Patent Grant
7995958
1. Field of the Invention
The present invention relates to an image forming apparatus including a fixing unit which fixes a heated and melted unfixed toner onto a sheet carrying a toner image while passing the sheet of paper through a nip defined between a pair of heating rollers or a heating belt and a roller.
2. Description of the Related Art
In this type of image forming apparatus, in order to meet demands such as shortening the warm-up time of a fixing unit and saving energy, attention has recently been drawn to a belt method capable of operating with a smaller amount of heat capacity (e.g., refer to Japanese Patent Laid-Open Publication No. H06-318001). In recent years, an electromagnetic induction heating method (IH) capable of rapid heating or high-efficient heating has also been notable, and taking into account saving energy when fixing a color image, the image forming apparatus employing the combination of the electromagnetic induction heating and belt methods have been put on the market. The combination of the belt method and the electro-magnetic induction heating has advantages in that a coil can be easily laid out and cooled and a belt can be directly heated. These and other advantages prompt an electromagnetic inductor to be arranged outside of the belt (so-called external IH type).
In the electro-magnetic induction heating method, various arts have been developed for the purpose of preventing an excessive temperature rise in a non-sheet conveyed region in accordance with the width (conveyed-sheet width) of a sheet conveyed through a fixing unit. Particularly, a means for the different sizes of sheets in the external IH is described in the following prior arts, for example, Japanese Patent Laid-Open Publication No. 2003-107941 and Japanese Patent Laid-Open Publication No. 2006-120523).
In a first prior art (Japanese Patent Laid-Open Publication No. 2003-107941 (FIGS. 2 and 3)), a magnetic member is divided into several parts and arranged in a conveyed-sheet width direction, and some of the divided parts of the magnetic member are moved close to and apart from an excitation coil in accordance with the width (conveyed-sheet width) of a conveyed sheet. In this case, some of the divided parts of the magnetic member are moved apart from the excitation coil in a non-sheet conveyed region, thereby lowering the heat-generation efficiency in the non-sheet conveyed region to make the generated-heat quantity smaller than that in a minimum sheet conveyed region for a sheet of a minimum width.
In a second prior art (Japanese Patent Laid-Open Publication No. 2006-120523), a magnetic shielding plate having a curved-surface is formed in advance with a plurality of steps in the longitudinal directions thereof, and these steps form an area for passing magnetism and an area screening out magnetism in the width direction of a sheet. Therefore, when the size of a sheet is changed, the magnetic shielding plate is turned in accordance with the conveyed-sheet width, thereby screening out magnetism in a non-sheet conveyed region to suppress an excessive rise in the temperature of a heated roller or the like.
However, the first prior art has the problem of requiring a wider motion space for the magnetic member, thereby making the whole apparatus larger.
In the second prior art, the positions of the steps formed beforehand in the shielding plate determine the shielding area and the non-shielding area, thereby making it difficult to handle sheets of paper having many different sizes. Besides, if the steps are formed in the direction in which the shielding plate turns, then the turning angle as a whole is restricted to hinder enlarging each step (e.g., a turning angle of approximately 15°-30°), thereby reducing the quantity of screened-out magnetism and making it impossible to suppress the generated-heat quantity sufficiently.
It is an object of the present invention to provide an image forming apparatus capable of decreasing the number of members arranged inside a heating member to reduce the heat capacity, shorten the warm-up time and save a space, and also capable of regulating magnetism for a variety of sheet sizes and producing a shielding effect enough.
In order to accomplish the object, an image forming apparatus according to the present invention includes an image forming section forming a toner image and transferring the toner image onto a sheet and a fixing unit including a heating member and a pressure member. The fixing unit is operable to fix the toner image onto the sheet while nipping and conveying the sheet between the heating member and the pressure member. The heating member has a sheet conveyed region that the sheet passes. The sheet conveyed region is set in accordance with the size of the sheet being conveyed. The fixing unit further includes a coil arranged along an outer surface of the heating member and generating a magnetic field, a fixed core arranged opposite to the heating member with respect to the coil and forming a magnetic path, a plurality of movable cores arranged between the fixed core and the heating member with respect to a direction in which the coil generates a magnetic field, to form the magnetic path together with the fixed core, and also arranged along the sheet conveyed region, a shielding member arranged along an outer surface of at least one movable core and shielding magnetism, and a magnetism adjustment unit rotating at least one movable core around a predetermined axis to switch the position of the shielding member between a shielding position where the shielding member is positioned inside the sheet conveyed region to shield the magnetism and a retracted position where the shielding member is positioned outside the sheet conveyed region to permit pass of the magnetism.
These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanied drawings.
Embodiments of the present invention will be described below in detail with reference to the drawings.
The image forming apparatus 1 of
The apparatus main body 2 houses a paper cassette 5 storing sheets in a lower part thereof and is provided on a side (the right side in
The apparatus main body 2 is provided inside at a left portion in
The paper cassette 5 can be drawn out of the apparatus main body 2 and then refilled with sheets, and includes a storage portion 16 selectively storing at least two kinds of sheets having different sizes. Sheets of paper stored in the storage portion 16 are delivered one by one to the first conveying path 9 by a sheet feeding roller 17 and a handling roller 18.
The stack tray 6 can be opened and closed on the right side of the apparatus main body 2 and includes a manual feeding portion 19 on which a single or a plurality of sheets are placed manually. Sheets placed on the manual feeding portion 19 are delivered one by one toward the second conveying path 10 by a pick-up roller 20 and a handling roller 21.
The first conveying path 9 and the second conveying path 10 join in front of a resist roller 22. A sheet supplied to the resist roller 22 waits once here, is sent to a secondary transfer portion 23 after undergoing a skew adjustment and a timing adjustment, and is given a secondary transfer of a full-color toner image on an intermediate transfer belt 40 in the secondary transfer portion 23. The sheet subjected to toner-image fixing in the fixing unit 14 is reversed, if necessary, in a fourth conveying path 12 and the side of the sheet reverse to the side subjected to the toner-image fixing undergoes the secondary transfer of a full-color toner image in the secondary transfer portion 23. After undergoing the toner-image fixing on the reverse side in the fixing unit 14, the sheet passes through the third conveying path 11 and is discharged to the paper discharge portion 3 by a discharge roller 24.
The image forming section 7 includes four image forming units 26 to 29 forming each toner image of black (B), yellow (Y), cyan (C) and magenta (M), and an intermediate transfer unit 30 superimposing and carrying toner images of each color formed by the image forming units 26 to 29.
Each of the image forming units 26 to 29 includes a photosensitive drum 32 rotating counterclockwise as shown by an arrow by a drive motor (not shown), a charger 33 mounted face to face with a peripheral surface of the photosensitive drum 32, a laser scanning unit 34 arranged downstream of the charger 33 in the rotational direction of the photosensitive drum 32 and applying a laser beam to a specified position on the peripheral surface of the photosensitive drum 32, a developer 35 arranged downstream of the laser-beam radiation position in the rotational direction of the photosensitive drum 32 and mounted face to face with the peripheral surface of the photosensitive drum 32, and a cleaner 36 arranged downstream from the developer 35 in the rotational direction of the photosensitive drum 32 and mounted face to face with the peripheral surface of the photosensitive drum 32.
Each developer 35 of the image forming units 26 to 29 includes a toner box 51 storing each of a black toner, a yellow toner, a cyan toner and a magenta toner.
The intermediate transfer unit 30 includes a rear roller (driving roller) 38 mounted near the image forming unit 26, a front roller (driven roller) 39 mounted near the image forming unit 29, the intermediate transfer belt 40 stretched between the rear roller 38 and the front roller 39, and four transfer rollers 41 pressed via the intermediate transfer belt 40 against the peripheral surface of the photosensitive drum 32 of each image forming unit 26 to 29.
In the intermediate transfer unit 30, toner images of each color are superimposed and transferred at the positions of the transfer rollers 41 from the photosensitive drums 32 onto the intermediate transfer belt 40, and a full-color toner image is formed on the intermediate transfer belt 40.
The first conveying path 9 conveys a sheet delivered from the paper cassette 5 to the intermediate transfer unit 30 and includes a plurality of conveying rollers 43 arranged in predetermined positions, and the resist roller 22 arranged in front of the intermediate transfer unit 30 and adjusting the timing between an image forming operation by the image forming section 7 and a paper feeding operation.
The fixing unit 14 heats and pressurizes a sheet, on which a toner image is transferred in the image forming section 7, to fix a toner image on the sheet. The fixing unit 14 includes, for example, a roller pair made up of a pressure roller 44 and a fixing roller 45 of a heating type. The pressure roller 44 has, for example, a metal core and an elastic surface layer (e.g., silicone rubber), and the fixing roller 45 has, for example, a metal core, an elastic surface layer (e.g., silicone sponge) and a mold-release layer (e.g., PFA). A heat roller 46 is arranged adjacent to the fixing roller 45, and a heating belt 48 is stretched between the heat roller 46 and the fixing roller 45. A specific structure of the fixing unit 14 will be further described later.
A conveying path 47 is formed on each of the upstream and downstream sides of the fixing unit 14 in the sheet conveying direction. Through the upstream conveying path 47, a sheet passed through the intermediate transfer unit 30 is introduced into the nip between the pressure roller 44 and the fixing roller 45, and through the nip, is guided to the third conveying path 11 via the downstream conveying path 47.
The third conveying path 11 forwards a sheet subjected to fixing in the fixing unit 14 to the paper discharge portion 3, and is provided in a proper position with a conveying roller pair 49 and at the outlet with the discharge roller 24.
Next, the fixing unit 14 of the image forming apparatus 1 according to a first embodiment of the present invention will be described in detail.
As described above, the fixing unit 14 includes the pressure roller 44, the fixing roller 45, the heat roller 46 and the heating belt 48. The surface layer of the fixing roller 45 is formed with the elastic silicone sponge layer to form a flat nip between the heating belt 48 and the fixing roller 45.
The heating belt 48 includes a substrate made of a ferromagnetic material (e.g., Ni), a thin-film elastic layer (e.g., silicone rubber) formed in the surface layer of the substrate, and a mold-release layer (e.g., PFA) formed in the outer surface of the elastic layer. The heating belt 48 may be a resin belt such as PI if designed to have no heat-generation function. The heat roller 46 includes a metal core made of magnetic metal (e.g., Fe or SUS) and a mold-release layer (e.g., PFA) formed in the surface of the metal core.
The pressure roller 44 includes, for example, a metal core made of Fe and Al, a Si rubber layer formed on the metal core, and a fluororesin layer formed in the surface of the rubber layer. The pressure roller 44 may be provided inside with, for example, a halogen heater 44a.
The fixing unit 14 further includes an IH coil unit 50 (not shown in
[Coil]
In the example of
[Fixed Core]
As shown in
The arrangement of the cores 54 and 56 is determined, for example, in accordance with the distribution of a magnetic-flux density (magnetic-field strength) of the induction heating coil 52. Although the arch cores 54 are arranged at predetermined intervals, the side cores 56 compensate for a magnetic-focusing effect in places where the arch cores 54 are not arranged, making the magnetic-flux density distribution (temperature difference) in the longitudinal direction of the heat roller 46 uniform. Outward from the arch cores 54 and the side cores 56, for example, a resinous core holder (not shown) is provided which supports the arch cores 54 and the side cores 56 and the material thereof may preferably be a heat-resistant resin (e.g., PPS, PET or LCP).
The heat roller 46 is provided inside with a thermistor 62 which can be arranged especially in a place where the heat roller 46 generates a large quantity of heat by induction heating. The thermistor 62 operates in response to an excessive temperature rise in the heat roller 46 to stop the heating conducted by the induction heating coil 52. Besides, a thermostat (not shown) can be provided inside the heat roller 46, improving the safety at the time of an abnormal temperature rise.
[Block-Shaped Core]
The center core 58 is, for example, a ferrite core having a cylindrical shape in section and a rotating-shaft member 59 is inserted through the center of the center core 58 in the axial direction of the center core 58. The rotating-shaft member 59 is formed from, for example, a non-magnetic metal (AL or the like) or a heat-resistant resin (PPS, PET, LCP or the like). The center core 58 is divided into a plurality of parts in the axial direction, and each part is formed as a block-shaped core 58a (movable core).
As can be seen in
[Shielding Member]
The outer surface of each block-shaped core 58a is attached with a shielding member 60. The shielding member 60 is a thin plate member and is curved in an arcuate shape corresponding to the shape of the outer surface of the center core 58a. The shielding member 60 may be, as shown in the figure, for example, embedded in the block-shaped core 58a, or affixed to the outer surface of the block-shaped core 58a. The shielding member 60 can be affixed, for example, with a silicon adhesive.
It is preferable that the shielding member 60 is made of a non-magnetic and electrically-conductive material, such as oxygen-free copper. The shielding member 60 generates opposing magnetic field by the influence of induction current induced when a magnetic field perpendicular to a surface of the shielding member 60 penetrates the surface of the shielding member 60, and then cancel interlinkage flux (perpendicular penetrating magnetic field) to thereby shield the magnetic field. Further, by using a good electrically conductive material, the generation of Joule heat by the induction current is suppressed and the magnetic field can be efficiently shielded. In order to improve electrical conductivity, it is effective, for example, to select a material with as small a specific resistance as possible and to increase the thickness of the members. Specifically, it is preferable that the thickness of the shielding member 60 is greater than 0.5 mm. The thickness of the shielding member 60 is selected to be 1 mm in this embodiment.
The center core 58 is arranged between the arch cores 54 and the heat roller 46 (the heating belt 48) with respect to the direction of the magnetic-field generation by the induction heating coil 52 to form a magnetic path together with the arch cores 54 and the side cores 56. In detail, an end 54a (magnetic-path inlet or outlet) of the arch core 54 is apart from the heating belt 48, and the center core 58 is a member forming an intermediate magnetic path between the end 54a and the heating belt 48.
As shown in
[Details of Center Core]
The block-shaped cores 58a, 58b and 58c are each arranged in a predetermined position in the sheet-width direction. The block-shaped core 58c may be divided into several core pieces in the axial direction if it is too large, thereby facilitating the manufacturing thereof.
[Cores at Both Ends and in the Middle]
The rotating-shaft member 59 penetrates the whole center core 58 and extends in the axial direction of the center core 58, and has a full length greater than the center core 58. Among the block-shaped cores 58a, 58b and 58c, two block-shaped cores 58b at both ends and the middle block-shaped core 58c in the width direction are fixed to the rotating-shaft member 59, and thereby, three block-shaped cores 58b and 58c are rotated together as the rotating-shaft member 59 rotates.
The IH coil unit 50 is provided with a driving motor 66 whose driving power rotates the rotating-shaft member 59. A driven gear 59a is attached to an end of the rotating-shaft member 59 and engaged with an output gear 66a of the driving motor 66. As the driving motor 66 is driven, the driving power rotates the rotating-shaft member 59, thereby rotating the three block-shaped cores 58b and 58c together.
[Independent Cores]
The four block-shaped cores 58a are all penetrated in the axial direction by the rotating-shaft member 59 and supported so as to be loosely rotated relative to the rotating-shaft member 59. Therefore, the driving motor 82 provided in each block-shaped core 58a is driven to rotate each block-shaped core 58a individually and independently.
[Rotation Control Method]
Next, a description will be given about a method of individually controlling the rotation of each block-shaped core 58a, 58b, 58c of the center core 58.
As shown in
As shown in
The shielding position and the retracted position are mutually opposite positions 180 degrees apart from each other, and the shielding member 60 is moved to the shielding position or the retracted position by switching the rotation direction of the driving roller 80 in a forward and reverse manner. For example, as shown in
Each block-shaped core 58a, 58b is provided with two photo-interrupters 86, 74. Instead of this constitution, however, the shielding position of each block-shaped core 58a, 58b is set as a reference position and one photo-interrupter 86, 74 may be arranged in a position where the position detecting member 73, 84 is detected. In this case, the position in which each driving motor 82, 66 stops is controlled in such a way that the position where each block-shaped core 58a, 58b is rotated by 180 degrees from the reference position (shielding position) becomes the retracted position.
[Individual Control Circuit]
In this embodiment, each driving motor 66, 82 may be, for example, a stepping motor and the operation thereof is controlled by a control circuit (not shown). This control circuit can be formed, for example, by a control IC, an I/O driver, a semiconductor memory and the like. A detection signal from each photo-interrupter 74, 86 is inputted via the input driver to the control IC, and on the basis of detection signal, the control IC detects a present rotation angle (position) of each driving motor 66, 82. The control IC is notified of information on a present sheet size from an image forming control unit (not shown). Upon receiving the information, the control IC reads information on the position (shielding position or retracted position) of the shielding member 60 suitable for the sheet size from the semiconductor memory (ROM) and outputs a drive pulse equivalent to the rotation angle (180 degrees) corresponding to the position information at that time. The drive pulse is applied to each driving motor 66, 82 via the output driver to operate each driving motor 66, 82.
[Individual Control Example]
Next, a description will be given about the control of each block-shaped core 58a, 58b, 58c in accordance with the size of a sheet. In this embodiment, each block-shaped core 58a, 58b, 58c is designed in size to correspond to each conveyed-sheet width equivalent to, for example, the longitudinal length of A5, A4 or B4, or the lateral length of A4.
[Minimum Conveyed-Sheet Width]
As shown in
[Maximum Conveyed-Sheet Width]
As shown in
[Intermediate Conveyed-Sheet Width]
As shown in
[Cores at Both Ends]
As shown in
[Two Cores Near Both Ends]
As shown in
[Two Cores Near Middle]
As shown in
Next,
As shown in
[Cores at Both Ends]
As shown in
[Two Cores Near Both Ends]
As shown in
[Two Cores Near Middle]
As shown in
[Magnetism Adjustment Unit]
In this embodiment, the rotating-shaft member 59 supporting the block-shaped cores 58b and 58c, the driving motor 66 driving the rotating-shaft member 59, the driving roller 80 pressed into contact with each peripheral surface of the block-shaped cores 58a and the driving motor 82 driving the driving roller 80 constitute a magnetism adjustment unit capable of switching each shielding member 60 of the cores 58a and 58b between the shielding position and the retracted position. The magnetism adjustment unit individually rotates the four block-shaped cores 58a and independently controls the position (shielding position and retracted position) of each shielding member 60, thereby adjusting the quantity of screened-out magnetism optimally in accordance with the intermediate conveyed-sheet widths W2 and W3 of various types. This makes it possible to control the heated range of the heat roller 46 precisely in accordance with the size (conveyed-sheet width) of the sheet determined in advance and to prevent an excessive temperature rise certainly outside the conveyed-sheet width. In some of the above figures, although clockwise and counterclockwise rotations are each shown by an arrow, each block-shaped core 58a, 58b may be rotated only in one direction, and further, the sheet-conveying direction may be opposite to the direction shown in some of the figures.
[Other Structural Examples]
Next,
Diverse variations are feasible in this embodiment. Each block-shaped core 58a, 58b, 58c has a cylindrical or columnar shape but is not limited to this, and hence, may have a polygonal shape in section. Further, the length of each block-shaped core 58a, 58b, 58c in the axial directions is not especially restricted, and hence, may be set suitably for the size of a sheet in use.
Besides, the specific form of each component element including the arch core 54 or the side core 56 is not limited to the one shown in the figures, and hence, may be properly variable.
Next, the fixing unit 14 of the image forming apparatus 1 according to a second embodiment of the present invention will be described in detail.
The fixing unit 14 further includes an IH coil unit 150 outside the heat roller 46 and the heating belt 48. The IH coil unit 150 includes an induction heating coil 52, a pair of arch cores 54, a pair of side cores 56 and a center core 158. The induction heating coil 52, arch cores 54 and side cores 56 of the IH coil unit 150 have configurations substantially similar to the IH coil unit 50 according to the first embodiment, and hence, the description thereof is omitted. The center core 158 will be below described in detail.
[Center Core]
The center core 158 is, for example, a ferrite core having a cylindrical shape in section and includes a shaft member 159 inserted through the center thereof in the axial direction. The shaft member 159 is formed from, for example, a non-magnetic metal (AL or the like) or a heat-resistant resin (PPS, PET, LCP or the like). The center core 158 is divided into a plurality of parts to form a plurality of block-shaped cores 158a. The cores 158a are arranged in the axial direction of the center core 158.
[Shielding Member]
Each block-shaped core 158a has a shielding member 60 attached to the outer surface thereof. The shielding member 160 is a thin plate member and is curved in an arcuate shape conforming to the shape of the outer surface of the core 158a. The shielding member 160 may be, as shown in the figure, for example, embedded in the block-shaped core 158a, or affixed to the outer surface of the block-shaped core 158a. The shielding member 60 can be affixed, for example, with a silicon adhesive.
It is preferable that the shielding member 160 is made of a non-magnetic and electrically-conductive material, such as oxygen-free copper. In the shielding member 160, a magnetic field perpendicular to the surface thereof penetrates to cause an induced current and thereby generate a reverse magnetic field and cancel an interlacing magnetic flux (perpendicular penetration magnetic field), thereby screening out a magnetic field. Further, an electrically-conductive member is employed, thereby suppressing Joule heat generation caused by an induced current to screen out the magnetic field efficiently. In order to improve the electrical conductivity, for example, it is effective to select a material having a low specific resistance and thicken the member, and specifically, the thickness of the shielding member 160 may preferably be 0.5 mm or above, and for example, it is 1 mm in the second embodiment.
As shown in
[Details of Center Core]
Although the block-shaped cores 158a arranged in the middle of the center core 158 in the axial direction are omitted in
[Axial Groove]
As shown in
[Circumferential Groove]
Among the ten block-shaped cores 158a, some of the cores 158a has an inner peripheral surface formed with a circumferential groove 158d extending in the circumferential directions of each core 158a. In
The shaft member 159 is shaped like a round bar and has a full length greater than that of the center core 158. The outer diameter of the shaft member 159 is slightly smaller than the inner diameter of the block-shaped core 158a, in other words, the diameter of the through path 158b, thereby enabling each block-shaped core 158a to rotate along the outer peripheral surface of the shaft member 159. The shaft member 159 can move or slide relative to the center core 158 (block-shaped core 158a) in the axial direction. The shaft member 159 is capable of moving in the axial direction by a moving mechanism 180 (
[Projection]
The shaft member 159 is provided on the outer peripheral surface with a plurality of projections 159a, 159b and 159c that are arranged at a predetermined interval and on the same line in the axial direction of the shaft member 159. The projections 159a, 159b and 159c have substantially the same shape and size.
The shape and size of each projection 159a, 159b, 159c are set in such a way that they can be received in the axial groove 158c and the circumferential groove 158d. Therefore, as shown in
If the shaft member 159 is rotated relative to the block-shaped cores 158a with any of the projections 159a, 159b and 159c aligned in the axial direction with the circumferential groove 158d, the projections 159a, 159b and 159c are received into the circumferential groove 158d and moved in the circumferential direction along the circumferential groove 158d.
[Magnetism Adjustment Method]
Each shielding member 160 of the block-shaped cores 158a is switched from the retracted position to the shielding position in accordance with the size of a sheet to be printed. In
When the block-shaped core 158a is required to have the shielding member 160 switched to the shielding position, the shaft member 159 is rotated with the projection 159a, 159b or 159c received in the axial groove 158c to thereby rotate the block-shaped core 158a together with the shaft member 159. On the other hand, when the block-shaped core 158a is not required to have the shielding member 160 switched to the shielding position, the shaft member 159 is rotated with the projection 159a, 159b or 159c received in the circumferential groove 158d. In this case, since the projection 159a, 159b or 159c moves along the circumferential groove 158d, the block-shaped core 158a is not rotated (or idled) even if the shaft member 159 is rotated. A description will be below given about a switch from the retracted position to the shielding position in accordance with the size of a sheet.
[Minimum Sheet-Conveyed Region W1]
As shown in
[Intermediate Sheet Conveyed Region W2]
As shown in
[Maximum Sheet Conveyed Region W3]
As shown in
[Switch to Shielding Position]
As shown in
As shown in
[Keeping in Retracted Position]
As shown in
As shown in
[Rotation Mechanism, Moving Mechanism]
Next, a configuration will be described for rotating or moving the shaft member 159.
The rotation mechanism 164 rotates the shaft member 159, for example, by transmitting the rotation of a stepping motor 166 via gears 167 and 168 to drive a drive shaft 170. In order to detect a rotation position (reference position in the rotation direction) of the shaft member 159, the gear 168 is provided on a side thereof with an index 172 and a photo-interrupter 174 combined therewith.
The drive shaft 170 is integrally connected with the shaft member 159 and has the same axial center as those of the shaft member 159 and the center core 158. The rotation angle (switch between the retracted position and the shielding position) of the shaft member 159 can be controlled, for example, with a drive-pulse number applied to the stepping motor 166, and the rotation mechanism 164 has a control circuit (not shown) for this purpose. The control circuit can be formed, for example, by a control IC, an I/O driver, a semiconductor memory and the like. A detection signal from the photo-interrupter 174 is inputted via the input driver to the control IC, and on the basis of the detection signal, the control IC can detect the shaft member 159 being in the reference position or not. In the second embodiment, the shielding member 160 stops in the retracted position as the shaft member 159 stops in the reference position, and the shielding member 160 is switched from the retracted position to the shielding position as the shaft member 159 is rotated by 180 degrees from the reference position.
The moving mechanism 180 moves the shaft member 159 in the axial direction through the drive shaft 170, for example, by transmitting the mechanical power of a stepping motor 182 via gears 184 and 185 to rotate a swash plate cam 186 which in turn drives the drive shaft 170. The swash plate cam 186 is formed with a cam plane 186a inclined with respect to an axial line thereof, and an end of the drive shaft 170 is in contact with the cam plane 186a to form a sliding pair therewith. The drive shaft 170 has a compression coil spring 188 connected to the other end (near the rotation mechanism 164) thereof and is given an initial thrust (or biasing force) by a repulsive force of the spring 188. Hence, the swash plate cam 186 is rotated to reciprocate the drive shaft 170 in the axial direction, thereby allowing the shaft member 159 to go and return in the axial direction. Although the other end of the drive shaft 170 penetrates the gear 168 of the rotation mechanism 164, the gear 168 and the drive shaft 170 are subjected to spline coupling using a key 171, thereby hindering the gear 168 from moving in the axial direction even if the drive shaft 170 moves in the axial direction.
The center core 158 is provided at both ends with sleeves 163 restricting the movement thereof in the axial direction. On the other hand, the shaft member 159 is provided at both ends with collar members 161 each fitted along the inner peripheral surface of the corresponding sleeve 163. When the shaft member 159 is moved in the axial direction, the collar members 161 are guided by the sleeves 163, realizing a smooth movement thereof.
[Control Method]
The stop position (movement distance) of the shaft member 159 in the axial direction varies according to the rotation angle of the swash plate cam 186. The stop position of the shaft member 159 can be controlled, for example, with a drive-pulse number applied to the stepping motor 182. The moving mechanism 180 also has a control circuit (not shown). This control circuit can also be formed, for example, by a control IC, an I/O driver, a semiconductor memory and the like and has control information on stop positions of the shaft member 159 according to sheet sizes stored in advance in the semiconductor memory (e.g., EEPROM). The control IC is notified of information on a present sheet size from an image forming control unit (not shown). Upon receiving the information, the control IC reads from the semiconductor memory information on the stop position of the shaft member 159 suitable for the sheet size and outputs, at a specified cycle, the predetermined number of drive pulses for allowing the shaft member 159 to reach the targeted stop position. The drive pulse is applied to the stepping motor 182 via the output driver to operate the stepping motor 182.
After confirming that the rotation mechanism 180 has finished controlling the stop position of the shaft member 159, the control circuit of the rotation mechanism 164 rotates the stepping motor 166. As described earlier, the block-shaped cores 158a outside the sheet conveyed region are rotated according to the sheet size at that time to switch the shielding members 160 from the retracted positions to the shielding positions.
[Cut-Out Portion]
The cut-out portion 90 is formed by cutting off a part of the block-shaped core 158a along the axial direction of the core 158a. The cut-out portion 90 may be formed in a molding die simultaneously when sintering ferrite powder, or formed by cutting a molded column (cylinder). As long as the cut-out portion 90 has an arcuate shape in section in the final form, the manufacturing process is not limited.
In the third embodiment, the block-shaped core 158a is formed inside with the axial groove 158c and the circumferential groove 158d, and the shaft member 159 is formed with the projections 159a, 159b and 159c. The axial groove 158c and the circumferential groove 158d are located, however, out of the way of the cut-out portion 90. The rotation or non-rotation of the block-shaped core 158 a by the projections 159a, 159b and 159c is the same as that in the second embodiment.
In the third embodiment, control is executed in such a way that the block-shaped cores 158a outside the sheet conveyed region in accordance with the size of a sheet are rotated to switch the cut-out portion 90 from the retracted position to a resistance position (shielding position). Specifically, as shown in
On the other hand, when the cut-out portion 90 is in the position 180 degrees apart from the position of
Since the heat roller 46 is a non-magnetic metal, a magnetic field generated by the induction heating coil 52 passes through the side cores 56, the arch core 54 and the intermediate core 55, penetrates the heat roller 46 and reaches the center core 158 inside of the heat roller 46. The penetration magnetic field gives induction heating to the heating belt 48.
In this structural example, as shown in
Next,
The internal type IH coil unit 250 includes only the center core 158 without such an arch core nor a side core as described above. A magnetic field generated by the induction heating coil 52 passes the peripheral surface of the heat roller 46 and enters the center core 158, then passes through the middle of the induction heating coil 52 from the center core 158, and reaches a vicinity of the nip between the heat roller 46 and the pressure roller 44. Although the center core 158 is inside of the heat roller 46, in the same way as the second embodiment, the block-shaped cores 158a are rotated together with the shaft member 159, thereby screening out magnetism outside the sheet conveyed region.
Diverse variations are feasible in the second embodiment and the third embodiments. For example, the number of the block-shaped cores 158a obtained by division is not limited especially to the embodiments, and hence, may be varied suitably for the size of a sheet in use.
In the first to third embodiments, the plate-shaped shielding member 160 is employed to adjust (screen out) magnetism. However, the shielding member 160 may be made of a non-magnetic metal (e.g., oxygen-free copper) and have a closed-ring shape. In this case, in the shielding member 160, a magnetic flux penetrating the closed ring generates a magnetic field working in a direction opposite to the direction in which the magnetic field generated by the induction heating coil 52 works. As a result, the opposite magnetic filed generated in the shielding member 160 cancels the magnetic field generated by the coil 52. Accordingly, the same magnetism-shielding effect as the first to third embodiments can be obtained.
Further, the specific forms of each component element including the arch core 54 or the side cores 56 are not limited to the ones shown in the figures, and thus, can be suitably varied.
The image forming apparatus and particularly, the fixing unit described so far mainly have the following configuration.
The image forming apparatus includes An image forming apparatus includes an image forming section forming a toner image and transferring the toner image onto a sheet and a fixing unit including a heating member and a pressure member. The fixing unit is operable to fix the toner image onto the sheet while nipping and conveying the sheet between the heating member and the pressure member. The heating member has a sheet conveyed region that the sheet passes. The sheet conveyed region is set in accordance with the size of the sheet being conveyed. The fixing unit further includes a coil arranged along an outer surface of the heating member and generating a magnetic field, a fixed core arranged opposite to the heating member with respect to the coil and forming a magnetic path, a plurality of movable cores arranged between the fixed core and the heating member with respect to a direction in which the coil generates a magnetic field, to form the magnetic path together with the fixed core, and also arranged along the sheet conveyed region, a shielding member arranged along an outer surface of at least one movable core and shielding magnetism, and a magnetism adjustment unit rotating at least one movable core around a predetermined axis to switch the position of the shielding member between a shielding position where the shielding member is positioned inside the sheet conveyed region to shield the magnetism and a retracted position where the shielding member is positioned outside the sheet conveyed region to permit pass of the magnetism.
The image forming apparatus having the above configuration employs the method (external IH) of giving induction heating to the heating member by a magnetic field generated by the coil to heat and melt a toner image. Therefore, there is no need to provide any particular member inside the heating member. Besides, in order to form a magnetic path for leading a magnetic field generated by the coil, the fixed core is arranged around the coil, and the plurality of movable cores are simply arranged between the fixed core and the heating member, thereby avoiding making the space occupied by the whole thereof larger.
Furthermore, the image forming apparatus having the above configuration is capable of adjusting the generated-heat quantity of the heating member only by rotating at least one movable core. Specifically, if the magnetism adjustment unit rotates the movable core to move the shielding member to the retracted position, a magnetic field generated by the coil is led to the fixed core and the movable core, causing the heating member to generate an eddy current and conducting magnetic induction heating. On the other hand, if the magnetism adjustment unit rotates the movable core to move the shielding member to the shielding position, the magnetic resistance in the magnetic path increases to lower the magnetic field strength, thereby reducing the generated-heat quantity of the heating member.
Moreover, in the image forming apparatus having the above configuration, there is no need to move the core away from the heating member in adjusting the generated-heat quantity of the heating member, thereby saving a space. Besides, there is no need to provide inside the heating member a core for magnetic induction or an electrically-conductive member for magnetic field adjustment, thereby suppressing an increase in the heat capacity and shortening the warm-up time.
In addition, in the image forming apparatus having the above configuration, it is preferable that the shielding member is provided on the outer surface of each movable core and the magnetism adjustment unit rotates the plurality of movable cores individually.
According to this configuration, the plurality of movable cores are individually rotated to switch the position of the shielding member of each movable core independently, thereby adjusting the generated-heat quantity of the heating member in accordance with a variety of sheet sizes (sheet conveyed regions). For example, when the sheet size is minimum, control is executed in such a way that the shielding member of the movable core outside the minimum sheet conveyed region with respect to the sheet width direction is switched to the shielding position, thereby preventing an excessive temperature rise in the heating member outside the minimum sheet conveyed region. Besides, if the sheet size is changed, control is executed in such a way that the shielding member of the movable core outside the sheet conveyed region in accordance with the sheet size is switched to the shielding position, thereby quickly responding to a switch of the sheet size while certainly preventing an excessive temperature rise in the heating member outside the sheet conveyed region.
Furthermore, in the image forming apparatus having the above configuration, preferably, the magnetism adjustment unit includes a common rotation unit simultaneously rotating the outer movable cores arranged at positions corresponding to ends of a maximum sheet conveyed region set when a sheet having a maximum size is conveyed, and a plurality of individual rotation units individually rotating a corresponding one of the other inner movable cores positioned between the outer movable cores.
According to this configuration, the common rotation unit rotates outer movable cores together to switch the respective shielding members simultaneously to the shielding positions, thereby screening out magnetism easily on the outermost side of the sheet conveyed region and quickly responding to a switch of the sheet size.
Moreover, in the image forming apparatus having the above configuration, it is preferable that the outer movable core and the inner movable core are each a cylindrical core having a through hole formed along the axis thereof. It is also preferable that the common rotation unit includes a rotating shaft member fitted in the through holes of the outer movable cores and fitted loosely in the through holes of the inner movable cores, and a drive source rotating the rotating shaft member whereas each of the individual rotation units includes a rotating roller pressed into contact with an peripheral surface of the corresponding inner movable core and undergoing rotation to transmit a friction force to the peripheral surface, and a drive source rotating the rotating roller.
In addition, in the image forming apparatus having the above configuration, it is preferable that the movable cores include a first movable core arranged inside a minimum sheet conveyed region set when a sheet having a minimum size is conveyed and a second movable core arranged outside the minimum sheet conveyed region and also that the shielding member is provided in not the first movable core but the second movable core.
According to this configuration, since the shielding member is not provided in the movable core arranged inside the minimum sheet conveyed region, screening out magnetism by the shielding member is not carried out, thereby constantly transmitting a magnetic flux to the heating member.
Furthermore, in the image forming apparatus having the above configuration, it is preferable that among the plurality of movable cores, the magnetism adjustment unit rotates a movable core arranged outside the sheet conveyed region set in accordance with the size of the sheet to switch the position of the shielding member of the movable core from the retracted position to the shielding position.
According to this configuration, the shielding member of the movable core inside the sheet conveyed region (within the heated range) is switched to the retracted position, a magnetic field generated by the coil passes the fixed core and the movable core, thereby causing the heating member to generate an eddy current and conducting magnetic induction heating. On the other hand, when the magnetism adjustment unit rotates the movable core outside the minimum sheet conveyed region to move the shielding member to the shielding position, the magnetic resistance inside the magnetic path increases to lower the magnetic-field strength, thereby reducing the generated-heat quantity of the heating member. This makes it possible to certainly prevent an excessive temperature rise in the heating member outside the sheet conveyed region.
Moreover, in the image forming apparatus having the above configuration, it is preferable that the plurality of movable cores are formed by dividing a single core into a plurality of cores and the single core has a through hole of a circular sectional shape formed along the axis thereof. It is also preferable that the magnetism adjustment unit includes a shaft member fitted loosely in the through holes of the movable cores and supporting the movable cores rotatably, a guide groove formed in an inner peripheral surface of each movable core, an engagement portion provided in the shaft member and engageable with the guide groove, and a drive mechanism driving the shaft member. The shape of the guide groove is preferably set in such a way that as the shaft member is driven, the engagement portion moves in the guide groove to rotate the movable cores.
The magnetism adjustment unit preferably has the following specific configuration. The engagement portion is a plurality of projections provided on an outer peripheral surface of the shaft member and spaced at a predetermined interval from each other in the axial direction of the shaft member. The drive mechanism includes a moving mechanism moving the shaft member in the through holes in the axial direction of the movable cores and a rotation mechanism rotating the shaft member in the through holes around the axis of the shaft member. The guide groove includes an axial groove formed at the inner peripheral surfaces of the movable cores over the movable cores in the axial direction of the movable cores, and a circumferential groove formed at the inner peripheral surface to extend from the axial groove in the circumferential direction of the movable core. The axial groove has a shape capable of receiving the projections. The projections move in the axial groove relative to the movable cores in the axial direction of the movable cores when the moving mechanism moves the shaft member. The circumferential groove has a shape capable of receiving the projections. The projections move in the circumferential groove relative to the movable cores in the circumferential direction of the movable core when the rotation mechanism rotates the shaft member. When the moving mechanism moves the shaft member in the axial direction, the projections are switched to a position where the projections are received in the circumferential groove or a position where the projections are not received in the circumferential groove. When the projections are switched to the position where the projections are received, the rotation of the shaft member by the rotation mechanism keeps the shielding member in the retracted position, while when the projections are switched to the position where the projections are not received, the rotation of the shaft member by the rotation mechanism switches the position of the shielding member from the retracted position to the shielding position.
The magnetism adjustment unit having the above configuration is capable of selectively rotating the movable cores individually only using the moving mechanism and the rotation mechanism, thereby making it unnecessary to employ a rotation mechanism having a motor for each movable core to simplify the structure.
In addition, in the image forming apparatus having the above configuration, it is preferable that the movable core is a cylindrical core and, instead of the shielding member, includes a cut-out portion so formed by cutting off a peripheral part thereof as to have an arcuate shape in section viewed from the axial direction. When the projections are switched to the position where the projections are received in the circumferential groove, the rotation of the shaft member by the rotation mechanism keeps the cut-out portion in the retracted position, while when the projections are switched to the position where the projections are not received in the circumferential groove, the rotation of the shaft member by the rotation mechanism switches the cut-out portion from the retracted position to the shielding position.
According to the above configuration, when the magnetism adjustment unit rotates the movable core to switch the cut-out portion to the retracted position, a magnetic field generated by the coil passes the fixed core and the movable core, thereby causing the heating member to generate an eddy current and conducting magnetic induction heating. On the other hand, when the magnetism adjustment unit rotates the movable core to switch the cut-out portion to a resistance position (shielding position), the magnetic resistance inside the magnetic path increases (an air gap is substituted for a part of the magnetic path) to lower the magnetic-field strength, thereby reducing the generated-heat quantity of the heating member. Likewise in this case, the movable cores are arranged in the width direction of a sheet, thereby preventing an excessive temperature rise in accordance with a variety of sheet sizes. Besides, the individual movable cores are rotated to switch the cut-out portion to the resistance position, thereby certainly suppressing the quantity of magnetism passing outside the sheet conveyed region.
This application is based on Japanese patent application serial Nos. 2008-085377 and 2008-170520, filed in Japan Patent Office on Mar. 28, 2008 and Jun. 30, 2008 respectively, the contents of which are hereby incorporated by reference.
Although the present invention has been fully described by way of example with reference to the accompanied drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-085377 | Mar 2008 | JP | national |
| 2008-170520 | Jun 2008 | JP | national |
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| Number | Date | Country | |
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| 20090245898 A1 | Oct 2009 | US |
