JP2018169491A - Image formation device and method for controlling the same - Google Patents

Abstract

To provide a conveyance technique of a sheet that hardly gives bad impression to a user while suppressing increase in temperature of a no-paper-feed area of a fixation device in an image formation device of an electrophotography method.SOLUTION: A printer 100 includes: a conveyance member for conveying a sheet S; a heating member 81 for thermally fixing a toner image on the sheet S; and a side thermistor 812. In a case where the sheet S is continuously conveyed with a passage-of-sheets interval being Da, when end temperature detected by a signal of the side thermistor 812 exceeds a high temperature threshold value, the printer 100 continuously conveys the sheet S with the passage-of-sheets interval of sheet conveyance being Db larger than Da. In a case where the sheet S is continuously conveyed with the passage-of-sheets interval being Db, when the end temperature detected by the signal of the side thermistor 812 drops below a low temperature threshold value, the printer 100 continuously conveys the sheet S with a passage-of-sheets interval of sheet conveyance being Dc, which is smaller than Db and larger than Da.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic method and a control method thereof.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus that includes a process unit that forms a toner image and a fixing device that thermally fixes the toner image transferred to the sheet to the sheet, when the sheet passes through the fixing device, the sheet It is known that a temperature difference is generated between the sheet passing area and the non-sheet passing area since the heat is taken away from the fixing device. The larger this temperature difference is, the more easily the fixing device is broken and the sheet is wrinkled. Therefore, it is desired to reduce this temperature difference.

  An example of a technique that focuses on the above-described temperature difference is Patent Document 1. Patent Document 1 discloses an image forming apparatus having means for detecting a surface temperature of an end portion of a heating roller of a fixing device, and when a detected temperature exceeds a predetermined temperature, a sheet interval during continuous conveyance of a sheet is disclosed. A configuration is disclosed in which the paper gap is returned to the original when the detected temperature is lowered after that.

Japanese Patent Laid-Open No. 5-80604

  However, the conventional technique described above has the following problems. That is, the fluctuation of the surface temperature in the non-sheet passing area is likely to increase, and the sheet conveyance control is difficult to stabilize. An improvement is desired because there is a possibility of giving a bad impression to the user, such as misunderstanding, if the paper interval frequently changes during the continuous conveyance of the sheet.

  The present invention has been made to solve the above-described problems of the prior art. That is, it is an object of the present invention to provide a sheet conveying technique in an electrophotographic image forming apparatus that suppresses a temperature rise in a non-sheet passing area of a fixing device and hardly gives a bad impression to a user.

  An image forming apparatus designed to solve this problem includes a conveyance member that conveys a sheet, and a heating member that thermally fixes a toner image on the sheet conveyed by the conveyance member, in the conveyance direction of the sheet. A heating member arranged along a sheet width direction which is an orthogonal direction, a temperature sensor which outputs a different signal depending on the temperature of the end of the heating member among the heating members, and a control unit, The control unit performs continuous conveyance of the sheet by the conveyance member, with the sheet conveyance interval of the sheet conveyance being a first sheet conveyance interval, and performs continuous conveyance of the sheet by the conveyance member at the first sheet conveyance interval. When the temperature detected by the signal from the temperature sensor exceeds the first high temperature threshold, the sheet passing interval for sheet conveyance by the conveying member is a second sheet passing interval larger than the first sheet passing interval. interval When the sheet is continuously conveyed by the conveying member and the sheet is continuously conveyed by the conveying member at the second sheet passing interval, the temperature detected by the signal from the temperature sensor is the first temperature. When the value falls below a first low temperature threshold value that is lower than the first high temperature threshold value, the third paper passing interval is smaller than the second paper passing interval and larger than the first paper passing interval. As the interval, the sheet is continuously conveyed by the conveying member.

  In the image forming apparatus disclosed in this specification, the temperature of the end of the heating member in the sheet width direction is the first when the sheet is continuously conveyed with the sheet conveying interval being the first sheet passing interval. If the high temperature threshold is exceeded, the second paper passing interval is set to be larger than the first paper passing interval. Further, when the sheet is continuously conveyed at the second sheet passing interval, if the temperature of the end of the heating member falls below the first low temperature threshold, the sheet passing interval is smaller than the second sheet passing interval and the first sheet passing interval. The third paper passing interval is larger than the paper interval.

  In other words, according to the image forming apparatus disclosed in the present specification, after the paper passing interval is increased due to the temperature rise at the end of the heating member, if the temperature decreases, the paper passing interval is reduced. At this time, by setting the paper passing interval to be smaller than the paper passing interval after the increase and larger than the paper passing interval before the increase, the temperature rise becomes more gradual than the previous temperature rise. That is, even if the edge temperature rises again by reducing the sheet passing interval, there is a possibility that the time until the first high temperature threshold is reached is longer than the case of continuous conveyance at the first sheet passing interval. high. Therefore, since the frequency of the change of the sheet passing interval can be reduced, it is difficult to give a bad impression to the user.

  A control method, a computer program, and a computer-readable storage medium storing the computer program for realizing the functions of the apparatus are also novel and useful.

  According to the present invention, in the electrophotographic image forming apparatus, it is possible to realize a sheet conveying technique that suppresses a temperature rise in a non-sheet passing area of the fixing device and hardly gives a bad impression to the user.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. FIG. 3 is an explanatory diagram illustrating a schematic configuration of a fixing unit. FIG. 2 is a block diagram illustrating an electrical configuration of a printer. It is explanatory drawing which shows the example of the change of edge part temperature, and the change between paper. 6 is a flowchart illustrating a procedure of sheet conveyance processing. It is a flowchart which shows the procedure of a high temperature side paper gap adjustment process. It is explanatory drawing which shows the example of the change of edge part temperature, and the change between paper. It is a flowchart which shows the procedure of a low temperature side paper gap adjustment process. It is explanatory drawing which shows the example of the change of edge part temperature, and the change between paper. 6 is a flowchart illustrating a procedure of sheet conveyance processing. It is a flowchart which shows the procedure of the high temperature difference side paper gap adjustment process. It is a flowchart which shows the procedure of the low temperature difference side paper gap adjustment process.

  Hereinafter, a first embodiment in which an image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a printer having an electrophotographic image forming function.

  As shown in FIG. 1, the printer 100 according to this embodiment forms a toner image on a sheet feeding tray 11 that stores a sheet S before printing, a paper discharge tray 12 that stores a printed sheet S, and the sheet S. A process unit 5 and a fixing unit 8 for fixing the toner image to the sheet S are provided. In addition, the printer 100 includes a sheet conveyance path 13 that is a path of the sheet S from the sheet feed tray 11 to the sheet discharge tray 12 via the process unit 5 and the fixing unit 8.

  The printer 100 includes various conveyance members for conveying the sheet S along the sheet conveyance path 13. As shown in FIG. 1, the printer 100 includes a pickup roller 21, a registration roller 22, and a paper discharge roller 23 as conveyance members that convey the sheet S.

  The pickup roller 21 is rotationally driven by a pickup motor 25 (see FIG. 3), pulls out one sheet S from the sheet feeding tray 11 and sends it out to the sheet conveyance path 13. The registration roller 22 and the paper discharge roller 23 are rotationally driven by a main motor 26 (see FIG. 3). The registration roller 22 conveys the sheet S drawn by the pickup roller 21 toward the process unit 5 in synchronization with the toner image forming operation of the process unit 5. The paper discharge roller 23 discharges the printed sheet S to the paper discharge tray 12.

  Of the various rotating members and various conveying members included in the process unit 5 and the fixing unit 8, at least the directions of the rotation axes of the members arranged along the sheet conveying path 13 are parallel to each other. 1 is a direction perpendicular to the paper surface. That is, all the rotating members arranged along the sheet conveyance path 13 are arranged so that the direction of the rotation axis is perpendicular to the conveyance direction of the sheet S.

  In addition, the printer 100 includes various sheet detection members on the sheet conveyance path 13 for detecting the passage of the sheet. Specifically, the sheet detection member includes a sheet sensor 71. The sheet sensor 71 is disposed downstream of the pickup roller 21 and upstream of the registration roller 22 in the sheet conveyance direction. The sheet sensor 71 outputs different signals depending on the presence or absence of a sheet at the detection location.

  The process unit 5 forms a toner image by electrophotography, and transfers the toner image to the sheet S conveyed through the sheet conveyance path 13. As shown in FIG. 1, the process unit 5 includes a photoreceptor 51, a charging unit 52, an exposure unit 53, a developing unit 54, a transfer unit 55, and a cleaner 56. The photoconductor 51 is rotated in the clockwise direction in FIG. 1, and the charging unit 52, the exposure unit 53, the developing unit 54, the transfer unit 55, and the cleaner 56 are arranged around the photoconductor 51 in the rotation direction of the photoconductor 51. They are arranged in this order.

  The charging unit 52 is, for example, a scorotron charger, and charges the surface of the photoreceptor 51 almost uniformly. The exposure unit 53 is, for example, a laser exposure unit, which partially exposes the photoconductor 51 by irradiating a laser beam, and forms an electrostatic latent image on the photoconductor 51 based on image data. The developing unit 54 stores toner, develops the toner by supplying the toner to the electrostatic latent image on the photoconductor 51, and forms a toner image on the photoconductor 51. The transfer unit 55 electrically draws the toner image on the photoreceptor 51 and transfers it to the sheet S. The cleaner 56 is, for example, a sponge roller, and removes toner or the like remaining on the photoconductor 51 after transfer from the photoconductor 51.

  The fixing unit 8 includes a heating member 81 and a pressure roller 82 disposed on both sides of the sheet conveyance path 13. When the heating member 81 and the pressure roller 82 are brought into pressure contact with each other, a fixing nip is formed between the heating member 81 and the pressure roller 82. The fixing unit 8 heat-fixes the toner image on the sheet S by conveying the sheet S on which the toner image has been transferred by the process unit 5 while heating at the fixing nip.

  The heating member 81 includes a heater 810 and heats the sheet S passing through the fixing nip by heating the surface of the heater 810. As the heating member 81, for example, a roller member or an endless belt member can be applied. Further, as the heater 810, for example, a halogen heater, a ceramic heater, or an IH heater (induction heating member) can be applied. The heater 810 only needs to be able to heat the surface of the heating member 81, and may be disposed inside the heating member 81 to heat the heating member 81 from the inside, or may be disposed outside the heating member 81 to be heated. The surface of 81 may be directly heated.

  The pressure roller 82 is a heat-resistant rubber roller. For example, a metal shaft is coated with an elastic layer made of silicone rubber or the like and a release layer having releasability. The pressure roller 82 is pressed toward the heating member 81 by a pressing member (not shown). The pressure roller 82 is driven to rotate counterclockwise in FIG. 1 when the sheet is conveyed, and the heating member 81 is rotated clockwise in FIG. 1 following the rotation of the pressure roller 82. The The heating member 81 may be on the driving side.

  The printer 100 can print on a plurality of types of sheets S in a direction orthogonal to the conveyance direction of the sheet S, that is, in a direction parallel to the axial direction of each conveyance member. Hereinafter, the length of the sheet S in the direction orthogonal to the conveyance direction is defined as the width of the sheet S. In the printer 100, the sheet S is conveyed so-called centered. That is, as shown in FIG. 2, the sheet S conveyed by the fixing unit 8 is a sheet S2 having a large width or a sheet S1 having a small width. It passes through a position closer to the center in the axial direction. Note that the axial lengths of the heating member 81 and the pressure roller 82 are larger than the width of the maximum printable sheet S.

  In addition, as shown in FIG. 2, the fixing unit 8 includes a center thermistor 811 and a side thermistor 812 as sensors for detecting the temperature of the heating member 81. The side thermistor 812 is an example of a temperature sensor. The center thermistor 811 and the side thermistor 812 output different signals according to the surface temperature of each detection location. The center thermistor 811 is used to detect the surface temperature of the paper passing area, and the side thermistor 812 is used to detect the surface temperature of the non-paper passing area. The printer 100 controls the power supplied to the heater 810 based on the output signal of the center thermistor 811 so that the temperature of the fixing nip becomes the target fixing temperature, for example.

  Specifically, since the printer 100 transports the sheet S in the center position as described above, the center thermistor 811 is the central portion in the axial direction of the heating member 81, and all the sheets S of various widths. Different signals are output according to the surface temperature in the passing paper passing area. Further, the side thermistor 812 is an end portion in the axial direction of the heating member 81, and outputs a different signal according to the surface temperature in the non-sheet passing region through which any sheet S of various widths does not pass.

  Note that the conveyance position of the sheet S is not limited to center alignment, and may be left alignment or right alignment. Even in that case, the detection location of the center thermistor 811 may be in the paper passing area of the various sheets S, and the detection location of the side thermistor 812 may be in the non-paper passing area of the various sheets S. Further, the number of thermistors is not limited to two, and three or more thermistors may be arranged in the axial direction of the heating member 81. Each thermistor may be a contact type that contacts the heating member 81 or a non-contact type that does not contact the heating member 81.

  Next, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 according to this embodiment includes a controller 30 including a CPU 31, a ROM 32, a RAM 33, and an NVRAM (nonvolatile RAM) 34. The printer 100 also includes a process unit 5, a fixing unit 8, a pickup motor 25, a main motor 26, a sheet sensor 71, a network interface (network IF) 37, and an operation panel 40. The controller 30 is electrically connected.

  The ROM 32 stores firmware, which is a control program for controlling the printer 100, various settings, initial values, and the like. The RAM 33 is used as a work area from which various control programs are read, or as a storage area for temporarily storing image data. The NVRAM 34 is used as a storage area for storing various setting values, cumulative values, and the like.

  The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 in accordance with a control program read from the ROM 32 and signals sent from various sensors. The CPU 31 is an example of a control unit. Further, the controller 30 may be a control unit. Note that the controller 30 in FIG. 3 is a general term that summarizes hardware used for controlling the printer 100 such as the CPU 31, and does not necessarily represent a single piece of hardware that actually exists in the printer 100.

  The pickup motor 25 rotates the pickup roller 21. The main motor 26 rotationally drives a conveying member other than the pickup roller 21 such as the registration roller 22, each rotating member of the process unit 5, and the pressure roller 82 of the fixing unit 8. Note that the pickup roller 21 may also be driven by the main motor 26.

  The network IF 37 is hardware for communicating with an external device connected via a network. For example, the printer 100 receives a print job from an external device via the network IF 37. The communication method using the network IF 37 may be wireless or wired. In addition to the network IF 37, the printer 100 may include a communication unit with an external device such as a USB interface.

  The operation panel 40 is hardware that is responsible for displaying a notification to the user and receiving an instruction input by the user. The operation panel 40 includes, for example, a liquid crystal display and a button group including a start key, a stop key, a numeric keypad, and the like. The printer 100 can also accept a print job via the operation panel 40.

  Next, conveyance control of the sheet S by the printer 100 will be described. In the fixing unit 8, when the sheet S passes through the fixing nip, the sheet S takes heat from the fixing nip, so that the surface temperature of the sheet passing region of the heating member 81 is likely to decrease. Therefore, during continuous conveyance of the sheet S, in the printer 100, the heating member 81 is frequently heated in order to set the sheet passing area to the target fixing temperature. On the other hand, since the sheet S does not deprive heat in the non-sheet passing region, the surface temperature of the heating member 81 tends to continue to rise due to the heating member 81 being heated.

  For example, based on the output signal of the side thermistor 812, the printer 100 stops power supply to the heater 810 when the surface temperature of the non-sheet passing region of the heating member 81 exceeds the upper limit temperature. When power supply to the heater 810 is stopped, continuous conveyance of the sheet cannot be continued, so that productivity may be significantly reduced. Hereinafter, the surface temperature of the non-sheet passing region of the heating member 81 is referred to as “end portion temperature”, and the surface temperature of the sheet passing region of the heating member 81 is referred to as “center temperature”.

  Therefore, when the end temperature reaches a predetermined high temperature threshold value lower than the upper limit temperature, the printer 100 increases the paper gap. The term “between sheets” in the present specification means the distance between the trailing edge of the preceding sheet S and the leading edge of the succeeding sheet S in the conveyance direction of the sheet S while continuous conveyance of the sheet S is continued. The sheet interval is an example of the sheet passing interval, and the high temperature threshold is an example of the first high temperature threshold.

  Since there is no sheet S passing between the sheets, it is difficult for the fixing unit 8 to lose heat. For this reason, heating by the heater 810 is hardly performed, and the heat of the non-sheet passing area moves to the sheet passing area due to the temperature difference between the non-sheet passing area and the sheet passing area. For this reason, the temperature of the non-sheet passing area decreases, and the temperature difference between the non-sheet passing area and the sheet passing area decreases. That is, the printer 100 can suppress the excessive temperature rise in the non-sheet passing area as the gap between the sheets is increased.

  The printer 100 continuously conveys sheets between set sheets. Based on the output signal from the sheet sensor 71, the printer 100 detects the change from the presence of sheet S to the absence of the sheet S, thereby acquiring the timing at which the trailing edge of the preceding sheet S passes the detection location of the sheet sensor 71. To do. The printer 100 starts conveying the subsequent sheet S after an interval time corresponding to the interval between the sheets has elapsed from the passage timing. Specifically, the printer 100 picks the subsequent sheet S by the pickup roller 21 and sends it to the sheet conveyance path 13. That is, the printer 100 switches between sheets by switching the interval time.

  The printer 100 includes a plurality of threshold values for the edge temperature, and switches between sheets based on the comparison result between the edge temperature and each threshold value. As described above, for example, when the edge temperature becomes higher than the high temperature threshold, the printer 100 reduces the surface temperature by increasing the gap between the sheets. On the other hand, the greater the gap between the sheets, the lower the number of sheets S transported per unit time and the lower the productivity. Therefore, the printer 100 includes a predetermined low temperature threshold lower than the high temperature threshold in addition to the above-described high temperature threshold as the edge temperature threshold. Then, after increasing the paper gap, the printer 100 improves the productivity by reducing the paper gap when the end temperature becomes lower than the low temperature threshold. The low temperature threshold is an example of a first low temperature threshold.

  However, simply repeating the increase in the sheet interval when the high temperature threshold is exceeded and the decrease in the sheet interval when the temperature is below the low temperature threshold causes frequent changes between the sheets during continuous conveyance of the sheet S. There is a possibility. In the printer 100 according to the present embodiment, when the edge temperature becomes lower than the low temperature threshold after the paper interval is increased, the paper interval is smaller than the paper interval after the previous increase and more than the paper interval before the previous increase. Enlarge.

  FIG. 4 shows an example of the relationship between the change in edge temperature and the change between papers by the printer 100 of this embodiment. In the example of FIG. 4, the printer 100 starts continuous conveyance of the sheet S at the interval Da from the time ta. After the start of continuous conveyance, the edge temperature rises. At time tb when the edge temperature exceeds the high temperature threshold, the printer 100 changes the sheet interval to the sheet interval Db larger than the sheet interval Da, and continues the continuous conveyance of the sheet S. By increasing the paper interval, the end temperature decreases after time tb.

  At time tc when the edge temperature becomes lower than the low temperature threshold, the printer 100 changes the sheet interval to a sheet interval Dc that is smaller than the sheet interval Db and larger than the sheet interval Da, and continuously conveys the sheet S. continue. By reducing the gap between the sheets, the edge temperature increases after time tc. However, since the current paper gap Dc is larger than the paper gap Da, the temperature rise rate is slower than during continuous conveyance with the paper gap Da. In the example of FIG. 4, the slope of the end temperature after time tc is smaller than the slope of the end temperature between time ta and time tb.

  If the continuous conveyance of the sheet S is continued after time tc, the edge temperature again exceeds the high temperature threshold at time td. Therefore, at time td, the printer 100 changes the sheet interval to the sheet interval Dd larger than the sheet interval Dc, and continues the continuous conveyance of the sheet S. Since the slope of the end temperature after time tc is small, the elapsed time from time tc to time td is longer than the elapsed time from time ta to time tb. That is, the frequency of changing the sheet interval after the second time is lower than the initial time from the start of continuous conveyance.

  Note that the paper interval Dd changed at time td is preferably larger than the paper interval Dc and smaller than the paper interval Db, as shown in FIG. In this way, the slope at which the end temperature decreases after time td is smaller than the slope between time tb and time tc, and the time until the end temperature again becomes lower than the low temperature threshold is long. Therefore, it is possible to further reduce the frequency of changing the sheet interval.

  Next, a sheet conveyance process procedure for realizing the above-described sheet S conveyance control will be described with reference to the flowchart of FIG. The sheet conveyance process is executed by the CPU 31 when a print instruction based on a print job is received in a state where the sheet S is not being conveyed.

  In the sheet conveyance process, the CPU 31 first starts temperature control of the fixing unit 8 (S101). The CPU 31 acquires the center temperature based on the output signal of the center thermistor 811 and controls the amount of power supplied to the heater 810 so that the center temperature is within a predetermined fixing temperature range.

  Further, the CPU 31 starts continuous conveyance of the sheet S with the sheet interval set as a predetermined initial sheet interval (S102). The initial paper interval is a paper interval set at the start of continuous conveyance of the sheet S. The initial sheet interval is set to an interval that can be appropriately printed by the printer 100 and can achieve the maximum productivity, and is the shortest sheet interval unless the printing conditions such as the conveyance speed of the sheet S are changed. . Therefore, the CPU 31 does not set the paper interval to a value smaller than the initial paper interval. Note that the printer 100 stores the initial sheet interval for each printing condition in the ROM 32 or the NVRAM 34. The initial sheet interval is an example of a first sheet passing interval.

  Then, the CPU 31 sets the short side limit between the initial sheets (S103). Further, the CPU 31 sets a predetermined long side limit between the longest sheets (S104). The short side limit and the long side limit are temporary limit values that limit the setting range between papers. Note that the CPU 31 may execute S102 to S104 in any order, and may execute them simultaneously in parallel.

  The longest paper interval is the longest paper interval that can be assumed to be long enough to reduce the edge temperature. The CPU 31 does not set the paper interval larger than the longest paper interval. The longest paper interval is, for example, a paper interval corresponding to the circumferential length of the heating member 81 and a paper interval corresponding to half of the length of the sheet S. The distance between the longest papers may be different for each printing condition. The printer 100 stores the longest sheet interval in the ROM 32 or the NVRAM 34.

  Then, the CPU 31 starts a printing operation based on the received print job (S105). In the printing operation, the printer 100 drives the main motor 26 to rotate various conveyance members and performs the sheet S conveyance operation.

  Further, the CPU 31 determines whether or not to continue the printing operation (S106). When the sheet S subsequent to the sheet S being printed is not transported, the CPU 31 determines that the printing operation is not continued. For example, if the received print job is a job that only prints on one sheet S and the next print job is not received, it is not necessary to start the conveyance of the subsequent sheet S. It is determined that the operation is not continued. If it is determined that the printing operation is not continued (S106: NO), the CPU 31 ends the sheet conveying process.

  On the other hand, when it is determined that the printing operation is to be continued (S106: YES), the CPU 31 acquires the end temperature based on the output signal of the side thermistor 812 (S107). Then, the CPU 31 determines whether or not the acquired end temperature is higher than a high temperature threshold (S108). If it is determined that the edge temperature is higher than the high temperature threshold (S108: YES), the CPU 31 executes a high temperature side paper gap adjustment process (S110).

  Next, the procedure of the high-temperature side paper gap adjustment process will be described with reference to the flowchart of FIG. In the high temperature side paper gap adjustment process, the CPU 31 first sets the short side limit to the paper gap set in the current sheet conveying operation (S201). Since the end temperature has become higher than the high temperature threshold during continuous conveyance of the sheet S between the current sheets, the end temperature is likely to further increase between the current sheets. Therefore, the CPU 31 does not set the sheet interval to a value less than or equal to the current sheet interval in the continuous conveyance of the sheet S being executed.

  Then, the CPU 31 changes the sheet interval to a value larger than the short side limit and smaller than the long side limit (S202). The initial value of the long side limit is the longest sheet interval set in S104 of the sheet conveying process. The long side limit is also changed by executing a low temperature side paper gap adjustment process described later. Since the short side limit is set in S201 at the current paper interval, the paper interval is changed to a value larger than the current paper interval in S202.

  Note that in S202, the CPU 31 may determine the sheet interval as, for example, an intermediate value between the short side limit and the long side limit, or a value obtained by adding a predetermined value (for example, 2 mm) to the short side limit. Alternatively, it may be determined based on a reference table that stores the changed sheet interval in association with each short side limit.

  FIG. 7 shows an example of a change between the edge temperature and the paper interval when the intermediate value between the short side limit and the long side limit is set. In the example of this figure, after the continuous conveyance of the sheet S is started between the initial sheets at time t0, the edge temperature becomes higher than the high temperature threshold at time t1. As a result, the CPU 31 starts execution of the high-temperature side paper gap adjustment process, and changes the paper gap to the paper gap d1 that is an intermediate value between the initial paper gap and the longest paper gap in S202. The sheet interval d1 is an example of a second sheet passing interval.

  Then, the CPU 31 determines whether or not to continue the printing operation (S203). S203 is the same process as S106 of the sheet conveying process. When it is determined that the printing operation is not continued (S203: NO), the CPU 31 ends the high-temperature side paper gap adjustment processing and returns to the sheet conveyance processing.

  When it is determined that the printing operation is to be continued (S203: YES), the CPU 31 causes each conveying member to continuously convey the sheet S between the sheets set in S202, and continuously performs the printing operation. And CPU31 acquires edge part temperature (S204). S204 is the same process as S107 of the sheet conveying process. The CPU 31 may set the execution timing of S204 to be, for example, after a predetermined time from the previous temperature acquisition, after the printing on one sheet S is completed, and after the start of conveyance of the next sheet S.

  Then, the CPU 31 determines whether or not the end temperature is higher than the above-described upper limit temperature (S205). When it is determined that the end temperature is higher than the upper limit temperature (S205: YES), the CPU 31 returns to the sheet conveying process as an error (S206).

  When it is determined that the end temperature is not higher than the upper limit temperature (S205: NO), the CPU 31 determines whether the end temperature is higher than the high temperature threshold (S207). If it is determined that the edge temperature is not higher than the high temperature threshold (S207: NO), the CPU 31 ends the high temperature side paper gap adjustment processing and returns to the sheet conveyance processing. As indicated by a broken line in the example of FIG. 7, if the edge temperature decreases due to the change to the sheet interval d1 at time t1, the temperature is not higher than the high temperature threshold. When the edge temperature becomes equal to or lower than the high temperature threshold, the CPU 31 returns to the sheet conveyance process and causes the conveyance member to continuously convey the sheet S at the interval d1 between the sheets.

  On the other hand, when it is determined that the end temperature is higher than the high temperature threshold (S207: YES), the CPU 31 determines whether the end temperature is higher than the second high temperature threshold (S208). . The second high temperature threshold is a temperature higher than the high temperature threshold and lower than the above-described upper limit temperature. When it is determined that the end temperature is not higher than the second high temperature threshold (S208: NO), the CPU 31 returns to S203 and determines whether or not to continue printing.

  When it is determined that the end temperature is higher than the second high temperature threshold (S208: YES), the CPU 31 returns to S201 and sets the short side limit to the current sheet interval d1. Since the edge temperature further increased during the continuous conveyance of the sheet S at the sheet interval d1, the CPU 31 continuously conveys the sheet S being executed as indicated by the diagonal lines in the graph between the sheets in FIG. In between, the paper interval is not set to a value less than the current paper interval d1.

  In step S202, the CPU 31 changes the sheet interval to a value larger than the short side limit and smaller than the long side limit, and causes the conveyance member to continuously convey the sheet S. In the example of FIG. 7, the CPU 31 changes the paper interval to a paper interval d2, which is an intermediate value between the paper interval d1 and the longest paper interval. The sheet interval d2 is an example of a fifth sheet passing interval. If the edge temperature exceeds the high temperature threshold and the gap between the papers is larger than the initial paper gap d1, if the rise in the edge temperature does not stop, it is better to give a larger paper gap and give priority to the suppression of the temperature rise. preferable.

  Note that the paper gap d2 may be larger than the paper gap d1, and may be the longest paper gap. Alternatively, even when the sheet interval is set to the sheet interval d2, the interval between the sheets may be set to the longest sheet interval when the rise in the end temperature does not stop.

  When the CPU 31 determines that printing is not continued, the end temperature reaches the upper limit temperature, or the end temperature becomes a temperature equal to or lower than the high temperature threshold, the high temperature is detected. The side paper gap adjustment process is terminated and the process returns to the sheet conveyance process. This concludes the description of the high-temperature side paper gap adjustment processing.

  Returning to the description of the sheet conveying process in FIG. After the high temperature side paper gap adjustment process in S110, the CPU 31 determines whether or not an error has occurred in S206 of the high temperature side paper gap adjustment process (S111). If it is determined that an error has occurred (S111: YES), the CPU 31 ends the sheet conveyance process and stops the continuous conveyance of the sheet S. Even if the gap between the sheets is increased, if the edge temperature does not stop rising and the edge temperature reaches the above-described upper limit temperature, it is better to stop the continuous conveyance of the sheet S.

  If it is determined that there is no error (S111: NO), the CPU 31 returns to S106 and determines whether or not to continue printing. If it is determined that the printing operation is not continued in the high-temperature side paper gap adjustment process (NO in S203), the CPU 31 determines that the printing operation is not continued in S106. finish.

  If it is determined in S106 that printing is to be continued, the edge temperature is acquired in S107, and it is determined whether or not the edge temperature acquired in S108 is higher than the high temperature threshold. If it is determined that the acquired edge temperature is not higher than the high temperature threshold value (S108: NO), the CPU 31 has a gap between sheets larger than the initial gap, and the edge temperature is low. It is determined whether the temperature is lower than the threshold (S109). The low temperature threshold is a temperature lower than the high temperature threshold, and is higher than the end temperature at the start of the sheet conveying process.

  If the CPU 31 determines that the paper interval is not larger than the initial paper interval, or that the end temperature is not lower than the low temperature threshold (S109: NO), the CPU 31 returns to S106 and further performs the printing operation. Determine whether to continue. During the continuous conveyance of the sheet S, the end temperature is less likely to be lower than the temperature at the time when the continuous conveyance is started. Even if the edge temperature is lower than the low temperature threshold, if the gap between the sheets is the initial gap, the edge temperature has not exceeded the high temperature threshold from the start of conveyance, and there is no need to change the gap. Even if the paper interval is larger than the initial paper interval, it is not necessary to change the paper interval if the edge temperature is not lower than the low temperature threshold. If the end temperature is in the temperature range below the high temperature threshold and above the low temperature threshold, the CPU 31 causes the conveyance member to continuously convey the sheet S while maintaining the space between the sheets at the current size, and performs printing. Let it continue.

  On the other hand, when it is determined that the paper interval is larger than the initial paper interval and the end temperature is lower than the low temperature threshold (S109: YES), the CPU 31 executes the low temperature side paper interval adjustment process. (S112).

  Next, the procedure of the low-temperature side paper gap adjustment process will be described with reference to the flowchart of FIG. In the low temperature side paper gap adjustment process, the CPU 31 first sets the long side limit to the paper gap set in the current sheet conveying operation (S301). Since the edge temperature has become lower than the low temperature threshold during continuous conveyance of the sheet S between the current sheets, the edge temperature is likely to further decrease between the current sheets. In other words, even when the sheet S is continuously conveyed with the paper gap slightly smaller than the current paper gap, the possibility that the edge temperature is too high is small. Therefore, in order not to reduce productivity too much, the CPU 31 does not set the paper interval to a value greater than the current paper interval in the continuous conveyance of the sheet S being executed.

  Then, the CPU 31 changes the sheet interval to a value larger than the short side limit and smaller than the long side limit (S302). Since the long side limit is set in S301 at the current paper interval, the paper interval is changed to a value smaller than the current paper interval in S302.

  Note that the short side limit may be changed by the above-described high temperature side paper gap adjustment processing. For example, as shown by the broken line in FIG. 7, when the edge temperature once exceeds the high temperature threshold and the paper gap is changed to the paper gap d1, the edge temperature becomes lower than the low temperature threshold. The limit is between the initial sheets. On the other hand, as indicated by a solid line in FIG. 7, when the end temperature is higher than the second high temperature threshold, the short side limit is changed to a value larger than the initial paper interval.

  FIG. 9 shows an example of a change between the edge temperature and the paper space when the edge temperature becomes lower than the low temperature threshold after the high temperature side paper space adjustment processing is changed to the paper space d1. In the example of this figure, the printer 100 starts continuous conveyance of the sheet at time t0 and changes the sheet interval to the sheet interval d1 at time t1. Furthermore, during the continuous conveyance of the sheet S with the sheet interval d1, the edge temperature became lower than the low temperature threshold at time t3. Therefore, at time t3, the CPU 31 changes the long side limit to the paper interval d1, and changes the paper interval to the paper interval d3, which is an intermediate value between the initial paper interval and the paper interval d1. The sheet interval d3 is an example of a third sheet passing interval.

  Then, the CPU 31 determines whether or not to continue the printing operation (S303). S303 is the same process as S203 of the high-temperature side paper gap adjustment process. If it is determined that the printing operation is not continued (S303: NO), the CPU 31 ends the low-temperature side paper gap adjustment processing and returns to the sheet conveyance processing.

  When it is determined that the printing operation is to be continued (S303: YES), the CPU 31 continues the continuous conveyance of the sheet S and the printing operation. And CPU31 acquires edge part temperature (S304). S304 is the same process as S204 of the high-temperature side paper gap adjustment process.

  Then, the CPU 31 determines whether or not the end temperature is lower than the low temperature threshold (S305). If it is determined that the end temperature is not lower than the low temperature threshold (S305: NO), the CPU 31 ends the low temperature side paper gap adjustment process and returns to the sheet conveyance process. As indicated by the broken line in the example of FIG. 9, when the edge temperature increases due to the change to the sheet interval d3 at time t3 and the temperature is not lower than the low temperature threshold, the CPU 31 transfers the sheet. Returning to the processing, the conveying member is caused to continuously convey the sheet S at the interval d3.

  On the other hand, when it is determined that the end temperature is lower than the low temperature threshold (S305: YES), the CPU 31 determines whether the end temperature is lower than the second low temperature threshold (S306). . The second low temperature threshold is a temperature lower than the low temperature threshold. When it is determined that the end temperature is not lower than the second low temperature threshold (S306: NO), the CPU 31 returns to S303 and determines whether or not to continue printing.

  If the CPU 31 determines that the end temperature is lower than the second low temperature threshold (S306: YES), the CPU 31 returns to S301 and sets the long side limit to the current sheet interval d3. Since the edge temperature further decreased during the continuous conveyance of the sheet S at the sheet interval d3, the CPU 31 detects the gap between the sheets during the continuous conveyance of the sheet S being executed, as indicated by the oblique lines in FIG. It is not set to a value greater than the current paper interval d3.

  Then, the CPU 31 proceeds to S202 and changes the sheet interval to a value larger than the short side limit and smaller than the long side limit. In the example of FIG. 9, the CPU 31 changes the paper interval to a paper interval d4 that is an intermediate value between the initial paper interval and the paper interval d3. The sheet interval d4 is an example of a seventh sheet passing interval. If the edge temperature further decreases even when the paper gap is changed to a paper gap d3 smaller than the paper gap d1, it is preferable to set a smaller paper gap d4 and give priority to productivity.

  When the CPU 31 determines that printing is not continued or when it is determined that the end temperature has become a temperature equal to or higher than the low temperature threshold, the low temperature side inter-sheet adjustment process is terminated and the process returns to the sheet conveying process. This concludes the description of the low-temperature side paper spacing adjustment process.

  Returning to the description of the sheet conveying process in FIG. After the low-temperature side paper gap adjustment process in S112, the CPU 31 returns to S106 and determines whether or not to continue printing. When it is determined that the printing operation is not continued in the low temperature side paper gap adjustment process (NO in S303), the CPU 31 determines that the printing operation is not continued in S106, and therefore the CPU 31 performs the sheet conveyance process. finish.

  That is, when the edge temperature becomes equal to or lower than the high temperature threshold and equal to or higher than the low temperature threshold during execution of the high temperature side paper interval adjustment processing and the low temperature side paper interval adjustment processing, the CPU 31 Thus, the conveying member continuously conveys the sheet S. On the other hand, when the edge temperature is higher than the high temperature threshold or lower than the low temperature threshold, the CPU 31 changes the sheet interval and causes the conveyance member to continuously convey the sheet S.

  For example, as shown by the broken line in FIG. 9, after changing the paper interval to the paper interval d3, when the edge temperature rises and becomes higher than the high temperature threshold at time t5, the CPU 31 changes the paper interval to The sheet interval d5 is changed to an intermediate value between the sheet interval d1 and the sheet interval d3. The sheet interval d5 is an example of a fourth sheet passing interval. In this case, the CPU 31 further sets the short side limit to the sheet interval d3.

  Further, for example, as shown by a solid line in FIG. 7, after changing the paper interval to the paper interval d2, the CPU 31 determines that the edge temperature decreases and becomes lower than the low temperature threshold at time t7. Is changed to an intermediate paper interval d7 between the paper interval d1 and the paper interval d2. The sheet interval d7 is an example of a sixth sheet passing interval. In this case, the CPU 31 further sets the long side limit to the sheet interval d2.

  Further, for example, as indicated by a solid line in FIG. 9, after the edge temperature falls below the second low temperature threshold and the sheet interval is changed to the sheet interval d4, the edge temperature rises and becomes high at time t6. When it becomes higher than the threshold value, the CPU 31 changes the sheet interval to an intermediate sheet interval d6 between the sheet interval d3 and the sheet interval d4. The sheet interval d6 is an example of an eighth sheet passing interval. In this case, the CPU 31 further sets the short side limit to the sheet interval d4.

  As described above, the printer 100 acquires the edge temperature during continuous conveyance of the sheet, and changes the sheet interval based on the result of comparing the acquired edge temperature with the high temperature threshold or the low temperature threshold. In particular, if the reverse side threshold is exceeded after changing the paper interval, the printer 100 does not return to the original paper interval, but the size of the paper between the original paper interval and the changed paper interval. The sheet S is conveyed between them. Accordingly, for example, the time from time t3 to time t5 in FIG. 9 or the time from time t4 to time t6 is both longer than the time from time t0 to time t1. In other words, the frequency of changing the gap is gradually decreasing.

  As described above in detail, according to the printer 100 of the first embodiment, the excessive temperature rise at the end can be suppressed by increasing the gap between the sheets in accordance with the increase in the end temperature of the heating member 81. After that, when the edge temperature is lowered, the gap between the sheets is reduced, but it is made larger than before the change, thereby reducing the degree of change in the edge temperature. That is, it is possible to converge the edge temperature and reduce the frequency of changing the sheet interval. As a result, a sheet conveying technique that does not easily give a bad impression to the user is realized.

  Next, a second embodiment in which the image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. In the present embodiment, control different from that of the first embodiment is performed by the printer 100 having the same configuration as that of the first embodiment. The same configurations and processes as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

  The printer 100 according to the second embodiment calculates a difference between the end temperature and the center temperature, and compares the calculated difference with a predetermined high temperature difference threshold value or a predetermined low temperature difference threshold value. Different from the first embodiment. The printer 100 continuously conveys the sheet S, so that the end temperature increases and the difference between the end temperature and the center temperature also increases. That is, the printer 100 can reduce the frequency of changing the paper interval even if the paper interval is changed based on the comparison between the difference and the threshold value. The procedure for changing the sheet interval based on the comparison result is the same as in the first embodiment.

  Note that the printer 100 according to the second embodiment stores the high temperature difference threshold and the low temperature difference threshold in the ROM 32 or the NVRAM 34. The high temperature difference threshold is an example of a first temperature difference threshold, and the low temperature difference threshold is an example of a second temperature difference threshold. In the second embodiment, the side thermistor 812 is an example of a first temperature sensor, and the center thermistor 811 is an example of a second temperature sensor.

  The procedure of the sheet conveying process of the second embodiment will be described with reference to the flowchart of FIG. The sheet conveyance process is executed by the CPU 31 when a print instruction based on a print job is received in a state where the sheet S is not being conveyed.

  In the sheet conveyance process, the CPU 31 first starts temperature control of the fixing unit 8 (S101). In addition, the CPU 31 sets a sheet interval to a predetermined initial sheet and starts continuous conveyance of the sheet S (S102). Then, the CPU 31 sets the short side limit between the initial sheets (S103). Further, the CPU 31 sets a predetermined long side limit between the longest sheets (S104). Then, the CPU 31 starts a printing operation based on the received print job (S105).

  Further, the CPU 31 determines whether or not to continue the printing operation (S106). If it is determined that the printing operation is to be continued (S106: YES), the CPU 31 acquires the end temperature based on the output signal of the side thermistor 812 (S107). Further, the CPU 31 acquires the center temperature based on the output signal of the center thermistor 811 (S401). Then, the CPU 31 calculates the difference between the center temperature and the end temperature (S402).

  Then, the CPU 31 determines whether or not the calculated difference is larger than the high temperature difference threshold (S403). When it is determined that the calculated difference is larger than the high temperature difference threshold value (S403: YES), the CPU 31 executes a high temperature difference side paper gap adjustment process (S405). Note that the high temperature difference side paper gap adjustment process is a process that uses the difference in place of the end temperature in the high temperature side paper gap adjustment process shown in FIG. The procedure of the high temperature difference side paper gap adjustment process will be described later.

  Further, in the sheet conveying process, as in the first embodiment, it is determined whether or not there is an error (S111). If it is determined that there is no error (S111: NO), the process returns to S106 and whether or not to continue printing. Judging. If it is determined that the calculated difference is not greater than the high temperature difference threshold value (S403: NO), the CPU 31 determines that the paper interval is larger than the initial paper interval and the difference calculated in S402 is low. It is determined whether it is smaller than the temperature difference threshold value (S404). The low temperature difference threshold is smaller than the high temperature difference threshold and larger than zero.

  If it is determined that the paper gap is not larger than the initial paper gap, or the calculated difference is not smaller than the low temperature difference threshold (S404: NO), the CPU 31 returns to S106 and continues printing. Judge whether or not. On the other hand, when it is determined that the paper interval is larger than the initial paper interval and the calculated difference is smaller than the low temperature difference threshold (S404: YES), the CPU 31 performs low temperature difference side paper interval adjustment processing. Is executed (S406). The low temperature difference paper spacing adjustment process is a process that uses the difference instead of the edge temperature in the low temperature side paper spacing adjustment process shown in FIG. The procedure of the low temperature difference side paper gap adjustment process will be described later.

  If the CPU 31 determines that the printing operation is not continued (S106: NO), or determines that an error has occurred (S111: YES), the CPU 31 ends the sheet conveyance process and stops the continuous conveyance of the sheets S. This is the end of the description of the sheet conveyance processing of the second embodiment.

  Next, the procedure of the high temperature difference side paper gap adjustment process will be described with reference to the flowchart of FIG. Note that the same procedures as those in the high-temperature side paper gap adjustment process shown in FIG. 6 are denoted by the same reference numerals in FIG.

  In the high temperature difference side paper gap adjustment processing, first, the short side limit is set to the paper gap set in the current sheet conveying operation (S201). Then, the CPU 31 changes the sheet interval to a value larger than the short side limit and smaller than the long side limit (S202). Further, the CPU 31 determines whether or not to continue the printing operation (S203).

  Then, the CPU 31 obtains the end temperature and the center temperature and calculates the difference (S501). Specifically, as in S107, S401, and S402 of the sheet conveying process shown in FIG. 10, the edge temperature and the center temperature are acquired, and the difference is calculated based on the acquired temperature.

  Further, the CPU 31 determines whether or not the end temperature is higher than the above-described upper limit temperature (S205). When it is determined that the end temperature is higher than the upper limit temperature (S205: YES), the CPU 31 returns to the sheet conveying process as an error (S206).

  When it is determined that the end temperature is not higher than the upper limit temperature (S205: NO), the CPU 31 determines whether or not the calculated difference is larger than the high temperature difference threshold (S502). If it is determined that the difference is not greater than the high temperature difference threshold value (S502: NO), the CPU 31 ends the high temperature difference side paper gap adjustment process and returns to the sheet conveyance process.

  On the other hand, when it is determined that the difference is larger than the high temperature difference threshold (S502: YES), the CPU 31 determines whether or not the difference is larger than the second high temperature difference threshold (S503). The second high temperature difference threshold value is larger than the high temperature difference threshold value. When it is determined that the difference is not greater than the second high temperature difference threshold (S503: NO), the CPU 31 returns to S203 and determines whether or not to continue printing.

  When it is determined that the difference is larger than the second high temperature difference threshold (S503: YES), the CPU 31 returns to S201, sets the short side limit to the current paper interval d1, and proceeds to S202 to change the paper interval. When the CPU 31 determines that printing is not continued, when the end temperature reaches the upper limit temperature, or when the difference is equal to or lower than the high temperature difference threshold, the high temperature difference is detected. The side paper gap adjustment process is terminated and the process returns to the sheet conveyance process. This concludes the description of the high temperature difference side paper gap adjustment processing.

  Next, the procedure of the low temperature difference side paper gap adjustment process will be described with reference to the flowchart of FIG. Note that the same steps as those in the low-temperature side paper gap adjustment process shown in FIG. 8 are denoted by the same reference numerals in FIG. 12, and detailed description thereof is omitted.

  In the low temperature difference side paper gap adjustment processing, first, the long side limit is set to the paper gap set in the current sheet conveying operation (S301). Then, the CPU 31 changes the sheet interval to a value larger than the short side limit and smaller than the long side limit (S302). Further, the CPU 31 determines whether or not to continue the printing operation (S303).

  Then, the CPU 31 obtains the end temperature and the center temperature and calculates the difference (S601). Specifically, as in S107, S401, and S402 of the sheet conveying process shown in FIG. 10, the edge temperature and the center temperature are acquired, and the difference is calculated based on the acquired temperature.

  Then, the CPU 31 determines whether or not the calculated difference is smaller than the low temperature difference threshold (S602). If it is determined that the difference is not smaller than the low temperature difference threshold value (S602: NO), the CPU 31 ends the low temperature difference side paper gap adjustment process and returns to the sheet conveyance process.

  On the other hand, when it is determined that the difference is smaller than the low temperature difference threshold value (S602: YES), the CPU 31 determines whether or not the difference is smaller than the second low temperature difference threshold value (S603). The second low temperature difference threshold is a value smaller than the low temperature difference threshold. When it is determined that the difference is not smaller than the second low temperature difference threshold (S603: NO), the CPU 31 returns to S303 and determines whether or not to continue printing.

  If it is determined that the difference is smaller than the second low temperature difference threshold value (S603: YES), the CPU 31 returns to S301, sets the long side limit to the current sheet interval d3, proceeds to S302, and changes the sheet interval. Then, the CPU 31 ends the low temperature difference side inter-sheet adjustment process to determine whether to continue printing, or when the difference is equal to or greater than the low temperature difference threshold value, and enters the sheet conveyance process. Return. This concludes the description of the low temperature difference side paper gap adjustment processing.

  That is, the printer 100 according to the second embodiment acquires the edge temperature and the center temperature during continuous conveyance of the sheet, calculates the difference, and calculates the calculated difference and the high temperature difference threshold value or the low temperature difference threshold value. Based on the comparison result, the paper interval is changed. Then, as in the first embodiment, when the reverse threshold is exceeded after changing the paper interval once, the printer 100 does not return to the original paper interval, but instead of returning to the original paper interval and the changed paper interval. The sheet S is transported between sheets of a size between.

  As described above in detail, the printer 100 of the second embodiment can also converge the edge temperature and reduce the frequency of changing the sheet interval, as in the first embodiment. As a result, a sheet conveying technique that does not easily give a bad impression to the user is realized.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a printer, and can be applied to any apparatus having an image forming function in an electrophotographic system, such as a copying machine, a multifunction machine, and a FAX apparatus.

  Further, for example, the printer 100 only needs to be able to adjust the sheet interval when passing through the fixing unit 8, and may switch the sheet interval using a sensor other than the sheet sensor 71. For example, when the conveyance timing of the sheet S can be changed by the registration roller 22, the printer 100 may switch between sheets using a sheet sensor upstream or downstream of the registration roller 22. Alternatively, the sheet interval may be switched using a sheet sensor upstream or downstream of the fixing unit 8 as long as the timing at which the sheet S enters the fixing unit 8 can be adjusted.

  Also, for example, when continuous conveyance is continued with a paper interval d3 that is smaller than the paper interval d1 and larger than the initial paper interval, and the end temperature exceeds the high temperature threshold again (broken line in FIG. 9), the paper interval is changed to the paper interval. You may return to d1. However, by setting the paper gap d5 smaller than the paper gap d1 and larger than the paper gap d3, the rising speed of the edge temperature can be lowered, and the change frequency between the papers can be further suppressed.

  Further, for example, the second high temperature threshold and the second low temperature threshold may be omitted. For example, if the inter-paper d1 after exceeding the high temperature threshold for the first time is sufficiently increased, the end temperature can be prevented from reaching the second high temperature threshold, so the second high temperature threshold can be eliminated and the processing is simplified. It becomes. On the other hand, if the second high temperature threshold value is provided, productivity is high because it is not necessary to make the gap d1 too large. Also, if the paper gap d3 is set to be smaller within the range larger than the initial paper gap, the edge temperature is unlikely to be lower than the second low temperature threshold, so the second low temperature threshold can be eliminated, and the processing is performed. It becomes simple. However, if the second low temperature threshold value is provided, the inter-paper interval d3 can be increased, so that the frequency of change between the papers can be suppressed.

  Further, for example, more threshold values may be provided in addition to the second high temperature threshold value and the second low temperature threshold value. By providing a large number of threshold values, it is possible to set a small change width when changing between sheets. And since edge part temperature can be converged, the change frequency between paper can be suppressed.

  The processing disclosed in the embodiments may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the processing disclosed in the embodiment can be realized in various modes such as a recording medium or a method recording a program for executing the processing.

21 Pickup roller 31 CPU
81 Heating member 811 Center thermistor 812 Side thermistor 100 Printer

Claims (9)

A conveying member for conveying the sheet;
A heating member for thermally fixing a toner image on a sheet conveyed by the conveying member, the heating member being disposed along a sheet width direction which is a direction orthogonal to the sheet conveying direction;
Among the heating members, a temperature sensor that outputs different signals depending on the temperature of the end in the sheet width direction, and
A control unit;
With
The controller is
With the sheet conveying interval of the sheet conveyance as the first sheet passing interval, the sheet is continuously conveyed by the conveying member,
When the sheet is continuously conveyed by the conveying member at the first sheet passing interval,
When the temperature detected by the signal from the temperature sensor exceeds the first high temperature threshold, the sheet passing interval of the sheet conveyance by the conveying member is set as a second sheet passing interval larger than the first sheet passing interval. The sheet is continuously conveyed by the conveying member,
When the sheet is continuously conveyed by the conveying member at the second sheet passing interval,
When the temperature detected by the signal from the temperature sensor falls below a first low temperature threshold value that is lower than the first high temperature threshold value, the sheet conveyance interval of the sheet conveyance by the conveyance member is made smaller than the second sheet conveyance interval. In addition, the sheet is continuously conveyed by the conveying member as a third sheet passing interval larger than the first sheet passing interval.
An image forming apparatus. The image forming apparatus according to claim 1,
The controller is
When the sheet is continuously conveyed by the conveying member at the third sheet passing interval,
When the temperature detected by the signal from the temperature sensor exceeds the first high temperature threshold, the sheet conveyance interval of the sheet conveyance by the conveyance member is larger than the third sheet conveyance interval and the second sheet conveyance interval. A sheet is continuously conveyed by the conveying member as a fourth sheet passing interval smaller than
An image forming apparatus. The image forming apparatus according to claim 1, wherein:
The controller is
When the sheet is continuously conveyed by the conveying member at the second sheet passing interval,
When the temperature detected by the signal from the temperature sensor exceeds the second high temperature threshold value that is higher than the first high temperature threshold value, the sheet conveyance interval of the sheet conveyance by the conveyance member is larger than the second sheet conveyance interval. As the fifth sheet passing interval, the sheet is continuously conveyed by the conveying member.
An image forming apparatus. The image forming apparatus according to claim 3,
The controller is
When performing continuous conveyance of the sheet at the fifth sheet passing interval by the conveyance member,
When the temperature detected by the signal from the temperature sensor falls below the first low temperature threshold, the sheet conveyance interval of the sheet conveyance by the conveyance member is larger than the second sheet conveyance interval and the fifth sheet conveyance interval. The sheet is continuously conveyed by the conveying member as a sixth sheet passing interval smaller than
An image forming apparatus. In the image forming apparatus according to any one of claims 1 to 4,
The controller is
When the sheet is continuously conveyed by the conveying member at the third sheet passing interval,
When the temperature detected by the signal from the temperature sensor is lower than the second low temperature threshold which is lower than the first low temperature threshold, the sheet conveyance interval of the sheet conveyance by the conveyance member is smaller than the third sheet conveyance interval. In addition, the sheet is continuously conveyed by the conveying member as a seventh sheet passing interval larger than the first sheet passing interval.
An image forming apparatus. The image forming apparatus according to claim 5,
The controller is
When the sheet is continuously conveyed by the conveying member at the seventh sheet passing interval,
When the temperature detected by the signal from the temperature sensor exceeds the first high temperature threshold, the sheet conveyance interval of the sheet conveyance by the conveyance member is larger than the seventh sheet conveyance interval and the third sheet conveyance interval. A sheet is continuously conveyed by the conveying member as an eighth sheet passing interval smaller than
An image forming apparatus. A conveying member for conveying the sheet;
A heating member for thermally fixing a toner image on a sheet conveyed by the conveying member, the heating member being disposed along a sheet width direction which is a direction orthogonal to the sheet conveying direction;
A first temperature sensor that outputs a different signal depending on the temperature of the end of the heating member in the sheet width direction;
A second temperature sensor that outputs a different signal depending on the temperature of the central portion in the sheet width direction of the heating member;
A control unit;
With
The controller is
With the sheet conveying interval of the sheet conveyance as the first sheet passing interval, the sheet is continuously conveyed by the conveying member,
When the sheet is continuously conveyed by the conveying member at the first sheet passing interval,
When the difference between the temperature detected by the signal from the first temperature sensor and the temperature detected by the signal from the second temperature sensor exceeds the first temperature difference threshold value, the sheet is conveyed by the conveying member. The sheet is continuously conveyed by the conveying member with the interval being a second sheet passing interval larger than the first sheet passing interval,
When the sheet is continuously conveyed by the conveying member at the second sheet passing interval,
If the difference between the temperature detected by the signal from the first temperature sensor and the temperature detected by the signal from the second temperature sensor is below a second temperature difference threshold lower than the first temperature difference threshold; The sheet conveyance interval of the sheet conveyance by the conveyance member is set as a third sheet conveyance interval that is smaller than the second sheet conveyance interval and larger than the first sheet conveyance interval, and the sheet is continuously conveyed by the conveyance member.
An image forming apparatus. A conveying member for conveying the sheet;
A heating member for thermally fixing a toner image on a sheet conveyed by the conveying member, the heating member being disposed along a sheet width direction which is a direction orthogonal to the sheet conveying direction;
Among the heating members, a temperature sensor that outputs different signals depending on the temperature of the end in the sheet width direction, and
An image forming apparatus control method comprising:
A first continuous conveyance step in which the conveyance member performs continuous conveyance of the sheet, with the sheet conveyance interval of the sheet conveyance being a first sheet conveyance interval;
When the sheet is continuously conveyed by the conveying member at the first sheet passing interval,
When the temperature detected by the signal from the temperature sensor exceeds the first high temperature threshold, the sheet passing interval of the sheet conveyance by the conveying member is set as a second sheet passing interval larger than the first sheet passing interval. A second continuous conveying step for causing the conveying member to continuously convey the sheet;
When the sheet is continuously conveyed by the conveying member at the second sheet passing interval,
When the temperature detected by the signal from the temperature sensor falls below a first low temperature threshold value that is lower than the first high temperature threshold value, the sheet conveyance interval of the sheet conveyance by the conveyance member is made smaller than the second sheet conveyance interval. And a third continuous conveying step for causing the conveying member to continuously convey the sheet as a third sheet passing interval larger than the first sheet passing interval;
A control method for an image forming apparatus. A conveying member for conveying the sheet;
A heating member for thermally fixing a toner image on a sheet conveyed by the conveying member, the heating member being disposed along a sheet width direction which is a direction orthogonal to the sheet conveying direction;
A first temperature sensor that outputs a different signal depending on the temperature of the end of the heating member in the sheet width direction;
A second temperature sensor that outputs a different signal depending on the temperature of the central portion in the sheet width direction of the heating member;
An image forming apparatus control method comprising:
A first continuous conveyance step in which the conveyance member performs continuous conveyance of the sheet, with the sheet conveyance interval of the sheet conveyance being a first sheet conveyance interval;
When the sheet is continuously conveyed by the conveying member at the first sheet passing interval,
When the difference between the temperature detected by the signal from the first temperature sensor and the temperature detected by the signal from the second temperature sensor exceeds the first temperature difference threshold value, the sheet is conveyed by the conveying member. A second continuous conveying step for causing the conveying member to continuously convey the sheet, with the interval being a second sheet passing interval larger than the first sheet passing interval;
When the sheet is continuously conveyed by the conveying member at the second sheet passing interval,
If the difference between the temperature detected by the signal from the first temperature sensor and the temperature detected by the signal from the second temperature sensor is below a second temperature difference threshold lower than the first temperature difference threshold; A sheet feeding interval for sheet conveyance by the conveying member is a third sheet passing interval that is smaller than the second sheet passing interval and larger than the first sheet passing interval. 3 continuous transport steps;
A control method for an image forming apparatus.

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