JPH05297759A - Fixing device - Google Patents

Abstract

PURPOSE:To uniformize the fixation of developer on a wide sheet when the wide sheet is allowed to pass after a narrow sheet. CONSTITUTION:A fixing device 11 which fixes the developer by heating a sheet material while it is held and carried is provided with a heating roller 21, a pressuring roller 22 which press-contacts with the roller 21, a pressuring device 25 which presses at least the center part and both end parts of the roller 22, temperature detecting means 24a, 24b and 24c which detect the temperature of at least the center part and both end parts of the heating roller, and a controller 50 which controls the device 25 to weaken the pressuring force of the narrow sheet non-passing part of the roller 21 when the temperature of the narrow sheet non-passing part is higher than that of a narrow sheet passing part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for heating and fixing a developer transferred to a sheet material such as paper in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art Conventionally, as the above-mentioned fixing device, a heating roller having a built-in heater and a pressure roller which comes into pressure contact with the heating roller are provided, and the sheet material is sandwiched and conveyed by the heating roller and the pressure roller. It is known to heat and fix the developer adhering to the sheet material. Further, the length of the roller is slightly longer than, for example, the vertical size of the A3 plate or the vertical size of the A4 plate, and only a sheet having a maximum width equal to or smaller than the size can be fed.

[0003]

However, when a narrow sheet is continuously passed through the fixing device, the heating roller does not contact the sheet (hereinafter referred to as "non-sheet passing portion"). Is higher than the temperature of the portion that contacts the sheet (hereinafter referred to as the "sheet passing portion"). Therefore, there is a problem that if a sheet of a size wider than the narrow size is passed after the sheet of a narrow size is passed, a difference in fixing rate occurs due to the temperature difference, resulting in poor image quality.

Therefore, conventionally, a fixing device in which the heater of the heating roller is divided in the axial direction so that the temperature can be partially adjusted and a fixing device provided with a cooling device have been proposed, but the responsiveness is poor. However, there is a problem that it is impossible to sufficiently improve the fixability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a fixing device according to the first invention is a heating roller having a heater and capable of rotating.
A pressure roller rotatably provided in parallel with the heating roller, a pressure device that presses at least the central portion and both ends of the pressure roller toward the heating roller, and at least the central portion of the heating roller. When the narrow sheet non-sheet passing portion of the heating roller is at a higher temperature than the narrow sheet passing portion by the temperature detecting means for detecting the temperature of both end portions and the temperature detecting means, the pressurizing device is driven. And a control device for weakening the pressure applied to the narrow sheet non-sheet passing portion.

In the fixing device according to the second aspect of the present invention, at least a heating roller having a heater, which is rotatable and driven, a pressure roller rotatably provided in parallel with the heating roller, and at least the pressure roller. A pressure device that presses the central portion and both end portions toward the heating roller, and temperature detection means that detects the temperature of the narrow sheet passing portion of the heating roller,
Calculation means for calculating the temperature of the narrow sheet non-sheet passing portion based on the sheet size of the narrow sheet, the number of continuous prints, and the elapsed time after the end of the printing process, and the narrow sheet non-sheet passing portion is a narrow sheet passing portion. And a control device for driving the pressurizing device to weaken the pressure applied to the non-sheet passing portion of the narrow sheet when the temperature is higher than the above.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the fixing device according to the present invention is applied to a printer will be described below. FIG. 1 is a sectional view showing a schematic configuration of a printer having a fixing device according to the present invention. In this printer 1, the host computer 2
The laser generator 3 is operated based on the image information input from the electrostatic latent image is formed on the outer peripheral surface of the photoconductor 5 charged by the charging device 4, and the electrostatic latent image is developed by the developing device 6. Is visualized as a toner image. A sheet, which is a transfer material, is supplied from a paper feeding unit 7, the toner image is transferred by a transfer device 8, and then separated from the photoconductor 5 by a separating device 9. Subsequently, the sheet is conveyed by the conveying device 10 to the fixing device 11, where the toner image is heated and fixed, and then ejected to the paper ejection unit 12.

The fixing device 11 is, as shown in FIG.
An upper heating roller 21 and a lower pressure roller 22 are provided. The heating roller 21 is a hard roller, is provided with a heater 23 at the center as a heating means, and is rotated in a direction of an arrow X by a motor (not shown). Are detected by the thermistors 24a, 24b, 24c. The pressure roller 22 is a soft roller whose outer peripheral portion is covered with rubber, and is arranged in parallel with the heating roller 21,
It is pressed against the heating roller 21 by the pressing device 25,
The heating roller 21 is driven to rotate.

The pressure device 25 includes a central pressure device 26 for pressing the central portion of the pressure roller 22, and a pressure roller 22.
End pressurizing devices 27 and 28 for pressing both ends of the. In the central pressure device 26, the backup roller 31 is disposed below the pressure roller 22 in parallel with the pressure roller 22, and is supported by the support base 32. The support 32 is provided with the shaft 3 of the cylinder 33 arranged vertically.
It is fixed to No. 4 and moves up and down according to the amount of hydraulic oil supplied from the pump 35 to the cylinder 33, and the pressure contact force of the backup roll 31 with respect to the pressure roller 22 can be adjusted. In the end pressurizing devices 27 and 28, the support bases 36 and 40 are arranged in the vertical direction of the cylinder 3
It is fixed to the shafts 38 and 42 of 7, 41 and the pump 3
The end portion of the heating roller 21 is moved up and down according to the amount of hydraulic oil supplied from 9, 43.

FIG. 3 shows a control device 50 of the fixing device. In this control device 50, a CPU 52 is connected to a RAM 52, a heater 23 and a ROM 53 which stores control programs for the pumps 35, 39 and 43. Also, C
The thermistors 24a to 24c are connected to the PU 51 via an input port (not shown), and are connected to the heater power supply 54 and the pump driver 55 via an output port (not shown).

The operation of the fixing device 11 based on the control device 50 will be described. In the fixing device 11, the heating roller 21 rotates in the direction of arrow X based on the driving of a motor (not shown), and a current is applied from the heater power supply 54 to the heater 23 to heat the heating roller 21. In addition, the pressurizing device 25
The pumps 35, 39, 43 of the cylinders 33, 37,
The hydraulic oil is supplied to each of the pressure rollers 41, and the pressure roller 22 is pushed upward at its central portion and both end portions to heat the heating roller 2.
Pressed to 1.

When a sheet having toner on the upper surface is conveyed in the direction of arrow Y, the sheet is conveyed while being sandwiched between the heating roller 21 and the pressure roller 22, and the developer is melted by the heat of the heating roller 21. It is fixed. The above-described printer adopts a so-called center-passing sheet conveyance mode in which the sheet is conveyed with the center of the photoconductor 5 aligned with the center of the sheet, and the sheet is aligned with the center of the roller. Be transported. Further, a signal is output from the CPU 51 to the heater power supply 54 to keep the temperature of the heating roller 21 at a temperature suitable for fixing, and a signal is output to the pump driver 55 to output the pumps 35, 39,
The pressure at 43 is adjusted.

The heating temperature control and the pressing force control of the fixing device 11 will be described. In the following description, the “narrow sheet” is a sheet that is narrower than the maximum size sheet that can be passed through the fixing device and that is narrower than the sheet that is conveyed after the printing process is completed. Say. On the contrary, the “wide sheet” is a sheet wider than the sheet conveyed before the start of the printing process.

When a narrow sheet is continuously conveyed to the fixing device 11, for example, the rollers 21 and 22 are slightly longer than the A3 plate vertical size, whereas the A4 plate or B is used.
When the sheet of the fifth plate is continuously fed in the vertical direction, heat is taken by the sheet at the sheet passing portion of the heating roller 21. Therefore, as shown in FIG. 14, the output of the heater power supply 54 is adjusted based on the temperature detection value from the central thermistor 24a, and the paper passing portion of the heating roller 21 is kept in a state necessary for melting the developer. .. Further, the non-sheet passing portion of the heating roller 21 takes less heat than the sheet passing portion, so that the temperature gradually rises. Therefore, in this state, the wide sheet is attached to the fixing device 1.
When it is conveyed to 1, the fixing property of the developer passing through the sheet passing portion and the sheet non-passing portion of the narrow sheet is different due to the temperature difference, and the image quality is deteriorated.

Therefore, the control device 50 performs the following processing in order to correct the difference in the fixing property due to the temperature difference by adjusting the pressing force of the pressure roller 22. That is, C
The PU 51 obtains the temperature difference between the central portion and the end portion of the heating roller 21 based on the temperature detection values from the thermistors 24a, 24b, 24c. Next, a chart (not shown) showing the relationship between the temperature difference and the pressure difference stored in the ROM 53 is displayed by C
The data is read out to the PU 51, the pressure difference corresponding to the temperature difference, that is, the pressure difference between the central pump 35 and the end pumps 39, 43 is calculated according to this chart, and the pumps 39, 43 are driven based on the calculated value. The pressure applied to the end portion of the pressure roller 22 is weakened. However, the pressing force of the central pump 35 is kept constant. The program in the ROM 53 is
It is created by experimentally obtaining the relationship between the temperature difference between the central portion and the end portion and the fixing pressure difference that provides good fixing properties as a whole.

By the above processing, even if a wide sheet is sent to the fixing device 11, the heating roller 21 is still kept at an appropriate temperature and pressure for fixing in the area corresponding to the sheet passing portion of the narrow sheet. A good fixing property can be obtained.
On the other hand, in the portion of the heating roller 21 located in the non-sheet passing portion of the narrow sheet where the temperature is rising, the fixing pressure is decreased although the fixing temperature is high, so that it is equivalent to the narrow sheet passing portion as a whole. Can be secured.

A second embodiment of the present invention will be described. In the fixing device 11 ′ of FIG. 4 according to the second embodiment, the thermistor 24 a is arranged only in the central portion of the heating roller 21. The other structure is the same as that of the fixing device 1 of the first embodiment, and the same parts are designated by the same reference numerals and the description thereof will be omitted. In the control device 60, as shown in FIG.
2, the sheet size memory 63, the continuous print number memory 64, the processing interval memory 65 and the ROM 66 are the CPU 6
It is connected to 1. Further, the thermistor 24a, the heater power supply 67, and the pump driver 68 are connected to the CPU 61 via an input / output port (not shown).

The sheet size memory 63 stores data regarding the size of the sheet to be printed by the printer 2 and the sheet conveying direction (longitudinal feed, horizontal feed).
The continuous print number memory 64 stores data regarding the number of prints when continuously printing on sheets of the same size, and the processing interval memory 65 starts one print process and then another print process. Stores data related to time to.

In the control device 60, the memory 63,
Data stored in 64, 65, etc. and the thermistor 24
The temperature difference between the central portion and both end portions of the heating roller 21 is calculated based on the detected temperature value of a, and the end portion pressing force of the pressure roller 22 is adjusted based on the result.

Specifically, as shown in FIG. 6, in the print processing program of the controller 60, the ΔT arithmetic processing is executed at # 101. The ΔT means a temperature difference between the central portion and both end portions of the heating roller 21. This process will be described in detail later. Next, in # 102, it is determined whether or not the wide sheet is being printed. If the wide sheet is being printed, the pressure changing process is performed in # 103, and if the narrow sheet is being printed, the other printing process is performed in # 106. Run. When the pressure changing process is completed, it is determined in # 104 whether or not it is the final print. If it is the final print, the fixing pressure is reset in # 105 to return to the initial state, and other print processes are executed in # 106. If printing is continued instead of printing, the fixing pressure is maintained as it is, and other printing processing is executed in # 106.

In the ΔT estimation process (# 101), # 3
In 01, # 302, and # 303, when the fixing device finishes printing the narrow sheet (mode M: 1), when changing from standby to printing operation (mode M: 2), during printing of wide size sheet ( Mode M: 3) and other operations, for example, it is determined whether the narrow width sheet is in printing or in standby.

Mode M: 1, ie, when the printer 1 has just finished printing the narrow sheet, # 2
At 11, the CPU 61 reads the sheet size of the sheet that has been printed until immediately before from the sheet size memory 63. The sheet size is input as print data for the printer 1 from the host computer 2 to the CPU 61, and is further output from the CPU 61 to the sheet size memory 63 for storage.

Next, at # 212, the chart 1 (see FIG. 9) stored in the ROM 66 is read. This chart 1 shows the relationship between the sheet passing time (or the number of sheets passed) of the narrow sheet and the temperature difference between the narrow sheet sheet passing portion and the narrow sheet non-sheet passing portion. The experiment is performed according to the above, and the result is used to create in advance. Subsequently, in # 213, the paper passing time Δt ₁ is read from the continuous print number memory 64, and in # 214, the temperature difference ΔT ₀ between the central portion and the end portion of the heating roller obtained last time is read from the RAM 62. Further, in # 215, the paper passing time Δt ₁ and the temperature differences ΔT ₀ to t ₀ and t ₁ are determined according to the chart 1, and # 216
Determine the temperature difference ΔT ₁ after passing a narrow sheet with.

In the mode M: 2, that is, at the timing when the printer 1 is switched from the standby mode to the printing mode based on the command from the host computer 2, # 22.
1, the waiting time for printing Δt ₂ from the processing interval memory 65
Is read, and the chart 2 (see FIG. 10) is read in # 222. This chart 2 represents the relationship between the waiting time and the temperature difference, and is obtained experimentally. Next, at # 223, the temperature difference ΔT ₀ between the central portion and the end portion of the heating roller previously obtained is read from the RAM 62, and at # 224, the standby time Δt ₂ and the temperature difference ΔT ₀ to t ₀ , according to the chart 2. t ₂ is determined, and the temperature difference ΔT ₂ after passing the narrow sheet is determined in # 226.

In mode M: 3, that is, during printing of a wide size sheet, the chart 3 (see FIG. 11) is read in # 231. This chart 3 shows the relationship between the continuous sheet passing time of a wide sheet and the temperature difference due to the continuous sheet passing, and is obtained experimentally. Next, in # 232, the continuous print time Δt ₃ is read from the continuous print number memory 64, and in # 233, the temperature difference ΔT between the central portion and the end portion of the heating roller obtained last time from the RAM 62 ΔT.
Reads _0, determining the t _0, t ₃ from the continuous printing time according chart 3 △ t ₃ and the temperature difference △ T ₀ in ♯234, the temperature difference △ T ₃ at each time point in the wide sheet printed with ♯235 decide.

In the pressure changing process (# 103), the process shown in FIG.
As shown in # 1, the temperature difference ΔT (ΔT ₁ to ΔT ₃ ) obtained in the above ΔT calculation process is read in # 301, and it is determined whether or not ΔT> 0 in # 302, and ΔT> When it is determined that the temperature is 0, that is, the temperature at both ends is higher than that at the center, the chart 4 is read at # 303. This chart 4 shows the above temperature difference Δ
4 shows the relationship between T and the pressure difference between the central portion and the end portion of the pressure roller 22. Next, in # 304, the pressure difference ΔP is obtained from the temperature difference ΔT according to Chart 4,
With # 305, pressurize the end pump with 2.0-ΔP (kg /
cm ₂ ). On the other hand, if there is no temperature difference ΔT, or if the central portion is colder than the end portion, it is determined in # 306 whether the pressure difference ΔP> 0. If ΔP> 0, the fixing pressure is determined in # 307. After resetting and returning to the initial state, the pressing force at the center is set equal to that at the end.

In the above two embodiments, the pressure device 2
5 is provided with three pumps 35, 39, 43 and their pressures are individually adjusted. However, as shown in FIG. 13, the backup roller 31 supporting the central portion of the pressure roller 22 and both end portions thereof are provided. The supporting plates 36 and 40 for supporting are urged toward the heating roller 21 by springs 71, 72 and 73, respectively, and the lever 74 rotatably instructed is locked to the upper ends of both ends of the support shaft of the pressure roller 22. Alternatively, the pressing force may be adjusted by pressing down the end portion of the pressure roller 22 with the lever 74 using the solenoid 75.

Further, in the above-described embodiment, the printer having a so-called center-passing mode in which the central portion of the photosensitive member 5 and the central portions of the rollers 21 and 22 are aligned with each other to convey the sheet has been described. , Photoconductor 5 and roller 2
The present invention can also be applied to a printer in which the sheet is conveyed with the ends of the sheets aligned with the reference lines of one end side of the sheets 1 and 22. In the above-described one-side sheet passing printer, the sheet always passes. Hold the fixing pressure at one end side constant,
The fixing pressure of the portion where the sheet passes or does not pass is adjusted according to the sheet size by the above method.

Further, in the above embodiment, the thermistor is 3
The case where one or one pump and three pumps for pressurization are provided has been described, but the number thereof is not limited.

[0030]

As is apparent from the above description, in the fixing device according to the present invention, when the wide sheet is passed after the narrow sheet, the pressing force of the narrow sheet is reduced. Then, the reduction of the pressing force can be immediately performed by a pump or the like. Therefore, it is possible to more quickly adjust the pressing force as compared with the conventional fixing device in which the heater is divided or the cooling device is provided, and it is possible to obtain a uniform fixing property.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a printer.

FIG. 2 is a perspective view of a fixing device.

FIG. 3 is a circuit diagram of a control device.

FIG. 4 is a perspective view of a second embodiment of the fixing device.

FIG. 5 is a circuit diagram of a control device according to a second embodiment.

FIG. 6 is a flowchart of print processing.

FIG. 7 is a flowchart of ΔT estimation processing.

FIG. 8 is a flowchart of pressure change processing.

FIG. 9 is a chart 1 showing a temperature change of a non-sheet passing portion.

FIG. 10 is a chart 2 showing a temperature change when paper is not passed.

FIG. 11 is a chart 3 showing a temperature change during continuous passage of wide sheets.

FIG. 12 is a chart 4 showing the relationship of ΔT−ΔP.

FIG. 13 is a perspective view of a third embodiment of the fixing device.

FIG. 14 is a diagram showing temperature changes in a sheet passing portion and a non-sheet passing portion.

[Explanation of symbols]

11 ... Fixing device, 21 ... Heating roller, 22 ... Pressing roller, 23 ... Heater, 24a, 24b, 24c ... Thermistor, 25 ... Pressing device, 26 ... Central part pressing device, 27, 2
8 ... End pressure device.

Claims (2)

[Claims] 1. A sheet material is sandwiched and conveyed while being heated,
In a fixing device for fixing the developer adhering to the sheet material, a rotatable heating roller having a heater, a pressure roller rotatably provided in parallel with the heating roller, and the pressure roller. Of at least the central portion and both ends of the heating roller against the heating roller, temperature detecting means for detecting the temperature of at least the central portion and both ends of the heating roller, the temperature detecting means of the heating roller When the narrow sheet non-sheet passing portion is hotter than the narrow sheet passing portion, a control device for driving the pressurizing device to weaken the pressing force of the narrow sheet non-passing portion is provided. And fixing device. 2. The sheet material is held and conveyed while being heated,
In a fixing device for fixing the developer adhering to the sheet material, a rotatable heating roller having a heater, a pressure roller rotatably provided in parallel with the heating roller, and the pressure roller. A pressure device that presses at least the central portion and both ends of the sheet toward the heating roller, temperature detection means for detecting the temperature of the narrow sheet passing portion of the heating roller, sheet size of the narrow sheet, continuous printing A calculating means for calculating the temperature of the narrow sheet non-sheet passing portion based on the number of sheets and the elapsed time after completion of the printing process, and the above-mentioned addition when the narrow sheet non-sheet passing portion is higher in temperature than the narrow sheet passing portion. A fixing device comprising: a control device that drives a pressure device to weaken the pressure applied to the narrow sheet non-sheet passing portion.