JP3167887B2 - Fixing device for image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic method, in which an unfixed toner on a sheet as an image carrier is heated and fixed. The present invention relates to a fixing device of an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, a latent image formed on a photosensitive member having a photosensitive layer as a recording medium is visualized with a powder toner, and the visualized image is formed. The transferred toner image is transferred onto a sheet of paper as an image carrier, and since the toner is not fixed, the toner is melted by heat and fused on the paper to fix the toner on the paper. ing. Therefore, the downstream side in the conveyance path of the paper passing through the image forming area, is a fixing apparatus for example in front of the discharge portion of the paper is provided.

FIG. 7 shows an example of this fixing device.
As shown in FIG. 7, a fixing device 70 is constituted by a heat roller 72 having a heater lamp 71 formed of a halogen lamp as a heating source inside, and a pressure roller 73 pressed by a predetermined pressure. I have.

A fixing device 70 shown in FIG. 7 is disposed before a discharge unit 74 in a transport path passing through an image forming unit 75 as shown in FIG. The toner image 76 on the paper P is brought into close contact with the upper heat roller 72, and is heated and fixed by the heat of the heat roller 72.

The image forming section 75 exposes a photoreceptor 77 having a photoconductive layer, which is uniformly charged by a charger 78, to optical information corresponding to a desired image via an optical system 79. An electrostatic latent image is formed on the surface, and a powder toner 81 as a colorant is attached to the latent image by a developing device 80 to visualize the latent image. The toner image on the surface of the photoreceptor 77 visualized by the developing device 80 is transferred to a transfer device 8 disposed at a transfer position.
At 2, the image is electrostatically transferred to the surface of the sheet paper P conveyed to that position. The unfixed toner image 76 is formed on the surface of the sheet paper P after the transfer, and the fixing device 70 described above is used.
Then, the toner image is fused and fixed by heat at the same time while being transported while being brought into close contact with the heat roller 72 by the action of the pressure roller 73.

Heat roller 72 constituting fixing device 70
Is provided with a heater lamp 71 in a cylinder having a core tube made of aluminum (Al) as a core metal, and the surface of the cylinder is covered with a member such as silicon rubber having good releasability from toner and the like. ing. The silicone rubber coating layer and the metal core are bonded and fixed using an adhesive called a primer, and a heater roller 72 is formed.

The surface of the heat roller 72 is maintained at a fixable temperature in order to heat and fix the toner on the sheet paper P. Therefore, the temperature sensor 83 or the like is provided et the thermistor in contact with the surface of the heat roller 72 is provided, in response to the temperature detection signal from the sensor 83, the drive control of the power supply of the heater lamp 71 Then, the temperature of the surface of the heat roller 72 is maintained at the set temperature at which the fixing can be performed.

In FIG. 7, reference numeral 84 denotes a heat roller 7.
2, a cleaning pad for preventing an offset for cleaning toner and the like adhering to the surface and transferring the toner to the sheet paper P again; 85, a cleaning device for removing toner remaining on the surface of the photoconductor 77 after transfer; and 86, a fixing device 70 This is a sheet detection microswitch for detecting the sheet sheet P that has passed and is discharged.

An example of the temperature control of the fixing device 70 in FIG. 7 is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-295873. This is, as shown in FIGS. 8 and 9, in response to turning on the power of the copying apparatus or the like.
First, the heater lamp 71 in FIG. 7 is continuously turned on to drive the heat roller 62 so that the surface temperature thereof quickly rises to the target set temperature Ts.

Then, the temperature T before the target set temperature Ts is set.
o, the heater 61 is periodically turned on or off to perform power supply control, to prevent overshoot due to a rapid rise in surface temperature, and to prevent overshoot due to the target set temperature Ts. Control is performed so that the ripple due to the temperature difference is reduced. At this time, after reaching the target set temperature Ts, as shown in FIG.
The power is supplied for a period of time from when the temperature falls below 1 to the set temperature Ts until the temperature reaches the set temperature Ts.

In this case, the thermal response of the heat roller 71 is very poor.
Even if 1 is turned off, the core metal of the heat roller is heated, the heat is further transmitted to the coating layer of the heat roller, and the surface of the heat roller is heated to a considerable temperature. Therefore, a large ripple due to the temperature of the surface of the heat roller 72 is formed.

In the above-described driving, the ripple for maintaining the set temperature Ts may be considerably large. In order to further reduce the ripple, when the temperature becomes equal to or lower than the temperature Ts as shown in FIG. fixed time (T o
n ) Turn on the heater lamp 71 and wait for a predetermined time (Tof
f) The heater lamp 71 is turned off. This allows
The control is such that the surface temperature of the heat roller 72 is maintained at a target set temperature Ts. Thus, the temperature is maintained so as to reduce the temperature ripple.

[0013]

[SUMMARY OF THE INVENTION According to by that heating control in the fixing apparatus according to the prior art of the above publications, is effective in controlling the heat roller 72 to the fixable temperature Ts.
That is, in the control for maintaining the set temperature Ts, the temperature ripple can be reduced, and stable fixing can be performed.

However, according to the above-described temperature control of the fixing device, when the temperature of the heat roller 72 is controlled to the set temperature Ts, if the temperature falls below the set temperature Ts, the heater lamp 7
1 is turned on for a predetermined long time. In particular, the ratio of the period in which the heater lamp 71 is turned on is much larger than the period in which the heater lamp 71 is turned off. for that reason,
If the temperature reaches the set temperature Ts within the period (Ton) during which the heater lamp 71 is turned on, the heater lamp 71 is overdriven at that point in time, similarly to the control in FIG. As a result, power is excessively supplied, and the surface of the heat roller 72 is heated to a temperature or more sufficient to fix the toner, and the temperature ripple increases.

Further, according to Japanese Patent Laid-open flat 4-295873, by paying attention to the temperature of the heat roller 72, and <br/> intended to maintain suppressing ripples its temperature to the set temperature Ts Therefore, the temperature of the interface between the Al core constituting the heat roller 72 and the coating layer of silicon rubber, that is, the interface temperature of the core is not a technique suggested at all.
Therefore, in the control process of performing control for maintaining the heat roller 72 at the set temperature Ts, the core metal may be heated to a temperature equal to or higher than the temperature at which the coating layer is separated from the core metal. In addition, this causes a problem that the silicone rubber is separated from the cored bar for a long time, that is, when used for a long time.

[0016] In particular, the metal core surface and the silicon rubber, for example, because it is adhered at 180 ° C. of about heat-resistant adhesive, silicone rubber adhesive is melted metal core and the metal core is overheated More peel off. When the surface temperature of the heat roller 72 is controlled at, for example, about 170 ° C. as a set temperature, the temperature of the core metal itself may be higher than 170 ° C. Therefore, if the core is heated to a temperature of 180 ° C. or higher, and if this is continued for a long time, the adhesive is peeled off due to the problem of heat resistance and the like, and the silicon rubber is separated from the core, making the fixing device unusable.

In this case, the heater lamp 7 described in the above publication is used.
According to the control of the power supply to the power supply 1, the power supply 10 is set at 10
The temperature which is lower by about ° C. is set as the first set temperature To, and at this time, the temperature of the core metal of the heat roller 72 exceeds 180 ° C. or more. Further, after the set temperature Ts, when the temperature falls below the set temperature Ts, the heater lamp 71
Since the OFF time is much shorter than the ON time, excessive heat is supplied even during the period in which the set temperature Ts is maintained. The temperature is maintained at or above the specified temperature, and the coating layer is peeled off over time.

An object of the present invention is to solve the above-mentioned problems and to prevent separation between a core of a heat roller for constituting a fixing device and a coating layer coated on the core. In this case, it is possible to control the amount of power to be supplied to the heating source. Achieving this objective also reduces temperature ripple.

It is another object of the present invention to prevent excessive heating and to apply a necessary minimum amount of heat in temperature control after a target temperature is reached when heating a heat roller. It is.

[0020]

According to the present invention, there is provided a heat roller having a heating source therein and having a surface heated to a desired temperature, and a pressure roller applied to the heat roller. An unfixed toner image formed on the sheet paper by controlling the supply of power to the heating source by controlling the supply of power to the heating source. the in the fixing device of the image forming apparatus was formed by maintaining the fixable temperature, the temperature to the set roller surface temperature never coating layer of the heat roller is separated from the metal core and the first set temperature, the Roller surface higher than the first set temperature capable of fixing toner image
The temperature of the second set temperature, a temperature detecting sensor for detecting the surface temperature of the heat roller, and the detected temperature of the temperature detection sensor, and comparison means for comparing the first and second set temperature, the comparison When the temperature is equal to or higher than the first set temperature according to the comparison of the means, the heating source is set to a first ON / OFF preset value.
Control means for maintaining the heat roller at the second set temperature by driving until the temperature reaches the second set temperature under the condition of the ratio.
The first ratio of / OFF is set so as not to exceed the upper limit temperature of the core metal in which the coating layer of the heat roller is not peeled off from the core metal, and the ON time is set to 1 or less with respect to the OFF time. Features.

The control means rotationally drives the heat roller and the pressure roller in response to turning on the power to the heating source, and in response to the heat roller reaching a second set temperature, the heat roller and the heating roller. It is characterized in that the rotation of the pressure roller is stopped.

[0022]

Further, the heating source control means increases the ON time ratio of the heating source in order to maintain the heat roller surface temperature at the second set temperature in response to the start of driving of the image forming apparatus. In addition, the second ON / OFF ratio is set larger than the first ON / OFF ratio.

[0024]

According to the fixing device of the image forming apparatus constructed as described above, at the start of power-on, power is continuously supplied to the heating source for heating the heat roller. Therefore, the rise to the target temperature, that is, the second set temperature, can be shortened as much as possible.

Then, when the temperature of the heat roller surface reaches the first set temperature, the supply is controlled at a predetermined first ON / OFF ratio without continuously supplying power to the heating source. For example, supply power to the heating source for one second,
The power supply to the heating source is stopped for seconds. That is, ON / O
The first ratio of the FF is 1/3 (the ON / OFF ratio is 1:
Controlled in 3). As a result, although the temperature rise of the heat roller becomes slower than at the time of rising, the temperature gradually rises to the target second set temperature.

Therefore, after the temperature reaches the second set temperature, the power supply to the heating source is stopped (OFF), and in order to maintain the second set temperature, if the temperature falls below the second set temperature,
As described above, the second set temperature is maintained by controlling the driving of the heating source at a predetermined ON / OFF ratio.

[0027] Here, in response to when the power is turned on in the falling Chiage of the heat roller to the second predetermined temperature of interest, by leaving the heat roller and the pressure roller is rotationally driven, even if the pressure roller It can be preheated. Therefore, the amount of heat taken by the pressure roller at the start of the image operation can be small, the drop in the surface temperature of the heat roller is small, and even if the first ratio of ON / OFF when driving the heating source is small, it is sufficient. Can be maintained at the second set temperature at which fixing can be performed. In this case, since there is no excessive power supply,
The core temperature of the heat roller does not exceed the upper limit temperature at which the coating layer will be peeled off.

In the above control, the first set temperature is set to the surface temperature of the heat roller when the upper limit temperature of the core metal constituting the heat roller is reached. The temperature of the heat roller surface is controlled so as to increase without exceeding the upper limit temperature at which the coating layer to be coated may be peeled off. As a result, the layer covered by the core is prevented from being peeled from the core, and the problem of the life of the fixing device can be solved. In particular, since the first set temperature is set to a temperature at which the core metal temperature of the heat roller does not exceed the upper limit, the driving of the heating source is thereafter performed at a preset first ON / OFF ratio. since the Ru-driven, will be transmitted as heat for heating the set temperature heat supplied via the core metal is an object of the heat roller.

At this time, the first ratio of ON / OFF is preferably such that the ON time is equal to or less than the OFF time. In other words, ON for 1 second and OF for 3 seconds
The ON time ratio at the time of F becomes 1/4, and ON / OF
The ratio of F is 1/3. By setting like this,
The overheating state can be prevented, the temperature of the heat roller surface can be controlled without largely deviating from the second set temperature, and the temperature ripple can be reduced accordingly. In addition, an increase in the core temperature of the heat roller can be suppressed.

Further, when there is a command to start the image forming operation while maintaining the second set temperature, the second ratio of ON / OFF for supplying power to the heating source becomes larger than the above-mentioned first ratio. It is set as follows. For example, the ON time ratio is set to be larger than the ON ratio of the first ratio. Specifically, the OFF time is shortened, the ON time is fixed, and O
After N, the operation of turning off for 2 seconds is repeated. for that reason,
The ON time ratio becomes 1/3, and the second ON / OFF ratio becomes 1/2, which is set to be larger than the first ratio.

As a result, the amount of heat supplied to the heat roller somewhat increases, and the temperature of the core metal tends to increase. At this time, when the roller is driven to rotate by the start command, the heat of the heat roller is taken away by the pressure roller, so that the increased heat amount is supplemented as the heat amount for heating the pressure roller. The temperature rise of the heat roller can be suppressed and the second set temperature can be maintained, and at the same time, the temperature rise of the core metal of the heat roller can be prevented. Further, even if the pressure roller is sufficiently heated, heat is taken away by the sheet paper as the image carrier passing through the fixing device. Therefore, the amount of heat taken can be covered by the above-mentioned drive ratio. As a result, to suppress the temperature rise of the metal core of the heat roller, and can maintain the surface temperature of the heat roller in the second set temperature.

[0032]

FIG. 1 is a time chart showing the temperature control of the fixing device according to the present invention, FIG. 2 is a time chart showing the rising state in FIG. 1 in detail, and FIG. FIG. 4 is a time chart showing a driving state after rising to a possible state, FIG. 4 shows a specific example of the fixing device of the present invention, FIG. 5 is a control block diagram relating to temperature control of the fixing device of the present invention, and FIG. 1 is an enlarged view of a main part in which a fixing device of the invention is applied to a color image forming apparatus.

In FIG. 6, reference numeral 1 denotes an image forming unit. The image forming unit includes a photoconductor 2, various process means (not shown) for forming a desired toner image on the photoconductor surface, and an image forming unit on the photoconductor surface. A transfer drum 3 for transferring the formed toner image to a sheet-like sheet.

As shown in FIG. 7, a charger for uniformly charging the surface, an optical system for exposing the charged surface with an optical image, and a formed latent image for each color are formed around the photosensitive member 2 as shown in FIG. A plurality of developing units for developing with the toner powder, a transfer unit configured to transfer the formed toner images of the respective colors on a sheet-like paper P closely adhered to the transfer drum 3, and a toner remaining after the transfer. A cleaning device for removing, a static eliminator for removing remaining electric charge, and the like are arranged.

The transfer drum 3 has a peripheral length set to a length capable of winding a sheet of the maximum size. The transfer drum 3 has an inner layer 31 and a surface layer 32 formed on a cylinder 30. The sheet P is electrostatically attracted, for example, and the leading edge of the sheet P sucked in synchronization with the rotation of the photoconductor 2 is driven to rotate so as to coincide with the formed toner image.

The straight line perpendicular to the straight line connecting the center of the photosensitive member 2 and the transfer drum 3, that is, the tangential direction 4 of the contact portion (nip portion) between the photosensitive member 2 and the transfer roller 3, is on the photosensitive member 2 side. The fixing device 5 according to the present invention is disposed at the upper part.
In particular, the heat roller 50 and the pressure roller 54 of the fixing device 5
The fixing device 5 is disposed so that the hip portion (contact portion) of the fixing device 5 is above the line 4.

Then, the transfer of the formed toner image to the sheet paper P in close contact with the transfer drum 3 is completed.
It is peeled off from the peeling claw 33 and guided to the fixing device 5.
The peeling claw 33 operates in synchronization with the rotation of the transfer drum 3, and is separated from the surface of the transfer drum 3 when transferring a toner image formed on the photoreceptor 1, and is in close contact with the sheet paper. When the transfer of the toner image is completed without separating the sheet P, the sheet P is separated from the leading end of the sheet paper P closely contacted with the surface of the transfer drum 3.

The leading end of the separated sheet P first comes into contact with the heat roller 50 side of the fixing device 5, and then is fed into a nip portion with the pressure roller 54. The sheet is guided in a substantially straight state without changing the posture of the sheet until the sheet is fed.

As a result, the sheet paper P is guided to the heat roller 50 without being forcibly changed in the direction , so that the transferred unfixed toner is not separated or scattered. , Good fixing becomes possible. Also,
After the sheet paper P comes into contact with the heat roller 50, it is guided to the nip portion in a preheated state, so that the fixing action is further improved.

Therefore, the fixing device 5 of the present invention comprises the heat roller 50 and the pressure roller 54 as described above, and as shown in FIG. 4, details of the core metal 51 made of aluminum Al. On the surface, a rubber coating layer 52 made of, for example, silicon rubber or the like, which is excellent in releasing property from toner
Is adhered and fixed with an adhesive called a primer, for example, to form the heat roller 50. This heat roller 50
A heater lamp 53 including a halogen lamp or the like as a heating source for maintaining the surface temperature of the heat roller 50 at a fixing temperature (set temperature) is provided inside the metal core.

The heat roller 50 is formed with a considerable contact width (nip width) in order to efficiently fix the toner on the sheet paper P with the heat roller 50.
In order to bring the sheet paper P into close contact with the heat roller 50 side, a rotatable supported metal core 55 is provided with a thick or low hardness or both silicone rubber or sponge with PF.
An A (perfluoroalkyl = ethylene copolymer resin) tube 56 is provided with a pressure roller 56 formed by coating. The pressure roller 56 is considered to improve the heat insulation by providing the thick covering layer 56 as described above, and to reduce the temperature drop on the surface of the heat roller 50 on the image surface side. As described above, the nip width in the transport direction in contact with the heat roller 50 is increased.

On the other hand, in order to maintain the surface temperature of the heat roller 50 at a predetermined set temperature, the power supply to the heater lamp 53 is drive-controlled. For this purpose, a temperature detection sensor 57 composed of a thermistor or the like arranged so as to be in contact with the surface of the heat roller 50 is provided. According to the output of the temperature detection sensor 57,
According to the control block diagram shown in FIG.
Is controlled.

In FIG. 5, the heater lamp 53 is
Power is supplied according to the driving of the heater driving circuit 6.
The heater driving circuit 6, a detection signal from the temperature sensor 5 7 digitized via an A / D converter 7, it is digitized at the sampling circuit 8. A comparison circuit (means) 10 compares the converted value with a value of a table (look-up table) 9 storing a value or the like corresponding to a predetermined set temperature or the like. The supply of power to the heater lamp 53 via the heater drive circuit 6 is controlled on the basis of the above.

The table 9 stores a value corresponding to the above-mentioned set temperature and the like, and a value corresponding to the amount of power to be supplied to the heater lamp 53 according to the comparison result of the comparison circuit 10. I have. As the control of the electric energy, a method of controlling a time width under a constant voltage, a method of controlling a current amount under a fixed period of time,
Alternatively, some control the voltage values, or control them in combination, and one of them is stored in the table 9.

In the present invention, the voltage value is fixed,
The amount of power is controlled by controlling the time. For example, the ON / OFF ratio between the supply (ON) time and the non-supply (OFF) time is stored in the heater lamp 53. As for the current amount, the current amount in a certain time is stored, and as the voltage value, the voltage value in a certain time is stored. In short, by controlling the ON / OFF ratio of the present invention described above, the amount of consumed power is controlled in exactly the same way as when controlling the amount of current or the voltage value. controlling the ratio of the OFF not only controls the width of the ON time, Ru <br/> Oh those containing controls the voltage value or current amount. For simplicity of explanation, the following simply ON / OF
The control of the ratio of F means that it is turned on in the power supply of a constant voltage.
The case where the time width and the OFF time width are controlled will be described.

An example of the temperature control of the fixing device 5 according to the present invention having the above configuration will be described with reference to the time chart shown in FIG.

In FIG. 1, the first set temperature T1 is lower than the second set temperature T2 at which the heat roller 50 can fix the toner image.
Is the surface temperature of the heat roller 50 when it reaches the upper limit temperature of the boundary temperature at which the core metal 51 and the rubber coating layer 52 can be prevented from peeling off. For example, if the upper limit temperature is 180 ° C., power is supplied to the heater lamp 53, and the temperature of the surface of the heat roller 50 when the core metal 51 reaches the upper limit of the boundary temperature is defined as the first set temperature T1. Set. That is, the surface temperature of the heat roller 50 when the temperature reaches 180 ° C., which is the upper limit temperature at which the rubber coating layer 52 is not peeled from the core metal, is set as the set temperature T1.

More specifically, the heat roller 50 has a core 2 made of aluminum having a thickness of 2 mm and a diameter of 30 mm.
High thermal conductivity L having a thickness of 900 to 940 μm as the coating layer 52
The pressure roller 54 has a thickness of 2 mm and a diameter of 30 mm to 50 μm, and a high release LTV layer (surface layer) having a thickness of 30 to 50 μm. 5.5 mm thick L on 30 mm core 55
The TV rubber 56 was configured by coating a PFA tube on the surface. Therefore, when a halogen lamp of 800 W is used as the heater lamp, the temperature of the core metal 51 is 170 ° C. to 180 ° C.
° C, especially 175 ° C (set as the upper limit temperature), since the surface temperature is 134 ° C.
It is set as the set temperature T1.

In particular, if the diameter of the heat roller 50, the thickness of the metal core 51 and the thickness of the coating layer 52, the material of the rubber coating layer 52, and the like are determined, the first set temperature T1 is determined when the fixing device 5 is assembled. The surface temperature of the heat roller 50 when the temperature reaches an allowable upper limit temperature at which the core metal 51 and the rubber coating layer 52 do not peel off is measured, and the temperature at this time is determined as a first set temperature T1. Therefore, it is best to set the temperature at which the peeling does not occur at a slightly lower temperature in consideration of safety than the upper limit temperature.

Therefore, when the power of the color image forming apparatus is first turned on, the power is continuously supplied to the heater lamp 53. Here, as described above, the heat roller 5
Until the upper limit of the boundary temperature between the zero cored bar 51 and the rubber coating 52 reaches the first set temperature T1 which does not exceed 180 ° C., for example, the heater drive circuit 6 supplies a constant voltage power to the heater lamp 53. Supplied. That is, when the comparison result by the comparison circuit 10 confirms that the temperature T detected by the temperature detection sensor 57 is lower than the first set temperature T1,
The heater drive circuit 6 supplies power to the heater lamp 53 continuously.

As a result, the heat roller 50 is rapidly heated, and the rise of the surface temperature to the target second set temperature T2 can be shortened. At this time, the heat roller 50 and the pressure roller 54
Are rotationally driven together in response to turning on of the power supply.

Then, by continuously supplying power to the heater lamp 53, the surface temperature of the heat roller 50, for example, 1
When the comparison circuit 10 confirms that the temperature has reached the first set temperature T1 of 34 ° C., from the continuous supply state of the power, under the condition according to the ON / OFF ratio stored in the table 9 , The heater lamp 53 via the heater drive circuit 6
Is driven. In this case, the ratio between ON and OFF is determined so that the temperature of the core metal 51 does not exceed the upper limit temperature and is stabilized near the upper limit temperature. In particular, when the ON / OFF ratio is 1 or less, the amount of heat supplied does not become excessive during heating control at the first set temperature T1 or more, and the surface temperature of the heat roller 50 gradually increases. The temperature of the gold 51 can be maintained near the upper limit.

The driving based on the ON / OFF ratio is as follows.
For example, after being turned on for 1 second (supplying power to the heater lamp 53 for 1 second), it is turned off for 3 seconds, and this is sequentially and repeatedly controlled. The ON / OFF ratio at this time is 1/3, and 1
It is as follows. In addition, the ON time ratio is the ON time during continuous supply.
If the ratio is "1", it is "1/4".

As shown in detail in FIG. 2, the above-described state is such that after the heat roller 50 is heated by the heater lamp 53 and reaches the first set temperature T1, the heater drive circuit 6 drives the heater lamp 53 continuously. Are sequentially and repeatedly driven at, for example, the ON / OFF ratio previously stored.
As a result, the temperature of the surface of the heat roller 50 is gradually increased without the temperature of the core metal 51 exceeding the upper limit temperature To.

Therefore, after the first set temperature T1, the surface temperature of the heater lamp 53 rises slightly gradually. At this time, the temperature of the core metal 51 has reached the upper limit temperature of, for example, 175 ° C. in the state where the first set temperature has been reached. Do not exceed, heater lamp 5
3 heats the rubber coating layer 52. Therefore, the rubber coating layer 52 is heated, and the surface temperature of the heat roller 50 gradually increases. And finally, the second set temperature T2,
That is, the temperature reaches the temperature T2 at which the toner can be heated and fixed.
When the temperature reaches the second set temperature T2, the temperature is detected by the temperature detection sensor 57, and the power supply to the heater lamp 53 is released, that is, the heater lamp 53 is turned off. At the same time, the rotation of both rollers 50 and 54 of the fixing device 5 is stopped.

The heat roller 50 is heated to the second set temperature T2.
Is heated, the color image forming apparatus can be used in this state, the roller is driven to rotate by a start command for image formation, and image formation is started.

On the other hand, when the heat roller 50 is at the second set temperature T
After reaching 2, the driving of the heater lamp 53 is controlled in accordance with the detection signal from the temperature detection sensor 57 so as to maintain the temperature. As shown in the time chart of FIG. 3 in detail, the power is supplied to the heater lamp 53 until the heat roller 50 reaches the second set temperature T2 in a period in which the temperature falls below the second set temperature T2. At this time, the heater lamp 53 is turned on / off in a predetermined manner in the same manner as after the temperature reaches the first set temperature T1.
Drive control is performed so that power is supplied at the ratio of F. Thereby, the temperature of the core metal 51 can be controlled to a temperature range in which the rubber coating layer 52 is not peeled, and therefore, the coating layer 52 is peeled without being maintained at or above the upper limit temperature at which the rubber coating layer 52 is peeled from the core metal 51. The heat roller 50
Life can be extended.

Therefore, when waiting in the above state,
When the image forming operation start command is output, the sheet paper P
Before the rollers pass through the fixing device 5, both rollers 5 of the fixing device 5
0 and 54 are rotationally driven. Therefore, the surface temperature of the heat roller 50 temporarily drops as shown in FIG. This is because the heat of the heat roller 50 is taken away by the pressure roller 54 side, and it is necessary to recover the heat.
For this purpose, the ON / OFF ratio is changed instead of the drive ratio of the heater lamp 53 during standby. This ratio is also stored in the above-described table 9 in advance.

[0059] In a second ratio for driving and controlling the heater lamp 53 at the start of image forming operation, since the heat of the heat roller 50 is taken away to the pressure roller 54 side, the first set temperature ON / OFF of the first ratio after T1
The ratio of ON time is set to be larger than the ratio of. As a specific example, the OFF time is shortened while the ON time is kept constant.

For example, in the standby state after the first set temperature T1 and after reaching the second set temperature, the ON / OFF state is set.
If the first OFF ratio is 1: 3 (for example, ON for one second)
Then, when the heater lamp 53 is turned off for 3 seconds, the ratio (1/3) of the ON time for driving the heater lamp 53 is set to be larger than the ON time ratio (1/4) at the first ratio, such as 1: 2. I'm making it big. As a result, the power supply amount of the heater lamp 53 is increased, and the supplied heat amount is increased.

As a result, the amount of heat taken to the pressure roller 55 side is compensated, and the heat roller 50 is kept at the second set temperature T.
It can also supplement the amount of heat required to maintain 2. In addition, by rotating the pressure roller 54 at the time of startup when the power is turned on,
Since the pressure roller 54 is also heated to some extent, the heat of the heat roller 50 is not taken away in a large amount even if the pressure roller 54 rotates when the image operation starts. Therefore, at the start of roller rotation,
The heat roller 50 can be sufficiently maintained at the second set temperature T2 even when the heater lamp 53 is driven without increasing the power supply ratio when the heater lamp 53 is driven and the first ratio controlled during standby is maintained.

However, when both the rollers 50 and 54 of the fixing device 5 are not rotated when the power is turned on, the amount of heat taken by the pressure roller 54 increases, so that it is effective to increase the ON ratio as described above. Become.

Then, in the color image forming apparatus, the toner image is transferred to the sheet
By the time the sheet P is sent to the fixing device 5,
As described above, even if both the rollers of the fixing device 5 are rotated and the temperature of the heat roller 50 temporarily drops, the temperature sufficiently recovers to the second set temperature T2 before that. Even if the ratio of the ON time of the power supply for driving the heater lamp 53 is increased, if the sheet paper P is conveyed, the sheet paper P
Since the heat of the heat roller 50 is deprived of the heat, an excessive amount of heat is not supplied, and the temperature of the core metal 51 of the heat roller 50 does not exceed the upper limit temperature. Therefore, the heater lamp 53 can be driven and controlled with the optimum amount of power, and unnecessary power consumption is not performed.

Next, the sheet paper P is guided between the rollers 50 and 54 of the fixing device 5 and passes therethrough, whereby the unfixed toner image on the sheet paper P is fixed. At this time, as described above, a large amount of heat is removed from the heat roller 50 and the pressure roller 55 in order to fix the sheet paper P and the toner image. Therefore, the temperature of the heat roller 50 decreases. Also in this case, the ON /
The second ratio of OFF is set to O with respect to the first ratio in the standby state.
Since the ratio of N hours is large, it is possible to supply an amount of power that can compensate for the amount of heat taken by the sheet paper P.

Therefore, when the heater lamp 53 is driven at the stage where the image forming operation, that is, the printing operation is started, the ON / OFF ratio is set to be smaller than the standby ratio at the timing when the heater lamp 53 is driven. The ratio is set large so that the ON time becomes long. Then, when the printing operation is completed, the rollers 50 and 54 of the fixing device 5 are stopped, thereby returning the second ratio of ON / OFF supplied to the heater lamp 53 to the first ratio in the standby state. Here, in the ON / OFF ratio, the ratio between the ON time and the OFF time is 1: 1 in any case.
Is set to a value (1 or less) that does not exceed the maximum temperature, the temperature rise of the cored bar 51 can be suppressed, and the temperature can be prevented from exceeding the upper limit temperature.

When changing the above ON / OFF ratio,
In particular, the OFF time is set short. This is advantageous in that the storage capacity of the table 9 can be reduced. That is, since the ON time is fixed,
By storing the OFF time, the memory capacity can be reduced. This can be similarly performed by setting the OFF time constant and setting the ON time long.

In this case, since the repetition cycle of ON and OFF for driving the heater lamp 53 becomes long, the temperature ripple tends to become large. Therefore, shortening the repetition period works very effectively by reducing the ripple. Therefore, it is best to shorten the OFF time, which has the effect of shortening the cycle.

Further, the amount of power supplied to the heater lamp 53 is controlled at the ON / OFF ratio. Therefore, when a voltage is supplied at a constant cycle or when the amount of electric power is changed, the same operation can be performed by changing a voltage value or a current value at the time of ON (supply) at a constant cycle. Is a large change in voltage or current instead of time, which is exactly the same. Therefore, controlling the ON / OFF ratio is
This includes the control of the current or the voltage value, in addition to the control described in the embodiment.

Next, if the printing operation is not started, in order to save energy and shorten the start-up time for making the image forming apparatus usable, for example, 2
If the printing operation does not start during the waiting time of one minute, the energy saving mode is set in which the amount of power supplied to the heater lamp 53 is reduced in order to reduce the power consumption in the fixing device 5. This eliminates unnecessary power consumption,
In addition, a preheating mode in which the fixing device 5 is preheated in advance.

For this purpose, without maintaining the surface temperature of the heat roller 50 at the second set temperature T2, a temperature lower than the first set temperature T1, for example, at a temperature of about 100 ° C. I do. Therefore, when driving the heater lamp 53, the ratio of the ON time is set as follows:
It is set to about 1 / N (N> 10). For example, if the power consumption at the time of ON by the heater lamp 53 is about 800 W, in order to supply power corresponding to 25 W,
If the ON / OFF ratio is turned on for 1 second and turned off for 31 seconds, for example, the total consumption (the ratio of the ON time) becomes 1 /
32, which is about 25 W of power consumption. At this time,
The above ratio may be appropriately set so that the surface temperature Tp of the heat roller 50 is, for example, about 100 ° C.

Further, if a heater lamp for energy saving is separately provided together with the heater lamp 53 and the heater lamp has a power amount of about 25 W, the heater lamp is always driven to be lit, so that the above-described 100 lamp can be easily obtained. It is possible to control the temperature around ℃. However, even if one heater lamp 53 is used as described above, if the purpose of easily setting the preheating mode can be achieved by controlling the ON / OFF ratio, when the fixing device 5 is assembled,
If there is no need to arrange two heater lamps, the assembly is simplified.

In the setting of the energy saving mode, 2
It has been described that the setting is automatically performed when the apparatus is left idle in a standby state in which the image forming apparatus is not used (usable state of the image forming apparatus) for 2 minutes. The required time may be arbitrarily set. Further, a specific key for setting the energy saving mode may be provided, and the energy saving mode may be set by operating the key.

[0073] release of this energy-saving mode, the mode release key provided by the operation of the release key. When this mode is released, as shown in FIG.
0 and 54 are driven to rotate, and the heater lamp 53 is driven.
At this time, the heater lamp 53 is continuously turned on without performing drive control at the first ON / OFF ratio as described above. When the temperature reaches the first set temperature T1, as described above, the heater lamp 53 is turned ON / OF.
Drive at the first ratio of F. By doing so, the core metal 51 can be maintained at a temperature not higher than the upper limit temperature at which the coating layer 52 does not peel off.

Further, since the surface temperature Tp of the heat roller 50 is maintained at, for example, about 100 ° C., the time required for the heat roller 50 to rise to the second set temperature T2 is very short. As a result, from the state where the signal of the print start command is output, the time when the image forming operation is started and the toner image is transferred to the sheet paper P, and the time when the toner image is conveyed to the fixing device 5, the heat roller 50 The temperature can be sufficiently raised to the second set temperature. As a result, printing can be started immediately without waiting for printing to start.

For this purpose, the energy-saving mode is released not only by operating a release key provided separately but also by receiving a print start command signal in response to a print switch operation. Is very effective. Then, the heat roller 50 at the time of the energy saving mode, the first sheet paper P in the image forming apparatus, by setting the temperature Tp rises sufficiently second set temperature within the time reaching to the fixing device 5 Good.

[0076]

According to the fixing device of the present invention, even if the surface temperature of the heat roller constituting the fixing device is controlled so as to maintain the temperature at which the fixing can be performed, the coating applied to the core metal of the heat roller can be achieved. There is no fear that the layer is peeled off, and the life of the fixing device can be extended. It also prevents overheating,
Control the temperature of the surface without greatly deviating from the second set temperature
And the temperature ripple can be reduced accordingly. Moreover,
It is possible to suppress an increase in the temperature of the core metal of the heat roller.

By rotating the heat roller or the like in advance, the pressure roller can also be heated, so that a large amount of heat is not removed from the heat roller in the image forming operation and a small amount of power is used as described above. The heat roller can be maintained at the set temperature in a state where the coating layer is prevented from peeling off.

Further, there is no waste of power supply to the heating source, and the effect of preventing overheating in an excessive state and preventing peeling of the coating layer is enhanced.

Further, when the image forming operation is started, an amount of electric power is supplied to compensate for the amount of heat taken by the image carrier, so that the heat roller can be maintained at a temperature at which the heat roller can be fixed in a state where the coating layer is prevented from peeling off. Poor fixing can also be prevented.

According to the fixing device of the present invention, the ripple of the surface temperature of the heat roller can be controlled to be very small, so that the fixing operation of the toner image is stabilized.

[Brief description of the drawings]

FIG. 1 is a time chart in temperature control of a fixing device according to the present invention.

FIG. 2 is a time chart showing a relationship between a core metal temperature and a heat roller surface temperature related to temperature control at the start of FIG. 1;

FIG. 3 is a time chart showing control of power supply for maintaining the temperature after the fixing device in FIG. 1 reaches a temperature at which fixing can be performed.

FIG. 4 is a sectional view showing a specific example of a fixing device according to the present invention.

FIG. 5 is a control block diagram relating to power supply of a fixing device according to the present invention.

FIG. 6 is a sectional view of a main part of an apparatus in which the fixing device of the present invention is applied to a color image forming apparatus.

FIG. 7 is a cross-sectional view illustrating a conventional example of an image forming apparatus including a fixing device.

FIG. 8 is a time chart illustrating a control example of power supply to a heating source in a conventional fixing device.

FIG. 9 is a time chart showing an example of control for maintaining a fixable temperature required for power supply to a heating source in a conventional fixing device.

FIG. 10 is a time chart showing another control example for maintaining a feasible temperature required for power supply to a heating source in a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming part 2 Photoreceptor 3 Transfer drum 5 Fixing device 50 Heat roller 51 Core bar 52 Coating layer 53 Heater lamp (heating source) 54 Pressure roller 57 Temperature detection sensor 6 Heater drive circuit 9 Look-up table 10 Comparison circuit T1 First 1 set temperature T2 2nd set temperature

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-295873 (JP, A) JP-A-52-2258 (JP, A) JP-A-58-4167 (JP, A) JP-A-59-258 83219 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (3)

(57) [Claims] 1. A heat roller having a heating source inside and having a surface heated to a desired temperature, and an image carrier pressed by the heat roller and brought into close contact with the heat roller. A fixing roller for an image forming apparatus, comprising: a pressure roller; and controlling the supply of power to the heating source to maintain the surface of the heat roller at a temperature at which an unfixed toner image formed on the sheet paper can be fixed. In the above, the roller surface temperature set to a temperature at which the coating layer of the heat roller does not peel off from the core metal , the first set temperature and
A temperature higher than the first set temperature at which the toner image can be fixed .
The chromatography La surface temperature to second set temperature, a temperature detecting sensor for detecting the surface temperature of the heat roller, and the detected temperature of the temperature detection sensor, and comparison means for comparing the first and second set temperature When the temperature is equal to or higher than the first set temperature by the comparison of the comparing means,
Control means for maintaining the heat roller at the second set temperature by driving the heat source under the condition of a first ON / OFF first ratio until the heat source reaches the second set temperature; Wherein the first ratio of ON / OFF for driving the heating source is set to a condition that does not exceed the upper limit temperature of the core metal in which the coating layer of the heat roller is not peeled off from the core metal , ON time OF
A fixing device for an image forming apparatus, wherein the fixing time is set to 1 or less with respect to the F time. 2. A heat roller having a heat source therein and having a surface heated to a desired temperature, and an image carrier pressed by the heat roller and brought into close contact with the heat roller. A fixing roller for an image forming apparatus, comprising: a pressure roller; and controlling the supply of power to the heating source to maintain the surface of the heat roller at a temperature at which an unfixed toner image formed on the sheet paper can be fixed. In the above, the roller surface temperature set to a temperature at which the coating layer of the heat roller does not peel off from the cored bar, and the first set temperature
A temperature higher than the first set temperature at which the toner image can be fixed .
The chromatography La surface temperature to second set temperature, a temperature detecting sensor for detecting the surface temperature of the heat roller, and the detected temperature of the temperature detection sensor, and comparison means for comparing the first and second set temperature In response to turning on the power to the heating source, the heating source is continuously turned on, and the heat roller and the pressure roller are driven to rotate. If it is, the heating source is driven under the condition of the first ON / OFF ratio set beforehand until the temperature reaches the second set temperature, and when the heat roller reaches the second set temperature, the heat roller and the heating roller are heated. Control means for stopping the rotation of the pressure roller, wherein the first ratio of ON / OFF for driving the heating source is such that the coating layer of the heat roller is not peeled off from the core metal. > Do not exceed the temperature limit It is set to matter, the ON time OF
A fixing device for an image forming apparatus, wherein the fixing time is set to 1 or less with respect to the F time. 3. An on / off control unit for driving the heating source ON or OFF in response to a start of an operation of the image forming apparatus, the ON / OFF driving the heating source to maintain the heat roller at a second set temperature. 3. The fixing device for an image forming apparatus according to claim 1, wherein the second ratio has a larger ON time ratio than the first ratio of ON / OFF after the first set temperature.