JP3215748B2 - Print density correction method and LED printer incorporating the correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting print density in an LED printer, and more particularly, to a linearly arranged LE.
The present invention relates to a print density correction method that effectively utilizes a divided exposure method of forming a print dot while lighting a D element group a plurality of times in a sub-scanning direction for each scanning line, and an LED printer incorporating the correction method.

[0002]

2. Description of the Related Art Conventionally, LED element groups arranged on a line in the main scanning direction are time-divisionally controlled to turn on the LED element rows corresponding to image information in units of n bits or in units of one main scanning line. An LED printer is known in which the dot exposure image is formed on the generatrix of the photosensitive drum to form an electrostatic latent image corresponding to the exposure image. In this type of apparatus, an LED head is generally used. A shift register, a latch circuit for serially inputting n-bit data to each of the chips in units of a plurality of elements, a drive driver for controlling the driving of the light emitting elements in the chip based on parallel data from the shift register, etc. Is connected to a driving IC incorporating the LED.
Chips have variations in luminance (light output) characteristics between chips or between elements due to differences in manufacturing conditions during wafer production. For this reason, conventionally, in order to obtain a stable light output between the LED chips, a method of correcting the luminance characteristics of the LED chips by controlling the energization time or the driving current in accordance with the luminance characteristics for each chip has been proposed. Various proposals have been made. (July 1-2805, JP-A-1-29
7271, Kokai 59-132276, etc.)

[0003] However, as in the prior art described above,
Even if the energization time or the drive current is controlled in accordance with the luminance characteristics of each chip, there is variation between the drive ICs incorporating the constant current circuit and also between the LED elements in the chip. Correcting these individually makes the control operation and control circuit extremely complicated. That is, as described above, the LED chip is connected to a drive driver for driving and controlling the respective light emitting elements, a common driver for setting the energization time while sequentially switching the LED chips, and the like. The rise or fall characteristics are different for each drive IC. Also, between the LED elements in the chip, there is a variation in the light emission intensity of each element due to the variation of the generated film and the etching.
The variation in the light emission intensity including the variation between the driving IC and the LED element in the chip is about ± 20%, so that one between adjacent dots is 80% and the other is 120%.
And in the worst case, the variation between them is 50% (120
/ 80), and a large variation occurs in the print density, that is, the potential of the latent image on the photosensitive member.

On the other hand, the exposure amount on the photoreceptor
It is determined by the product of the light output of the element and the exposure time,
For this reason, as shown in JP-A-4-212871, individual LED elements emit light in an apparatus using a static drive type LED head that simultaneously exposes a large number of LED elements arranged on a line according to image information. Signal is turned on in accordance with the contents input in advance to a rank correction output circuit indicating the light quantity rank of each LED element.
The time is set by the CPU, and a strobe signal is output at a timing to be printed. Based on the strobe signal, the exposure time of the LED element is controlled while correcting the emission time corresponding to the light amount rank of each LED element. Technology exists. Further, in this publication, a technique is disclosed in which the correction data of the rank correction output circuit is not set in units of dots but a density is selected based on the density of a target pixel and surrounding pixels.

[0005]

However, as described above, the technique of simply controlling the exposure time in accordance with the light quantity rank of each LED element is based on the static drive type LED for simultaneously exposing one scanning line as described above. Although effective in a head, there is a problem in a so-called time division type LED head. In other words, the time-division type LED head uses, for example, 2560 LED elements for one scanning line as 64
The LED is divided into 40 blocks (LED chips) bit by bit, and the LEDs are sequentially controlled to be turned on in units of the divided LED chips (blocks). Therefore, in the time division method, compared with the static drive method, The exposure time is 1/40.
It is currently difficult to further control the light emission time according to the light intensity rank of each ED element, and the horizontal synchronization cycle has been significantly reduced in response to the recent trend toward smaller photoconductor drum diameters and higher speeds. As a result, it is practically almost impossible to further control the exposure time in the time division method.

For this reason, Oki Electric R & D (No. 139 Vo)
L. 55 No3 July 1988 report) LED
Using a thick film resistor for current control connected to the element,
There is also a technique of controlling the conduction current for each element by laser-trimming the thick-film resistor according to the level of the LED output and adjusting the resistance value, but the number of laser-trimmings is large and the productivity is poor. . As the resolution increases, the distance between the thick-film antibodies becomes narrower, which makes it technically difficult.

In view of the above-mentioned drawbacks of the prior art, the present invention is to stabilize the amount of exposure on a photoreceptor, which is determined by the product of the light output of the LED element including the variation between the driving IC and the LED element in the chip and the exposure time. To achieve a uniform dot print density on the photoreceptor .
It is an object of the present invention to provide a print density correction method in a divided exposure system and an LED printer using the correction method.

[0008]

Conventionally, as shown in FIG. 1B, one pixel dot for generating a pixel pattern is divided into P unit elements in the sub-scanning direction, and each of the divided unit elements is repeated. While applying the same pixel signal, in other words, LED
In the case of a printer, an LED printer that forms one dot latent image on a photoreceptor while illuminating LED elements arranged in a line in a sub-scanning direction for each scanning line as appropriate several times is known. (Japanese Patent Publication No. 62-26626, Japanese Patent Application Laid-Open No. 60-134660, etc.)
The present invention is an LED printer which forms a dot latent image on a photoreceptor while effectively utilizing such a divided exposure method, and illuminating LED elements arranged in a line in a sub-scanning direction for each scanning line appropriately several times . Compensation of print density in split exposure system
Correct method, comprising : pixel information of an LED element;
And the lighting pattern information corresponding to the
Video data generated while performing a logical AND
Then, the LED element is turned on a plurality of times in the sub-scanning direction as appropriate.
Control the light amount variation between the LED elements.
It is characterized by performing correction in consideration of the above.

[0009] As means for realizing such a correction method, in an LED printer employing the above-mentioned divided exposure method, LED elements arranged in a line are arranged based on pixel information.
Lighting control several times in the sub-scanning direction for each scanning line
While forming a dot latent image on the photoreceptor.
Measuring the light intensity variation of between ED elements, storage means for correcting data corresponding to the variation is written, and a lighting pattern is selected based on the correction data read out from the storage means comprises the The pixel information of the LED element and the L
Both bits of the ED element and the corresponding lighting pattern information
Video data generated while performing a logical AND on information
The LED element in the sub-scanning direction several times
It is characterized in that a dot latent image is formed on the photosensitive member while controlling the lighting .

[0010]

The basic principle of the present invention, for example, a division exposure method repetitively scanning n (8) times for each scan line, 5 bits that ± 20% of the light amount variation with respect to the flat <br/> average amount Let us consider a case where the LED is corrected.

1) First, all the 5-bit LEDs are turned on, and the light quantity of each element is measured. (FIG. 2A) 2) Next, a latent element that can be formed on the photoconductor when the LED element (No. 1) having the minimum light amount is repeatedly turned on n times (for example, 8/8 or 16/16) for the number of divided exposures. The exposure time is set so that the image dot diameter becomes the dot diameter of the regular resolution. This setting is performed by controlling the strobe time, and all the LED elements are turned on based on the strobe time. In this case, it is not necessary to use the LED element (No. 1) having the minimum light amount value as a reference. Becomes easier. Also, the reference lighting number of the LED element having the minimum light amount value is not limited to the number of divided exposures n / n, but may be, for example, (n-1) / n (7/8 or 15/1) in relation to the print density.
6) may be set as the reference lighting frequency.

3) The number of times of lighting such that the LED element having the minimum light amount has the same exposure energy as the case where the number of times of the divided exposure is n is calculated for the other LED elements based on the correction formula of FIG. Then, the calculated divided lighting data is written into the light quantity correction ROM as correction data. 4) Next, the lighting pattern register shown in FIG. 2C is selected by reading the correction data (hereinafter referred to as resist selection data) from the ROM for each corresponding LED element.

5) Next, as shown in FIG. 1A, the same image data is repeatedly output serially for n divided scanning lines corresponding to the number of divided exposures n for each scanning line.
In each exposure line, bit data in the corresponding divided exposure line of the register, corresponding image data and AND are taken, and video data which is ON data in which an LED is turned on only when both the image data and the bit data are black Is output to the LED head side. 6) As a result, as shown in the right column of FIG. 2C and FIG.
Times, in the case of the LED element having the light amount of 0.9, for example, 7/8
Exposure is performed in a divided manner in inverse proportion to the variation in the amount of light, and the diameter of the exposure dots formed on the photosensitive drum can be made uniform.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. FIG.
FIG. 4 to FIG. 4 show an embodiment of the present invention showing the control section of the LED printer. The configuration will be described in detail according to the operation. The serial image data VDATA transferred from the bitmap memory 11 based on VCLK is an 8-bit serial data. Buffer memory 14 by parallel conversion circuit 12
After converting the 8-bit image data WDATA into 8-bit parallel data corresponding to the bus width of the address ADR and the WRITE cycle MWR transmitted from the memory control circuit 15 via the direction control 13,
Thus, the data is stored at a predetermined address of the selected one bank of the buffer memory 14. The buffer memory 14 temporarily stores the image data in order to convert the transfer speed VCLK of the serial image data read from the bitmap memory 11 to the transfer speed TCLK of the LED corresponding to the divided exposure speed. WRITE / READ is performed while the memory is controlled.

After the conversion into 8-bit parallel data is completed by the bit serial / parallel conversion circuit 12, the buffer memory 14 is stored in the buffer memory 14 within 8 VCLK until the next 8-bit parallel conversion is completed by the conversion circuit 12. Is controlled as shown in the timing chart of FIG. That is, the buffer memory 14 has memory areas BANK1 and BANK2 for two scanning lines, and when BANK1 is a write buffer, BANK2 becomes a read buffer, and BANK2 is input until the next horizontal synchronization signal Lsync is input.
The image data for the next one scanning line is stored in K1 in units of 8 bits. On the other hand, in BANK 2 in which image data for the current one scan line is stored, it is necessary to read out n × 8 dot image data within 8 VCLK time (hereinafter referred to as a read cycle) excluding the WRITE cycle for each 1 WRITE cycle. There is. Here, reading out the image data of n × 8 dots does not mean that the same image data of 8 dots is repeatedly read out n times. For example, in the case of 16-division exposure, one image from address 0000 to address 0127 is read.
This means reading out 28 image data. Therefore BANK
Each time 1/16 scan line image data is written in 1, the current one scan line image data is swept out from BANK2. This is repeated 16 times, and the current one scan line image data is repeated. Is repeated 16 times. The switching of the BANKs 1 and 2, that is, the toggle operation of writing / reading is performed based on the horizontal synchronization signal Lsync, and the above operation is repeated while the BANKs 1 and 2 are switched.

The image data read from the BANK 2 is held in the data latch & shift circuit 49 in units of 4 × 8 dots. Each time the data of 32 dots is latched, the image data is read out based on the LD of the control circuit 15. A 32-bit parallel-serial conversion circuit 1 for every 32 dots
6, and the parallel data is serially output from the conversion circuit 16 to the AND gate 17 based on TCLK having a transfer rate 16 times higher than the VCLK. The image data of one scan line is made to correspond to the resist pattern based on TCLK having a transfer speed 16 times as fast as VCLK while taking the AND with the corrected serial data input to the AND gate 17 in synchronization with the serial image data. The corrected image data that has been appropriately converted to black and white is transmitted to the LED head 30 for 16 divided exposure lines. The divided horizontal synchronizing signal SLsync is repeated every time the divided exposure line is swept out, and is output to the LED head side.

Next, a method of generating the corrected serial data will be described. First, as shown in FIG.
The light amount distribution data (normalized data) obtained by full lighting of the ED head is converted into a light emission pattern register 2 via a correction formula.
5 is converted into exposure correction data indicating the number of divisional lightings for selecting 5, and a light amount correction R corresponding to each LED head 30 is obtained.
Write it to OM21. Therefore, the light amount correction ROM 21 is attached to each LED head 30, and if the head 30 of the device is replaced, the ROM 21 is also replaced.
Note that a mask RAM or the like is used instead of the ROM 21 and LE
The correction data may be configured to be rewritable as the D head 30 deteriorates with time. The light amount correction ROM 21 has a memory width in which 8-bit data can be written. However, when the number of division exposures is 16, 4-bit data is sufficient, and the data written in the ROM 21 has an odd No. in the upper 4 bits of one address. , And the correction data of the even-numbered LED elements can be written in the lower 4 bits. As a result, correction data for each print dot is stored in the upper and lower parts of one address, respectively, so that the memory capacity of the ROM 21 can be reduced and two correction data can be swept out by one access. For this reason, there is an effect that the access speed of the ROM 21 can be reduced correspondingly.

After mounting the correction ROM 21, the correction circuit timing generator 22 inputs a clock ICLK of 1/2 of TCLK, which is the transfer speed of the divided exposure line, to the address counter 23 based on the horizontal synchronization signal Lsync and VCLK. As a result, 8-bit correction data of a pair of upper and lower printing dots corresponding to a predetermined address in the light amount correction ROM 21 designated by the counter 23 is transferred to the latch & data selector 24 and latched. Then, in the selector 24, the upper 4 bits are selected by the select signal SEL output from the generator 22.
Bits and correction data (resist selection data) of lower 4 bits are sequentially selected and input to the light emission pattern register 25 in synchronization with the transfer speed of TCLK. The light emission pattern register 25 can select 16 types of registers by the 4-bit register selection signal, and outputs the contents of the selected register 25 to the pattern selector 26 in parallel.

The 16-bit register data output in parallel selects 1-bit data corresponding to the divided exposure lines sequentially according to an output signal from a 4-bit binary counter 27 indicating the scanning order of the divided exposure lines. That is, 4
The bit binary counter 27 outputs the divided exposure synchronization signal SLsy
Each time nc is input, one bit is counted and the SL
It is configured to reset when sync is counted 16 times. Therefore, the corrected serial data input to the AND gate 17 in synchronization with the serial image data is obtained by first register data (1 bit) on the first divided exposure line by the binary counter 27 for one scan line to the AND gate side. The binary counter 27 counts up when the divided exposure synchronizing signal SLsync is input next, and the resist data (1 bit) on the second divided exposure line is serially transmitted to the AND gate 17 for one scanning line. Is output and the above operation is repeated thereafter. Note that the reference register of the light emission pattern register 25 does not necessarily need to be set to 16/16, and M
For example, 15/16 may be selected to be the reference register based on the print density control signal obtained via the PUBUS and the MPU I / F circuit 28.

An LED head strobe generating circuit 29 is formed on the photosensitive member when the LED element having the minimum light amount (0.8) is repeatedly turned on (8 or 16) as described above. A strobe time setting register 29a for setting the exposure time so that the obtained latent image dot diameter becomes the dot diameter of the regular resolution is built in, and the value of this register is printed by the MPUI / F circuit 28. It is configured to be adjustable based on the density control signal. .

FIG. 5A shows the configuration of the LED head circuit. The 32-bit serial correction image data DATA transferred from the AND gate 17 of the controller is transferred to the shift registers 31 and 31 every 32-bit serial transfer.
As shown in (B), clock timings CLK0 to CLKC
LK1 is shifted and latched by the 32 × 2 latch circuit 32. Each time 32 × 2 bits are latched by the latch circuit 32, the common driver circuit 33 is latched based on the latch data.
To drive the corresponding LE based on the strobe time.
Each LED element 30a of the D chip 30A is turned on.

The connection of the common driver circuit 33 is switched to the next LED chip 30B based on the switching signal from the block designating circuit 34 for each latch of 32 bits × 2 data in the latch circuit 32.
The lighting operation of each LED element 30a is controlled, and the same operation is continuously performed 40 times to output corrected image data for one divided exposure line. Further, by controlling the lighting of the next divided exposure line and the successive divided exposure line in a similar manner, the lighting of the LED elements of the 16 divided exposure lines is controlled. As a result, as shown in FIG. 4, in the case of an LED element having a light amount of 0.8, for example, 16/16 times, the light amount of 0.
In the case of the 9 LED elements, divisional exposure is performed in inverse proportion to, for example, 14/16 times corresponding to the variation in the amount of light, and the diameter of the exposure dots formed on the photosensitive drum can be made uniform.

[0023]

According to the present invention, as described above, the driving IC
The exposure amount on the photoreceptor, which is determined by the product of the light output of the LED element and the exposure time, including the variation between the LED elements in the chip, and the exposure time, is used to set the dot print density on the photoreceptor uniform. I can do it. Further, according to the present invention, in the divisional exposure method, simply performing AND operation on the image data for the divisional exposure and the correction resist data based on the variation in the light amount between the LED elements results in the divisional exposure in inverse proportion to the variation in the light amount. In addition, the uniformization of the diameter of the exposure dots formed on the photosensitive drum can be easily achieved. Further, since the present invention does not control the division of the exposure time but controls the number of exposures, it can be easily applied to a time division system.

[Brief description of the drawings]

FIG. 1 is an operation diagram showing a basic configuration of the present invention, in which (A) shows a lighting pattern formed by taking AND of register data and image data. (B) shows a separation exposure method and a conventional data transfer method.

2A and 2B show the operation of the present invention, wherein FIG. 2A is a light quantity distribution diagram between LED elements, FIG. 2B is a table showing a correction formula for deriving the number of divided lighting, and FIG. The type of the lighting pattern is shown.

FIG. 3 is an overall circuit diagram of a controller according to an embodiment of the present invention.

FIG. 4 is a time chart showing a data flow and an operation of FIG. 3;

FIG. 5 is an LED head circuit diagram used in the present embodiment.

[Explanation of symbols]

 12 8-bit serial / parallel conversion circuit 15 memory control circuit 14 buffer memory 49 data latch & shift circuit 17 AND gate 30 LED head 21 light quantity correction ROM 22 correction circuit timing generator 25 light emission pattern register 29 LED head strobe generation circuit

Claims (2)

(57) [Claims] 1. One scan of LED elements arranged in a line
Photoconductor while lighting multiple times in the sub-scanning direction as appropriate for each line
Form a latent dot image on topLED printer split exposure method
The print density correction method in the formula, The pixel information of the LED element and the LED element corresponding to the LED element
Logical AND of both bit information with lighting pattern information
LED based on video data generated while
By performing lighting control of the element several times in the sub-scanning direction as appropriate
Correction taking into account the variation in the amount of light between the LED elements
Thing LED printerSplit exposure methodSmell
Print density correction method. 2. A plurality of LED elements arranged in a line shape are scanned a plurality of times in the sub-scanning direction for each scanning line based on pixel information.
A dot latent image can be formed on the photoconductor while controlling lighting.
In the divided-exposure type LED printer, the variation of the light amount between the respective LED elements is measured, and a storage unit in which correction data corresponding to the variation is written, and a correction data read from the storage unit. A lighting pattern selected by the user, and corresponding to the pixel information of the LED element and the LED element.
Logical AND of both bit information with the lighting pattern information
L based on the video data generated while
Split exposure characterized by forming a dot latent image on a photoconductor while controlling the lighting of the ED element several times in the sub-scanning direction as appropriate
LED printer in the system .