JP2012118161A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve controllability of a fixing temperature by appropriately controlling power while separating a paper sheet from a fixing member with air flow for separation.SOLUTION: A fixing control unit 60 variably controls power to be supplied to a heating unit 53 in accordance with capacity of air flow for separation by setting a power instruction with a power table stored in a storage unit 63 referred to. The power table defines a relationship between a capacity of air flow for separation sent by a separation unit and an increased quantity of power supplied to the heating unit 53 increased beyond a reference power quantity. The fixing control unit 60 determines the increased quantity of power on the basis of the capacity of air flow for separation and sets a power instruction in consideration of the determined increased quantity of power in addition to the reference power quantity.

Description

  The present invention relates to a fixing device and an image forming apparatus using the same.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are known as printers, copiers, and the like. In this image forming apparatus, when a toner image is formed on a sheet, the toner image is transferred to the sheet, and then the sheet passes through a pressure contact portion (fixing nip portion) of a pair of fixing members constituting the fixing device. A process of fixing a toner image on a sheet is executed. By the way, in this type of fixing device, there is a problem that the paper that has passed through the fixing nip portion is wound around the fixing member (for example, a fixing roller) and is not separated from the fixing member. Therefore, a fixing device that separates a sheet from a fixing member using separation air is known.

  Patent Document 1 discloses a fixing device that suppresses winding of a sheet around a fixing member. In this fixing device, when the paper is an OHP sheet having a different fixing condition from that of plain paper, the fixing roller is switched to an optimum target fixing temperature, and the fixing roller is maintained at the target fixing temperature according to the detection temperature of the thermistor. The power supply from the power source to the heater is adjusted, and the drive of the fan that rapidly cools the fixing roller is adjusted.

JP 2000-47521 A

  However, since the separation air is blown also to the fixing member, this takes heat of the fixing member, and there is a problem that the fixing temperature is lowered. As described in Patent Document 1, power control has been performed to maintain the target fixing temperature, but power control has not been performed in consideration of the influence of the separation wind.

  The present invention has been made in view of such circumstances, and an object thereof is to improve the controllability of the fixing temperature by appropriately performing power control while separating the paper from the fixing member by the separation wind. It is.

  In order to solve such a problem, the first invention provides a pair of fixing members for fixing a toner image on a sheet by passing the sheet through a fixing nip portion, and a fixing member with a heating amount corresponding to the supplied electric power. Based on the detection results of the heating unit that heats the sheet, the separation unit that blows the separation air from the sheet discharge side in the fixing nip unit, the fixing temperature detection unit that detects the temperature of the fixing member, and the fixing temperature detection unit A temperature control unit that performs temperature control to switch the on / off operation of the heating unit, sets a power command that defines power to be supplied to the heating unit during the on operation, and an air volume control unit that controls the amount of separated air by the separation unit, A fixing device is provided that includes a storage unit that holds a power table that defines a correspondence relationship between the amount of separated air flow by the separation unit and the amount of power supplied to the heating unit. In this case, the temperature control unit variably controls the power supplied to the heating unit in accordance with the air volume of the separated air set by the air volume control unit by setting the power command with reference to the power table of the storage unit. A fixing device.

  Here, in the first invention, it is preferable that the power table defines a correspondence relationship between the amount of separated air by the separation unit and the amount of power increase with respect to a reference amount of power supplied to the heating unit. In this case, it is desirable that the temperature control unit determines the power increase amount based on the flow rate of the separated wind, and sets the power command by adding the reference amount to the determined power increase amount.

  In the first invention, the air volume control unit preferably sets the air volume of the separation air according to the paper type.

  In the first aspect of the invention, it is preferable that the temperature control unit performs a process of determining the amount of increase in power on the condition that the paper type of the paper has been selected. Or it is preferable that a temperature control part performs the process which determines an electric power increase amount on the conditions of the printing start command which is a command of the printing start from a user.

  In the first aspect of the invention, the temperature control unit forcibly turns on the heating unit on condition of a print start command that is a print start command from the user, and on condition that the sheet reaches the fixing nip unit. It is preferable to shift to temperature control.

  Furthermore, in the first invention, when the temperature control unit determines that the temperature of the fixing member has shifted to a stable state based on the target fixing temperature of the fixing member, the temperature control unit does not take into account the power increase amount. It is preferable to set only the amount as the power command.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image forming unit that transfers a toner image onto a sheet; and the fixing device according to the first aspect that fixes the transferred toner image onto the sheet. .

  According to the present invention, the power supplied to the heating unit can be set to an appropriate amount by setting the power command according to the air volume of the separated wind. As a result, appropriate power control can be performed in consideration of a temperature drop due to the separation wind, so that the controllability of the fixing temperature can be improved.

Explanatory drawing which shows the structure of the image forming apparatus 1 typically. Block diagram schematically showing a control system of the image forming apparatus 1 6 is a flowchart for explaining an operation centering on fixing processing of the image forming apparatus 1 according to the first embodiment. Explanatory diagram showing the transition of the temperature of the fixing upper roller 51 Flowchart for explaining an operation centering on fixing processing of the image forming apparatus 1 according to the second embodiment.

(First embodiment)
FIG. 1 is an explanatory diagram schematically showing a configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an electrophotographic image forming apparatus such as a copying machine, for example, and forms a full-color image by arranging a plurality of photoconductors facing a single intermediate transfer belt in a vertical direction. A tandem type color image forming apparatus.

  The image forming apparatus 1 includes a document reading unit 10, exposure units 20Y, 20M, 20C, and 20K, image forming units 30Y, 30M, 30C, and 30K, an intermediate transfer unit 40, a fixing device 50, a paper discharge reversing unit 70, and a refeed. The paper unit 80 and the paper supply unit 90 are mainly configured, and these are housed in one housing.

  The document reading unit 10 includes an automatic document feeder ADF at the top thereof. The documents D placed on the document placement table 15 of the automatic document feeder ADF are separated one by one, sent out to the document conveyance path, and conveyed by the conveyance drum 16. The first transport guide G 1 and the document discharge roller 17 discharge the document D transported by the transport drum 16 to the document discharge tray 18.

  The document reading unit 10 reads an image of the document D being conveyed by the conveyance drum 16 at the document image reading position RP. Specifically, the image of the document D is irradiated with the lamp L at the document image reading position RP. Reflected light by irradiation is guided by the first mirror unit 11, the second mirror unit 12, and the lens unit 13 and forms an image on the light receiving surface of the image sensor CCD. The imaging device CCD photoelectrically converts incident light and outputs a predetermined image signal. The output image signal is created as input image data by performing A / D conversion.

The image reading control unit 14 performs processing such as shading correction, dither processing, and compression on the input image data, and uses the data obtained by this processing as output image data in the RAM of the image formation control unit 5 (see FIG. 2). Stored in the storage unit. Note that the output image data may be received from a personal computer connected to the image forming apparatus 1 or another image forming apparatus as well as data output from the document reading unit 10.

  The exposure units 20Y to 20K are composed of a laser light source, a polygon mirror, a plurality of lenses and the like (not shown), and generate a laser beam. The exposure units 20Y to 20K correspond to the output information output from the image formation control unit 5 based on the output image data, and the photosensitive members 31Y, 31M, 31C, and 31K that are constituent elements of the image formation units 30Y to 30K. The surface is exposed by scanning with a laser beam. A latent image is formed on the photoconductors 31Y to 31K by scanning exposure of the laser beam.

  The image forming unit 30Y includes a photoreceptor 31Y, and a main charging unit 32Y, a developing unit 33Y, a first transfer roller 34Y, and a cleaning unit 35Y, which are disposed around the photoconductor 31Y. The other image forming units 30M, 30C, and 30K have the same configuration as that of the image forming unit 30Y. Around the photoreceptors 31M, 31C, and 31K, main charging units 32M, 32C, and 32K, developing units 33M, 33C, and 33K, First transfer rollers 34M, 34C, 34K and cleaning units 35M, 35C, 35K are arranged, respectively.

  The surfaces of the photoreceptors 31Y to 31K are uniformly charged by the main charging units 32Y to 32K. The developing units 33Y to 33K develop latent images on the photoreceptors 31Y to 31K by developing with toner. As a result, toner images are formed on the photoreceptors 31Y to 31K.

  The first transfer rollers 34 </ b> Y to 34 </ b> K sequentially transfer the toner images formed on the photoreceptors 31 </ b> Y to 31 </ b> K to predetermined positions on the intermediate transfer belt 41 of the intermediate transfer unit 40. The cleaning units 35Y to 35K remove the toner remaining on the surfaces of the photoreceptors 31Y to 31K after the transfer of the toner image.

  The second transfer roller 42 transfers the toner image transferred onto the intermediate transfer belt 41 to the paper P. The paper P to be transferred is supplied from one of the trays PG 1, PG 2, and PG 3 constituting the paper feed unit 90, and is sent to the second transfer roller 42 while being timed by the paper feed roller 91.

  The belt cleaning unit 43 cleans the surface of the intermediate transfer belt 41 that has finished transferring the toner image onto the paper P. The cleaned intermediate transfer belt 41 is used for the next image transfer.

  Here, the above-described elements, that is, the exposure units 20Y to 20K, the image forming units 30Y to 30K, the intermediate transfer unit 40, and the second transfer roller 42 constitute an image forming unit. That is, the image forming unit (1) charges the photosensitive drums 31Y to 31K, (2) forms electrostatic latent images on the photosensitive drums 31Y to 31K by the exposure units 20Y to 20K, and (3) is formed. (4) The toner images on the photoconductive drums 31Y to 31K are primarily transferred to the intermediate transfer belt 41. (5) The toner images on the intermediate transfer belt 41 are transferred to the sheet P two times. The toner image is transferred onto the paper P through a series of processes of next transfer. The sheet P having the transferred toner image, that is, the unfixed toner image on the surface to be fixed, is sent to the fixing device 50.

  The fixing device 50 fixes the toner image on the fixing target surface of the paper P by pressurizing and heating the paper P. The fixing device 50 includes a fixing unit and a separation unit.

  The fixing unit includes, for example, a pair of fixing members, an upper fixing roller 51 and a lower fixing roller 52, and a heating unit 53. The upper fixing roller 51 and the lower fixing roller 52 are arranged in pressure contact with each other, and a fixing nip portion NP is formed at the press contact portion between the upper fixing roller 51 and the lower fixing roller 52. Here, when the sheet P passes through the fixing nip NP, an upper fixing roller 51 is disposed above the sheet surface, and a lower fixing roller 52 is disposed below the sheet surface.

  The fixing upper roller 51 is configured by laminating an elastic layer such as silicone rubber or sponge on the surface of cylindrical steel or aluminum. The lower fixing roller 52 is configured by laminating an elastic layer such as silicone rubber and a release layer made of fluorine resin or the like on the surface of a cylindrical steel or aluminum pipe.

  The heating unit 53 is disposed around the fixing member and has a function of heating the fixing member. Specifically, the heating unit 53 is disposed around the outer side of the upper fixing roller 51 and heats the upper fixing roller 51 using radiant heat. The heating unit 53 is configured to be able to freely adjust the heating amount for the fixing upper roller 51 in accordance with the supplied electric power. In this embodiment, induction heating (IH: Induction Heating) is used. It is an IH heater.

  In this fixing unit, the sheet P is conveyed with the surface to be fixed facing the fixing upper roller 51 and passes through the fixing nip NP in the conveyance process of the sheet P. As a result, the toner image is fixed on the fixing target surface of the paper P through the pressure applied by the upper fixing roller 51 and the lower fixing roller 52 and the heat action of the upper fixing roller 51.

  On the other hand, the separation part is mainly composed of, for example, a blower fan 54 and a duct 55 for guiding air. The blower fan 54 and the duct 55 are connected to each other, and these members are disposed so that the front end portion (air outlet) of the duct 55 faces the paper discharge side of the paper P in the fixing nip portion NP. Yes. Specifically, the front end portion of the duct 55 is disposed at a position shifted from the front surface on the paper discharge side of the fixing nip NP toward the fixing upper roller 51 side. It is known that the arrangement of the duct 55 is such that the upper fixing roller 51 located on the fixing target surface side of the paper P is more likely to wind the paper P out of the upper fixing roller 51 and the lower fixing roller 52. It is based on.

  The blower fan 54 is a blower unit that takes in air with a rotating fan and generates separated wind by blowing out the taken-in air. For example, the blower fan 54 is a multi-blade fan that is rotatably provided with a large number of forward blades. The blower fan 54 of the present embodiment can blow the separated wind, stop blowing the separated wind, or adjust the wind speed (air volume) of the separated wind by controlling the rotation speed. it can.

  The shape / configuration of the blower fan 54 is not limited to the above, and any shape / configuration may be adopted as long as it can satisfy the function of sending air. Further, the blower fan 54 may blow air outside the apparatus instead of the air inside the image forming apparatus 1 or may blow a gas other than air. Furthermore, instead of the blower fan 54, a blower such as a compressor may be used.

  The duct 55 is a duct having a rectangular cross section made of metal such as aluminum. When the duct 55 is functionally grasped, the duct 55 is configured by an inlet that is connected to the blower fan 54, a guide portion that guides the separated air from the inlet, and an outlet that blows off the separated air.

  In this separation portion, the air (separation air) blown from the blower fan 54 is sent to the inlet of the duct 55, then guided by the guide portion of the duct 55, and finally fixed from the outlet of the duct 55. It is discharged toward the nip portion NP. The sheet P is separated from the fixing upper roller 51 by the separation air blown from the air outlet 59c (air separation).

  The paper discharge unit 70 conveys the paper P that has been subjected to the fixing process by the fixing device 50 and discharges it to the paper discharge tray 75. When the paper P is reversed and discharged, the paper discharge guide 72 once guides the paper P downward. The paper discharge reversing roller 73 holds the rear end of the paper P and then reversely conveys the paper P. Then, the paper discharge guide 72 guides the paper P to the paper discharge roller 74 so that the paper P is discharged to the paper discharge tray 75. Is done.

  In addition, in the case of double-sided printing in which image formation is performed on each of the front and back surfaces of the paper P instead of single-sided printing in which image formation is performed only on the front surface of the paper P, the paper discharge guide 72 is used for the toner image on the front surface of the paper P. The sheet P that has been subjected to the fixing process is conveyed to the refeed unit 80 located below. A refeed reverse roller 81, which is one of the components of the refeed unit 80, reverses the paper P by nipping the rear end of the paper P and feeds it to the refeed conveyance path 82. As a result, the paper P is used for image formation on the back surface via the re-feed conveyance path 82.

  FIG. 2 is a block diagram schematically showing a control system of the image forming apparatus 1 according to the present embodiment. The control system of the image forming apparatus 1 is mainly configured by an image formation control unit 5 and a fixing control unit 60. The image formation control unit 5 and the fixing control unit 60 are configured to be able to communicate with each other.

  As the image formation control unit 5, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The image formation control unit 2 performs various calculations according to a control program stored in the ROM, and controls the operation state of the image forming apparatus 1 based on the calculation results.

  This image formation control unit 5 is set together with information set through an input unit 6 provided at the upper part of the main body of the image forming apparatus 1 or output image data from a personal computer or other image forming apparatus connected to the image forming apparatus 1. From the received information, the printing conditions, for example, single-sided / double-sided printing type, paper type of the paper P to be printed (for example, paper type such as size, thin paper / plain paper / thick paper, etc.), image density and magnification And so on. In addition, as the input part 6, the touch panel which can perform input operation according to the information displayed on a display can be used, for example.

The image forming control unit 5 controls each unit (image forming unit) of the image forming apparatus 1 to execute the following series of processes, thereby transferring the toner image onto the conveyed paper P.
(1) Charge the photoreceptors 31Y to 31K. (2) Form electrostatic latent images on the photoreceptors 31Y to 31K by the exposure units 20Y to 20K. (3) Adhere toner to the formed electrostatic latent images ( 4) Primary transfer of toner images on photoreceptors 31Y-31K to intermediate transfer belt 41 (5) Transport of paper P (6) Secondary transfer of toner image on intermediate transfer belt 41 to paper P

  On the other hand, as the fixing control unit 60, for example, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The fixing control unit 60 performs various calculations according to a control program stored in the ROM, and controls the operation state of the fixing device 50 based on the calculation results.

  Sensor signals from various sensors and signals from the image formation controller 5 are input to the fixing controller 60. Here, the fixing temperature sensor 65 is disposed around the upper fixing roller 51 and detects the fixing temperature, that is, the temperature of the upper fixing roller 51 (specifically, the surface temperature). The paper detection sensor 66 is arranged on the upstream side of the fixing nip portion NP in the transport path of the paper P, and detects the presence or absence of the paper P reaching the fixing device 50 (fixing nip portion NP).

  The fixing control unit 60 includes an air volume control unit 61, an IH control unit 62, and a storage unit 63 when this is viewed functionally.

  The air volume control unit 61 controls the air volume of the separated air by the separation unit by controlling the rotational speed of the blower fan 54. The air volume of the separation air is set according to the paper type by referring to a separation air table described later.

  The IH control unit 62 performs temperature control for switching the on / off operation of the heating unit 53 based on the detection result of the fixing temperature sensor 65, and sets a power command that defines the power supplied to the heating unit 53 during the on operation ( Temperature controller). When the IH control unit 62 outputs a power command to the IH drive circuit 56, the power supplied to the IH heater as the heating unit 53 is controlled by the IH drive circuit 56. That is, the IH control unit 62 can arbitrarily adjust the heating amount for the upper fixing roller 51 through the power command.

  The IH control unit 62 has two switchable operation modes, and operates according to one of the operation modes. When the normal mode which is one of the two operation modes is set, the IH control unit 62 uses a preset reference amount (hereinafter referred to as “reference power amount”) as a power command to the IH drive circuit 56. Determine as. On the other hand, when the power-up mode, which is the other of the two operation modes, is set, the IH control unit 62 sets the power-up amount (in accordance with the amount of separated wind to the above-described reference power amount ( The power command is determined by adding the power increase amount). The amount of power increase is set according to the amount of separated air by referring to a power table described later.

  The storage unit 63 holds a table that defines the relationship between the paper type and the air volume of the separation air (hereinafter referred to as “separation air table”). This separated air table is referred to by the air volume control unit 61 described above. In general, the thinner the paper P is, the easier it is to wind the paper P around the fixing upper roller 51. In view of this, the separation air volume is set according to various paper types through experiments and simulations so that the paper type that easily winds around the fixing upper roller 51 has a larger separation air volume. Since the ease of winding the paper P depends on the paper quality such as coated paper and high-quality paper, the paper quality may be adopted as the paper type, or a combination of the paper quality and the thickness may be adopted. .

  In addition, the storage unit 63 holds a table (hereinafter referred to as “power table”) that defines the relationship between the volume of separated wind and the amount of power increase. This power table is referred to by the IH control unit 62 described above. Since the separation wind is blown, the heat of the upper fixing roller 51 is taken away, so that the surface temperature of the upper fixing roller 51 is lowered. Therefore, the fixing temperature controllability is improved by determining the power command in consideration of the power increase amount. For example, when the air volume of the separation wind is 50 m / s, the power increase amount is 500 W, and when the air volume of the separation wind is 30 m / s, the power increase amount is 300 W. In the power table, the amount of power increase is set according to the amount of various separated winds through experiments and simulations.

  FIG. 3 is a flowchart for explaining the operation centering on the fixing process of the image forming apparatus 1 according to the present embodiment. The processing shown in this flowchart is executed by the fixing control unit 60 with the power-on of the image forming apparatus 1 as a trigger.

  First, in step 10 (S10), the fixing control unit 60 selects a paper type of the paper P. For example, when the user sets the paper P on the trays PG1 to PG3, the paper type of the paper P is input through the input unit 6, and the fixing unit control unit 60 holds the paper type. Then, the fixing control unit 60 selects the paper type of the paper P based on the held input information.

  In step 11 (S11), the fixing control unit 60 refers to the separation wind table stored in the storage unit 63 and determines the separation air volume corresponding to the selected paper type.

  In step 12 (S12), the fixing control unit 60 refers to the power table stored in the storage unit 63, and determines the power increase amount corresponding to the air volume of the separated air.

  In step 13 (S13), the fixing control unit 60 determines whether printing has started. The print start is determined by receiving a print start command, which is a print start command from the user, through the input unit 6 or by issuing a print start command from a personal computer or other image forming apparatus connected to the image forming apparatus 1. It can be done by receiving.

  In step 14 (S14), the fixing control unit 60 starts air separation. Specifically, the fixing control unit 60 controls the blower fan 54 so that the air volume of the separated air determined in step 11 is obtained. This air separation is continuously executed until an affirmative determination is made in the determination process of step 20 described later.

  In step 15 (S15), the fixing control unit 60 sets the operation mode to the power-up mode.

  In step 16 (S16), the fixing controller 60 starts roller temperature adjustment control. In this roller temperature control, the detection result of the fixing temperature sensor 65 is referred to, and the IH heater as the heating unit 53 is turned on and off so that the surface temperature of the upper fixing roller 51 follows the target fixing temperature. . For example, when it is determined that the surface temperature of the upper fixing roller 51 is lower than the target fixing temperature by a predetermined temperature, the heating unit 53 is turned on, and the surface temperature of the upper fixing roller 51 returns to the target fixing temperature. For example, the heating unit 53 is turned off. When the heating unit 53 is turned on, the IH control unit 62 executes it by outputting a power command to the IH drive circuit 56. Therefore, when the heating unit 53 is turned on when the operation mode is the power up mode, a value obtained by adding the power up amount (step 12) set in accordance with the amount of separated air to the reference power amount is used as the power command. It is output to the drive circuit 56.

  In step 17 (S17), the fixing control unit 60 refers to the detection result of the paper detection sensor 66 and determines whether or not the paper P reaches the fixing nip NP. If the determination in step 17 is affirmative, that is, if the paper P reaches the fixing nip NP, the process proceeds to step 18 (S18). On the other hand, if a negative determination is made in step 17, that is, if the paper P does not reach the fixing nip NP, the determination in step 17 is performed again.

  In step 18, the fixing control unit 60 refers to the detection result of the fixing temperature sensor 65, and the surface temperature of the upper fixing roller 51 that has decreased due to the paper P being supplied to the fixing nip NP has reached the target fixing temperature. Determine whether or not. That is, based on the determination in step 18, it is determined whether or not the temperature of the fixing upper roller 51 once lowered due to the passage of the sheet P has shifted to a stable state. In this embodiment, the target fixing temperature is used as a guideline for determining a stable state, but other values can be used. For example, it is only necessary to determine that the temperature has shifted to a stable state based on the target fixing temperature, such as adopting an intermediate value between the lowered minimum temperature of the fixing upper roller 51 and the target fixing temperature.

  If the determination in step 18 is affirmative, that is, if the surface temperature of the upper fixing roller 51 has reached the target fixing temperature, the process proceeds to step 19 (S19). On the other hand, if a negative determination is made in step 18, that is, if the surface temperature of the upper fixing roller 51 has not reached the target fixing temperature, the process proceeds to step 20 (S20).

  In step 19, the fixing control unit 60 sets the operation mode to the normal mode. When the operation mode is set to the normal mode in step 19, the fixing control unit 60 continues the roller temperature control in the normal mode. That is, when the operation mode is the normal mode and the IH heater that is the heating unit 53 is turned on, the fixing control unit 60 outputs only the reference power amount to the IH drive circuit 56 as a power command.

  In step 20, the fixing control unit 60 determines whether or not the final sheet has passed through the fixing device 50. If an affirmative determination is made in step 20, that is, if the final sheet P in the job started by starting printing has passed through the fixing device 50, the process proceeds to step 21 (S21). On the other hand, if a negative determination is made in step 20, that is, if the final sheet has not passed through the fixing device 50, the process returns to step 18.

  In step 21 (S21), the fixing controller 60 determines whether or not the image forming apparatus 1 is powered off. If the determination in step 21 is affirmative, if the image forming apparatus 1 is powered off, this routine ends. On the other hand, if a negative determination is made in step 21, if the power of the image forming apparatus 1 is not turned off, the process proceeds to step 22 (S22).

  In step 22, the fixing control unit 60 determines whether or not the paper type of the paper P has been changed. If an affirmative determination is made in step 22, that is, if the paper type of the paper P is changed, the processing returns to step 10. On the other hand, if a negative determination is made in step 22, that is, if the paper type of the paper P has not been changed, the process returns to step 13.

  As described above, in the present embodiment, the fixing control unit 60 sets the power command with reference to the power table of the storage unit 63, thereby variably supplying the power supplied to the heating unit 53 according to the air volume of the separated air. Control. Here, the power table defines a correspondence relationship between the amount of separated air by the separation unit and the amount of power increase with respect to the reference power amount of power supplied to the heating unit 53. The fixing control unit 60 determines the power increase amount based on the air volume of the separated wind, and sets the power command by adding the reference power amount to the determined power increase amount.

  FIG. 4 is an explanatory diagram showing the transition of the temperature of the fixing upper roller 51. As shown in the figure, when printing starts, the sheet P sequentially passes through the fixing nip portion NP, so that the temperature of the upper fixing roller 51 decreases. In the following explanation, “thin paper” is assumed as the fixing target paper.

In FIG. 11A, L11 indicates a temperature transition when the roller temperature control is performed in a state where a value obtained by adding a predetermined power amount to a reference power amount is set as a power command, and L12 indicates a reference power amount. The temperature transition when the roller temperature control is performed in the state where is set as the power command is shown. In the case shown in FIG. 5A, the separation air accompanying the air separation is stopped.

  Comparing the two cases, the amount of decrease in the fixing temperature accompanying the passage of the paper P can be suppressed by adopting the amount of power increased from the reference amount of power as the power command, and thereafter the target fixing temperature. The temperature return to Tt can also be achieved early. As described above, the controllability of the fixing temperature can be improved by adding the power increase amount to the reference power amount.

  In FIG. 7B, L21 and L22 indicate temperature transitions when the roller temperature control is performed in a state where the power amount obtained by adding the power increase amount to the reference power amount is set as the power command. Here, the power-up amount set in L21 is set to be larger than the power-up amount set in L22. In the case shown in FIG. 5B, it is assumed that the separation air is blown to the fixing nip NP with a predetermined air volume.

  In the case shown in L21, the power command is set in consideration of the power-up amount, but this power command (power-up amount) is too large. In this case, although the time required to return to the target fixing temperature Tt is short, the upper fixing roller 51 is heated by a large amount of power, so that the temperature of the upper fixing roller 51 increases even after the heating section 53 is turned off, and this overshoots. Invite the situation to end. On the other hand, in the case indicated by L22, the power command (power increase amount) is too small although the power increase amount is taken into account. In this case, a situation such as overshoot does not occur, but there may be a problem that it takes a long time to return to the target fixing temperature Tt. As described above, the temperature of the fixing upper roller 51 decreases as the paper P passes, but when air separation is performed, the separation air also causes the temperature of the fixing upper roller 51 to decrease. Therefore, when determining the power command (power up amount), it is necessary to appropriately set the power command (power up amount) in accordance with the separated wind in order to consider the temperature drop due to the separated wind.

  In this regard, according to the present embodiment, the power supplied to the heating unit can be set to an appropriate amount by setting the power command according to the air volume of the separated wind. Specifically, as shown in FIG. 5C, by appropriately setting the power command, a situation such as an overshoot, that is, a temperature transition as indicated by L21 is eliminated, and an appropriate value as indicated by L31 is obtained. The temperature transition can be taken. Similarly, by appropriately setting the power command, the situation that the return to the target fixing temperature Tt is delayed, that is, the temperature transition as shown in L22 is eliminated, and the appropriate temperature transition shown in L32 can be taken. (L31 and L32 show the same temperature transition). Thereby, it is possible to effectively suppress an overshoot or a situation where the return to the target fixing temperature Tt is delayed. As a result, it is possible to perform power control in consideration of a temperature drop due to the separation wind, so that it is possible to improve controllability of the fixing temperature.

  Further, for example, a method of setting a power command based on a detection value of a temperature sensor is conceivable, but a delay due to a temperature time constant may occur. In this regard, according to the present embodiment, the temperature control can be performed with high responsiveness by setting the power command using the power table.

  In the present embodiment, the fixing control unit 60 sets the separation air volume according to the paper type. Thereby, the separation of the paper P from the fixing upper roller 51 can be performed appropriately.

  In the present embodiment, the fixing control unit 60 performs the power-up amount determination process on the condition that the paper type of the paper P has been selected. As a result, the amount of power increase can be reliably reflected during the fixing operation. Note that the power-up amount determination process is not limited to when the paper type is selected. For example, the power-up amount determination process may be performed based on a print start command that is a print start command from the user.

  In this embodiment, when it is determined that the temperature of the upper fixing roller 51 has shifted to a stable state based on the target fixing temperature, only the reference power amount is used as a power command without taking into account the power increase amount. Set. Immediately after printing is started, the amount of heat provided by the upper fixing roller 51, the lower fixing roller 52, and their peripheral members is small, and therefore the temperature is likely to decrease due to the passage of the paper P and the influence of separation wind. However, when the printing of the paper P proceeds to some extent, a stable amount of heat is ensured, and the temperature is easily stabilized. Therefore, when such a situation is determined, it is possible to suppress power consumption while maintaining stable fixing performance by setting the power command to only the reference power amount.

(Second Embodiment)
The following is a flowchart for explaining the operation centering on the fixing process of the image forming apparatus 1 according to the second embodiment. The processing shown in this flowchart is executed by the fixing control unit 60 with the power-on of the image forming apparatus 1 as a trigger.

  In step 30 to step 35 (S30 to S35), as in the first embodiment, the selection of the paper type of the paper P, the determination of the separation air volume, the determination of the power-up amount, and whether printing has started. Judgment, start of air separation, and setting of power-up mode are performed.

  In step 36 (S36), the fixing control unit 60 forcibly turns on the heating unit 53. When the heating unit 53 is forcibly turned on in this step 36, the heating unit 53 is kept on until the roller temperature control is started. When the heating unit 53 is turned on in this forced on, the value obtained by adding the power up amount set according to the air volume of the separated wind to the reference power amount is set because the operation mode is set to the power up mode. It is output to the IH drive circuit 56 as a power command.

  In step 37 (S 37), the fixing control unit 60 refers to the detection result of the paper detection sensor 66 and determines whether or not the paper P has reached the fixing device 50. If the determination in step 37 is affirmative, that is, if the paper P reaches the fixing device 50, the process proceeds to step 38 (S38). On the other hand, if a negative determination is made in step 37, that is, if the paper P has not reached the fixing device 50, the determination in step 37 is performed again.

  In step 38, the fixing control unit 60 releases the forced on of the heating unit, and in the subsequent step 39 (S38), the fixing control unit 60 starts roller temperature control.

  In steps S39 to S44 (S39 to S44), the fixing controller 60 determines whether or not the surface temperature of the upper fixing roller 51 has reached the target fixing temperature, sets the normal mode, and determines whether or not the final sheet has passed. Determination, whether the power is turned off, and whether the paper type has been changed.

  As described above, according to the present embodiment, the fixing control unit 60 forcibly turns on the heating unit 53 on the condition of a print start command that is a print start command from the user, and paper to the fixing nip NP. The process proceeds to roller temperature control on condition that P is reached.

  According to such a configuration, the fixing temperature can be increased before the paper P reaches the fixing nip NP by forcibly turning on the heating unit 53 in the initial printing stage. Accordingly, it is possible to suppress a situation in which the paper P reaches the fixing nip portion NP at a timing when the fixing temperature is low.

  The image forming apparatus according to the embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the invention. . Further, the fixing device itself constituting the image forming apparatus also functions as part of the present invention. Furthermore, in the above-described embodiment, the control unit that controls the fixing device is uniquely provided as the fixing control unit. However, the image forming control unit may serve as the fixing control unit. Moreover, although IH heater was illustrated as a heating part, if the heating amount can be adjusted freely according to the electric energy supplied, it will not be limited to this.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Image formation control part 6 Input part 10 Document reading part 20Y-20K Exposure part 30Y-30K Image formation part 40 Intermediate transfer part 41 Intermediate transfer belt 42 Second transfer roller 43 Belt cleaning part 50 Fixing device 51 On fixing Roller 52 Lower fixing roller 53 Heating unit 54 Blower fan 55 Duct 60 Fixing control unit 61 Air flow control unit 62 IH control unit 63 Storage unit 65 Fixing temperature sensor 66 Paper detection sensor 70 Paper discharge unit 72 Paper discharge guide 73 Paper discharge reverse roller 74 Paper discharge roller 80 Re-feed unit 81 Re-feed reversing roller 82 Re-feed conveyance path 90 Paper feed unit

Claims (8)

A pair of fixing members that fix the toner image on the paper by passing the paper through the fixing nip; and
A heating unit that heats the fixing member with a heating amount corresponding to the supplied power;
A separation unit that blows separation air on the paper from the paper discharge side in the fixing nip, and
A fixing temperature detector for detecting the temperature of the fixing member;
A temperature control unit that performs temperature control for switching the on / off operation of the heating unit based on the detection result of the fixing temperature detection unit, and sets a power command that defines power to be supplied to the heating unit during the on operation; and
An air volume control unit for controlling the air volume of the separated air by the separating unit;
A storage unit that holds a power table that defines a correspondence relationship between the amount of separated air flow by the separation unit and the power supplied to the heating unit;
The temperature control unit is configured to change the power supplied to the heating unit according to the air volume of the separated air set by the air volume control unit by setting the power command with reference to the power table of the storage unit. The fixing device is characterized by being controlled. The power table defines a correspondence relationship between the amount of separated air by the separation unit and the amount of power increase with respect to a reference amount of power supplied to the heating unit,
The temperature control unit determines the power increase amount based on the air volume of the separated wind, and sets the power command by adding the reference amount to the determined power increase amount. The fixing device described in 1.   The fixing device according to claim 1, wherein the air volume control unit sets the air volume of the separation air according to a paper type.   The fixing device according to claim 2, wherein the temperature control unit performs the process of determining the power increase amount on the condition that a paper type of the paper is selected.   The fixing device according to claim 2, wherein the temperature control unit performs a process of determining the power increase amount on condition of a print start command that is a print start command from a user.   The temperature control unit forcibly turns on the heating unit on the condition of a print start command that is a command to start printing from a user, and controls the temperature control on the condition that the sheet reaches the fixing nip unit. 5. The fixing device according to claim 1, wherein the fixing device is transferred to the fixing device.   When the temperature control unit determines that the temperature of the fixing member has shifted to a stable state based on the target fixing temperature of the fixing member, only the reference amount is taken into account without taking into account the power increase amount. The fixing device according to claim 1, wherein the fixing device is set as the power command. An image forming unit for transferring a toner image to paper;
A fixing device according to claim 1, wherein the transferred toner image is fixed on a sheet;
An image forming apparatus comprising:

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