Image-forming device

Abstract

To suppress occurrence of unusual sound because of deformation of a belt in a fixing device for sandwiching the belt between a heater and a pressure roller.SOLUTION: A control section can execute first control and second control in a process for increasing a temperature of a heating unit to a target temperature. The control section rotates a motor for rotating a pressure roller at a first rotational speed in the first control, and increases a duty ratio of energization to a heater as the deviation between a target temperature and a detection temperature of a first temperature sensor is larger. The control section rotates the rotor at a second rotational speed lower than the first rotational speed in the second control, and restricts a duty ratio of energization to a heater to a limitation value or smaller that is smaller than the upper-limit value of the duty ratio in the first control. The control section executes the second control when a detection temperature (Tout) of a second temperature sensor detected (S7) when a fixing device starts to be driven is equal to or less than a first threshold TH1 (S5).SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus.

Background Art

[0002] Conventionally, there has been known an image forming apparatus including an endless belt having grease applied to its inner peripheral surface, a heater disposed inside the belt, a pressure roller that sandwiches the belt between the heater, a motor that drives the pressure roller, and a control unit that controls the motor (see Patent Document 1). When starting the rotation of the pressure roller in a low-temperature environment, the control unit sets the rotation speed of the motor to be lower than the rotation speed during printing. This suppresses the motor from being out of synchronization due to the solidification of the grease in a low-temperature environment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the prior art, the control of the heater at the start of rotation of the pressure roller is not considered. In a fixing device that sandwiches the belt between the heater and the pressure roller, since the portion of the belt in contact with the heater is intensively heated, when starting to drive the fixing device in a low-temperature environment, the temperature distribution of the belt varies in the circumferential direction. As a result, the belt may be deformed and abnormal noise may occur.

[0005] Therefore, an object of the present disclosure is to suppress the occurrence of abnormal noise due to deformation of the belt in a fixing device that sandwiches the belt between a heater and a pressure roller.

Means for Solving the Problems

[0006] To solve the above problems, the image forming apparatus of the present disclosure includes a fixing device, a motor, a second temperature sensor, and a control unit. The fixing device includes a heating unit, a belt, a pressure roller, and a first temperature sensor. The heating unit has a heater. The belt is endless. The pressure roller sandwiches the belt with the heating unit. The first temperature sensor detects the temperature of the heating unit. The motor rotates the pressure roller. The second temperature sensor is a sensor different from the first temperature sensor. In the process of raising the temperature of the heating unit to the target temperature, the control unit can execute first control and second control. In the first control, the control unit rotates the motor at a first rotation speed, and increases the duty ratio of the power supply to the heater as the deviation between the target temperature and the detected temperature of the first temperature sensor increases. In the second control, the control unit rotates the motor at a second rotation speed lower than the first rotation speed, and limits the duty ratio of the power supply to the heater to a limit value lower than the upper limit value of the duty ratio in the first control. When the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is equal to or lower than the first threshold value, the control unit executes the second control.

[0007] When the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is equal to or lower than the first threshold value, by configuring the control unit to execute the second control, in a low temperature environment, the output of the heater is limited and the motor rotates at a low speed. As a result, the variation in the circumferential temperature distribution of the belt can be suppressed, the deformation of the belt can be suppressed, the generation of abnormal noise can be suppressed, and the generation of abnormal noise can be suppressed more when the belt rotates at a low speed than when it rotates at a high speed.

[0008] Further, in the second control, the control unit may fix the duty ratio to the limit value.

[0009] In the second control, by fixing the duty ratio to a limit value, the control can be simplified.

[0010] Further, when the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is higher than the first threshold value, the control unit may execute the first control without executing the second control.

[0011] Further, when the detected temperature of the first temperature sensor detected during the execution of the second control becomes equal to or higher than a second threshold value lower than the target temperature, the control unit may switch from the second control to the first control.

[0012] Further, at the start of driving of the fixing device, the control unit may execute a third control in which power is supplied to the heater with the motor stopped, and after the third control, execute the first control or the second control.

[0013] Further, in the process of raising the temperature of the heating unit to the target temperature, the control unit can execute a fourth control in which the motor is rotated at a second rotational speed, and the larger the deviation between the target temperature and the detected temperature of the first temperature sensor, the larger the duty ratio of power supply to the heater. In this case, the control unit executes the fourth control when the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is equal to or lower than the first threshold value and the detected temperature of the first temperature sensor detected at the start of driving of the fixing device is equal to or higher than the third threshold value. Also, when the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is equal to or lower than the first threshold value and the detected temperature of the first temperature sensor detected at the start of driving of the fixing device is lower than the third threshold value, the control unit executes the second control.

[0014] Further, when the control unit receives print data, when the power of the image forming apparatus is turned on, when the state of the image forming apparatus returns from an error state to a normal state, or when the state of the image forming apparatus shifts from the sleep mode to the ready mode, the control unit may start driving the fixing device.

Advantages of the Invention

[0015] According to the present disclosure, in a fixing device that sandwiches a belt between a heater and a pressure roller, generation of abnormal noise due to deformation of the belt can be suppressed.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] Next, the embodiment will be described in detail with reference to the drawings as appropriate. As shown in FIG. 1, a laser printer 100 as an example of an image forming apparatus includes a main body housing 120, a supply unit 130, an exposure device 140, a process cartridge 150, a fixing device 1, a motor M, a second temperature sensor SE2, and a control unit 500.

[0018] The main body housing 120 has an opening H1, a front cover 121, and a discharge tray 124. The opening H1 is an opening through which the process cartridge 150 can pass. The front cover 121 opens and closes the opening H1. The discharge tray 124 is a tray for supporting the sheet S discharged from the inside of the main body housing 120.

[0019] The supply unit 130 is a mechanism that supplies the sheet S toward the photosensitive drum 151 described later. The supply unit 130 includes a supply tray 131 that houses the sheet S, a pressing plate 132, and a supply mechanism 133. The sheet S in the supply tray 131 is pushed upward by the pressing plate 132 and separated one by one by the supply mechanism 133 and supplied to the process cartridge 150.

[0020] The exposure device 140 includes a laser light source, a polygon mirror, a lens, a mirror, etc. (not shown). The exposure device 140 exposes the surface of the photosensitive drum 151 with laser light based on image data emitted from the laser light source.

[0021] The process cartridge 150 is detachable from the main body housing 120 through the opening H1. The process cartridge 150 includes a photosensitive drum 151, a charger 152, a developing roller 153, and a transfer roller 154.

[0022] The charger 152 charges the surface of the photosensitive drum 151. The exposure device 140 forms an electrostatic latent image on the surface of the photosensitive drum 151 by exposing the charged surface of the photosensitive drum 151.

[0023] The developing roller 153 supplies the toner in the process cartridge 150 to the electrostatic latent image on the photosensitive drum 151. Thereby, a toner image is formed on the photosensitive drum 151. Then, the sheet S supplied from the supply unit 130 passes between the photosensitive drum 151 and the transfer roller 154, and the toner image on the photosensitive drum 151 is transferred to the sheet S.

[0024] The fixing device 1 is a device that fixes the toner image to the sheet S. The fixing device 1 includes a heating unit 2, a belt BL, and a pressure roller 3.

[0025] The heating unit 2 has a heater 10. The heater 10 heats the belt BL and heats the sheet S through the belt BL.

[0026] The belt BL is endless. The heating unit 2 is located inside the belt BL. The pressure roller 3 sandwiches the belt BL with the heating unit 2.

[0027] As the sheet S passes between the belt BL and the pressure roller 3, the toner image is fixed on the sheet S. The sheet S on which the toner image is fixed is discharged onto the discharge tray 124 by the discharge roller 125.

[0028] The motor M is a motor for rotating the pressure roller 3. The motor M is controlled by the control unit 500.

[0029] The second temperature sensor SE2 is a sensor for detecting the outside air temperature. The second temperature sensor SE2 is located in a space inside the main body housing 120 where the temperature is substantially the same as the outside air temperature. For example, the second temperature sensor SE2 is located near the air intake for taking in the outside air of the main body housing 120.

[0030] The temperature detected by the second temperature sensor SE2 is output to the control unit 500. In the following description, the temperature detected by the second temperature sensor SE2 is also referred to as the second detected temperature.

[0031] As shown in Fig. 2(a), the pressure roller 3 has a cylindrical shaft 3A and a cylindrical roller portion 3B. The shaft 3A is made of, for example, metal. The roller portion 3B is made of, for example, rubber. The roller portion 3B covers a part of the shaft 3A.

[0032] The heating unit 2 has a heater 10, a holder 20, a stay ST, and a heat conductive member 30 and a first temperature sensor SE1 shown in Fig. 2(b).

[0033] The first temperature sensor SE1 is a sensor different from the second temperature sensor SE2. The first temperature sensor SE1 detects the temperature of the heating unit 2, specifically, the temperature of the heater 10. The first temperature sensor SE1 is in contact with the heat conduction member 30. The temperature detected by the first temperature sensor SE1 is output to the control unit 500. In the following description, the temperature detected by the first temperature sensor SE1 is also referred to as the first detected temperature.

[0034] As shown in FIG. 2(b), the heater 10 forms a nip portion NP by sandwiching the belt BL between it and the pressure roller 3. The heater 10 includes a substrate 11, a resistive heating element 12 disposed on the substrate 11, and a cover 13. The substrate 11 is made of a ceramic elongated rectangular plate with aluminum oxide as the material. The heater 10 is a so-called ceramic heater.

[0035] The resistive heating element 12 is formed on one surface of the substrate 11 by printing. The resistive heating element 12 generates heat when energized.

[0036] The cover 13 covers the resistive heating element 12. The cover 13 is made of, for example, glass.

[0037] As shown in FIG. 2(a), the holder 20 supports the heater 10 and has a function of guiding the belt BL. The holder 20 is made of, for example, resin.

[0038] The stay ST supports the holder 20. The stay ST is made of, for example, metal.

[0039] The belt BL is made of metal, resin, or the like. The belt BL rotates around the heater 10 while being guided by the holder 20. The belt BL has an outer peripheral surface and an inner peripheral surface. The outer peripheral surface contacts the pressure roller 3 or the sheet S to be heated. The inner peripheral surface contacts the heater 10. Grease is applied to the inner peripheral surface.

[0040] The heat conduction member 30 is a member for conducting heat in the longitudinal direction of the heater 10 to equalize the temperature of the heater 10 in the longitudinal direction. The heat conduction member 30 is a plate-like member, located between the heater 10 and the holder 20, and contacts the other surface of the substrate 11. When the heating unit 2 sandwiches the sheet S with the pressure roller 3, the heat conduction member 30 is sandwiched between the heater 10 and the holder 20. The heat conduction member 30 is made of, for example, aluminum.

[0041] The control unit 500 has a CPU, ROM, RAM, non-volatile memory, etc., and is configured to perform various controls based on a pre-prepared program. The control unit 500 can appropriately select and execute the first control, second control, third control, and fourth control in the process of raising the temperature of the heating unit 2 to the target temperature. The target temperature is set to a fixing temperature suitable for fixing when the printing mode is executed, and is set to a ready temperature lower than the fixing temperature when the ready mode is executed.

[0042] The first control is a control for rotating the motor M at the first rotation speed and increasing the duty ratio of the energization to the heater 10 as the deviation between the target temperature and the first detected temperature is larger. The deviation is calculated, for example, by subtracting the first detected temperature from the target temperature. In this embodiment, the first rotation speed is set to the speed when the motor M rotates at full speed, and is also simply referred to as "full speed". The control unit 500 sets the duty ratio in the range of 0 to 100% in the first control.

[0043] The second control is a control for rotating the motor M at a second rotation speed lower than the first rotation speed and restricting the duty ratio of the energization to the heater 10 to be below a limit value lower than the upper limit value of the duty ratio in the first control. In this embodiment, the second rotation speed is set to half the full speed, and is also simply referred to as "half speed". Also, in this embodiment, in the second control, the duty ratio is fixed to the limit value. The limit value may be any value smaller than 100%, and can be, for example, 33%, that is, about 1 / 3 of the upper limit value.

[0044] The third control is a control for energizing the heater 10 while the motor M is stopped. In the present embodiment, in the third control, the duty ratio is fixed at 100%.

[0045] The fourth control is a control for rotating the motor M at the second rotational speed and increasing the duty ratio of the energization to the heater 10 as the deviation between the target temperature and the first detected temperature is larger. In other words, the fourth control is the same as the first control in terms of the control of the heater 10, except that the control of the motor M is different from that of the first control. The control unit 500 also sets the duty ratio to a value between 0 and 100% in the fourth control.

[0046] The control unit 500 executes the third control at the start of driving of the fixing device 1, and after the third control, executes the first control, the second control, or the fourth control according to the outside air temperature and the temperature of the heating unit 2. Specifically, the control unit 500 selects the first control, the second control, or the fourth control based on the table shown in FIG. 3.

[0047] When the second detected temperature (outside air temperature) detected at the start of driving of the fixing device 1 is equal to or lower than the first threshold value and the first detected temperature (temperature of the heating unit 2) detected at the start of driving of the fixing device 1 is lower than the third threshold value, the control unit 500 executes the second control.

[0048] When the second detected temperature detected at the start of driving of the fixing device 1 is equal to or lower than the first threshold value and the first detected temperature detected at the start of driving of the fixing device 1 is equal to or higher than the third threshold value, the control unit 500 executes the fourth control. When the second detected temperature detected at the start of driving of the fixing device 1 is higher than the first threshold value, the control unit 500 executes the first control regardless of the temperature of the heating unit 2. Note that when the control unit 500 executes the first control after the third control, the second control and the fourth control are not executed.

[0049] When the control unit 500 executes the second control or the fourth control, it terminates the second control or the fourth control based on the temperature of the heating unit 2, and then executes the first control. Specifically, when the first detected temperature detected during the execution of the second control becomes equal to or higher than a second threshold lower than the target temperature, the control unit 500 switches from the second control to the first control. When the first detected temperature detected during the execution of the fourth control becomes equal to or higher than the second threshold, the control unit 500 switches from the fourth control to the first control.

[0050] When the power of the laser printer 100 is turned on, when the state of the laser printer 100 shifts from the sleep mode to the ready mode, when print data is received, or when the state of the laser printer 100 returns from the error state to the normal state, the control unit 500 starts driving the fixing device 1. Specifically, when the power of the laser printer 100 is switched from OFF to ON, or when the state of the laser printer 100 shifts from the sleep mode to the ready mode, the control unit 500 starts the ready mode and starts driving the fixing device 1.

[0051] The transition from the sleep mode to the ready mode can be performed, for example, when the time required for receiving print data is equal to or longer than a predetermined time, such as when the capacity of the print data is large. In this case, the control unit 500 determines whether the reception of the print data is completed within a predetermined time from the reception of the print data. If it is determined that the reception is completed, the control unit 500 shifts from the sleep mode to the print mode. If it is determined that the reception is not completed, the control unit 500 shifts from the sleep mode to the ready mode. Note that the control unit 500 stops the motor M and turns off the heater 10 in the sleep mode.

[0052] When the control unit 500 receives print data, it starts the print mode and starts driving the fixing device 1. When the state of the laser printer 100 becomes an error state in the print mode and then returns from the error state to the normal state, the control unit 500 resumes the print mode and starts driving the fixing device 1.

[0053] Here, the error can be any error. For example, during printing, the control unit 500 determines whether the sheet S is jammed inside the main body housing 120 based on information from a sheet sensor that detects the passage of the sheet S. If it is determined that the sheet is jammed, an error is determined, and printing control is stopped.

[0054] After that, the control unit 500 determines whether it has returned from the error state to the normal state based on information from a cover sensor that detects the opening and closing of the front cover 121 and the sheet sensor. Specifically, based on information from the sheet sensor, it is determined that the sheet S is not in contact with the sheet sensor, and based on information from the cover sensor, when it is determined that the front cover 121 is closed, it is determined that it has returned from the error state to the normal state.

[0055] Next, the control of the control unit 500 will be described in detail. When the control unit 500 receives print data or when it returns from an error state, it executes the first heat treatment shown in FIG. 4 until the first detected temperature reaches the target temperature.

[0056] In the first heat treatment, the control unit 500 first obtains the outside air temperature Tout at the start of printing from the second temperature sensor SE2 and the temperature Tu of the heating unit 2 at the start of printing from the first temperature sensor SE1 (S1). After step S1, the control unit 500 sets the target temperature to the fixing temperature Tt (see FIG. 6) (S2).

[0057] After step S2, the control unit 500 executes the third control, specifically, turns on the heater 10 with the motor M stopped (S3). After step S3, the control unit 500 determines whether the current temperature Tn of the heating unit 2 obtained from the first temperature sensor SE1 is equal to or higher than the rotation start temperature THr (see FIG. 6) (S4).

[0058] Here, the rotation start temperature THr is a threshold value for starting the rotation of the motor M. In other words, the rotation start temperature THr is a threshold value for ending the third control. The rotation start temperature THr is set to a temperature lower than the second threshold value TH2.

[0059] Note that in this embodiment, the end condition of the third control is set based on temperature, but for example, it may be set based on time. For example, the third control may end after a predetermined time has elapsed since the start of the third control.

[0060] The control unit 500 repeats the process of step S4 until Tn≥THr (No). When it is determined in step S4 that Tn≥THr (Yes), the control unit 500 determines whether the outside air temperature Tout at the start of printing is equal to or less than the first threshold value TH1 (S5).

[0061] When it is determined in step S5 that Tout≤TH1 (Yes), the control unit 500 determines whether the temperature Tu of the heating unit 2 at the start of printing is lower than the third threshold value TH3 (S6). When it is determined in step S6 that Tu<TH3 (Yes), the control unit 500 executes the second control, specifically, rotates the motor M at half speed and limits the duty ratio to be equal to or less than the limit value (S7).

[0062] When it is determined in step S6 that Tu<TH3 is not satisfied (No), the control unit 500 executes the fourth control, specifically, rotates the motor M at half speed and sets the duty ratio in the range of 0 to 100% based on the deviation between the target temperature and the first detected temperature (Tn) (S8).

[0063] After step S7 or step S8, the control unit 500 determines whether the current temperature Tn of the heating unit 2 is equal to or higher than the second threshold value TH2 (S9). The control unit 500 repeats the process of step S9 until Tn≥TH2.

[0064] When it is determined in step S9 that Tn ≥ TH2 (Yes), or when it is determined in step S5 that Tout ≦ TH1 is not satisfied (No), the control unit 500 executes the first control. Specifically, the motor M is rotated at full speed, and the duty ratio is set in the range of 0 to 100% based on the deviation between the target temperature and the first detected temperature (Tn) (S10).

[0065] When the first detected temperature reaches the target temperature by the first control, the control unit 500 ends this process. After the first detected temperature reaches the target temperature, the same process as before may be performed.

[0066] When the power of the laser printer 100 is switched from OFF to ON, or when the state of the laser printer 100 shifts from the sleep mode to the ready mode, the control unit 500 executes the second heat treatment shown in FIG. 5 until the first detected temperature reaches the target temperature.

[0067] Here, the second heat treatment is only slightly different in the processes of steps S1 and S2 of the first heat treatment, and the other processes are the same as those of the first heat treatment. For the processes similar to those of the first heat treatment in the second heat treatment, the same reference numerals are used and the description is omitted.

[0068] In the second heat treatment, the control unit 500 first obtains the outside air temperature Tout at the start of the ready mode from the second temperature sensor SE2 and obtains the temperature Tu of the heating unit 2 at the start of the ready mode from the first temperature sensor SE1 (S31). After step S31, the control unit 500 sets the target temperature to the ready temperature Tr (see FIG. 6) (S32). After step S32, the control unit 500 executes the processes of steps S3 to S10 similar to those of the first heat treatment.

[0069] Next, a specific example of the operation of the control unit 500 will be described. As shown in Fig. 6(a), when the outside air temperature Tout is equal to or lower than the first threshold TH1 and the temperature Tu of the heating unit 2 is lower than the third threshold TH3, when the control unit 500 receives print data (at time t0), first, the third control is executed. Specifically, the heater 10 is turned on while the motor M is stopped (from time t0 to t1). As a result, the first detected temperature (Tn) rises at a relatively large first gradient.

[0070] When the first detected temperature (Tn) becomes equal to or higher than the rotation start temperature THr (at time t1), the control unit 500 switches from the third control to the second control. In the second control, the control unit 500 rotates the motor M at half speed and restricts the duty ratio to be equal to or lower than the limit value. As a result, the first detected temperature (Tn) rises at a second gradient smaller than the first gradient.

[0071] When the first detected temperature (Tn) becomes equal to or higher than the second threshold TH2 (at time t2), the control unit 500 switches from the second control to the first control. In the first control, the control unit 500 rotates the motor M at full speed and sets the duty ratio in the range of 0 to 100% based on the deviation between the target temperature and the first detected temperature (Tn). As a result, the first detected temperature (Tn) rises at a gradient larger than the second gradient.

[0072] As shown in Fig. 6(b), when the outside air temperature Tout is higher than the first threshold TH1, when the control unit 500 receives print data (at time t10), first, the third control is executed. As a result, the first detected temperature (Tn) rises at a relatively large first gradient.

[0073] When the first detected temperature (Tn) becomes equal to or higher than the rotation start temperature THr (at time t11), the control unit 500 switches from the third control to the first control. As a result, the first detected temperature (Tn) rises at a gradient substantially the same as the first gradient.

[0074] As described above, according to the present embodiment, the following effects can be obtained. When the second detected temperature (Tu) detected by the control unit 500 at the start of driving of the fixing device 1 is equal to or lower than the first threshold value TH1, the second control is executed. Thus, in a low-temperature environment, the output of the heater 10 is restricted and the motor M rotates at a low speed. By restricting the output of the heater 10 in this way, variations in the circumferential temperature distribution of the belt BL can be suppressed, deformation of the belt BL can be suppressed, and generation of abnormal noise can be suppressed. Further, generation of abnormal noise can be suppressed when the belt BL rotates at a low speed as compared with when it rotates at a high speed.

[0075] By fixing the duty ratio to a limit value in the second control, the control can be simplified.

[0076] Note that the present disclosure is not limited to the above-described embodiment, and can be used in various forms as exemplified below.

[0077] The heating unit is not limited to the structure of the above-described embodiment. The heating unit may have, for example, a metal plate heated by a heater and configured to sandwich the belt between the metal plate and the pressure roller.

[0078] The first temperature sensor may be any sensor that detects the temperature of the heating unit. For example, the first temperature sensor may be disposed at a position away from the heating unit.

[0079] The second temperature sensor may be a sensor different from the first temperature sensor. For example, the second temperature sensor may be disposed near the fixing device.

[0080] The first rotational speed and the second rotational speed are not limited to the above-described embodiment, and may be set to any values.

[0081] In the second control, the duty ratio does not have to be fixed. For example, in the second control, the heater may be controlled so that the detected temperature of the first temperature sensor is equal to or lower than a preset upper limit value. Specifically, in the second control, after setting the upper limit value, control similar to the energization control of the first embodiment may be performed. Note that the upper limit value can be set to a temperature lower than, for example, the fixing temperature and the ready temperature.

[0082] The condition for switching from the second control to the first control is not limited to temperature and may be determined by, for example, time. For example, after a lapse of a predetermined time from the start of the second control, the control may be switched from the second control to the first control.

[0083] In the first control, the duty ratio may be set based on an operation amount including a proportional term proportional to the deviation between the target temperature and the first detected temperature and a differential term proportional to the differential value of the deviation. Also in this case, the larger the deviation between the target temperature and the first detected temperature, the larger the duty ratio.

[0084] In the above embodiment, the control is selected based on the outside air temperature at the start of driving of the fixing device and the temperature of the heating unit. However, for example, the control may be selected based only on the outside air temperature at the start of driving of the fixing device. In this case, for example, the second control may be executed when the outside air temperature at the start of driving of the fixing device is equal to or lower than the first threshold value, and the first control may be executed when the outside air temperature at the start of driving of the fixing device is higher than the first threshold value. Also, in this case, the control unit may be configured not to execute the fourth control.

[0085] The third control is also optional and does not have to be executed. In this case, the control unit may execute the first control or the second control from the beginning based on the outside air temperature at the start of driving of the fixing device.

[0086] The image forming apparatus is not limited to a laser printer and may be other image forming apparatuses such as a copying machine or a multifunction peripheral.

[0087] Each element described in the above embodiment and modification example may be arbitrarily combined and implemented.

Explanation of Signs

[0088] 1 Fixing device 2 Heating unit 3 Pressing roller 10 Heater 100 Laser printer 500 Control unit BL Belt M Motor SE1 First temperature sensor SE2 Second temperature sensor TH1 First threshold value Tout Outside air temperature

Claims

1. a fixing device including a heating unit having a heater, an endless belt, a pressure roller for sandwiching the belt between the heating unit and a first temperature sensor for detecting a temperature of the heating unit; A motor that rotates the pressure roller; a second temperature sensor separate from the first temperature sensor; A control unit, The control unit is In the process of increasing the temperature of the heating unit to a target temperature, a first control for rotating the motor at a first rotation speed and increasing a duty ratio of power supply to the heater as a deviation between the target temperature and a temperature detected by the first temperature sensor increases; a second control in which the motor is rotated at a second rotation speed lower than the first rotation speed and a duty ratio of energization to the heater is limited to a limit value lower than an upper limit value of the duty ratio in the first control, When the temperature detected by the second temperature sensor at the start of driving of the fixing device is equal to or lower than a first threshold value, the image forming apparatus executes the second control.

2. 2 . The image forming apparatus according to claim 1 , wherein the control unit fixes a duty ratio to the limit value in the second control.

3. The control unit is 2. The image forming apparatus according to claim 1, wherein when the detected temperature of the second temperature sensor detected at the start of operation of the fixing device is higher than the first threshold value, the first control is executed without executing the second control.

4. The control unit is The image forming apparatus according to claim 1, characterized in that when the detected temperature of the first temperature sensor detected during execution of the second control becomes equal to or higher than a second threshold value lower than the target temperature, the image forming apparatus switches from the second control to the first control.

5. The control unit is a third control is executed to energize the heater while the motor is stopped when the fixing device starts to be driven; 2. The image forming apparatus according to claim 1, wherein the first control or the second control is executed after the third control.

6. The control unit is a fourth control is executed in which, in a process of increasing the temperature of the heating unit to the target temperature, the motor is rotated at the second rotation speed, and a duty ratio of current supply to the heater is increased as a deviation between the target temperature and the temperature detected by the first temperature sensor increases; executes the fourth control when the detected temperature of the second temperature sensor detected at the start of driving of the fixing device is equal to or lower than the first threshold value and the detected temperature of the first temperature sensor detected at the start of driving of the fixing device is equal to or higher than a third threshold value; The image forming apparatus according to claim 1, characterized in that the second control is executed when the detected temperature of the second temperature sensor detected at the start of operation of the fixing device is lower than the first threshold value and when the detected temperature of the first temperature sensor detected at the start of operation of the fixing device is lower than the third threshold value.

7. The control unit is The image forming apparatus according to any one of claims 1 to 6, characterized in that the fixing device is started to be driven when print data is received, when the power of the image forming apparatus is turned on, when the state of the image forming apparatus returns to a normal state from an error state, or when the state of the image forming apparatus transitions from a sleep mode to a ready mode.

Images