Patent Grant
7865119
This application is related to Japanese patent application Nos. 2006-112604 and 2006-199733 which are filed on Apr. 14, 2006 and Jul. 21, 2006 respectively whose priorities are claimed under 35 USC §119, the disclosure of which are incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a color registration method and a color image forming apparatus.
2. Description of the Related Art
There has been known a color image forming apparatus (so-called tandem-type color image forming apparatus) having a plurality of drum-type photoconductors. In the color image forming apparatus, it is important to suppress the positional deviation for every color (color misregistration) to an unnoticeable degree. When the color misregistration is great, it might be evaluated that the image quality is deteriorated. The greatest factor of the color misregistration is a periodic crude density on the output image caused by the eccentricity of each photoconductor. The ideal countermeasure is that the eccentric amount of each photoconductor is sufficiently reduced, but trade-off between cost and mass-productivity should be considered.
In view of this, various ideas have been provided to make the color misregistration unnoticeable even if the eccentric amount is the same. For example, an apparatus in which the peripheral length of each photoconductor drum and the peripheral length of the transfer belt is set to have ratios of whole numbers has been proposed (for example, Japanese Patent Laid-Open No. 7-261499). Further, an apparatus has been known in which a mark formed on a transfer belt is detected and, when the detected position is outside the fixed range, this position is stored and the formation of the mark is inhibited at this position (for example, Japanese Patent Laid-Open No. 2004-294471).
When the phase (rotational phase) of the eccentricity of each photoconductor is not matched, the color misregistration becomes noticeable. This point is focused, and various ideas have been given for matching the rotational phase of each photoconductor on the output image so as to make the color misregistration unnoticeable. In this case, in order to detect the rotational phase of each photoconductor, a toner pattern (toner image) having lines, parallel to the rotational axis of the photoconductor, arranged at equal intervals in the rotating direction is formed, and the deviation from the expected position is detected.
However, the cause of the crude density of the output image, in other words, the cause of the deviation of the formed toner pattern from the expected position, exists in the factors other than the eccentricity of the photoconductor. Upon detecting the rotational phase, the causes other than the eccentricity of the photoconductor become a disturbance. A sufficient precision cannot always be obtained in the detection of the rotational phase of each photoconductor using the toner pattern due to the disturbances.
In order to precisely detect the rotational phase of each photoconductor, a technique for effectively removing the disturbance component has been desired.
The color image forming apparatus performs the image formation by using three primary colors of yellow, cyan, and magenta, and black. The tandem-type image forming apparatus includes four photoconductors corresponding to each color. In the case of the monochromatic image formation, only the black photoconductor is used.
It is preferable that the diameter of the black photoconductor is increased from the viewpoint of achieving high-speed monochromatic image formation, compared to the color image formation, and of prolonging the service life of the black photoconductor to make its exchange cycle same as that of the other photoconductors. However, if only the diameter of the black photoconductor is greater than the diameter of the other photoconductors, various subjects involved with the color image formation arise. The representative one is the subject relating to the color misregistration. Since the rotational cycle of the black photoconductor is different from those of the other photoconductors, the technique for aligning the direction of the eccentricity to make the color misregistration unnoticeable cannot be taken.
A technique for making the color misregistration unnoticeable with a simple configuration has been desired even in case where a plurality of types of photoconductors, each type having a different diameter, are used.
The present invention is accomplished in view of the aforesaid circumstances, and firstly provides a technique for effectively removing a disturbance component included in a toner pattern used for a color registration, in order to be capable of precisely adjusting the rotational phase of each photoconductor. Secondly, the present invention provides a technique for suppressing a variation in an image pitch corresponding to the rotational cycle of each photoconductor with a simple configuration, even if a plurality of types of photoconductors, each having a different diameter, are used, whereby a color misregistration is made unnoticeable.
In order to solve the aforesaid subjects, the present inventors have conducted diligent researches and found that the disturbance component also has periodicity. The factors of the periodicity are caused by the following means driving the image forming apparatus.
(1) In an image forming apparatus including a plurality of photoconductors each having a different diameter, a cycle corresponding to the peripheral length of a second photoconductor having a second diameter in case where a toner pattern of a first photoconductor having a first diameter is formed.
(2) A cycle of a transfer drive roller that drives a transfer belt for transferring the toner patterns formed on each photoconductor and superimposing the toner patterns.
Describing in detail the aforesaid (1), the second photoconductor having the second diameter is brought into contact with an intermediate transfer belt when the toner pattern of the first photoconductor having the first diameter is formed. It is considered that the friction force due to the contact applies unintentional drive force to the intermediate transfer belt, so that the moving speed of the intermediate transfer belt is changed.
It is considered that the aforesaid item (1) appears since the image forming apparatus includes photoconductors each having a different diameter, and a transfer roller is used for the transfer from the photoconductor to the transfer belt.
In order to solve the first subject, the present invention provides a color registration method to be executed by a computer, in a color image forming apparatus including a plurality of drum-type photoconductors, each photoconductor having a peripheral surface on which images in a predetermined color are formed, the predetermined color being different in each photoconductor, in which some or all of the photoconductors having the same diameter are drived to match pitch fluctuations which are contained in the images formed on the respective photoconductors and which correspond to a rotational cycle of the photoconductors, the method including: a first measurement step for forming a first registration image for each color and measuring formation positions of a plurality of predetermined portions in each registration image; a second measurement step for forming a second registration image for each color and measuring formation positions of a plurality of predetermined portions in each registration image; a calculation step for obtaining deviations of the formation positions of each of the predetermined portions measured in the first and second measurement steps, from a reference position, and for calculating the deviations of each portion for every photoconductor; a step for calculating a periodic fluctuation component corresponding to the rotational cycle of the photoconductor on which the registration images are formed on the basis of the calculated deviation for each registration image, so as to obtain phases thereof; and a step for adjusting a rotational phase of each photoconductor in order for the obtained phases matching to each other, wherein the first and second registration images are formed on the peripheral surface of the same photoconductor at a predetermined interval, and the predetermined interval is an interval in the rotating direction, which is set such that disturbance components in which a cycle is assumed beforehand, cancel with each other by calculating the deviation.
In order to solve the first subject from the different viewpoint, the present invention provides a color image forming apparatus including: a plurality of drum-type photoconductors in which first and second registration images are respectively formed on a peripheral surface of the same photoconductor; a measurement section for measuring formation positions of a plurality of predetermined portions in each of the formed registration images; a deviation calculating section for obtaining deviations of the measured formation positions of each of the predetermined portions from a reference position, and for calculating the deviations of each portion for every photoconductor; a phase determining section for calculating a periodic fluctuation component corresponding to a rotational cycle of the photoconductor on which the registration images are formed on the basis of the calculated deviation for each registration image, so as to obtain phases thereof; and an adjustment section for adjusting a rotational phase of each photoconductor in order for the obtained phases matching to each other, wherein the first and second registration images are formed on the peripheral surface of the same photoconductor at a predetermined interval, and the predetermined interval is an interval in the rotating direction, which is set such that disturbance components in which a cycle is assumed beforehand, cancel with each other by calculating the deviation.
Further, in order to solve the first and second subjects, the present invention provides an image forming apparatus including: a plurality of drum-type photoconductors in which first and second registration images are respectively formed on a peripheral surface of the same photoconductor; a plurality of drive sections for rotatably driving each photoconductor at a predetermined drive speed; a measurement section for measuring formation positions of a plurality of predetermined portions in each of the formed registration images; a deviation calculating section for obtaining deviations of the measured formation positions of each of the predetermined portions from a reference position, and for calculating the deviations of each portion for every photoconductor; a phase determining section for calculating a periodic fluctuation component corresponding to a rotational cycle of the photoconductor on the basis of the calculated deviation for each registration image, so as to obtain phases thereof; an adjustment section for adjusting a rotational phase of each photoconductor in order for phases of speed fluctuation of each photoconductor matching to each other on the basis of the obtained phases; a correction signal output section for outputting a speed correction signal that is included in each of the formed images for correcting the fluctuation component corresponding to the rotational cycle of each photoconductor; and a drive control section for controlling the drive sections to correct the drive speed of each photoconductor by using the outputted speed correction signal, wherein the first and second registration images are formed on the peripheral surface of the same photoconductor at a predetermined interval, the predetermined interval is an interval in the rotating direction, which is set such that disturbance components in which a cycle is assumed beforehand, cancel with each other by calculating the deviation, and the speed correction signal is a signal having a cycle equal to the rotational cycle of each photoconductor.
In the present invention described above, the state in which the phases of the speed variation of each photoconductor match to each other means, for example, the state in which the times when the maximum point and minimum point of the variation in the peripheral speed of each photoconductor at the exposure position respectively match to each other.
In other words, the present invention performs the following with respect to the first subject.
(1) A first toner pattern is formed on a transfer belt, and the position of the formed toner pattern is measured to calculate a misregistration amount (deviation) 1 from the expected position.
(2) Then, a second toner pattern is formed at the position from the first toner pattern at a predetermined interval in the transporting direction of the transfer belt. The position of the formed second toner pattern is measured to calculate a misregistration amount 2 from the expected position.
(3) Next, the calculated misregistration amount 1 and the misregistration amount 2 are totaled to calculate a final misregistration amount. In this case, the predetermined interval is set such that the misregistration amount caused by the periodic disturbance factor is produced inversely in the misregistration amount 1 and the misregistration amount 2. By virtue of this configuration, the misregistration amount caused by the periodic fluctuation factor is in the direction in which it is canceled by the final misregistration amount, whereby its influence is prevented.
Thus, the rotational phase of the photoconductor can precisely be detected.
With respect to the first subject, the color registration method according to the present invention includes a first measurement step for forming a first registration image for each color and measuring the formation position of a plurality of predetermined portions in each registration image, and a second measurement step for forming a second registration image for each color and measuring the formation position of a plurality of predetermined portions in each registration image, wherein the first and second registration images are formed on the same photoconductor at a predetermined interval, and the predetermined interval is set such that disturbance components in which a cycle is presumed beforehand, cancel with each other by the calculation of the deviation.
Further, with respect to the first subject, the image forming apparatus according to the present invention includes a plurality of drum-type photoconductors, on which a first and a second registration images are formed on the surface of the same photoconductor, and a measurement section for measuring the formation position of a plurality of predetermined portions in each registration image, wherein the predetermined interval is set such that disturbance components in which a cycle is presumed beforehand, cancel with each other by the calculation of the deviation.
According to the aforesaid configuration, a plurality of color registration toner patterns (hereinafter simply referred to as toner patterns) are formed at the predetermined interval by which the periodic disturbances having a cycle different from the predetermined cycle cancel with each other, and the phase of the fluctuation component in the predetermined cycle can be obtained for each image, whereby the disturbance can effectively be suppressed with less number of toner patterns, and the phase of the fluctuation component in the predetermined cycle can precisely be obtained. From another viewpoint, the disturbance can be suppressed with less number of toner patterns, whereby the time taken for the image formation and measurement can also be shortened.
Although the above-mentioned case describes that the photoconductor has a drum shape, the present invention is applicable to a belt-like photoconductor, for example. In this case, the eccentricity of the photoconductor drive roller for driving the belt-like photoconductor becomes the cause of the periodic crude density. Therefore, the drum-type photoconductor may be replaced with the photoconductor drive roller. For example, the cycle to be measured may be a cycle corresponding to the peripheral length of the photoconductor drive roller, and the rotational phase of each photoconductor drive roller may be adjusted by measuring the toner pattern.
One example of a transfer member is the intermediate transfer belt on which the toner image formed on the photoconductor is transferred. The embodiment described later describes an image forming apparatus having such intermediate transfer belt. However, there is the one, in the tandem-type color image forming apparatus, in which the toner image formed on the photoconductor is directly transferred onto a print sheet. In this type of apparatus, the transfer belt directly supports and transports the sheet. The toner image is transferred onto the sheet transported by the transfer belt. The present invention is applicable to this type of image forming apparatus. In this case, the toner pattern to be measured may be formed on the sheet. Alternatively, in so far as the toner pattern to be measured, it may directly be transferred onto the transfer belt.
In the color registration method according to the present invention, each registration image may include a plurality of straight lines orthogonal to the rotating direction of the photoconductor, and each of the measurement steps may measure a formation position of each straight line.
The image forming apparatus may further include a transferring member for transferring each of the formed images, and a drive roller for superimposing the images in each color by moving the transferring member between the photoconductors, wherein the predetermined interval may be an interval in the rotating direction, which is set such that periodic disturbances corresponding to the rotational cycle of the drive roller cancel with each other.
Further, the predetermined interval may be an interval between front ends of each of the registration images or between rear ends of each of the registration images, and may be an interval substantially equal to the integral multiple of the peripheral length of the photoconductor and to the sum of the integral multiple of the peripheral length of the drive roller and its half rotation, and the calculation step may make a calculation by obtaining the sum of the deviations of each corresponding portion of the registration images.
Alternatively, the predetermined interval may be substantially equal to the sum of the integral multiple of the peripheral length of the photoconductor and its half rotation and to the integral multiple of the peripheral length of the drive roller, and the calculation step may make a calculation by obtaining the difference between the deviations of each corresponding portion of the registration images.
Moreover, in the color registration method according to the present invention, the image forming apparatus may include a first photoconductor having a first diameter and a second photoconductor having a second diameter, the registration images are formed on the first photoconductor, and the predetermined interval may be set such that periodic disturbances corresponding to the rotational cycle of the second photoconductor cancel with each other.
Further, the predetermined interval may be substantially equal to the integral multiple of the peripheral length of the first photoconductor and to the sum of the integral multiple of the peripheral length of the second photoconductor and its half rotation, and the calculation step may make a calculation by obtaining the sum of the deviations of each corresponding portion of the registration images.
Alternatively, the predetermined interval may be substantially equal to the sum of the integral multiple of the peripheral length of the first photoconductor and its half rotation and to the integral multiple of the peripheral length of the second photoconductor, and the calculation step may make a calculation by obtaining the difference between the deviations of each corresponding portion of the registration images.
Further, in the color registration method according to the present invention, the image forming apparatus may include a first photoconductor having a first diameter and a second photoconductor having a second diameter, the registration images are formed on the first photoconductor, and the predetermined interval may be set such that periodic components corresponding to the peripheral length of the second photoconductor cancel with each other, and periodic components corresponding to the peripheral length of a drive roller cancel with each other.
Moreover, the predetermined interval may be substantially equal to the integral multiple of the peripheral length of the first photoconductor, to the sum of the integral multiple of the peripheral length of the second photoconductor and its half rotation, and to the sum of the integral multiple of the peripheral length of the drive roller and its half rotation, and the calculation step may make a calculation by obtaining the sum of the deviations of each corresponding portion of the registration images.
Alternatively, the predetermined interval may be substantially equal to the sum of the integral multiple of the peripheral length of the first photoconductor and its half rotation, to the integral multiple of the peripheral length of the second photoconductor, and to the integral multiple of the peripheral length of the drive roller, and the calculation step makes a calculation by obtaining the difference between the deviations of each corresponding portion of the registration images.
Further, the image forming apparatus according to the present invention may further include a transferring member for transferring each of the formed images, and a drive roller for superimposing the images in each color by moving the transferring member between the photoconductors, wherein the predetermined interval may be an interval which is set such that periodic disturbances corresponding to the rotational cycle of the drive roller cancel with each other.
Further, a plurality of the drum-type photoconductors may include a first photoconductor having a first diameter and a second photoconductor having a second diameter, the registration images may be formed on the first photoconductor, and the predetermined interval may be set such that periodic components corresponding to the peripheral length of the second photoconductor cancel with each other, and periodic components corresponding to the peripheral length of a drive roller cancel with each other.
Moreover, the image forming apparatus for solving the first and second subjects according to the present invention may include: a plurality of drum-type photoconductors in which first and second registration images are respectively formed on a peripheral surface of the same photoconductor; a plurality of drive sections for rotatably driving each photoconductor at a predetermined drive speed; a measurement section for measuring formation positions of a plurality of predetermined portions in each of the formed registration images; a deviation calculating section for obtaining deviations of the measured formation positions of each of the predetermined portions from a reference position, and for calculating the deviations of each portion for every photoconductor; a phase determining section for calculating a periodic fluctuation component corresponding to a rotational cycle of the photoconductor on the basis of the calculated deviation for each registration image, so as to obtain phases thereof; an adjustment section for adjusting a rotational phase of each photoconductor in order for phases of speed fluctuation of each photoconductor matching to each other on the basis of the obtained phases; a correction signal output section for outputting a speed correction signal that is included in each of the formed images for correcting the fluctuation component corresponding to the rotational cycle of each photoconductor; and a drive control section for controlling the drive sections to correct the drive speed of each photoconductor by using the outputted speed correction signal, wherein the first and second registration images may be formed on the peripheral surface of the same photoconductor at a predetermined interval, the predetermined interval may be an interval in the rotating direction, which is set such that disturbance components in which a cycle is assumed beforehand, cancel with each other by calculating the deviation, and the speed correction signal may be a signal having a cycle equal to the rotational cycle of each photoconductor.
Further, in the image forming apparatus according to the present invention, the photoconductors may include a plurality of types having different diameters, and the speed correction signal may be a signal having a cycle equal to the rotational cycle of each photoconductor according to the diameter.
The image forming apparatus may further include: a registration image forming section for forming the registration images composed of a plurality of patterns on each photoconductor; a fluctuation component calculating section for calculating an amplitude and a phase of a pitch fluctuation component corresponding to the rotational cycle of the photoconductor from a measurement result of each pattern; and a correction signal generating section for generating the speed correction signal having a cycle equal to the rotational cycle on the basis of the calculated amplitude and phase for every diameter.
Further, in the image forming apparatus according to the present invention, the speed correction signal may be common to the photoconductors having the same diameter.
The image forming apparatus according to the present invention may further include: a transferring member for transferring the images formed by each photoconductor, and a rotational phase adjustment section for adjusting the rotational phase of the photoconductor, wherein each photoconductor may be composed of a black image forming photoconductor having a diameter of a first size and a plurality of color image forming photoconductors having a diameter of a second size, and each photoconductor may be arranged along the transferring member at a predetermined interval, and the rotational phase adjustment section may determine the rotational phase of each of the color image forming photoconductors on the basis of the calculated phase so that the phases of the pitch fluctuation component included in the image formed by the respective color image forming photoconductors and transferred to the transferring member are matched to each other, and may adjust the rotational phase of each of the color image forming photoconductors in such a manner that the respective rotational phases are shifted from the respective determined rotational phases at an angle determined beforehand according to the interval so as to align the rotational phases of the respective color image forming photoconductors.
The present invention will be explained in detail with reference to drawings. It is possible to better understand the present invention from the explanation described below. Notably, the explanation described below should be considered to be only illustrative, and not restrictive in all aspects.
(Outline of Image Forming Apparatus)
In the present embodiment, the outline of the mechanical structure of a color image forming apparatus according to one embodiment of the present invention will be explained.
The image data handled by the image forming apparatus is in accordance with a color image using each of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four developing units 2 (2a, 2b, 2c, 2d), four photoconductor drums 3 (3a, 3b, 3c, 3d), four chargers 5 (5a, 5b, 5c, 5d), and four cleaner units 4 (4a, 4b, 4c, 4d) are provided according to each color. The alphabets appended to each numeral represent such that “a” corresponds to black, “b” corresponds to cyan, “c” corresponds to magenta, and “d” corresponds to yellow. Four types of latent images are formed at the peripheral surface of each of the photoconductor drums 3. Specifically, four image stations are provided corresponding to each color.
The configuration of one of the image stations will be explained as the representative of four image stations. The other image stations have the same configuration. Accordingly, the alphabets appended to each numeral are omitted. The charger 5 is a charging means for uniformly charging the surface of the photoconductor drum 3 with a predetermined potential. Examples of the charging means include a brush-type charger and a charger-type charger in addition to a contact-type roller as shown in
The exposure unit 1 is an exposure means for selectively exposing the surface of the charged photoconductor. As the exposure means, a writing head in which light-emitting devices such as EL or LED are arranged in an array may be used instead of the laser scanning unit (LSU) shown in
The laser beam L is modulated in accordance with the image data produced by reading a document or produced by a computer.
The photoconductor drum 3 charged by the laser beam L modulated with the image data is scanned and exposed, whereby an image having a potential corresponding to the image data (electrostatic latent image) is formed on the surface of the photoconductor drum 3. The developing unit 2 develops the latent image formed on the photoconductor drum 3 (makes the latent image formed on the photoconductor drum 3 visible) with a toner of any one of colors of K, C, M, and Y. The cleaner unit 4 removes and collects the residual toner on the surface of the photoconductor drum 3 after the image is developed and transferred as described below.
The intermediate transfer belt unit 8 is arranged above the photoconductor drum 3. The intermediate transfer belt unit 8 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 8-1, an intermediate transfer belt tension mechanism 8-3, an intermediate transfer belt driven roller 8-2, an intermediate transfer roller 6 (6a, 6b, 6c, 6d), and an intermediate transfer belt cleaning unit 9.
The intermediate transfer belt drive roller 8-1, the intermediate transfer belt tension mechanism 8-3, the intermediate transfer roller 6, the intermediate transfer belt driven roller 8-2, and the like stretch the intermediate transfer belt 7 and drive the same to rotate in the direction shown by an arrow B.
The intermediate transfer roller 6 is rotatably supported at an intermediate transfer roller mounting section of the intermediate transfer belt tension mechanism 8-3 at the intermediate transfer belt unit 8. A transferring bias voltage for transferring the toner image formed on the photoconductor drum 3 to the intermediate transfer belt 7 is applied to the intermediate transfer roller 6.
The intermediate transfer belt 7 is provided to be in contact with the respective photoconductor drums 3. The toner image in each color formed on the surface of the photoconductor drum 3 is successively transferred to the intermediate transfer belt 7 by the transferring bias voltage applied to the intermediate transfer roller 6. Thus, a color toner image (multi-color toner image) is transferred onto the intermediate transfer belt 7 in a multi-layered manner. The intermediate transfer belt 7 is made by forming a film having a thickness of about 100 μm to 150 μm into an endless shape.
As described above, the intermediate transfer roller 6 is in contact with the back side of the intermediate transfer belt 7, and it is a transferring means for transferring the toner image onto the intermediate transfer belt 7 from the photoconductor drum 3. A transferring bias voltage of about several hundred volts (the voltage having a polarity (+) opposite to the charging polarity (−) of toner) for transferring the toner image is applied to the intermediate transfer roller 6.
The intermediate transfer roller 6 has a metallic (for example, stainless) shaft having a diameter of 8 to 10 mm as a base. A conductive elastic member (for example, EPDM, urethane foam) is covered on its surface. The conductive elastic member makes it possible to apply a generally uniform voltage to the intermediate transfer belt. In this embodiment, a manual transfer roller is used as the transferring means. However, in addition to this configuration, a brush-type transfer electrode (transfer brush) may be brought into contact with the back side of the intermediate transfer belt 7 for use as the transferring means.
The toner image transferred onto the intermediate transfer belt 7 moves to a transfer section 11, where the transfer roller 11e is arranged, with the rotation of the intermediate transfer belt 7.
The intermediate transfer belt 7 and the transfer roller 11e are brought into pressing contact with each other with a nip of a predetermined width. Further, a bias voltage (high voltage having a polarity (+) opposite to the charging polarity (−) of toner) for transferring the toner image onto a later-described sheet is applied to the transfer roller 11e. Either one of the transfer roller 11e and the intermediate transfer belt drive roller 8-1 is made of a hard material (metal or the like), and the other one is an elastic roller in which the surface of a core metal is covered by a soft material (elastic rubber roller, foaming-resin roller or the like). This can constantly provide a nip of a predetermined width.
The toner is adhered onto the intermediate transfer belt 7 at an area other than the area where the image is transferred onto the sheet by the contact with the photoconductor drum 3. Further, there exists a toner that is not transferred onto the sheet by the transfer roller 11e to remain on the intermediate transfer belt 7. These toners might cause the toner colors to be mixed in the subsequent processes. Thus, the intermediate transfer belt cleaning unit 9 is provided to remove and collect the toners on the intermediate transfer belt 7. The intermediate transfer belt cleaning unit 9 is provided with a cleaning blade serving as a cleaning member, the end of which is in contact with the intermediate transfer belt 7 for removing the toners. The portion of the intermediate transfer belt 7 in a portion where the intermediate transfer belt cleaning unit 9 is in contact with the intermediate transfer belt 7 is supported by the intermediate transfer belt driven roller 8-2 from the back side.
On the sheet feeding tray 10, sheets used for the image formation are stacked. The sheet feeding tray 10 is disposed below the exposure unit 1 of the image forming apparatus 50. On the other hand, the sheet exit tray 15 is disposed at an upper part of the image forming apparatus 50. On the sheet exit tray 15, printed sheets are ejected and stacked in such a way that the printed sides face downward.
Further, the image forming apparatus 50 is provided with the sheet transporting path S, having generally a perpendicular shape, through which a sheet on the sheet feeding tray 10 is conveyed to the sheet exit tray 15 via the transfer section 11 and the fuser unit 12. In the vicinity of the sheet transporting path S between the sheet feeding tray 10 and the sheet exit tray 15, for example a pick-up roller 16, a registration roller 14, the transfer section 11, the fuser unit 12, and transport rollers 25 (25-1 to 25-8) for transporting the sheet are disposed.
A plurality of transport rollers 25-1 to 25-4 are small rollers that facilitate and support conveying of the sheets and are provided along the sheet transporting path S. The pick-up roller 16 is disposed at an end portion of the sheet feeding tray 10, and conveys sheets, one by one, from the sheet feeding tray 10 to the sheet transporting path S.
The registration roller 14 temporarily holds the sheet being conveyed through the sheet transporting path S at a predetermined position. The registration roller 14 has a function of conveying the sheet to the transfer section 11 at such timing that the front end of the toner image formed on the intermediate transfer belt 7 is synchronized with the front end of the sheet.
The fuser unit 12 is provided with, for example, a heat roller 31 and a pressure roller 32. The heat roller 31 and the pressure roller 32 rotate with a sheet which is sandwiched between them.
The heat roller 31 is controlled by a control section of a control substrate 40 such that an unillustrated heater arranged in the heat roller 31 has a predetermined fusing temperature on the basis of a signal from a temperature detection unit (not illustrated). The heat roller 31 and the pressure roller 32 apply heat and pressure to the sheet, which is passed between the heat roller 31 and the pressure roller 32, so that the color toner images transferred onto the sheet are melted, mixed, and pressed. As a result, the color toner images are heat fused with the sheet.
The sheet with the fixed multi-color toner image is transported, by the transport rollers 25-5 and 25-6, to a reversed-sheet exit path of the sheet transporting path S. Then, the sheet, which has been reversed upside down (the multi-color toner image is facing downward), is ejected to the sheet exit tray 15.
Next, the sheet transporting path will be explained in detail. A sheet cassette 10 for accommodating sheets beforehand is provided in the image forming apparatus.
The sheet feeding tray 10 is provided with the corresponding pick-up roller 16, at its end portion, that supplies the sheets, one by one, to the sheet transporting path.
The sheet conveyed from the sheet feeding cassette 10 is conveyed to the registration roller 14 by the transport rollers 25-1 to 25-4 disposed on the sheet transporting path and then stops. The registration roller 14 sends the sheet to the transfer section 11 at such timing that the front end of the sheet meets the front end of the toner image on the intermediate transfer belt 7. At the transfer section 11, the toner image on the intermediate transfer belt 7 is transferred onto the sent sheet. Thereafter, the toner image passes the fuser unit 12. At this time, the non-fixed toner on the sheet is fused by heat, naturally cooled after passing through the fuser unit 12, and then, fixed onto the sheet. Then, the sheet is conveyed to the transport roller 25-5, then, to the sheet exit roller 25-6 and finally, ejected to the sheet exit tray 15.
The control substrate 40 is arranged below the sheet exit tray 15. The control substrate 40 has a microcomputer for controlling the operation of each section of the image forming apparatus 50, a ROM for storing a control program executed by the microcomputer, and a RAM for providing a working area for the process of the microcomputer and a storage area of image data. The microcomputer executes the control program to function as a control section. The above-described image formation, transfer of toner image, transport of sheet, temperature control of the fuser unit, and the like are realized by the function of the control section.
The control substrate has an input circuit and an output circuit. Inputted to the input circuit are signals from the sensors arranged at each section in the image forming apparatus 50, whereby the microcomputer can perform the processing by using the inputted signals. The output circuit is the one for outputting a signal for driving loads arranged at each section.
(Procedure 1 of Color Registration—Measurement of Misregistration Amount)
The diameter of each of Y, M, and C photoconductor drums is 30 mm, and the diameter of the K photoconductor drum 3a is 80 mm. The difference in the diameter depends upon the design conditions such as a service life of the photoconductor, a processing speed (the moving speed of the surface of the photoconductor and the intermediate transfer belt 7 upon the image formation), and the like. The processing speed upon the color image formation in which the color misregistration becomes a significant problem is 173 mm/sec. The distance between the transfer point of the Y photoconductor drum 3d and the transfer point of the M photoconductor drum 3c, and the distance between the transfer point of the Y photoconductor drum 3d and the transfer point of the C photoconductor drum 3b are respectively 100 mm. The distance between the transfer point of the C photoconductor drum 3b and the transfer point of the K photoconductor drum 3a is 200 mm.
A color registration sensor 42 for measuring the color misregistration is arranged at a 280 mm downstream side of the transfer point of the K photoconductor drum 3a. The color registration sensor 42 is an optical sensor for reading a toner pattern transferred onto the intermediate transfer belt 7. The read signal is inputted to the input circuit of the control substrate and processed by the control section.
A plurality of (seventeen in
When the pattern shown in
(Procedure 2 of Color Registration—Acquiring Phase of Main Fluctuation Component)
The control section obtains the periodic fluctuation phase corresponding to the peripheral length of the photoconductor drum 3, on which the toner pattern is formed, from the misregistration amount obtained for each straight line. This is because that the greatest cause for producing the misregistration amount is experientially found to be the eccentricity of the photoconductor.
As shown in
As shown in
On the contrary, when the peripheral speed at the exposure position is slower than the reference speed as shown in
The control section obtains the phase of the periodic fluctuation corresponding to the peripheral length of the photoconductor drum 3, on which the toner pattern is formed, from the misregistration amount obtained for each straight line.
It is to be noted that, in the present embodiment, the “misregistration amount” is a numeral with a positive or negative sign corresponding to the result of the measurement of each straight line in the toner pattern. Specifically, each misregistration amount is a value indicating the misregistration from the reference position. The positive or negative sign indicates the direction of the misregistration. For example, the “positive” sign represents the direction in which each straight line delays from the reference position (see
Each photoconductor drum 3 is driven by the photoconductor drive motor 45 provided to correspond to each photoconductor drum 3. The rotation of the drive motor 45 is controlled by the control section. A drive gear 46 is fitted to the output axis of the photoconductor drive motor 45. The drive gear 46 is engaged with the driven gear 47. It is considered from the result of the analysis of the periodic fluctuation component of the color misregistration that the color misregistration is greatly caused by the eccentricity of the photoconductor drum 3 and the driven gear 47.
Even if the color misregistration is for the most part caused by the eccentricity of the photoconductor drum 3 and the driven gear 47, there are other causes. It has been known that another main cause is the eccentricity of the transfer belt drive roller 8-1 and the eccentricity of the photoconductor having a different diameter. This is acquired by the analysis of the periodic fluctuation component of the color misregistration. The photoconductor having a different diameter means the photoconductor for black, when a yellow image is the subject, for example. Alternatively, the photoconductor having a different diameter means the photoconductor for Y, M and C, when a black image is the subject.
When the toner pattern is formed and measured, the other causes become disturbances to deteriorate the precision of the measurement. Therefore, in the image forming apparatus according to the present invention, a plurality of toner patterns are formed to prevent the disturbances. However, it takes much time for the measurement only by forming many toner patterns to average the disturbances. Therefore, the interval between the toner patterns is set such that the periodic fluctuations of the other main disturbance factors cancel with each other. Specifically, the interval between the first toner pattern and the second toner pattern is set such that the phase of the disturbance is reversed in the first toner pattern and the second toner pattern.
The misregistration amount obtained from the first toner pattern and the misregistration amount obtained from the second toner pattern are calculated, whereby the misregistration amount in which the disturbance is suppressed is obtained. The phase of the fluctuation component with the predetermined cycle is obtained from the obtained misregistration amount.
The interval between the toner patterns is, for example, the distance between the front ends thereof, or the distance between the rear ends thereof. Specifically, the interval between the toner patterns is the distance between the corresponding portions of the adjacent toner patterns.
The control section obtains the rotational phase of the photoconductor drum 3 upon forming the toner pattern in each color by performing the aforesaid measurement for each color. The eccentricity of the photoconductor drum 3 is a very small amount that cannot be observed only by the visual observation of the rotating photoconductor drum 3. The phase of the eccentricity is obtained only after the toner pattern is formed and measured.
For example, when the phase of the periodic fluctuation component of K is obtained, the interval Lt of each toner pattern of K may be set to 750 mm in order to remove the periodic fluctuation component of the transfer belt drive roller 8-1 included in the toner pattern of K. The interval Lt of the toner pattern generally corresponds to the integral multiple of the peripheral length of the K photoconductor drum 3a that forms the toner pattern of K, and the sum of the integral multiple of the peripheral length of the transfer belt drive roller 8-1 and the half rotation thereof. Specifically,
Peripheral length of K photoconductor drum that is the subject of the measurement: 80 (mm)×π≅251 (mm)
Peripheral length of transfer belt drive roller that is the disturbance: 31.8 (mm)×π≅100 (mm)
Interval Lt of toner patterns: 750 (mm)=100 (mm)×7.5≅251 (mm)×3
The interval Lt is set to the sum of the integral multiple of the peripheral length of the transfer belt drive roller that is the disturbance and the half rotation thereof. Specifically, it is set such that the disturbance agreeing with the rotational cycle of the drive roller takes the reverse phase. Accordingly, if the misregistration amount is composed in each corresponding straight line of two toner patterns, the disturbance components of the cycle are canceled with each other. The misregistration amount is a numerical value with a sign, so that composing the misregistration amounts means that the addition of the numerical values with signs is performed.
The interval Lt of each toner pattern of K may be set to 1131 mm in order to remove the periodic fluctuation component of each of the Y, M and C photoconductor drums 3d, 3c, and 3b included in the toner pattern of K. The interval Lt of the toner pattern generally corresponds to the sum of the integral multiple of the peripheral length of the K photoconductor drum 3a that forms the toner pattern of K and its half rotation, and the sum of the integral multiple of the peripheral length of each of Y, M, and C photoconductor drums 3d, 3c, and 3b. Specifically,
Peripheral length of K photoconductor drum that is the subject of the measurement: 80 (mm)×π≅251 (mm)
Peripheral length of each of Y, M, and C photoconductor drums that is the disturbance: 30 (mm)×π≅94.2 (mm)
Interval Lt of toner patterns: 1131 (mm)=94.2 (mm)×12≅251 (mm)×4.5
The interval Lt is set to the integral multiple of the peripheral length of each of the Y, M, and C photoconductor drums that is the disturbance. Specifically, it is set such that the disturbance agreeing with the rotational cycle of the photoconductor drum takes the same phase. Accordingly, if the difference between the misregistration amounts of each straight line corresponding to two toner patterns is calculated, the disturbance components of the cycle are canceled with each other. The misregistration amount is a numerical value with a sign, so that the calculation of the difference means that the subtraction of the numerical values with signs is performed.
As described above, the interval Lt of the toner patterns is within a range substantially equal to the integral multiple of the peripheral length of the photoconductor drum, which is the subject to be measured, or to the total sum of the integral multiple of the peripheral length and the half rotation, and may be within the range substantially equal to the total sum of the integral multiple of the peripheral length of the photoconductor drum having a diameter different from that of the photoconductor that is the subject to be measured and the half rotation, or to the integral multiple thereof.
The aforesaid substantially equal range may be the length corresponding to ±15° with respect to the phase angle in which one cycle of the periodic disturbance is 360°. Specifically, the aforesaid substantially equal range may be the range corresponding to the length of an arc of a sector having a central angle of ±15° in the transfer belt drive roller that is the disturbance, or the photoconductor drum that is the disturbance. According to the experience of the present inventor, the influence due to the periodic disturbance caused by the error in the processing precision corresponds to approximately four pixels in the misregistration amount shown in
More preferable value of the aforesaid range is ±15.7° of the phase angle with one cycle of the periodic disturbance defined as 360°. According to the experience of the present inventor, more preferable result could be obtained, when the interval Lt of the toner patterns was set to 750 mm with respect to 753.98 mm that is the length three times the peripheral length of the K photoconductor drum having a diameter of 80 mm. In this case, the angle corresponding to 3.98 mm, which is the difference between 753.98 mm and 750 mm, is 5.7°. Therefore, more preferable result can be obtained within the range of the phase angle of ±5.7° with one cycle of the periodic disturbance defined as 360°.
Next, the case where the phase corresponding to the periodic fluctuation component of Y, for example, will be explained. In this case, the color misregistration is relatively adjusted by the rotational phase adjustment for the M and C photoconductor drums having the diameter same as that of the Y photoconductor drum, so that they do not become the disturbance. However, even if the rotational phase is adjusted for the K photoconductor drum, the effect of reducing the color misregistration cannot be obtained, since the K photoconductor drum has the different diameter. Specifically, the periodic component of the deviation corresponding to the peripheral length of the K photoconductor drum 3a becomes the disturbance. The interval Lt of the toner patterns in this case generally corresponds to the integral multiple of the peripheral length of the Y photoconductor drum 3d, and to the sum of the integral multiple of the peripheral length of the K photoconductor drum 3a and its half rotation. Specifically,
Peripheral length of Y photoconductor drum 3d that is the subject to be measured: 30 (mm)×π≅94.2 (mm)
Peripheral length of K photoconductor drum 3a that is the disturbance: 80 (mm)×π≅251 (mm)
The interval Lt of toner patterns may be, for example, such that:
377 (mm)≅94.2 (mm)×4≅251 (mm)×1.5 or
1131 (mm)≅94.2 (mm)×12≅251 (mm)×4.5.
(Procedure 3 of Color Registration—Adjustment of Rotational Phase of Photoconductor Drum)
Even if the absolute value of the eccentric amount is constant, the color misregistration can be made unnoticeable by matching the phase of each color.
As shown in
It should be noted that the position of the projection 44 for each photoconductor drum is determined regardless of the direction of the eccentricity. This is because the eccentricity is produced due to the error in the precision in processing components or assembling precision, and the eccentricity is not provided intentionally. However, as described above, the relationship between the direction of the eccentricity and the projection 44 can be obtained by measuring the toner pattern to obtain the phase of the main fluctuation component.
In the aforesaid manner, the control section determines the reference rotation angle of each photoconductor drum from the measured toner pattern.
Further, the control section adjusts the rotational phase of each of Y, M, and C photoconductor drums in order that the reference phases of the Y, M, and C photoconductor drums, each having the same diameter, match to one another.
The rotational phase may be adjusted, for example, by exposing the front end of the printed image with the reference rotation angle of each photoconductor drum. Alternatively, the rotational phase may be adjusted by exposing the front end of the image with a delay of a predetermined angle from the reference phase. It is to be noted that the delay amount is the same in Y, M and C. By virtue of this configuration, the phases of each of the formed images of Y, M and C match to one another, whereby the color misregistration is unnoticeable.
The control section executes the adjustment of the rotational phase of each photoconductor drum at the time when it stops each photoconductor drum after the formation of the toner pattern, for example. The control section controls the rotation of the drive motor 45 of each photoconductor such that, upon stopping, the rotation angle when each photoconductor drum 3 is stopped takes a predetermined relationship.
(Calculating Process of Interval between Toner Patterns and Misregistration Amount)
The interval between the toner patterns formed for each color is set to the predetermined interval Lt according to the aforesaid procedure. The predetermined interval Lt will further be explained. The setting of the interval Lt between the toner patterns has a degree of freedom described below. The control section can remove the disturbance component of the predetermined cycle by calculating the sum or difference of the misregistration amounts. When the disturbance component is removed by calculating the sum of the misregistration amounts, the interval Lt may be set to the integral multiple of the fluctuation period of the subject to be measured and the sum of the integral multiple of the fluctuation period of the disturbance and its half rotation. On the other hand, when the disturbance component is removed by calculating the difference of the misregistration amounts, the interval Lt may be the sum of the integral multiple of the fluctuation period of the subject to be measured and its half rotation, and the integral multiple of the fluctuation period of the disturbance. A designer may select which interval is used.
Two patterns, i.e., a pattern 1 and a pattern 2, are formed as the toner pattern. In this case, the control section sets the pattern 1 and the pattern 2 to have a relationship shown in the figure. The fluctuation component corresponding to the K photoconductor drum 3a is the same phase, while the fluctuation component corresponding to the color photoconductor drums is the reverse phase. The control section calculates the sum of each deviation. This suppresses the disturbance component of the reverse phase and amplifies the fluctuation component corresponding to the K photoconductor drum 3a that is the subject to be measured.
On the other hand,
Two patterns, i.e., a pattern 1 and a pattern 2, are formed as the toner pattern. In this case, the control section sets the pattern 1 and the pattern 2 to have a relationship shown in the figure. The fluctuation component corresponding to the K photoconductor drum 3a is the reverse phase, while the fluctuation component corresponding to the color photoconductor drums is the same phase. The control section calculates the difference of each deviation. This suppresses the disturbance component of the reverse phase and amplifies the fluctuation component corresponding to the K photoconductor drum 3a that is the subject to be measured.
(Suppression of Disturbance Component having Composite Cycle)
In
The disturbance including the composite cycle means the following. When Y is the subject to be measured, the color misregistration is relatively adjusted by the rotational phase adjustment of the M and C photoconductor drums having the diameter same as that of the Y photoconductor drum, whereby M and C photoconductor drums do not become the disturbance. However, since the K photoconductor drum has the different diameter, the effect of reducing the color misregistration cannot be obtained only by adjusting the rotational phase. Specifically, the periodic component of the deviation corresponding to the peripheral length of the K photoconductor drum 3a is the disturbance. Further, the periodic component of the deviation corresponding to the peripheral length of the intermediate transfer belt 7 is the disturbance. The deviation obtained by the measurement contains both periodic components.
Therefore, if the interval Lt between the toner patterns is set as described below, both of the periodic component of the deviation corresponding to the peripheral length of the K photoconductor drum 3a and the periodic component of the deviation corresponding to the intermediate transfer belt 7 can be suppressed. Since Y (color photoconductor drum) is the subject to be measured, the interval Lt is set to satisfy the all three conditions described below.
(1) Integral multiple of the peripheral length of color photoconductor drum (94.2 mm)
(2) Integral multiple of peripheral length of K photoconductor drum 3a (251 mm)+half rotation
(3) Integral multiple of peripheral length of intermediate transfer drive roller 7 (100 mm)+half rotation
For example, 5655 mm that generally satisfies the three conditions of:
(1) 94.2 (mm)×60
(2) 251 (mm)×22.5
(3) 100 (mm)×56.5
is set as the interval Lt. If the sum of the deviations of the corresponding portions of the pattern 1 and the pattern 2 is calculated, the disturbance component is suppressed, whereby the target fluctuation component can be precisely measured.
When K is the subject to be measured, the effect of reducing the color misregistration cannot be obtained only by adjusting the rotational phase, since the color photoconductor drums have the different diameters. Specifically, the periodic component of the deviation corresponding to the peripheral lengths of the color photoconductor drums is the disturbance. Further, the periodic component of the deviation corresponding to the peripheral length of the intermediate transfer belt 7 is the disturbance. The deviation obtained by the measurement contains both periodic components.
Therefore, if the interval Lt between the toner patterns is set as described below, both of the periodic component of the deviation corresponding to the peripheral length of the color photoconductor drums and the periodic component of the deviation corresponding to the intermediate transfer belt 7 can be suppressed. Since K photoconductor drum 3a is the subject to be measured, the interval Lt is set to satisfy the all three conditions described below.
(1) Integral multiple of the peripheral length of K photoconductor drum 3a (251 mm)+half rotation
(2) Integral multiple of peripheral length of color photoconductor drum (94.2 mm)
(3) Integral multiple of peripheral length of intermediate transfer drive roller 7 (about 100 mm)
For example, 4901 mm that generally satisfies the three conditions of:
(1) 251 (mm)×19.5
(2) 94.2 (mm)×52
(3) 100 (mm)×49
is set as the interval Lt. If the difference of the deviations of the corresponding portions of the pattern 1 and the pattern 2 is calculated, the disturbance component is suppressed, whereby the target fluctuation component can be precisely measured.
Since the K photoconductor drum 3a has the different diameter as described above, the color misregistration cannot be reduced by matching the phase thereof to the phases of Y, M and C. Therefore, as for the K photoconductor drum 3a, the speed of the photoconductor drive motor 45a is periodically corrected to make the peripheral speed of the K photoconductor drum 3a constant on the basis of the reference signal that is the output from the K phase sensor 43a and the reference rotation angle of K. Thus, the pitch fluctuation component of K is suppressed, thereby reducing the color misregistration.
(Reduction in Color Misregistration by Correction of Drive Speed of Photoconductor)
As described above, the diameter of each of the color photoconductor drums and the diameter of the K photoconductor drum are different. The technique for suppressing the pitch fluctuation component of each image formed by the photoconductor drum having a different diameter will be explained hereinafter.
As shown in
The cycle of the modulation signal of K matches to the rotational cycle Tk of the photoconductor K. The cycle of the modulation signal (for color) matches to the rotational cycle Tc of the color photoconductors.
The detection signals from the color registration sensor 42 and the phase sensor 43 corresponding to each photoconductor drum 3 are inputted to the control section 40a. The control signals for the drive control circuit 53 corresponding to each photoconductor drum 3 and each of the modulation signal generating circuits 51 of K and color are outputted from the control section 40a. It is to be noted that input/output signals not shown in
As for the color registration, the control section 40a outputs the control signals to each drive control circuit 53 for controlling the drive of each photoconductor drum 3. Then, the control section 40a forms a registration toner patch, transfers the same onto the intermediate transfer belt 7, and reads the position of each pattern by the color registration sensor 42.
The control section 40a calculates the misregistration amount (deviation) of the position of the read pattern from the reference position, and obtains the phase of the eccentricity (rotational phase) of each photoconductor drum 3 on the basis of the calculated deviation. Then, the control section 40a adjusts the relative position of each photoconductor drum 3 in such a manner that the obtained rotational phases are matched.
Further, the control section 40a obtains the amplitude of the eccentricity of each photoconductor drum 3 from the result of the measurement of the toner pattern, and controls the phase and amplitude of the modulation signal generated at the modulation signal generating circuits 51a and 51b according to the obtained phase and amplitude.
The modulated drive signal must have the phase and the amplitude for canceling the fluctuation of the peripheral speed due to the eccentricity. Each modulation signal generating circuit 51 is a block that generates the modulation signal satisfying the aforesaid condition. More specifically, each modulation signal generating circuit 51 is a sine wave generating circuit that can adjust the amplitude and the phase of the output signal.
(Adjustment of Rotational Phase of Photoconductor Drum)
After the color registration is performed, the control section stores Δt=t2−t1 shown in
In the manner described above, the control section determines the reference rotation angle of each photoconductor drum on the basis of the reference phase of the measured toner pattern.
Further, the control section adjusts the rotational phases of Y, M and C photoconductor drums such that each of the reference phases are matched from the misregistration amount of the measured toner pattern from the reference phase.
The rotational phase may be adjusted, for example, by exposing the front end of the printed image with the reference rotation angle of each photoconductor drum. Alternatively, the rotational phase may be adjusted by exposing the front end of the image with the delay of the predetermined angle from the reference phase. It is to be noted that the delay amount is the same in Y, M and C. By virtue of this configuration, the phases of each of the formed images of Y, M and C are matched, whereby the color misregistration is unnoticeable.
The control section executes the adjustment of the rotational phase of each photoconductor drum at the time when it stops each photoconductor drum after the formation of the toner pattern, for example. The control section controls the rotation of each photoconductor drive motor 45 such that, upon stopping, the rotation angle when each photoconductor drum 3 is stopped takes the predetermined relationship. Specifically, the control section controls the rotation angle of the photoconductor upon stopping in such a manner that the synchronous signals of Y, M and C have the predetermined phase relationship shown in
Accordingly, with the state in which the rotational phase is adjusted, the rotational phase of the M photoconductor drum 3c is delayed by 21.96° from the rotational phase of the Y photoconductor drum 3d. Similarly, the rotational phase of the C photoconductor drum 3b is delayed by 21.96° from the rotational phase of the M photoconductor drum 3c. Specifically, the rotational phase of the C photoconductor drum 3b is delayed by 43.92° from the rotational phase of the Y photoconductor drum 3d.
If the distance between each transfer position is agreed with the peripheral length of the photoconductor, the rotational phase of each photoconductor is matched to each other. However, this imposes a limitation on a layout interval around each photoconductor or the size of the image forming apparatus.
In view of this, when the distance between the transfer positions and the peripheral length of the photoconductor do not agree with each other, the phase of the color modulation signal is controlled with any one of Y, M, and C defined as a reference. In the embodiment shown in
When the modulation signal from the modulation signal generating circuit 51b is inputted to each drive control circuit 51b, 51c, and 51d with the state in which the rotational phase of each of Y, M and C photoconductor drums 3 is adjusted, a deviation is produced between the peripheral speed fluctuation component of the photoconductor and the phase of the modulation signal.
For example, it is supposed that the amplitude of the peripheral speed fluctuation component of the C photoconductor drum 3b is the greatest, and the modulation signal generating circuit 51b generates the modulation signal having the phase reverse to that. In this case, the modulation signal is also inputted to the Y and M drive control circuits 51d and 51c from the modulation signal generating circuit 51b. As for the C photoconductor drum 3b, the phase is corrected, so that the peripheral speed fluctuation component is well suppressed, but the phase of the modulation signal to the peripheral speed fluctuation component is deviated for the Y and M photoconductor drums 3d and 3c.
Therefore, the control section corrects the rotational phase of each photoconductor from the state in which the rotational phase of each of Y, M and C photoconductor drums 3 is adjusted, in order that the phases of the pitch fluctuation component on the image match to each other. This makes it possible to match the rotational phase of each of Y, M and C photoconductors to one another and to reverse the phase of the peripheral speed fluctuation component of each photoconductor drum to the common modulation signal. Specifically, the rotational phase of the M photoconductor drum 3c is advanced in its rotating direction by 21.96°. Further, the rotational phase of the C photoconductor drum 3b is advanced in its rotating direction by 43.92°. Specifically, the rotational phase of the stopped photoconductors is controlled to match the M and C synchronous signals with the Y synchronous signal with the Y synchronous signal as a reference.
In this case, somewhat of a deviation occurs between the direction of the eccentricity of each of Y, M and C photoconductor drums 3 and the position of each image formed on the surface of the photoconductor drum, but the peripheral speed fluctuation component of each photoconductor is cancelled by using the modulation signal, whereby the absolute value of the color misregistration is reduced. Accordingly, the color misregistration becomes unnoticeable.
The rotational phase of the color photoconductor drum can be obtained by measuring the registration toner pattern. In other words, it is not until the toner pattern is measured that the rotational phase of each photoconductor is found. However, the adjustment amount for matching the rotational phase of each photoconductor drum from the state where the phases of the pitch fluctuation component on the image match to each other is found beforehand. The control section adjusts the rotational phase of each photoconductor drum 3 after it matches the phase of the pitch fluctuation component on the image by the measurement of the toner pattern. In this manner, the adjustment amount of the rotational phase of each photoconductor drum 3 is derived in two stages. It is to be noted that the process for physically deviating the rotational phase of each photoconductor drum may be executed at one time at the stage where the final adjustment amount is derived.
A black circle in
The amplitude of each modulation signal is adjustable. The amplitude of the color modulation signal is adjusted such that the amplitude of the pitch fluctuation component included in the image in each color is detected, and the maximum amplitude and the minimum amplitude among the amplitudes obtained for the pitch fluctuation component of each of Y, M and C colors are selected. Then, the intermediate values of the maximum amplitude and the minimum amplitude are obtained. Next, the variation amount of the rotation speed of the photoconductor corresponding to the obtained amplitude (intermediate value) is obtained. If the diameter of the photoconductor and the reference rotation speed are determined beforehand, the variation amount of the rotation speed corresponding to the amplitude of the pitch fluctuation can be calculated by using them. The control section determines the amplitude of the modulation signal (for color) that cancels the obtained variation amount.
More specifically, it is supposed that the speed variation amplitude of the C photoconductor having the greatest variation amount of the rotation speed is defined as Ac, and the speed variation amplitude of the M photoconductor having the smallest variation amount of the rotation speed is defined as Am. In this case, the control section employs the intermediate value of Ac and Am, i.e., (Ac+Am)/2, as the amplitude of the modulation signal. The reason is as follows. If the amplitude of the modulation signal (for color) is determined to completely cancel the peripheral speed variation component of the photoconductor drum having the greatest amplitude, the correction amount becomes too great to the photoconductor drum having the smallest amplitude.
(Formation of Registration Toner Pattern and Control of Measurement)
The reason for using the term “ideally” is because the aforesaid concept is achieved if there is no eccentricity of the photoconductor drum or other disturbances, but actually, an error is included with respect to the predetermined interval Lt due to these factors.
In
After the measurement for all lines is completed (step S17), the control section 40a waits until the timing of starting the formation of the pattern 2 comes (step S19). The timing of forming the pattern 2 is the timing apart from the start of the formation of the pattern 1 by the interval Lt in terms of the distance on the intermediate transfer belt. In the present embodiment, the interval Lt is sufficiently longer than the distance of 680 mm from the intermediate transfer roller 6d to the color registration sensor 42. When the interval Lt is shorter than 680 mm or substantially equal to 680 mm, the control section 40a forms the pattern 2 before the measurement of the pattern 1 or simultaneously.
The control section 40a controls each section of the image station to start the formation of the pattern 2 when the aforesaid timing has come (step S21). Then, the control section 40a transfers the formed pattern 2 onto the intermediate transfer belt 7, and detects the passing timing of each line on the basis of the detection signal from the color registration sensor 42 when each line of the transferred pattern 2 passes the color registration sensor 42 (step S23). Thus, the control section 40a calculates the misregistration amount (misregistration amount 2) from the reference timing for each line of the seventeen lines (step S25). The calculated misregistration amount is temporarily stored to be used for the later calculation.
After the measurement for all lines is completed (step S27), the control section 40a obtains the sum or difference between the misregistration amount 1 and the misregistration amount 2 for each of seventeen lines to obtain the composite misregistration amount d(n) (step S31). Whether the sum is obtained or the difference is obtained is determined according to the setting of the interval Lt. Specifically, when the disturbance component that should be removed has the same phase in the pattern 1 and the pattern 2, the difference is obtained, while when the disturbance component has the reverse phase, the sum is obtained, in order to cancel the disturbance components with each other.
Subsequently, the control section 40a executes a process for calculating the reference phase and amplitude of the pitch fluctuation component from the composite misregistration amount d(n) (step S33). An example of obtaining the reference phase and the amplitude is as stated in the explanation of
(Adjustment of Rotational Phase of Photoconductor Drum)
The technique for adjusting the rotational phase of each photoconductor drum will be explained in detail.
As described above, the rotational phase is adjusted by the control for realizing that the eccentric direction of each photoconductor drum 3 after being stopped becomes the predetermined direction, when the control section 40a stops each photoconductor drum 3. The control section 40a obtains the direction of the eccentricity of each photoconductor drum 3 by measuring the registration toner pattern, and outputs the synchronous signal at the timing when the position of the reference phase corresponding to the obtained eccentric direction is exposed by the laser beam L. As shown in
Thereafter, the control section 40a stops the Y photoconductor drum 3d, which is the reference, at the predetermined position. In
When the output of the M synchronous signal is delayed with respect to the Y synchronous signal, the M photoconductor drum 3c may be stopped with the delay of the delay amount MΔdr from the M synchronous signal that is outputted with delay from the Y synchronous signal that is the reference for stoppage.
It is preferable that the adjustment of the rotational phase is executed every time each photoconductor drum 3 is stopped. There may be a case in which the rotational phase of each photoconductor is gradually deviated unintentionally during the process of continuously printing many pages. This is considered that it is caused by the slight error in the diameter of each photoconductor drum or a disturbance factor of the dive control system. The effect of suppressing the color misregistration can be maintained by matching the rotational phase when the photoconductor drum 3 is stopped.
It is finally apparent that various modifications are possible within the scope of the present invention, in addition to the aforesaid embodiment. The modifications should not be construed not belonging to the feature and scope of the present invention. It is intended that the scope of the present invention includes all modifications within the meaning and scope equivalent to the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-112604 | Apr 2006 | JP | national |
| 2006-199733 | Jul 2006 | JP | national |
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| 6938351 | Kobayashi et al. | Sep 2005 | B2 |
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| 07-261499 | Oct 1995 | JP |
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| Number | Date | Country | |
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| 20070242986 A1 | Oct 2007 | US |
