Image forming apparatus

Abstract

By appropriately setting the timing for starting the fuser from a stopped state, unnecessary idle rotation of the fuser is reduced, thereby suppressing unnecessary lifespan consumption of the fuser. [Solution] The image forming apparatus 100 includes an imaging unit 90, a fixing device 30 that performs fixing processing, and a control unit 40 that can control the drive source 37 and heater 34 of the fixing device 30. In a start process that brings the device from a first state in which the drive of the drive source 37 and the temperature control of the heater 34 are stopped to a second state in which the drive of the drive source 37 and the temperature control of the heater 34 are started to enable fixing processing, the control unit 40 can perform control to change the timing at which the drive of the drive source 37 and the temperature control of the heater 34 are started based on the detected temperature detected by the temperature sensor 35 in the first state and the target temperature detected by the temperature sensor 35 in the second state, in relation to the timing at which the first recording material P after the start process reaches the fixing nip N.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, or a multifunction machine having a plurality of functions among these functions, using an electrophotographic method or an electrostatic recording method.

Background Art

[0002] In an image forming apparatus such as a copying machine using an electrophotographic method, a toner image is formed on a sheet-like recording paper, and the recording paper is heated and pressurized by a fixing device to fix the toner image on the recording paper (fixing process) is performed.

[0003] As a fixing device, for example, a belt heating type fixing device that heats a recording paper via a fixing belt is known (Patent Document 1). For example, in such a belt heating type fixing device, since the fixing belt rotates while sliding on the heater, friction occurs at the sliding portion. Therefore, the amount of wear of the fixing belt due to the friction is one of the factors that determine the life of the fixing belt. Increasing the total rotation time of the fixing belt promotes the wear of the fixing belt by that amount, leading to a shorter life of the fixing belt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The fuser unit stops operating after all fixing processes in a job are completed and restarts when the next job begins. In addition, for example, in a belt-heating type fuser unit, the following operation may be performed to extend the lifespan of the fuser belt: During continuous paper feeding, the fuser unit stops operating after the recording paper has passed the fuser nip, and restarts before the next recording paper enters the fuser nip.

[0006] Here, "starting up the fixing device" refers to initiating the operation of the fixing device (driving the drive motor, heating the heater) and bringing it to a stable state where fixing is possible. Starting up the fixing device can also be called "activating the fixing device." Furthermore, "starting up the drive motor" refers to starting the drive motor and bringing it to a stable state where fixing is possible. Furthermore, "starting up the heater" refers to starting the heater and raising it to the temperature required for fixing.

[0007] The time required to start up the fuser unit depends on the drive load applied to the fuser unit; a heavier drive load results in a longer start-up time. It is necessary for the fuser unit to start up before the recording paper enters the fuser nip. Therefore, sufficient time is allocated for the fuser unit to start up, even under heavy drive loads, to allow the drive to stabilize. Furthermore, the time required to start up the fuser unit depends on the time it takes to raise the temperature of the fuser nip to the required temperature. It is necessary for the temperature of the fuser nip to reach the required temperature before the recording paper enters the fuser nip. Therefore, sufficient time is allocated for the fuser unit to start up, even under long heating times for the fuser nip.

[0008] However, depending on how the fuser is used, the heat stored in the fuser may reduce the drive load or cause the temperature of the fuser nip to rise to the required temperature more quickly, resulting in the fuser starting up earlier than the pre-allocated time. In this case, unnecessary idle rotation of the fuser occurs between the completion of fuser startup and the arrival of the recording paper at the fuser nip. As mentioned above, a longer period of unnecessary idle rotation of the fuser leads to a shorter lifespan for the fuser.

[0009] Therefore, the objective of the present invention is to reduce unnecessary idle rotation of the fixing device and suppress unnecessary life consumption of the fixing device by appropriately setting the timing for starting the operation of the fixing device from a state in which the operation of the fixing device has stopped. [Means for solving the problem]

[0010] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image forming unit that forms a toner image on a recording material, and a fixing apparatus that performs a fixing process for fixing the toner image formed by the image forming unit to the recording material, comprising: a rotatable first fixing member; a rotatable second fixing member that forms a fixing nip together with the first fixing member; a heater that generates heat for heating the fixing nip; a drive source that generates a driving force for rotating the first fixing member and the second fixing member; and a temperature sensor that detects a temperature correlated with the temperature of the fixing nip, wherein the fixing apparatus heats the fixing nip with the heater and performs the fixing process by clamping the recording material between the first fixing member and the second fixing member at the fixing nip and transporting it, The image forming apparatus comprises a control unit capable of controlling the drive source and the heater, wherein the control unit is capable of performing control to change the timing at which the drive source and the heater are started in relation to the timing at which the first recording material after the start process reaches the fixing nip, based on a detected temperature which is the temperature detected by the temperature sensor in the first state and a target temperature which is the target value of the temperature detected by the temperature sensor in the second state, in a start process that brings the apparatus from a first state in which the drive source and the heater temperature control are started to a second state in which the fixing process is possible. [Effects of the Invention]

[0011] According to the present invention, by appropriately setting the timing for starting the operation of the fixing device from a state where its operation has stopped, it is possible to reduce unnecessary idle rotation of the fixing device and suppress unnecessary consumption of the fixing device's lifespan. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing the schematic configuration of an image forming apparatus. [Figure 2] This is a cross-sectional view showing the schematic configuration of the fixing device. [Figure 3]It is a block diagram showing a schematic control configuration of an image forming apparatus. [Figure 4] It is a graph diagram for explaining drive control and temperature control of a fixing device. [Figure 5] It is a schematic cross-sectional view near a fixing device for explaining the control timing of the fixing device. [Figure 6] It is a schematic diagram for explaining various times related to a recording sheet passing through a fixing nip portion. [Figure 7] It is a graph diagram for explaining stop and restart of temperature control and drive control of a fixing device. [Figure 8] It is a flowchart diagram of the overall operation of the fixing device in Example 1. [Figure 9] It is a flowchart diagram of paper gap control of the fixing device in Example 1. [Figure 10] It is a flowchart diagram of control for acquiring paper gap time. [Figure 11] It is a table showing the relationship between the temperature and the temperature rising time of the fixing device in Example 2. [Figure 12] It is a graph diagram showing the relationship between the temperature and the temperature rising time of the fixing device in Example 2. [Figure 13] It is a flowchart diagram of control for acquiring recovery time in Example 2. [Figure 14] It is a flowchart diagram of the operation of the fixing device after the timing when the recording sheet in Example 2 passes through the fixing nip portion.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0014] [Example 1] [Configuration of Image Forming Apparatus] First, the configuration of the image forming apparatus according to this embodiment will be described. FIG. 1 is a cross-sectional view showing the schematic configuration of the image forming apparatus 100 according to this embodiment. In this embodiment, the image forming apparatus 100 is a tandem type image forming apparatus adopting an intermediate transfer method, which can form a full-color image on a sheet-like recording paper using an electrophotographic method.

[0015] Note that, typically, paper is used as the recording material (recording medium) on which an image is formed in the image forming apparatus 100. Therefore, here, the recording material may be referred to as "paper", "recording paper", "sheet", etc. However, the recording material is not limited to paper, and may be made of a material other than paper such as a plastic sheet, or a material containing a material other than paper. Also, the type of recording paper includes attributes (so-called paper type categories) based on general characteristics such as plain paper, coated paper, cardboard, synthetic paper, numerical values and numerical ranges such as basis weight and thickness, and any information that can distinguish the recording paper, including brand (including manufacturer, product number, etc.). Generally, the type of recording paper is often specified by the paper type category and thickness (or basis weight).

[0016] The image forming apparatus 100 includes a printer unit 110 and an image reading unit (reader unit) 120. The image reading unit 120 reads a document placed on the document table glass 121. The image reading unit 120 has an optical unit 125 including a light source 122, optical system members 123 such as lenses, and a CCD sensor 124. In the optical unit 125, the light irradiated from the light source 122 is reflected by the document and imaged on the CCD sensor 124 through optical system members 23 such as lenses. Such an optical unit 125 moves in the direction of arrow A1 in FIG. 1 to scan the document, thereby converting the document into an electrical signal data series for each line. The image signal obtained by the CCD sensor 124 is sent to the control unit 40 provided in the printer unit 110 via the reader control unit 126. Then, in the control unit 40, image processing adapted to each of the image forming units described later is performed on this image signal. Also, the control unit 40 can receive an external input from an external host device such as a print server as an image signal.

[0017] The printer unit 110 has four image forming units 10Y, 10M, 10C, and 10K, each forming images in yellow (Y), magenta (M), cyan (C), and black (K), respectively, as multiple image forming units (stations). Note that elements with the same or corresponding functions or configurations provided for each color may be described collectively by omitting the Y, M, C, and K at the end of the symbols indicating that they belong to one of the colors. The image forming unit 10 consists of a photosensitive drum 11 (11Y, 11M, 11C, 11K), a charging roller 12 (12Y, 12M, 12C, 12K), an exposure device 13, a developing device 14 (14Y, 14M, 14C, 14K), a drum cleaning device 15 (15Y, 15M, 15C, 15K), and the like, which will be described later. The exposure apparatus 13 is configured as a single unit that irradiates light onto the photosensitive drum 11 of each image forming unit 10. In each image forming unit 10, image formation is performed based on the image signal described above.

[0018] The photosensitive drum 11, which serves as the first image carrier, is driven to rotate in the direction of arrow R1 (counterclockwise) in Figure 1. The surface of the rotating photosensitive drum 11 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 12, which is a roller-type charging member (charger) used as a charging means. The operation of charging the surface of the photosensitive drum 11 with the charging roller 12 is preparation for forming an electrostatic latent image on the photosensitive drum 11, and is an example of image formation preparation performed in the image forming apparatus 100. The charged surface of the photosensitive drum 11 is scanned and exposed by laser light irradiated by the exposure apparatus 13, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 11. The image signal is converted into PWM (pulse width modulation controlled) laser light by the control unit 40. The exposure apparatus 13 consists of a polygon scanner and scans the photosensitive drum 11 of each image forming unit 10 by irradiating it with laser light corresponding to the image signal. The electrostatic latent image formed on the photosensitive drum 11 is developed (visualized) by a developing device 14, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 11. In this embodiment, the developing device 14 deposits toner, which is charged with the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 11, onto the exposed area of ​​the photosensitive drum 11, where the absolute value of the potential has decreased after being uniformly charged and then exposed. In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative polarity.

[0019] An intermediate transfer unit 20 is positioned opposite the four photosensitive drums 11. The intermediate transfer unit 20 has an intermediate transfer belt 21, which is an intermediate transfer body composed of an endless belt, serving as a second image carrier. The intermediate transfer belt 21 is stretched over a plurality of tension rollers, namely drive rollers 22, tension rollers 23, and secondary transfer opposing rollers 24, and is taut with a predetermined tension. The intermediate transfer belt 21 rotates (moves in a circular motion) in the direction of arrow R2 (clockwise) in Figure 1 as the drive rollers 22 are rotationally driven. On the inner circumferential surface of the intermediate transfer belt 21, primary transfer rollers 25, which are roller-type primary transfer members serving as primary transfer means, are positioned corresponding to each of the photosensitive drums 11Y, 11M, 11C, and 11K. The primary transfer roller 25 is pressed toward the photosensitive drum 11 via the intermediate transfer belt 21, forming a primary transfer section (primary transfer nip section) T1, which is the contact area between the photosensitive drum 11 and the intermediate transfer belt 21. The toner image formed on the photosensitive drum 11 is transferred (primary transfer) onto the rotating intermediate transfer belt 21 in the primary transfer section T1. During primary transfer, a primary transfer bias (primary transfer voltage) with the opposite polarity to the normal charging polarity of the toner is applied to the primary transfer roller 25. As a result, the primary transfer roller 25 discharges from the inner surface of the intermediate transfer belt 21, transferring the toner image on the photosensitive drum 11 onto the intermediate transfer belt 21. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black formed on each of the photosensitive drums 11Y, 11M, 11C, and 11K are sequentially transferred so that they are superimposed on the same image forming area on the intermediate transfer belt 21. After the first transfer, the surface of the photosensitive drum 11 is cleaned by the drum cleaning device 15.

[0020] On the outer circumferential surface of the intermediate transfer belt 21, a secondary transfer roller 70, which is a roller-type secondary transfer member serving as a secondary transfer means, is positioned opposite the secondary transfer opposing roller 24 via the intermediate transfer belt 21. The secondary transfer roller 70 is pressed toward the secondary transfer opposing roller 24 via the intermediate transfer belt 21, forming a secondary transfer section (secondary transfer nip section) T2, which is the contact area between the intermediate transfer belt 21 and the secondary transfer roller 70. The toner image formed on the intermediate transfer belt 21 is transferred (secondary transfer) in the secondary transfer section T2 onto the recording paper P, which is being transported while being held between the intermediate transfer belt 21 and the secondary transfer roller 70. During secondary transfer, a secondary transfer bias (secondary transfer voltage) with the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer roller 70. As a result, the secondary transfer roller 70 forms a secondary transfer electric field in the secondary transfer section T2, transferring the toner image on the intermediate transfer belt 21 onto the recording paper P.

[0021] In this embodiment, the image forming unit 90, which forms a toner image on the recording paper P, is composed of each image forming unit 10, an intermediate transfer unit 20, a secondary transfer roller 70, and the like.

[0022] The recording paper P is fed from the paper feeding unit 50, which serves as a paper feeding means, and transported toward the secondary transfer unit T2. The paper feeding unit 50 is composed of a cassette 51 as a storage unit, a paper feeding roller 52 as a paper feeding member, and a transport roller 53 as a transport member. The recording paper P stored in the cassette 51 is separated one sheet at a time by the paper feeding roller 52 and other components and fed out of the cassette 51. This recording paper P is transported by the transport roller 53 to a pair of register rollers (register unit) 60, which serves as a synchronous transport member. After being held in a waiting position by the pair of register rollers 60, the timing of the recording paper P is controlled to align the position of the toner image on the intermediate transfer belt 21 with the position of the recording paper P, and then the pair of register rollers 60 transports it toward the secondary transfer unit T2.

[0023] The recording paper P onto which the toner image has been transferred is transported to the fixing device 30, which acts as an image heating device. The fixing device 30 constitutes a fixing means for fixing the toner image onto the recording paper P. The fixing device 30 heats and pressurizes the recording paper P carrying the unfixed toner image to fix (melt and solidify) the toner image onto the recording paper P (fixing process). After passing through the fixing device 30 and the toner image has been fixed onto the recording paper P, it is then discharged (output) to the outside of the image forming apparatus 100 (outside the machine) and loaded onto the output tray 80, which acts as an output section.

[0024] In the case of double-sided printing, once the transfer and fixing of the toner image to the first surface (first image-forming surface) of the recording paper P is complete, the recording paper P is transported to the inversion unit 55 located inside the printer unit 110. In the inversion unit 55, the toner image is then transferred and fixed to the second surface (second image-forming surface) of the recording paper P, which has been reversed. This recording paper P is then discharged from the machine and stacked on the output tray 80.

[0025] <Configuration of the fixing device> Next, the configuration of the fixing device 30 in this embodiment will be described. In this embodiment, the fixing device 30 is a belt heating type fixing device. Figure 2 is a cross-sectional view showing the schematic configuration of the fixing device 30.

[0026] Regarding the fixing device 30 and its constituent elements, "longitudinal direction" refers to the direction approximately perpendicular to the transport direction of the recording paper P on the surface of the recording paper P. Also, regarding the fixing device 30 and its elements, "short direction" refers to the direction approximately parallel to the transport direction of the recording paper P on the surface of the recording paper P (a direction approximately perpendicular to the longitudinal direction). Furthermore, regarding the fixing device 30 and its elements, "length" refers to the dimension in the longitudinal direction, and "width" refers to the dimension in the short direction. Furthermore, regarding the recording paper P, "width direction" refers to the direction approximately perpendicular to the transport direction of the recording paper P on the surface of the recording paper P, and "width" refers to the dimension in the width direction. Furthermore, the "leading end" of the recording paper P is the leading end in the transport direction of the recording paper P. Furthermore, the "rear end" of the recording paper P is the rear end in the transport direction of the recording paper P. Furthermore, the passage of the recording paper P through a predetermined position such as the fixing device 30 is also called "paper feeding".

[0027] The fixing device 30 includes a fixing belt 31 as a first fixing member (heating rotating body) and a pressure roller 33 as a second fixing member (pressure rotating body). The fixing belt 31 is made up of an endless belt. The fixing belt 31 can also be described as a fixing film made of an endless film. The pressure roller 33, together with the fixing belt 31, forms a fixing nip section (fixing section) N that grips and transports the recording paper P. The fixing device 30 also includes a ceramic heater (hereinafter simply referred to as "heater") 34 as a heater (heating element, heating body) that generates heat to heat the fixing nip section N, and a heater holder 32 as a support member. The fixing nip section N, which is the contact section (nip section) between the fixing belt 31 and the pressure roller 33, is formed when the pressure roller 33 contacts the heater 34 (heater holder 32) via the fixing belt 31. In this embodiment, the heater holder 32 is pressed toward the pressure roller 33, thereby forming the fixing nip portion N.

[0028] The heater holder 32 is made of a rigid, heat-resistant material and has a roughly trough-shaped (roughly U-shaped) cross-section. The heater holder 32 supports the heater 34 in a groove provided on the lower surface in the center of the shorter side of the heater holder 32. The fixing belt 31 is loosely fitted onto the outer circumference of the heater holder 32 that supports the heater 34. The heater 34 is in contact with the inner surface of the fixing belt 31. Grease is applied to the inner surface (inner surface) of the fixing belt 31 to improve sliding performance with the heater 34. The pressure roller 33 is driven to rotate in the direction of arrow R3 (counterclockwise) in Figure 2 by the drive motor 37 (Figure 3). When the pressure roller 33 is driven to rotate, the fixing belt 31, which is pressed against the pressure roller 33 at the fixing nip portion N, rotates (circumferentially moves) in the direction of arrow R4 (clockwise) in Figure 2, following the movement of the pressure roller 33. The drive motor 37 functions as a drive source that generates the driving force to rotate the fixing belt 31 and the pressure roller 33.

[0029] Furthermore, the fixing device 30 has a fixing thermistor 35 as a temperature sensor, which constitutes a fixing temperature detection means for detecting the temperature of the surface (or back) of the fixing belt 31 or the heater 34. In this embodiment, multiple fixing thermistors 35 are provided (for example, at multiple locations in the longitudinal direction, or on the heater 34 and at other locations).

[0030] Furthermore, the fixing device 30 has a post-fixing sensor (recording material rear end sensor) 36 as a recording material detection means for detecting when the recording paper P has finished passing through the fixing nip section N. Here, the distance from the fixing nip section N (downstream end) to the post-fixing sensor 36 in the transport direction of the recording paper P is denoted as "E [mm]". The position of the post-fixing sensor 36 is represented by the position where the post-fixing sensor 36 detects the recording paper P (the position where the timing of "post-fixing sensor OFF" in Figure 7 is detected).

[0031] <Control configuration of an image forming apparatus> Next, the control configuration of the image forming apparatus 100 in this embodiment will be described. Figure 3 is a block diagram showing the schematic control configuration of the image forming apparatus 100 in this embodiment.

[0032] The image forming apparatus 100 has a control unit 40 as a control means for comprehensively controlling the image forming apparatus 100. The control unit 40 is composed of a CPU 41 as an arithmetic processing means (arithmetic processing unit), ROM 42, RAM 43, and EEPROM 44 as storage means (storage unit), a timer 45 as a time measurement means (time measurement unit), and an input / output circuit (not shown) as an input / output means (input / output unit). The CPU 41 controls the image forming apparatus 100. The ROM 42 stores control programs and application programs executed by the CPU 41. The RAM 43 functions as a work area for executing the processing of control programs. The EEPROM 44 stores data such as various settings that are desired to be retained even when the power to the image forming apparatus 100 is turned off. The timer 45 is capable of generating periodic time intervals for control and measuring the elapsed time between two points.

[0033] The control unit 40 is connected to an operation unit (UI) 130 provided on the image forming apparatus 100. The operation unit 130 is configured to have a display unit that displays information to the user (operator) under the control of the control unit 40, and an input unit that inputs various settings and other information to the control unit 40 based on user operations. The operation unit 130 may be configured to have a touch panel or the like that has the functions of both a display unit and an input unit. In this case, the operation unit 130 displays information on the screen to the user and accepts touch input from the user.

[0034] Furthermore, the control unit 40 is connected to various loads and sensors that constitute the fixing device 30. Specifically, the drive motor 37, which is the driving source for the pressure roller 33 and the fixing belt 31, and the heater 34, which has multiple heat sources, are connected to the control unit 40. In addition, multiple fixing thermistors 35 that detect the temperature of the surface of the fixing belt 31 and the heater 34, and a post-fixing sensor 36 that detects the timing when the recording paper P has been transported after fixing are also connected to the control unit 40. The operation of these drive motors 37, heaters 34, fixing thermistors 35 and post-fixing sensor 36 is controlled based on control signals from the control unit 40.

[0035] Furthermore, the control unit 40 is connected to an ambient temperature sensor 140, which is provided in the image forming apparatus 100 as an ambient temperature detection means. The ambient temperature sensor 140 detects the temperature around the image forming apparatus 100 (the temperature of the environment in which the image forming apparatus 100 is installed). The control unit 40 acquires the temperature information detected by the ambient temperature sensor 140 and uses it for various controls.

[0036] The control unit 40 controls the image forming apparatus 100 to execute a job. A job is a series of operations that start with a single start command and involve forming and outputting an image on one or more sheets of recording paper P. The user can input information about various settings, such as the type of recording paper P used in the job and the number of copies to be printed, from the operation unit 130 (or an external host device) to the control unit 40. Based on the various settings (job details) input by the user, the control unit 40 then executes the operations of the job, including image formation based on the image signal and fixing processing in the fixing apparatus 30.

[0037] <Drive control of the fixing device> Next, the drive control (recording paper transport control) of the fixing device 30 will be explained using Figure 4(a). Figure 4(a) is a graph showing the change in the rotational speed of the drive motor 37 from the start of operation.

[0038] The drive control of the fixing device 30 involves driving the drive motor 37 in a predetermined direction to rotate the pressure roller 33. When the pressure roller 33 is rotated, the fixing belt 31, which is pressed against the pressure roller 33 at the fixing nip section N, is driven in accordance with the pressure roller 33.

[0039] The CPU 41 controls the rotation speed (drive speed) of the drive motor 37 to stabilize the rotation speed of the pressure roller 33 at a predetermined rotation speed. In this embodiment, multiple rotation speeds are pre-set for the drive motor 37 depending on the type of recording paper P. The rotation speed of the drive motor 37 is uniquely determined by the type of recording paper P specified in the job. This rotation speed of the drive motor 37 is referred to as the "target speed Vtarget". The target speed Vtarget is set according to the type of recording paper P and is pre-stored in the ROM 42. Here, it is assumed that the rotation speed of the drive motor 37 = the rotation speed of the pressure roller 33 (rotation speed of the fixing belt 31, movement speed of the recording paper P).

[0040] After the drive motor 37 starts, it takes time to reach the target speed Vtarget and for the drive to stabilize. This time from the start of the drive motor 37's operation until the drive stabilizes is called the "stable drive time Vtime". The drive motor 37 is connected to a gear group that transmits the drive force of the drive motor 37 to the pressure roller 33. Therefore, the drive motor 37 is subjected to the drive load of the gear group that rotates the pressure roller 33 and the drive load of the pressure roller 33. In addition, since the fixing belt 31 rotates in accordance with the rotation of the pressure roller 33, the rotational load of the pressure roller 33 also contributes to the drive load of the drive motor 37.

[0041] The drive load of the gear group and the pressure roller 33, as well as the rotational load of the pressure roller 33, change depending on the ambient temperature around the image forming apparatus 100 (the temperature of the environment in which the image forming apparatus 100 is installed), as detected by the ambient temperature sensor 140. The load tends to increase in low-temperature environments. Furthermore, as the load increases, the stable operating time Vtime tends to increase. In addition, the stable operating time Vtime changes for each of the multiple target speeds Vtarget.

[0042] Therefore, a standard stable operating time Vtime is pre-set under the conditions where the startup time for the drive motor 37 is the longest within the expected range. This standard stable operating time Vtime information is pre-stored in the ROM 42. Based on this standard stable operating time Vtime information, the CPU 41 can determine the timing to start driving the drive motor 37 in accordance with the timing at which the driving of the pressure roller 33 needs to be stabilized. In other words, it can manage the startup time of the drive motor 37.

[0043] <Temperature control of the fixing device> Next, the temperature control of the fixing device 30 will be explained using Figure 4(b). Figure 4(b) is a graph showing the change in the temperature detected by the fixing thermistor 35 from the start of heating of the heater 34.

[0044] In order to fix the toner image onto the recording paper P, the temperature of the fixing nip N must be maintained at a predetermined temperature according to the type of recording paper P. This predetermined temperature is called the "target temperature Ttarget". The target temperature Ttarget is set according to the type of recording paper P and stored in the ROM 42 in advance. To maintain the temperature of the fixing nip N at the target temperature Ttarget, the temperature is detected by the fixing thermistor 35. The CPU 41 then acquires the temperature information detected by the fixing thermistor 35 and changes the power supplied to the heater 34 so that the temperature detected by the fixing thermistor 35 becomes the target temperature Ttarget. In this way, the CPU 41 performs temperature control of the fixing device 30 (heater 34).

[0045] The fixing thermistor 35, as a fixing temperature detection means, only needs to be able to detect a temperature correlated with the temperature of the fixing nip N, and specifically, it may detect the temperature of the surface (or back) of the fixing belt 31 or the heater 34. Furthermore, the temperature detection results from multiple fixing thermistors 35 can be used individually for control, for example, in relation to their installation positions. Furthermore, the detection results from multiple fixing thermistors 35 can be used after appropriate processing, such as averaging. Here, the temperature detection result from one fixing thermistor 35 will be used as a representative example from among the multiple fixing thermistors 35 for explanation. Moreover, the present invention is not limited to a configuration in which multiple fixing thermistors 35 are provided as a fixing temperature detection means, but may also be a configuration in which only one temperature sensing element such as a thermistor is provided. Here, the temperature detected by the fixing thermistor 35 may be referred to as the "detected temperature of the fixing thermistor 35" or the "temperature of the fixing nip N".

[0046] When performing the fixing process in a job, the power supplied to the heater 34 is controlled, that is, the temperature control of the fixing device 30 is performed. This temperature control of the fixing device 30 includes "heater start-up control" to raise the temperature of the fixing nip N to the target temperature Ttarget, and "PI control" to maintain the temperature of the fixing nip N at the target temperature Ttarget. When power is supplied to the heater 34, the heater start-up control is performed first to raise the temperature of the fixing nip N to the target temperature Ttarget. Then, when the temperature detected by the fixing thermistor 35 reaches the target temperature Ttarget, the control switches from "heater start-up control" to "PI control".

[0047] The time required for heater startup control is defined as "heater startup time Ttime". Heater startup time Ttime varies depending on the conditions, even if the target temperature Ttarget is constant. For example, when heater startup control is performed when the fixing device 30 has already accumulated heat, the time will be longer when the fixing device 30 has not accumulated any heat. Therefore, a reference heater startup time Ttime is set in advance for the condition in which the time required to start up the heater 34 is the longest within the expected range. This reference heater startup time Ttime information is stored in ROM 42 in advance. Based on this reference heater startup time Ttime information, the CPU 41 can determine the timing to start temperature control of the heater 34 to match the timing when it wants to raise the temperature of the fixing nip section N to the required temperature. In other words, it can manage the time related to the startup of the heater 34.

[0048] Furthermore, it is desirable that the temperature control of the fixing device 30 be performed in such a way that the temperature of the pressure roller 33 in the circumferential direction and the temperature in the longitudinal direction are kept uniform. For this reason, temperature control is performed when the pressure roller 33 (drive motor 37) is being driven. If the temperature control of the fixing device 30 is performed at a high temperature while the drive motor 37 is stopped, only the fixing nip portion N where the pressure roller 33 and the heater 34 are pressed together will heat up, and more heat than that expected at the target temperature Ttarget will be applied to one point in the circumferential direction of the pressure roller 33 while the drive motor 37 is being driven. In this state, there is a possibility of a decrease in image quality due to temperature unevenness, and in some cases, an error due to overheating of the heater 34. For this reason, in this embodiment, the drive control and temperature control of the fixing device 30 are started and stopped in sync. In other words, in this embodiment, the timing of starting the drive of the drive motor 37 ("drive start timing") and the timing of starting the temperature control of the heater 34 ("temperature control start timing") are synchronized. In this embodiment, the drive of the drive motor 37 and the temperature control of the heater 34 are started substantially simultaneously. In this embodiment, the timing for stopping the drive of the drive motor 37 ("drive stop timing") and the timing for stopping the temperature control of the heater 34 ("temperature control stop timing") are synchronized. In this embodiment, the drive of the drive motor 37 and the temperature control of the heater 34 are stopped substantially simultaneously. However, if the above-mentioned problems can be sufficiently suppressed, the drive control and temperature control of the fixing device 30 may be started or stopped at timings that are, for example, slightly out of sync.

[0049] Here, the longer of the stable operating time Vtime and the heater start-up time Ttime can be adopted as the "start-up time Stime," which is the time required to start up the fixing device 30. In this embodiment, the heater start-up time Ttime is adopted as the start-up time Stime (Stime = Ttime) and this will be explained accordingly.

[0050] <Control timing of the fixing device> Next, using Figure 5, we will explain several timings in which the position of the recording paper P relative to the fixing device 30 differs, which can be used as the control timing for the fixing device 30. Figures 5(a), (b), and (c) are schematic cross-sectional views of the vicinity of the fixing device 30, respectively, to explain several timings in which the position of the recording paper P differs with respect to the fixing nip N.

[0051] As shown in Figure 5(a), the timing at which the leading edge of the recording paper P enters the fixing nip N is defined as the "recording paper leading edge entry timing." The act of the leading edge of the recording paper P entering the fixing nip N is also simply called "leading edge entry."

[0052] As shown in Figure 5(b), the timing when the trailing edge of the recording paper P has finished passing through the fixing nip section N is defined as the "recording paper nip exit timing." The moment when the trailing edge of the recording paper P has finished passing through the fixing nip section N is also simply called "nip exit."

[0053] As shown in Figure 5(c), the timing at which the trailing edge of the recording paper P has finished passing through the post-fixing sensor 36 is defined as the "recording paper trailing edge exit timing." Specifically, the recording paper trailing edge exit timing is the timing at which the post-fixing sensor 36 changes from detecting the presence of recording paper P to detecting the absence of recording paper P. The moment when the trailing edge of the recording paper P has finished passing through the post-fixing sensor 36 is also simply called "trailing edge exit."

[0054] The time (period) during which the recording paper P passes through the fixing nip section N is defined as the "paper passage time". The paper passage time is the time (period) from the state shown in Figure 5(a) to the state shown in Figure 5(b).

[0055] Furthermore, the time (period) during which the recording paper P does not pass through the fixing nip section N is defined as the "non-feeding time." In particular, the non-feeding time between the preceding recording paper P and the succeeding recording paper P during continuous feeding is defined as the "inter-paper time (or inter-paper time)." Inter-paper time is the time (period) during continuous feeding from the state shown in Figure 5(b) (preceding recording paper P) to the state shown in Figure 5(a) (successing recording paper P).

[0056] Next, using Figure 6(a), we will explain various timeframes related to the recording paper P passing through the fixing nip section N during continuous paper feeding. Figure 6(a) is a schematic diagram showing the positional relationship of the first to third sheets of recording paper P passing through the fixing nip section N during continuous paper feeding.

[0057] The time (period) between the entry of the leading edge of the preceding recording paper P and the entry of the leading edge of the following recording paper P is defined as "TopToTop".

[0058] Furthermore, the time (period) between the exit of the nip of the preceding recording paper P and the entry of the leading edge of the following recording paper P is defined as "EndToTop". This EndToTop coincides with the aforementioned inter-paper time. Therefore, the inter-paper time is also called "Inter-paper time EndToTop".

[0059] <Adjustment control for forming the toner image> In addition to forming an image on the recording paper P, the image forming apparatus 100 may also form a toner image for adjustment.

[0060] The following types of toner images may be formed for adjustment purposes: For example, a halftone toner patch image may be formed to detect the current toner density. Pattern images may also be formed to detect the amount of color shift for each color: yellow, magenta, cyan, and black. In addition, multi-tone patches may be formed to reflect the actual density of each step in the gradation of each color in the gamma curve.

[0061] As an example, let's explain color misalignment correction control. The image forming apparatus 100, which is capable of forming color images, superimposes multiple images of different colors. If the image formation position of each color is shifted from the desired position, color misalignment will occur. To suppress this color misalignment, the CPU 41 controls the laser light irradiated onto the photosensitive drums 11Y, 11M, 11C, and 11K of each color. For example, the CPU 41 corrects color misalignment in the sub-scanning direction (the direction of movement of the surface of the intermediate transfer belt 21) by adjusting the image writing timing of colors other than the reference color (e.g., yellow) (e.g., magenta, cyan, black). The CPU 41 controls the formation of a patch pattern on the intermediate transfer belt 21 in a non-paper-feeding state to adjust this image writing timing. The CPU 41 also controls the reading of this patch pattern by a patch sensor (not shown) composed of optical sensors to detect the amount of color misalignment. Then, the CPU 41 corrects color misalignment by correcting the writing timing of the toner images of colors other than the reference color based on the interval from the patch pattern of the reference color to the patch patterns of each color other than the reference color. The patch pattern for color shift correction is predetermined, and time is required for the patch sensor to read this patch pattern. This time for reading the patch pattern is called "color shift correction time Ctime".

[0062] As another example, let's explain density correction control. When the image forming apparatus 100 forms an image, it uses laser light to form an electrostatic latent image on the photosensitive drum 11. The amount of laser light (laser intensity) determines the depth of the electrostatic latent image on the photosensitive drum 11 (the amount by which the absolute value of the potential of the exposed area decreases from the absolute value of the potential of the unexposed area). The depth of the electrostatic latent image is related to the amount of toner transferred from the developing apparatus 14 to the photosensitive drum 11. Therefore, the laser intensity affects the density of the toner image. By setting the laser intensity and high-voltage output value to appropriate values, the maximum density and halftone gradation characteristics of each color are matched. Image density control to maintain a constant maximum density of each color is called "Dmax control". In addition, image density control to maintain the halftone gradation characteristics linear with respect to the image signal is called "Dhalf control". Dmax control is designed to suppress scattering and poor fixing of overlapping characters due to excessive toner application, and to improve the long-term stability of image density by correcting density fluctuations caused by increased cumulative usage of the image forming apparatus 100 and environmental changes. The CPU 41 corrects the laser light intensity as follows: The CPU 41 controls the formation of a patch pattern for density correction to adjust the laser light intensity on the intermediate transfer belt 21 when no paper is being fed. The CPU 41 also controls the formation of this patch pattern by reading it using a patch sensor (not shown) composed of optical sensors, and to detect the density level of each color. The timing of the laser light intensity update may be set as follows to form an image with stable density regardless of environmental changes or increased cumulative usage of the image forming apparatus 100: For example, Dmax control is performed between sheets of paper in the middle of a job, and the laser light intensity is updated. The patch pattern for density correction is predetermined, and time is required to read this patch pattern using the patch sensor. This time for reading the patch pattern is called the "density correction time Dtime".

[0063] The above color shift correction control and density correction control are performed at a reduced productivity in image formation, with extended inter-paper time due to the addition of color shift correction time Ctime and density correction time Dtime. In other words, color shift correction control and density correction control are performed with the transport of recording paper P temporarily suspended until the reading of the patch patterns for color shift correction and density correction is complete.

[0064] <Adjustment control to prevent toner image formation> As mentioned above, the image forming apparatus 100 has adjustment controls that form a toner image for adjustment, as well as adjustment controls that are necessary but do not form a toner image.

[0065] For example, if the amount of toner stored in the toner storage unit (not shown) that supplies toner to the developing unit 14 becomes low, toner replenishment control, which is an adjustment control that forcibly sends toner from the toner storage unit to the developing unit 14, may be performed. The time required for toner replenishment varies depending on the amount of toner remaining in the toner storage unit. The time required to replenish toner until a predetermined amount of toner can be supplied from the toner storage unit to the developing unit 14 in toner replenishment control is defined as "toner replenishment time TRtime".

[0066] Toner replenishment control is an adjustment control that prevents the formation of a toner image. However, when performed during a job, the toner replenishment time TRtime is taken into account, and the inter-paper time is extended. In other words, toner replenishment control is performed by temporarily suspending the transport of the recording paper P until the toner replenishment is complete.

[0067] <Productivity control of image forming apparatus> The productivity of the image forming apparatus 100 (the specified number of prints per unit time for each type of recording paper P used; hereinafter also referred to as "PPM") can be expressed by the aforementioned TopToTop (Figure 6(a)). TopToTop is the time it takes for the leading edge of one recording paper P to pass through a predetermined position from the leading edge of the preceding recording paper P to the leading edge of the following recording paper P. In other words, TopToTop is the sum of the paper passage time and the inter-paper time EndToTop.

[0068] Here, the adjustment controls for forming a toner image and those for not forming a toner image are performed in a non-paper-feed state. Therefore, the specified paper-to-paper time EndToTop (also referred to here as the "reference paper-to-paper time") is added to the color misalignment correction time Ctime, density correction time Dtime, and toner replenishment time TRTime, and the TopTopTop time is redetermined. The reference paper-to-paper time is set according to the information of the recording paper P (size, basis weight, etc.) and stored in the ROM 42 in advance. In other words, when color misalignment correction control, density correction control, and toner replenishment control are performed, the paper-to-paper time EndToTop becomes longer, resulting in decreased productivity. In this case, the non-paper-feed time at the fuser nip section N becomes longer, and the drive control and temperature control of the fuser 30 are performed in a non-paper-feed state where the recording paper P has not passed through. The operation of the fuser 30 in this state is also called "idle rotation" of the fuser 30.

[0069] <Lifespan of components in the fixing device> When the fixing device 30 is driven and its temperature is controlled, wear and tear occur in the components that make up the fixing device 30. The lifespan of the fixing device 30 is partly due to the aging of its components, but a large part is also due to wear and tear.

[0070] The purpose of operating the fuser unit 30 is to fix the unfixed toner image on the recording paper P to the recording paper P by applying heat and pressure to the recording paper P. Therefore, if the fuser unit 30 is operated idle for a long time without paper feeding, it will unnecessarily consume the lifespan of the fuser unit 30. In other words, by controlling the fuser unit 30 to minimize idle rotation, the lifespan of the fuser unit 30 can be extended.

[0071] <Stopping and restarting temperature control and drive control between sheets of paper> If the overall paper-to-paper time in the image forming apparatus 100 increases, the fuser unit 30 will unnecessarily perform temperature control and drive control. Therefore, it is effective to stop the temperature control and drive control of the fuser unit 30 when no paper is being fed.

[0072] Using Figure 7, the stopping and restarting of the temperature control and drive control of the fixing device 30 between sheets of paper during continuous paper feeding will be explained. Figure 7 shows a graph illustrating the changes in the rotational speed of the drive motor 37 and the changes in the detected temperature of the fixing thermistor 35, as well as a schematic diagram of the positional relationship of the recording paper P corresponding to the time axis of the graph.

[0073] Figure 7(a) is a graph showing the change in rotational speed of the drive motor 37 when the drive control of the fuser unit 30 is stopped and restarted between sheets of paper during continuous paper feeding. Figure 7(b) is a graph showing the change in the detected temperature of the fuser thermistor 35 when the temperature control of the fuser unit 30 is stopped and restarted between sheets of paper during continuous paper feeding. In particular, Figure 7(b) shows the change in the detected temperature of the fuser thermistor 35 when the temperature control of the fuser unit 30 is restarted when the fuser unit 30 has not accumulated heat.

[0074] First, to ensure that the recording paper P has completely passed through the fuser nip section N, it is necessary to determine whether or not to stop the drive control and temperature control of the fuser device 30 at the timing when the trailing edge of the recording paper is removed (Figure 5(c)) (Figure 7(a)).

[0075] However, even at the timing when the trailing edge of the recording paper is removed, it is desirable not to unconditionally stop the drive control and temperature control of the fuser unit 30. Generally, if the paper inter-page time EndToTop is longer than the startup time Stime, it is possible to stop the drive control and temperature control of the fuser unit 30. More specifically, see the following equation, Etime = Distance E ÷ Target Driving Speed ​​V The result of calculating the time using this method is called the "nip sensor time Etime". Here, distance E is the transport distance of the recording paper P from the nip exit to the trailing end exit of the recording paper P, and the nip sensor time Etime is the time it takes for the recording paper P to move distance E at the target drive speed Vtarget.

[0076] And then, EndToTop-Etime-Stime> 0 If the conditions are met, the drive control and temperature control of the fixing device 30 can be stopped.

[0077] Next, the "restart time Rtime" is calculated to determine the "restart timing TA" for restarting the temperature control and drive control of the fuser 30 so that the start-up of the fuser 30 is completed before the leading edge of the subsequent recording paper P enters the fuser nip section N (Figure 7(b)).

[0078] In other words, the time from the moment the drive control and temperature control of the fixing device 30 are stopped until the moment the drive control and temperature control of the fixing device 30 are restarted is defined as "restart time Rtime". The restart time Rtime is given by the following formula: Rtime = EndToTop - Etime - Stime This can be calculated using the formula. Furthermore, the timing at which the restart time Rtime elapses is the "restart timing TA" at which the drive control and temperature control of the fixing device 30 are restarted.

[0079] <Restarting control when the fuser is accumulating heat> Next, we will explain the control process when restarting the temperature control of the fixing device 30 while the fixing device 30 is accumulating heat between sheets of paper during continuous feeding.

[0080] Figure 7(c) is a graph showing the change in the detected temperature of the fixing thermistor 35 when the temperature control of the fixing device 30 is restarted while the fixing device 30 is accumulating heat, and the control of this embodiment is not applied (comparative example).

[0081] When the temperature control of the fixing device 30 is stopped while the fixing device 30 is not storing heat, the detected temperature of the fixing thermistor 35 changes as shown in Fig. 7(b). When the temperature control of the fixing device 30 is stopped while the fixing device 30 is not storing heat, the fixing device 30 can no longer maintain its temperature, and the temperature drops rapidly. Therefore, as the start-up time Stime of the fixing device 30, even in a state where the temperature drops rapidly like this, a reference paper interval time Ttimebase is set such that the temperature reaches the target temperature Ttarget before the leading end of the subsequent recording paper P enters the fixing nip portion N. Thereby, before the leading end of the subsequent recording paper P enters the fixing nip portion N, it is possible to control the detected temperature of the fixing thermistor 35 to rise to the target temperature Ttarget.

[0082] On the other hand, when the temperature control of the fixing device 30 is stopped while the fixing device 30 is storing heat, the detected temperature of the fixing thermistor 35 changes as shown in Fig. 7(c). Since the fixing device 30 is storing heat, the temperature of the fixing device 30 does not drop rapidly even when the temperature control of the fixing device 30 is stopped. In this case, the temperature rise time Ttime’ which is the actual time required for the temperature rise of the fixing device 30 may be shorter than the reference paper interval time Ttimebase (Ttime’ < Ttimebase). Therefore, if the restart time Rtime is set by referring to the reference paper interval time Ttimebase, since the actual temperature rise is faster, the idling time of the fixing device 30 becomes longer compared to the state where the fixing device 30 is not storing heat. This idling of the fixing device 30 is wasteful. Therefore, in this embodiment, it is possible to extend the restart time Rtime based on the detected temperature of the fixing thermistor 35 after the calculated restart time Rtime as described above has elapsed (before restarting the temperature control).

[0083] An example of a specific method for extending the restart time Rtime is described below. After the restart time Rtime calculated using the reference inter-paper time Ttimebase has elapsed (before restarting temperature control), the temperature detected by the fuser thermistor 35 is obtained. This temperature detected by the fuser thermistor 35 is defined as the "restart decision temperature CheckTemp". The difference between the restart decision temperature CheckTemp and the target temperature Ttarget is calculated, and if the difference is less than or equal to a predetermined value (10°C in this embodiment), the restart time Rtime is recalculated. In other words, if the restart decision temperature CheckTemp is 10°C or less lower than the target temperature Ttarget, the restart time Rtime is recalculated. The restart time Rtime can be recalculated, for example, as follows: The heater start-up time Ttime (=Stime) is set to a value obtained by adding -2 seconds to the reference inter-paper time Ttimebase (i.e., subtracting 2 seconds), and the restart time Rtime is recalculated. In other words, a fixed value (2 seconds) is added to the restart time Rtime calculated using the reference inter-page time Ttimebase to obtain the restart time Rtime after recalculation.

[0084] Furthermore, the method for recalculating the restart time Rtime is not limited to the method of subtracting a fixed value (2 seconds) from the heater start-up time Ttime (=Stime) as described above. For example, it may be possible to calculate the time required to start up the heater 34 by predicting the temperature start-up time Ttime' and feed that back into the heater start-up time Ttime. The calculation method is not limited as long as the restart time Rtime can be recalculated so that the restart time Rtime is extended to reduce unnecessary idle rotation of the fuser 30 and the fuser 30 starts up before the leading edge of the subsequent recording paper P enters the fuser nip section N.

[0085] Furthermore, in this embodiment, the restart decision temperature CheckTemp is obtained after the restart time Rtime has elapsed, but the restart decision temperature CheckTemp may be obtained approximately simultaneously with or before the restart time Rtime has elapsed. The initially set restart time Rtime can be extended to reduce unnecessary idle rotation of the fuser 30 and to complete the startup of the fuser 30 before the leading edge of the subsequent recording paper P enters the fuser nip section N.

[0086] Figure 7(d) shows the change in the temperature detected by the fuser thermistor 35 when the restart time Rtime is recalculated according to this embodiment and the restart timing TA is changed. In this case, as a result of recalculating the restart time Rtime, it is possible to delay the restart of the drive control and temperature control of the fuser device 30 by 2 seconds compared to the case in Figure 7(c). In other words, the restart time Rtime after recalculation in Figure 7(d) becomes the stop time of the fuser device 30. Therefore, the idle rotation of the fuser device 30 can be reduced compared to the case in Figure 7(c). In addition, since the time required to start up the heater 34 is also shorter, the start-up of the fuser device 30 can be completed before the leading edge of the subsequent recording paper P enters the fuser nip section N.

[0087] <Print control of the fuser unit> Next, we will describe the print control of the fuser 30, which is a series of controls for executing the fixing process in a job. Figure 8 is a flowchart of the print control of the fuser 30. Here, we will explain assuming that the drive control and temperature control of the fuser 30 are stopped and restarted between sheets of paper during continuous feeding. In the flowchart, the symbol "S" attached to each process means "step".

[0088] S101: CPU41 waits until a job start command is received, and then proceeds to process S102.

[0089] S102:CPU41 acquires job details (job information) that include information about the recording paper P specified in the job (size, basis weight, etc.).

[0090] S103: The CPU 41 sets a target temperature Ttarget according to the job details obtained in S102, and starts heating the heater 34 so that the temperature detected by the fixing thermistor 35 becomes the target temperature Ttarget (start process).

[0091] S104: The CPU 41 sets a target speed Vtarget according to the job details obtained in S102, and starts driving the drive motor 37 at the target speed Vtarget to rotate the pressure roller 33 and the fixing belt 31 (start process).

[0092] S105: The CPU 41 waits until the rotation speed of the drive motor 37 stabilizes at the target speed Vtarget set in S104, and then proceeds to process S106.

[0093] S106: The CPU 41 waits until the temperature detected by the fixing thermistor 35 reaches the target temperature Ttarget set in S103, and then proceeds to process S107.

[0094] S107: The CPU 41 maintains drive control and temperature control of the fuser 30 until the trailing edge of the recording paper P passes through the fuser nip section N and the post-fusing sensor 36 detects that the trailing edge of the recording paper P has come out.

[0095] S108: The CPU 41 performs paper spacing control of the fuser 30. Paper spacing control will be described later using Figure 9.

[0096] S109: CPU41 determines whether the output of all images in the job has finished, and repeats the processes from S107 to S109 until it is finished, then proceeds to process S110.

[0097] S110: Regardless of the target temperature Ttarget setting, the CPU 41 stops supplying power to the heater 34 (temperature control of the fuser unit 30).

[0098] S111: The CPU 41 stops the drive of the drive motor 37 (drive control of the fixing device 30).

[0099] Furthermore, once the CPU 41 stops the temperature control and drive control of the fuser unit 30 as described above, it waits until the next job is submitted.

[0100] <Paper spacing control> Next, we will explain the paper spacing control in S108 of Figure 8. Figure 9 is a flowchart of the paper spacing control.

[0101] S201: The CPU 41 obtains the paper-to-paper time EndToTop between the recording paper P whose trailing edge has been detected by the post-fixing sensor 36 and the subsequent recording paper P, and proceeds to processing S202. The control for obtaining the paper-to-paper time EndToTop will be described later using Figure 10.

[0102] S202: The CPU 41 sets a restart time Rtime to determine the restart timing TA for restarting the temperature control and drive control of the fuser 30, according to the acquired inter-paper time EndToTop. The restart time Rtime is the time determined by the method described in the section above, "<Stopping and restarting temperature control and drive control between papers>". The restart time Rtime set here is sufficient to guarantee the time required for the fuser 300 to start up through the drive control and temperature control of the fuser 30, even when the fuser 30 is under heavy drive load or has not accumulated heat. The CPU 41 stores the calculated restart time Rtime in the RAM 43 and then proceeds to the process in S203.

[0103] S203: The CPU 41 performs the process of stopping the temperature control of the fuser unit 30. The CPU 41 stores the currently set target fixing temperature Ttarget in RAM 43 in order to set it as the target temperature Ttarget when the fuser unit 30 is restarted, and then stops supplying power to the heater 34. After the CPU 41 has finished the process of stopping the temperature control of the fuser unit 30, it proceeds to the process in S204.

[0104] S204: The CPU 41 performs a stop operation for the drive control of the fuser unit 30. The CPU 41 stores the currently set target speed Vtarget of the drive motor 37 in the RAM 43 in order to set it as the target speed Vtarget when the fuser unit 30 is restarted, and then stops the drive of the drive motor 37. After the CPU 41 has finished the stop operation for the drive control of the fuser unit 30, it proceeds to the process in S205.

[0105] S205: The CPU 41 waits for the restart time Rtime set in S202 to elapse. The following methods can be used to determine the elapsed time. For example, an event timer (management timer) for the restart time Rtime is set as a trigger when the trailing edge of the recording paper P is pulled out, and the restart timing TA is determined after waiting for the time to expire. Alternatively, the following method may be used to wait for the elapsed time. For example, a countdown process may be performed by polling at predetermined intervals, and the restart timing TA may be determined when the counter reaches 0. During this restart time Rtime, the temperature control and drive control of the fuser 30 are stopped, so the amount of heat stored in the fuser 30 decreases. In particular, if the temperature of the environment in which the image forming apparatus 100 is installed, as detected by the ambient temperature sensor 140, is low, the amount of temperature drop of the fuser 30 will be large. On the other hand, for example, depending on the number of sheets of recording paper P that have been fed through before the fuser 30 stop process is executed by the paper spacing control, the amount of temperature drop of the fuser 30 may be small. If CPU41 determines that the restart time Rtime has elapsed (the restart timing TA has been reached), it proceeds to process S206.

[0106] S206: The CPU 41 obtains the restart decision temperature CheckTemp detected by the fuser thermistor 35. This allows the CPU 41 to understand the heat storage status of the fuser unit 30 while waiting for the restart time Rtime to elapse in S205. The CPU 41 stores the obtained restart decision temperature CheckTemp in the RAM 43 and proceeds to processing in S207.

[0107] S207: The CPU 41 calculates the temperature difference between the target temperature Ttarget stored in RAM 43 and the restart decision temperature CheckTemp also stored in RAM 43. By determining the temperature difference between the target temperature Ttarget and the restart decision temperature CheckTemp, information regarding the remaining time required for the temperature of the fuser 30 to rise can be obtained. Specifically in this embodiment, the restart time Rtime is updated by the method described in the section above, "<Restarting control when the fuser is accumulating heat>". At this point, the CPU 41 has timed out the management timer for the restart time Rtime, so it sets the timer to wait for the difference between before and after the update of the restart time Rtime, and proceeds to the process in S208.

[0108] S208: The CPU 41 waits for the restart time Rtime, which was reset in S207, to elapse (until the reset restart timing TA is reached). The elapsed time Rtime (until the restart timing TA is reached) is optimized in S206 and S207 according to the time required for the fuser unit 30 to rise in temperature. Therefore, at this timing, the CPU 41 restarts the fuser unit 30, that is, the drive control and temperature control of the fuser unit 30.

[0109] S209: The CPU 41 restarts heating the heater 34 so that the temperature detected by the fuser thermistor 35 becomes the target fuser temperature Ttarget stored in the RAM 43.

[0110] S210: The CPU 41 restarts the drive motor 37 so that its rotational speed becomes the target speed Vtarget stored in the RAM 43.

[0111] S211: The CPU 41 waits until the rotation speed of the drive motor 37 stabilizes at the target speed Vtarget set in S210, and then proceeds to process S212.

[0112] S212: The CPU 41 waits until the temperature detected by the fuser thermistor 35 reaches the target temperature Ttarget set in S209, and then terminates the paper spacing control.

[0113] Figure 10 is a flowchart of the control for obtaining the paper-to-paper time EndToTop in S201 of Figure 9.

[0114] S301: The CPU 41 sets the reference paper spacing time as the paper spacing time EndToTop and stores it in the RAM 43. The reference paper spacing time is stored in the ROM 42 and is uniquely determined according to the job details, including information about the recording paper P (size, basis weight, etc.).

[0115] S302: CPU41 determines whether toner replenishment control is required. If toner replenishment control is required, CPU41 proceeds to process S303. On the other hand, if toner replenishment control is not required, CPU41 skips process S303 and proceeds to process S304.

[0116] S303: The CPU 41 adds the toner replenishment time TRTime to the paper-to-paper time stored in RAM 43, and sets the paper-to-paper time EndToTop by adding the time required for correction control necessary for the reference paper-to-paper time. Then, the CPU 41 stores this paper-to-paper time EndToTop in RAM 43 and proceeds to processing S304.

[0117] S304: CPU41 determines whether concentration correction control is necessary. If concentration correction control is necessary, CPU41 proceeds to process S305. On the other hand, if concentration correction is not necessary, CPU41 skips process S305 and proceeds to process S306.

[0118] S305: The CPU 41 adds the density correction time Dtime to the paper-to-paper time stored in RAM 43, and sets the paper-to-paper time EndToTop by adding the time required for the correction control necessary for the reference paper-to-paper time. Then, the CPU 41 stores this paper-to-paper time EndToTop in RAM 43 and proceeds to the process in S306.

[0119] S306: CPU41 determines whether or not to perform color shift correction control. If color shift correction control is necessary, CPU41 proceeds to process S307. On the other hand, if color shift correction control is not necessary, CPU41 skips process S307 and terminates the control to acquire the inter-paper time.

[0120] S307: The CPU 41 adds the color shift correction time Ctime to the paper-to-paper time stored in RAM 43, and sets the time obtained by adding the time required for the correction control necessary for the reference paper-to-paper time as the paper-to-paper time EndToTop. Then, the CPU 41 stores the paper-to-paper time EndToTop in RAM 43 and terminates the control for acquiring the paper-to-paper time.

[0121] <Effects> As described above, the image forming apparatus 100 of this embodiment comprises an image forming unit 90 that forms a toner image on a recording material (recording paper) P, and a fixing apparatus 30 that performs a fixing process to fix the toner image formed by the image forming unit 90 to the recording material P, and includes a rotatable first fixing member (fixing belt) 31, a rotatable second fixing member (pressure roller) 33 that forms a fixing nip portion N together with the first fixing member 31, a heater (ceramic heater) 34 that generates heat to heat the fixing nip portion N, and a first The fixing device 30 includes a drive source (drive motor) 37 that generates a driving force to rotate the fixing member 31 and the second fixing member 33, and a temperature sensor (fixing thermistor) 35 that detects a temperature correlated with the temperature of the fixing nip section N, and a heater 34 that heats the fixing nip section N and performs fixing processing by sandwiching and transporting the recording material P between the first fixing member 31 and the second fixing member 33 in the fixing nip section N, and a control unit 40 that can control the drive source 37 and the heater 34. In this embodiment, the control unit 40 performs a start process (for example, S205-S212 in Figure 9) to change the timing at which the drive of the drive source 37 and the temperature control of the heater 34 are started in relation to the timing at which the first recording material P after the start process reaches the fixing nip section N, based on the detected temperature (CheckTemp), which is the temperature detected by the temperature sensor 35 in the first state, and the target temperature (Ttarget), which is the target temperature detected by the temperature sensor 35 in the second state. This control unit 40 performs a start process (for example, S206-S210 in Figure 9) to change the timing at which the drive of the drive source 37 and the temperature control of the heater 34 are started in relation to the timing at which the first recording material P after the start process reaches the fixing nip section N.

[0122] In this embodiment, if the temperature difference between the target temperature and the detected temperature is greater than a predetermined value (10°C in this embodiment), the control unit 40 controls the timing between the start of driving the drive source 37 and temperature control of the heater 34 and the timing when the first recording material P reaches the fixing nip section N to be a first time (for example, Ttime in Figure 7(b)). On the other hand, if the temperature difference between the target temperature and the detected temperature is less than or equal to the predetermined value, the control unit 40 controls the timing between the start of driving the drive source 37 and temperature control of the heater 34 and the timing when the first recording material reaches the fixing nip section N to be a second time (for example, Ttime' in Figure 7(d)) ​​which is shorter than the first time. In this embodiment, the first time (Ttimebase) is set in advance. Also, in this embodiment, the difference between the first time and the second time (2 seconds in this embodiment) is set in advance.

[0123] Furthermore, in this embodiment, when the control unit 40 performs a stop process to return to the first state by stopping the drive of the drive source 37 and the temperature control of the heater 34 after the timing when the first recording material P has finished passing through the fixing nip section N in the second state, during the execution of a job to form toner images on multiple recording materials P, it is possible to perform control to change the timing at which the drive of the drive source 37 and the temperature control of the heater 34 are started in the start process before the second recording material P, which is transported to the fixing nip section N after the first recording material, reaches the fixing nip section N. In this embodiment, the control unit 40 controls the system to perform the stop process if the time between the timing when the rear end of the first recording material P in the transport direction has finished passing through the fixing nip section N and the timing when the front end of the second recording material P in the transport direction reaches the fixing nip section (paper-to-paper time) is longer than a predetermined time. In this embodiment, the first fixing member 31 is composed of an endless belt, the heater 34 contacts the inner circumferential surface of the first fixing member 31, and the second fixing member 33 contacts the heater 34 via the first fixing member 31.

[0124] As mentioned above, if the timing for restarting the fuser unit 30 during continuous paper feeding is fixed regardless of the heat storage status of the fuser unit 30, the fuser unit 30 may complete its startup earlier than the preset time if it is storing heat. In this case, the idle time of the fuser unit 30 becomes unnecessarily long, leading to a shortened lifespan of the fuser unit 30.

[0125] In contrast, according to this embodiment, the timing for restarting the fuser 30 during continuous paper feeding can be readjusted and optimized according to the heat storage status of the fuser 30. This makes it possible to reduce unnecessary idle rotation of the fuser 30 while appropriately maintaining the amount of heat supplied to the recording paper P, thereby suppressing unnecessary consumption of the fuser 30's lifespan.

[0126] Thus, according to this embodiment, by appropriately setting the timing for starting the operation of the fixing device 30 from a stopped state, it is possible to reduce unnecessary idle rotation of the fixing device 30 and suppress unnecessary consumption of the fixing device 30's lifespan.

[0127] [Example 2] Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0128] In this embodiment, another example of a method for setting the timing for starting the operation of the fixing device 30 from a state in which the operation of the fixing device 30 has stopped will be described.

[0129] Furthermore, in Example 1, the control for restarting the operation of the fuser 30, which had been temporarily stopped between sheets of paper during continuous paper feeding, was described. However, the present invention can also be applied to the control for starting the operation of the fuser 30 at the start of a job. In this example, the control at the start of a job will also be described.

[0130] <Time (Tc) until the recording paper enters the fixing nip section> In this embodiment, the time from the timing of deciding whether to stop or restart (start) the temperature control and drive control of the fuser 30 until the recording paper P enters the fuser nip section N is defined as the "nip entry time (control time) Tc". The nip entry time Tc can be used not only for control to restart the operation of the fuser 30 that has been temporarily stopped between sheets of paper during continuous feeding, but also for control to start the operation of the fuser 30 at the start of a job.

[0131] Figure 6(b) is a schematic diagram showing the positional relationship between the first and second sheets of recording paper P as they are transported toward the fixing nip section N at the start of a job. As described in Example 1, when the image forming apparatus 100 receives a job, it prepares for image formation and begins forming a toner image on the photosensitive drum 11. Meanwhile, the transport mechanism for the recording paper P performs paper feeding and transport operations so that the toner image formed on the intermediate transfer belt 21 can be transferred to a predetermined position on the recording paper P. The time from when the image forming apparatus 100 receives a job until the recording paper P enters the fixing nip section N, including the time for such image formation preparation, paper feeding, and transport operations, is defined as "pre-rotation time PreRot".

[0132] The previous rotation time (PreRot) and the paper-to-paper time (EndToTop) are set as the initial values ​​for the nip entry time (Tc), as will be described later.

[0133] <Stopping and restarting temperature control and drive control between sheets of paper> As explained in Example 1, if the inter-paper time for the image forming apparatus 100 becomes long overall, the fuser 30 will unnecessarily perform temperature control and drive control. Therefore, it is effective to stop the temperature control and drive control of the fuser 30 when no paper is being fed.

[0134] In the following section, we will first describe how the method of this embodiment can be applied to control the operation of the fixing device 30, which has been temporarily stopped between sheets of paper during continuous paper feeding.

[0135] <Calculation of recovery time Ttime [sec]> As explained in Example 1, the longer of the stable operating time Vtime and the heater start-up time Ttime can be used as the time required to start up the fixing device 30 (start-up time Stime in Example 1). In this example, as in Example 1, the heater start-up time Ttime is used as the time required to start up the fixing device 30. In this example, the time required to start up the fixing device 30 (=Ttime) is referred to as the "recovery time Ttime".

[0136] The method for calculating the recovery time Ttime will now be explained. Figure 11 is a table showing the relationship between the temperature of the fixing device 30 (temperature detected by the fixing thermistor 35) and the time it takes to reach that temperature from 0°C in this embodiment. For example, if the current temperature is 0°C and the target temperature Ttarget is 160°C, the time it takes to reach 160°C from 0°C is 10.2 seconds.

[0137] Figure 12 is a linearly interpolated graph of the relationship between temperature and time shown in Figure 11. From the relationship between temperature and time shown in Figure 12, the recovery time Ttime can be calculated. For example, suppose the target temperature Ttarget is 170°C and the current temperature is 130°C. In this case, the time it takes to reach 170°C from 0°C is 12 seconds, and the time it takes to reach 130°C from 0°C is 6.4 seconds. Therefore, the time it takes to reach the target temperature Ttarget of 170°C from the current temperature of 130°C (hereinafter referred to as "recovery time Tf") can be calculated as the difference in time it takes to reach each of the above temperatures from 0°C. That is, recovery time f = 12 seconds - 6.4 seconds = 5.6 seconds.

[0138] In this embodiment, the recovery time Ttime is calculated by adding a predetermined time (1 second in this embodiment) set as the time it takes for heat to be transferred to the fixing belt 31 after the temperature control of the fixing device 30 is started, to the recovery time Tf (5.6 seconds + 1 second = 6.6 seconds).

[0139] <Conditions for stopping temperature control and drive control> Next, the stop conditions for temperature control and drive control of the fixing device 30 during continuous paper feeding in this embodiment will be described.

[0140] First, it is necessary to ensure that the recording paper P has completely passed through the fuser nip section N. Therefore, at the timing when the trailing edge of the recording paper is removed (Figure 5(c)), a decision is made as to whether or not to stop the drive control and temperature control of the fuser device 30.

[0141] However, even when the trailing edge of the recording paper is about to come off, it is desirable not to unconditionally stop the drive control and temperature control of the fuser unit 30. In this embodiment, the drive control and temperature control of the fuser unit 30 are stopped only when all of the following predetermined conditions are met.

[0142] The following conditions 1 and 2 are used to determine the relationship between the nip entry time Tc and the recovery time Ttime.

[0143] Condition 1: Tc ≥ Ttime + 5 seconds must be satisfied. "5 seconds" is a predetermined time set to prevent the fixing device 30 from being stopped and immediately restarted.

[0144] Condition 2: Tc ≥ 10 seconds must be satisfied. "10 seconds" is a predetermined time set to prevent frequent stopping of the fixing device 30. This reduces the operating noise caused by stopping and restarting the fixing device 30, and also reduces the consumption of parts.

[0145] Furthermore, the following conditions 3 to 6 are used to make decisions based on the type of job and the heat storage status of the fixing device 30 before and after job execution.

[0146] Condition 3: The prescribed control for reducing PPM is not being performed. Prescribed controls for reducing PPM include, for example, a control that reduces PPM when it is determined that there is insufficient power and heat during continuous paper feeding. Another example is a control that reduces PPM to prevent the temperature of the longitudinal end of the fixing nip section N from rising too high when narrow recording paper P is fed continuously.

[0147] Condition 4: The job must not contain mixed pages of different types of recording paper P, such as different basis weights, surface properties, and widths.

[0148] Condition 5: The job must not be undergoing post-processing temperature control after completion.

[0149] Condition 6: The temperature detected by the fixing thermistor 35 before the start of the job is not below a predetermined temperature (7.5°C in this embodiment).

[0150] <Conditions for restarting temperature control and drive control> Next, the restart conditions (recovery conditions) for the temperature control and drive control of the fixing device 30 during continuous paper feeding in this embodiment will be described.

[0151] If the aforementioned stopping conditions are met and the temperature control and drive control of the fixing device 30 are stopped, it is necessary to restart the temperature control and drive control of the fixing device 30 before the recording paper P enters the fixing nip section N, and to stabilize the fixing device 30 in a state where it can perform the fixing process.

[0152] In this embodiment, the temperature control and drive control of the fixing device 30 are restarted when any of the following predetermined conditions are met.

[0153] Condition 1: Tc ≤ Ttime must be satisfied. A time comparison is performed so that the temperature detected by the fuser thermistor 35 reaches the target temperature Ttarget before the recording paper P enters the fuser nip section N.

[0154] Condition 2: Tc ≤ 5 seconds. In this embodiment, the time it takes for the drive motor 37 to stabilize at the target speed Ttarget from a stopped state is set to 5 seconds.

[0155] <Timing for determining conditions for resumption> In this embodiment, as described above, the recovery time Ttime is calculated based on the time it takes for the detected temperature of the fuser thermistor 35 to reach the target temperature Ttarget from the current temperature. When the temperature control of the fuser device 30 is stopped, the heat stored in the fuser device 30 is not retained and escapes, and the detected temperature of the fuser thermistor 35 decreases. Therefore, the recovery time Ttime changes over time. To address this, the detected temperature of the fuser thermistor 35 is acquired at a first timing and at a second timing that follows the first timing. The recovery time Ttime, calculated based on the detected temperature of the fuser thermistor 35 acquired at the first timing, is then updated based on the detected temperature of the fuser thermistor 35 acquired at the second timing. In this embodiment, the detected temperature of the fuser thermistor 35 is acquired periodically to update the recovery time Ttime. The nip entry time Tc also decreases by the amount of time that has elapsed. Therefore, each time the recovery time Ttime is updated (periodically in this embodiment), it is determined whether the conditions for restarting the drive control and temperature control of the fuser device 30 are met.

[0156] In this embodiment, the determination period for the restart conditions of the drive control and temperature control of the fixing device 30 is set to 10 ms. However, it is not limited to this. Depending on the heat source and heater ignition timing of the fixing device 30, for example, the determination of the restart conditions may be triggered by the zero-crossing signal of the heater ignition timing.

[0157] <Control procedure for the fixing device> Figure 13 is a flowchart of the control process for determining the recovery time Ttime.

[0158] S401: CPU41 obtains the current detected temperature of the fuser thermistor 35 and proceeds to process S402.

[0159] S402: The CPU 41 obtains a target temperature Ttarget corresponding to the recording paper P that will next pass through the fixing nip section N, based on the information (size, basis weight, etc.) of the recording paper P included in the job description, and proceeds to the process in S403.

[0160] S403: Based on the current detected temperature obtained in S401 and the target temperature Ttarget obtained in S402, CPU41 calculates the recovery time Tf until the target temperature Ttarget is reached from the relationship between temperature and time (Figures 11 and 12), and proceeds to processing in S404.

[0161] S404:CPU41 calculates the recovery time Ttime by adding 1 second to the recovery time Tf obtained in S403.

[0162] Figure 14 is a flowchart of the control process from the moment the trailing edge of the recording paper P leaves the fixing nip section N during the job (the moment the trailing edge of the recording paper P in Figure 5(b) finishes passing through the fixing nip section N).

[0163] S501: The CPU 41 performs control to acquire the paper interlock time EndToTop, as shown in Figure 10, as described in Example 1. The paper interlock time EndToTop acquired by this control becomes the initial value of the nip entry time Tc, which is the time from the current point (when the trailing edge of the recording paper P has finished passing through the fixing nip section N) until the leading edge of the subsequent recording paper P enters the fixing nip section N. Therefore, the CPU 41 stores the acquired paper interlock time EndToTop as the nip entry time Tc in the RAM 43 and proceeds to the process in S502.

[0164] In this embodiment, for ease of understanding, the image forming apparatus 100 is configured to detect the timing when the rear end of the recording material P has finished passing through the fixing nip section N. The timing when the rear end of the recording material P has finished passing through the fixing nip section N can be detected by setting the position of the post-fixing sensor 36, etc. Alternatively, the same post-fixing sensor 36 as in Embodiment 1 may be used, and "EndToTop-Etime" may be set as the initial value of the nip entry time Tc.

[0165] S502: CPU41 executes the control to determine the recovery time Ttime shown in Figure 13, obtains the recovery time Ttime, and proceeds to process S503.

[0166] S503: The CPU 41 determines whether the stop conditions for the drive control and temperature control of the fuser unit 30 (the relationship between the nip entry time Tc and the recovery time Ttime, and all other conditions) are met. The stop conditions are as described in the section above, "<Stop conditions for temperature control and drive control>". If the stop conditions are not met (stopping is not possible), the CPU 41 terminates the control and waits for the next sheet of recording paper P to be transported. On the other hand, if the stop conditions are met (stopping is possible), the CPU 41 proceeds to the process in S504.

[0167] S504: CPU41 sets a predetermined time (10ms in this embodiment) for periodically updating the nip entry time Tc and recovery time Ttime, starts counting time, and proceeds to process S505.

[0168] S505: The CPU 41 performs the process of stopping the temperature control of the fuser unit 30. The CPU 41 stores the currently set target fixing temperature Ttarget in RAM 43 in order to set it as the target temperature Ttarget when the fuser unit 30 is restarted, and then stops supplying power to the heater 34. After the CPU 41 has finished the process of stopping the temperature control of the fuser unit 30, it proceeds to the process in S506.

[0169] S506: The CPU 41 performs a stop operation for the drive control of the fuser unit 30. The CPU 41 stores the currently set target speed Vtarget of the drive motor 37 in the RAM 43 in order to set it as the target speed Vtarget when the fuser unit 30 is restarted, and then stops the drive of the drive motor 37. After the CPU 41 has finished the stop operation for the drive control of the fuser unit 30, it proceeds to the process in S507.

[0170] S507: CPU41 determines whether the predetermined time set in S504 has elapsed. If the predetermined time has not elapsed (No), CPU41 continues counting the time; if the predetermined time has elapsed (Yes), it proceeds to process S508.

[0171] S508: The CPU 41 calculates the nip entry time Tc, which is the time from the current moment until the leading edge of the recording paper P reaches the fixing nip section N, using the following formula: Tc = Tc - elapsed time (10 ms). The CPU 41 stores the calculated nip entry time Tc in the RAM 43 and updates it, then proceeds to process S509.

[0172] S509: The CPU 41 executes the control to determine the recovery time Ttime again as shown in Figure 13, obtains the recovery time Ttime again, and proceeds to the process in S510. Here, if the current detected temperature of the fuser thermistor 35, obtained in S401 in Figure 13, has started to decrease because the temperature control of the fuser device 30 has stopped and the heat that the fuser device 30 was holding has escaped, the recovery time Ttime will be longer.

[0173] S510: The CPU 41 determines whether the restart conditions for the drive control and temperature control of the fuser unit 30 described above (the conditions relating the nip entry time Tc and recovery time Ttime, updated in S508 and S509 respectively, or any other conditions) are met. The restart conditions are as described in the section above, <Restart Conditions for Temperature Control and Drive Control>. If the restart conditions are not met (restart not possible), the CPU 41 proceeds to the process in S511. On the other hand, if the restart conditions are met (restart possible), the CPU 41 proceeds to the process in S512.

[0174] S511: CPU41 sets a time (10ms in this embodiment) to decide whether to resume again and restarts the count. CPU41 returns to processing S507 and repeats processing S507 to S511 until it is possible to resume.

[0175] S512: The CPU 41 restarts heating the heater 34 so that the temperature detected by the fuser thermistor 35 becomes the target fuser temperature Ttarget stored in the RAM 43.

[0176] S513: The CPU 41 restarts the drive motor 37 so that its rotational speed becomes the target speed Vtarget stored in the RAM 43. Then, the CPU 41 restarts the temperature control and drive control of the fuser unit 30, and then terminates the control and waits for the next sheet of recording paper P to be transported.

[0177] <Control during the previous rotation> The same control described above for restarting the operation of the fuser 30 between sheets of paper can be applied as control to start the operation of the fuser 30 before the first sheet of recording paper P at the start of the job reaches the fuser nip section N.

[0178] Even at the start of a job, the heat storage state of the fuser unit 30 at the start of the current job may differ depending on factors such as the number of sheets of recording paper P fed through before the fuser unit 30 stopped operating at the end of the preceding job, or the time between the preceding job and the current job. Therefore, if the timing for starting up the fuser unit 30 during the preceding job rotation time is fixed regardless of the heat storage state of the fuser unit 30, the fuser unit 30 may complete its startup earlier than the preset time if it is storing heat. In this case, the idle rotation time of the fuser unit 30 becomes unnecessarily long, leading to a shortened lifespan of the fuser unit 30.

[0179] Therefore, in the same manner as the control for restarting the operation of the fuser 30 between sheets of paper as described above, the timing for starting up the fuser 30 during the previous rotation time can be readjusted and optimized according to the heat storage status of the fuser 30. This makes it possible to reduce unnecessary idle rotation of the fuser 30 while appropriately maintaining the amount of heat supplied to the recording paper P, thereby suppressing unnecessary consumption of the fuser 30's lifespan.

[0180] In this embodiment, by using the nip entry time Tc, the above-described control between sheets of paper can be easily applied to the control at the start of a job. Specifically, in the above-described control between sheets of paper, the inter-sheet time EndToTop was set as the initial value of the nip entry time Tc, which is the time from the current point until the recording paper P enters the fixing nip section N. In the control at the start of a job, instead of this, the above-described pre-rotation time PreRot (Figure 6(b)) can be set as the initial value of the nip entry time Tc, which is the time from the current point until the recording paper P enters the fixing nip section N. Then, for example, from the time the job start instruction is input, a determination can be made periodically to determine whether or not the start conditions for drive control and temperature control of the fixing device 30 are met.

[0181] Furthermore, the same control method described in Example 1 can also be applied as a control method at the start of a job (a method of subtracting a fixed value from the recovery time Ttime).

[0182] <Effects> As described above, in this embodiment, the control unit 40 performs a start process (for example, S507 to S513 in Figure 14) to bring the system from a first state in which the drive of the drive source 37 and the temperature control of the heater 34 are stopped to a second state in which the drive of the drive source 37 and the temperature control of the heater 34 are started to enable the fixing process. If the temperature difference between the target temperature (Ttarget) detected by the temperature sensor 35 in the second state and the detected temperature detected by the temperature sensor 35 in the first state (for example, S401 in Figure 13) is a first temperature difference, the control unit 40 controls the timing between the start of the drive of the drive source 37 and the timing when the first recording material P after the start process reaches the fixing nip section N to be a first time. On the other hand, if the temperature difference between the target temperature and the detected temperature is a second temperature difference which is smaller than the first temperature difference, the control unit 40 controls the time between the start of driving the drive source 37 and temperature control of the heater 34 and the timing when the first recording material P reaches the fixing nip section N to be a second time which is shorter than the first time. In this embodiment, the first time is set in advance. In this embodiment, the control unit 40 also controls the second time to change based on information (for example, Figures 11 and 12) which is obtained in advance and shows the relationship between the temperature difference between the detected temperature and the target temperature and the time it takes for the temperature detected by the temperature sensor 35 to rise from the detected temperature to the target temperature due to the heating of the heater 34. In this embodiment, the control unit 40 sets the second time based on the first detected temperature and the target temperature, and also controls the system to update the second time based on the second detected temperature and the target temperature, which are acquired after the timing at which the first detected temperature is acquired (S508, S509 in Figure 14). The control unit 40 can also change the timing at which the drive source 37 is driven and the temperature control of the heater 34 is started during the start process after a start instruction for a job to form a toner image on one or more recording materials P is input, before the first recording material P reaches the fuser nip section N.

[0183] According to this embodiment, similar to Embodiment 1, the timing for restarting the fuser 30 during continuous paper feeding can be readjusted and optimized according to the heat storage status of the fuser 30. This makes it possible to reduce unnecessary idle rotation of the fuser 30 while appropriately maintaining the amount of heat supplied to the recording paper P, thereby suppressing unnecessary life consumption of the fuser 30. Furthermore, in this embodiment, by using the nip entry time Tc to control the timing of stopping or restarting (starting) the drive control and temperature control of the fuser 30, it becomes easy to apply the control according to the present invention not only to control between sheets of paper but also to control at the start of a job. In addition, in this embodiment, by using information showing the relationship between the detected temperature of the fuser thermistor 35 and the recovery time Tf, the recovery time Ttime can be determined with greater accuracy, and idle rotation of the fuser 30 can be reduced with greater accuracy. Thus, according to this embodiment, by appropriately setting the timing for starting the operation of the fuser 30 from a state where its operation has stopped, unnecessary idle rotation of the fuser 30 can be reduced, thereby suppressing unnecessary life consumption of the fuser 30.

[0184] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0185] In the above-described embodiment, the present invention was applied to an electrophotographic full-color image forming apparatus having multiple image forming units. However, the present invention is not limited thereto and can be applied to various types of image forming apparatuses, including monochrome image forming apparatuses.

[0186] Furthermore, in the above-described embodiment, the present invention was applied to an image forming apparatus equipped with a belt-heating type fixing device, but the fixing device is not limited to an image forming apparatus with a belt-heating type fixing device. In a belt-heating type fixing device, the fixing belt rotates while sliding against the heater, so the effect of reducing unnecessary idle rotation is significant. However, the present invention can also be applied to a hot roller fixing device. A hot roller fixing device generally consists of a heating roller (first fixing member), a pressure roller (second fixing member) that presses against it, and a heater that is non-contactingly provided inside the heating roller, and does not have a sliding part between the fixing member and the heater. Even in a hot roller fixing device, by applying the present invention, idle rotation can be reduced and unnecessary consumption of the lifespan of the members can be suppressed. [Explanation of Symbols]

[0187] 30 Fixing device 31 Fixing belt 33 Pressure roller 34 Ceramic Heaters 35 Fixing Thermistor 36. Sensor after fixing 40 Control Unit N Fixing nip section

Claims

1. An imaging unit that forms a toner image on the recording material, A fixing apparatus that performs fixing processing to fix a toner image formed by the image-making unit onto a recording material, comprising: a rotatable first fixing member; a rotatable second fixing member that forms a fixing nip together with the first fixing member; a heater that generates heat to heat the fixing nip; a drive source that generates a driving force to rotate the first fixing member and the second fixing member; and a temperature sensor that detects a temperature correlated with the temperature of the fixing nip, wherein the fixing apparatus performs the fixing processing by heating the fixing nip with the heater and by clamping and transporting the recording material between the first fixing member and the second fixing member at the fixing nip, A control unit capable of controlling the drive source and the heater, It has, The control unit is characterized in that, in a start process that brings the system from a first state in which the drive of the drive source and the temperature control of the heater are stopped to a second state in which the drive of the drive source and the temperature control of the heater are started to enable the fixing process, it is possible to perform control to change the timing at which the drive of the drive source and the temperature control of the heater are started relative to the timing at which the first recording material after the start process reaches the fixing nip, based on a detected temperature which is the temperature detected by the temperature sensor in the first state and a target temperature which is the target value of the temperature detected by the temperature sensor in the second state.

2. The control unit, in the start process, If the temperature difference between the target temperature and the detected temperature is greater than a predetermined value, the time between the start of the drive source operation and the start of the heater temperature control and the timing when the first recording material reaches the fixing nip section is controlled to be a first time. The image forming apparatus according to claim 1, characterized in that, if the temperature difference between the target temperature and the detected temperature is less than or equal to the predetermined value, the time between the timing of starting the drive of the drive source and the temperature control of the heater and the timing of the first recording material reaching the fixing nip portion is controlled to be a second time that is shorter than the first time.

3. The image forming apparatus according to claim 2, characterized in that the first time is set in advance.

4. The image forming apparatus according to claim 2, characterized in that the difference between the first time and the second time is set in advance.

5. The control unit, in the start process, If the temperature difference between the target temperature and the detected temperature is a first temperature difference, the time between the start of the drive source and the start of the heater temperature control and the timing when the first recording material reaches the fixing nip portion is controlled to be a first time. The image forming apparatus according to claim 1, characterized in that, if the temperature difference between the target temperature and the detected temperature is a second temperature difference smaller than the first temperature difference, the time between the timing of starting the drive of the drive source and the temperature control of the heater and the timing of the first recording material reaching the fixing nip portion is controlled to be a second time that is shorter than the first time.

6. The image forming apparatus according to claim 5, characterized in that the first time is set in advance.

7. The image forming apparatus according to claim 5, characterized in that the control unit controls the second time to change based on information that has been determined in advance, which shows the relationship between the temperature difference between the detected temperature and the target temperature and the time it takes for the temperature detected by the temperature sensor to rise from the detected temperature to the target temperature due to the heating of the heater.

8. The image forming apparatus according to claim 7, characterized in that the control unit sets the second time based on the first detected temperature as the detected temperature and the target temperature, and controls the second time to be updated based on the second detected temperature as the detected temperature and the target temperature, which are acquired after the timing at which the first detected temperature was acquired.

9. The image forming apparatus according to any one of claims 1 to 8, characterized in that, when the control unit performs a stop process to return to the first state by stopping the drive of the drive source and the temperature control of the heater after the timing when the first recording material has finished passing the fixing nip section in the second state during the execution of a job to form toner images on a plurality of recording materials, it is possible to perform control to change the timing at which the drive of the drive source and the temperature control of the heater are started in the start process before the second recording material, which is transported to the fixing nip section after the first recording material, reaches the fixing nip section.

10. The image forming apparatus according to claim 9, characterized in that the control unit controls the stopping process when the time between the timing when the rear end of the first recording material in the transport direction has finished passing the fixing nip and the timing when the front end of the second recording material in the transport direction reaches the fixing nip is longer than a predetermined time.

11. The image forming apparatus according to any one of claims 1 to 8, characterized in that the control unit can perform control to change the timing of starting the drive of the drive source and the temperature control of the heater in the start process after an instruction to start a job to form a toner image on one or more recording materials has been input and before the first recording material reaches the fixing nip section.

12. The image forming apparatus according to any one of claims 1 to 8, characterized in that the first fixing member is composed of an endless belt, the heater is in contact with the inner circumferential surface of the first fixing member, and the second fixing member is in contact with the heater via the first fixing member.

Images