JP2017223884A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that accurately detects a failure in a temperature detection element or a fixing member to prevent the generation of downtime more than necessary for a user.SOLUTION: There is provided an image forming apparatus that comprises a fixing part including a first rotating body that is in contact with a toner image carrying surface of a recording material to heat the recording material and a second rotating body that cooperates with the first rotating body to form a nip part sandwiching to convey the recording material, the image forming apparatus including a first temperature sensor and a second temperature sensor that respectively detect the temperatures on one end side and the other end side in the width direction of the first rotating body, and a control part that controls to change a conveyance interval of the recording materials between a first conveyance interval and a second conveyance interval longer than the first conveyance interval, wherein when the absolute value of the temperature difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor is equal to or larger than a first predetermined value and equal to or smaller than a second predetermined value larger than the first predetermined value, the control part controls to change the first conveyance interval to the second conveyance interval, and when the absolute value exceeds the second predetermined value, inhibits the execution of an image forming job.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as an electrophotographic system capable of forming an image on a recording material, such as a printer, a facsimile machine, and a copying machine.

  In such an image forming apparatus, toner (developer) of a toner image (unfixed image) formed on a recording material (hereinafter referred to as paper or paper) by an image forming unit is melted by heat. A fixing device (image heating device, image heating device) for fusing onto the paper is mounted.

  In order to increase the temperature at a high speed, the fixing device has a fixing roller that is a heating medium with a small diameter, a resin film rotating member that is pressed against the rotating member from the inside, and a thin metal rotating member that is induction heated. What is heated by heating is known. These are all intended to reduce the heat capacity of a rotating body (hereinafter referred to as a fixing member), which is a heating medium, and to heat it with a heat source with good heating efficiency.

  By shortening the temperature raising time of the fixing member, it becomes important to accurately determine a change in the temperature detecting element due to a failure of the temperature detecting element (temperature detecting element) or a damage of the fixing member. The conventional fixing device is configured to stop the device when the temperature detecting element detects an excessive temperature rise. For example, in Patent Document 1, the fixing device is stopped not only when the temperature of the fixing member exceeds the temperature assumed by the temperature detection element but also when the temperature difference between the two temperature detection elements exceeds a predetermined threshold. Yes. By performing the detection based on the temperature difference, it is possible to cope with not only an excessive temperature rise but also a failure mode such as a contact failure of the temperature detection element.

  On the other hand, Patent Document 2 proposes a fixing device in which the pressing force is variable in order to cope with various types of paper such as envelopes and thin paper.

JP 2006-243288 A JP 2014-025965 A

  In the conventional method, when temperature detection elements are provided at both ends in the width direction of the fixing member, if the paper is not set correctly and is set at a position shifted in a direction perpendicular to the conveyance direction, the temperature detection elements at both ends are It was found that there was a temperature difference, and it could be misdetected. When a malfunction is detected as a failure, not only the cost of dispatching a worker (serviceman) for maintenance, but also the apparatus is stopped until the serviceman arrives, which causes a great downtime for the user. Further, it was found that when the pressure is lowered as in Patent Document 2, a temperature difference between both end portions is likely to occur, and the possibility of erroneous detection increases.

  The present invention has been proposed in view of the above problems. An object of the present invention is to provide an image forming apparatus that accurately detects a failure of a temperature detecting element or a fixing member and does not cause a user to experience unnecessary downtime.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows:
A first rotating body that contacts the toner image carrying surface of the recording material and heats the recording material, and a fixing having a second rotating body that cooperates with the first rotating body and forms a nip portion that sandwiches and conveys the recording material. In an image forming apparatus having a section,
A first temperature sensor and a second temperature sensor that respectively detect temperatures on one end side and the other end side in the width direction of the first rotating body;
A control unit that controls to change the conveyance interval of the recording material to a first conveyance interval and a second conveyance interval that is wider than the first conveyance interval;
The control unit, when executing the image forming job, has an absolute value of a temperature difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor equal to or greater than a first predetermined value. When the value is equal to or smaller than the second predetermined value that is larger than the first predetermined value, the first transfer interval is controlled to be changed to the second transfer interval, and exceeds the second predetermined value. In this case, the execution of the image forming job is prohibited.

  According to the present invention, it is possible to provide an image forming apparatus capable of accurately detecting a failure without causing unnecessary downtime for a user due to erroneous detection.

Flow chart of control in embodiment 1 Configuration explanatory diagram of an example of an image forming apparatus FIG. 3 is a schematic cross-sectional view of the main part of the fixing device in Embodiment 1. Exploded perspective schematic view of the main part of the device Circuit diagram of induction heating device The block diagram of the control system of the apparatus in Example 1 Schematic diagram explaining the temperature transition Schematic diagram explaining the operation Schematic diagram explaining the operation of the comparative example Explanatory drawing when the paper is set at the center and when it is set at the back Schematic diagram explaining temperature transition (part 1) Schematic diagram explaining temperature transition (Part 2) Schematic diagram explaining temperature transition (Part 3) Schematic diagram explaining the operation Flow chart of control in embodiment 2 The perspective view of the fixing device of Example 3. (A) is a schematic cross-sectional left side view of the main part of the apparatus, (b) is a partially enlarged view of (a), and (c) is a cross-sectional view of a pressure applying member (pressure pad). (A) and (b) are a left side view of the same device and a left side view of a partly cutout. Schematic diagram of layer structure of fixing belt Eccentric cam shape illustration Illustration of belt unit position in each pressure mode Illustration in normal pressure mode Explanatory drawing in envelope pressure mode Flow chart of control (1) Control flow chart (2) Diagram explaining nip width in normal pressure mode and envelope pressure mode Diagram explaining nip width and end temperature

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention replaces part or all of the configuration of the embodiment with an alternative configuration as long as the productivity of the recording material is set according to the detected temperature difference between a plurality of temperature detection elements (temperature detection elements). Other embodiments can also be implemented.

  Therefore, the image heating device (image heating device: fixing unit) is not only a fixing device that heats a recording material on which an unfixed toner image is formed to fix the toner image on the recording material, but also semi-fixed or fixed. It includes a surface treatment apparatus that heat-treats the toner image and imparts a desired surface property to the image. The rotating body to be induction-heated and the rotating body to be brought into pressure contact include not only a roller but also a belt and a film.

  An image forming apparatus equipped with an image heating apparatus can carry out the present invention without distinction between monochrome / full color, sheet-fed type / recording material conveying type / intermediate transfer type, toner image forming method, and transfer method. In the present embodiment, only main parts relating to toner image formation / transfer / fixing will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used in various applications such as a multifunction peripheral.

<Image forming apparatus>
FIG. 2 is a diagram illustrating the configuration of the image forming apparatus according to this embodiment. The image forming apparatus 30 is a tandem-intermediate transfer type electrophotographic full-color printer, and performs an image forming operation based on an image forming job (print job) input from an external device 319 such as a PC to the control unit 100. Reference numeral 317 denotes a printer operation unit that can input various types of information to the control unit 100. Various information is displayed from the control unit 100 on the display unit of the operation unit 317.

  Four image forming units 1a, 1b, 1c, and 1d are disposed inside the printer main body 30A. Each image forming unit includes process units such as photosensitive drums a, b, c, and d, and chargers, developing units, drum cleaners, and the like (not shown) that act on the photosensitive drums. An intermediate transfer belt unit 2 is disposed above the image forming units 1a, 1b, 1c, and 1d, and a laser scanner unit 4 is disposed below the image forming units 1a, 1b, 1c, and 1d.

  In the image forming unit 1a, a yellow toner image is formed on the photosensitive drum a and transferred to the intermediate transfer belt 3 by the primary transfer unit Ta1. In the image forming unit 1b, a magenta toner image is formed on the photosensitive drum b and is transferred to the intermediate transfer belt 3 by the primary transfer unit Tb1. In the image forming portions 1c and 1d, a cyan toner image and a black toner image are formed on the photosensitive drums c and d, respectively, and transferred to the intermediate transfer belt 3 by the primary transfer portions Tc1 and Td1, respectively. As a result, a four-color superimposed toner image is formed on the intermediate transfer belt 3. Since the electrophotographic process mechanism and image forming operation of these image forming units are known, the description thereof will be omitted.

  On the other hand, one of the feeding rollers 6 of the recording material cassettes 5 (A, B, C) in a plurality of stages is driven to feed a recording material (sheet: hereinafter referred to as paper or paper) P to one sheet. . The sheet P passes through the conveyance path 7 and is introduced into the secondary transfer portion T2 that is a pressure contact portion between the intermediate transfer belt 3 and the secondary transfer roller 9 by the registration roller pair 8 at a predetermined control timing. As a result, the four-color superimposed toner images on the intermediate transfer belt 3 are secondarily transferred onto the sheet P at once.

  The sheet P is introduced into a fixing device (fixing unit) F, which is an image heating device, through the conveyance path 10 and is heated and pressurized, whereby an unfixed toner image is melted and softened and fixed as a fixed image (heat) Fixed). The paper P exiting the fixing device F is discharged onto the upper tray 12 by the discharge roller 11. Here, in the printer 30 of the present embodiment, conveyance of large and small width papers is performed based on a so-called central reference centered on the paper width.

<Image heating device>
3 is a schematic cross-sectional view of the main part of the fixing device F, FIG. 4 is a schematic exploded perspective view of the main part of the device F, FIG. 5 is a circuit diagram of the induction heating device, and FIG. 6 is a block diagram of the control system of the device. It is. The fixing device F includes a fixing roller (heating rotator) 20 serving as a first rotating body that heats a toner image on a sheet (on a recording material) at a nip N therebetween, and a pressure roller (pressing member) serving as a second rotating body. Pressure rotating body) 22. The fixing roller 20 is a fixing member that contacts the toner image carrying surface of the paper P and heats the paper. A pressure roller 22 that is a pressure member is pressed against the fixing roller 20 in the horizontal direction and the fixing roller 20. The nip portion N for nipping and transporting the paper is formed in cooperation with the above.

  In the fixing roller 20, an elastic layer 20b of silicone rubber is disposed on the outer periphery of a magnetic cored pipe 20a, and the outer peripheral surface of the elastic layer 20b is covered with a release layer 20c of fluororesin. The pressure roller 22 is disposed so as to face the fixing roller 20 and is urged toward the fixing roller 20 by a coil spring (not shown) disposed at the shaft ends on both sides.

  In the pressure roller 22, an elastic layer 22b of silicone rubber is disposed on the outer periphery of a magnetic cored pipe 22a, and the outer peripheral surface of the elastic layer 22b is covered with a release layer 22c of fluororesin. The fixing roller 20 and the pressure roller 22 are coupled by a gear train (not shown) arranged at one end in the longitudinal direction, and are driven integrally by a drive motor M1 connected to the gear train.

  The fixing roller 20 is heated by an induction heating device 70 mainly composed of an exciting coil 71, a magnetic core 72, and a magnetic circuit member 82 disposed on the outside thereof. The induction heating device 70 generates magnetic flux and heats the fixing roller 20. The fixing roller 20 serving as an induction heating element uses a ferromagnetic metal such as iron (a metal having a high magnetic permeability) to restrain more magnetic flux generated from the induction heating device 70 inside the metal. By increasing the magnetic flux density, an eddy current is generated on the metal surface, and the fixing roller 20 can efficiently generate heat.

  The exciting coil 71 and the magnetic core 72 are disposed inside the housing 76 of the induction heating device 70. The exciting coil 71 is formed in an oval shape in a direction perpendicular to the paper surface in FIG. A magnetic core 72 divided into a plurality of parts in the direction perpendicular to the paper surface of FIG. Reference numeral 73 denotes a magnetic core moving mechanism that selectively moves each of the divided magnetic cores in a direction toward the fixing roller 20 and a direction away from the fixing roller 20. Since this mechanism is outside the gist of the present invention, a detailed description thereof is omitted here.

  The magnetic circuit member 82 forms a magnetic circuit of magnetic flux generated by the exciting coil 71 so as to go around the magnetic core 72 and the cored bar pipe 20a of the fixing roller 20. The magnetic core 72 and the magnetic circuit member 82 are used for increasing the efficiency of the magnetic circuit of the alternating magnetic flux generated from the exciting coil 71 and for magnetic shielding. The magnetic core 72 uses a material having a low high magnetic permeability residual magnetic flux density, such as ferrite, in order to efficiently guide the alternating magnetic flux to the induction heating element constituting the fixing roller 20.

  As shown in FIG. 4, the exciting coil 71 has a substantially elliptical shape (horizontal boat) in the longitudinal direction, and is arranged along the outer peripheral surface of the fixing roller 20. The exciting coil 71 uses, as a core wire, a litz wire obtained by bundling about 80 to 160 fine wires of an insulation coated electric wire with a diameter of 0.1 to 0.3 mm. The core wire is wound 8 to 12 times around the magnetic core 72 to constitute the exciting coil 71.

  The magnetic cores 72 divided into a plurality are arranged in an array state in a direction orthogonal to the paper transport direction (recording material transport direction) Z. The magnetic core 72 is configured to connect the winding center portion of the exciting coil 71 and the outer peripheral surface in a circular arc shape in the axial vertical section of the fixing roller 20.

  In order to heat the fixing roller 20, the fixing device F employs an induction heating method in which an eddy current is generated in an induction heating element provided in the fixing roller 20 by a magnetic flux generated by the exciting coil 71 and heat is generated by Joule heat. In the induction heating method, since the heat generation position can be placed very close to the nip portion N, the surface temperature of the fixing roller 20 is fixed when the power is turned on, compared to the heat roller method using a halogen lamp heater. The time required to reach an appropriate temperature is short. In addition, since the heat transfer path from the heat generation position to the nip portion N is short and simple, the thermal efficiency of heating is high.

  When a high frequency current is applied to the exciting coil 71, the fixing roller 20 generates heat. The exciting coil 71 generates an alternating magnetic flux by the supplied alternating current, and the alternating magnetic flux is guided to the magnetic core 72 to generate an eddy current in the fixing roller 20 that is an induction heating element. The eddy current generates Joule heat by the specific resistance of the induction heating element. That is, by supplying an alternating current to the exciting coil 71, the fixing roller 20 enters an electromagnetic induction heat generation state.

  As shown in FIG. 5, the excitation circuit 310 supplies an alternating current of a high-frequency current to the excitation coil 71 of the fixing device F. Excitation coil 71 is connected between a connection point of switch elements 303 and 304 and a connection point of capacitors 305 and 306 in excitation circuit 310 of IH power supply device 300 that is supplied with power from commercial AC power supply 500. The exciting coil 71 generates magnetic flux to inductively heat the fixing roller 20.

  In the IH power supply device 300, the diode bridge 301 and the filter capacitor 302 constitute a rectifying / smoothing circuit to generate a DC voltage. The power control unit 313 applies the AC voltage to the excitation coil 71 by alternately operating the switch elements 303 and 304 via the drive unit 312. The capacitors 305 and 306 are resonance capacitors that form a resonance circuit together with the excitation coil 71. The drive unit 312 drives the two switch elements 303 and 304, respectively. The power detection unit 311 detects the input power of the IH power supply device 300.

  As described above, the fixing roller 20 and the pressure roller 22 are rotationally driven, and the fixing roller 20 is heated by the induction heating device 70. Then, as will be described below, the fixing roller 20 is temperature-controlled to a predetermined temperature, and the paper P carrying the unfixed toner image t is introduced into the nip portion N. The sheet P is nipped and conveyed by the nip portion N, and is heated by the fixing roller 20, and receives the nip pressure, and the unfixed toner image t is fixed to the sheet P by heat and pressure (thermal fixing). The paper P that has passed through the nip portion N is separated from the fixing roller 20 and discharged and conveyed from the fixing waste device F.

  As shown in FIG. 4, the temperature detection elements 314, 315, and 316 are arranged at positions facing the fixing roller 20, respectively, and a longitudinal center portion of the fixing roller 20 and one end side (hereinafter referred to as a back side); The temperature at each position on the other end side (hereinafter referred to as the front side) is detected. The temperature detection element is a temperature sensor such as a thermistor. That is, a plurality of temperature detection elements 314, 315, and 316 that detect temperatures at a plurality of locations that are separated from each other in the width direction of the fixing roller 20 are provided.

  The central temperature detection element 314 detects the temperature of the longitudinal center portion of the fixing roller 20 and controls the power control unit 313 so that the temperature of the fixing roller 20 is raised to a predetermined temperature and becomes constant. The back side temperature detection element (first temperature sensor) 315 and the near side temperature detection element (second temperature sensor) 316 are arranged at positions facing both ends of the fixing roller 20, and both longitudinal ends (width) of the fixing roller 20. The temperature at one end side and the other end side in the direction is detected (detected).

  In the present embodiment, the back side temperature detecting element 315 and the near side temperature detecting element 316 are arranged at a distance of 115 mm from the longitudinal center position of the fixing roller 20 with an equal distance from the central temperature detecting element 314. Hereinafter, the back side temperature detecting element 315 and the near side temperature detecting element 316 are also referred to as end temperature detecting elements.

  The power control unit 313 determines the power condition output by the drive unit 312 from the operation command from the control unit 100 of the image forming apparatus 30 and the state of the fixing device F such as the temperature detection result of the temperature detection unit 314. The drive unit 312 drives the two switch elements 303 and 304 according to the power condition determined by the power control unit 313.

<Example 1>
In this embodiment, even if the user sets the paper incorrectly, in the continuous print job, the paper passing interval is controlled by the temperature difference between the end temperature detecting elements 315 and 316, thereby detecting the device failure and the erroneous detection. Thus, a fixing device configured so as not to be performed is realized.

  The control unit 100 includes a CPU 201, a ROM 202, and a RAM 203. Using the external device 3196 such as the operation unit 317 or a PC as an input unit, information on the type of paper (recording material type) to be used (for which image heating processing is performed) (recording material information such as size “, basis weight, type”) is controlled. The control unit 100 controls the image formation control unit 318 and the drive motor (device drive source) M1.

  The control unit 100 controls the IH power supply device 300 based on the temperature detected by the central temperature detection element 314 so that the surface temperature of the fixing roller 20 becomes constant. The control unit 100 controls the image formation control unit 317 and the sheet conveyance control unit 320 based on the detected temperature difference between the back side temperature detection element 315 and the near side temperature detection element 316 to set the sheet conveyance interval to a predetermined conveyance interval. It is controllable to become.

  The operation in this embodiment will be described with reference to the flowchart of FIG. After starting the print job (when the image forming job is executed), the control unit 100 calculates the absolute value of the temperature difference between the detected temperatures of the back side temperature detecting element 315 and the front side temperature detecting element 316 (back side to front side temperature difference). get. Then, it is compared whether or not it is higher than a temperature difference (second predetermined value: ΔTerr) assuming a failure (S1000). In this embodiment, ΔTerr is set to 50 ° C., and if a temperature difference higher than this temperature occurs, an error is displayed on the display unit of the operation unit 317 and the job is interrupted (execution of the image forming job is prohibited: The operation of the apparatus is stopped) and the process ends (S1001).

  The actions to be performed by the user after the error display and the jub interruption in S1001 are the following a and b.

  a: Since a paper set failure is considered, the set state is confirmed. If the paper is not set correctly, the set is corrected and the job is restarted.

  b: If there is no paper setting failure in the set state at a, and if an error display and a jub are interrupted even when the job is re-executed at a, the temperature detecting element is broken, the fixing roller or the fixing belt is damaged, etc. Because it is possible, make a service man call.

  When the absolute value of the temperature difference between the back side temperature detecting element 315 and the near side temperature detecting element 316 is equal to or less than ΔTerr (less than the second predetermined value), the control unit 100 determines a predetermined value ΔTdwn (less than ΔTerr). It is determined whether it is larger than the first predetermined value (S1002). In this example, ΔTdwn was set to 40 ° C.

  When the back-front temperature difference is equal to or greater than ΔTdwn, the control unit 100 turns on the down sequence and controls the image formation control unit 318 and the paper transport control unit 320 to set the paper transport interval (paper passing interval) to a predetermined value. Control is performed so as to widen (S1003). In the down sequence, when the standard conveyance interval of a sheet at the time of executing a normal print job is the first conveyance interval, the conveyance interval is set to a second conveyance interval that is wider than the first conveyance interval by a predetermined amount. This is a sequence for performing change control.

  If the back-front temperature difference is smaller than ΔTdwn, it is determined whether the job is finished (S1004). If it is not finished, the process returns to S1000. When the job is finished, the job is finished. At this time, if the down sequence is ON, the down sequence is turned OFF, that is, the setting of the sheet conveyance interval is returned to the standard state (first conveyance interval), and the job is ended (S1005, S1006). .

  The temperature difference ΔTerr assuming a failure can be set in the failure mode as described below. For example, when foreign matter enters the nip portion N, either the back side or the near side of the surface layer 20c of the fixing roller 20 is peeled off, or the back side temperature detecting element 315 or the near side temperature detecting element 316 is used. Sets the temperature difference when a contact failure occurs. The threshold temperature ΔTdwn that enters the down sequence may be erroneously detected due to variations in temperature detection elements or the like when it is set to a temperature close to ΔTerr.

  The control of the first embodiment is summarized as follows. The control unit 100 acquires a temperature difference between the temperature detected by the back side temperature detection element 315 and the temperature detected by the front side temperature detection element 316 when executing the print job. When the absolute value of the temperature difference is not less than the first predetermined value ΔTdwn and not greater than the second predetermined value ΔTerr, which is greater than the first predetermined value, the first transport interval Is controlled to be changed to the second conveyance interval. If the second predetermined value ΔTerr is exceeded, execution of the print job is prohibited.

The operation of this embodiment will be described. In FIG. 7A, 500 sheets of A4 size plain paper having a basis weight of 105 [g / m ² ] set in the recording material cassette 5 in a 15 ° C. environment with a productivity of 80 sheets per minute by lateral feed. The schematic diagram of detection temperature transition of each temperature detection element 314, 315, 316 when paper is passed is shown.

  The control target temperature of the center temperature detecting element 314 in the experiment is 180 ° C. at the center of the fixing roller 20. Since the paper width of the A4 size paper is 297 mm, the fixing roller portion corresponding to the near-side temperature detection element 315 and the back-side temperature detection element 316 rises in temperature because the fixing roller 20 is not deprived of heat by the sheet (hereinafter, non-printing temperature). This is called the temperature rise of the paper passing section). The surface of the fixing roller that has been heated at the non-sheet passing portion converges to a predetermined temperature that can balance heat dissipation.

  In FIG. 7B, assuming the failure mode, the temperature detection elements 314, 315, and 316 of the temperature detection elements 314, 315, and 316 when the front side temperature detection element 316 is separated from the surface of the fixing roller and the same sheet is passed. The schematic diagram of detection temperature transition is shown.

  It can be seen that the detection temperature decreases as the near-side temperature detection element 316 moves away from the surface of the fixing roller. FIG. 8 shows the temperature difference between the back side and front side temperature detection elements 315 and 316 from the start of paper feeding (temperature difference between back and front) and the number of output sheets per minute. In FIG. 8, the productivity of 80 sheets per minute in this embodiment is 1.0, and 40 sheets of productivity per minute in the down sequence is represented as 0.5. It can be seen that when the temperature difference between the back and the front exceeds ΔTdwn, a down sequence is entered and productivity is lowered. When the back-front temperature difference exceeds ΔTerr, an error stops.

  As a comparative example, FIG. 9 also shows an operation of stopping due to an error when S1002 and S1003 in the flowchart of FIG. 1 are deleted and ΔTerr is exceeded. Also in the comparative example, as in this embodiment, the error is stopped when the temperature difference between the back and front exceeds ΔTerr.

  Next, the operation when the paper set in the recording material cassette 5 is set shifted in the longitudinal direction (width direction) will be described with reference to FIGS. When the user sets paper in the recording material cassette 5, it is set in a state of being biased to the back side (or the front side) as shown in FIG. 10 due to variations in the recording material cassette 5 or cutting accuracy of the paper. There is. At this time, the back side temperature detecting element 315 is in the sheet passing area, but the sheet does not pass through the portion of the near side temperature detecting element 316, and thus the temperature rise in the non-sheet passing part occurs.

  At this time, FIG. 11A shows a schematic diagram of the temperature transition when the paper passes continuously. When the preceding paper A passes, the near-side temperature detection element 316 rises in temperature at the non-sheet passing portion, so that the temperature rises, but the back-side temperature detection element 315 dissipates heat due to the passing paper and drops in temperature. In the interval between the sheets until the next sheet B enters the nip portion N, the back side temperature detecting element 315 rises in temperature because the amount of heat taken away by the sheet passage is recovered. As a result, while the paper is passing, the front temperature difference increases, and the temperature difference between the papers repeatedly decreases.

  FIG. 11B similarly shows the temperature transition when the paper interval is widened by the down sequence. Since the temperature interval of the back side temperature detecting element 315 can be sufficiently taken because the space between the papers is widened, it can be seen that the temperature difference in the front side is smaller than that when the paper space is narrow.

  For comparison, FIG. 11C shows a temperature transition when the back side temperature detecting element 315 is broken and separated from the fixing roller 20. It can be seen that when the temperature detecting element fails, the temperature difference between the sheets does not recover even if the gap between the papers is widened, so that the temperature difference at the back only increases.

  Next, the operation in this embodiment is shown in FIG. In the normal productivity of 80 sheets per minute, the ratio between papers is small, so the temperature difference between the back and front increases. It can be seen that when the temperature difference between the back and the front exceeds ΔTdwn, a down sequence is entered and productivity is lowered. Since the gap between the sheets is opened, the temperature difference between the back and the front is reduced, and the error is not stopped beyond ΔTerr.

  In the configuration of the comparative example, as a result of shifting the paper set in the recording material cassette 5 and passing the paper in the same manner as in this embodiment, it does not enter the down sequence, so that the temperature difference between the back and the front is ΔTerr as in FIG. The error was stopped due to a false detection.

  As described above, in the configuration of the present embodiment, even when the recording material is shifted and set, it is possible to prevent erroneous detection as a failure and an error stop.

<Example 2>
The second embodiment is different from the first embodiment in that the error stop is immediately stopped based on the temperature information of the back-front temperature difference before the back-front temperature difference exceeds the error stop threshold ΔTerr. The control in the second embodiment is the same as that in the first embodiment except for the apparatus configuration and image formation control except that the flowchart of FIG. Hereinafter, the flowchart of FIG. 13 will be described, but portions that perform the same operations as in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the second embodiment, after it is determined in the first embodiment that the back-front temperature difference does not exceed ΔTerr (S1000), it is determined in S2001 whether the current down sequence is in progress. When it is determined that the down sequence is not in progress, the flow for determining whether to enter the down sequence is entered as in the first embodiment (S1002). During the down sequence, the transition of the back-to-front temperature difference when the sheet does not pass through the nip portion N is confirmed. If the temperature difference increases, an error is displayed and stopped (S2002, S1001). ).

  Whether or not the sheet passes through the nip portion N is calculated in consideration of the sheet interval controlled by the control unit 100 and the sheet conveyance time from the recording material cassette 5 to the nip portion N. The sheet conveyance time from the recording material cassette 5 to the nip portion N is stored in advance in the ROM 202 of the control unit 100 in FIG.

  Whether or not the temperature difference has increased in S2002 is determined by determining the temperature difference between the back and front of the timing when the preceding paper P passes through the nip portion N and the temperature between the next paper and the next paper, for example, every 100 ms. Check sequentially. At this time, when the temperature difference between the back and the front increases three times in succession, it is determined that the temperature difference is widened (S2002), and an error display is performed (S1001).

  The control of the second embodiment is summarized as follows. When executing a print job in a state where the conveyance interval of the paper P is changed and controlled to the second conveyance interval, the control unit 100 determines that the absolute value of the temperature difference is when the paper is not nipped and conveyed by the nip portion N. When enlarging, execution of the print job is prohibited.

  The operation of the second embodiment will be described with reference to FIG. As shown in FIG. 11B, when the paper set in the recording material cassette 5 is set shifted in the longitudinal direction, an operation similar to that of the first embodiment can be performed to enter the down sequence and avoid the occurrence of an error. it can.

  When the back side temperature detecting element 315 breaks down and is separated from the fixing roller 20, the temperature difference between the sheets increases as shown in FIG. 11C, and an error is detected before the next sheet reaches the nip portion N. Can judge and stop. As a result, it is possible to stop immediately at the time of failure as compared with the first embodiment, so that the subsequent sheet B does not fall below the fixing temperature in FIG. 11C and does not output an unnecessary defective fixing image. .

<Example 3>
The third embodiment is applied to the fixing device in which the pressing force is variable in order to cope with various types of paper such as envelopes and thin paper in the first embodiment. The control and control such as image formation are the same as those in the first embodiment, except that the variable pressure mechanism is added to the apparatus configuration in the fourth embodiment. Hereinafter, the variable pressure mechanism and the effect thereof will be described, but portions that perform the same operation as in the embodiment will be given the same reference numerals and description thereof will be omitted.

  Here, in the following description, regarding the fixing device F, the front means the surface when the device F is viewed from the sheet entrance side, and the left and right are the left or right when the device is viewed from the main surface. The upstream side and the downstream side are the upstream side and the downstream side in the paper transport direction Z.

  FIG. 14 is a perspective view of the fixing device F according to the fourth embodiment. 15A is a schematic cross-sectional left side view of the main part of the apparatus, FIG. 15B is a partially enlarged view of FIG. 15A, and FIG. 15C is a cross-sectional view of the pressure applying member (pressure pad). is there. 16A and 16B are a left side view of the apparatus F and a left side view with a part cut away.

  The heating assembly 501 has a fixing belt (endless belt) 506 having a cylindrical shape and flexibility. The belt 506 has a magnetic member (metal layer, conductive member) that generates heat by electromagnetic induction when passing through a region where a magnetic field (magnetic field, magnetic flux) generated from the excitation coil 71 exists. Further, a metal stay 507 inserted into the belt 506 is provided. A pressure pad (nip pad) 508 as a pressure applying member is attached to the lower surface of the stay 507 along the longitudinal direction.

  The pad 508 is a member that forms a nip portion (fixing portion, fixing nip portion) N by applying a predetermined pressing force between the belt 506 and the pressure roller 22, and is made of a heat resistant resin. A portion of the pad 508 facing the inner surface of the belt 506 includes an upstream protrusion 508a, a main pressure portion 508b, and a downstream protrusion 508c as shown in FIGS.

  In other words, the pad 508 has a convex portion that is an upstream protrusion 508a in the upstream portion of the nip portion N, and a convex portion that is a downstream protrusion portion 508c in the downstream portion of the nip portion N. Between the convex portions 508a and 508b. The main pressure portion 508b is included. The main pressure portion 508b does not necessarily have to be flat, and may be farther from the inner surface of the belt 506 than a portion where the tip of the upstream protrusion 508a and the tip of the downstream protrusion 508c are connected by a plane. .

  More specifically, the pad 508 is a pressure applying member configured to apply a relative pressure toward the pressure roller 22 with the belt 506 interposed therebetween to form the nip portion N. The pad 508 has a main pressure portion 508b in the vicinity of the center of the nip portion N at a portion facing the inner surface of the belt 506 in the cross section. Further, convex portions 508a and 508c projecting from the main pressure portion 508b toward the belt 506 are provided on the upstream side and the downstream side in the paper conveyance direction X with the main pressure portion 508b being inside.

  The pad 508 is crowned to correct the deflection when pressure is applied, and the crown amount used in this embodiment is 1. at the longitudinal center and the end (position of 200 mm from the center) of the pad 508. 6 mm.

  The stay 507 is made of iron in this embodiment because it needs rigidity to apply pressure to the nip portion N. In addition, on the upper surface side (excitation coil 71 side) of the stay 507, a magnetic core (inner magnetic core) 509 for concentrating the induction magnetic field on the belt 506 in order to efficiently heat the belt 506 is provided on the stay 507. It is arranged over the length.

  The left and right ends of the stay 507 protrude outward from the left and right ends of the belt 506, respectively. The left and right symmetrical flange members (fixing flanges) 510L and 510R are fitted to both ends. The flange members 510L and 510R are regulating members that regulate the movement of the belt 506 in the longitudinal direction (width direction: left-right direction) and the shape in the circumferential direction. The belt 506 is loosely fitted to the assembly of the stay 507, the pad 508, and the core 509 described above. Movement of the belt 506 in the longitudinal direction is restricted by the inward surfaces of the flange members 510L and 510R.

  As will be described later, the base layer 506a (FIG. 17) of the belt 506 is made of a metal that generates electromagnetic induction heat. Therefore, it is sufficient to provide flange members 510 </ b> L and 510 </ b> R having a flange portion that simply receives the end portion of the belt 506 as a means for restricting the shift of the belt 506 in the rotating state in the longitudinal direction. Thereby, there is an advantage that the configuration of the fixing device F can be simplified.

  A temperature sensor such as a thermistor serving as a central temperature detecting element 314 that detects the temperature of the belt 506 is disposed through a support member 511 having elasticity at the central portion of the pad 508. The temperature detection element is in elastic contact with the inner surface of the belt 506 by a member 511. As a result, even if a position variation such as the temperature detecting element contact surface of the rotating belt 506 undulates, the central temperature detecting element 314 follows this and maintains a good contact state with the inner surface of the belt 506. The

  The heating assembly 501 is disposed by engaging the flange members 510L and 510R with the longitudinal guide slit portions 505a disposed on the side plates 505L and 505R of the apparatus housing 505, respectively. Therefore, the heating assembly 501 has a degree of freedom that it can move in the vertical direction along the slit portion 505a between the side plates 505L and 505R as a whole.

  FIG. 17 is a model diagram showing a layer structure of the belt 506. In this embodiment, the belt 506 has a nickel base layer (magnetic member, metal layer) 506a having an inner diameter of 30 mm and manufactured by electroforming. The base layer 506a has a thickness of 40 μm. A heat resistant silicone rubber layer is provided as an elastic layer 6b on the outer periphery of the base layer 506a. The thickness of the layer 506b is preferably set within a range of 100 to 1000 μm.

  In this embodiment, the thickness of the layer 506b is set to 300 μm in consideration of reducing the heat capacity of the belt 506 to shorten the warm-up time and obtaining a suitable fixed image when fixing a color image. Silicone rubber has a hardness of 20 degrees JIS-A and a thermal conductivity of 0.8 W / mK. Further, on the outer periphery of the layer 506b, a fluororesin layer (for example, PFA or PTFE) is provided as a surface release layer 506c with a thickness of 30 μm.

  In order to reduce the sliding friction between the inner surface of the belt and the central temperature detecting element 314, a resin layer (sliding layer) 506d such as a fluororesin or polyimide may be provided on the inner surface side of the base layer 506a with a thickness of 10 to 50 μm. good. In this example, a polyimide layer having a thickness of 20 μm was provided as the layer 506d.

  The belt 506 has a low heat capacity and flexibility (elasticity) as a whole, and maintains a cylindrical shape in a free state. In addition to nickel, a metal such as an iron alloy, copper, or silver can be selected for the metal layer 506a. Moreover, the structure of laminating | stacking these metals on a resin base layer may be sufficient. The thickness of the metal layer 506a may be adjusted according to the frequency of a high-frequency current that flows in the exciting coil 71 described later and the permeability / conductivity of the metal layer 506a, and may be set between about 5 and 200 μm.

  The pressure roller 22 is disposed such that both ends of the cored bar 22a are rotatably supported via bearings 512 with respect to the side plates 505L and 505R of the apparatus housing 505, respectively, and are driven to rotate by the drive motor M1. .

[Pressure mechanism 504 and changing mechanism]
In this embodiment, the pressure mechanism 504 presses the pad 508 of the heating assembly 501 with a predetermined pressing force (pressure) to the pressure roller 22 via the belt 506, and the belt 506 and the pressure roller 22. It is a pressurizing means for forming a predetermined nip portion N therebetween. In the present embodiment, the pressure (pressurized state) of the pressurizing mechanism 504 can be changed by the changing mechanism.

  Then, the control unit 100 controls the change mechanism based on the paper information acquired from the input unit 317 or 319 so that the pressurization state of the pressurization mechanism 504 is higher than that in the first pressurization mode and the first pressurization mode. Switching to the second pressurizing mode in which the pressing force is reduced is executed.

  Hereinafter, a specific mechanism configuration will be described. A pair of pressure levers 518L and 518R that are long in the left and right front and rear directions (paper transport direction) as pressure members are disposed on the outer upper portions of the side plates 505L and 505R, respectively.

  The lever 518L is positioned above the pressurized portion 510a of the flange member 510L, and the rear end portion pivots so as to be pivotable in the vertical direction around the support shaft 518a with respect to the side plate 505L behind the flange member 510L. It is worn. That is, the lever 518L can operate in a direction in which the pressed portion 510a of the flange member 510L is pressed against the supporting shaft 518a or a direction away from the pressed portion 510a.

  The front end portion of the lever 518L is located in front of the flange member 510L. The lever 518L is constantly urged to rotate downward about the shaft 518a by the spring force of a spring 519a of a spring-loaded screw 519L as an urging member disposed between the side plate 505L.

  The lever 518R is positioned above the pressurized portion 510a of the flange member 510R, and the rear end portion is pivotally pivotable in the vertical direction around the support shaft 518a with respect to the side plate 505R behind the flange member 510R. It is worn. In other words, the lever 518R can operate in a direction in which the pressed portion 510a of the flange member 510R is pressed against the supporting shaft 518a or in a direction away from the pressed portion 510a.

  The front end portion of the lever 518R is located in front of the flange member 510R. The lever 518R is constantly urged to rotate downward about the shaft 518a by a spring force of a spring 519a of a spring-loaded screw 519R as an urging member disposed between the side plate 505R.

  When the levers 518L and 518R are in a free state, the lower surfaces of the levers 518L and 518R are respectively subjected to a spring force defined by a spring 519a of a screw with a spring against the upper surface of the pressurized portion 510a of the flange members 510L and 510R. It's pushing enough. In this embodiment, this pressure is set to 550 N, for example. As a result, in the heating assembly 501, the stay 507 and the pad 508 are pushed down together with the flange members 510RL and 510R, and the pad 508 presses against the pressure roller 22 against the elasticity of the elastic layer 502b across the belt 506. .

  As a result of this pressure contact, a nip portion N having a predetermined width is formed between the belt 506 and the pressure roller 22 in the paper transport direction X. The pad 508 assists in forming the pressure profile at the nip N. The configuration at this time is hereinafter referred to as a pressurizing configuration.

  A cam shaft 521 is rotatably disposed between the side plates 505L and 505R via a bearing (not shown). On the left and right ends of the shaft 521, eccentric cams (pressure release members) 522L and 522R that are symmetrical and have the same shape on the outside of the side plates 505L and 505R are fixed and arranged in the same phase. The cam 522L is located below the front end portion of the pressure lever 518L. The cam 522R is located below the front end portion of the lever 518R.

  A gear (pressure releasing gear) 523 is fixedly disposed at the left end of the shaft 521. A driving force of a pressure roller detaching motor (for example, a stepping motor) M2 controlled by the control unit 100 is transmitted to the gear 523 through a transmitting means (not shown), and the shaft 521, that is, the cams 522L and 522R is rotated. Is controlled.

  That is, the control unit 100 rotates the motor M2 according to a predetermined signal to rotate the gear 523 by a predetermined amount in a predetermined direction. The shaft 521 rotates according to the rotation of the gear 523, and the cams 522L and 522R rotate accordingly.

  By controlling the rotation of the cams 522L and 522R, the levers 518L and 518R are lifted and rotated against the spring force of the springs 519a of the spring-loaded screws 519L and 519R, thereby changing the pressure on the pressure roller 22 of the pad 508. The

  The bearing (not shown), the shaft 521, the cams 522L and 522R, the gear 523, and the motor M2 are changing mechanisms that change the pressure of the nip portion N by the pressurizing mechanism 504. Details of the pressure change of the pressurizing mechanism 504 will be described later.

[Pressure change operation]
The cams 522L and 522R have two peak shapes as shown in FIG. The position of the belt 506 when the cams 522L and 522R rotate will be described with reference to FIG.

  FIG. 19A shows the normal pressure mode. In this mode, the flat portions of the cams 522L and 522R are in an upward rotation angle posture, and the cams 522L and 522R are not in contact with the levers 518L and 518R. Therefore, the spring force of the spring 519a of the spring-loaded screws 519L and 519R sufficiently acts on the levers 518L and 518R, and the pressure of the nip portion N is in a predetermined first pressure (normal pressure) (pressurization) Constitution).

  In this embodiment, in the normal pressure mode (first pressurization mode), the force (total pressure at the nip) applied to the heating assembly (belt unit) 501 is 500N. Examples of the normal pressure include 100N to 900N. Preferably it is 40N-600N.

  The cams 522L and 522R rotate clockwise in the normal pressure mode of FIG. 20A, and the levers 518L and 518R are counteracted against the spring force of the spring 519a of the spring-loaded screw 519R. Push it up to the position 1) ((a) → (b)). Then, the pressure on the flange members 510L and 510R is reduced by half, and the position of the belt 506 is raised by ΔY1 ((a) → (b)). As a result, the pressure in the nip portion N is lower (weaker, lighter) than the first pressure in the normal pressure mode, and a predetermined envelope pressure mode (second pressurization mode) is set (pressure reduction configuration).

  In this embodiment, in this envelope pressure mode, the force (total pressure at the nip) applied to the heating assembly (belt unit) 501 is set to 30N. Examples of the light pressure include 10N to 90N. Preferably it is 4N-60N.

  When the cams 522L and 522R further rotate and push the levers 518L and 518R up to the position of the second highest peak (peak 2), the belt 506 is further raised by ΔY2. Then, the pressure on the flange members 510L and 510R of the spring force of the spring 519a of the screw 519R with the spring is invalidated, and the belt 506 and the pressure roller 22 enter the pressure release mode (pressure release state: pressure release configuration) ((b) → (c)).

  The control unit 100 controls the heating assembly 501 to the pressure release mode shown in FIG. When the paper to be passed through the fixing device F is other than the envelope, the normal pressure mode shown in FIG. In the case of an envelope, the envelope pressure mode (pressure reduction configuration) shown in FIG. 19B is controlled.

[Pressure mode]
A pressurization form at the nip portion N in the normal pressure mode and the envelope pressure mode of the fixing device F in this embodiment will be described with reference to FIGS. 20 (a) and 21 (a) are cross-sectional views when the paper (plain paper) P other than the envelope passes through the nip portion N in each mode, and FIG. 20 (b) and FIG. b) shows cross-sectional views when the envelope passes through the nip portion N in each mode. 20 (c) and 21 (c) show the velocity distribution on the envelope cover when the envelope is passed in each mode.

  In the normal pressure mode, as shown in FIG. 20A, the upstream protrusion 508 a, the main pressure part 508 b, and the downstream protrusion 508 c of the pressure pad 508 that is a pressure applying member are all in pressure contact with the belt 506. When the paper P other than the envelope is passed, the nip portion N has an upwardly convex shape due to the protrusions 508a and 8c on the upstream and downstream sides of the pad 508. It has become. Thereby, even when a sheet having a small basis weight and a low rigidity is passed, the separation property to the fixing belt 506 is sufficiently secured.

  On the other hand, when the envelope passes through the nip portion N in the normal pressure mode as shown in FIG. Thus, the nip portion N has an upwardly convex shape. For this reason, due to the deformation of the envelope passing through the nip portion N, a difference in transport amount occurs between the upper surface and the lower surface of the envelope.

  FIG. 20C shows the transport amount (solid arrow) in the front and the feed amount of the reverse transport amount (dotted arrow) when the envelope is the long type No. 3. In the envelope, two sheets of front and back sheets are constrained on the front and back sides of at least one side in the belt width direction. In the case of long die No. 3, the position indicated by x is a restraint location. Since the front and back surfaces are continuous in the constrained portion, the nip portion N passes through an intermediate conveyance amount between the front and back conveyance amounts. Due to the difference in feed amount in the belt width direction between the constrained part and the non-constrained part of the envelope, a rotational moment as shown by the white arrow occurs, and the envelope 蓄積 w Will occur.

  In the present embodiment, since the purpose is to make the nip portion N convex in the normal pressure mode, the belt 506 need not be in contact with all the main pressure portions 508b of the pressure pad 508, and the main pressure portion A part of 508b may be in contact with the belt 506.

  In the envelope pressure mode, as shown in FIG. 21A, the upstream protrusion 508a and the downstream protrusion 508c of the pressure pad 508 are both in pressure contact with the belt 506, but the main pressure portion 508b is separated from the belt 506. It becomes a state. When the paper P other than the envelope is passed, the nip portion does not have an upward convex shape but a straight shape due to the rigidity of the protrusions 508a and 508c on the upstream and downstream sides of the pressure pad 508 and the belt 506. The sheet discharged from the nip portion N is discharged straight.

  In this case, there is no problem with the high-rigidity paper P that is two-layered like an envelope. However, when plain paper P with low basis weight and low rigidity is passed, the curvature of the belt 506 cannot be secured sufficiently. Separation may be insufficient.

  On the other hand, when the envelope passes through the nip portion N in the envelope pressure mode as shown in FIG. 21 (b), the nip portion N does not have an upward convex shape but a straight shape in the portion not restrained by the front and back of the envelope. It has become. Therefore, deformation of the envelope passing through the nip portion N can be suppressed, and a difference in feeding amount between the two sheets of the front and back of the envelope can be suppressed ((c) in FIG. 21). As a result, it is possible to suppress the occurrence of a speed deviation in the belt width direction between the constrained portion and the non-constrained portion of the envelope, thereby preventing the occurrence of envelope wrinkles.

  In the present embodiment, in the envelope pressure mode, the belt 506 is supported only by the upstream protrusion 508a and the downstream protrusion 508c of the pressure pad 508 as shown in FIG. The configuration in which the portion 508b does not contact the belt 506 has been described.

  In the envelope pressure mode, a part of the main pressure portion 508b may exceptionally come into contact. For example, there are cases where the upstream / downstream protrusions are not sufficiently high in the mechanical tolerance range, or where the upstream / downstream protrusions have become low due to durable wear. Further, when an envelope having high rigidity in the envelope pressure mode passes through the nip portion N, the belt 506 may be deformed and the belt 506 may come into contact with the main pressure portion 3b of the pressure pad 508.

However, there is no problem at all because the envelope is difficult to generate. As an envelope with high rigidity, for example, a product made by Yamagata Co., Ltd., long 3 Sumi sticking AR Ultra White 130 pear frame, 120 mm × 235 mm, basis weight 130 g / m ^{2 and the} like can be mentioned.

  The control of this embodiment will be described with reference to the flowchart shown in FIG. First, the image forming apparatus accepts an image forming job (JOB). Thereafter, the control unit 100 determines whether or not the sheet to be passed is an envelope job that is an envelope (S5000). If the sheet to be passed is not an envelope, the control unit 100 sets the pressure of the fixing device F to the normal pressure mode (S5001), and performs an image forming operation and a fixing operation (S5003). In S5000, if the paper to be passed is an envelope, the envelope pressure mode is set (S5002), and the image forming operation & fixing operation (S5003) is performed.

  The fixing operation in the normal pressure mode and the envelope pressure mode will be described with reference to the flowchart shown in FIG. First, the control unit 100 drives the pressure roller detachment motor M2 to adjust the pressure of the fixing device F to a normal pressure (S5100). Next, the control unit 100 drives the pressure roller 22 by the drive motor M, rotationally drives the pressure roller 22 and the belt 506, applies a voltage to the coil 15, and heats the belt 506 (S5101). Heating and rotation are continued until the belt 506 reaches a predetermined temperature control temperature (S5102).

  When the mode determined in the flow of FIG. 22 is the envelope pressure mode, the pressure of the fixing device F is switched to the envelope pressure (S5103, S5104). The control unit 100 introduces the paper P on which the unfixed toner is placed into the nip portion N by the image forming operation of the image forming unit, and fixes the unfixed toner on the paper P (S5105).

  Then, the control unit 100 performs the operations of S5103 to S5105 until the print job is finished (S5106), and when the print job is finished, stops the rotation of the drive motor M and the power supply to the excitation coil 71 (S5107). Depending on the setting after the end of the print job, the pressure roller detachment motor M2 is driven to change the pressure of the fixing device F to normal pressure or pressure release (S5108).

  FIG. 24A schematically shows the nip width of the nip N in the paper conveyance direction X in the envelope pressure mode and the normal pressure mode. In the normal pressure mode, since the nip pad 508 has a crown shape, the deflection of the stay 507 and the pressure roller 22 can be corrected to form a substantially uniform contact nip width over the entire length. . Accordingly, it is possible to ensure a long and uniform sheet separation performance with respect to the recording material other than the envelope.

  As shown in FIG. 24B, the longitudinal nip width distribution when the envelope is sandwiched during envelope pressure is shared by the portion where the envelope is sandwiched at the nip portion N, so that the nip width at the end is further narrowed. turn into.

  FIG. 25 shows the relationship between the contact nip width and the temperature of the end temperature detection element (315 or 316) when the temperature of the central temperature detection element 314 is adjusted to 180 ° C. at a constant temperature. From this result, it can be seen that the contact nip width of the end portion becomes narrower, and the temperature of the end portion temperature detecting element becomes higher when it is less than 0.5 mm. This is because the contact nip width is narrowed so that the heat of the fixing belt 106 is difficult to escape to the pressure roller 22, and the heat radiation amount is reduced, so that the fixing belt 106 temperature is kept high.

  From the relationship between FIG. 24 (b) and FIG. 25, when the pressure balance in the back and front of the envelope pressure mode is not good, or when the longitudinal sheet passing portion of the envelope varies, the back and front nip width may cause a difference. -A temperature difference in the foreground may occur. For example, if the pressure balance is lost and the near side nip width is 0.5 mm or more, the back side nip width becomes narrower than 0.5 mm. There may be a large temperature difference between the back and front.

  The envelope 1 was passed through in a state where the back-front contact nip widths were varied by actually changing the envelope pressure positions of the cam 522L and the cam 522R by 0.1 mm from the front to the back.

Envelope 1: Made by Yamagata Co., Ltd., Long 3 Sumi Attached AR Ultra White 130 Pear frame pear, 120 mm x 235 mm, basis weight 130 g / m ²
As is clear from the first embodiment, by performing the control of the third embodiment, the down sequence is not caused and no error occurs. However, in the case of the control in which the down sequence is not performed as a comparative example, an error has occurred due to the difference between the back and front contact nip widths.

  As described above, when the predetermined temperature difference occurs in the configuration in which the pressing force is variable, control is performed so as to reduce the productivity, thereby preventing erroneous detection as a failure and stopping the error. it can.

<Other matters>
(1) In the fixing device F of the embodiment, the pressure pad is pressed against the pressure roller via the belt. Conversely, the pressure roller is pressed against the pressure pad via the belt. It is also possible to adopt a mechanism configuration that pressurizes the pressure. Further, it is possible to adopt a mechanism configuration in which the pressure pad and the pressure roller are pressed against each other via a belt. That is, a mechanism configuration in which the pressure pad and the pressure roller are relatively pressurized via the belt can be provided.

  (2) The fixing device F that is a fixing unit is not limited to use as a device that heats and fixes an unfixed toner image formed on a sheet as a fixed image. It is also effective as a device for adjusting the surface properties of an image, such as improving the glossiness of an image by re-heating and pressurizing a toner image once fixed or presupposed on a sheet (a fixing device such as this also). Called).

  (3) The image forming apparatus is not limited to the image forming apparatus that forms a full-color image as in the embodiment, and may be an image forming apparatus that forms a monochrome image. In addition, the image forming apparatus can be implemented in various applications such as a copying machine, a FAX, and a multifunction machine having a plurality of these functions in addition to necessary equipment, equipment, and housing structure.

  30..Image forming apparatus, F..Fixing unit (fixing device), 20..First rotating body (fixing roller), 22..Second rotating body (pressure roller), N..Nip part, 314. 315, 316, .., a plurality of temperature sensors, 317, 319,... Recording material information input unit, 100 .. control unit, P .. recording material, t .. toner image

Claims (6)

A first rotating body that contacts the toner image carrying surface of the recording material and heats the recording material, and a fixing having a second rotating body that cooperates with the first rotating body and forms a nip portion that sandwiches and conveys the recording material. In an image forming apparatus having a section,
A first temperature sensor and a second temperature sensor that respectively detect temperatures on one end side and the other end side in the width direction of the first rotating body;
A control unit that controls to change the conveyance interval of the recording material to a first conveyance interval and a second conveyance interval that is wider than the first conveyance interval;
The control unit, when executing the image forming job, has an absolute value of a temperature difference between the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor equal to or greater than a first predetermined value. When the value is equal to or smaller than the second predetermined value that is larger than the first predetermined value, the first transfer interval is controlled to be changed to the second transfer interval, and exceeds the second predetermined value. An image forming apparatus that prohibits the execution of an image forming job in the case of an error.   When the recording material is not being nipped and conveyed by the nip portion during execution of an image forming job in which the recording material conveyance interval is controlled to be changed to the second conveyance interval, the control unit performs the temperature difference. The image forming apparatus according to claim 1, wherein execution of an image forming job is prohibited when the absolute value of is increased. An input unit for recording material information relating to a recording material to be subjected to image heating processing;
A pressurizing mechanism that presses the first rotating body and the second rotating body together;
A change mechanism capable of changing the pressing force of the pressurizing mechanism,
The control unit controls the change mechanism based on the recording material information acquired from the input unit, and applies the pressurization state of the pressurization mechanism more than the first pressurization mode and the first pressurization mode. The image forming apparatus according to claim 1, wherein switching to the second pressurizing mode in which the pressure is reduced is executed.   The first rotating body is an endless belt having flexibility, and has a pressure applying member that contacts the inner surface of the belt and forms the nip portion together with the second rotating body via the belt. The image forming apparatus according to claim 3.   The image forming apparatus according to claim 4, wherein the pressure applying member has a crown shape. In the cross section, the pressure applying member has a main pressure portion in the vicinity of the center of the nip portion at a portion facing the inner surface of the belt, and an upstream side and a downstream side in the recording material conveyance direction with the main pressure portion interposed therebetween, respectively. Having an upstream protrusion and a downstream protrusion protruding from the main pressure part toward the belt,
In the first pressurizing mode, the pressure applying member and the second rotating body are connected to the belt so that the upstream protrusion, the downstream protrusion, and the main pressure portion are in contact with the inner surface of the belt. Through a relatively pressurized state,
In the second pressurizing mode, the pressure applying member and the second pressure mode are set such that the upstream protrusion and the downstream protrusion are in contact with the inner surface of the belt and the main pressure portion is not in contact with the inner surface of the belt. The image forming apparatus according to claim 4, wherein the rotating body is in a state of being relatively pressurized through the belt.