JP3607528B2 - Image forming apparatus - Google Patents

Description

表１から湿度が高い場合、９９％以下の速度比で用紙Ｐを搬送すれば、画像の白抜けの発生を抑えれることがわかる。実験結果によると９８．５％の速度比まで良好な結果が得られたが、速度比を落とし過ぎると用紙Ｐをレジストローラ２１２とニップ部３００の間で引っ張り過ぎて転写ずれ等の不具合が発生するため、速度比は９８．５％が下限である。
【００４２】
また、他の実施形態として、用紙Ｐの吸湿に応じて用紙Ｐに張力を付加して用紙Ｐの表面状態を平滑にすればよいので、図５に示すように、一対の移動自在なガイドローラ３０２ａ，３０２ｂをレジストローラ２１２とニップ部３００との間に設け、用紙Ｐの吸湿具合、例えば湿度に応じて互いのガイドローラ３０２ａ，３０２ｂを近接する方向に移動させて、両ガイドローラ３０２ａ，３０２ｂの間で用紙Ｐを引き伸ばして表面の凸凹をなくすようにしてもよい。
【００４３】
なお、本発明は、上記実施形態に限定されるものではなく、本発明の範囲内で上記実施形態に多くの修正および変更を加え得ることは勿論である。本実施形態においては、カラー複写機への適用例を示したが、モノクロ複写機、あるいはプリンタ、ファクシミリにも本発明を適用できる。また、搬送ベルトの代わりに転写ローラを用いてもよく、感光体ドラムとの間にニップ部を形成し、転写ローラによって用紙が搬送されながら転写される。さらに、レジストローラの代わりにベルトを用いてもよい。
【００４４】
そして、レジストローラによる搬送速度と搬送ベルトによる搬送速度との速度比を湿度に応じて可変すればよいので、レジストローラの周速を一定にして、搬送ベルトによる搬送速度を湿度が高いときには速く、湿度が低いときには遅くしてもよい。なお、この場合は、搬送速度に応じて画像形成プロセスの速度も変化させる必要がある。
【００４５】
【発明の効果】
以上の説明から明らかな通り、本発明によると、湿気が多くて用紙の表面状態が悪くなっても、用紙の搬送速度を可変する等により、レジスト手段からニップ部までの間において用紙を引っ張った状態にして、用紙が吸湿したときに生じる表面の凸凹を小さくする。したがって、用紙の表面が平滑となるので、画像の転写時の白抜けを防止でき、画像品質を良好なものにすることができる。しかも、用紙のしわの発生も防止でき、用紙の搬送性が向上する。
【図面の簡単な説明】
【図１】本発明の実施形態のカラー複写機の全体構成図
【図２】湿度が低いときのレジストローラとニップ部との間の詳細図
【図３】湿度が高いときのレジストローラとニップ部との間の詳細図
【図４】湿度に応じて搬送速度を設定するときのフローチャート
【図５】他の実施形態のレジストローラとニップ部との間の詳細図
【符号の説明】
２１２ レジストローラ
２１６ 搬送ベルト
３００ ニップ部
３０１ 湿度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that transfers a toner image onto a sheet by a transfer member that forms an image carrier and a nip portion.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine or a printer, a sheet fed from a sheet tray is transported to a registration roller, the skew of the sheet is corrected by the registration roller, and then in accordance with the timing of the image forming process in the image forming unit. The sheet is conveyed toward a nip portion formed between a photosensitive drum (image carrier) and a transfer member such as a transfer belt and a transfer roller. The toner image formed on the photosensitive drum is transferred onto the sheet by passing through the nip while the sheet is conveyed by the transfer member.
[0003]
At this time, the sheet conveyance speed of the registration roller is set so that the transfer image does not have unevenness or color misregistration due to uneven rotation of the registration roller or uneven rotation of the conveyance roller upstream of the registration roller. The sheet is made faster, and an appropriate deflection is provided between the registration roller and the nip portion. That is, the conveyance speed is set so that the conveyance speed of the fixing device <the conveyance speed of the image forming unit including the photosensitive drum <the conveyance speed of the registration rollers, so that the upstream side of the sheet conveyance is not affected.
[0004]
[Problems to be solved by the invention]
By the way, the paper is easily affected by the usage environment, especially humidity. If the humidity is high and the surrounding humidity is higher than a predetermined level, the moisture content of the paper increases and the smoothness of the paper surface deteriorates. Unevenness occurs on the surface. If the paper is transported while maintaining the conventional transport speed relationship, the transferred image may be blanked or wrinkled on the paper due to irregularities on the surface of the paper, resulting in a reduction in image quality.
[0005]
Therefore, in order to suppress variations in paper conveyance accuracy due to moisture, Japanese Patent Laid-Open No. 8-262822 discloses that paper is fed from a paper tray to a registration roller in accordance with the output of a humidity sensor attached to the outer wall of the image forming apparatus. It is disclosed that control is performed such that the timing of feeding is varied, the sheet conveying speed from the sheet tray to the registration roller is varied, or the timing of feeding the sheet from the registration roller is varied.
[0006]
However, when the paper is bent between the registration roller and the nip portion, the unevenness of the paper surface is not eliminated, and therefore, the paper is wrinkled in the process of passing from the registration roller to the image forming portion, and the transferred image is not white. I can't deal with it.
[0007]
Therefore, in view of the above, the present invention controls the conveyance speed of the registration roller in accordance with the humidity, thereby adjusting the bending of the paper between the registration roller and the image forming unit, and is not affected by moisture. An object of the present invention is to provide an image forming apparatus capable of obtaining a stable image.
[0008]
[Means for Solving the Problems]
The problem-solving means according to the present invention comprises a transfer means comprising a belt or a roller for transferring an image while forming a nip portion between the image carrier and conveying the paper, and a sheet at a predetermined timing toward the nip portion. And a humidity sensor that detects the surrounding humidity when the conveyance speed by the registration means is set higher than the conveyance speed by the transfer means in order to prevent transfer deviation and the like. The relative relationship between the transfer speed by the transfer means and the transfer speed by the resist means is varied according to the humidity. That is, when the humidity is higher than a predetermined value, the conveying speed by the registration means is a conveying speed or less by the transfer means, when the humidity is lower than the predetermined value, the conveying speed by the registration means is larger than the conveying speed by the transfer means .
[0009]
As described above, since the moisture absorption amount of the paper increases when the moisture is high, the surface of the paper is likely to be uneven, and the paper bends between the nip portion and the registration means while maintaining the normal conveyance speed. Thus, the surface condition of the sheet is not improved at all, and when the sheet passes through the nip portion and an image is transferred, an image defect occurs. Therefore, as described above, humidity is detected as a measure of moisture, and when the humidity is high, the conveyance speed by the registration means is made slower than the conveyance speed by the transfer means, so that the paper is pulled and the surface unevenness is reduced. This prevents white spots and the like, and eliminates wrinkling of the paper. Therefore, the paper can be smoothly conveyed and the image quality can be kept good.
[0010]
By the way, the moisture absorption condition of the paper changes due to moisture, and unevenness occurs on the surface.If the moisture absorption condition of the paper is directly detected and the conveyance speed is controlled, the conveyance according to the surface condition of the paper can be performed. Image quality can be further improved. In order to detect the moisture absorption state of the sheet, an image sensor, an optical sensor, or the like that directly detects the surface state of the sheet may be provided on the upstream side of the registration unit in the sheet conveyance direction. If there is a lot of moisture and unevenness according to the surface state of the paper, the conveyance speed by the registration means is made slower than the conveyance speed by the transfer means. Even if the humidity is high, if the paper does not absorb much moisture, the unevenness is reduced, so the conveying speed by the transfer means is not slowed down.
[0011]
Also, if there are no irregularities on the surface of the paper, defects such as white spots on the image and paper wrinkles will not occur. Therefore, it is only necessary to apply tension to the paper according to the moisture absorption of the paper to smooth the surface state of the paper. . As one of means for smoothly correcting the surface of such a sheet, there is a means for changing the above-mentioned conveyance speed, and the sheet is pulled and tension is added. Alternatively, a movable guide roller and a deformable guide plate may be provided, and the sheet may be moved or deformed according to moisture absorption of the sheet so that the sheet is stretched to eliminate surface irregularities.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. In the digital color copying machine as the image forming apparatus, a document table 111 and an operation panel are provided on the upper surface of the copying machine main body, and an image reading unit 110 and an image forming unit 210 are provided inside the copying machine main body. . A double-sided automatic document feeder (RADF) 112 is mounted above the document table 111 so as to be openable and closable with respect to the document table 111 and having a predetermined positional relationship with respect to the upper surface of the document table 111. Has been.
[0013]
Further, the double-sided automatic document feeder 112 first transports the document so that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111, and after the image reading on this one side is completed. The document is reversed and conveyed toward the document table 111 so that the other side faces the image reading unit 110 at a predetermined position on the document table 111. The double-sided automatic document feeder 112 discharges the original after one-sided image reading for one original is completed, and executes a double-sided conveyance operation for the next original. The original conveying and front / back reversing operations are controlled by a control device built in the copying machine main body in relation to the operation of the entire copying machine.
[0014]
The image reading unit 110 is disposed below the document table 111 in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image reading unit 110 includes document scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.
[0015]
The document scanning bodies 113 and 114 are composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 114 includes an exposure lamp that exposes the surface of the document image and a first mirror that deflects a reflected light image from the document in a predetermined direction. While maintaining the distance, the robot moves back and forth in parallel at a predetermined scanning speed. The second scanning unit 114 includes second and third mirrors that further deflect the reflected light image from the original deflected by the first mirror of the first scanning unit 113 in a predetermined direction. The reciprocating unit 113 is reciprocated in parallel while maintaining a constant speed relationship.
[0016]
The optical lens 115 reduces the reflected light image from the original deflected by the third mirror of the second scanning unit 114 and forms the reduced light image at a predetermined position on the CCD line sensor 116. .
[0017]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 116 is a three-line color CCD that can read a black-and-white image or a color image and output line data that is color-separated into R (red), G (green), and B (blue) color components. is there. The document image information converted into an electrical signal by the CCD line sensor 116 is further transferred to an image processing unit in the control device and subjected to predetermined image data processing.
[0018]
An image forming unit 210 is disposed below the image reading unit 110. Below the image forming unit 210, the sheets (recording media) P stacked in a sheet tray are separated one by one and the image forming unit 210 is separated. A paper feed mechanism 211 having a plurality of rollers to be fed toward is provided. Then, the sheets P separated and supplied one by one are conveyed to the image forming unit 210 at a timing set by a pair of registration rollers 212 arranged in front of the image forming unit 210. Further, the paper P on which an image is formed on one side is also re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.
[0019]
Below the image forming unit 210, a transfer mechanism 213 that performs transfer while conveying a sheet is disposed. The transfer mechanism 213 includes a conveyance belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel. The conveyance belt 216 is charged by a suction charger (not shown) to transfer the paper P. It is configured to carry by electrostatic attraction.
[0020]
Further, a fixing device 217 for fixing the toner image transferred onto the paper P is disposed on the downstream side of the conveying belt 216. The sheet P that has passed through the nip portion between the pair of fixing rollers of the fixing device 217 passes through the conveyance direction switching gate 218 and is discharged onto the discharge tray 220 attached to the outer wall of the copier body 1 by the discharge roller 219. Is done.
[0021]
The switching gate 218 selectively switches between a path for discharging the fixed sheet P to the outside of the copying machine main body 1 and a path for re-feeding the sheet P toward the image forming unit 210. The paper P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image forming unit 210.
[0022]
In the image forming unit 210, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the fourth image forming station Pd are close to the upper side of the conveying belt 216. Then, they are arranged in order from the upstream side in the paper transport direction.
[0023]
The conveyance belt 216 is frictionally driven in the direction indicated by the arrow Z in FIG. 1 by the driving roller 214 and carries the paper P fed through the paper feed mechanism 211 as described above, and the paper P is fed to the image forming stations Pa to Pd. Sequentially.
[0024]
Each of the image stations Pa to Pd has substantially the same configuration, and includes photosensitive drums 222a to 222d that are rotationally driven in the direction of arrow F shown in FIG. Around the photosensitive drums 222a to 222d, the chargers 223a to 223d for uniformly charging the photosensitive drums 222a to 222d and the electrostatic latent images formed on the photosensitive drums 222a to 222d are developed. Developing devices 224a to 224d, transfer dischargers 225a to 225d for transferring the toner images on the photosensitive drums 222a to 222d to the paper P, and a cleaning device 226a for removing the toner remaining on the photosensitive drums 222a to 222d. To 226d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.
[0025]
Laser beam scanner units 227a to 227d are provided above the photosensitive drums 222a to 222d, respectively. The laser beam scanner units 227a to 227d are a semiconductor laser element (not shown) that emits dot light modulated in accordance with image data, and a polygon mirror (deflection) for deflecting the laser beam from the semiconductor laser element in the main scanning direction. (Apparatus) 240a to 240d, and fθ lenses 241a to 241d and mirrors 242a to 242d and 243a to 243d for forming an image of the laser beam deflected by the polygon mirrors 240a to 240d on the surface of the photosensitive drums 222a to 222d. Has been.
[0026]
The laser beam scanner unit 227a has a pixel signal corresponding to the black component image of the color document image, the laser beam scanner unit 227b has a pixel signal corresponding to the cyan component image of the color document image, and the laser beam scanner unit 227c has the pixel signal. A pixel signal corresponding to the magenta color component image of the color original image is input, and a pixel signal corresponding to the yellow color component image of the color original image is input to the laser beam scanner unit 227d. Thereby, electrostatic latent images corresponding to the color-converted document image information are formed on the respective photosensitive drums 222a to 222d. The developing device 227a contains black toner, the developing device 227b contains cyan toner, the developing device 227c contains magenta toner, and the developing device 227d contains yellow toner. The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. Thus, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.
[0027]
In addition, the paper P supplied from the paper feeding mechanism 211 is transported between the first image forming station Pa and the fourth image forming station Pd in a state where the paper P is reliably electrostatically attracted onto the transport belt 216. On the other hand, a static eliminator 229 is provided between the fourth image station Pd and the fixing device 217 almost directly above the driving roller 214. An AC current for separating the sheet P electrostatically attracted to the conveyor belt 216 from the conveyor belt 216 is applied to the static eliminator 229.
[0028]
In the digital color copying machine having the above configuration, the conveyance of the paper is controlled by the control device in accordance with the timing of the image forming process. A cut sheet-like paper is used as the paper P. When the paper P is fed out from the paper feed cassette and supplied into the guide of the transport path, the leading end of the paper P is detected by a sensor (not shown). Then, based on the detection signal output from this sensor, the pair of registration rollers 212 are temporarily stopped.
[0029]
Then, the paper P is fed onto the conveying belt 216 rotating in the arrow Z direction at the timing of image formation at each of the image stations Pa to Pd. At this time, the conveyance belt 216 is charged with a predetermined charging by a suction charger (not shown) as described above, so that the sheet P is stably displaced without passing through the image stations Pa to Pd. Be transported.
[0030]
In each of the image stations Pa to Pd, toner images of the respective colors are respectively formed on the photosensitive drums 222a to 222d, electrostatically attracted by the transport belt 216, transferred onto the transported paper P, and superimposed on the surface thereof. The When the transfer of the image by the fourth image station Pd is completed, the paper P is sequentially peeled off from the conveying belt 216 by the discharger 229 for discharging from the leading end portion thereof and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is discharged from the discharge roller 219 onto the paper discharge tray 220.
[0031]
In the above-described configuration, the laser beam scanner units 227a to 227d scan and expose the laser beam to perform optical writing on the photosensitive drums 222a to 222d. However, instead of the laser beam scanner unit, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used. The LED head is smaller than the laser beam scanner unit and has no moving parts and is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units.
[0032]
Here, as shown in FIG. 2, a conveying belt 216 exists between the photosensitive drums 222a to 222d and the transfer dischargers 225a to 225d, and the conveying belt 216 and the photosensitive drums 222a to 222d are used. Nip portions 300 are respectively formed. Then, the sheets P separated and supplied one by one by the sheet feeding mechanism 211 from the sheet tray are transported toward the nip portion 300 of the first image forming station Pa at the timing by the registration roller 212, and each nip portion 300 is conveyed. The toner images are transferred from the photosensitive drums 222a to 222d onto the paper when passing through the sheet. Note that the distance from the registration roller 212 to the nip portion 300 is smaller than the length of the paper P in the transport direction.
[0033]
At this time, the conveyance speed of the paper P by the registration roller 212, that is, the circumferential speed Vr of the registration roller is influenced by uneven rotation of the registration roller 212, uneven rotation of the conveyance roller upstream of the registration roller 212, and the like. The speed is set to be faster than the transport speed Vb (<Vr) by the transport belt 216 so that no deviation occurs. Therefore, the sheet P bends upward between the registration roller 212 and the nip portion 300. However, when the ambient humidity where the color copying machine is used is high, the paper P absorbs moisture, causing wrinkles and corner breakage during conveyance, and whitening of the transferred image when passing through the nip portion 300. To do. Therefore, in order to eliminate the adverse effect of humidity, a humidity sensor 301 for detecting ambient humidity is provided, and the relative relationship between the conveyance speed Vb by the conveyance belt 216 and the conveyance speed Vr by the registration roller 212 is determined according to the humidity by the control device. Perform variable transport control.
[0034]
The humidity sensor 301 is a general humidity sensor that detects the humidity of the atmosphere, and is disposed immediately before the upstream side of the registration roller 212 in the conveyance path. As described above, when the humidity sensor 301 is disposed not inside the copying machine main body but near the position where image formation is actually performed, the moisture absorption state of the paper P is reliably detected from the humidity. This improves the reliability of the transport control.
[0035]
Next, a method for determining the conveyance speed based on humidity will be described. The conveyance speed Vb by the conveyance belt 216 is kept constant, and the peripheral speed Vr of the registration roller 212 is determined according to the detection result of the humidity sensor 301. That is, when the humidity is less than the predetermined value, the motor driving the registration roller 212 is controlled so that Vr> Vb as usual because it is not affected by the humidity. When the humidity is equal to or higher than a predetermined value, the peripheral speed Vr of the registration roller 212 is controlled to be slow so that Vr ≦ Vb. Thus, since normal conveyance control is performed when the humidity is low, the sheet P bends as shown in FIG. 2, but when the humidity is high, both conveyance speeds are reversed, and the conveyance belt 216 and the registration roller are reversed. The sheet P is pulled by the speed difference from 212, and the deflection is smaller than that in the case of normal conveyance as shown in FIG.
[0036]
Specifically, as shown in FIG. 4, in STEP 1, it is determined whether or not the humidity is 70% or more. If 70% or more, the process proceeds to STEP 2, and if it is less than 70%, the process proceeds to STEP 4. In STEP 2, it is determined whether or not the humidity is 80% or more. If 80% or more, the process proceeds to STEP 3, and if it is less than 80%, the process proceeds to STEP 5.
[0037]
In STEP 3, the speed ratio between the peripheral speed Vr of the registration roller 212 and the transport speed Vb of the transport belt 216 is set to Vr / Vb = 99.5%. In STEP 4, the speed ratio between the peripheral speed Vr of the registration roller 212 and the transport speed Vb of the transport belt 216 is set to Vr / Vb = 100.5%. In STEP 5, the speed ratio between the peripheral speed Vr of the registration roller 212 and the transport speed Vb of the transport belt 212 is set to Vr / Vb = 100%. As described above, the peripheral speed Vr of the registration roller 212 is set according to the humidity, and the relative relationship between the conveyance speed Vr by the registration roller 212 and the conveyance speed Vb by the conveyance belt 216 is varied.
[0038]
Therefore, when the humidity is high, the speed at which the leading edge of the paper P passes through the nip portion 300 is equal to or faster than the speed at which the trailing edge is sent out by the registration rollers 212. The paper is conveyed between the registration roller 212 and the nip portion 300 while being pulled on both sides. Therefore, even if the paper P absorbs moisture and the surface has unevenness, the paper P is stretched. Therefore, the unevenness is reduced, the paper P is not wrinkled, white spots of the image can be prevented, and good image quality is achieved. can get.
[0039]
When the humidity is low, the speed ratio is set to 100.5%, but the deflection of the paper P between the registration roller 212 and the nip portion 300 is appropriate, and the paper P does not pull between the two. No transfer deviation or the like occurs when the image is transferred. However, when the speed ratio is set to 100.5% or more, the deflection between the two becomes larger than necessary, and problems such as paper jam at the nip portion 300 and Z-shaped folding of the paper P occur. The upper limit of the speed ratio is 100.5%.
[0040]
(Experimental example)
The installation environment of the image forming apparatus is a room temperature of 35 ° C. and a humidity of 85%, and the speed ratio Vr / Vb between the peripheral speed Vr of the registration roller 212 and the conveying speed Vb in the image forming unit 210 is 98.5% to 100.5%. When the image was shaken, the white spots of the image were confirmed. The results are shown in Table 1. In Table 1, “x” indicates a level where white spots occur, “Δ” indicates a level where white spots occur slightly, and “◯” indicates a level where white spots do not occur.
[0041]
[Table 1]

From Table 1, it can be seen that if the humidity is high and the paper P is conveyed at a speed ratio of 99% or less, the occurrence of white spots in the image can be suppressed. According to the experimental results, good results were obtained up to a speed ratio of 98.5%. However, if the speed ratio is decreased too much, the paper P is pulled too much between the registration roller 212 and the nip portion 300, causing problems such as transfer deviation. Therefore, the lower limit of the speed ratio is 98.5%.
[0042]
Further, as another embodiment, a tension may be applied to the paper P in accordance with the moisture absorption of the paper P to smooth the surface state of the paper P. Therefore, as shown in FIG. 5, a pair of movable guide rollers The guide rollers 302a and 302b are provided between the registration roller 212 and the nip portion 300, and the guide rollers 302a and 302b are moved toward each other in accordance with the moisture absorption condition of the paper P, for example, the humidity. The sheet P may be stretched between the two so as to eliminate the surface unevenness.
[0043]
In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention. In this embodiment, an example of application to a color copying machine has been shown, but the present invention can also be applied to a monochrome copying machine, a printer, or a facsimile. In addition, a transfer roller may be used in place of the conveyance belt, and a nip portion is formed between the transfer drum and the photosensitive drum, and the sheet is transferred while being conveyed by the transfer roller. Further, a belt may be used instead of the registration roller.
[0044]
And since the speed ratio between the conveyance speed by the registration roller and the conveyance speed by the conveyance belt may be varied according to the humidity, the peripheral speed of the registration roller is made constant, and the conveyance speed by the conveyance belt is high when the humidity is high, When the humidity is low, it may be delayed. In this case, it is necessary to change the speed of the image forming process according to the transport speed.
[0045]
【The invention's effect】
As is clear from the above description, according to the present invention, even when the humidity is high and the surface state of the paper is deteriorated, the paper is pulled between the resist means and the nip portion by changing the paper conveyance speed. In this state, the surface unevenness that occurs when the paper absorbs moisture is reduced. Accordingly, since the surface of the paper becomes smooth, white spots during image transfer can be prevented, and image quality can be improved. In addition, the occurrence of paper wrinkles can be prevented, and the paper transportability is improved.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a color copying machine according to an embodiment of the present invention. FIG. 2 is a detailed view between a registration roller and a nip when humidity is low. FIG. 3 is a registration roller and nip when humidity is high. FIG. 4 is a flowchart for setting the conveyance speed according to the humidity. FIG. 5 is a detailed diagram between the registration roller and the nip portion according to another embodiment.
212 Registration roller 216 Conveying belt 300 Nip part 301 Humidity sensor

Claims (5)

A transfer means for transferring an image while transporting the paper while forming a nip portion with the image carrier, a registration means for transporting the paper at a predetermined timing toward the nip portion, and detecting moisture absorption of the paper A humidity detector that controls the relative relationship between the conveyance speed by the transfer means and the conveyance speed by the registration means according to moisture absorption of the paper, and the control means is configured to control the humidity when the humidity is equal to or higher than a predetermined value. , the conveying speed by the registration means the following conveying speed of the transfer means, when the humidity is lower than the predetermined value, the image forming apparatus characterized by a greater than conveying speed of the transfer means the conveyance speed by the registration means. A transfer means for transferring an image while transporting the paper while forming a nip portion with the image carrier, a registration means for transporting the paper at a predetermined timing toward the nip portion, and detecting moisture absorption of the paper A humidity detector that controls the relative relationship between the conveyance speed by the transfer means and the conveyance speed by the registration means in accordance with moisture absorption of the paper, and the control means is configured to control the humidity when the humidity is 80% or more. When the conveyance speed by the resist means is less than the conveyance speed by the transfer means and the humidity is less than 70%, the conveyance speed by the registration means is larger than the conveyance speed by the transfer means, and when the humidity is 70% or more and less than 80%, An image forming apparatus characterized in that the conveying speed by the means is equal to the conveying speed by the transfer means. The image forming apparatus according to claim 1, wherein a humidity sensor that detects the humidity of the atmosphere is used as the moisture detector, and the humidity sensor is disposed in a conveyance path that is upstream of the registration unit in the sheet conveyance direction. 4. The image forming apparatus according to claim 1, wherein the conveyance speed by the registration means is variable within a range of 98.5 to 100.5% with respect to the conveyance speed by the transfer means. A transfer means for transferring an image while transporting the paper while forming a nip portion with the image carrier, a registration means for transporting the paper at a predetermined timing toward the nip portion, and detecting moisture absorption of the paper And a paper correction unit that applies tension to the paper according to moisture absorption of the paper and smoothes the surface state of the paper, and the paper correction unit is provided upstream of the transfer unit in the transport direction. An image forming apparatus that is arranged.

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