JP2012042756A - Fixing device, image forming device, and controlling method of fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of stabilizing a fixing performance by accurately detecting the changes of nip width due to the thermal expansion of an elastic layer of a fixing roller to adjust the nip width, an image forming device, and a controlling method of the fixing device.SOLUTION: When the nip width changes due to the thermal expansion of an elastic layer 15b of a fixing roller 15 during printing, the fixing roller 15 changes a position to a second position, and a fixing roller position change detecting sensor 19 is switched on. A control portion 20 controls the action of a pressurizing roller moving mechanism 18 to move a pressurizing roller 17 in a direction separating from the fixing roller 15, when the fixing roller position change detecting sensor 19 is switched on during printing. Therefore, even if the nip width changes due to the thermal expansion of the elastic layer 15b of the fixing roller 15 during printing, the changes of the nip width can be accurately detected to adjust the nip width to be a proper value, and the fixing performance can be stabilized.

Description

  The present invention relates to a fixing device that heats and melts a toner image on a recording medium and fixes the toner image on the recording medium, an image forming apparatus including the fixing device, and a control method for the fixing device.

  2. Description of the Related Art Image forming apparatuses such as electrophotographic copying machines and printers include a fixing device that heats and melts a toner image transferred onto a recording medium and fixes the toner image on the recording medium. The fixing device used in the image forming apparatus includes a belt fixing type fixing device that heats and melts the toner image on the recording medium with the heat of the fixing belt, and a roller that heats and melts the toner image on the recording medium with the heat of the fixing roller A fixing type fixing device or the like is widely known.

  Taking a belt fixing system as an example, this fixing device includes a fixing belt stretched and supported by a plurality of roller members such as a fixing roller and a heating roller, and a nip portion formed in pressure contact with the fixing roller via the fixing belt. A pressure roller to be formed, a pressure adjusting mechanism for setting the width of the nip portion by adjusting the position of the pressure roller, and the like are provided. Then, in the process in which the recording medium passes through the nip portion between the fixing belt and the pressure roller, the toner image on the recording medium is heated and melted by the heat of the fixing belt using the heating roller as a heat source, and pressure is applied. The toner image is fixed on the recording medium.

  In such a fixing device, there is a problem that the fixing property becomes unstable due to the variation of the width of the nip portion (hereinafter referred to as nip width). As a factor that the nip width fluctuates, there is deformation of the fixing roller due to expansion of an elastic layer such as rubber due to applied heat. When the nip width varies, the amount of heat applied to the toner image on the recording medium that passes through the nip portion changes, so that the fixing property is not stable. To solve such a problem, for example, a technique described in Patent Document 1 has been proposed as a technique for detecting a change in nip width and optimizing fixing conditions.

  In Patent Document 1, for the purpose of preventing the fixing property from being varied due to the variation from the target nip width, the variation in the nip width is detected from the position change of the tension roller (heating roller), and recording is performed based on the detection result. A technique of changing a medium conveyance speed and a fixing belt temperature is disclosed.

In the technique described in Patent Document 1 described above, a change in the nip width is detected from the position change of the tension roller (heating roller) using the following principles (1) to (3).
(1) Due to the deformation of the fixing roller, the tension of the fixing belt changes.
(2) Since the tension of the fixing belt is changed, the position of the displaceable tension roller is changed.
(3) The displacement of the tension roller is measured by a distance measuring sensor.

  For this reason, if the elastic characteristic of the fixing belt itself that is the premise of the above (1) changes with time, or if the displacement characteristic of the tension roller with respect to the tension change of the fixing belt that is the premise of (2) changes, the nip. It becomes impossible to accurately detect the fluctuation of the width. In other words, the technique described in Patent Document 1 is configured to detect the nip width change by using many mechanical characteristics that tend to change over time, and thus it is difficult to accurately detect the nip width change. There's a problem.

  The present invention has been made in view of the above, and it is possible to accurately detect a change in the nip width due to the thermal expansion of the elastic layer of the fixing roller, adjust the nip width, and stabilize the fixability. It is an object of the present invention to provide a fixing device, an image forming apparatus, and a control method for the fixing device.

  In order to solve the above-described problems and achieve the object, a fixing device according to the present invention includes a fixing roller having an elastic layer that thermally expands on an outer periphery and driven to rotate around a rotation shaft, and the fixing roller. A pressure member that presses against the elastic layer to form a nip portion; a fixing roller; a first position; and a second position at which the rotation shaft is separated from the pressure member relative to the first position. A supporting means for supporting the movement of the fixing roller, a detecting means for detecting that the fixing roller is in the second position, and when it is detected that the fixing roller is in the second position, Nip width adjusting means for adjusting the width of the nip portion by moving the pressure member in a direction away from the fixing roller.

  An image forming apparatus according to the present invention includes the fixing device according to the present invention.

  Further, the control method of the fixing device according to the present invention includes an elastic layer that thermally expands on the outer periphery, a fixing roller that is rotationally driven around a rotation shaft, and a nip portion that is in pressure contact with the elastic layer of the fixing roller. And a supporting means for supporting the pressure member to be formed and the fixing roller so as to be movable between a first position and a second position where the rotation shaft is separated from the pressure member than the first position. And a step of detecting that the fixing roller is in the second position, and when detecting that the fixing roller is in the second position, And a step of adjusting the width of the nip portion by moving the pressure member in a direction away from the fixing roller.

  According to the present invention, when the elastic layer of the fixing roller is thermally expanded, the fixing roller is moved to the second position, and it is detected by the detecting means that the fixing roller is in the second position, and the pressure member is moved from the fixing roller. Since the nip width is adjusted by moving in the away direction, the nip width can be accurately detected by detecting the fluctuation of the nip width due to the thermal expansion of the elastic layer of the fixing roller, and the fixing property can be stabilized. There is an effect that can be.

FIG. 1 is a schematic configuration diagram of a color laser printer. FIG. 2 is a configuration diagram illustrating details of the fixing device. FIG. 3 is a diagram illustrating an example of a fixing roller mounting structure. FIG. 4 is a diagram schematically illustrating how the nip width varies in the fixing device. FIG. 5 is a flowchart for explaining the outline of the nip width initial setting process executed by the control unit at the start of printing. FIG. 6 is a flowchart illustrating an example of a nip width adjustment process that is repeatedly executed at a predetermined cycle by the control unit during printing. FIG. 7 is a flowchart illustrating an example of processing for measuring the amount of movement of the pressure roller from the position where the fixing roller position variation detection sensor is turned on to the position where an appropriate nip width is obtained.

  Exemplary embodiments of a fixing device, an image forming apparatus, and a fixing device control method according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description, a tandem color laser printer is exemplified as an example of an image forming apparatus to which the present invention is applied, and a belt fixing type fixing apparatus is illustrated as an example of a fixing apparatus to which the present invention is applied.

  FIG. 1 is a schematic configuration diagram of a color laser printer 100 according to the present embodiment. The color laser printer 100 includes image forming units 1a, 1b, 1c, and 1d for four colors of Y (yellow), M (magenta), C (cyan), and K (black). A tandem type color laser printer in which 1a, 1b, 1c, and 1d are sequentially arranged along the traveling direction of the transfer belt 10 (the direction of arrow B in the figure).

  The image forming units 1a, 1b, 1c, and 1d include photosensitive members 2a to 2d, drum chargers 3a to 3d, exposure devices 4a to 4d, developing devices 5a to 5d, transfer devices 6a to 6d, and cleaning devices 7a to 7d, respectively. I have. The photoreceptors 2a to 2d are configured in a drum shape and are rotated in the direction of arrow A in the drawing. The drum chargers 3a to 3d uniformly charge the photoconductors 2a to 2d that are rotated. The exposure devices 4a to 4d scan the surfaces of the photoreceptors 2a to 2d charged by the drum chargers 3a to 3d with laser beams to form electrostatic latent images based on the image data. The developing units 5a to 5d develop the electrostatic latent images formed on the photoreceptors 2a to 2d by the exposure devices 4a to 4d with toner. The transfer units 6a to 6d transfer the toner images formed on the photoreceptors 2a to 2d to the transfer belt 10 by the development of the developing units 5a to 5d. The cleaning devices 7a to 7d clean the surfaces of the photoreceptors 2a to 2d.

  In the color laser printer 100, the Y, M, C, and K4 toner images formed by the image forming units 1a, 1b, 1c, and 1d are transferred onto the transfer belt 10 in a superimposed manner. A four-color full-color toner image is formed in. The toner image formed on the transfer belt 10 reaches the paper transfer unit 9 and is simultaneously conveyed in the direction of arrow H by the action of a high voltage applied to the paper transfer unit 9 to transfer the transfer belt 10 and the paper transfer The image is transferred onto the recording medium P that passes between the container 9 and the recording medium P. Untransferred toner on the transfer belt 10 is collected by a belt cleaning device 12. The toner image transferred onto the recording medium P is fixed on the recording medium P by the fixing device 11.

  FIG. 2 is a configuration diagram showing details of the fixing device 11. The fixing device 11 is a belt-fixing type fixing device using a fixing belt 13 as a fixing member. In addition to the fixing belt 13, a heating roller 14, a fixing roller 15, a tension roller 16, a pressure roller (pressure member). 17, a pressure roller moving mechanism 18, a fixing roller position variation detection sensor 19, a control unit 20, a memory 21, and the like.

  Here, the fixing belt 13 as a fixing member is an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer made of a resin material. The elastic layer of the fixing belt 13 is formed of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. The release layer of the fixing belt 13 is formed of PFA (tetrafluoroethylene barfluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. By providing the release layer on the surface layer of the fixing belt 13, the releasability (peelability) with respect to the toner image I is secured. The fixing belt 13 is stretched and supported by two roller members (the heating roller 14 and the fixing roller 15). The tension roller 16 has a role of applying a certain tension to the fixing belt 13 stretched between two roller members.

  The heating roller 14 is a thin cylindrical body made of a metal material, and a heater 22 (heat source) is fixedly provided inside the cylindrical body. The heater 22 is a halogen heater or a carbon heater, and both ends thereof are fixed to the side plate of the fixing device 11. The heating roller 14 is rotatably attached to the side plate of the fixing device 11 at both end shafts via bearings. The heater 22 generates heat when electric power whose output is controlled from a power supply unit (AC power supply) is supplied. The heating roller 14 is heated by the radiant heat from the heater 22, and heat is further applied to the toner image I on the recording medium P from the surface of the fixing belt 13 heated by the heating roller 14. The output control of the heater 22 is performed based on the detection result of the belt surface temperature by a temperature sensor (not shown) such as a thermopile facing the surface of the fixing belt 13.

  The fixing roller 15 is a roller member in which an elastic layer 15b such as fluorine rubber, silicone rubber, or foamable silicone rubber is formed on a core metal 15a made of stainless steel (for example, SUS304). A rotation shaft 15c is provided at the center of the cored bar 15a. The fixing roller 15 has both ends of a rotating shaft 15c rotatably attached to the side plate of the fixing device 11 via bearings, and is driven to rotate clockwise (in the direction of arrow C in the figure) by a fixing roller driving unit (not shown). As a result, the fixing belt 13 travels in the direction of arrow D in the figure.

  The pressure roller 17 has substantially the same configuration as the fixing roller 15, and an elastic layer 17 b such as fluorine rubber, silicone rubber, or foamable silicone rubber is formed on a core metal 17 a made of stainless steel (for example, SUS304). Roller member.

  In the fixing device 11, the pressure roller 17 is pressed against the fixing roller 15 via the fixing belt 13 to form a nip portion. In the fixing device 11, the elastic layer 15 b of the fixing roller 15 is made thicker than the elastic layer 17 b of the pressure roller 17 in order to form a nip portion. As an example, the elastic layer 17b of the pressure roller 17 is 3 mm, whereas the elastic layer 15b of the fixing roller 15 is 15 mm.

  The pressure roller moving mechanism 18 includes a swing arm 18a. Both end bearings of the pressure roller 17 are rotatably supported by the swing arm 18a. The swing arm 18a can swing around a swing shaft 18b provided at one end thereof. A bearing 18c is fixed to the other end of the swing arm 18a. An eccentric cam 18d having a rotating shaft is provided at a position deviating from the center of the circle at a position where the bearing 18c contacts the lower side in the figure. The eccentric cam 18d is driven by a motor (not shown). The eccentric cam 18d is provided with a shielding plate 18e, and the eccentric cam position detecting means 18f detects the position of the shielding plate 18e so that the reference position of the eccentric cam 18d can be grasped.

  The eccentric cam 18d is always kept in contact with the bearing 18c by the tension of the swing arm spring 18g connected to the swing arm 18a. When the eccentric cam 18d rotates in the direction of arrow E in the figure by driving the motor, the bearing 18c moves in the direction of arrow F in the figure. As a result, the pressure roller 17 supported by the swing arm 18a moves in the direction of arrow G in the drawing, that is, in the direction approaching the fixing roller 15. On the other hand, when the eccentric cam 18d rotates in the direction of arrow E 'in the figure by driving the motor, the bearing 18c moves in the direction of arrow F' in the figure. As a result, the pressure roller 17 supported by the swing arm 18 a moves in the direction of the arrow G ′ in the drawing, that is, in the direction away from the fixing roller 15.

  FIG. 3 is a diagram illustrating an example of a mounting structure of the fixing roller 15. The side plate 30 of the fixing device 11 has a long hole 31 having a longitudinal direction in the vertical direction in the figure corresponding to the arrangement direction of the fixing roller 15 and the pressure roller 17 at a position where the rotation shaft 15 c of the fixing roller 15 is attached. It is formed through. The long hole 31 is provided with a slider 32 that is slidable along the longitudinal direction. The rotation shaft 15 c of the fixing roller 15 is inserted into a long hole 31 formed in the side plate 30, and is attached to a slider 32 attached to the long hole 31 via a bearing 33. Further, between the slider 32 and the upper end portion of the long hole 31, two terminals 19a and 19b of a switch constituting the fixing roller position variation detection sensor 19 are provided.

  In a state where the fixing roller 15 is not pressurized by the pressure roller 17, as shown in FIG. 3A, the rotation shaft 15c is located at the lower end side (the pressure roller 17 side) of the long hole 31 (the pressure roller 17 side). Hereinafter, this is referred to as a first position. At this time, the switch constituting the fixing roller position variation detection sensor 19 is turned off with the two terminals 19a and 19b being separated. When the pressure roller 17 is pressed against the fixing roller 15 from this state, the fixing roller 15 is slightly pushed up by the pressure roller 17 and a nip portion is formed between the fixing roller 15 and the pressure roller 17. Then, by adjusting the position of the pressure roller 17 with respect to the fixing roller 15 and controlling the pressure of the fixing roller 15 by the pressure roller 17, the nip width is maintained in an appropriate range.

  Here, when the pressure of the pressure roller 17 on the fixing roller 15 becomes excessive, the fixing roller 15 is further pushed up by the pressure roller 17 and the nip width becomes larger than the appropriate range. As shown in FIG. 3B, the fixing roller 15 is referred to as a second position (hereinafter referred to as a second position) where the rotation shaft 15c is on the upper end side (the side away from the pressure roller 17) of the long hole 31. ) At this time, the switch constituting the fixing roller position variation detection sensor 19 is turned on when the two terminals 19a and 19b come into contact with each other.

  Even if the position of the pressure roller 17 is maintained appropriately, if the elastic layer 15b of the fixing roller 15 is thermally expanded due to a temperature change in the fixing device 11 and the diameter of the fixing roller 15 increases, As in the case where the pressure is excessive, the fixing roller 15 is pushed up to the second position shown in FIG. 3B, and the nip width is increased beyond the appropriate range. Also in this case, the switch constituting the fixing roller position variation detection sensor 19 is turned on when the two terminals 19a and 19b come into contact with each other.

  FIG. 4 is a diagram schematically showing how the nip width fluctuates due to thermal expansion of the elastic layer 15b of the fixing roller 15. FIG. 4A is a fixing device at the start of printing after the color laser printer 100 is turned on. 11B shows the state of the fixing device 11 when a predetermined number of prints have been completed. At the start of printing, the fixing roller 15 is in a relatively low temperature state. At this time, the diameter of the fixing roller 15 is R, and the nip width is N (see FIG. 4A). Thereafter, as the printing continues, the amount of heat received by the fixing roller 15 gradually increases, and the elastic layer 15b of the fixing roller 15 thermally expands, so that the diameter of the fixing roller 15 becomes R + ΔR (ΔR ≧ 0). As a result, the nip width increases to N + ΔN (ΔN ≧ 0) (see FIG. 4B). Here, the nip width is shown to change due to the deformation due to the thermal expansion of the elastic layer 15b of the fixing roller 15. However, similarly, when the position where the pressure roller 17 is in pressure contact with the fixing roller 15 changes, The nip width varies.

  In this state where the nip width varies, if continuous printing is performed while the pressure roller 17 is held at the same pressure contact position, the amount of heat applied to the toner image I on the recording medium P at the nip increases. As a result, the toner image I on the recording medium P adheres to the fixing belt 13 side, so that the fixing to the recording medium P cannot be performed normally or the glossiness of the color image is impaired. Can no longer be obtained. Therefore, in the fixing device 11 according to the present embodiment, the change in the nip width as described above is detected by the fixing roller position variation detection sensor 19, and the control unit 20 controls the operation of the pressure roller moving mechanism 18 to apply pressure. By adjusting the position of the roller 17, the nip width is adjusted to an appropriate value.

  FIG. 5 is a flowchart for explaining an outline of the nip width initial setting process executed by the control unit 20 at the start of printing. In the initial state before the start of printing, the pressure roller 17 is at a position separated from the fixing roller 15.

  When the initial setting process of the nip width shown in FIG. 5 is started, the controller 20 first starts the movement of the pressure roller 17 by the pressure roller moving mechanism 18 in step S101, and the pressure roller 17 is moved to the fixing roller. Move gradually to the 15th side. In step S102, the control unit 20 determines whether the fixing roller position variation detection sensor 19 is turned on.

  The control unit 20 continues the movement of the pressure roller 17 toward the fixing roller 15 by the pressure roller moving mechanism 18 until the fixing roller position variation detection sensor 19 is turned on (step S102: No). When the fixing roller position variation detection sensor 19 is turned on (step S102: Yes), the movement of the pressure roller 17 by the pressure roller moving mechanism 18 is temporarily stopped in step S103.

  Next, in step S104, the control unit 20 reads the moving amount (distance) of the pressure roller 17 for obtaining an appropriate nip width stored in advance in the memory 21. In step S105, the control unit 20 controls the operation of the pressure roller moving mechanism 18 to move the pressure roller 17 away from the fixing roller 15 by the distance read in step S104.

  Next, in step S106, the control unit 20 confirms whether or not the fixing roller position variation detection sensor 19 has been switched from on to off. If the fixing roller position variation detection sensor 19 is switched from on to off (step S106: Yes), it is determined that an appropriate nip width is obtained, and the nip correction counter is cleared in step S107. Thus, the series of initial setting processes shown in FIG. The nip correction counter is a counter that measures the number of steps when the pressure roller 17 is moved step by step to adjust the nip width.

  On the other hand, when the fixing roller position variation detection sensor 19 remains on (step S106: No), the control unit 20 determines in step S108 a motor (stepping) that is a driving source of the pressure roller moving mechanism 18. The motor) is operated by one step, and the pressure roller 17 is moved by one step in a direction away from the fixing roller 15. In step S109, the control unit 20 increments (increases by 1) the value of the nip correction counter.

  Next, in step S110, the control unit 20 determines whether or not the value of the nip correction counter has reached a predetermined specified value. If the value of the nip correction counter reaches the specified value (step S110: Yes), it is determined that some abnormality has occurred in the fixing device 11, and the operation panel of the color laser printer 100 is displayed in step S111. The error message display or the like notifies the operator that an abnormality has occurred in the fixing device 11, and the initial setting process is terminated. On the other hand, if the value of the nip correction counter has not reached the specified value (step S110: No), the process returns to step S106 and the subsequent processing is repeated. When the fixing roller position variation detection sensor 19 is switched from on to off (step S106: Yes), the nip correction counter is cleared (step S107), and the initial setting process is terminated.

  If there is no abnormality in the fixing device 11 by the above initial setting process, the nip width is adjusted to an appropriate value at the start of printing. Note that the movement amount (distance) of the pressure roller 17 for obtaining the appropriate nip width read from the memory 21 by the control unit 20 in step S104 of FIG. Or measured immediately after mechanical adjustment work is performed at the product delivery destination and stored in the memory 21. Here, in the initial setting process, when the nip width is adjusted while moving the pressure roller 17 by one step as described above, the process until the fixing roller position variation detection sensor 19 is switched from on to off. It is desirable to update the information in the memory 21 according to the amount of movement of the pressure roller 17.

  Even if the nip width is adjusted to an appropriate value by the initial setting process at the start of printing as described above and printing is started, the nip width varies when the elastic layer 15b of the fixing roller 15 is thermally expanded during printing. Therefore, in the fixing device 11 according to the present embodiment, the control unit 20 repeatedly executes the nip width adjustment process shown in the flowchart of FIG. 6 at a predetermined cycle during printing, and the nip width varies when the nip width varies during printing. Adjust the width to an appropriate value.

  When the nip width adjustment process shown in FIG. 6 is started, the control unit 20 first determines whether or not the fixing roller position variation detection sensor 19 is turned on in step S201. If the fixing roller position variation detection sensor 19 remains off (step S201: No), it is determined that the nip width is maintained at an appropriate value, and the nip width adjustment process in FIG. Wait until the processing cycle is reached.

  On the other hand, when the fixing roller position variation detection sensor 19 is turned on (step S201: Yes), the control unit 20 indicates that the nip width varies due to the thermal expansion of the elastic layer 15b of the fixing roller 15. In step S202, the printing operation is interrupted. In step S <b> 203, the control unit 20 operates a motor (stepping motor) that is a driving source of the pressure roller moving mechanism 18 for one step, and moves the pressure roller 17 away from the fixing roller 15 by one step. Move. In step S204, the control unit 20 increments (increases by 1) the value of the nip correction counter.

  Next, in step S205, the control unit 20 checks whether or not the fixing roller position variation detection sensor 19 has been switched from on to off. If the fixing roller position fluctuation detection sensor 19 has been switched from on to off (step S205: Yes), it is determined that the nip width has been adjusted to an appropriate value, and the nip correction counter is cleared in step S206. In S207, the printing operation is resumed, and the series of nip width adjustment processing shown in FIG.

  On the other hand, when the fixing roller position variation detection sensor 19 remains on (step S205: No), the controller 20 has reached the predetermined specified value of the nip correction counter in step S208. Determine whether or not. If the value of the nip correction counter has reached the specified value (step S208: Yes), it is determined that some abnormality has occurred in the fixing device 11, and the operation panel of the color laser printer 100 is determined in step S209. An error message is displayed to notify the operator that an abnormality has occurred in the fixing device 11, and the nip width adjustment process is terminated. On the other hand, if the value of the nip correction counter has not reached the specified value (step S208: No), the process returns to step S203 and the subsequent processing is repeated, and when the fixing roller position variation detection sensor 19 is switched from on to off (step S205). : Yes), the nip correction counter is cleared (step S206), the printing operation is restarted (step S207), and the nip width adjustment process is terminated.

  In the fixing device 11 according to this embodiment, the nip width adjustment process is repeatedly performed at a predetermined period during printing, so that the nip width is increased during printing due to the thermal expansion of the elastic layer 15b of the fixing roller 15. Even if it fluctuates, the nip width can be adjusted to an appropriate value, and the fixing property can be stabilized.

  FIG. 7 is a flowchart illustrating an example of a process of measuring the movement amount (distance) of the pressure roller 17 that the control unit 20 reads from the memory 21 in step S104 of FIG. This process is performed, for example, immediately after a mechanical adjustment operation is performed at a factory or a product delivery destination before the color laser printer 100 is shipped.

  When the processing shown in the flowchart of FIG. 7 is started, the control unit 20 first starts the movement of the pressure roller 17 by the pressure roller moving mechanism 18 in step S301, and moves the pressure roller 17 to the fixing roller 15 side. And gradually move. In step S302, the control unit 20 determines whether the fixing roller position variation detection sensor 19 has been turned on.

  Here, when the fixing roller position fluctuation detection sensor 19 remains off (step S302: No), the control unit 20 sets the movement amount of the pressure roller 17 to the fixing roller 15 side to a predetermined maximum movement amount. It is determined whether the pressure roller 17 has reached the maximum movement amount (step S303: No), and the fixing roller 15 of the pressure roller 17 by the pressure roller moving mechanism 18 is determined. Continue moving to the side. On the other hand, when the movement amount of the pressure roller 17 reaches the maximum movement amount while the fixing roller position variation detection sensor 19 is off (step S303: Yes), the control unit 20 determines that the fixing roller position variation detection sensor 19 It is determined that an abnormality such as a failure has occurred. In step S304, the movement of the pressure roller 17 is stopped. In step S305, an error message is displayed on the operation panel of the color laser printer 100 to detect the change in the fixing roller position. The operator is notified that an abnormality such as a failure of the sensor 19 has occurred, and the processing shown in FIG.

  When the fixing roller position variation detection sensor 19 is turned on (step S302: Yes), the control unit 20 temporarily stops the movement of the pressure roller 17 by the pressure roller moving mechanism 18 in step S306. In step S307, the control unit 20 operates the motor (stepping motor) that is the driving source of the pressure roller moving mechanism 18 for one step, and moves the pressure roller 17 away from the fixing roller 15 by one step. Move. In step S308, the control unit 20 increments (increases by 1) the value of the pressure roller movement counter. The pressure roller movement counter moves the pressure roller 17 step by step from the position where the fixing roller position variation detection sensor 19 is turned on in order to measure the amount of movement of the pressure roller 17 to obtain an appropriate nip width. It is a counter that measures the number of steps when moved.

  Next, in step S309, the control unit 20 confirms whether or not the fixing roller position variation detection sensor 19 has been switched from on to off. When the fixing roller position fluctuation detection sensor 19 is switched from on to off (step S309: Yes), in step S310, the value of the pressure roller movement counter at that time is determined by the fixing roller position fluctuation detection sensor 19. The movement amount (distance) of the pressure roller 17 from the ON position to the position where an appropriate nip width is obtained is stored in the memory 21. Then, the control unit 20 clears the pressure roller movement counter in step S311 and ends the series of processes shown in FIG.

  On the other hand, when the fixing roller position variation detection sensor 19 remains on (step S309: No), the control unit 20 sets the value of the pressure roller movement counter to a predetermined specified value in step S312. Determine if it has been reached. If the value of the pressure roller movement counter reaches the specified value (step S312: Yes), it is determined that some abnormality has occurred in the fixing device 11, and the operation of the color laser printer 100 is performed in step S313. By displaying an error message on the panel or the like, the operator is notified that an abnormality has occurred in the fixing device 11, and the series of processing shown in FIG. On the other hand, if the value of the pressure roller movement counter has not reached the specified value (step S312: No), the process returns to step S307 and the subsequent processing is repeated, and when the fixing roller position variation detection sensor 19 is switched from ON to OFF ( Step S309: Yes), the value of the pressure roller movement counter at that time is stored in the memory 21 as the movement amount (distance) of the pressure roller 17 to the position where an appropriate nip width is obtained (step S310), and pressure is applied. The roller movement counter is cleared (step S311), and the series of processing shown in FIG.

  As described above in detail with specific examples, in the fixing device 11 according to the present embodiment, when the nip width varies due to the thermal expansion of the elastic layer 15b of the fixing roller 15 during printing, The fixing roller 15 is moved to the second position, and the fixing roller position change detection sensor 19 is turned on. When the fixing roller position variation detection sensor 19 is turned on during printing, the control unit 20 controls the operation of the pressure roller moving mechanism 18 to move the pressure roller 17 away from the fixing roller 15. Thus, even if the nip width fluctuates due to the thermal expansion of the elastic layer 15b of the fixing roller 15 during printing, it is possible to accurately detect the fluctuation of the nip width and adjust the nip width to an appropriate value. And fixing stability can be achieved.

  In the fixing device 11 according to the present embodiment, at the start of printing, the pressure roller 17 is moved to the fixing roller 15 side until the fixing roller position variation detection sensor 19 is turned on, and the fixing roller position variation detection sensor 19 is turned on. Since the pressure roller 17 is moved in a direction away from the fixing roller 15 by a predetermined distance stored in the memory 21 from the position, the width of the nip portion is adjusted to an appropriate value. Even when the fixing roller 15 and the pressure roller 17 are deformed at the start of printing due to the above, the nip width can be adjusted to an appropriate value, and the fixing property can be stabilized.

  Further, in the fixing device 11 according to the present embodiment, even when the pressure roller 17 is moved away from the fixing roller 15 when adjusting the nip width, the fixing roller position variation detection sensor 19 remains on and does not switch off. In this case, since an operator is notified that an abnormality has occurred in the fixing device 11 by displaying an abnormality message on the operation panel of the color laser printer 100, an appropriate error recovery such as a customer call is appropriate. Treatment can be prompted to the operator.

  In addition, the color laser printer 100 according to the present embodiment can output a high-quality printed matter stably by including such a fixing device 11.

  In addition, this invention is not limited to said embodiment as it is, It can be embodied by adding various deformation | transformation and change in the range which does not deviate from the summary in an implementation stage. For example, the above embodiment is an example in which the present invention is applied to the belt fixing type fixing device 11. However, the present invention can be effectively applied to other types of fixing devices such as a roller fixing method. is there. The above embodiment is an example in which the present invention is applied to the tandem color laser printer 100. However, the present invention can be effectively applied to any image forming apparatus including a fixing device.

DESCRIPTION OF SYMBOLS 11 Fixing device 15 Fixing roller 15b Elastic layer 15c Rotating shaft 17 Pressure roller (Pressure means)
18 Pressure roller moving mechanism (nip width adjusting means)
19 Fixing roller position fluctuation detection sensor (detection means)
20 Control unit (nip width adjusting means, notifying means)
21 Memory (storage means)
30 Side plate (support means)
31 Long hole (support means)
32 Slider (supporting means)
33 Bearing (support means)
100 color laser printer (image forming device)

JP 2008-139724 A

Claims (7)

A fixing roller that has an elastic layer that thermally expands on the outer periphery and is driven to rotate about a rotation axis;
A pressure member that presses against an elastic layer of the fixing roller to form a nip portion;
Support means for supporting the fixing roller so as to be movable between a first position and a second position where the rotation shaft is separated from the pressure member than the first position;
Detecting means for detecting that the fixing roller is in the second position;
Nip width adjusting means for adjusting the width of the nip portion by moving the pressure member in a direction away from the fixing roller when it is detected that the fixing roller is in the second position; A fixing device comprising: a fixing device;   The nip width adjusting means moves the pressure member toward the fixing roller until the fixing roller is detected to be in the second position at the start of printing, and the fixing roller is moved to the second position. The position of the pressure member at the time when it is detected to be in the position is used as a reference position, and the pressure member is moved from the reference position by a predetermined distance in a direction away from the fixing roller. The fixing device according to claim 1, wherein initial setting is performed.   The fixing device according to claim 2, further comprising storage means for storing the predetermined distance.   Informing means for informing that the pressing roller is in an abnormal state when it is still detected that the fixing roller is in the second position even if the pressing member is moved away from the fixing roller. The fixing device according to claim 1, wherein   5. The switch according to claim 1, wherein the detection unit is a switch that is turned on when two contact points come into contact with the fixing roller moving to the second position. 6. Fixing device.   An image forming apparatus comprising the fixing device according to claim 1. A fixing roller that has an elastic layer that thermally expands on the outer periphery and is driven to rotate about a rotation axis;
A pressure member that presses against an elastic layer of the fixing roller to form a nip portion;
And a supporting unit that supports the fixing roller so as to be movable between a first position and a second position where the rotation shaft is separated from the pressure member relative to the first position. A control method,
Detecting that the fixing roller is in the second position;
And a step of adjusting the width of the nip portion by moving the pressure member in a direction away from the fixing roller when it is detected that the fixing roller is in the second position. The fixing device control method.

Images