JP2003345150A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a color drift regardless of the types of recording mediums by controlling a loop in the recording medium at the entrance of a fixing means. <P>SOLUTION: The image forming apparatus which fixes an image formed on the recording medium by an image forming part has: an electrostatic transfer belt 9a for carrying a transfer material S from the image forming part to a fixing part 10; the fixing part 10 for fixing the image while further transporting the recording medium transported by the electrostatic transport belt 9a; a detection sensor 22 for detecting an amount of loop made in the transfer material S during its transport from the image forming part to the fixing part 10; and a speed switching means which is capable of switching, in at least two steps, the speed at which the recording medium is transported by the fixing part 10. According to the detection result of the detection sensor 22, the speed switching means is switched to control the amount of loop in the transfer material. <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 such as a copying machine, a printer or a facsimile which forms an image by an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus for forming a color image at high speed, yellow (Y), magenta (M), cyan (C), black (B) along a conveyor belt.
k) The photosensitive drum is arranged for each color, and the transfer material is sequentially conveyed by the conveyor belt to sequentially transfer the images of the respective colors, or the toner images of the respective colors are sequentially transferred to the intermediate transfer belt so as to be superposed and finally transferred. There is a so-called in-line method in which the toner images are collectively transferred to the transfer material.

A major problem in this in-line type color image forming apparatus is color misregistration between colors of a color image. One of the causes of this color misregistration is the difference between the speed of the transfer belt that transfers the transfer material and the fixing speed. This is because the speed of the transfer material is governed by the fixing speed after entering the fixing, and therefore the transfer material cannot be fed at a constant speed after entering the fixing. Therefore, generally, as in Japanese Patent Laid-Open No. 7-234604, it is necessary to form a loop on the transfer material before the entrance of the fixing section and make the loop amount constant at that time (hereinafter, referred to as “loop control”). ) Minimizes the speed difference between transfer and fixing.

Further, as one of the image problems, there are image defects during fixing and paper wrinkles. One of the causes of this image defect and paper wrinkle is the angle (posture) of the paper at the time of fixing.
In order to avoid image defects and paper wrinkles at the time of fixing, the loop control shape for naturally performing the loop control is determined.

[0005]

However, even if the speed difference between transfer and fixing is eliminated, in the situation where a loop is formed to avoid image defects during fixing and paper wrinkles, paper strains such as paper types may be removed. Due to the difference, some external force is applied to the conveyor belt. This external force does not cause color misregistration if it is extremely small compared to the force attracted by the conveyor belt, but depending on the paper type, even if it has the same loop shape, the external force applied to the conveyor belt is large. As a result, the transfer material on the conveyor belt slips, causing color misregistration.

Therefore, it is necessary to reduce the external force applied to the conveyor belt by changing the shape of the loop depending on the paper type. However, in the conventional loop control, the loop control shape at the time of control is always determined, and it is difficult to switch depending on the paper type.

The present invention is to solve the above problems,
An object of the present invention is to provide an image forming apparatus capable of eliminating color misregistration regardless of the type of recording medium by controlling the loop of the recording medium at the entrance of the fixing unit.

[0008]

A typical configuration according to the present invention for achieving the above object is to form an image in an image forming apparatus in which an image formed on a recording medium in an image forming unit is fixed by a fixing unit. A conveying means for conveying the recording medium from the image forming section to the fixing means, a fixing means for fixing the recording medium conveyed by the conveying means while conveying the recording medium, and a recording medium during the conveyance from the image forming section to the fixing means. A loop detection unit that detects the amount of the generated loop, and a speed switching unit that can switch the recording medium conveyance speed by the fixing unit in at least two stages are provided, and the speed switching is performed according to the detection result of the loop detection unit. The loop amount of the recording medium is controlled by switching the means.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a sectional view showing the outline of a color image forming apparatus according to an embodiment of the present invention.

(Overall Structure) The color image forming apparatus shown in the figure has four photosensitive drums 1 (1a, 1b, 1c, 1).
d), charging means 2 (2a, 2b, 2c, 2) for uniformly charging the surface of the photosensitive drum 1 around the respective photosensitive drums 1 in order according to the rotation direction thereof.
d), exposure means 3 (3a, 3a, which irradiates a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 1)
3b, 3c, 3d), developing means 4 (4a, 4b, 4) that attaches toner to the electrostatic latent image and visualizes it as a toner image.
c, 4d), transfer means (transfer roller) 5 (5) for transferring the toner image on the photosensitive drum 1 to a transfer material (recording medium).
a, 5b, 5c, 5d), a cleaning unit 6 for removing post-transfer toner remaining on the surface of the photosensitive drum 1 after transfer.
(6a, 6b, 6c, 6d) and the like are arranged to form an image forming unit.

Here, the photosensitive drum 1, the charging means 2, the developing means 4, and the cleaning means 6 for removing the toner are integrally made into a cartridge to form a process cartridge 7 (7).
a, 7b, 7c, 7d) are formed.

Further, the transfer material S fed from the feeding portion 8 is conveyed to the image forming means by the conveying means 9 composed of an electrostatic conveying belt, and the toner images of respective colors are sequentially transferred to record a color image. After that, the image is fixed by the fixing section (fixing means) 10 and discharged to the discharge section 13 by the discharge rollers 11 and 12.

During double-sided printing, before the transfer material S is fixed by the fixing unit 10 and discharged by the discharge rollers 11 and 12, the discharge rollers 11 and 12 are reversed to move to the double-sided conveyance path 15. It is transported (direction of arrow A). The transfer material S transported to the double-sided transport path 15 is a skew feed roller on the front of the main body of the apparatus.
It passes through 16 and is conveyed vertically downward to the U-turn roller 17, and is conveyed to the image forming portion by the U-turn roller 17 and the registration roller 8d.

Next, the structure of each part will be described in sequence.

(Transfer Material Feeding Structure) The feeding unit 8 includes a feeding cassette 8a and a multi feeding tray 8 which is a multi feeding device.
b, a multi-feeding unit 8c, and a registration roller 8d.

The feeding cassette 8a contains a plurality of transfer materials S and is loaded in the bottom of the apparatus main body. Feed cassette 8a
The cassette pickup roller 8 when forming an image from the
The transfer materials S are separated and conveyed one by one by a1 and are conveyed to the image forming section by the cassette conveying rollers 8a2 and the registration rollers 8d.

Next, the multi-feed tray 8b is normally stored in the front of the main body of the apparatus, but at the time of use, the multi-feed tray 8b is rotated and opened to set a plurality of transfer materials S. To do. During image formation from the multi-feed tray 8b, the multi-pickup roller 8c1 separates and conveys the transfer materials S one by one, and the multi-conveyor roller 8c2.
Then, it is conveyed to the image forming section by the registration rollers 8d. At this time, the feeding path from the multi-feeding device, such as a thick paper, an envelope, a special paper, etc., which is relatively hard to be electrostatically attracted to the surface of the electrostatic transport belt 9a, or which has a high ratio of using a transfer material having a strong elasticity, is used. , When the transfer material reaches the surface of the electrostatic transport belt 9a, the front and rear ends are along the belt surface,
It is composed of only R with a curve that makes the center part float.

The feeding path from the feeding cassette 8a shown in FIG. 1 has a curve that warps with respect to the surface of the electrostatic transport belt 9a, but the transfer material fed from the feeding cassette 8a is compared. It is known that even if the cassette feeding path shown in FIG. 1 is taken, a transfer material, which has a weak elasticity and is easily electrostatically attracted to the surface of the electrostatic transport belt 9a, is used. .

Separation and conveyance of sheets in the feeding cassette 8a and the multi-feeding unit 8c are performed by a feeding motor (not shown) in the feeding unit via a gear drive train.

(Image Forming Structure) The photosensitive drum 1 as an image bearing member is constituted by coating an organic photoconductor layer (OPC) on the outer peripheral surface of an aluminum cylinder. The photosensitive drum 1 is rotatably supported at both ends by flanges, and by transmitting a driving force from a drive motor (not shown) to one end, the photosensitive drum 1 is rotated counterclockwise as shown by an arrow in FIG. It is driven to rotate.

Each charging means 2 is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photoconductor drum 1 and a charging bias voltage is applied by a power source (not shown) to cause photoconductor The surface of the drum 1 is uniformly charged.

The exposing means 3 has a polygon mirror, and the polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown).

The developing means 4 is adjacent to the toner storage portion storing the toner of each color of black, cyan, magenta, and yellow and the surface of the photosensitive member, and is rotationally driven by a driving portion (not shown) and a developing bias (not shown). It is composed of a developing roller or the like that develops by applying a developing bias voltage from a power source.

Further, inside the electrostatic transport belt 9a, which will be described later, transfer members 5a, 5 which face the four photosensitive drums 1a, 1b, 1c, 1d and contact the electrostatic transport belt 9a.
b, 5c and 5d are provided side by side. These transfer members 5 are connected by a transfer bias power source (not shown), and positive charges are transferred from the transfer members 5 to the transfer conveyance belt 9a.
Is applied to the transfer material via the transfer material, and by this electric field, the negative color toner images on the photosensitive material drum 1 are sequentially transferred to the transfer material in contact with the photosensitive material drum 1 to form a color image.

The toner image detecting sensor 20 detects a toner pattern formed on an endless belt for measuring the color shift amount, calculates the color shift amount based on the detection result, and based on the calculation result, the image is formed. Correct the formation position.

(Transfer Material Conveying Structure) The transfer material S is conveyed from the feeding portion 8 to the image forming area by the conveying means 9.

The electrostatic transport belt 9a as a transfer material carrier constituting the transport means 9 is stretched and supported by four rollers of a driving roller 9b and driven rollers 9c, 9d and 9e, and all the photosensitive drums 1a. , 1b, 1c, 1d are arranged to face each other. By the driving roller 9d, the transfer material is transported to the transfer position by the electrostatic transport belt 9a, and the toner image on the photosensitive drum 1 is transferred.

At the most upstream position of the electrostatic transport belt 9a, a suction roller 9f for sandwiching the transfer material together with the belt 9a and attracting the transfer material to the electrostatic transport belt 9a is arranged. When the transfer material is conveyed, a voltage is applied to the attraction roller 9f to form an electric field between the transfer roller 9c and the opposing grounded roller 9c, and the electrostatic conveyance belt 9f.
A dielectric polarization is generated between a and the transfer material to generate an electrostatic attraction force on both.

(Fixing Structure) The fixing unit 10 which is a fixing means,
The image formed on the transfer material is fixed by applying heat and pressure.

Reference numeral 10a denotes a cylindrical fixing belt having an electromagnetic induction heating layer, which is guided by a belt guide member 10c having a built-in magnetic field generating means including an exciting coil and a T-shaped magnetic core. An elastic pressure roller 10b sandwiches the fixing belt 10a and forms a fixing nip portion N having a predetermined width with a predetermined pressure contact force with the belt guide member 10c.

The pressure roller 10b is rotationally driven by a driving means (not shown), and the cylindrical fixing belt 10a is rotated accordingly, and electromagnetic induction heat generation of the fixing belt 10a is performed by feeding power from an exciting circuit (not shown) to the exciting coil. Is done.

In a state where the fixing nip portion N has risen to a predetermined temperature and is temperature-controlled, the transfer material S having the unfixed toner image formed thereon, which is conveyed from the image forming portion, is applied to the fixing belt 10a of the fixing nip portion N. The image surface is introduced upward between the pressure roller 10b, that is, facing the fixing belt surface, and at the fixing nip portion N, the image surface is in close contact with the outer surface of the fixing belt 10a and the fixing nip portion N together with the fixing belt 10a. Is sandwiched and conveyed.

(Loop Forming Structure) Next, a structure for forming a loop on the transfer material in the fixing section 10 will be described.

When the image on the transfer material is fixed, the transfer material holding force in the fixing nip is stronger than the transfer portion holding force. Therefore, if the transfer speed in the fixing part 10 is different from the transfer speed in the transfer part, transfer is performed. The material S is conveyed at the fixing speed.

Therefore, in the image forming apparatus of this embodiment, as shown in FIG. 2, the transfer material S is provided between the fixing section 10 and the transfer section.
Loop detection means for detecting the loop amount of is provided. This loop detecting means is rotatable by contacting the transfer material S with the lever member 23, and the flag 21 at the rotation source part thereof.
Is to detect whether or not the loop amount of the transfer material has become a certain amount or more depending on whether or not the detection sensor 22 configured by an optical sensor is shielded from light.

On the other hand, the driving speed of the elastic pressure roller 10b is
The speed switching means can switch the speed in at least two steps, and the driving speed is switched in accordance with the detection result of the detection sensor 22 so that the loop amount of the transfer material is made constant. ing. In this embodiment, switching can be performed in two steps.

That is, the detection sensor 22 is in the on state when the transfer material being conveyed has no loop, and when the loop becomes larger than a predetermined amount, the flag 21 is turned off because the detection sensor 22 is shielded from light. Therefore, when the detection sensor 22 is turned on, the conveyance speed by the fixing unit 10 is increased, and when the detection sensor 22 is turned off, the conveyance speed by the fixing unit 10 is decreased to loop the transfer material near the entrance of the fixing unit 10. The amount can be constant.

As described above, the transport speed in the fixing unit 10 is 2
It is possible to switch between stages (one that is faster and one that is slower than the transfer material transport speed by the electrostatic transport belt 9a). However, in practice, the suitable loop control shape is different depending on the paper type, double-sided printing, and the first half and the second half of the transfer material (for example, the loop control shapes A and B in FIG.
C), it is necessary to change the loop control shape depending on the type of transfer material.

Therefore, in the present embodiment, as shown in FIG. 3, by changing the speed switching times A and B in the fixing unit 10, the loop control shape is changed without changing the mechanical structure. There is.

For example, when the loop amount is made smaller in the case of thick paper than the normal loop amount (for example, in case of plain paper), as shown in FIG. The transfer material transfer speed by the fixing unit 10 is increased after a predetermined time (switching time A) from the time when the detection sensor 22 is transferred from the off state to the on state (the transfer material loop is reduced to a predetermined amount). Switch to. During this switching time A, the fixing unit 10 has a slow conveyance speed, and therefore the loop amount gradually increases.

Then, the fixing unit 10 is operated after a predetermined time (switching time B) from the time when the flag 21 shields the detection sensor 22 due to the increase of the loop amount and the sensor 22 is turned off (state in which the loop has grown to a predetermined amount). The transfer material transfer speed is switched so that the transfer material transfer speed becomes slower. During this switching time B, the conveyance speed in the fixing unit 10 is high, so the loop decreases.

By setting the switching time B longer to make the fixing speed as a whole faster than that of plain paper, the apparent loop control shape of thick paper can be delicately reduced. By setting the switching times A and B according to the type of transfer material, it is possible to finely adjust the loop shape according to the type of transfer material.

For example, if the switching time A for increasing the speed of plain paper is 14 msec and the switching time B for decreasing the speed of plain paper is 14 msec respectively, the switching time A for increasing the speed of thick paper is 5 msec and the switching time B for slowing is 25 msec. The loop control shape can be made smaller than the case.

As a means for changing the apparent loop control shape without changing the switching time, depending on the type of the transfer material, the fixing speed can be set higher by increasing the fixing speed on the faster side or slower on the lower side. By holding it, the apparent loop control shape can be changed.

In the process in which the transfer material is nipped and conveyed together with the fixing belt 10a through the fixing nip portion N, the unfixed toner image on the transfer material S is heated and fixed by the electromagnetic induction heat generation of the fixing belt 10a.

As described above, by having at least two loop control shapes and appropriately setting the switching of the transfer material conveying speed by the fixing unit 10, it is possible to strongly strain the paper such as thick paper.
If the external force applied to the conveyor belt is too large,
Color shift can be eliminated by reducing the loop and reducing the external force applied to the conveyor belt. Further, it is possible to eliminate the problems of image defects and paper wrinkles caused by the angle at which fixing is performed. In this way, by changing the loop shape for each type of paper, both sides, and the trailing edge of the paper, any problem can be easily dealt with.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, the same parts as those of the first embodiment will be designated by the same reference numerals and description thereof will be omitted, and only the case different from the first embodiment will be described. To do.

As shown in FIG. 4, the loop control shape formed in front of the entrance of the fixing unit described in the first embodiment is provided with two detection sensors 22 so that the rotational position of the flag 21 can be detected at two positions. . This avoids the risk of controlling with the wrong loop shape.

[Third Embodiment] A third embodiment of the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, the same parts as those of the first embodiment will be designated by the same reference numerals and description thereof will be omitted, and only the case different from the first embodiment will be described. To do.

In this embodiment, as shown in FIG. 5A, the detection sensor 22 can detect not only one end 21a of the flag 21 but also the other end 21b. Therefore, the conveyance speed of the transfer material by the fixing unit 10 can be switched in three steps, so that the detection sensor 22 can detect the end portion 21 of the flag 21.
It is possible to control a plurality of types of loop amounts by switching the fixing conveyance speed between when a and 21b are detected and when the flag 21 is not detected.

This is not only for detecting the ends 21a and 21b of the flag 21, but as shown in FIG. 5 (b), the flag 24 detected by the detection sensor 22 is provided with a plurality of detecting portions 24a to 24f. Alternatively, the transfer material conveying speed by the fixing unit 10 may be switched when the detection sensor 22 detects each of the detection units 24a to 24f. Further, as shown in FIG. 5 (c), not only the detection portion has a protrusion shape, but also a hole 25a is formed in the flag 25 so that the detection sensor 22 can detect a plurality of positions so that the fixing portion 10 can switch the conveyance speed. You may comprise.

Even in this case, the shape of the flag may be complicated, but the loop control shape suitable for each transfer material can be formed without increasing the cost.

In the above-described embodiment, an example in which the loop amount is changed according to the type of transfer material is shown, but it is also possible to set the loop amount to be changed depending on the print mode, for example. .

[0055]

As described above, according to the present invention, color misregistration can be eliminated regardless of the type of recording medium by stepwise switching the recording medium conveying speed by the fixing means in accordance with the detection result of the loop detecting means. it can.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a color image forming apparatus using loop control according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of loop detection means.

FIG. 3 is a diagram showing a relationship between a flag signal and a fixing speed.

FIG. 4 is an explanatory diagram of an embodiment in which two loop amount detection sensors are provided.

FIG. 5 is an explanatory diagram of an embodiment in which a plurality of locations of a flag can be detected.

[Explanation of symbols]

N: Fixing nip part S ... Transfer material 1 ... Photosensitive drum 2 ... Charging means 3 ... Exposure means 4 ... Developing means 5 ... Transfer roller 6 ... Cleaning means 7 ... Process cartridge 8 ... Feeding department 8a ... Feed cassette 8a1 ... Cassette pickup roller 8a2 ... Cassette transport roller 8b ... Multi-feed tray 8c ... Multi-feed unit 8c1 ... Multi pickup roller 8c2 ... Multi-conveyor roller 8d ... Registration roller 9 ... Transportation means 9a ... Electrostatic transport belt 9b ... Drive roller 9c, 9d, 9e ... Driven roller 9f ... Suction roller 10… Fixing unit 10a ... Fusing belt 10b ... Elastic pressure roller 10c… Belt guide member 11, 12… Ejection roller 13 ... Discharge part 15… Double-sided transport path 16… Slant feeding roller 17… U-turn roller 20 Toner image detection sensor 21… Flag 21a, 21b ... Edges 22… Detection sensor 23 ... Lever member 24… Flag 24a to 24f ... Detection unit 25… Flag 25a ... hole

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenji Watanabe             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA16 DA20 DA38 DC02 DC05                       DE02 DE07 DE10 EC06 EC10                       ED16 ED25 EE02 EF09 FA05                       FA11 FA28                 2H033 AA01 AA46 AA47 BA08 BA11                       BA12 BB28 BB33 BE06 CA16                       CA17 CA22 CA36 CA37                 2H072 AA07 AA16 AA22 AB09 CA01                       CA07                 3F048 AA02 AA04 AA05 AB01 BA26                       BB02 BB10 DA06 DC09 DC13                       EB29

Claims (7)

[Claims] 1. An image forming apparatus for fixing an image formed on a recording medium in an image forming section by a fixing means, a conveying means for conveying a recording medium from the image forming section to the fixing means, and a conveying means for conveying the recording medium. At least a fixing unit that fixes the recording medium while conveying the recording medium, a loop detecting unit that detects a loop amount generated in the recording medium during the conveyance from the image forming unit to the fixing unit, and a recording medium conveying speed by the fixing unit are at least An image forming method comprising: a speed switching unit capable of switching in two or more steps; and controlling a loop amount of the recording medium by switching the speed switching unit according to a detection result of the loop detection unit. apparatus. 2. The image according to claim 1, wherein the loop amount of the recording medium is controlled by switching the speed switching means after a predetermined delay time has elapsed after the loop amount is detected by the loop detecting means. Forming equipment. 3. The image forming apparatus according to claim 1, wherein the loop amount is changed according to a print mode. 4. The image forming apparatus according to claim 1, wherein the loop amount is changed according to the type of recording medium. 5. The image forming apparatus according to claim 1, wherein the loop amount is changed based on a detection result of the loop detecting means. 6. The image forming apparatus according to claim 1, wherein the loop amount is changed according to a detection result of two sensors. 7. The image forming apparatus according to claim 1, wherein the loop detecting means is capable of detecting a plurality of locations on the detection member, and the switching of the loop amount is changed by detecting a plurality of locations on the detection member. apparatus.