JP2006011154A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce color shift at an image formation starting position by multi-color superposition, particularly, to highly accurately perform the image alignment of 2nd color and 4th color images formed by a 2nd image forming unit, and to easily adjust the image position between respective image forming units. <P>SOLUTION: The image forming apparatus is provided with an intermediate transfer belt 1 having a 1st mark M1 as a reference of starting to write the 1st color image and a 2nd color mark M2 arranged at a distance equal to or below a moving distance obtained by the time of starting to write the 2nd color image, a mark detecting sensor 5 for detecting the marks M1 and M2, a counter for starting a counting operation after being reset when the mark M2 is detected, a counted value obtaining means for obtaining the counted value C2 of the counter when the mark M2 is detected, and a calculating means for calculating the counted value C1 by the time of starting to write the 2nd color image after the prescribed time of starting to write the 1st color image and the counted value C3 by the time of starting to write the 2nd color image after the mark M2 is detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that transfers a toner image formed on an image carrier such as a photosensitive drum to an intermediate transfer member and transfers the transferred image to a sheet-like recording medium. .

In an electrophotographic multicolor image forming apparatus, four color toner images of yellow, magenta, cyan, and black are formed on an intermediate transfer member such as an intermediate transfer belt, and the toner image is formed into a sheet-like recording medium. (Hereinafter, sometimes simply referred to as “recording medium”) is transferred onto the recording medium, and full color printing is performed. If the writing position of each color is deviated when performing full color printing, the toner image formed in an overlapping manner is transferred to the recording medium, resulting in color misregistration and deterioration in image quality.
Therefore, position control for matching the image writing start position is required. Conventionally, in an image forming apparatus that forms an image by transferring a toner image to an intermediate transfer member, an alignment mark is provided on the intermediate transfer member, the mark is detected by a sensor, and from the mark detection to the start of image writing. There is known an image forming apparatus that counts by a hardware counter and starts image writing when it matches a set value from mark detection to image writing start, and aligns the image of each color.

Further, a method is known in which a toner image having a pattern for alignment is formed on an intermediate transfer member, the pattern is detected by an optical sensor, the amount of positional deviation of the image is obtained, and the position of the image is corrected.
As a technique for setting various conditions for image formation by detecting a plurality of reference marks provided on an intermediate transfer member, the following is known.

  In Japanese Patent Laid-Open No. 2002-31926, a plurality of marks are formed on an intermediate transfer member, and the time until detection of adjacent marks is compared with a preset time, and the toner image carrier (intermediate transfer belt) is compared. Proposals have been made to provide speed control means so that the rotation speed becomes a normal rotation speed.

  Japanese Patent Laid-Open No. 7-325455 proposes to eliminate the positional deviation between the image areas of both belts by using a photoconductor belt having a reference mark formed thereon and transferring it to an intermediate transfer belt.

  In Japanese Patent Laid-Open No. 2000-305417, new image formation is performed on the basis of marks different from the preceding image formation, thereby preventing concentration of image forming positions on the intermediate transfer member and preventing deterioration of the intermediate transfer member. To do. Another proposal has been made to prevent deformation of the intermediate transfer member by stopping at a mark different from the preceding image formation and not waiting at the same position.

  Japanese Patent Laid-Open No. 2003-334989 also proposes a writing control for performing a control for suppressing the writing start position alignment between each rotation of the intermediate transfer body to 1/2 scan or less based on a mark reference.

JP 2002-31926 A JP 7-325455 A JP 2000-305417 A JP 2003-334899 A

  As an image forming apparatus that forms an image by transferring a toner image to an intermediate transfer member, an image forming apparatus having four sets of image forming units arranged facing each other along the moving surface of the intermediate transfer member is known. Hereinafter, such an image forming method is referred to as a first image forming method. In the image forming apparatus using the first image forming method, the alignment mark provided on the intermediate transfer member is detected, and the first color is written on the basis of the detection timing. The writing from the second color to the fourth color is performed sequentially after the time for the intermediate transfer member to move the distance between the image forming units from the reference of the first color so that the images overlap on the intermediate transfer member. Done.

  Therefore, it is necessary to adjust the writing start timing of the three colors from the second color to the fourth color with respect to the reference color of the first color, and there is a problem that the adjustment takes time and is difficult. In addition, when speed fluctuation occurs in the intermediate transfer member, there is a problem that the three colors of the second color to the fourth color are shifted from the reference color of the first color.

In the image forming apparatus described in Japanese Patent Application Laid-Open No. 2000-305417, that is, an image forming apparatus having two sets of image forming means arranged facing each other along the moving surface of the intermediate transfer body, the alignment provided on the intermediate transfer body The first mark is written on the basis of the detection timing. After the intermediate transfer member makes one round, the same mark is detected again, and writing of the third color is performed based on the detection timing.
The writing of the second color is performed after the time for the intermediate transfer member to move the distance between the image forming units from the reference of the first color. Similarly, after the intermediate transfer member has made one revolution, writing for the fourth color is performed after a time for the intermediate transfer member to move the distance between the image forming units from the reference for the third color. Hereinafter, such an image forming method is referred to as a second image forming method.

Therefore, although the image forming positions of the first color and the third color coincide with each other, when the speed variation occurs in the intermediate transfer body, the second color and the fourth color are different from the first color reference color. There is a problem that each shifts.
At this time, it is also necessary to adjust the writing start timing of the second color with respect to the first reference color and the writing start timing of the fourth color with respect to the third reference color. In addition, the first transfer and the second rotation of the intermediate transfer member have different timings at which the cleaning process and the transfer process to the recording medium are performed, causing load fluctuations. Therefore, the intermediate transfer member is rotated twice to form a four-color image, the first color and the second color, the third color and the fourth color image formation positions are detected, and the misregistration amount is confirmed. It is necessary to adjust the writing start position. Note that the writing process control by the second image forming method will be described in a later-described embodiment as a comparative example related to the prior art, as compared with Example 1 according to the present invention.
In addition, in the above two image forming methods, there is a problem that the amount of toner used for adjusting the writing start position increases, and adjustment takes time.

  On the other hand, when the technique related to the writing control apparatus and the image forming apparatus described in Japanese Patent Application Laid-Open No. 2003-33489 is applied to a known part (...) of the image forming apparatus according to claim 1 of the present invention, 1 of the intermediate transfer member. If the intermediate transfer member undergoes speed fluctuations in the second and second rotations, there is a problem that the writing start positions of the second and fourth color images are shifted from the first color.

  Accordingly, the present invention pays attention to the above points, and in an image forming apparatus having two sets of image forming units arranged facing each other along the moving surface of the intermediate transfer member, Color misregistration is reduced, and in particular, image alignment of the second color and the fourth color formed by the second image forming unit (second image forming station) is performed with high accuracy, and between each image forming unit It is a main object to provide an image forming apparatus capable of easily adjusting an image position.

In order to solve the above-described problems and achieve the above-described object, the invention according to each claim employs the following characteristic means and configuration.
According to the first aspect of the present invention, at least a latent image formed by a single image carrier and a scanning type writing unit that is disposed opposite to the image carrier and forms a latent image on the image carrier is obtained. First and second image forming units composed of a plurality of color-switchable developing means for developing with two color developers and toner images formed by the first and second image forming units are sequentially superimposed. An image forming apparatus comprising: an intermediate transfer member to be transferred; and transfer means for transferring a color image formed on the intermediate transfer member to a sheet-like recording medium. Are arranged at a distance equal to or less than the distance from the first detected means to the start of writing of the second color. Less with second detected means There are also two detected means, a first detecting means, a detecting means for detecting the second detected means at a predetermined position, and an initial time when the detecting means detects the first detected means. A count unit that starts counting the elapsed time after being converted, a count acquisition unit that acquires the count value C2 of the count unit when the detection unit detects the second detected unit, and a preset value from the count value C2 Counting the elapsed time from the detection of the second detected means to the start of writing of the second color, which is the difference from the count value C1 of the elapsed time from the start of writing of the first color to the start of writing of the second color. And a calculation means for calculating the value C3, and the first color of the first transfer is detected at the (2n-1) -th rotation (n ≧ 1: positive integer) of the intermediate transfer body with reference to the detection timing of the first detected means. image Initiating the writing, starting the image writing of the second color at the count value C1 on the basis of the detection timing of the first detected means, and detecting the first detected means at the 2nth rotation of the intermediate transfer member. The third color image writing is started based on the timing, and the fourth color image writing is started at the count value C3 based on the second detected unit detection timing.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the detected means that forms a set of the first detected means and the second detected means along the moving direction of the intermediate transfer member, etc. A plurality of the intermediate transfer members are arranged at intervals, and the second immediately preceding the distance moved from the arbitrary first detection means serving as the first color writing start reference to the second color writing start. The detected means is detected, and at the (2n-1) rotation of the intermediate transfer body, the first color image writing is started on the basis of the first detected means detection timing, and the first detected means The second color image writing is started at the count value C1 with the detection timing as a reference, and the third color image writing is performed at the 2n rotation of the intermediate transfer body with reference to the first detection means detection timing. Start, second detected means detection timing As a reference, characterized in that to start the image writing of the fourth color in the count value C3.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the count unit controls image writing timing by operating in synchronization with a main scanning synchronization signal of the scanning type writing unit. It is characterized by that.

  According to a fourth aspect of the present invention, at least a latent image formed by a single image carrier and scanning-type writing means disposed opposite to the image carrier and forming a latent image on the image carrier is provided. First and second image forming units composed of a plurality of color-switchable developing means for developing with two color developers and toner images formed by the first and second image forming units are sequentially superimposed. An image forming apparatus comprising: an intermediate transfer member to be transferred; and transfer means for transferring a color image formed on the intermediate transfer member to a sheet-like recording medium. Are arranged at a distance equal to or less than the distance from the first detected means to the start of writing of the second color. Less with second detected means There are also two detected means, a first detecting means, a detecting means for detecting the second detected means at a predetermined position, and an initial time when the detecting means detects the first detected means. A count unit that starts counting the elapsed time after being converted, a count acquisition unit that acquires the count value C2 of the count unit when the detection unit detects the second detected unit, and a preset value from the count value C2 Counting the elapsed time from the detection of the second detected means to the start of writing of the second color, which is the difference from the count value C1 of the elapsed time from the start of writing of the first color to the start of writing of the second color. A calculating means for calculating a value C3, and the detecting means measures an elapsed time from detection of the detected means serving as the writing start reference to the next main scanning synchronization signal. Measurement means, storage means for storing and holding a first reference value T / 2 that is ½ of the main scanning synchronization signal period T, and a measurement value of the first measurement means as a first value. A first determination means for determining the magnitude of the reference value and a measurement value after the detection of the detected means until the next main scanning synchronization signal after reaching the first reference value. A second measuring means for measuring and holding time; a calculating means for obtaining a difference between a measurement time by the first measuring means and a measurement result of the second measuring means; and a result of the calculating means as a first reference value. A second determination means for comparing and determining the magnitude of the first detection means at the (2n-1) -th rotation (n ≧ 1: positive integer) of the intermediate transfer member. When the result of the determination means 1 is determined to be large, the variable amount S1 is set to 1, and when the result is determined to be small, the variable amount S1 is set to 2, The variable amount S2 is 1 when the result of the first determining means is determined to be large in the detection of the second detected means at the (2n-1) th rotation of the subject, and the variable amount S2 is determined to be small. 2 and the second measurement time when the first detected means at the (2n-1) th rotation of the intermediate transfer body is detected, and when the first detected means at the 2nth rotation of the intermediate transfer body is detected. When the result of the second determination means is determined to be small during the first measurement time at 1, the variable amount S3 is set to 1, and when the result is determined to be large, the variable amount S3 is set to 2, and (2n− 1) Second determination at the second measurement time at the time of detection of the second detection target at the rotation and at the first measurement time at the detection of the second detection means at the 2nth rotation of the intermediate transfer member. When the result of the means is determined to be small, the variable amount S4 is set to 1, and when it is determined to be large, the variable amount S4 is set to 2. Then, the writing of the first color is started in synchronization with the S1 main scanning synchronization signal from the detection of the first detected means at the (2n-1) th rotation of the intermediate transfer member, and the second color Is started in synchronization with the (S1 + C1) -th main scanning synchronization signal from the detection of the first detected means at the (2n-1) -th rotation of the intermediate transfer member, and the writing of the third color is started. From the detection of the first detected means at the 2nth rotation of the intermediate transfer member, the fourth color writing is started in synchronization with the S3rd main scanning synchronization signal, and the second nth rotation of the intermediate transfer member is started. The detection is performed in synchronization with the (S1 + S4-S2) -th synchronization signal from the second detected means detection.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, storage means for storing and holding a preset count value for delaying the timing for starting image formation for each color is provided. And controlling to start writing the image of each color after the count has elapsed from the timing of starting the writing of the image of each color.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the means for adjusting the count value C1 and the count memory for storing and holding the count value C1 adjusted by the means. Means for controlling the write start position.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the count value C1 is adjusted by adjusting any one color of the first image forming unit and any one color of the second image forming unit. And a total of two colors.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth aspect, the image forming apparatus further comprises means for detecting the amount of residual toner of each color, and the adjustment of the count value C1 It is characterized in that it is performed in a total of two colors, one color with many colors and one color with much remaining toner of the second image forming unit.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a use condition storage that stores and holds at least one use condition information among an environmental temperature, the number of printed sheets, and a use time. And storage means for storing and holding a preset count value that delays the timing of starting image formation for each color, and according to at least one of the environmental temperature, the number of printed sheets, and the usage time Thus, control is performed so that the image writing of each color is started after the count has elapsed from the timing of starting the image writing of each color.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a use condition storage that stores and holds at least one use condition information among an environmental temperature, the number of printed sheets, and a use time. And a count storage unit that counts the detected unit serving as the writing start reference, and serves as the writing start reference according to at least one of the environmental temperature, the number of printed sheets, and the usage time. The detected means is changed to another detected means.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a length discriminating unit that discriminates a length of the sheet-like recording medium in the moving direction, and the intermediate transfer member. The writing start position is calculated from the transport speed of the sheet, the sheet-like recording medium length in the moving direction obtained by the length discriminating means, and the sheet-like recording medium interval set in advance by the length of the sheet-like recording medium. And a main scanning synchronization signal count value from the main scanning synchronization signal immediately after detection of the detected means serving as the writing start reference to the start of writing is calculated and set by the calculating means.

  According to the present invention, a novel image forming apparatus can be provided by solving the above-described problems. The effects of each claim are as follows.

According to the present invention, even when the speed variation occurs in the intermediate transfer member, the second and fourth color image head alignment can be performed with high accuracy in the same manner as the first and third color image head alignment. (Claims 1 and 2).
According to the present invention, by controlling at a timing synchronized with writing, it is possible to perform high-precision image head alignment in one scanning unit. In addition, since it is not necessary to provide a dedicated timer, the apparatus configuration can be simplified.

According to the present invention, the image head position shift can be suppressed to 1/2 scan or less.
According to the present invention, since the image forming position on the intermediate transfer member can be changed, deterioration of the intermediate transfer member can be prevented.
According to the present invention, it is possible to easily perform image head alignment adjustment between the first and second image forming units.

According to the present invention, since the four colors can be aligned by adjusting the two colors of the first rotation of the intermediate transfer member, the amount of toner used and the adjustment time during the adjustment can be reduced.
According to the present invention, since the four colors can be aligned by adjusting the two colors of the first rotation of the intermediate transfer member, the frequency of toner replacement can be reduced by adjusting the colors with a large amount of residual toner in each image forming unit. (Claim 8).
According to the present invention, since the image forming position on the intermediate transfer member can be changed, deterioration of the intermediate transfer member can be prevented (claims 9 and 10).

  According to the present invention, when two or more images are formed per intermediate transfer member circumferential length, the second and subsequent image writing start reference is set to the immediately preceding detected means reference (for example, the mark reference), so that the reference can be made. Since the time until the start of writing can be shortened, it is difficult to be influenced by the speed fluctuation of the intermediate transfer member, and the image head position shift can be reduced.

  Embodiments including the best mode for carrying out the present invention will be described below with reference to the drawings. In the embodiment and examples, components such as members and components having the same functions and shapes are described with the same reference numerals, and the description thereof is omitted. In order to simplify the drawings and the description, even components that are to be represented in the drawings may be omitted as appropriate without being specifically described in the drawings. When a constituent element such as a published patent gazette is cited and described, the reference numeral is shown in parentheses to distinguish it from that of the embodiment and examples.

First, with reference to FIG. 1 and FIG. 2, an outline of a configuration and a process of main parts of a color image forming apparatus will be described as an example of an image forming apparatus to which the present invention is applied.
a. Overview of Image Forming Apparatus An image forming apparatus 100 shown in FIG. 1 uses drum-shaped photoreceptors 14 and 14 ′ (hereinafter referred to as photoreceptor drums) as image carriers, and around the photoreceptor drums 14 and 14 ′. The first and second image forming units 140 and 240 are arranged with charging means 15 and 15 ', writing means 16 and 16', developing means 13 and 13 ', and cleaning means (not shown). The image forming units 140 and 240 are arranged at a constant interval along the same moving surface of the intermediate transfer belt 1 as an intermediate transfer member.

  If the image forming process is focused on one image forming unit, it follows a general electrostatic recording system, and a certain color is applied by a writing means on a photosensitive drum uniformly charged by a charger in the dark. The latent image is written, and the latent image is visualized by a developing means and transferred to an intermediate transfer belt.

  Assuming that the developing means in each image forming unit has a visualization function using toners of two different colors, four colors are added to the three primary colors, so these colors are shared by the developing means. Then, a full color image can be formed.

  Accordingly, while the same image forming area on the intermediate transfer belt sequentially passes through the two image forming units, the toner images are transferred one by one by each image forming unit. The same image formation can be achieved by allowing each image forming unit to superimpose and transfer a toner image of a color different from the previous one while the color-superimposed image area passes through the two image forming units once again. When the area passes through each image forming unit twice, the full-color toner image is overlaid and transferred. If this full-color toner image is transferred onto a transfer sheet as a sheet-like recording medium, a full-color image can be obtained on the transfer sheet. The toner image on the transfer paper can be fixed by a fixing unit to obtain a full-color final image on the transfer paper.

  This image forming apparatus makes it possible to obtain a high-speed print output in synchronization with the rotation of the intermediate transfer belt. The image forming apparatus includes a photosensitive drum as an image carrier, an LED as a writing unit, a converging light transmitter, and the like. As an example of this modified application, an endless belt-shaped image carrier may be used, and a laser light source may be used as a writing unit. Further, the image carrier is not limited to a photoconductor, but can be a medium that can form a latent image only by an action other than light, and an electromagnetic change due to an action other than light on such an image carrier. It is also possible to use writing means that can provide For example, in the case of a type using a magnetic recording drum instead of the photosensitive drum, a magnetic writing unit is used instead of the optical writing unit.

  In this way, the toner image formed with at least the three primary colors of A, B, and C is transferred to the image carrier and transferred to the intermediate transfer belt, and the color image on the intermediate transfer belt is transferred to the transfer paper by the transfer means. In the image forming method, as shown in FIG. 1, the photosensitive drum, the charging unit, and the developing unit are arranged at regular intervals along the same moving surface of the intermediate transfer belt 1 that runs in the direction of arrow a. The toner image is transferred onto the intermediate transfer belt 1 by the first image forming means 10 and the second image forming means 20 and the color image obtained on the intermediate transfer belt 1 is transferred onto the transfer paper by the transfer means. Is. The first image forming unit 10 is disposed in the first image forming unit 140, and the second image forming unit 20 is disposed in the second image forming unit 240.

b. Image Forming Process Here, when the total length of the intermediate transfer belt 1 is L and the length corresponding to the length in the moving direction at the time of transfer of the transfer paper is m, the color image forming process when L = m + α is sequentially performed. explain. Here, α is the length of the non-image forming area on the intermediate transfer belt 1 in the direction of movement of the intermediate transfer belt, and α <m. The length of α varies depending on the length of the image forming area on the intermediate transfer belt 1 or the length of the transfer paper used. Therefore, depending on the length of the transfer paper, there is a case where α> m.
(1) A toner image of A color is transferred to the intermediate transfer belt 1 by the first image forming unit 140 having A color developing means.
(2) Next, in the second image forming unit 240 having the B color developing means, the B color toner image is superimposed and transferred onto the A color toner image to obtain A and B color toner images. The C color toner image is superimposed and transferred onto the color toner image by the C color developing means of the first image forming unit 140 to obtain A, B, and C color toner images. At this point, the intermediate transfer belt 1 rotates approximately once.
(3) Obtained by transferring the D-color toner image by the D-color developing means of the second image forming unit 240 to the A, B, C-color toner images obtained in the step (2). A full-color image is transferred onto a transfer sheet (first sheet) by a transfer roller 110 as transfer means. Transfer onto the transfer paper (first sheet) is performed during the second rotation of the intermediate transfer belt 1.
(4) When a plurality of color prints are to be taken, the A color toner image in the first image forming unit 140 is simultaneously transferred with the overlap transfer of the D color toner image in the second image forming unit 240 in step (3). , And the B color toner image in the second image forming unit 240 is superimposed and transferred to obtain A and B color toner images.
(5) To the A and B toner images obtained in step (4), a C toner image in the first image forming unit 140, and then a D toner image in the second image forming unit 240. Are transferred to obtain a full-color image, which is transferred onto a second transfer sheet (second sheet). Transfer onto the transfer paper (second sheet) is performed during the fourth rotation of the intermediate transfer belt 1.
(6) The third and subsequent prints are obtained at the sixth rotation of the intermediate transfer belt 1 by repeating the steps from step (3).

c. Regarding the Intermediate Transfer Belt In the image forming apparatus 100 shown in FIG. 1, the intermediate transfer belt 1 as an intermediate transfer member is an endless belt, and is supported on each shaft (not shown) rotatably supported in the direction of the arrow in the figure. The drive roller 2 and the driven roller 3 that are attached are stretched over and are driven to rotate in the rotation direction indicated by the arrow a. A plurality of marks serving as detection means serving as a reference position on the intermediate transfer belt 1 along the rotational direction in a non-image forming region on one end side in the width direction orthogonal to the rotational direction a on the upper surface of the belt 1 Are provided at intervals in a row.

  A single mark may be provided or a plurality of marks may be provided. The mark has a line shape, and only this portion reflects light better than other portions. The example shown in FIG. 1 shows a case where two marks M1 and M2 are provided. Regardless of whether the mark is a single mark or a plurality of marks, a mark detection sensor 5 as a detecting means is provided on a non-illustrated immovable member and placed above the passing area of these marks. The mark detection sensor 5 includes a pair of a light emitter and a light receiver (not shown).

The mark detection sensor 5 includes a light emitting element such as an LED as a light emitter, and a light receiving element such as a photosensor (PT) as a light receiver. The approximate dimensions are about vertical (b) × horizontal (c) = 10 mm × 43 mm. The other detailed configuration of the mark detection sensor 5 is the same as the detection means (5) shown in FIGS. 2 to 4 of Japanese Patent Laid-Open No. 2000-305417. Omitted.
When the light emitted from the light emitter is reflected by the marks M1, M2 moving with the intermediate transfer belt 1 or other marks M (not shown), the reflected light is received by the light receiver, and the mark is controlled by the control means described later. M1, M2, and M are detected and controlled.

  With reference to FIG. 1 and FIG. 2, the overall configuration and operation of the image forming apparatus 100 will be supplementarily described. In both figures, a first image forming means 10 and a second image forming means 20 are provided at intervals along the same moving surface of the intermediate transfer belt 1 running in the rotation direction indicated by the arrow a. . The first image forming unit 10 and the second image forming unit 20 have the same configuration and form a toner image by electrophotography.

  The intermediate transfer belt 1 is given an optimum tension by a tension roller 60. On the lower running surface of the intermediate transfer belt 1, along the running direction of the intermediate transfer belt 1, a first image forming unit 140 including the first image forming means 10 in FIG. 1 and a second image in FIG. The second image forming unit 240 including the image forming unit 20 is disposed at a predetermined interval. The intermediate transfer belt 1 is longer than the length in the moving direction of the maximum size transfer paper used in the image forming apparatus 100 of the present embodiment by the non-image forming area.

In the first image forming unit 140, around the photosensitive drum 14 as an image carrier, a brush-like charging unit 15 that uniformly charges the surface of the photosensitive drum 14 in the rotation direction indicated by the arrows; Writing means 16 for optically writing an electrostatic latent image on the charged surface of the photosensitive drum 14, developing means 13 for developing an electrostatic latent image (hereinafter simply referred to as “latent image”) with toner, and the photosensitive drum 14 Cleaning means 21 for cleaning is disposed.
The developing means 13 includes a C-color developing device 11 and an A-color developing device 12. The developing device 11 and the developing device 12 can be switched and driven alternatively by a predetermined switching means.

Similarly to the first image forming unit 140, in the second image forming unit 240, a charging unit 15 ′ and a writing unit are arranged around the photosensitive drum 14 ′ serving as an image carrier in the order of the rotation directions indicated by arrows. 16 ', developing means 13', and cleaning means 31 are arranged.
The developing means 13 ′ includes a B color developing device 11 ′ and a D color developing device 12 ′. The developing unit 11 ′ and the developing unit 12 ′ can be selectively switched and driven by a predetermined switching unit.
The second image forming unit 240 is attached to the apparatus main body in the same posture as the first image forming unit 140.
The photoconductive drum 14 in the first image image forming unit 140 and the photoconductive drum 14 ′ in the second image image forming unit 240 are identical in shape, size, material, etc., and are shared. It is illustrated. The photosensitive drum 14 and the photosensitive drum 14 'are rotationally driven at the same peripheral speed.

  Each of the image forming units 140 and 240 is detachably attached to the apparatus main body. The rotation of each of the photosensitive drums 14 and 14 ′ is synchronized with the traveling of the intermediate transfer belt 1, and the peripheral speed thereof is determined to be exactly the same as the traveling speed of the intermediate transfer belt 1. Instead of the charging means 15 and 15 ', a charging means using a corona discharger or a roller can be employed.

  Each developing device uses a two-component developer. The developing unit 12 for A color is magenta toner and carrier, the developing unit 11 'for B color is yellow toner and carrier, the developing unit 11 for C color is cyan toner and carrier, and the developing unit 12 for D color. 'Contains black toner and a carrier, respectively, and latent images on the respective photosensitive drums 14 and 14' formed by a well-known method using the charging units 15 and 15 'and the writing units 16 and 16' are displayed. The developing is performed by the developing rollers 32, 33, 34, and 35, respectively.

  Each of these developing rollers 32, 33, 34, and 35 is a developing means, and adopts a magnetic brush developing system using a type in which a nonmagnetic sleeve is rotated around a fixed magnet.

  The four developing devices 11, 12, 11 ′, and 12 ′ each have a similar configuration including a paddle that is a developer agitator, a conveying screw that is a toner replenisher, and the like. Other known color developing devices described in Japanese Patent Publication No. Gazette can be adopted.

  The conveying screws 4M, 4C, 4Y, and 4B have a structure in which blades are spirally wound. The paddles 8M, 8C, 8Y, and 8B have spiral blades 9c and eight radial plates in order to have a developer agitating function and a conveying function. The paddle 8M and the conveying screw 4M respectively convey the developer in the opposite axial directions by rotation, and distribute the developer evenly in the longitudinal direction of the developing roller 32. The other paddles 8C, 8Y, 8B and the conveying screws 4C, 4Y, 4B are the same as described above.

  A first transfer brush 41 and a second transfer brush 42 serving as a transfer device to which a transfer bias voltage is applied are respectively contactable with and separated from the photosensitive drums 14 and 14 ′ with the intermediate transfer belt 1 interposed therebetween. In addition, the driven roller 3 is provided with a transfer roller 110 to which a bias voltage for transfer is applied, through the intermediate transfer belt 1 so as to be able to contact and separate. A transfer roller or a corona discharger can be used in place of the first and second transfer brushes 41 and 42.

  Each of the photosensitive drums 14 and 14 ′ is flat and slightly separated downward from the intermediate transfer belt 1, and the first transfer brush 41 and the second transfer brush 42 are slightly upward from the intermediate transfer belt 1. In the step of transferring the toner images on the photosensitive drums 14 and 14 ′ to the intermediate transfer belt 1, the intermediate transfer belt 1 is moved to the photosensitive member by the first transfer brush 41 and / or the second transfer brush 42. Contact drum 14 and / or 14 '.

The driven roller 3 and the transfer roller 110 constitute a color image transfer unit 45. Instead of the transfer roller 110, a transfer means using a corona discharger or a transfer brush can be employed. The driving roller 2 is provided with a cleaning device 61 that removes toner remaining on the surface of the intermediate transfer belt 1 so as to be able to contact and separate.
When forming a full-color image, the first image forming unit 10 and the second image forming unit 20 sequentially form toner images on the intermediate transfer belt 1, and transfer the color image obtained on the intermediate transfer belt 1. The image is transferred onto transfer paper by the roller 110.
The rotation of the photosensitive drums 14 and 14 ′ in each of the image forming units 10 and 20 is synchronized with the traveling due to the rotation of the intermediate transfer belt 1, and the peripheral speed thereof is determined to coincide with the traveling speed of the intermediate transfer belt 1. ing. The photosensitive drums 14 and 14 ′ are usually slightly separated from the intermediate transfer belt 1, and the first transfer brush 41 is transferred in the process of transferring the toner images on the photosensitive drums 14 and 14 ′ to the intermediate transfer belt 1. The intermediate transfer belt 1 is brought into contact with the photosensitive drums 14 and 14 ′ by the second transfer brush 42. The toner image transferred onto the intermediate transfer belt 1 is transferred onto transfer paper by a transfer roller 110 constituting a transfer device.

  As shown in FIG. 2, below the first and second image forming units 140 and 240, a sheet feeding device (not shown) that feeds the stacked transfer sheets one by one is arranged. The single transfer sheet P sent out from the paper feeding device is fed to the transfer unit 45 by a feed roller pair 43 and a pair of registration rollers 44. A fixing device 50 including a heating roller 47 that is rotationally driven in the direction of an arrow b and a pressure roller 48 that rotates in pressure contact with the heating roller 47 is disposed obliquely above and to the left of the transfer unit 45. A roller 51 for applying an anti-offset liquid contacts the surface of the heating roller 47 as necessary, and a transfer paper peeling claw 52 is in contact therewith.

  On the downstream side of the fixing device 50, a pair of paper discharge rollers 54 for sending the transfer paper sent from the fixing device 50 onto the paper discharge tray 53 is disposed. An exhaust fan 55 for exhaust heat is provided at the upper left portion of FIG. 2, whereby an electrical component (not shown) stored below the paper discharge tray 53 is heated by the heat of the fixing device 50. Is prevented.

  When the color images A, B, C, and D are finally formed on the intermediate transfer belt 1 by the above procedure, the color image is transferred by the transfer device onto the transfer paper sent from the paper supply unit (not shown). Is fixed. After the transfer of the color image, the intermediate transfer belt 1 is subjected to removal of residual toner by the cleaning device 61.

d. Control Unit The control of the image forming apparatus described above is performed by the control system shown in FIG. FIG. 2 shows a control system in the image forming apparatus 100 including the first and second image forming units 10 and 20 shown in FIG. The control unit 70 mainly controls the operation of the image forming apparatus 100 when writing an image, and also controls the overall operation of the image forming apparatus 100. The control means 70 includes a CPU 71 (central processing unit), an unillustrated I / O (input / output) port, a nonvolatile RAM 72 (a storage device capable of storing and reading data), a ROM 73 (read-only storage device), and The microcomputer includes a timer 74 and the like, which are connected by a signal bus (not shown).
However, the count acquisition means, the calculation means, and the counter of the timer 74 in the CPU 71 are functions unique to Example 1 described later, and are arranged as the control means 70 of the general image forming apparatus 100 to which the present invention is applied. Note that this is not done.

  The control means 70 includes an operation panel 22 having operation switches / keys for instructing image forming conditions and the like for the image forming apparatus 100, a mark detection sensor 5, a temperature sensor 7 for detecting an environmental temperature, and a total print so far. Information from a printed sheet counter 24 or the like that holds the number of sheets is input.

  The control unit 70 outputs control information necessary for image formation to the first image forming unit 10, the second image forming unit 20, and other controlled objects 23. When an intermediate transfer drum on the drum is used instead of the intermediate transfer belt 1, a control signal is output to the intermediate transfer drum drive system instead of the intermediate transfer belt drive system 40.

A supplementary description will be given of the configuration peculiar to the first embodiment.
As a specific example of the writing means 16, 16 ′, for example, the same one as the exposure apparatus (1a) shown in FIG. 16 of Japanese Patent Application Laid-Open No. 2003-334989 and described in the paragraph “0114” is used. That is, the writing means 16 and 16 ′, like the exposure apparatus (1a), reflect light beams from two light sources (not shown) by a rotating polygon mirror (polygon mirror) as one scanning means to write light (exposure). ). Then, as with the light receiving element (14) in the exposure apparatus (1) shown in FIG. 3 of the publication and described in the paragraphs “0011” to “0013” and “0015”, two pieces from the rotary polygon mirror are used. Are detected by two light receiving elements (not shown, but for convenience, 14MC (in the same publication, (14MY), 14YB (in the same publication, (14CK) is attached)). It has become.

  That is, the writing means 16 and 16 'have the same configuration as that of the single exposure apparatus (1a) and are provided with two light sources. One light source is a magenta or cyan image by a modulation means (not shown). In accordance with the information, the other light source is sequentially modulated in accordance with the image information of yellow and black colors by a modulation means (not shown), and the image information of each color of magenta and cyan, yellow and black is used. By emitting a laser beam as a sequentially modulated light beam, an image is formed as a laser spot on the surface of the photosensitive drums 14 and 14 '. These laser spots are rotated and driven by driving means (not shown) so that the photosensitive drums 14 and 14 'are repeatedly scanned in the main scanning direction, and latent images are formed on the photosensitive drums 14 and 14'. Form.

The light receiving elements (14MC, 14YB) as main scanning synchronization signal generating means are arranged outside the image range within the laser beam scanning range, receive the laser beam from the rotary polygon mirror, detect this, and perform main scanning. A main scanning synchronization signal for determining the image writing start position (lateral registration) in the direction is generated.
The specific examples of the writing means 16 and 16 ′ are not limited to the exposure apparatus (1a), and the exposure apparatus (1) described above may be provided in each of the writing means 16 and 16 ′. .

Next, with reference to FIG. 5, a supplementary description will be given of the control configuration unique to the first embodiment.
The timer 74 in the example shown in FIG. 5 is a so-called external timer 74 that is initialized when the mark detection sensor 5 detects the first mark M1, that is, a counter serving as a counting unit that starts counting elapsed time after being reset. It has the function of.
The counter is not limited to the external timer 74, but may be provided in a so-called internal timer provided in the CPU 71, or the external timer and the internal timer may be assigned functions as appropriate (examples and modifications described later). The same applies to examples).

  The CPU 71 has a function as count acquisition means for acquiring the count value C2 by the counter of the timer 74 when the mark detection sensor 5 detects the second mark M2, and also writes the first color set in advance from the count value C2. Calculation means for calculating a count value C3 of the elapsed time from the detection of the second mark M2 to the start of writing of the second color, which is a difference from the start to the count value C1 of the elapsed time from the start of writing of the second color. As well as a control function. Hereinafter, the CPU 71 is sometimes referred to as the control means 70 for the sake of simplicity.

  The control means 70 is provided in the control board arrangement part in the apparatus main body. The control means 70 (CPU 71) includes various signals from the operation panel 22, mark detection signals from the mark detection sensor 5, main scanning synchronization signals from the light receiving elements (14MC) and (14YK), and environmental temperature from the temperature sensor 7. A detection signal, a data signal related to the total number of printed sheets from the printed number counter 24, for example, a total driving time of the first or second image forming unit 140, 280 of the image forming apparatus 100 or a total of the intermediate transfer belt 1 Based on the usage time data relating to the drive time and the operation program called from the ROM 73, the operation of the first and second image forming means 10, 20, the intermediate transfer belt drive system 40 and other controlled objects 23 are controlled. The overall operation of the image forming apparatus 100 is controlled.

  The ROM 73 stores an operation program for the entire image forming apparatus 100, necessary data, and the like, and this operation program is appropriately called by the CPU 71. The RAM 72 temporarily stores and holds the calculation results of the CPU 71, various signals from the operation panel 22, mark detection signals from the mark detection sensor 5, main signals from the light receiving elements (14MC) and (14YK). A scanning synchronization signal, an environmental temperature detection signal from the temperature sensor 7, a data signal related to the total number of prints so far from the print number counter 24, for example, the first or second image forming unit 140, 280 of the image forming apparatus 100. For example, a function for storing use time data and on / off signals relating to the total drive time of the intermediate transfer belt 1 or the total drive time of the intermediate transfer belt 1 as needed.

  A first embodiment in which the present invention is applied to the image forming apparatus 100 shown in FIGS. 1 and 2 based on the above-described configuration will be described with reference to FIGS. In the timing chart of FIG. 3, the first rotation of the intermediate transfer belt 1 is detected by adding a comma “′” to the marks M1, M2, and the like detected at the second rotation of the intermediate transfer belt 1. (The same applies to the timing chart of FIG. 8 described later). Since this operation is performed under the control of the control means 70 (CPU 71), the control means 70 (when the detailed operations such as activation, operation, and stop of actuators (control target drive means) such as various motors are described. Expressions based on commands or command signals from the CPU 71) are omitted as much as possible.

  When the control means 70 receives a print instruction signal from a host computer (not shown), the image forming apparatus 100 shown in FIG. 2 starts printing in response to a command signal from the control means 70. First, the photosensitive drums 14, 14 'and the intermediate transfer The belt 1 is driven. In FIG. 1, when the intermediate transfer belt 1 is driven, the mark M <b> 1 is detected by the mark detection sensor 5 and a mark detection signal is output to the CPU 71. The image forming apparatus 100 starts an image forming operation with reference to a mark detection signal first detected after the peripheral speed of the intermediate transfer belt 1 reaches a constant speed. A known control method is used in which the peripheral speed of the intermediate transfer belt 1 reaches a constant speed by determining the constant speed arrival time in advance and measuring the driving time of the intermediate transfer belt 1.

When the mark M1 is detected by the mark detection sensor 5, the first image forming unit 10 starts the first color A light writing by the writing unit 16, and the latent image is formed on the photosensitive drum 14. Be started. The latent image is developed in the first color A by the developing device 12 of the developing means 13 to form a toner image on the photosensitive drum 14. This toner image is transferred to the intermediate transfer belt 1, and a first-color A-color toner image is formed on the intermediate transfer belt.
When the mark M1 is detected by the mark detection sensor 5, the counters shown in FIGS. 3 and 4 are reset and start counting elapsed time. At this time, immediately after the mark M1 is detected, the main scanning synchronization signal generated by the light receiving element (14MC) is inputted to the control means 70, so that the main detection signal next to the mark detection signal of the mark M1 as shown in FIG. Image writing of the first color is started at the timing of the scanning synchronization signal (write synchronization signal). Thus, the mark detection signal and the main scanning synchronization signal are asynchronous.

  Here, the first color A toner image formed by the first image forming unit 10 and the second color B formed by the second image forming unit 20 on the intermediate transfer belt 1 in advance. After the mark M1 is detected by the mark detection sensor 5 so that the toner images overlap each other and the first color light writing is started by the writing means 16, the second color light writing is started by the writing means 16 ′. The elapsed time until this is stored as a count value C1 (set value) of the counter. Then, as described later, when the count value of the counter (timer 74) of the control means 70 reaches a preset count value C1, that is, when it coincides with the count value C1, the second color optical writing is started.

The mark M2 is detected by the mark detection sensor 5 during the formation of the first-color A-color toner image before the start of the second-color B-color optical writing. The CPU 71 acquires the count value C2 of the counter at that time. The CPU 71 calculates the count value C3 of the time from the acquired count value C2 to the preset count value C1, and stores it in the RAM 72.
When the count value reaches C1, in the second image forming unit 20, the writing unit 16 'starts the second color B light writing, and the formation of a latent image on the photosensitive drum 14' is started. The latent image is developed by the developing unit 11 'of the developing means 13' for the second color, B, to form a toner image on the photosensitive drum 14 '. This toner image is transferred to the intermediate transfer belt 1 so as to overlap the first-color A-color toner image, and the first-color A color and the second-color B color are transferred onto the intermediate transfer belt. A synthetic toner image is formed.

When the developing unit 12 completes the development of the first-color A-color latent image, the first-color A-color developing unit 12 is switched to the third-colored C-color developing unit 11. Similarly, when the development of the second B-color latent image is completed by the developing device 11 ′, the second-color B-color developing device 11 ′ is switched to the fourth-color D-color developing device 12 ′. .
When the intermediate transfer belt 1 makes one turn and the mark M1 is detected again by the mark detection sensor 5, in the first image forming unit 10, the writing unit 16 changes the C color of the third color in the same manner as the first color. Optical writing is started, and formation of a latent image on the photosensitive drum 14 is started. At this time, immediately after the detection of the mark M1, the main scanning synchronization signal generated by the light receiving element (14MC) is inputted to the control means 70 as described with reference to FIG. The third color optical writing is started at the timing of the main scanning synchronization signal (write synchronization signal) that comes next.
Then, the latent image is developed by the developing unit 11 of the developing unit 13 for the third color C, and a toner image is formed on the photosensitive drum 14. This toner image is transferred to the intermediate transfer belt 1 so as to overlap the first color A color toner and the second color B color toner image, and the first color A color is transferred onto the intermediate transfer belt 1. As a result, a composite toner image of the second color B and the third color C is formed.

Next, when the mark M2 is detected again by the mark detection sensor 5, the counter shown in FIG. 3 is reset and starts counting elapsed time. When the count value coincides with the count value C3 stored and held at the first rotation of the intermediate transfer belt, the second image forming unit 20 starts writing the fourth color D light by the writing unit 16 '. Formation of a latent image on the body drum 14 'is started. The latent image is developed by the developing unit 11 ′ of the developing means 13 ′ for the fourth color, D, to form a toner image on the photosensitive drum 14 ′.
This toner image is transferred to the intermediate transfer belt 1 so as to overlap the synthesized toner image of the first color A, the second color B, and the third color C, and is transferred onto the intermediate transfer belt. In addition, a full-color toner image of the first color A, the second color B, the third color C, and the fourth color D is formed.

  The above-described control operation will be briefly described as follows. In other words, the image forming apparatus 100 according to the first exemplary embodiment basically operates at the same timing, except that the first transfer and the second rotation of the intermediate transfer belt 1 have different colors due to switching of the developing devices. Also, optical writing to the photosensitive drums 14 and 14 'is basically performed at the same timing, although the mark used as a reference for starting writing is different. The optical writing of the second color to the photosensitive drum 14 ′ at the first rotation of the intermediate transfer belt 1 is controlled based on a preset count value C1 from the time of detection of the mark M1, and thus apparently. The traveling distance on the intermediate transfer belt 1 is long.

On the other hand, the count value C3 that is the difference from the time of detection of the mark M2 immediately before the start of the second color optical writing (acquisition of the count value C2) to the count value C1 from the start of the second color optical writing is measured and calculated as described above. it can. Therefore, by storing the calculated count value C3, the elapsed time from the detection of the mark M2 ′ to the start of the fourth color optical writing on the photosensitive drum 14 ′ at the second rotation of the intermediate transfer belt 1 is stored. By using the count value C3, the distance from the reference on the intermediate transfer belt 1 can be substantially shortened, so that it is difficult to be affected by the speed fluctuation of the intermediate transfer belt 1 or the like.
Therefore, according to the first exemplary embodiment, even when the speed fluctuation occurs in the intermediate transfer belt 1 as the intermediate transfer member, the second color and the fourth color are similar to the first color and third color image head alignment. It is possible to align the top of the color image with high accuracy.

Next, various modifications of the first embodiment will be described.
A first modification will be described with reference to FIG. Compared to the first embodiment, the first modification has a distance equal to or less than the distance traveled from the mark M1 serving as the first color A write start reference to the second color B light write start. The mark M2 is a mark M2 in which a plurality of sets of two marks M1 and M2 are arranged on the intermediate transfer belt 1 at equal intervals, and an arbitrary reference mark detected by starting the image forming operation is marked M1. However, the main point is that the write start control is performed, and the other points are the same as in the first embodiment.

  In FIG. 6, a symbol L <b> 1 indicates a distance traveled from the mark M <b> 1 serving as the first color A light writing start reference to the start of the second color B light writing. The operation of the first modification can be easily performed by referring to the first embodiment shown in FIGS. 1 to 5 and FIG. 6, and thus further explanation is omitted (claim 2).

With reference to FIG. 7, a modified example different from the modified example 1 shown in FIG. 6 will be described. The modification shown in FIG. 7 is mainly different from the modification 1 shown in FIG. 6 in that marks are arranged on the intermediate transfer belt 1 with an interval smaller than the above interval.
In FIG. 7, marks M-1 (= M1) to M-7 (= M2) are provided in order from the mark M1 to the mark M2 at equal intervals in order from the right. Here, if the time difference at which adjacent marks are detected by the mark detection sensor 5 is, for example, 200 ms, the time from when the mark M1 is detected until the mark M2 is detected is 1200 ms. When the mark M1 is detected, a mark management timer (which may be an internal timer in the CPU 71) provided in the timer 74 shown in FIG. 5 is set to 1100 ms, for example, and countdown is started.

Next, the mark M-2 is detected after 200 ms have elapsed, and the count value of the mark management timer at this time is 900 ms. As described above, when the mark management timer is measuring time, control is performed so as to ignore the detected marks, and therefore all the detected marks M-3 to M-6 are sequentially ignored. The mark management timer count value becomes “0” after about 100 ms from the detection of the mark M-6, the mark management timer is stopped, and the marks detected thereafter are valid. Therefore, the mark M-7 to be detected next, that is, the mark M2, becomes valid.
In this manner, optical writing is performed such that the marks detected between the time when the reference mark having the two mark detection times as the mark M1 is detected and the time immediately before the mark M2 is detected are ignored. Perform start control. Therefore, according to the modification 1 and the modification shown in FIG. 7, the same advantages as those of the first embodiment can be obtained (claim 2).

The modification 2 is mainly different from the first embodiment in that the optical writing timing is controlled by using a counter that operates in synchronization with the main scanning synchronization signal of the writing means 16 and 16 ′.
As a means for measuring the elapsed time, instead of the timer 74 (which may be an internal timer in the CPU 71), a counter for detecting the main scanning synchronization signal shown in FIG. . The counter of the main scanning synchronization signal is reset (initialized) at the timing of the mark detection signal, and the count value of the counter is incremented by 1 each time the main scanning synchronization signal is detected. That is, when a mark detection interrupt is entered using the interrupt processing of the CPU, the main scanning synchronization signal counter is reset and counted every time the main scanning synchronization signal interruption occurs. Then, when the count value C1 set in advance is reached, the second color optical writing is controlled at the timing of the main scanning synchronization signal. In this way, since actual optical writing must be started at the timing of the main scanning synchronization signal, the optical writing timing can be adjusted by the count number of the main scanning synchronization signal. The above-described control method is also adopted on the second image forming unit 240 side.
As described above, it is possible to perform image head alignment, which is writing position control in one scanning unit, with high accuracy. Furthermore, since it is not necessary to provide a dedicated timer, the apparatus configuration can be simplified (claim 3).

In the third modification, compared with the first embodiment, a function as a storage unit that stores and holds a preset count value that delays the timing of starting image formation of each color is added to the nonvolatile RAM 72 of the control unit 70. The main difference is that the CPU 71 is added with a function for controlling the light writing of each color to start after the count has elapsed from the light writing start timing of each color.
An example of controlling with the main scanning synchronization signal shown in FIG. 4 will be described. When there is no delay, optical writing of the first color and the second color is started at the same timing as described with reference to FIG. Here, when the count value to be delayed is “2”, the optical writing is started at the timing of the main scanning synchronization signal obtained by delaying the optical writing of the first color and the second color by two. Therefore, the entire image can be formed at a position delayed by two lines. In other words, the position of the image formed on the intermediate transfer belt 1 can be arbitrarily changed and shifted by delaying the start timing of optical writing for each color by a predetermined count and starting optical writing. Can do.
Therefore, according to the third modification, the image forming position on the intermediate transfer belt 1 as an intermediate transfer member can be changed, so that the deterioration of the intermediate transfer belt 1 can be prevented.

The modification 4 is different from the first embodiment in that a function as a means for adjusting the count value C1 is added to the CPU 71 of the control means 70, and a count storage means for storing and holding the count value C1 adjusted by the CPU 71. The main difference is that is added to the nonvolatile RAM 72.
As described above, the count value C1 is adjusted and can be changed by the CPU 71, so that the first color and the second color can always be finely adjusted so that the heads of the images match. Therefore, according to the fourth modification, the count value C1 can be constantly updated, so that the image head alignment adjustment between the first and second image forming units 140 and 240 can be performed accurately and easily. 6).

  The modification 5 is different from the first embodiment in that a function as use condition storage means for storing use condition information of environmental temperature, number of printed sheets and use time is added to the nonvolatile RAM 72 of the control means 70, and each color. The function of the storage means for storing and holding a preset count value is added to the nonvolatile RAM 72 of the control means 70, the environmental temperature detection signal from the temperature sensor 7, and the number of printed sheets Data signals from the counter 24 relating to the total number of printed sheets up to now, for example, usage relating to the total driving time of the first or second image forming unit 140, 280 of the image forming apparatus 100 or the total driving time of the intermediate transfer belt 1 Based on the time data signal, the optical writing of each color according to at least one of the environmental temperature, the number of printed sheets, and the usage time. From write start timing, a point obtained by adding a function to CPU71 which controls so as to start the optical writing of each color after the count has elapsed differs mainly.

  In the fifth modification, the CPU 71 performs the same control as in the third modification according to the usage conditions information of the environmental temperature, the number of printed sheets, and the usage time stored and held in the nonvolatile RAM 72. By this control, the writing start timing is shifted, and the image position formed on the intermediate transfer belt 1 is arbitrarily shifted.

The modification 6 is different from the first embodiment in that a function as a use condition storage unit that stores and holds use condition information of the environmental temperature, the number of printed sheets, and the use time is added to the nonvolatile RAM 72 of the control unit 70. The function of the count storage means for counting the mark M1 as the start reference is added to the nonvolatile RAM 72 of the control means 70, the environmental temperature detection signal from the temperature sensor 7, and the total number of prints from the printed sheet counter 24 to date. Writing starts based on a data signal related to the number of printed sheets, for example, a use time data signal related to the total drive time of the first or second image forming unit 140 or 280 of the image forming apparatus 100 or the total drive time of the intermediate transfer belt 1 The main difference is that a function of changing the reference mark M1 to another mark is added to the CPU 71.
In the sixth modification, control is performed to change the mark M1 serving as a writing start reference to another mark based on the usage condition information of the environmental temperature, the number of printed sheets, and the usage time stored and held in the nonvolatile RAM 72. By this control, the writing start timing is shifted, and the image position formed on the intermediate transfer belt 1 is arbitrarily shifted.
Therefore, according to the modified examples 5 and 6, since the image forming position on the intermediate transfer belt 1 as the intermediate transfer member can be changed, the deterioration of the intermediate transfer belt 1 can be prevented.
The use condition storage means only needs to have a function of storing and holding at least one use condition information among the environmental temperature, the number of printed sheets, and the use time, and there is at least one means for detecting the use condition information. That's fine.

  The modified example 7 has a length discriminating unit that discriminates the sheet length of the transfer paper P in the moving direction of the intermediate transfer belt 1 as compared with the first embodiment, the conveyance speed of the intermediate transfer belt 1, and the length A function of calculating means for calculating the writing start position based on the sheet length of the transfer sheet P determined by the length determining means and the sheet interval set in advance by the sheet length, and a writing start reference The main difference is that the CPU 71 adds a function for calculating and setting the main scanning synchronization signal count value from the main scanning synchronization signal immediately after detection of the mark M1 to the start of writing.

  The length discriminating means is, for example, a well-known sensor disposed in a sheet feeding cassette of a sheet feeding unit (not shown) or a plurality of reflective optical sensors arranged in the sheet feeding direction of a sheet feeding tray (not shown). Can be identified. The conveyance speed of the intermediate transfer belt 1 is detected by a rotary encoder including an encoder sensor disposed in a drive system (not shown).

  When forming a plurality of images per circumferential length of the intermediate transfer belt 1, the distance from the beginning of the first image to the length of the sheet in the transport direction plus the interval between the first and second sheets Then, a second image is formed. When the paper size is selected, the paper length and the paper interval are determined in advance, and this distance can be obtained. Therefore, the mark immediately before the optical writing start timing of the second sheet can be specified from the mark M1 as the writing start reference of the first sheet. Further, the count value from the detection of this mark by the mark detection sensor 5 to the start of the second optical writing is also obtained. At this time, the number of marks from the mark M1 and the count number of timing from this mark to the start of writing of the second sheet are set, and the start of writing of the second sheet is controlled.

  Therefore, according to the modified example 7, when two or more images are formed per circumferential length of the intermediate transfer belt 1, writing is started from the reference by setting the optical writing start reference for the second and subsequent sheets as the previous mark reference. Can be shortened, so that it is difficult to be influenced by the speed fluctuation of the intermediate transfer belt 1, and the image head position deviation can be reduced.

  Next, for comparison with Example 1 according to the present invention, referring to FIG. 1, FIG. 2, and FIG. 8 for a comparative example according to a conventional technique (for example, a technique described in Japanese Patent Laid-Open No. 2000-305417). I will explain. Since operations other than the writing process are the same as those in the above-described embodiment and example 1, only the writing process timing after the detection of the writing reference mark M1 will be described here.

When the mark M1 is detected by the mark detection sensor 5, the first image forming unit 10 starts the first color A light writing by the writing unit 16, and the latent image is formed on the photosensitive drum 14. Be started. When the mark M1 is detected by the mark detection sensor 5, the counter of the comparative example shown in FIG. 8 is reset and time counting by the counter is started.
When the count value reaches C1, in the second image forming means 20, the writing means 16 ′ starts the second color B light writing and the formation of the latent image on the photosensitive drum 14 ′ is started. .

When the mark M1 is detected again by the mark detection sensor 5 after the intermediate transfer belt makes one round, in the first image forming unit 10, the third color C light is written by the writing unit 16 as in the first color. Writing is started and formation of a latent image on the photosensitive drum 14 is started.
When the count value reaches C1 ′, the second image forming unit 20 starts the fourth color D light writing by the writing unit 16 ′ and starts the formation of a latent image on the photosensitive drum 14 ′. The

  Here, similarly to the count value C1, a third color C toner image formed by the first image forming unit 10 and the second image forming unit 20 are formed on the intermediate transfer belt 1 in advance. The mark M1 is detected by the mark detection sensor 5 so that the fourth color D-color toner images overlap, and the writing means 16 starts the third color optical writing. The time until the optical writing of the fourth color is started is stored as a counter value C1 ′.

When the first embodiment according to the present invention is compared with the comparative example according to the prior art, the first color A, the third color C, the first color A, and the second color The B color alignment control method is the same. Since the first color A and the third color C are written with reference to the same mark M1 with a difference of one turn of the intermediate transfer belt, no positional deviation occurs.
However, in the comparative example according to the related art, when the speed variation occurs in the intermediate transfer belt 1, the second color B color and the fourth color D color are respectively positioned with respect to the first color A. Deviation occurs. Further, the load changes and the speed fluctuates easily due to the difference between the contact and separation of the cleaning device 61 with respect to the intermediate transfer belt 1 and the contact and separation of the transfer roller 110 between the first and second rotations of the intermediate transfer belt 1.

On the other hand, in Example 1 according to the present invention, even when the intermediate transfer belt 1 fluctuates in speed, the second B color and the fourth D color correspond to one turn of the intermediate transfer belt. Since there is a difference, writing is started at the timing of the count value C3 from the same mark M2, so that there is almost no displacement.
Accordingly, the count value of the counter corresponding to the time difference from the detection timing of the mark M1 at the first rotation of the intermediate transfer belt, that is, the writing start timing of the first color A to the writing start timing of the second color B is adjusted. By just doing this, it is possible to align the writing start positions of the four colors.

A second embodiment will be described with reference to FIGS. 1, 2, 9 and 10. Since the image forming method other than the control of the write timing is the same as that of the first embodiment, the description thereof is omitted.
Compared to the first embodiment, the second embodiment has a control configuration shown in FIG. 9 instead of the control configuration shown in FIG. 5 and a timing chart shown in FIGS. 10 is mainly different in that the write timing is controlled in the timing chart shown in FIG.

  Image formation for each color is started on the basis of marks M1 and M1 of the intermediate transfer belt 1 after the main scanning synchronization signal count value C1 has elapsed from the mark M1 and after the main scanning synchronization signal count value C3 has elapsed from the mark M2. When 16 ′ is a scanning type using the laser scanning optical system as described above, the detection of the mark M1 or M2 on the intermediate transfer belt 1 and the main scanning synchronization signal serving as the writing reference of the writing means 16 or 16 ′ are asynchronous. Therefore, even if image formation is started with the mark M1 or M2 on the intermediate transfer belt 1 as a reference, there is a deviation of a maximum of one scanning in the superimposed image of each color.

  The control configuration of this image forming apparatus is mainly different from that of the first embodiment shown in FIG. 5 in that it has a control means 70A having a microcomputer configuration shown in FIG. 9 instead of the control means 70. To do. Compared with the control means 70 shown in FIG. 5, the control means 70 </ b> A has a CPU 71 </ b> A instead of the CPU 71, a RAM 72 </ b> A instead of the RAM 72, a ROM 73 </ b> A instead of the ROM 73, and a timer 74. The main difference is that the timer 74A is provided.

The CPU 71A is mainly different from the CPU 71 in that it has functions of first and second determination means and calculation means, and is otherwise the same as the CPU 71.
The timer 74A is mainly different from the timer 74 in that it has the functions of the first and second measuring means, and is otherwise the same as the timer 74.

  The control means 70 </ b> A includes various signals from the operation panel 22, mark detection signals from the mark detection sensor 5, environmental temperature detection signals from the temperature sensor 7, and data signals related to the total number of prints so far from the print number counter 24. For example, based on the usage time data relating to the total driving time of the first or second image forming unit 140, 280 of the image forming apparatus 100 or the total driving time of the intermediate transfer belt 1, and the operation program called from the ROM 73A. The operations of the first and second image forming units 10 and 20, the intermediate transfer belt drive system 40 and other controlled objects 23 are controlled to control the overall operation of the image forming apparatus 100.

  The ROM 73A stores an operation program for the entire image forming apparatus 100, necessary data, and the like, and this operation program is appropriately called by the CPU 71A. The RAM 72A has a function of temporarily storing or storing the calculation result of the CPU 71A.

  As described above, the main control configuration of the second embodiment is based on the mark detection sensor 5 and the mark detection sensor 5 that detect the first mark M1 and the second mark M2 at predetermined positions, as shown in FIG. It has a function as a count acquisition means for acquiring the count value C2 of the counter when the second mark M2 is detected, and a lapse from the count value C2 to the second color write start from the preset first color write start The calculation means for calculating the elapsed time count value C3 from the time of detection of the second mark M2 until the start of writing of the second color, which is the difference up to the time count value C1, and the measurement value of the first measurement means. A first determination means for determining the magnitude of the first reference value, a calculation means for obtaining a difference between a measurement time by the first measurement means and a measurement result of the second measurement means; The CPU 71A having a function as a second determination means for comparing the result of the means with the first reference value and determining the magnitude thereof, and the reset of the mark detection sensor 5 when the first mark M1 is detected. A first measurement that has a function of a counter as a counting means for starting counting and that measures an elapsed time from detection of the mark M1 as a writing start reference by the mark detection sensor 5 to the next main scanning synchronization signal. A timer 74A having a function as a second measuring means for measuring and holding the time until the next main scanning synchronization signal after the measured value after detecting the means M1 and the mark M1 reaches the first reference value; It comprises a RAM 72A as a storage means for storing and holding a first reference value T / 2 which is set to ½ of the main scanning synchronization signal period T set in advance.

A second embodiment in which the present invention is applied to the image forming apparatus 100 shown in FIGS. 1 and 2 based on the above-described configuration will be described with reference to FIGS. 1, 2, 9, and 10.
In FIG. 1, when the mark M1 is detected by the mark detection sensor 5 in the first rotation of the intermediate transfer belt 1, the time t1 from this detection timing to the next main scanning synchronization signal is measured by the first measuring means. Is done. Next, the first determination means compares the time t1 with the first reference value T / 2 to determine the magnitude. As a result of the comparison, when it is determined that t1 is greater than T / 2, the first image forming unit 10 uses the writing unit 16 to set the first color A on the basis of the main scanning synchronization signal next to the mark M1 detection timing. Start color light writing. The value of the variable amount S1 at this time is stored as 1. The variable value of 1 means the first main scanning synchronization signal from the mark detection timing.

  Contrary to the above, when it is determined that t1 is smaller than T / 2 as a result of comparison, writing is performed in the first image forming unit 10 based on the second main scanning synchronization signal from the mark M1 detection timing. The optical writing of the first color A is started by means 16. The value of the variable amount S1 at this time is stored as 2. When the mark M1 is detected by the mark detection sensor 5, the second measuring means calculates a time t1 ′ from this detection timing to the next main scanning synchronization signal after the first reference value T / 2 has elapsed. measure.

  Next, in the second image forming unit 20, the mark M <b> 2 is detected by the mark detection sensor 5 at a timing before the second B color optical writing is started by the writing unit 16 ′. The count value C2 of the counter at this time is acquired. A count value C3 from the acquired count value C2 to a preset count value C1 is calculated and stored.

The time t2 from this detection timing to the next main scanning synchronization signal is measured by the first measuring means. Next, the first determination means compares the time t2 with the first reference value T / 2 to determine the magnitude. As a result of the comparison, when it is determined that t2 is greater than T / 2, the value of the variable amount S2 is stored as 1. As a result of comparison, when it is determined that t2 is smaller than T / 2, the value of the variable amount S2 is stored as 2.
When the mark M2 is detected by the mark detection sensor 5, the time t2 ′ from the detection timing to the next main scanning synchronization signal after the first reference value T / 2 has elapsed by the second measuring means. Measure.

  Next, when the counter value matches the preset count value C1, the second image forming unit 20 uses the main scanning synchronization signal as a reference and stores the variable amount S1th main scanning synchronization signal. 16 'starts optical writing of the second color, B color. That is, B-color optical writing of the second color is started in synchronization with the (S1 + C1) -th main scanning synchronization signal from the detection of the mark M1.

  When the mark M1 is detected again by the mark detection sensor 5 after the intermediate transfer belt makes one round, the time t3 from this detection timing to the next main scanning synchronization signal is measured by the first measuring means. Next, the second determination means compares the time t3 with the time t1 'obtained when the mark M1 for the first rotation of the intermediate transfer belt is detected, thereby determining the magnitude. As a result of the comparison, when it is determined that t1 ′ is smaller than T / 2, the first image forming unit 10 uses the writing unit 16 to set the third color on the basis of the main scanning synchronization signal next to the mark M1 detection timing. Start C-color optical writing. The value of the variable amount S3 at this time is stored as 1.

  Contrary to the above, when it is determined that t1 ′ is greater than T / 2 as a result of the comparison, the first image forming unit 10 uses the second main scanning synchronization signal from the mark M1 detection timing as a reference. The writing means 16 starts the third-color C-color optical writing. The value of the variable amount S3 at this time is stored as 2.

  Next, when the mark M2 is detected by the mark detection sensor 5 at the second rotation of the intermediate transfer belt, the time t4 from this detection timing to the next main scanning synchronization signal is measured by the first measuring means. . Next, the second determination means compares the time t4 with the time t2 'obtained when the mark M2 for the first rotation of the intermediate transfer belt is detected to determine the magnitude. As a result of the comparison, when it is determined that t2 'is smaller than T / 2, the value of the variable S4 is stored as 1. On the contrary, when it is determined that t2 'is larger than T / 2 as a result of comparison, the value of the variable S4 is stored as 2.

When the mark M2 is detected by the mark detection sensor 5 at the second rotation of the intermediate transfer belt, the counter is reset and starts counting.
In the second rotation of the intermediate transfer belt, after the mark M2 is detected by the mark detection sensor 5, the writing means in the second image forming means 20 is synchronized with the (S1 + S4-S2) -th main scanning synchronization signal. At 16 ', the fourth color D-color optical writing is started.

With the above control, writing of the first color A and the third color C is started within a time difference T / 2 or less after the writing start reference mark M1 is detected. Similarly, for the second color B and the fourth color D, writing starts at a time difference T / 2 or less after the writing start reference mark M2 is detected.
Therefore, according to the second embodiment, even when the intermediate transfer belt 1 fluctuates in speed during the first and second rotations of the intermediate transfer belt 1, the second color and the fourth color are compared with the first color. The image start position deviation, which is the image writing start position deviation, can be suppressed to ½ scanning or less.

  Also in the second embodiment, by adding the first to seventh modifications of the first embodiment, the advantages and effects of the first to seventh modifications can be obtained in addition to the advantages and effects of the second embodiment.

Still another embodiment 3 of the embodiments 1 and 2 will be described (claims 7 and 8).
In the third embodiment, a position detection mark (not shown) different from the marks M1 and M2 is formed on the intermediate transfer belt 1, and this position detection mark is detected by a detection means (not shown) separate from the mark detection sensor 5. Thus, the positional deviation amount of each color toner image is obtained, and the writing start timing is controlled so that the image positions of the respective colors overlap.

In FIG. 1, when the mark M 1 is detected by the mark detection sensor 5, the first image forming unit 10 starts optical writing of the first position detection mark by the writing unit 16, and the latent image onto the photosensitive drum 14. Image formation begins. The latent image is developed in the A or C color by the developing device 12 or 11 of the developing unit 13 to form a position detection toner image on the photosensitive drum 14.
The position detection toner image is transferred to the intermediate transfer belt 1, and a first or a position A or C toner image for position detection is formed on the intermediate transfer belt 1. When the mark M1 is detected by the mark detection sensor 5, the counter shown in FIG. 3 is reset and starts counting.

  Here, the mark M1 is detected in advance so that the toner image formed by the first image forming unit 10 and the toner image formed by the second image forming unit 20 overlap on the intermediate transfer belt 1 in advance. The time from the start of the A or C color light writing by the writing means 16 to the start of the B or D color light writing by the writing means 16 'is stored as the count value C1 of the counter. .

  The mark M1 is detected by the mark detection sensor 5, and after the count value C1 has elapsed from when the first image forming unit 10 starts optical writing of the first position detection mark by the writing unit 16, the second image is displayed. In the forming means 20, optical writing of the second position detection mark is started by the writing means 16 ′, and formation of a latent image on the photosensitive drum 14 ′ is started. This latent image is developed in B or D color by the developing device 11 'or 12' of the developing means 13 'to form a position detection toner image on the photosensitive drum 14'. The position detection toner image is transferred to the intermediate transfer belt 1, and a second or B position toner image for position detection is formed on the intermediate transfer belt 1.

  First and second position detection marks (not shown) formed on the intermediate transfer belt 1 are detected by a detection means (not shown), and a positional deviation amount of the toner image is obtained. From the obtained positional deviation amount, the count value C1 is corrected so that the positions of the first and second position detection marks (not shown) overlap, and the writing start timing of the second image forming means 20 is controlled.

  Here, using the corrected count value C1, a full color image is formed by the procedure shown in the first embodiment. When the first A color toner and the second B color toner image are formed, the writing start timing is adjusted by the above method, so an image in which the A color and the B color overlap is formed. In this writing start position adjustment, the adjustment operation of the positional deviation amounts of the third color and the fourth color for forming an image in the second rotation of the intermediate transfer belt 1 is omitted.

  The writing of the third color is started at the timing when the mark M1 that determines the writing start timing of the first color is detected by the mark detection sensor 5 and then the intermediate transfer belt makes one round and the mark M1 is detected again. The writing start positions of the first color and the third color are always the same and do not need to be adjusted. The writing of the second color is started at the timing of the count value C1 after the mark M1 that determines the writing start timing of the first color is detected by the mark detection sensor 5. When the mark M2 is taken as a reference, the mark M2 is detected by the mark detection sensor 5 at a timing immediately before the start of writing of the second color, and then performed with the count value C3.

The writing of the fourth color is performed with the count value C3 after the intermediate transfer belt 1 has made a full turn from the start of writing of the second color and the mark M2 is detected by the mark detection sensor 5. The writing start positions of the fourth color are almost the same and do not need to be adjusted.
As described above, as the simple writing start position adjustment mode, the writing start position adjustment of the full-color image of four colors can be performed by adjusting the two colors of the first rotation of the intermediate transfer belt 1.

As in the prior art, in the high-definition mode, the first color A is the mark M1 reference and the second color B is the count value C1 from the mark M1 at the first rotation of the intermediate transfer belt. Similarly, at the second rotation of the intermediate transfer belt, the third color C is used as a reference for the mark M1, and the fourth color D is used as a count value C1 ′ from the mark M1, and a position detection mark is formed. The four color position detection marks formed on the intermediate transfer belt 1 are detected by the detection means to determine the amount of positional deviation of the toner image, and the position of the four color position detection marks is determined from the obtained positional deviation amount. The count values C1 and C1 ′ may be corrected so that the positions overlap, and the write start timing may be controlled.
For example, in continuous image formation, the high-definition mode is used for the writing start position adjustment of the first image formation, and the simple adjustment mode is used during the image formation.

  When this method is used, the writing start position can be adjusted by one rotation of the intermediate transfer belt 1, so that the time can be adjusted in half as compared with the conventional method. Further, since the writing start position can be adjusted by forming the two color position adjusting toner images, the toner consumption can be halved and the toner replacement frequency can be reduced.

  The toner cartridge for each color is provided with a means for detecting the remaining toner amount, the remaining toner amount is detected, and the developing means 13 of the first image forming means 10 determines the remaining toner amount of A color or C color. The position detection marks are formed with a large number of colors, and similarly, the position detection marks are formed with a color having a large amount of residual toner out of the B color and the D color by the developing unit 13 ′ of the second image forming unit 20. As a result, the frequency of toner replacement can be reduced.

1 is a front view showing a main part of an image forming apparatus to which the present invention is applied. FIG. 2 is a front view illustrating an overall configuration of the image forming apparatus in FIG. 1. 3 is a timing chart according to the write timing of Example 1. FIG. 4 is a timing chart showing in detail an enlarged main part of the timing chart of FIG. 3. FIG. 2 is a block diagram schematically showing a control configuration of a main part of the image forming apparatus in FIG. 1. 10 is a plan view of a main part showing a mark formation state on an intermediate transfer belt in Modification 1. FIG. 12 is a plan view of a main part showing a mark formation state on an intermediate transfer belt in still another modified example of modified example 1. FIG. 10 is a timing chart relating to writing timing as a comparative example in a conventional image forming apparatus. It is a block diagram which shows simply the control structure of Example 2. 10 is a timing chart according to the write timing of Example 2.

Explanation of symbols

1 Intermediate transfer belt (intermediate transfer member)
5 Mark detection sensor (detection means)
10 First image forming means 13, 13 ′ Developing means 14, 14 ′ Photosensitive drum (image carrier)
16, 16 'writing means 20 second image forming means 70, 70A control means 71 CPU (calculation means, count acquisition means)
71A CPU (calculation means, first and second determination means)
72 ROM (storage means)
73 RAM (storage means)
74 timer (counting means, first and second measuring means)
100 Image forming apparatus 140 First image forming unit 240 Second image forming unit C1, C2, C3 Count values M1, M2 First and second marks (first and second detected means)
P transfer paper (example of sheet-like recording medium)

Claims (11)

The formed latent image is developed with at least two colors of developer by a single image carrier and a scanning type writing means that is arranged opposite to the image carrier and forms a latent image on the image carrier. A first and second image forming unit comprising a plurality of color-switchable developing units; an intermediate transfer member for transferring toner images formed by the first and second image forming units in a superimposed manner; In an image forming apparatus comprising transfer means for transferring a color image formed on an intermediate transfer member to a sheet-like recording medium,
On the intermediate transfer member, the first detected means that is arranged along the moving direction and serves as the first color writing start reference, and moves from the first detected means to the start of writing the second color. At least two detected means are arranged with a second detected means arranged at a distance equal to or less than the distance;
Detecting means for detecting the first detected means and the second detected means at a predetermined position;
A counting means that is initialized when the detecting means detects the first detected means and starts counting elapsed time;
A count acquisition means for acquiring a count value C2 of the count means upon detection of the second detected means by the detection means;
The difference from the count value C2 to the count value C1 of the elapsed time from the start of writing of the first color to the start of writing of the second color set in advance from the time of detection by the second detected means. Calculating means for calculating the count value C3 of the elapsed time until the start of writing,
At the (2n-1) -th rotation (n ≧ 1: positive integer) of the intermediate transfer member, the first color image writing is started on the basis of the first detection means detection timing,
With the first detection means detection timing as a reference, image writing of the second color is started with the count value C1,
At the 2nth rotation of the intermediate transfer member, the third color image writing is started with reference to the first detection means detection timing,
An image forming apparatus, wherein the fourth color image writing is started at the count value C3 on the basis of the second detected unit detection timing. The image forming apparatus according to claim 1.
A plurality of detected means that are paired with the first detected means and the second detected means are arranged on the intermediate transfer body at equal intervals along the moving direction of the intermediate transfer body to write the first color The second detected unit immediately before the distance from the arbitrary first detected unit serving as the start reference to the start of writing of the second color is detected, and (2n-1) of the intermediate transfer member is detected. In the rotation, the first color image writing is started with reference to the first detected means detection timing,
With the first detection means detection timing as a reference, image writing of the second color is started with the count value C1,
At the 2nth rotation of the intermediate transfer member, the third color image writing is started with reference to the first detection means detection timing,
An image forming apparatus, wherein the fourth color image writing is started at the count value C3 on the basis of the second detected unit detection timing. The image forming apparatus according to claim 1 or 2,
The image forming apparatus according to claim 1, wherein the counting unit controls image writing timing by operating in synchronization with a main scanning synchronization signal of the scanning type writing unit. The formed latent image is developed with at least two colors of developer by a single image carrier and a scanning type writing means that is arranged opposite to the image carrier and forms a latent image on the image carrier. A first and second image forming unit composed of a plurality of color-switchable developing means; an intermediate transfer member that sequentially superimposes and transfers toner images formed by the first and second image forming units; In an image forming apparatus comprising transfer means for transferring a color image formed on an intermediate transfer member to a sheet-like recording medium,
On the intermediate transfer member, the first detected means that is arranged along the moving direction and serves as the first color writing start reference, and moves from the first detected means to the start of writing the second color. At least two detected means are arranged with a second detected means arranged at a distance equal to or less than the distance;
Detecting means for detecting the first detected means and the second detected means at a predetermined position;
A counting means that is initialized when the detecting means detects the first detected means and starts counting elapsed time;
A count acquisition means for acquiring a count value C2 of the count means upon detection of the second detected means by the detection means;
The difference from the count value C2 to the count value C1 of the elapsed time from the start of writing of the first color to the start of writing of the second color, which is set in advance, from the time of detection by the second detected means. Calculating means for calculating the count value C3 of the elapsed time until the start of writing,
First measuring means for measuring an elapsed time from detection of the detected means serving as the writing start reference to the next main scanning synchronization signal by the detecting means;
Storage means for storing and holding a preset first reference value T / 2 that is ½ of the main scanning synchronization signal period T;
A first determination means for comparing the measurement value of the first measurement means with the first reference value and determining the magnitude thereof;
Second measuring means for measuring and holding the time until the next main scanning synchronization signal after the measured value after detecting the detected means reaches the first reference value;
A calculation means for obtaining a difference between a measurement time by the first measurement means and a measurement result of the second measurement means;
A second determination unit that compares the result of the calculation unit with a first reference value and determines the magnitude thereof;
When the first detected means is detected at the (2n-1) -th rotation (n ≧ 1: positive integer) of the intermediate transfer body and the result of the first determining means is determined to be large, the variable amount S1 is 1. When determined to be small, the variable amount S1 is set to 2,
When the second detected means is detected at the (2n-1) -th rotation of the intermediate transfer body and the result of the first determining means is determined to be large, the variable amount S2 is determined to be 1 and variable when it is determined to be small. Let the amount S2 be 2,
The second measurement time at the time of detection of the first detected means at the (2n-1) th rotation of the intermediate transfer body and the first time at the time of detection of the first detected means at the 2nth rotation of the intermediate transfer body. In the measurement time, when the result of the second determination means is determined to be small, the variable amount S3 is set to 1, and when it is determined to be large, the variable amount S3 is set to 2.
A second measurement time at the time of detection of the second detected means at the (2n-1) th rotation of the intermediate transfer member and a first time at the detection of the second detected means at the 2nth rotation of the intermediate transfer member. In the measurement time, when the result of the second determination means is determined to be small, the variable amount S4 is 1, and when it is determined to be large, the variable amount S4 is 2.
The writing of the first color is started in synchronization with the S1 main scanning synchronization signal from the detection of the first detected means at the (2n-1) th rotation of the intermediate transfer member,
The second color writing is started in synchronization with the (S1 + C1) -th main scanning synchronization signal from the detection of the first detected means at the (2n-1) th rotation of the intermediate transfer member,
The writing of the third color is started in synchronization with the S3rd main scanning synchronization signal from the detection of the first detected means of the 2n rotation of the intermediate transfer member,
The fourth color writing is started in synchronization with the (S1 + S4-S2) -th main scanning synchronization signal from the detection of the second detected means at the 2n-th rotation of the intermediate transfer member. apparatus. The image forming apparatus according to any one of claims 1 to 4,
Storage means for storing and holding a preset count value that delays the timing for starting image formation for each color, so that image writing for each color is started after the count has elapsed from the timing for starting image writing for each color. An image forming apparatus characterized in that the control is performed. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising: means for adjusting the count value C1; and count storage means for storing and holding the count value C1 adjusted by the means, and controlling the writing start position. The image forming apparatus according to claim 6.
2. The image forming apparatus according to claim 1, wherein the adjustment of the count value C1 is performed with a total of two colors, any one color of the first image forming unit and any one color of the second image forming unit. The image forming apparatus according to claim 6.
Means for detecting the amount of remaining toner of each color, and the count value C1 is adjusted by adjusting one color with a large amount of remaining toner in the first image forming unit and one color with a large amount of remaining toner in the second image forming unit; And an image forming apparatus characterized in that it is performed in a total of two colors. The image forming apparatus according to any one of claims 1 to 4,
Use condition storage means for storing and holding at least one use condition information among environmental temperature, number of printed sheets and use time, and storage means for storing and holding a preset count value for delaying the timing of starting image formation for each color In accordance with at least one of the environmental temperature, the number of printed sheets, and the usage time, the image writing of each color is started after the count has elapsed from the timing of starting the image writing of each color. An image forming apparatus that controls the image forming apparatus. The image forming apparatus according to any one of claims 1 to 4,
Use condition storage means for storing and holding at least one use condition information of environmental temperature, number of printed sheets and use time, and count storage means for counting the detected means as the writing start reference, and the environmental temperature An image forming apparatus characterized in that a detected unit serving as the writing start reference is changed to another detected unit according to at least one of the number of printed sheets and the usage time. The image forming apparatus according to any one of claims 1 to 4,
A length discriminating unit for discriminating the length of the sheet-like recording medium in the moving direction, a conveyance speed of the intermediate transfer member, a sheet-like recording medium length in the moving direction obtained by the length discriminating unit, A calculating means for calculating a writing start position based on the sheet-shaped recording medium interval set by the length of the sheet-shaped recording medium;
An image forming apparatus, wherein the arithmetic means calculates and sets a main scanning synchronization signal count value from a main scanning synchronization signal immediately after detection of the detected means serving as a writing start reference to writing start.

Images