Patent Grant
7238924
The present invention relates to an image heating apparatus for heating an image on recording medium. As an example of such an image heating apparatus, a fixing apparatus for fixing an unfixed image formed on recording medium, an apparatus for increasing in glossiness a fixed image on recording medium, by heating the image, etc., can be listed.
An electrophotographic copying machine, or the like, in accordance with the prior art is provided with a heating apparatus, which is for heating an unfixed image (image formed of toner) on recording medium (unfixed image having been transferred onto recording medium while recording medium is conveyed) so that the toner (developer) of which the unfixed image is formed is fused to recording medium by being thermally melted.
As for the type of such a heating apparatus, there have been known: a heating apparatus, the fixation roller, as a heating medium, of which has been reduced in wall thickness and diameter for faster temperature increase; a heating apparatus comprising a rotatable resin film, and a heating member placed in contact with the rotatable film from inside the loop of the rotatable film with the application of a predetermined amount of pressure; a heating apparatus comprising a rotatable metallic member with a thin wall, which can be heat by electromagnetic induction; etc. These heating apparatuses are characterized in that each of them is designed to minimize its rotatable member as a heating medium in thermal capacity and to heat the rotatable member with the use of a heat source higher in thermal efficiency. There are also heating apparatuses employing a heat source of the noncontact type. However, in the field of an image forming apparatus such as a copying machine, a heating apparatus of the type which thermally melts the developer on recording medium by placing a rotatable member with a thin wall, with the recording medium, has been proposed by a greater number than a heating apparatus employing a heat source of the noncontact type, from the standpoint of cost and energy efficiency.
However, if a rotatable member as a heating medium is reduced in wall thickness to reduce it in thermal capacity, it is also reduced in the size of the sectional area perpendicular to its axial line, being thereby reduced in the thermal transfer rate, in terms of the axial direction of the rotatable member, and the thinner the wall of a rotatable member, the more conspicuous this reduction in thermal transfer rate. Further, in the case of a rotatable member formed of resin or the like which is lower in coefficient of thermal conductivity, this characteristic is even more conspicuous.
When the coefficient of thermal conductivity of an object is λ; the difference in temperature between the two points of the object is (θ1−θ2); and the distance between the two points is L, the amount Q by which heat is transferred per unit of time between two points of the object is expressed by the following equation, which is obvious from Fourier s law:
Q=λùf(θ1−θ2)/L.
The above described characteristic does not causes any problem when an image to be fixed is borne on a recording medium of the largest size usable with a heating apparatus, that is, the recording medium on which the image to be fixed is borne is a widest recording medium, in terms of the lengthwise direction of the rotatable member, usable with the heating apparatus. However, when multiple recording mediums smaller in width in terms of the lengthwise direction of the rotatable member than the largest recording medium are used, the following problem occurs. That is, the temperature of the rotatable member increases above the target temperature (proper temperature for fixation) across the portions outside the path of the recording medium with the smaller width, in terms of the lengthwise direction of the rotatable member. As a result, the difference in temperature between the portion of the rotatable member within the path of the recording mediums of the smaller width and the portions of the rotatable member outside the path of the recording mediums with the smaller width becomes extremely large.
Since the components in the adjacencies of the heating medium are usually formed of resinous materials, there is a possibility that their service lives will be reduced in terms of heat resistance, and/or they will be thermally damaged, by this nonuniformity in the temperature of the heating medium in terms of its lengthwise direction. Moreover, there is the problem that as a recording medium of the larger size is conveyed through a heating apparatus immediately after multiple recording mediums of the smaller size are continuously conveyed through the heating apparatus, it is possible that the recording medium of the large size will be wrinkled and/or skewed, and/or the image on the recording medium will be nonuniformly fixed, by the nonuniformity in temperature across the parts of the heating medium. The difference in temperature between the portion of the heating medium within the path of a recording medium and the portion(s) of the heating medium outside the path of a recording medium is roughly proportional to the thermal capacity of a recording medium to be conveyed through a heating apparatus, and also, to the throughput (number of prints outputted per unit of time) of each job. Therefore, a heating apparatus, the heating medium of which is a rotatable member with a thin wall and is low in thermal capacity, has been difficult to satisfactorily use as the fixing apparatus for a copying machine or the like which is high in throughput.
As a means for solving the above described problem, there has been known a heating apparatus employing multiple halogen lamps or heat generating resistors, as heat sources, so that the portions of the heating medium can be selectively supplied with electric power according to the width of a recording medium to be conveyed through the heating apparatus.
Admittedly, there have been heating apparatuses which employ multiple heat sources comprising an induction coil so that the heat sources can be selectively supplied with electric power to solve the above described problem. However, providing a heating apparatus with multiple heat sources or dividing the heat source of a heating apparatus into multiple sections makes the control circuit of the heating apparatus more complicated and higher in cost. Moreover, the attempt to match the number of heat sources to the number of the types of the recording mediums (media) usable with a heating apparatus (image forming apparatus) and different in width, requires the heating apparatus to be further increased in the number of the heat sources, or the number of the sections into which the heat source of a heating apparatus is to be subdivided, further increasing the heating apparatus in cost. In addition, there is another problem in the case of a heating apparatus, the heating medium of which is a rotatable member with a thin wall. That is, the heat source becomes discontinuous and nonuniform in temperature distribution, across the joints between the subsections of the heat source, which will possibly affect the performance of a heating apparatus in terms of image fixation.
Thus, it has been proposed to provide a heating apparatus based on electromagnetic induction with a magnetic flux blocking means for partially blocking the magnetic flux directed toward the heating medium from the means for electromagnetically heating the heating medium, and a means for changing in position the magnetic flux blocking means (for example, Japanese Laid-open Patent Application 2004-265670). According to this proposal (invention), the portions of the magnetic flux, which are directed toward the portions of the heating medium, which do not need to be heated, are blocked by moving the magnetic flux blocking means. Therefore, heat is not generated in the portions of the heating medium, which do not need to be heated; in other words, the heating medium is controlled in terms of where in the heating medium heat is to be generated, being therefore controlled in terms of the heat distribution thereof. The heating apparatus (fixing apparatus) disclosed in Japanese Laid-open Patent Application 2004-265670 is structured so that its magnetic flux blocking plate can be rotated in the hollow of its fixation roller, having therefore the merit of being smaller in the dimension in terms of the lengthwise direction of the apparatus, compared to a heating apparatus (fixing apparatus) structured so that its magnetic flux blocking plate is moved in the direction parallel to the lengthwise direction its heat roller, for example.
According to Patent Document 1, the temperature increase, which occurs across the portions of the heating medium outside the path of a recording medium of a medium or small size, that is, the size smaller than the size of the largest recording medium conveyable through the heating apparatus (image forming apparatus), is dealt with by employing a magnetic flux blocking plate, the magnetic flux blocking portions of which are matched in size with the recording medium of the medium or small size. However, the market offers too many kinds of recording mediums in terms of size, making it difficult to deal with the above described problem by adjusting the magnetic flux according to each of the various recording medium sizes. It is possible to give the actual adjusting portion of a magnetic flux adjusting means a stepless shape. However, enabling the magnetic flux adjusting portions to adjust the magnetic flux according to all of the various recording medium sizes makes it necessary to reduce each of the magnetic flux adjusting portions of the magnetic flux adjusting member, which correspond one for one to the various recording medium sizes, in the dimension in terms of the circumferential direction of the rotatable heating medium, which creates the following problem. That is, even if the magnetic flux adjusting member is moved into the exact position to deal with multiple recording mediums of a given size in order to partially block the magnetic flux, the magnetic flux adjusting portions are too narrow, in terms of the circumferential direction of the rotatable heating medium, to fully shield the portions of the heating medium outside the path of the recording medium of the given size, from the magnetic flux. Therefore, eddy current is induced in the portions of the heating medium outside the coverage by the magnetic flux adjusting portions, in terms of the circumferential direction of the heating medium, and generates heat in the portions of the heating medium. Consequently, the portions of the rotatable heating medium outside the recording medium path are excessively increased in temperature by the heat generated therein.
On the other hand, if a magnetic flux adjusting member designed to accommodate a few of the representative sizes among various recording medium sizes is employed to prevent the temperature increase outside the recording medium path, the portions of the heating medium outside the recording medium path increases in temperature, and/or the heating medium becomes nonuniform across the portion to be used for heating the recording medium being conveyed, when the actual magnetic flux adjusting portions of the magnetic flux adjusting member do not match in size the recording medium being conveyed. More specifically, with the employment of the above described magnetic flux adjusting member, as the magnetic flux adjusting member is moved into the magnetic flux adjusting position when none of the actual magnetic flux adjusting portions of the magnetic flux adjusting member perfectly matches the size of the recording medium used currently for image formation, the magnetic flux adjusting member overlaps with the edge portions of a recording medium being conveyed. Thus, the portions of the heating medium, which correspond in position to the areas in which the magnetic flux adjusting member is overlapping with the recording medium, is robbed of heat each time a recording medium is conveyed through the heating apparatus, even though no heat is generated therein. As a result, these portions of the heating medium fall in temperature. It is possible to reposition the magnetic flux adjusting member so that the actual magnetic flux adjusting portions of the magnetic flux adjusting member, which is one size (step) smaller in terms of the amount by which the magnetic flux is adjusted, than the portions which overlap with the recording medium, blocks the magnetic flux, the excessive temperature increase occurs across the portions of the heating medium outside the recording medium path.
It is also possible to extend the recording medium conveyance interval between a transfer medium and the immediately following transfer medium, according to the size of the following transfer medium, in order to wait until the heating medium becomes normal in temperature level and temperature distribution. However, the employment of this method makes an image forming apparatus very inconvenient to use; for example, it makes the cumulative intervals substantially long when a set of originals are different in size.
Thus, the primary object of the present invention is to prevent, or reduce in extent, the temperature increase which occurs across the portions of a heating medium outside the recording medium path, even when none of the magnetic flux adjusting portions of the magnetic flux adjusting member match in size the recording medium being conveyed through a heating apparatus.
Another object of the present invention is to provide a magnetic flux adjusting means capable of reducing the nonuniformity in the temperature of a heating medium, which is caused by the continuous conveyance of multiple recording mediums different in size, even when none of the magnetic flux adjusting portions of a magnetic flux adjusting member match in size the recording medium being conveyed through a heating apparatus.
One of the typical image heating apparatuses structured in accordance with the present invention for accomplishing the above described object is characterized in that it comprises: a rotatable heating member for heating an image on recording medium, in the heating nip; a magnetic flux generating means for generating a magnetic flux for heating the rotatable heating member by electromagnetic induction; and a magnetic flux controlling means movable into the magnetic flux controlling position in order to control the magnetic flux directed toward the rotatable heating member from the magnetic flux generating means, and that when multiple recording mediums, the width of which is such that the recording mediums partially overlap with the magnetic flux controlling portions of the magnetic flux controlling means, are continuously conveyed through the image heating apparatus, the magnetic flux controlling means is alternately moved into the magnetic flux controlling position and the retreat position, that is, the position in which the magnetic flux controlling means does not control the magnetic flux, during the heating of the heating member (during image heating operation).
Another of the typical image heating apparatuses in accordance with the present invention for accomplishing the above described objects is characterized in that it comprises: a rotatable heating member for heating an image on recording medium, in the heating nip; a magnetic flux generating means for generating a magnetic flux for heating the rotatable heating member by electromagnetic induction; and a magnetic flux controlling means for controlling the magnetic flux directed toward the rotatable heating member from the magnetic flux generating means, and that the magnetic flux controlling means is provided with a first magnetic flux controlling portions for controlling, in the first controlling position, the magnetic flux directed toward the first portions of the rotatable heating member, and a second magnetic flux controlling portions for controlling, in the second position, the magnetic flux direction toward the second portions of the rotatable heating member, which include the first portions of the rotatable heating member and are greater in dimension in terms of the lengthwise direction of the heating member, and when multiple recording mediums, the width of which is such that the recording mediums partially overlap with the portion of each of the second controlling portions, which is outside the first controlling portion, are continuously conveyed through the image heating apparatus, the magnetic flux controlling means is alternately moved into the first magnetic flux controlling position and the second magnetic controlling position, during the heating of the heating member (during image heating operation).
According to an aspect of the present invention, there is provided an image heating apparatus comprising a heating rotatable member for heating an image on a recording material in a heating nip; magnetic flux generating means for generating a magnetic flux for induction heat generation in said heating rotatable member; magnetic flux confining means for confining the magnetic flux directed toward a predetermined region of said heating rotatable member from said magnetic flux generating means; and moving means for repeatedly moving said magnetic flux confining means during a heating operation between the operating position and a retracted position retracted from the operation position, when the recording material which has a predetermined width overlapping with a part of the predetermined region is continuously heated by said apparatus.
According to another aspect of the present invention, there is provided an image heating apparatus comprising a heating rotatable member for heating an image on a recording material in a heating nip; magnetic flux generating means for generating a magnetic flux for induction heat generation in said heating rotatable member; magnetic flux confining means for confining the magnetic flux directed toward said heating rotatable member from said magnetic flux generating means, wherein said magnetic flux confining means has a first magnetic flux confining portion for confining, at a first position, the magnetic flux toward a first region of said heating rotatable member, and a second magnetic flux confining portion for confining, at a second position, the magnetic flux toward a second region having a width larger than the first region of said heating rotatable member and including the first region; and moving means for moving said magnetic flux confining means at least between said first position and said second position during a heating operation when the recording material having a predetermined width overlapping partly with a region which is in said second region and outside said first region, is repeatedly heated by said apparatus.
According to a further aspect of the present invention, there is provided an image heating apparatus comprising a heating rotatable member for heating an image on a recording material in a heating nip; magnetic flux generating means for generating a magnetic flux for induction heat generation in said heating rotatable member; magnetic flux confining means for confining the magnetic flux directed toward said heating rotatable member from said magnetic flux generating means, wherein said magnetic flux confining means has a first magnetic flux confining portion for confining, at a first position, the magnetic flux toward a first region of said heating rotatable member, and a second magnetic flux confining portion for confining, at a second position, the magnetic flux toward a second region having a width larger than the first region of said heating rotatable member and including the first region; and moving means for moving stepwisely said magnetic flux confining means to said first position and then to said second position when the recording material having a size not overlapping with said second region is continuously heated.
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.
Embodiment 1
(1) Example of Image Forming Apparatus
Designated by a referential symbol 104 is an electrophotographic photosensitive member (which hereinafter will be referred to as photosensitive drum), which is in the form of a rotatable drum and is rotationally driven at a predetermined peripheral velocity in the clockwise direction indicated by an arrow mark. While the photosensitive drum 104 is rotated, its peripheral surface is uniformly charged by a charging apparatus 105 to predetermined polarity and potential level. Then, the uniformly charged peripheral surface of the photosensitive drum 104 is exposed to an image writing beam of light L projected by an image writing apparatus 106. As a result, the numerous points of the uniformly charged peripheral surface of the photosensitive drum 104, which have been exposed to the beam of light L, attenuate in potential level, creating thereby an electrostatic latent image which reflects the pattern in which the peripheral surface of the photosensitive drum 104 have been exposed. The image writing apparatus 106 in this embodiment is a laser scanner. In response to a command from an unshown controller, the image writing apparatus 106 outputs a beam of laser light L while modulating it with sequential digital electrical video signals reflecting the information of the original photoelectrically read by the above-mentioned photoelectric reading apparatus 103. To this beam of laser light L which is being oscillated in the direction perpendicular to the rotational direction of the photosensitive drum 104, the uniformly charged portion of the peripheral surface of the rotating photosensitive drum 104 is exposed. As a result, an electrostatic latent image reflecting the information (image formation data) of the original is created on the uniformly charged portion of the peripheral surface of the photosensitive drum 104.
Then, the electrostatic latent image is developed by a developing apparatus 107 into a visible image formed of toner (which hereinafter will be referred to as toner image). The toner image is electrostatically transferred by a transferring apparatus 108 (charging apparatus) from the peripheral surface of the photosensitive drum 104 onto a recording medium S delivered from a recording medium feeding/conveying mechanism, with a predetermined timing, to the transfer portion, which is where the photosensitive drum 104 opposes the transferring apparatus 108.
The recording medium feeding/conveying mechanism of the image forming apparatus in this embodiment comprises first to fourth recording medium feeding portions which accommodate first to fourth recording medium cassettes 109–112, an MP tray 113 (multi-pass tray), a recording medium reversing- and refeeding portion 114, from the selected one of which recording mediums S are conveyed to the transfer portion. Designated by a referential symbol 115 is a pair of registration rollers, which release each recording medium S with a predetermined timing toward the transfer portion.
In the transfer portion, the toner image on the peripheral surface of the photosensitive drum 104 is transferred onto the recording medium S. Then, the recording medium S is separated from the peripheral surface of the photosensitive drum 104, and is conveyed to a fixing apparatus 116, in which the unfixed image on the recording medium S is fixed. Then, the recording medium S is discharged by a pair of sheet discharge rollers 117 onto a delivery tray 118 located outside the main assembly of the image forming apparatus.
Meanwhile, the peripheral surface of the photosensitive drum 104 from which the recording medium S has just been separated is cleaned. That is, the contaminants such as the toner remaining on the peripheral surface of the photosensitive drum 104 after the toner image transfer are removed by a cleaning apparatus 119 to repeatedly use the surface for image formation.
When the image forming apparatus is in the two-sided copy mode, a recording medium S is conveyed in the following manner. That is, after the formation of an unfixed toner image on one (first) of the two surfaces of a recording medium S, the recording medium S is fed into the fixing apparatus 116. As soon as a recording medium is conveyed out of the fixing apparatus 116, it is introduced into the recording medium reversing- and refeeding portion 114, by which it is turned over and refed into the main assembly of the image forming apparatus so that another toner image can be transferred onto the other (second) surface of the recording medium S. After the transfer of the toner image onto the second surface of the recording medium, the recording medium S is conveyed for a second time through the fixing apparatus 116, and is discharged as a two-sided copy by the pair of sheet discharge rollers 117 onto the delivery tray 118 located outside the main assembly of the image forming apparatus.
Incidentally, the copying machine in this embodiment is a multifunction copying machine, which is provided with printing and facsimileing functions in addition to the copying function. However, the additional functions of the machine are not essential to the description of the present invention, and therefore, will not be described.
(2) Example of Fixing Apparatus
Designated by a referential symbol 7 is a cylindrical fixation roller as the member in the wall of which heat is generated by electromagnetic induction (which hereinafter may be referred to simply as electromagnetically heatable member). The fixation roller 7 is rotatably supported by and between the side plate 12a and 12b of the main assembly of the image heating apparatus, with a pair of bearings 11a and 11b placed between the side plate 12a and 12b and the lengthwise end portions of the fixation roller 7, one for one. As the material for the fixation roller 7, it is desired to use a metallic substance such as iron, nickel, cobalt, or the like. The usage of a ferromagnetic metal (metal greater in permeability) as the material for the fixation roller 7 makes it possible to confine a greater portion of the magnetic flux generated by a magnetic flux generating means, in the wall of the fixation roller 7; that is, it makes it possible to increase the wall of the fixation roller 7 in magnetic flux density. Therefore, it can induce eddy current in the surface portion of the fixation roller 7 at a higher level of efficiency, and therefore, can heat the fixation roller 7 at a higher level of efficiency. The thickness of the wall of the fixation roller 7 is made to be in a range of roughly 0.3–2 mm in order to render the fixation roller 7 relative low in thermal capacity. The surface layer of the fixation roller 7 is an unshown toner releasing layer, which normally is a 10–50 μm thick layer formed of PTFE or a 10–50 μm thick layer formed of PFA. The fixation roller 7 may be provided with a rubber layer, which is placed on the immediate inward side of the toner releasing layer. Designated by a referential symbol 1 is a heating assembly disposed within the hollow of the fixation roller 7. The heating assembly 1 is made up of a coil, a core, a holder as a supporting member, etc. The structure of this heating assembly 1 will be described in detail in the following Section (3).
Designated by a referential symbol 8 is an elastic pressure roller disposed under the fixation roller 7, in parallel to the fixation roller 7. The elastic pressure roller 8 is rotatably supported between a pair of pressure roller bearings 15a and 15b. It is kept pressed upon the downwardly facing portion of the peripheral surface of the fixation roller 7 with the application of a predetermined amount of pressure provided by a unshown pressure applying means, against the elasticity of the pressure roller 8, forming thereby a fixation nip N as a heating portion with a predetermined width. The pressure roller 8 is made up of a metallic core formed of iron, a silicone rubber layer coated on the peripheral surface of the metallic core, and a toner releasing layer, similar to that of the fixation roller 7, coated on the peripheral surface of the silicone rubber layer. The fixation roller 7 is provided with a pair of fixation roller gears 10a and 10b, which are attached to the lengthwise end portions of the fixation roller 7, one for one. As rotational force is transmitted to the fixation roller gear 10a from an unshown driving system, the fixation roller 7 is rotationally driven at a predetermined peripheral velocity in the clockwise direction indicated by an arrow mark A in
To the excitation coil 5 of the heating assembly 1 disposed within the hollow of the fixation roller 7, electric power (high frequency electric current) is supplied from an electric power controlling apparatus 13 (excitation circuit) through a pair of power lines 9 for supplying the coil with electric power. As a result, a magnetic flux (alternating magnetic field) is generated by the heating assembly 1, and this magnetic flux induces eddy current in the wall of the fixation roller 7 as a member in which heat is generated. The eddy current induced in the wall of the fixation roller 7 generates heat in the wall of the fixation roller 7 (Joule heat: heat resulting from current loss); in other words, the fixation roller 7 is heated. The temperature of the fixation roller 7 is detected by a first temperature detecting means 16 (thermistor or the like), and the signal representing the detected temperature level of the fixation roller 7 is inputted into a control circuit 17, which controls the fixation roller temperature by controlling the electric power supplied to the excitation coil 5 of the heating assembly 1 from the electric power controlling apparatus 13, so that the detected temperature level of the fixation roller 7 inputted from the first temperature detecting means 16 remains at a predetermined level for image fixation.
As described above, while the fixation roller 7 and pressure roller 8 are rotationally driven, the temperature of the fixation roller 7 is kept at a predetermined level for image fixation by the heat generated by the eddy current induced in the wall of the fixation roller 7 by the magnetic flux generated by the excitation coil 5 of the heating assembly 1, as the electric power is applied to the excitation coil 5. Referring to
Designated by a referential symbol 14 is a recording medium separating claw 14, which plays the role of separating the recording medium S from the fixation roller 7, preventing thereby the recording medium S from wrapping around the fixation roller 7, after being introduced into the fixation nip N and conveyed out of the fixation nip N.
As for the positional relationship between a recording medium S and the fixing apparatus in this embodiment, in terms of the direction perpendicular to the recording medium conveyance direction, while the recording medium S is conveyed through the fixing apparatus 116, the recording medium S is conveyed so that the center of the recording medium S coincides with the center of the fixing apparatus 116. Referring to
A recording medium with the largest width W1 conveyable through the fixing apparatus 116 in this embodiment is a recording medium of a size A4 (297 mm in width), and a recording medium of a size A4R (210 mm in width) is used as an example of a recording medium with a width less than that (width W1) of the widest recording medium. Hereinafter, a recording medium with the largest width W1 conveyable through the fixing apparatus in this embodiment will be referred to as recording medium of the normal size, and the width W1 will be referred to as normal width.
(3) Heating Assembly 1
Designated by a referential symbol 1 is a heating assembly as a magnetic flux generating means, which is disposed in (inserted into) the hollow of the cylindrical fixation roller 7. The heating assembly 1 is made up of a holder 2, the excitation coil 5, magnetic core 6 (a, b), a stay, etc. The excitation coil 5 and magnetic core 6 make up the actual magnetic flux generating portion of the heating assembly 1. The stay is for supporting the excitation coil 5 and magnetic core 6. The heating assembly 1 is also provided with a magnetic flux adjusting member 18 (magnetic flux blocking member (magnetic flux reducing member), shutter), which is rotatably disposed on the outward side of the holder 2, in terms of the radius direction of the fixation roller 7, so that its rotational axis coincides with the axial line of the holder 2. The holder 2 is in the form of a trough, which is roughly semicircular in cross section. The magnetic core 6 (which is made up of first portion 6a and second portions 6b, and hereinafter, will be referred to simply as core), which is T-shaped in cross section, is disposed in the hollow of this holder 2, in parallel to the lengthwise direction of the holder 2. The first portion 6a and second portions 6b of the magnetic core 6 are roughly the same in the dimension, in terms of the lengthwise direction of the fixation roller 7, as a recording medium of the normal width W1; they match, in width and location, the path of a recording medium of the normal size. The excitation coil 5 (which hereinafter will be referred to simply as coil) is also disposed in the hollow of the holder 2, being wound around the first portion 6a of the core 6. The coil 5 is roughly elliptic in contour, and its long axis is parallel to the lengthwise direction of the fixation roller 7. The overall shape of the coil 5 is such that the curvature of the contour of its outwardly facing portion matches the curvature of the internal surface of a cylindrical object such as the fixation roller 7. The coil 5 is characterized in that it is shaped so that even its lengthwise end portions, where it is bent in the shape of a letter U, are shaped so that the curvature of their contour matches that of the internal surface of the fixation roller 7. In other words, the coil 5 is disposed in the hollow of the holder 2 so that the contour of the outwardly facing portion of the coil 5 follows the internal surface of the fixation roller 7.
A holder cap 4, shown in
(4) Magnetic Flux Adjusting Apparatus
The magnetic flux adjusting apparatus of the fixing apparatus, which was mentioned regarding the example of a fixing apparatus, is provided with a magnetic flux adjusting (blocking) member 18 (magnetic flux reducing member), which is disposed in the gap between the heating assembly 1, and the fixation roller, as a member in which heat can be generated by electromagnetic induction, being enabled to be moved in the circumferential direction of the fixation roller 7 along the internal surface of the fixation roller 7. The magnetic flux adjusting apparatus is also provided with a means for moving the magnetic flux adjusting (blocking) member 18 into one of predetermined magnetic flux adjusting positions (operative positions) and a retreat position in which it does not adjust the magnetic flux. As the material for the magnetic flux reducing (blocking) member 18, a nonmagnetic and electrically conductive substance (for allowing eddy current to flow through magnetic flux adjusting member), which is low in specific resistance, is preferable; for example, copper, aluminum, silver, alloys thereof, or ferrite or the like, which is high in specific resistance, and therefore, is capable of confining a magnetic flux. Further, even a magnetic substance such as iron or nickel can be used as the material for the magnetic flux adjusting member, as long as a magnetic flux adjusting member formed thereof is provided with round through holes or through holes in the form of a slit so that the eddy current induced therein is prevented from generating heat. Referring to
(Shape of Magnetic Flux Adjusting Member)
The first magnetic flux adjusting portion essentially bears the role of blocking the portion of the magnetic flux, which corresponds in size and position to the portions of the fixation roller 7 outside the path of a recording medium of the large or medium size, to prevent the temperature increase across the portions of the fixation roller 7 outside the recording medium path, whereas the second magnetic flux adjusting portion bears the role of blocking the portion of the magnetic flux, which corresponds in size and position to the portions of the fixation roller 7 outside the path of a recording medium of the medium or small size.
(Positioning of Thermistor)
The thermistors 22 and 23 (shutter thermistors) as temperature detecting means are disposed so that they correspond in position to the first and second magnetic flux adjusting portions 18a and 18b. The magnetic flux adjusting member 18 is moved into one of the magnetic flux adjustment positions, or the retreat position, so that the temperature level of the fixation roller 7 detected by the thermistors 22 or 23 remains within a predetermined range.
To describe in more detail, in terms of the lengthwise direction of the fixation nip N (fixation roller 7), the first shutter thermistor 23 (which hereinafter will be referred to simply as first thermistor) is disposed in the range in which the magnetic flux is blocked by the first magnetic flux adjusting portion, and which corresponds in size and position to the area outside the path of a recording medium of the largest size, whereas the second shutter thermistor 22 is disposed in the range in which the magnetic flux is blocked by the second magnetic flux adjusting portion, and which is not only outside the path of a recording medium of the medium size, but also, outside the range in which the magnetic flux is blocked by the first magnetic flux adjusting portion.
In a case in which the magnetic flux adjusting portions of the magnetic flux adjusting member do not perfectly match in size and position to the recording medium being conveyed, for example, when the magnetic flux adjusting member is in one of the magnetic flux adjusting positions, in which the magnetic flux adjusting portions thereof overlap with the path of the recording medium being conveyed, the portions of the fixation roller 7, which correspond to the areas in which the magnetic flux adjusting portions overlap with the recording medium path, is deprived of heat even though no heat is generated therein. Therefore, these portions of the fixation roller 7 drastically reduce in temperature, being likely to cause fixation failure.
Thus, the position in which the magnetic flux adjusting member is placed to adjust the magnetic flux when the magnetic flux adjusting portions do not match in size and position to the recording medium being conveyed (when magnetic flux adjusting member is in one of magnetic flux adjusting positions, in which magnetic flux adjusting portions thereof overlap with recording medium edges) will be described.
(1) Shutter Drive Control Sequence (Medium Size)
Next, the shutter drive control in accordance with the present invention will be described.
As soon as a command for continuously producing a multiple copies of an original, using recording mediums of the medium size (hereafter, A4R), is inputted into the image forming apparatus in this embodiment, a copying operation begins. As the copying operation begins, the temperature of the lengthwise end portions of the fixation roller begins to rise (fixation roller rises in temperature so that its temperature distribution will become temperature distribution A shown in
Referring to
First, a control circuit 17 (control portion) determines whether the temperature level S-th 1 detected by the first thermistor, or the temperature level S-th 2 detected by the second thermistor, has reached a level in a range of 205° C.–210° C. As soon as the temperature level S-th 1 detected by the first thermistor, or the temperature level S-th 2 detected by the second thermistor, reaches 205° C., the control portion 17 moves the magnetic flux adjusting (blocking) member 18 into the first magnetic flux blocking position (
Normally, as multiple recording mediums of the medium size are continuously conveyed through the fixing apparatus, the portions of the fixation roller, which correspond in position to the out-of-path areas W3, that is, the areas in which the magnetic flux is blocked, continues to gradually rise in temperature as do the lengthwise end portions of the fixation roller as shown in
As described above, by adjusting in two stages the portions of the magnetic flux, which correspond in position to the out-of-path areas of the fixation nip, the temperature level of the fixation roller outside the path of the recording medium being conveyed can be kept within the predetermined range, even when multiple recording mediums, which do not match in size to any of the magnetic flux adjusting portions of the magnetic flux adjusting member, are continuously conveyed through the fixing apparatus.
Further, by providing the fixing apparatus with two or more temperature detecting means, it is possible to detect, as closely as possible, the peaks of the temperature distribution of the fixation roller, across the portions of the fixation roller outside the recording medium path, the size of which are changed by the size of a recording medium being conveyed. Therefore, the surface temperature of the fixation roller can be kept within the predetermined range.
In this embodiment, the temperature of the portions of the fixation roller outside the recording medium path is detected, and the shutter is moved in response to the detected temperature. However, this setup in this embodiment is not intended to limit the scope of the present invention. For example, the shutter may be controlled in multiple stages according to the size of a recording medium being conveyed, the number of the recording mediums being conveyed per unit of time, or length of time multiple recording mediums are being conveyed.
This embodiment was described with reference to the image forming operation in which multiple recording mediums of the medium size were continuously conveyed through the fixing apparatus. However, the effectiveness of the present invention is not affected even if an image forming operation carried out by an image forming apparatus employing a fixing apparatus in accordance with the present is such that a set of originals different in size are continuously copied, and therefore, multiple recording mediums different in size are continuously conveyed in a specific or random order through the fixing apparatus. Obviously, the effectiveness of the present invention is not affected by the size of a recording medium to be used for image formation, that is, whether recording mediums to be used for image formation is of the large or small size.
That is, the magnetic flux adjusting member has only to be controlled as follows: As the temperature of the portions of the fixation roller outside the recording medium path reaches a predetermined level, the magnetic flux adjusting member is moved so that the range, in terms of the lengthwise direction of the fixation roller (fixation nip), in which the magnetic flux is adjusted (blocked) by the magnetic flux adjusting portions of the magnetic flux adjusting member, increases one step (one size), or in steps. Then, as the temperature of the portions of the fixation roller outside the recording medium path falls below the predetermined level, the magnetic flux adjusting member is moved into the predetermined retreat position.
Incidentally, the service life of the drive gears can be extended by expanding in steps the range, in terms of the lengthwise direction of the fixation roller (fixation nip), in which the magnetic flux is adjusted (blocked) by the magnetic flux adjusting member, with the selective usage of the first and second magnetic flux adjusting portion 18a and 18b, respectively, when multiple recording mediums of the small size are continuously conveyed. In other words, this control method is smaller in the number of times the magnetic flux adjusting member is driven, compared to the control method in which the magnetic flux adjusting member is directly moved from the retreat position (home position) in which it does not block the magnetic flux, to the position in which its magnetic adjusting portions 18b adjust (block) the magnetic flux. Further, this method makes it possible to more precisely control in temperature the portions of the fixation roller outside the recording medium path.
Further, when moving, in Step 3, the magnetic flux adjusting member, out of the second magnetic flux adjusting position to move its magnetic flux adjusting portions 18b out of the magnetic flux blocking positions, the magnetic flux adjusting member may be rotated a certain angle, instead of retracting it all the way into the retreat position (home position), so that the range, in which the magnetic flux is blocked by the magnetic flux adjusting member, is reduced by one size. This controlling method makes it possible to even more precisely control in temperature the portions of the fixation roller outside the recording medium path.
The usage of an image heating apparatus in accordance with the present invention is not limited to the usage as a fixing apparatus such as the one in this embodiment. For example, an image heating apparatus in accordance with the present invention can be very effectively used as such an image heating apparatus as a fixing apparatus for temporarily fixing an unfixed image to an object to be heated, or a surface property changing apparatus for changing a fixed image in surface properties such as glossiness by reheating the fixed image and the object bearing the fixed image.
Even when the magnetic flux adjusting portions of the magnetic flux adjusting member do not match in size a recording medium being conveyed, the temperature of the entirety of the heating member, in terms of its lengthwise direction, can be kept within a predetermined range, by alternately carrying out the operation for increasing, in the dimension in terms of the lengthwise direction of the heating member, the range in which magnetic flux is blocked by the magnetic flux adjusting member, and the operation for decreasing the range.
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. 307529/2004 filed Oct. 22, 2004, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-307529 | Oct 2004 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5464964 | Okuda et al. | Nov 1995 | A |
| 5747774 | Suzuki et al. | May 1998 | A |
| 6373036 | Suzuki | Apr 2002 | B2 |
| 6492630 | Nagahira | Dec 2002 | B2 |
| 6713734 | Suzuki | Mar 2004 | B2 |
| 6782216 | Suzuki | Aug 2004 | B2 |
| 6969833 | Suzuki | Nov 2005 | B2 |
| 6970664 | Yamamoto | Nov 2005 | B2 |
| 7034261 | Suzuki | Apr 2006 | B2 |
| 7038178 | Suzuki | May 2006 | B2 |
| 7122769 | Nami et al. | Oct 2006 | B2 |
| 7132631 | Nami et al. | Nov 2006 | B2 |
| 20020148828 | Nagahira | Oct 2002 | A1 |
| 20030077093 | Sekiguchi | Apr 2003 | A1 |
| 20050006378 | Suzuki | Jan 2005 | A1 |
| 20050173415 | Yamamoto et al. | Aug 2005 | A1 |
| 20050252912 | Yamamoto | Nov 2005 | A1 |
| 20060086719 | Suzuki et al. | Apr 2006 | A1 |
| 20060086720 | Nakase et al. | Apr 2006 | A1 |
| 20060086724 | Yamamoto et al. | Apr 2006 | A1 |
| 20060086726 | Yamamoto et al. | Apr 2006 | A1 |
| 20060086730 | Kondo et al. | Apr 2006 | A1 |
| 20060088328 | Yoshimura et al. | Apr 2006 | A1 |
| 20060088329 | Suzuki et al. | Apr 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 2002-287563 | Oct 2002 | JP |
| 2002-323829 | Nov 2002 | JP |
| 2003-123957 | Apr 2003 | JP |
| 2004-170622 | Jun 2004 | JP |
| 2004-265670 | Sep 2004 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20060086730 A1 | Apr 2006 | US |
