JP2017151288A - Image forming apparatus, image forming apparatus control method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for shortening the time required for formation and detection of a mark for density correction in an image formation apparatus performing density correction.SOLUTION: A printer 100 includes: a left sensor 21 which has a regular reflection light reception element and a diffuse reflection light reception element; and a right sensor 22 which has only the regular reflection light reception element and has no diffuse reflection light reception element. The printer 100 forms a mark 28 for density correction in accordance with satisfaction of an execution condition of density correction. The printer 100 forms marks 28Y, 28M, 28C in colors other than black at a position including a detection range of the left sensor 21 as the mark 28 for density correction and forms a black mark 28K at a position including a detection range of the right sensor 22. The printer 100 forms the black mark 28K at a position where at least partial coordinates in the conveyance direction on a conveyor belt 7 is the same as coordinates of the marks 28Y, 28M, 28C in other colors.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus for forming a toner image, a control method for the image forming apparatus, and a program. More specifically, the present invention relates to a density correction technique performed by the image forming apparatus.

  In an image forming apparatus that forms a toner image, a technique for performing density correction is known. As a density correction procedure, the image forming apparatus forms, for example, a density correction mark on the conveyance belt prior to formation of a toner image to be printed. Then, the image forming apparatus detects a mark on the conveyance belt with a sensor, and acquires correction data based on the detection result. Then, the image forming apparatus adjusts the development bias and the like based on the acquired correction data.

  Further, as a document disclosing a sensor for detecting a mark, for example, there is Patent Document 1. In Patent Document 1, an image is formed with two types of sensors, a sensor including a light emitting element and a specular reflection light receiving element, a sensor including a light emitting element, a diffuse reflection light receiving element, and a specular reflection light receiving element. An apparatus configuration is disclosed.

JP 2012-194504 A

  However, the conventional technique described above has the following problems. That is, in the density correction, it is necessary to form a mark on the conveyor belt and detect the mark with a sensor. Therefore, the formation of a toner image to be printed cannot be started until the mark is detected. Therefore, the longer the time required for mark formation and detection, the longer the printing is delayed. Also, the longer the time required for mark formation and detection, the greater the amount of rotation of the conveyor belt, resulting in greater consumption of the conveyor belt. Therefore, it is desired to shorten the time required for mark formation and detection.

  The present invention has been made to solve the above-described problems of the prior art. That is, an object of the present invention is to provide a technique for shortening the time required for forming and detecting a density correction mark in an image forming apparatus that performs density correction.

An image forming apparatus for solving this problem includes a black forming portion that forms a black toner image, another color forming portion that forms a toner image other than black, and a toner formed in the black forming portion. An image and a toner belt formed in the other color forming unit in a predetermined conveying direction; a first sensor including a light emitting element, a regular reflection light receiving element, and a diffuse reflection light receiving element; And a second sensor that does not include the diffuse reflection light receiving element, and a control unit, and the control unit performs a density correction mark in response to satisfying the first condition. In the first forming process, the other color forming unit converts other color marks, which are density correction marks of colors other than black, in the width direction on the conveyor belt. The coordinates are the coordinates of the detection range of the first sensor A black mark, which is a black density correction mark, is formed by the black forming portion at a position where the coordinate in the width direction on the conveyor belt includes the coordinate of the detection range of the second sensor. In addition, at least a part of the coordinates in the conveying direction on the conveying belt is formed at the same position as the coordinates of the other color mark.

  An image forming apparatus disclosed in the present specification includes a first sensor including a regular reflection light receiving element and a diffuse reflection light receiving element, and a second sensor including only a regular reflection light receiving element. Then, the image forming apparatus forms a density correction mark in response to satisfying the first condition. The image forming apparatus forms, as a density correction mark, another color mark other than black at a position including the detection range of the first sensor, and the black black mark includes a detection range of the second sensor. To form. Further, the image forming apparatus forms the black mark at a position where at least a part of the coordinates in the transport direction on the transport belt is the same as the coordinates of the other color mark.

  That is, in the image forming apparatus disclosed in this specification, at least a part of the black mark is at the same position as the other color mark in the transport direction of the transport belt and at the position aligned with the other color mark in the width direction of the transport belt. It is formed. For this reason, as compared with the case where marks of all colors are formed in a line in the transport direction, the dimension in the transport direction of the entire mark is shortened. Therefore, the time required to form and detect the entire mark is also shortened. In other words, in an image forming apparatus that performs density correction, it can be expected that the time required for formation and detection of density correction marks will be shortened.

  A control method for realizing the functions of the image forming apparatus, a computer program, and a computer-readable storage medium storing the computer program are also novel and useful.

  According to the present invention, in an image forming apparatus that performs density correction, a technique for reducing the time required for forming and detecting a density correction mark is realized.

1 is a cross-sectional view illustrating an internal configuration of a printer according to an embodiment. It is explanatory drawing which shows a mark sensor. FIG. 2 is a block diagram illustrating an electrical configuration of a printer. It is a figure which shows the example of the mark for density correction. It is explanatory drawing which shows the relationship between the toner amount of colors other than black, and the amount of reflected light. It is explanatory drawing which shows the relationship between black toner amount and reflected light quantity. It is a flowchart which shows the procedure of a density correction process. It is explanatory drawing which shows the example of the mark for density correction. It is a flowchart which shows the procedure of a density correction process.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a printer having an electrophotographic image forming function.

  As shown in FIG. 1, the printer 100 of this embodiment is an electrophotographic image forming apparatus that can form a color image. As shown in FIG. 1, the printer 100 includes a process unit 5, an exposure unit 6, a conveyance belt 7, a fixing unit 8, and a belt cleaner 9.

  The conveyor belt 7 is an endless belt that is rotated by a plurality of rollers or the like, and is rotated clockwise in FIG. The conveyor belt 7 conveys the sheet on the outer peripheral surface. In addition, a toner image may be formed on the outer peripheral surface of the conveyor belt 7, and in this case, the conveyor belt 7 conveys the toner image. In the following, the direction of movement of the conveyor belt 7 at each location is defined as the conveyance direction, and the direction of the rotation axis of the roller or the like that rotates the conveyor belt 7, that is, the direction perpendicular to the paper surface in FIG. The width direction of The width direction of the conveyance belt 7 is a direction orthogonal to the conveyance direction on the conveyance belt 7.

  The printer 100 also includes a paper feed tray 91 that stores sheets before printing and a paper discharge tray 92 that stores printed sheets. Then, as shown by a two-dot chain line in FIG. 1, the printer 100 includes a paper discharge tray 91, a conveyance belt 7, an upper half circumference portion in FIG. 1, and a fixing unit 8. A conveyance path 11 that is a sheet path to 92 is provided. Further, the belt cleaner 9 is disposed in the lower half of the conveyor belt 7 in FIG. 1 and removes deposits on the conveyor belt 7.

  The process unit 5 includes a yellow process unit 50Y, a magenta process unit 50M, a cyan process unit 50C, and a black process unit 50K. The process unit 50K is an example of a black forming unit, and the process unit 50Y, the process unit 50M, and the process unit 50C are examples of other color forming units, respectively. The process sections 50Y, 50M, 50C, and 50K for the respective colors are arranged at equal intervals along the upper half circumference portion of the transport belt 7 in FIG. Note that the arrangement order of the process parts of each color is not limited to the example shown in FIG.

  As shown in FIG. 1, the process unit 50 </ b> K includes a drum-shaped photoconductor 51 and forms a black toner image on the photoconductor 51. The process unit 50K includes a charging unit 52, a developing unit 54, a transfer unit 55, and a cleaner 56 around the photoreceptor 51, and is arranged in this order in the clockwise direction in FIG. In addition, the printer 100 includes an exposure unit 6 that is common to the process units 50Y, 50M, 50C, and 50K for the respective colors above the process unit 5 in FIG.

  The charging unit 52 charges the surface of the photoconductor 51. The exposure unit 6 exposes the surface of the photoconductor 51 to form an electrostatic latent image. The developing unit 54 supplies toner to the electrostatic latent image to form a toner image. The developing unit 54 of the process unit 50K contains black toner and forms a black toner image. The transfer unit 55 transfers the toner image on the photoconductor 51 to the conveyance belt 7 or a sheet conveyed by the conveyance belt 7. The cleaner 56 removes deposits such as toner remaining on the photoconductor 51 after the transfer from the photoconductor 51.

  The other color process units 50Y, 50M, and 50C have the same configuration as the process unit 50K, and form the toner images of the respective colors on the transport belt 7 or the sheet transported by the transport belt 7. In the printer 100 of this embodiment, the exposure unit 6 is a member common to the process units 50Y, 50M, 50C, and 50K for each color. However, the exposure unit 6 is individually provided for each process unit 50Y, 50M, 50C, and 50K for each color. An exposure unit may be provided.

  The printer 100 takes out the sheet from the paper feed tray 91 and conveys it along the conveyance path 11. The process unit 5 forms a toner image and transfers the toner image formed on the conveyed sheet. At this time, in color printing, each process unit 50Y, 50M, 50C, 50K forms a toner image of each color on each photoreceptor 51, and the toner images of each color are superimposed on the sheet. On the other hand, in monochrome printing, a toner image is formed only by the process unit 50K and transferred to a sheet.

  As shown in FIG. 1, the fixing unit 8 is disposed on the downstream side of the conveyance belt 7 in the sheet conveyance direction, and includes a heating roller 81 and a pressure roller 82 on both sides of the conveyance path 11. . The fixing unit 8 heat-fixes the toner image on the sheet to the sheet at a fixing nip between the heating roller 81 and the pressure roller 82. Then, the printer 100 discharges the fixed sheet to the paper discharge tray 92.

  Further, as shown in FIG. 1, the printer 100 includes a left sensor 21 and a right sensor 22 at a position downstream of the process unit 5 and upstream of the belt cleaner 9 in the transport direction of the transport belt 7. ing. The left sensor 21 and the right sensor 22 are arranged at positions where they overlap when viewed in the width direction of the conveyor belt 7, and are overlapped in FIG.

  As shown in FIG. 2, the left sensor 21 and the right sensor 22 are actually provided at separate positions. That is, the left sensor 21 is provided near one end in the width direction of the conveyor belt 7, and the right sensor 22 is provided near the other end in the width direction of the conveyor belt 7. Specifically, when the transport direction of the transport belt 7 is viewed from the bottom upward, the left sensor 21 is disposed at the left end in the width direction, and the right sensor 22 is disposed at the right end in the width direction. Hereinafter, as shown by arrows in FIG. 2, the left and right in the width direction are defined in the above-described direction.

  Both the left sensor 21 and the right sensor 22 are reflective optical sensors. The left sensor 21 outputs a different signal according to the amount of toner on the conveyor belt 7 in the detection range 21E on the left side in the width direction on the conveyor belt 7. The right sensor 22 outputs a different signal according to the amount of toner on the conveyance belt 7 in the detection range 22E on the right side in the width direction on the conveyance belt 7. In FIG. 2, the detection ranges 21E and 22E are indicated by dotted line frames. The toner amount refers to the overlapping thickness or the amount of toner on the conveying belt 7 in the detection ranges 21E and 22E.

  As shown in FIG. 2, the left sensor 21 is one in which a light emitting element 211 such as an LED and two light receiving elements 212 and 213 such as a phototransistor are integrated. The light emitting element 211 irradiates light from an oblique direction with respect to the detection range 21E. The light receiving element 212 is provided at an angle to receive light regularly reflected by the conveyor belt 7 among the light emitted from the light emitting element 211. The light receiving element 213 receives diffuse reflected light at a position different from that of the light receiving element 212. The left sensor 21 is an example of a first sensor. The light emitting element 211 is an example of the light emitting element of the first sensor, the light receiving element 212 is an example of the regular reflection light receiving element of the first sensor, and the light receiving element 213 is the diffuse reflection of the first sensor. It is an example of a light receiving element.

  The left sensor 21 outputs a signal based on the amount of light received by the light receiving element 212 and a signal based on the amount of light received by the light receiving element 213, respectively. That is, the printer 100 detects both the regular reflection light amount and the diffuse reflection light amount in the detection range 21E based on the output signal of the left sensor 21.

  On the other hand, as shown in FIG. 2, the right sensor 22 is one in which one light emitting element 221 such as an LED and one light receiving element 222 such as a phototransistor are integrated. The light emitting element 221 emits light from an oblique direction with respect to the detection range 22E. The light receiving element 222 is provided at an angle to receive light regularly reflected by the transport belt 7 among the light emitted from the light emitting element 221. Unlike the left sensor 21, the right sensor 22 is not provided with a light receiving element other than the light receiving element 222 that receives specularly reflected light. The right sensor 22 is an example of a second sensor. The light emitting element 221 is an example of a light emitting element of the second sensor, and the light receiving element 222 is an example of a regular reflection light receiving element of the second sensor.

  The right sensor 22 outputs a signal based on the amount of light received by the light receiving element 222. That is, the printer 100 detects the amount of specular reflection in the detection range 22E based on the output signal of the right sensor 22. The positional relationship between the left sensor 21 and the right sensor 22 may be reversed.

  The printer 100 performs density correction and positional deviation correction using output signals from the left sensor 21 and the right sensor 22. For example, as shown in FIG. 2, the printer 100 forms a correction mark 27 on the conveyance belt 7, and at least before and after a period in which the formed mark 27 passes through the detection range 21 </ b> E of the left sensor 21. The output signal of the left sensor 21 is acquired. Further, the printer 100 acquires the output signal of the right sensor 22 before and after a period in which the formed mark 27 passes at least the detection range 22E of the right sensor 22. Furthermore, the printer 100 calculates the formation position of the mark 27 and the toner amount based on the output signals of the left sensor 21 and the right sensor 22, and corrects various biases and the like when forming an image thereafter based on the calculation result. To do.

  Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 of this embodiment includes a controller 30 having a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The printer 100 includes a process unit 5, a left sensor 21, a right sensor 22, a network IF (network interface) 37, a USBIF (USB interface) 38, and an operation panel 40, which are controlled by the CPU 31. Is done.

  The ROM 32 stores firmware, which is a control program for controlling the printer 100, various settings, initial values, and the like. The RAM 33 is used as a work area from which various control programs are read or as a storage area for temporarily storing image data. The NVRAM 34 is used as a storage area for storing various correction data for image correction, various set values, and the like.

  The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 in accordance with a control program read from the ROM 32 and signals sent from various sensors. The CPU 31 is an example of a control unit. Further, the controller 30 may be a control unit. Note that the controller 30 in FIG. 3 is a general term that summarizes hardware used for controlling the printer 100 such as the CPU 31, and does not necessarily represent a single piece of hardware that actually exists in the printer 100.

  The network IF 37 is hardware for communicating with devices connected via the network. The communication method may be wired or wireless. The operation panel 40 is hardware that is responsible for displaying a notification to the user and receiving an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a button group including a start key, a stop key, a numeric keypad, and the like.

  Next, operations for forming and detecting marks for various image corrections in the printer 100 will be described. In order to obtain the correction amount for image correction, the printer 100 first acquires the current degree of deviation. For this purpose, the printer 100 forms and detects marks that are toner images. There are a plurality of types of image correction, such as misregistration correction and density correction, and the printer 100 forms a different mark for each type of correction. The example shown in FIG. 2 is a state in which a misalignment correction mark 27 is formed on the transport belt 7.

  The misalignment correction marks 27 are two rows of mark groups formed at different positions in the width direction of the transport belt 7 as shown in FIG. In each row, belt-like marks 27Y, 27M, 27C, and 27K made of toner of each color are arranged at predetermined intervals in the transport direction of the transport belt 7, and the whole is repeated a plurality of times. Each mark 27 is a substantially rectangular mark having a dimension that is greater than the width of the detection ranges 21E and 22E in the width direction of the transport belt 7 and a short dimension within the detectable range in the transport direction of the transport belt 7.

  Further, each row of the marks 27 is formed at a position passing through the detection range 21E of the left sensor 21 or the detection range 22E of the right sensor 22 as the transport belt 7 moves. Specifically, the coordinate of the left mark 27 in the width direction of the transport belt 7 includes the coordinate of the detection range 21E of the left sensor 21. Further, the coordinates of the right mark 27 in the width direction of the transport belt 7 include the coordinates of the detection range 22E of the right sensor 22. The arrangement order of the colors of the marks 27 in each column is not limited to the order shown in FIG.

  The printer 100 uses the light receiving element 212 that is the specular reflection light receiving element of the left sensor 21 and the light receiving element 222 that is the specular reflection light receiving element of the right sensor 22 when reading the mark 27 to correct the positional deviation. . That is, the printer 100 acquires the presence / absence of toner in the detection ranges 21E and 22E at each time point based on the output signal of the light receiving element 212 and the output signal of the light receiving element 222. Furthermore, by detecting the presence or absence of toner while moving the conveyor belt 7, the printer 100 acquires the leading edge position or trailing edge position of each mark 27 in the conveying direction.

  The printer 100 compares the leading end positions or the trailing end positions of the marks 27 to determine whether or not there is a positional shift between the marks or a color shift when overlapping. If the printer 100 determines that there is a color shift based on the position of the mark 27 of each color, for example, the printer 100 corrects the writing timing of the toner image of one color. For this purpose, the printer 100 stores the current misregistration amount or the calculated correction amount in the NVRAM 34, and corrects misregistration and color misregistration by using the values stored in the subsequent image formation.

  In addition, in the image density correction, the printer 100 forms, for example, a density correction mark 28 different from the position deviation correction mark 27 as shown in FIG. As shown in FIG. 4, the density correction marks 28 are rectangular solid image marks 28Y, 28M, 28C, and 28K having a predetermined density for each color, for example, 100% density. The printer 100 forms and detects a mark 28 on the transport belt 7 in order to acquire the current image density. The arrangement order of the marks 28Y, 28M, and 28C is not limited to the order shown in FIG.

  The density correction mark 28 is a black color formed at a position passing through the detection range 22E of the right sensor 22 and a mark 28Y, 28M, 28C of each color other than black formed at a position passing through the detection range 21E of the left sensor 21. Mark 28K. Specifically, as shown in FIG. 4, the coordinate X1 of the marks 28Y, 28M, and 28C in the width direction (X-axis direction in the drawing) of the conveyor belt 7 includes the coordinate X21 of the detection range 21E of the left sensor 21. . Further, the coordinate X2 of the black mark 28K in the width direction of the transport belt 7 includes the coordinate X22 of the detection range 22E of the right sensor 22.

  Then, the marks 28Y, 28M, and 28C of colors other than black are formed side by side in the transport direction of the transport belt 7 as shown in FIG. Further, the black mark 28K is formed in the same position as the coordinates of the other color marks 28Y, 28M, and 28C in at least a part of the transport direction of the transport belt 7. Specifically, as shown in FIG. 4, the coordinate Y2 in the transport direction (Y-axis direction in the drawing) of the black mark 28K is within the range of the overall coordinate Y1 of the other color marks 28Y, 28M, and 28C. In. That is, in the example of FIG. 4, the overall dimension of the mark 28 in the conveyance direction is equal to the dimension of the range in which the marks 28Y, 28M, and 28C are formed.

  The printer 100 acquires the toner amounts of the other color marks 28Y, 28M, and 28C based on the output signal of the light receiving element 212 of the left sensor 21 and the output signal of the light receiving element 213. Further, the printer 100 acquires the toner amount of the black mark 28 </ b> K based on the output signal of the light receiving element 222 of the right sensor 22.

  Here, the reflection of light by each color toner will be described. As shown in FIGS. 5 and 6, the relationship between the toner amount and the amount of reflected light is different between black toner and non-black toner. FIG. 5 is a graph showing the relationship between the amount of toner on the conveyor belt 7 and the amount of specular reflection or diffuse reflection for toners of colors other than black. FIG. 6 is a graph showing the relationship between the amount of toner on the conveyor belt 7 and the amount of specularly reflected light or diffusely reflected light for black toner.

  The conveyance belt 7 is a material that reflects light well. When there is no toner in the detection range 21E, most of the light emitted from the light emitting element 211 is regularly reflected on the surface of the conveyance belt 7. That is, when the amount of toner in the detection range 21E is small, the amount of regular reflection received by the left sensor 21 is large and the amount of diffuse reflection is small. On the other hand, when the amount of toner in the detection range 21E increases, the amount of reflected light changes according to the amount of toner because it is affected by the reflection of the toner.

  For colors other than black, as shown in FIG. 5, as the toner amount increases from 0, the amount of specular reflection decreases and the amount of diffuse reflection increases due to the diffusion of light by the toner particles. When the toner amount exceeds a certain level, light is reflected by the overlapping toner particles. For this reason, the amount of specular reflection light starts to increase, and the amount of specular reflection light and diffuse reflection light amount increase as the amount of toner increases.

  That is, as can be seen from FIG. 5, it is difficult to estimate the amount of toner of colors other than black based only on the amount of specular reflection. The printer 100 forms marks 28 </ b> Y, 28 </ b> M, and 28 </ b> C of colors other than black at positions passing through the detection range 21 </ b> E of the left sensor 21, and is based on the output signal of the light receiving element 212 of the left sensor 21 and the output signal of the light receiving element 213. Thus, the toner amounts of the marks 28Y, 28M, and 28C are estimated. That is, since the toner amount is estimated based on both the regular reflection light amount and the diffuse reflection light amount, the toner amount of colors other than black can be estimated appropriately.

  On the other hand, since the black toner has the property of absorbing light, the relationship between the toner amount and the amount of reflected light is slightly different from colors other than black. In black, as shown in FIG. 6, the amount of specularly reflected light continues to decrease as the toner amount increases. Even if the amount of toner increases, the amount of specular reflection does not start to increase. Therefore, for the black mark 28K, the toner amount can be estimated based only on the regular reflection light quantity. Therefore, the printer 100 forms the black mark 28K at a position passing through the detection range 22E of the right sensor 22, and estimates the toner amount based on the output signal of the light receiving element 222 of the right sensor 22. That is, the printer 100 estimates the toner amount of the black mark 28K based only on the regular reflection light amount.

  The printer 100 determines that the density of the mark is appropriate if the acquired toner amount is within an allowable range of the reference amount corresponding to the image density of the mark. On the other hand, if the acquired toner amount is outside the allowable range of the reference amount corresponding to the image density of the mark, the printer 100 performs development bias correction, charging bias correction, exposure intensity correction, gamma in the next and subsequent image formation. Perform at least one of the corrections. For example, when the printer 100 determines that the toner amount is small, the absolute value of the developing bias is increased to increase the toner supply amount. Further, for example, when the printer 100 determines that the toner amount is large, the absolute value of the developing bias is decreased to reduce the toner supply amount. For example, the printer 100 determines a correction value that is a change width of the developing bias based on the difference between the estimated toner amount and the reference amount.

  Next, a first form of image correction processing executed by the printer 100 will be described with reference to the flowchart of FIG. This image correction process is executed by the CPU 31 when a print command is received. The printer 100 receives a print command via the network IF 37 and the operation panel 40, for example.

  In this image correction process, the CPU 31 first determines whether or not an execution condition for executing mark formation for density correction is satisfied (S101). There are a plurality of execution conditions for each type of correction. For example, cover open, power-on, printing more than a predetermined number of sheets, continuous activation for a predetermined time or more, environmental change such as humidity and temperature, or a combination thereof. The execution condition for executing mark formation for density correction is an example of the first condition.

  If it is determined that the density correction execution condition is not satisfied (S101: NO), the CPU 31 forms an image based on the print command (S103), and ends the image correction process. It should be noted that the correction process executed before image formation is other than density correction. If the execution conditions for other corrections are satisfied, the printer 100 executes a correction process that satisfies the execution conditions before execution of printing.

  When it is determined that the density correction execution condition is satisfied (S101: YES), the CPU 31 determines whether the type of the print target of the received print command is image data including image data (S101: YES). S111). Text data is an image that contains only text and does not include photos or illustrations to be printed. The image data is image data including photographs or illustrations that are images other than text data. The type of print target is included in the received print job information, for example. Further, the CPU 31 may analyze the contents of the print data and acquire the type of print target. The condition that becomes YES in S111 is an example of a second condition.

  When it is determined that the image data does not include image data (S111: NO), the CPU 31 displays two rows of density correction marks 28 as shown in FIG. Form (S112). S112 is an example of a first formation process.

  That is, the CPU 31 causes the process units 50Y, 50M, and 50C to sequentially form the marks 28Y, 28M, and 28C of the respective colors in order at positions passing through the detection range 21E of the left sensor 21. Further, the CPU 31 causes the process unit 50K to form a black mark 28K at a position passing through the detection range 22E of the right sensor 22. As shown in FIG. 4, the position of the mark 28K in the transport direction is within the range of the positions of the marks 28Y, 28M, and 28C in the transport direction. The marks 28Y, 28M, and 28C are examples of other color marks, and the mark 28K is an example of a black mark.

  In the printer 100 of this embodiment, as shown in FIG. 4, the mark 28K is formed larger than the marks 28Y, 28M, and 28C of the other colors in the transport direction. Since only the black mark 28K is formed at the position of the right sensor 22, even if the mark 28K is formed to be somewhat larger than the marks 28Y, 28M, and 28C of other colors, the size in the transport direction of the entire mark 28 is not affected. Absent. That is, the printer 100 forms the mark 28K larger than the marks 28Y, 28M, and 28C of the other colors within a range that does not exceed the dimension in the transport direction of the entire mark 28.

  For example, as shown in FIG. 4, the dimension LK in the conveyance direction of the mark 28K is larger than any of the dimension LY in the conveyance direction of the mark 28Y, the dimension LM in the conveyance direction of the mark 28M, and the dimension LC in the conveyance direction of the mark 28C. large. The dimension LK is, for example, about twice as large as the dimensions LY, LM, and LC. The dimension LK is shorter than the overall dimensions of the other color marks 28Y, 28M, 28C including the gaps between the marks. The overall dimension LT of the mark 28 is equal to the overall dimensions of the other color marks 28Y, 28M, 28C.

  Then, the CPU 31 detects the formed mark 28 based on the output signals from the left sensor 21 and the right sensor 22 (S113). That is, the CPU 31 causes the light emitting element 211 to emit light and receives the output signals of the light receiving elements 212 and 213 while the formed marks 28Y, 28M, and 28C pass at least the detection range 21E of the left sensor 21. Further, the CPU 31 causes the light emitting element 221 to emit light and receives the output signal of the light receiving element 222 while the formed mark 28K passes at least the detection range 22E of the right sensor 22.

  The CPU 31 samples the output signals of the left sensor 21 and the right sensor 22 a plurality of times in one mark 28, and estimates the toner amount by, for example, an average value. As described above, since the mark 28K is larger than the marks 28Y, 28M, and 28C of other colors, the number of sampling of the mark 28K by the right sensor 22 can be made larger than that of the other colors. As shown in FIG. 6 described above, when the amount of black toner exceeds a certain level, the amount of change in the amount of specular reflection with respect to the amount of change in toner amount is small. Therefore, the method for estimating the toner amount using only the regular reflected light amount of the right sensor 22 is slightly more accurate than the method for estimating the toner amount using both the regular reflected light amount and the diffuse reflected light amount. May be low. In this embodiment, since the mark 28K is formed large and the number of samplings is increased, it is possible to ensure the detection accuracy for black.

  Then, the CPU 31 estimates the toner amount of each mark 28 from the detection result, and calculates a correction value for density correction based on the difference from the reference amount (S114). The correction value for density correction is a correction value that increases the absolute value of the developing bias so as to increase the density, for example, if the estimated toner amount is small, and the density is decreased, for example, if the estimated toner amount is large. Thus, the correction value reduces the absolute value of the developing bias. Further, the CPU 31 stores the calculated correction value for density correction in the NVRAM 34. Then, the CPU 31 forms an image based on the print command using the development bias corrected with the calculated correction value (S103), and ends the image correction process.

  On the other hand, when it is determined that the image data to be printed of the received print command is image data including image data (S111: YES), the CPU 31 sends a density correction as shown in FIG. One row of marks 29 is formed (S116). S116 is an example of a second formation process. In S111, the CPU 31 determines YES even if the image data includes image data, if it includes image data.

  In S116, the CPU 31 causes the process units 50Y, 50M, 50C, and 50K to sequentially arrange marks 29Y, 29M, 29C, and 29K of the respective colors at positions passing through the detection range 21E of the left sensor 21. The marks 29Y, 29M, and 29C are the same as the marks 28Y, 28M, and 28C, respectively. The mark 29K is a mark with a black toner, the position of the conveyance belt 7 in the width direction including the coordinate of the detection range 21E of the left sensor 21, and the conveyance direction of the conveyance belt 7 is a mark 29Y of another color. , 29M, and 29C are marks formed at positions different from the coordinates.

  That is, as shown in FIG. 8, the dimension of the mark 29K in the transport direction is equal to the dimension of each of the other color marks 29Y, 29M, and 29C in the transport direction. The mark 29K is formed at a position that does not overlap with other color marks. For this reason, the overall dimension LS of the mark 29 in the transport direction is larger than the overall dimension LT of the mark 28 (see FIG. 4). The marks 29Y, 29M, and 29C are examples of other color marks, and the mark 29K is an example of a black mark.

  Then, the CPU 31 detects the formed mark 29 based on the output signal of the left sensor 21 (S117). Then, the CPU 31 estimates the toner amount of each mark 29 from the detection result, and calculates a correction value for density correction based on the difference from the reference amount (S118). The method for calculating the correction value for density correction is the same as that when the mark 28 is used. Further, the CPU 31 stores the calculated correction value for density correction in the NVRAM 34. Then, the CPU 31 forms an image based on the print command using the development bias corrected with the calculated correction value (S103), and ends the image correction process.

  As described above, the detection accuracy when the toner amount of the mark 28K is estimated using the right sensor 22 is slightly lower than the detection accuracy when the toner amount of the mark 29K is estimated using the left sensor 21. Since printing of image data including image data includes photographs, illustrations, and the like, high-precision density control tends to be desired for black. Therefore, the CPU 31 uses the mark 29 in density correction before printing an image including image data. Thereby, the black density control can be made with high accuracy according to the situation.

  On the other hand, in text data, the accuracy required for black density control is slightly lower than that of images including photographs and illustrations. Therefore, the printer 100 uses the mark 28 for density correction before printing of image data that does not include image data and includes only text data. The overall conveyance direction dimension of the mark 28 is shorter than the overall conveyance direction dimension of the mark 29. By using the mark 28, the time required for the formation and detection of the mark can be shortened, so the waiting time until the start of printing is short. Further, since the overall dimension of the mark is short, the conveyance amount of the conveyance belt 7 for forming and detecting the mark is small, and the degree of consumption of the conveyance belt 7 and the process unit 5 can be suppressed.

  Next, a second form of image correction processing executed by the printer 100 will be described with reference to the flowchart of FIG. This image correction process is executed by the CPU 31 when a print command is received. The second form is different from the first form in the condition for determining which of the two rows of marks 28 and the one row of marks 29 is used. About the process similar to a 1st form, the same code | symbol as the flowchart of FIG. 7 is attached | subjected and description is abbreviate | omitted.

  In the image correction processing of the second form, the CPU 31 first determines whether or not the execution condition for executing mark formation for density correction is satisfied, as in the first form (S101). If it is determined that the density correction execution condition is not satisfied (S101: NO), the CPU 31 forms an image based on the print command (S103), and ends the image correction process.

  If it is determined that the execution condition for density correction is satisfied (S101: YES), the CPU 31 determines whether the execution condition for positional deviation correction is satisfied (S201). The execution condition of the positional deviation correction is an example of a third condition.

  If it is determined that the execution condition for the misregistration correction is satisfied (S201: YES), the CPU 31 sequentially executes density correction and misregistration correction in this order. In this case, the CPU 31 estimates the toner amount by using the marks 28 which are two rows of density correction marks, and calculates a correction value for density correction based on the result. That is, the same processing as S112, S113, and S114 of the first form is executed.

  Thereafter, the CPU 31 causes the misalignment correction marks 27 to be formed in the process units 50Y, 50M, 50C, and 50K for the respective colors (S205). S205 is an example of a misalignment forming process. When forming the misalignment correction mark 27, the CPU 31 uses the developing bias corrected with the correction value calculated in S114. When both density correction and positional deviation correction are executed, the variation in detection accuracy due to the color of the mark 27 for positional deviation correction can be reduced by calculating and applying the correction value for density correction first.

  Then, the CPU 31 detects the mark 27 based on the output signal of the left sensor 21 and the output signal of the right sensor 22 (S206), and calculates a correction value for misalignment correction (S207). Further, the CPU 31 stores the calculated correction value for density correction and the correction value for positional deviation correction in the NVRAM 34, forms an image based on the print command (S103), and ends the image correction process.

  When the execution conditions for both density correction and positional deviation correction are satisfied, many processes are executed before printing, and the time until the start of printing tends to be long. In the printer 100 according to the second embodiment, when both execution conditions are satisfied, the correction value for density correction is calculated using the two rows of marks 28. The time required for formation and detection is short.

  On the other hand, when it is determined that the execution condition of the positional deviation correction is not satisfied (S201: NO), the CPU 31 estimates the toner amount using the mark 29 that is a density correction mark in one row, and based on the result. Thus, a correction value for density correction is calculated. That is, the same processing as S116, S117, and S118 of the first form is executed. Further, the CPU 31 forms an image based on the print command (S103), and ends the image correction process. When the formation and detection of the mark for correcting the misregistration are not executed, the time required for the correction process is not so long. Therefore, the printer 100 performs the high-precision density correction by performing the process using the mark 29. Do.

  As described above in detail, when the density correction execution conditions are satisfied, the printers 100 according to the first and second embodiments have two rows of marks 28 as density correction marks according to other conditions. Is used. That is, a mark other than black is formed at a position passing through the detection range 21E of the left sensor 21 having two light receiving elements, and a black mark is formed at a position passing through the detection range 22E of the right sensor 22 having one light receiving element. . Since the toner amount of the black mark can be estimated without using the diffusely reflected light amount, it can be estimated based on the output signal of the right sensor 22 having only a light receiving element that receives regular reflected light. Further, the printer 100 forms the black mark 28K among the marks 28 so that at least a part of the conveyance belt 7 in the conveyance direction is at the same position as any of the non-black color marks. Therefore, the dimension of the entire mark in the transport direction can be shortened as compared with the case where one row of marks 29 is used. As a result, the time required for mark formation and detection can be shortened.

  Further, even when the mark 28 is formed, the printers 100 according to the first and second embodiments estimate the toner amount of the mark 28K based only on the regular reflection light amount. That is, it is not necessary to replace the right sensor 22 with one having two light receiving elements similar to the left sensor 21. Therefore, the cost can be suppressed as compared with the case where a sensor including two light receiving elements is used for both the left sensor 21 and the right sensor 22.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a printer, and can be applied to any apparatus having an image forming function in an electrophotographic system, such as a copying machine, a multifunction machine, and a FAX apparatus.

  Further, in FIG. 4, the tip of the mark 28K and the tip of the mark 28Y are illustrated at the same coordinates in the transport direction, but this is not restrictive. 4 shows an example in which the entire mark 28K is formed within the range where the other color marks 28Y, 28M, and 28C are formed in the conveyance direction of the conveyance belt 7, but at least a part of the other color is in the other color. It may be within the range of the mark. Even if the portions are formed side by side, the overall dimension of the mark 28 is shorter than that of the mark 29. It is preferable to form the entire mark 28K within the range in which the other color marks 28Y, 28M, and 28C are formed because the overall dimension of the mark becomes shorter.

  In the first and second embodiments, the mark 28 and the mark 29 are illustrated by arranging one mark for each color, but two or more marks may be formed. For example, density correction can be performed more precisely by forming a plurality of marks having different densities and using the result of estimating the respective toner amounts.

  In the first and second embodiments, the mark 28K is made larger than the mark of the other color, but it may be the same size. However, it is preferable to increase the sampling number so that the estimation accuracy of the toner amount of the mark 28K increases. Instead of increasing the size, a plurality of marks having the same size as the other colors may be formed.

  Further, as a condition for using the mark 28 for the density correction mark, the first embodiment exemplifies the condition not including the image data, and the second embodiment exemplifies the execution condition of the positional deviation correction. It is not limited to form. In other words, it may be determined that both conditions are satisfied and at least one is satisfied. Further, both conditions may be provided, and either one may be selected in advance. Still other conditions may be provided. For example, selection between speed priority and image quality priority may be accepted as a setting by the user. In this case, if speed is prioritized, mark 28 is used, and if image quality is prioritized, mark 29 is used. The mark 28 may always be used as a density correction mark.

  In the first and second embodiments, the printer 100 that forms marks on the conveyance belt 7 that conveys a sheet has been described. However, the present invention is also applicable to a secondary transfer type image forming apparatus. That is, the belt on which the mark is formed may be an intermediate transfer belt.

  The processing disclosed in the embodiments may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the processing disclosed in the embodiment can be realized in various modes such as a recording medium or a method recording a program for executing the processing.

7 Conveyor belt 21 Left sensor 22 Right sensor 31 CPU
50Y, 50M, 50C, 50K Process unit 100 Printer

Claims (8)

A black forming portion for forming a black toner image;
Another color forming part for forming a toner image other than black,
A conveying belt that conveys the toner image formed in the black forming portion and the toner image formed in the other color forming portion in a predetermined conveying direction;
A first sensor including a light emitting element, a specular reflection light receiving element, and a diffuse reflection light receiving element;
A second sensor including a light emitting element and a regular reflection light receiving element, and not including a diffuse reflection light receiving element;
A control unit;
With
The controller is
In response to satisfying the first condition, a first forming process for forming a density correction mark is executed,
In the first forming process,
The other color forming unit forms another color mark, which is a density correction mark of a color other than black, at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the first sensor. ,
A black mark, which is a black density correction mark, is positioned by the black forming portion at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the second sensor, and the transport Forming at least some coordinates in the transport direction on the belt at the same position as the coordinates of the other color mark;
An image forming apparatus. The image forming apparatus according to claim 1,
The dimension of the black mark in the transport direction of the transport belt is larger than the dimension of the transport belt in the transport direction for one color of the other color mark,
An image forming apparatus. The image forming apparatus according to claim 1, wherein:
The controller is
In response to satisfying the second condition, a second forming process for forming a density correction mark is executed,
In the second forming process,
The other color forming unit forms the other color mark at a position where the coordinate in the width direction on the conveyor belt includes the coordinate of the detection range of the first sensor
By the black forming portion, the black mark is placed at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the first sensor, and the coordinate in the transport direction on the transport belt is Formed at a position different from the coordinates of the other color mark,
An image forming apparatus. The image forming apparatus according to claim 3,
The first condition includes a case where a print command is received and a print target is an image of data composed only of text,
The second condition includes a case where a print command is received and a print target is an image of data including image data.
An image forming apparatus. The image forming apparatus according to claim 3 or 4, wherein:
The controller is
In response to satisfying the third condition, a misalignment forming process for forming a misalignment correction mark is executed,
In the misalignment forming process,
A position misalignment mark that is a position misalignment correction mark by the black color forming section and the other color forming section; a position in which the coordinate in the width direction on the conveyor belt includes the coordinates of the detection range of the first sensor; and , Formed at positions including the coordinates of the detection range of the second sensor,
The first condition includes satisfying the third condition,
The second condition includes not satisfying the third condition.
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
The controller is
Perform at least one of development bias correction, charging bias correction, exposure intensity correction, and gamma correction based on the density correction data.
An image forming apparatus. A black forming portion for forming a black toner image;
Another color forming part for forming a toner image other than black,
A conveying belt that conveys the toner image formed in the black forming portion and the toner image formed in the other color forming portion in a predetermined conveying direction;
A first sensor including a light emitting element, a specular reflection light receiving element, and a diffuse reflection light receiving element;
A second sensor including a light emitting element and a regular reflection light receiving element, and not including a diffuse reflection light receiving element;
An image forming apparatus control method comprising:
A first forming step of forming a mark for density correction in response to satisfying the first condition;
In the first forming step,
The other color forming unit forms another color mark, which is a density correction mark of a color other than black, at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the first sensor. ,
A black mark, which is a black density correction mark, is positioned by the black forming portion at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the second sensor, and the transport Forming at least some coordinates in the transport direction on the belt at the same position as the coordinates of the other color mark;
A control method of the image forming apparatus. A black forming portion for forming a black toner image;
Another color forming part for forming a toner image other than black,
A conveying belt that conveys the toner image formed in the black forming portion and the toner image formed in the other color forming portion in a predetermined conveying direction;
A first sensor including a light emitting element, a specular reflection light receiving element, and a diffuse reflection light receiving element;
A second sensor including a light emitting element and a regular reflection light receiving element, and not including a diffuse reflection light receiving element;
In an image forming apparatus comprising
In response to satisfying the first condition, a first forming process for forming a density correction mark is executed,
In the first forming process,
The other color forming unit forms another color mark, which is a density correction mark of a color other than black, at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the first sensor. ,
A black mark, which is a black density correction mark, is positioned by the black forming portion at a position where the coordinate in the width direction on the transport belt includes the coordinate of the detection range of the second sensor, and the transport Forming at least some coordinates in the transport direction on the belt at the same position as the coordinates of the other color mark;
A program characterized by that.

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