JPH06270471A - Printing density correcting method and led printer in which correcting method is incorporated - Google Patents

Abstract

PURPOSE:To make the exposure quantity of a photosensitive member constant to uniformize dot printing density by controlling the number of times of lighting in a sub-scanning system on the basis of the correction value corresponding to the irregularity of the quantity of light between LED elements arranged in a line form. CONSTITUTION:Resist selection data is read from an ROM at every corresponding LED element to select a lighting pattern register. Next, the same image data is repeated by the quantity of (n) divided scanning lines corresponding to the number (n) of times of division exposure at every one scanning line to be serially outputted. The AND of the bit data in the divided exposure line corresponding to the register and the corresponding image data is taken in each exposure line and video data becoming ON data wherein an LED element is allowed to light only when both of the image data and the bit data are black is outputted to an LED head. As a result, in the case of the LED element with quantity of light of 0.8, for example, division exposure is performed in an inversely proportional manner corresponding to 8/8 times and the irregularity of quantity of light and the diameter of the exposure dot formed on a photosensitive member becomes uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print density correction method for an LED printer, and more particularly to LEs arranged in a line.
The present invention relates to an LED printer incorporating a print density correction method and a correction method that effectively utilize a divided exposure method in which print dots are formed while lighting a D element group for each scan line a plurality of times in the sub-scanning direction.

[0002]

2. Description of the Related Art Conventionally, LED element groups arranged on a line along a main scanning direction are time-divided in units of n bits or in units of one main scanning line to control the lighting of the LED element row in correspondence with image information. However, an LED printer is known in which the dot exposure image is formed on the generatrix of the photoconductor drum so that an electrostatic latent image corresponding to the exposure image can be formed. In this type of device, the LED head is generally used. A shift register for making a plurality of elements into chips and serially inputting n-bit data to each of the chips, a latch circuit, and 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 constructed by connecting a drive IC incorporating
Chips have variations in luminance (light output) characteristics between chips or between elements due to differences in manufacturing conditions during wafer production. Therefore, conventionally, in order to obtain a stable light output between the LED chips, there is a method of correcting the brightness characteristics of the LED chips by controlling the energizing time or the drive current corresponding to the brightness characteristics of each chip. Various proposals have been made. (Actual fairness 1-221805, JP-A-1-29
7271, S. Kaikai 59-132276, etc.)

However, as in the prior art, the LED
Even if the energization time or the drive current is controlled in accordance with the brightness characteristics of each chip, there are variations among the drive ICs that incorporate the constant current circuit and among LED elements within the chip. Correcting these individually makes the control operation and control circuit extremely complicated. That is, as described above, the LED chip is connected with a drive driver for driving and controlling each light emitting element, a common driver for setting the energization time while sequentially switching the LED chips, and the like. The rising or falling characteristics are different for each drive IC. In addition, the light emission intensity varies among the LED elements in the chip due to variations in the generated film and etching.
The variation of the light emission intensity including the variation between the drive IC and the LED elements in the chip is about ± 20%. Therefore, one between the adjacent dots is 80% and the other is 120%.
In the worst case, the variation between the two is 50% (120
/ 80), which causes a large variation in the print density, that is, the latent image potential on the photoconductor.

On the other hand, the exposure amount on the photoconductor is the same as that of the LED
It is determined by the product of the light output of the device and the exposure time,
Therefore, as shown in Japanese Patent Laid-Open No. 4-212871, each LED element is caused to emit light in a device using a static drive type LED head that simultaneously exposes a large number of LED elements arranged on a line in correspondence with image information. Strobe signal for turning on in accordance with the content that is input in advance to the rank correction output circuit or the like indicating the light intensity rank of each LED element.
The time is set by the CPU, and a strobe signal is output at the timing for printing. Based on the strobe signal, the exposure time of the element is controlled while correcting the light emission time corresponding to the light quantity rank of each LED element. Technology exists. Further, the publication discloses a technique of performing density selection based on the densities of the target pixel and surrounding pixels around it, instead of setting the correction data of the rank correction output circuit in dot units.

[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 a static drive type LED that simultaneously exposes every scanning line as described above. It is effective in the head, but there is a problem in the so-called time division type LED head. That is, the time-division type LED head has, for example, 2560 LED elements for one scanning line.
It 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 to the static drive method. The exposure time is 1/40.
It is quite difficult to further control the light emission time according to the light intensity rank of each ED element, and the horizontal synchronization cycle is drastically shortened in response to the downsizing and speeding up of the photosensitive drum as in recent years. Therefore, it is practically impossible to further control the exposure time in the time division method.

For this reason, Oki Electric Research and Development (No. 139 Vo
L. 55 No3 July 1988) Report on LED
Using a thick film resistor for current control connected to the element,
There is also a technique of controlling the energization current for each element by laser-trimming a thick film resistor according to the size of the LED output and adjusting the resistance value, but the number of laser trimming is large and the productivity is poor. . As the resolution increases, the interval between thick film antibodies becomes narrower, which is technically difficult.

In view of the above drawbacks of the prior art, the present invention makes the exposure amount on the photosensitive member constant, which is determined by the product of the light output of the LED element including the variation between the drive IC and the LED element in the chip and the exposure time. It is an object of the present invention to provide a print density correction method that can set the dot print density on the photoconductor to a uniform density, 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 the divided unit elements are 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 photoconductor while appropriately illuminating a plurality of LED elements arranged in a line in the sub-scanning direction for each scanning line is known. (Japanese Patent Publication No. 62-26626, JP-A No. 60-134660, etc.)
The present invention effectively utilizes such a divided exposure data transfer system to form a dot latent image on a photoconductor while appropriately lighting LED elements arranged in a line in a plurality of scanning lines in the sub-scanning direction. The number of lightings in the sub-scanning direction is controlled based on a correction value corresponding to the variation in the light amount between the LED elements.

As a means for realizing such a correction method, in the LED printer adopting the divided exposure method, the variation in the light amount between the LED elements is measured, and the correction data corresponding to the variation is stored in the memory. Means and a lighting pattern selected based on the correction data read from the storage means, while appropriately lighting the LED elements in the sub-scanning direction for each scanning line based on the lighting pattern information. The feature is that a dot latent image is formed on the photoconductor. In this case, as means for performing divided exposure based on the lighting pattern information, for example, video data generated by taking a logical product of both bit information of the pixel information of the LED element and the lighting pattern information corresponding to the LED element. On the basis of this, by performing lighting control of the LED elements in the sub-scanning direction a plurality of times as appropriate, it is possible to make a correction in consideration of variations in the amount of light between the LED elements, but the present invention is not limited to this.

[0010]

According to the basic principle of the present invention, for example, a 5-bit LED having a light quantity variation of ± 20% with respect to the average light quantity is corrected in a divided exposure method in which n (8) times are repeatedly scanned for each scanning line. Think about the case.

1) First, all the 5-bit LEDs are turned on and the light amount of each element is measured. (FIG. 2 (A)) 2) Next, the latent image that can be formed on the photoconductor when the LED element (No 1) having the minimum light amount value is repeatedly turned on n times (e.g., 8/8 or 16/16) divided exposure times The exposure time is set so that the image dot diameter becomes the dot diameter of the normal resolution. This setting is performed by controlling the strobe time, and all the LED elements are turned on with this strobe time as a reference. In this case, the LED element with the minimum light amount value (No1) does not have to be used as a reference, but by using the LED element with the minimum light amount value as the reference and setting this as the maximum value of the number of times of lighting, the calculation of the correction formula described below is performed. Will be easier. Also, the reference number of times of lighting of the LED element having the minimum light amount value is not limited to the number of divided exposures n / n, but is (n-1) / n (7/8 or 15/1) in relation to the print density.
6) may be set as the reference number of times of lighting.

3) The number of lightings for which the LED element having the minimum light amount value has the same exposure energy as the case where the number n of divided exposures is turned on is calculated for other LED elements based on the correction formula of FIG. 2B. The calculated divided lighting data is written in the light amount correction ROM as correction data. 4) Next, the correction pattern (hereinafter referred to as resist selection data) is read from the ROM for each corresponding LED element to select the lighting pattern register shown in FIG. 2 (C).

5) Next, as shown in FIG. 1A, the same image data is repeatedly serially output for n divided scanning lines corresponding to the number of divided exposures n for each scanning line.
Video data which is ON data in which each exposure line takes bit data in the corresponding divided exposure line of the register and corresponding image data and AND, and the 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. 2 (C) and FIG. 1 (A), in the case of an LED element with a light amount of 0.8, for example, 8/8
In the case of an LED element with the light amount of 0.9, for example, 7/8
The exposure is divided and exposed in inverse proportion to the variation in the number of turns and the amount of light, and the diameter of the exposure dot formed on the photosensitive drum can be made uniform.

[0014]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 3
4 to 4 show an embodiment of the present invention showing a control unit of an LED printer. To explain the configuration in detail according to the operation, the serial image data VDATA transferred from the bit map memory 11 based on VCLK is 8-bit serial / The parallel conversion circuit 12 allows the buffer memory 14
After converting the data into 8-bit parallel data corresponding to the bus width of, the 8-bit image data WDATA is transmitted from the memory control circuit 15 via the direction control 13 and the address ADR and WRITE cycle MWR.
Are stored in 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 bit map memory 11 into 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 of 8-bit parallel data by the bit serial / parallel conversion circuit 12 is completed, the buffer memory 14 is set within the time of 8 VCLK until the conversion circuit 12 completes the next 8-bit parallel conversion. Control as shown in the timing chart. That is, the buffer memory 14 has memory areas BANK1 and BANK2 for two scanning lines. When BANK1 is a write buffer, BANK2 becomes a read buffer, and BANK2 is supplied until the next horizontal synchronizing signal Lsync is input.
Image data for the next scanning line is stored in K1 in 8-bit units. On the other hand, in BANK2 in which the image data for the current one scanning line is stored, it is necessary to read the image data of n × 8 dots within the time of 8 VCLK excluding the WRITE cycle (hereinafter referred to as a read cycle) every 1 WRITE cycle. There is. Here, reading the image data of n × 8 dots does not mean that the same image data of 8 dots is repeatedly read n times. For example, in the case of 16-division exposure, 1 address from 0000 address to 0127 address is read.
It means to read 28 image data. Therefore BANK
Every time 1/16 scanning line image data is written in 1, the current one scanning line image data is swept out from BANK2. This is repeated 16 times, and the current one scanning line image data is repeated. However, the sweep will be repeated 16 times. The BANKs 1 and 2 are switched, that is, the write / read toggle operation is performed based on the horizontal synchronizing signal Lsync, and the 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, and every time the 32 dot data is latched, it is based on the LD of the control circuit 15. A 32-bit parallel-serial conversion circuit 1 for every 32 dots
6 is input in parallel to the input terminal 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 VCLK. Then, while taking AND with the corrected serial data input to the AND gate 17 in synchronization with this serial image data, the image data of one scanning line is made to correspond to the resist pattern based on TCLK having a transfer rate 16 times higher than VCLK. Then, the corrected image data that is appropriately converted into black and white is transmitted to the LED head 30 side for 16 exposure lines. The divided horizontal synchronizing signal SLsync is repeatedly output every time the divided exposure line is swept out and 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 fully lighting the ED head is used as a light emission pattern register 2 through a correction formula.
5 is converted into exposure correction data indicating the number of divided lighting for selecting 5, and the light amount correction R corresponding to each LED head 30 is converted.
Write in OM21. Therefore, the light amount correction ROM 21 is attached to each LED head 30, and when the head 30 of the device is replaced, the ROM 21 is also replaced.
A mask RAM or the like is used instead of the ROM 21, and LE
The correction data may be rewritable with the deterioration of the D head 30 with time. The light amount correction ROM 21 has a memory width in which 8-bit data can be written, but when the number of divided exposures is 16 divisions, 4-bit data is sufficient, so the data written in the ROM 21 is an odd No. in the upper 4 bits of one address. The correction data of the LED element of No. 4 and the correction data of the LED element of even No. can be written in the lower 4 bits. As a result, the correction data for each print dot is stored in the upper and lower positions of one address respectively, so that the memory capacity of the ROM 21 can be saved and two correction data can be swept out by one access. Therefore, the access speed of the ROM 21 can be reduced by that amount.

After the correction ROM 21 is mounted, the correction circuit timing generator 22 inputs the clock ICLK, which is 1/2 the transfer speed of the divided exposure line, to the address counter 23 based on the horizontal synchronizing signal Lsync and VCLK. As a result, 8-bit correction data of a pair of upper and lower print dots corresponding to a predetermined address in the light amount correction ROM 21 designated by the counter 23 is transferred to and latched by the latch & data selector 24. Then, according to the select signal SEL output from the generator 22 in the selector 24, the upper 4
The bit and the lower 4 bits of correction data (resist selection data) are sequentially selected and input to the light emission pattern register 25 in synchronization with the transfer rate 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 is sequentially selected by the output signal from the 4-bit binary counter 27, which indicates the scanning order of the divided exposure lines, to select 1-bit data corresponding to the divided exposure lines. That is, 4
The bit binary counter 27 uses the divided exposure synchronization signal SLsy.
Every time nc is input, one bit is counted and the SL
It is configured to reset when sync is counted 16 times. Therefore, in the corrected serial data input to the AND gate 17 in synchronization with the serial image data, the binary counter 27 first serializes the registration data (1 bit) on the first divided exposure line for one scanning line to the AND gate side. The binary counter 27 counts up when the divided exposure synchronizing signal SLsync is output next, and then the registration data (1 bit) on the second divided exposure line is serialized to the AND gate 17 side for one scanning line. Then, the above operation is repeated. The reference register of the light emission pattern register 25 does not necessarily need to be selected as 16/16.
For example, 15/16 may be selected as the reference register based on the print density control signal obtained via the PUBUS and MPUI / F circuit 28.

Reference numeral 29 denotes an LED head strobe generating circuit, which forms an LED element having a minimum light amount value (0.8) on the photoconductor when the LED element is repeatedly turned on the number of times of divided exposure (8 or 16) as described above. The strobe time setting register 29a for setting the exposure time so that the obtained latent image dot diameter becomes the dot diameter of the normal resolution is built in, and the value of the 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 structure of the LED head circuit. The 32 bits of the serial correction image data DATA transferred from the AND gate 17 of the controller are transferred to the shift registers 31 and 31 every 32 bits serial transfer.
As shown in (B), clock timings CLK0 to C
LK1 is shifted and transferred and latched in the 32 × 2 latch circuit 32, and every time the latch circuit 32 latches 32 × 2 bits, the common driver circuit 33 is based on the latch data.
Drive the corresponding LE based on the strobe time.
Each LED element 30a of the D chip 30A is turned on.

Then, based on a switching signal from the block designating circuit 34 for each latch of 32 bits × 2 data in the latch circuit 32, the connection of the common driver circuit 33 is switched to the next LED chip 30B, and the LED chip 30B.
The LED elements 30a are controlled to be turned on, and the same operation is repeated 40 times thereafter to output the corrected image data for one divided exposure line. Further, the lighting control of the LED elements of the 16 division exposure lines is performed by performing the lighting control of the next division exposure line and the next division exposure line in the same manner. As a result, as shown in FIG. 4, in the case of the LED element having the light amount of 0.8, the light amount of 0.
In the case of the LED element of No. 9, the exposure is divided in inverse proportion to the light quantity variation of 14/16 times, for example, and the diameter of the exposure dot formed on the photosensitive drum can be made uniform.

[0023]

As described above, according to the present invention, the drive IC
The exposure amount on the photoconductor, 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 chip, is made constant, and the dot printing density on the photoconductor is set to a uniform density. You can Further, according to the present invention, in the divided exposure method, the image data for the divided exposure and the correction resist data based on the variation in the light amount between the LED elements and AND are taken, and the divided exposure is performed in inverse proportion to the variation in the light amount. It is possible to easily achieve uniformization of the diameter of the exposure dot formed on the photosensitive drum. Further, since the present invention does not control the exposure time in a divided manner but controls the number of times of exposure, it can be easily applied to the time division method.

[Brief description of drawings]

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

2A and 2B show the operation of the present invention, FIG. 2A is a light intensity distribution chart between LED elements, FIG. 2B is a table showing a correction formula for deriving the number of divided lightings, and FIG. 2C is lighting pattern register data. 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 the flow and action of the data shown in FIG.

FIG. 5 is a circuit diagram of an LED head used in this 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 intensity correction ROM 22 correction circuit timing generator 25 light emission pattern register 29 LED head strobe generation circuit

Claims (3)

[Claims] 1. A dot latent image is formed on a photoconductor while appropriately illuminating a plurality of LED elements arranged in a line in the sub-scanning direction for each scanning line, and the variation in the light amount between the LED elements is dealt with. A method for correcting print density in an LED printer, wherein the number of times of lighting in the sub-scanning direction is controlled based on the corrected value 2. An LED printer configured so that a dot latent image can be formed on a photoconductor while controlling lighting of LED elements arranged in a line based on pixel information.
The light amount variation between the elements is measured, and a storage unit in which correction data corresponding to the variation is written and a lighting pattern selected based on the correction data read from the storage unit are provided, and the lighting is performed. L is characterized in that a dot latent image is formed on a photoconductor while appropriately turning on an LED element a plurality of times in the sub-scanning direction for each scanning line based on pattern information.
ED printer 3. The LED element is appropriately moved in the sub-scanning direction based on video data generated while taking a logical product of both bit information of the pixel information of the LED element and the lighting pattern information corresponding to the LED element. The LED printer according to claim 2, wherein the lighting control is performed a plurality of times.