Patent Grant
9557702
Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to a configuration of correcting a curl of a sheet.
Description of the Related Art
Hitherto, in an image forming apparatus such as a copying machine or a printer, a toner image formed by an image forming portion is transferred onto a sheet fed from a feeding portion, and thereafter, the sheet is guided to a fixing device to fix an unfixed toner image on the sheet to the sheet. As such a fixing device, there is a heat pressure fixing-type fixing device which fixes a toner image to a sheet by pressurizing and heating the sheet that passes through the fixing device.
Here, when the sheet is pressurized and heated to fix the toner image to the sheet, the sheet may be curled due to the toner on the sheet or moisture contained in the sheet. In the case where the sheet is curled as such, a jam (sheet clogging) occurs in a conveying portion. Furthermore, there is a concern that loading characteristics of the sheet on a discharge tray may be degraded. Therefore, in the fixing device according to the related art, a curl correcting portion which corrects a curl of a sheet by applying a pressure to the curled sheet in the reverse direction to the direction of the curl of the sheet is provided. In addition, as the curl correcting portion, there is a curl correcting portion which corrects a curl of a sheet using two rollers having different hardnesses (refer to U.S. Patent Application Publication No. 2011/0229178 A1).
However, in the image forming apparatus according to the related art provided with the curl correcting portion, there may be cases where a jam of a sheet occurs in the fixing device. Therefore, on the downstream of the fixing device in a sheet conveyance direction, a door for a jam recovery is provided to support one of the two rollers of the curl correcting portion and remove the jammed sheet. In addition, the door is provided with a guide portion which guides the sheet to a nip portion of the two rollers of the curl correcting portion in a state where the door is closed.
However, in the case where the guide portion is provided in the door as such, when the door is opened and closed, there is a concern that the guide portion may collide with the other roller of the two rollers of the curl correcting portion and thus the roller and the guide portion may be damaged.
The invention is accomplished in view of the circumstances described above. It is desirable to provide an image forming apparatus capable of opening and closing a door without damaging a roller or a guide portion.
In order to solve the problems, a representative configuration of the image forming apparatus according to the invention includes: an image forming portion which forms a toner image; a transfer portion which transfers the toner image onto a sheet; a fixing portion which includes a pressure roller and a heating member that forms a fixing nip to fix the toner image onto the sheet by coming in press contact with the pressure roller; a curl correcting unit which is provided on a downstream side of the fixing portion in a sheet conveyance direction and includes a first roller and a second roller that forms a correction nip to correct a curl of the sheet by coming in press contact with the first roller; a holding portion which movably holds the second roller; a biasing member which applies a force to the holding portion in such a direction that the second roller comes in press contact with the first roller; a door which rotatably holds the first roller, is supported to be opened and closed, and separates the first roller from the second roller by being opened; and a retracting portion which allows the holding portion to be retracted to a position where the second roller deviates from a movement path of the door against a biasing force of the biasing member according to a closing operation of the door.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, embodiments of the invention will be described in detail with reference to the drawings.
In
Here, the image forming portion 102 includes a process cartridge 104 including a photosensitive drum 2, a charging roller 3, a developing roller 4, a cleaning blade 5, and the like. In addition, a laser optical system 1 which is an exposure unit that exposes the surface of the photosensitive drum 2 to form an electrostatic latent image on the photosensitive drum 2 is provided. Further, the printer body 101 includes a transfer roller 14 that abuts on the photosensitive drum 2 and forms a transfer portion T together with the photosensitive drum 2, a fixing device 105 that fixes a toner image transferred from the transfer portion T onto the sheet S, and the like.
The sheet feeding device 103 includes a pickup roller (feeding roller) 7 which feeds the sheet S at the highest level stored in the sheet feeding cassette 6 which is a sheet storage portion. In addition, the sheet feeding device 103 includes a feed roller 7a that is rotated in a sheet conveyance direction and a retard roller 7b which comes in press contact with the feed roller 7a and forms a separation nip portion to separate the sheets between the retard roller 7b and the feed roller 7a one from another.
In
Next, the image forming operation performed in the laser beam printer 100 configured as such will be described. When the image forming operation is started, first, the pickup roller 7 of the sheet feeding device 103 is rotated to feed a sheet S1 at the highest level on the sheet feeding cassette 6. In addition, the sheet S1 fed by the pickup roller 7 as such is separated and conveyed by the pair of separation rollers 7a and 7b and is then conveyed to a pair of registration rollers 11 at a standstill by a conveying roller 8 so as to be subjected to tip end positioning (skew feeding correction).
After the tip end positioning is performed, the pair of registration rollers 11 is rotated, and the sheet S1 is conveyed by the pair of registration rollers 11. In addition, when the sheet S1 is conveyed to a top sensor 13, the control portion 150 allows the laser optical system 1 to emit a laser beam onto the photosensitive drum 2 charged by the charging roller 3 based on image information input from an external personal computer (PC). Accordingly, an electrostatic latent image is formed on the photosensitive drum. Next, toner that is appropriately charged is supplied to the photosensitive drum 2 and adheres to the electrostatic latent image as the developing roller 4 is rotated such that the electrostatic latent image is developed and visualized as a toner image.
Next, the sheet S1 conveyed by the pair of registration rollers 11 reaches the transfer portion T, and the image on the photosensitive drum 2 is transferred onto the sheet S1 by the transfer roller 14. In addition, the photosensitive drum 2 on which the toner image is transferred is cleaned by the cleaning blade 5 so that residual toner is removed. Thereafter, the sheet S1 on which the toner image is transferred is conveyed to the fixing device 105 and is heated and pressurized when passing through the fixing device 105 such that an unfixed toner image on the sheet is fixed to the sheet surface. The sheet S1 on which the toner image is fixed as such is discharged onto a discharge tray 120 by a discharge roller 106.
Here, as illustrated in
In this embodiment, the material of the decurl roller 18 is a foam silicone rubber having an ASKER C type hardness of approximately 30 degrees, and the material of the decurl counter roller 19 is iron. In addition, as the decurl roller 18 which is an elastic roller having such a low hardness is pressurized by the decurl counter roller 19 which is a non-elastic roller having a high hardness, the decurl nip 18a is formed along the outside diameter of the decurl counter roller 19. Accordingly, while the sheet is conveyed through the decurl nip 18a, the curl formed in the sheet by the fixing nip 17a is corrected.
In
When a print job is continuously performed, the temperature of the pressure roller 17 of which the material is a silicone rubber having an ASKER C type hardness of approximately 50 degrees is increased and thus the outside diameter thereof is increased due to thermal expansion. Since the decurl roller 18 is disposed in the vicinity of the fixing nip, the decurl roller 18 comes in contact with the sheet which is at a high temperature immediately after fixing and thus the outside diameter thereof is increased due to thermal expansion in the same manner. Accordingly, the conveyance speeds can be easily matched when the decurl roller 18 having a high thermal expansion like the pressure roller 17 is driven compared to when the decurl counter roller 19 made of iron having a low thermal expansion is driven. In addition, by allowing the conveyance speeds of the sheet at the fixing nip and the decurl nip to be matched, conveyance problems such as wrinkling and folding of the sheet are easily prevented.
In
In
Here, the pressure control cam 26 switches a pressurizing force applied to the pressure roller 17 by the fixing film 15 via the fixing pressure lever 27 using the outside cam shape 26a. In addition, the pressure control cam 26 switches a pressurizing force applied to the decurl roller 18 by the decurl counter roller 19 via the decurl pressure lever 28 using the inside cam shape 26b. As such, in this embodiment, a fixing nip pressure changing mechanism 105C which changes the pressurizing force of the fixing nip is configured by the outside cam shape 26a of the pressure control cam 26, the fixing pressure lever 27, and the fixing pressure spring 30. In addition, as illustrated in
At this time, the outside cam shape 26a of the pressure control cam 26 is separated from the fixing pressure lever 27 and the pressurizing force of the fixing pressure spring 30 is applied to the fixing film 15 via the fixing pressure lever 27 and the fixing flange 29. Therefore, the fixing nip pressure remains in the “strong” state. In addition, the inside cam shape 26b of the pressure control cam 26 comes in contact with the decurl pressure lever 28 to rotate the decurl pressure lever 28 clockwise. Accordingly, the spring length of the decurl pressure spring 31 is shortened, and thus the decurl nip pressure is in a “strong” state. That is, in a state where temperature and humidity are high and the amount of moisture in the air is high, that is, in a state where the curl formed in the sheet at the fixing nip is large, a state (third state) where the fixing nip pressure is “strong” and the decurl nip pressure is “strong” is set.
In addition, as illustrated in
In addition, when the power is “ON” from “OFF”, the control portion 150 drives the motor M which rotates the pressure control cam 26 to make at least one revolution of the pressure control cam 26, thereby setting the rotational phase of the pressure control cam 26, that is, the states of the fixing nip pressure and the decurl nip pressure. In addition, a controller 151 inputs a signal from an external PC 152 to the control portion 150.
Here, for example, an amount of moisture in the air of 19.1 g/m2 corresponds to a temperature 28C° and a humidity of 70%. In addition, in a high temperature and high humidity environment in which the amount of moisture in the air is high, the amount of moisture contained in the sheet is increased. In this case, a heat amount applied to the sheet at the fixing nip is less likely to be uniformly transferred to the front and rear of the sheet, and thus the curl is enlarged. In contrast, in a room temperature and normal humidity environment or a low temperature and low humidity environment, the amount of moisture contained in the sheet is reduced. In this case, a heat amount applied to the sheet at the fixing nip is more likely to be uniformly transferred to the front and rear of the sheet, and thus the curl is reduced.
In this embodiment, the fixing nip pressure and the decurl nip pressure are controlled to be set to the following three states by the pressure control cam 26, the fixing pressure lever 27, and the decurl pressure lever 28. That is, the fixing nip pressure and the decurl nip pressure are controlled to be set to an A state in which the fixing nip pressure is “weak” and the decurl nip pressure is “weak”, a B state in which the fixing nip pressure is “strong” and the decurl nip pressure is “weak”, and a C state in which the fixing nip pressure is “strong” and the decurl nip pressure is “strong”. That is, in this embodiment, the fixing nip pressure and the decurl nip pressure can be controlled by a simple and small configuration including the pressure control cam 26, the fixing pressure lever 27, and the decurl pressure lever 28.
Next, a control process of the fixing nip pressure and the decurl nip pressure when a print job is performed by the control portion 150 will be described using the flowchart illustrated in
Here, when the amount of moisture in the air is equal to or higher than 19.1 g/m2 (Y in S104), the control portion 150 drives the motor M to rotate the pressure control cam 26. By rotating the pressure control cam 26 as such, the control portion 150 sets the fixing nip pressure changing mechanism 105C and the decurl nip pressure changing mechanism 105D to the state (C state) in which the fixing nip pressure is “strong” and the decurl nip pressure is “strong” (S105). By setting to the C state in which the fixing nip pressure is “strong” and the decurl nip pressure is “strong”, even in the high temperature and high humidity environment in which fixing is easily performed but curling is likely to occur, both good fixability and a low degree of curling can be achieved.
In addition, when the amount of moisture in the air is less than 19.1 g/m2 (N in S104), the control portion 150 sets the fixing nip pressure changing mechanism 105C and the decurl nip pressure changing mechanism 105D to the state (B state) in which the fixing nip pressure is “strong” and the decurl nip pressure is “weak” (S106). By setting to the B state in which the fixing nip pressure is “strong” and the decurl nip pressure is “weak”, the curl of the sheet with a small curl can be appropriately corrected. Thereafter, the control portion 150 starts the conveyance of the sheet and the image forming operation and performs the print job (S107).
In a case where a jam occurs in a state where the sheet remains in the fixing device, the control portion 150 performs control to set the A state in which the fixing nip pressure is “weak” and the decurl nip pressure is “weak” illustrated in
As such, in this embodiment, the control portion 150 controls the fixing nip pressure changing mechanism 105C and the decurl nip pressure changing mechanism 105D to be set to an appropriate state in which both good fixability and a low degree of curling can be achieved based on the temperature information and the humidity information depending on the temperature and humidity. For example, under the high temperature and high humidity environment in which fixing is easily performed due to an increase in the temperature of the sheet as described above but curling is likely to occur due to a high amount of moisture contained in the sheet, the fixing nip pressure is weakened and the decurl nip pressure is increased.
As such, in this embodiment, the fixing nip pressure and the decurl nip pressure can be changed without being necessarily linked to each other. Therefore, both good fixability and a low degree of curling can be achieved regardless of environment. In addition, since the decurl nip pressure changing mechanism 105D has a simple and small configuration, the decurl roller 18 can be disposed near the downstream side of the fixing nip. Therefore, both a reduction in the size of the apparatus and a good ability to correct a curl can be achieved.
Here, in this embodiment, as illustrated in
As the decurl counter roller bearing 36 is moved upward as such, without the contact of the upper surface 37b of the conveyance guide 37 on the upstream side in the sheet conveyance direction with the decurl counter roller 19, and the jam recovery door 35 can be closed. That is, when the jam recovery door 35 is closed, the decurl counter roller bearing 36 is moved upward by a retracting portion 105F configured by the cam follower shape 36a of the decurl counter roller bearing 36 and the cam shape 37a of the conveyance guide 37.
In addition, when the jam recovery door 35 is closed, as the decurl counter roller bearing 36 is moved, the decurl counter roller 19 is also lifted to a position where the decurl counter roller 19 does not come in contact with the jam recovery door 35. In other words, when the jam recovery door 35 is closed, as the decurl counter roller bearing 36 is moved, the decurl counter roller 19 is lifted to a position that deviates from a rotational path O (of the conveyance guide 37) of the jam recovery door 35 illustrated in
In addition, even when the jam recovery door 35 is opened, similarly to when the jam recovery door 35 is closed, the decurl counter roller bearing 36 is pressed by the cam shape 37a of the conveyance guide 37 and is lifted upward. Accordingly, when the jam recovery door 35 is opened, flaws on the surfaces of the conveyance guide 37 and the decurl counter roller 19 can be prevented.
As described above, in this embodiment, when the jam recovery door 35 is opened and closed, the retracting portion 105F causes the decurl counter roller bearing 36 to be retracted to a position at which the decurl counter roller 19 deviates from the rotational path (movement path) of the jam recovery door 35. Accordingly, the jam recovery door 35 can be opened and closed without damaging the conveyance guide 37 and the decurl counter roller 19. In addition, when the jam recovery door 35 is opened and closed, the A state in which the fixing nip pressure is “weak” and the decurl nip pressure is “weak” is set, and thus the jam recovery door 35 can be opened with a small operating force, thereby enhancing jam recovery characteristics.
Next, a second embodiment of the invention will be described.
On the other hand, when the fixing pressure lever 27 is turned upward, the hook shape 27a locked to the decurl counter roller bearing 36 is also lifted, and thus the decurl counter roller bearing 36 is moved upward. Accordingly, as illustrated in
On the other hand, when the fixing pressure lever 27 is turned downward, the hook shape 27a is also lowered. Accordingly, the decurl counter roller bearing 36 is lowered, and the decurl roller 18 and the decurl counter roller 19 come in contact with each other. In addition, since the inside cam shape 26b of the pressure control cam 26 and the decurl pressure lever 28 are separated from each other at this time, the decurl nip pressure remains in the “weak” state. That is, in the state where temperature or humidity is low and the amount of moisture in the air is low, the state in which the fixing nip pressure is “strong” and the decurl nip pressure is “weak” is set by the fixing nip pressure changing mechanism 105C and decurl nip pressure changing mechanism 105D.
Here, when the jam recovery door 35 is opened, in addition to that the fixing nip pressure is approximately 0 as described above, the decurl counter roller 19 is lifted by the hook shape 27a. Therefore, the decurl roller 18 and the decurl counter roller 19 are separated from each other. As a result, an operating force required to open and close the jam recovery door 35 is further reduced.
In addition, in a case of a blackout, or in a case where the user turns off the power by mistake while the print job is performed, there is a possibility that the jam recovery door 35 may be opened and closed in the state where the decurl roller 18 and the decurl counter roller 19 form a nip as illustrated in
Here, as illustrated in
In the separation conveyance guide holder 39, a U-shaped groove (not illustrated) provided in the downstream side end (correction nip side end) in the sheet conveyance direction is fitted to the decurl counter roller bearing 36. Accordingly, when the decurl counter roller bearing 36 is moved, the separation conveyance guide 38 is turned (moved) integrally with the decurl counter roller bearing 36, in other words, the decurl counter roller 19.
Here, in the above description, a threshold of the amount of moisture for switching the states of the fixing nip pressure changing mechanism 105C and decurl nip pressure changing mechanism 105D is set to 19.1 g/m2. However, in a case where the threshold of the amount of moisture is constant, when the amount of moisture in the air is close to 19.1 g/m2, the decurl nip pressure is frequently switched for every print job. In addition, when the decurl nip pressure is frequently switched as such, there may be cases where the amount of curl is changed and paper discharging and loading characteristics are degraded. Therefore, in order to prevent the degradation of the paper discharging and loading characteristics, the threshold of the amount of moisture may be changed.
Next, an image forming apparatus according to a third embodiment of the invention in which the threshold of the amount of moisture is changed as described above will be described. In this embodiment, the threshold for switching the states of the fixing nip pressure changing mechanism 105C and the decurl nip pressure changing mechanism 105D is changed by a current decurl nip pressure.
When a print job is input to the controller from the external PC (S202), the control portion 150 acquires temperature information and humidity information from the temperature sensor 12a and the humidity sensor 12b (S203). In addition, the control portion 150 obtains the amount of moisture in the air from the acquired temperature information and humidity information and determines a current decurl nip pressure using the information from the state detection sensor 34.
In addition, when the current decurl nip pressure is “strong” (Y in S204), the control portion 150 determines whether or not the amount of moisture in the air is equal to or less than 18.1 g/m2 (smaller than 19.1 g/m2) (S205). When it is determined that the amount of moisture in the air is equal to or less than 18.1 g/m2 (Y in S205), the control portion 150 determines that the curl is small and sets the fixing nip pressure and decurl nip pressure to “strong” and “weak”, respectively (S208). When it is determined that the amount of moisture in the air is not equal to or less than 18.1 g/m2 (N in S205), the control portion 150 determines that the curl is large and holds the decurl nip pressure “strong” (S209). That is, when the amount of moisture in the air is not equal to or less than 18.1 g/m2, the decurl nip pressure is not switched to the “weak” state.
In a case where the current decurl nip pressure is not “strong” (N in S204), the control portion 150 determines whether or not the decurl nip pressure is “released” or “indeterminate” (S2041). In addition, when it is determined that the decurl nip pressure is “released” or “indeterminate” (Y in S2041), the control portion 150 determines whether or not the amount of moisture in the air is equal to or higher than 19.1 g/m2 (S206). Here, in a case where it is determined that the amount of moisture in the air is equal to or higher than 19.1 g/m2 (Y in S206), the control portion 150 sets the fixing nip pressure to “strong”, determines that the curl is large, and sets the decurl nip pressure to “strong” (S210). When it is determined that the amount of moisture in the air is equal to or less than 19.1 g/m2 (N in S206), the control portion 150 sets the fixing nip pressure to “strong”, determines that the curl is small, and sets the decurl nip pressure to “weak” (S211). That is, in the case where the decurl nip pressure is “released” or “indeterminate”, when the amount of moisture in the air is not equal to or higher than 19.1 g/m2, the decurl nip pressure is not switched to the “strong” state.
When it is determined that the decurl nip pressure is not “released” or “indeterminate” (N in S2041), that is, when it is determined that the decurl nip pressure is “weak”, the control portion 150 determines whether or not the amount of moisture in the air is equal to or higher than 20.1 g/m2 (greater than 19.1 g/m2) (S207). In addition, when it is determined that the amount of moisture in the air is equal to or higher than 20.1 g/m2 (Y in S207), the control portion 150 sets the fixing nip pressure to “strong”, determines that the curl is large, and sets the decurl nip pressure to “strong” (S212). When it is determined that the amount of moisture in the air is not equal to or higher than 20.1 g/m2 (N in S207), the control portion 150 sets the fixing nip pressure to “strong”, determines that the curl is small, and holds the decurl nip pressure “weak” (S213).
That is, in a case where a curl nip pressure is “weak”, when the amount of moisture in the air is not equal to or higher than 20.1 g/m2, the decurl nip pressure is not switched to the “strong” state. In addition, after setting the decurl nip pressure and the curl nip pressure by selecting the amount of moisture in the air based on the decurl nip pressure as such, the control portion 150 starts the conveyance of the sheet and the image forming operation and performs the print job (S214).
As described above, in this embodiment, the amount of moisture in the air (threshold) is selected based on the decurl nip pressure to set the decurl nip pressure and the curl nip pressure. Accordingly, when the amount of moisture in the air is close to 19.1 g/m2, the degradation of the paper discharging and loading characteristics which occurs because the decurl nip pressure is frequently switched for every print job and thus the amount of curl is changed can be prevented.
In this embodiment, the case where the threshold is changed based on the decurl nip pressure is described. However, the threshold may also be changed using not only the decurl nip pressure but also information regarding the fixing nip pressure. That is, the threshold for switching the fixing nip pressure and the decurl nip pressure may be changed based on a current fixing nip pressure and the decurl nip pressure.
When a print job is input to the controller from the external PC (S302), the control portion 150 acquires temperature information and humidity information from the temperature sensor 12a and the humidity sensor 12b (S303). In addition, the control portion 150 obtains the amount of moisture in the air from the acquired temperature information and humidity information and a table (not illustrated) and determines the current fixing nip pressure and the decurl nip pressure using the information from the state detection sensor 34.
In addition, when the current fixing nip pressure is “strong” and the decurl nip pressure is “strong” (Y in S304), the control portion 150 determines whether or not the amount of moisture in the air is equal to or less than 18.1 g/m2 (smaller than 19.1 g/m2) (S305). When it is determined that the amount of moisture in the air is equal to or less than 18.1 g/m2 (Y in S305), the control portion 150 sets the fixing nip pressure and decurl nip pressure to “strong” and “weak”, respectively (S308). When it is determined that the amount of moisture in the air is not equal to or less than 18.1 g/m2 (N in S305), the control portion 150 sets the fixing nip pressure and decurl nip pressure to “strong” and “strong”, respectively (S309). That is, when the amount of moisture in the air is not equal to or less than 18.1 g/m2, while the fixing nip pressure is “strong”, the decurl nip pressure is not switched to the “weak” state.
In a case where the decurl nip pressure is not “strong” (N in S304) while the current fixing nip pressure is “strong”, the control portion 150 determines whether or not the fixing nip pressure and the decurl nip pressure are “released” or “indeterminate” (S3041). In addition, when it is determined that the fixing nip pressure and the decurl nip pressure are “released” or “indeterminate” (Y in S3041), the control portion 150 determines whether or not the amount of moisture in the air is equal to or higher than 19.1 g/m2 (S306). In addition, when it is determined that the amount of moisture in the air is equal to or higher than 19.1 g/m2 (Y in S306), the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “strong”, respectively (S310). When it is determined that the amount of moisture in the air is equal to or less than 19.1 g/m2 (N in S306), the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “weak”, respectively (S311).
When it is determined that the fixing nip pressure and the decurl nip pressure are not “released” or “indeterminate” (N in S3041), the control portion 150 determines whether or not the amount of moisture in the air is equal to or higher than 20.1 g/m2 (greater than 19.1 g/m2) (S307). In addition, when it is determined that the amount of moisture in the air is equal to or higher than 20.1 g/m2 (Y in S307), the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “strong”, respectively (S312). When it is determined that the amount of moisture in the air is not equal to or higher than 20.1 g/m2 (N in S307), the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “weak”, respectively (S313). After setting the decurl nip pressure and the curl nip pressure by selecting the amount of moisture in the air based on the fixing nip pressure and the decurl nip pressure as such, the control portion 150 starts the conveyance of the sheet and the image forming operation and performs the print job (S314).
By performing the control process as described above, when the amount of moisture in the air is close to 19.1 g/m2, the degradation of the paper discharging and loading characteristics which occurs because the decurl nip pressure is frequently switched for every print job and thus the amount of curl is changed can be prevented.
Next, a fourth embodiment of the invention will be described.
Here, in a case of a thick sheet, the sheet is not easily fixed. Therefore, the fixing temperature adjustment is set to be high. However, since the thick sheet has high rigidity and has a small amount of curl caused by the fixing nip, the decurl nip pressure needs to be set to weak. In addition, in a case of a thin sheet having a good surface property, the sheet is easily fixed. Therefore, the fixing temperature adjustment is set to be low. However, the thin sheet has low rigidity and has a high amount of curl caused by the fixing nip, the decurl nip pressure needs to be set to “strong”. In a case of a thin sheet having a poor surface property, the sheet is not easily fixed, and thus the fixing temperature adjustment is set to be high. Furthermore, in the case of the thin sheet having a poor surface property, in addition to that the rigidity thereof is low and the amount of curl caused by the fixing nip is high, the fixing temperature adjustment is set to be high. Therefore, the amount of curl is further increased.
Here, a control process of setting the curl nip pressure according to the basis weight and the surface property of the sheet S according to this embodiment will be described by using a flowchart illustrated in
Next, the control portion 150 acquires information regarding the basis weight and the surface property of the sheet from the medium sensor 21 (S404) and determines whether or not the basis weight of the sheet is 90 g/m2 (S405). In addition, in a case of a sheet of which the basis weight is not 90 g/m2, that is, in a case of a thick sheet, the sheet is not easily fixed. Therefore, the control portion 150 sets the fixing temperature adjustment to “high” (S407). In addition, since the thick sheet has high rigidity and has a low amount of curl caused by the fixing nip, the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “weak”, respectively (S410).
In addition, it is determined whether or not the basis weight of the sheet is 90 g/m2 and the surface property of the sheet is equal to or less than a predetermined threshold (S406). In addition, in a case where the basis weight of the sheet is 90 g/m2 and the surface property thereof is equal to or less than the predetermined threshold (Y in S406), that is, in a case of a thin sheet having a good surface property, the sheet is easily fixed. Therefore, the control portion 150 sets the fixing temperature adjustment to “low” (S408). In addition, the thin sheet has low rigidity and has a large amount of curl caused by the fixing nip. Therefore, the control portion 150 subsequently determines whether or not the amount of moisture in the air is equal to or higher than 19.1 g/m2 (S411).
In addition, in a case where the amount of moisture in the air is equal to or higher than 19.1 g/m2 (Y in S411), that is, in a case of a high temperature and a high humidity, the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “strong”, respectively (S413). In a case where the amount of moisture in the air is not equal to or higher than 19.1 g/m2 (N in S411), that is, in a room temperature and normal humidity environment or a low temperature and low humidity environment, the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “weak”, respectively (S414).
In addition, in a case where the basis weight of the sheet is ≦90 g/m2 and the surface property of the sheet is not equal to or less than the threshold (N in S406), that is, in a case of a thin sheet having a poor surface property, the sheet is not easily fixed. Therefore, the control portion 150 sets the fixing temperature adjustment to “high” (S409). Here, in addition to that the thin sheet has low rigidity and a large amount of curl caused by the fixing nip, the fixing temperature adjustment is set to be high. Therefore, the amount of curl is further increased.
Accordingly, in this embodiment, “an amount of moisture in the air of 8.3 g/m2” corresponding to a temperature of 23° C. and a humidity of 40% other than “an amount of moisture in the air of 19.1 g/m2” corresponding to a temperature of 27° C. and a humidity of 70% is the threshold for switching between “strong” and “weak” of the decurl nip pressure. Therefore, the control portion 150 determines whether or not the amount of moisture in the air is equal to or higher than 8.3 g/m2 (S412), and in a case where the amount of moisture in the air is equal to or higher than 8.3 g/m2 (Y in S412), the fixing nip pressure is set to “strong” and the decurl nip pressure is set to “strong” (S415).
In addition, in a case where the amount of moisture in the air is not equal to or higher than 8.3 g/m2 (N in S412), that is, in the low temperature and low humidity environment, the control portion 150 sets the fixing nip pressure and the decurl nip pressure to “strong” and “weak”, respectively (S416). In addition, after setting the decurl nip pressure and the curl nip pressure according to the basis weight and the surface property of the sheet S as such, the control portion 150 starts the conveyance of the sheet and the image forming operation and performs the print job (S417).
As described above, in this embodiment, the decurl nip pressure and the curl nip pressure are set according to the basis weight and the surface property of the sheet. Accordingly, fixing temperature adjustment and the decurl nip pressure by which both good fixability and a low degree of curling can be achieved can be automatically set according to the basis weight and the surface property of the sheet.
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 modifications, equivalent structures and functions.
This application is a Continuation of U.S. application Ser. No. 14/065,658, filed on Oct. 29, 2013, and allowed on Feb. 27, 2015, which claims the benefit of Japanese Patent Application No. 2012-243667, filed Nov. 5, 2012, both of which are hereby incorporated by reference herein in their entireties.
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 14065658 | Oct 2013 | US |
| Child | 14719648 | US |
