JPH06332330A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent offset or the jam of a transfer material from occurring caused by the overheating of toner in a fixing device when the speed of an image forming action is switched to a low speed side. CONSTITUTION:By regulating positional relation between a photosensitive drum 32 and the fixing device 37 so that a distance L to a nip part formed by the upper roller 37A and the lower roller 37B of the fixing device 37 from the separation device 35 of the transfer paper provided on the circumferential surface of the photosensitive drum 32 becomes longer than the maximum length of the transfer paper to be used, the transfer paper separated from the photosensitive drum 32 is carried once only by a carrying belt 36. Thus, a fixing action can be executed by the fixed carrying speed and the set temperature of the fixing device 37 regardless of the switching of the rotational speed of the photoreceptor 32.

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 having a laser beam exposure device and a heat roller type fixing device.

[0002]

2. Description of the Related Art In an electrostatic image forming apparatus having a laser beam exposure device, a screen of an electrostatic latent image formed on a photosensitive member is main-scanned by a laser beam and sub-scanned by movement of the photosensitive member. It is formed by the synthesis with.

This electrostatic latent image is formed by main scanning (changing the linear velocity of a polygon mirror or a galvano mirror) by lowering the speed of the sub-scanning, that is, lowering the rotation speed of the photosensitive member when it is a drum. The recording linear density can be recorded densely. Therefore, if the moving speed of the photoconductor and the linear speed of the polygon mirror or galvano mirror can be switched to the low speed side, a high-quality image with a higher pixel density can be obtained.

[0004]

On the other hand, as for the fixing device, generally, a structure in which a pair of heat rollers constituting the fixing device is rotated in synchronism with the movement of the photosensitive member so as to synchronize with the transfer speed of the transfer material is adopted. Therefore, as described above, when the moving speed of the photoconductor is switched to the low speed side, the conveying speed of the heat roller pair also automatically decreases.

Therefore, when fixing the transfer image, the sandwiching time by the pair of heat rollers becomes long and an excessive pressure and heat amount are applied to the toner image to cause a so-called offset phenomenon. In an extreme case, the transfer material is a heat roller. It may be wrapped around and jammed.

As means for preventing such troubles in advance, JP-A-60-51866, JP-A-61-184577, and JP-A-SHO-5
No. 9-184365 and JP-A No. 1-221779 disclose proposals for controlling the supply amount of a release agent to a heat roller and a setting value for a fixing temperature, but each of them has a plurality of sensors. It is inevitable that the structure becomes complicated and expensive because it requires a control system.

The present invention solves this problem and improves the result.
It enables fixing under a fixed fixing condition regardless of the change of the moving speed of the photoconductor, or automatically changes and corrects the fixing temperature and condition according to the change of the moving speed of the photoconductor by an extremely simple means. It is an object of the present invention to provide an image forming apparatus capable of always performing an appropriate fixing action.

[0008]

The above-mentioned object is to change the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by changing the linear velocity of the photoconductor and a polygon mirror or a galvano mirror. In the image forming apparatus that changes
An image forming apparatus characterized in that the conveying speed of fixing means provided in the apparatus is always kept constant regardless of switching of the linear velocity of the photoconductor, and a static image formed on the photoconductor by exposure to laser light. In an image forming apparatus that changes the recording linear density of an electrostatic latent image by switching the linear velocities of the photoconductor and the polygon mirror or galvano mirror, the supply amount of the release agent to the fixing means provided in the device is set to the photoconductor. An image forming apparatus characterized in that the linear velocity is changed according to the switching of the linear velocity, and a recording linear density of an electrostatic latent image formed on a photoconductor by exposure to a laser beam is switched between the linear velocities of the photoconductor. In the image forming apparatus that is changed by
An image forming apparatus characterized by changing a set temperature of a fixing unit provided in the apparatus according to switching of a linear velocity of the photoconductor, and an electrostatic latent image formed on the photoconductor by exposure of a laser. In the image forming apparatus that changes the recording linear density by changing the linear velocity of the photoconductor and the polygon mirror or galvano mirror, the set temperature of the fixing unit provided in the device is set according to the reduction of the linear velocity of the photoconductor. An image forming apparatus characterized by being lowered by an air blowing cooling means to be operated, and a recording linear density of an electrostatic latent image formed on a photoconductor by exposure of a laser beam to change the linear velocity of the photoconductor. In the image forming apparatus, the set temperature of the fixing unit provided in the apparatus is changed by the heat radiation of the fixing roller which is rotated according to the reduction of the linear velocity of the photoconductor. It is achieved by an image forming apparatus characterized by lowering Te.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the image forming apparatus of the present invention is shown in FIGS.

The apparatus comprises an image reading section 10, a laser writing section 20, an image forming section 30, and a paper feeding section 40.

The image of the original document D placed on the original table is provided with the illumination lamp 11A of the image reading section 10 and the mirror 11B.
Exposure scanning is performed by parallel movement of the mirror unit 11 from a solid line to a position shown by a broken line, and by following movement of the second mirror unit 12 having a pair of facing mirrors 12A at a speed half that of the first mirror unit 11. Then, the image is formed on the image pickup device 14 via the projection lens 13, undergoes image processing, and is temporarily stored in a memory as an image signal.

Next, the image signal is transferred to the laser writing unit 20.
When a laser beam generated by a semiconductor laser (not shown) is rotated and scanned by the polygon mirror 22 rotated by the drive motor 21, the optical path is bent by the mirrors 24, 25 and 26 through the fθ lens 23 and the image is obtained. Forming part 30
Of the photoconductor drum 32, which has been previously charged by the charger 31
Is projected onto the peripheral surface to form a bright line. Therefore, an electrostatic latent image of the original image is formed on the peripheral surface of the photoconductor drum 32 by the main scanning by the laser beam and the sub-scanning accompanying the rotation of the photoconductor drum 32. This latent image is the developing sleeve 33 of the developing device 33.
The toner carried by A carries out reversal development to form a toner image.

On the other hand, each paper feed cassette loaded in the paper feed unit 40
A transfer paper P of a designated size is unloaded from 41 by the operation of the unloading roller 41A of the paper feed cassette 41 to be stored, and is fed toward the image transfer portion via the transport roller 43.

The transfer sheet P thus fed is fed to the transfer section in synchronism with the toner image on the peripheral surface of the photosensitive drum 32 adjusted in timing by the registration roller 44, and then fed to the transfer section 34. The toner image is transferred by being charged by.

Next, the transfer paper P is separated from the peripheral surface of the photosensitive drum 32 by the static eliminating action of the separator 35 and is conveyed to the fixing device 37 via the conveyor belt 36, and is sandwiched between the upper roller 37A and the lower roller 37B. After the toner is fused by heat, it is discharged from the fixing device 37 via the conveying roller 38.

The ejected transfer paper P is ejected onto the tray 50 via the paper ejection roller 45.

On the other hand, the photosensitive drum 32 from which the transfer paper P is separated
Is a blade 39A that is pressed against the cleaning device 39.
After the residual toner is removed and cleaned by, the charging device 31 again applies the electric charge to start the next image forming process.

In the above apparatus, the recording linear density of the electrostatic latent image formed on the photosensitive drum 32 is changed from the normal 400 dpi (400 dots per inch in length) to 600 dpi by the switching means provided in the operating section. It has a function to switch to and record a higher quality image.

The switching of the recording linear density is performed by a command from a control system based on a signal from the switching means.
This is achieved by lowering the linear velocities of 32 and the polygon mirror 22 and adaptively correcting the image forming conditions of the image forming members related thereto.

Table 1 shows an example of correction of image forming conditions when the recording linear density is switched from 400 dpi to 600 dpi.

[0021]

[Table 1]

Fixing device used in each embodiment described below
The specifications of 37 and the developer used for the developing unit 33 have the following specifications.

Fixing device Upper roller: length 324 mm, diameter φ50 mm, core metal material A5056TD (PFA coating 20 μm) Lower roller: length 310 mm, diameter φ50 mm, core metal material STKM (LTV rubber 5 mm ... rubber hardness 30)
° + PFA tube) Crimping load: 3.7kgf / cm Heater: Upper roller 1100W Lower roller 200W Setting temperature: 200 ° C (Upper roller) Developer toner: Polyester type average particle type 8.5μm Carrier: Resin coated Ferrite average particle size 60 μm Toner concentration: 4% FIGS. 2 and 3 show an embodiment (first embodiment) according to claim 1 of the present invention, in which the transfer paper P is provided only by the conveyor belt 36. The distance during conveyance, that is, the length L from the separator 35 in FIG. 2 to the nip portion between the upper roller 37A and the lower roller 37B of the fixing device 37 is larger than the maximum length of the transfer paper P used. Value eg transfer paper P is A
In the case of 3 sheets (297 × 420 mm) and lateral feed, it is set to 297 mm or more, and the transfer paper P on the conveyor belt 36 is temporarily not regulated by the photosensitive drum 32 and the fixing device 37 in terms of the conveying speed. It is supposed to be put in a state.

Therefore, when the recording linear density is switched,
As shown in FIG. 3, the signal from the CPU drives the photosensitive drum 32, the feeding speed of the transfer paper P, the voltage of the high voltage power supply, the developing device 33.
The driving of the fixing device 37, the conveying roller 38 located on the downstream side of the fixing device 37, and the discharge roller 45 are always driven at a constant conveying speed regardless of the switching of the rotation speed of the photosensitive drum 32. It becomes possible to do.

As a result, the fixing device 37 can keep the set temperature constant regardless of the switching of the recording linear density, and can exhibit a stable and efficient fixing action.

4 to 6 show an embodiment (second embodiment) according to claim 2 of the present invention.

In the fixing device 37, a sponge-like coating roller 373, which is impregnated with silicon oil in an oil pan 371 through a supply roller 372, is constantly in pressure contact with the peripheral surface of the upper roller 37A, and the fixing roller 37 is fixed to the upper roller 37A. By rotating the coating roller 373 counterclockwise with respect to the rotation in the time direction, silicon oil as a release agent is evenly coated on the peripheral surface of the upper roller 37A, and the melted toner on the transfer paper P is transferred to the upper roller. This prevents the occurrence of so-called offset that transfers to the peripheral surface of 37A.

The above-mentioned upper roller 37A and coating roller 373
Have their peripheral surfaces cleaned by a cleaning web 374A and a cleaning blade 375A, respectively, while the lower roller 3
The peripheral surface of 7B is also kept clean by the pressure contact between the cleaning web 374B and the cleaning blade 375B, and the predetermined temperature is maintained by the detection of each temperature sensor S.

The amount of silicone oil applied by the coating roller 373 changes in proportion to the linear velocity when the linear velocity of the coating roller 373 is higher than a certain speed as shown in FIG. The amount of oil supplied to the upper roller 37A can be increased by switching the linear velocity of the coating roller 373.

Therefore, when the recording linear density is changed, the result shown in FIG.
As shown in FIG. 5, the fixing device 37 is simply switched between the transport system and the drive of the coating roller 373 in response to a signal from the CPU, and the set temperature is not required to be switched, and the offset is avoided by the control of the silicone oil described above. You can do it.

As an example, when the recording linear density is 400 dpi, the linear velocities of the upper roller 37A and the coating roller 373 are 280 mm / sec, respectively.
Is 50 mm / sec and the linear velocity of the upper roller 37A is 125 mm / in accordance with the linear velocity of the photosensitive drum 32 when the density is switched to 600 dpi.
Decrease to sec, while increasing the linear velocity of the coating roller 373 to 150 mm / sec to increase the amount of oil supplied to the A4 size transfer paper P from 1 to 2 mg to 10 to 15 mg, which is nearly 10 times. Is possible.

7 and 8 show an embodiment (third embodiment) according to claim 3 of the present invention.

7A and 7B show the results of an investigation of the occurrence of offset due to the fixing action of the present invention when the recording linear density is 400 dpi and 600 dpi.
It was possible to confirm the proper range of each fixing temperature as shown in.

The hot offset region shown in the figure is a range in which offset occurs in the upper roller 37A of the fixing device 37 due to welding due to overheating of the toner, while the under offset region has insufficient heat and toner adheres to the transfer paper P. It shows the range that is not controlled.

Therefore, the intermediate area sandwiched between the hot offset area and the under offset area is an appropriate temperature range for image fixing, and from this result, the temperatures of the upper roller 37A and the lower roller 37B are recorded at a recording linear velocity of 400 dpi. In the case, the median value is 200 ℃, and in the case of 600dpi, the median value is 185 ℃ (both in the figure ×
It is desirable to switch to (indicated by a mark) and set.

The above-mentioned fixing temperature switching control is carried out by the control of the CPU which receives the recording linear density switching signal together with the drive switching of the photoconductor and the fixing device as shown in FIG.

FIGS. 9 and 10 show an embodiment (fourth embodiment) according to claim 4 of the present invention, in which the fixing device 37 is operated by changing the recording linear density from 400 dpi to 600 dpi. The heat generation amount of each heater H contained in the roller 37A and the lower roller 37B is controlled to switch the set temperature to the low temperature side, and at the same time, the inside of the container is forcibly cooled by the introduction of outside air by the operation of the blower cooling means. As a result, the temperature of each roller is rapidly lowered so that a low set temperature can be obtained within a short time.

The set temperature of the fixing device 37 is set to 200 ° C. when the recording linear density is 400 dpi and 185 ° C. when the recording linear density is 600 dpi, and the temperature is set to the upper roller 37A and the lower roller 37B.
Are detected by the respective temperature sensors S provided on the respective peripheral surfaces of the. When the temperature detected by each sensor S reaches a predetermined set temperature, the lamp of the operation unit is turned on to instruct the start of copying.

When the recording linear density of the apparatus is set to 400 dpi and then switched to 600 dpi, the set temperature of the fixing device 37 is set to 185 ° C.
By switching to, the intake fan F1 installed in the intake duct D1 as the blower cooling means starts to operate.

By the operation of the intake fan F1, the outside air outside the apparatus is sucked into the intake duct D1, filtered through the air filter f and sent into the container of the fixing device 37, and the upper roller 37A in a high temperature state. The lower roller 37B is cooled.

The air in the container, which has cooled each roller to a high temperature, is discharged to the outside of the device through the exhaust duct D2 by the continuous operation of the exhaust fan F2 of the exhaust device provided for ventilation of the device, and the circulation of this outside air. The action effectively lowers the temperature of each roller.

Next, the temperature sensor S detects the set temperature.
When 185 ° C. is detected, the operation of the intake fan F1 is stopped and the set temperature is kept constant.

The intake fan F1 does not operate when the temperature of the fixing device 37 is lower than the set temperature of the fixing device 37, that is, 185 ° C. in the case of the present embodiment. Therefore, the process of using the recording linear density as 400 dpi is not performed. The intake fan F1 is not operated when directly used as 600 dpi.

FIG. 11 shows an embodiment (fifth embodiment) according to claim 5 of the present invention.

When the set temperature of the fixing device 37 is set to the low temperature side in response to the switching of the recording linear density, as a means for obtaining the low set temperature within a short time, the air blowing described in the fourth embodiment above. In addition to the cooling means, it is also possible to put both the upper roller 37A and the lower roller 37B in an operating state, and to effectively lower the temperature of each of the upper and lower rollers by the heat radiation effect of the roller peripheral surface accompanying the rotation.

According to the experiment of the present invention, the temperature of each of the upper and lower rollers is set to 200 ° C. when the recording linear density is 400 dpi, and the temperature is set to 600 ° C.
When switching to a set temperature of 185 ℃ when switching to the density of dpi, the temperature decrease rate is 0.14 ℃ per second, which is unequal when the temperature is naturally cooled while both rollers are stationary. 0.4 ℃ per second when both are in the rotating state
It was confirmed that a high temperature drop rate of 0 was uniformly obtained.

Therefore, as shown in the figure, the recording linear density is switched from 400 dpi to 600 dpi and the set temperature of the fixing device 37 is set from 200 ° C. to 185 ° C.
Upper roller 37A and lower roller 37 of the fixing device 37
By placing 37B in a rotating state, the time required to switch the set temperature can be shortened.

In the case of the present embodiment, for the same reason as in the case of the fourth embodiment, when the temperature of the fixing device 37 is lower than the set temperature of the low temperature, each roller is not rotated and is in a stationary state. It is heated by and set to a predetermined temperature.

[0049]

According to the present invention, it is possible to realize an image forming apparatus capable of automatically corresponding to a fixing condition of a transferred toner image in accordance with switching of an image forming speed by scanning a laser beam. As a result, it is possible to provide an image forming apparatus capable of stably recording a high quality image without causing a trouble such as offset.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram of an image forming unit according to the first embodiment.

FIG. 3 is a control circuit diagram according to the first embodiment.

FIG. 4 is a cross-sectional configuration diagram of a fixing device according to a second embodiment.

FIG. 5 is a graph showing the amount of silicone oil applied.

FIG. 6 is a control circuit diagram according to a second embodiment.

FIG. 7 is a graph showing an appropriate temperature of a fixing roller.

FIG. 8 is a control circuit diagram according to a third embodiment.

FIG. 9 is a configuration diagram of a blast cooling unit according to a fourth embodiment.

FIG. 10 is a control circuit diagram according to a fourth embodiment.

FIG. 11 is a control circuit diagram according to a fifth embodiment.

[Explanation of symbols]

 10 Image reading unit 20 Laser writing unit 30 Image forming unit 31 Charging device 32 Photosensitive drum 33 Developing device 34 Transfer device 35 Separator 36 Conveyor belt 37 Fixing device 37A Upper roller 37B Lower roller 40 Paper feeding unit 41 Paper feeding cassette 371 Oil Pan 372 Supply roller 373 Coating roller P Transfer paper H Heater S Temperature sensor F1 Intake fan F2 Exhaust fan

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Nishida 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (5)

[Claims] 1. An image forming apparatus for changing the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by switching the linear velocity of the photoconductor, and a fixing unit provided in the device. The image forming apparatus is characterized in that the conveying speed of the photoconductor is always kept constant regardless of the change of the linear velocity of the photoconductor. 2. An image forming apparatus for changing the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by switching the linear velocity of the photoconductor and a polygon mirror or a galvano mirror. An image forming apparatus, wherein an amount of a release agent supplied to a fixing unit provided in the apparatus is changed according to switching of a linear velocity of the photoconductor. 3. An image forming apparatus for changing the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by switching the linear velocity of the photoconductor, and a fixing unit provided in the device. The image forming apparatus is characterized in that the set temperature is changed according to the switching of the linear velocity of the photoconductor. 4. An image forming apparatus for changing the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by switching the linear velocity of the photoconductor, and a fixing unit provided in the device. The image forming apparatus is characterized in that the set temperature is reduced by a blower cooling unit that operates in accordance with the reduction of the linear velocity of the photoconductor. 5. An image forming apparatus for changing the recording linear density of an electrostatic latent image formed on a photoconductor by exposure to laser light by switching the linear velocity of the photoconductor, and fixing means provided in the device. The image forming apparatus is characterized in that the set temperature is reduced by heat radiation of a fixing roller that is rotated according to the reduction of the linear velocity of the photosensitive member.