JP2011095557A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly obtain the density of an image in an image forming method and an image forming apparatus by which an image is formed by developing a latent image with a liquid developer containing a liquid carrier and a toner. <P>SOLUTION: After a solid patch image PI is formed on an intermediate transfer body 31, the intermediate transfer body 31 is idled, and when the solid patch image PI passes a detection range of an optical sensor PS for the second time, the image density of the image PI is acquired by a controller 10 based on a signal outputted from the optical sensor PS. During idling the intermediate transfer body 31, a developing device 24 is separated from a photoreceptor drum 21 to a retracting position to stop supplying a liquid developer to the photoreceptor drum 21, and the solid patch image PI passes a primary transfer nip NP1 under the described condition, thereby, a liquid carrier CL present in a surface layer of the solid patch image PI is peeled when the solid patch image PI passes the primary transfer nip NP1 to expose a toner T constituting the patch image PI. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming method and an image forming apparatus for forming an image by developing a latent image with a liquid developer containing a liquid carrier and toner and detecting the image.

  Conventionally, a latent image carrier such as a charged photosensitive drum is exposed by an exposure unit to form an electrostatic latent image on the latent image carrier, and toner is attached to the latent image carrier by a developing unit. An electrophotographic image forming apparatus in which a latent image is visualized to form a toner image, and the toner image is transferred onto a transfer sheet to obtain a predetermined image has been put into practical use. Here, as a developing method of the developing unit, a liquid developing method using a developer in which toner is dispersed in a liquid carrier is known. This liquid development system has advantages such as a high-resolution image can be obtained because the particle diameter of the toner is as small as 0.1 to 2 μm, and a uniform image can be obtained because the fluidity is high because of the liquid. Therefore, various liquid development type image forming apparatuses have been proposed (for example, Patent Document 1).

JP 2009-15351 A

  By the way, the image density of the toner image formed as described above depends on the electric field applied to the charged toner at the development position, and this electric field is caused by changes in the development bias, exposure energy, charging bias, and the development gap. Therefore, these changes may affect the image density of the toner image, leading to a decrease in image quality. Further, in the liquid development method, the image density, particularly the solid image density, may fluctuate due to a change in the mixing ratio of the toner and the liquid carrier or a change in the thickness of the toner formed on the developing roller constituting the developing unit. . Therefore, for example, in the invention described in Patent Document 1, a plurality of solid patch images are formed while changing the contrast potential, and each image density is detected by a reflective optical sensor (patch sensor) to increase the contrast potential. Therefore, a high density image forming condition is required in which the toner adhesion amount to the latent image carrier is substantially saturated. It has also been proposed to feedback control the toner mixing ratio and the rotation speed of the anilox roller so that the density of the solid image is constant.

  However, even if a solid patch image is formed in the liquid developing method, the upper surface of the toner layer constituting the patch image may be covered with a liquid carrier and the entire surface of the patch image is in a mirror state as will be described later. In this case, the light projected from the optical sensor is reflected on the surface of the patch image, and the density of the patch image may not be detected accurately. As a result, appropriate image forming conditions cannot be obtained, leading to a reduction in image quality.

  Some embodiments according to the present invention provide an image forming method and an image forming apparatus for developing a latent image with a liquid developer containing a liquid carrier and a toner to form an image. The goal is to find it accurately.

  According to one aspect of the image forming method of the present invention, a latent image is formed on a first latent image carrier, and the latent image formed on the first latent image carrier is a liquid developer containing a liquid carrier and toner particles. Is developed with a first developer carrier that is in contact with the first latent image carrier, and the image developed on the first latent image carrier is transferred between the first latent image carrier and the transfer medium. The image is transferred to the transfer medium at the first transfer nip formed by contact, the first latent image carrier and the first developer carrier are separated from each other, and the transfer medium on which the image is transferred moves around. The detection unit detects an image that has passed through the first transfer nip portion.

  An aspect of the image forming apparatus according to the present invention is a first latent image carrier on which a latent image is formed, and a liquid developer that is in contact with the first latent image carrier and includes a liquid carrier and toner. A first developer carrying member that develops the latent image, and a first transfer nip portion are formed in contact with the first latent image carrying member, and the first latent image carrier is formed at the first transfer nip portion. A transfer medium on which the developed image is transferred, a developer carrier moving portion for bringing the first developer carrier into contact with or separating from the first latent image carrier, and the image transferred to the transfer medium A control for controlling the image forming apparatus so that the image passes through the first transfer nip portion by moving the transfer medium after the first developer carrying member is separated from the first latent image carrying member by the developer carrying member moving unit. And a detection unit that detects an image that has passed through the first transfer nip.

  In the invention (image forming method and image forming apparatus) configured as described above, the image formed on the transfer medium is not detected by the detection unit immediately after the image formation, but the image detects the first transfer nip portion. The image is detected after passing. Further, the developer carrying member is separated from the latent image carrying member, and the transfer medium is moved so that the image passes through the first transfer nip portion. Therefore, no new liquid developer is supplied from the first developer carrier to the first latent image carrier, and as a result, the liquid developer exists on the surface layer portion of the image formed on the transfer medium. The liquid carrier is peeled off at the first transfer nip, and the toner constituting the image is exposed. Then, image detection is performed by the detection unit with the toner exposed. Accordingly, the density of the image formed on the transfer medium can be obtained with high accuracy based on the detection result of the detection unit.

  Here, a latent image is formed, a second latent image carrier that contacts the transfer medium to form a second transfer nip, and a second latent image that contacts the second latent image carrier. A second developer carrier that develops the latent image formed on the carrier with a liquid developer containing second toner particles different from the liquid carrier and toner particles, and the second latent image carrier; The image on which the transfer medium on which the image that moves around and separated from the second developer carrier passes through the second transfer nip portion and passes through the first transfer nip portion and the second transfer nip portion. May be configured to be detected by the detection unit.

  Further, when the image is transferred to the transfer medium at the first transfer nip portion, the second latent image carrier and the second developer carrier may be separated from each other.

  Further, a latent image is formed on the second latent image carrier, the latent image formed on the second latent image carrier is developed with the second developer carrier, and developed on the second latent image carrier. The transferred second image is transferred to the transfer medium at the second transfer nip portion, the second latent image carrier and the second developer carrier are separated from each other, and the second image moving around is transferred. The transfer medium passes through the first transfer nip part and the second transfer nip part, and the detection part detects the second image that has passed through the first transfer nip part and the second transfer nip part. May be.

  In addition, there is a recess on the peripheral surface, and a transfer roller with which the peripheral surface abuts through the transfer medium and the recording material. When the transfer medium on which the image has been transferred is moving around, the recess is opposed to the recording medium. In this case, the transfer medium and the transfer roller may be separated from each other.

1 is a diagram illustrating a first embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. 2 is a timing chart showing the operation of the image forming apparatus shown in FIG. FIG. 2 is a schematic diagram illustrating an operation of the image forming apparatus illustrated in FIG. 1. FIG. 5 is a diagram illustrating a second embodiment of an image forming apparatus according to the present invention. FIG. 6 is a block diagram showing an electrical configuration of the apparatus of FIG. 5. 6 is a timing chart showing patch image formation and density detection operations in the image forming apparatus shown in FIG. 5. FIG. 6 is a schematic diagram illustrating an operation of the image forming apparatus illustrated in FIG. 5. FIG. 9 is a diagram illustrating a third embodiment of an image forming apparatus according to the invention. The block diagram which shows the electric constitution of the apparatus of FIG. The figure which shows the structure of a secondary transfer part. The figure explaining the effect | action of the contact member in 2nd Embodiment. 10 is a timing chart showing patch image formation and density detection operations in the image forming apparatus shown in FIG. FIG. 10 is a diagram illustrating a fourth embodiment of an image forming apparatus according to the invention.

  FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 forms a monochrome image with a single color (black) toner. When an image forming command is given from an external device such as a host computer to a controller 10 having a CPU, a memory, etc., the controller 10 Controls each part of the apparatus to execute a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet-like recording medium RM such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  The image forming apparatus 1 is provided with a photosensitive drum 21 on which a toner image is formed. The photosensitive drum 21 is arranged so that the rotation shaft 21a thereof is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1). The rotating shaft 21a of the photosensitive drum 21 is connected to a main motor M1 disposed at the end of the photosensitive drum 21, and the photosensitive drum 21 is driven to rotate at a predetermined speed in the direction of arrow D21 in FIG.

  Around the photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and the surface of the photosensitive drum 21 is exposed according to an image signal to form an electrostatic latent image. An exposure unit 23 to be formed, a developing unit 24 that visualizes the electrostatic latent image as a toner image, a first squeeze unit 25, a second squeeze unit 26, and a cleaner blade 27 that cleans the surface of the photosensitive drum 21 after transfer. Are arranged along the rotation direction D21 (clockwise in FIG. 1) of the photosensitive drum 21 in these order.

  The charger 22 does not come into contact with the surface of the photosensitive drum 21, and a conventionally well-known and commonly used corona charger can be used as the charger 22. When a scorotron charger is used as the corona charger, a wire current flows through the charge wire of the scorotron charger and a direct current (DC) grid charging bias is applied to the grid. In this way, the photosensitive drum 21 is charged by corona discharge due to the application of the charging bias from the charging bias generator (not shown) to the charger 22, whereby the surface potential of the photosensitive drum 21 is set to a substantially uniform potential. Is done.

  The exposure unit 23 exposes the surface of the photosensitive drum 21 with a light beam in accordance with an image signal given from an external device to form an electrostatic latent image corresponding to the image signal. The exposure device 23 can be constituted by a light beam from a semiconductor laser scanned by a polycon mirror, or a line head in which light emitting elements are arranged in the main scanning direction.

  Toner is applied from the developing device 24 to the electrostatic latent image formed in this manner, and the electrostatic latent image is developed with the toner. The developing device 24 of the image forming apparatus 1 includes a developing roller 241, an anilox roller 242, a developer container 243 for storing a liquid developer in which a toner is dispersed in a liquid carrier in an approximate weight ratio of about 20%, a developer The toner compression corona generator 244 that mainly charges and compresses the toner is mainly configured. Of these main components, the developing roller 241 is a cylindrical member, and is provided with an elastic layer such as polyurethane rubber, silicon rubber, NBR, or PFA tube on the outer peripheral portion of an inner core made of metal such as iron. The developing roller 241 is connected to the developing motor M2, and is rotated counterclockwise on the paper surface of FIG. The developing roller 241 is electrically connected to a developing bias generator (not shown) so that the developing bias is applied at an appropriate timing.

  An anilox roller 242 is provided to supply the liquid developer to the developing roller 241, and the liquid developer is directly supplied from the anilox roller 242 to the developing roller 241. As described above, the anilox roller 242 has a function of supplying the liquid developer to the developing roller 241. The anilox roller 242 is a roller having a concave pattern formed by a spiral groove or the like engraved finely and uniformly on the surface so as to easily carry the liquid developer. Similar to the developing roller 241, a metal cored bar wrapped with a rubber layer such as urethane or NBR, or a PFA tube is used. The anilox roller 242 is connected to the developing motor M2, and is rotated counterclockwise on the paper surface of FIG. As described above, the liquid developer is supplied from the developer storage unit 246 to the developing roller 241 by a so-called two-roller configuration. However, the liquid developer is not limited to this form, and is temporarily applied from the anilox roller 242 to the intermediate roller. It is good also as a structure (3 roller structure) which apply | coats a liquid developer to the developing roller 241. FIG. According to such a three-roller configuration, the liquid developer passes through the nip portion a plurality of times, so that the liquid developer can be sufficiently kneaded, and a uniform liquid developer film is formed by the developing roller 241. It becomes possible.

  A regulating member 245 is in contact with the anilox roller 242. As the restricting member 245, a metal member or a member having elasticity formed by coating an elastic body on the surface can be used. The restricting member 245 according to the present embodiment is a urethane rubber that comes into contact with the surface of the anilox roller 242. Etc., and a plate made of metal or the like that supports the rubber part. The regulating member 245 has a function of regulating and adjusting the film thickness and amount of the liquid developer carried and conveyed by the anilox roller 242 and adjusting the amount of liquid developer supplied to the developing roller 241. . Further, the liquid developer scraped off by the regulating member 245 is returned to the developer storage unit 246.

  The liquid developer stored in the developer storage unit 246 is volatile at room temperature at a low concentration (1 to 2 wt%) and low viscosity using Isopar (trademark: exon) as a liquid carrier, which is generally used conventionally. A solid having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and a high viscosity at room temperature instead of a volatile liquid developer having an organic solvent, silicon oil, mineral oil Alternatively, a liquid developer having a high viscosity (about 30 to 10,000 mPa · s) added to a liquid solvent such as edible oil together with a dispersant and having a toner solid content concentration of about 20% is used.

  As described above, the developing roller 241 supplied with the liquid developer rotates so as to move in the direction opposite to the surface of the anilox roller 242, and moves in the same direction as the surface of the photosensitive drum 21. Rotate. In order to form a toner image, the rotation direction of the developing roller 241 needs to be rotated so that the surface thereof moves in the same direction as the surface of the photosensitive drum 21, but for the anilox roller 242, It may be configured to move in the opposite direction or the same direction.

  A toner compression corona generator 244 and a developing roller cleaning unit 247 are arranged along the rotation direction of the developing roller 241. More specifically, a toner compression corona generator 244 is arranged on the upstream side in the rotation direction of the developing roller with respect to the developing position where the surface of the developing roller 241 is in contact with the photosensitive drum 21 to form the developing nip portion. . The toner compression corona generator 244 is an electric field applying unit that increases the bias of the surface of the developing roller 241, and the toner of the liquid developer conveyed by the developing roller 241 is positioned close to the toner compression corona generator 244. Then, an electric field is applied, and charging and compression are performed. For the toner charging and compression, a compaction roller that is charged by contact may be used instead of corona discharge by applying electrolysis.

  On the other hand, a developing roller cleaning unit 247 is disposed on the downstream side in the developing roller rotation direction with respect to the developing position, and the leading end thereof is in contact with the surface of the developing roller 241. The developing roller cleaning unit 247 is made of an elastic material such as rubber, and scrapes and removes the liquid developer remaining on the developing roller 241 without contributing to development. The liquid developer thus scraped off is dropped into the developer recovery unit 248 and recovered.

  Further, the developing device 24 configured in this way is connected to the developing device separation / contact mechanism 240, and the rotational driving force from the development device separation / contact motor M3 is transmitted to the development device separation / contact mechanism 240. Accordingly, the developing device 24 can reciprocate between a developing position for developing the latent image on the photosensitive drum 21 (solid line position in FIG. 1) and a retracted position away from the photosensitive drum 21 (dashed line position in FIG. 1). It has become. Therefore, when the developing device 24 is moved to the retracted position and positioned, the supply of new liquid developer to the photosensitive drum 21 is stopped during that time.

  A first squeeze portion 25 is disposed on the downstream side of the developing position in the rotation direction D <b> 21 of the photosensitive drum 21, and a second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25. These squeeze portions 25 and 26 are provided with squeeze rollers 251 and 261, respectively. Then, the squeeze roller 251 rotates in response to the rotational driving force from the main motor M1 while contacting the surface of the photosensitive drum 21 at the first squeeze position to remove excess developer in the toner image. Further, in the rotation direction D21 of the photosensitive drum 21, the squeeze roller 261 receives the rotational driving force from the main motor M1 while rotating in contact with the surface of the photosensitive drum 21 at the second squeeze position downstream of the first squeeze position. Then, excess liquid carrier and fog toner in the toner image are removed. Further, in the present embodiment, in order to increase the squeeze efficiency, a squeeze bias generator (not shown) is electrically connected to the squeeze rollers 251 and 261 so that the squeeze bias is applied at an appropriate timing. Has been. In this embodiment, the two squeeze portions 25 and 26 are provided. However, the number and arrangement of the squeeze portions are not limited to this, and for example, one squeeze portion may be disposed.

  The toner image that has passed through these squeeze positions is primarily transferred to the intermediate transfer member 31 of the primary transfer unit 3. In the primary transfer unit 3, the intermediate transfer member 31 is constituted by an intermediate transfer drum having a drum shape, and the surface of the intermediate transfer member 31 abuts on the surface of the photosensitive drum 21 to form the primary transfer nip portion NP1. However, it receives the rotational driving force from the main motor M1 and rotates in the counterclockwise direction D31 on the paper surface of FIG. In addition, a primary transfer bias generator (not shown) is electrically connected to the intermediate transfer member 31, and a primary transfer bias is applied at an appropriate timing so that the toner image on the photosensitive drum 21 is transferred to the intermediate transfer member 31. Primary transfer efficiently.

  In the present embodiment, in order to detect the toner image transferred to the intermediate transfer member 31, a reflective optical sensor PS is disposed on the downstream side of the primary transfer nip NP1 in the moving direction D31 of the intermediate transfer member 31. Yes. The optical sensor PS has a projector and a light receiver. The light sensor irradiates the surface of the intermediate transfer body 31 from the light projector, and the light receiver receives the light reflected by the surface of the intermediate transfer body 31. A signal corresponding to is output to the controller 10. Therefore, the controller 10 can obtain the image density of a toner image formed on the intermediate transfer member 31 based on the signal, for example, a patch image formed as described later.

  Further, the outer peripheral surface of the secondary transfer roller 42 of the secondary transfer unit 4 abuts on the outer peripheral surface of the intermediate transfer member 31 on the downstream side of the optical sensor PS in the moving direction D31 of the intermediate transfer member 31, and the secondary transfer nip portion. NP2 is formed. The secondary transfer roller 42 is electrically connected to a secondary transfer bias generator not shown. Then, the recording medium RM is conveyed from the pair of gate rollers 51 and 51 toward the secondary transfer nip portion NP2, and the single color toner image formed on the intermediate transfer member 31 at the secondary transfer position is recorded on the recording medium RM. When transferring, a secondary transfer bias is applied to the secondary transfer roller 42 from the secondary transfer bias generation unit. On the other hand, when the patch image formed as described later is allowed to pass through the secondary transfer nip portion NP2 while remaining on the intermediate transfer member 31, the secondary transfer bias generating portion applies to the secondary transfer roller 42. A bias having a polarity opposite to that of the secondary transfer bias, that is, a reverse bias is applied.

  Further, the secondary transfer unit 4 is provided with a secondary transfer roller cleaning unit 45 for removing the developer remaining on the secondary transfer roller 42, and the tip blade of the secondary transfer roller cleaning unit 45 is subjected to secondary transfer. The developer is scraped off in contact with the surface of the roller 42.

  The recording medium RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 42 to the transport mechanism 6. The transport mechanism 6 transports the recording medium RM to the fixing unit 7 and heat or pressure is applied to the monochromatic toner image transferred to the recording medium RM to fix the toner image to the recording medium RM. Is called.

  In addition, in this embodiment, the secondary transfer is performed in the rotational direction D31 of the intermediate transfer body 31 in order to clean and remove the toner and liquid carrier remaining on the surface of the intermediate transfer body 31 after the secondary transfer as described above. An intermediate transfer member cleaning unit 39 is provided in a part of the range from the nip NP2 to the primary transfer nip NP1. The intermediate transfer member cleaning unit 39 is connected to the cleaner separation / contact mechanism 320, and the intermediate transfer member cleaning is performed in response to the rotational driving force from the cleaner separation / contact motor M4 being transmitted to the cleaner separation / contact mechanism 320. The tip blade of the portion 39 can be brought into and out of contact with the surface of the intermediate transfer member 31. Therefore, the toner and the liquid carrier remaining on the surface of the intermediate transfer body 31 can be removed by the front end blade coming into contact with the surface of the intermediate transfer body 31, while the front end blade is separated from the surface of the intermediate transfer body 31. As will be described later, the patch image formed on the surface of the intermediate transfer member 31 can be directly passed through the intermediate transfer member cleaning unit 39 and sent to the primary transfer nip NP1.

  In this embodiment, the photosensitive drum 21 having a diameter of 78 mm is used, whereas the diameter of the intermediate transfer member 31 is set to 66 mm. Further, drivers 11 to 14 are provided to drive and control the motors M1 to M4 in accordance with operation commands from the controller 10, respectively. In particular, the process speed is 250 (by controlling the main motor M1 by the driver 11). mm / sec), the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251, 261 are rotationally driven.

  In the image forming apparatus 1 configured as described above, it is desired to form an image under appropriate image forming conditions as in the image forming apparatus disclosed in Patent Document 1. Therefore, as in the same apparatus, a solid patch image is formed, and the image density of the solid patch image is detected by the optical sensor PS, and the controller 10 forms an image forming condition for forming a good high density image based on the detection result. Ask for. However, in this embodiment, in order to suppress the influence of the liquid carrier and accurately obtain the image density of the solid patch image, the intermediate transfer member 31 is rotated only once around the development unit 24 while being separated from the photosensitive drum 21 after the patch image is formed. It is spinning. Hereinafter, the solid patch image formation and the density detection operation in the present embodiment will be described in detail with reference to FIGS. 3 and 4.

  FIG. 3 is a timing chart showing the operation of the image forming apparatus shown in FIG. FIG. 4 is a schematic diagram showing the operation of the image forming apparatus shown in FIG. In the image forming apparatus 1 according to this embodiment, the controller 10 controls each part of the apparatus according to a program stored in a memory (not shown) of the controller 10 to execute solid patch image formation and density detection as follows. . That is, when the operation of the main motor M1 is started, the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251 and 261 start to rotate. At this time, the developing motor M2 stops rotating and the developing roller 241 and the anilox roller 242 are stopped rotating. In this state, the developing device 24 is separated from the photosensitive drum 21 (a broken line position in FIG. 1). ). Further, the tip blade of the intermediate transfer member cleaning unit 39 is positioned at a position separated from the surface of the intermediate transfer member 31 (see FIG. 4).

  Then, at timing T 1 when the rotation of the photosensitive drum 21 becomes a steady state, the charging bias is applied to the charger 22, the squeeze bias is applied to the squeeze rollers 251 and 261, and the primary transfer bias to the intermediate transfer member 31. Application is performed. At the same time or subsequently, application of a reverse bias to the secondary transfer roller 42 is started. As described later, by applying a reverse bias to the secondary transfer roller 42 in this way, the patch image is secondary transferred even if the patch image formed on the intermediate transfer body 31 passes through the secondary transfer nip NP2. It is possible to perform the idling operation while preventing the secondary transfer roller 42 from being contaminated by preventing transfer to the roller 42. The reverse bias application is stopped after the patch image has passed through the secondary transfer nip NP2 twice as will be described later.

  After a predetermined time has elapsed from the timing T1, the development motor M2 starts to rotate, the development roller 241 and the anilox roller 242 rotate, and the application of the development bias is started. From the subsequent timing T2, the developing device separation contact motor M3 operates for a predetermined time (in this embodiment, 2 seconds). Upon receiving this rotational driving force, the development device separation contact mechanism 240 causes the development device 24 to move to the photosensitive drum 21. Then, the developing roller 241 is brought into contact with the surface of the photosensitive drum 21 (contact state). Thereby, the development preparation is completed.

  At the next timing T3, an image signal corresponding to the solid patch image is given to the exposure unit 23, and a latent image corresponding to the solid patch image is formed on the surface of the photosensitive drum 21. In this embodiment, in order to generate an image signal corresponding to the solid patch image, the image signal generation unit is provided in the memory of the controller 10, but the supply mode of the image signal corresponding to the patch image is limited to this. Is not to be done. This also applies to the subsequent embodiments.

  When the latent image moves to the development position as the photosensitive drum 21 rotates, the latent image is developed by the liquid developer (liquid carrier CL + toner T), and a solid patch image PI is formed on the surface of the photosensitive drum 21. The Further, the patch image PI is conveyed to the primary transfer nip portion NP1 and is primarily transferred to the intermediate transfer member 31. When the solid patch image PI immediately after the primary transfer is observed in detail, as shown in FIG. 4A, the upper surface of the toner layer constituting the solid patch image PI is covered with the liquid carrier CL, and the entire surface of the patch image PI is mirror-finished. Often in a state. As the intermediate transfer member 31 rotates, the solid patch image PI moves to a position facing the optical sensor PS, that is, to a detection range of the optical sensor PS ((b) in the figure). At this stage, the solid patch image PI is moved by the optical sensor PS. Even if the image density of PI is detected, the light projected from the projector of the optical sensor PS is reflected on the surface of the solid patch image PI, that is, the liquid carrier surface Sc, and the density of the solid patch image PI cannot be detected accurately.

  Therefore, in the present embodiment, the patch image PI is not detected by the optical sensor PS in the first round when the solid patch image PI passes through the detection range of the optical sensor PS, and the signal output from the optical sensor PS in the second round. Based on the concentration detection. That is, at the timing T4 when the leading edge of the solid patch image PI enters the secondary transfer nip NP2, the developing device separation contact motor M3 operates for a predetermined time (in this embodiment, 2 seconds), and receives this rotational driving force to develop. The device separation contact mechanism 240 moves the developing device 24 from the photosensitive drum 21 to the retracted position, and separates the developing roller 241 from the surface of the photosensitive drum 21. Then, a reverse bias is applied to the secondary transfer nip portion NP2, the tip blade of the intermediate transfer member cleaning unit 39 is separated from the surface of the intermediate transfer member 31, and the developing roller 241 is separated from the surface of the photosensitive drum 21. In this state, the solid patch image PI is passed through the secondary transfer nip portion NP2 and the primary transfer nip portion NP1. As a result, as shown in FIG. 6C, the surface of the liquid carrier CL is peeled off at the secondary transfer nip portion NP2 and the primary transfer nip portion NP1, and the toner T constituting the solid patch image PI is transferred to the surface of the patch image PI. Exposed to. Then, as shown in FIG. 4D, a signal output from the optical sensor PS while the solid patch image PI passes through the detection range of the optical sensor PS is given to the controller 10 so that the image density of the solid patch image PI is accurate. Is required.

  When the solid patch image PI passes through the secondary transfer nip portion NP2 after passing through the second round sensor, the application of the charging bias, the developing bias, the squeeze bias, the primary transfer bias, and the reverse bias is stopped at a timing T5. Subsequently, the rotation of the main motor M1 is stopped, and the rotation of the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251 and 261 is temporarily stopped.

  Then, at timing T6, the cleaner separation / contact motor M4 operates for a predetermined time, and upon receiving this rotational driving force, the cleaner separation / contact mechanism 320 rotates the intermediate transfer member cleaning unit 39 to move the tip blade to the intermediate transfer member 31. Abut on the surface of Thereafter, the main motor M1 is temporarily operated while applying the squeeze bias, the primary transfer bias, and the reverse bias again for a predetermined time (= T8-T7), and the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251, 261. Rotate. As a result, the solid patch image PI that has passed through the secondary transfer nip NP2 moves to a cleaning position where the tip blade of the intermediate transfer member cleaning unit 39 contacts the surface of the intermediate transfer member 31, and is removed by the intermediate transfer member cleaning unit 39. Is done.

  The bias application and driving of the main motor M1 are stopped after the removal of the solid patch image PI, and the cleaner separation / contact motor M4 is operated for a predetermined time at a timing T9. 320 rotates the intermediate transfer member cleaning unit 39 to separate the tip blade from the surface of the intermediate transfer member 31. Thus, the formation of the solid patch image PI and the density detection are completed.

  As described above, in the first embodiment, immediately after the solid patch image PI is formed on the intermediate transfer member 31, the solid patch image PI is not detected by the optical sensor PS, but the intermediate transfer member 31 is idled to form a solid patch. When the image PI passes the detection range of the optical sensor PS for the second time, the controller 10 obtains the image density of the image PI based on a signal output from the optical sensor PS. Further, the developing device 24 is moved away from the photosensitive drum 21 to the retracted position while the intermediate transfer member 31 is idling, and the supply of the liquid developer to the photosensitive drum 21 is stopped. In this state, the solid patch image PI is primarily transferred. Since the toner passes through the nip portion NP1, the liquid carrier CL present on the surface layer portion of the solid patch image PI is peeled off when the solid patch image PI passes through the primary transfer nip portion NP1, so that the toner T constituting the patch image PI becomes the patch image PI. Exposed on the surface. In this way, the solid patch image PI is detected by the optical sensor PS after preventing the surface of the patch image PI from becoming a mirror surface. Therefore, the solid patch image PI can be accurately detected by the optical sensor PS, and the density of the solid patch image can be obtained with high accuracy based on the detection result.

  Thus, in the first embodiment, the photosensitive drum 21 corresponds to the “first latent image carrier” of the present invention, and the intermediate transfer member 31 corresponds to the “transfer medium” of the present invention. Further, the primary transfer nip portion NP1 formed by contacting the photosensitive drum 21 with the intermediate transfer member 31 corresponds to the “first transfer nip portion” of the present invention. The developing roller 241 corresponds to the “first developer carrier” of the present invention. Further, the developing device separation contact mechanism 240 and the development device separation contact motor M3 constitute the “developer carrier moving portion” of the present invention. Further, the optical sensor PS corresponds to the “detection unit” of the present invention.

  FIG. 5 is a diagram showing a second embodiment of the image forming apparatus according to the present invention. FIG. 6 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped to form a color image, and black (K). A monochrome mode in which a monochrome image is formed using only toner can be selectively executed. In this image forming apparatus, when an image forming instruction is given from an external device such as a host computer to a controller 10 having a CPU, a memory, etc., the controller 10 controls each part of the apparatus to execute a predetermined image forming operation, and copy An image corresponding to the image formation command is formed on a sheet-like recording medium RM such as paper, transfer paper, paper, and an OHP transparent sheet.

  Each of the image forming stations 2Y, 2M, 2C, and 2K has the same structure and function except for the toner color, and the configuration around the photosensitive drum 21 is basically the same as that of the first embodiment. . Therefore, in FIG. 5, in order to make the drawing easier to see, reference numerals are given only to the components constituting the image forming station 2 </ b> C, and description of reference numerals to be attached to the other image forming stations 2 </ b> Y, 2 </ b> M and 2 </ b> K is omitted. Further, the same configuration as that of the first embodiment is denoted by the same or corresponding reference numerals, and the description of the configuration is omitted. Further, in the following description, the structure and operation of the image forming station 2C will be described with reference to the reference numerals attached to FIG. 5, but the structure and operation of the other image forming stations 2Y, 2M, and 2K also differ in toner color. It is the same except that.

  The image forming station 2C is provided with a photosensitive drum 21 on which a cyan toner image is formed. The photosensitive drum 21 is arranged so that its rotation axis is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 5), and at a predetermined speed in the direction of arrow D21 in FIG. Driven by rotation.

  Around the photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and an electrostatic latent image is formed by exposing the surface of the photosensitive drum 21 according to an image signal. , A developing unit 24 that visualizes the electrostatic latent image as a toner image, a first squeeze portion 25, a second squeeze portion 26, and a belt-like intermediate transfer member. A primary transfer unit 3 that performs primary transfer to 31 and a cleaner blade 27 that cleans the surface of the photoconductor drum 21 after transfer are respectively rotated in the rotation direction D21 (clockwise in FIG. 5) of the photoconductor drum 21. It is arranged along.

  As described above, the configuration around the photosensitive drum 21 is basically the same as that of the first embodiment. However, in the second embodiment, four developing devices 24 are provided to form a four-color toner image, and an intermediate portion is provided. Four primary transfer nip portions NP1y, NP1m, NP1c, and NP1k are provided for transferring to the transfer body 31. Therefore, in the second embodiment, the four developing devices 24 are connected to the developing device separating / contacting mechanisms 2401 to 2404, respectively, and the four developing device separating / contacting motors M31 to M34 are provided. The device 24 can be brought into and out of contact with the photosensitive drum 21 independently. For example, in response to the rotational driving force from the developing unit separation contact motor M33 being transmitted to the development unit separation contact mechanism 2403, in the cyan image forming station 2C, the development unit 24 displays the latent image on the photosensitive drum 21. It can reciprocate between a developing position for developing and a retracted position away from the photosensitive drum 21. Therefore, when the developing device 24 is moved to the retracted position and positioned, the supply of new liquid developer to the photosensitive drum 21 is stopped during that time. In this respect, the image forming stations 2Y, 2M, and 2K for the other colors are exactly the same.

  In addition, four primary transfer nip portions NP1y, NP1m, NP1c, and NP1k are provided for transfer to the intermediate transfer member 31, and are configured as follows. That is, the intermediate transfer member 31 is an endless belt as an image carrier that can temporarily carry a toner image on its surface, more specifically on its outer peripheral surface, and a plurality of rollers 32, 33, 34, 35 and 36. It is stretched over. Among these, the roller 32 is connected to the main motor M1 and functions as a belt driving roller for driving the intermediate transfer member 31 in the direction of the arrow D31 in FIG.

  As will be described in detail later, among the rollers 32 to 35 over which the intermediate transfer body 31 is stretched, only the belt drive roller 32 is driven by the main motor M1, and the other rollers 33 to 36 are drive sources. The driven roller does not have Further, the belt driving roller 32 winds the intermediate transfer member 31 on the downstream side of the primary transfer position TR1 and the upstream side of the secondary transfer position TR2 described later in the belt moving direction D31.

  The primary transfer unit 3 includes a primary transfer backup roller 37, and the primary transfer backup roller 37 is disposed to face the photosensitive drum 21 with the intermediate transfer member 31 interposed therebetween. At the primary transfer position TR1 where the photosensitive drum 21 and the intermediate transfer member 31 are in contact, the outer peripheral surface of the photosensitive drum 21 is in contact with the intermediate transfer member 31 to form the primary transfer nip portion NP1c. Then, the toner image on the photosensitive drum 21 is transferred to the outer peripheral surface of the intermediate transfer member 31 (the lower surface at the primary transfer position TR1). Thus, the cyan toner image formed by the image forming station 2C is transferred to the intermediate transfer member 31. Similarly, the toner images are transferred at the other image forming stations 2Y, 2M, and 2K, so that the toner images of the respective colors are sequentially superimposed on the intermediate transfer member 31 to form a full-color toner image. On the other hand, when a monochrome toner image is formed, the toner image is transferred to the intermediate transfer member 31 only in the image forming station 2K corresponding to the black color. Further, as will be described later, solid patch images formed by the image forming stations 2Y, 2M, 2C, and 2K are primarily transferred to the intermediate transfer member 31 at the primary transfer nip portion.

  The toner image transferred to the intermediate transfer member 31 in this way is conveyed to the secondary transfer position TR2 via the winding position around the belt driving roller 32. At the secondary transfer position TR2, the secondary transfer roller 42 is disposed opposite to the roller 34 around which the intermediate transfer body 31 is wound, with the intermediate transfer body 31 interposed therebetween, and the surface of the intermediate transfer body 31 and the transfer roller 42 are disposed. The surface is in contact with each other to form the secondary transfer nip portion NP2. That is, the roller 34 functions as a secondary transfer backup roller. The rotation shaft of the backup roller 34 is supported elastically by a pressing portion 345 which is an elastic member such as a spring and can be moved toward and away from the intermediate transfer member 31.

  At the secondary transfer position TR2, the single-color or multi-color toner images formed on the intermediate transfer member 31 are transferred from the pair of gate rollers 51 to the recording medium RM conveyed along the conveyance path PT. Further, the recording medium RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 42 to the fixing unit 7 provided on the transport path PT. In the fixing unit 7, heat or pressure is applied to the toner image transferred to the recording medium RM to fix the toner image on the recording medium RM.

  Of the rollers around which the intermediate transfer body 31 is stretched, between the belt drive roller 32 and the secondary transfer backup roller 34, that is, on the downstream side of the belt drive roller 32 winding position in the belt moving direction D31, In addition, the driven roller 33 provided on the upstream side of the winding position of the secondary transfer backup roller 34 is a tension roller that adjusts the tension of the intermediate transfer member 31 with its rotating shaft elastically supported by a spring 331. . More specifically, the rotation shaft of the tension roller 33 is elastically supported by a spring 331 that can expand and contract in a direction substantially perpendicular to a virtual plane that is in contact with both the outer peripheral surface of the drive roller 32 and the outer peripheral surface of the secondary transfer backup roller 34. Thus, the tension roller 33 is movable by a predetermined amount in the same direction while the intermediate transfer member 31 is wound around. In a steady state, the tension roller 33 is urged by a spring 331 so as to push the intermediate transfer member 31 stretched between the belt driving roller 32 and the secondary transfer backup roller 34 outward. Yes.

  The tension roller 33 is in contact with the intermediate transfer member 31 from the inner side of the intermediate transfer member 31, that is, from the back side opposite to the surface that is the image carrying surface of the intermediate transfer member 31. The reason is as follows. First, the contact with the opposite side of the image carrying surface causes the tension roller 33 to disturb the toner image carried on the intermediate transfer member 31, or to be contaminated by the toner remaining on the intermediate transfer member 31. Absent. In order to increase the tension adjustment effect by the tension roller, it is effective to increase the winding angle of the intermediate transfer member 31. However, the tension roller is brought into contact with the image carrying surface and the winding angle is increased. If it is going to be, it is necessary to give the surface of the intermediate transfer body 31 a large negative curvature, there is a concern about the influence on the toner image, and there is a problem in the structure. For these reasons, the tension roller 33 is in contact with the back surface of the intermediate transfer member 31.

  Further, an intermediate transfer member cleaning unit 39 is provided to face one of the rollers 35 provided on the downstream side of the secondary transfer position TR2 in the transport direction D31 of the intermediate transfer member 31. More specifically, the intermediate transfer member cleaning unit 39 is in contact with the surface of the intermediate transfer member 31 wound around the roller 36 and removes deposits such as residual liquid carrier and toner, and the cleaning roller 391. And a blade 392 that scrapes off deposits on the roller 391. Further, a belt cleaning blade 393 is provided at a position downstream of the cleaning roller 391 so as to be able to be separated from and contacted with the intermediate transfer body 31 and finally remove the residue that the cleaning roller 391 could not remove. Yes. In the second embodiment, as in the first embodiment, the intermediate transfer member cleaning unit 39 is connected to the cleaner separation / contact mechanism 320, and the rotational driving force from the cleaner separation / contact motor M4 is applied to the cleaner separation / contact mechanism 320. The cleaning roller 391 and the belt cleaning blade 393 of the intermediate transfer member cleaning unit 39 can be separated from and brought into contact with the surface of the intermediate transfer member 31 in accordance with the transmission to the contact mechanism 320. Therefore, the toner and the liquid carrier remaining on the surface of the intermediate transfer body 31 can be removed by the cleaning roller 391 and the belt cleaning blade 393 coming into contact with the surface of the intermediate transfer body 31. As will be described later, the patch image formed on the surface of the intermediate transfer member 31 is allowed to pass through the intermediate transfer member cleaning unit 39 and sent to the primary transfer nips NP1y, NP1m, NP1c, and NP1k as described later. It is possible.

  In the present embodiment, the photosensitive drum 21 having a diameter of 78 mm is used, whereas the intermediate transfer member 31 uses an intermediate transfer belt having a circumferential length of 1890 mm. In addition, drivers 11, 12, 131 to 134, and 14 are provided to drive and control the motors M1, M2, M31 to M34, and M4 in accordance with operation commands from the controller 10, respectively. By driving M1, the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251 and 261 are rotationally driven so that the process speed becomes 250 (mm / sec).

  In the image forming apparatus 1 configured as described above, it is desirable to form an image under appropriate image forming conditions as in the image forming apparatus of Patent Document 1 and the first embodiment. Therefore, as in the same apparatus, a solid patch image is formed, and the image density of the solid patch image is detected by the optical sensor PS, and the controller 10 forms an image forming condition for forming a good high density image based on the detection result. Ask for. However, in this embodiment, in order to suppress the influence of the liquid carrier and accurately obtain the image density of the solid patch image, the intermediate transfer member 31 is rotated only once around the development unit 24 while being separated from the photosensitive drum 21 after the patch image is formed. It is spinning. Hereinafter, the formation and density detection operation of the first yellow solid patch image will be described in detail with reference to FIGS.

  FIG. 7 is a timing chart showing operations of yellow patch image formation and density detection in the image forming apparatus shown in FIG. FIG. 8 is a schematic diagram showing the operation of the image forming apparatus shown in FIG. In the image forming apparatus 1 according to this embodiment, the controller 10 controls each part of the apparatus according to a program stored in a memory (not shown) of the controller 10 to form a yellow (first color) solid patch image and detect the density. Run as follows: That is, when the operation of the main motor M1 is started, the photosensitive drum 21, the intermediate transfer body 31, and the squeeze rollers 251 and 261 start rotating for all colors, and the driving roller 32 rotates and the intermediate transfer body 31 moves. It starts to move around in the direction D31. At this time, the developing motor M2 stops rotating, and the developing roller 241 and the anilox roller 242 are stopped in rotation for all colors. In this state, the developing device 24 is located at a retracted position away from the photosensitive drum 21. is doing. Further, the cleaning roller 391 and the belt cleaning blade 393 of the intermediate transfer member cleaning unit 39 are positioned at positions separated from the surface of the intermediate transfer member 31.

  Then, at timing T 1 when the rotation of the photosensitive drum 21 becomes a steady state, the charging bias is applied to the charger 22, the squeeze bias is applied to the squeeze rollers 251 and 261, and the primary transfer bias to the intermediate transfer member 31. Application is performed. At the same time or subsequently, application of a reverse bias to the secondary transfer roller 42 is started. As described later, by applying a reverse bias to the secondary transfer roller 42 in this way, the patch image is secondary transferred even if the patch image formed on the intermediate transfer body 31 passes through the secondary transfer nip NP2. It is possible to perform the idling operation while preventing the secondary transfer roller 42 from being contaminated by preventing transfer to the roller 42. The reverse bias application is stopped after the patch image has passed through the secondary transfer nip NP2 twice as will be described later.

  After a predetermined time has elapsed from the timing T1, the development motor M2 starts to rotate, the development roller 241 and the anilox roller 242 rotate, and the application of the development bias is started. From the subsequent timing T2, the yellow (first color) developing unit separation / contact motor M31 operates for a predetermined time (in this embodiment, 2 seconds), and the developing unit separation / contact mechanism 2401 receives the rotational driving force for the yellow unit The developing device 24 is moved close to the photosensitive drum 21 to bring the developing roller 241 into contact with the surface of the photosensitive drum 21 (contact state). Thereby, the development preparation for the yellow color is completed. Note that the second-color (magenta) developer separation motor M32 remains stopped during the formation of the yellow solid patch image and density detection, which will be described later, and the downstream side of the image forming station 2Y in the moving direction D31 of the intermediate transfer member 31. The developing device 24 arranged on the side is positioned at a retracted position separated from the photosensitive drum 21. In this regard, although illustration in FIG. 7 is omitted, the third color (cyan) and the fourth color (black) are the same as the second color.

  At the next timing T3, an image signal corresponding to the solid patch image is given to the exposure unit 23, and a latent image corresponding to the solid patch image is formed on the surface of the photosensitive drum 21. In order to generate an image signal corresponding to a solid patch image, in this embodiment as well, the image signal generator is provided in the memory of the controller 10 as in the first embodiment.

  When the latent image moves to the development position as the photosensitive drum 21 rotates, the latent image is developed by the liquid developer (liquid carrier CL + toner T), and the yellow solid patch image PI becomes the surface of the photosensitive drum 21. Formed. Further, the patch image PI is conveyed to the primary transfer nip portion NP1y and is primarily transferred to the intermediate transfer member 31. When the yellow solid patch image PI immediately after the primary transfer is observed in detail, the upper surface of the toner layer constituting the solid patch image PI is covered with the liquid carrier CL as shown in FIG. Is often in a mirror state. With the rotation of the intermediate transfer member 31, the solid patch image PI has a primary transfer nip portion NP1m for the second color (magenta), a primary transfer nip portion NP1c for the third color (cyan), and a primary transfer nip portion NP1k for the fourth color (black). The optical sensor PS passes and moves to a position opposite to the optical sensor PS, that is, to the detection range of the optical sensor PS ((b) in the same figure). The light projected from the projector of the sensor PS is reflected by the surface of the solid patch image PI, that is, the liquid carrier surface Sc, and the density of the solid patch image PI cannot be detected accurately.

  Therefore, in the present embodiment, the patch image PI is not detected by the optical sensor PS in the first round when the solid patch image PI passes through the detection range of the optical sensor PS, and the signal output from the optical sensor PS in the second round. Based on the concentration detection. That is, as shown in FIG. 7, at the timing T4 when the rear end portion of the solid patch image PI passes through the primary transfer nip portion NP1m of the second color (magenta), the developing device separation contact motor M31 is set for a predetermined time (in this embodiment, 2 seconds). In response to this rotational driving force, the yellow developer unit contact mechanism 2401 moves the yellow developer unit 24 from the photosensitive drum 21 to the retracted position so that the developing roller 241 is moved from the surface of the photosensitive drum 21. Separate. Then, with the reverse bias applied to the secondary transfer nip NP2, the cleaning roller 391 and the belt cleaning blade 393 of the intermediate transfer member cleaning unit 39 are separated from the surface of the intermediate transfer member 31, and the developing roller 241 is set for all colors. The yellow solid patch image PI is passed through the secondary transfer nip portion NP2 and the primary transfer nip portions NP1y, NP1m, NP1c, and NP1k while being separated from the surface of the photosensitive drum 21. As a result, as shown in FIG. 6C, the toner T that forms the solid patch image PI by peeling off the surface layer portion of the liquid carrier CL at the secondary transfer nip portion NP2 and the primary transfer nip portions NP1y, NP1m, NP1c, and NP1k. Are exposed on the surface of the patch image PI. Then, as shown in FIG. 6D, a signal output from the optical sensor PS while the solid patch image PI passes through the detection range of the optical sensor PS is given to the controller 10, and the image density of the yellow solid patch image PI is changed. Accurately required.

  When the solid patch image PI passes through the secondary transfer nip portion NP2 after passing through the second round sensor, the application of the charging bias, the developing bias, the squeeze bias, the primary transfer bias, and the reverse bias is stopped at a timing T5. Subsequently, the rotation of the main motor M1 is stopped, and the rotation of the photosensitive drum 21, the intermediate transfer member 31, the squeeze rollers 251, 261, and the intermediate transfer member 31 is temporarily stopped.

  Then, at timing T6, the cleaner separation / contact motor M4 operates for a predetermined time, and receives the rotational driving force, the cleaner separation / contact mechanism 320 rotates the intermediate transfer member cleaning unit 39 to clean the cleaning roller 391 and the belt cleaning blade. 393 is brought into contact with the surface of the intermediate transfer member 31. After that, the main motor M1 is temporarily operated for a predetermined time from timing T7, and the squeeze bias, the primary transfer bias, and the reverse bias are applied again to rotate the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251 and 261. Let As a result, the solid patch image PI that has passed through the secondary transfer nip NP2 moves to a cleaning position where the cleaning roller 391 and the belt cleaning blade 393 of the intermediate transfer member cleaning unit 39 come into contact with the surface of the intermediate transfer member 31, and the intermediate transfer member. It is removed by the cleaning unit 39.

  The bias application and driving of the main motor M1 are stopped after the solid patch image PI is removed by cleaning, and the cleaner separating / contacting motor M4 is operated for a predetermined time. The transfer body cleaning unit 39 is rotated to separate the cleaning roller 391 and the belt cleaning blade 393 from the surface of the intermediate transfer body 31. Thus, the formation of the solid patch image PI and the density detection are completed.

  As described above, also in the second embodiment, as in the first embodiment, after the solid patch image PI is formed on the intermediate transfer member 31, the developing device 24 is separated from the photosensitive drum 21 for all colors. The transfer body 31 is rotated to pass the solid patch image PI through the secondary transfer nip NP2, the primary transfer nip NP1y, NP1m, NP1c, and NP1k. Therefore, the liquid carrier CL present on the surface layer portion of the solid patch image PI is peeled off to prevent the toner T constituting the patch image PI from being exposed from the patch image PI, that is, the surface of the patch image PI is prevented from being a mirror surface. The solid patch image PI is detected by the optical sensor PS. Therefore, the solid patch image PI can be accurately detected by the optical sensor PS, and the density of the solid patch image can be obtained with high accuracy based on the detection result.

  As described above, in the second embodiment, the yellow solid patch image PI is formed and the density is detected, and the photosensitive drum 21 of the image forming station 2Y corresponds to the “first latent image carrier” of the present invention. The primary transfer nip portion NP1y corresponds to the “first transfer nip portion” of the present invention. Further, the “developer carrying member moving portion” of the present invention is constituted by the developing device separating and contacting mechanisms 2401 to 2404 and the developing device separating and contacting motors M31 to M34. Note that when the solid patch image PI is formed and the density is detected for other toner colors, the density of the solid patch image is increased by preventing the surface of the patch image PI from being a mirror surface by performing the same as in the case of yellow. The accuracy can be obtained.

  By the way, when a toner image is formed by a wet development method in which a toner image is formed using a liquid developer (liquid carrier CL + toner T), an intermediate transfer is performed at the secondary transfer nip portion NP2 in order to obtain good transfer characteristics. It is desired that the recording medium RM is pressed against the body 31 with a high pressing force. Further, since the liquid developer is interposed, there is a high possibility that the recording medium RM is stuck to the intermediate transfer member 31 and jammed. Therefore, in the image forming apparatus 1, a secondary transfer roller 42 having a grip portion may be used as described below.

  FIG. 9 is a diagram showing an image forming apparatus according to a third embodiment of the invention. FIG. 10 is a block diagram showing an electrical configuration of the apparatus of FIG. The third embodiment is greatly different from the second embodiment in the configuration of the secondary transfer unit 4 and the operation during solid patch image PI formation and density detection, and the other configurations are the same. Therefore, the following description will focus on the differences.

  FIG. 11 is a diagram showing the configuration of the secondary transfer unit. More specifically, FIG. 11A is a perspective view showing the overall configuration of the secondary transfer unit 4, and FIG. 11B is a diagram for explaining the shape of the contact member 47. As shown in FIGS. 9 and 11A, the secondary transfer unit 4 has a secondary transfer roller 42 provided with a recess 41 formed by cutting out a part of the outer peripheral surface of the cylinder. In the secondary transfer roller 42, a rotation shaft 421 that is rotatable in the direction D 4 about the rotation shaft 4210 is disposed in parallel or substantially parallel to the rotation shaft of the secondary transfer backup roller 34.

  Further, side plates 422 and 422 are attached to both ends of the rotating shaft 421, respectively. More specifically, each of these side plates 422 and 422 has a shape in which a notch 422a is provided on a disk-shaped metal plate. As shown in FIG. 11, the notches 422 a and 422 a are attached to the rotary shaft 421 while facing each other and separated by a distance slightly longer than the width of the intermediate transfer member 31. In this way, the secondary transfer roller 42 is formed, which has a drum shape as a whole but has a recess 41 extending in parallel or substantially parallel to the rotating shaft 421 on a part of the outer peripheral surface thereof.

  Further, an elastic layer 43 such as rubber or resin is formed on the outer peripheral surface of the secondary transfer roller 42, that is, on the surface of the metal plate surface excluding the region corresponding to the inside of the recess 41. The elastic layer 43 forms a secondary transfer nip portion NP2 facing the intermediate transfer member 31 wound around the backup roller 34. At the secondary transfer nip portion NP2, the backup roller 34 is urged toward the secondary transfer portion 4 by the pressing portion 345, and between the secondary transfer portion 4 and the intermediate transfer body 31 wound around the backup roller 34. A predetermined load (60 kgf in this embodiment) is applied.

  In addition, a grip 44 for gripping the recording medium RM is disposed inside the recess 41. The gripping portion 44 includes a gripper support member 441 erected on the outer peripheral surface of the secondary transfer roller 42 from the inner bottom portion of the concave portion 41, and a gripper member supported so as to be able to contact with and separate from the distal end portion of the gripper support member 441. 442. The gripper member 442 is connected to a gripper driving unit (not shown). In response to the ungrip command from the controller 10, the gripper driving unit is actuated so that the leading end of the gripper member 442 is separated from the leading end of the gripper support member 441 and the recording medium RM is prepared for gripping or released. On the other hand, when the gripper driving unit is operated in response to a grip command from the controller 10, the leading end of the gripper member 442 moves to the leading end of the gripper support member 441 and grips the recording medium RM. In addition, about the structure of the holding part 44, it is not limited to this embodiment, You may employ | adopt other conventionally well-known holding mechanisms.

  At both ends of the secondary transfer roller 42, support members 46 are attached to the outer surfaces of the side plates 422 so that they can rotate integrally with the secondary transfer roller 42. Further, the support member 46 is formed with a planar region 461 corresponding to the recess 41. The transfer roller side contact member 470 is attached to the flat area 461, respectively. In the contact member 470, the base part 471 is attached to the support member 46, and the contact part 472 extends from the base part 471 in the normal direction of the planar region 461, and the distal end portion of the contact part 472 Extends to the vicinity of the opening side end of the recess 41. That is, when the secondary transfer roller 42 is viewed from the end of the rotating shaft 421, the contact member 470 is disposed so as to close the recess 41. Therefore, when the concave portion 41 reaches a position facing the intermediate transfer body 31 by the rotation of the secondary transfer roller 42, the contact member 470 comes into contact with the end surface of the secondary transfer backup roller 34.

  Further, as shown in FIG. 11B, the distal end peripheral surface of the contact portion 472 is formed so that the curvature Rct of the central portion of the peripheral surface on the distal end side is larger than the curvatures Rrs and Rls of both ends. . For example, in the present embodiment, the outer diameter of the secondary transfer roller 42 including the elastic layer 43 is set to about 191 mm, whereas the curvature Rct is set to 88.2 mm, and the curvatures Rrs and Rls at both ends are Both are set to 22.4 mm. The center of curvature CC of the center portion of the contact member 47 is disposed on the rotation axis of the secondary transfer roller 42, that is, the center axis 4210 of the rotation shaft 421, and the angle range α of the center portion is the opening range (60 of the recess 41). It is set to 63 °, which is slightly wider than (°). Therefore, when the secondary transfer roller 42 rotates, the concave portion 41 faces the intermediate transfer body 31 wound around the drive roller 32 over the angular range α.

The opening length (opening width) W41 of the recess 41 along the rotation direction D4 of the secondary transfer roller 42 is:
191 × π × (60/360) ≈100 mm
It is. On the other hand, in the angle range β (= 360 ° -60 °), the elastic layer 43 faces the intermediate transfer member 31 to form a nip NP as will be described below, and the secondary transfer roller 42 rotates in the rotational direction D4. The length of the elastic layer 43 along is
191 × π × {(300/360} ≈500 mm
Is set to This is so that the largest size of the recording medium RM usable in the apparatus 1 can be wound. That is, the length of the elastic layer 43 is determined to be longer than the length of the usable recording material having the maximum length along the rotational direction D4 of the secondary transfer roller 42.

In this embodiment, the length (nip width) Wnp of the nip NP along the rotation direction D4 of the secondary transfer roller 42 is about 11 mm.
(Opening width W41 of recess 41)> (nip width Wnp at nip NP)
Have the relationship. Accordingly, when the concave portion 41 of the secondary transfer roller 42 faces the intermediate transfer member 31, the transfer nip temporarily disappears.

  Since the secondary transfer backup roller 34 is configured to be movable toward and away from the secondary transfer roller 42, the recess 41 of the secondary transfer roller 42 faces the intermediate transfer body 31. Then, the secondary transfer backup roller 34 may be displaced toward the secondary transfer roller 42 side. The contact member 47 has a function of restricting such displacement of the secondary transfer backup roller 34.

  FIG. 12 is a view for explaining the operation of the contact member in this embodiment. More specifically, FIG. 12A is a view of the contact member 47 viewed from the axial direction when the concave portion 41 faces the secondary transfer position TR2, and FIG. 12B shows this in the axial direction. It is the figure seen from the orthogonal direction. As shown in FIG. 12A, the shape of the outer peripheral surface of the contact member 47 is a substantially arc shape centered on the rotation center 4210 of the secondary transfer roller 42 in the region facing the recess 41 of the secondary transfer roller 42. It has become. On the other hand, the end of the secondary transfer backup roller 34 has an outer diameter larger than the diameter of the secondary transfer backup roller 34, is coaxial with the secondary transfer backup roller 34, and is rotatable independently of this. The bearing 342 is provided. When the contact member 47 of the secondary transfer backup roller 34 faces the secondary transfer roller 42, the outer peripheral surface of the contact member 47 and the outer peripheral surface of the bearing 342 come into contact with each other, so that the pressing portion 345. The distance between the rotation center 4210 of the secondary transfer roller 42 and the surface of the intermediate transfer member 31 is regulated against the urging force.

  The elastic layer 43 forms an interval R0 from the rotation center 4210 of the secondary transfer roller 42 to the intermediate transfer member 31 when the concave portion 41 is located at the secondary transfer position TR2 and the contact member 47 is in contact with the bearing 342. The radius Rr of the secondary transfer roller 42 is set to be slightly smaller. More precisely, the interval R0 is set to be the same as the interval between the rotation center 4210 of the secondary transfer roller 42 and the intermediate transfer member 31 in the state where the secondary transfer nip NP2 is formed at the secondary transfer position TR2. Is set. Since the elastic layer 43 is elastically deformed by the pressing force of the pressing portion 345 when the secondary transfer nip portion NP2 is formed, the distance between the rotation center 4210 of the secondary transfer roller 42 and the intermediate transfer member 31 is the pressing force. This is slightly smaller than the radius Rr of the secondary transfer roller 42 in a state where no is added. In this state, that is, in the state where the secondary transfer nip portion NP2 is formed, the interval between the rotation center 4210 of the secondary transfer roller 42 and the intermediate transfer member 31 is R0. Therefore, in this embodiment, the interval between the rotation center 4210 of the secondary transfer roller 42 and the intermediate transfer body 31 is maintained at a substantially constant value R0 regardless of the rotation phase of the secondary transfer roller 42.

  A secondary transfer roller drive motor M5 is mechanically connected to the rotating shaft 421 of the secondary transfer roller. In the present embodiment, a driver 12 is provided to drive the secondary transfer roller drive motor M5. The driver 12 drives the motor M4 in accordance with a command given from the controller 10 to rotate the secondary transfer roller 42 in the direction of the clockwise direction D4 in FIG. 9, that is, the belt moving direction D31 in the width direction. The secondary transfer backup roller 34 is a driven roller having no drive source. By using the secondary transfer backup roller 34 facing the secondary transfer roller 42 that is driven by the motor as a driven roller, the secondary transfer roller 42 and the intermediate transfer body 31 in the secondary transfer nip portion NP2 or intermediate transfer. Slip between the body 31 and the secondary transfer backup roller 34 can be prevented.

  In the present embodiment, as shown in FIG. 10, a secondary transfer roller drive motor M <b> 5 is provided and is mechanically connected to the secondary transfer roller 42. When a command from the controller 10 is given to the driver 15, the secondary transfer roller drive motor M 5 is controlled by the driver 15 to rotate the secondary transfer roller 42, or the recess 41 is formed in the second position as will be described later. The positioning can be stopped in a posture toward the next transfer backup roller 34.

  In the image forming apparatus 1 according to the third embodiment, it is desired to form an image under appropriate image forming conditions as in the image forming apparatus disclosed in Patent Document 1, the first embodiment, and the second embodiment. Therefore, similarly to the second embodiment, after the solid patch image PI is formed, the circuit 10 is rotated once and then the image density of the solid patch image is detected by the optical sensor PS, and the controller 10 based on the detection result has a good high level. An image forming condition for forming a density image is obtained. However, in the present embodiment, since the secondary transfer roller 42 configured as described above is used, the secondary transfer roller 42 is positioned at a predetermined position before the solid patch image PI is formed, and the secondary transfer roller 42 The peripheral surface is separated from the intermediate transfer member 31, and solid patch image formation and density detection are performed in the separated state. Hereinafter, the solid patch image formation and density detection operation for the second magenta color will be described in detail with reference to FIG.

  FIG. 13 is a timing chart showing operations for forming a magenta patch image and detecting the density in the image forming apparatus shown in FIG. In the image forming apparatus 1 according to this embodiment, the controller 10 controls each part of the apparatus according to a program stored in a memory (not shown) of the controller 10 to form a magenta (second color) solid patch image and detect the density. Run as follows: That is, as in the second embodiment, the operation of the main motor M1 is started to rotate the photosensitive drum 21, the intermediate transfer member 31, and the squeeze rollers 251, 261, and at the same time, the controller 10 gives a control command to the driver 15. The secondary transfer roller 42 is rotated by driving the secondary transfer roller drive motor M5. Then, as shown in FIG. 12, when the concave portion 41 of the secondary transfer roller 42 faces the secondary transfer backup roller 34 and the outer peripheral surface of the secondary transfer roller 42 is separated from the intermediate transfer member 31, the secondary transfer is performed at that position. The rotation of the roller 42 is stopped and positioning is performed.

  When the solid patch image PI is formed and the density is detected while being positioned as described above, the secondary transfer roller 42 is soiled by the developer without applying a reverse bias to the secondary transfer roller 42 while the solid patch image PI is formed. Can be surely prevented. Therefore, in the third embodiment, the formation of the solid patch image PI and the density detection are performed without applying the reverse bias. That is, at timing T1 after the positioning of the secondary transfer roller 42 is completed, the charging bias is applied to the charger 22, the squeeze bias is applied to the squeeze rollers 251 and 261, and the primary transfer bias is applied to the intermediate transfer member 31. Is executed. Thereafter, as in the second embodiment, formation of a solid patch image PI and density detection are executed.

  As described above, according to the third embodiment, not only the same functions and effects as those of the second embodiment but also the following functions and effects can be obtained. That is, the intermediate transfer is performed in a state where the secondary transfer roller 42 is positioned so that the concave portion 41 of the secondary transfer roller 42 faces the intermediate transfer member 31 and the outer peripheral surface of the secondary transfer roller 42 is separated from the intermediate transfer member 31. Since the body 31 is idle, it is possible to reliably prevent the solid patch image PI formed on the intermediate transfer body 31 from adhering to the secondary transfer roller 42 and becoming dirty during the idle rotation.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the second and third embodiments, solid patch image formation and density detection are performed for each color unit. However, as in the above embodiment, solid patch image formation and density detection are performed for a plurality of colors including idle rotation. You may go. For example, in the fourth embodiment shown in FIG. 14, after the solid patch images PIy, PIm, PIc, and PIk are formed for all the colors as shown in FIG. 14A, each developing device 24 is moved away from the photosensitive drum 21. ((B) in the figure). Then, the intermediate transfer member 31 is idled in the separated state, and all the solid patch images PI are allowed to pass through the primary transfer nip portions NP1y, NP1m, NP1c, and NP1k ((c) in the figure). Then, as shown in FIG. 4D, the controller 10 causes the solid patch image PIy of each color to be based on a signal output from the optical sensor PS while the solid patch images PIy, PIm, PIc, and PIk pass through the detection range of the optical sensor PS. , PIm, PIc, and PIk may be obtained. Thereby, the effect similar to the said embodiment is acquired.

  In the second to fourth embodiments, the image forming stations 2Y, 2M, 2C, and 2K are arranged in a line. However, the arrangement relationship is not limited to this. Although four image forming stations are arranged in a line along the stretching direction of the belt-shaped intermediate transfer member 31, the number and arrangement of the image forming stations are not limited to this.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum (latent image carrier), 24 ... Developing device, 31 ... Intermediate transfer member (transfer medium), 240, 2401-2404 ... Developing device separation contact mechanism (Developing device moving part) ), CL ... Liquid carrier, D31 ... Transfer direction of transfer medium, M3, M31-34 ... Developer separation contact motor (developer mover), NP1, NP1y, NP1m, NP1c, NP1k ... Primary transfer nip PI, PIy, PIm, PIc, PIk: solid patch image, PS: optical sensor (detection unit), T: toner

Claims (7)

Forming a latent image on the first latent image carrier;
Developing the latent image formed on the first latent image carrier with a first developer carrier that carries a liquid developer containing a liquid carrier and toner particles and contacts the first latent image carrier. And
The image developed on the first latent image carrier is transferred to the transfer medium at a first transfer nip formed by bringing the first latent image carrier and the transfer medium into contact with each other.
Separating the first latent image carrier and the first developer carrier;
Moving the transfer medium on which the image has been transferred,
An image forming method, wherein a detection unit detects the image that has passed through the first transfer nip. A latent image is formed, and a second latent image carrier that forms a second transfer nip in contact with the transfer medium;
A second latent image formed on the second latent image carrier in contact with the second latent image carrier is developed with a liquid developer containing a liquid carrier and second toner particles different from the toner particles. A developer carrier of
Separating the second latent image carrier and the second developer carrier;
The transfer medium on which the image moving around is passed through the second transfer nip,
The image forming method according to claim 1, wherein the detection unit detects the image that has passed through the first transfer nip portion and the second transfer nip portion.   The image forming method according to claim 2, wherein the second latent image carrier and the second developer carrier are separated from each other when the image is transferred to the transfer medium at the first transfer nip portion. Forming a latent image on the second latent image carrier,
Developing the latent image formed on the second latent image carrier with the second developer carrier;
Transferring the second image developed on the second latent image carrier to the transfer medium at the second transfer nip;
Separating the second latent image carrier and the second developer carrier;
The transfer medium onto which the second image that moves around passes through the first transfer nip part and the second transfer nip part,
The image forming method according to claim 2, wherein the detection unit detects the second image that has passed through the first transfer nip and the second transfer nip. Having a recess on the peripheral surface, and having a transfer roller with which the peripheral surface abuts via the transfer medium and the recording material,
5. The apparatus according to claim 1, wherein when the transfer medium to which the image is transferred is rotating, the transfer medium and the transfer roller are separated from each other with the concave portion facing the recording medium. 6. The image forming method described. A first latent image carrier on which a latent image is formed;
A first developer carrier that contacts the first latent image carrier and develops the latent image with a liquid developer containing a liquid carrier and toner;
A transfer medium in contact with the first latent image carrier to form a first transfer nip portion, on which the developed image is transferred to the first latent image carrier at the first transfer nip portion; ,
A developer carrying member moving section for bringing the first developer carrying member into contact with or apart from the first latent image carrying member;
After transferring the image to the transfer medium, the developer carrier moving unit moves the first developer carrier away from the first latent image carrier and moves the transfer medium to move the image. A controller for controlling the first transfer nip to pass through;
A detector that detects the image that has passed through the first transfer nip;
An image forming apparatus comprising: A latent image is formed, and a second latent image carrier that forms a second transfer nip in contact with the transfer medium;
A second latent image formed on the second latent image carrier in contact with the second latent image carrier is developed with a liquid developer containing a liquid carrier and second toner particles different from the toner particles. A developer carrier of
The controller controls the image to pass through the second transfer nip by moving the transfer medium;
The image forming apparatus according to claim 6, wherein the detection unit detects the image that has passed through the first transfer nip portion and the second transfer nip portion.

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