Image forming device

Abstract

To provide an image forming apparatus that can reduce the influence of a change in the driving speed of a fan on fixation quality.SOLUTION: An image forming apparatus 1 comprises: a fixing unit 8 that has a heating unit 81 for heating a sheet S and fixes a toner image to the sheet S; a fan 10 for cooling the fixing unit 8, the fan 10 capable of changing its driving speed; and a control unit 100. The control unit 100 can execute standby control of, in changing the driving speed of the fan 10 during the fixation of the toner image to the sheet S, suspending the fixation of the toner image to the sheet S, controlling a temperature of the heating unit 81 to be a predetermined target temperature for a predetermined time after the suspension of the fixation of the toner image, and resuming the fixation of the toner image to the sheet S after the lapse of the predetermined time.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus including a fixing unit that fixes a toner image on a sheet and a fan that cools the fixing unit. [Background technology]

[0002] Conventionally, there is known an image forming apparatus equipped with a fixing unit that fixes a toner image to a sheet with heat, and a fan that cools the fixing unit by exhausting the air inside the image forming apparatus to the outside or by drawing in outside air into the image forming apparatus (Patent Document 1). With this technology, when no image forming operation is being performed, the fan rotates at a slower speed than when the image forming operation is being performed, and when the image forming operation is started, the temperature of the fixing unit is detected, and the lower the detected temperature is, the later the timing at which the fan switches from low speed to high speed is controlled. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-325873 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional technology, the fan driving speed may be changed when the image forming operation is started and the toner image is fixed to the sheet. If the fan driving speed is changed when the toner image is fixed, the temperature of the fixing unit changes, which may affect the fixing quality, for example, by reducing the fixing strength.

[0005] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS An object of the present invention is to provide an image forming apparatus capable of reducing the effect on fixing quality caused by changing the drive speed of the fan. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, an image forming apparatus has a heating section for heating a sheet, a fixing section for fixing a toner image onto the sheet, a fan for cooling the fixing section, the fan having a variable drive speed, and a control section. When the control unit changes the fan drive speed when fixing a toner image to a sheet, the control unit can perform standby control to interrupt the fixing of the toner image to the sheet, control the temperature of the heating unit to a predetermined target temperature for a predetermined time after the fixing of the toner image is interrupted, and resume fixing of the toner image to the sheet after the predetermined time has elapsed.

[0007] According to this configuration, when fixing a toner image to a sheet, by executing standby control when changing the fan drive speed, the impact of changing the fan drive speed on fixing quality can be reduced.

[0008] In addition, when the control unit changes the fan drive speed when fixing a toner image to a sheet, if the amount of change in the fan drive speed per unit time is greater than or equal to a predetermined amount, the control unit can be configured to execute standby control, and if the amount of change is less than the predetermined amount, to continue fixing the toner image to the sheet without executing standby control.

[0009] According to this, when the amount of change in the fan drive speed is large and the change in the fan drive speed is likely to affect the fixing quality, the standby control can be executed, and the effect of the change in the fan drive speed on the fixing quality can be effectively reduced. Also, when the amount of change in the fan drive speed is small and the change in the fan drive speed is unlikely to affect the fixing quality, the fixing of the toner image on the sheet can be continued without interruption.

[0010] In addition, the fan can be configured to change its drive speed to at least a first speed, a second speed faster than the first speed, and a third speed faster than the second speed, and the control unit can be configured to determine that when the fan drive speed is changed between the first speed and the third speed within a unit time, the amount of change is greater than or equal to a predetermined value.

[0011] This makes it possible to easily determine when the amount of change in the fan drive speed is large.

[0012] In addition, the fan can be configured to change its drive speed to at least a first speed, a second speed faster than the first speed, and a third speed faster than the second speed, and the control unit can be configured to determine that the amount of change is less than a predetermined amount when the fan drive speed is changed between the first speed and the second speed within a unit time, and / or when the fan drive speed is changed between the second speed and the third speed within a unit time.

[0013] This makes it possible to easily determine when the amount of change in the fan drive speed is small.

[0014] In addition, the image forming device may be equipped with a temperature sensor that detects the temperature inside the housing of the image forming device, and the control unit may be configured to change the fan drive speed based on the detection result of the temperature sensor when fixing a toner image to a sheet.

[0015] In addition, when fixing a toner image onto a sheet, if the temperature based on the detection result of the temperature sensor is equal to or higher than a predetermined temperature, the control unit can be configured to change the fan drive speed to a speed faster than before the change.

[0016] This makes it possible to prevent the temperature inside the housing from becoming too high when a toner image is fixed onto a sheet.

[0017] In addition, during standby control, the control unit can be configured to interrupt the supply of the sheet following the sheet being fixed to the fixing unit, and to interrupt the fixing of the toner image to the sheet by completing the fixing of the toner image to the sheet being fixed.

[0018] According to this, the toner image can be fixed to the end on the sheet during fixing.

[0019] Further, the control unit may be configured to restart the fixing of the toner image onto the sheet by restarting the supply of the next sheet to the fixing unit during standby control.

[0020] The heating section may be a heating roller that is heated by a heater. Effect of the Invention

[0021] According to the present invention, it is possible to reduce the effect on fixing quality caused by changing the driving speed of the fan. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 illustrates a configuration of an image forming apparatus. [Diagram 2] FIG. 1A is a diagram showing the configuration around the heating section of the fixing unit, and FIG. 1B is a graph showing the output of each heater. [Diagram 3] 4 is a flowchart showing the operation of a control unit. [Figure 4] 4 is a flowchart showing a fan control process. [Diagram 5] 13 is a flowchart showing a standby control process. [Figure 6] 4 is a timing chart showing an example of the operation of the control unit, in which the drive speed of the fan is changed from stopped to low speed within a unit time, and then changed from low speed to high speed within the unit time. [Figure 7] 5 is a timing chart showing an example of the operation of the control unit, in which the drive speed of the fan is changed from stopped to high speed within a unit time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. 1, the image forming apparatus 1 is an apparatus that forms an image on a sheet S while conveying the sheet S. The image forming apparatus 1 is a color printer capable of forming color images, and includes, within a housing 2, a sheet supply section 3, an image forming section 4, a fan 10, a post-fixing sensor 23, an internal temperature sensor 25 as a temperature sensor, and a control section 100. The housing 2 has a discharge tray 21 on the top surface.

[0024] The sheet supply unit 3 has a function of supplying sheets S to the image forming unit 4. The sheet supply unit 3 includes a supply tray 31 capable of accommodating a plurality of sheets S, and a sheet supply mechanism 32. The sheet supply mechanism 32 includes a pickup roller 33, a separation roller 34, a separation pad 35, a conveying roller 36, and a registration roller 37.

[0025] The sheet supply unit 3 sends out the sheets S in the supply tray 31 using a pickup roller 33, separates the sheets S one by one using a separation roller 34 and a separation pad 35, and conveys the sheets S toward a registration roller 37 using a conveyance roller 36. Thereafter, the sheet supply unit 3 aligns the position of the leading edge of the sheet S using the registration roller 37 to correct skew of the sheet S, and supplies the sheet S to the image forming unit 4.

[0026] The image forming section 4 has a function of forming an image on a sheet S. The image forming section 4 includes an exposure unit 5, a photosensitive drum 61, a charger 62, a developing cartridge 63, a transfer unit 7, and a fixing section 8. The image forming section 4 includes four photosensitive drums 61, four chargers 62, and four developing cartridges 63.

[0027] The exposure unit 5 includes a plurality of light sources, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). The exposure unit 5 emits a light beam (see dashed line) based on image data to expose the surface of the photosensitive drum 61, thereby forming an electrostatic latent image on the surface of the photosensitive drum 61.

[0028] The photosensitive drum 61 is a member in which a photosensitive layer is formed on the outer periphery of a cylindrical drum main body having electrical conductivity. The four photosensitive drums 61 are arranged side by side in the conveying direction of the sheet S. The charger 62 has a function of charging the surface of the photosensitive drum 61. The charger 62 has a charging wire, a grid electrode, and the like. Each of the developing cartridges 63 has a developing roller 64 capable of carrying toner. The developing cartridges 63 contain yellow, magenta, cyan, or black toner.

[0029] The transfer unit 7 includes a drive roller 71, a driven roller 72, a conveyor belt 73, and four transfer rollers 74. The conveyor belt 73 is an endless belt, and is stretched between the drive roller 71 and the driven roller 72. The transfer rollers 74 are disposed inside the conveyor belt 73 so as to sandwich the conveyor belt 73 between themselves and the corresponding photosensitive drums 61.

[0030] The fixing unit 8 has a function of fixing a toner image to the sheet S. The fixing unit 8 has a heating unit 81, a pressure unit 82, a first heater 83, and a second heater 84. The heating unit 81 is a cylindrical heating roller heated by the heaters 83 and 84, and heats the sheet S. The pressure unit 82 is disposed so as to sandwich the sheet S between itself and the heating unit 81, and has a function of applying pressure to the sheet S between itself and the heating unit 81. The pressure unit 82 includes an endless pressure belt, a pressure pad disposed so as to sandwich the pressure belt between itself and the heating unit 81, and a belt guide for rotatably guiding the pressure belt, all of which are shown without reference numerals. The heaters 83 and 84 are heaters that generate heat when energized to heat the heating unit 81, and are disposed inside the heating unit 81.

[0031] In the image forming unit 4, the surface of the photosensitive drum 61 is charged by the charger 62, and then exposed by the exposure unit 5. As a result, an electrostatic latent image based on image data is formed on the surface of the photosensitive drum 61. Next, the image forming unit 4 supplies toner from the developing roller 64 to the electrostatic latent image formed on the photosensitive drum 61. As a result, a toner image is formed on the photosensitive drum 61.

[0032] Next, the image forming unit 4 transfers the toner image formed on the photosensitive drum 61 onto the sheet S by passing the sheet S supplied from the sheet supply unit 3 between the photosensitive drum 61 and the transfer roller 74 while conveying the sheet S by the conveyor belt 73. As a result, the toner image is formed on the sheet S.

[0033] Thereafter, the image forming unit 4 conveys the sheet S on which the toner image has been formed between the heating unit 81 and the pressure unit 82, thereby fixing the toner image to the sheet S. As a result, an image is formed on the sheet S. The sheet S on which the image has been formed is conveyed by conveying rollers 91 and 92, and is discharged to the discharge tray 21 by discharge rollers 93.

[0034] The post-fixing sensor 23 has a function of detecting the sheet S transported from the fixing unit 8 toward the discharge tray 21. The post-fixing sensor 23 is disposed downstream of the heating unit 81 and the pressure unit 82 in the transport direction of the sheet S. More specifically, the post-fixing sensor 23 is disposed between the heating unit 81 and the pressure unit 82 and the transport roller 91 in the transport direction of the sheet S.

[0035] The post-fixing sensor 23 may be, for example, a sensor including a lever that rotates when the sheet S comes into contact with it, and an optical sensor that detects the position of the lever. The post-fixing sensor 23 outputs a detection signal to the control unit 100 when it detects the sheet S, and outputs a non-detection signal to the control unit 100 when it does not detect the sheet S. It does not matter which of the detection signal and the non-detection signal has a higher voltage.

[0036] The in-machine temperature sensor 25 is a sensor for detecting the temperature inside the housing 2 of the image forming apparatus 1. In this embodiment, the in-machine temperature sensor 25 is disposed between the developing cartridge 63 disposed most downstream in the conveying direction of the sheet S and the fixing unit 8. As the in-machine temperature sensor 25, for example, a thermistor or the like can be used.

[0037] The fan 10 is a fan for cooling the fixing unit 8 and the like. The fan 10 is provided at an exhaust port of the housing 2, and when driven, exhausts air inside the housing 2 to the outside of the housing 2. The housing 2 has a pair of left and right side frames (not shown), and the fan 10 is provided on the right side frame. The fan 10 is disposed above the fixing unit 8 when viewed from the left-right direction. Note that a duct (not shown) extending left and right is provided above the fixing unit 8, and the fan 10 is disposed on the right side of the duct.

[0038] The fan 10 is capable of changing the drive speed. More specifically, the fan 10 is capable of changing the drive speed to a first speed, a second speed faster than the first speed, and a third speed faster than the second speed. In this embodiment, the first speed is 0. That is, when the drive speed is the first speed, the fan 10 stops. Hereinafter, the first speed is also referred to as "stopped," the second speed is also referred to as "low speed," and the third speed is also referred to as "high speed."

[0039] 2(a), in addition to the heating unit 81, the first heater 83, and the second heater 84, the fixing unit 8 further includes a first temperature sensor 85 and a second temperature sensor 86. The first temperature sensor 85 and the second temperature sensor 86 are sensors for detecting the temperature of the heating unit 81.

[0040] The first heater 83 is a halogen heater having a glass tube 83A and a filament 83B provided inside the glass tube 83A. The heat generating portion of the filament 83B is concentrated in the center in the width direction of the sheet S compared to each end in the width direction of the sheet S. As a result, the first heater 83 heats the center region 811 of the heating portion 81 more strongly than the end regions 812. As shown by the dashed line in Fig. 2(b), the output of the first heater 83 is distributed so that it is highest in the center in the width direction and gradually decreases toward both ends in the width direction.

[0041] Here, the width direction of the sheet S is a direction perpendicular to the conveying direction of the sheet S in the image forming unit 4. Hereinafter, the width direction of the sheet S is also simply referred to as the "width direction". The central region 811 of the heating unit 81 is a region including the central portion of the heating unit 81 in the width direction. The end region 812 of the heating unit 81 is a region of the heating unit 81 located outside the central region 811 in the width direction. The heating unit 81 has, as the end region 812, a first end region 812A which is a region between one edge 81D of the heating unit 81 and the central region 811, and a second end region 812B which is a region between the other edge 81E of the heating unit 81 and the central region 811.

[0042] In this embodiment, the boundaries between the central region 811 and the end regions 812 (812A, 812B) are positions X1, X2 where the magnitude relationship between the maximum output of the first heater 83 shown by the dashed line and the maximum output of the second heater 84 shown by the solid line in Fig. 2(b) is reversed. Here, the maximum output of the heater refers to the output when power is supplied to the heater with the maximum current duty ratio (100%).

[0043] The second heater 84 is a halogen heater having a glass tube 84A and a filament 84B provided inside the glass tube 84A. The heat generating portion of the filament 84B is concentrated at each end in the width direction compared to the center in the width direction. As a result, the second heater 84 heats the end region 812 of the heating portion 81 more strongly than the center region 811. As shown by the solid line in FIG. 2(b), the output of the second heater 84 is distributed higher at both ends in the width direction than at the center.

[0044] In the fixing unit 8, the range (peak position) where the output of the first heater 83 is maximum and the range (peak positions P1, P2) where the output of the second heater 84 is maximum are set so as not to overlap in the width direction.

[0045] The peak position of the output of the first heater 83 in the width direction is located within the maximum contact area A21 in the width direction. More specifically, the peak position of the output of the first heater 83 in the width direction is located within the minimum contact area A11 in the width direction. The peak positions P1 and P2 of the output of the second heater 84 in the width direction are located within the maximum contact area A21 in the width direction.

[0046] Here, the heating portion 81 has a minimum contact area A11, a minimum non-contact area A12, a maximum contact area A21, and a maximum non-contact area A22.

[0047] The minimum contact area A11 is the minimum size of the sheet S that can be conveyed by the image forming unit 4 in the width direction. min When the smallest size sheet S is conveyed, min The minimum contact area A11 includes the center of the central area 811 in the width direction. The minimum non-contact area A12 includes the area where the sheet S has a minimum size in the width direction that can be conveyed by the image forming unit 4. min When the smallest size sheet S is conveyed, min This is an area that does not come into contact with the

[0048] The maximum contact area A21 is the maximum sheet S that can be conveyed by the image forming unit 4 in the width direction. max When the sheet S of the largest size is conveyed, max The maximum contact area A21 is a portion excluding the central area 811 and the outer ends in the width direction of the end area 812. The maximum non-contact area A22 is a portion excluding the central area 811 and the outer ends in the width direction of the end area 812. The maximum non-contact area A22 is a portion excluding the central area 811 and the outer ends in the width direction of the end area 812. max When the sheet S of the largest size is conveyed, maxThe maximum non-contact area A22 is the outer end of the end area 812 in the width direction.

[0049] The peak positions P1 and P2 of the output of the second heater 84 in the width direction are located outside the minimum non-contact area A12, in other words, the minimum contact area A11. The peak positions P1 and P2 of the output of the second heater 84 in the width direction are located inside the maximum non-contact area A22. In other words, the peak positions P1 and P2 of the output of the second heater 84 are located between the minimum contact area A11 and the maximum non-contact area A22 in the width direction.

[0050] Each heater 83, 84 has a regulated light distribution specification, and the specification is determined by a predetermined detection method. As a method for detecting the output (light distribution) of each heater 83, 84, for example, a method of arranging an optical sensor that detects the light of the heater at a predetermined distance from the heater and detecting the amount of light is given. The predetermined distance is the distance from the heater to the inner circumferential surface of the heating unit 81.

[0051] The first temperature sensor 85 detects the temperature of the central region 811. More specifically, the first temperature sensor 85 detects the temperature of the minimum contact region A11 of the central region 811. The detected temperature detected by the first temperature sensor 85 is output to the control unit 100.

[0052] The first temperature sensor 85 is positioned at a position shifted toward the first end region 812A side with respect to the center (conveyance center SC) of the heating section 81 in the width direction. The first temperature sensor 85 detects the temperature of the heating section 81 without contacting the heating section 81. More specifically, the first temperature sensor 85 is disposed at a distance from the outer peripheral surface of the heating section 81. For example, a non-contact thermistor can be used as the first temperature sensor 85. Note that in this embodiment, when the image forming apparatus 1 conveys the sheet S in the fixing section 8, the sheet S is conveyed with the center of the heating section 81 in the width direction being the conveyance center SC.

[0053] The second temperature sensor 86 detects the temperature of the end region 812. Specifically, the second temperature sensor 86 detects the temperature of a first end region 812A of the end region 812. More specifically, the second temperature sensor 86 detects the temperature of a maximum non-contact region A22 of the first end region 812A. The detected temperature detected by the second temperature sensor 86 is output to the control unit 100.

[0054] The second temperature sensor 86 is located at a position in the width direction different from the peak positions P1, P2 of the output of the second heater 84 in the width direction. More specifically, the second temperature sensor 86 is located outside the peak position P1 of the output of the second heater 84 in the width direction. More specifically, the second temperature sensor 86 is located outside the maximum contact area A21 in the width direction. The second temperature sensor 86 detects the temperature of the heating unit 81 in a state of contact with the heating unit 81. As the second temperature sensor 86, for example, a contact type thermistor can be used.

[0055] The control unit 100 (see FIG. 1) includes a CPU, RAM, ROM, input / output circuits, etc., and performs various types of arithmetic processing based on programs and data stored in the ROM or the like, thereby executing control.

[0056] The control unit 100 controls the output of the first heater 83 by controlling the power supply to the first heater 83 so that the temperature detected by the first temperature sensor 85 becomes a predetermined target temperature of the central region 811. In detail, the control unit 100 determines a power supply duty ratio of an AC voltage supplied to the first heater 83 based on the difference between the temperature detected by the first temperature sensor 85 and the target temperature, and performs a feedback process to control the amount of power supplied to the first heater 83 per unit time based on the determined power supply duty ratio.

[0057] Furthermore, the control unit 100 controls the output of the second heater 84 by controlling the power supply to the second heater 84 so that the temperature detected by the second temperature sensor 86 becomes a predetermined target temperature of the end region 812. In detail, the control unit 100 determines a power supply duty ratio of an AC voltage supplied to the second heater 84 based on the difference between the temperature detected by the second temperature sensor 86 and the target temperature, and performs a feedback process to control the amount of power supplied to the second heater 84 per unit time based on the determined power supply duty ratio.

[0058] The power supply duty ratio is determined so as to approach 100% as the value obtained by subtracting the detected temperature from the target temperature increases, and when the detected temperature is higher than the target temperature, the power supply duty ratio is determined to be 0%.

[0059] When a toner image is fixed to the sheet S, the control unit 100 changes the drive speed of the fan 10 based on the detection result of the in-machine temperature sensor 25. Specifically, in this embodiment, when the control unit 100 receives a print job including an instruction to start printing and image data and forms an image on the sheet S, if the temperature based on the detection result of the in-machine temperature sensor 25 is equal to or higher than a predetermined temperature, the control unit 100 changes the drive speed of the fan 10 to a speed faster than before the change.

[0060] In detail, when forming an image on the sheet S, if the temperature based on the detection result of the internal temperature sensor 25 is lower than a first predetermined temperature, the control unit 100 sets the drive speed of the fan 10 to the first speed. In other words, the control unit 100 stops the fan 10.

[0061] Furthermore, when forming an image on the sheet S, if the temperature based on the detection result of the internal temperature sensor 25 is equal to or higher than the first predetermined temperature and is lower than a second predetermined temperature higher than the first predetermined temperature, the control unit 100 sets the drive speed of the fan 10 to the second speed. In other words, the control unit 100 drives the fan 10 at a low speed.

[0062] Furthermore, when forming an image on the sheet S, if the temperature based on the detection result of the internal temperature sensor 25 is equal to or higher than the second predetermined temperature, the control unit 100 sets the driving speed of the fan 10 to the third speed. That is, the control unit 100 drives the fan 10 at a high speed.

[0063] Here, the temperature based on the detection result of the in-machine temperature sensor 25 may be a detected temperature detected by the in-machine temperature sensor 25, or may be a corrected temperature obtained by correcting the detected temperature of the in-machine temperature sensor 25.

[0064] When the control unit 100 changes the drive speed of the fan 10 , it outputs a control signal indicating the voltage to be applied to the fan 10 to a fan controller (not shown) that controls the supply of electricity to the fan 10 .

[0065] The control unit 100 can execute standby control when changing the drive speed of the fan 10 when fixing a toner image onto the sheet S. In the standby control, the control unit 100 interrupts the fixing of the toner image onto the sheet S, controls the temperature of the heating unit 81 to be a predetermined target temperature for a predetermined time after the fixing of the toner image is interrupted, and resumes the fixing of the toner image onto the sheet S after the predetermined time has elapsed.

[0066] In detail, during standby control, the control unit 100 controls the pickup roller 33 to interrupt the supply of the sheet S following the sheet S being fixed to the fixing unit 8, and also interrupts the fixing of the toner image to the sheet S by completing the fixing of the toner image to the sheet S being fixed and discharging the sheet S from between the heating unit 81 and the pressure unit 82.

[0067] After the fixing of the toner image onto the sheet S is interrupted, the control unit 100 controls the temperature of the heating unit 81 to be the target temperature until a predetermined time has elapsed from the point at which the post-fixing sensor 23 no longer detects the sheet S being fixed. More specifically, the control unit 100 controls the supply of electricity to the first heater 83 so that the temperature detected by the first temperature sensor 85 becomes the target temperature of the central region 811, and controls the supply of electricity to the second heater 84 so that the temperature detected by the second temperature sensor 86 becomes the target temperature of the end region 812.

[0068] After a predetermined time has elapsed, the control unit 100 controls the pickup roller 33 to resume the supply of the next sheet S to the fixing unit 8, thereby restarting the fixing of the toner image onto the sheet S.

[0069] The control unit 100 may be configured to transfer and fix, when fixing of the toner image on the sheet S is resumed, the same toner image as that on the previous sheet S that was being fixed at the start of the standby control, onto the next sheet S. In other words, the standby control may be executable not only when a print job having a next sheet S (next page to be printed), that is, a print job for forming images continuously on multiple sheets S, is received, but also when a print job for forming an image on one sheet S is received.

[0070] When the drive speed of the fan 10 is changed when fixing a toner image on the sheet S, the control unit 100 executes standby control if the amount of change in the drive speed of the fan 10 per unit time (hereinafter also referred to as "speed change amount") is greater than or equal to a predetermined amount. In this embodiment, when the drive speed of the fan 10 is changed between a first speed and a third speed during printing to form an image on the sheet S during a unit time, the control unit 100 determines that the amount of speed change is greater than or equal to a predetermined amount, and executes standby control.

[0071] In detail, the control unit 100 executes standby control when the drive speed of the fan 10 is changed from stopped to high speed during a unit time, and when the drive speed is changed from high speed to stopped during a unit time. The unit time is not particularly limited, but is, for example, about 5 to 10 seconds. Note that as long as the drive speed of the fan 10 is changed between stopped and high speed during the unit time, it does not matter if it goes through low speed on the way.

[0072] Furthermore, when the control unit 100 changes the drive speed of the fan 10 when fixing a toner image on the sheet S, if the amount of speed change is less than a predetermined amount, the control unit 100 does not execute standby control and continues fixing the toner image on the sheet S. In this embodiment, when the control unit 100 changes the drive speed of the fan 10 between the first speed and the second speed during a unit time and / or when the control unit 100 changes the drive speed of the fan 10 between the second speed and the third speed during a unit time during printing, the control unit 100 determines that the amount of speed change is less than a predetermined amount, and continues fixing the toner image on the sheet S without executing standby control.

[0073] In detail, when the drive speed of the fan 10 is changed from stopped to low speed during a unit time during printing (in other words, when it is changed only from stopped to low speed) and when it is changed from low speed to stopped during a unit time, the control unit 100 continues fixing of the toner image on the sheet S. Also, when the drive speed of the fan 10 is changed from low speed to high speed during a unit time during printing and when it is changed from high speed to low speed during a unit time (in other words, when it is changed only from high speed to low speed), the control unit 100 continues fixing of the toner image on the sheet S.

[0074] Next, the operation of the control unit 100 will be described with reference to a flowchart. As shown in FIG. 3, when the control unit 100 receives a print job, it starts a printing operation including fixing a toner image onto a sheet S (S110).

[0075] Furthermore, when the control unit 100 receives a print job, it repeatedly executes the fan control process shown in Fig. 4 until the print job is completed. In detail, the control unit 100 determines whether the temperature T based on the detection result of the internal temperature sensor 25 during printing is equal to or higher than a first predetermined temperature Tth1 (S11).

[0076] Then, when the temperature T based on the detection result of the internal temperature sensor 25 is less than the first predetermined temperature Tth1 (S11, No), the control unit 100 stops the fan 10 (S12). More specifically, the control unit 100 outputs a control signal to the fan controller to stop the fan 10.

[0077] In step S11, if the temperature T based on the detection result of the internal temperature sensor 25 is equal to or higher than the first predetermined temperature Tth1 (Yes), the control unit 100 determines whether the temperature T based on the detection result of the internal temperature sensor 25 is equal to or higher than the second predetermined temperature Tth2 (S13).

[0078] Then, when the temperature T based on the detection result of the internal temperature sensor 25 is lower than the second predetermined temperature Tth2 (S13, No), the control unit 100 drives the fan 10 at a low speed (S14). In detail, the control unit 100 outputs a control signal to the fan controller to drive the fan 10 at a low speed.

[0079] In step S13, if the temperature T based on the detection result of the internal temperature sensor 25 is equal to or higher than the second predetermined temperature Tth2 (Yes), the control unit 100 drives the fan 10 at high speed (S15). In detail, the control unit 100 outputs a control signal to the fan controller to drive the fan 10 at high speed.

[0080] 3, after starting to fix the toner image on the sheet S, the control unit 100 determines whether or not to change the drive speed of the fan 10, more specifically, whether or not a control signal has been output to the fan controller (S121). If the drive speed of the fan 10 is to be changed (S121, Yes), the control unit 100 determines whether or not to change the drive speed of the fan 10 between a stopped speed and a high speed during a unit time (S122).

[0081] When the drive speed of the fan 10 is changed between the stopped speed and the high speed speed during the unit time (S122, Yes), the control unit 100 executes standby control (S130). In detail, as shown in FIG. 5, in the standby control, the control unit 100 first suspends the fixing of the toner image onto the sheet S.

[0082] In this embodiment, the control unit 100 does not drive the pickup roller 33, and interrupts the supply of the sheet S following the sheet S being fixed to the fixing unit 8 (S131). The control unit 100 also completes the fixing of the toner image on the sheet S being fixed, and discharges the sheet S from between the heating unit 81 and the pressure unit 82. In detail, the control unit 100 determines whether the post-fixing sensor 23 has switched from a state in which it detects the sheet S being fixed to a state in which it does not detect the sheet S being fixed (whether it has changed from ON to OFF) (S132), and if it has not changed to OFF (S132, No), it waits until it changes to OFF, and if it has changed to OFF (S132, Yes), it proceeds to step S133.

[0083] In step S133, the control unit 100 starts control so that the temperature of the heating unit 81 becomes a predetermined target temperature. In detail, the control unit 100 controls the power supply to the heaters 83 and 84 so that the temperature of the heating unit 81 becomes a predetermined target temperature.

[0084] After starting the temperature control of the heating unit 81, the control unit 100 determines whether a predetermined time has elapsed since the post-fixing sensor 23 turned OFF (S134). If the predetermined time has not elapsed (S134, No), the control unit 100 returns to step S133 and continues the temperature control of the heating unit 81.

[0085] In step S134, if the predetermined time has elapsed (Yes), the control unit 100 resumes fixing of the toner image onto the sheet S. More specifically, the control unit 100 drives the pickup roller 33 to resume supplying the next sheet S to the fixing unit 8 (S135). Thereafter, the control unit 100 proceeds to step S140 in FIG. 3.

[0086] 3, if the drive speed of the fan 10 is not changed (No), the control unit 100 continues fixing the toner image on the sheet S and proceeds to step S140. If the drive speed of the fan 10 is not changed between stopped and high speed during the unit time (No) during step S122, that is, if the drive speed of the fan 10 is changed between stopped and low speed during the unit time or if the drive speed of the fan 10 is changed between low speed and high speed during the unit time, the control unit 100 continues fixing the toner image on the sheet S and proceeds to step S140.

[0087] In step S140, the control unit 100 determines whether the print job is completed. If the print job is not completed (S140, No), the control unit 100 returns to step S121 and executes the subsequent processes. If the printing is completed (S140, Yes), the control unit 100 ends the operation shown in FIG.

[0088] Next, an example of the operation of the control unit 100 will be described with reference to a timing chart.

[0089] As shown in FIG. 6, when a print job is received (time t11), the control unit 100 controls the temperature of the heating unit 81 to a predetermined target temperature TT, and at an appropriate timing (time t12), drives (turns ON) the pickup roller 33 to supply the sheet S from the supply tray 31 to the image forming unit 4, and transfers and fixes the toner image onto the sheet S.

[0090] During printing, when the drive speed of the fan 10 switches from stopped to low speed within a unit time (time t13), and when the drive speed of the fan 10 switches from low speed to high speed within a unit time (time t15), the effect on the temperature of the heating unit 81 is small, so the control unit 100 continues to fix the toner image onto the sheet S without interruption. Specifically, after time t12, at a predetermined timing (times t14, t16, etc.), the control unit 100 turns on the pickup roller 33 to supply the sheet S from the supply tray 31 toward the image forming unit 4, and continues the transfer and fixing of the toner image onto the sheet S.

[0091] 7, when the drive speed of fan 10 switches from stopped to high speed within a unit time during printing (time t13), for example, the temperature of heating unit 81 is likely to drop and the effect on the temperature of heating unit 81 is large, so control unit 100 executes standby control and first suspends the fixing of the toner image onto sheet S. Specifically, control unit 100 suspends the supply of sheet S from supply tray 31 to image forming unit 4 without driving pickup roller 33 (turning it OFF) at time t14.

[0092] Then, the control unit 100 controls the temperature of the heating unit 81 to be the target temperature TT for a predetermined time tp from the time when the sheet S being fixed is discharged from between the heating unit 81 and the pressure unit 82 and the post-fixing sensor 23 changes from ON to OFF at time t25. Then, when the predetermined time tp has elapsed at time t26, the control unit 100 turns on the pickup roller 33 to supply the sheet S from the supply tray 31 toward the image forming unit 4, and restarts the transfer and fixing of the toner image onto the sheet S.

[0093] According to the present embodiment described above, by executing standby control when changing the drive speed of the fan 10 when fixing a toner image on the sheet S, even if the temperature of the heating unit 81 drops due to the change in the drive speed of the fan 10, the fixing of the toner image on the sheet S can be temporarily interrupted, and the temperature of the heating unit 81 can be heated up to the target temperature TT, and then the fixing of the toner image on the sheet S can be resumed. This makes it possible to reduce the effect of the change in the drive speed of the fan 10 on the fixing quality, such as a decrease in fixing strength.

[0094] In addition, since the standby control is executed when the speed change amount is equal to or greater than a predetermined amount, the standby control can be executed when the change amount of the drive speed of the fan 10 is large and the change in the drive speed of the fan 10 is likely to affect the fixing quality. This makes it possible to effectively reduce the effect of the change in the drive speed of the fan 10 on the fixing quality.

[0095] Furthermore, since the fixing of the toner image onto the sheet S continues without executing standby control when the amount of change in speed is less than a predetermined amount, the fixing of the toner image onto the sheet S can be continued without interruption when the amount of change in the drive speed of the fan 10 is small and the effect of changing the drive speed of the fan 10 on the fixing quality is unlikely to be felt. This makes it possible to prevent the time until the received print job is completed from becoming longer than necessary.

[0096] In addition, when the drive speed of the fan 10 is changed between stopped and high speed within a unit time, it is determined that the amount of speed change is greater than or equal to a predetermined amount. Therefore, compared to the case where, for example, the gradient of change in the voltage applied to the fan is calculated, it is possible to easily determine when the amount of change in the drive speed of the fan 10 is large.

[0097] In addition, when the drive speed of the fan 10 is changed between stopped and low speed within a unit time, or when the drive speed is changed between low speed and high speed within a unit time, it is determined that the amount of speed change is less than a predetermined amount. Therefore, it is possible to easily determine when the amount of change in the drive speed of the fan 10 is small, compared to, for example, calculating the gradient of change in the voltage applied to the fan.

[0098] In addition, when the temperature based on the detection result of the internal temperature sensor 25 is equal to or higher than a predetermined temperature, the driving speed of the fan 10 is changed to a speed faster than before the change, so that it is possible to prevent the temperature inside the housing 2 from becoming too high when fixing a toner image to the sheet S.

[0099] In addition, in the standby control, the fixing of the toner image onto the sheet S is interrupted after the fixing of the toner image onto the sheet S is completed, so that the toner image on the sheet S being fixed can be fixed to the end.

[0100] Although the embodiment has been described above, the image forming apparatus can be modified as appropriate as exemplified below.

[0101] In the embodiment, the fan 10 can change the drive speed to three stages, namely, stop, low speed, and high speed, but the fan may be able to change the drive speed to four or more stages. For example, the fan may be able to change the drive speed to a first speed, a second speed faster than the first speed, a third speed faster than the second speed, and a fourth speed faster than the third speed. In this case, for example, when the drive speed of the fan is changed between the first speed and the third speed during a unit time, when the drive speed is changed between the first speed and the fourth speed during a unit time, and when the drive speed is changed between the second speed and the fourth speed during a unit time, the control unit may determine that the speed change amount is equal to or greater than a predetermined amount and execute standby control, and otherwise determine that the speed change amount is less than the predetermined amount and continue fixing of the toner image to the sheet.

[0102] Also, the drive speed of the fan may be changeable between two stages: stopped and driven. Also, in the above embodiment, the first speed is 0, but the first speed does not have to be 0.

[0103] In the embodiment, the drive speed of the fan 10 can be changed stepwise between stop, low speed, and high speed, but for example, the drive speed of the fan may be changed steplessly. Even in this case, the control unit can be configured to execute standby control when changing the drive speed of the fan when fixing a toner image on a sheet, if the amount of change in the drive speed of the fan per unit time (for example, the gradient of change in the voltage applied to the fan) is equal to or greater than a predetermined amount, and to continue fixing the toner image on the sheet without executing standby control, if the amount of change is less than the predetermined amount.

[0104] In the above embodiment, when the drive speed of the fan 10 is changed when fixing a toner image on the sheet S, standby control is executed if the amount of change in the drive speed of the fan 10 per unit time is equal to or greater than a predetermined amount, but, for example, a configuration may be adopted in which standby control is executed if the speed difference before and after the change in the drive speed of the fan is equal to or greater than a predetermined amount. Also, when the drive speed of the fan is changed when fixing a toner image on a sheet, a configuration may be adopted in which standby control is executed regardless of the amount of change in the drive speed of the fan per unit time or the speed difference before and after the change.

[0105] In the above embodiment, the starting point of the specified time in the standby control was the point at which the sheet S being fixed was discharged from between the heating section 81 and the pressure section 82, specifically, the point at which the post-fixing sensor 23 changed from ON to OFF, but, for example, the starting point of the specified time may also be the point at which the supply of the next sheet to the fixing section is interrupted.

[0106] In the above embodiment, the fan 10 is an exhaust fan provided at the exhaust port of the housing 2 to exhaust air from inside the housing 2, but for example, the fan may be an intake fan provided at the intake port of the housing to take in outside air into the housing. Also, the image forming apparatus may be equipped with both an exhaust fan and an intake fan.

[0107] In the above embodiment, when fixing a toner image on sheet S, the drive speed of fan 10 is changed based on the detection result of in-machine temperature sensor 25, but for example, the drive speed of fan 10 may be changed based on the detection result of a temperature sensor that detects the temperature of heating unit 81, such as second temperature sensor 86. Also, the drive speed of the fan may not only be changed based on the detection result of the temperature sensor, but may also be changed based on at least one of the detection result of the temperature sensor, the number of printed sheets, the sheet size, the sheet thickness, the sheet basis weight, etc. Also, in the above embodiment, a thermistor is exemplified as the temperature sensor, but any sensor capable of detecting temperature may be used.

[0108] In the above embodiment, the heating unit 81 is a heating roller, but the heating unit may be, for example, an endless heating belt. Also, in the above embodiment, the pressure unit 82 is configured to include a pressure belt, a pressure pad, a belt guide, etc., but the pressure unit may be, for example, a pressure roller. Also, in the above embodiment, the heaters 83 and 84 are halogen heaters that use radiant heat, but the heaters may be, for example, ceramic heaters or carbon heaters that use heat generated by resistors, or IH heaters that inductively heat the heating unit. Also, the heaters may be arranged outside the heating unit, rather than inside the heating unit.

[0109] In the above embodiment, a color printer is used as an example of the image forming apparatus, but the image forming apparatus may be, for example, a monochrome printer. Also, the image forming apparatus may be, for example, a copier, a multifunction machine, or the like, instead of a printer.

[0110] The elements described in the above embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0111] 1. Image forming device 2. Chassis 8 Fixing section 10 Fan 25 In-machine temperature sensor 81 Heating section 83 First heater 84 Second heater 100 Control section S Seat

Claims

1. a fixing section having a heating section for heating the sheet and fixing the toner image on the sheet; a fan for cooling the fixing unit, the fan having a variable driving speed; A control unit, The image forming apparatus is characterized in that, when the control unit changes the drive speed of the fan when fixing a toner image to a sheet, the control unit is capable of executing standby control in which the fixing of the toner image to the sheet is interrupted, the temperature of the heating unit is controlled to be a predetermined target temperature for a predetermined time after the fixing of the toner image is interrupted, and the fixing of the toner image to the sheet is resumed after the predetermined time has elapsed.

2. When the control unit changes the driving speed of the fan when a toner image is fixed on a sheet, When the change amount per unit time of the drive speed of the fan is equal to or greater than a predetermined value, the standby control is executed; 2. The image forming apparatus according to claim 1, wherein, when the amount of change is less than a predetermined amount, the standby control is not executed, and fixing of the toner image onto the sheet is continued.

3. the fan is capable of changing a drive speed to at least a first speed, a second speed faster than the first speed, and a third speed faster than the second speed; 3. The image forming apparatus according to claim 2, wherein the control unit determines that the amount of change in the drive speed of the fan is equal to or greater than a predetermined amount when the drive speed of the fan is changed between the first speed and the third speed during the unit time.

4. the fan is capable of changing a drive speed to at least a first speed, a second speed faster than the first speed, and a third speed faster than the second speed; The image forming apparatus of claim 2 or claim 3, characterized in that the control unit determines that the amount of change is less than a predetermined value when the fan drive speed is changed between the first speed and the second speed during the unit time, and when the fan drive speed is changed between the second speed and the third speed during the unit time.

5. A temperature sensor is provided to detect a temperature inside a housing of the image forming apparatus, 5. The image forming apparatus according to claim 1, wherein the control unit changes a drive speed of the fan based on a detection result of the temperature sensor when a toner image is fixed onto a sheet.

6. The image forming apparatus according to claim 5, characterized in that, when fixing a toner image onto a sheet, if the temperature based on the detection result of the temperature sensor is equal to or higher than a predetermined temperature, the control unit changes the drive speed of the fan to a speed faster than before the change.

7. 7. The image forming apparatus according to claim 1, wherein the control unit, in the standby control, interrupts the supply of the sheet following the sheet being fixed to the fixing unit, and interrupts the fixing of the toner image to the sheet by completing the fixing of the toner image to the sheet being fixed.

8. The image forming apparatus according to claim 7 , wherein the control unit, in the standby control, restarts the fixing of the toner image onto the sheet by restarting the supply of the next sheet to the fixing unit.

9. 9. The image forming apparatus according to claim 1, wherein the heating unit is a heating roller that is heated by a heater.

Images