Image forming apparatus

Abstract

The present invention provides an image forming apparatus that can automatically perform control of fixing conditions in environments where such control is necessary to suppress paper curling. [Solution] When the control unit 90 in the image forming apparatus 10 receives an image forming job on one or more sheets of paper P, it determines whether or not to perform fixing condition change control based on the humidity condition that the ambient humidity He of the image forming apparatus 10 exceeds the reference humidity, and at least one of the setting conditions of the paper length setting and the double-sided printing setting in the print job. As this fixing condition change control, the control unit 90 can perform control to change the pressure from the pressurizing member (42) from a first pressure when the ambient humidity He is below the reference humidity to a second pressure that is lower, and to make the amount of heat supplied by the heat source 45 greater than the amount of heat when the ambient humidity He is below the reference humidity.

Description

Technical Field

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

Background Art

[0002] Image forming apparatuses such as copiers, multifunction devices, printers, and facsimile machines that use an electrophotographic method include a fixing device. Generally, the fixing device is configured to form a fixing nip by pressing a fixing member such as a fixing belt with a pressing member. As the paper passes through this fixing nip, the toner and the paper are pressurized and heated, and the toner image is fixed on the paper. In such a fixing device, the paper may curl when it is subjected to heat and pressure at the fixing nip.

[0003] For example, in Patent Document 1, for the purpose of suppressing curling of the paper after double-sided printing, when performing double-sided printing, the pressure applied by the pressing member during printing of the first side of the double-sided printing is defined as the first pressure, and when the pressure applied by the pressing member during printing of the second side is defined as the second pressure, a fixing device is disclosed that performs an adjustment to make the second pressure weaker than the first pressure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In image forming apparatuses equipped with such a fixing device, when paper with a high moisture content is used for printing, the degree of curling that occurs when the paper passes through the fixing nip tends to be greater. When the printed paper is discharged into the output tray, if the degree of curling is large, the paper will not stack properly on the output tray, causing the paper on the output tray to be pushed out by the paper discharged later, or the paper to curl up on the output tray, resulting in a problem where the number of sheets that can be stacked in the output tray is extremely small, in other words, the stackability deteriorates.

[0006] Furthermore, when printing on long sheets of paper, such as A3 size, along the transport direction to the fuser, the deterioration of stackability becomes particularly noticeable. This is because, although the degree of curl does not change significantly depending on the length of the paper (in this disclosure, the length along the transport direction in the image forming apparatus), as the paper length increases, the amount of paper movement within the output tray increases, making it easier for problems such as paper falling out of the output tray to occur, even if the degree of curl is small.

[0007] Furthermore, when performing double-sided printing on paper, the paper may curl during the printing of the first side. This curled paper is then transported within the image forming apparatus for printing the second side, which can lead to paper jams (JAM) during transport.

[0008] To control the fixing conditions and suppress paper curling, reducing the pressure applied to the paper at the fixing nip, i.e., weakening the pressure of the pressurizing member, is effective. However, in order to fix toner to the paper, it is necessary to raise the fixing temperature instead of lowering the pressure of the pressurizing member. Raising the fixing temperature can cause the fixing member to deteriorate more easily due to the high temperature and reduce the energy efficiency of image formation, so it is desirable to not perform this control in environments where it is not necessary. Conventional image forming machines have prepared multiple fixing condition patterns that combine pressure reduction of the pressurizing member and the corresponding fixing temperature correction, allowing service technicians to select the appropriate pattern according to the degree of paper curling. However, because this is done manually according to the degree of paper curling, there were cases where this control remained performed even in environments where it was not necessary.

[0009] This disclosure has been made in view of the above-mentioned problems, and aims to provide an image forming apparatus that can automatically perform control of fixing conditions in an environment where it is necessary to control the conditions for suppressing paper curling. [Means for solving the problem]

[0010] To solve the above problems, the following image forming apparatus is provided. The image forming apparatus disclosed herein is Fixing belt and A nip-forming member is arranged on one side of the fixing belt, A pressure member presses the nip-forming member from the other side of the fixing belt to form a fixing nip between it and the fixing belt, thereby fixing an image onto the paper being transported to the fixing nip. A heat source for heating the fixing belt, An image forming apparatus having a fixing device that includes a pressure changing device for changing the pressure applied by the pressurizing member to the nip forming member, A humidity detection unit for detecting ambient humidity in the image forming apparatus, The system comprises one or more control units that control the heat source and the pressure changing device, The control unit, upon receiving a print job for image formation on one or more sheets of paper, determines whether or not to perform fixing condition change control based on the humidity condition that the ambient humidity exceeds the reference humidity and at least one of the paper length setting and double-sided printing setting conditions for the print job. The control unit is characterized in that, as fixing condition change control, it can change the pressure from the pressurizing member from a first pressure, which is the pressure when the ambient humidity is below the standard humidity, to a second pressure, which is lower than that, and can also perform control to make the amount of heat supplied by the heat source greater than the amount of heat when the ambient humidity is below the standard humidity.

[0011] In the image forming apparatus described above, the control unit may be configured to determine that the humidity condition is met when the ambient humidity exceeds the reference humidity for a predetermined period of time.

[0012] Furthermore, in the image forming apparatus described above, when printing continuously on multiple sheets of paper, the control unit may be configured to gradually reduce the pressure from the pressurizing member and gradually increase the amount of heat emitted by the heat source each time a predetermined number of sheets of paper pass through the fixing nip.

[0013] Furthermore, in the image forming apparatus described above, if the control unit determines that it should perform the fixing condition change control for a double-sided printing job, it may be configured to perform the fixing condition change control when printing the first side of the double-sided print, but not when printing the second side.

[0014] Furthermore, in the above-mentioned image forming apparatus, A paper feed tray for containing the paper to be supplied to the fuser device, The system further comprises a heater for heating the paper contained in the paper feed tray, The control unit may be configured not to perform the fixing condition change control if a predetermined time has elapsed since heating by the heater started. [Effects of the Invention]

[0015] According to the image forming apparatus of the present disclosure, excellent effects can be obtained, such as being able to automatically execute the control of the fixing conditions in an environment where control of the fixing conditions for suppressing the curling of paper is required.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present disclosure as viewed from the front. [Figure 2] It is a front view showing a schematic configuration of a fixing device included in the image forming apparatus shown in FIG. 1. [Figure 3] It is a front view of a pressing change device provided in the fixing device. [Figure 4] It is a system block diagram showing a control configuration of the image forming apparatus shown in FIG. 1. [Figure 5] It is a flowchart showing an example of a flow of a determination process for determining whether to execute fixing condition change control. [Figure 6] It is a graph exemplifying a state in which the temperature difference between the fixing belt and the pressure roller expands with the passage of time during continuous printing.

Modes for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present disclosure and is a schematic cross-sectional view of an image forming apparatus 10 as viewed from the front. In FIG. 1, reference numeral X indicates the front-rear direction (depth direction), reference numeral Y indicates the left-right direction (width direction), and reference numeral Z indicates the up-down direction (height direction). The same applies to FIG. 2.

[0018] The image forming apparatus 10 shown in Figure 1 is a color image forming apparatus that forms multi-color and monochrome images on paper P, such as recording paper, using an electrophotographic method, according to image data read by an image reading device 11 or image data transmitted from an external source. The image forming apparatus 10 may also be a monochrome image forming apparatus. Furthermore, the image forming apparatus 10 may be a color image forming apparatus of another form.

[0019] The image forming apparatus 10 comprises a document feeder 12 and an image forming apparatus body 13, the image forming apparatus body 13 being equipped with an image forming unit 14 and a paper transport system 15.

[0020] The image forming unit 14 includes an exposure device 30 (specifically, an exposure unit of the writing optical system), multiple developing devices 31-31 (specifically, developing units), multiple photoreceptor drums 32-32, multiple photoreceptor cleaner units 33-33, multiple chargers 34-34, a primary transfer belt device 35, multiple toner cartridge devices 36-36 (specifically, toner cartridge units), and a fuser device 40 (specifically, a fuser unit). The paper transport system 15 includes a paper feed tray 16, a manual feed tray 17 for which envelopes, etc., are set, and an output tray 18.

[0021] The top of the image forming apparatus body 13 is a document tray 19 made of transparent glass on which a document (not shown) is placed, and below the document tray 19 is an image reading device 11 for reading the image of the document. A document feeder 12 is also provided above the document tray 19. The image of the document read by the image reading device 11 is sent to the image forming apparatus body 13 as image data, and the image formed in the image forming apparatus body 13 based on the image data is recorded on paper P. An operation display unit 25 (operation panel) is provided near the document tray 19.

[0022] The image data handled by the image forming apparatus 10 corresponds to a color image using multiple colors (in this example, black (K), cyan (C), magenta (M), and yellow (Y)). Therefore, the developing units 31-31, photoreceptor drums 32-32, photoreceptor cleaner units 33-33, chargers 34-34, and toner cartridge units 36-36 are each set up in multiple quantities (in this example, four units each for black, cyan, magenta, and yellow) to form multiple types of images corresponding to each color (four types in this example), and these constitute multiple (four in this example) image stations.

[0023] In the image forming apparatus 10, when performing image formation, the paper to be printed, such as paper P, is supplied from the paper feed tray 16 or the manual feed tray 17, and the paper P is transported to the registration roller 21 by transport rollers 20a to 20a provided along the paper transport path S. Next, at the timing when the toner image on the primary transfer belt 22, which is moved in a circumferential direction M in the primary transfer belt device 35, aligns with the paper P, the paper P is transported by the secondary transfer belt device 23, and the toner image is transferred onto the paper P. After that, the paper P is passed between the nip forming member (specifically, the fixing roller 41) and the pressure member (specifically, the pressure roller 42) in the fixing device 40, so that the unfixed toner on the paper P is melted and fixed by heat, and discharged onto the paper output tray 18 via the transport rollers 20a and the discharge roller section 24. Furthermore, in the image forming apparatus 10, when image formation is performed not only on the front surface but also on the back surface of the paper P, that is, when double-sided printing is performed, the paper P is transported in the reverse direction from the discharge roller section 24 to the reversal path Sr, and the front and back surfaces of the paper P are reversed via the transport roller 20b and guided again to the register roller 21, where the toner image is fixed on the back surface of the paper P in the same way as on the front surface, and then discharged to the output tray 18. In this way, the image forming apparatus 10 completes a series of printing operations. That is, in this disclosure, "printing the first side in double-sided printing" means image formation on the front surface of the paper P, and "printing the second side in double-sided printing" means image formation on the back surface of the paper P.

[0024] It is also possible to form a monochrome image using at least one of the four image forming stations and transfer the monochrome image to the primary transfer belt 22 in the primary transfer belt device 35. This monochrome image, like the color image, is transferred from the primary transfer belt 22 to the paper P and fixed onto the paper P.

[0025] Next, a pressure changing device 50 applied to the fixing device 40 according to this embodiment will be described. The fixing device 40 comprises a plurality of belt rollers (fixing rollers 41 and heating rollers 44 in this example) and an endless belt (fixing belt 43 in this example) wrapped around the plurality of belt rollers. The fixing belt 43 is configured to transfer heat from the heating rollers 44 to the fixing rollers 41.

[0026] Figure 2 is a front view showing the schematic configuration of the fixing device 40. In the fixing device 40, a pressure roller 42 is pressed against a fixing roller 41 via a fixing belt 43, and the pressing part constitutes a fixing nip N that fixes the paper P. The fixing belt 43 is heated by a heat source 45 provided inside the heating roller 44 and is maintained at a predetermined fixing temperature based on a signal from a fixing temperature detection unit 46 (specifically a temperature sensor such as a thermistor). The fixing temperature detection unit 46 may also be capable of detecting humidity as well as temperature, and a humidity sensor may be provided separately from the temperature sensor. In Figure 2, the rotation direction of the pressure roller 42 and fixing belt 43, and the transport direction of the paper P are indicated by arrows.

[0027] Figure 3 is a front view of a pressure changing device 50 provided in the fixing device 40. The pressure changing device 50 adjusts the roller pressure of the pressure roller 42 toward the fixing roller 41. The pressure changing device 50 includes a first pressure lever 52 that can contact the pressure roller 42 by receiving a biasing force from a first biasing member 51, and a second pressure lever 54 that contacts the pressure roller 42 by receiving a biasing force from a second biasing member 53 having a smaller biasing force than the first biasing member 51. The second biasing member 53 is spanned between the levers 52 and 54. By rotating the eccentric cam 56, the first pressure lever 52 is rotated, thereby changing the biasing force from the biasing members 51 and 53 and changing the roller pressure. The rotation position of the eccentric cam 56 is defined according to the thickness of the material to be printed, and the device is configured to obtain the optimal roller pressure.

[0028] Figure 4 is a system block diagram showing the control configuration of the image forming apparatus 10. The control unit 90 controls the entire image forming apparatus 10. The control unit 90 realizes various functions by reading and executing various programs stored in the storage unit 92 (for example, storage or ROM). The control unit 90 may be realized by one or more control devices / arithmetic units [CPU (Central Processing Unit), SoC (System on a Chip)]. The control unit 90 may also be composed of one or more control circuits. The control unit 90 has a processing unit 91 consisting of a microcomputer such as a CPU, and a storage unit 92 including non-volatile memory such as ROM and volatile memory such as RAM. The control unit 90 controls the operation of various components by having the processing unit 91 load control programs pre-stored in the ROM of the storage unit 92 onto the RAM of the storage unit 92 and execute them.

[0029] The operation display unit 25 receives user operation instructions (operation data) and outputs the received operation instructions to the control unit 90. The operation display unit 25 also displays various information based on the display information (display data) output from the control unit 90.

[0030] <First Embodiment> The control unit 90 controls the heat source 45 and the pressure changing device 50. In this example, the control unit 90 includes a pressure changing control unit Q1 that controls the pressure changing device 50 (i.e., the pressure applied by the pressure roller 42 to the fixing roller 41) and a heat source heat quantity changing control unit Q2 that controls the amount of heat supplied by the heat source 45. This allows the control unit 90 to perform fixing condition change control. When the surrounding environment of the image forming apparatus 10 is such that the paper P curls when it passes through the fixing nip N, the control unit 90 can suppress the curling of the paper P by performing fixing condition change control.

[0031] As part of this fixing condition change control, the control unit 90 changes the pressure applied by the pressure roller 42 (pressure member) to the fixing roller 41 (nip forming member) from a first pressure, which is applied when the ambient humidity of the image forming apparatus 10 is below the standard humidity, to a second pressure, which is lower than that. At the same time, it increases the amount of heat supplied by the heat source 45 to be greater than the amount of heat supplied when the ambient humidity is below the standard humidity. By executing this control, the pressure applied to the paper P at the fixing nip N can be reduced, and consequently, curling of the paper P can be suppressed.

[0032] On the other hand, in this control, the amount of heat supplied by the heat source 45 is increased to fix the toner to the paper P, thereby raising the fixing temperature. Therefore, it is desirable to avoid executing this control as much as possible when the paper P does not curl or when the curling is not a problem. By doing so, it is possible to avoid thermal damage to the components of the fixing device 20 as much as possible, thereby extending the lifespan of those components, and to save energy in the image forming apparatus 10.

[0033] Incidentally, in image forming apparatus equipped with a fixing device, when paper with a high moisture content is used for printing, the degree of curl that occurs when passing through the fixing nip tends to be greater. The moisture content of the paper is influenced by the humidity of the environment in which the paper is placed.

[0034] Furthermore, the deterioration of paper stackability becomes apparent when printing on long sheets of paper along the transport direction to the fuser. This is because longer sheets require more movement within the output tray, making it easier for problems such as paper falling out of the output tray to occur, even with minimal curling. The deterioration of stackability due to paper length becomes particularly noticeable when ambient humidity exceeds a certain threshold. Hereafter, this threshold will be referred to as the first threshold.

[0035] In addition, when performing double-sided printing on paper, the paper may curl during the printing of the first side. This curled paper is then transported within the image forming apparatus for printing the second side, which can cause paper jams (JAM) during transport. The occurrence of JAM during double-sided printing becomes more pronounced when the ambient humidity exceeds a certain threshold. Hereafter, this threshold will be referred to as the second threshold.

[0036] Therefore, it is possible to determine whether paper curling causes poor stacking performance or jamming by distinguishing between humidity conditions, where the ambient humidity of the image forming apparatus exceeds the standard humidity, and at least one of the paper length setting and double-sided printing setting conditions in the print job.

[0037] In other words, in this embodiment, the control unit 90, which receives a print job for image formation on one or more sheets of paper P, determines whether or not to perform fixing condition change control based on the humidity condition that the ambient humidity of the image forming apparatus 10 exceeds the standard humidity, and at least one of the setting conditions for the paper length setting and the double-sided printing setting in the print job. By making this determination, the control can be automatically performed in environments where fixing condition change control is necessary, and the control can be avoided as much as possible in environments where it is not necessary.

[0038] To enable determination based on the ambient humidity of the image forming apparatus 10, the image forming apparatus 10 is equipped with an environmental detection unit 60 (see Figure 4) that detects the surrounding environment of the image forming apparatus 10. Within the image forming apparatus 10, the environmental detection unit 60 is located away from heat-generating devices such as the fixing device 40 in order to detect the surrounding environment of the image forming apparatus 10.

[0039] The environmental detection unit 60 includes a humidity detection unit 61 that detects the ambient humidity He of the image forming apparatus 10. The control unit 90 determines, based on the detection result of the humidity detection unit 61, whether or not the humidity condition that the ambient humidity He exceeds the reference humidity is met. The reference humidity used for the determination is set in advance through experiments or the like and is stored in the storage unit 92.

[0040] In this example, the environmental detection unit 60 includes a temperature detection unit 62 that detects the ambient temperature Te of the image forming apparatus 10, in addition to the humidity detection unit 61. The control unit 90 includes an ambient humidity detection control unit Q3 that detects the ambient humidity He from the detection signal of the humidity detection unit 61, an ambient temperature detection control unit Q4 that detects the ambient temperature Te from the detection signal of the temperature detection unit 62, and a determination control unit Q7 that determines whether or not to execute fixing condition change control.

[0041] It is preferable that the control unit 90 determines whether or not to perform fixing condition change control based on the humidity condition that the ambient humidity He exceeds the reference humidity, and the setting conditions for both the paper length setting and the duplex printing setting. In this case, two reference humiditys are provided, specifically a first reference humidity related to the paper length setting and a second reference humidity related to the duplex printing setting. The first reference humidity is set based on a first threshold, and the second reference humidity is set based on a second threshold.

[0042] Table 1 below shows an example of whether or not the control unit 90 in the image forming apparatus 10 according to this embodiment performs fixing condition change control. In Table 1, "JAM present" means that the conditions are such that jams are likely to occur, and "stacking deterioration" means that the conditions are such that stacking performance is likely to deteriorate. In this example, the first reference humidity for paper length setting is 60%, and the second reference humidity for double-sided printing setting is 70%.

[0043] [Table 1]

[0044] If the condition falls under the category of "JAM present" or "Stacking deterioration" in Table 1, the determination control unit Q7 in the control unit 90 determines to execute fixing condition change control. If the condition falls under the category of "No problem" in Table 1, the determination control unit Q7 in the control unit 90 determines not to execute fixing condition change control.

[0045] Furthermore, when the paper is long (in this example, A3 paper), the problem of poor stacking in single-sided printing occurs at ambient humidity He, and this problem is also present in double-sided printing. Therefore, if the ambient humidity He exceeds the first reference humidity (60%), the control unit 90 can determine that it will execute fixing condition change control, regardless of whether it is single-sided or double-sided printing. An example of this determination process will be described later.

[0046] (Examples) Here, an embodiment of the image forming apparatus 10 that performs fixing condition change control according to the classification in Table 1 will be described. The fixing device 40 of the image forming apparatus 10 in this embodiment includes a fixing roller 41 with a diameter of 25 mm, a pressure roller 42 with a diameter of 20 mm, and a fixing belt 43 with a diameter of 40 mm. In the fixing device 40, the pressure roller 42 is pressed against the fixing roller 41 via the fixing belt 43, and the pressing part constitutes a fixing nip N that fixes the paper P. When the paper P passes through the fixing nip N (i.e., is fed through), the toner on the paper P is fixed by temperature and pressure. A fixing lamp, which is a heat source 45, is provided inside the heating roller 44. The control unit 90 controls the lighting of the fixing lamp so that the temperature of the fixing belt 43 is maintained at a predetermined fixing temperature. In this example, the control unit 90 also includes a fixing temperature detection control unit Q5 (see Figure 4) that detects the fixing temperature Tf from the detection signal of the fixing temperature detection unit 46. The effective length of the fixing roller 41, pressure roller 42, and heating roller 44, excluding the bearing portion, is 330 mm, and the length of the fixing belt 43 is 320 mm.

[0047] If the determination control unit Q7 in the control unit 90 determines that it will not perform fixing condition change control, image formation on the paper P is performed under the first fixing conditions, which are the normal fixing conditions. In this example, the first fixing conditions are: pressure from the pressure roller 42 (pressure at the fixing nip N) of approximately 343 N (35 kgf), fixing nip width at the fixing nip N of 7 mm, and temperature control temperature of the fixing belt 43 during paper feeding of 150°C.

[0048] If the determination control unit Q7 in the control unit 90 determines that it should perform fixing condition change control, image formation on the paper P is performed under second fixing conditions, which are different from the first fixing conditions. In this example, the second fixing conditions are a pressure of approximately 245 N (25 kgf) from the pressure roller 42 (pressure at the fixing nip N), a fixing nip width of 5 mm at the fixing nip N, and a temperature control temperature of 170°C for the fixing belt 43 during paper feeding.

[0049] Thus, in the image forming apparatus 10, as a fixing condition change control, the pressure from the pressure roller 42 is changed to a lower level than normal, and the temperature control temperature of the fixing belt 43 is changed to a higher level than normal (i.e., the amount of heat supplied by the heat source 45 is increased compared to normal). By changing from the first fixing condition to the second fixing condition, the fixing temperature is increased to compensate for the decrease in the fixing nip width, thereby bringing the amount of heat supplied to the toner closer to the normal amount. As the fixing nip width decreases, the amount of heat supplied to the paper P decreases, thus suppressing curling of the paper P. In other words, the fixing condition change control functions as a control to suppress curling of the paper P.

[0050] (Example of processing) Next, an example of the process for determining whether or not to execute fixing condition change control will be explained below with reference to Figure 5. Figure 5 is a flowchart showing an example of the process for determining whether or not to execute fixing condition change control. As mentioned above, the fixing condition change control in this disclosure functions as curl suppression control, so in this flowchart, fixing condition change control will be simply referred to as curl suppression control.

[0051] As shown in Figure 5, when the control unit 90 receives a print job to form an image on one or more sheets of paper P, it first determines whether the length of the paper P is equal to or greater than the standard length (300 mm in this example) (S1).

[0052] If the length of the paper P is determined to be greater than or equal to the standard length (S1: Yes), the control unit 90 determines whether the ambient humidity He exceeds the first standard humidity (60% in this example) (S2). If the ambient humidity He exceeds the first standard humidity (S2: Yes), the control unit 90 performs fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P using the second fixing condition (fixing condition different from the normal condition). If the ambient humidity He is less than or equal to the first standard humidity (S2: No), the control unit 90 does not perform fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P using the first fixing condition (normal fixing condition).

[0053] If it is determined that the length of the paper P is less than the standard length (S1: No), it is determined whether the ambient humidity He exceeds the first standard humidity (60% in this example) (S3). If it is determined that the ambient humidity He exceeds the first standard humidity (S3: Yes), the process proceeds to S4. If it is determined that the ambient humidity He is less than or equal to the first standard humidity (S3: No), the control unit 90 does not perform fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P under the first fixing conditions.

[0054] In S4 shown in Figure 5, it is determined whether the print job is single-sided or double-sided. If the print job is single-sided (S4: Yes), the control unit 90 does not perform fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P with the first fixing condition. If the print job is double-sided (S4: No), the process proceeds to S5.

[0055] In S5 shown in Figure 5, it is determined whether the ambient humidity He exceeds the second reference humidity (70% in this example). If it is determined that the ambient humidity He exceeds the second reference humidity (S5: Yes), the control unit 90 executes fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P under the second fixing conditions. If it is determined that the ambient humidity He is at or below the second reference humidity (S5: No), the control unit 90 does not execute fixing condition change control when forming the image on the paper P. That is, the image is formed on the paper P under the first fixing conditions.

[0056] According to the above example of a process for determining whether or not to execute the fixing condition change control, it is possible to make a determination according to the categories shown in Table 1.

[0057] <Second Embodiment> Incidentally, the curl of paper P is influenced by the moisture content of the paper; the higher the moisture content, the greater the degree of curl that tends to occur when passing through the fixing nip N. However, for paper P to contain enough moisture to curl, the ambient humidity He must remain high for a period of time.

[0058] In this embodiment, the control unit 90 determines that the humidity condition for determining whether or not to perform fixing condition change control is met when the ambient humidity He exceeds the reference humidity for a predetermined period of time.

[0059] This configuration prevents the fixing condition change control (i.e., curl suppression control) from being executed before the paper P absorbs moisture and becomes prone to curling. Consequently, it reduces the thermal damage suffered by the components of the fixing device 20, extending their lifespan, and also allows for energy savings in the image forming apparatus 10.

[0060] Using the processing example shown in Table 5, in S2 and S3, the system is configured to determine "Yes" if the ambient humidity He exceeds the first reference humidity (60% in this example) for a predetermined time (e.g., 12 hours). In addition, in S5, the system may be configured to determine "Yes" if the ambient humidity He exceeds the second reference humidity (70% in this example) for a predetermined time (e.g., 12 hours), or in S5, the system may be configured to determine "Yes" without the condition of a predetermined time. Furthermore, the predetermined time in S2 and S3 may be different from the predetermined time in S5.

[0061] <Third Embodiment> Figure 6 is a graph illustrating how the temperature difference between the fuser belt 43 and the pressure roller 42 increases over time during continuous printing. In Figure 6, Ta represents the temperature of the fuser belt 43, and Tb represents the temperature of the pressure roller 42.

[0062] The pressure roller 42 is heated by heat supplied from the fixing belt 43. However, when printing is performed continuously on multiple sheets of paper P (continuous paper feeding), the heat supply from the fixing belt 43 to the pressure roller 42 is interrupted by the paper P, causing the temperature of the pressure roller 42 to decrease over time. As a result, as shown in Figure 6, the temperature difference between the fixing belt 43 and the pressure roller 42 increases over time. When the temperature difference between the fixing belt 43 and the pressure roller 42 increases, one side of the paper P that has passed through the fixing nip N becomes hotter than the other side, increasing the uneven heating of the paper P and thus increasing the degree of curling of the paper P.

[0063] In this embodiment, when printing continuously on multiple sheets of paper P, the control unit 90 gradually reduces the pressure from the pressurizing member (pressure roller 42 in this example) and gradually increases the amount of heat supplied by the heat source 45 each time a predetermined number of sheets of paper pass through the fuser nip N.

[0064] With this configuration, the curl suppression effect in the fixing condition change control can be enhanced as the number of sheets continuously fed increases. In other words, even if the number of sheets continuously fed increases, curling of the paper P can be suppressed. Furthermore, when the number of sheets continuously fed is small, the amount of heat supplied by the heat source 45 can be kept low, thereby reducing the thermal damage to the components of the fixing device 20, extending the lifespan of those components, and saving energy in the image forming apparatus 10.

[0065] <Fourth Embodiment> Incidentally, when printing on both sides, curling of the paper P occurs during the printing of the first side. Therefore, if the curling of the paper P is suppressed during the printing of the first side, the aforementioned problems of poor stackability and jamming during the printing of the second side will not occur.

[0066] In this embodiment, when the control unit 90 determines that it should perform fixing condition change control for a print job that performs double-sided printing, it performs fixing condition change control when printing the first side of the double-sided print job, but does not perform fixing condition change control when printing the second side.

[0067] This configuration reduces the number of times the fixing condition change control is executed, thus reducing the number of times the amount of heat supplied by the heat source 45 is increased (i.e., the number of times the fixing temperature is raised). As a result, thermal damage to the components of the fixing device 20 is reduced, extending the lifespan of those components, and the image forming apparatus 10 becomes more energy-efficient.

[0068] <Fifth Embodiment> The image forming apparatus 10 according to this embodiment is equipped with a heater (cassette heater) for heating the paper P contained in the paper feed tray 16 (see Figure 1). In this example, the image forming apparatus 10 is also equipped with a paper feed tray heating detection unit 70 (see Figure 4) for detecting heating of the paper feed tray 16 (that the heater is turned on), and the control unit 90 is equipped with a paper feed tray heating detection control unit Q6 (see Figure 4) for detecting the detection signal from the paper feed tray heating detection unit 70.

[0069] This heater keeps the paper P stored in the paper tray 16 warm, preventing the paper P from absorbing moisture and releasing any moisture contained in the paper P. After heating by this heater begins, it takes a certain amount of time for enough moisture to be released from the paper P so that curling does not occur during printing.

[0070] In this embodiment, the control unit 90 does not perform fixing condition change control if a predetermined time has elapsed since heating by the heater started. This predetermined time can be, for example, 24 hours.

[0071] With this configuration, when the heater eliminates the need to suppress curling of the paper P, the fixing condition change control is not executed. This reduces the thermal damage to the components of the fixing device 20, extending their lifespan and saving energy for the image forming apparatus 10.

[0072] The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined by the claims. This includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0073] 10 Image forming apparatus 11 Image reading device 12 Document feeder 13 Image forming apparatus main unit 14 Image forming unit 15. Paper transport system 16 Paper feed tray 17 Manual feed tray 18 Paper output tray 19. Manuscript Stand 20a, 20b Conveyor rollers 21 Registroller 22 Primary Transfer Belt 23 Secondary transfer belt 24 Discharge roller section 25 Operation display section 30 Exposure apparatus 31 Developing device 32 Photoconductor Drum 33 Photoconductor Cleaner Section 34 Charger 35 Primary Transfer Belt Device 36 Toner cartridge device 40 Fixing device 41 Fixing roller (an example of a nip-forming member) 42 Pressure roller (an example of a pressure component) 43 Fixing belt 44 Heating rollers 45 Heat source 46 Fixing temperature detection unit 50 Pressure changing device 51 First biasing member 52. First pressurizing lever 53 Second biasing member 54. Second pressure lever 56 Eccentric cam 60 Environmental detection unit 61 Humidity detection unit 62 Temperature detection unit 70 Paper feed tray heating detection unit 90 Control Unit 91 Processing Unit 92 Memory section He ambient humidity Flexible ambient temperature Tf fixing temperature Q1 Pressure Change Control Unit Q2 Heat Source Heat Quantity Change Control Unit Q3 Ambient Humidity Detection and Control Unit Q4 Ambient Temperature Detection and Control Unit Q5 Fixing temperature detection control unit Q6 Paper feed tray heating detection control unit Q7 Judgment control section

Claims

1. Fixing belt and A nip-forming member is arranged on one side of the fixing belt, A pressure member presses the nip-forming member from the other side of the fixing belt to form a fixing nip between it and the fixing belt, thereby fixing an image onto the paper being transported to the fixing nip. A heat source for heating the fixing belt, An image forming apparatus having a fixing device that includes a pressure changing device for changing the pressure applied by the pressurizing member to the nip forming member, A humidity detection unit for detecting ambient humidity in the image forming apparatus, The system comprises one or more control units that control the heat source and the pressure changing device, The control unit, upon receiving a print job for image formation on one or more sheets of paper, determines whether or not to perform fixing condition change control based on the humidity condition that the ambient humidity exceeds the standard humidity and at least one of the paper length setting and double-sided printing setting conditions for the print job. The control unit is capable of performing control as fixing condition change control, which involves changing the pressure from the pressurizing member from a first pressure when the ambient humidity is below the standard humidity to a second pressure lower than that, and increasing the amount of heat supplied by the heat source to a value greater than the amount of heat when the ambient humidity is below the standard humidity.

2. An image forming apparatus according to claim 1, The image forming apparatus is characterized in that the control unit determines that the humidity condition is met when the ambient humidity exceeds the reference humidity for a predetermined period of time.

3. An image forming apparatus according to claim 1 or claim 2, The image forming apparatus is characterized in that, when printing continuously on multiple sheets of paper, the control unit gradually reduces the pressure from the pressurizing member and gradually increases the amount of heat supplied by the heat source each time a predetermined number of sheets of paper pass through the fixing nip.

4. An image forming apparatus according to claim 1 or claim 2, The image forming apparatus is characterized in that, when the control unit determines to perform the fixing condition change control for a double-sided printing job, it performs the fixing condition change control when printing the first side of the double-sided print job, but does not perform the fixing condition change control when printing the second side.

5. An image forming apparatus according to claim 1 or claim 2, A paper feed tray for containing the paper to be supplied to the fuser device, The system further comprises a heater for heating the paper contained in the paper feed tray, The image forming apparatus is characterized in that the control unit does not perform the fixing condition change control if a predetermined time has elapsed since heating by the heater started.

Images