JP2003316184A - Image forming device and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which prevents the occurrence of image deterioration, such as disturbance of toner images, by preventing the occurrence of pulling of recording media to each other and suppressing the vibration at the rear ends of the recording media when the rear ends of the recording media pass transfer means. <P>SOLUTION: The image forming device has a transfer section for transferring the toner image formed on an image carrying member to the recording medium in a transfer position, a fixing section for fixing the toner image transferred to the recording medium, and control section for controlling the amount of the loop that the transfer section and the fixing section form on the recording medium by controlling a fixing and conveying speed transferring the recording media by the fixing section. The above control section controls a fixing and conveying speed so as to decrease the amount of the loop in response with the arrival of the rear end of the recording medium at the prescribed position on the upstream side in the conveying direction of the transfer position. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an image forming method.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, when a recording medium is conveyed by using a plurality of conveying portions such as rollers, the recording medium is bent to some extent (loop) by the plurality of conveying portions.
An image forming apparatus is known that controls a plurality of conveyance units so as to form a sheet.

Here, as an example of the image forming apparatus, a transfer section for transferring the toner image on the photosensitive drum to a recording medium,
2. Description of the Related Art There is known an electrophotographic image forming apparatus having a fixing unit that fixes a toner image sent from a transfer unit on a recording medium by, for example, a heat roller system.

Explaining such an electrophotographic image forming apparatus, the transfer speed given to the recording medium by the transfer section and the fixing section is caused by a change in the diameter of a roller such as a fixing roller constituting the fixing section due to heat. If they are different from each other, image deterioration may occur due to pulling of the recording medium by the transfer unit and the fixing unit, or generation of an unnecessarily large loop in the recording medium.

In order to solve this problem, a detection unit for detecting the loop amount formed on the recording medium by the transfer unit and the fixing unit is provided, and the loop amount formed by the transfer unit and the fixing unit on the recording medium is determined. A method of controlling a plurality of transport units such as rollers so as to hold a fixed amount is used (for example, refer to Patent Document 1).

[0006]

[Patent Document 1] Japanese Patent Laid-Open No. 2000-89534 (6th
-7, Fig. 5)

[0007]

However, in the conventional image forming apparatus, the recording medium is passed through the transfer portion while keeping the loop amount formed on the recording medium at a constant amount. When the trailing edge passes through the transfer section, the loop formed by a plurality of transport sections such as rollers is opened. As a result, the trailing edge of the recording medium vibrates and the unfixed toner image transferred onto the sheet is disturbed,
A problem that causes image deterioration occurs.

The present invention has been made in view of the above, and does not cause pulling of recording media and the like, and
An object of the present invention is to provide an image forming apparatus that does not cause image deterioration such as disturbance of a toner image by suppressing vibration of the trailing edge of the recording medium when the trailing edge of the recording medium passes through a transfer unit. And

[0009]

In order to achieve the above object, the present invention provides a transfer means for transferring a toner image formed on an image carrier to a recording medium at a transfer position, and the transfer means for transferring the toner image to the recording medium. A control unit that controls the amount of loop formed by the transfer unit and the fixing unit on the recording medium by controlling the fixing unit that fixes the toner image and the fixing conveyance speed that the fixing unit conveys the recording medium. And a control means for controlling the fixing conveyance speed so as to reduce the loop amount in response to the rear end of the recording medium reaching a predetermined position on the upstream side in the conveyance direction of the transfer position. And

Further, image formation in an image forming apparatus having a transfer means for transferring the toner image formed on the image carrier to a recording medium at a transfer position and a fixing means for fixing the toner image transferred on the recording medium. A first method for controlling a loop amount formed by the transfer unit and the fixing unit on a recording medium by controlling a fixing conveyance speed at which the transfer unit and the fixing unit convey a recording medium. In response to the control step and the rear end of the recording medium reaching a predetermined position on the upstream side in the transport direction of the transfer position, the loop amount formed on the recording medium in the first control step is reduced. A second control step for controlling the fixing and conveying speed.

Further, transfer means for transferring the toner image formed on the image carrier to the recording medium conveyed at a predetermined conveying speed at the transfer position, and the toner image transferred to the recording medium is fixed. A fixing unit and a control unit for controlling a fixing conveyance speed of the fixing unit, wherein the fixing conveyance is performed in response to the trailing end of the recording medium reaching a predetermined position upstream of the transfer position in the conveyance direction. A control means for controlling the speed to switch from a first speed lower than the predetermined transfer speed to a second transfer speed higher than the predetermined transfer speed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

(First Embodiment) The first embodiment will be described with reference to FIGS.

FIG. 1 is a diagram showing the overall configuration of a tandem type color image forming apparatus. The tandem type color image forming apparatus described in the first embodiment uses cyan (C), yellow (Y), magenta (M), and black (K) developers (toners) by an electrophotographic method. An image is formed by transferring and fixing it on a recording medium.

Reference numerals 1C, 1Y, 1M and 1Bk denote scanner units, which are semiconductor lasers (not shown), 2C, 2Y and 2B.
It is composed of a rotating polygon mirror of M and 2Bk.

Reference numerals 3C, 3Y, 3M, and 3Bk are cartridges which are constructed so that a developer storage device 4, a photoconductor 5, a developing sleeve 6 and the like, which will be described later, can be integrally attached to and detached from the main body of the image forming apparatus. The arrangement of the cartridges is not limited to that shown in FIG. 1, and the cartridges may be arranged in any order.

Reference numerals 4C, 4Y, 4M, and 4Bk denote developer storage devices which store a developer (toner) and 5
The waste toner is collected by cleaning the excess toner on the C, 5Y, 5M, and 5Bk photoconductors.

6C, 6Y, 6M, and 6Bk are developing sleeves, which are charged by a charging device (not shown), and the scanner units 1C to 1Bk irradiate laser light to form photoconductors 4C to 4C. Toner is supplied onto 4Bk to develop the toner image.

Transfer rollers 7C, 7Y, 7M and 7Bk are used to transfer the above-mentioned toner image onto the recording medium 10. More specifically, a cartridge drive motor, which will be described later, applies a rotational force to the photoconductor to transfer the toner image developed on the photoconductor to the recording medium while nipping and conveying the recording medium with the photoconductor and the transfer roller.

Reference numeral 8 is an endless conveyor belt for conveying a recording medium, 9 is a paper feeding unit, and 10 is a recording medium.

The recording medium 10 is fed to the fixing unit 11 by being given a feeding force by the photoconductor 5Bk, the transfer roller 7Bk and the feeding belt 8 which are located on the most downstream side in the feeding direction.

The fixing unit 11 is a unit for fixing the toner image on the recording medium. The heating unit 12 heats the recording medium, and the recording medium is conveyed, and the heating roller 12 is given a rotational force to apply pressure. It is composed of a pressure roller 13. As the heating roller 12, a coil is arranged in the film-shaped electromagnetic induction heating rotor, and an electric current is passed through the coil to heat the film-shaped electromagnetic induction heating rotor on the outer periphery, or a halogen. A device having a built-in heat source such as a heater is used.

A recording medium detection sensor 14 is provided upstream of the fixing unit 11 in the transport direction. Although the recording medium detection sensor 14 is provided on the downstream side in the transport direction of the cartridge 3Bk located at the most downstream side in the transport direction in this embodiment, it may be provided at an arbitrary position on the upstream side in the transport direction of the fixing unit 11.

FIG. 2 is an enlarged view of a main part of FIG. 1. Among the cartridges 3C to 3Bk, the cartridge drive motor 15 for driving the cartridge 3Bk including the photoconductor 5Bk and the most downstream in the transport direction, and the pressure roller of the fixing unit 11. A fixing unit drive motor 16 for driving the motor 13, a controller 17 for controlling the drive of the fixing unit drive motor 13, motor drivers 18, 19 for driving the above-mentioned motor in response to a control command from the controller 17, and a rotation of the motor A counter 20 that counts pulses from a pulse generator (encoder, MR sensor, etc.) that generates pulses is shown in FIG. 1
In addition to the above, The controller 17 may be configured by a CPU or the like, and the counter 20 may be provided separately from the CPU, or may be configured by incorporating the counter 20 in the CPU. Further, the cartridge drive motor 15 may be provided in each of the cartridges 3C to 3Bk or may be provided commonly to all the cartridges.

FIG. 3 is a control block diagram in the first embodiment.

Reference numeral 21 denotes a recording medium size detection sensor for detecting the size of the recording medium 10 loaded in the paper feeding unit 9,
A memory 22 has a table 23 for storing count values according to the size of the recording medium 10 used when counting by the counter 20. It should be noted that the count value stored in the table 23 indicates that the trailing end of the recording medium 10 is detected by the recording medium detection sensor 14 after the leading end of the recording medium 10 conveyed at the process speed Vp is detected, and then the photosensitive member 5Bk and the transfer roller 7Bk are detected. The value C1 counted by the counter 20 and the deceleration to Vpd slower than the process speed Vp from the time when the leading edge of the recording medium 10 is detected by the recording medium detection sensor 14 before the transfer nipping the transfer nip portion N1 where is close to. Further, it is the value C1d counted by the counter 20.

Reference numeral 24 denotes an encoder, which is attached to the drive shaft of the cartridge drive motor 15 and is composed of a disk having slits at equal intervals along the circumference and a photo interrupter. When the light of the photo interrupter passes through the slit of the disk. A pulse is output and output to the counter 20. Therefore, the controller 17 controls the recording medium 10 conveyed by the photoconductor 5Bk driven by the cartridge driving motor 15 based on the value of the counter 20.
Since the transport distance of the recording medium 10 can be calculated,
It is possible to determine whether or not the rear end has reached a predetermined position on the upstream side in the transport direction of the transfer nip portion N1.

Reference numeral 25 is a ferromagnetic magnetoresistive effect type sensor element (hereinafter referred to as MR sensor), which detects a pattern in which the rotor of the fixing unit drive motor 16 is uniformly magnetized, and a Sin waveform corresponding to the rotational speed of the rotor. Waveform converter 2 as
Output to 6. The waveform converter 26 converts the Sin waveform into a rectangular pulse wave (for example, 360 pulses / rotation) and outputs the rectangular pulse wave to the counter 20.

Then, the controller 17 determines the photosensitive member 5B based on the count value of the pulse output from the motor.
k, the transfer roller 7Bk, and the conveyor belt 8 are the recording medium 1.
The transport speed given to 0 and the transport speed given to the recording medium 10 by the fixing unit 11 can be calculated, and the measured count value is compared with the count value stored in advance in the table 23 to convey the recording medium 10. The position can be calculated. Then, based on the calculated transport speed and transport position, a control command is transmitted to the motor drivers 18 and 19 to control the cartridge drive motor 15 and the fixing unit drive motor 16.

Next, the operation of the image forming apparatus in this embodiment will be described with reference to the flowchart of FIG.

In step S401, the controller 17
Monitors whether or not image data transmitted from a video controller (not shown) or the like has been received.

In step S402, the image forming operation is started in response to the reception of the image data (YES in step S401), and at the same time, the paper feed unit 9 which is a paper feed port designated by the video controller, the operation panel or the like.
The recording media 10 stacked on the paper are fed by a paper feed roller (not shown).

In step S403, the fixing unit 11
Of the cartridges 3C to 3Bk, the transfer rollers 7C to 7Bk, the conveyor belt 8 and the like.
The process speed Vp, which is the conveyance speed of the image forming unit that transfers the toner image on 5 Bk, is set. This operation is performed by transmitting a control command from the controller 17 to the motor driver 18 and controlling the rotation speed of the cartridge drive motor 15. The recording medium 10 that has been fed is conveyed at the process speed Vp, and the cartridge 4
When passing through C, the toner image of C (cyan) formed on the photoconductor 5C is transferred, and then the toner image of Y (yellow) is transferred by the cartridge 4Y in the order of the carrying direction and the toner image of M (magenta) is transferred by the cartridge 4M. ), Finally, the Bk (black) toner image is sequentially transferred onto the recording medium 10 by the cartridge 4Bk, and finally the full-color toner image is transferred.

Steps S404 and 405 are step S
402 and 403 are steps executed in parallel,
In step S404, the recording medium size detection sensor 21
The recording medium size is detected by the table 23 in the memory 22 in step S405.
And count values C1 and C1d adapted to the size
Is selected.

The count value C1 means that the trailing edge of the recording medium 10 is the photosensitive member 5Bk and the transfer roller 7Bk after the leading edge of the recording medium 10 conveyed at the process speed Vp is detected by the recording medium detecting sensor 14. Is a value counted by the counter 20 until it comes out of the transfer portion nip portion N1 adjacent thereto, C1d is about half the count value C1, and the leading end of the recording medium 10 is detected by the recording medium sensor 14. This is a count corresponding to the time from when the intermediate point of the length of the recording medium 10 in the transport direction reaches the transfer nip portion N1.

In step S406, step S405
The count values C1 and C1d selected in 1 are set in the controller 17.

In step S407, the controller 17
However, it is determined whether or not the recording medium 10 onto which the full-color toner image has been transferred is conveyed to reach the recording medium detection sensor 14 and the output of the sensor is turned on.

In step S408, in response to the detection of the leading edge of the recording medium 10 (YES in step S407), the counter 20 causes the cartridge drive motor 1 to operate.
The counting of the output pulse of 5 is started.

In step S409, the controller 17
Sends a deceleration command to the motor driver 19 to lower the rotation speed of the fixing unit drive motor 16 so that the conveyance speed by the fixing unit 11 is Vpd lower than the process speed Vp.
And Vpd can be arbitrarily set as long as it is lower than the process speed Vp, but in the present embodiment, as an example,
Vpd is 95% of Vp Vpd = 0.95V
p.

In step S410, the controller 17
By monitoring whether or not the count started in step S408 reaches C1d, it is determined whether or not the rear end of the recording medium 10 has reached a predetermined position on the upstream side in the transport direction of the transfer nip portion N1, If C1d is reached, an acceleration command is sent from the controller 17 to the motor driver 19 in step S411, and the fixing unit drive motor 1
The rotation speed of 6 is increased, and the conveyance speed by the fixing unit 11 is set to Vpu higher than the process speed Vp. Here, Vpu can be arbitrarily set as long as it is higher than the process speed Vp, but the time for the recording medium 10 to pass through the fixing unit 11 at the normal process speed Vp is T, and the fixing unit 11 is at low speed Vpd. When the time for transporting the recording medium 10 is Td, it is preferable that the speed is represented by the following formula.

Vpu = (Vp · T−Vpd · Td) / (T−Td) (Equation 1) By defining Vpu in this way, the average speed of one recording medium passing is determined as the process. Since the fixing unit drive motor 16 is controlled so as to have the speed Vp, the recording medium 10 is finally ejected from the fixing unit 11 at the same timing as when an image is formed on the recording medium 10 with the process speed Vp. It

In step S412, it is monitored whether or not the count reaches C1. If the count reaches C1, the counter is reset in step S413.

In step S414, it is determined whether there is a page to be continuously image-formed. If there is a page to be continuously image-formed, the process returns to step S402, and if not, the image-forming operation is ended.

The carrying state of the recording medium 10 in the above operation will be described with reference to FIG.

FIG. 11A is a diagram showing the conveyance state of the recording medium 10 at the time when the leading edge of the recording medium 10 is detected by the recording medium detection sensor 14. As shown in step S409 in the flowchart of FIG. 4, at this time, the controller 17 reduces the transport speed of the fixing unit 11 from the process speed Vp to Vpd slower than Vp.

FIG. 11B is a diagram showing a state in which the fixing unit 11 conveys the recording medium 10 at a distance corresponding to L ₂ (= Vpd · Td) after the leading end of the recording medium 10 has entered the fixing nip portion N2. Is. Vpd is a speed slower than the process speed Vp, and the distance conveyed by the fixing unit 11 during the Td at the process speed Vp is Vp · Td. Therefore, the recording medium between the transfer nip portion N1 and the fixing nip portion N2. At 10, a loop corresponding to (Vp · Td−Vpd · Td) is formed.

At this point, the transfer nip portion N
The distance from 1 to the rear end of the recording medium 10 is half the length L ₁ of the recording medium 10 in the transport direction.
Then, at this point, the loop formed between the transfer nip portion N1 and the fixing nip portion N2 is reduced when the rear end of the recording medium 10 passes through the transfer nip portion N1. The transport speed is switched from Vpd to Vpu which is higher than Vp.

FIG. 11C shows the conveyance state of the recording medium 10 when the rear end of the recording medium 10 reaches the transfer nip portion N1.

By setting Vpu as described above, the loop formed by the amount corresponding to (Vp.Td-Vpd.Td) in FIG. 11B is further L ₁ / from FIG. 11B. When the trailing edge of the recording medium 10 passes through the transfer nip portion N1, the vibration of the trailing edge of the recording medium is suppressed.

In the first embodiment, the encoder 2 is used to detect the rotation speed of the cartridge drive motor 15.
4 uses an MR sensor to detect the rotation speed of the fixing unit drive motor 16, but the encoder 2 is used for both motors.
Any one of 4 and MR sensor may be used. Also,
When the motor is a stepping motor, the same control may be performed using a method in which the counter 20 counts the driving pulses transmitted to the motor driver by the controller 17 to drive the stepping motor. good.

Further, in the first embodiment, the recording medium detection sensor 14 detects the recording medium 10 before the recording medium 10 is detected.
The value of C1d was set so as to switch the transport speed of the fixing unit 11 from Vpd to Vpu in response to the transport of 1/2 of the transport direction length.
It may be set to an arbitrary length of 3/4. Here, for example, 1/3 means that the distance from the transfer nip portion N1 to the rear end of the recording medium 10 is 1/3 of the length of the recording medium 10 in the transport direction.

Further, in the first embodiment, the recording medium detection sensor 14 for detecting the recording medium 10 is provided between the transfer nip portion N1 and the fixing nip portion N2. It can be provided at any position as long as it is on the upstream side in the carrying direction. In that case, the count value C1 stored in the table 23 of the memory 22 is different from that described above, and after the recording medium detection sensor 14 detects the front end of the recording medium 10, the rear end of the recording medium 10 is transferred to the transfer portion nip portion N1. Is set to a value counted by the counter 20 before exiting. Further, in the count value C1d, the distance from the transfer nip portion N1 to the trailing edge of the recording medium 10 after the recording medium detection sensor 14 detects the leading edge of the recording medium 10 is a predetermined distance (for example, the recording medium conveyance direction). It is assumed that the count value required to reach a state in which the length becomes 1/2) is set.

As described above, according to the transport position of the recording medium 10 calculated by the controller 17, the mode for controlling to form a loop is switched to the mode for controlling to reduce the loop, so that the roller diameter of the fixing unit 11 can be reduced. It is possible to provide an image forming apparatus that does not cause an image defect due to fluctuations in the recording medium 10 and does not cause an image defect due to the trailing end of the recording medium 10 bouncing when passing through the transfer portion.

(Second Embodiment) The second embodiment will be described with reference to FIGS.

In the first embodiment, the recording medium detection sensor 14 is controlled so as to switch the conveying speed of the fixing unit 11 according to the count value after the recording medium 10 is detected. In the above embodiment, a sensor for detecting the loop amount formed on the recording medium 10 by the transfer unit and the fixing unit 11 is further used to provide a step of controlling the loop amount to a constant amount.

FIG. 5 shows a temporal change in the conveyance of the recording medium 10 (in the order of a, b, c, d) in the second embodiment, and 27 is a photoconductor 5Bk and a transfer roller 7B.
The transfer unit and the fixing unit 11, which are close to each other by
It is a loop detection sensor that detects whether or not the amount of loops formed at 0 has reached a certain amount. The loop detection sensor 2
As shown in FIG. 6, 7 is composed of a mechanical flag 28 and a photo interrupter 29. When a loop is formed on the recording medium 10, a recording medium contact member 28a of the mechanical flag 28 is formed.
Is pressed by the recording medium 10 to rotate the mechanical flag 28, and accordingly, the photo interrupter 29 is shielded from light (loop sensor OFF / FIG. 6-a).
b is rotated to release the light blocking (loop sensor ON / FIG. 6-b). As a result, the output of the loop detection sensor 27 is inverted, and it is detected that a certain amount of loop has been formed.

Next, the operation of the image forming apparatus according to the second embodiment will be described with reference to the flowchart of FIG.

Steps S701 to S704 are the first
Since it is the same as steps S401 to S404 in the above embodiment, the description thereof will be omitted.

In step S705, step S704.
The count values C2 and C2d are selected by referring to the recording medium size detected in step 23 with respect to the table 23, which means that after the leading edge of the recording medium 10 conveyed at the process speed Vp is detected by the recording medium detection sensor 14. , Recording medium 1
The trailing end of 0 is a value counted by the counter 20 until the photosensitive member 5Bk and the transfer roller 7Bk come out of the transfer portion nip portion N1 in proximity, and C2d is the leading end of the recording medium detected by the recording medium detection sensor. A value that is counted by the counter 20 and smaller than C2 until it forms a sufficient loop amount in the recording medium 10 that is conveyed at the process speed Vp after being detected may be any value. It is preferable to set the value to be counted by the counter 20 from the time when the leading edge is detected by the recording medium detection sensor 14 to the time when 1/3 to 3/4 of the length of the recording medium 10 in the conveying direction is conveyed. . Here, for example, 1/3 means that the distance from the transfer nip portion N1 to the rear end of the recording medium 10 is 1/3 of the length of the recording medium 10 in the transport direction.

In step S706, step S705
The count values C2 and C2d selected in step S7 are set in the controller 17, and in step S707, the recording medium 10 onto which the full-color toner image has been transferred leaves the image forming portion,
The recording medium detection sensor 14 detects the leading end of the recording medium 10 and monitors whether the output of the sensor is turned on.

In step S708, the leading edge of the recording medium is detected (YES in step S707 / Fig. 5-a).
The counter 20 starts counting the output pulses of the cartridge drive motor 15 according to the state (1).

In step S709, the controller 17
Sends a deceleration command to the motor driver 19 to lower the rotation speed of the fixing unit drive motor 16 so that the conveyance speed by the fixing unit 11 is Vpd lower than the process speed Vp.
And Vpd can be arbitrarily set as long as it is lower than the process speed Vp, but as in the first embodiment,
Vpd is 95% of Vp Vpd = 0.95V
p.

In step S710, step S708.
It is monitored whether or not the count started in step 2 has reached C2d, and if it has not reached C2d, step S
Proceed to 711.

In step S711, the output of the loop detection sensor is monitored, and if the loop sensor is ON, the process proceeds to step S712, and if it is OFF, the process proceeds to step S713.

In step S712, it is determined that a loop has been formed (state shown in FIG. 5-c, etc.), and the controller 1
7 sends an acceleration command to the motor driver 19, increases the number of rotations of the fixing unit drive motor 16, and causes the fixing unit 11 to rotate.
The transfer speed by Vp is higher than the process speed Vp.
As u, the loop amount is controlled to decrease. Note that Vp
u can be arbitrarily set as long as it is higher than the process speed Vp, but it is calculated by the same formula as in the first embodiment.

In step S713, it is determined that the loop amount has decreased (state shown in FIG. 5B), and the controller 1
7 sends a deceleration command to the motor driver 19, lowers the rotation speed of the fixing unit drive motor 16, and causes the fixing unit 11 to rotate.
The conveyance speed is set to Vpd, and control is performed to form a loop.

After steps S712 and S713, the process returns to step S710 to monitor again whether or not the count has reached C2d. If the count has reached C2d, the process proceeds to step S714. At this point, the recording medium 10 is being conveyed by both the image forming unit and the fixing unit 11 so as to maintain a constant loop amount, and the trailing end of the recording medium 10 is the photoconductor 5Bk located at the most downstream side of the image forming unit. And the transfer roller 7Bk are located upstream of the transfer nip portion N1 in the transport direction.

Then, in step S714, the controller 17 sets the loop amount when the trailing end of the recording medium 10 passes through the transfer nip portion N1 to be an appropriate amount (state of FIG. 5-d). The conveyance speed is set to Vpu2, which is higher than Vpu, and the loop amount is controlled to decrease. Here, Vpu2 can be arbitrarily set as long as the speed is higher than Vpu, but the time during which the recording medium 10 passes the fixing unit 11 at the normal process speed Vp is T, and the fixing unit 11 is at the high speed Vpu. It is preferable to set the speed represented by the following equation, where Tu is the time for carrying the recording medium and Td is the time for the fixing unit 11 to carry the recording medium 10 at the low speed Vpd.

Vpu2 = [Vp · T− (Vpu · Tu + Vpd · Td)] / (T−Tu−Td) (Equation 2) In step S715, the rear end of the recording medium 10 passes through the transfer unit. It is determined whether or not the count has reached C2. If the count has reached C2, the process proceeds to step S716, and the fixing unit transport speed is returned to Vp.

Then, in step S717, the counter 20
Is reset, and it is determined in step S718 whether there is a page to be continuously image-formed. If there is a page to be continuously image-formed, the process returns to step S702, and if not, the image-forming operation is ended.

The carrying state of the recording medium 10 in the above operation will be described with reference to FIG.

FIG. 5A is a diagram showing the conveyance state of the recording medium 10 at the time when the leading edge of the recording medium 10 is detected by the recording medium detection sensor 14. As shown in step S709 in the flowchart of FIG. 7, at this time, the controller 17 reduces the transport speed of the fixing unit 11 from the process speed Vp to Vpd slower than Vp. After that, Vpd and Vpu according to the ON (loop presence) / OFF (no loop) state of the loop detection sensor 27.
Transport while switching.

FIG. 5C is a diagram showing a state where the leading end of the recording medium 10 has entered the fixing nip portion N2 and has been conveyed by the fixing unit 11 a distance corresponding to (Vpu · Tu + Vpd · Td). . Steps S710 to S71
In FIG. 3, Vpu and Vpd are transferred while being switched, and the total time transferred by Vpu is Tu and the total time transferred by Vpd is Td. Further, since the distance by which the fixing unit 11 conveys the recording medium 10 at the process speed Vp for (Tu + Td) time is Vp · (Tu + Td), [Vp · (Tu + Td) − (Vpu · Tu +
Vpd · Td)] is formed.

The loop formed between the transfer nip portion N1 and the fixing nip portion N2 is reduced as the trailing edge of the recording medium 10 passes through the transfer nip portion N1.
The conveyance speed of the fixing unit 11 is Vpu higher than Vpu.
Switch to 2.

FIG. 5D shows the conveyance state of the recording medium 10 when the trailing edge of the recording medium 10 reaches the transfer nip portion N1.

By setting Vpu2 as described above,
In FIG. 5-c, [Vp · (Tu + Td) − (Vpu ·
[Tu + Vpd · Td)], the formed loop disappears, and the vibration of the trailing edge of the recording medium is suppressed when the trailing edge of the recording medium 10 passes through the transfer nip portion N1.

In the second embodiment, the recording medium detection sensor 14 for detecting the recording medium 10 is provided between the transfer nip portion N1 and the fixing nip portion N2. It can be provided at any position as long as it is on the upstream side in the carrying direction. In that case, although the count values C2 and C2d stored in the table 23 of the memory 22 are different from those described above, C2 is, after the front end of the recording medium 10 conveyed at the process speed Vp is detected by the recording medium detection sensor 14, The rear end of the recording medium 10 is the photoconductor 5B.
k and the transfer roller 7Bk are close to each other, a transfer portion nip portion N1
C2d is counted by the counter 20 after the leading edge of the recording medium is detected by the recording medium detection sensor until a sufficient loop is formed on the recording medium 10 conveyed at the process speed Vp. Value.

As described above, in accordance with the transport position of the recording medium 10 calculated by the controller 17, the mode for controlling to form a loop of a fixed amount is switched to the mode for controlling to reduce the loop amount, thereby fixing unit. 11
It is possible to provide an image forming apparatus that does not cause an image defect due to a change in the roller diameter of the recording medium 10 or an image defect due to the trailing end of the recording medium 10 bouncing when passing the transfer portion.

By controlling the average conveyance speed of one recording medium to be the process speed Vp, the loop amount when the rear end of the recording medium 10 passes the transfer portion becomes an appropriate amount, and It is possible to provide an image forming apparatus that does not cause image deterioration due to bouncing.

(Third Embodiment) A third embodiment will be described with reference to FIG. Since the third embodiment is a modification of the second embodiment, only differences from the second embodiment will be described.

In the second embodiment, step S
At 715, it is determined whether or not the trailing edge of the recording medium 10 has passed the transfer portion, depending on whether or not the count has reached C2. If it has reached C2, the process proceeds to step S716, and the fixing unit transport speed is set to Vp. Are returning.

On the other hand, in the third embodiment, the fixing unit conveyance speed is set to Vpu in step S816.
The recording medium is fixed and discharged at Vpu3, which has a higher speed than 2. Note that step S
At the time point when YES is determined in 815, the trailing edge of the recording medium 10 has passed through the image forming portion, and the recording medium 10 is conveyed only by the fixing unit 11. Even if the conveying speed at this time is increased, It does not cause tension between recording media.

As described above, by increasing the conveying speed after the trailing edge of the recording medium 10 passes through the transfer portion, it is possible to improve the throughput without causing a defect in image formation.

(Fourth Embodiment) A fourth embodiment will be described with reference to FIGS. 9 and 10.

Although the process speed Vp is constant in the first to third embodiments, there are a plurality of types of recording media on which the image forming apparatus can form an image. Then, by changing the process speed, it is possible to form an excellent image according to the type of recording medium. The fourth embodiment is a modification of the first to third embodiments, and allows a plurality of transport speeds to be set as the process speed Vp.

In the following description, an embodiment in which a plurality of process speeds Vp can be set in the first embodiment will be described. However, a plurality of process speeds Vp in the second and third embodiments are set. It goes without saying that you can enable it.

In this embodiment, the types of recording media are plain paper (64 g / mm2 to 105 g / mm2), thick paper (105 g / mm2), glossy film, and OHT.
Assuming species, Vp1, Vp2 (Vp1
/ 2), Vp3 (Vp1 / 3), Vp4 (Vp1 / 4)
The process speed is switched to.

FIG. 9 is a view showing the vicinity of the paper feeding unit 9 in FIG. 1, and 30 is a feeding roller for feeding the recording medium 10. Reference numeral 31 denotes a recording medium type detection sensor, which comprises a light emitting element 31a and a light receiving element 31b. As shown in the figure, the light receiving element 31b receives the light that has passed through the recording medium 10 by causing the light emitting element 31a to emit light.
The type of 0 is determined.

The operation of the fourth embodiment will be described with reference to the flowchart of FIG. Since the following example is a modified example of the first embodiment, steps S1003 to S1005 related to setting the process speed Vp will be mainly described.

In step S1003, it is determined whether or not there is a recording medium type setting made by the user from an operation panel (not shown) of the image forming apparatus. If the setting is made by the user (YES in step S1003), step S
In step 1005, process speeds Vp1 to Vp4 corresponding to the recording medium type are set as the process speed Vp.

In step S1004, step S10
If the recording medium type is not set by the user in 03, the recording medium type detection sensor 30 detects the recording medium type, and in step S1005, the process speed Vp1 corresponding to the recording medium type is set as the process speed Vp.
~ Set Vp4.

Then, Vpd set in step S1012 is set to a speed corresponding to Vp, and Vp is Vp1 to Vp4.
Vpd is also variably set according to which of the two is set. Note that Vpd can be arbitrarily set as long as it is lower than Vp, but in the present embodiment, as an example, Vpd =
It is set to 0.95 Vp.

Further, V set in step S1014
Pu is also set to a speed according to Vp, and Vpd is also variably set according to which of Vp1 to Vp4 Vp is set. It should be noted that Vpu can be arbitrarily set as long as it is faster than Vp, but it is set to a value calculated using Equation 1 in the first embodiment.

The count C1d is the same as that in the first embodiment.
However, by setting the count value according to the type of recording medium, it is possible to perform appropriate control according to the type of recording medium. For example, in the case of thick paper, there is more strain than plain paper, so when a loop is formed using the count C1d as in the case of plain paper, a larger repulsive force is generated than in plain paper. Therefore, in the case of thick paper, by setting a value smaller than the count C1d, it is possible to reduce the amount of loops to be formed and to form a good image. As for the value of the count C1d in the case of thick paper,
After the leading edge of the recording medium 10 is detected by the recording medium detection sensor 14, 1/3 to 1 of the length of the recording medium 10 in the transport direction is detected.
It is preferably set to a value counted by the counter 20 until the length of / 2 is transported.

As described above, when Vp is variably set and Vpu and Vpd are also set to appropriate values according to Vp, the process speed Vp is changed according to the type of recording medium. Also, an image that does not cause an image defect due to fluctuations in the roller diameter of the fixing unit 11 and does not cause an image defect due to the trailing edge of the recording medium 10 bouncing when passing through the transfer nip portion N1. A forming device can be provided.

Further, by changing the conveyance position of the rear end of the recording medium, which is the timing for switching the conveyance speed control of the fixing unit 11, depending on the type of recording medium, proper image formation is not affected by the type of recording medium. It can be performed.

[0097]

As described above, according to the present invention,
In response to the trailing edge of the recording medium reaching a predetermined position on the upstream side of the transfer position in the conveying direction, the fixing conveying speed is controlled so as to reduce the loop amount formed on the recording medium. And an image forming apparatus that does not cause image deterioration such as disturbance of a toner image by suppressing the vibration of the trailing edge of the recording medium when the trailing edge of the recording medium passes through the transfer unit. provide.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a tandem type color image forming apparatus.

FIG. 2 is an enlarged view of a main part of a tandem type color image forming apparatus.

FIG. 3 is a control block diagram of the image forming apparatus.

FIG. 4 is a flowchart for explaining the first embodiment.

FIG. 5 is an explanatory diagram of a temporal change in conveyance of a recording medium.

FIG. 6 is an operation explanatory diagram of a loop detection sensor.

FIG. 7 is a flowchart for explaining the second embodiment.

FIG. 8 is a flowchart for explaining a third embodiment.

FIG. 9 is an explanatory diagram of a recording medium type determination sensor.

FIG. 10 is a flowchart for explaining a third embodiment.

FIG. 11 is an explanatory diagram of a temporal change in conveyance of a recording medium.

[Explanation of symbols]

3C-3Bk developing cartridge 5C-5Bk photoconductor 7C-7Bk Transfer roller 8 conveyor belt 9 Paper feeding unit 10 recording media 11 fixing unit 12 Heating roller 13 Pressure roller 14 Recording medium detection sensor 15 Development cartridge drive motor 16 Fixing unit drive motor 17 Controller 18, 19 Motor driver 20 counter 21 Recording medium size detection sensor 22 memory 23 table 24 encoder 26 MR sensor 27 Loop detection sensor 31 Recording medium type detection sensor N1 transfer nip N2 fixing nip

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DC04 DC10 DE02 DE07 EB04                       EC06 EC11 ED16 ED25 EE01                       EE02 EE03 EE04 EF09 ZA10                 2H033 AA01 AA15 BA08 BA11 BB01                       BB28 CA09 CA13 CA22 CA30                       CA36 CA40                 2H200 FA04 FA10 FA20 GA02 GA04                       GA05 GA06 GA12 GA23 GA34                       GA44 GA47 GB30 HA02 HB12                       HB22 JA02 JB06 JB39 JB49                       JB50 PA10 PA11 PB12 PB39

Claims (15)

[Claims] 1. A transfer means for transferring a toner image formed on an image carrier to a recording medium at a transfer position, a fixing means for fixing the toner image transferred on the recording medium, and the fixing means for the recording medium. Is a control unit that controls the amount of loop formed by the transfer unit and the fixing unit on the recording medium by controlling the fixing conveyance speed for conveying the recording medium. An image forming apparatus comprising: a control unit that controls the fixing conveyance speed so as to reduce the loop amount in response to reaching a predetermined position on the upstream side. 2. The transfer means conveys the recording medium at a first speed, and the control means is responsive to the rear end of the recording medium reaching the predetermined position, the fixing conveying speed. The first
The image forming apparatus according to claim 1, wherein the second speed is higher than the second speed. 3. The transfer means and the fixing means have loop detection means for detecting the amount of the loop formed on a recording medium, and the control means causes the trailing end of the recording medium to reach the predetermined position. 3. The image forming apparatus according to claim 1, wherein the fixing conveyance speed is controlled so that the fixed loop amount is formed based on the detection result of the loop detection unit. 4. The loop detection means outputs a loop present signal or a loop non-signal according to the presence or absence of the constant loop amount, and the control means causes the trailing end of the recording medium to reach the predetermined position. Previously, in response to the loop present signal, the transfer unit controls the fixing conveyance speed to be higher than the transfer conveyance speed for conveying the recording medium, and in response to the loop non-signal, the fixing conveyance speed is lower than the transfer conveyance speed. The image forming apparatus according to claim 3, wherein the image forming apparatus is controlled to have a conveyance speed. 5. The control unit determines an average value of the fixing conveyance speed when one recording medium passes through the fixing unit,
5. The fixing / conveying speed is controlled so as to be substantially equal to the transfer / conveying speed of the transfer means.
The image forming apparatus according to any one of 1. 6. A recording medium detecting means for detecting a recording medium, and whether or not the trailing edge of the recording medium has reached a predetermined position upstream of the transfer position in the transport direction based on the detection result of the recording medium detecting means. The image forming apparatus according to any one of claims 1 to 5, further comprising a determining unit that determines whether or not it is. 7. A size setting means for setting a size of a recording medium, and a signal output means for outputting an output signal according to a conveying distance of the recording medium by the transfer means, wherein the determining means has the size setting. Whether the trailing edge of the recording medium has reached the predetermined position based on the size of the recording medium set by the means and the output signal of the signal output means after the recording medium detecting means detects the leading edge of the recording medium. The image forming apparatus according to claim 6, wherein the image forming apparatus determines whether or not the image forming apparatus is included. 8. The control means sets the fixing conveyance speed to a third speed higher than the second speed in response to the rear end of the recording medium reaching the transfer position. The image forming apparatus according to claim 2. 9. A transfer transport speed setting means for setting a transfer transport speed for transporting a recording medium by the transfer means, and the fixing transport speed according to the transfer transport speed set by the transfer transport speed setting means. 9. The image forming apparatus according to claim 1, further comprising a fixing / conveying speed setting unit for setting. 10. A recording medium discriminating unit for discriminating a type of a recording medium, wherein the transfer / conveying speed setting unit varies the transfer / conveying speed according to the type of the recording medium discriminated by the recording medium judging unit. The image forming apparatus according to claim 9, wherein the image forming apparatus is set to. 11. A recording medium discriminating unit for discriminating a type of a recording medium, wherein the control unit varies the predetermined position according to the type of the recording medium discriminated by the recording medium discriminating unit. The image forming apparatus according to claim 9. 12. The transfer device includes a plurality of transfer units that sequentially transfer toner images of different colors to a recording medium, and the control unit has the rear end of the recording medium at the most downstream side in the transport direction of the recording medium. 11. The image forming apparatus according to claim 1, wherein the fixing conveyance speed is controlled so as to reduce the loop amount in response to reaching the predetermined position by the means. 13. An image forming apparatus in which an image forming apparatus has a transfer unit that transfers a toner image formed on an image carrier to a recording medium at a transfer position, and a fixing unit that fixes the toner image transferred to the recording medium. A first method for controlling a loop amount formed by the transfer unit and the fixing unit on a recording medium by controlling a fixing conveyance speed at which the transfer unit and the fixing unit convey a recording medium. In a control step, in response to the trailing edge of the recording medium reaching a predetermined position on the upstream side in the transport direction of the transfer position, the loop amount formed on the recording medium in the first controlling step is reduced. A second control step of controlling the fixing and conveying speed. 14. In the second control step, when the rear end of the recording medium reaches a predetermined position on the upstream side in the transport direction of the transfer position, the transfer means sets the fixing transport speed to the recording medium. 14. The image forming method according to claim 13, wherein the step is a step of increasing the transfer conveyance speed for conveying the sheet. 15. Transfer means for transferring the toner image formed on the image carrier to a recording medium conveyed at a predetermined conveying speed at a transfer position, and fixing the toner image transferred to the recording medium. A fixing unit and a control unit for controlling a fixing conveyance speed of the fixing unit, wherein the fixing conveyance is performed in response to the rear end of the recording medium reaching a predetermined position on the upstream side in the conveyance direction of the transfer position. An image forming apparatus, comprising: a control unit configured to control the speed to switch from a first speed lower than the predetermined transfer speed to a second transfer speed higher than the predetermined transfer speed.