JPH0740162B2 - Image forming device - Google Patents

Description

The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine and a printer.

(Prior Art) Conventionally, as a fixing device of this type, a pair of fixing rollers, at least one of which has a heating source such as a halogen heater, nips and conveys a support such as copy paper carrying an unfixed image. There is a roller fixing device for fixing the unfixed image. The fixing roller is warmed up by turning on the power of the image forming apparatus and energizing the heating source at the same time to rapidly heat the fixing roller until it reaches a predetermined temperature. The surface temperature of this fixing roller is detected by a temperature detecting element, and when the warm-up is completed and the temperature reaches a predetermined temperature, the energization of the heating source is controlled so as to maintain the temperature thereafter, and the fixing roller is always stable. It is designed to maintain sex.

By the way, from the heated fixing roller, heat is released by conduction heat or radiant heat through the supporting member and the driving member, so that the temperature inside the machine remarkably rises and thermal deterioration of electric parts and mechanical parts, There is a problem that thermal damage is caused, and cleaner and toner blocking in the developing device occur.

Therefore, in order to solve the above problems, an exhaust heat fan is provided at the rear or side of the fixing device, and the exhaust heat fan is constantly rotated when the power is turned on to prevent the temperature rise inside the machine.

However, in this case, the so-called morning first just after the power is turned on,
Even though the inside of the machine is cold, the exhaust heat fan is rotating, so the components such as the fixing roller are cooled by the convection of the air around the fixing roller, and the thermal efficiency is about 30 to 45%, which is very bad. It was Therefore, immediately after the power of the apparatus is turned on, there is a problem that wasteful heat radiation from the fixing roller is large and the fixability of the copy is very poor as compared with the steady state. In particular, in the energy-saving type high-speed machine, the number of guaranteed fixing sheets in continuous copying immediately after turning on the power is significantly reduced.

Therefore, in order to solve this problem, immediately after the device is turned on, the set temperature of the fixing roller is set higher than the normal set temperature for a predetermined time to accelerate the temperature rise of the roller,
It has been proposed that by rotating the roller pair during weighting, heat is also applied to the pressure roller side to improve the fixing property.

However, in the former case, the wait time becomes longer,
In addition to the drawback of shortening the life of the fixing roller and the parts in contact with it, the
There is a limit to increase the wattage of the heater that heats the fixing roller with a limited electric power of 0 V and 15 A, and it was still incomplete when performing high-speed processing. Also, in the latter case, there are drawbacks that the wait time becomes long and the life of parts in the fixing device is shortened, and a problem such as noise is likely to occur. Even if the above measures are taken, it is difficult to guarantee complete fixing in the morning copy of the high speed copying machine.

Therefore, in the conventional high-speed machine, the temperature of the roller is detected, and when the temperature becomes lower than a predetermined temperature, copying is stopped, or as in Japanese Patent Publication No. 61-10070, according to the decrease of the surface temperature of the fixing roller. It is known to prevent the occurrence of fixing failure by sequentially increasing the copy cycle and controlling the fixing temperature so as not to drop below the fixable temperature.

(Problems to be Solved by the Invention) However, such a conventional technique has the following problems. That is, in the former case, the temperature of the fixing roller is detected, and when the temperature becomes lower than the predetermined temperature, the copying is stopped. It drops rapidly and falls below a predetermined temperature. Therefore, as the speed of the machine increases, the frequency of stoppage of copying increases, and since there is a time until the temperature of the fixing roller returns once stopped, not only does the user feel uncomfortable, but actually the temperature detection element There is a problem that accurate control is very difficult because the detected temperature varies greatly.

For example, a thermistor is generally used as the temperature detecting element. FIG. 11 shows the resistance-temperature characteristic of the thermistor, where the vertical axis shows the resistance value (R) of the thermistor and the horizontal axis shows the temperature (T). In FIG. 11, T ₁ is the controlled temperature and T ₂ is the temperature at which the copy operation is stopped. When the temperature of the thermistor is T ₁ and T ₂ , and its resistance is R ₁ and R ₂ , the temperature and resistance of this thermistor are: (B: Thermistor constant (° K)) holds, but in reality, as shown by a, b, c in Fig. 11,
Individual thermistors have variations. Normally, the thermistor resistance in the vicinity of the temperature control temperature T ₁ is controlled with high accuracy so as to minimize the variation in the temperature characteristic.Therefore, the resistance of the thermistor in the vicinity of the lower fixing temperature T ₂ ∽ temperature characteristic The variation is very large. Therefore, if you stop copying when the resistance of the thermistor becomes R ₂ ,
The variation in the surface temperature of the fixing roller when copying is stopped
It was very large, from T ₂ ′ to T ₂ ″.

For example, even if the temperature control temperature T _{1 is set} to 185 ° C and the temperature of the thermistor element is suppressed to ± 1 ° C at that temperature, if the temperature T _{2 at} which the copy operation is stopped is set to 150 ° C, the detected temperature of the thermistor element is The variation is about ± 4 ° C. Actually, when the variation that occurs during assembly when the thermistor is integrated with the thermistor holder and the variation in the contact state when the thermistor is brought into contact with the fixing roller are also included, it is 185 ° C.
The variation of the setting roller surface temperature is ± 5 ℃, 150
The variation of the fixing roller temperature when the temperature is ℃ is ± 9 to 10 ℃.

By the way, if a large number of copies are taken continuously in the morning when the thermal efficiency is very poor, the fixing roller temperature rapidly decreases, and then the inclination gradually becomes gentle as shown in FIG. The slope becomes small near T ₂ . Therefore, if the temperature of the fixing roller detected by the thermistor when the copying is stopped has a variation of ± 9 to 10 ° C, the copy number is small in a certain copying machine, and the fixing property is actually sufficiently good. In spite of this, copying has been stopped, and in other copying machines, there has been a problem that the copying operation is continued despite a large amount of fixing failure.

Also in the latter case, the surface temperature of the fixing roller is measured by a temperature detection element such as a thermistor, and the copy cycle is managed based on the result, so that it is very difficult to control accurately as in the above. The number of copies is small and the copy cycle is reduced even though the fixability is actually good enough, or conversely, the copy operation is continued even if fixing failure occurs. There was an inconvenience.

The thermal efficiency described here means that represented by the following formula.

Thermal efficiency η = (W _total -W _loss (T)) x 100 / W _total (%) W _loss = (H _ON / H _ON + H _OFF ) x W _total (W) where W _total : Heating in the fixing device Total power of the source (W) W _loss (T): Heat radiation amount (W) when the roller pair _{idles at the} roller temperature T (° C) H _ON : Time when the heating source is on H _OFF : Heating source The present invention has been made in order to solve the above-mentioned problems of the prior art, and its object is to ensure that there is no fixing failure without being influenced by the accuracy of the temperature detecting means. An object of the present invention is to provide an image forming apparatus configured so that a recording material can be discharged in a short time.

(Means for Solving Problems) In order to achieve the above-mentioned object, the present invention includes an image forming unit that forms a toner image on a recording material, and a fixing roller that fixes an unfixed toner image on the recording material. , A heater for heating the fixing roller, a temperature detecting means for detecting the surface temperature of the fixing roller, and the energization of the heater to be started after the power source is turned on to maintain the fixing roller surface at a predetermined temperature. As described above, the energization control unit that controls the energization of the heater according to the detection signal from the temperature detection unit, the timer that measures the time after the power is turned on to the apparatus main body, and the number of images formed on the recording material are measured. And a counter, and when a plurality of continuous image forming signals are set and input before the time measured by the timer reaches a predetermined value, the image forming unit starts image formation at a first speed, After this, the measurement of the counter When the temperature detected by the temperature detecting means when the number reaches a predetermined value is lower than a predetermined temperature, the image forming means forms an image at a second speed lower than the first speed. Has been done.

(Operation) In the present invention, when a plurality of continuous image forming signals are set and input before the time measured by the timer after the power is turned on reaches a predetermined value, the image forming unit causes the image to be formed at the first speed. If the temperature detected by the temperature detecting means when the number of sheets measured by the counter reaches a predetermined value after the formation is started and the temperature is lower than the predetermined temperature, the image forming means is slower than the first speed. Imaging at speed.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a sectional view showing the configuration of an entire embodiment of the image forming apparatus to which the present invention is applied.

In the figure, the surface of a drum 1 is composed of a photoconductor and a seamless photoconductor using a conductor, is rotatably supported by a shaft, and is a main motor 3 which operates in response to the pressing of a copy start key.
Starts rotation in the direction of the arrow. Then, when the predetermined rotation of the drum 1 and the potential control processing (preprocessing) are completed, the original placed on the original table glass 34 is illuminated by the illumination lamp 40 integrally formed with the first scanning mirror 39,
The reflected light is the first mirror 39, the second mirror 36, and the third mirror.
An image is formed on the drum 1 through the lens 37, the lens 35, and the fourth mirror 38.

The drum 1 is corona charged by the high voltage unit 2. After that, the image irradiated by the exposure lamp 40 is slit-exposed, and an electrostatic latent image is formed on the drum 1 by a known method.

Next, the electrostatic latent image on the photosensitive drum 1 is developed by the developing roller of the developing device 7 and visualized as a toner image, and the toner image is transferred by the transfer charger 5.

The transfer paper in the upper cassette 13 or the lower cassette 14 is
The sheet is fed into the main body apparatus by the sheet feeding roller 11 or 12, and is fed in the direction of the photosensitive drum 1 by the registration roller 15 at accurate timing so that the leading edge of the latent image and the leading edge of the transfer sheet are aligned. After that, the transfer paper passes between the transfer charger 5 and the drum 1, so that the toner image on the drum 1 is transferred.

After the transfer is completed, the transfer paper is separated from the drum 1 by the separation charger 8, guided by the conveyor belt 17 to the fixing device 32, fixed by pressing and heating, and then discharged by the discharge roller 19 to the outside of the apparatus.

After the transfer, the drum 1 is continuously rotated, and the surface thereof is cleaned by a cleaning device 6 including a cleaning roller and an elastic blade.

The pedestal 200 can be separated from the main body 100,
It has a deck 54 capable of storing 2000 sheets of transfer paper and an intermediate tray 59 for double-sided copying. Further, the lifter 54L of the deck 54 capable of accommodating 2000 sheets ascends according to the amount of transfer paper so that the transfer paper always contacts the paper feed roller 50.

When performing double-sided copying or multiplex copying, first raise the paper ejection flapper 33 of the main body 100 to pedestal the copied transfer paper.
It is stored in the intermediate tray 59 via the transport path 57 of 200. At this time, the multiple flapper 52 is lowered during double-sided copying, and the multiple flapper 52 is raised during multiple copying. The intermediate tray 59 can store up to 99 transfer sheets. The stored transfer paper is pressed by the intermediate tray weight 53.

At the time of the back side copy or the multiplex copy to be performed next, the transfer sheets stored in the intermediate tray 59 are operated one by one from the bottom by the action of the sheet feeding roller 51 and the weight 53, and the registration roller of the main body 100 through the path 58. Guided to 15.

Reference numeral 300 is a circulation type document feeder (RDF), 301 is a stacking tray for setting a document, and 302 and 303 are document size detection sensors, which are provided at a predetermined interval in the direction perpendicular to the paper surface. The size of the document in the width direction can be determined by checking whether both the sensors 302 and 303 detect the document or only the sensor 303 (assuming 303 is on the back side of the paper) detects the document. A more accurate size can be determined by increasing the number of sensors. Further, the size in the length direction can be determined by the time when the sensor 303 (302) is detecting the document.

Also, in this RDF300, from the stack tray 301 to the sheet path 304
The original sent to the exposure surface through the sheet path 305 can be stacked on the stack tray 301 again.

The detailed operation of RDF is described in Japanese Patent Application No. 59-
Since it is described in detail in No. 206619, it is omitted here.

400 is a finisher, and the copy ejected from the main body is half-folded or Z-folded at a paper folding unit 450 according to designation, and output to a swinging copy tray 401 or to a staple tray 402, and staples each part. The sheets are bound at 403 and dropped to the stacker tray 404.

In the paper folding unit 450, when the Z-folding is designated, the flapper 454 is turned on.
Then, the copy paper is guided to the lower path, the leading edge of the paper is stopped at 451 and the part that is folded into 1/4 through the roller 453 hits the 452 and is folded in half and is again guided from 453 to 455 to 400. . In the case of half-folding, it is folded in half at 451 and is not output to 452 but output from 455 to 400 as it is. When there is no folding, the flapper 454 is turned off and is output straight to 400.

When the staple mode is selected, the finisher 400 outputs a copy to the staple tray 402, turns on the staple 403 according to an instruction from the main body, and staples the sheets. After that, it is dropped to the stacker tray 404. With this repetition, a plurality of copies that are collated and bound are completed. If the staple is not selected, the copy is output to the swinging copy tray 401, and it is possible to make a copy of a plurality of copies by shifting 30 mm to the left and right at a place with a good nail according to an instruction from the main body.

FIG. 1 is an explanatory view showing an embodiment of a fixing device according to the present invention.

In the figure, a transfer material P such as a copy sheet onto which the toner image T has been transferred is separated from the image carrier 1 by the separation charger 8 and conveyed to the fixing device 32 by the conveyor belt 17.

The fixing device 32 has a heating roller 3201 and a pressure roller 3202, and the pressure roller 3202 is brought into pressure contact with the heating roller 3201 at least during fixing by a well-known pressure means. This heating roller 3201 is provided with a heat-resistant elastic body layer such as silicon rubber, fluorine rubber, fluorosilicone rubber or the like in a thickness of 0.05 to 2 mm on the outer peripheral surface of a metal hollow cylindrical roller core metal made of aluminum, stainless steel, copper or the like. , And preferably, a heat-resistant release resin layer such as PFA or PTFE is further provided thereon in an amount of 3 to 100 μm.
It is provided in m thickness. A heating heater 3203 such as a halogen heater and an auxiliary heater 3203 ′ are provided inside the heating roller 3201. The auxiliary heater 3203 ′ is normally in an OFF state and is activated only when the power supply is turned on. To do. On the other hand, the pressure roller 3202 is a metal hollow cylindrical roller core made of aluminum, stainless steel, copper, or the like, and a heat resistant elastic layer such as silicon rubber, fluorine rubber, or fluorosilicone rubber is formed on the outer peripheral surface of the metal core in a thickness of 2 to 10 mm. And preferably,
Further, a heat-resistant release resin layer such as PFA or PTFE having a thickness of 3 to 100 μm is provided on the upper layer. in this way,
The thick heat-resistant elastic layer of the pressure roller 3202 is the heating roller.
It is for forming a pressure contact area (nip portion) with 3201. Inside the hollow of the pressure roller 3202, a heater 3203 ″ for low heating such as a halogen heater is provided.

A temperature detecting element 3204 such as a thermistor or a thermocouple is arranged in contact with the outer peripheral surface of the heating roller 3201. The detection signal is guided to a known control means (not shown), and the heater 3203 is applied by the control means. By controlling the voltage and the like, the temperature of the outer peripheral surface of the heating roller 3201 is maintained at the toner image melting temperature.

Further, on the outer periphery of the heating roller 3201, the heating roller 32
01 A cleaning member 3205 is provided for removing foreign matter such as offset toner and paper dust attached to the surface from the roller surface. The cleaning member 3205 is configured such that a cleaning web 32051 made of heat-resistant non-woven fabric such as Nomex, Himeron, or polyester is wound from a supply roller 32054 to a winding roll 32053 and is brought into contact with a heating roller 3201 by a pressing roller 32052. . The cleaning web 32051 is rotationally driven by a driving means (not shown). When the take-up roll 32053 is taken up, the take-up roll 32054 is pulled out from the supply roll 32054 so as to slightly change its contact position, and the new surface of the kneading web 32051 is always in contact with the heating roller 3201. In addition, if the knurling web 32051 is impregnated with an offset prevention liquid such as dimethyl silicone oil, the kunning effect can be further enhanced.

Further, on the periphery of the heating roller 3201, curved reflecting plates 3206 and 3206 ′ having heat reflectivity are closely arranged over the entire longitudinal direction. The reflection plate 3206 is arranged around the heating roller 3201 so as to cover the entire surface of the heating roller between the pressing roller 32052 and the entrance of the transfer material P,
The reflection plate 3206 'includes a pressing roller 32052 and a separating claw 3 to be described later.
It is disposed so as to cover the entire surface of the heating roller between the heating roller 208 and the heating roller 208. Covers 3207 and 3207 'having a large thickness for preventing heat radiation, which are made of a heat insulating material such as glass wool, are attached to the outer peripheral surfaces of the reflectors 3206 and 3206'.
It prevents unnecessary heat dissipation from the. That is, the reflector 32
06, 3206 'and covers 3207, 3207' form a covering member for the heating roller 3201.

Further, a casing member 3209 having a substantially U-shaped cross section is provided on the upper side of the fixing device 32, and the cleaning member 3205, the reflection plates 3206 and 3206 ′, the covers 3207 and 3207 ′, and the temperature detection element 32 are provided.
Surrounding 04. On the outside of the casing member 3209, another casing having an L-shaped cross section is provided via an air layer 3210.
3211 is provided.

On the other hand, also on the pressure roller 3202 side, a reflection plate 3212 similar to the reflection plate 3206 and a cover 3213 similar to the cover 3207 are provided so as to cover most of the periphery of the pressure roller 3202. A casing 3214 similar to the casing 3209 is provided outside the cover 3213.

These reflectors 3206, 3206 ′, 3212 and covers 3207, 320
By providing 7 ', 3213, it is possible to reduce the heat wasted from the surfaces of the heating roller 3201 and the pressure roller 3202, and to stabilize the temperature measuring property of the temperature detecting element 3204. Therefore, the temperature control of the heating roller 3202 with respect to the set temperature can be stabilized and the power consumption can be reduced.

A guide plate 3215 for guiding the transfer material P to the heating roller 3201 side is provided in the vicinity of the ends of the reflection plate 3206 and the reflection plate 3212 which are close to each other, and the guide plate 3215 is formed of a heat insulating resin such as PBT. Has been done. A shutter 3216 that opens and closes the entrance of the fixing device is disposed at the lower end of the casing member 3209, and the shutter 3216 is rotatably driven by a plunger (not shown) with 3216 'as a fulcrum. The shutter 3216 is in an open state as shown in the figure during a copying operation, and when not copying, is rotated about a rotation fulcrum 3216 'and comes into contact with the guide plate 3215, and the inlet side is closed to waste heat dissipation. Is being prevented.

By the way, the transfer material P having the unfixed toner image T is nipped and conveyed between the heating and pressing rollers 3201 and 3202, and the toner image T is a permanent image on the paper surface by the heat applied by the heated rollers 3201 and 3202. Is fixed as its discharge roller
It is discharged from the device while being sandwiched by 3217 and 3218.

On the discharge port side of the heating roller 3201, a plurality of separation claws 3208 are provided so as to contact the roller surface along the roller axial direction in order to surely separate the transfer material P from the heating roller. In addition, the separation claw 32 is also attached to the outlet side of the pressure roller 3202.
08 'is provided so as to contact the surface of the roller 3202. The separation claw 3208 is held by a support plate 3219 arranged in a separated state from the casings 3209 and 3211, and the separation claw 3208 ′ is also held by a support plate 3220 separated from the casing member 3214. These separation claws 3208 and 3208 ′ are set to 322
With 0'as a fulcrum, the support plates 3219 and 3220 and the paper discharge roller pairs 3217 and 3218 can be moved integrally with the roller pairs 3201 and 3202 so as to be separated therefrom.

As the reflection plates 3206, 3206 ', 3212, it is desirable to use a metal plate having a glossy surface such as an aluminum or copper plate whose surface is polished, or an iron plate subjected to a surface treatment such as chrome plating. Further, the reflection plates 3206, 3206 ', 3212 preferably have a curvature such that they are concentric with the roller peripheral surface, and the thickness thereof is preferably relatively thin.

The covers 3207, 3207 ', 3213 are preferably composed of glass wool, rock wool, ceramic fiber, or foam such as phenol foam or epoxy foam, either individually or in combination.

By the way, in this embodiment, the opening 321 is formed in the support plate 3219.
9'is formed, and an exhaust heat fan 3221 as air cooling means is connected to the opening 3219 '. A heat exhaust fan 32 for exhausting heat around the drum is provided near the image carrier 1.
30 are arranged.

FIG. 2 shows a cross section taken along the line XX of FIG.

Heat-resistant heat insulating sleeves 3223 and 3223 ′ are fitted on the rotating shafts 3224 and 3224 ′ of the heating roller 3201, respectively, and these heat insulating sleeves 3223 and 3223 ′ are attached to the frame bodies 3225 and 3225 ′ of the fixing device, respectively. It is supported by bearings 3226, 3226 'that are mounted. The rotary shafts 3224 and 3224 'have heat-resistant gears 3227 and 322
The heat resistant gears 3227 'are engaged with the driving force transmission gears 3228 connected to the driving source M. Then, the heating roller 3201 is rotationally driven by the driving force of the driving source M being transmitted through the driving force transmission gear 3228 and the heat resistant gear 3227 '. A gear 3229 'fixed to the manual knob 3229 is meshed with the other heat-resistant gear 3227, and occupies most of the manual knob drive system. On the other hand, in the case of this configuration, heat loss to the drive system can be reduced or eliminated, so that the thermal efficiency can be highly improved and the power consumption can be reduced. Also, in this configuration, since heat resistant sleeves 3224 and 3224 'are used in addition to heat resistant gears 3227 and 3227', it is possible to prevent heat loss from the roller end portion to the frame bodies 3225 and 3225 'and further improve thermal efficiency. it can.

The heat-resistant sleeve may be a heat-insulating member such as polyimide, polyamide-imide, polyamide, PPS (polyphenylene sulfide), PBT (polybutylene terephthalate) resin, phenol resin, or the like, or a heat-insulating material made of a mixed material of this type. It is preferable to use a material made of a conductive material.

Further, the gears 3227, 3227 'are preferably made of a heat-resistant material having a good heat-insulating property such as polyimide, polyamide-imide, PPS, modified phenol, and tetrafluoroethylene with a reinforcing filler. .

As mentioned above, the heating roller 3201 has a heat resistant sleeve 3224,3
224 'and heat-resistant gears 3227, 3227' make them thermally isolated from the machine body and the frames 3225, 3225 ', and the heat loss transmitted through them becomes very small. As described above, thermally isolating the roller from the driving force transmission path is very effective in improving the thermal efficiency.

Next, the operation control of FIG. 3 of the present invention will be described.

FIG. 4 is a circuit block diagram for carrying out the present invention.
1 is a central processing unit (CPU), for example, NEC's μCOM87AD is used. 502 is a ROM memory that stores the control program
01 controls the device according to this program.
Reference numeral 503 is a RAM memory which is a main storage device, 504 is an interface for outputting a control signal to a load such as a main motor, 505 is an interface for inputting an input signal of an image sensor or the like, and 506 is an operation unit (not shown). This is an interface that controls the input and output of the key and display of.

Reference numerals 507 and 508 respectively denote a main switch and a copy size sensor, which detect the closing of the main switch and the size of copy paper.

A copy number sensor 509 detects the cumulative number of copies. The cumulative number of copies referred to here is the number of sheets that are continuously passed, and is cleared when the copying is stopped once, and is counted from the count 1 again in the next copying operation.

For example, in the copying machine shown in FIG. 3, when 20 sets of originals are set in the RDF300 and 25 copies of each original are made, 20 copies x
Since 25 sheets = 500 sheets are processed one after another without stopping at all, the final sheet becomes 500 sheets in cumulative number.

Reference numerals 510 and 511 respectively denote a fixing thermistor input from the fixing unit shown in FIG. 1 and a room temperature thermistor (not shown) installed in a place where heat is not easily received in the copying machine. Ambient temperature).

The resistance value of the thermistor is converted into a voltage, converted into digital data by the A / D converter 512, and read into the CPU 501.

FIG. 5 is a flow chart of an example of the control method of the fixing device of the present invention, which is stored in the ROM 502 of FIG.

In the fixing device according to the present embodiment having the above-described configuration, the fixing process is performed as follows. That is, CPU501
After the main switch is turned on, a predetermined device startup operation is performed to adjust the surface temperature of the fixing roller to a constant temperature. Hereinafter, control is performed based on the flowchart shown in FIG. First, the CPU 501 determines the time after the ON state of the main switch is detected by the main switch sensor 507, that is, the time after the power of the copying machine is turned on.
It is detected by an internal software timer or the like, and it is judged whether this time is within a predetermined time (step). If this time has passed the predetermined time t,
The CPU 501 unconditionally starts the copy operation in the high speed mode. Here, the high-speed mode is an image forming processing mode of speed which is executed by a normal high-speed copying machine. If the above time is within the predetermined time t, the process proceeds to step.

Next, CPU 501, based on a signal from the room temperature thermistor 511, room temperature performs determination of whether the predetermined temperature T ₀ ° C. or less (step), the step in the case of the predetermined temperature T ₀ ° C. or less, the predetermined temperature T If the temperature is higher than ₀ ° C, proceed to step.
In step, the CPU 501 detects by the copy size sensor 508 whether or not the size of the transfer paper is full size, and if it is full size, the process proceeds to step, and if not, the process proceeds to step. In step or, the CPU 501
Based on the signal from the copy number sensor 508, the continuous copy number reaches n ₁ or n ₂ while determining whether or not the number of consecutive copies has reached n ₁ or n _2. Until you run the copy in high speed mode.

That is, the CPU 501 starts the operation and then steps
However, time t from when the power was turned on
Even within the range, the copy operation is performed in the high speed mode until the number of continuous copies reaches n ₁ or n ₂ .

On the other hand, when the number of continuous copies reaches n ₁ or n ₂ , the CPU 501
Detects the temperature of the fixing roller by the fixing thermistor 510 and judges whether the temperature of the fixing roller is equal to or lower than a predetermined temperature T ₁ ° C (step). When the temperature of the fixing roller is higher than the predetermined temperature T ₁ , the judgment of whether the temperature of the fixing roller is T ₁ ° C or lower is repeated while continuing the copy operation in the high speed mode (step). On the contrary, when the temperature of the fixing roller is equal to or lower than the predetermined temperature T ₁ ° C, the copying operation is performed in the low speed mode, and it is determined whether the temperature of the fixing roller is equal to or lower than the copy stop temperature T ₃ ° C (step).
When the temperature of the fixing roller is higher than the copy stop temperature T ₃ ° C, the copy operation is continued in the low speed mode, and when the temperature becomes lower than the copy stop temperature T ₃ ° C, the copy operation is stopped. Here, the low speed mode is a mode that is lower by a predetermined ratio than the high speed mode, and the speed of the copy mode is controlled by, for example, changing the scanning interval of the optical system.

If the room temperature is higher than the predetermined temperature T ₀ ° C., the process proceeds to step, but from this step to step, the set values n ₃ , n ₄ , T ₂ , T ₄ are only different, and the same as step ~. Is done. By the way, the room temperature is the predetermined temperature T ₀ ℃
If it is higher, the thermal fixing condition becomes better, and the number of copies n ₃ , n ₄ that can be copied in the high-speed mode becomes larger than n ₁ , n ₂ , and the temperature T _{2 at which the} mode is switched to the low-speed mode and the copy stop mode is set. , T ₄ can also be made lower than T ₁ , T ₃ .

As described above, in this embodiment, within t minutes immediately after the power source is turned on, the thermal efficiency is low, and the copying is performed in the high-speed mode up to n ₁ or n ₂ sheets (depending on the size of the transfer paper) where good fixing can be secured. After that, the temperature of the fixing roller is the predetermined temperature T ₁ ℃
When it becomes the following, the mode is switched to the low speed mode and the copying is continued, and when the temperature becomes lower than the copy stop temperature T ₃ ° C, the copying is stopped. Therefore, the predetermined number of sheets that can be satisfactorily fixed even immediately after the power is turned on can be copied in a short time in the high speed mode. At that time, since it does not depend on the temperature of the fixing roller, the temperature of the fixing roller is erroneously detected by a sensor such as a thermistor, and the copy operation is stopped even if the number of copies is small and the temperature of the fixing roller is high. It is possible to prevent the copy cycle from being lengthened and the copy time from being unintentionally lengthened. Also, after copying a specified number of copies, copying is performed by switching to the low-speed mode depending on the temperature of the fixing roller, so the amount of heat radiation increases as in the case of continuing the high-speed mode, and fixing defects do not occur. Only when the temperature is reached does copying stop. At this time, the temperature of the fixing roller that can be switched to the low speed mode should be set higher considering the thermistor variation (that is, the fixing property should be set to be good even at the lowest value in the variation range). It became possible and there was no fear of fixing failure.

(Experimental Example) With the above configuration, the present applicant actually performed a fixing property test using a fixing device as described below.

As heating roller 3201, outer diameter φ59.3mm, reverse crown amount
150μm, aluminum roller core metal thickness 6.5mm, 0.25 on the surface layer
The pressure roller 3202 is a roller coated with mm-thick silicon rubber and 20 μm-thick PTFE, and is a 5 mm thick heat-vulcanizable silicone rubber layer and a 20 μm-thick layer on a stainless steel roller core having an outer diameter of φ60 mm and φ50 mm. The rollers coated with the fluorine-containing rubber latex layer were used respectively.

Also, the coating 3203 in the heating roller is 750 W, and the heater 3203 'is
Each of the 350 W halogen heaters was used, and the heater 3203 'was turned on only at the start-up (during weight). On the other hand, as the heater 3203 ″ in the pressure roller, a 70 W sheathed heater was used, and it was turned on only during the copying operation.

The nip width was 9.0 mm and the heating roller surface temperature was 195 ° C.

FIG. 6 illustrates a change diagram of the surface temperature of each roller with time for the experiment of the above specific example. Time t = t ₀
When the power is turned on, the heaters 3203 and 3203 'and the heater 320
3 ″ lights up. When the heating roller surface temperature rises as shown in the figure and reaches 170 ° C (point A, time t ₁ ), both rollers 3201 and 3202 that have been stopped start pressure contact rotation. The surface temperature of the pressure roller also rises sharply.

When the heating roller surface temperature reaches 195 ° C (point B, time
t ₂ ) Fixing is possible and both rollers 3201 and 3202 stop rotating. The heating roller 3201 is held by the control means (not shown) so that the surface temperature becomes around 195 ° C.
On the other hand, the surface temperature of the pressure roller 3202 drops because heat is not supplied from the fixing roller. After about 5 minutes (point C) from the fixing possible state, the pressure roller temperature becomes the lowest, and then the temperature of the pressure roller gradually increases due to the heat of the heater 3203 ″ from the inside. Therefore, the fixing ability at the point C is the lowest. Therefore, continuous copying at this point C is extremely preferable as a comparative experiment of fixing property.
Temperature change when continuous copying of 0 sheets is completed at the end of 250 sheets (D
(Dots) are included.

The experimental results shown below were performed under the following conditions between C and D. In other words, under the environment of 20 ℃, copy speed 445mm / sec (A3 size paper, 43 sheets / min), weighing 80g / m ² A3 paper is a flat black of φ24mm arranged in 3 rows at regular intervals. From the continuous copy of 250 sheets, the sample is extracted every 25 sheets, such as the first sheet, the 25th sheet, the 50th sheet ... Was evaluated as the fixability.

This fixing property was evaluated by using Silbon C (trade name, Kojin Co., Ltd., Silbon paper) for 10 reciprocating rubs at a pressure of 40 g / cm ² and measuring the density difference before and after rubbing with a Macbeth reflection densitometer. And digitized.

Ie D: φ24 reflection density before rubbing solid image (1.0 ≦ D ≦
Adjust the image density so that it becomes 1.1. D ': Reflection density after rubbing a φ24 solid black image ΔD: Density reduction rate Then, the average of the density reduction rates of the solid black portions at 9 locations was used to evaluate the fixability.

Further, FIG. 7 shows an operation sequence of the exhaust heat fans 3221 and 3230 in the present embodiment. In FIG. 7, t ₀ is when the power is turned on,
t ₁ is the start of the previous multi-rotation, t ₂ is the release of the wait after the previous multi-rotation is completed, t _{2 to} t ₃ are the standby (when the copy is possible but not copying), t ₄ is the start of the copying, t ₄ ~t ₅ during the copy, t ₅ is at the end of the copying operation, t ₅ ~ is the time of standby.

When the power is turned on at t ₀ , the exhaust heat fans 3221 and 3230 become OF
The F state is maintained, and the ON state occurs only at time t ₃ .
In this experimental example, the exhaust heat fan 3221 is turned on in a half speed state during standby and turned on in a full speed state during copying.

In addition, the exhaust heat fan 3230 is always in the full-speed state from time t _{3 on.}
Becomes

The main purpose of the exhaust heat fan 3221 to be turned on in the half speed state during standby is to prevent noise.

In this experimental example, the heat exhaust fan 322 is turned on after the power is turned on.
The time t ₃ until the 1,3230 is operated is variable according to the temperature of the fixing roller when the power is turned on.

In this experimental example, t ₃ was set as follows.

After the time t ₃ minutes has elapsed, even if the exhaust heat fans 3221 and 3230 are intermittently operated at predetermined intervals, or if the heating roller 3201
A temperature detecting element 3222 is provided in the vicinity, and when the detected temperature is higher than or equal to a predetermined temperature, it is strong and when it is lower than the predetermined temperature, it is operated weakly
It may be operated only when the temperature is equal to or higher than a predetermined temperature. In addition, the exhaust heat fans 3221 and 3230 must be synchronized with each other to turn ON-O.
You don't have to FF.

In addition, in this experimental example, in the flowchart of FIG.
= 45, T ₀ = 23, n ₁ = 100, n ₂ = 200, n ₃ = 300, n ₄ = 400, T ₁ = 16
4, T ₂ = 158, T ₃ 155, T ₄ = 150. The low speed mode is 3
5 sheets / A3 minutes.

The results of the fixability test under the above conditions are shown in FIG.

In the above-mentioned fixing evaluation method, the range showing good fixability in a normal line image is the case where the density reduction rate is 20 to 25% or less. It exhibited fixability.

Also, in the above experimental example, it can be seen that the copy speed changed to the low speed mode after 100 sheets were passed.

FIG. 9 shows changes in the surface temperature of the heating roller in this case. It can be seen that the rate of decrease in density (which means the fixing rate) and the rate of decrease in roller temperature have decreased due to the change to the low speed mode after 100 sheets have been passed.

In addition, in order to calculate the amount of heat that is effectively used for copy paper, Fig. 10 shows the change over time in the amount of heat dissipation when the paper is idled and not passed. Immediately after the power was turned on in this experimental example, the amount of heat radiated by idle rotation was 360 W. Immediately after the power was turned on, the thermal efficiency η was 59%. Further, for reference, the idling heat dissipation amount when the standby state was continued for 1 hour or more was 115 W, and the thermal efficiency η was 87%. The fixability at this point is
Even when the set temperature was 180 ° C, it was good.

In other words, there is a big difference between the thermal efficiency in the morning 1 and the thermal efficiency after completely warming up, and the time when the thermal efficiency is very poor is within 30 to 40 minutes after the power is turned on. As in the invention, it is very effective to introduce the low speed mode only for a predetermined time after the power is turned on. It is also very effective to define the number of copies (cumulative number of copies in this embodiment) before detecting the fixing roller temperature. If the input voltage is low (normal standard value is ± 10%, it is -10% because the standard value is -10%), and if the copy paper is thick paper, the number of copies can be guaranteed reliably under the worst conditions. It is preferable to investigate whether or not and make a decision based on it.

In addition, the fixing roller temperature of the control method of the present invention can be set on the safe side in which fixing failure never occurs in consideration of variations in the thermistor and the like.

In the embodiment, the case where the room temperature, the transfer paper size and the temperature of the fixing roller are detected in addition to the elapsed time immediately after the power is turned on and the number of continuous copies, and the condition is changed based on these detected values will be described. However, it is not always necessary to detect the room temperature, the transfer paper size and the like and change the conditions based on this, but when these are detected, the reliability can be further improved. That is, the detection amount essential in the present invention is the elapsed time immediately after the power is turned on and the number of continuous copies.

(Effects of the Invention) The present invention is configured as described above and has the above-described effects. It is possible to reliably discharge a recording material having no fixing failure in a short time without depending on the accuracy of the temperature detecting means, and to form an image unintentionally. It is possible to surely prevent the operation from stopping and the fixing failure.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a fixing device according to the present invention, FIG. 2 is a sectional view taken along the line XX in FIG. 1, and FIG. 3 is a structural view showing a copying machine to which the present invention is applied. 4, FIG. 4 is a block diagram showing the control system, FIG. 5 is a flowchart showing the operation of the control system, FIG. 6 is a graph showing the relationship between the roller surface temperature and time, and FIG. 7 is the operation of the exhaust heat fan. Time chart showing,
FIG. 8 is a graph showing the relationship between the density reduction rate and the number of copies,
FIG. 9 is a graph showing the relationship between the surface temperature of the heating roller and the number of copies, and FIG. 10 is a graph showing the relationship between the heat radiation amount and time.
FIG. 11 is a graph showing the relationship between the thermistor resistance and temperature. Explanation of symbols 32 …… Fusing device, 501 …… CPU 507 …… Main switch sensor 509 …… Copies sensor

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-57-81278 (JP, A) JP-A-57-67970 (JP, A) JP-A-48-81542 (JP, A)

Claims (1)

[Claims] 1. An image forming means for forming a toner image on a recording material, a fixing roller for fixing an unfixed toner image on the recording material, a heater for heating the fixing roller, and a surface temperature of the fixing roller. The heater is energized in response to a detection signal from the temperature detector so that the heater is energized after the power is turned on to the temperature detection unit and the main body of the apparatus is started to maintain the temperature of the fixing roller at a predetermined temperature. It has an energization control means for controlling, a timer for measuring the time after the power is turned on to the apparatus main body, and a counter for measuring the number of images formed on the recording material. When a plurality of continuous image forming signals are set and input before reaching, the image forming means starts image forming at a first speed, and then the temperature when the number of sheets measured by the counter reaches a predetermined value. Predetermined temperature detected by the detection means The image forming apparatus is characterized in that, when the temperature is lower than the temperature, the image forming unit forms an image at a second speed lower than the first speed.