JP2009036856A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is used so as to suppress specification of motors to a minimum, with respect to the image forming apparatus in which motor driving force driving a fixing unit (roller drive and pressure release) serves also as a transfer separation drive through a drive transmission means. <P>SOLUTION: The image forming apparatus has a sequence for starting the motor again after carrying out pressure release in the fixing device when the fixing motor is not rotated during an initial action of the image forming apparatus. In addition, it has a sequence for confirming a state of transfer separation when power is turned on and starting the motor after carrying out pressure release in the fixing unit when not normal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium.

  In recent years, in this type of image forming apparatus, a transfer apparatus in which a transfer member such as a transfer roller, a transfer belt, or a transfer brush is arranged in contact with an image carrier has been used because ozone generation is extremely small. . In a transfer device using such a transfer member, if the transfer member such as a transfer roller is left in contact with the image carrier for a long period of time, the press contact portion of the transfer member is deformed and cannot be restored. . As a result, there arises a problem that uneven rotation pitch of the transfer member occurs in the image feeding direction.

In order to solve the above problems, the transfer member may be separated from the image carrier except during image formation, and at least the transfer member may be in contact with the image carrier during image formation. For example, in Patent Document 1, a transfer roller is separated using a solenoid, and image formation is performed by using a basic operation signal (start signal, end signal) during an image forming operation of the image forming apparatus as a drive signal for the solenoid. A device that automatically separates the transfer roller at the end of the operation is disclosed.
Japanese Patent Laid-Open No. 2-82278

  However, in a color image forming apparatus having a plurality of transfer rollers, disposing a solenoid for contact / separation of each transfer roller (yellow, magenta, cyan, black) not only increases the size of the apparatus, It will also lead to an increase in cost. In addition, as a countermeasure, if all four transfer rollers can be contacted and separated by a single solenoid, the solenoid's cost will increase because the suction force required for the solenoid is quadrupled. Further, in the color image forming apparatus, since the color color transfer roller which is not necessary at the time of printing in the monochrome mode is pressed, the deformation of the transfer roller described above cannot be completely prevented. .

  In JP-A-07-230224, the transfer roller abutment / separation operation is not performed by a solenoid, but by using an image carrier drive source, and the transfer roller is rotated in the reverse direction to the image formation. Spacing is disclosed. However, in a color image forming apparatus, a brushless motor that can perform uniform rotation is generally used in order to prevent misalignment of an image formed on each color image carrier during image formation. In this brushless motor, reverse rotation is used. For this purpose, a circuit for driving the reverse rotation of the brushless motor and a signal for switching between the forward and reverse rotations are also required. Therefore, particularly in a configuration in which each color image carrier is independently provided with a driving source, the cost becomes high. End up.

  Therefore, the transfer roller is abutted and separated by one drive source different from the drive source of the image carrier, and the drive force is transmitted by one solenoid, and the transfer roller in color mode / monochrome mode As for the contact / separation switching, the transfer roller can be prevented from being deteriorated at low cost by using cams having different shapes (phases). In this case, although the torque specifications required for the drive source (for example, a brushless motor) are increased by the torque required for the contact / separation operation of the transfer roller, the timing of contact / separation of the transfer roller is shown in FIG. As shown in the figure, the transfer roller is separated when the torque required for the drive source is small, that is, when the brushless motor is driven to rotate at a steady rotation, not at the time of starting that requires a relatively large torque. For example, the torque specifications required for the brushless motor can be minimized. Here, when a solenoid (configuration that hooks to the missing gear mechanism) is used to transmit the driving force, the solenoid is not caught on the missing gear mechanism if a device failure or power failure occurs during contact / separation operations This will stop the device. In this case, when the brushless motor is started during the subsequent operation of the apparatus, the torque necessary for the contact / separation operation of the transfer roller is added as shown in FIG. There are problems that occur. Assuming such a case, if the torque specification of the brushless motor is increased, the cost increases.

  In this case, the brushless motor used for the transfer / separation operation can suppress the torque specifications of the brushless motor by using a combination of the load and the load required for the brushless motor. . For example, Japanese Patent Application Laid-Open No. 09-290975 describes the content of changing the pressure applied by pressing the pressure rotator against the fixing rotator of the fixing device. By using the fixing device having such a fixing pressure switching means as a load and using the fixing pressure switching and transfer separation timings at different timings, the torque specifications of the brushless motor can be suppressed.

  An object of the first to third aspects of the present application is to provide an image forming apparatus that can be used while minimizing the torque specifications required for the drive source used for the contact / separation drive of the transfer roller in the above configuration. It is to be.

In order to achieve the above object, the first means of the present invention is:
A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separating means;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
If the control unit detects an abnormal rotation of the driving unit during the initial operation of the image forming apparatus, the driving unit is held for a predetermined time in a state where the pressing force of the fixing unit is lowered than usual by the pressing force changing unit. And the initial operation is performed again in a state where the pressing force of the fixing unit is returned to the normal state by the pressing force changing unit.

The second means is
A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separation;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
State detecting means for detecting whether or not the transfer means is separated from the image carrier;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
If the transfer unit is not separated from the image carrier at the start of the initial operation of the image forming apparatus, the driving unit is set in a state where the pressing force of the fixing unit is lowered than usual by the pressing force changing unit. It is characterized in that it is rotationally driven for a time, and then the initial operation is performed again in a state where the pressure applied by the fixing means is returned to the normal state by the pressure change means.

Further, the third means is the first to second means,
The driving unit is configured to transmit a driving force to the fixing unit and the transfer separation unit during forward rotation, and to transmit the driving force to the pressure change unit during reverse rotation.

As explained above, according to the first invention of the present application,
A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separating means;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
If the control unit detects an abnormal rotation of the driving unit during the initial operation of the image forming apparatus, the driving unit is held for a predetermined time in a state where the pressing force of the fixing unit is lowered than usual by the pressing force changing unit. It is possible to minimize the torque specifications required for the drive means by performing the initial operation again with the applied pressure changing means returning to the normal state with the applied pressure changing means returned to the normal state. Thus, the cost of the driving means can be reduced.

Further, according to the second invention of the present application,
A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separation;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
State detecting means for detecting whether or not the transfer means is separated from the image carrier;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
If the transfer unit is not separated from the image carrier at the start of the initial operation of the image forming apparatus, the driving unit is set in a state where the pressing force of the fixing unit is lowered than usual by the pressing force changing unit. In addition to the effect of the first invention, it is in an irregular state by rotating it for the time and then performing the initial operation again with the pressure changing means returning the pressure of the fixing means to the normal state. Therefore, it is possible to reduce the time required to avoid an irregular state and shift to a normal initial operation.

According to the third invention of the present application,
The driving means transmits the driving force to the fixing means and the transfer separation means at the time of forward rotation, and transmits the driving force to the pressure change means at the time of reverse rotation, so that the first invention and the second invention are provided. Can be realized at a lower cost.

  Next, embodiments of the present invention will be described with reference to the drawings.

  The color image forming apparatus (hereinafter referred to as a main body) shown in FIG. 1 includes process cartridges 5Y, 5M, 5C, and 5K that are detachable from the main body. These four process cartridges 5Y, 5M, 5C, and 5K have the same structure, but images with toners of different colors, that is, yellow (Y), magenta (M), cyan (C), and black (Bk) are displayed. It differs in the point to form. Process cartridges 5Y, 5M, 5C, and 5K are photosensitive drums 1Y, 1M, 1C, and 1K that are image carriers, charging rollers 2Y, 2M, 2C, and 2K, developing rollers 3Y, 3M, 3C, and 3K, and drum cleaning blades, respectively. 4Y, 4M, 4C, 4K and a waste toner container.

  Laser units 7Y, 7M, 7C, and 7K are arranged below the process cartridges 5Y, 5M, 5C, and 5K, and exposure based on image signals is performed on the photosensitive drums 1Y, 1M, 1C, and 1K.

  The photosensitive drums 1Y, 1M, 1C, and 1K are charged to predetermined negative potentials by the charging rollers 2Y, 2M, 2C, and 2K, and then electrostatic latent images are formed by the laser units 7Y, 7M, 7C, and 7K, respectively. Is done. This electrostatic latent image is reversely developed by the developing rollers 3Y, 3M, 3C, and 3K, and negative toner is attached to form toner images of Y, M, C, and Bk, respectively.

  The intermediate transfer belt unit includes an intermediate transfer belt 8, a driving roller 9, and a secondary transfer counter roller 10. Further, primary transfer rollers 6Y, 6M, 6C, and 6K are disposed inside the intermediate transfer belt 8 so as to face the photosensitive drums 1Y, 1M, 1C, and 1K, and transfer bias is applied by a bias applying unit (not shown). Is applied.

  The toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are obtained by rotating the photosensitive drums in the direction of the arrows, the intermediate transfer belt 8 in the direction of the arrow A, and the primary transfer rollers 6Y, 6M, 6C, By applying a positive bias to 6K, the toner images on the photosensitive drum 1Y are sequentially transferred onto the intermediate transfer belt 8 and transferred to the secondary transfer roller 11 with the four color toner images superimposed. The

  The feeding / conveying device 12 includes a paper feed roller 14 that feeds the transfer material P from the paper feed cassette 13 that houses the transfer material P, and a transport roller pair 15 that transports the fed transfer material P. Yes. Then, the transfer material P conveyed from the feeding / conveying device 12 is conveyed to the secondary transfer roller 11 by the registration roller pair 16.

  In the transfer from the intermediate transfer belt 8 to the transfer material P, a positive bias is applied to the secondary transfer roller 11 so that the four color toner images on the intermediate transfer belt 8 are transferred to the transferred transfer material P. Secondary transfer.

  After the toner image is transferred, the transfer material P is conveyed to the fixing device 17 and heated and pressed by the fixing film 18 and the pressure roller 19 to fix the toner image on the surface. The fixed transfer material P is discharged by the paper discharge roller pair 20.

  On the other hand, the toner remaining on the surface of the photosensitive drums 1Y, 1M, 1C, and 1K after the toner image transfer is removed by the cleaning blades 4Y, 4M, 4C, and 4K, and the intermediate transfer belt after the secondary transfer to the transfer material P. The toner remaining on the toner 8 is removed by the transfer belt cleaning blade 21, and the removed toner is collected into a waste toner collecting container 22.

  Next, the contact / separation mechanism of the primary transfer rollers 6Y, 6M, 6C, 6K in this embodiment will be described.

  The toothless gear structure for performing drive transmission control is a structure in which three of the first toothless gear 70, the second toothless gear 71 having the structure shown in FIG. I'm taking it. The operation principle of this configuration will be described. The drive transmission is achieved by releasing the locking claw 72 with a locking claw stopper, for example, a solenoid flapper 73 typified by an electromagnetic solenoid, so that the first toothless gear 70 and the second toothless gear 71 on the same axis are springs 74. When the spring 74 is released, the phase of the first toothless gear 70 and the second toothless gear 71 is limited, the gear tooth profile is in phase, and the drive is connected. The

  The operation in the drive transmission control is interrupted because the driving force from the drive source is idled by the missing teeth immediately before the pair of missing gears. Therefore, when the solenoid flapper 73 is operated and the locking claw 72 is released, the second partial gear 71 starts rotating by the force of the spring 74 incorporated between the first partial gear 70 and the second partial gear 71. When the second toothless gear 71 is driven and the tooth shape of the second toothless gear 71 and the first toothless gear 70 are in the same phase, both gears are engaged and the drive is connected. The one-tooth gear 70 meshes with the input gear 75 from the drive source, and the drive is transmitted to the output shaft 76.

  When the gear makes a full turn, the solenoid flapper 73 is engaged with the locking claw 72, and the driving of the second toothless gear 71 is stopped. At that time, since the first partial gear 70 is connected to the drive, the first partial gear 70 continues to rotate, and the spring 74 between the first partial gear 70 and the second partial gear 71 is compressed, and the spring force is stored. Since the last tooth just before reaching the missing tooth portion of the first missing gear 70 must rotate against the energy of the spring 74 between the second missing gear 71, on the output drive side The first toothless gear 70 is rapidly rotated by the installed cam 77, rotates to the position of the toothless portion, stops, and the series of operations ends.

  The drive transmission control mechanism in this embodiment is adopted as a mechanism for contacting and separating the primary transfer roller when switching between the monochrome mode, the color mode, and the standby mode (including power OFF). The contact / separation mechanism of the primary transfer roller will be schematically described with reference to FIG. In the electrostatic transfer belt unit having the intermediate transfer belt 8, the primary transfer roller 6 (6Y, 6M, 6C, 6K) and the drive mechanism in FIG. 1, the drive mechanism is a system that drives the drive roller 9 and the primary transfer roller 6. Two systems of the system that separates are driven. The system for driving the normal drive roller 9 is continuously driven, and the system for separating the primary transfer roller 6 performs drive transmission control intermittently as necessary. Intermittent drive transmission control is performed through the toothless gear pair of the present invention, which will be described in detail below. When drive is transmitted from the pair of toothless gears, the final output gear 78 is configured to operate for a predetermined phase every time the pair of toothless gears makes one revolution. The primary transfer roller 6 (6Y, 6M, 6C, 6K) is separated from the final output gear 78 by a phase fixed on the same axis as the separation cams 79 and 80 (see FIG. 4). Reciprocatingly moves the primary transfer roller bearing 82 holding the primary transfer roller from the inclined surface of the slider 81 and separates the primary transfer roller 6 (6Y, 6M, 6C, 6K). Here, the separation cam 79 is a cam for moving the slider 81 on the left side in FIG. 3, and thereby the Bk primary transfer roller 6K is brought into contact with and separated from, while the separation cam 80 is in FIG. This is a cam for moving the right slider 81, whereby the primary transfer rollers 6Y, 6M, 6C of Y, M, C are contacted and separated. FIG. 4 shows the state of the separation cams 79 and 80 in this embodiment.

  Here, the contact / separation operation of the primary transfer roller 6 (6Y, 6M, 6C, 6K) in the present embodiment will be described using FIG. 5 as the relationship between the separation cams 79, 80 and the slider 81 in FIG. In this embodiment, every time the second toothless gear 71 in FIG. 2 rotates once, the final output gear 78 in FIG. 3 rotates by 1/3 rotation (120 °) counterclockwise. It is described. First, in the standby mode, the Bk separation cam 79 and the Y, M, and C separation cams 80 are in a phase for moving the slider 81, and all the primary transfer rollers 6 (6Y, 6M, 6C, 6K) are separated. Has been. Next, when the second toothless gear 71 rotates once, the separation cams 79 and 80 are in a phase in which the slider 81 does not move, and the color mode is reached in which all the primary transfer rollers 6 (6Y, 6M, 6C, 6K) are in contact. And transition. Next, when the second toothless gear 71 rotates once, the phase shifts the slider 81 only by the separation cam 79, and the mode shifts to the monochrome mode in which only the Bk transfer roller 6K contacts. Further, when the second toothless gear 71 rotates once, it shifts to the standby mode again.

  The contact / separation operation of the primary transfer roller obtains a driving force from the fixing motor 23 that rotationally drives the fixing device 17. Here, the operation principle of the fixing motor 23 (DC brushless motor as an example) will be described with reference to FIG.

  FIG. 6 shows the configuration of the drive circuit of the fixing motor 23, which has Y-connected coils 55 to 57 and a rotor 58. Furthermore, Hall elements 59 to 61 are provided as position detecting means for the rotor 58. These Hall elements 59 to 61 are elements in which a voltage appears at both ends of the semiconductor piece by detecting a magnetic field, and the position of the rotor can be detected. The output is amplified by the amplifier 62 and input to the motor drive control circuit 42.

  A motor drive circuit unit 41 drives the fixing motor 23, and includes a motor drive control circuit 42, high-side transistors 43 to 45, and low-side transistors 46 to 48. The transistors 43 to 48 are connected to U, V, and W, which are both ends of the coil, respectively, and ON / OFF control is performed according to the phase switching signal output from the motor drive control circuit 42 to sequentially switch the phases to be excited. Rotate. The phase switching signal is generated by the motor drive control circuit 42 by detecting the drive signal from the output port of the CPU 40 and the position signal of the rotor 58 generated from the Hall elements 59-61.

  Regarding the motor rotation for phase switching, the potential of (U, V, W) is changed from (+ voltage, OFF, 0V) to (OFF, + voltage, 0V) → (0V, + voltage, OFF) → (0V, OFF, By switching from (+ voltage) → (OFF, 0V, + voltage) → (+ voltage, 0V, OFF), each phase is sequentially excited and the motor rotates. For example, by setting the potential of (U, V, W) to (+ voltage, OFF, 0V), the coils 55 and 57 are excited. In order to set the potential of (U, V, W) to (+ voltage, OFF, 0V), a high signal is output from Tr1 and Tr6 of the motor drive control circuit 41, and the transistors 43 and 48 are turned on. . Here, the diodes 49 to 54 are provided for protecting each transistor. For example, when the transistor 43 changes from ON to OFF, the current due to the coil inductance circulates through the diode 49 to protect the transistor 43 from being destroyed.

  Next, the configuration of the fixing device 17 will be described with reference to FIG.

  Reference numeral 90 denotes a stay, which is a heat resistant and rigid member as a heating body holding member and a film guide member. Reference numeral 91 denotes a ceramic heater as a heating body, which is disposed and held on the upper surface of the stay 90 along the length of the stay. Reference numeral 18 denotes an endless (cylindrical) heat resistant film which is externally fitted to a stay 90 which is a film guide member including a heating body 91. The inner peripheral length of the endless heat-resistant film 18 and the outer peripheral length of the stay 90 including the heating body 91 are about 3 mm larger than that of the film 18, and therefore the film 18 is fitted with a margin in the peripheral length. ing.

  Reference numeral 93 denotes a pressure roller as film outer surface contact driving means for forming a nip portion N with the film 18 sandwiched between the heating body 91 and rotating the film 18. The pressure roller 19 is composed of a cored bar, an elastic body layer, and an outermost release layer, and a film 18 is sandwiched between the surface of the heating body 91 with a predetermined pressing force 94 by bearing means and biasing means (not shown). They are arranged in pressure contact. The pressure roller 19 is rotationally driven by the fixing motor 23 at a predetermined peripheral speed. By the rotational drive of the pressure roller 19, a rotational force acts on the film 18 by the frictional force between the pressure roller and the film outer surface at the nip portion N, and the film 18 has an inner surface side of the heating body 91 at the nip portion N. While being in close contact with the surface and sliding, the outer periphery of the stay 90 is driven to rotate in the direction of the arrow in the direction of the arrow at substantially the same peripheral speed as that of the pressure roller 19.

  Further, the fixing device 17 in the present embodiment is configured to be able to vary the pressing force 94, and the operation principle will be described. The pressing force 94 is generated by fixing a pressing spring 96 shown in FIG. 8 with a holding member 95 and sandwiching the holding member 95 between the pressing force changing cam 97 and the stay 90. The pressing force changing cam 97 changes the pressing force by being rotated by a driving source (not shown) (separate from the fixing motor 23).

  The flow of the present embodiment will be described below with reference to the flowchart of FIG.

  Turn on the main unit with S101. The main body starts a predetermined initial operation in S102, and activates the fixing motor in S103 in the series of initial operations. Here, when the rotation speed of the fixing motor reaches a predetermined rotation speed in S104 and other predetermined processing is completed, the initial operation is terminated in S105, and a standby state is entered. When a print command is entered in S106 during standby, the print mode (color print or monochrome print) is confirmed in S107, and in the case of color print, the primary transfer rollers of all Y, M, C, and Bk are contacted in S108. In the monochrome mode, only the primary transfer roller of Bk is brought into contact in S109. Thereafter, an actual printing operation (image forming operation) is started in S110. When printing is completed in S111, all the primary transfer rollers are separated in S112, and the standby state is entered again.

  On the other hand, if the rotation speed of the fixing motor does not reach the predetermined rotation speed in S104, the load torque of the fixing motor may be in the relationship shown in FIG. Therefore, by reducing the pressing force of the fixing device in S113, the load torque of the fixing device is reduced as shown in FIG. In step S114, the fixing motor is activated again. If the rotation speed of the fixing motor reaches a predetermined rotation speed in S115, the fixing motor is driven for a predetermined time in S116 (during this time, the transfer separation solenoid locks the missing gear clutch to cut off the drive transmission). Thereafter, the pressing force of the fixing device is returned to normal in S117, and the completion of the initial operation in S105 is awaited again. If the rotation speed of the fixing motor does not reach the predetermined rotation speed in S115, it is determined in S118 that the fixing motor has failed.

  The present embodiment is almost the same as the configuration of the first embodiment, except that a separation cam 79, 80 and a sensor flag 100 for position detection are provided coaxially with the final output gear 78 as shown in FIG. The sensor flag 100 is configured to transmit and shield a photo interrupter 101 provided separately. Further, in this embodiment, the sensor flag 100 has a disk shape and is provided with a slit in a part thereof, and the position where the photo interrupter 101 is transmitted in the standby mode in which the primary transfer rollers 6 (6Y, 6M, 6C, 6K) are all separated. It has become. In this embodiment, when the image is not formed, the primary transfer roller 6 (6Y, 6M, 6C, 6K) is put into the separated standby mode. Therefore, when the power is turned on, the primary transfer roller 6 (6Y, 6M, 6C, 6K) are all separated.

  The flow of this embodiment will be described below with reference to the flowchart of FIG.

  Turn on the main unit with S201. In S202, the main body starts a predetermined initial operation. In the series of initial operations, the state of the S203 sensor flag 100 is confirmed, and it is confirmed that all the primary transfer rollers are in the separated state. In S203, the separated state of the primary transfer roller can be confirmed. When other predetermined processing is completed, the initial operation is terminated in S204 and the standby state is entered. When a print command is entered in S205 during standby, the print mode (color print or monochrome print) is confirmed in S206. In the case of color print, the primary transfer rollers of all of Y, M, C, and Bk are contacted in S207. In the monochrome mode, only the primary transfer roller of Bk is brought into contact in S208. Thereafter, an actual printing operation (image forming operation) is started in S209. When printing is completed in S210, all the primary transfer rollers are separated in S211 and the standby state is entered again.

  On the other hand, if the primary transfer rollers are not all separated in S203, the load torque of the fixing motor may be in the relationship shown in FIG. Therefore, by reducing the pressing force of the fixing device in S212, the load torque of the fixing device is reduced as shown in FIG. In step S213, the fixing motor is activated. If the rotation speed of the fixing motor reaches the predetermined rotation speed in S214, the fixing motor is driven for a predetermined time in S215 (during this time, the transfer separation solenoid locks the missing gear clutch to cut off the drive transmission). Thereafter, the pressing force of the fixing device is returned to normal in S216, and the end of the initial operation in S204 is awaited. If the rotation speed of the fixing motor does not reach the predetermined rotation speed in S214, it is determined in S217 that the fixing motor has failed.

  The present embodiment is almost the same as the configuration of the first embodiment, except that the forward / reverse operation of the fixing motor serves to both rotate the fixing device and change the pressing force of the fixing device. The outline will be described with reference to FIG.

  The driving force of the fixing motor is transmitted to the common gear 110. The common gear 110 is connected to a rotation driving gear 111 of the fixing device and a pressing force change gear 112 of the fixing device, and both the rotation driving gear 111 and the pressing force change gear 112 have a one-way clutch that rotates only in one direction. It has been incorporated. In the present embodiment, the rotation driving gear 111 rotates only in the counterclockwise direction, and the driving force is transmitted to the pressure roller 19 via a gear (not shown). The pressing force changing gear 112 rotates only in the clockwise direction, and the driving force is transmitted to the pressing force changing cam 97 via a gear (not shown).

  In this embodiment, when the fixing motor is rotated in the forward rotation direction, the common gear 110 in FIG. 15 rotates clockwise (rotation drive of the fixing device), and when the fixing motor is rotated in the reverse rotation direction, Assuming that the common gear 110 in FIG. 15 rotates counterclockwise (changing the pressing force of the fixing device), the flow of this embodiment will be described with reference to the flowchart of FIG.

  Turn on the main unit in S301. In step S302, the main body starts a predetermined initial operation, and in the series of initial operations, the main body starts normal rotation in step S303 (rotation drive of the fixing device). Here, in S304, when the rotation speed of the fixing motor reaches the predetermined rotation speed and other predetermined processes are completed, the initial operation is terminated in S305 and the standby state is entered. When a print command is entered in S306 during standby, the print mode (color print or monochrome print) is confirmed in S307. In the case of color print, the primary transfer rollers in contact with all Y, M, C, and Bk are contacted in S308. In the monochrome mode, only the primary transfer roller of Bk is brought into contact in S309. Thereafter, the actual printing operation (image forming operation) is started in S310. When printing is completed in S311, all the primary transfer rollers are separated in S312 and the standby state is entered again.

  On the other hand, if the rotation speed of the fixing motor does not reach the predetermined rotation speed in S304, there is a possibility that the load torque of the fixing motor has the relationship shown in FIG. Therefore, the fixing motor is stopped in S313, and the fixing motor is driven in reverse rotation (change of pressing force of the fixing device) to reduce the pressing force of the fixing device in S314, thereby reducing the load torque of the fixing device as shown in FIG. Let When the reduction of the pressing force is completed, the fixing motor is stopped in S315, and the fixing motor is activated in the normal direction again (rotation drive of the fixing device) in S316. When the rotation speed of the fixing motor reaches the predetermined rotation speed in S317, the fixing motor is driven for a predetermined time in S318 (during this time, the transfer separation solenoid locks the missing gear clutch to cut off the drive transmission). Thereafter, the fixing motor is stopped in S319, and the fixing motor is again driven in reverse (change in pressing force of the fixing device) to return the pressing force to normal in S320, and the fixing motor is stopped in S321. In step S322, the fixing motor is rotated forward (rotation driving of the fixing device), and the completion of the initial operation in step S305 is awaited again. If the rotation speed of the fixing motor does not reach the predetermined rotation speed in S317, it is determined in S323 that the fixing motor has failed.

1 is a schematic diagram of an image forming apparatus according to the present invention. Schematic of the missing gear mechanism in the 1st example of the present invention. 1 is a schematic diagram of a primary transfer separation mechanism in a first embodiment of the present invention. The cam arrangement of the primary transfer separation mechanism in the first embodiment of the present invention. The cam phase relationship of the primary transfer separation mechanism in the first embodiment of the present invention. 1 is a drive circuit for a brushless motor according to a first embodiment of the present invention. 1 is a schematic diagram of a fixing device according to a first embodiment of the present invention. FIG. 2 is a configuration for switching the pressing force of the fixing device according to the first embodiment of the present invention. FIG. 3 is a flowchart in the first embodiment of the present invention. FIG. 3 is a load relationship of the fixing motor in the first embodiment of the present invention (normal time). FIG. 3 is a load relationship of the fixing motor according to the first embodiment of the present invention (in an irregular case). FIG. FIG. 3 is a load relationship of the fixing motor in the first embodiment of the present invention (when the pressing force is reduced). FIG. 10 is a state detection mechanism of a primary transfer separation mechanism in the second embodiment of the present invention. 7 is a flowchart in the second embodiment of the present invention. FIG. 6 shows a driving configuration of a fixing device according to a third embodiment of the present invention. 10 is a flowchart in the third embodiment of the present invention.

Explanation of symbols

1 Photosensitive drum
5 Process cartridge
6 Primary transfer roller
8 Intermediate transfer belt
11 Secondary transfer roller
17 Fixing device
18 Fixing film
19 Pressure roller
23 Fixing motor
72 Locking claw
73 Solenoid flapper
79 Separation cam (Bk)
80 Separation cam (Y, M, C)
81 Slider
96 Pressure spring
97 Pressing force change cam
100 Sensor flag
101 photo interrupter
111 Rotation drive gear
112 Pressure change cam

Claims (3)

A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separating means;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
When the control unit detects an abnormal rotation of the driving unit during the initial operation of the image forming apparatus, the driving unit is determined in a state where the pressing force of the fixing unit is lowered than usual by the pressing force changing unit. An image forming apparatus, wherein the image forming apparatus is driven to rotate for a period of time, and then the initial operation is performed again in a state where the pressure applied by the fixing means is returned to a normal state by the pressure changing means. A sheet feeding unit for separating and feeding the transfer material one by one; a developing unit for forming a toner image on the image carrier; and the toner image formed on the image carrier for the transfer material. In an image forming apparatus comprising transfer means for transferring, and fixing means for nipping and conveying the transfer material between a fixing rotator and a pressure rotator to fix the toner image to the transfer material,
The image forming apparatus includes:
A pressing force changing means for changing a pressing force between the fixing rotating body and the pressure rotating body of the fixing means;
Transfer separation means for separating the transfer means from the image carrier;
Drive means for driving both the fixing means and the transfer separation means;
A toothless gear mechanism for transmitting the driving force of the driving means to the transfer separation;
Lock means for locking the rotation operation of the toothless gear mechanism by hooking a claw-like member on the toothless gear mechanism;
State detecting means for detecting whether or not the transfer means is separated from the image carrier;
A controller for monitoring ON / OFF control of the locking means and the rotation state of the driving means,
The control unit
The lock means is unlocked when the fixing means is driven to rotate at a steady rotation, and the rotation of the fixing means is stopped, and the lock mechanism is locked by the lock means. A later control,
If the transfer means is not separated from the image carrier at the start of the initial operation of the image forming apparatus, the driving means is determined in a state where the pressure applied by the fixing means is lowered than usual by the pressure change means. An image forming apparatus, wherein the image forming apparatus is rotated for a predetermined time, and then the initial operation is performed again in a state where the pressure applied by the fixing unit is returned to a normal state by the pressure change unit.   3. The drive unit according to claim 1, wherein the drive unit is configured to transmit a driving force to the fixing unit and the transfer separation unit during forward rotation, and to transmit the driving force to the pressure change unit during reverse rotation. Image forming apparatus.

Images