JP5486770B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system, and more particularly to an image forming apparatus including a fixing device that conveys paper by a pressure member. is there.

  A fixing device in a conventional image forming apparatus includes a heating roller maintained at a predetermined temperature, and a pressure roller that is in pressure contact with the heating roller, and a nip portion formed by the pressure contact between the pressure roller and the heating roller. Thus, there is known a roller fixing system in which a sheet (transfer material) carrying an unfixed toner image is heated while being nipped and conveyed. In addition, recently, the apparatus includes a fixing roller disposed opposite to the pressure roller, a heating roller, and an endless fixing belt stretched between the fixing roller and the heating roller. A belt fixing system in which an unfixed toner image is pressure-fixed on a transfer material by applying heat from a heating roller to the transfer material via a fixing belt at a nip portion formed by the pressure contact is performed.

  However, when the transfer material is introduced into the nip portion and heated and pressed as in the roller fixing method and the belt fixing method, the transfer member is sandwiched depending on the temperature state of the constituent members such as the pressure roller and the heating roller. In some cases, the conveyance speed fluctuated.

  For example, in the belt fixing system, the pressure roller is driven to rotate, the fixing belt is driven to rotate, and the transfer material is nipped and conveyed to the nip portion. When the heat of the belt is transmitted to the pressure roller, the temperature of the pressure roller rises, and the pressure roller formed of a rubber material or the like thermally expands and the outer diameter of the pressure roller increases. On the other hand, when the pressure roller is driven at a constant rotational speed, the outer diameter of the pressure roller increases as the pressure roller becomes higher in temperature, thereby increasing the peripheral speed of the pressure roller. In addition, the nipping and conveying speed of the transfer material is increased. The same applies to the roller fixing method, and as the apparatus is driven, the outer diameter of the pressure roller increases, so the speed at which the transfer material is nipped and conveyed also increases.

  On the other hand, since transfer of the transfer material at, for example, the image transfer unit upstream of the fixing device is controlled at a predetermined constant speed, the transfer material is held in a nipped and transported state in both the image transfer unit and the nip portion of the fixing device. In this state, depending on the temperature of the nip portion, the conveying speed of the fixing device becomes faster than the conveying speed of the image transfer portion, so that the fixing device pulls the transfer material, and the image to be transferred is transferred in the image transfer portion. There was a gap.

  In order to eliminate such transfer image misalignment, the nipping / conveying speed of the fixing device is set so that a loop as a slack is formed on the transfer material conveyed between the image transferring portion and the fixing device. If the transfer speed is set slower than the initial speed, the occurrence of a phenomenon that the transfer material is pulled during that time can be prevented. On the other hand, if the transfer speed of the transfer material in the image transfer unit exceeds the clamping transfer speed of the fixing device, an unnecessarily loop is formed in the transfer material. Becomes unstable, causing an offset in the fixing device. Therefore, it is necessary that the transfer material is transported in an appropriate loop between the image transfer unit and the fixing device.

  Therefore, in Patent Document 1, a loop amount detection unit that detects the amount of loop formed by the transfer material between the image transfer unit and the fixing device in a state where the transfer material is simultaneously held by the image transfer unit and the fixing device. In order to switch and control the nipping and conveying speed of the transfer member at the nip portion of the fixing device in accordance with the detection result of the loop amount detecting means, the rotation speed of the fixing motor that rotates the pressure roller is switched. At this time, a thermistor is disposed on the surface of the pressure roller, and the nipping and conveying speed of the fixing device is set based on the detected temperature of the thermistor in consideration of the thermal expansion of each component in accordance with the fixing temperature control status. In another embodiment, the temperature of the thermistor installed on the side surface opposite to the nip portion is monitored, and the temperature of the pressure roller, that is, the amount of expansion is simply predicted.

However, in the above-described prior art, the dedicated thermistor for calculating the thermal expansion is arranged in the pressure roller, so that the thermal expansion of the pressure roller is led based on the temperature detected from the pressure roller itself, Although the nipping and conveying speed of the nip portion of the fixing device can be set accurately, there is an inconvenience that the thermistor and the number of parts related to it increase and the production cost increases. In addition, when a thermistor is installed on the opposite side of the nip, the amount of expansion can only be predicted simply, and a wide range from the initial heating temperature of the heating belt etc. to the temperature at the time of fixing. In the temperature range, there is a problem that it is difficult to accurately predict the change in the pressure roller diameter due to thermal expansion, and it is difficult to correct the nipping and conveying speed of the nip portion.
JP 2007-72289 A (paragraphs [0037] to [0040], [0055], FIG. 2)

  The present invention has been made to solve the above-described problems, and an image forming apparatus that accurately corrects the nipping / conveying speed of the fixing nip portion according to a temperature change of the fixing apparatus with a simple apparatus configuration. The purpose is to provide.

  To achieve the above object, the present invention provides a heating member having a heat source, a pressure member disposed in pressure contact with the heating member, a temperature detection member for detecting the temperature of the heating member, and the pressure member. And a control unit for controlling the rotation of the driving unit. A sheet carrying an unfixed toner image is formed in a nip formed by the press contact between the heating member and the pressing member. In the image forming apparatus that passes the paper and performs heat fixing, the control unit controls the number of rotations of the driving unit based on the temperature detected by the temperature detecting member, regardless of the temperature of the pressure member. The pressurizing member is set to a predetermined peripheral speed.

  According to this configuration, when the heating member heated by the heat source is pressed against the pressure member, the heat of the heating member is transmitted to the pressure member, and the temperature of the heating member is lowered. This falling temperature is detected by the temperature detection member. The control unit estimates the temperature of the pressure member based on the descending temperature of the heating member, and controls the rotation speed of the driving unit so as to rotate the pressure member at a predetermined peripheral speed.

  In the invention according to claim 2, the control unit detects the temperature detected by the temperature detecting member at the start of rotation of the driving means and the detected temperature detected by the temperature detecting member after a predetermined time from the start of rotation. The number of rotations of the driving means is controlled based on the difference in temperature of the heating member. According to this configuration, when heat is transmitted from the heating member to the pressure member, the temperature of the heating member decreases, but the temperature detection member detects a temperature difference at which the heating member descends from the start of rotation of the driving means to a predetermined time. Then, the control unit estimates the temperature of the pressure member based on the temperature difference.

  According to a third aspect of the present invention, the control unit is based on a heating member temperature difference from a detected temperature of the temperature detecting member that is detected after the first and second predetermined time from the start of rotation of the driving unit. The rotational speed of the driving means is controlled. According to this configuration, when the heat is transmitted from the heating member to the pressure member, the temperature of the heating member decreases. However, the temperature difference between the temperature detection member and the heating member is lowered while the heating member is uniformly heated by the heat source. , And the control unit estimates the temperature of the pressure member based on the temperature difference.

  According to a fourth aspect of the present invention, when the temperature difference of the heating member is lower than a predetermined temperature, the control unit reduces the rotational speed of the driving means to be smaller than the predetermined rotational speed of the driving means at the predetermined temperature. And when the said heating member temperature difference is higher than the said predetermined temperature, the rotation speed of the said drive means is made larger than the said predetermined rotation speed. According to this configuration, when the temperature difference of the heating member is lower than the predetermined temperature, the temperature is increased and the outer diameter is increased by making the rotational speed of the driving means smaller than the predetermined rotational speed at the predetermined temperature. When the peripheral speed of the pressure member is reduced and the temperature difference of the heating member is higher than the predetermined temperature, the temperature is lowered and the outer diameter is reduced by increasing the rotational speed of the driving means above the predetermined rotational speed. The peripheral speed of the pressure member is increased.

  According to a fifth aspect of the present invention, when the sheet is continuously passed through the nip portion, the control unit sets the number of rotations of the driving unit to the predetermined number of rotations when the number of sheets to be passed increases. It is characterized by being close to.

  According to a sixth aspect of the present invention, when the driving unit continuously drives the pressure member to rotate, the control unit rotates the driving unit when the rotation driving time of the driving unit becomes longer. The number is made close to the predetermined number of rotations.

  According to the first aspect of the present invention, when the heating member heated by the heat source is pressed against the pressure member, the heat of the heating member is transmitted to the pressure member, and the temperature of the heating member is lowered. This falling temperature is detected by the temperature detection member. The control unit estimates the temperature of the pressure member based on the descending temperature of the heating member, and controls the rotation speed of the driving means so as to rotate the pressure member at a predetermined peripheral speed. Regardless of the temperature of the pressure member, even if a temperature detection member or the like is not provided, the nipping / conveying speed of the paper in the nip is constant, and the paper conveyance that suppresses the transfer image misalignment and paper wrinkles is suppressed. Can be done.

  According to the second aspect of the present invention, when heat is transmitted from the heating member to the pressurizing member, the temperature of the heating member decreases. Is detected, and the controller estimates the temperature of the pressure member based on the temperature difference and rotates the pressure member at a predetermined peripheral speed. It is corrected.

  According to the invention described in claim 3, when the heat is transmitted from the heating member to the pressure member, the temperature of the heating member is lowered, but the temperature detection member is in a state where the heating member is uniformly heated by the heat source. The temperature difference that the heating member descends is detected, the control unit estimates the temperature of the pressure member based on the temperature difference, and rotates the pressure member at a predetermined peripheral speed. Corrected accurately.

  According to the fourth aspect of the present invention, when the temperature difference of the heating member is lower than the predetermined temperature, the temperature is increased by making the rotational speed of the driving means smaller than the predetermined rotational speed at the predetermined temperature. Since the peripheral speed of the pressure member whose outer diameter is increased is reduced, the nipping and conveying speed of the nip portion can be made constant regardless of the temperature of the pressure member. Further, when the temperature difference of the heating member is higher than the predetermined temperature, the peripheral speed of the member whose temperature is lowered and the outer diameter is reduced is increased by increasing the rotational speed of the driving means to be higher than the predetermined rotational speed. Therefore, the nipping and conveying speed of the nip portion can be made constant regardless of the temperature of the pressure member.

  According to the invention described in claim 5, when the number of sheets to be passed increases, the pressure member approaches the temperature corresponding to the predetermined temperature. Regardless of the number of sheets, the nipping and conveying speed of the nip portion can be made constant.

  According to the sixth aspect of the present invention, when the rotation driving time of the pressure member increases, the pressure member approaches the temperature corresponding to the predetermined temperature, so that the rotation speed of the driving means approaches the predetermined rotation speed. Thus, the nipping and conveying speed of the nip portion can be made constant regardless of the rotational drive time.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. The embodiment of the present invention shows the most preferable form of the invention, and the use of the invention and the terms shown here are not limited thereto.

(First embodiment)
FIG. 1 is a cross-sectional front view schematically showing an internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a tandem type color printer. As the photosensitive members 11a to 11d that are rotatable, an organic photosensitive member (OPC photosensitive member) is used as a photosensitive material for forming a photosensitive layer, and black (B), It is arranged corresponding to each color of yellow (Y), cyan (C) and magenta (M). The photosensitive layer may be amorphous silicon. Around each of the photoreceptors 11a to 11d, developing devices 2a to 2d, an exposure unit 12, chargers 13a to 13d, and static eliminators 14a to 14d are disposed.

  The developing devices 2a to 2d are arranged opposite to the lower right of the photoconductors 11a to 11d and supply toner to the photoconductors 11a to 11d. The chargers 13a to 13d are arranged on the upstream side of the developing device 2a to 2d in the rotation direction of the photosensitive member and opposed to the surfaces of the photosensitive members 11a to 11d, and uniformly charge the surfaces of the photosensitive members 11a to 11d. The static eliminators 14a to 14d are arranged on the downstream side of the photoconductor rotation direction of the developing devices 2a to 2d and to face the surfaces of the photoconductors 11a to 11d, and charge remaining on the surfaces of the photoconductors 11a to 11d after development. Remove static electricity.

  The exposure unit 12 scans and exposes each of the photoconductors 11a to 11d based on image data such as characters and patterns input from a personal computer or the like to an image input unit (not shown). The developing device 2a Is provided downstream of the chargers 13a to 13d in the rotation direction of the photosensitive member. The exposure unit 12 is provided with a laser light source and a polygon mirror, and a reflection mirror and a lens are provided corresponding to each of the photoreceptors 11a to 11d. Laser light emitted from the laser light source is applied to the surfaces of the photoconductors 11a to 11d via a polygon mirror, a reflection mirror, and a lens, and the surfaces of the photoconductors 11a to 11d are electrostatically applied to the surfaces of the photoconductors 11a to 11d. A latent image is formed. The electrostatic latent images are developed into toner images by the developing devices 2a to 2d.

  The intermediate transfer belt 17 is stretched around the tension roller 6, the driving roller 25, and the driven roller 27. The photoreceptors 11a to 11d are arranged below the intermediate transfer belt 17 so as to be in contact with the intermediate transfer belt 17 so as to be adjacent to each other from the upstream side in the transport direction (arrow direction in FIG. 1). . The primary transfer rollers 26a to 26d are arranged so as to face the photoreceptors 11a to 11d and contact the intermediate transfer belt 17 with the intermediate transfer belt 17 interposed therebetween, and are movable in the vertical direction in FIG. If necessary, a primary transfer nip portion is formed by being pressed against each of the photoreceptors 11a to 11d via the intermediate transfer belt 17, and is separated. In the primary transfer nip portion, the toner images formed by the photoconductors 11a to 11d are transferred to the surface of the intermediate transfer belt 17. The toner images on the photoconductors 11a to 11d are sequentially transferred to the intermediate transfer belt 17 at a predetermined timing along with the rotation of the intermediate transfer belt 17, whereby cyan, magenta, yellow, and black are transferred onto the surface of the intermediate transfer belt 17. A full color toner image is formed by superimposing the four color toner images. The belt cleaning 31 cleans the toner remaining on the intermediate transfer belt 17 after the transfer.

  The secondary transfer roller 34 is opposed to the driving roller 25 with the intermediate transfer belt 17 interposed therebetween, and presses against the intermediate transfer belt 17 to form a secondary transfer nip portion. In the secondary transfer nip portion, the intermediate transfer belt The toner image on the surface 17 is transferred to the paper P.

  A paper feed cassette 32 that stores paper P is disposed below the image forming apparatus 1, and a stack tray 35 that supplies manual paper is disposed in the middle of the image forming apparatus 1. On the left side of the image forming apparatus 1, a first conveyance path 33 that conveys the paper P fed from the paper feed cassette 32 to the secondary transfer nip portion formed by the intermediate transfer belt 17 is disposed. On the left side, a second conveyance path 36 for conveying the sheet fed from the stack tray 35 to the secondary transfer nip portion is provided. In the upper left part of the image forming apparatus 1, a fixing device 18 that performs a fixing process on the paper P on which an image has been formed, and a third transport path that transports the paper on which the fixing process has been performed to the paper discharge unit 37. 39 is disposed.

  The paper feed cassette 32 can be replenished by pulling it out of the apparatus (front side in FIG. 1), and the stored paper P is first fed one by one by the pick-up roller 33b and the separating roller 33a. It is fed out to the conveyance path 33 side.

  The first conveyance path 33 and the second conveyance path 36 are merged before the registration roller 33c, and the registration roller 33c takes the timing of the image forming operation and the paper feeding operation in the intermediate transfer belt 17 to form the sheet P. Is conveyed to the secondary transfer nip portion. The full color toner image on the intermediate transfer belt 17 is secondarily transferred to the sheet P conveyed to the secondary transfer nip portion by the secondary transfer roller 34 to which a bias potential (a polarity opposite to the toner charging polarity) is applied. Then, it is conveyed to the fixing device 18.

  The fixing device 18 includes a fixing belt heated by a heater, a pressure roller disposed in pressure contact with the fixing belt, and the like, and heats and presses the paper P on which the toner image as a transfer material is transferred. The fixing process is performed by After the sheet P is fixed by the fixing device 18, the sheet P is reversed by the fourth conveyance path 40 as necessary, and the full-color toner image is secondarily transferred to the back surface of the sheet by the secondary transfer roller 34. And is discharged to the paper discharge portion 37 by the discharge roller 19a through the third conveyance path 39.

  FIG. 2 is a cross-sectional front view showing a schematic configuration of the fixing device 18 used in the image forming apparatus 1 described above. The fixing device 18 is a belt fixing method, and includes a fixing belt 52 as a heating member, a fixing roller 53, a pressure roller 54 as a pressure member, a heat roller 55, a driving means 57 having a motor and a reduction gear. And a thermostat unit 60 and a thermistor 84. In the hollow of the heat roller 55, a heater lamp 55 a is provided as a heat source for the fixing device 18. The fixing roller 53, the pressure roller 54, and the heat roller 55 are rotatably supported in the longitudinal direction of the casing (not shown) of the fixing device 18, and drive means 57, a heater lamp 55a, a thermostat unit 60, and a thermistor 84. Is fixedly held in a housing (not shown).

  The fixing belt 52 is wound around the fixing roller 53 and the heat roller 55, and is driven to rotate in the direction of the arrow x shown in FIG. The fixing belt 52 is an endless belt formed of a nickel thin plate having a thickness of 40 μm, and has an outer peripheral surface coated with an offset preventive agent such as a silicone rubber film.

  The fixing roller 53 and the pressure roller 54 are rubber rollers arranged to face each other. When the pressure roller 54 is pressed toward the center of the fixing roller 53 via the fixing belt 52, the pressure roller 54. A nip portion N is formed between the fixing belt 52 and the fixing belt 52. The heat roller 55 applies tension to the fixing belt 52 and is formed of a cylindrical aluminum tube. Since the fixing roller 53 and the pressure roller 54 are formed longer than the fixing belt 52 in the longitudinal direction, the pressure roller 54 is in pressure contact with the fixing roller 53 together with the fixing belt 52.

  The drive unit 57 includes a motor and a reduction gear train, and is gear-connected to the pressure roller 54. When the drive unit 57 is rotationally driven in the arrow direction shown in FIG. 2, the pressure roller 54 rotates in the arrow direction. The rotation of the pressure roller 54 causes the fixing roller 53 and the fixing belt 52 that are in pressure contact with the pressure roller 54 to rotate at the same speed in the direction of the arrow shown in FIG. Heat from the heater lamp 55a disposed in the hollow of the heat roller 55 is transmitted to the fixing belt 52 through the heat roller 55, and the fixing belt 52 is heated. By the reverse rotation of the pressure roller 54 and the fixing belt 52, the paper P is conveyed upward of the apparatus while the toner image T of the paper P is heated and melted at the nip portion N.

  In the fixing device 18 configured as described above, the paper P on which the toner image T is formed is conveyed in the direction of the arrow y shown in FIG. 2 from the pre-fixing guide 21 arranged on the upstream side of the fixing belt 52 in the paper conveying direction. The toner image on the paper P is heated and melted at the nip portion N, whereby the toner image T is fixed. Thereafter, the paper P is discharged to the paper discharge unit 37 (see FIG. 1) by the post-fixing guide 22 and the transport rollers 23a and 23b arranged on the downstream side in the paper transport direction.

  Next, the thermostat unit 60 and the thermistor 84 will be described. The thermostat unit 60 is arranged toward the peripheral surface of the heat roller 55, detects the temperature of the heat roller 55 one by one, and when the temperature of the heat roller 55 exceeds a preset temperature range, the heater lamp 55a. This prevents the roller from being overheated by interrupting energization of the roller. The thermostat unit 60 is disposed in a hollow portion formed inside the fixing belt 52, and includes a thermostat 62, a thermostat support member 63, a coil spring 64, and a holding member 61 that holds them inside, and the thermostat 62 includes the coil spring 64. Due to this urging force, the thermostat 62 protrudes from the holding member 61 in the direction of the heat roller 55 so that the detection surface of the thermostat 62 is always in contact with the circumferential surface of the heat roller 55 and can detect the temperature.

  The thermistor 84 as temperature detecting means is disposed outside the fixing belt 52 and in a portion stretched by the heat roller 55, and detects the temperature of the fixing belt 52 that is in contact therewith. Based on this detected temperature, the temperature of the nip portion N related to the fixing of the toner image T is controlled, and as will be described later, the rotational speed of the driving means 57 is controlled to change the temperature of the nip portion N at the time of fixing. Regardless, the sheet P can always pass through the nip portion N at a constant nipping and conveying speed.

  Next, control of the main part of the image forming apparatus by the control unit will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of an image forming apparatus including a control unit.

  The image forming apparatus 1 includes an image forming unit 71 including a charging unit 13, a developing device 2, a photoconductor 11, a transfer unit 72 such as an intermediate transfer belt, a pressure roller 54, a heat lamp 55a, a thermostat 62, and a thermistor 84. In addition to the fixing device 18, driving means 57 for driving each part of the device such as the pressure roller 54, and the paper feed cassette 32, a control unit 74, a storage unit 75, an operation panel 79, a main power supply 83, and development A motor 81 and a paper feed motor 82 are provided.

  The storage unit 75 includes a RAM 76, a ROM 77, and an image memory 78. The RAM 76 and the ROM 77 store processing programs and processing contents of the control unit 74, and the image memory 78 receives an image input unit (see FIG. Image data such as characters and designs input in (Omitted) is stored.

  The operation panel 79 includes an operation unit composed of a plurality of operation keys, and a display unit (all of which is not shown) that displays setting conditions, device statuses, and the like. The user can turn on / off the main power supply 83 of the device. When the image forming apparatus 1 has a facsimile function, the facsimile transmission destination is registered in the storage unit 75 in addition to setting the printing conditions such as OFF, the paper size / type, and the number of printed sheets. It is also used for various settings such as reading and rewriting the transmission destination.

  The driving unit 57 drives the photosensitive member 11, the driving roller 25 (see FIG. 1) of the transfer unit 72, and the pressure roller 54 of the fixing device 18 in response to a control signal from the control unit 74. The developing motor 81 drives the toner stirring screw and the developing roller in the developing device 2 in accordance with a control signal from the control unit 74. The paper feed motor 82 drives the paper feed roller in the paper feed cassette 32 in accordance with a control signal from the control unit 74.

  The thermostat 62 detects the temperature of the heat roller 55 (see FIG. 2). When the heat roller 55 exceeds a preset upper limit temperature in accordance with the detected temperature, the contact of the thermostat 62 is opened and the supply of power to the heat lamp 55a is stopped. The thermistor 84 detects the surface temperature of the fixing belt 52 and sends the detected temperature signal to the controller 74. Based on the temperature signal, the control unit 74 controls on / off of the heat lamp 55a so as to maintain a fixing temperature at which the fixing belt 52 can perform the fixing satisfactorily. The number of rotations of the motor of the drive unit 57 is controlled so that the peripheral speed of the pressure roller 54 is constant.

  The control unit 74 is constituted by a microcomputer or the like, and generally controls the image forming unit 71, the paper feed cassette 32, the fixing device 18, the motors 81 and 82, and the driving unit 57 in accordance with programs set in the RAM 76 and the ROM 77. To do. Further, the control unit 74 controls the rotational speed of the motor of the driving unit 57 based on the temperature detected by the thermistor 84 and the rotational speed correction table stored in the ROM 77.

  The rotation speed correction table relates to the temperature of the fixing belt 52 and the rotation speed of the driving unit 57, and will be described based on FIGS. 4 and 5 together with FIGS. FIG. 4 is a diagram showing temperature changes of the pressure roller 54 and the fixing belt 52 when the driving unit 57 is driven to rotate the pressure roller 54 and the fixing belt 52 after being left for a predetermined time after the previous fixing. The vertical axis indicates temperature (unit: ° C.), and the horizontal axis indicates time (unit: seconds). 4 shows a state in which the motor of the driving unit 57 is driven after being left for one hour, and FIG. 5 shows a state in which the motor of the driving unit 57 is driven after being left for one minute.

  In the apparatus model for creating the rotation speed correction table, the thermistor 84 is disposed on the outer periphery of the pressure roller 54 of the present embodiment, and the outer peripheral temperature of the pressure roller 54 is measured. However, a thermistor for the pressure roller is not provided, and a rotation speed correction table created by this apparatus model is mounted.

  As shown in FIG. 4, the fixing belt 52 maintains a fixing possible temperature (180 to 190 ° C.), heat is transferred from the fixing belt 52, and the pressure roller 54 maintains a substantially constant temperature (60 ° C.). Then, driving of the driving means 57 is started. When the pressure roller 54 is rotated by the rotation of the driving unit 57 and the fixing belt 52 is rotated, the heat of the fixing belt 52 is transmitted to the pressure roller 54 and the temperature of the transmission fixing belt 52 is lowered by the amount of the heat transfer. . Similarly, the fixing belt 52 is maintained at a fixing temperature (180 to 190 ° C.), and the temperature at which the fixing belt 52 is lowered due to heat transfer to the pressure roller 54 is also examined at other temperatures of the pressure roller 54. At this time, if the temperature difference between the fixing belt 52 and the pressure roller 54 is large, the temperature of the fixing belt 52 rapidly decreases. If the temperature difference is small, the temperature of the fixing belt 52 slowly decreases. The temperature of the pressure roller 54 is estimated from the descending temperature per time of the fixing belt 52, and the number of rotations of the motor of the driving unit 57 is determined in accordance with the descending temperature.

  Specifically, in FIG. 4, the detected temperatures by the thermistor 84 of the fixing belt 52 are 169 ° C. and 154 ° C. after 1 second and 2 seconds from the start of driving of the driving unit 57, respectively. The detected temperature is 60 ° C. The difference in temperature between 1 second and 2 seconds is 15 °, and it can be seen that when the pressure roller 54 is 60 ° C., heat corresponding to 15 ° is transmitted from the fixing belt 52. Next, as shown in FIG. 5, the detected temperature of the pressure roller 54 is 120 ° C. after 1 minute from the previous drive of the drive unit 57, and 1 second after the drive start of the drive unit 57. The detected temperatures by the thermistor 84 of the fixing belt 52 after 2 seconds are 176 ° C. and 167 ° C., respectively. The difference in temperature between 1 second and 2 seconds is 9 °, and when the pressure roller 54 is 120 ° C., it can be seen that heat corresponding to 9 ° is transmitted from the fixing belt 52. Here, the temperature is detected 1 second and 2 seconds after the start of driving because the fixing belt 52 is moved once from the start of driving and the heat from the heater lamp 55a is uniformly distributed on the entire circumference of the fixing belt 52. This is for detecting the descending temperature of the fixing belt 52 accompanying the rotation of the pressure roller 54 in a state where the pressure roller 54 is heated.

Similarly, when the temperature detected by the pressure roller 54 at 60 ° C. to 120 ° C. is checked, the temperature difference between the pressure roller 54 and the detected temperature of the pressure roller 54 is 13 ° when the temperature detected by the pressure roller 54 is 80 ° C. When the detected temperature of 54 is 100 ° C., the temperature difference is 10 °, and the temperature difference between the pressure roller 54 and the fixing belt 52 is as shown in Table 1.

In the present embodiment, the pressure roller 54 is a rubber roller having an outer diameter of 35 mm, and the fluctuation temperature range of the peripheral surface of the pressure roller 54 is 60 to 120 ° C. The temperature change in this range causes thermal expansion, The outer diameter of the pressure roller 54 changes by about 0.4 mm. Therefore, in order to make the peripheral speed of the pressure roller 54 substantially constant even when the outer diameter changes, the temperature of the fixing belt 52 shown in Table 1 and the temperature of the pressure roller 54 are changed based on the temperature of the driving means 57. Correct the rotation speed. This rotation speed correction table is shown in Table 2.

In Table 2, in the area C where the temperature difference of the fixing belt 52 is 10 <ΔX ≦ 13, the temperature of the pressure roller 54 is in the range of 80 to 100 ° C. (reference temperature). Normally, during continuous paper feeding, the reference temperature is maintained, and the rotation speed of the drive means 57 is set at the reference temperature. Therefore, the rotation speed of the drive means 57 in the area C is set as the reference rotation speed, The rotational speed of the drive means 57 is corrected according to the temperature difference.

  That is, in the areas A and B, the temperature difference of the fixing belt 52 is smaller than that of the area C, that is, the temperature of the pressure roller 54 is higher than the reference temperature of the pressure roller 54 in the area C. The diameter is larger than that of area C. Therefore, the rotation speed of the driving means 57 is reduced by 0.8% with respect to the reference rotation speed in the area A, and is reduced by 0.4% with respect to the reference rotation speed in the area B. Here, since the temperature of the pressure roller 54 is higher in the area A than in the area B, the number of rotations of the driving unit 57 is made smaller than that in the area B. On the other hand, in the areas D and E, the temperature difference of the fixing belt 52 is larger than that of the area C, that is, higher than the reference temperature of the pressure roller 54, so that the pressure roller diameter is smaller than that of the area C. Yes. Accordingly, the rotation speed of the driving means 57 is increased by 0.4% with respect to the reference rotation speed in the area D, and is increased by 0.8% with respect to the reference rotation speed in the area E. Here, since the temperature of the pressure roller 54 is lower in the area E than in the area D, the rotational speed of the driving unit 57 is made larger than that in the area D.

  In this manner, the rotation speed correction table shown in Table 2 multiplies the reference rotation speed by the rotation speed correction coefficient to correct the rotation speed of the driving unit 57, so that the pressure roller 54 can be used regardless of the fixing temperature. Is stored in the ROM 77.

  Next, driving control of the driving unit 57 of the fixing device will be described based on FIG. 3 together with FIG.

  The controller 74 controls the heat lamp 66a of the heat roller 55 (see FIG. 2). Control is performed so that the energization-on state is maintained (warm-up) until the heat lamp 55a is energized and the fixing belt 52 (see FIG. 2) rises to a fixable temperature. When the surface temperature of the fixing belt 52 reaches the fixable temperature by detecting the temperature of the thermistor 84, the energization of the heat lamp 55a is continued as it is, and the detected temperature of the thermistor 84 is maintained so as to stably maintain the fixable temperature. On / off control of the heat lamp 55a is performed based on the above.

  When the start signal of the image forming operation is input to the control unit 74, the control unit 74 controls the driving unit 57. If the input of the start signal is during the warming up of the fixing belt, the process waits until the fixing temperature is reached. When the fixing temperature is reached, the driving means 57 is driven to rotate at the reference rotational speed, and the driving means 57 rotates the pressure roller. 54 is rotated.

  When the fixing belt 52 rotates as shown in FIG. 2 by the rotation of the pressure roller 54, the control unit 74 sets the detected temperature of the thermistor 84 that is input 1 second and 2 seconds after the drive of the drive unit 57 starts. Based on this, the temperature difference between 1 second and 2 seconds is calculated. With reference to the rotational speed correction table (Table 2) in the ROM 77, the rotational speed correction coefficient corresponding to this temperature difference is determined, and the rotational speed of the driving means 57 is corrected. When the peripheral speed of the pressure roller 54 is also corrected by correcting the rotation speed, the paper P conveyed in the direction of the arrow y shown in FIG. 2 enters the nip portion N and is heated and pressurized in the nip portion N. As a result, the toner image T is conveyed to the post-fixing guide 22 at a predetermined nipping and conveying speed while being fixed.

  When the paper P on which the toner image is formed is continuously passed, the control unit 74 counts the number of sheets passing through the nip portion N, and when the counted value exceeds a predetermined number (for example, 25), the driving unit 57. Is corrected so as to approach the reference rotation speed of the rotation speed correction table (Table 2) (if the rotation speed is in area A, it is corrected in area B, or if it is in area E, it is corrected in area D). Further, when the count value of the number of sheets becomes large (for example, 50 sheets), the driving means 57 is corrected to the reference rotation number (area B or area D is corrected to area C) and driven to rotate.

  Further, when the driving unit 57 is continuously driven, the time is calculated from the start of driving of the driving unit 57, and when a predetermined time (for example, 1 minute) elapses, the rotational speed of the driving unit 57 is corrected to approach the reference rotational speed. (Correct from area A to area B or from area E to area D), and when the time (for example, 2 minutes) elapses, the drive means 57 is corrected to the reference rotational speed (from area B or area D to area C) and rotationally drive.

  According to the first embodiment, the image forming apparatus 1 includes the endless fixing belt 52 stretched between the heat roller 55 including the heater lamp 55 a and the fixing roller 53, and the pressure contact with the fixing belt 52. The pressure roller 54 arranged in this manner, the thermistor 84 for detecting the temperature of the fixing belt 52, drive means 57 having a motor for rotating the pressure roller 54, and a control unit for controlling the rotation of the drive means 57. 74, a sheet P carrying an unfixed toner image is passed through a nip portion N formed by pressure contact between the fixing belt 52 and the pressure roller 54, and heat fixing is performed. Based on the temperature detected by the thermistor 84, the control unit 74 controls the rotational speed of the driving unit 57 so that the pressure roller 54 has a predetermined peripheral speed regardless of the temperature of the pressure roller 54.

  According to this configuration, when the heated fixing belt 52 is pressed against the pressure roller 54, the heat of the fixing belt 52 is transmitted to the pressure roller 54, and the temperature of the fixing belt 52 decreases. This lowered temperature is detected by the thermistor 84. The control unit 74 estimates the temperature of the pressure roller 54 based on the descending temperature of the fixing belt 52 and controls the rotation speed of the driving unit so as to rotate the pressure roller 54 at a predetermined peripheral speed. As a result, without providing a dedicated thermistor to the pressure roller, the nipping and conveying speed of the paper P in the nip portion N becomes constant regardless of the temperature of the pressure roller 54, and the transfer image deviation and paper wrinkle of the paper are constant. Thus, the sheet conveyance with the occurrence of the occurrence of the ink can be performed at the nip portion.

  Further, according to the first embodiment, the control unit 74 detects the temperature difference from the detected temperature of the thermistor 84 detected after the first and second predetermined times (1 second and 2 seconds) from the start of rotation of the driving unit 57. Based on the above, the rotational speed of the drive means 57 is controlled. When heat is transmitted from the fixing belt 52 to the pressure roller 54, the temperature of the fixing belt 52 decreases. However, the thermistor 84 decreases the temperature of the fixing belt 52 while the entire circumference of the fixing belt 52 is uniformly heated by the heater lamp 55a. In order to estimate the temperature of the pressure roller 54 based on the descending temperature and rotate the pressure roller 54 at a predetermined peripheral speed, the nipping and conveying speed of the nip portion N is accurately corrected.

  Further, according to the first embodiment, the controller 74 determines that the temperature difference after the first and second predetermined times (after 1 second and after 2 seconds) is lower than the predetermined temperature (area C of the rotation speed correction table). In this case, the peripheral speed of the pressure roller 54 whose temperature is increased and the outer diameter is increased is reduced by making the rotational speed of the driving means 57 smaller than a predetermined rotational speed (reference rotational speed) at a predetermined temperature. Therefore, regardless of the temperature of the pressure roller 54, the nipping and conveying speed of the paper P in the nip portion N can be made constant. Further, the nipping and conveying speed of the nip portion N is accurately corrected. In addition, when the temperature difference between the first and second predetermined times (after 1 second and 2 seconds) is higher than the predetermined temperature, the rotational speed of the driving unit 57 is set larger than the predetermined rotational speed (reference rotational speed). As a result, the peripheral speed of the pressure roller 54 whose temperature is lowered and the outer diameter is reduced is increased, so that the nipping and conveying speed of the paper P in the nip portion N is increased regardless of the temperature of the pressure roller 54. Can be constant.

  Further, according to the first embodiment, when the paper P is continuously passed through the nip portion N, the controller 74 sets the rotational speed of the driving unit 57 to a predetermined rotational speed (reference speed) when the number of paper passes increases. When the number of sheets to be passed increases by approaching the number of revolutions), the pressure roller 54 approaches the temperature corresponding to the reference temperature, so that the number of revolutions of the driving unit 57 is brought close to the predetermined number of revolutions (reference number of revolutions). Regardless of the number of sheets, the nipping and conveying speed of the sheet P in the nip portion N can be made constant.

  Further, according to the first embodiment, when the driving unit 57 continuously drives the pressure roller 54 to rotate, the control unit 74 sets the rotational speed of the driving unit 57 to a predetermined rotational speed (when the rotational driving time becomes longer). When the rotation driving time of the pressure roller 54 increases by approaching the reference rotation speed), the pressure roller 54 approaches the temperature corresponding to the reference temperature, so that the rotation speed of the driving unit 57 is set to a predetermined rotation speed (reference rotation). The holding and conveying speed of the paper P in the nip portion N can be made constant regardless of the rotational drive time.

(Second Embodiment)
The present invention is not limited to the first embodiment described above, and in the fixing belt system having the same configuration as that of the first embodiment, a rotation speed correction table is created based on the descending temperature of the fixing belt 52 for a predetermined time from the start of driving. Thus, the rotation speed correction table may be stored in the ROM 77. This will be described with reference to FIGS. 2, 4 and 5.

  In FIG. 4, the detected temperatures of the fixing belt 52 by the thermistor 84 are 191 ° C. and 169 ° C. at the start of driving of the driving means 57 and one second after the start of driving, and the detected temperatures of the pressure roller 54 are 60 ° C. It is. The temperature difference between the start of driving and one second after that is 22 °, and it can be seen that when the pressure roller 54 is 60 ° C., heat corresponding to 22 ° is transmitted from the fixing belt 52. Next, in FIG. 5, the detected temperature of the pressure roller 54 is 120 ° C., and the detected temperatures by the thermistor 84 of the fixing belt 52 at the start of driving of the driving means 57 and after 1 second are 189 ° C. And 176 ° C. The temperature difference between the start of driving and one second after that is 13 °, and it can be seen that when the pressure roller 54 is 120 ° C., heat corresponding to 13 ° is transmitted from the fixing belt 52.

Similarly, when the detected temperature of the pressure belt 54 at 60 to 120 ° C. is examined, the temperature difference of the pressure roller 54 is 21 ° when the detected temperature of the pressure roller 54 is 80 ° C. When the detected temperature of 54 is 100 ° C., the temperature difference is 17 °, and the temperature difference between the pressure roller 54 and the fixing belt 52 is as shown in Table 3.

In the present embodiment, in consideration of the size and material of the pressure roller 54, even if the outer diameter of the pressure roller 54 changes due to thermal expansion in the above-described variable temperature range of 60 to 120 ° C., If the rotational speed of the driving unit 57 is corrected based on the temperature difference of the fixing belt 52 and the temperature of the pressure roller 54 shown in Table 3 to make the peripheral speed substantially constant, the rotational speed correction table shown in Table 4 is obtained. Become.

In Table 4, in area C where the temperature difference of the fixing belt 52 is 17 <ΔX ≦ 21, the temperature of the pressure roller 54 is in the range of 80 to 100 ° C. (reference temperature). Normally, during continuous paper feeding, the reference temperature is maintained, and the rotation speed of the drive means 57 is set at the reference temperature. Therefore, the rotation speed of the drive means 57 in the area C is set as the reference rotation speed, The rotational speed of the drive means 57 is corrected according to the temperature difference.

(Third embodiment)
As in the second embodiment, the third embodiment creates a rotation speed correction table based on the temperature drop of the fixing belt 52 from the start of driving to a predetermined time, and stores the rotation speed correction table in the ROM 77. However, the predetermined time is different from that of the second embodiment. This will be described with reference to FIGS. 2, 4 and 5.

In FIG. 4, based on the temperature difference by the thermistor 84 of the fixing belt 52 at the start of driving of the driving means 57 and 2 seconds after the start of driving, and the detected temperature 60 ° C. of the pressure roller 54, and in FIG. Based on the temperature difference by the thermistor 84 of the fixing belt 52 at the detection temperature 120 ° C. of the roller 54 and the detection temperatures 80 ° C. and 100 ° C. of the pressure roller 54, the results shown in Table 5 are obtained.

In order to make the peripheral speed of the pressure roller 54 substantially constant even if the outer diameter of the pressure roller 54 changes due to thermal expansion in consideration of the size and material of the pressure roller 54 within the fluctuating temperature range in the above table. Further, when the rotational speed of the driving unit 57 is corrected based on the temperature difference of the fixing belt 52 and the temperature of the pressure roller 54 shown in Table 5, the rotational speed correction table shown in Table 6 is obtained.

  According to the second and third embodiments, the control unit 74 detects the temperature of the thermistor 84 that is detected when the rotation of the driving unit 57 is started, and the thermistor 84 that is detected after a predetermined time (1 second or 2 seconds) from the start of rotation. The rotational speed of the drive means 57 is controlled based on the temperature difference from the detected temperature. When heat is transmitted from the fixing belt 52 to the pressure roller 54, the temperature of the fixing belt 52 decreases. The thermistor 84 detects the temperature at which the fixing belt 52 is lowered from the start of rotation to a predetermined time, and based on the decreasing temperature. In order to estimate the temperature of the pressure roller 54 and rotate the pressure roller 54 at a predetermined peripheral speed, the nipping and conveying speed of the nip portion N is accurately corrected.

  The present invention can be used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, an image including a fixing device that conveys paper by a pressure member or the like. It can be used for a forming apparatus.

1 is a cross-sectional front view illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional front view showing a schematic configuration of a fixing device according to a first embodiment of the present invention. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 4 is a diagram showing a temperature change of the fixing device in a state where a fixing motor is driven after being left for one minute from the previous fixing of the image forming apparatus according to the first to third embodiments of the present invention. FIG. 4 is a diagram illustrating a temperature change of the fixing device in a state where a fixing motor is driven after being left for one hour from the previous fixing of the image forming apparatus according to the first to third embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2a-2d Developing device 11a-11d Photoconductor 17 Intermediate transfer belt 18 Fixing device 52 Fixing belt 53 Fixing roller 54 Pressure roller 55 Heating roller 55a Heater lamp (heat source)
57 driving means 60 thermostat unit 62 thermostat 71 image forming unit 74 control unit 83 main power supply 84 thermistor (temperature detection member)
N Nip part P Paper (transfer material)
T Toner image

Claims (6)

A fixing belt heated by a heat source;
A pressure roller disposed on an outer periphery of the fixing belt;
A fixing roller disposed on an inner periphery of the fixing belt and pressed against the pressure roller via the fixing belt;
A roller disposed on an inner periphery of the fixing belt and stretching the fixing belt together with the fixing roller;
A temperature detecting member for detecting the temperature of the fixing belt;
Drive means for rotationally driving the pressure roller;
A storage unit for storing a rotation speed correction table for correcting the rotation speed of the driving means ;
A control unit that controls the heat source based on the detection result of the temperature detection member, and that controls the rotation of the driving unit based on the detection result of the temperature detection member and the rotation speed correction table;
An image forming apparatus that heats and fixes a sheet carrying an unfixed toner image through a nip formed by pressure contact between the fixing belt and the pressure roller,
When the temperature of the fixing belt is lowered when the heat of the fixing belt is transmitted to the pressure roller between the start of driving of the driving unit and before the sheet is conveyed to the nip portion and on the basis of the lowered temperature of the temperature detection member has detected, with reference to the rotational speed correction table, by controlling the rotational speed of the drive means, the pressure irrespective of the temperature of the pressure roller An image forming apparatus characterized in that a roller has a predetermined peripheral speed.   The controller is based on a temperature difference between a detected temperature of the temperature detecting member detected at the start of rotation of the driving unit and a detected temperature of the temperature detecting member detected after a predetermined time from the start of rotation. The image forming apparatus according to claim 1, wherein the number of rotations is controlled.   The control unit detects the temperature of the temperature detection member detected after a first predetermined time from the start of rotation of the driving means, and the temperature detection member detected after a second predetermined time from the start of rotation of the driving means. The image forming apparatus according to claim 1, wherein the rotational speed of the driving unit is controlled based on a temperature difference from the detected temperature.   When the temperature difference detected by the temperature detection member is lower than a predetermined temperature, the control unit reduces the rotational speed of the driving means relative to the predetermined rotational speed of the driving means at the predetermined temperature, and the temperature 4. The image formation according to claim 2, wherein when the temperature difference detected by the detection member is higher than the predetermined temperature, the rotational speed of the driving unit is increased with respect to the predetermined rotational speed. apparatus.   When the sheet is continuously passed through the nip portion, the control unit brings the rotational speed of the driving unit closer to the predetermined rotational speed when the number of passed paper sheets exceeds a predetermined number. The image forming apparatus according to claim 4.   When the driving means continuously drives the pressure roller to rotate, the control unit brings the rotational speed of the driving means closer to the predetermined rotational speed when the rotational driving time of the driving means becomes longer than a predetermined time. The image forming apparatus according to claim 4.

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