JP5089119B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material.

  In image forming apparatuses such as electrophotographic copying machines, printers, and facsimile machines, an electrostatic latent image is formed on the outer peripheral surface (surface) of a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) that is an image carrier. The latent image is developed as a toner image by a developing device. Then, the toner image (development image) on the surface of the photosensitive drum is transferred onto a recording material by a transfer device, and the toner image on the recording material is heated and fixed on the recording material surface by an image heating fixing device (fixing device).

  As the fixing device, a heating body that generates heat when energized, a heat-resistant film that slides with the heating body, and a pressure member that presses the heating body across the film to form a film and a nip portion. There is something to have. In this film heating type fixing device, a heating body is heated and adjusted to a predetermined temperature, and a recording material on which an unfixed toner image is formed and held is nipped and conveyed at the nip portion, and the toner on the recording material is conveyed during the conveyance process. The image is applied with heat from the heating element and pressure from the pressure member. As a result, the toner image is fixed on the surface of the recording material.

  In the fixing device, a thin plate-like heating body having a low heat capacity such as a so-called ceramic heater can be used as the heating body, and a thin film having a low heat capacity can be used as the film. Therefore, it is possible to quickly raise the temperature of the nip portion to the set temperature (target temperature). For this reason, it is possible to suppress power consumption as much as possible without supplying power to the apparatus during standby, so that power saving and wait time reduction (quick start performance) can be realized.

  In the fixing device, when a recording material (for example, an envelope or a postcard) having a narrow width with respect to the heat generation area width in the longitudinal direction of the plate-like heating body is nipped and conveyed at the nip portion, an area through which the recording material passes (paper passing area) And the region that does not pass through (non-paper passing region), the amount of heat taken away from the heating body is greatly different. Therefore, when a narrow recording material is continuously nipped and conveyed at the nip portion, heat is not taken away by the recording material in an area where the recording material does not pass. Therefore, the temperature of the area gradually increases as the number of conveyed recording materials increases. The temperature rises to exceed the set temperature, so-called non-sheet passing portion temperature rise occurs. Excessive temperature rise of the non-sheet passing portion significantly exceeding the set temperature may damage constituent members such as a film and a pressure member, thereby reducing the device life (durability life).

Therefore, a method of lowering the interval between recording materials to be continuously conveyed, so-called throughput (the number of recording materials to be conveyed (output) per unit time) to a point where there is no problem even in the worst condition (widening the recording material conveyance interval) is attempted. It has been. Japanese Patent Application Laid-Open No. 2004-228561 proposes that temperature detection means such as a thermistor provided in a non-sheet passing region detects temperature rise of the non-sheet passing portion and performs control to change the throughput according to the temperature condition. In Patent Document 2, the recording material width detecting means provided in the non-sheet passing portion region detects the recording material width, and when the recording material width is narrow, the power supply to the heating body is temporarily reduced or the throughput is changed. It has been proposed to perform control.
Japanese Patent Laid-Open No. 5-80604 JP-A-8-305188

The present invention is a further development of the above prior art. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of more accurately determining whether or not a recording material is conveyed out of the conveyance reference and suppressing the temperature rise of the non-sheet passing portion .

A typical configuration of an image forming apparatus according to the present invention is a recording material width restriction that can move symmetrically with respect to a conveyance reference set at the center of a recording material conveyance path in a direction orthogonal to the recording material conveyance direction. A member, an image forming unit that forms a toner image on the recording material, a recording material width detecting unit that is provided in the recording material conveyance path and detects the width of the recording material, a heating unit, and the conveyance reference First temperature detecting means for detecting the temperature of the heating means in a region through which recording materials of all sizes usable in the conveying apparatus pass, and the side on which the recording material width detecting means is provided with respect to the conveyance reference A second temperature detecting means for detecting the temperature of the heating means in a region opposite to the control section, and a control for controlling electric power supplied to the heating means so that the detected temperature of the first temperature detecting means maintains a target temperature. Means, and having toner on the recording material In an image forming apparatus having a fixing unit that heat-fixes an image on a recording material, the recording material width detection unit does not detect the passage of the recording material even though the recording material is conveyed, and the first When the temporal change amount of the difference between the detection temperature of the temperature detection means and the detection temperature of the second temperature detection means is smaller than a predetermined threshold value, the recording material width detection means does not detect the passage of the recording material and The number of recording materials conveyed per unit time is greatly reduced compared to when the temporal change amount is larger than the predetermined threshold value.

According to the present invention, it is possible to provide an image forming apparatus capable of more accurately determining whether or not the recording material is conveyed out of the conveyance reference and suppressing the temperature increase of the non-sheet passing portion.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 1 is a structural model diagram of an example of an image forming apparatus according to the present invention. This image forming apparatus is a laser printer using an electrophotographic system.

  In the following description, regarding the printer and the components of the printer, the width direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The width direction is also the axial direction of a photosensitive drum as an image carrier.

  In the printer A shown in this embodiment, the maximum width of the usable recording material (recording paper, OHP sheet, etc.) is the LETTER size, and the recording material having the maximum width size is conveyed in the center in the width direction of the recording material and described later. Transport is performed with a central transport reference that matches the transport reference position of the means. The process speed for forming an image on the recording material is 200 mm / sec, the conveyance interval of the recording material is 1.714 sec, and a print is output at 35 sheets / min (ppm).

In the printer A of the present embodiment, when a print command is input from a host device such as a personal computer (not shown), a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier in an image forming unit is provided. It is rotated in the direction of the arrow at a predetermined peripheral speed (process speed). In addition, driving of the laser scanner 2 as an exposure unit is started.

  The photosensitive drum 1 is uniformly charged at a predetermined polarity and potential by a charging roller 3 serving as a charging device during its rotation. The surface of the photosensitive drum 1 is subjected to scanning exposure with a laser beam L by a laser scanner 2. As a result, an electrostatic latent image corresponding to image data input from the host device is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed as a toner image (developed image) by the developing device 4.

  On the other hand, at a predetermined control timing, a multi-tray (MP tray: multi-purpose tray) 5 as a conveying means or a recording material (hereinafter referred to as paper) P from a feeding cassette 6 one by one is fed one by one. To the registration roller pair 8.

  The tray 5 includes a plate 5a for setting the paper P and a feeding roller 5b provided in the width direction on the plate 5a. The feeding roller 5b has a rotating shaft 5b1 (FIG. 5). Both ends of the rotating shaft 5b1 are rotatably supported by holding portions 5aR and 5aL provided at both ends in the width direction of the plate 5a via bearings (not shown). A drive gear G is provided at one end of the rotating shaft 5b1. The feeding roller 5b is rotated in the direction of the arrow by the driving gear G being rotated by a conveying motor 70 as driving means, and conveys the paper P set on the plate 5a to the roller pair 8.

  The plate 5a of the tray 5 is provided with sheet width restriction guides 9R and 9L (FIG. 2) as recording material width restriction members. FIG. 2 is a structural model diagram of an example of the regulation guides 9R and 9L. The regulation guides 9R and 9L are arranged symmetrically in the width direction of the plate 5a and are connected by a synchronous movement mechanism (not shown). As a result, the regulation guides 9R and 9L can move in a symmetrical manner with respect to the conveyance reference position CL virtually set at the center in the width direction of the plate 5a. That is, the interval between the regulation guides 9R and 9L can be adjusted to be wide or narrow with the conveyance reference position CL as the center. As a result, the left and right end surfaces of the paper P set on the plate 5a are regulated by the inner surfaces of the corresponding regulation guides 9R and 9L, and the width direction center Pc of the paper P can coincide with the conveyance reference position CL. Accordingly, the sheet P is conveyed to the roller pair 8 by the feeding roller 5b in a state where the center Pc in the width direction coincides with the conveyance reference position CL.

  Sheets P are stacked and stored in the cassette 6, and the sheets P are conveyed to the roller pair 8 through the feeding guide 7 by the rotation of the feeding roller 6a.

  The sheet P conveyed from the tray 5 or the cassette 6 is conveyed by the roller pair 8 to the transfer nip T between the photosensitive drum 1 and the transfer roller 10 as a transfer device through the feeding guide 7.

  Reference numeral 71 denotes a top sensor as recording material detection means. The top sensor 71 is disposed on the conveyance reference position CL between the roller pair 8 and the transfer portion T (FIG. 5). The top sensor 71 detects that the paper P is passing by detecting that a lever (not shown) is tilted at the front end of the paper P when the paper P passes. That is, the state where the paper P is present is continuously detected until the rear end of the paper P passes the lever. Accordingly, the length of the paper P in the transport direction can be detected based on the time during which the top sensor 71 is in the paper presence state. The lever of the top sensor 71 returns to the original position when the trailing edge of the paper P passes, and it is detected that the trailing edge of the paper P has passed the position of the top sensor 71. The throughput of the paper P in the case of continuous printing is maintained by feeding the next paper P after a predetermined time has elapsed since the top sensor 71 detects the leading edge of the paper P or the trailing edge of the paper P.

  Reference numeral 72 denotes a paper width sensor as recording material width detection means. The paper width sensor 72 is arranged on either the left or right side in the width direction orthogonal to the transport direction of the paper P with respect to the transport reference position CL (FIG. 5). In this embodiment, the paper width sensor 72 is arranged on the left side in the width direction perpendicular to the transport direction of the paper P with respect to the transport reference position CL. If the size of the paper P is equal to or larger than the predetermined size, the paper width sensor 72 detects that a lever (not shown) is tilted at the front end of the paper P when the paper P passes, and the sensor P is turned on. Is detected. If the lever is not tilted, the sensor is turned off.

  In the transfer nip T, the paper P is nipped and conveyed by the photosensitive drum 1 and the transfer roller 10. Meanwhile, a transfer bias is applied to the transfer roller 10. As a result, the toner image on the surface of the photosensitive drum 1 is electrostatically transferred sequentially onto the sheet P surface.

  The surface of the photosensitive drum 1 after the transfer of the toner image to the paper P is cleaned by the cleaning device 11 after removal of transfer residual toner, paper dust, and the like, and is repeatedly used for image formation.

  The sheet P that has received the transfer of the toner image at the transfer nip T is introduced into an image heating and fixing device 13 as an image heating unit via a conveyance guide 12. Then, when the paper P receives heat and pressure from the fixing device 13, the toner image is fixed on the paper P surface. The recording material P exiting the fixing device 13 is discharged onto the discharge tray 16 by the discharge guide 14 and the discharge roller 15.

(2) Fixing device (fixing unit)
1) Configuration of Fixing Device FIG. 3 is an enlarged schematic cross-sectional view of the main part of the fixing device 13. The fixing device 13 is a pressure member driving type / film heating type fixing device.

  Reference numeral 21 denotes a cylindrical (endless belt-shaped) fixing film as a fixing rotating body. The film 21 may be a single layer composed mainly of heat-resistant PTFE, PFA, FEP, or the like, or polyimide, polyamideimide, PEEK, PES, or PPS, in order to reduce the heat capacity as part of speeding up the fixing process. Or a composite layer in which PTFE, PFA, FEP, or the like is coated on the outer peripheral surface of an endless substrate mainly composed of a resin such as SUS, Al, Ni, or Zn. Things can be used. Alternatively, an outer peripheral surface of the substrate may be coated with an elastic member such as silicone rubber, and the outer peripheral surface may be coated with PTFE, PFA, FEP, or the like. This film 21 is loosely fitted on a heater holder 23 as a holding member.

  The heater holder 23 is a heat-resistant and rigid member having a substantially semicircular arc shape in cross section. The holder 23 is made of a liquid crystal polymer resin having high heat resistance. The holder 23 is arranged inside the film 21 to guide the film 21 and to play a role of holding the heater 22 as a heating body (heat source). The heater 22 is held by the holder 23 along the paper P width direction.

  Reference numeral 25 denotes an elastic pressure roller 25 as a pressure rotator. The pressure roller 25 has an elastic layer 25b mainly composed of heat-resistant and releasable silicone rubber or the like on the outer peripheral surface of a columnar or substantially columnar core 25a mainly composed of iron, aluminum or the like. It is configured by covering. The pressure roller 25 is rotatably held at both ends of the cored bar 25a by a pair of side plates of a device frame (not shown) via a bearing. On the upper side of the pressure roller 25, a heating assembly including the heater 22, the holder 23, the film 21 and the like is arranged in parallel with the pressure roller 25 with the heater 22 facing downward. Then, both ends of the holder 23 are urged toward the pressure roller 25 by a pressure mechanism (not shown) to press the heater 22 against the outer peripheral surface (surface) of the pressure roller 22 through the film 21. Thereby, the elastic layer 25b of the pressure roller 25 is elastically deformed, and a nip portion (fixing nip portion) N is formed between the surface of the pressure roller 22 and the surface of the film 21.

  FIG. 4 is a structural model diagram of the heater 22. The heater 22 has a thin plate-like substrate 22a whose main component is ceramics typified by alumina, aluminum nitride or the like. On the surface (surface on the nip portion N side) of the substrate 22a, a resistance heating element 22b mainly composed of Ag / Pd (silver palladium) is applied by screen printing or the like along the paper P width direction. It is. Further, electrode portions 22c1 and 22c2 for energizing the heating element 22b are formed on the surface of the substrate 22a. The heating element 22b is covered with a protective layer 22d whose main component is glass or fluorine. The protective layer 22d is formed on the surface of the substrate 22a so as to cover the heating element 22b.

  In the heater 22, a main thermistor 51 as a first temperature detecting means and a sub thermistor 52 as a second temperature detecting means are provided on the back surface (the surface opposite to the surface on the nip portion N side) of the substrate 22a. (Figure 5). The main thermistor 51 is disposed in an area through which all sizes of paper P usable in the image forming apparatus M pass in the heater 22. In this embodiment, the main thermistor 51 is arranged on the left side of the conveyance reference position CL in the paper P width direction. The sub-thermistor 52 is disposed in an area where the relatively narrow paper P does not pass among the papers P of all sizes usable in the image forming apparatus M in the heater 22. In this embodiment, the sub-thermistor 52 is disposed on the right side of the conveyance reference position CL in the paper P width direction.

2) Heat-fixing operation of the fixing device The pressure roller 25 is driven in the direction of the arrow at a predetermined peripheral speed (process speed) by a driving motor (not shown) provided at the end of the core metal 25a by a fixing motor 26 as fixing driving means. It is rotated. Although the fixing motor 26 is not shown, the driving is controlled by the MPU 60. A rotational force acts on the film 21 by the pressure frictional force at the nip N between the surface of the pressure roller 25 and the surface of the film 21 due to the rotation of the pressure roller 25. With this rotational force, the film 21 is driven to rotate around the outer circumference of the holder 23 while the inner surface of the film 21 is in close contact with the surface of the protective layer 22d of the heater 22 and slides.

  In the rotating state of the pressure roller 25 and the film 21, an MPU (micro processor unit) 60 as a control unit starts driving a heater driving unit 61 as a power supply unit. The heater driving unit 61 energizes the heating element 22b through the electrode portions 22c1 and 22c2 of the heater 22. As a result, the heating element 22b generates heat and the heater 22 quickly rises in temperature. Further, the MPU 60 takes in temperature information detected by the main thermistor 51 in real time. The MPU 60 controls the heater driving unit 61 based on the temperature information, and the energization amount to the heater 22 so that the heater 22 maintains a predetermined set temperature (target temperature) (hereinafter, the set temperature is referred to as a fixing temperature). To control. In the fixing device 13 of this embodiment, when the size of the paper P is the LETTER size, the energization amount to the heater 22 is controlled so that the temperature of the heater 22 is maintained at 200 ° C. Control of the heater drive unit 61 by the MPU 60 is control in which the energization amount to the heating element 22b is adjusted over an arbitrary fixed time with respect to the AC bias energized to the heating element 22b of the heater 22, so-called phase control. Alternatively, wave number control can be used. Among these controls, the wave number control has an advantage that noise accompanying the energization is less than that of the phase control. Therefore, the fixing device 13 of this embodiment employs the wave number control. Although the output signal of the sub thermistor 52 is not used for the temperature control, the MPU 60 takes in temperature information detected by the sub thermistor 52 in real time.

  In a state where the heater 22 is maintained at the fixing temperature, the paper P carrying the unfixed toner image t is introduced into the nip portion N (FIG. 3). The paper P is nipped and conveyed by the film 21 and the pressure roller 25 in the nip portion N. During the conveyance process, the heat of the heater 22 is applied to the paper P through the film 21. As a result, the unfixed toner image t is fixed on the sheet P surface by receiving the heat from the heater 22 and the nip pressure. The sheet P exiting the nip portion N is separated from the surface of the film 21 by the curvature, and is discharged to the discharge guide 14 (FIG. 1).

3) Positional relationship between the paper width sensor 72, the main thermistor 51, and the sub-thermistor 52 FIG. 5 is a schematic plan view showing the relationship between the tray 5, the photosensitive drum 1, and the heater 22 of the image forming apparatus M.

In the image forming apparatus M of the present embodiment, the sub-thermistor 52 is disposed on one side (right side) straddling the conveyance reference position CL, and the sheet width sensor 72 is disposed on the other side (left side). In the sub thermistor 52 and the paper width sensor 72, the distance from the conveyance reference position CL is preferably equal. However, the distance may be slightly different as long as necessary functions can be satisfied for the sub-thermistor 52 and the paper width sensor 72. In this embodiment, the distance A from the conveyance reference position CL to the paper width sensor 72 and the distance F from the conveyance reference position CL to the sub-thermistor 52 are both equal to 100 mm. Since the distance from the sub thermistor 52 to the paper width sensor 72 is 200 mm, the width of the paper P detected by the paper width sensor 72 is less than 200 mm. Accordingly, the paper P having a width of less than 200 mm is handled as a narrow paper (hereinafter referred to as a narrow paper) P1. A paper P having a width of 200 mm or more is handled as a wide paper (hereinafter referred to as a wide paper) P2. The arrangement positions of the paper width sensor 72 and the sub-thermistor 52 differ depending on the size of the image forming apparatus M, and are not limited to the above distance.

  Further, the maximum opening width B from the conveyance reference position CL for each of the regulation guides 9R and 9L is set to B = 110 mm by providing a slight clearance with respect to the wide paper P2. Accordingly, the left and right regulating guides 9R and 9L are respectively provided from the position of the maximum opening width B to the left and right side surfaces of the narrow paper P1 when the narrow paper P1 is transported on the basis of the central transport as indicated by arrows. The range can be moved back and forth. Here, the center transport reference means that the narrow paper P1 and the wide paper P2 are transported in a state where the center Pc in the width direction coincides with the transport reference position CL (FIGS. 5 and 8).

  Further, since the left and right regulation guides 9R and 9L can be moved to arbitrary positions in the left and right direction, some users do not use the narrow regulation sheet P1 with respect to the conveyance reference position CL. There is a case where the sheet is to be transported in a state where it is brought close to the left side (other side) or the right side (one side) of the center Pc in the width direction. This is an irregular usage that is out of specification different from the central conveyance standard originally set in the apparatus, and has a high risk of damaging the apparatus. Here, irregular use outside this specification is referred to as a one-sided conveyance reference. When the user uses the left regulation guide 9L as the one-sided conveyance reference regulation guide, the regulation guide 9L is opened to the vicinity of the maximum opening width B, and the regulation guide 9L is brought into contact with the left side surface of the narrow paper P1. In this state, the narrow paper P1 is conveyed (FIG. 7). When the right regulation guide 9R is used as a regulation guide for the one-sided conveyance reference, the regulation guide 9R is opened to the vicinity of the maximum opening width B, and the right side surface of the narrow paper P1 is in contact with the regulation guide 9R. Then, the narrow paper P1 is conveyed (FIG. 9).

  Next, the positions of the sheet width sensor 72, the main thermistor 51, and the sub-thermistor 52 will be described based on the relationship between the above-mentioned center conveyance reference and the one-sided conveyance reference. The paper width sensor 72 has a narrow width that is transported on the basis of a one-sided transport reference in which the wide paper P2 transported based on the central transport reference passes and the center in the width direction is brought closer to the left side in the width direction with respect to the transport reference position CL. It is arranged in an area (sheet passing area) through which the sheet P1 passes. The main thermistor 51 passes through the narrow paper P1 and the wide paper P2 conveyed on the central conveyance reference, and is shifted to the left side or right side in the width direction with respect to the conveyance reference position CL. It is arranged in an area (sheet passing area) through which narrow paper P1 conveyed on the conveyance reference passes. The sub-thermistor 52 passes through the wide sheet P2 conveyed based on the central conveyance reference, and is a narrow sheet conveyed based on the one-sided conveyance reference where the center in the width direction is brought closer to the right side in the width direction with respect to the conveyance reference position CL. It is arranged in the area where P1 passes. That is, the sub-thermistor 52 is a narrow sheet P1 that is transported based on the center transport reference, and a narrow sheet P1 that is transported based on the one-sided transport reference where the center in the width direction is brought closer to the left side in the width direction with respect to the transport reference position CL. Is disposed in an area that does not pass through (non-sheet passing area).

4) Description of erroneous determination of narrow sheet P1 conveyed on the basis of the one-sided conveyance reference When the narrow sheet P1 is conveyed based on the central conveyance reference, the detection temperature of the sub-thermistor 52 that detects the temperature of the non-sheet passing region is described above. Based on this, it can be directly determined whether or not the temperature of the non-sheet passing region has exceeded the protection temperature for maintaining the performance of the heater 22. In addition, it is possible to perform control such as switching the throughput of the narrow paper P1 in accordance with the temperature of the non-sheet passing area of the heater 22 and lowering the fixing temperature at a more accurate timing, thereby improving the performance of the image forming apparatus M. Can be made.

  In this way, when the sub-thermistor 52 is arranged on one side of the conveyance reference position CL and the paper width sensor 72 is arranged on the other side, a method of determining conveyance of the narrow sheet P1 by the one-sided conveyance reference. As follows, the following method can be adopted.

  When the wide paper P2 is transported based on the central transport standard, the paper width sensor 72 is in the paper passing area, so that the sensor is turned on and it is detected that the wide paper is being transported. Further, since the sub-thermistor 52 is also in the sheet passing region, the temperature does not rise abnormally compared with the main thermistor 51. Therefore, in such a case, it is determined that the wide paper P2 is transported based on the central transport standard, and the wide paper P2 is transported with a normal throughput.

  When the narrow paper P1 is transported based on the central transport reference, the paper width sensor 72 becomes a non-sheet passing area and the sensor is turned off. Further, since the sub-thermistor 52 also becomes a non-sheet passing region, the temperature rises abnormally compared to the main thermistor 51. Therefore, in such a case, it is determined that the narrow sheet P1 is being conveyed based on the central conveyance reference. When the narrow paper P1 is being conveyed, as described above, the fixing condition such as the fixing temperature is changed or the paper feed interval is increased (the throughput is decreased) to prevent the temperature increase of the non-sheet passing portion. Process.

  Two cases are conceivable when the narrow sheet P1 is conveyed on the basis of the one-sided conveyance reference.

  [Case 1]: The sub-thermistor 52 is in a non-sheet passing area and the sheet width sensor 72 is in a sheet passing area.

  [Case 2]: The sub-thermistor 52 is in the paper passing area, and the paper width sensor 72 is in the non-paper passing area.

・ Case 1
In this case, the sub-thermistor 52 is abnormally heated while the sheet width sensor 72 is on. At this time, since the paper width sensor 72 is initially sensor-on, the narrow paper P1 is continuously transported with a normal throughput in the same manner as the wide paper P2 is transported based on the central transport standard. However, on the other hand, the temperature of the sub thermistor 52 gradually increases as the temperature of the non-sheet-passing portion is increased, so that a temperature difference occurs between the detected temperature of the sub thermistor 52 and the fixing temperature of the main thermistor 51. Eventually, when this temperature difference becomes equal to or higher than a predetermined determination reference temperature and the paper width sensor 72 is ON, it is determined that the one-sided conveyance reference is performed.

・ Case 2
In this case, first, the paper width sensor 72 is turned off, and it is detected that the narrow paper P1 is not the central conveyance reference. On the other hand, since the sub-thermistor 52 is in the sheet passing area, the temperature does not rise abnormally even when a plurality of narrow sheets P1 are conveyed. In order to detect that the sub-thermistor 52 does not have an abnormal temperature rise, it is not sufficient to transport only one narrow sheet P1, and it is necessary to transport a plurality of sheets. Therefore, for example, when the temperature difference between the detected temperature of the sub-thermistor 52 and the fixing temperature of the main thermistor 51 after transporting a plurality of sheets is less than the determination reference temperature, and the sheet width sensor 72 is sensor off, Judge that it is done.

  If it can be determined that the narrow paper P1 is conveyed based on the one-sided conveyance reference, the narrow paper P1 is conveyed based on the central conveyance reference when the narrow paper P1 is conveyed based on the one-sided conveyance standard. It is possible to perform a control different from the case where it is performed. The state where the narrow paper P1 is conveyed on the basis of the one-sided conveyance reference has a larger non-sheet passing region than the state where the narrow paper P1 is conveyed based on the central conveyance reference. For this reason, when the narrow paper P1 is conveyed on the basis of the one-sided conveyance reference, the temperature of the non-sheet passing region is likely to rise more than the case of being conveyed on the central conveyance reference, and the heater 22 can exceed the protection temperature faster. There is sex. For this reason, for example, in the case of the one-sided conveyance reference, the fixing temperature is further lowered, or the conveyance interval is widened to reduce the throughput, or the image forming apparatus M is urgently used, compared with the case where the narrow paper P1 is conveyed based on the central conveyance reference. Control such as stopping can be performed. Further, it is possible to display on the display panel or the like of the image forming apparatus M and notify the user that the paper is being used irregularly at a normal position.

  In the case 1 and the case 2, it is determined whether or not it is the one-sided conveyance reference based on whether the temperature difference between the sub-thermistor 52 and the main thermistor 51 is equal to or higher than the determination reference temperature. However, when the fixing device 13 is in the following state, there is a possibility that it cannot be accurately determined whether or not it is the reference transporting standard.

  For example, when there is a temperature difference between the detected temperatures of the sub-thermistor 52 and the main thermistor 51, the above control does not work normally. In such a state, when the sub-thermistor 52 and the main thermistor 51 have a temperature difference element as the fixing device 13 at the position where the temperature detection is performed, specifically, the heater 22 in which the thermistors 51 and 52 are arranged is in the width direction. This can happen when the heat distribution is. Since this heat generation distribution is not intentional and is caused by variations, it is difficult to make it completely flat.

  In addition, there may be a difference between the detected temperatures of the sub-thermistor 52 and the main thermistor 51 due to variations in temperature detection capability. The detection temperature characteristics of the thermistors 51 and 52 have a variation of about ± 3 deg.

  In such a case, there is a possibility that the detected temperature of the sub-thermistor 52 is higher than the detected temperature of the main thermistor 51 from the beginning, and the temperature difference is equal to or higher than the determination reference temperature. Therefore, even when the wide paper P2 is transported based on the central transport standard, the routine of the case 1 may be entered, and it may be determined that the wide paper P2 is transported based on the one-side transport standard.

  Even in the case 2 where the narrow paper P1 is actually conveyed on the basis of the one-sided conveyance reference, since the temperature difference is originally detected to be equal to or higher than the determination reference temperature, even if a plurality of sheets are conveyed, the temperature is below the determination reference temperature. Never become. Therefore, it may not be possible to determine that the paper is being transported based on the one-sided transport standard.

  On the other hand, even if the detected temperature of the sub-thermistor 52 is much lower than the detected temperature of the main thermistor 51 due to the above-described variation, and the narrow paper P1 is conveyed on the basis of the one-sided conveyance reference in the case 1, it is quite easy to determine the temperature difference. There may be cases where the reference temperature is not exceeded. In such a case, as a matter of course, it cannot be determined that the sheet is conveyed based on the one-sided conveyance reference.

  In order to solve these problems, in the image forming apparatus M of the present embodiment, based on the detection result of the paper width sensor 72 and the temporal change of the temperature difference detected by the main thermistor 51 and the sub-thermistor 52, The drive of the feeding roller 5b is controlled. The control (hereinafter referred to as a recording material conveyance control sequence) is executed by the MPU 60.

5) Recording Material Transport Control Sequence FIG. 6 is a flowchart of an example of the recording material transport control sequence.

  When the MPU 60 receives a print command (print start), the MPU 60 drives the carry motor 70 to rotate the feed roller 5b of the tray 5. By the rotation of the feed roller 5b, the narrow paper P1 or the wide paper P2 set in advance on the plate 5a is conveyed (S1).

  When the leading edge of the narrow paper P1 or the wide paper P2 conveyed by the feed roller 5b reaches the paper width sensor 72, a detection signal is taken from the paper width sensor 72 and a first determination is made (S2). As described above, since the paper width sensor 72 is turned on / off according to the paper width, the width of the paper P is determined based on this result. However, at this point in time, only the position of the paper width sensor 72 can be understood only by whether or not the paper P has passed, whether the actual width of the paper P is being transported based on the central transport standard, I don't know if it is being transported.

If the paper width sensor 72 is on, it is determined that the paper is wide paper P2, and the normal throughput of 35 ppm is maintained (S3). When the paper width sensor 72 is off, it is certain that the paper is narrow paper P1 regardless of the center conveyance reference or the side-by-side conveyance reference, and in this embodiment, the throughput is reduced corresponding to the narrow paper P1. The process proceeds to control, that is, control to increase the conveyance interval of the narrow paper P1 per unit time (S6). In this example, it was set to 12 ppm.
Note that it is also possible to switch the throughput after waiting for the second determination without decreasing the throughput just because it is the narrow paper P1. Further, as described above, it is also possible to perform control for changing the fixing conditions such as lowering the fixing temperature.

  Next, when the narrow paper P <b> 1 or the wide paper P <b> 2 reaches the fixing device 13, a second determination is made by the sub thermistor 52.

  First, the case where the normal throughput of 35 ppm is maintained based on the first determination result (S3) will be described.

  In this case, a second determination is made according to the value of the detected temperature TS of the sub-thermistor 52 that is constantly monitored during the operation of the image forming apparatus M (S4). If the detected temperature TS is equal to or lower than the protection temperature of the heater 22 in S4, the operation is continued with a normal throughput of 35 ppm.

  If the detected temperature TS exceeds the protection temperature of the heater 22, it is determined that the temperature rise of the non-sheet passing portion is large at that time, and control for significantly reducing the normal throughput is performed. In this embodiment, when the detected temperature TS exceeds the protection temperature 270 ° C. of the heater 22, the throughput is reduced to 2 ppm (S5). This protection temperature is a temperature set with a certain margin within a range where the heater 22 is not damaged in terms of heat resistance.

  As described above, when the detection temperature TS of the sub-thermistor 52 greatly exceeds the fixing temperature 200 ° C. of the heater 22 in spite of the paper width sensor 72 being turned on in S3 and being determined to be wide paper P2, FIG. As shown in FIG. 4, in reality, the narrow sheet P1 is likely to be conveyed to the side where the sheet width sensor 72 is present on the basis of the one-sided conveyance reference. When the narrow sheet P1 is conveyed on the basis of the one-sided conveyance standard, the non-sheet passing area is much larger than the central conveyance standard in the heater 22, and therefore the temperature rise in the non-sheet passing area (non-sheet passing part temperature rise). ) Gets worse. Therefore, in order to prevent the heater 22 from being damaged due to the temperature rise of the non-sheet passing portion, control is performed to further lower the throughput than when the narrow paper P1 is transported based on the central transport reference. In this embodiment, the throughput is drastically reduced to 2 ppm at a conveyance interval of 30 sec, and the non-sheet passing portion temperature rise is reduced between the narrow paper P1 that is continuously conveyed.

  In this case (when the paper width sensor 72 is on), the control is performed directly based on the detected temperature of the sub-thermistor 52, unlike when the paper width sensor 72 described later is off. This is because the position where the non-sheet passing region occurs in the heater 22 is always on the sub-thermistor 52 side, and the direct control according to the temperature of the sub-thermistor 52 can surely prevent the heater 22 from being damaged. .

  Next, the case where the sheet width sensor 72 is turned off, the first determination result is determined as the narrow sheet P1 (S6), and the throughput is reduced to 12 ppm (S6) will be described.

  First, a difference TS0−TM0 = ΔT0 between the detection temperature TS0 of the sub-thermistor 52 and the detection temperature TM0 of the main thermistor 51 at the timing when the leading edge of the first narrow sheet P1 enters the nip portion N is obtained. Hold (S7). In this embodiment, the value ΔT0 is the value immediately before entering the first sheet, but actually, even after the leading edge of the narrow paper P1 enters the nip portion N, if it is not yet conveyed so much, ΔT0 at that time There is no problem to ask for.

  The difference TSn−TMn = ΔTn between the detection temperature TSn of the sub-thermistor 52 and the detection temperature TMn of the main thermistor 51 is obtained again at the timing when the rear end of the nth narrow sheet P1 passes through the nip N (S8). .

  n is the number of sheets from which detection of narrow paper P1 is started. After the detection of the nth sheet is completed, n = n + 1 is set and the same detection is continued until the end of the print job (image forming process) on the next narrow paper P1.

Next, in order to detect how ΔTn changes with respect to the difference ΔT0 between the detection temperatures of the first sub-thermistor 52 and the main thermistor 51, the difference between ΔTn and ΔT0 [ΔTn−ΔT0] (temporal change) Amount) is calculated (S9). When [ΔTn−ΔT0] is a positive value, the non-sheet-passing portion temperature rises. When the value is zero or negative, the non-sheet-passing portion temperature is not increased. However, even if the position of the sub-thermistor 52 is not in the non-sheet passing region, [ΔTn−ΔT0] may become positive due to a slight temperature rise. Therefore, when [ΔTn−ΔT0] is equal to or higher than a predetermined value (specified temperature difference) that is somewhat high, it is determined that the non-sheet-passing portion temperature rise (S9). In this embodiment, when [ΔTn−ΔT0] is equal to or greater than +10 deg (threshold value) , it is determined that the non-sheet passing portion temperature rise has occurred.

  In S9, when [ΔTn−ΔT0] is equal to or greater than +10 deg as the second determination result, the narrow sheet P1 is conveyed based on the central conveyance reference as shown in FIG. 8 based on the first determination result. Can think. That is, since the narrow sheet P1 is conveyed based on the central conveyance reference, a non-sheet passing area is formed as expected, and thus the non-sheet passing portion temperature rises. In this case, the throughput is maintained at 12 ppm as the mode for the narrow paper P1.

  In this way, even when the narrow paper P1 is transported based on the central transport reference, if the narrow paper P1 is continuously transported, the non-sheet passing area may be heated up to the protection temperature of the heater 22. is there. For this reason, for example, whenever the detection temperature of the sub-thermistor 52 exceeds 270 ° C., the throughput may be gradually decreased from 12 ppm → 6 ppm → 4 ppm.

  When the second determination result [ΔTn−ΔT0] is less than +10 deg, the position of the sub-thermistor 52 is not in the non-sheet passing region even though the first determination result is the narrow sheet P1. Is shown. Therefore, it can be said that there is a high possibility that the narrow paper P1 is not transported on the basis of the central transport standard and is transported on the side where the sub-thermistor 52 exists as shown in FIG. Therefore, in this case, since the state is irregular, the throughput is reduced to 2 ppm in order to prevent the heater 22 from being damaged (S5).

  Thus, the amount [ΔTn−ΔT0] in which the difference ΔT between the detected temperature of the sub-thermistor 52 and the detected temperature of the main thermistor 51 changes due to the passage of the narrow paper P1 is calculated for the following reason.

  As described in the above item 4), when the determination is performed only by ΔT, if there is a temperature difference between the detection temperatures of the sub-thermistor 52 and the main thermistor 51 from the beginning, there is a very high possibility of erroneous detection. Become.

  For example, even if there is no temperature rise at the non-sheet passing portion, if the heat distribution of the heater 22 is large, there may actually be a case where the sub-thermistor 52 detects 220 ° C. when the main thermistor 51 is 200 ° C. In such a heater 22 having a large heat generation distribution, ΔT is always +20 deg or more at a minimum, and it is detected as if the temperature of the non-sheet passing portion is being raised at any time.

  On the other hand, [ΔTn−ΔT0] is calculated to detect how the temperature difference ΔT has changed due to the passage of the narrow paper P1. Then, even if there is a difference in the detected temperature between the sub-thermistor 52 and the main thermistor 51 due to the heat generation distribution, it is canceled out and only the value where the temperature of the non-sheet passing portion is raised by passing the narrow paper P1 is taken out. Can do.

  For example, even if ΔT0 is +20 deg immediately before the narrow paper P1 enters the nip N, if ΔTn when the trailing edge of the narrow paper P1 passes through the nip N is also +20 deg, ΔTn−ΔT0 = 0 deg. It can be detected that there is no temperature rise in the non-sheet passing portion.

  Here, in particular, such control must be performed in consideration of the fact that the narrow sheet P1 is transported to the side of the sub-thermistor 52 without being transported based on the central transport standard. Because.

  If the narrow paper P1 is always transported based on the central transport reference, the non-sheet passing area can be always left and right as shown in FIG. 8, and the sub-thermistor 52 can directly detect the temperature rise of the non-sheet passing portion. Therefore, damage to the heater 22 can be prevented by monitoring whether the detected temperature of the sub-thermistor 52 exceeds the protection temperature of the heater 22.

  However, when the narrow paper P1 is conveyed to the sub thermistor 52 side as shown in FIG. 9 on the basis of the one-sided conveyance reference, the position of the sub thermistor 52 becomes the sheet passing area. Therefore, while the temperature detected by the sub-thermistor 52 does not increase, the opposite side becomes a non-sheet passing region, so the temperature of the heater 22 increases rapidly. In this state, the sub-thermistor 52 cannot directly detect the temperature rise of the non-sheet passing portion, so it is not known at all whether or not the heater 22 has reached the protection temperature. Therefore, compared to the case where the temperature of the non-sheet passing area is directly detected, it is necessary to judge that the conveyance is performed based on the one-sided conveyance standard more quickly and surely because the control has to be performed as expected. Don't be.

  By the way, if the paper width sensor 72 is off and it can be detected that the detection temperature of the sub-thermistor 52 does not rise, it can be determined that the narrow paper P1 is conveyed to the sub-thermistor 52 side on the basis of the one-sided conveyance reference. Is possible.

  Here, in order to quickly determine that the narrow paper P1 is being conveyed on the basis of the one-sided conveyance standard, is the non-sheet passing temperature rising occurring in a state in which the number of continuous conveyance of the narrow paper P1 is small? You have to make a decision. In a state where the number of continuous sheets of narrow paper P1 is small, the non-sheet passing temperature rise is still relatively small even if the narrow paper P1 is transported based on the central transport standard. Therefore, the threshold value for determination (determination reference temperature (= determination reference value)) must be set as small as possible.

  At this time, as described above, if only the temperature difference ΔT between the sub-thermistor 52 and the main thermistor 51 is used, the central conveyance reference is used despite the fact that it is the one-sided conveyance reference due to the influence of the heat generation distribution that the heater 22 originally has. It becomes easy to make a misjudgment to judge that.

  Therefore, as in this embodiment, the determination is made with a smaller threshold value by making a determination with a value [ΔTn−ΔT0] to which a temporal parameter such as a change in the temperature difference ΔT due to the passage of the narrow paper P1 is added. In addition, the above-mentioned misjudgment can be eliminated.

  In this embodiment, the temporal change of the temperature difference ΔT is observed. However, in terms of the temporal change, the same effect can be obtained even if the temporal change of the detected temperature itself of the sub-thermistor 52 is observed. That is, the temperature change [TSn−TS0] from the detection temperature TS0 of the sub thermistor 52 at the start of printing to the detection temperature TSn of the sub thermistor 52 in the nth narrow sheet P1 is used as a threshold value. The influence of the heat generation distribution can be eliminated. As a result, it is possible to accurately detect how many degrees the non-sheet passing area has been heated. For example, if [TSn−TS0] is equal to or greater than +10 deg, the temperature of the non-sheet passing portion has risen, and it is determined that the narrow paper P1 is being transported based on the central transport standard, and the throughput is maintained as it is. On the other hand, if it is less than +10 deg, it is determined that the narrow sheet P1 is conveyed based on the one-sided conveyance standard, and the throughput is reduced to 2 ppm. Thus, the temporal change may be detected not by the temperature difference but by the temperature of the sub-thermistor 52 itself.

  However, assuming that the fixing temperature required for fixing is lowered by warming the fixing device due to continuous paper passing, etc., control such as changing the fixing temperature controlled by the main thermistor 51 stepwise according to the number of paper sheets, etc. When performing the above, the detected temperature of the sub-thermistor 52 also changes accordingly, and thus the above-described control for judging only by the temperature of the sub-thermistor 52 is not suitable. For example, if the fixing temperature controlled by the main thermistor 51 is lowered by 10 degrees, the temperature at the position of the sub-thermistor 52 is also lowered by 10 degrees. Then, although the temperature rise itself in the non-sheet passing area with respect to the sheet passing area has not changed, the temperature detected by the sub-thermistor 52 itself is lowered, so that it is determined that the temperature change has changed to the minus side. become. This will induce misjudgment.

  On the other hand, the temperature difference ΔT between the sub-thermistor 52 and the main thermistor 51 always detects the temperature rise at the position of the sub-thermistor 52 relative to the position of the main thermistor 51, so that even if the temperature of the main thermistor 51 changes. The temperature difference itself does not change. Therefore, it can be said that the temperature of the heater 22 can be detected with higher accuracy when the temperature difference ΔT is taken in view of the value of the temperature rise of the non-sheet passing portion.

  By the way, in the above example, the non-sheet passing portion temperature rise is determined based on the nth sheet ΔT0 and ΔTn for the narrow sheet P1 passing through the non-sheet passing area, but of course the determination starts from the first sheet. Is possible. However, depending on the type of the narrow paper P1, there may be a case where the temperature rise of the non-sheet passing portion is hardly known by only transporting one sheet. For example, a paper having a small basis weight or a paper having a short length has a small non-sheet passing portion temperature rise and is transported based on a one-sided transport standard even though the narrow paper P1 is transported based on the central transport standard. May be misdetected.

  Therefore, in order to determine that these papers are transported based on the one-sided transport standard, a few sheets are transported. If the transport is based on the central transport standard, the determination is made when the temperature rise of the non-sheet passing portion can be reliably detected. This is better for preventing misjudgment. However, on the other hand, the paper non-passage area may rise to a temperature at which the heater 22 may be damaged even if several sheets of paper having a large basis weight or a long length are transported. It is dangerous to make a decision after transporting. Therefore, it is preferable to set a balance between the number of sheets to be determined. In addition, since the threshold value at this time is erroneously judged whether it is large or small, an optimum value must be selected. For example, if the threshold value is too small, it is determined that the non-sheet-passing portion temperature rise is caused even by a slight temperature rise of the sub-thermistor 52. Conversely, if the threshold value is too large, there is a non-sheet-passing portion temperature rise. Can no longer be detected. Therefore, the threshold value is set so that [ΔTn−ΔT0] does not surely exceed this value when there is no temperature increase in the non-sheet passing portion and exceeds this value when there is a temperature increase in the non-sheet passing portion. Must-have.

  In the apparatus of this embodiment, it is necessary to convey five or more continuous sheets of narrow paper P1 in terms of preventing the above-mentioned erroneous determination, and if the number of sheets in order to prevent the heater 22 from being damaged is about five. There was no problem. Also, it was optimal to set the threshold value (threshold temperature) at this time to +10 deg. Of course, this numerical value varies depending on the configuration of the image forming apparatus M, and is not limited thereto.

  A case will be described below in which the determination is made after the continuous conveyance of five sheets of narrow paper P1 from the above results.

  First, the sheet width sensor 72 is turned off, and the first determination result is determined as the narrow sheet P1.

  Then, a difference TS0−TM0 = ΔT0 between the detection temperature TS0 of the sub-thermistor 52 and the detection temperature TM0 of the main thermistor 51 at the timing when the leading edge of the first narrow sheet P1 enters the nip portion N is detected.

  The continuous paper passing is performed as it is, and the detection temperature TS5 of the sub-thermistor 52 and the main thermistor 51 are again detected at the timing when the rear end of the fifth narrow paper P1 of the continuous conveyance number of the narrow paper P1 passes through the nip portion N. A difference TS5-TM5 = ΔT5 of the detected temperature TM5 is detected.

  Here, ΔT5−ΔT0 is calculated, and when [ΔT5−ΔT0] is +10 deg or more, it is determined that the narrow paper P1 is conveyed based on the central conveyance reference, and the throughput is maintained at 12 ppm. When [ΔT5−ΔT0] is less than +10 deg, it is determined that the narrow paper P1 is being conveyed to the sub-thermistor 52 side on the basis of the one-sided conveyance standard, and the throughput is set to 2 ppm.

  Further, the detection of the difference TSn−TMn = ΔTn between the detection temperature TSn of the sub-thermistor 52 and the detection temperature TMn of the main thermistor 51 is continued even after the sixth continuous conveyance number of the narrow paper P1. When [ΔTn−ΔT0] becomes +10 deg or less, it is more preferable to determine that the sheet is conveyed based on the one-sided conveyance reference.

  This is based on the assumption that what has been conveyed based on the central conveyance standard is switched to conveyance based on the one-sided conveyance standard, and there is a misjudgment on the fifth consecutive conveyance number of narrow sheets P1. Considering the case. That is, when it is determined that the temperature of the sub-thermistor 52 does not increase even after the sixth continuous conveyance number of the narrow sheets P1, it can be immediately determined that the conveyance is based on the one-sided conveyance standard. it can.

  By the way, in the above example, when it is determined that the conveyance is based on the one-sided conveyance standard, the throughput is significantly reduced to 2 ppm to suppress the temperature rise of the non-sheet passing portion and prevent the heater 22 from being damaged. It is also possible to reduce the temperature rise of the non-sheet passing portion by lowering. For example, when the temperature of the heater 22 is controlled to 200 ° C. during the normal fixing operation, the fixing temperature is lowered by 30 degrees and changed to 170 ° C. when it is determined that the conveyance is based on the one-sided conveyance reference. As a result, the temperature of the non-sheet passing area also decreases. As a result, it is possible to prevent the heater 22 from being damaged at the time of conveyance based on the one-sided conveyance reference while maintaining the throughput at 12 ppm.

  Alternatively, both a decrease in throughput and a decrease in fixing temperature may be combined. For example, when it is determined that the conveyance is based on the one-sided conveyance standard, the fixing temperature is first lowered by 10 degrees and the throughput is also changed to 6 ppm. When only the fixing temperature is lowered and the conveyance based on the one-sided conveyance standard is supported, the deterioration of the fixing property becomes conspicuous because it is not effective for preventing the heater 22 from being damaged unless the amount of decrease in the fixing temperature is increased. . Also, when dealing with only the throughput, the throughput must be greatly reduced. On the other hand, if both the throughput and the fixing temperature are reduced at the same time, they can be transported in a single-sided manner with a faster throughput and better fixability than when dealing with the temperature rise of the non-sheet passing part alone. It can handle standard transport.

  Therefore, according to the image forming apparatus M of the present embodiment, it is possible to suppress the temperature rise in the non-sheet passing region of the heater 22 when the narrow paper P1 is continuously transported based on the center transport reference or the side-by-side transport reference. it can.

  In the image forming apparatus M of the present embodiment, the printing is continued even if it is determined that the conveyance is based on the side-by-side conveyance, but the printing can also be stopped.

  Further, even when printing is stopped or when printing is continued, a warning message may be issued on a display panel (not shown) of the image forming apparatus M.

  By the way, in the image forming apparatus M of the present embodiment, in the width direction of the paper P, the paper width sensor 72 is arranged on the left side of the conveyance reference position CL, and the sub-thermistor 52 is arranged on the right side. In this configuration, the abnormal temperature rise can be detected by the right sub-thermistor 52 when the narrow paper P1 on the left side is conveyed on the basis of the one-sided conveyance reference. The reason for this configuration is that when the user who intends to transport the narrow paper P1 on the basis of the one-sided transport standard sets the narrow paper P1 on the plate 5a of the tray 5, the user approaches the left regulation guide 9L. This is because there is a tendency. This is considered to be because the horizontal writing text is generally written on the left side as a reference, and the user can easily adjust the text writing position when the text is conveyed on the basis of the justified conveyance standard. In other words, by adopting this configuration, it is possible to directly detect the transport of the one-sided transport reference with an abnormal temperature rise at the position of the sub-thermistor 52 for a larger number of users, and to increase safety. Can do. However, the position of the paper width sensor 72 is not limited to the left side, and the position of the sub thermistor 52 is not limited to the right side. The sub thermistor 52 is disposed on the left side, and the paper width sensor 72 is disposed on the right side. It doesn't matter.

  Further, the arrangement position of the paper width sensor 72 is not limited to between the tray 5 and the transfer nip portion T, and may be arranged, for example, between the transfer nip T portion and the fixing device 13.

  Further, the fixing device 13 is not limited to the film heating type shown in the present embodiment, and similar effects can be obtained even with a heat roller type.

  Another example of the image forming apparatus according to the present invention will be described.

  The image forming apparatus shown in the present embodiment has the same configuration as the image forming apparatus M of the embodiment except for a recording material conveyance control sequence described later. In this embodiment, the same reference numerals are given to members / portions common to the image forming apparatus of Embodiment 1, and the description thereof is omitted. The same applies to Example 3 to be described later.

  The image forming apparatus M of this embodiment has a plurality of threshold values for performing the determination of [ΔTn−ΔT0] when the narrow paper P1 is transported on the sub-thermistor 52 side on the side-by-side transport standard, and the narrow paper An appropriate threshold value is used according to the number of transported sheets of P1. That is, a process of changing the threshold value for performing the determination of [ΔTn−ΔT0] according to the detected number of narrow sheets P1 detected by the sub-thermistor 52 is performed.

  FIG. 10 is a flowchart illustrating an example of a recording material conveyance control sequence in the image forming apparatus according to the present exemplary embodiment.

  S11 to S18 are the same as S1 to S8 of the embodiment, respectively.

  In S19, when n = 3, that is, the difference [ΔT3−ΔT0] between ΔT3 and ΔT0 is calculated from the third sheet of the narrow paper P1, and when [ΔT3−ΔT0] is +5 deg or more, the non-sheet passing portion ascending is calculated. Judge that it is warm. In this case, as shown in FIG. 8, since the sheet is conveyed based on the central conveyance reference, the throughput is set to 12 ppm as it is. If [ΔT3−ΔT0] is less than +5 deg, it is determined that the narrow paper P1 is being conveyed on the basis of the one-sided conveyance reference as shown in FIG. 9, and the throughput is switched to 2 ppm (S15).

  Next, the difference TS4-TM4 = ΔT4 between the detection temperature TS4 of the sub-thermistor 52 and the detection temperature TM4 of the main thermistor 51 is detected again at the timing when the trailing edge of the fourth narrow sheet P1 passes through the nip portion N. ΔT4−ΔT0] is calculated (S20). When [ΔT4-ΔT0] is +7 deg or more, 12 ppm is maintained as it is, and when it is less than +7 deg, the throughput is switched to 2 ppm (S15).

  For the fifth and subsequent narrow sheets P1, that is, when n ≧ 5, if [ΔTn−ΔT0] is +10 deg or more, 12 ppm is maintained as it is (S21), and if it is less than +10 deg, the throughput is 2 ppm. (S15). This control is continued until the end of printing for n = n + 1 and the fifth and subsequent sheets.

  In the above example, the threshold values of [ΔTn−ΔT0] are gradually increased to +5 deg, +7 deg, and +10 deg when the third, fourth, fifth and subsequent sheets, ie, n = 3, n = 4, and n ≧ 5, respectively. It is getting bigger. The reason for controlling in this way will be described below.

  If the threshold value of [ΔTn−ΔT0] for judging the conveyance based on the one-sided conveyance standard is set to be large, the central conveyance standard is used for a sheet with a relatively small non-sheet passing portion temperature rise and a small basis weight. In spite of being conveyed correctly, the non-sheet passing portion temperature rise cannot be detected. For this reason, as described above, there is a high possibility of misjudgment as conveyance based on the one-sided conveyance standard. At this time, once an erroneous determination is made, the throughput is reduced to 2 ppm, so the temperature rise in the non-sheet passing portion is reduced at a stretch. Then, even if the narrow paper P1 is conveyed on the basis of the central conveyance reference, the temperature rise of the non-sheet passing portion does not increase thereafter, and accordingly, the erroneous determination cannot be corrected. For this reason, in the first embodiment, even if the paper has a small basis weight, the paper is continuously conveyed until the temperature of the non-sheet-passing portion is sufficiently increased, and then the misregistration is prevented by making a judgment of conveyance based on the one-sided conveyance standard. Yes. This is because the temperature rise in the non-sheet passing portion due to the conveyance of the narrow paper P1 usually increases as the number of the continuous conveyance of the narrow paper P1 increases, and the determination becomes easier. However, in order to prevent the heater 22 from being damaged or the like, it is necessary to make the judgment of conveyance based on the one-sided conveyance reference as early as possible.

  In the present embodiment, in order to make the determination of the conveyance based on the one-sided conveyance reference at an earlier stage, the first determination is performed on the third continuous conveyance number of the narrow sheets P1.

  At this time, since the temperature rise in the non-sheet passing portion is still small in the third continuous conveyance number of the narrow paper P1, if the threshold value is set to a large value, the temperature in the non-sheet passing portion is actually increased. However, the temperature rise of the non-sheet passing portion cannot be detected, and the above-described erroneous determination occurs. If +10 deg is set as a threshold value as in the first embodiment, the threshold value is too large to be determined by the third continuous conveyance number of the narrow paper P1, so that even if the conveyance is performed based on the central conveyance reference, it is not necessary. The temperature of the paper passing section cannot be detected and the throughput is reduced to 2 ppm. Therefore, the threshold value for the third continuous conveyance number of narrow paper P1 is set low. In this embodiment, +5 deg is set as the threshold value.

  On the contrary, if the threshold value is set to a low value, there is a high possibility that the non-sheet-passing portion temperature is erroneously determined even when the non-sheet-passing portion temperature is not increased. The mechanical configuration of the image forming apparatus M of the present embodiment is the same as that of the first embodiment. Therefore, in the third continuous conveyance number of the narrow paper P1, [ΔTn−ΔT0] when there is no temperature increase in the non-sheet passing portion is surely [ΔTn−ΔT0] when there is a temperature increase in the non-sheet passing portion. However, the possibility of misjudgment is considerable.

  However, even if an erroneous determination is made for the third continuous conveyance number of narrow sheets P1, damage to the heater 22 can be prevented if the determination is correct for the fourth and subsequent sheets.

  In this case, the misjudgment due to the small threshold is different from the case where the threshold is too large to detect a temperature rise in the non-sheet-passing portion. is not. Thus, the throughput remains maintained at 12 ppm. For this reason, when there is a non-sheet-passing portion temperature rise, the non-sheet-passing portion temperature rise is greater at the fourth continuous conveyance number of narrow sheets P1. In other words, the misjudgment can be corrected with the fourth continuous conveyance number of narrow paper P1, and the possibility of misjudgment becomes smaller than the third continuous conveyance number of narrow paper P1.

  At this time, the threshold value is changed in order to reduce misjudgment at the fourth continuous conveyance number of the narrow paper P1, and the fourth threshold value than the third continuous conveyance number of the narrow paper P1. Increase This is because, in the third and fourth sheets, the temperature rise in the non-sheet passing portion is naturally larger in the fourth sheet, so the threshold value is increased accordingly. If the threshold value of the fourth sheet is the same as that of the third sheet, even the fourth sheet repeats misjudgment made in the third sheet, which is meaningless. By increasing the threshold value of the fourth sheet, it is easier to correct the misjudgment of the third sheet. For this reason, in the present embodiment, the threshold value for the fourth continuous conveyance number of narrow paper P1 is set to +7 deg.

  Similarly, the fifth sheet of the continuous conveyance number of the narrow sheets P1 is set to be larger than the fourth sheet so that correction can be made even if erroneous detection occurs in the fourth sheet.

  As described in the first exemplary embodiment, by setting the threshold value to +10 deg from the fifth continuous conveyance number of the narrow sheets P1, it is possible to almost certainly determine the one-sided conveyance reference.

  In Example 1, since only one threshold is provided, the temperature rise of the non-sheet passing portion is detected after continuous conveyance of five or more sheets that can reliably determine the conveyance based on the one-sided conveyance standard.

  On the other hand, in this embodiment, the threshold value is changed in accordance with the number of continuously conveyed narrow sheets P1, so that the judgment of conveyance based on the one-sided conveyance reference is made from the third number of continuously conveyed narrow sheets P1. Can be corrected by the fifth sheet even if misjudgment is made.

  Therefore, according to the image forming apparatus M of the present embodiment, the following operational effects can be obtained in addition to the same operational effects as the first embodiment. That is, as compared with the first embodiment, it is possible to start the judgment of the conveyance based on the side-by-side conveyance with a smaller number of continuously conveyed sheets of narrow paper P1, and it is possible to reduce the possibility that the heater 22 is damaged or the like. .

  Another example of the image forming apparatus according to the present invention will be described.

  The image forming apparatus shown in the present embodiment has the same configuration as the image forming apparatus M of the embodiment except for a recording material conveyance control sequence described later.

  The image forming apparatus M according to the first embodiment and the second embodiment determines whether the narrow sheet P1 is transported based on the one-sided transport reference by using a certain threshold value regardless of the state of the image forming apparatus M at the start of printing. It was. In the image forming apparatus M of the present embodiment, the printing operation (image forming operation) history corresponding to the number of detected narrow sheets P1 detected by the sub-thermistor 52 and the previous printing operation of the history printing operations are completed. The process of changing the threshold value is performed based on the relationship with the elapsed time from the time when it was performed.

  FIG. 11 is a flowchart illustrating an example of a recording material conveyance control sequence in the image forming apparatus according to the present exemplary embodiment. FIG. 12 is an explanatory diagram showing a control table used for executing the throughput reduction control based on the second determination in the recording material conveyance control sequence.

  S31 to S38 are the same as S1 to S8 in the embodiment, respectively. In S39, it is determined whether the previous print job performed immediately before the current print job, that is, the previous print job was the narrow paper P1 or the wide paper P2. When the previous print job is the wide paper P2, the same control as that performed on the narrow paper P1 in the first embodiment is performed. That is, the difference TS5-TM5 = ΔT5 between the detection temperature TS5 of the sub-thermistor 52 and the detection temperature TM5 of the main thermistor 51 at the timing when the rear end of the fifth and subsequent sheets of the narrow sheet P1 passes through the nip portion N. To detect. Then, the difference [ΔT5-ΔT0] between ΔT5 and ΔT0 is calculated, and it is determined whether [ΔT5-ΔT0] is greater than or equal to +10 deg (S40). When [ΔT5−ΔT0] is +10 deg or more, the throughput is maintained at 12 ppm as it is. When [ΔT5−ΔT0] is less than +10 deg, it is determined that the narrow paper P1 is transported based on the one-sided transport standard, and the throughput is switched to 2 ppm (S35). This control is continued until the end of printing for n = n + 1 and the fifth and subsequent sheets.

  On the other hand, if the previous print job was narrow paper P1, it is determined as the next step how many seconds have passed since the end of the previous print job (S41). If 60 seconds or more have elapsed since the end of the previous print job, the process proceeds to S40 described above. If printing has been performed again in less than 60 seconds from the end of the previous print job, the process proceeds to the next step S42.

  In S42, different thresholds and determination timings are used for determining the conveyance based on the one-sided conveyance reference. In S42, the difference TS3-TM3 = ΔT3 between the detection temperature TS3 of the sub-thermistor 52 and the detection temperature TM3 of the main thermistor 51 immediately after the trailing edge of the third narrow-width sheet P1 of the continuously conveyed number of narrow sheets P1 passes. And the difference [ΔT3−ΔT0] between ΔT3 and ΔT0 is calculated. If [ΔT3−ΔT0] is 5 deg or more, it is determined that the sheet is conveyed based on the central conveyance reference, and the throughput of 12 ppm is maintained. If [ΔT3−ΔT0] is less than 5 deg, it is determined that the conveyance is based on the one-sided conveyance standard, and the throughput is switched to 2 ppm (S35). This control is continued until the end of printing for the third and subsequent sheets with n = n + 1.

  The reason why the threshold value and the determination timing are made different depending on the previous print history is described below.

  When the previous print job is narrow paper P1, the temperature of the non-sheet passing area is always increased. The temperature rise history of the non-sheet passing area remains to some extent when the time until the next print job is short, and affects the next print job. In experiments conducted by the inventor using the image forming apparatus M having the configuration of the present embodiment, when the interval from the end of the previous print job to the start of the next print job is less than 60 seconds, The effect was confirmed. Specifically, at the start of printing, the temperature of the non-sheet passing area is already higher than that of the sheet passing area. That is, the temperature detected by the sub-thermistor 52 is higher than the temperature detected by the main thermistor 51. In such a case, the difference TS0−TM0 = ΔT0 between the detection temperature TS0 of the sub-thermistor 52 and the detection temperature TM0 of the main thermistor 51 at the timing when the leading edge of the first narrow sheet P1 enters the nip portion N is already somewhat high. Value. On the other hand, even if several sheets of narrow paper P1 are conveyed based on the central conveyance reference from that state, the temperature of the sub thermistor 52 is already high from the beginning, and thus does not increase so much. That is, the difference TSn− between the detection temperature TSn of the sub-thermistor 52 and the detection temperature TMn of the main thermistor 51 immediately after the rear end of the nth narrow paper P1 passes when n sheets of narrow paper P1 are continuously conveyed. TMn = ΔTn does not increase with the value of ΔT0. That is, [ΔTn−ΔT0] becomes a small value because ΔT0 is high. This means that the temperature change from the leading edge of the first sheet to the trailing edge of the nth sheet of the narrow paper P1 is small, but the sub-thermistor is already at the leading edge of the first sheet due to the previous temperature rise of the non-sheet passing portion. It is natural that 52 is heated. In such a state, when the same determination condition is used after the wide paper P2 or when the heater 22 is cooled and there is no history of non-sheet passing portion temperature rise, that is, when ΔT0 is substantially zero, This makes it easy to make a mistake as described above.

  For example, if ΔT0 is already +7 deg, even if ΔT5 becomes +15 deg on the fifth sheet of narrow paper P1 by conveying the narrow paper P1 based on the central conveyance reference, [ΔT5−ΔT0] is 15 deg−7 deg. = 8 deg. According to the judgment condition of the first registration in the first embodiment, since [ΔT5−ΔT0] is less than 10 deg for the fifth sheet, the judgment is made as a single registration. Accordingly, this example is 2 ppm even though the case is conveyed based on the central conveyance standard. Throughput drops.

  As described above, when the previous print job is narrow paper P1 and the time elapsed from the end of the print job is short, the temperature change from ΔT0 to ΔTn is small, and an erroneous determination is made.

  The phenomenon in which the temperature difference between the sub-thermistor 52 and the main thermistor 51 from the start of printing due to the history of printing operations is different from the case where there is a temperature difference from the beginning due to the heat generation distribution of the heater 22 described in the first embodiment. . In other words, this phenomenon cannot be eliminated even if the amount of change in temperature difference between the sub-thermistor 52 and the main thermistor 51 is detected, which is clear from the above description.

  On the other hand, if there is a history of non-sheet passing portion temperature rise during the previous printing, the temperature of the sub-thermistor 52 is already higher than the temperature of the main thermistor 51 at the start of printing. For this reason, if the narrow paper P1 is transported on the basis of the one-sided transport reference in this state, the temperature of the sub-thermistor 52 is surely lowered. That is, since ΔT0 is already high in the conveyance based on the one-sided conveyance reference, ΔTn is almost certainly smaller than ΔT0.

  In the case of the first embodiment, it is assumed that ΔT0 is almost zero or slightly negative. Therefore, there is a possibility that [ΔTn−ΔT0] may become a positive value even if the conveyance is performed based on the one-sided conveyance reference. . Therefore, the threshold value of [ΔT5−ΔT0] is set to +10 deg.

  However, [ΔTn−ΔT0] hardly becomes positive under the condition of reprinting in a state in which the time has elapsed little after the conveyance of the narrow sheet P1 based on the one-sided conveyance reference. Therefore, even if the threshold value for performing the shift determination of [ΔTn−ΔT0] is reduced, it is possible to determine the transfer based on the shift alignment reference.

  Further, when the temperature of the sub-thermistor 52 has increased to some extent due to the history of the temperature rise of the non-sheet passing portion from the start of printing, the temperature of the sub-thermistor 52 immediately decreases due to the conveyance based on the one-sided conveyance. For this reason, even if the determination timing is made earlier, it is possible to accurately determine the conveyance based on the side-by-side conveyance.

  The present embodiment is based on this idea. That is, when the previous print job is the narrow paper P1 and the next print job is performed in less than 60 seconds, the determination condition is changed, and [ΔT3−ΔT0] is set for the third sheet of the narrow paper P1. Based on whether or not +5 deg.

  By the way, the example shown in the present embodiment is essentially the threshold value and determination when the detection temperature of the sub-thermistor 52 is somewhat higher than the detection temperature of the main thermistor 51 at the start of printing, that is, when ΔT0 is already a certain value. It is synonymous with switching timing. That is, for example, as shown in FIG. 12, it seems that the determination condition may be switched according to the value of ΔT0 immediately before the first print. However, the temperature difference value ΔT0 originally includes an element of the heat generation distribution that the heater 22 has. For this reason, in this embodiment, the control is performed by detecting the change amount of the temperature difference of [ΔTn−ΔT0], but it is not preferable to simply add the determination based on the temperature difference of ΔT0. Absent.

  In this embodiment, the threshold value switching condition for determining the conveyance based on the one-sided conveyance reference is set to less than 60 seconds from the end of the previous print job, but this value is not limited to this, and image formation is not limited to this. Needless to say, it differs depending on the configuration of the apparatus M. For example, in an image forming apparatus having a configuration in which a cooling device for reducing the temperature rise of a non-sheet passing portion such as a fan is disposed after the conveyance of the narrow paper P1, this time may naturally be shortened.

  Therefore, according to the image forming apparatus M of the present embodiment, the following operational effects can be obtained in addition to the same operational effects as the first embodiment. That is, it is possible to prevent misjudgment of the conveyance of the narrow sheet P1 based on the one-sided conveyance reference, and it is possible to further reduce the possibility that the heater 22 is damaged as compared with the first and second embodiments.

Structural model diagram of an example of the image forming apparatus of Embodiment 1 Model diagram of an example of a tray regulation guide Expanded cross-sectional model view of the main part of the fixing device Heater configuration model diagram FIG. 3 is a schematic plan view illustrating the relationship among the tray, the photosensitive drum, and the heater of the image forming apparatus according to the first embodiment. 6 is a flowchart illustrating an example of a recording material conveyance control sequence in the image forming apparatus according to the first exemplary embodiment. Explanatory drawing when narrow paper is transported to the side where the paper width sensor is present based on the one-sided transport standard Explanatory drawing when narrow paper is transported based on the central transport standard. Explanatory drawing when narrow paper is transported to the side where the sub-thermistor is present on the basis of the one-sided transport standard 7 is a flowchart illustrating an example of a recording material conveyance control sequence in the image forming apparatus according to the second exemplary embodiment. 7 is a flowchart illustrating an example of a recording material conveyance control sequence in the image forming apparatus according to the third exemplary embodiment. Explanatory drawing showing the control table of the recording material conveyance control sequence in the image forming apparatus of Embodiment 3.

Explanation of symbols

P: paper (recording material), P1: narrow paper, P2: wide paper, 1: photosensitive drum, 5: multi-tray, 13: fixing device, 22: heater, 51: main thermistor, 52: sub-thermistor, 60: MPU, 70: transport motor, 72: paper width sensor

Claims (4)

A recording material width regulating member that can move symmetrically with respect to a conveyance reference set in the center of the recording material conveyance path in a direction orthogonal to the recording material conveyance direction, and an image forming unit that forms a toner image on the recording material Recording material width detection means for detecting the width of the recording material, heating means, and recording materials of all sizes that can be used in the apparatus for conveying in accordance with the conveyance reference. First temperature detecting means for detecting the temperature of the heating means in the passing area and temperature of the heating means in the area opposite to the side where the recording material width detecting means is provided with respect to the conveyance reference A second temperature detecting means for controlling the power supplied to the heating means so that the temperature detected by the first temperature detecting means maintains a target temperature, and recording a toner image on the recording material A fixing portion that heat-fixes to the material. In the image forming apparatus,
Although the recording material is being conveyed, the recording material width detection unit does not detect the passage of the recording material and the difference between the detection temperature of the first temperature detection unit and the detection temperature of the second temperature detection unit is not detected. When the temporal change amount is smaller than the predetermined threshold value, the recording material width detecting means does not detect the passage of the recording material and the unit time change is greater than when the temporal change amount is larger than the predetermined threshold value. An image forming apparatus characterized in that the number of recording materials to be conveyed is greatly reduced. The image forming apparatus according to claim 1, wherein the predetermined threshold value is larger as a time for calculating the temporal change amount is longer . When the width orthogonal to the recording material conveyance direction of the recording material at the time of the previous printing is smaller than the predetermined width and the elapsed time from the end of the previous printing is shorter than the reference time, the time change amount is calculated. time, the image forming apparatus according to claim 1 or claim 2 wherein the width of the recording material and wherein the shorter than said predetermined width is greater than or the elapsed time is longer than the reference time. The heating means has a cylindrical fixing film and a heater in contact with the inner surface of the fixing film, and the first temperature detecting means and the second temperature detecting means detect the temperature of the heater. The image forming apparatus according to any one of claims 1 to 3 .

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