JP4431410B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a latent image carrier, a plurality of developing means for developing the latent image carried on the latent image carrier into a visible image, and optical scanning for carrying the latent image by scanning the latent image carrier. The present invention relates to an image forming apparatus such as a copying machine or a facsimile.

  Optical scanning in this type of image forming apparatus is divided into sub-scanning, which is scanning in the surface movement direction of the latent image carrier, and main scanning, which is scanning in a direction perpendicular thereto. A light beam emitted from a light source such as a laser diode is deflected in a main scanning direction by a deflecting means such as a polygon mirror, thereby performing main scanning on the latent image carrier. Further, the surface of the latent image carrier is relatively moved with respect to the irradiation position of the light beam, so that the latent image carrier is sub-scanned. These scans are started when the light beam comes to the writing start position in the main scanning direction along with the deflection. Whether or not the light beam has reached the writing start position is determined based on a beam detection signal from a beam detection unit that detects the light beam at a predetermined position in the main scanning direction.

  In the image forming apparatus having such a configuration, one latent image carrier and a plurality of developing units corresponding to the latent image carrier are provided, and a plurality of visible images individually developed by each developing unit are intermediate-transferred from the latent image carrier. Those which are sequentially superimposed on the body and transferred are known. In this type of image forming apparatus, the surface of the intermediate transfer member is moved by the number of times of overlapping. For example, in a system that obtains a quadruple image by superimposing and transferring four visible images of yellow, magenta, cyan, and black, first, the latent image carried on the latent image carrier is developed by yellow developing means. Development is performed to obtain a yellow image (hereinafter, yellow, magenta, cyan, and black are referred to as Y, M, C, and K). Then, the obtained Y image is transferred onto the first transfer intermediate transfer member. Next, the M image, the C image, and the K image developed on the latent image carrier are sequentially superimposed and transferred to the intermediate transfer member on the second, third, and fourth turns, and finally the quadruple image is transferred. obtain.

  In the image forming apparatus having such a configuration, it is necessary to start optical scanning with respect to the latent image carrier at a timing at which the leading edge of each color image can be superimposed on the intermediate transfer member without deviation for each turn of the intermediate transfer member. . Therefore, with respect to the start timing of the optical scanning with respect to the latent image carrier, the intermediate transfer member is synchronized with the leading edge of the visible image on each surface at the transfer position where the intermediate transfer member and the latent image carrier are opposed to each other. Each lap is determined as follows. That is, based on the mark detection signal from the mark detection means for detecting the reference mark attached to the predetermined position in the surface movement direction of the intermediate transfer member and the above-described beam detection signal, the main and secondary of the latent image carrier are detected. The scanning start position in both directions is determined for each turn. In this way, the leading edge of the latent image to be formed on the latent image carrier from now on can be superimposed at the transfer position on the leading edge of the visible image previously transferred onto the intermediate transfer member. Then, the optical scanning of the electrostatic latent image is started.

  However, when such timing arrives, the light beam is not always at the writing start position in the main scanning direction. This is for the reason explained below. That is, for example, it is assumed that the peripheral length of the intermediate transfer member is 600 [mm], the linear velocity is 40 [mm / sec], and the scanning speed in the main scanning direction of the optical scanning unit is 1000 [times / sec]. In this case, the number of times of optical scanning performed per rotation of the intermediate transfer member is exactly 15000 times. In such a configuration, the light beam coincides with the writing start position in the main scanning direction at the moment of detecting the mark on the first circumference of the intermediate transfer body, and at that moment, the optical scanning for the electrostatic latent image of the first color is performed. Suppose you started. Theoretically, the polygon mirror rotates by the number that scans the light beam exactly 15000 times in the main scanning direction from the moment until the intermediate transfer member makes one round. For this reason, the reference mark for the second turn is detected at the time when the intermediate transfer member has just made one turn, and the light beam comes to the optical writing start position in the main scanning direction and the electrostatic latent image for the second color is detected. For this purpose is started. However, in practice, since the speed of the intermediate transfer member varies, the light beam in the main scanning direction is often not at the writing start position when the intermediate transfer member makes one round. Then, the next optical scanning is started when the surface of the intermediate transfer member is moved a little more than one round, and the leading edge shift of the visible image in the sub-scanning direction occurs.

  When an intermediate transfer belt is used as the intermediate transfer member, a slight slip of the belt may occur on the driving roller. For this reason, the front end shift is more likely to occur than when an intermediate transfer drum having no slip is used.

  As an image forming apparatus capable of suppressing such tip misalignment, the one described in Patent Document 1 is known. This image forming apparatus detects the deviation between the writing start position entry timing of the light beam and the transfer position entry timing of the visible image on the intermediate transfer body, which is caused by the speed fluctuation of the intermediate transfer body, as described above. And the beam detection signal. Then, according to the deviation, the phase of the change in the light deflection angle by the deflecting means is corrected so that both timings can be synchronized. More specifically, the rotational phase of the polygon mirror that is a part of the deflecting unit is corrected according to the timing deviation described above, and the phase of change in the light deflection angle is corrected. By such correction, it is possible to effectively suppress the leading edge deviation due to the speed fluctuation of the intermediate transfer member.

  However, in order to obtain a superimposed image with this image forming apparatus, for example, the surface of the intermediate transfer body can be obtained by the number of times of the overlay transfer, for example, the surface of the intermediate transfer body is rotated four times to obtain a four-color image. Must move around. As a result, the image forming time is significantly increased as compared with a monochromatic image forming apparatus that does not perform superposition.

  On the other hand, as a conventional image forming apparatus for forming a superimposed image, a visible image forming unit having a latent image carrier and a developing unit corresponding to the latent image carrier is provided in the same number as the number of overlapping of visible images. Is also known (described in Patent Document 2 and Patent Document 3). For example, if this type of image forming apparatus forms the above-described quadruple image as a superimposed image, 4 for individually forming four colors of Y, M, C, and K visible images. Two visualization means are provided. Then, the Y, M, C, and K colors on each latent image carrier are transferred to a surface moving body such as an intermediate transfer belt that moves the surface endlessly or a transfer body such as transfer paper that is conveyed while being held on the surface. The visible images are sequentially superimposed and transferred. According to this configuration, it is possible to obtain a superimposed image without moving the surface of the surface moving body around the number of times of overlapping. Therefore, it is possible to avoid an increase in the image forming time due to the circular movement corresponding to the number of times of overlapping.

  However, even in this type of image forming apparatus, when the speed fluctuation of the surface moving body occurs, the optical writing start position with respect to the latent image carrier and the visible image front end on the surface moving body between the respective visible image forming means. Are displaced relatively, leading to misalignment of the tip.

JP-A-10-202944 JP 2001-337510 A JP 2000-94747 A

  As in the image forming apparatuses described in Patent Document 2 and Patent Document 3 described above, in the case where a plurality of latent image carriers are provided, the time lag from the start of optical scanning for the first color to the start of optical scanning for the second color is This is much shorter than the image forming apparatus disclosed in Patent Document 1. This is for the reason explained below. That is, in the image forming apparatus disclosed in Patent Document 1, the time lag is the same as the time required to make one rotation of the intermediate transfer member, which is a considerably long time. For example, in an intermediate transfer body having a circumference corresponding to the vertical dimension of A4 size, the time is required to move the surface by about 300 [mm]. On the other hand, in the image forming apparatuses of Patent Document 2 and Patent Document 3, the time lag causes the intermediate transfer member to move from the position facing the latent image carrier for the first color to the latent image carrier for the second color. It is the same as the time to phase to the facing position. This time is much shorter than that described in the above-mentioned Patent Document 1, and may be a time required to move the intermediate transfer member by several tens [mm], for example. In such a short time, the speed fluctuation of the intermediate transfer member does not occur so much, and the leading edge deviation due to the speed fluctuation hardly occurs. However, the distance between the latent image carrier for the first color and the latent image carrier for the fourth color is shorter than the peripheral length of the intermediate transfer member, but is relatively long, for example, 200 [mm]. Therefore, the speed of the intermediate transfer member varies between the position facing the latent image carrier for the first color and the position of moving the intermediate transfer member to the position facing the latent image carrier for the fourth color. Probability is high. Therefore, in the image forming apparatuses of Patent Document 2 and Patent Document 3 described above, the light emitted from the deflecting unit is changed according to the speed fluctuation of the intermediate transfer body from the start of the optical scan for the first color to the start of the optical scan for the fourth color. It is desirable to correct the phase of the change in deflection angle.

  However, in the image forming apparatus described in Patent Document 2, it is not possible to employ a method of correcting the phase of the change in the deflection angle by the deflecting unit to suppress the tip deviation caused by the speed fluctuation of the surface moving body. This is for the reason explained below. That is, this image forming apparatus includes a plurality of light sources individually corresponding to a plurality of latent image carriers, but the light beams emitted from the respective light sources are deflected by one common polygon mirror, Optical scanning is performed on each latent image carrier. In such a configuration, a plurality of latent image carriers are simultaneously scanned using a single polygon mirror. For this reason, for example, when the rotational phase of the polygon mirror is corrected to correct the optical writing start position for the latent image carrier of the fourth color corresponding to the speed fluctuation of the surface moving body, Optical scanning for the third color latent image carrier is disturbed. Therefore, it is not possible to adopt a method of correcting the rotational phase of the polygon mirror in accordance with the speed fluctuation of the surface moving body in the same manner as the image forming apparatus of Patent Document 1. However, the following advantages can be obtained by performing optical scanning on all the latent image carriers using one polygon mirror. That is, by performing optical scanning on each latent image carrier using a separate polygon mirror, the rotation of each polygon mirror must be controlled separately, complicating the configuration. It can be avoided.

  On the other hand, the image forming apparatus of Patent Document 3 includes a plurality of polygon mirrors individually corresponding to each light source in addition to a plurality of light sources individually corresponding to a plurality of latent image carriers. In such a configuration, if the rotational phase of the polygon mirror is corrected in accordance with the speed fluctuation of the surface moving body in the same manner as in the image forming apparatus of Patent Document 1, the leading edge deviation caused by the speed fluctuation is prevented without disturbing the optical scanning. Can be suppressed. In addition, the start timing of the optical scanning of the second, third, and fourth colors is corrected in accordance with the speed fluctuation of the intermediate transfer body from the start of the first color optical scanning, so that the speed fluctuation of the intermediate transfer body among all colors is corrected. The resulting tip misalignment can be suppressed. However, the above-described merit that occurs in the image forming apparatus of Patent Document 2 cannot be obtained. Specifically, the configuration of the optical scanning means is complicated by providing dedicated polygon mirrors, polygon motors, motor control circuits, etc. corresponding to all the latent image carriers. And the cost increase by this complication becomes serious. This image forming apparatus includes a phase control unit for correcting the rotational phase of each polygon mirror. However, this correction is performed in order to suppress the tip misalignment caused by the distance error between each latent image carrier and the tilt error, and is performed in order to suppress the tip misalignment caused by the speed fluctuation of the surface moving body. is not.

The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of realizing both the items (1) and (2) listed below. It is.
(1) The superposition transfer is completed without moving the surface of the surface moving body over a plurality of circumferences, and the image forming time is shortened.
(2) By correcting the phase of the change in the light deflection angle by the deflecting unit while simplifying the configuration of the optical scanning unit as compared with the image forming apparatus of Patent Document 3, the tip due to the speed fluctuation of the surface moving body The deviation is suppressed to some extent, and the optical scanning disturbance caused by the correction is avoided.

In order to achieve the above-mentioned object, the invention according to claim 1 allows a plurality of latent image carriers that carry latent images, and latent images on the surface of the latent image carrier to be individually associated with these latent image carriers. A plurality of developing means for developing a visual image and each latent image carrier by irradiating the moving surface of each latent image carrier while deflecting the light emitted based on the image information by the deflecting means and performing optical scanning Optical scanning means for carrying a latent image on the body, a surface moving body that moves endlessly so that the surface sequentially passes through the position facing each latent image carrying body, and a predetermined position in the endless movement direction of the surface moving body. First mark detection means and second mark detection means for detecting the generated reference mark, and a visible image developed on each latent image carrier, respectively, on the surface moving body or a transfer body held on the surface thereof Transfer means for transferring images in a superimposed manner and light deflection by the deflection means In an image forming apparatus provided with a reference angle detecting means for detecting that a predetermined reference angle is detected with respect to degrees, adjacent pairs that can be established in each latent image carrier (2 arranged adjacent to each other) At least one of the pairs of latent image carriers) is subjected to optical scanning using the same first deflecting unit with respect to each latent image carrier, For at least one of the latent image carriers whose optical scanning starts after the two latent image carriers included in the pair, the second deflecting unit different from the first deflecting unit is used for the light scanning. The optical scanning unit is configured to perform scanning, and after the surface moving body has entered the mark detection position by the first mark detection unit, of the two latent image carriers included in the pair, Latent image on the upstream side of the surface moving direction of the surface moving body A moving distance from the holder to the transfer position for transferring the visible image to the surface moving body, and the surface moving body entering the mark detection position by the second mark detection means; The first mark is made to have the same moving distance from the latent image carrier that undergoes optical scanning by the second deflecting means to the transfer position for transferring the visible image to the surface moving body. Detection means and second mark detection means are arranged, and as the reference angle detection means, a first reference angle detection means corresponding to the first deflection means and a second reference angle detection means corresponding to the second deflection means. And at least a first mark detection signal from the first mark detection means, a second mark detection signal from the second mark detection means, and a first reference angle detection from the first reference angle detection means Signal and second reference angle detection hand The optical scanning means is provided with a deflection angle phase correcting means for correcting the phase of the change in the optical deflection angle by the second deflecting means based on the second reference angle detection signal from the stage. .
Also, the second aspect of the present invention, there is provided an image forming apparatus according to claim 1, a plurality of the image bearing member, first, second, includes four third and fourth latent image bearing member The two adjacent pairs are the first adjacent pair formed by the first and second latent image carriers and the second adjacent pair formed by the third and fourth latent image carriers. While making one round of the surface of the moving body, the visible images of the respective surfaces are sequentially superimposed and transferred onto the surface moving body in the order of the first, second, third and fourth latent image carriers. From the time Ta at which a quadruple image is formed and the optical scanning unit obtains the first mark detection signal by the first mark detection unit prior to the start of optical scanning on the first latent image carrier. After storing the time difference dt1 up to the time point Tb when the first reference angle detection signal is first obtained by the first reference angle detection means, the second mark detection hand The time difference dt2 from the time point Tc at which the second mark detection signal is obtained by the time point Td at which the second reference angle detection signal is first obtained by the second reference angle detection means is obtained and stored in advance. The phase is corrected based on the time difference dt1.
The invention according to claim 3 is the image forming apparatus according to claim 2 , wherein the optical scanning unit stores a predetermined reference correction time t1 in advance, and the reference correction time t1 has passed from the time point Ta. Based on the first reference angle detection signal obtained after the time Te, the optical scanning of the first latent image carrier is started, and the time difference dt1 from the time Tc until the reference correction time t1 passes. The phase of the second deflecting means is corrected based on the time difference dt2, and thereafter, the optical scanning of the third latent image carrier is started.
According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect , the optical scanning unit stores a predetermined standard time difference ts, and a difference Δ between the time difference dt1 and the time difference dt2. When t is calculated and “standard time difference ts ≧ difference Δt” is satisfied, the correction of the phase of the second deflecting unit is omitted.
The invention according to claim 5 is the image forming apparatus according to claim 4 , wherein when the optical scanning unit determines that the correction of the phase of the second deflecting unit is omitted, a predetermined time from the time Tc. Starting the optical scanning on the third latent image carrier based on the time when the first second reference angle detection signal obtained after passing through, and the reference correction time t1 for the predetermined time, Whether the value is longer or shorter than this, at least the time Tf when the optical scanning of the first latent image carrier is started, the time Te, the reference correction time t1, and the time difference. It is determined based on dt1 and the time difference dt2.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect , when the optical scanning unit determines that the correction of the phase of the second deflecting unit is omitted, the time Te and the time The time difference tx from Tf is stored, and the predetermined time is determined based on at least the magnitude relationship between the time difference dt1 and the time difference dt2 and the time difference tx. .
The invention according to claim 7 is the image forming apparatus according to claim 5 , wherein when the optical scanning unit determines to omit correction of the phase of the second deflecting unit, the time Te and the time The time difference tx with respect to Tf is added to the reference correction time t1 and stored as the post-addition correction time t1 ′, and at least the magnitude relationship between the time difference dt1 and the time difference dt2 and the post-addition correction time t1 ′ Based on the above, the predetermined time is determined.
The invention according to claim 8 is the image forming apparatus according to any one of claims 2 to 7 , wherein the arrangement pitch of the two latent image carriers in the adjacent pair is n (integer) as the reference mark. A plurality of devices arranged in the endless moving direction of the surface moving body at equal pitches, and the time when the optical scanning means obtains the first mark detection signal for any one reference mark is the time Ta If the optical scanning of the first latent image carrier has already been completed at the time Tg when n first mark detection signals for n are obtained, the first reference angle detection is started first from the time Tg. Based on the time difference dt3 until the signal is obtained and the time difference dt1, the phase of the first deflecting means is corrected from the time Tg until the reference correction time t1 is passed. Start optical scanning for latent image carrier It is characterized in that it is shall.
The invention according to claim 9 is the image forming apparatus according to claim 8 , wherein the time Tc is the time when the optical scanning unit obtains the second mark detection signal for any one of the reference marks. If the optical scanning of the third latent image carrier is already completed at the time Th when the n second mark detection signals for n are obtained, the second reference angle detection is started first from the time Th. Based on the time difference dt4 until the signal is obtained and the time difference dt2, the phase of the second deflecting means is corrected from the time Th until the reference correction time t1 is passed. This is characterized in that the optical scanning for the latent image carrier is started.
A tenth aspect of the present invention is the image forming apparatus according to any one of the second to seventh aspects, wherein the third mark detection detects the reference mark at a position different from the first and second mark detection means. And the optical scanning means obtains the first mark detection signal at the time Ta, and then obtains the third mark detection signal by the third mark detection means at the time Ti, the first latent image carrier. Is already completed, based on the time difference dt5 from the time Ti to the time when the first reference angle detection signal is first obtained and the time difference dt1, the reference correction is performed from the time Ti. The phase of the first deflecting means is corrected until the time t1 passes, and thereafter, the optical scanning of the second latent image carrier is started.
The invention of claim 1 1, an image forming apparatus according to claim 1 0, said first, fourth mark detecting means for detecting the reference mark in a position different from the second and third mark detecting means And the optical scanning means obtains the second mark detection signal at the time Tc, and then obtains the fourth mark detection signal by the fourth mark detection means at the time Tj. When the optical scanning has already been completed, the reference correction time from the time Tj to the time difference dt6 from the time Tj to the time when the second reference angle detection signal is first obtained and the time difference dt2 are used. The phase of the second deflecting means is corrected until time t1, and thereafter the optical scanning of the fourth latent image carrier is started.

In these image forming apparatuses, visible images developed individually on a plurality of latent image carriers are sequentially superimposed and transferred onto a surface moving body or a transfer body held on the surface, thereby transferring the surface. Superposition transfer is completed without moving the surface of the moving body over a plurality of circumferences. By performing the overlay transfer in this way, it is possible to shorten the image forming time as compared with the case of performing the overlay transfer with the surface of the surface moving body being rotated many times.
Further, in these image forming apparatuses, at least one of the adjacent pairs that can be established in each latent image carrier performs optical scanning using the same first deflecting means. The configuration of the optical scanning unit can be simplified as compared with the image forming apparatus disclosed in Patent Document 3 in which optical scanning is performed on the body using different deflecting units. In such a configuration, it becomes impossible to correct the phase of the change of the light deflection angle between the latent image carriers in the adjacent pair that performs the optical scanning by the same first deflecting unit, but the first color and the second color As described above with reference to the example, there is a relatively low possibility of leading edge misalignment between these latent image carriers. On the other hand, as already described by taking the first color and the fourth color as an example, there is a relatively high possibility of leading edge misalignment between two latent image carriers that are not located adjacent to each other and are located at relatively distant positions. However, such tip misalignment can be suppressed without disturbing the optical scanning by the first deflecting unit by correcting the phase of the change of the light deflection angle in the second deflecting unit. Therefore, although not at the same level as when deflecting means are provided corresponding to all the latent image carriers, the optical scanning is disturbed by correcting the phase of the change in the deflection angle while suppressing the tip deviation to some extent. Can be avoided.
As a result, both of the items (1) and (2) described above can be realized.

Hereinafter, a tandem color laser printer (hereinafter referred to as “printer”) will be described as an embodiment of an image forming apparatus to which the present invention is applied.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment. This printer includes four sets of toner image forming units 10Y, 10M, 10C, and 10K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). . Further, an optical scanning device 30 as optical scanning means, a transfer unit 20 as transfer means, a paper feed cassette 1, a plurality of conveying roller pairs 2, a registration roller pair 3, a secondary transfer roller 4, a bottle mounting portion 5, a fixing unit 6, A pair of discharge rollers 7 is also provided. Hereinafter, the subscripts Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively.

  The bottle mounting portion 5 is detachably mounted with Y, M, C, and K toner bottles 51Y, M, C, and K that store Y, M, C, and K toners. These Y, M, C, and K toner bottles 51Y, M, C, and K are respectively developed by the toner image forming units 10Y, 10M, 10C, and 10K via Y, M, C, and K toner replenishing devices (not shown). Connected to the device.

  The toner image forming portions 10Y, 10M, 10C, and 10K, which are visible image forming means, are arranged in parallel at a predetermined interval below a transfer unit 20 to be described later, and each intermediate transfer belt 21 of the transfer unit 20 is provided. Opposite to. These toner image forming units have drum-shaped photoconductors 11Y, 11M, 11C, and 11K, which are latent image carriers that carry latent images.

  The photoconductors 11Y, 11M, 11C, and 11K are driven to rotate clockwise in the drawing by driving means (not shown). Then, it is optically scanned in the dark by an optical scanning device 30 that emits a laser beam modulated based on image information sent from a personal computer (not shown) or the like, and electrostatic latent images for Y, M, C, and K are obtained. Carry.

  The four toner image forming units 10Y, 10M, 10C, and 10K have substantially the same configuration except that the colors of the toners used are different. Hereinafter, the configuration of the Y toner image forming unit 10Y using Y toner will be described as an example, and description of other colors will be omitted.

  The Y toner image forming unit 10Y includes, in addition to the photoreceptor 11Y, a brush roller 12Y for applying a lubricant, a swingable counter blade 13Y for performing a cleaning process, and a discharge lamp 14Y for performing a discharge process. Etc. Further, a charging roller 15Y for uniformly charging the photoconductor 11Y, a developing device 16Y as developing means, and the like are also provided.

  The charging roller 15Y to which an AC charging bias is applied by a power source (not shown) is disposed so as to contact the photoreceptor 11Y. Then, the surface of the photoconductor 11Y is uniformly charged while being rotated by the driving means (not shown) so that the surface thereof is moved in the direction opposite to the surface movement of the photoconductor 11Y. When the laser beam L modulated and deflected by the optical scanning device 30 is scanned on the surface of the photoreceptor 11Y that has been uniformly charged in this way, an electrostatic latent image for Y is formed on the surface. Although the example using the charging roller 15Y has been described as the charging means for uniformly charging the photoconductor 11Y, a charging charger or the like may be used.

  The developing device 16Y has a developing roll disposed so as to expose a part from the opening of the casing. Further, it also has a first transport screw, a second transport screw, a doctor blade, a toner concentration sensor, and the like. A Y developer containing a magnetic carrier and negatively chargeable Y toner is included in the casing. The Y developer is frictionally charged while being agitated and conveyed by the first conveying screw and the second conveying screw, and is then carried on the surface of the developing roll as the developer carrying member. Then, after the layer thickness is regulated by the doctor blade, the layer is conveyed to a developing region facing the photoconductor 11Y, where Y toner is attached to the electrostatic latent image for Y on the photoconductor 11Y. This adhesion forms a Y toner image on the photoreceptor 11Y. The Y developer that has consumed Y toner by development is returned to the casing as the surface of the developing roll (developing sleeve) rotates. On the other hand, the developed Y toner image is primarily transferred onto an intermediate transfer belt 21 described later. The developing roll has a developing sleeve made of a non-magnetic pipe that is rotationally driven by a driving means (not shown), and a magnet roller (not shown) that is included so as not to be rotated. The Y developer is attracted and carried on the surface of the developing sleeve by the magnetic force generated by the magnet roller.

  The toner concentration sensor Y composed of a magnetic permeability sensor outputs a voltage having a value corresponding to the magnetic permeability of the Y developer conveyed by the first conveying screw. Since the magnetic permeability of the developer shows a good correlation with the toner density of the developer, the toner density sensor outputs a voltage having a value corresponding to the Y toner density. This output voltage value is sent to a control unit (not shown). The control unit includes storage means such as an RMA, in which a Vtref for Y, which is a target value of an output voltage from the toner density sensor, and an output voltage from a toner density sensor mounted on another developing device. The data of Vtref for M, C, and K, which are target values, are stored. For the developing device 16Y for Y, the value of the output voltage from the toner density sensor is compared with the Vtref for Y, and a Y toner replenishing device (not shown) is driven for a time corresponding to the comparison result. As a result, the toner in the Y toner bottle 51Y is supplied into the Y developing device 16Y. By controlling the drive of the Y toner replenishing device in this way (toner replenishment control), an appropriate amount of Y toner is replenished to the Y developer whose Y toner density has been reduced with development, and the inside of the developing device 16Y. The Y toner density of the Y developer is maintained within a predetermined range. The same toner replenishment control is performed for the developing devices for other colors.

  The Y toner image developed on the photoconductor 11Y by the Y developing device 16Y is transported to a Y primary transfer position described later with the rotation of the photoconductor 11Y. Then, primary transfer is performed on the photoreceptor 11Y to an intermediate transfer belt 21 described later. Similarly, in the toner image forming units 10M, C, and K for M, C, and K, electrostatic latent images are formed on the photoreceptors 11M, C, and K, and developed into M, C, and K toner images. . Then, the toner image is primary-transferred on the Y toner image that has been primarily transferred onto the photoreceptor 11Y. By this superimposing primary transfer, a quadruple toner image in which Y, M, C, and K toner images are superimposed is formed on the intermediate transfer belt 21.

  A predetermined amount of lubricant is applied by the brush roller 12Y to the surface of the photoreceptor 11Y after the Y toner image is transferred to the intermediate transfer belt 21, and then the cleaning process is performed by the counter blade 13Y. Then, the static electricity is removed by the light emitted from the static elimination lamp 14Y to prepare for the formation of the next electrostatic latent image.

  The transfer unit 20 includes an endless intermediate transfer belt 21, a driving roller 22, a nip inlet roller 23, a nip outlet roller 24, four primary transfer chargers 25Y, M, C, and K.

  The intermediate transfer belt 21 is stretched counterclockwise in the figure by a driving roller 22 that is stretched counterclockwise in the figure by a driving means (not shown) while being stretched around the driving roller 22, the nip inlet roller 23, and the nip outlet roller 24. Can be moved endlessly.

  The four primary transfer chargers 25Y, 25M, 25C, 25K are respectively disposed inside the loop of the intermediate transfer belt 21 and face the photoreceptors 11Y, 11M, 11C, 11K via the intermediate transfer belt 21. ing. The opposing regions are the Y, M, C, and K primary transfer positions, respectively. At these Y, M, C, and K primary transfer positions, transfer charges are applied to the back surface of the belt by the intermediate transfer belt 21 and the primary transfer chargers 25Y, M, C, and K, and the belt and the photoreceptors 11Y, M, and C. , K, a transfer electric field is formed. Note that a transfer bias roller or the like may be used instead of the transfer charger.

  The secondary transfer roller 4 is in contact with the intermediate transfer belt 21 between the nip entrance roller 23 and the nip exit roller 24 from the belt front surface side to form a secondary transfer nip. A secondary transfer electric field is formed between the secondary transfer roller to which a secondary transfer bias is applied from a power source (not shown) and the intermediate transfer belt 21.

  A paper feed cassette 1 is disposed at the bottom of the printer body. The paper feed cassette 1 accommodates a plurality of transfer papers P in a stack of transfer papers, and presses a paper feed roller 1a against the uppermost transfer paper P. Then, the sheet feeding roller 1a is rotated at a predetermined timing, and the transfer sheet P is sent out to the sheet feeding path. This paper feed path has a plurality of conveying roller pairs 2. Further, a registration roller pair 3 is provided near the end thereof. Then, the transferred transfer paper P is conveyed toward the registration roller pair 3 by the conveyance roller pair 2. The registration roller pair 3 sends the received transfer paper P toward the above-described secondary transfer nip at a timing at which the transfer paper P can be synchronized with the quadruple toner image on the intermediate transfer belt 21. On the transfer paper P that has entered the secondary transfer nip, a quadruple toner image is collectively secondary transferred by the influence of the secondary transfer electric field and nip pressure. The quadruple toner image after the secondary transfer is combined with the white color of the transfer paper P to form a full color image.

  The transfer paper P on which the full-color image is formed in this way passes through the secondary transfer nip, and then is transferred from the intermediate transfer belt 21 to the fixing unit 6. The fixing unit 6 is rotated so that the heating roller 6a and the pressure roller 6b are brought into contact with each other and moved in the same direction at the contact portion to form a fixing nip. The transfer paper P delivered to the fixing unit 6 is sandwiched between the fixing nips in such a posture that the image transfer surface is brought into contact with the heating roller 6a. Then, it passes through the fixing unit 6 while the full color image is fixed on the image transfer surface by heating or pressing.

  After passing through the fixing unit 6, the transfer paper P passes through the reversing guide plate, and then passes through the paper discharge roller pair 7 and is discharged toward the stack portion provided on the upper surface of the printer housing.

Next, a characteristic configuration of the printer will be described.
In this printer, the primary transfer process of the toner image from the toner image forming unit to the intermediate transfer belt 21 starts from the Y toner image forming unit 10Y. Thereafter, the primary transfer process in the M, C, and K toner image forming units 10M, C, and K is started with a little delay. That is, the Y toner image forming unit 10Y is disposed on the most upstream side of the overlay transfer process, and the K toner image forming unit 10K is disposed on the most downstream side of the overlay transfer process. is there.

  The Y photoconductor 11Y arranged on the most upstream side of the superposition transfer process and the M photoconductor 11M on the second most upstream side are arranged adjacent to each other, and the first photoconductor 11Y is arranged next to the first photoconductor 11Y. An adjacent pair 18 is formed. Further, the C photoconductor 11C which is the third upstream side and the K photoconductor 11K which is the most downstream side are arranged adjacent to each other, and constitute the second adjacent pair 19. is doing.

  On one end side in the width direction of the intermediate transfer belt 21, a reference mark (not shown) is attached to a predetermined portion of the belt circumference. The reference mark is detected by the first mark detection means 60 including a reflection type photosensor disposed above the developing device 16Y in the Y toner image forming unit 10Y. Further, the detection is also performed by the second mark detection means 61 including a reflective photosensor or the like disposed above the developing device 16C in the C toner image forming unit 10C. The distance from when the reference mark on the intermediate transfer belt 21 enters the detection position by the first mark detection means 60 until it enters the primary transfer position for Y on the most upstream side of the overlay transfer process is as follows. It is the same as the distance described in. That is, from the time when the reference mark on the intermediate transfer belt 21 enters the detection position by the second mark detection means 61 to the time when it enters the C primary transfer position on the third upstream side of the overlay transfer process. Distance.

  The first mark detection signal from the first mark detection means 60 and the second mark detection signal from the second mark detection means 61 are sent to a time difference detection circuit (not shown). Based on these mark detection signals, the optical scanning start timing for each of the photoconductors 11Y, 11M, 11C, and 11K is determined.

  The optical scanning device 30 includes a first optical scanning unit 31, a second optical scanning unit 41, and an optical scanning control unit (not shown). The Y photoconductor 11Y and the M photoconductor 11M in the first adjacent pair 18 are optically scanned by the first optical scanning unit 31 disposed below them. In addition, the C photoconductor 11C and the K photoconductor 11K in the second adjacent pair 19 are optically scanned by the second optical scanning unit 41 disposed below them.

  The first optical scanning unit 31 includes two laser diodes (hereinafter referred to as LD) which are not shown, which are light sources, a first polygon device 32 which is a deflecting means, a collimator lens 33, five reflecting mirrors 34a, b, c, d and e. have. One of the two LDs in the first optical scanning unit 31 emits a laser beam Ly that is modulated in accordance with Y-color image information by a modulation unit (not shown). As shown in FIG. 2, the emitted laser light Ly is sequentially deflected in the main scanning direction while being reflected by any one of the six deflecting reflecting surfaces of the first polygon mirror 32a having a regular hexagonal prism shape that is driven to rotate. I'm damned. Then, as shown in FIG. 1, after collimating through the collimating lens 33, the light is sequentially reflected by the reflecting mirrors 34a, b, c, and then the surface of the Y photoconductor 11Y is optically scanned. Each time the deflecting / reflecting surface that reflects the laser light L1 is switched in accordance with the rotation of the first polygon mirror 32a, scanning in the main scanning direction is performed once. Then, as shown in FIG. 2, every time, the beam is deflected to a predetermined angle by the first beam detecting means 62 as the first reference angle detecting means provided on the side of the Y photoconductor 11Y. The instantaneous laser beam Ly is detected. Scanning in the sub-scanning direction is performed by moving the surface of the photoconductor 11Y in the sub-scanning direction. The first beam detection means 62 outputs a first beam detection signal every time the laser beam Ly is detected. In FIG. 2, reference numeral 35 denotes an LD that emits the laser light Ly.

  In FIG. 1, the other LD (not shown) in the first optical scanning unit 31 emits a laser beam Lm modulated in accordance with M image information by a modulation means (not shown). The emitted laser beam Lm is sequentially deflected in the main scanning direction while being reflected by the deflection reflection surface of the first polygon mirror 32a on the upper side in the vertical direction than the Y laser beam Ly. Then, after passing through the collimating lens 33 and collimated, it is sequentially reflected by the reflecting mirrors 34d and 34e, and the surface of the M photoconductor 11M is optically scanned. Since the laser beam Lm is deflected by the same first polygon mirror 32a as the Y laser beam Ly, the relationship between the phase of the deflection and the phase of the deflection of the laser beam Ly is always constant. Therefore, in FIG. 2 described above, the value of the deflection angle θ of the Y laser light Ly at the moment detected by the first beam detector 62 and the M laser light (Lm) (not shown) at that moment. The difference from the value of the deflection angle is the same.

  In FIG. 1, the second optical scanning unit 41 has the same configuration as the first optical scanning unit 31, and includes two LDs (not shown) as light sources, a second polygon device 42 as deflection means, collimating lenses 43, 5 and so on. Two reflecting mirrors 44a, b, c, d, e and the like are provided. Then, similarly to the first optical scanning unit 31, the C photoconductor 11C and the K photoconductor 11K are optically scanned. A second beam detecting means 63 serving as a second reference angle detecting means is disposed on the side of the C photoconductor 11C, and the instantaneous laser beam Lc (C laser) deflected to a predetermined angle is provided. Light) is detected.

  As described above, the first optical scanning unit 31 uses the first polygon device 32 which is the same deflecting unit for the Y photoconductor 11Y and the M photoconductor 11M in the first adjacent pair 18. To perform optical scanning. Therefore, the phase difference of main scanning is always constant between the Y photoconductor 11Y and the M photoconductor 11M. Similarly, the phase difference of main scanning is always constant between the C photoconductor 11C and the K photoconductor 11K optically scanned by the second optical scanning unit 41.

  1 indicates a distance between the Y photoconductor 11Y and the M photoconductor 11M, and a distance between the C photoconductor 11C and the K photoconductor 11K. The combination of the distance L1, the peripheral speed of the intermediate transfer belt 21, and the scanning speed in the main scanning direction (rotational speed of the polygon mirrors 32a and 42a) by the first light scanning unit 31 and the second light scanning unit 41 is as follows. It is set like this. That is, the number of scans in the main scanning direction performed while the intermediate transfer belt 21 moves the distance L1 is set to an integer. In such a configuration, the optical writing position in the main scanning direction is shifted between the two photosensitive members in the adjacent pair because the distance L1 is set to a value that does not make the number of scans an integer. Such a situation can be solved.

  In the case of forming a toner image of each color by the tandem method as in this printer, optical scanning for each color can be performed substantially in parallel. Therefore, compared to the case where only one photoconductor is provided and one color is superimposed and transferred for each rotation of the intermediate transfer belt, the optical scanning of the color preceding the overlay transfer process is started. The time until the subsequent color light scanning starts is significantly shortened. Further, the moving distance of the intermediate transfer belt 21 within that time is also significantly shortened. This moving distance is the distance L1 described above. There is not much change in the moving speed of the intermediate transfer belt 21 which is the surface moving body while moving such a small moving distance. Therefore, in this printer, the first polygon device 32 as the first deflecting unit is used for the two photosensitive members (11Y, M) of the first adjacent pair 18 that are adjacent to each other at the distance L1. The optical scanning is performed. Further, the two photoconductors (11C, K) of the second adjacent pair 19 which are adjacent to each other at the distance L1 are optically scanned using the second polygon device 42 which is the second deflecting means. Like to do. By doing so, an increase in cost due to the provision of dedicated polygon devices corresponding to all the photoconductors 11Y, 11M, 11C, and 11K is avoided.

  However, as in the relationship between the Y photoconductor 11Y that is the first color and the K photoconductor 11K that is the fourth color, the two photoconductors that are not formed as adjacent pairs but are relatively apart from each other. In the meantime, there is a high possibility of causing the speed fluctuation of the intermediate transfer belt 21. Therefore, the second polygon device 42 different from the first polygon device 32 is used for the two photosensitive members (11C, K) of the second adjacent pair 19 whose optical scanning starts later than the first adjacent pair. The optical scanning is performed using the. Then, the first color (second color) and the fourth color (third color) are corrected by correcting the phase of the change of the light deflection angle by the second polygon device 42 by a later-described optical scanning control unit which is a deflection angle phase correcting means. The misalignment between the two is suppressed.

  FIG. 3 is a block diagram showing a part of an electric circuit in the optical scanning control unit of the optical scanning device (30). In the figure, an optical scanning control unit 50 includes a main control unit 51, a data storage unit 52 including a RAM, a time difference measurement unit 53, a first optical writing control unit 54, a second optical writing control unit 55, and a third. An optical writing control unit 56, a fourth optical writing control unit 57, and the like are included. The first polygon motor control unit 58 and the second polygon motor control unit 59 are also provided.

  The first polygon motor controller 58 is connected to the first polygon motor 32b which is a part of the first polygon device (32) described above. The second polygon motor control unit 59 is connected to a second polygon motor 42b which is a part of the second polygon device (42) described above. The first polygon motor 32b and the second polygon motor 42b rotate and drive the first polygon mirror (32a) and the second polygon mirror (42a) described above, and are stepping motors capable of delicate control of the rotation angle. Become.

  The time difference measuring means 53 receives the first mark detection signal from the first mark detection means (60) and the second mark detection signal from the second mark detection means (61). The first beam detection signal from the first beam detection means (62) and the second beam detection signal from the second beam detection means (63) are also input.

  The main control unit 51 starts at a predetermined timing with respect to the first optical writing control unit 54, the second optical writing control unit 55, the third optical writing control unit 56, and the fourth optical writing control unit 57, respectively. An instruction signal is output. When the first optical writing control unit 54, the second optical writing control unit 55, the third optical writing control unit 56, and the fourth optical writing control unit 57 detect this start instruction signal, they are based on the image information. Controls driving of Y, M, C, and K LDs.

  Further, the main control unit 51 outputs a correction signal to the second polygon motor control unit 59 at a predetermined timing. The second polygon motor control unit 59 shifts the rotational phase of the second polygon motor 42b by adjusting the number of step pulses to the second polygon motor 42b based on the correction signal. Accordingly, the rotational phase of the second polygon mirror (42a) is also shifted.

  The first mark detection means (60) described above outputs a first mark detection signal when it detects a reference mark attached to a predetermined location of the intermediate transfer belt (21). The time difference measuring means 53 performs the following measurement in the process of superimposing and transferring four colors. That is, first, after measuring the time difference dt1 from the time Ta when the first mark detection signal is detected to when the first beam detection signal is first detected, the result is output to the main control unit 51. Next, after measuring a time difference dt2 from the time point Tc at which the second mark detection signal is detected to when the second mark detection signal is first detected, the result is output to the main control unit 51.

  FIG. 4 is a timing chart showing the relationship between the generation times of the signals in the printer. When driving of the intermediate transfer belt (21) (not shown) is started, the reference mark on the belt is eventually detected by the first mark detection means (60). As a result, when the first mark detection signal is issued, the time difference measuring means (53) recognizes the time point Ta and starts measuring the time difference dt1. Further, the countdown of the reference correction time t1 stored in advance in the data storage means (52) is started. The reference correction time t1 is set to be longer than the time necessary for establishing the main scanning phase adjustment under the control of the second polygon motor control unit (59).

  When the first beam detection signal is issued after the time Ta, the time Tb is recognized by the time difference measuring means (53) and the time difference dt1 is counted. The measurement result of this time difference dt1 is stored in the data storage means (52). Next, when the countdown of the reference correction time t1 ends (when the reference correction time t1 elapses from the time Ta), the time difference Te (53) recognizes the time Te at that moment. After that, when the first beam detection signal is generated for the first time, the light beam comes to the writing start position in the main scanning direction of the Y photoconductor (11Y), and the Y photoconductor (11Y). ) Is started.

  Thereafter, when the reference mark passes the primary transfer position for the second color M with the endless movement of the intermediate transfer belt (21) and the second mark detection signal is issued, the time difference measuring means (53) The time point Tc is recognized, and the time difference dt2 is started. At the same time, the countdown of the reference correction time t1 is also started.

  When the first second beam detection signal is issued after the time Tc, the time Td is recognized by the time difference measuring means (53) and the time difference dt2 is counted. The main control unit (51) calculates a difference Δt between the measurement result of the time difference dt2 sent from the time difference measuring means (53) and the time difference dt1 previously stored in the data storage means (52). . Then, based on the calculation result, a deviation from the normal phase is calculated for the phase of the C laser light Lc in the main scanning direction. The normal phase is a C electrostatic image so that the C toner image on the C photoconductor (11C) is perfectly superimposed on the YM toner image superimposed and transferred on the intermediate transfer belt (21). This is the phase at which optical writing of the latent image can be started. Specifically, for the C photoconductor (11C), optical writing is started at a timing at which the C electrostatic latent image can be perfectly superimposed on the YM toner image on the intermediate transfer belt (21). Must. This timing can be known based on the second mark detection signal from the second mark detection means (61) that has detected the reference mark on the belt. This is because the time when a predetermined time has elapsed from the moment of detection of the second mark detection signal is such timing. However, at this time, the C laser beam Lc is not necessarily positioned exactly at the writing start position in the main scanning direction. Depending on the phase of the deflection angle, the position is shifted from the writing start position. Then, it becomes impossible to start optical writing for C at the above-described timing. Therefore, the main control unit (51) calculates a deviation from the normal phase with respect to the phase of the deflection angle of the laser beam Lc at the present time based on the above-described difference Δt. Then, a correction signal is constructed based on the deviation, and the result is output to the second polygon motor control unit (59).

  The second polygon motor control unit (59) corrects the rotational phase of the second polygon mirror (42a) by changing the number of step pulses to the second polygon motor (42b) based on the received correction signal. To do. With this correction, as can be seen from the change in the output interval of the second beam detection signal in the figure, the phase of the second beam detection signal is changed from the time Tc until the reference correction time t1 elapses. Relative to the signal. This means that the phase of the deflection angle in the main scanning direction of the laser light (Lc, Lk) output from the second optical scanning unit (41) is matched with the normal phase. Therefore, even if the speed of the intermediate transfer belt (21) changes from the primary transfer position for Y to the primary transfer position for C, optical writing of the electrostatic latent image for C is performed. Can be started at an appropriate timing. And the overlay shift resulting from the speed fluctuation can be suppressed.

  In addition, as a reference mark, although the thing fixed to the belt surface at the time of manufacture of the intermediate transfer belt (21) is used, the following may be used. That is, the patch toner image formed by any one of the toner image forming portions is transferred to the intermediate transfer belt (21).

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described.
[Example 1]
The difference Δt between the time difference dt1 and the time difference dt2 is correlated with the amount of misalignment between the Y toner image and the C toner image when the rotational phase of the second polygon mirror (42a) is not corrected. Therefore, if the difference Δt is equal to or smaller than the predetermined threshold value, it is possible to keep the amount of misalignment within an allowable range without correcting the rotational phase of the second polygon mirror (42a). Therefore, the printer according to the first embodiment stores data of a predetermined standard time difference ts in the data storage means (52), and when “standard time difference ts ≧ difference Δt” is satisfied, the phase This correction is omitted.

  However, if the correction is simply omitted, a color shift exceeding an allowable range may occur depending on the magnitude relationship between the time difference dt1 and the time difference dt2. Hereinafter, this reason will be described on the assumption that the standard time difference ts is 1/4 of the main scanning period T.

  FIG. 5 shows a timing chart when “time difference dt1 <time difference dt2” and “time difference Tx <time difference Ty”. This time Tx is the time Te when the reference correction time t1 has elapsed after the first mark detection signal is generated, and then the first first beam detection signal is detected and the optical writing to the Y photoconductor (11Y). This is the time difference from the time point Tf at which the recording can be started. Further, the time difference Ty is the time Tm when the reference correction time t1 has elapsed after the second mark detection signal is generated, and then the first second beam detection signal is detected and the light to the C photoconductor (11C). This is the time difference from the time Tn when writing can be started. When “time difference dt1 <time difference dt2” and “time difference Tx <time difference Ty” are satisfied, the time Tf precedes the time Tn as shown in the figure. Then, the first line (line extending in the main scanning direction) of optical writing for the C photoconductor (11C) is ¼ dot than the first line of optical writing for the Y photoconductor (11Y). The amount of deviation is within an acceptable range although it is shifted by a minute.

  FIG. 6 shows a timing chart when “time difference dt1 <time difference dt2” and “time difference Tx> time difference Ty”. In this case, as shown in the drawing, the time point Tn precedes the time point Tf relatively. Then, the first line of optical writing for the Y photoconductor (11Y) is shifted by about one dot after the first line of optical writing for the C photoconductor (11C). Therefore, even if Δt becomes ¼ of the main scanning period T, the amount of misalignment does not always fall within ¼ dot, and the magnitude relationship between the time difference dt1 and the time difference dt2, or the time Tx difference Depending on the magnitude relationship with the time difference Ty, a deviation of nearly one dot occurs.

  From the comparison between FIG. 5 and FIG. 6, when “time difference dt1 <time difference dt2”, in order to make the shift amount ¼ of the allowable range without correcting the phase, the third color C photoconductor (11C It is understood that it is necessary to delay the writing start time for the first color Y relative to the writing start time for the Y color photoreceptor (11Y). Here, relative sending means that the writing start time for C based on the detection timing of the second mark detection signal is the start of writing for Y based on the detection timing of the first mark detection signal. It means sending more than the time.

  Further, from FIG. 6, when “time difference tx> time difference ty” is satisfied, the amount of deviation can be increased by delaying the writing start time for the C photoconductor (11C) by one cycle (T) from the time Tn. It can be seen that can be accommodated in 1/4 dots.

  FIG. 7 shows a timing chart when “time difference dt1> time difference dt2” and “time difference Tx> time difference Ty”. In this case, as shown in the drawing, the time point Tn precedes the time point Tf relatively. Then, the first optical writing line for the Y photoconductor (11Y) is shifted by 1/4 dot from the first optical writing line for the C photoconductor (11C). The amount is within an acceptable range.

  FIG. 8 shows a timing chart when “time difference dt1> time difference dt2” and “time difference Tx <time difference Ty”. In this case, as shown in the figure, the time point Tf precedes the time point Tn relatively. As a result, the first line of optical writing for the C photoconductor (11C) is shifted by about one dot after the first line of optical writing for the Y photoconductor (11Y).

  From comparison between FIG. 7 and FIG. 8, when “time difference dt1> time difference dt2”, in order to set the deviation amount to ¼ of the allowable range without correcting the phase, the writing to the photoconductor for C (11C) is performed. It can be seen that it is necessary for the start time of the recording to precede the writing start time relative to the Y photoconductor (11Y). Further, from FIG. 8, when “time difference tx <time difference ty” is satisfied, if the writing start time for the C photoconductor is preceded by one cycle (T) from time Tn, the amount of deviation is 1 It can be seen that / 4 dots can be accommodated.

  Therefore, the printer performs the following control. That is, the time difference tx between the time Te and the time Tf is measured by the time difference measuring means (53), and the measurement result is stored in the data storage means (52). At the time when the time difference dt2 is measured, the time difference ty between the time Tm and the time Tn is calculated from the relationship between the measurement result and the reference correction time t1. Since the reference correction time t1 and the main scanning period T are predetermined invariable values, if the time difference dt2 is obtained, the time difference ty can be obtained by calculation. If it is determined that the correction of the main scanning phase is omitted based on the comparison between the standard time difference ts and the difference Δt, the first second beam detection signal after a predetermined time from the time Tc is obtained. When it is obtained, optical writing for C is started. The predetermined time is determined based on the time difference dt1, the time difference dt2, the time difference tx, and the time difference ty, whether the reference correction time t1, the longer value, or the shorter value.

  Specifically, when “time difference dt1 <time difference dt2” and “time difference Tx <time difference Ty”, or when “time difference dt1> time difference dt2” and “time difference Tx> time difference Ty” are satisfied, The predetermined time is determined as the reference correction time t1. That is, optical writing is started when the first second beam detection signal is obtained after the time Tm (examples in FIGS. 5 and 7).

  When “time difference dt1 <time difference dt2” and “time difference Tx> time difference Ty”, the predetermined time is determined as “reference correction time t1 + main scanning period T” (in FIG. 6, time Tn is set to 1). Example of shifting by the period).

  If “time difference dt1> time difference dt2” and “time difference Tx <time difference Ty” are satisfied, the predetermined time is determined as “reference correction time t1—main scanning period T” (in FIG. Example of shifting by one cycle)

  With these determinations, when it is determined that the correction of the main scanning phase is omitted, the amount of misalignment can be reliably kept within the allowable range. That is, when it is determined that the correction of the main scanning phase is omitted, the predetermined amount of time is determined based on the magnitude relationship between the time difference dt1 and the time difference dt2 and the time difference tx, thereby reliably allowing the amount of misalignment. It can fit within the range.

[Example 2]
The printer of Example 1 described above employs the following method. That is, as a method for determining the predetermined time based on the time point Tf, the time point Te, the reference correction time t1, the time difference dt1, and the time difference dt2, the time difference tx between the two time points (Te, Tf) This is a method for obtaining the time difference ty. On the other hand, although the printer according to the second embodiment is based on the time point Tf, the time point Te, the time difference dt1, and the time difference dt2, the predetermined time is determined by a different method.

  This method will be described. FIG. 5 and FIG. 6 described above show examples where “time difference dt1 <time difference dt2” as described above. In FIG. 5, since “time difference tx <time difference ty”, the time point Tn is after the time point “reference correction time t1 + time difference tx” from the time point Tc. Therefore, if the addition value of the reference correction time t1 and the time difference tx is defined as the post-addition correction time t1 ′, the timing at which the first second beam detection signal is obtained after the post-addition correction time t1 ′ from the time Tc is also the time Tn. On the other hand, when “time difference Tx> time difference Ty” as shown in FIG. 6, as described above, optical writing is started at a timing shifted by one main scanning period after the time Tn. It is desirable. In this case, since “time difference Tx> time difference Ty”, when the post-addition correction time t1 ′ (t1 + tx) passes from the time point Tc, the time point Tn always elapses. For this reason, the timing at which the first second beam detection signal is obtained after the addition time t1 '(t1 + tx) after the time Tc is shifted from the time Tn by one main scanning period. Accordingly, when “time difference dt1 <time difference dt2” is satisfied, optical writing is performed at the timing at which the first second beam detection signal after the addition time t1 ′ (t1 + tx) after the time Tc is obtained. Just start.

  FIG. 7 and FIG. 8 described above show examples where “time difference dt1> time difference dt2” as described above. In any of the figures, it can be seen that if the added value of the reference correction time t1 and the time difference tx is defined as the post-addition correction time t1 ', the following results. That is, it can be seen that the timing earlier by the difference Δt is relatively synchronized with the first beam detection signal than when the post-addition correction time t1 '(t1 + tx) has elapsed from the time Tc. It can also be seen that if the optical writing for C is started at this timing, the amount of misalignment can be within an allowable range. Therefore, when “time difference dt1> time difference dt2” is satisfied, optical writing for C may be started at this timing.

  Therefore, the printer determines the optical writing start timing for C as follows. That is, the post-addition correction time t1 '(t1 + tx) is calculated during the optical writing by the first optical scanning unit (31), and the time measuring process is started at the time Tc. Next, as soon as the difference Δt is obtained based on the time difference dt2, “post-addition correction time t1′−difference Δt” is calculated, and the measured time value is sequentially compared with the calculation result. Then, the clocking process is terminated immediately before the clocked value reaches the calculation result (for example, calculation result−T / 10), and the optical writing for C is started when the first second beam detection signal thereafter is obtained. By determining the writing start timing for C in this way, as in the printer of the first embodiment, when it is determined that correction of the main scanning phase is omitted, the overlay deviation amount is surely within the allowable range. Can fit in. That is, when it is determined that the correction of the main scanning phase is omitted, the above-described predetermined time is determined based on the magnitude relationship between the time difference dt1 and the time difference dt2 and the post-addition correction time t1 ′. The amount can be reliably within an acceptable range.

[Example 3]
The printer of the third embodiment has a plurality of reference marks arranged on the intermediate transfer belt (21) at a predetermined pitch in the endless movement direction. This pitch is “distance L1 (distance between photoconductors in adjacent pairs) −distance L2.” The distance L2 is a distance that the intermediate transfer belt (21) moves within the reference correction time t1. In such a configuration, due to the formed toner image being relatively small, optical writing to the Y photoconductor (11Y) is started based on the first mark detection signal, and then the next first mark It is assumed that the optical writing is completed when the detection signal is obtained. In such a case, even if the driving of the first polygon motor (32b) is controlled at that time and the phase of the main scanning by the first optical scanning unit (31) is shifted, the optical writing for Y that has already been completed is completed. Will not disturb you. Furthermore, when correction for shifting the main scanning phase by one cycle is started from that point, the timing until the subsequent optical writing to the M photoconductor (11M) must be started is reached. The correction can be finished. Therefore, if there is a sudden belt speed fluctuation due to slip between the start of optical writing and the time point, if the correction of the main scanning phase is started at that point, the following becomes possible. That is, it is possible to suppress the misalignment due to the sudden belt speed fluctuation without disturbing the Y toner image.

  In this way, the printer suppresses misalignment caused by a sudden change in belt speed due to slip between adjacent pairs of photoconductors. Specifically, as shown in FIG. 9, when the optical writing on the Y photoconductor (11Y) is completed at the time Tg when the next first mark detection signal is obtained after the time Ta. Measures the time difference dt3 from the time Tg until the first first beam detection signal is obtained. If there is no sudden belt speed fluctuation due to slip from the time point Ta to this time, the time difference dt1 and the time difference dt3 are equal to each other. When this difference exceeds a predetermined threshold, the phase of main scanning is adjusted by the drive control of the first polygon motor (32b) based on the difference to match the phase before the slip. As a result, the optical writing start on the Y photoconductor (11Y) and the optical writing start on the M photoconductor (11M) are relatively synchronized as shown in FIG. After t1, the time difference tx has passed.

  In the second optical scanning unit (41), the phase of main scanning is corrected as described above prior to the start of optical writing on the C photoconductor (11C). Then, after the time Tc, when the optical writing to the C photoconductor (11C) is completed at the time Th when the next second mark detection signal is obtained, the second beam is firstly started from the time Th. The time difference dt4 until the detection signal is obtained is measured. When the difference between the time difference dt2 and the time difference dt4 exceeds a predetermined threshold, the main scanning phase is adjusted by the drive control of the second polygon motor (42b) based on the difference, and the phase before the slip is obtained. Adapted. As a result, in the first, second, third, and fourth colors, all optical writing starts are relatively synchronized as shown in the figure, and after all the reference correction time t1 has elapsed, the time difference tx has passed.

[Example 4]
The printer according to the fourth embodiment is also configured to suppress the misalignment caused by a sudden change in belt speed due to slip between adjacent pairs of photoconductors. However, only one reference mark is provided on the intermediate transfer belt (21). Instead, as shown in FIG. 10, in addition to the first and second mark detection means (60, 61), a third mark detection means 64 and a fourth mark detection means 65 are provided.

  The third mark detection means 64 is arranged so as to detect the reference mark on the intermediate transfer belt 21 between the first color Y photoconductor 11Y and the second color M photoconductor 11M. Yes. The time required for the reference mark on the intermediate transfer belt 21 to enter the primary transfer position for Y after entering the detection position by the first mark detection means 62 is determined by the third mark detection means 64. This is the same as the time required to enter the primary transfer position for M after entering the detection position. That is, the distance between the first mark detection means 62 and the Y photoconductor 11Y is the same as the distance between the third mark detection means 64 and the M photoconductor 11M.

  The fourth mark detection means 65 is arranged so as to detect a reference mark on the intermediate transfer belt 21 between the third color C photoconductor 11C and the fourth color K photoconductor 11K. Yes. The time required for the reference mark on the intermediate transfer belt 21 to enter the primary transfer position for C after the reference mark enters the detection position by the second mark detection means 63 is determined by the fourth mark detection means 65. This time is the same as the time required to enter the primary transfer position for K after entering the detection position. That is, the distance between the second mark detection means 63 and the C photoconductor 11C is the same as the distance between the fourth mark detection means 65 and the K photoconductor 11K.

  In such a configuration, the time difference in mark detection timing between the first to third mark detection means is the same as the detection time difference between the preceding reference mark and the subsequent reference mark in the printer of the third embodiment. Also, the time difference in mark detection timing between the second to fourth mark detection means is the same as the detection time difference between the preceding reference mark and the subsequent reference mark in the printer of the third embodiment.

  Here, after the time point Ta, the timing at which the third mark detection signal is obtained by the third mark detection means 64 is defined as the time point Ti, and the time difference from when the first beam detection signal is first obtained is defined as dt5. Further, after the time Tc, the timing at which the third mark detection signal is obtained by the third mark detection means 64 is defined as time Tj, and the time difference from when the first beam detection signal is first obtained is defined as dt6. Then, by controlling the time Tg, the time difference dt3, the time Th, and the time difference dt4 shown in FIG. 9 with the time Ti, the time difference dt5, and the time difference dt6, respectively, the same belt belt speed fluctuation can be obtained. The resulting overlay misalignment can be suppressed.

  Up to now, each color toner image is superposed on the intermediate transfer belt 21 which is a surface moving body from each of the photoconductors 11Y, 11M, 11K, and primary transfer is performed, and the resulting quadruple toner image is transferred to the transfer paper at the secondary transfer nip. Although an example of batch secondary transfer to P has been described, the following may be performed. That is, the respective color toner images are superposed on the transfer paper P held on the surface of the paper transport belt as the surface moving body from the respective photoreceptors 11Y, 11M, 11K, and primary transfer, and the secondary transfer is omitted. May be.

  As described above, in the printer according to the embodiment and each example, the first mark detection unit 60 and the second mark detection unit 61 arranged to detect at different positions are used as the mark detection unit. Further, as reference angle detection means, a first beam detection means 62 corresponding to the first polygon device 32 as the first deflection means and a second beam detection means 63 corresponding to the second polygon device 42 as the second deflection means. Used. Further, the phase of the change in the light deflection angle by the second polygon device 42 is set to at least the first mark detection signal from the first mark detection means 60, the second mark detection signal from the second mark detection means 61, the first beam. Deflection so as to correct based on the first beam detection signal (first reference angle detection signal) from the detection means 62 and the second beam detection signal (second reference angle detection signal) from the second beam detection means 63 An optical scanning control unit 50 serving as an angular phase correction unit is configured. In such a configuration, on the basis of these detection signals, the phase of the deflection angle in the main scanning direction of the laser light (Lc, Lk) output from the second optical scanning unit (41) is matched with the normal phase, and the overlay deviation is corrected. Can be suppressed.

  Further, in the printer according to the embodiment and each example, as a plurality of latent image carriers, a Y photoconductor 11Y as a first latent image carrier, an M photoconductor 11M as a second latent image carrier, Four photoconductors 11C for C serving as a third latent image carrier and a photoconductor 11K for K serving as a fourth latent image carrier are provided. Further, as the adjacent pair, a first adjacent pair 18 by the Y photoconductor 11Y and the M photoconductor 11M, and a second adjacent pair 19 by the C photoconductor 11C and the K photoconductor 11K, It has two. Further, while the surface of the intermediate transfer belt 21 that is a surface moving member makes one round, the toner images on the respective surfaces are sequentially superimposed on the belt in the order of the first, second, third, and fourth latent image carriers. To form a quadruple toner image. Further, from the time Ta when the optical scanning device 30 as the optical scanning means obtains the first mark detection signal prior to the start of the optical scanning with respect to the Y photoconductor 11Y to the time Tb when the first beam detection signal is first obtained. After the time difference dt1 is stored, the time difference dt2 from the time point Tc at which the second mark detection signal is obtained to the time point Td at which the second beam detection signal is first obtained is obtained, and this time difference dt1 stored previously. Based on the above, the phase is corrected. In such a configuration, as described with reference to FIG. 4, the phase of the deflection angle in the main scanning direction of the laser light (Lc, Lk) output from the second optical scanning unit (41) is perfectly matched to the normal phase. , Overlay deviation can be effectively suppressed.

  In the printer according to the embodiment or each example, the optical scanning device 30 stores a predetermined reference correction time t1 in advance, and is obtained after a time Te that has passed the reference correction time t1 from the time Ta. On the basis of the one-beam detection signal, optical scanning on the Y photoconductor 11Y is started, and the second polygon is based on the time difference dt1 and the time difference dt2 from the time point Tc to the passage of the reference correction time t1. The phase of the device 42 is corrected, and thereafter, optical scanning on the C photoconductor 11C is started. In such a configuration, as shown in FIG. 4, while providing a time lag of the reference correction time t1 between the time Ta and the time Te, the reference correction time t1 is also between the time Tc and the time Tm. By providing a minute time lag, the phase of the second polygon device 42 can be reliably corrected within the latter time lag.

  In the printers of the first and second embodiments, when the optical scanning device 30 satisfies “standard time difference ts ≧ difference Δt”, the correction of the phase of the second polygon device 42 is omitted. It has become. In such a configuration, when the amount of misalignment between the first color Y toner image and the third color C toner image falls within an allowable range for the above-described reason, the correction of the phase misalignment is omitted. Deterioration of the second polygon device 42 due to a forced change in driving speed during phase correction can be suppressed while keeping the amount within an allowable range.

  Further, in the printer of the first embodiment, when the optical scanning device 30 determines that the correction of the phase of the second polygon device 42 is omitted, the first second beam detection after a predetermined time from the time point Tc. Based on the time when the signal is obtained, optical scanning for the C photoconductor 11C is started. Whether the reference correction time t1, the value longer than this, or the value shorter than the predetermined time is at least the time point Tf when the optical scanning of the Y photoconductor 11Y is started, and It is determined based on the time Te, the reference correction time t1, the time difference dt1, and the time difference dt2. In such a configuration, when it is determined that the correction of the phase of the second polygon device 42 is omitted, the overlay deviation amount can be easily within an allowable range.

  In the printer according to the first embodiment, the optical scanning device 30 stores the time difference tx between the time point Te and the time point Tf, and at least the magnitude relationship between the time difference dt1 and the time difference dt2. The predetermined time is determined based on the time difference tx. In this configuration, as described with reference to FIGS. 5 to 8, the timing of the optical writing start with respect to the C photoconductor 11 </ b> C is appropriately adjusted based on the time difference tx and the above magnitude relationship, and the overlay is performed. The amount of deviation can be reliably kept within the allowable range.

  In the printer of the second embodiment, when the optical scanning device 30 determines that the correction of the phase of the second polygon device 42 is omitted, the time difference tx between the time Te and the time Tf is calculated as the reference correction time. It is added to t1 and stored as post-addition correction time t1 ′. Then, the predetermined time is determined based on at least the magnitude relationship between the time difference dt1 and the time difference dt2 and the post-addition correction time t1 '. Even in such a configuration, as described with reference to FIGS. 5 to 8, the optical writing start timing for the C photoconductor 11 </ b> C is appropriately set based on the post-addition correction time t <b> 1 ′ (t <b> 1 + tx) and the above magnitude relationship. Thus, the amount of misalignment can be reliably kept within the allowable range.

  Further, in the printer of the third embodiment, a plurality of references arranged on the intermediate transfer belt 21 at a predetermined pitch in the endless moving direction at a pitch obtained by dividing the arrangement pitch of the two photosensitive members in the adjacent pair 18 by n (integers) Has a mark. Then, the time point when the optical scanning device 30 obtains the first mark detection signal for any one of the reference marks is set as the time point Ta. Further, when the optical scanning on the Y photoconductor 11Y has already been completed at the time Tg when the n first mark detection signals are obtained from this point, the time from the time Tg to the time when the first beam signal is first obtained. The phase of the first polygon device 32 is corrected between the time point Tg and the reference correction time t1 based on the time difference dt3 and the time difference dt1, and thereafter the optical scanning of the M photoconductor 11M is performed. To start. In such a configuration, even if there is a sudden belt speed fluctuation due to slip between the primary transfer position for Y and the primary transfer position for M, it is possible to suppress the misalignment caused by that.

  In the printer of the third embodiment, the time point when the optical scanning device 30 obtains the second mark detection signal for any one of the reference marks is the time point Tc, and a predetermined number of second mark detection signals are obtained therefrom. When the optical scanning on the C photoconductor 11C has already been completed at the time Th, based on the time difference dt4 from the time Th to the time when the second beam detection signal is first obtained, and the time difference dt2, The phase of the second polygon device 42 is corrected from the time Th until the reference correction time t1 passes, and thereafter the optical scanning for the K photoconductor 11K is started. In such a configuration, even if there is a sudden belt speed fluctuation due to slip between the primary transfer position for C and the primary transfer position for K due to the above-described reason, an overlay deviation caused by the belt is suppressed. be able to.

  In addition, the printer according to the fourth embodiment includes the third mark detection unit 64 that detects the reference mark at a position different from the first and second mark detection units (60, 61). Then, after the optical scanning device 30 obtains the first mark detection signal at the time Ta, the optical scanning of the Y photoconductor 11Y is performed at the time Ti when the third mark detection signal is obtained by the third mark detection means 64. If it has already been completed, the time period from the time point Ti to the time point when the first beam detection signal is first obtained and the time difference dt1 to the time point from the time point Ti until the reference correction time t1 is passed. Then, the phase of the first polygon device 32 is corrected, and thereafter optical scanning on the M photoconductor 11M is started. Even in such a configuration, even if there is a sudden belt speed fluctuation due to slip between the primary transfer position for Y and the primary transfer position for M for the above-described reason, the overlay deviation caused by it is suppressed. be able to.

  Further, the printer according to the fourth embodiment includes a fourth mark detection unit 65 that detects the reference mark at a position different from the first, second, and third mark detection units (60, 61, 64). Then, after the optical scanning device 30 obtains the second mark detection signal at the time Tc, it performs optical scanning on the C photoconductor 11C at the time Tj when the fourth mark detection signal is obtained by the fourth mark detection means 65. If already completed, based on the time difference dt6 from the time Tj to the time when the second beam detection signal is first obtained and the time difference dt2, the time from the time Tj until the reference correction time t1 is passed. Then, the phase of the second polygon device 42 is corrected, and thereafter, optical scanning for the K photoconductor 11K is started. Even in such a configuration, even if there is a sudden belt speed fluctuation between the primary transfer position for C and the primary transfer position for K due to the reasons described above, it is possible to suppress the misregistration due to the belt speed fluctuation. .

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 3 is a plan view showing a part of a first light scanning unit and a Y photoconductor of the printer. FIG. 2 is a block diagram showing a part of an electric circuit of an optical scanning control unit in the printer. 6 is a timing chart showing a relationship between generation times of signals in the printer. 4 is a timing chart showing the relationship between signals when “time difference dt1 <time difference dt2” and “time difference Tx <time difference Ty” in the printer of Embodiment 1. FIG. 4 is a timing chart showing the relationship between signals when “time difference dt1 <time difference dt2” and “time difference Tx> time difference Ty” in the printer. 4 is a timing chart showing the relationship between signals when “time difference dt1> time difference dt2” and “time difference Tx> time difference Ty” in the printer. 4 is a timing chart showing the relationship between signals when “time difference dt1> time difference dt2” and “time difference Tx <time difference Ty” in the printer. 9 is a timing chart showing the relationship between signals in the printer according to Embodiment 3. FIG. 10 is a schematic configuration diagram illustrating a printer according to a fourth embodiment.

Explanation of symbols

11Y Photoconductor for Y (first latent image carrier)
11M M photoreceptor (second latent image carrier)
11C C photoreceptor (third latent image carrier)
11K K photoconductor (fourth latent image carrier)
16Y Y developing device (developing means)
18 First Adjacent Pair 19 Second Adjacent Pair 20 Transfer Unit (Transfer Unit)
21 Intermediate transfer belt (surface moving body)
30 Optical scanning device (optical scanning means)
32 First polygon device (first deflection means)
42 Second polygon device (second deflection means)
50 Optical scanning controller (deflection angle phase correction means)
60 first mark detection means 61 second mark detection means 62 first beam detection means (first reference angle detection means)
63 Second beam detection means (second reference angle detection means)
64 Third mark detection means 65 Fourth mark detection means

Claims (11)

Based on image information, a plurality of latent image carriers that carry a latent image, a plurality of developing means for developing the latent image on the surface of the latent image carrier into a visible image individually corresponding to each of these latent image carriers By irradiating the surface of each latent image carrier to which the latent image carrier moves while deflecting the light emitted by the deflecting means and performing optical scanning, the optical scanning means for carrying the latent image on each latent image carrier, and the surface A surface moving body that moves endlessly so as to sequentially pass through a position facing the latent image carrier, and a first mark detecting means and a second mark detecting means for detecting a reference mark attached to a predetermined position in the endless moving direction of the surface moving body. Mark detection means, transfer means for transferring the visible image developed on each latent image carrier on the surface moving body or a transfer body held on the surface thereof, and transfer of light by the deflection means Detects that the deflection angle has reached the specified reference angle In the image forming apparatus and a reference angle detecting means,
At least one of the adjacent pairs (a pair consisting of two latent image carriers arranged adjacent to each other) that can be established in each latent image carrier is assigned to each latent image carrier. On the other hand, while performing optical scanning using the same first deflecting means, the latent image carrier whose optical scanning starts later than the two latent image carriers included in the pair of latent image carriers. For at least one of the bodies, the optical scanning means is configured to perform optical scanning using a second deflecting means different from the first deflecting means,
After the surface moving body enters the mark detection position by the first mark detecting means, the position of the surface moving body is positioned upstream of the surface moving direction of the surface moving body among the two latent image carriers included in the pair. The moving distance from the latent image carrier to the surface moving body to the transfer position for transferring the visible image, and the surface moving body at the mark detection position by the second mark detection means. The moving distance from entering the transfer position for transferring the visible image from the latent image carrier that receives the optical scanning by the second deflecting means to the surface moving body is made the same. The first mark detection means and the second mark detection means are disposed,
As the reference angle detection means, a first reference angle detection means corresponding to the first deflection means and a second reference angle detection means corresponding to the second deflection means are provided,
And at least a first mark detection signal from the first mark detection means, a second mark detection signal from the second mark detection means, a first reference angle detection signal from the first reference angle detection means, and the above A deflection angle phase correction unit that corrects the phase of the change in the light deflection angle by the second deflection unit based on the second reference angle detection signal from the second reference angle detection unit is provided in the optical scanning unit. An image forming apparatus . The image forming apparatus according to claim 1 ,
As the plurality of latent image carriers, four first, second, third, and fourth latent image carriers are provided, and the first pair by the first and second latent image carriers is provided as the adjacent pair. The first, second, third, and second pairs are provided while the surface moving body makes one round. A visible image of each surface is sequentially superimposed and transferred onto the surface moving body in the order of four latent image carriers to form a quadruple image, and the optical scanning unit is configured to carry the first latent image carrier. Prior to the start of optical scanning on the body, from the time Ta when the first mark detection signal is obtained by the first mark detection means to the time Tb when the first reference angle detection signal is first obtained by the first reference angle detection means. After storing the time difference dt1, from the time Tc when the second mark detection signal is obtained by the second mark detection means, The time difference dt2 up to the time point Td at which the second reference angle detection signal is first obtained by the angle detection means is acquired, and the phase is corrected based on this and the previously stored time difference dt1. An image forming apparatus. The image forming apparatus according to claim 2 ,
The optical scanning means stores a predetermined reference correction time t1 in advance, and the first latent angle detection signal is obtained based on the first reference angle detection signal obtained after the time Te that has passed the reference correction time t1 from the time Ta. The optical scanning of the image carrier is started, and the phase of the second deflecting unit is corrected based on the time difference dt1 and the time difference dt2 from the time point Tc to the passage of the reference correction time t1. An image forming apparatus for starting optical scanning on the third latent image carrier later. The image forming apparatus according to claim 3 ,
When the optical scanning means stores a predetermined standard time difference ts and calculates a difference Δt between the time difference dt1 and the time difference dt2, and “standard time difference ts ≧ difference Δt” is satisfied. An image forming apparatus characterized in that the correction of the phase of the second deflecting means is omitted. The image forming apparatus according to claim 4 ,
When the optical scanning unit determines that the phase correction of the second deflecting unit is omitted, based on the time when the first second reference angle detection signal is obtained after a predetermined time from the time Tc. At least whether the optical scanning for the third latent image carrier is started and the predetermined time is set to the reference correction time t1, a value longer than this, or a shorter value than the above. It is determined on the basis of the time Tf when the optical scanning of the first latent image carrier is started, the time Te, the reference correction time t1, the time difference dt1, and the time difference dt2. Image forming apparatus. The image forming apparatus according to claim 5 , wherein
When the optical scanning unit determines that the correction of the phase of the second deflecting unit is omitted, the time difference tx between the time point Te and the time point Tf is stored, and at least the time difference dt1 and the time difference dt2 are stored. And the time difference tx to determine the predetermined time. The image forming apparatus according to claim 5 , wherein
When the optical scanning unit determines that the correction of the phase of the second deflecting unit is omitted, a time difference tx between the time point Te and the time point Tf is added to the reference correction time t1, and an added correction time t1 And the predetermined time is determined based on at least the magnitude relationship between the time difference dt1 and the time difference dt2 and the post-addition correction time t1 '. . The image forming apparatus according to any one of claims 2 to 7 ,
The reference mark includes a plurality of reference marks arranged in the endless movement direction of the surface moving body at a pitch obtained by dividing the arrangement pitch of the two latent image carriers in the adjacent pair by n (integer). The time when the means obtains the first mark detection signal for any one of the reference marks is defined as the time Ta, and the first latent image carrier is obtained at time Tg when n first mark detection signals are obtained. Is already completed, based on the time difference dt3 from the time Tg to the time when the first reference angle detection signal is first obtained and the time difference dt1, the reference correction is performed from the time Tg. An image forming apparatus characterized in that the phase of the first deflecting means is corrected before time t1, and thereafter optical scanning on the second latent image carrier is started. 9. The image forming apparatus according to claim 8 , wherein
The time when the optical scanning unit obtains the second mark detection signal for any one of the reference marks is the time Tc, and the time Th when the n second mark detection signals are obtained from the time Tc. If the optical scanning on the three latent image carrier has already been completed, the time point dt4 from the time point Th to the time point at which the second reference angle detection signal is first obtained and the time difference dt2 The image formation is characterized in that the phase of the second deflecting means is corrected between Th and the reference correction time t1, and thereafter the optical scanning of the fourth latent image carrier is started. apparatus. The image forming apparatus according to any one of claims 2 to 7 ,
A third mark detecting means for detecting the reference mark at a position different from the first and second mark detecting means; and after the optical scanning means obtains the first mark detection signal at the time Ta, When the optical scanning on the first latent image carrier has already been completed at the time Ti when the third mark detection signal is obtained by the third mark detection means, the first reference angle detection signal is started first from the time Ti. On the basis of the time difference dt5 up to the point of obtaining the time difference dt5 and the time difference dt1, the phase of the first deflection means is corrected from the time point Ti to the passage of the reference correction time t1. An image forming apparatus for starting optical scanning on an image carrier. An image forming apparatus according to claim 1 0,
A fourth mark detection unit configured to detect the reference mark at a position different from the first, second, and third mark detection units, and the optical scanning unit obtains the second mark detection signal at the time Tc. Thereafter, when the optical scanning on the third latent image carrier is already completed at the time Tj when the fourth mark detection signal is obtained by the fourth mark detection means, the second reference is first started from the time Tj. Based on the time difference dt6 up to the time when the angle detection signal is obtained and the time difference dt2, the phase of the second deflecting means is corrected from the time Tj until the reference correction time t1 is passed. An image forming apparatus for starting optical scanning on a fourth latent image carrier.

Images