JP2000310928A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a good image quality by preventing generation of an image void at a time of transfer and wrinkling of the paper by making uneveness generated on a surface of paper small in high humidity. SOLUTION: In this device, the humidity is detected by a humidity sensor 301 upstream of a resist roll 212. Thus, when the humidity is high, circumferential speed Vr of the resist roll 212 is made slower than carrying speed Vb of a carrying belt 216 and the projections and the recessions on the surface of the paper P are made small by making a state where the paper P is pulled tight between the resist roll 212 and a nip part 300.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for transferring a toner image to a sheet by a transfer member forming a nip portion with an image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a sheet fed from a sheet tray is conveyed to a registration roller, and the skew of the sheet is corrected by the registration roller. The paper is conveyed toward a nip formed between a photosensitive drum (image carrier) and a transfer member such as a transfer belt and a transfer roller in accordance with the timing. The toner image formed on the photosensitive drum is transferred onto the paper by the paper passing through the nip while being conveyed by the transfer member.

At this time, the paper transport speed of the registration roller is adjusted so that unevenness of the transferred image and color shift do not occur due to the uneven rotation of the registration roller and the uneven rotation of the transport roller upstream of the registration roller. And the paper is appropriately bent between the registration roller and the nip. That is, the transport speed is set so that the transport speed of the fixing device <the transport speed of the image forming unit including the photosensitive drum <the transport speed of the registration roller, so that the transport speed is not affected by the upstream side of the paper transport.

[0004]

By the way, paper is susceptible to the use environment, especially humidity, and when the humidity is high and the surrounding humidity is higher than a predetermined value, the water content of the paper increases, and The surface smoothness deteriorates, and the paper surface becomes uneven. If the paper is transported in the conventional relationship of the transport speed, white spots on the transferred image and wrinkles on the paper will occur due to the unevenness of the paper surface, and the image quality will be degraded.

Therefore, in order to suppress variations in sheet transport accuracy due to moisture, Japanese Patent Application Laid-Open No. 8-262822 discloses a registration roller from a sheet tray in accordance with an output of a humidity sensor attached to an outer wall of an image forming apparatus. It is disclosed that control is performed such as changing the timing of sending the sheet to the paper tray, changing the sheet conveyance speed from the sheet tray to the registration roller, or changing the timing of sending the sheet from the registration roller.

However, if the paper bends between the registration roller and the nip, the unevenness of the paper surface will not be eliminated, so that wrinkles of the paper that occur during the process of the paper passing through the registration roller and the image forming unit, and the whiteness of the transferred image will occur. I cannot cope with the omission.

Accordingly, the present invention has been made in view of the above, and by controlling the conveyance speed of a registration roller in accordance with humidity,
It is an object of the present invention to provide an image forming apparatus that can adjust the bending of a sheet between a registration roller and an image forming unit and obtain a high-quality image that is not affected by moisture.

[0008]

Means for solving the problems according to the present invention are: transfer means comprising a belt or a roller for forming an nip portion between the image bearing member and transferring an image while conveying a sheet; A registration means comprising a belt or a roller for conveying the paper at a predetermined timing toward the printer, and when the conveyance speed by the transfer means is set to be faster than the conveyance speed by the registration means in order to prevent a transfer deviation, etc. A humidity sensor for detecting the humidity of the transfer means is provided, and the relative relationship between the transfer speed by the transfer means and the transfer speed by the registration means is changed according to the humidity.
That is, when the humidity is higher than the predetermined value, the transport speed by the registration unit is equal to or lower than the transport speed by the transfer unit, and when the humidity is lower than the predetermined value, the transport speed by the register unit is equal to or higher than the transport speed by the transfer unit.

As described above, when the humidity is high, the amount of moisture absorption of the paper increases, so that the surface of the paper tends to have irregularities,
At the normal transport speed, the paper is bent between the nip and the registration means, the surface condition of the paper is not improved at all, and the paper passes through the nip and the image is transferred. Then, an image defect occurs. Therefore, as described above, the humidity is detected as a measure of the humidity, and if the humidity is high, the transport speed by the registration unit is made slower than the transport speed by the transfer unit. White spots can be prevented, and wrinkles of the paper can be eliminated, so that the paper can be transported smoothly and the image quality can be kept good.

[0010] By the way, since the degree of moisture absorption of the paper changes due to the humidity and the surface becomes uneven, if the degree of moisture absorption of the paper is directly detected and the transport speed is controlled, the transport according to the surface condition of the paper is performed. And the image quality can be further improved. In order to detect the degree of moisture absorption of the sheet, an image sensor, an optical sensor, or the like that directly detects the surface state of the sheet may be provided upstream of the registration unit in the sheet transport direction. Then, if the humidity is large and the unevenness is large according to the surface condition of the sheet, the transport speed by the registration unit is made slower than the transport speed by the transfer unit. Even if the humidity is high, if the paper does not absorb much moisture, the irregularity is reduced, so that the transfer speed by the transfer means is not reduced.

Further, if there is no unevenness on the surface of the paper, defects such as white spots on the image and wrinkles of the paper do not occur. Therefore, tension is applied to the paper in accordance with the moisture absorption of the paper to smooth the surface condition of the paper. do it. As one of means for smoothing the surface of such a sheet, there is a means for varying the above-mentioned conveyance speed, and the sheet is pulled and tension is applied. Alternatively, a movable guide roller and a deformable guide plate may be provided, and the paper may be moved or deformed in accordance with the moisture absorption of the paper, so that the paper is stretched to eliminate unevenness on the surface.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to 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 an 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. . The platen 1 is located above the platen 111.
11 is supported so as to be openable and closable with respect to the platen 111.
A two-sided automatic document feeder (RADF; Reversing Automat) with a predetermined positional relationship with respect to the upper surface
ic Document Feeder) 112 is mounted.

Further, the automatic two-sided automatic document feeder 112
First, the document is conveyed such that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111,
After the image reading for this one side is completed,
The original is inverted so that the other surface faces the image reading unit 110 at a predetermined position on the original
To be conveyed toward. Then, after the two-sided image reading for one document is completed, the double-sided automatic document feeder 112 discharges this document and performs a double-sided conveyance operation for the next document. The operation of transporting the original and reversing the original is controlled by a control device built in the main body of the copying machine in relation to the operation of the entire copying machine.

The image reading section 110 is arranged below the document table 111 for reading an image of the document conveyed onto the document table 111 by the automatic duplex document feeder 112. The image reading unit 110 includes original scanning bodies 113 and 1 that reciprocate in parallel along the lower surface of the original table 111.
14, an optical lens 115, and a photoelectric conversion element CC
And a D line sensor 116.

The original 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 the reflected light image from the document in a predetermined direction. It reciprocates in parallel at a predetermined scanning speed while maintaining the distance. The second scanning unit 114 is the first scanning unit 113
A second mirror and a third mirror for further deflecting the reflected light image from the document deflected by the mirror toward a predetermined direction are provided, and reciprocate in parallel with the first scanning unit 113 while maintaining a constant speed relationship. Things.

The optical lens 115 reduces the reflected light image from the original document deflected by the third mirror of the second scanning unit 114, and converts the reduced light image into the CCD line sensor 11.
6 to form an image at a predetermined position.

The CCD line sensor 116 photoelectrically converts the formed light image sequentially and outputs it as an electric signal. The CCD line sensor 116 reads a black-and-white image or a color image, and outputs R (red), G (green), B
This is a three-line color CCD that can output line data that is color-separated into each color component of (blue). This CC
The document image information converted into an electric signal by the D-line sensor 116 is further transferred to an image processing unit in the control device and subjected to predetermined image data processing.

An image forming unit 210 is disposed below the image reading unit 110. Under the image forming unit 210, sheets (recording media) P stacked and stored in a sheet tray are separated one by one to form an image. A paper feed mechanism 211 having a plurality of rollers for supplying the paper toward the forming unit 210 is provided. The sheets P separated and supplied one by one are transferred to the image forming unit 2.
The sheet is conveyed to the image forming unit 210 at a timing set by a pair of registration rollers 212 arranged before the ten. Further, the sheet 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.

Below the image forming section 210, a transfer mechanism 213 for performing transfer while transporting a sheet is arranged.
The transfer mechanism 213 includes a driving roller 214 and a driven roller 21.
5, a transport belt 216 stretched so as to extend substantially in parallel with the transport belt 5, and the transport belt 216 is charged by a suction charger (not shown) to electrostatically attract and transport the paper P. I have.

Further, on the downstream side of the conveyor belt 216,
A fixing device 217 for fixing the toner image transferred onto the sheet P is provided. The sheet P passing through the nip between the pair of fixing rollers of the fixing device 217 is
After the transfer direction switching gate 218, the discharge roller 21
9, the paper is discharged onto a paper discharge tray 220 attached to the outer wall of the copying machine body 1.

The switching gate 218 has a path for discharging the sheet P after fixing outside the copying machine main body 1 and the image forming section 210.
And a path for re-supplying the paper P toward. The sheet P whose conveyance direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback conveyance path 221, and is again supplied to the image forming unit 210.

The image forming section 210 includes a first image forming station Pa and a second image forming station P
b, a third image forming station Pc, and a fourth image forming station Pd are arranged side by side from the upstream side in the sheet conveying direction in the vicinity of the upper side of the conveying belt 216.

The transport belt 216 is frictionally driven by a drive roller 214 in a direction indicated by an arrow Z in FIG.
As described above, the sheet P that is fed through the sheet feeding mechanism 211 is carried, and the sheet P is transferred to the image forming stations Pa to Pd.
Sequentially.

Each of the image stations Pa to Pd has substantially the same configuration, and includes photosensitive drums 222a to 222d which are driven to rotate in the direction of arrow F shown in FIG. Around the photoconductor drums 222a to 222d, chargers 223a to 223d for uniformly charging the photoconductor drums 222a to 222d, and electrostatic latent images formed on the photoconductor drums 222a to 222d are developed. Developing devices 224a to 224d, transfer discharging devices 225a to 225d for transferring the toner images on the photosensitive drums 222a to 222d to the paper P, and the photosensitive drum 22
Cleaning devices 226a to 226d for removing toner remaining on the photosensitive drums 222a to 222d
To 222d in order of rotation.

Each of the photosensitive drums 222a to 222d
Above the laser beam scanner unit 227a
To 227d are provided respectively. The laser beam scanner units 227a to 227d include a semiconductor laser element (not shown) that emits dot light modulated according to image data, and a polygon mirror (deflection) for deflecting a laser beam from the semiconductor laser element in the main scanning direction. Apparatus) 240a to 240d and polygon mirror 240a
Lenses 241a to 241d, mirrors 242a to 242d, and fθ lenses 241a to 241d for forming an image of the laser beam deflected by
43a to 243d.

Laser beam scanner unit 227a
Is a pixel signal corresponding to a black component image of a color original image, a laser beam scanner unit 227b is a pixel signal corresponding to a cyan component image of a color original image, and a laser beam scanner unit 227c is a magenta image of a color original image. A pixel signal corresponding to the color component image is input to the laser beam scanner unit 227d, and a pixel signal corresponding to the yellow component image of the color original image is input to the laser beam scanner unit 227d. As a result, the electrostatic latent images corresponding to the color-converted original image information are formed on the respective photosensitive drums 222a to 222d.
Formed on top. Then, black toner is applied to the developing device 227a, cyan toner is applied to the developing device 227b,
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. As described above, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.

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 securely attracted onto the transport belt 216. Is done. On the other hand, a static eliminator 229 is provided almost directly above the drive roller 214 between the fourth image station Pd and the fixing device 217.
An AC current is applied to the neutralizer 229 to separate the paper P electrostatically attracted to the transport belt 216 from the transport belt 216.

In the digital color copying machine having the above-described structure, the control of the paper transport control is performed by the control device in accordance with the timing of the image forming process. Cut sheet-shaped paper is used as the paper P. When the paper P is sent 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 a detection signal output from this sensor, the pair of registration rollers 212 temporarily stop the operation.

The paper P is stored in each image station Pa.
Pd is fed onto the conveyor belt 216 rotating in the direction of arrow Z at the same timing as the image formation of Pd. At this time, since the transport belt 216 has been given a predetermined charge by a suction charger (not shown) as described above, the sheet P is stably maintained without being displaced while passing through the image stations Pa to Pd. Conveyed.

In each of the image stations Pa to Pd, a toner image of each color is applied to each of the photosensitive drums 222a to 222a.
The sheet P is formed on a sheet 222d, is transferred onto a sheet P conveyed by being electrostatically attracted by the conveying belt 216, and is superposed on the surface thereof. When the transfer of the image by the fourth image station Pd is completed, the paper P is sequentially moved from the leading end thereof.
The discharge belt 229 is peeled off from the conveyor belt 216 by the discharging device 229, and is guided to the fixing device 217. Finally, the paper P on which the toner image has been fixed is discharged from the discharge roller 219 onto the paper discharge tray 220.

In the above arrangement, the laser beam scanner units 227a to 227d scan and expose the laser beam by the laser beam so that the photosensitive drum 2 is exposed.
Optical writing to 22a to 222d is performed. However, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used instead of the laser beam scanner unit. The LED head is smaller in size 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 type digital color copying machine which requires a plurality of optical writing units.

Here, as shown in FIG. 2, the photosensitive drums 222a to 222d and the transfer dischargers 225a to 225d
A conveyor belt 216 exists between the conveyor belt 216 and the conveyor belt 216 and the photosensitive drums 222a to 222d, respectively, forming nip portions 300. Then, the paper P separated and supplied one by one from the paper tray by the paper feeding mechanism 211 is timed by the registration roller 212, and the nip portion 3 of the first image forming station Pa is adjusted.
The toner image is transferred from the photoconductor drums 222a to 222d to the paper when the paper is conveyed toward 00 and passes through each nip 300. Note that the distance from the registration roller 212 to the nip 300 is smaller than the length of the sheet P in the transport direction.

At this time, the conveying speed of the sheet P by the registration roller 212, that is, the peripheral speed Vr of the registration roller
Is faster than the transport speed Vb (<Vr) of the transport belt 216 so that unevenness and color shift of the transfer image do not occur due to the uneven rotation of the registration roller 212 or the unevenness of the rotation of the transport roller upstream of the resist roller 212. Is set. Therefore, the sheet P bends upward between the registration roller 212 and the nip 300. However, when the surrounding humidity at which the color copier is used is high, the paper P absorbs moisture, causing wrinkles and corner breaks during conveyance, and white spots on the transferred image when passing through the nip 300. I do. Therefore, in order to eliminate the adverse effect of humidity, a humidity sensor 301 for detecting the surrounding humidity is provided, and the control device controls the transfer speed Vb of the transfer belt 216 and the registration roller 212 according to the humidity.
Is performed to change the relative relationship with the transport speed Vr.

As the humidity sensor 301, a general humidity sensor for detecting the humidity of the atmosphere is used, and is disposed immediately before the resist roller 212 on the conveyance path on the upstream side. As described above, when the humidity sensor 301 is disposed inside the copier main body, not outside, and near the position where image formation is actually performed, the degree of moisture absorption of the paper P is reliably detected from the humidity. And the reliability of the transport control is improved.

Next, a method of determining the transport speed based on the humidity will be described. The transport speed Vb of the transport 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 drive of the motor for rotating the registration roller 212 is controlled so that Vr> Vb as usual since the influence of the humidity is not exerted. When the humidity is equal to or higher than the predetermined value, the peripheral speed Vr of the registration roller 212 is controlled so as to decrease so that Vr ≦ Vb. As described above, when the humidity is low, the normal transport control is performed, so that the sheet P bends as shown in FIG.
The paper P is pulled by the speed difference between the registration roller 16 and the registration roller 212, and the bending is reduced as compared with the case where the normal conveyance is performed as shown in FIG.

More specifically, as shown in FIG.
In step 1, it is determined whether or not the humidity is 70% or more.
If above, go to STEP2, if less than 70%, STE
Proceed to P4. In STEP 2, it is determined whether or not the humidity is 80% or more.
If it is less than%, the flow proceeds to STEP5.

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 STEP4,
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% is set. The peripheral speed Vr of the registration roller 212 is set according to the humidity as described above,
The relative relationship between the transport speed Vr of the registration roller 212 and the transport speed Vb of the transport belt 216 is varied.

Therefore, when the humidity is high, the paper P
Since the speed at the time when the front end of the sheet passes through the nip portion 300 is equal to or higher than the speed at which the rear end is sent out by the registration roller 212, the bending becomes small.
The paper P is pulled by the registration rollers 21 with both sides being pulled.
2 and the nip 300. Therefore, even if the paper P absorbs moisture and has irregularities on the surface, the paper P is stretched, so that the irregularities are reduced, the wrinkles of the paper P are not generated, and white spots on the image can be prevented, and good image quality can be obtained. can get.

When the humidity is low, the speed ratio is 100.
Although set to 5%, the deflection of the paper P between the registration roller 212 and the nip 300 is appropriate, and the paper P is not pulled by both, and a transfer deviation or the like occurs when transferring an image. Absent. However, when the speed ratio is 100.
If it is set to 5% or more, the bending between the two becomes unnecessarily large, and the paper jam or the paper P
The speed ratio is 10
0.5% is the upper limit.

(Experimental Example) The installation environment of the image forming apparatus was set to a room temperature of 35 ° C. and a humidity of 85%, and the speed ratio Vr between the peripheral speed Vr of the registration roller 212 and the transport speed Vb in the image forming unit 210.
The white spot state of the image when / Vb was varied from 98.5% to 100.5% was confirmed. Table 1 shows the results. In Table 1, “x” indicates a level at which white spots occurred, “Δ” indicates a level at which white spots slightly occurred, and “○” indicates a level at which no white spots occurred.

[0041]

[Table 1] From Table 1, when the humidity is high, the paper P at a speed ratio of 99% or less
It can be seen that the occurrence of white spots in the image can be suppressed by transporting According to the experimental results, good results were obtained up to the speed ratio of 98.5%. However, if the speed ratio was excessively reduced, the paper P was pulled too much between the registration roller 212 and the nip portion 300, causing problems such as transfer deviation. Speed ratio is 9
8.5% is the lower limit.

In another embodiment, the surface of the sheet P may be smoothed by applying tension to the sheet P in accordance with the moisture absorption of the sheet P. Therefore, as shown in FIG. The guide rollers 302a and 302b are provided between the registration roller 212 and the nip 300, and the guide rollers 302a and 302b are arranged in accordance with the degree of moisture absorption of the sheet P, for example, humidity.
The sheet P may be stretched between the guide rollers 302a and 302b by moving the sheet 302b in the approaching direction so as to eliminate unevenness on the surface.

It should be noted that the present invention is not limited to the above embodiment, and it goes without saying that many modifications and changes can be made to the above embodiment within the scope of the present invention. In the present embodiment, an example of application to a color copying machine has been described.
The present invention can be applied to a monochrome copying machine, a printer, and a facsimile. Further, a transfer roller may be used in place of the transfer belt, a nip portion is formed between the transfer roller and the photosensitive drum, and the transfer is performed while the sheet is transferred by the transfer roller. Further, a belt may be used instead of the registration roller.

Since the speed ratio between the transport speed of the registration roller and the transport speed of the transport belt may be varied in accordance with the humidity, the peripheral speed of the resist roller is kept constant, and the transport speed of the transport belt is high. Sometimes it is fast and when the humidity is low it may be slow. In this case, it is necessary to change the speed of the image forming process according to the transport speed.

[0045]

As is apparent from the above description, according to the present invention, even if the surface condition of the paper is deteriorated due to high humidity,
The paper is pulled from the registration means to the nip by changing the paper conveyance speed, for example, to reduce the unevenness of the surface that occurs when the paper absorbs moisture. Therefore, since the surface of the paper becomes smooth, white spots at the time of image transfer can be prevented, and the image quality can be improved. In addition, the occurrence of wrinkles on the sheet can be prevented, and the sheet 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 portion when humidity is low.

FIG. 3 is a detailed view between a registration roller and a nip portion when humidity is high.

FIG. 4 is a flowchart for setting a transport speed according to humidity.

FIG. 5 is a detailed view of a registration roller and a nip portion according to another embodiment.

[Explanation of symbols]

 212 registration roller 216 transport belt 300 nip 301 humidity sensor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masashi Hirai 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 2H027 DA14 DE10 ED16 ED17 ED24 EE03 2H032 AA05 BA15 CA00 CA14 3F102 AA06 AB01 DA08 FA04 FA08 9A001 BB06 HH34 HZ23 JZ35 KK42

Claims (6)

[Claims] A transfer unit configured to form a nip between the image carrier and transfer an image while transporting the paper; a registration unit configured to transport the paper at a predetermined timing toward the nip; Image forming apparatus, comprising: a moisture detector for detecting the degree of moisture absorption of the image forming apparatus; and control means for changing a relative relationship between the transport speed by the transfer means and the transport speed by the registration means in accordance with the moisture absorption of the sheet. apparatus. 2. The image according to claim 1, wherein a humidity sensor for detecting the humidity of the atmosphere is used as the humidity detector, and the humidity sensor is disposed on a conveyance path upstream of the registration unit in the sheet conveyance direction. Forming equipment. 3. The image forming apparatus according to claim 1, wherein when the humidity is higher than a predetermined value, the conveying speed by the registration unit is set to be lower than the conveying speed by the transfer unit. 4. The image forming apparatus according to claim 1, wherein when the humidity is lower than a predetermined value, the conveying speed by the registration unit is set to be higher than the conveying speed by the transfer unit. 5. The image forming apparatus according to claim 1, wherein the transport speed of the registration unit is variable within a range of 98.5% to 100.5% of the transport speed of the transfer unit. 6. A transfer means for forming an nip between the image bearing member and transferring an image while conveying a sheet, a registration means for conveying the sheet at a predetermined timing toward the nip, and a sheet. An image forming apparatus, comprising: a moisture detector for detecting the degree of moisture absorption of the sheet; and sheet correction means for applying tension to the sheet in accordance with the moisture absorption of the sheet to smooth the surface state of the sheet.