JP2024037562A - Fixing device and image forming device - Google Patents

Abstract

The present invention provides an image forming apparatus that does not limit the heater when there is no abnormality in driving the fixing belt even when the heater is restricted due to an abnormality in the moving speed of the belt. SOLUTION: The image forming apparatus includes a belt rotating body (201), its driving means (311) and heating means (210), and a pressure roller (203) that forms a nip portion between the belt member. means (220, 221) for measuring the rotational speed of the belt rotating body; means (300) for determining an abnormality when the measured belt rotational speed is out of a predetermined range; The means includes a limiting means (300) for stopping energization to one or more heaters, and a means (300) for determining whether the heater limitation can be canceled, and the heater limitation has been canceled (302) and the restriction has been canceled. When the flag is set, power supply to the heater is not stopped regardless of whether the belt speed is abnormal. [Selection diagram] Figure 7

Description

The present invention relates to a fixing device that heats a toner image on a recording material and an image forming apparatus equipped with the fixing device.

In image forming devices such as electrophotographic devices and electrostatic recording devices, a toner image is formed on a sheet of recording material, and the toner image is heated and pressurized by a fixing device to fix it on the recording material. .

One of the conventional fixing devices includes a pressure roller, a pad member disposed opposite to the pressure roller, a heating roller, and an endless fixing belt stretched between the pad member and the heating roller. A belt-type fixing device that fixes a toner image onto a recording material by applying heat from a heating roller to the recording material via the fixing belt at a nip formed by pressure contact between a pressure roller and a fixing belt. It has been known. This fixing method is especially adopted in image forming apparatuses that output a large amount of output per hour because it is possible to fix toner on the recording material in a short time because the contact area between the recording material and the fixing belt is large. It is a method.

In Patent Document 1, in order to stably convey a recording material in a belt-type fixing device, a belt moving speed detecting means for detecting the moving speed of a belt member is provided, and the fixing roller driving speed is controlled based on the detected belt moving speed. A fixing device has been proposed. It is also proposed that using this configuration, if the belt moving speed detecting means detects that the moving speed of the belt member is slower than the target, it is determined that an abnormality has occurred within the image forming apparatus. There is.

In a fixing device, if the fixing belt, which is a heated portion, does not operate at a target speed, it is assumed that heat will be locally concentrated and the device will be damaged. As a safety measure for such a case, in Patent Document 2, when the rotation detection means detects that the pressure roller is not rotating, the device is prevented from generating heat by limiting part of the electric power supplied to the heating element. Proposals to minimize damage are known.

According to the above literature, if the fixing device has a means for detecting the speed of the heated member, it is possible to operate the device without damage even when the speed of the heated member is abnormal.

By the way, if we classify the reasons why the speed detection means of the heated member detects an abnormality, there are cases where driving at the target speed cannot be achieved due to heavy load due to a malfunction of the heated member, jammed paper, etc., and cases where the speed detection means itself cannot be achieved. It is assumed that the speed cannot be detected correctly due to an abnormality.

If the cause of the speed abnormality is the former, it is effective to implement the power restriction proposed in Patent Document 2, but if it is the latter, there is no need to implement the restriction.

When power restrictions are implemented, the fuser device cannot utilize its original heat generation capacity, resulting in an increase in start-up time at the start of a job, and control to restore the fusing temperature by increasing the paper feeding interval. , since this results in waiting time for the user, implementing restrictions when unnecessary is a disadvantage for the user.

Japanese Patent Application Publication No. 2013-44868 Japanese Patent Application Publication No. 2012-155340

Therefore, in the present invention, when the belt movement speed detecting means detects an abnormality and the heater restriction is activated, it is determined that there is no abnormality in the fuser belt drive, and if it is determined that there is no abnormality in the fuser belt, the heater restriction is activated. The purpose is to prevent this from happening.

In order to solve the above problems, the image forming apparatus of the present invention includes an endless belt rotating body (201), a driving means (311) for rotationally driving the belt rotating body, and heating the belt rotating body. heating means (210) consisting of a plurality of heaters; a pressure roller (203) circumscribing the belt rotating body and forming a nip portion with the belt member; belt rotational speed measuring means (220, 221) for measuring the belt rotational speed, and a belt speed abnormality that is determined to be abnormal when the belt rotational speed measured by the belt rotational speed measuring means deviates from the target speed by more than a predetermined range. determination means (300); and heater restriction means (300) for stopping energization of at least one heater among the plurality of heaters in the heating means when the belt speed abnormality determination means determines that the belt speed is abnormal. , a heater restriction release determining means (300) for determining whether or not the heater restriction by the heater restriction means can be released, and when the heater restriction is removed, a restriction release flag is set (302), and the restriction is released. When the completed flag is set, the heater limiting means does not stop energizing the heater, regardless of the determination result of the belt speed abnormality determining means.

According to the present invention, even if the belt movement speed detection mechanism detects an abnormality, unnecessary heater restriction can be suppressed, and the waiting time for the user can be reduced.

1 is a schematic diagram of an image forming apparatus. FIG. 3 is a diagram for explaining the fixing device of the present embodiment. FIG. 3 is a diagram for explaining the fixing device of the present embodiment. FIG. 3 is a diagram for explaining the fixing device of the present embodiment. FIG. 2 is a control block diagram of the image forming apparatus. FIG. 3 is a diagram showing temperature control of the fixing device. FIG. 3 is a diagram for explaining speed control of a fixing device. FIG. 3 is a diagram for explaining speed control of a fixing device. FIG. 7 is a diagram for explaining protection control based on heater restriction of the fixing device. FIG. 6 is a diagram for explaining protection control based on heater restriction of the fixing device. FIG. 7 is a diagram for explaining protection control based on heater restriction of the fixing device. FIG. 7 is a diagram for explaining protection control based on heater restriction of the fixing device. FIG. 7 is a diagram for explaining protection control based on heater restriction of the fixing device. FIG. 3 is a diagram for explaining heater restriction and release control of the fixing device.

Embodiments of an image forming apparatus according to the present invention will be described below based on the drawings. In the following, an example in which the present invention is applied to an electrophotographic full-color image forming apparatus having a plurality of photosensitive drums will be described. It can also be applied to forming devices, etc.

<Image forming device>
A schematic configuration of the image forming apparatus of this embodiment will be described using FIG. 1.

FIG. 1 is a diagram showing a full-color image forming apparatus according to this embodiment. The image forming apparatus 1 includes an image reading section 2 and an image forming apparatus main body 3. The image reading unit 2 reads a document placed on a document table glass 21. Light emitted from a light source 22 is reflected by the document, and an image is formed on a CCD sensor 24 via an optical system member 23 such as a lens. be done. By scanning in the direction of the arrow, such an optical system unit converts the original into an electric signal data string for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, and a control section 30 performs image processing in accordance with each image forming section, which will be described later. The control unit 30 also receives external input from an external host device such as a print server as an image signal.

The image forming apparatus main body 3 includes a plurality of image forming sections Pa, Pb, Pc, and Pd, and each image forming section forms an image based on the above-mentioned image signal. That is, the image signal is converted by the control section 30 into a laser beam subjected to PWM (pulse width modulation control). In FIG. 1, 31 is a polygon scanner serving as an exposure device, which scans with a laser beam according to an image signal. Then, a laser beam is irradiated onto the photosensitive drums 200a to 200d, which serve as image carriers of each of the image forming units Pa to Pd. Note that Pa is a yellow (Y) image forming section, Pb is a magenta (M) image forming section, Pc is a cyan (C) image forming section, and Pd is a black (Bk) image forming section, which correspond to each other. Form a color image. Since the image forming sections Pa to Pd are substantially the same, details of the Y image forming section Pa will be explained below, and explanations of the other image forming sections will be omitted. In the Y image forming section Pa, a photosensitive drum 200a forms a toner image on its surface based on an image signal, as described below.

A primary charger 201a charges the surface of the photosensitive drum 200a to a predetermined potential in preparation for forming an electrostatic latent image. A laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which is charged to a predetermined potential. A developing device 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. Reference numeral 203a denotes a transfer roller, which generates discharge from the back surface of the intermediate transfer belt 204, applies a primary transfer bias having a polarity opposite to that of the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

Further, the toner image on the intermediate transfer belt 204 is conveyed to the next image forming section, and the toner images of each color formed at each image forming section are sequentially transferred in the order of Y, M, C, and Bk. A colored image is formed on the surface. The toner image that has passed through the Bk image forming section is subjected to a secondary transfer electric field having a polarity opposite to that of the toner image on the intermediate transfer belt 204 in a secondary transfer section composed of a pair of secondary transfer rollers 205 and 206. As a result, the image is secondarily transferred onto the paper P. After the fed paper waits at the register section 208, the timing is controlled to align the toner image on the intermediate transfer belt with the paper, and the paper is conveyed from the register section. Thereafter, the toner image on the paper is fixed onto the paper by a fixing device 200 serving as an image heating device. After passing through the fixing device, the paper is ejected outside the machine. In the case of a double-sided job, when the transfer and fixing of the toner on the first side (first side) of image formation is completed, the paper passes through a reversing section provided inside the image forming apparatus after fixing, and the front and back of the paper are reversed, and the image is The toner on the second side (second side) is transferred and fixed, then discharged outside the machine and stacked on the paper discharge tray 7.

The image forming apparatus main body 3 is provided with a fixing door 251 (not shown) that can be opened and closed and forms a part of its casing, and its open/closed state can be detected by a fixing door sensor 250 (not shown).

By opening the fixing door 251, the user can access the fixing device 200, and can perform replacement and maintenance of the fixing device 200, and clear jamming of recording paper P that has become jammed during transportation.

When the fixing door sensor 250 detects that the door is open, the fixing device 200 is prohibited from operating, and is allowed to operate only when the fixing door sensor 250 detects that the door is closed, so that the user can safely access the fixing device. Ru.

<Control block of image forming apparatus>
<Fixing device>
FIG. 2a shows a schematic diagram of the overall configuration of a belt heating type fixing device 200 according to an embodiment of the present invention. In FIG. 2a, the recording material P is conveyed from right to left. The fixing device 200 includes a fixing belt (hereinafter referred to as a belt) 201 as an endless rotatable heating rotating body, a pressure pad (hereinafter referred to as a pad) 202 as a fixing member, an auxiliary drive roller 204, and a tension roller 205. and a pressure roller 203 as a pressure rotating body that faces the belt 201 and forms a nip portion 262 together with the belt 201.

The belt 201 is stretched by a pad 202, an auxiliary drive roller 204, and a tension roller 205. Pad 202 is pressed by pressure roller 203 with belt 201 in between.

A halogen heater 210 (hereinafter referred to as a heater) is disposed inside the auxiliary drive roller 204, and is capable of generating heat up to a predetermined temperature. The belt 201 is heated while being in contact with the auxiliary drive roller 204 in a section from a contact point 260 to a separation point 261 . The heater temperature is controlled by changing the power input to the heater 210 so that the temperature detection result of the heater thermistor 231 becomes a predetermined target temperature depending on the paper type. Further, the auxiliary drive roller 204 has a gear fixed to one end of the shaft, and is connected to a drive source (not shown) via the gear to be rotationally driven. The rotation of the auxiliary drive roller 204 provides the belt 201 with auxiliary driving force.

The tension roller 205 is biased by a spring supported by the frame of the heater 210, is a tension roller that applies a predetermined tension to the belt 201, and rotates as a result of the belt 201. The tension by the spring is 50N, and by applying tension to the belt 201, the belt 201 is made to follow the pad 202.

The pressure roller 203 is connected to a pressure roller drive source (not shown) via a gear and is rotationally driven. Further, the pressure roller 203 is pressed against the pad 202 via the belt 201 by the movement of the pressure frame by a drive source and a cam (not shown).

In the nip portion 262 formed between the belt 201 and the pressure roller 203, the recording material P carrying the toner image is held between them and the toner image is heated while being conveyed. In this way, the fixing device 200 fixes the toner image on the recording material P while nipping and conveying the recording material P.

There is a belt thermistor 230 near the nip portion 262 that measures the temperature at the nip portion 262 of the belt 201.

The contact roller 220 is disposed in contact with the auxiliary drive roller 204 and rotates as the auxiliary drive roller 204 rotates. A slit (not shown) is formed in the contact roller 220, and the rotation detection sensor 221 reads this. As the contact roller rotates, the output of the rotation detection sensor 221 becomes a pulse signal, and the rotation speed of the belt 201 is detected by measuring the time it takes to count the number of pulses to a predetermined count number. be able to.

FIG. 2b is a diagram schematically showing a cross section taken along the rotation axis of the auxiliary drive roller 204 along a plane parallel to the rotation axis of the auxiliary drive roller 204. FIG. The halogen heaters 211 to 216 are disposed inside the auxiliary drive roller 204 and supported by a holder (not shown). Thermistors 231a and 231b are in contact with the auxiliary drive roller 204, and detect the surface temperature of the center and end portions of the auxiliary drive roller 204, respectively.

FIG. 2c shows the light distribution of the six halogen heaters 211 to 216 in this example. The horizontal axis represents the position in the front-rear direction, and the vertical axis represents the heat generation performance at that position. As can be seen from FIG. 2c, each of the six halogen heaters has a different light distribution, and the halogen heaters (halogen heater 211, halogen heater 216) mainly heat the central area with D1 and D2 as boundaries. There are halogen heaters (halogen heater 212, halogen heater 214, halogen heater 215) that mainly heat the end regions bordering on D1 and D2, and a halogen heater 213 that heats the entire center and end regions. The halogen heaters 211 to 216 have a configuration in which the input current value can be set independently, and the power of the halogen heaters is 1000W for the halogen heaters 211, 212, 213, and 216, and 500W for the halogen heaters 214 and 215. It has become. This allows the lighting ratio of the halogen heaters (halogen heater 212, halogen heater 214, and halogen heater 215) that mainly heats the edge region to be reduced even when recording material P having a small width in the front and back direction is continuously passed through. By lowering the height, it is possible to suppress heat accumulation at both ends of the auxiliary drive roller 204. Thermistors 231a and 231b detect temperatures at the center and at the ends, respectively.Thermistor 231a is placed at the center, and thermistor 231b is placed outside D1. By arranging the thermistors 231a and 231b so as not to overlap D1 and D2, it is possible to reliably detect the temperatures in the central region and the end regions.

When the heat distribution portions of the halogen heaters 211 to 216 are 500 mm, and D1 and D2 are 125 mm and 375 mm, respectively, the outside of D1 of the halogen heater 211 is 100 W, the inside of D1 and D2 is 800 W, and the outside of D2 is 100 W.

<Control block of image forming apparatus>
FIG. 3 shows a control block diagram of the image forming apparatus 1 according to the embodiment of the present invention. The control unit 30 includes a CPU 300 that performs basic control of the image forming apparatus 1, a ROM 301 that stores control programs and application programs, a RAM 302 that functions as a work area for executing processing of the control program, and a RAM 302 that stores data even when the power is turned off. , a timer 304 capable of generating periodic time intervals for control and measuring elapsed time between two points, and a UI 305 that displays a screen for the user and receives touch input from the user.

The control unit 30 includes a pressure drive motor 310 that drives the pressure roller 203 as a drive source, a belt drive motor 311 that drives the fixing belt 201, and a fixing heater 210 that has a plurality of heat sources used to adjust the temperature of the fixing device 200. are connected and controlled based on control signals from the control section 30, respectively.

The control unit 30 also includes sensors such as a belt thermistor 230 for detecting the temperature of the belt surface, a fixing thermistor 231 for detecting the temperature of the fixing heat source, and a fixing thermistor 231 for detecting the driving speed of the belt 201 so as to be in contact with the belt. A speed detection sensor 221 that detects the rotation of the contact roller 220, a pre-fixing sensor 240 that is installed upstream of the fixing device 200 and detects the timing at which the paper is transported, and a fixing sensor that detects the timing at which the paper is transported after fixing. A rear sensor 241 and a fixing door sensor 250 that detects that the fixing door 251 is opened are connected. Each is controlled based on a control signal from the control section 30.

When CPU 300 detects that fixing door sensor 250 is open, it immediately stops the JOB, stops fixing heater 210, and stops driving pressurization drive motor 310 and belt drive motor 311.

<About fixing temperature control>
FIG. 4 shows warm-up control to warm up the fixing device 200 to a predetermined temperature from the time the power is turned on to prepare for printing, standby control to maintain the predetermined temperature until the job starts, and temperature setting according to the job content. The flowchart shows a series of temperature controls during print control.

In step 400, the CPU 300 starts driving the belt at the speed setting for warm-up control. The fixing device 200 of this embodiment is driven at 348 mm/s during warm-up.

In step 401, the CPU 300 sets a warm-up target temperature and starts heating the heater.

In step 402, the CPU 300 waits until the temperature detected from the fixing thermistor 231 reaches the target temperature, and when the temperature reaches the target temperature, the process proceeds to step 403.

In step 403, CPU 300 sets the belt speed to a standby speed. The fixing device 200 of this embodiment is driven at the lowest speed from the viewpoint of quietness, and the speed is reduced to 50 mm/s during standby.

In step 404, CPU 300 sets the heater to the standby target temperature.

In step 405, the CPU 300 waits until the JOB starts, and when the JOB starts, the process proceeds to step 406.

In step 406, the CPU 300 obtains the job contents including information such as the paper size to be fixed and the basis weight.

In step 407, the CPU 300 changes the speed of the belt 201 to the target speed according to the job details obtained in step 406. In the fixing device 200 of this embodiment, the target speed is switched between 348 mm/s, 248 mm/s, and 174 mm/s depending on the basis weight of the paper.

In step 408, CPU 300 sets a target fixing temperature according to the JOB details obtained in step 406.

In step 409, the CPU 300 determines whether the JOB is completed, and repeats step 409 until the JOB is completed. When the JOB is completed, the CPU 300 returns to step 403 and stands by until the next JOB.

In this way, the temperature control of the fixing device 200 includes warm-up control that is performed immediately after the power is turned on, standby control that maintains the fixing temperature with the belt at a low speed until the start of the next job, and control that is performed during a job and when the job starts. There is a print control that sets the belt speed and temperature accordingly.

<Fuser belt speed detection>
FIG. 5A shows a flow of feedback speed correction control of the fixing belt 201 using the rotation detection sensor 221.

The rotation detection threshold of the rotation detection sensor 221 in this embodiment is 100 mm/s. Therefore, except for the standby drive in step 403 in FIG. 4 where the rotation detection threshold is exceeded, feedback speed control is performed during warm-up drive in step 400 in FIG. 4 and print drive in step 407.

In step 500, the CPU 300 determines whether the belt drive motor 311 is being driven. If it is being driven, the process proceeds to step 501; otherwise, the flow is ended.

In step 501, the CPU 300 compares whether the target belt speed of the belt driven in step 500 is faster than the standby belt speed, and if it is faster than the standby belt speed, step 502; otherwise, ends the process.

In step 502, the CPU 300 uses the timer 304 to start measuring the elapsed time since the drive was started in step 500.

In step 503, the CPU 300 obtains the elapsed time of the timer 304 measured in step 501, waits until the time required for stable driving has elapsed, and if the time required for stable driving has elapsed, proceeds to step 504. .

In step 504, the CPU 300 checks whether a pulse signal is input from the rotation detection sensor 221, and if it can be obtained, proceeds to step 505. If not, it determines that the speed cannot be detected normally and ends the flow. .

In step 505, the CPU 300 counts the number of pulses of the pulse signal input from the rotation detection sensor 221 and stores it in the RAM 302. Further, the CPU 300 uses the timer 304 to measure the time required to count a predetermined number of pulses. In this embodiment, the number of pulses corresponding to three revolutions of the contact roller 220 is measured.

In step 506, the CPU 300 waits until a predetermined number of pulses can be counted, and when the count is completed, the process proceeds to step 506.

In step 507, the CPU 300 compares the elapsed time since step 504 with the theoretical time. If the pulse measurement time is longer, the process proceeds to step 508; otherwise, the process proceeds to step 509.

In step 508, CPU 300 sets the speed of belt 200 to be reduced according to the speed difference.

In step 509, CPU 300 accelerates the speed of belt 200 according to the speed difference.

In step 510, CPU 300 returns to step 505 and repeats until the belt stops. If the belt stops, end the flow.

FIG. 5b shows a timing chart when the feedback speed control of FIG. 5a is implemented.

The belt speed is a waveform of the speed at which the belt 201 is actually rotating.

The input waveform is a pulse signal from which the rotation detection sensor 221 reads out the slid mounted on the contact roller.

The motor speed setting is a speed value set for the belt drive motor 311 by the CPU 300.

T550 corresponds to step S500 in FIG. 5a, and is the timing to start driving the belt.

T551 is the timing at which the belt stable drive time has elapsed in step S503 of FIG. 5a.

T552, T553, and T554 are the timings at which pulses are acquired in steps S505 to S506 in FIG. 5a and feedback is applied to the belt speed in steps 508 and 509 in FIG. 5a, and the motor speed setting is the same as the ideal motor speed 560. Fine adjustments will be made depending on the difference.

In this way, the rotation speed of the contact roller 220 that contacts the belt 201 and rotates in conjunction with the belt 201 can be calculated using the pulse signal output from the rotation detection sensor 221. By comparing the calculated rotation speed with the ideal rotation speed, the belt speed can be finely adjusted and belt drive control can be performed with higher precision.

<Protection control by heater restriction>
In the belt-type fixing method, the temperature of the belt 201 decreases by applying heat from the heater 204 to the memory material P at the fixing nip 262 as it goes around its path, and by dissipating heat during the movement. The CPU 300 predicts the amount of temperature drop in the belt 201 and determines the power input to the heater 204 so that the belt temperature at the nip portion 261 is always maintained. However, if the belt 201 is stopped or not operating at the target speed, this prediction will deviate from the actual situation, which may cause excessive heat to be applied to the belt 201, leading to equipment failure. There is a possibility of connection.

Therefore, when it is assumed that the rotation of the belt 201 is not as intended, a heater limiting operation is performed in which the output of the heater 204 is reduced to avoid device failure.

The heater limiting operation will be described below using the group of FIG.

FIG. 6a shows a flowchart for determining whether to implement heater restriction using the rotation detection sensor 221. Note that for the same reason as the above-mentioned fixing belt speed detection, this flow is performed during warm-up drive in step 400 in FIG. 4 and print drive in step 407, except for the standby drive in step 403 in FIG. 4 when the rotation detection threshold is below. Implemented from time to time.

In step 600, the CPU 300 obtains the control status of the belt drive motor 311, and if the belt drive motor 311 is being driven, the process proceeds to step 601, and if the belt drive motor 311 is not being driven, the CPU 300 executes step 600 again.

In step 601, the CPU 300 checks whether a pulse signal is input from the rotation detection sensor 221, and if it can be obtained, the process proceeds to step 602; otherwise, it determines that the belt may have stopped, and in step 606 Proceed to.

In step 602, the CPU 300 obtains the control status of the belt drive motor 311, and if the speed change control is in progress, the pulse detection result will constantly change, so one cycle is considered completed and the process proceeds to step 600, and if the speed change is not in progress, the process proceeds to step 603.

In step 603, the CPU 300 counts the number of pulses of the pulse signal input from the rotation detection sensor 221 and stores it in the RAM 302. Further, the CPU 300 uses the timer 304 to measure the time required to count a predetermined number of pulses. In this embodiment, the number of pulses corresponding to three revolutions of the contact roller 220 is measured.

In step 604, the CPU 300 waits until a predetermined number of pulses can be counted, and when the counting is completed, the process proceeds to step 605.

In step 605, CPU 300 compares the elapsed time since step 504 with the theoretical time. The logical time has a positive and negative margin, and if the pulse measurement time is within this range, the process proceeds to step 600; otherwise, the process proceeds to step 606 as a rotation speed abnormality.

In step 606, CPU 300 executes heater restriction. Specifically, CPU 300 fixes the output current values of halogen heaters 213 and 216 to zero. Once heater restriction is executed, detection control is terminated since the restriction state continues.

FIG. 6b is a graph that focuses on a certain point on the fixing belt (201) and shows the temperature transition when this point goes around the belt path during printing without heater restriction.

The vertical axis is the temperature t, and the horizontal axis is the belt travel distance d. Further, L in the figure is a length indicating the circumferential length of the belt.

First, T601 indicates the temperature at the point (261) where the fixing belt (201) leaves the heating roller (210). After leaving the heating roller (210), the belt temperature gradually decreases due to heat radiation, so the belt leaves the heating roller (210) at a temperature tHeat higher than the target temperature tTarget.

Next, T602 indicates the temperature at the timing when it reaches the temperature detection sensor (230). At this point, the belt temperature is controlled to be around the target temperature tTarget.

Subsequently, T603 indicates the belt temperature at the nip portion (262). In the nip portion, the fixing belt (201) applies heat to the paper, so the temperature drops by dTd (° C.). The amount of decrease in temperature varies depending on the size and basis weight of the paper being passed, the state of heat storage in the heating roller, etc.

Subsequent T604 indicates the temperature at the point (260) where the fixing belt (201) contacts the heating roller (210). From here, the fixing belt (201) is again given heat by dTu(b) by the heating roller (210), and the temperature returns to tHeat by the timing (T605) of reaching the heating roller detachment point (261).

By repeating this cycle, the temperature of the fixing belt (201) is maintained while paper is being passed. T606 is the temperature at the timing when the temperature detection sensor (230) reaches the temperature in the second round, and it can be seen that it is lower by dTl than near tTarget (°C) in the first round.

Next, using FIG. 6c, the temperature transition when the belt goes around the belt during sheet passing under heater restriction will be explained.

The timings of T611, T612, T613, T614, T615, and T616 in the figure correspond to the positions of T601, T602, T603, T604, T605, and T606 in FIG. 6b, respectively.

The difference between the non-heater limiting time and the heater limiting time is that the temperature increase width dTu(c) from T614 to T615 is reduced due to a reduction in the amount of heat generated by the heating roller (210). This shows that the temperature at the timing when the temperature detection sensor (230) reaches the second rotation of the belt has not reached tTarget (° C.).

FIG. 6d shows the belt temperature change that can be observed by the temperature detection sensor (230) when paper continues to be passed with the heater restricted. Timings T620 to T625 shown in the figure indicate timings each time the traveling distance L has progressed.

As explained in FIG. 6c, during the heater restriction, the temperature of the fixing belt (201) decreased by dTl every revolution. If paper continues to pass while maintaining the paper spacing, the belt temperature decreases by dTl each time it goes around, and it can be seen that the belt temperature deviates from the target temperature, dTarget. If printing continues in this state, the belt temperature at the nip portion (262) will drop below the temperature that allows the toner to be fixed on the paper, which is undesirable because the toner will not be fixed.

FIG. 6e shows the belt temperature transition when paper is fed with the paper feeding interval twice the belt length L while the heater is restricted. At temperature detection timing T621 after the sheet passes through the nip, the belt temperature shows a value lower than the target temperature tTarget by dT1. After this, the belt moves toward the nip portion (262) again, but because the paper feeding interval is spaced, a temperature drop in dTd due to heat being taken away by the paper does not occur. From this, it can be seen that the temperature of the fixing belt has returned to tTarget by the second rotation T622. In this way, by widening the paper feeding interval, it is possible to compensate for the decrease in heat generation due to heater restriction. Note that this time we have shown an example in which the paper gap is twice the belt length, but this is just an example, and if the temperature drop dTl per belt revolution caused by the size of the belt temperature drop dTd caused by the paper or the heater restriction changes. In this case, the paper feed interval must be increased or decreased.

<About heater restriction and cancellation>
In the fixing device 200 of this embodiment, when the rotation detection sensor 221 cannot output a pulse signal, it is difficult to determine whether the rotation detection sensor 221 or the contact roller 220 is malfunctioning or whether the belt 201 is rotating. Therefore, by limiting the heater output as shown in FIG. 6, excessive temperature rise can be prevented even if the belt is not rotating correctly.

On the other hand, by limiting the heater output, heating efficiency decreases, and in order to raise the temperature to the target temperature, paper must be spaced apart and productivity must be reduced.

If the belt drive is normal and there is only a failure in the rotation detection sensor 221 or the contact roller 220, the heater output is unnecessarily restricted, resulting in an unnecessary drop in productivity.

Therefore, once it is determined that the belt is rotating, it is necessary to cancel the heater restriction and minimize the drop in productivity.

FIG. 7 shows a flow of heater restriction and cancellation depending on whether rotation of the belt 201 can be detected.

In step 700, CPU 300 sets the confirmation skip flag to FALSE. The confirmation skip flag is flag information for determining whether or not to implement heater restriction. If it is confirmed in advance that the belt 201 can rotate, if it is TRUE, the JOB can be executed without heater restriction.

In step 701, the CPU 300 determines whether the fixing door sensor 250 detects that the door is open. If the door is open, the process proceeds to step 702; otherwise, the process proceeds to step 703.

In step 702, CPU 300 sets the confirmation skip flag to FALSE. When the fixing door 251 is opened, the state of the fixing device 200 and rotation detection sensor 221 may change due to parts replacement, etc., so the heater restriction determination is executed again in the next job.

In step 703, the CPU 300 determines whether the JOB has been started, and if the JOB has started, the process advances to step 704; if not, the process returns to step 701, and repeats until the JOB starts.

In step 704, the CPU 300 reads the rotation detection sensor 221 and checks whether a pulse signal like the input waveform shown in FIG. If the speed can be detected, the process advances to step 705.

In step 705, CPU 300 sets the confirmation skip flag to TRUE.

In step 706, the CPU 300 determines whether the confirmation skip flag is FALSE. If it is FALSE, the process proceeds to step 707; otherwise, the process proceeds to step 708.

In step 707, the CPU 300 restricts the heater because the state of the fixing device 200 may have changed since the last JOB was executed due to replacement work being performed before the power was turned on or while the door was open. .

In step 708, the CPU 300 determines that even if the speed was not detected in step 704, the power has never been turned off or the door has been opened since the last job in which belt rotation was confirmed, and the state of the fixing device 200 has changed. If not, do not enforce heater limits.

In step 709, the CPU 300 initializes a paper passing counter to 0 in order to store in the RAM 302 the number of sheets that have been passed since the start of the JOB.

In step 710, CPU 300 passes one sheet.

In step 711, the CPU 300 adds 1 to the paper passing count stored in the RAM 302.

In step 712, the CPU 300 determines whether the heater is being restricted in step 707, and determines whether the passed paper count added in step 710 exceeds a predetermined number of sheets. If the conditions are met, the CPU 300 proceeds to step 713, If not, proceed to step 715.

In step 713, CPU 300 sets the confirmation skip flag to TRUE.

In step 714, CPU 300 cancels the heater restriction.

In step 715, the CPU 300 determines whether the JOB has ended. If the JOB has ended, the process returns to step 701; if the JOB is continuing, the process returns to step 710.

In this way, even if the rotation cannot be detected and the heater is restricted in step 707, if the check skip flag is set to TRUE in step 713, the next job will refer to the check skip flag in step 706 and set the heater limit. can be canceled.

This can prevent a decrease in productivity due to unnecessary heater restrictions.

200 Fixing device 201 Fixing belt (belt)
202 Pressure pad (pad)
203 Pressure roller 204 Auxiliary drive roller 205 Stretching roller 210 Heater (heater)
220 Contact roller 221 Rotation detection sensor 230 Belt thermistor 231 Fixing thermistor 240 Pre-fixing sensor 241 Post-fixing sensor 250 Fixing door sensor 251 Fixing door 260 Belt contact start point 261 Belt contact end point 262 Fixing nip section 300 CPU
301 ROM
302 RAM
303 EEPROM
304 Timer 305 UI

Claims (4)

An endless belt rotating body,
a driving means for rotationally driving the belt rotating body;
a heating means consisting of a plurality of heaters that heats the belt rotating body;
a pressure roller circumscribing the belt rotating body and forming a nip portion with the belt member;
Belt rotation speed measuring means for measuring the rotation speed of the belt rotating body;
Belt speed abnormality determining means for determining an abnormality when the belt rotational speed measured by the belt rotational speed measuring means deviates from a target speed by more than a predetermined range;
Heater limiting means for stopping energization to at least one heater among the plurality of heaters in the heating means when the belt speed abnormality determining means determines that the belt speed is abnormal;
Heater restriction release determination means for determining whether the heater restriction by the heater restriction means can be canceled;
When the heater restriction is canceled, the restriction canceled flag is set, and when the restriction canceled flag is set, the heater limiting unit energizes the heater regardless of the determination result of the belt speed abnormality determining unit. An image forming apparatus characterized in that it does not stop. The image forming apparatus according to claim 1, wherein the restriction-released flag is cleared when the user is expected to touch the belt rotation body or the belt rotation speed detection means. . The image forming apparatus further includes one or more doors that can be opened and closed so that a user does not touch the belt rotating body or the belt rotation speed detection means during operation of the apparatus, and the opening and closing status of the door is controlled. door opening/closing detection means capable of determining whether or not the door is open/closed, and the condition for clearing the restriction-released flag is a case where the door opening/closing means detects that one of the doors is opened. The image forming apparatus according to claim 2. 4. The image forming apparatus according to claim 2, wherein the condition for clearing the restriction-released flag is when the image forming apparatus is powered off or started.