JP5962959B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

  In an image forming apparatus such as a copying machine or a printer, for example, a fixing device that fixes a toner image on a sheet includes a pair of rolls including a fixing roll (fixing rotator) and a pressure roll (pressure rotator). There are known systems such as a belt system composed of an endless heating belt (heating rotator) and a pressure roll (pressure rotator) that are rotationally driven by a fixing roll (fixing rotator).

  Further, the fixing roll is provided with a heater as a heating element and a motor (driving means) for driving the fixing roll.

  In such a fixing device, a sheet or the like on which an unfixed toner image is transferred is sent to a fixing nip formed between opposing pairs of rolls, and the toner image is applied to a sheet or the like by applying heat and pressure. Established.

  At this time, the motor is provided with a fan for cooling itself by air blowing on the rotating shaft in order to suppress temperature rise due to self-heating such as a motor coil and a substrate and heat transfer from the heater, Has a separate fan.

  On the other hand, when the temperature of the motor is excessively lowered by these fans, a situation occurs in which the fixing temperature of the fixing nip portion falls below the minimum fixing temperature due to the air blown by the fans.

  As for temperature control in the fixing device, for example, there is a technique disclosed in Patent Document 1.

Japanese Patent No. 4444223

  An object of the present invention is to provide a technique capable of suppressing a temperature decrease of a fixing rotator while suppressing a temperature increase of a driving unit that drives a fixing rotator of a fixing device.

In order to solve the above problem, the fixing device of the present invention according to claim 1 includes a pressure rotator and a fixing rotator, and feeds the recording medium while sandwiching the recording medium between the pressure rotator and the fixing rotator. A fixing unit that fixes the developer image transferred to the recording medium to the recording medium, a first cooling unit that cools the developer image by blowing air, a driving unit that drives the fixing rotator, and the blowing unit A second cooling unit that cools the driving unit; and the second cooling unit is driven based on at least one of the fixing speed of the fixing unit and the basis weight of the recording medium, and the temperature of the driving unit is And control means for controlling the temperature so as to be suppressed below the allowable temperature of the means.

  According to a second aspect of the present invention, in the first aspect of the present invention, information relating to the fixing speed of the fixing unit and the basis weight of the recording medium and the air volume of the second cooling unit are stored. Storage means, and the control means refers to the information stored in the storage means and refers to the information regarding at least one of the actual fixing speed of the fixing means and the basis weight of the recording medium. The air volume of 2 cooling means is controlled, It is characterized by the above-mentioned.

  According to a third aspect of the present invention, in the first aspect of the present invention, there is provided an air volume determination formula relating to at least one of the fixing speed of the fixing unit and the basis weight of the recording medium and the air volume of the second cooling unit. A storage unit stored therein, and the control unit applies information regarding at least one of an actual fixing speed of the fixing unit and a basis weight of the recording medium to an air volume determination formula stored in the storage unit. The air volume of the second cooling means is controlled.

  In order to solve the above-described problem, an image forming apparatus according to a fourth aspect of the present invention includes an image holding body on which a developer image is held, and the developer image held on the image holding body is transferred to a recording medium. And a fixing device according to any one of claims 1 to 3 for fixing the unfixed developer image transferred to the recording medium to the recording medium. .

  According to the first aspect of the present invention, it is possible to suppress the temperature decrease of the fixing rotator while suppressing the temperature increase of the driving means for driving the fixing rotator of the fixing device as compared with the case where the present invention is not adopted. It becomes possible.

  According to the second aspect of the present invention, as compared with the case where the present invention is not adopted, the temperature rise of the driving means for driving the fixing rotator of the fixing device is finely suppressed in steps, and the temperature of the fixing rotator is lowered. Is minimized.

  According to the third aspect of the present invention, as compared with the case where the present invention is not adopted, the temperature rise of the driving means for driving the fixing rotator of the fixing device is continuously finely suppressed, and the temperature of the fixing rotator is decreased. Is minimized.

  According to the fourth aspect of the present invention, as compared with the case where the present invention is not adopted, the fixing temperature is stabilized, and deterioration of the fixing property of the image on the recording medium and uneven gloss of the image are suppressed.

1 is a conceptual diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a conceptual diagram illustrating an example of a fixing device of the image forming apparatus in FIG. 1. FIG. 3 is a perspective view illustrating an example of a fixing device in FIG. 2. FIG. 2 is a circuit block diagram of a main part of the image forming apparatus in FIG. 1. It is a graph shown about the relationship between the drive speed of a motor, and the temperature of a motor. 6 is a graph showing the relationship between the axial position of the fixing roll and the temperature of the fixing roll. It is a figure which shows an example of the control pattern of the external fan stored in memory. 6 is a graph showing the relationship between the motor driving speed and the motor temperature in the image forming apparatus of the present embodiment. It is a figure which shows another example of the control pattern of the external fan stored in memory.

  Hereinafter, an embodiment as an example of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  FIG. 1 is a conceptual diagram of an example of an image forming apparatus 1 according to an embodiment of the present invention.

  The image forming apparatus 1 according to the present embodiment is, for example, a tandem color printer, and includes a plurality of image forming units 20, an intermediate transfer belt (an example of an image carrier) 30, a backup roll 41, and a secondary transfer roll ( An example of a transfer unit) includes a pair of sheets 42, paper supply trays 50 a and 50 b, a paper transport system 60, and a fixing device 70.

  The image forming unit 20 includes, for example, four color image forming units 20Y, 20M, 20C, and 20K that form yellow, magenta, cyan, and black toner images, and a transparent color that transfers, for example, a transparent toner image. Image forming units 20CL and 20CL, and these six image forming units 20CL, 20Y, 20M, and 20C so as to primarily transfer a toner image formed according to image information of each color to the intermediate transfer belt 30. , 20K are arranged in the order of transparent color, transparent color, yellow, magenta, cyan and black along the rotation direction of the intermediate transfer belt 30. Instead of a transparent color, a light color image forming unit for transferring a light color toner image such as light yellow, light magenta, light cyan, or light black may be provided. Also, both the transparent color image forming unit 20CL and the light color image forming unit may be provided side by side.

  Each image forming unit 20 includes a photosensitive drum (an example of an image carrier) 21, a charging device 22 that charges the surface of the photosensitive drum 21 to a predetermined potential, and a laser beam L on the charged photosensitive drum 21. , An exposure device 23 for forming an electrostatic latent image by irradiating the toner, a developing device 24 for developing the electrostatic latent image formed on the photosensitive drum 21 by the exposure device 23 to form a toner image, and a photosensitive drum A primary transfer roll 25 for transferring the toner image on the toner image 21 to the intermediate transfer belt 30 in a primary transfer portion, and a drum cleaner 26 for removing residual toner and paper dust from the surface of the photosensitive drum 21 after the toner image is transferred. I have. A toner cartridge 27 that supplies developer to the developing device 24 is installed above each image forming unit 20.

  The primary transfer roll 25 of each image forming unit 20 is arranged so that the intermediate transfer belt 30 is sandwiched between each photosensitive drum 21. An electric field is formed between the photosensitive drum 21 and the primary transfer roll 25 by applying a transfer bias voltage having a reverse polarity with respect to the charging electrode of the toner to each primary transfer roll 25, and the photosensitive drum 21. The charged toner image is transferred onto the intermediate transfer belt 30 by Coulomb force. Note that the photosensitive drum 21 rotates in the clockwise direction during the primary transfer.

  The intermediate transfer belt 30 is a member for sequentially transferring (primary transfer) the toner images of the respective color components formed by the respective image forming units 20 and holding them. The intermediate transfer belt 30 is formed in an endless shape in a state where it is stretched over a plurality of support rolls 31a to 31f and a backup roll 41, and rotates in the counterclockwise circumferential direction for each color image forming unit 20CL, The toner image formed by 20Y, 20M, 20C, and 20K is subjected to primary transfer.

  The pair of the backup roll 41 and the secondary transfer roll 42 forms a full-color image by collectively transferring (secondary transfer) the toner images transferred onto the intermediate transfer belt 30 onto a sheet (an example of a recording medium). And is disposed in a state of being opposed to each other with the intermediate transfer belt 30 interposed therebetween. The opposite portion between the backup roll 41 and the secondary transfer roll 42 is a secondary transfer portion.

  The backup roll 41 is rotatably installed on the back side of the intermediate transfer belt 30, and the secondary transfer roll 42 is rotatably installed in a state facing the toner image transfer surface of the intermediate transfer belt 30. The backup roll 41 and the secondary transfer roll 42 are arranged such that their respective rotational axis directions (directions perpendicular to the paper surface of FIG. 1) are along each other.

  In transferring the toner image on the intermediate transfer belt 30, a voltage having the same polarity as the charging polarity of the toner is applied to the backup roll 41, or a voltage having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roll 42. . Thereby, a transfer electric field is formed between the backup roll 41 and the secondary transfer roll 42, and the toner image held on the intermediate transfer belt 30 is transferred onto the paper.

  The sheet supply trays 50a and 50b contain sheets of various sizes and thicknesses. The paper in the paper supply trays 50a and 50b is pulled out by a pick-up roll (not shown) of the paper transport system 60, and then the timing is controlled by a resist roll 62 of the paper transport system 60 and introduced into the secondary transfer unit. The toner image is transferred and then conveyed to the fixing device 70 through the conveyance belts 63 and 64 of the paper conveyance system 60.

  The fixing device 70 is a device that fixes an unfixed toner image transferred onto a sheet or the like in a secondary transfer unit to the sheet by thermocompression bonding, and includes a fixing roll (an example of a fixing rotating body) 71 and a heating belt 73. The fixing unit includes a heating belt unit 78 and a pressure roll (an example of a pressure rotator) 72 provided so as to face the heating belt unit 78. The heating belt 73 is provided so as to pass through a fixing nip portion between the fixing roll 71 and the pressure roll 72.

  The sheet after the secondary transfer is conveyed to a fixing nip portion between the fixing roller 71 and the pressure roller 72 facing each other, and is discharged while being sandwiched between the heating belt 73 and the pressure roller 72. At this time, the paper or the like is heated by the fixing roll 71 and the heating belt 73 and is pressed by the pressure roll 72, whereby the toner image is fixed on the paper or the like. The sheet or the like that has passed through the fixing device 70 is sent to a discharge roll (not shown) through the conveyance belt 65 and discharged to the outside of the image forming apparatus 1.

  Next, the configuration of the above-described fixing device 70 will be described with reference to FIGS. 2 is a conceptual diagram of an example of the fixing device 70 used in the image forming apparatus of FIG. 1, and FIG. 3 is a perspective view of an example of the fixing device 70 of FIG. 3, the left side of the drawing is the rear side of the image forming apparatus 1 (the back side with respect to the direction in which the paper supply trays 50a and 50b are mounted on the image forming apparatus 1), and the right side of the drawing is the front side of the image forming apparatus 1. It has become.

  The fixing device 70 includes a peeling pad 74, an internal heating roll 75, an external heating roll 76, and support rolls 77 a and 77 b, in addition to the heating belt unit 78 including the fixing roll 71 and the heating belt 73 and the pressure roll 72. I have. Furthermore, a motor (an example of a driving unit) 81 that rotates the heating belt unit 78 that drives the fixing roll 71 and an external fan (second cooling unit) 80 for cooling the motor 81 are provided. The motor 81 is provided with a control board 81a for controlling the rotation of the motor 81 and a heat sink 81b for radiating heat from the control board 81a. Cooling means) 81c is attached. Accordingly, the motor 81 rotates and the heating belt unit 78 is driven to rotate at the same time as the internal fan 81c rotates, and a motor coil (not shown) constituting the motor 81 is cooled by the air blown by the internal fan 81c. That is, the motor 81 itself is cooled. In the external fan 80 described above, more specifically, the control board 81a is cooled via the heat sink 81b, and the motor coil of the motor 81 is cooled by blowing air.

  The fixing roll 71 is a member that receives the driving force of the motor 81 and rotationally drives the pressure roll 72 and the heating belt 73, and is installed in a state of being rotatable in a counterclockwise direction. The sheet P is conveyed by the rotation of the fixing roll 71, and the pressure roll 72 and the heating belt 73 are rotated (driven). A first fixing nip portion N1 is formed between the fixing roll 71 and the pressure roll 72.

  The fixing roll 71 is also a member that heats the paper P and the heating belt 73. The fixing roll 71 is made of a metal such as aluminum, iron, or stainless steel, and three heating sources 71L such as a halogen lamp are installed therein. However, the number of the heat sources 71L may be two or less or four or more.

  Next to the fixing roll 71 (on the downstream side of the conveyance of the paper P), the above-described peeling pad 74 is installed adjacent to the entire axial direction of the fixing roll 71. The peeling pad 74 has a function of peeling the paper P after the fixing process from the heating belt 73. In addition, a second fixing nip portion N2 is formed between the peeling pad 74 and the pressure roll 72, and the fixing nip portion of the fixing device 70 is longer than when the peeling pad 74 is not provided.

  Oil is interposed between the fixing roll 71 and the peeling pad 74 and the heating belt 73. Thereby, the contact resistance between the fixing roll 71 and the peeling pad 74 and the heating belt 73 is reduced, so that the rotational movement of the heating belt 73 becomes smooth. Therefore, damage to the heating belt 73 due to contact between the fixing roll 71 and the peeling pad 74 and the heating belt 73 is suppressed or prevented.

  The above-described pressure roll 72 includes a hollow cylindrical cored bar 72A, an elastic layer 72B covering the outer periphery thereof, and a release layer 72C covering the outer periphery of the elastic layer 72B. The core metal 72A is made of a metal such as aluminum, iron or stainless steel, the elastic layer 72B is made of an insulating material having heat resistance such as silicone rubber, and the release layer 72C is made of, for example, a fluorine resin. Consists of.

  The pressure roll 72 is installed so as to be movable in a direction approaching the fixing roll 71 and in a direction away from the fixing roll 71, and is pressed against the fixing roll 71 by an elastic member (spring) during the fixing process. ing. Thus, the first and second fixing nip portions N1 and N2 described above are formed between the fixing roll 71 and the peeling pad 74 and the pressure roll 72 facing each other.

  The heating belt 73 is an endless belt in which a release layer made of, for example, a fluorine resin is laminated on a heat-resistant insulating base material such as polyimide resin, and includes a fixing roll 71 and an internal heating roll 75. And rotatably provided in the circumferential direction (counterclockwise direction) in a state of being stretched around the support rolls 77a and 77b.

  The heating belt 73 is stretched so as to pass through the first and second fixing nip portions N1 and N2. The paper P transported to the first and second fixing nips N1 and N2 is heated by the fixing roll 71 and the heating belt 73 while being sandwiched between the heating belt 73 and the pressure roll 72, and also the pressure roll 72. Is pressurized. As a result, the unfixed toner image on the paper P is fixed on the paper P. When such a heating belt 73 is used, a decrease in heating temperature is suppressed as compared with the case where the sheet P is heated only by the fixing roll without using the heating belt 73. Further, since the heating belt 73 can be taken longer than the size of the paper, the occurrence of a gloss level difference is suppressed or prevented.

  A speed detector (an example of speed detecting means) 79 for detecting the speed of the heating belt 73 is installed on the outer periphery of the heating belt 73 (on the paper P carrying-in side). The speed detector 79 is a photoelectric speed detector that includes a light emitting unit and a light receiving unit such as a rotary encoder, for example, generates a pulse signal as the heating belt 73 rotates, and outputs the pulse signal to a CPU (described later) Central Processing Unit) 83 is transmitted. The peripheral speed of the heating belt 73, that is, the fixing speed of the fixing unit is measured by this pulse signal.

  The above-described internal heating roll 75 is a member that heats the heating belt 73 and is rotatable so as to follow the rotation of the heating belt 73 at a position farther from the pressure roll 72 than the fixing roll 71 and the external heating roll 76. It is installed in a state.

  The internal heating roll 75 is made of a metal such as aluminum, iron or stainless steel, and four heating sources 75L such as halogen lamps are installed therein. However, the number of heating sources 75L may be three or less or five or more.

  The external heating roll 76 described above is a member that heats the heating belt 73, and is in contact with the fixing belt 71 and the internal heating roll 75 so as to push the heating belt 73 out of the frame of the heating belt 73. It is installed in a state. The external heating roll 76 is also installed in a rotatable state so as to follow the rotation of the heating belt 73.

  The external heating roll 76 is made of a metal such as aluminum, iron or stainless steel, and three heating sources 76L such as a halogen lamp are installed therein. However, the number of the heat sources 76L may be two or less or four or more.

  Next, FIG. 4 shows a circuit block diagram of the main part of the image forming apparatus 1 described above.

  A CPU (an example of a control unit) 83 is a device that controls image processing of the image forming apparatus 1. The CPU 83 is electrically connected to a memory (an example of a storage unit) ME, and the speed detector 79, the external fan 80, the motor 81, and various information relating to image formation by the operator (basis weight of paper) And an operation panel 82 to which commands (same size / enlargement / reduction, number of formed images, monochrome / color, etc.) are input are electrically connected.

  The CPU 83 measures the peripheral speed (that is, the fixing speed) of the heating belt 73 based on the pulse signal sent from the speed detector 79 during the fixing process of the fixing device 70, and also from the operation panel 82. To recognize the paper thickness (that is, paper basis weight). The driving of the external fan 80 is controlled based on the fixing speed and the paper basis weight.

  Here, the relationship between the driving speed of the motor 81 and the temperature of the motor 81 due to the cooling effect by the external fan 80 and the internal fan 81c driven by the motor 81 is shown in FIG.

  As shown in the figure, in the absence of the external fan 80 and the internal fan 81c, no cooling effect can be obtained, so that the temperature of the motor 81 (the temperature of the motor coil and the substrate) is relatively low from the motor allowable temperature. It exceeds the upper limit. As the driving speed of the motor 81 increases, the temperature of the motor 81 also increases.

  Further, when only the internal fan 81c is provided, when the driving speed of the motor 81 is low, the rotation speed of the internal fan 81c is also low, so that an effective cooling effect cannot be obtained, and the temperature of the motor 81 rises. The upper limit of the allowable temperature is exceeded. However, when the rotational speed of the internal fan 81c increases as the driving speed of the motor 81 increases, the cooling effect gradually appears and the temperature of the motor 81 decreases, and the upper limit of the allowable motor temperature from a certain driving speed. Below.

  When the internal fan 81c is provided and the external fan 80 is turned on, the external fan 80 rotates regardless of the driving speed of the motor 81 and a cooling effect is obtained. Therefore, the driving speed of the motor 81 is low. However, the temperature of the motor 81 is lower than the upper limit of the allowable motor temperature. Then, as the driving speed of the motor 81 increases, the cooling effect by the internal fan 81c is gradually added, and the temperature of the motor 81 becomes lower than the upper limit of the allowable motor temperature.

  Next, the relationship between the axial position of the fixing roll 71 and the temperature of the fixing roll 71 is shown in FIG.

  As shown in FIG. 5, when both the internal fan 81c and the external fan 80 are driven, the temperature of the motor 81 falls below the upper limit of the allowable motor temperature from when the driving speed is low.

  Here, as shown in FIG. 6, the minimum fixing temperature when the fixing speed is high is higher than the minimum fixing temperature when the fixing speed is low. This is because, when the fixing speed is increased, the time for the sheet P to pass through the first and second fixing nips N1 and N2 is shortened, so that it is necessary to give the sheet P a necessary amount of heat in a shorter time. It is.

  As shown in the figure, when viewed from the axial position of the fixing roll 71, when the external fan 80 is turned on on the rear side of the fixing roll 71 where the external fan 80 is installed, the fixing speed becomes high. (In other words, when the driving speed of the motor 81 is increased), the cooling effect by the two fans of the external fan 80 and the internal fan 81c is exerted, so that fixing on the rear side of the fixing roll 71 on which the external fan 80 is installed is performed. The temperature drops excessively, and the fixing speed falls below the minimum fixing temperature at high speed. Further, the temperature balance between the front side and the rear side of the fixing roll 71 is also deteriorated.

  On the other hand, when the external fan 80 is turned off, the cooling effect by the external fan 80 does not occur, so the rear side of the fixing roll 71 on which the external fan 80 is installed is below the minimum fixing temperature when the fixing speed is high. The temperature balance with the front side is maintained well.

  In addition, the minimum fixing temperature when the fixing speed is low is lower than that when the fixing speed is high. Therefore, whether the external fan 80 is turned on or off, Even the rear side of the fixing roll 71 does not fall below.

  Therefore, the present inventor has come up with the idea that the driving of the external fan 80 may be controlled in accordance with the fixing speed in this way. Further, as the thickness of the paper P increases, that is, as the basis weight of the paper P increases, the load of the motor 81 that drives the internal fan 81c increases and the temperature rises. I also came up with the idea of controlling the drive of 80. That is, by controlling the driving of the external fan 80 based on the fixing speed and the paper basis weight, the temperature of the axial end portion (especially the rear side) of the fixing roll 71 can be reduced well while the temperature increase of the motor 81 is suppressed. I came up with a good idea.

  Here, it is described that the driving of the external fan 80 is controlled based on the fixing speed and the paper basis weight, but it may be controlled based on either the fixing speed or the paper basis weight. In other words, the present invention only needs to control the driving of the external fan 80 based on at least one of the fixing speed and the paper basis weight. In the present embodiment, the external fan 80 and the internal fan 81c are provided on the rear side of the fixing device 70, but may be on the front side.

Now, the control pattern of the external fan 80 derived from the above knowledge is shown in FIG. As shown in FIG. 7, the fixing speed is divided into three categories of low speed (˜300 mm / s), medium speed (300 to 400 mm / s), and high speed (400 to mm / s), and the paper basis weight is small ( ~100g ^{/ m} 2), middle (100~200g ^{/ m} 2), it was divided into three categories: large (200~g / ^{m 2).} The fixing speed and the paper basis weight may be divided into two sections or four sections or more instead of three sections. Also, the numerical division may not follow this embodiment.

  In FIG. 7, the driving of the external fan 80 is controlled in four stages. In other words, it is “OFF” that is not rotating, “weak” that is rotated at the lowest speed, “strong” that is rotated at the highest speed, and intermediate between “weak” and “strong” It is “medium” which is in a state of being rotationally driven at a speed of 5 mm.

  When the fixing speed is high, the motor 81 is sufficiently cooled only by the cooling effect of the internal fan 81c, so that the external fan 80 is controlled to be “off”. Further, when the paper basis weight is small, the load on the motor 81 is small and the temperature rise of the motor 81 is small, so the external fan 80 is similarly controlled to “off”.

  Further, when the fixing speed is low and the paper basis weight is large, the cooling effect of the internal fan 81c is not expected, and in addition, the load on the motor 81 is maximized and the temperature rise of the motor 81 is maximized. Therefore, the external fan 80 is controlled to “strong”.

  Further, when the fixing speed is medium and the sheet basis weight is medium, the cooling effect of the internal fan 81c is expected to some extent, but the load on the motor 81 is larger than when the sheet basis weight is small. As the temperature of the motor 81 increases, the external fan 80 is controlled to be “weak”.

  When the fixing speed is medium and the paper basis weight is large, the cooling effect of the internal fan 81c is expected to some extent, but the load on the motor 81 is maximized and the temperature rise of the motor 81 is the largest. Since it becomes large, the external fan 80 is controlled to “medium”. In addition, when the fixing speed is low and the paper basis weight is medium, the cooling effect of the internal fan 81c is not expected, and the temperature rise of the motor 81 is larger than when the paper basis weight is small. Similarly, the external fan 80 is controlled to “medium”.

  The table shown in FIG. 7 is stored in the memory ME shown in FIG. When fixing the toner image onto the paper P, the CPU 83 causes the CPU 83 to determine the actual fixing speed, which is the peripheral speed of the heating belt 73 measured by the speed detector 79, and the actual paper P input from the operation panel 82. A sheet basis weight as a thickness is input, and the CPU 83 refers to the table shown in FIG. Then, referring to the tables stored in these memories ME (that is, information relating to the fixing speed and the paper basis weight), the driving speed of the external fan 80 is determined from the information relating to the actual fixing speed and the paper basis weight in the above four steps. Controlled.

  FIG. 8 shows the relationship between the driving speed of the motor 81 and the temperature of the motor 81 accompanying the cooling effect by the external fan 80 controlled by the CPU 83 and the internal fan 81c driven by the motor 81 along the table shown in FIG. .

  As shown in the figure, when the external fan 80 is controlled and driven as described above, the external fan 80 is driven when the driving speed of the motor 81 is low and the cooling effect by the internal fan 81c is not expected. As a result, the motor 81 is cooled, and the temperature rise of the motor 81 is suppressed.

  Then, as the driving speed of the motor 81 increases, the driving speed of the external fan 80 decreases as the cooling effect by the internal fan 81c gradually appears. Therefore, the temperature of the motor 81 is equal to the motor allowable temperature. The upper limit is maintained at a level, and temperature rise is suppressed. Thereby, the temperature drop of the fixing roll 71 (particularly the temperature drop at the end in the axial direction) is minimized.

  In the above description, driving of the external fan 80 is controlled in four stages, but it is controlled in two stages, “ON” and “OFF”, which are not rotating. What is necessary is that the rotational speed, that is, the air volume of the external fan may be any number of stages.

  Here, FIG. 9 shows a table referred to by the CPU 83 when the driving of the external fan 80 is controlled in two stages of “ON” and “OFF”, that is, when the air volume is not controlled.

  As shown in FIG. 9, “OFF” in the table shown in FIG. 7 is “OFF”, and “strong”, “medium”, and “weak” locations are “ON”. In the case shown in FIG. 9, since the temperature rise of the motor 81 is finely suppressed, as a result, the temperature drop of the fixing roll 71 (particularly the temperature drop at the end portion in the axial direction) is minimized. As a result, in the image forming apparatus 1 using the fixing device 70, the fixing temperature is stabilized, and deterioration of the fixing property of the image on the recording medium and uneven gloss of the image are suppressed to the minimum.

  In contrast, in the case shown in FIG. 7, the temperature rise of the motor 81 is not as finely controlled as in the case shown in FIG. 9, but the temperature drop of the fixing roll 71 (particularly the temperature drop at the end in the axial direction) is effective. To be suppressed.

  Furthermore, the air volume of the external fan 80 may be continuous control instead of such stepwise control.

  As an example of continuously controlling the air volume of the external fan 80, an air volume determination formula for obtaining the fan air volume from the sheet basis weight and the fixing speed is stored in the memory ME instead of the table shown in FIGS. In addition, it is conceivable to control the driving of the external fan 80 based on numerical values obtained by applying the paper basis weight and the fixing speed to the air volume determination formula, that is, the fan air volume.

  Here, an example of an air volume determination formula is shown in Formula (1). However, the formula shown here is only an example, and the present invention is not limited to the formula.

Fan air volume y = α × (paper basis weight x ₁ / fixing speed x ₂ ) + β (1)

  In Expression (1), α is an air volume determination coefficient, and β is a corrected air volume.

  In this way, instead of obtaining the fan air volume from the paper basis weight and the fixing speed, the fan air volume is determined by associating the fan air volume with either the paper basis weight or the fixing speed, and the fan air volume is calculated from the paper basis weight or the fixing speed. You may make it ask.

  Although the invention made by the present inventor has been specifically described based on the embodiment, the embodiment disclosed in this specification is an example in all respects and is limited to the disclosed technology. Should not be considered. That is, the technical scope of the present invention should not be construed restrictively based on the description in the above-described embodiment, but should be construed according to the description of the scope of claims. All modifications are included without departing from the technical scope equivalent to the described technique and the gist of the claims.

  For example, in the above description, information on the fixing speed is obtained from the peripheral speed of the heating belt 73 by the speed detector 79, and information on the paper basis weight is obtained from the operation panel 82 input as the thickness of the paper P. The fixing speed may be obtained from the rotational speed of the motor 81, the rotational speed of the pressure roll 72, the transport speed of the paper P, or the like. Further, the basis weight of the paper P may be obtained by measuring with a thickness sensor.

  Further, in the above description, the fixing device 70 is a belt system including the endless heating belt 73 and the pressure roll 72 that are rotationally driven by the fixing roll 71, but for example, the fixing roll 71 and the pressure roll. 72 may be a roll pair method.

  In the above description, the image forming apparatus is applied to the secondary transfer method using an intermediate transfer belt. However, the image forming apparatus may be a direct transfer method in which an image on an image carrier is directly transferred to a recording medium. Good.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor drum 22 Charging apparatus 23 Exposure apparatus 24 Developing apparatus 25 Primary transfer roll 30 Intermediate transfer belt 42 Secondary transfer roll 70 Fixing apparatus 71 Fixing roll 72 Pressing roll 73 Heating belt 74 Peeling pad 78 Heating belt unit 79 Speed detector 80 External fan 81 Motor 81a Control board 81b Heat sink 81c Internal fan 82 Operation panel 83 CPU
ME memory N1, N2 Fixing nip P Paper

Claims (4)

Fixing means comprising a pressure rotator and a fixing rotator, and fixing the developer image transferred to the recording medium by feeding the recording medium while sandwiching the recording medium between the pressure rotator and the fixing rotator. When,
A first cooling means for cooling itself by blowing air, and a driving means for driving the fixing rotating body;
Second cooling means for cooling the drive means by blowing air;
Based on at least one of the fixing speed of the fixing unit and the basis weight of the recording medium, the second cooling unit is driven to control the temperature of the driving unit to be less than the allowable temperature of the driving unit. Control means to
A fixing device. A storage unit that stores information on at least one of a fixing speed of the fixing unit and a basis weight of the recording medium and an air volume of the second cooling unit;
The control means refers to the information stored in the storage means and controls the air volume of the second cooling means from information on at least one of the actual fixing speed of the fixing means and the basis weight of the recording medium. To
The fixing device according to claim 1. A storage unit that stores an air volume determination formula relating to at least one of a fixing speed of the fixing unit and a basis weight of the recording medium and an air volume of the second cooling unit;
The control unit applies the information regarding at least one of the fixing speed of the fixing unit and the basis weight of the recording medium to the air volume determination formula stored in the storage unit to control the air volume of the second cooling unit. To
The fixing device according to claim 1. An image carrier for holding a developer image;
Transfer means for transferring the developer image held on the image carrier to a recording medium;
The fixing device according to any one of claims 1 to 3, wherein the unfixed developer image transferred to the recording medium is fixed to the recording medium.
An image forming apparatus comprising:

Images