JP6733348B2 - Image forming device - Google Patents

Description

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

In image forming apparatuses such as copiers, printers, and facsimiles, a heat fixing method is widely adopted as a method for fixing an unfixed toner image transferred onto a sheet such as a sheet onto the sheet. As a fixing device, there is known a fixing device including a fixing belt which is formed in an endless shape, is wrapped around a first pressure roller and a tension roller, and is sandwiched between a first pressure roller and a second pressure roller. ing.

Nowadays, there is an increasing need for image formation on a relatively thin sheet. However, in an electrophotographic image forming apparatus, it is difficult to obtain a suitable fixing property for a thin sheet. The reason is that a thin sheet has low separability from the fixing belt on the downstream side of the fixing nip portion in the sheet conveying direction after fixing.

In order to improve the separability of the sheet with respect to the fixing belt, the winding area of the fixing belt with respect to the first pressure roller on the downstream side of the fixing nip portion in the sheet conveying direction (hereinafter, may be simply referred to as “belt winding area”). ) Is increased and the tension of the fixing belt is lowered. However, with the configuration in which the area around the fixing belt is increased and the tension in the fixing belt is reduced, the slack is likely to occur in the fixing belt on the downstream side of the fixing nip portion in the sheet conveying direction. Then, after the slack has occurred, the tension of the fixing belt returns to its original position so that the fixing belt suddenly bounces (hereinafter, this phenomenon is referred to as “belt bounce”). As a result, there is a problem that noise is likely to occur in the image formed on the sheet.

Therefore, the tension of the fixing belt that does not cause the belt bounce has been designed in advance according to the belt winding area and the surface friction coefficient of the first pressure roller. However, when the cumulative output number of sheets increases, the surface coating of the first pressure roller may peel off. As a result, the surface friction coefficient of the first pressure roller increases, and the belt bounce is likely to occur. Therefore, when the integrated output number of sheets is increased and peeling of the surface coating of the first pressure roller is predicted, it is conceivable to replace the first pressure roller before the belt bounces. However, there was concern that the printing cost would increase.

Then, the prior arts relating to the fixing device, which are considered to be applicable in order to solve the above problems, are disclosed in Patent Documents 1 and 2.

The fixing device described in Patent Document 1 includes a fixing belt wound around a plurality of rollers including a fixing roller, and a pressure roller that comes into pressure contact with the fixing roller via the fixing belt. This fixing device executes control such that the surface speed of the pressure roller is slower than the surface speed of the fixing belt until the front end (downstream end in the transport direction) of the recording medium (sheet) is separated from the fixing belt. That is, since the surface speed of the fixing belt is higher than the surface speed of the pressure roller, it can be expected that the occurrence of belt bounce is suppressed.

The heating device described in Patent Document 2 includes a driving roller, a tension roller, and a fixing film (endless belt) wound around a low heat capacity heating body, and a pressure roller that presses and contacts the low heat capacity heating body via the fixing film. And a biasing means for the tension roller. When this heating device detects the deviation of the fixing film in the direction of the rotation axis, the heating device controls the tension roller to move the tension roller to change the tension of the fixing film and return the fixing film to a predetermined position.

JP 2012-47905 A JP-A-3-260682

However, in the fixing device described in Patent Document 1, the surface speed of the fixing belt is set to be higher than the surface speed of the pressure roller in response to the increase in the surface friction coefficient of the fixing roller due to the increase in the cumulative output number of recording media (sheets). Is not increasing. Further, this fixing device controls the surface speed of the pressure roller to be equal to the surface speed of the fixing belt after the front end (downstream end in the transport direction) of the recording medium is separated from the fixing belt. For these reasons, there has been a problem that it may not be possible to suppress the occurrence of belt bounce of the fixing belt. Further, if the surface speed of the fixing belt is made higher than the surface speed of the pressure roller from the start of the operation of the fixing device, abrasion of the surface of the fixing roller is promoted, which may lead to shortening of the life of the fixing roller.

In addition, the heating device described in Patent Document 2 also fixes in the same manner as the fixing device of Patent Document 1 in response to an increase in the surface friction coefficient of the low heat capacity heating element due to an increase in the cumulative output number of recording materials (sheets). It does not change the tension of the film. Therefore, there is a problem in that the occurrence of belt bounce of the fixing film may not be suppressed.

The present invention has been made in view of the above points, and even when the integrated output number of sheets is increased, the separability of the sheet after fixing with respect to the fixing belt is suppressed while suppressing an increase in printing cost. An object is to provide an image forming apparatus that can be realized.

In order to solve the above problems, the present invention has an endless fixing belt which is wound around a first pressure roller and a tension roller and is sandwiched between the first pressure roller and the second pressure roller. In the image forming apparatus, the unfixed toner image transferred onto the sheet is fixed on the sheet at the fixing nip portion where the first pressure roller and the second pressure roller contact each other with the fixing belt interposed therebetween. (1) A detection unit that detects information relating to the surface state of the pressure roller, and two drive sources individually provided for the first pressure roller and the second pressure roller or the tension of the fixing belt is changed. At least one of the tension changing portions for fixing, and as an operation mode at the time of fixing, the first pressure roller and the second pressure roller are set to a predetermined surface speed at the time of normal fixing, and the fixing belt is provided. Has a normal mode in which a predetermined tension is set, and a belt splash avoiding mode selected based on information related to the surface state of the first pressure roller detected by the detector, and the belt splash avoiding mode is When selected, a speed change is performed to increase the surface speed of the fixing belt in the fixing nip portion above the surface speed of the second pressure roller, or a tension to increase the tension of the fixing belt from that in the normal mode. Characterized by performing at least one of the changes.

With this configuration, by changing the speed of the fixing belt or changing the tension of the fixing belt, it is possible to suppress the occurrence of belt bounce on the downstream side of the fixing nip portion in the sheet conveying direction. Therefore, even if the cumulative output number of sheets increases, the first pressure roller need not be replaced. At this time, the tension (exit curvature) on the exit side of the fixing nip becomes equal to that before the surface coat of the first pressure roller is peeled off, and the separability can be maintained while avoiding the belt bounce.

Further, in the image forming apparatus having the above-mentioned configuration, the detection unit detects the integrated output number of sheets as the information related to the surface state of the first pressure roller.

Further, in the image forming apparatus having the above-mentioned configuration, the detection unit detects the light reflectance of the surface of the first pressure roller as the information related to the surface state of the first pressure roller.

Further, in the image forming apparatus having the above-mentioned configuration, the detection unit detects displacement of slack of the fixing belt around the fixing nip portion as the information related to the surface state of the first pressure roller. ..

Further, the image forming apparatus having the above configuration is provided with an operation unit capable of setting either automatic selection of the belt splash avoiding mode or manual selection by the user of the belt splash avoiding mode.

Further, in the image forming apparatus having the above-mentioned configuration, the speed increase in the speed change or the tension increase in the tension change is executed stepwise or continuously in the belt splash avoiding mode.

According to the configuration of the present invention, even when the cumulative output number of sheets is increased, the first pressure roller does not need to be replaced, and belt bounce is generated at the downstream side of the fixing nip portion in the sheet conveying direction. It is possible to suppress. Therefore, it is possible to provide the image forming apparatus capable of favorably realizing the separability of the sheet after fixing with respect to the fixing belt while suppressing the increase of the printing cost.

1 is a front view of a partial vertical cross section of an image forming apparatus according to a first exemplary embodiment of the present invention. FIG. 3 is a schematic front view of the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration of a fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. 6 is a graph showing the relationship between the number of durable prints and the surface friction coefficient of the first pressure roller. 6 is a graph showing the relationship between the surface speed of the fixing belt and the belt bounce occurrence period in the fixing device of the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 6 is a schematic front view of a fixing device of an image forming apparatus according to a second exemplary embodiment of the present invention. FIG. 6 is a schematic front view of the fixing device of the image forming apparatus according to the second exemplary embodiment of the present invention, showing a state in which the tension of the fixing belt is changed. FIG. 7 is a schematic front view of a fixing device of an image forming apparatus according to a third exemplary embodiment of the present invention. FIG. 6 is a schematic front view of a fixing device of an image forming apparatus according to a third exemplary embodiment of the present invention, showing a state in which the tension of the fixing belt is changed.

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the contents below.

<First Embodiment>
First, with respect to the image forming apparatus of the first embodiment of the present invention, the image output operation will be described while explaining the outline of the structure using FIG. FIG. 1 is an example of a partial vertical sectional front view of an image forming apparatus. The two-dot chain line with an arrow in the figure indicates the sheet conveyance path and the conveyance direction.

The image forming apparatus 1 is a so-called tandem type color copying machine as shown in FIG. 1, and includes an image reading unit 2 that reads an image of a document, a printing unit 3 that prints the read image on a sheet such as paper, and a printing unit. An operation unit 4 for inputting conditions and displaying the operating status, and a main control unit 5 are provided.

The image reading unit 2 is a known unit that reads an image of an original placed on the upper surface of a platen glass (not shown) by moving a scanner (not shown). The image of the original is separated into three colors of red (R), green (G), and blue (B), and converted into an electric signal by a CCD (Charge Coupled Device) image sensor (not shown). As a result, the image reading unit 2 obtains image data for each color of red (R), green (G), and blue (B).

The image data for each color obtained by the image reading unit 2 is subjected to various processes in the main control unit 5, and image data of each reproduced color of yellow (Y), magenta (M), cyan (C), and black (K). Is stored in the storage unit 5b (see FIG. 3) of the main control unit 5. The image data for each reproduced color stored in the storage unit 5b is subjected to processing for positional deviation correction, and then scanned in synchronization with sheet conveyance to perform optical scanning on the photosensitive drum 21 which is an image carrier. It is read line by line.

The printing unit 3 forms an image by an electrophotographic method and transfers the image to a sheet. The printing unit 3 includes an intermediate transfer belt 11 in which the intermediate transfer body is formed as an endless belt. The intermediate transfer belt 11 is wound around a driving roller 12 and driven rollers 13 and 14. The intermediate transfer belt 11 is rotationally moved counterclockwise in FIG. 1 by the drive roller 12.

The driving roller 12 presses and contacts the secondary transfer roller 15 that faces the intermediate transfer belt 11 with the intermediate transfer belt 11 interposed therebetween. At the position of the driven roller 14, the intermediate transfer cleaning unit 16 provided so as to face the driven roller 14 with the intermediate transfer belt 11 interposed therebetween contacts the outer peripheral surface of the intermediate transfer belt 11. After the toner image formed on the outer peripheral surface of the intermediate transfer belt 11 is transferred onto the sheet, the intermediate transfer cleaning unit 16 removes and cleans the adhered substances such as toner remaining on the outer peripheral surface of the intermediate transfer belt 11.

Below the intermediate transfer belt 11, image forming units 20Y, 20M, 20C, and 20K corresponding to reproduced colors of yellow (Y), magenta (M), cyan (C), and black (K) are provided. In this description, the identification symbols “Y”, “M”, “C”, and “K” are omitted, unless otherwise specified, and are collectively referred to as, for example, “image forming unit 20”. There is something to do. The four image forming units 20 are arranged in a line along the rotation direction of the intermediate transfer belt 11 from the upstream side to the downstream side in the rotation direction. The four image forming units 20 have the same configuration, and a charging unit, an exposing unit, a developing unit, a drum cleaning unit, and a primary transfer roller are arranged around the photosensitive drum 21 that rotates clockwise in FIG. Prepare

Above the intermediate transfer belt 11, a toner bottle 31 and a toner hopper 32 corresponding to the four image forming units 20 of respective reproduced colors are provided. For the developing unit and the toner hopper 32, a toner remaining amount detecting unit (not shown) that detects the amount of toner inside is provided. Further, a toner replenishing device (not shown) is provided between the developing unit and the toner hopper 32 and between the toner hopper 32 and the toner bottle 31, respectively. When the remaining amount detecting unit detects a decrease in the amount of toner inside the developing unit, the replenishing device drives the toner hopper 32 to replenish the developing unit with toner. Further, when the remaining amount detecting section detects a decrease in the amount of toner inside the toner hopper 32, the replenishing device drives the toner bottle 31 to replenish the toner hopper 32 with toner. The toner bottle 31 is detachably attached to the main body of the apparatus, and can be replaced with a new one as needed.

A scanning optical device 23, which is an exposure unit, is arranged below the image forming unit 20. The scanning optical device 23 corresponds to the four image forming units 20 by one unit, and has four light sources such as semiconductor lasers (not shown) individually corresponding to each of the four photosensitive drums 21. The scanning optical device 23 modulates four semiconductor lasers according to image gradation data of each reproduced color, and individually emits laser light corresponding to each reproduced color to the four photoconductor drums 21.

Below the scanning optical device 23, there is provided a sheet supply device 91 in which a plurality of sheets S such as sheets are stacked and housed. The sheets S accommodated in the sheet feeding device 91 are sequentially fed to the sheet conveying path Q one by one from the uppermost layer. The sheet S sent from the sheet stacking device 91 to the sheet conveying path Q reaches the position of the registration roller pair 94. Then, the registration roller pair 94 corrects the skew feeding of the sheet S (skew correction) and in synchronism with the rotation of the intermediate transfer belt 11, and the contact portion between the intermediate transfer belt 11 and the secondary transfer roller 15 (secondary transfer). The sheet S is sent out toward the (nip portion).

In the image forming unit 20, an electrostatic latent image is formed on the surface of the photosensitive drum 21 by the laser light emitted from the scanning optical device 23, and the electrostatic latent image is visualized as a toner image by the developing unit. The toner image formed on the surface of the photoconductor drum 21 is primarily transferred to the outer peripheral surface of the intermediate transfer belt 11 at a position where the photoconductor drum 21 faces the primary transfer roller with the intermediate transfer belt 11 interposed therebetween. Then, as the intermediate transfer belt 11 rotates, the toner images of the image forming units 20 are sequentially transferred to the intermediate transfer belt 11 at a predetermined timing, so that yellow, magenta, cyan, and black are formed on the outer peripheral surface of the intermediate transfer belt 11. A color toner image is formed by superposing the four color toner images.

The color toner image primarily transferred onto the outer peripheral surface of the intermediate transfer belt 11 is formed by contacting the intermediate transfer belt 11 and the secondary transfer roller 15 with the sheet S sent in synchronization by the registration roller pair 94. And is transferred at the secondary transfer nip portion.

A fixing device 40 is provided above the secondary transfer nip portion. The sheet S to which the unfixed toner image is transferred at the secondary transfer nip portion is sent to the fixing device 40, and the toner image is heated and pressed to be fixed on the sheet S. The sheet S that has passed through the fixing device 40 is discharged to a sheet discharge section 96 provided above the intermediate transfer belt 11.

The operation unit 4 is provided on the front side of the image reading unit 2. The operation unit 4 inputs settings such as printing conditions such as the type and size of the sheet S used for printing by the user, enlargement/reduction, presence/absence of double-sided printing, and settings such as fax number and sender name in facsimile transmission. Accept. The operation unit 4 also serves as an informing unit for informing the user of the device state, cautions, error messages, and the like by displaying them on the display unit 4w.

Further, the image forming apparatus 1 is provided with a CPU 5a, an image processing unit, and a main control unit 5 including other electronic components (not shown) for controlling the entire operation of the image forming apparatus 1 (see FIG. 3). The main control unit 5 uses the central processing unit CPU 5a and the image processing unit, and controls the components such as the image reading unit 2 and the printing unit 3 based on the programs and data stored and input in the storage unit 5b. A series of image forming operation and printing operation are realized.

Next, the configuration of the fixing device 40 of the image forming apparatus 1 will be described with reference to FIGS. FIG. 2 is a schematic front view of the fixing device 40. FIG. 3 is a block diagram showing the configuration of the fixing device 40 of the image forming apparatus 1. FIG. 4 is a graph showing the relationship between the number of durable prints and the surface friction coefficient of the first pressure roller. In FIG. 2, the fixing device 40 is shown with the sheet conveying path Q substantially horizontal. In FIG. 2, the left side is the upstream side with respect to the fixing device 40 in the sheet conveying direction, and the right side is the downstream side with respect to the fixing device 40 in the sheet conveying direction.

As shown in FIGS. 2 and 3, the fixing device 40 includes a first pressure roller 41, a second pressure roller 42, a tension roller 43, a fixing belt 44, a first heating section 45, a second heating section 46, and a first heating section 46. A drive motor 47, a second drive motor 48, a biasing unit 50, and an information detection unit 60 are provided.

The first pressure roller 41 and the second pressure roller 42 have a cylindrical shape, and are arranged side by side so that their peripheral surfaces face each other with the sheet conveyance path Q in between. The rotation axes of the first pressure roller 41 and the second pressure roller 42 extend in the sheet width direction, that is, in the front-back direction of the image forming apparatus 1. The first pressure roller 41 and the second pressure roller 42 have a length corresponding to the entire area of the sheet conveyance path Q in the sheet width direction. A rotation shaft (not shown) of the first pressure roller 41 is rotatably supported by a bearing provided in the casing of the fixing device 40. A rotation shaft (not shown) of the second pressure roller 42 is rotatably supported by a bearing provided in the casing of the fixing device 40.

The first pressure roller 41 and the second pressure roller 42 have a laminated structure in which, for example, a release layer (for example, fluorine coating), a heat generating layer, an elastic layer, and the like are sequentially provided from the outer peripheral surface side toward the radial center. .. The first pressure roller 41 and the second pressure roller 42 have a diameter of, for example, about 40 mm to 60 mm, and each elastic layer has a thickness of, for example, about several mm. The sheet on which the surface of the first pressure roller 41 is heated by the action of the first heating unit 45, the surface of the second pressure roller 42 is heated by the action of the second heating unit 46, and the unfixed toner image is transferred. The S is heated to fix the toner on the sheet S. The second pressure roller 42 houses the second heating unit 46 therein.

A predetermined pressure is applied to the second pressure roller 42 by a pressure mechanism (not shown) such as a pressure spring, and the peripheral surface of the second pressure roller 42 presses the peripheral surface of the first pressure roller 41 to make contact with the fixing nip portion. Form N. In the fixing nip portion N, for example, the first pressure roller 41 is in a state of being depressed inward in the radial direction. The fixing device 40 fixes the unfixed toner image transferred to the sheet S on the sheet S at the fixing nip portion N where the first pressure roller 41 and the second pressure roller 42 contact each other with the fixing belt 44 interposed therebetween.

Two drive sources, a first drive motor 47 and a second drive motor 48, are provided individually for each of the first pressure roller 41 and the second pressure roller 42. For example, a stepping motor is used as the first drive motor 47, and an AC servo motor is used as the second drive motor 48. The first pressure roller 41 receives power from the first drive motor 47 and rotates counterclockwise in FIG. The second pressure roller 42 receives power from the second drive motor 48 and rotates clockwise in FIG.

The tension roller 43 has a cylindrical shape and accommodates a first heating unit 45 for heating the first pressure roller 41 therein. The tension roller 43 is arranged such that its peripheral surface faces the peripheral surface of the first pressure roller 41 with a space therebetween. The rotation axis of the tension roller 43 is parallel to the rotation axis of the first pressure roller 41 and extends along the paper width direction, that is, the front-back direction of the image forming apparatus 1. The tension roller 43 has a length corresponding to the entire area of the sheet conveyance path Q in the sheet width direction. A rotating shaft 43 a of the tension roller 43 is rotatably supported by a bearing 51 of the biasing unit 50, which will be described later. Further, the tension roller 43 is supported so as to be displaceable in a direction in which the tension roller 43 approaches and separates from the first pressure roller 41.

The fixing belt 44 is formed in an endless shape, and its length in the paper width direction is the same as that of the first pressure roller 41 and the tension roller 43. The fixing belt 44 has a laminated structure in which an elastic layer, a release layer, etc. are provided on a base material layer made of, for example, a polyimide film. The fixing belt 44 has a diameter of, for example, about 100 mm. The fixing belt 44 is wound around the first pressure roller 41 and the tension roller 43, and is sandwiched between the first pressure roller 41 and the second pressure roller 42 at the fixing nip portion N. A predetermined tension is applied to the fixing belt 44 by the urging unit 50.

The biasing unit 50 includes a bearing 51, a biasing spring 52, and a support member 53. The bearing 51 rotatably supports the rotating shaft 43a of the tension roller 43. The biasing spring 52 is composed of, for example, a tension spring, one end of which is connected to the bearing 51 and the other end of which is connected to the support member 53, and is interposed between the bearing 51 and the support member 53. The support member 53 is fixed to the casing of the fixing device 40 so as not to be displaced. The biasing spring 52 exerts a biasing force on the tension roller 43 in a direction in which the tension roller 43 is separated from the first pressure roller 41 via the bearing 51, and generates a predetermined tension on the fixing belt 44.

The information detection unit 60 is arranged near the first pressure roller 41, for example. The information detection unit 60 detects information related to the surface state of the first pressure roller 41.

The information detection unit 60 detects, for example, the cumulative output number of sheets S as the information related to the surface state of the first pressure roller 41. In this case, the information detection unit 60 has, for example, a sheet detection sensor, detects the sheets S passing through the fixing nip portion N, and counts the number of sheets. The main controller 5 may be provided with the information detector 60 to detect the cumulative output number of sheets S as digital information.

Alternatively, the information detection unit 60 detects, for example, the light reflectance of the surface of the first pressure roller 41 as the information related to the surface state of the first pressure roller 41. In this case, the information detection unit 60 has, for example, a non-contact type color discrimination sensor, and detects a change in the glossiness of the surface of the first pressure roller 41 as a light reflectance.

Alternatively, the information detection unit 60 detects displacement of the slack of the fixing belt 44 around the fixing nip portion N, for example, as information on the surface state of the first pressure roller 41. In this case, the information detection unit 60 has, for example, a non-contact type displacement sensor, and detects the displacement of the slack of the fixing belt 44.

The image forming apparatus 1 has a normal mode and a belt splash avoiding mode as operation modes at the time of fixing.

The normal mode is an operation mode used during normal fixing. In the normal mode, the first pressure roller 41 and the second pressure roller 42 are set to a predetermined surface speed, and the fixing belt 44 is set to a predetermined tension.

On the other hand, the belt bounce avoidance mode is automatically selected based on the information related to the surface state of the first pressure roller 41 detected by the information detection unit 60.

For example, the belt bounce avoidance mode is automatically selected based on the cumulative output number of sheets S detected by the information detection unit 60. Here, FIG. 4 shows the relationship between the number of durable prints and the surface friction coefficient of the first pressure roller 41, the vertical axis represents the surface friction coefficient of the first pressure roller 41, and the horizontal axis represents the number of durable prints. Represent Then, "100%" of the number of durable prints in FIG. 4 means the standard number of durable prints in the image forming apparatus 1 preset in the design stage.

According to FIG. 4, it can be seen that the surface friction coefficient of the first pressure roller 41 increases when the number of durable printed sheets exceeds 100%. It is considered that this is because the surface coating (release layer or the like) of the first pressure roller 41 is peeled off. As a result, there is a possibility that the belt bounce is likely to occur. Therefore, for example, when the durable print number exceeds 100%, the belt bounce avoidance mode is selected.

Alternatively, for example, the belt bounce avoidance mode is automatically selected based on the light reflectance of the surface of the first pressure roller 41 detected by the information detection unit 60. When the surface coating of the first pressure roller 41 is peeled off as described above, the glossiness of the surface of the first pressure roller 41 is increased. Therefore, when the information detector 60 detects the change in the glossiness of the surface of the first pressure roller 41, the belt splash avoiding mode is selected.

Alternatively, for example, the belt bounce avoidance mode is automatically selected based on the displacement of the slack of the fixing belt 44 detected by the information detection unit 60. When the surface friction coefficient of the first pressure roller 41 increases as described above, the fixing belt 44 is likely to loosen near the downstream side of the fixing nip portion N in the sheet conveying direction. Therefore, the belt bounce avoidance mode is selected when the information detector 60 detects the displacement of the slack of the fixing belt 44. For example, when the slack displacement of the fixing belt 44 reaches 500 μm in the direction normal to the surface of the fixing belt 44, the belt splash avoiding mode is selected.

In the belt splash avoidance mode, either automatic selection or manual selection by the user can be set using the operation unit 4. For example, the user can judge by looking at the state of the image, text, pattern, etc. printed on the sheet S, and manually select the belt splash avoiding mode.

Next, the operation of the fixing device 40 in the belt bounce avoidance mode will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the surface speed of the fixing belt 44 in the fixing device 40 and the belt bouncing cycle.

Here, the surface speed of the fixing belt 44 and the surface speed of the second pressure roller 42 at the time of separation before the first pressure roller 41 and the second pressure roller 42 contact each other across the fixing belt 44. Is, for example, about 290 mm/s to 300 mm/s and 320 mm/s. In the configuration of this embodiment, when the number of pulses of the first drive motor 47, which is a stepping motor, is about 24100, the surface speed of the fixing belt 44 becomes substantially equal to the surface speed of the second pressure roller 42.

Then, when the belt splash avoiding mode is selected, the image forming apparatus 1 executes a speed change to increase the surface speed of the fixing belt 44 in the fixing nip portion N above the surface speed of the second pressure roller 42. At this time, the number of pulses of the first drive motor 47, which is a stepping motor, is increased in order to increase the surface speed of the fixing belt 44. Specifically, the image forming apparatus 1 controls the transmission of a command to the first drive motor 47 to increase the number of pulses of the first drive motor 47 from about 24100 when the belt splash avoidance mode is selected. Execute.

As a result, according to FIG. 5, it can be seen that when the surface speed of the fixing belt 44 is made higher than the surface speed of the second pressure roller 42, the occurrence of belt bounce can be suppressed. On the other hand, according to FIG. 5, when the surface speed of the first pressure roller 41 is lower than the surface speed of the second pressure roller 42 in the state where the fixing operation in the belt splash avoidance mode is required. That is, when the number of pulses of the first drive motor 47 is lower than about 24100, it can be seen that belt bounce is likely to occur.

As in the above-described embodiment, the fixing device 40 has the information detection unit 60 that detects information related to the surface state of the first pressure roller 41 and the first pressure roller 41 and the second pressure roller 42. A first drive motor 47 and a second drive motor 48 that are individually provided are provided. In the image forming apparatus 1, as an operation mode at the time of fixing, the first pressure roller 41 and the second pressure roller 42 are set to a predetermined surface speed and the fixing belt 44 is set to a predetermined tension at the time of normal fixing. The normal mode and the belt splash avoiding mode selected based on the information related to the surface state of the first pressure roller 41 detected by the information detection unit 60 are provided. Further, the image forming apparatus 1 executes a speed change to increase the surface speed of the fixing belt 44 in the fixing nip portion N higher than the surface speed of the second pressure roller 42 when the belt splash avoiding mode is selected.

According to this configuration, by changing the speed of the fixing belt 44, it is possible to suppress the occurrence of belt bounce on the downstream side of the fixing nip portion N in the sheet conveying direction. Therefore, even when the cumulative output number of sheets S increases, the first pressure roller 41 does not have to be replaced. At this time, the tension (exit curvature) on the exit side of the fixing nip becomes equal to that before the surface coat of the first pressure roller is peeled off, and the separability can be maintained while avoiding the belt bounce. Therefore, it is possible to preferably realize the separability of the sheet S after fixing from the fixing belt 44 while suppressing an increase in printing cost.

Further, since the information detection unit 60 detects the integrated output number of the sheets S as the information related to the surface state of the first pressure roller 41, the surface friction coefficient of the first pressure roller 41 that causes the belt bounce increases. Can be predicted based on the cumulative output number of sheets S. Therefore, it is possible to effectively suppress the occurrence of belt bounce.

Further, since the information detection unit 60 detects the light reflectance of the surface of the first pressure roller 41 as the information related to the surface state of the first pressure roller 41, the first pressure roller 41 that causes the belt to bounce. It is possible to predict the increase in the surface friction coefficient of the above based on the light reflectance of the surface of the first pressure roller 41. Therefore, it is possible to effectively suppress the occurrence of belt bounce.

Further, since the information detection unit 60 detects the displacement of the slack of the fixing belt 44 around the fixing nip N as the information related to the surface state of the first pressure roller 41, the first pressure that causes the belt bounce. The increase in the surface friction coefficient of the roller 41 can be predicted based on the displacement of the slack of the fixing belt 44. Therefore, it is possible to effectively suppress the occurrence of belt bounce.

Further, since the operation unit 4 capable of setting either the automatic selection of the belt splash avoiding mode or the manual selection of the belt splash avoiding mode by the user is provided, the selection of the belt splash avoiding mode and the release of the selection are appropriately performed as necessary. It can be arbitrarily selected.

<Second Embodiment>
Next, an image forming apparatus according to the second exemplary embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic front view of the fixing device of the image forming apparatus. FIG. 7 is a schematic front view of the fixing device and shows a state in which the tension of the fixing belt is changed. Since the basic configuration of this embodiment is the same as that of the first embodiment described above, the same components as those of the first embodiment are designated by the same names and the same reference numerals as before, and detailed description thereof will be given. The description may be omitted.

As shown in FIG. 6, the fixing device 40 of the image forming apparatus 1 of the second embodiment includes a cam member 54 in which the urging portion 50 is a tension changing portion.

The cam member 54 is arranged between the support member 53 and the tension roller 43 and adjacent to the support member 53. The cam member 54 has, for example, an elliptical shape when viewed from the seat width direction, and is rotatable about an axis extending parallel to the seat width direction. When the cam member 54 is rotated, the support member 53 adjacent to the cam member 54 is displaced along the outer shape of the cam member 54. That is, the support member 53 is guided by a guide portion (not shown) and is displaced in a direction in which the tension roller 43 approaches and separates.

When the support member 53 is displaced in the direction away from the tension roller 43, the urging spring 52 extends, and the urging force of the urging spring 52 moves in the direction away from the first pressure roller 41. To increase. As a result, the tension of the fixing belt 44 also increases.

Then, when the belt bounce avoidance mode is selected, the image forming apparatus 1 executes a tension change for increasing the tension of the fixing belt 44 as compared with the normal mode. At this time, the cam member 54 is rotated in order to increase the tension of the fixing belt 44.

According to the configuration of the second embodiment, by changing the tension of the fixing belt 44, it is possible to suppress the occurrence of belt bounce on the downstream side of the fixing nip portion N in the sheet conveying direction. Therefore, even when the integrated output number of sheets S increases, the first pressure roller 41 does not need to be replaced, and the fixing nip portion N after fixing of the relatively thin sheet S is downstream in the sheet conveying direction. It becomes possible to maintain the separability of the fixing belt 44 with respect to the fixing belt 44 while avoiding the bounce of the belt.

<Third Embodiment>
Next, an image forming apparatus according to a third exemplary embodiment of the present invention will be described with reference to FIGS. 8 and 9. FIG. 8 is a schematic front view of the fixing device of the image forming apparatus. FIG. 7 is a schematic front view of the fixing device and shows a state in which the tension of the fixing belt is changed. Since the basic configuration of this embodiment is the same as that of the first embodiment described above, the same components as those of the first embodiment are designated by the same names and the same reference numerals as before, and detailed description thereof will be given. The description may be omitted.

As shown in FIG. 6, the fixing device 40 of the image forming apparatus 1 of the third embodiment includes a tension changing roller 55 whose biasing portion 50 is a tension changing portion.

The tension changing roller 55 is arranged adjacent to the inside of the fixing belt 44 between the support member 53 and the tension roller 43. The tension changing roller 55 is rotatable about an axis extending parallel to the sheet width direction. The tension changing roller 55 is displaced in the direction from the inside to the outside of the fixing belt 44 by using a cam mechanism or the like (not shown).

When the tension changing roller 55 is displaced in the direction from the inner side to the outer side of the fixing belt 44, the outer shape of the fixing belt 44 is pushed outward and the fixing belt 44 extends. As a result, the tension of the fixing belt 44 increases.

The tension changing roller 55 may be arranged adjacent to the outside of the fixing belt 44 in advance, and may be displaced in the direction from the outside to the inside of the fixing belt 44.

Then, when the belt bounce avoidance mode is selected, the image forming apparatus 1 executes a tension change for increasing the tension of the fixing belt 44 as compared with the normal mode. At this time, the tension changing roller 55 is displaced in order to increase the tension of the fixing belt 44.

According to the configuration of the third embodiment, by changing the tension of the fixing belt 44, it is possible to suppress the occurrence of belt bounce on the downstream side of the fixing nip portion N in the sheet conveying direction. Therefore, even when the integrated output number of sheets S increases, the first pressure roller 41 does not need to be replaced, and the fixing nip portion N after fixing of the relatively thin sheet S is downstream in the sheet conveying direction. It becomes possible to maintain the separability of the fixing belt 44 with respect to the fixing belt 44 while avoiding the bounce of the belt.

<Fourth Embodiment>
Next, an image forming apparatus according to the fourth exemplary embodiment of the present invention will be described. Since the basic configuration of this embodiment is the same as that of the first embodiment described above, the same components as those of the first embodiment are designated by the same names and the same reference numerals as before, and detailed description thereof will be given. The description may be omitted.

In the belt bounce avoidance mode, the image forming apparatus 1 of the fourth embodiment increases the speed of changing the speed of the fixing belt 44 or increasing the tension of changing the tension of the fixing belt 44 as the number of durable prints increases as shown in Table 1. To execute.

Table 1 shows the difference between the surface speed of the second pressure roller 42 and the surface speed of the fixing belt 44 when the speed of the fixing belt 44 is changed when the number of durable printed sheets increases, for example, 100%, 175%, and 250%. For example, it means increasing stepwise to 0.2%, 0.4%, and 0.6%.

Further, Table 1 shows that when the number of durable prints is increased to 100%, 175%, and 250%, for example, when the tension of the fixing belt 44 is changed, the tension of the fixing belt 44 is twice or four times that in the normal mode. , 6 times stepwise.

According to the configuration of the fourth embodiment, the speed of the fixing belt 44 is changed stepwise or the fixing belt 44 is gradually changed in response to the increase in the surface friction coefficient of the first pressure roller 41 with the increase in the cumulative number of output sheets S. Tension change can be performed. Accordingly, it is possible to effectively suppress the occurrence of belt bounce on the downstream side of the fixing nip portion N in the sheet conveying direction.

When the number of durable printed sheets increases from 100% to 250%, the speed change of the fixing belt 44 or the tension change of the fixing belt 44 may be continuously increased.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

For example, in the image forming apparatus 1, the first drive motor 47 and the second drive motor 48, which are two drive sources individually provided for the first pressure roller 41 and the second pressure roller 42, or the fixing belt. At least one of the cam member 54 and the tension changing roller 55, which is a tension changing portion for changing the tension of 44, may be provided, but both the drive source and the tension changing portion may be provided.

The present invention can be used in an image forming apparatus provided with a fixing device.

1 Image Forming Device 40 Fixing Device 41 First Pressure Roller 42 Second Pressure Roller 43 Tension Roller 44 Fixing Belt 47 First Drive Motor (Drive Source)
48 Second drive motor (drive source)
50 urging portion 54 cam member (tension changing portion)
55 Tension changing roller (tension changing unit)
60 Information detector (detector)
N fixing nip area S sheet

Claims (3)

An endless fixing belt wound around the first pressure roller and the tension roller and sandwiched between the first pressure roller and the second pressure roller is provided. In an image forming apparatus for fixing an unfixed toner image transferred onto a sheet at a fixing nip portion where a pressure roller and the second pressure roller contact each other,
A detection unit that detects information relating to the surface state of the first pressure roller;
At least one of two drive sources provided separately for the first pressure roller and the second pressure roller or a tension changing unit for changing the tension of the fixing belt;
Equipped with
As the information related to the surface state of the first pressure roller, the detection unit detects the light reflectance of the surface of the first pressure roller or the displacement of the slack of the fixing belt around the fixing nip portion,
As an operation mode at the time of fixing, a normal mode in which the first pressure roller and the second pressure roller are set to a predetermined surface speed and a fixing belt is set to a predetermined tension at the time of normal fixing, An avoidance mode selected based on information related to the surface state of the first pressure roller detected by the detection unit,
When the avoidance mode is selected, the speed of the surface of the fixing belt in the fixing nip portion is changed to be higher than the surface speed of the second pressure roller, or the tension of the fixing belt is set to be higher than that in the normal mode. An image forming apparatus, characterized in that at least one of the tension changes for increasing is also performed. Automatic selection, or the image forming apparatus according to claim 1, characterized in that it comprises an operating unit capable of any of the settings of the manual selection by a user of the avoidance mode of the avoidance mode. 3. The image forming apparatus according to claim 1, wherein in the avoidance mode , speed increase in the speed change or tension increase in the tension change is executed stepwise or continuously.