JP2005345989A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain proper images free of the occurrence of fixing defects etc., due to the temperature fall of a heating roller, even when paper sheets are continuously fed at a high speed. <P>SOLUTION: The heating device is provided with a temperature-detecting member 7 for detecting the temperature of the heating roller 1 having an elastic body layer 1b, an electric power detection means for detecting the supply electric power of an excitation circuit 4 for supplying the electric power to a heating source 3 for heating the heating roller 1, and a controller 6 for deciding whether fixing operation should be carried out, based on the comparison result of the output values of the temperature-detecting member 7 and the electric power detection means and a preset reference value, and thereby the warming-up is shortened, due to the lowering of the heat capacity of an exothermic layer and the proper image quality free of the occurrence etc., of the fixing defects etc., is maintained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heating device that fixes a toner image on a recording material by thermocompression bonding using a heating member and a pressure member that presses the heating member, and an image forming apparatus including the same.

  An electrophotographic image forming apparatus is provided with a heating device for heating and fixing a powder developer (toner) on a recording sheet. As a heating device used in an image forming apparatus, a heating roller type heating device using a heating roller has been widely put into practical use.

  A heating roller type heating device includes a heating roller that conveys a recording sheet on which a toner image made of a powder developer is transferred, and a pressure roller that conveys the recording sheet while pressing the recording sheet against the heating roller. It has. In such a heating apparatus, a fixing nip portion that is a pressure contact portion between the heating roller and the pressure roller serves as a fixing point. In other words, by passing the recording paper through the fixing nip (pressure contact portion), the toner image can be fused and fixed on the recording paper.

  Conventionally, a cylindrical aluminum member having a large wall thickness and a large heat capacity has been used as a heating roller used in a heating device. However, since the heat roller having such a configuration has a large heat capacity, the time required to raise the temperature to a predetermined temperature required for the fixing process, that is, the rise time becomes long. Further, there is a problem that the power consumption required for raising the temperature of the heating roller is increased. For these problems, it is effective to reduce the thickness of the heating roller, thereby reducing the heat capacity of the heating device and reducing the rise time and power consumption.

  In addition, a heating source for heating the heating roller of the heating device is disposed inside the heating roller or outside the heating roller. As a heating method for heating the heating device with this heating source, a heater lamp method for heating a heating roller using a heater lamp such as a halogen lamp or an electromagnetic induction heating using an induction heating coil is used. An induction heating method for generating heat in a film is known. Among these, the induction heating method can reduce the rise time and power consumption of the heating device as compared with the heater lamp method, and therefore, the development of a heating device using the induction heating method is actively performed. .

  In an induction heating type heating device, (a) a method using a metal roller that generates heat with a relatively thick metal roller, (b) a film having a heat generation layer of about several tens of μm, A method of heating while sliding, (c) a method of using a roller structure by providing an elastic body such as a heat insulating sponge inside a hollow metal cylinder of about several tens of μm, and further providing a cored bar on the inside thereof is known. It has been.

  Among these, (a) the method using a metal roller can obtain the rigidity of the roller itself, while the heat capacity of the heating element layer is increased, so that it is difficult to significantly shorten the rise time. Further, in the (b) film sliding method, since the film is used without using a roller, the heat capacity is small and the rise time can be shortened. However, since a film is used, stable rotational driving is difficult, and it is not suitable for speeding up the fixing process.

  On the other hand, in the method using the roller structure of (c), a heating coil is installed on the surface of the heating roller, and a thin heating element layer having a small heat capacity is heated from the surface, that is, the image surface side. Since the elastic body layer having excellent heat insulating properties is provided inside the heat generating body layer, heat escape from the heat generating body layer to the elastic body layer or the core metal provided inside thereof can be prevented. Therefore, although it is a roller structure, it can implement | achieve the outstanding temperature rising performance and reduction of power consumption. In addition, since it is a roller structure, high speed and stable rotation drive can be easily realized, and furthermore, since it has an elastic layer inside the heating element layer, it is easy to realize a wide fixing nip. Therefore, it can be applied to a high-speed color fixing device. A heating device using such a roller structure as a heating roller is disclosed in Patent Document 1, for example.

This patent document 1 discloses an embodiment in which the roller structure is used as a heating roller, a metal sleeve as a thin metal cylinder is provided, and an induction heating coil is used as a heating source.
JP 2000-214714 A

  By the way, in the above-mentioned patent document 1, since the heat capacity of the heat generating layer is small and the heat generating layer is thermally insulated and held by the sponge layer which is a heat insulating elastic body layer, the elasticity on the heating roller surface layer side as viewed from the heat generating layer. The body layer or release layer can be heated quickly, and the surface of the heating roller quickly reaches the temperature required for fixing, and even if heat is taken away by the media such as recording paper, the supply of heat catches up. However, it does not describe how much fixing speed can be dealt with.

  Therefore, the present applicants conducted a continuous paper feeding experiment using a heating roller type heating device as shown in FIG. 9 and measured the heating roller temperature, so that the heat supply to the heating roller sufficiently caught up. It was confirmed whether it was able to follow the temperature. The results will be described below.

  First, in the heating device of FIG. 9, an induction coil 3 a that is a heating source is arranged in a form facing the heating roller 1. The heating roller 1 has an outer diameter of 40 mm, an aluminum core 1 a having a thickness of 3 mm in order from the inside, a silicon sponge 1 b which is an elastic body layer having a thickness of 6 mm, a Ni heat generating layer 1 c having a thickness of 40 μm, and measures against uneven gloss of the image. The elastic layer 1d is made of silicon rubber having a thickness of 400 μm and the PFA tube 1e having a thickness of 30 μm for releasing the toner. On the other hand, the pressure roller 2 has an outer diameter of 30 mm, and in order from the inside, an aluminum cored bar 2a, a silicon sponge 2b that is an elastic body layer with a thickness of 5 mm, and a PFA tube with a thickness of 30 μm for releasing the toner. 2c.

FIG. 10 shows a printing speed of 50 sheets per minute when the fixing temperature of the heating device shown in FIG. 9 is set to 170 ° C. and the A4 width paper P (basis weight 105 g / m ² ) is relatively thick. It is a graph which shows the relationship between the paper passing time and the temperature of the heating roller 1 when the paper is continuously passed for about 2 minutes (70 sheets) at (50 ppm). In addition, in order to be able to evaluate the fixability, the image pattern was formed up to about every 50th sheet, such as 1st sheet, 10th sheet,..., 40th sheet, and 50th sheet. The recording paper was passed. The image pattern was a patch pattern in which yellow, magenta, and cyan toners were superposed from one to three layers, and the amount of adhesion per toner layer was 0.5 mg / cm ² .

  As is apparent from FIG. 10, it can be seen that the temperature of the heating roller 1 is greatly reduced from the initial setting temperature of 170 ° C. to about 150 ° C. by continuously passing paper. In addition, it was confirmed that defective fixing occurred in all patterns after the 10th sheet except for the first sheet.

  As described above, in the heating apparatus shown in FIG. 9 as well, particularly when outputting at a high speed, the amount of heat lost to the medium such as recording paper is quickly replenished, and the surface temperature of the heating roller 1 is set to the fixing set temperature or It was found that it was difficult to maintain the temperature at which no fixing failure occurred.

  Therefore, in order to clarify the reason why the heating roller temperature cannot follow when the paper is continuously fed at a high speed, an idling heating experiment was conducted using the heating device of FIG. Specifically, the temperature of the heating roller 1 is increased from room temperature to 170 ° C. while rotating the heating roller 1 at a speed of 240 mm / sec. The power required to maintain the roller 1 at a constant temperature was measured.

  FIG. 11 is a graph showing the relationship between the idling time and the power required to maintain the heating roller 1 at a constant temperature. As shown in FIG. 11, it can be seen that a particularly large electric power is required immediately after the heating roller 1 is started up. That is, in order to maintain the heating roller 1 at a constant temperature immediately after the start-up as a cause of the temperature drop of the heating roller at the time of continuous paper feeding at high speed, that is, the cause of the heat supply not catching up. It can be seen that a larger amount of heat supply is required. Here, in the configuration of the heating roller 1 of the heating device shown in FIG. 9, a highly heat-insulating sponge layer is provided inside the thin heat generating layer to suppress the movement of heat from the heat generating layer to the inside of the heating roller. However, the heat transfer from the heat generation layer to the sponge layer cannot be eliminated at all, and as long as there is a temperature difference between the heat generation layer and the sponge layer, heat transfer is not possible. It seems that it is happening.

  And it is considered that the larger the temperature difference between the heat generating layer and the sponge layer, the greater the amount of heat transfer from the heat generating layer to the sponge layer. Therefore, the amount of heat transfer from the heat generation layer to the sponge layer during idling heating was calculated by thermal analysis.

  FIG. 12 shows the relationship between the idling time and the amount of heat transfer from the heat generating layer to the sponge layer when the heating roller 1 is heated from room temperature to a fixing temperature and then kept at the fixing temperature while idling. It is the graph which showed. As can be seen from FIG. 12, the heat transfer amount from the heat generation layer to the sponge layer is particularly large immediately after start-up. From this result, in the heating apparatus having the structure shown in FIG. 9, the temperature drop of the heating roller 1 particularly when it is continuously output at a high speed immediately after the temperature rise from room temperature is due to the heat transfer from the heat generating layer to the sponge layer. It is thought that this has an effect. As described above, in the structure shown in FIG. 9, it was found that when the recording paper is continuously output at a high speed, the temperature of the heating roller 1 is lowered, and as a result, fixing failure or the like occurs.

  The present invention has been made in view of such circumstances, and it is possible to shorten the warm-up by reducing the heat capacity of the heating layer of the heating member (heating roller), and at the same time, continuously outputs at high speed. In particular, it is possible to quickly replenish the amount of heat taken by the recording paper and other media at the start of paper feeding, and there is no occurrence of a temperature drop of the heating member, and there is no occurrence of defective fixing or the like. It is an object of the present invention to provide a heating device capable of maintaining image quality and to provide an image forming apparatus provided with the heating device having such characteristics.

  The heating device of the present invention includes a heating member having an elastic layer, a pressure member arranged in pressure contact with the heating member, a heating source for heating the heating member from the outside, and power to the heating source. In a heating apparatus that includes power supply means (for example, an excitation circuit) to supply and heat-fixes an image on a recording material, temperature detection means for detecting the temperature of the heating member, and power supplied from the power supply means are detected. And a control unit that determines whether or not to perform the fixing operation based on a comparison result between the output values of the temperature detection unit and the power detection unit and a preset determination reference value. Characterized by.

  According to the heating device of the present invention, since the fixing operation is controlled to start based on the temperature information and the power information after reaching the fixing temperature, it is possible to obtain a good image without occurrence of fixing failure or the like. Can do. The reason is described below.

  First, in the heating method in which heating is performed from the surface of the heating roller by an external heating source, when a fixing operation is started based on only the fixing temperature information, a large amount of recording material is required for continuous paper feeding under high-speed output conditions. The amount of heat is lost. In particular, immediately after startup from normal temperature, the amount of heat transferred to the elastic layer, which is a heat insulating layer, is large, and the amount of heat lost to the recording material and the heat insulating layer cannot be supplied. It may be significantly reduced and fixing failure may occur.

  On the other hand, in the heating device of the present invention, after detecting the amount of power supplied to the heating roller and determining that the amount of power is below the reference value, that is, the temperature detection means reaches the predetermined temperature. After that, the heating roller is idled for a necessary time, and the heat quantity taken away by the heat insulating material is reduced, so that the fixing operation is started, that is, the sheet passing is started. A good image can always be obtained.

  In the heating device of the present invention, the power detection means is a calculation unit that counts the power supply signal output from the control unit, and the fixing operation is performed by comparing the count result of the calculation unit with a preset criterion value. It is good also as a structure from which a control part judges whether it performs. By adopting such a configuration, it is not necessary to newly provide a circuit or the like for detecting electric power, it is possible to make a determination for starting the fixing operation, and it is possible to always obtain a good image without occurrence of fixing failure or the like. it can.

  In the heating device of the present invention, the power detection means has a configuration including a current detection circuit and a voltage value circuit, and actually measures the electric power supplied to the heating source from each detection value of the current detection circuit and the voltage value circuit. Alternatively, a comparison determination with a predetermined determination reference value may be performed. When the current and voltage are detected in this way, the amount of electric power supplied to the heating source can be determined by actual measurement, so that the determination accuracy is improved and a good image without occurrence of fixing failure or the like can always be obtained.

  In the heating device of the present invention, it is preferable that the determination reference value of power for determining whether or not to perform the fixing operation can be switched between color output and monochrome output. As described above, when the power determination reference value is switched between monochrome output and color output, it is possible to obtain a good image without occurrence of fixing failure or the like in the tandem color image forming apparatus.

  That is, in a tandem color image forming apparatus, the number of recording materials that can be processed per unit time is almost the same in both monochrome output and color output, but per color recording material is one per recording material. Since a large amount of toner is used, the energy for fixing the toner to the recording material is larger than that for monochrome output. In other words, it is necessary to reduce the amount of heat escaped to the elastic layer, which is a heat insulation layer, in color output compared to monochrome output, and the power criteria for monochrome output and color output. Thus, the fixing operation is started under optimum conditions, so that it is possible to always obtain a good image with no occurrence of fixing failure without prolonging the waiting time of the user more than necessary.

  Also, the power criterion value may be switched according to the number of recording materials that can be processed per unit time. In this way, it is possible to obtain a good image without occurrence of fixing failure. That is, in a color image forming apparatus constituted by a four-rotation process, the number of recording materials processed per unit time is about one-fourth of the number of sheets for monochrome output. In both color output and monochrome output, the time for the recording material to pass through the fixing nip is constant, but in the case of color output, after the recording material passes through the fixing nip, the next recording material It takes a long time to reach the fixing nip, and the temperature of the heating roller can be recovered within that time. That is, since the degree of temperature drop of the heating roller varies depending on the number of recording materials processed per unit time, the power criterion value depends on the number of recording materials that can be processed per unit time. By performing switching and starting the fixing operation under optimum conditions, a good image without occurrence of fixing failure or the like can always be obtained without increasing the waiting time of the user more than necessary.

  In the heating apparatus of the present invention, the power determination reference value for determining whether or not to perform the fixing operation may be changed according to the number of processed recording materials input by the user. Specifically, in the case of single copy (single print), since the temperature drop of the heating roller is small, in such a case, the power criterion is lowered or the fixing operation is started only with temperature information. By doing so, the waiting time of the user can be further reduced.

  In the heating apparatus of the present invention, the power determination reference value for determining whether or not to perform the fixing operation may be configured to be changed based on the thickness information of the recording material. Specifically, for example, the power criterion is set low for thin paper, and high for thick paper. Latency can be minimized.

  In the heating apparatus according to the present invention, the heating member includes at least an elastic layer, a heat generation layer, and a release layer that are sequentially stacked from the inside, and the heating source is an induction heating unit that induction-heats the heat generation layer. It is good. In this way, the heat generating layer is heated from the outside of the heating roller by induction heating, so that the rise time required to raise the heating roller to a predetermined temperature is shortened and the power consumption can be reduced. In addition, an excellent heating device can be provided.

  According to the image forming apparatus of the present invention, since the fixing device having the above features is provided, the user will not be kept waiting more than necessary. Further, when the sheet is continuously fed at a high speed. However, it is possible to always obtain a good image quality without occurrence of fixing failure due to a temperature drop of the heating roller.

  According to the heating device of the present invention, the temperature detection means for detecting the temperature of the heating member having the elastic layer, and the power detection means for detecting the supply power of the power supply means for supplying power to the heating source for heating the heating member. And a control unit for determining whether or not to perform the fixing operation based on a comparison result between the output values of the temperature detection unit and the power detection unit and a predetermined determination reference value. The heat capacity can be reduced by reducing the heat capacity of the heat generation layer, and at the same time, even when continuously outputting at high speed, the amount of heat lost to the media such as recording paper at the start of paper feeding can be quickly replenished, and heating Occurrence of roller temperature drop is eliminated. As a result, it is possible to maintain good image quality without occurrence of fixing failure or the like.

  According to the image forming apparatus of the present invention, since the fixing device having the above characteristics is provided, even when the sheet is continuously fed at a high speed, there is no occurrence of a fixing defect due to a decrease in the temperature of the heating roller. Good image quality can always be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Embodiment 1>
-Heating device-
An example of the heating device of the present invention will be described with reference to FIG.

  The heating device 10 of this example is provided in, for example, an electrophotographic image forming apparatus, and melts an unfixed toner image made of unfixed toner (developer) on a recording paper (recording material) P. The apparatus performs heating and pressure fixing of the toner image on the recording paper P.

  As shown in FIG. 1, the heating device 10 includes a heating roller (heating member) 1, a pressure roller (pressure member) 2, a heating source 3, an excitation circuit (power supply means) 4, a temperature detection member (temperature detection means). ) 7, a control unit 6, a fixing entrance guide 8, and the like.

  The heating roller 1 melts the toner on the recording paper P and fixes the toner image on the recording paper P by the pressure applied by the heating roller 1 and the pressure roller 2. The heating roller 1 receives a driving force from a driving means (not shown) and is driven to rotate at a peripheral speed V1 in the direction of an arrow R1 in FIG.

  As shown in FIG. 1, the heating roller 1 includes a first elastic body layer 1b having heat insulation, an adhesive layer (not shown), and a Ni (nickel) heating layer 1c on the outer surface of a core metal (metal layer) 1a. The second elastic layer 1d and the release layer 1e are formed in this order. In FIG. 2, the fragmentary sectional view of the layer structure of the heating roller 1 is shown.

  The cored bar 1a of the heating roller 1 is composed of a metal element tube such as aluminum, iron, and stainless steel. The cored bar 1a can be formed of a heat resistant resin such as PPS (polyphenylene sulfite) or ceramic.

  The first elastic body layer 1b of the heating roller 1 is a heat insulating layer provided so as to retain heat generated in a Ni heat generating layer 1c described later and not radiate heat to the core metal 1a side. The first elastic layer 1b is provided to secure a fixing nip portion N formed when the heating roller 1 and the pressure roller 2 are in pressure contact with each other with a predetermined width. By providing such a first elastic body layer 1b, the heating roller 1 is elastically deformed, and a fixing nip portion N having a wider nip width can be formed. The first elastic body layer 1b is formed of an elastic body such as silicon sponge formed by foaming silicon rubber, for example.

  The Ni heat generating layer 1c of the heating roller 1 is a heat generating layer that generates heat by the action of an alternating magnetic field generated in the heating source 3, as will be described in detail later. In this example, the Ni heat generating layer 1c is formed of Ni, but is not limited thereto, and may be a metal such as silver, copper, and aluminum, in particular, iron, cobalt, manganese, magnetic stainless steel, It is preferably formed of a ferromagnetic material such as ferrite.

  The second elastic layer 1d of the heating roller 1 is provided so that the surface of the heating roller 1 is elastically deformed following the unevenness of the unfixed toner image on the recording paper P. By providing such a second elastic layer 1d, the toner can be uniformly melted and fixed even when the toners of the respective colors overlap each other as in color printing or the like. The second elastic layer 1d is not limited to silicon rubber, and may be formed of an elastic material such as fluororubber.

  The release layer 1e of the heating roller 1 is provided in order to improve the releasability from the toner and prevent the toner from adhering to the surface of the heating roller 1. That is, since the heating roller 1 is in direct contact with the toner on the recording paper P, the melted toner tends to adhere. Therefore, toner adhesion is prevented by improving the releasability of the surface of the heating roller 1. In this example, a PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) tube is used as the release layer 1e, and the second elastic layer 1d is covered with a PFA tube. The release layer 1e may be formed by coating the surface with a fluorine-based resin such as PTFE (polytetrafluoroethylene) as long as it has excellent release properties.

  As shown in FIG. 1, the pressure roller 2 is in pressure contact with the heating roller 1 and sandwiches a recording paper P carrying an unfixed toner image between the pressure roller 2 and the heating roller 1. Then, the toner image is fixed on the recording paper P. The pressure roller 2 is pressed against the heating roller 1 with a predetermined pressing force (contact pressure) by an urging means (not shown) such as a pressure spring. The pressure roller 2 is driven to rotate at a peripheral speed V2 in the direction of arrow R2 in FIG. 1 as the heating roller 1 rotates.

  The pressure roller 2 has a structure in which an elastic body layer 2b and a release layer 2c are formed in this order on the outer surface of the cored bar 2a.

  The cored bar 2a of the pressure roller 2 is configured by a metal base tube that is a cylindrical rotating body such as iron, aluminum, and stainless steel. The core metal 2a can also be formed of a heat resistant resin such as PPS (polyphenylene sulfite) or ceramic.

  The elastic body layer 2b of the pressure roller 2 is formed of, for example, an elastic body such as silicon rubber or silicon sponge formed by foaming silicon rubber. The release layer 2c is provided to make the surface of the pressure roller 2 excellent in releasability, and may be formed by coating the surface with a fluorine-based resin such as a PFA tube or PFA or PTFE. . In this example, the release layer 2c can be formed so as to cover the elastic layer 2b with, for example, a PFA tube.

  The heating source 3 is provided to generate heat from the Ni heat generating layer 1 c of the heating roller 1. The heating source 3 includes an induction coil (heating source) 3a and a holder case 3b.

  The induction coil 3a includes an aluminum single wire coated with an oxide film, a copper wire having an insulating coating, a litz wire in which a plurality of them are bundled in the longitudinal direction of the heating roller 1, which is a direction parallel to the central axis of the heating roller 1, and the like. Wrapped around. Here, the litz wire is a bundle of about 10 to 150 copper wires coated with an insulating material having a strand diameter of about 0.05 to 0.8 mm. When a litz wire is used as the induction coil 3a, the litz wire may be wound about 5 to 20 times.

  The holder case 3b is an insulating support that accommodates the induction coil 3a therein. As shown in FIG. 1, the holder case 3 b has a size so as to cover substantially half of the circumference of the heating roller 1 along the outer circumferential surface of the heating roller 1.

  The excitation circuit 4 is connected to the induction coil 3a and applies an alternating current to the induction coil 3a to generate an alternating magnetic field. The excitation circuit 4 is controlled so that a high-frequency current of about 10 to 100 kHz flows through the induction coil 3a, for example, by the control unit 6 described later.

  As shown in FIG. 1, the temperature detection member 7 contacts the outer peripheral surface of the heating roller 1 and detects the temperature of the surface of the heating roller 1. Although the details will be described later, the temperature detection member 7 detects the temperature rise state of the surface temperature of the heating roller 1, and therefore detects the temperature in the most heat generating region on the surface of the heating roller 1 or in the vicinity thereof. Is preferred. In general, the temperature detection member 7 may be a thermistor.

  The control unit 6 is configured by, for example, a CPU (Central Processing Unit) and the like. From the control circuit of the image forming apparatus based on information such as the temperature of the surface of the heating roller 1 detected by the temperature detection member 7 described above. Is supplied to the induction coil 3a by controlling a switching element (not shown) such as an IGBT (Insulated Gate Bipolar Transistor) in the excitation circuit 4 based on an ON / OFF signal or power signal of heating inputted. The high frequency current is controlled. Further, the control unit 6 gives a rotation drive signal for rotating the heating roller 1 to the drive circuit 5. Details of the control operation of the control unit 6 will be described later.

  The fixing entrance guide 8 is a contact between the heating roller 1 and the pressure roller 2 on the recording sheet P holding the unfixed toner image conveyed to the heating device 10 from an image forming means (not shown) of the image forming apparatus. Guide to the fixing nip N, which is a part. That is, the fixing inlet guide 8 is disposed upstream of the fixing nip portion N along the arrow Kp direction, which is the conveyance direction of the recording paper P shown in FIG. Then, when the recording paper P is supplied to the heating device 10, the recording paper P is brought into contact with the back surface of the recording paper P that is not holding an unfixed toner image, and the leading edge of the recording paper P is smoothly and appropriately placed. Enter the fixing nip N.

  In the heating apparatus 10 including the heating roller 1, the pressure roller 2, the heating source 3, the temperature detection member 7, and the like having the above-described configuration, as shown in FIG. 1, the pressure roller is in pressure contact with the heating roller 1. 2 is placed and held. Since the first elastic body layer 1 b is provided on the heating roller 1, the heating roller 1 is elastically deformed when the pressure roller 2 is in pressure contact with the heating roller 1. As a result, a wide band-shaped nip portion N which is a contact portion between the heating roller 1 and the pressure roller 2 is formed. Specifically, the nip width of the fixing nip portion N is set to about 7 mm.

  Further, a heating source 3 is locally provided so as to face a region other than the formation position of the fixing nip portion N on the outer surface of the heating roller 1. The heating source 3 has a predetermined curvature along the outer peripheral surface of the heating roller 1 and covers almost half of the circumference of the heating roller 1 as described above. The heating source 3 and the outer peripheral surface of the heating roller 1 are arranged with an interval of about 3 mm.

  Further, a temperature detection member 7 is disposed between the heating source 3 and the heating roller 1. The temperature detection member 7 is preferably provided in a region of the surface of the heating roller 1 where heat is generated by the heating source 3 in consideration of heating the heating roller 1 during standby in a stopped state. In the heating device 10 of this example, as shown in FIG. 1, a temperature detection member 7 is provided between the heating source 3 and the heating roller 1 so as to contact the heating roller 1.

-Image forming device-
FIG. 3 is a diagram schematically illustrating an example of a color image forming apparatus including the heating device 10 having the above-described configuration.

  The color image forming apparatus 100 of this example is a so-called tandem type printer in which four color visible image forming units 100Y, 100M, 100C, and 100B are arranged along a recording sheet conveyance path. Specifically, four sets of visible image forming units 100Y, 100M, 100C, and 100B are arranged along a recording paper conveyance path that connects the recording paper P (recording material) supply tray 120 and the heating device 10. Then, after each color toner is multiplex-transferred onto the recording paper P conveyed by the recording paper conveying means 130 of the endless belt, it is fixed by the heating device 10 having the above-described configuration to form a full color image. The heating device 10 has the same configuration as that shown in FIG. 1, and includes a heating roller 1, a pressure roller 2, a heating source 3, an excitation circuit 4, a temperature detection member 7, a control unit 6, and a fixing inlet guide. 8 and so on.

  Next, the configuration of each part of the color image forming apparatus 100 will be described.

  The recording paper conveying means 130 has an endless conveying belt 133 that is stretched by a pair of driving rollers 131 and idling rollers 132 and that rotates by being controlled at a predetermined peripheral speed (for example, 240 mm / s). The recording paper P is electrostatically adsorbed onto the belt 133 and conveyed.

  Each of the visible image forming units 100Y, 100M, 100C, and 100B includes a photosensitive drum 111, and around the photosensitive drum 111, a charging roller 112, a laser beam irradiation unit 113, a developing device 114, and a transfer unit. The roller 115 and the cleaner 116 are arranged in this order.

  The developing devices 114 of the visible image forming units 100Y, 100M, 100C, and 100B contain yellow (Y), magenta (M), cyan (C), and black (B) toners. Each visible image forming unit 100Y, 100M, 100C, 100B forms a toner image on the recording paper P by the following process.

  That is, after the surface of the photosensitive drum 111 is uniformly charged by the charging roller 112, the surface of the photosensitive drum 111 is laser-exposed according to image information by the laser light irradiation unit 113 to form an electrostatic latent image. Thereafter, a toner image is developed on the electrostatic latent image on the photosensitive drum 111 by the developing device 114, and the visualized toner image is recorded by the transfer roller 115 to which a bias voltage having a polarity opposite to that of the toner is applied. Transfer is sequentially performed on the recording paper P conveyed by the paper conveying means 130.

  The recording paper P onto which the toner image has been transferred is peeled off from the transport belt 133 by the curvature of the drive roller 131 and then transported to the heating device 10. Therefore, an appropriate temperature and pressure are given by the heating roller 1 and the pressure roller 2 maintained at a predetermined temperature. Then, the toner is dissolved and fixed to the recording paper P to form a robust image.

  Next, in the color image forming apparatus 100 having the above-described configuration, an operation when performing a fixing process of an unfixed toner image on the recording paper P will be described in detail with reference to FIG.

  When a job processing request is made to the image forming apparatus 100, in the heating apparatus 10, a rotation drive signal for rotating the heating roller 1 is given from the control unit 6 to the drive circuit 5. Start rotation at desired speed. After the heating roller 1 starts rotating, or at approximately the same timing, the control unit 6 performs a process of raising the heating roller 1 of the heating device 10 to a fixable temperature and setting it in a fixable state, so-called warm-up operation. Therefore, the heating signal and the power signal are input to the excitation circuit 4, and energization of the induction coil 3a of the heating source 3 is started.

  Specifically, first, the control unit 6 of the heating device 10 sends a heating ON signal to the excitation circuit 4 so that the heating roller 1 reaches a predetermined fixing temperature based on the temperature information detected by the temperature detection member 7. And give a power signal. The power signal at this time is desirably the maximum input power in order to shorten the warm-up time. However, if the heating roller 1 is in a warm state based on the detected temperature of the heating roller 1, the comparison is performed. You may make it start up with low electric power. The heating roller 1 generates heat due to the influence of an alternating magnetic field generated by the induction coil 3a. The principle of the heat generation will be described again with reference to FIG.

  An alternating current is supplied to the induction coil 3a to generate an alternating magnetic field. When this alternating magnetic field acts on the Ni heat generating layer 1c of the heating roller 1, an eddy current is generated in the Ni heat generating layer 1c. Since the Ni heat generating layer 1c has a specific resistance, Joule heat is generated by the eddy current generated in the Ni heat generating layer 1c. As a result, the heating roller 1 generates heat.

  In general, when a high-frequency magnetic field such as the alternating magnetic field is applied to a conductive member (hereinafter referred to as a “conductor”) such as the Ni heat generating layer 1c, under the influence of the skin effect of the conductor, The alternating magnetic field is shielded. For this reason, the alternating magnetic field acts only near the surface of the conductor. Specifically, the depth δ from the surface of the conductor on which the alternating magnetic field acts (hereinafter referred to as “skin depth δ”) is expressed by the equation [δ = √ (ρ / π · f · μ)]. . Where ρ is the electrical resistivity of the conductor, μ is the magnetic permeability, and f is the frequency of the alternating magnetic field.

  Such skin depth δ is an index indicating the amount of absorption of the alternating magnetic field. That is, at a position where the depth from the surface of the conductor on which the alternating magnetic field acts is deeper than δ, the amount of absorption of the alternating magnetic field by the conductor is attenuated to 1 / e or less. In this position, even if an alternating magnetic field acts, it hardly contributes to the heat generation of the conductor. Therefore, if the thickness of the heat generating layer 1c is too thick, the heat capacity increases and, at the same time, the region that does not contribute to heat generation also increases, so the heating time of the heating roller becomes longer. In addition, since the hardness of the surface of the heating roller is increased, there is a problem that a desired nip width cannot be obtained. On the other hand, even if the thickness of the heat generating layer 1c is too thin, the magnetic field penetrates and is not sufficiently absorbed by the heat generating layer, and the heating efficiency is lowered. Considering such points, the thickness of the heat generating layer is preferably about several tens of μm.

  Based on the principle as described above, the surface of the heating roller 1 is rapidly heated to the target temperature. For example, when the set temperature is 170 ° C., the heating roller 1 is normally rotated with the maximum power that can be supplied while rotating the heating roller 1. Thereafter, when the control unit 6 detects that the heating roller 1 has reached the set temperature of 170 ° C. based on the detected temperature information from the temperature detection member 7 brought into contact with the heating roller 1, the set temperature is maintained. While continuing to rotate at a desired speed (this state is hereinafter referred to as “idle state”). Until the heating roller 1 reached the set temperature, the heating was continued at the maximum power. However, when the idling state was reached, to maintain the set temperature, the temperature of the heating roller 1 was subsequently changed to 1000 W and 300 W. Heat to maintain.

  More specifically, when the control unit 6 determines that the temperature of the heating roller 1 is below 170 ° C. and the temperature of the heating roller 1 needs to be increased based on the temperature information of the temperature detection member 7, excitation is performed. When a power signal of 1000 W is given to the circuit 4 and, conversely, when the control unit 6 determines that the temperature of the heating roller 1 exceeds 180 ° C. and the temperature of the heating roller 1 needs to be lowered, the control unit 6 makes an excitation circuit. By supplying a power signal of 300 W to 4, the temperature of the heating roller 1 is controlled to a fixed fixing temperature.

  At this time, the control unit 6 calculates the power per section time. Specifically, as shown in FIG. 4, the control unit 6 includes a calculation unit 61 that calculates how many times a 1000 W signal is given per unit time. Here, the minimum time unit for supplying the power signal is about several μsec to several tens μsec. For example, assuming that the section time is 1 second, the number of times the 1000 W signal is supplied in this section time is counted, By calculating the average power, the power required for the idling operation is calculated. As the idling operation continues, the amount of electric power for maintaining the fixing temperature decreases. As a result, this calculated value also gradually decreases.

  Further, the control unit 6 stores the storage unit 63 that stores the reference value of the electric energy during the idling operation for starting the fixing operation, and the comparison that compares the reference value with the calculation value in the calculation unit 61. The comparison unit 62 compares the reference value and the calculated value. When the calculated value falls below the reference value, the control unit 6 outputs a fixing operation start signal, that is, a printable signal, and the image The forming / fixing operation is performed.

  In the above example, the calculation is performed based on a high power value, that is, based on an output signal of 1000 W. However, there is no problem even if the calculation is performed for a low power of 300 W. Conventionally, the fixing operation is started based on the temperature information of the heating roller 1. However, as described above, the fixing operation is started from the temperature information and the power information in addition to the power information during the idling operation. The amount of heat transferred to the elastic layer provided inside the layer is reduced, and even when continuous paper feeding is performed, the amount of heat transferred to the recording material and the elastic layer greatly exceeds the amount of input power, and the heating roller 1 Thus, the temperature of the toner is not significantly lowered, and fixing failure or the like does not occur, and a good fixed image can be obtained.

<Embodiment 2>
In the above-described example (Embodiment 1), power information in the idling state is obtained based on the power signal from the control unit 6 and compared with the determination reference value in the control unit 6. In this example, as shown in FIG. 5, a current detection circuit 11 for measuring the coil current and a voltage detection circuit 12 for measuring the coil voltage are provided to measure the power value, and the fixing operation is performed using the measured value. Whether or not it is determined. In the case of this example, the actual measurement value is transmitted to the control unit 6, and the control unit 6 similarly compares with the determination reference value, and starts the fixing operation with that value.

  Thus, starting the fixing operation based on the power information in addition to the temperature information has the following advantages.

  That is, so far, the state where the heating apparatus is started up from room temperature (approximately 25 to 30 degrees), that is, the case where the heat insulation layer is sufficiently cooled has been described. In the case where the heating roller 1 is warmed immediately after many printings, that is, in a state where the elastic layer is sufficiently warmed, the amount of heat transferred from the heat generating layer to the elastic layer is raised from room temperature. Less than immediately after. When printing is performed from such a state, it is a case where almost no heat is stored in the heat insulating layer by the idling operation. After the heating roller 1 reaches the fixing temperature, it is possible to determine the warming state of the heat insulating layer of the heating roller 1 by determining and determining the power required for the idling operation at intervals of several seconds. Therefore, the idling operation is not performed more than necessary, and the user is not kept waiting.

  Further, in this example, the power determination reference value may be switched between monochrome output and color output. The advantages in this case will be described below.

  In general, in a color output apparatus (color image forming apparatus) configured in a tandem system, the number of recording sheets that can be processed per unit time is almost the same in both monochrome output and color output. Since a large amount of toner is used per recording sheet at the time of color output, a larger amount of energy is required for fixing the toner on the recording sheet than at the time of monochrome output. In other words, when outputting color, it is necessary to reduce the amount of heat escape to the elastic layer, which is a heat-insulating layer, compared to when outputting monochrome. By setting it to a value smaller than the power judgment reference value at the time, it becomes possible to start the fixing operation under optimal power conditions in both color output and monochrome output, A good image without occurrence of fixing failure or the like can always be obtained without unnecessarily increasing the waiting time of the user.

  On the other hand, in a color output device constituted by a four-rotation process, the number of recording sheets processed per unit time is usually about one-fourth of the number of sheets for monochrome output. In both color output and monochrome output, the time for the recording paper to pass through the fixing nip is constant, but in the case of color output, after the recording paper passes through the fixing nip, the next recording paper It takes a long time to reach the fixing nip, and the temperature of the heating roller can be recovered within that time.

  That is, since the degree of temperature drop of the heating roller varies depending on the number of recording sheets processed per unit time, the power determination reference value is switched according to the number of recording sheets that can be processed per unit time. If the number of recording sheets processed per unit time is small, it is possible to start the fixing operation under optimum conditions by increasing the power judgment reference value. A good image without occurrence of fixing failure or the like can always be obtained without increasing the waiting time.

  In addition, since the temperature of the heating roller gradually decreases as the paper is passed, if the number of print requests from the user is small, for example, in the case of single copy, it is not necessary to reduce the power criterion value. There is no. Further, when thin paper is used, the amount of heat taken away by the paper decreases, so the power criterion value may be lowered. In the case of single copy of thin paper, it is also possible to control by only the temperature information of the heating roller, that is, immediately after reaching the fixing temperature, based on the thickness information and the number information of the recording paper. As described above, by switching the power determination reference value based on the requested number of prints and the thickness information of the recording paper, it is possible to suppress fixing failure and the like while minimizing the waiting time of the user.

  Note that the number of printed sheets is input from an operation panel (including a numeric keypad, a setting button for setting an image mode, and a display unit such as a liquid crystal display) provided in the image forming apparatus, and returns to a power criterion value. It is reflected. Also, the recording paper thickness information can be selected by selecting the paper type such as thin paper, plain paper, thick paper, etc. by the user operating the operation panel.

  Here, in each of the above embodiments, the induction coil 3a is disposed as the heating source 3 outside the heating roller 1, but the present invention is not limited to this, and the heating source 3 may be a halogen lamp or a ceramic heater. Or the like, and an external heating roller for heating the heating roller from the outside may be used.

  Further, in the heating device 10 shown in FIG. 1, no heat source is provided inside the pressure roller 2, but as shown in FIG. 6, the pressure roller 2 is a relatively thin core metal 2 e such as aluminum, As a configuration in which the release layer 2 c is provided on the outer side, a heat source 21 such as a halogen lamp may be provided inside the pressure roller 2 to heat the pressure roller 2. Further, a silicon rubber (not shown) of about 400 μm may be provided between the cored bar 2e of the pressure roller 2 and the release layer 2c.

  Examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these examples.

<Example 1>
In the heating apparatus 10 shown in FIG. 1, a heating roller 1, a pressure roller 2, a heating source 3, and a temperature detection member 7 having the following configuration are used.

  That is, as the heating roller 1, a first elastic layer 1b formed of a silicon sponge having a thickness of 6 mm and a Ni heating layer having a thickness of 40 μm are formed on the outer surface of a hollow aluminum base tube having an outer diameter of 28 mm and a thickness of 3 mm. A second elastic layer 1d made of silicon rubber having a thickness of 1c and a thickness of 400 μm was formed in this order, and a PFA tube having a thickness of 30 μm was provided as a release layer 1e on the outermost layer.

  As the pressure roller 2, an elastic body layer 2b formed of a silicon sponge having a thickness of 5 mm is provided on an iron columnar core 2a having a diameter of 20 mm, and a PFA tube having a thickness of 30 μm is provided on the surface of the elastic body layer 2b. What provided the layer was used. The nip width of the fixing nip N formed by the contact between the heating roller 1 and the pressure roller 2 was set to about 7 mm.

  Further, a litz wire was used as the induction coil 3a of the heating source 3, and the heating roller 1 was arranged at a distance of 3 mm from the surface of the heating roller 1. Further, a thermistor is used as the temperature detecting member 7, and the temperature detecting member 7 is disposed between the induction coil 3 a and the heating roller 1.

  In the heating apparatus 10 having such a structure, after turning on the power, a heating operation was performed while rotating the heating roller 1 at 240 mm / sec, and the heating roller 1 was heated to 170 ° C. Subsequently, the heating operation was continued at a constant temperature of 170 ° C. while rotating the heating roller 1, and the heating was continued until the electric power during the idling operation decreased to 150 W.

Then, after detecting that the power during idling is 150 W and determining that the fixing operation is possible, a relatively thick A4 width paper (basis weight 105 g / m ² ) is set to 100 at a speed of 50 ppm. The sheets were passed continuously. In addition, in order to evaluate the fixing property, a recording sheet on which an image pattern was formed was passed through the first sheet, the tenth sheet,. The image pattern is a patch pattern in which yellow, magenta, and cyan toners are superposed from one to three layers, and the amount of adhesion per toner layer is 0.5 mg / cm ² .

  FIG. 7 is a result showing the temperature state of the heating roller 1 during paper feeding under the above-described conditions. As is apparent from FIG. 7, the temperature of the heating roller 1 hardly decreases even though continuous paper feeding is performed at a high speed of 50 ppm, and the amount of heat taken by the paper can be sufficiently compensated. It was confirmed that Also, regarding the fixing strength, there was no problem in all patterns from 1 layer to 3 layers.

<Comparative example>
Using the heating device 10 having the configuration described in Example 1, immediately after the temperature of the heating roller 1 reached 170 ° C., the temperature of the heating roller 1 was measured when paper feeding was started immediately. The measurement results are shown in FIG. In this comparative example, as shown in FIG. 8, the temperature of the heating roller 1 decreased by about 20 ° C. at maximum, and a clear cold offset occurred.

  From the above Example 1 and the comparative example, when the fixing operation is started based on the power information at the time of idling in addition to the temperature information of the heating roller, the temperature of the heating roller is not lowered and the continuous paper feeding is performed. It was also found that a good image with no occurrence of fixing failure can be obtained.

  The heating device according to the present invention is applied to an image forming apparatus such as a printer, a copier, a fax machine, or a digital multi-function machine having these functions for forming an image on a recording material by fixing a toner image on the recording material. It can be used effectively. Since the heating device of the present invention can quickly eliminate the temperature unevenness of the heating roller when the heating device is returned from the standby state, it is possible to provide an image forming apparatus capable of warming up in a short time. it can. In addition, since the return time when the heating device is returned from the standby mode can be shortened, there is also an effect of reducing power consumption, so that power saving of the image forming apparatus can be realized.

It is a figure which shows typically the structure of embodiment of the heating apparatus of this invention. It is a partial expanded sectional view which shows typically the structure of the heating roller used for the heating apparatus of FIG. 1 is a diagram schematically illustrating a configuration of an embodiment of an image forming apparatus of the present invention. It is a block diagram which shows an example of the control system of a heating apparatus. It is a block diagram which shows another example of the control system of a heating apparatus. It is a figure which shows typically the structure of another embodiment of the heating apparatus of this invention. It is a figure which shows the result of the Example of this invention, and is a graph which shows the temperature state of the heating roller in continuous paper passing. It is a figure which shows the result of the comparative example of this invention, and is a graph which shows the temperature state of the heating roller during continuous paper passing. It is a figure which shows typically an example of a heating roller type heating apparatus. 10 is a graph showing the relationship between the sheet passing time and the temperature of the heating roller 1 when the sheet is continuously fed in the heating apparatus of FIG. 9. It is a graph which shows the relationship between idling time and electric power required in order to maintain a heating roller at fixed temperature. It is a graph showing the relationship between the idling time and the amount of heat transfer from the heat generating layer to the sponge layer when the heating roller is heated from room temperature to a fixing temperature and then maintained at the fixing temperature while idling the heating roller. .

Explanation of symbols

10 Heating device 1 Heating roller (heating member)
DESCRIPTION OF SYMBOLS 1a Metal core 1b 1st elastic body layer 1c Ni heat generating layer 1d 2nd elastic body layer 1e Release layer 2 Pressure roller (pressure member)
3 Heating source 3a Induction coil 4 Excitation circuit (power supply means)
DESCRIPTION OF SYMBOLS 5 Drive circuit 6 Control part 7 Temperature detection member 8 Fixing entrance guide 100 Image forming apparatus 100Y, 100M, 100C, 100B Visible image forming unit 111 Photoconductor drum 112 Charging roller 113 Laser light irradiation means 114 Developer 115 Transfer roller 116 Cleaner

Claims (9)

A heating member having an elastic layer; a pressure member arranged in pressure contact with the heating member; a heating source for heating the heating member from the outside; and a power supply means for supplying power to the heating source. In a heating device that heats and fixes an image on a recording material,
Temperature detection means for detecting the temperature of the heating member; power detection means for detecting power supplied from the power supply means; output values of the temperature detection means and power detection means; and preset determination reference values; A heating device, comprising: a control unit that determines whether or not to perform a fixing operation based on the comparison result.   The power detection unit is a calculation unit that counts a power supply signal output from the control unit, and the control unit compares a count result of the calculation unit with a preset determination reference value to perform a fixing operation. The heating apparatus according to claim 1, wherein it is determined whether or not to perform.   The heating apparatus according to claim 1, wherein the power detection unit includes a current detection circuit and a voltage detection circuit.   The heating apparatus according to claim 1, wherein the determination reference value can be switched between color output and monochrome output.   The heating apparatus according to claim 1, wherein the determination reference value is switched according to the number of recording materials that can be processed per unit time.   The heating apparatus according to claim 1, wherein the determination reference value can be changed according to the number of processed recording materials input by a user.   The heating apparatus according to claim 1, wherein the determination reference value can be changed based on thickness information of the recording material.   The heating member includes at least an elastic body layer, a heat generation layer, and a release layer that are stacked in order from the inside, and the heating source is induction heating means that induction heats the heat generation layer. The heating apparatus according to any one of claims 1 to 7. An image forming apparatus comprising the heating device according to claim 1.

Images