JP6036194B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In general, printers, copiers, facsimiles, and the like, which are electrophotographic image forming apparatuses, form an electrostatic latent image by irradiating a charged photosensitive drum with laser light based on image data. By attaching toner, which is colored particles, to the latent image, the electrostatic latent image is visualized to form a toner image. Then, after the toner image is directly or indirectly transferred onto the recording paper, the toner image is fixed on the recording paper at the fixing nip portion, and the recording paper is discharged onto a paper discharge tray by a paper discharge roller.

  In the conventional transfer method, as shown in FIG. 6A, the intermediate transfer belt 30 and the recording paper 40 which are belt-shaped image carriers are sandwiched between the secondary transfer counter roller 10 and the secondary transfer roller 20. Thus, a secondary transfer nip portion 50 is formed between the intermediate transfer belt 30 and the recording paper 40. By applying a transfer voltage to the secondary transfer counter roller 10 or the secondary transfer roller 20, the toner image formed on the intermediate transfer belt 30 is transferred to the recording paper 40 at the secondary transfer nip portion 50.

  As a technique related to toner image transfer, pre-transfer due to poor adhesion between the intermediate transfer belt and transfer paper (recording paper) on the upstream side of the secondary transfer nip in the moving direction of the intermediate transfer belt cannot be visually confirmed. A technique for suppressing the level to a level has been proposed (see, for example, Patent Document 1).

  Further, a technique has been proposed for reducing rear transfer blur by reducing the amount of deflection of the transfer material when the transfer material is released from the entrance guide member, regardless of the rigidity of the transfer material (recording paper) ( For example, see Patent Document 2).

JP 2002-14550 A JP 2011-112774 A

  By the way, in the transfer method described above, when the rear end portion of the recording paper 40 (thick paper) having a high basis weight enters the secondary transfer nip portion 50, the rear end portion of the recording paper 40 pushes up the intermediate transfer belt 30. In the area A immediately before the secondary transfer nip 50, a gap is generated between the intermediate transfer belt 30 and the recording paper 40. Due to this gap, discharge occurs in region A. Due to the discharge generated between the recording paper 40 and the toner image on the intermediate transfer belt 30, the charge of the toner particles forming the toner image on the intermediate transfer belt 30 is reversed in polarity. As a result, as shown in FIG. 6B, even if a transfer voltage is applied at the secondary transfer nip portion 50, a phenomenon in which the toner image is not transferred to a part 60 of the recording paper 40 occurs, resulting in an image defect (later This is the cause of edge repellency.

  A technique for solving the problem of transfer omission will be described with reference to FIG. FIG. 7 is a configuration diagram of a secondary transfer portion of a transfer system that is an improvement of the transfer system of FIG. In this method, when the rear end portion of the recording paper 40 enters the secondary transfer nip portion 50, the pressing member 70 is brought into contact with the position immediately before the secondary transfer nip portion 50 on the inner peripheral surface side of the intermediate transfer belt 30. Thus, the gap between the intermediate transfer belt 30 and the recording paper 40 is to be eliminated. With this configuration, since no discharge occurs between the intermediate transfer belt 30 and the recording paper 40, the toner image is transferred to the rear end portion 60 of the recording paper 40, and occurrence of rear end repelling can be suppressed.

  However, the gap between the intermediate transfer belt 30 and the recording paper 40 cannot be sufficiently eliminated by merely bringing the pressing member 70 into contact with the inner peripheral surface side of the intermediate transfer belt 30, and the occurrence of rear end repelling is suppressed. There was a problem that it might not be possible. Further, when the pressing member 70 is brought into contact with the inner peripheral surface side of the intermediate transfer belt 30, there is a problem that the intermediate transfer belt 30 fluctuates in speed and streaky image noise due to the speed fluctuation occurs. .

  The techniques described in Patent Documents 1 and 2 are intended to prevent the occurrence of trailing edge repelling of thick paper and the occurrence of streak-like image noise when the pressing member 70 is brought into contact with the intermediate transfer belt 30. Therefore, it does not have the structure for it.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of preventing the trailing edge of cardboard and the generation of streak-like image noise.

An image forming apparatus according to the present invention includes:
An intermediate transfer belt;
A rotating body provided on the inner peripheral surface side of the intermediate transfer belt in the vicinity of the entrance of a secondary transfer nip formed between the secondary transfer counter roller and the secondary transfer roller;
A contact / separation portion for bringing the rotating body into contact with an inner peripheral surface of the intermediate transfer belt, and for separating the rotating body from an inner peripheral surface of the intermediate transfer belt;
A rotating body driving unit for rotating the rotating body;
From the state in which the rotating body is separated from the inner peripheral surface of the intermediate transfer belt, after the leading edge of the recording paper passes through the secondary transfer nip portion, the rotating body is moved in the same direction and at the same speed as the intermediate transfer belt. in while rotating in contact with the inner peripheral surface of the intermediate transfer belt, then, before the rear end of the recording sheet passes through the secondary transfer nip portion, so as to vary the rotational speed of the rotary body A control unit for controlling the rotating body drive unit and the contact separation unit;
Equipped with a,
The controller is configured so that a rotational speed ratio θ (= V1 / V2) between the rotational speed (V1) of the rotating body after the change and the rotational speed (V2) of the intermediate transfer belt is 1> θ ≧ −0. The rotational speed of the rotating body is changed so as to be .5 .

  According to the present invention, it is possible to provide an image forming apparatus capable of preventing the trailing edge of cardboard and the generation of streak-like image noise.

3 is a control block diagram of the image forming apparatus in the present embodiment. FIG. It is a figure which shows the structure which forms the secondary transfer nip part NP in this Embodiment. 3 is a flowchart showing an operation of the image forming apparatus in the present embodiment. It is a figure which shows the structure which forms the secondary transfer nip part NP in this Embodiment. It is a table | surface which shows the experimental result in an Example and a comparative example. It is a figure explaining a prior art. It is a figure explaining a prior art.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 100]
An image forming apparatus 100 shown in FIG. 1 forms an image on a recording sheet by an electrophotographic process. The image forming apparatus 100 includes a control unit 101, a document reading unit 110, an operation display unit 120, an image processing unit 130, an image forming unit 140, a conveyance unit 150, a fixing unit 160, a communication unit 171, a storage unit 172, and a first drive unit. 180, a second driving unit 182 and a third driving unit 184 are provided.

  The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads a program corresponding to the processing content from the ROM 103 and develops it in the RAM 104, and centrally controls the operation of each block of the image forming apparatus 100 in cooperation with the developed program. At this time, various data stored in the storage unit 172 are referred to. The storage unit 172 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 101 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 171. Do. For example, the control unit 101 receives image data transmitted from an external device, and forms an image on a recording sheet based on the image data (input image data). The communication unit 171 includes a communication control card such as a LAN card, for example.

  The original reading unit 110 optically scans the original conveyed on the contact glass, forms an image of reflected light from the original on a light receiving surface of a CCD (Charge Coupled Device) sensor, and reads the original. The document is conveyed onto the contact glass by an automatic document feeder (ADF). However, the document may be manually placed on the contact glass.

  The operation display unit 120 has a touch panel screen. The user can perform input operations for various instructions and settings (for example, setting of basis weight of recording paper) via a touch panel screen.

  The image processing unit 130 includes a circuit that performs analog-digital (A / D) conversion processing and a circuit that performs digital image processing. The image processing unit 130 generates digital image data by A / D conversion processing from the analog image signal acquired by the CCD sensor of the document reading unit 110 and outputs the digital image data to the image forming unit 140.

  The image forming unit 140 emits laser light based on the digital image data generated by the image processing unit 130, and irradiates the photosensitive drum with the emitted laser light, whereby an electrostatic latent image is formed on the photosensitive drum. Is formed (exposure process).

  The image forming unit 140 is configured to execute a charging process performed before the exposure process, a development process performed after the exposure process, a transfer process after the development process, and a cleaning process after the transfer process in addition to the exposure process described above. It has.

  In the charging step, the image forming unit 140 uniformly charges the surface of the photosensitive drum by corona discharge from the charging device. In the developing step, the image forming unit 140 forms a toner image on the photosensitive drum by attaching toner contained in the developer in the developing device to the electrostatic latent image on the photosensitive drum.

  In the transfer process, the image forming unit 140 primarily transfers the toner image on the photosensitive drum to the intermediate transfer belt 200. The image forming unit 140 secondarily transfers the toner image on the intermediate transfer belt 200 onto the recording paper conveyed by the conveyance unit 150. In the cleaning process, the image forming unit 140 removes the toner remaining on the photosensitive drum after the transfer process.

  The fixing unit 160 includes a heating roller, a fixing roller, a fixing belt, and a pressure roller. The heating roller and the fixing roller are arranged apart from each other by a predetermined distance. A fixing belt is stretched between the heating roller and the fixing roller. The pressure roller is disposed in a state of being in pressure contact with the fixing belt in a region where the fixing belt and the fixing roller are in contact with each other. A fixing nip portion is formed at a portion where the fixing belt and the pressure roller are in contact with each other.

  The fixing unit 160 fixes the toner image on the recording sheet by applying heat and pressure to the toner image on the recording sheet introduced into the fixing nip (heating fixing) (fixing step). As a result, a fixed toner image is formed on the recording paper. The recording paper heated and fixed by the fixing unit 160 is discharged to the outside of the image forming apparatus 100.

  The first drive unit 180 receives a control command from the control unit 101 and rotates a pressing roller 250 described later. The first drive unit 180 is configured by a combination of a motor and a gear, for example. The first drive unit 180 functions as a rotating body drive unit. Moreover, the pressing roller 250 functions as a rotating body.

  The second drive unit 182 receives a control command from the control unit 101 and rotates a slide cam 190 described later. The 2nd drive part 182 is comprised by the combination of a motor, a gear, etc., for example. The second drive unit 182 functions as a contact separation unit.

  The third drive unit 184 receives the control command from the control unit 101 and rotates the intermediate transfer belt 200. The 3rd drive part 184 is constituted by combination of a motor, a gear, etc., for example. The third drive unit 184 functions as a belt drive unit.

[Configuration for forming secondary transfer nip NP]
Next, a configuration for forming the secondary transfer nip portion NP will be described. As shown in FIG. 2, the intermediate transfer belt 200 is sandwiched between the secondary transfer counter roller 210 and the secondary transfer roller 220. With this configuration, a secondary transfer nip NP where the secondary transfer counter roller 210 and the secondary transfer roller 220 are in contact with each other via the intermediate transfer belt 200 is formed.

  The toner image formed on the intermediate transfer belt 200 is secondarily transferred to the recording paper 240 by applying a transfer voltage having a reverse polarity to the toner to the secondary transfer roller 220 at the secondary transfer nip NP.

  The intermediate transfer belt 200 is looped around a secondary transfer counter roller 210, a support roller 230, and the like. The intermediate transfer belt 200 travels at a constant speed in the direction of arrow A by the rotation of the support roller 230.

  The intermediate transfer belt 200 is an endless belt, and is formed of, for example, a semiconductive belt made of polyimide (PI). When the intermediate transfer belt 200 is pressed against the recording paper 240 by the secondary transfer roller 220, the toner image primarily transferred to the intermediate transfer belt 200 is secondarily transferred to the recording paper 240.

  A pressing roller 250 is provided on the inner peripheral surface side of the intermediate transfer belt 200 in the vicinity of the entrance of the secondary transfer nip NP. The pressing roller 250 is provided at a position upstream by a predetermined distance L (for example, 15 [mm]) from the secondary transfer opposing roller 210 in the conveyance direction of the recording paper 240. Note that the conveyance direction of the recording paper 240 coincides with the traveling direction A of the intermediate transfer belt 200.

  The pressing roller 250 has conductivity and is electrically grounded. The pressing roller 250 moves in the direction of arrow B in FIG. 2, thereby contacting the inner peripheral surface of the intermediate transfer belt 200 or moving away from the inner peripheral surface of the intermediate transfer belt 200. Specifically, the pressing roller 250 is connected to the second driving unit 182 via the pressing spring 192 and the slide cam 190. The second drive unit 182 rotates the slide cam 190 about the shaft center 191 when receiving a drive command from the control unit 101. The control unit 101 controls the biasing force of the pressing spring 192 against the pressing roller 250 by controlling the amount of rotation of the slide cam 190 by the second driving unit 182. The control unit 101 increases the biasing force of the pressing spring 192 against the pressing roller 250 to bring the pressing roller 250 into contact with the inner peripheral surface of the intermediate transfer belt 200, and reduces the biasing force to transfer the pressing roller 250 to the intermediate transfer surface. The belt 200 is separated from the inner peripheral surface.

Next, the control operation of the image forming apparatus 100 will be described with reference to the flowchart of FIG. It should be noted that the pressing roller 250 is separated from the inner peripheral surface of the intermediate transfer belt 200 before the process of step S100 is started. Each process shown in FIG. 3 is executed each time an image forming process is performed on one recording sheet 240.
[Control Operation of Image Forming Apparatus 100]
First, the control unit 101 determines whether or not the basis weight of the recording paper 240 set by the user via the operation display unit 120 is a predetermined basis weight (for example, 200 [gsm]) or more. If the result of this determination is that it is not equal to or greater than a predetermined basis weight (for example, 200 [gsm]) (step S100, NO), the image forming apparatus 100 ends the processing in FIG.

  On the other hand, when the weight is equal to or greater than the predetermined basis weight (step S100, YES), the control unit 101 is based on a detection result of a paper position detection unit (not shown; Then, it is determined whether or not the leading end of the recording paper 240 has passed through the secondary transfer nip NP (step S120). If the result of this determination is that the leading edge of the recording paper 240 has not passed through the secondary transfer nip NP (step S120, NO), the processing returns to before step S120. FIG. 4A shows a state when the leading end of the recording paper 240 passes through the secondary transfer nip NP.

  On the other hand, when the leading end of the recording paper 240 passes through the secondary transfer nip NP (step S120, YES), the control unit 101 controls the first drive unit 180 and the second drive unit 182 to perform the first timing. In step S140, the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 in a state where it is rotated with the same direction (counterclockwise direction) and the same speed as the intermediate transfer belt 200 (step S140).

  The first timing is, for example, a predetermined position between the position where the distance from the leading edge of the recording paper 240 is 30 [mm] and the position where the distance from the trailing edge is 40 [mm] is 2 This is the timing of passing through the next transfer nip NP. FIG. 4B shows a state where the pressing roller 250 is in contact with the inner peripheral surface of the intermediate transfer belt 200.

  Next, the control unit 101 determines whether or not the rear end of the recording paper 240 has reached the second timing before passing through the secondary transfer nip NP (step S160). The second timing is, for example, the position where the distance from the rear end of the recording paper 240 is 40 [mm] after the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200. It is a predetermined timing until it passes the part NP. If the result of this determination is that the second timing has not been reached (step S160, NO), the processing returns to before step S160.

  On the other hand, when it is the second timing (step S160, YES), the control unit 101 controls the first drive unit 180 to change the rotation speed of the pressing roller 250 (step S180). Further, the control unit 101 changes the rotation speed of the pressing roller 250 at a predetermined change speed. FIG. 4C shows a state when the rotation speed of the pressing roller 250 is changed. As shown in FIG. 4C, when the rotational speed of the pressing roller 250 changes, the intermediate transfer belt 200 is subjected to a pulling force in the direction of arrow C, and the intermediate transfer belt 200 in the vicinity of the secondary transfer nip NP. The tension of this increases locally.

In the present embodiment, the control unit 101 has a rotational speed ratio θ (= V 1 / V 2 ) between the rotational speed (V1) of the pressing roller 250 after being changed and the rotational speed (V2) of the intermediate transfer belt 200. ) Is changed so that 1> θ ≧ −0.5. Here, when θ is a negative value, it means that the pressing roller 250 is counter-rotated in the reverse direction (clockwise direction) to the intermediate transfer belt 200. When θ is 0, it means that the pressing roller 250 is stationary.

  Next, the control unit 101 determines whether the trailing edge of the recording paper 240 has passed through the secondary transfer nip NP based on the detection result of the paper position detection unit (step S200). If the result of this determination is that the trailing edge of the recording paper 240 has not passed through the secondary transfer nip NP (step S200, NO), the processing returns to before step S200.

  On the other hand, when the rear end portion of the recording paper 240 passes through the secondary transfer nip NP (step S200, YES), the control unit 101 controls the second drive unit 182 to move the pressing roller 250 of the intermediate transfer belt 200. Separated from the inner peripheral surface (step S220). When the process of step S220 is completed, the image forming apparatus 100 ends the process in FIG.

[Effects of the present embodiment]
As described above in detail, in this embodiment, intermediate transfer is performed in the vicinity of the entrance of the secondary transfer nip NP formed between the intermediate transfer belt 200, the secondary transfer counter roller 210, and the secondary transfer roller 220. The pressing roller 250 provided on the inner peripheral surface side of the belt 200, the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200, and the pressing roller 250 is separated from the inner peripheral surface of the intermediate transfer belt 200. From the state where the second driving unit 182, the first driving unit 180 that rotates the pressing roller 250, and the pressing roller 250 are separated from the inner peripheral surface of the intermediate transfer belt 200, the leading end of the recording paper 240 is moved to the secondary transfer nip. After passing through the portion NP, the pressing roller 250 is rotated and brought into contact with the inner peripheral surface of the intermediate transfer belt 200. A control unit 101 that controls the first driving unit 180 and the second driving unit 182 so as to change the rotation speed of the pressing roller 250 before the trailing end of the recording paper 240 passes through the secondary transfer nip NP. .

  According to the present embodiment configured as described above, when the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200, the speed variation of the intermediate transfer belt 200 is suppressed, and then the image to be formed has a streak shape. It is possible to prevent the occurrence of image noise. Further, when the rear end portion of the recording paper 240 enters the secondary transfer nip portion NP, the tension of the intermediate transfer belt 200 in the vicinity of the secondary transfer nip portion NP is locally changed by changing the rotation speed of the pressing roller 250. To increase. Therefore, the amount by which the intermediate transfer belt 200 is pushed up by the rear end portion of the recording paper 240 is reduced, and no discharge is generated between the recording paper 240 and the toner image on the intermediate transfer belt 200, thereby preventing the occurrence of rear end repelling. can do.

  In this embodiment, the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 in a state where the pressing roller 250 is rotated in the same direction and at the same speed as the intermediate transfer belt 200. With this configuration, the speed of the intermediate transfer belt 200 is kept constant before and after the contact between the pressing roller 250 and the inner peripheral surface of the intermediate transfer belt 200, and then streak-like image noise is generated in the formed image. It can be surely prevented.

  Further, in the present embodiment, the control unit 101 determines between the position where the distance from the leading edge of the recording paper 240 is 30 [mm] and the position where the distance from the trailing edge is 40 [mm]. The pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 at a timing when the predetermined position passes through the secondary transfer nip NP. When the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 at the timing when the leading end portion of the recording paper 240 enters the secondary transfer nip portion NP, the pressing roller 250 hitting the leading end portion of the recording paper 240 is pushed up. Then, the intermediate transfer belt 200 floats. As a result, in the region immediately before the secondary transfer nip NP, a gap is generated between the intermediate transfer belt 200 and the recording paper 240, and a discharge is generated accordingly. As a result, even if a transfer voltage is applied at the secondary transfer nip NP, a leading edge repelling (transfer omission) phenomenon in which the toner image is not transferred to the leading edge of the recording paper 240 occurs. Therefore, by causing the pressing roller 250 to contact the inner peripheral surface of the intermediate transfer belt 200 after the leading end of the recording sheet 240 has surely passed through the secondary transfer nip NP, the leading edge of the recording sheet 240 is generated. Can be prevented.

  In the present exemplary embodiment, the control unit 101 makes the position where the distance from the rear end of the recording paper 240 is 40 [mm] after the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200. The rotation speed of the pressing roller 250 is changed at a predetermined timing until it passes through the secondary transfer nip NP. With this configuration, it is possible to prevent the pressing roller 250 from pressing the intermediate transfer belt 200 more than necessary at a timing when the trailing edge repelling phenomenon does not occur, that is, when the trailing edge of the recording paper 240 does not pass through the secondary transfer nip NP. As a result, it is possible to prevent the intermediate transfer belt 200 from being damaged by the pressing.

In the present embodiment, the control unit 101 also rotates the rotation speed ratio θ (= V 1 / V) between the rotation speed (V1) of the pressing roller 250 after the change and the rotation speed (V2) of the intermediate transfer belt 200. The rotation speed of the pressing roller 250 is changed so that V 2 ) satisfies 1> θ ≧ −0.5. With this configuration, the frictional force increases between the pressing roller 250 and the intermediate transfer belt 200, and the tension of the intermediate transfer belt 200 in the vicinity of the secondary transfer nip portion NP can be effectively increased. Therefore, there is no gap between the intermediate transfer belt 200 and the recording paper 240, and no discharge occurs between the intermediate transfer belt 200 and the recording paper 240, so that it is possible to reliably prevent the occurrence of rear end repelling. From the viewpoint of more reliably preventing the occurrence of rear end repelling, the rotational speed ratio θ is preferably a small value, that is, a value close to −0.5.

  Further, in the present embodiment, the pressing roller 250 has conductivity and is electrically grounded. With this configuration, it is possible to prevent static electricity from being charged in the pressing roller 250 due to frictional contact between the pressing roller 250 and the intermediate transfer belt 200. Therefore, when the halftone image is transferred to the recording paper 240, the halftone image on the intermediate transfer belt 200 is prevented from being disturbed by the influence of static electricity charged on the pressing roller 250 before the transfer, and as a result, Generation of halftone noise can be prevented.

  In the above embodiment, the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 only when the basis weight of the recording paper 240 is equal to or greater than the predetermined basis weight. With this configuration, the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200 only when the trailing edge of the thick paper and streak-like image noise are likely to be generated. It is possible to prevent the intermediate transfer belt 200 from being damaged due to unnecessary contact with the toner, and consequently with the contact.

[Modification]
In the above embodiment, the control unit 101 determines that the pressing roller 250 is moved between the secondary transfer counter roller 210 and the secondary transfer roller 220 after the leading end of the recording paper 240 has passed through the secondary transfer nip NP. The pressing amount with respect to the intermediate transfer belt 200 may be set to 0 to 5 [mm] while being pressed, and may be brought into contact with the inner peripheral surface of the intermediate transfer belt 200. With this configuration, when the rear end portion of the highly rigid recording paper 240 enters the secondary transfer nip NP, the intermediate transfer belt 200 is pushed down, and a gap is generated between the intermediate transfer belt 200 and the recording paper 240. Is prevented. Therefore, no discharge occurs between the recording paper 240 and the toner image on the intermediate transfer belt 200, and the occurrence of trailing edge repelling at the rear end portion of the recording paper 240 can be prevented. Note that the control unit 101 sets the pushing amount to a large value because the higher the basis weight of the recording paper 240, the higher the possibility that a gap is generated between the intermediate transfer belt 200 and the recording paper 240. Is desirable. From the same point of view, the control unit 101 is closer to the situation where the rear end of the recording paper 240 having higher rigidity enters the secondary transfer nip NP as the humidity around the image forming apparatus 100 decreases. It is desirable to set the pushing amount to a large value. Further, it is desirable that the control unit 101 sets the pushing amount to a larger value as the rigidity of the recording paper 240 becomes higher.

  In the above-described embodiment, the control unit 101 may change the rotation speed of the pressing roller 250 at a predetermined change speed (for example, constant speed, double speed, and half speed). However, from the viewpoint of suppressing the speed fluctuation of the intermediate transfer belt 200 as much as possible, it is desirable to change the rotation speed of the pressing roller 250 at a constant speed. Here, the constant speed is a change speed per unit time set in advance in order to suppress the speed fluctuation of the intermediate transfer belt 200 as much as possible when the rotation speed of the pressing roller 250 is changed. The double speed and the half speed are the double speed and the half speed of the change speed, respectively.

  In the above embodiment, the control unit 101 may control the third driving unit 184 to increase the rotation speed of the intermediate transfer belt 200 when the rotation speed of the pressing roller 250 is changed. With this configuration, when the rotation speed of the pressing roller 250 changes, it is possible to prevent the speed fluctuation from occurring in the intermediate transfer belt 200 that is in contact with the pressing roller 250. Regarding the amount of increase in the rotational speed of the intermediate transfer belt 200, the friction coefficient between the pressing roller 250 and the intermediate transfer belt 200 differs depending on the material of the pressing roller 250 (for example, rubber or metal). It is desirable to set. In this case, the increase amount of the rotation speed of the intermediate transfer belt 200 corresponding to the material of the pressing roller 250 may be stored in the storage unit 172 in advance, and the control unit 101 may appropriately read it.

  In the above-described embodiment, the control unit 101 increases the basis weight of the recording paper 240 when the rear end portion of the recording paper 240 enters the secondary transfer nip NP and the recording with the intermediate transfer belt 200. Since there is a high possibility that a gap is generated between the sheet 240 and the sheet 240, the rotation speed ratio θ between the rotation speed (V1) of the pressing roller 250 and the rotation speed (V2) of the intermediate transfer belt 200 after the change is small. The rotational speed of the pressing roller 250 may be changed so that From the same point of view, the control unit 101 is closer to the situation where the rear end of the recording paper 240 having higher rigidity enters the secondary transfer nip NP as the humidity around the image forming apparatus 100 decreases. It is desirable to change the rotation speed of the pressing roller 250 so that the rotation speed ratio θ becomes a small value. Further, it is desirable that the control unit 101 changes the rotation speed of the pressing roller 250 so that the rotation speed ratio θ becomes a smaller value as the rigidity of the recording paper 240 becomes higher.

  Moreover, in the said embodiment, the pressing roller 250 may have elasticity. For example, the pressing roller 250 has a conductive resin sheet layer on the outermost layer on the inner peripheral surface side (contact surface side) of the intermediate transfer belt 200 and a foamed layer such as a sponge as the second layer. The resin sheet layer and the foamed layer have low rebound resilience. With this configuration, when the halftone image is transferred to the recording paper 240, even if the trailing end of the recording paper 240 jumps up after passing through the paper guide (not shown) and contacts the intermediate transfer belt 200, The impact on the recording paper 240 is reduced. Therefore, the disturbance of the halftone image formed on the intermediate transfer belt 200 is suppressed, and as a result, generation of halftone noise at the rear end portion of the recording paper 240 can be prevented.

  In the above embodiment, the distance L between the pressing roller 250 and the secondary transfer counter roller 210 may be arbitrarily set. However, from the viewpoint of eliminating the gap between the intermediate transfer belt 200 and the recording paper 240 and suppressing the occurrence of rear end repelling, it is desirable that the distance L between the pressing roller 250 and the secondary transfer counter roller 210 be as small as possible. For example, it is 10-20 [mm].

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

[Example]
Finally, the results of an experiment conducted by the present inventor for confirming the effectiveness in the above embodiment will be described.

[Configuration of Image Forming Apparatus According to First to Sixth Embodiments]
As the experimental image forming apparatus, the image forming apparatus 100 having the configuration shown in FIGS. In the first to sixth embodiments, the basis weight of the recording paper 240, the first timing at which the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200, and the second timing at which the rotation speed of the pressing roller 250 is changed. The rotation speed ratio θ between the rotation speed (V1) of the pressing roller 250 after the change and the rotation speed (V2) of the intermediate transfer belt 200, and the change per unit time when the rotation speed of the pressing roller 250 is changed. The speed, the distance between the secondary transfer counter roller 210 and the pressing roller 250, and the pressing amount of the pressing roller 250 against the intermediate transfer belt 200 were set as shown in FIG. Here, the first timing is the sheet leading edge XX [mm], which is the timing at which the position where the distance from the leading edge of the recording sheet 240 is XXX [mm] passes through the secondary transfer nip NP. This means that the pressing roller 250 is brought into contact with the inner peripheral surface of the intermediate transfer belt 200. The second timing is the leading edge of the sheet ●●● [mm], which is pressed at the timing when the position where the distance from the leading edge of the recording paper 240 is ●●● [mm] passes through the secondary transfer nip NP. It means that the rotation speed of the roller 250 is changed.

[Configuration of Image Forming Apparatus According to First Comparative Example]
As an experimental image forming apparatus, a configuration in which a fixing member is brought into contact with the intermediate transfer belt 200 instead of the pressing roller 250 after the leading end of the recording paper 240 passes through the secondary transfer nip NP.

[Configuration of Image Forming Apparatus According to Second Comparative Example]
The experimental image forming apparatus employs a configuration in which the pressing roller 250 is not provided, that is, nothing is brought into contact with the intermediate transfer belt 200 after the leading end of the recording paper 240 has passed through the secondary transfer nip NP.

[experimental method]
In the experiment, a black halftone image was transferred to a recording paper 240 of A3 size (paper length: 420 [mm]). FIG. 5B shows the result of evaluating the occurrence of trailing edge flickering and streak-like image noise on the halftone image transferred to the recording paper 240 according to the following evaluation criteria.

(Occurrence of rear edge repellency)
○: No trailing edge repelling occurred on the recording paper 240.
Δ: The trailing edge of the recording paper 240 is generated but at an acceptable level.
X: The trailing edge of the recording paper 240 is repelled and is an unacceptable level.

(Situation of streak-like image noise)
○: No streak-like image noise is generated on the recording paper 240.
×: Striped image noise is generated on the recording paper 240.

[Experimental result]
In the first to sixth embodiments, it was possible to prevent the trailing edge repelling and the generation of streak-like image noise. On the other hand, in the first comparative example, the gap between the intermediate transfer belt 200 and the recording paper 240 could not be sufficiently eliminated, and the occurrence of rear end repelling could not be prevented completely. Further, when the fixing member was brought into contact with the inner peripheral surface side of the intermediate transfer belt 200, a speed change occurred in the intermediate transfer belt 200, and streak-like image noise was generated due to the speed change. In the second comparative example, a gap was generated between the intermediate transfer belt 200 and the recording paper 240, and it was not possible to prevent the trailing edge from being repelled. Since nothing is brought into contact with the inner peripheral surface side of the intermediate transfer belt 200, no speed fluctuation occurs in the intermediate transfer belt 200, and no streak-like image noise occurs.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 102 CPU
103 ROM
104 RAM
110 Document Reading Unit 120 Operation Display Unit 130 Image Processing Unit 140 Image Forming Unit 150 Conveying Unit 160 Fixing Unit 171 Communication Unit 172 Storage Unit 180 First Drive Unit 182 Second Drive Unit 184 Third Drive Unit 190 Slide Cam 191 Axis Center 192 Pressure spring 200 Intermediate transfer belt 210 Secondary transfer counter roller 220 Secondary transfer roller 230 Support roller 240 Recording paper 250 Pressing roller NP Secondary transfer nip

Claims (16)

An intermediate transfer belt;
A rotating body provided on the inner peripheral surface side of the intermediate transfer belt in the vicinity of the entrance of a secondary transfer nip formed between the secondary transfer counter roller and the secondary transfer roller;
A contact / separation portion for bringing the rotating body into contact with an inner peripheral surface of the intermediate transfer belt, and for separating the rotating body from an inner peripheral surface of the intermediate transfer belt;
A rotating body driving unit for rotating the rotating body;
From the state in which the rotating body is separated from the inner peripheral surface of the intermediate transfer belt, after the leading edge of the recording paper passes through the secondary transfer nip portion, the rotating body is moved in the same direction and at the same speed as the intermediate transfer belt. in while rotating in contact with the inner peripheral surface of the intermediate transfer belt, then, before the rear end of the recording sheet passes through the secondary transfer nip portion, so as to vary the rotational speed of the rotary body A control unit for controlling the rotating body drive unit and the contact separation unit;
Equipped with a,
The controller is configured so that a rotational speed ratio θ (= V1 / V2) between the rotational speed (V1) of the rotating body after the change and the rotational speed (V2) of the intermediate transfer belt is 1> θ ≧ −0. An image forming apparatus that changes the rotation speed of the rotating body so as to be .5 . The control unit sets the pushing amount of the rotating body with respect to the intermediate transfer belt to 0 to 5 [mm] after the leading end of the recording paper passes through the secondary transfer nip portion, and performs the intermediate transfer. The image forming apparatus according to claim 1 , wherein the image forming apparatus is brought into contact with an inner peripheral surface of the belt. The control unit has a predetermined position between the position where the distance from the leading edge of the recording sheet is 30 [mm] and the position where the distance from the trailing edge is 40 [mm] is the secondary transfer nip. 3. The image forming apparatus according to claim 1, wherein the rotating body is brought into contact with an inner peripheral surface of the intermediate transfer belt at a timing of passing through a portion. After the rotating unit is brought into contact with the inner peripheral surface of the intermediate transfer belt, the control unit passes through the secondary transfer nip portion at a position where the distance from the rear end of the recording paper is 40 [mm]. at a predetermined time before, the image forming apparatus according to any one of claim 1 to 3 for changing the rotational speed of the rotating body. Wherein the control unit, the image forming apparatus according to any one of claims 1-4 for changing the rotational speed of the rotating body at a predetermined rate of change. A belt driving unit for rotating the intermediate transfer belt;
Wherein, when changing the rotational speed of the rotating body, an image forming according to any one of claim 1 to 5 for controlling the belt drive to increase the rotational speed of the intermediate transfer belt apparatus. The rotating body, an image forming apparatus according to any one of claim 1 to 6 provided upstream of the position by a predetermined distance from the secondary transfer opposing roller in the transport direction of the recording paper. The rotating body has conductivity, and an image forming apparatus according to any one of claim 1 to 7, which is electrically grounded. The image according to any one of claims 1 to 8 , wherein the control unit causes the rotating body to contact the inner peripheral surface of the intermediate transfer belt only when the basis weight of the recording paper is equal to or greater than a predetermined basis weight. Forming equipment. The image forming apparatus according to claim 2 , wherein the control unit sets the pushing amount to a larger value as the basis weight of the recording sheet becomes higher. The image forming apparatus according to claim 1 , wherein the control unit changes the rotation speed of the rotating body so that the rotation speed ratio θ becomes a smaller value as the basis weight of the recording sheet becomes higher. The image forming apparatus according to claim 2 , wherein the controller sets the push amount to a larger value as the humidity around the image forming apparatus becomes lower. The image forming apparatus according to claim 1 , wherein the control unit changes the rotation speed of the rotating body so that the rotation speed ratio θ becomes a smaller value as the humidity around the image forming apparatus becomes lower. The image forming apparatus according to claim 2 , wherein the control unit sets the pushing amount to a larger value as the rigidity of the recording sheet becomes higher. The image forming apparatus according to claim 1 , wherein the control unit changes the rotation speed of the rotating body so that the rotation speed ratio θ becomes a smaller value as the rigidity of the recording sheet becomes higher. The rotating body, an image forming apparatus according to any one of claim 1 to 15 having an elasticity.

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