JPH09288432A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deflection caused by the left and right deviation of recording paper by moving a nip position formed by a pair of fixing rollers in accordance with deviation detected by a detecting means. SOLUTION: A skew sensor is installed on the upstream side of the carrying path of a fixing device 7 and in the vicinity of the exist of a transferring part 5. The skew sensors are installed at two points so as to be a left skew sensor 15a and a right skew sensor 15b. That the top end of the recording paper passes the right skew sensor 15a is detected, and that it passes the left skew sensor 15a delaying from it is detected. The left and right deviation θ of the top end of the recording paper is deduced from a lag time, and is transmitted to the movement control part of the fixing device 7, so that the fixing device 7 is moved so as to position at a point I' deviated by the quantity θ from the defined position I of a nip. Thus, the nip position of the pair of the fixing rollers is moved in accordance with the left and right deviation of the recording paper, the entire width of the top end of the recording paper is simultaneously caught by the nip.

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 facsimile and a printer.

[0002]

2. Description of the Related Art The basic structure of an image forming apparatus comprises a charger, a photoconductor, a developing unit, a resist roller, a transfer section, a cleaning unit, a fixing device, an optical reading section and the like. In the image process, first, the surface of the photoconductor is uniformly charged by a charger, and light is applied to a part other than the image part from the writing part based on the information obtained by the optical reading part to form an electrostatic latent image on the photoconductor. To form. Next, in the developing unit, toner charged to the opposite polarity to the electrostatic latent image is attached to the electrostatic latent image to form a visible image. Then, the recording paper output from the paper supply unit is conveyed to the photoconductor at timing by the registration rollers. Then, an electric charge having a polarity opposite to the charging polarity of the toner on the photoconductor is applied from the transfer portion located on the back surface of the recording paper, and the toner is transferred to the recording paper by electrostatic force. The recording paper carrying the transferred toner image is conveyed to a fixing device and enters a fixing step. The fixing device has a fixing roller having a built-in heat source and a pressure roller in pressure contact with the fixing roller, and these rollers are generally called a fixing roller pair. The fixing device is maintained at a high temperature in order to sufficiently fuse the toner carried on the recording paper to the recording paper, and the recording paper carrying the toner image is formed by the fixing roller and the pressure roller. When passing through the nip, it is fixed by heat and pressure. After the transfer, the electric charge remaining on the photoconductor is removed by a static eliminator, and the residual toner left on the photoconductor without being transferred is removed when passing through the cleaning unit.

[0003]

In the fixing device of the image forming apparatus as described above, when the recording paper is fed in a curved state when reaching the fixing roller pair, the paper is transferred between the transfer portion and the fixing portion. There is a bias of. This means that when the leading edge of the recording paper enters the nip portion of the fixing roller pair, one of the leading edges of the recording paper reaches the nip portion before the other, and the side that arrives later is between the fixing portion and the transfer portion. It will be in a bent state. If this bent state deteriorates, the recording paper will have creases or wrinkles, or it will contact the fixing roller before it reaches the nip, resulting in a so-called blank image, or by touching the fixing entrance guide plate and unfixed image It rubs and produces an abnormal image.

[0004]

In order to solve the above-mentioned problems, the present invention has a registration roller for timing the recording paper sent from the paper feeding unit and sending it to the image forming unit,
In an image forming apparatus having a fixing roller pair for fixing a recording sheet carrying an unfixed image transferred by the transfer section of the image forming section, the image forming apparatus is being conveyed downstream of the registration roller and upstream of the fixing roller pair. And an image forming apparatus provided with a moving means for moving the nip position formed by the fixing roller pair according to the amount of deviation detected by the detecting means. Achieve by providing.

[0005]

According to the image forming apparatus configured as described above, even if the recording paper is left / right misaligned upstream of the fixing device, the misalignment amount is detected before reaching the nip position, and the nip position is detected according to the misalignment amount. Is moved and the recording paper reaches the nip, no lateral displacement occurs with respect to the nip.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the basic configuration of the image forming apparatus includes a charger 1, a photoconductor 2, a developing unit 3, a registration roller 4, a transfer unit 5, a cleaning unit 6, a fixing device 7, an optical reading unit, and the like. ing. In the image process, first, the surface of the photoconductor 2 is uniformly charged by the charger 1.
Writing unit (not shown) based on the information obtained by the optical reading unit
Light is applied to a portion other than the image portion to form an electrostatic latent image on the photoconductor 2. Next, in the developing unit 3, the toner charged to the opposite polarity to the electrostatic latent image is attached to the electrostatic latent image to form a visible image. Then, the recording paper output from the paper supply unit 9 is conveyed to the photoconductor 2 with the timing set by the registration rollers 4. Then, an electric charge having a polarity opposite to the charging polarity of the toner on the photoconductor 2 is applied from the transfer portion 5 located on the back surface of the recording paper, and the toner is transferred to the recording paper by electrostatic force. The recording paper carrying the transferred toner image is conveyed to the fixing device 7 and enters a fixing step. The fixing device 7 includes an upper guide plate 12, a lower guide plate 13, a fixing roller 10 having a built-in heat source, a pressure roller 11 in pressure contact with the fixing roller 10, a pair of paper discharge rollers 14, and the like. The fixing device 7 is maintained at a high temperature in order to sufficiently fuse the toner carried on the recording paper to the recording paper. The recording paper carrying the toner image is fixed on the fixing roller 1.
When passing through the nip portion formed by 0 and the pressure roller 11, the toner is fixed by heat and pressure. After the transfer, the charge remaining on the photoconductor 2 is removed by a charge remover (not shown), and the residual toner left on the photoconductor 2 without being transferred is removed when passing through the cleaning unit 6. A skew sensor 15 is installed upstream of the transfer path of the fixing device and near the exit of the transfer section.

Next, the left / right deviation between the skew sensor 15 and the recording paper will be described. The skew sensor 15 is shown in FIG.
Like the left skew sensor 15a and the right skew sensor 1
It is installed in two places like 5b. Then, it is detected that the leading edge of the recording paper has passed over the right skew sensor 15b, and then, after a delay, it has passed over the left skew sensor 15a. From this delay time, the left-right deviation amount θ of the leading edge of the recording paper is calculated, and this is transmitted to the movement control section of the fixing device 7 so that the fixing device 7 is moved from the prescribed position I of the nip by θ.
Move it so that it is located at the offset I '. Although not shown, this moving means may be configured such that the right side of the fixing device 7 is a fulcrum and the left side is moved by a motor. in this way,
Since the nip position of the fixing roller pair moves in accordance with the lateral displacement of the recording paper, the entire width of the leading edge of the recording paper is simultaneously added to the nip, so that the recording paper is stably conveyed.

Here, when the image forming operation is continuously performed, the next recording sheet is controlled to return to the normal position I before being detected by the skew sensor 15, so that the next recording sheet is recorded. The moving distance of the nip with respect to the deviation amount θ ′ can be easily calculated, and the movement becomes easy. Therefore, it is possible to easily cope with the difference in the left-right deviation for each conveyed recording sheet.

Further, by returning the nip to the normal position I while the recording paper is present in the nip, it is possible to convey the recording paper without any left / right misalignment. However, in this case,
There is no other limitation as long as it is only for correcting the left / right deviation of the recording paper, but in order to prevent the transfer deviation on the recording paper and the stress on the recording paper between the transfer and the fixing, the rear end of the recording paper is a transfer means. It is desirable to do it after it is not affected by.
For example, as shown in FIG. 3, the movement control unit reads the information from the recording paper size detecting unit and the information from the skew sensor 15, and when the control unit determines that there is no recording paper in the transfer unit. It can be realized by operating the motor so as to return to the normal position I. Further, a paper discharge roller pair 14 is provided downstream of the fixing roller pair. When returning the nip to the normal position with the recording paper sandwiched in the nip, there is no problem when the fixing roller pair and the paper discharge roller pair 14 move at the same time as in the above-described embodiment, but the paper discharge is performed. When the roller pair 14 is provided outside the fixing device or when only the fixing roller pair is moved, the relationship of the holding force of the recording material between the fixing roller pair and the paper discharge roller pair 14 is increased. However, the paper holding force of the fixing roller pair is considerably higher than the paper holding roller pair 14 holding force (to the extent that one sheet of recording paper is conveyed), and the paper ejection roller pair 14 has a slightly higher conveyance speed. Since the recording paper is slightly slipped between the pair of paper ejection rollers 14 due to, the lateral deviation amount is corrected and sent to the paper ejection unit without affecting the recording paper itself or the image quality. Further, if the sheet is discharged without any left-right misalignment in this way, it is possible to smoothly perform subsequent post-processing devices such as a double-sided conveyance device, a sorter, a stapler device, a finisher, and a paper folding device. .

It goes without saying that the moving means, the left / right deviation detecting means, the installation position and the like of the present invention are not limited to those in the above-mentioned embodiment.

[0011]

According to the present invention, when the recording paper reaches the nip of the pair of fixing rollers even if the recording paper is displaced laterally upstream of the fixing device, the leading end of the recording paper reaches the nip at the same time over the entire width. Therefore, it is possible to prevent the bending caused by the lateral displacement of the recording paper.

[0012]

[Brief description of drawings]

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

FIG. 2 is a top view of the vicinity of the fixing unit according to the exemplary embodiment of the present invention.

FIG. 3 is a control block diagram of the embodiment of the present invention.

[Explanation of symbols]

 4 Registration Roller 5 Transfer Part 7 Fixing Device 10 Fixing Roller 11 Pressure Roller 14 Paper Ejection Roller Pair 15 Skew Sensor

Claims (3)

[Claims] 1. A registration roller for feeding a recording sheet sent from a sheet feeding section to an image forming section at a timing, and fixing a recording sheet carrying an unfixed image transferred by a transfer section of the image forming section. In an image forming apparatus having a pair of fixing rollers, a left / right deviation detecting unit for detecting a left / right deviation amount of a leading edge of a recording sheet being conveyed is provided downstream of the registration rollers and upstream of the fixing roller pair. An image forming apparatus comprising: a moving unit that moves a nip position formed by the pair of fixing rollers in accordance with the amount of deviation detected in Step. 2. The image forming apparatus according to claim 1,
An image forming apparatus, wherein after the entire width of the leading edge of a recording paper reaches the nip position, the nip position is returned to the normal position before the next recording paper reaches the detection means. 3. The image forming apparatus according to claim 1, wherein the nip is formed after the trailing edge of the recording sheet passes through the transfer section and before the trailing edge of the recording sheet finishes passing through the fixing roller pair. An image forming apparatus that returns a position to a normal position.