JP2005338698A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device wherein slip predictive detection is performed at low cost in a film heating fixing device. <P>SOLUTION: When a thermistor temperature rise speed during pre-rotation is higher than a prescribed range, splip prediction is detected, or when temperature ripple during temperature adjustment in pre-rotation is larger than a prescribed range, slip prediction is detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a printer, a copier, and a facsimile machine. More specifically, the present invention relates to an improvement in an image forming apparatus using a film heating type heat fixing device (fixing device) as a device for fixing an unfixed image formed and supported on a recording material.

  Conventionally, a heat roller type or a film heating type is known as a fixing device in an image forming apparatus such as a copying machine or a printer.

  In particular, a film heating type fixing device has been proposed in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like, and it can suppress power consumption as much as possible without supplying power during standby. It is effective as an energy-saving on-demand fixing device.

  The basic configuration includes a heater (heating member, heating body) fixedly supported by a film guide member, and a heat-resistant and thin film (fixing film) that slides on the heater and the film guide member. A fixing member, and a pressure roller as a pressure member that forms a fixing nip by pressure contact with a heater via the film, and sandwiches and conveys a recording material on which an unfixed image is formed at the fixing nip portion. The unfixed image is heated and fixed as a permanent image by heat from a heater through a film.

  As a film driving method in a film heating type fixing device, a driving roller is provided on the inner peripheral surface of the film and the film is driven while tension is applied to the film. Although a system is known in which the film is driven to rotate with respect to the pressing rotator by driving, the latter pressure roller driving system is often adopted in recent years because the number of components is small.

In the pressure roller driving system, as disclosed in Patent Document 5, a fixing film and a film guide member are provided by interposing a heat-resistant lubricant (grease) between the fixing film and the film guide member. It is customary to ensure the slidability between the two.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP-A-5-27619

  However, especially in the above-described film heating and fixing apparatus of the pressure roller driving system, the rotation of the film is driven rotation depending on the rotation driving of the pressure roller, and depending on the recording material passing condition, the conveyance abnormality (between film and recording material) Image disturbance due to slip, or jamming due to conveyance failure due to slippage between the pressure roller and the recording material, etc. was likely to occur.

  Occurrence of the conveyance abnormality occurs in a state where sliding resistance between the film and the film guide member (or heater) becomes large, and sliding resistance between the film and the recording material or the pressure roller and the recording material. When the inventor confirmed the occurrence conditions of slip, it was found that the occurrence occurred easily under the following conditions.

Condition (1): At the time of heating drive of a fixing device left in a low temperature condition Condition (2): At the time of heat driving of a durable fixing device Condition (3): At the time of printing a thin recording material with a high water content Condition (4): Low hardness During intermittent printing with a rubber / surface tube pressure roller

[Condition (1)]
The fixing device left in a low temperature environment is difficult to work with lubrication because the grease interposed between the film and the film guide member or the heater is cooled, and the sliding resistance of the inner surface of the film increases. Rotation failure) and recording material conveyance force decrease easily. For condition (1), there may be a case where a heater is heated immediately before the fixing driving (when the driving is stopped) and the driving of the apparatus is started after the grease in the fixing nip is sufficiently melted. Many.

[Condition (2)]
The printing endurance fixing device has a reduced film slip and recording material conveyance force due to the increase in sliding resistance of the film inner surface due to exhaustion of the oil component of the grease or generation of abrasion powder during film sliding. Is likely to occur. For condition (2), countermeasures such as preventing an increase in sliding resistance due to durability are often taken by improving the grease member or the heater surface / film guide surface.

[Condition (3)]
A recording material left in a high-humidity environment has a high water content, and when the high-humidity recording material is sandwiched in the fixing nip, a large amount of water vapor is likely to be generated from the inside of the recording material due to the heat of the pressure roller and the film. The large amount of water vapor generated at this time is interposed between the recording material and the pressure roller, or between the recording material and the film, so that each sliding resistance is lowered and the conveying force of the recording material is significantly reduced. It becomes easy to cause a film slip and a decrease in conveying force of the recording material. As a result of verification of a slip-prone recording material, it occurred in the case of smooth paper with a moisture content of 8.0% or more and a basis weight of 70 g / m2 or less that was left in a high humidity environment such as a 23 ° C. and 70% RH environment. I found it easy.

  For condition (3), the moisture content of the recording material is estimated by disposing a humidity sensor and a paper resistance sensor in the image forming apparatus, and the fixing temperature is lowered when the moisture content is judged to be large. It is conceivable to take measures to suppress the generation amount of water vapor by preventing excessive heating of the pressure roller and the film by suppressing the heating amount during rotation.

[Condition (4)]
In a fixing device using a low-hardness rubber / surface tube type pressure roller, the surface pressure of the fixing nip is low and the frictional resistance (μ) of the surface is small, so the material is conveyed from the pressure roller to a film or recording material. The transmission force is small and the slip is likely to occur. Further, in intermittent printing, the pressure roller is heated and stored for a long time due to residual heat in each printing process, etc., so the pressure roller temperature tends to be higher than that in continuous printing. When the pressure roller temperature is high, the amount of water vapor generated from the inside of the recording material described in the condition (3) increases, and slip is more likely to occur. When the inventor verified with the above-mentioned high-humidity paper, by performing intermittent printing with a short stop interval using a rubber hardness of 45 ° or less (Asker-C hardness meter: 500 gf load), a surface PFA tube pressure roller, When the pressure roller surface temperature exceeded 150 ° C., significant slip jamming was observed.

  For condition (4), measures by improving the pressure roller member, such as increasing the rubber hardness, increasing the surface frictional resistance, etc., or placing a pressure roller temperature sensor in the image forming apparatus, the pressure roller temperature is A countermeasure by fixing control such as lowering the fixing temperature when the temperature exceeds a predetermined temperature or suppressing the heating amount during rotation before printing can be considered.

  The above-mentioned film slip or the conveyance failure jam caused by the slip not only deteriorates the image quality on the recording material but also gives the user troublesome jam processing and the like, so slip suppression is important for ensuring the quality of the image forming apparatus. Although it is a proposition, it is not preferable to take measures such as lowering the fixing temperature over a variety of recording materials among the above-described measures against slip, because it is in the direction of sacrificing fixing properties. Since the slip generation condition is limited as described above, it is more preferable that the slip suppression control is performed only when the generation condition is concerned. However, as means for detecting the generation condition, the humidity sensor, paper, etc. It is not preferable to additionally provide a resistance sensor, a pressure roller temperature detection sensor, or the like in the image forming apparatus because the cost of the apparatus increases. Further, a film rotation speed detection device as disclosed in JP-A-2001-203072 is also expensive as a method that can directly detect film slip. Further, although the sliding surface between the heater or the film guide and the film inner surface has been improved or the grease member has been improved, it is difficult to completely suppress the sliding resistance.

  The present invention has been made in view of the above problems, and detects a film slip in a film heating type fixing device or a conveyance failure jam caused by a slip of a recording material by a low-cost predictive detection method, and based on the detection result. An object of the present invention is to provide an image forming apparatus capable of performing slip prevention control and to improve the reliability of this type of fixing device.

An image forming apparatus according to the present invention for solving the above-mentioned problems is as follows.
(1) a fixing member having a heating body, a thin film that slides on the heating body, and a pressure member that presses the heating body through the thin film to form a fixing nip, An image having a fixing device that sandwiches and conveys a recording material on which an unfixed image is formed at a fixing nip portion, and fixes the unfixed image as a permanent image on the recording material by heat from the heating body via the thin film. In the forming device,
The fixing device includes a temperature detection unit that detects a temperature of the heating body, and the image forming apparatus includes a temperature monitoring unit that monitors a temperature detected by the temperature detection unit, and sets the temperature of the heating body to a predetermined value. It has a heating element heat generation control means for controlling the temperature range,
An abnormal state of conveyance of the recording material in the fixing nip portion is predicted or detected based on a monitoring result by the temperature monitoring unit.

  (2) In the image forming apparatus according to (1), when the heating member starts heat generation by the heating member control unit while the recording material is not sandwiched in the fixing nip, the temperature monitoring unit obtains the temperature. The abnormal conveyance state is predicted when the rising temperature rising rate of the temperature detecting means is faster than a predetermined range.

  (3) During the predetermined temperature control of the heating body in the fixing device according to (1), when the amplitude of the temperature detected by the temperature detection unit by the temperature monitoring unit is larger than a predetermined range, the abnormal conveyance state Is predicted or detected.

  (4) In the image forming apparatus according to any one of (1) to (3), heating body input power detecting means for detecting start-up power input to the heating body in the fixing device, or the start-up power Heating element input power control means for controlling the temperature detection means to a predetermined value, and based on the detection result by the heating element input power detection means or the control power value by the heating element input power control means, A predetermined range of the temperature speed or a predetermined range of the detected temperature amplitude during the predetermined temperature control of the heating body is determined.

  (5) In the image forming apparatus according to (4), the heating body input power detection unit is configured to start up the temperature detection unit when the predetermined amount of electric power is applied while driving of the fixing device is stopped. On the basis of any of the above, the input power to the heating body is detected.

  (6) In the image forming apparatus according to any one of (1) to (3), when the conveyance abnormality state is predicted or detected, the image forming apparatus performs temperature rise prevention control of the pressure member. It is a feature.

  (7) In the image forming apparatus according to (6), the temperature rise prevention control of the pressure member is control for suppressing a heat generation amount of the heating body by the heating body heat generation control means. Is.

  (8) In the image forming apparatus described in (6), the temperature rise prevention control of the pressure member is characterized in that the sheet feeding timing of the recording material is advanced earlier than usual.

  (9) In the image forming apparatus according to any one of (1) to (3), the image forming apparatus includes a conveyance abnormality warning unit that warns a user of the abnormal conveyance state, and predicts or detects the conveyance abnormality. In this case, the image forming apparatus issues a warning by the conveyance abnormality warning means.

  The operation of the present invention will be described below. In the case of the fixing device condition in which the abnormal conveyance state (recording material slip) occurs, the film rotation occurs because the film inner surface sliding resistance becomes larger than usual or the outer surface sliding resistance becomes smaller than usual. The speed becomes unstable. In a state where the film rotation speed is slower than a predetermined value, the temperature increase rate of the inner surface of the film sandwiched between the heaters by the film heat insulating effect, and consequently the temperature increase rate of the heater itself increases. In addition, since the film inner surface temperature rapidly varies according to the variation of the film rotation speed, the detection temperature ripple (temperature difference) increases when the heater heating constant temperature control is performed. By monitoring the temperature rise rate and temperature fluctuation with a temperature detection element (thermistor), it is possible to easily detect and detect film slip or slip occurrence during rotation before printing or when the recording material enters the fixing nip. It becomes.

  According to the present invention, film slip or recording material slip jam in a film heating type fixing device is detected by a low-cost predictive detection method that does not require a new device, and slip prevention control is performed based on the detection result. It is possible to provide an image forming apparatus capable of performing the above.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  The details of the present invention will be described by way of specific examples with reference to the drawings.

  FIG. 1 is a schematic sectional view of a film heating type fixing device mounted in an image forming apparatus according to the present invention. The fixing device of this embodiment is a pressure roller drive type, and a film support 71 holding a heating body 73 is pressed against a pressure roller 74 with a predetermined pressing force via a cylindrical heat resistant film 72. A fixing nip portion N is formed between the heating member 73 and the heating member 73.

  The rotational force acts on the film 72 by the frictional force with the outer surface of the heat resistant film 72 due to the rotation of the pressure roller 74, and the film 72 rotates around the outer periphery of the film support 71 holding the heating body 73 in the direction of arrow a. In the state where the heating body 73 is heated by the temperature monitoring means 20 and the heat generation control means 21 to be described later, and the heating body 73 is adjusted to a print temperature, for example, 180 ° C., the fixing nip N When the recording material P carrying the unfixed toner image T that is the material to be heated is input, the heat of the heating body 73 is applied to the recording material P through the heat resistant film 72, and the unfixed toner image T is formed. It is heat-fixed on the surface of the recording material P. The recording material P that has passed through the fixing nip N is separated from the surface of the heat-resistant film 72 and is discharged.

  The film support 71 has heat insulation, high heat resistance, and rigidity, such as polyphenylene sulfide (PPS), polyamide imide (PAI), polyimide (PI), polyether ether ketone (PEEK), liquid crystal polymer, etc. Resins and composite materials of these resins and ceramics, metal, glass and the like.

  The cylindrical heat-resistant film 72 is, for example, a thin film cylinder having a base layer of polyimide having a thickness of about 30 μm to 100 μm. The base layer is coated with PFA, PTFE or the like via a conductive primer, and is separated from the toner. Maintains type. In addition, a sliding grease (not shown) is applied between the inner surface of the film 72 and the film support 71 to maintain the sliding property of the film 72.

  The pressure roller 74 is provided with a silicone rubber layer 74b as a base layer on a metal core 74a, and a PFA top layer 74c having a thickness of about 10 to 100 μm is provided on the silicone rubber layer 74b through a primer layer (not shown). It is configured and maintains releasability from the toner.

  Reference numeral 73 denotes a heating body. For example, Ag / Pd is formed on one side of a heater substrate 73a using a heat-resistant, electrically insulating, low heat capacity ceramic base material such as alumina having a length of 270 mm, a width of 8 mm, and a thickness of 1 mm. A resistance heating element (energization heating element) layer 73b, a surface protection layer 73c covering the resistance heating element layer 73b, a power supply electrode pattern 73d, and the like are formed, and the heating element 73 is attached based on the energization control from the heat generation control means 21. Electric heating is performed (FIG. 2).

  The power control to the heating element 73 by the heat generation control means 21 includes zero-cross wave number control for controlling the execution and stop of energization for each half wave of the power waveform, and a phase for controlling the phase angle for energizing for each half wave of the power waveform. A multi-stage power control method such as control is used.

  FIG. 3 shows a schematic configuration diagram of the temperature monitoring means 20 of the heating body 73. The temperature monitoring means 20 has a temperature detection element (hereinafter referred to as a thermistor) 75, a pull-up resistor 76, and a temperature monitoring power source 77 on the circuit, and controls the temperature of the heating body 73. The thermistor 75 is composed of a thermistor holder 75a fixed by a fixing member (not shown), a ceramic fiber layer 75b having heat resistance, heat insulation, and elasticity, an NTC thermistor 75c, and a polyimide thin film 75d as a unit. Is pressed. When, for example, DC 5 V is applied by the temperature monitoring power supply 77, the temperature of the NTC thermistor 75c is detected by monitoring the divided voltage Vth based on the resistance ratio between the NTC thermistor 75c and the pull-up resistor 76.

  The temperature control of the heating element 73 is caused to function as follows. When the resistance heating element layer 73 b is energized by the heat generation control means 21, the heating element layer generates heat and the heater substrate 73 a rises in temperature, and the temperature of the heater substrate 73 a passes through the thermistor 75 and the temperature monitoring means 20. The temperature is detected and fed back to the heat generation control means 21, and energization control is performed on the heating element layer 73 b to control the temperature of the heating element 73 to the print temperature, and in this embodiment 1, the temperature is controlled to 180 ° C.

  The heat generation control means 21 in the first embodiment fixes an initial input power (hereinafter also referred to as “start-up power”) that is energized to start up the heating element 73 to a predetermined temperature when heating of the fixing device is started. The temperature control is controlled to a value, for example, 600 W and raised to a predetermined temperature, and the above-described feedback energization control is performed.

  Next, the details of the slip prediction control according to the present invention will be described with reference to the flowchart of FIG. In the first embodiment, an expected startup time range is set for the startup power 600W. When the fixing device of Example 1 is used to start up 600 W, the time for the temperature of the thermistor 75 to rise from 60 ° C. to 130 ° C. depends on the components constituting the fixing device, the ambient temperature environment, and the periphery of the fixing device. It is known from prior examination that it is usually 2.0 sec ± 10% including variation in temperature environment, and the expected start-up time range is set to [1.8 to 2.2] sec. With respect to this expected start-up time range, the temperature monitoring means 20 measures the time Δt until the thermistor 75 rises from 60 ° C. to 130 ° C. after actually starting energization heating to the heating element 73 (S 43). Then, it is determined whether or not it is faster than the lower limit 1.8 sec of the above time range, and if it is fast, a slip prediction flag is set and slip occurrence prediction is detected (S44).

  In the first embodiment, when the slip prediction flag is raised during the startup of the heating element 73, the target temperature during pre-printing rotation (pre-rotation temperature adjustment) is 140 ° C., which is 40 degrees lower than the normal target temperature of 180 ° C. Control to switch to print temperature adjustment 180 ° C. immediately before the recording material P enters the fixing nip N is performed as slip prevention control (S 46 to 47). This control change prevents an excessive temperature rise of the pressure roller 74 by suppressing the heat generation amount of the heating body 73 during the pre-rotation, and reduces the amount of water vapor generated when the recording material P enters the fixing nip, thereby reducing the recording material. The purpose is not to drop the friction coefficient μ between P and the pressure roller 74 (film 72). If the slip prediction flag is not set in S44, temperature control is performed with the print temperature adjustment of 180 ° C. as the target temperature.

Next, Table 1 shows the results of a verification experiment of Example 1 using thin paper smooth paper (60 g / m ² ) left for 48 hours in a high humidity environment (32 ° C./80% Rh). Here, the fixing device conditions for verification are as follows, and the presence / absence of slip occurrence in Example 1 and the conventional example is indicated by ○ (no occurrence) and × (occurrence).

Verification (1): Durable fixing device depleted of sliding grease (film 72 inner surface-film support
71 large μ)
Verification (2): Pressure roller rubber hardness 42 ° (Asker-C hardness meter: 500 gf load)
Fixing device (μ surface between film 72 outer surface and pressure roller 74 is small)
Normal: Pressure roller rubber hardness 47 ° (Asker-C hardness meter: 500 gf load)
Normal fuser (normal state)

  According to Table 1, while the temperature rise time from 60 ° C. to 130 ° C. is 2.0 sec in the normal fixing device, both the verification (1) and (2) are set to the expected start-up time range [1.8-2. .2] less than sec. This mechanism will be described below.

  The verifications (1) and (2) are conditions that apply to the slip generation conditions described above as the fixing unit conditions. (1) has a large frictional resistance between the inner surface of the film 72 and the film support 71. ) Has a small frictional resistance between the outer surface of the film 72 and the surface of the pressure roller 74. In such a state, the rotational movement of the film 72 is not stable even during the pre-printing rotation without the recording material P interposed, and there is a state that is extremely slow compared to the film rotation speed of the normal fixing device.

  FIG. 5 shows a conceptual diagram of heat transfer from the resistance heating element 73b during rotation before printing (in a state where the recording material P is not interposed). The amount of heat Q from the resistance heating element 73b is divided into heat Qn moving to the fixing nip N side and heat Qh moving to the heater substrate 73a side. Further, the heat Qn is divided into heat Qf held by the film 72 and heat Qp held by the pressure roller 74. Normally, both the heat Qf and the heat Qp leave the fixing nip N due to the rotational movement of the pressure roller 74 and the film 72, whereas when the rotational speed of the film 72 is extremely slow as described above, Although Qp leaves the fixing nip N by rotational movement, the heat Qf tends to stay in the fixing nip N, and the temperature of the fixing nip portion on the inner surface of the film 72 tends to rise rapidly. When the thermal conductivity of the film 72 (polyimide base layer) is larger than that of the heater (alumina, glass), the heat of the fixing nip portion on the inner surface of the film 72 that has been heated is more easily transferred to the heating body 73 side than the pressure roller 74 side. Therefore, the heating rate of the heating body 73 itself is also increased. Therefore, it is considered that the temperature increase rate of the thermistor 75 arranged on the back side of the heater substrate 73a is also higher than usual, resulting in the rise time results as shown in Table 1.

  As described above, according to the configuration of the first embodiment, the temperature rise rate of the heating body (thermistor) during rotation before printing is monitored, and if the recording material slips faster than the expected start-up time range, the recording material can slip. Therefore, it is possible to perform slip occurrence prevention control accompanying detection.

  In the first embodiment, only the temperature rise rate measurement of the start-up time during the rotation before printing has been described. However, the temperature rise measurement is not limited to this, and is performed between the recording material and the next recording material (between sheets). The same effect can be obtained even when performing the above.

  In the first embodiment, only the control for preventing the excessive temperature rise of the pressure roller by lowering the temperature control target temperature during the rotation before printing has been described as the slip generation prevention control when the slip prediction is detected. Not limited to this, this control can be implemented if control to suppress the heating temperature of the pressure roller, such as control to reduce the amount of heat generated by the heating element during the previous rotation, such as a reduction in the amount of control power, or advance the recording material feed timing, etc. The same effect as in Example 1 is obtained. Furthermore, if control is performed to suppress the amount of heat generation, such as printing temperature adjustment of the heating member while the recording material is nipping and conveying the fixing nip, a further slip prevention effect can be obtained.

  Further, in an image forming apparatus having a conveyance abnormality warning means for warning a user of a conveyance abnormality state, a warning can be given to the user when detected by the slip prediction detection method of the present invention, and a recording material conveyance failure jam or the like can occur in advance. It can also be prevented.

  An image forming apparatus according to the second embodiment will be described.

  In the first embodiment, the slip prediction is detected by measuring the rising temperature increase rate of the heating element 73 during the rotation before printing. In the second embodiment, the detected temperature ripple during the target temperature control, that is, the constant temperature control is performed. The point that slip prediction is detected by measuring the detected temperature amplitude of the thermistor 75 is different from that of the first embodiment, and the other configurations are the same as those of the first embodiment.

  Details of the slip prediction control in the second embodiment will be described with reference to the flowchart of FIG. In the second embodiment, the expected temperature ripple range is set for the startup power 600W. When the fixing device in Example 2 is used to start up 600 W and the temperature control is performed at 180 ° C. by the multi-stage power control method such as the zero cross wave number control or the phase control described above, the temperature of the thermistor 75 becomes 180 ° C. It has been found in advance that the detected temperature ripple for 1 second after reaching this temperature is usually 180 ° C ± 3 deg., Including variations in each part of the fixing device, ambient temperature environment, and fixing device ambient temperature environment. The expected temperature ripple range was set to [177 to 183] ° C. In S62, temperature control is performed by setting the target temperature during rotation before printing to 180 ° C., and the temperature monitoring means 20 monitors the detected temperature ripple of the thermistor 75 within a time range of 1 second after reaching 180 ° C. (S63). ), It is determined whether or not the detected temperature T within the time range is out of the temperature range (S64). When the detected temperature T is out of the temperature range, a slip prediction flag is set and slip occurrence prediction is detected (S65).

  In the second embodiment, when the slip prediction flag is set during the pre-rotation temperature adjustment control of the heating body 73, the heat generation of the heating body 73 is turned off and turned on again at a predetermined timing to enter the recording material P in the fixing nip N. Switching control is performed as anti-slip control so that the print temperature control rises to 180 ° C. before the ink enters (S66 to 67). As in the first embodiment, this control change prevents excessive heating of the pressure roller 74 by suppressing the amount of heat generated by the heating body 73 during the pre-rotation, and water vapor is generated when the recording material P enters the fixing nip. The purpose is to prevent the friction coefficient μ between the recording material P and the pressure roller 74 (film 72) from being reduced by reducing the amount. If the slip prediction flag is not set in S64, the temperature control is continued with the print temperature control of 180 ° C. as the target temperature.

Next, Table 2 shows the results of the verification experiment of Example 2 using thin paper smooth paper (60 g / m ² ) left for 48 hours in a high humidity environment (32 ° C./80% Rh). Here, there are three fixing device conditions for verification: “Verification (1)”, “Verification (2)”, and “Normal” in the first embodiment.

  According to Table 2, while the detected temperature during the 180 ° C. temperature control is within the expected range in the normal fixing device, both the verification (1) and (2) have the set temperature ripple expected range [177− 183] ° C., and the detected temperature ripple is larger than usual. This phenomenon is also a phenomenon caused by the same mechanism as described in the first embodiment. Even when a constant temperature control is performed with a predetermined energization control amount, the rotational speed of the film 72 during the previous rotation is unstable. Since heat transfer also becomes unstable, the detected temperature ripple of the thermistor 75 increases.

  As described above, according to the configuration of the second embodiment, it is possible to monitor the detected temperature ripple of the thermistor during the constant temperature control of the heating body and determine the possibility of the occurrence of the slip of the recording material when it is out of the set range. It has become possible to carry out slip occurrence prevention control accompanying detection.

  In the second embodiment, only the case where the temperature ripple during the constant temperature control during the rotation before printing is monitored has been described. However, the present invention is not limited to this, and the interval between the recording material and the next recording material (between sheets). Even when the temperature ripple is monitored in a state where the recording material is held in the fixing nip N, the same effect can be obtained by setting an appropriate temperature ripple range for each.

  In the second embodiment, as the slip occurrence prevention control when the slip prediction is detected, the energization heating is turned off during the rotation before printing. However, the present invention is not limited to this, and the control for suppressing the excessive temperature rise of the pressure roller or the recording material is not limited. Then, the same effect as in the second embodiment can be obtained.

  An image forming apparatus based on the third embodiment will be described.

  In the first and second embodiments, the startup power value of the heating element 73 is controlled to 600 W by the heat generation control means 21, and in this third embodiment, the AC power supply voltage or a predetermined duty ratio to the power supply voltage is set. The difference is that slip prediction is detected after the startup power is input. In the configuration of the third embodiment, a constant power control circuit is not required in the heat generation control means 21, and slip prediction detection can be performed at a lower cost.

  However, since the temperature increase rate and temperature ripple of the thermistor 75 during rotation before printing in Examples 1 and 2 change only with different startup power, slip prediction cannot be detected as it is. In the third embodiment, the start-up power input to the fixing device is detected at low cost, and the “estimated start-up time” and “temperature ripple range” are set based on the detected start-up power to predict the slip. It is characterized by detecting.

  First, the heating body 73 startup power detection in the third embodiment will be described. The rising power detection in the third embodiment is a detection method in which energization heating is performed for a predetermined time while driving of the fixing device is stopped, and electric power is estimated from the temperature rise of the thermistor 75 at that time. When the inventor conducted a preliminary study, using the fixing device of this embodiment, when the temperature reached by the thermistor 75 was plotted when the fixed power was applied for 0.5 seconds while the drive was stopped, the input power and the temperature increase were plotted. It was found that there was a very linear correlation with the degree as shown in FIG. From this correlation, a power supply voltage is applied to the heating element 73 for a predetermined time (0.5 sec in the third embodiment) while the fixing device is stopped, and the temperature monitoring means 20 determines the temperature rise of the thermistor 75. The rising power supplied to the heating body 73 can be detected. The reason why the current is heated while the drive is stopped is that there is a possibility that the temperature rise may change depending on the coefficient of friction of the fixing member if it is driven to rotate, and that the heat transfer described above is performed when the drive is stopped. This is because the heater can easily rise in temperature, and the power detection accuracy is improved. Furthermore, when the heating device is energized and heated before the fixing device is driven, the sliding grease (not shown) interposed between the heating body 73 and the film 72 can be efficiently melted. This is because it is possible to prevent the occurrence of slip when the apparatus is heated.

  Next, details of the slip prediction control of the third embodiment will be described with reference to the flowchart of FIG. In the third embodiment, after the printing is started and before the fixing device is driven, the AC power supply voltage is continuously applied to the heating body 73 for 0.5 seconds, and the heat generation is temporarily turned off (S82 to 83). Then, the temperature increase ΔT0 of the thermistor 75 is obtained by the temperature monitoring means 20, and the corresponding “estimated rise time from 60 ° C. to 130 ° C.” (or “expected temperature ripple range during constant temperature control at 180 ° C.”) is displayed. 3 is set based on 3 (S84).

  Since the flow after the setting is the same as that of the first embodiment (or the second embodiment), the description thereof is omitted.

  According to the configuration of the third embodiment, the power input to the heating body can be easily detected even in a low-cost image forming apparatus that does not require a constant power control circuit, regardless of the power supply voltage. The slip of the recording material can be predicted or detected by setting the degree of temperature rise or the temperature ripple.

  In the third embodiment, the AC power supply voltage is applied 100% as the voltage application value while the fixing device driving is stopped, and the applied power is detected. However, the power detection is performed by applying a predetermined duty (for example, 50% application). May be. In the third embodiment, the temperature rise of the thermistor (temperature difference from the initial temperature before heating to the ultimate temperature) is used when detecting power, but the power may be estimated from the rate of temperature increase of the thermistor.

  Further, in the third embodiment, after power detection, the power supply voltage is input as it is as the rising voltage applied during driving of the fixing device. However, the present invention is not limited to this, and the predetermined voltage is determined based on the power detection result. You may determine the starting duty for starting up with an electric power value (for example, 600W).

Schematic sectional view of a film heating type fixing device according to the present invention Partially cutaway plan view of a heating element according to the present invention Schematic configuration sectional view around the thermistor according to the present invention Control flow chart of image forming apparatus based on first embodiment Conceptual diagram of heat transfer from the resistance heating element in the heating element in Example 1 Control flow chart of image forming apparatus based on second embodiment Correlation diagram between input power and thermistor temperature when the fixing device is stopped in the third embodiment Control flow chart of image forming apparatus based on third embodiment

Explanation of symbols

71 Film support means 72 Fixing film 73 Heating body 74 Pressure roller 75 Thermistor

Claims (9)

A fixing member having a heating body, a thin film that slides on the heating body, and a pressure member that presses the heating body through the thin film to form a fixing nip; An image forming apparatus having a fixing device that sandwiches and conveys a recording material on which an unfixed image is formed and fixes the unfixed image as a permanent image on the recording material by heat from the heating body via the thin film ,
The fixing device includes a temperature detection unit that detects a temperature of the heating body, and the image forming apparatus includes a temperature monitoring unit that monitors a temperature detected by the temperature detection unit, and sets the temperature of the heating body to a predetermined value. It has a heating element heat generation control means for controlling the temperature range,
An image forming apparatus that predicts or detects an abnormal conveyance state of the recording material in the fixing nip portion based on a monitoring result by the temperature monitoring unit.   2. The image forming apparatus according to claim 1, wherein the temperature obtained by the temperature monitoring unit when the heating body control unit starts to generate heat while the recording material is not sandwiched in the fixing nip. 3. An image forming apparatus characterized in that the abnormal conveyance state is predicted when a rising temperature rising rate of the detection means is faster than a predetermined range.   2. The abnormal conveyance state is predicted or detected when an amplitude of a temperature detected by the temperature detection unit by the temperature monitoring unit is larger than a predetermined range during the predetermined temperature control of the heating body in the fixing device according to claim 1. An image forming apparatus.   4. The image forming apparatus according to claim 1, wherein heating body input power detection means for detecting start-up power input to a heating body in the fixing device, or the start-up power is controlled to a predetermined value. A heating body charging power control means, based on a detection result by the heating body charging power detection means or a control power value by the heating body charging power control means, a predetermined range of the rising temperature rising rate of the temperature detection means, Alternatively, the predetermined range of the detected temperature amplitude during the predetermined temperature control of the heating body is determined.   5. The image forming apparatus according to claim 4, wherein the heating body input power detection unit is set to any one of a rising speed and a reached temperature of the temperature detection unit when a predetermined amount of power is input while driving of the fixing device is stopped. An image forming apparatus that detects input power to the heating body based on the image forming apparatus.   The image forming apparatus according to claim 1, wherein when the abnormal conveyance state is predicted or detected, the image forming apparatus performs temperature rise prevention control of the pressure member. .   The image forming apparatus according to claim 6, wherein the temperature rise prevention control of the pressure member is control for suppressing a heat generation amount of the heating body by the heating body heat generation control unit.   7. The image forming apparatus according to claim 6, wherein the temperature rise prevention control of the pressurizing member advances the paper feeding timing of the recording material earlier than usual.   The image forming apparatus according to claim 1, wherein the image forming apparatus includes a conveyance abnormality warning unit that warns a user of the conveyance abnormality, and the image formation is performed when the conveyance abnormality state is predicted or detected. The image forming apparatus is characterized in that the apparatus gives a warning by the conveyance abnormality warning means.

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