JP2012042755A - 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 properly controlling nip width and keeping stable fixing performance, an image forming device, and a controlling method of the fixing device.SOLUTION: The position of a pressurizing roller 17, when the change rate of temperature of the pressurizing roller 17 exceeds a reference value, is detected as a contact starting position where the pressurizing roller 17 starts to contact with an elastic layer 15b of a fixing roller 15. The moving amount of the pressurizing roller 17 from the contact starting position which can obtain the optimal nip width according to a kind of a recording medium P is calculated, and the pressurizing roller 17 is moved to the fixing roller 15 side only by the calculated moving amount.

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. As a fixing device of an image forming apparatus, a fixing device of a belt fixing method that heats and melts a toner image on a recording medium with the heat of a fixing belt, or a roller fixing method that heats and melts a toner image on a recording medium with the heat of a fixing roller Such fixing devices are 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, and a moving mechanism for moving the pressure roller in a direction in which the pressure roller comes in contact with and separates from the fixing roller are provided. Then, in the process of sandwiching and feeding out the recording medium to the nip formed between the fixing roller and the pressure roller via the fixing belt, the toner image on the recording medium is formed by the heat of the fixing belt using the heating roller as a heat source. The toner image is fixed on the recording medium by heating and melting and applying pressure.

  In such a fixing device, in order to obtain an optimum amount of heat to the toner image on the recording medium passing through the nip portion to obtain stable fixing performance, the width of the nip portion (hereinafter referred to as nip width) is appropriately set. It is important to control. Here, since the optimum nip width varies depending on the type of the recording medium that passes through the nip portion, the nip width depends on the type of the recording medium, particularly in a fixing device of an image forming apparatus that uses a plurality of types of recording media. Variable control is also performed (for example, refer to Patent Document 1).

  By the way, in a conventional fixing device that performs variable control of the nip width, variable control of the nip width is performed based on an adjustment value at the time of manufacturing the image forming apparatus. Specifically, in the adjustment work performed at the time of manufacturing the image forming apparatus, the distance between the centers of the fixing roller and the pressure roller of the fixing apparatus is obtained, and the distance between the centers is specific to the fixing apparatus of the image forming apparatus. It is stored in the memory as a reference value for nip width control. When the image forming apparatus actually forms an image on a recording medium, the optimum nip for each recording medium to be used is controlled by controlling the position of the pressure roller based on the reference value stored in the memory. A width is obtained.

  However, in the thermal transient state between the start of the image forming apparatus and the entire fixing device reaching the thermal equilibrium state, the fixing roller is affected by the expansion of the elastic layer of the fixing roller as the temperature rises. Even when the center-to-center distance with the pressure roller does not change, the nip width varies. For this reason, as in the conventional fixing device, the nip width is controlled with the distance between the centers of the fixing roller and the pressure roller of the fixing device obtained in the adjustment work performed at the time of manufacturing the image forming apparatus as a reference value. In such a case, the nip width may not be appropriately controlled, and there is a problem that it is difficult to maintain stable fixing performance.

  The present invention has been made in view of the above, and provides a fixing device, an image forming apparatus, and a fixing device control method capable of maintaining a stable fixing performance by appropriately controlling the nip width. With the goal.

  In order to solve the above-described problems and achieve the object, a fixing device according to the present invention includes a heat source, a fixing roller in which an elastic layer is formed on the outer periphery of a core metal, and the fixing roller with respect to the heat source. A pressure member that is disposed at a remote position and presses against the elastic layer of the fixing roller to form a nip portion, and a moving unit that moves the pressure member in a direction to contact with and separate from the fixing roller; A first temperature detecting means for detecting the temperature of the pressure member; and the moving means moving the pressure member from a position away from the fixing roller toward the fixing roller while moving the first member. The position of the pressure member at the time when the rate of change in temperature of the pressure member detected by the temperature detection means exceeds a reference value, and the pressure member starts to contact the elastic layer of the fixing roller. Contact detected as contact start position Nip width adjusting means for adjusting the width of the nip portion by controlling the amount by which the moving means moves the pressure member from the contact start position to the fixing roller side. It is characterized by that.

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

  The fixing device control method according to the present invention includes a heat source, a fixing roller in which an elastic layer is formed on an outer periphery of a cored bar, and a position farther from the fixing roller than the heat source. A pressure member that presses against an elastic layer of the fixing roller to form a nip portion; a moving unit that moves the pressure member in a direction to move toward and away from the fixing roller; and a temperature of the pressure member. And a first temperature detecting unit, wherein the moving unit moves the pressure member from a position away from the fixing roller toward the fixing roller. The position of the pressure member when the rate of change of the temperature of the pressure member detected by the temperature detection means exceeds a reference value, and the pressure member contacts the elastic layer of the fixing roller. Detected as the contact start position that started And adjusting the width of the nip portion by controlling the amount by which the moving means moves the pressure member from the contact start position to the fixing roller side. .

  According to the present invention, the contact start position at which the pressure member starts to contact the elastic layer of the fixing roller is detected from the rate of change in temperature of the pressure member, and the pressure unit is moved from the contact start position to the fixing roller. Since the width of the nip portion is adjusted by controlling the amount of movement to the side, there is an effect that stable fixing performance can be maintained by appropriately controlling the nip width.

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 block diagram showing a configuration of a control system related to adjustment of the nip width. FIG. 4 is a graph showing the temperature change of the pressure roller when the pressure roller is gradually moved from the position away from the fixing roller to the fixing roller side. FIG. 5 is a graph illustrating temperature control in the fixing device. FIG. 6 is a flowchart showing a series of processes related to contact start position detection that is performed during the period from when the color laser printer is started until the fixing device reaches a thermal equilibrium state. FIG. 7 is a flowchart showing processing for adjusting the nip width in accordance with the type of recording medium used for printing.

  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 to be 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 (moving means) 18, a fixing belt temperature sensor 19, a pressure roller temperature sensor (first temperature detecting means) 20, a fixing roller core metal temperature sensor (second temperature detecting means) 21, A control unit 22 and a memory 23 are provided.

  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 T is ensured. 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 24 (heat source) is fixedly provided inside the cylindrical body. The heater 24 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 24 generates heat when electric power whose output is controlled is supplied from the power supply unit (AC power supply) of the color laser printer 100. The heating roller 14 is heated by the radiant heat from the heater 24, and heat is further applied to the toner image T on the recording medium P from the surface of the fixing belt 13 heated by the heat conduction from the heating roller 14. The surface temperature of the fixing belt 13 is detected by a fixing belt temperature sensor 19 such as a thermopile disposed opposite to the surface of the fixing belt 13, and the surface temperature of the fixing belt 13 becomes constant at a desired control temperature (fixing temperature). Thus, the output of the heater 24 is controlled.

  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). The fixing roller 15 has shafts at both ends rotatably attached to side plates of the fixing device 11 via bearings, and is rotationally driven 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 is driven and 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, while 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.

  In order to heat and melt the toner image T on the recording medium P to be stably fixed to the recording medium P, the width of the nip portion (the portion where the recording medium P is sandwiched between the fixing roller 15 and the pressure roller 17 ( It is necessary to appropriately set the nip width) according to the type of the recording medium P to be used so as to give an optimum amount of heat to the toner image T. The nip width can be adjusted by controlling the position of the pressure roller 17 with respect to the fixing roller 15 by moving the pressure roller 17 in the direction of contacting and separating from the fixing roller 15 using the pressure roller moving mechanism 18 described above. . However, due to the influence of the elastic layer 15b of the fixing roller 15 expanding as the temperature rises, the nip width fluctuates even if the position of the pressure roller 17 with respect to the fixing roller 15 is set to a predetermined position, resulting in fixing. May cause a variation in sex. Therefore, in the fixing device 11 according to the present embodiment, when the nip width is adjusted, the position where the pressure roller 17 starts to contact the elastic layer 15b of the fixing roller 15 (contact start position) is detected. By controlling the amount by which the pressure roller moving mechanism 18 moves the pressure roller 17 toward the fixing roller 15 with the detected contact start position as a reference, an optimum nip width corresponding to the type of the recording medium P to be used is obtained. I try to get it.

  Specifically, a pressure roller temperature sensor 20 such as a thermopile for detecting the temperature of the pressure roller 17 is provided at a position facing the surface of the pressure roller 17, for example. Then, from the rate of change of the temperature of the pressure roller 17 detected by the pressure roller temperature sensor 20, the contact start position where the pressure roller 17 starts to contact the elastic layer 15 b of the fixing roller 15 is detected. That is, when the pressure roller 17 moves from the position away from the fixing roller 15 to the fixing roller 15 side and contacts the elastic layer 15b of the fixing roller 15, heat conduction from the fixing roller 15 to the pressure roller 17 occurs. A steep temperature rise appears on the pressure roller 17. Therefore, while the pressure roller 17 is moved to the fixing roller 15 side, the temperature of the pressure roller 17 detected by the pressure roller temperature sensor 20 is monitored, and the rate of change in the temperature of the pressure roller 17 is the reference value. It is possible to detect the position of the pressure roller 17 at a time point exceeding the above-mentioned position as the contact start position. Then, the pressure roller moving mechanism 18 controls the amount by which the pressure roller 17 is moved to the fixing roller 15 with the detected contact start position as a reference, so that the optimum according to the type of the recording medium P to be used. A nip width can be obtained.

  In addition, when the color laser printer 100 is started from a state where it is not sufficiently warmed up, it takes several minutes for the temperature of the fixing belt 13 in the fixing device 11 to reach the temperature necessary for fixing and melting the toner image T. However, even if the fixing belt 13 reaches the control temperature, the whole including the inside of the fixing device 11 is in a thermal transient state. When the load on the fixing device 11 increases as the high-speed full-color color laser printer 100 increases, the fixing device 11 itself also increases in size. Therefore, it takes several tens of minutes to reach the thermal equilibrium state including the inside of the fixing device 11. There is also. Even when the fixing device 11 is ready for printing, the thermal equilibrium is not reached inside the fixing device 11. For example, the nip width after the color laser printer 100 is started from the cool-down state is the thermal transient of the fixing device 11. Especially fluctuates while in the state.

  Therefore, in the fixing device 11 according to the present embodiment, the fixing roller core metal temperature sensor 21 that detects the temperature of the core metal 15b of the fixing roller 15 is provided in order to detect that the fixing device 11 is in a thermal transient state. Yes. The fixing roller mandrel temperature sensor 21 is provided in a portion where the influence from the heater (heat source) 24 inside the fixing device 11 is small and the temperature change has a large influence on the nip width fluctuation. For example, as the fixing roller core temperature sensor 21, a thermistor or the like that is installed in pressure contact with the core 15b of the fixing roller 15 and directly detects the surface temperature of the core 15b can be used.

  In the fixing device 11 according to the present embodiment, a fixing belt temperature sensor 19, a pressure roller temperature sensor 20, and a fixing roller core metal temperature sensor 21 are connected to the control unit 22. As described above, the control unit 22 controls the output of the heater 24 so that the surface temperature of the fixing belt 13 detected by the fixing belt temperature sensor 19 becomes constant at a predetermined control temperature. Further, as described above, the control unit 22 contacts the pressure roller 17 that starts to contact the elastic layer 15 b of the fixing roller 15 based on the temperature of the pressure roller 17 detected by the pressure roller temperature sensor 20. Detect the starting position. The detected contact start position information (specifically, position information of the eccentric cam 18d of the pressure roller moving mechanism 18 when the pressure roller 17 is at the contact start position) is used as the contact start position information 25. The data is stored in a memory 23 accessible from the control unit 22.

  Further, the control unit 22 determines whether or not the fixing device 11 is in a thermal transient state based on the temperature of the core metal 15 b of the fixing roller 15 detected by the fixing roller core temperature sensor 21. Here, the thermal transient state refers to the following state. That is, when the color laser printer 100 is in a non-operating state for a long time, the fixing device 11 inside the color laser printer 100 is in a state equal to the ambient temperature. When the surface temperature of the fixing belt 13 is heated to a predetermined control temperature (fixing temperature) at which the toner image T can be fixed in the process of making the color laser printer 100 ready for printing, the printing becomes possible. Even in a possible state, the temperature inside the fixing device 11, particularly the member located at a position away from the heater 24 as a heat source, continues to rise. Such a state is referred to as a thermal transient state. In the thermal transient state, the elastic layer 15b of the fixing roller 15 expands and causes a variation in the nip width. For this reason, when the fixing device 11 is in a thermal transient state, the control unit 22 repeatedly detects the contact start position, and updates the contact start position information 25 stored in the memory 23 with newly obtained information as needed. To do. The state in which the temperature rise of the members inside the fixing device 11 is called a thermal equilibrium state, and when the fixing device 11 is in a thermal equilibrium state, detection of the contact start position by the control unit 22 is stopped. .

  FIG. 3 is a block diagram showing a configuration of a control system related to adjustment of the nip width. This control system includes a fixing belt temperature sensor 19, a pressure roller temperature sensor 20, a fixing roller core temperature sensor 21, a control unit 22, a memory 23, a pressure roller moving mechanism 18, and a heater 24. Composed. The control unit 22 includes a heater output control unit 101, a determination unit 102, a contact start position detection unit 103, and a nip width adjustment unit 104 as functional configurations. The control unit 22 is configured using, for example, a microcomputer equipped with a CPU, RAM, ROM, input / output interface, and the like, and the CPU executes a control program stored in the ROM using the RAM as a work area. Thus, the function as the heater output control unit 101, the function as the determination unit 102, the function as the contact start position detection unit 103, and the function as the nip width adjustment unit 104 are realized.

  The heater output control unit 101 controls the output of the heater 24 so that the surface temperature of the fixing belt 13 detected by the fixing belt temperature sensor 19 becomes constant at a predetermined control temperature (fixing temperature).

  The determination unit 102 determines whether the fixing device 11 is in a thermal transient state or a thermal equilibrium state. Specifically, if the temperature of the cored bar 15a of the fixing roller 15 detected by the fixing roller cored bar temperature sensor 21 is equal to or lower than the cored bar temperature saturation value, the determination unit 102 causes the fixing device 11 to enter a thermal transient state. Judge that there is. On the other hand, if the temperature of the core metal 15a of the fixing roller 15 detected by the fixing roller core metal temperature sensor 21 exceeds a core metal temperature saturation value described later, it is determined that the fixing device 11 is in a thermal equilibrium state. The core metal temperature saturation value is a value obtained by subtracting the temperature difference determined by the thermal resistance of the fixing roller 15 from the fixing temperature controlled to a constant temperature by the heater output control unit 101.

  When the fixing device 11 is in a thermal transient state, the contact start position detection unit 103 detects that the pressure roller 17 is based on the temperature of the pressure roller 17 detected by the pressure roller temperature sensor 20. The contact start position at which contact with the elastic layer 15 b is started is detected, and information on the detected contact start position is stored in the memory 23 as contact start position information 25. Specifically, the contact start position detector 103 controls the operation of the pressure roller moving mechanism 18 to gradually move the pressure roller 17 from a position away from the fixing roller 15 toward the fixing roller 15. The output of the pressure roller temperature sensor 20 is sampled at regular intervals. Then, the temperature change rate of the pressure roller 17 is obtained from the difference between the previous sampling value and the current sampling value, and the position of the pressure roller 17 when the temperature change rate of the pressure roller 17 exceeds the reference value is contacted. The position information is detected as the start position, and the position information is stored in the memory 23 as the contact start position information 25. While the fixing device 11 is in a thermal transient state, the contact start position detection unit 103 repeats the above processing and updates the contact start position information 25 in the memory 23 to the latest information.

  FIG. 4 is a graph showing the temperature change of the pressure roller 17 when the pressure roller 17 is gradually moved from the position away from the fixing roller 15 to the fixing roller 15 side. In the drawing, the vertical axis indicates the temperature of the pressure roller 17, and the horizontal axis indicates time (the pressure roller 17 moves toward the fixing roller 15 as time elapses). Moreover, the upward arrow in the figure indicates that the contact start position detection unit 103 of the control unit 22 is sampling the output of the pressure roller temperature sensor 20 at regular intervals.

  Since the pressure roller 17 does not have a heat source inside, if there is no influence by heat conduction from the fixing roller 15, the temperature rise is only caused by radiant heat, and the influence is small, so the temperature rise is moderate. Here, when the pressure roller 17 approaches the fixing roller 15 and heat conduction from the fixing roller 15 to the pressure roller 17 occurs, the temperature rise of the pressure roller 17 increases. Since the heat is directly transferred from the fixing roller 15 to the pressure roller 17 when contacting the 15 elastic layers 15b, the temperature rise of the pressure roller 17 becomes steep.

  Assuming that the temperature change rate of the pressure roller 17 between the upward arrows in FIG. 4 is Δ, when the value of Δ exceeds a certain reference value k, the pressure roller 17 is elastic layer 15 b of the fixing roller 15. It can be determined that the contact has been made. In FIG. 4, since the value of Δ exceeds the reference value k at the time T0, the position of the pressure roller 17 at the time T0 is detected as the contact start position.

  When actually printing on the recording medium P, the nip width adjusting unit 104 controls the operation of the pressure roller moving mechanism 18 so that the pressure roller 17 is moved from the contact start position according to the type of the recording medium P. Thus, the nip width is adjusted by moving the fixing nip 15 to the position where the optimum nip width is obtained. Specifically, the nip width adjusting unit 104 reads the contact start position information 25 from the memory 23 when actually printing on the recording medium P, and the current state of the elastic layer 15b of the fixing roller 15 ( The contact start position of the pressure roller 17 corresponding to the state of thermal expansion is grasped. Then, the amount of movement from the contact start position of the pressure roller 17 necessary to obtain the optimum nip width is calculated according to the type of the recording medium P used for printing, and the pressure roller 17 is moved to the contact start position. The operation of the pressure roller moving mechanism 18 is controlled so as to move toward the fixing roller 15 by the amount of movement calculated from the above. The optimum amount of movement of the pressure roller 17 according to the type of the recording medium P used for printing is, for example, for obtaining the type of the recording medium P supported by the color laser printer 100 and the optimum nip width. A table in which the amount of movement of the pressure roller 17 from the contact start position is associated with each other can be created in advance and held in the memory 23 or the like, and can be obtained with reference to this table.

  FIG. 5 is a graph illustrating temperature control in the fixing device 11, where the vertical axis of the diagram is temperature, the horizontal axis is time, the solid line graph in the figure is the temperature change of the surface temperature of the fixing belt 13, and the broken line graph Indicates the temperature change of the fixing roller 15, and the dashed line graph indicates the temperature change of the pressure roller 17.

  When the surface temperature of the fixing belt 13 reaches the control temperature, the heater output control unit 101 turns on and off the heater 24 and controls the surface temperature of the fixing belt 13 to be maintained at the control temperature. In such a control state (hereinafter, referred to as “fixing temperature constant value control”), the contact start position detection unit 103 performs the above-described process of detecting the contact start position. Here, when the pressure roller 17 contacts the elastic layer 15 b of the fixing roller 15, a steep temperature gradient M is detected in the temperature of the pressure roller 17 due to heat conduction from the fixing roller 15 to the pressure roller 17. The contact start position detection unit 103 detects the position of the pressure roller 17 at the time when the temperature gradient M of the pressure roller 17 is detected as the contact start position.

  Even after the contact start position is detected, the temperature of the cored bar 15a of the fixing roller 15 continues to rise gently until the temperature becomes saturated. Here, if the thermal resistance of the fixing roller 15 is Rth and the heat radiation amount of the fixing roller 15 is Q, the temperature of the cored bar 15a of the fixing roller 15 is saturated because C = Rth × Q with respect to the control temperature. When the temperature reaches the temperature obtained by subtracting the temperature difference C defined by The thermal resistance Rth of the fixing roller 15 is a fixed value determined by the material constituting the fixing roller 15. The heat dissipation amount Q of the fixing roller 15 is affected by the ambient temperature environment, but the upper limit value is a fixed value depending on the use environment conditions of the color laser printer 100. Therefore, C (min.), Which is the minimum value of the temperature difference C, is also defined as a fixed value.

  In the present embodiment, a value obtained by adding a predetermined margin ΔC to a minimum value C (min.) Of the temperature difference C defined as a fixed value is defined as a temperature difference C, and a value obtained by subtracting the temperature difference C from the control temperature. The core metal temperature is saturated. The determination unit 102 determines that the fixing device 11 is in a thermal transient state while the temperature of the cored bar 15a of the fixing roller 15 is equal to or lower than the cored bar temperature saturation value, and the temperature of the cored bar 15a of the fixing roller 15 is When the core metal temperature saturation value is exceeded, it is determined that the fixing device 11 has reached a thermal equilibrium state.

  FIG. 6 is a flowchart showing a series of processes related to contact start position detection that is performed from when the color laser printer 100 is started until the fixing device 11 reaches a thermal equilibrium state. FIG. 7 is a flowchart showing processing for adjusting the nip width according to the type of the recording medium P used for printing. Hereinafter, the operation of the fixing device 11 will be specifically described with reference to FIGS. 6 and 7.

  A series of processes shown in the flowchart of FIG. 6 is started when the color laser printer 100 is turned on. First, in step S101, energization of the motor that rotationally drives the fixing roller 15 is started, and driving of the fixing belt 13 is started. In step S102, energization of the heater 24 in the heating roller 14 is started, and heating of the heating roller 14 is started.

  Next, in step S103, it is determined whether or not the surface temperature of the fixing belt 13 detected by the fixing belt temperature sensor 19 has reached a predetermined control temperature. If the surface temperature of the fixing belt 13 has not reached the control temperature as a result of this determination (step S103: No), the heating roller 14 continues to be heated, and when the surface temperature of the fixing belt 13 reaches the control temperature (step S103). : Yes), in the next step S104, the fixing temperature constant value control by the heater output control unit 101 of the control unit 22 is started. When the fixing temperature constant value control is started, thereafter, the output of the heater 24 is controlled so that the surface temperature of the fixing belt 13 is maintained at the control temperature.

  Next, in step S <b> 105, the operation of the pressure roller moving mechanism 18 is controlled by the contact start position detection unit 103 of the control unit 22, and the pressure roller 17 moves from the position away from the fixing roller 15 to the fixing roller 15 side. Move gradually. In step S106, the pressure roller temperature sensor 20 detects the temperature of the pressure roller 17, and in step S107, it is determined whether the temperature change rate of the pressure roller 17 exceeds a reference value.

  If the temperature change rate of the pressure roller 17 is equal to or less than the reference value as a result of the determination in step S107 (step S107: No), the movement of the pressure roller 17 in step S105 and the temperature detection of the pressure roller 17 in step S106 are detected. Repeatedly, when the temperature change rate of the pressure roller 17 exceeds the reference value (step S107: Yes), in the next step S108, the position of the pressure roller 17 at that time is detected as the contact start position, and the contact start position. Information 25 is stored in the memory 23. In step S <b> 109, the operation of the pressure roller moving mechanism 18 is controlled, and the pressure roller 17 moves to a position away from the fixing roller 15.

  When the processing from step S101 to step S109 is completed, the color laser printer 100 can execute printing processing for forming an image on the recording medium P. When a print execution instruction is input, the nip width adjustment process shown in the flowchart of FIG. 7 is executed by the nip width adjustment unit 104 of the control unit 22 as an interrupt process for the process shown in the flowchart of FIG. The nip width adjustment process will be described later.

  Next, in step S110, the temperature of the core metal 15a of the fixing roller 15 is detected by the fixing roller core metal temperature sensor 21, and in step S111, the determination unit 102 of the control unit 22 detects the temperature of the core metal 15a of the fixing roller 15. It is determined whether or not has changed by more than a specified value. If the temperature of the cored bar 15a of the fixing roller 15 has changed by more than a specified value (Step S111: Yes), the elastic layer 15b of the fixing roller 15 may be thermally expanded to change the contact start position. Since the property is high, the process returns to step S105 and the process of detecting the contact start position is repeated. On the other hand, if the temperature of the cored bar 15a of the fixing roller 15 has not changed more than the specified value (step S111: No), the temperature of the cored bar 15a of the fixing roller 15 exceeds the cored bar temperature saturation value in the next step S112. Is determined.

  As a result of the determination in step S112, if the temperature of the cored bar 15a of the fixing roller 15 is equal to or lower than the cored bar temperature saturation value (step S112: No), the fixing device 11 is in a thermal transient state, and thus step S110 and step S111 The process is repeated. On the other hand, when the temperature of the cored bar 15a of the fixing roller 15 exceeds the cored bar temperature saturation value (step S112: Yes), the fixing device 11 has reached a thermal equilibrium state, and thus a series of processes shown in the flowchart of FIG. To do.

  When an instruction to execute printing is input to the color laser printer 100, the processing shown in the flowchart of FIG. 7 is started by the nip width adjusting unit 104 of the control unit 22. First, in step S201, the recording medium P used for printing is started. The type is identified. Identification of the type of the recording medium P can be realized, for example, by inputting print condition setting information set by the user.

  Next, in step S202, the contact start position information 25 stored in the memory 23 is read. In step S203, the amount of movement of the pressure roller 17 from the contact start position for obtaining an optimum nip width according to the type of the recording medium P used for printing is calculated.

  Next, in step S204, the operation of the pressure roller moving mechanism 18 is controlled, and the pressure roller 17 is controlled to move to the fixing roller 15 side from the contact start position by the amount of movement calculated in step S203. The process shown in the flowchart of FIG. 7 ends. As a result, even when the elastic layer 15b of the fixing roller 15 is in a thermally expanded state, it is possible to adjust the nip width to the optimum according to the type of the recording medium P used for printing. The fixing performance can be stabilized.

  As described above in detail with reference to specific examples, according to the fixing device 11 according to the present embodiment, the contact start position detecting unit 103 of the control unit 22 is separated from the fixing roller 15 by the pressure roller 17. The operation of the pressure roller moving mechanism 18 is controlled so as to gradually approach the fixing roller 15 side from the determined position, and the change rate of the temperature of the pressure roller 17 detected by the pressure roller temperature sensor 20 during that time becomes a reference value. The position of the pressure roller 17 at the time of exceeding is detected as a contact start position at which the pressure roller 17 starts contact with the elastic layer 15 b of the fixing roller 15. Then, the nip width adjusting unit 104 of the control unit 22 can move from the contact start position detected by the contact start position detecting unit 103 to obtain an optimal nip width according to the type of the recording medium P used for printing. And the operation of the pressure roller moving mechanism 18 is controlled so that the pressure roller 17 moves toward the fixing roller 15 by the calculated amount of movement. Therefore, even when the elastic layer 15b of the fixing roller 15 is in a thermally expanded state, the nip width is appropriately adjusted so that an optimum nip width corresponding to the type of the recording medium P used for printing can be obtained. And stable fixing performance can be maintained.

  Further, according to the fixing device 11 according to the present embodiment, the determination unit 102 of the control unit 22 determines that the temperature of the core metal 15a of the fixing roller 15 detected by the fixing roller core metal temperature sensor 21 has the core metal temperature saturation value. Whether or not the fixing device 11 is in a thermal transient state or a thermal equilibrium state is determined depending on whether or not it exceeds, and when the fixing device 11 is in a thermal transient state, the contact start position detecting unit 103 The contact start position detection process is repeatedly performed to update the contact start position information 25 stored in the memory 23 as needed. Therefore, even when the elastic layer 15b of the fixing roller 15 gradually expands due to thermal transition of the fixing device 11 and the contact start position fluctuates, the nip width can be adjusted appropriately and stable. Fixing performance can be maintained.

  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.

11 Fixing Device 15 Fixing Roller 17 Pressure Roller (Pressure Member)
18 Pressure roller moving mechanism (moving means)
20 Pressure roller temperature sensor (first temperature detection means)
21 Fixing roller core temperature sensor (second temperature detecting means)
22 Control unit 24 Heater (heat source)
100 color laser printer (image forming device)
102 determination unit (determination means)
103 Contact start position detection unit (contact start position detection means)
104 Nip width adjusting part (nip width adjusting means)

JP 2001-154525 A

Claims (6)

A heat source,
A fixing roller in which an elastic layer is formed on the outer periphery of the metal core;
A pressure member disposed at a position farther than the fixing roller with respect to the heat source, and press-contacting an elastic layer of the fixing roller to form a nip portion;
Moving means for moving the pressurizing member in a direction of coming into contact with and separating from the fixing roller;
First temperature detecting means for detecting the temperature of the pressure member;
A rate of change in temperature of the pressure member detected by the first temperature detection means while the moving means moves the pressure member from a position away from the fixing roller toward the fixing roller. Contact start position detecting means for detecting the position of the pressure member at the time when the reference value is exceeded as a contact start position at which the pressure member starts contact with the elastic layer of the fixing roller;
And a nip width adjusting unit that adjusts a width of the nip portion by controlling an amount by which the moving unit moves the pressure member from the contact start position to the fixing roller side. apparatus. Determination means for determining whether the fixing device is in a thermal transient state or in a thermal equilibrium state;
The contact position detection unit repeatedly detects the contact start position and updates the information of the contact start position based on a new detection result when the determination unit determines that the fixing device is in a thermal transient state. The fixing device according to claim 1, wherein when the determination unit determines that the fixing device is in a thermal equilibrium state, detection of the contact start position is stopped. A second temperature detecting means for detecting the temperature of the core of the fixing roller;
If the temperature of the core metal of the fixing roller detected by the second temperature detecting means is equal to or lower than a predetermined temperature, it is determined that the fixing device is in a thermal transient state, and the temperature of the core metal of the fixing roller is the predetermined temperature. The fixing device according to claim 2, wherein when the temperature is exceeded, the fixing device is determined to be in a thermal equilibrium state.   The predetermined temperature is a value obtained by subtracting a temperature difference determined by a thermal resistance of the fixing roller from a fixing temperature controlled to be a constant temperature by controlling a heat generation amount of the heat source. The fixing device according to claim 3.   An image forming apparatus comprising the fixing device according to claim 1. A heat source,
A fixing roller in which an elastic layer is formed on the outer periphery of the metal core;
A pressure member disposed at a position farther than the fixing roller with respect to the heat source, and press-contacting an elastic layer of the fixing roller to form a nip portion;
Moving means for moving the pressurizing member in a direction of coming into contact with and separating from the fixing roller;
A first temperature detecting means for detecting the temperature of the pressure member, and a control method of a fixing device,
A rate of change in temperature of the pressure member detected by the first temperature detection means while the moving means moves the pressure member from a position away from the fixing roller toward the fixing roller. Detecting the position of the pressure member at a time when the reference value is exceeded as a contact start position at which the pressure member starts contact with the elastic layer of the fixing roller;
Adjusting the width of the nip portion by controlling the amount by which the moving means moves the pressure member from the contact start position to the fixing roller side. Method.

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