JP6331417B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus employing an electrophotographic system.

  2. Description of the Related Art As an image forming apparatus employing an electrophotographic system, there is known an image forming apparatus that includes a heat source and includes a fixing unit that fixes an image on a sheet and a control unit that controls the temperature of the fixing unit.

  As such an image forming apparatus, for example, an image forming apparatus including a sheet tray for placing a sheet and a sheet presence / absence detecting sensor for detecting whether or not the sheet is placed on the sheet tray is known. ing. In this image forming apparatus, during the image forming operation, the presence / absence of the sheet on the sheet tray is detected by the sheet presence / absence detection sensor. If no sheet on the sheet tray is detected, the control unit controls the fixing unit so as to lower the temperature of the fixing unit. As a result, the temperature of the fixing unit can be lowered in accordance with the absence of sheets on the sheet tray (see, for example, Patent Document 1).

JP-A-4-289888

  However, in the image forming apparatus described in Patent Document 1, the temperature of the fixing unit may be lowered in a state where the sheet is positioned at the fixing unit. Specifically, in some cases, such as after the last sheet is fed from the sheet tray, the sheet on the sheet tray may be lost in a state where the fed sheet remains in the conveyance path. In this case, there is a possibility that the temperature of the fixing unit is lowered despite the sheet remaining in the conveyance path. As a result, there arises a problem that the image is not satisfactorily fixed on the sheet. In addition, when there is a sheet on the sheet tray but the sheet feeding operation is not performed well and the sheet is not fed from the sheet tray, the temperature of the fixing unit is kept high while the sheet does not reach the fixing unit. The problem of sagging occurs.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of reliably fixing an image on a recording medium while preventing overheating of a heating member.

(1) In order to achieve the above object, an image forming apparatus of the present invention includes a heating member that contacts a recording medium carrying a developer image and fixes the developer image on the recording medium by heating, and a recording medium. A sheet feeding unit that feeds the sheet toward the heating member, a first detection unit that detects the temperature of the heating member, a second detection unit that detects that the recording medium is fed from the sheet feeding unit, A controller that controls the temperature based on the set temperature. The control unit controls the heating member to lower the temperature of the heating member when the recording medium is not in contact with the heating member based on whether or not the recording medium is detected by the second detection unit.

  According to such a configuration, when the control unit determines that the recording medium is not in contact with the heating member based on the presence / absence of detection of the feeding of the recording medium by the second detection unit, the temperature of the heating member is determined. Lower.

  Therefore, the temperature of the heating member can be lowered at a timing when the recording medium is not in contact with the heating member.

As a result, when the recording medium is in contact with the heating member while preventing the heating member from overheating, the image can be reliably fixed on the recording medium by the heating member.
(2) Further, the control unit controls the heating member to lower the temperature of the heating member when the temperature detected by the first detection unit is higher than the set temperature, and fixes the developer image to the recording medium by heating. When the recording medium is set to the first temperature, the first detection temperature is determined when it is determined that the recording medium is not in contact with the heating member based on whether the recording medium is detected by the second detection unit. The second temperature may be lower than the temperature.

  According to such a configuration, when the control unit determines that the recording medium is not in contact with the heating member based on the presence / absence of the detection of the feeding of the recording medium by the second detection unit, the control unit sets the preset temperature. A second temperature lower than the first temperature is set. And a control part controls a heating member so that the temperature of a heating member may be lowered | hung, when the temperature which the 1st detection part detected is higher than preset temperature.

  Therefore, the temperature of the heating member can be lowered by changing the set temperature from the first temperature to the second temperature.

As a result, the temperature of the heating member can be lowered with simple control.
(3) The control unit may set the set temperature to a third temperature lower than the second temperature while the image forming operation is stopped.

  According to such a configuration, the second temperature can be higher than the third temperature and lower than the first temperature.

  Therefore, when the set temperature is set to the first temperature, the temperature of the heating member is set to a temperature suitable for fixing by changing the second temperature to the first temperature as compared with the case where the third temperature is set to the first temperature. Easy to return.

As a result, the image can be reliably fixed on the recording medium.
(4) In addition, the control unit controls to lower the temperature of the heating member when the temperature detected by the first detection unit is higher than the set temperature, and detects the feeding of the recording medium of the second detection unit. When it is determined that the recording medium is not in contact with the heating member based on the presence or absence, the temperature detected by the first detection unit may be corrected to be higher than the set temperature.

  According to such a configuration, when the control unit determines that the recording medium is not in contact with the heating member based on whether or not the recording medium is detected by the second detection unit, the first detection unit Correct the detected temperature higher. And a control part controls a heating member so that the temperature of a heating member may be lowered | hung, when the temperature which the 1st detection part detected is higher than preset temperature.

  Therefore, the temperature of the heating member can be lowered by correcting the temperature detected by the first detection unit.

As a result, the temperature of the heating member can be lowered with simple control.
(5) Further, the control unit detects the feeding of the recording medium in the second detecting unit without detecting the feeding of the recording medium in the second detecting unit. Based on the above, the heating member may be controlled to lower the temperature of the heating member when it is determined that the previous recording medium is separated from the heating member.

  According to such a configuration, in the control unit, the second detection unit detects the previous feeding of the recording medium, does not detect the feeding of the current recording medium, and the previous recording medium is separated from the heating member. When it is determined that the temperature has been determined, the temperature of the heating member is controlled to be lowered.

  Therefore, when the previous recording medium is fed and the current recording medium is not fed, when the previous recording medium is in contact with the heating member, the temperature of the heating member is set to a temperature suitable for fixing. Can keep.

As a result, the image can be reliably fixed on the recording medium by the heating member.
(6) Further, the control unit controls the heating member to lower the temperature of the heating member until it determines that the next recording medium comes into contact with the heating member based on the detection of the feeding of the recording medium by the second detection unit. You may control.

  According to such a configuration, the control unit controls the heating member to lower the temperature of the heating member until it is determined that the next recording medium comes into contact with the heating member.

  Therefore, when the next recording medium comes into contact with the heating member, the temperature of the heating member can be set to a temperature suitable for fixing.

As a result, the image can be reliably fixed on the recording medium by the heating member.
(7) The heating member may be configured to generate heat when power is supplied. The control unit may lower the temperature of the heating member by stopping the supply of power to the heating member.

  According to such a structure, a control part controls a heating member so that the temperature of a heating member may be lowered | hung by stopping supply of the electric power to a heating member.

Therefore, the temperature of the heating member can be reliably lowered.
(8) The first detection unit may be a non-contact type temperature sensor.

According to such a configuration, when the first detection unit is a non-contact type temperature sensor, an image can be effectively fixed on the recording medium.
(9) The temperature sensor may have a thermistor.

According to such a configuration, when the temperature sensor is a thermistor, the image can be effectively fixed on the recording medium.
(10) In addition, the first type is transported at a first speed and transports a first type of recording medium that is in contact with the heating member for a predetermined time. The first type is transported at a second speed slower than the first speed. A second transport mode for transporting a second type of recording medium that is in contact with the heating member longer than the recording medium. When the recording medium is transported in the first transport mode, the control unit sets the time for lowering the temperature of the heating member as the first period, and when the recording medium is transported in the second transport mode, the controller sets the temperature of the heating member. The time to be lowered may be a second period longer than the first period.

  According to such a configuration, the image forming apparatus has a first transport mode in which the recording medium is transported at the first speed, and a second transport mode in which the recording medium is transported at a speed slower than the first speed. . The control unit lowers the temperature of the heating member in the first period when the recording medium is transported in the first transport mode, and more than in the first period when the recording medium is transported in the second transport mode. The heating member is controlled to lower the temperature of the heating member in the long second period.

  Therefore, the temperature of the heating member can be lowered in a time corresponding to the speed at which the recording medium is conveyed.

  As a result, overheating of the heating member can be reliably prevented.

  In the image forming apparatus of the present invention, the heating member can be prevented from being overheated and the image can be reliably fixed on the recording medium.

FIG. 1 is a central sectional view showing an embodiment of the image forming apparatus of the present invention. FIG. 2 is a block diagram showing the main part of the electrical configuration of the printer shown in FIG. FIG. 3 is a flowchart for explaining the sheet feeding operation of the image forming apparatus shown in FIG. FIG. 4 is a flowchart illustrating control of the set temperature in the control unit of the image forming apparatus shown in FIG. FIG. 5 is a flowchart illustrating control of the heating roller in the control unit of the image forming apparatus shown in FIG. FIG. 6A is a timing chart illustrating the operation of the image forming apparatus illustrated in FIG. 1, and is a timing chart illustrating the operation of the image forming apparatus in a state where the paper feeding operation is achieved. FIG. 6B is a timing chart illustrating the operation of the image forming apparatus illustrated in FIG. 1, and is a timing chart illustrating the operation of the image forming apparatus in a state where the sheet feeding operation has not been continuously achieved. FIG. 7 is a timing chart illustrating the operation of the image forming apparatus illustrated in FIG. 1, and is a timing chart illustrating the operation of the image forming apparatus in a state where the sheet feeding operation has been achieved but has not been achieved. FIG. 8 is a flowchart illustrating control of the set temperature in the control unit of the image forming apparatus according to the second embodiment. FIG. 9 is a flowchart illustrating control of the set temperature in the control unit of the image forming apparatus according to the third embodiment.

1. Overall Configuration of Printer As shown in FIG. 1, a printer 1 as an example of an image forming apparatus is a horizontal type direct tandem color printer.

  In the following description, when referring to the direction of the printer 1, the state in which the printer 1 is horizontally placed is used as the upper and lower reference. That is, the upper side of the drawing in FIG. 1 is the upper side, and the lower side of the drawing is the lower side. Further, the left side of FIG. 1 is the front, and the right side of FIG. 1 is the rear. In addition, when the printer 1 is viewed from the front, the left and right reference is used. That is, the back of the paper surface of FIG.

  The printer 1 includes a main body casing 2 as an example of a substantially box-shaped housing. A top cover 4 that opens and closes the main body opening 3 is provided at the upper end of the main body casing 2 so as to be swingable with the rear end serving as a fulcrum. The printer 1 includes a paper feeding unit 9, a plurality of process units 5, a plurality of LED units 6, a transfer unit 7, and a fixing unit 8 in the main body casing 2.

  The paper feed unit 9 is located in the front lower end of the main casing 2. The paper feeding unit 9 includes a pickup roller 10 as an example of a paper feeding unit and a pair of registration rollers 24.

  The pickup roller 10 is positioned above the front end portion of a paper feed tray 22 described later at the lower end portion of the paper feed unit 9.

  The pair of registration rollers 24 are rotatably supported at the upper end portion of the paper feeding unit 9 so as to contact each other. Each of the pair of registration rollers 24 has a substantially cylindrical shape extending in the left-right direction.

  All the process units 5 are detachably provided in the main casing 2. The plurality of process units 5 correspond to one of yellow, magenta, cyan, and black, respectively, and are positioned so as to be parallel to each other in the front-rear direction.

  The process unit 5 includes a photosensitive drum 11, a scorotron charger 12, a developing roller 13, and a supply roller 14.

  The photosensitive drum 11 has a substantially cylindrical shape extending in the left-right direction, and is provided rotatably at the rear lower end of the process unit 5.

  The scorotron charger 12 is positioned above and behind the photosensitive drum 11 at an interval.

  The developing roller 13 is rotatably supported in front of and above the photosensitive drum 11 so as to be in contact with the photosensitive drum 11. The developing roller 13 has a substantially cylindrical shape extending in the left-right direction.

  The supply roller 14 is rotatably supported on the front upper side of the developing roller 13. The supply roller 14 has a substantially cylindrical shape extending in the left-right direction. The rear lower end portion of the supply roller 14 is in contact with the front upper end portion of the developing roller 13.

  Further, the process unit 5 includes a layer thickness regulating blade 15 that regulates the thickness of the toner supplied to the developing roller 13. The process unit 5 stores toner above the developing roller 13 and the supply roller 14.

  Each of the plurality of LED units 6 is positioned above the photosensitive drums 11 of the plurality of process units 5.

  The transfer unit 7 is located below the plurality of process units 5. The transfer unit 7 includes a driving roller 16, a driven roller 17, a conveyance belt 18, and a plurality of transfer rollers 19.

  The driving roller 16 is rotatably supported at the rear end portion of the transfer unit 7.

  The driven roller 17 is rotatably supported at the front end portion of the transfer unit 7.

  The conveyor belt 18 is wound around the driving roller 16 and the driven roller 17 so that the upper portion thereof is in contact with all the photosensitive drums 11 from below. The conveyor belt 18 is moved by the driving roller 16 and the driven roller 17 so that the upper portion thereof moves from the front toward the rear.

  Each of the plurality of transfer rollers 19 is positioned below each of the plurality of photosensitive drums 11 so as to sandwich an upper portion of the conveyance belt 18.

  The fixing unit 8 is located behind the transfer unit 7. The fixing unit 8 includes a heating roller 20 as an example of a heating member, and a pressure roller 21.

  The heating roller 20 is rotatably supported at the upper end portion of the fixing unit 8. The heating roller 20 has a substantially cylindrical shape extending in the left-right direction. The heating roller 20 includes a heater and is configured to generate heat when electric power is supplied.

  The pressure roller 21 is rotatably supported behind the heating roller 20. The pressure roller 21 has a substantially cylindrical shape extending in the left-right direction. The front upper end of the pressure roller 21 is in contact with the rear lower end of the heating roller 20.

  When a print job is input to the printer 1, an image forming operation is started. Then, the toner in the process unit 5 is triboelectrically charged positively between the supply roller 14 and the developing roller 13 and is carried on the surface of the developing roller 13 as a thin layer having a constant thickness by the layer thickness regulating blade 15. The

  On the other hand, the surface of the photosensitive drum 11 is uniformly positively charged by the scorotron charger 12 and then exposed by the LED unit 6 based on predetermined image data. Thereby, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 11. The toner carried on the developing roller 13 is supplied to the electrostatic latent image on the surface of the photosensitive drum 11, whereby the toner image is carried on the surface of the photosensitive drum 11.

  A sheet P as an example of a recording medium is accommodated in a sheet feed tray 22 provided at the bottom of the main casing 2 and is picked up by the rotation of the pickup roller 10 and then U-turns to the rear upper side by various rollers. And is fed one by one between the photosensitive drum 11 and the conveyor belt 18 at a predetermined timing by the rotation of the registration roller 24. Then, the transport belt 18 transports between all the photosensitive drums 11 and all the transfer rollers 19 from the front side to the rear side. At this time, the toner image is transferred to the paper P by the transfer bias applied to the transfer roller 19.

  The paper P is heated and pressed when it passes between the heating roller 20 and the pressure roller 21. At this time, the toner image is thermally fixed on the paper P.

Thereafter, the paper P is conveyed so as to make a U-turn to the front upper side, and is discharged onto a paper discharge tray 23 provided on the top cover 4.
2. Configuration Regarding Control of Fixing Unit As shown in FIGS. 1 and 2, the printer 1 includes a paper feed detection sensor 31 as an example of a second detection unit, a temperature detection sensor 32 as an example of a first detection unit, and a control. Part 30.

  The paper feed detection sensor 31 is positioned in front of the pickup roller 10 with a gap. The paper feed detection sensor 31 is configured to detect whether or not the paper is being transported in the paper transport path in front of the pickup roller 10.

  The temperature detection sensor 32 is located behind the heating roller 20 with an interval. The temperature detection sensor 32 is a non-contact type temperature sensor having a thermistor, and is configured to detect the temperature of the raw tube of the heating roller 20.

  As shown in FIG. 2, the control unit 30 includes a control board 40, and the control board 40 has a pickup roller control unit 41, a set temperature control unit, and a configuration realized by software by program processing by the CPU. 42 and a heating roller control unit 43.

  The pickup roller control unit 41 controls the operation of the pickup roller 10 based on a signal input from the paper feed detection sensor 31.

  The set temperature control unit 42 holds a set temperature value for controlling the heating roller 20, and changes the set temperature value in accordance with a signal input from the pickup roller control unit 41.

The heating roller control unit 43 controls the heating roller 20 based on the signal input from the temperature detection sensor 32 and the value of the set temperature held by the set temperature control unit 42. Specifically, the heating roller control unit 43 controls the temperature of the heating roller 20 by controlling the power supplied to the heater of the heating roller 20.
3. Image Forming Operation (1) Fixing Control in Normal Image Forming Operation As shown in FIGS. 2 and 6A, when a print job is input in the printer 1, the set temperature control unit 42 sets the set temperature to the first temperature. The fixing temperature A1 is set as an example (S20, see FIG. 4). The fixing temperature A1 is 210 ° C., for example. The fixing temperature A1 may be in the range of 180 ° C. to 220 ° C., may be in the range of 160 ° C. to 240 ° C., and may be outside these ranges.

Then, the pickup roller control unit 41 drives the pickup roller 10 at time _{t 1} (S1, see FIG. 3). Then, as described above and as shown in FIG. 1, the paper P is picked up from the paper feed tray 22, and the paper P comes into contact with the paper feed detection sensor 31. Then, as shown in FIG. 6A, the sheet feeding sensor 31 at time _{t 2} is turned on (S2: YES, see FIG. 3).

Then, the pickup roller control unit 41, after the drive time T1 of the pickup roller 10 has passed the predetermined time _{T A} (S3: YES, see FIG. 3), at time _{t 3,} stops the driving of the pickup roller 10 (S4 FIG. 3).

Thereafter, the sheet P is fed between the photosensitive drum 11 and the transport belt 18 by the rotation of the registration roller 24 as described above. Then, the sheet P is separated from the sheet feeding sensor 31, the paper feed sensor 31 at time t ₄ is turned off.

  Next, as described above, the paper P passes between the photosensitive drum 11 and the transfer roller 19 and then passes between the heating roller 20 and the pressure roller 21. At this time, when the paper P comes into contact with the heating roller 20, the heat of the heating roller 20 is transferred to the paper P, and the temperature of the heating roller 20 decreases. Then, the temperature detection sensor 32 detects the surface temperature K of the heating roller 20 after contacting the paper P. When the detected temperature K of the temperature detection sensor 32 is lower than the set temperature A1 (S40: YES, see FIG. 5), the heating roller control unit 43 supplies power to the heating roller 20 (S41, see FIG. 5). When the detected temperature K of the temperature detection sensor 32 is higher than the set temperature A1 (S40: NO, see FIG. 5), the power supply to the heating roller 20 is stopped (S43, see FIG. 5). Thereby, the temperature of the heating roller 20 is maintained at a temperature suitable for fixing, specifically, within a range of ± 5 ° C. with respect to the fixing temperature A1. The temperature of the heating roller 20 may be kept within a range of ± 10 ° C. with respect to the fixing temperature A1, or may be kept within a range of ± 15 ° C. with respect to the fixing temperature A1.

Then, the pickup roller control unit 41, after the driving of the pickup roller 10 has passed the predetermined time _{T B} from the time _{t 3} when stopped (S5: YES, see FIG. 3), at time _{t 5,} the print job is not completed If not (S7: NO, see FIG. 3), the pickup roller 10 is driven again (S1, see FIG. 3), and the second sheet P is fed.

  The above operation is repeated until the print job is completed.

That is, after the time t ₅ the pickup roller 10 is driven, at time t _6, the paper feed sensor 31 is turned on. Then, the pickup roller control unit 41 (see S3, FIG. 3) at time _{t 7} the pickup roller 10 has passed a predetermined time _{T A} from the drive to stop the driving of the pickup roller 10 (S4, see Fig. 3 ). Subsequently, the rotation of the registration rollers 24, the paper feed sensor 31 at time t ₈ is turned off.

Further, at time _{t 9} the pickup roller 10 has passed the predetermined time _{T B} from the time _{t 7} was stopped, the pickup roller control unit 41 (see S1, FIG. 3) is driven pick-up roller 10, a third sheet paper P is fed. After time _{t 9} the pickup roller 10 is driven, at time _{t 10,} the paper feed sensor 31 is turned on. Then, the pickup roller control unit 41 (see S3, FIG. 3) at time _{t 11} to the pickup roller 10 has passed a predetermined time _{T A} from the drive to stop the driving of the pickup roller 10 (S4, see Fig. 3 ). Then, after that, by the rotation of the registration roller 24, the paper feed sensor 31 at time _{t 12} is turned off.

Note that the first sheet P is discharged to the paper feed tray 22 at a time t ₅₀ between the time t ₆ and the time t ₇ .

When the print job ends (S27: YES, see FIG. 4), the set temperature control unit 42 sets the set temperature to the standby temperature A3 (S28, see FIG. 4). The standby temperature A3 is 165 ° C., for example.
(2) Fixing control when paper cannot be fed in image forming operation As shown in FIG. 6B, when the paper P in the paper feeding tray 22 runs out during the above-described image forming operation, the pickup roller control unit 41 determines that the time t _{Even if the} pickup roller 10 is driven at ₂₁ (S1, see FIG. 3), if the paper P is not fed (S2: NO, see FIG. 3), the paper feed detection sensor 31 remains off.

Then, the pickup roller control unit 41, after the pick-up roller 10 has passed the predetermined time T _C from the time t ₂₁ which is driven, at time t _22, and stops driving of the pickup roller 10, it is determined that no possible paper feed (See S9, FIG. 3). Time T _C from the time t ₂₁ to the pickup roller 10 is driven to the point t ₂₂ where the driving of the pickup roller 10 is stopped, the paper feeding detection sensor 31 from the time t ₁ when the pickup roller 10 is driven in the normal image forming operation shorter than the time T _a of up to time t ₂ which is turned on.

  Then, the pickup roller control unit 41 counts the number of times the pickup roller 10 is driven (S10, see FIG. 3).

Then, the pickup roller control unit 41, when the driving frequency of the pickup roller 10 is less than 3 (S11: NO, see FIG. 3), the predetermined time T _D from the time t ₂₂ it is determined that the paper feed miss occurs the last after There has elapsed, at time _{t 23,} is again driven, the pickup roller 10 (S1, see FIG. 3). That is, the second driving of the pickup roller 10 is started. Time T _D, in the normal image forming operation is longer than the paper discharge time t ₅₀ until the pickup roller 10 the sheet P from the start of the drive is discharged to the discharge tray 23.

Then, the pickup roller control unit 41, the t ₂₄ is the time from the time point t ₂₃ the predetermined time T _C has elapsed, stops driving of the pickup roller 10, it is determined that no possible paper feed (S9, Fig. 3 reference).

Similarly, the set temperature control unit 42 sets the set temperature to the second temperature at t ₂₄ when the predetermined time _TF has elapsed from the time t ₂₂ when the paper feed error occurs (S22: YES, see FIG. 4). The temperature is set to the overheat prevention temperature A2 as an example of the temperature (S23, see FIG. 4). The overheat prevention temperature A2 is lower than the fixing temperature A1 and higher than the standby temperature A3. The overheat prevention temperature A2 is 170 ° C., for example.

  Then, since the detection temperature K of the temperature detection sensor 32 is higher than the overheat prevention temperature A2 (S40: NO, see FIG. 5), the heating roller control unit 43 stops the power supply to the heating roller 20 (S43, FIG. 4). As a result, the temperature of the heating roller 20 decreases.

Next, the set temperature control unit 42 sets the set temperature to the fixing temperature at the time t ₂₅ when a predetermined time _TG has elapsed from the time t ₂₂ when the driving of the first pickup roller 10 is stopped (S24: YES, see FIG. 4). Set to A1 (S25, see FIG. 4).

  Similarly, the driving of the pickup roller 10 for the third time is started.

That is, at time _{t 26} that the predetermined time _{T D} has passed from the time _{t 24} of the drive stop of the previous pickup roller 10 (S12: see YES, FIG. 3), the pickup roller 10 is driven (S1, see FIG. 3) . Then, the pickup roller 10 at time _{t 27} from the time _{t 26} the predetermined time _{T C} has elapsed for driving (S8: see YES, FIG. 3), the drive is stopped the pick-up roller 10 (S9, see FIG. 3). Further, time _{t 27} are the time when the set time _{T F} from the time _{t 24} the drive stop has passed the last of the pickup roller 10 (S22: YES, see FIG. 4), setting the temperature control unit 42, the time t _{In 27} , the set temperature is set to the overheat prevention temperature A2 (S23, see FIG. 4). Then, setting the temperature control unit 42, at the time _{t 28} the set time _{T G} from time _{t 24} of the drive stop has passed the last of the pickup roller 10, the set temperature to the fixing temperature A1 (S25, see FIG. 4).

Thereafter, when the number of times of driving of the pickup roller 10 is 3 (S11: YES, see FIG. 3), after a predetermined time _{T E} has elapsed from the time _{t 27} of the drive stop of the third pick-up roller 10, at time _{t 29,} The set temperature control unit 42 sets the set temperature to the standby temperature A3 (S28, see FIG. 4).
(3) Fixing control when paper cannot be fed after normal image forming operation As shown in FIG. 7, when a print job is input in the printer 1, the same timing as the normal image forming operation described above is initially set. The operation is performed. That is, the same, at time _{t 1,} the pickup roller 10 is driven (S1, see FIG. 3), then the paper feeding detection sensor 31 at time _{t 2} is turned on (S2: YES, see FIG. 3). That is, the first sheet P is fed by the first driving of the pickup roller 10. After the pickup roller 10 has passed a predetermined time _{T A} from the time _{t 1} has been driven (S3, see FIG. 3), at time _{t 3,} the driving of the pickup roller 10 is stopped (S4, see Fig. 3). Thereafter, the rotation of the registration rollers 24, the first sheet paper P is conveyed in the sheet feeding sensor 31 at time t ₄ is turned off. Further, at time _{t 5} that the pickup roller 10 has passed the predetermined time _{T B} from the time _{t 3} when stopped (S7: NO, see FIG. 3), the pickup roller 10 is driven (S1, see FIG. 3).

  Then, the pickup roller 10 is driven, but the paper P is not fed well by the pickup roller 10 (S2: NO, see FIG. 3), that is, the paper P is fed by the start of driving of the pickup roller 10 for the second time. If no paper is fed, the paper feed detection sensor 31 remains off.

Then, the pickup roller control unit 41 judges after the pick-up roller 10 has passed the predetermined time T _C from the time point t ₅ was driven, at time t _30, and stops driving of the pickup roller 10, paper feed miss occurs (S9, see FIG. 3).

  Then, the pickup roller control unit 41 counts the number N of paper feeding errors (S10, see FIG. 3).

Thereafter, at time t ₅₀ , the first sheet P is discharged to the sheet feed tray 22.

Then, the pickup roller control unit 41, if the number N of misfeeds is less than 3 (S11: NO, see FIG. 3), from the time t ₃₀ it is determined that the paper feed miss occurs the last predetermined time T _D after There has elapsed (S12: YES, see FIG. 3), at time _{t 31,} again, to drive the pickup roller 10 (S1, see FIG. 3).

When the second sheet P is normally picked up from the sheet feed tray 22, the sheet P comes into contact with the sheet feed detection sensor 31. Then, paper feed sensor 31 is turned on at time _{t 32} (S2: YES, see FIG. 3).

Then, setting the temperature control unit 42, after misfeeds has passed a predetermined time _{T F} from the time _{t 30} that occurred (S22: YES, see FIG. 4), at time _{t 33,} the overheat prevention temperature A2 the set temperature (S23, see FIG. 4). In other words, when the set temperature control unit 42 determines that the previous paper P has been separated from the heating roller 20 by securing a predetermined time _TF from the time point t ₃₀ when the paper feed error occurs to the time point t _33. Further, the set temperature is set to the overheat prevention temperature A2.

  Then, since the detection temperature K of the temperature detection sensor 32 is higher than the overheat prevention temperature A2 (S40: NO, see FIG. 5), the heating roller control unit 43 stops the power supply to the heating roller 20 (S43, FIG. 5). As a result, the temperature of the heating roller 20 decreases.

Then, the pickup roller control unit 41, after the lapse of a predetermined time _{T A} from the time _{t 31} which drives the pickup roller 10 (S3, see FIG. 3), at time _{t 34,} to stop the driving of the pickup roller 10 (S4 FIG. 3).

Thereafter, the second sheet P is fed between the photosensitive drum 11 and the conveyor belt 18 by the rotation of the registration roller 24 as described above. Then, the second sheet P is separated from the sheet feeding sensor 31, the paper feed sensor 31 at time t ₃₅ is turned off.

Then, setting the temperature control unit 42, at the time _{t 36} from the time _{t 30} to misfeeds occur a predetermined time _{T G} has elapsed (S24: YES, see FIG. 4), the set temperature to the fixing temperature A1 (S25 FIG. 4).

  Then, since the detection temperature K of the temperature detection sensor 32 is lower than the fixing temperature A1 (S40: YES, see FIG. 5), the heating roller control unit 43 supplies power to the heating roller 20 (S43, see FIG. 4). . Thereby, the temperature of the heating roller 20 is maintained at a temperature suitable for fixing.

  Then, the pickup roller control unit 41 resets the number N of sheet feeding errors (S6, see FIG. 3).

Next, at time t ₆₀ , the second sheet P comes into contact with the heating roller 20. That is, before the second sheet P comes into contact with the heating roller 20, the set temperature control unit 42 sets the set temperature to the fixing temperature A1. In other words, the set temperature control unit 42 keeps the set temperature at the overheat prevention temperature A2 until it is determined that the next sheet P is in contact with the heating roller 20.

Thereafter, the normal image forming operation is repeated.
4). Operation and Effect (1) According to the printer 1, as shown in FIG. 3, the control unit 30 determines that the paper P is not in contact with the heating roller 20 based on the presence or absence of a signal from the paper feed detection sensor 31. The heating roller 20 is controlled so as to lower the temperature of the heating roller 20.

  Therefore, the temperature of the heating roller 20 can be lowered at a timing when the paper P is not in contact with the heating roller 20.

As a result, when the recording medium is in contact with the heating member while preventing the heating member from overheating, the image can be reliably fixed on the recording medium by the heating member.
(2) According to the printer 1, as shown in FIG. 4, the set temperature control unit 42 does not contact the heating roller 20 with the paper P based on the presence or absence of a signal from the paper feed detection sensor 31. Is determined, the set temperature is set to the overheat prevention temperature A2 lower than the fixing temperature A1. Then, the heating roller control unit 43 controls the heating roller 20 so as to lower the temperature of the heating roller 20 when the temperature detected by the temperature detection sensor 32 is higher than the set temperature.

  Therefore, the temperature of the heating roller 20 can be lowered by changing the set temperature from the fixing temperature A1 to the overheat prevention temperature A2.

As a result, the temperature of the heating roller 20 can be lowered with simple control.
(3) According to the printer 1, as shown in FIG. 4, the set temperature control unit 42 sets the set temperature to the standby temperature A3 lower than the overheat prevention temperature A2 while the image forming operation is stopped. That is, the overheat prevention temperature A2 is higher than the standby temperature A3 and lower than the fixing temperature A1.

  Therefore, when the set temperature is set to the fixing temperature A1, the temperature of the heating roller 20 is suitable for fixing by changing the overheat prevention temperature A2 to the fixing temperature A1 as compared with the case where the standby temperature A3 is changed to the fixing temperature A1. Easy to return to temperature.

As a result, the image can be reliably fixed on the paper P.
(4) Also, according to the printer 1, as shown in FIG. 3, the control unit 30 causes the paper feed detection sensor 31 to detect the previous feeding of the paper P and to detect the current feeding of the paper P. In addition, when it is determined that the previous paper P has been separated from the heating roller 20, the heating roller 20 is controlled to lower the temperature of the heating roller 20.

  Therefore, if the previous paper P is fed and the current paper P is not fed, and the previous paper P is in contact with the heating roller 20, the temperature of the heating roller 20 is suitable for fixing. Can be kept at temperature.

As a result, the image can be reliably fixed on the paper P by the heating roller 20.
(5) Also, according to the printer 1, as shown in FIG. 4, the control unit 30 lowers the temperature of the heating roller 20 by stopping the supply of power to the heating roller 20.

Therefore, the temperature of the heating roller 20 can be reliably lowered.
(6) Moreover, according to this printer 1, as shown in FIG. 1, the temperature detection sensor 32 is a non-contact type temperature sensor.

Therefore, the image can be effectively fixed on the paper P.
(7) Moreover, according to this printer 1, as shown in FIG. 1, the temperature detection sensor 32 has a thermistor.

Therefore, the image can be effectively fixed on the paper P.
5. Modified Example A modified example of the printer 1 will be described with reference to FIGS. In the following modified example, the same reference numerals are given to the same members and controls as those in the first embodiment, and the description thereof is omitted.
(1) Second Embodiment (1-1) Basic Control of Printer of Second Embodiment In the first embodiment, the set temperature control unit 42 changes the set temperature from the fixing temperature A1 to the overheat prevention temperature A2. Thus, the temperature of the heating roller 20 is controlled.

  On the other hand, in the second embodiment, the temperature of the heating roller 20 is controlled by correcting the measured value of the temperature detected by the temperature detection sensor 32.

Specifically, as shown in FIG. 8, the set temperature control unit 42 measures the temperature detected by the temperature detection sensor 32 when a time _TF has elapsed after determining that a paper feed error has occurred (S22: YES). The value K is corrected. The set temperature control unit 42 corrects the temperature detected by the temperature detection sensor 32 to add 10 ° C. Thereby, the control unit 30 recognizes a value 10 ° C. higher than the temperature value detected by the temperature detection sensor 32 as the measurement value K. The set temperature control unit 42 may correct the temperature value detected by the temperature detection sensor 32 so as to add 15 ° C. or correct the value so as to add 19 ° C.

  As a result, the value recognized as the measurement value by the set temperature control unit 42 becomes higher than the fixing temperature A1 (S42: NO, see FIG. 5), so that the power supply to the heating roller 20 is stopped (S43, FIG. 5). reference). Thereby, the temperature of the heating roller 20 is lowered.

Thereafter, the set temperature control unit 42 stops the correction (S71) when the set time _TG has elapsed after the time T7 after determining that a paper feed error has occurred (S24: YES). Accordingly, the set temperature control unit 42 recognizes the temperature value detected by the temperature detection sensor 32 as a measured value.
(1-2) Effects of Second Embodiment According to the printer 1 of the second embodiment, as shown in FIG. 8, the set temperature control unit 42 is based on the presence or absence of a signal from the paper feed detection sensor 31. When it is determined that the paper P is not in contact with the heating roller 20, the temperature value detected by the temperature detection sensor 32 is corrected to be high. Further, the heating roller control unit 43 controls the temperature of the heating roller 20 to be lowered when the temperature detected by the temperature detection sensor 32 is higher than the set temperature.

  Therefore, the temperature of the heating roller 20 can be lowered by correcting the temperature value detected by the temperature detection sensor 32.

As a result, the temperature of the heating roller 20 can be lowered with simple control.
(2) Third Embodiment (2-1) Basic Control of Printer of Third Embodiment In the third embodiment, the printer 1 is an example of a first print mode and a second transport mode as an example of the first transport mode. As a second print mode. In the first printing mode, the same printing operation as in the first embodiment is performed.

On the other hand, in the second printing mode, the paper P such as cardboard or postcard is overheated in the fixing unit 8 for a longer time than in the first printing mode. Therefore, the speed at which the paper P is conveyed is slower than that in the first printing mode, and specifically, is about half. Therefore, the time from the pickup roller 10 is driven to pickup roller 10 is driven to the next (time corresponding to the time t ₂₁ to time t ₂₃₎ is long.

  Note that the normal paper is an example of the first type of recording medium, the transport speed of the paper P in the first print mode is the first speed, and the transport speed of the paper P in the second print mode is the second speed. .

  As shown in FIG. 9, in the second print mode, when the paper P is fed by the pickup roller 10 and the paper feed detection sensor 31 is not turned on, the set temperature control unit 42 sets the set temperature to the overheat prevention temperature. Set to A2 (S23).

Next, since a job in the second print mode is input (S70: YES), the set temperature control unit 42 sets the time T7 after determining that a paper feed error has occurred as an example of the second period. to determine whether the elapsed time _{T I} (S71). Set time T _I is longer than the set time T _G as an example of a first period in a first printing mode. Then, setting the temperature control unit 42, when the time T7 has passed a set time _{T I} (S71: YES), the pickup roller 10 next to the fixing temperature A1 the set temperature before being driven (S25).

That is, the time set temperature control unit 42 in the second printing mode is the set temperature to the overheat prevention temperature A2, the partial time corresponding to the time t ₂₁ to time t ₂₃ is long, set in the first printing mode It is longer than the time during which the temperature control unit 42 sets the set temperature to the overheat prevention temperature A2.
(2-2) Effects of Third Embodiment According to the printer 1 of the third embodiment, the printer 1 has the first print mode and the second print mode having a lower conveyance speed than the first print mode. . Then, the control unit 30 lowers the temperature of the heating roller 20 at the set time _TG when normal paper is transported in the first print mode, and the set time when the thick paper is transported in the second print mode. long setting time than T _G T _I, and controls to lower the temperature of the heating roller 20 and the set temperature to A2.

  Therefore, the temperature of the heating roller 20 can be lowered in a time corresponding to the speed at which the paper is conveyed.

  As a result, overheating of the heating roller 20 can be reliably prevented.

DESCRIPTION OF SYMBOLS 10 Pickup roller 20 Heating roller 30 Control part 31 Paper feed detection sensor 32 Temperature detection sensor

Claims (10)

A heating member that comes into contact with the recording medium carrying the developer image and fixes the developer image to the recording medium by heating;
A paper feeding unit that feeds the recording medium toward the heating member;
A first detector for detecting the temperature of the heating member;
A second detector for detecting that a recording medium has been fed from the paper feeder;
A controller that controls the temperature of the heating member based on a set temperature,
The control unit is based on the detection of the feeding of the recording medium by the second sensing unit, and the second sensing unit detects the feeding of the recording medium of the previous time and does not detect the feeding of the recording medium of the current time. An image forming apparatus that controls the heating member to lower the temperature of the heating member when it is determined that the previous recording medium is separated from the heating member. The controller is
When the temperature detected by the first detection unit is higher than the set temperature, the heating member is controlled to lower the temperature of the heating member,
When fixing the developer image to the recording medium by heating, the set temperature is set to the first temperature,
A second temperature that is lower than the first temperature when the recording medium is determined not to be in contact with the heating member based on whether or not the recording medium is detected by the second detector. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 2, wherein the control unit sets the set temperature to a third temperature lower than the second temperature while the image forming operation is stopped. The controller is
When the temperature detected by the first detection unit is higher than a set temperature, control to lower the temperature of the heating member,
The temperature detected by the first detection unit is determined based on the set temperature when it is determined that the recording medium is not in contact with the heating member based on whether the recording medium is detected by the second detection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus corrects the image to be higher.   The control unit controls the heating member to lower the temperature of the heating member until it determines that the next recording medium comes into contact with the heating member based on the detection of the feeding of the recording medium by the second detection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled. The heating member is configured to generate heat when power is supplied;
The controller is
The image forming apparatus according to claim 1, wherein the temperature of the heating member is lowered by stopping the supply of electric power to the heating member.   The image forming apparatus according to claim 1, wherein the first detection unit is a non-contact type temperature sensor.   The image forming apparatus according to claim 7, wherein the temperature sensor includes a thermistor. A first transport mode for transporting a first type of recording medium transported at a first speed and in contact with the heating member for a predetermined time;
A second transport mode for transporting a second type of recording medium that is transported at a second speed that is slower than the first speed and that is in contact with the heating member longer than the first type of recording medium;
The controller is
When the recording medium is transported in the first transport mode, the time for lowering the temperature of the heating member is a first period,
9. The method according to claim 1, wherein when the recording medium is transported in the second transport mode, the time for lowering the temperature of the heating member is a second period longer than the first period. The image forming apparatus described in the item. A heating member that comes into contact with the recording medium carrying the developer image and fixes the developer image to the recording medium by heating;
A paper feeding unit that feeds the recording medium toward the heating member;
A detector for detecting the temperature of the heating member;
A controller that controls the temperature of the heating member based on a set temperature,
When the control unit determines that the recording medium being transported is separated from the heating member when a paper feeding error has occurred in which the recording medium is not fed from the paper feeding unit in a state where the print job has not ended. In addition, the heating member is controlled to lower the temperature of the heating member.

Images