Image forming device

Abstract

To control the conveyance interval between recording materials to prevent an increase in temperature of a non-paper feed area of a fixing nip part according to the conveyance speed of the recording materials or the type of the recording materials.SOLUTION: An image forming apparatus comprises: an image forming unit 101 that performs image formation on a recording material P; a fixing film 24 that forms a nip part with a pressure roller 30; a ceramic heater 21; a sub thermistor 22b that is provided on an end side of the ceramic heater 21; and a control unit 60 that controls a conveyance interval from when a rear end of a preceding sheet passes through the nip part until when a leading end of a subsequent sheet reaches the nip part. When the conveyance speed of the preceding sheet and the subsequent sheet is a full speed and a temperature detected by the sub thermistor 22b is a first temperature, the control unit 60 controls the conveyance interval to be a first interval (S4-S19), and when the conveyance speed of the preceding sheet and the subsequent sheet is a half speed slower than the full speed and the temperature detected by the sub thermistor 22b is the first temperature, controls the conveyance interval to be a second interval smaller than the first interval (S20-S31).SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a recording material. [Background technology]

[0002] In electrophotographic image forming apparatuses, a toner image transferred onto a recording material is heated and pressurized by a fixing device to be fixed to the recording material. A widely known fixing method for fixing devices is a film fixing method using a heat-generating member and a cylindrical film. In the fixing device, if a recording material passes through a fixing nip portion of the fixing device continuously, the non-paper-passing area of ​​the fixing nip, where the recording material does not pass, experiences excessive temperature rise. To prevent this temperature rise in the non-paper-passing area, the following configuration is known for image forming apparatuses. Specifically, the image forming apparatus is provided with a temperature detection element that detects the temperature of a heater corresponding to an area on the edge of the fixing nip portion that is inside the maximum paper width of the conveyable recording material and outside the minimum paper width of the conveyable recording material. The temperature detection element then widens (lengthens) the interval between conveyance of the recording material based on the heater temperature, thereby suppressing the temperature rise in the non-paper-passing area of ​​the fixing nip (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-169413 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, in an image forming apparatus, in order to suppress a temperature rise in the non-paper passing portion in the fixing nip, the interval between conveyance of the recording material is controlled in accordance with the heater temperature detected by the temperature detection element. However, when the interval between conveyance of the recording material is controlled, the interval between conveyance of the recording material is not adapted to the conveyance speed of the recording material or the type of recording material, which causes a problem of affecting throughput (the number of sheets that can be printed per hour).

[0005] The present invention was made under these circumstances, and aims to control the conveying interval of the recording material in order to suppress temperature rise in the non-paper passing areas of the fixing nip depending on the conveying speed of the recording material or the type of recording material. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] (1) An image forming device includes: an image forming unit that forms an image on a recording material; a first rotating body; a second rotating body that is in contact with the outer circumferential surface of the first rotating body and forms a nip portion between the first rotating body and the second rotating body; a heater that is disposed in the internal space of the second rotating body; a first temperature detecting means that is provided at a position corresponding to the center in the longitudinal direction of the heater; a second temperature detecting means that is provided at a position closer to the end than the first temperature detecting means in the longitudinal direction of the heater; and a control means that controls a conveyance interval that is the interval from when the rear end of a preceding sheet passes through the nip portion until the front end of a succeeding sheet reaches the nip portion, and the control means controls the conveyance interval of the preceding sheet and the succeeding sheet. Basis weight is the first basis weight and the temperature detected by the second temperature detection means is the first temperature reached In this case, the conveying interval is set to the first interval, and the conveying interval of the preceding paper and the succeeding paper is set to the second interval. a second basis weight having a basis weight greater than the first basis weight; and the temperature detected by the second temperature detection means is the first temperature reached In this case, the conveying interval is set to a second interval that is narrower than the first interval. [Effects of the Invention]

[0009] According to the present invention, it is possible to control the conveyance speed of the recording material or the interval between conveyances of the recording material in order to suppress a rise in temperature in the non-paper passing portion of the fixing nip in accordance with the type of recording material. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 1 is a cross-sectional view showing a schematic configuration of a fixing device according to an embodiment of the present invention; [Figure 3] Schematic cross-sectional view showing the configuration of a heater according to an embodiment. [Figure 4] Schematic diagram showing the configuration of a heater according to an embodiment. [Figure 5] Schematic diagram showing the placement position of the thermistor in the embodiment. [Figure 6] FIG. 1 is a control block diagram illustrating a control unit that controls the power supply to the heater in the embodiment. [Figure 7] 1 is a flowchart showing a control sequence of the throughput control in the first configuration example of the embodiment. [Figure 8] 10 is a flowchart showing a control sequence of the throughput control in the second embodiment of the present invention; [Figure 9] Schematic diagram showing the arrangement position of the thermistor in Configuration Example 3 of the embodiment. [Figure 10] FIG. 10 is a diagram illustrating the transition of throughput in the configuration example 1 of the embodiment and the conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following examples, passing a recording material through the fixing nip portion of a fixing device is referred to as "paper passing." Furthermore, in the fixing nip portion, an area where the recording material does not pass is referred to as a non-paper passing area (or non-paper passing portion), and an area where the recording material passes is referred to as a paper passing area (or paper passing portion). Furthermore, the phenomenon where the temperature of the non-paper passing area of ​​the fixing nip portion becomes higher than that of the paper passing area is referred to as non-paper passing area temperature rise. [Example]

[0012] [Configuration of Image Forming Apparatus and Image Forming Operation] 1 is a cross-sectional view showing the configuration of an image forming apparatus 100 equipped with a fixing device 50. The process speed, which is the speed at which the recording material is conveyed in the image forming apparatus 100 of this embodiment, is 180 mm / s at full speed, and the throughput at full speed is 30 ppm, which enables printing of 30 sheets of A4-sized recording material per minute. In addition to the full speed as a process speed, the image forming apparatus 100 of this embodiment also has a half-speed process speed, which is approximately half the full speed, for printing on recording materials such as cardboard.

[0013] In FIG. 1, image forming unit 101 (enclosed by a dashed line in the figure) that forms toner images on recording material P has four image forming stations Pa, Pb, Pc, and Pd. Yellow, magenta, cyan, and black toner images are formed at image forming stations Pa, Pb, Pc, and Pd, respectively. Furthermore, image forming unit 101 is provided with laser scanners 3a, 3b, 3c, and 3d that form electrostatic latent images on the photosensitive drums 1 of the image forming stations Pa, Pb, Pc, and Pd, respectively. Each image forming station Pa, Pb, Pc, and Pd is equipped with photosensitive drums 1a, 1b, 1c, and 1d that serve as image carriers, charging rollers 2a, 2b, 2c, and 2d, and developing units 4a, 4b, 4c, and 4d that have developing rollers 41a, 41b, 41c, and 41d, respectively. Each of the image forming stations Pa, Pb, Pc, and Pd has the same configuration, and the suffixes a, b, c, and d added to the names of the components of each of the image forming stations Pa, Pb, Pc, and Pd indicate that the component is that of the image forming station Pa, Pb, Pb, or Pd. Hereinafter, the suffixes a, b, c, and d will be omitted except when referring to a component of a specific image forming station.

[0014] At each of the image forming stations Pa, Pb, Pc, and Pd, a charging roller 2 charges the surface of the photosensitive drum 1 to a uniform potential. The photosensitive drum 1, charged to a uniform potential, is irradiated with a laser beam from a laser scanner 3 in accordance with image data, forming an electrostatic latent image on the photosensitive drum 1 (image carrier) in accordance with the image data. The developing roller 41 of the developing unit 4 then deposits toner onto the electrostatic latent image formed on the photosensitive drum 1, forming a toner image on the photosensitive drum 1. The toner images formed on the photosensitive drum 1 at each of the image forming stations Pa, Pb, Pc, and Pd are sequentially transferred, superimposed on one another, to an intermediate transfer belt 7, which rotates in the direction of the arrow (clockwise) in the figure, by a primary transfer member 6 disposed opposite the photosensitive drum 1. Any toner remaining on the photosensitive drum 1 that has not been transferred to the intermediate transfer belt 7 is removed by a cleaning blade 5C of a cleaner 5. The toner image transferred onto the intermediate transfer belt 7 is conveyed to a secondary transfer nip portion formed by contact between the intermediate transfer belt 7 and a secondary transfer roller 8 in order to be transferred onto a recording material P.

[0015] On the other hand, recording materials P are stored in a paper feed cassette 9, which serves as a paper feed unit, and when an image forming operation starts, the recording materials P are fed one by one to a conveyance path by a feed roller 10. The recording materials P fed by the feed roller 10 are conveyed by a conveyance roller 11 to a secondary transfer nip portion, where the toner image on the intermediate transfer belt 7 is transferred onto the recording material P. Note that toner remaining on the intermediate transfer belt 7 without being transferred to the recording material P is removed by a cleaning blade 80C of an intermediate transfer belt cleaner 80.

[0016] The recording material P onto which the toner image has been transferred at the secondary transfer nip is conveyed to the fixing device 50, where it is subjected to heating and pressure treatment, and the toner image is fixed to the recording material P. Then, the recording material P that has passed through the fixing device 50 is discharged to a discharge section 13 by a discharge roller 12.

[0017] [Configuration and Operation of Fixing Device] Next, the configuration of the fixing device 50 and the fixing operation of the fixing device 50 on the recording material P will be described. FIG. 2 is a cross-sectional view showing the general configuration of the fixing device 50 of this embodiment. FIG. 3 is a schematic cross-sectional view showing the general configuration of the ceramic heater 21 of the fixing device 50. The film sliding surface side refers to the surface of the ceramic heater 21 that slides against the film 24, and the film non-sliding surface side refers to the surface of the ceramic heater 21 that does not slide against the film 24. FIG. 4 is a schematic diagram showing the configuration of the ceramic heater 21 as viewed from the film sliding surface side that slides against the fixing film 24. FIG. 5 is a schematic diagram showing the position of the thermistor as viewed from the film non-sliding surface side opposite the film sliding surface. FIG. 6 is a control block diagram explaining a control system that controls the power supply to the ceramic heater 21.

[0018] [Configuration of fixing device] First, the configuration of the fixing device 50 of this embodiment will be described. As shown in Fig. 2, the fixing device 50 of this embodiment has a heating unit 20 and a pressure roller 30, which is a first rotating body that comes into contact with a fixing film 24 belonging to the heating unit 20 to form a fixing nip portion N. Both the heating unit 20 and the pressure roller 30 are members that are long in a direction (hereinafter referred to as the longitudinal direction) perpendicular to the recording material conveyance direction (the direction of the arrow shown in Fig. 2) in which the recording material P, onto which the toner image T has been transferred, is conveyed to the fixing nip portion N.

[0019] (heating unit) The heating unit 20 includes a ceramic heater (hereinafter referred to as the heater) 21, a thermistor 22a, a sub-thermistor 22b, a cylindrical fixing film 24 serving as a second rotating body, and a fixing film guide 23. The fixing film guide 23 is made of a heat-resistant material and has a recess at the top of the cross section shown in FIG. 2, and a longitudinal groove on the pressure roller 30 side (the fixing nip N side). The fixing film 24 is cylindrically formed so that the inner circumferential length of the film is a predetermined length longer than the outer circumferential length of the fixing film guide 23, and is loosely fitted around the fixing film guide 23 without tension. The fixing film 24 has a two-layer structure in which the outer circumferential surface of an endless strip-shaped film base layer made primarily of polyimide is covered with an endless strip-shaped surface layer made primarily of PFA.

[0020] As shown in FIG. 2, the heater 21, thermistor 22a, and sub-thermistor 22b are supported in a groove in a fixing film guide 23. The heater 21 is disposed in the internal space of a cylindrical fixing film 24. The heater 21 has a thin plate-shaped substrate 21a made primarily of ceramic, such as alumina or aluminum nitride. As shown in FIG. 3, a heating resistor 21b made primarily of silver, palladium, or the like is disposed along the longitudinal direction of the substrate 21a on the surface of the substrate 21a facing the film sliding surface. A protective layer 21c made primarily of glass or a heat-resistant resin, such as fluororesin or polyimide, is formed to cover the heating resistor 21b. As shown in FIG. 4, in addition to the heating resistor 21b, a conductive portion 21d electrically connected to the heating resistor 21b and an electrode 21e connected to the conductive portion 21d are pattern-printed along the longitudinal direction of the substrate 21a on the surface of the substrate 21a facing the film sliding surface. A protective layer 21c (the area surrounded by a broken line in FIG. 4) is formed to cover the heating resistor 21b.

[0021] 3, a main thermistor 22a as a first temperature detection means and a sub-thermistor 22b as a second temperature detection means are disposed in contact with the substrate 21a on the substrate surface on the non-film sliding surface side of the substrate 21a. More specifically, as shown in FIG. 5, the main thermistor 22a is disposed near the center of the substrate 21a of the heater 21, and detects the temperature of a region of the heater 21 corresponding to a region (paper passing region) of the fixing nip N through which a recording material P of the minimum width that can be passed through the fixing nip N passes. In FIG. 5, the area surrounded by a dashed line indicates the heating resistor 21b on the film sliding surface side of the heater 21. Meanwhile, the sub-thermistor 22b is disposed in a region near the end of the substrate 21a of the heater 21, corresponding to a region (non-paper passing region) of the fixing nip N through which a recording material P of the maximum width that can be passed passes but a recording material P of the minimum width that can be passed does not pass through. When performing continuous printing on recording material P having a width smaller than the maximum paper-passable width, the control unit 60 described later uses the sub-thermistor 22b to detect the temperature of the heater 21 corresponding to the non-paper-passing area of ​​the fixing nip portion N.

[0022] (Pressure roller) As shown in Fig. 2, the pressure roller 30 has a core 30a made of a metal material such as iron, SUS, or aluminum. An elastic layer 30b, mainly made of silicone rubber, is formed on the outer peripheral surface of the shaft portion connecting both longitudinal ends of the core 30a, and a release layer 30c, mainly made of PTFE, PFA, or FEP, is formed on the outer peripheral surface of the elastic layer 30b. The shaft portions at both longitudinal ends of the core 30a are rotatably supported by the frame of the fixing device 50, and a gear driven by a motor (indicated as M in Fig. 2) is fixed to one longitudinal end of the core 30a.

[0023] [Operation of the fixing device] (heat fixing operation) Next, the heat fixing operation of the fixing device 50 will be described. In FIG. 2, a control unit 60, which is a control means, has a CPU (not shown), a ROM (not shown), and a RAM (not shown), and controls the heat fixing operation of the fixing device 50. The ROM stores control programs and data executed by the CPU to control the fixing device 50, and the RAM is used to store temporary data. The control unit 60 drives the motor M in response to a print signal, and the motor M rotates the pressure roller 30 in the direction of the arrow (counterclockwise) in FIG. 2. Following the rotation of the pressure roller 30, the fixing film 24 of the heating unit 20 rotates in the direction of the arrow (clockwise) in FIG. 2 while its inner circumferential surface (inner surface) slides against the heater 21 and the fixing film guide 23. The recording material P onto which the unfixed toner image T has been transferred is nipped and conveyed between the pressure roller 30 and the outer peripheral surface (surface) of the fixing film 24 at the fixing nip N, and the toner image T is heated by the heat of the surface of the fixing film 24 heated by the heater 21, and fixed onto the recording material P. Then, the control unit 60 stops driving the motor M after the recording material P onto which the toner image T has been fixed passes through the fixing nip N and is discharged from the fixing device 50.

[0024] 6, the control of the fixing device 50 by the control unit 60 will be described. The control unit 60 acquires the detected temperature of the main thermistor 22a, which detects the temperature of the heater 21, via an A / D conversion circuit 63. The control unit 60 controls the amount of power supplied to the heater 21 by switching the on / off state of a bidirectional thyristor (hereinafter referred to as a triac) 62 so that the acquired detected temperature of the main thermistor 22a maintains the fixing temperature (target temperature) of the fixing device 50. In detail, the control unit 60 controls the on / off state of the triac 62 to supply (apply) an AC voltage input from a commercial AC power supply 61 to the heater 21. An AC voltage from the commercial AC power supply 61 is input to the electrode 21e (FIG. 4) of the heater 21 via the triac 62, and power is supplied to the heating resistor 21b via the conductive portion 21d (FIG. 4). The heating resistor 21b generates heat when power is supplied from the commercial AC power supply 61, and the heater 21 rapidly rises in temperature to heat the fixing film 24 in the fixing nip portion N. When the recording material P passes through the fixing nip portion N and the image forming process is completed, the control portion 60 turns off the triac 62 and stops the supply of AC voltage from the commercial AC power supply 61.

[0025] (Detection of temperature rise in non-paper passing areas) As described above, the control unit 60 controls the heating and fixing operation of the recording material P in the fixing nip N of the fixing device 50 based on the temperature of the heater 21 detected by the main thermistor 22a. The control unit 60 also acquires the temperature of the heater 21 corresponding to the non-paper passing area of ​​the fixing nip N detected by the sub-thermistor 22b via the A / D conversion circuit 63, and detects the temperature of the heater 21 corresponding to the non-paper passing area of ​​the fixing nip N. As shown in FIG. 5, when printing is continuously performed on recording materials P with the minimum allowable width, the temperature of the heater 21 corresponding to the paper passing area of ​​the fixing nip N through which the recording material P passes decreases as the recording material P passes. On the other hand, the temperature of the heater 21 corresponding to the non-paper passing area of ​​the fixing nip N where the sub-thermistor 22b is located and through which the recording material P does not pass rises to a high temperature. In this way, the control unit 60 acquires the temperature detected by the sub-thermistor 22b arranged on the longitudinal end side of the heater 21, which corresponds to the non-paper passing region of the fixing nip N where small-sized recording materials P do not pass. This makes it possible to detect the temperature of the heater 21 corresponding to the non-paper passing region of the fixing nip N.

[0026] (Process speed setting) In this embodiment, the process speed of the image forming apparatus 100 is set according to the basis weight of the recording material P to be printed. The basis weight of the recording material P is determined by the user specifying the recording material P to be used for printing at the time of printing. Paper types of the recording material P include plain paper as well as thick paper, and recording material P with a large basis weight, such as thick paper, requires long periods of heating and pressurization in the fixing nip N of the fixing device 50 to achieve sufficient fixation when passed through the fixing device 50. Therefore, in this embodiment, the process speed can be switched between full speed (first conveying speed) and half speed (second conveying speed), and full speed is set when plain paper is specified, and half speed is set when thick paper is specified.

[0027] [Control of recording material transport interval] In this embodiment, the control unit 60 controls the conveyance interval of the recording material P fed from the paper feed cassette 9 in accordance with the temperature detected by the sub-thermistor 22b, which detects the temperature of the heater 21, corresponding to the non-paper passing region of the fixing nip N. The conveyance interval of the recording material P is also the interval from when the trailing edge of the preceding recording material P (preceding sheet) passes through the fixing nip N until the leading edge of the succeeding recording material P (subsequent sheet) reaches the fixing nip N. More specifically, if the temperature detected by the sub-thermistor 22b is lower than a predetermined temperature, the control unit 60 feeds the recording material P from the paper feed cassette 9 at a predetermined conveyance interval. If the temperature detected by the sub-thermistor 22b is higher than the predetermined temperature, the control unit 60 feeds the recording material P from the paper feed cassette 9 at a conveyance interval obtained by adding a waiting time corresponding to the detected temperature to the predetermined conveyance interval. The standby time to be added increases (increases) as the detected temperature increases, and decreases (decreases) as the detected temperature decreases. Then, when the temperature detected by the sub-thermistor 22b again drops below the predetermined temperature, the control unit 60 feeds the recording material P from the paper feed cassette 9 at a predetermined conveying interval. This makes it possible to mitigate the temperature rise in the non-paper passing portions of the fixing nip N. Furthermore, although the throughput decreases when the conveying interval of the recording material P is made longer than the predetermined conveying interval, after the temperature rise in the non-paper passing portions of the fixing nip N has been mitigated, the control unit 60 returns the conveying interval of the recording material P to the predetermined conveying interval. This makes it possible to prevent a decrease in productivity of the recording material.

[0028] [Configuration example 1] In configuration example 1, when small-sized plain paper is passed as the recording material P, the process speed is set to full speed, which is the maximum value. On the other hand, when small-sized thick paper is passed as the recording material P, more heat is required to ensure fixability when passing through the fixing nip N. Therefore, the set temperature (target temperature) of the heater 21 is lowered and the process speed is set to half speed. Table 1 shown below shows the relationship between the temperature (unit: °C) detected by the sub-thermistor 22b (referred to as sub-thermistor temperature in the table, and the same applies to the following tables) and the waiting time (unit: seconds) between recording materials P when the process speed is full speed. Table 2 shows the relationship between the temperature (unit: °C) detected by the sub-thermistor 22b and the waiting time (unit: seconds) between recording materials P when the process speed is half speed. Here, the paper passage waiting time between recording materials P refers to the waiting time added to the predetermined transport interval between the preceding recording material P (preceding sheet) fed from the paper feed cassette 9 and the recording material P (subsequent sheet) fed thereafter. For example, in Table 1 for a full process speed, when the detected temperature of the sub-thermistor 22b is 190°C or lower, the paper passage waiting time is 0 seconds, and the transport interval between the preceding and subsequent sheets remains the predetermined transport interval. On the other hand, when the detected temperature of the sub-thermistor 22b is 240°C or higher, the paper passage waiting time is 4 seconds, and the subsequent sheet is fed from the paper feed cassette 9 after (predetermined transport interval + 4 seconds) has elapsed since the preceding sheet was fed. Also, in Table 2 for a half process speed, when the detected temperature of the sub-thermistor 22b is 210°C or lower, the paper passage waiting time is 0 seconds, and the transport interval between the preceding and subsequent sheets remains the predetermined transport interval. On the other hand, when the detected temperature of sub-thermistor 22b is 240°C or higher, the paper passage standby time is 4 seconds, and the subsequent paper is fed from paper feed cassette 9 after (predetermined conveying interval + 4 seconds) has elapsed since the preceding paper was fed. As will be described later, due to the configuration of image forming apparatus 100, it is difficult to stop image formation or the conveying of recording material P at a timing after an electrostatic latent image has started to be formed on photosensitive drum 1. Therefore, the feeding interval of recording material P fed from paper feed cassette 9 is controlled by adding the paper passage standby time to the predetermined feeding interval of recording material P.Therefore, the longer (greater) the waiting time between sheets of recording material P, the lower the throughput, but the more the temperature rise in the non-sheet passing portion of the fixing nip N is alleviated.

[0029] [Table 1]

[0030] [Table 2]

[0031] Whether the process speed is full or half speed, if the temperature detected by the sub-thermistor 22b (sub-thermistor temperature) exceeds a predetermined temperature, it is preferable to lengthen the paper-passage waiting time shown in Tables 1 and 2 by adding it to the predetermined conveyance interval between recording materials P. This is because the higher the temperature detected by the sub-thermistor 22b, the higher the temperature in the non-paper-passage area of ​​the fixing nip N, and a longer waiting time is required to alleviate the temperature rise. Furthermore, it is preferable that the paper-passage waiting time shown in Table 2 at half speed is equal to or shorter than the paper-passage waiting time at the same sub-thermistor temperature at full speed shown in Table 1. Furthermore, it is preferable that the sub-thermistor temperature required for the paper-passage waiting time shown in Table 2 is higher than that shown in Table 1. This is related to the slow process speed and the low fixing temperature setting of the heater 21. A slow process speed provides more time for the heat stored in the non-paper-passage area of ​​the heating resistor 21b of the heater 21 to diffuse in the longitudinal direction of the heater 21. Furthermore, setting a low fixing temperature when the process speed is half speed means that the power consumed per unit time by the fixing device 50, i.e., the heat generated per unit time by the fixing device 50, is less than when the process speed is full speed. As a result, when the process speed is half speed, the temperature rise of the heater 21 corresponding to the non-paper passing area of ​​the fixing nip N while printing one sheet of recording material P is smaller than when the process speed is full speed. Therefore, the temperature rise in the non-paper passing area can be mitigated with a short paper passing wait time relative to the temperature detected by the sub-thermistor 22b.

[0032] In Configuration Example 1, as shown in Tables 1 and 2, the paper feed standby time is set to its maximum when the detected temperature of sub-thermistor 22b is 240°C to prevent image defects such as uneven fixing, uneven gloss, and high-temperature offset due to temperature increases in non-paper-passing areas. The fact that the paper feed standby time is maximized when the detected temperature of sub-thermistor 22b is 240°C is the same for both full speed (Table 1) and half speed (Table 2), but it does not necessarily have to be the same. Furthermore, to further increase productivity while suppressing temperature increases in non-paper-passing areas, it is preferable to set multiple sub-thermistor temperature thresholds that determine the paper feed standby time and change the relationship between the sub-thermistor temperature and the paper feed standby time depending on the process speed. In this configuration example, the sub-thermistor temperature thresholds that determine the paper feed standby time are set in 10°C increments, but they may be set more precisely. Furthermore, if it is possible to set different process speeds, such as 1 / 3 speed or 1 / 4 speed in addition to full speed and half speed, it is desirable to separately define the relationship between the sub-thermistor temperature and the paper feed waiting time according to the set process speed.

[0033] Table 3 shows the relationship between the paper feed wait time (unit: seconds) shown in Tables 1 and 2 and the throughput (unit: ppm) when printing on A4-sized recording material P. Table 3 shows the throughput when printing on A4-sized recording material P (A4 paper) at full speed and half speed process speeds. For example, when the paper feed wait time is 0 seconds, the throughput is 30 ppm when the process speed is full speed and 15 ppm when the process speed is half speed. However, as the paper feed wait time increases, the throughput decreases. When the paper feed wait time is 4 seconds (for example, when the sub-thermistor temperature in Tables 1 and 2 is 240°C or higher), the throughput is 10 ppm when the process speed is full speed and 7 ppm when the process speed is half speed.

[0034] [Table 3]

[0035] [Control sequence for recording material feeding control] Next, the recording material feed control of this configuration example will be described. Fig. 7 is a flowchart showing the control sequence for recording material feed control of this configuration example. The process of Fig. 7 is started when a print signal for recording material P is received, and is executed by control unit 60. Note that here, the size of recording material P is assumed to be small (for example, a recording material with a paper width of the minimum width that can be passed as shown in Fig. 5). Furthermore, the waiting time WT, which is the paper passing waiting time described above, is set based on the paper passing waiting time corresponding to the sub-thermistor temperature in Tables 1 and 2 described above.

[0036] In step (hereinafter referred to as S) 1, the control unit 60 determines whether printing is to be performed on multiple sheets of recording material P. If the control unit 60 determines that printing is to be performed on multiple sheets of recording material P, the control unit 60 proceeds to S3, and if the control unit 60 determines that printing is to be performed on one sheet of recording material P, the control unit 60 proceeds to S2. In S2, the control unit 60 starts printing (printing) one sheet of recording material P, and ends the process when printing is completed.

[0037] In S3, the control unit 60 determines whether the set process speed is full speed. If the control unit 60 determines that the set process speed is full speed, the process proceeds to S4, and if the control unit 60 determines that the set process speed is not full speed (the process speed is half speed), the process proceeds to S20.

[0038] In S4, the control unit 60 starts printing on the recording material P at full process speed. In S5, the control unit 60 acquires the detected temperature (sub-thermistor temperature) of the heater 21 corresponding to the non-paper passing region of the fixing nip N, detected by the sub-thermistor 22b, via the A / D conversion circuit 63, and determines whether the sub-thermistor temperature is 200°C or higher. If the control unit 60 determines that the sub-thermistor temperature is 200°C or higher, the process proceeds to S7, and if the control unit 60 determines that the sub-thermistor temperature is less than 200°C, the process proceeds to S6. In S6, the control unit 60 sets the waiting time WT to 0 seconds, and the process proceeds to S16.

[0039] In S7, the control unit 60 determines whether the acquired sub-thermistor temperature is equal to or higher than 210°C. If the control unit 60 determines that the sub-thermistor temperature is equal to or higher than 210°C, the process proceeds to S9, and if the control unit 60 determines that the sub-thermistor temperature is lower than 210°C, the process proceeds to S8. In S8, the control unit 60 sets the waiting time WT to 1 second, and the process proceeds to S16.

[0040] In S9, the control unit 60 determines whether the acquired sub-thermistor temperature is equal to or higher than 220° C. If the control unit 60 determines that the sub-thermistor temperature is equal to or higher than 220° C., the process proceeds to S11, and if the control unit 60 determines that the sub-thermistor temperature is lower than 220° C., the process proceeds to S10. In S10, the control unit 60 sets the waiting time WT to 1.5 seconds, and the process proceeds to S16.

[0041] In S11, the control unit 60 determines whether the acquired sub-thermistor temperature is equal to or higher than 230° C. If the control unit 60 determines that the sub-thermistor temperature is equal to or higher than 230° C., the process proceeds to S13, and if the control unit 60 determines that the sub-thermistor temperature is lower than 230° C., the process proceeds to S12. In S12, the control unit 60 sets the waiting time WT to 2 seconds, and the process proceeds to S16.

[0042] In S13, the control unit 60 determines whether the acquired sub-thermistor temperature is 240°C or higher (a predetermined temperature or higher). If the control unit 60 determines that the sub-thermistor temperature is 240°C or higher, the process proceeds to S15, and if the control unit 60 determines that the sub-thermistor temperature is less than 240°C, the process proceeds to S14. In S14, the control unit 60 sets the waiting time WT to 2.5 seconds and proceeds to S16. In S15, the control unit 60 sets the waiting time WT to 4 seconds and proceeds to S16.

[0043] In S16, the control unit 60 determines whether an image to be printed on the next recording material P (next sheet) is being formed on the photosensitive drum 1. If the control unit 60 determines that an image to be printed on the next sheet is being formed on the photosensitive drum 1, the process proceeds to S18. If the control unit 60 determines that an image to be printed on the next sheet is not being formed on the photosensitive drum 1, the process proceeds to S17. In S17, if an image has not yet been formed on the photosensitive drum 1, the control unit 60 can stop the transport of the next sheet and wait, so it sets a waiting time WT for the paper passage of the next recording material P (next sheet), and the process proceeds to S19. In S18, if an image of the next sheet has already been formed on the photosensitive drum 1, the control unit 60 cannot stop the transport of the next sheet, so it sets a waiting time WT for the paper passage of the recording material P (next sheet) after the next sheet, and the process proceeds to S19. In S19, the control unit 60 determines whether printing on all recording materials P has been completed. If the control unit 60 determines that printing on all recording materials P has been completed, it ends the process. If it determines that printing on recording materials P has not been completed, it returns the process to S4 and prints the next recording material P. Note that, when the control unit 60 has executed the process of S17, after conveying the preceding recording material P, it feeds the next recording material P after the time obtained by adding the waiting time WT to the predetermined conveying interval of the recording material P has elapsed. Similarly, when the control unit 60 has executed the process of S18, it conveys the recording material P (next sheet) following the preceding recording material P, and after the time obtained by adding the waiting time WT to the predetermined conveying interval of the recording material P has elapsed, it feeds the recording material P (next sheet) following the next recording material P.

[0044] In S20, the control unit 60 starts printing on the recording material P at half process speed. In S21, the control unit 60 acquires the detected temperature (sub-thermistor temperature) of the heater 21 corresponding to the non-paper passing region of the fixing nip N, detected by the sub-thermistor 22b, via the A / D conversion circuit 63, and determines whether the sub-thermistor temperature is 220°C or higher. If the control unit 60 determines that the sub-thermistor temperature is 220°C or higher, the process proceeds to S23, and if the control unit 60 determines that the sub-thermistor temperature is less than 220°C, the process proceeds to S22. In S22, the control unit 60 sets the waiting time WT to 0 seconds, and the process proceeds to S28.

[0045] In S23, the control unit 60 determines whether the acquired sub-thermistor temperature is equal to or higher than 230° C. If the control unit 60 determines that the sub-thermistor temperature is equal to or higher than 230° C., the process proceeds to S25, and if the control unit 60 determines that the sub-thermistor temperature is lower than 230° C., the process proceeds to S24. In S24, the control unit 60 sets the waiting time WT to 1 second, and the process proceeds to S28.

[0046] In S25, the control unit 60 determines whether the acquired sub-thermistor temperature is 240°C or higher (a predetermined temperature or higher). If the control unit 60 determines that the sub-thermistor temperature is 240°C or higher, the process proceeds to S27, and if the control unit 60 determines that the sub-thermistor temperature is less than 240°C, the process proceeds to S26. In S26, the control unit 60 sets the waiting time WT to 1.5 seconds and proceeds to S28. In S27, the control unit 60 sets the waiting time WT to 4 seconds and proceeds to S28.

[0047] In S28, the control unit 60 determines whether an image to be printed on the next recording material P (next sheet) is being formed on the photosensitive drum 1. If the control unit 60 determines that an image to be printed on the next sheet is being formed on the photosensitive drum 1, the process proceeds to S30. If the control unit 60 determines that an image to be printed on the next sheet is not being formed on the photosensitive drum 1, the process proceeds to S29. In S29, if an image has not yet been formed on the photosensitive drum 1, the control unit 60 can stop the transport of the next sheet and wait, so it sets a waiting time WT for the paper passage waiting time of the next recording material P (next sheet), and the process proceeds to S31. In S30, if an image of the next sheet is already being formed on the photosensitive drum 1, the control unit 60 cannot stop the transport of the next sheet, so it sets a waiting time WT for the paper passage waiting time of the recording material P (next sheet) after the next sheet, and the process proceeds to S31. In S31, the control unit 60 determines whether printing on all recording materials P has been completed. If the control unit 60 determines that printing on all recording materials P has been completed, it ends the process. If it determines that printing on recording materials P has not been completed, it returns the process to S20 and prints the next recording material P. Note that, when the control unit 60 has executed the process of S29, after conveying the preceding recording material P, it feeds the next recording material P after the time obtained by adding the waiting time WT to the predetermined conveying interval of the recording material P has elapsed. Similarly, when the control unit 60 has executed the process of S30, it conveys the recording material P (next sheet) following the preceding recording material P, and after the time obtained by adding the waiting time WT to the predetermined conveying interval of the recording material P has elapsed, it feeds the recording material P (next sheet) following the next recording material P.

[0048] As described above, in the recording material feed control of this configuration example shown in FIG. 7 , the paper feed wait time is determined based on the temperature detected by the sub-thermistor 22b, thereby optimizing the transport interval for transporting the recording material P, including the paper feed wait time. In particular, when continuous printing of small-sized recording materials P causes the temperature of the non-paper-passing areas of the fixing nip N to rise and the sub-thermistor temperature to rise, the wait time is increased, lengthening the transport interval for the recording material P. This reduces throughput, but it can mitigate the temperature rise in the non-paper-passing areas of the fixing nip N. Furthermore, when the temperature rise in the non-paper-passing areas of the fixing nip N is mitigated and the sub-thermistor temperature drops, the wait time can be shortened in accordance with the sub-thermistor temperature to increase throughput. In this way, by controlling the feeding of the recording material P according to the flowchart in FIG. 7 , it is possible to mitigate the temperature rise in the non-paper-passing areas of the fixing nip N and quickly improve throughput.

[0049] It is desirable to control the conveyance interval of the recording material P by continuously updating the standby time WT in accordance with the sub-thermistor temperature at short time intervals. However, if a sudden change in the sheet passing standby time causes a phenomenon such as repeated increases and decreases in the sheet passing standby time (i.e., repeated increases and decreases in the temperature of the non-sheet passing portion of the fixing nip N), the control may be such that the standby time is increased and decreased in stages.

[0050] Furthermore, it is desirable that the timing for feeding the recording material P, which is calculated by adding the paper waiting time to the predetermined conveyance interval of the recording material P, be as early as possible after the sub-thermistor temperature is detected. Due to the configuration of the image forming apparatus 100, it is difficult to stop image formation or the conveyance of the recording material P after the electrostatic latent image begins to form on the photosensitive drum 1. The timing for feeding the recording material P and the timing for forming an image on the photosensitive drum 1 differ due to the difference between the distance the toner image formed on the photosensitive drum 1 travels to the secondary transfer nip and the distance the recording material fed from the paper feed cassette 9 travels to the secondary transfer nip. For example, if the distance the recording material fed from the paper feed cassette 9 travels to the secondary transfer nip is longer, image formation on the photosensitive drum 1 begins after the recording material P is fed. Therefore, if image formation on the photosensitive drum 1 has not started at the time when the paper waiting time according to the sub-thermistor temperature is determined, the recording material on which the image is to be formed (i.e., the next sheet mentioned above) can be fed at a conveying interval that includes the determined paper waiting time.

[0051] On the other hand, if the distance traveled by the toner image formed on the photosensitive drum 1 to the secondary transfer nip portion is longer, the recording material P is fed from the paper feed cassette 9 after image formation on the photosensitive drum 1 has started. Since image formation on the photosensitive drum 1 has started, the timing at which the toner image on the photosensitive drum 1 reaches the secondary transfer portion is determined. The timing at which the recording material P is fed from the paper feed cassette 9 is determined so that it is transported to the secondary transfer nip portion at the timing at which the toner image on the photosensitive drum 1 reaches the secondary transfer portion, and it cannot be fed at a transport interval that includes the paper passage wait time. Therefore, if image formation on the photosensitive drum 1 has started at the time the paper passage wait time corresponding to the sub-thermistor temperature is determined, the following transport control is performed. That is, the subsequent recording material P (i.e., the above-mentioned second-next paper) that is fed after the recording material on which image formation is being performed (i.e., the above-mentioned next paper) is fed at a transport interval that includes the determined paper passage wait time. In this way, in the control of feeding the recording material P in this configuration example, the timing of feeding the recording material P can be controlled based on the waiting time WT for the next sheet or the sheet after that, which makes it possible to suppress temperature rise in the non-sheet passing areas of the fixing nip N and also to suppress a decrease in throughput, thereby improving productivity.

[0052] [Configuration example 2] In the configuration example 1, the paper passage standby time for the temperature detected by the sub-thermistor 22b was determined according to the process speed when printing the recording material P, but the configuration example 2 differs from the configuration example 1 in that the paper passage standby time is determined according to the basis weight of the recording material P. Table 4 shown below shows the results when the basis weight of the recording material P is 90 g / m 2 This is a table showing the relationship between the detected temperature (unit: °C) of the sub-thermistor 22b and the paper passing waiting time (unit: seconds) between recording materials P in the following cases. Table 5 also shows the relationship between the detected temperature (unit: °C) of the sub-thermistor 22b and the paper passing waiting time (unit: seconds) between recording materials P in the following cases: 2 10 is a table showing the relationship between the detected temperature (unit: °C) of the sub-thermistor 22b and the waiting time (unit: seconds) between sheets of recording material P when the temperature is greater than 100°C. The basis weight of the recording material P is determined by specifying the type of recording material P used during printing. In this configuration example, the basis weight of the recording material P is 90 g / m 2In the following cases, the process speed is full speed, and the basis weight of the recording material P is 90 g / m 2 When the temperature is larger than the predetermined temperature, the process speed is half the normal speed. The waiting times for the recording material P to pass in Tables 4 and 5 with respect to the detected temperatures of the sub-thermistor 22b are the same as those in Tables 1 and 2 of the first configuration example.

[0053] [Table 4]

[0054] [Table 5]

[0055] [Control sequence for recording material feeding control] Next, the recording material feeding control of this configuration example will be described. Fig. 8 is a flowchart showing the control sequence of the recording material feeding control of this configuration example. The processing of Fig. 8 is started when a print signal for the recording material P is received, as in Fig. 7 of the configuration example 1, and is executed by the control unit 60. Note that here, the size of the recording material P is assumed to be small (for example, a recording material with a paper width of the minimum width that can be passed as shown in Fig. 5). Also, the waiting time WT, which is the above-mentioned paper passing waiting time, is set to 100 seconds when the basis weight of the recording material P is 90 g / m 2 In the following cases, the paper feed standby time is set to correspond to the sub-thermistor temperature in Table 4. On the other hand, when the basis weight of the recording material P is 90 g / m 2 If it is greater than this, the paper passage waiting time corresponding to the sub-thermistor temperature in Table 5 is set.

[0056] In S41, the control unit 60 determines whether printing is to be performed on multiple sheets of recording material P. If the control unit 60 determines that printing is to be performed on multiple sheets of recording material P, the process proceeds to S43, and if the control unit 60 determines that printing is to be performed on one sheet of recording material P, the process proceeds to S42. In S42, the control unit 60 starts printing on one sheet of recording material P, and ends the process when printing is completed.

[0057] In S43, the control section 60 determines that the basis weight of the recording material P is 90 g / m2 Whether it is below (predetermined value or less) (basis weight ≦ 90 g / m 2 The control section 60 determines that the basis weight of the recording material P is 90 g / m 2 If it is determined that the basis weight of the recording material P is 90 g / m 2 or less, the process proceeds to S44. 2 Not less than (grammage > 90g / m 2 If it is determined that the value is 0, the process proceeds to S60.

[0058] The basis weight of the recording material P is 90 g / m 2 The processes in the following cases, S44 to S59, are the same as the processes in S4 to S19 in Fig. 7, and therefore the description thereof will be omitted here. 2 The processing in steps S60 to S71, which is the processing when the number of times ...

[0059] High basis weight recording material P (basis weight > 90 g / m 2 ) is the same temperature, the waiting time for paper passage is 2 It is preferable to set the waiting time for the recording material P having a large basis weight (basis weight > 90 g / m) to be equal to or shorter than the waiting time for the recording material P having a large basis weight (basis weight > 90 g / m) 2 ) is the temperature of the sub-thermistor where the paper feed waiting time occurs, and the recording material P with a small basis weight (basis weight ≦ 90 g / m 2 ), which is preferable. This is related to the amount of heat removed from the fixing nip portion N when the recording material P passes through the fixing device 50. A recording material P with a larger basis weight removes more heat from the fixing nip portion N, and therefore the temperature rise in the non-sheet passing areas of the fixing nip portion N is smaller than that of a recording material P with a smaller basis weight. As a result, the temperature rise in the non-sheet passing areas of the fixing nip portion N is smaller for a recording material P with a larger basis weight while printing one sheet of recording material than for a recording material P with a smaller basis weight, and the temperature rise in the non-sheet passing areas can be mitigated with a shorter sheet passing wait time for the same sub-thermistor temperature.

[0060] [Configuration example 3] Configuration example 3 is a configuration example in which the method of determining the paper passage wait time is similar to configuration example 1, but the number and arrangement of sub-thermistors and the method of determining the sub-thermistor temperature are different. In configuration examples 1 and 2, sub-thermistor 22b was installed at one longitudinal end of heater 21. In configuration example 3, sub-thermistors 22b and 22c are installed at both longitudinal end of heater 21, and the higher of the temperatures detected by the two sub-thermistors 22b and 22c is used as the sub-thermistor temperature when determining the paper passage wait time.

[0061] (Ceramic heater configuration) FIG. 9 is a schematic diagram showing the positions of the thermistor 22a and sub-thermistors 22b and 22c of the ceramic heater 21 used in the fixing device 50 of this configuration example, when viewed from the non-film sliding surface side, which is the side that does not slide against the film 24. In FIG. 9, the area surrounded by a dashed line indicates the heating resistor 21b located on the film sliding surface side of the heater 21. As shown in FIG. 9, the main thermistor 22a, sub-thermistor 22b, and sub-thermistor 22c are in contact with the substrate 21a of the heater 21. The main thermistor 22a detects the temperature of the heater 21 corresponding to the paper passing region of the fixing nip N through which the minimum-width recording material P can pass. Meanwhile, the sub-thermistors 22b and 22c are located in regions of the heater 21 corresponding to the non-paper passing region of the fixing nip N through which the maximum-width recording material P can pass and the minimum-width recording material P cannot pass. The regions corresponding to the non-paper passing region of the fixing nip portion N are located on the left and right end sides of the substrate 21a in the longitudinal direction of the drawing, with two regions sandwiching the center of the substrate 21a corresponding to the paper passing region of the fixing nip portion N. Sub-thermistor 22b is located in the non-paper passing region on the left side of FIG. 9, and sub-thermistor 22c is located in the non-paper passing region on the right side of FIG.

[0062] The control unit 60 acquires the temperature Tb of the heater 21 corresponding to the non-paper passing region of the fixing nip N detected by the sub-thermistor 22b, and the temperature Tc of the heater 21 corresponding to the non-paper passing region of the fixing nip N detected by the sub-thermistor 22c. The control unit 60 then adopts the higher of the temperatures Tb and Tc as the sub-thermistor temperature. As a result, even if the recording material P is biased toward one of the non-paper passing regions in the paper feed cassette 9 (FIG. 1), the control unit 60 can accurately detect the temperature rise in the non-paper passing region in the other non-paper passing region.

[0063] [Configuration example 4] Configuration example 4 is a configuration example in which the paper passing standby time is calculated by adding paper passing standby time 1, which is calculated in accordance with configuration example 1, to paper passing standby time 2, which is determined by the size of the recording material P. Here, the size of the recording material refers to the paper length of the recording material P (the length of the recording material P in the conveying direction) and the paper width (the length of the recording material P in the direction perpendicular to the conveying direction). In other words, the recording material conveyance interval in configuration example 4 is the addition of paper passing standby time 1 and paper passing standby time 2 to a predetermined conveyance interval. In this configuration example, because paper passing standby time 2, which depends on the size of the recording material P, is added to the predetermined conveyance interval, the recording material conveyance interval is longer than in configuration example 1.

[0064] Table 6 below shows the paper passage standby time 2 determined according to the paper length and paper width of the recording material P. The narrower the paper width, the less heat is absorbed by the recording material P as it passes through the fixing nip N, resulting in a higher temperature in the non-paper passing area of ​​the fixing nip N. For this reason, in Table 6, when the paper width is less than 155 mm, the paper passage standby time 2 is set longer than when the paper width is 155 mm or greater. Also, the shorter the paper length, the higher the temperature in the non-paper passing area of ​​the fixing nip N when the recording material P passes through the fixing nip N. For this reason, in Table 6, when the paper length is less than 210 mm, the paper passage standby time 2 is set longer than when the paper length is 210 mm or greater. In this configuration example, the paper passage standby time is determined based on the size of the recording material P in addition to the paper passage standby time according to the process speed in configuration example 1, thereby further mitigating the temperature rise in the non-paper passing area.

[0065] [Table 6]

[0066] [Comparative Example] The comparative example is an embodiment in which the paper passage standby time is determined using only the detected temperature of the sub-thermistor 22b, as in conventional image forming apparatuses. Therefore, the paper passage standby time in the comparative example does not change depending on the process speed or the basis weight of the recording material P, as in configuration examples 1 and 2. Table 7 shown below shows the relationship between the detected temperature of the sub-thermistor 22b (unit: °C) and the paper passage standby time (unit: seconds) between recording materials P. In this comparative example, the paper passage standby time shown in Table 7 is set depending on the detected temperature of the sub-thermistor 22b, regardless of the process speed or basis weight. Note that the paper passage standby time for the detected temperature of the sub-thermistor 22b shown in Table 7 is determined when the process speed is at full speed in configuration example 1 and when the basis weight of the recording material P is 90 g / m 2 This is the same as the paper passage waiting time for the same detected temperature of the sub-thermistor 22b in the following cases.

[0067] [Table 7]

[0068] [Productivity in Configuration Examples 1 to 4 and Comparative Example] Table 8 shows the productivity and the average detected temperature of the sub-thermistor when the throughput control in the above-mentioned configuration examples 1, 2, 3, 4, and the comparative example is applied to the continuous printing of small-sized A5-size recording material P for 3 minutes. The A5-size recording material P is made of plain paper and thick paper, and the basis weight of the thick paper is 100 g / m. 2 is.

[0069] [Table 8]

[0070] As shown in Table 8, the basis weight is 100 g / m2 When the process speed for printing on thick paper is half speed, the productivity of Configuration Examples 1, 2, and 3 is significantly improved compared to the Comparative Example. As described above, the Comparative Example determines the paper passage wait time between recording materials P based only on the sub-thermistor temperature, regardless of the process speed. On the other hand, Configuration Examples 1 and 3 determine the paper passage wait time between recording materials P based on the sub-thermistor temperature and the process speed, and Configuration Example 2 determines the paper passage wait time based on the sub-thermistor temperature and the basis weight of the recording material P, so the productivity of Configuration Examples 1, 2, and 3 is greater than that of the Comparative Example.

[0071] When the process speed is half speed or the basis weight is 90 g / m 2 When the process speed is full speed or the basis weight is 90 g / m, the temperature rise in the non-paper passing area is gradual. 2 Compared to the following cases, the waiting time between recording materials P can be shortened, achieving higher productivity than the comparative example. Furthermore, in this test, no clear difference in productivity was observed between Configuration Examples 1, 2, and 3. This is because the throughput control in Configuration Examples 1, 2, and 3 uses the same control sequence based on Figures 7 and 8 described above. Furthermore, as described above, the difference in productivity between Configuration Examples 1, 2, and 3 occurs when the recording materials P are unevenly loaded in the paper feed cassette 9. Configuration Example 4 is effective in further lowering the average detected temperature of the sub-thermistor 22b during printing. For example, even when printing is performed under strict conditions that limit the temperature rise in the non-paper-passing areas of the fixing nip N, such as when a long, thin strip of recording paper P is passed through the fixing nip N, the printing operation can be performed more safely.

[0072] Furthermore, as shown in Table 8, the average detected temperature of the sub-thermistor during printing was 231°C for the comparative example using thick paper (half speed), which is lower than the 238°C for configuration examples 1, 2, and 3. This indicates that when the process speed of the comparative example is half speed, there is ample room for the heater 21 to heat up in the non-paper passing areas, i.e., the paper passing wait time is the same as at full speed, so at half speed the paper passing wait time is longer than necessary. On the other hand, configuration examples 1, 2, and 3 were able to achieve maximum productivity while allowing for a temperature rise in the non-paper passing areas.

[0073] [Change in throughput between configuration example 1 and comparison example when process speed is in half-speed mode] Figure 10 shows the basis weight of 100 g / m 210 is a graph showing the change in throughput versus the number of prints when A5-sized recording material P is continuously printed. In FIG. 10, the solid line shows the change in throughput when the paper feed wait time in Table 2 of Configuration Example 1 is applied, and the dashed line shows the change in throughput when the paper feed wait time in Table 6 of Comparative Example is applied. Note that the horizontal axis of FIG. 10 shows the number of prints of recording material P (unit: sheets), and the vertical axis shows throughput (unit: ppm). When Configuration Example 1 and the Comparative Example are applied, printing is performed at the maximum throughput of 15 ppm at the start of printing. However, when Configuration Example 1, shown by the solid line, is applied, the maximum throughput is maintained for a larger number of prints than when the Comparative Example, shown by the dashed line. Furthermore, as the number of prints of recording material P increases, the throughput when Configuration Example 1 is applied becomes higher than the throughput when the Comparative Example is applied for the same number of prints. This is because, if the sub-thermistor temperature is the same in Configuration Example 1 and the comparative example, i.e., the temperature rise in the non-sheet-passing section is the same, the sheet-passing wait time in Configuration Example 1 is the same as or shorter than the sheet-passing wait time in the comparative example. That is, the throughput control when Configuration Example 1 is applied at half-speed processing speed is performed to achieve a throughput equal to or greater than that of the comparative example, in which the throughput control is performed at half-speed processing speed in the same way as that at full speed. As a result, the application of Configuration Example 1 allows a longer period of time for maintaining high throughput compared to the application of the comparative example. In this way, the image forming apparatus 100 to which the present invention is applied can achieve optimization of productivity while suppressing temperature rise in the non-sheet-passing section of the heater 21.

[0074] As described above, according to this embodiment, it is possible to control the conveying speed of the recording material or the conveying interval of the recording material to suppress the temperature rise in the non-paper passing portion of the fixing nip portion depending on the type of recording material. [Explanation of symbols]

[0075] 21 Ceramic heater 22b Sub-thermistor 24 Fixing film 30 Pressure roller 50 Fixing device 60 Control Unit 101 Image forming unit

Claims

1. an image forming means for forming an image on a recording material; A first rotating body; a second rotating body that contacts an outer peripheral surface of the first rotating body and forms a nip portion between the second rotating body and the first rotating body; a heater disposed in the internal space of the second rotating body; a first temperature detecting means provided at a position corresponding to the center in the longitudinal direction of the heater; a second temperature detecting means provided at a position closer to an end of the heater than the first temperature detecting means in the longitudinal direction of the heater; a control means for controlling a transport interval, which is an interval from when the trailing edge of the preceding sheet passes through the nip portion until when the leading edge of the succeeding sheet reaches the nip portion; Equipped with the control means sets the conveying interval to a first interval when the basis weight of the preceding sheet and the succeeding sheet is a first basis weight and the temperature detected by the second temperature detection means reaches a first temperature; An image forming apparatus characterized in that the basis weight of the preceding paper and the following paper is a second basis weight that is greater than the first basis weight, and when the temperature detected by the second temperature detection means reaches the first temperature, the conveying interval is set to a second interval that is narrower than the first interval.

2. 2. The image forming apparatus according to claim 1, wherein the control means increases the conveying interval in accordance with the size of the recording material.

3. 3. The image forming apparatus according to claim 1, wherein the control means sets the conveying interval to a third interval longer than the first interval when the temperature detected by the second temperature detection means reaches or exceeds a predetermined temperature higher than the first temperature.

4. a paper feed section on which recording material is placed, 4. The image forming apparatus according to claim 1, wherein the control unit controls the paper feed unit to feed the recording material after the conveying interval has elapsed since the preceding recording material was fed.

5. The image forming apparatus according to claim 4, wherein, when the image forming means has not started image formation on the next recording material to be fed, the control means causes the paper feeding unit to feed the next recording material after the conveying interval has elapsed from the timing at which the preceding recording material was fed, and when the image forming means has started image formation on the next recording material to be fed, the control means causes the paper feeding unit to feed the next recording material after the conveying interval has elapsed from the timing at which the next recording material was fed.

6. the second temperature detecting means are disposed on each end side of the heater in the longitudinal direction, 6. The image forming apparatus according to claim 1, wherein the control unit sets the higher of the temperatures detected by the second temperature detection unit as the temperature detected by the second temperature detection unit.

7. the second rotating body is a cylindrical film, the first rotating body is a pressure roller that forms the nip portion with the film, 7. The image forming apparatus according to claim 1, wherein 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.

Images