JPH11184184A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change a fixing speed in accordance with a transfer speed and a feeding speed, and to attain the miniaturization of a device without the reduction of productivity by controlling a transfer performance so that a fixed condition of transferring a visible image on a recording material may be maintained cooperatively with a speed change operation of changing the recording material feeding speed in accordance with the fixing speed. SOLUTION: On condition that the fixing speed is changed in accordance with the transfer speed and the feeding speed, the feeding speed of the recording material P in a transfer nip area(n) and the feeding speed of the recording material P by a recording material feeding means 4 are controlled by a feeding speed control means 5. And, under such a situation that the recording material P is nipped at the transfer nip area (n) and the material P does not reach the fixing means 3, the recording material P feeding speed is changed in accordance with the recording material P fixing speed by the fixing means 3. The transfer performance is controlled by the transfer performance control means 6 so that the fixed condition of transferring the visible image on the recording material P may be maintained cooperatively with the operation of changing the speed of the recording material P by the feeding speed control means 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a laser printer, and other image forming apparatuses employing an electrophotographic system, an electrostatic recording system, or the like, and more particularly, to conveying a recording material between a transfer unit and a fixing unit. The present invention relates to an image forming apparatus of a type including a means.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, for example, an intermediate transfer type image forming apparatus is exemplified. After a toner image formed on a photoreceptor is primarily transferred to an intermediate transfer body, the intermediate image is formed. 2. Description of the Related Art There has been known an image forming apparatus in which a toner image on a transfer body is collectively transferred onto a recording material by a secondary transfer device, and the recording material is fixed by a fixing device. In such an image forming apparatus, a conveying device including a conveying belt or the like is usually provided between the transfer device and the fixing device in order to convey the transferred recording material to the fixing device in a stable state. ing.

In this type of image forming apparatus, usually,
From the viewpoint of securing productivity, the image forming process for plain paper, which is the most frequently used as a recording material, is set as a standard, and the conveying speed of the recording material in the transfer device (hereinafter, referred to as “transfer speed”).
The transfer speed of the recording material in the transfer device (hereinafter, referred to as a transfer speed as necessary) and the transfer speed of the recording material in the fixing device (hereinafter, referred to as a fixation speed as necessary) are substantially referred to. The apparatus is designed so as to set the same.

Accordingly, in such an image forming apparatus, when thick paper such as a postcard is used as a recording material, the transfer of the toner image to the recording material by the transfer device and the conveyance of the recording material by the conveyance device are performed. Does not cause a problem, but the heat capacity of the thick paper is larger than that of the plain paper in the fixing device, so the fixing heat amount is insufficient, and the toner constituting the toner image may remain on the recording material without being heated and melted. .

Therefore, when a recording material having a large basis weight and a large heat capacity such as thick paper is used, the amount of fixing heat in the fixing device is increased to sufficiently heat and fuse the toner constituting the toner image. Is needed. As a method of increasing the fixing heat amount in the fixing device, for example, a method of increasing the fixing temperature by increasing the fixing power, a method of increasing the nip time by increasing the fixing pressure to increase the nip width, and a method of decreasing the fixing speed To increase the nip time.

Here, the method of increasing the fixing temperature by increasing the fixing power is not preferable from the viewpoint of energy saving because the power consumption increases. In particular, a copying machine or a laser to which this type of image forming apparatus is applied is used. In a printer, the power consumption of the entire device is often limited to 1.5 kVA or less, so that an increase in power consumption is a major problem. Further, in the method of increasing the nip width and increasing the nip time by increasing the fixing pressure, it is difficult to switch the nip pressure itself, and an apparatus for switching the nip pressure is separately required, which complicates the apparatus. In this regard, it can be said that a method in which the nip time is lengthened by lowering the fixing speed is advantageous in that the above problems do not occur.

[0007]

However, if only the fixing speed of the fixing device is reduced and the conveying speed is kept at the conventional value, the leading end of the recording material conveyed on the conveying device at the conventional conveying speed is fixed to the fixing device. When the recording material enters the recording medium, there is a possibility that the recording material forms a loop, and the unfixed toner on the recording material is rubbed by peripheral members, thereby causing smudge or wrinkling of the recording material during fixing. Also, if the speed difference between the two is large, the impact on the recording body when entering the fixing device becomes large,
If the recording material is clogged, the unfixed toner image on the recording material is displaced, and the transfer on the transfer device side is affected, image disturbance occurs. Even if the fixing speed and the conveyance speed are similarly reduced, the recording material forms a loop when the leading end of the recording material conveyed from the transfer device at the previous transfer speed enters the conveyance device. As a result, the unfixed toner on the recording material may be rubbed by peripheral members to cause smudge.

Therefore, as means for solving such a problem, for example, the transfer speed and the transport speed are made variable in accordance with the change in the fixing speed, and when the fixing speed is lowered at the time of fixing, the entire process speed is substantially reduced to the fixing speed. Image forming apparatus of a system in which the recording material is returned to a normal process speed after the recording material has passed through the fixing device.
67174, JP-A-4-125676 and JP-A-6-161191), and the transfer speed is fixed at all times, and the transfer speed is fixed when the rear end of the recording material in the transfer direction passes through the transfer device. An image forming apparatus of a type in which the speed is reduced to a speed close to the speed and the recording material returns to a normal conveyance speed after passing through a fixing device (see Japanese Patent Application Laid-Open No. 1-134582).

However, in the former prior art, when the fixing speed is reduced, the transfer speed and the transport speed must be reduced at the same time, which increases the time required to form one image. Therefore, there is a technical problem that productivity is reduced.

In the latter prior art, when a recording material having a short length in the conveyance direction such as a postcard is used, the recording material undergoes rapid deceleration on the conveyance device. If the recording material on the conveyance device is not sufficiently stabilized by suction or the like due to scattering of the toner on the recording material due to suction or the like, the recording material may exhibit abnormal behavior and cause image disorder or the like. There is.

Further, it is necessary that the leading end of the recording material in the conveying direction does not reach the fixing device at the time when the rear end of the recording material in the conveying direction has passed through the transfer device. The length must be longer than the length of the recording material that is expected to be used in actual use, and it must be long enough to obtain sufficient acceleration / deceleration time. There is a problem that it leads to conversion.

[0012] Further, even in an image forming apparatus of a type in which a recording material is directly transferred from a photosensitive member to a recording material, a transport device is provided between the transfer device and the fixing device to transport the recording material after the transfer. For those that have similar technical issues.

The present invention has been made to solve such a technical problem, and is based on the premise that the fixing speed is changed with respect to the transfer speed and the transport speed, while preventing a decrease in productivity. When the fixing speed in the fixing device is changed, the recording material conveyed toward the fixing unit does not bend at the fixing unit, clogging, disturbance of the developed image, influence on the transfer unit, and the like. It is an object of the present invention to provide an image forming apparatus that can be downsized.

[0014]

That is, according to a first aspect of the present invention, as shown in FIG. 1, an image carrier 1 on which a visible image T is formed and carried, and the image carrier 1 and a transfer nip area are formed. transfer means 2 for forming the visible image T on the image carrier 1 and transferring the visible image T on the recording material P; fixing means 3 for fixing the visible image T transferred on the recording material P; In an image forming apparatus including a recording material conveying unit 4 for conveying the recording material P from the transfer unit 2 to the fixing unit 3, the recording material P in the transfer nip area n
Conveying speed and the recording material P in the recording material conveying means 4
Under the condition that the recording material P is nipped in the transfer nip area n and does not reach the fixing unit 3, the conveying speed of the recording material P corresponds to the fixing speed of the recording material P of the fixing unit 3. Transfer speed control means 5 for shifting to a set speed
And a transfer force control means 6 for controlling a transfer force in such a manner as to maintain a constant condition for transferring a visible image onto the recording material P in conjunction with a shifting operation of the recording material P by the transport speed control means 5. It is characterized by having.

Here, the present invention is based on the premise that the fixing speed is changed with respect to the transfer speed and the conveying speed. Examples include a toner having a different amount of toner to be fixed (for example, a single-color image and a multi-color image) and a toner having a different heat capacity of a recording material (for example, plain paper and thick paper). Further, for example, the capability of the fixing device must be reduced due to the device configuration due to the limitation of power consumption, and the same applies to the type in which the fixing speed is set lower than the transfer speed and the transport speed.

In such technical means, the image carrier 1 is not limited to a photosensitive member or a dielectric on which the visible image T is formed and supported, as long as the image carrier 1 carries the visible image T. And an intermediate transfer member on which the visible image T is temporarily transferred and held. The shape of the image carrier 1 may be appropriately selected, such as a drum shape or a belt shape.
Further, as for the image forming method applied in the present application, an electrophotographic method, an electrostatic recording method, or the like may be appropriately selected as long as the visible image T is formed by at least a charged coloring material such as toner.

The fixing means 3 may be appropriately selected from various methods as long as it fixes the recording paper P and the visible image T transferred thereon by heating.
From the viewpoint of ensuring safety and stability, for example, a heating and pressing method in which a fixing nip area is formed by a roll pair or a belt pair or a combination of a roll and a belt, and a heating source is provided in at least one of them. It is preferable to employ

Further, the recording material conveying means 4 may be appropriately selected as long as it conveys the recording material P from the exit of the transfer nip area n to the entrance of the fixing means 3; From the viewpoint, it is preferable to stabilize the recording material P conveyed on the belt by suction using the conveyance belt.

The transfer speed control means 5 controls the transfer speed of the recording material P in the transfer nip area n and the recording material transfer means 4. Of these, the transfer speed control in the transfer nip area n is performed. With regard to the above, one of the image carrier 1 and the transfer unit 2 may be driven and the other driven, or both may be driven and controlled. Furthermore, from the viewpoint of preventing the occurrence of a loop or the like of the recording paper P when changing the transport speed of the recording material P in the transfer nip area n and the recording material transporting means 4 to a speed corresponding to the fixing speed, It is preferable that the transport speed control unit 5 controls the transport speed of the recording material P in the transfer nip area n and the transport speed of the recording material P in the recording material transport unit 4 to be changed at the same rate of change.

Further, as long as the transfer means 2 forms the image carrier 1 and the transfer nip area n, the shape thereof may be appropriately selected, such as a roll shape or a belt shape. , May be appropriately selected from various methods. In the present application, in the state where the recording material P is nipped in the transfer nip area n between the image carrier 1 and the transfer unit 2, the shift from the transfer speed to the speed corresponding to the fixing speed is started. From this viewpoint, it is necessary to control the transfer force of the transfer unit 2 in order to keep the condition for transferring the visible image T onto the recording material P constant. It is necessary to provide the transfer force control means 6 which performs the transfer. Here, from the viewpoint of facilitating the control of the transfer force of the transfer unit 2, the transfer method employs a method in which the transfer force is easily controlled, for example, a method in which transfer is performed by forming a transfer electric field. It is preferable to control the transfer force by controlling the voltage applied to the transfer unit 2 or the amount of current supplied.

In addition, the above control is performed for the recording material P
It is preferable to perform the recording based on the transport position of the recording material P. From such a viewpoint, it is preferable to provide a recording material position detecting unit 9 for detecting the position of the recording material P.

Further, for example, when it is necessary to change the fixing speed between when a single color image is formed and when a plurality of colors are formed, or when it is necessary to change the fixing speed depending on the type of the recording material P, etc. Image forming mode discriminating means 8 for discriminating the image forming mode from information on the visual image T, information on the type and size of the recording material P, environmental information and the like, and fixing speed control for controlling the fixing speed of the fixing means 3 based on these information. Means 7 are preferably provided.

When the distance from the exit of the transfer nip area n to the fixing means 3 is larger than the length of the recording material P in the transport direction, the rear end of the recording material P in the transport direction passes through the transfer nip area n. In this case, the leading end of the recording material P in the transport direction does not reach the fixing unit 3. Therefore, in a range where the visible image T on the recording material P is hardly affected, the productivity can be further improved by changing the transfer speed to near the fixing speed.

That is, in the second embodiment of the present invention, the image carrier 1 on which the visible image T is formed and carried, and the image carrier 1 and the transfer nip area n are formed to form the image carrier 1 on the image carrier 1. Transfer means 2 for transferring the visual image T onto the recording material P, fixing means 3 for fixing the visible image T transferred on the recording material P, and transfer means 2 for transferring the recording material P from the transfer means 2 to the fixing means 3. In the image forming apparatus including the recording material conveying means 4 for conveying, the conveying speed of the recording material P in the transfer nip area n and the conveying speed of the recording material P in the recording material conveying means 4 are controlled, and the conveying direction of the recording material P Under the condition that the rear end is nipped in the transfer nip area n and does not reach the fixing unit 3, the conveying speed of the recording material P is changed to a speed corresponding to the fixing speed of the recording material P of the fixing unit 3. It is characterized by comprising speed control means 5.

In such technical means, it is preferable to control the conveyance speed of the recording material P based on the conveyance position of the recording material P to be conveyed. It is preferable to provide a recording material position detecting means 9 for detecting the position.

Further, when changing the transport speed of the recording material P in the transfer nip area n and the recording material transporting means 4 to a speed corresponding to the fixing speed, from the viewpoint of preventing the occurrence of a loop or the like of the recording paper P. Then, the transport speed control means 5
It is preferable to control so that the conveying speed of the recording material P in the transfer nip area n and the conveying speed of the recording material P in the recording material conveying means 4 are changed at the same rate of change.

Further, for example, when it is necessary to change the fixing speed between when a single color image is formed and when a plurality of colors are formed, or when it is necessary to change the fixing speed depending on the type of the recording material P, etc. Image forming mode discriminating means 8 for discriminating the image forming mode from information on the visual image T, information on the type and size of the recording material P, environmental information and the like, and fixing speed control for controlling the fixing speed of the fixing means 3 based on these information. Means 7 are preferably provided.

Next, the operation of the above technical means will be described. First, in the first invention of the present application, in FIG. 1, a visible image T formed on an image carrier 1 is transferred onto a recording material P by a transfer unit 2 at a normal transfer speed, and the transferred recording material is transferred. P is sequentially conveyed to the recording material conveying means 4 side. Then, under the condition that the recording material P is nipped in the transfer nip area n and has not reached the fixing unit 3, the conveyance speed control unit 5 sets the transfer speed and the conveyance speed to correspond to the fixing speed of the recording material P in the fixing unit 3. And the transfer force control means 6 controls the transfer force so that the condition for transferring the visible image T onto the recording material P is kept constant. Therefore, at the time of transfer, the visible image T on the recording material P is conveyed from the recording material conveying means 4 to the fixing means 3 without causing density unevenness or the like, and thereafter, a fixing process is performed.

In the second aspect of the present invention, in FIG. 1, the visible image T formed on the image carrier 1 is transferred onto the recording material P by the transfer means 2 at a normal transfer speed. Is sequentially conveyed to the recording material conveying means 4 side. Under the condition that the rear end of the recording material P in the conveying direction is nipped in the transfer nip area n and does not reach the fixing unit 3, the conveying speed control unit 5 sets the transfer speed and the conveying speed to the recording material in the fixing unit 3. The speed is changed to a speed corresponding to the fixing speed of P. For this reason, the visible image T on the recording material P is transferred with almost no density unevenness or the like, and then the recording material P is transported from the recording material transporting means 4 to the fixing means 3 so that the fixing process is performed. Will be applied.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of a color image forming apparatus to which the present invention is applied. In the same figure, reference numeral 11 denotes a photosensitive drum (latent image carrier), which has a charging device 12 and an exposure device (not shown in FIG. An electrostatic latent image corresponding to image information is formed by a known electrophotographic process such as that shown in FIG. Around the photosensitive drum 11, developing units 14 to 17 corresponding to black (Bk), yellow (Y), magenta (M), and cyan (C) are provided. The toner image T is formed by developing the electrostatic latent image formed on the developing unit 11 by one of the developing units 14 to 17.

Reference numeral 20 denotes an intermediate transfer belt arranged so as to be in contact with the surface of the photosensitive drum 11;
It is stretched around a plurality of (four in the present embodiment) rolls 21 to 24 and rotates in the direction of arrow B. Here, in the present embodiment, reference numeral 21 is a driven roll, and reference numeral 2
Reference numeral 2 denotes a driving roll for the intermediate transfer belt 20, reference numeral 23 denotes a tension roll for controlling the tension of the intermediate transfer belt 20 to a constant value, and reference numeral 24 denotes an opposing roll (backup roll) for secondary transfer.

The toner image T formed on the photosensitive drum 11 is transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 20 at a primary transfer position where the photosensitive drum 11 contacts the intermediate transfer belt 20. At this primary transfer position, a primary transfer device (corona charger in this embodiment) 18 is provided on the back side of the intermediate transfer belt 20, and the corona charger 18 has a polarity opposite to that of the toner. By applying a voltage, the toner image T on the photosensitive drum 11 is electrostatically attracted to the intermediate transfer belt 20. Reference numeral 19 denotes a drum cleaner for removing residual toner on the photosensitive drum 11.

Further, a secondary transfer device 40 is provided at a secondary transfer position of the intermediate transfer belt 20 facing the conveyance path of the sheet P as a recording material. And a backup roll 24 disposed on the back side of the intermediate transfer belt 20 and serving as a counter electrode of the secondary transfer roll 25. Then, a transfer bias having the same polarity as the charged polarity of the toner is stably applied to the backup roll 24 via the power supply roll 26.

Further, the secondary transfer roll 25 is provided with a cleaning blade 28 made of, for example, urethane rubber. Further, on the downstream side of the secondary transfer device 40 in the moving direction of the intermediate transfer belt 20, A belt cleaner 41 for removing the residual toner is provided.

The secondary transfer roll 25 and the belt cleaner 41 are disposed so as to be able to contact and separate from the intermediate transfer belt 20. When a color image is formed, the toner image before the final color is subjected to the secondary transfer. These members are separated from the intermediate transfer belt 20 until they pass through the roll 25 and the belt cleaner 41.

In the present embodiment, the paper transport system is configured to feed the paper P from the paper tray 50 to the feed roll 51.
The paper P is sent to the secondary transfer position at a predetermined timing after the positioning is once stopped by the registration roll (registration roll) 52.

Further, on the downstream side in the transport direction of the paper P discharged from the secondary transfer device 40, the paper transport guide 29, the transport belt system 53, the fixing transport guide 58, and the fixing device 57
Are arranged so that the paper P after the secondary transfer is sequentially conveyed. In the present embodiment, the transport belt system 53 includes a driven roll 54, a drive roll 55, and a transport belt 56 stretched over the plurality of rolls. Suction is performed by a suction device that does not perform the operation, and the stability of sheet conveyance is ensured. Reference numeral 31 denotes a sheet P on the transport belt 56.
This is a jam sensor for detecting the jam. The fixing device 57 includes a heating roll 5 having a heating source (not shown) therein.
7a and a pressure roll 57b.

Further, in this embodiment, as shown in FIG. 3, a process control system 100 for controlling an image forming process according to the type of paper is provided. In the figure, reference numeral 101 denotes a registration sensor using a reflection-type optical sensor provided on the registration roll 52 to detect the passage time of the leading end and the trailing end of the sheet P, and 102 detects the type of sheet to be used. A paper type detection device 103, a paper size detection device 103 for detecting the size of the paper to be used, 105 a drive motor of the drive roll 22 of the intermediate transfer belt 20, 106 a drive motor of the drive roll 55 of the transport belt 56, 107
A drive motor 108 for the heating roll 57a of the fixing device 57;
Is a DC variable bias power supply for the power supply roll 26 of the secondary transfer device 40, and 109 is a control device for controlling these.

FIG. 4 is a block diagram of the process control system 100. In the figure, a paper passage timing detection signal 111 from a registration sensor 101, a paper type detection device 1
02 and the paper size detection signal 113 from the paper size detection device 103 are input to the CPU 122 via the input interface 121, and then the CPU 122 executes a drive control program stored in the ROM 123 in advance. After executing the data processing as appropriate with the RAM 124, the driving roll 22 of the intermediate transfer belt 20 is output via the output interface 125.
The intermediate transfer belt speed control signal 131 is supplied to the drive motor 105 for driving the transport belt 55, and the transport belt speed control signal 131 is supplied to the drive motor 106 for driving the drive roll 55 of the transport belt 56.
32, a driving motor 107 for driving the heating roll 57a of the fixing device 57, a fixing speed control signal 133, and
The secondary transfer bias control signal 134 is supplied to the DC variable bias power supply 108 for the power supply roll 26 of the secondary transfer device 40.
Are transmitted.

Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. Specifically, the photosensitive drum 11
If the electrostatic latent image written thereon corresponds to, for example, yellow image information, this electrostatic latent image is developed by the developing device 15 containing yellow (Y) toner, and the photosensitive drum 1
1 is formed with a yellow toner image T. The unfixed toner image T formed on the photoconductor drum 11 is transferred from the photoconductor drum 11 to the surface of the intermediate transfer belt 20 at a primary transfer position where the photoconductor drum 11 and the intermediate transfer belt 20 are in contact.

At this time, when forming a monochrome image,
The toner image T primarily transferred to the intermediate transfer belt 20 is immediately secondary-transferred. However, when a color image in which toner images of a plurality of colors are superposed is formed, the photosensitive drum 1
The process of forming the toner image on the surface 1 and the primary transfer of the toner image is repeated by the number of colors. For example, when a toner image in which four color toner images are superimposed is formed, black, yellow,
Magenta and cyan toner images T are formed, and these toner images T are sequentially primary-transferred onto the intermediate transfer belt 20 in order.
On the other hand, the intermediate transfer belt 20 rotates at the same cycle as the photosensitive drum 11 while holding the first primary-transferred black toner image T, and the yellow and magenta And a cyan toner image T are formed. The toner image T primarily transferred to the intermediate transfer belt 20 in this manner is conveyed to a secondary transfer position as the intermediate transfer belt 20 rotates.

On the other hand, at the same time when the start switch is turned on, the type of the paper P on which the toner image T is to be transferred is detected by the paper type detecting device 102. To the secondary transfer position, and the secondary transfer roll 25 nips the paper P with respect to the backup roll 24.

At this time, as shown in FIG. 5, when the paper type detecting device 102 confirms that the paper P is not thick paper, the paper type detecting device 102 outputs a paper type detection signal 112 indicating the fact. It is sent out and a normal fixing process is performed.

In the normal fixing process, the moving speed of the intermediate transfer belt 20 (hereinafter referred to as a normal secondary transfer speed) is V1, the moving speed of the conveyor belt 56 (hereinafter referred to as a normal belt conveyor speed) is V2, and the fixing is performed. Assuming that the rotation speed of the device 57 (hereinafter referred to as a normal fixing speed) is V3, these are set in the following relationship. V2 = V1 × 1.002 V3 = V1 × 0.997 Here, the normal belt transfer speed V2 is slightly increased from the normal secondary transfer speed V1 because the transfer of the sheet P after the secondary transfer is performed. This is for preventing the occurrence of a paper loop or the like at the time of entering the belt 56.
On the other hand, the degree of increase in the normal fixing speed V3 is small.
This is to prevent the sheet P from being pulled by the fixing roll pair of the fixing device 57 and the fixed image to be stretched when V3> V2. In the present embodiment, the normal secondary transfer speed V1
Is set to 220 mm / sec, and the secondary transfer bias I is usually set to 30 μA.

FIG. 6 shows a timing chart of the normal fixing process. In FIG. 1, a toner image T is primary-transferred sequentially from a photosensitive drum 11 onto an intermediate transfer belt 20.
At this time, a DC primary transfer bias is applied to the primary transfer corona charger 18. Also, the control device 109
Controls the speed of the intermediate transfer belt 20 (secondary transfer speed), the speed of the conveyor belt 56 (conveyance speed), and the speed of the fixing device 57 (fixing speed) to V1, V2, and V3, respectively.

Next, with the end of the primary transfer, the primary transfer bias to the primary transfer corona charger 18 is cut off, and then the conveyance of the paper P is started. And the cash register sensor 10
When the entry of the sheet P is detected by the control unit 1, the control device 109 supplies power to the secondary transfer roll 25 by pressure until the sheet P reaches the nip area between the secondary transfer roll 25 and the backup roll 24. A secondary transfer bias control signal for starting the application of the normal transfer bias is sent to the DC variable bias power supply 108 that supplies power to the roll 26.

At the secondary transfer position shown in FIG. 2, the transfer electric field formed between the secondary transfer roll 25, which is the secondary transfer device 40, and the backup roll 24 acts on the intermediate transfer belt 20. The transferred toner image T is transferred to the sheet P at the secondary transfer position. This toner image T
Is transferred to the fixing device 5 by the transport belt 56.
7 to fix the toner image. Further, the toner remaining on the intermediate transfer belt 20 after the transfer is cleaned by the belt cleaner 41.

On the other hand, in FIG.
If the paper P is detected to be thick paper in step 02, a paper type detection signal 112 indicating this is sent from the paper type detection device 102, and the special fixing process A is executed.

The special fixing process A is performed by the process shown in FIG. First, as shown in FIG.
Until the toner image T primarily transferred on the intermediate transfer belt 20 reaches the secondary transfer position and the secondary transfer on the paper P is started, the secondary transfer speed, The transport speed, the fixing speed, and the secondary transfer bias are controlled to V1, V2, V3, and I, respectively, and the secondary transfer is started. This state is shown in the timing chart of FIG.

Next, as shown in FIG. 7B, the sheet P is nipped in the transfer nip area n _T and the leading end of the sheet P in the transport direction reaches the fixing nip area n _F. The secondary transfer speed, the transport speed, and the fixing speed are V1,
V2 and V3 are decelerated at the same speed change rate from V2 and V3 to V1 ', V2' and V3 ', respectively, and at the same time, the secondary transfer bias is reduced from I to I' in proportion to the degree of deceleration of the secondary transfer speed.

This control will be described in more detail.
FIG. 9A shows the position of the sheet P in the transport direction. In the figure, the symbol S indicates the leading end of the sheet P in the transport direction, the symbol α indicates the deceleration start position at which the secondary transfer speed is reduced from V1 to V1 ', and the symbol β indicates the deceleration end at which the secondary transfer speed is reduced. The position and the symbol E indicate the rear end of the sheet P in the transport direction. Here, the deceleration start position α and deceleration end position β is suitably selected from the region where the sheet P has not reached the nipped and fixing nip area n _F to the transfer nip region n _T.

FIG. 9B shows the relationship between the position in the sheet conveying direction, the secondary transfer speed, and the secondary transfer bias. In the figure, during the period from the sheet leading end position S to the deceleration start position α, the toner image
1 (220 mm / sec in the present embodiment) and the normal secondary transfer bias I (30 μA in the present embodiment). Next, during the period from the deceleration start position α to the deceleration end position β, the normal secondary transfer speed V1 to the special fixing speed V1 ′ (110 mm / sec in the present embodiment).
, And at the same time, the secondary transfer bias is reduced from the normal secondary transfer bias I to the special secondary transfer bias I ′ (15 μA in the present embodiment) in proportion thereto. At this time, the toner image T is secondarily transferred onto the sheet P under the same transfer conditions as before the start of deceleration. Then, during the period from the deceleration end position β to the sheet rear end position E, the special secondary transfer speed V
It is controlled to be constant by 1 'and the special secondary transfer bias I'. Also at this time, the toner image T is secondarily transferred onto the sheet P under the same transfer conditions as before the start of deceleration and during deceleration. This state is shown in FIG.

Then, as shown in FIG.
There Once discharged through the transfer nip region n _T, the secondary transfer speed returns to V1 from V1 ', a secondary transfer bias is disconnected. This state is shown in FIG.

Next, as shown in FIG. 7D, when the paper P passes over the transport belt 56, the transport speed returns from V2 'to V2. This state is shown in FIG. Further, when the sheet P passes through the fixing nip area n _F, the fixing speed V3 'ends the series of processes return to V3.

Here, in the present embodiment, the special secondary transfer speed V1 ', the special belt conveying speed V2', and the special fixing speed V3 'are set in the following relationship. V1 ′ = V3 × 1.003 V2 ′ = V3 × 1.005

In this embodiment, from the viewpoint of preventing a decrease in productivity, it is preferable to set the period during which the secondary transfer speed is reduced to a short period. The position α at which the shift is started from the secondary transfer speed V1 to the special secondary transfer speed V2 is set to the rear end E side of the sheet P in the transport direction, or the deceleration start position α
And the deceleration end position β are preferably made close to each other.

By performing the control as described above, FIG.
As shown in FIG. 7, before the secondary transfer is started, the secondary transfer speed is reduced to the fixing speed of the thick paper (the special fixing speed V3 ′ in this embodiment).
1.5 times the productivity is secured. Further, when the secondary transfer speed is reduced during the secondary transfer, the secondary transfer bias is reduced in proportion to the reduction in the secondary transfer speed so as not to change the transfer conditions. No image unevenness occurs in the transferred toner image.

In this embodiment, the secondary transfer speed, the belt conveyance speed, and the fixing speed are sequentially returned to the normal speed as the paper P passes. However, the present invention is not limited to this. When the rear end E of the sheet P in the conveying direction has passed the fixing device 57, the speed may be returned to the normal speed at the same time. Further, when the next sheet P is also a thick sheet, it is also possible to return only the secondary transfer speed to the normal speed and keep the belt conveyance speed and the fixing speed at the speed in the special fixing step.

Furthermore, in the present embodiment, only the thick paper is subjected to the special fixing step. However, the present invention is not limited to this. For example, for a recording material such as an OHP sheet which requires a higher fixing heat than plain paper. It is also possible to apply. Furthermore, the determination of the type of the paper P is subdivided, a plurality of special fixing speeds in the special fixing process are set, and the secondary transfer speed and the belt conveyance speed in the special fixing process are set in accordance with the fixing speed. It is also possible to set. Further, the present invention can be applied not only to a color image forming apparatus but also to a monochrome image forming apparatus.

Embodiment 2 This embodiment is substantially the same as Embodiment 1, except that the amount of toner of the toner image T to be transferred is detected and the fixing speed is set according to the amount of toner. In addition, the secondary transfer speed, the belt conveyance speed, and the secondary transfer bias are controlled in accordance with the fixing speed.

In this embodiment, the process control system 100 includes a registration sensor 101 as shown in FIG.
In addition to the paper passage timing detection signal 111 from the printer, the paper type detection signal 112 from the paper type detection device 102, and the paper size detection signal 113 from the paper size detection device 103,
An image toner amount detection signal 114 from the image toner amount detection device 104 in FIG. 3 is input to the CPU 122 via the input interface 121, and substantially the same control as in the first embodiment is executed. In particular, in the present embodiment, as shown in FIG. 11, the amount of image forming toner to be transferred is compared with the fixed toner amount that is set as a standard when the normal fixing step is performed, and the amount of toner to be transferred is determined. Even when the amount of toner for image formation is large, the special fixing process A is executed.

In the present embodiment, similarly to the first embodiment, when the secondary transfer speed is reduced during the secondary transfer in order to fix the toner image T on the thick paper, the transfer conditions are not changed. In addition, since the secondary transfer bias is reduced in proportion to the reduction in the secondary transfer speed, the toner image T transferred onto the sheet P is free from image unevenness and the like, and a large amount of toner is fixed. Even when the fixing speed has to be reduced in order to make the toner image T
No image unevenness or the like occurs.

[0063] ◎ Embodiment 3 present embodiment is substantially the same as the first embodiment, postcard or the like, the length of the conveying direction of the sheet P, the fixing nip of the fixing device 57 from the fixing nip area n _F When the distance is shorter than the distance to the area, the toner image T to be transferred is not affected.
From the time the conveying direction trailing end of the sheet P reaches the transfer nip area n _T, the secondary transfer speed is obtained by so controlling the transport speed and fixing speed.

FIG. 12 shows a flowchart in the present embodiment. In the figure, first, it is determined whether or not the sheet P is a thick sheet. If the sheet P is not a thick sheet, the above-described normal fixing process is performed. Also, paper P
There when was cardboard, the length in the conveyance direction of the length and the sheet P to the fixing nip region of the fixing device 57 are compared from the transfer nip region n _T of the secondary transfer device 40, the transport direction length of the paper P Is larger, the special fixing process A described above is performed, and if smaller, the special fixing process B is performed.

FIG. 13 is a timing chart of the special fixing process B. In the special fixing process step B, respectively in a state in which the conveying direction trailing end of the sheet P is nipped in the transfer nip region n _T, the secondary transfer speed, the transport speed and the fixing speed, from each V1, V2, and V3 s V1 ', V2' and V3 'are decelerated at the same speed change rate.

This control will be described in more detail.
FIG. 14A shows the position of the sheet P in the transport direction. In the figure, reference symbol S indicates the leading end of the sheet P in the transport direction, and reference symbol γ indicates the deceleration start position at the rear end side of the sheet P in the transport direction where the secondary transfer speed is reduced from V1 to V1 ′.
Reference numeral δ (E) denotes the rear end of the sheet P in the conveyance direction at which the deceleration of the secondary transfer speed ends, and indicates the deceleration end position of the secondary transfer speed. Here, the deceleration start position γ is appropriately selected from a range within 7 mm from the rear end of the sheet P in the transport direction.

FIG. 14B shows the relationship between the position in the paper transport direction, the secondary transfer speed, and the secondary transfer bias. In the drawing, during the period from the sheet leading end position S to the deceleration start position γ, the toner image T has a normal secondary transfer speed V1 (220 mm / sec in the present embodiment) and a normal secondary transfer bias I (the present embodiment). At 30 .mu.A). Next, during the period from the deceleration start position γ to the sheet rear end position and the deceleration end position δ (E), the normal secondary transfer speed V1 is changed to the special fixing speed V1 ′ (110 mm / sec in the present embodiment). While the deceleration is performed, the toner image T is secondarily transferred onto the paper P.

As described above, in this embodiment, since the position at which the secondary transfer speed starts to be reduced is the rear end of the sheet P in the transport direction, the period during which the secondary transfer speed is reduced is shortened. High productivity is ensured. Further, since the position at which the secondary transfer speed starts to be reduced is the rear end of the sheet P in the transport direction, the toner image T that is secondarily transferred onto the sheet P
Is hardly affected. In particular, as shown in FIG. 14A, if the deceleration start position γ is set in a margin area 82 other than the area 81 of the sheet P where the toner image T is transferred, the toner image T transferred to the sheet P Will have no effect at all.

[0069]

As described above, according to the present invention,
Before the recording material is nipped in the transfer nip area and enters the fixing means, the transfer speed of the recording material is changed to a speed corresponding to the fixing speed while maintaining the transfer conditions constant, so that the fixing speed is reduced. Even in the case where it is necessary to make the recording material flexible at the fixing portion of the recording material without increasing the size of the apparatus by increasing the distance between the transfer means and the fixing means,
Clogging, disturbance of a developed image, influence on a transfer portion, and the like can be prevented. Further, in a mode in which the conveying speed of the recording material is changed to a speed corresponding to the fixing speed before the rear end of the recording material in the conveying direction is nipped in the transfer nip area and enters the fixing means, The productivity can be improved by only controlling the conveyance speed while preventing the recording material from being bent at the fixing portion, clogged, disordered developed image, and adversely affecting the transfer portion.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of an image forming apparatus according to Embodiments 1 to 3.

FIG. 3 is an explanatory diagram illustrating a control system of the image forming apparatus according to the first to third embodiments.

FIG. 4 is a block diagram showing a control system of the color image forming apparatus according to the first to third embodiments.

FIG. 5 is a flowchart illustrating a sheet fixing process of the image forming apparatus according to the first embodiment.

FIG. 6 is a timing chart illustrating operation timings of the image forming apparatus according to the first embodiment when a normal fixing process is performed.

FIGS. 7A to 7D are schematic views for explaining a process of a special fixing process A. FIG.

FIG. 8 is a timing chart showing operation timings of the image forming apparatus according to the first embodiment when the special fixing process A is performed.

FIGS. 9A and 9B are explanatory diagrams showing a relationship between a sheet transport position, a secondary transfer speed, and a secondary transfer bias when a special fixing process A is performed.

FIG. 10 is a timing chart showing the operation timing of the comparison mode according to the first embodiment.

FIG. 11 is a flowchart illustrating a sheet fixing process of the image forming apparatus according to the second embodiment.

FIG. 12 is a flowchart illustrating a sheet fixing process of the image forming apparatus according to the third embodiment.

FIG. 13 is a timing chart showing operation timings of the image forming apparatus according to Embodiment 3 when a special fixing process B is performed.

FIGS. 14A and 14B are explanatory diagrams showing a relationship between a sheet transport position, a secondary transfer speed, and a secondary transfer bias when a special fixing process B is performed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Transfer means, 3 ... Fixing means, 4 ... Recording material conveyance means, 5 ... Conveyance speed control means, 6 ... Transfer force control means, 7 ... Fixing speed control means, 8 ... Image formation mode discrimination Means 9: Recording material position detecting means P: Recording material T: Visible image

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code FI G03G 15/16 103 G03G 15/16 103 15/20 102 15/20 102 21/14 21/00 372 (72) Inventor Masateru Kazeoka 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Co., Ltd.

Claims (5)

[Claims] An image carrier on which a visible image is formed and carried; transfer means for forming a transfer nip area with the image carrier to transfer a visible image on the image carrier to a recording material; In an image forming apparatus including a fixing unit that fixes a visible image transferred thereon and a recording material conveying unit that conveys a recording material after transfer from the transfer unit to the fixing unit, a conveying speed of the recording material in a transfer nip area And controlling the conveying speed of the recording material in the recording material conveying means, and setting the conveying speed of the recording material to the fixing of the recording material by the fixing means under the condition that the recording material is nipped in the transfer nip area and does not reach the fixing means. Transport speed control means for shifting the speed to a speed corresponding to the speed, and a transfer force so as to maintain a constant condition for transferring a visible image onto the recording material in conjunction with a shift operation of the recording material by the transport speed control means. Force control to control An image forming apparatus characterized by comprising a stage. 2. An image carrier on which a visible image is formed and carried; transfer means for forming a transfer nip area with the image carrier to transfer a visible image on the image carrier to a recording material; In an image forming apparatus including a fixing unit that fixes a visible image transferred thereon and a recording material conveying unit that conveys a recording material after transfer from the transfer unit to the fixing unit, a conveying speed of the recording material in a transfer nip area And controlling the conveying speed of the recording material in the recording material conveying means, and fixing the conveying speed of the recording material under the condition that the rear end in the conveying direction of the recording material is nipped in the transfer nip area and does not reach the fixing means. An image forming apparatus comprising: a conveying speed control unit that changes a speed to a speed corresponding to a fixing speed of a recording material of the unit. 3. The image forming apparatus according to claim 1, wherein the image forming mode determining unit determines an image forming mode;
An image forming apparatus, comprising: controlling a fixing speed of a fixing unit based on image forming mode information determined by the image forming mode determining unit. 4. The image forming apparatus according to claim 1, further comprising: a recording material position detecting unit configured to detect a conveying position of the recording material, wherein the conveying speed control unit includes a recording material position detecting unit. An image forming apparatus that controls a control start timing of a recording material conveyance speed based on detected position information of a recording material. 5. The image forming apparatus according to claim 1, wherein the transport speed control unit controls the transport speed of the recording material in the transfer nip area and the transport speed of the recording material in the recording material transport unit. An image forming apparatus, wherein the image forming apparatus performs control so as to change at a speed change rate.