JPH09309223A - Led writing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the correction of luminescence irregularity due to a change with time elapse by detecting the brightness of luminescence of plural LED elements on an LED array arranged in the main scan direction and controlling the LED elements based on the detected brightness of luminescence so that the brightness of each of the LED elements is set to the specified value. SOLUTION: A quantity of light correction part 518 sequentially turns ON plural LED elements in the process of warming-up at a specific drive current and a specific duty ratio to seek a correction amount by detecting each of the luminescence brightnesses, and further, update and store the correction results. In addition, the quantity of light correction part 518 has a comparision circuit for determining a quantity of light measuring signal detected and outputs an LED abnormality signal to a printer CPU, if the measured quantity of light is below the specified value. The printer GPU connects this LED abnormality signal to a system control part to display it on a control panel. A quantity of light control part 517 corrects a quantity of light of luminescence based on a signal for setting a quantity of light of luminescence from the printer CPU and a quantity of light correction signal per LED element from the quantity of light correction part 518 to output a luminescence enable signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED in which a latent image is written by selectively lighting each element of an LED array in which light emitting diode (LED) elements are arranged in a line and irradiating the light on a photoconductor. Regarding a writing device.

[0002]

2. Description of the Related Art Generally, an LED printer selectively illuminates each element of an LED array and irradiates light onto a photoreceptor. Therefore, the LED printer has no moving parts such as a polygon mirror of a laser printer and has high reliability. Also, in the case of a wide printer that requires a large-format print output, a laser printer is substituted because a large optical space for scanning light in the main scanning direction is not required and the size can be reduced.

In a laser printer, the output is 10
While one light source (laser diode) of about mW is turned on and its beam is scanned through a polygon mirror, an f-θ lens, and the like, an LED printer emits one beam per pixel.
LED elements are arranged in a row in the main scanning direction,
A drive current of about 10 mA is applied to the ED element to emit light. Therefore, when it is applied to a printer whose main purpose is to output characters and which has a relatively low image density, or a plotter which outputs only line drawings such as graphics, each LED element is selectively turned on or not turned on. The light emission variation of each LED element does not pose a problem with only on / off control (binary control), but when applied to a digital copying machine, when it is applied to a digital copy machine, for example, a manuscript with many black solids such as a poster manuscript or an intermediate image such as a photograph. Since a document having many tones (halftones) is copied, variations in the light emission of the LED elements appear as uneven density or white streaks.

Conventionally, as a method of correcting the light emission variation of the LED elements, as shown in, for example, Japanese Patent Laid-Open No. 62-200966, correction data corresponding to the light emission variation of each LED element of the LED head is stored in advance in the ROM. Then, a method has been proposed in which the drive current of each LED element is corrected based on the correction data to reduce the light emission variation of each LED element and to make the light amount distribution uniform.

[0005]

However, in the above-mentioned conventional method, since the correction data corresponding to the light emission variation at the time of manufacturing the LED element is stored in the ROM in advance and is corrected,
If the light emission variation of the LED element occurs due to the change over time, there is a problem that it cannot be corrected.

In view of the above conventional problems, the present invention is an LED
It is an object of the present invention to provide an LED writing device capable of correcting light emission variations due to changes over time of elements.

[0007]

In order to achieve the above-mentioned object, the first means is a one-dimensional LED array in which a plurality of LED elements are arranged in the main scanning direction, and the light emission brightness of each of the plurality of LED elements. And a light emission luminance control means for controlling the light emission luminance of each of the plurality of LED elements to be a predetermined value based on the light emission luminance detected by the light emission luminance detection means. Is characterized by.

In the second means, the light emission luminance control means in the first means changes the duty ratio of the drive signal for lighting the plurality of LED elements, whereby each light emission luminance of the plurality of LED elements is predetermined. The feature is that the value is controlled to be a value.

The third means is characterized in that the abnormality is notified when the light emission luminance detected by the light emission luminance detecting means in the first or second means is below a correctable value.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an LED according to the present invention.
2 is a block diagram showing a copying machine to which an embodiment of a writing device is applied, FIG. 2 is a block diagram showing the original reading device of FIG. 1, FIG. 3 is a block diagram showing the copying machine of FIG. 1, and FIG. FIG. 5 is an explanatory view showing the operation panel, FIG. 5 is a block diagram showing the LED writing control circuit of FIG. 1 in detail, and FIG. 6 is a block diagram showing the LED driver circuit and LED head of FIG. 1 in detail.

In FIG. 1, the copying machine schematically includes a document reading device 100 for reading a document, a copying device 200 for copying a document image read by the document reading device 100 onto a sheet, and an operating device 400. . The copying apparatus 200 includes an image information storage device 300 having an image memory 301 and a system control device 302, and a copying circuit 5
00, the operation device 400 outputs an operation panel 420 as shown in FIG. 4 and operation information input via the operation panel 420 to the system control device 302, and operates based on the control of the system control device 302. It has an operation control circuit 410 for performing display control of the panel 420.

In the document reading apparatus 100, as shown in FIG. 2, when an operator inserts a document into the insertion opening of the roller 1, the document is conveyed by the roller 1 on the contact glass 2, and the document being conveyed is fluorescent lamp. The light is reflected by the lens 4, and the reflected light is reflected by the lens 5 by the image sensor (CCD) 6
Is formed on the light-receiving surface of the original, and photoelectrically converted by the CCD 6 to read an original image. The analog image signal photoelectrically converted by the CCD 6 is controlled by the reading control circuit 106 as shown in FIG.
The signal is output to the image amplification circuit 101 in synchronization with the clock from No. 5 and amplified, and then converted into a multi-value digital image signal for each pixel by the A / D conversion circuit 102.

The following shading correction circuit 103 is used for the uneven light amount of the fluorescent lamp 4, dirt on the contact glass 2 and CCD 6.
Is corrected for unevenness in sensitivity of each element. The image signal corrected by the shading correction circuit 103 is stored in the image page memory unit 301 after being converted into digital recording image information by the image processing circuit 104. This image information is read out as appropriate, output to the copying circuit 500, and applied to the LED head 503 shown in FIG. 6 through the LED write control circuit 501 and the LED driver circuit 502 shown in FIG. It is converted into infrared light modulated according to the image information.

The structure of the copying apparatus 200 will be described with reference to FIG. The surface of the photosensitive drum 25 is uniformly charged to, for example, −850 V by the charging device 26, and the LED head 50 is charged.
A latent image is formed by the infrared light of No. 3. Here, the LED head 503 is configured so that a large number of LEDs are arranged in an array, and each of the infrared lights is irradiated on the photosensitive drum 25 via the SELFOC lens array. And
L is set in the area where the original density is light (the binary signal is the non-recording level)
The ED element is not turned on, and the LED element is turned on in a portion where the document density is high (a binary signal is a recording level).
V, the irradiation section has a potential of about -100 V, and as a result,
An electrostatic latent image corresponding to the density of the image is formed on the photosensitive drum 25.

The latent image on the photosensitive drum 25 is developed by the developing unit 27. Here, the developing unit 27
The toner inside is agitated and negatively charged, and a bias of -600 V is applied, and the toner adheres only to the infrared light irradiation portion on the photosensitive drum 25, so that the latent image is developed with the toner. The toner image on the photoconductor drum 25 is transferred to the paper by the transfer charger 23, then the paper is separated from the photoconductor drum 25 by the separation charger 28, and the remaining toner on the photoconductor drum 25 is removed by the cleaning unit 29. You.

The paper is set in advance in the form of roll papers 11a, 11b, 11c having different widths on the three paper feed tables 9a, 9b, 9c. Roll paper 11a to 11c
Is a feed roller 12a corresponding to the size of the image.
12a to 13c and selectively supplied to the cutters 13a to 13c.
c, and then conveyed by the rollers 14a to 14c, then conveyed by the registration roller 24 so as to match the toner image on the photosensitive drum 25, and the toner image is transferred by the transfer charger 23. Next, the sheet separated from the photosensitive drum 25 is conveyed by a conveying belt 31, the toner is fixed by a fixing unit 30, and is discharged onto a discharge tray 32. Such a copying apparatus 200 is driven by the printer driving device 505 under the control of the printer driving control circuit 504 shown in FIG.

On the operation panel 420, as shown in FIG.
As keys for specifying various functions, for example, the paper size key, paper type specification key, paper feed stage specification key, numeric keypad, start key, mode clear key, stop key, density adjustment key, image quality adjustment key, scaling key, etc. Further, a copy number display section, a magnification change display section, an original insertable display section, and the like are provided as display sections.

Next, the LED writing control circuit 5 shown in FIG.
01 and the LED head 503 shown in FIG. 6 will be described in detail. Here, the LED head 503 is an even number (EVE
Shift register 602 for N) lines and odd number (OD
A shift register 603 for D) lines, the LED array 604 consisting of 14336 pieces of LED elements 604 _{1 to 604 14336,} LED elements 604 _{1 to 604 14336} respectively monitor photodiodes each emitting light quantity of (P
D) PD array 605 having 605 _{1 to} 605 ₁₄₃₃₆
And has a CCD606, LED elements 604 _{1 to 604
The} amount of each emitted light of ₁₄₃₃₆ is detected and fed back to the LED writing control circuit 501.

An image input from the reading device 100 to the copying device 200 is temporarily stored in the image memory 301 and is input to the LED writing control circuit 501 as it is, or after being edited or processed, in synchronization with a synchronizing signal and an image clock. To do. In the LED writing control circuit 501, image data of two lines (nth line and n + 1th line) are simultaneously transferred to the line memory group 512 via the input buffer 511.
(FIG. 5).

The image data stored in the line memory group 512 is first selected by the selector 513 for the nth line and then for the nth line in order to reduce the processing frequency of the LED head 503.
The image data of the + 1st line is read and output to the shift registers 602 and 603 as the odd line (ODD) data and the even line (EVEN) through the output buffer 514 and the LED driver 502 shown in FIG. . Along with this image data, a synchronization signal, a pixel transfer clock signal, and a duty ratio control signal (enable signal) that determines the amount of emitted light are also sent to the LED driver 502.
Is output to

This series of processing is performed within the time when the data of the n + 2 and n + 3 lines are input and stored in the same line memory 512, and this processing is repeated thereafter. L
The image data transferred to the ED head 503 is conveyed to each LED dot position in the even-numbered line shift register 602 and the odd-numbered line shift register 603, and then each LED is determined by the duty ratio control signal and its correction signal. Only the light is selectively turned on to illuminate the photosensitive drum 25.

The control timing generator 515 is a CPU (printer CP) in the printer drive control circuit 504 shown in FIG.
U) to generate various timing signals. The transfer clock control unit 516 sets the transfer clock of the image data together with the image data to the L level via the output buffer 514.
Output to the ED driver 502. The light amount correction unit 518 is L
And it outputs a light quantity correction signal for correcting the variation of each element based on the light emission amount and a data table of the LED elements 604 _{1 to 604 14336} fed back from ED head 503 to the light amount control unit 517.

[0023] In this case, the light quantity correction unit 518, for example once a day, the LED elements 604 _{1 to 604 14336} sequentially lighted at a predetermined drive current and the duty ratio during the warm-up of the first power on, the light emitting luminance The correction amount is detected to obtain the correction amount, and the result is updated and stored for the next day. Further, the light amount correction unit 518 has a comparison circuit for determining whether or not the detected light amount measurement signal is less than or equal to a predetermined value that cannot be corrected even if the light emission amount is increased. The LED abnormality signal is output to. The printer CPU sends this LED abnormality signal to the system control unit 302 to display the LED abnormality on the operation panel 420.

The light amount control unit 517 corrects the light emission amount based on the light emission amount setting signal from the printer CPU and the light amount correction signal for each LED element (dot) from the light amount correction unit 518, and the LED element lighting time ( A light emission enable signal for determining the duty ratio) is output. here,
The light emission amount setting signal from the printer CPU is supplied to the photoconductor 25.
An appropriate value is set in advance at the time of factory shipment in order to correct the variation in the sensitivity and the like, and is reset by a service person at the time of maintenance such as replacement of the photoconductor 25.

The LED driver 502 shown in FIG.
ODD data from the D write control circuit 501, EVE
A buffer that transfers N data, a transfer clock, an enable signal, etc. to the shift registers 602 and 603 of the LED head 503, and a CCD drive that applies a clock to the CCD 606 and extracts its output, and feeds it back to the light amount correction unit 518 as a light amount measurement signal. It has a circuit.
The LED lighting DC power source 607 is the LED head 50.
3 and the LED driver 502 are supplied with necessary DC power.

[0026]

As described above, according to the first aspect of the present invention, since the respective light emission luminances of the plurality of LED elements are detected and controlled so as to reach the predetermined value, the light emission variation due to the change over time of the LED elements. Can be corrected.

According to the second aspect of the present invention, a plurality of LEs
By controlling the duty ratio of the signal for turning on the D element so that each light emission luminance becomes a predetermined value,
It is possible to correct variations in light emission due to changes over time in the LED elements.

According to the third aspect of the invention, the abnormality can be notified when the detected light emission luminance is less than or equal to the correctable value.

[Brief description of drawings]

FIG. 1 is a block diagram showing a copying machine to which an embodiment of an LED writing device according to the present invention is applied.

FIG. 2 is a configuration diagram illustrating the document reading apparatus of FIG. 1;

FIG. 3 is a configuration diagram illustrating the copying machine of FIG. 1;

FIG. 4 is an explanatory diagram showing an operation panel of FIG. 1;

FIG. 5 is a block diagram showing the LED write control circuit of FIG. 1 in detail.

6 is a block diagram showing in detail the LED driver circuit and the LED head of FIG. 1. FIG.

[Explanation of symbols]

 501 LED writing control circuit 503 LED head 517 Light amount control unit 518 Light amount correction unit 604 LED array 605 Photodiode array 606 CCD

Claims (3)

[Claims] 1. A one-dimensional LED array in which a plurality of LED elements are arrayed in a main scanning direction, a light emission luminance detection unit that detects each light emission luminance of the plurality of LED elements, and a light emission luminance detection unit that detects the light emission luminance. And a light emission brightness control unit that controls each light emission brightness of the plurality of LED elements to have a predetermined value based on the light emission brightness. 2. The light emission brightness control means includes a plurality of Ls.
2. The LED writing device according to claim 1, wherein each of the plurality of LED elements is controlled to have a predetermined value by changing a duty ratio of a drive signal for lighting the ED element. 3. The LED writing device according to claim 1, wherein when the light emission luminance detected by said light emission luminance detecting means is equal to or less than a correctable value, an abnormality is notified.