Patent Application
20110236083
The present invention relates to a fixing apparatus employable by an image forming apparatus, such as a copying machine, a laser beam printer, a facsimile machine, a multifunction image forming apparatus, etc., to fix a toner image. A multifunction image forming apparatus is an image forming apparatus capable of performing a combination of the functions of the preceding examples of an image forming apparatus, etc. A fixing apparatus is used, as necessary, with an image formation process, such as an electrophotographic process, an electrostatic recording process, a magnetic recording process, etc., in which an unfixed toner image, which is in accordance with the formation of an image to be formed, is formed on a sheet of recording medium, through direct or indirect transfer, with the use of toner made up of thermally meltable resin, etc. More specifically, a fixing apparatus is an apparatus for permanently fixing an unfixed toner image on a sheet of recording medium to the sheet of recording medium by heating the unfixed toner image. The recording medium usable with a fixing apparatus is recording paper, printing paper, transfer sheet, OHT sheet, glossy paper, glossy film, electro-facsimile paper, electrostatic recording paper, etc.
Generally, an image forming apparatus has such a fixing apparatus that uses heat and pressure to fix an unfixed toner image on a sheet of recording medium to the sheet. Generally, a fixing apparatus such as the one described above has a fixation roller and a pressure roller, which form a fixation nip by being pressured upon each other. In operation, it feeds a sheet of recording medium, on which an unfixed toner image is present, into the fixation nip, and conveys the sheet through the fixation nip while applying heat and pressure to the sheet of recording medium and the toner image thereon, so that the unfixed toner image becomes fixed to the sheet of recording medium.
A fixing apparatus, such as the one described above, suffers from the following phenomenon (problem): As a fixing apparatus is continuously used for image formation for a substantial length of time, some of the toner particles of which the toner image on the sheet of recording medium is made up of, transfer onto the peripheral surface of the fixation roller and remain adhered thereto. This phenomenon is caused by the deterioration of the properties of the peripheral surface of the fixation roller, static electricity, and/or excessiveness or insufficiency in the amount by which heat is given to the sheet of recording medium from the fixation roller. This phenomenon is likely to occur when the temperature of the fixation roller is significantly higher or lower than the proper level. Further, the amount by which toner is transferred onto the fixation roller is greater when the temperature of the fixation roller is significantly higher or lower. The toner particles having adhered to the peripheral surface of the fixation roller contaminate the recording medium by transferring back onto the recording medium in the fixation nip.
Thus, in order to prevent the above described contamination of the recording medium, a fixing apparatus is provided with a web-based cleaning apparatus for removing the toner particles on the peripheral surface of the fixation roller, by rubbing the peripheral surface of the fixation roller with its cleaning web.
However, as the amount of the recovered (collected) toner (amount of toner on peripheral surface of fixation roller 131) increases because of the continuation of an image forming operation, the cleaning surface of the cleaning web 140 becomes contaminated, gradually reducing the cleaning apparatus in performance in terms of the recovery of the toner from the fixation roller 131 to the cleaning web 140. Eventually, the contamination of recording medium occurs.
Recently, as one of the means for solving this problem, a cleaning apparatus which feeds the cleaning nip N with an unused portion of the cleaning web 140, with a preset timing, for example, for every preset length of fixation time, has come to be known (Japanese Laid-open Patent Application H11-24484). In the case of this cleaning apparatus, in order to feed its fixation nip N with an unused portion of its cleaning web 140, the take-up roller 141 is rotated by a preset amount (angle) with preset timing, based on such information as cumulative print count, cumulative number of revolution of the fixation roller, or the like.
If an anomaly, such as paper jam, occurs, a large amount of toner sometimes transfers onto the peripheral surface of the fixation roller 131, which results in the intrusion of a large amount of toner into the cleaning nip N. In such a case, the problem that the fixation roller 131 fails to be properly cleaned, and/or abnormal noises are caused by the “slip-and-stick” between the fixation roller 131 and cleaning web 40. As for the countermeasure for this problem, there has been known a cleaning apparatus which is controlled in such a manner that if an anomaly such as paper jam is detected, an unused portion of the cleaning web is fed into the cleaning nip N by a length longer than the normal length by which it is fed when an on-going image forming operation is normal, in anticipation of the contamination of the peripheral surface of the fixation roller 131 by a greater amount.
The art described in Japanese Laid-open Patent Application H11-24484 is about a predicative control for taking up the cleaning web for every preset length of fixation time. Therefore, a cleaning web is conveyed by a preset length even if the amount by which toner is recovered in the cleaning nip N is small, and therefore, the cleaning surface of the cleaning web is not contaminated much. Therefore, a cleaning web roll has to be increased in the length of cleaning web in order to ensure that the fixation roller is satisfactorily cleaned for a long time before the cleaning apparatus has to be supplied with a fresh cleaning web roll. In other words, the art in the aforementioned patent document is problematic in that it requires for a fixing apparatus to be large in size, which results in cost increase.
Further, it is a common practice to require a user to select a printing mode based on paper type, so that the temperature of the fixation roller is set to a level which is optimum for the proper fixation of a toner image to recording medium (selected paper). However, this set-up creates the following problem. That is, if the user selected a wrong print mode, that is, a mode which should not be selected (this selection will be referred to as mode selection error), the temperature of the fixation roller is sometimes set to a level which is seriously higher or lower than the proper level. For example, if an image formed on a sheet of cardboard is fixed in the normal mode for ordinary paper, the amount by which heat is supplied to the recording medium (cardboard) is insufficient, possibly causing a large amount of toner to be transferred from the recording medium onto the peripheral surface of the fixation roller (cold offset). On the contrary, if an image is printed on a sheet of ordinary paper in the cardboard mode, the amount by which heat is supplied to the recording medium (ordinary paper) from the fixing apparatus is excessive, possibly causing a large amount of toner to be transferred onto the fixation roller (hot offset). In the abovementioned cases, it is liable that a large amount of toner having transferred onto the peripheral surface of the fixation roller enters the cleaning nip N.
In the case of the mode selection error described above, however, it is unlikely for an anomaly of this type to be detected, and therefore, the cleaning nip N is not fed with an unused portion of the cleaning web as it is if the mode selection error is not made. Therefore, it occurs sometimes that the fixation roller is poorly cleaned, and/or abnormal noises are generated by the “slip-and-stick” between the peripheral surface of the fixation roller and the cleaning web. Further, in some cases, the fixing apparatus is subjected to an excessive amount of internal stress, which results in the damages to the components, such as a motor, cleaning web, etc., of the fixing apparatus.
Thus, the primary object of the present invention is to provide a fixing apparatus which takes up the cleaning web by the length proportional to the amount of the contamination of the peripheral surface of the fixation roller.
According to an aspect of the present invention, there is provided a fixing apparatus for fixing a toner image formed on a recording material, said fixing apparatus comprising a rotatable member; a cleaning unit for cleaning said rotatable member, said cleaning unit including a cleaning fabric for cleaning said rotatable member, a feeding roller on which said cleaning fabric is wound, and a winding-up roller for winding up said cleaning fabric fed from said feeding roller; and a load applying mechanism for applying a retarding force against a winding-up operation of said winding-up roller such that when a frictional force between said rotatable member and said cleaning fabric which is in a standstill state and which is in contact with said rotatable member which is rotating exceeds the retarding force of said load applying mechanism, said winding-up roller rotates to wind up said cleaning fabric.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
Hereinafter, the preferred embodiments of the present invention are described in detail with reference to the appended drawings. Incidentally, the dimensions and materials of the structural components of the image forming apparatus, and the positional relationship among the structural components, in the following preferred embodiments of the present invention, are not intended to limit the present invention in scope, unless specifically noted.
First, referring to
Each image forming portion forms an electrostatic latent image with the use of a beam of exposure light which is turned on and off with intervals which correspond to the length of the exposure time obtained by the image processing portion which converts the image formation data into image formation signals. Then, it forms a monochromatic image of toner by developing the electrostatic latent image. Monochromatic images, different in color, made of toner (which hereafter is referred to simply as toner image), are layered in alignment, effecting thereby a multicolor toner image (unfixed). The unfixed multicolor toner image is transferred onto a sheet of recording medium. Then, the unfixed multicolor toner image on the sheet of recording medium is fixed. The operation of each image forming portion is controlled by a CPU 200. Photosensitive drums 22Y, 22M, 22C, and 22K, which are photosensitive members are in the stations for forming yellow (Y), magenta (M), cyan (C), and black (K) monochromatic images, respectively. Each of the photosensitive drums 22Y, 22M, 22C, and 22K is made of an aluminum cylinder, and an organic photoconductive layer coated on the peripheral surface of the cylinder. It is rotated in the counterclockwise direction by the force transmitted to the drum 22 from an unshown motor, in synchronism with the progression of an image forming operation.
The four image forming stations are provided with four charging devices 23Y, 23M, 23C, and 23K, respectively, which are first charging means. The four charging devices 23Y, 23M, 23C, and 23K have charging sleeves 23YS, 23MS, 23CS, and 23KS, respectively, which charge the photosensitive drums 22Y, 22M, 22C, and 22K, respectively.
After the charging of the photosensitive drums 22Y, 22M, 22C, and 22K by the corresponding charging devices, one for one, four beams of exposure light are sent to them from four scanners 24Y, 24M, 24C, and 24K, respectively, selectively exposing the points (pixels) of the charged peripheral surface of each photosensitive drum 22. Consequently, an electrostatic latent image is effected on the peripheral surface of each photosensitive drum 22.
The four image forming stations are also provided with four developing devices 26Y, 26M, 26C, and 26K for developing the four electrostatic latent images, one for one, with the use of four toners, one for one, different in color. The four developing devices 26Y, 26M, 26C, and 26K have four sleeves 26YS, 26MS, 26CS, and 26KS, respectively. The normal polarity to which the four toners used in this embodiment become charged is negative. Between the sleeves 26YS, 26MS, 26CS, and 26KS, and photosensitive drums 22Y, 22M, 22C, and 22K, respectively, development bias is applied from an unshown electric power source. By this development bias, four monochromatic toners, different in color, are supplied from the developing devices onto the corresponding photosensitive drums, forming thereby four monochromatic toner images on the four photosensitive drums 22, one for one. The four developing devices 26 are independently and removably mountable in the image forming apparatus.
During the formation of a color image forming operation, the intermediary transferring member 28 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and is rotated in the clockwise direction, at the same velocity as the peripheral velocity of each photosensitive drum 22, so that the monochromatic toner images are transferred onto the intermediary transfer member 28. More concretely, the first transfer bias is applied between the first transfer rollers 27Y, 27M, 27C, and 27K, and corresponding photosensitive drums 22Y, 22M, 22C, and 22K, respectively. Thus, the four monochromatic toner images, different in color, are transferred from the intermediary transfer member 28 by the first transfer bias, in such a manner that the four monochromatic toner images, different in color, are sequentially layered on the intermediary transfer member 28 in alignment with each other. Consequently, a multicolor toner image is formed on the intermediary transfer member 28.
The sheet feeding portion, which is a sheet feeding means, has a sheet feeder cassette 21a and a sheet feeder tray 21b. The sheet feeding portion holds multiple sheets 11 of recording medium in layers. The multiple sheets 11 of recording medium are fed one by one into the main assembly of the image forming apparatus by a pair of sheet feeder rollers 20a and 20b, and sent to a pair of registration rollers 16. As each sheet 11 of recording medium reaches the pair of registration rollers 16, its arrival at the rollers 16 is detected by a sensor 17 which is on the upstream side of the rollers 16 in terms of the sheet conveyance direction. During an image forming operation, as the sheet 11 arrives at the registration rollers 16, it is held there for a preset length of time by the rollers 16, and then, is released by the rollers 16 with such a timing that the sheet 11 will arrive at a second transfer roller 29 at the same time as the arrival of the multicolor toner image at the second transfer roller 29.
The second transfer roller 29 is in contact with the intermediary transfer member 28. As the sheet 11 of recording medium arrives at the roller 29, the roller 29 transfers the multicolor toner image from the intermediary transfer member 28 onto the sheet 11 of recording medium while conveying the sheet 11 by keeping the sheet 11 pinched between itself and intermediary transfer member 28. Then, the sheet 11 is sent from the second transfer roller 29 to the fixing apparatus 30 which is an image heating apparatus. While the second transfer roller 29 is transferring the multicolor toner image onto the sheet 11 of recording medium, it is kept in the position 29a in which it pressed on the sheet 11. However, as soon as the image forming operation ends, the second transfer roller 29 is moved back to the position 29b where the second transfer roller 29 is kept separated from the intermediary transfer member 28. Further, during an image forming operation, the second transfer bias is applied between the second transfer roller 29 and intermediary transfer member 28 from an unshown electric power source. It is by the second transfer bias that the multicolor toner image is transferred from the intermediary transfer member 28 onto the sheet 11 of recording medium.
The fixing apparatus 30 is an apparatus that fixes the unfixed multicolor toner image on the sheet 11 of recording medium to the sheet 11 by melting the multicolor toner image with the application of heat thereto, while conveying the sheet 11 through the fixing apparatus 30. It is made up of a pair of sheet conveying rollers, that is, a fixation roller 31 and a pressure roller 32. The pressure roller 32 is kept pressed upon the fixation roller 31. The sheet 11 of recording medium on which the unfixed multicolor toner image is present is conveyed through the fixation nip which the fixation roller 31 and pressure roller 32 form. As it is conveyed through the fixation nip, heat and pressure are applied to the sheet 11 and the multicolor toner image thereon, whereby the multicolor toner image is fixed to the surface of the sheet 11. Then, the sheet 11 is conveyed to a pair of discharge rollers 61. The contaminants on the peripheral surface of the fixation roller 31 are removed by the web-based cleaning apparatus 34.
The structure of the fixing apparatus 30 is described later.
The discharge rollers 61 discharge the sheet 11 of recording medium into an unshown delivery tray, and the image forming portions end the above described image formation sequence.
The recording medium sheet conveyance speed in this embodiment is 40 mm/sec.
a) is a sectional view of the fixing apparatus in this embodiment, and shows the basic structure of the apparatus. The fixation roller 31 is made up of a substrate 31a, an elastic layer 31b, and a surface layer 31c. The substrate 31a is metallic, and is the core of the fixation roller 31. It is a hollow iron cylinder, and is 1.5 mm in wall thickness. The elastic layer 31b is a silicon rubber layer, and covers virtually the entirety of the peripheral surface of the metallic (iron) core 31a. It is 2 mm in thickness. The surface layer 31c, which is a parting layer, is made of fluorinated resin. It covers the entirety of the peripheral surface of the elastic layer 31b. It is 50 μm in thickness. The external diameter of the fixation roller 31 is 35 mm. One of the end portions of the metallic core 31a is fitted with a gear (unshown), through which the force for rotating the fixation roller 31 is transmitted to the fixation roller 31 from a fixation roller driving motor 50 as the fixation roller driving means. The fixation roller 31 is rotated by this force. The basic structure of the pressure roller 32 is the same as that of the fixation roller 31. That is, the pressure roller 32 is made up of a substrate 32a, an elastic layer 32b, and a surface layer 32c. The substrate 32a is metallic, and is the core of the pressure roller 32. It is a hollow iron cylinder and is 1.5 mm in thickness. The elastic layer 32b is a silicon rubber layer, and covers virtually the entirety of the peripheral surface of the metallic (iron) core 32a. It is 2 mm in wall thickness. The surface layer 32c, which is a parting layer, is made of fluorinated resin. It covers the entirety of the peripheral surface of the elastic layer 32b. It is 50 μm in thickness. The external diameter of the pressure roller 32 is 35 mm, which is the same as that of the fixation roller 31. The pressure roller 32 is kept pressed upon the fixation roller 31 by roughly 400 N of pressure generated by a combination of unshown springs and supporting members, forming thereby a heating nip NF between its peripheral surface and the peripheral surface of the fixation roller 31. The heating nip NF is for fixing the multicolor toner image on the sheet 11 of recording medium, to the surface of the sheet 11 by melting the image with the application of heat.
A halogen heater 33 is the heat source for heating the fixation roller 31, and is in the hollow of the fixation roller 31. The surface temperature of the fixation roller 31 is detected by a thermopile 73, which is a noncontact temperature detecting means, and is positioned so that it faces the peripheral surface of the fixation roller 31. The detected surface temperature of the fixation roller 31, which is in the form of an analogue signal, is converted into a digital signal by the CPU 200 (A/D conversion). The CPU 200 keeps the surface temperature of the fixation roller 31 at a preset level by controlling (turning on or off) an electric power circuit 201, which is the means for supplying the halogen heater 33 with electric power, based on the detected surface temperature of the fixation roller 31.
Next, the web-based cleaning unit 34, which is the cleaning apparatus in this embodiment, is described. A cleaning web 40, which is the cleaning cloth, is an unwoven cloth made of aramid fiber. The cleaning web 40 is kept stretched between a supply roller 41 and a take-up roller 42, and is kept pressed upon the peripheral surface of the fixation roller 31 by 4.9 N of pressure applied by the take-up roller 42 by which the cleaning web 40 is taken up. The cleaning web 40 removes the contaminants on the peripheral surface of the fixation roller 31, by its portion which is kept pressed upon the peripheral surface of the fixation roller 31 by the take-up roller 42. Hereafter, the area of contact between the fixation roller 31 and cleaning web 40 is referred to as a cleaning nip NCL. That is, the portion of the cleaning web 40, which is in the cleaning nip NCL, provides the cleaning apparatus with the cleaning surface, which faces the peripheral surface of the fixation roller 31. In this embodiment, the dimension of the cleaning nip NCL in terms of the rotational direction of the fixation roller 31 is 2.0 mm. That is, the cleaning web 40 cleans the peripheral surface of the peripheral surface of the fixation roller 31 (which is one of the pair of recording medium sheet conveyance rollers), by wiping the peripheral surface of the fixation roller 31 with its cleaning surface, that is, the portion of the cleaning web 40, which is in the cleaning nip NCL.
The cleaning web 40 in this embodiment is moved by the friction between itself and the peripheral surface of the fixation roller 31, which increases as the amount of the toner on its cleaning surface increases. Thus, as the cleaning surface of the cleaning web 40, which is in the cleaning nip NCL, becomes significantly contaminated, it is replaced by the immediately upstream portion of the cleaning web 40 in terms of the rotational direction of the fixation roller 31. The cleaning apparatus 34 in this embodiment is structured so that the take-up roller 42 is kept pressed against the fixation roller 31, with the presence of the cleaning surface of the cleaning web 40 between the take-up roller 42 and fixation roller 31, and takes up the cleaning web 40 as the portion of the cleaning web 40, which is in the cleaning nip NCL, is moved out of the cleaning nip NCL by the interaction between the rotation of the fixation roller 31 and the friction between the cleaning web 40 and peripheral surface of the fixation roller 31. More specifically, as the amount of the toner on the cleaning surface exceeds a certain value, the portion of the cleaning web 40, which is in the cleaning nip NCL, is moved downstream out of the cleaning nip NCL by the rotation of the fixation roller 31. As the portion of the cleaning web 40, which is in the cleaning nip NCL is moved out of the cleaning nip NCL, the take-up roller 42 rotates in the direction to take up the cleaning web 40. Further, as the cleaning web 40 is moved by being pulled by the rotation of the fixation roller 31, the supply roller 41 rotates by being pulled by the cleaning web 40. In other words, the portion of the cleaning web 40, which is on the supply roller 41, is unrolled from the supply roller 41 while allowing its portion in the cleaning nip NCL to be moved out downward from the cleaning nip NCL. The supply roller 41 and take-up roller 42 are 8 mm in external diameter. The width (dimension in terms of direction perpendicular to recording medium conveyance direction) is 224 mm. The take-up roller 42 is placed in contact with, or separated from, the fixation roller 31 with a preset timing by an unshown take-up roller moving mechanism.
In this embodiment, the web-based cleaning apparatus 34 is positioned so that it is placed in contact with the fixation roller 31. However, the web-based cleaning apparatus 34 may be positioned so that it is placed in contact with the pressure roller 32 as shown in
Further, the load applying rotational member has two pieces 110a and 110b of silicon rubber, which are 1 mm in thickness. The silicon rubber piece 110a is between one of the lengthwise ends of the compression spring 80 and the corresponding end surface of the take-up roller 42, and is solidly glued to the lengthwise end surface of the take-up roller 42. The silicon rubber piece 110b is between the other end of the compression spring 80 and the side plate 90, and is solidly glued to the side plate 90.
Therefore, the torque (rotational force) with which the shaft 42a of the take-up roller 42 is provided, and works in the direction to make the take-up roller 42 take up the cleaning web 40, is subjected to the friction generated between the silicone rubber piece 110a and the end surface of the take-up roller 42 by the resiliency of the compression spring 80, and the friction generated between the silicone rubber piece 110b and the side plate 90 also by the resiliency of the compression spring 80. Thus, as the fixation roller 31 rotates, the friction is generated between the two silicone rubber pieces 110a and 110b and corresponding surfaces. This friction functions as the load which is against the friction which is generated between the cleaning surface and the peripheral surface of the fixation roller 31 and increases as the amount of toner on the cleaning surface increases. Thus, when the torque with which the shaft 42a of the take-up roller 42 is provided by the friction between the cleaning surface of the cleaning web 40 and the peripheral surface of the fixation roller 31 is no more than roughly 0.04 N·m (no more than threshold value), the take-up roller 42 is prevented from rotating; the take-up roller 42 rotates only when the torque of the shaft 42a is no less than 0.4 N·m. The torque of the shaft 42a of the take-up roller 42, which is roughly 0.04 N·m, corresponds to the threshold value preset for the friction between the peripheral surface of the fixation roller 31 and the cleaning surface, which increases with the increases in the amount of toner on the cleaning surface of the cleaning web 40. Therefore, when the torque of the shaft 42a of the take-up roller 42 is no more than roughly 0.04 N·m, the take-up roller 42 is prevented by the friction generated by the silicone rubber pieces 110a and 110b from rotating. However, as the torque of the shaft 42a of the take-up roller 42 becomes no less than roughly 0.04 N·m, becoming therefore greater than the friction generated by the silicone rubber pieces 110a and 110b, the take-up roller 42 rotates.
As described above, the cleaning unit in this embodiment has the load applying mechanism (80, 110a, and 110b) which functions as a brake for regulating the rotation of the take-up roller 42 for taking up the cleaning web 40 (cleaning cloth). That is, as the friction between the peripheral surface of the rotational member 31, and the portion of the cleaning web 40 (cleaning cloth), which is remaining stationary in the cleaning nip NCL, becomes greater than the friction (retarding or braking force) generated by the load applying mechanism, the take-up roller 42 is rotated by the friction between the peripheral surface of the fixation roller 31 and the cleaning surface, in the direction to take up the cleaning web 40 (cleaning cloth).
In
As the amount of torque applied to the shaft 42a of the take-up roller 42 became no less than roughly 0.06 N·m, the “slip-and-slick” occurred between the fixation roller 31 and the cleaning web 40, which sometimes resulted in the generation of such abnormal noises that were in 100-200 Hz in frequency, and/or unsatisfactory cleaning of the fixation roller 31 attributable to the reduction of the toner recovery capacity of the portion of the cleaning web 40 in the cleaning nip NCL. As the amount of the toner applied to the shaft 42a of the take-up roller 42 was increased by the further increase of the amount of the recovered toner on the portion of the cleaning web 40 in the cleaning nip NCL, the components of the fixing member were subjected to an excessive amount of stress; in some cases, the components of the fixing member were damaged.
b) shows the relationship between the amount of the recovered toner on the portion of the cleaning web 40 in the cleaning nip NCL, and the amount of the torque applied to the shaft 42a of the take-up roller 42, when the take-up roller 42 was not kept absolutely stationary. As the amount of the recovered toner on the portion of the cleaning web 40 in the cleaning nip NCL increased, the amount of the friction between the cleaning web 40 and the peripheral surface of the fixation roller 31 in the cleaning nip NCL also increased. However, as the amount of the torque exceeded 0.04 N·m, the take-up roller 42 rotated in such a direction that its peripheral surface moved in the same direction in which the peripheral surface of the fixation roller 31 moved, whereby a fresh portion of the cleaning web 40 was moved into the cleaning nip NCL, reducing thereby the friction between the cleaning surface of the cleaning web 40 and the peripheral surface of the fixation roller 31. Thus, the amount of the torque applied to the shaft 42a of the take-up roller 42 reduced, preventing thereby the aforementioned problem that abnormal noises were generated by the “slip-and-stick” attributable to the increase in the amount of the friction between the cleaning web 40 and fixation roller 31; the fixation roller 31 fails to be properly cleaned; and/or the components of the fixing member were damaged. Further, as the cleaning nip NCL was supplied with a fresh portion of the cleaning web 40, the amount of the torque applied to the shaft 42a of the take-up roller 42 reduced, and therefore, the take-up roller 42 did not rotate. Thus, it did not occur that the cleaning nip NCL is unnecessary supplied with a fresh portion of the cleaning web 40.
As described above, in this embodiment, as the torque of the shaft 42a of the take-up roller 42, which is related to the amount of the recovered toner, exceeds a preset amount, that is, roughly 0.04 N·m, the cleaning nip NCL is supplied with a fresh portion of the cleaning web 40, by rotating the take-up roller 42 in such a direction that its peripheral surface moves in the same direction as the peripheral surface of the fixation roller 31 moves. Because of this structural arrangement, when the amount of the recovered toner is small, the take-up roller 42 is not rotated, and therefore, the cleaning nip NCL is not supplied with a fresh portion of the cleaning web 40. In other words, the employment of this embodiment of the present invention can reduce the amount of the cleaning web consumption. That is, it can significantly reduce the initial amount (length) by which the supplied roller 41 needs to be supplied with the cleaning web 40, compared to any of fixing apparatuses in accordance with the prior art, which is controlled in such a manner that the cleaning nip NCL is predicatively supplied with a preset amount (length) of cleaning web 40 per preset length of fixation time. Therefore, it can reduce a fixing apparatus in size and cost.
Next, a case in which a user selected a wrong recording medium mode is described. It is assumed here that the user selected the mode for ordinary paper when the mode for cardboard should have been selected. In such a case, the amount by which heat is supplied to the sheet 11 of recording medium is insufficient for cardboard, and therefore, a large amount of toner adheres (offsets from sheet 11 of recording medium) to the peripheral surface of the fixation roller 31, and reaches the cleaning nip NCL. In the case of a fixing apparatus controlled so that its cleaning nip NCL is fed with a preset length of cleaning web 40 per preset length of fixation time, the friction between the cleaning web 40 and the peripheral surface of the fixation roller 31 in the cleaning nip NCL increases, increasing thereby the amount of the torque to which the shaft 42a of the take-up roller 42 is subjected. The conventional fixing apparatus, however, does not have a means for detecting the increase of the torque of the shaft 42a. Therefore, the problems that the fixation roller 31 failed to be properly cleaned; abnormal noises are generated by the “slip-and-stick”; and/or the components of the fixing apparatus are damaged, sometimes occurred.
In the case of the fixing apparatus in this embodiment, as the torque to which the shaft 42a of the take-up roller 42 is subjected is increased by the friction between the cleaning web 40 and the peripheral surface of the fixation roller 31 is increased by the recovered toner (toner wiped away from peripheral surface of fixation roller 31 by cleaning web 40) in the cleaning nip NCL, the take-up roller 42 is automatically rotated in such a direction that its peripheral surface moves in the same direction as the direction in which the peripheral surface of the fixation roller 31 moves, and the cleaning nip NCL is supplied with a fresh portion of the cleaning web 40, preventing thereby the torque from increasing further. Therefore, the problems that the fixation roller 31 fails to be properly cleaned; abnormal noises are generated by the “slip-and-stick”; and/or components of the fixing apparatus are damaged, is unlikely to occur.
In this embodiment, a torque limiter is employed as a load applying member. Otherwise, the structure of the fixing apparatus in this embodiment is the same as that in the first embodiment, and therefore, is not described. Referring to
In this embodiment, the employment of the above described torque limiter makes it possible to more precisely regulate the torque for rotating take-up roller 42 than in the first embodiment. Therefore, this embodiment is superior to the first embodiment in terms of the effectiveness and preciseness with which the torque can be regulated.
Incidentally, in the preceding preferred embodiments of the present invention, the shaft 42a of the take-up roller 42 was provided with the mechanical load applying member. However, the preceding embodiments are not intended to limit the present invention in scope. That is, it may be to any rotational shaft of the fixing apparatus that the mechanical load applying member is attached, as long as the shaft is in connection to the shaft 42a of the take-up roller 42, that is, the shaft to which the torque generated by the friction between the cleaning web and the peripheral surface of the fixation roller (or pressure roller) is to be transmitted. That is, regardless of which of the rotational shafts of the fixing apparatus is provided with the mechanical load applying member, the effects of the present invention remain the same as those obtained by the preceding embodiments.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 075765/2010 filed Mar. 29, 2010 which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-075765 | Mar 2010 | JP | national |
