JP2012018268A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in productivity in feeding a recording material of a size having a predetermined width or less for the subsequent job after image formation by controlling the start/stop timing of cooling means in an image forming device.SOLUTION: An image forming device comprises a cooling device 60 for cooling a non-feeding region in which a recording material of a size having a predetermined width or less is not passed among the whole feeding region of a fixing device for feeding a recording material and a control part 39 for controlling the operation of the cooling device 60. The control part 39 starts the operation of the cooling device 60 until the first recording material enters the fixing device after generation of a printing job for the recording material of the size having the predetermined width or less and continues the operation of the cooling device 60 while performing the printing job for the recording material of the size having the predetermined width or less.

Description

  The present invention relates to an electrophotographic type or electrostatic recording type image forming apparatus such as a printer, a copying machine, and a facsimile machine, which is equipped with a fixing device for heating and fixing an image.

  Conventionally, in an electrophotographic image forming apparatus, a method of forming a toner image on a recording material such as paper by a method called a Carlson process and fixing the toner image as a fixed image is generally used. Various fixing methods have been proposed for this purpose. From the viewpoint of fixing properties, a method of fixing a toner image by heating (thermal fixing method) is generally used. In particular, a method of fixing by directly contacting a toner image with a rotating body containing a heating source is widely used.

  In this thermal fixing method, it is important to make the temperature distribution on the heating rotary member such as a roller or a film uniform with respect to the axial direction, including the region through which the recording material (hereinafter referred to as paper) passes. . This is because if there is a part where the temperature is lower than the predetermined temperature, fixing failure may occur, while if it is too high, the heating rotating member and the proximity member may be thermally damaged. is there.

  In recent years, for example, a variety of paper sizes from a relatively large size paper (large size paper) such as A3 size to a small size paper (small size paper) commonly used such as A4R and B5 sizes are supported. There is a need for an image forming apparatus. For this reason, it is necessary to configure the axial lengths of the heating rotary member and the pressure rotary member so as to correspond to a relatively large size such as an A3 size. However, when such a configuration is adopted, when a small-sized sheet having a small width such as A4R or B5 passes through the fixing device, there is a non-sheet passing area in which the sheet does not pass in the effective fixing area of the heating rotating member. Become more. When such small-size paper is continuously copied, the surface temperature of the non-sheet passing area becomes very high because heat is not taken away by the sheet from the surface of the heating rotating member corresponding to the non-sheet passing area.

  In order to solve the above non-sheet passing portion overheating, the following proposal has been made.

  Conventional Example 1: Responding by stopping the supply of heat to the heating rotating member between the papers and idling so that the surface temperature of the heating rotating member in the non-sheet passing area is the same as the surface temperature of the sheet passing area To do.

  Conventional Example 2: Heating means such as a heater built in the heating rotary member so that the amount of heat supplied to the non-sheet passing area is smaller than the amount of heat supplied to the sheet passing area for fixing small size paper. Change the light distribution ratio (heat generation distribution).

  However, the above-described conventional example has the following problems.

  In the above-mentioned conventional example 1, it is necessary to widen the gap between the sheets because the idle rotation for cooling the heating rotating member is necessary between the sheets that are the sheet passing interval when continuously passing the small size paper. The problem that productivity at the time of passing small size paper worsens arises. In recent years, the user's demand for productivity has gradually increased, and reducing the productivity during continuous paper feeding may not satisfy the product specifications required by the user.

  In the case of adopting the configuration as in Conventional Example 2, it is necessary to arrange a heater having a plurality of light distributions in order to cope with a plurality of paper sizes, which may increase the cost.

  In order to prevent an increase in the surface temperature of the non-sheet passing area when a small size sheet is passed, a configuration in which the non-sheet passing area is cooled by cooling air has been proposed as in Patent Documents 1 and 2.

  In the technique described in Patent Document 1, the periphery of the pressure roll in the fixing device is divided into a sheet passing area side and a non-sheet passing area side by a partition plate, and the non-sheet passing is performed from a cooling fan disposed inside the fixing apparatus. Cooling air is blown to the pressure roll on the region side.

  In the technique described in Patent Document 2, a cooling fan is disposed above the top plate that covers the fixing roll, and the air is normally blown above the top plate to prevent the temperature around the fixing device from rising. When the paper passing through the fixing area is a small size paper, a window as a guide device provided on the top plate is opened, and cooling air is supplied to the non-sheet passing area of the surface portion of the rotating fixing roll.

  The technique described in Patent Document 3 differs by adjusting the length in the width direction of the blower opening according to the width of the paper to be used when the cooling air is blown from the cooling fan to the non-sheet passing region. This prevents overheating of the non-sheet passing portion even for paper of different sizes.

  The proposals in Patent Documents 1 to 3 have the following problems. That is, in the conventional example in which the cooling air is blown to the heating rotating member, since the cooling fan is provided inside the fixing device, it is necessary to use a cooling fan with high heat resistance, which may increase the cost. In addition, a cooling fan with a relatively large air flow is required, and the fixing device itself becomes large. Furthermore, even if a partition plate is provided, cooling air flows from the non-sheet passing area side to the sheet passing area, the temperature decreases near the boundary between the non-sheet passing area and the fixing temperature at the partition boundary area. Problem of fixing failure.

Japanese Patent Application Laid-Open No. 60-136779 JP-A-5-181382 JP 2003-076209 A JP 2007-187816 A

  As means for solving the above problems, a fixing device having the following configuration has been proposed (see Patent Document 4). The fixing device includes a non-sheet-passing area cooling duct in which a blower port is formed facing the non-sheet-passing area surface of the heating rotating member to cool the surface of the heating-rotating member. A cooling device having a blower fan for blowing cooling air. The cooling fan that blows the cooling air has a control unit that is started / stopped (ON / OFF) at a predetermined timing using the temperature detection result of the non-sheet passing region. Therefore, it is possible to provide a fixing device that can efficiently prevent an excessive increase in the temperature of the cooling fan section and is excellent in safety without using a cooling fan having high heat resistance, at low cost / space-saving.

  However, in any of the conventional techniques, even if an end cooling fan is provided and cooling is performed, the temperature of the end rises in the middle of continuous passing of small-size paper. There was a case.

For example, the control timing of the cooling fan as the prior art performed by the applicant of the present invention before the present invention is as follows.
ON timing: The temperature of the temperature detection element (TH = thermistor) is detected after the passage of small-size paper to the fixing device, and the temperature difference between MTH (center) and STH (edge), that is, the non-sheet passing portion and the non-passing portion The cooling means is started when the temperature difference of the paper passing portion exceeds a predetermined temperature (for example, 10 ° C.).
OFF timing: After the end of the print job, the cooling means is stopped when the temperature difference between the sheet passing portion and the non-sheet passing portion is equal to or lower than a predetermined temperature (10 ° C.)

  However, in such a control method, the current situation is that the temperature rise suppression at the end is not always satisfactory and the productivity may be affected.

  In this background, in the image forming apparatus as described above, by controlling the start / stop timing of the cooling unit, it is possible to pass a recording material having a size equal to or smaller than a predetermined width of the next job after image formation. The purpose is to prevent a decrease in productivity.

  An image forming apparatus according to the present invention includes a fixing device that heat-fixes an unfixed image formed on a recording material, and extends a paper feed conveyance time interval when the temperature of the fixing device becomes an excessively high temperature state. In the image forming apparatus that performs the interval control, a cooling unit that cools a non-sheet passing region where a recording material having a size equal to or less than a predetermined width does not pass among all the sheet passing regions of the fixing device that passes the recording material; Control means for controlling the operation, and the control means activates the cooling means after the occurrence of a print job for a recording material having a size less than the predetermined width and before the first recording material enters the fixing device. And the operation of the cooling means is continued during execution of a print job for a recording material having a size smaller than the predetermined width.

  In this way, after detecting that the recording material size to be image-formed is smaller than the predetermined width, the cooling unit is started before the image formation is started earlier than before, By continuing the operation of the cooling means during the image forming operation of the size of the predetermined width or less, it is possible to delay the time to reach the overheated state in the paper gap control. As a result, it is possible to reduce the degree of temperature rise in the non-sheet passing area even when recording materials having a size equal to or smaller than the predetermined width are continuous.

  In one aspect of the image forming apparatus, the control unit applies a recording material having a recording material size exceeding the predetermined width as a next printing job after a printing job for the recording material having a size equal to or smaller than the predetermined width is completed. When the print job is generated, the operation of the cooling means is stopped. In another aspect, the control means determines that the temperature difference between the center and the edge in the width direction of the entire sheet passing area of the fixing device is a predetermined temperature after the end of the print job for the recording material having a size smaller than the predetermined width. When the temperature becomes below or when the temperature of the end portion matches the environmental temperature, the operation of the cooling means is stopped.

  According to the present invention, by controlling the start / stop timing of the cooling unit, the excessive temperature rise of the non-sheet passing portion in the fixing device is suppressed when a recording material having a size of a predetermined width or less is passed. As a result, it is possible to improve productivity in passing a recording material having a size equal to or smaller than a predetermined width of the next job after image formation.

1 is a schematic configuration diagram of a main part of an image forming apparatus including a fixing device according to the present invention. FIG. 2 is an enlarged schematic diagram of a fixing device of the image forming apparatus shown in FIG. 1. It is an expansion schematic diagram of the heating body shown in FIG. FIG. 3 is a schematic diagram of a layer configuration of the fixing film shown in FIG. 2. FIG. 3 is a schematic diagram of a layer configuration of a pressure roller shown in FIG. 2. FIG. 4 is a diagram illustrating an example in which a cooling fan is used as a cooling device in the fixing device according to the embodiment of the present invention. It is explanatory drawing of the prior art which cools based on the temperature difference of a paper passing part and a non-paper passing part. It is explanatory drawing of operation | movement of embodiment of this invention. It is a flowchart of the cooling fan control process in this Embodiment which comprehensively includes the operation examples 1 and 2 in embodiment of this invention. It is the block diagram which showed the outline hardware constitutions in embodiment of this invention.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 1 shows a schematic configuration of a main part of an image forming apparatus provided with a fixing device according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process. However, the exposure method is not limited to the one using a laser beam. The image forming apparatus of the present invention is not limited to a printer. For example, it can be applied to a copying machine and a facsimile. In any image forming apparatus, the image forming operation is also referred to as “printing”. The fixing device is a device that heat-fixes an unfixed image formed on a recording material.

  In FIG. 1, an electrophotographic photosensitive drum 31 functions as an image carrier for forming an electrostatic latent image on its peripheral surface. Hereinafter, the electrophotographic photosensitive drum is simply abbreviated as a drum. The drum 31 is rotationally driven at a predetermined process speed (image forming speed) in the clockwise direction indicated by the arrow. The process speed is not particularly limited but is, for example, 230 mm / sec.

  In the rotation process, the drum 31 undergoes a primary charging process uniformly with a predetermined polarity and potential from a charging bias application power source S1 for the charging roller 32 via a charging roller 32 as a charging means.

  Next, the drum 31 receives scanning exposure L by laser light whose intensity is modulated in accordance with the time-series electric digital pixel signal of the target image information output from the laser scanner 33 on the primary charging surface. As a result, the drum potential of the bright exposure portion is attenuated, and an electrostatic latent image corresponding to the target image information is formed on the drum peripheral surface.

  Further, the electrostatic latent image is reversely developed as a toner image by a negative developer (negatively charged toner) by a developing device 34 as a developing unit (toner is attached to an exposed bright portion of the drum surface). This development is performed from the development bias application power source S2 via the development roller (or development sleeve) 34a.

  Next, the toner image is fed at a predetermined timing from a sheet feeding unit (not shown) in a transfer unit 35a which is a pressure nip between the drum 31 and a transfer roller 35 as a transfer unit. The toner images are sequentially transferred onto the surface of the recording material or transfer material P). This transfer is performed via a transfer roller 35 from a transfer bias application power source S3. In this example, the transfer roller 35 to which a transfer bias is applied charges the back surface of the paper P to a positive polarity that is opposite to the toner charging polarity (minus). As a result, the negative polarity toner image on the drum 31 surface side is transferred to the paper P surface side by electrostatic force.

  The paper that has passed through the transfer portion 35a is neutralized by a static elimination needle 36 (or a separation charger) and separated from the surface of the drum 31. Further, the toner image is conveyed and introduced into the fixing device 37, and is subjected to a heat fixing process of the toner image and is output as a printed matter. The fixing device 37 cools a non-sheet-passing region (a sheet-passing region end) where a sheet having a size equal to or smaller than a predetermined width does not pass among all the sheet-passing regions through which the maximum size sheet that can be printed by the image forming apparatus passes. A cooling device 60 is incorporated as a cooling means. In the double-sided print mode or the multiple print mode, the sheet is fed again to the transfer section 35a after fixing (not shown).

  The surface of the drum 31 after the paper separation is subjected to removal of residual deposits such as transfer residual toner by the cleaning device 38 and is repeatedly used for image formation.

  The control unit 39 includes a CPU and a memory, and controls each unit of the image forming apparatus. In this example, a detection signal such as a temperature is received from the fixing device 37 and a control signal such as a heater or a cooling fan described later is output to the fixing device 37.

(2) Fixing device 37
FIG. 2 is an enlarged schematic view of the fixing device 37.

a) Overall Configuration and Operation of Fixing Device The fixing device 37 of this example is a so-called tensionless type film heating type device. In other words, a cylindrical (endless) film is used as the fixing film 2, and at least a part of the circumference of the film is tension-free (a state in which no tension is applied), and the film 2 is pressed as a pressure rotating body. The roller 9 (pressure roller, backup roller) is rotationally driven by the rotational driving force.

  The heat-resistant and heat-insulating stay 3 having a substantially semicircular arc shape in cross section functions as a heating body supporting member and a film inner surface guide member. In this example, it is a plastic stay made of heat-resistant molding material. The heating element (heater) 1 is fitted into a groove formed along the length of the stay at a substantially central portion of the lower surface of the stay 3 and fixedly supported by a heat-resistant adhesive. The stay 3 is backed up by a sheet metal stay 3a made of Fe or Al in order to suppress the pressure of the pressure roller 9 and the bending due to the heating element 1.

  The cylindrical fixing film 2 is loosely fitted on an assembly including the stay 3, the heating body 1, and the sheet metal stay 3a.

  The pressure roller 9 is rotatably held at both end shaft portions of the core metal 9a. An assembly composed of the stay 3, the heating body 1, and the sheet metal stay 3a with the fixing film 2 fitted outside is disposed on the upper side of the pressure roller 9 with the heating body 1 facing downward, and an urging means (not shown) is applied to the metal stay 3a. A pressing force with a total pressure of 4 to 20 kg is applied. Thus, the heating body 1 is pressed against the elasticity of the pressure roller 9 while the fixing film 2 is sandwiched between the heating body 1 and the pressure roller 9. A fixing nip portion N is formed between the heating body 1 and the pressure roller 9 sandwiching the fixing film 2.

  The cleaning roller 10 removes residual toner that could not be fixed from the pressure roller 9 and prevents the pressure roller 9 from being soiled by the stain. By forming the cleaning roller with a material with high thermal conductivity (Al etc.), not only the pressure roller 9 is cleaned, but also the effect of suppressing the excessive temperature rise in the non-sheet passing portion and making the temperature distribution uniform is expected. it can.

  The pressure roller 9 is driven to rotate by a driving means (not shown) through a power transmission system (not shown) and rotated counterclockwise as indicated by an arrow. When the pressure roller 9 is rotationally driven, a rotational force acts on the fixing film 2 due to a frictional force between the pressure roller 9 and the outer surface of the fixing film 2 in the fixing nip portion N, and the fixing film 2 is brought into close contact with the heating body 1. However, the outer periphery of the stay 3 is driven to rotate in the clockwise direction a indicated by the arrow. In order to reduce the sliding resistance between the heating element 1 and the fixing film 2 in the fixing nip portion N, it is preferable that a lubricant such as heat-resistant grease is present between the two.

  When a print job (JOB) occurs, or based on a recording material detection signal from a recording material detection means (not shown) disposed in the paper conveyance path upstream of the fixing device 37 in the paper conveyance direction. The rotational driving of the pressure roller 9 is started, and the heating of the heating body 1 is started. In this specification, when a print job is generated, in a printer, when a print start signal is generated from a host computer (for example, a PC), in a copying machine, when a copy start button is pressed or a paper cassette is selected. Further, it is when an image signal is received in a facsimile.

  When the rotation peripheral speed of the fixing film 2 is stabilized by the rotation of the pressure roller 9 and the temperature of the heating body 1 rises to a predetermined temperature, the fixing film 2 is fixed between the fixing film 2 and the pressure roller 9 in the fixing nip N. The paper P carrying the toner image T as the material to be heated is introduced with the toner image carrying surface side of the fixing film 2 side, so that the paper P is heated at the fixing nip portion N via the fixing film 2. It moves in close contact with the fixing nip portion N together with the fixing film 2. In the moving and passing process, the heat of the heating body 1 is applied to the paper P through the fixing film 2 and the toner image T is heated and fixed on the surface of the paper P. The paper P that has passed through the fixing nip N is separated from the surface of the fixing film 2 and conveyed.

  The tension-less type film heating type apparatus of this example includes a fixing nip portion N, an outer surface portion of the stay 3 on the upstream side of the fixing nip portion in the rotation direction of the fixing film 2 and the fixing film 2 when the fixing film is rotationally driven. The tension acts only on the fixing film 2 portion in the contact sliding portion region, and the tension does not act on the remaining most film 2 portion. Therefore, there are features such as a small driving torque of the fixing film 2 and a small moving force along the longitudinal direction of the stay 3 of the fixing film 2.

b) Heating body 1
The heating element 1 is a horizontally long linear heating element having a low heat capacity and having a direction perpendicular to the conveyance direction of the paper P as a longitudinal direction. In this example, it is a ceramic heater. As shown in the enlarged schematic diagram of the heating body 1 in FIG. 3, the heater substrate 1 a has a good thermal conductivity, insulating property, and high heat resistance with a thickness of 1.0 mm, whose longitudinal direction is the direction orthogonal to the conveyance direction of the paper P. And a low heat capacity substrate, for example, a ceramic substrate such as alumina. The energization heating element layer 1b is a layer that is patterned in a thin strip shape by screen printing or the like along the length of the substrate at the substantially central portion in the substrate width direction on one surface (front surface) of the heater substrate 1a. Is a layer. The withstand voltage glass layer 1c is an insulating protective layer formed so as to cover the energization heating element layer 1b. The conductive layer 1e is an electrode layer formed on the surface of the withstand voltage glass layer 1c. The temperature detection element 1d is an element for detecting the temperature of the heating body 1, for example, a thermistor, provided in contact with the other surface (back surface) side of the heater substrate 1a. When detecting the temperature difference between the center and the end of the heating element 1 (temperature difference between the sheet passing area and the non-sheet passing area), the temperature detecting element 1d is installed in at least two places, the center and the end. The conductive layer 1f is an electrode layer of the temperature detecting element 1d formed on the surface of the withstand voltage glass layer 1c.

  The heating element 1 is exposed to the outer surface on the energization heating element layer forming surface side, and is fitted into a groove formed along the length of the stay at a substantially central portion of the lower surface of the stay 3 to be heat resistant. Fixed and supported with adhesive.

  The conductive layer 1e formed on the surface of the withstand voltage glass layer 1c is in close contact with the inner surface of the fixing film 2 at the fixing nip portion N. The conductive layer 1e is grounded via a rectifier (diode) and a resistor (not shown).

  The energization heating element layer 1b is supplied with electric power by an A / C driver (not shown) between both longitudinal ends. Thereby, the energization heating element layer 1b generates heat, and the entire heating element 1 is quickly heated. The temperature rise of the heating body 1 is detected by the temperature detection element 1d on the back side of the heating body. The detected heating body temperature is sent as an electrical signal to an A / D converter (not shown), and is input to the control unit 39 (FIG. 1) via this converter. The control unit 39 controls the A / C driver based on this input signal, and the energization power to the energization heating element layer 1b is controlled so that the heating body temperature is adjusted to a predetermined appropriate temperature.

c) Fixing film 2
In the case of this example, the fixing film 2 has a three-layer structure of a base film layer (base layer) 2a, a primer layer (adhesive layer) 2b, and a coat layer (release layer) 2c, as shown in the schematic diagram of the layer structure of FIG. It is a film.

  The base film layer 2a is based on a heat-resistant and insulating material such as polyimide, polyetherketone, polyethersulfone, polyetherimide, polyparabanic acid, etc., and has a high thermal conductivity such as metal boride powder. Are mixed and dispersed into a cylindrical film having a thickness of about 20 to 80 μm.

  A primer layer 2b is laminated and coated on the outer peripheral surface of the base film layer 2a to a thickness of about 5 μm, and then a release layer 2c made of a fluororesin such as PFA or PTFE or a silicone resin is formed with a thickness of about 5 to 20 μm. It is.

  If the adhesion between the base film layer 2a and the release layer 2c is good, there is no problem even if the two-layer film without the primer layer 2b is used. Also, the fixing film 2 can be used even if it is composed of two or more layers by interposing a layer having other functions between them. However, in order to maintain the fixability, it is desirable to have a layer structure in which the overall thickness is made as thin as possible and the thermal conductivity is improved.

d) Pressure roller 9
The pressure roller 9 of this example is provided with an elastic rubber layer 9b made of silicone rubber, fluorine rubber or the like around a metal core 9a of Fe, Al or the like, as shown in the schematic diagram of the layer structure of FIG. Further, an insulating release layer 9c is provided on the outer periphery. The elastic rubber layer 9b of the pressure roller 9 of this example is made to have a low resistance (for example, 10 ⁸ Ωcm or less) by dispersing a conductive filler such as carbon black or graphite in a rubber material.

  The insulating release layer 9c is formed by coating an insulating fluororesin such as PFA, PTFE, FEP, ETFE or the like in a thickness of about 20 to 100 μm or a tube shape.

  With the above configuration, when 100 sheets with a width of 148.5 mm (A5R) were flowed at a rate of 30 sheets per minute, the temperature of the non-sheet passing portion of the heating element 1 exceeded 240 ° C., and the pressure was increased. The temperature of the non-sheet passing portion of the roller was raised to 200 ° C. or higher.

  FIG. 6 shows an example in which a cooling fan 61 is used as the cooling device 60 in the fixing device 37 according to the present embodiment. The cooling fans 61 are separately disposed at both ends of the film 2 and cool by blowing air to both ends of the film 2. Both cooling fans 61 are controlled to start / stop (that is, ON / OFF) by the control unit 39. In the present embodiment, the control unit 39 starts the cooling fan 61 after the occurrence of a print job for a sheet having a size of a predetermined width or less until the first sheet enters the fixing device. That is, when a small size print instruction is issued, for example, when a print job such as that described above occurs, the size of the paper on which the image is to be formed is smaller than a predetermined width (hereinafter simply referred to as “small size”). The cooling device 60 starts to be started immediately (that is, the cooling fan 61 is turned on) immediately after the detection of the first sheet or until the first sheet enters the fixing device 37 at the latest. The operation of the cooling fan 61 is continued during execution of a print job for a sheet having a size equal to or smaller than a predetermined width.

  In the present specification, the “size of a predetermined width or less” refers to a size that is smaller than the maximum width size of paper that can be used by the image forming apparatus. The present invention is particularly suitable for application to a size having a width that is 25% or more smaller than the maximum width. Such a size corresponds to the width S shown in FIG. 6. For example, when the size of the maximum width is A3 vertical, the size is A4 vertical and smaller.

  In the case of a printer, when a small-size paper print instruction is issued from the host computer, it can be determined that “small size is detected”. In the case of a copying machine, when a small size paper is selected as a paper size to be copied, it can be determined that “small size is detected”. In the case of a facsimile, it can be determined that “small size has been detected” when a print job of small size paper is received. On the other hand, when the large size paper is selected, the cooling fan 61 is not turned ON.

  FIG. 10 shows a schematic hardware configuration of the image forming apparatus of the present embodiment.

  The image forming apparatus includes an operation panel 21, a scanner unit 22, a communication unit 23, a paper feeding unit 25, a paper size detecting unit 26, a paper conveying unit 27, and an image recording unit 28 in addition to the fixing device 37 and the control unit 39 described above. Have.

  The operation panel 21 includes a liquid crystal display unit for a user interface, a key input unit, and the like. The scanner unit 22 is an image scanner for a copying function. The communication unit 23 is a part that performs communication for a printer interface and a facsimile function. The paper supply unit 25 is a part that picks up and supplies paper from a paper cassette. The paper size detection unit 26 is a unit that detects the paper size of an image formation target based on the selection of a paper cassette or an instruction from the host computer. In addition to the case where a hardware sensor or the like is provided, the paper size detection unit 26 is also provided. In some cases, the control unit 39 may be responsible for some or all of the functions. The paper transport unit 27 is a part that transports the paper supplied from the paper supply unit 25 to the image recording unit 28. The image recording unit 28 is a part that records a toner image on the conveyed paper. The fixing device 37 is means for thermally fixing the toner image as described above, and includes the heating body 1, the temperature detection element 1 d, and the cooling device 60.

  For comparison with the present embodiment, in FIG. 7 and FIG. 8, the prior art that performs cooling based on the temperature difference between the paper passing portion and the non-paper passing portion of the heating body 1 and the operation of the present embodiment are described. The comparison will be described. 7 and 8, the thin line graph shows the conventional operation, and the thick line graph shows the operation of the present embodiment.

<Operation example 1 Control during small-size sheet feeding after large-size sheet feeding>
As this operation example 1, an operation example at the time of passing a small size after passing a large size paper is considered. In the present embodiment, the size is the width of a sheet on which printing is performed, and a size equal to or smaller than a predetermined width (predetermined width) is a small size.

Prior art controls are as follows.
(1) Fan_ON timing: The cooling fan is activated at a time t1 when the temperature difference between the sheet passing portion and the non-sheet passing portion exceeds a predetermined temperature (for example, 10 ° C.) after the start of passing small-size paper to the fixing device.
(2) Fan_OFF timing: After passing the number of print jobs, the cooling fan is stopped when the temperature difference between the temperature detection elements at the center and at the end of the heating element 1 becomes a predetermined temperature (for example, 10 ° C.) or less.

On the other hand, the control method in the present embodiment is as follows.
(1) The cooling fan (FAN) is stopped when passing large-size paper. When a small-size print job occurs after printing by passing large-size paper, immediately or after that, at the latest, until the first paper enters the fixing device 37 (typically small-size paper) At the same time as the print job occurs, control is performed to activate the cooling fan. Even when “immediate” activation is employed, if the large-size image forming operation is being performed at that time, the end of the large-size image forming operation is awaited.
(2) When continuously passing small-size paper, the cooling fan is rotated regardless of the number of papers to be passed.

  In the examples of FIGS. 7 and 8, “printing (during image forming operation)” means that a print job is being executed, and feeding of the first sheet after the occurrence of the print job is started. Until the paper is discharged. Further, a case where the next print job occurs immediately after or before the end of the previous print job is shown.

  As an effect, in the prior art, the temperature at which paper interval control (so-called throughput down: TPD) is performed to widen the paper feed conveyance time interval in order to prevent excessive edge temperature rise at a certain timing by continuous small size paper passing. The time until reaching the TPD temperature can be extended compared to the prior art (time L1 in FIG. 7), while the TPD transition temperature (240 ° C. in this embodiment) is reached. As a result, the effect of improving the productivity of small size printing can be expected from the prior art. Throughput reduction usually refers to control that extends the paper feed and conveyance time interval of continuous paper when the fixing temperature is overheated (higher than the expected temperature). However, there is a demerit that the number of printed sheets per hour is reduced because the interval between the sheets fed and conveyed is widened.

<Operation example 2 Control during small-size sheet feeding after small-size sheet feeding>
As operation example 2, the cooling fan control at the time of small-size paper passing after small-size paper feeding was performed by a method different from the prior art.

  In the prior art, as described above, even if the cooling fan is turned on in the previous job, it is turned off when the temperature difference between the paper passing portion and the non-paper passing portion is equal to or lower than a predetermined temperature (for example, 10 ° C.). Turns on at time t2 when the temperature difference between the sheet passing portion and the non-sheet passing portion exceeds a predetermined temperature (for example, 10 ° C.) after the start.

The control of the present embodiment is as follows.
(1) FAN_ON timing: When a print job of a small size occurs, the cooling fan is activated immediately before the start of image formation or immediately before the first sheet enters the fixing device 37 at the latest. As described above, even when “immediate” activation is adopted, if a large-size image forming operation is being performed at that time, the end of the large-size image forming operation is awaited. The cooling fan is rotated while small-size paper is being fed. When continuously passing a plurality of small size sheets, the cooling fan is rotated regardless of the number of sheets.
(2) FAN_OFF timing: When it is detected that the paper size of the next print job is not small after the end of a small print job (for example, when a large print job occurs), or The cooling fan is stopped at the earlier time when the predetermined condition is satisfied after the completion. “Predetermined conditions are satisfied” as used herein refers to, for example, a case where the temperature difference between the temperature detection elements at the center and the end of the heating element 1 is equal to or lower than a predetermined temperature (for example, 10 ° C.), This is a case where the environmental temperature detected by the detecting means (sensor) to detect and the temperature of the end portion substantially coincide. Even if the cooling fan is stopped after the small size print job is finished, if the small size print job is generated again, the cooling fan is operated again regardless of the temperature difference between the sheet passing portion and the non-sheet passing portion.

  As described above, in the operation example 2, basically, the operation of the cooling fan is continued during the period from the end of the printing of the small size paper to the start of the printing of the next small size paper. Also in the operation example 2, the time until the temperature reaches the TPD temperature can be extended (time L2 in FIG. 8), and the effect of improving the productivity of small size printing can be expected. Further, when a large size print job occurs after the small size print job is completed, the cooling fan is immediately stopped, so that the large size printing can be immediately performed without any problem.

  FIG. 9 shows a flowchart of the cooling fan control process in the present embodiment that comprehensively includes such operation examples 1 and 2. This process is realized by the CPU of the control unit 39 described above reading and executing the control program from the memory.

  This process is started when the main body of the image forming apparatus is turned on.

  First, after a predetermined initial operation is performed, generation of a print job is awaited (S11). When a print job is generated, it is determined whether or not the paper width size is a small size (S12).

  If the size is not small, the cooling fan is turned off (S13), and the printing operation is started (S14). In step S13, if the cooling fan is already in the OFF state, the state is maintained. After printing is completed (S15), the next job is waited (S16).

  If the paper width is small in step S12, the cooling fan is turned on immediately or before the first paper enters the fixing device 37 (S20), and printing is started (S21). In step S20, if the cooling fan is already in the ON state, that state is maintained. When printing is completed (S22), the next job is waited (S16).

  When the next job is generated, the paper size is confirmed again (S19), and the process proceeds to step S13 or S20 depending on whether the size is small. However, when the next job is detected as a small size, if the large size is being printed at that time (S23), the process proceeds to step S20 after the large size printing is completed. That is, it waits until the last sheet in at least large size printing is discharged from the fixing device 37.

  When there is no next job in step S16, when the above-mentioned “predetermined condition” is satisfied, for example, when the temperature difference between the sheet passing portion and the non-sheet passing portion is equal to or lower than a predetermined temperature (S17a, Yes) or an end portion. When the temperature of the cooling fan substantially matches the environmental temperature (S17b, Yes), the cooling fan is turned off (S18). In this step S18, if the cooling fan is already in the OFF state, that state is maintained.

  As described above, in the cooling fan control processing according to the present embodiment, the cooling fan operation is continued during the small-size image forming operation, and the paper size of the next print job is not small after the print job is completed. When detected, the cooling fan is stopped. Although not essential in the present invention, the cooling fan is stopped when the predetermined condition is satisfied even before it is detected that the paper size of the next print job is not small. In other words, after the end of the print job, the cooling fan continues to operate until it is detected that the paper size of the next print job is not small or until the predetermined condition is satisfied after the end of the print job. To do.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, a cooling fan as a cooling unit is disposed at both ends of the heater in correspondence with an example in which non-sheet passing portions are generated at both ends of the heater when fixing small size paper, but a non-sheet passing portion is generated at one end of the heater. In the example, it may be arranged only on one end side. Moreover, although the cooling fan was mentioned as an example of a cooling means, it is not restricted to a cooling fan, It is possible to employ | adopt the arbitrary cooling means which can be utilized.

DESCRIPTION OF SYMBOLS 1 ... Heating body 2 ... Fixing film 3 ... Stay 9 ... Pressure roller 10 ... Cleaning roller 31 ... Electrophotographic photosensitive drum 32 ... Charging roller 33 ... Laser scanner 34 ... Developing device 35 ... Transfer roller 35a ... Transfer part 36 ... Static elimination Needle 37 ... Fixing device 38 ... Cleaning device 39 ... Control unit 60 ... Cooling device 61 ... Cooling fan

Claims (5)

An image forming apparatus that includes a fixing device that heat-fixes an unfixed image formed on a recording material, and that performs paper interval control to increase a paper feeding conveyance time interval when the temperature of the fixing device becomes an excessively high temperature state. ,
A cooling means for cooling a non-sheet passing area through which a recording material having a size of a predetermined width or less does not pass among all the sheet passing areas of the fixing device for passing the recording material;
Control means for controlling the operation of the cooling means,
The control means starts the cooling means after the occurrence of a print job for a recording material having a size smaller than the predetermined width and before the first recording material enters the fixing device, The image forming apparatus characterized in that the operation of the cooling unit is continued during execution of a print job for a recording material of a size.   When the print job for the recording material having a size exceeding the predetermined width is generated as the next print job after the print job for the recording material having a size equal to or smaller than the predetermined width is completed, the control unit The image forming apparatus according to claim 1, wherein the operation is stopped.   When the temperature difference between the center and the edge in the width direction of the entire sheet passing area of the fixing device is equal to or lower than a predetermined temperature after the end of the print job for the recording material having a size equal to or smaller than the predetermined width, or 3. The image forming apparatus according to claim 1, wherein the operation of the cooling unit is stopped when the temperature of the end matches the environmental temperature.   The image forming apparatus according to claim 1, wherein the size equal to or smaller than the predetermined width is a size having a width smaller than that of a maximum width of a sheet that can be used by the image forming apparatus.   The control means activates the cooling means after the end of the image forming operation when an image forming operation having a size exceeding the predetermined width is in progress when a print job for a recording material having a size smaller than the predetermined width is generated. The image forming apparatus according to claim 1, wherein the image forming apparatus is started.

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