit 30, where the toner is fixed on the transfer paper. . The transfer paper on which the toner has been fixed is sent to a paper discharge tray 32 and discharged outside the apparatus. A cleaning unit 29 removes residual toner on the photosensitive drum 25.

Next, the operation panel 420 of the operation device 400 shown in FIG. 2 will be described with reference to FIG. FIG. 5 is a layout diagram illustrating a configuration example of the operation panel 420. The operation device 400 includes an operation control circuit 410 and an operation panel 42.
Consists of zero. The operation panel 420 has a start key 42
1, stop key 422, mode clear key 423, setting key 424, numeric keypad 425, paper type designation key 426,
A density adjustment key 427, an image quality adjustment key 428, a paper size key 429, a scaling key 430;
1, a copy number display 432, a magnification display 433, and a document insertable display 434.

Next, the LED write control circuit 501 of FIG. 2 will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration example of the LED write control circuit 501. Digitally recorded image information (hereinafter, referred to as “image data”) input to the copying machine main body 200 by the image reading apparatus 100 is temporarily stored in the image memory unit 301, and as it is, or after data editing / processing, a synchronization signal and The data is input to the LED write control circuit 501 in synchronization with the image clock.

The image data of two lines (the nth line and the (n + 1) th line) simultaneously inputted to the LED write control circuit 501 are stored in the line memory group 512 via the input buffer 511 for each line. Line memory group 51
2 is divided into an odd number (ODD) and an even number (EVEN). Note that this division processing is performed by L
This is performed to lower the processing frequency of the ED head 503.

Then, among the image data stored in the line memory group 512, first the image data of the n-th line,
Subsequently, the image data of the (n + 1) th line is read out by the selector 513 in a time-division manner. Then, the image data of the n-th line is output to the L through the LED driver circuit 502 in FIG. 2 together with a synchronization signal (not shown), a transfer clock, and an enable signal (duty signal) via the output buffer 514.
The data is transferred to the ED head 503.

Thereafter, the same processing is performed on the image data of the (n + 1) th line.
This is performed within the time when each image data of the line and the (n + 3) th line is input and stored in the same line memory group 512, and the above is repeated.

The control timing generator 515 is a CPU (printer CP) in the printer control circuit 504 shown in FIG.
U) to generate various timing signals. The transfer clock control section 516 outputs a transfer clock in synchronization with the control timing signal from the control timing generation section 515.

The light amount control unit 517 synchronizes with the control timing signal from the control timing generation unit 515 and converts the light amount setting signal from the printer CPU and the light amount correction signal for each of the LED elements 604 _{1 to} 604 ₁₄₃₃₆ from the light amount correction unit 518. The respective light emission amounts are corrected based on the respective LED elements 604.
_{1 to} 604 An enable signal for determining the time (light emission duty ratio) at which the ₁₄₃₃₆ lights up (emits light) is output.

Here, the light quantity setting signal from the printer CPU is preset to an appropriate value at the time of shipment from the factory in order to correct variations in sensitivity and the like of the photosensitive drum 25. It is reset by man. Light quantity correction signal, the LED elements 604 ₁
Provided by the light quantity correction unit 518 having a data table for correcting the variation of the light emission amount of ～604 _14336.

The light amount correction unit 518 includes an LED head 503
Each LED element is fed back from 604 _through 603
4 Based on the signal indicating the light emission amount of ₁₄₃₃₆ (light amount measurement signal), a correction amount for correcting each light emission amount to an optimum value is calculated, and each calculated value is stored as a data table and then calculated. The value is output to the light amount controller 517 as a light amount correction signal in synchronization with the control timing signal from the control timing generator 515.

Here, each part of the LED write control circuit 501 functions as a light amount detecting means and a light amount correcting means according to claims 1 to 3. Next, the LED driver circuit 502 and the LED head 503 in FIG. 2 will be described with reference to FIG. FIG. 6 is a block diagram illustrating a configuration example of the LED head 503.

The LED driver circuit 502 includes ODD data, EVEN data,
The transfer clock, the enable signal, etc.
, And a CCD drive circuit for inputting a clock to the CCD 606 to extract the output and feeding it back to the light quantity correction unit 518 as a light quantity measurement signal.

The LED head 503 has an even number (EVEN).
Line shift register 602, an odd (ODD) line shift register 603, and a large number of LED elements 6.
04 _1-604 and LED array 604 consisting of _14336, a photodiode (PD) 605 ₁ ~ for detecting the light emission amount of the LED elements 604 _{1 to 604 14336} respectively
PD array 605 consisting of 605 ₁₄₃₃₆ and CCD 60
6 is provided. LED lighting DC power supply 607 is L
A necessary DC power supply voltage is supplied to the ED driver circuit 502 and the LED head 503.

Here, the LED write control circuit 501 outputs L
Each image data (ODD data, EVEN data) transferred via the ED driver circuit 502 is sequentially transferred to the corresponding LED element position by the shift registers 602 and 603, and each LED element is determined by the enable signal. Light up for hours. Thereby,
The surface of the photosensitive drum 25 in FIG. 4 is selectively exposed to form an electrostatic latent image.

Next, the control according to the present invention by the digital writing device 506 configured as described above will be described more specifically. The digital writing device 506 is, for example, once a day, enters a light quantity measurement mode in response to an instruction from the printer CPU during a warm-up when the first power is turned on,
Performs data updating processing for correcting the amount of light emission of the LED elements 604 _{1 to 604 14336.}

That is, each LED of the LED head 503
The elements 604 _{1 to} 604 ₁₄₃₃₆ are sequentially caused to emit light by predetermined image data and an enable signal having a light emission duty ratio (pulse width), and the light amount correction unit 518 detects each light emission amount (light amount measurement signal) and detects each light emission amount. Are respectively calculated to correct the values to the optimum values, and stored as a data table.

A detection circuit (not shown) detects each of the above-mentioned detection values (light amount detection value) and a predetermined value (for example, 5 times the rated value of the light emission amount of each of the LED elements 604 _{1 to} 604 ₁₄₃₃₆ ).
0%) is sequentially determined to determine whether each light amount detection value is equal to or less than a predetermined value. If there is a light amount detection value equal to or less than the predetermined value, correction cannot be performed even if the light emission amount of the LED element is increased. The following processing is performed.

That is, the correction amount is calculated again so that the light emission amount of another LED element (adjacent LED element) adjacent to both sides (only one side) of the LED element may be increased (as a result, the LED element may be recalculated). And other LEs adjacent to it
The light emission duty ratio of the D element is changed), and the contents of the data table are partially changed. This data table is used until the next day's data update processing is started.

As described above, according to the detected light amount, the LE
When changing the light emission duty ratio of the D element, if necessary (when there is a light amount detection value equal to or less than a predetermined value), the LE
By changing the light emission duty ratio so that the light emission amount of another LED element adjacent to the D element is increased, even if one of the LED elements is greatly deteriorated,
It is possible to equalize the light intensity distribution by elements 604 _{1 to 604 14336.} That is, each LED element 604 _{1 to 604
The} light quantity distribution by ₁₄₃₃₆ can be made uniform over a long period of time.

[0043]

As described above, according to the digital writing device of the present invention, each LED of the LED head
It is possible to make the light quantity distribution by the elements uniform over a long period of time.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an LED write control circuit 501 in FIG. 2;

FIG. 2 is a block diagram illustrating a configuration example of a digital copying machine according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram illustrating an example of a mechanical unit of the image reading apparatus 100 of FIG. 2;

FIG. 4 is a schematic configuration diagram showing an example of a mechanical unit of the copying machine main body 200;

FIG. 5 is a layout diagram showing a configuration example of an operation panel 420;

FIG. 6 is a block diagram showing a configuration example of the LED head 503, respectively.

[Explanation of symbols]

100: Image reading device 200: Copy machine main body 300: Image information storage device 301: Image memory unit 500: Printer device 501: LED writing control circuit 502: LED driver circuit 503: LED head 504: Printer control circuit 506: Digital writing 511: Input buffer 512: Line memory group 513: Selector 514: Output buffer 515: Control timing generator 516: Transfer clock controller 517: Light amount controller 518: Light amount corrector 602: Shift for even number (EVEN) line Register 603: Odd (ODD) line shift register 604 _{1 to} 604 ₁₄₃₃₆ : LED element 604: LED array 605 _{1 to} 605 ₁₄₃₃₆ : Photodiode 605: PD array 606: CCD 607: DC power supply for LED lighting

Claims (3)

[Claims] A one-dimensional LED head in which a plurality of LED elements are arranged at a predetermined density in a main scanning direction;
A digital writing device comprising: a light amount detecting unit for detecting a light emitting amount of each element; and a light amount correcting unit for correcting a light emitting amount by changing a light emitting duty ratio of a corresponding LED element in accordance with each detection value by the unit. In the above, when the light quantity correction means changes the light emission duty ratio of the LED element in accordance with the value detected by the light quantity detection means, the light emission duty ratio of another LED element adjacent to the LED element is changed as necessary. A digital writing device, which is a means for changing. 2. The light quantity correction means changes a light emission duty ratio so that a light emission quantity of another LED element adjacent to the LED element increases when a value detected by the light quantity detection means is equal to or less than a predetermined value. 2. The digital writing device according to claim 1, wherein the digital writing is performed. 3. The digital writing device according to claim 2, wherein the predetermined value is set to 50% of a rated value of a light emission amount of each of the LED elements.