JP2013101300A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of adjusting a density, without soiling a transfer member with a toner pattern, even during an image forming operation and capable of minimizing a shutter opening time.SOLUTION: A secondary transfer roller 15 can be moved between a contact position where the secondary transfer roller 15 comes into contact with an intermediate transfer belt 3 and a separation position where the secondary transfer roller 15 is separated from an image carrier, a density sensor 30 includes outer sensors 30R and 30F for detecting a toner image outside the contact area of the secondary transfer roller 15 and the intermediate transfer belt 3, and a shutter 40 and the secondary transfer roller 15 are made into three states: a state (A) where the shutter 40 is in a closed position where the sensor is blocked and the secondary transfer roller 15 is in the contact position; a state (B) where the shutter 40 is in an open position and the secondary transfer roller 15 is in the contact position; and a state (C) where the shutter is in the open position and the secondary transfer roller 15 is in the separation position.

Description

  The present invention relates to an image forming apparatus that transfers a toner image carried on the surface of an image carrier onto a transfer material by a transfer member.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile machine, or a multifunction machine having at least two functions thereof is well known. When a toner image is transferred onto the surface of a transfer material passing between the transfer roller and the image carrier, the contact type transfer roller used in such an image forming apparatus has a charging polarity of toner constituting the toner image. A reverse polarity voltage is applied, and the toner image on the surface of the image carrier is transferred onto the transfer material by the action of the electric field formed thereby.

  In this type of image forming apparatus, a toner pattern is formed on the surface of the image carrier at predetermined conditions, for example, every time when the power is turned on, and the image density is detected from the information of the detecting means that detected the image. Conventionally, density adjustment for determining the state of the image forming apparatus and controlling each element of the image forming apparatus to a state suitable for forming a toner image has been performed. For example, when a two-component developer having toner and carrier is used in a developing device that forms a toner image on the surface of the image carrier, the toner of the two-component developer is detected by detecting the image density of the toner pattern. When the density is detected and it is determined that the toner density is low, the toner is supplied to the developing container of the developing device.

  At this time, in order to perform normal density control, it is required to keep the sensor detection surface clean, but the detection surface may become dirty due to toner scattering in the apparatus during the printing operation. Therefore, a configuration in which a shutter member that protects the detection surface is provided and the shutter is opened only when a density adjustment operation is necessary is described in Patent Document 1 and the like.

  Further, in an image forming apparatus using a transfer roller of a type in contact with the surface of the image carrier, when the toner pattern described above is formed on the surface of the image carrier, the toner of the pattern is transferred when the toner pattern reaches the transfer roller. When the transfer material adheres to the roller and the transfer material is fed between the image carrier and the transfer roller, the toner attached to the transfer roller may adhere to the back surface of the transfer material, and the transfer material may be soiled by the toner.

  Therefore, conventionally, when the toner pattern passes through the portion of the transfer member, the transfer member is separated from the surface of the image carrier to prevent the toner of the toner pattern from adhering to the transfer member.

  However, with such a configuration, there is a problem that density adjustment is limited to a non-printing operation such as when the machine power is turned on or after printing is completed. This is because the density adjustment pattern formed on the image carrier adheres to the transfer roller, and the density adjustment is performed in a state where the transfer roller is separated from the image carrier in order to avoid the problem of fouling the back side of the printed paper. This is because of Therefore, there is a problem that the density adjustment by performing a predetermined number of prints during continuous printing or the like must be performed after the printing operation is temporarily stopped and the transfer roller is separated.

  In view of the above-described conventional circumstances, the present invention can adjust the density without staining the transfer member with a toner pattern even during an image forming operation, and can minimize the opening time of the shutter that covers the sensor detection surface. It is an object of the present invention to provide an image forming apparatus that can be used.

  To achieve the above object, the present invention provides an image carrier that carries a toner image on its surface, a sensor that detects a toner image on the image carrier, a closed position that protects the detection surface of the sensor, and a sensor And a transfer member that contacts the image carrier, and a toner image on the image carrier between the image carrier and the transfer member. In the image forming apparatus for transferring the image to the transfer material, the transfer member is movable between a contact position where the transfer member contacts the image carrier and a separated position away from the image carrier, and the sensor includes the transfer member and the image. An external sensor for detecting a toner image outside the contact area of the carrier is provided, and the shutter and the transfer member are transferred when the shutter is in the closed position and the transfer member is in the contact position (A), and when the shutter is in the open position. A state where the member is in a contact position (B); Yatta proposes an image forming apparatus characterized by taking three states with state of the separated position transfer member in the open position (C).

  According to the present invention, the density can be adjusted without smearing the transfer member with the toner pattern even during the image forming operation, a stable and good image can be obtained, and the detection surface of the sensor during the operation that is easily contaminated is protected. An image forming apparatus capable of minimizing the shutter opening time is provided.

1 is a schematic configuration diagram illustrating an image forming apparatus according to the present invention. FIG. 2 is an explanatory plan view showing a main part of an intermediate transfer unit according to an embodiment of the present invention. FIG. 6 is an explanatory diagram illustrating an intermediate transfer unit in a state (C). FIG. 6 is an explanatory diagram illustrating an intermediate transfer unit in a state (B). FIG. 6 is an explanatory diagram illustrating an intermediate transfer unit in a state (A). It is explanatory drawing which shows the positional relationship of the filler at the time of a state (C), and a transmission type photosensor. It is explanatory drawing which shows the positional relationship of the filler at the time of a state (B), and a transmission type photosensor. It is explanatory drawing which shows the positional relationship of the filler and transmission photosensor in a state (A). It is explanatory drawing which shows a transmissive photosensor. It is explanatory drawing which shows other embodiment of this invention. FIG. 15 is an explanatory plan view showing a main part of an intermediate transfer unit in a state (C) in still another embodiment of the present invention. It is plane explanatory drawing which shows the time of the state (B) in further another embodiment of this invention. It is plane explanatory drawing which shows the time of the state (A) in other embodiment of this invention. It is a figure which shows the cam diagram in the cam part of the end surface cam with a gear shown in FIG. FIG. 12 is an explanatory plan view showing a main part of an intermediate transfer unit in a state (E) in still another embodiment of the present invention. (A) is a state (D), (b) is a state, (c) is explanatory drawing which shows the relationship between the sensor and shutter at the time of a state (F). FIG. 16 is an explanatory plan view showing a main part of the intermediate transfer unit in the state (F) in the embodiment of FIG. It is a figure which shows the cam diagram in the cam part of the end surface cam with a gear shown in FIG. It is explanatory drawing which shows the transmission type photosensor and filler in the state E. It is explanatory drawing which shows the transmission type photosensor and filler in the state F. It is explanatory drawing which shows the relationship between the sensor and shutter in the state (D) in the modification of embodiment of FIG. It is explanatory drawing which shows the relationship between the sensor and shutter in the state (E) in the modification of embodiment of FIG. It is explanatory drawing which shows the relationship between the sensor and shutter at the time of the state (F) in the modification of embodiment of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view showing an example of an image forming apparatus configured as an electronic copying machine, a printer, a facsimile, or a composite machine of these. An image forming unit having first to fourth photoconductors 2Y, 2C, 2M, and 2K formed in a drum shape is disposed in the image forming apparatus main body 1 shown here. An intermediate transfer belt 3 as an image carrier made up of an endless belt is disposed facing the body. The intermediate transfer belt 3 is wound around two rollers 4 and 5, and one of the rollers is driven counterclockwise in FIG.

  The image forming apparatus illustrated in FIG. 1 includes the first to fourth four photoconductors 2Y to 2K, but the number of photoconductors may be four or more. In the image forming apparatus shown in FIG. 1, the intermediate transfer belt 3 is wound around two rollers 4 and 5, but the number of rollers may be three or more.

  The first to fourth photoconductors 2Y to 2K are rotated in the counterclockwise direction in FIG. 1 while being in contact with the surface of the intermediate transfer belt 3, respectively. At this time, the first photoconductor 2Y is charged to a predetermined polarity by the charging roller 6, and a light-modulated laser beam 7 emitted from an optical writing unit (not shown) is irradiated on the charging surface. As a result, an electrostatic latent image is formed on the first photoconductor 2Y, and this electrostatic latent image is visualized as a yellow toner image by the developing device 8. On the other hand, a transfer voltage is applied to the primary transfer roller 9, whereby the toner image on the photoreceptor 2Y is primarily transferred onto the surface of the intermediate transfer belt 3 that is rotationally driven in the direction of the arrow. The residual transfer toner adhering to the photoreceptor 2C after the toner image transfer is removed by the cleaning device 10.

  In exactly the same manner as described above, a cyan toner image, a magenta toner image, and a black toner image are formed on the second to fourth photoconductors 2C, 2M, and 2K, respectively, and each toner image is transferred to a yellow toner image. Then, the toner images are sequentially superimposed and transferred onto the intermediate transfer belt 3, and four color toner images are carried on the intermediate transfer belt 3.

  On the other hand, a paper feeding device 11 is arranged at the lower part of the image forming apparatus main body 1. The paper feeding device 11 includes a paper feeding tray 12 containing a recording medium P made of, for example, a recording medium or a resin film, and a topmost sheet. The uppermost recording medium P is sent out in the direction of the arrow by the rotation of the paper feeding roller 13. The sent recording medium is fed between the intermediate transfer belt 3 and the secondary transfer roller 15 as a transfer member disposed on the intermediate transfer belt 3 at a predetermined timing by the rotation of the positioning roller pair 14. A transfer voltage is applied to the secondary transfer roller 15, whereby the superimposed toner image on the intermediate transfer belt 3 is secondarily transferred to the recording medium. The secondary transfer roller 15 is pressed against the driven roller 5 via the intermediate transfer belt 3 and is rotationally driven in the clockwise direction in FIG. 1 while being in contact with the surface of the intermediate transfer belt 3. The recording medium P is fed between the secondary transfer roller 15 and the intermediate transfer belt 3, and the superimposed toner image on the intermediate transfer belt 3 is secondarily transferred to the recording medium P. The transfer member is not limited to the transfer roller but may be a transfer belt or the like.

  The recording medium P to which the toner image has been transferred passes through the fixing device 16, and at this time, the toner image on the recording medium is fixed to the recording medium by the action of heat and pressure. The recording medium that has passed through the fixing device 16 is discharged to a paper discharge unit on the image forming apparatus main body 1.

  In the image forming apparatus configured as described above, the process speed of the intermediate transfer belt 3 is adjusted to 200 mm / sec. The primary transfer roller 9 is disposed at a contact portion between the photoreceptor 1 and the intermediate transfer belt 3 and is pressed by a spring 21. The load is set to 1N on one side. A predetermined transfer bias is applied to the primary transfer roller 9 by each voltage applying device 22 (only the yellow image forming portion is shown). In this example, + 1800V is set to be applied.

The intermediate transfer belt 3 is made of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) or the like in a single layer or a plurality of layers, and is made of conductive material such as carbon black. The volume resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹² Ωcm, and the surface resistivity is adjusted to be in the range of 10 ⁹ to 10 ¹³ Ωcm. If necessary, a release layer may be coated on the surface of the intermediate transfer belt 3. Materials used for the coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluorocarbon resin), FEP (four-fluorocarbon). Fluorine resin such as ethylene fluoride-propylene hexafluoride copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto. The method of manufacturing the intermediate transfer belt 3 includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary.

  If the volume resistivity of the intermediate transfer belt 3 exceeds the above-described range, the bias necessary for transfer increases, which increases the power supply cost. In addition, the charge potential of the intermediate transfer belt 3 becomes high in the transfer process, the recording medium peeling process, and the like, and self-discharge becomes difficult. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays quickly, which is advantageous for static elimination by self-discharge, but toner scatter occurs because the current during transfer flows in the surface direction. End up. Therefore, the volume resistivity and surface resistivity of the intermediate transfer belt 3 in the present invention must be within the above ranges. The volume resistivity and the surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP), and the intermediate transfer belt 3. The measured value 10 seconds after applying the voltage of 100V (surface resistivity is 500V) to the front and back of the was used.

  Reference numeral 23 denotes a belt cleaning unit for cleaning the intermediate transfer belt 3. A cleaning blade 24 made of urethane rubber is pressed against the intermediate transfer belt 3 to block the toner and clean it.

  Reference numeral 25 denotes a brush roller for applying the lubricant 26 to the intermediate transfer belt 3. A counter roller 27 is disposed at a position facing the brush roller 25 and the intermediate transfer belt 3. The counter roller 27 rotates with the intermediate transfer belt 3, and the driving of the brush roller 25 is transmitted from the counter roller 27 by a gear (not shown). The counter roller 27 is made of metal and has a diameter of φ8.

  As the lubricant 26, a fatty acid metal salt having a linear hydrocarbon structure is used. The fatty acid metal salt contains at least one fatty acid selected from stearic acid, palmitic acid, myristic acid and oleic acid, and at least one metal selected from zinc, aluminum, calcium, magnesium and lithium The fatty acid metal salt containing is mentioned. Among them, zinc stearate is the most preferable material in terms of cost, quality stability, and reliability because it is produced on an industrial scale and has been used in many fields. However, the higher fatty acid metal salt generally used industrially is not a single compound composition of its name, but includes other fatty acid metal salts, metal oxides, and free fatty acids that are more or less similar. Fatty acid metal salts are no exception.

  In order to scrape off the lubricant 26 with the brush roller 25, the lubricant 26 is pressed against the brush roller 25 by a compression coil spring 28 with a force of 1N to 2N. Further, in this example, the brush roller 25 is made by bonding a flock of polyester on a metal core such as SUS, and the density of the hair is about 100,000 per square inch and the length of the hair is 2.5 mm. The outer diameter is 9 m. The brush roller 25 is rotationally driven with a speed difference from the intermediate transfer belt 3 in order to improve the coating efficiency. In this embodiment, the rotation direction is the same as the belt moving direction, and the rotation speed is set to 220 mm / sec. This is a value of 10% increase of the belt moving speed of 200 mm / sec.

  The lubricant 26 is applied to maintain the friction coefficient of the intermediate transfer belt 3 in an appropriate range. In this example, the appropriate range is 0.2 to 0.35. When the lubricant is not applied, the friction coefficient is increased by the toner that has not been transferred to the recording medium P, and the transfer residual toner passes through the cleaning blade 24, resulting in poor cleaning or the cleaning blade 24 turning up. Further, when the friction coefficient of the intermediate transfer belt 3 is low, there is a problem in that the transfer efficiency to the recording medium is reduced and a part of the image is lost (blurred image, worm-eaten image).

The secondary transfer roller 15 is configured by coating an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material on a metal core such as SUS. Here, if the resistance value of the secondary transfer roller 15 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, resulting in an increase in power supply cost. . In addition, since a high voltage is applied, a discharge occurs in the gap before and after the transfer portion nip, so that white spots are lost due to the discharge on the halftone image. On the other hand, if the resistance value of the secondary transfer roller 15 is below the above range, transferability between a multi-color image portion (for example, a three-color superimposed image) and a single-color image portion existing on the same image cannot be achieved. This is because the resistance value of the secondary transfer roller 15 is low, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. Since a voltage value higher than the voltage is required, setting a voltage that can transfer a plurality of color image portions causes an excessive transfer current in a single-color image, resulting in a reduction in transfer efficiency. The resistance value of the secondary transfer roller 15 is measured by installing the secondary transfer roller 15 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. In this state, it was calculated from the value of the current flowing when a voltage of 1000 V was applied between the metal core and the metal plate. The secondary transfer roller 15 is in contact with the driven roller 5 with a load of 50 N, and is configured to rotate with the roller 5. In order to transfer the toner image on the intermediate transfer belt 3 to the recording medium P, a transfer bias is applied to the roller 5 facing the secondary transfer by the voltage applying device 29. In this example, constant current control is performed, and the current setting value is −30 μA.

  1 to 3, a sensor for detecting a toner image formed on the belt is provided on the apparatus main body side immediately after the downstream side of the secondary transfer portion in the rotation direction of the intermediate transfer belt 3. The sensor is a density sensor 30 that detects the density of the detected toner image. As clearly shown in FIG. 2, two density sensors 30 are provided, one on each end side in the width direction of the intermediate transfer belt 3, and an operation panel (not shown) is shown below in FIG. On the front side of the arranged image forming apparatus, the density sensor is provided with a density sensor 30F on the front side of the image forming apparatus and a density sensor 30R on the back side. Note that the density sensor will be described with the reference numeral 30 when collectively describing, and F on the front side and R on the back side when describing the front side and the back side separately.

  This density sensor 30 is an optical density sensor composed of a light emitting element and a light receiving element, and its detection surface is set to be disposed about 5 mm above the surface of the intermediate transfer belt 3. If toner or the like adheres to the detection surface of the density sensor 30 and becomes dirty, the detection accuracy decreases. Therefore, a shutter 40 that protects the detection surface from contamination is provided in the apparatus main body 1. As shown in FIG. 2, the shutter 40 viewed from above is formed in a long rectangular shape, and the length in the width direction of the intermediate transfer belt 3, which is the longitudinal direction thereof, is longer than the belt width (see FIG. 2). ), Both sensors 30R and 30F can be moved simultaneously to open and close. The installation positions of the density sensors 30R and 30F will be described later.

  Next, the opening / closing mechanism of the shutter 40 of the density sensor 30, the contact / separation mechanism of the secondary transfer roller 15, and the arrangement relationship thereof will be described with reference to FIGS. 3 is an enlarged view of the density sensor and the secondary transfer portion of FIG. 1, and FIG. 2 is a view of the portion shown in FIG. 3 as viewed from above.

  2 and 3, the shutter 40 that covers the detection surfaces of the density sensors 30R and 30F and protects them from dirt and the like enters the gap between the density sensors 30R and 30F and the intermediate transfer belt 3, and detects the detection surface of the density sensor 30. A DC brush motor 31 (hereinafter referred to as a motor) capable of normal rotation and reverse rotation is movable as a drive source. Used. The motor 31 is disposed on the back side of the image forming apparatus, and an output gear 32 is attached to its output shaft. The output gear 32 meshes with a large-diameter gear 33A of a main body coupling gear 33 configured as a two-stage gear provided in the image forming apparatus main body 1. When the intermediate transfer unit U is set in the image forming apparatus main body 1, the main body coupling gear 33 is a small-diameter gear of a unit side coupling gear whose small-diameter gear 33 </ b> B is configured as a two-stage gear provided in the intermediate transfer unit U. Mesh with 34B.

  The unit side coupling gear 34 extends in parallel with the width direction of the intermediate transfer belt 3 and is fixed to one end of a through shaft 35 longer than the width of the belt 3. The through shaft 35 is rotatably attached to the intermediate transfer unit, and the front end, which is the other end, has the same diameter, the same number of teeth and the same tooth position as the large diameter gear 34R of the unit side coupling gear. Is fixed. Therefore, when the unit side coupling gear rotates, the gears 34R and 34F are rotated simultaneously and in the same direction. The large-diameter gear 34R and the gear 34F of the unit side coupling gear mesh with the gear portions 36R and 36F of the geared shutter opening / closing cams 37R and 37F, respectively. The shutter opening / closing cams 37R and 37F with gears on the both sides are the same parts, and the gear parts 36R and 36F and the cam parts 37R and 37F are integrated parts. The cam surfaces of the cam portions 37R and 37F of the shutter opening / closing cam with gear are in contact with both ends of the shutter 40, and the detection surfaces of the density sensors 30R and 30F can be opened and closed by the rotation of the motor 31. The shutter 40 is urged by a pair of compression springs 41R and 41F, which are urging members, to move in such a direction that the cam portions 37R and 37F of the shutter opening and closing cam are always in contact with the shutter 40. At this time, the compression springs 41 are arranged at symmetrical positions on both sides in the longitudinal direction of the shutter 40 so that the long rectangular shutter 40 can be pressed on both sides in the longitudinal direction with good balance.

  Next, the operation of the contact / separation mechanism of the secondary transfer roller 15 will be described. The drive source is the same motor 31 as the shutter 40. The large-diameter gear 34R and the gear 34F of the unit side coupling gear mesh with the gear portions 42R and 42F of the geared secondary transfer contact / separation cam, respectively. The geared secondary transfer contact / separation cam is the same component, and is a component in which the gear portions 42R, 42F and the cam portions 43R, 43F are integrated. The cam surfaces of the cam portions 43R and 43F of the geared secondary transfer contact / separation cam are in contact with rollers 44R and 44F provided at both ends of the secondary transfer roller 15, and the secondary transfer roller 15 is rotated by the rotation of the motor 31. Can be brought into contact with and separated from the intermediate transfer belt 3. In this example, the secondary transfer roller 15 is loaded on the side where a force of 20 N abuts by biasing members as compression springs 45R and 45F at both ends.

In order to drive the opening / closing operation of the shutter 40 and the contact / separation operation of the secondary transfer roller 15 with the same motor 31, it is necessary to synchronize the operations of the shutter 40 and the secondary transfer roller 15. In the present embodiment, the gear portions 36R, 36F of the geared shutter opening / closing cam and the gear portions 42R, 42F of the geared secondary transfer contact / separation cam have the same number of gear teeth. Furthermore, the phase relationship between the shutter 40 and the secondary transfer roller 15 is also necessary. In the present embodiment, the three states (A), (B), and (C) shown in FIGS. 3, 4, and 5 and Table 1 are configured. In the state (A) shown in FIG. 3, the shutter 40 is shut off, and the secondary transfer roller 15 is in contact. In the state (B) shown in FIG. 4, the shutter 40 is open, and the secondary transfer roller 15 is in contact, shown in FIG. In the state (C), the shutter 40 is opened and the secondary transfer roller 15 is separated. The unit side coupling gears 34R and 34F, the geared shutter opening / closing cams 36R and 36F, and the geared secondary transfer contact / separation cams 42R and 42F are assembled so as to have such a phase relationship.

Next, the relationship between the operation of the image forming apparatus and the above three states (A), (B), and (C) will be described.
In the standby state of the machine or in the operation stop state of the image forming apparatus in the sleep mode, the shutter 40 is opened and the secondary transfer roller 15 is separated (C). If the secondary transfer roller 15 is left in contact with the intermediate transfer belt 3 for a long time, the rubber layer of the secondary transfer roller is dented, and a lateral band image is generated at a one-round pitch of the secondary transfer roller 15. is there. In order to prevent this problem, the state (C) in which the secondary transfer roller 15 is separated from the intermediate transfer belt 3 is set at the standby after the end of the printing operation or after the transition to the sleep mode. Further, after the image forming apparatus is turned on or after the toner bottle is replaced, a density adjustment operation for grasping the toner density in the developing device 8 and controlling it to an appropriate density may be performed. Since this density adjustment process is not in a printing operation, it is not necessary to keep the secondary transfer roller 15 in contact with the intermediate transfer belt. In order to prevent the dirt toner on the intermediate transfer belt 3 from adhering to the secondary transfer roller, it is desirable to keep the secondary transfer roller 15 in a separated state. Therefore, the state (C) is also taken at this time.

  During a normal printing operation, the shutter 40 is opened and the state (A) in which the secondary transfer roller 15 is brought into contact is taken. During the printing operation, the fixing unit is at a high temperature, and an air current is generated in the apparatus by a fan (not shown) in order to suppress the temperature increase in the apparatus. Unfixed toner is placed on the photosensitive member 2, the intermediate transfer belt 3 and the recording medium P, and is rotated or transported. The influence of the airflow causes the toner to be in the machine. . When the scattered toner accumulates on the detection surface of the density sensor 30, there is a problem that the detection performance deteriorates and the density cannot be controlled to an appropriate level. Therefore, in order to protect the detection surface during the printing operation, the shutter 40 is configured to take a blocking state.

  When density adjustment is performed during printing, the shutter 40 is opened and the secondary transfer roller 15 is brought into contact (B). In a conventional image forming apparatus, density adjustment is limited to non-printing. This is because the density adjustment pattern formed on the intermediate transfer belt 3 adheres to the secondary transfer roller 15, and the secondary transfer transfer roller 15 performs the intermediate transfer in order to avoid the problem of fouling the back side of the printed paper. This is because the operation is performed while being separated from the belt 3. In general, the density adjustment is performed once every several tens to 100 sheets. Therefore, it is necessary to temporarily stop the printing operation for density adjustment in the case of conventional large-scale printing, which increases the waiting time of the user. I was doing it.

  The width of the intermediate transfer belt 3, the width of the secondary transfer roller 15, and the maximum sheet passing width are W when the width of the intermediate transfer belt 3 is W, the width of the secondary transfer roller 15 is W1, and the maximum sheet passing width is W2. > W1> W2. Therefore, in the present invention, the density sensors 30R and 30F are arranged outside the width W1 of the secondary transfer roller 15 in the intermediate transfer belt 3 shown in FIG. This is a major feature. With this configuration, even if a density adjustment pattern is formed during printing, the pattern can be detected without soiling the secondary transfer roller 15. By performing density adjustment during printing, not only can the user wait time be reduced, but density adjustment can be performed more frequently than before, so it is possible to provide a good image with reduced variations in image density. It becomes.

Next, a method for detecting the states (A), (B), and (C) will be described.
As shown in FIG. 2, an arc-shaped filler 46 is fixed to the upper end surface of the main body side coupling gear 33. 6 to 8, the angle formed by both ends of the arc-shaped filler 46 at the center of the main body side coupling gear 33 is 120 °. Transmission type photosensors 47 and 48 are arranged so as to sandwich the arc filler 46. The transmission type photosensors 47 and 48 are the same part, and the position of both is set to 120 ° from the center of the main body side coupling gear 33. As shown in FIG. 9, the transmissive photosensors 47 and 48 are optical sensors composed of a light-emitting element P and a light-receiving element Q. An output signal (voltage) from the sensor is determined depending on whether there is a shield that does not transmit light between them. ) Will change.

6 to 8 showing the relationship between the arc-shaped filler 46 and the transmission type photosensors 47 and 48, FIG. 6 shows the state (C), FIG. 7 shows the state (B), and FIG. 8 shows the state (A). Each is shown. In the present embodiment, since the motor 31 can be driven in both the forward direction and the reverse direction, the state (A), (B), (C), (A) transition and the state (C ), (B), (A), and (C) can be transferred. Therefore, the three states (A), (B), and (C) can be shifted from any state to any of the other two states. Specific operation examples are: state (C) when the apparatus power is on, state (C) during normal density adjustment, (A) during printing, and (B) when density adjustment is entered during printing. When returning to the printing operation (A), the standby state after the end of printing is (C). If only the state is written, (C), (A), (B), (A), and (C) are obtained. Since the motor 31 can perform both forward rotation and reverse rotation, the control shown in Table 2 can be performed, and the above process can be executed smoothly. In the above process, since the time for which the shutter 40 is opened can be minimized, the density detection surface is prevented from being contaminated with toner, and normal density control is possible.

  Table 2 shows a method for detecting the completion of the transition from the current state to the next state. It can be detected from the rotation direction of the motor 31 and changes in the signals of the two sensors. If the driving of the motor is stopped based on the trigger shown in Table 2, the shutter opening / closing cam and the secondary transfer contact / separation cam cannot be stopped accurately at the respective positions shown in FIGS. It passes a little). However, in this embodiment, even if the stop position varies somewhat, the cam shape is such that the shutter can be shut off / opened and the contact / separation of the secondary transfer roller can be guaranteed, and there is no particular problem.

FIG. 10 shows a density detection sensor unit of a color image forming apparatus showing another embodiment of the present invention.
In this embodiment, the opening / closing operation of the shutter 40 and the contact / separation operation of the secondary transfer roller 15 are the same as in the above embodiment, but the cleaning member 50 for cleaning the detection surface of the density sensor 30 is provided on the shutter 40. Is different. With this configuration, the detection surface of the density sensor 30 is cleaned each time the shutter is opened and closed, so that the density of the density adjustment pattern on the intermediate transfer belt can be accurately detected. In the illustrated example, the cleaning member 50 is configured by a brush, but the cleaning member 50 may be configured by sponge, felt, or the like.

  The amount of toner replenished to the developing means 8 and the replenishment timing are determined by the density of the density adjustment pattern. For example, if the detected density is lower than a specified value, control is performed to increase the toner density in the developing means by increasing the replenishment amount or making the timing frequent. On the other hand, when the detected density is high, supply is stopped and control is performed so that the toner density in the developing means does not increase. In the above-described present invention, since the density adjustment pattern can be detected with high accuracy, it is possible to provide a good image with small variations in image density.

11 to 15 are explanatory views of main parts showing still another embodiment of the present invention.
This embodiment is different from the embodiment shown in FIG. 2 in that the shutter 40 is operated by the cam portion 52 of the geared end face cam, and the other configurations are almost the same. Therefore, the same reference numerals are given to common members and the description thereof is omitted.

  In FIG. 11, only the gear portion 42 </ b> R of the geared secondary transfer contact / separation cam is engaged with the unit side coupling gear 34 </ b> R provided at one end of the through shaft 35, but is provided at the other end of the through shaft 35. The gear portion 42F of the geared secondary transfer contact / separation cam and the gear portion 51 of the geared end face cam mesh with the unit side coupling gear 34F. The geared end face cam is formed by integrating a gear portion 51 and a cam portion 52, and one end in the longitudinal direction of the shutter 40 mounted so as to be swingable in the longitudinal direction is in contact with the cam portion 52. A pressing action in a direction of contacting the cam portion 52 is urged by a pressing spring 53 provided at the other end in the longitudinal direction. In the shutter 40, openings 40aR and 40aF are formed at positions corresponding to the density sensors 30R and 30F. The openings 40aR and 40aF move to the vertical direction of FIG. 11 to move the density sensors 30R and 30F. Open or shut off the detection surface.

  In order to drive the opening / closing operation of the shutter 40 and the contact / separation operation of the secondary transfer roller with the same motor 31, it is necessary to link the operations of the shutter 40 and the secondary transfer roller 15 in association with each other. In this example, the number of gear teeth of the gear part 51 of the geared end face cam and the gear part 42 of the geared secondary transfer contact / separation cam are the same. Furthermore, the phase relationship between the shutter 40 and the secondary transfer roller is also necessary. This example is configured to take the three states shown in Table 1. In the state (A), the shutter is shut off, the secondary transfer roller is in contact, in the state (B), the shutter is open, the secondary transfer roller is in contact, and in the state (C), the shutter is open, and the secondary transfer roller is separated. is there. The unit side coupling gear 34F, the gear portion 42F of the geared secondary transfer contact / separation cam, and the gear portion 51 of the geared end face cam are assembled so as to have such a phase relationship.

The operation of the image forming apparatus when taking the above three states will be described with reference to FIGS.
When the machine is on standby or in sleep mode, the state (C) of FIG. 11 is taken. If the secondary transfer roller 15 is left in contact with the intermediate transfer belt 3 for a long time, the rubber layer of the secondary transfer roller is dented, and there is a problem that a horizontal band image is generated at a one-round pitch of the secondary transfer roller. . In order to prevent this problem, measures are taken to separate the secondary transfer roller from the intermediate transfer belt during standby after the end of the printing operation or after transition to the sleep mode. Further, after the image forming apparatus is turned on or after the toner bottle is replaced, a density adjustment operation for grasping the toner density in the developing device 8 and controlling it to an appropriate density may be performed. Since this density adjustment process is not in a printing operation, the secondary transfer roller 15 does not need to be in contact with the intermediate transfer belt 3. In order to prevent the dirt toner on the intermediate transfer belt 3 from adhering to the secondary transfer roller 15, it is desirable to keep the secondary transfer roller 15 in a separated state.

  During a normal printing operation, the state (A) in FIG. 12 is taken. During the printing operation, the fixing unit is at a high temperature, and an air current is generated in the apparatus by a fan (not shown) in order to suppress the temperature increase in the apparatus. Unfixed toner is placed on the photosensitive member, the intermediate transfer belt 3 and the recording medium, and is rotated or transported. The influence of the airflow also causes the toner to be in the machine. When the scattered toner accumulates on the detection surface of the density sensor 30, there is a problem that the detection performance deteriorates and the density cannot be controlled to an appropriate level. Therefore, in order to protect the detection surface of the density sensor 30 during the printing operation, it is desirable that the shutter 40 be in a blocking state.

  When density adjustment is performed during printing, the state (B) in FIG. 13 is taken. In a conventional image forming apparatus, density adjustment is limited to non-printing. This is because the density adjustment pattern formed on the intermediate transfer belt is attached to the secondary transfer roller 15 and the back side of the paper for subsequent printing is fouled. This is because the operation is performed in a separated state. The density adjustment is performed once every several tens to 100 sheets. However, when printing a large amount, it is necessary to temporarily stop the printing operation for the density adjustment, which increases the waiting time of the user. It was.

  Therefore, in the present invention, the density can be adjusted even during the printing operation. In FIG. 11, the density sensors 30R and 30F are characterized in that they are arranged outside the secondary transfer roller width W1 wider than the maximum sheet passing width W2. With this configuration, even if a density adjustment pattern is formed during printing, the pattern can be detected without soiling the secondary transfer roller 15 or the recording medium P. By performing density adjustment during printing, not only can the user wait time be reduced, but density adjustment can be performed more frequently than before, so it is possible to provide a good image with reduced variations in image density. It becomes.

  A cam diagram in the cam portion 52 of the geared end face cam for operating the shutter 40 is shown in FIG. The positions of 0 °, 120 °, and 240 ° in the cam diagram correspond to the state (C), the state (A), and the state (B), respectively.

  In the above embodiment, the density sensor 30 is placed on both sides of the contact area of the secondary transfer roller 15 in the width direction of the intermediate transfer belt 3. Concentration may not be stable. Furthermore, it is more advantageous to increase the image density information from the sensor in order to increase the accuracy of image density adjustment. At this time, it is meaningless to place a plurality of sensors at the same level position in the width direction of the intermediate transfer belt 3, and it is preferable to obtain information from different positions in the width direction of the intermediate transfer belt 3.

  Therefore, in still another embodiment of the present invention shown in FIG. 15, an inner density sensor 30C is provided at the center in the width direction of the intermediate transfer belt 3, and the inner density sensor 30C is similar to the outer density sensors 30R and 30F. The detection surface is opened and closed by the shutter 40.

Next, the opening / closing mechanism of the shutter 40 of the density sensor 30, the contact / separation mechanism of the secondary transfer roller 15, and the arrangement relationship thereof will be described.
The opening / closing mechanism of the shutter 40 and the contact / separation mechanism of the secondary transfer roller 15 shown in FIG. 15 are very similar to the opening / closing mechanism of the shutter 40 and the contact / separation mechanism of the secondary transfer roller 15 shown in FIG. Explain mainly. In FIG. 15, the same members as those in FIG.

  In FIG. 15, DC brush motor 31, output gear 32, main body coupling gear 33, unit side coupling gear 34R, gear 34F, through shaft 35, secondary transfer contact / separation cam gear portions 42R and 42F, and geared secondary transfer contact. The cam portions 43R and 43F of the separation cam, the rollers 44R and 44F, the compression springs 45R and 45F, the geared end face cam having the gear portion 51 and the cam portion 52, and the pressing spring 53 are similar in form and operation to those shown in FIG. It is. 11 differs from that shown in FIG. 11 in that three density sensors 30 are provided, that is, the outer density sensors 30R and 30F and the inner density sensor 30C. Therefore, the shutter 40 also has openings 40aR, 40aF, and 40aC for each sensor. Is provided, and there is one filler 46 on the upper end surface of the main body side coupling gear 33 and one transmissive photosensor 47 that detects the filler 46.

  The openings 40aR and 40aF for the outer density sensors 30R and 30F of the shutter 40 have an opening 40aC for the inner density sensor 30C, and the width of the openings 40aR and F for the outer density sensors 30R and 30F in the moving direction of the shutter 40. Is set to approximately twice the length of the opening 40aC for the inner concentration sensor 30C.

And in this embodiment, it sets so that the states (D), (E), and (F) shown in Table 3 may be taken.

  In the present embodiment, the shutter 40 for the density sensor 30 is set to take three states shown in FIG. 16, and these three states are states (D), (E), and (F) shown in Table 3. .

  In the state (D), the intermediate transfer unit U is not set, the openings 40aR, 40aF, and 40aC for the three density sensors 30 are blocked, and the secondary transfer roller 15 is in the separated position. The situation in which this state (D) is taken is, for example, at the time of product assembly in a factory. As long as there is no failure, the density sensor unit including the shutter 40 and the density sensor 30 is a unit that is used until the end of its product life. Therefore, the density sensor unit is often assembled to the product body at the initial stage of assembly. If the detection surface of the density sensor 30 is in an open state until the other units such as the intermediate transfer unit U, the photosensitive unit, and the toner bottle are assembled, toner, dust, foreign matter, etc. may adhere to the detection surface. It is desirable to be blocked by a shutter. In addition, even after the start of product use, the toner inside the machine may be scattered during maintenance such as replacement of the intermediate transfer unit U that has reached the end of its life, and the detection surface of the density sensor may be soiled, so the intermediate transfer unit U is removed. In this case, it is desirable to block the detection surfaces of all density sensors 30 by the shutter 40.

  In the state (E), the intermediate transfer unit U shown in FIG. 15 is set, the openings 40aR and 40aF of the outer density sensors 30R and 30F are opened, the opening 40aC of the inner density sensor 30C is shut off, and the secondary transfer roller 15 is turned on. It is in the contact position. The situation that takes the state (E) is a situation in which the density adjustment operation can be executed during the printing operation, which is a major feature of the present invention. Since the outer density sensors 30R and 30F in the contact area between the secondary transfer roller 15 and the intermediate transfer belt 3 are disposed, the toner pattern does not adhere to the secondary transfer roller 15 and the transfer paper backside stain of the next print can be prevented. Further, since the maximum sheet passing width W2 is shorter than the length W1 of the secondary transfer roller 15, the density adjustment pattern does not adhere to the secondary transfer roller 15 even during sheet passing. Since the toner remaining on the intermediate transfer belt 3 without being transferred to the transfer paper is different in position in the main scanning direction from the outer density sensors 30R and 30F, the toner does not scatter on the detection surface, and the detection surface is also soiled. Does not occur. As described above, since the density can be adjusted during the printing operation, it is possible to sequentially detect and correct a change in toner density, so that a user can wait for a good image with little variation in the image density. Can be provided. Since the internal density sensor 30C in the state (E) is in a printing operation, the detection surface is blocked to prevent the transfer residual toner on the intermediate transfer belt 3 from adhering.

  In the state (F), the intermediate transfer unit U shown in FIG. 17 is set, the openings 40aC of all the density sensors 30R, 30F, and 30C are opened, and the secondary transfer roller 15 is in the separated position. The situation that takes this state (F) corresponds to a normal density adjustment operation that is executed other than during the printing operation. Other than during the printing operation is, for example, when the power is turned on, when returning from the sleep mode, after the printing operation is completed, after the toner bottle is replaced. When the power is turned on, when returning from the sleep mode and after the print operation is completed, the printer does not immediately shift to the print operation. Therefore, all the density sensors 30R, 30F, and 30C are opened and all the density sensors are used. Execute the density adjustment operation. Compared with the density adjustment operation during the printing operation in the state (E), since all the density sensors 30R, 30F, and 30C are used, density adjustment with higher accuracy can be performed. Further, when the print job start signal is issued, the state immediately shifts to the state (E), and the inner density sensor 30C is blocked by the shutter 40, so that the detection surface of the inner density sensor 30C is prevented from being soiled.

  Then, it is desirable to execute the density adjustment operation using all the density sensors 30 in order to accurately determine the toner replenishment amount when the toner bottle is replaced. After the density adjustment operation is completed, the process immediately shifts to the state (E), and the density sensor 30C is blocked by the shutter 40, so that contamination can be prevented.

  Normally, the state (F) is maintained in the sleep mode or when the power is turned off. This is because when the secondary transfer roller 15 is left in contact with the intermediate transfer belt 10 for a long period of time, a dent is generated in the contact portion of the secondary transfer roller, and the secondary transfer roller has one circumferential pitch during printing. This is because a horizontal band occurs.

  Further, the state (E) and the state (F) are switched by rotating the shutter opening / closing cam 51 by driving the motor 31. FIG. 18 shows a cam curve of the cam 51. A total of 120 ° of 0 to 60 ° and 300 to 360 ° corresponds to the phase of the state (F). 120 to 240 ° corresponds to the phase of the state (E). The position difference between the state (E) and the state (F) is set to 5 mm. In the present embodiment, the state (D) and the state (E) are set to a stroke of 7 mm, and the state (E) and the state (F) are set to a stroke of 5 mm (see FIG. 18).

  Furthermore, in the movement from the state (F) to the state (D), when the intermediate transfer unit U is taken out from the image forming apparatus main body, the cam portion 52 provided in the intermediate transfer unit U is separated from the shutter 40. As a result, the shutter 40 is pushed by the pressing spring 53 as shown in FIG. 16A, and all the openings 40a of the shutter 40 are disengaged from the detection surface of the sensor 30, and the detection surfaces of all the sensors are blocked (D). become. Since the intermediate transfer unit U is not removed from the image forming apparatus main body during the printing operation, it does not move from the state (E) to the state (D).

Next, a method for detecting the states (E) and (F) will be described.
As shown in FIGS. 15 and 17, an arc-shaped filler 48 is attached to the end face of the main body side coupling gear 33. The angle of the arc is 180 °. A transmissive photosensor 47 is arranged so as to sandwich the arc. The transmissive photosensor 47 is an optical sensor comprising a light emitting element P and a light receiving element W ¥ Q similar to those in FIG. 9, and an output signal (voltage) from the sensor is determined depending on whether there is a shield that does not transmit light between them. change. FIG. 19 is a view as seen from the Z direction shown in FIG. FIG. 20 is a view as seen from the Z direction shown in FIG. The main body side coupling gear 33 rotates in the direction of the arrow shown in FIGS. 18 and 19, and one rotation is synchronized with one rotation of the shutter opening / closing cam 51 and the secondary transfer contact / separation cams 43R and 43F. At the time of transition from the state E to the state F, the output of the transmissive photosensor 47 changes from cutoff to open. If the driving of the motor 31 is stopped at the moment of change, the motor 31 stops before the state F is reached, and the open / close state of the shutter and the contact / separation state of the secondary transfer roller are not appropriate. For this reason, a time difference is provided between the timing at which the motor stop signal is output and the output change timing of the transmission type photo sensor. In this embodiment, it is set to 100 msec. Similarly, the set time difference from state F to state E is also 100 msec.

  21, FIG. 22, and FIG. 23 show the density detection sensor unit in the modification of the embodiment shown in FIG. In this example, cleaning members 50R, 50C, and 50F that clean the detection surface of the density sensor 30 are provided on the shutter 40. In the illustrated example, the cleaning member 50 is configured by a brush, but the cleaning member 50 may be configured by sponge, felt, or the like.

  If comprised in this way, in the state (D), as shown in FIG. 21, the cleaning members 50R and 50F clean the test surfaces of the sensors 30R and 30F. Therefore, the detection surface can be cleaned and kept clean every time the intermediate transfer unit is replaced. In the state (F), as shown in FIG. 22, the cleaning member 50C cleans the test surface of the sensor 30C. Therefore, the test surface of the sensor 30C is cleaned during printing. Since all the sensors can be detected in the state (E), the cleaning members 50R, 50C, and 50F are separated from the detection surfaces of the sensors as shown in FIG.

  The amount of toner to be replenished to the developing device 8 and the replenishment timing are determined by the density of the density adjustment pattern. For example, if the detected density is lower than a specified value, control is performed to increase the toner density in the developing device 8 by increasing the replenishment amount or making the timing frequent. On the other hand, when the detected density is high, replenishment is stopped and control is performed so that the toner density in the developing device 8 does not increase.

  According to the present invention, the image density can be detected with high accuracy, and the detection surface of each density sensor 30 can always be kept clean. Therefore, the toner pattern on the intermediate transfer belt 3 can be accurately detected, and the image density variation can be detected. It is possible to provide a good image with a small size.

3 Intermediate transfer belt 4, 5 Support roller 15 Secondary transfer roller 30 Density sensor 31 Motor 40 Shutter 46 Filler 47, 48 Transmission type photo sensor

JP 2009-145778 A

Claims (10)

Moveable between an image carrier that carries a toner image on the surface, a sensor that detects the toner image on the image carrier, a closed position that protects the detection surface of the sensor, and an open position that the sensor can detect An image forming apparatus for transferring a toner image on the image carrier to a transfer material between the image carrier and the transfer member.
The transfer member is movable between a contact position that contacts the image carrier and a separation position that is separated from the image carrier,
The sensor includes an outer sensor that detects a toner image outside the contact area between the transfer member and the image carrier,
The shutter and the transfer member are transferred when the shutter is in the closed position and the transfer member is in the contact position (A), the shutter is in the open position and the transfer member is in the contact position (B), and the shutter is in the open position. An image forming apparatus characterized in that a member takes three states: a separated position state (C).   2. The image forming apparatus according to claim 1, wherein the three states can be changed directly to the other two states in any state.   3. The image forming apparatus according to claim 1, wherein the driving source for switching between the three states is a motor capable of switching between normal rotation and reverse rotation. An image carrier that carries a toner image on the surface, a plurality of sensors that detect the toner image on the image carrier, a closed position that protects the detection surface of the sensor, and an open position that the sensor can detect In an image forming apparatus, comprising: a movable shutter; and a transfer member that contacts the image carrier, and transferring a toner image on the image carrier to a transfer material between the image carrier and the transfer member. ,
The transfer member is movable between a contact position that contacts the image carrier and a separation position that is separated from the image carrier,
The sensor includes an inner sensor that detects a toner image in a contact area between the transfer member and the image carrier, and an outer sensor that detects a toner image outside a non-contact area between the transfer member and the image carrier.
When the shutter of the inner sensor is in the closed position, the shutter of the outer sensor is in the closed position and the transfer member is in the separated position (D), the shutter of the inner sensor is in the closed position, and the shutter of the outer sensor is opened. A state where the transfer member is in the contact position at the position (E), a state where the shutter of the inner sensor is in the open position, and a state where the shutter of the outer sensor is in the open position and the state where the transfer member is in the separated position (F). An image forming apparatus.   5. The image forming apparatus according to claim 1, wherein opening and closing of the shutter and contact and separation of the transfer member are driven by the same drive source.   6. The image forming apparatus according to claim 5, wherein the shutter opening / closing cam rotated by the driving source and the transfer member contacting / separating cam are rotated simultaneously.   7. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt provided in an intermediate transfer unit that is detachably attached to the image forming apparatus main body. Image forming apparatus.   8. The image forming apparatus according to claim 1, wherein a cleaning member for cleaning a detection surface of the density sensor by opening and closing the shutter is provided on the shutter.   5. The image forming apparatus according to claim 4, wherein the inner / outer sensor, the shutter, and an urging unit that presses the shutter against an opening / closing cam are provided in an image forming apparatus body, and the shutter opening / closing cam is the intermediate transfer. The direction in which the intermediate transfer unit is pulled out from the image forming apparatus main body is the same as the direction in which the urging means presses the shutter, and when the intermediate transfer unit is pulled out from the image forming apparatus main body, the shutter is An image forming apparatus, wherein the image forming apparatus is in a closed state (D) that is pushed by the urging unit and takes all the internal and external sensors.   5. The image forming apparatus according to claim 4, wherein the inner sensor and the outer sensor are opened / closed by a single shutter.

Images