JP2020024313A - Image formation apparatus and method of controlling the same - Google Patents

Abstract

To precisely determined whether or not a recording medium is carried one-sidedly.SOLUTION: An image formation apparatus 1 comprises: conveying means 220 which can convey a recording medium of a first type not perforated in a conveying direction CD of a recording medium and a recording medium of a second type perforated at an end part in the conveying direction, and conveys the recording medium; image forming means 210 which forms a toner image on the recording medium carried by the conveying means; fixing means 230 which heats the recording medium having the toner image formed to fix the toner image on the recording medium; temperature detecting means 51a, 51b which detect temperatures of the fixing means at two different position in a width direction MS orthogonal to the conveying direction of the recording medium; and determining means 200 which determines whether or not the recording medium is conveyed one-sidedly in a width direction based upon a temperature difference between the two positions detected by the temperature detecting means and a reference value set according to the recording medium is the first type or second type.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus having a fixing unit that thermally fixes a toner image on a recording medium.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus has a fixing device for fixing a toner image to a recording medium by applying heat and pressure to the recording medium on which the toner image is formed. The fixing device has a fixing nip section for nipping and conveying the recording medium on which the toner image is formed, and applies heat and pressure to the recording medium passing through the fixing nip section to fix the toner image on the recording medium. The recording medium is fed from a feeding cassette or a manual feed tray to the image forming unit, where a toner image is formed by the image forming unit, and is conveyed to the fixing device. If the recording medium is not set at an appropriate position on the feeding cassette or the manual feed tray, the recording medium is shifted from the reference position to either the rear side or the near side in the direction (width direction) orthogonal to the transport direction. It is transported in a state (hereinafter, referred to as a one-sided state). If the recording medium is conveyed in an offset state, the temperature of the non-sheet passing area of the fixing device through which the recording medium does not pass excessively increases (hereinafter, referred to as excessive temperature increase). Excessive temperature rise on one side of the fixing device in the width direction causes image deterioration. Therefore, a temperature rise suppression operation such as aging is performed to suppress excessive temperature rise. Note that aging is a method of making the temperature distribution on the surface of the fixing roller uniform by rotating the fixing roller while the image forming is not performed and the fixing heater is also stopped.

  Japanese Patent Application Laid-Open No. H11-163873 discloses detecting temperatures of both ends of a fixing device and determining whether a recording medium is conveyed in a one-sided state based on a difference between the detected temperatures. If the difference between the detected temperatures is equal to or more than the first value, a message is displayed to prompt the user to stop the image forming operation and correct the bias of the recording medium. When the difference between the detected temperatures is equal to or more than a second value smaller than the first value, aging is performed for a predetermined time to equalize temperature unevenness of the fixing device in the width direction.

JP 2011-27885 A

  However, as a recording medium, paper such as pre-punched paper having a plurality of binding holes (hereinafter referred to as punch holes) near the end, paper having a chipped end, and paper having a part of the end cut off is used. May be used. When the pre-punched paper is passed through the fixing device in a state in which a plurality of punched holes are arranged in the transport direction, the temperature of the area where the punched holes of the fixing device pass is harder to be deprived, and the temperature is higher than that of the other paper passing areas. Therefore, an excessive temperature rise occurs in a region where the punch holes pass. According to the technique disclosed in Japanese Patent Application Laid-Open No. H11-163, since a difference in the detected temperatures at both ends of the fixing device occurs due to an excessive temperature rise in a region where a punch hole passes, aging is performed to suppress the excessive temperature increase. However, since an image is hardly formed in the area around the punched hole of the pre-punched paper, if aging is performed to suppress excessive temperature rise in the area where the punched hole passes, the productivity of the image forming apparatus is reduced.

  Accordingly, the present invention provides an image forming apparatus that can accurately determine whether a recording medium is being conveyed to one side based on a reference value set according to the type of the recording medium.

An image forming apparatus capable of transporting a first type of recording medium that is not perforated in a transport direction of a recording medium and a second type of recording medium that has a perforated end in the transport direction according to an embodiment of the present invention. Is
Conveying means for conveying the recording medium,
Image forming means for forming a toner image on the recording medium conveyed by the conveying means,
Fixing means for applying heat to the recording medium on which the toner image is formed to fix the toner image on the recording medium;
Temperature detection means for detecting the temperature of the fixing means at two different positions in the width direction orthogonal to the transport direction of the recording medium,
The recording medium shifts to one side in the width direction based on a temperature difference between the two positions detected by the temperature detecting unit and a reference value set according to whether the recording medium is the first type or the second type. Determining means for determining whether or not the sheet has been conveyed;
Is provided.

  According to the present invention, it is possible to accurately determine whether or not a recording medium is being conveyed to one side based on a reference value set according to the type of the recording medium.

FIG. 2 is a cross-sectional view of the image forming apparatus. FIG. 2 is a block diagram of a control system of the image forming apparatus. FIG. 3 is a diagram illustrating an internal structure of the fixing device. 9 is a flowchart illustrating a print job waiting process executed by the CPU. 5 is a flowchart illustrating a printing process executed by the CPU. 9 is a flowchart showing a process of setting a deviation state determination reference value executed by a CPU. The figure which shows the screen which notifies on the operation display part of "the offset state". FIG. 3 is a diagram illustrating a sheet, a bias state, and a temperature difference.

<Configuration of Image Forming Apparatus>
The configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. The image forming apparatus 1 forms an image on a recording medium by an electrophotographic method. The image forming apparatus 1 is a copying machine that forms a monochrome image, but the present invention is not limited to this. The image forming apparatus 1 may be a color copying machine, a color printer, a facsimile, or a multifunction peripheral. The image forming apparatus 1 may form an image on a recording medium by an electrostatic recording method. FIG. 1 is a sectional view of the image forming apparatus 1. The image forming apparatus 1 includes an operation display unit 190, an image reading unit 191, an image forming unit 210, a conveying unit 220, and a fixing device 230. The image forming apparatus 1 further includes a discharge roller 142 and a discharge tray 160. The operation display unit 190 is an interface that allows the user to set print information, instruct printing start, and notify the user of information. The operation display unit 190 functions as a type setting unit that allows a user to set the type of a recording medium (hereinafter, referred to as paper) P. Examples of the type of the paper P include plain paper (non-pre-punched paper), pre-punched paper, paper with a missing end, and paper with a part of the end missing. The image reading section 191 reads an image of a document and generates image data. The image forming unit 210 as an image forming unit forms a toner image on the paper P. The transport unit 220 as a transport unit transports the paper P from the feeding cassette 100 disposed below the image forming apparatus 1 to the image forming unit 210. The fixing device 230 as a fixing unit heats and pressurizes the sheet P to fix the toner image on the sheet P, and forms an image on the sheet P.

  The image forming unit 210 has a rotatable photosensitive drum (photoconductor) 120. Around the photosensitive drum 120, a charging roller (charging device) 125, a laser scanner unit (exposure device) 123, a developing device 121, a transfer roller (transfer member) 122, and a collected toner box (cleaning device) 124 are arranged. . The transport unit 220 includes the pickup roller 102 and the registration roller 110 that transport the sheets P stored in the feed cassette 100 to the transport path 103 one by one. The fixing device 230 as a fixing unit has a fixing roller (heating rotator) 41 as a fixing member and a pressing roller 42 as a pressing member. The fixing member is not limited to the cylindrical fixing roller 41, and may be a film-shaped rotating body.

<Control system>
Next, a control system 10 that controls the image forming apparatus 1 will be described. FIG. 2 is a block diagram of the control system 10 of the image forming apparatus 1. The control system 10 has a central processing unit (hereinafter, referred to as a CPU) 200 as control means (controller) for controlling the image forming apparatus 1. The control system 10 includes a read-only memory (hereinafter, referred to as ROM) 201 as a storage unit for storing a control program and a random access memory (hereinafter, referred to as RAM) 202 as a storage unit for storing data. The control system 10 further includes an external interface (hereinafter, referred to as an external I / F) 111 such as a USB cable for communicating with an external device 300 such as a personal computer. The CPU 200 is electrically connected to the external I / F 111, the operation display unit 190, the image reading unit 191, the ROM 201, the RAM 202, the image forming unit 210, the transport unit 220, and the fixing device 230. The CPU 200 is further electrically connected to the first thermistor 51a, the second thermistor 51b, and the third thermistor 51c provided in the fixing device 230. The CPU 200 acquires operation information of the user from the operation display unit 190. CPU 200 displays information such as print information and a warning on operation display section 190. CPU 200 reads an image of a document by image reading unit 191.

<Image forming operation>
Next, an image forming operation (hereinafter, referred to as a printing operation) of the image forming apparatus 1 will be described. When the CPU 200 acquires print information from the external device 300 via the external I / F 111, the CPU 200 starts a printing operation. When the user instructs the start of copying using the image reading unit 191 via the operation display unit 190, the CPU 200 acquires print information from the operation display unit 190 and the image reading unit 191 and starts a printing operation. The CPU 200 causes the image forming apparatus 1 to execute a printing operation using print information according to a control program stored in the ROM 201. In the printing operation, the CPU 200 writes and reads data necessary for the printing operation in the RAM 202.

  When the printing operation is started, the CPU 200 feeds the sheets P one by one from the feeding cassette 100 to the transport path 103 by the pickup roller 102. The sheet P is transported to the registration roller 110 through the transport path 103. On the other hand, the charging roller 125 uniformly charges the surface of the photosensitive drum 120. The CPU 200 emits laser light (light beam) from the laser scanner unit 123 to the uniformly charged surface of the photosensitive drum 120 in accordance with image information to form an electrostatic latent image on the surface of the photosensitive drum 120. The developing device 121 develops the electrostatic latent image formed on the surface of the photosensitive drum 120 with toner (developer) to form a toner image (developer image). The CPU 200 conveys the sheet P to the transfer roller 122 by the registration roller 110 such that the tip of the toner image formed on the surface of the photosensitive drum 120 coincides with the tip of the sheet P. The transfer roller 122 transfers the toner image on the photosensitive drum 120 to the paper P. The toner remaining on the surface of the photosensitive drum 120 without being transferred is collected by the collection toner box 124. The paper P on which the toner image is formed is transported from the transfer roller 122 to the fixing device 230. The CPU 200 controls the fixing device 230 to apply heat and pressure to the sheet P passing through the fixing device 230, fix the toner image on the sheet P, and form an image on the sheet P. The paper P on which the image is formed is discharged to the discharge tray 160 by the discharge roller 142 with the surface on which the image is formed facing downward. The configuration and the image forming operation of the image forming apparatus 1 described above are merely examples, and the present invention is not limited to these.

<Fixing device>
Next, the fixing device 230 will be described with reference to FIGS. FIG. 3 is a diagram showing the internal structure of the fixing device 230. As shown in FIG. 1, the fixing device 230 includes a fixing roller 41 and a pressure roller 42. The fixing device 230 has a heating element (heater) 60 longer than the maximum length of the main scanning direction (hereinafter, referred to as the width direction) MS of the sheet P permitted to be used in the image forming apparatus 1. The fixing device 230 has at least two temperature detecting units that detect the temperature of the fixing roller 41 at different positions in the width direction MS orthogonal to the transport direction CD in which the sheet P is transported. In order to detect the temperature of the fixing roller 41, a first temperature detecting section (hereinafter, referred to as a first thermistor) 51a, a second temperature detecting section (hereinafter, referred to as a second thermistor) 51b, and a third temperature detecting section as temperature detecting means. (Hereinafter, referred to as a third thermistor) 51c. The first thermistor 51a and the second thermistor 51b are provided at both ends of the fixing device 230 in the width direction MS. The third thermistor 51c is provided at the center of the fixing device 230 in the width direction MS. The CPU 200 sets the temperature of the fixing roller 41 based on the detected temperatures (detection results) of the first thermistor 51a, the second thermistor 51b, and the third thermistor 51c so that the temperature of the fixing roller 41 becomes a temperature suitable for fixing the toner to the paper P. The output of the heating element 60 is controlled. The temperature detecting means is not limited to a thermistor, but may be a temperature detector such as a thermocouple or a non-contact thermometer using infrared rays.

  The first thermistor 51a is provided at one end (hereinafter, referred to as a first position) 230a on the front side of the fixing device 230 in the width direction MS. The CPU 200 detects the temperature of one end on the front side of the fixing roller 41 by the first thermistor 51a. The second thermistor 51b is provided at the other end (hereinafter, referred to as a second position) 230b on the back side opposite to the first position 230a of the fixing device 230 in the width direction MS. The second position 230b is different from the first position 230a in the width direction MS. The CPU 200 detects the temperature at the other end on the far side of the fixing roller 41 by the second thermistor 51b. The third thermistor 51c is provided at a central third position 230c of the fixing device 230 between the first position 230a and the second position 230b. The CPU 200 detects the temperature near the center of the fixing roller 41 by the third thermistor 51c. The CPU 200 determines the transport position of the sheet P in the width direction MS based on the temperature detected by the first thermistor 51a and the temperature detected by the second thermistor 51b.

  In the present embodiment, the first thermistor 51a and the second thermistor 51b are provided at both ends of the fixing device 230 in the width direction MS, but the present invention is not limited to this. The first thermistor 51a and the second thermistor 51b may be arranged at positions corresponding to both ends of the sheet P to be conveyed. In an image forming apparatus capable of transporting a plurality of types of sheets having different widths in the width direction MS, three or more thermistors may be arranged at a plurality of positions corresponding to ends of sheets having different widths. Further, a plurality of thermistors are arranged near each end of the fixing roller 41 in the width direction MS, and the temperature is predicted based on the detection results of the plurality of thermistors near the end in the width direction MS of the paper P being conveyed. May be. Further, two thermistors that can move to positions corresponding to both ends of the conveyed sheet P in the width direction MS may be provided.

<Offset state detection>
Next, referring to FIGS. 1 and 3, a state in which the center of the conveyed sheet P is shifted from the reference position to one of the front side and the back side in the width direction MS perpendicular to the conveyance direction CD (hereinafter, referred to as one side) A shift state detection for detecting whether the shift state is a shift state) will be described. The reference position is, for example, the third position 230c at the center of the fixing device 230 in the width direction MS in the present embodiment.

  When replenishing the paper P to the feed cassette 100, the user may set the paper P in the feed cassette 100 in a state where the paper P is moved to the back side or the near side. When the printing operation is performed in a state where the sheet P is set to be closer to one side of the feeding cassette 100, the balance of the size of the non-sheet passing area generated at both ends of the fixing device 230 is lost. Since the toner transferred to the portion of the sheet P passing near the portion of the fixing roller 41 where the large non-sheet passing area of the fixing roller 41 has been excessively heated does not melt at an appropriate temperature, the toner on the sheet P is fixed. There is a possibility that an image defect that adheres to the roller 41 or becomes a blurred image may occur.

  Therefore, the CPU 200 executes the detection of the deviation state of the sheet P using the detection temperatures of the first thermistor 51a and the second thermistor 51b in order to prevent an image defect. When the sheet P passes through the fixing roller 41, the sheet P takes heat of the fixing roller 41. When the sheet P is set at the reference position of the feeding cassette 100, the center of the sheet P in the width direction passes through the center of the fixing roller 41. Therefore, the difference between the detected temperature of the first thermistor 51a and the detected temperature of the second thermistor 51b is small or almost nonexistent. When the sheet P is set in a state in which the sheet P is shifted toward the back side of the feeding cassette 100 in the width direction, the non-sheet passing area on the back side of the fixing roller 41 becomes smaller than the non-sheet passing area on the near side. As a result, the amount of the paper P that takes away heat from the back side of the fixing roller 41 becomes larger than the amount that takes away the heat from the front side, so that the detected temperature of the first thermistor 51a located on the near side is the second thermistor located on the back side. It becomes higher than the detection temperature of 51b. Further, when the sheet P is set in a state of being shifted toward the front side of the feeding cassette 100, the non-sheet passing area on the front side of the fixing roller 41 is smaller than the non-sheet passing area on the back side. As a result, the amount by which the paper P removes heat from the near side of the fixing roller 41 is greater than the amount by which the sheet P removes heat from the back side, so that the temperature detected by the second thermistor 51b located on the back side is increased by the first thermistor located on the near side. It becomes higher than the detection temperature of 51a. As described above, when the sheet P is set in the feeding cassette 100 in a state where it is moved to one side, a temperature difference occurs between the detected temperatures of the first thermistor 51a and the second thermistor 51b. Therefore, in the shift state detection according to the present embodiment, when the difference between the detected temperature of the first thermistor 51a and the detected temperature of the second thermistor 51b is equal to or more than the reference value, it is determined that the sheet P is in the shift state. . When it is determined that the sheet P is in the offset state, the CPU 200 equalizes the temperature distribution in the width direction MS of the fixing roller 41 by providing an interval (hereinafter, referred to as a sheet interval) between the conveyed sheets P, and Prevent defects. In the present embodiment, the temperature difference between the first position 230a and the second position 230b of the fixing device 230 is reduced by making the length of the sheet 300 milliseconds (ms) longer than the sheet interval in normal continuous printing.

  However, if the paper P is pre-punched paper and the row of punched holes is parallel to the paper transport direction, the punched hole portion of the pre-punched paper is fixed even if the pre-punched paper is set at the reference position of the feeding cassette 100. The heat is not taken from the roller 41. Therefore, a difference occurs in the detected temperature between the first thermistor 51a and the second thermistor 51b. If an excessive temperature rise occurs in the portion of the fixing roller 41 corresponding to the position of the punched hole of the pre-punched paper, an image is not usually formed near the punched hole of the pre-punched paper. There is no. That is, when the paper P is pre-punched paper, it is not always necessary to take measures to prevent the occurrence of image defects by lengthening the paper interval based on the temperature difference between the first thermistor 51a and the second thermistor 51b. Rather, if the paper P is pre-punched paper and the paper interval is lengthened based on the temperature difference between the first thermistor 51a and the second thermistor 51b, productivity may be unnecessarily reduced. Therefore, in the present embodiment, when the pre-punched paper is conveyed, erroneous determination of the deviation state detection is prevented, thereby preventing a reduction in productivity.

<Print job waiting process>
Next, a main flow of the CPU 200 that controls the operation of the image forming apparatus 1 will be described with reference to FIG. FIG. 4 is a flowchart showing a print job waiting process executed by the CPU 200. The CPU 200 executes a print job waiting process according to a program stored in the ROM 201.

  When the power of the image forming apparatus 1 is turned on, the CPU 200 starts a print job waiting process. The CPU 200 determines whether a request to turn off the power has been received (S101). If a request to turn off the power has not been received (NO in S101), CPU 200 determines whether a print job has been received (S102). If a print job has not been received (NO in S102), CPU 200 returns the process to S101. If a print job has been received (YES in S102), CPU 200 executes a printing process (S103). When the printing process ends, the image forming apparatus 1 enters the standby state, and the CPU 200 returns the process to S101. When a request to turn off the power is received (YES in S101), the CPU 200 turns off the power after executing predetermined necessary processing.

<Print processing>
Next, the printing process executed in step S103 in FIG. 4 will be described with reference to FIG. FIG. 5 is a flowchart showing a printing process executed by the CPU 200. The CPU 200 executes a printing process according to a program stored in the ROM 201.

  When the printing process is started, the CPU 200 starts a printing operation (S201). The CPU 200 detects the temperature of the first position 230a by the first thermistor 51a while the sheet P passes through the fixing device 230 (S202). At the same time, the CPU 200 detects the temperature at the second position 230b using the second thermistor 51b (S203). The CPU 200 executes the deviation state determination reference value setting (S204). In setting the offset state determination reference value, the CPU 200 sets a reference value for determining whether or not the sheet P is in the offset state in the offset state determination. The setting of the offset state determination reference value will be described later with reference to FIG. The CPU 200 determines that the absolute value of the difference between the temperature detected at the first position 230a detected by the first thermistor 51a and the temperature detected at the second position 230b detected by the second thermistor 51b (hereinafter referred to as the difference) is equal to or greater than a reference value. It is determined whether or not there is (S205). If the difference between the detected temperatures is smaller than the reference value (NO in S205), the CPU 200 determines that the sheet P is not in the offset state as a result of the offset state determination, and notifies the operation display unit 190 of the "offset state". The screen is erased (S206). When the screen for notifying the “skew state” is not displayed on the operation display unit 190, the CPU 200 does not change the screen of the operation display unit 190.

  When the difference between the detected temperatures (temperature difference) is equal to or greater than the reference value (YES in S205), CPU 200 as the judging means judges that sheet P is in the unbalanced state as a result of the unbalanced state determination, and displays operation display unit 190. Display a screen for notifying the "displacement state" (S207). With reference to FIG. 7, an example of a screen for notifying the user that the paper P is in a non-uniform state, which is displayed on the operation display unit 190 as the display unit by the CPU 200 as the notification unit, will be described. FIG. 7 is a diagram showing a screen 192 displayed on the operation display unit 190 and notifying of the “displacement state”. The left side of the screen 192 indicates that the sheet P is set to be offset. The user is prompted to set the paper P again as shown on the right side of the screen 192 and correct the biased state of the paper P. Also, at the bottom of the screen 192, the message "Productivity has decreased because the paper is shifted to the back or near side. It is recommended that you temporarily stop or set the paper at the reference position after printing is completed." Is displayed.

  The CPU 200 adds 300 ms to the interval (time interval) between the conveyed sheets P so that the temperature difference between the first position 230a and the second position 230b of the fixing device 230 is reduced (S208). When the printing on one sheet P is completed, the CPU 200 determines whether there is print information on the next sheet P (S209). If there is print information for the next sheet P (YES in S209), CPU 200 returns the process to step S201. As a result, the printing process is performed on the paper P while performing the deviation state determination of whether or not the paper P is in the deviation state for each sheet. If there is no print information for the next sheet P (NO in S209), CPU 200 ends the printing process.

<Setting of reference value for judging deviation state>
Hereinafter, the setting of the offset state determination reference value performed in step S204 of FIG. 5 will be described with reference to FIG. FIG. 6 is a flowchart showing a process of setting a deviation state determination reference value performed by CPU 200. The CPU 200 executes a process of setting a bias state determination reference value according to a program stored in the ROM 201.

  When the setting of the bias state determination reference value is started, the CPU 200 acquires the paper type information of the paper P stored in the feeding cassette 100 from the RAM 202 (S301). The paper type information of the feed cassette 100 is preset by the user from the operation display unit 190 and stored in the RAM 202. In the present embodiment, the first type of paper that has not been perforated in the paper transport direction is supplied to the feed cassette 100 such that the paper is perforated at the end in advance, and the perforated direction is the transport direction of the paper. The stored paper is a second type. The CPU 200 determines whether the paper P stored in the feeding cassette 100 is non-pre-punched paper or pre-punched paper based on the paper type information (S302). If the sheet P is pre-punched paper (YES in S302), the sheet is determined based on whether or not the punched hole row of the pre-punched paper is stored in the feeding cassette 100 so as to be parallel to the transport direction CD based on the paper type information. Is determined to be the first type or the second type (S303). If the row of punch holes is not parallel to the transport direction CD (if it is orthogonal), the temperature difference between the back side and the front side of the fixing roller 41 is small. Therefore, when the punch holes are orthogonal to the transport direction CD (NO in S303), the CPU 200 sets the reference value used in the determination of the offset state to 15 and saves it in the RAM 202 (S305), Finish setting the value. On the other hand, if the punched holes are parallel to the transport direction CD (YES in S303), the CPU 200 sets the reference value to 25, saves it in the RAM 202 (S304), and ends the setting of the bias state determination reference value. If the paper P is not pre-punched paper (NO in S302), the CPU 200 sets the reference value to 15 and saves it in the RAM 202 (S305), and ends the setting of the bias state determination reference value.

  Here, a reference value (threshold) used in the determination of a bias state will be described with reference to FIG. FIG. 8 is a diagram illustrating a sheet, a bias state, and a temperature difference. FIG. 8 shows the maximum value, the minimum value, and the average value of the temperature difference when the plain non-pre-punched paper and the plain paper pre-punched paper are in the non-centered state and in the non-centered state, respectively. When the non-pre-punched paper is set at the reference position of the feeding cassette 100 so as not to be shifted, the maximum value of the temperature difference between the first thermistor 51a and the second thermistor 51b is 8 ° C., and the minimum value is 3 ° C. The value is 5 ° C. When the non-pre-punched paper is set in the feeding cassette 100 in a biased state, the maximum value of the temperature difference between the first thermistor 51a and the second thermistor 51b is 19 ° C, the minimum value is 5 ° C, and the average value is 15.6 ° C. It is. When the pre-punched paper is set at the reference position of the feeding cassette 100 so as not to be shifted, the maximum value of the temperature difference between the first thermistor 51a and the second thermistor 51b is 20 ° C, the minimum value is 5 ° C, and the average value is Is 17.1 ° C. When the pre-punched paper is set in the feeding cassette 100 in a biased state, the maximum value of the temperature difference between the first thermistor 51a and the second thermistor 51b is 37 ° C, the minimum value is 5 ° C, and the average value is 31.1 ° C. is there.

  As shown in FIG. 8, when the non-pre-punched paper is set in the feeding cassette 100 in a biased state, the temperature difference is set at the reference position of the feeding cassette 100 so that the pre-punched paper is not biased. It can be seen that the temperature difference is almost the same as the case. Therefore, in this embodiment, the reference value is set according to the type of paper. Specifically, when the type of paper is plain paper (non-pre-punched paper), the CPU 200 as the reference value setting means sets the reference value used in the deviation state determination to 15 ° C. (first reference value). . When the type of paper is pre-punched paper, the CPU 200 sets the reference value used for determining the deviation state to 25 ° C. (second reference value). The second reference value for the type in which the end or part of the end of the sheet is missing is larger than the first reference value for the type in which the end or part of the end of the sheet is not missing. In addition, even if the type of paper is pre-punched paper, when a plurality of punched holes are arranged in a direction perpendicular to the transport direction CD, the reference value used in the determination of the bias state as described above is 15 ° C. (first reference). Value). Note that the reference values shown here are merely examples, and the reference values may be appropriately set according to the configuration of the image forming apparatus 1, the number of punched holes in the pre-punched paper, the paper partially covered with the edge, and the like. . Further, the configuration may be such that a user can set a set value for each sheet.

  According to the present embodiment, it is possible to accurately detect whether or not a sheet is conveyed in a shifted state by setting a reference value for detecting the shifted state according to the paper type. As a result, it is possible to prevent a decrease in productivity due to an erroneous detection of a deviation state when the pre-punched paper is passed. According to the present embodiment, there is no need to change parts or add expensive parts, so that it is possible to accurately detect the state of deviation of the pre-punched paper without increasing the cost. According to this embodiment, it is possible to accurately determine whether or not the recording medium is being conveyed to one side based on the reference value set according to the type of the recording medium.

1. Image forming apparatus 51a First thermistor (temperature detecting means)
51b... Second thermistor (temperature detecting means)
200 CPU (judgment means)
210: Image forming unit (image forming means)
220 ... Conveying unit (conveying means)
230: fixing device (fixing means)
CD: transport direction MS: width direction P: paper (recording medium)

Claims (8)

An image forming apparatus capable of transporting a first type of recording medium that is not perforated in a transport direction of the recording medium and a second type of recording medium that has a perforated end in the transport direction.
Conveying means for conveying the recording medium,
Image forming means for forming a toner image on the recording medium conveyed by the conveying means,
Fixing means for applying heat to the recording medium on which the toner image is formed to fix the toner image on the recording medium;
Temperature detection means for detecting the temperature of the fixing means at two different positions in the width direction orthogonal to the transport direction of the recording medium,
The recording medium shifts to one side in the width direction based on a temperature difference between the two positions detected by the temperature detecting unit and a reference value set according to whether the recording medium is the first type or the second type. Determining means for determining whether or not the sheet has been conveyed;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the determining unit determines that the recording medium is being conveyed by the one side in the width direction when the temperature difference is equal to or greater than the reference value.   The image forming apparatus according to claim 1, further comprising a type setting unit configured to set a type of the recording medium to the first type or the second type. A reference for setting the reference value to a first reference value when the recording medium is the first type, and for setting the reference value to a second reference value when the recording medium is the second type Equipped with value setting means,
The image forming apparatus according to claim 1, wherein the second reference value is larger than the first reference value.   The image forming apparatus according to claim 4, wherein the second type of recording medium includes a pre-punched paper in which a plurality of the perforations are arranged in the transport direction.   The image forming apparatus according to claim 4, wherein the first type of recording medium includes a pre-punched paper in which a plurality of the perforations are arranged in the width direction.   4. The apparatus according to claim 1, further comprising a notification unit configured to notify that the recording medium is in a state of being shifted when it is determined that the recording medium is being conveyed to the one side in the width direction. 7. The image forming apparatus according to claim 6.   8. The apparatus according to claim 1, wherein when it is determined that the recording medium is being conveyed toward the one side in the width direction, an interval between the recording media conveyed by the conveying unit is increased. The image forming apparatus according to claim 1.

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