JP2004109165A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a flicker level in automatic double-sided printing by using a switchback system. <P>SOLUTION: The image forming apparatus having a switchback system automatic double-sided mechanism performs control so that temperature control gain is lowered for a fixed period in the case of transiting from inter-paper controlled temperature between paper sheets in switchback to ordinary controlled temperature when next paper advances to a fixing device. Since the temperature control gain is lowered only in automatic double-sided printing so as to be advantageous in terms of fixing property, the flicker level is improved without sacrificing the fixing property. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus having a heat fixing heater for toner.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fixing heater has been used in an image forming apparatus (hereinafter, printer) to fix a toner image on paper.
[0003]
When a printer requests printing from a connected external device, the printer feeds and conveys the paper, performs an image forming operation according to a predetermined electrophotographic process, and conveys the paper on which the toner image is placed to a fixing heater. The printer controls the fixing heater to a fixed temperature to heat and fix.
[0004]
In particular, in recent years, the number of opportunities for performing double-sided printing has been increasing in order to make effective use of paper resources even in view of the environment. Among them, printers equipped with a compact automatic double-sided mechanism that can provide a low-cost double-sided printing mechanism with a small installation area are increasing.
[0005]
In FIG. 1, a sheet material stacked on a paper cassette 103 of a laser beam printer main body 101 is fed by a cassette sheet feeding roller 103a, and a conveying path of an image forming section of the sheet material in the printer by a pair of conveying rollers 103b and 103c. The sheet is fed onto L2, and the sheet leading edge detection sensor S2 detects the image timing and the positions of the leading edge and the trailing edge of the sheet material. The registration roller pair 103c adjusts the leading end parallelism of the sheet material, and conveys the sheet material to the transfer roller 105d and the photosensitive drum 105a. The sheet material on which the toner has been transferred by the transfer roller 105d and the photosensitive drum 105a is conveyed to a pressure roller 106a, a fixing film 106b, and a ceramic heater 106c for fixing the toner to the sheet material, and after being pressure-fixed, is discharged face-up. After passing through the paper roller pair 107, if the recording is one-sided, the paper is discharged to the paper discharge tray 114 by rotating the face-down paper discharge roller pair 110 driven by a paper discharge motor (not shown) forward.
[0006]
In automatic duplex printing, the sheet material on which the toner image is formed on the first surface is fixed by the fixing device 106, and then discharged face-down until the rear end of the sheet material passes the face-up discharge roller 107. By rotating the roller pair 110 forward by a paper discharge motor (not shown), the face-down discharge roller pair 110 is reversed at an appropriate timing after the rear end of the sheet material passes through the face-up paper discharge roller. The sheet is guided to the reversing sheet conveyance path L3 by the face-down sheet ejection roller pair 110, is guided to the re-feeding sheet conveyance path L4 by the reversing guide roller 111, and the reversing sheet introduction detection sensor S5, the reversing sheet conveyance roller pair 112, The sheet enters the double-sided printing conveyance path section 102 in the order of the paper sensor S6 and the reverse paper re-feeding roller pair 113, and again passes through the registration roller 103c. After being guided to the image forming unit paper conveyance path L2 and forming the image of the second surface of the sheet material in the same manner as the printing of the first surface described above, the face-down discharge roller pair 110 is moved in the same manner as in the case of single-sided recording. By rotating the paper forward, the paper on which double-side recording has been performed is discharged to the face-down discharge tray 114.
[0007]
In this printer, one sheet is recorded in the image forming unit paper conveyance path L2 and one sheet of the first-side recorded paper is simultaneously recorded in the conveyance path from the reversing paper conveyance path L3 to the re-feeding paper conveyance path L4. The image forming is performed and the reverse re-feeding is carried out at the same time. In this configuration, when performing single-sided continuous printing, it is possible to increase the throughput with a short sheet interval. However, when performing automatic double-sided printing, the face-down sheet discharge unit 109 is used to perform a switchback tray. Therefore, in the case of automatic double-sided printing, it is necessary to prevent a collision between the sheet on which the switchback reversal is performed and the next sheet by making a large space between the sheets after the first side. As shown in FIG. 2, immediately after printing on the front side (first side), it is necessary to open a gap for switching back. Since it is not necessary to perform switchback reversal after printing the back surface (second surface), the paper interval may be small.
[0008]
When a large sheet gap is opened, such as after the front side (first side), the amount of heat carried by the sheet is lost, and the target sheet gap temperature is lowered to prevent the fixing unit from being overheated and causing hot offset or the like. Immediately before the paper reenters the fixing device, control is performed to return the target temperature to the normal target temperature.
[0009]
As shown in FIGS. 4 (a) and 4 (b), when performing temperature control, the power supplied to the heater is changed by changing the power supplied to the heater depending on how many of the control blocks (all 15 waves) are supplied. The target temperature is controlled. As shown in FIG. 5, the difference ΔT between the thermistor detected temperature and the target temperature is calculated during the execution of the fixing temperature control, and when the temperature difference ΔT is not 0, the temperature control gain G is calculated by a certain equation. On the other hand, if the thermistor detection temperature is higher than the target temperature, the wave number N-G1 obtained by subtracting the gain G1 from the immediately preceding fixing temperature harmonic number N, that is, the power supplied to the heater is reduced, and the temperature is lowered. Conversely, if the thermistor detection temperature is lower than the target temperature, the fixing temperature harmonic number N + G2, which is obtained by adding G2 calculated from a fixed equation to the immediately preceding fixing temperature harmonic number N, that is, the power supplied to the heater is increased to increase the temperature. Wait to go up.
[0010]
This gain G has a larger value as the temperature difference ΔT is larger.
[0011]
[Problems to be solved by the invention]
However, when the target temperature is changed when the paper interval becomes large during the above-described conventional automatic double-sided printing, the power fluctuation becomes large and flicker (a phenomenon such as the incandescent lamp connected to the same power outlet flickering due to the power change) occurs. It was getting worse.
[0012]
To prevent this, if the gain calculation formula is changed so that the gain becomes smaller when the target temperature is changed, the rise in temperature will be worse, and the temperature will not rise enough by the time the paper enters the fixing nip. As a result, a fixing defect at the leading end of the sheet may occur.
[0013]
[Means for Solving the Problems]
In order to solve the above problem, an image forming apparatus according to the present invention has the following configuration, and performs the following control.
[0014]
In an image forming apparatus having a switchback type automatic double-sided apparatus, when the interval between sheets is increased after printing on the first side of the automatic duplex printing, the target temperature is decreased from the normal temperature to the interval between sheets, and Usually, the gain of the temperature control is reduced for a certain period when the temperature is raised to the target temperature.
[0015]
By controlling as described above, in the present invention, only the gain at the time of automatic double-sided is advantageous in that the fixing property is advantageous because the paper passes through the fixing device twice while securing the fixing property during single-sided printing, It is possible to improve flicker during automatic double-sided printing while securing the fixing property.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
(First embodiment)
1 and 3 are diagrams illustrating an embodiment of the present invention.
[0017]
In FIG. 1, a sheet material stacked on a paper cassette 103 of a laser beam printer main body 101 is fed by a cassette sheet feeding roller 103a, and a conveying path of an image forming section of the sheet material in the printer by a pair of conveying rollers 103b and 103c. The sheet is fed onto L2, and the sheet leading edge detection sensor S2 detects the image timing and the positions of the leading edge and the trailing edge of the sheet material.
[0018]
The registration roller pair 103c adjusts the leading end parallelism of the sheet material, and conveys the sheet material to the transfer roller 105d and the photosensitive drum 105a. The sheet material on which the toner has been transferred by the transfer roller 105d and the photosensitive drum 105a is conveyed to a pressure roller 106a, a fixing film 106b, and a ceramic heater 106c for fixing the toner to the sheet material, and after being pressure-fixed, is discharged face-up. After passing through the paper roller pair 107, if the recording is one-sided, the paper is discharged to the paper discharge tray 114 by rotating the face-down paper discharge roller pair 110 driven by a paper discharge motor (not shown) forward.
[0019]
In automatic duplex printing, the sheet material on which the toner image is formed on the first surface is fixed by the fixing device 106, and then discharged face-down until the rear end of the sheet material passes the face-up discharge roller 107. By rotating the roller pair 110 forward by a paper discharge motor (not shown), the face-down discharge roller pair 110 is reversed at an appropriate timing after the rear end of the sheet material passes through the face-up paper discharge roller. The sheet is guided to the reversing sheet conveyance path L3 by the face-down sheet ejection roller pair 110, is guided to the re-feeding sheet conveyance path L4 by the reversing guide roller 111, and the reversing sheet introduction detection sensor S5, the reversing sheet conveyance roller pair 112, The sheet enters the double-sided printing conveyance path section 102 in the order of the paper sensor S6 and the reverse paper re-feeding roller pair 113, and again passes through the registration roller 103c. After being guided to the image forming unit paper conveyance path L2 and forming the image of the second surface of the sheet material in the same manner as the printing of the first surface described above, the face-down discharge roller pair 110 is moved in the same manner as in the case of single-sided recording. By rotating the paper forward, the paper on which double-side recording has been performed is discharged to the face-down discharge tray 114.
[0020]
At this time, in the flowchart of FIG. 3, it is checked whether double-sided printing is being performed (301). In the case of single-sided printing, a normal temperature control gain is used (302). If double-sided printing is being performed, the process stands by until the paper enters the fixing nip 120 mm (303). When the paper reaches 120 mm before entering the fixing nip, the target temperature is switched as shown in FIG. 2 (304), and at the same time, the temperature control gain is reduced to half the gain G / 2 (305). When the sheet reaches 60 mm before the paper enters the fixing nip (306), the temperature control gain is returned to the original gain G (307).
[0021]
As described above, according to the present invention, by controlling as described above, in the present invention, while the fixing property at the time of one-sided printing is ensured, the sheet is passed twice through the fixing device and the fixing property is advantageous during automatic double-sided printing. Since only the gain is reduced, it is possible to improve flicker during automatic double-sided printing while securing the fixing property.
[0022]
In the present invention, in an image forming apparatus having a switchback type automatic double-sided apparatus, when the interval between the sheets is increased after printing the first side of the automatic duplex printing, when the target temperature is lowered from the normal temperature to the interval between the sheets, In addition, the gain of the temperature control is reduced for a certain period when the temperature is increased from the sheet interval temperature to the normal target temperature.
[0023]
By controlling as described above, in the present invention, only the gain at the time of automatic double-sided is advantageous in that the fixing property is advantageous because the paper passes through the fixing device twice while securing the fixing property during single-sided printing, It is possible to improve flicker during automatic double-sided printing while securing the fixing property.
[0024]
【The invention's effect】
In the present invention, in an image forming apparatus having a switchback type automatic double-sided apparatus, when the interval between the sheets is increased after printing the first side of the automatic duplex printing, when the target temperature is lowered from the normal temperature to the interval between the sheets, Further, the gain of the temperature control is reduced for a certain period when the temperature is raised from the sheet interval temperature to the normal target temperature.
[0025]
By controlling as described above, in the present invention, only the gain at the time of automatic double-sided is advantageous in that the fixing property is advantageous because the paper passes through the fixing device twice while securing the fixing property during single-sided printing, It is possible to improve flicker during automatic double-sided printing while securing the fixing property.
[Brief description of the drawings]
FIG. 1 is an image forming apparatus according to an embodiment of the present invention.
FIG. 2 illustrates an embodiment of the present invention.
FIG. 3 is a flowchart illustrating an embodiment of the present invention.
FIG. 4 is a diagram illustrating a conventional example. FIG. 5 is a flowchart illustrating a conventional example.
101 laser beam printer main body 102 double-sided conveying path section 103 paper cassette 104 laser scanner unit 105 process cartridge 106 thermal fixing device 107 ... Face-up discharge roller pair 108 ... Face-up tray 109 ... Face-down discharge unit 110 ... Face-down discharge roller pair 111 ... Reversing paper guide roller 112 ... ..Reverse paper transport roller pair 113... Reverse paper re-feed roller pair

Claims (3)

A fixing unit for fixing a toner image on a sheet, a temperature detecting unit for detecting a temperature of the fixing unit, a control unit for performing temperature control based on temperature information of the fixing unit, and controlling the fixing unit to a specified target temperature. Control means;
Paper transport means, paper position detection means for detecting a paper transport position,
In an image forming apparatus having an automatic double-sided printing mechanism that switches the sheet conveyance direction by turning over the sheet on which one-side recording has been performed,
The image forming apparatus according to claim 1, wherein the control unit changes the gain of the temperature control according to the information of the sheet transport position detecting unit when performing automatic double-sided printing using the automatic double-sided printing mechanism. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the automatic double-sided printing mechanism performs switchback using a single-sided paper discharge unit. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the control unit changes the gain of the temperature control according to information that the first side of the automatic double-sided printing is being printed or the second side is being printed.

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