JP5470027B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus, and more particularly to a color misregistration determination function.

  There is a type of color image forming apparatus in which a color toner image is formed on a transfer belt by superimposing and transferring a toner image of a pattern of each color on a transfer belt, and the color toner image is transferred to a sheet. In order to prevent color misregistration when a toner image of each color pattern is superimposed, a technique (registration technique) that detects and corrects color misregistration by detecting a toner image of a predetermined pattern has been proposed (for example, a patent). Reference 1).

JP 2002-55506 A

  If the predetermined pattern partially includes a high density region, there is a problem that accuracy of detecting the predetermined pattern is lowered. In addition, there are the following two problems concerning optical conditions for forming an electrostatic latent image having a predetermined pattern.

  One problem is related to a plurality of light deflection surfaces provided in the polygon mirror. An electrostatic latent image having a predetermined pattern is formed on the photosensitive drum by deflecting the light beam modulated by the predetermined pattern data on the light deflection surface of the polygon mirror and scanning the photosensitive drum. Since differences in light reflectance and surface tilt amount inevitably occur on each light deflection surface, the optical conditions of each light deflection surface are not exactly the same.

  Another problem is related to the multi-beam method. The multi-beam method is a method in which a plurality of light sources are used for forming an electrostatic latent image in order to improve the printing speed. Since differences in the direction of the optical axis, wavelength, etc. inevitably occur in each light source, the optical conditions of each light source are not exactly the same.

  In order to improve the accuracy of color misregistration determination, it is preferable to form an electrostatic latent image of a determination pattern in consideration of the difference in the optical conditions.

  The present invention provides a color image forming apparatus capable of detecting a toner image of a determination pattern used for determination of color misregistration when a toner image of each color pattern is superimposed on a transfer belt with high accuracy and low cost. The purpose is to provide.

  A color image forming apparatus according to an aspect of the present invention that achieves the above object has a function of superimposing a toner image of each color pattern to form a color toner image and superimposing a toner image of each color pattern. A color image forming apparatus having a function of determining a color misregistration using a toner image of a determination pattern for each color, and that operates at the time of color misregistration and applies light to the toner image of the determination pattern for each color. And the toner image of the determination pattern has a smaller dimension in the sub-scanning direction than the diameter of the spot of the light irradiated from the optical sensor, and the determination pattern A plurality of narrow-width pattern toner images, which are narrower than the toner image, are arranged in the sub-scanning direction at intervals smaller than the spot diameter. A pattern data storage unit in which data of the determination pattern for forming a toner image of a pattern for use is stored in advance; and a light beam modulated by data of a corresponding color pattern during normal operation; At the time of deviation determination, a light source that emits a light beam modulated by the data of the determination pattern stored in the pattern data storage unit, a light beam emitted from the light source is irradiated, and the irradiated light beam is deflected An electrostatic latent image of a pattern of each color during the normal operation by drawing a scanning line with a light beam deflected by the polygon mirror, and a plurality of exposure apparatuses including a polygon mirror having a plurality of light deflection surfaces. And a photosensitive drum on which an electrostatic latent image of the determination pattern for each color is formed at the time of the color misregistration determination, and at the time of the normal operation Develops the electrostatic latent image of the corresponding color pattern to form a toner image on the photosensitive drum, and develops the toner image by developing the electrostatic latent image of the corresponding pattern for the determination at the time of the color misregistration. A plurality of developing devices formed on the photosensitive drum and a toner image of each color pattern developed by the plurality of developing devices during the normal operation are superimposed and transferred, and developed by the plurality of developing devices when the color misregistration is determined. The transfer sensor onto which the toner image of the determination pattern of each color transferred is transferred and the toner image of the determination pattern of the color transferred onto the transfer belt is reflected by the light sensor being irradiated with light. A determination pattern detection unit that detects a toner image of the determination pattern based on a signal output from the optical sensor by receiving light. The determination pattern data stored in the pattern data storage unit includes data in which the light deflection surfaces irradiated with the light beam are the same in forming the electrostatic latent image of each narrow pattern. And

  According to this configuration, the toner image of the determination pattern has a plurality of narrow-width pattern toner images whose dimensions in the sub-scanning direction are smaller than the spot diameter of the light emitted from the optical sensor, and the interval is smaller than the spot diameter. And arranged in the sub-scanning direction. Therefore, in the determination of color misregistration, the toner image of the determination pattern can be detected with high accuracy and at low cost.

  Further, according to the above configuration, the determination pattern data includes data in which the light deflection surfaces irradiated with the light beam are the same in forming the electrostatic latent image of each narrow pattern. Therefore, even if there are differences in the optical conditions of the light deflection surfaces of the polygon mirror, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform. In this way, since the electrostatic latent image of the determination pattern is formed in consideration of the difference in optical conditions, the accuracy of color misregistration determination can be improved.

  In the above configuration, the data of the determination pattern stored in the pattern data storage unit is data in which the order of the light deflection surfaces that irradiate the light beam in forming the electrostatic latent image of each narrow pattern is the same. Including.

  According to this configuration, the determination pattern data includes data in which the order of the light deflection surfaces to be irradiated with the light beam is the same in forming the electrostatic latent image of each narrow pattern. Therefore, even if there are differences in the optical conditions of the light deflection surfaces of the polygon mirror, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform. Therefore, the accuracy of color misregistration determination can be improved.

  In the above configuration, a rotation position detector that detects a rotation position of a predetermined light deflection surface among the plurality of light deflection surfaces, and light that irradiates a light beam in forming an electrostatic latent image of each narrow pattern Irradiation control for controlling the timing of irradiating the light deflection surface with the light beam based on the rotation position of the light deflection surface detected by the rotation position detector so that the deflection surface becomes the same at each color misregistration determination And a portion.

  According to this configuration, the light deflection surface that irradiates the light beam in the formation of the electrostatic latent image of each narrow pattern can be made the same in each color misregistration determination. Therefore, the accuracy of color misregistration determination can be improved.

  A color image forming apparatus according to another aspect of the present invention that achieves the above object has a function of forming a color toner image by superimposing a toner image of each color pattern, and superimposing a toner image of a pattern of each color A color image forming apparatus having a function of determining a color misregistration using a toner image of a determination pattern for each color, and that operates at the time of color misregistration and applies light to the toner image of the determination pattern for each color. And the toner image of the determination pattern has a smaller dimension in the sub-scanning direction than the diameter of the spot of the light irradiated from the optical sensor, and the determination pattern A plurality of narrow-width pattern toner images, which are narrower than the toner image, are arranged in the sub-scanning direction at intervals smaller than the spot diameter. A pattern data storage unit in which data of the determination pattern for forming a toner image of a pattern for use is stored in advance; and a light beam modulated by data of a corresponding color pattern during normal operation; At the time of deviation determination, a light source that emits a light beam modulated by the data of the determination pattern stored in the pattern data storage unit, a light beam emitted from the light source is irradiated, and the irradiated light beam is deflected An electrostatic latent image of a pattern of each color during the normal operation by drawing a scanning line with a light beam deflected by the polygon mirror, and a plurality of exposure apparatuses including a polygon mirror having a plurality of light deflection surfaces. And a photosensitive drum on which an electrostatic latent image of the determination pattern for each color is formed at the time of the color misregistration determination, and at the time of the normal operation Develops the electrostatic latent image of the corresponding color pattern to form a toner image on the photosensitive drum, and develops the toner image by developing the electrostatic latent image of the corresponding pattern for the determination at the time of the color misregistration. A plurality of developing devices formed on the photosensitive drum and a toner image of each color pattern developed by the plurality of developing devices during the normal operation are superimposed and transferred, and developed by the plurality of developing devices when the color misregistration is determined. The transfer sensor onto which the toner image of the determination pattern of each color transferred is transferred and the toner image of the determination pattern of the color transferred onto the transfer belt is reflected by the light sensor being irradiated with light. A determination pattern detection unit that detects a toner image of the determination pattern based on a signal output from the optical sensor by receiving light. A plurality of light sources provided in each of the plurality of exposure apparatuses, and a plurality of light beams arranged in the sub-scanning direction and drawing a scanning line in the main scanning direction are emitted by the plurality of light sources, and the pattern data The determination pattern data stored in the storage unit includes data that uses the same light source for forming the electrostatic latent images of the narrow patterns.

  According to this configuration, the toner image of the determination pattern has a plurality of narrow-width pattern toner images whose dimensions in the sub-scanning direction are smaller than the spot diameter of the light emitted from the optical sensor, and the interval is smaller than the spot diameter. And arranged in the sub-scanning direction. Therefore, in the determination of color misregistration, the toner image of the determination pattern can be detected with high accuracy and at low cost.

  Further, according to the above configuration, the determination pattern data includes data that uses the same light source for forming the electrostatic latent image of each narrow pattern. Therefore, even if there are differences in the optical conditions of each light source in the multi-beam method, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform. In this way, since the electrostatic latent image of the determination pattern is formed in consideration of the difference in optical conditions, the accuracy of color misregistration determination can be improved.

  In the above configuration, the data of the determination pattern stored in the pattern data storage unit is the width of each narrow pattern as viewed in the sub-scanning direction of the scanning line on which the electrostatic latent image of each width pattern is formed. The data including the same order of the light sources used for forming the electrostatic latent image can be included.

A color image forming apparatus according to still another aspect of the present invention that achieves the above object has a function of forming a color toner image by superimposing the toner images of the respective color patterns, and the toner images of the respective color patterns are formed. A color image forming apparatus having a function of determining a color shift at the time of superimposing using a toner image of a determination pattern for each color, and operates at the time of determining a color shift to the toner image of the determination pattern for each color An optical sensor that receives light reflected by light irradiation and a toner image of the determination pattern have a size in the sub-scanning direction smaller than the diameter of the light spot irradiated from the optical sensor, and the determination image A plurality of narrow pattern toner images, which are narrower than the pattern toner image, are arranged along the sub-scanning direction at intervals smaller than the spot diameter; A pattern data storage unit in which data of the determination pattern for forming a toner image of the determination pattern is stored in advance, and a light beam modulated by data of a corresponding color pattern during normal operation; At the time of color misregistration determination, a light source that emits a light beam modulated by the data of the determination pattern stored in the pattern data storage unit, and a light beam emitted from the light source are irradiated. A plurality of exposure apparatuses including a plurality of light deflecting surfaces for deflecting light, and drawing a scanning line with a light beam deflected by the polygon mirror. A photosensitive drum on which a latent image is formed and an electrostatic latent image of the determination pattern for each color is formed when the color misregistration is determined; The electrostatic latent image of the corresponding color pattern is developed at the time of production to form a toner image on the photosensitive drum, and the electrostatic latent image of the determination pattern of the corresponding color is developed at the time of color misregistration. A plurality of developing devices for forming the image on the photosensitive drum, and a toner image of each color pattern developed by the plurality of developing devices during the normal operation is superimposed and transferred, and when the color misregistration determination is performed by the plurality of developing devices. A transfer belt onto which the toner image of the determination pattern of each color developed is transferred, and the light sensor irradiates and reflects the toner image of the determination pattern of each color transferred onto the transfer belt. And a determination pattern detection unit that detects a toner image of the determination pattern based on a signal output from the optical sensor by receiving the received light. Each of the plurality of exposure apparatuses includes a plurality of light sources, and the plurality of light sources emit a plurality of light beams arranged in the sub-scanning direction so as to draw a scanning line in the main scanning direction, The determination pattern data stored in the pattern data storage unit includes a plurality of narrow patterns drawn by selecting the plurality of light sources in the plurality of narrow patterns constituting the determination pattern. is constituted by the scanning lines and the combination of a plurality of light sources seen contains data having the same, one of the light deflection surfaces of the plurality of light deflecting surfaces is used to draw the narrow pattern, the plurality of light sources By irradiating the plurality of light beams generated in Step 1, and drawing the plurality of scanning lines on the photosensitive drum, an electrostatic latent image having one narrow pattern is formed. And forming an electrostatic latent image of each narrow pattern of a plurality of narrow pattern.

  According to the present invention, it is possible to detect a toner image of a determination pattern used for determination of color misregistration when a toner image of a pattern of each color is superimposed on a transfer belt with high accuracy and low cost.

1 is a diagram illustrating an outline of an internal structure of a color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. FIG. 6 is a plan view of a toner image of a determination pattern of a first comparative example transferred to a transfer belt. It is a flowchart of an example of the process which detects edge E1, E2 and performs color shift determination. FIG. 4 is a cross-sectional view taken along line II in FIG. 3. It is a top view which shows the relationship between the spot of irradiation light, and the size of the toner image of the pattern for determination. It is a figure which shows the toner image of the pattern for determination of a 1st comparative example, and the toner image of the pattern for determination of a 2nd comparative example. It is a figure which shows the toner image of the pattern for determination of a 1st comparative example, and the toner image of the pattern for determination of a 3rd comparative example. It is a figure which shows the toner image of the pattern for determination of a 1st comparative example, and the toner image of the pattern for determination concerning this embodiment. FIG. 6 is a plan view of a toner image of a determination pattern according to the embodiment transferred to a transfer belt. It is a schematic diagram which shows the state which irradiated the light beam to the light deflection surface of the polygon mirror in this embodiment. It is a block diagram which shows the irradiation control system of the light beam which concerns on this embodiment. It is a flowchart explaining formation of the electrostatic latent image of the pattern for determination. It is a diagram showing a toner image of a determination pattern according to the present embodiment. FIG. 15 is a diagram illustrating determination pattern data for forming a toner image of the determination pattern illustrated in FIG. 14. It is a diagram showing a toner image of a determination pattern according to the present embodiment. FIG. 17 is a diagram showing determination pattern data for forming a toner image of the determination pattern shown in FIG. 16. It is a figure which shows the scanning line SL in which the electrostatic latent image of each narrow pattern was formed. It is a figure which shows the scanning line SL in which the electrostatic latent image of each narrow pattern was formed. It is a flowchart explaining the control which makes the light deflection | deviation surface which irradiates a light beam, and the order to irradiate the same in every color misregistration determination in formation of the electrostatic latent image of each narrow pattern. It is a schematic diagram which shows the state which irradiated the light beam to the light deflection surface of the polygon mirror in this embodiment to which a multi-beam system is applied. It is the figure which looked at four light sources from the light emission surface side of the light beam. It is a diagram showing a toner image of a determination pattern according to the present embodiment. FIG. 24 is a diagram showing determination pattern data for forming a toner image of the determination pattern shown in FIG. 23. It is a diagram showing a toner image of a determination pattern according to the present embodiment. FIG. 26 is a diagram showing determination pattern data for forming a toner image of the determination pattern shown in FIG. 25. It is a figure which shows the scanning line SL in which the electrostatic latent image of each narrow pattern was formed. It is a figure which shows the scanning line SL in which the electrostatic latent image of each narrow pattern was formed. It is a diagram showing a toner image of a determination pattern according to the present embodiment. FIG. 30 is a diagram illustrating determination pattern data for forming a toner image of the determination pattern illustrated in FIG. 29.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of a color image forming apparatus 1 according to an embodiment of the present invention. The color image forming apparatus 1 can be applied to, for example, a digital multifunction machine having a color copy, a color printer, and a color facsimile function. The color image forming apparatus 1 is a tandem system, and includes an apparatus main body 100 and an image reading unit 200 disposed on the apparatus main body 100.

  The image reading unit 200 reads an image (character, figure, photograph, etc.) with a CCD (Charge Coupled Device) or the like and outputs it as image data. The image reading unit 200 has a function of reading a color image. As a result, color copy and color facsimile can be transmitted.

  The apparatus main body 100 includes a sheet storage unit 110, an image forming unit 130, and a fixing unit 160.

  The paper storage unit 110 is disposed at the lowermost part of the apparatus main body 100 and includes a paper tray 111 that can store a bundle of paper P. The paper tray 111 is inserted into the apparatus main body 100 and attached. When the paper P is replenished, the paper tray 111 is pulled out from the apparatus main body 100. In the bundle of sheets P stored in the sheet tray 111, the uppermost sheet P is fed out toward the sheet conveyance path 115 by driving the pickup roller 113. The paper P is transported to the image forming unit 130 through the paper transport path 115.

  The image forming unit 130 forms a toner image on the conveyed paper P. The image forming unit 130 includes a magenta unit 133M, a cyan unit 133C, a yellow unit 133Y, and a black unit 133K, which are arranged in the order in which the toner images are transferred to the transfer belt 131. These units have the same configuration, and a magenta unit 133M will be described as an example.

  The magenta unit 133M includes a photosensitive drum 135 and an exposure device 137. Around the photosensitive drum 135, a charger 139, a developing device 141, and a cleaner 143 are disposed. The charger 139 uniformly charges the peripheral surface of the photosensitive drum 135. The exposure device 137 generates light corresponding to magenta data among image data (image data output from the image reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and uniformly. Irradiate the circumferential surface of the charged photosensitive drum 135. As a result, an electrostatic latent image having a magenta pattern is formed on the peripheral surface of the photosensitive drum 135. In this state, by supplying magenta toner from the developing device 141 to the peripheral surface of the photosensitive drum 135, a toner image having a magenta pattern is formed on the peripheral surface.

  The transfer belt 131 can move clockwise while being sandwiched between the photosensitive drum 135 and the primary transfer roller 145. A toner image having a magenta pattern is transferred from the photosensitive drum 135 to the transfer belt 131. The magenta toner remaining on the peripheral surface of the photosensitive drum 135 is removed by the cleaner 143. The above is the description of the magenta unit 133M.

  Above the magenta unit 133M, the cyan unit 133C, the yellow unit 133Y, and the black unit 133K, containers that store toner of corresponding colors, that is, a magenta toner container 147M, a cyan toner container 147C, and a yellow toner. A container for toner 147Y and a container for black toner 147K are arranged. Each color developing device 141 is supplied with toner from a corresponding container.

  As described above, a toner image having a magenta pattern is transferred to the transfer belt 131, and a toner image having a cyan pattern is transferred on the toner image. Similarly, a toner image having a yellow pattern and a toner having a black pattern are transferred. The image is transferred in layers. As a result, a color toner image is formed on the transfer belt 131. In this way, a color toner image is formed on the transfer belt 131 by transferring the toner image of each color pattern superimposed on the transfer belt 131. The color toner image is transferred by the secondary transfer roller 149 onto the paper P conveyed from the paper storage unit 110 described above.

  The sheet P on which the color toner image is transferred is sent to the fixing unit 160. The fixing unit 160 has a structure in which a fixing belt 165 is hung on a heating roller 161 and a fixing roller 163. The fixing belt 165 is sandwiched between the fixing roller 163 and the pressure roller 167. The paper P onto which the color toner image is transferred is sandwiched between these rollers. Accordingly, heat and pressure are applied to the color toner image and the paper P, and the color toner image is fixed to the paper P. The paper P is discharged to a paper discharge tray 169.

  FIG. 2 is a block diagram showing an electrical configuration of the color image forming apparatus 1 shown in FIG. The color image forming apparatus 1 has a configuration in which an apparatus main body 100, an image reading unit 200, a control unit 300, an operation display unit 400, a communication unit 500, and an optical sensor 11 are connected to each other by a bus. The apparatus main body 100 and the image reading unit 200 have been described with reference to FIG.

  The control unit 300 includes an MPU (Micro Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The MPU performs control necessary for operating the color image forming apparatus 1 on the hardware constituting the color image forming apparatus 1. The ROM stores software necessary for controlling the operation of the color image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (image data output from the image reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  The operation display unit 400 is provided with operation keys including hard keys. Specifically, a function key for switching between a start key, a numeric keypad, a stop key, a reset key, a copy, a printer, a scanner, and a facsimile are provided. The operation display unit 400 is provided with a touch panel. On the screen of the touch panel, various operations and details of operations are displayed and operation keys including soft keys are displayed.

  The communication unit 500 includes a facsimile communication unit 501 and a network I / F unit 503. The facsimile communication unit 501 includes an NCU (Network Control Unit) that controls connection of a telephone line with a destination facsimile and a modulation / demodulation circuit that modulates / demodulates a signal for facsimile communication. The facsimile communication unit 501 is connected to the telephone line 505.

  A network I / F unit 503 is connected to a LAN (Local Area Network) 507. A network I / F unit 503 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 507.

  The optical sensor 11 operates at the time of color misregistration determination, and receives light reflected by irradiating the toner image of the determination pattern for each color transferred to the transfer belt 131 with light.

  The control unit 300 includes functions of a pattern data storage unit 301, a determination pattern detection unit 303, and a threshold setting unit 305. The pattern data storage unit 301 stores in advance determination pattern data for forming a color misregistration determination pattern toner image. The determination pattern detection unit 303 detects the toner image of the determination pattern based on the output from the optical sensor 11. The threshold setting unit 305 sets a threshold used for detecting the toner image of the determination pattern based on the light reflectance of the transfer belt 131.

  As described above, a color toner image is formed on the transfer belt 131 by superimposing and transferring the toner image of each color pattern of magenta, cyan, yellow, and black on the transfer belt 131. In order to prevent color misregistration when the toner images of the respective color patterns are superimposed, the color misregistration is determined using the toner images of the determination patterns for the respective colors.

  As a premise for understanding the toner image of the determination pattern according to the present embodiment, the toner image of the determination pattern of the first to third comparative examples will be described. FIG. 3 is a plan view of the toner image of the determination pattern of the first comparative example transferred to the transfer belt 131. Reference sign D1 indicates the sub-scanning direction, and reference sign D2 indicates the main scanning direction. Reference sign D3 indicates the moving direction of the transfer belt 131, and this direction is along the sub-scanning direction D1.

  As the determination pattern toner images, magenta determination pattern toner images 21M and 23M, cyan determination pattern toner images 21C and 23C, yellow determination pattern toner images 21Y and 23Y, and black determination pattern toner images There are toner images 21K and 23K. If it is not necessary to distinguish the toner images of these color determination patterns, they are simply referred to as determination pattern toner images 21 and 23.

  The toner images 21 and 23 of the determination pattern each have a rectangular shape and have longitudinal edges E1 and E2. The edge E1 is in front of the edge E2 with respect to the moving direction D3 of the transfer belt 131.

  The toner image 21 of the determination pattern extends in the main scanning direction D2. On the other hand, the toner image 23 of the determination pattern extends obliquely with respect to the main scanning direction D2.

  The edges E1 and E2 are used for determining color misregistration. A process for detecting the edges E1 and E2 and determining color misregistration will be described. FIG. 4 shows a flowchart of an example of this process. The edges E1 and E2 are detected using the optical sensor 11 shown in FIG. FIG. 5 is a cross-sectional view taken along the line II in FIG. 3 and shows the positional relationship between the optical sensor 11 and the transfer belt 131. The optical sensor 11 is disposed above the transfer belt 131. The optical sensor 11 includes a light projecting unit 13 and a light receiving unit 15.

  Light (hereinafter referred to as reflected light RL) reflected by the light irradiated from the light projecting unit 13 (hereinafter referred to as irradiated light IL) to the transfer belt 131 passing under the optical sensor 11 is reflected by the light receiving unit 15. Light is received (step S1). The irradiation light IL is applied to an area on the transfer belt 131 where the toner images 21 and 23 of the determination pattern are transferred. The diameter of the spot SP that is irradiated with the irradiation light IL on the transfer belt 131 is, for example, about 3 mm. FIG. 6 is a plan view showing the relationship between the spot SP of the irradiation light IL and the size of the toner images 21 and 23 of the determination pattern. The widths of the toner images 21 and 23 of the determination pattern are made larger than the diameter of the spot SP. Thereby, the reflected light RL having sufficient intensity is obtained.

  The reflected light RL is received by the light receiving unit 15, and a signal SG having a waveform corresponding to the intensity of the reflected light RL is output from the light receiving unit 15 as shown in FIG. 3. A position where the signal SG becomes a predetermined threshold value TH is set as a position of the edges E1 and E2. The threshold value TH is set in advance based on the light reflectance of the transfer belt 131. The optical sensor 11 is used for the measurement of the reflectance.

  When the edges E1 and E2 are not detected (No in step S3), the process of step S3 is repeated. When the edges E1 and E2 are detected (Yes in step S3), the center point CP is calculated (step S5).

  A central position with respect to the edge E1 and the edge E2 is defined as a center point CP. That is, the edges E1 and E2 of the toner images 21 and 23 of the determination pattern are detected using the optical sensor 11, and the center point CP is obtained by calculation from the positions of the edges E1 and E2.

  After obtaining the center point CP, color misregistration is determined (step S7). A time interval at which the center point CP passes under the optical sensor 11 is measured, and color misregistration is determined based on this time interval. When the time interval deviates from a predetermined value, it is determined that the color shift is present. The reason why the determination pattern 23 is provided in addition to the determination pattern 21 is to determine the shift in the main scanning direction D2 of each color. For example, in the case of a magenta pattern toner image, the time interval between the center point CP of the determination pattern toner image 21M and the determination pattern toner image 23M is measured, and the deviation in the main scanning direction D2 is detected. Determined.

  By the way, a high density region may occur in the toner image due to a cause called an edge effect. This will be described with reference to FIG. FIG. 7 is a diagram showing a toner image 21 of the determination pattern of the first comparative example and a toner image 25 of the determination pattern of the second comparative example. The first comparative example is an ideal toner image in which a high density region caused by the edge effect is not generated. On the other hand, the second comparative example is a toner image in which a high density region 27 is generated due to the edge effect. A signal SG for the determination pattern toner image 21 is denoted by reference numeral SG (21), and a signal SG for the determination pattern toner image 25 is denoted by reference numeral SG (25). The spot SP of the irradiation light IL is described in order to compare the size of the spot SP with the toner images 21 and 25 of the determination pattern.

  In the sub-scanning direction D1, a high density area 27 caused by the edge effect is generated in the front end area of the toner image 25 of the determination pattern. The edge effect is caused by a difference in rotational speed between a roller (such as a magnet roller) in the developing device 141 and the photosensitive drum 135 in FIG. Due to the edge effect, a high density region 27 is generated in the front end region and / or the rear end region in the sub-scanning direction D1.

  In order to increase the accuracy of detecting the edges E1 and E2, the toner image of the determination pattern is filled with the same color. For this reason, the high density region 27 caused by the edge effect is likely to occur. Since the rotational speed difference is related to the printing system of the color image forming apparatus 1, it is difficult to eliminate the rotational speed difference. Therefore, the high density region 27 caused by the edge effect is inevitably generated.

  The waveform of the signal SG (21) is symmetrical with respect to the center point CP. On the other hand, the waveform of the signal SG (25) is asymmetrical, and the signal SG (25) is stronger on the edge E1 side than the center point CP. This is because the intensity of the reflected light RL is higher in the high concentration region 27 than in other regions. Since the signal SG (25) becomes stronger on the edge E1 side than the center point CP, the edge E1 is detected with a deviation from the original position. As a result, the center point CP of the toner image 25 of the determination pattern becomes a value deviated from the original value.

  The width of the high concentration region 27 due to the edge effect is about 0.5 to 1.0 mm. Accordingly, if the width of the toner image of the determination pattern is set to 0.5 to 1.0 mm, the toner image of the determination pattern is composed only of the high density region 27. Therefore, the toner image of the determination pattern includes the high density region. 27 and other areas do not occur. A toner image of a determination pattern having a width of 0.5 to 1.0 mm will be described as a third comparative example with reference to FIG.

  FIG. 8 is a view showing a toner image 21 of the determination pattern of the first comparative example and a toner image 29 of the determination pattern of the third comparative example. A signal SG for the toner image 29 of the determination pattern is indicated by reference numeral SG (29). Since the toner image 29 of the determination pattern is composed of only the high density region 27, the signal SG (29) is symmetrical. Since the toner image 29 of the determination pattern has a uniform density, it seems that the edges E1 and E2 can be detected correctly.

  However, since the width of the toner image 29 of the determination pattern is smaller than the diameter of the spot SP of the irradiation light IL, the reflected light RL having sufficient intensity cannot be obtained. For this reason, since the level of the signal SG (29) decreases, the signal SG (29) does not exceed the threshold value TH. Even if the signal SG (29) exceeds the threshold value TH, the inclination of the waveform is small, so that an error occurs in the determination that the signal SG (29) exceeds the threshold value TH. Therefore, the accuracy of detecting the edges E1 and E2 decreases.

  If the diameter of the spot SP is made smaller than the width of the toner image 29 of the determination pattern, the reflected light RL having sufficient intensity can be obtained even for the toner image 29 of the determination pattern. It can be detected accurately. However, since the sensor that can control the diameter of the spot SP to be small is expensive, the cost of the color image forming apparatus 1 increases.

  The toner image of the determination pattern according to the present embodiment is a toner image having a discontinuous pattern in the sub-scanning direction D1, and the toner image 29 of the determination pattern of the third comparative example is constant along the sub-scanning direction D1. It has the structure arranged at intervals. FIG. 9 is a view showing the toner image 21 of the determination pattern of the first comparative example and the toner image 31 of the determination pattern according to the present embodiment. A signal SG for the toner image 31 of the determination pattern is indicated by reference numeral SG (31).

  The determination pattern toner image 31 includes a plurality of narrow-width pattern toner images 35 extending in the same direction as the toner image. The width of the toner image 35 having the narrow pattern is smaller than the width of the toner image 31 having the determination pattern. The width of the narrow-width pattern toner image 35, in other words, the dimension in the sub-scanning direction D1, is smaller than the diameter of the spot SP of the irradiation light IL. The toner images 35 having a plurality of narrow patterns are periodically arranged in the sub-scanning direction D1 at intervals smaller than the diameter of the spot SP.

  The narrow-width pattern toner image 35 is filled with the same color. The width dimension of the narrow-width pattern toner image 35 is 0.5 to 1.0 mm. As a result, even when the high density region 27 caused by the edge effect occurs, the toner image 35 of the narrow pattern is configured only by the high density region 27. Accordingly, it is possible to prevent the high density region 27 and other regions from being formed in the toner image 35 having a narrow width pattern.

  The signal SG (31) for the determination pattern toner image 31 is smaller than that of the determination pattern toner image 21, but the two or more narrow pattern toner images 35 are located in the spot SP. A decrease in the level of (31) can be prevented. Since the toner image 31 of the determination pattern has a configuration in which the toner image 35 of the narrow pattern and the pattern of the base (transfer belt 131) are alternately arranged, the light reflected by the toner image 31 of the determination pattern is averaged. Is done. Thus, the waveform of the signal SG (21) can be made symmetrical with respect to the center point CP. The accuracy of detecting the edges E1 and E2 can be increased by being able to make this left-right symmetric and preventing the level of the signal SG (31) from being lowered.

  FIG. 10 is a plan view of the toner image of the determination pattern according to the present embodiment transferred to the transfer belt 131, and corresponds to FIG. As the determination pattern toner images according to the present embodiment, magenta determination pattern toner images 31M and 33M, cyan determination pattern toner images 31C and 33C, yellow determination pattern toner images 31Y and 33Y, and black. There are toner images 31K and 33K of the determination pattern. If it is not necessary to distinguish the toner images of these color determination patterns, they are simply referred to as determination pattern toner images 31 and 33.

  The determination pattern toner images 31 and 33 each include a plurality of narrow width toner images 35. The toner images 35 having a plurality of narrow patterns extend in the main scanning direction D2. The toner images 31 and 33 of the determination pattern each have a rectangular shape and have longitudinal edges E1 and E2. The toner image 31 of the determination pattern extends in the main scanning direction D2. On the other hand, the toner image 33 of the determination pattern extends obliquely with respect to the main scanning direction D2.

  The magenta determination pattern toner images 31M and 33M are formed by the magenta unit 133M in FIG. 1, and the cyan determination pattern toner images 31C and 33C are formed by the cyan unit 133C and the yellow determination pattern toner. The images 31Y and 33Y are formed by the yellow unit 133Y, and the toner images 31K and 33K of the black determination pattern are formed by the black unit 133K. The determination pattern toner images 31 and 33 are transferred in the order of magenta, cyan, yellow, and black at a predetermined interval along the sub-scanning direction D1.

  The formation of the determination pattern toner images 31 and 33 will be briefly described. The determination pattern data for each color, which is the basis of the determination pattern toner images 31 and 33, is stored in advance in the pattern data storage unit 301 shown in FIG. At the time of color misregistration determination, an electrostatic latent image of a corresponding color determination pattern is formed on each color photosensitive drum 135. Each color developing device 141 develops the electrostatic latent image of the corresponding color determination pattern to form a toner image. The toner images 31 and 33 of the determination patterns for the respective colors developed by the respective color developing devices 141 are transferred to the transfer belt 131.

  As described above, the determination pattern toner images 31 and 33 according to the present embodiment are formed based on the determination pattern data of each color stored in advance in the pattern data storage unit 301. The determination pattern toner images 31 and 33 are constituted by a plurality of narrow width toner images 35. The narrow-width pattern toner images 35 are periodically arranged along the sub-scanning direction D1 at a distance smaller than the diameter of the spot SP of the irradiation light IL and smaller than the diameter of the spot SP. Yes. Therefore, since the toner images 35 having two or more narrow patterns can be positioned in the spot SP, it is possible to prevent a decrease in the level of the signal output from the optical sensor 11 even if the spot SP has a large diameter.

  Further, since the toner images 31 and 33 of the determination pattern are configured by alternately arranging the toner image 35 of the narrow pattern and the pattern of the base (transfer belt 131), they are reflected by the toner images 31 and 33 of the determination pattern. The light is averaged. Thereby, the waveform of the signal SG output from the optical sensor 11 can be made symmetrical with respect to the center point CP.

  Therefore, according to the present embodiment, the edge E1, E2 of the determination pattern toner images 31, 33 used for the determination in the determination of color misregistration when the toner image of each color pattern is superimposed on the transfer belt 131 is set to be high. It can be detected with accuracy and at low cost.

  The toner images 35 having a plurality of narrow patterns may be arranged at intervals smaller than the diameter of the spot SP, and may not be arranged periodically.

  The number of toner images 35 having a plurality of narrow patterns may be two or more.

  The determination pattern toner images 31 and 33 are formed by arranging a plurality of narrow pattern toner images 35 at regular intervals along the sub-scanning direction D1. It can be said that the magenta (cyan, yellow) pattern and the background (transfer belt 131) color pattern are alternately arranged along the sub-scanning direction D1. The present invention is not limited to this, and a configuration in which a toner image 35 having a narrow pattern having a high density and a toner image 35 having a narrow pattern having a low density are alternately arranged along the sub-scanning direction D1 may be employed.

  In this embodiment, the light beam modulated by the determination pattern data is irradiated onto the light deflection surface of the polygon mirror, deflected by the light deflection surface, and a scanning line is drawn in the main scanning direction D2, so that the photosensitive drum 135 is irradiated. An electrostatic latent image of the determination pattern is formed. A light beam irradiation control system for forming the electrostatic latent image will be described with reference to FIGS. FIG. 11 is a schematic diagram showing a state in which the light deflection surface 43 of the polygon mirror 41 is irradiated with the light beam LB in the present embodiment. FIG. 12 is a block diagram showing a light beam irradiation control system 45 according to the present embodiment. The irradiation control system 45 is provided corresponding to each color. The optical components such as the collimator lens and the fθ lens are not shown. The irradiation control system 45 includes a polygon mirror 41, a light beam generation unit 47, and the like.

  The light beam generation unit 47 includes a light source 49 that emits the light beam LB, a drive circuit that drives the light source 49, and the like. For example, a semiconductor laser is used as the light source 49. Corresponding color image data (in other words, corresponding color pattern data) among the image data to be printed during normal operation is sent to the light beam generation unit 47. At the time of color misregistration determination, determination pattern data is sent to the light beam generation unit 47. The determination pattern data is stored in advance in the pattern data storage unit 301.

  The light source 49 emits a light beam LB modulated by data of a corresponding color pattern during normal operation, and the light beam LB modulated by data of a determination pattern stored in the pattern data storage unit 301 at the time of color misregistration determination. Is emitted.

  The polygon mirror 41 is rotated in the rotation direction R about the rotation shaft 53 by the motor 51. The polygon mirror 41 has a regular hexagonal side surface. This side surface is constituted by six light deflecting surfaces 43-1 to 43-6. The optical deflection surface 43-1, the optical deflection surface 43-3, the optical deflection surface 43-4, the optical deflection surface 43-5, and the optical deflection surface 43-6 along the rotation direction R with respect to the optical deflection surface 43-1. Is located. The light deflection surfaces 43-1 to 43-6 are referred to as the light deflection surface 43 if they need not be distinguished, and are referred to as the light deflection surfaces 43-1 to 43-6 if they need to be distinguished.

  Here, formation of the electrostatic latent image of the determination pattern will be described with reference to the flowchart shown in FIG. The polygon mirror 41 is rotated by the motor 51 (step S1). The light source 49 emits the light beam LB modulated by the determination pattern data (step S3). The light beam LB is applied to the rotating light deflection surface 43 and deflected by the light deflection surface 43 to draw a scanning line SL on the photosensitive drum 135 in the main scanning direction D2. One scanning line SL is drawn by one light deflection surface 43. By repeating drawing of one scanning line SL on the rotating photosensitive drum 135, an electrostatic latent image of a determination pattern is formed along the sub-scanning direction D1 (step S5). The sub-scanning direction D1 corresponds to the rotation direction of the photosensitive drum 135.

  Returning to the explanation of the irradiation control system 45. In the present embodiment, a predetermined rotational position of the light deflection surface 43 among the six light deflection surfaces 43 can be detected. This predetermined light deflection surface 43 is indicated by a mark 55. The cylindrical member 57 on which the mark 55 is arranged is fixed to the rotation shaft 53 coaxially with the rotation shaft 53 of the polygon mirror 41. As a result, the cylindrical member 57 rotates together with the polygon mirror 41, so that the mark 55 rotates together with the predetermined light deflection surface 43. In the present embodiment, since the mark 55 is arranged under the light deflection surface 43-1, the light deflection surface 43-1 corresponds to a predetermined light deflection surface 43 among the six light deflection surfaces 43. . By detecting the mark 55, the rotational position of the light deflection surface 43-1 is detected.

  The mark 55 is detected by the rotational position detector 59. In this embodiment, an optical sensor is used as the rotational position detector 59. The light reflectance of the mark 55 is different from the light reflectance of the cylindrical member 57. Thereby, the mark 55 can be detected by the rotational position detector 59. As the rotational position detection unit 59, a sensor other than the optical sensor (for example, a magnetic sensor), an encoder, or the like can be used.

  The irradiation control unit 61 controls the timing of irradiating the light deflection surface 43 with the light beam LB based on the rotation position of the light deflection surface 43-1 detected by the rotation position detection unit 59. The above is the description of the irradiation control system 45 of the light beam LB according to the present embodiment.

  In the present embodiment, as shown in FIG. 9, the toner image 31 of one determination pattern is composed of a plurality of narrow-width pattern toner images 35. Therefore, the electrostatic latent image of one determination pattern is constituted by a plurality of electrostatic latent images of narrow patterns. In this embodiment, the light deflection surface 43 that irradiates the light beam LB is the same in forming the electrostatic latent image of each narrow pattern. As an assumption for understanding this, an example in which the light deflection surfaces 43 that irradiate the light beam LB are not the same will be described with reference to FIGS. FIG. 14 shows a toner image 31 of a determination pattern according to this embodiment. The determination pattern toner image 31 includes six narrow-width toner images 35.

  The toner image 35 of each narrow pattern is composed of four lines 63. One line 63 corresponds to a part of one scanning line SL shown in FIG. In FIG. 14, four lines 63 are displayed at intervals, but the intervals cannot be recognized with the naked eye. Accordingly, the toner image 35 having a narrow pattern appears as one line. Between the adjacent narrow-width toner images 35, there is a blank portion 65 corresponding to four lines.

  FIG. 15 shows determination pattern data for forming the determination pattern toner image 31 shown in FIG. The six light deflection surfaces 43 are formed in order along the rotation direction R as a first light deflection surface 43, a second light deflection surface 43,..., A sixth light deflection surface 43. For example, if the light deflection surface 43-5 is first irradiated with the light beam LB among the six light deflection surfaces 43, the first light deflection surface 43 is the light deflection surface 43-5, the second light. The deflection surface 43 is the light deflection surface 43-6, the third light deflection surface 43 is the light deflection surface 43-1, the fourth light deflection surface 43 is the light deflection surface 43-2, and the fifth light deflection surface 43 is the light. The deflection surface 43-3 and the sixth light deflection surface 43 become the light deflection surface 43-4.

  ON-OFF on the vertical axis indicates ON or OFF of the light source 49. If the light source 49 is ON, the light source 49 emits the light beam LB, and the light deflection surface 43 is irradiated with the light beam LB during the ON period. If the light source 49 is OFF, the light source 49 does not emit the light beam LB. Therefore, the light deflection surface 43 is not irradiated with the light beam LB during the OFF period. The 1st, 2nd,..., 8th rotation of the vertical axis represents the first rotation of the polygon mirror 41, the 2nd rotation,.

  In drawing one scanning line SL, a portion drawn during the ON period corresponds to one line 63. data1 is data for forming an electrostatic latent image corresponding to the toner image 35 of one narrow pattern, that is, an electrostatic latent image of one narrow pattern. On the other hand, data2 is data for forming an electrostatic latent image corresponding to one blank portion 65, that is, an electrostatic latent image between the electrostatic latent images of the narrow pattern.

  In forming an electrostatic latent image of each narrow pattern, (1) a light beam is applied to the first light deflection surface 43, the second light deflection surface 43, the third light deflection surface 43, and the fourth light deflection surface 43. When LB is irradiated, (2) When the third light deflection surface 43, the fourth light deflection surface 43, the fifth light deflection surface 43, and the sixth light deflection surface 43 are irradiated with the light beam LB. (3) There are three cases where the light beam LB is irradiated on the fifth light deflection surface 43, the sixth light deflection surface 43, the first light deflection surface 43, and the second light deflection surface 43.

  Therefore, in the toner image 31 of the determination pattern shown in FIG. 14, the light deflection surface 43 that irradiates the light beam in forming the electrostatic latent image of each narrow pattern is not the same. Since each light deflection surface 43 inevitably has a difference in light reflectance and surface tilt amount, the optical conditions of each light deflection surface 43 are not exactly the same. For this reason, the toner image 35 of each narrow pattern shown in FIG. 14 may be uneven in density, reflectance, and the like.

  On the other hand, an example in which the light deflection surface 43 for irradiating the light beam is the same will be described with reference to FIGS. FIG. 16 shows the toner image 31 of the determination pattern according to the present embodiment. The toner image 35 of each narrow pattern is composed of six lines 63. The blank portion 65 corresponds to six lines. These points are different from the toner image 31 of the determination pattern shown in FIG. FIG. 17 is a diagram corresponding to FIG. 15 with respect to the toner image 31 of the determination pattern shown in FIG.

  In the toner image 31 of the determination pattern shown in FIG. 16, in the formation of the electrostatic latent image of each narrow pattern, the first light deflection surface 43, the second light deflection surface 43, the third light deflection surface 43, There is only one of the cases where the fourth light deflection surface 43, the fifth light deflection surface 43, and the sixth light deflection surface 43 are irradiated with the light beam LB. Therefore, the light deflection surface 43 that irradiates the light beam LB is the same in forming the electrostatic latent image of each narrow pattern. Therefore, even if there is a difference in the optical conditions of each light deflection surface 43 of the polygon mirror 41, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform. In this way, since the electrostatic latent image of the determination pattern is formed in consideration of the difference in optical conditions, the accuracy of color misregistration determination can be improved.

  Furthermore, according to the determination pattern data shown in FIG. 17, the order of the light deflection surfaces 43 that irradiate the light beam can be made the same in forming the electrostatic latent image of each narrow pattern. This will be described with reference to FIGS. 18 and 19 are diagrams showing scanning lines SL on which electrostatic latent images having narrow patterns are formed. The scanning line SL shown in FIG. 18 is based on the determination pattern data shown in FIG. The scanning line SL shown in FIG. 19 is based on the determination pattern data corresponding to the five lines 63 having the blank portion 65 shown in FIG.

  In FIG. 18, the order of the light deflection surfaces 43 used for forming the electrostatic latent image of each narrow pattern as viewed from the order of the scanning line SL in which the electrostatic latent image of each narrow pattern is formed in the sub-scanning direction D <b> 1. Of the first light deflection surface 43, the second light deflection surface 43, the third light deflection surface 43, the fourth light deflection surface 43, the fifth light deflection surface 43, and the sixth light deflection surface 43. Only if. On the other hand, in FIG. 19, in addition to the above case, the sixth light deflection surface 43, the first light deflection surface 43, the second light deflection surface 43, the third light deflection surface 43, the fourth light deflection surface 43, For example, the optical deflection surface 43 and the fifth optical deflection surface 43 may be used.

  As described above, according to the determination pattern data shown in FIG. 17, the order of the light deflection surfaces 43 to which the light beams are irradiated can be made the same in forming the electrostatic latent image of each narrow pattern. The conditions for forming the electrostatic latent image of the width pattern can be made uniform. Therefore, the accuracy of color misregistration determination can be improved.

  In the formation of the electrostatic latent image of each narrow pattern, the light deflection surface 43 that irradiates the light beam LB and the data in which the irradiation order is the same are not limited to the data shown in FIG. Number of light deflection surfaces 43 used when forming electrostatic latent images of each narrow pattern (corresponding to data1), and used when forming electrostatic latent images between electrostatic latent images of narrow patterns The number of light deflection surfaces 43 to be used (corresponding to data2) may be an integer multiple of 6. For example, 12 light deflecting surfaces 43 are used for forming the electrostatic latent image of each narrow pattern, and 6 light deflections are used for forming the electrostatic latent image between the electrostatic latent images of the narrow pattern. Surface 43 is used. The number of light deflecting surfaces 43 used for forming the electrostatic latent image of each narrow pattern is not limited to an integral multiple of 6, for example, five electrostatic deflection images between the electrostatic latent images of the narrow pattern. The number of the light deflection surfaces 43 used when forming the latent image may be seven.

  “6”, which is an integral multiple of 6, corresponds to the number of light deflection surfaces 43 constituting the polygon mirror 41. Therefore, for example, if the number of the light deflection surfaces 43 constituting the polygon mirror 41 is eight, it becomes an integer multiple of eight.

  In the light deflection surface 43 that irradiates the light beam LB and the control that makes the irradiation order the same as described above, the reference light deflection surface 43 is not determined. For this reason, there is a possibility that the light deflection surface 43 that irradiates the light beam LB and the order in which the light beam LB is irradiated may be different at each color misregistration determination. For example, in the previous color misregistration determination, the light deflection surface 43 that irradiates the light beam and the irradiation order are the light deflection surface 43-1, the light deflection surface 43-2, the light deflection surface 43-3, and the light deflection surface 43-4. The optical deflection surface 43-5 and the optical deflection surface 43-6. However, in this color misregistration determination, the light deflection surface 43-4, the light deflection surface 43-5, the light deflection surface 43-6, the light deflection surface 43-1, the light deflection surface 43-2, and the light deflection surface 43-3 There is a case. In order to improve the accuracy of color misregistration determination, it is preferable that the light deflection surface 43 that irradiates the light beam LB and the irradiation order be the same in each color misregistration determination.

  Therefore, in the present embodiment, a predetermined rotational position of the light deflection surface 43 (light deflection surface 43-1) can be detected by the rotation position detector 59 of FIG. In the formation of the electrostatic latent image of each narrow pattern, the light deflection surface 43 that irradiates the light beam LB and the irradiation order of the detected light deflection surface 43-1 are the same in each color misregistration determination. The timing of irradiating the light deflection surface 43 with the light beam LB is controlled based on the rotation position. FIG. 20 is a flowchart for explaining this control.

  First, the polygon mirror 41 is rotated in the rotation direction R by the motor 51 (step S11). The mark 55 indicates the light deflection surface 43-1 and rotates together with the light deflection surface 43-1. The rotational position detector 59 performs an operation of detecting the mark 55, that is, an operation of detecting a predetermined rotational position of the light deflection surface 43 (step S13). If the mark 55 cannot be detected (No in step S13), the operation in step S13 is repeated.

  When the rotational position detector 59 can detect the mark 55 (Yes in step S13), the light deflection surface 43 that is first irradiated with the light beam LB is controlled by controlling the timing of irradiation with the light beam LB. 43-1 (step S15). As a result, in each color misregistration determination, the first light deflection surface 43 can be changed to the light deflection surface 43-1, so that the light deflection surface 43 that irradiates the light beam LB and the order in which the light is deflected can be changed each time. It can be made the same by judgment.

  By irradiating the light deflection surface 43-1 with the light beam LB, formation of the electrostatic latent image having the first narrow pattern is started. By forming an electrostatic latent image of each narrow pattern, an electrostatic latent image of a determination pattern is formed (step S17).

  As described above, according to the control shown in FIG. 20, in the formation of the electrostatic latent image of each narrow pattern, the light deflection surface 43 that irradiates the light beam and the irradiation order are made the same in each color misregistration determination. be able to. Therefore, the accuracy of color misregistration determination can be improved.

  Up to this point, the light source 49 that emits the light beam LB has been described as an example. This embodiment can also be applied to a multi-beam method using a plurality of light sources 49. FIG. 21 is a schematic diagram showing a state in which the light beams LB-1 to LB-4 are irradiated on the light deflection surface 43 of the polygon mirror 41 in the present embodiment to which the multi-beam method is applied, and corresponds to FIG. The difference from FIG. 11 is that four light sources 49-1 to 49-4 are provided, and four light beams LB-1 to LB-4 are irradiated to the respective light deflection surfaces 43. FIG. 22 is a view of the light sources 49-1 to 49-4 as viewed from the light emitting surface side of the light beams LB-1 to LB-4.

  The light beams LB-1, LB-2, LB-3, and LB-4 respectively emitted from the light sources 49-1, 49-2, 49-3, and 49-4 are irradiated on the same light deflecting surface 43 to each light. The deflection surface 43 is irradiated. The four light beams LB-1 to LB-4 are in the order of the light beams LB-1, LB-2, LB-3, and LB-4 in the sub-scanning direction D1 (corresponding to the rotation direction of the photosensitive drum 135 in FIG. 21). And the scanning lines SL are drawn in the main scanning direction D2.

  In the present embodiment to which the multi-beam method is applied, the same light source is used for forming the electrostatic latent image of each narrow pattern. As an assumption for understanding this, an example in which the above is not the same will be described with reference to FIGS.

  FIG. 23 shows the toner image 31 of the determination pattern according to the present embodiment. The toner image 35 of each narrow pattern is composed of three lines 63. The blank portion 65 corresponds to three lines 63. These points are different from the toner image 31 of the determination pattern shown in FIG. FIG. 24 is a view corresponding to FIG. 15 with respect to the toner image 31 of the determination pattern shown in FIG.

  In the multi-beam method, a plurality of scanning lines SL (four scanning lines in the present embodiment) can be drawn in the main scanning direction D1 with one light deflection surface 43. data1 is data for forming an electrostatic latent image of one narrow pattern. data2 is data for forming an electrostatic latent image between the electrostatic latent images of narrow patterns.

  The light sources used for forming the electrostatic latent image of each narrow pattern are (1) the light source 49-1, the light source 49-2, and the light source 49-3; and (2) the light source 49-3, the light source 49-4, There is a case of the light source 49-1. Therefore, in the toner image 31 of the determination pattern shown in FIG. 23, the light source used for forming the electrostatic latent image of each narrow pattern is not the same. Since the light sources 49-1 to 49-4 inevitably have different optical axis directions and wavelengths, the optical conditions of the light sources 49-1 to 49-4 are not exactly the same. For this reason, the toner image 35 of each narrow pattern shown in FIG. 23 may be uneven in density, reflectance, and the like.

  On the other hand, an example in which the same light source is used for forming the electrostatic latent image of each narrow pattern will be described with reference to FIGS. FIG. 25 shows the toner image 31 of the determination pattern according to the present embodiment. The toner image 35 of each narrow pattern is composed of four lines 63. The blank portion 65 corresponds to four lines 63. FIG. 26 is a diagram corresponding to FIG. 15 with respect to the toner image 31 of the determination pattern shown in FIG.

  In the toner image 31 of the determination pattern shown in FIG. 25, when the light source used for forming the electrostatic latent image of each narrow pattern is the light source 49-1, the light source 49-2, the light source 49-3, and the light source 49-4. There is only. Therefore, even if there is a difference in the optical conditions of each light source, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform. As described above, since the electrostatic latent image of the determination pattern is formed in consideration of the difference in the optical conditions, the accuracy of the color misregistration determination can be improved.

  Further, according to the determination pattern data shown in FIG. 26, the following effects are obtained. 27 and 28 are diagrams showing scanning lines SL on which electrostatic latent images of respective narrow patterns are drawn. The scanning line SL shown in FIG. 27 is based on the determination pattern data shown in FIG. The scanning line SL shown in FIG. 28 uses the same light source for forming the electrostatic latent image of each narrow pattern, but the blank portion 65 is based on the pattern data for determination corresponding to three lines 63. Yes.

  In FIG. 27, the order of the light sources used for forming the electrostatic latent images of the respective narrow width patterns as viewed from the order of the scanning lines SL in which the electrostatic latent images of the respective narrow width patterns are formed is the light source 49. -1, light source 49-2, light source 49-3, and light source 49-4 only. On the other hand, in FIG. 28, there are cases of the light source 49-4, the light source 49-1, the light source 49-2, the light source 49-3, etc. in addition to the above case.

  As described above, according to the determination pattern data shown in FIG. 26, in the formation of the electrostatic latent image of each narrow pattern, the order of the scanning lines SL in which the electrostatic latent image of the narrow pattern is formed in the sub-scanning direction D1. Accordingly, the order of the light sources used for forming the electrostatic latent image having the narrow pattern can be made the same. Thereby, the conditions for forming the electrostatic latent image of each narrow pattern can be made uniform, so that the accuracy of the color misregistration determination can be improved.

  Note that the data used in forming the electrostatic latent image of each narrow pattern is the same and the data in the same order is not limited to the data shown in FIG. For example, the case shown in FIGS. 29 and 30 may be used. FIG. 29 shows the toner image 31 of the determination pattern according to the present embodiment. The toner image 35 of each narrow pattern is composed of three lines 63. The blank portion 65 corresponds to five lines 63. FIG. 30 is a diagram corresponding to FIG. 15 with respect to the toner image 31 of the determination pattern shown in FIG.

  In the data shown in FIG. 30, light sources 49-1, 49-2, and 49-3 are used as the light sources used to form the electrostatic latent images of the narrow patterns. An electrostatic latent image of one narrow pattern is formed by data1. An electrostatic latent image between the electrostatic latent images of the narrow pattern is formed by data2. According to the data shown in FIG. 30, the number of light sources used for forming the electrostatic latent image having a narrow pattern can be reduced, so that a circuit (such as a drive circuit for driving the light source) used for forming the electrostatic latent image having the determination pattern is used. Can be reduced.

  Finally, the overall configuration of the color image forming apparatus 1 according to the present embodiment will be supplemented with reference to FIGS. 1 and 2. The color image forming apparatus 1 has a function of forming a color toner image by superimposing a toner image of each color pattern, and the color misregistration when the toner image of each color pattern is superimposed is determined. It has a function of making a determination using the images 31 and 33. The color image forming apparatus 1 includes a plurality of exposure devices 137, a plurality of photosensitive drums 135, a plurality of developing devices 141, and a transfer belt 131.

  The plurality of exposure apparatuses 137 include a light source 49 and a polygon mirror 41. The light source 49 emits a light beam LB modulated by the corresponding color pattern data during normal operation, and the light beam modulated by the determination pattern data stored in the pattern data storage unit 301 at the time of color misregistration determination. Emits light. The polygon mirror 41 is irradiated with the light beam LB emitted from the light source 49 and has a plurality of light deflection surfaces 43 that deflect the irradiated light beam LB.

  The plurality of photosensitive drums 135 are provided corresponding to the respective colors and arranged in tandem. On the plurality of photosensitive drums 135, by drawing the scanning line SL with the light beam LB deflected by the polygon mirror 41, an electrostatic latent image having a corresponding color pattern is formed in the normal operation, and the color misregistration is determined. An electrostatic latent image of the determination pattern of the color to be formed is formed.

  The plurality of developing devices 141 develop the electrostatic latent image of the corresponding color pattern during normal operation to form a toner image, and develop the electrostatic latent image of the corresponding determination pattern for the corresponding color during color misregistration determination. To form a toner image.

  The transfer belt 131 is transferred by superimposing and transferring a toner image of each color pattern developed by the plurality of developing devices 141 during normal operation, and when determining color misregistration, the toner of the determination pattern for each color developed by the plurality of developing devices 141. Images 31 and 33 are transferred.

  In this embodiment, the case where the color image forming apparatus 1 has a plurality of photosensitive drums 135 has been described. However, the present invention can also be applied to a color image forming apparatus having one photosensitive drum. In this case, an electrostatic latent image of each color pattern is formed on one photosensitive drum during normal operation, and each color determination based on determination pattern data stored in the pattern data storage unit 301 at the time of color misregistration determination. An electrostatic latent image of the pattern for use is formed.

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 11 Optical sensor 31 Toner image 33 of judgment pattern Toner image 35 of judgment pattern Toner image 41 of narrow pattern Polygon mirror 43 (43-1 to 43-6) Light deflection surface 49 (49-1) 49-4) Light source 55 Mark 59 Rotation position detection unit 61 Irradiation control unit 63 Line 65 Blank portion 131 Transfer belt 135 Photosensitive drum 137 Exposure device 141 Development device 301 Pattern data storage unit 303 Determination pattern detection unit D1 Sub-scanning direction D2 Main scanning direction D3 Movement direction of transfer belt IL Light irradiated from optical sensor (irradiated light)
RL Reflected light SP Spot E1 of irradiated light Edge E2 of determination pattern toner image Edge CP of determination pattern toner image CP Center point TH Threshold SG Signal LB (LB-1 to LB-4) Light beam R Rotation direction SL Scanning line

Claims (3)

It has a function to form a color toner image by superimposing the toner images of each color pattern, and determines the color shift when superimposing the toner images of the respective color patterns using the toner image of the judgment pattern for each color. A color image forming apparatus having a function of:
An optical sensor that operates at the time of color misregistration determination and receives light reflected by irradiating the toner image of the determination pattern of each color with light;
The determination pattern toner image has a plurality of narrow patterns whose dimensions in the sub-scanning direction are smaller than the diameter of the spot of the light emitted from the photosensor and are narrower than the determination pattern toner image. Are arranged in the sub-scanning direction at intervals smaller than the spot diameter, and the determination pattern data for forming the determination pattern toner image is stored in advance. A stored pattern data storage unit;
During normal operation, a light beam modulated by the corresponding color pattern data is emitted, and when the color misregistration is determined, the light beam modulated by the determination pattern data stored in the pattern data storage unit is emitted. A plurality of exposure apparatuses including: a light source; and a polygon mirror having a plurality of light deflection surfaces that are irradiated with the light beam emitted from the light source and deflect the irradiated light beam;
By drawing a scanning line with a light beam deflected by the polygon mirror, an electrostatic latent image of each color pattern is formed during the normal operation, and an electrostatic latent image of the determination pattern for each color is determined during the color shift determination. A photosensitive drum on which is formed,
During the normal operation, the electrostatic latent image of the corresponding color pattern is developed to form a toner image on the photosensitive drum, and when the color misregistration is determined, the electrostatic latent image of the corresponding pattern for the determination is developed. A plurality of developing devices for forming a toner image on the photosensitive drum;
During the normal operation, the toner images of the patterns of the respective colors developed by the plurality of developing devices are superimposed and transferred, and at the time of the color misregistration determination, the toner images of the determination patterns of the respective colors developed by the plurality of developing devices are transferred. A transfer belt to be transferred;
Based on the signal output from the optical sensor, the optical sensor irradiates light to the toner image of the determination pattern of each color transferred to the transfer belt and receives the reflected light. A determination pattern detection unit that detects a toner image of the determination pattern,
There are a plurality of light sources provided in each of the plurality of exposure apparatuses, and a plurality of light beams that are arranged in the sub-scanning direction and draw a scanning line in the main scanning direction are emitted by the plurality of light sources,
The data of the determination pattern stored in the pattern data storage unit is drawn by selecting each of the plurality of light sources in the plurality of narrow patterns constituting the determination pattern. is composed of a plurality of scan lines, and viewing contains a data combination of said plurality of light sources to be used for drawing the narrow patterns are the same,
One light deflection surface of the plurality of light deflection surfaces is irradiated with the plurality of light beams generated by the plurality of light sources, and the plurality of scanning lines are drawn on the photosensitive drum to form one narrow pattern. A color image forming apparatus , wherein an electrostatic latent image of each of the plurality of narrow patterns is formed by forming an electrostatic latent image .   The data of the determination pattern stored in the pattern data storage unit is the electrostatic latent of each narrow pattern as viewed from the order in the sub-scanning direction of the scanning line on which the electrostatic latent image of each narrow pattern is formed. The color image forming apparatus according to claim 1, comprising data in which the order of the light sources used for forming the image is the same. A rotational position detector for detecting a rotational position of a predetermined light deflection surface among the plurality of light deflection surfaces;
In the formation of the electrostatic latent image of each narrow pattern, the rotational position of the light deflection surface detected by the rotational position detection unit is set so that the light deflection surface irradiated with the light beam becomes the same at every color misregistration determination. The color image forming apparatus according to claim 1, further comprising: an irradiation control unit that controls a timing of irradiating the light deflection surface with the light beam based on the light source.

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