JP2019028277A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can reduce erroneous detection of winding of paper around a fixing member during paper feed to increase detection accuracy even during conveyance of thin paper.SOLUTION: An image forming apparatus comprises: a fixing unit that includes a heating rotary body, a pressure rotary body, and a heat source built in the heating rotary body; and paper conveyance direction detection means that is arranged downstream of the fixing unit and detects a conveyance direction of paper. When detecting with the paper conveyance direction detection means that the conveyance direction of paper is reversed during paper feed, the image forming apparatus determines the occurrence of paper jam.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus capable of forming an image on a recording material such as a copying machine, a printer, or a facsimile employing an electrophotographic system.

  In recent years, it has been desired that an image forming apparatus can output a product corresponding to various media, and various media compatible technologies are required. In the fixing device of the image forming apparatus, in the middle of paper passing, the middle of the paper is wound around the fixing member and pulled back, making it impossible to pass the paper quickly and reliably. One of the media support technologies that need to be done.

  Up to now, it has been common to detect a jammed paper winding using a paper presence / absence detection sensor provided in a paper transport unit. Specifically, a plurality of paper presence / absence detection sensors are provided in the paper transport unit on the downstream side in the transport direction of the fixing device, and (1) a predetermined time that the paper leading edge should reach for each paper presence / absence detection sensor. When there is a paper presence / absence detection sensor that does not detect “presence” in the range, or (2) in the “presence” state of the paper presence / absence detection sensor, the paper is switched to the “no” state other than when the paper trailing edge is reached When the presence / absence detection sensor is present, it is determined that winding has occurred in the fixing device and the paper has been pulled back to the fixing device and jammed, and the operation of the image forming apparatus is urgently stopped.

  However, in the above method, a long sheet having the conveyance direction as the longitudinal direction is passed, and the sheet presence / absence detection sensor at the most downstream side of the image forming apparatus detects “Yes”, and the sheet is conveyed more than a predetermined distance. Later (when the transport distance at this time is set to L0), when winding is started in the fixing device unit, the occurrence of winding in the middle may not be detected unless pull back is generated for L0.

  When the amount of L0 is longer than the outer peripheral length of the fixing member, a paper jam is detected on the way, and when the stop of the image forming apparatus is completed, the paper is wound around the fixing member one or more times. As a result, there arises a problem that the jam handling power becomes heavy.

  In order to solve this problem, as disclosed in Patent Document 1, a method has been proposed in which the load torque of the fixing member is detected, and when the load exceeds a certain value, it is determined that the jam occurs during winding.

JP-A-9-236958

  By the way, when detecting the load torque of the fixing member as described in Patent Document 1 and reliably determining the intermediate winding jam, the load torque of the fixing member that is determined as the intermediate winding jam is It is necessary to set it above the maximum torque and below the minimum torque when a jam occurs.

  If the load torque is set outside this range, (1) When the set load torque is low: there is a possibility that a winding jam will be erroneously detected even during normal operation. (2) When the set load torque is high: Even if winding occurs midway, it may be detected as normal operation and cannot be detected.

  FIG. 16 is a diagram illustrating a change in the load torque of the fixing member when winding is caused in the middle. In the case of thick paper, winding occurs halfway with respect to the normal load torque, the load torque at the other time is sufficiently large, and there is a margin in the set load torque range.

  On the other hand, in the case of thin paper, the difference between the torque at the normal time and the torque at the time of jam occurrence is reduced, and the settable load torque region becomes very small. In addition, with the recent market demand for ultra-thin paper, the load torque range that can be set further decreases (or disappears). Therefore, since it is likely to be in a state such as (1) or (2) and there is a risk of erroneous detection, it is necessary to propose an intermediate winding jam detection means with further improved detection accuracy.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can suppress erroneous detection of an intermediate winding jam and increase detection accuracy even during thin paper conveyance.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a fixing unit that includes a heating rotator, a pressure rotator, and a heating source built in the heating rotator, and a downstream of the fixing unit. And a paper transport direction detecting means for detecting the paper transport direction. When the paper transport direction detecting means detects that the paper transport direction has been reversed during paper feeding, a paper jam is detected. It is characterized by judging.

  According to the present invention, it is possible to provide an image forming apparatus that can suppress erroneous detection of an intermediate winding jam and increase detection accuracy even during thin paper conveyance.

1 is a schematic overall configuration diagram showing an image forming apparatus having a fixing device according to an embodiment of the present invention. It is a block diagram concerning a 1st embodiment. FIG. 3 is a cross-sectional view showing the inside of the fixing device according to the embodiment of the present invention. FIG. 2 is an exploded view showing the inside of the fixing device according to the embodiment of the present invention. FIG. 3 is a cross-sectional view and a configuration diagram of a paper discharge transport unit illustrating a transport unit of the fixing device according to the first embodiment. It is a schematic diagram showing the state at the time of normal paper passing based on 1st Embodiment It is a schematic diagram showing the state at the time of the occurrence of end winding according to the first embodiment. It is a schematic diagram showing the state at the time of the middle winding based on 1st Embodiment It is a flowchart of detection with halfway winding based on 1st Embodiment. It is a graph which shows the detection state at the time of the middle winding generation | occurrence | production of 1st Embodiment and a comparative example. It is a schematic diagram showing the state at the time of normal paper passing based on 2nd Embodiment. It is a schematic diagram showing the state at the time of the middle winding based on 2nd Embodiment. It is a block diagram based on 2nd Embodiment. It is a flowchart of the middle winding detection based on 2nd Embodiment. It is a graph which shows the detection state at the time of the middle winding generation | occurrence | production of 2nd Embodiment and a comparative example. It is the figure which showed the subject of the prior art.

  Hereinafter, specific examples (embodiments) of embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

<First Embodiment>
FIG. 1 is a schematic cross-sectional view of an image forming apparatus including a fixing device (fixing unit) having an endless rotating body in the present embodiment. The image forming apparatus shown in FIG. 1 includes an image forming unit 10 for each color of Y (yellow), M (magenta), C (cyan), and Bk (black). The photosensitive drums a to d included in the image forming units 1 a to 1 d are charged in advance by a charger, and then a latent image is formed by the laser scanner 6. The latent image becomes a toner image by the developing device. The toner images on the photosensitive drums a to d are sequentially transferred to, for example, an intermediate transfer belt 2 that is an image carrier by primary transfer rollers 2a to 2d.

  On the other hand, the recording material P is sent one by one from the paper feed cassette 4, passes through the post-feed conveyance path 45, and is sent to the registration roller pair 9. The registration roller pair 9 once receives the recording material P and straightens it when the recording material P is skewed. The registration roller pair 9 sends the recording material P between the intermediate transfer belt 2 and the secondary transfer roller 3a in synchronization with the toner image on the intermediate transfer belt 2. The color toner image on the intermediate transfer belt is transferred to the recording material P by, for example, a secondary transfer roller 3a which is a transfer body. Thereafter, the toner image on the recording material P passes through the pre-fixing conveyance path 30 and is fixed to the recording material P by being heated and pressurized by the fixing device 40.

  When a toner image is formed only on one side of the recording material P, the recording material P is discharged to the paper discharge tray 12 via the paper discharge roller 11 by switching the switching flapper 46. When toner images are formed on both sides of the recording material P, the recording material P on which the toner image has been fixed by the fixing device 40 is conveyed to the paper discharge roller 11 and discharged when the trailing edge of the paper reaches the reversal point 42. After being switched back and conveyed by the reverse rotation of the paper roller 11 and passing through the double-sided conveyance path 47, a toner image is formed on the other side through the same process as the single-sided image formation, and discharged to the paper discharge tray 12. Is done. The portion constituted by the switchback operation of the flapper 46 and the paper discharge roller 11 is an example of a reversing unit.

  For the purpose of removal when the recording material P is jammed in the conveyance path, maintenance, and the like, a door 80 is provided in the apparatus main body so as to be rotatable about the hinge 90 to the right in the figure. One of the conveyance path 30 before fixing, the secondary transfer roller 3a, and the registration roller pair 9 (right side in the figure) is provided on the door 80. When the door 80 is opened, the conveyance path 45 after the sheet feeding to the discharge roller 11 is provided. In the meantime, the conveyance path other than the fixing device 40 is opened.

  FIG. 2 is a schematic block diagram illustrating a control unit provided in the image forming apparatus 12 in the present embodiment. As shown in FIG. 2, the CPU 81 includes control units (a temperature detection unit 89, a heater control unit 91, a drive control unit 92, and a paper discharge transport unit 96), a paper feed cassette 4, and an I / F unit 85 of the fixing device 40. The timer 86, the controller 87, the image processing unit 84, the ROM 83, and the RAM 82 are electrically connected, and are further connected to the operation unit 95 through the I / F unit 85.

  The CPU 81 forms an image on the recording material P stored in the paper feed cassette 4 based on the printing conditions. The operation unit 95 receives an operation by the user, and is configured by a liquid crystal touch panel, for example. The operation unit 95 may be an external terminal such as a personal computer connected to the image forming apparatus 12. Further, the CPU 81 performs time measurement with the timer 86.

  Image information 88 such as printing conditions is sent to the CPU 81 through the controller 87. The CPU 81 can form an image by processing the received image information 88 by the image processing unit 84.

  The ROM 83 stores a program for controlling the image processing unit 84, the paper feeding unit 4, the operation unit 95, each control unit of the fixing device 40, and the like. The RAM 82 is used as a work area when the CPU 81 executes a program.

  By being controlled by the CPU 81 with such a configuration, the fixing device 40 can control the conveyance speed of the recording material P, the surface temperature of the fixing film 113, and the like, and can fix the toner image on the recording material P.

  Next, the configuration and mechanism of the fixing device 40 mounted in the image forming apparatus according to the embodiment of the present invention will be described with reference to FIGS. 3 is a cross-sectional view showing the inside of the fixing device, FIG. 4 is an exploded view showing the inside of the fixing device, and FIG. 5 is a cross-sectional view showing a conveying portion of the fixing device.

  The heating device 110 provided in the fixing device 40 is pressed against the elasticity of the pressure roller 120 by the following configuration to form a fixing nip portion N. The heating device 110 includes flanges 116 at both ends, and the flanges 116 are connected to the metal stay 114. One end of the pressure spring 115 is connected to a fixing device housing (not shown), and the other end is connected to the pressure arm 123.

  The pressure arm 123 is rotatably held around the rotation center C. One end of the pressure arm 123 is urged by the pressure spring 115, whereby the pressure arm 123 applies a biasing force to the flange 116, The flange 116 is pressed toward the pressure roller 120. The urging force transmitted to the flange 116 acts on both ends of the metal stay 114. As a result, the metal stay 114 is pressed in the direction of the pressure roller 120, so that the heat insulating holder 112 and the heat insulating holder are arranged in contact with the metal stay 114. The heater 111 disposed in contact with the 112 is integrally pressed toward the pressure roller 120.

  That is, as shown in FIG. 3, the metal stay 114 has both ends in the longitudinal direction protruding from the heat insulating holder 112 and inserted into the flange 116, and the pressure arm 123 disposed on the flange 116 is a pressure spring. 115 is pressurized. The load is uniformly transmitted through the stay 114 over the longitudinal direction of the heat insulating holder 112.

  In the fixing nip portion N, the fixing film 113 is bent by being sandwiched between the heater 111 and the pressure roller 120 by the applied pressure, and is in close contact with the heating surface of the heater 111. The pressure roller 120 obtains a driving force that rotates in the direction of the arrow in FIG. 2 by a driving gear 117 provided at the end of the cored bar. The driving force is transmitted from a motor M1 (not shown) through a drive control unit 92 in accordance with a command from the CPU 81 that controls the control means. By driving the pressure roller 120, the recording material P existing in the fixing nip portion N is controlled so as to receive the conveying force at the speed PS.

  As the pressure roller 120 is driven to rotate, the fixing film 113 is driven and rotated (moved) by the frictional force with the pressure roller 120. At this time, the fixing film 113 slides with respect to the heater 111. Between the fixing film 113 and the heater 111, a lubricant such as fluorine-based or silicone-based heat-resistant grease is interposed, so that the frictional resistance is kept low and the fixing film 113 can be rotated smoothly (movable). It becomes.

  Further, the temperature control of the heater 111 is controlled by a temperature detection element such as the thermistor 118 provided on the back surface of the ceramic substrate and a temperature detection element such as the thermistor 119 provided for directly detecting the temperature of the fixing film 113 on the inner surface of the fixing film 113. In response to this signal, the heater controller 90 determines the duty ratio, wave number, and the like of the voltage applied to the energization heating resistor layer and appropriately controls the temperature in the fixing nip to maintain a desired fixing set temperature.

  Further, the metal stay 114 is provided with a grounding means 121 for the purpose of grounding the fixing film 113. The grounding means 121 and the thermistor 119 are projected in a spring state with a spring property outside the projected shape when the fixing film 113 is attached in a natural state so that the fixing film 113 is slidably contacted with the fixing film 113 attached. Is attached.

  Further, the fixing device 40 is provided with an inner discharge roller pair 70 as shown in FIG. The inner discharge roller pair 70 includes an inner discharge driving roller 70a and an inner discharge driven roller 70b. The inner discharge driving roller 70a is provided with a driving gear (not shown) at its end, and driving is input from a driving source M2 (not shown) by the driving control unit 92. Further, the inner discharge driven roller 70b is urged by the urging means (not shown) to the inner discharge driving roller to form a nip portion and convey the recording material P through the nip portion. In order to keep the posture of the recording material P being conveyed appropriately, the inner paper discharge driving roller 70a is rotated at a speed that is set to be several percent faster than the rotation speed of the pressure roller 120.

  The recording material P holding the unfixed toner image is appropriately supplied along the inlet guide 132 by a supply unit (not shown) at a predetermined timing, and is nipped and conveyed by the fixing nip portion N to be heated and fixed. The recording material P discharged from the fixing nip N is guided by the discharge guide 131 and conveyed to the inner discharge roller pair 70.

  Next, an intermediate winding jam detection method according to the present embodiment will be described with reference to FIGS. In the middle of the discharge guide 131 of the fixing device 40, a paper discharge sensor 133 is provided as a paper conveyance direction detecting means (FIG. 5A), and before and after the paper discharge sensor 133, as shown in FIG. In order to detect the state of the paper discharge sensor 133, a photo interrupter 134a and a photo interrupter 134b are arranged.

  A spring 135 is attached to the paper discharge sensor 133, and the paper discharge sensor 133 can move in the direction of the arrow in FIG. Further, the sheet discharge sensor 133 can detect a conveyance state after the recording material P is separated from the fixing film 113 by using a surface material having good followability with the recording material P, for example, silicon rubber for the surface layer. It becomes possible.

  First, when the recording material P is normally conveyed, the paper discharge sensor 133 operates as shown in FIG. 6A, and this is detected by the photo interrupter 134a (FIG. 6B). Thereby, it can be determined that the paper transport direction is normal. Further, when a leading end jam occurs due to the leading end of the recording material P being wound around the fixing film 113 or the pressure roller 120, the paper discharge sensor 133 does not operate as shown in FIG. No conveyance is detected. From the state of the photo interrupter 134a different from the normal state, the CPU 81 can determine that the leading edge jam has occurred.

  Then, after the leading edge of the recording material P is normally conveyed, if a mid-winding jam occurs due to a mid-section of the recording material P being wound around the fixing film 113, the paper discharge sensor 133 is shown in FIG. Operate to state. That is, when the recording material P is wrapped around the fixing film 113, the downstream portion of the recording material P in the transport direction as viewed from the fixing film 113 is in the direction of the arrow shown in FIG. Moving. At this time, the paper discharge sensor 133 follows the recording material P and changes to the state shown in FIG. 8B, and the reverse of paper conveyance can be detected by the photo interrupter 134b. It is possible to determine an intermediate winding from this information and to make an emergency stop.

  Next, according to the flowchart of FIG. 9, a method for detecting an intermediate winding jam in the present embodiment will be described. When the job instruction is input by the user, the CPU 81 starts the job (S9-1). Accordingly, the CPU 81 controls the heating device 110 through the drive control unit 92 and the heater control unit 91 of the fixing device and rotates the pressure roller 120 (S9-2), and detects the thermistor 119 disposed on the fixing film 113. Temperature control is performed until the temperature reaches the temperature control temperature (S9-3). When the temperature detected by the thermistor 119 reaches the target value, the CPU 81 starts paper feeding (S9-5). When the sheet feeding starts, the recording material P enters the fixing nip N (S9-6).

  Thereafter, the recording material P is transported along the discharge guide, the leading edge of the recording material P operates the paper discharge sensor 133, and the paper discharge transport unit 96 detects the forward direction of the sheet passing (S9-7). When the paper discharge conveyance unit 96 detects the normal direction of the paper passing, the CPU 81 starts detecting the winding in the middle (S9-8). First, the CPU 81 stores the time t1 when the paper discharge sensor 133 is operated, and calculates the time T seconds until the trailing edge of the recording material P reaches the paper discharge sensor 133 (S9-9). If the paper discharge conveyance unit 96 detects the reverse direction of the paper passing during the time T seconds from the time t1 (S9-10), the CPU determines that the recording material P has been jammed midway, and the heater control unit The heater 111 is turned on by 91 and the drive of the pressure roller 120 is immediately stopped by the drive controller 92 (S9-12).

  On the other hand, when time T seconds have elapsed from time t1, when the paper discharge transport unit 96 detects the absence of paper (S9-11), the CPU 81 continues the job without making an emergency stop. However, the time T seconds generally has a margin of several milliseconds as a detection error. In the present embodiment, the margin is ± 20 milliseconds.

  Here, in order to explain the effect of the present embodiment, as a comparative example of the configuration of the present embodiment, the paper discharge sensor does not follow the paper, and only the presence or absence of the paper is detected. Went. FIG. 10 is a graph comparing the state change of the paper discharge sensor of the comparative example and the state change of the paper discharge sensor according to the present embodiment in the case where a winding jam occurs.

  First, when the recording material P enters the paper discharge sensor, in both the comparative example and the present embodiment, the paper discharge sensor detects the paper entry, and both the state changes to the paper presence state and the paper forward direction state. Next, when a paper jam occurs halfway after a certain time Δt after the recording material P enters the paper discharge sensor, in the comparative example, there is no paper after the time Δt when the paper returns backward and the front edge of the paper passes the paper discharge sensor again. Is detected. Therefore, it takes Δt seconds from the occurrence of the jam to the judgment of the jam. On the other hand, in the present embodiment, since the paper discharge sensor can react to the paper behavior in which the paper is reversed at time Δt, it is possible to detect a jam almost simultaneously with the occurrence of a paper jam.

  That is, in the comparative example, the longer the time Δt is, the longer the detection is delayed. In the present embodiment, the detection can be performed almost simultaneously with the time when the recording material is wound halfway regardless of the time Δt. In this way, by implementing this embodiment, it was possible to significantly improve midway winding detection responsiveness compared to the conventional example.

  As described above, according to the present embodiment, it is possible to detect the reverse of the paper transport direction by using the paper transport direction detection unit that detects the paper transport direction after fixing. Detection can be performed quickly and reliably without increasing the size of the apparatus. In addition, even during the transport of ultra-thin paper, it is possible to detect the occurrence of an intermediate winding jam with high detection accuracy with no detection failure.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the present embodiment, the paper conveyance direction detection unit is different from that in the first embodiment, and the other components are the same as those in the first embodiment, and common portions are omitted. In the present embodiment, as shown in FIGS. 11 and 12, a rotation detection unit 97 of the internal paper discharge driven roller 70b is provided as a paper transport direction detecting means, and the reverse of the rotation direction of the internal paper discharge driven roller 70b is detected. Detects winding jam.

  FIG. 13 is a block diagram according to the present embodiment, FIG. 14 is a flowchart of the present embodiment, and FIG. 15 is a graph relating to the response of halfway winding detection according to the present embodiment and a comparative example. A method for detecting an intermediate winding jam in the present embodiment will be described with reference to the flowchart of FIG.

  When a job command is input by the user, the CPU 81 starts job (S14-1). Accordingly, the CPU 81 controls the heating device 110 through the drive control unit 92 and the heater control unit 91 of the fixing device, and rotates the pressure roller 120 (S14-2), and detects the thermistor 119 disposed on the fixing film 113. Temperature control is performed until the temperature reaches the temperature control temperature (S14-3). When the temperature detected by the thermistor 119 reaches the target value, the CPU 81 starts paper feeding (S14-5). When the paper feeding is started, the recording material P enters the fixing nip portion N (S14-6).

  Thereafter, the recording material P is transported along the discharge guide 131, and the leading end of the recording material P causes the paper discharge sensor 133 to transition to the paper presence state (S14-7). When the paper discharge sensor 133 detects the presence of paper, the CPU 81 starts detecting the winding halfway (S14-8). First, the CPU 81 stores the time t1 when the paper discharge sensor 133 is operated, and calculates the time T seconds until the trailing edge of the recording material P reaches the paper discharge sensor 133 (S14-9). If the inner discharge roller rotation detection unit 97 detects that the rotation of the inner discharge driven roller 70b is reversed before the time T1 has elapsed from the time t1, the CPU winds the recording material P halfway around (S14-10). It is determined that a jam has occurred, and the heater controller 91 immediately turns on the heater 111 and the drive controller 92 stops the driving of the pressure roller 120 (S14-12).

  About the effect of this embodiment, as shown in FIG. 15, it turns out that the effect equivalent to 1st Embodiment is acquired. Therefore, also by using this embodiment, it is possible to detect midway winding detection with higher responsiveness than in the past, as in the first embodiment.

  As described above, according to the present embodiment, it is possible to detect the reverse of the paper transport direction by using the paper transport direction detection unit that detects the paper transport direction after fixing. Detection can be performed quickly and reliably without increasing the size of the apparatus. In addition, even during the transport of ultra-thin paper, it is possible to detect the occurrence of an intermediate winding jam with high detection accuracy with no detection failure.

40 ... fixing device 70 ... inner paper discharge roller pair 12 ... image forming device 92 ... drive mechanism 110 ... heating device 111 ... heater 112 ... heat insulating holder 113 ... Fixing film 114 ... metal stay 115 ... pressure spring 116 ... flange 117 ... drive gear 118 ... thermistor 119 ... thermistor 120 ... pressure roller 121 ... grounding means 123 ... Pressure arm 126 ... Cam 131 ... Discharge guide 132 ... Inlet guide 81 ... CPU
84: Image processing unit

Claims (3)

A fixing unit including a heating rotator, a pressure rotator, and a heating source built in the heating rotator;
A paper transport direction detecting means disposed downstream of the fixing unit and detecting a paper transport direction;
In an image forming apparatus having
An image forming apparatus characterized in that a paper jam is determined when the paper transport direction detecting means detects that the paper transport direction has been reversed during paper passing.   2. The paper conveyance direction detection means includes a flag that follows a paper conveyance direction arranged in a paper conveyance path, and is a flag position detection means that detects a position of the flag. The image forming apparatus described in 1.   2. The image according to claim 1, wherein the paper conveyance direction detection unit is a driven roller rotation detection unit that detects a rotation direction of the driven roller of a pair of paper conveyance rollers including a driving roller and a driven roller. Forming equipment.