JP2004188845A - Print head characteristic measuring device, light exposure correcting method, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out measurement of exposure energy distribution at a print head, with high accuracy and high resolution and at high speed. <P>SOLUTION: There is provided an LED print head (LPH) 14 characteristic measuring device for calculating correction data for calculating development concentration corresponding to each light emitting point, based on the exposure energy distribution. The device is comprised of a line CCD 61, a moving stage 62, a CCD board 70, a CCD interface 80, and a PC 66. The line CCD 61 is arranged so as to be opposed to the LPH 14 which is an array of light emitting elements, and measures an exposure of each light emitting element of the LPH 14. The moving stage 62 enables uniform movement of the line CCD 61 while maintaining the position of the line CCD 61 so as to be inclined by a predetermined angle toward a moving direction of the same. The CCD board 70 arithmetically operates output from the line CCD 61 to obtain data for correcting the quantity of light of each light emitting element constituting the LPH 14. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure amount correction method for a print head that performs optical writing, and more particularly, to an exposure amount correction method for correcting variations in exposure amounts for a plurality of light emitting elements.
[0002]
[Prior art]
In an image forming apparatus such as a printer, a copying machine, a facsimile, etc., which adopts an electrophotographic system, an electrostatic latent image is obtained by irradiating image information on a uniformly charged photoconductor by an optical recording unit. An image is formed by adding toner to the electrostatic latent image to visualize the image, transferring the image onto recording paper and fixing the image. As such an optical recording means, besides an optical scanning method in which a laser beam is scanned in a main scanning direction using a laser to expose the light, in recent years, an LED (Light Emitting Diode: light emitting diode) has been used in response to a demand for miniaturization of the apparatus. Optical recording means using an LED print head (LPH: LED Print Head) arranged in a large number in the main scanning direction is employed.
[0003]
The LPH generally includes an LED array in which a plurality of LED chips in which a large number of LEDs are arranged in a line are arranged, and a large number of rod lenses for forming light output from the LEDs on the surface of a photoconductor (photoconductor drum). And a SELFOC lens in which are arranged. In the image forming apparatus, each LED of the LPH is driven based on input image data, light is output toward the photoconductor, and the light is imaged on the photoconductor surface by the selfoc lens. Then, an electrostatic latent image is formed in the sub-scanning direction by relatively moving the photoconductor and the LPH.
[0004]
In this LPH, since a plurality of light emitting elements are arranged in a line in the main scanning direction, variations in light emitting points greatly affect image quality. In particular, when there is a variation in the light amount at the light emitting point, a streak or density unevenness in the sub-scanning direction occurs, which is likely to cause an image quality defect. Therefore, as a conventional technique, there is a technique of measuring a characteristic value in an exposure intensity distribution of a light emitting element by a two-dimensional CCD, and obtaining a correction value for each light emitting element from the measurement result to obtain a light emission amount (for example, see Patent Document 1). .). Further, there is a technique for measuring characteristic points of a light emitting element based on a light emission intensity distribution of the light emitting element obtained by a slit and determining light amount correction data (for example, see Patent Document 2).
[0005]
[Patent Document 1]
JP-A-2002-127492 (pages 7, 9; FIGS. 16, 21)
[Patent Document 2]
JP-A-11-227254 (pages 3-4, FIG. 9, FIG. 13)
[0006]
[Problems to be solved by the invention]
Here, in the measurement method described in Patent Literature 1, since the position resolution of measurement is determined by the pixel size of the CCD, the resolution is improved by using an enlargement optical system. However, the optical system has different reflectance and transmittance depending on the incident position and incident angle of the incident light, and has problems such as aberration and vignetting, so that it is difficult to perform highly accurate measurement. Further, when the magnifying optical system is used, the exposure energy on the sensor decreases, and it is necessary to lengthen the accumulation time, so that high-speed measurement is difficult. Further, in the technique described in Patent Literature 2, the exposure energy distribution is calculated from the exposure distribution integrated in a certain direction, and the information of the actual distribution is lost. As a result, there is a problem that the accuracy is reduced. Was.
[0007]
The present invention has been made to solve the above-described technical problems, and an object of the present invention is to measure an exposure amount of a light emitting element constituting a print head with high resolution.
Another object is to make the development density in the image forming apparatus uniform by appropriately grasping the light amount of each light emitting element constituting the print head using a line CCD having a low positional resolution.
[0008]
[Means for Solving the Problems]
With this object in mind, the present invention relates to a printhead characteristic measuring device for calculating correction data for calculating a development density corresponding to each light emitting point from an exposure energy distribution, wherein the printhead has light emitting elements arranged therein. The amount of exposure from each light-emitting element is measured by a line CCD provided opposite to the CCD, and the line CCD is moved at a constant speed by a moving stage while the line CCD is inclined at a fixed angle in the moving direction. The output from the line CCD is arithmetically processed to obtain data for correcting the light amount of the light emitting elements constituting the print head.
[0009]
Here, the line CCD can be characterized in that the CCD accumulation time is set to an integral multiple of the scan period of the print head. Further, the processing unit may be characterized in that the outputs from the line CCDs are rearranged, and the oblique arrangement due to the inclination of the line CCDs by a fixed angle is corrected using a buffer memory.
[0010]
Further, when grasping the present invention from the category of the method, the present invention is a method for measuring an exposure amount of a print head in which a plurality of light emitting elements are arranged, and an image is formed by exposing a photosensitive member with the light emitting elements, Measuring the exposure amount by moving the line CCD, which is provided opposite to the illuminated light emitting element and arranged obliquely to the moving direction, at a constant speed, and correcting the exposure amount in the light emitting element from the measured exposure amount Calculating the correction data for performing the correction. Here, the step of calculating the correction data includes rearranging data relating to the exposure amount measured by the line CCDs arranged obliquely on the buffer memory, and based on the rearranged data, the light amount of each light emitting element. It is characterized in that data for correcting the variation is calculated.
[0011]
From another viewpoint, the present invention relates to an exposure correction method for correcting an exposure of a print head in which light emitting points are arranged using a line CCD having a predetermined positional resolution. It is characterized in that the exposure amount is measured in a state where the substantial positional resolution is improved without relying on an optical system for a predetermined position resolution, and correction data is obtained based on the measured exposure amount. Here, the line CCD is moved with respect to the print head, so that the exposure amount of the arranged light emitting points is measured. It is characterized by improving the resolution.
[0012]
Further, the image forming apparatus to which the present invention is applied includes a photoconductor, and a print head that forms an electrostatic latent image by exposing the photoconductor with a plurality of light emitting elements arranged, and the print head includes: A memory is provided for storing a correction characteristic value or light quantity correction data based on data in which the position resolution of the line CCD for measuring the exposure amount of each light emitting element is substantially improved without using an optical system with respect to the position resolution of the line CCD. The exposure amount of each light emitting element is determined based on the correction characteristic value or light amount correction data stored in the memory. The correction characteristic value stored in the memory can be characterized in that it is a value that can correlate an exposure profile obtained from an exposure amount measured by a line CCD with a development density.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus using an LED printhead to be measured in the present embodiment, and shows a so-called tandem type digital color printer. The image forming apparatus shown in FIG. 1 includes, in a main body 1, an image processing system 10 for forming an image corresponding to gradation data of each color, an image output control unit 30 for controlling the image processing system 10, for example, a personal computer (PC). 2 and an image reading device (IIT) 3, and includes an image processing unit (IPS: Image Processing System) 40 that performs predetermined image processing on the image data received from these devices.
[0014]
The image processing system 10 includes an image forming unit 11 including a plurality of engines arranged in parallel at a predetermined interval in a 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). A photoconductor drum 12 which is an image carrier (photoconductor) for forming an image and carrying a toner image; a charger 13 for uniformly charging the surface of the photoconductor drum 12; a photoconductor charged by the charger 13 An LED print head (LPH) 14, which is a print head for exposing the drum 12, is provided with a developing unit 15 for developing a latent image obtained by the LPH 14. Further, the image processing system 10 conveys the recording paper in order to 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 in a multiplex manner. The image forming apparatus includes a sheet conveying belt 21, a driving roller 22 for driving the sheet conveying belt 21, and a transfer roller 23 for transferring the toner image on the photosensitive drum 12 to a recording sheet.
[0015]
Each of the image forming units 11Y, 11M, 11C, and 11K has substantially the same structure except for the toner stored in the developing device 15. The image signal input from the PC 2 or IIT 3 is subjected to image processing by the image processing unit 40, and is supplied to each of the image forming units 11Y, 11M, 11C, and 11K via an interface. The image processing 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 by the LPH 14 on the surface of the photosensitive drum 12 charged by the charger 13 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 device 15, and the formed yellow toner image is transferred onto a recording sheet on a sheet conveying belt 21 that rotates in the direction of the arrow in FIG. Transcribed. Similarly, magenta, cyan, and black toner images are formed on the respective photosensitive drums 12 and are multiplex-transferred onto recording paper on a paper transport belt 21 by using a transfer roll 23. The multiply-transferred toner image on the recording sheet is conveyed to the fixing device 24 and fixed on the recording sheet by heat and pressure.
[0016]
FIG. 2 is a diagram showing a configuration of an LED print head (LPH) 14 which is a print head. The LPH 14 includes an LED array 51 in which a large number of LEDs are arranged as light emitting elements, a printed circuit board 52 supporting the LED array 51 and having a circuit for controlling the driving of the LED array 51 formed thereon, and light emitted from each LED. A selfoc lens array (SLA) 53 for forming an image of the beam on the photosensitive drum 12 is provided. The printed circuit board 52 and the selfoc lens array 53 are held by a housing 54. In the LED array 51, LEDs are arranged by the number of pixels in the main scanning direction. For example, when the short side (297 mm) of the A3 size is set as the main scanning direction, 7020 LEDs are arranged at intervals of about 42.3 μm at a resolution of 600 dpi. Note that the array may be arranged in a staggered pattern in addition to being arranged in a line. A memory (ROM or the like) in which the printed circuit board 52 stores data relating to correction characteristic values obtained by the exposure amount measuring method to which the present embodiment is applied (or light amount correction data calculated from the correction characteristic values). The light amount of the LEDs constituting the LED array 51 is corrected based on the data stored in the memory.
[0017]
Next, an exposure profile measurement system for the LPH 14 will be described.
FIG. 3 is a diagram for explaining an exposure profile measurement system to which the present embodiment is applied. The exposure profile measuring device 60 constituting the measurement system includes a line CCD (Charge Coupled Device) 61 in which a light receiving surface is provided to face the light emitting unit of the LPH 14 and a plurality of pixels are arranged in a line, and the line CCD 61. A CCD board 70 for measuring the exposure energy distribution from the LPH 14 using the output from the line CCD 61, a moving stage 62 for moving the CCD board 70 with the main scanning direction in which the LEDs of the LPH 14 are arranged as a moving direction, and on the moving stage 62 A stage driver 63 for moving the CCD board 70 at a constant speed, an LPH driver 64 for outputting a drive signal to the LPH 14 to turn on each LED, and a CCD interface 80 for processing a data signal transferred from the CCD board 70. ing. The line CCD 61 provided on the CCD board 70 has a CCD light receiving surface disposed near the focal plane of the print head of the LPH 14, and in this embodiment, no optical element such as a lens is used.
[0018]
Processing of the obtained data signal, movement control of the CCD board 70, control of the LPH driver 64, and the like are executed by a personal computer (PC) 66 as a processing unit. The PC 66 includes a frame grabber 67 for capturing image data, a digital I / O 68 for controlling input of a status signal and a data signal, output of a control signal, and the like, a motor controller 69 for controlling driving of the stage driver 63, and the like. I have. The moving stage 62 has, for example, a non-contact structure using an air bearing and a linear motor. The motor controller 69 performs PLL control based on feedback from a linear encoder, thereby realizing constant-speed movement control of the CCD board 70. are doing.
[0019]
The exposure profile measuring device 60 performs measurement at a constant time period while moving the CCD board 70 having the line CCD 61 at a constant speed in the main scanning direction, converts the data into digital values, and takes the data into the PC 66. Here, if an optical system such as a lens is used, differences in transmittance, reflectance, and the like occur due to the path and incident angle of light, and these differences cannot be ignored in highly accurate measurement of exposure energy. The line CCD 61 to which the present embodiment is applied does not use an optical system (a magnifying lens or the like) except that an ND-filter with an antireflection film for adjusting sensitivity is attached. However, if the optical system is eliminated as much as possible, there arises a problem that the position resolution of the measurement is determined by the pixel size of the line CCD 61. Therefore, in the present embodiment, as will be described later, the line CCD 61 is inclined at a fixed angle with respect to the moving direction, thereby improving the substantial positional resolution without relying on the magnifying optical system.
[0020]
FIG. 4 is a diagram for explaining the positional relationship between the line CCD 61 and the LED exposure spot of the LPH 14. Here, a state in which the line CCD 61 inclined at an angle θ from the moving direction (main scanning direction, X direction) with respect to the LED exposure spot moves at a moving speed of 1 mm / s is shown. The LED exposure spot is narrowed to 30 to 40 μm. The line CCD 61 used here has a pixel size of 4.7 × 4.7 μm, an inclination angle θ of 8.6 degrees, a transmittance of an optical filter (ND-filter) of 2%, and a storage time of 0.5. 95 ms. Note that the CCD accumulation time is a time during which the line CCD 61 performs photoelectric conversion for an external light input, and has a role of a shutter. The line CCD 61 receives the light from the LPH 14 during the accumulation time, performs photoelectric conversion, and sequentially outputs an analog voltage proportional to the amount of light × time = exposure energy through an analog shift register.
[0021]
As the position resolution of the measurement, the position resolution in the main scanning direction (X direction) is determined by the drive timing of the line CCD 61, and is determined by the moving speed and the time for capturing one line of the line CCD 61. As for the position resolution in the sub-scanning direction (Y direction), the inclination of the line CCD 61 as shown in FIG. 4 substantially reduces the CCD pixel pitch and increases the resolution. In the example shown in FIG. 4, the position resolution in the main scanning direction is 0.93 μm, and the position resolution in the sub scanning direction is 0.70 μm.
[0022]
FIG. 5 is a diagram for explaining the positional resolution of the line CCD 61, and shows the positional relationship between the CCD pixels. The line CCD 61 is inclined at θ = 8.6 deg with respect to the main scanning direction, which is the moving direction, and moves at the moving speed v. Here, it is assumed that the pixel interval of the line CCD is P, the pixel interval in the main scanning direction is Px, and the pixel interval in the sub-scanning direction is Py. If the CCD accumulation time is t, the pixel interval Px in the main scanning direction is
Pixel interval Px in the main scanning direction = CCD accumulation time t × moving speed v
Or using a positive integer K
Pixel interval Px in the main scanning direction = CCD accumulation time t × moving speed v × K
Is represented by The resolution in the main scanning direction at this time is
Main scanning direction resolution = Main scanning direction pixel interval Px / K
It becomes.
[0023]
At the time of rearrangement, the measurement timing is determined so that the measurement positions are arranged on a straight line. Further, even when measurement is performed at a position where the pixel interval Px in the main scanning direction is equally divided by an integer K, linearity at the time of rearrangement can be obtained. In the present embodiment, for example, actual measurement is performed at K = 5. In this case, if θ = 8.6 deg and CCD pixel interval P = 4.7 μm, the main scanning resolution becomes
cos (8.6 deg) × 4.7 μm / 5 (K) = 0.93 μm
Thus, the substantial positional resolution can be improved without relying on the magnifying optical system. In the present embodiment, the cycle of the CKS (scanning start signal of the LED constituting the LPH 14) (CCD accumulation time = CKS cycle × M) is finely adjusted to match the main scanning resolution. That is, the accumulation time of the CCD is configured to be an integral multiple of the scanning cycle of the LPH 14.
[0024]
Here, the accumulation time of the CCD is determined by SH (shift pulse). When a self-scanning LED (SLED: Selfscanning LED) is used, an arbitrary lighting pattern can be measured by synchronizing SH with a start pulse CKS. Further, even if there is stray light generated by light emitting points that emit light at different timings in time, light can be captured at a position where the light is emitted. In addition, even when using an LED of static drive or dynamic drive instead of the SLED, the same measurement can be performed by synchronizing with a line sync (LSYNC: horizontal synchronization signal).
[0025]
The line CCD 61 used has a pixel pitch of 4.7 μm. However, such a line CCD 61 having a narrow pixel pitch is generally used for an image scanner used in the image reading device 3 or the like. , The total number of pixels is often large. If not many pixels are required for measurement use, this large number of pixels will extend the CCD transfer cycle time, making it difficult to complete all transfer and data sorting within the desired accumulation time. Become. Therefore, by switching the frequency of the transfer pulse (reset: RS, clamp: CMP, clock: CLK) of the CCD between the necessary pixels and the unnecessary pixels, the total time of the transfer cycle is shortened even when the total number of pixels is large. can do.
[0026]
Next, measurement and data transfer processing will be described.
FIG. 6 is a timing chart showing the processing of measurement and data transfer. In FIG. 6, CKS is an SLED scan start signal, and the CCD accumulation time is calculated using Tcks, a positive integer M, which is the interval between start pulses.
CCD accumulation time = M x Tcks
Is represented by SH is a CCD accumulation time control signal, CLK is a CCD transfer clock, CVALID is a CCD required pixel signal output period, CTRCK is a signal for transferring CCD data to a buffer, RDCK is a buffer read clock, and TRCK is a data transfer to a frame grabber 67. The clock is shown.
[0027]
First, an SH pulse is sent to the CCD in synchronization with CKS. In the example shown in FIG. 6, a measurement cycle in which CKS is two cycles and SH is one cycle is shown. When the measurement cycle N + 1 is entered, the CCD data accumulated in the measurement cycle N is transferred by CMP, RS, and CLK. Here, for example, the CCD may be configured to have 7,500 pixels, and the 3200th to 4223rd pixels are used. In such a case, unnecessary pixels 1 to 3199 are transferred at 25 MHz, 3200 to 4223 pixels are transferred at 5 MHz, and 4224 to 7500 pixels are transferred at 25 MHz. In the high-speed transfer, electric noise is easily taken, and it is desirable to transfer at a low speed as much as possible at the time of measurement. However, if data is transferred to unnecessary pixels at 5 MHz, the entire data transfer time of the line CCD exceeds the measurement time. Therefore, it is during the 5 MHz transfer section that the data is actually obtained by the A / D conversion, and the data (1024 pixels × 16 bits) during this period is written to the buffer memory (described later). This writing period to the buffer memory is indicated as a CVALID buffering cycle. At this time, CTRCK is output. Then, the data is read from the buffer memory at the address indicated by the data rearrangement by the clock indicated by RDCK, and is transferred to the frame grabber 67 by the clock of TRCK. 6 is executed.
[0028]
Next, a circuit configuration of a processing unit for enabling the above processing to be executed will be described.
FIG. 7 is a diagram for explaining a circuit configuration of a CCD board 70 which is one of the processing units. The CCD board 70 receives a scanning start signal (CKS) of the SLED from the LPH driver 64 and outputs a CLK signal and the like, a CCD timing generator 71, a register 72 for outputting a set value, and a line based on the set value from the register 72. A post-processing circuit 73 for performing post-processing on the data read from the CCD 61, an AD converter 74 for converting an analog output from the post-processing circuit 73 to digital, and a logical product of the output of the AD converter 74 and the CCD timing generator 71. And an AND gate 75 for outputting a CCD digital signal.
[0029]
In the circuit configuration shown in FIG. 7, the following processing is performed on the data output from the line CCD 61, and the data is output as an exposure profile measurement value. As the processing, first, since the line CCD 61 has sensitivity unevenness for each pixel, the sensitivity unevenness is corrected. Further, as described above, since the line CCD 61 is used at an angle, the data is rearranged to simplify post-processing.
[0030]
Since the line CCD 61 to which this embodiment is applied adopts a structure in which odd-numbered pixels and even-numbered pixels are output through different analog shift registers, the line CCD 61 has two output terminals of EVEN and ODD. I have. Therefore, each of the post-processing circuits 73 performs post-processing. Here, a difference in characteristics between EVEN and ODD is canceled by specifying an offset value and a gain value.
[0031]
As described above, CVALID, which is a signal indicating the CCD required pixel signal output period, does not use all the data of the CCD but employs some of the data as required pixels. "TRUE" is output from the CCD timing generator 71 only when the CTRCK is a transfer clock for synchronously transferring CCD data to the CCD interface 80, and is output from the CCD timing generator 71 only when required pixel data is output, like CVALID.
[0032]
FIG. 8 is a diagram for explaining a circuit configuration of the CCD interface 80 which is one of the processing units. Here, the processing of the data transferred from the CCD board 70 is executed. The CCD interface 80 includes a trigger processing unit 81 that triggers based on the output of the line CCD 61, a WRITE address generation unit 82 that receives a CVALID and CTRCK from the CCD board 70 and outputs a WRITE address, and an enable from the trigger processing unit 81. CCD sensitivity in-plane unevenness correction unit 83 that receives and outputs WRITE data, and memory 84 that stores various values such as in-plane unevenness correction values such as black level and white level provided to CCD sensitivity in-plane unevenness correction unit 83. , A buffer memory 85 for temporarily storing data, a CCD tilt correction unit 86 for specifying a rearrangement address, etc., based on the profile measurement data output from the CCD tilt correction unit 86 and the development characteristics stored in the memory 84. Processing unit that executes the processing of the developing characteristics 7. Based on the output from the development characteristic processing section 87, a conversion processing to a correction characteristic value described later is executed, and a sub-scanning integration processing section 88 for outputting the calculation result to the memory 84; A PC-IF 89 is provided for interfacing with the PC 66, such as receiving signals and outputting data signals.
[0033]
Upon receiving the CVALID, CTRCK, and CCD digital signals from the CCD board 70, the trigger processing unit 81 determines whether light enters the line CCD 61 and the output exceeds a set threshold. If not exceeded, the operation is performed until the buffering cycle, and the subsequent data rearrangement / frame grabber transfer cycle is not operated. When a trigger is applied, the operation of the data rearrangement / frame grabber transfer cycle starts from the next measurement cycle.
[0034]
The CCD sensitivity in-plane unevenness correction unit 83 corrects the sensitivity unevenness of each pixel of the line CCD 61. That is, black level correction and white level correction are performed, and the intercept and inclination of each pixel are corrected. In order to correct the inclination of the line CCD 61, data is temporarily written to the buffer memory 85. After that, when the rearrangement data is prepared, the rearrangement address is designated by the CCD tilt correction unit 86, and the data (READ data) is read. The read data is transferred to the frame grabber 67 by a transfer clock (TRCK). Further, it is also possible to provide a function of performing further processing and writing the processing result to the buffer memory 85. Since the buffer memory 85 is used for temporarily storing data rearrangement, data that has been used for rearrangement and becomes unnecessary is sequentially used for buffering new data.
[0035]
In the CCD interface 80 shown in FIG. 8, after the processing is started, the WRITE address generation unit 82 generates a buffer WRITE row address in response to the rise of CVALID, and generates a buffer WRITE column address in response to CTRC. . These are combined and output to the buffer memory 85 as a WRITE address. In the CCD tilt correcting section 86, a rearranging row address and a rearranging column address are generated, and these are combined and output to the buffer memory 85 as a READ address. The CCD tilt correction unit 86 reads data from the buffer memory 85 and outputs profile measurement data to the frame grabber 67 with the read clock RDCK shown in FIG.
[0036]
In the example shown in FIG. 8, the profile measurement data is directly output to the frame grabber 67. However, by implementing the necessary processing in the CCD interface 80, the processing on the PC 66 and the data transferred to the PC 66 can be reduced. In the example shown in FIG. 8, for example, a configuration in which a development characteristic processing unit 87 and a sub-scanning integration processing unit 88 are mounted, the processing result is written into the memory 84 again, and data is acquired from the PC 66 using the digital I / O 68 Contains. In the case of the above setting, that is, when the spatial resolution is 0.93 μm × 0.70 μm, 1 data = 16 bits, and the A3 width is measured using 1024 pixels as the line CCD 61, for example, raw data of profile measurement data = 650 Mbytes , The data after processing = 640 Kbytes.
[0037]
FIG. 9 is a diagram for explaining a memory map for rearranging CCD outputs in the buffer memory 85. Here, it is shown using the address (x, y), where x is a buffer row address indicating a CCD scan number, and y is a buffer column address indicating a CCD pixel number. p indicates the number of CCD effective pixels, and in this embodiment, p = 1024. The integer K is set to K = 5.
[0038]
First, in the buffer WRITE address generation, (0, 0), (0, 1),..., (0, p−1), (1, 0), (1, 1),. , (1, p-1), (2,0), ..., (K. (p-1) + K-1, p-2), (K. (p-1) + K-1, p-1) , (0,0), (0,1),... Are generated. On the memory map shown in FIG. 9, addresses are specified from left to right and from top to bottom, and when the final address is reached, the process returns to the upper left. When the rearrangement becomes unnecessary, the data is sequentially overwritten with the data from the line CCD 61. The row address is incremented (Increment) at the rising edge of CKS, and the column address is incremented by the data transfer clock from the line CCD 61 to generate a memory address.
[0039]
Next, in the generation of the rearrangement READ address, the data of the address (0, 0), (K, 1), (K · 2, 2),..., (K · (p−1), p−1) , X = 0 is overwritten with the CCD output in the next buffering cycle. Similarly, after reading the data at the address of (1, 0), (K + 1, 1), (K · 2 + 1, 2),..., (K · (p−1) +1, p−1), In the buffering cycle, x = 1 is overwritten with the CCD output. By repeating such processing, (K, 0), (K · 2, 1), (K · 2 + 2, 3),..., (K · (p−1) +1, p−2), (0, p Data reading and overwriting are repeatedly performed in the order of -1) data reading. The row address is incremented by K at the rise of CKS, and the column address is incremented by a read (READ) clock to the buffer memory 85. As described above, in the buffer memory 85, the outputs of the line CCDs 61 are rearranged, and the oblique arrangement is corrected.
[0040]
Next, a conversion process to a correction characteristic value performed by the PC 66 will be described.
FIG. 10 is a flowchart for explaining the conversion process to the correction characteristic value. Here, the obtained exposure profile is converted into a correction characteristic value that can be correlated with the development density. First, after acquiring the profile measurement data via the frame grabber 67, a sub-scanning direction multiplexing process for calculating a value obtained by shifting and adding the profile measurement data in the sub-scanning direction is executed (step 101). Next, a development characteristic process for converting the obtained exposure energy distribution into a development density is executed (step 102). Then, sub-scan integration is performed to convert the estimated development density into a value corresponding to each light emitting point (step 103). Finally, main scan integration is performed to calculate the position of each light emitting point from the shape of the exposure profile and calculate the development density corresponding to each light emitting point (step 104), and the correction characteristic value is output (step 105). , The process ends.
[0041]
First, the sub-scanning direction multiplexing process shown in step 101 will be described with reference to FIGS. FIGS. 11A and 11B are diagrams for explaining sub-scanning direction multiplexing processing in the presence of stray light. FIGS. 12A to 12D show a plurality of SLEDs constituting the line CCD 61. FIG. 9 is a diagram for explaining an exposure distribution when the patterns are arranged in a staggered pattern. Here, the “stray light” is light emitted from the LPH 14 outside the predetermined path. Since this stray light may also exist in the sub-scanning direction as a light emitting point that affects each other, it is preferable to flatten the light profile in consideration of superimposition in the sub-scanning direction.
[0042]
In the case where minute light (such as stray light) as shown in FIG. 11A is present, the effect on the development density is ignored by the development characteristic processing in step 102. In the example shown in FIG. 11A, the portion exceeding the threshold does not include the influence of stray light. Therefore, as shown in FIG. 11B, by calculating the value obtained by shifting the measured exposure profile in the sub-scanning direction, it is possible to include the influence of the stray light in the portion exceeding the threshold value, Correction that avoids the problem described above becomes possible.
[0043]
In the staggered arrangement for explaining the exposure distribution in FIGS. 12A to 12D, the positions of the SLEDs constituting the line CCD are shifted in the sub-scanning direction due to, for example, miniaturization or wiring. When such an arrangement is adopted, as shown in FIGS. 12A and 12B, the exposure energy distribution during printing and the exposure distribution during measurement may have different cross sections in the sub-scanning direction in the exposure energy distribution. . In the example shown in FIGS. 12A and 12B, a state where the amount exceeding the threshold is completely different is shown. In such a case, similarly to the above, the sections in the sub-scanning direction of the measured exposure energy distribution are shifted in the sub-scanning direction and added, and the exposure energy in consideration of the overlap in the sub-scanning direction as shown in FIG. By obtaining the cross section in the sub-scanning direction of the distribution, an exposure energy distribution substantially equivalent to the exposure energy distribution at the time of printing (at the time of image formation) shown in FIG. 12C can be obtained, and the amount exceeding the threshold becomes almost equal. Such an exposure distribution can be obtained.
[0044]
Next, the development characteristic processing shown in step 102 will be described.
FIGS. 13A and 13B are diagrams for explaining the contribution of the exposure energy to the density when the development characteristics are considered. There is a relationship (development characteristic) between the exposure energy and the developed image density (development density) as shown in FIG. 13A, and by adjusting the exposure energy using this development characteristic, A desired image density can be obtained. FIG. 13B shows a simplified development characteristic shown in FIG. FIG. 13B shows a linear region in which the exposure energy amount and the image density are substantially proportional to each other, and a dead band region in which the image density does not appear (ie, is not developed) when the exposure is performed on the lower exposure energy side than the linear region. And a saturated region on the higher exposure energy side than the linear region, where the image density does not increase even if the exposure amount is increased. In this embodiment, the exposure energy distribution is converted into the development density using the input / output characteristics when the input is the exposure energy and the output is the development density. For example, the development characteristics are processed using simple development characteristics using threshold values and saturation values.
[0045]
Next, the sub-scan integration shown in step 103 will be described.
FIG. 14 is a diagram for explaining sub-scan integration. In this step and the next step 104, the estimated developing density is converted into a value corresponding to each light emitting point, so that the light amount correction amount of each light emitting point can be calculated. Data is added in the sub-scanning direction for light emitting points as shown in FIG. FIG. 14 (b) shows the exposure energy distribution, where the horizontal axis is the position and the vertical axis is the exposure energy. This example is an example of a light profile acquired when the 1200 dpi LPH 14 is lit in a 2on2off pattern, and shows a value obtained by integrating a threshold value and a saturation value in the sub-scanning direction after applying the threshold value and the saturation value.
[0046]
Next, the main scanning integration shown in step 104 will be described.
FIGS. 15A and 15B are views for explaining integration in the main scanning direction. Here, the estimated development density is converted into a value corresponding to each light emitting point, so that the light amount correction amount of each light emitting point can be calculated. FIG. 15A shows the flow of processing, and FIG. 15B shows the result of executing the measurement and calculation based on the integration in the sub-scanning direction shown in FIG. 14, where the horizontal axis represents the position and the vertical axis represents the exposure energy. Has taken. The example shown in FIG. 15B is an example of an optical profile acquired when the 1200 dpi LPH 14 is lit in a 2on2off pattern, similarly to FIG. 14B. Taking into account the variation of the LED chip assay constituting the LPH 14, the elongation due to heat, and the like, dividing the position of each light emitting point based on the absolute position of the moving stage lacks versatility. Therefore, the position of each light emitting point is calculated from the shape of the exposure profile, and then the development density corresponding to each light emitting point is calculated.
[0047]
Referring to the flowchart shown in FIG. 15A, first, a measurement / calculation result by sub-scan integration as shown in FIG. 15B is obtained (step 201). Next, a peak is detected from the obtained exposure profile, and a valley is detected (step 202). Then, the exposure energy amount from the valley to the valley in this exposure profile is integrated, and an integrated value Sn as shown by oblique lines in FIG. 15B is obtained (step 203). The integrated value thus obtained is divided by the distance between valleys to obtain En = Sn / Ln (step 204). Here, En indicates a correction characteristic value for the n-th light emitting point.
[0048]
The correction characteristic value obtained as described above is obtained by measuring the exposure profile obtained by measuring the amount of light of the LPH 14 in a state where the line CCD 61 is tilted in the moving direction and the substantial positional resolution is increased, and the development profile and the development density. Is converted to a value that can be correlated. In the image forming apparatus shown in FIG. 1, this correction characteristic value is stored in a memory such as a ROM provided inside the LPH 14, for example. It may be configured to be stored in the memory of the image output control unit 30. Further, the light amount correction data calculated from the correction characteristic value may be stored in the memory. In the image forming apparatus, the output light amount of each LED in the LPH 14 is corrected using the correction characteristic value stored in the ROM or the like, so that the variation of each light emitting point is suppressed, the unevenness is small, and the It is possible to obtain a high-quality image with suppressed streaks. In addition, since a highly accurate correction characteristic value can be obtained, it is possible to achieve high image quality in a state where there is little impact on cost from the viewpoint of structure.
[0049]
FIGS. 16A and 16B are diagrams illustrating a configuration example of the exposure profile measurement device 60 during mass production. In FIG. 16A, the LPH 14 is measured using two line CCDs 61, a first line CCD 61-1 and a second line CCD 61-2. The first line CCD 61-1 and the second line CCD 61-2 are each inclined at the same angle with respect to the moving direction, and are arranged on the same moving stage 62 at a constant interval, as described above. Have been. The two line CCDs 61 move on the moving stage 62 at the same time. The measurement is performed by using the first line CCD 61-1, which is the first line CCD 61, and after correcting the light amount of the LPH 14 in real time, the measurement is performed by the second line CCD 61-2. By employing such a plurality of measurement methods, the measurement step and the inspection step can be performed simultaneously, and the work steps can be shortened.
[0050]
On the other hand, in FIG. 16 (b), two line CCDs 61, a first line CCD 61-1 and a second line CCD 61-2, are provided in parallel on a moving stage 62, move at the same time, and each has a different LPH 14 (The first LPH 14-1 and the second LPH 14-2). By simultaneously measuring the plurality of LPHs 14, it is possible to reduce the work time required for the measurement.
[0051]
As described above in detail, according to the present embodiment, the exposure amount of each light emitting element in the LPH 14 is measured in a state where the line CCD 61 is inclined at a certain angle with respect to the moving direction. Accordingly, even when a lens such as an enlargement optical system is not provided, the exposure amount can be measured with a higher resolution than the position resolution of the line CCD 61. Further, the correction data obtained as a result of the measurement is stored in a memory such as a ROM provided inside the LPH 14 of the image forming apparatus, and the exposure amount is corrected for each light emitting element. It is possible to obtain good image quality in which vertical stripes and density unevenness of an image generated in the sub-scanning direction are suppressed.
[0052]
【The invention's effect】
As described above, according to the present invention, the measurement of the exposure energy distribution in the print head can be performed with high accuracy, high resolution, and high speed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus using an LED print head to be measured in the present embodiment.
FIG. 2 is a diagram illustrating a configuration of an LED print head (LPH) that is a print head.
FIG. 3 is a diagram for explaining an exposure profile measurement system to which the present embodiment is applied;
FIG. 4 is a diagram for explaining a positional relationship between a line CCD and an LED exposure spot of an LPH.
FIG. 5 is a diagram for explaining a position resolution of a line CCD.
FIG. 6 is a timing chart showing processing of measurement and data transfer.
FIG. 7 is a diagram for explaining a circuit configuration of the CCD board.
FIG. 8 is a diagram illustrating a circuit configuration of a CCD interface.
FIG. 9 is a diagram for explaining a memory map for rearranging CCD outputs in a buffer memory.
FIG. 10 is a flowchart illustrating a conversion process to a correction characteristic value.
FIGS. 11A and 11B are diagrams for explaining sub-scanning multiplex processing when stray light exists.
FIGS. 12A to 12D are views for explaining an exposure distribution when a plurality of SLEDs constituting a line CCD are arranged in a staggered manner.
FIGS. 13A and 13B are diagrams for explaining the contribution of exposure energy to density when development characteristics are considered.
FIG. 14 is a diagram for explaining sub-scan integration.
FIGS. 15A and 15B are diagrams for explaining integration in the main scanning direction.
FIGS. 16A and 16B are diagrams showing an example of a configuration at the time of mass production in an exposure profile measuring apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Main body, 10 ... Image processing system, 11 ... Image forming unit, 12 ... Photoconductor drum, 14 ... LED print head (LPH), 51 ... LED array, 52 ... Printed circuit board, 53 ... Selfoc lens array, 60 ... Exposure profile measuring device, 61: line CCD, 62: moving stage, 63: stage driver, 66: personal computer (PC), 67: frame grabber, 68: digital I / O, 69: motor controller, 70: CCD board, 80: CCD interface, 81: Trigger processing unit, 82: WRITE address generation unit, 83: CCD sensitivity in-plane unevenness correction unit, 85: Buffer memory, 86: CCD tilt correction unit

Claims (10)

A line CCD that is provided to face a print head in which light emitting elements are arranged, and that measures an exposure amount from each light emitting element;
A moving stage that moves the line CCD at a constant speed in a state where the line CCD is inclined at a fixed angle in the moving direction;
A processing unit for calculating the output from the line CCD to obtain data for correcting the light amount of the light emitting elements constituting the print head. 2. The printhead characteristic measuring apparatus according to claim 1, wherein the line CCD has a CCD accumulation time that is an integral multiple of a scan cycle of the printhead. 2. The print head characteristic measuring apparatus according to claim 1, wherein the processing unit rearranges the output from the line CCD and corrects the oblique arrangement due to the line CCD being tilted by the predetermined angle. A plurality of light emitting elements are arranged, a method for measuring the exposure amount of a print head that forms an image by exposing a photoconductor by the light emitting elements,
Measuring the exposure amount by moving at a constant speed a line CCD provided opposite the illuminated light emitting element and disposed obliquely to the moving direction;
Calculating correction data for correcting the exposure amount of the light emitting element from the measured exposure amount. The step of calculating the correction data includes rearranging data on the exposure amount measured by the line CCDs arranged obliquely on a buffer memory, and based on the rearranged data, a light amount variation due to each light emitting element. 5. The exposure amount correcting method according to claim 4, wherein data for correcting is calculated. An exposure correction method for correcting the exposure of a print head in which light emitting points are arranged using a line CCD having a predetermined positional resolution,
For the predetermined position resolution of the line CCD, the exposure amount is measured in a state where the substantial position resolution is improved without relying on an optical system,
An exposure correction method, wherein correction data is obtained based on the measured exposure. The line CCD moves with respect to the print head to measure the exposure amount of the arranged light emitting points, and is arranged obliquely with respect to the moving direction so that the substantial position is obtained. 7. The method according to claim 6, wherein the resolution is improved. A photoreceptor,
A print head that forms the electrostatic latent image by exposing the photoconductor by a plurality of light emitting elements that are arranged,
The print head has a memory for storing a correction characteristic value based on data having substantially improved position resolution without using an enlargement optical system with respect to the position resolution of the line CCD for measuring the exposure amount of each light emitting element. An image forming apparatus, wherein an exposure amount of each light emitting element is determined based on the correction characteristic value stored in the memory. 9. The image forming apparatus according to claim 8, wherein the correction characteristic value stored in the memory is a value that allows a correlation between an exposure profile obtained from the exposure amount measured by the line CCD and a development density. apparatus. A photoreceptor,
A print head that forms the electrostatic latent image by exposing the photoconductor by a plurality of light emitting elements that are arranged,
The print head has a memory for storing light amount correction data based on data having substantially improved position resolution without using an enlargement optical system with respect to the position resolution of the line CCD for measuring the exposure amount of each light emitting element. An image forming apparatus, wherein an exposure amount of each light emitting element is determined based on the light amount correction data stored in the memory.

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