Patent Application
20050067407
This application is based on an application No.2003-339749 filed in Japan, the contents of which are hereby incorporated by reference.
The present invention relates to an induction heating device for inductively heating an object to be heated which is formed of conductive material.
The invention also relates to an induction heating fixing device of induction heating type for fixing to a sheet a toner image formed on the sheet while conveying the sheet.
The invention also relates to an image forming apparatus having an image forming unit for forming a toner image on a sheet and an induction heating fixing device of induction heating type for fixing to the sheet the toner image formed on the sheet while conveying the sheet having the toner image formed thereon by the image forming unit. Among image forming apparatus of this type are copying machines, laser printers, facsimiles and the like, typically.
Recently, fixing devices of induction heating type that achieve high thermal conversion efficiencies have been proposed in terms of energy saving.
For example, a fixing device disclosed in patent literature (Japanese Patent Laid-Open Publication 2002-93566) has a heating roller (a member to be heated including a metal sleeve) that is rotated by a motor, a pressurizing roller that is in pressure contact with the heating roller, and a coil that is provided along part of outer periphery of the heating roller and that is tightly wound so as to form a layer. A thermistor (temperature detecting means) is provided so as to face a part of the outer periphery of the heating roller wherein the part is far from a region which the coil faces. In operation, a high-frequency current is fed through the coil and the heating roller is heated by an induced current (eddy current) caused thereby. The temperature of the heating roller is controlled so as to be held at a predetermined temperature on basis of detection signal from the thermistor. A sheet is conveyed while being nipped between the heating roller and the pressurizing roller and a toner image formed on the sheet is fixed to the sheet.
The fixing device, however, has a defect in that it is difficult to accurately detect the temperature because the part of the outer periphery of the heating roller of which temperature is detected by the thermistor is far from the region (heating region) which is inductively heated by the coil. In particular, failure in the motor might cause the heating roller to stop rotating and to undergo an abnormal local temperature increase, which could not be detected accurately in the above example and might entail a danger of firing.
In such an external coil type in which a coil is placed outside a heating roller as described above, it is often impossible to provide a temperature sensor inside the heating roller because thermal insulating material such as sponge rubber is provided inside the roller. In an internal coil type in which a coil is placed inside a heating roller, it is possible to provide a temperature sensor outside the heating roller so as to face a heating region, however, the placement of major elements inside and outside the heating roller results in increase in scale and cost of the device.
Therefore, an object of the present invention is to provide an induction heating device and an induction heating fixing device which are capable of accurately detecting temperature of heating region of an object to be heated, at low cost, and capable of increasing stability and safety in control of the temperature.
Another object of the invention is to provide an image forming apparatus having such an induction heating fixing device.
In order to achieve the object, the present invention provides an induction heating device for inductively heating an object to be heated which is formed of conductive material, comprising:
Herein, “conductor section” refers to a part of the “conductor” that forms the coil.
In the induction heating device of the invention, the layer of conductor that forms the coil is positioned so as to extend along the object. In an operation, a high-frequency current is passed through the coil, and the object is heated by an induced current (eddy current) caused by the current passage. In the induction heating device, a gap is formed between conductor sections of the coil through which electric currents respectively flow in the same direction, the gap being used for detecting temperature of the object. Therefore a temperature sensor can be provided in the gap so as to face the object, for example. Alternatively, a temperature sensor of infrared type may be provided in a position farther than the coil from the object so that temperature of part of the object corresponding to the gap can be detected with use of the gap as a path for the detection. In those configurations, the part of which the temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. The temperature of the object is controlled to a predetermined temperature on basis of detection signal from the temperature sensor. As a result, stability and safety in temperature control for the object can be improved.
The gap is provided between the conductor sections that form the coil, so that the coil is cooled by passage of air through the gap. Accordingly, heat generating efficiency can be kept high.
The gap in the coil is formed simply by a change in winding of the coil. Besides, the coil and the temperature sensors are positioned on the same side (all outside or all inside) of the object, and therefore the device is not required to have a large scale. As a result, the induction heating device can be configured at low cost.
The object may contain material other than conductive material. The coil may be in the form of a plurality of layers stacked in a direction perpendicular to layer direction, which are composed of a plurality of turns of conductor respectively. The “layer direction” refers to directions along the layer as a whole. In this configuration, the “gap” between conductor sections means a gap along the layer direction.
In an embodiment of the induction heating device, the holder comprises a core made of magnetic material.
In the embodiment of the induction heating device, magnetic flux produced by the coil is guided to the object, through the magnetic material that forms the core. Thus heat generating efficiency is improved. As a result, the induction heating device can be configured compactly and miniaturized.
In an embodiment of the induction heating device, a temperature sensor is provided in the gap so as to face the object.
In the embodiment of the induction heating device, a temperature sensor is provided in the gap so as to face the object. Thus the part of which temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. As a result, stability and safety in temperature control for the object can be improved.
Preferably, the temperature sensor is a thermosensitive switch (thermostat). The thermosensitive switch performs on-off control action with use of thermal energy emitted by an object to be detected, and a structure of a temperature controlling circuit for controlling the temperature of the object can be simplified by use of the thermosensitive switch.
An embodiment of the induction heating device is characterized in that a temperature sensor of infrared type is provided in a position farther than the coil from the object so that temperature of part of the object corresponding to the gap can be detected with use of the gap as a path for the detection.
More particularly, the embodiment of the induction heating device is an induction heating device for inductively heating the object which is formed of conductive material, comprising:
In the embodiment of the induction heating device, similarly, the part of which temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. As a result, stability and safety in temperature control for the object can be improved.
In an embodiment of the induction heating device, the object consists of a body of rotation, and the holder and the coil are positioned outside the body of rotation.
Herein, “body of rotation” refers to a solid formed by rotating a two-dimensional figure about an axis.
In the embodiment of the induction heating device, the holder and the coil are positioned outside the body of rotation that forms the object, and temperature of outer surface of the body of rotation is detected from outside of the body of rotation through the gap of the coil. Such a configuration is useful for an object inside which heat insulating material such as sponge rubber is provided and inside which no space exists for provision of a temperature sensor.
In an embodiment of the induction heating device, the object consists of a hollow body of rotation, and the holder and the coil are positioned in hollow space in the hollow body of rotation.
In the embodiment of the induction heating device, the holder and the coil are positioned in hollow space in the hollow body of rotation that forms the object, and temperature of inner surface of the hollow body of rotation is detected from inside of the body of rotation through the gap of the coil. In the embodiment, it is unnecessary to provide the holder and the coil outside the object and therefore the induction heating device can be configured compactly.
In another aspect, the present invention provides an induction heating fixing device of induction heating type for fixing a toner image to a sheet while conveying the sheet, comprising:
Herein, “width direction of the sheet” refer to a direction substantially perpendicular to a direction in which the sheet is conveyed, and “conductor section” refers to a part of the “conductor” that forms the coil.
In an operation of the induction heating fixing device of the invention, a high-frequency current is passed through the coil, and the fixing member is heated by an induced current (eddy current) caused by the current passage. Then the sheet is conveyed through the pinching part between the fixing member and the pressurizing member, and a toner image formed on the sheet is thereby fixed to the sheet. In the induction heating fixing device, a gap is formed between conductor sections of the coil which extend in a direction parallel to width direction of the sheet being conveyed through pinching part between the fixing member and the pressurizing member and through which electric currents respectively flow in the same direction, the gap being used for detecting temperature of the fixing member. Therefore, a temperature sensor can be provided in the gap so as to face the fixing member, for example. Alternatively, a temperature sensor of infrared type may be provided in a position farther than the coil from the fixing member so that temperature of part of the fixing member corresponding to the gap can be detected with use of the gap as a path for the detection. In those configurations, the part of which temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. The temperature of the fixing member is controlled to a predetermined temperature on basis of detection signal from the temperature sensor. As a result, stability and safety in temperature control for the fixing member can be improved.
The gap is provided between the conductor sections that form the coil, so that the coil is cooled by passage of air through the gap. Accordingly, a heat generating efficiency can be kept high.
The gap in the coil is formed simply by a change in winding of the coil. Besides, the coil and the temperature sensors are positioned on the same side (all outside or all inside) of the fixing member, and therefore the device is not required to have a large scale. As a result, the induction heating fixing device can be configured at low cost.
The fixing member may contain material other than conductive material. The coil may be in the form of a plurality of layers stacked in a direction perpendicular to layer direction, which are composed of a plurality of turns of conductor respectively. The “layer direction” refers to directions along the layer as a whole. In this configuration, the “gap” between conductor sections means a gap along the layer direction.
In an embodiment of the induction heating fixing device, the holder comprises a core made of magnetic material.
In the embodiment the induction heating fixing device, magnetic flux produced by the coil is guided to the fixing member through the magnetic material that forms the core. Thus heat generating efficiency is improved. As a result, the induction heating fixing device can be configured compactly and miniaturized.
In an embodiment of the induction heating fixing device, a temperature sensor is provided in the gap so as to face the fixing member.
In the embodiment of the induction heating fixing device, a temperature sensor is provided in the gap so as to face the fixing member. Thus the part of which temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. As a result, stability and safety in temperature control for the fixing member can be improved.
Preferably, the temperature sensor is a thermosensitive switch (thermostat). The thermosensitive switch performs on-off control action with use of thermal energy emitted by an object to be detected, i.e., the fixing member. Therefore structure of temperature controlling circuit for controlling the temperature of the fixing member can be simplified by use of the thermosensitive switch.
An embodiment of the induction heating fixing device is characterized in that a temperature sensor of infrared type is provided in a position farther than the coil from the fixing member so that temperature of part of the fixing member corresponding to the gap can be detected with use of the gap as a path for the detection.
More particularly, the embodiment of the induction heating fixing device is an induction heating fixing device for inductively heating a fixing member which is formed of conductive material, comprising:
In the embodiment of the induction heating fixing device, similarly, the part of which the temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. As a result, stability and safety in temperature control for the fixing member can be improved.
In an embodiment of the induction heating fixing device, the fixing member consists of a body of rotation, and the holder and the coil are positioned outside the body of rotation.
Herein, “body of rotation” refers to a solid formed by rotating a two-dimensional figure about an axis.
In the embodiment of the induction heating fixing device, the holder and the coil are positioned outside the body of rotation that forms the fixing member, and temperature of outer surface of the body of rotation is detected from outside of the body of rotation through the gap of the coil. Such a configuration is useful for a fixing member inside which heat insulating material such as sponge rubber is provided and inside which no space exists for provision of a temperature sensor.
In an embodiment of the induction heating fixing device, the fixing member consists of a hollow body of rotation, and the holder and the coil are positioned in hollow space in the hollow body of rotation.
In the embodiment of the induction heating fixing device, the holder and the coil are positioned in hollow space in the hollow body of rotation that forms the fixing member, and temperature of inner surface of the hollow body of rotation is detected from inside of the body of rotation through the gap of the coil. In the embodiment, it is unnecessary to provide the holder and the coil outside the fixing member and therefore the induction heating fixing device can be configured compactly.
In an embodiment of the induction heating fixing device, the fixing member consists of a body of rotation that is rotated about a central axis, the holder has a protrusion extending toward the body of rotation and wound in the coil, and the gaps in the coil are provided on upstream side and downstream side of the protrusion of the holder with respect to rotation direction of the fixing member.
Herein, “central axis” refers to the central axis of the body of rotation.
In the embodiment of the induction heating fixing device, the gaps in the coil are provided on upstream side and downstream side of the protrusion of the holder with respect to the rotation direction of the fixing member. Accordingly, distribution of generated heat on the fixing member is symmetrical about a part of the fixing member corresponding to the protrusion of the holder, on upstream side and downstream side of the protrusion with respect to the rotation direction of the fixing member. Therefore temperature of part of the fixing member corresponding to the gap on the downstream side, for example, can be found by provision of a temperature sensor in the gap on the upstream side, for example, and by detection of temperature of part of the fixing member corresponding to the gap. Thus the temperature can be detected more accurately. As a result, stability and safety in temperature control for the fixing member can be improved.
In an embodiment, the induction heating fixing device further comprises a second coil for heating a second region of the fixing member wherein the second region is different from a first region of the fixing member heated by the first coil with respect to the width direction of the sheet.
Herein, the “second region” is not entirely superimposed on the first region, i.e., the “second region” is partially superimposed on the first region.
Typically, the first region of the fixing member which is heated by the first coil with respect to the width direction of the sheet (which will be referred to as “first heating width”) is determined in accordance with a sheet having the largest width that is fed to the device. That is intended for achieving satisfactory fixing over the whole area of the sheet having the largest width. When a sheet having a width smaller than the sheet having the largest width is fed, there is produced a part of the first heating width that does not contribute to heating of the sheet. Then the temperature of the part may become higher than that of the other part that contributes to heating of the sheet, and the temperature of the fixing member may vary with respect to the width direction of the sheet. Therefore, the embodiment of the induction heating fixing device has a second coil for heating a second region of the fixing member wherein the second region is different from a first region of the fixing member heated by the first coil with respect to the width direction of the sheet, as described above. The second region of the fixing member which is heated by the second coil (which will be referred to as “second heating width”) may be determined in accordance with sheets that are fed to the device. For example, the second region is determined in accordance with a sheet smaller in width than the sheet having the largest width that is fed to the device. With such a setting, the whole second heating width can be made to contribute to heating of the sheet. Thus the temperature of the fixing member becomes uniform with respect to the width direction of the sheet. Consequently, stability and safety in the temperature control for the fixing member can further be improved.
In another aspect, the present invention provides an image forming apparatus comprising an image forming unit for forming a toner image and an induction heating fixing device of induction heating type for fixing to a sheet the toner image formed by the image forming unit while conveying the sheet, comprising:
The image forming unit may form the toner image directly on the sheet or may form the toner image temporarily on a transferring body and may thereafter transfer the toner image onto the sheet.
In an operation of the image forming apparatus of the invention, a high-frequency current is passed through the coil of the induction heating fixing device, and the fixing member is heated by an induced current (eddy current) caused by the current passage. Then a toner image is formed by the image forming unit, a sheet is conveyed through the pinching part between the fixing member and the pressurizing member, and the toner image formed by the image forming unit is thereby fixed to the sheet. In the image forming apparatus, a gap is formed between conductor sections of the coil which extend in a direction parallel to width direction of the sheet being conveyed through pinching part between the fixing member and the pressurizing member and through which electric currents respectively flow in the same direction, the gap being used for detecting temperature of the fixing member. Therefore, a temperature sensor can be provided in the gap so as to face the fixing member, for example. Alternatively, a temperature sensor of infrared type may be provided in a position farther than the coil from the fixing member so that temperature of part of the fixing member corresponding to the gap can be detected with use of the gap as a path for the detection. In those configurations, the part of which the temperature is detected by the temperature sensor is positioned within the region (heating region) that is inductively heated by the coil, and therefore the temperature can be detected accurately. The temperature of the fixing member is controlled to a predetermined temperature on basis of detection signal from the temperature sensor. As a result, stability and safety in temperature control for the fixing member can be improved.
The gap is provided between the conductor sections that form the coil, so that the coil is cooled by passage of air through the gap. Accordingly, heat generating efficiency can be kept high.
The gap in the coil is formed simply by a change in winding of the coil. Besides, the coil and the temperature sensor are positioned on the same side (all outside or all inside) of the fixing member, and therefore the device is not required to have a large scale. As a result, the image forming apparatus can be configured at low cost.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
Hereinbelow, the present invention will be described in detail with reference to embodiments shown in the drawings.
The fixer has in a casing 10 a cylindrical fixing roller 1 as an object to be heated or a fixing member, a cylindrical pressurizing roller 2 as a pressurizing member, a ferrite core 5 as a holder, a layer-like coil 6 that is positioned so as to extend along outer periphery of the fixing roller 1, a first temperature sensor 7 composed of a thermostat, a second temperature sensor 8 of infrared type, and guides 3, 4, and 9 for guiding a paper form 90 as a sheet.
As shown in
The fixing roller 1 in
The ferrite core 5 is composed of magnetic material and is positioned outside and below the fixing roller 1 so as to extend along and face the outer periphery of the fixing roller 1. The ferrite core 5 has a section generally shaped like a letter E as a whole and extends along axial direction of the fixing roller 1. Specifically, the ferrite core 5 has a main body 5p having a cross section shaped like a circular arc with the same curvature that the outer periphery of the fixing roller 1 has, and three protrusions extending from the main body 5p toward the fixing roller 1, i.e., a center protrusion 5a and end protrusions 5b and 5c.
As shown in
Specifically, the coil 6 includes an outward conductor section 6-1 and a return conductor section 6-2 both of which extend in longitudinal direction (in lateral direction in
The longitudinal direction of the coil 6 correspond to a direction parallel to the central axis of the fixing roller 1 in
As shown in
The first temperature sensor 7 composed of a thermostat is positioned in the gap 6b of the coil 6 so as to face the fixing roller 1. In this example, the first temperature sensor 7 is placed generally at longitudinal center (a position shown by a broken line in
The ferrite core 5, the coil 6, and the first temperature sensor 7 form a coil unit for induction heating as the induction heating device.
Upon passage of a current through the coil 6 in such an arrangement, most of a magnetic field produced by the coil 6 is guided by the ferrite core 5 to pass through the Ni alloy layer 1c of the fixing roller 1, eddy currents are produced there, and heat is generated in a region of the outer periphery of the fixing roller 1 that faces the coil 6. Thus most of the magnetic field produced by the exciting coil 6 is guided to the fixing roller 1 through the ferrite core 5 that is magnetic material, and therefore heat generating efficiency is increased. As a result, this fixer can be made compact and can be miniaturized.
As shown in
Angle positions of the gaps 6b and 6c of the coil 6 are made to correspond to positions of peaks in the distribution of generated heat. That is, the thermostat 7 provided in the gap 6b is capable of detecting temperature of a peak of the distribution of generated heat. Since the distribution of generated heat is symmetrical on both sides of the origin O, temperature of part corresponding to the gap 6c on the downstream side can be found by providing the temperature sensor in the gap 6b on the upstream side, as shown in this example, and detecting the temperature of the part corresponding to the gap 6b.
As shown in
On basis of signal representing an operation mode from a CPU (Central Processing Unit) 15 for performing control over a whole printer (signal on a target temperature of the fixing roller 1 in printing mode, standby mode or the like) and signal representing a detected temperature from the second temperature sensor 8, the control unit 14 performs ON/OFF control over the IGBT 13 so as to approach the detected temperature to the target temperature. As shown in
In a printing operation, the temperature of the fixing roller 1 is controlled to be kept at a target temperature according to a printing mode by the temperature controlling circuit 20 including the control unit 14. Then a paper form 90 is conveyed through the nipping part between the fixing roller 1 and the pressurizing roller 2, and a toner image 91 formed on the paper form 90 is thereby fixed to the paper form 90.
On condition that the rotation of the fixing roller 1 is stopped or retarded by failure in the motor or the like, in particular, the heating region of the fixing roller 1 may extraordinarily rise in temperature. In the fixer, the thermostat 7 as the first temperature sensor provided in the gap 6b of the coil described above detects the temperature of the peak of the distribution of generated heat. Therefore, the peak temperature of the distribution of generated heat can be detected accurately. If the peak temperature of the distribution of generated heat exceeds a temperature specified in a predetermined safety standard, the thermostat 7 is turned off and the passage of the current through the coil 6 is thereby interrupted. As a result, stability and safety in the temperature control for the fixing roller 1 are improved.
The gaps 6b and 6c are provided between the conductor sections forming the coil 6, so that the coil 6 is cooled by passage of air through the gaps 6b and 6c. Accordingly, copper loss is restrained from increasing and the heat generating efficiency can be kept high.
The gaps 6b and 6c between the conductor sections that form the coil 6 are formed simply by the change in winding of the coil. Besides, the coil 6 and the temperature sensors 7 and 8 are positioned on the same side (outside, in this example) of the fixing roller 1, and therefore the device is not required to have a large scale. As a result, the fixer can be configured at low cost.
For example, sizes of gaps 6b and 6c may vary with longitudinal positions as in the coils 6A and 6B shown in
As in the coil 6C shown in
The gaps do not have to exist in the center of a length of the coil and a large number of gaps may be provided.
Specifically, the fixer has a cylindrical fixing roller 21 as an object to be heated or a fixing member and a cylindrical pressurizing roller 22 as a pressurizing member with which the fixing roller 21 is in pressure contact. As is the case with the embodiment described above, a nipping part as a pinching part is formed between the fixing roller 21 and the pressurizing roller 22. As shown in
As shown in
In the holder 23 are installed a ferrite core 25 having a T-shaped cross section and a layer-like coil 26 provided along the inner periphery of the fixing roller 21.
The ferrite core 25 has a center protrusion 25a extending toward the fixing roller 21 and two end protrusions 25b and 25c extending toward the fixing roller 21 in directions opposite to each other.
The coil 26 is identical with the coil 6 shown in
In this example, a first temperature sensor 27 composed of a thermostat is positioned in one gap 26b and a second temperature sensor 28 is positioned in the other gap 26c. Thus temperature of inner surface of the fixing roller 21 is detected from inside of the fixing roller 21 through the gaps 26b and 26c of the coil 26.
In a printing operation, the temperature controlling circuit 20 shown in
The embodiment improves stability and safety in the temperature control for the fixing roller 21, as is the case with the embodiment described above. Besides, the fixer can compactly be configured because it is unnecessary to provide a holder, a coil and the like outside the fixing roller 21.
As shown in
A configuration of the second coil 36 except the longitudinal size is the same as the configuration of the first coil 6. That is, the second coil 36 has a center gap 36a and gaps 36b, 36c positioned symmetrically about the center gap 36a. The gaps 36b and 36c are provided between conductor sections through which electric currents respectively flow in the same direction. On condition that the second coil 36 is stacked on the first coil 6 as shown in
Consequently, a distribution of generated heat provided by the second coil 36 coincides with the distribution of generated heat provided by the first coil 6, according to observation along the outer periphery of the fixing roller 1. That is, the distribution of generated heat is symmetrical and have peaks on the upstream side and the downstream side with respect to the rotation direction of the fixing roller 1.
According to observation in direction along the central axis of the fixing roller 1, i.e., in direction along the width of the paper form 90, the region that is heated by the second coil 36 (which will be referred to as “second heating width”) is narrower than the region that is heated by the first coil 6 (which region will be referred to as “first heating width”).
A first temperature sensor 7 composed of a thermostat is positioned so as to extend through the gap 6b of the first coil 6 and the gap 36b of the second coil 36 and so as to face the fixing roller 1. A second temperature sensor 8 faces a part of the outer periphery of the fixing roller 1 that is far from the heating region, as is the case with the embodiment of
In a printing operation, the temperature controlling circuit 20 shown in
When a paper form of A3 size having the largest width is fed, in this arrangement, the whole first heating width that is heated by the first coil 6 can be made to contribute to heating of the paper form. When a paper form of B4 size having a width smaller than A3 form has is fed, the whole second heating width that is heated by the second coil 36 can be made to contribute to heating of the paper form. Thus the temperature of the fixing roller 1 becomes uniform along the width of a paper form. Consequently, stability and safety in the temperature control for the fixing roller can further be improved.
In accordance with the embodiment, the peak temperature of the distribution of generated heat is detected with use of the single thermostat 7 that is common on occasion of the current passage through the first coil 6 and on occasion of the current passage through the second coil 36, and therefore the fixer can be configured compactly at low cost. Complication of circuit structure is also avoided.
Specifically, the fixer has a ferrite core 35 obtained by enlargement of the ferrite core 5 in
The first coil 6 is mounted on the ferrite core 35 in such a manner that a center gap 6a of the coil 6 is fit on the inner protrusion 35a of the ferrite core 35 and that the coil 6 as a whole is surrounded by and enclosed between the inner protrusion 35b and the end protrusion 35c of the ferrite core 35. The second coil 36 is mounted on the ferrite core 35 in such a manner that a center gap 36a of the coil 36 is fit on the inner protrusion 35b of the ferrite core 35 and that the coil 36 as a whole is surrounded by and enclosed between the inner protrusion 35a and the end protrusion 35d of the ferrite core 35.
A first temperature sensor 7 composed of a thermostat is positioned so as to extend through the gap 6b of the first coil 6 and through the gap 36c of the second coil 36 and so as to face the fixing roller 1. A second temperature sensor 8 faces a part of the outer periphery of the fixing roller 1 that is far from the heating region, as is the case with the embodiment of
When a paper form of A3 size having the largest width is fed (i.e., when a current is passed through the first coil 6), there are used the protrusions 35a, 35b, and 35c out of the protrusions of the ferrite core 35. When a paper form of B4 size having a width smaller than A3 form has is fed (i.e., when a current is passed through the second coil 36), there are used the protrusions 35a, 35b, and 35d out of the protrusions of the ferrite core 35.
In accordance with the embodiment, a magnetic circuit can be optimized for the first coil 6 and for the second coil 36, individually, though the coil unit is enlarged in comparison with the embodiment of
In a main body 5p of the ferrite core 5, a through hole 5w is provided in a position corresponding to the first temperature sensor 7 shown in
In the fixer, both the first temperature sensor 7A and a second temperature sensor 8 are of infrared type and therefore a configuration of a temperature controlling circuit can be made common to the two temperature sensors 7A and 8. Accordingly, a circuit structure in the fixer can be simplified and the fixer can be configured at low cost.
The color printer has a four-color developing unit 50 as a image forming unit, loop-like transfer felt 51 as an object to be heated or a fixing member wound around a roller 52 and a fixing roller 53, a cylindrical pressurizing roller 54 as a pressurizing member, a coil unit 59 for induction heating that is positioned so as to extend along a flat section (a lower side section 51b) inside the transfer felt 51, a second temperature sensor 58, and guides (not shown) for guiding a paper form 92 as a sheet.
The developing unit 50 has a yellow developing section 50Y, a magenta developing section 50M, a cyan developing section 50C, and a black developing section 50K, which are disposed along a direction of circulation of the transfer felt 51. A toner image 93 with four colors is transferred onto the transfer felt 51 by the developing sections.
The transfer felt 51 is configured like a belt wound around the roller 52 and the fixing roller 53. In the transfer felt 51, for convenience, an upper section between the roller 52 and the fixing roller 53 is referred to as an upper side section 51a, and a lower section between the roller 52 and the fixing roller 53 is referred to as the lower side section 51b. The transfer felt 51 is driven by the roller 52 and the fixing roller 53 so as to circulate in a direction such that the upper side section 51a moves leftward and such that the lower side section 51b moves rightward, as shown by an arrow in
As shown in
In
The coil unit 59 for induction heating has a ferrite core 55 as a holder, a layer-like coil 56 positioned along the flat section (the lower side section 51b) inside the transfer felt 51, and a first temperature sensor 57 composed of a thermostat.
The ferrite core 55 has a cross section generally shaped like a letter E as a whole, and extends along axial direction of the fixing roller 53. Specifically, the ferrite core 55 has a main body 55p having a cross section shaped like a flat plate and three protrusions extending from the main body 55p toward the transfer felt 51, i.e., a center protrusion 55a and end protrusions 55b and 55c.
A configuration of the coil 56 is the same as the configuration of the coil 6 shown in
The coil 56 is mounted on the ferrite core 55 with adhesive such as glue in such a manner that the center gap 56a of the coil 56 is fit on the center protrusion 55a of the ferrite core 55 and that the coil 56 as a whole is surrounded and enclosed by the end protrusions 55b and 55c of the ferrite core 55.
A first temperature sensor 57 composed of a thermostat is provided in the gap 56b of the coil 56 so as to face the transfer felt 51.
A second temperature sensor 58 is provided above the fixing roller 53 so as to face the transfer felt 51.
The color printer has a CPU 70 for controlling operations of the whole printer, and a temperature controlling circuit 60 having the same configuration that the temperature controlling circuit 20 shown in
In a printing operation, the temperature of the transfer felt 51 is controlled to a target temperature according to a printing mode by the temperature controlling circuit 60. Then a paper form 92 is conveyed through the nipping part between the transfer felt 51 and the pressurizing roller 54, and a toner image 93 formed on the transfer felt 51 is thereby transferred onto and fixed to the paper form 92.
On condition that the circulation of the transfer felt 51 is stopped or retarded by failure in a motor or the like, in particular, a heating region of the transfer felt 51 may extraordinarily rise in temperature. In the fixer, the thermostat 57 as the first temperature sensor provided in the gap 56b of the coil described above detects temperature of peak of a distribution of generated heat. Therefore, the peak temperature of the distribution of generated heat can be detected accurately. If the peak temperature of the distribution of generated heat exceeds a temperature specified in a predetermined safety standard, the thermostat 57 is turned off and the passage of the current through the coil 56 is thereby interrupted. As a result, stability and safety in the temperature control for the transfer felt 51 can be improved.
The gaps 56b and 56c are provided between the conductor sections that form the coil 56, so that the coil 56 is cooled by passage of air through the gaps 56b and 56c. Accordingly, copper loss is restrained from increasing and heat generating efficiency can be kept high.
The gaps 56b and 56c between the conductor sections that form the coil 56 are formed simply by the change in winding of the coil. Besides, the coil 56 and the temperature sensor 57 are positioned on the same side (inside, in this example) of the transfer felt 51, and therefore the device is not required to have a large scale. As a result, the color printer can be configured at low cost.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-339749 | Sep 2003 | JP | national |
