JP2008046568A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an occurrence of an action failure in a peripheral device due to unnecessary rise in surface temperature of a heat roller and an increase in consumed amount of power, etc., by evading an unnecessary setting change of target temperature to a high temperature side in an image forming apparatus provided with a setting change function for the target temperature in the heat roller. <P>SOLUTION: Returning time A required for a detected temperature T<SB>1</SB>by a thermistor 25 to be returned to the target temperature T<SB>f</SB>after going lower than the target temperature T<SB>f</SB>is compared with a threshold value B and then the target temperature T<SB>g</SB>for the heat roller 20 has its setting changed to the high temperature side T<SB>h</SB>only when the returning time A is greater than the threshold value B. Thus, problems such as; the action failure of the peripheral device due to the surface temperature of the heat roller 20 being made unnecessarily high in the summer, etc., increase in load to such as a heat exhausting apparatus or an increase in consumed amount of power due to energizing time for a halogen lamp 22 being prolonged can be surely solved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine, and more particularly to a temperature control technique for a fixing device that performs a heat fixing operation of a toner image.

  In this type of image forming apparatus, when the power switch is turned on, a preparatory operation called a preheating operation is performed prior to the printing operation. Some preheating operations are periodically performed when the printer is in a standby state in which printing operation is possible. When the preheating operation is performed in this way and the surface of the heat roller (hereinafter, abbreviated as a roller as appropriate) constituting the fixing device is raised to a predetermined standby temperature prior to the printing operation, it is necessary for toner fixing. Since the time required to reach the fixing temperature (standby time) can be shortened, a rapid printing operation can be realized.

In the temperature control of the fixing surface of the roller including such preheating operation, maintaining the roller surface temperature at a constant level in continuous printing is one of the important issues in preventing poor toner fixing and maintaining print quality. It is.
FIG. 11 shows a conventional temperature control method for the heat roller during continuous printing. In the figure, _Tf indicates a target temperature, and the halogen lamp, which is a heating means incorporated in the heat roller, is on / off controlled so that the surface temperature of the heat roller matches the target temperature _Tf. . The first sheet of the print at the start of the continuous printing, since the overshoot due to the increase from the standby temperature T ₀ is generated, the surface temperatures T ₁ is higher than the target temperature T _f. Therefore, when the first sheet of the prints, the passage of the recording paper, the recording paper by heat of the roller deprived, as the surface temperature T ₁ is lowered, it is rarely below the target temperature T _f In other words, the fixing operation is normally executed, and toner fixing failure hardly occurs.

In contrast, when the subsequent second sheet printing, in a state in which lowered the surface temperature T ₁ of the passage of the recording paper on the previous page, go further takes heat of coming next recording sheet roller. Therefore, as shown in FIG. 11, the temperature (T ₁ ) of the roller surface gradually decreases as the printing proceeds from the third sheet to the fourth sheet, greatly lowering the target temperature _Tf , and the toner is not sufficiently melted. Thus, a toner fixing failure may occur. This problem becomes prominent in winter when the recording paper is cold.

  For example, Patent Documents 1 to 3 can be cited as countermeasures against such a decrease in the surface temperature of the heat roller. In Patent Document 1, when it is confirmed that the print is continuous, the target temperature is set to the high temperature side after the first recording sheet is printed. According to this, since the temperature difference between the roller surface temperature and the fixing temperature necessary for toner fixing can be taken large, it is possible to prevent the roller surface temperature from becoming lower than the fixing temperature, and thus fixing. The occurrence of defects can be effectively prevented.

In Patent Document 2, the fixing speed for the first OHT sheet is set to 1/3 that of plain paper, and the second sheet is further set to 1/4. When the fixing speed is set to be low in this way, it is possible to secure a sufficient time until the surface temperature of the heat roller recovers to the fixing temperature, so that it is possible to prevent the occurrence of fixing failure during continuous printing operation. it can. In Patent Document 3, the exhaust fan is driven to rotate at a low speed until the number of recording sheets after the fixing process reaches a predetermined number. According to this, by keeping the ambient temperature of the roller at a high temperature, it is possible to suppress a decrease in the surface temperature of the roller and prevent occurrence of fixing failure.
Japanese Patent Laid-Open No. 9-230736 Japanese Patent Laid-Open No. 10-20706 JP 2005-43667 A

  Of the above three types of countermeasures, it can be said that the invention method according to Patent Document 1 is the most direct countermeasure. In other words, the method of setting and changing the value of the target fixing temperature as in Patent Document 1 is to control the surface temperature of the heat roller through on / off control of the halogen lamp, so compared to the other two methods, This is the most direct countermeasure.

However, in the control method according to Patent Document 1, since the target temperature setting change is determined only based on the criterion of whether or not continuous printing is performed, there is a risk that the surface of the roller will become unnecessarily high temperature. is there. In other words, this measure is useful in situations where the recording paper is extremely cold, such as in winter, and the surface temperature of the roller may fall below the fixing temperature due to the recording paper passing through the fixing device. This is not a necessary measure under circumstances where the temperature of the recording paper is high and there is no possibility that the roller surface temperature will decrease, such as in summer.
For this reason, the method of Patent Document 1 that shifts the surface temperature of the roller to the high temperature side every time it is determined that the print is continuous prints the surface of the roller and its peripheral devices unnecessarily in a high temperature state in summer. Therefore, an increase in the load of the heat exhausting device is caused, and in the worst case, there is a possibility of causing a malfunction of the peripheral device. Since the energization time of the halogen lamp is prolonged, there is a disadvantage in that the printing time is prolonged and the power consumption is increased.

  An object of the present invention is to avoid an unnecessarily setting change of the target temperature to the high temperature side in an image forming apparatus having a setting change function of the target temperature of the heat roller, and to prevent the surface temperature of the heat roller from being changed. The purpose is to prevent the peripheral devices from malfunctioning and increasing the amount of power consumption due to the necessary increase.

According to a first aspect of the present invention, there is provided a fixing device for performing a heat fixing operation of a toner image transferred onto a recording sheet, a roller temperature detecting means for detecting a surface temperature of a heat roller constituting the fixing device, The heating control means for controlling the heating means of the heat roller and the detection temperature from the roller temperature detecting means are compared with a preset reference temperature so that the surface temperature approaches the preset target temperature, and this comparison is performed. A target temperature changing means for setting and changing the target temperature based on the result, and the target temperature changing means determines that the temperature detected by the roller temperature detecting means when receiving the continuous print command is lower than the reference temperature. An object of the present invention is an image forming apparatus in which the target temperature is set to a high temperature side prior to the heat fixing operation for the first recording sheet by the fixing device.
In this image forming apparatus, in the heat fixing operation for the first recording sheet in continuous printing, the recovery time required until the temperature detected by the roller temperature detecting means falls below the target temperature before the setting change and returns to the target temperature. Is provided with a return time measuring means. Then, the target temperature changing means compares the return time from the return time measuring means with a preset threshold value. If the return time is larger than the threshold value, the target temperature changing means performs the heat fixing operation on the second recording sheet. In advance, the target temperature is set and changed to the high temperature side.

  Specifically, as in the present invention of claim 2, the return time measuring means compares the output value from the roller temperature detecting means with the target temperature and counts the output time from the comparator. It can be.

According to a third aspect of the present invention, there is provided a fixing device responsible for the heat fixing operation of the toner image transferred onto the recording paper, a roller temperature detecting means for detecting the surface temperature of the heat roller constituting the fixing device, The heating control means for controlling the heating means of the heat roller and the detection temperature from the roller temperature detecting means are compared with a preset reference temperature so that the surface temperature approaches the preset target temperature, and this comparison is performed. A target temperature changing means for setting and changing the target temperature based on the result, and the target temperature changing means determines that the temperature detected by the roller temperature detecting means when receiving the continuous print command is lower than the reference temperature. An object of the present invention is an image forming apparatus in which the target temperature is set to a high temperature side prior to the heat fixing operation for the first recording sheet by the fixing device.
The image forming apparatus includes a time measuring unit that measures an energization time during which the heating unit is on-controlled by the heating control unit during the heat fixing operation for the first recording sheet in continuous printing. Then, the target temperature changing means compares the energization time measured by the time measuring means with a preset threshold value, and when the energization time is larger than the threshold value, the heat fixing for the second recording sheet is performed. Prior to operation, the target temperature is set and changed to the high temperature side.

In the first and third aspects, the target temperatures that are set and changed prior to the heat welding operation for the first recording sheet and the second recording sheet need not be the same temperature. That is, as shown in FIG. 4, the present invention is not limited to the form in which the target temperature in the heat welding operation of the first and second recording sheets is the same temperature (T _h ), but as shown in FIG. the target temperature of the recording sheet T _h, handsome can take a form to be changed and set to a different target temperature T _{h 'to} this, short when the return time and the current time exceeds the threshold value The target temperature may be set and changed to a higher temperature side than the target temperature _Tf in the normal state.

  According to the first aspect of the present invention, since the target temperature is changed to the high temperature side only when the recovery time is larger than the threshold value, the image forming apparatus according to the conventional Patent Document 1 is used. In the form where the target temperature is changed to the high temperature side every time continuous printing is unavoidable, the malfunction of surrounding equipment caused by the surface temperature of the heat roller becoming unnecessarily high in summer etc. Further, problems such as an increase in the load of the heat exhausting device or the like, or an increase in power consumption due to a prolonged energization time of the heating means can be reliably solved.

  As in the present invention of claim 2, when the output value from the roller temperature detecting means and the target temperature are compared by a comparator, and the return time is measured by counting the output time from the comparator, Since the return time can be reliably measured with a simple configuration, an increase in manufacturing cost can be minimized and an image forming apparatus excellent in reliability free from malfunctions can be provided at low cost.

  According to the third aspect of the present invention, the target temperature is set to the high temperature side only when the energization time is larger than the threshold value, so that the image forming apparatus according to the conventional Patent Document 1 is used. In the form where the target temperature is changed to the high temperature side every time continuous printing is unavoidable, the malfunction of surrounding equipment caused by the surface temperature of the heat roller becoming unnecessarily high in summer etc. Further, problems such as an increase in the load of the heat exhausting device or the like, or an increase in power consumption due to a prolonged energization time of the heating means can be reliably solved.

(First embodiment)
Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of the image forming apparatus, and FIG. 2 is a schematic configuration diagram of the fixing device. In FIG. 1, a sheet feeding path R for conveying the recording paper P drawn from the paper feeding device 2 is formed inside the image forming apparatus 1, and the sheet feeding path R in the sheet conveying direction is formed. A paper feeding device 2, a developing device 3, a photosensitive device 4, and a fixing device 5 are arranged along the downstream side from the upstream side.

  The paper feeding device 2 includes a paper feeding cassette 7 that stores the paper P and a paper feeding roller 8 that feeds the recording paper P in the paper feeding cassette 7. The paper feed roller 8 is connected to the motor 10 via a clutch 9 so that the drive can be transmitted, and is driven intermittently to feed out the recording paper P. The developing device 3 includes a toner chamber 11 that contains toner, a developing roller 12 that supplies toner to the photosensitive drum 15, and a supply roller 13 that supplies toner to the developing roller 12.

  The photosensitive device 4 includes a photosensitive drum 15 that contacts the recording paper P and transfers toner, a transfer roller 16 that is disposed to face the photosensitive drum 15, and a charging roller that negatively charges the surface of the photosensitive drum 15. 17 and a memory removal brush 18 for cleaning the surface of the photosensitive drum 15. Further, an LED 19 that is a light emitter that forms an electrostatic latent image on the photosensitive drum 15 is disposed above the photosensitive drum 15.

  The LED 19 irradiates the photosensitive drum 15 on the basis of image information transmitted from an image reading apparatus attached to the image forming apparatus 1 or another image forming apparatus connected via a communication line or the like. Form an image. Then, toner is supplied to the electrostatic latent image from the developing roller 12 to form a toner image on the photosensitive drum 15. When the toner image is conveyed between the photosensitive drum 15 and the transfer roller 16 with the recording paper P sandwiched therebetween, a predetermined bias voltage is applied to the transfer roller 16 so that the toner image is transferred to the recording paper P. Transcript to.

As shown in FIG. 2, the fixing device 5 includes a heat roller 20 and a press roller 21 disposed to face the heat roller 20. A halogen lamp (heating means) 22 is provided as a heating means of the heat roller 20 at the axial center position in the heat roller 20. The heat generated by the halogen lamp 22 is transmitted to the outer peripheral portion of the heat roller 20 formed of metal (aluminum).
The press roller 21 is configured by disposing a sponge roller 21b on the outer periphery of a metal cored bar 21a. The press roller 21 is pressed against the heat roller 20 by an urging means (not shown).
Then, the recording paper P holding the toner image is nipped and conveyed along the sheet feeding path R while being heated and pressurized by the heat roller 20 and the press roller 21, thereby fixing the toner image on the recording paper P. To do. In FIG. 2, the right side of the heat roller 20 shows a state in which the toner 23a after transfer is attached to the recording paper P, and the left side of the heat roller 20 shows a state in which the toner 23b after fixing is fixed. Show.

  The fixing device 5 is provided with a thermistor 25 that detects the temperature of the outer peripheral surface of the heat roller 20. The thermistor 25 is disposed so as to be in contact with the surface 20 a of the heat roller 20 and transmits the detected temperature to the control device 30.

A control device 30 responsible for overall control of the image forming apparatus 1 is provided with a key input unit 31 for input operation of the number of copies, a display unit 32 which is a liquid crystal display screen, and a timer 33 for measuring time. Has been. In FIG. 1, reference numeral 34 indicates a switch for switching the energization state of the halogen lamp 22. Controller 30, the heating control unit for controlling turning on and off the switch 34 and (heating control means) 30a, and the monitor unit 30b for monitoring the detected temperature from the thermistor 25, sets changes the target temperature T _g of the heat roller 20 target temperature changing unit and the (target temperature changing means) 30c, the temperature detected by the thermistor 25, the target temperature T _g of below by target temperature T _g time required for returning to the (return time) return time for measuring the measuring portion (Return time measuring means) 30d.

Here, the target temperature _Tg is the surface temperature of the heat roller 20 targeted by the control device 30 during the heat fixing operation, and is set higher than the fixing temperature necessary for toner fixing. Heating control section 30a, while monitoring the detected temperature from the thermistor 25 in the monitor unit 30b, the detection temperature to match the target temperature T _g, for on-off control of the halogen lamp 22. In the memory of the control device 30 according to the present embodiment, two types of target temperatures T _{g of} T _h and T _f (T _h > T _f ) are stored, and the target temperature changing unit 30c has a basic target temperature. as the T _f, it changes the target temperature T _h if necessary.

As shown in FIG. 4, the target temperatures T _h and T _f include an off temperature close to a high temperature at which the energization of the halogen lamp 22 is turned off within a predetermined temperature range centered on the temperatures, and the energization of the halogen lamp 22. It is set and the low temperature side of the on temperature and on the, when the detected temperature T ₁ of the thermistor 25 exceeds off temperature, the halogen lamp 22 is controlled to be turned off, if the detected temperature T ₁ is greater than on the temperature, The halogen lamp 22 is on-controlled.

Return time measurement unit 30d in this embodiment, counting the detected temperature T ₁ of the thermistor 25 includes a comparator circuit for comparing the target temperature T _f which is stored in memory, the output time from the comparator circuit Thus, the return time A is measured.

Next, the control operation of the image forming apparatus 1 when receiving a continuous print command will be described with reference to FIGS. 4 to 6 are simplified for ease of explanation, and the detected temperature change by the thermistor 25 is shown as a polygonal line, but in actuality, it becomes a curve-like change.
3, in the image forming apparatus 1, when receiving the continuous printing command is compared with the reference temperature T _s which is set to detect the temperature T ₀ by the thermistor 25 in advance (S1). In this comparison, when the detected temperature T ₀ is higher than the reference temperature T _s (No in S1, FIG. 5), the target temperature setting unit does not change the target temperature (S2: T _g = T _f ). the detected temperature _{T 0} from the thermistor _25, in comparison with the _T f _-оff temperature and _T f _-оn temperature, the halogen lamp 22 and on-off control, to perform a continuous printing (S3, FIG. 5). That is, when the detected temperature T ₀ by the thermistor 25 exceeds the reference temperature T _s , it is determined that the temperature is not in a low temperature environment, and a normal continuous printing operation is performed.

On the other hand, in comparison with the reference temperature _{T s} in S1, when the detected temperature _{T 0} is less than or equal to the reference temperature _{T s} is prior to the heat fixing operation for the recording sheet P by (Yes, 4 in S1), the fixing device 5 Te, set changes the target temperature _{T g} to higher temperatures side of _{T h (S4: T g =} T h). That is, if the detected temperature T ₀ when receiving the continuous print command is lower than the reference temperature T _s , it is determined that the ambient environment temperature is low, and the target temperature T _f in the normal state is determined from the temperature. to the target temperature T _h of the high-temperature side, and changes the setting of the target temperature T _g. The detected temperature T ₁ is raising the surface temperature of the heat roller 20 until the target temperature T _h, the start of the feeding operation of the recording paper P by the paper feed roller 8 (pickup), one in the continuous printing The first sheet is printed (S5). When the pickup is started to return the target temperature from _{T h} to _{T f (S6: T g =} T f).

As shown in FIG. 4, gradually decreases by the detected temperature T ₁ is deprived of heat to the recording paper P in the first sheet, it reaches the on temperature of the target temperature T _f (T _{f -on),} the halogen lamp 22 Is turned on and reversely increased to return to the target temperature _Tf . In the present embodiment, when printing to the recording paper P in the first sheet in the above-described continuous printing, the detected temperature T ₁ is from below one end of the target temperature T _f from the thermistor 25 to return to the target temperature T _f The time required for the recovery (return time A) is measured by the return time measuring unit 30d.

6, when the recording paper P in the first sheet passes through the fixing device 5, which shows the time course of the detected temperature T ₁ of the thermistor 25, (a) has a recording sheet P in winter such as low temperature the time course of the detected temperature T ₁ of the case in, (b) shows the time course of the detected temperature T ₁ of the case where the recording sheet P is warmer than (a). As shown in FIG. 6 (a), when the recording sheet P is low, the detected temperature T ₁ is the target temperature T from below the _f target temperature T time required for returning to _f (return time A) is As shown in FIG. 6B, the recording paper P becomes longer than when the recording paper P is warm. This is because a large amount of heat by cold recording paper P is taken from the heat roller 20, the temperature change of the roller surface temperature T ₁ is a steep, due to the drop width from the target temperature T _f is increased .

Next, the control device 30 compares the return time A measured in S7 with the threshold value B stored in the memory (S8). If the return time A exceeds the threshold value B (Yes in S8), recording paper P is determined to be in the cold state, prior to the second sheet of printing operation, it returns the target temperature T _g again from T _f to T _h (S9), leading to оff temperature of the target temperature T _h The surface temperature of the heat roller 20 is raised until the second sheet is printed (S10, FIG. 4). Printing operation using such a target temperature T _h is continued until the printing operation of the number of sheets set in advance is completed (No in S11), the printing operation of the predetermined number is completed (Yes in S11), the target temperature T _Returning to _f , the printing operation is performed (S2, S3).

On the other hand, if the return time A is equal to or smaller than the threshold B is (No in S8), and the target temperature _{T g} was maintained while the _{T f,} performs the printing operation (S2, S3). This is because the surface temperature of the heat roller 20 was quickly returned to the target temperature _Tf , so the recording paper P is not so low in temperature, and the influence of the temperature of the recording paper P on the surface temperature of the heat roller 20 is It depends on the judgment that it is insignificant.

As described above, in the image forming apparatus 1 according to the present embodiment, during the heat fixing operation for the first recording sheet P in continuous printing, the temperature T ₁ detected by the thermistor 25 falls below the target temperature T _{f. The} time required to return to _f (return time A) was measured, and the return time A was compared with a preset threshold B. When return time A is smaller than the threshold value B, the stationary target temperature T _g while the target temperature T _f, when the return time A is larger than the threshold value B, the sheet of recording paper P of handsome prior to heat fixing operation, the target temperature T _g by changing set target temperature T _h of the high-temperature side, and shall make the printing operation after continuous printing handsome.
That is, in this image forming apparatus, the temperature state of the recording paper P is given to the heat roller 20 based on the return time A of the detected temperature T1 to the target temperature _Tf in the heat fixing operation for the _first recording paper P. Only when the return time A is greater than the threshold B, it is determined that the recording paper P is in a low temperature state and the influence on the heat roller 20 is large, and the target temperature _Tg is set to a high temperature. The setting was changed to _Th on the side.

Therefore, according to this image forming apparatus 1, when the recording paper P is in a low temperature state, the target temperature _Tg is changed to the high temperature side _Th to change the surface temperature of the heat roller 20 and necessary for toner fixing. Therefore, it is possible to prevent the surface temperature of the heat roller 20 from becoming lower than the fixing temperature, and thus to reliably prevent the occurrence of fixing failure.
Above all, in the image forming apparatus 1 only when the return time A is greater than the threshold B, from the target temperature Tg to a high temperature side of the T _h, a conventional image forming apparatus according to Patent Document 1 as in the ambient surface temperature of the target temperature was unavoidable in the form of configuration changes to the high temperature side of the T _h, the heat roller 20 is unnecessarily in summer or the like every time the continuous printing is caused by a high temperature It is possible to reliably eliminate the malfunction of the device, an increase in the load of the exhaust heat device, etc., or an increase in power consumption due to the prolonged energization time of the halogen lamp 22.
Thus, according to the present embodiment, an image forming apparatus that is free from fixing defects and excellent in print quality and reliability can be obtained. Further, according to this image forming apparatus, the target temperature _Tg is not unnecessarily changed to the high temperature side (T _h ), and an increase in power consumption of the heat roller 20 is minimized, It is also excellent in that the increase in running cost can be suppressed.

(Second Embodiment)
A second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. In the second embodiment, in addition to the two target temperatures T _g of T _f and T _h , the second sheet is used by using the target temperature of T _h ′ (T _h > T _h ′> T _f ). This is different from the first embodiment in that the halogen lamp 22 is turned on / off in the subsequent printing operation. Specifically, in the image forming apparatus 1 according to the second embodiment, when the detected temperatures T ₁ by the thermistor 25 has reached the target temperature T _h, a pickup for recording paper P in the first sheet by the sheet feeding roller 8 Start operation. When return time A is greater than the threshold value B, prior to the heat fixing operation for the recording paper P handsome, the target temperature T _g low temperature than the target temperature T _h, and than the target temperature T _f Also, the setting operation is changed to the high target temperature T _h ′, and the printing operation for the second and subsequent sheets of continuous printing is performed.

Thus, at a lower temperature than the target temperature T _h, and the than the target temperature T _f is to perform the second sheet subsequent print operation using a high-temperature target temperature T _{h ',} the surface temperature of the roller 20 the with temperature higher than the target temperature T _f, the occurrence of faulty fixing was effectively prevented, it is possible to ensure good print quality, moreover, than the target temperature T _h of the surface temperature of the roller 20 By making the temperature low, the energization time of the halogen lamp 22 can be shortened compared to the first embodiment, which can contribute to a reduction in power consumption and a reduction in printing time.

(Third embodiment)
8 and 10 show a third embodiment of the image forming apparatus according to the present invention. As shown in FIG. 8, in this image forming apparatus 1, in place of the return time measurement unit 30d (see FIG. 1), a halogen lamp is used by the heating control unit 30a in the heat fixing operation for the first recording sheet in continuous printing. The point provided with the time measuring part (time measuring means) 30e which measures the energization time in which 22 is on-controlled is different from FIG. 1 of the first embodiment. Since other than that is the same as that of 1st Embodiment, the same code | symbol is attached | subjected to the same member and the description is abbreviate | omitted.

9, when the recording paper P in the first sheet passes through the fixing device 5, which shows the time course of the detected temperature T ₁ of the thermistor 25, (a) has a recording sheet P in winter such as low temperature (B) shows a state in which the recording paper P is warmer than (a). FIG. 10 is a flowchart showing a control method of the image forming apparatus 1 according to this embodiment.
In this image forming apparatus 1, the detection temperature T ₁ by the thermistor 25 decreases to the T _f -on temperature and the halogen lamp 22 is turned on, and then the detection temperature T ₁ increases to the T _f -off temperature. Then, the energization time C until the halogen lamp 22 is turned off is measured, and this is compared with the threshold value D stored in the memory (S27 in FIG. 10). If the energization time C exceeds the threshold D (Yes in S28), it is determined that the recording paper P is in a low temperature state, and the target temperature T is determined prior to the printing operation for the second recording paper P. and _{T h} a _g from _{T f} (S29). Other control operations are the same as those in the first embodiment.

This image forming apparatus 1 can also provide the same effects as those of the first embodiment. That is, when the recording sheet P is in a cold state, the target temperature T _g By setting change to the high temperature side of the T _h, a large temperature difference between the fusing temperature required for the surface temperature and the toner fixing of the heat roller 20 Therefore, it is possible to effectively prevent the surface temperature of the heat roller 20 from becoming lower than the fixing temperature, and thus it is possible to reliably prevent the occurrence of fixing failure.
Further, only when the energizing time C is greater than the threshold D, from the target temperature T _g to a high temperature side of the T _h, as in the conventional image forming apparatus according to Patent Document 1, the continuous printing was inevitable the target temperature in the form of configuration changes to the high temperature side of the T _h each time, in summer or the like operation or failure of the peripheral device the surface temperature of the unnecessary heat roller 20 is caused by a high temperature, the exhaust An increase in power consumption due to an increase in the load of the heat device or the energization time of the halogen lamp 22 can be reliably eliminated.

1 is a schematic configuration diagram of an image forming apparatus of the present invention according to a first embodiment. FIG. 2 is a schematic configuration diagram illustrating a configuration of a fixing device. It is a flowchart which shows the process sequence of a control apparatus. It is a time chart which shows the time change of the detection temperature of a thermistor and the on / off control of a halogen lamp when the return time exceeds a threshold value. It is a time chart which shows the time change of the detection temperature of the thermistor and the on / off control of the halogen lamp when the detection temperature T ₀ of the thermistor exceeds the reference temperature T _s when receiving the continuous print command. When recording paper one sheet passes through the fixing device, a time chart showing changes with time of the detected temperature T ₁ of the thermistor, (a) shows the case where the recording sheet in winter or the like is in a low temperature state, (b) Indicates that the recording paper is warmer than (a). FIG. 10 is a time chart for explaining a processing procedure of the image forming apparatus according to the second embodiment, and shows a time change between the detected temperature of the thermistor and the on / off control of the halogen lamp when the recovery time exceeds a threshold value. . It is a schematic block diagram of the image forming apparatus of this invention which concerns on 3rd Embodiment. A time chart showing changes with time of the detected temperature T ₁ of the thermistor when the recording paper one sheet passes through the fixing device, (a) shows the case where the recording sheet in winter or the like is in a low temperature state, (b) is The recording paper is warmer than (a). It is a flowchart which shows the process sequence of a control apparatus. It is a figure for demonstrating the problem of the conventional temperature control method, and has shown the state of the change of the surface temperature of the heat roller in continuous printing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Fixing apparatus 20 Heat roller 22 Heating means (halogen lamp)
25 Roller temperature detection means (thermistor)
30 Heating control means (heating control unit)
30d Target temperature changing means (target temperature changing unit)
30d Return time measuring means (return time measuring unit)
30e Timekeeping means (timer)
P recording paper _{T g, T h, T h} ', T f target temperatures T ₁ detected by the thermistor temperature

Claims (3)

A fixing device responsible for the heat fixing operation of the toner image transferred onto the recording paper;
Roller temperature detecting means for detecting the surface temperature of the heat roller constituting the fixing device;
A heating control means for controlling the heating means of the heat roller so that the surface temperature of the heat roller approaches a preset target temperature;
A target temperature changing means for comparing the detected temperature from the roller temperature detecting means with a preset reference temperature and changing the target temperature based on the comparison result;
When the target temperature changing means determines that the temperature detected by the roller temperature detecting means when receiving the continuous print command is lower than the reference temperature, prior to the heat fixing operation for the first recording paper by the fixing device, the target temperature changing means In an image forming apparatus that changes the temperature setting to a high temperature side,
During the heat-fixing operation for the first sheet of recording paper in continuous printing, a recovery time that measures the recovery time required for the roller temperature detection means to return to the target temperature after the temperature detected by the roller temperature detection means falls below the target temperature before the setting change. Equipped with measuring means,
The target temperature changing means compares the return time from the return time measuring means with a preset threshold value, and if the return time is greater than the threshold value, prior to the heat fixing operation for the second recording sheet. And changing the setting of the target temperature to the high temperature side.   2. The image forming apparatus according to claim 1, wherein the return time measuring unit compares an output value from the roller temperature detecting unit with a target temperature by a comparator and counts an output time from the comparator. A fixing device responsible for the heat fixing operation of the toner image transferred onto the recording paper;
Roller temperature detecting means for detecting the surface temperature of the heat roller constituting the fixing device;
A heating control means for controlling the heating means of the heat roller so that the surface temperature of the heat roller approaches a preset target temperature;
A target temperature changing means for comparing the detected temperature from the roller temperature detecting means with a preset reference temperature and changing the target temperature based on the comparison result;
When the target temperature changing means determines that the temperature detected by the roller temperature detecting means when receiving the continuous print command is lower than the reference temperature, prior to the heat fixing operation for the first recording paper by the fixing device, the target temperature changing means In an image forming apparatus that changes the temperature setting to a high temperature side,
In the heating and fixing operation for the first recording paper in continuous printing, the heating control unit includes a time measuring unit that measures the energization time during which the heating unit is on-controlled,
The target temperature changing unit compares the energization time measured by the time measuring unit with a preset threshold value. If the energization time is greater than the threshold value, the target temperature changing unit performs the heat fixing operation on the second recording sheet. An image forming apparatus, wherein the target temperature is set and changed to a high temperature side in advance.

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