JP2013097099A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that, in an electrophotography type image forming apparatus, an external additive contained in a developer, in particular, is attached to an image carrier for forming an electrostatic latent image and causes an image defect.SOLUTION: The image forming apparatus includes: a photosensitive drum 31 for carrying an electrostatic latent image on the surface; a transfer roller 12 that transfers a developer image formed on the surface of the photosensitive drum 31 onto a recording medium; pressing means (21, 22, and 28) that press the transfer roller 12 towards the photosensitive drum 31 by first pressing force and second pressing force that is larger than the first pressing force; and control means (103-111) for controlling the operation of the whole apparatus. The control means controls the pressing means to press the transfer roller 12 by the first pressing force when forming the image, and to press the transfer roller 12 by the second pressing force in cleaning.

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus.

  Conventionally, in an electrophotographic printer, an electrostatic latent image formed on an image carrier is developed with a developer containing at least a colorant, the developer development is transferred onto a recording sheet by a transfer member, and developed on the recording sheet. An agent image was formed. The pressure between the transfer member and the image carrier is kept constant (see, for example, Patent Document 1).

JP 2000-172148 A (page 3, FIG. 2)

  However, there is a problem that an external additive contained in the developer adheres to an image carrier that forms an electrostatic latent image and causes an image defect.

An image forming apparatus according to the present invention is an image forming apparatus capable of taking an image forming state and a cleaning state for cleaning an electrostatic latent image carrier.
The electrostatic latent image carrier that carries an electrostatic latent image on the surface, a transfer member that transfers a developer image formed on the surface of the electrostatic latent image carrier to a recording medium, and a first pressing force And a pressing means for pressing the transfer member against the surface of the electrostatic latent image carrier with a second pressing force larger than the first pressing force, and a control means for controlling the operation of the entire apparatus. ,
The control unit controls the pressing unit to press the transfer member with the first pressing force during the image formation and to press the transfer member with the second pressing force during the cleaning. Features.

  According to the present invention, the developer or the external additive attached or fixed to the electrostatic latent image carrier can be scraped off by the transfer member that is strongly pressed and finally recovered.

1 is a schematic configuration diagram for explaining a main configuration of an image forming apparatus according to a first embodiment of the present invention. It is a schematic block diagram which shows typically the structure of a developing device with an exposure apparatus. FIG. 2 is a schematic configuration diagram of a photosensitive drum, a transfer roller, and a pressure mechanism of the transfer roller, as viewed from a recording paper discharge side. (A) shows the state where the cam is in the first position, and (b) is an operation explanatory view showing the state where the cam is in the second position. FIG. 2 is a control system block diagram showing a configuration of a main part of a part particularly related to the present invention in the control system of the image forming apparatus in the first embodiment. It is a time chart for demonstrating the operation | movement of each part at the time of the cleaning process performed based on this invention, and the applied bias voltage. 7 is a time chart showing, as a comparative example, the operation of each unit during image formation of the image forming apparatus that does not perform the photosensitive drum cleaning operation and the bias voltage applied. (A) is an explanatory diagram showing a state of a defective image in which black spots are generated in a white background image of printing paper, and (b) is a defective image in which white spots are generated in a black background image of printing paper. FIG. 5 is a control system block diagram showing a main configuration of a part particularly related to the present invention in the control system of the image forming apparatus in the second embodiment.

Embodiment 1 FIG.
FIG. 1 is a schematic configuration diagram for explaining a main configuration of the image forming apparatus according to the first embodiment of the present invention.

  In FIG. 1, an image forming apparatus 1 has a configuration as an electrophotographic printer capable of printing with, for example, black (K). In the apparatus, a paper transport path having transport rollers 8, 9, and 10 is formed. A paper feed tray 3 for storing the recording paper 4 is disposed in the uppermost stream of the paper transport path, and is disposed in the lowermost stream. Is provided with a stacker 15 on which the printed recording paper 4 is placed.

  The recording paper 4 in the paper feed tray 3 is fed out one by one by the hopping roller 7 to the paper transport path. A transport roller 8 for transporting the fed recording paper 4 is disposed downstream of the hopping roller 7, and an electrostatic latent image carrier on which a toner image is formed by development as will be described later, downstream of the transport roller 8. And a transfer roller 12 as a transfer member for transferring a toner image formed on the photosensitive drum 31 to the recording paper 4, together with the photosensitive drum 31, the recording paper 4. A fixing device 11 including a heat roller and a backup roller is disposed downstream of the toner image so as to fix the toner image on the recording paper 4. The recording paper 4 on which the toner image is fixed by the fixing device 11 is sent to the stacker 15 outside the device by the transport rollers 9 and 10.

  As will be described later, the transfer roller 12 is configured such that the transfer roller shaft 12 a is urged or pressed against the photosensitive drum 31 by the action of the transfer roller spring 21 and the cam 22.

  The X, Y, and Z axes in FIG. 1 take the X axis in the transport direction when the recording paper 4 passes through the developing device 2, and take the Y axis in the rotational axis direction of the photosensitive drum 31. The Z axis is taken in a direction perpendicular to the axis. Moreover, when each axis | shaft of X, Y, and Z is shown in the other figure mentioned later, these axial directions shall show a common direction. That is, the XYZ axes in each figure indicate the arrangement direction when the depicted portion of each figure constitutes the image forming apparatus 1 shown in FIG.

  FIG. 2 is a schematic configuration diagram schematically showing the configuration of the developing device 2 together with the exposure device 33.

  As shown in the figure, in the developing device 2, a photosensitive drum 31 that can store charges on the surface and can remove charges on the surface by exposure is disposed so as to be rotatable in the direction of the arrow. Around the drum 31, in order from the upstream side in the rotation direction, the surface of the photosensitive drum 31 is contacted with a constant pressure and rotated in the direction of the arrow, and a predetermined bias voltage is applied by the charging voltage control unit 105 (FIG. 5). An exposure apparatus that forms an electrostatic latent image by irradiating light from a light source such as an LED head onto the surface of a charging roller 32 as a charging member that is applied and charged by supplying electric charge, and the charged photosensitive drum 31 33 is arranged. Further, a developing unit 30 is provided that forms a toner image by attaching and developing charged toner 37 as a developer on the surface of the photosensitive drum 31 on which the electrostatic latent image is formed.

  The developing unit 30 stores unused toner 37, and a toner cartridge 40 that supplies the toner 37 from a lower toner supply port 40 a having a long hole shape formed in the longitudinal direction is supplied to the lower part of the developing unit 30. A toner sensor 38 for detecting the remaining amount of toner in the toner storage chamber, a developing roller 34 as a developing member disposed in contact with the photosensitive drum 31, a toner supply roller 35 for supplying toner 37 to the developing roller 34, and a developing roller 34 The toner on the developing roller 34 is formed on the electrostatic latent image formed on the surface of the photosensitive drum 31 by including a layer forming blade 39 for uniformly thinning the toner 37 on the upper surface and a film 36 for preventing the toner 37 from leaking. The toner image is formed by developing 37, and a toner image is formed. Further, a predetermined bias voltage is applied to the developing roller 34, the toner supply roller 35, and the layer forming blade 39 by a developing voltage control unit 106 (FIG. 5) described later.

  The developing roller 34 and the toner supply roller 35 are arranged in parallel with each other so as to be in contact with each other at a constant pressure, and rotate in the direction of the arrow shown in FIG. The toner 37 is supplied from the toner supply roller 35 to the developing roller 34 by the bias voltage supplied in 5). As shown in the figure, the layer forming blade 39 and the developing roller 34 are arranged in parallel to each other so that, for example, a bent portion of the layer forming blade 39 contacts the peripheral surface of the developing roller 34 with a constant pressure. The developing roller 34 to which the developing bias voltage is applied contacts the photosensitive drum 31 with a constant pressure, and the electrostatic latent image formed by the exposure device 33 is formed by the toner 37 thinned by the layer forming blade 39. develop.

  Here, each configuration of the toner 37 and the developing device 2 will be further described.

The toner 37 is not particularly limited, but here, a negatively charged black toner having an average particle diameter of 6.5 to 7.5 μm and an average circularity of 0.97 prepared by an emulsion polymerization method was used. The degree of circularity was measured using “Flow type particle image analyzer FPIA-2100” manufactured by Sysmex Corporation based on the following formula (1).
Circularity = L1 / L2 (1)
Here, L1 is the circumference of a circle having the same area as the area of the particle projection image, and L2 is the circumference of the particle projection image. If the circularity is 1.00, it is a true sphere, and the particle shape becomes indefinite as the circularity becomes smaller than 1.00.

  The charging roller 32 is formed of epichlorohydrin rubber around the shaft, and the surface thereof is subjected to an isocyanate treatment so as to have an outer diameter of φl2.0 mm. The surface roughness is a contact type 10-point average roughness according to JISBO601-1994, and Rz = 7 to 12 μm. The entire surface is in contact with the photosensitive drum 31 with a pressing force of 1000 gf (one side 500 gf).

  The developing roller 34 has an elastic layer formed of polyether urethane on a SUS developing roller shaft 34a, and has a desired outer diameter value (here, the finished outer diameter is 5 mm from the end). The surface of the rubber layer was subjected to rough polishing, finisher polishing, etc. in order to obtain φ15.9 mm on both sides and φ15.92 mm at the center. Here, the outer diameter of the roller was measured 32 times between two rotations using a Mitutoyo LSM-6100 laser at a roller rotation speed of 35 rpm, and the average was taken. Further, a coating (for example, an isocyanate treatment, a polyether urethane coating, etc.) for imparting charging properties to the toner 37 was applied.

  Further, carbon black (for example, acetylene black, ketjen black, etc.) was added in order to adjust the resistance value and increase the strength. The resistance (R) of the developing roller 34 is measured by bringing a ball bearing made of SUS having a width of 2.0 mm and a diameter of 6.0 mm into contact with a force of 20 gf. At this time, the resistance (R) is 100 V between the shaft and the shaft. Is applied, the ratio of voltage (V) to current (I) (R = V / I) is 1 M to 100 MΩ. The roller hardness is 77 degrees with a load of 9.8 N according to JIS K6252. The surface roughness is a contact type 10-point average roughness according to JIS BO601-1994, and Rz = 2 to 6 μm. Further, it is arranged to be pushed into the photosensitive drum 31 by about 0.1 mm, and the load at this time is in contact with a pressing force of 1000 gf (500 gf on one side) as a whole.

  The toner supply roller 35 is formed by forming semiconductive foamed silicon rubber on a supply roller shaft 35a made of SUS, and is polished so as to have a predetermined outer diameter (for example, φ15.5 mm). The compound is obtained by adding a reinforcing silica filler, a vulcanizing agent necessary for vulcanization and a foaming agent, to various raw rubbers such as dimethyl silicon raw rubber and methylphenyl silicon raw rubber. As the foaming agent, an inorganic foaming agent such as sodium bicarbonate or an organic foaming agent such as ADCA is used.

  The method for measuring the outer diameter of the toner supply roller 35 is the same as that for the developing roller 34 described above. Moreover, the sponge is a single bubble and the hardness as a roller is 50-65 degrees in Asker F. The cell diameter of the sponge is 300 to 500 μm near the surface by a method of observing and measuring the cross section with a CCD. In addition, when the outer diameter is 15.5 mm, the roller resistance measured by the same method as in the case of the developing roller 34 is 1.0 mm pressed against the developing roller 34 in a stationary state, when 300 V is applied. 1 M to 100 MΩ.

  The photoreceptor drum 31 is a negatively charged organic photoreceptor (OPC), and a photosensitive layer including a charge generation layer and a charge transport layer is formed on an aluminum base tube having an outer diameter of φ30 mm. The photosensitive layer has a thickness of 18 μm. The linear velocity on the surface of the photosensitive drum 31 is about 114 mm / s, which corresponds to A4 longitudinal feed of 20 ppm.

  The photosensitive drum gear 51 (FIG. 3) is connected to the drum drive motor 25 (FIG. 5) and receives a driving force. The developing roller 34 rotates in a rotating direction at a linear velocity of about 1.26 times on the surface thereof with respect to the photosensitive drum 31 by gear transmission, and the toner supply roller 35 rotates with respect to the developing roller 34 by gear transmission. Rotate in the counter direction at a speed of 0.68 times.

  FIG. 3 is a schematic configuration diagram of the photosensitive drum 31, the transfer roller 12, and the pressure mechanism of the transfer roller 12 as viewed from the side where the recording paper 4 is discharged, and FIGS. 4 (a) and 4 (b). These are operation | movement explanatory drawings with which the operation | movement description is provided.

  The transfer roller 12 has an elastic layer made of an elastic semi-conductive foamed EPDM (ethylene propylene diene rubber) formed on a transfer roller shaft 12a made of SUS, and is polished to an outer diameter of φ16.4 mm. The length of the rubber part is 216 mm, and the foamed sponge is a single cell and has a cell diameter of 200 to 400 μm. The roller hardness was measured at three locations in the axial direction under a load of 9.8 N according to JIS K6252, and the average was 38 degrees. The roller resistance measured by the same method as in the case of the developing roller 34 is 50 M to 100 MΩ.

  Further, the transfer roller 12 has a transfer roller shaft 12a guided by a guide member 18 (only a partial shape of the guide groove is indicated by a dotted line in FIG. 4) so that the transfer roller 12 approaches or separates from the photosensitive drum 23. It is held slightly movable.

  The pair of transfer roller springs 21 is placed in a compressed state between the apparatus main body and the transfer roller shaft, and presses both sides of the transfer roller shaft 12a with a total of 1000 gf (one side 500 gf) during the image forming operation, thereby transferring the transfer roller 12. 4 is pressed against the photosensitive drum 31, and the pair of cams 22 is moved by the cam motor 28 as shown in FIG. As shown in (2), it is configured to be able to act on both sides of the transfer roller shaft 12a at a second position selected during a cleaning operation described later.

  When the cam 22 is in the first position shown in FIG. 4A, the transfer roller 12 is controlled by the biasing force of the pair of transfer roller springs 21, and the biasing force (first set pressure) of 1000 gf (one side 500gf) as a whole. ) And the cam 22 is in the second position of FIG. 4B, the transfer roller 12 further receives the pressing force of the pair of cams 22 and approaches the photosensitive drum 31. Then, it is pressed against the photosensitive drum 31 with a pressing force (second set pressure) of 3000 gf (one side 1500 gf) as a whole. The cam 22, the transfer roller spring 21, and the cam motor 28 correspond to the pressing means.

  In the present embodiment, the transfer roller 12 receives the driving force when the transfer roller gear 52 is connected to the same drum driving motor 25 (FIG. 5) as the photosensitive drum gear 51 via the driving force transmission system. With respect to 31, it moves in the direction of rotation (in the direction of the arrow shown in FIG. 1) at a linear velocity of about 1.03 times on its surface.

  FIG. 5 is a control system block diagram showing the configuration of the main part of the control system of the image forming apparatus 1 particularly related to the present invention.

  In the figure, an interface unit 101 is a part that takes a physical hierarchy interface with an external computer. The command / image processing unit 102 includes a print setting processing unit that transmits / receives data of the interface unit 101 and processes print information obtained from the interface unit 101. Further, the command / image processing unit 102 interprets commands and image data from the external computer side or develops them into a bitmap, and outputs the image data to the exposure control unit 103. The exposure control unit 103 processes the image data expanded into the bitmap from the command / image processing unit 102 in accordance with the interface of the exposure apparatus 33 and transmits the processed data to the exposure apparatus 33. Detailed description of the exposure apparatus is omitted.

  The charging voltage control unit 105 applies a bias voltage to the charging roller 32 in the developing device 2 (FIG. 2) in accordance with an instruction from the printing control unit 104 that controls the entire apparatus to charge the surface of the photosensitive drum 31. I do. The development voltage control unit 106 attaches the toner 37 to the electrostatic latent image generated by the exposure device 33 on the surface of the photosensitive drum 31 (FIG. 2), and thus the development roller 34 and the toner supply roller 35 in the development device 2. Control for applying a bias voltage to the layer forming blade 39 is performed. The transfer voltage control unit 107 transfers the toner image generated on the surface of the photosensitive drum 31 (FIG. 1) to the recording paper 4 and receives an instruction from the print control unit 104 to the transfer roller 12 (FIG. 1). Control for applying a bias voltage is performed.

  The image forming drive control unit 108 receives an instruction from the print control unit 104, and is provided in the developing device 2 (FIG. 2). The photosensitive drum 31, the charging roller 32, the developing roller 34, and the toner supply roller 35 are provided. A drum driving motor 25 that drives the transfer roller 12 is controlled, and a conveyance motor control unit 109 controls a conveyance motor 26 for driving the conveyance rollers 8, 9, 10 according to an instruction from the printing control unit 104, and controls a hopping motor. The unit 110 controls the hopping motor 27 for driving the hopping roller 7 in accordance with an instruction from the print control unit 104.

The cam control unit 111 controls the cam motor 28 that is driven so that the cam 22 selectively selects the first and second positions in response to an instruction from the print control unit 104.
The print control unit 104, the exposure control unit 103, the charging voltage control unit 105, the development voltage control unit 106, the transfer voltage control unit 107, the image formation drive control unit 108, the transport motor control unit 109, the hopping motor control unit 110, and The cam control unit 111 corresponds to control means.

  In the above configuration, first, an operation at the time of image formation will be described with reference to FIGS.

  When printing starts, the recording paper 4 fed out from the paper feed tray 3 by the hopping roller 7 is transported along the transport path by the transport roller 8, and its leading end reaches the developing device 2. On the other hand, in the developing device 2, a toner image is formed on the surface of the photosensitive drum 31 during this time, and the toner image is transferred while the recording paper 4 is nipped between the photosensitive drum 31 and the transfer roller 12. It is transferred onto the recording surface of the recording paper 4. At this time, a predetermined bias voltage, for example, a positive voltage of +2400 V is applied to the transfer roller 12 by the transfer voltage control unit 107 (FIG. 5).

  The recording paper 4 onto which the toner image has been transferred is conveyed further downstream and reaches the fixing device 11. The fixing device 11 includes a heat roller and a backup roller arranged in parallel in contact with each other, and fixes a toner image on the recording paper 4 by heat and pressure applied at a nip portion formed between these rollers. Let The printed recording paper 4 on which the toner image has been fixed and sent from the fixing device 11 is discharged to the stacker 15 outside the device by the transport rollers 9 and 10.

  In the developing device 2, the photosensitive drum 31 starts rotating in synchronization with the conveyance of the recording paper 4, and accordingly, the developing roller 34 and the toner supply roller 35 are connected via a gear and the charging roller 32. Rotate by rotation with contact. At the same time, a bias voltage of −1150 V is applied to the charging roller 32, a bias voltage of −200 V is applied to the developing roller 34, and a bias voltage of −300 V is applied to the supply roller 35 and the layer forming blade 39. However, these voltage values are adjusted according to the required print density.

  Then, the exposure device 33 forms an electrostatic latent image by exposing the charged surface of the photosensitive drum 31 with, for example, an LED based on the print data received by the image forming apparatus 1 from the host device, and the developing unit 30. The developing roller 34 attaches the thinned toner formed on the surface to the electrostatic latent image and develops it, thereby forming the above-described toner image.

  FIG. 6 is a time chart for explaining the operation of each unit and the applied bias voltage during the cleaning process performed according to the present invention. The cleaning process will be described with reference to the time chart.

  When the image forming operation (printing) starts at time t0, as described above, the hopping roller 7 rotates to feed out the recording paper 4 from the paper feed tray 3, and in synchronization with this, the transport rollers 8, 9, 10 rotate. Then, the conveyance of the recording paper 4 on the conveyance path is started, and the photosensitive drum 31 of the developing device 2 is rotationally driven. Accordingly, the transfer roller 12, the charging roller 32, the developing roller 34, and the toner supply roller 35 are rotated. At the same time, the charging roller 32 has a negative voltage of −1150 V, the developing roller 34 has a negative voltage of −200 V, the toner supply roller and the layer forming blade 39 have a negative voltage of −300 V, and the transfer roller A positive voltage of + 2400V is applied to 12 respectively. At this time, the cam 22 is in the first position, and the transfer roller 12 is biased against the photosensitive drum 31 by a pair of transfer roller springs 21 with a biasing force (first set pressure) of 1000 gf (one side 500 gf) as a whole. Has been.

  Under the above settings, the image forming process described above is executed, the image forming operation (printing) is finished at time t1, and the photosensitive drum cleaning operation described later is started at time t2.

  The objects to be cleaned by this photosensitive drum cleaning operation include the normally charged toner, the reversely charged toner, and the external additive detached from the toner 37. Here, the regular charged toner is a negative (−) charged toner, the reverse charged toner is a positive (+) charged toner, and the external additive is a friction between the developing roller 34 and the photosensitive drum 31. It is a component of the toner released from the toner 37 and is mainly silica. This silica has a strong negative chargeability and is generally negatively charged.

  When the photosensitive drum cleaning operation starts at time t2, the conveyance rollers 8, 9, and 10 that convey the recording paper 4 are stopped, and first, collection of reversely charged (+) toner is started. At this time, biases having the same polarity as toner charging, for example, −200 V, −300 V, and −300 V, are applied to the developing roller 34, the toner supply roller 35, and the layer forming blade 39, respectively. Is applied with a bias voltage having a polarity opposite to that of the toner charging, for example, + 2400V and + 1100V, respectively. Further, the cam 22 is changed from the first position to the second position, and the developing roller 34 is pressed against the photosensitive drum 31 with a stronger force than that at the time of printing, that is, a pressing force (second set pressure) of 3000 gf (one side 1500 gf) as a whole. To do.

  In this state, the photosensitive drum 31, the charging roller 32, the transfer roller 12, the developing roller 34, and the toner supply roller 35 are rotated. As a result, reversely charged (+) toner is discharged from the transfer roller 12 and the charging roller 32 and adheres to the surface of the photosensitive drum 31, and further reaches the developing roller 34 as the photosensitive drum 31 rotates. Since the charging roller 32 is applied with +1100 V having a polarity opposite to that at the time of printing, the surface potential of the photosensitive drum 31 at this time is about +500 V, and reverse charging (attached to the surface of the photosensitive drum 31 ( +) The toner is collected by the developing roller 34 and further by the toner supply roller 35 due to the bias difference.

  At time t3, the collection of the reversely charged (+) toner is finished and the collection of the normally charged (−) toner and silica is started.

  Therefore, at time t3, biases having a polarity opposite to that of toner charging, for example, +200 V, +300 V, and +300 V, are applied to the developing roller 34, the toner supply roller 35, and the layer forming blade 39, respectively. The roller 32 is applied with a bias voltage having the same polarity as that of toner charging, for example, -900 V and -1150 V, respectively. The cam 22 remains in the second position.

  In this state, the photosensitive drum 31, the charging roller 32, the transfer roller 12, the developing roller 34, and the toner supply roller 35 are rotated. As a result, the normally charged (−) toner and silica are discharged from the transfer roller 12 and the charging roller 32, adhere to the surface of the photosensitive drum 31, and reach the developing roller 34 as the photosensitive drum 31 rotates. Since −1150 V at the time of printing is applied to the charging roller 32, the surface potential of the photosensitive drum 31 at this time is about −550 V, and normal charging (−) attached to the surface of the photosensitive drum 31 is performed. The toner and silica are collected on the developing roller 34 and further on the toner supply roller 35 due to the bias difference.

  At time t4, the recovery of the toner and silica ends. Therefore, at time t4, the cam 22 is returned to the first position, and the bias voltages applied to the transfer roller 12, the developing roller 34, the toner supply roller 35, and the layer forming blade 39 are returned to the state at the time of printing.

  Thereafter, in this state, the photosensitive drum 31, the charging roller 32, the transfer roller 12, the developing roller 34, and the toner supply roller 35 are rotated. At time t5, the rotational driving is stopped, and the developing roller 34, toner The bias voltage to the supply roller 35, the layer forming blade 39, the charging roller 32, and the transfer roller 12 is set to 0 V, and the photosensitive drum cleaning operation is finished.

  From time t4 to time t5, the rotating operation was performed with the bias voltage applied to the cam 22 and each part being in the printing state. The cleaning of the photosensitive drum 31 was performed under pressure contact with the cam 22 set to the second position. If this is done, there is a possibility that the potential of the photosensitive drum 31 may vary due to the charging by the transfer roller bias, and this variation is prevented. It is known that when there is this variation, image unevenness occurs in subsequent printing. Each time from time t2 to time t3, time t3 to time t4, and time t4 to time t5 may be long, but it is necessary to set at least the time for which the photosensitive drum 31 makes one rotation. .

  FIG. 7 is a time chart showing, as a comparative example, the operation of each unit during image formation of the image forming apparatus that does not perform the photosensitive drum cleaning operation, and the applied bias voltage. In this case, in the time chart shown in FIG. 6, when the image formation at the time t1 is finished, the cleaning is finished at the time t5.

  That is, when the image forming operation (printing) starts at time t10, as described above, the hopping roller 7 rotates to feed the recording paper 4 from the paper feed tray 3, and in synchronization with this, the transport rollers 8, 9, 10 Starts rotating and the conveyance of the recording paper 4 on the conveying path is started, and the photosensitive drum 31 of the developing device 2 is driven to rotate. Along with this, the transfer roller 12, the charging roller 32, the developing roller 34, and the toner supply roller 35 At the same time, the charging roller 32 has a negative voltage of −1150 V, the developing roller 34 has a negative voltage of −200 V, the toner supply roller and the layer forming blade 39 have a negative voltage of −300 V, and A positive voltage of +2400 V is applied to the transfer roller 12. The transfer roller 12 is urged against the photosensitive drum 31 by a pair of transfer roller springs 21 with an urging force (first set pressure) of 1000 gf (one side 500 gf).

  Under the above settings, the image forming process described above is executed. At time t11, the photosensitive drum 31, the transfer roller 12, the developing roller 34, the toner supply roller 35, and the transport rollers 7, 8, and 9 are driven to rotate. And the bias voltage applied to the developing roller 34, the toner supply roller 35, the layer forming blade 39, the charging roller 32, and the transfer roller 12 is set to 0 V, and the image forming operation (printing) is finished.

  Next, a print test (Example 1) performed using a test apparatus having the same configuration as that of the image forming apparatus 1, for example, and a print evaluation result thereof are performed based on the time chart of FIG. explain.

The test environment was low-temperature and low-humidity (temperature 10 ° C., humidity 20% RH) where defects are likely to occur.
Based on IS0 / IEC 19752 with Xerox 4200 Letter size (201b), printing was performed three pages at a time (three pages every 20 seconds), and 300 sheets were printed a day for a total of 2,100 pages. That is, after printing 300 sheets, the test for printing an image by printing one blank sheet and one solid black sheet was repeated for 7 days after being left overnight (12 hours) in the same low-temperature and low-humidity environment. The reason for leaving it overnight is that the external additive released from the toner is cooled and fixed to the photosensitive drum 31, and image defects are likely to occur.

  As a comparative example, a similar printing test (comparative example) was performed using an image forming apparatus that does not perform the photosensitive drum cleaning operation based on the above-described time chart of FIG. 7 under the same conditions.

  Table 1 is a table showing test results of Example 1 in which the photosensitive drum cleaning operation was performed and a comparative example in which it was not performed.

In addition, what can confirm visually a black spot on a white background or a white spot on a black background was set to NG (x).
An example of the defective image is shown in FIG. As shown in FIG. 5A, the black spots are generated in the white background image because the toner on the developing roller 34 is mechanically caught by the substance adhering to the photosensitive drum 31, mainly the external additive. . As shown in FIG. 5B, white spots are generated in the black background image because the external additive mainly attached to the photosensitive drum 31 is strongly negatively charged and the drum potential is kept high even after exposure. This is probably because the toner is not developed. In both charging characteristics, once the adhesion occurs, it becomes a starting point, and when the adhesion grows, it becomes a size that can be visually confirmed or grows linearly.

  As is clear from Table 1, in the case of the printing test of Example 1, the life of the developing device was extended compared to the case of the printing test of Comparative Example 1, and at least 1800 sheets could be printed normally. In the case of the comparative example, about 300 sheets were successfully printed.

  Based on the test results described above, the photosensitive drum cleaning after time t2 in the time chart of FIG. 6 will be considered. In the image forming apparatus 1 according to the present embodiment, toner (developer) and silica (external additive) are pressurized by the developing roller 34, the transfer roller 12, and the charging roller 32, and are mainly applied to the photosensitive drum 31. It adheres by mirror image force + van der Waals force. Since the transfer roller 12 is made of foamed rubber, countless fuzz caused by increasing the pressure scrapes off such deposits on the photosensitive drum 31 and temporarily takes them into the foamed cell. Then, it can be discharged by the reverse bias voltage applied at time t3 and finally returned to the developing roller 34. For this reason, in the printing test of Example 1, it seems that the influence of the external additive was able to be suppressed.

  The collection of the reversely charged (+) toner is started at time t2, and the collection of the normally charged (−) toner is performed at the subsequent time t3. The reversely charged toner is separated from the photosensitive drum 31 and each roller by the collecting operation. This is because normal charging may be caused by the friction of. Such a charged toner cannot be collected when the reversely charged toner is collected, but can be collected when the regular charged toner is collected thereafter.

In the present embodiment, the drive source of the transfer roller 12 and the drive source of the photosensitive drum 31 are described as the same drive motor. However, the present invention is not limited to this, and is driven to rotate by separate drive motors. You may comprise as follows.
Further, in the present embodiment, the description has been made so that the photosensitive drum cleaning is performed for each recording sheet. However, the present invention is not limited to this, and the configuration is such that the photosensitive drum cleaning is performed for each predetermined number of printings. Various modes can be taken.

  As described above, according to the image forming apparatus of the present embodiment, the external additive and toner adhering to the photosensitive drum are scraped off by pressing the transfer roller against the photosensitive drum with a high pressure and rotating it idly. Therefore, it is possible to prevent deterioration in printing quality due to the adhered matter.

Embodiment 2. FIG.
The image forming apparatus according to the present embodiment is different from the image forming apparatus 1 according to the first embodiment described above in that the cam 22 is disposed in the photosensitive drum cleaning operation, for example, between time t2 and time t4 shown in FIG. In the second position shown in (b), the linear velocity on the surface of the transfer roller 12 with respect to the photosensitive drum 31 is about 1.3 times (1.03 times in other cases). Therefore, in the present embodiment, as shown in FIG. 9, the image forming drive control unit 108 individually controls the rotation of the drum drive motor 25 that drives the photosensitive drum 31 and the transfer roller motor that drives the transfer rotor 12. Is configured to do.

  Since the other configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus 1 of the first embodiment described above, different points will be mainly described and description of common parts will be omitted.

  A printing test (Example 2) performed using a test apparatus having the same configuration as the image forming apparatus according to the present embodiment that performs the photosensitive drum cleaning operation based on the time chart of FIG. explain.

  The test conditions such as the test environment were the same as in the first embodiment, and a total of 3,000 pages were printed. That is, after printing 300 sheets a day, after leaving it overnight (12 hours) in a low-temperature and low-humidity environment, a test of printing a blank sheet and a solid black sheet to evaluate an image was repeated over 10 days.

  As a comparative example, a similar printing test (comparative example) was performed using an image forming apparatus that does not perform the photosensitive drum cleaning operation based on the above-described time chart of FIG. 7 under the same conditions.

  Table 2 is a table showing test results of Example 2 in which the photosensitive drum cleaning operation was performed and a comparative example in which the operation was not performed.

  As is apparent from Table 2, in the case of the printing test of Example 2, the life of the developing device was extended compared with the case of the printing test of Comparative Example 1, and at least 2700 sheets could be printed normally. In the case of the comparative example, about 300 sheets were successfully printed.

  According to the test results described above, in the printing test of Example 2, the peripheral speed difference between the photosensitive drum 31 and the transfer roller 12 during cleaning of the photosensitive drum was larger than in the printing test of Example 1. In particular, the ability to scrape off toner (developer) and silica (external additive) adhering to the photosensitive drum 31 by van der Waals force is promoted, and the number of sheets that can be printed normally is increased as compared with the first embodiment. I think that the.

  In the present embodiment, the drive source of the transfer roller 12 and the drive source of the photosensitive drum 31 are configured by separate drive motors, and the rotation control is appropriately performed. However, the present invention is not limited to this. The drive source of the transfer roller 12 and the drive source of the photosensitive drum 31 are the same drive motor, and at the time of cleaning the photosensitive drum, the gear ratio of the rotation transmission path to the transfer roller 12 is changed and the linear velocity is set in two stages. It may be configured to switch.

  As described above, according to the image forming apparatus of the present embodiment, the life of the developing device having the photosensitive drum can be further extended by increasing the peripheral speed of the transfer roller at the time of cleaning the photosensitive drum.

  Further, in each of the above-described embodiments, the cleanerless development method has been described. However, there are various methods such as a cleaning blade that scrapes off the developer on the photosensitive drum, a cleaning roller that collects by bias, or the like. It can take an aspect.

  In the above-described embodiments, the monochrome direct printing method has been described as the image forming apparatus. However, the present invention can also be applied to an intermediate transfer image forming apparatus and a color image forming apparatus including a plurality of developing devices. is there. In addition, the present invention can be applied to anything that performs printing / printing by an electrophotographic method, such as a multifunction printer, a fax machine, and a copying machine.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2 Developing apparatus, 3 Paper feed tray, 4 Recording paper, 7 Hopping roller, 8 Transport roller, 9 Transport roller, 10 Transport roller, 11 Fixing apparatus, 12 Transfer roller, 12a Transfer roller shaft, 13 Exposure apparatus , 15 stacker, 18 guide member, 21 transfer roller spring, 22 cam, 23 drive unit, 25 drum drive motor, 26 transport motor, 27 hopping motor, 28 cam motor, 29 transfer roller motor, 30 developing unit, 31 photosensitive drum, 32 Charging roller, 33 exposure device, 34 developing roller, 34a developing roller shaft, 35 toner supply roller, 35a supply roller shaft, 36 film, 37 toner, 38 toner sensor, 39 layer forming blade, 40 toner cartridge, 40a lower toner supply port 51 Photosensitive drum gear, 52 Transfer roller gear, 101 Interface unit, 102 Command / image processing unit, 103 Exposure control unit, 104 Print control unit, 105 Charging voltage control unit, 106 Development voltage control unit, 107 Transfer voltage control unit, 108 Image Forming drive control unit, 109 transport motor control unit, 110 hopping motor control unit, 111 cam control unit.

Claims (6)

In an image forming apparatus capable of taking an image forming state and a cleaning state for cleaning an electrostatic latent image carrier,
The electrostatic latent image carrier carrying the electrostatic latent image on the surface;
A transfer member for transferring a developer image formed on the surface of the electrostatic latent image carrier to a recording medium;
A pressing means for pressing the transfer member against the surface of the electrostatic latent image carrier with a first pressing force and a second pressing force larger than the first pressing force;
Control means for controlling the operation of the entire apparatus,
The control means controls the pressing means to press the transfer member with the first pressing force during the image formation and to press the transfer member with the second pressing force during the cleaning. An image forming apparatus.   The image forming apparatus according to claim 1, wherein a peripheral speed of the transfer member is greater during the cleaning than during the image formation.   3. The image forming apparatus according to claim 1, wherein the cleaning state is set after the image forming state is finished.   4. The image forming apparatus according to claim 3, wherein after the cleaning state is finished, the transfer member is pressed with the first pressing force for a predetermined time. A charging member for charging the surface of the electrostatic latent image carrier;
A developing member for developing the electrostatic latent image with a charged developer;
Have
At the time of the cleaning, first, a bias voltage having the same polarity as that at the time of image formation is applied to the developing member and the transfer member, and a bias voltage having a polarity opposite to that at the time of image formation is applied to the charging member. 5. The developer is collected, and then the normally charged developer is collected by reversing the polarity of each bias voltage applied to the developing member, the transfer member, and the charging member. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 1, wherein the developer is a developer prepared by a polymerization method.

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