JP2002182543A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which is capable of preventing the temperature in the apparatus from excessively rising and maintaining excellent image quality free from a fixation defect, etc. SOLUTION: This image forming apparatus has a fixing device having a fixing roller in which at least two or more heaters having different light emission distributions are incorporated, a pressure roller which is pressed rotatably to the fixing roller, a temperature detecting means which detects the surface temperature of the fixing roller, and a control means which controls the heaters to turn on according to the detected value of the temperature detecting means and an air discharge fan with which its air capacity can be switched in two or more stages so as to prevent the temperature in the apparatus from being raised by the fixing device; and the switching of the air capacity by the air discharging fan is controlled respectively when transfer paper passes through, when the device is started up, and when the device is in standby mode.

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 PPC copier, a printer, and a facsimile provided with a heat roller fixing device having a fixing roller having at least two or more heaters.

[0002]

2. Description of the Related Art In recent years, as global environmental measures,
Each model supports a reduction in warm-up of the image forming apparatus by reducing the thickness of the fixing roller. However, the fixing property is remarkably deteriorated particularly in the case of thick paper for the following reasons. (1) Since the strength of the fixing roller itself is significantly reduced due to the thinning of the fixing roller, the fixing method in which a pressure roller having extremely low rubber hardness is brought into contact with the fixing roller at a low pressure is used. The effect is extremely reduced. In other words, simply speaking, the principle of thermal fixing is to apply pressure and heat to the toner on the transfer paper from the fixing roller to crush the toner, fuse it, and fix it on the transfer paper. This is because the thinner fixing roller has low strength, so the pressure roller has low rubber hardness.
Naturally, the pressure in the nip is also quite low. For this reason, the force for crushing the toner is weak, so that a gap is formed between the toners, heat conduction is deteriorated, and the action of pushing the toner into the fiber of the paper is also weakened, so that the fixability is weakened. Further, since the heat capacity of the thin fixing roller is small, when the paper passes through the nip portion, the heat of the fixing roller is taken by the transfer paper, and the temperature of the fixing roller drops significantly. Further, when the paper is thick paper, since the heat capacity of the paper is large, the amount of heat taken from the fixing roller is large, and as a result, the temperature of the fixing roller greatly decreases, so that the fixing property is weakened. (2) As the thickness of the fixing roller is reduced, the heat capacity of the fixing roller is also reduced, so that the temperature of the fixing roller at the time of sheet passing is significantly reduced. (3) The amount of power that can be supplied to the fixing device is reduced due to the abundance of post-processing devices in the apparatus. (4) The size of the apparatus itself is reduced due to space saving, and the degree of influence of heat from the fixing apparatus on other parts is increased. Therefore, the exhaust fan for cooling the fixing apparatus is closer, Need to be powerful. For this reason, the temperature distribution in the axial direction of the fixing roller is not uniform, and a portion where the fixing failure occurs (a roller end portion or the like) occurs.

Therefore, conventionally, in order to cope with the above-mentioned problem, a thick paper mode control and a control in which two heaters are independently controlled are performed. Examples of the prior art include “Japanese Patent Publication No. 2-81076” and “Japanese Unexamined Patent Application Publication No. 11-23171.
No. 6 "is disclosed.

[0004]

However, the above-mentioned prior art has the following problems. That is, as described above, the thick paper mode control and the independent control of the two heaters are performed in order to prevent the fixing failure. However, the specific control contents of the thick paper mode are as follows. Set. (2) Pre-rotation of the fixing device is performed, and the fixing roller and the pressure roller are warmed before passing the sheet. (3) A gap between the three paper passages is opened to prevent the temperature of the fixing roller from dropping. (4) The transport speed is reduced and the amount of heat applied to the paper is increased, but in any case, the situation is actually reversed from the viewpoint of productivity. In general, independent control by two heaters is constituted by light-emitting heaters at the center and both ends. In this case, as pointed out in (4) of the prior art, the temperature distribution of the rollers is not uniform. Therefore, there is a problem that the temperature at both ends of the roller cannot be made uniform.

[0005] As described in the above (4),
In the image forming apparatus, each model supports energy saving and space saving. To realize this space saving, the size of each unit is reduced and the distance between each unit is inevitably close. Therefore, the heat of the fixing device is likely to adversely affect other units, particularly the image forming unit. Further, since the units are very close to each other, a space for flowing air for cooling is narrowed, and it is difficult for the air to flow. Therefore, it is necessary to increase the air volume by the exhaust fan. Here, FIG. 5 shows an airflow path inside the image forming apparatus 1. As shown in FIG. 5, the blowing paths of the exhaust fan 31 serving as a fixing system cooling fan for cooling the fixing device 8 are a, b, c, and d, and the blowing paths of the electrical system cooling fan 32 are l, b. m, f, g, h, and the air supply path of the PSU cooling fan 33 is e, f, g,
h. The natural convection airflow is i, j, k. As is apparent from the airflow shown in FIG. 5, since the exhaust fan 31 is located immediately behind the fixing device 8 to be cooled most, the cooling air naturally flows through the fixing device 8. In other words, it can be easily guessed that the cooling air flows most easily inside the fixing roller, which is a large passage directly in front of the exhaust fan 31.

Accordingly, in addition to extremely deteriorating heat conduction in the axial direction of the roller due to the reduction in thickness of the fixing roller, if the cooling air flows inside the fixing roller,
Even when the two heaters for emitting light at both ends are independently controlled, it is difficult to make the temperatures at both ends substantially uniform. In order to solve this problem, it would be possible to perform independent control using three heaters with different light emission corresponding to the center, the front end, and the back end, but in reality, cost, space, etc. It is difficult to achieve from a viewpoint. As described above, if the temperature distribution at both ends of the fixing roller is not uniform due to the exhaust fan 31, the heat conduction in the roller axis direction is extremely deteriorated. Is not easily improved. For this reason, the fixing property is further deteriorated on the lower temperature side. In order to improve the fixing performance when the thin fixing roller is employed as described above, it is natural to prevent the fixing roller temperature from dropping immediately after passing the paper, and it is important to improve the fixing roller temperature distribution as an important point. It has become.

Here, the problems of the prior art will be further described with reference to FIGS. That is, FIG.
Is turned on when the image forming apparatus 1 is at the room temperature level (the temperature of the fixing device 8). Two minutes after the power is turned on, ten sheets of thick paper (135K, A3 size) are continuously passed from the manual feed unit to form an image. The temperature change of the fixing roller until the operation is completed is shown. The solid line indicates the center temperature of the fixing roller, the dashed line indicates the temperature on the back side, and the dotted line indicates the temperature on the front side. At this time, the exhaust fan 31 has a maximum (MAX) air volume. First, when the power is turned on, the fixing heater is energized, and the temperature of the center / front / back of the fixing roller starts to rise all at once. Here, the temperature at the center rises fastest, then the back side is fastest, and the near side rises the most lately. The reason is that the center rises quickly because it receives the heat of the center heater and the heat of the end heater, but the end is delayed compared to the center because the heat escapes from the roller opening. Further, the front side of the front air hits the inlet through which the outside cooled air flows by the exhaust air fan 31, so that the temperature rise is further delayed as compared with the back side. After about 15 seconds, the fixing roller temperature reaches the target of 185 degrees, and thereafter, the center heater / both end heaters start controlling around 185 degrees. However, the control of the heaters at both ends is normally controlled by a thermistor provided on the back side of the roller, and the front side is an inlet through which the outside cooled air flows through the inside of the roller by the exhaust fan 31 as described above. In comparison, the temperature gradually decreased, and after 2 minutes, the center / back was 18
While control is performed at around 5 degrees, the near side drops to about 160 degrees. In this state, for example, when 10 sheets of 135 K / A3 are continuously fed by manual sheet feeding, the heat taken by the pressure roller and the heat taken by the transfer paper drop by about 25 degrees, and from there, the heater is gradually turned off. Returns to 185 degrees due to the heat received. Accordingly, as shown in FIG. 6, the center / end portion undergoes the temperature change as described above, but the temperature on the near side where the temperature drop is large at the time of the start of sheet feeding decreases to about 135 degrees, and then gradually returns. .

Next, when the paper passing is completed and the rotation operation by the fixing device 8 is completed, the temperature rises (overshoots) momentarily due to the heat which is not suddenly taken away by the paper and the pressure roller. The temperature immediately drops due to the cooling air, and control starts again around 185 degrees. Naturally, if you leave it in this state (if the machine standby state continues),
The temperature in the foreground starts to fall again compared to the back. Then, what is the fixability in this state?
Since the temperature slightly exceeds the lower limit temperature of K of 155 degrees which is the fixing temperature of K, the fixing property can be satisfied.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional image forming apparatus, and to switch the air volume of an exhaust fan in accordance with the state of a machine or a paper passing state, thereby achieving a temperature inside the apparatus. It is an object of the present invention to provide an image forming apparatus which can prevent an excessive rise of the image quality and maintain good image quality without causing a fixing failure or the like.

[0010]

SUMMARY OF THE INVENTION At least two or more fixing rollers each having a built-in heater having a different light emission distribution, a pressure roller rotatably pressed against the fixing roller, and detecting a surface temperature of the fixing roller. And a control unit for controlling lighting of each heater in accordance with a value detected by the temperature detecting unit. The unfixed toner image is formed at a nip formed by pressing the fixing roller and the pressing roller. Device for hot-melt fixing the toner onto transfer paper, and an image forming apparatus having an exhaust fan whose air volume can be switched at least two or more stages in order to prevent an increase in the temperature inside the apparatus due to the fixing device. The switching of the air volume is controlled and performed when the transfer paper is passed, when the machine is started up, and when the machine is on standby. In addition, when the relationship of the air volume by the exhaust fan is set so that the time of paper passing> the time of machine standby> the time of machine start-up, it is possible to prevent an excessive rise in the temperature inside the machine and to prevent the occurrence of fixing failure and the like. Image quality can be maintained.

[0011]

FIG. 1 shows an embodiment of an image forming apparatus according to the present invention. That is, FIG. 1 shows an overall configuration diagram of the image forming apparatus 1 in a state where peripheral devices are mounted,
An ADF 2, a finisher 3, and a double-sided tray 4 are mounted as the peripheral devices. Hereinafter, the configuration and the transfer path of the transfer sheet will be described in detail. Reference numeral 5 denotes a paper feed tray. The transfer paper fed from the paper feed tray 5 is transported by transport rollers 6, and after a predetermined image is formed by image forming means 7, the image is fixed by a fixing device 8 and relay unit 9. The sheet is discharged via the finisher 3. The finisher 3 has a stapler 10 therein, and the transfer paper stapled by the stapler 10 is discharged onto a discharge tray 13 by a transport belt 12 after a predetermined number of staples (binding operation) in a jogger stack unit 11.

Here, the transport path for transporting the transfer paper toward the finisher 3 in the "non-staple mode" is indicated by a solid line, and the transport path in the "staple mode" is indicated by a dotted line. In this case, the paper thickness that can be fed from the paper feed tray 5 is a general “55 kg to 90 kg paper”, and the paper can be passed through the respective transport paths of “finisher staple / finisher non-staple” from the discharge port on the relay unit 9. Paper thickness setting. Reference numeral 14 denotes a manual tray. The paper thickness that can be fed by the manual tray 14 is 45 kg to 135 kg paper compatible with various application papers. The paper thickness is set so that the path can be passed. This is because staples are not commonly used when the transfer paper is application paper.

FIG. 2 shows the structure of the fixing device 8. The fixing device 8 is provided on a fixing roller 15, a pressure roller 16 which rotates by pressing against the fixing roller 15, and a pressure roller 16 side. A pressure lever 28 for transmitting a pressing force by the pressing spring 17;
The toner on the transfer paper is fixed by utilizing the heating by fixing heaters 18 and 18a provided inside 15. In this example, the fixing heater 18 is a central light emitting heater (600 W) corresponding to a size width (210 mm) of A4T or less, and the fixing heater 18a is A3T.
Light emitting heaters (4
00W). Here, the outer diameter of the fixing roller 15 is 40
mm, the core metal is a thin roller of 0.4 mm made of iron, the calorie of the fixing heater 18 is 1000 W, the outer diameter of the pressure roller 16 is a low-hardness roller made of foamed silicone of 30 mm, and a warm-up time of 15 sec or less is achieved with a 35 CPM machine. It is an example of a fixing device.
Reference numeral 19 denotes a fixing separation claw, reference numeral 20 denotes a pressure separation claw, and reference numeral 21 denotes a discharge branch claw. When the “copy mode” is selected to the “double-sided mode”, the transfer paper is temporarily stored in the double-sided tray 4 by the switching operation of the discharge branch claw 21.

The fixing roller 15 is heated by fixing heaters 18 and 18a, and its surface temperature is detected by a thermistor 22 slidably contacting the outer peripheral surface of the fixing roller 15 so that the fixing roller 15 is maintained at a fixed fixing temperature. Temperature control is performed.
23 is a thermal fuse for preventing excessive temperature rise. Fixing device 8
The fixing roller 15 and the pressure roller 16 rotate in the direction of the arrow in the drawing by the rotation drive from a drive system (not shown), and the transfer paper fed from the paper feed tray 5 After passing through the nip between the rollers 15 and 16 via the entrance guide 25 and being fixed, the sheet is discharged by driving the sheet discharging roller 26. The paper discharge from the fixing device 8 is detected by a paper discharge sensor 27. Further, as described above, the fixing device 8 is provided with the exhaust fan 31.
It is cooled by the exhaust air (FIG. 5).

FIG. 3 is a flowchart showing an example of a control method in the image forming apparatus of the present invention. As shown in this flowchart, in the present invention, the air volume of the exhaust fan 31 is switched at the time of paper passing / at the start of the machine / at the time of machine standby, and the air volume of the exhaust fan 31 is switched according to the paper feed port of the transfer paper. The air flow rate of the exhaust fan 31 is switched according to the number of sheets passed.
31 is characterized by operating. FIG. 4 shows a temperature change diagram of the fixing roller according to the present invention. That is, FIG.
As shown in (1), the machine is turned on from the state where the temperature of the fixing unit is at the room temperature level. Two minutes after the machine is turned on, 10 sheets of thick paper (135K, A3 size) are continuously passed from the manual feed unit to form an image. 9 shows a change in the fixing roller temperature until the operation is completed. The solid line indicates the center temperature of the fixing roller, the dashed line indicates the temperature on the back side, and the dotted line indicates the temperature on the front side.

However, the condition of the exhaust fan 31 at this time is as follows. (1) At startup, the exhaust fan 31 is turned off. (2) During standby / sheet passing, the exhaust fan 31 is decelerated (the voltage is reduced to half in this embodiment). When the power is turned on, the fixing heater is energized and the temperature of the center / front / back of the fixing roller starts rising all at once. . Here, the exhaust fan 31 is turned off as described above.
So the center is slightly higher, but almost at the center / front /
The temperature rises in the same way. After about 15 seconds, the fixing roller temperature reaches the target temperature of 185 degrees. Thereafter, the heater control is started. Here, the exhaust fan 31 is controlled at a voltage half that of the exhaust air amount (MAX) in FIG. 6 (conventional example). , The air volume is reduced. Therefore, the temperature drop on the near side is reduced,
After 2 minutes, the center / back is controlled at around 185 degrees, while the near side calms down at about 175 degrees. In that state,
When 10 sheets of 135K / A3 are continuously fed from the manual feeder,
Although the temperature drops in the same way due to the heat taken by the pressure roller and the heat taken by the transfer paper, since the air volume of the exhaust fan 31 is reduced, the drop is about 20 degrees, and from there the heat is gradually received from the heater. Return to 185 degrees by heat. Therefore, as shown in FIG. 4, the center / end portion undergoes the temperature change as just described, and the front side is improved to a drop of about 155 degrees.

Here, when the paper passing is completed and the rotation operation is completed, the temperature rises momentarily (overshoot) due to the heat which is not suddenly taken away by the paper and the pressure roller, but the air volume of the exhaust fan 31 is reduced. Because of this, the temperature drops gradually, so the exhaust fan 31 is kept in the MAX state for a predetermined time immediately after the completion of paper passing, and the fixing fan temperature is reduced to around 185 degrees, and the exhaust fan 31 is decelerated again. Obviously, it is better to put it in a state. The fixability in this state is about 135 K at the center / both ends. Since the angle is slightly higher than 155 degrees, the fixing property can be satisfied.

Here, the exhaust fan 31 is completely turned off at the time of start-up. However, there is a case where the fixing heat at the time of start-up adversely affects other parts depending on the machine configuration.
It is possible that the air is exhausted by the exhaust fan 31 in the decelerating state.
Next, in the examples up to this point, the case of paper passing from the manual feed is taken as an example, but control when paper is passed from the main body paper supply will be described.

That is, in the main body sheet feeding, a large number of sheets can be stacked (ex. 500 sheets).
The paper thickness that can be passed is the level of plain paper (ex. 55K to 90K)
It is. On the other hand, in the case of manual sheet feeding, the number of sheets that can be stacked is about 50 sheets, and the sheet thickness that can be passed is the level of plain paper (ex. 45K to 135K), so there is a great difference between the two. Therefore, the maximum continuous sheet feeding in the manual sheet feeding is 50 sheets in the present embodiment, and even if the sheet is continued to be fed while the exhaust fan 31 is being decelerated, the temperature rise in the apparatus is not significantly affected. However, the number of sheets
It is possible to set nine sheets manually and pass the sheets sequentially while passing the sheets. On the other hand, if the main body is fed, 500 sheets can be fed per sheet, and if sheets of the same size are stored in all four steps, a maximum of 2000 sheets can be continuously fed.
If the exhaust fan 31 continues to be decelerated continuously in this state, the temperature inside the machine will rise steadily, and the possibility that a problem will occur becomes very high. Therefore, in the present invention, when the main body is fed, the deceleration state is maintained until a predetermined number of sheets are reached, and thereafter, the airflow by the exhaust fan 31 is maximized, so that the temperature inside the apparatus can be prevented from rising. Further, since the paper thickness corresponding to the main body feeding is thinner than the manual feeding as described above, it is possible to set the exhaust fan 31 to MAX from the beginning depending on the machine. At the same time, as described above, even in the case of manual paper feeding, a large number of continuous papers can be passed if additional paper is passed, so that the deceleration state is similarly reduced to a predetermined number, and then the exhaust fan 31 is set to the maximum. By doing so, it is possible to prevent an excessive rise in temperature inside the machine.

[0020]

The present invention is as described above. According to the first aspect of the present invention, there is provided a fixing roller including at least two or more heaters having different light emission distributions, and a rotatable fixing roller. A pressure roller in contact with the pressure roller, a temperature detecting means for detecting a surface temperature of the fixing roller, and a control means for controlling lighting of each heater in accordance with a value detected by the temperature detecting means; A fixing device that heat-fuses and fixes an unfixed toner image on transfer paper at the nip formed by pressure contact with the printer, and its air volume can be switched at least two or more steps to prevent temperature rise inside the machine due to this fixing device In the image forming apparatus having the exhaust fan, the switching of the air volume of the exhaust fan is controlled and performed when the transfer paper is passed, when the machine is started, and when the machine is on standby. In, thereby preventing an excessive increase in the internal temperature, fixing failure or the like there is an effect that it is possible to maintain good image quality does not occur. According to a second aspect of the present invention, in the first aspect of the present invention, the relationship of the air volume by the exhaust fan is set so as to satisfy a condition of paper passing> machine standby time ≧ machine start-up. In addition to the above, there is an effect that it is possible to prevent a sharp rise and to maintain a good image quality without causing a fixing failure or the like.

According to a third aspect of the present invention, in the first aspect of the present invention, the switching of the air volume of the exhaust fan is controlled in accordance with the sheet feeding port of the transfer sheet, thereby preventing an excessive rise in the internal temperature of the apparatus. In addition, there is an effect that it is possible to maintain good image quality without causing a fixing failure or the like. According to a fourth aspect of the present invention, in the first aspect of the present invention, since the relationship of the air flow rate by the exhaust fan is set so that main body feeding ≧ external multi-tray feeding, the internal temperature of the apparatus excessively increases. In addition to the above, there is an effect that it is possible to maintain good image quality without causing fixing defects and the like. According to a fifth aspect of the present invention, in accordance with the first aspect of the present invention, since the switching control of the air volume of the exhaust fan is performed in accordance with the number of sheets passed, an excessive increase in the internal temperature of the apparatus is prevented, and a fixing failure is prevented. There is an effect that it is possible to maintain a good image quality in which no problem occurs. The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the maximum air flow is maintained for a predetermined time immediately after the completion of the transfer sheet irrespective of the sheet feeding port of the transfer sheet and the number of sheets passed. Since the air is exhausted by the exhaust fan for a predetermined period of time, it is possible to prevent an excessive rise in the internal temperature of the apparatus, and to maintain an excellent image quality without causing a fixing failure or the like.

[0022]

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an image forming apparatus of the present invention.

FIG. 2 is an overall configuration diagram showing an identification landing device.

FIG. 3 is a flowchart illustrating an example of a control method according to the present invention.

FIG. 4 is an explanatory diagram showing a change transition of a fixing temperature in the present invention.

FIG. 5 is an explanatory diagram illustrating a state of an air flow path in the image forming apparatus.

FIG. 6 is an explanatory view showing a change transition of a fixing temperature in the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 2 ADF 3 finisher 4 double-sided tray 5 paper feed tray 7 image forming means 8 fixing device 9 relay unit 10 stapler 11 jogger stack unit 15 fixing roller 16 pressure roller 18, 18 a fixing heater 19 fixing separation claw 20 pressure Separating Claw 21 Paper Discharge Branch Claw 23 Thermal Fuse 27 Paper Discharge Sensor 31 Air Discharge Fan (Fixing Cooling Fan) 32 Electrical Cooling Fan 33 PSU Cooling Fan

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H027 DA12 DA32 DA33 DA34 DA35 DA46 DC10 EA12 ED25 EE03 EF04 EF09 EF13 JA11 JB24 JC08 2H033 AA02 AA41 BA29 BA30 BB01 BB28 CA07 CA28 CA30 CA32 CA53 3K058 AA12 AA21 BA

Claims (6)

[Claims] 1. A fixing roller including at least two heaters having different light emission distributions, a pressure roller rotatably pressed against the fixing roller, and a temperature detecting unit for detecting a surface temperature of the fixing roller. And control means for controlling the lighting of each heater in accordance with the value detected by the temperature detecting means. The unfixed toner image is transferred onto the transfer paper at a nip formed by pressing the fixing roller and the pressure roller. In an image forming apparatus having a fixing device for performing hot-melt fixing and an exhaust fan capable of switching its air volume at least two or more stages in order to prevent an increase in the temperature inside the apparatus due to the fixing device, switching of the air volume by the exhaust fan An image forming apparatus is controlled and controlled when a transfer sheet is passed, when the machine is started, and when the machine is on standby. 2. The relationship between the air flow rate of the exhaust fan and the air flow rate is as follows:
2. The image forming apparatus according to claim 1, wherein a setting is made such that a time when the machine stands by is equal to or more than a time when the machine stands up. 3. A switching control of an air volume of an exhaust fan according to a paper feed port of a transfer sheet.
4. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein the relationship of the air volume by the exhaust fan is set such that main body feeding ≧ external multi-tray feeding. 5. The image forming apparatus according to claim 1, wherein switching control of the air volume of the exhaust fan is performed according to the number of sheets passed. 6. Immediately after the completion of the passage of the transfer paper, air is discharged by the exhaust fan for a predetermined time at a maximum air flow for a predetermined time regardless of the paper feed port of the transfer paper and the number of sheets passed. The image forming apparatus according to claim 1.