JP2014222276A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption when thermally fixing toner images formed on recording sheets to the recording sheets.SOLUTION: When, of recording sheets P1 to P3 that are consecutively conveyed, the recording sheets P1 and P2 include a standard heating area Sr to be heated at a standard fixing temperature T1, and the recording sheet P3 includes the standard heating area Sr to be heated at the standard fixing temperature T1 and a high-temperature heating area Hr to be heated at a high fixing temperature T2 higher than the standard fixing temperature T1, an image forming apparatus sets a heating start timing tp with a heater so that the heating temperature of the recording sheet P3 reaches the high fixing temperature T2 at a timing at which the high-temperature heating area Hr in a first recording sheet P3 including the high-temperature heating area Hr reaches a fixing nip Nf, and starts heating to the high fixing temperature T2 from the set heating start timing tp.

Description

  The present invention relates to an image forming apparatus in which an unfixed toner image is formed on a recording sheet and thermally fixed.

In an image forming apparatus that forms a toner image by an electrophotographic method, a toner image is usually formed on a recording sheet, and the toner image is thermally fixed on the recording sheet in a fixing device.
An appropriate fixing temperature (heating temperature) of the recording sheet in the fixing device varies depending on the toner adhesion amount of the toner image formed on the recording sheet. In the case of a toner image having a large amount of toner adhesion, the amount of heat taken away by the toner increases. Therefore, it is preferable to increase the heating temperature of the recording sheet in order to ensure the toner fixability. However, when the recording sheet is heated at a high temperature, power consumption in a heating means such as a heater increases, so that power saving cannot be ensured, and the economy may be impaired.

  Patent Document 1 discloses a configuration in which the fixing target temperature of a recording sheet (recording medium) is changed based on the presence / absence of halftone processing of an image in one recording sheet and the type of gradation processing. . According to such a configuration, the recording sheet can be heated at a fixing target temperature corresponding to the toner adhesion amount of the toner image formed on the recording sheet.

JP 2012-118496 A

In the configuration described in Patent Document 1, information regarding the amount of toner adhesion is acquired for each recording sheet, and the fixing target temperature is set. However, when a region where a large amount of toner is attached and a region where a small amount of toner is mixed in one recording sheet, if the fixing target temperature is set to a high temperature, the entire recording sheet It will be heated uniformly.
In this case, the area where the toner adhesion amount on the recording sheet is small is also heated at a high temperature, and in the area where the toner adhesion quantity is small, the amount of heat more than the amount of heat necessary to ensure the toner fixability is obtained. Given. As a result, heating means such as a heater consumes more power than is required for one recording sheet. When the number of such recording sheets increases, the power consumed in the heating means is increased, and the power saving performance may be impaired.

  The present invention has been made in view of such a problem, and can ensure the fixability of a toner image formed on a recording sheet and can suppress the loss of power saving performance. Is to provide.

  In order to achieve the above object, an image forming apparatus according to the present invention is secured between a heating body heated by a heating unit and a pressure body pressed against the heating body after a toner image is formed on a recording sheet. An image forming apparatus that heat-fixes the recording sheet by passing the recording sheet through a fixing nip, and sets the heating temperature of the recording sheet to be higher than the standard fixing temperature based on information on the toner amount of the toner image formed on the recording sheet. A determination unit that determines whether the recording sheet includes a high-temperature heating region that should have a high fixing temperature, and a heating temperature of the recording sheet that is determined to include the high-temperature heating region is a temperature increase of the heating unit. As a result, the temperature rises from the standard fixing temperature toward the high fixing temperature until the high temperature heating area reaches the fixing nip, and the high temperature heating area reaches the fixing nip. To reach the high fusing temperature at ring, characterized in that it comprises a control means for controlling the temperature increase start timing of the heating means.

In the image forming apparatus according to the present invention, the recording sheet that is determined to include the high-temperature heating area starts to be heated at the high fixing temperature at the timing when the high-temperature heating area reaches the fixing nip. Thereby, the high-temperature heating area of the recording sheet is appropriately heated at the high fixing temperature, and the fixability of the toner image in the high-temperature heating area can be ensured.
In addition, the recording sheet including the high temperature heating region is heated at a temperature lower than the high fixing temperature at the leading end side in the sheet conveying direction than the high temperature heating region. As a result, it is possible to reduce the power consumption in the heating means compared with the case where the entire recording sheet is uniformly heated at a high fixing temperature, and to suppress the loss of power saving in the image forming apparatus. it can.

Preferably, when the new job is a process of forming a toner image on a plurality of recording sheets, the control unit first includes a high-temperature heating area by the determination unit among the continuously conveyed recording sheets. The control of the temperature rise start timing is applied to the recording sheet determined as follows.
Preferably, the control unit sets the temperature rise start timing for a recording sheet determined to include a high-temperature heating region by the determination unit among the recording sheets conveyed after the first recording sheet. The heating means is controlled so that the entire recording sheet has a high fixing temperature without applying control.

  Preferably, the control unit includes a time required for the heating of the recording sheet by the heating unit to increase from the standard fixing temperature to the high fixing temperature, and among the plurality of recording sheets, From the start of conveyance of the first recording sheet conveyed first to the fixing nip until the high temperature heating area of the recording sheet first determined to include the high temperature heating area arrives at the fixing nip. The temperature rise start timing is set based on the required conveyance time.

  Preferably, the control means starts the temperature increase when the required temperature increase time is equal to the required transfer time based on the transfer start timing at which the first recording sheet starts to be transferred. The timing is made to coincide with the transfer start timing, and when the temperature increase required time is shorter than the transfer required time, the temperature increase start timing is set to a timing later than the transfer start timing.

Preferably, the control means sets the temperature rise start timing earlier than the transfer start timing when the temperature rise required time is longer than the transfer required time.
Preferably, the required temperature increase time changes for each predetermined different execution condition at the time of job execution, and the control means corresponds to the required temperature increase time when the different execution conditions are satisfied. Temperature rise time information is stored, and it is determined which of the different execution conditions is satisfied, and the temperature rise time corresponding to the determined execution condition is used to determine the rise time information. A temperature start timing is set.

Preferably, in addition to the determined execution condition, the control unit extends the temperature increase time by the extended amount when the specific condition for prolonging the temperature increase time is also satisfied. The time is corrected.
Preferably, auxiliary heating means for heating the pressure body is further provided, and the control means adds to the determined execution condition when the temperature of the pressure body is lower than a predetermined reference temperature. The pressurizing body is heated by the auxiliary heating means on the assumption that a specific condition for prolonging the temperature increase time is also satisfied.

Preferably, the determination unit determines a region of a toner image to be formed on one recording sheet, and includes an image image region that uses a larger amount of toner than a character region. It is determined that the high temperature heating region is included in the sheet.
Preferably, based on data described in a page description language, the charged image carrier is exposed and scanned to form an electrostatic latent image on the image carrier, and the formed electrostatic latent image is A process unit for forming the toner image by developing with toner is provided, and the determination unit analyzes the page description language and determines whether or not the image image area is included based on the analysis. It is characterized by.

  Preferably, the charged image carrier is exposed and scanned based on the image data, an electrostatic latent image is formed on the image carrier, and the formed electrostatic latent image is developed with toner. A process unit for forming the toner image, and the determination means determines whether the image area is included based on the number of dots of each of a plurality of scanning lines when the image carrier is exposed and scanned. It is characterized by determining.

FIG. 2 is a schematic diagram for explaining a configuration of an MFP according to the embodiment. 2 is a block diagram showing a configuration of a control system provided in the MFP. FIG. It is a flowchart which shows the content of the high temperature heating area | region determination process performed in a PDL process part. It is a flowchart which shows the content of the high temperature heating area | region determination process performed in an image process part. It is a flowchart which shows the content of the fixing control performed in an engine control part. It is a flowchart which shows the content of the subroutine of temperature rising timing control. It is a flowchart which shows the content of the subroutine of image formation timing control. It is a flowchart which shows the content of the subroutine of a standard heating mode. It is a flowchart which shows the content of the subroutine of high temperature heating mode. FIG. 4 is a schematic diagram virtually illustrating a state in which three recording sheets on which toner images are formed are conveyed in this order toward a fixing nip. It is a figure which illustrates the content of temperature rising time information. FIG. 4 is a schematic diagram virtually illustrating a state in which three recording sheets are conveyed toward a fixing nip in this order when image forming timing control is executed.

An embodiment of an image forming apparatus according to the present invention will be described based on an MFP (Multi-Function Peripheral).
FIG. 1 is a schematic diagram for explaining the configuration of the MFP according to the present embodiment.
As shown in FIG. 1, the MFP includes an image reading unit A that reads an image of a document, and an image forming unit B that forms a toner image by an electrophotographic method.

<Image reading unit>
The image reading unit A is provided with an image reading unit 10 provided on the upper side of the image forming unit B, and an ADF unit (automatic document feeder) 20 provided on the upper side of the image reading unit 10.
On the upper surface of the image reading unit 10, a strip-shaped first document glass 13 and a plate-shaped second document glass 16 are provided. The first original glass 13 faces the front side of the MFP on the left side (hereinafter simply referred to as “left side” and the opposite side is called “right side”), and in the main scanning direction (from the front side of the MFP to the back side). (Direction along). The second original glass 16 is arranged on the right side with respect to the first original glass 13.

The ADF unit 20 includes an ADF main body 21 disposed above the first original glass 13 and an original table 22 extending rightward from the ADF main body 21. The ADF main body 21 conveys the originals placed on the original table 22 one by one to the internal conveyance path 21 a and passes them over the first original glass 13 of the image reading unit 10.
Inside the image reading unit 10, a linear light source 11 that emits light upward is arranged along the main scanning direction. The linear light source 11 is configured to be slidable along the sub-scanning direction in the lower area of the second original glass 16. The linear light source 11 irradiates light in the main scanning direction with one sheet (one page) passing through the first original glass 13 along the sub-scanning direction in a stopped state. The linear light source 11 moves in the sub-scanning direction with respect to the original while irradiating light along the main scanning direction with respect to the one-page original placed on the second original glass 16. .

  The light reflected from the original after being irradiated from the linear light source 11 is irradiated to the line sensor 15 by the optical system 14 provided inside the image reading unit 10. The line sensor 15 receives light reflected by the document while the linear light source 11 relatively moves from one end side to the other end side in the sub-scanning direction of the document. The line sensor 15 outputs a signal corresponding to the amount of received light as scan data.

<Image forming unit>
The image forming unit B provided below the image reading unit A is based on scan data output from the line sensor 15 of the image reading unit 10 or based on image data transmitted from an external terminal device. A toner image is formed on the recording sheet P.
An intermediate transfer belt 31 that can move around in the direction indicated by the arrow X is provided along the horizontal direction at substantially the center in the vertical direction inside the image forming unit B. The intermediate transfer belt 31 is wound around a driving roller 31a provided at the right end and a driven roller 31b provided at the left end.

Below the intermediate transfer belt 31, four process units 40Y, 40M, 40C, and 40K for forming toner images by electrophotography are arranged side by side along the lower traveling direction of the intermediate transfer belt 31. ing.
The process units 40Y, 40M, 40C, and 40K form toner images of respective colors of Y (yellow), M (magenta), C (cyan), and K (black). The process units 40Y, 40M, 40C, and 40K have substantially the same configuration, and each include a photosensitive drum 41, a charging device 42, an exposure device 43, and a developing device 44.

The respective photoconductive drums 41 of the four process units 40Y, 40M, 40C, and 40K are arranged to face the running portion on the lower side of the intermediate transfer belt 31. The photosensitive drum 41 is rotationally driven in the direction indicated by the arrow Z.
The charging device 42 is provided on the downstream side in the rotation direction of the photosensitive drum 41 with respect to the position of the photosensitive drum 41 facing the intermediate transfer belt 31. The charging device 42 uniformly charges the surface of the rotating photosensitive drum 41.

The exposure device 43 is disposed downstream of the charging device 42 in the rotation direction of the photosensitive drum 41 and below the photosensitive drum 41. The exposure device 43 emits laser light from the laser diode, and exposes and scans the surface of the photosensitive drum 41 for each scanning line along the axial direction (main scanning direction) of the photosensitive drum 41 in a rotated state. To do.
The laser diode is driven when the laser diode is driven by exposure data based on scan data output from the line sensor 15 of the image reading unit 10 or image data (drawing data) transmitted from an external terminal device. It is emitted from.

The developing device 44 is provided downstream of the exposure device 43 in the rotation direction of the photosensitive drum 41. The developing device 44 of each process unit 40Y, 40M, 40C, 40K converts the electrostatic latent image formed on the surface of the photosensitive drum 41 into Y (yellow), M (magenta), C (cyan), K ( Develop with black toner.
In the circumferential movement area of the intermediate transfer belt 31, four primary transfer rollers 32Y, 32M, 32C, and 32K are provided above the process units 40Y, 40M, 40C, and 40K. Each of the primary transfer rollers 32Y, 32M, 32C, and 32K is opposed to the photosensitive drum 41 of each of the process units 40Y, 40M, 40C, and 40K, with the belt running portion below the intermediate transfer belt 31 interposed therebetween. . The respective toner images formed on the respective photosensitive drums 41 are transferred onto the lower belt running portion (on the lower surface) of the intermediate transfer belt 31 by the opposing primary transfer rollers 32Y, 32M, 32C, and 32K. Is transferred (primary transfer).

In this case, the image formation by each process unit 40Y, 40M, 40C, 40K, that is, the exposure by the exposure device 43 is shifted by a predetermined time so that the toner images of the respective colors are multiplex-transferred onto the same one-page region on the intermediate transfer belt 31. It starts at the timing.
In the case of forming a single color image, a toner image is formed only on the photosensitive drum 41 of a predetermined process unit (for example, the process unit 40K) and transferred to the belt running portion below the intermediate transfer belt 31. The

A secondary transfer roller 33 is pressed against the right end of the intermediate transfer belt 31. The secondary transfer roller 33 presses the drive roller 31 a via the intermediate transfer belt 31, and a transfer nip Nt is formed (secured) between the intermediate transfer belt 31 and the secondary transfer roller 33.
A paper feed unit 35 is provided below the image forming unit B. A plurality of recording sheets P are accommodated in the paper feeding unit 35, and the recording sheets P are fed out from the paper feeding unit 35 by a paper feeding roller 35b. The recording sheet P fed out by the paper feed roller 35 b is supplied to the sheet conveyance path 37.

  The sheet conveyance path 37 is provided in a substantially vertical state above the paper feed roller 35b, and is disposed above the transfer nip Nt where the intermediate transfer belt 31 and the secondary transfer roller 33 are pressed. It passes through the inside of the fixing device 38. The upper part of the sheet conveying path 37 is bent in the left direction above the fixing device 38. A sheet discharge roller 39 is provided at the end of the sheet conveyance path 37.

  In the sheet conveyance path 37, a timing roller pair 34 is provided upstream of the transfer nip Nt in the sheet conveyance direction. The timing roller pair 34 is rotated by a timing motor 55 (see FIG. 2). The recording sheet P fed out from the sheet feeding unit 35 into the sheet conveyance path 37 is conveyed to the transfer nip Nt by the timing roller pair 34 being rotated at a predetermined timing by the timing motor 55.

  The recording sheet P conveyed by the timing roller pair 34 passes through the transfer nip Nt at a predetermined conveyance speed. The toner image primarily transferred onto the intermediate transfer belt 31 is secondarily transferred to the recording sheet P while the recording sheet P passes through the transfer nip Nt. In this case, the process units 40Y to 40K are configured so that the leading edge in the sheet conveyance direction of the one-page region of the toner image primarily transferred onto the intermediate transfer belt 31 and the leading edge in the sheet conveyance direction of the recording sheet P to be conveyed coincide. The conveyance timing of the recording sheet P by the timing roller pair 34 is controlled based on the toner image formation timing.

  The recording sheet P on which the toner image is secondarily transferred is conveyed to a fixing device 38 provided above the transfer nip Nf. The fixing device 38 fixes the toner image on the recording sheet P by heating and pressurizing the recording sheet P being conveyed. The recording sheet P on which the toner image is fixed is discharged onto a paper discharge tray 36 provided above the image forming unit B by a paper discharge roller 39.

<Fixing device>
The fixing device 38 includes a heating roller 38a and a fixing roller 38b, a fixing belt 38c wound around the heating roller 38a and the fixing roller 38b, and a pressure roller 38d that presses the fixing belt 38c.
The fixing belt 38c is wound around the fixing roller 38b and the heating roller 38a in a state where tension is applied. The pressure roller 38d is pressed against the fixing belt 38c and presses the fixing belt 38c against the fixing roller 38b. A fixing nip Nf is secured (formed) between the pressure roller 38d and the fixing belt 38c.

  The pressure roller 38d is rotated at a predetermined rotation speed by a fixing conveyance motor 38g (see FIG. 2). As a result, the fixing roller 38b pressed against the pressure roller 38d with the fixing belt 38c interposed therebetween rotates following the pressure roller 38d. Also, the fixing belt 38c moves (runs) in the direction of arrow F together with the fixing roller 38b and the pressure roller 38d.

The heating roller 38a is formed in a hollow cylindrical shape, and a heater lamp (halogen heater lamp) 38e for heating the heating roller 38a is provided therein. When the heating roller 38a is heated by the heater lamp 38e, the fixing belt 38c that runs around the heating roller 38a is heated.
The recording sheet P onto which the toner image has been transferred is conveyed to the fixing nip Nf with the surface onto which the toner image has been transferred facing the fixing belt 38c, and passes through the fixing nip Nf. The recording sheet P passing through the fixing nip Nf is pressed by the fixing belt 38c and heated. As a result, the toner image is fixed on the recording sheet P.

  In the vicinity of the heating roller 38a, a temperature sensor 38f for detecting the surface temperature of the fixing belt 38c wound around the heating roller 38a is provided. The temperature sensor 38f is disposed to face an upstream portion in the running direction of the fixing belt 38c wound around the heating roller 38a. The temperature sensor 38f detects a temperature corresponding to the heating temperature of the recording sheet P in the fixing nip Nf.

<MFP control system>
FIG. 2 is a block diagram showing a configuration of a main part of a control system provided in the MFP.
The MFP includes a main control unit 51 that executes various data processing in the MFP, and an engine control unit 52 that controls the image reading unit A and the image forming unit B based on instructions from the main control unit 51.

The main control unit 51 includes a CPU 51a, a RAM 51b, a ROM 51c, a communication interface (I / F) unit 51d, a PDL processing unit 51e, an image data storage unit 51f, and an image processing unit 51g.
The communication I / F 51d receives image data (drawing data) transmitted from an external terminal, a server, or the like (not shown) via a network such as a LAN. The drawing data is described in a page description language (PDL). The image data received by the communication I / F 51d is given to the PDL processing unit 51e.

  The PDL processing unit 51e obtains drawing data (page data) in units of print jobs (image forming jobs), and for each page of data (page data), a character area that is a character (text) image, a photograph Analyzes the distinction of each region such as a photographic region that is an image, the drawing start position and end position of each region, and generates print data for forming toner images of Y, M, C, and K colors from the analysis results Then, the generated print data is sent to the image processing unit 51g.

Further, the PDL processing unit 51e determines whether or not an image image (high temperature heating area) that requires high temperature heating at the time of fixing based on the analysis result (here, a region other than a character area, such as a photograph) is included in one page. I do. This determination method will be described later.
The image data storage unit 51f stores the scan data output from the line sensor 15 of the image reading unit A for each page of the document and stores them in units of print jobs.

  The image processing unit 51g reads the scan data stored in the image data storage unit 51f, generates print data for forming Y, M, C, and K toner images, and generates the generated Y to K colors Correction processing including predetermined gradation correction is performed on the print data for use. This correction processing is similarly performed when Y to K print data is received from the PDL processing unit 51e.

When executing the print job, the image processing unit 51g generates exposure data for driving the laser diodes in the exposure devices 43 of the process units 40Y to 40K based on the Y to K color print data after the correction processing is performed. To do.
This exposure data is obtained by causing the laser diode to emit light in units of dots for the image forming area on the photosensitive drum 41 when the photosensitive drum 41 is exposed and scanned for each of the process units 40Y to 40K. Is a signal used to form an electrostatic latent image of one scanning line by turning off the laser diode in units of one dot, and is composed of, for example, a rectangular waveform.

The generated exposure data for Y to K colors is output from the image processing unit 51g to the engine control unit 52 in accordance with an instruction from the CPU 51a.
The engine control unit 52 performs light emission control of the laser diode in the exposure device 43 for each of the process units 40Y to 40K based on the exposure data output from the image processing unit 51g. Thereby, laser light is emitted from the exposure device 43 to the rotating photosensitive drum 41 for each of the process units 40Y to 40K, and the photosensitive drum 41 is exposed and scanned.

  An electrostatic latent image for one page is formed on each photosensitive drum 41 by the exposure data generated from the print data for one page. The formed electrostatic latent image is developed by the developing device 44 to be a toner image of each color of Y, M, C, and K. Here, when executing a print job for printing an image of a plurality of (Mn) pages on one recording sheet P per page, printing is executed in the order of the pages, that is, in the order of one page, two pages, and Mn pages. The

Further, the engine control unit 52 controls the timing motor 55 so that the timing roller pair 34 is rotated and stopped at a predetermined timing during execution of the print job.
The recording sheet P conveyed from the paper supply unit 35 is temporarily stopped by the timing roller pair 34 in a rotation stopped state. Thereafter, the rotation of the timing roller pair 34 is resumed in accordance with the timing at which the front end of the one-page region in the sheet conveyance direction reaches the transfer nip Nt of the toner image primarily transferred onto the intermediate transfer belt 31 by the process units 40Y to 40K. Is done. As a result, the recording sheet P is conveyed to the transfer nip Nt at a predetermined conveyance speed.

The engine controller 52 is given a surface temperature Ts of the fixing belt 38c detected by the temperature sensor 38f. Further, the engine control unit 52 controls the heater lamp 38e to an on state and an off state. Further, the engine control unit 52 also controls a fixing conveyance motor 38g that rotates the pressure roller 38d.
The engine control unit 52 performs fixing control for controlling the heater lamp 38e based on the detection result of the temperature sensor 38f so that the recording sheet P passing through the fixing nip Nf is heated at a predetermined fixing temperature. Further, the engine control unit 52 rotationally drives the rotating members such as the photosensitive drums 41 and the intermediate transfer belts 31 of the process units 40Y to 40K so as to rotate at a predetermined system speed during execution of the print job. In addition to controlling a main motor (not shown), the timing motor 55 and the fixing and conveying motor 38g are controlled so that the recording sheet P is conveyed on the sheet conveying path 37 at the same constant speed as the system speed. Hereinafter, the conveyance speed of the recording sheet S is referred to as a sheet conveyance speed.

<Outline of fixing control and high-temperature heating area determination processing>
When the toner image forming operation (print job) is instructed, the engine control unit 52 executes fixing control in units of the instructed print job. In the fixing control, when the heating temperature of each recording sheet P on which the toner image is formed is controlled to the standard fixing temperature T1, the “standard heating mode” is set. Further, when controlling to a high fixing temperature T2 higher than the standard fixing temperature T1, the “high temperature heating mode” is set.

The standard fixing temperature T1 in the standard heating mode can secure the fixing property of the toner image having an average printing rate as in the case where the toner image of only the character (text) image is formed on the recording sheet P. Temperature. In the present embodiment, the standard fixing temperature T1 is set to 160 ° C.
The high fixing temperature T2 in the high-temperature heating mode is a temperature that can secure the fixing property of a toner image (image image) such as a photograph that uses a larger amount of toner per unit area than a character (text) image. . In the present embodiment, the high fixing temperature T2 is set to 180 ° C.

  In order for the engine control unit 52 to execute such fixing control, the main control unit 51 determines whether the toner image formed on one recording sheet P includes a region to be heated at the high fixing temperature T2. Execute the process of determining. In the following, in one recording sheet P (one page), an area to be heated at the high fixing temperature T2 is referred to as a “high temperature heating area”, and the other area is referred to as a “standard heating area”. The process for determining whether or not the high-temperature heating area is included is referred to as “high-temperature heating area determination process”.

  When the image data to be printed is image data (drawing data) received from an external terminal or the like, the high-temperature heating area determination processing is executed on the basis of the image data (page data) for each page in the PDL processing unit 51e. If it is scan data, it is executed on the basis of exposure data obtained from the scan data (page data) for each page in the image processing unit 51g.

Each of the PDL processing unit 51e and the image processing unit 51g determines whether a high-temperature heating region is included in the toner image for each page data in units of one page.
In the high temperature heating area determination process, the page data determined to include the high temperature heating area in the toner image is set to “high temperature page”. The recording sheet P on which the toner image is formed based on the page data set to “high temperature page” is heated in the “high temperature heating mode” in the fixing control.

Further, the page data determined not to include the high temperature heating area is set to “standard page”. The recording sheet P on which the toner image is formed based on the page data set to “standard page” is heated in the “standard heating mode” in the fixing control.
Further, when page data set to “hot page” is included in the print job, the heating temperature of the hot heating area on the first recording sheet P on which the toner image of “hot page” is formed is The timing for raising the temperature from the standard fixing temperature T1 to the high fixing temperature T2 is also controlled. That is, the heater lamp 38e is controlled so that the heating temperature of the recording sheet P in the fixing nip Nf becomes the high fixing temperature T2 at the timing when the first high-temperature heating area in the print job arrives at the fixing nip Nf (heater temperature increase). control).

For this heater temperature rise control, in the high temperature heating area determination process, for the page data first determined to include the high temperature heating area in the print job, the position of the high temperature heating area in the sub-scanning direction within one page is determined. Identify.
The position of the high-temperature heating area in the sub-scanning direction is the position downstream of the sheet conveyance direction in the high-temperature heating area when the high-temperature heating area is formed on one recording sheet P (closest to the front end in the sheet conveyance direction). This position corresponds to the position of the leading end edge (see Pr in FIG. 10), and this position is the first heating position on the recording sheet P at the high fixing temperature T2. This position is hereinafter referred to as “high temperature heating start position”.

<High temperature heating area determination processing>
Next, the high temperature heating region determination process executed in each of the PDL processing unit 51e and the image processing unit 51g will be described.
First, the high temperature heating region determination process executed in the PDL processing unit 51e will be described based on the flowchart of FIG.

The PDL processing unit 51e performs PDL analysis of the drawing data received for each print job in the communication I / F unit 51d. When the received drawing data includes a plurality of page data, the PDL processing unit 51e generates print data by PDL analysis of each page data in the page order.
The PDL processing unit 51e performs a high-temperature heating region determination process in parallel with the generation of print data. In the high-temperature heating area determination process, it is determined whether all the page data in the print job includes a high-temperature heating area based on information on the toner amount of the toner image.

In the high temperature heating region determination process, first, the specific unnecessary flag Fp is set to the reset state (Fp = 0), and the count value of the number of pages in the print job is set to an initial value (M = 1: first page) (FIG. 3 step S11). Here, the specific unnecessary flag Fp is a flag set to “1” in step S21 described later.
Next, page data of the first page is acquired (step S12), and it is confirmed by PDL analysis whether the page drawing reference position is included in the page data (step S13). The drawing reference position of this image is information relating to the toner amount of the toner image.

  If the image drawing reference position is not included (“No” in step S13), there is no image such as a photograph or a figure, and only character (text) drawing is performed. Based on the assumption that the high-temperature heating area is not included in the toner image formed based on this, the M (= 1) page is set to “standard page” (step S16). Thereafter, the process proceeds to step S22.

  On the other hand, when the drawing reference position of the image is included (“Yes” in step S13), it is confirmed whether or not an image embedding is instructed at the drawing reference position of the image (step S14). When there is one or more drawing reference positions instructed to embed an image (“Yes” in step S14), the area instructed to embed the image is set as a high-temperature heating area, and M (= 1) page is set to a high temperature. The “hot page” including the heating area is set (step S17), and the process proceeds to step S18.

When the image embedding is not instructed (“No” in step S14), it is confirmed whether there is one or more drawing reference positions for which the paint processing is instructed (step S15). This image embedding instruction is also one piece of information relating to the toner amount of the toner image.
If there is no drawing reference position for which the filling process is instructed (“No” in step S15), the page data of the M (= 1) page does not include the high-temperature heating area, and the M (= 1) page. Is set to “standard page” (step S16).

In step S15, when there is one or more drawing reference positions for which the filling process is instructed (“Yes” in step S15), the M (= 1) page is set as a high temperature page (step S17). Thereafter, the process proceeds to step S18. This paint processing instruction is also one piece of information relating to the toner amount of the toner image.
In step S18, it is confirmed whether the specific unnecessary flag Fp is in the set state (Fp = 1). If the specific unnecessary flag Fp is not set (“No” in step S18), the toner formed on the recording sheet P based on the page data with the M page as the first high-temperature page in the print job. The high temperature heating start position of the first high temperature heating area is specified in the image, and the specified high temperature heating start position is stored (step S19).

The high temperature heating start position is specified by setting the drawing start position in the sub-scanning direction in the high temperature heating area based on the page data, the distance Le in the sheet conveyance direction from the leading edge in the sheet conveyance direction on the recording sheet P to be used (FIG. 10). This is done by converting to
This conversion is performed by referring to conversion information that associates the position in the sub-scanning direction specified by the page data in advance with the distance in the sheet conveyance direction on the recording sheet P. If the high-temperature heating start position can be specified, the conversion is performed. Other methods may be used.

When a plurality of high-temperature heating areas are present in one page area, the high-temperature heating area located on the most downstream side in the sheet conveying direction (sheet front end side) in the recording sheet P is extracted, and the high-temperature heating area is extracted. The high temperature heating start position is specified.
When the high temperature heating start position (distance Le) is stored, the specific unnecessary flag Fp is set (Fp = 1) (step S20), and the process proceeds to step S21.

If the specific unnecessary flag Fp is already set (“Yes” in step S18), steps S19 and S20 are skipped and the process proceeds to step S21. In this case, storage of the high temperature heating start position is not executed. The same applies to the standard page setting (step S16).
In step S21, it is confirmed whether or not the determination of the high-temperature heating region has been completed for all page data (page total number Mn) in the instructed print job. If the determination of the high temperature heating region for all the page data is not completed (M <Mn) (“No” in step S21), the current page number M is incremented by 1 (step S22), and step S12 Return to.

  For example, if M = 2, in step S12, page data of M (= 2) pages is acquired, and the processes after step S12 are executed. If the M (= 2) page does not include the high temperature heating area, the M (= 2) page is set as the standard page (step S16), and if the M (= 2) page includes the high temperature heating area, it is set as the high temperature page. (Step S17) If the specific unnecessary flag Fp is already set (“Yes” in Step S18), Step S19 is skipped, so the high-temperature heating of the high-temperature heating region included in the M (= 2) page The starting position is never stored.

  On the other hand, if the specific unnecessary flag Fp is not in the set state (“No” in step S18), the high temperature heating start position of the high temperature heating region included in the M (= 2) page is stored (step S19), and the specific unnecessary flag Fp is stored. Is set (Fp = 1) (step S20). That is, only the high temperature heating start position of the high temperature heating region included in the page when the specific unnecessary flag Fp is set to the first state is stored.

This is because the heater lamp is set so that the high temperature heating area in the page is fixed at the high fixing temperature T2 with respect to the first printed page among one or more pages including the high temperature heating area. This is because the heater temperature increase control for increasing the temperature of 38e is executed.
Until the number of pages M reaches Mn, the processing from steps S12 to S22 is repeatedly executed for each page.

When the number of pages M reaches Mn and the determination of the high temperature heating region for all page data is completed (“Yes” in step S21), information on “standard page” or “high temperature page” set for each page, Information on the stored high-temperature heating start position is notified to the CPU 51a as a determination result (step S23), and the high-temperature heating region determination process ends.
In addition, the high temperature heating area | region determination process of the PDL process part 51e is not limited to the process based on the flowchart shown in FIG. For example, instead of steps S13 to S15, if there is one or two of the fact that there is a drawing reference position of an image, an instruction to fill in, or an instruction to embed an image, there is a character region Alternatively, the recording sheet P may be determined to include an image area where a larger amount of toner is used, that is, a high-temperature heating area.

Next, the high-temperature heating region determination process executed in the image processing unit 51g will be described based on the flowchart of FIG.
When a print job is instructed, the image processing unit 51g generates print data for each of Y to K colors from one page of scan data stored in the image data storage unit 51f, and generates the generated Y to K colors. Based on the print data, exposure data for driving the laser diode in the exposure device 43 of the process units 40Y to 40K is generated.

When the high temperature heating area determination process is started, the image processing unit 51g first sets the high temperature heating area specific unnecessary flag Fp to the reset state (Fp = 0) and sets the count value of the number of pages in the print job to the initial value. (M = 1) is set (step S31 in FIG. 4).
Next, page data of the M page in the print job, here, the first first page is acquired (step S32). The page data is acquired by reading out data corresponding to the first page in the generated exposure data for each of Y to K colors.

Then, the total number of dots Dc for one scanning line is obtained (step S33). This total dot number Dc is information relating to the toner amount of the toner image.
Specifically, the acquired page data corresponding to the first page for each of Y to K colors is divided into data in units of scanning lines for each of Y to K colors.
All the scanning lines for exposing and scanning one page are defined as a first line, a second line, and a z-th (final) line in order from the front end to the rear end side in the sheet conveyance direction of the recording sheet P. The data corresponding to the first line is the data for the first line, the data corresponding to the second line is the data for the second line, and the data corresponding to the z-th line is the data for the z-th line. For example, the data for the first line is the data of the scanning line closest to the front end in the sheet conveyance direction in one page, and the data for the zth line is the data of the scanning line closest to the rear end in the sheet conveyance direction in one page. become.

Then, for each of Y to K colors, the data for the first line is referred to, the number of dots for exposing and scanning the image forming area is counted, and the total value obtained by adding the counted number of dots is the total number of dots Dc. To do.
It is determined whether or not the calculated dot total number Dc of one scanning line, here the first line, is equal to or less than a preset threshold value D1 (step S34).

If the total number of dots Dc ≦ threshold value D1 is determined (“Yes” in step S34), the first line is determined to be the A line (step S39), and the process proceeds to step S40.
The A line is a line that includes an image formed by an amount of toner that is equal to or less than the amount of toner that can secure the fixability on the recording sheet P if fixing is performed at the standard fixing temperature T1. The threshold value D1 is a value for determining whether or not it is the A line, and is determined in advance by experiments or the like.

On the other hand, if the total dot number Dc> threshold value D1 is determined (“No” in step S34), it is determined whether the total dot number Dc is smaller than the preset threshold value D2 (step S35). If the threshold value D2 <the total number of dots Dc is determined (“Yes” in step S35), the first line is determined to be the B line (step S38), and the process proceeds to step S40.
The B line is a line in which the toner adhesion amount of the formed image on the recording sheet P on one scanning line is larger than the A line, and in order to ensure the fixing property on the recording sheet P, the high fixing temperature T2 is used. It is a preferable line to perform fixing.

  If threshold D2 ≧ dot total number Dc is determined (“NO” in step S35), the number of edges Ec of the image included in the first line is counted (step S36). The number of edges Ec refers to the data (exposure data) of the first line, and when there are two or more dots indicating an image in the main scanning direction continuously in the first line, the number of edges is determined from the consecutive dots. This is done by accumulating and counting the number of dots at one end and the other end of the dot row in the main scanning direction by the number of existing images. Note that when there is no image area on the first line and only a non-image area, the edge number Ec of the image is zero.

  It is determined whether or not the number of edges Ec of the image is equal to or less than a threshold value E1 or greater than a threshold value E2 (> E1) (step S37). When a positive determination is made (“Yes” in step S37), the process proceeds to step S38. In this case, the first line is determined as the B line. On the other hand, when a negative determination is made (“No” in step S37), the process proceeds to step S39. In this case, the first line is determined as the A line.

  As described above, whether the A line or the B line is determined based on the size of the edge number Ec is determined based on the size of the edge number Ec to determine which attribute of the photograph or character the formed image has. Based on the attribute determination result, the first line for which the total number of dots Dc is determined to be larger than the threshold D1 for determining the A line should be the B line for which fixing at the high fixing temperature T2 is desirable, or depending on the attribute, the standard fixing temperature T1. This is to determine whether there is no problem even if the A line is suitable for fixing by the above.

That is, a solid image such as a photograph or a figure often has a relatively large area, and the larger the area, the longer the dot row indicating the image on one scan line, and thus the number of edges Ec on one scan line. Less.
On the other hand, in a character area including only characters, for each character, a line segment of the character becomes an image area, and a portion other than the line segment becomes a non-image area. The number of character segments existing on one scan line increases and the number of edges Ec on one scan line increases accordingly.

  Further, when the gradation of the output image is reproduced using pseudo gradation correction such as dithering, the number of edges Ec on one scanning line becomes extremely large. This is because pseudo gradation is performed by changing the ratio of dots (images) to be exposed and dots not to be exposed (non-images) of m × n dots indicated by the dither matrix in accordance with the gradation value. However, depending on the gradation value, the dots to be exposed and the dots not to be exposed are likely to be alternately arranged adjacent to each other in the main scanning direction, and the more the dots are alternately arranged, the more the dots to be exposed on one scanning line are not exposed. This is because the number of edges that are dot boundaries increases.

Normally, pseudo-tone reproduction methods such as dithering are applied to half-tone images such as photographs. Half-tone images have a larger amount of toner adhesion than character areas, and image areas with a large amount of toner adhesion. Since the amount of heat required for fixing increases, fixing at a high fixing temperature T2 is preferable. The same applies to the above-described solid image having a large area.
On the other hand, regarding the character area, if the size of the character itself is small, even if the toner adhesion amount in one scanning line is increased to some extent (Dc> D1), it is still a character, and the standard fixing temperature T1. However, the fixability on the recording sheet P can often be secured.

  Therefore, when the relationship of the number of edges Ec ≦ E1 or E2 <the number of edges Ec is satisfied under the condition of D1 <the total number of dots Dc ≦ D2, there is a probability that the line is a line constituting a halftone image region such as a photograph. If it is determined as B line because it is high and the relationship of E1 <number of edges Ec ≦ E2 is satisfied, the probability that it is a line constituting the character area is high, so the configuration is determined as A line, which is more suitable for image attributes Judgment can be made. Therefore, the number of edges can be said to be one piece of information regarding the toner amount of the toner image.

  In step S40, it is confirmed whether the setting of “A line” or “B line” for all the scanning lines (1 to z) in the page data of the M (= 1) page is completed for each of Y to K colors. If the settings for all the scan lines have not been completed (“No” in step S40), the process returns to step S33. In this case, the process after step S33 is executed for the line to be exposed and scanned after the scanning line for which determination has been completed, in the above example, the second line, and the setting of “A line” or “B line” is set. Done.

Steps S33 to S40 are repeated for each scanning line until the setting of the lines for all the z scanning lines in the M (= 1) page is completed for each of the Y to K colors, and the setting for the scanning lines for the total number z is performed. Is completed (“Yes” in step S40), the process proceeds to step S41.
In step S41, whether or not “B lines” of a preset number (N) or more among all the scanning lines 1 to z are continuous in the sub-scanning direction in the M (= 1) page is Y to. Check for each K color.

If it is determined that one or more of the Y to K colors includes N or more B lines (“Yes” in step S41), the M (= 1) page is set to “high temperature page” (step S42). In other cases (“No” in step S41), the M (= 1) page is set to “standard page” (step S47).
The B line is a line determined to constitute a halftone image area such as a photograph as described above. However, depending on the number and size of characters in the character area, the B line is originally a line constituting the character area. However, the relationship of the number of edges Ec ≦ E1 or E2 <the number of edges Ec may be satisfied, and the line may be erroneously determined. In the case of a character region, the space between characters is usually a non-image region, and in the non-image region, it should be determined as an A line instead of a B line. It is rare that the number of continuous B lines becomes extremely large.

On the other hand, in the case of a halftone image region such as a photograph having a certain area, the relationship of the number of edges Ec ≦ E1 or E2 <the number of edges Ec is satisfied. In most cases, the continuous number of the is increased.
Therefore, considering the possibility of erroneous determination in the image area determination (steps S34 to S39) in units of one scanning line, even if the determination of the B line is made, the continuous number in the sub-scanning direction is a threshold value. If the number is less than N (“No” in step S41), it is regarded as a scanning line that should originally be determined as the A line, and only when the number of continuous B lines is N or more, the high temperature page is displayed. It is set (step S42), and in other cases, the standard page is set (step S47).

The threshold values D1, D2, E1, E2, and N are set in advance based on experiments or the like so that the standard page and the high temperature page can be appropriately determined.
In step S42, when the M (= 1) page is set to “high temperature page”, it is confirmed whether or not the specific unnecessary flag Fp is set (Fp = 1) (step S43). If it is not in the set state (“No” in step S43), the high temperature heating start position of the first high temperature heating area in the toner image is specified and stored (step S44).

This high-temperature heating start position is the sheet in the high-temperature heating area located closest to the front end (downstream) of the recording sheet P in the sheet conveyance direction among one or more high-temperature heating areas on one recording sheet P as described above. This is the position in the sub-scanning direction of the edge (front edge) on the front end (downstream) side in the transport direction (Pr in FIG. 10).
Among all the scanning lines (first to zth lines) in one page, the line number corresponding to the high temperature heating start position is specified, and the circumference of the photosensitive drum 41 by one scanning line is assigned to the specified line number. By multiplying the scanning line width [mm / line] on the surface, the distance Le (FIG. 10) on the recording sheet P from the leading edge of the recording sheet P to the high temperature heating start position can be calculated. it can. This calculated distance Le is used as information for specifying the high temperature heating start position.

Specifically, for example, if the resolution is 400 [dpi], the scanning line width on the circumferential surface of the photosensitive drum 41 by one scanning line is 0.063 [mm / line], so the specified line number Is 1000, the high temperature heating start position on the recording sheet P is a position away from the leading edge of the recording sheet P by a distance Le (= 63) [mm] in the sub-scanning direction.
When the specified high-temperature heating start position (distance Le) is stored, the identification unnecessary flag Fp is set (Fp = 1) (step S45). Thereafter, the process proceeds to step S46.

  On the other hand, if it is determined in step S41 that N or more B lines are not continuous (“No” in step S41), the M (= 1) page is set to “standard page” (step S47). . In this case, the recording sheet P on which the toner image is formed based on the page data of M (= 1) page is heated in the standard heating mode in the fixing control. Thereafter, the process proceeds to step S46.

In step S46, it is confirmed whether the setting process of “standard page” or “hot page” has been completed for all pages (total number of pages Mn) in the print job.
If the setting process for all the pages Mn has not been completed (“No” in step S46), the count value of the number of pages M is incremented by 1 (step S48), the process returns to step S32, and the M page, the above In the example, processing for page data of two pages (steps S32 to S47) is executed. In this process, when the M (= 2) page is set to “high temperature page” (step S42), if the first page is set to “standard page”, the specific unnecessary flag Fp is in a reset state (Fp = 0). ) (“No” in step S43), the high temperature heating start position for the high temperature heating region included in the M (= 2) page is specified (step S44).

On the other hand, if the first page has already been set to the “high temperature page”, the specific unnecessary flag Fp has already been set (Fp = 1) (“Yes” in step S43), and therefore step S44. Is skipped, and the high temperature heating start position for the high temperature heating region included in the M (= 2) page is not specified.
As described above, the high temperature heating start position of the high temperature heating area is specified (step S44) only for the pages that are determined to include the high temperature heating area first in the print order among all the pages Mn in the print job. Is done.

  The processes in steps S32 to S48 are repeatedly executed until the page setting for all the pages Mn is completed. When the process is completed (“Yes” in step S46), the page setting result and the page set as “high temperature page” are displayed. If included, the CPU 51a is notified of the information specified as the high temperature heating start position as a determination result (step S49), and the high temperature heating region determination process is terminated.

<Fixing control>
Next, the fixing control executed in the engine control unit 52 will be described based on the flowchart of FIG.
When a print job is instructed, the engine control unit 52 receives exposure data for all pages in the print job from the CPU 51a (see step S51 in FIG. 5). Next, it is confirmed whether all pages of the print job are set to “standard pages” (step S52).

If all pages are set to “standard pages” (“Yes” in step S52), the fixing control for all recording sheets P in the print job is set to the standard heating mode and executed (step S65). ).
In the standard heating mode, the heater lamp 38e is controlled so that the recording sheet P passing through the fixing nip Nf is heated at the standard fixing temperature T1 (160 ° C.).

FIG. 8 is a flowchart showing the contents of a subroutine of the standard heating mode.
In the standard heating mode, the surface temperature Ts of the fixing belt 38c detected by the temperature sensor 38f is compared with the standard fixing temperature T1 (step S111). When the surface temperature Ts becomes higher than the standard fixing temperature T1 (“Yes” in step S111), the heater lamp 38e is turned off (step S112), and when the surface temperature Ts of the fixing belt 38c falls below the standard fixing temperature T1 (step S112). "No" in S111), the heater lamp 38e is turned on (step S113). Thereafter, the process returns to step S66.

In step S66, it is confirmed whether printing for all pages in the instructed print job has been completed. When it is determined that printing for all pages has been completed (“Yes” in step S66), fixing control for the instructed print job is completed.
In step S52, when all pages are not set as “standard pages” but include pages set as “high temperature pages” (“No” in step S52), the process proceeds to step S53. In the processing after step S53, the recording sheet P is heated in the fixing nip Nf at the timing when the most high-temperature heating area formed on the first “hot page” recording sheet P reaches the fixing nip Nf. Temperature increase control for increasing the temperature to the high fixing temperature T2 is executed.

The outline of the temperature rise control to the high fixing temperature T2 will be described first with reference to the schematic diagram of FIG. 10, and then the control method will be described using the flow.
FIG. 10 virtually illustrates how three recording sheets P1 to P3 on which toner images are formed based on page data of the first to third pages in a print job are conveyed toward the fixing nip Nf in this order. It is a schematic diagram shown.

In the example of the figure, the first page and the second page are set as “standard pages” including only the standard heating region Sr, and the third page is set as “high temperature page” including the standard heating region Sr and the high temperature heating region Hr. An example is shown.
The front end edge (side edge on the downstream side in the sheet conveyance direction) of the high-temperature heating region Hr in the recording sheet P3 is at a position Pr that is separated by a distance Le from the front end in the sheet conveyance direction to the rear end side in the sub-scanning direction. This position corresponds to the high temperature heating start position Pr.

  Each of the recording sheets P1 to P3 has a certain length Ls along the sheet conveying direction, and each of the recording sheets P1 to P3 is spaced from the timing roller pair 34 at a certain sheet conveying speed Sp with a certain sheet interval Lk. It is conveyed to the fixing nip Nf. The sheet interval Lk corresponds to the time from the end of the image forming operation on the nth page to the start of the image forming operation on the (n + 1) th page, and is determined in advance.

Each recording sheet P that has arrived at the fixing nip Nf maintains the sheet conveyance speed Sp and passes through the fixing nip Nf.
In the figure, in addition to the recording sheets P1 to P3, a graph showing how the surface temperature Ts of the fixing belt 38c changes with the passage of time after the conveyance of the recording sheet P1 is started by the timing roller pair 34 ( A solid line, a broken line, a one-dot chain line, a two-dot chain line) and a timing chart showing the image formation start timing are also shown.

The recording sheets P1 and P2 for the first page and the second page set as the standard page do not need to be heated at the high fixing temperature T2, but need to be heated at least at the standard fixing temperature T1.
On the other hand, the high temperature heating region Hr on the recording sheet P3 for the third page set as the high temperature page should be heated at the high fixing temperature T2, but the standard heating region Sr other than the high temperature heating region Hr is to be heated. Although it is necessary to heat at the standard fixing temperature T1, it is not necessary to heat at the high fixing temperature T2.

On the other hand, time tu is required to raise the surface temperature Ts of the fixing belt 38c from the standard fixing temperature T1 to the high fixing temperature T2.
If the time tu required for this temperature rise and the arrival timing at which the high temperature heating start position Pr on the recording sheet P3 (the front edge of the high temperature heating region Hr) arrives at the fixing nip Nf are known in advance, the temperature rise from this arrival timing. When the temperature of the fixing belt 38c goes back from the standard fixing temperature T1 to the high fixing temperature T2, the high temperature heating start position Pr on the recording sheet P3 becomes the fixing nip. The surface temperature Ts of the fixing belt 38c can be made to reach the high fixing temperature T2 just at the timing of arriving at Nf.

The arrival timing at which the high temperature heating start position Pr on the recording sheet P3 arrives at the fixing nip Nf is based on the conveyance start timing (time point tf) of the recording sheet P1 by the timing roller pair 34, and the distance Lf in FIG. It can be obtained by obtaining the time ta divided by the transport speed Sp.
Here, the conveyance start timing (time point tf) of the recording sheet P1 indicates a time point when a predetermined time te has elapsed from the image formation start timing (time point tc).

The image formation start timing (time tc) indicates, for example, the time when a signal indicating the start of printing rises in a printable state due to the end of warm-up.
The predetermined time te is a waiting time from the start of image formation by the process units 40Y to 40K to the start of conveyance of the recording sheet P by the timing roller pair 34, and specifically, on the photosensitive drum 41 of the process unit 40Y. The time required for the leading edge of the formed image area to reach the secondary transfer position Nt via the intermediate transfer belt 31 from the start of formation is tb, and the conveyance of the recording sheet P by the timing roller pair 34 is started. The time required for the leading edge of the recording sheet P1 to reach the secondary transfer position Nt is tc, which is a time indicated by (tb−tc), and is determined in advance.

  At the image formation start timing (time point tc), the conveyance of the recording sheet P1 from the sheet feeding unit 35 to the timing roller pair 34 is started. At this time, the timing roller pair 34 is in a rotation stop state, and when the leading edge of the recording sheet P1 in the sheet conveyance direction reaches the timing roller pair 34 and reaches the conveyance start timing (time point tf) of the recording sheet P1, the timing roller pair 34 The conveyance of the recording sheet P1 by the pair 34 is started.

The distance Lf is obtained by the formula [Lp + (2 × Ls) + (2 × Lk) + Le].
The distance Lp corresponds to the distance on the sheet conveyance path 37 from the timing roller pair 34 to the fixing nip Nf, and is determined in advance and stored in the ROM 51c or the like.
The distance Ls corresponds to the length in the sheet conveyance direction of the recording sheets P1 to P3, and information detected or designated by the user is acquired by a detection unit (not shown).

The distance Lk corresponds to a sheet interval, and is determined in advance as an interval when a plurality of recording sheets P are continuously conveyed, and is stored in the ROM 51c or the like.
The distance Le corresponds to the distance in the sheet conveyance direction from the leading end on the recording sheet P3 to the high temperature heating start position Pr, and the high temperature heating start position Pr (distance Le) stored in the above steps S19 and S44 is read out. To be acquired.

The sheet conveyance speed Sp is determined in advance and stored in the ROM 51c or the like.
A time ta obtained by dividing the distance Lf by the sheet conveyance speed Sp is required from the start of conveyance of the recording sheet P1 by the timing roller pair 34 (time tf) until the high temperature heating start position Pr on the recording sheet P3 arrives at the fixing nip Nf. It corresponds to time. Hereinafter, this time ta is referred to as a required time ta in the high temperature heating region.

On the other hand, the time required for temperature increase (temperature increase required time) tu can be obtained from the heating characteristics of the heater lamp 38e and the magnitude of the temperature to be increased (temperature increase temperature). In this embodiment, temperature rise time information indicating the relationship between the heating characteristics and the temperature rise temperature is held in advance, and a method for obtaining the temperature rise required time tu by referring to this temperature rise time information is taken. Yes.
FIG. 11 is a diagram exemplifying the contents of the temperature rise time information. For each of the cases where the input power of the heater lamp 38e changes in three stages of A, B, and C (where C <B <A), the heater The relationship between the continuous heating time of the lamp 38e and the temperature rise temperature of the surface temperature Ts of the fixing belt 38c is shown in a table format.

  The input power B is a standard power supplied from a commercial power source, and is a time required for increasing the surface temperature Ts of the fixing belt 38c by 10 [° C.] by continuous heating of the heater lamp 38e (temperature increase required). Time) is 1.2 seconds. In addition, the required temperature increase time for increasing the surface temperature Ts of the fixing belt 38c by 15 [° C.] is 1.8 seconds, and the required temperature increase time for increasing the temperature 20 [° C.] is 2.5 seconds.

On the other hand, when the input power A is in a higher power state than the input power B, the required temperature increase time is slightly shorter than in the input power B, and when the input power C is in a lower power state than the input power B, It can be seen that the time required for temperature increase is slightly longer than that for the input power B.
This is because, in the present embodiment, the heater lamp 38e having a heating characteristic in which the heat generation amount per unit time increases as the input power increases, so that the temperature increase required time tu when the input power is A is the maximum. This is because the temperature increase required time tu when C is the shortest and the input power is the shortest is the longest. In this sense, the input voltages A to C can be said to be predetermined different conditions that make the required temperature increase time different.

  The case where the input voltage changes in three stages as described above is specified depending on the MFP installation environment (power supply circumstances, etc.), and the input power of the heater lamp 38e is less than the original standard (input power B). This is because it may fluctuate slightly up and down. Thus, by determining the required temperature increase time tu suitable for the input power according to the input power, it is possible to further reduce the error in the required temperature increase time tu due to fluctuations in the input power.

  Further, the temperature rise temperature is made to correspond to three stages of 10, 15, and 20 [° C.] because the surface temperature Ts of the fixing belt 38c is set to the original standard fixing temperature T1 (= 165 [° C.]) due to temperature ripple. On the other hand, the temperature may actually decrease to about 160 [° C.] or may increase to about 170 [° C.]. Considering such a case, the temperature rise temperature is set to the high fixing temperature T2. (= 180 [° C.])) in addition to 15 [° C.], which is the difference between the standard and (10) and 20 [° C.].

The current input power of the heater lamp 38e is detected by a wattmeter (not shown) provided in the image forming unit B, and the current surface temperature Ts of the fixing belt 38c is detected by a temperature sensor 38f.
For example, when the current input power matches the input power A and the current surface temperature Ts of the fixing belt 38c is 160 [° C.], the temperature rise temperature is 20 [° C.]. It can be calculated as 2.0 seconds.

When the actual input power does not match any of A, B, and C, the closest input power among the input powers A to C can be applied. The same applies to the temperature rise.
In the above description, the case where the input power and the temperature rising temperature are each divided into three stages has been described. However, the present invention is not limited to this, and the input power and the temperature rising temperature are set in multiple stages. Can be taken.

  Returning to FIG. 10, the required conveyance time ta and the required temperature increase time tu in the high-temperature heating region are obtained, and then the time Δtu (= ta−tu) which is the difference between them is obtained, and the recording sheet P1 by the timing roller pair 34 is obtained. If the temperature rise to the high fixing temperature T2 of the fixing belt 38c by continuous lighting (continuation of ON) of the heater lamp 38e is started from the time tp when the time Δtu has elapsed from the start of conveyance of the recording sheet, a recording sheet as shown by the solid line in the graph The surface temperature Ts of the fixing belt 38c reaches the high fixing temperature T2 at the timing when the high temperature heating start position Pr on P3 arrives at the fixing nip Nf. In this sense, the time point tp can be said to be the temperature rise start timing.

Since the temperature rise start timing (time point tp) in the figure corresponds to the time point when the first recording sheet P is passing through the fixing nip Nf, the solid line graph indicates that the first recording sheet P is in the fixing nip Nf. That is, an example in which the temperature of the fixing belt 38c is started to be raised to the high fixing temperature T2 during the passage of the toner.
Also, depending on the length of time Δtu, the start of the temperature increase to the high fixing temperature T2 may occur when the rear end of the second recording sheet P in the sheet conveyance direction passes through the fixing nip Nf as indicated by a dashed line graph, for example. Or the conveyance of the recording sheet P1 by the timing roller pair 34 may be started as shown by a two-dot chain line graph. In this case, the time Δtu becomes zero.

On the other hand, the broken line graph shows a comparative example in which the surface temperature Ts of the fixing belt 38c is controlled to reach the high fixing temperature T2 at the timing when the leading edge of the recording sheet P3 arrives at the fixing nip Nf. ing.
In the case of this comparative example, the temperature rise start time tq to the high fixing temperature T2 is earlier than the temperature rise start timing (time tp) according to the solid line graph, and the recording sheet P3 is originally heated at the high fixing temperature T2. Since the standard heating region Sr that does not require heating is also heated at the high fixing temperature T2, the amount of wasted power supplied to the heater lamp 38e is increased and the power saving performance is impaired.

  On the other hand, if the temperature rising start to the high fixing temperature T2 is controlled as shown by the solid line, the alternate long and short dash line graph according to the present embodiment, one or more recording sheets P conveyed one by one. Among these, for the first recording sheet P3 including the high temperature heating area Hr, the standard heating area Sr on the recording sheet P3 is heated at a temperature higher than the standard fixing temperature T1 and lower than the high fixing temperature T2, and the high temperature heating area Since Pr can be heated at a high fixing temperature T2, it is possible to improve the power saving property as compared with the comparative example while ensuring the toner fixing property.

The control for starting the temperature increase to the high fixing temperature T2 when the time Δtu has elapsed since the start of conveyance of the recording sheet P1 by the timing roller pair 34 is referred to as “temperature increase timing control”.
In the above description, the case where the relationship of the required heating time ta in the high temperature heating area ta ≧ the required temperature rising time tu is described. However, depending on the print job, the page where the high temperature heating area Pr exists is, for example, the second page. In some cases, the required time ta for conveyance in the high-temperature heating region is shortened and the relationship ta <tu is satisfied.

In this case, the temperature is raised to the high fixing temperature T2 from the time point tz that goes back before the start of conveyance of the recording sheet P1 by the timing roller pair 34 (time point tf) by the difference Δtz (= tu−ta) between the times tu and ta. You can also start.
Furthermore, even if the page where the high-temperature heating region Pr exists is, for example, the third page, there may be a relationship of time (ta + te) <tu depending on the temperature rise characteristics of the heater lamp 38e. Even if the temperature rise to the high fixing temperature T2 is started from the image formation start timing (time tc), the temperature rise may not be in time.

Therefore, when the relationship of time (ta + te) <tu is satisfied, control (image forming timing control) is executed to delay the image forming start timing from the original timing (time tc).
FIG. 12 is a schematic diagram virtually illustrating a state in which the three recording sheets P1 to P3 are conveyed toward the fixing nip Nf in this order when image forming timing control is executed, and the surface temperature of the fixing belt 38c. A graph (solid line) showing how Ts changes and a timing chart showing image formation start timing are also shown.

In the figure, the time points tc, tf, and the time te correspond to the time points tc, tf, and the time te shown in FIG. 10 (corresponding to the original image formation start timing without delay control), and are indicated by two-dot chain lines. Sheets P1 to P3 show the conveyance states of the recording sheets P1 to P3 when conveyance of the recording sheet P1 by the timing roller pair 34 is started from the time point tf.
On the other hand, the time point td indicates a time point when the image formation start timing is delayed by Δtw from the original time point tc, and the time point tg is the original timing of the conveyance start timing of the recording sheet P1 by the timing roller pair 34. A time point delayed by Δtw from the time point tf is shown. Further, the recording sheets P1 to P3 indicated by solid lines indicate the conveyance states of the recording sheets P1 to P3 when the conveyance of the recording sheet P1 by the timing roller pair 34 is started from the time point tg.

  When the relationship of time (ta + te) <tu is satisfied, if the conveyance of the recording sheet P1 by the timing roller pair 34 is started at the original conveyance start timing (time tf) based on the original image formation timing (time tc), the time tc Even if the temperature rise from the high fixing temperature T2 is started, it takes time tu to raise the temperature, so that the high temperature heating start position Pr arrives at the fixing nip Nf as in the recording sheet P3 indicated by a two-dot chain line tx. In this case, the surface temperature Ts of the fixing belt 38c is raised only to a temperature T3 lower than the high fixing temperature T2.

  Therefore, the temperature rise is started with reference to the time point tc, and the conveyance of the recording sheet P1 is started at a time point tg delayed by a time Δtw (= tu-te-ta) from the original conveyance start timing (time point tf). Thus, the surface temperature Ts of the fixing belt 38c reaches the high fixing temperature T2 at the timing (time ty) when the high temperature heating start position Pr arrives at the fixing nip Nf as in the recording sheet P3 indicated by the solid line. it can.

Thus, with respect to the first recording sheet P3 including the high temperature heating area Hr among the one or more recording sheets P that are sequentially conveyed, the standard heating area Sr is higher than the standard fixing temperature T1 and the high fixing temperature T2. The high-temperature heating region Pr can be heated at a high fixing temperature T2, and the power saving can be improved while ensuring the toner fixing property.
As described above, the conveyance of the recording sheet P by the timing roller pair 34 and the image formation timing are interlocked, and the image formation operation by the process units 40Y to 40K is delayed by the time Δtw from the original start timing (time tc). By starting at td and delaying the start of conveyance of the recording sheet P1 by the timing roller pair 34 by the time Δtw, the timing of conveyance of the recording sheet P and the temperature rise of the surface temperature Ts of the fixing belt 38c can be taken.

Returning to FIG. 5, in step S53, information on the high temperature heating start position Pr is acquired. This acquisition is performed by receiving information about the high temperature heating start position included in the determination results in steps S23 and S49.
Next, the sheet conveyance speed Sp is acquired (step S54). This acquisition is performed by reading information on the sheet conveyance speed Sp stored in the ROM 51c or the like.

And the conveyance required time ta of a high temperature heating area | region is calculated | required (step S55). The required conveyance time ta in the high-temperature heating area is obtained by dividing the distance Lf by the sheet conveyance speed Sp.
Subsequently, the required temperature increase time tu is obtained (step S56). The required temperature increase time tu refers to the temperature increase time information (FIG. 11), and the temperature increase required corresponding to the respective detection results of the current input power of the heater lamp 38e and the current surface temperature Ts of the fixing belt 38c. It is obtained by reading the time.

Then, the transfer required time ta in the high-temperature heating region and the temperature increase required time tu are compared, and it is determined whether or not tu ≦ ta (step S57).
If tu ≦ ta (“Yes” in step S57), the temperature rise timing control is executed (step S58). On the other hand, if tu> ta (“No” in step S57), image formation timing control is executed (step S59).
<Contents of temperature rise timing control>
FIG. 6 is a flowchart showing the contents of a subroutine for temperature rise timing control executed in step S58 of FIG.

  In this temperature rise timing control process, first, it is determined whether or not the surface temperature Ts of the fixing belt 38c detected by the temperature sensor 38f is equal to or higher than the standard fixing temperature T1 (step S71). When the standard fixing temperature T1 ≦ the surface temperature Ts of the fixing belt 38c (“Yes” in step S71), the heater lamp 38e is turned off (step S72), and the process proceeds to step S74. As a result, heating of the fixing belt 38c is stopped, and the surface temperature Ts of the fixing belt 38c is lowered.

When the standard fixing temperature T1> the surface temperature Ts of the fixing belt 38c (“No” in step S71), the heater lamp 38e is turned on (step S73), and the process proceeds to step S74. As a result, the heater lamp 38e generates heat, the fixing belt 38c is heated, and the surface temperature Ts of the fixing belt 38c is raised.
In step S74, it is determined whether or not the conveyance start timing of the recording sheet P1 has been reached. This determination is made by measuring that a predetermined time te has elapsed from the image formation start timing (time tc).

If it is determined that the conveyance start timing of the recording sheet P1 has not yet been reached ("No" in step S74), the process returns to step S71, and the processes of steps S71 to S74 are repeatedly executed. As a result, the surface temperature Ts of the fixing belt 38c is substantially maintained at the standard fixing temperature T1.
When it is determined that the recording sheet P1 conveyance start timing has been reached ("Yes" in step S74), conveyance of the recording sheet P1 by the timing roller pair 34 is started (step S75).

It is determined whether or not the time Δtu (= ta−tu) has elapsed since the conveyance of the recording sheet P1 by the timing roller pair 34 was started (step S76).
If it is determined that the time Δtu has not yet elapsed (“No” in step S76), if the standard fixing temperature T1 ≦ the surface temperature Ts of the fixing belt 38c (“Yes” in step S77), the heater lamp 38e is turned on. The state is turned off (step S78), and the process returns to step S76. On the other hand, when the standard fixing temperature T1> the surface temperature Ts of the fixing belt 38c (“No” in step S77), the heater lamp 38e is turned on (step S79), and the process returns to step S76.

The processes in steps S73 to S79 are repeatedly executed until it is determined that the time Δtu has elapsed. As a result, the surface temperature Ts of the fixing belt 38c is substantially maintained at the standard fixing temperature T1.
For example, as shown in FIG. 10, when the first recording sheet P including the high temperature heating region Hr is the third page, the first page and the second page should be set as standard pages. The recording sheets P1 and P2 on which the set first and second toner images are formed can be heated at the standard fixing temperature T1.

When the elapse of time Δtu is determined (“Yes” in step S76) (time point tp shown in FIG. 10), the heater lamp 38e is continuously turned on (step S80), thereby indicating a solid line in the graph of FIG. As described above, the heating of the fixing belt 38c by the heater lamp 38e is started, and the surface temperature Ts of the fixing belt 38c increases.
If the time Δtu is 0, that is, if the required heating time ta in the high-temperature heating region is equal to the required heating time tu, the process proceeds to step S80 simultaneously with the start of transferring the recording sheet P1, and the heater lamp 38e is continuously turned on. An on state is set (a graph indicated by a two-dot chain line in FIG. 10).

Until the surface temperature Ts of the fixing belt 38c reaches the high fixing temperature T2 (“No” in Step S81), the heater lamp 38e is kept on (Step S80), and the surface temperature Ts of the fixing belt 38c becomes the high fixing temperature T2. When it reaches (“Yes” in step S81), the heater lamp 38e is turned off (step S82).
At the timing when the surface temperature Ts of the fixing belt 38c reaches the high fixing temperature T2, the first recording sheet P including the high temperature heating area Hr, in the above example, the high temperature heating area Hr of the recording sheet P3 arrives at the fixing nip Nf and is fixed. Passes through the nip Nf. As a result, the high temperature heating region Hr of the recording sheet P3 is heated by the fixing belt 38c having reached the high fixing temperature T2.

  Then, it is determined whether or not the recording sheet P3 has passed through the fixing nip Nf (step S83). In this determination, a sheet detection sensor (not shown) is arranged on the upstream side of the sheet conveyance path 37 from the fixing nip Nf in the sheet conveyance direction, and the sheet conveyance path 37 is detected from the detection position of the recording sheet P by the sheet detection sensor. When the distance to the upper fixing nip Nf is Lz, the time tj (= Lz / sheet conveyance speed Sp) is measured from the detection of the trailing edge of the recording sheet P3 in the sheet conveyance direction by the sheet detection sensor. Is called. Note that the present invention is not limited to this method, and other methods may be used.

  When it is determined that the recording sheet P3 has not yet passed through the fixing nip Nf (“No” in step S83), if the surface temperature Ts of the fixing belt 38c <the high fixing temperature T2 (“Yes” in step S84). Then, the heater lamp 38e is turned on (step S85), and the process returns to step S83. On the other hand, when the surface temperature Ts of the fixing belt 38c ≧ the high fixing temperature T2 (“No” in step S84), the heater lamp 38e is turned off (step S86), and the process returns to step S83.

Until it is determined that the recording sheet P3 has passed through the fixing nip Nf, the processes in steps S83 to S86 are repeated. As a result, the surface temperature Ts of the fixing belt 38c is substantially maintained at the high fixing temperature T2.
When it is determined that the recording sheet P3 has passed through the fixing nip Nf (“Yes” in step S83), the process returns to step S61 in FIG. The processing after step S61 will be described later.
<Contents of image formation timing control>
FIG. 7 is a flowchart showing the contents of the image formation timing control subroutine executed in step S59 of FIG.

This image formation timing control is executed when the relationship of time (ta + te) <tu is satisfied as described above. In this case, the image formation start timing td (FIG. 12) is delayed by a time Δtw (= tu-te-ta) from the temperature rise timing of the heater lamp 38e. Hereinafter, this time Δtw is referred to as a delay time.
In the image forming timing control, first, it is determined whether or not the surface temperature Ts of the fixing belt 38c detected by the temperature sensor 38f has become equal to or higher than the standard fixing temperature T1 (step S91). If the temperature is not equal to or higher than the standard fixing temperature T1 (“No” in step S91), the heater lamp 38e is turned on (step S92), and the surface temperature Ts of the fixing belt 38c is continuously increased to the standard fixing temperature T1 or higher. And heat (warm up).

If the surface temperature Ts of the fixing belt 38c has reached the standard fixing temperature T1 (“Yes” in step S91), it is confirmed whether the heater lamp 38e is in an off state (step S93).
If the heater lamp 38e is off ("Yes" in step S93), the heater lamp 38e is turned on (step S94). Thereafter, the process proceeds to step S95. If the heater lamp 38e is on ("No" in step S93), step S94 is skipped to proceed to step S95 in order to keep the heater lamp 38e on. As a result, the heating of the fixing belt 38c from the standard fixing temperature T1 to the high fixing temperature T2 is started (time tc in FIG. 12).

In step S95, it is determined whether or not the delay time Δtw has elapsed since the temperature of the fixing belt 38c was raised to the high fixing temperature T2.
When it is determined that the delay time Δtw has elapsed (“Yes” in step S95), image formation is started (step S96) (time td in FIG. 12).
It is determined whether time te has elapsed since the start of image formation (step S97). If it is determined that the time te has elapsed since the start of image formation (“Yes” in step S97), the conveyance of the recording sheet P1 is started (step S98). As a result, the recording sheets P after the recording sheet P1 are sequentially conveyed with a certain sheet interval Lk. The heater lamp 38e is kept on.

  When conveyance of the recording sheet P is started, the recording sheet P set to the “standard page” before the recording sheet P in which the high temperature heating region Hr is set, that is, P3 in the above example, is conveyed to the fixing nip Nf. P is conveyed to the fixing nip Nf. In this case, the heater lamp 38e is kept on without controlling the heater lamp 38e so that the surface temperature Ts of the fixing belt 38c becomes the standard fixing temperature T1. As a result, the recording sheet P set to “standard page” is heated at a temperature slightly higher than the standard fixing temperature T1. In this case as well, the toner fixability is ensured without affecting the toner fixability.

Thereafter, the recording sheet P3 in which the high temperature heating area Hr is set arrives at the fixing nip Nf. At the same time, the surface temperature Ts of the fixing belt 38c becomes the high fixing temperature T2. Thereby, the high temperature heating region Hr of the recording sheet P is heated at the high fixing temperature T2 when passing through the fixing nip Nf.
The heater lamp 38e is controlled so that the surface temperature Ts of the fixing belt 38c becomes the high fixing temperature T2 while the recording sheet P3 in which the high temperature heating region Hr is set passes through the fixing nip Nf.

That is, when the surface temperature Ts of the fixing belt 38c becomes equal to or higher than the high fixing temperature T2 (“Yes” in step S99), the heater lamp 38e is turned off (step S100), and the process proceeds to step S103.
On the other hand, if the surface temperature Ts of the fixing belt 38c is lower than the high fixing temperature T2 (“No” in step S99), the heater lamp 38e is off (“Yes” in step S101). 38e is turned on (step S102), and the process proceeds to step S103. If the heater lamp 38e is not off ("No" in step S101), step S102 is skipped and the process proceeds to step S103.

In step S103, it is determined whether or not the recording sheet P3 in which the high temperature heating area Hr is set has passed through the fixing nip Nf.
If it is determined that the recording sheet P3 has not passed through the fixing nip Nf (“No” in step S103), the process returns to step S99, and the processes after step S99 are executed. Steps S99 to S103 are repeated until it is determined that the recording sheet P3 has passed through the fixing nip Nf.

When it is determined that the recording sheet P3 has passed through the fixing nip Nf (“Yes” in step S103), the process returns to step S61 in FIG.
As described above, since the surface temperature Ts of the fixing belt 38c reaches the high fixing temperature T2 at the timing when the first high temperature heating area Hr in the print job starts to pass through the fixing nip Nf, the high temperature heating area Hr has a high fixing temperature. Heated appropriately at temperature T2. Thereby, the fixability of the toner in the high temperature heating region Hr is ensured.

In this case, the standard heating area Sr on the front side in the sheet conveying direction from the high temperature heating start position Pr in the recording sheet P3 including the high temperature heating area Hr is heated at a temperature lower than the high fixing temperature T2. Thereby, the power consumption in the heater lamp 38e can be reduced as compared with the case where the entire recording sheet P3 including the high temperature heating region Hr is heated at the high fixing temperature T2.
Returning to FIG. 5, in step S61, it is determined whether printing for all pages in the instructed print job has been completed. If the printout has not ended ("No" in step S61), it is determined whether the next page in the page order is set to "standard page" (step S62).

  When the next page is set to “standard page” (“Yes” in step S62), the fixing of the recording sheet P of the next page is set to the standard heating mode (step S63). Also in this case, as shown in FIG. 8, when the surface temperature Ts of the fixing belt 38c is higher than the standard fixing temperature T1 (“Yes” in step S111), the heater lamp 38e is turned off (step S112). If the temperature is equal to or lower than the standard fixing temperature T1 (“No” in step S111), the heater lamp 38e is turned on (step S113). Thereafter, the process returns to step S61.

If the next page is not set to “standard page” (“No” in step S62), it is assumed that the “high temperature page” is set, and the fixing of the recording sheet P of the next page is performed in the high temperature heating mode. (Step S64).
In the high temperature heating mode, the heater lamp 38e is controlled so that the recording sheet P passing through the fixing nip Nf is heated at the high fixing temperature T2 (180 [° C.]).

FIG. 9 is a flowchart showing the contents of a subroutine for the high temperature heating mode.
In the high temperature heating mode, the surface temperature Ts of the fixing belt 38c detected by the temperature sensor 38f is compared with the high fixing temperature T2 (step S115 in FIG. 9). When the surface temperature Ts of the fixing belt 38c becomes higher than the high fixing temperature T2 (“Yes” in step S115), the heater lamp 38e is turned off (step S116), and when it is equal to or lower than the high fixing temperature T2 (in step S115). “No”), the heater lamp 38e is turned on (step S117). Thereafter, the process returns to step S61.

If all the printouts are not completed in step S61, the processes in steps S62 to S64 are repeated. When all the printouts are finished (“Yes” in step S61), the fixing control is finished.
As described above, in this embodiment, for each print job, the recording sheet P at the high fixing temperature T2 is the timing at which the high temperature heating area Hr in the first recording sheet P including the high temperature heating area Hr arrives at the fixing nip Nf. The heating of is started. Thereby, since the high temperature heating area Hr is appropriately heated at the high fixing temperature T2, it is possible to ensure the fixability of the toner in the high temperature heating area Hr. In addition, the recording sheet P set in the high temperature heating region Hr is heated at a temperature lower than the high fixing temperature T2 in the standard heating region Sr on the leading side (downstream side) in the sheet conveying direction than the high temperature heating region Hr. Thereby, the power consumption of the heater lamp 38e is reduced as compared with the case where the entire recording sheet P is uniformly heated at the high fixing temperature T2. Therefore, even if the number of executions of a print job including a page set as a high-temperature page increases, it is possible to prevent the power saving performance from being impaired.

<Modification>
(1) In the above embodiment, the temperature rise time information shown in FIG. 11 is information in which the temperature rise required time tu of the fixing belt 38c is associated with each of different input powers A to C. However, the present invention is not limited to this. I can't. If the change in the input power has little effect on the temperature rise control, instead of the input power, for example, information in which different temperature rise required times tu are associated with different types of recording sheets P being conveyed. You can also

As the type of the recording sheet P to be conveyed, the amount of heat taken away from the fixing belt 38c by the recording sheet P when the thick sheet passes through the fixing nip Nf at a constant speed rather than the plain sheet increases. Tends to be longer than plain paper. On the other hand, since the heat consumed by thin paper is less than that of plain paper, the temperature increase required time tu is likely to be shorter than that of plain paper.
For example, thin paper can be used instead of the input power A shown in FIG. 11, plain paper can be used instead of the input power B, and thick paper can be used instead of the input power C.

  (2) In step S55 of FIG. 5 in the above embodiment, the temperature increase time tu of the fixing belt 38c is acquired with reference to the temperature increase time information shown in FIG. Depending on the execution conditions, the acquired required temperature increase time tu may not match the actual required temperature increase time. In this case, even if continuous heating of the heater lamp 38e is started at the set temperature rise start timing (time point tp), the surface temperature of the fixing belt 38c is reached at the timing when the high temperature heating start position Pr arrives at the fixing nip Nf. There is a possibility that Ts cannot be raised to the high fixing temperature T2.

From this, the specific temperature required for the fixing belt 38c is longer than the required temperature increase time tu obtained from the temperature increase time information shown in FIG. 11 (the required temperature increase time tu is prolonged). If it is determined whether or not the specific condition is satisfied, the temperature increase required time tu may be corrected to the extended time tua by the extended amount.
The temperature raising time information shown in FIG. 11 is normally set under the condition that the recording sheet P is plain paper and the surface temperature of the pressure roller 38d is a predetermined reference temperature, for example, 165 [° C.].

  If the surface temperature of the pressure roller 38d is lower than the reference temperature when starting to raise the temperature of the fixing belt 38c to the high fixing temperature T2, the pressure roller out of the heat amount of the fixing belt 38c at the fixing nip Nf. The amount of heat taken away by 38d increases from the reference temperature. The case where the surface temperature of the pressure roller 38d is lower than the reference temperature is likely to occur when sufficient heat has not yet spread over the entire area of the pressure roller 38d, for example, immediately after the end of warm-up.

Even when the recording sheet P to be conveyed is not plain paper but thick paper, the amount of heat taken away from the fixing belt 38c by the thick paper increases when the recording sheet P passes through the fixing nip Nf. This is not limited to the case where the recording sheet P is thick paper, and the same applies to the case where the recording sheet P is made of a material that can easily remove heat from the fixing belt 38c as compared to plain paper.
In these cases, the actual required temperature increase time tua required for increasing the surface temperature Ts of the fixing belt 38c from the standard fixing temperature T1 to the high fixing temperature T2 is the temperature increasing time shown in FIG. It becomes longer than the required temperature increase time tu acquired from the information. In this sense, the fact that the surface temperature of the pressure roller 38d varies depending on the environment can be a specific condition for prolonging the temperature increase time tu. The same applies to the case where the types of recording sheets P are different.

  From the above, for example, a sensor for detecting the surface temperature of the pressure roller 38d is provided to check whether the surface temperature of the pressure roller 38d is equal to or lower than a preset threshold value, and the surface temperature of the pressure roller 38d. Is equal to or less than the threshold value, the temperature increase required time tu obtained from the temperature increase time information shown in FIG. It is possible to adopt a configuration in which the temperature increase start time (time point tp) is set using the corrected temperature increase required time tua (> tu) that is extended by a time corresponding to the surface temperature and using the corrected temperature increase required time tua. .

For example, if the difference between the actual surface temperature of the pressure roller 38d and the reference temperature is large and how long the time required for the temperature increase should be determined in advance through experiments or the like, The time to be extended can be obtained according to the magnitude of the difference.
Similarly, when the type of the recording sheet is set to a specific condition, the recording sheet P of a type that easily takes heat of the fixing belt 38c such as cardboard is used instead of the surface temperature of the pressure roller 38d. Assuming that a specific condition is satisfied, a configuration may be adopted in which the temperature increase time is corrected to tua. The use of a recording sheet of a type satisfying a specific condition can be determined based on the setting, for example, if the configuration allows a setting operation by the user. In addition, the temperature increase required time tu can be corrected based on both conditions of the surface temperature of the pressure roller 38d and the type of the recording sheet.

Instead of the above correction, the surface of the pressure roller 38d may be heated. Specifically, as shown by a broken line in FIG. 1, an auxiliary heater 38h for heating the pressure roller 38d of the fixing device 38 can be provided.
Even in this configuration, when a sensor for detecting the surface temperature of the pressure roller 38d is provided, and it is confirmed that the surface temperature of the pressure roller 38d is equal to or lower than a preset threshold value, the auxiliary heater 38h To heat the pressure roller 38d. As a result, it is possible to suppress an increase in the time required for heating the heater lamp 38e for raising the surface temperature Ts of the fixing belt 38c from the standard fixing temperature T1 to the high fixing temperature T2.

Accordingly, the surface temperature Ts of the fixing belt 38c can be set to the high fixing temperature T2 at the timing when the high temperature heating start position Pr arrives at the fixing nip Nf without correcting the temperature increase start timing (time tp).
(3) In the above embodiment, in the print job, the temperature rise start timing (time point tp) is controlled only for the first recording sheet P including the high temperature heating region Hr. However, the present invention is not limited to this. For example, the temperature rise start timing (time point tp) may be controlled for all recording sheets P including the high temperature heating region Hr.

  For example, when it is determined that the M page is a high temperature page, the (M + 1) page is a standard page, and the (M + 2) page is a high temperature page, the high temperature heating region Hr in the M page is heated at the high fixing temperature T2, and then the heater lamp 38e. Is turned off, the standard heating region Sr of the entire (M + 1) page is heated at a temperature higher than the standard fixing temperature T1 and lower than the high fixing temperature T2, the heater lamp 38e is turned on again, and the high temperature in the (M + 2) page A configuration is conceivable in which the heater lamp 38e is turned on and off by setting a temperature rise start timing (time point tp) at which the heating region Hr is heated at the high fixing temperature T2.

  (4) In the above embodiment, the standard page and the high temperature page are determined based on the analysis of the page description language (PDL) or the number of dots of the exposure data. However, the present invention is not limited to this. For example, each area existing in a page is determined on a page-by-page basis using a known method such as character area determination, photo area determination, or graphic area determination, and a page including a photo or graphic area is defined as a high-temperature page. It is also possible to use a method for specifying the photograph and figure area in FIG.

(5) In the above embodiment, control for starting conveyance of the recording sheet P by the timing roller pair 34 when the predetermined time te has elapsed (time tf) from the image formation start timing (time tc) by the process units 40Y to 40K. Although the example of was demonstrated, it is not restricted to this.
For example, in an image forming apparatus that forms only a monochrome image, if the image formation is started after the conveyance of the recording sheet P by the timing roller pair 34 is started, the conveyance start timing of the recording sheet P is the temperature rise start timing. It becomes a reference when performing control of (time tp). In this case, instead of the conveyance timing control, the image formation timing control described above can be configured to delay the conveyance start timing of the recording sheet P by the determined delay time, and to delay the image formation start timing accordingly. .

Further, although the required time ta in the high temperature heating region is determined based on the conveyance start timing of the recording sheet P by the timing roller pair 34, the present invention is not limited to this. Depending on the configuration of the apparatus, instead of the conveyance start timing by the timing roller pair 34, for example, a configuration in which the supply start timing of the recording sheet P from the sheet feeding unit 35 is obtained as a reference may be employed.
When this configuration is adopted, the high temperature of the high temperature heating region Hr in the first recording sheet P on which the toner image of the high temperature page is formed from the start of feeding of the first recording sheet P first fed out from the paper feeding unit 35. The time assumed to be required for the heating start position Pr to reach the fixing nip Nf is obtained as ta. For example, when the distance ta on the sheet conveyance path 37 from the paper supply unit 35 to the fixing nip Nf is α and the pause time of the recording sheet P by the timing roller pair 34 is β, the time ta is [(α / sheet conveyance). Speed Sp) + β]. Note that the time β is set to 0 if the timing roller pair 34 is not provided and the image forming is performed according to the feeding start timing by the paper feeding unit 35.

  (6) In the above embodiment, an example in which the image forming apparatus is applied to a tandem type MFP that forms a color image has been described. However, the present invention is not limited to this. An image forming apparatus that only forms a monochrome image instead of a color image may be used. After a toner image is formed on the recording sheet P, it is secured between a heating body such as a fixing belt 38c heated by heating means such as a heater lamp 38e and a pressure body such as a pressure roller 38d pressed against the heating body. Any image forming apparatus that allows the recording sheet P to pass through the fixing nip Nf to be thermally fixed can be applied to, for example, a copying machine, a printer, and a facsimile machine.

  The heater lamp 38e is not limited to the heating means, and a nichrome wire heater or the like may be used. The heating means such as the heater lamp 38e and the nichrome wire heater is not limited to the configuration arranged inside the heating roller 38a, but may be arranged outside the heating roller 38a to directly heat the fixing belt 38c. Further, the fixing nip Nf may be formed by the fixing roller 38b and the pressure roller 38d without providing the fixing belt 38c. In this case, the fixing roller 38b becomes a heating body. Further, the pressurizing body is not limited to the roller-shaped one, and may be, for example, a belt-shaped one or a configuration using a pressurizing body that is fixedly arranged so as not to rotate.

  Further, the contents of the above embodiment and the above modification may be combined as much as possible.

  The present invention is useful as a technique for reducing power consumption in an image forming apparatus that thermally fixes a toner image on a recording sheet.

DESCRIPTION OF SYMBOLS 10 Image reading unit 15 Line sensor 38 Fixing apparatus 38a Heating roller 38b Fixing roller 38c Fixing belt 38d Pressure roller 38e Heater lamp 38f Temperature sensor 40Y, 40M, 40C, 40K Process unit 41 Photosensitive drum 43 Exposure apparatus 51 Main control part 51e PDL processing unit 51g Image processing unit 52 Engine control unit

Claims (12)

Image formation in which, after forming a toner image on a recording sheet, the recording sheet is passed through a fixing nip secured between a heating body heated by a heating means and a pressure body pressed against the heating body, and thermally fixed. A device,
Based on information on the toner amount of the toner image formed on the recording sheet, it is determined whether the recording sheet includes a high-temperature heating area in which the heating temperature of the recording sheet should be a high fixing temperature higher than the standard fixing temperature. Determination means to perform,
The heating temperature of the recording sheet determined to include the high-temperature heating area is from the standard fixing temperature to the high fixing temperature until the high-temperature heating area reaches the fixing nip due to the temperature rise of the heating unit. Control means for controlling the temperature rise start timing of the heating means so as to reach the high fixing temperature at the timing when the high temperature heating area reaches the fixing nip,
An image forming apparatus comprising: The control means includes
When a new job is a process for forming a toner image on a plurality of recording sheets, among the recording sheets that are continuously conveyed, the recording sheet that is first determined to include the high-temperature heating area by the determination unit. The image forming apparatus according to claim 1, wherein control of the temperature rise start timing is applied. The control means includes
Of the recording sheets conveyed after the first recording sheet, the recording temperature of the recording sheet that is determined to include the high-temperature heating region by the determination unit is not applied, and the recording start control is not applied. The image forming apparatus according to claim 2, wherein the heating unit is controlled so that the entire sheet has a high fixing temperature. The control means includes
A heating time required for the heating temperature of the recording sheet by the heating means to rise from the standard fixing temperature to the high fixing temperature; and
Among the plurality of recording sheets, the high temperature heating of the recording sheet first determined to include the high temperature heating region from the start of conveyance of the first recording sheet conveyed first toward the fixing nip. 4. The image forming apparatus according to claim 2, wherein the temperature rise start timing is set based on a required conveyance time until the area reaches the fixing nip. 5. The control means includes
When based on the conveyance start timing at which the conveyance of the first recording sheet is started,
When the required temperature increase time is equal to the required transfer time, the temperature increase start timing is matched with the transfer start timing,
5. The image forming apparatus according to claim 4, wherein when the temperature increase required time is shorter than the transfer required time, the temperature increase start timing is set to a timing later than the transfer start timing. The control means includes
6. The image forming apparatus according to claim 5, wherein when the temperature increase required time is longer than the conveyance required time, the temperature increase start timing is set to a timing earlier than the conveyance start timing. The temperature increase time is as follows:
It changes for each different execution condition at the time of job execution,
The control means includes
Each of the different execution conditions stores temperature increase time information formed by associating a temperature increase required time when the condition is satisfied,
5. The temperature increase start timing is set using a temperature increase required time corresponding to the determined execution condition by determining which of the different execution conditions is satisfied. The image forming apparatus according to claim 1. The control means includes
In addition to the determined execution condition, when the specific condition for prolonging the temperature increase time is satisfied, the temperature increase time is corrected to a time extended by the protracted time, The image forming apparatus according to claim 7. Auxiliary heating means for heating the pressure body is further provided,
The control means includes
If the temperature of the pressurizing body is lower than a predetermined reference temperature, it is assumed that the specific condition for prolonging the temperature increase time is satisfied in addition to the determined execution condition. The image forming apparatus according to claim 7, wherein the pressure member is heated by a heating unit. The determination means includes
When a region of a toner image to be formed on one recording sheet is determined and an image image region that uses a larger amount of toner than a character region is included, the recording sheet includes the high-temperature heating region. The image forming apparatus according to claim 1, wherein the image forming apparatus determines whether the image is to be printed. Based on the data described in the page description language, the charged image carrier is exposed and scanned to form an electrostatic latent image on the image carrier, and the formed electrostatic latent image is developed with toner. A process unit for forming the toner image,
The determination means includes
The image forming apparatus according to claim 10, wherein the page description language is analyzed, and whether or not the image image area is included is determined based on the analysis. Based on the image data, the charged image carrier is exposed and scanned to form an electrostatic latent image on the image carrier, and the formed electrostatic latent image is developed with toner. A process unit for forming an image;
The determination means includes
11. The image forming apparatus according to claim 10, wherein whether or not the image image area is included is determined based on the number of dots of each of a plurality of scanning lines when the image carrier is exposed and scanned. .

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