JP2006011317A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing fatigue and wrinkles of material due to the repeated rotational movement of a transfer body and the transfer irregularities of an image caused thereby by maintaining the stable start and the stable rotation of the transfer body and reducing the rotational resistance caused by the difference of surface moving speed between an image carrier and the transfer body at the starting of driving. <P>SOLUTION: The image forming apparatus has a movable image carrier 1 carrying a toner image, a 1st drive means 111 for moving the image carrier 1, the movable transfer body 11 for transferring the toner image on the image carrier 1, and a 2nd driving means 121 moving the transfer body 11, and the image carrier 1 and the transfer body 11 come into contact with each other at a contact part. In the apparatus, the 1st drive means 111 works earlier than the 2nd driving means 121, when the image carrier 1 and the transfer body 11 start moving, and the speed of the transfer body 11 at the contact part exceeds the speed of the image carrier, while the moving of the transfer body 11 is in acceleration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic method or an electrostatic recording method such as a printer, a copying machine, and a facsimile, and in particular, an image carrier and a transfer member having a contact portion in contact with the image carrier. The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus, particularly a color image forming apparatus that forms a color image with a plurality of color developers, there are problems of small space, low cost, image quality, and high speed.

  In such a color copying machine, for speeding up, an image forming unit constituted by integrating image forming means such as a photosensitive drum as an image carrier, a developing device, a cleaner, a charger, etc. By implementing a color image forming process called a tandem system in which a plurality of colors are mounted and arranged in parallel with the transfer direction of a transfer material on which an image is transferred and the movement direction of an intermediate transfer body or the like, the speed is increased.

  In the tandem image forming apparatus, for each color of developer to be used, an image forming unit is provided for each of yellow, magenta, cyan, and black, for example, and a photosensitive drum that is an image carrier inside the image forming unit An image forming process is performed until a developer image (toner image) is formed on the surface. The image forming unit is arranged along one transfer body that is a transfer material conveyance body or an intermediate transfer body that conveys the transfer material, and the circumference of the photosensitive drum is directed to the transfer body side in each image formation section. The toner image formed on the surface is directly transferred onto the transfer material conveyed to the transfer body by moving the transfer body to each image forming unit, or transferred onto the intermediate transfer body as the transfer body. Then, it is further transferred to a transfer material at a time to form a color toner image, and the color toner image is fixed on the transfer material by heat and pressure by a fixing means to form an image formed product. Executed. A tandem type color image forming apparatus is disclosed in, for example, Patent Document 1.

  In such a tandem color image forming apparatus, for example, an electrostatic conveyance belt (conveyance belt) that is a transfer material conveyance body is used as the transfer body, and the belt conveyance for driving the image forming unit to move the electrostatic conveyance belt is performed. A device is provided.

  In such a belt conveyance device, the conveyance belt is often formed in an endless belt shape and is rotationally driven by a driving roller that supports the belt. Then, the photosensitive drum circumferential surface in the image forming unit contacts the belt surface of the conveyance belt, and both rotate so that the photosensitive drum circumferential surface and the conveyance belt surface move in the same direction at the contact portion.

  However, in order to remove residual toner after toner image transfer, the photosensitive drum often has a blade that is always in sliding contact with the image forming surface as a cleaning unit, which is a large driving load for the photosensitive drum. .

  For this reason, the photosensitive drum is delayed in the start of rotation (movement) as compared with a conveyance belt that is driven to rotate by a drive roller having a relatively small diameter and immediately responds to an instruction to start movement. Therefore, when the control unit of the image forming apparatus gives a movement start instruction to both the photosensitive drum and the conveyance belt at the same time, only the photosensitive drum starts to rotate after a predetermined time has elapsed.

  That is, when a movement start instruction is given to the photosensitive drum and the electrostatic conveyance belt at the same time, the largest speed difference is generated at the moment of starting rotation. As a result, the conveyance belt is subjected to rotational resistance from the photosensitive drum. In the tandem type color image forming apparatus, the electrostatic conveyance belt is in contact with a plurality of photosensitive drums, and receives a larger rotational resistance from each photosensitive drum.

  Due to the rotational resistance caused by such a difference in peripheral speed, the conveyor belt undergoes permanent deformation due to fatigue due to repeated stress. When permanent deformation further proceeds, a wave or wrinkle is generated on the belt. Wrinkles generated on the electrostatic conveyance belt cause transfer unevenness.

  Further, the wrinkles on the belt are irregularities with a depth of about several μm. Normally, the electrostatic conveyance belt is always in contact with the image forming surface of the photosensitive drum for transferring the toner image from the photosensitive drum. Therefore, rubbing unevenness is generated on the photosensitive drum, which causes uneven development and appears as a vertical pattern on the formed image.

  In addition, the wrinkles of the conveyor belt become larger each time the start-up is repeated, and there is a risk that the image quality of the output image will be significantly impaired as the apparatus durability progresses. In order to prevent such image quality defects, it is necessary to frequently replace the photosensitive drum and the electrostatic conveyance belt, which may lead to high running costs.

  It is also conceivable that feedback control is performed between the photosensitive drum and the conveying belt to synchronize the rotation. For example, as disclosed in Patent Document 2, one speed is detected by an encoder or the like between the photosensitive drum and the conveyor belt, and the other drive source is turned ON / OFF based on the detection result. Measures to make it follow can be considered.

  However, in this case, since one speed is corrected to the other speed, the positional relationship between the photosensitive drum and the conveyor belt can be controlled so as to be always constant. Resistance is generated.

  Another possible measure is to drive the photosensitive drum at a time earlier than the conveyor belt to reduce the load on the conveyor belt.

  However, the portion of the conveying belt that has moved following the photosensitive drum on the contact surface with the photosensitive drum causes slack between the belt driving roller and the photosensitive drum, which hinders stable start-up and stable rotation of the belt. Bring

  Also, if the photosensitive drum and the conveyor belt have a peripheral speed difference from the viewpoint of transferability, and the conveyor belt is moving fast, the sag of the electrostatic conveyor belt disappears over time. There is also.

However, from the viewpoint of shortening the time from the print job signal to the end of printing, it is not desirable to eliminate the slack depending on the peripheral speed difference.
JP-A-9-288396 JP-A 64-72176

  It is an object of the present invention to maintain stable start-up and stable rotation of a transfer member such as a conveyance belt or an intermediate transfer belt, and to reduce a rotational resistance generated by a surface movement speed difference from an image carrier at the start of movement. It is an object of the present invention to provide an image forming apparatus in which material fatigue, wrinkles, and image defects caused thereby are prevented by repeated rotational movements of

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a movable image carrier that carries a toner image, a first driving means that moves the image carrier, and a movable device for transferring a toner image on the image carrier. In the image forming apparatus, the image carrier and the transfer body are in contact with each other at a contact portion, and a second driving unit that moves the transfer body.
At the start of movement of the image carrier and the transfer body, the first driving unit operates before the second driving unit, and the transfer body at the contact portion is accelerated during the movement of the transfer body. The image forming apparatus is characterized in that the speed of the image exceeds the speed of the image carrier.

  An image forming apparatus according to the present invention includes a movable image carrier that carries a toner image, a first drive unit that moves the image carrier, and a movable transfer that transfers a toner image on the image carrier. In the image forming apparatus in which the image carrier and the transfer body are in contact with each other at the contact portion, when the movement of the image carrier and the transfer body starts, Since the drive means operates before the second drive means and the speed of the transfer body at the contact portion exceeds the speed of the image carrier during acceleration of movement of the transfer body, stable start and stable rotation of the transfer body are achieved. An image forming apparatus that can maintain and reduce the rotational resistance generated by the difference in surface movement speed from the image carrier at the start of movement, and prevent material fatigue, wrinkles, and image defects caused by the repeated rotational movement of the transfer body Was able to provide.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

Example 1
With reference to FIG. 2, the image forming apparatus of this embodiment will be described. Here, a side sectional view of the tandem type color image forming apparatus is shown.

  The tandem type image forming apparatus according to the present exemplary embodiment includes four image forming units 7 (7a, 7b, 7c, and 7d) for each color, and includes Bk (black) toner, C (cyan) toner, and M ( For each color of magenta toner and Y (yellow) toner, respective images are formed on the photosensitive drum 1 which is each drum-shaped image carrier provided therein, and an electrostatic conveyance belt (conveyance belt) 11 which is a transfer body. This is a color image forming system in which the transfer material S carried on the surface is sequentially transferred by a transfer unit corresponding to each image forming unit 7 and finally fixed on the sheet S as a transfer material.

  In this color image forming apparatus, a belt conveyance device 5 including the transfer unit and the conveyance belt 11 is mounted on the front side surface (right side in FIG. 2) of the main body device. The sheet S as a transfer material set in the belt conveying device 5 is picked up one by one by a paper feed roller 18 and fed into the device by a feed roller (roll pair) 19.

  In the belt conveyance device 5, the conveyance belt 11 that conveys the sheet S is supported by a plurality of rotatable winding rollers 13, 14 a, 14 b, and 15, and is flattened in the sheet conveyance direction by the rollers 13 and 14 a. This portion becomes the transfer surface 50 which is a contact portion between the photosensitive drum 1 and the conveyance belt 11, and the suction roller 22 is disposed on the upper surface side (outer surface side) of the electrostatic conveyance belt 11 at the most upstream portion in the belt 11 movement direction. Is provided. By applying a bias to the suction roller 22, the sheet S is electrostatically attracted to the transport belt 11.

  Opposite to the transfer surface 50, four photosensitive drums 1 (1a, 1b, 1c, 1d) provided in each of the image forming units 7 are linearly arranged. In each image forming unit 7 (7a, 7b, 7c, 7d), each photosensitive drum 1 is sequentially surrounded by the vicinity of its peripheral surface, and a charger 2 (2a, 2b, 2c, 2d), a developing device. 4 (4a, 4b, 4c, 4d) are arranged. Further, transfer members 12 (12a, 12b, 12c, 12d) as the transfer means are disposed at positions where the conveyance surface of the conveyance belt 11 is sandwiched with respect to each photosensitive drum 1.

  In the housing of each of the developing devices 4, Bk (black) toner and C (cyan) are transferred from the upstream side in the moving direction of the conveying belt 11 (downward in the drawing) in each of the image forming units 7 a, 7 b, 7 c, and 7 d. Toner, M (magenta) toner, and Y (yellow) toner are accommodated, respectively.

  In addition, a predetermined gap is provided between the charger 2 and the developing unit 4, and the peripheral surface of the photosensitive drum 1 is exposed from the scanner unit 3 (3 a, 3 b, 3 c, 3 d) as exposure means through this gap. Irradiation takes place.

  In this color image forming apparatus, the conveyance belt 11 circulates (rotates) in the clockwise direction in the figure to convey the sheet S. On the other hand, the photosensitive drum 1 rotates (moves), and a toner image is formed on the surface by the surrounding image forming means in the rotation process. That is, each charger 2 uniformly charges the corresponding peripheral surface of the photosensitive drum 1 with a predetermined charge, and the scanner unit 3 uniformly charges the peripheral surface of the photosensitive drum 1 as image information. In response, an electrostatic latent image is formed by exposure. The developing device 4 transfers toner to the low potential portion of the electrostatic latent image to form a toner image (development).

  The toner images formed (developed) on the peripheral surface of each photosensitive drum 1 are attracted to the electric charges generated on the conveyed sheet S by the transfer electric field formed by the transfer member 12 corresponding to the toner image, and the sheet S. It is transferred to the surface. The sheet S on which the toner image has been transferred is discharged to the outside by the discharge roller pair 23 after the toner image is thermally fixed on the surface of the sheet S by the fixing unit 20 having the pressure roller 21b and the heat generating roller 21a.

  Each photosensitive drum 1 includes a blade 6 (6a, 6b, 6c, 6d) that is a cleaning member in order to clean the residual toner remaining after the toner image transfer on the photosensitive drum 1. The blade 6 is always in sliding contact with the toner image surface side of the photosensitive drum 1, and the rotational resistance of the photosensitive drum 1 is large, about 8 kgf · cm.

  As described above, in the image forming process, a toner image is formed on the surface of the photosensitive drum 1 in the rotation process of the photosensitive drum 1 and the electrostatic conveyance belt 11 in each image forming unit 7. It is executed by transferring the sheet onto the sheet S carried on the electrostatic conveyance belt 11 in a superimposed manner. When the toner image is transferred from the photosensitive drum 1 to the sheet S on the conveying belt 11 by the transfer member 12, both are brought into contact with each other through the sheet S while rotating. At that time, depending on the rotational movement of the two, they affect each other by rubbing against each other. Here, at the time of image formation, both rotate at substantially the same speed (within 2% even if there is a speed difference), and the rotational movement mechanism of the photosensitive drum 1 and the conveyor belt 11 will be described below with reference to a block diagram shown in FIG. Will be described.

  The photosensitive drum 1 is transmitted with a drive through a large-diameter gear and a triangular coupling 112 from a drum drive motor 111 provided as a first drive means. The drum drive motor 111 includes a DC servo motor and the like, and operates according to the controller 100 that is a drive control unit that controls the operation of each unit in the image forming process in the apparatus main body connected to the drum drive motor 111.

The electrostatic conveyance belt 11 is composed of a film-like member having a thickness of about 110 μm and having a volume resistivity of 10 ¹² Ω · cm or less. The electrostatic conveyance belt 11 is a winding roller that constitutes a belt suspension tension member. The transfer roller 50 includes a downstream driving roller 13, an upstream driven roller 14a, and a driven roller 15 and a tension roller 14b. Since the sheet S is wound in the direction in which the sheet S is conveyed, in this case, is vertically arranged, it moves from the bottom to the top in the direction of gravity (rotation 9).

  The volume resistivity is a value obtained by applying 100 V with a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe compliant with JIS method K6911. As a material, PVDF was used, and Young's modulus was 1000 MPa. This was stretched under the condition that the belt tension was 8 g / mm.

  These rollers 13, 14 a, 14 b, and 15 are all arranged substantially in parallel with their both ends being rotatably held between bearings (not shown). The driving roller 13 is composed of a metal roller having a rubber layer with a large friction coefficient on the surface layer, and its diameter is set to 26 mm. The driving roller 13 is driven to rotate at a predetermined speed in the direction in which the sheet S is conveyed by the belt driving motor 121. The The driven roller 14 a has a function of regulating problems such as deviation and meandering that occur in the electrostatic conveyance belt 11.

  As shown in FIG. 4, the rotation mechanism of the belt 11 rotates the driving roller 13 by a belt driving motor 121 provided as a second driving unit, and the conveying belt 11 moves in the direction in which the sheet S is conveyed. Then, the driving force is transmitted to the conveying belt 11 by the frictional force between the outer peripheral surface of the driving roller 13 and the inner peripheral surface of the electrostatic conveying belt 11. Then, the electrostatic conveyance belt 11 starts to move in the direction in which the sheet S is conveyed between the four members of the driving roller 13, the driven rollers 14a and 15 and the tension roller 14b. The belt drive motor 121 includes a DC motor and the like, and operates according to the controller 100 connected to the belt drive motor 121.

  That is, the operation of both motors 111 and 121 is controlled by signals output from the controller 100 as drive control means provided in the apparatus control mechanism.

  The speed profiles of the drum drive motor 111 / belt drive motor 121 and the photosensitive drum 1 / electrostatic transport belt 11 are shown in FIG. 1A is a comparison of the surface movement (rotation) speeds of the drum 1 and the belt 11, and FIG. 1B is a comparison of the rotation speeds of the drum drive motor 111 and the belt drive motor 121.

  In operating the drum drive motor 111 and the belt drive motor 121, the drum drive motor 111 is first operated. However, the photosensitive drum 1 has a large rotational resistance, and has stopped without rotating for a certain time from the operation of the motor 111, and starts rotating (moving) after T seconds. Here, the time T from the operation of the motor to the start of rotation (movement) of the photosensitive drum 1 is a specific value based on the magnitude of the rotational resistance. That is, when the photosensitive drum 1 is large, it is set in advance from the relationship with its moment of inertia. Here, the rotation speed of the motor 111 increases at a certain inclination: A1 during the start-up from the operation of the motor 111 until the rotation speed reaches the set speed. In other words, by operating the motor 111 faster than the photosensitive drum 1 by T of several seconds at the acceleration A1, the rotational speed of the photosensitive drum 1 is changed almost at the same time as the rotational speed of the motor 111 becomes the set speed. 11 to a set speed that is substantially the same as the rotation speed.

  As the photosensitive drum 1 rotates, the conveyance belt 11 starts to rotate (move) by obtaining driving force from the four photosensitive drums 1 in contact before the rotation (movement) starts. That is, the photosensitive drum 1 also serves as a drive source for the transport belt 11.

  Next, the controller 100 operates the belt drive motor 121 after ΔT from the start of rotation of the drum 1, that is, after T + ΔT from the operation of the drum drive motor 111. Here, ΔT is a time for ensuring that the electrostatic conveyance belt 11 receives rotational driving after receiving the rotational force from the photosensitive drum 1.

  The rotating belt 11 is further subjected to a rotational force by a belt driving roller 13 that has obtained a driving force from a belt driving motor 121. At this time, in starting up from the operation of the motor 121 to the set rotational speed, the speed increases at a certain inclination: B1. That is, the motor 121 reaches a set speed in a few seconds at the acceleration B1, and at that time, the moving speed of the belt 11 also becomes a set speed that is substantially the same as the rotational speed of the photosensitive drum 1.

  At this time, the start-up time from the operation of the belt drive motor 121 until the rotation (movement) speed of the belt 11 reaches the set speed is shorter than that of the drum drive motor 111. That is, there is a relationship of A1 <B1.

  As a feature of the present embodiment, the controller 100 conveys the above A1, B1, T, and T + ΔT to the photosensitive drum 1 at the crossing point X in the middle of starting up in the time until the drum 1 and the belt 11 start up. It is set so that the surface layer speed of the belt 11 is reversed. That is, the drum 1 starts to rotate first, and the speed of the belt 11 is set so as to overtake the rotation speed of the drum 1 during the acceleration at which the rotation speed of the conveyor belt 11 becomes the set speed.

  As described above, the controller 100 operates in accordance with the predetermined operation timings T and T + ΔT and the start-up accelerations A1 and B1 when the drum drive motor 111 and the belt drive motor 121 are operated, and the conveyor belt 11 is moved to the photosensitive drum. 1, the belt driving motor 121 is operated so that the moving speed of the conveying belt 11 overtakes the rotating speed of the photosensitive drum 1 later.

  Therefore, in this image forming apparatus, material fatigue due to excessive tensile stress of the belt 11 due to a difference in activation time between the photosensitive drum 1 and the electrostatic conveyance belt 11 can be suppressed. Further, since the control is performed so that the speed of the conveyor belt 11 exceeds during the start-up, the rotation of the conveyor belt 11 is stable until the toner image is transferred, and image defects such as color misregistration do not occur.

  Specifically, the image defect accompanying material fatigue can be suppressed as follows. In the conventional start-up method, a starting shock occurs, and a high stress is instantaneously applied to the transport belt 11. After starting up repeatedly and starting up 50K times, 90% of the image defects occurred. On the other hand, this image forming apparatus can suppress the occurrence rate to a level where no image defect occurs after starting 50K times.

  During printing, the belt 11 and the photosensitive drum 1 are electrostatically attracted by the transfer bias, and the frictional force between the photosensitive drum 1 and the belt 11 tends to increase. On the other hand, after the printing is completed or the transfer to the sheet S is completed, the potential of the photosensitive drum 1 is dropped to 0V. Then, the transport belt 11 is also neutralized as a result. Further, when the rotation of the belt 11 and the drum 1 is started, no transfer bias is applied to the transfer member 12 positioned opposite the drum 1. For this reason, during the next printing, the electrostatic attraction force between the photosensitive drum 1 and the conveyor belt 11 is not generated. Therefore, since the slack of the belt 11 at the time of start-up is less than the influence of the electrostatic attraction force, the speed of the photosensitive drum 1 is somewhat higher than the speed of the transport belt 11 at the start-up. It is acceptable.

  Here, the set speeds of the photosensitive drum 1 and the conveyor belt 11 are the same, but are not necessarily limited thereto.

Example 2
With reference to FIG. 3, an image forming apparatus according to Embodiment 2 of the present invention will be described. This figure is a side sectional view of a tandem type color image forming apparatus that uses an intermediate transfer member as a transfer member that moves to face the photosensitive drum 1.

  This image forming apparatus includes an image forming unit 7 (7a, 7b, 7c, 7d) corresponding to each color of cyan, yellow, magenta, and black, a primary transfer roller 12 (12a, 12b, 12c, 12d) for each color, an intermediate An intermediate transfer belt 51 as a transfer member, a counter roller 52 and a driving roller 55, a driven roller 54, a paper feeding cassette 61, a paper feeding roller 62, a conveying roller pair 63, a registration roller pair 64, and a fixing roller that stretch the intermediate transfer belt 51. A roller pair 65, a paper discharge roller pair 66, and the like are included.

  Each image forming unit 7 includes a photosensitive drum 1 (1a, 1b, 1c, 1d), a charging device 2 (2a, 2b, 2c, 2d), a developing device 4 (4a, 4b, 4c, 4d), and a photosensitive member. It has a cleaning member 6 (6a, 6b, 6c, 6d), and has a scanner device unit 3 (3a, 3b, 3c, 3d) which is an exposure device common to each image forming unit 7.

  These image forming units 7 are arranged along the intermediate transfer belt 51, and the intermediate transfer belt 51 is wound around a driving roller 55, a driven roller 54, and a counter roller 52 that constitute a belt suspension member. Thus, a transfer surface 50 is formed between the driving roller 55 and the driven roller 54 as a contact portion that comes into contact with the photosensitive drum 1 in the image forming portion 7 and rotates in the forward direction with respect to the rotation of the photosensitive drum 1 ( Move). Each of these rollers 52, 54, and 55 is disposed substantially in parallel so that both ends thereof are rotatably held between bearings (not shown). The drive roller 55 is on the downstream side in the moving direction of the belt 51 on the transfer surface.

  The drive roller 55 is composed of a metal roller having a rubber layer with a large friction coefficient on the surface layer, and has a diameter set to 26 mm, for example, and is predetermined in a direction in which the intermediate transfer belt 51 is rotated by a belt drive motor 121 described below. It is rotationally driven at a speed of The driven roller 54 has a function of regulating problems such as deviation and meandering that occur in the intermediate transfer belt 51.

  The outline of the image forming operation in this apparatus will be described below. The operation of each image forming unit 7 is the same as that of the image forming unit 7 of the first embodiment.

  The surface of each photosensitive drum 1 that is driven to rotate is uniformly charged by each charging device 2. Then, an image forming signal is transmitted to the image forming apparatus via various networks and the like, and the scanner device 3 irradiates each photosensitive drum 1 with laser light corresponding to each part based on the image forming signal. The developing device 4 develops the electrostatic latent image due to the potential difference thus formed on the photosensitive drum 1 with the toner of each color, and visualizes it.

  Each color toner image formed on the surface of each photosensitive drum 1 is primarily transferred to an intermediate transfer belt 51 that is electrostatically driven to rotate by an electric field at a position facing each primary transfer roller 12. At this time, first, a black toner image is primarily transferred onto the intermediate transfer belt 51 on the transfer surface 50 at the primary transfer position where the primary transfer roller 12a faces. Subsequently, a yellow toner image is primarily transferred onto the intermediate transfer belt 51 on the intermediate transfer belt 51 at a primary transfer position facing the primary transfer roller 12b. Similarly, a magenta toner image and a cyan toner image are sequentially superimposed to form a full-color toner image on the intermediate transfer belt 51.

  The full-color toner image is conveyed to the secondary transfer position where the opposing roller 52 and the secondary transfer roller 56 face each other as the intermediate transfer belt 51 rotates. On the other hand, the recording sheet S, which is a single transfer material stored in the paper feed cassette 61, is similarly conveyed to the secondary transfer position via the paper feed roller 62, the conveyance roller pair 63, and the registration roller pair 64, The intermediate transfer belt 51 and the recording sheet S reach the secondary transfer position at the same time with the passage of the registration roller pair 64, and the transfer electric field generated by the intermediate transfer belt 51 and the secondary transfer roller 56 acts. The toner image is electrostatically transferred to the recording sheet S.

  Then, the recording sheet S holding the full-color toner image on the surface passes through the nip portion of the fixing roller pair 65. At that time, the full-color toner image is melted by the action of heat and pressure and fixed on the recording sheet S as a permanent image, and the image formation is completed.

  Each photosensitive drum 1 includes a blade 6 (6a, 6b, 6c, 6d) that is a cleaning member in order to clean the residual toner remaining after the toner image transfer on the photosensitive drum 1. The blade 6 is always in sliding contact with the toner image surface side of the photosensitive drum 1, and the rotational resistance of the photosensitive drum 1 increases.

  As described above, in the image forming process of the intermediate transfer method of the present embodiment, the direct transfer method of the first embodiment until the image forming operation for forming the toner image on the photosensitive drum 1 in each image forming unit. The same operation is performed. Also in this embodiment, a toner image is formed on the surface of the photosensitive drum 1 in the rotation process of each photosensitive drum 1 in each image forming unit 7. In this embodiment, this is a transfer body. The image is transferred onto the intermediate transfer belt 51 in a superimposed manner. Also in this case, when the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 51 by the primary transfer roller 12, both contact with each other while rotating. At that time, depending on the rotational movement of the two, they affect each other by rubbing against each other.

  Here, during image formation, both rotate at substantially the same speed (within 2% even if there is a speed difference). Therefore, the rotational movement mechanism of the photosensitive drum 1 is shown in FIG. This is the same as described above.

  As shown in FIG. 4, the intermediate transfer belt 51 drives the drive roller 55 by a belt drive motor 121 as a second drive unit, and friction between the outer peripheral surface of the drive roller 55 and the inner peripheral surface of the intermediate transfer belt 51. The driving force is transmitted to the intermediate transfer belt 51 by the force. The intermediate transfer belt 51 is rotationally driven in the direction in which the sheet S is conveyed between the three members of the driving roller 55, the driven roller 54, and the counter roller 52.

  Also in the intermediate transfer belt 51, the belt drive motor 121 includes a DC motor or the like and operates according to the controller 100 connected to the belt drive motor 121, similarly to the conveyance belt 11 in the first embodiment.

  That is, also here, the operations of the motors 111 and 121 of the photosensitive drum 1 and the intermediate transfer belt 51 are controlled by signals output from the controller 100 as drive control means provided in the apparatus control mechanism.

  Therefore, the speed profiles of the drum drive motor 111 / belt drive motor 121 and the intermediate transfer belt 51 / photosensitive drum 1 are infinitely close to those described in the first embodiment. By considering the electrostatic conveyance belt 11 as the intermediate transfer belt 51, the same explanation is given with reference to FIG.

  That is, first, the drum drive motor 111 is operated as shown in FIG. Then, the photosensitive drum 1 starts to rotate after T seconds from the start of driving and from the operation to the set speed as shown in FIG. 1 (b) due to rotational resistance caused by rubbing against the cleaning blade 6 or the like. In the increase, the speed increases at a certain inclination: A1, and reaches the set speed in a few seconds. As a result, the photosensitive drum 1 serves as a driving source for the intermediate transfer belt 51, and the intermediate transfer belt 51 obtains a driving force from the four photosensitive drums 1 in contact and starts to rotate.

  Next, the controller 100 operates the belt drive motor 121 after T + ΔT from the operation of the drum drive motor 121. The intermediate transfer belt 51 is further subjected to a rotational force by a belt driving roller 55 that has obtained a driving force from the belt driving motor 121, and has a rotational speed with a certain inclination: B1 during the start-up from operation to the set rotational speed. Rises and reaches the set speed in a few seconds.

  Also in this case, the start-up time from the operation of the belt drive motor 121 until the rotation speed of the belt 51 reaches the set speed is shorter than that of the drum drive motor 111, and there is a relationship of A1 <B1, and the controller 100 In the time until the drum 1 and the belt 51 rise, the surface movement (rotation) speed of the photosensitive drum 1 and the intermediate transfer belt 51 at the intersection point X in the middle of the above-described A1, B1, T, T + ΔT. Set to reverse.

  As described above, when the drum driving motor 111 and the belt driving motor 121 are operated, the controller 100 operates according to the predetermined start timings T, T + ΔT, and the starting accelerations A1, B1, and the rotational speed of the intermediate transfer belt 51. During the acceleration until the speed reaches the set speed, the belt drive motor 121 is operated so as to overtake the speed later while rotating the belt 51 on the photosensitive drum 1.

  Therefore, in this image forming apparatus, material fatigue due to excessive tensile stress of the belt 51 due to a difference in the activation time between the photosensitive drum 1 and the intermediate transfer belt 51 can be suppressed. Further, since the control is performed so that the speed of the intermediate transfer belt 51 exceeds during the start-up, the rotation of the intermediate transfer belt 51 is stable until the toner image is transferred and does not cause image defects such as color misregistration. .

  Here, paying attention to the difference between the electrostatic transfer belt 11 and the intermediate transfer belt 51, the point that the present invention is effective for the intermediate transfer belt 51 will be described.

  The transfer process of the intermediate transfer belt 51 is transferred from the photosensitive drum 1 to the sheet S via the intermediate transfer belt 51 as described above. In other words, the photosensitive drum 1 and the intermediate transfer belt 51 are always in contact with each other and are repeatedly rubbed. The process in which the belt wrinkle becomes an image defect is caused by the unevenness generated on the belt 51 repeatedly rubbing against the photosensitive drum 1, creating uneven rubbing on the photosensitive drum 1, and causing uneven charging.

  In view of this, it can be seen that the intermediate transfer belt 51 having a long rubbing time with respect to the photosensitive drum 1 has a disadvantageous structure for belt wrinkling because it rubs against the photosensitive drum 1 for a longer time. Thus, the present invention can be said to be an advantageous invention for the image forming apparatus having the intermediate transfer belt 51 configuration.

  As in the first embodiment, during printing, the belt 51 and the photosensitive drum 1 are electrostatically attracted by the transfer bias, and the frictional force between the photosensitive drum 1 and the belt 51 tends to increase. . On the other hand, after printing or after transfer to the sheet S, the surface potential of the photosensitive drum 1 is dropped to 0V. Then, the intermediate transfer belt 51 is also neutralized as a result.

  Again, when the rotation of the belt 51 and the drum 1 is started, no transfer bias is applied to the primary transfer roller 12 positioned opposite the drum 1. For this reason, during the next printing, the electrostatic attraction force between the photosensitive drum 1 and the intermediate transfer belt 51 is not generated. Therefore, since the slack of the belt 51 at the time of start-up is less than the influence of the electrostatic attraction force, the speed of the photosensitive drum 1 is greater than the speed of the intermediate transfer belt 51 at the time of start-up. Tolerable to some extent.

  In other words, as described above, the present invention can be applied to an intermediate transfer type image forming apparatus in the same manner as the direct transfer type described in the first embodiment, and has a great disadvantage in the intermediate transfer type. It is possible to prevent the belt wrinkle.

  In the first embodiment, a vertically arranged tandem type image forming apparatus is used as an example, and in the second embodiment, a tandem type image forming apparatus having a configuration in which image forming portions are arranged in the horizontal direction is exemplified. It goes without saying that the present invention is effective even if the configuration is an intermediate transfer system or a direct transfer system, and the present invention is effective for such a tandem system. The present invention can also be applied to a configuration in which a plurality of developing devices are provided and a monochrome image forming apparatus.

3 is a timing chart showing how the image carrier (FIG. 1 (a)) and the transfer member (FIG. 1 (b)) are driven when the first and second driving means according to the present invention are started up. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. It is a block diagram which shows an example of the control means of the 1st and 2nd drive means which concerns on this invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
7 Image forming unit 5 Belt conveying device 6 Cleaning member 11 Conveying belt (transfer body)
14a, 55 Drive roller 51 Intermediate transfer belt (intermediate transfer member)
100 controller (drive control means)
111 Drum drive motor (first drive means)
121 belt drive motor (second drive means)

Claims (4)

A movable image carrier for carrying a toner image, a first driving means for moving the image carrier, a movable transfer member for transferring a toner image on the image carrier, and the transfer member An image forming apparatus in which the image carrier and the transfer body are in contact with each other at a contact portion.
At the start of movement of the image carrier and the transfer body, the first driving unit operates before the second driving unit, and the transfer body at the contact portion is accelerated during the movement of the transfer body. The image forming apparatus is characterized in that the speed of the image exceeds the speed of the image carrier.   The image forming apparatus according to claim 1, wherein the transfer body is an intermediate transfer body.   The image forming apparatus according to claim 1, wherein the transfer body conveys a transfer material.   The image forming apparatus according to claim 1, wherein the transfer body includes a belt body.

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