Method of detecting a rolled paper and image forming apparatus

Abstract

The application discloses a method for detecting a rolled paper, and executes the following steps: starting printing, obtaining a paper length L1 of a job command; determining a theoretical trigger time: determining a trigger time T1 of a paper passing through a front paper sensor according to the paper length L1 and a speed of passing through the front paper sensor; judging whether an actual trigger time t1 of the paper passing through the front paper sensor satisfies a condition: t1 >= T1 + T1 余量 , T1 余量 representing a remaining time or an excess time of the paper passing through the front paper sensor; selecting a theoretical time T3 of a rear paper sensor according to the length L1 of the recognized paper; and judging whether an actual time tn is greater than the theoretical time, and issuing an alarm information and controlling a roller device to stop working if the actual time tn is greater than the theoretical time. The application can quickly recognize a rolled paper of the roller device before the rolled paper occurs, so that a user can easily take out the rolled paper, improve user experience, reduce safety risks, and improve the accuracy of the rolled paper recognition.

Description

Technical Field

[0001] This invention relates to the field of electronic imaging technology, and more specifically to a method for detecting the pressure of rolled paper and an image forming apparatus. Background Technology

[0002] In image forming apparatuses such as printers and copiers, it is necessary to detect paper jams or paper roll issues caused by the fuser rollers. For example, in the case of paper roll detection in the fuser unit, paper sensors are used for identification. In existing technology, the detection time required to detect the paper from the leading edge to the trailing edge is used. If this detection time exceeds the paper detection time corresponding to the specified paper size, a paper jam error occurs unconditionally. Another method is to wait until the timer value reaches a paper detection time corresponding to a small distance shorter than the maximum paper size. If the condition is met, the detection time is changed to the detection time of the maximum size. However, using this detection method, if the specified paper size is longer than the actual paper size, it cannot be detected when the fuser rollers cause paper rolls. Furthermore, if a shorter sheet of paper gets stuck at the paper feed tray, and the next sheet is detected when the fuser rollers actually cause paper rolls, the detection time is the maximum size detection time. At this point, there is a large amount of paper roll on the fuser rollers, making it impossible for the user to remove the paper roll, and posing a safety risk. Summary of the Invention

[0003] The method for detecting roll-pressed paper of the present invention can effectively solve the problem that the method of detecting roll-pressed paper of the fixing device in the prior art is not conducive to improving the accuracy of identification.

[0004] According to one aspect of the present invention, a method for detecting the roll pressure of paper is provided.

[0005] Including a roller pressing device, a front paper sensor, and a rear paper sensor, the following steps are performed:

[0006] Start printing, and set the print media length L1 for issuing the job command;

[0007] Calculate the theoretical trigger duration: Based on the length L1 of the printing medium and the speed at which the printing medium passes through the front paper sensor, determine the trigger duration T1 of the printing medium passing through the front paper sensor;

[0008] Determine whether the actual time t1 for the printing medium to pass through the front paper sensor meets the condition: t1≥T1+T1 余量 T1 余量 This indicates the remaining or excessive time that the theoretical printing medium will have passed through the front paper sensor;

[0009] Based on the paper type information of the printing medium, select the theoretical duration corresponding to the rear paper sensor;

[0010] If the actual duration tn is greater than the theoretical duration, an alarm message is issued and the roller pressing device is controlled to stop working.

[0011] In some implementations, when selecting the theoretical duration T3 corresponding to the rear paper sensor, if the condition t1≥T1+T1 is not satisfied... 余量 Then perform the following steps:

[0012] Based on the printing medium length L1 and the speed at which the printing medium passes through the rear paper sensor, the triggering time T2 for the printing medium passing through the rear paper sensor is determined; T2 余量 This represents the remaining time for the theoretical printing medium to pass through the rear paper sensor. The actual time t2 of the printing medium passing through the rear paper sensor is used to determine whether it satisfies the condition: t2 ≥ T2 + T2 余量 If the above conditions are met, an alarm message is issued and the roller pressing device is controlled to stop working.

[0013] In some implementations, if the condition t2≥T2+T2 is satisfied... 余量 If the alarm is triggered, the roller pressing device will control the stop of the drive device's rotation and heating / pressurization operations.

[0014] In some embodiments, the following steps are further included after the printing medium enters the front paper sensor:

[0015] The preset time T for the printing medium to travel from the front paper sensor to the rear paper sensor. m The actual time T for the printing medium to travel from the front paper sensor to the rear paper sensor. n Determine whether the condition is met: T m ≥T n If the above conditions are not met, an alarm message will be issued and the roller pressing device will be stopped.

[0016] In some implementations, when selecting the theoretical duration T3 corresponding to the rear paper sensor, if the condition t1≥T1+T1 is satisfied... 余量 Then perform the following steps:

[0017] If the paper type for the printing media does not match, the following steps are performed without reporting an error or canceling the process:

[0018] Identify the marker, set the maximum supported printing media length L3, and determine the trigger duration T3 for the printing media passing through the rear paper sensor based on the printing media length L3 and the speed at which it passes through the rear paper sensor. 余量 This represents the remaining time of the theoretical printing medium passing through the rear paper sensor. The determination is made to whether the actual time t3 of the printing medium passing through the rear paper sensor satisfies the condition: t3 ≥ T3 + T3余量 If the above conditions are met, an alarm message is issued and the roller pressing device is controlled to stop working; otherwise, after printing all the printing media in the machine, the printing is stopped.

[0019] In some implementations, if the condition: t3≥T3+T3 is not met... 余量 It issues an alarm message and controls the roller pressing device to stop working, and reminds the user to put in the correct paper pattern.

[0020] In some embodiments, when the printing medium passes through the front paper sensor, if the condition t1≥T1+T1 is not met... 余量 If the condition is met, a prompt will be issued; otherwise, an alarm message will be issued that is the opposite of the prompt.

[0021] On the other hand, an image forming apparatus is provided that can roll and press a printing medium to perform the above-described method for detecting the roll pressing of paper.

[0022] The roller pressing device is used to press the printing medium moving in the first direction;

[0023] The front paper sensor is located on the upstream side of the roller pressing device in the first direction and is used to measure the actual triggering time t1 of the printing medium to identify the paper type of the printing medium.

[0024] The rear paper sensor is located on the downstream side of the roller pressing device in the first direction and is used to measure the actual time tn for the printing medium to pass through.

[0025] Also includes:

[0026] The memory is used to record the motion information and preset information of the printing medium;

[0027] A controller is used to control the roller pressing device;

[0028] The controller identifies the paper type of the printing medium based on the front paper sensor, selects the theoretical time for the printing medium to pass through the rear paper sensor, and then compares the received actual time tn with the theoretical time. Given the paper type of the printing medium, it determines whether the actual time tn is within the theoretical time to determine whether there is a roll pressing of the paper.

[0029] In some embodiments, the roller pressing device is one of a fixing device, a conveying roller assembly, or a developing device.

[0030] The method for detecting roll pressure of paper rolls according to the present invention has the following advantages compared with the prior art:

[0031] This application uses a front paper sensor and a rear paper sensor to detect the paper roll status of the roller pressing device. When the printing medium passes through the front paper sensor, the execution of the printing medium can be identified. After the front paper sensor identifies the paper type, it determines whether the actual time for the printing medium to pass through the rear paper sensor is within the theoretical time, thereby determining whether there is paper roll in the printing medium passing through the roller pressing device. This application can quickly identify the paper roll situation of the roller pressing device before paper roll occurs, allowing users to easily remove the paper roll, improving user experience, reducing safety risks, and improving the accuracy of paper roll identification. Attached Figure Description

[0032] Figure 1 This is a simplified reference diagram of the structure of the image forming apparatus in this invention;

[0033] Figure 2 This is a simplified reference diagram of the fixing device portion of the image forming apparatus of the present invention;

[0034] Figure 3 This is a reference flowchart of the method for detecting roll-pressed paper in this invention;

[0035] Figure 4 The diagram shows the correspondence between the paper jam error indicator and the panel display of the image forming apparatus in this invention.

[0036] In the diagram: 1-Main body of the equipment, 2-Paper feed roller, 3-Transfer roller, 31-Discharge roller, 4-Developing roller, 5-Photosensitive drum, 6-Fixing roller, 7-Pressure roller, 8-Heating element, 9-Temperature detection element, 10-Temperature protection element, 11-Front paper sensor, 12-Rear paper sensor. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] This invention relates to a method for detecting paper roll curling during rolling and an image forming apparatus. The method for detecting paper roll curling can be applied to image forming apparatuses such as laser printers and electrophotographic copiers. This method can accurately detect situations where paper rolls up during the rolling process of a printing medium, such as paper or other media capable of carrying images.

[0040] The present invention will now be described in further detail with reference to the accompanying drawings.

[0041] Figure 1 An image forming apparatus according to an embodiment of the present invention is schematically shown. For example... Figure 1 As shown, the image forming apparatus includes a main body 1, a paper feeding module, an imaging module, a transfer module, and a fixing device.

[0042] The main body 1 of the device has an external frame for supporting and protecting other mechanisms. The paper feeding module is located at the bottom of the main body 1 and has a printing tray for storing paper. The paper feeding module has a paper feed roller 2, which picks up the paper from the printing tray and moves it to the paper feeding channel. The main body 1 also has a transfer roller 3 for transferring paper along the paper feeding channel. The imaging module is used to form an image and then attach the image to the paper. The imaging module has a developing roller 4 and a photosensitive drum 5. The developing roller 4 contacts the photosensitive drum 5 and rotates relative to it, which can generate... The developing latent image and the transfer module have a transfer belt. The imaging module transfers the image onto the transfer belt as a first transfer. The transfer belt with the image transfers the image onto the paper as a second transfer. When the paper with the image is conveyed to the fixing device through the paper feeding channel, the fixing device fixes the image onto the paper by heating and pressurizing. The main body 1 of the equipment is also equipped with a discharge roller 31, which is located on the downstream side of the fixing device. After the paper is fixed, the printed paper is discharged to the outside of the main body 1 or onto the paper tray through the discharge roller 31.

[0043] Among them, such as Figure 2 As shown, the fixing device includes a fixing roller 6 and a pressure roller 7. The fixing roller 6 is equipped with a heating element 8 to heat the fixing roller 6 to the fixing temperature. The fixing roller 6 abuts against the pressure roller 7, so that the paper can be heated and pressurized when passing between the fixing roller 6 and the pressure roller 7. The fixing device also has a temperature detection element 9 and a temperature protection element 10. The temperature detection element 9, such as a temperature control resistor or a thermometer, can detect the temperature of the fixing roller 6. The temperature protection element 10 is used to protect the fixing roller 6 from high temperature damage. It works in conjunction with the temperature detection element 9. When the temperature of the fixing roller 6 is detected to be higher than the preset temperature, the heating element 8 is disconnected by the temperature protection element 10.

[0044] This invention provides a method for detecting the pressure of rolled paper, implemented using the image forming apparatus described above, wherein, as... Figure 1As shown, the image forming apparatus also includes a pressing device, a controller (not shown), a memory (not shown), a front paper sensor 11, and a rear paper sensor 12. In this embodiment, a fixing device is used as a pressing device. In other embodiments, the pressing device may be a set of three conveying rollers, a developing device, or other transfer mechanism capable of pressing and conveying paper. The controller is specifically a microcontroller or control chip, used to process information acquired by other components. The memory is used to store and record the movement information and preset information of the paper, as well as preset information of other components. The controller is electrically connected to the fixing device, the memory, the front paper sensor 11 and the rear paper sensor 12. The front paper sensor 11 and the rear paper sensor 12 are used to detect whether paper has passed by and to calculate the duration of the paper's passage. The paper moves along the first direction and passes through the fixing device. The front paper sensor 11 is located upstream of the fixing device in the first direction, and the rear paper sensor 12 is located downstream of the fixing device in the first direction. That is, the fixing device is located between the front paper sensor 11 and the rear paper sensor 12, and the paper can pass through the front paper sensor 11 and the rear paper sensor 12 in sequence.

[0045] The front paper sensor 11 is used to detect the actual trigger time t1 of the paper passing through, so as to identify the paper type. The rear paper sensor 12 is used to detect the actual time tn of the paper passing through. The present invention is based on the following theory: the controller selects the theoretical time for the paper to pass through the rear paper sensor 12 according to the paper type identified by the front paper sensor 11, and then compares the detected actual time tn with the theoretical time. Under the known paper type, it determines whether the actual time tn is within the theoretical time, so as to determine whether there is a paper roll during roller pressing.

[0046] In this embodiment, the image forming apparatus sets the length of the paper sent by the PC to L1. Based on the preset conveying speed V1 of the front paper sensor 11, the theoretically calculated time for the paper to pass through the front paper sensor 11 is T1 (i.e., T1 = L1 / V1). Based on the preset conveying speed V2 of the rear paper sensor 12, the time for the paper to pass through the rear paper sensor 12 is T2 (i.e., T2 = L2 / V2). The maximum paper length supported by the image forming apparatus is set to L3, and the theoretically calculated time for the paper to pass through the rear paper sensor 12 is T3. Here, T1, T2, and T3 are the calculated theoretical durations. The memory can pre-store the actual trigger time t1 for the paper to pass through the front paper sensor 11 and the preset times L1, L2, T1, T2, and T3.

[0047] like Figure 3 As shown, the method for detecting roll pressure of paper according to the present invention includes the following steps:

[0048] S1. Start printing, obtain the paper length L1 of the job command and the maximum paper length L3 supported by the machine;

[0049] For example, if the user selects A4 or A3 paper size for printing, the controller will send the paper length to be detected as the corresponding A4 or A3 paper length L1, and the maximum paper length L3 corresponding to A4 or A3 paper size. The maximum paper length L3 is the safe paper length that the corresponding paper size can enter the transmission. If it exceeds the limit, it may easily cause paper jams or cause other mechanisms in the machine to jam and be scrapped.

[0050] S2. Determine the theoretical trigger duration. The trigger duration of the front paper sensor 11 is T1, the trigger duration of the rear paper sensor 12 is T2, and the maximum trigger duration of the rear paper sensor 12 is T3.

[0051] Similarly, the durations T1 and T2 are calculated using L1. However, since the paper passes through the front paper sensor 11 and the rear paper sensor 12 at different speeds, the values ​​of T1 and T2 may differ. The magnitudes of these values ​​are not limited. T3 is the theoretical duration calculated based on the maximum length corresponding to the paper type and the speed at which the paper passes through the rear paper sensor 12. The selection of T2 and T3 requires a comparison between T1 and the actual duration of the paper passing through the front paper sensor 11. In other words, the selection of T2 and T3 is related to the actual duration of the paper passing through the front paper sensor 11.

[0052] S3. Determine whether the actual triggering time t1 of the paper passing through the front paper sensor 11 meets the condition: t1≥T1+T1 余量 T1 余量 This indicates the remaining time for the theoretical paper to pass through the front paper sensor 11;

[0053] The paper needs to pass through the front paper sensor 11 first. The paper type is identified by the time it takes for the paper to pass through the front paper sensor 11. The actual trigger time t1 represents the actual time it takes for the paper to pass through the front paper sensor 11. T1+T1 余量 T1 represents the theoretical time it takes for the paper to pass through the front paper sensor 11 plus the remaining theoretical time for the paper. 余量 It can also be expressed as the time elapsed after the paper actually passes through the front paper sensor 11, satisfying t1≥T1+T1 余量 If the actual paper type does not match the preset paper type, it means that the actual paper type does not match. Otherwise, it means that the actual paper type matches, and the machine can issue a "paper type matches" prompt.

[0054] S4. Based on the detected paper length L1 or paper type information, select the theoretical duration of the corresponding rear paper sensor 12.

[0055] This step is based on step S3, and includes step S40 before the paper passes the rear paper sensor 12: The preset time Tm for the paper to travel from the front paper sensor 11 to the rear paper sensor 12, and the actual time Tn for the paper to travel from the front paper sensor 11 to the rear paper sensor 12 are determined. It is then determined whether the condition Tm ≥ Tn is met, i.e., whether the paper has traveled between the front and rear paper sensors within the specified time. If the above condition is not met, it indicates that abnormal paper feeding or paper jamming has occurred between the front and rear paper sensors, and an "abnormal paper feeding" alarm is issued, and the fixing device is stopped (same as step S5); otherwise, the following steps are performed:

[0056] After step S3, the paper is divided into two cases, each corresponding to a different theoretical time, as follows:

[0057] If step S3 does not satisfy the condition t1≥T1+T1 余量 Then, proceed to step S41: determine whether the actual time t2 of the paper passing the rear paper sensor 12 satisfies the condition: t2≥T2+T2 余量 T2 余量 This indicates the remaining or excessive time for the theoretical paper to pass through the rear paper sensor 12. If the above condition is met, step S5 is executed; otherwise, normal paper feeding is determined. Since the paper is determined to be conforming to the paper type when it passes the front paper sensor 11, the condition t2≥T2+T2 is still satisfied after passing through the rear paper sensor 12. 余量 This means that when the paper passes the rear sensor, the paper that matches the paper type still exceeds the preset time, and this happens after passing the fixing device. Therefore, it can be indicated that there is abnormal paper feeding after the paper passes the fixing device.

[0058] If S3 satisfies the condition t1≥T1+T1 余量 If the paper passing through the front paper sensor 11 does not match the preset paper type, then step S42 is executed:

[0059] S42. If the paper type of the marked paper does not match, do not report an error or cancel step S43;

[0060] S43. Identify the marker and determine whether the actual time t3 of the paper passing through the rear paper sensor 12 meets the condition: t3≥T3+T3 余量 T3 余量This indicates the remaining or excessive time for the theoretical paper to pass through the rear paper sensor 12. If the above condition is met, step S5 is executed; otherwise, printing is stopped after all the paper in the machine has been printed. This can be understood as follows: if the paper size is mismatched, the paper is marked, and the controller processes the excessive time for that paper to pass through the rear paper sensor 12 (i.e., selects a preset excessive time). Therefore, if a longer piece of paper passes through the rear paper sensor 12, its actual time t3 satisfies the condition t3≥T3+T3 余量 If the paper size is mismatched and the preset time limit of the rear paper sensor 12 is exceeded, then abnormal paper feeding occurs after the paper passes through the fixing unit. Otherwise, if the paper passes through the rear paper sensor 12 within the specified time without abnormal paper feeding, the controller sends a signal that all paper in the machine has been printed, and then executes a command to stop printing. At this time, the machine can issue a paper size mismatch prompt to remind the user to insert the correct paper size.

[0061] S5. If the actual duration tn is greater than the theoretical duration, issue a "paper feeding abnormality" alarm and control the roller pressing device to stop working.

[0062] The actual duration tn is greater than the theoretical duration, meaning that the paper in the above steps satisfies the condition t2≥T2+T2. 余量 Or t3≥T3+T3 余量 If Tm ≥ Tn (the paper does not reach the rear paper sensor 12 within the specified time), it indicates that there is a paper feeding abnormality in the fixing device, such as paper roll. In this case, the controller needs to send a stop command to the fixing device, such as stopping the rotation of the fixing motor (drive device) so that the fixing roller 6 no longer rotates, and stopping the fixing heating and pressurization. The paper may be stacked at the paper discharge port. The controller can quickly detect paper jams according to the paper type and prevent paper roll from occurring in advance.

[0063] In one implementation, the detection of paper jams is handled by the printing engine. Once an error is detected, the data control is notified via an error code mechanism to provide a corresponding panel prompt.

[0064] As shown in the table below, when a paper jam is detected, it will first determine whether the paper jam type requires forced flushing. If forced flushing is required, it will first perform forced flushing and report error code 0x3A, and the panel will report the corresponding paper jam. If forced flushing is not required or forced flushing fails, it will report error code 0x3B, and the panel will prompt the user to remove the paper jam and perform subsequent operations.

[0065]

[0066]

[0067] In addition to error codes, error parameters are set for different paper jam scenarios, such as 0x02. Therefore, in the event of a paper jam, an error identifier can be generated based on whether forced paper can be ejected and the paper jam scenario. The error identifier includes an error code and error parameters.

[0068] Specifically, the printing engine determines whether a paper jam exists based on the electrical signals output by each sensor. For example, each sensor can be a photoelectric sensor. When paper passes by a photoelectric sensor, the sensor is in a light-blocking state (outputting a high level); when no paper is at the position of the photoelectric sensor, the sensor is in an unblocking state (outputting a low level). Therefore, the duration for which the photoelectric sensor is in a light-blocking state (outputting a high level) at a specific position can be used to determine the duration for which paper has passed that specific position, thus determining whether a paper jam has occurred at that specific position.

[0069] Therefore, if a paper jam occurs, the system determines whether the paper jam can be forcibly cleared based on its location or type. If it can be forcibly cleared, a first error identifier (error code + error parameter) is generated. The data firmware then uses the first error identifier to find the corresponding first prompt message and displays it on the control panel. If the paper jam cannot be forcibly cleared, a second error identifier is generated. The data firmware then uses the second error identifier to find the corresponding second prompt message and displays it on the control panel. Figure 4 The diagram shows the correspondence between error identifiers and panel displays.

[0070] It is understood that this application can quickly identify the occurrence of paper roll in the fixing device before the paper roll is generated, so that users can easily remove the paper roll, improve the user experience, reduce safety risks, and improve the accuracy of paper roll detection.

[0071] The above description is merely a preferred embodiment of the present invention. To simplify the description, not all possible combinations of the various technical features in the above embodiments have been described, and this is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for detecting roll-fed paper, applied in an image forming apparatus for detecting printing media, characterized in that, The image forming apparatus includes a roller pressing device, a front paper sensor, and a rear paper sensor. The roller pressing device is used to press the printing medium moving along a first direction. The roller pressing device is a fixing device. The front paper sensor is located upstream of the roller pressing device in the first direction and is used to measure the actual triggering time t1 of the printing medium passing through the front paper sensor to identify the paper type of the printing medium. The rear paper sensor is located downstream of the roller pressing device in the first direction and is used to measure the actual time of the printing medium passing through the rear paper sensor. The method performs the following steps: Start printing and obtain the print media length L1 from the job command issued; Determine the theoretical trigger duration: Based on the length L1 of the printing medium and the speed at which the printing medium passes through the front paper sensor, determine the trigger duration T1 of the printing medium passing through the front paper sensor; Determine whether the actual triggering time t1 of the printing medium through the front paper sensor satisfies the condition: t1≥T1+T1 余量 T1 余量 This indicates the remaining or excessive time that the theoretical printing medium will have passed through the front paper sensor; Based on the paper type information of the printing medium, select the theoretical duration corresponding to the rear paper sensor; If the actual duration is greater than the theoretical duration, an alarm message is issued and the roller pressing device is controlled to stop working. When selecting the theoretical duration corresponding to the rear paper sensor, if the condition t1≥T1+T1 is not satisfied... 余量 Then, the following steps are performed: Based on the length L1 of the printing medium and the speed at which it passes through the rear paper sensor, the triggering time T2 of the printing medium passing through the rear paper sensor is determined. Determine whether the actual time t2 of the printing medium passing through the rear paper sensor satisfies the condition: t2≥T2+T2 余量 T2 余量 This indicates the remaining or exceeded time of the theoretical printing medium passing through the rear paper sensor. If the above conditions are met, an alarm message is issued and the roller pressing device is controlled to stop working. When selecting the theoretical duration corresponding to the rear paper sensor, if the condition t1≥T1+T1 is satisfied... 余量 Then perform the following steps: The print media paper type mismatch is marked without an error message, and the following steps are performed: Identify the marker, set the maximum supported printing media length L3, and based on the maximum length L3 and the speed at which the printing media passes through the rear paper sensor, confirm the trigger time T3 for the printing media to pass through the rear paper sensor. Determine whether the actual time t3 for the printing media to pass through the rear paper sensor satisfies the condition: t3 ≥ T3 + T3 余量 T3 余量 This indicates the remaining or exceeded time of the theoretical printing medium passing through the rear paper sensor. If the above conditions are met, an alarm message is issued and the roller pressing device is controlled to stop working. Otherwise, after printing all the printing media in the machine, stop printing. After the printing medium enters the front paper sensor, the following steps are also included: The preset time T for the printing medium to travel from the front paper sensor to the rear paper sensor. m The actual time T for the printing medium to travel from the front paper sensor to the rear paper sensor. n Determine whether the condition is met: T m ≥T n If the above conditions are not met, an alarm message will be issued and the roller pressing device will be stopped.

2. An image forming apparatus, characterized in that, The method for detecting rolled paper as described in claim 1; the image forming apparatus includes a rolling device, a front paper sensor, and a rear paper sensor; The roller pressing device is used to press the printing medium moving in the first direction, and the roller pressing device is a fixing device. The front paper sensor is located on the upstream side of the roller pressing device in the first direction and is used to measure the actual triggering time t1 of the printing medium passing through the front paper sensor in order to identify the paper type of the printing medium. The rear paper sensor is located on the downstream side of the roller pressing device in the first direction and is used to measure the actual time it takes for the printing medium to pass through the rear paper sensor. The image forming apparatus further includes: The memory is used to record the motion information and preset information of the printing medium; A controller is used to control the roller pressing device; The controller selects the theoretical time for the printing medium to pass through the rear paper sensor based on the paper type identified by the front paper sensor, and then compares the actual time for the printing medium to pass through the rear paper sensor with the theoretical time. Given the paper type of the printing medium, the controller determines whether the actual time for the printing medium to pass through the rear paper sensor is within the theoretical time to determine whether there is a roll-fed paper.

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