JP2006154649A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the hot offset which occurs in a part trough which a small-sized paper doesn't pass when being fed, occurs due to this part remaining at high temperature even after the end of the small-sized paper feed, and occurs when feeding a normal-sized paper next. <P>SOLUTION: A post-rotation time from the end of heat treatment to the stop of an apparatus is extended in accordance with a temperature difference between a main thermistor and a sub-thermistor at the time of the end of heat treatment, or a fixing temperature for the next print is reduced by a prescribed amount in accordance with a temperature difference between the main thermistor and the sub-thermistor before the start of print. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a heating apparatus for a material to be heated, an electrophotographic apparatus, an electrostatic recording apparatus, and the like provided as an apparatus for heating and fixing an unfixed image formed and supported on a recording material (hereinafter also referred to as a sheet). The present invention relates to a heating apparatus and an image forming apparatus.

  An image forming apparatus such as a printer / copier forms and supports an unfixed toner image of image information by a transfer method or a direct method on an image forming unit such as an electrophotographic process or an electrostatic recording process on a recording material, The recording material is conveyed and introduced into a heating device (fixing device, fixing device) to heat and fix the image as a permanently fixed image, and output as an image formed product.

  As a heating device, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like have proposed a film heating type heating device (Patent Documents 1 to 4). This is a system in which the heat of the heating body is applied to the recording material through a film and the unfixed image on the recording material is heated and fixed as a permanent image. Other known heat roller systems and hot plate systems Compared with image heating and fixing devices such as heat chambers, it is possible to use a heating element with a low heat capacity or a thin film that has a high temperature rise, thus saving power and shortening the wait time (quick start). It becomes. In addition, there is an advantage that various disadvantages of other conventional heating devices can be eliminated, which is effective.

  Incidentally, recording materials having various widths and lengths are passed through the image forming apparatus and its heating device. Here, when a particularly narrow recording material such as an envelope is continuously fed, the temperature rises in the portion that does not pass due to the difference in heat consumption between the portion where the recording material passes and the portion that does not pass in the heating device. The so-called “non-sheet passing portion temperature rise” occurs. If this phenomenon becomes severe, the thermal expansion of the pressure roller of the heating device will become uneven, and the rubber will break, or in the case of a film heating type heating device, a difference will occur in the film feed rate, resulting in twisting. To do. In addition, when the heat resistance temperature of the apparatus is exceeded, the surface of the pressure roller and the heater holder are melted.

  Alternatively, if the normal size paper is passed immediately after the small size paper is passed, the non-passage portion of the small size paper is at a high temperature, so excessive melting of toner occurs here, and the small size paper is not passed. A hot offset also occurs in a portion corresponding to the portion.

  Therefore, in order to prevent such a phenomenon, a configuration in which a temperature detection element is arranged in a region that becomes a non-sheet passing portion when a narrow sheet on a heater is passed and a temperature of the non-sheet passing portion is detected in recent years. Is often used (for example, Patent Document 5).

  FIG. 2 is a schematic cross-sectional view of a film heating type heating apparatus, and FIG.

  A heater 22 is supported by a heater holder 23 and is in pressure contact with a pressure roller 25 via a fixing film 21 by a pressure unit (not shown). The fixing film 21 is driven to rotate by the rotational driving of the pressure roller 25, conveys the recording material P introduced into the nip H, and applies heat of the heater 22 to the recording material P through the film 21. Reference numeral 51 denotes a main thermistor disposed at a position that always becomes a sheet passing area regardless of the size of the recording material, and controls the amount of heat generated by the heater 22 by maintaining the detected temperature at a predetermined temperature. To obtain the optimum heating amount for fixing the recording material.

  Reference numeral 52 denotes a sub-thermistor disposed at a position that becomes a non-sheet passing area when a recording material having a width smaller than the B5 size is passed. The sub-thermistor 52 is not used for temperature control, and only detects an abnormal temperature rise of the heater, such as a non-sheet temperature rise.

  When the recording material heating process ends, the apparatus performs a predetermined post-rotation and stops.

  In this configuration, when a recording material having a narrow width is continuously passed, the sub-thermistor 52 detects a temperature significantly higher than the detection temperature of the main thermistor 51 during the passing of the recording material. Here, if the sub-thermistor 52 rises to a predetermined temperature, control is performed such as waiting for a predetermined time to feed the paper and lowering the throughput or lowering the heating temperature, thereby reducing the temperature of the non-sheet passing portion. Prevent destruction.

  In addition, a configuration is also proposed in which the heating device is controlled to rotate in a non-heated state in which the energization of the heater 22 is stopped until the temperature of the sub-thermistor 52 is lowered to a predetermined temperature after the completion of the heat treatment of the small size paper. (For example, patent document 6).

  In order to prevent hot offset that occurs when normal size paper is passed immediately after passing small size paper, it is effective to wait for the next heat treatment until the temperature of the non-paper passing portion drops to some extent, If it stops immediately and waits, it will take a long time for the temperature to drop. On the other hand, when the heating device is rotated without causing the heater to generate heat, the temperature of the non-sheet passing portion that has been overheated can be lowered more quickly than when the device is stopped without rotating. Therefore, the waiting time can be shortened.

  Therefore, the above configuration is extremely effective for preventing hot offset.

  As another method for preventing hot offset, when a print command is issued after continuously passing a small size, when the temperature of the sub-thermistor 52 immediately before printing is higher than a predetermined temperature, In some cases, the heating temperature is set lower than usual.

  If normal size paper is heated at the same temperature as normal time immediately after passing small size paper, the heat storage amount of the non-paper passing portion is large, and this portion is excessively heated, so that the toner melts too much. This is a hot offset mechanism, but if the heating temperature is lowered in accordance with the temperature of the non-sheet passing portion, such excessive heating can be prevented. At this time, the portion that was a paper passing portion at the time of small-size paper passing has a smaller amount of heat storage than the non-paper passing portion, so the fixing property of the paper passing portion is slightly lower than normal. Therefore, the amount of decrease in the heating temperature is set in a balanced manner to a level where there is no problem in fixing performance while preventing hot offset.

Thus, by detecting the temperature of the non-sheet passing portion and applying feedback to the control in accordance with the detected temperature, the apparatus can be controlled so that a good image without hot offset can be output.
JP-A-63-313182 Japanese Patent Laid-Open No. 1-263679 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075-44083 Japanese Patent Laid-Open No. 5-80604 JP-A-6-348175

  However, when the control is performed only according to the temperature of the sub-thermistor as in the above-described conventional apparatus, the control is not necessarily optimal for preventing hot offset.

  The temperature of the sub-thermistor rises to a certain high temperature even when a normal size recording material is passed instead of a small size. However, when a small size is passed from this state, the temperature is originally high. The temperature of the non-sheet passing portion rises to a considerably high temperature just by passing the sheet. At this time, if the configuration is such that the post-rotation is extended and rotated in a non-heated state until the temperature of the sub-thermistor is lowered to a predetermined temperature as in the prior art, a small size is passed for a long time just by passing one sheet. It will rotate afterwards. However, in practice, even if the detection temperature of the sub-thermistor is high, hot offset does not occur if only one small size is passed. Therefore, even if the post-rotation is extended here, there is no meaning, and the user's convenience is impaired because the waiting time until the next printing is unnecessarily prolonged.

  In addition, there is a similar problem in the control for reducing the heating temperature at the next printing when the detected temperature of the sub-thermistor is high.

  In other words, when the amount of heat stored in the device itself has increased due to continuous paper passing of normal size, the non-sheet passing part becomes hot just by passing one small size paper. The control that ends up works. However, in practice, there is no hot offset even at the normal heating temperature, and this control only makes the fixing property meaningless.

According to the first invention of the present application, a heating body, a pressure member that directly or indirectly contacts the heating body to form a pressure nip portion, and a temperature detection element that detects the temperature of the heating body. And the pressure member rotates to heat the heated material conveyed and introduced into the pressure nip, and then the heated material is discharged to stop driving the apparatus. In the heating device, when a material to be heated whose width is shorter than a predetermined size is conveyed, at least one of the temperature detection elements is disposed at a position to be a sheet passing portion, and at least the other of the temperature detection elements. One is arranged at a position to be a non-sheet passing portion, and heating of the heated material is performed according to a temperature difference detected by the temperature detecting element of the non-sheet passing portion and the temperature detecting element of the sheet passing portion. Time from the end of processing to the stop of device drive Further, according to the second invention of the present application, in the first invention, the heating body is not in the period from the end of the heat treatment of the material to be heated to the stop of driving of the apparatus. It is in a heated state.

  According to the third invention of the present application, in the first and second inventions, the time from the end of the heat treatment of the material to be heated to the stop of driving of the apparatus is shorter than a predetermined size. It changes only after a to-be-heated material is conveyed.

  According to the fourth invention of the present application, the heating body and at least two temperature detection elements for detecting the temperature of the heating body are provided, and the heat energy generated by the heating body is conveyed and introduced. When a heated material having a width smaller than a predetermined size is conveyed, the temperature sensing element is disposed at a position to be a sheet passing portion, and is applied to the heating material. In the heating device arranged at least at the position where the non-sheet passing portion is located, the temperature detected by the temperature detecting element of the non-sheet passing portion and the temperature detecting element of the sheet passing portion before the heating body is heated. The heating temperature of the heating body is changed according to the difference.

  According to the fifth invention of the present application, in the first to fourth inventions, the pressure member is brought into contact with the fixedly supported heater through the heat resistant film, and the film member and the pressure member The recording medium is introduced into the press-contact nip formed therebetween, and the recording medium is moved and moved together with the film member, whereby the heat energy of the heating body is applied to the recording medium and the heat treatment is performed.

  According to the sixth invention of the present application, in the first to fifth inventions, the material to be heated is a recording material on which an unfixed image is formed and supported, and the apparatus heats the unfixed image to the recording material. It is a heat fixing device for fixing.

  According to a seventh aspect of the present application, in the image forming apparatus, the image forming unit includes an image forming unit that forms and supports an unfixed image on the recording material, and a fixing unit that fixes the unfixed image formed and supported on the recording material. The fixing unit is the heating device according to any one of the first to sixth inventions.

  1st-3rd invention which concerns on this application WHEREIN: The temperature detection which detects the temperature of the heating body, the pressurization member which contacts the said heating body directly or indirectly, and forms a press-contact nip part, and the said heating body Having at least two elements, the pressure member rotates, heats the heated material conveyed and introduced into the pressure nip, then discharges the heated material and stops driving the device. In the heating device, when a material to be heated having a width smaller than a predetermined size is conveyed, at least one of the temperature detection elements is disposed at a position to be a sheet passing portion, and at least one of the temperature detection elements The other is arranged at a position to be a non-sheet passing portion, and according to the temperature difference detected by the temperature detecting element of the non-sheet passing portion and the temperature detecting element of the sheet passing portion, From the end of heat treatment to the stop of the device drive By changing the interval, even after transporting a small size paper with a short width, the temperature of the portion that was a non-sheet passing portion when passing the small size paper can be kept sufficiently low, It is possible to prevent the occurrence of hot offset when a wide normal size paper is conveyed immediately thereafter. Furthermore, since the time from the end of the heat treatment to the stop of driving of the apparatus can be optimized as compared with the conventional case, it is possible to prevent the apparatus from being driven wastefully after the end of the heat treatment. Thereby, the lifetime of the apparatus can be further extended.

  In addition, in the fourth invention according to the present application, the material to be heated has at least two or more heating elements and temperature detection elements for detecting the temperature of the heating elements, and the heat energy generated by the heating elements is conveyed and introduced. When the heated material having a width smaller than a predetermined size is conveyed, at least one of the temperature detection elements is disposed at a position to be a sheet passing portion, and at least the other of the temperature detection elements One is the difference between the temperatures detected by the temperature detecting element of the non-sheet passing portion and the temperature detecting element of the sheet passing portion before the heating body is heated in the heating device arranged at the position to be the non-sheet passing portion. By changing the heating temperature of the heating body according to the temperature, it is possible to set a more appropriate heating temperature and prevent high temperature offset that occurs in a portion that has become a non-sheet passing portion when a small size paper is passed. And was the paper passing department Deterioration of fixability minute can be prevented.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus according to the present embodiment is a laser printer using an electrophotographic method, has a maximum sheet width of LETTER size, a process speed of 140 mm / sec, a sheet passing interval of 53 mm, and A4 size sheets of 24 sheets / min (ppm). It is a printer that outputs in

  When a print command from a host computer (not shown) is input to the apparatus and driving of the apparatus is started, the paper P as a recording material is fed from the paper feed cassette 10 or the multi-tray 9. The paper P is guided to the paper feed guide 7 and eventually the lever of the top sensor 13 on the transport path is tilted, and it is detected that the leading edge of the paper has passed the position of the top sensor 13. Thereafter, the top sensor 13 continues to detect the paper presence state until the trailing edge of the paper passes the top sensor 13. The lever of the top sensor 13 returns to the original position when the trailing edge of the sheet passes, and it is detected that the trailing edge of the sheet has passed the position of the top sensor 13.

  Eventually, the paper reaches the transfer portion T facing the transfer roller 6 below the photosensitive drum 1. The photosensitive drum 1 is uniformly and uniformly charged by the charging roller 11 and then irradiated with a laser beam L corresponding to an image signal from the laser scanning exposure device 3 to form an electrostatic latent image on the surface. Is done. The laser scanning exposure apparatus 3 reflects laser light on a rotating polygon mirror 31, focuses the reflected light on a lens 32, and irradiates the photosensitive drum 1 with a folding mirror 33 or the like.

  The latent image formed in this manner is selectively made to adhere toner by the developing device 2 and visualized as a toner image, and is conveyed to the transfer portion T as the photosensitive drum 1 rotates. In the transfer portion T, the transfer roller 6 applies an electric field having a polarity opposite to that of the toner from the back surface (back surface) of the paper, thereby transferring the toner image onto the paper.

  The sheet on which the toner image is transferred is guided to the conveyance guide 15 and reaches a fixing device (fixing device) 12 as a heating device, where heat and pressure are applied, and the toner image is fixed on the sheet from the leading edge of the sheet. To go.

  The sheet that has undergone the toner image fixing process is guided to the conveyance guide 16 and discharged as an image formed product (print, copy).

  FIG. 2 is a schematic cross-sectional view of the fixing device 12. A heater 22 as a heating body is supported on a heater holder 23, and is pressed against a pressure roller 25 via a fixing film 21 by a pressing means (not shown). Yes.

  The fixing film 21 may be a single layer mainly composed of heat-resistant PTFE, PFA, FEP or the like, or polyimide, polyamideimide, PEEK, PES, or PPS, in order to reduce the heat capacity as part of speeding up the fixing process. The outer peripheral surface of an endless substrate mainly composed of, for example, PTFE, PFA or FEP is coated with a composite layer, and the total thickness of the film 21 is 100 μm or less, preferably 20 μm or more and 50 μm or less. It has been.

  The heater 22 is formed by applying a heating resistor 222 mainly composed of Ag / Pd (silver palladium) to one surface of a thin plate-like substrate 221 mainly composed of ceramics typified by alumina or the like by screen printing or the like. Then, the thermistor 51 is in contact with or in proximity to the other surface of the substrate 221 as shown in FIG. And is supported.

  The heater holder 23 has a function of supporting the heater and guiding the inner surface of the fixing film 21 over the entire longitudinal direction.

  The pressure roller 25 has a cylindrical elasticity mainly composed of heat-resistant and releasable silicone rubber on the outer peripheral surface of a columnar or substantially columnar core 251 mainly composed of iron, aluminum or the like. The pressure roller 25 rotates in one direction when the core 251 receives a driving force from a driving mechanism (not shown). ing.

  Then, the fixing film 21 is rotated by the rotational driving of the pressure roller 25, conveys the paper P introduced into the nip H, and applies heat of the heater 22 to the paper P through the film 21.

  At this time, the fixing device 12 maintains the heater 22 at a predetermined temperature to obtain an optimum heating amount for fixing the paper. In the fixing device 12 of this embodiment, the normal size (A4 size) is set to 200 ° C. when the paper is passed. The temperature control of the heater 22 is performed by controlling energization to the heater 22 so that the detection temperature of the temperature detection element (thermistor) 51 disposed on the heater 22 becomes constant.

  The output signal of the thermistor 51 is input to the CPU 62 via the A / D converter 61. Based on this input signal, the CPU 62 controls the power supplied to the heating resistor 222 of the heater 22 as a heating body via the AC driver 63 and adjusts the temperature of the heater 22 to a predetermined temperature.

  As a control of the heating operation of the heater 22 by the CPU 62, in addition to the control of switching the amplitude or period of the AC bias energized to the heating resistor 222 according to the detected temperature of the thermistor 51, an external operation over an arbitrary fixed time is performed. Control of adjusting the energization amount from the power source to the heating resistor 222, so-called phase control or wave number control is performed. In particular, the wave number control has an advantage that the noise accompanying the energization is less than that of the phase control. Therefore, in the heating device 12, the wave number control is adopted as the control of the heating operation of the heater 22. ing.

  On the heater 22, in addition to the thermistor 51 used for temperature control, a thermistor 52 is arranged in a region that becomes a non-sheet passing portion when a small size is passed, and the temperature rise of the non-sheet passing portion itself is detected.

  Similarly to the thermistor 51, the output signal of the thermistor 52 is also input to the CPU 62 via the A / D converter 61. The CPU 62 detects the temperature information of the thermistor 52 in real time.

  FIG. 3 is a schematic sectional view of the fixing device 12 in the longitudinal direction.

  51 is a main thermistor arranged at a position that always becomes a paper passing area regardless of which size paper is passed, and 52 is a non-paper passing area when a paper having a width smaller than B5 size is passed. It is a sub thermistor arranged at the position. The sub-thermistor 52 is not used for temperature control, and only detects an abnormal temperature rise of the heater, such as a non-sheet temperature rise.

  When the trailing edge of the paper P passes the position of the top sensor 13, the lever of the top sensor 13 returns to the original position, and it is detected that the trailing edge of the paper has passed the position of the top sensor 13. That is, the top sensor 13 detects that there is no paper (paper out state). In the case of continuous printing, the next sheet is fed at regular intervals, and a print is generated through a similar process.

  The throughput of the sheet is maintained by feeding the next sheet after a predetermined time has elapsed since the top sensor 13 detected the leading edge or the trailing edge of the sheet. In this embodiment, as described above, the sheet passing interval is set to 53 mm with a normal throughput.

  When small-size paper is passed, the time for the top sensor 13 to detect the presence of paper is shorter than when normal-size paper is passed. As a result, the normal size paper and the small size paper are discriminated, and when the paper is shorter than the B5 size, the throughput is switched, and the paper is passed with the throughput lower than the normal 24 ppm. In this embodiment, for example, the sheet passing interval is set to 228 mm, and the throughput is switched to 16 ppm.

  The reason for performing such throughput control is that a sheet having a length shorter than the B5 size is generally short in width, and the temperature rise in the non-sheet passing portion is large. When the temperature detected by the sub-thermistor 52 rises due to the temperature rise of the non-sheet passing portion and exceeds the predetermined temperature, the throughput is further reduced. For example, when the detection temperature of the sub-thermistor 52 exceeds 250 ° C., the throughput is switched to 8 ppm. In this way, by sequentially decreasing the throughput in accordance with the temperature rise of the non-sheet passing portion, the highest possible throughput is maintained and the apparatus is prevented from being damaged.

  When the fixing process for all the sheets set as a print job is completed, the heating device enters a post-rotation and stops after a predetermined time of rotation. It is not necessary to heat at the time of post-rotation. Rather, in order to actively cool the heating device, the heater is turned off and the rotation is performed in a non-heated state.

  After passing a small size shorter than the B5 size, it is necessary to lower the temperature of the non-sheet passing portion that has been overheated in order to prevent hot offset when the next normal size printing is performed. .

  For this reason, after passing the small size paper, control is performed to extend the post-rotation more than usual.

  By the way, in the experiment of the present inventor, data on the occurrence of hot offset depends on the temperature difference between the main thermistor 51 and the sub-thermistor 52 rather than the detected temperature of the sub-thermistor 52.

  FIG. 4 shows an example of the experiment.

  In FIG. 4, the detection temperature of the main thermistor 51 is Tm, the detection temperature of the sub-thermistor 52 is Ts, and the temperature difference between the main thermistor 51 and the sub-thermistor 52 is Ts−Tm.

  The temperature detected by the thermistor here is just before the start of printing.

  In the above example, hot offset does not occur even if the temperature of the sub-thermistor is relatively high at 160 ° C. Conversely, even if the temperature is as low as 90 ° C, the temperature difference between the main thermistor and the sub-thermistor is It turns out that it may become a hot offset when it is large.

  This is natural, and even if the sub-thermistor part is hot, if the main thermistor part is also hot, when the heater is heated as it is, the temperature difference between the main thermistor and the sub-thermistor is almost maintained. Reaches the heating temperature.

  For example, when the temperature difference between the main thermistor and the sub thermistor immediately before the start of printing is 3 degrees, if the heating temperature of the heater controlled by the main thermistor is raised to 200 ° C., the sub thermistor section will be only about 203 ° C. This is not a hot offset.

  Conversely, if the temperature difference before the start of printing is 10 degrees, the main thermistor section is adjusted to 200 ° C., whereas the sub-thermistor section is 210 ° C., which may cause hot offset.

  That is, no matter what the temperature of the sub-thermistor is, the offset does not occur unless the temperature difference from the main thermistor is large, and it can be generated if the temperature difference is large.

  From the above examples, it can be seen that when the control is performed by paying attention only to the detected temperature of the sub-thermistor as in the conventional apparatus, the optimum control is not achieved.

  Therefore, in this embodiment, the post-rotation extension is determined not from the temperature of the sub-thermistor 52 but from the difference in temperature detected by the main thermistor 51 and the sub-thermistor 52.

  Specifically, first, the temperature difference between the main thermistor 51 and the sub-thermistor 52 when the heat treatment is finished and the energization to the heater 22 is turned off is detected. The temperature difference is detected by the CPU calculating Ts−Tm from the detected temperature Tm of the main thermistor 51 and the detected temperature Ts of the sub-thermistor.

Here, when Ts−Tm is 5 degrees or more, the post-rotation is extended, and the post-rotation is continued until the temperature difference becomes 3 deg or less in a non-heated state in which the heater is turned off.
If the post-rotation is performed until Ts−Tm becomes 3 deg or less, the temperature difference between the main thermistor and the sub-thermistor immediately before the start of printing can be reliably made 3 deg or less at the next printing, and the occurrence of hot offset can be prevented. The value of 3 deg is set from the above experimental value, but may be changed as appropriate depending on the characteristics of the toner and the configuration of the apparatus.

  By the way, since the temperature difference is relatively easily eliminated when Ts−Tm is small, the post-rotation extension time is short, and when Ts−Tm is large, the post-rotation is long.

  Here, if the temperature difference Ts−Tm is not easily reduced and the post-rotation is too long, it is not preferable from the viewpoint of the life of the apparatus, and the state where only the rotation is continued is also a source of noise. A time limit may be set. In this embodiment, the maximum post-rotation time is set to 30 seconds.

  When the post-rotation extension time is set as described above, hot offset cannot be completely prevented, but normal-size paper is often printed immediately after a small size is continuously fed. In addition, even if a hot offset occurs, it is very slight, so it is not a problem in actual use. Rather, the problem is that the rear rotation continues forever.

  Further, during the non-rotation after the end of the post-rotation, control may be performed to prohibit the print operation and wait until the temperature difference Ts−Tm becomes equal to or lower than a predetermined temperature by natural cooling.

  By configuring as described above, the post-rotation time can be controlled more appropriately as compared with the conventional configuration in which the rotation time is controlled according to the temperature of the sub-thermistor. That is, it is not necessary to perform unnecessary post-rotation, and the durability of the apparatus and the convenience of the user can be improved.

  The configuration in which the post-rotation time is extended after the small-size paper is passed as in the first embodiment and the heating device is cooled during this time is entered every time regardless of when the next print job comes.

  The reason for this control is that it is not known when the next print job will come at the time when the post-rotation of the apparatus is performed. Therefore, the control must always be performed assuming the worst situation for hot offset, in which the next print job comes immediately after the apparatus is stopped.

  However, in practice, the next print job rarely comes immediately after the apparatus is stopped, and it is normal that the non-sheet passing portion that is excessively heated during the stop of the apparatus is naturally cooled. If the non-sheet passing portion is naturally cooled, no offset occurs even if the normal size paper is passed.

  Essentially, every time a small-size sheet is passed, regardless of whether or not the next printing is performed, the control of continuing the rotation for a long time in the post-rotation is not preferable in terms of durability and noise of the apparatus.

  Ideally, the cooling control of the device should be performed only when it is really necessary.

  Therefore, in this embodiment, the post-rotation is not extended as in the first embodiment, and when the print command is received, the pre-rotation time until the start of paper feeding is extended.

  The image forming apparatus and the fixing device used in this embodiment are the same as those in the first embodiment, and the description of the configuration is omitted.

  First, small-size paper is passed through the image forming apparatus, and when a series of printing operations is completed, the apparatus performs normal post-rotation and immediately stops.

  Thereafter, when a normal size paper print command is received, the CPU 62 compares the detected temperatures of the main thermistor 51 and the sub-thermistor 52 and calculates a temperature difference Ts−Tm. When this temperature difference Ts−Tm is smaller than the predetermined temperature, no hot offset occurs, so the heater 22 is heated as it is, and the paper feeding is started as usual to perform image formation and fixing processing on the paper.

  On the other hand, when the temperature difference Ts−Tm is larger than the predetermined temperature, the heating of the heater 22 is once waited, the heating device is rotated in an unheated state, and the device is cooled. When the temperature difference Ts−Tm becomes smaller than the predetermined temperature, heating of the heater 22 is started and image formation is performed as usual.

  In this embodiment, when the temperature difference Ts−Tm is 3 degrees or more, non-heating rotation is performed in the pre-rotation, and when the temperature difference is 3 degrees or less, normal image formation is started.

  In the above configuration, the apparatus is rotated without heating for cooling only when the temperature difference Ts−Tm before the start of printing is large and a hot offset occurs. Therefore, compared with Example 1, the frequency with which the apparatus performs cooling rotation is significantly reduced, and the durability of the apparatus is improved. Moreover, the opportunity for the user to feel the noise caused by driving the device can be reduced.

  In this embodiment, in order to prevent hot offset, when normal size paper is printed after passing through small size paper, control is performed so that the heating temperature of the heater is lower than normal.

  The operation will be described in detail below.

  The image forming apparatus and the fixing device used in this embodiment are the same as those in the first embodiment, and the description of the configuration is omitted.

  First, small-size paper is passed through the image forming apparatus, and when a series of printing operations is completed, the apparatus performs normal post-rotation and immediately stops. Thereafter, when a normal size paper print command is received, the CPU compares the detected temperatures of the main thermistor 51 and the sub-thermistor 52 and calculates a temperature difference Ts−Tm. The heating temperature for the next printing is determined according to the temperature difference Ts−Tm, and the apparatus starts the printing operation. The control table shown in FIG. 5 is used for determining the heating temperature.

  Since the hot offset does not occur when the temperature difference Ts−Tm is small, the heating temperature can be set high as usual, and when the temperature difference Ts−Tm is large, the heating temperature is set low to prevent the hot offset.

  By controlling the heating temperature in accordance with the temperature difference Ts−Tm in this way, the heating temperature is not unnecessarily lowered, and hot offset can be prevented with higher accuracy than in the prior art, and the fixability is also deteriorated. It wo n’t happen.

  By the way, when printing of normal size paper continues continuously, if a certain number of sheets are passed, the temperature difference generated between the main thermistor portion and the sub-thermistor portion is eliminated.

  Therefore, it is necessary to return the heating temperature to the normal setting during the continuous printing. As a timing for returning the heating temperature, the number of sheets to be restored may be determined uniformly according to the temperature difference Ts-Tm before the start of printing as in the control table shown in FIG.

  Alternatively, if the temperature difference Ts−Tm is continuously calculated even during the heating operation and is returned when the temperature difference Ts−Tm becomes equal to or lower than the predetermined temperature, more appropriate control is achieved. For example, when the paper is passed at a heating temperature of 190 ° C., the temperature may be set to return to the normal 200 ° C. when the temperature difference Ts−Tm becomes 3 deg or less. Further, the heating temperature may change stepwise according to the temperature difference Ts−Tm during the heating operation. An example of the control table in such a case is shown in FIG.

  In the example of FIG. 6, when the temperature difference Ts−Tm is initially 7 deg or more, the heating temperature is set to 190 ° C., and the temperature difference Ts−Tm becomes less than 7 deg during continuous paper feeding, the heating temperature is 195 ° C. When the temperature difference Ts−Tm is less than 3 deg, the control is performed to return to the normal heating temperature of 200 ° C.

  By the way, in the above example, the control for extending the post-rotation and the pre-rotation after the small-size sheet passing as in the first and second embodiments is not included. In this way, the waiting time until the next printing is shortened because the rotation of the apparatus is not extended, and the usability of the apparatus is improved. However, on the other hand, when the printing operation is started after the small-size paper, there is a relatively high possibility that the temperature difference between the main thermistor portion and the sub-thermistor portion is large. As a result, the amount by which the heating temperature is lowered in order to prevent hot offset becomes relatively large, and the deterioration of the fixing property is increased accordingly.

  Therefore, it can be said that it is better to combine the configuration of the present embodiment with the configurations of Embodiments 1 and 2 in order to achieve both prevention of hot offset and fixability. That is, by combining the present embodiment and the first embodiment, post-rotation is performed until the temperature difference Ts−Tm between the main thermistor and the sub-thermistor becomes a predetermined temperature or less after the small-size paper is passed, and the temperature difference Ts in the post-rotation. It is more preferable in terms of image quality to compensate for the fact that −Tm cannot be fully reduced by lowering the heating temperature at the next printing.

  For example, if the temperature difference temperature difference Ts-Tm is 7 deg or more even after 30 seconds of post-rotation after the end of the heat treatment to a small size, the heating temperature according to the temperature difference Ts-Tm before the start of printing. The heat treatment can be performed at 190 ° C., which is 10 degrees lower than usual, to prevent hot offset.

  Alternatively, it is possible to set the predetermined temperature at which the post-rotation is finished slightly higher to reduce the post-rotation time. For example, post-rotation is performed until the temperature difference Ts-Tm becomes less than 7 deg after the heat treatment is finished in a small size, and when the temperature difference Ts-Tm is 3 deg or more at the start of the next printing, the heating temperature is lowered by 5 deg. Control may be performed such that the heat treatment is performed at a temperature of ° C. Alternatively, when the normal size paper is printed after passing the small size paper by combining the present embodiment and the second embodiment, the non-heated state is maintained until the temperature difference Ts−Tm between the main thermistor and the sub thermistor becomes a predetermined temperature or less. The pre-rotation may be performed and control may be performed to reduce the heating temperature at the time of printing when the temperature difference Ts−Tm becomes small to some extent.

  For example, when the temperature difference Ts−Tm is 7 deg or more at the start of printing, non-heating rotation is performed in the previous rotation until it becomes less than 7 deg. Thereafter, the heating temperature is set to 195 ° C., which is 5 deg lower than normal, and the paper is heated. . By performing such control, it is possible to improve the convenience for the user by reducing the extension time of the pre-rotation compared to the case where the second embodiment is performed alone.

  In addition, although the said Example 1, 2, 3 demonstrated as an example the heating apparatus of a film heating system, application of this structure is not limited to this, It is the same also with other heating systems, such as a heat roller system. An effect can be obtained.

Schematic configuration model diagram of image forming apparatus in embodiment Schematic configuration schematic diagram of heating device (fixing device) in the embodiment Schematic schematic diagram of longitudinal configuration of heating device (fixing device) in embodiment Examples of experiments conducted by the present inventors Control table of heating temperature in Example 3 Control table of heating temperature in Example 3

Explanation of symbols

P paper (recording material)
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Developing apparatus 3 Laser scanning exposure apparatus 6 Transfer roller 9 Multi tray 10 Paper feed cassette 11 Charging roller 12 Heating apparatus 13 Top sensor 21 Fixing film 22 Heater 23 Heater holder 25 Pressure roller 51 Main thermistor 52 Sub thermistor

Claims (7)

The pressure member includes at least two heating members, a pressure member that directly or indirectly contacts the heating body to form a pressure nip portion, and a temperature detection element that detects a temperature of the heating body. In the heating device that rotates and stops the drive of the device after discharging the heated material after performing the heat treatment of the heated material conveyed and introduced into the pressure nip part,
When a material to be heated whose width is shorter than a predetermined size is conveyed, at least one of the temperature detection elements is disposed at a position to be a sheet passing portion, and at least one other of the temperature detection elements is not. From the end of the heat treatment of the material to be heated according to the difference in temperature detected by the temperature detecting element of the non-sheet passing part and the temperature detecting element of the sheet passing part. A heating device characterized in that the time until the drive of the device stops is changed.   The heating apparatus according to claim 1, wherein the heating body is in an unheated state from the end of the heat treatment of the material to be heated to the stop of driving of the apparatus.   The time from the end of the heat treatment of the material to be heated to the stop of driving of the apparatus changes only after the material to be heated whose width is shorter than a predetermined size is conveyed. Heating device. It has at least two heating elements and two or more temperature sensing elements for detecting the temperature of the heating elements, and the thermal energy generated by the heating elements is applied to the heated material to be conveyed and discharged, and is wider than a predetermined size. When a short material to be heated is conveyed, at least one of the temperature detection elements is disposed at a position to be a sheet passing portion, and at least one of the temperature detection elements is disposed at a position to be a non-sheet passing portion. In the heating device that is
Before starting the heating of the heating body, the heating temperature of the heating body is changed according to the difference in temperature detected by the temperature detection element of the non-sheet passing portion and the temperature detection element of the sheet passing portion. apparatus.   A pressure member is brought into contact with a fixedly supported heating body via a heat resistant film, a recording medium is introduced into a pressure nip formed between the film member and the pressure member, and the recording medium is placed together with the film member. The heating apparatus according to any one of claims 1 to 4, wherein the heat treatment is performed by applying the heat energy of the heating body to the recording medium by traveling and moving the recording medium.   6. The heat fixing apparatus according to claim 1, wherein the material to be heated is a recording material on which an unfixed image is formed and supported, and the apparatus is a heat fixing device that heat-fixes an unfixed image on the recording material. The heating device according to 1.   The image forming means for forming and carrying an unfixed image on a recording material and the fixing means for fixing the unfixed image formed and supported on the recording material, wherein the fixing means is any one of claims 1 to 6. An image forming apparatus characterized by being a heating apparatus.