JP4319696B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and more particularly to transport control of a recording medium.

  In an image forming apparatus such as a copying machine, a facsimile machine, or a printer, a toner image is formed on a photoreceptor used as a latent image carrier, and the toner image is electrostatically applied to a recording medium such as paper, an OHP sheet, or tracing paper. The toner electrostatically transferred from the photoconductor to the recording medium is peeled off from the recording medium simply by adhering by electrostatic force, so that the recording medium such as a sheet can be obtained by heating or pressurizing the toner. It is necessary to fix it permanently. The step of permanently fixing the toner to the recording medium is called a fixing process.

As a configuration used in the fixing process, a heat roller fixing system in which a pair of rollers are opposed to each other, one of the rollers is a fixing roller that has a built-in heat source and is in contact with toner, and the other roller is a pressure roller Or a belt fixing system in which a belt heated at a position different from a position facing the pressure roller is brought into contact with toner instead of the fixing roller.
The heat roller fixing method is most widely used because of its high thermal efficiency and safety, and the belt fixing method has an advantage that a nip width formed between the belt and the pressure roller can be increased.

  The recording medium transported to the fixing device may be transported in a direction perpendicular to the transport direction, that is, without skew (skew) caused by a shift in the recording medium width direction. This is important in preventing the occurrence of so-called deviation. The cause of such skew (skew) is that the feeding failure from the member that transports the recording medium, that is, the feeding is performed while the feeding amount in the width direction is different, or the positioning error of the feeding device. Non-uniformity of pressure distribution due to a change in outer diameter due to a non-uniform application of a conveying force due to a difference in temperature distribution in a fixing device, or the like. For this reason, if the recording medium is skewed, wrinkles will occur and abnormalities such as white spots may occur due to defective adhesion at the transfer position where the photoconductor and transfer device face each other, resulting in part of the image missing. An image is obtained.

  Conventionally, in order to prevent loosening or image rubbing due to non-uniform contact with a recording medium in a fixing device, one of a pair of rollers provided in the fixing device can be tilted with respect to the axis of the opposing roller. A configuration has been proposed in which the contact pressure in the axial direction of the roller is changed or the conveyance speed of the recording medium in the fixing device is changed (for example, Patent Document 1). With the configuration disclosed in this publication, the tension of the recording medium in the fixing device can be made constant.

JP-A-5-341675

  In addition to the fixing device, the image forming apparatus includes a photosensitive member as a latent image carrier, a transfer device using a roller or a belt disposed opposite to the photosensitive member as a latent image carrier, and both. A registration roller capable of setting and feeding the registration timing toward the transfer position formed by the image forming apparatus, and a feeding device that conveys the recording medium toward each of these devices and from the transfer position toward the fixing device. It has been.

As a method of preventing skew of the recording medium in the recording medium conveyance path using each of the above apparatuses, the conveyance speed in the fixing device is set to be higher than the conveyance speed at the position where the recording medium passes before. There is a method of applying tension to the recording medium.
When changing the conveyance speed of the recording medium depending on the position through which the recording medium passes, the tension is applied when the leading edge of the recording medium reaches the fixing device and the trailing edge is pinched by another conveyance unit. It becomes the premise of. However, depending on the length of the recording medium in the conveyance direction, the rear end may be disengaged from the conveyance unit. In this case, the conveyance speed, that is, the linear velocity, of the fixing device with which the front end is clamped is determined by the photosensitive member and the transfer device. Is higher than the conveying speed at the transfer position at which the recording medium and the recording medium face each other, the recording medium is stretched, and the magnification between the image on the photoreceptor and the image transferred to the recording medium may change. Such a phenomenon cannot be solved only by applying a tension of a recording medium intended for the fixing device, that is, applying a tension, as in the above publication. The reason for this is that when only the transport speed at the fixing device is switched to the speed for applying tension, the recording medium is driven by the fixing device if the transport speed at the previous transport section remains unchanged. As a result, a speed difference may occur with the conveyance unit before reaching the fixing device, and this speed difference may appear as an extension of the transferred image.

  In view of the problems in the conventional image forming apparatus described above, an object of the present invention is due to a change in image magnification particularly when the conveyance speed in the fixing device is different from the conveyance speed at the position where the recording medium passes before. An object of the present invention is to provide an image forming apparatus having a configuration capable of preventing the occurrence of abnormal images.

According to a first aspect of the present invention, there is provided at least one paper feeding device for transporting a recording medium from a paper feeding cassette toward a registration roller, and the recording medium transported by the paper feeding device by a latent image carrier and a transfer device. A registration roller that feeds out toward a transfer position to be formed, and a pressure mechanism that changes a clamping pressure of the recording medium in order to fix an unfixed image carried on the recording medium from the latent image carrier at the transfer position. A fixing device, and at least the speed of a driving device provided in the fixing device is changed to change the transport speed of the recording medium at the transfer position and the transport speed of the recording medium at the fixing device. in the image forming apparatus having a control unit which can be different, in the control unit, and fed from the sheet feeding device conveying speed of the recording medium between leading to the fixing device The conveyance speed V1 in the range from the paper feeding device to the registration roller, the conveyance speed V2 at the registration roller, the conveyance speed V3 at the transfer position constituted by the latent image carrier and the transfer device, and the conveyance at the fixing device A speed relationship (V1 <V2 ≦ V3 <V4) is set so that tension can be applied to the recording medium using the speed V4, and after the leading edge of the recording medium passes through the fixing device, the trailing edge of the recording medium is The timing for releasing the nipping at a position other than the fixing device is determined , and the nipping pressure and the conveyance speed at the fixing device preset in the control unit are determined according to the nipping pressure of the recording medium at the fixing device. Based on the map, the conveyance speed at the fixing device and the conveyance speed from the registration roller to the transfer position so that the conveyance speed of the recording medium at the transfer position matches the speed of the latent image carrier. It is characterized in that it comprises a structure for switching.

According to a second aspect of the present invention, at least one paper feeding device that transports a recording medium from a paper feeding cassette toward a registration roller, and the recording medium transported by the paper feeding device by a latent image carrier and a transfer device. A registration roller that feeds out toward a transfer position to be formed, and a fixing device capable of temperature control for fixing an unfixed image carried on the recording medium from the latent image carrier at the transfer position, A control unit capable of changing the conveyance speed of the recording medium at the transfer position and the conveyance speed of the recording medium at the fixing device by changing the speed of a driving device provided in the fixing device ; Rejisutoro An image forming apparatus comprising, in the control unit, and fed from the paper feeding device as the conveying speed of the recording medium between leading to the fixing device, the sheet feeding apparatus The above-mentioned recording is carried out using the transport speed V1 in the range up to 3), the transport speed V2 at the registration roller, the transport speed V3 at the transfer position constituted by the latent image carrier and the transfer device, and the transport speed V4 at the fixing device. A speed relationship (V1 <V2 ≦ V3 <V4) is set so that tension can be applied to the medium, and after the leading edge of the recording medium passes through the fixing device, the trailing edge of the recording medium is clamped at a position other than the fixing device. The recording timing at the transfer position is determined based on the map of the surface temperature and the conveyance speed at the fixing device preset in the control unit according to the fixing temperature at the fixing device. characterized in that it comprises a structure for switching the conveying speed of up to the transfer position from the conveying speed and the resist rollers in the fixing device so that the speed of the conveyor speed and the latent image carrier of the medium is matched There.

According to a third aspect of the present invention, there is provided at least one paper feeding device for transporting a recording medium from a paper feeding cassette toward a registration roller, and the recording medium transported by the paper feeding device by a latent image carrier and a transfer device. A registration roller that feeds toward a transfer position to be formed; and a fixing device that fixes an unfixed image carried on the recording medium from the latent image carrier at the transfer position, and is provided at least in the fixing device. By changing the speed of the driving device, it is possible to make the conveyance speed of the recording medium at the transfer position different from the conveyance speed of the recording medium at the fixing device, and the temperature distribution at the fixing device. in the image forming apparatus having a possible control unit indexes the, in the control unit, and fed from the sheet feeding device conveying speed of the recording medium between leading to the fixing device The conveyance speed V1 in the range from the paper feeding device to the registration roller, the conveyance speed V2 at the registration roller, the conveyance speed V3 at the transfer position constituted by the latent image carrier and the transfer device, and the conveyance at the fixing device A speed relationship (V1 <V2 ≦ V3 <V4) is set so that tension can be applied to the recording medium using the speed V4, and after the leading edge of the recording medium passes through the fixing device, the trailing edge of the recording medium is Based on the map of the temperature distribution and the conveyance speed in the fixing device preset in the control unit according to the distribution state of the fixing temperature , by determining the time when the nipping is released at a position other than the fixing device , cut, based on the conveying speed of the conveying speed and the resist rollers in the fixing device so that the speed of the conveyor speed and the image bearing member of the recording medium at the transfer position coincides to the transfer position It is characterized in that it comprises obtaining configuration.

  According to a fourth aspect of the present invention, in the image forming apparatus according to one of the first to third aspects, the transport speed can be switched according to the type of the recording medium.

  According to the present invention, when tension is applied to the recording medium by changing the conveyance speed at the position where the recording medium is conveyed before the fixing device, the conveyance process according to the clamping pressure of the recording medium at the fixing device The transfer speed of the recording medium is switched between the transfer position and the fixing device regardless of the difference in the slip ratio generated between the recording medium and the holding portion due to the change in the holding pressure. It is possible to prevent the change in the magnification of the image from occurring by eliminating the difference in the conveyance speed. In addition, since the conveyance speed of the recording medium at the time of passing through the fixing device coincides between the fixing device and the transfer position, a change in image magnification at the transfer position is prevented, and an abnormal image is surely prevented from occurring. It becomes possible.

  In addition, according to the present invention, when tension is applied to the recording medium by changing the conveyance speed between the fixing device and a position where the recording medium is conveyed before, the conveyance is performed according to the fixing temperature of the recording medium in the fixing device. Since the conveyance speed of the recording medium in the process is switched, the nipping in the fixing device is performed regardless of the change in the conveyance speed based on the difference in the fixing temperature and the change in the shape of the conveyance member caused by the distribution state of the fixing temperature. It is possible to make the tension constant on the recording medium by making the state constant and eliminate the difference between the transfer position and the conveyance speed of the recording medium at the fixing device, thereby preventing wrinkles and deviation in the width direction. It is possible to surely prevent white spots and reliably prevent a change in image magnification due to a difference in speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing an example of an image forming apparatus to which a sheet-like medium feeding device according to an embodiment of the present invention is applied. The image forming apparatus shown in FIG. 1 can be written with a laser beam. A copier. Note that the image forming apparatus according to the present invention includes not only the copying machine shown in FIG. 1 but also a printer, a facsimile machine, a printing machine, and the like. Further, the copying machine shown in FIG. 1 has a configuration capable of forming a two-color image in accordance with document information obtained in a document scanning section B described later or image information transferred.

In FIG. 1, the copying machine 1 has an image formation processing unit A positioned at the center in the vertical direction, and an original document scanning unit B at the upper part and a paper feeding unit C at the lower part with the image formation processing unit A as a boundary. ing.
The image forming processing unit A is provided with a photosensitive member 2 that forms a cylindrical latent image carrier, and around the photosensitive member 2 is along the rotation direction of the photosensitive member 2 that rotates clockwise in FIG. The second charging device 3, the first writing device 4, the first developing device 5, and the first writing device 4 for performing image forming processing are capable of writing in accordance with image information separated into different colors. A writing device 4 ′, a second developing device 5 ′ capable of supplying toner of a color different from that of the first developing device 5, a transfer device 6 and a cleaning device 7 are arranged.

The photosensitive member 2 is uniformly charged by the charging device 3 during the rotation process, and then an electrostatic latent image is formed by the writing device 4 and the second writing device 4 ′ in accordance with the image information for each color separation. When the latent image is subjected to visible image processing by the first developing device 5 and the second developing device 5 ′ to form a toner image, the toner image is fed to the paper feeding unit C by the transfer device 6. Is transferred to a sheet which is an example of a recording medium fed from (hereinafter, the recording medium will be described as a sheet).
After the transfer, the photosensitive member 2 is freed of residual toner and residual charges by the cleaning device 7 and is uniformly charged by the charging device 3 to be ready for the next image formation.

  A sheet feeding unit C that feeds a sheet for transferring a toner image includes a plurality of sheet feeding cassettes 8A, 8B, 8C, and 8D including one disposed in the image forming processing unit A. The paper feed cassettes 8A to 8D are provided with FRR-type paper feed devices 57A, 57B, 57C, and 57D that can separate sheets in a double feed state. Reference numeral 8E denotes a refeed cassette that can be temporarily accommodated by reversing sheets to be image-formed on both sides, and reference numeral 8F denotes a registration roller that sets the registration timing of the sheet. From the sheet feeding devices 57A to 57D, the sheet is fed out in the direction indicated by the one-dot chain line so as to reach the position of the registration roller 8F.

Each of the paper feed cassettes 8A to 8D has a configuration capable of instructing the size and orientation of the stored sheet, and the configuration is shown in FIG.
In FIG. 5, the paper feed cassettes 8A to 8D are provided with a size lever that can slide on the upper end wall (for convenience, the paper feed cassette 8A is indicated by reference numeral 8A1). A push switch disposed at the loading position of the sheet feeding cassette by positioning the size lever 8A1 at the position of the sheet size and sheet feeding direction (longitudinal or laterally long) written on the end wall 8A ′ as the moving surface The size data and the direction data can be discriminated by corresponding to any of the actuators 8A3 of 8A2.

  The transfer device 6 uses a belt made of a dielectric, performs electrostatic transfer of a toner image by applying a transfer bias, and electrostatic adsorption of a sheet, and also has a function of conveying the adsorbed sheet toward a fixing device 9. ing.

  The fixing device 9 has a configuration in which a heat roller system including a fixing roller 9A and a pressure roller 9B is employed. Heating via a heat source built in the fixing roller 9A and pressure applied by the pressure roller are provided. Thus, the toner carried on the sheet is fused and penetrated into the sheet.

The configuration of the fixing device 9 is shown in FIG.
In FIG. 6, the fixing device 9 includes a fixing roller 9A having a heat source 9A1 such as a halogen lamp and an infrared heater, and a pressure roller 9B in contact with the fixing roller. The fixing roller 9A includes: A heat-resistant release layer such as PFA or PTFE is provided on the surface of the core metal, and the pressure roller 9B is configured by providing a heat-resistant rubber layer such as silicon rubber on the surface of the core metal. A fixing temperature sensor 9C and a pressure temperature detecting sensor 9D capable of detecting temperature are provided on the surfaces of the fixing roller 9A and the pressure roller 9B, respectively, so that temperature management necessary for fixing is performed. That is, the output control of the heat source 9A1 is performed according to the temperature detected by the fixing temperature sensor 9C and the pressurization temperature detection sensor 9D. The temperature detection signals from the temperature detection sensors 9C and 9D are output to a control unit 15 (see FIG. 7) for image formation, which will be described in detail later, and the control mode for the heat source 9A1 is set in the control unit 15. It has become.

The pressure roller 9B is rotatably supported at both ends of the rotation shaft, and the contact pressure against the fixing roller 9A is controlled by a pressure mechanism denoted by reference numeral 11 in FIG.
In FIG. 6, the pressure mechanisms 11 are provided at both axial ends of the rotation shaft 9B1 of the pressure roller 9B, respectively, and a pressing member 11A capable of swinging the rotation shaft 9B1 toward the fixing roller 9A, and a pressing member The drive lever 11B has one end engaged with one of the swing ends of 11A and can swing in a direction perpendicular to the pressing member 11A, and one end in the longitudinal direction is hooked to the other end of the drive lever 11B. The other end in the longitudinal direction of the elastic body 11C such as a spring is connected, and an anchor member 11D that can reciprocate in a direction to swing the drive lever 11B, and a screw rod 11E that meshes with a bent piece 11D1 formed on the anchor member 11D. Driven gear 11F having a shaft as a support shaft, idler 11G meshing with driven gear 11F, and drive teeth attached to the output shaft of drive motor 11H capable of rotating forward and reverse And a 11J.

In the pressurizing mechanism 11, when the rotation of the drive motor 11H is transmitted to the driven gear 11F, the moving direction of the anchor member 11D engaged with the screw rod 11E is set according to the rotating direction of the driven gear 11F, and the anchor member 11D The drive lever 11B swings through the elastic body 11C according to the moving direction.
The amount of swing of the drive lever 11B varies depending on the amount of rotation of the drive motor 11H, and the amount by which the rotary shaft 9B1 of the pressure roller 9B is displaced toward the fixing roller 9A by the pressing member 11A varies. As a result, the pressure roller 9B changes the pressing force against the fixing roller 9A, in other words, the clamping pressure of the sheet passing through the nip portion formed by the opposed contact portion between the fixing roller 9A and the pressure roller 9B. become.

The elastic body 11C whose one end in the longitudinal direction is hooked on the drive lever 11B maintains the contact pressure against the fixing roller 9A at the preset nip portion. For this reason, the anchor member 11D Is provided with a position sensor 11K capable of detecting the backward movement position thereof.
The position sensor 11K can detect the position where the anchor member 11D moves backward depending on the rotation direction of the drive motor 11H, and the fixing roller 9B is displaced when the pressure roller 9B is displaced in a direction to weaken the pressure with respect to the fixing roller 9A. This is a member that can control the rotation of the drive motor 11H so as to stop the anchor member 11D at a position where the initial contact pressure of the pressure roller 9B with respect to 9A is obtained.

  The fixed sheet may be discharged toward the paper discharge tray 10C, or may be sorted according to the page order or each image, and the sorted sheets are separated into the plurality of paper discharge trays 10A and the stapler 10B, respectively. It is discharged toward the aftertreatment device 10 provided. Further, the sheet after fixing may be used for image formation on both sides in addition to the case of the post-processing apparatus 10 described above. In this case, the reverse conveyance branched from the paper discharge unit in the fixing apparatus 9. It is discharged toward the road (indicated by the symbol RP for convenience).

  The reverse conveyance path RP reaches the position of the registration roller 8F via the refeed cassette 8E, and the reversed sheet is fed out again toward the transfer position of the photosensitive member 2. For this reason, in the reverse conveyance path RP, the switching claw P1, which switches the conveyance direction of the sheet discharged from the fixing device 9, the feeding roller P2, the feeding roller P3A and the feeding roller P3A, and the rotation direction pushes back the sheet. A sheet separation mechanism P3 including a separation roller P3B that rotates in the direction is provided, so that the sheet discharged from the fixing device 9 and reversed can be fed toward the registration roller 9F. Although FIG. 1 shows a state in which the paper discharge tray 10C is disposed above the post-processing apparatus 10, when the post-processing apparatus 10 is not provided, the sheet conveying direction in the fixing apparatus 9 is extended. A sheet discharge tray 10C is positioned on the line.

  The original scanning unit B is applied to a scanning optical system B2 for reading a document placed on a document placing table B1 disposed on the upper surface of the image forming processing unit A, an automatic document feeder B3, and a double-sided image. The reverse conveying member B4 is provided in a lid member B5 that can be opened and closed. The automatic document feeder B3 is also equipped with a document conveying belt B7 for introducing the document loaded on the document loading tray B6 onto the document loading table B1.

The scanning optical system B2 includes a light source B2A for irradiating illumination light to the document on the document table B1 and a first mirror B2B for switching the optical path of reflected light from the document, and is capable of reciprocating. The second and third mirrors B2C and B2D are set to have a relationship of 1: 2 in moving speed with B20 and the first scanning carriage B20 and can reciprocate and reverse the optical path of the reflected light from the first scanning carriage B20. And an optical lens B2F that forms an image of reflected light from the original toward a full-color CCD B2E capable of color separation.
In the scanning optical system B2, image information separated into R, G, and B colors by the full-color CCD B2E is output to a control unit used for image formation.

  The automatic document feeder B3 is a reverse roller as a feed roller B3A for feeding a document on the document placement tray B6 toward the document placement table B1, a document size detection sensor B3B, a document length detection sensor B3D, and a reverse conveyance member B4. A claw and a discharge roller B3E are provided, respectively, and a document from the document placement tray B6 is brought to the document placement table B1 and scanned by the feed roller B3A and the document transport belt B7, and then discharged by the discharge roller B3E. The case where the sheet is conveyed toward the discharge tray B3F and the case where the sheet is reversed not by the discharge roller B3E but reversed by the reverse conveying member B4 and brought back on the document placing table B1 for the duplex scanning can be selected. It has become. In any case, the document fed from the document placing tray B6 is fed in the width direction by the document size detection sensor B3B and the length detection sensor B3C in the process of being fed toward the document transport belt B7 by the feed roller B3A. The length in the feeding direction is detected. Detection data relating to the detected document size and orientation is output from each sensor to the control unit 15 (see FIG. 7) used for image formation.

  As shown in FIG. 2, the automatic document feeder B3 is provided so as to be openable and closable with respect to the document placing table B1 via a hinge B3A. The document placing table B1 is provided in the vicinity of one hinge B3A1. The claw B3B disposed on the upper surface of the apparatus main body is located. The claw B3B is opposed to the hole B31 formed on the automatic document feeder B3 side, and can enter the hole B31 when the automatic document feeder B3 is closed. The claw B3B entering the hole B31 can be opposed to the lift-up detection sensor B3C and the document detection timing sensor B3D provided on the automatic document feeder B3 side. The lift-up detection sensor B3C The state of entering, in other words, the state in which the automatic document feeder B3 is closed is detected, and the timing for detecting the size of the document located on the document table B1 is set by the document detection timing sensor B3D. ing. In FIG. 2, reference numerals B1A and B1B indicate the end face scale of the document.

As shown in FIG. 3, document size detection sensors 12 to 14 are arranged below the document table B1.
The document size detection sensors 12 to 14 all have the same configuration, and details thereof are shown in FIG.
In FIG. 4, an original size detection sensor (explained for the sake of convenience with reference to a sensor denoted by reference numeral 14) irradiates the original by dispersing light from one light-emitting diode 14A into three beams and reflects the reflected light. A reflection type sensor that receives light by three light receiving elements 14B to 14D disposed inside the optical system, and transmits light from below the document table B1 to the document table B1 and reflects from the document surface. The presence or absence of a document can be detected by receiving light. The document size detection sensors 12 to 14 always irradiate three beams, and the document is detected based on the position where the light receiving element received by the presence or absence of a signal from the light receiving element when the document detection timing sensor B3D is turned on. The document size can be detected along with the presence or absence of.

In FIG. 1, a first writing device 4 includes a laser output unit 4A capable of emitting laser light, and for writing and scanning the laser light in the main scanning direction corresponding to the axial direction when the photosensitive member 2 has a drum shape. The rotary polygon mirror 4B, the fθ lens 4C, and the mirror 4D are provided, and one of the color images separated by the full-color CCD B2E located in the scanning optical system B2, according to the image information corresponding to the black image in this embodiment. Writing processing for forming the electrostatic latent image, that is, laser beam emission control is performed.
Although not shown in detail in the second writing device 4 ′ in FIG. 1, the second writing device 4 ′ is composed of a writing unit that uses a plurality of LEDs juxtaposed in the main scanning direction as a light source.

On the other hand, the paper feeding devices 57A, 57B, 57C, and 57D for feeding the sheet toward the transfer position where the photosensitive member 2 and the transfer device 6 face each other are different only in the size and orientation of the sheets to be accommodated. Since the configuration for feeding is the same, the lowermost sheet feeding device 57D will be described as a representative. The sheet feeding device 57D includes a pickup roller 11 for feeding out the sheets stacked on the sheet feeding tray 8D, and a feed roller. A roller 12, a reverse roller 13 pressed against the feed roller 12, a guide 8G, and a conveying roller 8H are arranged.
The copying machine shown in FIG. 1 is provided with a manual feed tray 81 that can feed different or different size sheets that are not accommodated in the paper feeding device. An FRR paper feeding device 57E is provided correspondingly. Is provided. The paper feeding device 57E has the same configuration as the paper feeding device 57D.

In the copying machine having the above-described configuration, the image forming process is controlled by the control unit 15 shown in FIG.
In FIG. 7, the control unit 15 includes a system controller 15A corresponding to a configuration in which a main part is configured by a microcomputer and can control the sheet conveyance speed. The system controller 15A includes an operation unit. A controller 15B, an image processing controller 15C, an ADF controller 15D that controls the automatic document feeder B3, a paper feed tray controller 15E that controls the paper feeder, a FAX controller 15F, and a printer controller 15G are connected to each other.
The system controller 15A is a process controller capable of sequence control for sheet feeding, conveyance, fixing, double-sided printing and the like related to image forming processing, and the operation unit controller 15B is an operation unit using an operation panel or the like. It is a part that controls display control for the liquid crystal display unit 15B1 and various LED display units and input control of various input keys 15B2. The image processing controller 15C is used for image information processing used for image formation, manuscript and writing. The FAX controller 15F is a part that performs transmission / reception management and file management when the copying machine 1 used as image forming processing has a function as a facsimile machine. The printer controller 15G is a part that performs scanning control. Printer function when equipped with It is a part for data reception management and file management.

The system controller 15A including the image processing controller 15C is configured as shown in FIG.
Referring to FIG. 8 together with the configuration and functions, the reflected light from the original on the original table B1 is read by the full-color CCD B2E provided in the scanning optical system B2. The color-separated analog image signal photoelectrically converted by the full color CCDB 2E is amplified and corrected by the signal processing unit 16, is subjected to digital signal processing by the AD converter 17 and is subjected to shading correction by the shading correction circuit 18, and is then processed by the image processing unit. 19 is output.

  In the image processing unit 19, image processing such as MTF correction, γ correction, black image generation, color image generation, binary processing and multi-value processing is performed, and black image data and other color image data, that is, color image data. Is output to the selector 20. In the selector 20, the destination of the image signal is switched to the scaling unit 21 or the image memory controller 22.

The image signal that has passed through the scaling unit 21 is enlarged / reduced in accordance with the scaling ratio and sent to the writing unit 23. The image memory controller 22 and the selector 20 are configured to be able to input and output image signals in both directions.
In addition, a CPU 24 for setting the image memory controller 22 and the like and controlling the reading unit and the writing unit, and a ROM 24A and a RAM 24B for storing programs and data thereof are provided. Further, the CPU 24 can write and read data in the image memory 22 </ b> A via the memory controller 22.
The image sent to the image memory controller 22 </ b> A 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 22. By performing image compression, a limited image memory can be used effectively. In addition, since a large amount of original image data can be stored at a 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 22A is output while being blown out by the expansion device in the memory controller 22. On the other hand, at the time of FAX transmission, the selector 20 transfers black data to the FAX image memory 15F1. At the time of FAX reception, the received data is demodulated and expanded from the line, and then developed in the FAX image memory 15F1, and then sent to the writing unit 22 by the selector 20. Further, when receiving the printer data, the data is expanded in the printer image memory 15G1 and then sent to the writing unit 23 by the selector 20.

In the present embodiment, the control unit 15 performs the following control.
(1) When a sheet longer than the distance from the position of the registration roller 8F to the fixing device 9 is conveyed, the relationship of the sheet conveyance speed in this section is as follows:
V1 <V2 ≦ V3 <V4
However, V1: Conveying speed (linear speed) in the range from the paper feeder to the registration roller 8F
V2: Conveying speed (linear speed) by registration roller 8F
V3: Conveying speed (linear speed) at the transfer position constituted by the photosensitive member 2 and the transfer device 6
V4: Conveying speed (linear speed) in the fixing device 9
Is set.
Such a speed-related setting is intended to apply tension to the long sheet.
(2) When the relationship described in (1) is assumed, the conveyance speed at each position is adjusted based on the type and size of the sheet to be conveyed so as not to cause an image magnification error, and the sheet is conveyed. By adjusting the conveyance speed at each position in response to changes in (1) temperature, (2) temperature distribution, and (3) nipping pressure on the sheet at the fixing device 9 at the time, a magnification error is caused. The difference between the conveyance speed at the fixing device 9 and the conveyance speed at the transfer position is eliminated, and the conveyance speed is made to coincide. The following items are listed as conditions in this case.
In this embodiment, when the items listed in the above (1) to (3) are changed, the time when the tension applied to the sheet is changed is determined, and the sheet conveyance speed is fixed corresponding to the time. It is characterized in that the apparatus 9 and the transfer position are changed so as to coincide with each other.

Hereinafter, the contents of the control will be described as follows.
In the present embodiment, the sheet size specified by the user in the sheet feeding cassettes 8A to 8D and the direction when feeding are determined by the size lever 8A1 (see FIG. 5) and the push switch 8A2 (see FIG. 5) and various inputs. Based on the thickness specified by the operation unit controller 15B using the key 15B2 and the type of sheet such as plain paper, tracing paper or film, the fixing conditions in the fixing device 9, that is, the fixing temperature, fixing pressure and fixing time. When determined, the sheet conveying speed by the driving device in the fixing device 9 and the device provided before the sheet passes is set. In this case, the speed (linear speed) is set so that the initial set speed (linear speed) at each position is Vr0, the speed at the registration roller 8F to the transfer device (transfer belt) 6 is Vr0, and the speed at the fixing device 9 is set. Is set to Vh0, and the speed of the photosensitive member 2 is set to Vd, the relationship of the linear velocity of the sheet fed from the sheet feeding device <Vr0 = Vd <Vh0 is set on condition that tension can be applied to the sheet.

On the other hand, when the leading end of the sheet is clamped by the fixing device 9 due to the setting of the speed relationship, the tension is gradually weakened when the clamping is released at a position before the fixing device 9 except for the leading end. Depending on the relationship, the sheet speed in the fixing device 9 and the speed at the transfer position with respect to the photosensitive member 2 are different. For this reason, the above-described initial setting speed is changed in consideration of the occurrence of an image magnification error due to a relative speed shift.
In this embodiment, the timing (timing) at which the sheet tension is weakened is determined with respect to the sheet conveyance speed in the fixing device 9 that is set in advance according to the fixing conditions in the fixing device 9, and the sheet in each device is determined at that time. The sheet conveying speed at the fixing device 9 side is made to coincide with the sheet conveying speed at the transfer position with respect to the photoconductor.

The timing for changing the speed (timing: Tn) is obtained by the following equation.
Tn = T01 + (L0−L1) / (Vh0−Vr0)
However, T01: distance from the registration roller 8F to the leading edge of the sheet at the nip portion of the fixing device 9
L0: The distance at which the leading edge of the sheet is conveyed toward the transfer position with the photoreceptor 2 as indicated by the solid line in FIG.
L1: As indicated by a broken line in FIG. 9, the linear distance between the transfer position with the photosensitive member 2 and the fixing device 9 The timing Tn at which the speed is changed is a timer count when the leading edge of the sheet is fed out from the registration roller 8F. The speed is changed when the time is reached. For example, when the change time (T1) based on the initial speed setting described above is reached, the speed of the registration roller 8F to the transfer device (transfer belt) 6 is changed from Vr0 to Vr1 with the speed Vd of the photoconductor 2 as a reference, and the fixing device. The speed at 9 is changed from Vh0 to Vh1, and the speed relationship at this time is set to Vr1 <Vd ≦ Vh1. As a result, the sheet is set so that the speed at the transfer position becomes the speed of the photosensitive member 2 in a state where the tension application by the fixing device 9 is maintained.

  On the other hand, while the leading end side of the sheet is nipped by the fixing device 9 in the sheet size, the tension applied to the sheet is weakened when the trailing end passes through the nipping portion located before the fixing device, and the fixing device 9 speed is increased. Will move depending on. In this case, the sheet moving speed is faster than the speed of the photoconductor 2 due to the speed relationship between the fixing device 9 and the photoconductor 2, so that the time when such a phenomenon occurs is determined and the position at each position is determined. Change the sheet transport speed. The opportunity for such a phenomenon to occur includes a time point when the trailing edge of the sheet finishes passing through the registration roller 8F.

  In this embodiment, when the back tension is weakened, T2 is the time when the trailing edge of the sheet comes out of the nipping portion of the paper feeding device, and T3 is the time when the trailing edge of the sheet comes off from the registration roller 8F. When T2 reaches T2, the speed at the registration roller 8F to the transfer position is changed to Vr2, and the speed at the fixing device 9 is changed to Vh2. When the timer count reaches T3, the speed from the registration roller 8F to the transfer position is changed to Vr3, and the speed at the fixing device 9 is changed to Vh3.

The speed to be changed according to the time when the tension is weakened is set to the following relationship.
Linear velocity at paper feed position <Vr1 <Vr2 <Vr3 ≦ Vd ≦ Vh3 <Vh2 <Vh1
Note that the timer count is not limited to the time when the leading edge of the sheet is fed out from the registration roller 8F as described above, but the time when the feeding of the sheet from the paper feeding device is started, and the paper discharge sensor after fixing (illustrated). It is also possible to assume the time when the leading edge of the sheet reaches the fixing device and the trailing edge comes out of the other clamping portion.

The speed change timing determination and speed change processing will be executed according to the following procedure as described in the flowchart shown in FIG.
In FIG. 10, a data check regarding the sheet size and type specified by the user is performed in advance (ST1), and fixing conditions (fixing temperature, fixing pressure, fixing time) are set according to the contents of the specified data ( ST2). Of the fixing conditions, the fixing time affects the sheet conveyance speed.

When a paper cassette containing a sheet of a specified size and orientation is selected (ST3), initial speeds in the above-described apparatuses are set including the speed when the sheet is fed out from the paper cassette. (ST4) Sheet feeding is started (in FIG. 10, “Feed start” is displayed: ST5).
When it is detected by the sensor that the sheet has been fed out and reaches the registration roller 8F (ST6), the timer count is started with the timing when the leading edge of the sheet is fed out from the registration roller 8F as a start time (ST7). As described above, the sheet speed at this time is set to Vr0 from the registration roller 8F to the transfer position, and to Vh0 at the fixing device 9 (ST8).
When the timer count is determined (ST9) and it is determined that the change time (T1) has been reached, the initially set speed is changed to the next speed (ST10). Thereafter, the speed is changed every time the timer count reaches the change time (ST11 to ST14).

  The timer count is set at a time when the tension of the sheet is weakened, and the speed is changed at each time to suppress the difference in the moving speed of the sheet due to the tension between the transfer position with the photosensitive member 2 and the fixing device 9. Therefore, the magnification error between the transferred image at the transfer position and the image carried on the photosensitive member 2 can be eliminated.

  On the other hand, it is necessary to consider that the slip rate in the nipping and conveying unit varies depending on the material of the conveyed sheet. In the present embodiment, with respect to the slip ratio, which is one of the causes of skew, skew is more likely to occur due to the fact that the leading edge curl is more likely to occur in tracing paper than plain paper. Therefore, in the case of tracing paper, unlike other sheets, it is necessary to increase the back tension and stabilize the conveyance. Therefore, as shown in FIG. 11, the speeds (Vr0, Vr1, Vr2, Vr3, Vh0, Vh1, Vh3, Vh3) at the above-described change time are set differently depending on the material of the sheet. In the present embodiment, the speed can be calculated by a paper type coefficient α set in advance according to the sheet material. Assuming that the paper type coefficient α is αp for plain paper, αt for tracing paper (shown as trepe in FIG. 11), and αf for film, the initial setting is 1 ≦ αf. ≦ αp ≦ αt ≦ 1.0005 is established. The paper type coefficient is used to change the change time (Tn) or change the speed. As a result, even if the slip rate varies depending on the sheet material, the tension application efficiency during sheet conveyance can be kept high by changing the speed.

  In the present embodiment, the speed is changed in accordance with the temperature change, temperature distribution and pressure applied by the fixing device 9, that is, the clamping pressure on the sheet, based on the above premise. Hereinafter, embodiments relating to speed change will be described for each claim.

First Embodiment In this embodiment, the speed is changed based on a change in the fixing pressure in the fixing device 9, that is, the pressure applied to hold the sheet.
The fixing pressure is set in advance in the initial condition, but as the number of image formation increases, the heat supply from the heat source 9A1 provided in the fixing roller 9A may not catch up. For this reason, the surface temperature of the fixing roller 9A is lowered, which may cause a pressure drop at the nip portion due to a change in outer diameter. In this embodiment, the fixing pressure is increased according to the temperature drop of the fixing roller, the contact pressure to the sheet is made uniform, and the amount of heat supplied to the sheet is made constant. Therefore, as shown in FIG. 12, the control unit 15 registers the relationship between the fixing temperature and the pressing force (one-side pressing force) in advance as a map, and according to the result of detecting the surface temperature of the fixing roller 9A. The drive amount and drive direction of the drive motor 11H in the pressurizing mechanism 11 shown in FIG. 6 are controlled. As a result, the fixing pressure changes, and the sheet conveyance speed is changed in accordance with the change. The speed at this time is selected from the map shown in FIG.

In the present embodiment, the procedure shown in the flowchart shown in FIG. 14 is executed by the configuration as described above.
In FIG. 14, while the surface temperature of the fixing roller 9A is detected, the driving of the registration roller 8F is waited (ST15). When the detection data of the fixing temperature is output, the fixing pressure is changed according to the temperature change. (ST16, 17). The change value in this case is based on the maps shown in FIGS.
When the sheet conveyance speed (linear speed) at each position is determined according to the fixing temperature, the fixing pressure (pressing force), and the fixing temperature, the leading edge of the sheet is fed out from the registration roller 8F. The change time is monitored.

Second Embodiment In this embodiment, the speed is changed based on a change in fixing temperature in the fixing device 9.
The surface temperature of the fixing roller 9A is maintained at a predetermined fixing temperature by heating by the heat source 9A1, but when the temperature changes, the peripheral speed is not constant due to a change in the outer diameter. For this reason, even when a predetermined transport speed is set in the fixing device 9, the actual transport speed may change. Therefore, this embodiment is characterized in that the conveyance speed in the fixing device 9 is corrected according to the detection result of the surface temperature of the fixing roller. The correction amount in this case is based on the map shown in FIG.

Third Embodiment In this embodiment, the sheet conveyance speed is changed based on a change in the temperature distribution in the axial direction of the rollers constituting the sheet nip portion in the fixing device 9.
The sheet to be fixed in the fixing device 9 has various sizes, and when a small-sized sheet is continuously subjected to fixing, a surface that is in continuous contact with a roller surface that does not contact the sheet. And the temperature distribution is different. When small-size sheets are continuously fixed in large quantities, the temperature drop on the end side is less than the central part in the axial direction of the roller, and the difference in outer diameter increases, resulting in a shape in the axial direction. Becomes a drum shape, and the peripheral speed at the axial end is increased. For this reason, deviation tends to occur in the width direction of the sheet passing through the nip portion, and image blurring and wrinkles occur. Therefore, in this embodiment, a plurality of temperature detection sensors (not shown) for detecting the temperature distribution on the roller surface in the fixing device 9 are provided in the axial direction on the surface of the fixing roller 9A, and the temperature distribution on the surface is detected. In accordance with the result, the speed (linear speed) of each apparatus that affects the sheet conveyance speed at each position is changed based on the map shown in FIG. In this case, the temperature distribution is determined by providing a temperature detection sensor at each of the passing positions of the minimum size and the maximum size on the roller surface, and determining the temperature difference between the temperature detection sensors.

1 is a schematic diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view showing a configuration of an automatic document feeder used in a copying machine that is the image forming apparatus shown in FIG. 1. FIG. 2 is a perspective view illustrating an arrangement configuration of document size detection sensors provided on a document placement table used in the document scanning unit illustrated in FIG. 1. FIG. 4 is a diagram illustrating a configuration of a document size detection sensor illustrated in FIG. 3. FIG. 6 is a perspective view showing a sheet size and orientation designation structure provided in a paper feed cassette used in the paper feed device. FIG. 2 is a partial perspective view illustrating a configuration of a fixing device used in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a block diagram for explaining a configuration of a control unit corresponding to a configuration for changing a sheet speed in the image forming apparatus shown in FIG. 1. It is a block diagram for demonstrating the structure and function of the system controller and image processing controller which are used for the control part shown in FIG. FIG. 6 is a schematic diagram for explaining a distance relationship between a fixing device and a transfer position in a sheet conveyance process. It is a flowchart for demonstrating one of the effect | actions of the control part shown in FIG. It is a table for demonstrating the relationship between the material of a sheet | seat, and a change speed. FIG. 6 is a table for explaining a relationship between a sheet material, a fixing temperature, and a pressure. FIG. 6 is a table for explaining the relationship between a fixing pressure used for holding a sheet and a change speed. It is a flowchart for demonstrating the control based on the relationship between the fixing pressure shown in FIG. 13, and a change speed. It is a table for explaining the relationship between the fixing temperature and the change speed. It is a table for explaining the relationship between the temperature distribution due to the fixing temperature difference and the change speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copying machine which is image forming apparatus 2 Photoconductor which is latent image carrier 6 Transfer device 8A-8D Paper feed cassette 8F Registration roller 9 Fixing device 9A Fixing roller 9B Pressure roller 9C Fixing temperature detection sensor 9D Pressure temperature detection sensor 15 Control unit for changing speed

Claims (4)

At least one paper feeding device that transports the recording medium from the paper feeding cassette toward the registration roller, and the recording medium transported by the paper feeding device is fed toward a transfer position formed by the latent image carrier and the transfer device. A registration roller, and a fixing device having a pressurizing mechanism for changing a clamping pressure of the recording medium in order to fix an unfixed image carried on the recording medium from the latent image carrier at the transfer position,
Control capable of making the conveyance speed of the recording medium at the transfer position different from the conveyance speed of the recording medium at the fixing device by changing at least the speed of the driving device provided in the fixing device. In an image forming apparatus having a section ,
In the control unit, the conveyance speed of the recording medium from the sheet feeding device to the fixing device is defined as a conveyance speed V1 in a range from the sheet feeding device to the registration roller, and a conveyance speed at the registration roller. V2 is a speed relationship (T1 <V2 ≦ V3 <V4) where tension can be applied to the recording medium using a transport speed V3 at a transfer position constituted by the latent image carrier and a transfer device, and a transport speed V4 at the fixing device. )
After the leading edge of the recording medium passes through the fixing device, the timing at which the trailing edge of the recording medium is released at a position other than the fixing device is determined, and according to the clamping pressure of the recording medium at the fixing device. Thus , based on the map of the clamping pressure and the conveyance speed in the fixing device preset in the control unit, the conveyance speed of the recording medium at the transfer position and the speed of the latent image carrier are matched. An image forming apparatus comprising a configuration for switching between a conveyance speed in the fixing device and a conveyance speed from the registration roller to the transfer position . At least one paper feeding device that transports the recording medium from the paper feeding cassette toward the registration roller, and the recording medium transported by the paper feeding device is fed toward a transfer position formed by the latent image carrier and the transfer device. A registration roller, and a fixing device capable of temperature control for fixing an unfixed image carried on the recording medium from the latent image carrier at the transfer position,
Control capable of making the conveyance speed of the recording medium at the transfer position different from the conveyance speed of the recording medium at the fixing device by changing at least the speed of the driving device provided in the fixing device. In an image forming apparatus having a section ,
In the control unit, the conveyance speed of the recording medium from the sheet feeding device to the fixing device is defined as a conveyance speed V1 in a range from the sheet feeding device to the registration roller, and a conveyance speed at the registration roller. V2 is a speed relationship (T1 <V2 ≦ V3 <V4) where tension can be applied to the recording medium using a transport speed V3 at a transfer position constituted by the latent image carrier and a transfer device, and a transport speed V4 at the fixing device. )
After the leading edge of the recording medium has passed through the fixing device, the timing at which the trailing edge of the recording medium is released at a position other than the fixing device is determined , and according to the fixing temperature in the fixing device, On the basis of a map of the surface temperature and the conveying speed at the fixing device preset in the control unit, the fixing device so that the conveying speed of the recording medium at the transfer position matches the speed of the latent image carrier. And an image forming apparatus, wherein the image forming apparatus is configured to switch between a conveying speed at the transfer roller and a conveying speed from the registration roller to the transfer position . At least one paper feeding device that transports the recording medium from the paper feeding cassette toward the registration roller, and the recording medium transported by the paper feeding device is fed toward a transfer position formed by the latent image carrier and the transfer device. A registration roller, and a fixing device for fixing an unfixed image carried on the recording medium from the latent image carrier at the transfer position,
By changing the speed of at least the driving device provided in the fixing device, it is possible to make the conveyance speed of the recording medium at the transfer position different from the conveyance speed of the recording medium at the fixing device. In addition, in the image forming apparatus provided with a control unit capable of determining the temperature distribution in the fixing device ,
In the control unit, the conveyance speed of the recording medium from the sheet feeding device to the fixing device is defined as a conveyance speed V1 in a range from the sheet feeding device to the registration roller, and a conveyance speed at the registration roller. V2 is a speed relationship (T1 <V2 ≦ V3 <V4) where tension can be applied to the recording medium using a transport speed V3 at a transfer position constituted by the latent image carrier and a transfer device, and a transport speed V4 at the fixing device. )
After the leading edge of the recording medium passes through the fixing device, the timing at which the trailing edge of the recording medium is released at a position other than the fixing device is determined , and the control is performed according to the distribution state of the fixing temperature. In the fixing device, the conveyance speed of the recording medium at the transfer position and the speed of the latent image carrier coincide with each other based on a map of the temperature distribution and the conveyance speed in the fixing device preset in the unit. An image forming apparatus comprising: a switching speed between the registration roller and the transfer speed from the registration roller to the transfer position . The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein the conveyance speed can be switched according to the type of the recording medium.

Images