JP2006309189A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the occurrence of noise or poor images, etc., due to switching of conveyance speed of a fixing roller pair, while preventing image deterioration attributable to recording materials that are stretched or bend too much between a transfer roller pair and the fixing roller pair. <P>SOLUTION: Conveyance speed of recording materials P by the fixing roller pair 5 can be set to conveyance speed based on detected results of a recording material detection means 13, 14 and a loop detecting sensor S, and information on the recording material P that has been prestored in a memory 100. The fixing roller pair 5 conveys the recording material P that runs into the fixing roller pair 5, at such a constant conveyance speed that loop length of the recording material P becomes a lower limit length La after the loop detecting sensor S detects a loop of the recording material P and before the rear end of the recording material P passes through the transfer roller pair 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which an unfixed image is transferred to a recording material by a transfer unit, and the unfixed image is fixed to a recording material by a fixing unit.

  Conventionally, in an electrophotographic image forming apparatus, as shown in FIG. 14, an unfixed image carried on an intermediate transfer belt 102 is transferred onto a recording material P by a transfer roller pair 103, and the unfixed image is transferred by a fixing roller pair 105. The image is fixed on the recording material P, and the recording material on which the image is fixed by the discharge roller pair 111 is discharged to a discharge tray 107 outside the apparatus.

  The fixing roller pair 105 heat-fixes the unfixed image on the recording material, and the heat temporarily taken away from the fixing roller by the fixing processing forms a developer that forms the unfixed image transferred to the recording material. The amount varies depending on the amount of adhesion of the recording material, the number of recording materials passing through the fixing roller pair per unit time, the difference in heat capacity of the recording materials, and the like. The temporary temperature change generated in the fixing roller pair 105 appears as a change in the outer diameter of the roller. For this reason, there may be a difference between the recording material conveyance speed by the fixing roller pair 105 and the recording medium conveyance speed by the transfer roller pair 103.

  If there is a difference in the recording material conveyance speed between the fixing roller pair 105 and the transfer roller pair 103 as described above, image deterioration may be caused. That is, when the recording material conveyance speed by the fixing roller pair 105 is faster than the recording material conveyance speed by the transfer roller pair 103, the recording material P is pulled between the fixing roller pair 105 and the transfer roller pair 103, and the transfer roller pair 103. When the image is transferred to the recording material P, the image may be disturbed and the image may be deteriorated. On the other hand, when the recording material conveyance speed by the fixing roller pair 105 is slower than the recording material conveyance speed by the transfer roller pair 103, the recording material P forms an excessive loop between the fixing roller pair 105 and the transfer roller pair 103, The recording material P in which this excessive loop is formed is strongly pressed against the conveying guide 120 and rubbed, and the rubbing against the conveying guide 120 may cause image disturbance during transfer, leading to image deterioration.

  Therefore, conventionally, a predetermined loop is formed in the recording material P between the transfer roller pair 103 and the fixing roller pair 105 to prevent the recording material P from being pulled or excessively bent. Thus, the following proposals have been made to solve the above-described image degradation.

  As shown in FIG. 14, a loop detection sensor 12 for detecting a loop of the recording material P is provided in the conveyance guide 120 portion between the fixing roller pair 105 and the transfer roller pair 103, and the fixing roller pair 105 is detected according to the detection result. Is switched to the first speed slower than the recording material conveyance speed by the transfer roller pair 103 or the second speed faster than the first speed so that a predetermined loop is maintained ( For example, see Patent Document 1).

JP 05-107966 A

  However, in order to maintain the recording material in a predetermined loop between the fixing roller pair and the transfer roller pair, the fixing roller pair is switched to the first speed or the second speed. For this reason, there is a possibility that noise may be generated by switching the conveyance speed of the fixing roller pair. In addition, there is a risk that image defects such as image blurring at the transfer portion and uneven fixing at the fixing portion may occur due to periodic fine vibration caused by switching the conveyance speed of the fixing roller pair.

  It is an object of the present invention to prevent image deterioration caused by a recording material being pulled or excessively bent between a transfer roller pair and a fixing roller pair, while also preventing noise and image caused by switching the conveyance speed of the fixing roller pair. It is to reduce the occurrence of defects.

  The present invention provides a transfer means for transferring an unfixed image carried by an image carrier onto a recording material, a fixing means for fixing the transferred unfixed image on a recording material, and a transfer means and a fixing means. A loop detection means for detecting a loop of the recording material formed therebetween, a recording material detection means for determining that the recording material has reached the fixing means, and a control for controlling the conveyance speed of the recording material by the fixing means And the control means detects the recording material loop after the recording material loop is detected by the loop detection means based on the detection result of the recording material detection means and the loop detection means and the length of the recording material. The conveyance speed of the fixing unit is set so that the loop length of the recording material becomes the lower limit length when the end is removed from the transfer unit, and the fixing unit is controlled at the set conveyance speed. To do.

  According to the present invention, noise or image failure due to switching of the conveyance speed of the fixing unit, while preventing image deterioration due to the recording material being pulled or excessively bent between the transfer unit and the fixing unit. Can be reduced.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. Unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[First embodiment]
An image forming apparatus according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart showing the operation of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a block diagram of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a cross-sectional view showing an example of a loop shape between the transfer roller pair and the fixing roller pair. FIG. 5 is a table showing each setting information regarding the recording material stored in advance in the memory. FIG. 13 is a cross-sectional view showing the overall configuration of the image forming apparatus according to the embodiment of the present invention.

  First, the schematic configuration of the entire image forming apparatus will be described with reference to FIG. 13, and then the loop control of the recording material according to the information regarding the recording material will be described with reference to FIGS.

  An image forming apparatus 30 shown in FIG. 13 includes, for example, a photosensitive drum a that is four image carriers (electrophotographic photosensitive members) arranged in parallel to form toner images of colors of yellow, magenta, cyan, and black. (Yellow), b (magenta), c (cyan), d (black), and an intermediate transfer belt 2 serving as an intermediate transfer member disposed in an upper portion of the photosensitive drums a to d in a vertically cut manner. Prepare.

  Around each photosensitive drum a, b, c, d driven by a motor (not shown), a primary charger, a developer, etc. (not shown) are arranged, and they are attached to and detached from the image forming apparatus main body 30. It is unitized as a free process cartridge 1a, 1b, 1c, 1d.

  An exposure device 6 composed of a polygon mirror or the like is disposed below the photosensitive drums a to d.

  First, laser light based on a yellow component color image signal is projected onto the photosensitive drum a in the first image forming unit through a polygon mirror of the exposure device 6 to form an electrostatic latent image on the photosensitive drum a. Then, the yellow toner is supplied from the developing device to develop it, and the electrostatic latent image is visualized as a yellow toner image.

  When this toner image reaches the primary transfer portion where the photosensitive drum a and the intermediate transfer belt 2 come into contact with the rotation of the photosensitive drum a, the photosensitive drum is applied by the primary transfer bias applied to the transfer charging member 2a. The yellow toner image on the drum a is transferred to the intermediate transfer belt 2 (primary transfer).

  When the portion of the intermediate transfer belt 2 carrying the yellow toner image moves to the next image forming unit, a magenta toner image is formed on the photosensitive drum b by the same process as that of the previous image forming unit so far. The magenta toner image is superimposed and transferred onto the yellow toner image on the intermediate transfer belt 2 at the primary transfer portion where the body drum b and the intermediate transfer belt 2 abut. Similarly, as the intermediate transfer belt 2 moves, a cyan toner image and a black toner image are sequentially superimposed and transferred onto the yellow toner image and the magenta toner image at each primary transfer portion of each image forming unit. .

  On the other hand, the recording material P is stored in the cassette 4. The recording material P is fed one by one from the cassette 4 by the pick-up roller 8, is timed by the registration roller 9, reaches the secondary transfer portion, and is applied to the secondary transfer roller pair 3 as transfer means. The four color toner images on the intermediate transfer belt 2 are collectively transferred onto the recording material P by the transfer bias (secondary transfer).

  The recording material P onto which the four color toner images have been transferred is guided by a conveyance guide 20 and conveyed to a fixing roller pair 5 as a fixing unit disposed above the transfer roller pair 3, where heat and pressure are transferred. In response, the four color toner images are fixed. As a result, the toner of each color is melted and mixed to be fixed on the recording material P as a full-color print image. Thereafter, the recording material P on which the image is fixed is guided by the conveyance guides 21 and 22 and is discharged onto the discharge tray 7 by a discharge roller pair 11 as discharge means provided downstream of the fixing roller pair 5.

  In the single-side mode in which image formation is performed on one surface of the recording material P, the recording material P on which an image is formed on one surface as described above is discharged onto the discharge tray 7 by the discharge roller pair 11. . On the other hand, in the double-sided mode in which image formation is performed on both sides of the recording material P, the recording material P on which the image is formed on one side as described above is reversed through the double-sided path (not shown). Then, it is conveyed to the registration roller pair 9. Thereafter, the back surface recording is completed in the same image forming process as the front surface recording, and the recording material P on which images are formed on the front and back surfaces is discharged onto the discharge tray 7 by the discharge roller pair 11.

  Next, the recording material loop control performed between the transfer roller pair 3 and the fixing roller pair 5 in the image forming apparatus will be described with reference to FIGS.

  As shown in FIGS. 1 and 3, the image forming apparatus according to the present embodiment includes a CPU 17 as a control unit, and a recording material P loop formed between the transfer roller pair 3 and the fixing roller pair 5. Information relating to the recording material P is stored in advance, a loop detection sensor 12 as a loop detecting means for detecting the recording material, a recording material detection means capable of detecting or calculating that the recording material P has entered the fixing roller pair 5, and recording material P. And a memory 50 as storage means.

  In the present embodiment, the recording material detecting means includes a clutch 13 that transmits (ON) or shuts off (OFF) driving force to the registration roller pair 9, and a timer 14 that measures the time after the clutch 13 is turned ON. And the fact that the recording material P has reached the nip of the fixing roller pair 5 is calculated.

  The CPU 17 controls driving of a fixing motor M as a fixing driving unit that rotationally drives the fixing roller pair 5. The CPU 17 calculates an arbitrary conveyance speed based on the detection result of the recording material detection unit and the loop detection sensor 12 and information on the recording material P stored in the memory 50 in advance. The CPU 17 can set the conveyance speed of the recording material by the fixing roller pair 5 to the arbitrary conveyance speed. That is, the CPU 17 controls the driving of the fixing motor M so that the fixing roller pair 5 conveys the recording material at the set conveying speed.

  Further, the fixing roller pair 5 for which the conveyance speed is set by the CPU 17 is fixed after the recording material P entering the nip of the fixing roller pair 5 is detected by the loop detection sensor 12 after the loop of the recording material P is detected. The recording material is conveyed at a conveyance speed Vfa. The set recording material conveyance speed Vfa of the fixing roller pair 5 will be described in detail later. The loop length of the recording material P is the lower limit length until the trailing edge of the recording material comes out of the transfer roller pair 3. It is a constant conveyance speed that becomes La (see FIG. 4).

  Here, a control system of the image forming apparatus will be described. As shown in FIG. 3, reference numeral 17 denotes a CPU as the control means. A fixing motor M is controlled by the CPU 17 as described above. A loop detection sensor 12 detects a loop of the recording material P between the transfer roller pair 3 and the fixing roller pair 5. Reference numeral 13 denotes a clutch, and reference numeral 14 denotes a timer, which constitutes the recording material detecting means described above. Reference numeral 50 denotes a memory in which information regarding the recording material P is stored in advance. Reference numeral 15 denotes user setting information, which detects mode information, paper thickness information, and paper type information, which will be described later. Reference numeral 16 denotes an environmental sensor as environmental information detection means, which detects humidity in this embodiment.

  The information relating to the recording material P is at least one of mode information indicating image formation on one or both surfaces of the recording material P, recording material thickness, type information, and environmental information. is there. In the present embodiment, as shown in FIG. 5, the mode information indicating the single-side mode or the double-side mode, the recording material thickness information, the recording material type information, and the humidity information as the environmental information are related to the recording material P. The case where it uses as information is illustrated. As setting information corresponding to the combination of these pieces of information, data c1 to c12, d1 to d12, and e1 of recording material loop lengths L0, L1, La, and Lb and a recording material conveyance direction length S, which will be described later, are used. To e12, f1 to f12, and b1 to b9 are stored in the memory 50 in advance.

  Hereinafter, the operation of the fixing roller pair 5 including the recording material loop control performed between the transfer roller pair 3 and the fixing roller pair 5 in the image forming apparatus having the above configuration will be described.

  The recording material P is fed one by one from the cassette 4 by the pickup roller 8 and is timed by the resist roller 9 that is stopped. When the clutch 13 is turned on (step S21), the drive is transmitted to the registration roller 9, and the recording material P is conveyed toward the secondary transfer roller pair 3 by the registration roller 9. At the same time as the clutch 13 is turned on, the timer 14 starts counting (step S22).

  The recording material P onto which the four color toner images have been collectively transferred (secondary transfer) by the secondary transfer roller pair 3 is guided by the conveyance guide 20 to form the L0 loop shown in FIG. It rushes into the nip part. Here, the fixing roller pair 5 is driven by a fixing motor M which is a fixing driving unit independent of driving sources such as a photosensitive drum and an intermediate transfer belt. The recording material conveyance speed Vf of the fixing roller pair 5 is set in advance slower than the recording material conveyance speed Vt of the secondary transfer roller pair 3 (Vf <Vt), and the recording material P gradually forms a loop.

  When the loop length of the recording material P between the secondary transfer roller pair 3 and the fixing roller pair 5 becomes L1 shown in FIG. 4, that is, the loop detection flag 12a swings and the loop detection sensor 12 is turned on. (Step S23), the count time T0 of the timer 14 is detected (step S24). From this detected count time T0, a loop formation time T (= T0−T1) is calculated by subtracting a time T1 from when the clutch 13 is turned on until the recording material P enters the fixing roller pair 5. (Step S25). The time T1 is a constant set in advance in the table of the memory 50. The loop formation time T is a loop formation time from when the recording material enters the fixing roller pair 5 until the loop detection sensor 12 detects a loop of the recording material P.

  Next, an actual speed Vf = Vt− (L1−L0) of the recording material conveyance speed Vf of the fixing roller pair 5 is calculated from the loop formation time T.

  The recording material P that has entered the nip of the fixing roller pair 5 and whose loop L1 has been detected by the loop detection sensor 12 is transported at a constant level by the fixing roller pair 5 whose transport speed is set by the CPU 17 as described above. It is conveyed at a speed Vfa. The recording material conveyance speed Vfa of the fixing roller pair 5 is based on the detected count time T0 and setting information (see FIG. 5) stored in advance in the memory 50, and the following equations (1) and ( It is set to be within the range represented by 2) (step S26).

  The conveyance speed Vfa until the trailing edge of the sheet passes through the secondary transfer roller pair 3 is set so that a loop is not formed too large between the secondary transfer roller pair 3 and the fixing roller pair 5 or tension is generated. Satisfy the following relationship. T2 is the time from when the loop detection sensor detects the loop until the trailing edge of the sheet passes through the secondary transfer roller pair 3.

  Vt + (L1−Lb) / T2 ≦ Vfa ≦ Vt + (L1−La) / T2

  Here, since the sheet length is S, T2 = (S−Vt × T−L0) / Vt. When this is added to the previous equation, the following equation is obtained.

Vt + (L1−Lb) × Vt / (S−Vt × T−L0) ≦ Vfa (1)
Vfa ≦ Vt + (L1−La) × Vt / (S−Vt × T−L0) (2)

  The recording material conveyance speed Vfa of the fixing roller pair 5 set within the range represented by the above formulas (1) and (2) is the recording material P's speed until the trailing edge of the recording material P comes out of the transfer roller pair 3. This is the conveyance speed so that the loop length becomes the lower limit length La. The recording material conveyance speed Vfa is a constant conveyance speed faster than the recording material conveyance speed Vt by the transfer roller pair 3.

  In the above equation, L 0 is the loop length of the recording material P between the transfer roller pair 3 and the fixing roller pair 5 when the recording material enters the fixing roller pair 5. L1 is the loop length of the recording material P between the transfer roller pair 3 and the fixing roller pair 5 when the loop is detected by the loop detection sensor 12. La is a loop lower limit length of the recording material P between the transfer roller pair 3 and the fixing roller pair 5. In the present embodiment, the loop lower limit length La is defined as follows. When the loop length of the recording material between the transfer roller pair 3 and the fixing roller pair 5 is less than this, the transfer roller pair 3 and the fixing roller pair 5 The lower limit of the loop length that causes the recording material P to be pulled between. However, the loop lower limit length La is not limited to the boundary where the recording material is pulled from the state where the loop is formed (the lower limit value of the loop length), and the recording material P is the transfer roller pair 3. It is also possible to have a state where there is a slight degree of deflection that is unlikely to cause the trailing edge of the recording material to jump up when leaving the recording medium. Lb is a loop upper limit length of the recording material P between the transfer roller pair 3 and the fixing roller pair 5. The loop upper limit length Lb is the recording material between the transfer roller pair 3 and the fixing roller pair 5 when the loop length of the recording material P between the transfer roller pair 3 and the fixing roller pair 5 exceeds this length. P is the upper limit of the loop length that causes excessive deflection. The relationship between the loop lengths of these recording materials is La <L0 <L1 <Lb. Vt is the recording material conveyance speed of the transfer roller pair 3, and S is the length of the recording material in the conveyance direction.

  A loop shape (loop lengths L0, L1, La, Lb) between the secondary transfer roller pair 3 and the fixing roller pair 5 is shown in FIG. Here, the recording material loop lengths L0, L1, La, and Lb and the recording material transport direction length S are constants previously stored in the memory 50 as setting information, as described above. As shown in FIG. 5, these constants are set based on mode information such as single-sided printing or double-sided printing, recording material thickness information, recording material paper type information, and environment information as information on the recording material. ing. Here, the magnitude relationship of each setting information shown in FIG. 5 will be described.

  With respect to the loop length L0 of the recording material P between the transfer roller pair 3 and the fixing roller pair 5 when the recording material enters the fixing roller pair 5, as shown in FIG. Since the recording material itself is more rigid than the thin paper, the loop does not form much. That is, the loop length L0 of the recording material P is c3 <c2 <c1 as an example of the setting method shown in FIG. Also, since the recording material P in the double-sided mode is more curled than in the single-sided mode, a different set value is assigned to the loop length L0 of the recording material P. In the present embodiment, c1 <c7.

  Regarding the loop length L1 of the recording material P between the transfer roller pair 3 and the fixing roller pair 5 when the loop is detected by the loop detection sensor 12, the deflection in the vicinity of the nip of each roller pair depends on the rigidity (thickness) of the recording material P. The corners are different. That is, the loop length L1 of the recording material P is relatively longer for thin paper than for thick paper. For this reason, the loop length L1 of the recording material P is d3 <d2 <d1 as an example of the magnitude relationship of the setting information shown in FIG.

  With respect to the loop lower limit length La of the recording material P between the transfer roller pair 3 and the fixing roller pair 5, if the recording material P is thick paper, the loop length may be approximately equal to the loop length in the tension state. However, when the recording material is plain paper that is thinner than thick paper and is in a high humidity environment, the recording material P may wave in the width direction intersecting the transport direction as shown in FIG. In this case, before the recording material P having an unfixed image enters the nip of the fixing roller pair 5, the peak portion on which the unfixed image of the recording material P is placed on the fixing roller 5 a on the unfixed image side. This may cause image disturbance. Therefore, the loop lower limit length La of the recording material P is set to the loop limit length that does not cause image disturbance as described above. That is, the loop lower limit length La of the recording material P is e3 <e2 <e1 as an example of the magnitude relationship shown in FIG.

  Regarding the loop upper limit length Lb of the recording material P between the transfer roller pair 3 and the fixing roller pair 5, if the recording material P is thin paper, the sag limit state immediately before the recording material P touches the conveyance guide 20 may be sufficient. However, when the recording material is thicker than the thin paper, if the loop is made large like the thin paper, the recording material P nipped between the transfer roller pair 3 slips, and the image in the conveying direction of the recording material expands and contracts. There is a possibility. Therefore, the loop upper limit length Lb of the recording material P is set to a loop length that does not affect the image expansion / contraction. That is, the loop upper limit length Lb of the recording material P is f3 <f2 <f1 as an example of the magnitude relationship shown in FIG.

  The set values L0, L1, La, and Lb described above are based on the rigidity (paper thickness) of the recording material. However, the set values L0, L1, La, and Lb are also determined by the humidity as environmental information in addition to the paper thickness. May be different. For example, even if the recording materials have the same thickness, the recording material loop becomes larger when the humidity as the environmental information is high than when the humidity is low. For this reason, if the magnitude relationship of each setting information is illustrated with humidity as environmental information, it becomes c1> c4, d1> d4, e1> e4, f1> f4.

  As for the conveyance direction length S of the recording material P, a setting value related to the paper type information of the user setting information 15 is stored. In this embodiment, the environmental information is detected by the environmental sensor 16, and the paper type information and mode information are detected by the user setting information 15.

  In the image forming apparatus of the present embodiment, when the rear end of the recording material P passes through the transfer roller pair 3 with the loop upper limit length Lb shown in FIG. 4, the rear end of the recording material P jumps up, resulting in an image defect. Therefore, as described above, the recording material conveyance speed Vfa by the fixing roller pair 5 is set so that the rear end of the recording material P is removed from the transfer roller pair 3 in the state of the loop lower limit length La shown in FIG. Yes. As a result, it is possible to minimize the trailing edge of the recording material P from jumping up when the trailing edge of the recording material P comes off the transfer roller pair 3, and image defects caused by the jumping of the trailing edge of the recording material can be prevented. Can be reduced.

  After that, after the trailing edge of the recording material P passes through the secondary transfer roller pair 3, if the recording material is continuously conveyed by the fixing roller pair 5 at the above-described conveyance speed Vfa, the recording material conveyance speed Vt by the transfer roller pair 3 is maintained. Since the conveyance speed Vfa is faster than the recording speed, the recording material P may be rubbed against the guides in the conveyance guides 21 and 22 after fixing.

  Therefore, the timing at which the trailing edge of the recording material P passes through the secondary transfer roller pair 3 is set by the value of the count time of the timer 14, and when the predetermined time is reached, the recording material conveyance speed Vfb of the fixing roller pair 5 is reached. Is set equal to the recording material conveyance speed Vt of the transfer roller pair 3 (step S27).

  Thereafter, the recording material P is discharged to the discharge tray 7 by the discharge roller pair 11 provided downstream of the fixing roller pair 5.

  In the present embodiment, the recording material detecting means for detecting or calculating that the leading edge of the recording material has reached the nip of the fixing roller pair is the timing at which the leading edge of the recording material P reaches the nip of the fixing roller pair 5. The configuration calculated from the ON timing of the clutch 13 of the registration roller 9 is exemplified. However, the recording material detection means is not limited to this. As a recording material detection means for detecting that the leading edge of the recording material has reached the nip of the fixing roller pair, for example, as shown in FIG. It is good also as a structure which reads the timing which this torque fluctuates.

  As described above, according to the present embodiment, image deterioration caused by the recording material P being pulled or excessively bent between the transfer roller pair 3 and the fixing roller pair 5 is prevented. It is possible to reduce the occurrence of noise and image defects due to switching of the conveyance speed of the fixing roller pair 5.

  Further, since the recording material conveyance speed Vfa of the fixing roller pair 5 can be calculated according to the information regarding the recording material P, the recording material P is nipped by the fixing roller pair 5 and then passes through the nip of the transfer roller pair. Therefore, it is possible to reduce image defects caused by the loop state of the recording material.

  In calculating the recording material conveyance speed Vfa of the fixing roller pair 5, the recording material P uses a constant preset in the memory 50, so the recording material conveyance speed Vfa of the fixing roller pair 5 is calculated. It is possible to calculate with a simple and inexpensive configuration.

  Further, even when mode information such as single side / double side, paper thickness, paper type, environment, and the like change, an appropriate recording material loop can be formed, and image defects caused by the recording material loop state can be reduced. be able to.

  Further, the jumping of the recording material P when the trailing edge of the recording material passes through the nip of the transfer roller pair 3 can be reduced, and image defects caused by this can be eliminated.

  Further, in the post-fixing conveyance path after the trailing edge of the recording material passes through the nip of the transfer roller pair 3, it is possible to optimize the loop state of the recording material and eliminate image defects in the post-fixing conveyance path. be able to. Further, the curled state of the recording material can be stabilized, and jamming and poor loading can be prevented.

[Second Embodiment]
An image forming apparatus according to a second embodiment of the present invention will be described. In the image forming apparatus according to the present embodiment, the loop detection sensor 12 serving as the loop detection unit also serves as an operation detection function for detecting whether the recording material conveyance operation by the fixing roller pair 5 is normal. ing. This loop detection sensor 12 is used when the loop detection operation is not normally performed when printing is performed out of the specification, such as a user's erroneous operation, printing on a recording material outside the specification, or component deterioration due to durability. It has a motion detection function.

  Hereinafter, the image forming apparatus according to the second embodiment will be described in detail with reference to FIGS. FIG. 9 is a flowchart illustrating an example of the operation detection function. 10 to 12 are sectional views showing an example of a loop shape between the transfer roller pair and the fixing roller pair. Since the schematic configuration of the image forming apparatus is the same as that of the above-described embodiment, members having the same function are denoted by the same reference numerals and description thereof is omitted.

  First, the operation detection function is started by the ON timing of the clutch 13 or the like. Then, as shown in FIG. 10, after the leading edge of the recording material P enters the nip of the fixing roller pair 5, the loop detection sensor 12 detects whether the recording material P forms a loop within a predetermined time ( Step S91). At this time, since the fixing roller pair 5 transports the recording material P at a transport speed slower than the transport speed of the transfer roller pair 3, if it is normal, a loop is formed in the arrow direction 33 shown in FIG. The loop detection sensor 12 is turned on. On the other hand, if the loop detection sensor 12 is not turned on within a certain time after the clutch 13 of the registration roller 9 is turned on, the print job is stopped (step S92), and a jam processing display and a warning display are given to the user (step S93). .

  In this case, the recording material conveyance speed of the fixing roller pair 5 is faster than the normal state. Therefore, the warning display here indicates whether or not the user setting is performed according to the specification, or a message of the part replacement time.

  When the loop detection sensor 12 is normally turned on within a predetermined time in step S91, the recording material conveyance speed of the fixing roller pair 5 is set to be a constant conveyance speed Vfa as shown in the first embodiment. (Step S94). As a result, the recording material P is transported at the constant transport speed Vfa by the fixing roller pair 5 while being transported at the transport speed Vt by the transfer roller pair 3.

  Then, it is detected by the loop detection sensor 12 whether or not the loop of the recording material P is eliminated within a predetermined time (step S95). When the fixing roller pair 5 transports the recording material P at a constant transport speed Vfa, if it is normal, the loop is canceled in the arrow direction 31 shown in FIG. 11, and the loop detection sensor 12 is turned off within a predetermined time. On the other hand, if the loop detection sensor 12 is not turned off within a certain time, the recording material enlarges the loop in the direction indicated by the arrow 32 shown in FIG. In this case, the recording material conveyance speed of the fixing roller pair 5 is slower than the normal state. Therefore, if the loop detection sensor 12 does not turn OFF even after a certain period of time, the print job is stopped (step S92), and the jam processing display and warning display are performed to the user (step S93).

  According to the present embodiment, in addition to the effects of the above-described embodiment, the loop state of the recording material can be detected when the transfer roller pair or the fixing roller pair is deteriorated in durability or is out of specification. If it is not operating normally, the operation can be stopped and the user can be warned.

[Other Embodiments]
In the above-described embodiment, mode information, recording material thickness information, paper type information, and environmental information are used as information relating to the recording material, and the loop lengths L0, L1, and La of the recording material based on these pieces of information. Although the loop control using Lb and the recording material length S in the conveyance direction is illustrated, the present invention is not limited to this. As the information related to the recording material, other information related to the recording material such as mode information such as a mode for forming a monochrome image and a mode for forming a color image may be used. Further, information on these recording materials may be used individually or in appropriate combinations, and the recording material loop lengths L0, L1, La, Lb and the length of the recording material in the transport direction are based on the information. By storing the length S in the storage means in advance, the same effect as that of the above-described embodiment can be expected.

  In this embodiment, after the loop is detected by the loop detection sensor 12, the loop length is set to the lower limit length when the speed of the fixing roller pair 5 is changed and the trailing edge of the sheet passes through the secondary transfer roller pair 3. However, the changed speed is not necessarily constant. That is, the loop length may be set to the lower limit length when the sheet trailing edge passes through the secondary transfer roller pair 3 by gradually increasing or decreasing the speed.

  In the above-described embodiment, an image forming apparatus using four image forming units for color image formation is illustrated. However, the number of use is not limited, and can be set as needed. It ’s fine.

  In the above-described embodiment, the printer is exemplified as the image forming apparatus. However, the present invention is not limited to this, and other image forming apparatuses such as a copying machine and a facsimile apparatus, or their functions are provided. Another image forming apparatus such as a combined machine, an image forming apparatus that uses a recording material carrier, and sequentially superimposes and transfers the toner images of each color onto the recording material carried on the recording material carrier, as described above. A drum-shaped intermediate transfer member is used instead of a belt-shaped intermediate transfer member, and toner images of each color are sequentially transferred onto the intermediate transfer member, and the toner images carried on the intermediate transfer member are collectively recorded on a recording material. The image forming apparatus may transfer the image, and the same effect can be obtained by applying the present invention to the image forming apparatus.

1 is a cross-sectional view of an essential part showing an embodiment of an image forming apparatus to which the present invention is applied. FIG. 6 is a flowchart illustrating an example of control of the image forming apparatus. 2 is a block diagram illustrating a control system of the image forming apparatus. FIG. FIG. 4 is a cross-sectional view of a main part showing an example of a loop shape between a transfer roller pair and a fixing roller pair. 6 is a table illustrating various setting information stored in advance in a memory. FIG. FIG. 6 is a cross-sectional view of a main part showing a recording material loop length between a transfer roller pair and a fixing roller pair when the recording material enters the fixing roller pair. It is the perspective view which illustrated the corrugated shape of the recording material. It is principal part sectional drawing which shows the other form of the image forming apparatus to which this invention is applied. FIG. 10 is a flowchart illustrating another example (operation detection function) of control of the image forming apparatus. FIG. 6 is a cross-sectional view of a main part showing an example of a loop shape between a transfer roller pair and a fixing roller pair. FIG. 6 is a cross-sectional view of a main part showing an example of a loop shape between a transfer roller pair and a fixing roller pair. FIG. 6 is a cross-sectional view of a main part showing an example of a loop shape between a transfer roller pair and a fixing roller pair. 1 is a cross-sectional view illustrating an example of an image forming apparatus. It is a principal part sectional view of an image forming apparatus showing a loop state between conventional transfer and fixing.

Explanation of symbols

L0, L1, La, Lb ... Loop length M of recording material ... Fixing motor (fixing drive unit)
P: Recording material S: Loop detection sensor (loop detection means)
a, b, c, d... photosensitive drum (image carrier)
1a, 1b, 1c, 1d Process cartridge 2 Intermediate transfer belt 3 Secondary transfer roller pair (transfer means)
5: Fixing roller pair (fixing means)
9: Registration rollers 10, 11: Discharge roller pair (discharge means)
12 ... Loop detection flag 13 ... Registration clutch (recording material detection means)
14: Timer (recording material detection means)
15 ... User setting information 16 ... Environmental sensor (environmental information detection means)
17 ... CPU (control means)
20, 21, 22 ... conveyance guide 30 ... image forming apparatus main body 50 ... memory (storage means)

Claims (6)

Transfer means for transferring an unfixed image carried by the image carrier to a recording material;
Fixing means for fixing the transferred unfixed image on a recording material;
A loop detection means for detecting a loop of a recording material formed between the transfer means and the fixing means;
A recording material detecting means for determining that the recording material has reached the fixing means;
Control means for controlling the conveyance speed of the recording material by the fixing means;
With
The control means detects the recording material loop by the loop detection means based on the detection result of the recording material detection means and the loop detection means and the length of the recording material, and the trailing edge of the recording material from the transfer means. An image forming apparatus, wherein a conveying speed of the fixing unit is set so that a loop length of a recording material becomes a lower limit length when the recording material is pulled out, and the fixing unit is controlled at the set conveying speed. The recording material loop length between the transfer means and the fixing means when the recording material enters the fixing means is L0, the recording material loop length between the transfer means and the fixing means at the time of loop detection is L1, and the transfer means. The lower limit loop length of the recording material between the fixing unit and the fixing unit is La, the upper limit loop length of the recording material between the transfer unit and the fixing unit is Lb, and the relationship between the recording material loop lengths is La <L0 <L1 <Lb. The recording material conveyance speed of the transfer means is Vt, the recording material conveyance speed of the fixing means before loop detection is Vf, the length of the recording material in the conveyance direction is S, and the loop detection means records after the recording material enters the fixing means. When the loop formation time until the material loop is detected is T, the recording material conveyance speed Vfa by the fixing unit set by the control unit is
Vt + (L1−Lb) × Vt / (S−Vt × T−L0) ≦ Vfa
Vfa ≦ Vt + (L1−La) × Vt / (S−Vt × T−L0)
The image forming apparatus according to claim 1, wherein the image forming apparatus has a constant conveyance speed that satisfies the following relationship.   The image forming apparatus according to claim 2, further comprising a storage unit that stores in advance setting information of loop lengths L0, L1, La, and Lb corresponding to the type of recording material.   3. The image forming apparatus according to claim 2, further comprising a storage unit that stores in advance setting information of loop lengths L0, L1, La, and Lb according to environmental conditions.   The recording apparatus further comprises storage means for previously storing setting information of loop lengths L0, L1, La, and Lb corresponding to mode information indicating image formation on one or both surfaces of the recording material. The image forming apparatus according to 2.   The image forming apparatus according to claim 1, wherein the loop detection unit also has an operation detection function of detecting whether or not the recording material conveyance operation by the fixing unit is normal. .

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