Image forming apparatus

Abstract

To control the rotation time of a pressure roller for cooling a fixing member of a fixing device according to the temperature of non-paper feed parts of the fixing member.SOLUTION: An image forming apparatus comprises: a fixing device 50 that has a cylindrical fixing film 51, a pressure roller 53 in contact with an outer peripheral surface of the fixing film 51 and forming a fixing nip part N, and a heater 40 having heating elements 42a, 42b, and fixes a toner image on a sheet P to the sheet P with heat of the heater 40 at the fixing nip part N; and a CPU 94 that, when an area of the fixing nip part N through which the sheet P conveyed to the fixing nip part N passes is a paper feed part and areas of the fixing nip part N through which the sheet P conveyed to the fixing nip part N does not pass are non-paper feed areas, calculates the integrated amount of power supplied to the heating elements 42, 42b corresponding to the non-paper feed areas. The CPU 94 determines operations to equalize the temperature of the fixing nip part N after the sheet P passes through the fixing nip part N based on the calculated integrated power amount (S100 to S109).SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus including a fixing device.

Background Art

[0002] In electrophotographic image forming apparatuses such as laser printers, copiers, and facsimiles, a fixing device is provided to fix a toner image transferred onto a recording material. A film heating type fixing device includes a fixing film and a pressure roller that contacts the fixing film, and has a heater substrate inside the fixing film. Since the film heating type fixing device has a low heat capacity, by supplying power to the heater substrate, components such as the fixing film can reach a predetermined temperature state in a short time. Therefore, the film heating type fixing device is a fixing device having the advantage of a short FPOT (First Print Out Time).

[0003] On the other hand, when continuously passing a recording material with a small paper width, which is the length in the direction orthogonal to the conveyance direction, through the fixing device, the non-paper passage portion, which is the area where the recording material does not pass through the fixing film or the pressure roller, reaches a higher temperature than the paper passage portion where the recording material passes. In such a state, when a recording material with a large paper width passes through the fixing device, the recording material is in a state of excessive heating in the area of the non-paper passage portion of the fixing film, and there is a risk of image defects such as hot offset.

[0004] For example, in Patent Document 1, a method for avoiding the occurrence of hot offset is proposed. In the image forming apparatus disclosed in Patent Document 1, the number of recording materials with a small paper width passing through the fixing device is counted, and when the count value exceeds a certain number, in order to cool the fixing device after the recording material with a small paper width has passed, the rotation time of the pressure roller is increased. Thereby, the temperature of the non-paper passage portion of the fixing member of the fixing device is lowered, and the occurrence of hot offset can be avoided even when a large-size recording material passes through the fixing device after a small-size recording material has passed.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 11-73055 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, with the method proposed in the above-mentioned Patent Document 1, it may not be possible to flexibly cope with changes in the basis weight (weight per unit area) of the recording material or the paper width of the recording material. For example, when the basis weight of the recording material is large (the recording material is heavy), the amount of power supplied to the heater, which is the heat source, increases, and the amount of power supplied to the non-paper-passing part of the heater where the recording material does not pass also increases. Therefore, the speed at which the temperature of the non-paper-passing part rises also increases. In addition, when the amount of power supplied to the non-paper-passing part of the heater increases, the temperature of the non-paper-passing part of the fixing member (fixing film) also rises. On the other hand, when the basis weight of the recording material is small (the recording material is light), the amount of power supplied to the heater, which is the heat source, is small, and the amount of power supplied to the non-paper-passing part where the recording material does not pass also becomes small. Therefore, the speed at which the temperature of the non-paper-passing part rises becomes slow. Also, when the paper width of the recording material is small, the amount of power supplied to the non-paper-passing part where the recording material does not pass increases, and the speed of temperature rise in the non-paper-passing part becomes fast. On the other hand, when the paper width of the recording material is large, the amount of power supplied to the non-paper-passing part becomes small, and the speed of temperature rise in the non-paper-passing part also becomes slow.

[0007] In the image forming apparatus of Patent Document 1 described above, in order to cool the fixing member (fixing film) of the fixing device as the number of recording materials passing through the fixing device increases, the rotation time of the pressure roller in contact with the fixing member is increased. However, with this method, it is not possible to cope with the difference in the speed of temperature rise in the non-paper-passing part due to the difference in the basis weight and width of the recording material. Therefore, if the speed of temperature rise in the non-paper-passing part is too fast, there is a risk of hot offset. On the other hand, if the speed of temperature rise is too slow, there is a problem that the rotation time of the pressure roller for cooling the fixing member (fixing film) becomes longer than necessary.

[0008] The present invention has been made under such circumstances, and an object thereof is to control the rotation time of a pressure roller for cooling a fixing member according to the temperature of a non-paper-passing portion of the fixing member of a fixing device.

Means for Solving the Problems

[0009] In order to solve the above-described problems, the present invention includes the following configuration.

[0010] (1) A fixing device having a cylindrical film, a pressure roller that abuts on the outer peripheral surface of the film to form a nip portion, and a heater having a heating element, and fixing a toner image on a recording material to the recording material by the heat of the heater in the nip portion; when a region of the nip portion through which the recording material conveyed to the nip portion passes is defined as a first region, and a region of the nip portion through which the recording material conveyed to the nip portion does not pass is defined as a second region, an integrated amount of electric power supplied to the heating element corresponding to the second region and the saturation temperature rise value of the second region calculating control means; and the control means controls the rotation time of the pressure roller for cooling the nip portion after the recording material has passed through the nip portion based on the calculated integrated amount of electric power. An image forming apparatus characterized by the above. and the saturation temperature rise value

Effects of the Invention

[0011] According to the present invention, the rotation time of the pressure roller for cooling the fixing member can be controlled according to the temperature of the non-paper-passing portion of the fixing member of the fixing device.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 16

Best Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following examples, passing the recording material through the fixing nip portion of the fixing device is referred to as paper passing. Further, in the region where the heating element is generating heat, the region where the recording material is not passing is referred to as the non-paper-passing region (or non-paper-passing part), and the region where the recording material is passing is referred to as the paper-passing region (or paper-passing part). Furthermore, the phenomenon that the temperature of the non-paper-passing region becomes higher than that of the paper-passing region is referred to as non-paper-passing part temperature rise.

Examples

[0014] [Overall Configuration of Image Forming Apparatus] FIG. 1 is a cross-sectional view showing the configuration of an in-line color image forming apparatus, which is an example of an image forming apparatus equipped with the fixing device of Example 1. The configuration of the electrophotographic color image forming apparatus will be described with reference to FIG. 1. Note that the first station is a station for forming a yellow (Y) toner image, the second station is a station for forming a magenta (M) toner image, the third station is a station for forming a cyan (C) toner image, and the fourth station is a station for forming a black (K) toner image.

[0015] At the first station, the photosensitive drum 1a, which is an image carrier, is an OPC photosensitive drum. The photosensitive drum 1a is formed by laminating a plurality of functional organic materials such as a carrier generation layer that generates charges by photosensitization on a metal cylinder and a charge transport layer that transports the generated charges. The outermost layer has low electrical conductivity and is substantially insulated. The charging roller 2a, which is a charging means, contacts the photosensitive drum 1a and uniformly charges the surface of the photosensitive drum 1a while rotating passively as the photosensitive drum 1a rotates. A voltage obtained by superimposing a DC voltage or an AC voltage is applied to the charging roller 2a, and discharge occurs in minute air gaps on the upstream and downstream sides in the rotation direction of the photosensitive drum 1a from the nip portion between the charging roller 2a and the surface of the photosensitive drum 1a, thereby charging the photosensitive drum 1a. The cleaning unit 3a is a unit that cleans the toner remaining on the photosensitive drum 1a after transfer, which will be described later. The developing unit 8a, which is a developing means, stores the non-magnetic one-component toner 5a and has a developing roller 4a and a developer coating blade 7a. The photosensitive drum 1a, the charging roller 2a, the cleaning unit 3a, and the developing unit 8a are housed in an integrally formed process cartridge 9a that is detachable from the image forming apparatus.

[0016] The exposure device 11a, which is an exposure means, is composed of a scanner unit that reflects laser light by a rotating polygon mirror and scans the photosensitive drum 1a, or an LED (light-emitting diode) array, and irradiates a scanning beam 12a modulated based on an image signal onto the photosensitive drum 1a. Further, the charging roller 2a is connected to a charging high-voltage power supply 20a, which is a voltage supply means for the charging roller 2a. The developing roller 4a is connected to a developing high-voltage power supply 21a, which is a voltage supply means for the developing roller 4a. The primary transfer roller 10a is connected to a primary transfer high-voltage power supply 22a, which is a voltage supply means for the primary transfer roller 10a. The above is the configuration of the first station, and the second, third, and fourth stations also have the same configuration. For other stations, components having the same functions as those of the first station are given the same reference numerals, and the suffixes b, c, and d are added to the reference numerals for each station. In the following description, the suffixes a, b, c, and d are omitted unless a specific station is described.

[0017] The intermediate transfer belt 13 is supported by three rollers, namely, a secondary transfer opposing roller 15, a tension roller 14, and an auxiliary roller 19, as its stretching members. A force in the direction of stretching the intermediate transfer belt 13 is applied only to the tension roller 14 by a spring (not shown), so that an appropriate tension force is maintained on the intermediate transfer belt 13. The secondary transfer opposing roller 15 rotates under the rotational drive from a main motor (not shown), and the intermediate transfer belt 13 wound around the outer periphery rotates. The intermediate transfer belt 13 moves at substantially the same speed in the direction of the arrow (for example, clockwise in FIG. 1) with respect to the photosensitive drums 1a to 1d (for example, rotating counterclockwise in FIG. 1). Further, the primary transfer roller 10 is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 13 interposed therebetween, and rotates idly as the intermediate transfer belt 13 moves. The position where the photosensitive drum 1 and the primary transfer roller 10 are in contact with each other with the intermediate transfer belt 13 interposed therebetween is called the primary transfer position. The auxiliary roller 19, the tension roller 14, and the secondary transfer opposing roller 15 are electrically grounded. Note that the second to fourth stations also have the same configuration as the primary transfer rollers 10b to 10d of the first station, so the description thereof is omitted.

[0018] Next, the image forming operation of the image forming apparatus shown in FIG. 1 will be described. When the image forming apparatus receives a print command in the standby state, it starts the image forming operation. The photosensitive drum 1, the intermediate transfer belt 13, etc. start rotating in the direction of the arrow in the figure at a predetermined process speed by a main motor (not shown). The photosensitive drum 1a is uniformly charged by the charging roller 2a to which a voltage is applied by the charging high voltage power supply 20a, and then an electrostatic latent image based on the image information is formed by the scanning beam 12a irradiated from the exposure device 11a. The toner 5a in the developing unit 8a is charged to a negative polarity by the developer application blade 7a and applied to the developing roller 4a. Then, a predetermined developing voltage is applied to the developing roller 4a by the developing high voltage power supply 21a. When the electrostatic latent image formed on the photosensitive drum 1a reaches the developing roller 4a as the photosensitive drum 1a rotates, the electrostatic latent image is visualized by the adhesion of the negative-polarity toner, and a toner image of the first color (for example, Y (yellow)) is formed on the photosensitive drum 1a. Each station (process cartridge 9b to 9d) of the other colors M (magenta), C (cyan), and K (black) also operates in the same manner. While delaying the write signal from the controller (not shown) at a timing corresponding to the distance between the primary transfer positions of each color, an electrostatic latent image is formed on each of the photosensitive drums 1a to 1d by the scanning beam 12 from the exposure device 11. A DC high voltage having a polarity opposite to that of the toner is applied to each of the primary transfer rollers 10a to 10d. As a result, the toner images on the photosensitive drums 1a to 1d are sequentially transferred to the intermediate transfer belt 13 (hereinafter referred to as primary transfer), and a multi-color toner image is formed on the intermediate transfer belt 13.

[0019] Subsequently, in accordance with the formation of the toner image, the paper P, which is the recording material loaded in the cassette 16, is fed (picked up) by a paper feed roller 17 that is rotationally driven by a paper feed solenoid (not shown). The fed paper P is conveyed by a conveyance roller (not shown) to a registration roller (hereinafter referred to as a registration roller) 18. The paper P is conveyed to a transfer nip portion, which is the contact portion between the intermediate transfer belt 13 and the secondary transfer roller 25, by the registration roller 18 in synchronization with the toner image on the intermediate transfer belt 13. A voltage of the opposite polarity to the toner is applied to the secondary transfer roller 25 by a secondary transfer high voltage power supply 26, and the four-color multi-layer toner image carried on the intermediate transfer belt 13 is collectively transferred onto the paper P (on the recording material) (hereinafter referred to as secondary transfer). On the other hand, after the secondary transfer is completed, the toner remaining on the intermediate transfer belt 13 is cleaned by a cleaning unit 27. The paper P after the secondary transfer is conveyed to a fixing device 50, which is a fixing means, and the paper P on which the toner image is fixed is discharged to a discharge tray 30 as an image formation product (print, copy). Note that the fixing film 51, nip forming member 52, pressure roller 53, and heater 40 of the fixing device 50 will be described later.

[0020] [Control Block Diagram of Image Forming Apparatus] FIG. 2 is a block diagram showing the configuration of the control unit of the image forming apparatus, and the printing operation of the image forming apparatus will be described with reference to this figure. A host computer, PC110, transmits a printing command including image data of a printing image and printing information to a video controller 91 inside the image forming apparatus.

[0021] The video controller 91 converts the image data received from the PC110 into exposure data, transfers it to an exposure control device 93 inside the engine controller 92, and transmits the printing command to the CPU 94. The exposure control device 93 is controlled by the CPU 94 and controls the exposure device 11 that turns the laser light on and off according to the exposure data. When the CPU 94, which is a control means, receives a printing command from the video controller 91, it starts the image forming operation.

[0022] The engine controller 92 is equipped with a CPU 94, a memory 95, etc. The CPU 94 operates according to a program stored in advance in the memory 95. Further, the CPU 94 has a timer for measuring time, and various information for controlling the fixing device 50 described later is stored in the memory 95. The high-voltage power supply 96 is composed of the charging high-voltage power supply 20, the developing high-voltage power supply 21, the primary transfer high-voltage power supply 22, and the secondary transfer high-voltage power supply 26 described above. Also, the fixing power control device 97 is composed of a bidirectional thyristor (hereinafter referred to as a triac) 56 which is a supply control unit, a heating element switching device 552 (see FIG. 11) which is a switching unit for exclusively selecting a heating element for supplying power, etc. The fixing power control device 97 selects a heating element for supplying power in the fixing device 50 and determines the amount of power to be supplied.

[0023] The drive device 98 is composed of a main motor 99, a fixing motor 100, etc. Also, the sensor 101 consists of a fixing temperature sensor 60 which is a temperature detection means for detecting the temperature of the fixing device 50, a paper width sensor 102 for detecting the width of the paper P, a voltmeter 58, an ammeter 59, etc. The detection result of the sensor 101 is transmitted to the CPU 94. The CPU 94 acquires the detection results of the sensors 101 in the image forming apparatus and controls the exposure device 11, the high-voltage power supply 96, the fixing power control device 97, and the drive device 98 based on the detection results. Thereby, the CPU 94 forms an electrostatic latent image, transfers the developed toner image onto the paper P, fixes the transferred toner image onto the paper P, etc., and controls the image forming process in which the image data received from the PC 110 is printed as a toner image on the paper P. Note that the image forming apparatus to which the present invention is applied is not limited to the image forming apparatus having the configuration described with reference to FIG. 1, and any image forming apparatus that can print papers P of different widths and is provided with a fixing device 50 having a heater 40 described later may be used.

[0024] [Configuration of Fixing Device] FIG. 3 is a diagram showing the configuration of the fixing device 50 used in the image forming apparatus of the present embodiment. FIG. 3(a) is a perspective view showing the configuration of the fixing device 50, and FIG. 3(b) is a cross-sectional view when the fixing device 50 shown in FIG. 3(a) is cut at the center in the longitudinal direction.

[0025] The fixing device 50 includes a cylindrical fixing film 51, a pressure roller 53 that forms a fixing nip portion N together with the fixing film 51, a heater 40 that heats the fixing film 51, a nip forming member 52 that holds the heater 40, and a stay 55 that maintains the strength in the longitudinal direction.

[0026] The fixing film 51 is composed of a silicone rubber layer with a thickness of 200 μm on a polyimide substrate with a thickness of 50 μm, and a PFA release layer with a thickness of 20 μm on top of that. The pressure roller 53 is composed of a SUM mandrel with an outer diameter of 13 mm, a silicone rubber elastic layer with a thickness of 3.5 mm on top of it, and a PFA release layer with a thickness of 40 μm on top of that. By rotating the pressure roller 53 by a drive source (not shown), the fixing film 51 is driven by the rotation of the pressure roller 53 and rotates passively. The heater 40, which is a heating member, is disposed in the internal space of the fixing film 51, held by the nip forming member 52, and the inner peripheral surface of the fixing film 51 contacts the surface of the heater 40. Both ends of the stay 55 press the nip forming member 52, and the pressing force is received by the pressure roller 53 via the nip forming member 52 and the fixing film 51. Thereby, a fixing nip portion N is formed where the outer peripheral surface of the fixing film 51 and the pressure roller 53 are in pressing contact, and the fixing film 51 is sandwiched between the pressure roller 53 and the heater 40. The paper P passes through the fixing nip portion N in the paper conveyance direction in the figure. Since the nip forming member 52 needs to have rigidity, heat resistance, and heat insulation properties, it is formed of a liquid crystal polymer.

[0027] At the central portion in the longitudinal direction on the back surface of the heater 40 (the side opposite to the surface facing the fixing film 51), a fixing temperature sensor 60 (a thermistor is used here), which is a temperature detecting means, and a thermoswitch, which is a safety element (not shown), are arranged in contact with each other. The fixing temperature sensor 60 of the present embodiment is a chip resistor type thermistor (hereinafter referred to as the thermistor 60). The CPU 94 described above detects the resistance value of the thermistor 60 and controls the temperature of the heater 40 based on the detection result of the resistance value. Further, the thermistor 60 can also detect excessive temperature rise. Thermistors are arranged at both ends in the longitudinal direction of the heater 40, and the heater temperature of the heater 40 at each end in the longitudinal direction can be detected. The thermoswitch is a bimetal thermoswitch, and the heater 40 and the thermoswitch are electrically connected. When the thermoswitch detects an excessive temperature rise of the heater 40, the bimetal inside the thermoswitch operates, and the power supply to the heater 40 is cut off.

[0028] [Configuration of Heater] Fig. 4(a) is a diagram for explaining the configuration of the heater 40 of the present embodiment. In Fig. 4(a), the upper right diagram is a top view of the heater 40 when viewed from the pressure roller 53 side, and the left diagram is a cross-sectional view of the heater 40 shown in the right diagram when cut at the central portion in the longitudinal direction. On the other hand, the lower diagram is a cross-sectional view of the heater 40 shown in the upper right diagram when cut at the central portion in the short-side direction.

[0029] The heater 40 has a structure in which heating elements 42a and 42b mainly composed of silver and palladium, a conductive path 43 having a lower resistance value than the heating elements 42a and 42b, and power supply contacts 44a and 44b are formed on a plate-shaped ceramic substrate 41 made of alumina or the like. Regions other than the contacts 44a and 44b are coated with insulating glass 45. When a voltage is applied between the power supply contacts 44a and 44b, the heating elements 42a and 42b on the ceramic substrate 41 generate heat. The dimensions of the ceramic substrate 41 are a thickness t = 1 mm, a width w = 7.0 mm, and a length l = 280 mm. The heating elements 42a and 42b have the same dimension with a length of 222 mm in the longitudinal direction and are arranged in parallel in the short side direction of the ceramic substrate 41. The resistance values of the heating elements 42a and 42b are 21 Ω, and since the heating elements 42a and 42b are connected in parallel, the combined resistance value of the two heating elements 42a and 42b is 10.5 Ω. As described above, the heating elements 42a and 42b and the conductive path 43 are covered with glass 45 to maintain insulation. A thermistor 60 for detecting the temperature of the heater 40 through the ceramic substrate 41 is arranged at the central portion in the longitudinal direction of the ceramic substrate 41. The CPU 94 controls the amount of electric power supplied to the heating elements 42a and 42b based on the detection result of the temperature of the heater 40 by the thermistor 60.

[0030] FIG. 4(b) is a schematic diagram for explaining the power supply path for supplying power to the heater 40 of the present embodiment. As shown in FIG. 4(b), power is supplied to the heating elements 42a and 42b of the heater 40 from an AC power supply 57 (indicated as AC in the figure) via power supply contacts 44a and 44b. Further, in the power supply path, there are arranged a voltmeter 58 (indicated as V in the figure), which is voltage detection means for measuring the voltage applied to the heating elements 42a and 42b, and an ammeter 59 (indicated as A in the figure), which is current detection means for measuring the current value flowing through the heating elements 42a and 42b. The triac 56, which is a switch, connects / disconnects the power supply path from the AC power supply 57 to the heating elements 42a and 42b. The CPU 94 performs PI control using the temperature information of the heater 40 detected by the thermistor 60 so that the fixing nip portion N reaches a predetermined temperature, and calculates the ratio (duty) of the on / off time of the triac 56. Then, the CPU 94 controls the triac 56 based on the calculated duty.

[0031] An object of the present invention is to accurately calculate the temperature in the non-paper-passing portion of the fixing film 51, which is a fixing member, and thereby shorten the cooling time of the pressure roller 53 after passing the small-size paper P according to the temperature of the non-paper-passing portion. Further, it is to prevent the occurrence of hot offset when passing the large-size paper P after passing the small-size paper P. Therefore, in the present embodiment, the integrated power amount supplied to the non-paper-passing portion of the heater 40 is calculated, and the temperature of the non-paper-passing portion of the fixing film 51 is calculated from the calculated integrated power amount. By accurately calculating the temperature of the non-paper-passing portion of the fixing film 51, the cooling time of the pressure roller 53 after passing the small-size paper P can be set to the minimum necessary time. Hereinafter, a specific method for calculating the temperature of the fixing member of the present embodiment will be described.

[0032] [Power amount supplied to the paper-passing portion and non-paper-passing portion of the heater] FIG. 5 is a diagram for explaining the positional relationship between the heater 40 and the small-sized paper P (displayed as small-sized paper in the figure) through which the paper passes, using FIG. 4(b). In FIG. 5, it is assumed that the center in the width direction of the small-sized paper P passes through the center in the longitudinal direction (left-right direction in the figure) of the heating elements 42a and 42b of the heater 40. In the heating elements 42a and 42b shown in FIG. 5, the area of the paper passage portion through which the paper P passes is defined as area A, and among the non-paper passage portions on both sides of area A where the paper P does not pass, one non-paper passage portion is defined as area B (the non-paper passage portion on the left side in the figure), and the other non-paper passage portion is defined as area C (the non-paper passage portion on the right side in the figure). Also, let the length in the longitudinal direction of the heating elements 42a and 42b of the heater 40 be H, the paper width (length in the width direction) of the small-sized paper P be ha, the width in the longitudinal direction of area B which is a non-paper passage portion be hb, and the width in the longitudinal direction of area C be hc. As described above, since the paper P passes through the center in the longitudinal direction of the heating elements 42a and 42b of the heater 40, the width hb of area B and the width hc of area C are of the same length. The paper width ha may be determined based on the paper size information of the paper P included in the print information transmitted from the PC110, or the paper width ha of the paper P may be determined based on the detection result by the paper width sensor 102 provided in the image forming apparatus.

[0033] In this embodiment, based on the voltage information applied to the heating elements 42a and 42b measured by the voltmeter 58 and the current information flowing through the heating elements 42a and 42b measured by the ammeter 59, the amount of electric power supplied to the heating elements 42a and 42b of the heater 40 is calculated. Let the amount of electric power supplied from the AC power supply 57 to the heating elements 42a and 42b of the heater 40 be WS, the amount of electric power supplied to the area A which is the paper-passing part of the heating elements 42a and 42b be WSa, and the amounts of electric power supplied to the non-paper-passing areas B and C be WSb and WSc respectively. The amount of electric power WS can be calculated by WS = WSa + WSb + WSc. The amount of electric power WSa in the area A which is the paper-passing area can be calculated by the calculation formula WSa = (WS × paper width ha / length H of the heating element). Also, the amount of electric power WSb in the non-paper-passing area B is calculated by the calculation formula WSb = (WS × area width hb / length H of the heating element). Similarly, the amount of electric power WSc in the non-paper-passing area C is calculated by the calculation formula WSc = (WS × area width hc / length H of the heating element). Note that the area widths hb and hc are of the same length and are calculated by (length H of the heating element - paper width ha) / 2.

[0034] In this embodiment, the amount of electric power supplied to the non-paper-passing part of the heating element of the heater 40 is integrated, and from the integrated amount of electric power, the increased temperature (hereinafter referred to as the temperature rise value) of the non-paper-passing part of the fixing member is calculated. Let the integrated amount of electric power supplied from the AC power supply 57 to the heater 40 be IWS, the integrated amount of electric power in the non-paper-passing area B be IWSb, and the integrated amount of electric power in the non-paper-passing area C be IWSc. In this embodiment, since the area widths hb and hc of the areas B and C are of the same length, the amount of electric power supplied to the area B and the amount of electric power supplied to the area C are the same. Therefore, hereinafter, the integrated amount of electric power in the area B is calculated, and the calculation of the temperature rise value in the area B will be described, and the description of the area C will be omitted.

[0035] [Transition of Temperature Rise Value and Integrated Amount of Electric Power of Non-Paper-Passing Part of Fixing Member] First, three types of papers with different paper widths were prepared for a continuous paper feeding test. The temperature rise value (maximum value) in the non-paper feeding part of the fixing member and the integrated power consumption IWSb of the non-paper feeding part were obtained at that time, and it was confirmed whether there was a correlation between the integrated power consumption IWSb in region B and the temperature rise value of the non-paper feeding part. The paper feeding conditions for the continuous paper feeding test are as follows. The paper widths ha of the three types of papers L, M, and N are 210 mm, 205 mm, and 200 mm respectively, and the lengths and basis weights of papers L, M, and N in the conveying direction are all 297 mm and 128 g / m 2 respectively. In the continuous paper feeding test, temperature control was performed so that the detected temperature of the thermistor 60 in contact with the heater 40 was maintained at 200°C, the paper conveying speed was 200 mm / sec, and the feeding interval of each paper was 0.2 seconds. Here, the fixing member is the fixing film 51 of the fixing device 50.

[0036] Figure 6(a) is a graph showing the transition of the temperature rise value of the surface temperature in the region of the non-paper feeding part of the fixing film 51 when papers L, M, and N are continuously passed through the fixing nip part N of the fixing device 50. In Figure 6(a), the vertical axis represents the temperature rise value (unit: °C) of the surface temperature in the non-paper feeding part of the fixing film 51, and the horizontal axis represents time (unit: sec (seconds)). Also, the solid line graph in the figure shows the temperature change when paper L is continuously passed through, the two-dot chain line graph shows the temperature change when paper M is continuously passed through, and the dashed line graph shows the temperature change when paper N is continuously passed through.

[0037] In the figure, the points indicated by black circles show the time when the temperature rise value of the non-paper feeding part of the fixing film 51 reached 200°C when papers L, M, and N were continuously passed through. In Figure 6(a), the time T L200 when the temperature rise value of the non-paper feeding part of the fixing film 51 reached 200°C when paper L was passed through is 26 seconds. Similarly, the time T M200 when the temperature rise value of the non-paper feeding part of the fixing film 51 reached 200°C when paper M and paper N were passed through, and T N200They were 17 seconds and 12 seconds respectively. As shown in FIG. 6(a), for the sheet N with the smallest paper width, the temperature rising speed of the fixing film 51 was fast, and the temperature rising value of the fixing film 51 saturated at the highest temperature among the three types of sheets.

[0038] FIG. 6(b) is a graph showing the transition of the integrated power consumption IWSb in the non-paper-passing area B of the heating elements 42a and 42b when the sheets L, M, and N are continuously passed through the fixing nip portion N of the fixing device 50. In FIG. 6(b), the vertical axis represents the integrated power consumption IWSb (unit: W·S) supplied to the non-paper-passing area B of the heating elements 42a and 42b, and the horizontal axis represents time (unit: sec (seconds)). Also, the solid-line graph in the figure shows the change in the integrated power consumption IWSb when the sheet L is continuously passed, the two-dot chain-line graph shows the change in the integrated power consumption IWSb when the sheet M is continuously passed, and the broken-line graph shows the change in the integrated power consumption IWSb when the sheet N is continuously passed. As described above, the power consumption WSb in the non-paper-passing area B is calculated by the calculation formula WSb = (power consumption WS × area width hb / length H of the heating element). And the integrated power consumption IWSb in the area B is obtained by integrating the calculated power consumption WSb.

[0039] As explained in FIG. 6(a), when the sheets L, M, and N are continuously passed, the times when the temperature rising value of the non-paper-passing part of the fixing film 51 reaches 200°C are 26 seconds, 17 seconds, and 12 seconds respectively. In FIG. 6(b), when the sheets L, M, and N are continuously passed and 26 seconds, 17 seconds, and 12 seconds have elapsed respectively, the integrated power consumption IWSb in the area B is 220 (W·S), 220 (W·S), and 215 (W·S) for the sheets L, M, and N respectively. That is, when the sheets L, M, and N are continuously passed and the surface temperature of the non-paper-passing area of the fixing film 51 reaches 200°C, the integrated power consumption IWSb supplied to the non-paper-passing area B of the heating elements 42a and 42b is almost the same value.

[0040] Also, regarding the correlation between the surface temperature of the non-paper-passing area of the fixing film 51 at 190°C and 180°C and the integrated power consumption IWSb supplied to the non-paper-passing area B of the heating elements 42a and 42b, the above-mentioned continuous paper-passing test was conducted to confirm the presence or absence of the correlation. As shown in Fig. 6(a), when the continuous paper-passing of papers L, M, and N was performed, the times when the temperature rise value of the non-paper-passing area of the fixing film 51 reached 190°C were 19 seconds, 12 seconds, and 9 seconds, respectively. And in Fig. 6(b), when the continuous paper-passing of papers L, M, and N was performed and 19 seconds, 12 seconds, and 9 seconds had elapsed respectively, the integrated power consumption IWSb in the area B was 165 (W·S), 170 (W·S), and 170 (W·S) for papers L, M, and N, respectively. Also, as shown in Fig. 6(a), when the continuous paper-passing of papers L, M, and N was performed, the times when the temperature rise value of the non-paper-passing area of the fixing film 51 reached 180°C were 14 seconds, 9 seconds, and 6 seconds, respectively. And in Fig. 6(b), when the continuous paper-passing of papers L, M, and N was performed and 14 seconds, 9 seconds, and 6 seconds had elapsed respectively, the integrated power consumption IWSb in the area B was 130 (W·S), 135 (W·S), and 130 (W·S) for papers L, M, and N, respectively. As a result, it was confirmed that there is a strong correlation between the integrated power consumption IWSb supplied to the non-paper-passing area B of the heating elements 42a and 42b even when the surface temperature of the area corresponding to the non-paper-passing area of the fixing film 51 is 190°C and 180°C.

[0041] Figure 7(a) is a graph showing the relationship between the temperature rise value of the non-paper-passing portion of the fixing film 51 and the integrated power consumption IWSb supplied to the non-paper-passing portions of the heating elements 42a and 42b based on the results of the continuous paper-passing test described above. The vertical axis (Y-axis) of Figure 7(a) indicates the temperature rise value (unit: °C) of the non-paper-passing portion of the fixing film 51, and the horizontal axis (X-axis) indicates the integrated power consumption (unit: W·S) supplied to the region B of the non-paper-passing portions of the heating elements 42a and 42b. The graph in Figure 7(a) shows a straight line representing an approximate formula passing through the plotted points of the integrated power consumption IWSb supplied to the non-paper-passing portions of the heating elements 42a and 42b when the temperature rise values of the non-paper-passing portion of the fixing film 51 are 180°C, 190°C, and 200°C. If the formula representing the straight line shown in Figure 7(a) is defined as relational expression 1 (the first calculation formula), relational expression 1 is represented by Y = 0.23X + 150. Note that a table associating the integrated power consumption IWSb supplied to the non-paper-passing portions of the heating elements 42a and 42b with the temperature rise value of the non-paper-passing portion of the fixing film 51 may be created using relational expression 1, and the temperature rise value of the non-paper-passing portion of the fixing film 51 may be calculated from the integrated power consumption IWSb.

[0042] Also, in the graph of the temperature rise value of the non-paper-passing portion of the fixing film 51 shown in Figure 6(a), it can be seen that the temperature rise values of the non-paper-passing portions of the fixing film 51 corresponding to the papers L, M, and N are saturated so as to converge to a certain temperature. Specifically, the temperature rise values of the non-paper-passing portions of the fixing film 51 for the papers L, M, and N are saturated at 210°C, 230°C, and 255°C, respectively. Here, this temperature is defined as the saturation temperature rise value (saturation temperature). Next, a method for calculating the saturation temperature rise value will be described.

[0043] Figure 6(b) is a graph showing the transition of the integrated power consumption IWSb in region B of the non-paper-passing portions of heating elements 42a and 42b when sheets of paper L, M, and N are passed through continuously. Here, when the graphs of sheets of paper L, M, and N shown in Figure 6(b) are represented by a linear approximation formula with the integrated power consumption shown on the vertical axis as Y and the time shown on the horizontal axis as X, the ratio (rate of change), that is, the slope α of the linear approximation formula, of the change in Y with respect to the change in X is obtained. The slopes α for sheets of paper L, M, and N were 7.2, 10.2, and 13.3, respectively. Here, the slope of the graph after 4 seconds when sheets of paper L, M, and N are passed through the fixing nip portion N of the fixing device 50 of the fixing device 50 is calculated. Therefore, the linear expressions indicating the integrated power consumption y of sheets of paper L, M, and N shown in Figure 6(b) are approximated by y = 7.2x, y = 10.2x, and y = 13.3x, respectively.

[0044] Figure 7(b) is a graph showing the relationship between the saturation temperature rise value of the non-paper-passing portion of the fixing film 51 and the slope α calculated from the graph of Figure 6(b) based on the results of the above-described continuous paper-passing test. The vertical axis (Y-axis) of Figure 7(b) indicates the saturation temperature rise value (unit: °C) of the non-paper-passing portion of the fixing film 51, and the horizontal axis (X-axis) indicates the slope of the graph shown in Figure 6(b), that is, the change in the integrated power consumption IWSb in region B of the non-paper-passing portions of heating elements 42a and 42b with respect to the paper-passing time. The graph of Figure 7(b) shows a straight line representing an approximation formula passing through the plotted points of the slopes α calculated from the graphs of Figure 6(b) for sheets of paper L, M, and N with saturation temperature rise values of 210 °C, 230 °C, and 255 °C, and it can be confirmed that there is a correlation between the slope α and the saturation temperature rise value. When the expression showing the relationship between the slope α (X) and the saturation temperature rise value (Y) shown in Figure 7(b) is defined as relational expression 2 (second calculation formula), relational expression 2 is represented by Y = 7.4X + 156.

[0045] [Relationship between the integrated power consumption in the non-paper-passing portion of the heater and the temperature rise value of the non-paper-passing portion of the fixing film] Next, based on relational expression 1 showing the relationship between the integrated power consumption IWSb in region B of the non-paper-passing parts of the heating elements 42a and 42b of the heater 40 shown in FIG. 7(a) and the temperature rise value of the non-paper-passing part of the fixing film 51, a method for calculating relational expression 3 considering the above-described saturation temperature rise value will be described. Here, in relational expression 1 shown in FIG. 7(a), when the temperature rise value of the non-paper-passing part calculated by relational expression 1 is higher than the above-described saturation temperature rise value, a relational expression 3 is created in which the non-paper-passing part temperature rise value calculated from relational expression 1 is replaced with the saturation temperature rise value. As a specific example, a sheet P with a sheet width of 207 mm will be described as an example. The slope α when passing the sheet P with a sheet width of 207 mm is 11. Then, by substituting the slope α = 11 (that is, X = 11) into the above-described relational expression 2, the saturation temperature rise value Y is calculated to be 238°C (≈7.4°C × 11 + 156°C). Further, in relational expression 1, all non-paper-passing part temperature rise values corresponding to the integrated power consumption at which the non-paper-passing part temperature rise value is higher than 238°C are replaced with 238°C, which is the saturation temperature rise value. Thereby, the relationship between the integrated power consumption of the non-paper-passing parts of the final heating elements 42a and 42b and the temperature rise value of the non-paper-passing part of the fixing film 51 can be represented as a graph shown in FIG. 8.

[0046] FIG. 8 is a graph showing the relationship between the integrated power consumption supplied to the non-paper-passing parts of the heating elements 42a and 42b and the temperature rise value of the non-paper-passing part of the fixing film 51. In FIG. 8, the vertical axis (Y-axis) indicates the temperature rise value (unit: °C) of the non-paper-passing part of the fixing film 51, and the horizontal axis (X-axis) indicates the integrated power consumption supplied to the non-paper-passing parts of the heating elements 42a and 42b. Relational expression 3 representing the graph shown in FIG. 8 is such that when the integrated power consumption of the non-paper-passing part is X and the temperature rise value of the non-paper-passing part is Y, when the value of X is from 0 to 383, the value of Y is calculated using Y = 0.23X + 150 of relational expression 1, and when the value of X exceeds 383, Y = 238. Based on relational expression 3 and the integrated power consumption of the non-paper-passing parts of the heating elements 42a and 42b after printing, the temperature rise value of the non-paper-passing part of the fixing film 51 after printing can be calculated.

[0047] [Cooling time of the fixing device according to the temperature rise value of the non-paper-passing part] Next, the cooling time with respect to the temperature rise value of the non-paper-passing portion of the fixing film 51 will be described. The cooling time (also referred to as the cooling period) is the time (the period during which an operation for soaking is performed) for reducing the temperature of the non-paper-passing portion in the high-temperature state of the fixing film 51 of the fixing device 50 to a predetermined temperature by passing a small-size paper with a narrow paper width. The predetermined temperature is a temperature at which no hot offset occurs even when the paper width of the paper P to be printed next is wider than the paper width of the paper P printed immediately before. By reducing the temperature of the non-paper-passing portion of the fixing film 51 to the predetermined temperature and soaking it, the occurrence of hot offset can be suppressed even when a large-size paper with a wide width is passed after passing a small-size paper. In this embodiment, the temperature rise value of the non-paper-passing portion of the fixing film 51 after passing a small-size paper is calculated, and the cooling time for reducing the temperature of the non-paper-passing portion of the fixing film 51 is determined according to the calculated temperature rise value. The cooling time is determined such that the higher the temperature rise value of the non-paper-passing portion of the fixing film 51, the longer it is, and the lower the temperature rise value, the shorter it is. Note that for the cooling time, the pressure roller 53 of the fixing device 50 may be in a rotating state or in a stopped state without rotation.

[0048] [Control Sequence for Cooling of Fixing Device] FIG. 9 is a flowchart showing a control sequence for cooling to reduce the temperature rise value of the non-paper-passing portion of the fixing film 51 of the fixing device 50 described above. The process shown in FIG. 9 is started when printing is performed on the paper P and is executed by the CPU 94. Note that the CPU 94 controls the power supply to the heating elements 42a and 42b of the heater 40 to control the temperature of the fixing film 51 of the fixing device 50, but it is assumed that this is executed in a process different from the process shown in the flowchart of FIG. 9. Also, it is assumed that the memory 95 stores in advance the length information in the longitudinal direction of the heating elements 42a and 42b, the above-described relational expressions 1 and 2. Further, it is assumed that the memory 95 stores a table associating the temperature rise value of the non-paper-passing portion of the fixing film 51 with the cooling time for reducing the temperature of the non-paper-passing portion of the fixing film 51 to a predetermined temperature.

[0049] In the image forming apparatus, when the video controller 91 receives a print command from the PC 110, it transmits a print command including information on the paper P to the CPU 94. The CPU 94 that has received the print command from the video controller 91 starts the printing operation of the paper P. Note that the print job based on the print command from the PC 110 is a print job for the paper P of the same paper size.

[0050] In step (hereinafter referred to as S) 100, the CPU 94 acquires the paper width ha from the information on the paper P included in the print command received from the video controller 91, and the longitudinal length information H of the heating elements 42a and 42b from the memory 95. In S101, the CPU 94 sets the integrated power consumption IWSb in the non-paper-passing area B of the heating elements 42a and 42b to 0.

[0051] In S102, the CPU 94 acquires the voltage information applied to the heating elements 42a and 42b measured by the voltmeter 58 and the current information flowing through the heating elements 42a and 42b measured by the ammeter 59. In S103, the CPU 94 calculates the power consumption WS (= voltage × current) supplied to the heating elements 42a and 42b based on the voltage information and current information acquired in S102. Then, the CPU 94 calculates the power consumption WSb of the non-paper-passing part described above using the calculated power consumption WS, the paper width ha of the paper P, and the longitudinal length (the length H of the heating element - the paper width ha) / 2 of the non-paper-passing area B of the heating elements 42a and 42b. Further, the CPU 94 adds the calculated power consumption WSb to the value of the integrated power consumption IWSb in the non-paper-passing area B of the heating elements 42a and 42b, updates the value of the integrated power consumption IWSb, and stores the updated integrated power consumption IWSb in the memory 95. In S104, the CPU 94 determines whether the print job has ended. If it determines that the print job has not ended, the process returns to S102. If it determines that the print job has ended, the process proceeds to S105.

[0052] In S105, the CPU 94 reads out the integrated power consumption IWSb stored in the memory 95 every time an update is performed, and calculates a slope α indicating the change amount of the integrated power consumption IWSb over time. In S106, the CPU 94 reads out the above-described relational expression 2 from the memory 95, substitutes the slope α calculated in S105 into the read relational expression 2, and calculates the saturation temperature rise value of the non-paper passage portion of the fixing film 51 with respect to the paper P.

[0053] In S107, the CPU 94 uses the saturation temperature rise value calculated in S106 and the relational expression 1 (non-paper passage portion integrated power consumption and non-paper passage portion temperature rise value) read from the memory 95 to generate the above-described relational expression 3 in which all non-paper passage portion temperature rise values higher than the saturation temperature rise value are replaced with the saturation temperature rise value. In S108, the CPU 94 reads out the integrated power consumption IWSb at the end of the print job stored in the memory 95, substitutes the read integrated power consumption IWSb into the relational expression 3 generated in S107, and calculates the temperature rise value of the non-paper passage portion of the fixing film 51 at the end of the print job.

[0054] In S109, the CPU 94 acquires the cooling time corresponding to the temperature rise value of the non-paper passage portion of the fixing film 51 calculated in S108 from a table in which the temperature rise value of the non-paper passage portion of the fixing film 51 stored in the memory 95 and the cooling time of the fixing film 51 are associated. In S110, the CPU 94 stops the pressure roller 53 of the fixing device 50, resets the timer, and starts it. In S111, the CPU 94 refers to the timer and determines whether the timer value has elapsed the cooling time. If the CPU 94 determines that the timer value has not elapsed the cooling time, the process returns to S111, and if the CPU 94 determines that the timer value has elapsed the cooling time, the process ends.

[0055] Here, for the cooling time, a process of stopping the rotation of the pressure roller 53 is performed to lower the temperature of the non-paper passage portion of the fixing film 51. For example, for the cooling time, the pressure roller 53 may be rotated to lower the temperature of the non-paper passage portion of the fixing film 51, and after the cooling time has elapsed, a process of stopping the rotation of the pressure roller 53 may be performed.

[0056] In addition, in this embodiment, a printing job for printing on sheets P of the same size is described as an example. For example, in the case of a printing job for printing on a plurality of sheets P of different sizes, when the sheet size is changed, a cooling process of the pressure roller 53 may be performed, and after the cooling process is completed, printing on the next sheet P may be performed.

[0057] As described above, in this embodiment, based on the integrated power consumption amount of the non-sheet-passing portion of the heating element and the saturation temperature rise value of the non-sheet-passing portion, the temperature rise value of the non-sheet-passing portion of the fixing member is accurately calculated, thereby shortening the cooling time of the fixing device after passing a small-sized sheet. And by appropriately performing the cooling of the fixing member according to the temperature of the fixing member, it is possible to prevent the occurrence of hot offset even when passing a large-sized sheet after passing a small-sized sheet.

[0058] As described above, according to this embodiment, the rotation time of the pressure roller for cooling the fixing member can be controlled according to the temperature of the non-sheet-passing portion of the fixing member of the fixing device.

Embodiment

[0059] In Example 1, an example of calculating the power consumption amount of the non-sheet-passing portion of the heating element of the heater based on the voltage information and current information measured by a voltmeter and an ammeter was described. In Example 2, a method for calculating the power consumption amount of the non-sheet-passing portion of the heating element of the heater in a fixing device in which a voltmeter and an ammeter are not provided will be described.

[0060] [Configuration of Heater] FIG. 10(a) is a schematic diagram showing a power supply path for supplying power to the heater 40 of this embodiment. In FIG. 10(a), compared with FIG. 5 of Example 1, the difference is that a voltmeter 58 and an ammeter 59 are not provided. Regarding other configurations of the image forming apparatus, they are the same as those in Example 1, and the same reference numerals as those in Example 1 are used for the same members, and the description here is omitted.

[0061] In this embodiment, the memory 95 has an applied voltage table that associates the temperature difference between the target temperature of the heater 40 and the temperature of the heater 40 detected by the thermistor 60 with the voltage to be applied to the heater 40. The memory 95 also has a control signal table that associates the voltage to be applied to the heater 40 with the timing and output interval of the control signal for turning on the triac 56. The CPU 94 periodically detects the temperature difference from the target temperature of the heater 40 based on the temperature detection result of the heater 40 by the thermistor 60, and obtains the applied voltage corresponding to the detected temperature difference from the applied voltage table. Further, the CPU 94 determines the output timing of the control signal of the triac 56 corresponding to the obtained applied voltage from the control signal table, and outputs the control signal to the triac 56 according to the output timing. In this embodiment, the CPU 94 outputs the control signal in the half-wave period (every half period) of the AC voltage waveform of the AC power supply 57. When the control signal is output from the CPU 94, the triac 56 is turned on during the half period of the AC voltage waveform, and the AC voltage from the AC power supply 57 is supplied to the heater 40.

[0062] [Relationship between AC voltage and control signal of triac] Figure 10(b) is a diagram for explaining the relationship between the AC voltage of the AC power supply 57 and the control signal for driving the triac 56. In Figure 10(b), the lower diagram shows the control signal of the triac 56 output from the CPU 94, and the triac 56 is turned on only during the half period of the AC voltage when the control signal is output. The upper diagram shows the waveform of the AC voltage (described as AC voltage in the figure) from the AC power supply 57 supplied to the heater 40, and the AC voltage is supplied to the heater 40 only during the half period when the control signal is output. The hatched part in the figure indicates the state where the AC voltage is being supplied to the heater 40. The AC power supply 57 has a voltage of 100V and a power supply frequency of 50Hz, and the combined resistance of the heating elements 42a and 42b of the heater 40 is 10.5Ω. Then, the maximum amount of electric power WS supplied to the heater 40 per second is WS = V 2 / R = 100(V) × 100(V) / 10.5(Ω) ≒ 952 [W]. 50 Hz means 50 cycles per second (= 100 half - waves), and one half - wave is 1 (second) / 100 (times) = 0.01 second. Therefore, the amount of electric power supplied to the heater 40 for each half - wave is (100(V) × 100(V) / 10.5(Ω)) × 0.01 (second) = 9.52 [W·S].

[0063] In this embodiment, each time the CPU 94 outputs a control signal to the triac 56, it adds the amount of electric power 9.52 [W·S] to the integrated amount of electric power IWS. The integrated amount of electric power IWSb in the non - paper - passing area B of the heater 40 can be calculated by the formula for the integrated amount of electric power IWSb = hb / H × IWS described in Example 1. After calculating the integrated amount of electric power in the non - paper - passing part of the heater 40, the calculation methods for the saturation temperature rise value in the non - paper - passing part, Relational Expression 3, the temperature rise value in the non - paper - passing part, etc. are the same as those in Example 1, so the description here is omitted.

[0064] In this embodiment, the combined resistance value of the heating elements 42a and 42b is 10.5 Ω, and the AC voltage value of the AC power supply 57 is 100 V to calculate the amount of electric power. Since the variation in the resistance values of the heating elements 42a and 42b is as small as ±7%, the influence on the measurement accuracy of the amount of electric power is small. On the other hand, since the variation in the power supply voltage value of the AC power supply 57 changes depending on the usage environment, it may affect the measurement accuracy of the amount of electric power. Since the integrated amount of electric power in the non - paper - passing part of the heater 40 must not be calculated too little, it is desirable that the power supply voltage value of the AC power supply 57 be the maximum voltage value assumed. Information on the resistance values of the heating elements 42a and 42b and the power supply voltage value of the AC power supply 57 may be stored in the memory 95 in advance, and the CPU 94 may refer to it as needed.

[0065] Also, the flowchart shown in FIG. 9 of Example 1 is also applicable to Example 2. In FIG. 9, in the process of S102, the CPU 94 acquires the voltage information and current information measured by the voltmeter 58 and the ammeter 59, and in the process of S103, it calculates the amount of electric power using the acquired voltage information and current information and updates the integrated amount of electric power. In the case of Example 2, different from Example 1, the voltmeter 58 and the ammeter 59 are not provided.

[0066] Therefore, in order to apply the flowchart of FIG. 9 to the second embodiment, the processes of S102 and S103 may be changed as follows. In the process of S102, the CPU 94 determines whether to output a control signal to the triac 56. If a control signal is to be output, the process proceeds to S103. If no control signal is to be output, the process proceeds to S104. Further, in the process of S103, the CPU 94 adds the amount of power 9.52 [W·S] supplied to the non-printing area B of the heater 40 during the half-wave cycle of the AC voltage to the integrated power consumption IWSb, and stores the updated integrated power consumption IWSb in the memory 95.

[0067] Alternatively, in the process of S103, the number of times the control signal of the triac 56 is output is counted. When it is determined in the process of S104 that the printing job has ended, the integrated power consumption may be calculated by multiplying the count value by the amount of power 9.52 [W·S].

[0068] As described above, in this embodiment, each time a control signal of the triac 56 is output, the amount of power supplied to the heater 40 during the half-wave cycle of the power supply frequency from the AC power supply 57 is integrated to calculate the integrated power consumption of the non-printing area. Then, similar to the first embodiment, based on the integrated power consumption of the non-printing area of the heating element and the saturated temperature rise value of the non-printing area, the temperature rise value of the non-printing area of the fixing member is accurately calculated, so that the cooling time of the fixing device after passing a small-sized sheet can be shortened. And by appropriately performing the cooling of the fixing member according to the temperature of the fixing member, it is possible to prevent the occurrence of hot offset even when a large-sized sheet is passed after passing a small-sized sheet.

[0069] As described above, according to this embodiment, the rotation time of the pressure roller for cooling the fixing member can be controlled according to the temperature of the non-printing area of the fixing member of the fixing device.

Embodiment

[0070] The heaters of Examples 1 and 2 each had only one type of heating element. The heater of Example 3 has a plurality of heating elements, and a method for controlling the amount of electric power supplied to the non-paper-passing portion of the heating element by changing the usage ratio of the heating elements will be described.

[0071] [Configuration of Heater] FIG. 11(a) is a diagram for explaining the configuration of the heater 54 of this embodiment. The heater 54 has a heating element using a conductive material mainly composed of silver and palladium, a conduction path mainly composed of silver, and a contact for power supply on a heater substrate 549 made of Al2O3 material (thickness t = 1 mm, width w = 6.3 mm, length l = 280 mm). Note that the width w indicates the length in the short side direction in the figure, and the length l indicates the length in the long side direction in the figure. The heater 54 has heating elements 541 and 542 with the maximum length in the longitudinal direction, then a heating element 543 with a longer length in the longitudinal direction, and a heating element 544 with the shortest length in the longitudinal direction. The dimensions of the heating elements 541 and 542 are thickness t = 10 μm, width w = 0.7 mm, and length l = 222 mm, corresponding to the paper width of 210 mm of A4-sized paper. The dimensions of the heating element 543 are thickness t = 10 μm, width w = 0.7 mm, and length l = 188 mm, corresponding to the paper width of 182 mm of B5-sized paper. And the dimensions of the heating element 544 are thickness t = 10 μm, width w = 0.7 mm, and length l = 154 mm, corresponding to the paper width of 148.5 mm of A5-sized paper.

[0072] One end of each of the heating elements 541 and 542 (the first heating elements) is electrically connected to the contact 545 for power supply, and the other end is electrically connected to the contact 546 for power supply. One end of the heating element 543 (the second heating element) is connected to the contact 547 for power supply, and the other end is electrically connected to the contact 546 for power supply. And one end of the heating element 544 (the second heating element) is connected to the contact 547 for power supply, and the other end is electrically connected to the contact 548 for power supply.

[0073] The electric resistances of the heating elements 541 and 542 are both 21 Ω, and the combined resistance value of the heating elements 541 and 542 between the power supply contacts 545 and 546 is 10.5 Ω. Also, the resistance value of the heating element 543 is 24 Ω, and the resistance value of the heating element 544 is 28 Ω. The intervals in the short side direction in the figure of each of the heating elements 541, 542, 543, and 544 are all 0.7 mm.

[0074] [Arrangement of Heating Elements] Next, the arrangement of each of the heating elements 541, 542, 543, and 544 on the heater substrate 549 will be described. The heating elements 541 and 542, which are the first heating elements, are the heating elements with the maximum power supply amount from the AC power supply 57, and can heat the fixing device 50 to a state where paper can be passed through in a short time. The heating elements 541 and 542 can be heated in a short time, but there is a large thermal unevenness on the heater substrate 549 when the maximum voltage is applied, and there is a possibility that the heater substrate 549 may be distorted. Therefore, in the present embodiment, the two heating elements 541 and 542 are arranged in parallel so that the power is not concentrated at one location. Further, the heating elements 541 and 542 are arranged symmetrically with respect to the center in the short side direction of the heater substrate 549 to reduce the thermal unevenness of the heater substrate 549.

[0075] On the other hand, the heating element 543, which is the second heating element, and the heating element 544, which is the third heating element, are each provided as one in order to suppress the increase in the size of the heater 54. Also, since the heating elements 543 and 544 have a shorter length in the longitudinal direction compared to the heating elements 541 and 542 and have a configuration that is disadvantageous for the thermal unevenness of the heater substrate 549, the power supply amount from the AC power supply 57 is reduced to reduce the thermal unevenness of the heater substrate 549.

[0076] [Control of Power Supply Path] Next, the control of the power supply path for supplying power to each heating element will be described. FIG. 11(b) is a schematic diagram for explaining the power supply path for supplying power from the AC power supply 57 to the heater 54. In FIG. 11(b), one end of the AC power supply 57 is connected to one ends of the triacs 550 and 551, and the other end is connected to the contacts 546 for power supply of the heater 54 and the C-contact relay which is the heating element switching device 552 (hereinafter referred to as relay 552). The other end of the triac 550 is connected to the contact 545 for power supply of the heater 54. On the other hand, the other end of the triac 551 is connected to the relay 552 and the contact 548 for power supply of the heater 54. The relay 552 which is a switch has three contacts, that is, three contacts including the contact connected to the other end of the triac 551, the contact connected to the other end of the AC power supply 57, and the contact connected to the contact 547 for power supply of the heater 54. The contact connected to the contact 547 of the relay 552 is connected to the contact connected to the other end of the triac 551 or the contact connected to the other end of the AC power supply 57 by the relay control signal output from the CPU 94.

[0077] As shown in FIG. 11(b), the configuration of the power supply path of this embodiment is different from the configuration of the power supply path shown in FIG. 4(b) of the first embodiment in that the number of triacs has increased from one to two, the relay 552 has been added, and the voltmeter 58 and the ammeter 59 have been deleted. The configurations of the other image forming apparatuses are the same as those of the first embodiment, and the same reference numerals are used for the same members, so the description here is omitted.

[0078] When supplying power from the AC power supply 57 to the heating elements 541 and 542, the CPU 94 outputs a control signal to the triac 550 to turn on the triac 550, and applies an AC voltage between the contact 545 and the contact 546 of the heater 54. When supplying power from the AC power supply 57 to the heating element 543, the CPU 94 outputs a control signal to the triac 551 to turn on the triac 551, and applies an AC voltage between the contact 547 and the contact 546 of the heater 54. At this time, since the CPU 94 does not output a relay control signal to the relay 552, in the relay 552, the contact connected to the contact 547 of the heater 54 and the contact connected to the triac 551 are connected. When supplying power from the AC power supply 57 to the heating element 544, the CPU 94 outputs a relay control signal, and the relay 552 connects the contact connected to the contact 547 of the heater 54 and the contact connected to the AC power supply 57. Then, after switching the connection of the relay 552, the CPU 94 outputs a control signal to the triac 551 to turn on the triac 551, and applies an AC voltage between the contact 547 and the contact 548 of the heater 54.

[0079] As described above, the combined resistance value of the heating elements 541 and 542 is 10.5 Ω, and the resistance values of the heating elements 543 and 544 are 24 Ω and 28 Ω, respectively. For example, assuming that the maximum voltage that can be supplied by the AC power supply 57 is 120 V (volts), the maximum current value in the heating elements 541 and 542 is 11.43 A (amperes), the maximum current value in the heating element 543 is 5 A, and the maximum current value in the heating element 544 is 4.29 A. The current value that can be supplied by a household AC voltage line is generally 15 A or less. If an AC voltage is applied to a plurality of heating elements (for example, heating elements 541, 542, and heating element 543) simultaneously, the current value may exceed 15 A. Therefore, in this embodiment, when an AC voltage is applied (power is supplied) to any one of the heating elements, the AC voltage from the AC power supply 57 is not applied to the other two heating elements for control. That is, while the CPU 94 outputs a control signal to the triac 550 shown in FIG. 11(b), no control signal is output to the triac 551. As a result, the triacs 550 and 551 do not simultaneously enter the on state, so the AC voltage of the AC power supply 57 is not applied to a plurality of heating elements.

[0080] [Power Supply Control of Heater] Next, the power supply control to the heater 54 will be described. For example, when passing a B5-sized sheet of paper, the heating elements 541 and 542 and the heating element 543, whose width and longitudinal length in the B5-sized sheet are similar, are used as the heating elements to which power is supplied from the AC power supply 57. When passing an A5-sized sheet of paper, the heating elements 541 and 542 and the heating element 544, whose width and longitudinal length in the A5-sized sheet are similar, are used as the heating elements to which power is supplied from the AC power supply 57.

[0081] The CPU 94 detects the temperature difference between the target temperature of the heater 54 based on the temperature detection result of the heater 54 by the thermistor 60, and obtains the applied voltage corresponding to the detected temperature difference from the applied voltage table described in the second embodiment. Further, the CPU 94 determines the output timing of the control signals of the triacs 550 and 551 corresponding to the obtained applied voltage from the control signal table described in the second embodiment, and outputs the control signal to either one of the triacs 550 and 551 according to the output timing. The CPU 94 determines which heating element to supply power to by referring to the predetermined usage ratio of the heating elements. For example, when the usage ratios of the heating elements 541 and 542 are 30% and the usage ratio of the heating element 543 is 70%, power is supplied to the heating elements 541 and 542 for 0.3 seconds, and power is supplied to the heating element 543 for 0.7 seconds. The power supply is controlled in such a usage time ratio.

[0082] Incidentally, as the state of the fixing device 50 when passing paper, there are two states: a state where the heater 54 is not heated and is cold, and a state where the heater 54 is heated and warm. When the fixing device 50 is in a cold state, in addition to the paper being passed, there are members that need to be heated by supplying power, and it is necessary to supply a larger amount of electric power to the heater 54 to warm (heat) the entire heater 54 by the heating elements 541 and 542. On the other hand, if the fixing device 50 is in a warm state, it is not necessary to supply as high an amount of electric power as in the cold state, but the power supply amounts of the heating elements 543 and 544 are small as described above. Therefore, it is necessary to change the usage ratio of the heating elements 541 and 542 depending on whether the fixing device 50 is in a cold state or a warm state. That is, the CPU 94 increases the usage ratio of the heating elements 541 and 542 with a large power supply amount when the fixing device 50 is in a cold state, and increases the usage ratio of the heating elements 543 and 544 in order to reduce the power supply amount to the non-paper-passing part of the heater 54 when the fixing device 50 is in a warm state.

[0083] The determination of whether the fixing device 50 is in a cold state or a warmed state is made based on the detected temperature by the thermistor 60 that is in contact with the heater substrate 549. The higher the detected temperature by the thermistor 60, the warmer the fixing device 50 is. In this embodiment, the detected temperature of the thermistor 60 is divided into four temperature ranges, which are respectively defined as heating levels 1, 2, 3, and 4, indicating that the higher the heating level, the warmer the fixing device 50 is.

[0084] Table 1 is a table showing the temperature definition of the heating level of the fixing device 50 and the usage ratios of the heating elements 541, 542, 543, and 544 corresponding to each heating level. In Table 1, the fixing device heating level indicates heating levels 1 to 4, and the thermistor detected temperature indicates the range of the detected temperature of the thermistor 60 corresponding to each heating level. For example, when the temperature of the heater 54 detected by the thermistor 60 is less than 50°C, the heating level of the fixing device 50 is level 1. Similarly, when the detected temperature of the heater 54 detected by the thermistor 60 is, for example, 80°C, 120°C, or 155°C, the heating levels are level 2, level 3, and level 4, respectively. Also, the usage ratio of the heating element (unit: %) indicates the usage ratio of the heating element corresponding to the heating level. The usage ratio of the left heating element indicates the usage ratios of the heating elements 541, 542, and 543 used according to the heating level of the fixing device 50 when passing a B5-size paper. On the other hand, the usage ratio of the right heating element indicates the usage ratios of the heating elements 541, 542, and 544 used according to the heating level of the fixing device 50 when passing an A5-size paper. As shown in Table 1, the lower the heating level and the less warmed the fixing device 50 is, the higher the usage ratios of the heating elements 541 and 542 are set.

[0085]

Table 1

[0086] [Calculation of the amount of power supplied to the heater] As shown in Table 1, when passing B5-sized paper, heating elements 541, 542 and heating element 543 are used. FIG. 12 is a diagram for explaining the relationship between the B5-sized paper and the sizes of heating elements 541, 542, and heating element 543. FIG. 12(a) shows the positional relationship between heating elements 541, 542 and the B5-sized paper, and FIG. 12(b) shows the positional relationship between heating element 543 and the B5-sized paper. In FIG. 12(a), the paper width ha of the B5-sized paper, which is a small-sized paper, is 182 mm. The lengths of heating elements 541, 542 in the longitudinal direction in the figure are the same, and the length H1 is 222 mm. Also, the lengths hb1, hc1 of the non-paper-passing regions where the B5-sized paper does not pass through heating elements 541, 542 are each 20 mm (= (222 mm - 182 mm) / 2). Further, in FIG. 12(b), the length H2 of heating element 543 in the longitudinal direction in the figure is 188 mm, and the lengths hb2, hc2 of the non-paper-passing regions where the B5-sized paper does not pass through heating element 543 are each 3 mm (= (188 mm - 182 mm) / 2).

[0087] The power supply amount to the heating elements of the heater 54 is integrated based on the number of control signals output by the CPU 94 to the triacs 550, 551, in the same manner as in Example 2. For example, assuming the combined resistance value of heating elements 541, 542 is 10.5 Ω, the AC voltage of the AC power supply 57 is 100 V, and the power supply frequency is 50 Hz. Then, the power amount per half-wave (0.01 seconds) of the power supply frequency is (100 (V) × 100 (V) / 10.5 (Ω)) × 0.01 (seconds) = 9.52 [W·S]. On the other hand, assuming the resistance value of heating element 543 is 24 Ω, the AC voltage of the AC power supply 57 is 100 V, and the power supply frequency is 50 Hz, the power amount per half-wave of the power supply frequency is (100 (V) × 100 (V) / 24 (Ω)) × 0.01 (seconds) = 4.16 [W·S].

[0088] FIG. 13 is a diagram showing the relationship between the AC voltage waveforms applied to the heating elements 541 and 542 and the control signals for turning on the triacs 550 and 551 when the usage ratios of the heating elements 541, 542, and 543 are 50%:50%. In FIG. 13, eight half-cycles in the AC voltage waveform are used as the control unit. In FIG. 13, after power is supplied to the heating elements 541 and 542 for 0.08 seconds, which is the time for eight half-cycles (= 0.01 second / half-cycle × eight half-cycles), the power supply destination is switched to the heating element 543. Then, after power is supplied to the heating element 543 for 0.08 seconds, which is the time for eight half-cycles, the power supply destination is switched back to the heating elements 541 and 542 again.

[0089] The CPU 94 counts the number of control signals T1 output to the triac 550 to apply an AC voltage to the heating elements 541 and 542, and adds the amount of power 9.52 [W·S] to the integrated power amount IWS1 of the heating elements 541 and 542 each time a control signal is output. The integrated power amount IWSb1 in the non-paper-passing area when the heating elements 541 and 542 are in use can be calculated by the formula IWSb1 = integrated power amount IWS1 × (length hb1 of the non-paper-passing part of the heating elements 541 and 542 / length H1 of the heating elements of the heating elements 541 and 542). Similarly, the CPU 94 counts the number of control signals T2 output to the triac 551 to apply an AC voltage to the heating element 543, and adds the amount of power 4.16 [W·S] to the integrated power amount IWS2 of the heating element 543 each time a control signal is output. The integrated power amount IWSb2 in the non-paper-passing area when the heating element 543 is in use can be calculated by the formula IWSb2 = integrated power amount IWS2 × (length hb2 of the non-paper-passing part of the heating element 543 / length H2 of the heating element of the heating element 543). Then, the CPU 94 adds up the calculated integrated power amount IWSb1 of the non-paper-passing part of the heating elements 541 and 542 and the integrated power amount IWSb2 of the non-paper-passing part of the heating element 543 to calculate the integrated power amount IWSb of the non-paper-passing part in the heater 54.

[0090] [Relationship between the integrated power amount in the non-paper-passing part of the heater and the temperature rise value of the non-paper-passing part of the fixing film] FIG. 14(a) is a graph showing the time change of the integrated power consumption IWSb in the non-paper-passing area of the heater 54 when the heating level of the fixing device 50 is 1 (Lv1) (the usage ratio of the heating elements 541 and 542 to the heating element 543 is 50%:50%). In FIG. 14(a), the vertical axis represents the integrated power consumption IWSb (unit: W·S) in the non-paper-passing area of the heater 54, and the horizontal axis represents time (unit: sec (seconds)). Since the lengths of the heating elements are different, the power consumption in the non-paper-passing area of the heater 40 when the heating elements 541 and 542 are used and when the heating element 543 is used is different. Also, as described above, since the heating elements 541 and 542 and the heating element 543 are used alternately, as shown in FIG. 14(a), the integrated power consumption IWSb in the non-paper-passing area changes in a stepwise manner. As described in Examples 1 and 2, the CPU 94 calculates the slope α based on the time change of the integrated power consumption. The slope α of the graph shown in FIG. 14(a) was 14.9. Using the relational expression 2 in FIG. 7(b) described in Example 1, Y = 7.4X + 156, when the slope α is 14.9, the saturation temperature rise value is calculated, and the saturation temperature rise value is calculated to be 266 °C (≈7.4 °C × 14.9 + 156 °C).

[0091] Next, in the relational expression 1 (Y = 0.23X + 150) in FIG. 7(a) of Example 1, when the temperature rise value in the non-paper-passing area is higher than the saturation temperature rise value, the temperature rise value in the non-paper-passing area of the relational expression 1 is replaced with the saturation temperature rise value calculated by the relational expression 2. FIG. 14(b) is a graph showing a relational expression 3 indicating the relationship between the integrated power consumption (unit: W·S) of the non-paper-passing part of the heater 54 and the temperature rise value (unit: °C) of the non-paper-passing part of the fixing film 51 after replacing the saturation temperature rise value. The CPU 94 calculates the temperature rise value of the non-paper-passing part of the fixing film 51 after printing based on the relational expression 3 and the integrated power consumption in the non-paper-passing area of the heater 54 after printing. Then, the CPU 94 determines the cooling time of the fixing device 50 from the calculated temperature rise value in the non-paper-passing part of the fixing film 51 and executes a cooling operation on the fixing device 50 in the same manner as in Examples 1 and 2. The above description was for the case of passing a B5-sized sheet, but in the case of passing an A5-sized sheet using the heating elements 541, 542, and 544, the same procedure may be used. Note that also in this embodiment, in the flowchart shown in FIG. 9 of Example 1, it is necessary to change the process of calculating the integrated power consumption of the non-paper-passing part of the heating element, but it is possible to apply the flowchart of FIG. 9 to Example 3.

[0092] As described above, in this embodiment, even when the heater 54 has a plurality of heating elements with different lengths, the power consumption of the non-paper-passing part of the entire heater 54 is calculated based on the power consumption of the non-paper-passing part of each heating element. By calculating the power consumption of the non-paper-passing part of the entire heater 54, the temperature rise value of the non-paper-passing part of the fixing member can be accurately calculated based on the integrated power consumption of the non-paper-passing part of the heating element and the saturation temperature rise value of the non-paper-passing part, in the same manner as in Examples 1 and 2. Thereby, the cooling time of the fixing device after passing a small-sized sheet can be shortened. And by appropriately performing the cooling of the fixing member according to the temperature of the fixing member, the occurrence of hot offset can be prevented even when passing a large-sized sheet after passing a small-sized sheet.

[0093] As described above, according to this embodiment, the rotation time of the pressure roller for cooling the fixing member can be controlled according to the temperature of the non-paper-passing portion of the fixing member of the fixing device.

Embodiment

[0094] In the above-described Embodiments 1 to 3, the temperature rise value of the non-paper-passing portion area was calculated based on the amount of electric power supplied to the non-paper-passing portion of the heating element of the heater, and the cooling time of the fixing device was determined based on the calculated temperature rise value. In Embodiment 4, a method for calculating the saturation temperature rise value of the heating element of the heater in a simple manner and determining the cooling time of the fixing device using the calculated saturation temperature rise value as the temperature rise value of the non-paper-passing portion area will be described. Note that the configurations of the image forming apparatus, fixing device, and heater in this embodiment are the same as those in Embodiment 3, and the same reference numerals are used for the same devices and members, so the description here is omitted.

[0095] [Relationship between usage ratio of heating element and saturation temperature rise value when passing B5 paper] A paper passing test was conducted to check the relationship between the usage ratios of the heating elements 541, 542, 543 and the saturation temperature rise value in the non-paper-passing portion area of the fixing film 51 when using B5-sized paper. The usage ratios of the heating elements 541, 542, 543 were set to four types according to the heating levels 1 to 4 of the fixing device 50, similar to Table 1 described above. In the paper passing test, B5-sized paper with a basis weight of 128 g / m 2 was used, temperature control was performed so that the detected temperature of the thermistor 60 placed in contact with the heater 54 was maintained at 200°C, the paper conveyance speed was 200 mm / sec, and the feeding interval between each paper was 0.2 seconds.

[0096] Table 2 is a table summarizing the results of the paper passing test for B5-sized paper. Table 2 consists of the heating level (1 - 4) of the fixing device 50, the usage ratios of the heating elements 541, 542, and 543 corresponding to the heating level when passing B5 paper (unit: %), and the saturation temperature rise values (unit: °C) according to the heating level of the non-paper-passing area of the fixing film 51. As shown in Table 2, the usage ratios of the heating elements 541, 542, and 543 at heating level 1 are 50%:50%, and the saturation temperature rise value at this time was 227 °C. Similarly, the usage ratios of the heating elements 541, 542, and 543 at heating level 2 are 30%:70%, and the saturation temperature rise value at this time was 211 °C. Also, the usage ratios of the heating elements 541, 542, and 543 at heating level 3 are 20%:80%, and the saturation temperature rise value at this time was 203 °C. And the usage ratios of the heating elements 541, 542, and 543 at heating level 4 are 10%:90%, and the saturation temperature rise value at this time was 195 °C.

[0097]

Table 2

[0098] Figure 15(a) is a graph plotting the usage rate of the heating element 543 shown in Table 2 and the corresponding saturation temperature rise value. The vertical axis represents the saturation temperature rise value of the fixing film 51 (unit: °C), and the horizontal axis represents the usage rate of the heating element 543 (unit: %). As shown in Figure 15(a), it can be seen that there is a high correlation between the usage rate of the heating element 543 and the saturation temperature rise value. If the straight line connecting the points plotted in Figure 15(a) is defined as relational expression 4 when passing B5-sized paper, relational expression 4 is represented as Y = -0.8X + 267, where X is the usage rate of the heating element 543 and Y is the saturation temperature rise value.

[0099] [Relationship between the usage ratio of the heating element and the saturation temperature rise value when passing A5 paper] A paper feed test was also conducted for A5-sized paper to confirm the relationship between the usage ratios of heating elements 541, 542, 544 and the saturation temperature rise value in the non-paper-passing area of the fixing film 51. The usage ratios of heating elements 541, 542, 544 were set to four types according to the heating levels 1 to 4 of the fixing device 50, similar to Table 1 described above. In the paper feed test, paper with a basis weight of 128 g / m 2 of A5 size was used, temperature control was performed so that the detected temperature of the thermistor 60 placed in contact with the heater 54 was maintained at 200°C, the paper conveyance speed was 200 mm / sec, and the paper feed interval for each sheet was 0.2 seconds.

[0100] Table 3 is a table summarizing the results of the paper feed test for A5-sized paper. Table 3 consists of the heating levels (1 to 4) of the fixing device 50, the usage ratios (unit: %) of heating elements 541, 542, 544 corresponding to the heating levels when passing A5 paper, and the saturation temperature rise values (unit: °C) according to the heating levels in the non-paper-passing area of the fixing film 51. As shown in Table 3, the usage ratios of heating elements 541, 542, 544 at heating level 1 were 50%:50%, and the saturation temperature rise value at this time was 220°C. Similarly, the usage ratios of heating elements 541, 542, 544 at heating level 2 were 30%:70%, and the saturation temperature rise value at this time was 204°C. Also, the usage ratios of heating elements 541, 542, 544 at heating level 3 were 20%:80%, and the saturation temperature rise value at this time was 196°C. And the usage ratios of heating elements 541, 542, 544 at heating level 4 were 10%:90%, and the saturation temperature rise value at this time was 185°C.

[0101]

Table 3

[0102] FIG. 15(b) is a graph plotting the saturation temperature rise values corresponding to the usage rates of the heating elements 544 shown in Table 3. The vertical axis represents the saturation temperature rise value (unit: ° C) of the fixing film 51, and the horizontal axis represents the usage rate (unit: %) of the heating elements 544. As shown in FIG. 15(b), it can be seen that there is a high correlation between the usage rate of the heating elements 544 and the saturation temperature rise value. If the straight line connecting the points plotted in FIG. 15(b) is defined as relational expression 4 (the third calculation formula) when passing through A5 size paper, relational expression 4 is represented by Y = -0.86X + 263.6, where X is the usage rate of the heating elements 544 and Y is the saturation temperature rise value.

[0103] For papers of other sizes, a paper passing test is also performed in the same manner, and relational expression 4 corresponding to each paper is calculated. Then, the calculated relational expressions are stored in the memory 95, including relational expression 4 for B5 size and A5 size. In this embodiment, based on relational expression 4 stored in the memory 95 in advance and the usage ratios of the heating elements 543 and 544 according to the heating level, the saturation temperature rise value in the non-paper passing portion of the fixing film 51 is calculated. Then, the calculated saturation temperature rise value is used as the temperature rise value of the non-paper passing portion of the fixing film 51, and the cooling time corresponding to the temperature rise value of the non-paper passing portion is determined.

[0104] [Control Sequence for Cooling of Fixing Device] FIG. 16 is a flowchart showing a cooling control sequence for reducing the temperature rise value of the non-paper-passing portion of the fixing film 51 of the fixing device 50 in this embodiment. The process shown in FIG. 16 is activated when printing is performed on the paper P and is executed by the CPU 94. The CPU 94 controls the power supply to the heating elements 541, 542, 543, 544 of the heater 54 based on the usage ratios shown in Tables 2 and 3 described above, thereby controlling the temperature of the fixing film 51 of the fixing device 50. Note that the temperature control of the fixing film 51 of the fixing device 50 is executed in a process different from the process shown in the flowchart of FIG. 16. Also, it is assumed that the information of Tables 2 and 3 and the relational expression 4 described above are stored in the memory 95 in advance. Further, it is assumed that a table associating the temperature rise value of the non-paper-passing portion of the fixing film 51 with the cooling time for reducing the temperature of the non-paper-passing portion of the fixing film 51 to a predetermined temperature is stored in the memory 95. Note that the print job based on the print command from the PC 110 is a print job for the paper P of the same paper size.

[0105] In S200, the CPU 94 acquires the type information (B5 size, A5 size, etc.) of the paper P from the information of the paper P included in the print command received from the video controller 91. Also, the CPU 94 determines the heating level (1 to 4) of the fixing device 50 based on the temperature of the heater 40 detected by the thermistor 60. In S201, the CPU 94 acquires the usage ratio of the heating element from Table 2 or Table 3 stored in the memory 95 based on the type information of the paper P acquired in S200 and the heating level of the fixing device 50 determined in S200. For example, when the paper used for the print job is B5 size, the CPU 94 acquires the usage ratio of the heating element 543 corresponding to the heating level of the fixing device 50 using Table 2. Similarly, when the paper used for the print job is A5 size, the CPU 94 acquires the usage ratio of the heating element 544 corresponding to the heating level of the fixing device 50 using Table 3.

[0106] In S202, the CPU 94 reads relational expression 4 corresponding to the heating element of the usage ratio obtained in S201 from the memory 95, and calculates the saturation temperature rise value of the fixing film 51 by substituting the usage ratio of the heating element corresponding to relational expression 4. In S203, the CPU 94 determines whether the printing job has ended. If it determines that the job has ended, the process proceeds to S204. If it determines that the job has not ended, the process returns to S203.

[0107] In S204, the CPU 94 determines the saturation temperature rise value of the fixing film 51 calculated in S202 as the temperature rise value of the non-paper-passing area of the fixing film 51. In S205, the CPU 94 obtains the cooling time corresponding to the temperature rise value of the non-paper-passing area of the fixing film 51 determined in S204 from the table associating the temperature rise value of the non-paper-passing area of the fixing film 51 stored in the memory 95 with the cooling time of the fixing film 51.

[0108] In S206, the CPU 94 stops the pressure roller 53 of the fixing device 50, resets the timer, and starts it. In S207, the CPU 94 refers to the timer and determines whether the timer value has elapsed the cooling time. If the CPU 94 determines that the timer value has not elapsed the cooling time, the process returns to S207. If the CPU 94 determines that the timer value has elapsed the cooling time, the process ends. Here, for the cooling time, a process of stopping the rotation of the pressure roller 53 is performed to lower the temperature of the non-paper-passing area of the fixing film 51. For example, for the cooling time, the pressure roller 53 may be rotated to lower the temperature of the non-paper-passing area of the fixing film 51, and after the cooling time has elapsed, a process of stopping the rotation of the pressure roller 53 may be performed.

[0109] As described above, in this embodiment, the saturation temperature rise value of the fixing film 51 is calculated based on the usage ratio of the heating element determined according to the size of the paper used and the heating level of the fixing device, and the calculated saturation temperature rise value is used as the temperature rise value of the non-paper-passing portion. Since Embodiment 4 determines the temperature rise value of the non-paper-passing portion of the fixing film 51 by a simple method, compared with the above-described Embodiments 1 to 3, the accuracy of the temperature rise value of the non-paper-passing portion will decrease, and the cooling time will become longer. However, since the cooling time corresponding to the heating level of the fixing device 50 is ensured, the occurrence of hot offset can be prevented.

[0110] As described above, according to this embodiment, the rotation time of the pressure roller for cooling the fixing member can be controlled according to the temperature of the non-paper-passing portion of the fixing member of the fixing device.

Explanation of Signs

[0111] 40 Heater 42a, 42b Heating element 50 Fixing device 51 Fixing film 53 Pressure roller 94 CPU

Claims

1. A cylindrical film, A pressure roller that contacts the outer peripheral surface of the film and forms a nip portion, A heater having a heating element, And a fixing device that fixes the toner image on the recording material to the recording material by the heat of the heater at the nip portion, When the area of the nip portion through which the recording material conveyed to the nip portion passes is defined as a first area, and the area of the nip portion through which the recording material conveyed to the nip portion does not pass is defined as a second area, control means for calculating the integrated power amount supplied to the heating element corresponding to the second area and the saturation temperature rise value of the second area; Comprising, The control means controls the rotation time of the pressure roller to cool the nip portion after the recording material has passed through the nip portion based on the calculated integrated power amount and the saturation temperature rise value. An image forming apparatus characterized by that.

2. The image forming apparatus according to claim 1, wherein the heater is supplied with power from an AC power source.

3. A switch for connecting or disconnecting the power supply path from the AC power source to the heater is provided, The control means outputs a control signal for controlling the switch every half cycle of the power supply frequency of the AC power source. The image forming apparatus according to claim 2, characterized by that.

4. Voltage detection means for detecting the voltage applied to the heater from the AC power source, Current detection means for detecting the current flowing from the AC power source to the heater, Comprising, The control means is based on the voltage value detected by the voltage detection means, the current value detected by the current detection means, the length in the direction orthogonal to the conveyance direction of the recording material passing through the nip portion, and the length in the longitudinal direction of the heater. The image forming apparatus according to claim 3, characterized in that the integrated power amount supplied to the second region of the heating element is calculated.

5. The image forming apparatus according to claim 4, wherein the power amount supplied to the heating element is calculated based on the voltage value and the current value.

6. The control means is based on the power amount supplied to the heating element during a half cycle of the power supply frequency, the number of the control signals output to connect the power supply path to the heater, the length in the direction orthogonal to the conveyance direction of the recording material passing through the nip portion, and the length in the longitudinal direction of the heater. The image forming apparatus according to claim 3, characterized in that the integrated power amount supplied to the second region of the heating element is calculated.

7. The image forming apparatus according to claim 6, wherein the amount of electric power supplied to the heating element is calculated based on the voltage value of the AC power supply and the resistance value of the heating element.

8. The heater has a plurality of heating elements with different lengths in the longitudinal direction, and includes a plurality of switches for connecting or disconnecting a power supply path from the AC power supply to the plurality of heating elements, wherein the control means outputs a control signal for controlling the plurality of switches according to the length in a direction orthogonal to the conveyance direction of the recording material passing through the nip portion every half cycle of the power supply frequency of the AC power supply, and supplies power to the plurality of heating elements. The image forming apparatus according to claim 2.

9. The image forming apparatus according to claim 8, wherein the control means controls the plurality of switches so as not to supply power to two or more of the heating elements in a half cycle of the power supply frequency.

10. having temperature detection means for detecting the temperature of the heater when printing of the recording material is started, wherein the control means determines, based on the temperature of the heater detected by the temperature detection means, among the plurality of heating elements, a first heating element, and a second heating element having a length in the longitudinal direction shorter than that of the first heating element and close to the length in a direction orthogonal to the conveyance direction of the recording material passing through the nip portion, a ratio of supplying power. The image forming apparatus according to claim 9.

11. The image forming apparatus according to claim 10, wherein the ratio of supplying power to the first heating element increases as the temperature of the heater detected by the temperature detection means decreases, and the ratio of supplying power to the second heating element increases as the temperature of the heater detected by the temperature detection means increases.

12. The control means calculates the integrated power amount supplied to the second regions of the first heating element and the second heating element based on the power amount supplied to the first heating element during a half cycle of the power supply frequency, the number of the control signals output to connect the power supply path to the first heating element, the power amount supplied to the second heating element during a half cycle of the power supply frequency, the number of the control signals output to connect the power supply path to the second heating element, the length in a direction orthogonal to the conveyance direction of the recording material passing through the nip portion, the length in the longitudinal direction of the first heating element, and the length in the longitudinal direction of the second heating element. The image forming apparatus according to claim 11, characterized in that.

13. The power amount supplied to the first heating element is calculated based on the voltage value of the AC power supply and the resistance value of the first heating element. The image forming apparatus according to claim 12, characterized in that the power amount supplied to the second heating element is calculated based on the voltage value of the AC power supply and the resistance value of the second heating element.

14. It includes temperature calculation means for calculating the temperature of the second region of the film. The temperature calculation means has a first calculation formula for calculating the temperature of the second region of the film from the integrated power amount calculated by the control means. The image forming apparatus according to any one of claims 5, 7, and 13, characterized in that.

15. The temperature calculation means has a second calculation formula for calculating the saturation temperature of the second region of the film from the rate of change per unit time of the integrated power amount calculated by the control means. When the temperature of the second region of the film calculated by the first calculation formula is higher than the saturation temperature calculated by the second calculation formula, the saturation temperature is set as the temperature of the second region of the film. The image forming apparatus according to claim 14, characterized in that.

16. It includes temperature calculation means for calculating the temperature of the second region of the film. The temperature calculation means has a third calculation formula for calculating the saturation temperature of the second region of the film from the ratio of supplying power to the first heating element and the second heating element. The image forming apparatus according to claim 13, characterized in that the saturation temperature calculated by the third calculation formula is set as the temperature of the second region of the film.

17. The control means has information associating the temperature of the second region of the film with the cooling time of the film for reducing the temperature of the second region of the film to a predetermined temperature, and determines the cooling time of the film based on the information and the temperature of the second region of the film calculated by the temperature calculating means. The image forming apparatus according to claim 15 or claim 16, characterized in that.

18. The control means determines a cooling time for cooling the nip portion. The image forming apparatus according to any one of claims 1 to 16, characterized in that.

19. The heater is disposed in the internal space of the film, the film is sandwiched between the heater and the pressure roller, and the image on the recording material is heated through the film at the nip portion. The image forming apparatus according to any one of claims 1 to 18.

Images