JP2006076121A - Light emitting apparatus, image forming apparatus, and density variation correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To readily correct the density variation of IN-OUT by use of IN-OUT variation correction values obtained at a plurality of densities, that is varied, for example, when elements of an image formation unit are replaced in an image forming apparatus using a light emitting apparatus for sequentially lighting light emitting arrays. <P>SOLUTION: The light emitting apparatus comprises an LED print head (LPH) in which a plurality of light emitting apparatuses are aligned, and a lighting signal generating unit 61 for generating light signals to the plurality of light emitting elements in the LED print head according to input image data. The lighting signal generating unit 61 comprises a light quantity variation correction value storage unit 73 for storing the light quantity variation correction value to a light emitting array, and a correction calculation unit 74 for performing the correction calculation of the IN-OUT variation in density D1 and density D2 to the light amount correction value, when the light emitting array is mounted in the image forming apparatus having a lighting target. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile, and more particularly to an image forming apparatus including a print head for performing optical writing.

  Among image forming apparatuses such as printers, copiers, and facsimiles, for example, in an image forming apparatus adopting an electrophotographic method, an electrostatic recording is performed by irradiating light onto a uniformly charged photosensitive member by an optical recording unit. After obtaining the latent image, toner is added to the electrostatic latent image to make it visible, and the image is formed by transferring and fixing on the recording paper. As such an optical recording means, in addition to an optical scanning method in which a laser is used to scan and expose a laser beam in the main scanning direction, in recent years, in response to a request for downsizing of an apparatus, an LED (Light Emitting Diode) which is a light emitting element. : An optical recording means using an LED print head (LPH) in which a number of light emitting diodes) are arranged in the main scanning direction.

  This LPH generally has a plurality of LED chips in which a large number of LEDs are arranged in a line, and as a result, an LED array in which the LEDs are arranged in the main scanning direction (scanning direction), and the light output from the LEDs as a photoreceptor. A (photosensitive drum) includes a lens array in which a number of rod lenses are arranged in the main scanning direction in order to form an image on the surface. In the image forming apparatus, each LED of the LPH is driven to emit light based on the input image data, light is output toward the photoconductor, and light is imaged on the photoconductor surface by the lens array. An electrostatic latent image is formed in the sub-scanning direction by relatively moving the photoconductor and LPH.

  Here, in the image forming apparatus using the LED as the recording head, the unevenness of the recording head appears as the unevenness of the image as it is, and therefore an operation of correcting the unevenness of the recording head is performed. As a method for correcting the unevenness of the recording head, for example, there is a technique for correcting the unevenness of the recording head by actually forming a test pattern with the recording head and reading the obtained test pattern with a scanner or the like. Further, as a conventional technique described in the publication that employs LPH, for example, in an image forming apparatus that corrects LPH unevenness from a density reading value, a technique for correcting exposure unevenness caused by causes other than LPH with LPH is disclosed (for example, , See Patent Document 1).

JP-A-11-177824 (page 7-8, FIG. 1)

  By the way, in an image forming apparatus employing the above-described electrophotographic method, for example, due to variations during manufacturing and assembly, variations during parts replacement during maintenance, etc. In some cases, the gap between each component differs in the scanning direction between the front side (OUT side) and the back side (IN side) of the apparatus. The difference in the gap between the front side (OUT side) and the back side (IN side) of such an apparatus is caused by density unevenness (In-Out unevenness, scanning direction) between the front side (OUT side) and the back side (IN side). It appears as mura). In particular, for example, when a full color image is formed by superimposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K), In-Out unevenness for each color. As a result, non-uniform density in each color toner image finally becomes uneven when superimposed. The occurrence of such color unevenness greatly violates the recent demand for higher image quality, and its improvement is strongly desired.

  Here, unlike ROS (Raster Output Scanner), which is an exposure apparatus using laser light, LPH originally has a light amount correction function for correcting density unevenness as described above. Therefore, for example, this In-Out unevenness can be corrected at the same time during scanner correction. However, the cause of In-Out unevenness is not only the initial cause at the time of manufacturing and assembly, but also non-uniformity in sensitivity due to film thickness fluctuation due to wear of the photosensitive drum, for example, due to replacement of elements of the image forming unit. There are variations in the gap between the photosensitive drum and the LPH, and variations in the depth of field (DOF) of the LPH. For example, when it is desired to adjust later only the In-Out unevenness component caused by these temporal fluctuations, for example, in the conventional technique described in Patent Document 1, it is necessary to perform scanner correction again. In order to perform scanner correction, it is necessary to perform very complicated operations such as actually forming a test pattern with a recording head, reading the obtained test pattern with a scanner, and calculating a correction value for each LED. There is a demand for a function of simply adjusting only the -Out density difference.

  Further, this In-Out unevenness changes as the concentration changes. For this reason, when the In-Out unevenness is corrected at a specific density, the In-Out unevenness may be further deteriorated at other concentrations. For example, when the In-Out unevenness is corrected when the density is 50%, the In-Out unevenness is worsened when the density reaches 20%. For example, in the case of LPH, correction is performed with the exposure energy amount (light amount or time) of the spot shape on the photoconductor. However, when the spot shape varies, the low density portion and the high density portion One reason is that the amount of energy contributing to development changes. Further, for example, the electrophotographic process itself has sensitivity variations in the main scanning direction.

In view of the above, a main object of the present invention is to provide a light-emitting device that suppresses in-out unevenness regardless of writing density.
Another object is to obtain an image without in-out unevenness in an image forming apparatus that performs in-out unevenness correction in consideration of the difference in density.

  For such a purpose, a light emitting device to which the present invention is applied includes a light emitting array in which a plurality of light emitting elements are arranged, and a lighting that generates lighting signals for the plurality of light emitting elements of the light emitting array according to input image data. Signal generation means, and correction value providing means for providing a correction value for the light amount of the light emitting array to the lighting signal generating means. The correction value providing means performs scanning when the light emitting array is mounted on a device having an irradiation target. It is characterized in that each of the scanning direction unevenness in a plurality of densities is grasped with respect to the direction unevenness, and a correction value corresponding to the scanning direction unevenness is provided according to the density of the input image data. In the present invention, the unevenness in the scanning direction can be paraphrased as In-Out unevenness. The same applies to the following.

  Here, storage means for storing in advance light amount unevenness correction values in a plurality of light emitting elements of the light emitting array is further provided, and the correction value providing means uses the light amount unevenness correction values read from the storage means as the first density. The correction value is calculated by performing correction using the scanning direction unevenness correction value at and the scanning direction unevenness correction value at the second density. Note that the present invention does not prevent correction by further using the scanning direction unevenness correction value at the third density. The same applies hereinafter.

  The image forming apparatus further includes density determination means for determining the density of the input image data, and the correction value providing means includes the density of the image data determined by the density determination means, the first density and / or the second density. From the above relationship, it is possible to correct the unevenness in the scanning direction.

From another viewpoint, the light emitting device to which the present invention is applied includes a light emitting array in which a plurality of light emitting elements are arranged, and a light amount unevenness correction value at the first density as a light amount unevenness correction value of the light emitting array. And a light amount unevenness correction value storage means for storing a light amount unevenness correction value at the second density, and a light amount unevenness correction value at the first density and a light amount unevenness correction at the second density stored in the light amount unevenness correction value storage means. Correction value calculation means for calculating a correction value according to the density of the input image data from the value, and generating a lighting signal for a plurality of light emitting elements of the light emitting array using the correction value calculated by the correction value calculation means The correction value storage means compensates for the first scanning direction unevenness at the first density, which is calculated when the light emitting array is mounted on the device having the irradiation target. It is characterized by storing a first light amount unevenness correction value, and the second light amount unevenness correction value obtained using the second scanning direction unevenness correction value in the second concentration obtained by using the value.
Further, it may be characterized by further comprising a calculation means for calculating the first scanning direction unevenness correction value and the second scanning direction unevenness correction value at a predetermined timing when the light emitting element is turned on.

  On the other hand, when grasping the present invention from an image forming apparatus adopting an electrophotographic method, the image forming apparatus to which the present invention is applied includes an image carrier and a light emitting element array in which a plurality of light emitting elements are arranged in an array. And a print head that exposes the image carrier to form an electrostatic latent image, and a lighting that generates a lighting signal for the plurality of light emitting elements of the light emitting element array. Signal generation means, and scanning direction unevenness correcting means for correcting unevenness in the scanning direction with a plurality of densities with respect to the unevenness in the scanning direction when the print head is arranged opposite to the image carrier. The means generates a lighting signal corrected by the scanning direction unevenness correction means in accordance with the density of the image data to be output.

Here, the scanning direction unevenness correcting means can grasp and correct unevenness in the scanning direction of a plurality of densities when the image carrier or the print head is replaced.
Further, the scanning direction unevenness correcting means can provide the lighting signal generating means with a value determined by a linear function connecting the IN side and the OUT side in the scanning direction as a scanning direction unevenness correction value. .
Further, the lighting signal generation means reads the current light amount unevenness correction value, corrects the gradient of the density obtained from the scanning direction unevenness correction value provided by the scanning direction unevenness correction means, and generates a lighting signal. Can be a feature.

On the other hand, when grasping the present invention from the category of the method, the present invention is a density unevenness correction method in an image forming apparatus having an image carrier and a print head that exposes the image carrier to form an electrostatic latent image. Then, when the print head is disposed facing the image carrier, a step of acquiring an IN-OUT unevenness correction value that occurs in the scanning direction at a plurality of densities, and a current light amount unevenness correction value in the print head, And calculating a new light amount unevenness correction value using the obtained IN-OUT unevenness correction values at a plurality of obtained densities.
Here, the acquired IN-OUT unevenness correction value is a linear function of density change between the IN side and the OUT side in the scanning direction with respect to each of the first density and the second density that are input. It can be.

  According to the present invention, for example, the In-Out unevenness that occurs in the main scanning direction of image formation that has been changed due to replacement of each element of the image forming unit is suppressed regardless of the writing density. It is possible to obtain a finished image.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing the overall configuration of an image forming apparatus to which this embodiment is applied, and shows a so-called tandem type digital color printer. An image forming apparatus shown in FIG. 1 includes an image processing system 10 that forms an image corresponding to gradation data of each color, an image output control unit 30 that controls the image processing system 10, such as a personal computer (PC). 2 and an image reading apparatus (IIT) 3 and an image processing unit (IPS: Image Processing System) 40 that performs predetermined image processing on image data received from these.

  The image processing system 10 includes an image forming unit 11 composed of a plurality of engines arranged in parallel at regular intervals in the horizontal direction. The image forming unit 11 includes four image forming units 11Y, 11M, 11C, and 11K of yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 11 (11Y, 11M, 11C, and 11K) respectively include a photosensitive drum 12 that is an image carrier (photosensitive member) that forms an electrostatic latent image and carries a toner image, and a photosensitive drum 12. A charger 13 for uniformly charging the surface of the toner, an LED print head (LPH) 14 which is a print head for exposing the photosensitive drum 12 charged by the charger 13, and a developer for developing a latent image obtained by the LPH 14. 15 is provided. Further, the image process system 10 conveys the recording paper in order to multiplex-transfer the toner images of the respective colors formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K onto the recording paper. A sheet conveying belt 21, a driving roll 22 which is a roll for driving the sheet conveying belt 21, and a transfer roll 23 for transferring the toner image on the photosensitive drum 12 onto a recording sheet are provided.

  Each of the image forming units 11Y, 11M, 11C, and 11K includes substantially similar components. Image signals input from the PC 2 or IIT 3 are subjected to image processing by the image processing unit 40 and supplied to the image forming units 11Y, 11M, 11C, and 11K through the interface. The image process system 10 operates based on a control signal such as a synchronization signal supplied from the image output control unit 30. First, in the yellow image forming unit 11Y, an electrostatic latent image is formed on the surface of the photosensitive drum 12 charged by the charger 13 by the LPH 14 based on the image signal obtained from the image processing unit 40. A yellow toner image is formed on the electrostatic latent image by the developing unit 15, and the formed yellow toner image is transferred to the recording paper on the paper transport belt 21 that rotates in the direction of the arrow in the figure. It is transcribed using. Similarly, magenta (M), cyan (C), and black (K) toner images are formed on the respective photosensitive drums 12, and are transferred onto the recording paper on the paper conveying belt 21 using the transfer roll 23. Is done. The multiple transferred toner images on the recording paper are conveyed to the fixing device 24 and fixed on the recording paper by heat and pressure.

  FIG. 2 is a diagram showing a configuration of an LED print head (LPH) 14 that is a light emitting device. The LPH 14 is an LED array 51 in which a large number of LEDs are arranged as a light emitting element, a printed circuit board 52 that supports the LED array 51 and controls a drive of the LED array 51, and light emitted from each LED. A SELFOC lens array (registered trademark) (SLA) 53 for imaging the beam on the photosensitive drum 12 is provided. The printed circuit board 52 and the SELFOC lens array 53 are held in a housing 54. In the LED array 51, LEDs are arranged in the main scanning direction by the number of pixels, for example. For example, when an A3 size short (297 mm) is used as the main scanning direction, at a resolution of 600 dpi, it is necessary to arrange at least 7040 LEDs every about 42.3 μm. In addition to the case where the arrangement is arranged in a line, there are cases where the LED chips formed by a group of several LEDs are alternately arranged in a staggered manner. The printed circuit board 52 is a memory (ROM or the like) in which data relating to a correction value obtained by the exposure amount measuring method to which the present embodiment is applied (which may be light amount correction data calculated from the correction value) is stored. And the light quantity of the LEDs constituting the LED array 51 is corrected based on the data stored in the memory.

  FIG. 3 is a hardware configuration diagram of the LPH 14 to which the present embodiment is applied, and employs a self-scanning light emitting element (SLED) system having a thyristor structure. The LPH 14 receives, for example, video data (Video Data) from the image processing unit (IPS) 40 and supplies a lighting signal to each LED chip 63, and a clock and a synchronization signal from the image output control unit 30. A transfer signal generator 62 is provided for receiving and generating a transfer signal. The LPH 14 to which the present embodiment is applied has, for example, 58 LED chips 63 having 128 LEDs, and each LED chip 63 emits 128 dots, and the entire LPH 14 emits 7424 dots. Is possible. The lighting signal generator 61 generates 58 lighting signals (CKI1 to CKI58) for the 58 LED chips 63. The transfer signal generation unit 62 generates six transfer signals (CKS_1 to CKS_6) and six sets of transfer signals (CK1_1 to CK1_6, CK2_1 to CK2_6). For example, in the example shown in FIG. 3, the number of dots of each LED chip 63 is sequentially turned on by sequentially lighting 128 times in one main scanning line, and the number of simultaneous lighting in one scanning line is 58 is the maximum.

  FIG. 4 is a block diagram showing a configuration of the lighting signal generator 61, and shows a first configuration example to which the present embodiment is applied. For example, the lighting signal generation unit 61 may be provided in the image output control unit 30 illustrated in FIG. 1 in addition to the case where it is provided on the printed board 52 of the LPH 14. The lighting signal generator 61 shown in FIG. 1 performs in-out unevenness (unevenness in the scanning direction) in real time when the light intensity unevenness correction value at a specific density is obtained. The lighting signal generator 61 includes a buffer 71 that performs processing such as rearranging video data that is input raster data in the order of light emission, a density determination unit 72 that determines the density of each pixel, and each LED mounted in the LPH 14. A light amount unevenness correction value storage unit 73 in which a light amount unevenness correction value for correcting light amount unevenness is stored. Further, the light amount unevenness correction value f (x) stored in the light amount unevenness correction value storage unit 73, and the In-Out unevenness correction values (for example, (a1, b1) and the density D1 and the density D2). (a2, b2)) is used to provide a correction calculation unit 74 that performs a correction calculation on the density value h (x) determined by the density determination unit 72. In addition, a lighting clock number calculation unit 75 that performs correction using the correction value g (x) obtained from the correction calculation unit 74 on the input image data and calculates the number of lighting clocks is provided. Further, the calculated number of lighting clocks is converted into parallel data, and a pulse width calculation unit 76 for calculating a pulse width for performing pulse width modulation on each parallel-converted signal, PWM for generating each lighting signal A (Pulse Width Modulation) circuit 77 is provided. An LED lighting signal is output from the PWM circuit 77 to each LED chip 63.

  When the image data input to the density determination unit 72 is 1-bit image data (either one pixel is on or off), the density determination unit 72, for example, focuses on the lit pixel. The density determination is performed by counting the number of ON pixel dots in a predetermined area such as 15 × 15 dots.

  The light amount unevenness correction value storage unit 73 stores (stores) the light amount unevenness correction value f (x) as a fixed value corresponding to each pixel in the main scanning direction (scanning direction: x) of the LED print head (LPH) 14. Has been. Even if a special function is not added to the light amount unevenness correction value f (x) stored in the light amount unevenness correction value storage unit 73, the In-Out unevenness (scanning direction unevenness observed in the initial state or the like). ) Is included. When the LPH 14 is mounted on the image forming apparatus, this In-Out unevenness is expressed in a form expressed by a linear function, for example, across the scanning direction on the near side (OUT side) and the far side (IN side) of the apparatus. The amount of light that appears is uneven. For example, the in-out sensitivity of the photosensitive drum 12 varies due to film thickness variation due to wear, and the depth of field (DOF) of the LPH 14 varies, for example, when the image forming unit 11 is replaced. Etc. are the main factors of in-out unevenness. In-Out unevenness such as the initial state is corrected by the light amount unevenness correction value f (x) stored in the light amount unevenness correction value storage unit 73. However, when the In-Out unevenness varies with time, the conventional technique cannot readjust the In-Out unevenness by a simple method. In the present embodiment, the correction calculation is performed so that the current light amount unevenness correction value (the current value stored in the light amount unevenness correction value storage unit 73) is read and then the inclination of the In-Out unevenness is corrected. In-Out unevenness is adjusted by a simple method by recalculation in the unit 74.

  The In-Out unevenness correction value (a1, b1) at the density D1 and the In-Out unevenness correction value (a2, b2) at the density D2 provided to the correction calculation unit 74 are obtained in advance by inputting or reading the correction value. The stored value is stored in a predetermined memory (not shown) and read at a predetermined timing. Further, the value obtained by inputting or reading the correction value may be provided as it is. This In-Out unevenness correction value is, for example, the density difference information of IN-OUT specified (input) by the user via a predetermined user interface, or the density difference of IN-OUT read by the image reading device (IIT) 3. It can be determined by the degree of in-out unevenness based on information. As an example of the input by the user, there is an example in which the sensitivity evaluation by the user is replaced with a numerical value. As an example of sensitivity evaluation by the user, for example, a configuration in which the main body 1 is provided with a control panel including a liquid crystal display device as a user interface, and a user selection for a predetermined item displayed on the control panel can be recognized. As a display example for the user, for example, “the density on the back side is light”, “the density on the back side is high”, and the like are selected, and the levels are “pretty”, “medium”, and “slightly”. And so on. In the present embodiment, these inputs are performed at a plurality of concentrations. By recognizing user selection results based on these displays, In-Out unevenness correction values (a1, b1) and (a2, b2) in a predetermined function as shown in FIG. 6 described later can be determined. .

Further, as an example of reading from the image reading device (IIT) 3, the image data printed out from the main body 1 is read by the image reading device (IIT) 3, and the density in specific images on the IN side and OUT side is read. By recognizing the difference, a simple correction function can be obtained. Using the obtained correction function, it is possible to determine in-out unevenness correction values (a1, b1) and (a2, b2) as shown in FIG. In reading from the image reading device (IIT) 3, it is sufficient to obtain a correction function from recognition of a density difference between specific images on the IN side (back side) and OUT side (near side). The process is very simple.
In the example shown in FIG. 4, the case where an In-Out unevenness correction value based on two densities of the density D1 and the density D2 is input is described as an example, but the number is not limited to two. There are cases where a plurality of In-Out unevenness correction values are input. By increasing the number of in-out nonuniformity correction values, it becomes possible to perform an accurate correction value calculation more realistically.

Here, correction value calculation for In-Out unevenness will be described.
FIGS. 5A and 5B are diagrams illustrating an example of correction value calculation processing when the correction calculation unit 74 performs calculation processing using only a specific In-Out nonuniformity correction value. For the light amount unevenness correction value f (x) as shown in FIG. 5A, the In-Out unevenness correction value calculation is performed, and the correction value g (x) as shown in FIG. 5B is output. Yes. In each case, the horizontal axis x indicates the number (No) of the light emitting point, and the vertical axis indicates the density level. In FIG. 5A, the effect of In-Out unevenness appears, and the original light amount unevenness correction value f (x) has a tendency to fall to the right with low frequency components. The correction calculation unit 74 performs correction so as to cancel the influence of the inclination of “y = ax + b” from the input In-Out unevenness correction value (a, b). In particular,
g (x) = f (x) + ax + b
The inclination is corrected by the following equation, and a correction value g (x) as shown in FIG. 5B can be obtained.

  Furthermore, in the present embodiment, In-Out unevenness correction is independently performed at a plurality of concentrations, and In-Out unevenness that differs for each concentration is corrected. This is because, as a result of a sharp study by the inventor, when In-Out unevenness is corrected at a specific concentration, In-Out unevenness may remain at a different concentration, or In-Out unevenness at a specific concentration. This is because it has been discovered that the density unevenness at other densities may be worsened when the above correction is performed. For example, when the LPH 14 is used, the spot shape variation on the photosensitive drum 12 is corrected by the exposure energy amount (light quantity or time). It is considered that one of the causes is that the amount of energy contributing to development changes between the high density portion and the high density portion.

FIG. 6 is a diagram for explaining the respective In-Out unevenness correction values (a1, b1) and (a2, b2) of the density D1 and the density D2 provided to the correction calculation unit 74. In this example, the In-Out unevenness correction values (a1, b1) and (a2, b2) are as follows when the position in the main scanning direction is the x-axis and the density is y as shown in FIG.
Are determined as coefficients a1 and a2 and b1 and b2 for uniquely determining the linear function. In the example shown in FIG. 6, the density on the IN side and the density on the OUT side are expressed by a linear function as shown on the back side (IN side) and the near side (OUT side) of the main body 1 of the apparatus. At this time, the In-Out unevenness differs depending on the concentration, and the slopes a1 and a2 and the y-intercepts b1 and b2 are different. If the correction of In-Out unevenness is performed without taking this difference into consideration, the above-described problem occurs.

  Therefore, in the present embodiment, the correction calculation unit 74 of the lighting signal generation unit 61 shown in FIG. 4 is caused to function as correction value providing means for correcting In-Out unevenness (scanning direction unevenness) at a plurality of densities, thereby providing a plurality of correction values. Correction processing is executed using an In-Out unevenness correction value for density. More specifically, the correction calculation unit 74 corrects the In-Out unevenness correction value (a1, b1) at the first density D1 and the In-Out unevenness at the second density D2. The values (a2, b2) are input, the light amount unevenness correction value is changed according to the density value determined by the density determination unit 72, and the correction value g (x) is output.

即ち、濃度値ｈ(ｘ)が第１の濃度Ｄ１よりも小さい場合等、濃度がある程度下がれば、Ｉｎ−Ｏｕｔむらが飽和すると考え、濃度Ｄ１におけるＩｎ−Ｏｕｔむらの補正値(ａ１，ｂ１)だけを用いた補正が実行される。 For example, the correction calculation unit 74 is configured to change the light amount unevenness correction value according to the value of the density value h (x) determined by the density determination unit 72.
First, when the density value h (x) is smaller than the first density D1, the correction value g (x) is expressed by the following equation.

That is, if the density value h (x) is smaller than the first density D1, the In-Out unevenness is saturated when the density drops to some extent, and the correction value (a1, b1) of the In-Out unevenness at the density D1 is considered. Correction using only is performed.

かかる場合には、第１の濃度Ｄ１および第２の濃度Ｄ２の両者におけるＩｎ−Ｏｕｔむらの影響を受けると考えられる。そこで、この両者のＩｎ−Ｏｕｔむら補正値によって補間された補正が実行される。 On the other hand, when the density value h (x) is larger than the first density D1 and smaller than the second density D2, the correction value g (x) is expressed by the following equation.

In such a case, it is considered that both the first concentration D1 and the second concentration D2 are affected by in-out unevenness. Therefore, the correction interpolated by the both In-Out unevenness correction values is executed.

即ち、濃度値ｈ(ｘ)が第２の濃度Ｄ２よりも大きい場合等、濃度がある程度より大きくなれば、Ｉｎ−Ｏｕｔむらが飽和すると考え、濃度Ｄ２におけるＩｎ−Ｏｕｔむらの補正値(ａ２，ｂ２)だけを用いた補正が実行される。 Further, when the density value h (x) is larger than the second density D2, the correction value g (x) is expressed by the following equation.

That is, when the density value h (x) is higher than the second density D2, the In-Out unevenness is considered to be saturated when the density is higher than a certain level, and the correction value (a2, In-Out unevenness at the density D2 is considered). Correction using only b2) is performed.

  FIG. 7 is a flowchart showing a flow of processing executed by the lighting signal generator 61 with the above-described configuration. The lighting signal generator 61 first inputs image data (video data) composed of, for example, 1200 × 4800 × 1 bits, and stores it in the buffer 71 (step 101). In the density determination unit 72, for example, the density of the target pixel is determined using the density (on / off) of peripheral pixels including 15 × 15 dots centered on the target pixel (lighted pixel), and the density value h (x) is determined. Output (step 102). In the correction calculation unit 74, first, the light amount unevenness correction value f (x) of the target pixel is read from the light amount unevenness correction value storage unit 73 (step 103). Further, for example, when a correction start signal for In-Out unevenness correction or the like is input and In-Out unevenness correction is required, the In-Out unevenness correction value (a1, b1) at the density D1 and the In at the density D2 -Out unevenness correction values (a2, b2) are read (step 104). In addition, according to the density | concentration determined by the density | concentration determination part 72, it can also be comprised so that any one of the density | concentration D1 and the density | concentration D2 may be read.

  Thereafter, the correction calculation unit 74 determines the determined density value h (x), the read light amount unevenness correction value f (x), the correction value (a1, b1) of the in-out unevenness of the density D1, and / or Using the correction value (a2, b2) of the in-out unevenness of the density D2, the correction calculation is performed based on the above-described formula, and the correction value g (x) is output (step 105). For example, when a correction start signal or the like is not input and in-out unevenness correction is not necessary, the correction value g (x) is output in a state where the light amount unevenness correction value f (x) is equal.

Thereafter, the lighting clock number calculator 75 outputs the number of lighting clocks based on the image data (video data) and the unevenness correction value B obtained from the correction value g (x) (step 106). For example, if the video data rearranged in the light emission order is A, the number of lighting clocks Y is, for example,
Y = A · (1 + B / 255)
It can be expressed as In the above equation, the unevenness correction value B changes from 0 to 255, and as a result, the lighting clock number Y output from the lighting clock number calculator 75 changes from A to 2A.
After that, pulse width modulation is performed by the pulse width calculation unit 76 and the PWM circuit 77, an LED lighting signal is output (step 107), and the process ends.

Next, a second configuration example of the lighting signal generation unit 61 to which the present embodiment is applied, which is different from the block diagram of FIG. 4, will be described.
FIG. 8 is a block diagram showing a second configuration example of the lighting signal generator 61. The same reference numerals are used for the same functions as those in the first configuration example shown in FIG. In the second configuration example, for example, unevenness correction values different for each density, such as density 20% and density 50%, are stored in the memory. In addition, in-out unevenness correction is recalculated at a predetermined timing with a plurality of concentrations. Therefore, in the second configuration example shown in FIG. 8, instead of the light amount unevenness correction value storage unit 73 shown in FIG. 4, the light amount unevenness correction value storage unit 73a at the density D1, and the light amount unevenness correction value storage unit at the density D2. 73b, the light amount unevenness correction value f1 (x) from the light amount unevenness correction value storage unit 73a at the density D1, and the light amount unevenness correction value f2 (x) from the light amount unevenness correction value storage unit 73b at the density D2 74 is output. The light amount unevenness correction value storage unit 73a at the density D1 and the light amount unevenness correction value storage unit 73b at the density D2 read the unevenness correction values calculated by the In-Out unevenness correction calculation unit 81. When In-Out unevenness correction is performed at three or more densities, third and fourth light amount unevenness correction value storage units are provided. However, it is not always necessary to provide a plurality of memories as hardware. A mode in which a single or a plurality of memories are provided and a storage area is divided into a plurality (two or more, the number corresponding to the correction density) is stored. It does not matter.

The In-Out unevenness correction calculation unit 81 starts an unevenness correction calculation in response to an In-Out unevenness correction start trigger generated by an instruction from a user who uses the image forming apparatus. In the calculation, the In-Out unevenness correction value (a1, b1) of the density D1 and the In-Out unevenness correction value (a2, b2) of the density D2 are read. As for these correction values read out, those obtained in advance by input from the user or reading from the image reading device (IIT) 3 are stored in a memory (not shown) or the like, as described with reference to FIG. It is conceivable that the data is stored and read out in accordance with the operation timing. Of course, in-out unevenness correction values having three or more densities may be prepared. The In-Out nonuniformity correction calculation unit 81 performs the nonuniformity correction calculation from the nonuniformity correction value storage unit 73a for the light amount at the density D1 and the nonuniformity correction value storage unit 73b for the light quantity at the density D2, respectively. Read f2 (x). Then, using the obtained In-Out unevenness correction value (a1, b1) of the density D1 and In-Out unevenness correction value (a2, b2) of the density D2, the calculation (recalculation) of In-Out unevenness correction is executed. To do. The executed calculation results are again stored in the light amount unevenness correction value storage unit 73a at the density D1 and the light amount unevenness correction value storage unit 73b at the density D2.
In the correction calculation unit 74, the light amount unevenness correction value f1 (x) of the density D1 and the light amount unevenness correction value f2 (of the density D2) such as linear interpolation, for example, according to the density value h (x) obtained by the density determination unit 72. Interpolation processing with x) is performed, and a correction value g (x) for unevenness in the amount of light corresponding to the density of the target pixel is output. Thereafter, processing similar to that described with reference to FIG. 4 is executed.

  In this way, the lighting signal that has been subjected to the in-out unevenness correction is output from the lighting signal generator 61 by the configuration shown in the first configuration example or the second configuration example. This lighting signal is provided to the LED chip 63 shown in FIG.

Next, the LED chip 63 shown in FIG. 3 will be described.
FIG. 9 is a circuit diagram for explaining the configuration of the LED chip 63, and here, Chip 1 which is the first array chip is taken as an example. Although the input transfer signal and the lighting signal are different, Chip2 to Chip58 have the same configuration. The LED chip 63 shown in FIG. 9 includes, for example, 128 thyristors (S1 to S128), 128 LEDs (LED1 to LED128), 127 diodes (CR1 to CR127), 128 resistors (R1 to R128), Furthermore, it is composed of transfer current limiting resistors (R1A, R2A, R3A) that prevent excessive current from flowing through the signal lines.
The anode terminals (A1 to A128), which are input terminals of the thyristors (S1 to S128), are connected to the power supply line 65. A power supply voltage VDD (VDD = 5.0 V) is supplied to the power supply line 65. The transfer signal CK1 from the transfer signal generator 62 passes through the transfer current limiting resistor R1A to the cathode terminals (K1, K3,..., K127) that are the output terminals of the odd-numbered thyristors (S1, S3,..., S127). Supplied. Further, the transfer signal CK2 from the transfer signal generator 62 is applied to the transfer current limiting resistor R2A at the cathode terminals (K2, K4,..., K128) that are the output terminals of the even-numbered thyristors (S2, S4,..., S128). Is supplied through.

  On the other hand, the gate terminals (G1 to G128), which are the control terminals of the thyristors (S1 to S128), are respectively connected to the power supply line 66 via resistors (R1 to R128) provided corresponding to the thyristors. The power line 66 is grounded (GND). The gate terminals of the LEDs (LED1 to LED128) provided corresponding to the thyristors (S1 to S128) are connected to the gate terminals (G1 to G128) of the thyristors (S1 to S128), respectively. Furthermore, the anode terminals of the diodes (CR1 to CR127) are connected to the gate terminals (G1 to G128) of the thyristors (S1 to S128). The cathode terminals of the diodes (CR1 to CR127) are connected to the gate terminals of the next-stage thyristors, respectively. That is, the diodes (CR1 to CR127) are connected in series. The anode terminal of the diode CR1 is connected to the transfer signal generator 62 via the transfer current limiting resistor R3A and receives the transfer signal CKS. Further, the cathode terminals of the LEDs (LED1 to LED128) receive the lighting signal CKI1 from the lighting signal generator 61.

Next, the operation of the LED chip 63 will be described with reference to the timing chart shown in FIG.
First, when the chip 1 of the LED chip 63 is instructed to start the operation, the transfer signal generator 62 supplies a high-level transfer signal CKS as shown in FIG. That is, a high level is input to the gate terminal G1 of the thyristor S1 shown in FIG. When the transfer signal CKS is at a high level, the thyristor S1 is turned on when the transfer signal CK1 output from the transfer signal generator 62 becomes a low level as shown in FIG. 10B.

  As described above, among the odd-numbered thyristors (S1, S3,...) To which the transfer signal CK1 is supplied when the transfer signal CKS is at a high level, the gate terminal has the highest potential, that is, a gate equal to or higher than the thyristor threshold voltage. The voltage thyristor S1 is turned on. At this time, since the transfer signal CK2 is at a high level as shown in FIG. 10C, the potentials of the cathode terminals (K2, K4,...) Of the even-numbered thyristors (S2, S4,...) Remain high. The even-numbered thyristors (S2, S4,...) Are kept off. Further, since the lighting signal CKI1 is at a high level as shown in FIG. 10D, the potential of the cathode terminals of the LEDs (LED1 to LED128) is high, and the LEDs (LED1 to LED128) are not lit. Then, when the lighting signal CKI1 changes from the high level to the low level as shown in FIG. 10D, the potential of the cathode terminal of the LED1 becomes low and the LED1 lights up.

Next, when the thyristor S1 is on, as shown in FIG. 10C, when the transfer signal CK2 becomes low level and the lighting signal CKI1 becomes high level, the even-numbered thyristor (S2 to which the transfer signal CK2 is supplied). , S4,...), The thyristor S2 having the highest potential at the gate terminal, that is, the gate voltage equal to or higher than the threshold voltage of the thyristor is turned on, and the LED 1 is turned off. When the transfer signal CK1 becomes high level as shown in FIG. 10B, the thyristor S1 is turned off, the potential of the gate terminal G1 is gradually lowered by the resistor R1, and the potential of the gate terminal G2 is increased. Along with this, the potentials of the gate terminals G3 and G4 also rise.
Thereafter, when the lighting signal CKI1 changes from the high level to the low level as shown in FIG. 10D, the LED 2 is turned on. Similarly, when the thyristor S2 is on, as shown in FIG. 10B, when the transfer signal CK1 becomes low level again and the lighting signal CKI1 becomes high level, the thyristor S3 is turned on and the LED 2 is not lit. Become. Then, as shown in FIG. 10C, when the transfer signal CK2 becomes high level, the thyristor S2 is turned off.

As described above, in the Chip 1 of the LED chip 63, the thyristor is switched by alternately switching between the high level and the low level while providing the overlapping period (the period of Ta shown in FIG. 10) in which the transfer signals CK1 and CK2 are both at the low level. The LEDs (LED1 to LED128) can be sequentially lit by sequentially turning on (S1 to S128) and sequentially setting the lighting signal CKI1 to the low level in synchronization with this. Therefore, the signal lines connected to Chip 1 of the LED chip 63 include three for the transfer signals CKS, CK1, and CK2, one for the lighting signal CKI1, and two power lines (one of which is grounded). Therefore, it is possible to drive only with these six signal lines.
The same applies to Chip2, Chip3,..., Chip58 of the LED chip 63, and the LEDs are sequentially turned on by the transfer signals CKS, CK1, CK2, and the lighting signals CKI2 to CKI58, respectively.

  As described above in detail, according to the present embodiment, the light amount unevenness correction value of each LED of the LPH 14 is read, and the inclination of the In-Out unevenness, which is unevenness in the scanning direction, is further converted into the light amount unevenness correction value. Recalculated to correct. At this time, even if the In-Out density unevenness is corrected at a certain density, the In-Out density unevenness may remain at a different density, and adjustment with a single density may not be sufficient to obtain a good image. is there. In this embodiment, the configuration is such that the In-Out density unevenness is corrected using the In-Out unevenness information obtained at a plurality of densities, so that there is no In-Out unevenness regardless of the writing density. A good image can be obtained.

  As an example of use of the present invention, for example, an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic method, or a print that forms an electrostatic latent image by exposing, for example, a photosensitive drum in the image forming apparatus. Can be applied to the head.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is the figure which showed the structure of the LED print head (LPH). It is a hardware block diagram of LPH to which this Embodiment is applied. It is the block diagram which showed the structure of the lighting signal generation part. (a), (b) is a figure which showed an example of the correction value calculation process at the time of performing a calculation process using only a specific In-Out nonuniformity correction value in the correction calculation part. It is a figure for demonstrating each In-Out nonuniformity correction value (a1, b1) and (a2, b2) of density | concentration D1 and density | concentration D2 which are provided to a correction | amendment calculating part. It is the flowchart which showed the flow of the process performed in a lighting signal generation part. It is the block diagram which showed the 2nd structural example of the lighting signal generation part. It is a circuit diagram for demonstrating the structure of a LED chip. It is a timing chart which shows operation | movement of a LED chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image process system, 11 ... Image forming unit, 12 ... Photosensitive drum, 13 ... Charger, 14 ... LED print head (LPH), 15 ... Developer, 51 ... LED array, 52 ... Printed circuit board, 53 ... Cell Fock lens array (SLA) 61 ... Lighting signal generator 62 ... Transfer signal generator 63 ... LED chip 71 ... Buffer 72 ... Density determination unit 73 ... Uneven light intensity correction value storage 73a ... Density D1 Light intensity unevenness correction value storage section 73b ... Light intensity unevenness correction value storage section at density D2, 74 ... Correction calculation section, 75 ... Lighting clock number calculation section, 76 ... Pulse width calculation section, 77 ... PWM circuit, 81 ... In-Out Unevenness correction calculation unit

Claims (11)

A light emitting array in which a plurality of light emitting elements are arranged;
Lighting signal generating means for generating a lighting signal for the plurality of light emitting elements of the light emitting array according to input image data;
Correction value providing means for providing a correction value of the light amount of the light emitting array to the lighting signal generating means,
The correction value providing means grasps each of the scanning direction unevenness at a plurality of densities with respect to the scanning direction unevenness when the light emitting array is mounted on the apparatus having the irradiation target, and sets the density of the input image data. Accordingly, a correction value corresponding to the unevenness in the scanning direction is provided. Further comprising storage means for preliminarily storing light amount unevenness correction values in the plurality of light emitting elements of the light emitting array;
The correction value providing means corrects the light amount unevenness correction value read from the storage means using the scanning direction unevenness correction value at the first density and the scanning direction unevenness correction value at the second density, and The light-emitting device according to claim 1, wherein a correction value is calculated. A density determination means for determining the density of the input image data;
The correction value providing means corrects unevenness in the scanning direction from the relationship between the density of the image data determined by the density determination means and the first density and / or the second density. Item 3. A light emitting device according to Item 2. A light emitting array in which a plurality of light emitting elements are arranged;
A light amount unevenness correction value storage means for storing a light amount unevenness correction value at the first density and a light amount unevenness correction value at the second density as the light amount unevenness correction value of the light emitting array;
Correction for calculating a correction value corresponding to the density of the input image data from the light intensity unevenness correction value at the first density and the light intensity unevenness correction value at the second density stored in the light intensity unevenness correction value storage means. A value calculating means;
Lighting signal generating means for generating lighting signals for the plurality of light emitting elements of the light emitting array using the correction value calculated by the correction value calculating means,
The correction value storage means is a first light amount unevenness obtained by using a first scanning direction unevenness correction value at the first density, which is calculated when the light emitting array is mounted on a device having an irradiation target. A light-emitting device that stores a correction value and a second light amount unevenness correction value obtained using the second unevenness correction value in the scanning direction at the second density.   5. The calculation device according to claim 4, further comprising calculation means for calculating the first scanning direction unevenness correction value and the second scanning direction unevenness correction value at a predetermined timing when the light emitting element is turned on. Light emitting device. An image carrier;
A print head that includes a light emitting element array in which a plurality of light emitting elements are arranged in an array and a lens array that forms an image of light from the light emitting elements, and that exposes the image carrier to form an electrostatic latent image;
Lighting signal generating means for generating a lighting signal for the plurality of light emitting elements of the light emitting element array;
Scanning direction unevenness correcting means for correcting the scanning direction unevenness with a plurality of densities with respect to the scanning direction unevenness when the print head is arranged facing the image carrier,
The image forming apparatus, wherein the lighting signal generating unit generates a lighting signal corrected by the scanning direction unevenness correcting unit according to the density of image data to be output.   The image forming apparatus according to claim 6, wherein the scanning direction unevenness correcting unit grasps and corrects scanning direction unevenness of a plurality of densities when the image carrier or the print head is replaced.   The scanning direction unevenness correcting means provides the lighting signal generating means with a value determined by a linear function connecting the IN side and the OUT side in the scanning direction as a scanning direction unevenness correction value. Image forming apparatus.   The lighting signal generation unit reads the current light amount unevenness correction value, corrects a density gradient obtained from the scanning direction unevenness correction value provided by the scanning direction unevenness correction unit, and generates the lighting signal. The image forming apparatus according to claim 8. A density unevenness correction method in an image forming apparatus having an image carrier and a print head that exposes the image carrier to form an electrostatic latent image,
Obtaining an IN-OUT unevenness correction value generated in the scanning direction at a plurality of densities when the print head is disposed facing the image carrier;
And calculating a new light amount unevenness correction value using the IN-OUT unevenness correction values at a plurality of acquired densities as the current light amount unevenness correction value in the print head. .   The obtained IN-OUT unevenness correction value is a linear function of density change between the IN side and the OUT side in the scanning direction with respect to each of the inputted first density and second density. The method for correcting uneven density in an image forming apparatus according to claim 10.

Images