JP2008225069A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to reliably detect the occurrence of paper winding jam in rollers without having to add a new device to an image forming device. <P>SOLUTION: In the normal state, the paper winding jam in rollers is detected by decreasing the rotation speed of a paper discharge roller to a predetermined speed and monitoring the state of the paper passage between a fixing roller and a paper discharge outlet from the time when the paper passes through the fixing roller until it passes through the paper discharge roller. A decreased speed V2 of the paper discharge roller is calculated by the arithmetic expression of ((a)÷(L+(a)-2S))×V1 based on the distance (a) between the back-end position of the paper and a paper discharge sensor at the time when the decrease in the speed of the paper discharge roller is started, the distance S between the fixing roller and the paper discharge sensor, the paper length L, and the rotation speed V1 of the fixing roller and the paper discharge roller. The decrease in the rotation speed of the paper discharge roller is started (L-S)÷V1 after the paper discharge sensor has detected the forward end of the paper. Whether or not to decrease the speed of the paper discharge roller is determined depending on the operational conditions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser printer using an electrophotographic process, and more particularly to an image forming apparatus that detects a winding jam with respect to a fixing device.

  A schematic diagram of a laser printer using a conventional electrophotographic process is shown in FIG. The main body of the laser printer is composed of a paper supply / discharge section, a transport section, an image forming section, and a paper detection section. The paper supply / discharge unit includes a paper supply tray, a manual paper supply port 21, and a paper output port. The transport unit includes a paper feed roller 20, a registration roller 22, and a paper discharge roller 24. The image forming unit includes a transfer belt 10, a secondary transfer roller 11, a toner unit including cyan, magenta, yellow, and black colors, and a fixing unit. Further, the fixing device includes a fixing roller 23 and a heating device. The paper detection unit includes a registration sensor 25 and a paper discharge sensor 26. Both sensors are filler-type sensors.

  The paper feed tray is housed in the lower layer portion of the main body, and feeds paper from here through the paper feed roller 20. Similarly, paper can be fed from the manual paper feed port 21 and the conveyed paper is discharged from the paper discharge port. The paper feed roller 20 is a roller for transporting the paper in the paper feed tray, and the registration roller 22 holds the transported paper for a predetermined time and then transports it downstream. The paper discharge roller 24 is a roller for discharging paper from a paper discharge port. The paper is conveyed along a paper conveyance path from the paper supply roller 20 to the paper discharge roller 24. The transfer belt 10 conveys the toner image formed by the toner portion, and transfers the toner image to the sheet at the position of the secondary transfer roller 11. The fixing device fixes the toner image transferred to the paper with heat and pressure. The registration sensor 25 is provided on the upstream side in the vicinity of the registration roller 22 and detects the paper conveyed to the registration roller 22. The paper discharge sensor 26 is provided on the upstream side in the vicinity of the paper discharge roller 24, and detects paper to be discharged.

  A paper transport operation when an image is formed on the paper stacked on the paper feed tray will be specifically described. The sheets stacked on the sheet feeding tray are conveyed one by one from the stacked sheets to the conveying path by rotating the sheet feeding roller counterclockwise. Even after the registration sensor detects the arrival of the leading edge of the paper, the paper feed roller continues to rotate for a predetermined time, and the paper is kept waiting with the leading edge abutted against the registration roller. At that time, the leading edge of the sheet is brought into contact with the registration roller to make the sheet bend and correct the sheet conveyance start position and the sheet direction. The driving of the registration roller is started when the toner image conveyed by the transfer belt on the secondary transfer roller and the image forming position on the paper overlap. After the toner image is transferred to the paper, the toner image is fixed by a fixing device and discharged to a paper discharge port by a paper discharge roller that is driven to rotate counterclockwise. The paper feeding roller, registration roller, and fixing roller are given driving force by a driving motor (not shown) (for example, a DC motor). The paper discharge roller is given a driving force by a paper discharge motor (for example, a stepping motor) (not shown) whose rotation speed can be changed.

  In a fixing device in an image forming apparatus, a fixing roller 23 for fixing toner transferred onto a sheet and a pressure roller rotate in contact with each other. Since the toner melted by the fixing device on the paper has high adhesiveness, the paper may wrap around the fixing roller 23 or the pressure roller and may not be discharged normally. This is called fixing wrapping jam. If the fixing wrap jam is left unattended, the paper may be heated, generating a strange odor and producing smoke or failure. A paper discharge sensor 26 is disposed in the vicinity of the upstream side of the paper discharge roller 24 to detect the occurrence of such a fixing wrap jam. When the paper discharge sensor 26 does not turn on after fixing, or when the paper discharge sensor 26 does not turn off a predetermined time after the paper discharge sensor 26 is turned on, it is determined that a fixing winding jam has occurred.

  In general, the criterion for determining that the sheet has been normally conveyed is set not as a single fixed time but as a time having a time width in view of some margins such as roller slip and sensor error. The above-mentioned predetermined time has a sufficient time width on the basis of the time from when the paper discharge sensor 26 detects the leading edge of the paper until the trailing edge of the paper is detected when the paper is normally discharged. Point to time. As shown in FIG. 6B, the time from when the paper discharge sensor 26 is turned on until the time T2 elapses after the time T1 elapses is defined as a predetermined time. Therefore, if the paper discharge sensor 26 is turned off at a time other than the predetermined time, it can be determined that a jam has occurred.

  FIG. 7 is a general flowchart for detecting a fixing wrap jam that occurs after the leading edge of the paper reaches the paper discharge sensor 26 and is turned on. The paper length is L and the paper transport speed is V1. When the paper on which the toner image has been transferred passes through the fixing roller 23 and the paper discharge sensor 26 detects the leading edge of the paper, timer counting is started (the timer value is T). When the paper is normally conveyed, the paper discharge sensor 26 is turned off when the timer value T becomes (L ÷ V1). Conversely, a jam occurred when the paper discharge sensor 26 was turned off when the timer value T was less than (L ÷ V1), and when the paper discharge sensor 26 did not turn off even when the timer value T exceeded (L ÷ V1). It can be judged. Below are some examples of prior art related to this.

  The “image forming apparatus” disclosed in Japanese Patent Application Laid-Open No. 2004-228620 determines that a jam occurs when the paper discharge sensor is turned off before the sensor before the fixing roller is turned off, thereby determining that the paper is jammed with fixing wrapping. In this way, the recording material is prevented from being damaged by winding. The presence or absence of a recording material is detected on the upstream side and the downstream side of the fixing roller. While the recording material is detected on the upstream side, if the recording material is changed from the presence to the absence on the downstream side, the driving is stopped. When there is a recording material on the upstream side, it can be detected that the recording material is not discharged from the fixing roller. Therefore, when there is no recording material on the downstream side even though there is a recording material on the upstream side, it is erroneously detected as paper discharge. There is nothing. Accordingly, the winding of the recording material can be detected, and damage to the image forming apparatus can be prevented.

  The “image forming apparatus” disclosed in Patent Document 2 detects the amount of reflected light on the surface of the fixing roller to detect fixing wrapping jams, thereby reliably detecting wrapping of the transfer paper even if a reflective sensor is used. It can be done. The winding detection sensor is moved to a position where the fixing roller contacts the transfer paper and a position where the fixing roller does not contact the transfer paper. At each position, the amount of reflected light from the fixing roller is read and stored. The two stored data are compared, and it is checked whether the difference is equal to or greater than a predetermined value. When the value is equal to or greater than the predetermined value, a warning is displayed on the LCD on the operation unit and a predetermined abnormality process is performed to indicate that the transfer paper is wound around the fixing roller.

  The “image forming apparatus” disclosed in Patent Document 3 detects a fixing wrap jam by a paper discharge sensor and stops driving the main body, thereby detecting a wrap jam and performing a recovery process. This is to prevent progress. The photosensitive drum is scanned by the laser scanner unit according to the image signal. The latent image on the photosensitive drum is developed to form a toner image. After the toner image is transferred to the recording paper, it is thermally fixed and discharged. At this time, a state in which the recording paper passes a predetermined position is detected by a paper discharge sensor. By detecting the detection state of the leading and trailing edges of the recording paper for a predetermined time, the occurrence of winding of the recording paper is detected. When a winding jam occurs, the drive of the apparatus is stopped and the user is informed accordingly.

The “image forming apparatus” disclosed in Patent Document 4 detects a winding jam and a paper jam in a fixing device easily and reliably with an inexpensive configuration, and prevents a paper jam from recurring. When the surface temperature of the fixing member reaches a set temperature, two temperatures are detected and a reference temperature value is set in advance. During operation, a temperature value is calculated based on the detected temperatures at two locations when the surface temperature of the fixing member reaches a set temperature. A comparison is made between the temperature value and the reference temperature value to determine whether or not a paper winding jam has occurred on the fixing member. If a paper wrap jam has occurred, the power supply to the heat source is stopped.
Japanese Patent No. 2854441 (Japanese Patent Laid-Open No. 04-110880) Japanese Unexamined Patent Publication No. 07-319333 JP 2000-344395 A Japanese Patent Laid-Open No. 2002-156868

  However, the conventional fixing wrap jam detection method has the following problems. If a paper jam occurs when the paper ejection sensor detects the center of the paper after the paper ejection sensor is turned on, it may not be detected. The time from when the paper is caught in the fixing roller, when the paper is pulled in the opposite direction, and the leading edge of the paper passes through the paper discharge sensor is the predetermined time when the paper is normally transported (T2 after the paper discharge sensor is turned on, T2 If it matches the time until the elapsed time), it is indistinguishable from the case of normal transport.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional problems, and to reliably detect the occurrence of fixing winding jam without adding a new device to the image forming apparatus.

  In order to solve the above problems, according to the present invention, an image forming apparatus includes a fixing roller that heats and fixes a toner image transferred onto a sheet, and a discharge that discharges the sheet located downstream of the fixing roller to the outside of the apparatus. Located between the paper port, the fixing roller, and the paper discharge port, and positioned between the fixing roller and the paper discharge port to detect the state of paper passing, and transports the paper to the paper discharge port. A paper discharge roller that controls the drive of the paper discharge roller, and a jam determination unit that monitors a detection state of the paper by the paper detection unit for a predetermined time to determine a paper jam around the paper. The control means includes means for decelerating the rotation speed of the paper discharge roller to a predetermined speed from the time when the rear end of the paper passes through the fixing roller to the time when the rear end of the paper passes through the paper discharge roller in a normal state. did.

  In addition, the conveyance control means sends a distance a between the trailing edge position of the paper and the paper detection means when the discharge roller starts decelerating, a distance S between the fixing roller and the paper detection means, a paper length L, a fixing roller and a discharge roller. Based on the rotational speed V1 of the paper roller, a speed calculating means for calculating the deceleration speed V2 of the paper discharge roller by an arithmetic expression (a ÷ (L + a−2S)) × V1, and the rotational speed after deceleration of the paper discharge roller is V2. Means. The speed calculation means includes means for calculating a deceleration speed V2 of the paper discharge roller by an arithmetic expression (S ÷ (LS)) × V1, and the conveyance control means has the rear end of the paper exiting the fixing roller in a normal state. Means is provided for decelerating the rotational speed of the paper discharge roller to V2 at the time.

  The conveyance control means includes means for decelerating the rotational speed of the paper discharge roller after (LS) ÷ V1 after the paper detection means detects the leading edge of the paper. The second paper detection unit is disposed at a distance of S2 upstream of the fixing roller, and the conveyance control unit rotates the discharge roller after S2 / V1 after the second paper detection unit detects the trailing edge of the paper. Means for reducing the speed are provided. Deceleration determining means for determining whether or not to decelerate the discharge roller according to the operating condition is provided, and the conveyance control means decelerates the discharge roller according to the determination that the deceleration determination means performs deceleration. Means. The deceleration determination means determines that the discharge roller is decelerated when the sheet length L of the sheet is 2S or more, or determines that the discharge roller is decelerated according to the characteristics of the toner image transferred to the sheet. Or a means for determining that the discharge roller is to be decelerated when a solid image in the toner image is present on the rear end side from the center of the sheet.

  With the above configuration, the paper discharge roller is decelerated to a speed calculated by a predetermined arithmetic expression after the time when the trailing edge of the paper should pass the fixing roller, thereby erroneously detecting the paper discharge. Since there is no possibility, it is possible to reliably detect the fixing wrap jam. In addition, the timing at which the paper discharge roller is decelerated is determined based on the detection of the paper edge by a sensor installed upstream or downstream of the fixing roller, so that the trailing edge of the paper passes after the fixing roller. The discharge roller can be decelerated until the end passes through the discharge roller. Further, since it is determined whether or not the discharge roller is decelerated according to the sheet length and the toner image characteristics, unnecessary discharge roller deceleration is eliminated, and the productivity of the image forming apparatus is improved. be able to.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to FIGS.

  In Embodiment 1 of the present invention, when the sheet is in a normal state, the rotation speed of the sheet discharge roller is reduced to a predetermined speed from when the sheet passes through the fixing roller to the sheet discharge roller. The image forming apparatus determines whether a paper sheet has a fixed winding jam by monitoring the passage state of the paper between and a predetermined time.

  The basic configuration of the image forming apparatus according to the first embodiment of the present invention is the same as that of the conventional one shown in FIG. FIG. 1A is a block diagram of a main part of the image forming apparatus in Embodiment 1 of the present invention. The image forming apparatus includes a CPU 1, an image memory 2, an I / O (input / output) 3, an I / F (interface) 4, a ROM 5 and a RAM 6. The CPU 1 is an arithmetic device that interprets and executes program instructions. An arithmetic unit 7 and a timer 8 are provided inside the CPU 1. The calculator 7 is means for processing each data sent to the CPU 1 when calculating the distance. The timer 8 is means for measuring time with the exchange with the I / O 3 as a trigger. The image memory 2 is a memory that stores data to be printed by the image forming apparatus. The I / O 3 is a means for controlling input / output of electrical components such as sensors, motors, and clutches. The I / F 4 is an interface between the image forming apparatus and a terminal that issues a print request to the image forming apparatus. The ROM 5 is a read-only semiconductor memory that stores a program executed by the CPU 1. The RAM 6 is a semiconductor memory that can be read and written by designating an arbitrary address. The operation panel 9 is an input means and a display means for operation.

  FIG. 2 is a flowchart of the jam detection processing procedure and the discharge roller deceleration processing procedure when the discharge roller is decelerated at the time when the trailing edge of the sheet should pass the fixing roller.

The function and operation of the laser printer according to the first embodiment of the present invention configured as described above will be described. First, the operation principle of the present invention will be described. The case where the fixing roll-in jam cannot be detected is when the following two conditions are simultaneously satisfied.
(1) A critical position where the time until the trailing edge of the paper turns off the paper ejection sensor and the time until the front edge of the paper turns off the paper ejection sensor due to a fixing wrap jam when the paper is normally ejected Is present on the paper.
(2) When the paper discharge sensor is in the dangerous position, the fixing roll-in occurs.

  After the trailing edge of the paper passes through the fixing roller, the paper discharge speed (the speed of the paper discharge roller) is decreased so that it can be distinguished whether the paper is normally discharged or a fixing winding jam has occurred. As shown in FIG. 1B, the distance between the fixing roller and the discharge sensor is S, the sheet length is L, the rotation speed of the fixing roller is V1, and the changed discharge roller speed is V2. . In the case of 2S> L, since the paper is short and there is no danger position, it can be solved by using an apparatus that satisfies 2S> L. However, the size of the device becomes large. Similarly, there is no problem in the case of paper where 2S> L.

  Initially, the paper discharge roller is rotated at the same speed (V1) as that of the fixing roller, and the speed of the paper discharge roller is set to be higher than V1 from the time when the rear end of the paper should pass through the fixing roller if normally conveyed. Slow V2. The reason why the rear end passes through the fixing roller is that the image quality changes if the fixing time is different. The timing of deceleration may be after the time when the fixing roller should be removed.

Further, assuming that the dangerous position of the condition (1) is an X position from the rear end of the sheet, the condition “1 until the rear end of the sheet turns off the discharge sensor when the sheet is normally discharged” is set. The “time of” is ((X−S) ÷ V1 + S ÷ V2). Since the speed of the fixing roller remains V1, the “time until the leading edge of the paper turns off the paper discharge sensor due to the fixing winding jam” is ((L−X) ÷ V1). The position X where both equations are equal is the value of equation (A).
X = (1/2) {L + (1- (V1 / V2)) S} (A)
Here, if V2 is made sufficiently small, the solution of equation (A) becomes a negative number, and the dangerous position does not exist on the sheet. That is, since the condition (1) is not satisfied, there is no case where it is not possible to distinguish between normal discharge and fixing winding jam.

However, when continuous printing or productivity (throughput) is required, it is not practical to make V2 extremely small because the paper discharge speed becomes slow. However, when the condition (1) is satisfied but the condition (2) is not satisfied, V2 is maximized when X and S are equal. This is because, in order to prevent the condition (2) from being satisfied, X must be equal to or less than S, and it can be seen from equation (b) that is a modification of equation (b) that V2 increases as X increases.
V2 = S / (L + S-2X) × V1 (b)
That is, if V2 is a value represented by the formula (c), there is no case where it is not possible to distinguish between normal paper discharge and fixing winding jam, and V2 is maximized.
V2 = S / (LS) × V1 (C)

  Next, the operation procedure will be described with reference to the flowchart of FIG. Processing control is executed by the CPU 10. The symbol V1 used is the rotational speed of the fixing roller and the paper discharge roller, the symbol V2 is the rotational speed of the paper discharge roller after deceleration, the symbol L is the length of the paper, and the symbol S is The distance between the fixing roller and the paper discharge sensor. The time point at which the rear end of the paper should pass the fixing roller is determined based on the time when the paper discharge sensor detects the front edge of the paper. A process for reducing the rotational speed of the paper discharge roller to V2 is added to the conventional jam occurrence detection process flow.

  ((LS) ÷ V1) is the time taken from when the paper discharge sensor is turned on to when the paper trailing edge passes through the fixing roller when the paper is conveyed at the conveyance speed V1. The rotation speed of the paper discharge roller is V2. V2 is calculated by an arithmetic expression (a ÷ (L + a−2S)) × V1, and decelerating the discharge roller when the trailing edge of the sheet passes through the fixing roller is a = S, so V2 = ( The paper discharge roller is decelerated to S ÷ (LS)) × V1. Since the speed is decelerated during the conveyance, the time from when the paper discharge sensor is turned on to when it is normally conveyed is ((LS) ÷ V1 + (S ÷ V2)). . Therefore, if the paper discharge sensor is turned off earlier than this time, or if the paper discharge sensor does not turn off even after this time has elapsed, it is determined that a jam has occurred. Such control makes it possible to reliably detect the occurrence of fixing jam.

  In step 1 shown in FIG. 2, the sheet onto which the toner image has been transferred is conveyed to the fixing device at a speed V1. In step 2, it waits until the paper discharge sensor is turned on. In step 3, timer timing is started. Let T be the elapsed time. In step 4, it is checked whether the paper discharge sensor is turned off. If not, step 5 checks whether the elapsed time T is ((LS) / V1). If so, in step 6, the rotation speed of the paper discharge roller is lowered to V2. In step 7, it is checked whether the elapsed time T is longer than ((LS) / V1 + (S / V2)). Otherwise, go back to step 4. If it is longer, it is determined that a jam has occurred. If the paper discharge sensor is off in step 3, it is checked in step 8 whether the elapsed time T is shorter than ((LS) / V1 + (S / V2)). If it is shorter, it is determined that a jam has occurred. Otherwise, it is determined that the paper discharge is completed normally.

  As described above, in the first exemplary embodiment of the present invention, when the image forming apparatus is in a normal state, the rotation speed of the paper discharge roller is set to a predetermined speed from when the paper passes through the fixing roller until it passes through the paper discharge roller. Since the configuration is such that the paper passing state between the fixing member and the paper discharge port is monitored for a predetermined time to determine the paper fixing wrap jam, there is no possibility of erroneous detection of paper discharge, Fixing and winding jam can be reliably detected.

  In the second embodiment of the present invention, the time point at which the rotational speed of the paper discharge roller is decelerated is determined with reference to the time point when the registration sensor detects the rear edge of the paper, and the time when the rear edge of the paper should pass the fixing roller. An image forming apparatus that decelerates a paper discharge roller.

  The basic configuration of the image forming apparatus according to the second embodiment of the present invention is the same as the conventional one shown in FIG. FIG. 3 is a flowchart of the discharge roller deceleration processing procedure based on the registration sensor being turned off. Symbol S2 is the distance between the registration sensor and the fixing roller. V2 is calculated by the same arithmetic expression as in the first embodiment. FIG. 4 is a flowchart of the jam detection processing procedure when the paper discharge roller is decelerated at the time when the trailing edge of the paper should pass the fixing roller. It is a flowchart of the same form as the conventional jam detection processing flowchart, and the criterion for determining that a jam has occurred is the same as in the first embodiment.

  When the trailing edge of the sheet passes through the registration sensor, that is, when the registration sensor is turned off, timer counting is started (timer value T). The time S2 ÷ V1 hours after the registration sensor is turned off is the time when the trailing edge of the sheet passes the fixing roller when it is normally conveyed. Therefore, when T = S2 ÷ V1, the rotation speed of the paper discharge roller is reduced by setting the rotation speed of the paper discharge roller to V2. By performing the processing in FIG. 3 and the processing in FIG. 4, it is possible to reliably detect the occurrence of the fixing jam even when the rotation speed of the paper discharge roller is decelerated with reference to the registration sensor OFF. In FIG. 3 and FIG. 4, T is a different timer value.

  In step 11 shown in FIG. 3, the sheet on which the toner image is transferred is conveyed to the fixing device at a speed V1. In step 12, wait until the registration sensor is turned off. In step 13, timer timing is started. Let T be the elapsed time. In step 14, the process waits until the elapsed time T becomes (S2 ÷ V1). In step 15, the rotation speed of the paper discharge roller is lowered to V2.

  In step 21 shown in FIG. 4, the sheet on which the toner image has been transferred is conveyed to the fixing device at a speed V1. In step 22, the process waits until the paper discharge sensor is turned on. In step 23, timer timing is started. Let T be the elapsed time. In step 24, it is checked whether the paper discharge sensor is turned off. If not, step 25 checks whether the elapsed time T is longer than ((LS) / V1 + (S / V2)). Otherwise, go back to step 24. If it is longer, it is determined that a jam has occurred. If the paper discharge sensor is off in step 24, it is checked in step 26 whether the elapsed time T is shorter than ((LS) / V1 + (S / V2)). If it is shorter, it is determined that a jam has occurred. Otherwise, it is determined that the paper discharge is completed normally.

  As described above, in the second exemplary embodiment of the present invention, the image forming apparatus determines the time point at which the rotation speed of the paper discharge roller is decelerated with reference to the time point when the registration sensor detects the paper rear edge, and the paper rear edge. Since the paper discharge roller is decelerated at the time when the paper should pass through the fixing roller, there is no possibility of erroneous detection of paper discharge, and the fixing wrap jam can be detected reliably.

  In Embodiment 3 of the present invention, it is determined whether or not the rotation speed of the paper discharge roller is reduced. Depending on the sheet length and the position of the solid image in the toner image transferred to the sheet, a fixing winding jam occurs. Since the possibility is small, the rotation speed of the paper discharge roller is not reduced, and the image forming apparatus reduces the rotation speed of the paper discharge roller only when there is a possibility of fixing winding jam.

  The basic configuration of the image forming apparatus according to the third embodiment of the present invention is the same as that of the conventional one shown in FIG. FIG. 5 is a flowchart of a procedure for determining whether to decelerate the discharge roller according to the sheet length and the position of the solid image.

  If the paper length L is less than 2S, there is no risk of misjudgment of occurrence of fixing wrapping jam as normal paper discharge even if paper discharge is performed without decelerating the paper discharge roller. Do not slow down. Also, the fixing wrap jam is likely to occur at a solid image position on the paper. When the paper is discharged without decelerating the paper discharge roller, it is erroneously determined that the occurrence of the fixing wrap jam is normal discharge when the fixing wrap jam occurs on the rear end side from the center of the paper. . That is, if the solid image does not exist on the rear end side from the center of the sheet, the possibility of erroneous determination is small. Therefore, in the above case, it is only necessary to detect a jam as in the prior art without decelerating the paper discharge roller. On the contrary, the discharge roller is decelerated only when the sheet length L is 2S or more and the solid image exists on the rear end side from the sheet center. Thereby, unnecessary deceleration of the paper discharge roller can be eliminated, and productivity as an image forming apparatus can be improved.

  In step 31 shown in FIG. 5, it is checked whether the sheet length L is 2S or more. If it is not 2S or more, the paper discharge roller is not decelerated. In the case of 2S or more, in step 32, it is checked whether or not the solid image exists on the rear end side from the center of the sheet. Otherwise, the paper discharge roller is not decelerated. If so, the paper discharge roller is decelerated.

  As described above, in the third exemplary embodiment of the present invention, the image forming apparatus determines whether to reduce the rotation speed of the paper discharge roller, and only when there is a possibility that fixing winding jam may occur. Since the configuration is such that the rotation speed of the paper discharge roller is reduced, there is no possibility of erroneous detection of paper discharge, fixing wrapping jams can be reliably detected, and efficiency is improved.

  The image forming apparatus of the present invention is optimal for detecting a winding jam to a fixing device such as a copying machine or a laser printer using an electrophotographic process.

FIG. 2 is a block diagram of a main part of the image forming apparatus according to the first exemplary embodiment of the present invention and a conceptual diagram around a paper discharge sensor. FIG. 6 is a flowchart of a jam detection processing procedure and a discharge roller deceleration processing procedure in a case where the discharge roller is decelerated at the time when the trailing edge of the sheet of the image forming apparatus according to Embodiment 1 of the present invention should pass the fixing roller. FIG. 10 is a flowchart of a discharge roller deceleration processing procedure based on the OFF state of the registration sensor of the image forming apparatus according to the second exemplary embodiment of the present invention. FIG. 10 is a flowchart of a jam detection processing procedure when the paper discharge roller is decelerated at the time when the rear end of the sheet of the image forming apparatus according to the second exemplary embodiment of the present invention should pass the fixing roller. FIG. 10 is a flowchart of a determination procedure for determining whether or not to decelerate a discharge roller in accordance with a sheet length and a position of a solid image of an image forming apparatus according to a third exemplary embodiment of the present invention. It is the schematic of the laser printer using the conventional electrophotographic process, and the timing diagram of a paper discharge sensor. FIG. 9 is a general flowchart for detecting a fixing winding jam that occurs after the leading edge of a conventional paper reaches a paper discharge sensor and is turned on.

Explanation of symbols

1 ... CPU, 2 ... Image memory, 3 ... I / O, 4 ... I / F, 5 ... ROM, 6 ... RAM, 7 ... Calculator, 8. ..Timer, 9 ... operation panel, 10 ... transfer belt, 11 ... secondary transfer roller, 20 ... feed roller, 21 ... feed port, 22 ... registration roller, 23 ... Fixing roller, 24 ... Discharge roller, 25 ... Registration sensor, 26 ... Discharge sensor.

Claims (18)

  A fixing roller that heats and fixes the toner image transferred onto the paper, a paper discharge port that discharges the paper located downstream of the fixing roller to the outside of the apparatus, and a space between the fixing roller and the paper discharge port. A sheet detecting means for detecting a state of passing of the sheet, a sheet discharge roller disposed between the fixing roller and the sheet discharge port, and conveying the sheet to the sheet discharge port; A conveyance control unit that controls driving; and a jam determination unit that monitors a detection state of the sheet by the sheet detection unit for a predetermined time to determine a fixing winding jam of the sheet. The conveyance control unit is in a normal state. In this case, there is provided means for reducing the rotation speed of the paper discharge roller to a predetermined speed from the time when the rear end of the paper passes through the fixing roller to the time when the rear end of the paper passes through the paper discharge roller. Image forming equipment characterized by .   The conveyance control means includes a distance a between the trailing edge position of the paper and the paper detection means when the discharge roller starts to decelerate, a distance S between the fixing roller and the paper detection means, and a paper length L. Speed calculation means for calculating a deceleration speed V2 of the paper discharge roller by an arithmetic expression (a ÷ (L + a−2S)) × V1 based on the rotation speed V1 of the fixing roller and the paper discharge roller, and deceleration of the paper discharge roller The image forming apparatus according to claim 1, further comprising means for setting a subsequent rotation speed to V2.   The speed calculating means includes means for calculating a deceleration speed V2 of the paper discharge roller by an arithmetic expression (S ÷ (LS)) × V1, and the transport control means is configured such that the trailing edge of the paper is in a normal state. 3. The image forming apparatus according to claim 2, further comprising a unit that decelerates the rotation speed of the paper discharge roller to V <b> 2 when the fixing roller exits.   The conveyance control means includes means for decelerating the rotational speed of the paper discharge roller after (LS) ÷ V1 after the paper detection means detects the leading edge of the paper. The image forming apparatus according to claim 1.   A second paper detection unit disposed at a distance of S2 upstream of the fixing roller; and the conveyance control unit detects the discharge after S2 / V1 after the second paper detection unit detects the trailing edge of the paper. The image forming apparatus according to claim 1, further comprising a unit that decelerates a rotation speed of the paper roller.   The paper discharge roller includes a deceleration determination unit that determines whether or not to decelerate the discharge roller according to an operating condition, and the conveyance control unit determines whether the deceleration determination unit performs deceleration. The image forming apparatus according to claim 1, further comprising a unit that decelerates.   The image forming apparatus according to claim 6, wherein the deceleration determination unit includes a unit that determines that the discharge roller is decelerated when a sheet length L of the sheet is 2S or more.   The image forming apparatus according to claim 6, wherein the deceleration determining unit includes a unit that determines to decelerate the discharge roller according to a characteristic of the toner image transferred onto the sheet.   9. The apparatus according to claim 8, wherein the deceleration determination unit includes a unit that determines that the discharge roller is to be decelerated when a solid image in the toner image is present on the rear end side from the center of the sheet. The image forming apparatus described.   The toner image transferred onto the sheet is heated and fixed by a fixing roller, a state in which the sheet passes is detected by a sheet detecting unit downstream of the fixing roller, and the sheet is discharged by a sheet discharge roller downstream of the fixing roller. From the time when the rear end of the paper passes through the fixing roller to the time when the rear end of the paper passes through the paper discharge roller in a normal state. The sheet conveyance control method is characterized in that the conveyance speed of the sheet is reduced to a predetermined speed, and the detection state of the sheet is monitored for a predetermined time to determine the fixing winding jam of the sheet.   Based on the distance a between the rear end position of the sheet and the sheet detection unit at the time of starting deceleration, the distance S between the fixing roller and the sheet detection unit, the sheet length L, and the sheet conveyance speed V1, The paper conveyance control method according to claim 10, wherein the deceleration speed V2 is calculated by a ÷ (L + a−2S)) × V1 and the conveyance speed after deceleration is V2.   The deceleration speed V2 is calculated by an arithmetic expression (S ÷ (LS)) × V1, and if it is normal, the conveyance speed is reduced to V2 when the trailing edge of the sheet passes the fixing roller. The paper conveyance control method according to claim 11.   13. The paper transport control method according to claim 10, wherein the transport speed is reduced after (LS) / V1 after detecting the leading edge of the paper.   13. The conveyance speed is decelerated after S2 ÷ V1 after the second sheet detecting means arranged at a distance of S2 upstream of the fixing roller detects the trailing edge of the sheet. The paper conveyance control method according to claim 1.   The paper conveyance control method according to claim 10, wherein it is determined whether or not to perform deceleration according to an operation condition, and the deceleration is performed only when it is determined to perform deceleration.   16. The paper conveyance control method according to claim 15, wherein when the paper length L of the paper is 2S or more, it is determined that deceleration is performed.   The paper conveyance control method according to claim 15 or 16, wherein it is determined whether or not to decelerate according to characteristics of the toner image transferred to the paper.   18. The paper conveyance control method according to claim 17, wherein it is determined that deceleration is performed when a solid image in the toner image exists on the rear end side from the center of the paper.

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