Patent Application
20130034363
The present invention relates to an image heating apparatus to be mounted in an image forming apparatus, such as a copying machine, a printer or a facsimile machine, for forming an image on a recording material. Particularly, the present invention relates to an image heating apparatus for heating the image by an image heating member of an induction heating type.
An image forming apparatus in which after a toner image is transferred onto a recording material fed from a feeding portion to an image forming portion, the recording material on which the toner image is transferred is nip-conveyed through a heating nip of a heat generating member (fixing roller or fixing belt) of a fixing device to fix an image on the recording material has been widely known. Also an image heating apparatus using an induction heating device as a heating source of the heat generating member has been put into practical use (Japanese Laid-Open Patent Application (JP-A) 2001-194940 and JP-A 2006-120533).
In the image heating apparatus using the induction heating device, when sheets of the recording material with a length smaller than a length of the heat generating member with respect to a rotation axis direction of the heat generating member are continuously passed through the image heating apparatus, a phenomenon that a temperature in non-sheet-passing regions located at end portions of the heat generating member is increased is caused to occur. This phenomenon is hereinafter referred to as non-sheet-passing portion temperature rise.
In JP-A 2001-194940, a plurality of magnetic cones are provided with respect to the rotation axis direction of the heat generating member (fixing belt) and with respect to the magnetic cones at both end portions, an opposing gap from the heat generating member is enlarged, so that the non-sheet-passing portion temperature rise is avoided.
In JP-A 2006-120533, a size of a magnetic flux shielding plate for covering an end portion of the heat generating member (fixing roller) is switched to keep a heating range at an outside position of the recording material at a certain width even when a size of the recording material is changed, so that the non-sheet-passing portion temperature rise is avoided. Further, a temperature sensor is provided at the end portion of the heat generating member to actually measure the non-sheet-passing portion temperature rise and then the number of sheets per unit time of the recording material fed by the feeding portion is controlled.
A principal object of the present invention is to provide an image heating apparatus, in which a limiter of electric power supplied to a coil is provided for suppressing temperature rise at a non-sheet-passing temperature rise at a non-sheet-passing portion, capable of reinforcing an application performance to a recording material having a large thermal capacity in an operation in a mode in which an image on the recording material is heated at a low speed.
According to an aspect of the present invention, there is provided an image heating apparatus comprising: a coil for generating magnetic flux; a rotatable heat generating member for generating heat by the magnetic flux from the coil; a nip forming member for forming a nip, together with the heating member, in which an image on a recording material is to be heated; a power source for supplying electric power to the coil; a sensor for detecting a temperature of the heat generating member; a controller for controlling, on the basis of a detection result of the sensor, the power source so that the temperature of the heat generating member is a set image heating temperature; an executing portion for executing an operation in a first mode in which the heat generating member is rotated at a first speed when the recording material with a first thickness is conveyed into the nip and for executing an operation in a second mode in which the heat generating member is rotated at a second speed lower than the first speed when the recording material with a second thickness larger than the first thickness is conveyed into the nip; and a prohibiting portion for prohibiting the electric power, supplied from the power source to the coil by the controller, from exceeding a limiter value, wherein the limiter value when the operation in the second mode is executed is set so as to be higher than that when the operation in the first mode is executed.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Parts (a) and (b) of
Parts (a) to (c) of
Hereinbelow, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be carried out also in other embodiments in which a part or all of constitutions of the respective embodiments are replaced by their alternative constitutions so long as in a constitution in which productivity is lowered with a larger fixing necessary heat quantity per sheet of a recording material, electric power for induction heating is limited.
Therefore, an image heating apparatus includes not only a fixing device for fixing a toner image on a recording material by heating the recording material on which the toner image is transferred but also an image adjusting apparatus for providing a desired surface property to an image by heating a toner image which is partly fixed or completely fixed. The image heating apparatus may also include a glossiness imparting apparatus for improving glossiness of an image by re-heating the image fixed on the recording material. A heat generating member may be either of a belt member or a roller member.
A constitution for variably setting a heating region is not limited to a constitution for moving magnetic cones in a contact and separation direction relative to an exciting coil but may also be the constitution as described in JP-A 2006-120533 in which the heating region is set by moving the magnetic flux shielding member.
An image forming apparatus can mount the image heating apparatus of the present invention irrespective of the types of monochromatic/full-color, sheet-feeding/recording material conveyance/intermediary transfer, a toner image forming method and a transfer method.
In the following embodiments, only a principal portion concerning formation/transfer/fixing of the toner image will be described but the present invention can be carried out in image forming apparatuses with various uses including printers, various printing machines, copying machines, facsimile machines, multi-function machines, and so on by adding necessary equipment, options, or casing structures.
In the image forming portion PY, a yellow toner image is formed on a photosensitive drum 21(Y) and then is transferred onto the intermediary transfer belt 26. In the image forming portion PC, a cyan toner image is formed on a photosensitive drum 21(C) and is transferred onto the intermediary transfer belt 26. In the image forming portions PM and PK, a magenta toner image and a black toner image are formed on photosensitive drums 21(M) and 21(K), respectively, and are transferred onto the intermediary transfer belt 26.
The intermediary transfer belt 26 is constituted by an endless resin belt and is stretched around a driving roller 27, a secondary transfer opposite roller 28 and a tension roller 26, and is driven by the driving roller 26.
A recording material P is pulled out from a recording material cassette 31, which is an example of a feeding portion, one by one by a sheet feeding roller 32 and is in stand-by between registration rollers 33.
The recording material P is sent by the registration rollers 33 to a secondary transfer portion T2 where the toner images are transferred from the intermediary transfer belt 26 onto the recording material P. The recording material P on which the four color toner images are transferred is conveyed into a fixing device A is, after being heated and pressed by the fixing device A to fix the toner images thereon, discharged onto an external tray 37 via a discharge conveying path 36. Incidentally, during image formation of only a monochromatic (single) color (monochromatic (single) color mode), with respect to only an intended color, the toner image is formed and then carried on the intermediary transfer belt 26, and thereafter is transferred onto the recording material.
The image forming portions PY, PC, PM and PK have the substantially same constitution except that the colors of toners of yellow, cyan, magenta and black used in developing devices 23(Y), 23(C), 23(M) and 23(K) are different from each other. In the following description, the image forming portion PY will be described and other image forming portions PC, PM and PK will be omitted from redundant description.
The image forming portion PY includes the photosensitive drum 21 around which a charging roller 22, an exposure device 25, the developing device 23, a transfer roller 30, and a drum cleaning device 24 are disposed.
The charging roller 22 electrically charges the surface of the photosensitive drum 21 to a uniform potential. The exposure device 25 writes (forms) an electrostatic image for an image on the photosensitive drum 21 by scanning with a laser beam. The developing device 23 develops the electrostatic image to form the toner image on the photosensitive drum 21. The transfer roller 30 is supplied with a DC voltage, so that the toner image on the photosensitive drum 21 is transferred onto the intermediary transfer belt 26.
As shown in
The core metal 2a is tapered, so that the thickness of the elastic layer 2b is different between the central portion and each of the end portions. For this reason, a length of the fixing nip N between the fixing belt 1 and the pressing roller 2 is, when the fixing nip pressure is 600 N, about 9 mm at each of the end portions and about 8.5 mm at the central portion. As a result, a conveying speed of the recording material P at each of the end portions is higher than that at the central portion, so that there is such an advantage that paper creases are not readily gaped.
The pressure-applying member 3 is held by a metal stay 4 at its inner surface and supports an inner surface of the fixing belt 1 by its outer surface. The pressure-applying member 3 applies an urging force (pressure) to the pressing roller 2 via the fixing belt 1, thus forming the fixing nip N between the fixing belt 1 and the pressing roller 2. The pressure-applying member 3 is formed of a heat-resistant resin material. In a side where the stay 4 opposes an exciting coil 6, a magnetic flux shielding core 5 as a magnetic flux shielding member for preventing temperature rise of the stay 4 caused due to induction heating is provided.
As shown in
The fixing flanges 10 are left and right preventing members (regulating members) for preventing (regulating) rotation axis directional movement of and circumferential shape of the fixing belt 1 are provided. A stay urging spring 9b is compressedly provided between each end portion of the stay 4 provided by being inserted into the flanges 10 and a spring receiving portion 9a provided in a device chassis side, so that a pressing-down force is applied to the stay 4. As a result, the lower surface of the pressure applying member 3 and the upper surface of the pressing roller 2 are press-contacted to the fixing belt 1 therebetween, so that the fixing nip N for the image on the recording material is formed. A base layer of the rotating fixing belt 1 is formed of metal and therefore even in the rotation state, as a means for preventing deviation (shift) in a widthwise direction, provision of the fixing flanges only for simply receiving the end portions of the fixing belt 1 suffice. As a result, there is the advantage such that the constitution of the fixing device can be simplified.
As shown in
As a material for the base layer 1a, in addition to nickel, an iron alloy, copper, silver or the like is appropriately selectable. Further, the base layer 1a may also be constituted so that a layer of the metal or metal alloy described above is laminated on a resin material base layer. The thickness of the base layer 1a may be adjusted depending on a frequency of a high-frequency current caused to flow through the exciting coil described later and depending on magnetic permeability and electrical conductivity of the base layer and may be set in a range from 5 μm to 200 μm.
On the other peripheral surface of the base layer 1a, an elastic layer 1b which is a heat-resistant silicone rubber layer is provided. The thickness of the elastic layer 1b may preferably be set within a range of 100-1000 μm. In this embodiment, in consideration of reduction in a warming-up time by decreasing thermal capacity of the fixing belt 1 and obtaining of a suitable fixed image when the color images are fixed, the thickness of the elastic layer 1b is 300 μm. The silicone rubber layer as the elastic layer 1b has a hardness (JIS-A) of 20 degrees and is 0.8 W/mK in thermal conductivity. On the other peripheral surface of the elastic layer 1b, a parting layer 1c of fluorine-containing resin (such as PFA or PTFE) is formed in a thickness of 30 μm. On the inner surface of the base layer 1a, in order to lower sliding friction between the fixing belt inner surface and a central thermistor (TH1 in
As shown in
The exciting coil 6 uses Litz wire as an electric wire and is prepared by winding Litz wire in an elongated ship's bottom-like shape so that the exciting coil 6 opposes a part of the peripheral surface of the fixing belt 1. The exciting coil 6 is 352 mm in inner diameter and 392 mm in outer diameter with respect to the longitudinal direction.
Magnetic cores 7a are provided so as to cover the exciting coil 6 so that the magnetic field generated by the exciting core 6 is not substantially leaked to a portion other than the metal layer (electroconductive layer) of the fixing belt 1. The magnetic cores 7a have the function of efficiently guiding AC magnetic flux generated from the exciting coil 6 to the fixing belt 1. The magnetic cores 7a are used for increasing an efficiency of a magnetic circuit of the AC magnetic flux and for shielding the magnetic flux so as to avoid induction heating of peripheral members caused by leakage of the magnetic flux to the peripheral members. As a material for the magnetic cores 7a, a material such as ferrite having high permeability and low residual magnetic flux density.
A mold member 7c supports the exciting coil 6 and the magnetic cores 7a by an electrically insulating resin material. The fixing belt 1 and the magnetic cores 7a are kept in an electrically insulating state by the mold member 7c having a thickness of 0.5 mm. A spacing between the fixing belt 1 and the exciting coil 6 is constant at 1.5 mm (i.e., a distance between the mold surface and the fixing belt surface is 1.0 mm).
In the rotation state of the fixing belt 1, to the exciting coil 6 of the induction heating device 70, a high-frequency current of 20-50 Hz is applied from a power source (supply) device (exciting circuit) 101, so that the metal layer (electroconductive layer) of the fixing belt 1 is induction-heated by the magnetic field generated by the exciting coil.
The central thermistor TH1 is a temperature sensor (temperature detecting element) and is provided at a widthwise central portion of the fixing belt 1 in contact to the fixing belt 1. The central thermistor TH1 is mounted to the pressure applying member 3 via an elastic supporting member and therefore even when positional fluctuation such as waving of a contact surface of the fixing belt 1 is generated, the central thermistor TH1 follows the positional fluctuation and is kept in a good contact state to the fixing belt 1. The central thermistor TH1 detects the temperature of the inner surface of the fixing belt 1 substantially at a center of a recording material conveying region, so that detected temperature information is fed back to the controller 102.
The controller 102 controls the electric power supplied from the power supply device 101 to the exciting coil 6 so that the detected temperature inputted from the central thermistor TH1 is kept at a predetermined target temperature (fixing temperature). The controller 102 interrupts energization to the exciting coil 6 in the case where the detected temperature of the fixing belt 1 is increased up to the predetermined temperature.
The controller 102 changes, on the basis of a detected value of the central thermistor TH1, the frequency of the high-frequency current so that the detected temperature of the fixing belt 1 is constant at 180° C. as the target temperature of the fixing belt 1, thus controlling the electric power inputted into the exciting coil 6 to adjust the temperature. The exciting coil 6 of the induction heating device 70 connected to the power supply device 101 is controlled by the controller 102, so that the fixing belt 1 is heated to the predetermined fixing temperature.
As described above, to the exciting coil 6, the high-frequency current of 20-50 kHz is applied, so that the metal layer 1a of the fixing belt 1 is induction-heated. Temperature adjustment is made by controlling the electric power inputted into the exciting coil 6 by changing, on the basis of the detected value of the central thermistor TH1, the frequency of the high-frequency current so that the fixing belt temperature is kept at 180° C. as the target temperature of the fixing belt 1.
The induction heating device 70 including the exciting coil 6 is not disposed inside the fixing belt 1 which becomes a high temperature but is disposed inside the fixing belt 1 and therefore the temperature of the exciting coil 6 is not readily increased to the high temperature. Further, also an electric resistance is not increased, so that even when the high-frequency current is carried, it becomes possible to alleviate loss caused by Joule heat generation. Further, by externally disposing the exciting coil 6, the fixing belt 1 is downsized (low thermal capacity), so that it can be said that the induction heating device 70 is excellent in an energy saving property.
With respect to the warming-up time of the fixing device A in this embodiment, a constitution in which the thermal capacity is very low is employed and therefore when, e.g., 1200 W is inputted into the exciting coil 6, the temperature of the fixing device A can reach 165° C. as the target temperature in about 15 sec. There is no need to perform a heating operation and therefore electric power consumption can be suppressed at a very low level.
The fixing belt is rotationally driven at a peripheral speed, substantially equal to a conveying speed of the recording material P conveyed from the secondary transfer portion T2 in
The recording material P on which an unfixed toner image T is guided by a guide member 7 with its toner image carrying surface toward the fixing belt 1 to be introduced into the fixing nip N formed between the fixing belt 1 and the pressing roller 2 under pressure. The recording material P is, in the fixing nip N, intimately contacted to the outer peripheral surface of the fixing belt 1, thus being nip-conveyed together with the fixing belt 1 through the fixing nip N.
The unfixed toner image T is fixed on the surface of the recording material P by being pressed in the fixing nip N while being supplied with heat of the fixing belt 1. The surface of the recording material P passing through the fixing nip N is deformed at an exit portion of the fixing nip N, so that the recording material P is self-separated from the outer peripheral surface of the fixing belt 1 to be conveyed to the outside of the fixing device A.
Parts (a) and (b) of
As shown in
As shown in
On the other hand, at the non-sheet-passing portion, by increasing the gap between the exciting coil 6 and the magnetic cores 7a, the density of the magnetic flux passing through the fixing belt 1 is decreased, so that an amount of heat generation of the fixing belt 1 is decreased.
As shown in (a) of
As shown in
The plurality of the magnetic cones 7a are movable in a contact and separation direction relative to the fixing belt 1. The plurality of the magnetic cones 7a are arranged in the rotation axis direction of the fixing belt 1 and guide the magnetic flux generated by the exciting coil 6 to the fixing belt 1 in the respective regions. The controller 102 sets the region of the image heating temperature by moving the magnetic cones 7a in the number corresponding to the length of the recording material with respect to the widthwise direction close to the fixing belt 1 than other magnetic cones 7a.
The magnetic cores 7a are accommodated in a housing 76 while being held by a magnetic core holder 77. The magnetic core holder 77 is movable in a direction in which the gap between the exciting coil 6 and the magnetic cores 7a is changed. A link member 75 is assembled rotatably about a rotation shaft 76 and is connected to the magnetic core holder 77 at an elongated hole portion provided at its end portion. When the link member 75 is rotated about the rotation shaft 78 in Q1 direction, the magnetic core holder 77 and the magnetic cores 7a are moved in P1 direction. When the link member 75 is rotated about the rotation shaft 78 in Q2 direction, the magnetic core holder 77 and the magnetic cores 7a are moved in P2 direction. The link member 75 is surged by an exciting coil spring 74 in a direction in which it is rotated in the Q1 direction, but is prevented from moving in the Q1 direction by a regulating (preventing) member 73.
In a state in which the link member 75 is pressed-in by the regulating member 73, the link member 75 is rotationally moved in the Q2 direction against the exciting coil spring 74. At this time, the magnetic core holder 77 is moved in the arrow P2 direction, so that the magnetic cores 7a approach the exciting coil 6.
When the pressing-in of the link member 75 by the regulating member 73 is released (eliminated), the link member 75 is rotationally moved in the Q1 direction by being urged by the exciting coil spring 74 and thus is abutted against a frame 79 to be stopped. As a result, the magnetic core holder 77 is moved in the arrow P1 direction, so that the magnetic cores 7a are moved away from the exciting coil 6.
As shown in
Parts (a) to (c) of
Also from the viewpoints of material cost and energy efficiency, in the image forming apparatus E, it is a desirably tendency that the thermal capacity is decreased by using a thin heat generating member and the fixing belt is heated by the induction heating device with a good heating efficiency.
However, in the case where the thin heat generating member is used, a cross-sectional area of a cross section perpendicular to the rotation axis direction is very small and therefore a heat transfer efficiency with respect to the rotation axis direction is not good. This tendency is conspicuous with a smaller thickness of the heat generating member, and is further low for a resin material with a low thermal conductivity.
This is also clear from the Fourier's law such that a heat quantity Q transmitted per unit time is, when the thermal conductivity is λ, a temperature difference between two point is θ1−θ2 and a length between the two points is L, represented by the following formula:
Q=λ×f(θ1−θ2)/L.
In a state in which a heat transfer efficiency of the heat generating member with respect to the rotation axis direction is not good, when the small-sized recording material is subjected to the continuous sheet passing, the temperature of the heat generating member in the non-sheet-passing region is increased more than in the sheet passing region, so that a problem of a so-called non-sheet-passing portion temperature rise such that temperature non-uniformity of the heat generating member with respect to the rotation axis direction occurs is caused to be generated.
When this non-sheet-passing portion temperature rise occurs, when a large-sized recording material is heated immediately after sheets of a small-sized recording material are continuously heated, heating non-uniformity occurs on the recording material, thus causing paper creases and improper fixing. In the case where remarkable non-sheet-passing portion temperature rise occurs, a lifetime of peripheral members of a resin material is lowered in some cases. The degree of the non-sheet-passing portion temperature rise is enlarged with a larger thermal capacity of the recording material to be conveyed and with a larger print number per unit time. For this reason, in a copying machine with the high throughput, a fixing device using the thin rotatable member and the induction heating device with a good heating efficiency in combination could not be employed. In the copying machine with high productivity, in many cases, the non-sheet-passing portion transfer was avoided by dividing a halogen lamp heater or a heat generating resistor into a plurality of portions and then by heating a region depending on the recording material size.
As in JP-A 2001-194940 described above, also in the fixing device using the thin heat generating member and the induction heating device with the good heating efficiency in combination, an example in which the heating region of the heat generating member with respect to the rotation axis direction is settable depending on the recording material size is proposed. However, when the induction heating device is provided in the plurality of portions, or is divided, the control circuit is complicated and is increase in cost correspondingly. In the case of the thin heat generating member, there is also a problem such that a temperature distribution is discontinuous in the neighborhood of boundaries of divided heating regions and thus the heat generating member cannot satisfy a necessary temperature uniformity.
Therefore, in the fixing device A, between the fixing belt 1 and the exciting coil 6, the magnetic cores 7a capable of setting, a region, every 10 mm in width, of the magnetic flux guided from the exciting coil 6 to the fixing belt 1 are disposed. In order to meet various sizes of the recording material, the divided magnetic cores 7a extend in a convey width direction perpendicular to the recording material conveyance direction and is made movable by the core moving mechanism 71, so that a movement distance is changed depending on the recording material size. By moving the magnetic cores 7a in a number corresponding to a conveying widthwise size of the recording material, a degree of the magnetic flux sent from the induction heating device 70 in a region other than a region necessary to be heated is decreased, so that the heat generation of the fixing belt 1 itself is suppressed. As a result, control of the heating region is effected, so that it becomes possible to precisely control the temperature distribution of the fixing belt 1 to be increased in temperature.
As shown in
However, in the fixing device A using the induction heating device 70, there arises the following problem. As shown in
Therefore, in the image forming apparatus E in which the recording materials of various sizes can be passed through the fixing device A, it is difficult to always detect the temperature of the fixing belt 1 at the maximum temperature portion. It would be not impossible that the temperature of the fixing belt 1 at the maximum temperature portion is detected by providing a plurality of temperature detecting elements in the number corresponding to the number of sizes of the recording material but this is not practical from the viewpoints of a cost and an arrangement space.
In the thus-constituted fixing device A, in the case where the temperature of the fixing belt 1 at the maximum temperature portion becomes an unexpected temperature for some reason, there is a possibility that the fixing belt 1 is exposed to a temperature exceeding a design temperature and thus a durable lifetime of the fixing belt 1 is shortened.
For example, when image formation is started at an interval (rate) of 75 sheets/min on the assumption that the recording material of plain paper of 80 g/m2 in basis weight (weight per unit area) is used, in some cases, the recording material of thick paper of 160 g/m2 in weight per unit area is fed from the feeding portion. At this time, the induction heating device 70 heats the entire heating region more than the case of the plain paper in order to supplement heat quantity taken by the thick paper, so that the degree of the non-sheet-passing portion temperature rise is higher than that in the case of the plain paper.
Therefore, in the following embodiments, an output limiter of the induction heating device 70 is set at a level where the non-sheet-passing portion temperature does not exceed the design temperature, so that the temperature of the fixing belt 1 at the maximum temperature portion is prevented from being increased unexpectedly to exceed the design temperature.
The reason for this will be described. In order to ensure a fixing property for the recording material such as the thick paper with a large thermal capacity, setting of a low-speed mode in which a conveying speed is lowered is effective. In order to widen a range of the thick paper to which an operation in the low-speed mode is applicable, an increase in electric power supplied to the coil is effective. That is, a limiter of the electric power usable in the operation in the low-speed mode may desirably be as large as possible.
Incidentally, in this embodiment, the electric power limiter is provided in order to suppress that the fixing belt temperature at the non-sheet-passing portion reaches a limit temperature. According to study by the present inventor, it was understood that when the conveyance speed is lowered, an amount of heat dissipation from the fixing belt 1 to the pressing roller 2 at the non-sheet-passing portion becomes large. That is, even when the supplied electric power is the same, at a lowered conveyance speed, the fixing belt temperature is not readily increased at the non-sheet-passing portion. That is, in the operation in the low-speed mode, an electric power limiter value can be set at a high level. Therefore, in a constitution in which the electric power limiter is provided in order to suppress that the fixing belt temperature at the non-sheet-passing portion reaches the limit temperature, by increasing the supplied electric power in the operation in the low-speed mode, an applicable thick paper range can be widened.
As shown in
As shown in
The power source device 101 constitutes a rectifying smoothing circuit by a diode bridge 301 and a filter capacitor 302 to generate a DC voltage. The electric power controller 313 alternately actuates the switch elements 303 and 304 via a driver 312 to apply an AC voltage to the exciting coil 6. The capacitors 305 and 306 are a resonant capacitor for forming a resonant circuit together with the exciting coil 6. The driver 312 independently drives the two switch elements 303 and 304 in synchronism with each other.
A central thermistor TH1 functioning as a temperature sensor is provided in a contact state at an inner surface of the fixing belt 1 which is an electroconductive heat generating member, and detects the temperature of the fixing belt 1. An electric power detecting portion 311 detects an input electric power of the power source device.
The electric power controller 313 controls, on the basis of a command from the controller 102, the power source device 101 to actuate/stop the induction heating device 70. The electric power controller 313 determines a condition of the electric power, outputted from the driver 312, so that a detection temperature of the central thermistor TH1 converges to a control temperature designated by the controller 102. The electric power controller 313 determines the condition of the electric power, outputted from the driver 312, so that a detection output of the electric power detecting portion 311 does not exceed a set value of the maximum electric power designated by the controller 102. The driver 312 drives the two switch elements 303 and 304 in accordance with the electric power condition determined by the electric power controller 313.
As shown in Table 1 below, in the controller 102, every range of the basis weight of the recording material, a set value of each of the control temperature, the throughput (productivity) which is the number of sheets per unit time of the recording material to be heated, and the maximum electric power, the combination of the throughput (productivity) and the electric power value (maximum electric power setting) is set so that the temperature at the non-sheet-passing portion in the continuous image formation converges to the design temperature even when the weight per unit area of the recording material designated for the image formation is changed. Particularly, in Embodiment 1, the productivity is set depending on the designated recording materials so that the non-sheet-passing portion temperature is kept at the design temperature. However, the maximum electric power is set at a roughly constant value irrespective of the designated recording materials.
As shown in
Next, with respect to Comparative Embodiment in which no setting of the maximum electric power is made and Embodiment 1 in which the setting of the maximum electric power is made, the image formation was effected under conditions of the following experiments 1 to 3 to compare an occurrence state of the non-sheet-passing portion temperature rise.
As shown in
The temperature at the sheet passing portion is a measured temperature value of the fixing belt 1 at a longitudinal central recording material passing portion, and the temperature at the non-sheet-passing portion is a measured temperature value of the fixing belt 1 at a portion, where the temperature of the fixing belt 1 is increased, located outside the recording material passing portion of the fixing belt 1. With the feeding of the recording material, the sheet passing portion temperature indicated by a solid line was lowered to 160° C., and at the non-sheet-passing portion indicated by a broken line, the non-sheet-passing portion temperature rise occurred, but as indicated by a dotted line, the supplied electric power to the exciting coil 6 was 900 W and thus did not reach an upper limit of 1000 W.
As shown in
As shown in Table 2, in Experiment 1, with respect to both of Embodiment 1 and Comparative Embodiment, the sheet passing portion temperature is kept at the control temperature of 160° C. and the non-sheet-passing portion temperature is kept at 200° C. which is not more than the design temperature of 220° C. and therefore particularly no problem arises.
As shown in
The sheet passing portion temperature indicated by a solid line was lowered to 160° C., and at the non-sheet-passing portion indicated by a broken line, the non-sheet-passing portion temperature rise occurred, but as indicated by a dotted line, due to the lowering in productivity, the supplied electric power to the exciting coil 6 was 900 W and thus did not reach an upper limit of 1000 W.
As shown in
As shown in Table 3, in Experiment 2, with respect to both of Embodiment 1 and Comparative Embodiment, the sheet passing portion temperature is kept at the control temperature of 160° C. and the non-sheet-passing portion temperature is kept at 200° C. which is not more than the design temperature of 220° C. and therefore particularly no problem arises.
As shown in
In Comparative Embodiment, there is no limitation of the maximum electric power. For this reason, the electric power was supplied to the exciting coil 6 without limitation, so that the sheet passing portion temperature during the sheet passing was kept at 160° C. but the electric power of 1500 W was supplied in order to keep 160° C. As a result, as indicated by the broken line, at the non-sheet-passing portion, the non-sheet-passing portion temperature rise to 240° C. occurred.
As shown in
On the other hand, as shown in
As shown in
An experiment result of Experiment 3 is summarized in Table 4.
As shown in Table 4, in the control in Comparative Embodiment, the non-sheet-passing portion temperature rise is kept at 240° C. which exceeds the fixing belt design temperature of 220° C. and therefore there is a possibility that a durable lifetime of the fixing belt 1 is shortened. On the other hand, in the control in Embodiment 1, the non-sheet-passing portion temperature rise is kept at 200° C. which is less than the design temperature of 220° C. and therefore there is no possibility that the durable lifetime of the fixing belt 1 is shortened.
As described above, according to the control in Embodiment 1, even in the case where the setting of the basis weight of the recording material is erroneously made, by limiting the supplied electric power to the exciting coil 6, it is possible to prevent the fixing belt 1 from being exposed to the temperature which exceeds the design temperature.
Further, the setting of the maximum electric power supplied to the exciting coil 6 may be set depending on not only the basis weight of the recording material but also an ambient temperature where the image forming apparatus E is placed, so that more accurate control can be effected. The electric power value depending on the recording material type designated for the image formation is increased with a lower ambient temperature.
According to the control in Embodiment 1, even in the case where the user erroneously sets the basis weight of the recording material, it is possible to prevent the durable lifetime of the fixing belt 1 from decreasing.
As shown in
Therefore, in Embodiment 2, the central thermistor TH1 which is an example of the detecting means detects the temperature of the fixing belt 1 in a range, with respect to the conveyance width direction, in which the fixing belt 1 is contacted to the recording material. The controller 102 stops feeding of the recording material by the cassette 31 in the case where the detection temperature by the central thermistor TH1 is below a predetermined value and cannot be maintained.
The controller 102 stops the image formation in the case where the measured temperature of the fixing belt 1 does not reach the design temperature even when the supplied electric power to the exciting coil 6 is increased up to the set value of the maximum electric power. As a result, the fixing belt 1 can be used at a temperature which does not exceed its heat-resistant limit temperature and it is also possible to prevent formation of an image for which the toner cannot be sufficiently fixed.
As shown in
The controller 102 starts the image formation (S104) and when the supplied electric power to the exciting coil 6 does not reach a maximum (YES of S105), the image formation is continued (YES of S106 and S104). When setting of the print number is ended (NO of S106), the controller 102 ends the image formation (S107).
In a state in which the supplied electric power to the exciting coil 6 reaches the maximum thereof, when the sheet passing portion temperature is below a lower limit fixable temperature (NO of S105), the image formation is interrupted (paused) (S110).
According to the control in Embodiment 2, even in the case where the user erroneously sets the basis weight of the recording material, it is possible to prevent the durable lifetime of the fixing belt 1 from decreasing, and it is also possible to prevent the fixing non-uniformity of an outputted image. It is possible to detect, with reliability, the case where a fixing performance cannot be satisfied, except for the case where the fixing performance can be sufficiently ensured only by temporary reaching of the electric power, supplied to the exciting coil 6, at the maximum. It is possible to prevent unnecessary image formation by using the user (operator) to check the recording material accommodated in the recording material cassette 31 and/or the setting of the recording material in the image forming job.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 170802/2011 filed Aug. 4, 2011, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-170802 | Aug 2011 | JP | national |
