JP6658034B2 - Fixing device and image forming device - Google Patents

Description

  The present disclosure relates to a fixing device, and more particularly, to a fixing device that fixes toner containing a release agent.

  2. Description of the Related Art An image forming apparatus, such as a copying machine, a printer, a facsimile, and a multifunction peripheral having these functions, which conforms to an electrophotographic method, generally forms a latent image corresponding to image data on a photoconductor, and forms a toner on the latent image. The developed toner image is transferred to a sheet, the toner image transferred on the sheet is fixed, and the sheet is discharged.

  As a fixing device for fixing a toner image in this manner, a sheet on which a toner image is transferred is nipped and transported by a nip formed by a fixing roller having a built-in halogen heater or the like and a pressure roller for pressing the fixing roller. Meanwhile, a fixing device of a heat roller fixing type for heating and pressing is widely used.

  Here, since the toner of the toner image on the paper is heated when passing through the nip portion, the toner has an adhesive force, and the paper that has passed through the nip portion adheres to the surface of the fixing roller and is wound and separated. May cause jams. In particular, when a sheet having a small basis weight is used as the sheet, the separation performance is further reduced.

  On the other hand, the speed of image forming apparatuses has been increasing, and if the fixing roller is enlarged to secure a sufficiently long nip width, the roller curvature at the exit of the fixing nip becomes smaller, so that the separation performance is reduced. Decrease.

  Various technologies have been devised in order to easily separate a sheet from a fixing member even in a fixing device that secures such a sufficient nip width. As the technology, a method using a heat-resistant resin having a high release property on the surface layer of the fixing member, or providing a separation claw coated with a fluorine resin having a good release property on the paper discharge side of the nip portion, and fixing the paper to a fixing roller, There is a method of separating from.

  There is also a method of improving the performance of separating a paper from a fixing member by incorporating a wax that functions as a release agent by being melted in the toner by heating.

  Japanese Patent Application Laid-Open Publication No. 2014-081610 (Patent Document 1) discloses an image forming apparatus using a toner containing wax, which is configured such that when a toner is fixed on a sheet, the surface speed of a pressure roller and the surface speed of a fixing belt are reduced. A configuration is disclosed in which a difference is set to prevent a glossy memory that is generated in response to the history of the previous fixing process.

  Japanese Patent Application Laid-Open No. 2010-217466 (Patent Literature 2) discloses a fixing device having no cleaning member. Before starting a printing operation, a speed difference is provided between the fixing member and the pressing member to slide both members. That is, a configuration for cleaning the surface of the fixing member and the pressing member is disclosed.

JP 2014-081610 A JP 2010-217466 A

  Increasing the wax content in the toner can improve the separation performance of the paper from the fixing member, but has the problem that gloss (gloss) in the printing portion of the paper becomes noticeable.

  The technique disclosed in Patent Document 1 is a technique for suppressing unevenness in gloss (gloss memory) of a sheet and uniformly controlling the gloss of the sheet, and mentions nothing about improving the performance of separating the sheet from a fixing member. It has not been. Also, with respect to the technology disclosed in Patent Document 2, there is no mention of improving the performance of separating paper from a fixing member.

  The present disclosure has been made in order to solve the above-described problem, and an object in one aspect is to separate a sheet from a fixing member or a pressing member while suppressing gloss of a printing unit. An object of the present invention is to provide a fixing device using a toner containing a release agent and an image forming apparatus equipped with the fixing device, which can improve performance.

A fixing device that fixes toner containing a release agent attached to a sheet is disposed on a sheet conveyance path, and is configured such that a nip region where outer peripheral surfaces of the first and second nips are in contact with each other is formed. A rotating member, a separating member disposed at a first distance from the downstream end of the nip area, and separating the sheet from the first or second rotating member, and a position on the sheet transport path. And a control unit that controls the rotation speeds of the first and second rotating bodies based on the detection result by the detection unit. The control unit is configured to control the first area including at least a part of the area of the sheet whose distance from the leading end of the sheet is within the first distance during the first period in which the first area passes through the upstream end of the nip area. The difference in the peripheral speed between the first rotating body and the second rotating body is the peripheral speed in the second period in which the area other than the first area of the sheet passes through the upstream end of the nip area. The rotation speeds of the first and second rotating bodies are controlled so as to be larger than the difference.

Preferably, the lower flow end of the first region is the leading edge of the sheet.
Preferably, the upstream end of the first area is located at a first distance from the leading edge of the sheet .

  Preferably, in the first period, the control unit determines whether the first rotating body and the second rotating body are on the basis of the peripheral speed of one of the first and second rotating bodies. The rotation speeds of the first and second rotating bodies are controlled so that the peripheral speed difference becomes 1 to 10%.

  Preferably, the control unit individually drives the first and second rotating bodies during the first period, and controls the rotation speed of one of the first and second rotating bodies during the second period. Is set, and the other rotating body is driven to rotate by contact friction with one rotating body.

  More preferably, the apparatus further includes a first motor connected to the first rotating body, and a second motor connected to the second rotating body. The control unit individually sets the rotation speeds of the first and second motors in the first period.

  More preferably, a common motor that drives the first and second rotating bodies, a first gear that connects one rotating body to the motor, and a first gear that connects the other rotating body to the motor. The motor further includes a second gear having a number of teeth different from the number of teeth of the gear, and a clutch connecting the motor and the second gear. The control unit connects the motor and the second gear by the clutch during the first period, and disconnects the motor and the second gear by the clutch during the second period.

Preferably, the detection unit optically detects the position of the leading end of the sheet on the transport path.
Preferably, the detection unit is a timing roller that temporarily stops the sheet conveyed toward the nip area and adjusts the timing of supplying the sheet to the nip area.

  According to another aspect, an image forming apparatus that uses a toner containing a release agent includes an image forming unit that forms a toner image on a sheet, a fixing device that fixes a toner image attached to the sheet, and And a control unit for detecting the position of. The fixing device is disposed on a paper transport path, and includes first and second rotating bodies configured to form a nip region where their outer peripheral surfaces are in contact with each other, and from a downstream end of the nip region. A separation member that is arranged at a first distance and separates the sheet from the first or second rotating body. The controller controls the first rotation during a first period in which a first area including at least a part of the area of the sheet whose distance from the leading end of the sheet is within the first distance passes through the nip area. The first and second peripheral speed differences between the body and the second rotating body are larger than the peripheral speed difference during a second period in which an area other than the first area of the sheet passes through the nip area. The rotation speed of the second rotating body is controlled.

  Preferably, the control unit has an acquiring unit that acquires an index relating to the basis weight of the sheet, and the smaller the basis weight of the sheet, the more the distance between the first rotating body and the second rotating body in the first period. The rotational speeds of the first and second rotating bodies are controlled so that the peripheral speed difference becomes large.

More preferably, the index relating to the basis weight includes the type of paper.
More preferably, the apparatus further includes a thickness acquisition unit that acquires information on the thickness of the sheet. The index relating to the basis weight includes information relating to the thickness of the sheet.

  Preferably, the control unit includes a calculating unit that calculates a toner adhesion amount in the first region of the sheet, and the larger the calculated toner adhesion amount, the more the first rotating body and the second rotating member in the first period. The rotation speeds of the first and second rotators are controlled so that the peripheral speed difference between the rotator and the rotator is increased.

  More preferably, the calculating means calculates the toner adhesion amount based on the printing rate in the first area of the sheet.

  More preferably, the calculation means calculates the toner adhesion amount in consideration of the color overlap in which a plurality of toners are overlapped.

  Preferably, the control unit includes a measuring unit for measuring a margin distance from a leading edge of the sheet to an upstream position of the toner image, and the shorter the margin distance, the more the first rotating body and the second rotating body in the first period. The rotation speeds of the first and second rotators are controlled so that the peripheral speed difference between the first and second rotators increases.

  A fixing device using a toner including a release agent according to an embodiment can improve the performance of separating a sheet from a fixing member or a pressing member while suppressing gloss of a printing unit from being conspicuous.

FIG. 3 is a diagram illustrating an outline of a fixing device according to the embodiment. FIG. 2 is a diagram illustrating a configuration example of an image forming apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a fixing device according to the first embodiment. FIG. 3 is an enlarged view of the vicinity of a nip portion where a heating roller and a pressure roller are in contact with each other in the fixing device according to the first embodiment. 6 is a flowchart illustrating control of the fixing device according to the first embodiment. FIG. 9 is a diagram illustrating a configuration example of a fixing device according to a second embodiment. 9 is a flowchart illustrating control of the fixing device according to the second embodiment. 8 is a timing chart of the control shown in FIG. 7. FIG. 9 is a diagram illustrating a configuration example of a fixing device according to a third embodiment. 9 is a flowchart illustrating control of a fixing device according to a third embodiment. FIG. 3 is a diagram illustrating types of sheets set in each sheet cassette. FIG. 3 is a diagram illustrating a configuration example of a thickness detection unit for acquiring information on a thickness of a sheet. FIG. 15 is a diagram illustrating control of a fixing device according to a fifth embodiment. FIG. 19 is a diagram illustrating control of a fixing device according to a sixth embodiment. FIG. 2 is a block diagram illustrating a main hardware configuration of the image forming apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

[A. Overview]
FIG. 1 is a diagram illustrating an outline of a fixing device according to the embodiment. Referring to FIG. 1A, paper Pa to which toner To has been transferred is fixed with toner To by a fixing device. The fixing device includes a heating roller Rh having a heater He therein, a pressure roller Rp for applying pressure in contact with the heating roller Rh, and a separating claw Se for separating the sheet on which the toner To has been transferred from the heating roller Rh. And

  Generally, only one of the heating roller Rh and the pressing roller Rp is controlled by a motor to rotate, and the other roller is driven to rotate by contact friction with one roller. At this time, since the peripheral speed Vh of the heating roller Rh and the peripheral speed Vp of the pressure roller Rp are substantially equal, there is almost no difference in the peripheral speed between the two rollers.

  As shown in FIG. 1B, the toner To includes a pigment Pi and wax Wa as a release agent inside the resin Re. When only one of the rollers is rotated by the motor as described above, when the paper Pa passes through the nip portion Ni, the pressing force of the heating roller Rh and the pressing roller Rp acts on the toner To.

  On the other hand, when a peripheral speed difference between the peripheral speeds Vh and Vp is generated by controlling the peripheral speeds of the heating roller Rh and the pressure roller Rp, the toner To is applied to the toner To in the nip Ni in addition to the pressing force. Power works.

  FIG. 1C is a diagram showing the relationship between the amount of wax present on the toner surface after passing through the nip portion Ni and the speed ratio between the peripheral speeds Vh and Vp. These experimental data are obtained by measuring, with a component analyzer, the ion intensity contained in the toner surface transferred and fixed on the paper Pa when the speed ratio between the peripheral speeds Vh and Vp is changed. The rotation intensity of only one of the heating roller Rh and the pressure roller Rp is controlled, and the ion intensity when the other roller is driven to rotate is defined as 1, and the vertical axis is the ion intensity ratio. The higher the ionic strength ratio, the larger the amount of wax contained on the toner surface.

  As shown in FIG. 1C, when there is almost no difference between the peripheral velocities Vh and Vp, in other words, when only the pressing force is applied to the toner To in the nip portion Ni, the wax Wa oozing out of the toner To is removed. The amount is small. On the other hand, as the difference between the peripheral speeds Vh and Vp increases, in other words, as the shearing force applied to the toner To at the nip Ni increases, the amount of the wax Wa oozing out of the toner To increases.

  The fixing device according to the embodiment causes a peripheral speed difference between the fixing member and the pressing member when the leading end of the sheet passes through the nip. Thus, the fixing device according to the embodiment increases the amount of wax oozing from the toner, and improves the performance of separating the paper from the fixing member. Hereinafter, a detailed configuration and control of the fixing device will be described.

[B. First Embodiment Detecting Paper Position Downstream of Nip Section]
(B1. Image forming apparatus 100)
FIG. 2 is a diagram illustrating a configuration example of image forming apparatus 100 according to the first embodiment. The image forming apparatus 100 is an electrophotographic image forming apparatus such as a laser printer or an LED printer. As shown in FIG. 1, the image forming apparatus 100 includes an intermediate transfer belt 1 as a belt member at a substantially central portion inside. Below the lower horizontal portion of the intermediate transfer belt 1, four image forming units 2Y, 2M, 2C, and 2K corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively. Are arranged side by side along the intermediate transfer belt 1 and have photoconductor drums 3Y, 3M, 3C and 3K, respectively.

  Around each photoconductor drum 3Y, 3M, 3C, 3K, the chargers 4Y, 4M, 4C, 4K, the print head units 5Y, 5M, 5C, 5K, and the developing unit 6Y are arranged in this order along the rotation direction. , 6M, 6C, and 6K, and primary transfer rollers 7Y, 7M, 7C, and 7K opposed to the photosensitive drums 3Y, 3M, 3C, and 3K with the intermediate transfer belt 1 interposed therebetween, respectively.

  A secondary transfer roller 9 is pressed against a portion of the intermediate transfer belt 1 supported by the intermediate transfer belt driving roller 8, and the secondary transfer is performed in the area. A fixing device 20 is disposed downstream of the secondary transfer area.

  At the lower part of the image forming apparatus 100, a sheet feeding device 30 including sheet feeding cassettes 30a, 30b, and 30c configured to accommodate different sheets is detachably disposed. The paper Pa loaded and accommodated in the paper feeding device 30 is sent out one by one from the uppermost paper to the transport path R1 by the rotation of the paper feeding roller 31 corresponding to each paper feeding cassette.

  In the present embodiment, the image forming apparatus 100 employs, for example, an intermediate transfer method having a plurality of image forming units (2Y, 2M, 2C, and 2K), but is not limited thereto. The image forming apparatus may be of an electrophotographic type and include a fixing device. Specifically, the image forming apparatus may include a single image forming unit or may be a rotary type.

(B2. Schematic operation of image forming apparatus 100)
Next, a schematic operation of the image forming apparatus 100 having the above configuration will be described. When an image signal is input from an external device (for example, a personal computer or the like) to the image forming apparatus 100, the image forming apparatus 100 creates a digital image signal in which the image signal is color-converted into yellow, cyan, magenta, and black. Based on the input digital signal, each print head unit 5Y, 5M, 5C, 5K of each image forming unit 2Y, 2M, 2C, 2K emits light to perform exposure.

  Thus, the electrostatic latent images formed on the photosensitive drums 3Y, 3M, 3C, and 3K are developed by the developing units 6Y, 6M, 6C, and 6K, respectively, to become toner images of the respective colors. The toner of each color contains wax as a release agent in addition to the pigment corresponding to each color. The primary transfer of the toner images of each color is sequentially superimposed on the intermediate transfer belt 1 moving in the direction of arrow A in FIG. 1 by the operation of the primary transfer rollers 7Y, 7M, 7C, and 7K.

  The toner image formed on the intermediate transfer belt 1 in this manner is secondarily transferred to the paper Pa by the action of the secondary transfer roller 9.

  The toner image secondarily transferred to the paper Pa reaches the fixing device 20. The toner image is fixed on the paper Pa by the fixing device 20. The paper Pa on which the toner image has been fixed is discharged to a paper discharge tray 60 via a paper discharge roller 50. Hereinafter, the configuration and control of the fixing device 20 will be described.

(B3. Configuration of the fixing device 20)
FIG. 3 is a diagram illustrating a fixing device 20 according to the first embodiment. The fixing device 20 includes, as main components, a heating roller 21, a pressure roller 23, a detection unit 24, a separation claw 25, and a control unit 40.

  The heating roller 21 and the pressure roller 23 are arranged on the transport path R1 and form a nip Ni where their outer peripheral surfaces are in contact with each other. The heating roller 21 has a fluorine-based release layer, an elastic layer such as silicone rubber, and a core metal such as iron, stainless steel, and aluminum from the outside. The heating roller 21 includes a heater 22 inside. As the heater 22, for example, a halogen heater (infrared heating device) can be used. The heater 22 is not limited to this, and for example, a resistor heating device such as a thermal heater or a ceramic heater may be used. Further, the heating roller 21 may be induction-heated using a magnetic flux generator (not shown).

  Motors 26 and 27 are connected to the heating roller 21 and the pressure roller 23, respectively. The control unit 40 is electrically connected to the motors 26 and 27 and controls the rotational driving of these motors.

  The detection unit 24 detects that the downstream end (hereinafter, also simply referred to as “front end”) of the paper Pa has reached the separation claw 25 in the transport path R1. As the detection unit 24, for example, a light reflection type sensor including a light projecting unit and a light receiving unit can be used. In this case, the light from the light projecting unit is applied to the position of the upstream end Nt of the separation claw 25 in the transport path R1.

  FIG. 4 is an enlarged view of the vicinity of the nip portion Ni where the heating roller 21 and the pressure roller 23 contact the fixing device 20 according to the first embodiment. Referring to FIG. 4, sheet Pa conveyed along conveyance path R1 passes through nip portion Ni, thereby fixing a toner image to be carried.

(B4. Control of fixing device 20)
An elastic layer is provided on the surface of the pressure roller 23, and the elastic layer collapses at the nip portion Ni. Therefore, after passing through the nip portion Ni, the paper Pa is discharged toward the heating roller 21 according to the curvature of the heating roller 21. In another aspect, an elastic layer is provided on the surface of the heating roller 21, and the paper Pa is discharged to the pressure roller 23 side according to the curvature of the pressure roller 23 after passing through the nip portion Ni. There may be. In this case, the separation claw 25 needs to be arranged on the pressure roller 23 side.

  Here, the toner on the paper Pa has an adhesive force by being heated when passing through the nip portion Ni. Therefore, the possibility that the paper Pa adheres to the surface of the heating roller 21 and is conveyed after passing through the nip portion Ni increases.

  The separation claw 25 is arranged close to the surface of the heating roller 21. Further, a plurality of separation claws 25 are provided at predetermined intervals in the axial direction of the heating roller 21 extending in the direction perpendicular to the paper surface. The separation claw 25 separates the paper Pa existing in the vicinity of the surface of the heating roller 21 from the heating roller 21, thereby preventing occurrence of an abnormality such as a paper jam.

  However, for example, when the thickness (basis weight) of the paper Pa is small, the performance of separating the paper from the heating roller may decrease. In this case, the paper Pa may not be able to be separated from the heating roller by the separation claw 25, and a paper jam may occur.

  In order to solve this problem, the fixing device 20 according to the first embodiment determines the difference between the peripheral speed Vh of the heating roller 21 and the peripheral speed Vp of the pressing roller 23 when the paper Pa passes through the nip portion Ni. Cause. As a result, as shown in FIG. 1, the amount of wax (release agent) that oozes out on the toner surface on the paper Pa increases, and the performance of separating the paper Pa from the heating roller 21 can be improved.

  In the first embodiment, as an example, the control unit 40 controls the motors 26 and 27 so that the peripheral velocities Vh and Vp satisfy the following relational expression (1).

  Hereinafter, | (Vh−Vp) / Vp | in Expression (1) is also referred to as a peripheral speed difference between the heating roller 21 and the pressing roller 23. The reason for setting the peripheral speed difference to 0.01 or more is that if the peripheral speed difference is too small, the amount of wax oozing out on the toner surface is small, and the performance of separating the paper Pa from the heating roller 21 cannot be improved. This is because a paper jam may occur.

  On the other hand, the reason for setting the peripheral speed difference to 0.10 or less is that if the peripheral speed difference is too large, there is a possibility that an image shift occurs in which unfixed toner is shifted from a position where it should be fixed. .

  Therefore, in the fixing device 20 according to the first embodiment, by setting the peripheral speed difference so as to satisfy the relationship of the expression (1), the separation performance of the paper Pa from the heating roller 21 is improved while suppressing the image shift. be able to. Note that in Expression (1), the peripheral speed difference between the heating roller 21 and the heating roller 21 is set to fall within 1 to 10% based on the peripheral speed of the pressure roller 23, but is not limited thereto. In another aspect, the difference between the peripheral speed of the heating roller 21 and the peripheral speed of the pressing roller 23 may be set to fall within 1 to 10%.

  However, if the peripheral speed difference is set so as to always satisfy the expression (1) and the rotational driving of the heating roller 21 and the pressure roller 23 is controlled, another problem occurs. The first problem will be described. When the peripheral velocities of the heating roller 21 and the pressure roller 23 are generated, a roller having a low peripheral velocity is in a state where a brake is applied to a roller having a high peripheral velocity. Therefore, in the nip portion Ni, the load of the roller is increased, which may lead to shortening of the life of the fixing device such as damage to the silicone rubber forming the elastic layer, damage to the rotating shaft of the roller, and separation of the elastic layer from the core metal. There is.

  The second problem will be described. If the peripheral speed difference is constantly generated while the paper Pa passes through the nip portion Ni, the amount of wax oozing on the toner surface over the entire area of the paper increases, and the gloss of the printing portion may be conspicuous.

  Therefore, in the fixing device 20 according to the first embodiment, a peripheral speed difference that satisfies the expression (1) is generated by the motors 26 and 27 until the leading end of the paper Pa reaches the separation claw 25. This is because, after the leading end of the paper Pa is separated from the heating roller 21 by the separation claw 25, the paper Pa is conveyed along the conveyance path R1, so that a situation in which the paper Pa is not separated from the heating roller 21 cannot occur.

  The fixing device 20 stops the motor 27 after the leading end of the paper Pa reaches the separation claw 25. Thereby, the pressure roller 23 rotates following the heating roller 21. In other words, the fixing device 20 sets a larger peripheral speed difference in the period until the leading end of the paper Pa reaches the separation claw 25 than in other periods.

  In this case, the downstream end of the area of the sheet passing through the nip portion Ni during the period in which the peripheral speed difference is larger than the other periods (hereinafter, also referred to as “wax increasing area”) is the leading end of the sheet. On the other hand, the upstream end of the wax increasing area is located at a position (hereinafter referred to as a distance) from the leading end of the sheet, which is equivalent to the distance between the upstream end Nt of the separation claw 25 and the upstream end Nis of the nip Ni on the transport route R1. , "Nt-Nis position"). This shortens the period in which the difference between the peripheral speeds of the heating roller 21 and the pressure roller 23 is generated, reduces the load applied to both rollers, and suppresses the glossiness of the printing unit.

  FIG. 5 is a flowchart illustrating control of fixing device 20 according to the first embodiment. Hereinafter, the above-described series of controls will be described with reference to the flowchart shown in FIG. The process illustrated in FIG. 5 is realized by the control unit 40 executing a control program. In another aspect, some or all of the processing may be performed by circuit elements or other hardware.

  Referring to FIG. 5, in step S10, control unit 40 receives an input of a print job for forming an image on paper Pa. In step S12, the control unit 40 drives the motors 26 and 27. More specifically, the control unit 40 sets the peripheral speed Vh of the heating roller 21 and the peripheral speed Vp of the pressure roller 23 so as to satisfy the above equation (1).

  In step S <b> 14, the control unit 40 receives from the detection unit 24 a signal indicating that the leading end of the paper Pa has reached the end Nt of the separation claw 25.

  In step S16, the control unit 40 stops the motor 27 that drives the pressure roller 23 to rotate. Thus, the pressure roller 23 is driven to rotate by contact friction at the nip portion Ni with the heating roller 21.

  In steps S18 and S20, the control unit 40 ends the print job and stops the motor 26 that drives the heating roller 21 to rotate. Thus, the rotation of the pressure roller 23 is also stopped.

  According to the above, the fixing device 20 according to the first embodiment can make the peripheral speed difference larger in the period until the leading end of the paper Pa reaches the separation claw 25 than in other periods. As a result, the fixing device 20 can increase the amount of wax oozing on the toner surface in the wax-increased area including the leading end of the paper Pa. Thereby, the fixing device 20 can improve the performance of separating the sheet from the heating roller.

  In addition, after the leading end of the sheet reaches the separation claw, the fixing device 20 stops the motor 27 and rotates the pressure roller 23 by following the heating roller 21. Therefore, the fixing device 20 can reduce the load applied to both rollers and suppress the gloss of the printing unit.

  In the above-described example, the nip portion Ni is formed by the contact between the heating roller 21 and the pressure roller 23, but is not limited thereto. In another aspect, the fixing device stretches an endless fixing belt around a heating roller and a fixing roller including a halogen heater and the like, and fixes the toner image at a nip portion where the fixing belt and the pressure roller are in contact. It may be the one that causes it. Such a fixing device has the advantages that the heat capacity of the fixing belt is small, the warm-up time is reduced, and the energy efficiency is excellent.

  In the above example, the control unit 40 stops the motor 27 that drives the pressure roller 23 to rotate when the leading end of the paper Pa reaches the separation claw 25. The motor 26 may be stopped.

  Further, in the above example, the light reflection type sensor is used as the detection unit 24, but is not limited thereto. In another aspect, the detection unit 24 may be a light transmission type sensor.

[C. Second Embodiment Detecting Paper Position Upstream of Nip Section]
(C1. Overview)
In the first embodiment, the fixing device 20 performs control to change the peripheral speed difference between the peripheral speed Vh of the heating roller 21 and the peripheral speed Vp of the pressure roller 23 before and after the leading end of the paper Pa reaches the separation claw 25. Was. However, as described above, the shorter the time for increasing the peripheral speed difference, the more the load applied to both rollers can be reduced.

  Therefore, in the second embodiment, a description will be given of the configuration and control of a fixing device 20A capable of reducing the time for increasing the peripheral speed difference as compared with the fixing device 20 according to the first embodiment. Note that the basic configuration of the fixing device 20A is substantially the same as that of the fixing device 20, and therefore only different points will be described.

(C2. Configuration and control of fixing device 20A)
FIG. 6 is a diagram illustrating a configuration example of a fixing device 20A according to the second embodiment. Referring to FIG. 6, fixing device 20A arranges detection unit 24 not on the downstream side of nip portion Ni but on the upstream side.

  The detection unit 24 detects the leading end of the paper Pa conveyed along the conveyance path R1 on the upstream side of the nip portion Ni, and transmits a signal to that effect to the control unit 40.

  The fixing device 20 according to the first embodiment sets the wax increase area to an area from the leading edge of the paper Pa to the Nt-Nis position. However, the problem of the actual adhesion / separation of the paper Pa and the heating roller 21 is that the leading edge of the paper Pa reaches the end Nt of the separation claw 25 after passing through the downstream end Nie of the nip portion Ni. Until you do.

  Therefore, the fixing device 20A according to the second embodiment sets the upstream end of the wax-increased area at the interval between the end Nt of the separation claw 25 and the downstream end Nie of the nip Ni on the transport path R1 from the leading end of the sheet. It is set to a position at a corresponding distance (hereinafter, also referred to as “Nt-Nie position”).

  Hereinafter, the control will be described with reference to FIG. FIG. 7 is a flowchart illustrating control of fixing device 20A according to the second embodiment. Referring to FIG. 7, in steps S21 and S22, control unit 40 receives an input of a print job for forming an image on paper Pa, and drives motor 26 for rotating heating roller 21.

  In step S24, the detection unit 24 detects that the leading end of the paper Pa has passed at a predetermined position on the transport path R1 upstream of the nip portion Ni, and notifies the control unit 40 of that fact. Send a signal.

  In step S26, the control unit 40 calculates a timing T1 at which the leading end of the paper Pa reaches the upstream end Nis of the nip Ni. More specifically, the control unit 40 divides the distance from the detection position of the detection unit 24 on the transport path R1 to the upstream end Nis by the transport speed of the paper Pa. Thereby, the control unit 40 can calculate the time from when the detection unit 24 detects the leading end of the paper Pa to when it reaches the upstream end Nis. The distance from the detection position of the detection unit 24 to the upstream end Nis, and the transport speed of the paper Pa are stored in the storage device 120 described later. The control unit 40 also calculates the timing T2 at which the Nt-Nie position of the paper Pa reaches the upstream end Nis in the same manner as described above.

  In step S28, the control unit 40 drives the motor 27 at the calculated timing T1. At this time, the control unit 40 sets the peripheral speed Vh of the heating roller 21 and the peripheral speed Vp of the pressure roller 23 so as to satisfy the above equation (1).

  In step S30, the control unit 40 stops the motor 27 at timing T2 when the Nt-Nie position of the paper Pa reaches the upstream end Nis. Thus, the pressure roller 23 is driven to rotate by contact friction at the nip portion Ni with the heating roller 21.

  In steps S32 and S34, the control unit 40 ends the print job and stops the motor 26 that drives the heating roller 21 to rotate. Thus, the rotation of the pressure roller 23 is also stopped.

  FIG. 8 is a timing chart of the control shown in FIG. FIG. 8A shows that the area from the upstream end (front end) of the paper Pa to the Nt-Nie position in the transport direction is a wax increasing area.

  Referring to FIG. 8B, at timing T0, control unit 40 inputs a job for forming an image on paper Pa and drives motor 26. At timing Td, the detection unit 24 detects the leading end of the paper Pa at a predetermined position on the transport path R1 located upstream of the nip Ni. Further, based on the detection result of the detection unit 24, the control unit 40 determines the timing T1 at which the leading end of the paper Pa reaches the upstream end Nis of the nip Ni, and sets the Nt-Nie position of the paper Pa to the upstream end Nis. The timing T2 to reach Nis is calculated.

  The control unit 40 starts driving the motor 27 at a timing T1, and stops driving the motor 27 at a timing T2. At timing T3, the control unit 40 ends the print job and stops driving the motor 26.

  According to the above, in the fixing device 20A according to the second embodiment, the peripheral speed difference can be set to be large during the period in which the increased wax region from the leading end of the paper Pa to the Nt-Nie position passes through the nip portion Ni. Thus, the fixing device 20A can reduce the load on the heating roller 21 and the pressure roller 23 as compared with the fixing device 20 according to the first embodiment.

  In the second embodiment, the wax-increased region extends from the leading edge of the paper Pa to the Nt-Nie position, but is not limited to this. The controller 40 controls the nip portion Ni to pass a region including at least a part of the region from the leading end of the sheet Pa to the Nt-Nie position through the nip portion Ni, other than the region including the at least a portion. It is also possible to use a wax-increased region in which the peripheral speed difference is set to be larger than the period during which Ni passes. The reason is that the separation performance of the paper Pa from the heating roller 21 can be improved by increasing the amount of wax oozing on the toner surface in at least a part of the area from the leading end of the paper Pa to the Nt-Nie position. This is because it can be done.

  In another aspect, the detection unit 24 according to the second embodiment may be a timing roller that controls the supply timing of the paper Pa to the nip Ni, instead of the optical sensor. More specifically, the image forming apparatus abuts the leading end of the paper Pa on the timing roller whose rotation is stopped, then starts the rotation of the timing roller, and conveys the paper Pa toward the nip portion Ni.

[D. Embodiment 3 Means for Generating Peripheral Speed Difference]
The fixing device according to the first and second embodiments has a configuration in which the heating roller 21 and the pressure roller 23 are independently controlled by the motors 26 and 27, respectively. The fixing device 20B according to the third embodiment drives the heating roller 21 and the pressure roller 23 using a common motor. Hereinafter, the configuration and control of fixing device 20B according to the third embodiment will be described.

  FIG. 9 is a diagram illustrating a configuration example of a fixing device 20B according to the third embodiment. Referring to FIG. 9, a heating rotating body gear 44 is connected to heating roller 21, and a pressing rotating body gear 45 is connected to pressure roller 23. The heating rotator gear 44 is connected to the motor drive gear 42. On the other hand, the pressurizing rotator gear 45 is connected to the motor drive gear 42 via the clutch 43. The clutch 43 is configured to connect / disconnect the pressure rotating body gear 45 and the motor drive gear 42. The motor drive gear 42 is connected to the motor 41. The control unit 40 is electrically connected to the motor 41 and the clutch 43, and controls driving of the motor 41 and controls connection / disconnection of the pressurizing rotating body gear 45 and the motor driving gear 42.

  The heating rotator gear 44 and the pressurizing rotator gear 45 differ in the number of teeth constituting the gear. More specifically, when the motor 41 is driven at a predetermined speed in a state where the pressurizing rotator gear 45 and the motor driving gear 42 are connected by the clutch 43, the peripheral speeds Vh and Vp are expressed by the formulas ( The number of teeth satisfies the relationship of 1). The predetermined speed is a speed at which the motor 41 rotates when the paper Pa passes through the fixing device 20B.

  FIG. 10 is a flowchart illustrating control of fixing device 20B according to the third embodiment. Note that the parts denoted by the same reference numerals as those in FIG. 5 are the same and will not be described repeatedly.

  Referring to FIG. 10, in step S12A, control unit 40 drives motor 41 in a state in which pressurizing rotating body gear 45 and motor driving gear 42 are connected by clutch 43.

  In step S16A, the control unit 40 disconnects the pressurizing rotator gear 45 and the motor drive gear 42 by the clutch 43. Thus, the pressure roller 23 is driven to rotate by contact friction at the nip portion Ni with the heating roller 21.

  According to the above, in the fixing device 20 </ b> B according to the third embodiment, the peripheral speed difference between the peripheral speeds Vh and Vp can be controlled by the common motor 41. For this reason, the fixing device 20B can reduce the cost as compared with the fixing devices according to the first and second embodiments, and can realize simpler control.

  In another aspect, the fixing device includes a braking member that is close to one of the heating roller 21 and the pressure roller 23, and moves the braking member close to the other during a process of increasing the peripheral speed difference. The configuration may be such that the peripheral speed of the roller is reduced by pressing the roller. Also in this configuration, the fixing device can control the peripheral speed difference between the peripheral speeds Vh and Vp by the common motor 41.

[E. Embodiment 4 Controlling Difference in Circumferential Speed by Weight of Paper]
As described above, when the basis weight of the paper Pa is small, the separation performance of the paper Pa from the heating roller 21 is reduced. Thus, the fixing device according to the fourth embodiment sets the peripheral speed difference when the wax-increased area passes through the nip Ni as the basis weight of the paper Pa is smaller. The basic configuration of the fixing device according to the fourth embodiment is the same as that of fixing device 20 according to the first embodiment, and therefore, description thereof will not be repeated.

  As shown in FIG. 2, the image forming apparatus 100 has sheet cassettes 30a, 30b, and 30c. The user of the image forming apparatus 100 can set the type of paper set in these paper cassettes by using an operation panel 107 described later.

  FIG. 11 is a diagram illustrating the types of sheets set in each sheet cassette. In the example shown in FIG. 11, the user sets plain paper in the paper feed cassette 30a, thick paper in the paper feed cassette 30b, thin paper in the paper feed cassette 30c, and forms the information using the operation panel 107. Input to the device 100.

  For example, when the user prints using thick paper, the control unit 40 stops the motor 27 and drives only the motor 26. That is, the control unit 40 does not set the peripheral speed difference large even when the wax-increased area passes through the nip portion Ni. The reason for this is that thick paper has a high basis weight and therefore has a high separation performance from the heating roller 21, and there is a high possibility that paper jam will not occur even if the amount of wax oozing out on the toner surface is not increased.

  On the other hand, thin paper has low separation performance from the heating roller 21. For this reason, the control unit 40 determines the peripheral speed difference when the wax-enhanced region passes through the nip portion Ni by using the peripheral speed difference when printing using thin paper as the peripheral speed difference when printing using plain paper. Is also set to be large.

  According to the above, the fixing device 20 according to the fourth embodiment appropriately sets the peripheral speed difference when the wax-increased area passes through the nip portion Ni, based on the type of paper as an index regarding the basis weight of the paper. be able to. Thus, the fixing device according to the fourth embodiment can minimize the burden on the heating roller 21 and the pressure roller 23.

  In another aspect, the fixing device may be configured to acquire information on the thickness of the sheet instead of the type of the sheet. FIG. 12 is a diagram illustrating a configuration example of the thickness detection unit 32 for acquiring information on the thickness of a sheet. Referring to FIG. 12, thickness detecting unit 32 includes a roller 33, a housing 34 supporting roller 33, a spring 36, and a pressure sensor 38. The image forming apparatus 100 receives the input of the print job, drives the paper feed roller 31 to rotate, and sends out the paper Pa to the transport path R1.

  The rollers 33 are configured to rise as the paper Pa passes. As the rollers 33 rise, pressure is applied to the pressure sensor 38 via the spring 36. The control unit 40 monitors the amount of change in the pressure applied to the pressure sensor 38, that is, information about the thickness of the sheet, and the smaller the amount of change, the larger the peripheral speed difference when the wax-increased area passes through the nip Ni. May be set.

  Depending on the maker that manufactures the paper, the thickness may be different even though the type of paper is the same. Therefore, a configuration in which the peripheral speed difference is set by measuring the thickness of the paper actually printed is more appropriate than a configuration in which the peripheral speed difference is set according to the type of paper input to the image forming apparatus. Speed difference can be set. Further, the configuration in which the peripheral speed difference is set according to the type of paper input to the image forming apparatus is used when an item set by the user is incorrect, for example, when thin paper is set in a paper cassette of thick paper setting, Paper jams can occur. On the other hand, a configuration in which the peripheral speed difference is set by measuring the thickness of the sheet to be actually printed can avoid such a situation.

  Note that the thickness detection unit 32 is provided immediately downstream of the paper feed roller 31, but is not limited thereto. The thickness detection unit 32 may be provided on the transport route R1 on the upstream side of the nip portion Ni.

[F. Fifth Embodiment Controlling Difference in Circumferential Speed by Amount of Toner in Wax Increase Area]
In the fourth embodiment, a configuration in which a peripheral speed difference is set based on an index (a paper type and a thickness) regarding the basis weight of the paper Pa to be printed as a parameter affecting the performance of separating the paper Pa from the heating roller 21. explained. The parameter affecting the separation performance is not limited to the basis weight of the paper Pa, but also depends on the amount of toner attached to the paper Pa. As described above, the toner heated in the nip portion Ni has an adhesive force. Therefore, when the amount of toner adhered to the paper Pa increases, the separation performance from the heating roller 21 decreases. Therefore, the fixing device according to the fifth embodiment sets the peripheral speed difference when the wax-enhanced area passes through the nip portion Ni as the toner adhesion amount in the wax-enhanced area increases. Since the basic configuration of the fixing device according to the fifth embodiment is the same as that of fixing device 20 according to the first embodiment, description thereof will not be repeated.

  FIG. 13 is a diagram illustrating control of fixing device 20 according to the fifth embodiment. The control unit 40 according to the fifth embodiment specifies a wax-increased area (for example, from the leading edge of the sheet to the Nt-Nie position) from the input image data. Next, the control unit 40 calculates the toner adhesion amount in the wax increased area. More specifically, the control unit 40 calculates the number of print pixels (print ratio) in the wax-increased area. The control unit 40 sets the peripheral speed difference when the wax-increased area passes through the nip Ni as the calculated number of print pixels is higher.

  According to the above description, the fixing device 20 according to the fifth embodiment performs the peripheral speed difference when the wax-enhanced area passes through the nip portion Ni based on the number of print pixels in the wax-enhanced area as an index relating to the amount of toner adhered to the sheet. Can be set appropriately. Thus, the fixing device 20 according to the fifth embodiment can minimize the burden on the heating roller 21 and the pressure roller 23.

  In another aspect, the fixing device according to the fifth embodiment may consider the color overlap of the toner when calculating the toner adhesion amount. This is because the color-superimposed pixels have a larger toner adhesion amount than the non-color-superimposed pixels. As an example of control, it is assumed that the wax-increased area is 100 dots, of which 40 dots are print pixels, and 20 dots of the print pixels are pixels that are color-superimposed in two colors. In such a case, the printing rate is 40/100, but a correction to 60/100 may be performed in consideration of the color overlap.

[G. Embodiment 6: Set peripheral speed difference according to margin area]
The fixing device according to the sixth embodiment sets the peripheral speed difference based on the margin distance from the leading edge of the paper Pa to the upper end of the image as a parameter affecting the performance of separating the paper Pa from the heating roller 21. The basic configuration of the fixing device according to the sixth embodiment is the same as that of fixing device 20 according to the first embodiment, and therefore, description thereof will not be repeated.

  FIG. 14 is a diagram illustrating control of the fixing device according to the sixth embodiment. Referring to FIG. 14, control unit 40 according to the sixth embodiment has a position at the upstream end in the transport direction of an image formed on paper Pa from the leading end of paper Pa (hereinafter, also referred to as “image upper end”). ) Is calculated. Hereinafter, a specific calculation method will be described.

  Generally, a user of the image forming apparatus sets a non-printing area where printing is not performed up to a predetermined distance (for example, 2 mm) from the leading edge of the sheet. Therefore, the control unit 40 calculates the margin distance by adding the above-mentioned predetermined distance to the distance from the position of the upstream end of the print area where printing is performed to the position of the upper end of the image. The control unit 40 according to the sixth embodiment sets such that the shorter the calculated margin distance is, the larger the peripheral speed difference when the wax-increased area passes through the nip Ni is. When the calculated margin distance exceeds a predetermined distance (for example, 5 mm), the control unit 40 determines that the paper Pa has sufficient separation performance from the heating roller 21 and determines that the wax-increased region has a nip Ni , Only one of the motors 26 and 27 may be driven.

  According to the above, the fixing device 20 according to the sixth embodiment can appropriately set the peripheral speed difference when the wax-increased area passes through the nip portion Ni based on the margin distance of the sheet. Thus, the fixing device 20 according to the sixth embodiment can minimize the burden on the heating roller 21 and the pressure roller 23.

[H. Hardware configuration of image forming apparatus 100]
An example of a hardware configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 15 is a block diagram illustrating a main hardware configuration of the image forming apparatus 100.

  As shown in FIG. 15, the image forming apparatus 100 includes a control unit 40, a read only memory (ROM) 102, a random access memory (RAM) 103, a network interface 104, an operation panel 107, and a storage device 120. And

  The control unit 40 is configured by, for example, at least one integrated circuit. The integrated circuit includes, for example, at least one CPU (Central Processing Unit), at least one ASIC (Application Specific Integrated Circuit), at least one FPGA (Field Programmable Gate Array), or a combination thereof.

  The control unit 40 controls the operation of the entire image forming apparatus 100 including the fixing device 20 by executing various programs such as the control program 122 according to the present embodiment. The control unit 40 reads the control program 122 from the storage device 120 to the ROM 102 based on receiving the execution instruction of the control program 122. The RAM 103 functions as a working memory, and temporarily stores various data necessary for executing the control program 122.

  An antenna (not shown) and the like are connected to the network interface 104. The image forming apparatus 100 exchanges data with an external communication device via the antenna. The external communication device includes, for example, a mobile communication terminal such as a smartphone, a server, and the like. The image forming apparatus 100 may be configured so that the control program 122 can be downloaded from a server via an antenna.

  The operation panel 107 includes a display unit and a touch panel. The display unit and the touch panel are overlapped with each other, and the operation panel 107 receives a touch operation on the display unit. Operation panel 107 receives, for example, a printing operation on image forming apparatus 100.

  The storage device 120 is, for example, a storage medium such as a hard disk or an external storage device. Storage device 120 stores control program 122 and the like according to the present embodiment.

  The control program 122 may be provided as a part of an arbitrary program, not as a single program. In this case, the control processing according to the present embodiment is realized in cooperation with an arbitrary program. Even a program that does not include such some modules does not depart from the gist of the control program 122 according to the present embodiment. Further, some or all of the functions provided by the control program 122 may be realized by dedicated hardware. Further, the image forming apparatus 100 may be configured in a form such as a so-called cloud service in which at least one server executes a part of the processing of the control program 122.

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. Also, the disclosed embodiments are capable of performing any combination. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  20, 20A, 20B Fixing device, 21 heating roller, 23 pressure roller, 24 detecting unit, 25 separating claw, 26, 27, 41 motor, 100 image forming device, Ni nip portion, Pa paper, R1 transport path, Wa wax .

Claims (17)

A fixing device for fixing a toner containing a release agent attached to a sheet,
A first and a second rotating body arranged on the paper transport path and configured to form a nip area where their outer peripheral surfaces are in contact with each other;
A separation member that is arranged at a first distance from a downstream end of the nip area and separates the paper from the first or second rotating body;
A detection unit that detects a position on the transport path of the sheet,
A control unit that controls a rotation speed of the first and second rotating bodies based on a detection result by the detection unit,
The control unit may be configured such that a first area including at least a part of an area of the sheet whose distance from the leading end of the sheet is within the first distance passes through an upstream end of the nip area. In the first period, the peripheral speed difference between the first rotating body and the second rotating body is such that an area other than the first area of the sheet passes through the upstream end of the nip area. A fixing device that controls the rotation speeds of the first and second rotating bodies so as to be larger than the peripheral speed difference during the second period.   The fixing device according to claim 1, wherein a downstream end of the first area is a leading end of the sheet. The fixing device according to claim 1 , wherein an upstream end of the first area is located at the first distance from a leading end of the sheet .   In the first period, the control unit may determine whether the first rotator and the second rotator are based on a peripheral speed of one of the first and second rotators. 4. The fixing device according to claim 1, wherein the rotation speeds of the first and second rotating bodies are controlled so that a peripheral speed difference between the rotation speeds is 1 to 10%. 5. The control unit includes:
In the first period, the first and second rotating bodies are individually driven,
The rotation speed of one of the first and second rotating bodies is set in the second period, and the other rotating body is driven to rotate by contact friction with the one rotating body. The fixing device according to any one of claims 1 to 4. A first motor connected to the first rotating body;
A second motor connected to the second rotating body,
The fixing device according to claim 5, wherein the control unit sets the rotation speeds of the first and second motors individually during the first period. A common motor for driving the first and second rotating bodies,
A first gear connecting the one rotating body and the motor;
A second gear having a number of teeth different from the number of teeth of the first gear, for connecting the other rotating body and the motor;
A clutch that connects the motor and the second gear;
The control unit connects the motor and the second gear by the clutch during the first period, and disconnects the motor and the second gear by the clutch during the second period. Item 6. A fixing device according to item 5.   The fixing device according to claim 1, wherein the detection unit optically detects a position of a leading end of the sheet on the transport path.   8. The detection unit according to claim 1, wherein the detection unit is a timing roller that temporarily stops the sheet conveyed toward the nip area and adjusts a timing of supplying the sheet to the nip area. 9. Item 6. The fixing device according to item 1. An image forming apparatus using a toner containing a release agent,
An image forming unit that forms a toner image on paper;
A fixing device for fixing the toner image attached to the sheet,
A detection unit that detects a position on the transport path of the sheet,
And a control unit,
The fixing device includes:
A first and a second rotating body arranged on the paper transport path and configured to form a nip area where their outer peripheral surfaces are in contact with each other;
A separating member that is arranged at a first distance from a downstream end of the nip region and separates the paper from the first or second rotating body;
In the first period, the first region including at least a part of the region of the sheet whose distance from the leading edge of the sheet is within the first distance passes through the nip region. The difference in peripheral speed between the first rotating body and the second rotating body is the peripheral speed in a second period in which an area other than the first area of the sheet passes through the nip area. An image forming apparatus that controls a rotation speed of the first and second rotating bodies so as to be larger than the difference. The control unit includes:
An acquisition unit for acquiring an index regarding the basis weight of the paper,
The first and second rotations are performed so that the peripheral speed difference between the first rotator and the second rotator during the first period increases as the basis weight of the sheet decreases. The image forming apparatus according to claim 10, wherein the image forming apparatus controls a rotation speed of a body.   The image forming apparatus according to claim 11, wherein the index regarding the basis weight includes a type of the paper. Further comprising a thickness acquisition unit for acquiring information on the thickness of the paper,
The image forming apparatus according to claim 11, wherein the index regarding the basis weight includes information regarding a thickness of the sheet. The control unit includes:
Calculating means for calculating a toner adhesion amount in the first area of the sheet,
The first and second rotation speeds are set so that the peripheral speed difference between the first rotation body and the second rotation body during the first period increases as the calculated toner adhesion amount increases. The image forming apparatus according to claim 10, wherein the rotation speed of the rotating body is controlled.   The image forming apparatus according to claim 14, wherein the calculation unit calculates the toner adhesion amount based on a printing rate of the paper in the first area.   The image forming apparatus according to claim 15, wherein the calculation unit calculates the toner adhesion amount in consideration of a color overlap in which a plurality of toners are overlapped. The control unit includes:
Measuring means for measuring the margin distance from the leading edge of the paper to the upstream position of the toner image,
As the margin distance is shorter, the peripheral speed difference between the first rotator and the second rotator during the first period is larger, so that the peripheral speed difference between the first rotator and the second rotator is larger. The image forming apparatus according to claim 10, wherein the rotation speed is controlled.

Images