Patent Application
20180004149
The present disclosure relates to an image forming apparatus such as a copying machine or a printer employing an electrophotographic method.
In an image forming apparatus employing an electrophotographic method, a toner image borne by an image bearing member is electrostatically transferred to a transfer material such as a sheet of paper or anoverhead projector (OHP) sheet by applying voltage to the transfer member arranged to face the image bearing member such as a drum-shape photosensitive member (hereinafter, referred to as “photosensitive drum”) or an intermediate transfer member. Thereafter, the transfer material to which the toner image has been transferred is conveyed to a fixing unit, and the fixing unit applies heat and pressure to the transfer material to fix the toner image thereon.
An amount of moisture contained in a transfer material varies according to an environment where the image forming apparatus is used. For example, a transfer material absorbs moisture to have a relatively high moisture content in a high-humidity environment (hereinafter, referred to as “moist sheet”), and the transfer material is dried to have a relatively low moisture content in a low-humidity environment (hereinafter, referred to as “dried sheet”).
In the technique discussed in Japanese Patent Application Laid-Open No. 2013-130709, in order to precisely acquire a moisture content of the transfer material, an electric current value flowing in an image bearing member from a transfer member is detected, and the moisture content of the transfer material is acquired from the detected current value. In Japanese Patent Application Laid-Open No. 2013-130709, an electric current value flowing in the image bearing member from the transfer member without interposing the transfer material and an electric current value flowing in the image bearing member from the transfer member via the transfer material are detected. Then, the misture content of the transfer material is acquired from a difference of electric resistances of the transfer material acquired from the respective electric current values.
However, according to the technique described in Japanese Patent Application Laid-Open No. 2013-130709, although the moisture content of the transfer material can be acquired, it is difficult to reduce image defect when water droplets are adhered to a fixing unit due to dew condensation. When a moist sheet is fed to the fixing unit, water vapor is generated from the moist sheet rapidly heated at high temperatures, so that water droplets may be adhered to the fixing unit due to dew condensation. If water droplets are adhered to the fixing unit when a toner image is transferred to the transfer material from the image bearing member, a part of the transfer current necessary to transfer the toner image to the transfer material flows in an apparatus main unit or the ground via the water droplets, so that there is a risk in which the transfer current becomes insufficient to cause image defect to occur.
The present disclosure is directed to an image forming apparatus capable of reducing occurrence of image defect by executing dehumidification control in a case where water droplets are adhered to a fixing unit due to dew condensation.
According to anaspect of the present invention, an image forming apparatus includes an image bearing member configured to bear a toner image, a transfer member abutting on the image bearing member and configured to transfer a toner image to a transfer material from the image bearing member, a power source configured to apply voltage to the transfer member, a detection unit configured to detect electric current flowing in the transfer member when voltage is applied to the transfer member from the power source, a fixing unit configured to fix a toner image to a transfer material by heating the transfer material to which a toner image has been transferred by a heating unit, and a control unit configured to control the heating unit to heat the fixing unit, wherein the control unit controls the heating unit to heat the fixing unit in a state where conveyance of a subsequent transfer material stops after the transfer material that is in contact with the fixing unit is discharged from the fixing unit, in a case where a second current value that is detected by the detection unit when voltage is applied to the transfer member from the power source in a state where a transfer material is in contact with the fixing unit and the transfer member is greater than a first current value that is detected by the detection unit when voltage is applied to the transfer member from the power source before the transfer material reaches the fixing unit by a predetermined value or more.
Further features of the present invention will become apparent from the following description of embodiments with reference to the attached drawings.
Hereinafter, embodiments will be described in detail with reference to the appended drawings. Sizes, materials, shapes and relative arrangements of constituent members described in the below-described embodiments should be changed as appropriate according to a configuration and various conditions of an apparatus to which the present disclosure is applied. Accordingly, the below-described embodiments are not intended to limit the scope unless such limitations are explicitly mentioned hereinafter.
The image forming operation executed by the image forming apparatus 100 of the present embodiment will be described with reference to
The image forming unit S includes a photosensitive drum 1 as a drum-shape photosensitive member, a charging roller 2 as a charging unit, a development roller 3 as a development unit, and a cleaning blade 5 as a cleaning unit.
The photosensitive drum 1 is rotationally driven a direction indicated by an arrow R1 in
An endless intermediate transfer belt 7 as an image bearing member stretched by tension rollers 6a, 6b, and 6c serving as stretching members is arranged to face the photosensitive drums 1Y, 1M, 1C, and 1K of respective colors. The intermediate transfer belt 7 is rotationally driven in a direction indicated by an arrow B in
A secondary transfer roller 13 as a transfer member is arranged to face the tension roller 6b via the intermediate transfer belt 7 as an image bearing member. The intermediate transfer belt 7 is pressed by the tension roller 6b to abut on the secondary transfer roller 13, so that a secondary transfer portion is formed on a position where the intermediate transfer belt 7 abuts on the secondary transfer roller 13. In the present embodiment, a roller member having an outer diameter of 18 mm, which is configured of a nickel-plated steel rod having an outer diameter of 8 mm covered with a formed body that mainly consists of a nitrile rubber (NER) material and an epichlorohydrin rubber material adjusted to have a volume resistance of 108 Ω/cm and a thickness of 5 mm, is used. as the secondary transfer roller 13. Further, the secondary transfer roller 13 is connected to a transfer power source 26 having a detection circuit 25 as a detection unit, and a toner image in a plurality of colors is secondarily transferred to a transfer material P from the intermediate transfer belt 7 when voltage is applied to the secondary transfer roller 13 from the transfer power source 26.
The transfer materials P stacked on a sheet feeding cassette 9 are fed by a sheet feeding roller 10, individually separated by a separation roller pair 11, and conveyed by a conveyance roller pair 12 in a direction indicated by the arrow A in
The transfer material P to which the toner image in the plurality of colors is transferred at the secondary transfer portion is conveyed to a fixing unit 14 so as to be heated and pressurized by the fixing unit 14, so that the toner of respective colors is fused and intermingled with each other and fixed to the transfer material P. The toner that has left on the intermediate transfer belt 7 after the secondary transfer is cleaned and removed by a cleaning blade 16 provided on a downstream side of the secondary transfer portion in a moving direction of the intermediate transfer belt 7.
In the image forming apparatus 100 of the present embodiment, a full-color image is formed on the transfer material P through the above-described operation, and the transfer material P on which image formation has been performed is discharged to a discharge tray 18 by a discharge roller pair 17.
In the present embodiment, a film fixation type fixing, unit is employed. However, the fixing unit is not limited to the above, and embodiments are applicable to a configuration employing a fixing unit of another type such as a heat roller type.
As illustrated in
The fixing frame 32 is a conductive housing that covers the pressure roller 30 and the heating unit 31. The fixing frame 32 is electrically connected to the ground so as to be prevented from being charged electrically, and the insulating member 33 is arranged between the fixing frame 32 and the pressure roller 30.
The pressure roller 30 is a conductive roller having a core metal 30a, anelastic layer 30b formed on the outer circumferential surface of the core metal 30a, and a release layer 30c formed an the outer circumferential surface of the elastic layer 30b. A silicon rubber material or a fluorine-containing rubber material can be used as the elastic layer 30b, and a fluorine-containing resin material such as tetrafluoroethylene-perfluoro (alkoxy vinyl ether)-copolymer (PFA) can be used as the release layer 30c. In the present embodiment, the silicon rubber elastic layer 30b having a thickness of approximately 3.5 mm and a width of approximately 226 mm in the lengthwise direction is formed by executing injection molding on the stainless steel core metal 30a having the outer diameter of 11 mm. Further, the release layer 30c is formed on an outer circumferential surface of the elastic layer 30b by covering the elastic layer 30c with a PFA resin tube having a thickness of approximately 40 μm. In addition, conductive carbon filler is added to the elastic layer 30b and the release layer 30c, so that the pressure roller 30 has an electrical resistance of approximately 10 kΩ.
The pressure roller 30 is rotatably supported at both ends in the lengthwise direction of the core metal 30a and grounded via a grounding resistor Rg having a grounding resistance of 1 GΩ. The pressure roller 30 has an outer diameter of 18 mm, and a hardness thereof measured by the Asker-C hardness meter is 54° at a weight of 9.8 N. In order to ensure a fixing portion N and durability of the pressure roller 30 or the heating unit 31, the pressure roller 30 may have a hardness within a range of 40° to 70° when the hardness is measured at a weight of 9.8 N by using the Asker-C hardness meter.
The heating unit 31 includes a film 31a, a plate-like heater 31b, a supporting portion 31c for supporting the heater 31b, and a pressure stay 31d for reinforcing the supporting portion 31c. In addition, the heater 31b is in contact with an inner circumferential surface of the film 31a at a position facing the pressure roller 30 via the film 31a.
The film 31a is a tubular flexible member having a base layer (not illustrated), an elastic layer (not illustrated) formed on the outer circumferential surface of the base layer, and a release layer (not illustrated) formed on the outer circumferential surface of the elastic layer. In the present embodiment, the film 31a has an inner diameter of 18 mm, a polyimide material having a thickness of approximately 60 μm is used as the base layer, a silicone rubber material having a thickness of approximately 150 μm is used as the elastic layer, and a PFA resin tube having a thickness of approximately 15 μm is used as the release layer.
The heater 31b is configured of a substrate made of ceramics such as alumina, a heat generating resistor made of silver-palladium alloy formed on the substrate through screen printing, and an electric contact point made of silver connected to the heat generating resister. In the present embodiment, the substrate of the heater 31b consists of a rectangular parallelepiped-shape alumina material having a length of 5.8 mm in the conveyance direction of the transfer material P and a thickness of 1.0 mm. The heat generating resistor is protected by a protection layer such as a glass coating. In order to increase the sliding performance of the heat generating resistor and the film 31a, heat-resisting grease is applied to a portion between the heat generating resistor and the inner circumferential surface of the film 31a. A thermistor 31e is attached to one surface of the heater 31b on the opposite side of another surface brought into contact with the film 31a.
The supporting portion 31c is formed of liquid crystalline polymer, so as to have rigidity, heat-resisting property, and heat-insulating property. The supporting portion 31c has a function of supporting the inner circumferential surface of the film 31a that is in contact with the supporting portion 31c and a function of supporting the heater 31b.
In order to increase the bending rigidity of the heating unit 31, the pressure stay 31d is formed of a bent stainless steel having a plate thickness of 1.6 mm, having a U-shape cross-sectional face when viewed in the lengthwise direction. The heater 31b supported by the pressure stay 31d and the supporting portion 31c is pressed against and brought into contact with the pressure roller 30 via the film 31a, so as to form a fixing portion N having a width of approximately 6.2 mm in the conveyance direction of the transfer material P. In the present embodiment, the film 31a and the pressure roller 30 have a press-contact force of 180 N in total.
When a toner image is fixed to the transfer material P by the fixing unit 14, rotational force from a driving source (not illustrated) is transmitted to the pressure roller 30, so that the pressure roller 30 is rotationally driven in a clockwise direction at a predetermined speed as illustrated in
In a state where a temperature detected by the thermistor 31e of the heater 31b reaches a target temperature after the film 31a and the pressure roller 30 rotate and the power is supplied to the heater 31b, the transfer material P is guided by a conveyance guide 38 and introduced to the fixing portion N. While the transfer material P is passing through the fixing portion N, the toner image secondarily transferred to the transfer material P at the secondary transfer portion is heated and pressurized, so that the toner image is fused and fixed to the transfer material P. The transfer material P that has passed the fixing portion N is separated from the film 31a due to a curvature of the film 31a and discharged to the discharge tray 18 by the discharge roller pair 17.
In the present embodiment, a distance between the secondary transfer portion and the fixing portion N of the image forming apparatus 100 is 50 mm. Accordingly, when an image is formed on a transfer material P having a normal A4 size or a letter-size, at the same time the toner image is fixed to the transfer material P at the fixing, unit 14, the toner image is secondarily transferred to the transfer material P from the intermediate transfer belt 7 at the secondary transfer portion.
The image defect occurring when water droplets are adhered to the fixing unit 14 due to dew condensation will be described in detail with reference to
When the voltage is applied to the secondary transfer roller 13 from the transfer power source 26, a predetermined electric current flows in the secondary transfer roller 13, and a predetermined transfer current Itr flows in the intermediate transfer belt 7 from the secondary transfer roller 13 at the secondary transfer portion. However, in a. case where the transfer material P contains a large amount of moisture (hereinafter, referred to as “moist sheet HP”), as illustrated in
The transfer material P is likely to become a moist sheet HP if the transfer material P is kept in an environment having high temperature and high humidity, so that the electric current Ip flows to the ground via the pressure roller 30 when the moist sheet HP having low electrical resistance reaches the fixing unit 14 to be in contact with the conductive pressure roller 30. If a value of the electric current ip is too large, image defect may occur because the transfer current Itr necessary for secondarily transferring the toner image to the transfer material P at the secondary transfer portion becomes insufficient. Accordingly, in the present embodiment, by grounding the conductive pressure roller 30 via the grounding resistor Rg having a relatively large grounding resistance value, image defect caused by the electric current Ip is suppressed. In
However, in a case where the moist sheets HP are fed to the fixing unit 14 consecutively, as illustrated in
In the present embodiment, the control unit 110 determines that water droplets are adhered to the fixing unit 14 when the water droplets M adhered to the fixing frame 32 are in contact with the surface of the pressure roller 30 to cause the electric current Ip to flow to the ground via the water droplets M. Unless the pressure roller 30 and the fixing flame 32 are conducted via the water droplets M to cause the electric current Ip to flow to the ground, the control unit 110 determines that the water droplets are not adhered to the fixing unit 14 even if the water droplets M are adhered to the fixing frame 32.
Hereinafter, with reference to
In step S103, the transfer material P reaches the secondary transfer portion, and in step S104, the transfer material P reaches the fixing portion N of the fixing unit 14. Then, when the transfer material P is concurrently passing through the secondary transfer portion and the fixing unit 14 after reaching the fixing portion N, in step S105, the current value I1a (i.e., a second current value) flowing in the detection circuit 25 is detected. A secondary transfer operation is executed until the processing in steps S103 to S105 is completed, so that the predetermined voltage V0 is continuously applied to the secondary transfer roller 13 from the transfer power source 26 through constant voltage control.
In the present embodiment, a distance between the secondary transfer portion and the fixing portion N is 50 mm, a conveyance speed of the transfer material P is 100 mm/sec., and the detection circuit 25 detects 100 electric values per one second. For example, if a length of the transfer material P is 280 mm, a time period in which the transfer material P concurrently passes the secondary transfer portion and the fixing unit 14 in step S105 is 2.3 sec., so that 230 current values I1a are recorded.
In step S106, as to whether the image forming operation should be continuously executed is determined based on the image signal transmitted to the control unit 110. In a case where the image signal for forming an image on the subsequent transfer material P does not exist (NO in step S106), the image forming operation ends. In a case where the image signal for forming animage on the subsequent transfer material P exists (YES in step S106), the processing proceeds to step S107. In step S107, the current value I1a and the reference current value I0a are compared to each other. In a case where the current value I1a is greater than the reference current value I0a by a preset predetermined value ΔIa or more, there is a high possibility that the water droplets adhered to the fixing unit 14 causes the current Ip to flow to the ground, and thus image defect can be reduced by the control unit 110 executing the dehumidification control.
Herein, a value of the predetermined value ΔIa is determined according to the amount of electric current Ip flowing in the fixing unit 14, and the value thereof depends on the configuration of the image forming apparatus 100 such as a distance between the secondary transfer portion and the fixing portion N. By appropriately setting the value of the predetermined value ΔIa, precision of determination with respect to presence or absence of water droplets caused by dew condensation adhered to the fixing unit 14 can be increased. In the present embodiment, the value ΔIa is set as 30 μA.
As described above, when the current value I1a is greater than the reference current value I0a by the preset predetermined value ΔIa or more, the control unit 110 can determine that water droplets are adhered to the fixing unit 14. However, if a state where the current value I1a is greater than the reference current value I0a by the preset predetermined value ΔIa or more is continued for a predetermined time ΔTa, as to whether the water droplets adhered to the fixing unit 14 cause the electric current Ip to flow to the ground can be determined more precisely. This is because even in a state where the water droplets are not adhered to the fixing unit 14, electric current for the electrostatic capacitance of the fixing unit 14 may flow in the fixing unit 14 when the transfer material P reaches the fixing, unit 14.
Accordingly, by setting the predetermined time ΔTa, it is possible to suppress erroneous detection caused by the electric current temporarily flowing in the fixing unit 14 and to perform detection of water droplets caused by dew condensation more precisely. In the present embodiment, the predetermined time ΔTa is set as 0.3 sec. In other words, if a state where the current value I1a is greater than the reference current value I0a by the preset predetermined value ΔIa or more is continued for the predetermined time ΔTa (YES in step S107), the control unit 110 determines that water droplets are adhered to the fixing unit 14 due to dew condensation, and executes processing in step S108. In a case where the current value I1a is not in the above-described state (NO in step S107), the processing returns to step S103.
In step S108, as the dehumidification control executed by the control unit 110, the heating unit 31 of the fixing unit 14 and the pressure roller 30 are rotated while the heating unit 31 is being heated. Through the above operation, water droplets can be evaporated by increasing the temperature of the fixing unit 14. In the present embodiment, when adhesion of water droplets to the fixing unit 14 caused by dew condensation is determined, the control unit 110 executes the dehumidification control of the fixing unit 14 for 30 seconds in a state where the conveyance of the subsequent transfer material P stops after the transfer material P that is in contact with the fixing unit 14 is discharged from the fixing unit 14. When the dehumidification control is completed, the image forming apparatus 100 notifies a user that image forming operation can restart. Then, after the user has confirmed the notification, the processing returns to step S103, so that the control unit 110 restarts the image forming operation.
For example, providing a notification screen and a confirmation button on the image forming apparatus 100 may be considered as a specific method which allows the image forming apparatus 100 and the user to mutually provide or receive the notification and the confirmation. Further, in the present embodiment, although a control method of restarting the image forming operation after making the user confirm the notification has been described, the control method is not limited thereto, and the image forming operation may automatically start after the dehumidification control is completed by the control unit 110.
As illustrated. in.
In the present embodiment, the current value I1a of the first transfer material P detected in step S105 is 40 μA, and a value thereof has not reached 80 μA. Accordingly, the control unit 110 determines that water droplets are not adhered to the fixing unit 14 when the first transfer material P passes through the fixing unit 14, and starts the image forming operation of the subsequent transfer material P. In addition, when the water droplets are not adhered to the fixing unit 14, the transfer current Itr is less likely to flow due to electrical resistance of the transfer material P, so that the current value I1a is less thanthe reference current value I0a.
Thereafter, a detection operation similar to that of the first transfer material P is executed with respect to the subsequent transfer materials P. In the present embodiment, no adhesion of water droplets to the fixing unit 14 is determined when the n−1th transfer material P passes through the fixing unit 14, so that the image forming operation of the n-th sheet starts continuously. Herein, as illustrated in
In the present embodiment, description has been given to the case where water droplets are adhered to the fixing unit 14 when the n-th transfer material P (n≧3) passes through the fixing unit 14 while transfer materials P are being fed consecutively. However, the embodiment is not limited to the above, and presence or absence of water droplets can be determined through the method described in the present embodiment in a case where the water droplets are adhered to the fixing unit 14 when the first or the second transfer material P passes through the fixing unit 14.
In the present embodiment, as the dehumidification control for eliminating water droplets from the fixing unit 14, the heating unit 31 of the fixing unit 14 and the pressure roller 30 are rotated while the heating unit 31 is being heated. However, the embodiment is not limited thereto. As the dehumidification control for eliminating water droplets from the fixing unit 14, water droplets can be eliminated by increasing an interval between the transfer materials P passing through the fixing unit 14.
For example, when adhesion of water droplets to the fixing unit 14 caused by dew condensation is determined, an interval before the subsequent transfer material P passes through the fixing unit 14 may be increased. With this configuration, a time for waiting the water droplets adhered to the fixing unit 14 to evaporate can be provided, so that the fixing unit 14 can be dehumidified. Further, in a case where a plurality of subsequent transfer materials P exists, conveyance intervals between respective transfer materials P may be increased. With this configuration, the dehumidification control of the fixing unit 14 can be executed by gradually evaporating the water droplets when the transfer material P does not pass through the fixing unit 14. In addition, at this time, even if the heating unit 31 is not being heated, evaporation of water droplets canbe prompted by residual heat if the fixing unit 14 is still warm.
As described above, according to the present embodiment, by comparing the reference current value I0a before the transfer material P reaches the fixing unit 14 and the current value I1a when the transfer material P passes through the fixing unit 14, it is possible to determine presence or absence of water droplets adhered to the fixing unit 14. Further, when adhesion of water droplets to the fixing unit 14 is determined, water droplets can be eliminated through the dehumidification control executed by the control unit 110. With this configuration, it is possible to reduce occurrence of image defect caused by shortage of the transfer current Itr for transferring the toner image to the transfer material P from the intermediate transfer belt 7 at the secondary transfer portion.
In the present embodiment, in steps S102 and S105, the voltage V0 of a same value is applied to the secondary transfer roller 13 from the transfer power source 26, and presence or absence of water droplets adhered to the fixing unit 14 is determined based on the comparison between the reference current value I0a and the current value I1a detected by the detection circuit 25. However, the embodiment is not limited to the above, and presence or absence of water droplets adhered to the fixing unit 14 may be determined through constant current control in which the voltage applied to the secondary transfer roller 13 from the transfer power source 26 is detected by the detection circuit 25 serving as a detection unit. When water droplets are adhered to the fixing unit 14 to cause the electric current Ipr to flow to the ground, electric resistance thereof is lowered in comparison to the case where the electric current Ipr does not flow to the ground, and thus a value of the voltage applied to the secondary transfer roller 13 from the transfer power source 26 is lowered.
In other words, first, in step S102, voltage is applied from the transfer power source 26 so as to make a value of an electric current I0′ flowing in the secondary transfer roller 13 be the same, and a reference applied voltage V0a′ (first voltage) of the transfer power source 26 in step S102 is detected by the detection circuit 25. Then, in step S105, voltage is applied from the transfer power source 26 to make a value of the electric current I0′ flowing in the secondary transfer roller 13 be the same, and an applied voltage V1a′ (second voltage) of the transfer power source 26 in step S105 is acquired. Thereafter, if a state where the applied voltage V1a′ in step S105 is lower than the reference applied voltage V0a′ in step S102 by a preset predetermined value ΔVa or more is continued for a predetermined time ΔTa′, the control unit 110 determines that water droplets are adhered to the fixing unit 14. At this time, similar to the present embodiment, the predetermined value ΔVa. and the predetermined time ΔTa′ have to be set as appropriate according to the specification of the image forming apparatus 100.
In the first embodiment, in step S102, before the transfer material P reaches the secondary transfer portion, the predetermined voltage V0 is applied to the secondary transfer roller 13 from the transfer power source 26, and the reference current value I0a flowing in the secondary transfer roller 13 is detected by the detection circuit 25. On the other hand, as illustrated in
Hereinafter, with reference to
In step S204, the transfer material P reaches the fixing portion N of the fixing unit 14. Then, similar to the first embodiment, when the transfer material P is concurrently passing through the secondary transfer portion and the fixing unit 14 after reaching the fixing portion N, in step S205, the current value I1b (a second current value) flowing in the detection circuit 25 is detected. A secondary transfer operation is executed until the processing in steps S202 to S205 is completed, so that the voltage V0 is continuously applied to the secondary transfer roller 13 from the transfer power source 26. In the present embodiment, a distance between the secondary transfer portion and the fixing portion N is 50 mm, and a conveyance speed is 100 mm/sec., so that the reference current value In is detected within 0.5 sec. when the transfer material P passes through a region from the secondary transfer portion to the fixing portion N having a distance of 50 mm.
In step S206, in a case where it is determined that the image signal for forming an image on the subsequent transfer material P exists (YES in step S206), the processing proceeds to step S207. In step S207, the current value I1b and the reference current value I0b are compared to each other. If a state where the current value I1b is greater than the reference current value I0b by the preset predetermined value ΔIb or more is continued for the predetermined time ΔTb (YES in step S207), the control unit 110 determines that water droplets are adhered to the fixing unit 14 and executes processing in step S208. In a case where the current value I1b is not in the above-described state (NO in step S207), the processing returns to step S202. In step S208, as the dehumidification control executed by the control unit 110, an operation of rotating the heating unit 31 of the fixing unit 14 and the pressure roller 30 while heating the heating unit 31 is executed for 30 seconds. Thereafter, the image forming apparatus 100 notifies a user that image forming operation can restart. Then, after the user confirms the notification, the processing returns to step S202, and the image forming operation restarts. In the present embodiment, the predetermined value ΔIb and the predetermined time ΔTb are set as 40 μA and 0.3 sec., respectively.
A method of determining presence or absence of water droplets adhered to the fixing unit 14 by applying a voltage to the secondary transfer roller 13 from the transfer power source 26 and by detecting the electric current flowing in the secondary transfer roller 13 will be described with reference to
As illustrated in
Herein, as illustrated in
As described above, in the present embodiment, the reference current value I0b is detected by the detection circuit 25 before the transfer material P reaches the fixing portion N after reaching the second transfer portion. Then, presence or absence of water droplets adhered to the fixing unit 14 is determined by comparing the current value I1b and the reference current value I0b detected by the detection circuit 25 when the transfer material P concurrently passes through the secondary transfer portion and the fixing portion N after reaching the fixing unit 14. Because the dehumidification control of the fixing unit 14 is executed by the control unit 110 when adhesion of water droplets to the fixing unit 14 is determined thereby, an effect similar to the effect acquired in the first embodiment can be also acquired in the present embodiment.
In the first embodiment, if a state where the current value I1a is greater than the reference current value I0a by the predetermined value ΔIa or more is continued for the predetermined time ΔTa, adhesion of water droplets to the fixing unit 14 caused by dew condensation is determined, and the dehumidification control of the fixing unit 14 is executed by the control unit 110. On the other hand, as illustrated in
As illustrated in
Next, in step S309, the control unit 110 determines presence or absence of water droplets adhered to the fixing unit 14. Specifically, if a state where the current value I1c is greater than the reference current value I0c by a preset predetermined value ΔIcβ or more is continued for the predetermined time ATc (YES in step S309), the control unit 101 determines that water droplets are adhered. to the fixing unit 14 and executes processing in step S310. In a case where the current value I1c is not in the above-described state (NO in step S309), the processing returns to step S303.
Herein, the predetermined values ΔIcα (a first predetermined value) and ΔIcβ (a second predetermined value) respectively set in steps S307 and S309 are in a relationship of “ΔIcα>ΔIcβ”. In the present embodiment, the predetermined values ΔIcα and ΔIcβ are set as 50 μA and 30 μA, respectively. When the volume of water droplets adhered to the fixing unit 14 is increased, a conduction path between the fixing frame 32 and the pressure roller 30 is increased, and thus the electric current Ip flowing to the ground from the secondary transfer portion is increased. In other words, because the current value I1c detected by the detection circuit 25 is also increased, it is possible to determine whether the volume of water droplets adhered to the fixing unit 14 is large by setting a plurality of different predetermined values when the current value I1c and the reference current value I0c are compared to each other.
In the present embodiment, as the dehumidification control executed by the control unit 110 in step S308, an operation of rotating the heating unit 31 of the fixing unit 14 and the pressure roller 30 while heating the heating unit 31 is executed for 60 seconds, in a case where the volume of water droplets adhered to the fixing unit 14 is large. On the other hand, as the dehumidification control executed by the control unit 110 in step S310, the operation of rotating the heating unit 31 of the fixing unit 14 and the pressure roller 30 while heating the heating unit 31 is executed for seconds, in a case where the volume of adhered water droplets is not so large although the water droplets are adhered to the fixing unit 14.
As described above, according to the present embodiment, in addition to acquiring the effect described in the first embodiment, the dehumidification control more appropriate for each state of water droplets adhered to the fixing unit 14 can be selected.
In the present embodiment, as the dehumidification control executed by the control unit 110, the heating unit of the fixing unit 14 and the pressure roller 30 are rotated while the heating unit 31 is being heated. Further, a period for executing the dehumidification control by the control unit 110 is changed according to the magnitude of a difference between the current value I1c and the reference current value I0c detected by the detection circuit 25. However, the configuration is not limited to the above. As the dehumidification control executed by the control unit 110, an interval between the transfer materials P passing through the fixing unit 14 may be increased, and the interval between the transfer materials P passing through the fixing unit 14 may be changed according to the magnitude of a difference between the current value I1c and the reference current value I0c detected by the detection circuit 25. Furthermore, as the dehumidification control executed by the control unit 110, either one or both of the operation of rotating the heating unit 31 of the fixing unit 14 and the pressure roller 30 while heating the heating unit 31 and the operation of changing the interval between the transfer materials P passing through the fixing unit 14 may be executed.
Although the embodiments relate to applied to a color image forming apparatus have been described as the above, the present invention is not limited to the above-described embodiments. Embodiments are applicable as long as the image forming apparatus includes a transfer member for transferring a toner image to a transfer material P from an intermediate transfer belt and a fixing unit. In other words, as illustrated in
An image forming unit of an image forming apparatus 400 of the present embodiment includes a photosensitive drum 401K as an image bearing member, a charging roller 402K as a charging unit, a development roller 403K as a development unit, and a cleaning blade 405K as a cleaning unit.
Image forming operation starts when a control unit 410 receives an image signal, and the photosensitive drum 401K is rotationally driven in a direction indicated by an arrow R2 in
The photosensitive drum 401K as an image bearing member faces a transfer roller 413 as a transfer member to form a transfer portion. A transfer material P fed from a sheet feeding cassette 409 is conveyed to the transfer portion by a conveyance roller pair 412. Then, at the transfer portion, voltage is applied to the transfer roller 413 from a transfer power source 426 having a detection circuit 425 as a detection unit, so that the toner image is transferred to the transfer material P from the photosensitive drum 401K. Thereafter, a fixing unit 414 applies heat and pressure to the transfer material P to fix the toner image thereto, and the transfer material P is discharged to a discharge tray 418 by a discharge roller pair 417.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit f Japanese Patent Application No. 2016-132601, filed Jul. 4, 2016, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-132601 | Jul 2016 | JP | national |
