JP4048761B2 - Print head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a print head and a density correction method, and more particularly to a print head in which a plurality of light emitting elements are arranged in a line and an exposure amount correction method, which are used to form an image by exposing a photoreceptor. .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a print head in which a plurality of recording elements are arranged in a line is used as a print head of an image forming apparatus such as a printer, a copying machine, and a facsimile. A typical example is an LED print head (LPH) that is used in an electrophotographic image forming apparatus and uses LEDs as recording elements.
[0003]
In general, an LED print head has an LED array in which a plurality of LED chips each having a large number of LEDs arranged in a line are arranged, and a plurality of rod lenses arranged to form an image of light output from the LEDs on the surface of the photoreceptor. The SELFOC lens. In the image forming apparatus, each LED of the LED print head is driven based on the image data, light is output toward the photoconductor, and the light output by the Selfoc lens is imaged on the surface of the photoconductor. Perform exposure based on the image data of the photoconductor, and move the photoconductor and the LED print head relative to each other (this movement direction is referred to as the “sub-scanning direction”) to move the exposure position and form an image on the photoconductor To do.
[0004]
In an image forming apparatus using such a print head in which a plurality of recording elements are arranged, variations in the output energy amount cause unevenness in the exposure energy distribution, which appears on the image as streaks in the sub-scanning direction, degrading image quality. Cause it. The causes of the variation in the output energy amount can be broadly classified into the following three.
・ Difference between chips due to variations in chip manufacturing
・ Difference between light emitting points due to variations in chip manufacturing
・ Periodic unevenness due to the structure of the SELFOC lens
Variation in the amount of output energy due to these causes is an unavoidable problem. Usually, a print head has a driver configuration for correcting variations in output energy of each recording element, and variations due to the above-mentioned causes that occur in manufacturing. Is corrected.
[0005]
For example, in JP-A-2-36962, in a line recording head, image density is measured for each pixel, and correction data for each recording element is obtained in comparison with a reference density and stored in a memory. A technique for driving a recording element based on corresponding correction data has been proposed. Specifically, driving conditions (pulse width) and gradation correction (TRC) are used as correction data, and actual correction is corrected only by a density signal for the corresponding recording element.
[0006]
Japanese Patent Laid-Open No. 11-342650 discloses that an LED print head measures a beam profile (output light amount distribution) of each light emitting element so that a light emission amount exceeding a predetermined threshold in the beam profile becomes constant. In addition, a technique for controlling the output of each light emitting element has been proposed. In this technique, the amount of light emission is determined by excluding the skirt portion of the beam spot, so that the exposure energy at each light emission point is made uniform.
[0007]
In JP-A-11-227254, a plurality of light emitting elements are turned on except for adjacent light emitting elements, and the light emission intensity distribution (output light quantity distribution) of each light emitting element turned on by a PD (Photo Diode) is measured. Then, a feature point based on the emission intensity distribution, specifically, a displacement amount of the peak position, a change in the peak value, a change in the emission diameter, an emission diameter, an amount of light, and an emission area are derived. A technique for correcting the light emission intensity of a light emitting element has been proposed.
[0008]
Japanese Patent Laid-Open No. 2000-198233 discloses a technique for controlling the light energy (output light amount) of a target dot based on the peripheral dots for each target dot in consideration of the points (peripheral dots) that affect each other. Proposed. Specifically, the light energy is controlled according to the distance from the peripheral dots. At this time, the influence from the peripheral dots is held in advance as a matrix, and the influence from the peripheral dots is stored as image data. It is calculated from
[0009]
By the way, in addition to the amount of output energy of each recording element, the cause of unevenness in the output exposure energy distribution in a print head in which a plurality of recording elements are arranged in a line is the spread of the output energy from each recording element and its position. And variations in characteristic values such as superimposition of output energy between adjacent pixels. The cause of the variation in each characteristic value will be described below.
[0010]
First, the spread of output energy shows a gradual change due to the structure of the Selfoc lens. That is, the rate of change is small. This is because the light output from each light emitting point (LED) passes through a plurality of rod lenses per light emitting point, and the light output from the adjacent light emitting points passes through the rod lens in the SELFOC lens. It is for passing. For example, even if a change in the spread of output energy occurs due to dust adhesion or lens scratches, it gradually changes within a range of several mm width, and the rate of change is small. Even if the characteristics of the adjacent rod lenses are different, the influence similarly causes a change in the spread of the output energy gradually within the range of several mm width.
[0011]
Next, regarding the position of the output energy, this variation is mainly caused by the positional accuracy of the light emitting point. The positional accuracy of the light emitting point is sufficient in the chip, which is not a problem. If the relative position between the chips is shifted due to the variation in ASSY, a large positional variation (variation) occurs between the chips.
[0012]
Next, superimposition is caused by the variation in the output energy amount of each recording element, the spread of output energy, and the position of the output energy described above. In other words, if there is no variation in the amount of output energy of each recording element, the spread of output energy, and the position of the output energy, unevenness in the exposure energy distribution due to superposition does not occur.
[0013]
[Problems to be solved by the invention]
However, all of the conventional techniques control the output (signal, drive current value, etc.) supplied to drive each recording element individually to a predetermined characteristic value to achieve uniform exposure energy distribution. Therefore, the unevenness of the exposure energy distribution due to superimposition has not been considered. In particular, when the resolution exceeds 600 dpi (dot per inch), it is known that the contribution ratio of the influence of superimposition on the unevenness of the exposure energy distribution is markedly increased, which hinders the formation of high-quality images at high resolution. There was a problem.
[0014]
Even if the exposure energy distribution unevenness including the influence of superimposition can be corrected by the light amount control of the prior art, there is an effect for a specific image density, but the exposure energy for a different image density. In some cases, the non-uniform distribution was further exacerbated. This is because, in general, what appears in the image is not the total energy that is exposed, but the amount of energy that exceeds a certain threshold appears in the image. For example, when the print head has an exposure energy distribution as shown in FIG. 23, the energy distribution shown in FIGS. 24 and 25 has an effect on the image density. That is, if it is a low concentration part, it is a high energy part near the peak of energy distribution, and the influence of a low energy part comes out as it becomes high concentration.
[0015]
In the technique described in Japanese Patent Laid-Open No. 2-36962, it is shown that the output energy is changed depending on the density, but the output to each recording element is corrected from the output density obtained from the corresponding storage element. The influence from the memory element is not considered at all. That is, the influence of superposition cannot be removed, which is insufficient for high-quality image formation.
[0016]
Further, in the technique described in Japanese Patent Application Laid-Open No. 2000-198233, the influence from surrounding dots around the target dot is taken into account. However, as described above, variation in characteristic values such as output energy amount, No consideration is given to the unevenness of the exposure energy distribution due to the variation. In other words, this technology assumes that there is no variation in the profile of each light emitting element, and focuses on the size of the target dot on the recording paper for the shape of the composite profile that combines the light emission profiles without variation. Since the above-mentioned variation is unavoidable in a print head in which recording elements are arranged on a line, this technique cannot obtain a good image quality.
[0017]
The present invention has been made to solve the above-described problems, and provides a print head and an exposure amount correction method capable of correcting unevenness of exposure energy distribution including the influence of superposition by neighboring recording elements. For the purpose.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 is a print head that is used to form an image by exposing a photoreceptor, and a plurality of light emitting elements are arranged in a line, The exposure amount distribution between the light emitting elements to be lit is superimposed so as to affect at least the image density. Multiple light emitting elements Point When lighted Dew of Light intensity distribution A threshold value for high density is set so as to include a skirt portion of an exposure amount distribution of each light emitting element that constitutes a region that overlaps to an extent that affects the image density, and each light emitting element that constitutes the overlapping region A low density threshold value is set so as not to include the tail part of the exposure quantity distribution, and the exposure quantity distribution part exceeding the high density threshold value of the exposure quantity distribution is preset so as to be substantially flattened in the line direction. The correction data for the high-density image for each of the light-emitting elements, and the light emission set in advance so as to substantially flatten the exposure amount distribution portion exceeding the low density threshold of the exposure amount distribution in the line direction. Correction data for low-density images for each element From storage means for storing and correction data stored in the storage means, For each light emitting element, the dot density near the light emitting element (the light emitting element and its surrounding light emitting elements) And a correction means for selecting the correction data, and a correction means for correcting the exposure amount of the light emitting element based on the correction data selected by the selection means.
[0019]
According to the invention of claim 1, The exposure amount distribution between the light emitting elements to be lit is superimposed so as to affect at least the image density. Multiple light emitting elements In the exposure amount distribution when the light is turned on, a threshold value for high density is set so as to include a skirt portion of the exposure amount distribution of each light emitting element that constitutes a region to be superimposed to an extent that affects the image density, and the superposition is performed The threshold value for low density is set so as not to include the tail part of the exposure amount distribution of each light emitting element that constitutes the area to be exposed, and the exposure amount distribution part that exceeds the high density threshold value of the exposure amount distribution is substantially flat in the line direction. The correction data for the high-density image for each light emitting element set in advance and the exposure amount distribution portion exceeding the low density threshold of the exposure amount distribution are set in advance so as to be substantially flattened in the line direction. Correction data for low density images for each light emitting element is stored in the storage means. That is, in the storage means, correction data set in consideration of the influence of superposition by neighboring light emitting elements is prepared according to the image density, and the correction data stored in the storage means is stored by the selection means. home, For each light emitting element, the dot density near the light emitting element (the light emitting element and its surrounding light emitting elements) The correction data corresponding to is selected, and the exposure amount of each light emitting element is corrected by the correction means based on the selected correction data.
[0020]
Thereby, since the exposure amount of each light emitting element is corrected using correction data set in consideration of the influence of superimposition, unevenness of the exposure energy distribution including the influence of superposition can be corrected, and the vicinity of the light emitting element can be corrected. Since the correction data used for the correction is changed according to the image density, the correction data can be appropriately corrected regardless of the image density, and a high-quality image can be formed.
[0024]
Claims 2 As described in , The light emitting element may be turned on with a lighting pulse width based on image data, and the output light amount may be adjusted by the correction unit based on the correction data.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Next, a first embodiment according to the present invention will be described in detail with reference to the drawings.
[0037]
[Optical profile measuring device]
FIG. 1 shows a configuration of an optical profile measuring apparatus for measuring an exposure energy distribution of a print head used in an image forming apparatus.
[0038]
As shown in FIG. 1, an optical profile measuring apparatus 10 includes an LED array 12 in which a plurality of LEDs are arranged on a line in the direction of arrow A, and a selfoc lens array (SLA) 14. A sensor 18 for measuring an exposure energy distribution by a head (hereinafter referred to as “LPH”) 16 (details will be described later) is provided. The LPH 16 is set at a predetermined position by a holder member (not shown).
[0039]
The sensor 18 is configured by attaching a magnifying lens (in this embodiment, × 10 magnification) 22 to the light receiving surface side of a line CCD 20 in which a plurality of CCDs (Charge Coupled Devices) are arranged in a line. Further, the sensor 18 has the light receiving surface of the line CCD 20 opposed to the light output direction of the LPH 16 and the CCD array with respect to the LED array direction of the LPH 16 indicated by the arrow A (hereinafter referred to as “main scanning direction”). It is installed on a sensor moving stage 24 that can move at a constant speed in the main scanning direction so that the directions are orthogonal.
[0040]
That is, the sensor 18 receives light incident on each light receiving surface by each CCD while moving at a constant speed in the main scanning direction (LED arrangement direction), and outputs an electrical signal corresponding to the received light amount (this book). In the embodiment, the output energy distribution of the LPH 16 in a direction orthogonal to the LED arrangement direction (hereinafter referred to as “sub-scanning direction”) can be measured.
[0041]
The sensor 18 is connected to a personal computer (PC) 28 via a driver 26, and the personal computer 28 is also connected to the LPH 16 via a driver 26. The personal computer 28 is also connected to a driving unit (not shown) of the sensor moving stage 24.
[0042]
The personal computer 28 outputs lighting data to the LPH 16 via the driver 26, controls lighting of each LED of the LPH 16, and outputs a moving stage control signal to a driving unit (not shown) of the sensor moving stage 24 to move the sensor. By controlling the driving of the stage 24, the sensor 18 is moved at a constant speed in the main scanning direction, and a measurement timing signal is output to the sensor 18, and exposure energy measurement by the sensor 18 is ON / OFF controlled.
[0043]
The output of the sensor 18 is connected to the arithmetic processing unit 30, and the measurement result by the line CCD 20 from the sensor 18, that is, an electric signal (8-bit data) corresponding to the amount of light received by each CCD is serially input to the arithmetic processing unit 30. Is done.
[0044]
As shown in FIG. 2, the arithmetic processing unit 30 includes a memory 32, a memory 34, a comparator 36, and an adder 38 for each of the relatively low density and high density. In the following description, when the low concentration and the high concentration are distinguished from each other, the low concentration memory 34, the comparator 36, and the adder 38 have “A” at the end of their respective symbols. The memory 34, the comparator 36, and the adder 38 will be described with “B” added to the end of each code.
[0045]
The memory 34A stores a predetermined low concentration threshold value set in advance, and the memory 34B stores a predetermined high concentration threshold value set in advance. The low density threshold and the high density threshold are values corresponding to the minimum exposure amount required to obtain the image densities of low density and high density, and correspond to the threshold values of the present invention.
[0046]
The measurement results of each CCD input from the line CCD 20 are input to each of the comparators 36A and 36B. The comparator 36A compares the measurement result of each CCD with the low density threshold value stored in the memory 34A, and outputs data indicating the excess of the low density threshold value as the comparison result. The comparator 36B The CCD measurement result is compared with the high density threshold value stored in the memory 34B, and data indicating the excess of the high density threshold value is output as the comparison result.
[0047]
Adders 38A and 38B add the output data from comparators 36A and 36B, respectively. That is, the adders 38A and 38B add the amount exceeding the low density threshold or the high density threshold that affects the image density among the measurement results of each CCD of the line CCD 20, and add one line of the line CCD 20. After the addition is performed on the output data from the CCD, the addition result is stored in the memory 32 and the addition value is reset.
[0048]
That is, for each measurement by the line CCD 20, the memory 32 sequentially stores data corresponding to the addition (integration) value of the exposure energy amount exceeding a predetermined low density threshold and high density threshold for one line CCD. When the measurement is performed in the main scanning direction of the print head, the profile of the data in the main scanning direction for low density and high density (hereinafter referred to as “light profile for low density”, “for high density”). Respectively).
[0049]
The arithmetic processing unit 30 is connected to the personal computer 28 via the driver 26, and the light profile for low density and the light profile for high density stored in the memory 32 are respectively transferred. The personal computer 28 calculates correction data for low density based on the light profile for low density, and calculates correction data for high density based on the light profile for high density (details will be described later). Explained in the section).
[0050]
[Image forming equipment]
Next, an image forming apparatus 40 that forms an image using the LPH 16 will be described with reference to FIG. As shown in FIG. 3, the image forming apparatus 40 includes a photosensitive drum 42 that rotates at a constant speed in the direction of arrow B. The rotation direction (arrow B) of the photosensitive drum 42 corresponds to the sub-scanning direction.
[0051]
Around the photosensitive drum 42, a charger 44, an LPH 16, a developing unit 46, a transfer roller 48, a cleaner (not shown), and an erase lamp (not shown) are arranged in this order along the rotation direction of the photosensitive drum 42. It is installed.
[0052]
That is, the surface of the photosensitive drum 42 is uniformly charged by the charger 44 and then irradiated with a light beam by the LPH 16 to form a latent image on the photosensitive drum 42. The LPH 16 is connected to an LPH driving unit 100, which will be described later, and is controlled to be lit by the LPH driving unit 100. Based on the image data, the low-density correction data is obtained at low density, and the high-density data is obtained at high density. A light beam corrected based on the density correction data is emitted.
[0053]
To the formed latent image, toner is supplied by the developing device 46 to form a toner image on the photosensitive drum 42. The toner images on the photosensitive drum 42 are taken out one by one from the paper tray 50 by the transfer roller 48 and transferred to the paper 54 conveyed by the paper conveying belt 52. The toner remaining on the photosensitive drum 42 after the transfer is removed by a cleaner (not shown), neutralized by an erase lamp (not shown), charged by the charger 44 again, and the same processing is repeated.
[0054]
On the other hand, the paper 54 onto which the toner image has been transferred is conveyed to a fixing device 56 composed of a pressure roller 56A and a heating roller 56B and subjected to a fixing process. As a result, the toner image is fixed and a desired image is formed on the paper 54. The paper 54 on which the image is formed is discharged out of the apparatus.
[0055]
[Configure printhead details]
FIG. 4 shows a configuration diagram of the LPH 16 in which a large number of LEDs are used in the present embodiment. As shown in FIG. 4, the LPH 16 includes an LED array 12, a printed circuit board 60 on which a circuit for supplying various signals for supporting the LED array 12 and controlling driving of the LED array 12 is formed, and the SLA 14. I have.
[0056]
The printed circuit board 60 is disposed in the housing 62 with the mounting surface of the LED array 50 facing the photosensitive drum 42, and is supported by a plate spring 64.
[0057]
As shown in FIG. 5, the LED array 12 has a plurality of SLED (Self-Scanning LED) chips 68 in which a plurality of LEDs 66 are arranged in series along the axial direction of the photosensitive drum 42. Has been configured. The axial direction of the photosensitive drum 42 corresponds to the main scanning direction.
[0058]
In the LED array 12, by using this SLED chip 68, irradiation can be performed while scanning a light beam at a predetermined resolution in the axial direction of the photosensitive drum 42.
[0059]
Specifically, in the present embodiment, four SLED chips 68 are arranged in series to form the LED array 12, and 128 LEDs 66 are arranged in each SLED chip 68. In addition, below, when distinguishing each SLED chip | tip 68, the chip number of 1-4 is provided and demonstrated.
[0060]
In the present embodiment, the case where the self-scanning SLED chip 68 is used will be described as an example. However, the present invention may not be self-scanning. Of course, the number of SLED chips 68 need not be four.
[0061]
As shown in FIG. 4, the SLA 14 is supported by an SLA holder 70 and forms an image on the photosensitive drum 42 with the light beams emitted from the respective LEDs 66.
[0062]
[SLED circuit configuration]
Next, the circuit configuration of each SLED chip 68 will be described.
[0063]
As shown in FIG. 5, the lighting control signal ΦI (1 to 4: chip number), the transfer signals CK1 and CK2, and the start signal CKS for each SLED chip 68 are input to each SLED chip 68 from the LPH driving unit 100. It has come to be.
[0064]
As shown in FIG. 6, the SLED chip 68 is provided with a power supply line 80 and a GND (ground) line 82, and a predetermined voltage VDD (5 V) is supplied from a power supply device (not shown).
[0065]
In FIG. 6, in order to distinguish each SLED chip 68, the chip numbers 1 to 4 are shown in parentheses at the end of the reference numerals, and the following explanation follows this. Similarly, the members provided for each SLED chip 68 and the generated signals will be described with the chip numbers shown in parentheses at the end of the reference numerals. In FIG. 6, since the configuration of each SLED chip 68 (1-4) is the same, only the SLED chip 68 (1) is shown in detail, and the remaining SLED chips (2-4) are omitted. It shows.
[0066]
The SLED chip 68 includes a thyristor 84 for each of the plurality of LEDs 66 arranged in the SLED chip 68. The operation of the SLED chip 68 will be described with reference to the equivalent circuit of FIG. When the trigger is sometimes set to the high level, the current Itr flows to the point G, and at the same time, the current Ib2 flows from the point G to the base of the transistor Q2 (Itr≈Ib2). Thereby, the transistor Q2 is turned on, and the collector current of the transistor Q2 flows. That is, the base current Ib1 of the transistor Q1 flows, and the transistor Q1 is also turned on.
[0067]
When the transistor Q1 is turned on, the collector current IC1 of the transistor Q1 flows, the voltage at the point P increases, and the current Itr stops flowing. However, since the collector current Ic1 of the transistor Q1 flows to the base of the transistor Q2 (current Ib2), the transistor Q2 is kept on.
[0068]
Thereby, even if the trigger becomes a low level, the transistors Q1 and Q2 maintain the on state. In this state, the voltage VDD is held, the LED can be turned on, and a predetermined light amount can be obtained by performing pulse width modulation.
[0069]
As shown in FIG. 6, the anode side of each thyristor 84 is connected to the power supply line 80 and supplied with a predetermined voltage VDD. The first-stage thyristor 84 uses a start signal CKS (voltage) as a trigger to turn on the LEDs 66 of the SLED chip 68 from the point G1 connected to the gate side (the number following the point G indicates the order of the plurality of LEDs 66 arranged). Is applied. Further, the point G (1 to 128) connected to the gate side of the thyristor 84 at each stage is connected in series via the diode 86. Further, the points G (1 to 128) of each stage are connected to the GND line 82 through the resistors 88, respectively. The GND line 82 maintains a predetermined voltage at the first stage and decreases by a predetermined potential as it goes to each stage.
[0070]
Further, the point G (1 to 128) is connected to the anode side of the LED 66, and the lighting control signal ΦI (1 to 4: chip number) from the LPH driving unit 100 is supplied to the cathode side of the LED 66. It is connected to the. When the lighting control signal ΦI is at a low level (L), the LED 66 is lit if the thyristor 84 whose gate is the point G (1 to 128) is ON.
[0071]
The cathode side of the odd-numbered thyristor 84 is connected to the transfer signal CK1, and the cathode side of the even-numbered thyristor 90 is connected to the transfer signal CK2. According to the transfer signals CK1 and CK, the potential of the point G (1-128) is increased by a predetermined potential. That is, the potential at the point G reaches the predetermined potential at which the LED 66 can be turned on in order from the first point G1 to the subsequent stage, and the SLED chip 68 can be self-scanned.
[0072]
[Printer circuit configuration]
Next, a circuit configuration on the printed circuit board 60 for generating various control signals for controlling the driving of the SLED chip 68 having the above configuration will be described. As shown in FIG. 8, a circuit having a configuration in which the EEPROM 102, the screen processing unit 104, and the peripheral density determination unit 106 are connected to the LPH driving unit 100 is formed on the printed circuit board 60. In the EEPROM 102, correction data obtained by the personal computer 28 is stored in advance.
[0073]
The screen processing unit 104 reads and inputs image data to be processed from a memory (not shown) under the control of a main controller (not shown) that controls the entire operation of the image forming apparatus 40, and outputs the image data to the screen processing unit 104. Screen processing is performed and the data is sent to the LPH drive unit 100. Further, the image data is also input to the peripheral density determination unit 106, and the peripheral density determination unit 106 calculates either the low density correction data or the high density correction data based on the target pixel and the density of the peripheral pixels. Tag data for selection is generated and sent to the LPH drive unit 100. That is, the peripheral density determination unit 106 corresponds to the selection unit of the present invention.
[0074]
The LPH drive unit 100 generates a drive signal for driving the SLED chip 68 based on the screen-processed image data and Tag data, and outputs the drive signal to the SLED chip 68. The SLED chip 68 is driven based on this drive signal, that is, the LED 66 is turned on. More specifically, the LED 66 emits light that is pulse-modulated based on screen-processed image data and intensity-modulated based on low-density correction data or high-density correction data selected based on Tag data. Is output.
[0075]
Next, each circuit configuration of the screen processing unit 104, the peripheral density determination unit 106, and the LPH driving unit 100 will be described in detail. FIG. 9 shows detailed configurations of the screen processing unit 104 and the peripheral density determination unit 106.
[0076]
As shown in FIG. 9, image data is serially input to the peripheral density determination unit 106 from a main controller (not shown) together with the video clock VCLK and in synchronization with the video clock VCLK. In this embodiment, the image data is 8-bit data and takes a value from 0 to 240.
[0077]
The peripheral density determination unit 106 includes three FIFO (First In First Out) memories 108A, 108B, and 108C as a line memory for three lines. Image data is input to the FIFO memory 108A, and the output is the FIFO memory. The output of the FIFO memory 108B is input to the FIFO memory 108C. A video clock VCLK is supplied to the FIFO memories 108A, 108B, and 108C, and image data for three consecutive lines is stored in the FIFO memories 108A, 108B, and 108C in accordance with the video clock VCLK.
[0078]
Two flip-flops 110 and 112 are connected in series at the subsequent stage of each FIFO memory. In the following description, when distinguishing the corresponding FIFO memories, as shown in FIG. 9, an alphabet at the end of the code of the corresponding FIFO memory is given to the end of each code.
[0079]
The video clock VCLK is supplied to the clock terminals (CK) of the flip-flops 110 and 112, and the output terminal (Q) of the flip-flop 112 is connected to the full adder 114.
[0080]
The full adder 114 is also branched and input to the flip-flops 110 and 112, and the full adder 114 outputs the addition result of these input values. That is, the full adder 114 adds the image data Pdot of the target pixel and the image data of the surrounding pixels, that is, image data for a total of 9 pixels of 3 × 3 pixels.
[0081]
In this embodiment, a case where 3 × 3 pixel image data is added will be described as an example. However, the present invention is not limited to this, and it may be n × n pixels (n ≧ 1).
[0082]
The output of the full adder 114 is input to the positive terminal side of the comparator 116, and a predetermined TAG threshold value set in advance is input to the negative terminal side of the comparator 116. The comparator 116 compares the addition result of 9-pixel image data (hereinafter referred to as “SUM9DOT”) with the TAG threshold value, and outputs the result.
[0083]
Specifically, in the present embodiment, the TAG threshold value is preset to “432”, which is a value corresponding to a density of about 20% of all black. The comparator 116 outputs a signal indicating a value of “1” when “SUM9DOT> TAG threshold” and “0” when “SUM9DOT ≦ TAG threshold”.
[0084]
The output of the comparator 116 is input to the rearrangement unit 118. The rearrangement unit 118 rearranges the output of the comparator 116, that is, the comparison result between the SUM9DOT and the TAG threshold so as to match the lighting order of the LEDs 66 (see FIG. 20), and sends it as TAG data to the LPH drive unit 100. . In the present embodiment, an image for one pixel is formed by 4 × 4 light emitting points (LEDs).
[0085]
Further, as shown in FIG. 9, the screen processing unit 104 receives a video clock VCLK and a line synchronization signal LSYNC from a controller (not shown). The screen processing unit 104 includes an image threshold generation unit 120, a VDATA generation unit 122, and a rearrangement unit 124, and the video clock VCLK and the line synchronization signal LSYNC are supplied to the image threshold generation unit 120.
[0086]
As shown in FIG. 10, the image threshold generation unit 120 includes two 2-bit counters 126A and 126B. In the 2-bit counter 126A, the video clock VCLK is input to the clock input terminal (CLK), and the line synchronization signal LSYNC is input to the clear signal terminal (CLR). That is, the 2-bit counter 126A counts the number of clocks of the video clock VCLK and resets the count value by the input of the line synchronization signal LSYNC.
[0087]
The 2-bit counter 126B receives the line synchronization signal LSYNC at the clock input terminal, and counts the number of times the line synchronization signal LSYNC is input (generated). The counter results from the 2-bit counters 126A and 126B are output as an HPIC signal and a VPIC signal, respectively, and are used for addressing the image threshold generation ROM 128 that stores a 4 × 4 image threshold matrix in advance. The reason why the 4 × 4 image threshold value matrix is used is that in the present embodiment, an image corresponding to the image data of one pixel of interest is formed by 4 × 4 light emitting points (LEDs).
[0088]
The image threshold values stored in the addresses specified by the HPIC signal and the VPIC signal are sequentially read from the image threshold value generation ROM 128 and output from the image threshold value generation unit 120 to the VDATA generation unit 122 in the subsequent stage.
[0089]
The output of the flip-flop 110A, that is, the image data Pdot of the target pixel is also input to the VDATA generator 122. The VDATA generating unit 122 compares the image data Pdot with the 4 × 4 image threshold values sequentially input, performs an operation according to the comparison result, and performs image data Pdot of one target pixel. Lighting data VDATA for 4 × 4 light emitting points (LEDs) is generated.
[0090]
Specifically, in the present embodiment, the following comparison / calculation is performed based on the image threshold value and the image data Pdot of the target pixel to generate 4-bit data as the lighting data VDATA.
[0091]
When threshold <Pdot <(threshold + 15), VDATA = Pdot−threshold
When Pdot ≦ threshold, VDATA = 0
When (threshold value + 15) ≦ Pdot, VDATA = 15
In the above formula, the image threshold is abbreviated as “threshold”.
[0092]
Each LED 66 is lit for a time corresponding to the corresponding lighting data VDATA. FIG. 11 shows an example of the lighting data VDATA when Pdot is 0, 15, 37, 202, 240. In FIG. 11, when VDATA = 0, the area is outlined, when VDATA = 1 to 14, a part of the area is painted black, and when VDATA = 15, the entire area is painted, and the generated VDATA is generated. The value of is shown.
[0093]
The output of the VDATA generation unit 122 is input to the rearrangement unit 124. The rearrangement unit 124 rearranges the output of the VDATA generation unit 122, that is, the lighting data VDATA in accordance with the lighting order of the LEDs 66 (see FIG. 20), and sends the rearranged data to the LPH driving unit 100.
[0094]
As shown in FIG. 9, the video clock VCLK and the line synchronization signal LSYNC from the main controller are also input to the timing signal generator 130 provided on the printed circuit board 60. In the timing signal generation unit 130, based on the video clock VCLK and the line synchronization signal LSYNC, the line synchronization signal LS indicating one main scanning start timing (one main scanning interval) and the transfer indicating the transfer timing of the lighting data VDATA and TAG data are transferred. A clock SCLK is generated (see FIG. 20) and sent to the LPH drive unit 100.
[0095]
As shown in FIG. 6, the LPH drive unit 100 includes a drive signal generation unit 140, three flip-flops 142A1 to A3, and three flip-flops 142B1 to B3. In addition, the LPH driving unit 100 includes, for each of the SLED chips 68 (1 to 4) included in the LPH 16, a correction memory 144 (1 to 4) and a flip-flop 146A (1 to 4) as storage means of the present invention. 4) It has 146B (1-4) and the drive element part 148 (1-4) which bears the function as a correction | amendment means of this invention.
[0096]
The flip-flops 142A1 to A3, the flip-flops 142B1 to B3, the correction memories 144 (1 to 4), the flip-flops 146A (1 to 4), 146B (1 to 4), and the drive element units 148 (1 to 4) are driven. A signal generated by the drive signal generator 140 is connected to the signal generator 140.
[0097]
The drive signal generation unit 140 receives the line synchronization signal LS and the transfer clock SCLK from the timing signal generation unit 130.
[0098]
The drive signal generator 140 generates the transfer signals CK1, CK2 and the start signal CKS at a predetermined timing synchronized with the line synchronization signal LS and the transfer clock SCLK, and outputs them to the SLED chips 68 (1-4). Then, a lighting strobe signal STB indicating a lighting possible period of each LED 66 is generated and output to each driving element unit 148 (1 to 4).
[0099]
In addition, the drive signal generation unit 140 generates select signals SCK1, SCK2, and SCK3 at predetermined timings synchronized with the line synchronization signal LS and the transfer clock SCLK, and the select signal SCK1 is a clock terminal of the flip-flops 142A1 and 142B1 ( CK), the select signal SCK2 is output to the clock terminals of the flip-flops 142A2 and 142B2, and the select signal SCK3 is output to the clock terminals of the flip-flops 142A3 and 142B3.
[0100]
In addition, the drive signal generation unit 140 generates the latch signal LCH at a predetermined timing synchronized with the line synchronization signal LS and the transfer clock SCLK, and the flip-flops 146A (1-4) and flip-flops 146B (1-4). To each output. Further, the drive signal generation unit 140 generates a 7-bit address signal ADL for designating an address, and outputs it to the correction memory 144 (1 to 4).
[0101]
The lighting data VDATA from the screen processing unit 104 is branched and input to the input terminals (D) of the flip-flops 142A1 to A3. The output terminals (Q) of the flip-flops 142A1 to A3 are connected to the input terminals (D) of the flip-flops 146A (1 to 3), respectively, and the input lighting data VDATA is input to the flip-flops 146A (1 to 3). Is output. The lighting data VDATA from the screen processing unit 104 is input as it is to the input terminal (D) of the flip-flop 146A (4). The output terminals (Q) of the flip-flops 146A (1 to 4) are connected to the corresponding drive element units 148 (1 to 4).
[0102]
The flip-flops 142A1 to A3 output signals based on select signals SCK1, SCK2, and SCK3 input from the respective clock terminals, and the flip-flops 146A (1 to 4) output latch signals LCH input from the clock terminals. Input and output signals based on Thus, the lighting signals VD (1 to 4) of the corresponding SELD chips 68 (1 to 4) are input to the drive element units 148 (1 to 4) from the flip-flops 146A (1 to 4), respectively. It has become.
[0103]
On the other hand, the TAG data from the peripheral density determination unit 106 is branched and input to the input terminals (D) of the flip-flops 142B1 to B3. The output terminals (Q) of the flip-flops 142B1 to B3 are connected to the correction memories 144 (1 to 3), respectively, and the inputted TAG data is output to the correction memories 144 (1 to 3). The TAG data from the peripheral density determination unit 106 is input to the correction memory 144 (4) as it is.
[0104]
The correction memory 144 (1 to 4) stores correction data for low density and correction data for high density of each of the 128 LEDs 66 provided in the corresponding SLED chips 68 (1 to 4). This storage is performed by reading from the EEPROM 102 when the power is turned on, for example. In the present embodiment, the storage location of each correction data in the correction memory 144 is designated by an 8-bit address, the upper 1 bit indicates low / high density, and the lower 7 bits indicate an LED.
[0105]
The correction memory 144 (1 to 4) is a flip-flop corresponding to each of the TAG data as the correction signal COR (1 to 4) stored as the correction signal COR (1 to 4) with the address specified as the upper 1 bit and the address signal ADL as the lower 7 bits. 146B (1-4). That is, it is specified by the address signal ADL which correction data corresponding to the LED 66 of the LEDs 66 provided in the SLED chip 68 is read out, and the correction data for low density or the correction data for high density is selected by the TAG data. Whether to read is specified. The outputs (Q) of the flip-flops 146B (1-4) are connected to the corresponding drive element units 148 (1-4).
[0106]
The flip-flops 142B1 to B3 input / output signals based on select signals SCK1, SCK2, and SCK3 input from the respective clock terminals, and the flip-flops 146B (1 to 4) are input from the respective clock terminals. A signal is input / output based on the latch signal LCH. Thereby, the correction signals COR (1-4) of the corresponding SELD chips 68 (1-4) are read from the correction memories 144 (1-4) to the drive element units 148 (1-4), The signal is input from the flip-flop 146B (1 to 4).
[0107]
As shown in FIG. 12, each driving element unit 148 (1-4) includes a 4-bit counter 150, a comparator 152, AND circuits 154A, 154B, 154C, 154D, and transistors (n-channel MOSFETs) 156, 158A. 158B, 158C, 158D.
[0108]
In the 4-bit counter 150, a pulse modulation clock PWMCLK that divides the lighting-enabled period of each LED 66 indicated by the lighting strobe signal STB into 16 is input to a clock terminal (CLK), and a drive signal generation unit is input to a clear terminal (CLR). The strobe signal STB from 140 is input. The 4-bit counter 150 counts the number of pulses of the input pulse modulation clock PWMCLK, outputs the count value CD, and resets the count value CD when the strobe signal STB is input.
[0109]
The output terminal (Q) of the 4-bit counter 150 is connected to the negative side input terminal of the comparator 152, and the comparator 152 receives the count value of the number of pulses of the pulse modulation clock PWMCLK. The lighting signal VD (1-4) input from the corresponding flip-flop 146A (1-4) to the drive element unit 148 is input to the plus side input terminal of the comparator 152.
[0110]
The comparator 152 compares the input count value with the lighting signal VD, and the comparison result is “1” when “count value CD ≦ VD” and “0” when “count value CD> VD”. Is output. The output of the comparator 152 branches to the AND circuits 154A to 154D and the gate side of the transistor 156 and is input to each of them.
[0111]
To the AND circuits 154A to 154D, the 4-bit correction signals COR (1 to 4) input from the corresponding flip-flops 146B (1 to 4) are branched and input to the bits (COR0 to COR3). The outputs of the AND circuits 154A to 154D are connected to the gate sides of the transistors 158A to 158D, and the AND circuits 154A to 154D output the output of the comparator 152 and each bit value (COR0 to COR3) of the correction signal COR. An AND operation is performed, and the result is input to the gate side of the transistors 158A-D.
[0112]
The sources of the transistors 156 and 158A to 158D are grounded, and the drain sides are connected in parallel via resistors R, RA, RB, RC, and RD. The potential at the connection point P of the resistors R, RA, RB, RC, and RD is supplied from the drive element unit 148 to the corresponding SLED chips 68 (1 to 4) as the lighting control signal ΦI (1 to 4). .
[0113]
[Action]
Next, the operation of the present embodiment will be described.
[0114]
[Correction data calculation process]
First, correction data calculation processing by the personal computer 28 will be described. FIG. 13 shows a control routine for correction data calculation processing executed by the personal computer 28. When performing the correction data calculation process, the LPH 16 used for the image forming apparatus 40 is held in advance in the optical profile measuring apparatus 10 by a holder member (not shown) and set at a predetermined position.
[0115]
First, the personal computer 28 outputs lighting data instructing all lighting to the LPH 16 in step 200 of FIG. Accordingly, the LPH 16 receives the lighting data and lights all the LEDs 66 of the LPH 16 (all lighting).
[0116]
In the next step 202, the personal computer 28 outputs a movement stage signal to a drive unit (not shown) of the sensor movement stage 24, and causes the sensor movement stage 24 to move the sensor 18 at a constant speed in the main scanning direction. In the next step 204, a measurement timing signal is output to the sensor 18 to cause the sensor 18 to measure a cross section in the sub-scanning direction of the exposure energy distribution of the LPH 16.
[0117]
Then, until the movement of the sensor 18 in the main scanning direction is completed, the process proceeds from step 206 to step 208, the process returns from step 208 to step 204 every time a predetermined time elapses, and the measurement timing signal is output again. Thereby, until the movement of the sensor 18 in the main scanning direction is completed, the cross section in the sub-scanning direction of the exposure energy distribution of the LPH 16 is measured by the sensor 18 every predetermined time.
[0118]
In other words, in this embodiment, the personal computer 28 turns on all the LEDs 66 of the LPH 16 (all lights up), and the sensor 18 moves at a constant speed in the main scanning direction, as shown in FIG. A lighting signal, a moving stage control signal, and a measurement timing signal are output so that a cross section in the sub-scanning direction of the distribution is measured at a predetermined time period. The predetermined time period is determined so that the measurement result of the sensor 18 has a resolution of about several μm.
[0119]
At this time, the measurement result by the sensor 18, that is, each CCD output provided in the line CCD 20 of the sensor 18 is input to the arithmetic processing unit 30, and among the CCD outputs for one line of the line CCD 20, a low density threshold value. The amount exceeding the threshold value is added, and separately from the addition, the amount exceeding the high concentration threshold is added. That is, of the measurement results, an integral value obtained by rounding down the threshold value for low concentration and an integral value obtained by rounding down the threshold value for high concentration are calculated. This calculation result is stored in the memory 32.
[0120]
As a result, the sensor 18 is repeatedly measured at a predetermined cycle interval while moving at a constant speed in the main scanning direction, the calculation processing unit 30 performs the calculation, and the integrated values are sequentially stored in the memory 32. Finally (when the movement of the sensor 18 in the main scanning direction is completed), the exposure energy amount profile exceeding the low density threshold value in the main scanning direction (light profile for low density), and the exposure exceeding the high density threshold value. Each profile in the main scanning direction of the amount of energy (light profile for high density) is obtained.
[0121]
When the movement of the sensor 18 in the main scanning direction is completed, the process proceeds from step 206 to step 210. In step 210, the personal computer 28 reads out the low-density and high-density optical profiles stored in the memory 32, and in the next step 212, the low-density and high-density optical profiles are substantially omitted. The correction data for the low density and the correction data for the high density are respectively calculated so as to be flattened.
[0122]
The correction data calculated at this time is specifically correction data for adjusting the light quantity of each LED 66. This is because the LPH16 characteristic values that can be used for correction are only light amounts that can be adjusted easily electrically, and it is impossible to make fine adjustments after ASSY for spread, position, and superposition. is there.
[0123]
Next, using a specific example, correction data for low density and correction data for high density will be described in detail.
[0124]
FIG. 15 shows an example of a cross section in the sub-scanning direction of the exposure profile measured by the sensor 18 when the LPH 16 is fully lit. FIG. 16 shows a high-density optical profile obtained when the cross section in the sub-scanning direction of FIG. 15 was obtained, and a 0.2 mm wide moving average graph. FIG. The graph of the obtained optical profile for low density | concentration and the moving average of the 0.2 mm width is shown. FIGS. 16 and 17 are specific cases where the high concentration threshold TH (high) = 6 and the low concentration threshold Th (low) = 46, respectively.
[0125]
The reason why the moving average is set to 0.2 mm is that the human eye can identify only the unevenness of about 0.2 mm or more. For example, in the case of 600 dpi, the unevenness of the optical profile itself is 42.3 μm pitch, and the frequency is too high for human eyes to identify as uneven. That is, the unevenness when the moving average is taken with a width of 5 dots corresponding to 0.2 mm is confirmed by human eyes.
[0126]
As can be seen from the moving average graphs shown in FIGS. 16 and 17, the moving average of the high-density optical profile has a small variation (that is, uneven exposure energy distribution), and the moving average of the low-density optical profile. The variation is large. That is, when an image is formed using the LPH 16 in the image forming apparatus, an image with little unevenness in the high density area and noticeable unevenness in the low density area is formed. Therefore, the correction data obtained when this measurement is performed may be used as high-density correction data.
[0127]
Next, correction data for correcting unevenness in the low density region is obtained. Specifically, all peak values are detected from the light profile data, and an average value of data for ± 2 dots is calculated from the detected peak values. The calculated average value is used as an exposure value corresponding to each LED 66, an error from a predetermined target value is calculated, and correction data of each LED 66 is obtained from the correction resolution so that the error is minimized.
[0128]
At this time, the diffusion error method is adopted, the error remaining in the first LED 66 is added to the exposure value of the second LED 66, and the error between the addition result and a predetermined target value is calculated. In addition, correction data for the second LED 66 is obtained so that this error is minimized. Similarly, the error remaining in the second LED 66 is added to the exposure value of the third LED, and the error remaining in the third LED is sequentially added to the fourth LED exposure data. The correction data of each LED 66 is obtained by adding.
[0129]
FIG. 18 is a graph showing a light profile for high density obtained by re-measurement of the exposure profile at the time of full lighting using the correction data determined in this way, and a moving average graph having a width of 0.2 mm. FIG. 19 shows a low concentration light profile obtained in the same manner and its 0.2 mm graph of the moving average of the field. FIGS. 18 and 19 are specific cases where the high concentration threshold TH (high) = 6 and the low concentration threshold TH (low) = 46, respectively.
[0130]
As can be seen from the moving average graphs shown in FIGS. 18 and 19, the moving average of the low-density optical profile has a small variation, and the moving average of the high-density optical profile has a large variation. That is, when an image is formed by using the LPH 16 in the image forming apparatus, an image with less unevenness in the low density region and noticeable unevenness in the high density region is formed. Therefore, the correction data obtained when this measurement is performed may be used as low-density correction data.
[0131]
In this example, the case where good correction data is used for the high density region in the initial state has been described. However, when good correction data cannot be obtained for the high density region in the initial state, the low correction data is used. Correction data may be obtained in the same manner as the density region. Actually, there are more cases where it is necessary to obtain correction data for the high density area in the same manner as for the low density area.
[0132]
In this way, when the correction data capable of satisfactorily correcting unevenness is determined for each of the high density region and the low density region, the personal computer 28 stores the correction data in the EEPROM 102 of the LPH 16 in step 214 of FIG. Store and end the process.
[0133]
Thereafter, the LPH 16 is loaded into the image forming apparatus 40 and used for image formation by the image forming apparatus 40. That is, in the image forming apparatus 40, light corresponding to the image data is transmitted from the LPH 16 toward the photosensitive drum 42 whose surface is uniformly charged by the charger 44 while adjusting the light amount based on the determined correction data. Irradiation forms an electrostatic latent image on the photosensitive drum 42. The electrostatic latent image is developed by the developing device 46 and transferred onto the paper 54 by the transfer roller 48. In this way, the paper 54 onto which the toner image has been transferred is subjected to a fixing process by the fixing device 56 and then discharged out of the apparatus.
[0134]
[Lighting control processing]
Next, a lighting control process for outputting light according to image data while adjusting the amount of light from the LPH 16 during image formation will be described.
[0135]
When image formation is performed, a video clock VDCLK and a line synchronization signal LSYNC are supplied from a main controller (not shown). The timing signal generation unit 130 generates a line synchronization signal LS and a transfer clock SCLK based on these signals, and supplies the generated line synchronization signal LS and transfer clock SCLK to the LPH drive unit 100.
[0136]
At the same time, image data to be processed is input from the memory (not shown) to the peripheral density determination unit 106 under the control of the main controller (not shown). In the peripheral density determination unit 106, image data is sequentially stored in the FIFO memory 108 for three lines, and the image data Pdot of the target pixel and the image data for 3 × 3 pixels of the image data of the peripheral pixels are stored from the FIFO memory 108. The extracted result is added by the full adder 114, and the addition result is compared with a predetermined TAG threshold by the comparator 116 to generate TAG data of the target pixel. Then, the rearrangement unit 118 rearranges the TAG data in the order in which the LEDs 66 are turned on, and sequentially sends them to the LPH drive unit 100 in synchronization with the transfer clock SCLK generated by the timing signal generation unit 130.
[0137]
Specifically, in the present embodiment, the TAG threshold value is set to “432”, which is a value corresponding to a density of about 20% of all black. That is, by comparing the addition result with the TAG threshold value, it is determined whether or not the average density of the pixel of interest and the surrounding 3 × 3 pixels is higher than the density of 20% of all black, and the TAG data corresponds to This indicates whether the target pixel is in a high density area higher than the density of 20% of all black or in a low density area of 20% or less of all black.
[0138]
At the same time, the image data Pdot of the target pixel is input from the peripheral density determination unit 106 to the screen processing unit 104. In the screen processing unit 104, the image threshold generation unit 120 generates an image threshold based on the video clock VCLK and the line synchronization signal LSYNC, and the VDATA generation unit 122 compares and calculates the image threshold and the image data of the target pixel. Thus, lighting data VDATA for each light emitting point (LED) is generated. The rearrangement unit 124 rearranges the lighting data VDATA in the order in which the LEDs 66 are turned on, and sequentially sends the lighting data VDATA to the LPH driving unit 100 in synchronization with the transfer clock SCLK generated by the timing signal generation unit 130.
[0139]
That is, the line synchronization signal LS, the transfer clock SCLK, the TAG data, and the lighting data VDATA are input to the LPH driving unit 100, and based on these, the LED 66 provided in the SLED chip 68 is driven.
[0140]
The operation of the LPH driving unit 100 at this time will be described with reference to the timing chart of FIG. In the following, each LED 66 is distinguished by a serial number (No.) of the plurality of LEDs 66 arranged in the main scanning direction across the SLED chip 68 (see the numbers following L in FIG. 5).
[0141]
In the LPH driving unit 100, as shown in FIG. 20, the lighting data VDATA and the TAG data are sequentially synchronized with the transfer clock SCLK and in order of the chip number with reference to the falling edge of the line synchronization signal LS. Data corresponding to the first LED 66 (No. 0, 128, 256, 384) arranged in the No. 2, data corresponding to the second LED 66 (No. 1, 129, 257, 385), etc. are input. Is done.
[0142]
In the LPH driving unit 100, the input lighting data VDATA is input to the input terminals (D) as input data of the flip-flops 142A1 to A3 and the flip-flop AA4, and the TAG data is input to the flip-flops 142B1 to B3. Data is input to each input terminal (D) and also input to the correction memory 144 (4).
[0143]
In addition, the LPH driving unit 100 synchronizes with the input line synchronization signal LS and the transfer clock SCLK by the driving signal generation unit 140 to select signals SCK1, SCK2, SCK3, a latch signal LCH, an address signal ADL, and a lighting strobe signal. STB, start signal CKS, and transfer signals CK1 and CK2 are generated.
[0144]
The flip-flops 142A1 to A3 and the flip-flops 142B1 to B3 operate using the select signals SCK1, SCK2, and SCK3 as clock signals, and input data that is input when the select signals SCK1, SCK2, and SCK3 rise are output terminals (Q). And the output is held until the next rising edge of the select signals SCK1, SCK2, and SCK3.
[0145]
Thus, for example, during the period T1 from the rising edge of the select signal SCK1 to the next rising edge, the lighting data VDATA and TAG data for the No. 1 LED are output from the flip-flop 142A1 and the flip-flop B1, respectively. Similarly, during the period T2 from the rising edge of the select signal SCK2 to the next rising edge, the lighting data VDATA and TAG data for the No. 128 LED are output from the flip-flop 142A2 and the flip-flop 142B2. Further, during the period T3 from the rising edge of the select signal SCK3 to the next rising edge, the lighting data VDATA and TAG data for the No. 256 LED are output from the flip-flop 142A3 and the flip-flop 142B3.
[0146]
Outputs (lighting data) from the flip-flops 142A1 to A3 are input to the input terminals (D) as input data to the flip-flops 146A (1 to 3). Further, the lighting data VDATA from the screen processing unit 104 is input as input data to the flip-flop 146A (4), and the flip-flop 146A (1-4) operates using the latch signal LCH as a clock signal, The input data input at the rising edge of the latch signal LCH is output until the next rising edge of the latch signal LCH.
[0147]
Thus, for example, during the period T4 from the rising edge of the latch signal LCH to the next rising edge, the flip-flop 146A (1) is No. 0, the flip-flop 146A (2) is No. 128, and the flip-flop 146A (3) Is No. 256, and the flip-flop 146A (4) outputs the lighting data VDATA corresponding to the LED of No. 384 as the lighting signal VD (1-4) instructing the lighting of each SLED chip 68. That is, during the period T4, the lighting signals VD (1 to 4) corresponding to the first-stage LEDs 66 of the SLED chips 68 (1 to 4) are output. Similarly, in the next period T5, the SLED chips 68 are output. The lighting signals VD (1 to 4) corresponding to the second stage LED 66 (1 to 4), and the lighting signals VD (1 to 4) corresponding to the third stage LED 66 are output in the period T6.
[0148]
On the other hand, the outputs (TAG data) of the flip-flops 142B1 to B3 are input to the correction memory 144 (1 to 3), and the TAG data from the peripheral density determination unit 106 is input to the correction memory 144 (4). From the correction memory 144 (1-4), the data stored at the address specified by the input (TAG data) and the address signal ADL is read out, and the input data is input to the flip-flop 146B (1-4). Is entered as
[0149]
Specifically, the address signal ADL specifies which LED of correction data to be read out among the LEDs provided in the SLED chip 68 is specified, and the TAG data indicates the density of the region near the target pixel (the target pixel and its pixel). Depending on the average density of the surrounding 3 × 3 pixels, it is specified which of the low-density correction data and high-density correction data to be read out.
[0150]
The flip-flop 146B (1 to 4) operates using the latch signal LCH as a clock signal, and outputs the input data input at the rise of the latch signal LCH until the next rise of the latch signal LCH.
[0151]
Thus, for example, during period T4, flip-flop 146B (1) is No. 0, flip-flop 146B (2) is No. 128, flip-flop 146B (3) is No. 256, and flip-flop 146B (4) is Among the correction data for high density and low density for the No. 384 LED, one of the correction data designated by the TAG data of each LED is output as a correction signal COR (1 to 4). That is, during the period T4, the correction signal COR (1-4) corresponding to the first-stage LED 66 of each SLED chip 68 (1-4) is output. Similarly, in the next period T5, each SLED chip 68 is output. The correction signal COR (1-4) corresponding to the second stage LED 66 (1-4), and the correction signal COR (1-4)... Corresponding to the third stage LED 66 are output in the period T6.
[0152]
Thus, the lighting signals VD (1-4) output from the flip-flops 146A (1-4) and the correction signals COR (1-4) output from the flip-flops 146B (1-4) correspond respectively. Is input to the driving element unit 148 (1 to 4).
[0153]
As shown in FIG. 21, the drive element unit 148 uses the 4-bit counter 150 to count the number of pulses of the input pulse modulation clock PWMCLK from the falling edge of the strobe signal STB, and the falling edge of the next strobe signal STB. To clear the count value CD. That is, the count value CD from 0 to 15 is output from the 4-bit counter 150.
[0154]
The count value CD is compared with the lighting signal VD in the comparator 152, and the comparison result is output. The output of the comparator 152 is input to the gate of the transistor 156, so that during “count value CD ≦ lighting signal VD”, a gate current flows through the transistor 156 and the transistor 156 is turned on.
[0155]
The output of the comparator 152 is ANDed with each bit value (COR0 to COR3) of the correction signal COR by AND circuits 154A to 154D, and the calculation result is output. Thus, during the “count value CD ≦ lighting signal VD”, only the transistors 156A to 156D connected to the AND circuits 154A to 154D having the bit value of the input correction signal COR being “1”. A gate current flows and it becomes ON state.
[0156]
When the transistors 156A to 156D are turned on, as shown in FIG. 22A, the lighting signal VD is applied to the SLED chips 68 (1 to 4) corresponding to the drive element units 148 (1 to 4). While supplying the lighting control signal ΦI (1-4) with a pulse width corresponding to (1-4), as shown in FIG. 22B, according to the ON / OFF state of the AND circuits 154A-D, That is, the current value of the lighting control signal ΦI (1-4) is changed according to the value of the correction signal COR (1-4).
[0157]
At the same time, as shown in FIG. 20, in the drive signal generation unit 140, in the period T4, the start signal CKS is input to each SLED chip 68 as the H level, and the transfer signals CK1 and CK2 are set to H for each strobe signal STB. Switches between level / L level. As a result, the LED 66 can be lit in order from the first stage G1 of each SLED chip 68 to the subsequent stage for each strobe signal STB from the input of the start signal CKS, and the lighting control signal ΦI (1 to 1) supplied in this lit state. Each LED 66 lights up according to 4).
[0158]
That is, the SLED chips 68 (1 to 4) are turned on in order from the first stage to the rear stage LEDs 66 according to the lighting control signals ΦI (1 to 4) supplied from the corresponding drive element units 148 (1 to 4). Then, a light beam having an intensity corresponding to the corresponding correction signal COR (1 to 4) is output with a pulse width corresponding to the lighting signal VD (1 to 4).
[0159]
As described above, in the first embodiment, the light profile when the LPH 16 is fully lit is measured, and the exposure that exceeds a predetermined threshold (low density threshold, high density threshold) in the light profile when fully lit. The correction data is determined so as to flatten the energy amount. That is, by using the light profile at the time of full lighting, the correction data is determined in consideration of not only each LED 66 but also the LED around the LED 66, so that the influence due to superposition can be removed. .
[0160]
Even when not all of the lights are turned on, the same effect can be obtained by using a light profile obtained when at least a plurality of LEDs that affect each other are turned on.
[0161]
In the first embodiment, a plurality of correction data (in this embodiment, two for low density and two for high density) are prepared in accordance with the density, and when the image forming apparatus 40 forms an image. The correction data is selected according to the image density of the region near the target pixel (the target pixel and its surrounding pixels), and the light amount is adjusted. Therefore, the influence of superposition can be removed regardless of the image density, and high-quality image formation can be performed. Is possible.
[0162]
In the first embodiment, the case where the correction data is selected according to the image density in the vicinity region and the light amount adjustment is performed at the time of image formation has been described. However, the present invention is not limited to this. Instead, the correction data may be switched depending on the number of lighting of peripheral LEDs.
[0163]
Specifically, for example, the light profile in each of a plurality of predetermined lighting patterns is measured, for example, the LED 66 of the LPH 16 is turned on one by one (1 on 1 off), and correction data for each lighting pattern is calculated. deep. And when the image is formed, the surrounding LED lights To number Accordingly, correction data may be selected and light amount adjustment may be performed.
[0164]
However, ideally, it is desirable to obtain the light profile by obtaining the light profile according to the actual lighting pattern for each concentration, but it is necessary to calculate the correction data for every lighting pattern. It is not realistic considering the resource. Here, the exposure energy distribution when the LPH 16 is used in an image forming apparatus generally has the following characteristics.
(1) In high-resolution exposure (for example, 1200 × 2400 dpi × 2 bits), the exposure energy distribution due to the adjacent light emitting point (light emitting point adjacent to the target light emitting point) with respect to the exposure energy distribution of the light emitting point of interest (LED 66) is very large. The exposure energy distribution shape is greatly affected by the overlap of exposure energy at adjacent light emitting points. The overlap of exposure energy due to neighboring light emitting points other than adjacent light emitting points has a small contribution to the exposure energy distribution shape and greatly affects the average level of exposure energy.
(2) Since the light beam from the proximity light emitting point of LPH passes through the position in the vicinity of the pole within the SELFOC lens, there is little sudden change in the shape of the exposure energy distribution. For example, a 2on2off lighting pattern (LED 66 of LPH16) Are alternately turned on two by two), when the LEDs 66 of Nos. 1, 2, 5, 6, 9, 10,... Are turned on and the LEDs 66 of Nos. 3, 4, 7, 8, 11, 12,. There is almost no difference in the shape of exposure energy distribution between when it is lit.
(3) A completely isolated point that does not have a lighting area around it cannot achieve a stable resolution due to the limitations of development, and it is possible to develop stably only after multiple points of light emission overlap. The light emitting point is turned on. Therefore, it is necessary to consider the overlap of the exposure energy distribution between the adjacent light emitting points in the low density region and the high density region as well.
[0165]
Due to the above characteristics, the light profile is measured by a lighting pattern that lights adjacent light emitting points such as 2 on 2 off, and the average level of exposure energy is different for each of the low density and the high density as shown in FIG. It is practical to apply the above development characteristics by converting the scale for each density in consideration of the average level difference k. In FIG. 26, (1) indicates the exposure energy distribution during low density writing, and (2) indicates the exposure energy distribution during high density writing.
[0166]
By the way, in the so-called electrophotographic process in which a uniformly charged photosensitive drum 42 is exposed to form an electrostatic latent image and then developed, as in the image forming apparatus 40, generally, the exposure energy and the developed image are developed. There is a relationship (development characteristics) as shown in FIG. 27A between the densities, and a desired image density can be obtained by adjusting the exposure energy using these development characteristics. When this development characteristic is simplified, as shown in FIG. 27B, a linear region in which the exposure energy amount and the image density are approximately proportional to each other, and an image density is produced even when exposure is performed on the lower exposure energy side of the linear region. There is no dead (not developed) dead zone and a saturated region where the image density does not increase even if the exposure amount on the high exposure energy side is increased from the linear region. That is, the image density has a correlation with the exposure energy in the linear region and is hardly affected by the exposure amount in the dead zone and the saturated region.
[0167]
In the first embodiment, in order to obtain the low-density and high-density optical profiles in the light profile measuring apparatus 10, the dead zone of the development characteristics is set at each of the relatively low density and high density. In consideration of the case where the low density threshold and the high density threshold or less corresponding to the minimum exposure necessary for obtaining the image density are each rounded down from the exposure energy amount measured by the sensor 18, the case of high density is described. Since the measured exposure energy amount may reach the saturation region, it is more preferable to determine the saturation region as well as the dead zone. Specifically, when the light profile is calculated considering only the dead zone, if there is a part where the exposure amount reaches the saturation region, it is corrected to flatten the light profile including the exposure amount that reached the saturation region. Since the data is determined, if correction is performed as described above using this correction data, the image density of the portion that has reached the saturation region will be lighter than that of the other portions, causing streaks on the image. Because it will end up.
[0168]
In the first embodiment, the case where the optical profile in the main scanning direction is flattened taking into consideration only the superimposition in the main scanning direction has been described as an example. However, for example, stray light (LPH passing outside a predetermined path) The light emitting points that affect each other may exist not only in the main scanning direction, but also in the sub scanning direction. It is preferable to flatten the optical profile in consideration.
[0169]
<Second Embodiment>
Next, as a second embodiment, a case will be described in which a high-density optical profile is obtained in consideration of the dead zone and the saturation region, and the optical profile is flattened in consideration of superimposition in the sub-scanning direction. Since the second embodiment may be the same as the first embodiment except for the arithmetic processing unit 30 of the optical profile measuring apparatus 10, only the arithmetic processing unit 30 will be described in detail here. The same members as those of the first embodiment will be described using the same reference numerals.
[0170]
FIG. 28 shows a detailed configuration of the arithmetic processing unit according to the second embodiment. As shown in FIG. 28, the arithmetic processing unit 30 according to the second embodiment performs overlay calculation in the sub-scanning direction based on each CCD measurement result of the line CCD 20 with respect to the first embodiment. A computing unit 31 is newly provided. This computing unit 31 adds the sub-scanning direction cross sections (exposure energy distribution in the sub-scanning direction) of the exposure energy distribution obtained by the measurement of each CCD of the line CCD 20 by shifting the sub-scanning direction by a predetermined interval. A cross section in the sub-scanning direction of the exposure energy distribution considering the overlap in the scanning direction is obtained. The predetermined interval is set according to the writing resolution in the sub-scanning direction of the image forming apparatus.
[0171]
As a result, the computing unit 31 shifts by a predetermined interval in the sub-scanning direction when the influence of stray light is included in the sub-scanning direction as in the cross section in the sub-scanning direction of the exposure energy distribution shown in FIG. 29B, the cross section in the sub-scanning direction of the exposure energy distribution can be obtained in consideration of the influence of stray light, that is, the overlap in the sub-scanning direction.
[0172]
The arithmetic processing unit 30 stores a high density saturation value SAT (high) corresponding to an exposure amount at which image density is saturated, together with a high density threshold TH (high), in a memory 34B provided for high density. ing. The comparator 36B compares the calculation result of the calculator 31 with the high concentration threshold and the high concentration saturation value, and outputs data indicating the excess of the high concentration threshold up to the high concentration saturation value to the adder 38B. In the adder 38B, the data indicating the excess is added in the sub-scanning direction. That is, by extracting and adding only the exposure energy that affects the image density, a characteristic value correlated with the image density is obtained, and the image density is indirectly measured.
[0173]
This is because the input / output characteristics of the comparator 36B are based on the high density threshold value and the high density saturation value, as in the simplified development characteristics shown in FIG. The exposure energy amount is converted to image density by converting the input calculation result based on this input / output characteristics, with the linear region from the high density threshold to the high density saturation value, and the saturation region above the high density saturation value. Output to the adder 38B. Specifically, the hatched portions in FIG. 29D are integrated by the addition by the adder 38B, and the integrated values are sequentially stored in the memory 32.
[0174]
On the other hand, the low density threshold TH (low) is stored in the memory 34A provided for the low density similarly to the first embodiment, and the low density is calculated by the calculator 31 in the comparator 36A. The result is compared with the low density threshold TH (low), and the amount exceeding the low density threshold is added by the adder 38A, so that only the exposure energy that affects the image density is extracted and added. A characteristic value correlated with the density is obtained, and the image density is indirectly measured. In this case, the input / output characteristics of the calculator 31A are the same as the dead zone below the low concentration threshold and the linear region above the low concentration threshold. Specifically, the hatched portion in FIG. 29C is integrated by the addition by the adder 38A, and the integrated values are sequentially stored in the memory 32.
[0175]
As described above, the personal computer 28 moves the line CCD 20 in the main scanning direction as in the first embodiment in a state where the LPH 16 is lit in a lighting pattern that considers the overlap in the main scanning direction such as 2 on 2 off. The control is performed so as to perform the calculation in the main scanning direction. As a result, an optical profile for high density (exposure energy distribution in the main scanning direction) taking into account the overlap in the sub-scanning direction and taking into account the dead zone and saturation region for high density, and low taking into account the dead zone for low density. An optical profile for concentration can be obtained.
[0176]
The personal computer 28 reads each of the obtained high-density optical profile and low-density optical profile from the memory 32, and obtains high-density and low-density correction data so that they are substantially flattened. Thereby, low density and high density correction data can be obtained in consideration of the overlap in the main scanning direction and the overlap in the sub scanning direction.
[0177]
However, in order to perform correction for actually flattening the light profile in the image forming apparatus 40, it is necessary to convert the obtained light profile into a “characteristic value” corresponding to each light emitting point (LED 66) on a one-to-one basis. is there. Therefore, in this embodiment, as an example, as shown in FIG. 30, first, peak detection is performed from the obtained light profile, and the exposure energy amount from valley to valley in the light profile is integrated, and this integration is performed. The exposure energy density between the valleys is obtained by dividing the value by the distance from the valley to the valley. The exposure energy density of each valley obtained in this way is used as the characteristic value of each light emitting point, and the exposure amount is increased / decreased according to the difference from the target value so that this characteristic value matches the predetermined target value. The leveling is performed. The graph of FIG. 30 is an example of a light profile acquired when the LPH corresponding to 1200 dpi is lit in a 2 on 2 off pattern using the arithmetic processing unit 30 shown in FIG.
[0178]
By performing such flattening for each of the relatively low density and high density, a plurality of correction data corresponding to each density can be calculated. FIGS. 31 and 32 show comparison values of the target values of the characteristic values before and after correction at low density and high density, respectively, in the case where the light quantity of LPH 16 is corrected using the correction data determined in this way, and the values of 0. An example of a moving average of 2 mm width (5 sections) is shown. When the characteristic value matches the target value, it is 100%. As can be seen from FIG. 31 and FIG. 32, in both the low density and the high density, the characteristic values can be substantially matched with the target values by the correction and can be substantially flattened. Therefore, in the image forming apparatus, an image with less unevenness can be formed by correcting the output light amount of each LED 66 of the LPH 16 using this correction data.
[0179]
In the above description, the LPH 16 in which a plurality of SLEDs 68 are linearly arranged in the main scanning direction has been described as an example. However, due to downsizing and wiring convenience, a plurality of SLEDs 68 such as a staggered arrangement are positioned in the sub-scanning direction. As shown in FIG. 33, the cross section (A) of the exposure energy distribution at the time of measurement may differ from the cross section (B) of the exposure energy distribution at the time of image formation. Even in such a case, as described above, the sub-scanning direction section of the exposure energy distribution in consideration of the overlap in the sub-scanning direction by adding the offsets in the sub-scanning direction of the measured exposure energy distribution in the sub-scanning direction. As shown in (C) and (D), an exposure energy distribution substantially equivalent to the exposure energy distribution at the time of image formation can be obtained. In other words, the present invention can be applied even when a plurality of SLEDs 68 are arranged with their positions shifted in the sub-scanning direction by considering the overlap in the sub-scanning direction.
[0180]
In the above description, the case where the image density is divided into two density areas of a relatively low density and a high density has been described. However, in the present invention, correction is performed by obtaining correction data for each of a plurality of density areas. The present invention can be similarly applied when the image density is divided into three or more density regions.
[0181]
【The invention's effect】
As described above, the present invention has an excellent effect that the unevenness of the exposure energy distribution can be corrected including the influence of superposition by neighboring recording elements.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical profile measuring apparatus according to a first embodiment.
2 is a block diagram showing a detailed configuration of an arithmetic processing unit in FIG.
FIG. 3 is a schematic configuration diagram of an image forming apparatus according to the first embodiment.
FIG. 4 is a cross-sectional view showing an internal configuration of the LED print head (LPH) according to the first embodiment.
5 is a diagram showing an input signal from the printed board in FIG. 4 to the SLED.
FIG. 6 is a circuit diagram illustrating a detailed configuration of an SLED and an LPH driving unit.
FIG. 7 is a drive circuit diagram of a single LED in the SLED.
FIG. 8 is a block diagram showing a schematic circuit configuration on a printed circuit board.
FIG. 9 is a circuit diagram illustrating a detailed configuration of a peripheral density determination unit and a screen processing unit.
FIG. 10 is a circuit diagram showing a detailed configuration of a VDATA generation unit.
11 is an example of lighting data generated by the VDATA generator in FIG.
FIG. 12 is a circuit diagram showing a detailed configuration of a drive element unit.
FIG. 13 is a flowchart showing a control routine executed by a personal computer.
FIG. 14 is a conceptual diagram for explaining optical profile measurement by the optical profile measurement device.
FIG. 15 is an example of a sub-scanning direction profile when all lights are on.
FIG. 16 is a graph showing an example of the acquired high-density light profile and moving average when all lighting is performed.
FIG. 17 is a graph showing an example of an acquired light profile for low concentration and a moving average when all lighting is on.
FIG. 18 is a graph showing an example of a light profile and a moving average at a high density when correction is performed using correction data for low density calculated based on FIG.
FIG. 19 is a graph showing an example of a light profile at low density and a moving average when correction is performed using correction data for low density calculated based on FIG. 17;
FIG. 20 is a timing chart of various signals in the LPH driving unit.
FIG. 21 is a timing chart of various signals in the drive element section.
22A shows the relationship between the pulse width of the lighting control signal ΦI generated by the driving element unit and the lighting signal, and FIG. 22B shows the current value and correction of the lighting control signal ΦI generated by the driving element unit. It is a graph which shows the relationship of a signal.
FIG. 23 is a diagram illustrating an example of an exposure energy distribution of a print head.
FIG. 24 is a contour diagram showing an example of an exposure energy distribution appearing in an image when a threshold value corresponding to density is provided.
FIG. 25 is a graph showing an example of exposure energy distribution appearing in an image when a threshold value corresponding to density is provided.
FIG. 26 is a graph for explaining a difference in average value of exposure energy distribution for each density.
27A is a diagram showing general development characteristics, and FIG. 27B is a diagram showing development characteristics obtained by simplifying (A).
FIG. 28 is a block diagram illustrating a detailed configuration of an arithmetic processing unit according to the second embodiment.
29A shows a case where there is an influence of stray light in the sub-scanning direction, FIG. 29B shows a case where overlap in the sub-scanning direction is not considered, and FIG. 29B shows a sub-scanning direction of the exposure energy distribution when considering overlap in the sub-scanning direction. (C) and (D) are conceptual diagrams showing an integrated value by an adder for low density and an integrated value by an adder for high density when overlapping in the sub-scanning direction is considered.
FIG. 30 is a diagram for explaining a characteristic value calculation method for each LED for obtaining correction data for each LED according to the second embodiment;
FIG. 31 is a graph showing an example of a comparison value and a moving average of a characteristic value before and after correction using correction data for low density and a target value.
FIG. 32 is a graph showing an example of a comparison value with a target value of a characteristic value before and after correction using correction data for high density and a moving average.
FIGS. 33A and 33B are cross-sectional views in the sub-scanning direction of the exposure energy distribution at the time of printing and when measuring the optical profile when the overlap in the sub-scanning direction is not taken into consideration when the SLEDs are staggered. (D) is a conceptual diagram showing a cross section in the sub-scanning direction of the exposure energy distribution at the time of printing and light profile measurement in consideration of the overlap in the sub-scanning direction.
[Explanation of symbols]
10 Optical profile measuring device
12 LED array
16 LED print head
18 sensors
20 line CCD
24 Sensor movement stage
28 PC
30 arithmetic processing unit
32 memory
40 Image forming apparatus
42 Photosensitive drum
66 LED
68 SLED chip
100 LPH drive
104 Screen processor
106 Ambient concentration determination unit

Claims (2)

A print head that is used to form an image by exposing a photoreceptor, and in which a plurality of light emitting elements are arranged in a line,
The degree exposure distribution between the light emitting element to be lit, giving the exposure light amount distribution when was lit point a plurality of light emitting elements to overlap to such an extent that affects at least the image density, the influence on the image density The threshold value for high density is set so as to include the skirt portion of the exposure amount distribution of each light emitting element that constitutes the overlapping region, and does not include the skirt portion of the exposure amount distribution of each light emitting element that constitutes the overlapping region. A high density image for each of the light emitting elements set in advance so as to substantially flatten the exposure amount distribution portion exceeding the high concentration threshold value in the line direction by setting a low density threshold value Correction data for low-density images for each of the light-emitting elements set in advance so as to substantially flatten the exposure amount distribution data and the exposure amount distribution portion of the exposure amount distribution exceeding the low density threshold value in the line direction. Storage means for storing data, respectively,
Selection means for selecting the correction data from the correction data stored in the storage means for each light emitting element according to the dot density in the vicinity of the light emitting element (the light emitting element and its surrounding light emitting elements). When,
Correction means for correcting the exposure amount of each light emitting element based on the correction data selected by the selection means;
A print head comprising: The light emitting element is turned on with a lighting pulse width based on image data, and the output light amount is adjusted by the correction unit based on the correction data.
The print head according to claim 1.

Images