JP2005181894A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the occurrence of erroneous detection by a sensor is restrained in the case of correcting a toner transfer position so that a toner image may be transferred to a desired position on a body to be transferred. <P>SOLUTION: The image forming apparatus is equipped with: a means to irradiate a mark pattern directly transferred to a recording material feeding member 60 with light from the sensor to detect the position of the mark pattern transferred from an image carrier 11 with the use of reflected light from the mark pattern; a deviation detection means to detect deviation between the position of the mark pattern detected by the sensor 69 and an ideal position; and a correction means to correct a mark pattern transfer position so as to coincide with the ideal position based on the deviation detected by the deviation detection means. The apparatus is equipped with a sensor counter rotating member 62 opposed to the sensor 69, and the length in a subscanning direction being the moving direction of a mark pattern group being the assembly of the mark patterns is made shorter than the peripheral length of the sensor counter rotating member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions using an electrophotographic system. More specifically, the present invention relates to an image forming apparatus capable of superimposing and transferring each color toner image for forming a color image at the same position on a transfer material.

  2. Description of the Related Art Conventionally, in a color image forming apparatus, a tandem type image forming apparatus for forming a color image by arranging a plurality of image carriers such as a photoconductor along an endless transfer belt as a transfer member is known. Yes. In this tandem image forming apparatus, an electrostatic latent image is formed for each color of yellow (Y), magenta (M), cyan (C), and black (K) for each image carrier, and development, etc. An electrophotographic process is performed. Then, the images of different colors on the respective image carriers are superposed to finally form a color image on the transfer paper.

  There are mainly two transfer systems that can be employed in such a tandem color image forming apparatus. The first transfer method is an intermediate transfer method in which each color toner image formed on a latent image carrier is sequentially superimposed and transferred onto an intermediate transfer member and then transferred onto a recording material. The second transfer method is a direct transfer method in which the color toner images formed on the latent image carrier are sequentially superimposed and directly transferred onto the recording material conveyed while being supported by the recording material conveying member. .

In such a transfer system, in order to form a high-quality image, it is necessary to accurately align the toner transfer positions between the color toner images. If there is a positional deviation between the color toner images, the superimposed toner image formed on the transfer paper will be deteriorated in the reproducibility of the color image such as a positional deviation between the colors or a color deviation. In order to form a high-precision image, it is necessary to maintain the accuracy of color superposition of each color from 50 [μm] to 150 [μm] or less. In order to perform such high-precision alignment, it is difficult to maintain only the accuracy and adjustment of each component for image formation. Even if the members are adjusted with high accuracy, problems such as dimensional changes and slips may occur depending on the environment or over time. Moreover, when the necessity for parts replacement | exchange etc. arises, advanced adjustment is needed again. In fact, it is impossible for the user to accurately align the toner transfer position between the color toner images only by the user.
In view of this, an apparatus has been proposed in which a position is detected using a sensor after a mark pattern for alignment is formed, and position correction is automatically performed according to the detection result.
For example, the technique proposed in Patent Document 1 can be used. In this technique, a mark pattern is formed on the intermediate transfer belt, which is an array of marks made of toners of respective colors arranged in the belt moving direction. Then, each mark of each mark pattern is detected by a sensor, and a deviation amount between the detected position and the ideal position is calculated to correct the toner transfer position of each color toner.
This technique employs an intermediate transfer system (the first transfer system described above), and is a technique for correcting a toner transfer position that occurs during primary transfer from a latent image carrier to an intermediate transfer belt. It can also be applied to the (second transfer method). That is, if a plurality of mark patterns are similarly formed on the recording material conveying member, this is detected by a sensor, and the amount of deviation between the detected position and the ideal position is calculated, so that the toner transfer position is similarly set. It can be corrected.

However, in actuality, the sensor misdetects due to scratches or dirt on various members over time or attachment errors, and the toner transfer position between the color toner images is accurately aligned. There is a problem that it becomes difficult.
Therefore, the applicant of Patent Document 2 accurately aligns the toner transfer position between the toner images of each color even if the image carrier is scratched or soiled or an error in mounting the specular reflection type optical sensor occurs. An image forming apparatus that can do this is proposed.

Japanese Patent Application Laid-Open No. 8-234531 JP 2001-318502 A

  According to the technique disclosed in the above-mentioned Patent Document 2, scratches and dirt are attached to the image carrier over time, or attachment errors of the specular reflection type optical sensor occur over time. It is said that the position detection of the toner image can be reliably performed even if the light amount falls with time. However, scratches and dirt that may be erroneously detected as mark patterns by the sensor may occur. In such a case, even with the technique of Patent Document 2, the toner transfer position between the toner images of the respective colors cannot be accurately aligned.

  The present invention has been made in view of the above-described background, and an object of the present invention is to ensure that a toner image is transferred to a desired position on a transfer medium onto which a toner image such as a recording material or an intermediate transfer body is transferred. An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of erroneous detection by a sensor when correcting a transfer position.

In order to achieve the above-mentioned object, the invention of claim 1 includes a plurality of image carriers that form toner images of different colors, and a toner image forming unit that forms toner images on the plurality of image carriers, A transmissive recording material conveying member that conveys a recording material carried on the surface, and a transfer unit that transfers the toner on the plurality of image carriers onto the recording material conveyed by the recording material conveying member Forming a mark pattern of each color made of toner on the plurality of image carriers, and transferring the mark pattern directly onto the recording material conveying member by the transfer means; Means for irradiating the mark pattern with light from a sensor and detecting the position of the mark pattern transferred from the plurality of image carriers by the reflected light; and the position of the mark pattern detected by the sensor; Deviation from ideal position And a correction for correcting the toner transfer position to the recording material so that the mark pattern transfer position coincides with the ideal position based on the deviation amount detected by the deviation amount detection means. A timing at which the mark pattern passes through the sensor from a timing at which the mark pattern is transferred to the recording material conveying member, and a period during which the mark pattern passes through the sensor. Means for reading by the sensor, and a sensor-facing rotating member facing the sensor via the recording material conveying member, and in the sub-scanning direction which is a moving direction of the mark pattern group which is an aggregate of the mark patterns The length is shorter than the circumferential length of the sensor-facing rotating member.
According to a second aspect of the present invention, there are provided a plurality of image carriers that form toner images of different colors, a toner image forming unit that forms toner images on the plurality of image carriers, and an image on the image carrier. A transmissive intermediate transfer member to which toner is primarily transferred; a primary transfer means for primarily transferring the toner on the image carrier onto the intermediate transfer member; and the recording material and the recording material on the conveyed recording material. Secondary transfer means for secondary transfer of the toner image on the intermediate transfer body while being in contact with the intermediate transfer body, and the mark pattern made of toner are formed on the plurality of image carriers, and this is transferred to the primary transfer Means for transferring onto the intermediate transfer body by means, and the mark pattern transferred directly onto the intermediate transfer body is irradiated with light from a sensor, and the reflected light is transferred from the plurality of image carriers. Means for detecting the position of the mark pattern and the sensor A deviation amount detecting means for detecting a deviation amount between the detected position of the mark pattern and the ideal position, and the mark pattern transfer position matches the ideal position based on the deviation amount detected by the deviation amount detecting means. As described above, in the image forming apparatus including the correcting unit that corrects the toner transfer position to the recording material, the timing at which the mark pattern passes through the sensor from the timing at which the mark pattern is transferred to the intermediate transfer member. A set of mark patterns, comprising: means for performing reading by the sensor during a period in which the mark pattern passes through the sensor; and a sensor-facing rotating member facing the sensor via the recording material conveying member. The length of the mark pattern group as the body in the sub-scanning direction, which is the moving direction, is shorter than the circumferential length of the sensor-facing rotating member.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the opposed sensor is rotated before the mark pattern of each color is formed on the recording material conveying member or the intermediate transfer member. A false detection position detecting means for irradiating the rotating member with light from the sensor, detecting the reflected light, and detecting the position on the sensor-facing rotating member where the detected reflected light is erroneously detected as the mark pattern; And a means for detecting the position of the mark pattern at a timing such that the position detected by the erroneous detection position detecting means is not erroneously detected as the mark pattern.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, when there are a plurality of erroneous detection factor positions detected by the erroneous detection position detecting means in the length of the mark pattern group in the sub-scanning direction. In addition, a system is provided that issues a warning when the mark pattern group cannot be detected at a timing that does not overlap the erroneous detection position.

  According to these inventions, when correcting the toner transfer position so that the toner image is transferred to a desired position on the transfer target body onto which the toner image such as the recording material or the intermediate transfer body is transferred, an error caused by the sensor. There is an excellent effect that the occurrence of detection can be suppressed.

The reason why such an effect is obtained will be described below.
The light emitted from the light emitting part of the sensor passes through the recording material conveying member or the intermediate transfer member made of a light transmissive material and reaches the sensor-opposing rotating member. Then, the light is reflected from the surface of the rotation member facing the sensor and becomes reflected light, and is transmitted again through the recording material conveying member or the intermediate transfer member and detected by the light receiving unit.
When the mark pattern image for alignment of each color passes through the optical path of the sensor as the belt moves, the amount of received light is greatly reduced. By detecting the output change based on this reduction, the position of the mark pattern image for alignment of each color is grasped. The sensor is configured to calculate the period during which the mark pattern passes through the sensor from the timing of transfer to the recording material conveying member or the intermediate transfer member, and to read from the sensor only at that timing.
Here, if there is a scratch or dirt on the sensor facing rotating member, the amount of reflected light changes when reflected on the surface of the sensor facing rotating member, and it is erroneously detected as a mark pattern when detected by the light receiving unit There is.
In the present invention, the length of the mark pattern group in the sub-scanning direction, which is the moving direction of the mark pattern group (a collection of mark patterns of each color), is shorter than the circumferential length of the sensor facing rotating member. Therefore, when detecting the position of the mark pattern of each color transferred from the plurality of image carriers by the reflected light from the sensor, scratches, dirt, etc. on the sensor-facing rotating member are mistaken as the mark pattern. The probability of detection can be reduced as compared with the case where the length of the mark pattern group is made longer than the circumferential length of the sensor-facing rotating member.

Hereinafter, an embodiment in which the present invention is applied to a direct transfer tandem type laser printer (hereinafter referred to as “laser printer”) as an electrophotographic image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a schematic configuration of a laser printer according to the present embodiment. This laser printer includes toner image forming units 1Y, 1M, and 1C as four sets of image forming units for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). 1K. Hereinafter, the subscripts Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively. The four sets of toner image forming portions 1Y, 1M, 1C, and 1K are sequentially arranged from the upstream side in the moving direction of the transfer paper 100 as the transfer material (the direction in which the belt 60 travels along the arrow A in the drawing). ing. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. The arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel to each other and arranged at a predetermined pitch in the transfer paper moving direction.

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer includes an optical writing unit 2, paper feed cassettes 3 and 4, a registration roller pair 5, a transfer conveyance unit 6 as a transfer conveyance device, and belt fixing. A fixing unit 7 of a system, a paper discharge tray 8 and the like are provided. The transfer conveyance unit 6 has an endless transfer conveyance belt 60 as a transfer conveyance member that carries the transfer paper 100 and conveys the transfer paper 100 so as to pass through the transfer position of each toner image forming unit. In addition, the laser printer includes a manual feed tray MF and a toner supply container TC, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on the image data. To do.

  FIG. 2 is an enlarged view showing a schematic configuration of the transfer conveyance unit 6. The transfer conveyance belt 60 used in the transfer conveyance unit 6 is a high-resistance endless single layer belt having a volume resistivity of 109 to 1011 Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer conveyance belt 60 is wound around support rollers 61 to 68 so as to pass through the transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units.

  Out of these support rollers, the outer periphery of the transfer conveyance belt 60 faces the entrance roller 61 on the upstream side in the transfer paper moving direction so that the electrostatic adsorption roller 80 for transferring the transfer material to which a predetermined voltage is applied from the power source 80a is opposed. Arranged on the surface. The transfer paper 100 that has passed between the two rollers 61 and 80 is carried on the transfer conveyance belt 60 by electrostatic attraction. A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow.

  As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60. ing. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.

The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.
The entrance roller 61 and the electrostatic adsorption roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state of FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoconductors 11Y, 11M, 11C, and the entrance roller 61 is electrostatically charged. The suction roller 80 also moves downward. It is possible to avoid contact between the photosensitive drums 11Y, 11M, and 11C and the transfer conveyance belt 60 in the monochrome mode in which an image of only black is formed.
As described above, the contact / separation means for contacting / separating the upstream portion of the transfer transport belt 60 in the transfer sheet transport direction with respect to the photosensitive drums 11Y, 11M, 11C is the swing bracket 93, the cam 96, and the entrance roller bracket 90. Etc.

  On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by an outlet bracket 98, and are rotatable about a shaft 99 coaxial with a sensor-facing rotating member 62, which will be described later, serving as the outlet roller. When the transfer / conveyance unit 6 is attached to or detached from the main body, the transfer bias applying member 67K and the backup roller 68 adjacent thereto are rotated from the black image forming photosensitive member 11K by rotating clockwise by operating a handle (not shown). Are separated from each other.

  A cleaning device (not shown) composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer / conveying belt 60 wound around the driving roller 63. This cleaning device removes foreign matters such as toner adhering to the transfer conveyance belt 60. Further, a roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction for pushing the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 63 is ensured. A tension roller 65 for applying tension to the belt is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.

  The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming portions 1Y, 1M, 1C, and 1K, and formed at the transfer positions. Passes through the transfer nip.

In the color mode for forming a full-color image, each toner image developed on each of the toner image forming units 1Y, 1M, 1C, and 1K on the photosensitive drums 11Y, 11M, 11C, and 11K is transferred to the transfer paper 100 at each transfer nip. Is superimposed. Then, the image is transferred onto the transfer paper 100 under the action of the transfer electric field and nip pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100.
The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.
On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or is registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

FIG. 3 is an explanatory view showing the transfer conveyance belt 60 together with the reflection type photosensor 69 and the sensor facing rotation member 62.
A sensor facing rotating member 62 as a light reflecting member is in contact with a position facing the reflective photosensor 69 via the transfer conveyance belt 60. The sensor facing rotation member 62 also serves as a roller for stretching the transfer conveyance belt 60. The surface of the sensor facing rotating member 62 is mirror-finished with high reflectivity so as to reflect light well. The reason why the sensor facing member is a rotating body is to suppress an increase in belt driving torque. Further, when a fixed member is used instead of the sensor-facing rotating member 62, scraping with the transfer / conveying belt causes scraping on the back surface of the belt, and the surface of the fixed member becomes dirty and the amount of reflected light varies. This is because the toner transfer position may not be corrected accurately.

As shown in FIG. 4, the printer includes two reflective photosensors 69a and 69b. Light emitted from a light emitting portion (not shown) of the reflection type photosensors 69 a and 69 b passes through the transparent or milky white light transmitting portion of the transfer conveyance belt 60 and reaches the sensor facing rotation member 62. Then, the light is reflected by the surface of the sensor-facing rotating member 62 to become reflected light, passes through the transfer conveyance belt 60 again, and is detected by a light receiving unit (not shown) of the reflective photosensors 69a and 69b.
In the present embodiment, PVDF (polyvinylidene fluoride) having a high light transmission amount is used as the transfer conveyance belt 60. As a member of the transfer conveyance belt 60, a material having a high light transmission amount may be used instead of PVDF.

  FIG. 5 is a block diagram showing a part of the electric circuit of the laser printer. In the figure, a control unit 150 includes electrically connected toner image forming units 1Y, 1M, 1C, and 1K, an optical writing unit 2, a paper feed cassette 3, 4, a registration roller pair 5, a transfer unit 6, and a reflection type. It is connected to photo sensors 69a and 69b. The control unit 150 includes a CPU 150a that performs arithmetic processing, a RAM 150b that stores data, and a DSP (Digital Signal Processor) 150c.

  When a heating roller temperature of 60 [° C.] or less is detected immediately after the main power supply (not shown) is turned on, or when a printout of a predetermined number or more is performed, the control unit 150 performs the misalignment correction control. It is configured. Specifically, first, the photosensitive drums 11Y, 11M, 11C, and 11K are uniformly charged while rotating, and four electrostatic latent images of mark patterns as reference toner images are respectively provided by scanning the laser beam. Let it form. These electrostatic latent images are developed by developing devices 20Y, 20M, 20C, and 20K. The four toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11K by the development are transferred onto the transfer conveyance belt 60 so as not to overlap each other. By this transfer, one mark pattern group P is formed in the vicinity of both ends of the transfer conveyance belt 60.

  FIG. 6 is a schematic diagram showing one mark pattern group P. As shown in FIG. As shown in the figure, the mark pattern group P includes four mark patterns L301K, L301C, L301M, and L301Y that extend straight in the belt width direction, and four mark patterns s101K, s101C, and s101M that are inclined 45 [°] from the belt width direction. , S101Y. The mark patterns L301K, L301C, L301M, L301Y, s101K, s101C, s101M, and s101Y are each formed at a pitch of distance d, and the length of the mark pattern group is L3. Of these eight mark patterns, those marked with K, C, M, and Y are respectively transferred from the photosensitive drums 11K, C, M, and Y, and are K toner image, C toner image, and M toner. Image and Y toner image. The mark patterns L301K, L301C, L301M, and L301Y are formed with a length A and a width W. The remaining mark patterns s101K, s101C, s101M, and s101Y are formed with a length A√2 and a width W. Further, the other mark pattern group P formed in the vicinity of the opposite end of the transfer conveyance belt 60 has the same configuration, and the two mark pattern groups P each include eight mark patterns in the belt width direction. It is formed so as to face each other.

  When mark pattern images for alignment of each color in the two mark pattern groups P formed near both ends of the transfer conveyance belt 60 pass through the optical paths of the reflection type photosensors 69a and 69b as the belt moves, Each received light amount is greatly reduced. When the output change based on this reduction is detected by the control unit 150, the control unit 150 recognizes the detection of the mark pattern image for alignment of each color by the reflective photosensors 69a and 69b.

  Here, it is assumed that the situation described below does not occur. That is, the photosensitive drums 11Y, 11M, 11C, and 11K are tilted due to an assembly error or misaligned in the sub-scanning direction, or the reflection mirrors for Y, M, C, and K in the optical writing unit 2 are used. This is a situation in which the inclination in the longitudinal direction has occurred or the optical characteristics such as magnification in the main scanning direction of the Y, M, C, and K laser beams are different. Then, as shown in FIG. 6, the two mark pattern groups P in the vicinity of both ends of the belt are formed so that the paired mark patterns face each other straight in the belt width direction. Therefore, the mark patterns that are paired with each other pass through the optical paths of the reflective photosensors 69a and 69b almost simultaneously. Also, as shown in FIG. 4, the optical path entry intervals (time intervals) t1b, t2b, t3b of the reflective photosensor 69 in the mark patterns L301K, L301C, L301M, L301Y of one mark pattern group P, and the other mark The same optical path entry intervals t1a, t2a, t3a in the pattern group P are equal. These optical path entry intervals t1a (t1b), t2a (t2b), and t3a (t3b) are respectively from the optical path entry of the mark pattern L301K to the optical path entry of the mark pattern L301C, from the optical path entry of the mark pattern L301C to the optical path entry of the mark pattern L301M. From the optical path approach of the mark pattern L301M to the optical path entrance of the mark pattern L301Y.

  However, if the photoconductor drum 11C is tilted due to an assembly error or if the C reflecting mirror in the optical writing unit 2 is tilted in the longitudinal direction, for example, as shown in FIG. A positional deviation due to skew occurs between the two opposing mark patterns L301C. When the positional deviation due to skew occurs in this way, a time lag Δt occurs between the optical path entry timing of one mark pattern L301C and the optical path entry timing of the other mark pattern L301C. The skew angle θ can be obtained based on the time lag Δt and the moving speed of the transfer conveyance belt 60. Further, even when skew occurs not in the mark pattern L301C but in other mark patterns L301K, L301M, and L301Y, the skew angle θ can be obtained in the same manner.

  Therefore, the control unit 150 sequentially stores the optical path entry timings of the mark patterns L301K, L301C, L301M, and L301Y for the two mark pattern groups P in the RAM 150a, and the optical path entry intervals t1a, t2a, t3a, t1b, t2b and t3b are obtained respectively. Then, the skew angle θ of the mark pattern having the time lag Δt is calculated, and based on the calculation result, the corresponding reflecting mirror is tilted by the mirror tilting means to suppress the skew.

  On the other hand, for example, if the relative displacement of the photosensitive drums 11K, 11C, 11M, and 11Y in the sub-scanning direction occurs, the mark pattern L301C is displaced by the resist in the sub-scanning direction as shown in FIG. Will occur. When the positional deviation occurs as described above, the optical path entry intervals t1a, t2a, and t3a have different values, and the optical path entry intervals t1b, t2b, and t3b have the same values as the optical path entry intervals t1a, t2a, and t3a, respectively. However, as shown in FIG. 7, the optical path entry intervals t1a, t2a, and t3a are different from each other even when a position shift due to skew occurs. Therefore, the control unit 150 corrects the optical path entry intervals t1a, t2a, t3a, t1b, t2b, and t3b based on the time lag Δt caused by the skew to remove the influence of the skew, and then the optical path entry intervals t1a, t2a, Based on each displacement of t3a, the amount of displacement due to the resist in the sub-scanning direction is obtained. Then, based on this misregistration amount, the drive timing for K, C, M, and Y is corrected to suppress registration in the sub-scanning direction.

  When the skew and the misregistration due to registration in the sub-scanning direction are corrected in this way, next, in the main scanning direction based on the respective mark patterns s101K, s101C, s101M, and s101Y in the two mark pattern groups P. The misalignment due to the resist is corrected. Specifically, if there is no registration shift in the main scanning direction, the optical path entry intervals for the mark patterns s101K, s101C, s101M, and s101Y are equal in the vicinity of both ends of the belt. However, for example, as shown in FIG. 9, when a registration shift in the main scanning direction occurs in the upper mark pattern s101C in the drawing, the optical path entry intervals t1b (s101K to s101C), t2b (s101C to s101M), t3b (s101M). ˜s101Y) have different values. At this time, if the size of the mark pattern s101C in the main scanning direction is a regular size (the magnification in the main scanning direction is 1), the mark in the mark pattern group PP1 (lower side in the figure) as shown in the figure. The pattern s101C is registered in the same manner, and the optical path entry intervals t1a, t2a, and t3a have different values, and are synchronized with the optical path entry intervals t1b, t2b, and t3b, respectively. On the other hand, when the size of the mark pattern s101C in the main scanning direction is larger than the normal size (the magnification in the main scanning direction exceeds 1), for example, the upper mark pattern s101C in the figure is registered (main scanning direction). Nevertheless, the other mark pattern s101C is not resisted or the resist amount is reduced.

Therefore, the control unit 150 determines the mark patterns s101K, s101C, s101M, and the like in the two pattern images P based on the optical path entry intervals t1a, t2a, t3a, t1b, t2b, t3b and the moving speed of the transfer conveyance belt 60. The registration deviation (main scanning direction) amount and magnification (main scanning direction) of s101Y are respectively calculated. Then, based on the calculation result, the laser light irradiation timing for each color is corrected, or the pixel clock frequency is corrected, thereby suppressing such registration deviation and magnification deviation.
The mark pattern group P on the transfer conveyance belt 60 moves along with the endless movement of the belt and is detected by the reflection type photosensor 69, and then enters the contact position with the bias roller of the transfer unit 6. And electrostatically transferred to the bias roller and removed. In this way, by correcting the toner transfer position, it is possible to provide high-accuracy image quality without color misregistration or the like.
As described above, by suppressing the skew, the resist in the sub-scanning direction, and the resist in the main scanning direction for each color, the color shift of the full-color toner image formed during the printing process can be suppressed.

  However, even if the color misregistration is suppressed as described above, a serious defect may occur when correcting the toner transfer position. This is because it is not possible to completely prevent the sensor facing rotating member 62 from being contaminated by toner scattering or the like, or foreign matter mixing. The contamination due to the scattering of toner or the like, contamination by foreign matter, etc. appears at the sensor facing portion and is erroneously detected as a mark pattern, resulting in an error in correcting the toner transfer position. In such a case, the signal is output to the reflective photosensor 69 at the rotation period of the sensor-facing rotation member 62 that is being rotated. For this reason, the toner transfer position is not accurately corrected, and there is a possibility that a very serious defect that the position correction of the superposition of the respective color components is not accurately performed.

  FIG. 10 is a diagram for explaining an output waveform when the mark pattern is output by the reflective photosensor 69. This figure shows the waveform when the mark pattern group L1 in FIG. 6 passes the sensor section. As shown in FIG. 10, normally four output drop portions (valleys) are detected. However, the output waveform shown in FIG. 10 may not be obtained. As described above, this is a case where dirt, scratches, etc. occur on the sensor facing rotation member 62. Due to these stains and scratches, the amount of reflected light fluctuates and is erroneously detected as a mark pattern. Once it is erroneously detected as a mark pattern, it has a fatal effect on image quality. In addition, an error may occur and image formation may become impossible.

Therefore, in the present invention, the position correction for overlaying each color component is performed in the following procedure.
In the present embodiment, the length L3 (L1 and L2 in FIG. 4) of the mark pattern group based on the toner image necessary for one correction is shorter than the circumferential length D2 of the sensor facing rotation member 62. Is set. By adopting such a configuration, even when scratches or dirt adhere to the surface of the sensor-facing rotating member 62 used as a member facing the sensor, the probability that they are erroneously detected as mark patterns in the mark pattern group is reduced. It becomes possible. A larger diameter of the sensor facing rotation member 62 is more effective. When the length L3 of the mark pattern group in the sub-scanning direction is longer than the circumferential length D2 of the sensor facing rotation member 62, an abnormal output due to dirt or a flaw is always detected when the mark pattern group is detected. Become. Therefore, making the length L3 of the mark pattern group in the sub-scanning direction shorter than the circumferential length D2 of the sensor facing rotating member 62 is an effective means for reducing erroneous detection. In this embodiment, the length of the mark pattern group is L3 as shown in FIG. 6, but only L1 may be used, or n sets of L1 and L2 may be combined. Other patterns can also be adopted. These can be appropriately changed depending on the model and the required image quality.

FIG. 11 is a flowchart for performing alignment in the printer according to the present embodiment.
When it is determined that the registration correction timing is reached, the reflection type photosensor 69 is operated to detect whether there is a mark pattern erroneous detection factor such as dirt or a flaw in the sensor facing rotation member 62 (S1). The presence / absence of erroneous detection is determined (S2). If there is an erroneous detection factor, the number of erroneous detection factors is determined (S9). If there are a plurality of erroneous detection factors, it is determined whether or not the mark pattern can be detected at a timing such that a scratch or a stain on the sensor facing rotation member 62 is not erroneously detected as a mark pattern when detecting the position of the mark pattern. (S10). If no in S10, a warning is displayed to the user (S11). If a warning is given, the process ends without correcting the position of superimposing the color components.

If NO in S9 or YES in S10, a mark pattern for alignment is read (S12). Subsequently, the mark pattern is transferred to the transfer / conveying belt 60 at a timing such that the erroneous detection factor is not erroneously detected as a mark pattern (S13). Then, this mark pattern is detected by the reflective photosensor 69 (S5). It is confirmed whether or not the reading of the mark pattern is completed (S6), and the positional deviation amount of the overlapping position of each color component is calculated (S7). The superimposed position of each color component is finally corrected (S8), and the process is terminated.
When it is determined in S2 that there is no error detection factor, a mark pattern for alignment correction is read (S3). Subsequently, the mark pattern is transferred to the transfer conveyance belt 60 (S4). Then, this mark pattern is detected by the reflective photosensor 69 (S5). After confirming whether or not the reading of the mark pattern is completed (S6), the positional deviation amount of the overlapping position of each color component is calculated (S7). The superimposed position of each color component is finally corrected (S8), and the process is terminated.

  By performing such processing, the following effects can be obtained. Since the length L3 of the mark pattern group is set to be shorter than the circumferential length of the sensor facing rotating member 62, when a mark pattern erroneous detection factor such as a scratch or dirt occurs in the sensor facing rotating member 62 In addition, the probability of erroneous detection by the reflective photosensor 69 can be reduced. Accordingly, it is possible to improve the correction accuracy of the toner transfer position. This effect is better as the diameter of the sensor facing rotation member 62 is larger.

  Furthermore, in this embodiment, as described above, whether or not there is a mark pattern erroneous detection factor in the sensor facing rotation member 62 is determined before the mark pattern is formed on the transfer conveyance device. Therefore, when the fall of the reflected light is detected due to scratches, dirt, etc., the position is stored, and the toner image on the photosensitive member is recorded at such a timing that it does not enter the mark pattern group of the toner image for automatic alignment. Is configured to start writing. Therefore, even when a mark pattern erroneous detection factor such as a scratch or a dirt occurs in the sensor facing rotating member 62, the erroneous detection can be surely prevented, and the toner transfer position correction system can be enhanced.

  When there are a plurality of mark pattern erroneous detection factors in the sensor-facing rotation member 62 and it is determined that the mark pattern group cannot be detected at a timing that does not overlap with these erroneous detection factor positions, a warning is displayed. Yes. As a result, it is possible to reliably prevent a situation in which the correction accuracy of the toner transfer position is out of order, with the user or serviceman prompting repair or maintenance.

  The printer used in the above embodiment is an example of an apparatus to which the present invention can be applied, and is not limited to this apparatus. In a color image forming apparatus having an endless belt stretched around a plurality of rollers and having a belt driving device that is rotationally driven by at least one of these rollers, a toner transfer position is formed like a transfer belt. Any belt driving device that forms a toner mark pattern for correction and has a position correction function can be applied.

1 is a schematic configuration diagram of a laser printer according to an embodiment. FIG. 3 is an enlarged view showing a schematic configuration of a transfer unit. The schematic explanatory drawing of the reflection type photosensor 69 and a sensor opposing part. FIG. 5 is a schematic diagram showing a part of each of two pattern images that do not cause skew or resist displacement. The block diagram which shows a part of electric circuit. The schematic diagram which shows one of these pattern images. FIG. 5 is a schematic diagram showing a part of each of two pattern images that do not cause skew or resist displacement. The schematic diagram which shows the state which the position shift by skew produced in the mark pattern in one pattern image. The schematic diagram which shows the state in which the resist shift | offset | difference to the sub-scanning direction each occurred in the mark pattern in both pattern images. Explanatory drawing of the output waveform of a sensor. FIG. 5 is a flowchart showing a toner transfer position correction method according to the present embodiment.

Explanation of symbols

1Y, 1M, 1C, 1K Toner image forming portions 11Y, 11M, 11C, 11K Photosensitive drum 60 Transfer conveyance belt 62 Sensor counter rotating member 69 Reflective photosensor

Claims (4)

A plurality of image carriers that form toner images of different colors;
Toner image forming means for forming toner images on the plurality of image carriers;
A transmissive recording material conveying member that conveys the recording material in a state of being supported on the surface;
Transfer means for transferring toner on the plurality of image carriers onto a recording material conveyed by the recording material conveying member;
Means for forming a mark pattern of each color made of toner on the plurality of image carriers, and transferring the pattern directly onto the recording material conveying member by the transfer means;
Means for irradiating light from a sensor to the mark pattern directly transferred onto the recording material conveying member, and detecting the position of the mark pattern transferred from the plurality of image carriers by the reflected light;
A deviation amount detecting means for detecting a deviation amount between the position of the mark pattern detected by the sensor and an ideal position;
An image forming apparatus comprising: a correction unit that corrects a toner transfer position to the recording material based on a shift amount detected by the shift amount detection unit so that the mark pattern transfer position matches the ideal position. ,
Means for calculating a timing at which the mark pattern passes through the sensor from a timing at which the mark pattern is transferred to the recording material conveying member, and reading by the sensor during a period in which the mark pattern passes through the sensor;
A sensor-facing rotating member that faces the sensor via the recording material conveying member, and the length of the mark pattern group that is an assembly of the mark patterns in the sub-scanning direction is the length of the sensor-facing rotating member. An image forming apparatus characterized in that it is shorter than the circumference. A plurality of image carriers that form toner images of different colors;
Toner image forming means for forming toner images on the plurality of image carriers;
A transmissive intermediate transfer body onto which the toner on the image carrier is primarily transferred;
Primary transfer means for primarily transferring the toner on the image carrier onto the intermediate transfer member;
A secondary transfer means for secondary transfer of the toner image on the intermediate transfer member while bringing the recording material and the intermediate transfer member into contact with each other on the conveyed recording material;
Means for forming the mark pattern made of toner on the plurality of image bearing members and transferring the mark pattern onto the intermediate transfer member by the primary transfer unit;
Means for irradiating light from a sensor to the mark pattern directly transferred onto the intermediate transfer body, and detecting the position of the mark pattern transferred from the plurality of image carriers by the reflected light;
A deviation amount detecting means for detecting a deviation amount between the position of the mark pattern detected by the sensor and an ideal position;
An image forming apparatus comprising: a correction unit that corrects a toner transfer position to the recording material based on a shift amount detected by the shift amount detection unit so that the mark pattern transfer position matches the ideal position. ,
Means for calculating a timing at which the mark pattern passes through the sensor from a timing at which the mark pattern is transferred to the intermediate transfer member, and reading by the sensor during a period in which the mark pattern passes through the sensor;
A sensor-facing rotating member that faces the sensor via the recording material conveying member, and the length of the mark pattern group that is an aggregate of the mark patterns in the sub-scanning direction is the length of the sensor-facing rotating member. An image forming apparatus characterized in that it is shorter than the circumference. The image forming apparatus according to claim 1 or 2,
Before the mark pattern of each color is formed on the recording material conveying member or the intermediate transfer member, the sensor-irradiated rotating member is irradiated with light from the sensor, and the reflected light is detected and detected. Erroneous detection position detecting means for detecting a position on the rotation member facing the sensor, in which the reflected light is erroneously detected as the mark pattern,
An image forming apparatus comprising: means for detecting the position of the mark pattern at a timing such that the position detected by the erroneous detection position detection means is not erroneously detected as the mark pattern. The image forming apparatus according to claim 3.
When there are a plurality of misdetection factor positions detected by the misdetection position detecting means in the length of the mark pattern group in the sub-scanning direction, the mark pattern group is selected at a timing that does not overlap the misdetection position. An image forming apparatus comprising a system for issuing a warning when detection is impossible.

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