JP4686081B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile.
[0002]
[Prior art]
2. Description of the Related Art An image forming apparatus including a fixing device that fixes a toner image onto a sheet by nipping and conveying the sheet onto which the toner image formed by the image forming unit is transferred by a fixing rotating body such as a fixing roller is well known. . In this type of image forming apparatus, in an apparatus capable of forming an image on a long paper, a long paper is output from the fixing device without being skewed, and therefore, a back tension is applied to the paper passing through the fixing device. is there. A device that outputs a long sheet of paper while applying a back tension can prevent the sheet from meandering and convey it straight, which helps to prevent wrinkles and image blurring.
[0003]
By the way, in recent image forming apparatuses, due to the compactness of the machine, the interval between the fixing unit and the photosensitive member as the image carrier is narrowed, and there is no room for white spots and wrinkles due to the skew of the cut sheet. Therefore, even in such an apparatus, if the above-described long sheet conveyance method is employed, stable sheet conveyance can be obtained, and therefore, occurrence of white spots and wrinkles due to skew can be suppressed.
[0004]
[Problems to be solved by the invention]
However, since the linear speed of the fixing unit is set to be higher than the linear speed of the photosensitive member in the above-described long paper conveyance method, when the back tension starts to be applied to the paper being conveyed through the fixing unit, the paper conveyance speed is increased. However, there is a problem that the image is transferred faster than the photosensitive member linear velocity, the image transferred onto the paper is stretched in the transport direction (sub-scanning direction), and a magnification error occurs.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described conventional problems and can suppress the occurrence of magnification error even when a fixing rotary member is passed through while applying back tension to the paper.
[0006]
[Means for Solving the Problems]
  In order to achieve the above object, an image forming apparatus according to the present invention is arranged on a registration roller that regulates the position of the leading edge of a conveyed sheet, and on the downstream side in the conveyance direction of the registration roller, and is formed on an image carrier. Transfer means for transferring the toner image to the paper, and fixing means for fixing the toner image transferred by the transfer means to the paper. The linear speed of the fixing means is the registration roller or the transfer When transporting a sheet that is higher than the linear speed of the unit and whose length in the conveyance direction of the sheet is longer than the length of the sheet conveyance path from the registration roller to the fixing unit,Using time parameters based on the linear speed of the registration roller, the linear speed of the transfer means, the linear speed of the image carrier, and the linear speed of the fixing means,When it is determined that the paper enters the nip portion of the fixing unit and the back tension is applied to the paper, or when it is determined that the back tension changes, the paper conveyance speed at the transfer position of the transfer unit is the image. The linear speed of the registration roller is decelerated so that the linear speed of the carrier is substantially the same.
[0007]
  Furthermore, the present invention providesUsing time parameters based on the linear speed of the registration roller, the linear speed of the transfer means, the linear speed of the image carrier, and the linear speed of the fixing means,When it is determined that the paper enters the nip portion of the fixing unit and the back tension is applied to the paper, or when it is determined that the back tension changes, the paper conveyance speed at the transfer position of the transfer unit is the image. It is effective to decelerate the linear speed of the registration roller and increase the linear speed of the fixing unit so as to be commensurate with the deceleration so that the linear speed of the carrier is substantially the same.
[0008]
  In the present invention,Using time parameters based on the linear speed of the registration roller, the linear speed of the transfer means, the linear speed of the image carrier, and the linear speed of the fixing means,When it is determined that the paper enters the nip portion of the fixing unit and the back tension is applied to the paper, or when it is determined that the back tension changes, the paper conveyance speed at the transfer position of the transfer unit is the image. It is effective to increase the linear speed of the fixing unit so as to be substantially the same as the linear speed of the carrier and to reduce the linear speed of the registration roller so as to match the increased speed.
  Further, the present invention is effective if the sheet conveyance linear velocity by the fixing unit is changed to substantially the same speed as the sheet conveyance linear velocity by the transfer unit when the trailing edge of the sheet has passed through the registration roller.
[0009]
  In the present invention, the fixing condition of the fixing unit is selected according to the size or type of the sheet or the humidity inside the apparatus, and the sheet by the registration roller, the transfer unit, and the fixing unit is selected according to the fixing condition. It is effective to provide a control means for changing the conveying linear velocity.
  Furthermore, the present invention is effective when the registration roller, the transfer unit, and the fixing unit are driven by different driving sources.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory view showing a wide digital copying machine as an embodiment of an image forming apparatus according to the present invention.
[0011]
In FIG. 1, the digital copying machine of this example is schematically shown as a copying machine main body 1 having an image creating unit, an automatic document feeder (ADF) 100, a paper discharge tray 200, and a paper feeding unit (bank) in the copying machine main body. ) 300. The automatic document feeder 100 feeds the documents stacked on the document feeding table 101 one by one onto the contact glass 10 on the copying machine main body 1 side, and discharges them onto the discharge tray 105 after reading the image. It is configured. Documents on the document feeder 101 are aligned in the width direction by a side fence (not shown), separated from the lowermost document by the document feed roller 102, and fed onto the contact glass 10 by the conveyor belt 103. Paper is fed. The feeding unit 107 is provided with a document width detection sensor 108 and a document length detection sensor 109. The size of the document fed from the automatic document feeder 100 can be detected by the both sensors. The original on the contact glass 10 is discharged onto the discharge tray 105 by the conveyance belt 103 and the discharge roller 104 after the reading is completed.
[0012]
When reading a double-sided document, the document on the document feeding table 101 is separated from the bottom document by the document feeding roller 102 and fed, and passes through the contact glass 10 by the transport belt 103. Then, it is reversed by the reversing claw 106, fed again onto the contact glass 10, and the back surface is read. Next, the original on the contact glass 10 is transported by the transport belt 103 after being read from the back surface, reversed by the reversing claw 106, fed again onto the contact glass 10, and the front surface is read. Then, the original after the front surface reading is discharged onto the discharge tray 105 by the transport belt 103 and the discharge roller 104.
[0013]
As shown in FIG. 2, the automatic document feeder 100 is opened and closed around hinges 81 and 82, and a claw 83 is provided on the upper surface of the copier body 1 in the vicinity of the hinge 81, A hole 84 is provided in the lower surface of the automatic document feeder 100 at a position where the claw 83 faces when the conveying device 100 is closed. When the automatic document feeder 100 is closed, the claw 83 is inserted into the hole 84. ing. Inside the automatic document feeder 100 adjacent to the hole 84, a lift-up detection sensor 85 and a document detection timing sensor 86 for detecting the presence or absence of the claw 83 inserted through the hole 84 are provided. The lift-up detection sensor 85 detects the claw 83 when the automatic document feeder 100 is completely closed (lifted down) and is turned on, and when the automatic document feeder 100 is opened (lifted up). Will be off. The completely closed state refers to a state in which a part of the lower surface side of the automatic document feeder 100 is in contact with the upper surface of the copying machine main body 1.
[0014]
On the other hand, the document detection timing sensor 86 is provided to control the timing of detecting the size of the document on the contact glass 10 based on the detection result of the document size detection sensor described later. When the opening angle is within a predetermined angle, the claw 85 is detected and turned on. This predetermined angle is a slight angle, and when the operator manually opens the automatic document feeder 100, both the lift-up detection sensor 85 and the document detection timing sensor 86 are turned off. 87 and 88 are end face scales.
[0015]
As shown in FIG. 3, document size detection sensors 91 to 93 are provided below the contact glass 10. As shown in FIG. 4, each of the document size detection sensors 91 to 93 irradiates the light emitted from one light emitting diode 91a by dispersing it into three beams, and irradiates the reflected light to three light beams inside the optical system. It is a reflective sensor that receives light by the light receiving element 91b, and detects the presence or absence of a document by receiving only reflected light from the document surface through the contact glass 10 from the inside of the optical system.
[0016]
The document size detection sensors 91 to 93 are always in operation, and each light receiving element is turned on when a document on the contact glass 10 is detected, and is turned off when a document is not detected. The document size detection sensors 91 to 93 are arranged according to the sizes of a plurality of types of documents placed at predetermined positions on the contact glass 10. From this, it is determined whether or not there is a document on the contact glass 10, and the size of the document on the contact glass 10 is detected.
[0017]
The copier body 1 includes a scanner that reads a document, an image processing unit, a plotter, and the like. The scanner has a contact glass 10 for placing a document and an optical scanning system. The optical scanning system includes an exposure lamp 11, a first mirror 12, a second mirror 13, a third mirror 14, a lens 15, a full color CCD 16, and the like. Have.
[0018]
The exposure lamp 11 and the first mirror 12 are mounted on the first carriage, and the first carriage moves in the sub-scanning direction at a constant speed by a stepping motor when reading a document. The second mirror 13 and the third mirror 14 are mounted on the second carriage, and the second carriage moves at a speed half that of the first carriage by a stepping motor when reading a document. The original on the contact glass 10 is optically scanned by the movement of the first and second carriages, and is imaged on the light receiving surface of the CCD 16 by the lens 15 and subjected to photoelectric conversion.
[0019]
The image signal separated into red (R), green (G), and blue (B) by the full color CCD 16 is A / D converted by an image processing circuit and then subjected to various image processing by an image processing unit 611. Then, at the time of copying, it is copied onto a sheet by the writing unit. The writing unit includes a laser output unit 20, an fθ lens 21, and a mirror 22. The laser output unit 20 includes a laser diode (LD) that is a laser light source, a polygon mirror and a polygon motor (not shown). The laser output unit 20 emits a black signal laser beam modulated according to the image read by the scanner during copying, and forms a latent image on the photosensitive member 30.
[0020]
Around the photosensitive member 30, a black developing device 32, an LED writing unit 31 for writing a red signal image, a red second developing device 33, and the like are arranged, and the toner image on the photosensitive member 30 is transferred to the transfer rotator. Is transferred to a sheet by the transfer belt 54.
[0021]
The paper is selectively fed from the duplex unit 40 and the first tray 50 in the copying machine main body 1 and one of the second tray 310, the third tray 320, and the fourth tray 330 in the paper feeding unit 300, respectively. Paper is fed by the roller pair of the separation roller 43, the first paper feeding device 51, the second paper feeding device 311, the third paper feeding device 321, and the fourth paper feeding device 331. As shown in FIG. 7, the size and setting direction of the paper set in each tray are detected by the combination of ON / OFF of a plurality of push switches 401 in the position of the size lever 400 in the tray. The paper fed from the duplex unit 40 and the first tray 50 is transported upward by the vertical transport unit 60, and the paper fed from the second tray 310, the third tray 320, and the fourth tray 330 is banked. It is transported upward by the vertical transport unit 340 and the vertical transport unit 60. Then, after a predetermined time after the leading edge of the sheet is detected by the registration sensor 52, the sheet hits the registration roller 53 and temporarily stops, and is conveyed by the registration roller 53 in synchronization with the sub-scanning effective period signal (FGATE). The toner image on the body 30 is transferred. Next, the sheet is separated from the photoreceptor 30 and then conveyed by the transfer belt 54, and the toner image is fixed by the fixing device 55. The sheet after fixing is discharged to the discharge tray 200 by the switching claw 57 and the discharge roller 56 during single-sided printing and after double-sided printing. On the other hand, the paper after surface printing at the time of duplex printing is guided to the duplex conveyance path 41 by the switching claw 57, reversed by the feed roller 42 and the separation roller 43, and accumulated on the duplex unit 40. The sheet on the duplex unit 40 comes into contact with the feed roller 42 as the tray rises, and is fed to the vertical conveyance unit 60 when the feed roller 42 rotates to form an image on the back surface. In the present embodiment, the transport means up to the vertical transport unit 60 is configured as a paper feed transport body.
[0022]
FIG. 5 is a block diagram showing a control system of the digital copying machine. In the figure, an operation unit controller 500 performs liquid crystal display and various LED display controls and various key input controls on the operation unit, and a system controller 501 performs sheet feeding, conveyance, fixing, duplex printing, process control, and the like. The image processing controller 502 performs image control and scanner reading control, and the ADF controller 503 controls the automatic document feeder 100. The paper feed tray controller 504 controls the paper feed tray, the fax controller 505 performs fax transmission / reception management and file management, and the printer controller 506 performs printer data reception management and file management.
[0023]
FIG. 6 is a block diagram showing an image processing circuit of this digital copying machine. The document 600 on the contact glass 10 is illuminated by the exposure lamp 11 and the reflected light is read by the color CCD 16. Next, the analog image signal separated into R, G, and B by the color CCD 16 is amplified by the signal processing circuit 601 and corrected for light amount, converted into a digital image signal by the AD converter 602, and shading correction by the shading correction circuit 603. And sent to the image processing unit 604. The image processing unit 604 performs image quality processing such as MTF correction, γ correction, black image generation, color image generation, binary processing, and multi-value processing, and outputs black data and color data to the selector 605. In the selector 605, the destination of the image signal is switched to the scaling unit 606 or the image memory controller 608. The image signal that has passed through the scaling unit 606 is enlarged / reduced in accordance with the scaling factor and sent to the writing unit 607. The image memory controller 608 and the selector 605 are configured to be able to input and output image signals in both directions. In addition, a CPU 609 for setting the image memory controller 608 and the like and controlling the reading unit and the writing unit, and a ROM 610 and a RAM 611 for storing the program and data are provided. Further, the CPU 609 can write and read data in the image memory 612 via the memory controller 608.
[0024]
The image sent to the image memory controller 608 as a document image is sent to the image memory 612 after the image data is compressed by an image compression device in the image memory controller 608. By performing image compression, a limited image memory can be used effectively. Further, since a large amount of original image data can be stored at one time, the stored original image data can be output in page order. In this case, when the image is output, the data in the image memory 612 is output while being sequentially expanded by the expansion device in the memory controller 608.
[0025]
On the other hand, at the time of FAX transmission, the black data is transferred to the FAX image memory 613 by the selector 605. At the time of FAX reception, the received data is demodulated and expanded from the line, and is expanded in the FAX image memory 613 and then sent to the writing unit 607 by the selector 605. Further, when the printer data is received, the data is expanded in the printer image memory 614 and then sent to the writing unit 607 by the selector 605.
[0026]
FIG. 8 shows an internal configuration of the fixing device 55. As illustrated, the fixing device 55 includes a fixing roller 700 and a pressure roller 701 that presses against the fixing roller 700 as a fixing rotating body. The surface of the fixing roller 700 is coated with a heat-resistant release layer such as PFA or PTFE, and a heat source 702 is provided inside. As the heat source 702, a halogen heater, an infrared heater (nichrome wire), or the like is used. A fixing temperature sensor 703 as temperature detecting means is provided on the peripheral surface of the fixing roller 700, and a pressure temperature sensor 704 as temperature detecting means is provided on the peripheral surface of the pressure roller 701. This fixing temperature sensor. 703. Based on the temperature detection signal from the pressure temperature sensor 704, the heat source 702 is controlled so that the temperature of the fixing roller 700 and the pressure roller 701 becomes a certain temperature, and the amount of heat supplied to the transfer paper P is controlled. For control, the pressure mechanism is controlled so that the nip width between the fixing roller 700 and the pressure roller 701 can be changed. The fixing roller 700 is rotated by a driving mechanism (not shown), and performs fixing processing by applying heat and pressure to the transfer paper P while conveying the transfer paper P in cooperation with the pressure roller 701. The pressure roller 701 has a surface made of a heat-resistant rubber layer such as silicon rubber. The pressure roller 701 is pivotally supported at both ends of the shaft so as to be rotatable, and is always urged in a direction away from the fixing roller 700 by an urging means (not shown). On the other hand, the pressure roller 701 is lifted from below the shaft by a pressure mechanism and pressed against the lower portion of the fixing roller 700. In the pressurizing mechanism, the stepping motor 710 rotates forward (direction A), and the gear 713 is driven from the coaxial gear 711 through the idler gear 712. The shaft of the gear 713 is a feed screw 714 that pulls the anchor 715 in the horizontal direction (C direction). A spring 716 is hung on the anchor 715, and one is hung on the link 717. As the anchor 715 moves horizontally, the link 717 rotates around the fulcrum 718. A lever 719 is fitted to one end of the link 717 and rotates around a fulcrum 720 to push up the pressure roller 701 and apply pressure. Further, when the stepping motor 710 reversely rotates (B direction), the anchor 715 is pushed back in the horizontal direction (D direction), the lever 719 rotates about the fulcrum 720, and the pressure roller 701 is pulled down to release pressure. At this time, the anchor 715 is provided with a home position detection 721, and the pressure instructed can be applied to the pressure roller 701 by adjusting the amount of movement of the anchor 715. This mechanism is provided at both ends of the pressure roller 701.
[0027]
In the image forming apparatus configured as described above, as soon as the power is turned on, the heat source 702 is activated to start heating the fixing roller 700, and the surface of the fixing roller 700 and the pressure roller 701 is detected by the temperature detection unit. Start temperature detection. When the surface temperature of the fixing roller 700 and the pressure roller 701 reaches a temperature at which an unfixed image on the transfer paper P can be fixed, copying can be started, and this is displayed on an operation panel (not shown).
[0028]
The temperature control of the fixing device 55 is a so-called ON-OFF control method in which temperature control is performed while alternately supplying and not supplying power to a heater with a reference temperature (fixing temperature) generally required for performing a fixing operation being performed. There is a so-called proportional control method in which the pulse width or pulse density of the pulse signal for controlling energization of the heater is changed proportionally as the temperature approaches the fixing temperature. Furthermore, in order to compensate for the disadvantages of each of these methods, after fixing the thermal fixing device linearly to the proportional start point by full energization heating of the heater, the fixing temperature required for the fixing operation while maintaining thermal equilibrium by proportional control Control methods for shifting to and maintaining the above are already known. In any case, in the heat roller fixing device, the fixing roller is maintained at a certain set temperature when the machine is on standby, and the sheet sent by the image output start signal is sandwiched between the fixing roller pair to apply heat. The toner on the paper is fused and fixed.
[0029]
When passing through the fixing device 55, the paper may be wrinkled, and one of the causes is the skew of the conveyed paper. The cause of the skew of the paper is that the paper feed from the paper feeder is transported in a non-uniform state, the accuracy of the positional relationship of the units involved in each transport is not achieved, and the fixing device It can be considered that the temperature distribution is uneven and the pressure distribution is uneven.
[0030]
Therefore, in this embodiment, in order to obtain stable paper conveyance, when the paper in the conveyance direction is longer than the conveyance path from the registration roller 53 to the fixing nip, a back tension is applied when passing through the fixing device 55. It is constituted so that it can be conveyed. In this case, if a back tension is applied to the paper, there is a possibility that a magnification error may occur. Therefore, the paper conveyance is controlled based on the flowchart of FIG.
[0031]
In FIG. 9, the user sets the paper size and paper type of the paper feed tray, and the paper of each paper feed tray is set by the paper size and paper type detection means shown in FIG. Also, the fixing conditions (fixing temperature, pressure) can be selected for each paper type according to the paper thickness, and when the paper feed stage to be output is determined, the paper set in the paper feed stage Check the size and type of paper (plain paper, tracing paper, film) and determine the fixing conditions. Depending on the fixing conditions, each conveyance speed (paper feeding unit, registration roller / transfer unit, fixing unit) is determined. In the case of this embodiment, each of the driving means of the paper feed unit, registration roller / transfer unit, and fixing unit is provided with a drive motor separately, and the speed can be changed.
[0032]
The type, size, fixing condition, etc. of the paper to be fed are determined by the selected paper feed stage. The initial speed (Vr0) of the registration roller / transfer belt, the initial fixing speed (Vh0), the deceleration time (T1) of the paper, the registration roller 53 after T1 and the transfer belt, depending on the type of paper to be fed and the fixing conditions. The speed 54 (Vr1) and the linear speed (Vh1) of the fixing device 55 are determined in advance.
[0033]
  When paper feeding starts and the registration sensor 52 detects the leading edge of the paper and is turned on, the paper is in a state where the leading edge is held by the registration roller 53.Image writing signal (Fgate)Wait until it starts. When the Fgate signal is transmitted, the registration roller 53 is driven, and the toner image is transferred onto the sheet by the transfer belt 54 toward the photoreceptor 50. Thereafter, the sheet is conveyed as shown by the solid line in FIG. 10 and is sent to the fixing device 55, and the conveying force of the fixing device 55 is applied. Note that the image forming apparatus may hold the sheet with the leading edge of the sheet abutting against the nip of the registration roller 53.
[0034]
In such paper conveyance, the time is counted when the paper starts the registration roller 53. Further, in each conveyance unit, when the linear velocity of the registration roller / transfer belt is Vr0, the linear velocity of the photosensitive member is Vd, and the linear velocity Vh0 of the fixing unit, the feeding system linear velocity <Vr0 = Vd <Vh0. Is set. Therefore, when the conveyance force of the fixing device 55 is applied to the sheet, a back tension acts on the sheet, and a stable conveyance operation that prevents skew and the like is obtained.
[0035]
However, when the back tension is applied to the paper, the paper linear speed becomes faster than the linear speed Vd of the photosensitive member 50 due to the conveying force of the fixing device 55, which causes a problem of causing a magnification error.
[0036]
Therefore, when the back tension acts on the paper is T1, this time (T1) is calculated by T1 = T01 + (L0−L1) / (Vh0−Vr0).
Here, T01 is the time from when the leading edge of the paper starts the registration roller to enter the fixing nip, and L0 is the transport distance (FIG. 10) where the leading edge of the paper is transported from the transfer position of the photosensitive member to the fixing nip. In FIG. 10, L1 indicates a linear distance (broken line portion in FIG. 10) between the photosensitive member transfer portion and the fixing nip. In the case of the present embodiment, each linear velocity varies depending on the paper type, paper size, fixing conditions, and the like, so T1 is calculated by the above formula.
[0037]
If the time count value t exceeds T1, back tension is applied to the paper, and Vd cannot maintain the linear velocity of the transfer portion. Therefore, the linear velocity of the resist is changed to Vr1, which is slower than Vr0, and is fixed so as to balance it. Is changed to Vh1, which is faster than Vh0. At this time, the relationship between the respective linear velocities is Vr1 <Vd ≦ Vh1, and the sheet is conveyed at the same conveying linear velocity as the photosensitive member linear velocity Vd while the back tension is applied.
[0038]
With this configuration, when the back tension is applied to the paper, the resist linear velocity is changed to Vr1, and the fixing linear velocity is changed to Vh1, and the paper conveyance speed at the transfer portion is the same as the linear velocity Vd of the photosensitive member. Can be held quickly. Therefore, it is possible to prevent the occurrence of problems such as a magnification error, and the sheet is conveyed with the back tension applied, so that stable conveyance without skew is obtained.
[0039]
By the way, the back tension applied to the sheet conveyed by the fixing device 55 is not always a constant magnitude but changes depending on the position of the sheet. That is, each time the trailing edge of the sheet passes through the sheet conveying section and the registration roller of the sheet feeding system, the conveying force holding the sheet against the conveying force of the fixing section is weakened and the back tension changes. Specifically, when the back end of the paper passes through the paper feed and the back tension decreases, and when the back end of the paper passes through the registration roller, the speed at the paper transfer portion increases. Therefore, if the relationship between the respective linear velocities is maintained as Vr1 <Vd ≦ Vh1, depending on the position of the rear end of the sheet, the sheet conveying linear speed at the transfer unit may be maintained at the same speed as the linear speed Vd of the photosensitive member. It becomes difficult and a magnification error occurs.
[0040]
Therefore, if the trailing edge of the sheet exits the paper feed system is T2, and the time when the trailing edge is removed from the registration roller is T3, when the time count t reaches T2, the registration / transfer belt linear velocity is changed to Vr2. Then, the fixing linear velocity is changed to Vh2. When the time count t reaches T3, the resist / transfer belt linear velocity is changed to Vr3, and the fixing linear velocity is changed to Vh3. Here, the relationship between the respective linear velocities is such that the feeding linear velocity <Vr1 <Vr2 <Vr3 Vd Vh3 <Vh2 <Vh1. In this embodiment, the time count is started from the registration start. This count start position is counted from the paper feed start or the paper discharge sensor ON after fixing, and the time spent for conveyance is taken into consideration. Of course, it is also possible.
[0041]
By the way, the slip rate of each conveying means differs depending on the type of paper. Also, the skew generation margin varies depending on the paper type. In general, tracing paper (hereinafter referred to as “trepe”) or the like tends to cause curling of the leading edge of the paper, and therefore the paper itself is easily skewed. Therefore, the conveyance is not stable unless the amount of back tension of the paper is not more than that of plain paper. Therefore, in this embodiment, Vr0, Vr1, Vr2, Vr3, Vh0, Vh1, Vh2, and Vh3 have different values depending on the type of paper. The value is controlled to be set as shown in FIG. 11, for example. In the case of this embodiment, the set value is set for each paper type by the paper type coefficient α. Of course, this can be changed within the range of 1 ≦ α ≦ 1.0005 for each paper type in the operation unit, and can be changed according to the paper type used by the user. Is improved. Here, the paper type coefficient α is set to 1 ≦ αf ≦ αp ≦ αt ≦ 1.0005 in the initial setting, assuming that αp for plain paper, αt for trepe, and αf for film. This paper type coefficient changes T1, or changes the linear velocity. In addition, the conveyance quality is further improved by changing the linear velocity according to the paper size.
[0042]
In the transfer belt system according to the present embodiment, the sheet is electrostatically attracted to the transfer belt and conveyed. For this reason, the suction force of the transfer belt and the paper changes depending on the environmental humidity, and the paper transport speed in a state where the back tension is applied changes depending on the environmental humidity.
[0043]
  Therefore, in the present invention, there is provided a humidity detecting means for detecting the humidity inside the machine (not shown), and taking into account the change in the paper conveyance speed according to the humidity detected by the means, as shown in FIG. The linear velocities Vr0, Vr1, Vr2, Vr3, Vh0, Vh1, Vh2, Vh3 of each conveying means are set.InTherefore, the conveyance quality can be further improved.
[0044]
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the said embodiment, Various modifications can be made.
For example, although the transfer belt system is employed in the above-described embodiment, it can be applied to an apparatus using a transfer roller, and can also be applied to an apparatus using a charger that does not generate a conveyance force in the transfer unit.
[0045]
Further, in the above-described embodiment, the fixing roller system is adopted as the fixing rotating body, but it can also be applied to an apparatus using a fixing belt.
[0046]
【The invention's effect】
  Claims 1 to3According to the configuration, by using the back tension of the paper, it is possible to obtain a good transportability and to suppress the occurrence of a magnification error due to the back tension.
[0047]
  Claim4With this configuration, it is possible to more reliably suppress the occurrence of magnification error due to back tension.
  Claim5 and 6With this configuration, by using the back tension of the paper, good transportability can be obtained, and even if the transport slip rate varies depending on the paper type, the transport speed is controlled according to the properties of the paper type. The quality is further improved. In addition, because the humidity is detected and the speed control is carried out against the difference in environment due to humidity, the transport quality is improved,HiAs a result, the equality of the image quality can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view showing a wide digital copying machine as an embodiment of an image forming apparatus according to the present invention.
2 is a perspective view showing a state where an automatic document feeder of the copying machine of FIG. 1 is opened.
FIG. 3 is a perspective view illustrating an arrangement example of document size detection sensors.
FIG. 4 is a perspective view showing a detection method of a document size detection sensor.
FIG. 5 is a block diagram illustrating a control unit of the copying machine.
FIG. 6 is a block diagram showing an image processing circuit of the copying machine.
FIG. 7 is an explanatory perspective view illustrating an example of size detection of a paper feed cassette.
FIG. 8 is a perspective view illustrating a configuration of a fixing device.
FIG. 9 is a flowchart illustrating a flow of conveyance control of the copying machine.
FIG. 10 is an explanatory diagram illustrating a sheet conveyance path from a transfer unit to a fixing unit.
[Figure 11] Paper typeAccordingIt is a figure which shows the amount of change of each conveyance means.
[Figure 12] Environmental humidityAccordingIt is a figure which shows the amount of change of each conveyance means.
[Explanation of symbols]
    50 photoconductor
    53 Registration Roller
    54 Transfer belt
    55 Fixing device

Claims (6)

A registration roller that regulates the position of the leading edge of the conveyed paper;
A transfer unit disposed on the downstream side of the registration roller in the conveying direction and transferring the toner image formed on the image carrier to the paper;
Fixing means for fixing the toner image transferred by the transfer means to the paper,
In the image forming apparatus in which the linear speed of the fixing unit is higher than the linear speed of the registration roller or the transfer unit,
When conveying a sheet whose conveyance direction length is longer than the length of the sheet conveyance path from the registration roller to the fixing unit, the linear velocity of the registration roller, the linear velocity of the transfer unit, and the image carrying Using the time parameter based on the linear velocity of the body and the linear velocity of the fixing means, when the paper enters the nip portion of the fixing means and it is determined that the paper is back tensioned or the back tension changes Then, when it is determined, the linear speed of the registration roller is reduced so that the paper conveyance speed at the transfer position of the transfer means is substantially the same as the linear speed of the image carrier. . The image forming apparatus according to claim 1.
Using the time parameters based on the linear speed of the registration roller, the linear speed of the transfer means, the linear speed of the image carrier, and the linear speed of the fixing means, the paper enters the nip portion of the fixing means and When it is determined that the back tension is applied to the paper or when the back tension is changed, the paper transport speed at the transfer position of the transfer unit is substantially the same as the linear speed of the image carrier. An image forming apparatus comprising: decelerating a linear speed of the registration roller and increasing a linear speed of the fixing unit so as to balance the deceleration. The image forming apparatus according to claim 1.
Using the time parameters based on the linear speed of the registration roller, the linear speed of the transfer means, the linear speed of the image carrier, and the linear speed of the fixing means, the paper enters the nip portion of the fixing means and When it is determined that the back tension is applied to the paper or when the back tension is changed, the paper transport speed at the transfer position of the transfer unit is substantially the same as the linear speed of the image carrier. An image forming apparatus, wherein the linear speed of the fixing unit is increased and the linear speed of the registration roller is reduced so as to match the increased speed. The image forming apparatus according to claim 1 to 3,
An image forming apparatus, wherein when the trailing edge of the sheet passes through the registration roller, the sheet conveyance linear speed by the fixing unit is changed to substantially the same speed as the sheet conveyance linear speed by the transfer unit. The image forming apparatus according to claims 1 to 4,
The fixing condition of the fixing unit is selected according to the size or type of the sheet or the humidity inside the apparatus, and the linear conveying speed of the sheet by the registration roller, the transfer unit, and the fixing unit is changed according to the fixing condition. An image forming apparatus comprising a control unit. The image forming apparatus according to claims 1 to 5,
The image forming apparatus, wherein the registration roller, the transfer unit, and the fixing unit are driven by different driving sources.

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