Image forming apparatus

Abstract

To provide an image forming device which offers shorter FPOT and suppresses an increase in the amount of overshoot.SOLUTION: A control unit controls power supplied to a heater such that the temperature gradient used when warming up a fixing unit to a target temperature changes according to the time it takes for a recording material to enter a fixing nip from the time the supply of power to the heater is started.SELECTED DRAWING: Figure 6

Description

Technical Field

[0005] ,

[0001] The present invention relates to an electrophotographic recording type image forming apparatus such as a copying machine or a printer.

Background Art

[0002] An electrophotographic recording type image forming apparatus includes a fixing unit that forms a toner image on a recording material such as plain paper and fixes the toner image on the recording material to the recording material. In order to fix the toner image to the recording material, it is necessary for the fixing unit to reach a target temperature suitable for fixing when the conveyed recording material reaches the fixing unit. When the fixing unit is warmed up so as to reach the target temperature, an overshoot occurs in which the temperature of the fixing unit exceeds the target temperature. If the overshoot amount is too large, the toner image on the recording material that has reached the recording material is overheated, and a hot offset occurs in which the toner adheres to the fixing unit. Therefore, it is necessary to keep the overshoot amount small.

[0003] As a method for suppressing the overshoot amount during warm-up, Patent Document 1 describes setting the parameters of PID control to different values in the warm-up process and the fixing process (constant temperature control process). That is, the parameters of PID control in the warm-up process are set to different values from those during fixing so that the overshoot becomes small.

Prior Art Documents

[0006] However, if, during the warm-up process to increase the heating rate, the timing of the recording material entering the fixing unit is delayed due to some factor, an overshoot will occur.

[0007] The object of the present invention is to provide an image forming apparatus that can shorten FPOT while suppressing an increase in the amount of overshoot. [Means for solving the problem]

[0008] The present invention, for solving the above-mentioned problems, provides an image forming apparatus comprising: an image forming unit for forming a toner image on a recording material; a nip forming member for forming a fixing nip for gripping and transporting the recording material; a heater; a fixing unit for heating and fixing the toner image formed on the recording material to the recording material at the fixing nip; and a control unit for controlling the power supplied to the heater, wherein the control unit controls the time from when power is supplied to the heater until the recording material enters the fixing nip. of The system calculates the time required to warm up the fixing unit to the target temperature and controls the power supplied to the heater so that the temperature gradient decreases as the time increases. The control unit calculates the time from when power is supplied to the heater until the recording material enters the fixing nip as the sum of the time from when the print start command is sent until the image data is sent and the time required for image formation based on the image data. It is characterized by the following: [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an image forming apparatus that can shorten FPOT while suppressing an increase in the amount of overshoot. [Brief explanation of the drawing]

[0010] [Figure 1] Cross-sectional view of an image forming apparatus [Figure 2] Cross-sectional view of the fixing unit of Example 1 [Figure 3] Heater configuration diagram of Example 1 [Figure 4] Heater control circuit diagram of Example 1 [Figure 5] Explanatory diagram of the sequence required time Δts of Example 1 [Figure 6] Diagram showing the control parameters of Example 1 [Figure 7] Diagram showing the temperature transition of Example 1 [Figure 8] Diagram showing the control parameters of the comparative example of Example 1 [Figure 9] Diagram showing the temperature transition of the comparative example of Example 1 [Figure 10] Diagram showing the control parameters of Example 2 [Figure 11] Diagram showing the temperature transition of Example 2 [Figure 12] Diagram showing the control parameters of the comparative example of Example 2 [Figure 13] Diagram showing the temperature transition of the comparative example of Example 2 [Figure 14] Cross-sectional view of the fixing unit of Example 3 [Figure 15] Diagram showing the temperature estimation unit of Example 3

Mode for Carrying Out the Invention

[0011] Hereinafter, with reference to the drawings, modes for carrying out this invention will be exemplarily and specifically described based on examples. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of this invention to the following embodiments.

[0012] (Example 1) (Overall description of the image forming apparatus) FIG. 1 is a cross-sectional view of an electrophotographic recording type image forming apparatus 1000. Note that the characters YMCK attached to the end of the reference numerals indicate the colors of the toner, and are omitted when explaining matters common to the four colors.

[0013] The image forming apparatus 1000 is a full-color printer of an in-line type in which four photosensitive drums 1 are arranged in a row. The image forming apparatus 1000 is equipped with an automatic duplex printing mechanism, and the resolution is 600 dpi.

[0014] An image forming unit 101 that forms a toner image on a recording material has four image forming stations 100Y, 100M, 100C, and 100K. Each image forming station 100 has a photosensitive drum 1, a charging roller 2 as a primary charging unit, a laser scanner unit 11, a developing unit 8, toner containers 7 as toner supply units, a primary transfer roller 4, and a drum cleaner 16. The image forming unit 101 further has an intermediate transfer belt 24, a secondary transfer roller 25, a driving roller 26, a tension roller 13, and an auxiliary roller 23. The driving roller 26 functions as an opposing roller to the secondary transfer roller 25 while driving the intermediate transfer belt 24.

[0015] Reference numeral 200 is a fixing unit 200 that fixes the toner image formed on the recording material P to the recording material P. Reference numeral 113 is an engine controller, and reference numeral 120 is a video controller 120. The engine controller 113 is connected to the video controller 120 and controls each part of the image forming apparatus 1000 according to an instruction from the video controller 120. Reference numeral 400 is a heater control circuit 400 connected to a commercial AC power supply 401.

[0016] When the video controller 120 receives a print instruction from an external device, the video controller 120 starts a process of converting the image data received from the external device into printable image data. Then, the video controller 120 transmits an image forming start instruction (hereinafter referred to as a print start command) to the engine controller 113.

[0017] When a print start command is sent from the video controller 120, the warm-up operation of the fuser unit 200 and the motor drive of the laser scanner unit 11 are initiated. At the same time, the recording material P is fed from the paper feed cassette 15A into the image forming apparatus 1000 by the pickup roller 14 and the paper feed rollers 17 and 18. The recording material P is temporarily held between the transport (resist) roller 19a and the transport (resist) opposing roller 19b, which synchronize the image forming operation and the transport of the recording material P, as described later, and then stops and waits.

[0018] Subsequently, once the image data conversion process in the video controller 120 is completed and the image data is transmitted to the engine controller 113, the engine controller 113 issues instructions for the print sequence. The engine controller 113 controls the image forming unit 101 in YTOP mode if the received image data is full color (YMCK), or in KTOP mode if it is monochrome (black only).

[0019] First, let's explain image formation in YTOP mode. The laser scanner unit 11 scans the surface of the photosensitive drum 1, which is charged to a constant potential by the action of the charging roller 2, with laser light corresponding to the image data, and forms an electrostatic latent image on the photosensitive drum 1. The developer unit 8 is equipped with a developing roller 5. A bias voltage is applied to the developing roller 5 to supply toner to the photosensitive drum 1. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed with toner supplied from the developer unit 8. As a result, toner images of different colors are formed on the surface of each of the four photosensitive drums 1.

[0020] The intermediate transfer belt 24 is in contact with the photosensitive drum 1 and rotates in sync with the rotation of the photosensitive drum 1. The toner images formed on the four photosensitive drums 1 are sequentially transferred to the intermediate transfer belt 24 by the action of the primary transfer bias applied to the primary transfer roller 4. As a result, a superimposed toner image of four colors (full-color image) is formed on the intermediate transfer belt 24. Toner that is not transferred to the intermediate transfer belt 24 and remains on the photosensitive drum 1 is collected by the drum cleaner 16. The drum cleaner 16 has a cleaner blade 161 that contacts the photosensitive drum 1 and a toner collection container 162.

[0021] The full-color image formed on the intermediate transfer belt 24 is transported to the secondary transfer nip section formed by the intermediate transfer belt 24 and the secondary transfer roller 25. Synchronized with this, the recording material P, which had been waiting while being held between the transport roller pair 19a and 19b, is transported to the secondary transfer nip section by the action of the transport roller pair 19a and 19b. Then, the toner image is transferred to the recording material P all at once by the action of the secondary transfer bias applied to the secondary transfer roller 25.

[0022] The fixing unit 200 includes a film unit (heating unit) 200U and a pressure roller 208 that, together with the film unit 200U, forms a fixing nip section N. The recording material P holding the toner image T is transported by the pressure roller 208 and subjected to heat and pressure at the fixing nip section N. This fixes the toner image T to the recording material P. The recording material P with the fixed toner image T is discharged to the output tray 31 by the discharge rollers 20a and 20b, and the image forming operation is completed.

[0023] The belt cleaner 28 cleans the toner remaining on the intermediate transfer belt 24 using the action of the cleaner blade 281, and the toner collected here is stored as waste toner in the cleaner container 282.

[0024] Next, we will explain image formation in KTOP mode. KTOP mode differs from YTOP mode in that development is performed only at image formation station 100K; other processes are the same as in YTOP mode. Since image formation is not required at image formation stations 100Y, 100M, and 100C other than image formation station 100K, the time required for image formation in KTOP mode is shorter than in YTOP mode.

[0025] The image forming apparatus 1000 has a maximum paper feed width of 216 mm in the width direction of the recording material P, which is perpendicular to the transport direction of the recording material P, and is capable of printing recording material of LETTER size (216 mm x 279 mm). In addition, the transport speed (process speed) of the recording material P can be selected by the user according to the type of recording material P, and two types are available: 300 mm / s and 150 mm / s.

[0026] (Explanation of the fixing unit) Figure 2 is a cross-sectional view of the fixing unit (fixing section) 200. The fixing unit 200 has a film unit (heating unit) 200U and a pressure roller 208 that together with the film unit 200U form a fixing nip section N. The film unit 200U has a cylindrical fixing film 202 and a heater 300 etc. provided in the internal space of the fixing film 202 and in contact with the inner surface of the fixing film 202. The fixing nip section N is formed by the heating roller 208 together with the heater 300 via the fixing film 202.

[0027] The fixing film 202 is a tubular, multi-layered heat-resistant film, with a base layer made of a thin-walled heat-resistant resin such as polyimide or a metal such as stainless steel. Furthermore, a release layer, such as tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), is provided on the surface of the fixing film 202 to prevent toner adhesion and ensure separation from the recording material P. In addition, a heat-resistant rubber layer, such as silicone rubber, is provided between the base layer and the release layer.

[0028] The pressure roller 208 has a core metal 209 made of iron or aluminum, and an elastic layer 210 made of silicone rubber or the like. It also has a release layer on its surface, similar to the fixing film 202. The pressure roller 208 is in contact with the outer surface of the fixing film 202.

[0029] The heater 300 has a ceramic substrate 305, a heat-generating resistor 308 provided on the substrate 305 along the longitudinal direction of the substrate 305, and a surface protection layer 307 which is a glass layer covering the heat-generating resistor 308. The heater 300 is positioned in the internal space of the fixing film 202 along the longitudinal direction of the fixing film 202. Details of the heater 300 will be described later. Reference numeral 201 denotes a heater holding member made of a heat-resistant resin such as liquid crystal polymer, and is positioned in the internal space of the fixing film 202 along the longitudinal direction of the fixing film 202. The heater 300 is held by the heater holding member 201. The heater holding member 201 also has a guide function that guides the rotation of the fixing film 202.

[0030] Reference numeral 204 denotes a metal stay that reinforces the heater holding member 201 and is positioned in the internal space of the fixing film 202 along the longitudinal direction of the fixing film 202. The metal stay 204 biases the heater holding member 201, which holds the heater 300, toward the pressure roller 208 by a spring (not shown). This pressure forms a fixing nip portion N between the fixing film 202 and the pressure roller 208. The temperature of the heater 300 is detected by a thermistor (temperature sensing element) TH. The thermistor TH detects the temperature of the heater approximately in the center of the heater in the longitudinal direction. The temperature of the fixing film 202 is detected by a thermopile (temperature sensing element) TF. The thermopile TF detects the surface temperature of the fixing film 202 upstream of the fixing nip portion N in the recording material transport direction and in the central part of the fixing film 202 in the longitudinal direction.

[0031] The pressure roller 208 receives power from the motor 30 and rotates in the direction of arrow R1. As the pressure roller 208 rotates, the fixing film 202 is driven to rotate in the direction of arrow R2. By gripping and conveying the recording material P at the fixing nip section N and applying heat from the fixing film 202 to the recording material P, the toner image T on the recording material P is heated and fixed to the recording material P. In this embodiment, the fixing film 202, heater 300, pressure roller 208, etc., correspond to the nip section forming members that form the fixing nip section N that grips and conveys the recording material P.

[0032] (Heater description) Figure 3 is a diagram of the heater 300. The heater 300 has conductors 301 (301a, 301b) provided on the substrate 305 along the longitudinal direction of the substrate 305. The conductors 301 are separated into a conductor 301a located on the upstream side in the transport direction of the recording material P and a conductor 301b located on the downstream side. Between the conductors 301a and 301b is a heating resistor 302 which generates heat due to the power supplied through these conductors. Electrodes Ea and Eb are the parts to which terminals of a power supply connector (not shown) are connected. The surface protective layer 308, which is a glass layer, is the surface that contacts the fixing film 202. The surface protective layer 308 covers the heating resistor 302 so that electrodes Ea and Eb are exposed. The thermistor TH is positioned so as to contact the back surface layer of the heater 300 (the surface opposite to the sliding surface) at the center of the heater 300 in the longitudinal direction of the heater 300.

[0033] (Explanation of the control circuit) Figure 4 is a circuit diagram of the heater control circuit 400. Reference numeral 401 denotes the commercial AC power supply to which the image forming apparatus 1000 is connected. Power control to the heater 300 is performed by the engine controller 113 controlling the triac 410. The triac 410 operates according to the FUSER signal from the CPU 420 (control unit) built into the engine controller 113. The zero-cross detection unit 430 is a circuit that detects the zero-crossing of the AC waveform of the AC power supply 401 and outputs a ZEROX signal to the CPU 420. The ZEROX signal is used as a reference signal when controlling the phase or wavenumber of the triac 410.

[0034] The CPU 420 calculates the control duty cycle D (%), which corresponds to the power supplied to the heater 300, at a predetermined calculation cycle. In this embodiment, cascade PID control is employed to control the temperatures of both the fixing film 202 and the heater 300. Specifically, the target temperature Htgt of the heater 300 is calculated based on the difference ΔTf between the target temperature Ttgt of the fixing film 202 and the temperature detected by the thermopile TF. Then, the control duty cycle D is calculated based on the difference ΔTh between the target temperature Htgt of the heater 300 and the temperature detected by the thermistor TH. In this embodiment, the former is referred to as the film PID controller and the latter as the heater PID controller.

[0035] The CPU420 calculates the target temperature Htgt of the heater 300 based on the following formula, using the P gain Kfp, I gain Kfi, D gain Kfd, and constant term Cf. Htgt=Kfp×ΔTf+Kfi×∫ΔTfdt+Kfd×dΔTf / dt+Cf (Formula 1) However, to prevent damage to the heater 300 due to overheating, an upper limit is set for the target temperature Htgt of the heater 300. In this embodiment, the upper limit is set to 290°C.

[0036] Furthermore, the CPU420 calculates the control duty cycle D based on the following formula, using the P gain Khp, I gain Khi, D gain Khd, and constant term Ch. D=Khp×ΔTh+Khi×∫ΔThdt+Khd×dΔTh / dt+Ch (Formula 2) The calculation period for Equations 1 and 2 is assumed to be 80 ms.

[0037] The CPU420 converts the control duty cycle D into a phase angle (phase control) or wavenumber (wavenumber control) corresponding to the power, and outputs a FUSER signal at a timing based on the converted value to control the triac 410.

[0038] (Temperature control method) Using Figures 5, 6, and 7, the temperature control method for heating the fixing film 202 from temperature Tini at the start of power supply to the heater 300 to the target temperature Ttgt will be explained. In this embodiment, Tini = 23°C and Ttgt = 180°C.

[0039] First, Figure 5 will be used to explain the sequence duration Δts and the temperature gradient α. Figure 5(A) is a time series diagram for explaining the sequence duration Δts. The sequence duration Δts is the time from when power is supplied to the heater 300 until the leading edge of the recording material P enters the fixing nip section N in the transport direction. The sequence duration Δts is calculated in advance by the CPU 420 when the print start command is sent from the video controller 120. The sequence duration Δts is calculated as time Δtv + time Δtp. Time Δtv is the time from when the print start command is sent from the video controller 120 until the image data is sent. Time Δtp is the time required for image formation after the print sequence instruction is given by the engine controller 113.

[0040] Time Δtv is initially set to the shortest possible value of 0.5 seconds when the print start command is sent from the video controller 120. However, depending on the image, the conversion process from the original image to printable image data may be delayed. In that case, time Δtv is updated to a new value when the image data is sent from the video controller 120.

[0041] The time Δtp is 5.62 seconds in YTOP mode and 4.64 seconds in KTOP mode when the process speed is 300 mm / s. The sequence duration Δts is calculated as Δtv + Δtp, and the shortest time Δts in YTOP mode is 6.12 seconds, while the shortest time Δts in KTOP mode is 5.14 seconds.

[0042] Figure 5(B) is a temperature transition graph of the fixing film 202 to explain the temperature gradient α of the fixing film 202. The temperature gradient α of the fixing film 202 is defined as (Ttgt-Tini) / Δtw. Time Δtw is the time Δtw (warm-up time) from when power supply to the heater 300 is started until the temperature of the fixing film 202 reaches the target temperature Ttgt. Time Δtw is a predetermined value that was experimentally measured during the design stage of the image forming apparatus 1000 using the PID control parameters described later.

[0043] Figure 6 shows the parameter setting table for PID control. The parameter setting table differs before (warm-up process) and after (paper feeding process) when the recording material P enters the fixing nip N. Also, the parameters Kfp, Kfi, Kfd, and Cf of the film PID controller and the parameters Khp, Khi, Khd, and Ch of the heater PID controller are different. In the warm-up process, the parameters Kfp, Kfi, Kfd, and Cf of the film PID controller are set to change the temperature gradient α according to the sequence duration Δts.

[0044] Figure 7 shows the temperature progression of the fixing film 202 from the starting temperature Tini to the target temperature Ttgt. Figures 7(A), (B), (C), and (D) show the temperature progression for time Δts = 5.14 seconds, 5.5 seconds, 6.12 seconds, and 7 seconds, respectively. Figure 7(E) shows the temperature progression when the warm-up process time is set to 7 seconds with a control parameter setting of time Δts = 5.14 seconds. All cases are for a process speed of 300 mm / s.

[0045] In Figure 7(E), the temperature of the fixing film 202 significantly overshoots the target temperature Ttgt at the moment the tip of the recording material P enters the fixing nip N. In contrast, in Figures 7(A), (B), and (C), the amount of temperature overshoot of the fixing film 202 at the moment the tip of the recording material P enters the fixing nip N is kept to a minimum.

[0046] In Figure 7(D), there is a time lag between when the temperature of the fixing film 202 reaches the target temperature Ttgt and when the recording material P enters the fixing nip N. However, during this time, the temperature of the fixing film 202 is able to warm up without overshooting. Thus, in this embodiment, the power supplied to the heater 300 is controlled so that, at the same process speed, the temperature gradient α when warming up the fixing film 202 to the target temperature Ttgt changes according to the time Δts.

[0047] Figure 8 shows the parameter setting table for the PID control of the comparative example. The parameters Kfp, Kfi, Kfd, and Cf of the film PID controller in the warm-up process are the values ​​used in this embodiment (Figure 6) when the time Δts ≥ 6.12 seconds. In other words, even if the recording material P does not enter the fixing nip N for a long period of time, the values ​​are set so that the temperature of the fixing film 202 does not overshoot the target temperature Ttgt.

[0048] Figure 9 shows the temperature progression of the comparative example fixing film 202 from the starting temperature Tini to the target temperature Ttgt. Figures 9(A), (B), (C), and (D) show the temperature progression for times Δts = 5.14 seconds, 5.5 seconds, 6.12 seconds, and 7 seconds, respectively. As with Figure 7, time Δtv = 0.5 seconds. All cases are for a process speed of 300 mm / s.

[0049] In Figure 9, a graph showing the temperature range expanded to 150-200°C is shown to the right of the graph showing the temperature range of 0-300°C. In the cases of Figures 9(A) and (B), looking at the graph for the temperature range of 150-200°C, the recording material P enters the fixing nip N before the temperature of the fixing film 202 reaches the target temperature Ttgt. This can lead to fixing failure. To prevent this, in the comparative example, the engine controller 113 needs to delay the print sequence instruction so that Δts ≥ 6.12 seconds.

[0050] Thus, in this embodiment, when the time Δts is short, as in the KTOP mode, the FPOT can be shortened while suppressing the amount of temperature overshoot of the fixing film 202. On the other hand, even when the time Δts is long, as in the YTOP mode, the amount of temperature overshoot of the fixing film 202 can be suppressed.

[0051] As described above, the control unit controls the power supplied to the heater so that the temperature gradient when warming up the fixing section to the target temperature changes according to the time from when power supply to the heater is started until the recording material enters the fixing nip section. In particular, the power supplied to the heater is controlled so that the temperature gradient during warm-up changes at the same process speed. This makes it possible to provide an image forming apparatus that shortens the FPOT while suppressing an increase in the amount of overshoot.

[0052] (Example 2) Example 2 differs from Example 1 in that power is supplied to the heater 300 using PID control that uses only the temperature of the fixing film 202, rather than cascade PID control that controls the temperatures of both the fixing film 202 and the heater 300. The configuration of the image forming apparatus 1000 and the fixing unit 200 are the same as in the example. In Example 2, the output of the thermistor TH, which detects the temperature of the heater 300, is used to determine if the temperature of the heater 300 is abnormal.

[0053] (Temperature control method) The CPU420 calculates the control duty cycle D based on the following formula, using the difference ΔTf between the target temperature Ttgt of the fixing film 202 and the temperature detected by the thermopile TF, with a calculation period of 80ms. D=Kp×ΔTf+Ki×∫ΔTfdt+Kd×dΔTf / dt+C (Formula 3) Using Figures 10 and 11, the temperature control method for heating the fixing film 202 from temperature Tini at the start of power supply to the heater 300 to the target temperature Ttgt will be explained. In this embodiment, Tini = 23°C and Ttgt = 180°C.

[0054] Figure 10 shows the parameter setting table for PID control in this embodiment. The sequence duration Δts in this embodiment is at least 5.14 seconds and may be delayed depending on the preparation status of image formation. The parameters Kp, Ki, Kd, ​​and C of the PID controller in the warm-up process are set to change the temperature gradient α according to the sequence duration Δts.

[0055] Figure 11 shows the temperature progression of the fixing film 202 from the starting temperature Tini to the target temperature Ttgt. Figures 11(A), (B), (C), and (D) show the temperature progression for time Δts = 5.14 seconds, 5.3 seconds, 5.46 seconds, and 6 seconds, respectively. Figure 11(E) is a comparative example, showing the temperature progression when the warm-up process time is set to 6 seconds with a control parameter setting of time Δts = 5.14 seconds. All cases are for a process speed of 300 mm / s.

[0056] In Figure 11(E), the temperature of the fixing film 202 has significantly overshot the target temperature Ttgt. In contrast, in Figures 11(A), (B), and (C), the amount of overshoot has been kept to a minimum. Furthermore, in Figure 11(D), there is a time lag between when the temperature of the fixing film 202 reaches the target temperature Ttgt and when the recording material P enters the fixing nip N, but the amount of overshoot during this time has been kept to a minimum.

[0057] Figure 12 shows the parameter setting table for the PID control of the comparative example. The parameters Kp, Ki, Kd, ​​and C of the PID controller during the warm-up process are the same as those used in this embodiment (Figure 10) when the time Δts ≥ 5.46 seconds. However, the parameters Kp, Ki, Kd, ​​and C of the PID controller are not changed even when the time Δts changes.

[0058] Figure 13 shows the temperature progression of the comparative example fixing film 202 from the starting temperature Tini to the target temperature Ttgt. Figures 13(A), (B), (C), and (D) show the temperature progression for times Δts = 5.14 seconds, 5.3 seconds, 5.46 seconds, and 6 seconds, respectively.

[0059] In Figures 13(A) and (B), the recording material P enters the fixing nip N before the temperature of the fixing film 202 reaches the target temperature Ttgt, which may result in a fixing failure. To prevent this, in the comparative example, the engine controller 113 needs to delay the print sequence instruction so that Δts ≥ 5.46 seconds. In other words, in the comparative example, FPOT must be made longer. Also, in this embodiment, the shortest time from the start of power supply to the heater 300 until the tip of the recording material P enters the fixing nip N is 5.14 seconds, whereas in the comparative example, the shortest time is 5.46 seconds.

[0060] Thus, in this embodiment as well, it is possible to provide an image forming apparatus that can shorten FPOT while suppressing an increase in the amount of overshoot.

[0061] (Example 3) Example 3 differs from Example 1 in that the temperature of the fixing film 202 is estimated by a temperature estimation unit rather than a thermopile TF. As shown in Figure 14, the fixing unit 200B in this example does not have a thermopile TF.

[0062] (Temperature estimation part) The temperature estimation section of the fixing film 202 in this embodiment will be explained with reference to Figure 15. Figure 15 shows a simplified representation of the heat transfer paths between the components constituting the fixing unit 200B, with the arrows in the figure indicating the heat transfer paths between components in contact with each other. Figure 15(A) is a model when the recording material P is passing through the fixing nip section N, and Figure 15(B) is a model when the recording material P is not passing through the fixing nip section N.

[0063] The equation for estimating the temperature of each component model at a given time t in Figure 15(A) can be expressed as the following difference equation, given a sampling time period of Δt (e.g., 20 msec). Furthermore, the heat transfer coefficients αlf, αlh, αfh, αfp, and αrp are values ​​fitted to minimize the error between the experimentally measured temperatures of each component and the estimated values ​​obtained from the following equation. {Tl(t)-Tl(t-Δt)} / Δt=αlf{Tf(t-Δt)-Tl(t-Δt)}+αlh{Th(t-Δt)-Tl(t-Δt)} (Formula 4) {Tf(t)-Tf(t-Δt)} / Δt=αfh{Th(t-Δt)-Tf(t-Δt)}+αfp{Tp(t-Δt)-Tf(t-Δt)} (Formula 5) {Tr(t)-Tr(t-Δt)} / Δt=αrp{Tr(t-Δt)-Tp(t-Δt)} (Formula 6) Tp: recording material temperature, Tf: film temperature, Th: heater temperature, Tl: heater holding member temperature, Tr: pressure roller temperature However, the heater temperature Th is determined using the detection result of the thermistor TH, and the recording material temperature Tp is set to 23°C.

[0064] Similarly, the temperature of each component model in Figure 15(B) can be estimated using the following formula. Note that, except for the film temperature and pressure roller temperature, the same formula as in Figure 15(A) is used. Furthermore, the heat transfer coefficients αfr and αrf are values ​​fitted to minimize the error between the measured values ​​of each component temperature measured experimentally and the estimated values ​​obtained from the following formula. {Tf(t)-Tf(t-Δt)} / Δt=αfh{Th(t-Δt)-Tf(t-Δt)}+αfr{Tr(t-Δt)-Tf(t-Δt)} (Equation 7) {Tr(t)-Tr(t-Δt)} / Δt=αrf{Tf(t-Δt)-Tr(t-Δt)} (Formula 8) These temperature estimations are performed by CPU420, which also serves as the temperature estimation unit.

[0065] As described above, the temperature of the fixing film 202 is estimated, and the warm-up process is performed using the same temperature control method as in Example 1. In this embodiment as well, an image forming apparatus can be provided that shortens the FPOT while suppressing an increase in the amount of overshoot. [Explanation of Symbols]

[0066] 200 Fuser Unit 300 Heater 400 Heater control circuit

Claims

1. An image forming unit that forms a toner image on the recording material, A fixing unit comprising a nip-forming member that forms a fixing nip section for gripping and transporting recording material, and a heater, which heats and fixes the toner image formed on the recording material to the recording material using the fixing nip section, A control unit that controls the power supplied to the heater, In an image forming apparatus having, The control unit calculates the time from the start of power supply to the heater until the recording material enters the fixing nip section, and controls the power supplied to the heater such that the temperature gradient when warming up the fixing section to the target temperature becomes smaller as the time increases. The image forming apparatus is characterized in that the control unit calculates the time from the start of power supply to the heater until the recording material enters the fixing nip as the sum of the time from the timing when the print start command is transmitted until the image data is transmitted and the time required for image formation based on the image data.

2. The image forming apparatus according to claim 1, characterized in that the control unit controls the power supplied to the heater such that, at the same process speed, the temperature gradient when warming up the fixing unit to the target temperature becomes smaller as the time increases.

3. The image forming apparatus according to claim 1 or 2, characterized in that the nip portion forming member has a cylindrical film and a roller that contacts the outer surface of the film, the heater is arranged in the internal space of the film, and the fixing nip portion is formed by the heater and the roller via the film.

4. The image forming apparatus according to claim 3, characterized in that, at the same process speed, the control unit changes the value of the temperature gradient α = (Ttgt - Tini) / Δtw according to the time Δts from the start of power supply to the heater until the front end of the recording material enters the fixing nip, where Tini is the temperature of the film at the time when power supply to the heater is started, Ttgt is the temperature of the film when the front end of the recording material enters the fixing nip in the transport direction, and Δtw is the time from the start of power supply to the heater until the temperature of the film reaches Ttgt.

5. The image forming apparatus according to claim 1, characterized in that the control unit sets the time from when the print start command is sent until the image data is sent as a provisional time, updates the provisional time to an actual value when the image data is sent, and recalculates the time from when power supply to the heater is started until the recording material enters the fixing nip.

Images