Color image formation apparatus

Abstract

To provide a color image formation apparatus capable of outputting high-quality images even at low cost.SOLUTION: An electrophotographic color image formation apparatus comprises: a photosensitive body; an optical writing device; a light-emitting element 28; a light-emission control element 22; a deflection element 29 composed of a multifaceted reflector; a synchronization detection element 200 that detects a writing start timing of scanning; a color deviation correction function unit 26 that adjusts the writing start timing; a storage unit 27 that stores a color deviation correction value and a detection deviation characteristic value accompanying light quantity variation to the synchronization detection element; a detection deviation correction function unit 26; and an updating unit 26 that updates the detection deviation characteristic value stored in the storage unit 27. The execution result includes a first light quantity used in color deviation correction. The detection deviation correction function unit 26 calculates a detection deviation correction value using the first light quantity, a second light quantity determined as a lighting condition of the light-emitting element 28, and the detection deviation characteristic value, and adds the detection deviation correction value to the color deviation correction value.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a color image forming apparatus. [Background technology]

[0002] In electrophotographic image forming devices, particularly those configured to expose a photosensitive member with an LD (laser diode), the beam output from the LD is reflected by a rotating polygon mirror, and when the LD beam is irradiated from one end of the polygon mirror to the other, the beam (laser beam) is deflected according to the angle of the polygon mirror and scans one line on the photosensitive member. At this time, an electrostatic latent image for one line can be formed on the photosensitive member by switching the LD on or off according to the input image data, and by repeating line scanning while rotating the photosensitive member, an electrostatic latent image of the desired image can be formed.

[0003] When repeating line scanning, it is necessary to synchronize the write start timing for starting image formation. To determine this write start timing, a light detection sensor is installed just before scanning the photosensitive member to detect the beam scanning position. This light detection sensor is called a synchronous detection sensor, and the write start timing for image data is determined according to the output signal of the synchronous detection sensor.

[0004] A light detection sensor is equipped with a photodiode and uses an amplifier and gain resistor to detect minute changes in current. The light detection sensor can determine whether or not a beam is input based on this change in current. A light detection sensor can be made into a circuit by combining elements, but photo ICs that have slits and cover glass to improve detection accuracy and stabilize the sensor are commercially available and can be used inexpensively.

[0005] The amount of light from the beam changes depending on the imaging conditions. In addition to changes in the resolution of the output image, imaging conditions also include changes in productivity (linear speed) and temperature environment. When the imaging conditions change, the amount of light from the beam input to the synchronous detection sensor also changes. When the amount of light from the beam changes, the amount of current flowing through the optical detection sensor changes, causing a change in the detected waveform of the optical detection sensor. When the detected waveform of the optical detection sensor changes, the timing at which the image data starts to be written shifts, causing a positional deviation in the scanning direction (main scanning direction).

[0006] The above-mentioned misalignment is only a few tens of nanoseconds at most, so it is not a problem for a single color such as a monochrome machine, but for a color machine it will cause color shifts and color misalignment, degrading image quality. There are already known solutions to the technical issues that degrade image quality.

[0007] Patent Document 1 discloses a configuration in which waveform shaping is performed when a beam is detected by a light detection sensor in order to prevent deviations in the timing at which writing starts. Patent Document 2 discloses a method in which the pulse width of a beam detected by a light detection sensor is measured and the half cycle (center) of the measured pulse width is used as the timing at which writing starts, in order to prevent deviations in the timing at which writing starts. Summary of the Invention [Problem to be solved by the invention]

[0008] However, the configuration described in Patent Document 1 increases the number of parts, raising costs and making it impossible to provide an inexpensive color multifunction device (printer). Furthermore, the method described in Patent Document 2, when consolidating parts to create an inexpensive configuration, cannot completely suppress the effects of color shift due to changes in light intensity.

[0009] SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has as its object to provide a color image forming apparatus that is inexpensive yet capable of outputting high-quality images. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, the present invention provides an electrophotographic color image forming apparatus that forms an image by developing a developer on an electrostatic latent image formed on a photosensitive member, the color image forming apparatus having an optical writing device that exposes the photosensitive member, the optical writing device including a light-emitting element that irradiates the photosensitive member with light, an emission control element that controls the emission of the light-emitting element, a multi-faceted reflector that is provided on an optical path of light emitted from the light-emitting element, rotated and driven by an externally input signal, and deflecting the light irradiated onto the surface of the reflector to scan the photosensitive member in one direction, a synchronous detection element that detects the timing at which writing of an electrostatic latent image by irradiating the photosensitive member with light, and emission control by the emission control element in accordance with image data after the synchronous detection element detects the light. a memory unit that stores the execution result of the color shift correction, the color shift correction value, and a detection shift characteristic value that indicates the characteristics of the detection shift that occurs when the light intensity of light incident on the synchronous detection element fluctuates; a detection shift correction unit that corrects the detection shift of the synchronous detection element; and an update unit that updates the detection shift characteristic value stored in the memory unit, wherein the execution result includes a first light intensity of the light-emitting element when correcting the color shift, and the detection shift correction unit calculates a detection shift correction value for correcting the detection shift of the synchronous detection element using the first light intensity, a second light intensity determined as a lighting condition of the light-emitting element, and the detection shift characteristic value, and adds the detection shift correction value to the color shift correction value. [Effects of the Invention]

[0011] According to the present invention, it is possible to output high-quality images at low cost. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 1A is a diagram showing an example of the configuration of a color image forming apparatus according to this embodiment. [Figure 1B] FIG. 1B is a diagram showing an example of the hardware configuration of an MFP to which the color image forming apparatus according to this embodiment is applied. [Figure 2] FIG. 2 is a functional block diagram of an example of an optical writing device included in the color image forming apparatus according to this embodiment. [Figure 3] FIG. 3 is a diagram for explaining an example of a correction function for the writing start timing in the color image forming apparatus according to the present embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a synchronization detection plate in the color image forming apparatus according to the present embodiment. [Figure 5] FIG. 5 is a diagram showing an example of the configuration of an optical writing device of a color image forming apparatus according to this embodiment. [Figure 6] FIG. 6 is a diagram showing an example of a detection signal and an output signal of a beam from a light detection sensor of the color image forming apparatus according to this embodiment. [Figure 7] FIG. 7 is a diagram showing an example of the relationship between the amount of light of a beam irradiated onto the light detection sensor of the color image forming apparatus according to this embodiment and the detection signal and output signal. [Figure 8] FIG. 8 is a diagram showing another example of the configuration of the optical writing device of the color image forming apparatus according to the present embodiment. [Figure 9] FIG. 9 is a diagram showing an example of a detection signal and an output signal of a beam from a light detection sensor of the color image forming apparatus according to this embodiment. [Figure 10] FIG. 10 is a diagram showing an example of a detection signal and an output signal of a beam from a light detection sensor of the color image forming apparatus according to this embodiment. [Figure 11] FIG. 11 is a diagram showing an example of a change in the timing of starting writing in the color image forming apparatus according to the present embodiment. [Figure 12] FIG. 12 is a diagram showing an example of a detection deviation characteristics table in the color image forming apparatus according to the present embodiment. [Figure 13] FIG. 13 is a diagram for explaining an example of a method for using the detection deviation characteristics table in the color image forming apparatus according to the present embodiment. [Figure 14]FIG. 14 is a diagram for explaining an example of a method for correcting the write start timing when a detection deviation characteristic curve of an Nth-order polynomial is used instead of the detection deviation characteristic table in the color image forming apparatus according to the present embodiment. [Figure 15] FIG. 15 is a diagram for explaining an example of updating the detection deviation characteristic table or the detection deviation characteristic curve in accordance with the characteristics of the optical writing device in the color image forming apparatus according to the present embodiment. [Figure 16] FIG. 16 is a diagram for explaining an example of a process for updating the detection deviation characteristic table or the detection deviation characteristic curve in the color image forming apparatus according to the present embodiment. [Figure 17] FIG. 17 is a diagram for explaining an example of details of a method for updating the detection deviation characteristics table in the color image forming apparatus according to the present embodiment. [Figure 18] FIG. 18 is a diagram for explaining an example of details of a method for updating the detection deviation characteristic curve in the color image forming apparatus according to the present embodiment. [Figure 19] FIG. 19 is a flowchart showing an example of the flow of color matching processing in the color image forming apparatus according to this embodiment. [Figure 20] FIG. 20 is a flowchart showing an example of the flow of a printing operation in the color image forming apparatus according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a color image forming apparatus will be described in detail with reference to the accompanying drawings.

[0014] (First embodiment) 1A is a diagram showing an example of the configuration of a color image forming apparatus according to the present embodiment. The color image forming apparatus is an example of an electrophotographic color image forming apparatus that forms an image by developing an electrostatic latent image formed on a photosensitive member with a developer, and forms the image on a recording sheet being transported by registration rollers or the like.

[0015] 1A, the color image forming apparatus according to this embodiment includes primary transfer rollers 15K, 15C, 15M, and 15Y, photoconductors 16K, 16C, 16M, and 16Y (hereinafter, when the photoconductors 16K, 16C, 16M, and 16Y are not to be distinguished from one another, they are also referred to as photoconductors 16), an intermediate transfer belt 18 (see FIG. 3), a tension roller 11, a TM / P sensor 12, a drive roller 13, and a secondary transfer roller 14. In the following description, when the primary transfer rollers 15K, 15C, 15M, and 15Y are not to be distinguished from one another, they are referred to as primary transfer rollers 15.

[0016] The photoconductors 16K, 16C, 16M, and 16Y are arranged along the intermediate transfer belt 18 in the order of photoconductors 16Y, 16M, 16C, and 16K from the upstream side in the transport direction of the intermediate transfer belt 18.

[0017] Around the photoconductor 16K, a charger, a developer, a primary transfer roller 15K, a photoconductor cleaner, a static eliminator, etc. are arranged. In the following description, the photoconductor 16K, the charger, the developer, the primary transfer roller 15K, the photoconductor cleaner, the static eliminator, etc. will be collectively referred to as the image forming unit 19K.

[0018] Note that photoconductors 16C, 16M, and 16Y all have components common to photoconductor 16K arranged around them. In the following description, photoconductor 16C, charger, developer, primary transfer roller 15C, photoconductor cleaner, static eliminator, etc. will be collectively referred to as image forming unit 19C. Photoconductor 16M, charger, developer, primary transfer roller 15M, photoconductor cleaner, static eliminator, etc. will be collectively referred to as image forming unit 19M. Photoconductor 16Y, charger, developer, primary transfer roller 15Y, photoconductor cleaner, static eliminator, etc. will be collectively referred to as image forming unit 19Y.

[0019] In this embodiment, when color images are produced, photosensitive elements 16K, 16C, 16M, and 16Y contact intermediate transfer belt 18, and when monochrome images are produced, photosensitive element 16K contacts intermediate transfer belt 18, and photosensitive elements 16C, 16M, and 16Y are spaced apart from intermediate transfer belt 18.

[0020] Then, the image forming unit 19K and the LD (Laser Diode) 28 (see FIG. 2) perform an image forming process (charging process, exposure process, development process, transfer process, cleaning process, and charge removal process) while the photoconductor 16K is in contact with the intermediate transfer belt 18, thereby forming a black toner image on the intermediate transfer belt 18. The LD 28 is an example of a light emitting element that irradiates the photoconductor 16 with light (beam).

[0021] Similarly, image forming units 19C and LD28 perform an image forming process with photoconductor 16C in contact with intermediate transfer belt 18 to form a cyan toner image on intermediate transfer belt 18. Image forming units 19M and LD28 perform an image forming process with photoconductor 16M in contact with intermediate transfer belt 18 to form a magenta toner image on intermediate transfer belt 18. Image forming units 19Y and LD28 perform an image forming process with photoconductor 16Y in contact with intermediate transfer belt 18 to form a yellow toner image on intermediate transfer belt 18.

[0022] That is, in this embodiment, when a color image is formed, the photoconductors 16K, 16C, 16M, and 16Y perform the image forming process. Also, in this embodiment, when a monochrome image is formed, the photoconductor 16K performs the image forming process, but the photoconductors 16C, 16M, and 16Y do not perform the image forming process.

[0023] In the following, the image forming process by the image forming unit 19K will be mainly described, and the image forming processes by the image forming units 19C, 19M, and 19Y will not be described.

[0024] The photosensitive member 16K is rotated by a drive motor.

[0025] First, in the charging step, the charger uniformly charges the outer circumferential surface of the photosensitive member 16K, which is being rotated, in the dark.

[0026] Subsequently, in the exposure step, the LD 28 exposes the outer peripheral surface of the photoreceptor 16K, which is being rotated, with a beam, and forms an electrostatic latent image based on the black image on the photoreceptor 16K.

[0027] Subsequently, in the developing step, the developing unit develops the electrostatic latent image formed on the photoreceptor 16K with black toner, forming a black toner image on the photoreceptor 16K.

[0028] Next, in the transfer process, primary transfer roller 15K, at the primary transfer position where it contacts photoreceptor 16K, transfers the black toner image formed on photoreceptor 16K onto intermediate transfer belt 18. Note that even after the toner image is transferred, a small amount of untransferred toner remains on photoreceptor 16K.

[0029] Subsequently, in the cleaning process, the photoreceptor cleaner wipes off any untransferred toner remaining on the photoreceptor 16K.

[0030] Finally, in the charge removal step, the charge remover removes the residual potential on the photoconductor 16K, and the photoconductor 16K then waits for the next image formation.

[0031] The intermediate transfer belt 18 is an endless belt wound around a tension roller 11 and a drive roller 13, and moves endlessly over the photosensitive elements 16K, 16C, 16M, and 16Y in this order as the drive roller 13 is rotated by a drive motor.

[0032] 1A, when a color image is formed, a yellow toner image is first transferred onto the intermediate transfer belt 18 by the photoreceptor 16Y, followed by a magenta toner image by the photoreceptor 16M, a cyan toner image by the photoreceptor 16C, and a black toner image by the photoreceptor 16K. As a result, the toner images of each color are superimposed on the intermediate transfer belt 18 to form a full-color image.

[0033] When a monochrome image is to be formed, a black toner image is transferred onto the intermediate transfer belt 18 by the photosensitive member 16K. As a result, a monochrome image is formed on the intermediate transfer belt 18.

[0034] Then, when the image formed on the intermediate transfer belt 18 is transported to the secondary transfer position where it contacts the drive roller 13, the secondary transfer roller 14 presses the recording paper being transported by the registration rollers 17 and the like against the image formed on the intermediate transfer belt 18 at the secondary transfer position, thereby transferring the image from the intermediate transfer belt 18 to the recording paper.

[0035] The tension roller 11 applies tension to the intermediate transfer belt 18, thereby absorbing all of the expansion of the intermediate transfer belt 18 due to the influence of temperature changes. In other words, in this embodiment, the intermediate transfer belt 18 does not expand uniformly due to the influence of temperature changes, but rather the expansion of the intermediate transfer belt 18 due to the influence of temperature changes is concentrated in the tension roller 11 portion.

[0036] Here, in this embodiment, the tension roller 11 is arranged on the path of the intermediate transfer belt 18 from the TM / P sensor 12 to the most upstream primary transfer position (the primary transfer position where the photosensitive element 16Y and the primary transfer roller 15Y come into contact).

[0037] The TM / P sensor 12 is a photosensor or the like, and reads the color matching patterns formed on the intermediate transfer belt 18. In this embodiment, as shown in FIG. 1A, when a color image is formed, color matching patterns of four colors are formed on the intermediate transfer belt 18 by photoreceptors 16K, 16C, 16M, and 16Y.

[0038] 1B is a diagram showing an example of the hardware configuration of an MFP to which a color image forming apparatus according to this embodiment is applied. As shown in FIG. 1B, an MFP (Multi-Function Peripheral / Product / Printer) 9 includes a controller 910, a short-range communication circuit 920, an engine control unit 930, an operation panel 940, and a network I / F 950.

[0039] Of these, the controller 910 has a CPU 901, which is the main part of the computer, a system memory (MEM-P) 902, a north bridge (NB) 903, a south bridge (SB) 904, an ASIC (Application Specific Integrated Circuit) 906, a local memory (MEM-C) 907, which is a storage unit, an HDD controller 908, and an HD 909, which is also a storage unit, and is configured such that the NB 903 and the ASIC 906 are connected by an AGP (Accelerated Graphics Port) bus 921.

[0040] Of these, the CPU 901 is a control unit that performs overall control of the MFP 9. The NB 903 is a bridge that connects the CPU 901 with the MEM-P 902, the SB 904, and the AGP bus 921, and includes a memory controller that controls reading and writing to and from the MEM-P 902, a PCI (Peripheral Component Interconnect) master, and an AGP target.

[0041] The MEM-P902 has a ROM 902a, which is memory for storing programs and data that realize the functions of the controller 910, and a RAM 902b, which is used for expanding the programs and data and as a drawing memory during memory printing. The programs stored in the RAM 902b may be provided by being recorded in an installable or executable file format on a computer-readable recording medium such as a CD-ROM, CD-R, or DVD.

[0042] The SB 904 is a bridge for connecting the NB 903 with PCI devices and peripheral devices. The ASIC 906 is an integrated circuit (IC) for image processing applications that has hardware elements for image processing and serves as a bridge connecting the AGP bus 921, PCI bus 922, HDD controller 908, and MEM-C 907. The ASIC 906 includes a PCI target and AGP master, an arbiter (ARB) that forms the core of the ASIC 906, a memory controller that controls the MEM-C 907, multiple direct memory access controllers (DMACs) that perform image data rotation and other operations using hardware logic, and a PCI unit that transfers data between the scanner unit 931 and printer unit 932 via the PCI bus 922. A USB (Universal Serial Bus) interface and an IEEE 1394 (Institute of Electrical and Electronics Engineers) interface may also be connected to the ASIC 906. In this embodiment, printer unit 932 has the configuration of the color image forming apparatus shown in FIG. 1A.

[0043] The MEM-C907 is a local memory used as an image buffer for copying and a code buffer. The HD909 is a storage device for storing image data, font data used during printing, and forms. The HD909 controls the reading and writing of data from and to the HD909 under the control of the CPU901. The AGP bus 921 is a bus interface for a graphics accelerator card proposed to speed up graphics processing, and direct high-throughput access to the MEM-P902 enables the graphics accelerator card to operate at high speed.

[0044] The short-range communication circuit 920 is a communication circuit such as NFC (Near Field Communication) or Bluetooth (registered trademark). The engine control unit 930 is composed of a scanner unit 931 and a printer unit 932. The operation panel 940 includes a panel display unit 940a, such as a touch panel, that displays current settings and selection screens and accepts inputs from an operator, and an operation panel 940b that includes a numeric keypad that accepts settings for image formation conditions such as density settings and a start key that accepts a copy start command. The controller 910 controls the entire MFP 9, controlling, for example, drawing, communication, and inputs from the operation panel 940. The scanner unit 931 or the printer unit 932 includes an image processing unit that performs error diffusion, gamma conversion, and the like.

[0045] The MFP 9 can sequentially switch among the document box function, copy function, printer function, and facsimile function using the application switching key on the operation panel 940. When the document box function is selected, the MFP 9 enters document box mode, when the copy function is selected, the MFP 9 enters copy mode, when the printer function is selected, the MFP 9 enters printer mode, and when the facsimile mode is selected, the MFP 9 enters facsimile mode.

[0046] The network I / F 950 is an interface for performing data communication using a communication network. The short-range communication circuit 920 and the network I / F 950 are electrically connected to the ASIC 906 via a PCI bus 922.

[0047] 2 is a functional block diagram of an example of an optical writing device included in a color image forming apparatus according to this embodiment. As shown in FIG. 2, the optical writing device according to this embodiment includes an optical writing control unit 20, a light detection sensor 200, an LD 28, a polygon motor 29, etc., and is an example of an optical writing device that exposes a photoconductor 16.

[0048] The light detection sensor 200 is an example of a synchronous detection element that detects the start timing of writing an electrostatic latent image by irradiating the photoconductor 16 with light. The light-emission control unit 22 of the optical writing control unit 20 is an example of a light-emission control element that controls the light emission of the LD 28 and has the functions of turning the LD 28 on and off and adjusting the light intensity of the LD 28. To form an electrostatic latent image on the photoconductor 16, the light-emission control unit 22 transmits a turn-on signal and a turn-off signal for the LD 28 at a desired timing according to input image data. Hereinafter, the timing at which the transfer of the turn-on signal and turn-off signal for the LD 28 begins is referred to as the write start timing. The light-emission control unit 22 may also control the light intensity of the LD 28 to be constant while the beam irradiated from one end to the other of one surface of the polygon mirror 52 (see FIG. 5) scans in one direction. The light-emission control unit 22 may also have the function of varying the light intensity of the LD 28 at specific timings in the scanning direction. However, to reduce manufacturing costs, as in the present embodiment, such a configuration may be omitted and a uniform light intensity may be maintained throughout the entire scanning period. The optical detection sensor 200 detects the beam output from the LD 28 to determine the timing to start writing. The output signal of the optical detection sensor 200 is input to the optical writing control unit 20, which resets the internal count value counted by the count unit 23. The internal count value is automatically counted up during image formation, and when the internal count value reaches a predetermined value, the transfer of a turn-on signal and a turn-off signal for the LD 28 according to the image data is started.

[0049] The above-mentioned predetermined value is a value determined by the sum of a reference value determined based on the arrangement of the photoconductor 16 and the arrangement of the light detection sensor 200 and a correction value for the misalignment in the scanning direction for each color (color misalignment correction value). The color misalignment correction value in the main scanning direction is stored in the correction value storage unit 27 and is read from the correction value storage unit 27 before image formation starts. The correction value storage unit 27 is an example of a storage unit that stores the result of color misalignment correction, the color misalignment correction value, and the detected misalignment characteristic value in association with each other. Here, the result of color misalignment correction includes the light intensity of the LD 28 when correcting the color misalignment (an example of a first light intensity).

[0050] The correction value calculation unit 26 (an example of a color shift correction function unit) corrects color shift by adjusting the writing start timing from when the light detection sensor 200 detects the beam to when the light emission control unit 22 starts light emission control according to the image data. The correction value calculation unit 26 determines the writing start timing using the color shift correction value read out from the correction value storage unit 27 and a predetermined reference value read out from the reference value storage unit 25.

[0051] In this embodiment, in addition to the above-mentioned reference value and color shift correction value, a detection shift correction value is added to correct the shift in the writing start timing caused by fluctuations in the light intensity of the LD 28. Here, the detection shift characteristic value is a value that indicates the characteristics of the detection shift that occurs when the light intensity of the beam incident on the synchronization detection plate 41 (see FIG. 5) fluctuates.

[0052] The correction value calculation unit 26 is an example of a detection error correction function unit that corrects the detection error of the optical detection sensor 200. Specifically, the correction value calculation unit 26 calculates a detection error correction value for correcting the detection error of the optical detection sensor 200 using a first light amount included in the execution result of the color shift correction, a light amount (an example of a second light amount) determined as the lighting condition of the LD 28, and a detection error characteristic value. Here, the lighting condition is the lighting condition of the LD 28 when performing a printing operation. Next, the correction value calculation unit 26 adds the detection error correction value to the color shift correction value. The correction value calculation unit 26 (an example of an update unit) updates the detection error characteristic value stored in the correction value storage unit 27.

[0053] The color misregistration correction values ​​stored in the correction value storage unit 27 are updated during a color matching operation to correct misregistration between colors. By performing the color matching operation, an electrostatic latent image can be formed at a targeted position on the photoconductor 16, thereby forming a high-quality image. The correction value calculation unit 26 may update the color misregistration correction values ​​stored in the correction value storage unit 27 and the first light amount at approximately the same time.

[0054] In addition, the correction value calculation unit 26 must enable the function of calculating the detection misalignment correction value when it receives a print request, among requests for operating the optical writing device of the color image forming device, and must disable this function when it receives a request for color misalignment correction.

[0055] The correction value calculation unit 26 includes a light intensity setting step for setting the light intensity of the LD 28, a pattern forming step for forming a deviation amount calculation pattern (an example of a pattern) for detecting a detection deviation that occurs when the light intensity of the beam incident on the light detection sensor 200 varies, and a pattern detection step for detecting the formed deviation amount calculation pattern. The correction value calculation unit 26 then repeatedly performs the light intensity setting step, the pattern forming step, and the pattern detection step. The correction value calculation unit 26 calculates a detection deviation characteristic value based on the detection result of the deviation amount calculation pattern, and therefore the detection result of the detection deviation, and updates the detection deviation characteristic value stored in the correction value storage unit 27.

[0056] Furthermore, the pattern forming step and pattern detecting step may be performed by forming and detecting the deviation amount calculation pattern using the pattern forming unit and pattern detecting unit used when the correction value calculation unit 26 corrects color deviation. This makes it possible to update the detected deviation characteristic value without increasing the number of unnecessary parts.

[0057] Furthermore, the misalignment amount calculation pattern may be identical in all respects, such as angle, length, width, and formation interval, to the color matching pattern formed by the correction value calculation unit 26. This allows the misalignment amount calculation pattern to have the same shape as the color matching pattern when correcting color misalignment, thereby improving the calculation accuracy of the detected misalignment characteristic value.

[0058] Furthermore, when it is determined that the update of the detected deviation characteristic value has been completed successfully, the correction value calculation unit 26 may update the detected deviation characteristic value and notify the completion of the update process so that the update of the detected deviation characteristic value will not be performed the next time the color image forming apparatus is turned on. This allows the process of updating the detected deviation characteristic value to be performed only once when the optical writing device is replaced.

[0059] The detection deviation characteristic (the amount of change in the writing start timing when the light intensity of the LD 28 changes) differs for each optical writing device, and is affected by, for example, the beam spot diameter of the LD 28 as described above. Because this characteristic is less susceptible to time and corresponds to the characteristics of the optical writing device, it is sufficient to initiate the update process of the detection deviation characteristic value only once, immediately after assembling the color image forming apparatus. Alternatively, it is sufficient to initiate the update process only once when the optical writing device of the color image forming apparatus is replaced. Therefore, it is detected whether the optical writing device has been replaced, and if it is detected that it is a new device, the update process is automatically executed only once. In this embodiment, the CPU 901 (an example of a new device detection unit) detects whether the optical writing device has been replaced. Then, the CPU 901 may execute the update process when it detects that the optical writing device is new when the color image forming apparatus is powered on.

[0060] Alternatively, the detection error characteristic values ​​may be stored in the correction value storage unit 27 as a detection error characteristic table in which the detection errors are arranged in a table format. In this case, the correction value calculation unit 26 refers to the detection error characteristic values ​​closest to the first and second light amounts from the table-like arrangement, or calculates two detection error characteristic values ​​by performing interpolation processing, and calculates a detection error correction value based on the difference between the two detection error characteristic values. Then, the correction value calculation unit 26 performs interpolation processing of the detection error correction value based on multiple detection error detection results obtained by changing the light intensity setting of the LD 28, and updates each detection error characteristic value in the table-like arrangement stored in the correction value storage unit 27.

[0061] Furthermore, the correction value calculation unit 26 operates the LD 28 at three light intensity settings to obtain three detection results of the detection error, thereby realizing a high-quality correction system while suppressing an increase in the processing time for updating the detection error characteristic value.

[0062] Furthermore, the correction value calculation unit 26 may perform linear interpolation of the detection result of the detection error between two neighboring points to obtain the detection error correction value. This makes it possible to realize a high-quality correction system while suppressing an increase in the processing time required for updating the detection error characteristic value.

[0063] The detection error characteristic value may be stored in the correction value storage unit 27 as coefficients of an Nth-order polynomial. In this case, the correction value calculation unit 26 calculates the detection error characteristic value corresponding to the first light amount and the second light amount using the coefficients of the Nth-order polynomial, and calculates the detection error correction value from the difference between the two detection error characteristic values. The correction value calculation unit 26 also calculates the coefficients of the Nth-order polynomial based on the detection result of the detection error obtained by changing the light amount setting of the LD 28, and updates the coefficients of each Nth-order polynomial stored in the correction value storage unit 27.

[0064] Furthermore, the correction value calculation unit 26 operates the LD 28 at a light intensity setting of N+1 to obtain multiple detection results of the detection error, thereby realizing a high-quality correction system while suppressing an increase in the processing time for updating the detection error characteristic value.

[0065] Furthermore, the detection deviation characteristic values ​​may be stored as coefficients of a third-order or fourth-order polynomial in the correction value storage unit 27. The correction value calculation unit 26 calculates the detection deviation characteristic values ​​corresponding to the first and second light amounts using the coefficients of the third-order or fourth-order polynomial, and calculates the detection deviation correction value from the difference between the two detection deviation characteristic values. This makes it possible to realize a high-quality correction system while suppressing an increase in the processing time for updating the detection deviation characteristic values.

[0066] The polygon motor 29 drives the polygon mirror 52 (see FIG. 5). The deflection control unit 24 controls the driving of the polygon motor 29. The sensor control unit 21 controls the detection of the beam by the light detection sensor 200.

[0067] 3 is a diagram for explaining an example of a function for correcting the write start timing in a color image forming apparatus according to this embodiment. An electrostatic latent image formed on a photoreceptor 16 is developed with toner and transferred onto an intermediate transfer belt 18. A plurality of TM / P sensors 12 are provided opposite the intermediate transfer belt 18 and detect the toner on the intermediate transfer belt 18, and are installed in a direction (main scanning direction) perpendicular to the belt conveyance direction.

[0068] When performing color matching, a color matching pattern is formed so as to pass through the detection section of each TM / P sensor 12 and is detected by the TM / P sensor 12. The correction value calculation section 26 uses the detection result to calculate a color misregistration correction value for correcting registration misregistration or magnification misregistration between colors.

[0069] Fig. 4 is a diagram showing an example of a synchronization detection plate in a color image forming apparatus according to this embodiment. For the sake of simplicity, Fig. 4 shows the synchronization detection plate 41 placed directly beside the photosensitive member 16. In practice, a reflecting mirror may be placed on the beam path of the LD 28, and the synchronization detection plate 41 may be placed in a completely different location.

[0070] The optical detection sensor 200 mounted on the synchronization detection plate 41 is positioned on the scanning path of the beam emitted from the LD 28. Just before or just after one scan of the photosensitive member 16, the optical detection sensor 200 on the synchronization detection plate 41 detects the beam from the LD 28 and outputs a synchronization signal. The timing at which writing on the photosensitive member 16 starts is determined based on the synchronization signal input to the optical writing control unit 20. That is, the optical detection sensor 200 detects the timing at which writing of an electrostatic latent image starts when the beam is irradiated onto the photosensitive member 16.

[0071] FIG. 5 illustrates an example of the configuration of an optical writing device in a color image forming apparatus according to this embodiment. Light (beams) emitted from LDs 28, which scan the photoconductors 16 installed for each color, travels via lens 51, is deflected by the surface of polygon mirror 52, and then passes through an opposing fθ lens 53 to irradiate the photoconductors 16. As polygon mirror 52 rotates, the beams scan the photoconductors 16 in one direction, forming electrostatic latent images on the photoconductors 16 according to image data. Specifically, polygon mirror 52 is a multifaceted reflector, which is disposed on the optical path of the beams emitted from LDs 28. It is driven to rotate by an externally input signal and deflects the light irradiated onto the reflector surface to scan the photoconductors 16 in one direction. Since the width of the electrostatic latent image is the image width, the area outside the width of the electrostatic latent image formed on the photoconductors 16 is treated as outside the image area. The angle at which the beam is reflected varies depending on the rotation angle of the polygon mirror 52 , and the beam outside the image area is deflected by a mirror 54 and irradiated onto the synchronization detection plate 41 via an fθ lens 53 .

[0072] As explained in FIG. 4 , the synchronization detection plate 41 is provided with a light detection sensor 200, which detects the incident beam and outputs a synchronization signal to the optical writing control unit 20. In the optical writing device mounted on the color image forming apparatus, an LD 28 corresponding to each color is provided, and a beam is irradiated toward a different surface of the polygon mirror 52, and the beam scans the photoconductor 16 of the different color via a different fθ lens 53. Another synchronization detection plate 41 is also provided. Each of the two synchronization detection plates 41 is provided with a light detection sensor 200, and each light detection sensor 200 detects the beam incident from the LD 28 and outputs the corresponding synchronization signal to the optical writing control unit 20.

[0073] FIG. 6 is a diagram showing an example of a beam detection signal and an output signal of the optical detection sensor 200 of the color image forming apparatus according to this embodiment. In the graph shown in FIG. 6, the vertical axis represents the signal output from the optical detection sensor 200, and the horizontal axis represents time. The optical detection sensor 200 is composed of a semiconductor element, such as a photodiode, that generates a current when exposed to light. To improve the detection accuracy of the optical detection sensor 200, a slit or lens may be provided to reduce ambient light and narrow the direction of incident light. That is, the optical detection sensor 200 may have a slit that limits the incident optical path of the beam from the LD 28. Although the beam detection accuracy may be reduced depending on the characteristics of the optical detection sensor 200, providing a slit can suppress variations in detection accuracy.

[0074] When the beam from the LD 28 is irradiated onto the light receiving part of the light detection sensor 200, a current is generated and amplified by the built-in operational amplifier circuit. The amplified current then flows through an adjusted fixed-value gain resistor and becomes the detection signal of the light detection sensor 200. This detection signal is an analog value and is difficult to handle as is. Therefore, the magnitude of the detection signal from the light detection sensor 200 is compared using a comparator, and the signal is converted into a digital output signal (synchronization signal) that indicates that only the period during which the signal exceeds a certain voltage has been detected as a beam. The output signal from the light detection sensor 200, converted into a digital value, is passed to the optical writing control unit 20, which determines whether the light detection sensor 200 has detected the beam from the LD 28.

[0075] FIG. 7 shows an example of the relationship between the amount of light emitted by the light detection sensor 200 and the detection and output signals of the color image forming apparatus according to this embodiment. In the graph shown in FIG. 7, the vertical axis represents the signal output from the light detection sensor 200, and the horizontal axis represents time. When the amount of light from the LD 28 fluctuates, the detection signal from the light detection sensor 200 also fluctuates. If the amount of light is large, the analog detection signal also increases; if the amount of light is small, the detection signal decreases. As a result, the detection period of the LD 28 beam in the output signal from the light detection sensor 200 expands or contracts. The falling or rising edge of the detection signal is used as the detection position of the LD 28 beam incident on the synchronization detection plate 41. Therefore, if the amount of light increases or decreases, the edge position fluctuates, causing a shift in the write start timing.

[0076] To prevent deviations in the write start timing, the following solutions have been proposed in the past. Patent Document 1 discloses a method of adjusting the reference voltage of a comparator in a light detection sensor to maintain a constant LD beam detection period. Patent Document 2 discloses a method of measuring the LD beam detection period and determining the center position of the LD beam detection period as the detection position, thereby enabling LD beam detection regardless of the light intensity. However, the technologies described in Patent Documents 1 and 2 require one synchronization detection plate 41 per color to prevent deviations in the write start timing between multiple LDs 28 used for development with different developers, which increases the number of parts and increases costs.

[0077] FIG. 8 is a diagram showing another example of the configuration of an optical writing device of a color image forming apparatus according to this embodiment. Compared to the optical writing device shown in FIG. 5, the optical writing device shown in FIG. 8 has a single synchronization detection plate 41, and beams emitted from two LDs 28 are incident on the single synchronization detection plate 41 at different angles. This configuration eliminates the need for one synchronization detection plate 41, contributing to reduced manufacturing costs for the optical writing device. While Patent Document 2 reduces the detection accuracy of the LD beam, the configuration shown in FIG. 8 corrects the detection error of the optical detection sensor 200, thereby preventing a decrease in the detection accuracy of the beams emitted from the multiple LDs 28 by the optical detection sensor 200.

[0078] Although a single optical detection sensor 200 can detect the beams of all LDs 28, it reduces the manufacturing cost of the optical writing device, but it also presents a problem. While the method disclosed in Patent Document 1, which adjusts the reference voltage of the comparator to maintain a constant detection period for the LD beam, can adjust the light intensity of one LD, it cannot simultaneously adjust the light intensity of the other LD, making it impossible to optimize the timing for starting writing for each color. This results in degradation of image quality. Therefore, when a common optical detection sensor 200 is used to detect beams emitted from LDs 28 with different light intensities, it is no longer possible to maintain a constant detection period for the beams of each LD 28.

[0079] 9 and 10 are diagrams showing examples of the detection signal and output signal of the beam of the light detection sensor 200 of the color image forming apparatus according to this embodiment. In the graphs shown in FIGS. 9 and 10, the vertical axis represents the signal output from the light detection sensor 200, and the horizontal axis represents time. Compared to FIG. 6, the angle of the beam of the LD 28 incident on the light detection sensor 200 is tilted. As shown in FIG. 8, when multiple beams are incident on one light detection sensor 200, an incident angle may occur for each beam. In this case, the detection signal of the light detection sensor 200 may not be symmetrical but may have a distorted waveform.

[0080] The example shown in Figure 10, compared to Figure 7, shows how the beam angle of the LD 28 incident on the light detection sensor 200 changes when it is tilted. When the beam incident angle is tilted, the detection signal from the light detection sensor 200 becomes distorted and not symmetrical. Increasing or decreasing the light intensity of the LD 28 causes variations in the rising edge of the detection waveform (left side of the figure) and the falling edge of the detection waveform (right side of the figure) to become uneven. This indicates that the peak position of the beam is not located in the center of the detection period of the LD 28. In other words, the method described in Patent Document 2, which measures the detection period of the LD beam and determines the beam detection position as half the period after the falling edge, cannot determine the peak position appropriately, making it impossible to optimize the write start timing. This results in degradation of image quality.

[0081] FIG. 11 shows an example of changes in the write start timing of a color image forming apparatus according to this embodiment. In the graph in the center of FIG. 11, the vertical axis represents the signal output from the light detection sensor 200, and the horizontal axis represents time. In the graph on the right side of FIG. 11, the vertical axis represents the change in the write start timing, and the horizontal axis represents the amount of light from the LD 28. When the amount of light from the LD 28 incident on the light detection sensor 200 increases or decreases, the falling edge of the output signal from the light detection sensor 200 shifts, causing the image write start timing to fluctuate. A graph of this change results in a nonlinear shape. When the amount of light is small, the peak voltage is close to the reference voltage, resulting in high sensitivity to changes in the light amount and a large amount of change. When the amount of light is large, the reference voltage is easily exceeded, resulting in low sensitivity to changes in the light amount and a small amount of change.

[0082] The amount of change in the write start timing described above is uniquely determined by the physical configuration, such as the incident angle of the beam from the LD 28 entering the light detection sensor 200, the shape of the slit, lens, and light receiving unit. To uniquely determine the amount of change determined by the physical configuration, it is necessary to appropriately focus the beam from the LD 28 that irradiates the light detection sensor 200 and narrow the beam spot diameter before irradiating it. However, narrowing the beam spot diameter requires a high-precision focusing lens for the light detection sensor 200, which increases manufacturing costs. This embodiment presents a method for optimizing the image write start timing and providing high-quality images while suppressing increases in the manufacturing costs of the optical writing device, without using a high-precision focusing lens for narrowing the beam spot diameter before irradiating it.

[0083] Fig. 12 is a diagram showing an example of a detection deviation characteristics table in the color image forming apparatus according to this embodiment. Specifically, Fig. 12 shows an example of a detection deviation characteristics table that associates the amount of light from the LD 28 incident on the light detection sensor 200 mounted on the synchronization detection plate 41 with the amount of change in the write start timing. A detection deviation characteristics table is provided for each LD 28 with a different beam path. When a single amount of light incident on the light detection sensor 200 is determined, the correction value calculation unit 26 corrects the write start timing in accordance with the detection deviation characteristics table.

[0084] For example, when the light output of the LD 28 (LD1) is set to 1.3 mW and the light output of the LD 28 (LD2) is set to 1.1 mW, the detection deviation characteristics table indicates that the write start timing of LD1 needs to be delayed by 8.640 ns and the write start timing of LD2 needs to be advanced by 2.526 ns. By using such a detection deviation characteristics table, even if the light output of each LD 28 is changed, deviations in the write start timing can be suppressed, providing high-quality images. When referencing the detection deviation characteristics table, the input value can be the light output (mW) of the LD 28 or the ratio (%) of the light output of the LD 28 to the reference light output.

[0085] Fig. 13 is a diagram for explaining an example of how to use the detection deviation characteristics table in the color image forming apparatus according to this embodiment. The detection deviation characteristics table is a table of detection deviation characteristics values ​​when the light intensity of the LD 28 fluctuates, as explained in Fig. 12. Here, we will explain how to use the detection deviation characteristics table in an image processing apparatus such as a color image forming apparatus.

[0086] Misalignment between colors in a color image forming apparatus is corrected during color matching. Because a color matching pattern must be formed on the intermediate transfer belt 18, the color matching pattern is formed with a certain amount of light for each LD 28. The timing at which writing starts is determined based on the output signal of the light detection sensor 200, and is the same whether the color matching pattern is being formed or during printing; any fluctuation in the amount of light from the LD 28 will result in a similar misalignment. When forming the color matching pattern, the timing at which writing starts shifts depending on the amount of light, but the color misalignment correction value calculated to perform color matching in that state also includes the detection misalignment correction value.

[0087] Taking Figure 13 as an example, if the light intensity of LD28 (LD1) during color matching is 4.1 mW, the write start timing will be off by 32.542 ns, but the color misregistration correction value calculated during color matching will include this 32.542 ns offset. Therefore, if the light intensity of LD1 during printing is 4.1 mW, adjustments will be made so that the image can be formed in the position optimized by color matching.

[0088] The method for using the detection deviation characteristic table in this embodiment is defined as follows: The correction value calculation unit 26 stores the light intensities of the LDs 28 as operating conditions during color matching, and corrects the write start timing to cancel the difference between the detection deviation characteristic value caused by the light intensities during printing and the detection deviation characteristic value caused by the light intensities during color matching.

[0089] 13 as an example, if the light intensity of LD1 during color matching is 4.1 mW and the light intensity during printing is 3.8 mW, the write start timing of LD1 can be corrected by correcting the difference between the two detection deviation characteristic values ​​in the detection deviation characteristic table, that is, -0.862 ns, as shown in the following formula (1). Also, if the light intensity of LD2 during color matching is 4.2 mW and the light intensity during printing is 4.0 mW, the write start timing of LD2 can be corrected by correcting the difference between the two detection deviation characteristic values ​​in the detection deviation characteristic table, that is, 0.463 ns, as shown in the following formula (2).

number

[0090] In this way, by calculating the detection deviation correction values ​​for each of LD1 and LD2, deviations in the timing at which writing starts occur during image formation can be suppressed, and high-quality images can be provided.

[0091] FIG. 14 is a diagram illustrating an example of a method for correcting the write start timing when an Nth-order polynomial detection error characteristic curve is used instead of a detection error characteristic table in a color image forming apparatus according to this embodiment. In FIG. 14, the vertical axis represents the detection error characteristic value, and the horizontal axis represents the light intensity of the LD 28. As shown in FIGS. 12 and 13, this embodiment proposes a method for adjusting the write start timing using a detection error characteristic table. However, highly accurate correction using a detection error characteristic table requires detailed data storage, which consumes a large amount of storage space. Therefore, this embodiment also proposes a method for correcting the write start timing using a polynomial detection error characteristic curve as an alternative form.

[0092] Specifically, the correction value calculation unit 26 calculates a polynomial approximation curve as a detection deviation characteristic curve from each plot point of the amount of change in the writing start timing in FIG. 11, and calculates the coefficients a0 to a nThe correction value calculation unit 26 determines in advance the light intensity LDp of the LD 28 and the coefficients a0 to a6. n and summing up each term from the 0th power to the nth power of LDp, the detection deviation characteristic value is calculated.

[0093] The method for using the polynomial detection deviation characteristic curve in this embodiment is defined as follows: The correction value storage unit 27 stores the light intensities of the LDs 28 as operating conditions during color matching. The correction value calculation unit 26 calculates the difference (detection deviation correction value) between the detection deviation characteristic value caused by the light intensities during printing and the detection deviation characteristic value caused by the light intensities during color matching, and corrects the write start timing to cancel this difference.

[0094] For example, suppose the coefficients are a0 = -42.249, a1 = 62.972, a2 ​​= -24.779, a3 = 5.0273, a4 = -0.4872, a5 = 0.0151, and a6 = 0.0003. If the light intensity of the LD 28 (LD1) during color matching is 4.1 mW and the light intensity during printing is 3.8 mW, the correction value calculation unit 26 calculates the detection deviation characteristic values ​​on the detection deviation characteristic curve to be 27.1360 ns and 26.3738 ns, respectively, as shown in the following equations (3) and (4).

number

[0095] Then, the correction value calculation unit 26 calculates the difference between these two detection deviation characteristic values, −0.7622 ns, as the detection deviation correction value, as shown in the following equation (5), and corrects the color deviation based on this detection deviation correction value, thereby correcting the writing start timing of LD1.

number

[0096] The polynomial detection error characteristic curve is also stored for each color, similar to the detection error characteristic table.

[0097] 15 is a diagram illustrating an example of updating the detection deviation characteristic table or the detection deviation characteristic curve to match the characteristics of the optical writing device in the color image forming apparatus according to this embodiment. As shown in FIGS. 12, 13, and 14, this embodiment adjusts the writing start timing using the detection deviation characteristic table or the detection deviation characteristic curve. However, even in a configuration that uses the detection deviation characteristic table or the detection deviation characteristic curve, it may not be possible to correct the writing start timing with high accuracy.

[0098] As described above, if the beam spot diameter of the LD 28 that illuminates the optical detection sensor 200 of the synchronization detection plate 41 is not narrowed, the beam spot diameter varies greatly for each optical writing device. As a result, the amount of change in the writing start timing when the light intensity of the LD 28 changes varies greatly for each optical writing device. This can cause a detection deviation characteristic table that can be properly corrected in one optical writing device to not be properly corrected in another optical writing device.

[0099] Therefore, in this embodiment, as described above, the correction value calculation unit 26 updates the detection deviation characteristics table or the detection deviation characteristics curve.

[0100] 16 is a diagram for explaining an example of a process for updating the detection deviation characteristic table or the detection deviation characteristic curve in the color image forming apparatus according to this embodiment. When the detection deviation characteristic table is used, the values ​​of the detection deviation characteristic table are stored in correction value storage unit 27. When the detection deviation characteristic curve is used, the coefficients of the detection deviation characteristic curve are stored. Therefore, a method for updating the stored values ​​will be explained.

[0101] The correction value calculation unit 26 executes a light intensity setting step to set the light intensity of the LD 28 (step S1601). Next, the correction value calculation unit 26 executes a detection pre-processing step to perform pre-processing for pattern detection (step S1602). Specifically, the detection pre-processing step performs preparations before forming and detecting a misalignment amount calculation pattern. In the pre-preparation, the optical writing control unit 20 adjusts the emission intensity of the TM / P sensor 12 while rotating the intermediate transfer belt 18, etc.

[0102] Next, the correction value calculation unit 26 performs a deviation amount calculation pattern formation step of forming a deviation amount calculation pattern for calculating the detected deviation characteristic value (step S1603). Furthermore, the correction value calculation unit 26 performs a deviation amount calculation pattern detection step of detecting a deviation amount calculation pattern (step S1604). Furthermore, the correction value calculation unit 26 determines whether or not the detection of the deviation amount calculation pattern has been successful (step S1605).

[0103] If a deviation amount calculation pattern is not detected (step S1605: No), the correction value calculation unit 26 proceeds to step S1607 without calculating the detected deviation characteristic value. On the other hand, if a deviation amount calculation pattern is detected (step S1605: Yes), the correction value calculation unit 26 performs a deviation amount calculation step to calculate the detected deviation characteristic value (step S1606). Next, the correction value calculation unit 26 determines whether the detected deviation characteristic value has been calculated under all conditions (step S1607). If the detected deviation characteristic value has not been calculated under all conditions (step S1607: No), the process returns to step S1601.

[0104] If the detection error characteristic values ​​have been calculated under all conditions (step S1607: Yes), the correction value calculation unit 26 determines whether or not the detection error characteristic table or the detection error characteristic curve can be updated based on the calculation results of the detection error characteristic values ​​(step S1608). If the detection error characteristic table or the detection error characteristic curve cannot be updated (step S1608: No), the update process ends. On the other hand, if the detection error characteristic table or the detection error characteristic curve can be updated (step S1608: Yes), the correction value calculation unit 26 executes the update process of the detection error characteristic table or the detection error characteristic curve (step S1609).

[0105] Processing the series of steps from step S1601 to step S1606 outputs the calculation result of the detection deviation characteristic value for one light intensity of the LD 28. By repeatedly processing the series of steps from step S1601 to step S1606 while changing the light intensity of the LD 28, calculation results of a plurality of detection deviation characteristic values ​​are output, and based on these calculation results, if it is a detection deviation characteristic table, the respective values ​​stored in the detection deviation characteristic table are updated, and if it is a detection deviation characteristic curve, the coefficients of the respective polynomials are updated.

[0106] Here, the misalignment calculation pattern is a pattern that can detect misalignment in the main scanning direction. Basically, the misalignment calculation pattern is composed of a combination of patterns with different angles, such as horizontal and diagonal line patterns. This embodiment uses a pattern with the same shape as the color matching pattern used in the color matching process of the color image forming device. This reduces the effect of differences in pattern shape on the misalignment calculation results, and makes it possible to ideally estimate the characteristics of the detected misalignment of the optical writing device (the amount of change in the writing start timing when the light intensity of the LD changes).

[0107] 17 is a diagram for explaining an example of the details of a method for updating the detection deviation characteristics table in the color image forming apparatus according to this embodiment. The detection deviation characteristics of the optical writing device can be estimated by repeatedly processing the series of steps from step S1601 to step S1605 shown in FIG. 16. However, if an attempt is made to calculate the detection deviation characteristic values ​​for all the light intensities of the LDs 28 in the detection deviation characteristics table, the number of calculations of the detection deviation characteristic values ​​becomes enormous, and the update process takes a long time.

[0108] Therefore, in this embodiment, a series of steps from step S1601 to step S1605 of the detection deviation characteristic value update process are repeatedly performed with a number of light intensity settings that is smaller than the number of arrays in the detection deviation characteristic table. Then, after estimating the detection deviation characteristics of the optical writing device from the calculation results of the detection deviation characteristic value, interpolation processing is performed according to the number of arrays in the detection deviation characteristic table. By processing in this manner, the values ​​stored in the detection deviation characteristic table can be updated accurately in a short time.

[0109] Furthermore, when updating the values ​​stored in the detection deviation characteristics table, the calculation result of one detection deviation characteristic value is used as a reference value, and the difference from that reference value is stored. By performing calculations in this manner, the values ​​stored in the detection deviation characteristics table can be kept at a constant level, preventing overflow of stored values ​​and reducing memory consumption.

[0110] Furthermore, in this embodiment, the number of calculation points for the detection deviation characteristic value is three. As explained in FIG. 11, the detection deviation characteristic of an optical writing device has a nonlinear shape. To minimize the number of calculation points for the detection deviation characteristic value and perform accurate interpolation, calculation results for the detection deviation characteristic value at least three points are required. This is because the calculation results for the detection deviation characteristic value at two points do not become nonlinear. Furthermore, in this embodiment, the correction value calculation unit 26 performs linear interpolation processing. Even with simple interpolation processing, deviation can be corrected with high accuracy, and high-quality images can be provided.

[0111] 18 is a diagram for explaining an example of details of a method for updating the detection deviation characteristic curve in the color image forming apparatus according to the present embodiment. As explained in FIG. 14, another embodiment of the present embodiment uses a detection deviation characteristic curve instead of a detection deviation characteristic table, and therefore, here, the update process when using the detection deviation characteristic curve will be explained.

[0112] In another embodiment of the present invention, a series of steps from step S1601 to step S1606 of the update process are repeatedly performed with the number of calculation points (N+1) which is larger than the order N of the approximation formula of the detection deviation characteristic curve. Then, the coefficients a of the respective orders of the approximation formula that pass through all of the calculation results of N+1 are calculated. n This allows the detected deviation characteristic value of the optical writing device to be approximated with high accuracy in a short time.

[0113] Additionally, the order N of the approximation formula that approximates the detection deviation characteristic value of the optical writing device is set to 3 or 4. This is because if the order of the approximation formula is set to 5 or more, there is a risk that the distortion of the detection deviation characteristic curve will become large locally between calculation points. By performing calculations in this manner, accurate approximation can be achieved while reducing the number of calculation points.

[0114] Fig. 19 is a flowchart showing an example of the flow of color matching processing in a color image forming apparatus according to this embodiment. Fig. 20 is a flowchart showing an example of the flow of printing operations in a color image forming apparatus according to this embodiment. The method for correcting the writing start timing is processed in these two flowcharts.

[0115] First, an example of the flow of color matching processing in a color image forming apparatus will be described. The optical writing control unit 20 executes pre-detection processing (step S1901). Specifically, the optical writing control unit 20 performs preparations before forming and detecting a color matching pattern. The optical writing control unit 20 also adjusts the emission intensity of the TM / P sensor 12 while rotating the intermediate transfer belt 18 and the like.

[0116] Next, the optical writing control unit 20 forms a color matching pattern (step S1902). Specifically, the optical writing control unit 20 performs settings related to the formation of the color matching pattern.

[0117] Next, the optical writing control unit 20 detects a color matching pattern (step S1903). Furthermore, the optical writing control unit 20 determines whether or not the detection of the color matching pattern has been successful (step S1904). Specifically, the optical writing control unit 20 performs processing related to the detection of the color matching pattern, and when detection of all the formed color matching patterns is completed (step S1904: Yes), the optical writing control unit 20 ends the color matching pattern detection processing and proceeds to step S1905. On the other hand, when a color matching pattern is not detected (step S1904: No), the optical writing control unit 20 ends the color matching processing.

[0118] Next, the correction value calculation unit 26 performs a process of calculating a color misregistration correction value (step S1905). Specifically, the correction value calculation unit 26 calculates a color misregistration correction value that corrects misregistration between colors using the detection result of the color matching pattern. Here, the misregistration between colors includes misregistration in the main scanning direction, misregistration in the sub-scanning direction, skew misregistration, magnification misregistration, partial magnification misregistration, and other misregistrations. The misregistration in the writing start timing is included in the main scanning registration misregistration, and a color misregistration correction value that corrects the main scanning registration misregistration between colors is calculated at the time of color matching.

[0119] Next, if the calculated color misregistration correction value is normal (step S1906: Yes), the correction value calculation unit 26 updates the color misregistration correction value and the first light amount (step S1907). Specifically, the correction value calculation unit 26 updates the color misregistration correction value and the first light amount stored in the correction value storage unit 27. However, if color matching is not performed normally, such as due to color matching pattern detection or correction value calculation results, the update process of the color misregistration correction value and the first light amount is skipped. In other words, if color matching is not performed normally, the first light amount stored in the correction value storage unit 27 is not updated.

[0120] Next, the correction value calculation unit 26 updates the execution results of the color matching process (step S1908). Specifically, the correction value calculation unit 26 updates the execution results of the color matching stored in the correction value storage unit 27. Here, the execution results of the color matching include the internal temperature at the time of execution and the light intensity of the LD 28. However, if the color matching is not performed normally, such as the detection of the color matching pattern and the calculation results of the correction value, the process of updating the execution results of the color matching process is skipped.

[0121] Next, an example of the flow of the printing operation of the color image forming apparatus according to this embodiment will be described. First, the optical writing control unit 20 executes a pre-printing operation process (step S2001). Specifically, the optical writing control unit 20 performs a startup process for the optical writing device after a print job is received. Here, the startup process for the optical writing device includes starting the LD driver, rotating the polygon motor 29, and determining the light amount of the LD 28 during the printing operation.

[0122] Next, the optical writing control unit 20 executes initialization processing of the LD 28 (step S2002). Specifically, the optical writing control unit 20 initializes the LD 28 so that the light intensity of the LD 28 becomes a target light intensity. The optical writing control unit 20 also starts synchronous lighting so that the light detection sensor 200 of the synchronization detection plate 41 can detect the beam of the LD 28.

[0123] Next, if the LD 28 is properly initialized (step S2003: Yes) and a synchronization signal is detected (step S2004: Yes), the correction value calculation unit 26 reads out the execution conditions for color matching (step S2005). Specifically, the correction value calculation unit 26 reads out the light amount of the LD 28 at the time of color matching execution, which was stored when the color matching process was executed. Note that if the LD 28 is not properly initialized (step S2003: No) or if a synchronization signal is not detected (step S2004: No), the optical writing control unit 20 forcibly terminates the printing process (step S2010).

[0124] Next, the correction value calculation unit 26 adjusts the timing to start writing (step S2006). Specifically, the correction value calculation unit 26 refers to the detection deviation characteristics table and adjusts the timing to start writing for each color using the light amount of the LD 28 during printing and the light amount of the LD 28 during color matching.

[0125] Next, the optical writing control unit 20 executes a process during the printing operation (step S2007). Specifically, the optical writing control unit 20 turns on and off the LD 28 in accordance with the image data, and executes a process for forming a desired electrostatic latent image on the photoconductor 16.

[0126] Thereafter, when all print jobs are completed (step S2008: Yes), the optical writing control unit 20 executes post-printing process (step S2009). Specifically, the optical writing control unit 20 performs the following operations after printing: neutralizing the photosensitive member 16, stopping the LD driver, stopping the polygon motor 29, etc.

[0127] In the color matching process, a color matching pattern is formed, and a color misregistration correction amount is calculated by detecting the color matching pattern, and the writing start timing is corrected to eliminate color misregistration. As described above, in this embodiment, when the color matching pattern is formed, the function (correction function) for calculating the detected misregistration correction value of the optical writing device described in FIGS. 12 to 18 is disabled. Then, the light intensity of the LD 28 when forming the color matching pattern is stored. The writing start timing is shifted by the difference between the light intensity of the LD 28 during printing and the light intensity of the LD 28 stored in the storage unit due to the detected misregistration characteristics of the optical writing device. The color image forming apparatus corrects the deviation in the writing start timing by adding the detected misregistration correction amount calculated using the detected misregistration characteristics table or detected misregistration characteristic curve to the color misregistration correction amount calculated in the color matching process.

[0128] The light amount of the LD 28 is stored in the color matching execution result update step (step S1908), and the write start timing of the print operation is corrected in the write start timing adjustment step (step S2006). Note that although the above describes the timing for disabling the correction function, there is also a timing for enabling the correction function. The correction function needs to be enabled when forming an image or pattern of such high quality that the influence of the detection deviation characteristic value of the optical writing device becomes a concern. In a color image forming apparatus, the correction function of the optical writing device is enabled during the print operation.

[0129] In this way, according to the color image forming apparatus of this embodiment, even if an inexpensive LD driver without a shading correction function is used, a technique can be provided to suppress deviations in the timing at which image data starts to be written, so that high-quality images can be output at low cost.

[0130] In the above embodiment, the image forming apparatus of the present invention is described as being applied to a multifunction peripheral having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function, but the present invention can be applied to any image forming apparatus such as a copier, printer, scanner device, or facsimile device.

[0131] For example, aspects of the present invention are as follows. <1> In an electrophotographic color image forming apparatus, an image is formed by developing an electrostatic latent image formed on a photosensitive member with a developer, the color image forming apparatus has an optical writing device that exposes a photosensitive member; The optical writing device a light emitting element that irradiates the photosensitive member with light; a light-emission control element that controls light emission of the light-emitting element; a deflection element, which is a multi-faceted reflector provided on an optical path of light emitted from the light-emitting element, rotated by an externally input signal, and deflects the light irradiated onto the surface of the reflector to scan the photosensitive member in one direction; a synchronization detection element for detecting the timing at which writing of an electrostatic latent image is started by irradiating the photosensitive member with light; a color shift correction function unit that corrects color shift by adjusting the writing start timing from when the synchronous detection element detects light to when the light emission control element starts light emission control according to image data; a storage unit that stores a result of the color shift correction, a color shift correction value, and a detection deviation characteristic value that indicates a characteristic of the detection deviation that occurs when the amount of light incident on the synchronous detection element fluctuates; a detection error correction function unit that corrects a detection error of the synchronous detection element; an update unit that updates the detection deviation characteristic value stored in the storage unit, the execution result includes a first light amount of the light-emitting element when correcting color misregistration; The detection error correction function unit calculates a detection error correction value for correcting the detection error of the synchronous detection element using the first light amount, a second light amount determined as a lighting condition of the light-emitting element, and the detection error characteristic value, and adds the detection error correction value to the color error correction value. <2> the light emission control element controls the light amount of the light emitting element to be constant while the light irradiated from one end to the other of one surface of the deflection element scans in one direction; <1> 10. The color image forming apparatus according to claim 19. <3> the optical writing device irradiates one of the synchronous detection elements with light from a plurality of the light emitting elements, each of which is configured to irradiate a different one of the photosensitive elements; <1> or <2> 10. The color image forming apparatus according to claim 19. <4> The synchronous detection element has a slit that limits the incident optical path of the light from the light emitting element. <1> from <3> 10. The color image forming apparatus according to claim 19, <5> Among the requirements for the operation of the optical writing device of the color image forming apparatus, When a print request is received, the detection deviation correction function unit enables a function of calculating the detection deviation correction value for correcting the detection deviation of the synchronous detection element, and when a color deviation correction request is received, disables the function. <1> from <4> 10. The color image forming apparatus according to claim 19, <6> the color misregistration correction value and the first light amount stored in the storage unit are updated at approximately the same timing; <1> from <5> 10. The color image forming apparatus according to claim 19, <7> The update unit a light intensity setting step for setting the light intensity of the light emitting element; a pattern forming step of forming a pattern for detecting a detection error that occurs when the amount of light incident on the synchronous detection element fluctuates; a pattern detection step of detecting the formed pattern, repeating the light amount setting step, the pattern forming step, and the pattern detecting step while changing the light amount; calculating the detection deviation characteristic value based on the pattern detection result, and updating the detection deviation characteristic value stored in the storage unit; <1> from <6> 10. The color image forming apparatus according to claim 19, <8> the pattern forming step and the pattern detecting step perform formation and detection of the pattern using a pattern forming unit and a pattern detecting unit that are used when the color shift correction function unit corrects color shift, respectively. <7> 10. The color image forming apparatus according to claim 19. <9> the pattern formed in the pattern forming step has the same angle, length, width, and formation interval as the pattern formed by the color shift correction function unit; <7> 10. The color image forming apparatus according to claim 19. <10> the color image forming apparatus includes a new product detection unit for detecting whether the optical writing device has been replaced; When the color image forming apparatus is powered on, the new product detection unit detects that the optical writing device is new, and the update unit operates. <1> from <9> 10. The color image forming apparatus according to claim 19, <11> When it is determined that the update unit has completed normally, the detected deviation characteristic value is updated, and a notification is given that the update process has been completed so that the update unit will not operate the next time the color image forming apparatus is powered on. <10> 10. The color image forming apparatus according to claim 19. <12> the detected deviation characteristic values ​​are stored in the storage unit in a table-like arrangement; the detection deviation correction function unit calculates the two detection deviation characteristic values ​​by referring to the detection deviation characteristic values ​​that are closest to the first light amount and the second light amount from the table array or by performing interpolation processing, and calculates the detection deviation correction value based on the difference between the two detection deviation characteristic values. <1> from <11> 10. The color image forming apparatus according to claim 19, <13> the update unit performs interpolation processing of the detection error correction value based on a plurality of detection results of the detection error obtained by operating the light emitting element at three light intensity settings, and updates each of the detection error characteristic values ​​in the table-like array stored in the storage unit. <12> 10. The color image forming apparatus according to claim 19. <14> The update unit a linear interpolation process for the detection result of the detection deviation and the detection deviation correction values ​​of two neighboring points; <12> or <13> 10. The color image forming apparatus according to claim 19. <15> the detected deviation characteristic value is stored in the storage unit as a coefficient of an N-th degree polynomial; the detection error correction function unit calculates the detection error characteristic values ​​corresponding to the first light amount and the second light amount using coefficients of the Nth-order polynomial, and calculates the detection error correction value from a difference between the two detection error characteristic values. <1> from <11> 10. The color image forming apparatus according to claim 19, <16> the update unit calculates coefficients of the Nth-order polynomial based on a plurality of detection results of the detection deviation obtained by operating the light emitting element at a light intensity setting of N+1, and updates the coefficients of each of the Nth-order polynomials stored in the storage unit. <15> 10. The color image forming apparatus according to claim 19. <17> the detected deviation characteristic value is stored in the storage unit as a coefficient of a third-order polynomial or a fourth-order polynomial; the detection error correction function unit operates to calculate the detection error characteristic value corresponding to the first light amount and the second light amount using coefficients of a third-order polynomial or a fourth-order polynomial, and to calculate the detection error correction value from a difference between the two detection error characteristic values. <15> or <16> 10. The color image forming apparatus according to claim 19. [Explanation of symbols]

[0132] 16K, 16C, 16M, 16Y photoconductor 18 Intermediate transfer belt 19K,19C,19M,19Y Imaging section 20 Optical writing control unit 21 Sensor control unit 22 Light emission control unit 23 Counting section 24 Deflection control section 26 Correction value calculation unit 27 Correction value memory section 28LD 29 Polygon Motor 52 Polygon Mirror 200 Light detection sensor [Prior art documents] [Patent documents]

[0133] [Patent Document 1] Patent No. 2815183 [Patent Document 2] Japanese Patent Application Publication No. 61-025363

Claims

1. In an electrophotographic color image forming apparatus, an image is formed by developing an electrostatic latent image formed on a photosensitive member with a developer, the color image forming apparatus has an optical writing device that exposes a photosensitive member; The optical writing device a light emitting element that irradiates the photosensitive member with light; a light-emission control element that controls light emission of the light-emitting element; a deflection element, which is a multi-faceted reflector provided on an optical path of light emitted from the light-emitting element, rotated by an externally input signal, and deflects the light irradiated onto the surface of the reflector to scan the photosensitive member in one direction; a synchronization detection element for detecting the timing at which writing of an electrostatic latent image is started by irradiating the photosensitive member with light; a color shift correction function unit that corrects color shift by adjusting the writing start timing from when the synchronous detection element detects light to when the light emission control element starts light emission control according to image data; a storage unit that stores a result of the color shift correction, a color shift correction value, and a detection deviation characteristic value that indicates a characteristic of the detection deviation that occurs when the amount of light incident on the synchronous detection element fluctuates; a detection error correction function unit that corrects a detection error of the synchronous detection element; an update unit that updates the detection deviation characteristic value stored in the storage unit, the execution result includes a first light amount of the light-emitting element when correcting color misregistration; The detection error correction function unit calculates a detection error correction value for correcting the detection error of the synchronous detection element using the first light amount, a second light amount determined as a lighting condition of the light-emitting element, and the detection error characteristic value, and adds the detection error correction value to the color error correction value.

2. 2. The color image forming apparatus according to claim 1, wherein said light emission control element controls the light amount of said light emitting element to be constant while the light irradiated from one end to the other of one surface of said deflecting element scans in one direction.

3. 3. The color image forming apparatus according to claim 1, wherein said optical writing device irradiates one of said synchronous detecting elements with light from a plurality of said light emitting elements, each of said light emitting elements being configured to irradiate a different one of said photosensitive elements.

4. 2. A color image forming apparatus according to claim 1, wherein said synchronous detection element has a slit for restricting an incident optical path of light from said light emitting element.

5. Among the requirements for the operation of the optical writing device of the color image forming apparatus, 2. The color image forming apparatus according to claim 1, wherein the detection error correction function unit enables a function of calculating the detection error correction value for correcting the detection error of the synchronous detection element when a print request is received, and disables the function when a request for color error correction is received.

6. 2. The color image forming apparatus according to claim 1, wherein the color misregistration correction value and the first light amount stored in the storage unit are updated at substantially the same timing.

7. The update unit a light intensity setting step for setting the light intensity of the light emitting element; a pattern forming step of forming a pattern for detecting a detection error that occurs when the amount of light incident on the synchronous detection element fluctuates; a pattern detection step of detecting the formed pattern, repeating the light amount setting step, the pattern forming step, and the pattern detecting step while changing the light amount; 2. The color image forming apparatus according to claim 1, wherein the detected deviation characteristic value is calculated based on the detection result of the pattern, and the detected deviation characteristic value stored in the storage unit is updated.

8. 8. The color image forming apparatus according to claim 7, wherein the pattern forming step and the pattern detecting step form and detect the pattern using a pattern forming section and a pattern detecting section that are used when the color misregistration correcting function section corrects color misregistration.

9. 8. The color image forming apparatus according to claim 7, wherein the pattern formed in the pattern forming step has the same angle, length, width, and forming interval as the pattern formed by the color shift correction function unit.

10. the color image forming apparatus includes a new product detection unit for detecting whether the optical writing device has been replaced; 2. The color image forming apparatus according to claim 1, wherein when the color image forming apparatus is powered on, the new product detection unit detects that the optical writing device is new, and the updating unit operates.

11. 11. The color image forming apparatus according to claim 10, wherein when it is determined that the update unit has completed normally, the detected deviation characteristic value is updated, and a notification is given that the update process has been completed so that the update unit will not operate the next time the color image forming apparatus is powered on.

12. the detected deviation characteristic values ​​are stored in the storage unit in a table-like arrangement; 2. The color image forming apparatus according to claim 1, wherein the detection deviation correction function unit calculates the two detection deviation characteristic values ​​by referring to the detection deviation characteristic values ​​closest to the first light amount and the second light amount from the table-like array or by performing interpolation processing, and calculates the detection deviation correction value based on the difference between the two detection deviation characteristic values.

13. 13. The color image forming apparatus according to claim 12, wherein the update unit performs interpolation processing of the detection error correction value based on a plurality of detection results of the detection error obtained by operating the light-emitting element at three light intensity settings, and updates each of the detection error characteristic values ​​in the table-like arrangement stored in the memory unit.

14. 14. The color image forming apparatus according to claim 12, wherein the update unit performs linear interpolation of the detection error correction values ​​of two neighboring points on the detection result of the detection error.

15. the detected deviation characteristic value is stored in the storage unit as coefficients of an N-th degree polynomial; 2. The color image forming apparatus according to claim 1, wherein the detection error correction function unit calculates the detection error characteristic value corresponding to the first light amount and the second light amount using coefficients of the Nth-order polynomial, and calculates the detection error correction value from the difference between the two detection error characteristic values.

16. 16. The color image forming apparatus according to claim 15, wherein the update unit calculates coefficients of the Nth-order polynomial based on a plurality of detection results of the detection deviation obtained by operating the light-emitting element at a light intensity setting of N+1, and updates the coefficients of each of the Nth-order polynomials stored in the memory unit.

17. the detection deviation characteristic value is stored in the storage unit as a coefficient of a third-order polynomial or a fourth-order polynomial; 17. The color image forming apparatus according to claim 15, wherein the detection error correction function unit calculates the detection error characteristic value corresponding to the first light amount and the second light amount using coefficients of a third-order polynomial or a fourth-order polynomial, and calculates the detection error correction value from the difference between the two detection error characteristic values.

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