JP2010032953A - Fixing device and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device for shortening a warm-up time when a fixing mode at the time of power-off or sleeping is a low pressure mode. <P>SOLUTION: The fixing device 22 includes: a heat roller (heating member) 24 and a pressure roller (pressing member) 25 which abut on each other; a heater (heating source) 28 for heating the heat roller 24; and an automatic switching mechanism for automatically switching the fixing mode between a high pressure mode where the fixing pressure is high and the low pressure mode where the fixing pressure is low, wherein when the fixing mode at the power-on or at the recovery from sleeping is the low pressure mode, an aging time for rotationally driving the heat roller 24 and the pressure roller 25 during the warm-up time until they become in a ready state capable of performing the fixing operation is set shorter than that at the high pressure mode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device including a mechanism for automatically switching a pressing force (fixing pressure) of a pressure member to a heating member, and an image forming apparatus including the fixing device.

  In an image forming apparatus such as a copying machine or a printer that forms an image on a sheet by electrophotography, the electrostatic latent image formed on the image carrier is developed by a developing device and visualized as a toner image. Transfer the image onto the paper. The sheet onto which the toner image has been transferred is conveyed to a fixing device, and after the toner image is fixed by heat and pressure by the fixing device, it is discharged out of the apparatus, thereby completing a series of image forming operations. .

  The fixing device includes a heating roller that is a heating member that rotates in contact with each other and a pressure roller that is a pressure member, and presses the pressure roller against the heating roller to fix a predetermined amount therebetween. The pressure (nip pressure) is ensured.

  For example, when an envelope is passed through such a fixing device, the envelope is manufactured by folding and bonding the paper, and this causes distortion when passing through the fixing nip between the heating roller and the pressure roller. It is easy to generate my own. For this reason, when feeding envelopes, it is common to reduce the fixing pressure as much as possible, and a fixing device with an automatic switching mechanism that automatically switches the fixing pressure according to the type of paper is proposed. (For example, see Patent Documents 1 and 2).

  By the way, since a very strong nip pressure is applied to the fixing portion of the fixing device, if the fixing device is left for a long time with this strong nip pressure applied, the rubber layer or sponge layer of the pressure roller becomes a nip shape. If the fixing is performed in this state, there is a problem that unevenness occurs in the fixing pressure and causes unevenness in the image.

However, even if the rubber layer or sponge layer of the pressure roller is deformed into a nip shape, if the aging of rotating the pressure roller together with the heating roller is performed, the rubber layer or the sponge layer is restored to the original by thermal expansion. It is known that the shape can be restored (for example, see Patent Documents 3 and 4).
JP 2001-166627 A Japanese Patent Laid-Open No. 7-225528 JP 11-119588 A JP 2003-122177 A

  Thus, if the fixing device is left for a long time with the power turned off, or if the sleep state in which the heater is turned off for a long period of time continues for a long time, if the aging time is increased during warm-up, image unevenness may occur. Although the problem is solved, there is a problem that the warm-up time until the ready state in which image formation is possible becomes long.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to provide a fixing device capable of shortening the warm-up time when the fixing mode at the time of power-off or sleep is the low-pressure mode, and the fixing device. An image forming apparatus is provided.

  In order to achieve the above object, the invention according to claim 1 is directed to a heating member and a pressure member that are in contact with each other, a heating source that heats the heating member, and a high-pressure mode with a high fixing pressure or a low fixing pressure. In a fixing device equipped with an automatic switching mechanism that automatically switches to the low pressure mode, the heating member and the pressure member can be fixed at the time of warm-up when the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode. The aging time for rotational driving until reaching a ready state is set shorter than that in the high pressure mode.

  According to a second aspect of the present invention, in the first aspect of the invention, when the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the heating source is turned on after the fixing mode is switched to the high pressure mode. The aging is performed when the heating member reaches a predetermined temperature.

  According to a third aspect of the present invention, in the first or second aspect of the invention, when the fixing mode at the time of turning on the power or returning from the sleep mode is unknown, the heating source is turned on after the fixing mode is switched to the high pressure mode. The aging is performed only for a set time in the high pressure mode.

  An image forming apparatus according to a fourth aspect includes the fixing device according to any one of the first to third aspects.

  According to the first aspect of the present invention, when the fixing mode at the time of power OFF or sleep is the low pressure mode, the rubber layer or sponge layer of the pressure member that has been deformed is returned to the original shape. Since the aging time is set to be shorter than the aging time in the high pressure mode, the warm-up time until Ready that enables image formation is shortened, and the convenience for the user is enhanced.

  According to the second aspect of the present invention, when the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the fixing mode is switched to the high pressure mode, and the heater is pressed in the state where the pressure member is strongly pressed against the heating member. ON, and after the heating member reaches a predetermined temperature, the heating member and the pressure member are rotationally driven to perform the aging to remove the deformation of the pressure member. The original shape is reliably restored, and fixing pressure unevenness and image unevenness associated therewith are prevented.

  According to the third aspect of the present invention, it is a case where the power is turned off during the switching of the fixing mode, and whether the fixing mode before turning on the power or returning from the sleep mode is the high pressure mode or the low pressure mode. If it is unknown, the heating source is turned on after switching the fixing mode to the high pressure mode, and for safety, aging is performed only for a long setting time in the high pressure mode, so even before turning on the power or returning to sleep Even if the previous fixing mode is a high pressure mode and the rubber layer or sponge layer of the pressure member is greatly deformed, the rubber layer of the pressure member is formed by aging for a time sufficient to remove the deformation. Alternatively, the sponge layer can be completely restored to the original shape, and a high-quality image without image unevenness can be stably obtained.

  According to the fourth aspect of the invention, it is possible to stably obtain a high-quality image without image unevenness while shortening the warm-up time.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a cross-sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a perspective view of the color laser printer with an open / close cover opened.

  The color laser printer according to the present embodiment is a tandem type, and as shown in FIG. 1, a magenta image forming unit 1M, a cyan image forming unit 1C, and a yellow image forming unit 1Y are arranged at the center of the main body 100. The black image forming units 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, and charging rollers 3a, 3b, 3c, and 3d are disposed around the photosensitive drums 2a to 2d. 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (clockwise) by a variable speed stepping motor (not shown). The charging rollers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  The transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d via the intermediate transfer belt 7 in the respective primary transfer portions. Here, the intermediate transfer belt 7 is stretched between the secondary transfer counter roller 8 and the tension roller 9 and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. The roller 8 is disposed so as to be in contact with the secondary transfer roller 10 via the intermediate transfer belt 7 in the secondary transfer portion. A belt cleaning device 11 is provided in the vicinity of the tension roller 9.

  Incidentally, toner containers 12a, 12b, 12c, and 12d for supplying toner to the developing devices 4a to 4d are arranged in a line above the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100. It is installed.

  In addition, a laser scanner unit (LSU) 13 is disposed below the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, and a paper feed cassette 14 is detachably attached to the bottom of the main body 100 below the image forming units. is set up. A plurality of sheets (not shown) are stacked and accommodated in the paper feed cassette 14, and a pickup roller 15 for taking out the paper one by one from the paper feed cassette 14 is taken out in the vicinity of the paper feed cassette 14. A feed roller 16 and a retard roller 17 are provided for feeding the fed paper to the transport path L.

Further, the conveyance path L extending in the vertical direction on the side of the apparatus main body 100 includes a conveyance roller pair 18 that conveys the sheet, and the secondary transfer counter roller 8 and the second transfer opposing roller 8 at a predetermined timing after the sheet is temporarily held. A registration roller pair 19 is provided to be supplied to a secondary transfer portion which is a contact portion with the next transfer roller 10. Next to the transport path L, another transport path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of transport roller pairs 20 are appropriately used in the transport path L ′. Are provided at regular intervals.
By the way, the conveyance path L disposed in the vertical direction on one side portion in the apparatus main body 100 extends to the paper discharge tray 21 provided on the upper surface of the apparatus main body 100, and the fixing device 22 and the discharge path are disposed in the middle. A paper roller pair 23 is provided. As shown in FIG. 2, an opening / closing cover (front cover) 101 that can be opened and closed is provided on the front surface of the main body 100. When a sheet jams in the fixing device 22 or the like, the opening / closing cover 101 is provided. Is opened as shown in the figure and processing such as removing jammed paper is performed.

  Next, an image forming operation by the color laser printer having the above configuration will be described with reference to FIG.

  When an image formation start signal is issued, the photosensitive drums 2a to 2d are driven to rotate at a predetermined process speed in the direction of the arrow in FIG. 1 (clockwise) in each of the image forming units 1M, 1C, 1Y, and 1K. The drums 2a to 2d are uniformly charged by the charging rollers 3a to 3d. The laser scanner unit 13 emits a laser beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d with the laser beam, and each color is applied to each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to the color image signal is formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is transferred to the arrow shown in FIG. 1 by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied at the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 which is rotationally driven in the direction.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  Then, the pickup from the paper feed cassette 14 is performed in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 8 and the secondary transfer roller 10. The sheet fed to the conveyance path L by the roller 15, the feed roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 19. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 22, and the sheet on which the full-color toner image has been fixed by being heated and pressurized and thermally fixed on the surface of the sheet. Then, the paper is discharged onto the paper discharge tray 21 by the paper discharge roller pair 23 to complete a series of image forming operations. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 11, and the intermediate transfer belt 7 is prepared for the next image formation.

[Fixing device]
Next, details of the fixing device 22 according to the present invention will be described with reference to FIGS.

  3 is a cross-sectional view of the fixing device portion of the color laser printer (part A enlarged view of FIG. 1), FIG. 4 is a perspective view of the fixing device, and FIG. 6 is a sectional view showing a state when the fixing pressure of the identification fixing device is released, FIG. 7 is a sectional view showing a state when the fixing pressure of the identification fixing device is reduced, and FIG. FIG. 9 is a side view showing the positional relationship between the actuator and the PI sensor when the fixing pressure is reduced.

  As shown in FIG. 3, the fixing device 22 includes a heating roller 24 that is a heating member that rotates in contact with each other, a pressure roller 25 that is a pressure member, and a tension roller 26 that is disposed below the pressure roller 25. The heating roller 24, the pressure roller 25, and the tension roller 26 are arranged so as to be parallel and rotatable along the direction perpendicular to the paper surface of FIG. An endless fixing belt 27 is wound between the pressure roller 25 and the tension roller 26. The pressure roller 25 is connected to the heating roller 24 via the fixing belt 27 by a pressure mechanism described later. By being pressed, a fixing nip having a predetermined pressure (fixing pressure) is formed between the rollers 24 and 25.

  Two heaters 28 as upper and lower heaters are passed through the hollow heating roller 24, and a thermistor 29 for detecting the surface temperature of the heating roller 24 is provided on the outer periphery of the heating roller 24. Is provided. In addition to the heater 28, IH or the like can be used as a heating source.

  Thus, as described above, the sheet on which the full-color toner image is secondarily transferred collectively from the intermediate transfer belt 7 by the secondary transfer roller 10 is conveyed to the fixing device 22, and the fixing device 22 is heated. A full-color toner image is fixed by being heated and pressed in the process of being sandwiched and conveyed by a fixing nip between the roller 24 and the pressure roller 25. Then, the sheet on which the toner image is fixed is discharged to the discharge tray 21 by the discharge roller pair 23.

  By the way, in the fixing device 22 according to the present embodiment, the fixing mode is automatically switched to the high pressure mode in which the fixing pressure (the pressure applied to the heating roller 24 of the pressure roller 25) is high or the low pressure mode in which the fixing pressure is low. A switching mechanism is provided. The configuration of this automatic switching mechanism will be described below.

  That is, a pair of left and right pressure levers 31 are rotatably supported at both ends in the axial direction of the rotation shaft 30 of the pressure roller 25. As shown in FIGS. Is formed with a claw 31a, and the claw 31a is engaged with a hole formed in a body frame (not shown). Therefore, if each pressure lever 31 is rotated about the claw 31a, the pressure roller 25 is also rotated about the claw 31a together with the rotary shaft 30, and each pressure lever 31 is moved to the timepiece of FIGS. By rotating in the direction, the pressure roller 25 is pressed against the heating roller 24 via the fixing belt 27, and a fixing nip having a predetermined pressure is formed between the rollers 24 and 25.

  In addition, an engagement groove 31b is formed at the other end (tip) of each pressure lever 31, and a pair of left and right pressure plates 32 bent in an L shape in side view are engaged with the engagement groove 31b. Match. That is, as shown in FIG. 4, each pressurizing plate 32 is formed with a rectangular engagement hole 32a that is long in the vertical direction, and the tip of each pressurization lever 31 is passed through the engagement hole 32a. The engagement groove 31 b formed at the tip end portion is engaged with the engagement hole 32 a of the pressure plate 32.

  On the other hand, as shown in FIG. 4, in the vicinity of the pair of left and right pressure levers 31, the left and right rotating around the shaft 33 in conjunction with the opening / closing operation of the opening / closing cover 101 (see FIGS. 1 and 2). A pair of opening / closing levers 34 is provided on the main body frame side, and one end of each opening / closing lever 34 is connected to the upper end of the rod 35. Here, the pair of left and right rods 35 penetrates the pressure plate 32 and extends downwardly. A pressure spring 36 is interposed between the opening / closing lever 34 on the outer periphery of each rod 35 and the pressure plate 32.

  As shown in FIG. 4, a shaft 37 is disposed in the vicinity of the tension roller 26 so as to be rotatable along the axial direction of the tension roller 26 and the pressure roller 25. A pair of left and right cams 38 are attached. Each cam 38 is divided into left and right across the rod 35.

  Each of the cams 38 rotates when the fixing mode is switched to the low pressure mode, abuts against the pressure plate 32 as shown in FIG. 7, and pushes up the pressure plate 32 to pressurize as will be described later. This is for reducing the pressure (fixing pressure) applied to the pressure roller 25 by the spring 36. A gear G1 and a plate-like actuator 39 are connected to one end of the shaft 37.

  Further, as shown in FIG. 4, a DC motor 40 is vertically arranged on the side where the gear G1 is provided, and a pinion G2 attached to the output shaft of the DC motor 40 is a gear train G. And is connected to the gear G1. Therefore, when the DC motor 40 is driven, the rotation of the output shaft is transmitted to the shaft 37 while being decelerated through the pinion G2, the gear train G, and the gear G1, and the pair of left and right attached to the shaft 37 is connected to the shaft 37. The cam 38 and the actuator 39 are simultaneously rotated.

  Further, as shown in FIGS. 4, 8 and 9, near the actuator 39, the position of the cam 38, specifically, the position where the applied pressure of the pressure roller 25 is reduced in the low pressure mode is optically arranged. A PI sensor 41 is arranged for detection.

  When plain paper is passed through the fixing device 22 configured as described above, the high pressure mode is selected as the fixing mode and the fixing pressure is set high.

  That is, when the fixing mode opening / closing cover 101 is closed as shown in FIG. 1, as shown in FIG. 5, the opening / closing lever 34 is rotated by the opening / closing cover 101 in the direction of the arrow a about the shaft 33 as shown in FIG. In order to push down 35, the pressure spring 36 interposed between the opening / closing lever 34 and the pressure plate 32 is pressed and contracted, and the reaction force (spring force) F is applied to the pressure lever 31 via the pressure plate 32. Then, the tip of the pressure lever 31 is pushed down by the reaction force F of the pressure spring 36. Therefore, the pressure lever 31 rotates about the claw 31a in the clockwise direction in FIG. 5 to press the pressure roller 25 to the heating roller 24 via the fixing belt 27, and thereby the pressure roller 25 and the heating roller 25 are heated. A fixing nip having a predetermined pressure is formed between the rollers 24, and the plain paper passes through the fixing nip, whereby the toner image is heated and pressurized to be fixed on the plain paper (high pressure mode). In this high pressure mode, the actuator 39 stands as shown in FIG. 8, and the light from the light emitting portion to the light receiving portion of the PI sensor 41 is not blocked by the actuator 39. Therefore, the PI sensor 41 is in the fixing mode. Detect that is in high pressure mode.

  Then, for example, when the opening / closing cover 101 is opened as shown in FIG. 2 because a jam has occurred in the fixing device 22, the restriction of the opening / closing lever 34 by the opening / closing cover 101 is released, and the pressure spring 36 extends to a free length. As shown in FIG. 6, the open / close lever 34 rotates in the direction of arrow b about the shaft 33. For this reason, the reaction force F that has been pushing down the pressure plate 32 by the pressure spring 36 until now becomes 0, and therefore the pressure applied by the pressure roller 25 becomes 0 and the fixing pressure is released (fixing pressure released state). The jammed paper that has been held in the fixing nip between the pressure roller 25 and the fixing roller 24 can be easily removed.

  By the way, when a thick paper such as an envelope is passed while the image forming operation is performed with the open / close cover 101 closed, the fixing mode is switched from the high pressure mode to the low pressure mode by a signal to that effect, and the DC motor 40 is turned on. As described above, the rotation of the drive motor 40 is transmitted to the shaft 37, and the shaft 37 and the pair of left and right cams 38 and the actuator 39 are rotated.

  When the cam 38 rotates as described above, as shown in FIG. 7, the cam 38 comes into contact with the pressure plate 32 and pushes it up, so that the reaction force of the pressure spring 36 increases, but the pressure plate Since 32 moves upward with respect to the pressure lever 31, the pressing force F ′ of the pressure lever 31 by the pressure plate 32 becomes small (F ′ <F), and as a result, the pressure roller by the pressure lever 31. The pressing force on the pressure roller 25 is weakened, the pressure applied by the pressure roller 25 is reduced, and problems such as wrinkling of thick paper such as an envelope passing through the fixing nip do not occur.

  As described above, when the fixing mode is switched to the low pressure mode and the cam 38 rotates to reduce the pressure (fixing pressure) of the pressure roller 25, as shown in FIG. Since the moving actuator 39 blocks the light traveling from the light emitting portion to the light receiving portion of the PI sensor 41, the PI sensor 41 detects the position of the cam 38 where the pressure applied by the pressure roller 25 is reduced, thereby fixing the user. You can see that the mode is in low pressure mode. When the PI sensor 41 detects the position of the cam 38 at which the pressure applied by the pressure roller 25 is reduced, the DC motor 40 is reversely rotated for a predetermined time from that point, and the shaft 37, the cam 38, and the actuator 39 are reversed. The pressure roller 25 is returned to the pressure state as shown in FIG.

  By the way, when the fixing mode of the fixing device 22 is particularly the high pressure mode, the pressure roller 25 is pressed against the heating roller 24 with a very strong force, and thus the fixing device 22 is applied with this strong force. When the power is turned off for a long time or the sleep time for turning off the heater 28 for power saving becomes longer, the rubber layer or sponge layer of the pressure roller 25 is deformed into a nip shape, and this state As described above, there is a problem in that when fixing is performed, unevenness occurs in the fixing pressure, leading to image unevenness.

  However, even if the rubber layer or sponge layer is deformed into a nip shape, the pressure roller 25 is rotated again and thermally expanded, so that the rubber layer or sponge layer returns to its original shape. In addition, aging for rotating the heating roller 24 and the pressure roller 25 is performed during warm-up when the sleep state is canceled (sleep return) and the heater 28 is turned on. In this case, when the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the pressure applied to the pressure roller 24 is weak, so even if the aging time is shortened, the pressure roller 25 The rubber layer or sponge layer can return to its original shape.

  Therefore, in the fixing device 22 according to the present embodiment, when the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the Ready state in which the heating roller 24 and the pressure roller 25 can be fixed at the warm-up time. The aging time for rotational driving until it is reached is set shorter than that in the high pressure mode, so that the warm-up time is shortened.

  By the way, when the power is turned off while the fixing mode is being switched, it is unclear whether the fixing mode at the time of turning on the power or returning from the sleep mode is the high pressure mode or the low pressure mode. In order to set the initial position, the fixing mode is set to the high-pressure mode, and for safety, the aging time is set to be longer than the value in the high-pressure mode.

  The above control will be described below based on the flowchart shown in FIG.

  When the power is turned off or the heater 28 is turned off and then the power is turned on after the sleep state continues or the sleep state is released (sleep return) (step S1), the fixing mode at that time is the high pressure mode. Is determined (step S2). When the fixing mode is the high pressure mode (when the determination result in step S2 is Yes), the heater 28 is turned on and warm-up is started (step S3).

  On the other hand, when the fixing mode is not the high pressure mode (when the determination result of step S2 is No), that is, when the fixing mode is the low pressure mode or when the power is turned off during the switching of the fixing mode. If it is unclear whether the fixing mode before turning on the power or returning from the sleep mode is the high pressure mode or the low pressure mode, the fixing mode is switched to the high pressure mode and the fixing pressure is increased (step S4). ), The heater 28 is turned on and the warm-up is started (step S3).

  The warm-up is continued until the heating roller 24 reaches a predetermined fixing temperature (repeat from step S3 to step S5). When the heating roller 24 reaches a predetermined fixing temperature, the fixing mode at the time of turning on the power or returning from sleep is low. If the fixing mode is other than the low pressure mode (if the high pressure mode or the fixing mode is unknown and the determination result in Step S6 is No), it is determined whether or not the mode is the mode (step S6). Aging for rotationally driving the heating roller 24 and the pressure roller 25 is performed for a predetermined time T1 (step S7), and the rubber layer or sponge layer of the pressure roller 24 that has been deformed when stopped is returned to its original shape.

  On the other hand, when the fixing mode is the low pressure mode when the power is turned on or when returning from the sleep mode, the nip pressure applied to the pressure roller 25 at the time of stop is weak, and the rubber layer or sponge layer of the pressure roller 25 is weak. Since the amount of deformation is small, the aging time for rotationally driving the heating roller 24 and the pressure roller 25 is set to a time T2 (<T1) shorter than the time T1 in the high pressure mode, and the heating roller 24 and the pressing roller 25 are added for the time T2. Aging is performed by rotating the pressure roller 25, and the rubber layer or sponge layer of the pressure roller 25 is returned to its original shape (step S8).

  When aging is performed as described above and the rubber layer or sponge layer of the pressure roller 25 returns to its original shape, it is displayed that the ready state is ready for fixing (step S9).

  As described above, in the present embodiment, when the fixing mode at the time of power OFF or sleep is the low pressure mode, the rubber layer or sponge layer of the pressure roller 25 that has been deformed is returned to its original shape. For this reason, the aging time T2 is set to be shorter than the aging time T1 in the high pressure mode, so that the warm-up time until Ready to enable image formation is shortened and the convenience for the user is enhanced.

  In this embodiment, when the fixing mode at the time of turning on the power or returning from the sleep mode is other than the high pressure mode (when the low pressure mode or the fixing mode is unknown), the fixing mode is switched to the high pressure mode and pressurization is performed. The heater 28 is turned on while the roller 25 is strongly pressed against the heating roller 24, and after the heating roller 24 reaches a predetermined fixing temperature, the heating roller 24 and the pressure roller 25 are rotationally driven to remove the deformation of the pressure roller 25. Since the aging is performed, the rubber layer or the sponge layer of the pressure roller 25 is reliably returned to the original shape by aging, and the unevenness of the fixing pressure and the accompanying image unevenness are prevented.

  In this embodiment, the power is turned off during the switching of the fixing mode, and it is unknown whether the fixing mode before turning on the power or returning from the sleep mode was the high pressure mode or the low pressure mode. In some cases, the heater 28 is turned on after the fixing mode is switched to the high pressure mode, and the aging is performed only for the set time T1 in the high pressure mode for safety, so even before the power is turned on or before returning from the sleep mode. Even if the fixing mode is the high pressure mode and the rubber layer or sponge layer of the pressure roller 25 is largely deformed, the rubber of the pressure roller 25 is aged by performing aging for a time T1 necessary and sufficient to remove the deformation. The layer or the sponge layer can be completely returned to the original shape, and a high-quality image without image unevenness can be stably obtained.

  In the above embodiment, the fixing device in which the fixing belt is interposed between the heating roller as the heating member and the pressure roller as the pressure member has been described. However, the roller type in which the heating roller and the pressure roller are in direct contact with each other. The present invention can also be applied to a fixing device of this type or a belt-type fixing device in which either one of a heating member and a pressure member is a belt. In addition, the present invention can be similarly applied to any other image forming apparatus including a monochrome image forming apparatus of a single color other than a color laser printer and a fixing device provided therefor.

1 is a cross-sectional view of a color laser printer according to the present invention. FIG. 3 is a perspective view of the color laser printer according to the present invention with an open / close cover opened. FIG. 2 is a cross-sectional view of the fixing device portion of the color laser printer according to the present invention (enlarged detail view of part A in FIG. 1). 1 is a perspective view of a fixing device according to the present invention. FIG. 3 is a cross-sectional view illustrating a state of the fixing device according to the present invention during normal pressure application. FIG. 3 is a cross-sectional view showing a state when the fixing pressure is released by the fixing device according to the present invention. FIG. 3 is a cross-sectional view showing a state when the fixing pressure of the fixing device according to the present invention is reduced. FIG. 5 is a side view showing a positional relationship between an actuator and a PI sensor during normal pressurization in the fixing device according to the present invention. FIG. 4 is a side view showing a positional relationship between an actuator and a PI sensor when fixing pressure is reduced in the fixing device according to the present invention. 3 is a flowchart showing a control procedure of the fixing device according to the present invention.

Explanation of symbols

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a-2d Photosensitive drum 3a-3d Charging roller 4a-4d Developing device 5a-5d Transfer roller 6a-6d Drum cleaning device 7 Intermediate transfer belt 8 Secondary transfer counter roller 9 Tension roller 10 Secondary transfer roller 11 Belt cleaning device 12a to 12d Toner container 13 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Pickup roller 16 Feed roller 17 Retard roller 18 Conveyance roller pair 19 Registration roller pair 20 Conveyance roller pair 21 Paper discharge tray 22 Fixing device 23 Paper discharge roller pair 24 Heating roller (heating member)
25 Pressure roller (Pressure member)
26 Tension roller 27 Fixing belt 28 Heater (heating source)
29 Thermistor 30 Pressure roller rotating shaft 31 Pressure lever 31a Pressure lever claw 31b Pressure lever engagement groove 32 Pressure plate 32a Pressure plate engagement hole 33 Opening / closing lever shaft 34 Opening / closing lever 35 Rod 36 Pressure spring 37 Shaft 38 Cam 39 Actuator 40 DC motor 41 PI sensor 42 Handle 43 Switch 100 Image forming apparatus body 101 Opening / closing cover G Gear train G1 Gear G2 Pinion L, L 'Conveyance path

Claims (4)

A fixing device having a heating member and a pressure member that are in contact with each other, a heating source that heats the heating member, and an automatic switching mechanism that automatically switches the fixing mode to a high pressure mode with a high fixing pressure or a low pressure mode with a low fixing pressure. In
When the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the aging time during which the heating member and the pressure member are rotationally driven until the ready state capable of fixing at the warm-up time is set in the high pressure mode. A fixing device characterized by being set shorter than that.   When the fixing mode at the time of turning on the power or returning from the sleep mode is the low pressure mode, the heating source is turned on after switching the fixing mode to the high pressure mode, and the aging is performed when the heating member reaches a predetermined temperature. The fixing device according to claim 1, wherein:   If the fixing mode at power-on or sleep recovery is unknown, the heating source is turned on after switching the fixing mode to the high-pressure mode, and the aging is performed for a set time in the high-pressure mode. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1.

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