JP2010185983A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of suppressing the break of periodicity in the velocity variation of a latent image carrier drum, in an image forming apparatus and an image forming method, in which a toner image is formed by using a liquid developer and a squeeze roller. <P>SOLUTION: The image forming apparatus includes a latent image carrier drum rotating and carrying a latent image formed thereon; a developing unit supplying a liquid developer containing a liquid carrier and a toner to the latent image carrier drum and developing the latent image; and a squeeze roller which rotates, while removing the liquid carrier from the toner image formed on the latent image carrier drum developed by the developing unit, wherein the rotation cycle of the latent image carrier drum is an integral multiplication of the rotation cycle of the squeeze roller. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for developing a latent image formed on a latent image carrier drum with a liquid developer.

  2. Description of the Related Art Conventionally, an image forming apparatus that develops a latent image using a liquid developer obtained by dispersing toner in a liquid carrier is known. For example, in the image forming apparatus described in Patent Document 1, a developing unit supplies a liquid developer onto the surface of a photosensitive drum on which a latent image is formed. As a result, the latent image on the surface of the photosensitive drum is developed and a toner image is formed. The toner image thus formed is conveyed to a predetermined transfer position as the photosensitive drum rotates, and transferred to a transfer medium (“intermediate transfer belt” in the same document) at this transfer position.

  Further, the image forming apparatus described in Patent Document 1 includes a squeeze roller. The squeeze roller is provided between the developing position where the developing unit supplies the liquid developer and the transfer position. Then, the squeeze roller squeezes excess liquid carrier from the toner image on the upstream side in the rotation direction of the photosensitive drum with respect to the transfer position (that is, the preceding stage of the transfer position). As a result, the toner image having an improved toner ratio is conveyed to the transfer position.

JP 2008-310368 A

  By the way, a latent image carrier drum such as the above-described photosensitive drum may be decentered with respect to the rotation axis. When such a latent image carrier drum is decentered, the surface speed of the latent image carrier drum ( Peripheral speed) may vary at the transfer position. That is, when the latent image carrier drum is decentered with respect to the rotation axis, the distance from the rotation axis to the latent image carrier drum surface changes depending on the position on the latent image carrier drum surface. As a result, on the surface of the latent image carrier drum, the surface speed increases when the distance from the rotation axis is far, and the surface speed decreases when the distance from the rotation axis is short. When the speed fluctuation of the surface of the latent image carrier drum at the transfer position is caused, the toner image may be transferred out of the desired position on the transfer medium, and a good image may not be formed.

  However, as will be described in detail later, the surface speed fluctuation of the latent image carrier drum due to the eccentricity of the latent image carrier drum has a property of appearing periodically with the rotation period of the latent image carrier drum. Therefore, it is considered that the positional deviation of the toner image on the transfer medium is periodically reproduced with the rotation period of the latent image carrier drum. Therefore, if the positional deviation of the toner image formed on the transfer medium is detected in advance over the rotation period of the latent image carrier drum, it can be expected that the positional deviation of the toner image on the transfer medium can be suppressed based on the detection result. .

  However, in the above configuration in which the toner image is formed using the liquid developer and the liquid carrier is removed by the squeeze roller, the speed fluctuation on the surface of the latent image carrier drum may not appear in the rotation cycle of the latent image carrier drum. there were. That is, the squeeze roller removes excess liquid carrier from the toner image. Therefore, the amount of the liquid carrier tends to be small in the vicinity of the squeeze roller (for example, compared to the vicinity of the developing position). When the amount of the liquid carrier is reduced, the operation of the squeeze roller may affect the surface speed of the latent image carrier drum, and the periodicity of the speed fluctuation on the surface of the latent image carrier drum may be lost.

  The present invention has been made in view of the above problems, and in the image forming apparatus and the image forming method using a squeeze roller while forming a toner image using a liquid developer, the period of fluctuation in the speed of the latent image carrier drum. The purpose is to provide a technology that can suppress the collapse of sex.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier drum that rotates on a rotating shaft and forms a latent image, and a liquid developer containing a liquid carrier and toner. A latent image carrier drum, comprising: a developing unit that supplies the drum to develop the latent image; and a squeeze roller that rotates while removing the liquid carrier from the image formed on the latent image carrier drum by development of the developing unit. The rotation period is an integral multiple of the rotation period of the squeeze roller.

  Further, in order to achieve the above object, the image forming method according to the present invention includes a first step of forming a latent image on a latent image carrier drum rotating on a rotating shaft, and a liquid developer including a liquid carrier and toner. Is supplied to the latent image carrier drum to develop the latent image, and a third step is used to take the liquid carrier from the image developed on the latent image carrier drum in the second step by a rotating squeeze roller. A rotation cycle of the latent image carrier drum is an integral multiple of a rotation cycle of the squeeze roller.

  In the invention thus configured (image forming apparatus, image forming method), the rotation cycle of the latent image carrier drum is an integral multiple of the rotation cycle of the squeeze roller. Therefore, even if the amount of liquid carrier decreases near the squeeze roller and the operation of the squeeze roller affects the surface speed of the latent image carrier drum, the fluctuation in the periodicity of the speed fluctuation of the latent image carrier drum is suppressed. It is possible to do.

  In addition, a drive unit that drives the rotation shaft of the latent image carrier drum, a first gear disposed on the rotation shaft of the latent image carrier drum, and a second gear that is provided on the squeeze roller and meshes with the first gear. The number of teeth of the first gear may be an integral multiple of the number of teeth of the second gear. With this configuration, the rotation cycle of the latent image carrier drum can be set to the rotation cycle of the squeeze roller, and it is possible to suppress the disruption of the periodicity of the speed fluctuation of the latent image carrier drum. .

  As described above, according to the present invention, the disruption of the periodicity of the speed fluctuation of the latent image carrier drum is suppressed. Therefore, it is considered that the displacement of the image position on the transfer medium is periodically reproduced with the period of the latent image carrier drum. Therefore, the transfer medium on which the developed image is transferred to the latent image carrier and the image developed on the latent image carrier drum in a period longer than the rotation period of the latent image carrier drum are transferred to the transfer medium. And a control unit for detecting the image transferred to the head. This is because by effectively utilizing the detection result, it is possible to suppress the positional deviation of the image on the transfer medium in the subsequent image formation.

  For example, in a configuration that includes a light emitting element and includes an exposure head that forms a latent image on the latent image carrier drum by light from the light emitting element, the control unit determines the light emission timing of the light emitting element based on the detection result of the image. It is good to comprise so that it may control. Thereby, it is possible to suppress the positional deviation of the image on the transfer medium.

  At this time, the control unit obtains positional deviation data indicating the positional deviation of the image on the transfer medium from the result of detecting the position of the image transferred to the transfer medium, and controls the light emission timing of the light emitting element based on the positional deviation data. You may comprise so that it may do. Thereby, it is possible to reliably suppress the positional deviation of the image on the transfer medium.

  Furthermore, the control unit may be configured to control the light emission timing of the light emitting element based on the rotation period component of the latent image carrier drum calculated from the positional deviation data. Thereby, it is possible to more reliably suppress the image position shift on the transfer medium due to the speed fluctuation of the latent image carrier drum that occurs in the rotation cycle of the latent image carrier drum.

  Further, the control unit may be configured to form an image in a period not less than 3 times and not more than 5 times the rotation period of the latent image carrier drum. That is, a sufficient amount of misalignment data can be obtained by setting the image formation period to be three times or more the rotation period of the latent image carrier drum. In addition, by setting the period for forming an image to be not more than 5 times the rotation period of the latent image carrier drum, it is possible to suppress the time required to obtain the positional deviation data.

1 is a diagram illustrating an embodiment of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. The fragmentary perspective view which shows the structure of a line head. The fragmentary sectional view which shows the width direction cross section of a line head. FIG. 3 is a partial view showing a configuration of a developing unit. The partial side view which shows the rotation mechanism of a squeeze roller. The figure which shows the influence which the eccentricity of a photoconductive drum has on the surface speed of a photoconductive drum. The perspective view which shows the mechanical structure used by the detection operation | movement of a registration mark. The side view which shows the encoder which is one of the mechanical structures shown in FIG. 6 is a flowchart showing a registration mark detection operation. FIG. 11 is a perspective view showing a registration mark detection operation of FIG. 10. The top view which shows the registration mark formed by the detection operation of a registration mark. The figure which shows how to obtain | require the positional offset amount of a registration mark. The graph which shows the positional offset amount of a registration mark. The graph which plotted the rotation period component of the photosensitive drum of position shift amount. 5 is a flowchart showing an image forming operation. The graph which shows the horizontal request signal corrected with the resist profile. The timing chart which shows an example of correction | amendment operation | movement of a horizontal request signal. The graph which shows the position shift amount of the registration mark by the corrected request signal. The graph which shows the registration mark in the condition where the periodicity of the photoconductor speed fluctuation | variation collapsed. The graph which shows the resist mark formed with the profile based on FIG.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present embodiment. FIG. 2 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC, and based on this, an engine The controller EC controls each part of the device, such as the engine unit ENG and the head controller HC, and executes predetermined image forming operations, and responds to image formation commands on recording sheets such as copy paper, transfer paper, paper, and OHP transparent sheets. The image to be formed is formed.

  In the housing main body (not shown) included in the image forming apparatus according to this embodiment, an electrical component box (not shown) containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided. Yes. Further, the image forming unit 2, the transfer belt unit 8, and the secondary transfer unit 12 are also arranged in the housing body.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each of the image forming stations 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photosensitive drum 21 is arranged such that the rotation axis AR21 thereof is parallel or substantially parallel to the main scanning direction MD (direction perpendicular to the paper surface of FIG. 1). Further, the rotation axis AR21 of each photosensitive drum 21 is connected to a dedicated drive motor DM and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD. As described above, in this embodiment, the rotation shaft AR21 of the photosensitive drum 21 is directly driven by the drive motor DM without providing a power transmission mechanism such as a gear between the rotation shaft AR21 of the photosensitive drum 21 and the drive motor DM. Direct drive method is adopted.

  A charging unit 23, a line head 29, a developing unit 25, a squeeze roller SQ, and a photoconductor cleaner 27 are disposed around the photoconductor drum 21 along the rotation direction thereof. These functional units execute a charging operation, a latent image forming operation, a toner developing operation, and the like. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  The charging unit 23 includes a so-called corona charger, and is a non-contact type charger that does not contact the surface of the photosensitive drum 21. The charging unit 23 is connected to a charging voltage generation unit (not shown), receives the power from the charging voltage generation unit, and the surface of the photosensitive drum 21 at a charging position where the charging unit 23 faces the photosensitive drum 21. Is charged to a predetermined surface potential.

  The line head 29 is arranged such that its longitudinal direction LGD is parallel or substantially parallel to the main scanning direction MD, and its width direction LTD is parallel or substantially parallel to the sub-scanning direction SD. The line head 29 includes a plurality of light emitting elements arranged in the longitudinal direction LGD, and is disposed to face the photosensitive drum 21. Then, light from the light emitting element is imaged on the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image.

  FIG. 3 is a partial perspective view showing the structure of the line head. FIG. 4 is a partial cross-sectional view showing a cross-section in the width direction of the line head. Since these are partial views, they do not represent all parts. On the back surface 294-t of the head substrate 294 included in the line head 29, a plurality of light emitting elements E are arranged in the longitudinal direction LGD at a pitch corresponding to the resolution. Each light emitting element E is an organic EL element formed on the back surface 294-t of the head substrate, and is a so-called bottom emission type organic EL element. Further, a gradient index rod lens array 297 is disposed opposite to the surface 294-h of the head substrate 294. Therefore, the light beam emitted from the light emitting element E is transmitted from the back surface 294-t of the head substrate 294 to the front surface 294-h, and then imaged by the rod lens array 297 at an equal magnification. As a result, a spot SP is formed on the surface of the photosensitive drum 21 and a latent image is formed on the surface of the photosensitive drum 21.

  Such a latent image forming operation by the line head 29 is controlled by the main controller MC and the head controller HC. The main controller MC, the head controller HC, and each line head 29 are configured as separate blocks, which are connected to each other via a serial communication line. The data exchange operation between the blocks will be described with reference to FIG. When an image formation command is given from the external device to the main controller MC, the main controller MC transmits a control signal for starting the engine unit ENG to the engine controller EC. In addition, the image processing unit 100 provided in the main controller MC performs predetermined signal processing on the image data included in the image formation command, and generates video data VD for each toner color.

  On the other hand, the engine controller EC receiving the control signal starts initialization and warm-up of each part of the engine part ENG. When these are completed and the image forming operation can be executed, the engine controller EC outputs a synchronization signal Vsync that triggers the start of the image forming operation to the head controller HC that controls each line head 29.

  The head controller HC is provided with a head control module 400 that controls each line head 29 and a head-side communication module 300 that controls data communication with the main controller MC. On the other hand, the main communication module 200 is also provided in the main controller MC. The main communication module 200 outputs video data VD for one line to the head communication module 300 for each request from the head communication module 300. The head side communication module 300 passes this video data VD to the head control module 400. Then, the head control module 400 causes the light emitting elements of the line heads 29 to emit light based on the received video data VD. As will be described later, the light emission timing of the light emitting element is controlled based on the horizontal request signal H-req. That is, the horizontal request signal H-req is a signal that gives the light emission timing of the light emitting element, and the light emitting element emits light in synchronization with the horizontal request signal H-req. In this way, a latent image corresponding to the image formation command is formed on the surface of the photosensitive drum 21. The latent image is developed as a toner image by the developing unit 25 (FIG. 1).

  FIG. 5 is a partial view showing the configuration of the developing unit. The developing unit 25 includes a developer container 250, and a liquid developer AD is stored in the developer container 250. The liquid developer AD is a high viscosity (about 100 to 10,000 mPa · s) developer in which toner particles are dispersed at a high concentration (about 5 to 40 wt%) in a non-volatile and insulating liquid carrier such as silicone oil. is there. The toner particles are made of resin, pigment or the like having an average particle diameter of about 0.1 to 5 μm and are charged. In order to make the dispersion state of the toner particles in the liquid carrier AD uniform, a stirring member 251 for stirring the liquid developer AD is provided inside the developer container 250.

  Further, the developing unit 25 includes a scooping roller 252. A part of the pumping roller 252 is immersed in the liquid developer AD in the developer container 250, and rotates in the rotation direction D252 (clockwise direction in the figure) to pump up the liquid developer AD. The liquid developer AD thus pumped up is supplied to the developing roller 254 through the intermediate roller 253 (supply roller).

  The intermediate roller 253 is disposed between the scooping roller 252 and the developing roller 254, and rotates in the rotation direction D253 (counterclockwise direction in the figure). Since the rotation direction D253 of the intermediate roller 253 is opposite to the rotation direction D252 of the drawing roller 252, the surface of the intermediate roller 253 and the surface of the drawing roller 252 in the region where the intermediate roller 253 and the drawing roller 252 face each other. And move in the same direction. On the other hand, since the rotation direction D253 of the intermediate roller 253 is the same as the rotation direction D254 (counterclockwise direction in the figure) of the developing roller 254, the intermediate roller 253 and the developing roller 254 face each other (supply) At the position SR), the surface of the intermediate roller 253 and the surface of the developing roller 254 move in opposite directions. Then, the intermediate roller 253 supplies the liquid developer AD to the developing roller 254 at the supply position SR. Further, the liquid developer AD remaining on the intermediate roller 253 after passing through the supply position SR is scraped off by the cleaner blade 255.

  The developing roller 254 has a configuration in which an outer periphery of a metal inner core made of iron or the like is covered with an elastic body such as urethane resin, and forms a nip portion at a developing position DR that contacts the photosensitive drum 21. The developing roller 254 rotates in the rotation direction D254 and transports the liquid developer AD from the supply position SR to the development position DR. A voltage application charger 256 is disposed between the supply position SR and the development position DR. The voltage applying charger 256 is a corona charger, and applies a voltage to the developing roller 254 without contacting the developing roller 254. The charged toner particles in the liquid developer AD carried on the developing roller 254 are driven to the surface of the developing roller 254 and aggregate by the applied voltage. Thus, a toner layer having a predetermined layer thickness is formed on the surface of the developing roller 254.

  Incidentally, the thickness of the toner layer formed at this time can be controlled by adjusting the rotational speed of the intermediate roller 253. In other words, when the rotation speed of the intermediate roller 253 changes, the supply amount of the liquid developer AD per unit time to the developing roller 254 changes, so the supply amount of toner particles contained in the liquid developer AD per unit time ( The supply amount to the developing roller 254 also changes. As a result, the layer thickness of the toner layer formed by aggregation of the toner particles also changes. In short, when a thick toner layer is desired to be formed, the rotational speed of the intermediate roller 253 may be increased. Conversely, when a thin toner layer is desired to be formed, the rotational speed of the intermediate roller 253 may be decreased. The speed adjustment of the intermediate roller 253 can be executed by the engine controller EC.

  A developing bias generator (not shown) is electrically connected to the inner center of the developing roller 254. When the developing bias generator applies a developing bias to the inner center of the developing roller 254, the charged toner moves from the developing roller 254 to the surface of the photosensitive drum 21 at the developing position DR. Thus, the latent image on the surface of the photosensitive drum 21 is developed, and a toner image is formed. Further, the liquid developer AD remaining on the developing roller 254 after passing through the developing position DR is scraped off by the cleaner blade 257.

  The toner image that has become apparent at the development position DR is conveyed in the rotational direction D21 (clockwise direction in the figure) of the photosensitive drum 21, and then at the primary transfer position TR1 where the transfer belt 81 and the photosensitive drum 21 come into contact with each other. Primary transfer is performed on the transfer belt 81. However, in the present embodiment, the squeeze roller SQ is disposed to face the photosensitive drum 21 between the development position DR and the primary transfer position TR1. The squeeze roller SQ is an elastic roller whose surface is finished with an elastic member, and abuts on the photosensitive drum 21 while rotating in the rotation direction Ds (counterclockwise direction in the figure).

  FIG. 6 is a partial side view showing the rotation mechanism of the squeeze roller. In the figure, the photosensitive drum 21 and the squeeze roller SQ are indicated by broken lines. As shown in the figure, a power transmission gear G 21 is attached to the photosensitive drum 21. Therefore, when the photosensitive drum 21 rotates in the rotation direction D21 in response to the driving force from the drive motor DM (FIG. 2), the power transmission gear G21 also rotates in the rotation direction D21. On the other hand, a squeeze roller gear Gs is attached to the squeeze roller SQ, and the squeeze roller gear Gs rotates as the squeeze roller SQ rotates. The power transmission gear G21 and the squeeze roller gear Gs mesh with each other. Therefore, when the power transmission gear G21 rotates in the rotation direction D21, the squeeze roller gear Gs rotates in the rotation direction Ds opposite to the rotation direction D21. Thus, since the rotation direction of the squeeze roller SQ is opposite to the rotation direction D21 of the photosensitive drum 21, the movement direction of the surface of the squeeze roller SQ in the region where the squeeze roller SQ and the photosensitive drum 21 are in contact with each other. The moving direction of the surface of the photosensitive drum 21 is the same.

  The number of teeth of the power transmission gear G21 is 60, which is four times (integer multiple) the number of teeth of the squeeze roller gear (15). Therefore, the rotation cycle of the photosensitive drum 21 is four times (integer multiple) the rotation cycle of the squeeze roller SQ. Here, the rotation period is the time required for one rotation of the rotating object (photosensitive drum 21, squeeze roller SQ). Further, the ratio between the diameter R21 of the photosensitive drum 21 and the diameter Rs of the squeeze roller SQ is four times the same as the ratio of the number of teeth described above. Accordingly, the surface speed of the photosensitive drum 21 and the surface speed of the squeeze roller SQ are equal or approximately equal.

  Returning to FIG. The squeeze roller SQ contacts the photosensitive drum 21 while rotating as described above. As a result, the squeeze roller SQ squeezes (squeezes) excess liquid carrier from the toner image formed on the surface of the photosensitive drum 21. Thus, the toner image having an improved toner particle ratio is conveyed to the primary transfer position TR1 and is primarily transferred to the transfer belt 81.

  A photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The description of the entire image forming apparatus will be continued with reference to FIG. The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated by rotation of the driving roller 82 stretched between these rollers. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIG. 1, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is positioned on the image forming station 2Y. The primary transfer position TR1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  Further, the transfer belt unit 8 includes a transfer belt squeeze portion 87 disposed downstream of the black primary transfer roller 85K and upstream of the drive roller 82. The transfer belt squeeze part 87 functions to remove excess carrier liquid from the surface of the intermediate transfer belt 81 and improve the toner particle ratio of the toner image transferred to the surface of the intermediate transfer belt 81.

  A registration sensor RS is provided to face the surface of the transfer belt 81. The registration sensor RS optically detects a change in reflectance on the surface of the transfer belt 81 to detect a position of a registration mark formed on the transfer belt 81 as necessary.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). Then, in a state where the secondary transfer roller 121 is in contact with the transfer belt 81, a secondary transfer position TR2 is formed between the secondary transfer roller 121 and the intermediate transfer belt 81. The registration roller pair 80 feeds the sheet along the paper discharge path Dpe while adjusting the paper feed timing, and feeds the sheet to the secondary transfer position TR2. Then, at the secondary transfer position TR2, the toner image on the surface of the intermediate transfer belt 81 is secondarily transferred to the sheet.

  By the way, in such an image forming apparatus, the photosensitive drum 21 may be eccentric with respect to the rotation axis AR21, so that the surface speed of the photosensitive drum 21 may periodically fluctuate with the rotation cycle of the photosensitive drum 21. Yes (Figure 7). Here, FIG. 7 is a diagram showing the influence of the eccentricity of the photosensitive drum on the surface speed of the photosensitive drum. The column of “photosensitive drum side view” in the figure corresponds to the case where the side face of the photoconductive drum 21 is viewed from the longitudinal direction LGD. As shown in the same column, the center CT21 of the photosensitive drum 21 is shifted to the right side of the drawing with respect to the center CTcy of the rotation axis AR21, and the eccentricity of the photosensitive drum 21 occurs. When such eccentricity occurs, the distance from the center CTcy (rotation center) of the rotation axis AR21 to the surface of the photosensitive drum 21 changes depending on the position on the surface. As a result, on the surface of the photosensitive drum 21, the peripheral speed may increase at a distance far from the rotation center CTcy, and the peripheral speed may decrease at a distance near the rotation center CTcy.

  This is shown in the graph shown in the “photosensitive drum surface speed” column in FIG. In this graph, the horizontal axis represents the rotation angle θ (deg) of the photosensitive drum, and the vertical axis represents the peripheral speed V [SP] of the photosensitive drum 21. The rotation angle θ of the photosensitive drum 21 is an angle from the origin θ 0 fixed to the photosensitive drum 21 to a position where the line head 29 forms the spot SP, and is a value that changes as the photosensitive drum 21 rotates. Yes ("photosensitive drum side view"). Note that the origin θ0 is arbitrarily determined, and the origin θ0 illustrated in FIG. 7 is an example. In the graph, the surface speed V [TR1] of the photosensitive drum 21 at the spot SP formation position is shown. As shown in the graph, due to the eccentricity of the photosensitive drum 21, the surface speed of the photosensitive drum 21 fluctuates substantially sinusoidally with a period of 360 ° centering on the average surface speed Vav. That is, the surface speed of the photosensitive drum 21 varies with the rotation period of the photosensitive drum 21.

  Such surface speed fluctuations of the photosensitive drum 21 occur not only at the spot SP formation position but also at the primary transfer position TR1. If such a surface speed fluctuation of the photosensitive drum 21 occurs at the primary transfer position TR1, there is a possibility that a positional deviation of the toner image transferred to the intermediate transfer belt 81 may occur. However, as described above, the surface speed fluctuation of the photosensitive drum 21 periodically appears in the rotation cycle of the photosensitive drum 21. Therefore, it is considered that the positional deviation of the toner image on the intermediate transfer belt 81 is also periodically reproduced with the rotation cycle of the photosensitive drum 21. Therefore, in this embodiment, a plurality of registration marks are formed on the surface of the intermediate transfer belt 81 over the rotation period of the photosensitive drum 21 to detect the positional deviation of each registration mark. Next, the registration mark detection operation will be described.

  FIG. 8 is a perspective view showing a mechanical configuration used in the registration mark detection operation, and FIG. 9 is a side view showing an encoder which is one of the mechanical configurations shown in FIG. In the registration mark detection operation, a plurality of registration marks are formed while measuring the rotation angle θ of the photosensitive drum 21 with the encoder ECD, and the position of each registration mark is detected with the registration sensor RS. Here, the rotation angle θ of the photosensitive drum 21 is an angle from a reference slit SL1 (described later) to a spot SP (FIG. 9). As shown in FIG. 8, in the conveyance direction D81 of the intermediate transfer belt 81, two registration sensors RS and RS are provided on the downstream side of the four photosensitive drums 21 provided corresponding to the respective colors. . These registration sensors RS, RS are arranged side by side in the main scanning direction MD.

  As shown in FIGS. 8 and 9, an encoder ECD is provided at one end of a rotation axis AR21 that is parallel or substantially parallel to the main scanning direction MD. The encoder ECD has a disk-shaped encoder disk ED and a transmissive photosensor SC. The central portion of the encoder disk ED is attached to the rotation shaft AR21 of the photosensitive drum 21, and is configured to be rotatable as the photosensitive drum 21 rotates.

  The encoder disk ED is provided with a plurality of (64) slits SL radially about the rotation axis AR21. Then, a slit detection signal output from the photosensor SC that detects the slit SL is output to the engine controller EC. Of the 64 slits SL, the slit SL1 (reference slit SL1) at the position corresponding to the origin is longer than the other slits SL (SL2 to SL64). Therefore, the slit detection signal of the reference slit SL1 is different from the slit detection signals of the slits SL (SL2 to SL64) other than the reference slit SL1. Therefore, the engine controller EC determines the number of times the slit detection signal received from the photosensor SC is from the slit detection signal of the reference slit SL1, and detects the rotation angle θ of the photosensitive drum 21. Can do. In other words, the engine controller EC can detect the rotation angle θ with the reference slit SL1 as a base point. The engine controller EC can also detect the angular velocity from the time change of the rotation angle θ.

  FIG. 10 is a flowchart showing the registration mark detection operation. FIG. 11 is a perspective view showing the registration mark detection operation of FIG. In the figure, only the yellow (Y) line head 29 (Y) and the photosensitive drum 21 (Y) are represented by solid lines, and the other color (M), (C), and (K) line heads 29 (M). ), 29 (C), 29 (K) and the photosensitive drums 21 (M), 21 (C), 21 (K) are represented by broken lines. FIG. 12 is a plan view showing a registration mark formed by the registration mark detection operation.

  In step S101, a linear latent image LI (line pattern latent image LI) extending in the main scanning direction MD is formed on the surface of each of the photosensitive drums 21 (Y), 21 (M), 21 (C), and 21 (K). Is formed. A plurality of line pattern latent images LI are formed at predetermined time intervals by the line heads 29 (Y), 29 (M), 29 (C), and 29 (K). Further, every time each line pattern latent image LI is formed, the rotation angle θ of the photosensitive drums 21 (Y), 21 (M), 21 (C), and 21 (K) is measured (step S102). It is stored in the memory MM (step S103). The line pattern latent image LI thus formed on the photosensitive drum 21 (Y) or the like is developed with the corresponding color toner to form a registration mark RM (step S104). These registration marks RM are transferred to the surface of the intermediate transfer belt 81 (step S105). Thus, as shown in FIG. 12, the registration marks RM (Y), RM (M), RM (C), and RM (K) of the respective colors (Y), (M), (C), and (K) They are formed at intervals in the transport direction D81 (sub-scanning direction SD). Note that the registration mark forming operation is executed during a period five times the rotation period of the photosensitive drum 21. As a result, the registration marks RM (Y), RM (M), RM (C), and RM (K) are formed side by side over a length five times the circumferential length L21 of the photosensitive drum 21.

  The registration mark RM formed in this way is detected by the registration sensor RS while moving in the belt conveyance direction D81 (step S106). Then, based on the detection result of the registration sensor RS, the engine controller EC obtains the positional deviation amount of the registration mark RM. Specifically, the registration marks RM (Y), RM (M), and RM (C) of the colors (Y), (M), and (C) for the registration mark RM (K) of black (K) that is the reference color. ) Each positional deviation amount is obtained (step S107). The processing for determining the amount of misalignment (step S107) and the processing following step S107 (steps S108 and S109) are the same for yellow (Y), magenta (M), and cyan (C). Therefore, in the following, the processing after step S107 will be specifically described for yellow (Y).

  FIG. 13 is a diagram showing how to obtain the registration mark misregistration amount. In the figure, registration marks RM (K) and RM (Y) indicated by solid lines are registration marks actually formed on the surface of the intermediate transfer belt 81, and registration marks RM (Y) -id indicated by broken lines are misaligned. This is a virtual yellow (Y) registration mark at an ideal position. The interval IV-id between the black (K) registration mark RM (K), which is the reference color, and the virtual yellow (Y) registration mark RM (Y) -id is stored in advance in the memory MM or the like. . Then, in the engine controller EC, based on the detection result of the registration sensor RS, the black (K) registration mark RM (K) as the reference color and the actually formed yellow (Y) registration mark RM (Y) Interval IV-rl is calculated, and the difference between the interval IV-rl calculated in this way and the interval IV-id stored in the memory MM is obtained as a positional deviation amount ΔIV (FIG. 14). Here, FIG. 14 is a graph showing the misregistration amount of the registration mark. In FIG. 14, the yellow (Y) registration mark RM (Y) with respect to the position [mm] (horizontal axis) in the belt conveyance direction D81. The positional deviation amount ΔIV [μm] (vertical axis) is plotted. As shown in FIG. 14, the positional deviation amount ΔIV of the registration mark RM (Y) is substantially reproduced for each circumferential length L 21 of the photosensitive drum 21. This indicates that the positional deviation amount ΔIV of the registration mark RM (Y) appears in the rotation cycle of the photosensitive drum 21.

  In step S108, a component that varies with the rotation period of the photosensitive drum 21 is extracted by Fourier analysis from the positional deviation amount ΔIV shown in FIG. 14 (FIG. 15). Here, FIG. 15 is a graph plotting the result of extracting the rotation period component of the photosensitive drum from the positional deviation amount. In FIG. 15, the position [mm] in the belt conveyance direction and the rotation angle θ [deg] of the black (K) photosensitive drum 21 (K) corresponding to the position are shown along the horizontal axis. . The extraction results shown in FIG. 15 are also obtained for colors (M) and (C) other than yellow (Y), and are stored in the memory MM for each color (Y), (M), and (C) as a resist profile. Stored (step S109). Subsequent image formation is controlled based on this resist profile. The details are as follows.

  FIG. 16 is a flowchart showing the image forming operation. First, in step S201, as an initial setting, the photosensitive drum 21 (for each color (Y), (M), and (C) with respect to the rotation angle θ of the photosensitive drum 21 (K) for black (K), which is the reference color, is used. Y), phase differences Δθy, Δθm, and Δθc of rotation angles θ of 21 (M) and 21 (C) are set. Thus, in the image forming operation to be executed later, the photosensitive drums 21 (Y), 21 (M), and 21 (C) of the respective colors (Y), (M), and (C) are black (K). The photosensitive drum 21 (K) rotates with predetermined phase differences Δθy, Δθm, and Δθc.

  Then, while measuring the rotation angle θ of the black (K) photosensitive drum 21 (K) (step S203), the line heads 29 (Y), 29 (M), 29 (C), and 29 (K) A latent image is formed on each of the corresponding photosensitive drums 21 (Y), 21 (M), 21 (C), and 21 (K) (step S204). At this time, the light emission timings of the line heads 29 (Y), 29 (M), and 29 (C) of the respective colors (Y), (M), and (C) other than black (K) are the respective colors (Y), (M ) And (C) are adjusted based on the resist profile. Specifically, the horizontal request signal H-req supplied to each line head 29 (Y), 29 (M), 29 (C) is corrected based on the resist profile. Since the correction operation of the horizontal request signal H-req is the same for each color (Y), (M), and (C), the correction operation of the horizontal request signal H-req will be described below for yellow (Y). Only the other colors (M) and (C) are omitted.

  FIG. 17 is a graph showing the horizontal request signal corrected based on the resist profile shown in FIG. In FIG. 17, the correction amount ΔTreq of the horizontal request signal H-req interval is shown as the vertical axis. Here, the interval between the horizontal request signals H-req is a time interval at which the horizontal request signal H-req is output. In FIG. 17, the position [mm] in the belt conveyance direction D81 and the rotation angle θ [deg] of the black (K) photosensitive drum 21 (K) corresponding to the position are shown along the horizontal axis. Yes. As shown in FIG. 17, the horizontal request signal H-req interval is corrected so as to cancel out the positional deviation amount of the registration mark RM in the registration profile of FIG.

  FIG. 18 is a timing chart showing an example of the horizontal request signal correction operation. The figure shows the horizontal request signal H-req for the yellow (Y) line head 29 (Y) at time t1 when the rotation angle θ of the black (K) photosensitive drum 21 (K) becomes the rotation angle θ1. Is output. In this case, the engine controller EC reads the correction amount ΔTreq (FIG. 17) corresponding to the rotation angle θ1 from the memory MM, adds this correction amount ΔTreq to the standard H-req interval Treq-id, and then corrects the corrected H-req. The interval Treq-rl is obtained. Here, the standard H-req interval Treq-id is a time interval at which the uncorrected horizontal request signal H-req is output. Then, the next horizontal request signal H-req is output with a corrected H-req interval Treq-rl, and the light emitting element E of the line head 29 (Y) emits light in synchronization with the horizontal request signal H-req. To form a latent image. As described above, the engine controller EC of the present embodiment adjusts the light emission timing of the light emitting element E by correcting the horizontal request signal H-req.

  Each of the latent images formed by the line heads 29 (Y), 29 (M), and (C) and the latent image formed by the line heads 29 (K) is developed as a corresponding color toner image. (Step S204). Subsequently, the toner images of the respective colors (Y), (M), (C), and (K) are superimposed on the surface of the intermediate transfer belt 81 to form a color image (step S205). Then, the color image on the surface of the intermediate transfer belt 81 is secondarily transferred to the paper (step S206).

  As described above, in the present embodiment, the horizontal request signal H-req is corrected based on the registration profile, and the line head 29 forms a latent image in synchronization with the corrected horizontal request signal H-req. Therefore, even if the surface speed of the photosensitive drum 21 fluctuates, the positional deviation of the toner image on the surface of the intermediate transfer belt 81 can be suppressed. Such an effect can be confirmed by measuring the positional deviation of the registration mark RM when the registration mark detection operation is executed with the corrected horizontal request signal H-req.

  FIG. 19 is a graph showing the amount of misalignment of the yellow registration mark formed by the corrected horizontal request signal. The positional deviation amount ΔIV of the registration mark RM (Y) shown in FIG. 19 is 10 [mm] or less. On the other hand, as shown in FIG. 14, the positional deviation amount ΔIV of the registration mark RM (Y) formed by the horizontal request signal before correction is 40 [mm] at the maximum. In this way, by correcting the horizontal request signal H-req using the registration profile, the positional deviation amount ΔIV can be suppressed to about a quarter.

  As described above, in the present embodiment, the positional deviation amount ΔIV of the registration mark RM is obtained from the registration mark RM formed over the rotation period of the photosensitive drum 21, and the photosensitive member periodic component of the positional deviation amount ΔIV is a resist profile. Extracted as Then, image formation is executed with the horizontal request signal H-req corrected by the resist profile. Thereby, it is possible to suppress the positional deviation of the toner image on the surface of the intermediate transfer belt 81. However, in order for such a method to function effectively, it is important that the surface speed variation of the photosensitive drum 21 periodically varies with the rotation cycle of the photosensitive drum 21. However, in the configuration in which the toner image is formed using the liquid developer AD and the liquid carrier is removed by the squeeze roller SQ, the speed fluctuation on the surface of the photosensitive drum 21 may not appear in the rotation cycle of the photosensitive drum 21. .

  FIG. 20 is a graph showing the amount of misregistration of a registration mark formed in a situation where the periodicity of the speed fluctuation on the surface of the photosensitive drum is broken due to the influence of the squeeze roller. As shown in the figure, the positional deviation amount ΔIV of the registration mark RM (Y) is not reproduced by the circumferential length L21 of the photosensitive drum 21 and does not have periodicity in the rotation cycle of the photosensitive drum 21. Therefore, even if the rotational profile component of the photosensitive drum 21 is extracted from the positional deviation amount ΔIV in FIG. 20 to obtain a resist profile, and the horizontal request signal H-req is corrected by this resist profile, the surface of the intermediate transfer belt 81 is corrected. The position of the toner image is greatly shifted (FIG. 21). Here, FIG. 21 is a graph showing the positional deviation amount of the registration mark formed by the horizontal request signal corrected by the registration profile obtained from FIG. As shown in the figure, the positional deviation amount ΔIV of the registration mark RM (Y) varies substantially sinusoidally with the circumferential length Lsq of the squeeze roller SQ.

  Such a problem is caused by an inappropriate rotation period of the squeeze roller SQ. On the other hand, in this embodiment, the rotation cycle of the photosensitive drum 21 is an integral multiple of the rotation cycle of the squeeze roller SQ. Therefore, even if the amount of the liquid carrier is reduced in the vicinity of the squeeze roller SQ and the operation of the squeeze roller SQ affects the surface speed of the photosensitive drum 21, the collapse of the periodicity of the speed fluctuation of the photosensitive drum 21 is suppressed. It is possible to do. As a result, it is possible to suppress the displacement of the toner image on the surface of the intermediate transfer belt 81 (FIG. 19).

  In the present embodiment, the light emission timing of the light emitting element E is controlled based on the rotation period component of the photosensitive drum 21 extracted from the positional deviation amount ΔIV. Therefore, it is possible to more reliably suppress the displacement of the toner image on the intermediate transfer belt 81 due to the speed fluctuation of the photosensitive drum 21 that occurs in the rotation cycle of the photosensitive drum 21.

  Further, the present embodiment is preferable because the registration mark RM is formed between 3 times and 5 times the rotation period of the photosensitive drum. That is, by setting the period for forming the registration mark RM to be three times or more the rotation period of the photosensitive drum 21, a sufficient amount of data (positional deviation data) indicating the positional deviation amount ΔIV of the registration mark RM can be obtained. . In addition, by setting the period for forming the registration mark RM to be not more than 5 times the rotation period of the photosensitive drum 21, the time required to obtain the misregistration data can be suppressed.

  As described above, in this embodiment, the photosensitive drum 21 corresponds to the “latent image carrier drum” of the present invention, the drive motor DM corresponds to the “drive unit” of the present invention, and the power transmission gear G21 The squeeze roller gear Gs corresponds to the “second gear” of the present invention, the intermediate transfer belt 81 corresponds to the “transfer medium” of the present invention, and corresponds to the engine controller. EC corresponds to the “control unit” of the present invention, the line head 29 corresponds to the “exposure head” of the present invention, and the positional shift amount of the registration mark RM shown in FIG. It corresponds.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, the time for forming the registration mark RM is not limited to the above, and may be any time as long as it is equal to or longer than the rotation cycle of the photosensitive drum 21.

  Moreover, in the said embodiment, although one squeeze roller SQ is provided, the number of squeeze rollers is not restricted to this, Two or more may be sufficient. In this case, the rotation cycle of the photosensitive drum 21 may be an integral multiple of the rotation cycle of each squeeze roller.

  In the above embodiment, the rotation cycle of the photosensitive drum 21 is four times the rotation cycle of the squeeze roller SQ, but the ratio of the rotation cycle of the photosensitive drum 21 and the rotation cycle of the squeeze roller SQ is not limited to four. Any integer can be used.

  In the above embodiment, the squeeze roller SQ is driven by driving the squeeze roller gear Gs to the power transmission gear G21 attached to the photosensitive drum 21. However, the drive mechanism for the squeeze roller SQ is not limited to this, and a drive mechanism for the squeeze roller SQ may be provided completely separate from the drive mechanism for the photosensitive drum 21. In short, it is only necessary that the rotation cycle of the photosensitive drum 21 is an integral multiple of the rotation cycle of the squeeze roller SQ, and the drive mechanisms of the squeeze roller SQ and the photosensitive drum 21 have different configurations from those described above. Also good.

  In the above embodiment, in the region where the squeeze roller SQ and the photosensitive drum 21 are in contact with each other, the movement direction of the squeeze roller SQ surface is the same as the movement direction of the photosensitive drum 21 surface. The surface speed of 21 and the surface speed of the squeeze roller SQ are equal or substantially equal. However, the rotation direction and surface speed of the squeeze roller SQ are not limited to this. In short, it is sufficient that the rotation cycle of the photosensitive drum 21 is an integral multiple of the rotation cycle of the squeeze roller SQ.

  In the above-described embodiment, the plurality of light emitting elements E are arranged in a straight line in the longitudinal direction LGD. However, the plurality of light emitting elements E may be arranged in a zigzag of two rows or three or more rows in the longitudinal direction LGD.

  Moreover, in the said embodiment, although the organic EL element was used as the light emitting element E, you may use LED (Light-Emitting Diodes) as the light emitting element E. FIG.

  Further, the configuration of the line head 29 is not limited to the above-described one, and for example, the line head 29 described in JP 2008-036937 A, JP 2008-36939 A, or the like can be used. However, in the line head 29 described in these publications, a plurality of light emitting elements are arranged in a staggered manner to form one light emitting element group, and the plurality of light emitting element groups are two-dimensionally arranged. Therefore, a plurality of light emitting elements are arranged at different positions in the sub scanning direction SD. Therefore, for example, as described in FIG. 12 of Japanese Patent Laid-Open No. 2008-36937, in such a line head 29, light emission of light emitting elements arranged at different positions in the sub-scanning direction SD is controlled at different light emission timings. is doing. Therefore, when the present invention is applied to such a line head 29, it is preferable to provide a horizontal request signal H-req for each of a plurality of light emitting elements arranged at different positions in the sub-scanning direction SD. Then, each horizontal request signal H-req may be corrected according to the registration profile shown in FIG.

  In the above embodiment, the rotation axis AR21 of each photosensitive drum 21 is directly rotated by the dedicated drive motor DM. However, a drive force transmission system such as a gear may be provided between the rotation shaft AR21 and the drive motor DM.

  DESCRIPTION OF SYMBOLS 21 ... Photosensitive drum, 25 ... Developing part, 250 ... Developer container, 251 ... Stirring member 251, 252 ... Pumping roller, 253 ... Intermediate roller, 254 ... Developing roller, 256 ... Charger for voltage application, 29 ... Line 81, intermediate transfer belt, AD, liquid developer, AR21, rotating shaft AR21 (of the photosensitive drum), DM, drive motor, E, light emitting element, EC, engine controller, ECD, encoder, G21, for power transmission Gear, Gs ... Squeeze roller gear, H-req ... Horizontal request signal, MM ... Memory, RM ... Registration mark, RS ... Registration sensor, SQ ... Squeeze roller, TR1 ... Primary transfer position

Claims (8)

A latent image carrier drum that rotates on a rotating shaft and forms a latent image;
A developing section for supplying a liquid developer containing a liquid carrier and toner to the latent image carrier drum to develop the latent image;
A squeeze roller that rotates while taking out the liquid carrier from the image formed on the latent image carrier drum by development of the developing unit;
With
The image forming apparatus according to claim 1, wherein the rotation cycle of the latent image carrier drum is an integral multiple of the rotation cycle of the squeeze roller. A drive unit for driving the rotation shaft of the latent image carrier drum;
A first gear disposed on the rotating shaft of the latent image carrier drum;
A second gear provided on the squeeze roller and meshing with the first gear;
The image forming apparatus according to claim 1, wherein the number of teeth of the first gear is an integral multiple of the number of teeth of the second gear. A transfer medium onto which the developed image is transferred to the latent image carrier;
A controller that transfers the image developed on the latent image carrier drum to the transfer medium in a period equal to or greater than the rotation period of the latent image carrier drum, and detects the image transferred to the transfer medium;
The image forming apparatus according to claim 1, further comprising: An exposure head having a light emitting element and forming a latent image on the latent image carrier drum by light from the light emitting element;
The image forming apparatus according to claim 3, wherein the control unit controls a light emission timing of the light emitting element based on a detection result of the image.   The control unit obtains positional deviation data indicating the positional deviation of the image on the transfer medium from the result of detecting the position of the image transferred to the transfer medium, and based on the positional deviation data, The image forming apparatus according to claim 4, wherein the light emission timing is controlled.   The image forming apparatus according to claim 5, wherein the control unit controls a light emission timing of the light emitting element based on a rotation period of the latent image carrier drum calculated from the positional deviation data.   The image forming apparatus according to claim 5, wherein the control unit forms the image in a period not less than 3 times and not more than 5 times the rotation period of the latent image carrier drum. A first step of forming a latent image on a latent image carrier drum rotating about a rotation axis;
A second step of developing the latent image by supplying a liquid developer containing a liquid carrier and toner to the latent image carrier drum;
A third step of taking the liquid carrier from the image developed on the latent image carrier drum in the second step by a rotating squeeze roller;
With
An image forming method, wherein a rotation cycle of the latent image carrier drum is an integral multiple of a rotation cycle of the squeeze roller.

Images