Patent Grant
8036574
1. Field of the Invention
The present invention generally relates to an image forming apparatus using an electrophotographic recording method, such as a laser printer, a copying machine, a facsimile machine, or the like.
2. Description of the Related Art
Conventionally, image forming apparatuses using an electrophotographic method include a plurality of photosensitive drums that contribute to enhancing the speed of image forming. Various types of methods have been proposed for sequentially transferring toner images having different colors onto a recording material conveyed by an intermediate transfer belt or a conveying belt.
In such an image forming apparatus, a cartridge including a photosensitive drum or an intermediate transfer unit including an intermediate transfer belt is in a removable configuration. A driving force of a motor that is a drive unit of the main body of the image forming apparatus is transmitted to the photosensitive drum or a drive roller that is a drive member for the intermediate transfer belt or the conveying belt via a coupling unit. The coupling unit includes a first coupling provided on the side of the main body and a second coupling provided on the side of the photosensitive drum or the drive roller. The first coupling and the second coupling are configured such that a disconnected state as well as a connected state can be assumed.
When the first coupling and the second coupling are connected, the surface speed of the photosensitive drum or the belt is typically proportional to the speed of the motor. However, if the motor is started when the state of the couplings is changing from the disconnected state to the connected state, the photosensitive drum or the belt does not rotate (i.e., the surface speed is zero) even though the motor is activated. If this state continues, the surface of the photosensitive drum or the belt may be damaged, which may lead to image quality issues.
In these circumstances, Japanese Patent Application Laid-Open No. 2002-182537 discusses a method in which a low motor speed, compared to the speed that is used when an image is formed, is used until one of the couplings, which is used for transmitting a driving force generated by a motor to a photosensitive drum, is connected to the other coupling. In other words, the motor speed will be low during the connection time of the couplings. This time is based on the couplings that take the longest time in the connection.
According to an aspect of the present invention, an image forming apparatus for forming an image on a recording medium includes a photosensitive member, a motor, a belt configured to contact the photosensitive member, a drive member configured to rotate the belt and including a driven coupling, a drive coupling configured to rotate by a driving force generated by the motor, the drive coupling being movable in an axial direction such that the drive coupling can take an engagement position, at which the driving force is transmittable to the driven coupling while in engagement with the driven coupling, and a release position, at which the engagement with the driven coupling is released, a transfer member configured to transfer a toner image formed on the photosensitive member onto the recording medium carried on the belt or onto the belt, a voltage application unit configured to apply a voltage to the transfer member, and a control unit configured to execute control for causing the voltage application unit to apply the voltage to the transfer member after the drive coupling moves to the engagement position by drive of the motor and the driving force generated by the motor is transmitted to the driven coupling.
According to another aspect of the present invention, an image forming apparatus for forming an image on a recording medium includes a photosensitive member, a charging member configured to charge the photosensitive member, a motor, a belt configured to contact the photosensitive member, a drive member configured to rotate the belt and including a driven coupling, a drive coupling configured to rotate by a driving force generated by the motor, the drive coupling being movable in an axial direction such that the drive coupling can take an engagement position, at which the driving force is transmittable to the driven coupling while in engagement with the driven coupling, and a release position, at which the engagement with the driven coupling is released, a voltage application unit configured to apply a voltage to the charging member, and a control unit configured to execute control for causing the voltage application unit to apply the voltage to the charging member such that a portion charged by the charging member on the photosensitive member comes to a contact position where the portion contacts the belt after the drive coupling moves to the engagement position by drive of the motor and the driving force generated by the motor is transmitted to the driven coupling.
According to yet another aspect of the present invention, an image forming apparatus for forming an image on a recording medium includes a motor, a main-body coupling configured to rotate by a driving force generated by the motor, a process cartridge removable from a main body of the image forming apparatus and including a photosensitive drum and a drum coupling configured to transmit the driving force to the photosensitive drum by engaging with the main-body coupling at a predetermined phase angle when the process cartridge is mounted into the main body, a belt configured to contact the photosensitive member, a drive member configured to rotate the belt and including a driven coupling, a drive coupling configured to rotate by the driving force generated by the motor, the drive coupling being movable in an axial direction such that the drive coupling can take an engagement position, at which the driving force is transmittable to the driven coupling while in engagement with the driven coupling at a phase angle larger than the predetermined phase angle, and a release position, at which the engagement with the driven coupling is released, a transfer member configured to transfer a toner image formed on the photosensitive member onto the recording medium carried on the belt or onto the belt, a voltage application unit configured to apply a voltage to the transfer member, and a control unit configured to execute control for causing the voltage application unit to apply the voltage to the transfer member after the drive coupling moves to the engagement position by drive of the motor and the driving force generated by the motor is transmitted to the driven coupling.
According to yet another aspect of the present invention, an image forming apparatus for forming an image on a recording medium includes a motor, a main-body coupling configured to rotate by a driving force generated by the motor, a process cartridge removable from a main body of the image forming apparatus and including a photosensitive drum, a charging member configured to charge the photosensitive drum, and a drum coupling configured to transmit the driving force to the photosensitive drum by engaging with the main-body coupling at a predetermined phase angle when the process cartridge is mounted into the main body, a belt configured to contact the photosensitive member, a drive member configured to rotate the belt and including a driven coupling, a drive coupling configured to rotate by the driving force generated by the motor, the drive coupling being movable in an axial direction such that the drive coupling can take an engagement position, at which the driving force is transmittable to the driven coupling while in engagement with the driven coupling at a phase angle larger than the predetermined phase angle, and a release position, at which the engagement with the driven coupling is released, a voltage application unit configured to apply a voltage to the charging member, and a control unit configured to execute control for causing the voltage application unit to apply the voltage to the charging member such that a portion charged by the charging member on the photosensitive member comes to a contact position where the portion contacts the belt after the drive coupling moves to the engagement position by drive of the motor and the driving force generated by the motor is transmitted to the driven coupling.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
According to this embodiment, an image forming apparatus 100 includes four process cartridges 9a, 9b, 9c, and 9d, which are removable from an apparatus main body 100A. The process cartridges 9a to 9d are used for forming images of yellow (Y), magenta (M), cyan (C), and black (K), respectively.
The process cartridge 9a to 9d is an all-in-one cartridge including an organic photosensitive (OPC) drum 1a to 1d as a photosensitive member, a charging roller 2a to 2d as a charging member, a cleaning unit 3a to 3d used for removing residual toner on the photosensitive drum 1a to 1d, and a developing unit 8a to 8d. The developing unit 8a to 8d includes a developing sleeve 4a to 4d, nonmagnetic one-component developer (toner) 5a to 5d, and a developer blade 7a to 7d. The process cartridges 9b to 9d have a similar configuration as the process cartridge 9a except that they include developers 5b to 5d having respective different colors.
Exposure units 11a to 11d are provided above the process cartridges 9a to 9d. Each of the exposure units 11a to 11d includes a scanner unit configured to direct laser beams onto a polygonal mirror for scanning or a light emitting diode (LED) array. Scanning beams 12a to 12d, which are modulated by image signals, are directed on the photosensitive drums 1a to 1d, respectively.
Further, an intermediate transfer belt 13, which contacts all of the four photosensitive drums 1a to 1d, is arranged under the process cartridges 9a to 9d. The intermediate transfer belt 13 is stretched and supported by a secondary transfer counter roller 24, a drive roller 14 as a drive member, and a tension roller 15. These three rollers provide appropriate tension to the intermediate transfer belt 13. According to drive of the drive roller 14, the intermediate transfer belt 13 moves in the direction indicated by the arrow B, which is the same as the movement direction indicated by the arrow A of the photosensitive drums 1a to 1d, at a speed approximately the same as that of the drive roller 14.
According to the present exemplary embodiment, the intermediate transfer belt 13 is a 100 micrometer-thick polyvinylidene fluoride (PVDF) belt having a volume resistivity of 1010 ohm cm. The drive roller 14 as the stretching member is a 20-mm diameter roller with an aluminum cored bar coated with a 1.0 mm-thick layer of ethylene propylene diene M-class (EPDM) rubber which has an electric resistance of 104 ohms and in which carbon is distributed as an electroconductive agent. The tension roller 15 as the stretching member is a 20-mm diameter aluminum metal bar and provides a tension of 19.6 N for each one side and 39.2 N in total. The secondary transfer counter roller 24 as the stretching member is a 20-mm diameter roller with an aluminum cored bar coated with a 1.5 mm-thick layer of EPDM rubber which has an electric resistance of 104 ohms and in which carbon is distributed as an electroconductive agent.
Further, primary transfer rollers 10a to 10d as primary transfer members are arranged opposite the photosensitive drums 1a-1d with the intermediate transfer belt 13 in between. According to the present exemplary embodiment, each of the primary transfer rollers 10a to 10d is a roller having an outside diameter of 14 mm and includes a 6-mm-diameter nickel plated steel bar coated with a 4-mm thick elastic layer of nitrile butadiene rubber (NBR) foam sponge having an electric resistance of 107 ohms.
Further, the apparatus main body 100A includes a charge bias power supply unit 20a to 20d as a voltage supply unit for supplying a bias voltage to the charging roller 2a to 2d, a developing bias power supply unit 21a to 21d as a voltage supply unit for supplying a bias voltage to the developing sleeve 4a to 4d, and a primary transfer bias power supply unit 22a to 22d as a voltage supply unit for supplying a bias voltage to the primary transfer roller 10a. The intermediate transfer belt 13, the drive roller 14, the tension roller 15, the secondary transfer counter roller 24, the primary transfer rollers 10a-10d, and a toner charge unit 27 constitute an all-in-one belt unit 103. The belt unit 103 is removably mounted in the apparatus main body 10A.
Next, an example of an image forming operation will be described. When the image forming operation is started, the photosensitive drums 1a to 1d and the intermediate transfer belt 13 start to rotate in the direction indicated by the arrows A and B at a predetermined process speed. By the power supplied by the charge bias power supply unit 20a, the charging roller 2a charges the photosensitive drum 1a to a uniform negative polarity at its surface. Then, an electrostatic latent image corresponding to image information is formed on the photosensitive drum 1a by the scanning beam 12a emitted from the exposure unit 11a. According to the present exemplary embodiment, a voltage of −1000 V is applied to the charging roller 2a by the charge bias power supply unit 20a so that the surface of the photosensitive drum 1a is electrically charged to −500 V.
The toner 5a in the developing unit 8a is coated onto the developing sleeve 4a. The toner 5a on the developing sleeve 4 is regulated to have a predetermined thickness by the developer blade 7a. A predetermined bias voltage is supplied to the developing sleeve 4a from the developing bias power supply unit 21a. When the electrostatic latent image formed on the photosensitive drum 1a reaches the developing sleeve 4a by the rotation of the photosensitive drum 1a, the electrostatic latent image is made visible with the negatively chargeable toner. Accordingly, a toner image of the first color (yellow (Y), in this embodiment) is formed on the photosensitive drum 1a. Since the configuration of the process cartridges 9b, 9c, and 9d is similar to that of the process cartridge 9a, their description will be omitted.
An electrostatic image is formed on each of the photosensitive drums 1a to 1d according to exposure by the exposure units 11a to 11d while a controller as a control unit outputs a writing signal which is delayed depending on each primary transfer position of the corresponding color. Then, by each of the developing units 8a to 8d, an electrostatic latent image is developed into a toner image. Further, a bias voltage of a polarity opposite to a charge polarity of the toner is applied to the primary transfer rollers 10a to 10d by the primary transfer bias power supply units 22a to 22d, respectively. Through the above-described processes, toner images can be successively transferred onto the intermediate transfer belt 13, and a multiple superimposed image can be formed on the intermediate transfer belt 13.
Subsequently, in synchronization with the image formation, a transfer material P stacked in a transfer material cassette 16 is picked up by a feeding roller 17 and conveyed to registration rollers 18. Then, the transfer material P is further conveyed to an abutment portion which is formed between the intermediate transfer belt 13 and a secondary transfer roller 25 in synchronization with the toner image formed on the intermediate transfer belt 13. Subsequently, a bias voltage opposite in polarity to the toner is applied to the secondary transfer roller 25 by a secondary transfer bias power supply unit 26, so that the four-color superimposed images carried on the intermediate transfer belt 13 are simultaneously secondary-transferred onto the transfer material P. According to this exemplary embodiment, the secondary transfer roller 25 is a roller having an outside diameter of 18 mm and includes a 8-mm-diameter nickel plated steel bar coated with a 5-mm thick elastic layer of NBR foam (sponge) having an electric resistance of 108 ohms.
On the other hand, after the secondary transfer is completed, residual toner remaining on the intermediate transfer belt 13 is positively charged by the toner charge unit 27 which abuts the intermediate transfer belt 13. Then, by the primary transfer process in which a bias voltage of positive polarity is applied to each of the primary transfer members 10a to 10d, the residual toner is transferred onto the photosensitive drums 1a to 1d from the surface of the intermediate transfer belt 13 and collected by the cleaning units 3a to 3d.
According to the image forming apparatus of the present exemplary embodiment, a roller member including a 6-mm-diameter nickel plated steel bar 27a coated with a foam sponge layer 27b of EPDM rubber in which carbon black is distributed, and with a protective layer 27c made of water-soluble nylon as a surface layer, is used as the toner charge unit 27. Further, the toner charge unit 27 is connected to a toner charge bias power supply unit 28. In order to positively charge the untransferred residual toner, a direct voltage of 1 kV superposed on an alternating voltage of 2.5 kVpp is applied to the toner charge unit 27 by the toner charge bias power supply unit 28.
The transfer material P onto which the secondary-transfer-completed toner image is transferred is conveyed to a fixing unit 19. After the toner image is fixed by the fixing unit 19, the transfer material P is discharged to a discharging portion 112.
As illustrated in the example shown in
Now, the transmission of driving force to the photosensitive drum 1a in the process cartridge 9a will be described referring to the example shown in
Next, the transmission of driving force to the intermediate transfer belt 13 will be described referring to the example shown in
Further, as illustrated in the examples shown in
As illustrated in the example shown in
When the open/close door 102 is closed from an open state, a force is applied to the drive coupling 42 by the spring 44 in the direction indicated by the arrow E. However, since the recessed portion 43a and the raised portion 42a of this embodiment are triangular in section as illustrated in the example shown in
As illustrated in the block diagram shown in the example of
According to the image forming apparatus 100 of the present exemplary embodiment, since the resistance value of each of the intermediate transfer belt 13, the transfer rollers 10a to 10d, and the charging roller 2a varies depending on the environment, a preparation operation may be performed before the image forming operation. The preparation operation is an operation by which a bias voltage that is to be applied is corrected. This preparation operation may be performed when the open/close door 102 is opened or closed, or when the power of the image forming apparatus 100 is turned on.
However, since the movement of the drive coupling 42 is in synchronization with the movement of the open/close door 102 as described above, if the open/close door 102 is opened, the drive coupling 42 moves to the release position. On the other hand, if the open/close door 102 is closed, the drive coupling 42 also moves, but will be at the abutting position if it is not in phase with the driven coupling 43.
In this state, if the driving forces of the motors 30a to 30d and 31 are transmitted to the photosensitive drums 1a to 1d before they are transmitted to the intermediate transfer belt 13 in a preparation stage, then the photosensitive drum 1a will rotate while the intermediate transfer belt 13 is not rotating. In this case, if a bias voltage is applied to the charging roller 2a, a potential difference is generated between the surface of the photosensitive drum 1a and the intermediate transfer belt 13, which may then cause the photosensitive drum 1a to electrostatically attract the intermediate transfer belt 13. Accordingly, the photosensitive drum 1a may make the intermediate transfer belt 13 follow its movement in the same direction. Thus, the intermediate transfer belt 13 may rotate. This rotation may also cause the drive roller 14, to which the driven coupling 43 is arranged, to rotate. As a result, the state where the drive coupling 42 is not in phase with the driven coupling 43 (i.e., the unconnected state of the drive coupling 42 and the driven coupling 43) may continue. Thus, even if the image forming operation of the image forming apparatus 100 is started, the intermediate transfer belt 13 may rotate while being attracted to the photosensitive drum 1a, and the toner image will be formed on the photosensitive drum 1a in such a state.
When the toner image reaches a nip portion of the intermediate transfer belt 13 and the photosensitive drum 1a, the attracting force between the photosensitive drum 1a and the intermediate transfer belt 13 is reduced by the influence of the toner image. Thus, the rotation of the intermediate transfer belt 13 due to the electrostatic attraction between the photosensitive drum 1a and the intermediate transfer belt 13 may be stopped, but the transfer of the toner image onto the intermediate transfer belt 13 from the photosensitive drum 1a is continued. Then, the phase angle of the drive coupling 42 which is rotating according to the driving force generated by the motor 31 may match the phase angle of the driven coupling 43 which is not rotating. Subsequently, the couplings 42 and 43 are connected and move to the engagement position. Then, the drive roller 14 starts rotating as it receives the driving force of the motor 31. In such a state, the toner image is superposed on the intermediate transfer belt 13 and transferred, and thereby a defective image may be generated.
Further, a similar state may occur if the driving forces of the motors 30a to 30d and 31 are transmitted to the photosensitive drums 1a to 1d before they are transmitted to the intermediate transfer belt 13 in the preparation stage, and a bias voltage is applied to the charging roller 2a. That is, if the surface of the photosensitive drum 1a is charged, a potential difference may be generated between the surface of the photosensitive drum 1a and the intermediate transfer belt 13, which may then cause the photosensitive drum 1a to electrostatically attract the intermediate transfer belt 13. Accordingly, the photosensitive drum 1a may make the intermediate transfer belt 13 follow its movement in the same direction. Thus, the intermediate transfer belt 13 may rotate. This rotation can also cause the drive roller 14, to which the driven coupling 43 is arranged, to rotate. As a result, the state where the drive coupling 42 is not in phase with the driven coupling 43 (i.e., the unconnected state of the drive coupling 42 and the driven coupling 43) may continue. Thus, the toner image may be formed on the photosensitive drum 1a while the intermediate transfer belt 13 rotates while being attracted to the photosensitive drum.
When the toner image reaches a nip portion of the intermediate transfer belt 13 and the photosensitive drum 1a, the attracting force between the photosensitive drum 1a and the intermediate transfer belt 13 may be reduced by the influence of the toner image. Thus, the rotation of the intermediate transfer belt 13 due to the electrostatic attraction between the photosensitive drum 1a and the intermediate transfer belt 13 may be stopped, but the transfer of the toner image onto the intermediate transfer belt 13 from the photosensitive drum 1a may be continued. Then, the phase angle of the drive coupling 42 which is rotating according to the driving force generated by the motor 31 may be brought to match the phase angle of the driven coupling 43 which is not rotating. Subsequently, the couplings 42 and 43 are connected and move to the engagement position. Then, the drive roller 14 starts rotating as it receives the driving force of the motor 31. In such a state, the toner image may be superposed on the intermediate transfer belt 13 and transferred, and thereby a defective image may be generated.
Thus, according to the present exemplary embodiment, a bias voltage is not applied to the primary transfer rollers 10a to 10d during the connection time, which is the time for the connection of the drive coupling 42 and the driven coupling 43, after the motors 30a to 30d and 31 are started. That is, the controller 104 drives the motor 31 so that the drive coupling 42 is moved to the engagement position, and after a driving force of the motor 31 is transmitted to the driven coupling 43, the controller 104 controls each of the primary transfer bias power supply units 22a to 22d as a voltage application unit so that the voltage is applied to each of the transfer rollers 10a to 10d.
Details of the control will now be described referring to the examples shown in
The controller 104 outputs signals for starting the motors 30a to 30d and 31a time Tm after the power is turned on or the open/close door 102 is closed. Further the controller 104 outputs signals for starting application of voltage to the primary transfer bias power supply units 22a to 22d to start applying voltages to the primary transfer rollers 10a to 10d a time Td after the signals for starting the motors 30a to 30d and 31 are output. Here, the time Td is longer than a maximum connection time Tc which is a maximum time for connecting the drive coupling 42 to the driven coupling 43. According to the present exemplary embodiment, the maximum connection time Tc is a time for drive coupling 42 to rotate approximately 120 degrees at the maximum, since the recessed portion 43a and the raised portion 42a are triangular. If the process speed Vps (mm/sec) is defined using the middle point of the thickness of the intermediate transfer belt 13, since the outer diameter of the drive roller 14 of the present exemplary embodiment is 20 mm, T equals to or greater than 1000×120/360×(20π+50/1000)/Vps (msec). Further, the motors 30a to 30d and 31 are stopped and the voltage application to the primary transfer rollers 10a to 10d is stopped at a time Ts after the application of the voltage to the primary transfer rollers 10a to 10d is started. Then, the controller 104 may enter into a print signal waiting state and wait until it receives the print signal used for image forming.
According to the configuration of the present exemplary embodiment, when the process cartridge 9a is mounted in the apparatus main body 100A, the gear 37a which is provided at one end of the photosensitive drum 1a meshes with the gear 36a on the side of the main body. As described above, in some cases, however, the end face 42b of the drive coupling 42 illustrated in the example shown in
When the above-described preparation operation is finished, the driven coupling 43 and the drive coupling 42 are generally relatively securely connected. This may help improve throughput of the image forming operation. Further, since the image forming operation is started based on the securely-connected couplings, the generation of a defective image due to poor connection of the couplings may be prevented.
Since the voltage application to the primary transfer roller 10a has been described above, now, timing of voltage application to the charging roller 2a will be described referring to the examples shown in
However, if a voltage is applied to the charging roller 2a by the charge bias power supply unit 20a, the portion of the photosensitive drum 1a that has been charged by the charging roller 2a takes the time Te to reach the position where the photosensitive drum 1a contacts the intermediate transfer belt 13. This means that timing Tf, which is the time the voltage application to the charging roller 2a is started after the signals for starting the motors 30a and 31 are output, may be set so that it comes after the time obtained by subtracting the time Te from the time Tc, which is a maximum connection time for the driven coupling 43 and the drive coupling 42, has passed after the start of the motors. Further the controller 104 may control the charge bias power supply unit 20a to start applying a voltage to the charge roller 2a so that the portion of the photosensitive drum 1a charged by the charge roller 2a does not reach the position where the portion contacts the intermediate transfer belt 13 until the driving force is transmitted to the driven coupling 43 after the motors 30a and 31 are started. In other words, the controller 104 may drive the motor 31 so that the drive coupling 42 is moved to the engagement position, and may control the charge bias power supply unit 20a to apply a voltage to the charging roller 2a so that a portion of the photosensitive drum 1a charged by the charging roller 2a reaches the position where the portion contacts the intermediate transfer belt 13 after the driving force is transmitted to the driven coupling 43 by the driving force of the motor 31.
The above-described control may be performed when the power is turned on, for example since the open/close door 102 can be opened and closed while the power is turned off. According to the present exemplary embodiment, a voltage is applied to at least one of the charging roller 2 and the primary transfer roller 10 at a certain time after the signals for starting the motors 30 and 31 are output. However, voltage can be also be applied to both the charging roller 2 and the primary transfer roller 10 a certain time after the signals for starting the motors 30 and 31 are output.
Next, a second exemplary embodiment of the present invention will be described.
According to the present exemplary embodiment, components similar to those in the first exemplary embodiment are denoted by the same reference numerals and their description is omitted for simplification.
According to the first exemplary embodiment, independent motors 30a to 30d are provided for the photosensitive drums 1a to 1d for CMYK colors, respectively, and the motor 31 is provided for the drive roller 14 of the intermediate transfer belt 13.
As illustrated in the example shown in
Next, the transmission of driving force to the photosensitive drum 1a of the process cartridge 9a will be described in detail referring to the example shown in
Further, as illustrated in the examples shown in
When the open/close door 102 is closed from an open state, a force is applied to the main-body coupling 81 in the direction of the drum coupling 82 by the spring 144. However, since the raised portion 81a and the recessed portion 82a are triangular in section as illustrated in the example shown in
Further, as illustrated in the example shown in
Further, the raised portion 91a of the drive coupling 91 includes a protrusion 91c formed on its side so that the drive coupling 91 and the driven coupling 92 are connected at a phase angle of 360 degrees. Further, the driven coupling 92 includes a notch 92b. The protrusion 91c fits into the notch 92b. When the drive coupling 91 and the driven coupling 92 are connected, the driving force is transmitted to the driven coupling 92 by the rotation of the drive coupling 91.
Next, referring to
The example of the drive coupling 91 as shown includes an intermediate part 91e and a cap 91g. The intermediate part 91e is fixed to the drive shaft 81 by a pin 84. A force is applied to the cap 91g by a spring 91f against the intermediate part 91e in the axial direction. A raised portion 91b is provided on one end of the cap 91g. A flange 91d is provided on the other end. The flange 91b is connected to a release member 146 described below. Further, as illustrated in the example shown in
Next, an example of a state where the open/close door 102 is opened and the connection of the drive coupling 91 and the driven coupling 92 is released will be described.
With this configuration, the photosensitive drum 1a may rotate before the rotation of the intermediate transfer belt 13 is started without exception. According to the present exemplary embodiment, although the photosensitive drum 1a slides over the intermediate transfer belt 13 which is in a stop state, the damage of the photosensitive drum 1a will be smaller compared to when the intermediate transfer belt 13 slides over the photosensitive drum 1a which is in a stop state. This is because, if the intermediate transfer belt 13 slides over the photosensitive drum 1a in a stopped state, a particular portion of the photosensitive drum 1a will intensively receive friction contact. However, if the photosensitive drum 1a slides over the intermediate transfer belt 13 in a stop state, the whole circumference of the photosensitive drum 1a will receive the friction, and thus the damage will be smaller.
According to the present exemplary embodiment, the photosensitive drum 1a will rotate before the intermediate transfer belt 13 starts rotating as is with the first exemplary embodiment.
As illustrated in the block diagram shown in the example of
Details of the control will now be described referring to the examples shown in
According to this example, the controller 204 outputs a signal for starting the motor 70 a time Tm after the power is turned on or the open/close door 102 is closed. Further the controller 104 outputs signals for starting application of voltage to the primary transfer bias power supply units 22a to 22d to start applying voltages to the primary transfer rollers 10a to 10d a time Td after the signal for starting the motor 70 is output. Here, the time Td comes after a maximum connection time Tc, which is a maximum time for connecting the drive coupling 91 to the driven coupling 92, has passed.
According to the present exemplary embodiment, the maximum connection time Tc is the time for the drive coupling 91 to rotate approximately 360 degrees at the maximum, since the raised portion 81a fits into the recessed portion 82a at a phase angle of 360 degrees. If the process speed Vps (mm/sec) is defined using the middle point of the thickness of the intermediate transfer belt 13, since the outer diameter of the drive roller 14 of the present exemplary embodiment is 20 mm, T equals to or greater than 1000×360/360×(20π+50/1000)/Vps (msec). Further, the motor 70 is stopped and the voltage application to the primary transfer rollers 10a to 10d is stopped at a time Ts after the application of the voltage to the primary transfer rollers 10a to 10d is started. Then, the controller 204 enters into a print signal waiting state and waits until it receives the print signal used for image forming.
According to the configuration of the present exemplary embodiment, as illustrated in the examples shown in
The main-body coupling 81 rotates 120 degrees at the maximum before it is connected to the drum coupling 82. On the other hand, the driven coupling 92 provided on the drive roller 14 is not connected to the driven coupling 92 unless the drive coupling 91 rotates approximately 360 degrees if the open/close door 102 is closed or the power is turned on. This means that each of the photosensitive drums 1a to 1d starts rotating prior to the intermediate transfer belt 13. Thus, at that time, the timing of voltage application to each of the primary transfer rollers 10a to 10d will be delayed. In this way, the intermediate transfer belt 13 can be prevented from being attracted to the photosensitive drums 1a to 1d due to the electrostatic attraction force that is generated by the electric potential difference between the surface of each of the photosensitive drums 1a to 1d and the intermediate transfer belt 13. Since the intermediate transfer belt 13 is not attracted, and since the drive roller 14 is not affected by the rotation of the intermediate transfer belt 13, the drive coupling 91 is connected to the driven coupling 92 before the drive coupling 91 rotates 360 degrees at the maximum.
Since the driven coupling 92 and the drive coupling 91 can be relatively securely connected in the above-described preparation operation, throughput of the image forming operation can be improved. Further, since the image forming operation may be started based on the securely-connected couplings, the generation of defective images due to poor connection of the couplings may be prevented.
Since the voltage application to the primary transfer roller 10a from the primary transfer bias power supply unit 22a has been described above, now, timing of voltage application to the charging roller 2a will be described referring to the examples shown in
That is, according to this example, voltage application to the primary transfer roller 10a by the primary transfer bias power supply unit 22a may not be started until the driven coupling 92 and the drive coupling 91 are connected after the motor 70 is started. However, if a voltage is applied to the charging roller 2a by the charge bias power supply unit 20a, the portion of the photosensitive drum 1a that has been charged by the charging roller 2a takes the time Te to reach the position where the photosensitive drum 1a contacts the intermediate transfer belt 13. This means that timing Tf, which is the time the voltage application to the charging roller 2a is started after the signals for starting the motor 70 is output, is set so that it comes after the time obtained by subtracting the time Te from the time Tc, which is a maximum connection time of the driven coupling 92 and the drive coupling 91, has passed after the start of the motors. Further, the controller 204 may control the charge bias power supply unit 20a to start applying a voltage to the charge roller 2a so that the portion of the photosensitive drum 1a charged by the charge roller 2a does not reach the position where the portion contacts the intermediate transfer belt 13 until the driving force is transmitted to the driven coupling 92 after the motor 70 is started. In other words, the controller 204 drives the motor 70 so that the drive coupling 91 is moved to the engagement position, and controls the charge bias power supply unit 20a to apply a voltage to the charging roller 2a so that a portion of the photosensitive drum 1a charged by the charging roller 2a reaches the position where the portion contacts the intermediate transfer belt 13 after the driving force is transmitted to the driven coupling 92 by the driving force of the motor 70.
It is to be noted that the above-described control may be performed when the power is turned on since the open/close door 102 can be opened and closed while the power is turned off.
According to the present exemplary embodiment, a voltage is applied to the charging roller 2 or the primary transfer roller 10 a certain time after the signal for starting the motor 70 is output. However, the voltage can be applied to both the charging roller 2 and the primary transfer roller 10 a certain time after the signal for starting the motor 70 is output.
According to the first and the second exemplary embodiments, the image forming apparatus 100 including the intermediate transfer belt 13 to which a toner image on the photosensitive drum 1 is directly transferred to form a superimposed image has been described.
According to exemplary embodiments of the invention, an image forming apparatus may be provided having a relatively simple configuration used for enabling fairly secured connection of a coupling provided on a photosensitive member or a drive member for or a belt to a coupling provided on a main body of the image forming apparatus. Aspects according to the present invention may provide an image forming apparatus capable of inhibiting and even preventing defective images due to connection failure of the couplings.
According to another exemplary embodiment of the present invention, as illustrated in the example shown in
As describe above, according to an exemplary embodiment of the present invention, a voltage is applied to the transfer member after the drive of the motor is started and the driving force is transmitted to the couplings. Further, a voltage is applied to the charging member so that a portion of the photoreceptor charged by the charging member is moved to the position where that portion contacts the belt after the drive of the motor is started and the driving force is transmitted to the couplings. Accordingly, the belt can be prevented from being attracted to the photosensitive member due to electrostatic attraction force that is generated between the surface of the photosensitive member and the belt. Further, since the driven coupling and the drive coupling can be relatively securely connected, it may be possible to prevent defective images due to poor connection of the couplings. Further, by performing the control in the preparation operation, enhanced throughput considering image forming can be achieved.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Applications No. 2008-095125 filed Apr. 1, 2008 and No. 2009-053711 filed Mar. 6, 2009, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-095125 | Apr 2008 | JP | national |
| 2009-053711 | Mar 2009 | JP | national |
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| 20090257779 A1 | Oct 2009 | US |
